JPH0138132B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing polyester having a high crystallization rate.

More specifically, the present invention relates to a method for effectively utilizing components discharged or used during solid-phase processing of polyester and for obtaining polyester having a high crystallization rate.

Polyester, particularly polyethylene terephthalate, has properties that allow it to be used to form fibers, films, containers, etc. of excellent quality, but in order to improve the strength of these molded products, it is necessary to increase the degree of polymerization.

Solid-phase treatment is known as a method for further increasing the degree of polymerization of polyesters obtained by conventional melt polymerization methods.

To put it simply, solid-phase processing is a process in which polyester with a medium molecular weight obtained by melt polymerization is finely granulated to an appropriate size, and then the particles are granulated while being kept at a temperature below the melting point. This is a method of increasing the degree of polymerization of the polymer by simultaneously flowing an inert gas through the polymer layer or maintaining it under high vacuum.

As the amount of treatment increases, it becomes difficult to maintain the reaction system in a high vacuum and heat conduction deteriorates, so a method of circulating an inert gas is preferred industrially.

Note that the purpose of solid phase treatment is not limited to simply increasing the degree of polymerization, but may also be performed for the purpose of simultaneously lowering the content of carboxyl terminal groups or reducing the content of acetaldehyde.

By the way, in a continuous solid-phase processing system in which an inert gas is circulated, water, acetaldehyde, polyester oligomers, and fine particles and fine particles of polyester chips are entrained in the discharged inert gas in addition to ethylene glycol. Usually, in order to reuse the inert gas, the gas stream containing these impurities is introduced into an ethylene glycol contact tower and contacted with ethylene glycol in a countercurrent manner, and these compounds are absorbed or transferred to ethylene glycol to purify the inert gas. conduct.

In this case, it is recommended to install a filter near the outlet of the solid-phase processing equipment because the fine particles and fine polyester chips contained in the air flow may adhere to the inside of the inert gas piping, clogging the piping and hindering smooth operation. It was always hot.

Conventionally, the air stream from which fine polyester powder was removed was led to an ethylene glycol contact tower to purify the inert gas, but in this case, although a considerable amount of ethylene glycol was used, the Ethylene glycol has not been actively used effectively because it contains impurities.

By the way, polyethylene terephthalate has not been able to fully achieve its significance as a molding material. The reason for this is that polyethylene terephthalate has a slower crystallization rate than the same crystalline polymers such as nylon, polyacetal, polypropylene, polybutylene terephthalate, etc. Particularly below 100°C, crystallization hardly progresses, so it is not suitable for molded products under normal injection conditions. This is because it was not possible to obtain

80 to 120℃, where thermoplastic resin molding is usually performed.
In a mold at a temperature of , crystallization only partially progresses, resulting in a non-uniform product and poor dimensional stability.

In order to eliminate these drawbacks, attempts have been made to raise the mold temperature and lengthen the pressure holding time by taking advantage of the fact that polyethylene terephthalate crystallizes fastest at 160 to 170°C, but at temperatures above 140°C These molds are not common, and work efficiency is extremely low, making them impractical.

In view of the above-mentioned circumstances, the present inventors conducted intensive studies on a method for industrially easily obtaining polyethylene terephthalate with a high crystallization rate. The present inventors have discovered that this objective can be achieved by blending an ethylene glycol slurry containing ethylene glycol, and that it is also possible to effectively utilize ethylene glycol used in an ethylene glycol contact tower, which has never been considered before, leading to the completion of the present invention.

That is, the present invention uses ethylene terephthalate units.
A method for producing polyester is characterized in that when producing polyester having a content of 95 mol% or more, ethylene glycol containing high melting point polyester fine powder is used as part of the raw material discharged from a solid phase treatment zone.

The present invention will be explained in more detail below.

The polyester in the present invention refers to a polyester obtained by performing an esterification or transesterification reaction using terephthalic acid or its ester-forming derivative, such as dimethyl terephthalate and ethylene glycol as main starting materials, followed by a polycondensation reaction. However, a part of it may be replaced with another third component.

For example, part of the acid component may be replaced with isophthalic acid, naphthalene dicarboxylic acid, p-hydroxybenzoic acid, adipic acid, sebacic acid, or lower alkyl esters thereof, and part of the glycol component may be replaced with trimethylene glycol, tetra It may be replaced with methylene glycol, hexamethylene glycol, etc.

In any case, what is polyester as used in the present invention?
It refers to a polyester in which 95 mol% or more, preferably 97 mol% or more, of ethylene terephthalate units.

If the amount of the copolymerized component increases, the object of the present invention, which is to obtain a polyester with a high crystallization rate, cannot be sufficiently achieved, so the amount must be kept at 5 mol % or less.

The present invention is characterized in that when producing such polyester, a specific ethylene glycol discharged from an ethylene glycol contact tower attached to an adjacent solid-phase processing device is used.

FIG. 1 shows an example of an embodiment of the present invention.

