JP2006199830A - Polyester resin pellet and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester resin pellet resistant to the fusion of the pellets in solid-phase polycondensation process, giving a molded article having high transparency, and enabling the solid-phase polycondensation without lowering the polycondensation rate while suppressing the mutual fusion of the pellets. <P>SOLUTION: The polyester resin pellet has a surface crystalline layer containing a spherulite having a diameter of <5 μm. The thickness of the surface crystalline layer is ≥15 μm and ≤110 μm and the ratio of the thickness of the surface crystalline layer to the minor diameter of the pellet is ≤80%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polyester resin pellet and a method for producing the same. Specifically, the present invention relates to a polyester resin pellet capable of suppressing the fusion of the polyester resin pellet at the time of solid phase polycondensation and obtaining a highly transparent polyester resin molded product and a method for producing the same.

  Polyester resins are widely used as materials such as fibers, fabrics, molding resins and beverage bottles. And in order to draw out the moldability and mechanical properties necessary for various applications, the polymerization degree of the polyester resin is increased to a predetermined level. For example, a method is known in which a polyester resin prepolymer (polyester prepolymer) is obtained by melt polycondensation, and then the prepolymer is pelletized and the degree of polymerization is increased by solid phase polycondensation. This method is widely used in the production of polyester resin pellets on an industrial scale.

In this method, generally, a method is employed in which a drying step is provided before the polyester prepolymer pellets are put into the solid phase polycondensation step to suppress hydrolysis. Further, since the polyester prepolymer pellets may be fused in this drying step, various improved methods have been proposed in order to avoid such fusion. For example, a polyester prepolymer pellet is immersed in warm water at a temperature 10 ° C. or lower than its Tg, and the temperature is increased at a rate not exceeding 100 ° C. per hour to a temperature exceeding 15 ° C. while giving a linear velocity to the water. A method for avoiding the problem by warming has been proposed (see Patent Document 1). And before the drying process, a method of treating polyester prepolymer pellets with heated steam at 110 ° C. or higher (see Patent Document 2) and a method of treating with water or steam at 80 ° C. to 100 ° C. for 5 minutes to 25 minutes are also proposed. (See Patent Document 3). In addition, as a treatment of the polyester prepolymer, a method has been proposed in which polyethylene terephthalate prepolymer pellets obtained using a polycondensation catalyst containing a titanium-containing compound are brought into contact with water to reduce oligomers (see Patent Document 4).
JP-A-1-180309 JP 59-25815 A British Patent No. 83742 JP 2004-67964 A

  However, the method described in Patent Document 1 has a problem that it is not suitable for implementation on a chemical industry scale because it requires a large facility and requires a long time for processing. And in the method of patent document 2, there exists a problem that the superposition | polymerization speed in a solid-phase polycondensation process falls, and in the method of patent document 3, it fuse | melts pellets immediately after taking out from hot water. Or the solid phase polycondensation rate decreases.

In addition, the method described in Patent Document 4 is not a technique for preventing fusion of polyester resin prepolymer pellets, and the described hot water treatment time is as long as 30 minutes or more, which is not suitable for implementation on an industrial scale. Furthermore, the polyester resin pellets subjected to such treatment also have a problem that the solid-phase polycondensation rate decreases.
The present invention has been made in view of such problems, and suppresses fusion during solid-phase polycondensation of polyester resin pellets and suppresses a decrease in solid-phase polycondensation rate in the solid-phase polycondensation step. An object of the present invention is to provide a polyester resin pellet from which a highly transparent molded product can be obtained.

As a result of intensive studies, the present inventors have found that the above object can be achieved by forming a surface crystal layer having fine spherulites on the surface of the polyester resin pellets to a specific thickness, and have reached the present invention.
And it discovered that such a polyester resin pellet was obtained by treating the polyester resin pellet which has a density below a specific with the hot water which does not exceed 100 degreeC for the specific time, and completed this invention.

That is, the gist of the present invention is a polyester resin pellet having a surface crystal layer in which the diameter of the spherulite contained is less than 5 micrometers, and the thickness of the surface crystal layer is not less than 15 micrometers and not more than 110 micrometers. And the ratio of the surface crystal layer thickness to the pellet minor axis is 80% or less. Another aspect of the present invention is that raw material polyester resin pellets having a density of 1.36 g / cm ³ or less are heated with hot water at a temperature not lower than 100 ° C. and not higher than the glass transition temperature of the polyester resin. It is related with the manufacturing method of the polyester resin pellet characterized by performing the process for t [second] which satisfy | fills.

