JPH0764920B2 - polyethylene terephthalate - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a polyethylene terephthalate used for forming a film, a sheet, etc., including a bottle, and more specifically, a polyethylene terephthalate which is less likely to cause mold stains during molding and the polyethylene terephthalate. The present invention relates to a preform made of polyethylene terephthalate, a stretched hollow molded article, and an injection molded product.

TECHNICAL BACKGROUND OF THE INVENTION AND ITS PROBLEMS Conventionally, various resins have been adopted as materials for containers such as seasonings, oils, beverages, cosmetics and detergents according to the type of filling contents and the purpose of use thereof. .

Among these, polyethylene terephthalate is excellent in mechanical strength, heat resistance, transparency and gas barrier property, and is therefore particularly suitable as a material for a beverage filling container such as juice, soft drink, carbonated drink and the like.

Such polyethylene terephthalate is supplied to a molding machine such as an injection molding machine to mold a preform for a hollow molded body, and the preform is inserted into a mold having a predetermined shape, stretch blow molded, and then heat treated (heat set). It is then generally molded into a hollow molded container.

However, conventional polyethylene terephthalate contains oligomers such as a cyclic trimer, and the oligomers such as the oligomers adhere to the inner surface of the mold, the gas exhaust port of the mold, and the exhaust pipe. It was easy to occur.

Such mold stains cause the surface roughness and whitening of the obtained bottle. If the bottle becomes white, it must be discarded. For this reason, when molding a bottle using a conventionally known polyethylene terephthalate, it is necessary to frequently remove mold stains, resulting in a serious problem that the productivity of the bottle is significantly reduced.

In view of the above-mentioned circumstances, the inventors of the present invention have earnestly studied in order to obtain polyethylene terephthalate that is less likely to cause mold fouling during molding, and the main cause of mold fouling during molding is molding of polyethylene terephthalate. It has been found that at times, a large amount of oligomers such as cyclic trimers is produced, and the total amount of oligomers such as cyclic trimers contained in polyethylene terephthalate increases.

The present inventors further studied based on the above findings, and the oligomer content of the molded product obtained by injection molding after water-treating polyethylene terephthalate used for molding under specific conditions is set to W _1. , W ₀ -W ₁ whereas the oligomer content of the molded article obtained by directly injection molding the polyethylene terephthalate used for molding the case of the W ₀
It was found that the mold is less likely to be soiled during the molding when the value is within the specific range, and the present invention has been completed.

Incidentally, JP-A-69-25815 discloses a method of treating polyethylene terephthalate powder or granules with heated steam at 110 ° C. or higher in order to crystallize polyethylene terephthalate prior to solid-phase polycondensation of polyethylene terephthalate. It is disclosed.

Further, JP-A-59-219328 discloses that a polyester having an ethylene terephthalate unit as a main repeating unit having an intrinsic viscosity of at least 0.4 dl / g or more and a density of 1.35 g / cm ³ or less has a moisture content of Step of adjusting the humidity to at least 0.2% by weight, step of pre-crystallization at a temperature of 140 ° C or higher, and step of solid-state polymerization at a temperature of 180 ° C to 240 ° C in an inert gas atmosphere or under reduced pressure A method for producing a high-polymerization polyester, which comprises:

An object of the present invention is to solve the problems associated with the prior art as described above, in which a small amount of oligomers such as a cyclic trimer is produced during molding, which causes mold fouling. An object of the present invention is to provide polyethylene terephthalate that is difficult to prevent, a preform made of the polyethylene terephthalate, a stretched hollow molded article, and an injection molded article. Needless to say, the present invention can also be used to eliminate stains due to oligomers such as cyclic trimers for forming films and sheets other than bottles.

SUMMARY OF THE INVENTION Polyethylene terephthalate according to the present invention has an intrinsic viscosity of 0.70 dl / g or more and a density of 1.37 g / cm ³ or more, and an oligomer content of 0.5 wt% or less, and the polyethylene terephthalate As it is 29
The molded product obtained by injection molding at a molding temperature of 0 ° C. has an oligomer content of W ₀ % by weight, while the polyethylene terephthalate is immersed in hot water at a temperature of 95 ° C. for 8 hours and then dried, and then When the oligomer content of the molded product obtained by injection molding is W ₁ % by weight, W ₀ -W ₁ is 0 to 0.10% by weight.