The chip-shaped polyester to be subjected to solid phase treatment is continuously heated to about 220 to 250°C using a screw feeder or the like and supplied from 1 to a solid phase treatment apparatus.
In the present invention, an inert gas is circulated through the apparatus from 2 in order to enhance the effect of solid phase treatment. Examples of the inert gas used in this case include nitrogen, carbon dioxide, argon, and helium. , nitrogen or carbon dioxide gas, which is industrially easily available, and particularly nitrogen is preferably used.

In addition to ethylene glycol, water,
It contains acetaldehyde, polyester oligomers, etc., and fine particles and fine particles of polyester chips are also entrained in the air flow.

This is because the polyester used in solid-phase processing is made into small chips in order to increase the processing effect, but at this time, polyester debris called "beards" always get mixed in, and also when solid-phase processing is performed, During this time, the surface of the polyester chips becomes brittle, and when the chips collide with each other or with the inner wall as they move through the equipment, fine polyester powder is generated and is carried out by the airflow flowing through the equipment. .

The amount of polyester fine powder discharged from the solid phase processing equipment depends on the amount of polyester scraps in the raw polyester chips, solid phase processing temperature, inert gas flow rate, etc. It accounts for 20-50% of the total amount of entrained compounds.

The present inventors investigated the properties of this fine polyester powder from various angles, and found that the fine polyester powder has a high melting point because it has been heat-treated for a long time at a high temperature near the melting point of polyester. The present invention was achieved by discovering that if a certain amount of the polyester fine powder having a high melting point is added during the production of polyester, the crystallization rate of the newly obtained polyester becomes faster.

The high melting point polyester fine powder discharged from the solid-phase processing equipment is transported to the ethylene glycol contact tower together with an inert gas, but during this time, care must be taken to ensure that the diameter and curvature of the piping and the flow rate within the piping do not clog the piping. There is a need to. The flow rate of the inert gas in the piping is preferably 5 times or more, preferably 10 times or more, than that in the solid phase processing apparatus.

The inert gas conveyed to the ethylene glycol contact tower is here countercurrently contacted with the ethylene glycol from 4 to be purified and sent to the solid phase processing device again. The high melting point polyester fine powder moves to the ethylene glycol side together with other compounds and is extracted from the bottom of the column. Usually, a part of it is often returned to the ethylene glycol contact tower, but in any case, the ethylene glycol slurry containing the high melting point polyester fine powder is finally stored in the storage tank through 5.
It is supplied to the adjacent polyester manufacturing equipment continuously or intermittently as necessary.

In this case, the amount of high melting point polyester fine powder in ethylene glycol depends on the degree of concentration, but is usually about 0.1 to 10% by weight.

Ethylene glycol containing such high melting point polyester fine powder may be added at any time in the polyester manufacturing process, but in order to maximize the effects of the present invention, it should be added at the point when the esterification or transesterification reaction is completed. It's good to do that. The amount of high melting point polyester fine powder relative to the produced polyester is preferably about 0.1 to 5% by weight.

In this way, if ethylene glycol containing high melting point polyester fine powder discharged from a solid-phase processing equipment is used as part or all of the ethylene glycol component, which is one of the raw materials for polyester production, the resulting polyester will be extremely crystallized. It has been found that the polyester has a high speed and is particularly suitable for use in molding applications.

Another feature of the present invention is the effective use of ethylene glycol used in the ethylene glycol contact tower.

Conventionally, the ethylene glycol extracted from the bottom of the ethylene glycol contact tower has no solid content, but contains impurities such as water and acetaldehyde, making it unsuitable for use as a raw material for polyester manufacturing, as well as for general industrial purposes. It was considered.

However, according to the knowledge of the present inventors, even if such ethylene glycol containing high-melting-point polyester fine powder is used as part or all of the ethylene glycol component, which is one of the raw materials for polyester production, high-purity ethylene glycol cannot be used. It became clear that there was no difference between the two cases.

That is, there was no substantial difference between the two in terms of the polymerization rate during polyester production, the color tone of the resulting polyester, or the dispersibility of inert inorganic compounds added for the purpose of coloring, erasing, etc. in the polyester. .

Another advantage of using the ethylene glycol of the present invention is its effective thermal utilization. In other words, in the ethylene glycol contact tower, high-temperature inert gas and low-temperature ethylene glycol are in countercurrent contact, so the ethylene glycol that exchanges heat there is heated and is advantageous when added to the polyester manufacturing process. becomes.

As detailed above, in the present invention, when producing polyester, if ethylene glycol containing high melting point polyester fine powder discharged from an adjacent solid phase processing device is used as part of the raw material,
In particular, polyester with a fast crystallization rate suitable for use in molding can be easily obtained industrially,
Furthermore, it has been discovered that ethylene glycol used in ethylene glycol contact towers, which has never been considered before, can be used effectively, and its utilization is large.

Furthermore, the polyester fine powder that was conventionally removed near the exit of the solid-phase processing equipment can be actively used, and the heat exchange inside the ethylene glycol contact tower can be used effectively, resulting in resource and energy savings. It is an extremely excellent system from this point of view.

The present invention will be explained in more detail below using examples.

