JPS5945107A - Storing of polyester grnule - Google Patents

Abstract

PURPOSE:To prevent the moisture content rate of granules during in-stock from increasing, when polyester granules having alkilene terephthalate as the main recurring unit are stored, by a method wherein directly after polymerized polyester is formed into granules, the skin at least of the granules is crystallized. CONSTITUTION:Polyethylene terephthalate obtained by melt-polymerizing dimethyl terephthalate and ethylene glycol is discharged, cooled and then cut to obtain cylindrical pellets having a diameter 3mm. and a length 4mm. each. These pellets are divided into units of 300g. These units are brought into crystallizing treatment at 110-180 deg.C, in heated steam for 2-5sec. Then, each sample is put in a beaker of 500cc, the upper portion of the beaker is kept open, left for a prescribed time in a room with a relative humidity 65%, a temperature 23 deg.C and then the hygroscopic amount is measured. After being stored for seven more days, pellets are dried for 3hr on a fluidized bed in hot air of 150 deg.C, the moisture rate of the pellets is maeasured to obtain always good results of approx. 0.005%.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a storage method for minimizing the increase in moisture content of polyester powder when storing it in a bunker or the like. After melt polymerization, polyester is usually made into powder such as pellets, chips, or powder and stored in a hopper or bunker for a long time, taken out as needed, and formed into threads, films, bottles, etc.

By the way, when polyester is melted while containing water, the ester bonds are hydrolyzed and the degree of polymerization decreases, causing a significant deterioration in the quality of products obtained by spinning or molding.

For this reason, when polyester is melt-spun or melt-molded, the polyester is sufficiently heated and dried in the form of powder or granules to remove as much moisture as possible before melting.

In this drying process, the powder and granules are heated and dried at a sufficient temperature and time to prevent the degree of polymerization from decreasing due to moisture in the G melting process. It is not possible to prevent large fluctuations in the moisture content of powder and granules.

As a result of various investigations into the cause of this, the present inventors found that if the powder or granule before drying absorbs moisture during storage, sufficient drying cannot be performed in one drying process. They discovered that the moisture content increases, and discovered that this problem could be solved by preventing the granular material during storage from absorbing moisture, leading to the present invention.

That is, in the present invention, when storing a polyester powder having alkylene terephthalate as a main repeating unit, after the polyester is made into a powder after completion of polymerization, at least the surface layer of the powder is compressed for one hour. This is a method for storing polyester powder, which is characterized by crystallizing and storing a portion of the polyester powder.

The polyester in the present invention has alkylene terephthalate as its main repeating unit, and particularly preferably has ethylene terephthalate as its main repeating unit. Examples of the third component include adipic acid, sebacic acid, and isophthalic acid.

Dibasic acids such as 5-sodium sulfoisophthalic acid and naphthalene dicarboxylic acid 1, oxyacids such as oxybenzoic acid, and diethylene glycol, propylene glycol, neopentyl glycol, pentaerythritol, polyethylene glyfur, 1,4-butanediol, 10% or less of glycols may be copolymerized, or other polymers may be blended with 10% by weight or less.

The polyester also contains matting agents such as titanium oxide, flame retardants, weather and heat resistant agents, coloring stabilizers such as phosphorus compounds, antistatic agents, optical brighteners, known viscosity stabilizers such as boron compounds, etc. May be included.

The polyester powder in the present invention means chips, pellets, flakes, and powdered polyester.

Prior to melt spinning and molding, the powder and granule must be stored in a state where at least the surface layer thereof is crystallized until the powder and granule are dried. This prevents moisture from being absorbed into the powder and granules, and the moisture content of the powder before drying does not increase. Therefore, the moisture content of the powder and granules after drying does not increase. There is no such thing as rising. In order to prevent moisture from being absorbed into the inside of the powder, it is sufficient to crystallize only the P-shape part, and the thickness of the crystallized layer in the inclined part in Table 1 is as follows:
It is preferable that the thickness is 20μ or more, and the special thickness is 40μ or more. It goes without saying that the entire powder or granule may be completely crystallized.