40 / (Tt−Tg) ≦ t ≦ 6000 / (Tt−Tg) (1)
(In the formula, t represents the hot water treatment time (seconds), Tt represents the treated hot water temperature (° C.), and Tg represents the glass transition temperature of the polyester resin.)

The polyester resin pellet of the present invention is one in which fusion during solid-phase polycondensation is suppressed and a decrease in solid-phase polycondensation rate is also suppressed. Moreover, a highly transparent polyester resin molded product can be obtained by using the polyester resin pellet of the present invention. This is thought to be due to the disappearance of the highly oriented layer generated on the outermost surface of the pellet by the hot water treatment.
The highly oriented layer on the surface of the polyester resin pellets generated by shearing between the die and the resin generated when pelletizing the polyester prepolymer, shearing generated by cutting the strands during pelletizing, etc., is also caused by melting. The history is hard to disappear, and when it is melted and solidified, it first crystallizes, causing fogging of the molded product (decrease in transparency). As in the present invention, it is considered that a highly transparent polyester resin molded product can be obtained by plasticizing by performing a specific hydrothermal treatment and removing the shear history.

Hereinafter, the present invention will be described in detail.
The polyester resin pellet of the present invention has a surface crystal layer in which the diameter of the spherulite contained is less than 5 micrometers, the thickness of the surface crystal layer is not less than 15 micrometers and not more than 110 micrometers, and relative to the short axis of the pellet. The ratio of the surface crystal layer thickness is 80% or less.
In the polyester resin pellets of the present invention, the thickness of the surface crystal layer having a spherulite diameter of less than 5 micrometers is too thin, and if it is too thin, stickiness suppression caused by an amorphous part in the surface crystal layer becomes insufficient, The effect of suppressing fusion between the polyester resin pellets may be reduced. On the other hand, even if it is too thick, the outflow of by-products generated during solid phase polycondensation to the outside of the pellet is reduced, so that the speed of the solid phase polycondensation reaction is reduced. Therefore, the thickness of the surface crystal layer is preferably 15 micrometers or more, more preferably 20 micrometers or more, and 110 micrometers or less, and particularly preferably 100 micrometers or less.

  Further, the thickness of the surface crystal layer with respect to the minor axis of the polyester resin pellet of the present invention is 80% or less of the minor axis, preferably 70% or less. When the surface crystal layer exceeds 80% with respect to the minor axis, the polycondensation speed decreases. In general, a polyester resin pellet has a transcrystal layer having a thickness of about 10 micrometers on its outermost surface. The surface crystal layer in the polyester resin pellet of the present invention also includes this transcrystal layer.

  The method for measuring the diameter of the spherulite in the surface crystal layer of the polyester resin pellet of the present invention is arbitrary, but, for example, wide-angle X-ray diffraction analysis, which is an effective method for detecting an amorphous state with plasticization and advanced arrangement Is mentioned. In the present invention, instead of directly measuring the pellet, the surface crystal layer on the surface of the polyester resin pellet was set to a value obtained by the following measurement method in the state of the pellet.

First, polyester prepolymer pellets are sandwiched between spacers having a thickness of 200 microns, held at 300 ° C. for 3 minutes, held at 300 ° C. for 5 minutes under a pressure of 100 kg / cm ² , rapidly cooled, and polyester having a thickness of 200 μm. In order to produce a resin prepolymer sheet and increase the detection sensitivity, six sheets of this sheet were stacked and the state was measured by wide-angle X-ray diffraction. For the measurement, CuKα rays with an acceleration voltage of 50 kV and a current of 100 mA were used, and the 2θ / θ angle was counted from 5 ° to 40 ° at 0.1 ° step intervals for 1 step for 10 seconds. From the measurement results, it was confirmed that the polyester amorphous peak shifted to the wide-angle side by hydrothermal treatment. This suggests that the amorphous arrangement proceeds by hydrothermal treatment (reference document: Macromolecules 1991, 24, 1185).

  There is no restriction | limiting in the dicarboxylic acid component and diol component which are the main structural repeating units, and the polyester resin used for this invention can use arbitrary things. Among them, the dicarboxylic acid component is preferably one containing terephthalic acid and its derivative as the main component, and the diol component is preferably one containing ethylene glycol as the main component. Here, the main component indicates, for example, that the proportion of the carboxylic acid component or the diol component is 90 mol% or more, especially 95 mol% or more, particularly 99 mol% or more. Examples of derivatives of terephthalic acid include ester-forming derivatives, specifically, alkyl esters of about 1 to 4 carbon atoms of terephthalic acid such as dimethyl terephthalate; halides such as terephthalic acid dichloride. It is done.

