JP5288677B2 - Polyethylene terephthalate resin - Google Patents

Description

  The present invention relates to a polyethylene terephthalate resin capable of forming a hollow container such as a bottle having a small amount of an aldehyde compound such as acetaldehyde.

  Conventionally, as a material for containers such as seasonings, oils, beverages, cosmetics, and detergents, various resins have been adopted depending on the type of filling contents and the purpose of use.

  Among these, polyethylene terephthalate resin is excellent in mechanical strength, heat resistance, transparency and gas barrier properties, and is particularly suitable as a material for hollow containers for filling beverages such as mineral water, tea, carbonated drinks and juices. . Moreover, it classify | categorizes into a heat-resistant hollow container and a non-heat-resistant hollow container as a kind of bottle. Conventionally, mineral water, tea, juice and the like are heat resistant hollow containers to which heat resistance is imparted in order to fill the hollow containers at a high temperature (eg, 80 ° C. to 95 ° C.) in order to sterilize them. However, with recent advances in filling technology, a system has been established that can fill beverages that have been high-temperature sterilized and filled in aseptic conditions, and mineral water and tea are filled in non-heat-resistant hollow containers that do not require heat resistance. There are many more.

Such polyethylene terephthalate resin is formed into pellets by esterifying terephthalic acid or its ester-forming derivative and ethylene glycol or its ester-forming derivative, followed by liquid phase polycondensation in the presence of a polycondensation catalyst. Is done. Next, in the solid phase polymerization step, the polymer is further polymerized to prepare a resin having an appropriate intrinsic viscosity.
As a method for forming a bottle using the polyethylene terephthalate resin pellet as a raw material, for example, first, it is supplied to a melt molding machine such as an injection molding machine to form a preform called a preform. In this step, the pellet is put into a cylinder on which a screw is mounted, and the resin is plasticized (melted) by rotating the screw, then injected into a mold, cooled, solidified, and taken out to obtain a preform.

This preform is then fed to a blow molding machine. The blow molding machine comprises two steps, a heating step and a blowing step. In the heating step, the preform is heated to a predetermined temperature using, for example, an infrared heater to soften the material. Next, the heated preform is transferred to a blow process, inserted into a mold having a predetermined shape, stretch blow-molded with a rod called a stretch rod and high-pressure air, and taken out from the mold to form a hollow container. Normally, blow molding is a molding system that performs heating and blow continuously.
There are two major blow molding methods. When molding a non-heat-resistant hollow container, the heated preform is blow-molded in a mold and immediately taken out from the mold. On the other hand, when molding a heat-resistant hollow container, the strain generated at the time of blowing (stretching) by adjusting the mold temperature to a high temperature of, for example, 130 ° C. and contacting the high-temperature mold by a method called heat setting is used. Relax and give heat resistance.

  In the above-described injection molding, the resin is once melted at a temperature of, for example, 280 ° C. or more, but in this molten state, the resin undergoes a decomposition reaction and increases by-products such as aldehyde compounds such as acetaldehyde and formaldehyde. The aldehyde compound thus produced is also contained in the pelletized polyethylene terephthalate resin after the polymerization is completed. In the blow molding process, the molding temperature is, for example, about 90 ° C. to 120 ° C. At this temperature, the resin is difficult to decompose and the aldehyde compound does not increase.

Since this aldehyde compound remains in the container material, it elutes into the contents such as a beverage filled while the container is stored, and its flavor, fragrance, etc. are significantly reduced.
In order to prevent such a problem, elution of acetaldehyde into the filled contents must be suppressed, that is, the amount of acetaldehyde in the container material must be reduced. Furthermore, in order to reduce the amount of acetaldehyde in the container material, it is necessary to suppress an increase in the amount of acetaldehyde produced in the melt molding process.

  To date, methods to suppress the formation of acetaldehyde include adding a compound that chemically reacts with aldehyde to trap aldehyde, removing acetaldehyde from molten resin in the injection molding process, and lowering the melting point of the resin. Examples thereof include a method for suppressing resin decomposition by molding at a temperature.

  Examples of the method of adding a compound that traps aldehyde include Patent Document 1, Patent Document 2, Patent Document 3, and the like. However, the addition of these compounds leads to quality problems such as yellowing the color tone of molded products and deterioration of transparency, as well as cost increases such as the need to install equipment for adding these compounds in the molding process. There is a problem that it is easy. On the other hand, as a method for removing acetaldehyde from a molten resin in an injection molding process, Patent Document 4 includes a method in which a vent hole is provided in the middle of an injection cylinder and is removed therefrom under reduced pressure. This method requires that a special injection cylinder or screw be mounted on the molding machine.