Further, the preform, stretched hollow molded article and injection molded article according to the present invention are characterized by being made of such polyethylene terephthalate.

The polyethylene terephthalate according to the present invention has the oligomer content of a molded product obtained by injection molding the polyethylene terephthalate as it is at a molding temperature of 290 ° C.
W of ₀ % by weight, while the polyethylene terephthalate was immersed in hot water at a temperature of 95 ° C. for 8 hours, dried, and then injection-molded as described above to obtain an oligomer content of W ₁ % by weight. In that case, since W ₀ -W ₁ is 0 to 0.10% by weight, the amount of oligomers such as a cyclic trimer produced at the time of molding is small, and therefore mold stains are less likely to occur.

Specific Description of the Invention The polyethylene terephthalate according to the present invention will be specifically described below.

The polyethylene terephthalate according to the present invention has a specific intrinsic viscosity and density as described below, and has an oligomer content of 0.5% by weight or less, and moreover, the polyethylene terephthalate is directly injection-molded at a molding temperature of 290 ° C. The oligomer content of the obtained molded product was set to W ₀ % by weight, while the polyethylene terephthalate was heated to 95%.
When the oligomer content of the molded product obtained by immersing in hot water of ℃ for 8 hours and then drying, and then injection molding as described above is W ₁ % by weight, W ₀ -W ₁ is 0 to 0. It is 0.10% by weight.

Thus, the W ₀ -W ₁ of polyethylene terephthalate is 0 to
When it is 0.10% by weight, when a molded product is obtained by using this polyethylene terephthalate, it is difficult to generate an oligomer, and therefore, it is possible to effectively prevent mold stains from occurring.

In the present invention, polyethylene terephthalate is injection-molded to produce a molded article, and the content of oligomer contained in this molded article is measured. Here, the production of a molded product whose oligomer content is measured will be described first.

First, granular polyethylene terephthalate 2k as raw material
g is dried at a temperature of 140 ° C. and a pressure of 10 torr for 16 hours or more using a tray dryer to reduce the water content of granular polyethylene terephthalate to 50 ppm or less.

Next, the dried granular polyethylene terephthalate was molded by an M-70A injection molding machine manufactured by Meiki Seisakusho Co., Ltd. at the time of molding with nitrogen having a dew point of −70 ° C. at the upper part of the hopper and the screw feeder chute part of 5 normal cubic meters / hour each Feed in a ratio and set the barrel set temperature to 290 ℃, and the temperature of the C1 / C2 / C3 / nozzle tip of the molding machine to 260/290/290/300 ℃, and the mold cooling temperature to 15 ℃. Injection molding,
A stepped rectangular plate-shaped molded product is obtained.

Injection molding of a stepped rectangular plate-shaped molded article is performed by supplying dried granulated polyethylene terephthalate from a popper to an injection molding machine in such a manner that the weighing is 12 seconds and the injection is 60 seconds. The residence time of the molten resin in the molding machine is about 72 seconds. The weight of each stepped rectangular plate-shaped molded product is 75 g, and any one of the 11th to 15th oligomer measurement samples is used after the start of injection molding.

The stepped rectangular plate-shaped molded product 1 has a shape as shown in FIG. 1, the thickness of the A portion is about 6.5 mm, and the thickness of the B portion is about 5 mm.
mm, and the thickness of part C is about 4 mm. Using this part C, the amount of increase in the oligomer of the molded product is examined.

Next, the molded plate-shaped product having a thickness of 4 mm is cut into chips, and the amount of oligomer is measured as a sample for measuring oligomer.

Moreover, the amount of the oligomer contained in the polyethylene terephthalate molded body is measured as follows.

