JP-2026075958-A - Polyester resin composition and resin molded product

Abstract

[Problem] To provide a recycled polyester resin composition with excellent flame retardancy and mold release properties. [Solution] A polyester resin composition comprising polybutylene terephthalate resin, recycled polyethylene terephthalate resin, a transesterification inhibitor, and a flame retardant, wherein the amount of terminal hydroxyl groups of the polybutylene terephthalate resin is 30 to 70 mmol/kg relative to the total amount of the polybutylene terephthalate resin and the recycled polyethylene terephthalate resin. [Selection Diagram] None

Inventors

• 斎藤 樹

Assignees

• ポリプラスチックス株式会社

Dates

Publication Date

20260511

Application Date

20241023

Claims (6)

1. A polyester resin composition comprising polybutylene terephthalate resin, recycled polyethylene terephthalate resin, a transesterification inhibitor, and a flame retardant, wherein the amount of terminal hydroxyl groups of the polybutylene terephthalate resin is 30 to 70 mmol/kg relative to the total amount of the polybutylene terephthalate resin and the recycled polyethylene terephthalate resin.
2. The polyester resin composition according to claim 1, wherein the sum of the terminal hydroxyl groups of the polybutylene terephthalate resin and the recycled polyethylene terephthalate resin is 60 to 90 mmol/kg, relative to the total amount of the polybutylene terephthalate resin and the recycled polyethylene terephthalate resin.
3. The polyester resin composition according to claim 1 or 2, wherein the transesterification inhibitor comprises a phosphorus-based compound containing a sodium atom or a calcium atom.
4. The polyester resin composition according to claim 1 or 2, further comprising a crystal nucleating agent.
5. The polyester resin composition according to claim 1 or 2, further comprising 5 to 50% by mass of an inorganic filler relative to the total amount of the polyester resin composition.
6. A resin molded article obtained using the polyester resin composition described in claim 1 or 2.

Description

Embodiments of the present invention relate to polyester resin compositions and resin molded articles. In recent years, highly recyclable resins have been in demand for the realization of a sustainable society. Resins such as polyethylene, polystyrene, polypropylene, and polyethylene terephthalate, used in packaging and containers, have a high polymer ratio in packaging containers. Therefore, waste collected from the market is crushed, washed, and repelled for use as recycled products. On the other hand, polybutylene terephthalate resin (hereinafter also referred to as PBT resin) is often used with various additives such as inorganic fillers, impact absorbing agents, and flame retardants added according to market requirements. Because the polymer ratio of polybutylene terephthalate resin itself is low, it is difficult to obtain stable quality through the aforementioned processes. Therefore, methods such as recovering energy through thermal recycling or decomposing the polymer through chemical recycling, and then polymerizing the recovered monomers or using them as raw materials for other substances, are being considered. However, these methods consume a lot of energy and have not been widely adopted. Therefore, studies are underway to increase the proportion of recycled plastics used in polybutylene terephthalate resin compositions by blending readily available recycled resins, such as recycled polyethylene terephthalate resin (hereinafter also referred to as recycled PET resin) and recycled polystyrene resin, with polybutylene terephthalate resin. The compounding of polybutylene terephthalate resin with polyethylene terephthalate resin (hereinafter also referred to as PET resin) or polystyrene resin is commonly used to improve dimensional accuracy, reduce warping, and improve appearance. However, since polystyrene resin reduces heat resistance, polyethylene terephthalate resin, which has a higher melting point, is used in automotive parts and electrical equipment such as induction cooktops where heat resistance is required. However, polyethylene terephthalate resin inhibits the crystallization of polybutylene terephthalate resin, resulting in problems with moldability. Patent Document 1 describes a polyester resin composition containing polybutylene terephthalate resin, polyethylene terephthalate resin, an aluminum salt of diethylphosphinic acid, melamine cyanurate, and a phosphate ester, which exhibits excellent balance of physical properties such as fluidity. Patent Document 2 describes a resin composition containing polybutylene terephthalate resin, polyethylene terephthalate resin, and a flame retardant, wherein the polyethylene terephthalate resin contains 1.0 to 100 μg/g of iron, and it is presumed that the iron contributes to improving the release properties of molded articles obtained by molding the resin composition. International Publication No. 2024/043533Japanese Patent Publication No. 2023-81366 This is a schematic perspective view showing the molded product used to evaluate the release properties in the example. The following describes preferred embodiments of the present invention, but the present invention is not limited to these embodiments. <Polyester resin composition> The polyester resin composition of this embodiment comprises PBT resin, recycled PET resin, a transesterification inhibitor, and a flame retardant, wherein the amount of terminal hydroxyl groups of the PBT resin is 30 to 70 mmol/kg relative to the total amount of PBT resin and recycled PET resin. In resin compositions containing PBT resin and PET resin, transesterification reactions tend to occur easily between the PBT resin and PET resin under high-temperature conditions such as during melting. If the transesterification reaction proceeds too far, the melting point and crystallization temperature of the resin composition change, and temperature characteristics such as the temperature of deflection under load, as well as tensile strength and elastic modulus, may decrease, making it impossible to obtain the expected physical properties. Furthermore, if the crystallization temperature changes and crystallization becomes difficult, the amount of shrinkage during injection molding decreases, the solidification rate decreases, rigidity decreases, deformation occurs when releasing from the mold, and productivity decreases due to longer molding cycle times. The same applies when PET resin is replaced with recycled PET resin. Transesterification is a reaction in which the main chain is replaced by the reaction of ester groups and hydroxyl groups. Although it is affected by the concentration of hydroxyl groups, even if the total amount of hydroxyl groups in the resin composition is small, the release properties may not improve. The polyester resin composition of this embodiment, comprising PBT resin, recycled PET resin, a transesterification inhibitor, and a flame retardant, wherein the amount of terminal hydroxyl groups of the PBT