Moreover, the polyester resin used for this invention may contain copolymerization components other than a terephthalic-acid component and an ethylene glycol component as a repeating unit which comprises a polyester resin in the range which does not impair the effect. In general, the content of such other copolymer components is preferably 10 mol% or less, more preferably 5 mol% or less in the entire polyester resin.
Examples of dicarboxylic acid components other than terephthalic acid or derivatives thereof include phthalic acid, isophthalic acid, 1,3-phenylenedioxydiacetic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenylether dicarboxylic acid, 4,4 Aromatic dicarboxylic acids such as' -diphenyl ketone dicarboxylic acid, 4,4'-diphenoxyethane dicarboxylic acid, 4,4'-diphenylsulfone dicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and about 1 to 4 carbon atoms thereof Ester-forming derivatives such as alkyl esters and halides; alicyclic dicarboxylic acids such as hexahydroterephthalic acid; and ester-forming derivatives such as alkyl esters and halides having about 1 to 4 carbon atoms; succinic acid , Glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, urine Decane dicarboxylic acid, and aliphatic dicarboxylic acids such as dodecane dicarboxylic acid, ester-forming derivatives thereof such as alkyl esters or halides having about 1 to 4 carbon; and the like.

  Examples of diol components other than ethylene glycol include diethylene glycol, triethylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, decamethylene glycol, neopentyl glycol, 2-ethyl-2-butyl-1,3-propanediol, Aliphatic diols such as polyethylene glycol and polytetramethylene ether glycol; Alicyclic diols such as 1,4-cyclohexanediol and 1,4-cyclohexanedimethylol; Aromatic diols such as xylene glycol; 2,2- Examples thereof include an ethylene oxide adduct or a propylene oxide adduct of bis (4′-hydroxyphenyl) propane.

Furthermore, as copolymerization components other than the dicarboxylic acid component and diol component as described above, for example, monofunctional components such as stearyl alcohol, stearic acid, benzoic acid, trimellitic acid, trimesic acid, pyromellitic acid, trimethylolethane, Trifunctional or more polyfunctional components such as trimethylolpropane, glycerol, pentaerythritol and the like can be mentioned.
There is no restriction | limiting in particular in the manufacturing method of the polyester resin used for this invention, Conventionally well-known arbitrary methods can be used. In general, a polyester resin used for a polyester resin pellet is obtained by, for example, subjecting a dicarboxylic acid component such as terephthalic acid or an ester-forming derivative thereof and a diol component such as ethylene glycol to an esterification reaction or a transesterification reaction. It is obtained by carrying out a melt condensation reaction using a polycondensation catalyst. In order to make this into a polyester resin pellet, for example, it is obtained by cutting the polyester resin into a strand or the like while cutting it into an amorphous or low crystalline pellet, treating the pellet with hot water, and then crystallizing it. It is done. Moreover, in order to obtain a pellet with a higher degree of polycondensation, the pellet after hot water treatment or crystallization treatment may be subjected to solid phase polycondensation. Hereinafter, the polyester resin subjected to such solid phase polycondensation is particularly referred to as a polyester prepolymer.

  As a method for producing a polyester prepolymer, for example, a dicarboxylic acid containing terephthalic acid or a derivative thereof as a main component and a diol containing ethylene glycol as a main component are usually subjected to a temperature condition of about 240 to 280 ° C. in an esterification reaction vessel. Usually, a method of performing esterification reaction for about 1 to 10 hours under stirring under normal pressure to about 0.5 MPa is mentioned. In this case, the molar ratio of the diol component to the dicarboxylic acid component is usually 1 or more, preferably 1.05 or more, and usually 1.6 or less, preferably 2 or less.

  As another production method, a transesterification reaction between a dicarboxylic acid component and a diol component in the presence of a transesterification reaction catalyst is performed, and then the obtained esterification reaction product or polyester as a transesterification reaction product is used. The low molecular weight substance is transferred to a polycondensation tank, and in the presence of a polycondensation catalyst, usually at a temperature of about 250 to 290 ° C., gradually from normal pressure to gradually reduced pressure, and finally at a reduced pressure of usually about 1333 to 13.3 Pa. A method of melt polycondensation with stirring for about 1 to 20 hours can be mentioned. Such a production method may be performed either continuously or batchwise, and each of the esterification reaction tank and the polycondensation tank may be a single stage or a multistage.