  Therefore, as a method for suppressing the production of acetaldehyde, a method that can use an existing molding apparatus (for example, an injection molding machine) without significantly changing the physical properties of the polyethylene terephthalate resin is preferable. Among them, a method of forming at a low temperature is desirable from the viewpoint of cost reduction. For example, the method (Saturated polyester resin handbook P.10-16) of copolymerizing other components with the acid component or glycol component of a polyethylene terephthalate resin and lowering melting | fusing point is mentioned. However, even if the intrinsic viscosity, copolymerization component, and copolymerization amount are the same, the moldable temperature is not always constant during actual injection molding, that is, it is not always possible to melt at a low temperature simply by reducing the melting point of the resin. It has been found by the present inventors that molding is not possible.

  In other words, the process for plasticizing (melting) pellets is described. In melt molding with screws, heat is generated by the friction (shear) between the pellets and the inner wall of the cylinder due to the rotation of the screws, and the pellets receive the heat. It leads to plasticization. A screw is generally composed of three zones: a feed zone, a compression zone, and a metering zone. First, the pellets are continuously fed into the feed zone from the on-machine hopper, and moved forward while receiving shear as the screw rotates. And the plasticization of the pellet starts gradually from the feed zone to the compression zone. In the flight of the screw, it is divided into a melting zone (melt bed) and a solid zone (solid bed), and the pellets in the solid zone undergo plastic shearing due to shearing of the screw, move to the melting zone, and in front of the cylinder As it moves, the melting zone increases and the solid zone decreases. Particularly in the compression zone, the groove depth of the screw flight gradually becomes shallow, and the solid pellets are subjected to higher shearing of the screw. Further, the resin moves to the metering zone. Here, the flight groove depth is the shallowest, and the remaining solid (unmelted) is completely plasticized.

In the case of not completely plasticizing in the metering zone, for example, in the case of an injection molding machine, it is injected into a mold without being melted, and unmelted material is recognized in a molded product (preform), and molding defects such as whitening are caused. Become. In such a case, it is necessary to perform molding at a higher temperature, for example, by increasing the screw rotation speed or by increasing the set temperature of the heater attached to the cylinder. Accordingly, a larger amount of by-products such as acetaldehyde is generated. It may not always be possible to suppress this whitening simply by reducing the melting start temperature of the resin.
US Pat. No. 5,340,884 JP-A-1-22956 Japanese Patent Laid-Open No. 62-257959 Japanese Patent Laid-Open No. 7-60803 Saturated polyester resin handbook published by Nikkan Kogyo Shimbun

That is, the present invention is to solve the problems associated with the prior art as described above, and by controlling the difference between the melting point on the low temperature side and the melting point on the high temperature side to a specific range, the polyethylene terephthalate resin An object of the present invention is to provide a polyethylene terephthalate resin capable of producing a very high quality hollow container in which the melt plasticization temperature in melt molding is reduced and the production of aldehyde compounds such as acetaldehyde is suppressed.

  As a result of diligent investigation on this cause, the present inventors have found that the number of melting point peaks of the pellets detected under specific measurement conditions, and when there are a plurality of melting points, the melting point on the low temperature side and the melting point difference on the high temperature side are molded. The present invention has been completed by finding that it greatly affects the possible temperature.

That is, the present invention
Pellets made of polyethylene terephthalate resin,
(A) A dicarboxylic acid component excluding terephthalic acid and a glycol component excluding ethylene glycol are contained in a total amount of 1.5 to 6.0 mol% as a comonomer unit,
(B) the intrinsic viscosity (IV) is in the range of 0.70 dl / g to 1.10 dl / g,
(C) the density is in the range of 1390 kg / m3 to 1410 kg / m3;
(D) The microcrystal size of the pellet measured by small-angle X-ray is L1, and the pellet is left in a 50/50 wt% mixture of hexafluoroisopropanol and chloroform for 2 hours. When the measured crystallite size is L2, the values of L1 and L2 are both in the range of 60 to 70 mm.
The present invention relates to a polyethylene terephthalate resin pellet.
A molded product or preform obtained by melt molding the polyethylene terephthalate resin pellets, or a hollow container obtained by blow molding is a preferred embodiment of the present invention.