Note that "parts" in the Examples and Comparative Examples indicate "parts by weight." The measurement method used is shown below.

Intrinsic viscosity: 1.0 g of polymer was dissolved in 100 ml of phenol/tetrachloroethane (50/50 weight ratio) and measured at 30.0°C.

Color tone of polyester: The yellow tone of the obtained polymer was measured using a Tokyo Denshoku color difference meter (TC-5D type). The larger the b value, the stronger the yellowness.

Measurement of crystallization rate: Using a Perkin Elmer differential calorimeter DSC-IB model, 15 mg of the sample was heated and melted at 280°C for 5 minutes, then cooled at a rate of 16°C/min.
The temperature at the top of the exothermic peak due to crystallization was defined as the crystallization temperature and expressed as Tc ²⁸⁰ . The higher this value is, the faster the crystallization rate is.

Example 1 (Solid phase processing of polyester) Vertically installed inner diameter 20 cm, length equipped with a hopper type dryer and screw feeder
A 1.8 m cylindrical moving bed solid phase processing device with an intrinsic viscosity of 0.66 and approximately 4 mm in length, width, and height.
Polyester chips of 2 mm and 2 mm were fed at a rate of 4 kg/hour, while nitrogen gas was fed at 100 ml (standard state) per hour from the bottom of the solid phase processing apparatus in the opposite direction to the moving direction of the polyester chips.
Solid-phase processing was performed at °C.

At this time, the average residence time of the polyester chips was about 8 hours, and the average flow velocity in the pipe was about 0.3 m/sec.

After reaching a steady state, polyester chips with an intrinsic viscosity of 0.81 could be obtained at the outlet of the solid phase processing apparatus.

On the other hand, about 30 g of fine polyester powder per 100 kg of polyester supplied to the solid phase treatment apparatus was conveyed to the ethylene glycol contact tower together with the nitrogen gas discharged from the solid phase treatment apparatus.

When the melting point of the polyester fine powder was measured using a differential calorimeter, it was found to be approximately 265 to 285° C., although it varied depending on the thermal history of each fine powder, confirming that it had a high melting point.

The high melting point polyester fine powder, which was conveyed to the ethylene glycol contact tower with a nitrogen stream, was transferred there to the ethylene glycol side, concentrated, and stored as a 5% by weight ethylene glycol slurry.

(Manufacture of polyester) In the presence of 100 parts of bis-(β-hydroxyethyl) terephthalate oligomer, 87 parts of terephthalic acid and 42 parts of ethylene glycol were reacted at 260° C. under atmospheric pressure to perform esterification. After 4 hours, a polyester oligomer with an esterification rate of 98% was obtained.

Next, take 106 parts (equivalent to 100 parts of polyester) of this reaction mixture, hold it at 260°C, add 0.05 part of antimony trioxide as a polymerization catalyst, and further contain 5% by weight of the high melting point polyester fine powder obtained earlier. 10 parts of ethylene glycol was added and polymerization was carried out according to a conventional method.

In other words, the temperature gradually increases from 260℃ and finally
The temperature was 275°C, and the pressure was gradually reduced from normal pressure to 0.1 mmHg. After 4 hours, the system was returned to normal pressure and the polymer was discharged.

The obtained polyester has an intrinsic viscosity of 0.65 and a b value of +
Tc ²⁸⁰ , which is a guideline for crystallization rate, was 4.8, and the presence of high melting point nuclei was observed at 210°C.

Next, this polymer was injection molded using an Anchorberg V-10-30 injection molding machine manufactured by Japan Steel Works at a cylinder temperature of 275 to 280°C and a mold temperature of 90°C to a thickness of 4.
mm test pieces were prepared. The degree of crystallinity of this test piece was measured using a density gradient tube manufactured by Shibayama Kagaku Kikai Seisakusho and was found to be 41%, which was sufficiently satisfactory.

Comparative Example 1 A polyester was obtained in the same manner as in Example 1, except that ethylene glycol containing high melting point polyester fine powder was not added.

The obtained polyester has an intrinsic viscosity of 0.65 and a b value of +
At 4.6, Tc ²⁸⁰ was 201°C.

Next, a test piece was prepared in the same manner as in Example 1, and its crystallinity was measured and found to be 30%.
The crystallinity of the molded product was worse than that of the previous one.

As is clear from the Examples and Comparative Examples, the crystallization rate of the polyester of the present invention is extremely high due to the presence of high melting point nuclei.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram showing the flow of main substances around the solid phase treatment equipment, ethylene glycol contact tower, and polyester manufacturing equipment. Symbols: 1... polyester chip inlet for solid phase treatment, 2... purified nitrogen gas distribution tube, 3... nitrogen gas distribution tube containing high melting point polyester fine powder,
4...Ethylene glycol inlet, 5...Ethylene glycol flow pipe containing high melting point polyester fine powder.

Claims (1)

[Claims] 1. Production of polyester characterized by using ethylene glycol containing high melting point polyester fine powder discharged from a solid phase processing zone of polyester as a raw material when producing polyester having 95 mol% or more of ethylene terephthalate units. Law.