That is, a predetermined amount of a sample for oligomer measurement was dissolved in o-chlorophenol, reprecipitated with tetrahydrofuran and filtered to remove linear polyethylene terephthalate, and then the obtained filtrate was subjected to liquid chromatography (Shimadzu LC7A ) To obtain the amount of oligomer contained in polyethylene terephthalate, and divide this value by the amount of polyethylene terephthalate used in the measurement to obtain the amount of oligomer contained in polyethylene terephthalate (% by weight).
And

The polyethylene terephthalate according to the present invention as described above can be produced, for example, as follows.

The polyethylene terephthalate according to the present invention is produced by using terephthalic acid or its ester-forming derivative and ethylene glycol or its ester-forming derivative as raw materials. This polyethylene terephthalate contains 20 mol% or less of other dicarboxylic acid and / or Alternatively, another glycol may be copolymerized.

Specific examples of the dicarboxylic acid used in the copolycondensation other than terephthalic acid include aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, diphenoxyethane dicarboxylic acid, adipic acid, sebacic acid. And aliphatic dicarboxylic acids such as azelaic acid and decanedicarboxylic acid, and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid.

Specific examples of glycols used for copolycondensation other than ethylene glycol include trimethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, dodecamethylene glycol and other aliphatic glycols, cyclohexanedimethanol and the like. Alicyclic glycols, bisphenols, hydroxone, and aromatic diols such as 2,2-bis (4-β-hydroxyethoxyphenyl) propane.

A raw material containing terephthalic acid or its ester-forming derivative as described above and ethylene glycol or its ester-forming derivative is esterified in the presence of an esterification catalyst, and then liquid phase in the presence of a polymerization catalyst. After the polymerization, solid phase polymerization is performed.

As the method for producing polyethylene terephthalate according to the present invention, either a batch method or a continuous method may be adopted. However, an example of a preferable production method will be described below. Specifically, first, terephthalic acid or its ester forming property is described. A slurry containing the derivative and ethylene glycol or an ester-forming derivative thereof is prepared.

Such a slurry contains 1.02 to 1.4 mol, preferably 1.03 to 1.3 mol, of ethylene glycol or its ester-forming derivative with respect to 1 mol of terephthalic acid or its ester-forming derivative. This slurry is continuously supplied to the esterification reaction step.

The esterification reaction is carried out under a condition in which ethylene glycol is refluxed by using a device in which at least two esterification reactors are connected in series, while removing water generated by the reaction from the system in a rectification column. . The reaction conditions for carrying out the esterification reaction are that the temperature of the first step 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 0.5 to ² kg / cm ² , the temperature of the final stage esterification reaction is usually 250 to 280 ° C., preferably 255 to 275 ° C., and the pressure is usually 0 to 1.5 kg. / cm ² G It is preferably 0 to 1.3 kg / cm ² G.

Therefore, 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 or more stages, the second stage is carried out. The reaction conditions for the esterification reaction from the first stage to the stage immediately before the final stage are those 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 for the esterification reaction in the second stage is usually 245-2.
75 ℃ is preferably 250 ~ 270 ℃, the pressure is usually 0 ~ 2kg /
cm ² G It is 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 increase and the degree of the esterification reaction rate in each stage be smoothly distributed. 90 in the reaction product
% Or more, preferably 93% or more.

A low-order condensate is obtained by these esterification steps, and the number-average molecular weight of the low-order condensate is usually 500 to 5000.

Such an esterification reaction can be carried out without adding an additive other than terephthalic acid and ethylene glycol, or can be carried out in the coexistence of a polycondensation catalyst which will be described later. , Tri-n-butylamine, benzyldimethylamine, etc.
Add a small amount of a quaternary ammonium hydroxide such as a tertiary amine, tetraethylammonium hydroxide, tetra-n-butylammonium hydroxide or trimethylbenzylammonium hydroxide and a basic compound such as lithium carbonate, sodium carbonate, potassium carbonate or sodium acetate. Is preferable because the proportion of the dioxyethylene terephthalate component unit in the main chain of polyethylene terephthalate can be maintained at a relatively low level.