The effect of the melting point on the low temperature side and the melting point on the high temperature side of the pellet on the molding temperature will be described below. Solid phase polymerized pellets are crystallized polyethylene terephthalate resin, its melting point is measured by shows difference scanning calorimetry (DSC). When the dried pellet is attached to the DSC and the temperature is increased from 30 ° C. to 290 ° C. at a rate of 10 ° C./min, the two melting points of the low temperature side melting point Tm1 and the high temperature side melting point Tm2 are Generally detected. When such a polyethylene terephthalate resin is melt-molded, for example, by injection molding, the process until it is melted in the injection cylinder and plasticized is a process in which the temperature of the pellet rises due to screw rotation (shear). Melting with the melting point starts, and further melting with the melting point on the high temperature side proceeds, and by having fluidity, plasticization is completed, and melt molding such as injection molding and extrusion molding becomes possible.

When the difference between the melting point Tm1 on the low temperature side and the melting point Tm2 on the high temperature side is large, that is, when the temperature difference from the start to the end of melting is large, the outer surface of the pellet remains in a semi-molten state as plasticization starts. The outside of the pellets are fused together to form a large lump. This agglomerate is the same as a large pellet and takes longer to plasticize than a small pellet. Therefore, even if it reaches the screw metering zone, more solid remains. In such a case, the screw rotation speed is increased. Alternatively, molding must be performed at a higher temperature, for example, by increasing the set temperature of the heater mounted on the cylinder. That is, more by-products such as acetaldehyde are generated.

  Therefore, as a result of diligent investigation on this problem, the present inventors optimized the crystal structure of the pellets, thereby controlling the temperature difference between the melting point range and the melting point peak, and fusing the pellets in the melt plasticization process during molding. The inventors have found a technique for suppressing the phenomenon and melt-plasticizing the pellet more quickly at a low temperature, and have completed the present invention.

  The polyethylene terephthalate resin pellet of the present invention can be molded at a low temperature in melt molding such as injection molding or extrusion molding when molding a hollow container, and the production amount of by-products such as acetaldehyde can be reduced.

Hereinafter, a method for producing a polyethylene terephthalate resin according to the present invention and a method for molding a hollow molded body will be specifically described.

(Method for producing polyethylene terephthalate resin)
The polyethylene terephthalate resin of the present invention uses terephthalic acid or an ester-forming derivative thereof and ethylene glycol or an ester-forming derivative thereof as raw materials, and further includes a dicarboxylic acid component excluding terephthalic acid phthalic acid and a glycol component excluding ethylene glycol. A total of 1.5 to 6.0 mol% copolymerized polyester resin is used as the monomer unit. The total amount of the comonomer may be in the range of 1.5 to 6.0 mol%, but it is preferable to use one of the dicarboxylic acid component or the glycol component. It is preferable to use aromatic as the dicarboxylic acid and aliphatic as the glycol component.
When the amount of the copolymerization monomer is 6.0 mol% or less, the crystallinity is moderately high, so that the crystallization rate of the pellets does not decrease in the solid phase polymerization process, and the pellets are used in the solid phase polymerization process and the molding process. It is preferable because mutual fusion is difficult to occur. When the amount of the copolymerization monomer is 1.5 mol% or more, the melting point is appropriately lowered, and therefore, melt molding is possible at a temperature at which no by-product is generated, which is preferable.

  Specific examples of the aromatic dicarboxylic acid other than terephthalic acid include isophthalic acid, naphthalene dicarboxylic acid, diphenyldicarboxylic acid, diphenoxyethanedicarboxylic acid, and the like. The amount of copolymerization is preferably from 0.5 mol% to 5.0 mol%, more preferably from 1.0 mol% to 3.0 mol%, from the viewpoint of resin productivity. When the copolymerization amount of isophthalic acid is 5.0 mol% or less, it is preferable because the crystallinity is high, so that the crystallization rate of the pellet does not decrease in the solid phase polymerization step, and in the solid phase polymerization process and the molding process. It is preferable because fusion between pellets hardly occurs.

  Specific examples of the aliphatic diol other than ethylene glycol include diethylene glycol, trimethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, and dodecamethylene glycol, and the copolymerization amount thereof is aliphatic. The diol is preferably 3.0 mol% or less. A copolymerization amount of 3.0 mol% or less is preferable for the same reason as in the case of the dicarboxylic acid copolymerization.