  In the esterification reaction, a catalyst may or may not be used, and may be selected and determined as appropriate. Examples of esterification reaction catalysts include germanium dioxide, germanium tetroxide, germanium hydroxide, germanium oxalate, germanium tetraethoxide, germanium tetra-n-butoxide, and other germanium compounds, antimony trioxide, antimony pentoxide, antimony acetate, and antimony. Antimony compounds such as trisethyleneglycoxide, titanium compounds such as titanium tetraethoxide, titanium tetra-n-propoxide, titanium tetra-i-propoxide, titanium tetra-n-butoxide, titanium oxalate, potassium titanium oxalate, etc. A well-known catalyst is mentioned.

  As the transesterification reaction catalyst, one or more kinds of conventionally known metal compounds such as titanium, magnesium, calcium, manganese, lithium and zinc can be used. Specific examples include organic acid salts, alcoholates, and carbonates of these metals. Among these, magnesium acetate, calcium acetate, manganese acetate, lithium acetate, and hydrates thereof are preferable.

  Examples of the polyester polycondensation reaction catalyst include germanium compounds such as germanium dioxide, germanium tetroxide, germanium hydroxide, germanium oxalate, germanium tetraethoxide, germanium tetra-n-butoxide; titanium tetraethoxide, titanium tetra-n-propoxy , Titanium alkoxides such as titanium tetra-i-propoxide, titanium tetra-n-butoxide, and titanium compounds such as titanium oxalate and potassium titanium oxalate; cobalt formate, cobalt acetate, cobalt stearate, cobalt oxalate, cobalt carbonate, And cobalt compounds such as cobalt bromide; tin compounds such as tin acetate, tin oxalate and tin bromide. These may be used alone or in combination of two or more in any proportion. Among them, the condensation condensation reaction rate is fast, the load on the environment is small, and the amount of by-products such as acetaldehyde can be suppressed. Titanium compounds are preferred, and titanium alkoxides are particularly preferred from the viewpoint that the crystallization rate of the prepolymer can be kept low and the effects of the present invention become remarkable.

The amount of the catalyst used in the polycondensation reaction of the polyester is preferably such that the content as a metal atom derived from the catalyst is usually about 1 to 500 ppm with respect to the obtained polyester. If the amount of catalyst is too small, polycondensation does not proceed. Conversely, if the amount of catalyst is too large, coloring due to side reactions may occur.
Moreover, you may use a phosphorus compound as a stabilizer at the time of esterification reaction or transesterification reaction, and a polycondensation reaction. The amount of such a phosphorus compound used is preferably such that the content as a phosphorus atom derived from the phosphorus compound is usually about 1 to 200 ppm with respect to the resulting polyester. Examples of such phosphorus compounds include phosphate esters such as trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, triphenyl phosphate, tricresyl phosphate; triphenyl phosphite, trisdodecyl phosphate, Phosphites such as trisnonylphenyl phosphite; acid phosphates such as methyl acid phosphate, ethyl acid phosphate, isopropyl acid phosphate, butyl acid phosphate, dibutyl phosphate, monobutyl phosphate, dioctyl phosphate; Examples include phosphoric acid, hypophosphorous acid, and polyphosphoric acid.

  Moreover, you may use a basic compound as an ether bond production | generation inhibitor. Specific examples include tertiary amines such as triethylamine, tri-n-butylamine, and benzyldimethylamine; quaternary ammonium hydroxides such as tetraethylammonium hydroxide, tetra-n-butylammonium hydroxide, and trimethylbenzylammonium hydroxide. A lithium carbonate, sodium carbonate, potassium carbonate, sodium acetate, magnesium acetate and the like.

  The polyester prepolymer obtained by melt polycondensation may be extracted from the molten state into a strand, and may be cut with a cutter while cooling with water or with water, and may be cut into a prepolymer pellet, or a molten droplet may be dropped into water. It is good also as a prepolymer pellet. The size of the polyester prepolymer pellet is arbitrary, but usually the lower limit is 1 mm or more in the minor axis, preferably 2 mm or more, and it is desirable to have an average particle diameter of 5.5 mm, preferably 4 mm. If the particle size is too small, it may be difficult to handle because it floats in the air. Conversely, if the particle size is too large, the solid phase polycondensation speed may decrease.

The method for producing polyester resin pellets of the present invention comprises a specific hydrothermal treatment, specifically, a raw material polyester resin pellet (polyester prepolymer) having a density of 1.36 g / cm ³ or less, and a glass transition temperature of the polyester prepolymer. As described above, the treatment for t [seconds] satisfying the following general formula (1) is performed with hot water of less than 100 ° C.