Then, the obtained low-order condensate is heated under reduced pressure in the presence of a polycondensation catalyst to a temperature equal to or higher than the melting point of the obtained polyethylene terephthalate, and the glycol produced at this time is distilled out of the system to perform polycondensation. It is supplied to the liquid phase condensation polymerization process.

Such a polycondensation reaction in the liquid phase may be carried out in one step or in a plurality of steps. When carried out 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 200 to 30 Torr, and the temperature of the final polycondensation reaction is usually 265-300.
℃ is preferably 275 ~ 295 ℃, the pressure is usually 10 ~ 0.1 Tor
r It is preferably 5 to 0.5 Torr.

When the polycondensation reaction is carried out in two stages, the polycondensation reaction conditions in the first and second stages are in the above ranges, respectively, and when carried out in three or more stages, from the second stage The reaction conditions of the polycondensation reaction up to the first stage before the final stage are those between the reaction conditions of the first stage and the reaction conditions of the final 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, 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 the intrinsic viscosity at each stage is distributed smoothly. The intrinsic viscosity (IV) of polyethylene terephthalate obtained from the reactor is usually 0.35 to 0.80 dl / g, preferably 0.
It is desirable that the range is 45 to 0.75 dl / g, and more preferably 0.55 to 0.75 dl / g.

In this specification, the intrinsic viscosity is calculated from the solution viscosity measured at 25 ° C. after dissolving 1.2 g of polyethylene terephthalate in 15 cc of o-chlorophenol by heating and cooling.

The polycondensation reaction is preferably carried out in the presence of a catalyst and a stabilizer. As the catalyst, germanium compounds such as germanium dioxide, germanium tetraethoxide and germanium tetra n-butoxide, antimony catalysts such as antimony trioxide and titanium catalysts such as titanium tetrabutoxide can be used. Among these catalysts, the use of a germanium dioxide compound is preferable because the produced polyethylene terephthalate has excellent hue and transparency. Further, as the stabilizer, trimethyl phosphate, triethyl phosphate, tri-n-
Butyl phosphate, trioctyl phosphate, triphenyl phosphate, tricresyl phosphate and other phosphoric acid esters, triphenyl phosphite, trisdodecyl phosphate, trisnonyl phenyl phosphite and other phosphorous acid esters, methyl assid phosphate, isopropyl Acid phosphates such as acid phosphate, butyl acid phosphate, dibutyl phosphate, monobutyl phosphate and dioctyl phosphate, and phosphorus compounds such as phosphoric acid and polyphosphoric acid are used. The proportion of these catalysts or stabilizers used is usually 0.0005 to 0.2% by weight, preferably 0.001 to 0.05% by weight, as polymerization of the metal in the catalyst in the case of a catalyst, with respect to the polymerization of a mixture of terephthalic acid and ethylene glycol. In the case of a stabilizer, the weight of phosphorus atoms in the stabilizer is usually 0.001 to 0.1% by weight, preferably 0.002 to 0.02% by weight. The catalyst and the stabilizer may be supplied at the stage of the esterification reaction step or may be supplied to the reactor at the first stage of the polycondensation reaction step.

The polyethylene terephthalate used in the present invention may contain a dicarboxylic acid other than terephthalic acid or a diol other than ethylene glycol in an amount of 20 mol% or less as described above, but polyethylene terephthalate particularly preferably used in the present invention Is a general formula [1] The content of the ethylene terephthalate component unit (a) represented by the formula (I) is in the range of 95.0 to 99.0 mol%,
I] The content of the dioxyethylene terephthalate component unit (b) represented by is preferably in the range of 1.0 to 5.0 mol%.

The polyethylene terephthalate obtained in such a liquid phase polycondensation step is usually formed into particles (chip shape) by a melt extrusion molding method.

Such granular polyethylene terephthalate is usually 2.
It is desirable to have an average particle size of 0-5.0 mm, preferably 2.2-4.0 mm.

The density of polyethylene terephthalate obtained from the final polycondensation reactor is usually 1.33 to 1.35 g / cm ³ .

