JPS5845229A - Preparation of polyester chip for blow molding - Google Patents

Abstract

PURPOSE:To obtain the titled chip having low acetaldehyde content and excellent transparency, by heat treating a particular polyethylene therephthalate chip under specific conditions, and polymerizing in a moving-bed solid-phase polymerization apparatus in an inert gas stream. CONSTITUTION:Polyethylene terephthalate chips having a solution haze of <=10% are heat-treated at a temperature below the solid-phase polymerization temperature and not lower than the solid-phase polymerization temperature by 20 deg.C, preferably by 15 deg.C until the crystallinity of the chip reaches >=50%. The objective chips can be prepared by subjecting the heat-treated chips to the continuous solid-phase polymerization in a moving-bed solid-phase polymerization apparatus in an inert gas stream. The solid-phase polymerization temperature is usually >=190 deg.C, and it is preferable to set the temperature to somewhat higher level to lower the acetaldehyde content of the pellet efectively. EFFECT:A high-quality blow-molded article can be manufactured in high efficiency. USE:Food container, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing polyester chips for blow molding.

More specifically, the present invention relates to a method for producing polyester chips for blow molding that have excellent transparency, contain little acetaldehyde, and are particularly suitable for food container applications.1. Polyester, especially polyethylene terephthalate, has excellent physical properties. Arc fibers with physical and chemical properties,
Widely used in film and plastic molding fields.

Conventionally, polyvinyl chloride has been mainly used as the resin for plastic blow-molded products, but in recent years its use has been restricted due to sanitary issues, particularly in the field of blow-molded containers for food products.

On the other hand, although polyethylene tere-7 tallate has excellent percent properties as mentioned above, it has not been sufficiently penetrated into the blow molding field, particularly in the food container field. The cause of this is
The main problems were that the viscosity of the polymer when melted was low, crystallization was extremely rapid, the resulting product was prone to whitening, and acetaldehyde remained in the product. Regarding the first two of these problems, various improvements have been made from the perspective of molding technology, and it has come to function as a substitute for polyvinyl chloride, but polyethylene terephthalate still contains acetaldehyde. Therefore, there is a drawback that the taste and odor of the filling are likely to change. As a method for completely reducing the acetaldehyde in this polyethylene terephthalate and increasing the degree of polymerization so as to obtain a sufficient melt viscosity for blow molding, specifically, the method is to increase the degree of polymerization at a temperature of 190°C or higher and below the melting point under reduced pressure or inert gas flow. A so-called in-phase polymerization method is known in which the treatment is carried out for several hours to several tens of hours.

Among these, the in-phase polymerization method, which is carried out under a high-temperature inert gas flow, has the advantage of being excellent in economical efficiency and productivity because it allows chips to be processed continuously.

However, in the solid phase polymerization method carried out under a still-temperature inert gas flow, blocking and fusion between chips may occur under conditions where all the acetaldehyde in polyethylene terephthalate is sufficiently reduced and the degree of polymerization is sufficiently increased. The drawback is that it is difficult to process chips easily and stably.

In particular, polyethylene terephthalate chips for blow molding with a solution height of 10 inches or less exhibit this tendency more markedly than ordinary polyethylene terephthalate chips. The present inventors have conducted intensive studies on a method for converting polyethylene terephthalate with a solution haze of 10% or less into chips that can reduce acetaldehyde in the polymer and efficiently produce high-quality hollow molded products. We have arrived at the remarkable invention.

That is, in the present invention, when carrying out all-solid phase polymerization of polyethylene terephthalate chips having a solution haze of 10% or less, the crystallinity of the chips is at least within a temperature range lower than the same phase polymerization temperature but not lower than the same temperature by 20°C. The present invention provides a complete method for producing polyester chips for blow molding, which comprises heat-treating the polyester chips until they reach 50% and then subjecting them to continuous homopolymerization in a moving bed type homopolymerization apparatus under an inert gas flow.