The pellet made of the polyethylene terephthalate resin of the present invention has an intrinsic viscosity (IV) in the range of 0.70 dl / g to 1.10 dl / g. When the intrinsic viscosity is in the same range, it is preferable because moldability during injection molding or hollow molding is improved. The intrinsic viscosity was calculated from the solution viscosity measured at 25 ° C. after cooling and dissolving 0.5 g of polyethylene terephthalate resin in 100 cc of a mixed solution of tetrachloroethane / phenol = 50/50 (wt% / wt%). .

  The pellet made of the polyethylene terephthalate resin of the present invention has a density in the range of 1390 to 1410 kg / m 3. When the density is in the same range, it is preferable because the mechanical strength and heat resistance of the hollow body obtained by molding become good. The density is measured according to JISK-7112-1980. The density can be adjusted by changing the degree of crystallinity with the time of precrystallization and / or solid phase polymerization.

Pellets of polyethylene terephthalate resin of the present invention, the shown difference scanning calorimeter, one or two Tsude melting peaks detected from 30 ° C. at a heating rate 10 ° C. / min when the temperature was raised to 290 ° C. Yes,
When there is one melting peak, the peak temperature Tm is 220 ° C. or higher,
When there are two melting peaks, when the melting peak temperature on the low temperature side is Tm1 and the melting peak temperature on the high temperature side is Tm2, Tm1 is 220 ° C. or higher, and Tm2-Tm1 is greater than 0 ° C. and 15 ° C. It is in the following range.

One melting peak or two melting peaks with a temperature difference of 15 ° C. or less is preferable because the pellets hardly adhere to each other during molding and plasticization proceeds rapidly. In view of moldability, it is particularly preferred that there is one melting peak.
The temperature and temperature difference of the melting peak can be adjusted by the precrystallization temperature and the solid-state polymerization temperature as described later.

The raw material containing the aromatic dicarboxylic acid or the ester-forming derivative thereof and the aliphatic diol or the ester-forming derivative thereof as described above is esterified. Specifically, first, a slurry containing an aromatic dicarboxylic acid or an ester-forming derivative thereof and an aliphatic diol or an ester-forming derivative thereof is prepared.
In this slurry, 1.02-1.4 mol, preferably 1.03-1.3 mol of an aliphatic diol or an ester-forming derivative thereof is added to 1 mol of an aromatic dicarboxylic acid or an ester-forming derivative thereof. included. This slurry is continuously supplied to the esterification reaction step.

  The esterification reaction is preferably carried out using an apparatus in which two or more esterification reactors are connected in series under conditions where the aliphatic diol is refluxed while removing water generated by the reaction out of the system using a rectification column. To be implemented. The reaction conditions for carrying out the esterification reaction are such that the temperature of the first stage esterification reaction is usually 240 to 270 ° C., preferably 245 to 265 ° C., and the pressure is usually 0.2 to 3 kg / cm 2 G, Preferably, it is 0.5-2 kg / cm 2 G, the temperature of the esterification reaction in the final stage is usually 250-280 ° C., preferably 255-275 ° C., and the pressure is usually 0-1.5 kg / cm 2 G, preferably Is 0 to 1.3 kg / cm @ 2 G.

  When the esterification reaction is carried out in two stages, the esterification reaction conditions of the first stage and the second stage are within the above ranges, respectively, and when carried out in three stages or more, the second stage The reaction conditions for the esterification reaction up to one stage before the final stage are conditions between the reaction conditions of the first stage and the reaction conditions of the final stage.

For example, when the esterification reaction is carried out in three stages, the reaction temperature of the second stage esterification reaction is usually 245 to 275 ° C., preferably 250 to 270 ° C., and the pressure is usually 0 to 2 kg / cm 2 G, preferably 0.2 to 1.5 kg / cm 2 G. The reaction rate of these esterification reactions is not particularly limited in each stage, but it is preferable that the degree of increase in the esterification reaction rate in each stage is smoothly distributed, and further the esterification in the final stage. In the reaction product, it is usually 90% or more, preferably 93% or more.