In the present specification, the density is measured at a temperature of 23 ° C. by a density gradient tube using a mixed solvent of carbon tetrachloride and heptane.

The granular polyethylene terephthalate obtained as described above is supplied to the solid phase polycondensation step.

The granular polyethylene terephthalate supplied to the solid-phase polymerization step may be heated to a temperature lower than the temperature used for solid-phase polycondensation in advance to carry out pre-crystallization, and then supplied to the solid-phase polycondensation step.

The pre-crystallization step can also be carried out by heating the granular polyethylene terephthalate in a dry state, usually at a temperature of 120 to 200 ° C., preferably 130 to 180 ° C. for 1 minute to 4 hours, or alternatively, the granular polyethylene terephthalate containing steam or steam. It can also be carried out by heating to a temperature of 120 to 200 ° C. for 1 minute or more in an inert atmosphere.

The solid phase polycondensation step of supplying the above-mentioned granular polyethylene terephthalate comprises at least one stage, the polycondensation temperature is usually 190 to 230 ° C., preferably 195 to 225 ° C., and the pressure is usually 1 kg / cm ² G ~ 10 Torr, preferably normal pressure to 100T
The solid-phase polycondensation reaction is carried out under an orr condition in an atmosphere of an inert gas such as nitrogen gas, argon gas or carbon dioxide gas. Of these inert gases, nitrogen gas is preferred.

The intrinsic viscosity of the polyethylene terephthalate thus obtained is usually 0.70 dl / g or more, preferably 0.72 dl / g or more.

The density of this polyethylene terephthalate is usually 1.37 g /
cm ³ or more, preferably 1.38 g / cm ³ or more, more preferably
It is preferably 1.39 g / cm ³ or more.

Further, the oligomer contained in such polyethylene terephthalate [mainly represented by the formula The amount of cyclic trimer] is 0.5 wt% or less, preferably 0.4
It is desirable to be 5% by weight or less, and more preferably 0.40% by weight or less.

Next, the granular polyethylene terephthalate obtained as described above is subjected to water treatment. This water treatment is carried out by bringing the granular polyethylene terephthalate into contact with water, steam, steam-containing gas, steam-containing air or the like.

Granular polyethylene terephthalate and water The contact between granular polyethylene terephthalate and water at 40-110 ° C for 3 minutes
It is performed by soaking for 5 hours. Particularly preferably, it is carried out by immersing the granular polyethylene terephthalate in hot water at 50 to 100 ° C. for 5 minutes to 3 hours.

Further, the contact between the granular polyethylene terephthalate and the steam or the steam-containing gas, the steam or the steam-containing gas at a temperature of 50 ~ 110 ℃ or steam-containing air is preferably supplied in an amount of 0.5 g or more as steam per 1 kg of granular polyethylene terephthalate. Or present by contacting the particulate polyethylene terephthalate with steam.

The catalyst of the particulate polyethylene terephthalate and steam is usually 5 minutes to 14 days, more preferably 10 minutes to 2 days.
It is carried out for a day, particularly preferably for 20 minutes to 10 hours.

The method for industrially carrying out the contact treatment with water, water vapor or a gas containing water vapor will be exemplified below, but the method is not limited to this. Further, the treatment method may be either a continuous method or a batch method.

When the granular polyethylene terephthalate is subjected to a contact treatment with water by a batch method, a silo type treatment apparatus can be used. That is, granular polyethylene terephthalate is received in a silo, and water, steam, or a steam-containing gas is supplied in a batch method to perform contact treatment. Alternatively, the granular polyethylene terephthalate may be received in a rotating tube type contact treatment device, and the contact treatment may be performed while rotating to make the contact more efficient.

When the granular polyethylene terephthalate is continuously contacted with water, the tower-type processing unit continuously receives the granular polyethylene terephthalate from the upper part, and continuously supplies water or steam or a steam-containing gas in a cocurrent or countercurrent contact treatment with water. Can be made. Then, when treated with water, the granular polyethylene terephthalate is shaken with a vibrating screener,
Drain with a drainer such as Simon Carter and transfer to the next drying process. When treated with steam or a steam-containing gas, it can be directly transferred to the drying step.