40 / (Tt−Tg) ≦ t ≦ 6000 / (Tt−Tg) (1)
(In the formula, t represents the hot water treatment time (seconds), Tt represents the treated hot water temperature (° C.), and Tg represents the glass transition temperature of the polyester resin.)

  And after such a hot-water treatment, the polyester resin pellet of this invention can be manufactured by selecting and selecting suitably conventionally well-known arbitrary crystallization conditions. Furthermore, solid phase polycondensation may be performed as necessary. By performing the hydrothermal treatment as described above, it is considered that only the surface of the polyester resin pellet is plasticized, the arrangement of the non-crystalline parts is increased, and the generation of microcrystalline nuclei is promoted. In other words, when the non-crystallized plastic layer that is plasticized is crystallized, the number of spherulites is increased by about 10 to 100 times compared to a normal crystal layer, so that the crystallization speed becomes very fast. Therefore, it is considered that the surface crystal layer thickness can be optimized.

  As a result, the polyester resin pellets of the present invention can suppress “stickiness” caused by non-crystal parts even when the temperature rises in the drying process or the like, can suppress fusion between the polyester resin pellets, Even during condensation, the surface crystal layer is not too thick, so that by-products generated during solid-phase polycondensation can be easily removed from the pellets, and further, a decrease in the rate of solid-phase polycondensation reaction can be suppressed. It is done.

  In the present invention, the hot water treatment may be contact with hot water, such as immersion in hot water, etc., but contact with heated steam is also possible. Treatment is preferred. Specifically, the pellets obtained by strand-cutting the strand-like polyester prepolymer that has come out of the melt polycondensation tank of the polyester resin, in a pipe that is transported to the dehydration step or in a tank provided in the middle thereof The method of making it contact with hot water and the method of making it contact with hot water in a cooling tank before pelletization are mentioned. Or the method of putting the polyester prepolymer pellet which dehydrated adhering cooling water after pelletization into a hot-water-treatment tank, and making this prepolymer pellet contact with water-vapor-containing inert gas or water-vapor-containing air is mentioned.

  The temperature of the hot water is less than 100 ° C, more preferably 95 ° C or less. The lower limit of the hot water treatment temperature is higher than the glass transition temperature, preferably 1 ° C. or more, and particularly preferably 5 ° C. or more higher than the glass transition temperature. Usually, the lower limit of the hot water treatment temperature is 60 ° C. or more, especially 65 ° C. or more. It is preferable that Even if the treatment is performed with hot water having a temperature equal to or lower than the glass transition temperature, suppression of fusion between pellets in the drying step is not reduced. Moreover, since the treatment with hot water at a temperature exceeding 100 ° C. is accompanied by deactivation of the catalyst, the solid phase polycondensation speed may be reduced.

  The hydrothermal treatment time t (seconds) is at least 40 / (Tt-Tg) seconds or more, preferably 100 / (Tt-Tg) seconds or more, and the upper limit is 6000 / (Tt-Tg). In particular, it is preferably 5000 / (Tt−Tg) seconds or less. If the hydrothermal treatment time t is too short (below the range of the general formula (1)), the effect of suppressing fusion between the polyester resin pellets may be reduced, and conversely too long (the general formula (1) If it exceeds the range, the solid phase polycondensation rate of the resulting polyester resin pellets may decrease.

  In the method for producing polyester resin pellets of the present invention, this may be solid phase polycondensed to obtain polyester resin pellets having a desired degree of polycondensation. In the case of solid phase polycondensation, the polyester prepolymer pellets that have undergone the hydrothermal treatment step are usually pre-crystallized and dried, followed by solid phase polycondensation. The precrystallization step is usually performed by heating the polyester prepolymer pellets with stirring or under flow. If the preliminary crystallization temperature is too low, the crystallization progress rate in the subsequent stage may be reduced, and if it is too high, deterioration may occur due to the influence of moisture and the pellet may be colored. Therefore, the temperature at this time is usually 120 ° C. or higher, preferably 130 ° C. or higher and 190 ° C. or lower, preferably 180 ° C. or lower, and the holding time is usually 1 to 15 minutes.