By these esterification steps, an esterified product (low-order condensate) is obtained, and the number average molecular weight of the esterified product is usually 500 to 5,000. Such an esterification reaction can be carried out without adding additives other than aromatic dicarboxylic acids and aliphatic diols, and can also be carried out in the presence of a polycondensation catalyst described later. .
Tertiary amines such as triethylamine, tri-n-butylamine, and benzyldimethylamine; quaternary ammonium hydroxides such as tetraethylammonium hydroxide, tetra-n-butylammonium hydroxide, and trimethylbenzylammonium hydroxide; lithium carbonate, sodium carbonate It is preferable to add a small amount of a basic compound such as potassium carbonate or sodium acetate because the proportion of dioxyethylene terephthalate component units in the main chain of the polyethylene terephthalate resin can be maintained at a relatively low level.

  Next, the obtained esterified product is supplied to a liquid phase polycondensation step. In this liquid phase polycondensation step, heating is performed at a temperature equal to or higher than the melting point of the resulting polyethylene terephthalate resin under reduced pressure in the presence of a polycondensation catalyst, and the resulting glycol is distilled out of the system to remove the esterified product. To condense.

  Such a polycondensation reaction in the liquid phase may be performed in one stage or may be performed in a plurality of stages. When the reaction is conducted in a plurality of stages, the polycondensation reaction conditions are such that the reaction temperature of the first stage polycondensation is usually 250 to 290 ° C, preferably 260 to 280 ° C, and the pressure is usually 500 to 20 Torr, preferably Is 200 to 30 Torr, the temperature of the final polycondensation reaction is usually 265 to 300 ° C., preferably 270 to 295 ° C., and the pressure is usually 10 to 0.1 Torr, preferably 5 to 0.5 Torr. .

  When the polycondensation reaction is carried out in two stages, the first and second stage polycondensation reaction conditions are within the above ranges, respectively, and when carried out in three or more stages, the second stage The reaction conditions of the polycondensation reaction up to the first stage before the last stage are conditions between the reaction conditions of the first stage and the reaction conditions of the last stage.

  For example, when the polycondensation reaction is carried out in three stages, the reaction temperature of the second stage polycondensation reaction is usually 260 to 295 ° C., preferably 270 to 285 ° C., and the pressure is usually 50 to 2 Torr. The range is preferably 40 to 5 Torr. The intrinsic viscosity (IV) reached in each of these polycondensation reaction steps is not particularly limited, but it is preferable that the degree of increase in intrinsic viscosity at each stage is smoothly distributed. The intrinsic viscosity of the polyester obtained from the final stage polycondensation reactor is usually 0.45 to 0.75 dl / g, preferably 0.55 to 0.65 dl / g.

  In the present specification, the intrinsic viscosity is a solution viscosity measured at 25 ° C. after cooling and dissolving 0.5 g of polyester in 100 cc of a mixed solution of tetrachloroethane / phenol = 50/50 (wt% / wt%). Is calculated from

  The polycondensation reaction as described above is performed in the presence of a polycondensation catalyst such as a germanium-based compound described in JP-A-3-72524, an antimony-based compound, or a titanium-based compound described in, for example, WO 03/72633. To be implemented.

Further, a cobalt compound or a magnesium compound may be added as a co-catalyst compound, and the addition location may be added to the reactor in the esterification reaction step, or the first stage of the liquid phase polycondensation reaction step. It can also be added to the reactor.
In this way, the polyester obtained from the final polycondensation reactor is usually formed into pellets (chips) by a melt extrusion molding method.

  Such granular polyethylene terephthalate resin has an average cut surface diameter of usually 1.0 to 4.0 mm, preferably 1.5 to 3.0 mm. Moreover, it is preferable that the height of a longitudinal direction is 1.5 mm-4.0 mm normally, Preferably it is 2.0 mm-3.5 mm. The granular polyester thus subjected to the liquid phase polycondensation step is supplied to the solid phase polymerization step as desired.

  The polyethylene terephthalate pellet of the present invention has one melting peak measured by DSC or two melting peaks having a temperature difference of 15 ° C. or less. It is particularly preferable that the melting point is one. The value of the microcrystal size L in the polyethylene terephthalate resin is desirably 60 to 70 cm. In order to produce polyethylene terephthalate pellets having such characteristics, it is preferable to perform the following precrystallization step and solid phase polymerization step.