For drying the granular polyethylene terephthalate that has been contact-treated with water, a commonly used drying treatment for polyethylene terephthalate can be used. As a continuous drying method, a hopper type ventilation dryer is generally used in which granular polyethylene terephthalate is supplied from the upper part and a drying gas is aerated from the lower part. As a method of reducing the amount of dry gas and efficiently drying, a rotating disk type continuous dryer is selected, and while supplying a small amount of dry gas, heating steam and heating medium are supplied to the rotating disk and the outer jacket. The granular polyethylene terephthalate can be indirectly dried by heating.

A double-cone rotary dryer is used as a dryer for batch-type drying, and can be dried under a vacuum or under a vacuum while a small amount of dry gas is passed through. Alternatively, it may be dried under atmospheric pressure while aerating a dry gas.

Although atmospheric air may be used as the dry gas, dry nitrogen and dehumidified air are preferable from the viewpoint of preventing a decrease in molecular weight due to hydrolysis of polyethylene terephthalate.

The preform, stretched hollow molded article, and injection molded article according to the present invention are formed from polyethylene terephthalate as described above.

In addition, the polyethylene terephthalate according to the present invention has a small increase in acetaldehyde at the time of molding, so that a molded product such as a bottle film or a sheet having a low acetaldehyde content can be obtained. When polyethylene terephthalate having a high acetaldehyde content is used as a molded product, it may cause an offensive odor or an offensive odor, or the flavor and aroma of the contents may change. Further, when a photographic film is produced from polyethylene terephthalate having a high acetaldehyde content, it is likely to cause fogging.

In the present specification, the acetaldehyde content of polyethylene terephthalate is 2 g of a sample cooled and ground, and after returning to room temperature, 1 g is sampled and charged into a container, and the internal standard solution 2c is added to this container.
c was added and the mixture was sealed, then extracted in an oven at 120 ° C. for 1 hour and then cooled with ice, and 5 μ of the supernatant was prepared by Shimadzu Corporation.
It is determined by measuring with GC-6A manufactured by.

Effect of the Invention The polyethylene terephthalate according to the present invention has an intrinsic viscosity of 0.70 dl / g or more and a density of 1.37 g / cm ³ or more, preferably 1.38 g / cm ³ or more, and an oligomer content of 0.5% by weight or less. Furthermore, the oligomer content of the molded product obtained by injection molding the polyethylene terephthalate as it is at a molding temperature of 290 ° C. was set to W ₀ wt%, while the polyethylene terephthalate was immersed in hot water at a temperature of 95 ° C. for 8 hours. If the oligomer content of the molded product obtained by injection molding as described above is W ₁ % by weight, W ₀ -W ₁ is 0 to 0.10% by weight. Sometimes the amount of oligomers such as cyclic trimers is small,
In addition, since the total amount of oligomers such as cyclic trimers contained in polyethylene terephthalate during molding is small, mold stains are less likely to occur during molding.

Therefore, the polyethylene terephthalate according to the present invention does not need to be washed frequently when producing a molded product, so that it is possible to improve the productivity of a molded product such as a bottle, a film, a sheet, and the like. Alternatively, it is possible to prevent whitening of a film or sheet.

Further, the polyethylene terephthalate according to the present invention has a small increase in acetaldehyde at the time of molding, and therefore the flavor and aroma of the contents do not change due to an offensive odor or an offensive odor.

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

Example 1 has an intrinsic viscosity of 0.80 dl / g and a density of 1.40 g / cm ³ ,
5 kg of granular polyethylene terephthalate having an oligomer content of 0.33% by weight was immersed in 6.5 kg of distilled water in a stainless steel container. Next, a stainless steel container containing polyethylene terephthalate and distilled water is heated from the outside,
The internal temperature was controlled to 95 ° C., the mixture was kept for 4 hours for hot water treatment, and then dehydrated and dried to obtain the polyethylene terephthalate according to the present invention.