After precrystallization, the polyester resin pellets are dried. If the drying temperature is too low, it takes a long time for drying. Conversely, if the drying temperature is too high, deterioration may occur due to the influence of moisture, and the pellets may be colored. Therefore, the drying temperature is 140 ° C. or higher and 190 ° C. or lower, preferably under inert gas flow. The drying time is usually 30 minutes to 6 hours.
Next, the dried polyester resin pellets are heated at a high temperature to perform solid phase polycondensation. The solid phase polycondensation temperature may be appropriately selected and determined from a conventionally known temperature range, but is generally 190 ° C. or higher, preferably 195 ° C. or higher, preferably 235 ° C. or lower, particularly 230 ° C. or lower. Preferably it is done. The pressure of the solid-phase polycondensation atmosphere is nitrogen, argon, when carried out in an inert gas atmosphere such as carbon dioxide, 1 kg / cm ² or less, preferably 0.2 kg / cm ² or less. When the reaction is carried out in a reduced pressure atmosphere, the pressure is 0.1 to 50 Torr, preferably 0.5 to 10 Torr. The solid phase polycondensation time reaches a desired physical property in a shorter time as the temperature is higher, but is usually 1 to 30 hours, preferably 5 to 25 hours. By appropriately selecting these temperatures and pressures, polyester resin pellets having a desired degree of polycondensation can be obtained.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist. In the following examples, “parts” means parts by weight. The measuring methods for various physical properties in the present invention are as follows.
(1) Glass transition temperature (Tg)
Measurement was performed using a differential scanning calorimeter DSC7 manufactured by PerkinElmer. A sample prepared by cutting 10 mg of the dried prepolymer with a stainless steel razor blade made of Feather without shearing as much as possible and putting it in a standard pan for aluminum solid was used as a sample. An empty pan was used as a blank, and the temperature was increased from room temperature to 300 ° C. at a temperature increase rate of 20 ° C./min in a nitrogen atmosphere. Tg is calculated | required from the specific heat change behavior by the glass transition of a calorimetric curve. Specifically, the temperature at the intersection of the tangent at the midpoint of the specific heat change due to the glass transition and the tangent at the point before the specific heat change was defined as Tg.

(2) Thickness measurement of surface crystal layer One pellet after crystallization is coated with epoxy resin (bond quick 5) on the whole, and left in an oven at 40 ° C. for 2 hours to cure the epoxy resin, A sample for measurement was obtained. This was fixed so that the surface of the pellet was perpendicular to the blade of a microtome for optical microscope manufactured by Rights Co., Ltd., and the vicinity of the center of the chip was cut to a thickness of about 5 μm. A section obtained by cutting was taken out on a slide glass with tweezers, immersed in oil, covered with a cover glass, and smoothed by pressing to form a pellet cross-sectional observation sample. The observation sample was observed under the crossed Nicols of a polarizing microscope and focused, and the morphology of the crystals near the surface was photographed with a polaroid film at 400 × and 100 × magnification. The thickness of a region where spherulites of 5 microns or more were not formed perpendicularly from the photographed pellet surface was measured, and corrected by a 10 micron scale for an optical microscope to obtain a crystal surface layer thickness.

(3) Intrinsic viscosity (IV)
0.50 g of the freeze-pulverized pellets were mixed with phenol / 1,1,2,2-tetrachloroethane (weight ratio 1/1) and the concentration (c) was 1.0 g / dl at 140 ° C. for 30 minutes. Then, the relative viscosity (ηrel) with the stock solution was measured at 30 ° C. using an Ubbelohde capillary viscosity tube, and the specific viscosity (ηsp) and concentration (ηsp) and concentration (ηsp) determined from the relative viscosity (ηrel) -1 were measured. The ratio (ηsp / c) with respect to c) is obtained. Similarly, when the concentration (c) is 0.5 g / dl, 0.2 g / dl, and 0.1 g / dl, the respective ratio (ηsp / c) is From these values, the ratio (ηsp / c) when the concentration (c) was extrapolated to 0 was obtained as the intrinsic viscosity [η] (dl / g).

(4) Evaluation of fusion after hydrothermal treatment The prepolymer pellets after hydrothermal treatment were extracted into a sieve and air-cooled, and then the prepolymer pellets were fused together, and when there were 10 or more lumps, it was assumed that there was fusion. .

(5) Heat-fusion test 7 g of prepolymer pellets after the hot water treatment were spread on a vat, crystallized by heating at 143 ° C. for 3 minutes in an inert oven, and then taken out and air-cooled. This was packed in a 50 ml beaker, a weight was placed so that a pressure of 50 g per square centimeter was uniformly applied to the beaker opening, heated to 175 ° C., and nitrogen was circulated at a flow rate of 20 liters / minute for 30 minutes. Removed after heating. After returning to room temperature, when the pellet was taken out from the beaker, if the pellet was fused and a lump of 10 grains or more was present, it was determined that fusion was present.