First, polyethylene terephthalate resin pellets are preliminarily crystallized by heating to a temperature lower than the temperature for solid phase polymerization, and then charged into a reaction vessel.
Such a precrystallization step is preferably carried out at a temperature of 110 to 200 ° C., preferably 120 to 180 ° C., more preferably 130 to 150 ° C. with the granular polyester in a dry state. The time is in the range of 10 minutes to 4 hours.

  The solid-state polymerization temperature is 200 to 230 ° C, preferably 205 to 225 ° C, more preferably 210 to 220 ° C. If the precrystallization temperature is too high or the solid state polymerization temperature is too low, the crystallite size in the polyethylene terephthalate solid structure will be small and the melting of the polyethylene terephthalate resin will start at a relatively low temperature. Therefore, the melting point Tm1 on the low temperature side detected from the DSC may decrease, and the difference from the melting point Tm2 on the high temperature side may exceed 15 ° C. In addition, you may perform precrystallization by heating a pellet to the temperature of 120-200 degreeC for 1 minute or more in water vapor | steam atmosphere, water vapor | steam containing inert gas atmosphere, or water vapor | steam containing air atmosphere.

The value of the microcrystal size L1 and L2 in the polyethylene terephthalate resin is desirably 60 to 70 cm. If the crystallite size is less than 60 mm , the melting point Tm1 on the low temperature side decreases, and if the difference in the melting point Tm2 on the high temperature side is large and exceeds 15 ° C, the fusion phenomenon between pellets on the screw tends to occur and low temperature molding becomes difficult. May be. On the other hand, when the value of the microcrystal size is larger than 70 mm, the melting points Tm1 and Tm2 become too high, and conversely, the energy necessary for melting increases and low temperature molding may become difficult.
The values of the microcrystal sizes L1 and L2 can be adjusted from 60 to 70 by performing the preliminary crystallization process and the solid-phase polymerization process at the temperature described above. If the precrystallization temperature is too high, the crystallite size may be less than 60 mm.

Crystallite size, determined long period by small-angle X-ray scattering measurement of the pellets, calculated by multiplying the value of the period obtained ChoAmane crystallinity of pellets (crystal parts). The crystallinity is calculated from the measured density of the pellet and the crystal density and amorphous density of the polyethylene terephthalate resin. A specific method will be described in the section of Examples.

The solid phase polycondensation step in which such granular polyester is supplied comprises at least one stage, and the polycondensation temperature is usually 200 to 230 ° C, preferably 205 to 225 ° C, more preferably 210 ° C to 220 ° C, The solid phase polycondensation reaction is carried out under an inert gas atmosphere such as nitrogen gas, argon gas, carbon dioxide gas, etc., under a pressure of usually 1 kg / cm 2 G to 10 Torr, preferably normal pressure to 100 Torr. Of these inert gases, nitrogen gas is preferred.
If the solid-phase polymerization temperature is higher than the above, the pellets are in a semi-molten state, causing a fusing phenomenon between the pellets, impairing the productivity of the resin, and the density, Tm2, and crystal size are increased and the plasticization is worse. Cause problems.

The polyethylene terephthalate resin pellet of the present invention can be used as a raw material for various molded products. For example, it is melt-molded and used for hollow containers such as bottles, sheets, films, fibers, etc., but used for hollow containers. Is preferred.
According to the present invention, a conventionally known method can be adopted as a method for forming a hollow container, a sheet, a film, a fiber or the like from polyethylene terephthalate resin pellets.

(Method of forming a hollow container made of polyethylene terephthalate resin)
The polyethylene terephthalate resin pellets of the present invention have a low molding temperature in melt molding such as injection molding and extrusion molding, and therefore there are few by-products such as acetaldehyde in the molded product, for example, preforms and hollow container materials.
As a method for forming a hollow container, the hollow container is generally formed by two steps of injection molding and blow molding.

First, the polyethylene terephthalate resin pellet is adjusted to a moisture content of 50 ppm or less by dehumidifying air drying. Next, the preform is supplied to a molding machine such as an injection molding machine to form a preform called a preform. In this step, the pellet is put into a cylinder on which a screw is mounted, and the resin is plasticized (melted) by rotating the screw, then injected into a mold, cooled, solidified, and taken out to obtain a preform.
This preform is then fed to a blow molding machine. The blow molding machine comprises two steps, a heating step and a blowing step. In the heating step, the preform is heated to a predetermined temperature using, for example, an infrared heater to soften the material. Next, the heated preform is transferred to a blow process, inserted into a mold having a predetermined shape, stretch blow-molded with a rod called a stretch rod and high-pressure air, and taken out from the mold to form a hollow container. Normally, blow molding is a molding system that performs heating and blow continuously.

