JP-7855834-B2 - Method for manufacturing polyester resin pellets

Inventors

• 倉田 崇
• 北里 翔大
• 岸下 稔

Assignees

• 三菱ケミカル株式会社

Dates

Publication Date

20260511

Application Date

20210330

Claims (4)

1. A method for manufacturing polyester resin pellets, comprising the step of extruding molten crystalline polyester resin from a die hole of an underwater cutter into cooling water and cutting it to a predetermined length with a cutter to form pellets, A method for producing polyester resin pellets by polymerizing terephthalic acid, 1,4-butanediol, and a polyether polyol to produce the crystalline polyester resin, and extruding the resulting pellets from a die hole into cooling water, wherein A method for producing polyester resin pellets, characterized in that the temperature of the cooling water is 45 to 65°C.
2. A method for producing polyester resin pellets according to claim 1, wherein the polyether polyol is polytetramethylene glycol.
3. A method for producing polyester resin pellets according to claim 2, wherein the content of polytetramethylene glycol in terephthalic acid, 1,4-butanediol, and polytetramethylene glycol is 30% by mass or less.
4. The method for producing polyester resin pellets according to any one of claims 1 to 3, wherein the crystalline polyester resin is a resin whose semi-crystallization time, measured by differential scanning calorimeter (DSC) using the following method, is 1 second or more and 200 seconds or less. <Method for measuring semi-crystallization time> The sample is heated to 300°C and held for 3 minutes to melt, then rapidly cooled to 180°C and kept isothermal while continuously detecting the heat generation. The point at which the temperature reaches 180°C is defined as zero seconds, and the time until the temperature reaches half of the heat generation for crystallization after 10 minutes is defined as the semi-crystallization time.

Description

This invention relates to a method for producing polyester resin pellets. Polyester resins occupy an important industrial position due to their excellent mechanical and chemical properties. For example, crystalline polyesters, such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), are resins with excellent hygiene, heat resistance, and chemical resistance. Due to their ease of molding and cost-effectiveness, they are widely used in extrusion molding applications, including various industrial sheets and films, as well as in injection molding applications for food packaging, electrical and electronic components, automotive parts, and precision instrument parts. Polyester resins are obtained by melt polycondensation of dicarboxylic acid components, such as terephthalic acid, and diol components, such as ethylene glycol and 1,4-butylene glycol. After melt polycondensation is complete, they are usually processed into granular form called pellets. The conventional method for manufacturing these resin pellets involves extruding molten resin in strand form, cooling it to below the glass transition temperature by contacting it with cooling water using a slider or similar device, and then cutting it. For resins that are difficult to cure as strands due to reasons such as a low glass transition temperature, an underwater cutting method (hereinafter sometimes referred to as the "underwater cutter method") is known, in which molten resin is directly extruded from a die hole of an underwater cutter into cooling water, and at the same time, the molten resin is cut on the spot to obtain pellets (Patent Document 1). Molten resin cut underwater usually deforms into a spherical shape due to surface tension, and then crystallizes to fix the pellet shape. However, in the case of Patent Document 1, the composition of the cooling water used during cutting is a mixture of water and an organic solvent, and the temperature of the cooling liquid is high (100-190°C), which is undesirable from a safety standpoint, in terms of equipment costs for high-pressure equipment, and because it requires a subsequent solvent removal process. On the other hand, when the cooling water temperature is around normal room temperature, resins with relatively slow crystallization rates, such as polyethylene terephthalate, produce perfectly spherical pellets. However, resins with fast crystallization rates result in pellets that are bent into a "V" shape (hereinafter, this shape may be referred to as "bent"). Bent pellets have poor supply stability to the molding machine. For example, in extrusion molding, this can cause production problems due to fluctuations in discharge pressure and torque, and in injection molding, it leads to reduced productivity due to longer metering times. It is presumed that the reason for the pellet deformation is that the cooling water flow hits the polyethylene resin extruded from the die hole from the side (approximately perpendicular to the extrusion direction). Japanese Patent Publication No. 2005-349811 The present invention will be described in detail below, but the following descriptions of constituent elements are representative examples of embodiments of the present invention, and the present invention is not limited to these contents. [Crystalline polyester resin] The polyester resin of the present invention is a crystalline polyester, and refers to polyesters in general that possess crystalline properties. That is, it is a polyester resin obtained by polycondensation of a dicarboxylic acid component and a diol component, and which crystallizes at a temperature above its glass transition temperature. In the present invention, it is preferable that the resin has a fast crystallization rate when crystallized from a molten state. Specifically, when the resin is melted and then the semi-crystallization time at 180°C is measured using a differential scanning calorimeter (DSC), it is preferable that the resin has a semi-crystallization time of 1 second or more and 200 seconds or less, and more preferably 30 seconds or more and 100 seconds or less. Examples of dicarboxylic acid components include aromatic dicarboxylic acids such as terephthalic acid, phthalic acid, isophthalic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 4,4'-benzophenonedicarboxylic acid, 4,4'-diphenoxyethanedicarboxylic acid, 4,4'-diphenylsulfondicarboxylic acid, and 2,6-naphthalenedicarboxylic acid; alicyclic dicarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid; and aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. These dicarboxylic acid components can be introduced into the polymer backbone as dicarboxylic acids or as dicarboxylic acid derivatives such as dicarboxylic acid esters and dicarboxylic acid halides. Terephthal