The polyethylene terephthalate used in the present invention is
The ethylene terephthalate units are at least 85 mol, preferably more than 90 mol Fi, and obtained after esterification reaction of terephthalic acid and ethylene glycol or transesterification reaction between lower alkyl ester of terephthalic acid and ethylene glycol. The bisdiol ester and/or its low polymer are polycondensed in the presence of a polymerization catalyst, such as one or more of conventionally known antimony compounds, germanium compounds, and titanium compounds, at a cylinder temperature under high vacuum. A small amount of dicarboxylic acid residue or diol residue other than terephthalic acid residue may be present in i7. Dicarboxylic acid residues other than terephthalic acid residues include isophthalic acid, phthalic acid, 2
, 6-naphthalene dicarboxylic acid, trimellitic acid, pyromellitic acid, adipic acid, and 5-sodium sulfoisophthalic acid.

5-Although the diol component is mainly ethylene glycol, small amounts of other glycols may be used in combination. Examples include propylene glycol, trimethylene glycol, tetramethylene glycol, neopentyl glycol, cyclohexane dimetatool, diethylene glycol, and the like.

On the other hand, in order to impart excellent transparency to polyester blow molded products, it is necessary to reduce Preferably, it does not contain so-called internal particles, or even if it does contain them, they are fine and in very small quantities.

From this point of view, the polyethylene terephthalate used in the method of the present invention must have a solution haze of 10% or less, preferably 5% or less. Added to Vrs mixed solvent 30CC6-, stirred at 102℃ for 1 hour, cooled after dissolving, collected the solution into a 20m thick cell made of quartz glass, and transferred to an integrating sphere type HTR.
The haze value was measured using a meter 5EP-H-2 (manufactured by Nippon Seimitsu Kogaku) and is expressed as -.

The polyethylene terephthalate having an F6 liquid haze of 10% or less to be used in the method of the present invention preferably has an extreme viscosity of 0.5 or more and 0.72 or less, particularly 0.53 or more and 0.68Ji or less.

Prior to homopolymerization of polyethylene tere-7-talate brevolimer ζ that satisfies these requirements, the temperature is below the solid phase polymerization temperature and the temperature is t-20°C, preferably Fi15°C.
Heat treatment is performed to obtain a crystallinity of at least 50% within a temperature range not exceeding 50%. The heat treatment atmosphere may be air, inert gas, or under high vacuum. Moreover, whether or not the chips are stirred is not particularly limited. When the heat treatment temperature falls below the lower limit specified in the present invention, even if the degree of crystallinity becomes 50% or more through heat treatment, blocking of the chips with each other occurs in the next moving bed continuous solid phase polymerization apparatus9, resulting in stability. Ejection d4 becomes possible. If the crystallinity is less than 50, severe fusion occurs in the same phase polymerization apparatus.

Further, in order to efficiently reduce the acetaldehyde content in the solid phase polymerization temperature, which is usually 190C or higher, in the chip, it is preferable to set the temperature at a high temperature.

The crystallinity of polyethylene terephthalate as used in the present invention is determined from the density. The density was determined using a density gradient tube method, using a continuous mixture of bebutane as a light liquid and carbon tetrachloride as a heavy liquid. The following formula is used to determine the degree of crystallinity from the density. .

However, P is the density of the sample, p is the density of the amorphous part 1.3
35 (t/cd) pc is the density of the crystal part 1. +55(r/
j) As mentioned above, before solid-phase polymerizing polyethylene terephthalate chips with a solution haze of 105 GJ%, a crystallinity of at least 50 GJ is obtained within a temperature range below the in-phase polymerization temperature and not less than 20 °C below said temperature. By carrying out heat retention treatment, followed by solid phase polymerization in a moving bed type solid phase polymerization apparatus under inert gas flow, efficient solid phase polymerization can be carried out, and chips that are highly effective for blow molding can be obtained. It will be done.

The polyethylene terephthalate prepolymer used in the method of the present invention usually contains 50 to 300 ppm of acetaldehyde, but by subjecting it to the method of the present invention, it is possible to increase the intrinsic viscosity i by 0.05 or more and reduce the acetaldehyde content to less than 3 ppm. F4t? ! It is possible to obtain a hollow molded product with excellent quality.