  There are two major blow molding methods. When molding a non-heat-resistant hollow container, the heated preform is blow-molded in a mold and immediately taken out from the mold. On the other hand, the heat-resistant hollow container relaxes the distortion generated at the time of blowing (stretching) and imparts heat resistance by a technique called heat setting by adjusting the mold temperature to a high temperature of 130 ° C. or higher.

(Example)
EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

(Manufacture of polyester)
A slurry composed of a dicarboxylic acid and a glycol component was continuously supplied to the reactor, and an esterification reaction was performed under a condition of 260 ° C. and 0.9 kg / cm 2 -G under stirring and a nitrogen atmosphere. As the dicarboxylic acid component, terephthalic acid and isophthalic acid were supplied at a total rate of 6458 parts by weight / hour, and as the glycol component, ethylene glycol was supplied at a rate of 2615 parts by weight / hour. The copolymerization amount of isophthalic acid is shown in Table 1. The conditions were such that 33500 parts by weight of the slurry and the reaction product remained in the reactor during steady operation.

In the esterification reaction, a mixed solution of water and ethylene glycol was distilled off. The esterification reaction product (low-order condensate) was continuously extracted out of the system while controlling the average residence time to be 3.5 hours.
The number average molecular weight of the low-order polycondensate of ethylene glycol and terephthalic acid obtained above was 600 to 1300 (3 to 5 mer).

A catalyst solution in which antimony acetate was dissolved in ethylene glycol was added to the low-order condensate thus obtained, and a liquid phase polycondensation reaction was performed under the conditions of 285 ° C. and 1 torr.
The time required for the intrinsic viscosity of the obtained amorphous polyethylene terephthalate to reach 0.60 dl / g was 60 minutes.
Further, this polyethylene terephthalate resin pellet was precrystallized at 130 ° C., and then solid phase polycondensation was performed at 217 ° C. in the presence of circulating nitrogen gas. The intrinsic viscosity of the obtained polyethylene terephthalate was 0.80 dl / g.

(Measurement of intrinsic viscosity (IV))
The intrinsic viscosity is calculated from the solution viscosity measured at 25 ° C. after cooling and dissolving 0.5 g of polyethylene terephthalate resin pellets in 100 cc of a mixed solution of tetrachloroethane / phenol = 50/50 (wt% / wt%). did.

(Density measurement)
The density was measured using a density gradient tube based on JIS K-7112-1980. The density gradient solution was adjusted to 1360 kg / m3 to 1411 kg / m3 by adjusting and mixing light and high density solutions using zinc chloride, hydrochloric acid, and water, respectively.
The sample is wetted with methanol and then gently placed in a gradient tube and the reading is taken after 120 minutes. The value is rounded to the fourth digit by rounding the fifth significant digit according to JIS Z8401. At least two samples were prepared and measured, and the average value was taken as the measured value. The measured value difference between samples was 1 kg / m 3 or less.

(Measurement of melting point)
The polyethylene terephthalate resin pellet was vacuum-dried at 150 ° C. for 5 hours, and then the cut surface of the pellet was removed with a razor blade to collect the central portion. The dried pellet was heated from 30 ° C. to 290 ° C. at a rate of 10 ° C./min using a differential scanning calorimeter (DSC manufactured by Perkin Elmer). The temperature at which the crystal melts (melting peak temperature on the low temperature side) was Tm1, and the temperature at which the primary structure (amorphous) melted (melting peak temperature on the high temperature side) was Tm2. In this example, Tm1 was 24 2 ° C and Tm2 was 25 2 ° C.