After drying this granular polyethylene terephthalate, 290 ° C
The oligomer content of the square plate obtained by injection molding at the cylinder temperature of 0.35 wt% was measured, and the acetaldehyde concentration of the square plate was 7.6 ppm. This oligo content
W ₀ .

Next, dry polyethylene terephthalate was used at an internal temperature of 95 ° C for 8 hours.
After further hot water treatment in time, dehydration and drying, 29
The square plate obtained by injection molding at a cylinder temperature of 0 ° C. had an oligomer content of 0.34% by weight. Assuming that this oligomer content is W ₁ , W ₀ -W ₁ was 0.01% by weight.

Example 2 In Example 1, the intrinsic viscosity was 0.78 dl / g and the density was 1.
Example 1 was repeated except that a granular polyethylene terephthalate having a content of 40 g / cm ³ and an oligomer content of 0.28% by weight was used.

The results are shown in Table 1.

Example 3 Intrinsic viscosity is 0.80 dl / g, density is 1.40 g / cm ³ ,
5 kg of granular polyethylene terephthalate having an oligomer content of 0.33% by weight was filled in a stainless steel container, and steam at 100 ° C. was steamed at a rate of 0.5 kg per hour for 0.5 hours.

Using the polyethylene terephthalate thus obtained, the same procedure as in Example 1 was performed.

The results are shown in Table 1.

Example 4 Example 3 was performed in the same manner as Example 3 except that the steam passing time was 4 hours.

The results are shown in Table 1.

Example 5 The procedure of Example 3 was repeated, except that the steam passing time was changed to 2 hours.

The results are shown in Table 1.

Example 6 In Example 1, the intrinsic viscosity was 0.80 dl / g and the density was
Granular polyethylene terephthalate with an amount of 1.40 g / cm ³ and an oligomer content of 0.33 wt% was controlled in a stainless steel container at an internal temperature of 95 ° C for 16 hours to perform hot water treatment, and then dehydrated and dried. Example 1 was repeated except that polyethylene terephthalate according to the present invention was obtained.

The results are shown in Table 1.

Example 7 Example 1 was performed in the same manner as Example 1 except that the hot water treatment time was 0.5 hours. At this time, the acetaldehyde concentration of the square plate was 7.9 ppm.

Other results are shown in Table 1.

Example 8 In Example 1, the intrinsic viscosity was 0.80 dl / g and the density was
Example 1 was repeated except that a granular polyethylene terephthalate having a content of 1.40 g / cm ³ and an oligomer content of 0.29% by weight was used. At this time, the acetaldehyde concentration of the square plate was 3.3 ppm.

Other results are shown in Table 1.

Example 9 In Example 1, the intrinsic viscosity was 0.82 dl / g and the density was
Example 1 was repeated except that a granular polyethylene terephthalate having a content of 1.40 g / cm ³ and an oligomer content of 0.39% by weight was used.

The results are shown in Table 1.

Example 10 In Example 1, the intrinsic viscosity was 0.79 dl / g and the density was
Example 1 except that 5 kg of granular polyethylene terephthalate having a content of 1.40 g / cm ³ and an oligomer content of 0.29% by weight was treated in an atmosphere of a temperature of 40 ° C. and a relative humidity of 90% for 1 week.
Same as.

The results are shown in Table 1.

Comparative Example 1 The raw material polyethylene terephthalate of Example 1 was dried and injection-molded at a cylinder temperature of 290 ° C. without water treatment to measure the oligomer content of a square plate of 0.51% by weight.
Met. Let this oligomer content be W ₀ .

The acetaldehyde concentration of the square plate was 15 ppm.

Next, the granular polyethylene terephthalate was heated to an internal temperature of 95 ° C.
After hot water treatment for 8 hours, dehydration drying, and injection molding at a cylinder temperature of 290 ° C., the square plate obtained had an oligomer content of 0.35% by weight. When this oligomer content and W _1, W ₀ -W ₁ was 0.16 wt%.