In addition, the blow molding using the chips obtained in this way is as follows:
It can be carried out according to conventional melt molding techniques such as injection molding and extrusion molding.

9- The present invention will be specifically explained below with reference to Example 1, but the present invention is not limited to these Examples.

In the examples, the acetaldehyde content in polyethylene terephthalate was determined by pulverizing the entire polyethylene terephthalate in liquid nitrogen and converting this powder into 4CM manufactured by Shimadzu Corporation.
The mixture was heated to 165° C. by gas chromatography, and the produced peak was compared with that of a standard to determine the amount of free acetaldehyde M. Also, the intrinsic viscosity is O
- Measured at 25°C using chlorophenol solvent. The transparency of the molded product is ASTM-D for an injection square plate with a thickness of 3 mm.
The haze was measured according to -1003-59TK.

Example: 150 parts by weight of dimethyl terephthalate, 92 parts by weight of ethylene glycol, and 0.135 parts by weight of magnesium acetate were mixed together and methanol was distilled off at 145 to 225°C under a nitrogen stream, followed by an ester exchange reaction. Ta. Subsequently, the reactants were transferred to a polycondensation reactor and 0.0451i of methyl and phosphate was added.
Part i, 0.03 parts by weight of germanium dioxide as a polymerization catalyst was added, and the system was gradually heated to 285°C under reduced pressure.
Polycondensation alloy was processed at 0.21Hf for 2 hours and 50 minutes, and the intrinsic viscosity was 0.
．． 55, Solution haze 0.9, Contains acetaldehyde 1
l 8ppm average length 3■, major axis 3.0■, minor axis 2
．． A cylindrical polyethylene terephthalate chip of zero size was obtained.

The chips were treated under hot air at 150°C for 1 hour, and then
Processed for 2.5 hours at 95°C under nitrogen flow, crystallinity 52%
got a tip.

Subsequently, the crystallized chips are not cooled at all, and heated nitrogen is blown from the bottom and discharged to the top, and the chips are continuously supplied from the top and discharged from the bottom. Structure AT! -205 in a moving bed continuous homopolymerizable group
Even though the treatment was carried out for a residence time of 20 hours at .degree. C., no polymer fusion or blocking was observed in the column.

The obtained polymer had an intrinsic viscosity of 0.80, contained 1 pptyh of 1-acetaldehyde, had a haze of 1.5 s, and was excellent in transparency.

Experimental Examples Table 1 shows custom-made polymers in which the heat treatment conditions were changed in the same manner as in the examples for various polymers.

Experiments JfI & 1, 4, 5I/'i According to the scope of the present invention, acetaldehyde contained in chips after solid-phase polymerization was reduced to less than LP without causing fusion in a moving-bed continuous solid-phase polymerization tower. It was found that the transparency of the injection molded plate was also excellent.

In Experiment A2, the heat treatment temperature exceeded the range of the present invention by 1.
In Experiment 43, the degree of crystallinity did not increase sufficiently. In both cases, severe fusion occurred within the solid phase polymerization tower.

Experiment A7tj: The solution haze, heat treatment conditions, and crystallinity of the polymer are beyond the scope of the present invention.If the solution haze of the shiborima is high, even if the heat treatment conditions are insufficient, in-column melting N will not occur, but injection molded products It can be seen that the transparency is inferior.

Similarly, in Experiment A6, it can be seen that the injection molded product was inferior in transparency.

13-

Claims (1)

[Claims] When solid-phase polymerizing polyethylene terephthalate chips with a liquid haze of 10% or less, the chips are subjected to solid phase polymerization at a temperature lower than the homopolymerization temperature but not lower than the base temperature of 20°C until the degree of crystallinity reaches at least 5 ots. A method for producing a polyester tep for blow molding, which comprises heat-treating and then continuously solid-phase polymerizing it in a moving bed type solid-phase polymerization apparatus under an inert air flow.