(Measurement of crystallite size (L1))
Using an X-ray diffractometer (high-resolution small-angle X-ray scatterer manufactured by Rigaku Corporation), one pellet was attached to a holder for measurement. The microcrystal size (L1) was obtained by multiplying the obtained value (long period) by the crystallinity of the pellet (ratio of crystal part) obtained by the following formula. The results are shown in Table 1.
Crystallinity = 1455 × (density of pellet—1335)
/ (Density of pellet × (1455-1335))
1335 (kg / m3): Amorphous density of polyethylene terephthalate resin 1455 (kg / m3): Crystal density of polyethylene terephthalate resin

(Measurement of microcrystal (L2) size)
A mixed liquid (50% by weight / 50% by weight) of hexafluoroisopropanol and chloroform was prepared, and 100 g of pellets were put therein. After leaving the pellet in the mixed solution for 2 hours, the pellet and the mixed solution were separated using a funnel and filter paper. The pellets were dried in an incubator at 50 ° C. under a nitrogen stream. For the dried pellets, the crystallite size (L2) was determined by the same calculation method as L1 using an X-ray diffractometer (manufactured by Rigaku Corporation, high resolution small angle X-ray scattering device). The results are shown in Table 1.

(Observation of pellet fusion)
The polyethylene terephthalate resin pellets were dried for 4 hours using dehumidified air at 170 ° C., and the water content was adjusted to 50 ppm or less. Next, a Ti-80G2 injection molding machine manufactured by Toyo Kikai Kogyo Co., Ltd. was used, and an apparatus capable of observing the inside of the cylinder with a quartz glass window attached to the cylinder was used. The cylinder was set at a temperature of 250 ° C. and the rotation speed of the screw was set at 90 rpm. Molding was performed, and the plasticizing state of the pellets while the screw was rotating was visually observed from the quartz glass window.

(Measurement of plasticization lower limit temperature)
The polyethylene terephthalate resin pellets were dried for 4 hours using dehumidified air at 170 ° C., and the water content was adjusted to 50 ppm or less. The dried pellets were put into an LX160PET injection molding machine manufactured by Husky, and molding was carried out at a cylinder set temperature of 280 ° C. and a screw rotation speed of 24 rpm. Observe the appearance of the preform at that time, confirm the presence or absence of unmelted whitened material, and if no whitening is observed, reduce the set temperature of the cylinder by 3 ° C, perform molding, and then confirm whether the preform is whitened again did. In this example, since a whitened product was recognized for the first time at 264 ° C., the minimum plasticization temperature was 267 ° C.

(Measurement of acetaldehyde content)
Weigh 2.0 g of sample and freeze-grind using a freezer mill. The ground sample is put into a vial bottle purged with nitrogen, and further an internal standard substance (acetone) and water are added and sealed. The vial was heated with a dryer at 120 ± 2 ° C. for 1 hour, and then the supernatant was injected into a gas chromatography and measured. The results are shown in Table 1.

  Polyethylene terephthalate resin pellets and preforms were obtained in the same manner as in Example 1 except that the solid-state polymerization temperature was 220 ° C. The results are shown in Table 1.

(Comparative Example 1)
Polyethylene terephthalate resin pellets and preforms were obtained in the same manner as in Example 1 except that the precrystallization temperature was 170 ° C. and the solid-state polymerization temperature was 220 ° C. The results are shown in Table 1.

(Comparative Example 2)
Polyethylene terephthalate resin pellets and preforms were obtained in the same manner as in Example 1 except that the precrystallization temperature was 170 ° C. and the solid-state polymerization temperature was 210 ° C. The results are shown in Table 1.

Claims (4)

Pellets made of polyethylene terephthalate resin,
(A) A dicarboxylic acid component excluding terephthalic acid and a glycol component excluding ethylene glycol are contained in a total amount of 1.5 to 6.0 mol% as a comonomer unit,
(B) the intrinsic viscosity (IV) is in the range of 0.70 dl / g to 1.10 dl / g,
(C) density there from 1390kg / m ³ in the range of 1410kg / m ^3,
(D) The microcrystal size of the pellet measured by small-angle X-ray is L1, and the pellet is left in a 50/50 wt% mixture of hexafluoroisopropanol and chloroform for 2 hours. When the measured crystallite size is L2, the values of L1 and L2 are both in the range of 60 to 70 mm.
Polyethylene terephthalate resin pellets characterized by that.   A molded article or preform obtained by melt-molding the polyethylene terephthalate resin pellets according to claim 1.   A hollow container obtained by blow molding the polyethylene terephthalate resin pellet according to claim 1. It is a manufacturing method of the polyethylene terephthalate resin pellet according to claim 1,
Polyethylene terephthalate resin pellets obtained by subjecting polyethylene terephthalate resin pellets obtained through the liquid phase polycondensation step to pre-crystallization at 110 to 150 ° C. and further to solid-phase polymerization at 210 to 230 ° C. Production method.