Comparative Example 2 In Comparative Example 1, the intrinsic viscosity was 0.78 dl / g and the density was
The same procedure as in Comparative Example 1 was carried out except that granular polyethylene terephthalate having a content of 1.40 g / cm ³ and an oligomer content of 0.28% by weight was used.

The results are shown in Table 1.

Comparative Example 3 In Comparative Example 1, the intrinsic viscosity was 0.80 dl / g and the density was
The same procedure as in Comparative Example 1 was carried out except that a granular polyethylene terephthalate having a content of 1.40 g / cm ³ and an oligomer content of 0.29% by weight was used. At this time, the acetaldehyde concentration of the square plate was 14.0 ppm.

Other results are shown in Table 1.

Comparative Example 4 In Comparative Example 1, the intrinsic viscosity was 0.82 dl / g and the density was
The same procedure as in Comparative Example 1 was carried out except that a granular polyethylene terephthalate having a content of 1.40 g / cm ³ and an oligomer content of 0.39% by weight was used.

The results are shown in Table 1.

Example 11 The granular polyethylene terephthalate used in Example 1 was treated with hot water in the same manner as in Example 1, dehydrated and dried, and then dried under reduced pressure.
After drying at ℃ for about 16 hours, under nitrogen atmosphere, Meiki Seisakusho Co., Ltd.
Barrel set temperature of 28 using M-100A-SJ type injection molding machine
It is melted at 0 ℃ and injection-molded into a preform mold cooled at 10 ℃ at a molding pressure of 700kg / cm ² , with a caliber of 38mm and a body diameter of 28m.
A preform of m and having a body thickness of 4.5 mm and a weight of 64 g was produced in a molding cycle of 60 seconds.

The oligomer in the preform was 0.35% by weight.

Then, only the mouth plug was crystallized in an oil bath at 160 ° C to prepare a preform. This caliber crystallized preform is a biaxial stretch blow molding machine [CORPOPLA
ST) LB010], using a blowing pressure of about 20 kg / cm ² ,
Preform heating time of about 60 seconds, stretching temperature of 105 ℃ biaxially stretched 2.2 times in the longitudinal direction and 3.0 times in the transverse direction, and further 160 times
After holding for 60 seconds in a mold having a surface temperature of ℃, heat setting was performed by cooling the mold with water for 20 seconds. ,
A biaxially stretched bottle having a bottom-up bottom was prepared.

The heating (heat setting) for 60 seconds after stretching is for accelerating the whitening of the bottle for evaluation, and the heating (heat setting) time during the production of the bottle is 0.1 to 30 seconds.

Although 500 bottles were molded, all transparent bottles were obtained.

Comparative Example 5 The polyethylene terephthalate used in Example 1 was dried and molded in the same manner as in Example 1 without heat treatment and in the same manner as in Example 1.

Although 500 bottles were molded in the same manner as in Example 11, cloudy patterns occurred at around 400 bottles.

The oligomer in the obtained preform was 0.46% by weight.

[Brief description of drawings]

 FIG. 1 is a perspective view of a stepped rectangular plate-shaped product.

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Claims (4)

[Claims] 1. A polyethylene terephthalate having an intrinsic viscosity of 0.70 dl / g or more, a density of 1.37 g / cm ³ or more, and an oligomer (cyclic trimer) content of 0.5 wt% or less, Moreover, the oligomer content of the molded product obtained by injection molding the polyethylene terephthalate at a molding temperature of 290 ° C. is set to W ₀ wt%, while the polyethylene terephthalate is immersed in hot water at a temperature of 95 ° C. for 8 hours and then dried. Polyethylene, characterized in that W ₀ -W ₁ is 0 to 0.10% by weight when the oligomer content of the molded product obtained by injection molding as described above is W ₁ % by weight. Terephthalate. 2. A preform made of the polyethylene terephthalate according to claim 1. 3. A stretched hollow molded article made of the polyethylene terephthalate according to claim 1. 4. An injection-molded article made of the polyethylene terephthalate according to claim 1.