(6) Haze The pellet after completion of solid polycondensation was packed in a square spacer with a thickness of 2 mm and a side of 30 mm, and both sides were sandwiched by a Kapton film with a thickness of 50 μm, for preheating in a press machine heated to 290 ° C. 5 After being allowed to stand for 100 minutes, the pressure was increased to 100 kg / cm 2 and left for 5 minutes, immediately transferred to a water-cooled press at 25 ° C., pressurized at 100 kg / cm 2 and cooled for 3 minutes. Thereafter, the haze of the press sheet taken out was measured using a haze meter (“NDH-300A” manufactured by Nippon Denshoku Co., Ltd.).

Example 1
Terephthalic acid and ethylene glycol were continuously supplied to a slurry preparation (hereinafter the same) tank so that 13.0 parts of terephthalic acid and 5.82 parts of ethylene glycol were obtained to prepare a slurry. The slurry was continuously supplied to the first stage esterification reaction tank, and the esterification reaction was continuously carried out at about normal pressure at 260 ° C., and bis (2-hydroxyethyl) terephthalate having an ester reaction rate of 84% and its low A polymer was prepared. Bis (2-hydroxyethyl) terephthalate having low ester reaction rate of 95% and its low polymer are continuously fed to the second stage esterification reaction tank and reacted at 255 ° C. under normal pressure. Was prepared.

  Further, the reaction product was continuously supplied to the first stage polycondensation reaction tank, 0.00135 parts of orthophosphoric acid and 0.0080 parts of germanium dioxide were continuously added to the above preparation, and the pressure was reduced to 2.6 kPa. The reaction was continuously carried out at 270 ° C. and an average residence time of 1.2 hours. Subsequently, the reaction product was continuously supplied to the second stage polycondensation reaction tank, and melt polycondensation reaction was carried out under a reduced pressure of 0.5 kPa at 278 ° C. and an average residence time of 1.2 hours. The reaction was carried out in a polycondensation reaction tank at 280 ° C. and 0.3 kPa with an average residence time of 1.2 hours. Thereafter, the pressure was restored, and the resin was extracted in the form of a strand from an extraction port provided at the bottom of the polycondensation reaction tank, and after cooling with water, the resin was cut into chips to obtain polyethylene terephthalate prepolymer pellets. The obtained prepolymer had an intrinsic viscosity of 0.64 dl / g and a glass transition temperature of 73 ° C.

The prepolymer pellets were poured into hot water heated to 83 ° C. with a water bath, held with stirring for 30 seconds, immediately taken out through a sieve, drained, allowed to stand and air-cooled. No fusion was observed after air cooling. Further, when this prepolymer pellet was subjected to a heat fusion test, no fusion was observed. Haze was 2.3%. The results are shown in Table 1.
The prepolymer pellets thus obtained were spread on a stainless steel vat, heated in an inert oven (Yamato DN410I) at 160 ° C. for 3 hours under a nitrogen stream of 20 liters / minute, and then increased to 205 ° C. at 10 ° C. The temperature was raised at a rate of every minute and a solid phase polycondensation reaction was carried out for 20 hours. Subsequently, it returned to room temperature and took out from oven. After removal, the pellets had an intrinsic viscosity of 0.83 dl / g and a surface crystal layer thickness of 50 micrometers.

(Example 2)
The catalyst compound added during the polycondensation reaction was changed in the same manner as in Example 1 except that 0.00135 parts of orthophosphoric acid, 0.000794 parts of magnesium acetate tetrahydrate, and 0.000324 parts of tetrabutoxytitanium were used. Polymer pellets were obtained. The obtained prepolymer had an intrinsic viscosity of 0.62 dl / g and a glass transition temperature of 72 ° C. The obtained prepolymer pellets were poured into hot water heated to 83 ° C. with a water bath, held with stirring for 30 seconds, then immediately taken out into a sieve, water was removed, allowed to stand, and air-cooled. No fusion was observed between the pellets after air cooling. Further, when this pellet was subjected to a heat fusion test, no fusion was observed. Further, as a result of conducting a solid phase polycondensation reaction under the same conditions as in Example 1, the obtained polymer had an intrinsic viscosity of 0.84 dl / g and a surface crystal layer thickness of 40 micrometers.