In order to crystallize powder and granules, it is preferable to treat them with heated steam at a temperature of 110°C or higher. good. In order to prevent an increase in the moisture content of the granular material, superheated steam at 120° C. to 200° C. is preferable. Further, the heating steam temperature is preferably as high as possible, but if the temperature is too high, the decomposition reaction of the polyester will be accelerated, so it is preferable to perform the crystallization treatment at about 200° C. or lower.

Furthermore, when crystallizing with heated steam, if the powder or granules are exposed to a steam atmosphere for a long time, the moisture content of the powder or granules will increase, so the treatment should be done in as short a time as possible. is preferable. It is preferable to shorten the processing time from the viewpoint of energy saving and improvement of production efficiency.

Furthermore, in the present invention, it is necessary to perform the crystallization treatment of the granular material immediately after the completion of polymerization and the formation of the granular material. If the crystallization treatment is performed after a period of time has elapsed after the formation of the powder, the effect will be halved as the powder will absorb water during that time.

As described above, according to the method of the present invention, it is possible to prevent an increase in the moisture content of the powder or granular material during storage, prevent an increase in the moisture content of the powder or granular material after drying, and prevent the product from becoming hydrated during melt spinning or molding. Deterioration due to decomposition can be prevented. In addition, in the method of the present invention, since the powder or granules during storage are already crystallized, there is no need to crystallize the powder or granules immediately before drying to prevent sticking, as is conventionally done. .

The method of the present invention will be explained below with reference to Examples.

6- Examples 1-3. Comparative Examples 1 to 2 A polyethylene terephthalate foot obtained by melt polymerizing dimethyl terephthalate and ethylene glycol and having a melting point of 257°C and an ultimate viscosity change of ηJ of 0.64 was discharged, rapidly cooled, and then cut into pieces with a diameter of 3 m and a length. The pellets were made into cylindrical pellets with a size of 4 ml+, each of which was taken in 300 f portions, and immediately subjected to a crystallization treatment using heated steam in the form shown in the following table. The moisture content of the pellet immediately after being discharged and cut was 0.05 weight.

Next, each sample was placed in a 500 cr beaker and left in a room at a relative humidity of 65% and a temperature of 23° C. for a predetermined period of time with the top open, and the amount of moisture absorbed was measured.1. After further storage for 7 days, the pellets were dried on a fluidized bed using hot air at 150° C. for 3 hours, and the moisture content of the pellets was measured.

For comparison, the same test as in the example was also conducted on pellets that were not subjected to crystallization treatment (Comparative Example 1). However, in Comparative Example 1, the pellet was heated at 110°C immediately before drying.
A crystallization treatment was performed for 2 seconds using heated steam.

The results are shown in the table below. According to the method of the present invention for crystallizing and storing pellets, the moisture absorption I of pellets during storage is
It is clear that the moisture content of the pellet after drying is also low.

91 Examples 4-6. Comparative Examples 3 to 4 In Examples 1 to 3 and Comparative Examples 1 to 2, the pellets were changed to be stored in an atmosphere with a relative humidity of 95 degrees and a temperature of 23 degrees Celsius, and the experiments were carried out with the other conditions unchanged. Repeat 1. The results are shown in the table below. From this result also, according to the uninvented method.

It is clear that the pellets absorb less moisture during storage and the moisture content of the pellets after drying is also lower.

Patent applicant Teijin Ltd. Agent Patent Attorney Former 1) Jun Hiroshi 10-

Claims (1)

[Scope of Claims] 1. When storing polyester powder containing alkylene terephthalate as a main repeating unit, immediately after the polyester is made into powder after completion of polymerization, at least the surface layer of the powder is stored. A method for storing polyester powder, which comprises crystallizing and storing it. 2. The method according to claim 1, wherein the thickness of the crystallized layer on the surface layer of the granular material is 20 μm or more. 3. The method according to claim 1 or 2, wherein the crystallization is carried out using heated steam at 110° C. or higher.