(Example 3)
A slurry of 16.47 parts terephthalic acid, 0.626 parts 1,4-cyclohexanedicarboxylic acid and 5.82 parts ethylene glycol was prepared, and 0.30 parts bis (2-hydroxyethyl) terephthalate was added in advance. A low polymer was prepared by sequentially supplying the esterification tank maintained at ° C. over 4 hours. Prepolymer pellets were obtained from this low polymer in the same manner as in Example 2. The obtained prepolymer had an intrinsic viscosity of 0.59 dl / g and a glass transition temperature of 66 ° C. Next, the obtained prepolymer pellets were put into hot water heated to 80 ° C. with a water bath, held with stirring for 80 seconds, immediately taken out into a sieve, water was removed, allowed to stand, and air-cooled. No fusion was observed between the pellets after air cooling. Further, when this pellet was subjected to a heat fusion test, no fusion was observed. The pellet was subjected to solid phase polycondensation reaction in the same manner as in Example 1. As a result, the obtained polymer had an intrinsic viscosity of 0.84 dl / g and a surface crystal layer thickness of 90 micrometers.

(Comparative Example 1)
When the prepolymer pellet obtained in Example 1 was subjected to a heat fusion test without a hot water treatment step, fusion was observed. The polymer obtained by solid-phase polycondensation as in Example 1 had an intrinsic viscosity of 0.85 dl / g and a surface crystal layer thickness of 8 micrometers.

(Comparative Example 2)
The prepolymer pellets obtained in Example 1 were put into hot water heated to 93 ° C., held with stirring for 10 minutes, then immediately taken out into a sieve, water was cut off, allowed to stand, and air-cooled. The pellets after air cooling were fused. Further, when this prepolymer pellet was subjected to a heat fusion test, no fusion was observed. The intrinsic viscosity of the polymer obtained by subjecting this prepolymer pellet to solid phase polycondensation in the same manner as in Example 1 was 0.69 dl / g, and the surface crystal layer thickness was 190 micrometers.

(Comparative Example 3)
The prepolymer pellet obtained in Example 1 was put into hot water heated to 65 ° C., held with stirring for 5 minutes, then immediately taken out into a sieve, water was cut off, allowed to stand, and air-cooled. No fusion was observed in the pellets after air cooling. When this prepolymer pellet was subjected to a heat fusion test, fusion between the pellets was observed. The polymer obtained by solid phase polycondensation of the prepolymer pellets in the same manner as in Example 1 had an intrinsic viscosity of 0.84 dl / g and a surface crystal layer thickness of 8 microns.

(Comparative Example 4)
The prepolymer pellet obtained in Example 1 was held in steam heated to 130 ° C. for 30 seconds, then immediately taken out into a sieve, water was cut off, allowed to stand, and air-cooled. The pellets after air cooling were fused. When this prepolymer pellet was subjected to a heat fusion test, no fusion was observed. The polymer obtained by solid-phase polycondensation of this prepolymer pellet in the same manner as in Example 1 had an intrinsic viscosity of 0.72 dl / g and a surface crystal layer thickness of 150 micrometers.

(Comparative Example 5)
The prepolymer pellet obtained in Example 2 was put into hot water heated to 90 ° C., held with stirring for 30 minutes, then immediately taken out into a sieve, water was cut off, allowed to stand, and air-cooled. Fusion was observed in the pellets after air cooling. Further, when this prepolymer pellet was subjected to a heat fusion test, fusion between the pellets was observed. The polymer obtained by subjecting this prepolymer pellet to a solid phase polycondensation reaction in the same manner as in Example 1 had an intrinsic viscosity of 0.72 dl / g and a surface crystal layer thickness of 210 micrometers.

Claims (3)

  Polyester resin pellets having a surface crystal layer in which the diameter of spherulites contained is less than 5 micrometers, the thickness of the surface crystal layer being 15 micrometers or more and 110 micrometers or less, and the surface relative to the minor axis of the pellet Polyester resin pellets having a crystal layer thickness ratio of 80% or less. The raw material polyester resin pellets having a density of 1.36 g / cm ³ or less are treated with hot water not lower than the glass transition temperature of the polyester resin and lower than 100 ° C. for t [seconds] satisfying the following general formula (1). A method for producing polyester resin pellets, comprising:
40 / (Tt−Tg) ≦ t ≦ 6000 / (Tt−Tg) (1)
(In the formula, t represents the hot water treatment time (seconds), Tt represents the treated hot water temperature (° C.), and Tg represents the glass transition temperature of the polyester resin.) 3. The polyester resin pellet according to claim 2, wherein the raw material polyester resin pellet is obtained by polycondensation of dicarboxylic acids and diols using a polycondensation catalyst containing a titanium compound or a germanium compound. Manufacturing method.