Method for producing recycled material containing polybutylene terephthalate resin

Abstract

To provide a method for producing a recycled material containing polybutylene terephthalate resin, enabling production of a recycled material with stable color tone by using molded articles containing polybutylene terephthalate resin recovered from the market.SOLUTION: A method for producing a recycled material containing polybutylene terephthalate resin, comprises: conditioning a crushed product of a molded article containing polybutylene terephthalate resin recovered from the market so that the moisture content of the crushed product reaches a predetermined level; and kneading the conditioned crushed product.SELECTED DRAWING: None

Description

[Technical Field]

[0001] SUMMARY OF THE INVENTION Embodiments of the present invention relate to a method for producing recycled materials comprising polybutylene terephthalate resin. [Background technology]

[0002] In recent years, recovering and reusing reusable plastics from waste has become an important issue in order to protect the global environment. Plastics are primarily made from petroleum, and when incinerated or landfilled as waste, they are prone to causing environmental problems, making recycling increasingly important.

[0003] As a method for recycling recovered plastics, Patent Document 1 describes a method for recycling thermoplastic resins, which includes adding a phenolic antioxidant and a phosphorus-based antioxidant to a thermoplastic resin and a thermoplastic resin recovered from waste, and mixing them.

[0004] Polybutylene terephthalate resin (hereinafter also referred to as "PBT resin") has excellent heat resistance, moldability, etc., and is used in many applications in the automotive, electrical and electronic fields, etc. Various properties can be imparted to PBT resin by adding various additives, so PBT resin compositions containing additives appropriate for the application are often used in the automotive and electrical and electronic fields. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-284495 Summary of the Invention [Problem to be solved by the invention]

[0006] For example, in the case of PBT resin compositions, non-product parts such as sprues and runners generated during injection molding are sometimes recovered, crushed, mixed with virgin material, and reused in products. This type of reuse tends to result in a stable color because the same material is reused and the reuse is not commercially available, making it less susceptible to deterioration due to the usage environment. However, when attempting to recycle molded products using molded products containing PBT resin recovered from the market, even if the molded products are made of the same material, the color may not be stable due to factors such as the usage environment. An embodiment of the present invention is to provide a method for producing a recycled material containing polybutylene terephthalate resin, which can produce a recycled material having a stable color using molded articles containing polybutylene terephthalate resin recovered from the market. [Means for solving the problem]

[0007] The present invention encompasses the following aspects, but is not limited to the following aspects. [1] A method for producing a recycled material containing polybutylene terephthalate resin, comprising: adjusting the moisture content of crushed molded products containing polybutylene terephthalate resin recovered from the market so that the moisture content of the crushed product is 400 ppm or less relative to the total mass of the crushed product; and kneading the crushed product after adjusting the moisture content. [2] A method for producing a recycled material containing polybutylene terephthalate resin, comprising: adjusting the moisture content of crushed molded products containing polybutylene terephthalate resin recovered from the market so that the moisture content of the crushed product is 1000 ppm or more and 1500 ppm or less relative to the total mass of the crushed product; and kneading the moisture-adjusted crushed product. [Effects of the Invention]

[0008] According to an embodiment of the present invention, it is possible to provide a method for producing a recycled material containing polybutylene terephthalate resin, which can produce a recycled material having a stable color using molded articles containing polybutylene terephthalate resin recovered from the market. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 shows the relationship between the moisture content of the pulverized material after humidity conditioning (moisture content (ppm) relative to the total mass of the pulverized material) and the b* value of the pellet-shaped recycled material (recycled pellets) obtained for each of molded products A and B in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0010] Preferred embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments.

[0011] A method for producing a recycled material containing polybutylene terephthalate resin (PBT resin) according to an embodiment of the present invention includes adjusting the moisture content of a pulverized product of a molded product (hereinafter also referred to as "molded product X") containing polybutylene terephthalate resin collected from the market so that the moisture content of the pulverized product is a predetermined amount (hereinafter also referred to as "step 1"), and kneading the adjusted moisture content pulverized product (hereinafter also referred to as "step 2"). The recycled material containing PBT resin may be in the form of pellets, for example.

[0012] In step 1, a pulverized product of a molded product (molded product X) containing a PBT resin recovered from the market may be humidified so that the moisture content of the pulverized product is 400 ppm or less, or 1000 ppm to 1500 ppm, relative to the total mass of the pulverized product. Step 1 may be humidifying the pulverized product of molded product X so that the moisture content of the pulverized product is 400 ppm or less, relative to the total mass of the pulverized product (hereinafter also referred to as "step 1A"), or humidifying the pulverized product of molded product X so that the moisture content of the pulverized product is 1000 ppm to 1500 ppm, relative to the total mass of the pulverized product (hereinafter also referred to as "step 1B").

[0013] There are no particular limitations on the method for obtaining a molded article (molded article X) containing PBT resin recovered from the market. Molded articles containing PBT resin can be sorted, for example, by spectroscopic measurement from resin molded articles collected from the market as general industrial waste, etc. Examples of the sorting method by spectroscopic measurement include a method in which near-infrared light is irradiated onto a sample and the type of resin is determined based on the transmitted light that passes through the sample or the reflected light that is reflected from the sample.

[0014] Furthermore, molded products containing halogen elements such as bromine and antimony derived from flame retardants can be separated in advance using fluorescent X-ray analysis, etc.

[0015] Some molded products containing PBT resin that have been collected from the market contain metal inserts such as terminals and collars. These can be removed by, for example, using a magnetic material such as a magnet, or by shredding the material in a crusher and then removing it with a magnetic material.

[0016] The molded articles containing PBT resin separated in this manner may be separated into molded articles containing flame retardants, molded articles containing inorganic fillers, molded articles that are mostly PBT resin, etc., by utilizing differences in density using, for example, liquid or wind.

[0017] In step 1, a crushed molded article (molded article X) containing PBT resin collected from the market is subjected to humidity control. The size and shape of the crushed molded article X are not particularly limited. For example, a commercially available crusher may be used to crush molded articles. Crusher manufacturers include Morita Seiki Co., Ltd., Kawata Co., Ltd., and Horai Co., Ltd. Furthermore, if the number of molded articles to be crushed is small, a crusher such as a Wiley crusher may be used.

[0018] In step 1, the pulverized product of the molded product X is conditioned to have a predetermined moisture content, but the method for this is not particularly limited. For example, the molded product X may be pulverized in advance, and the pulverized product may be conditioned to have a predetermined moisture content. Alternatively, for example, the molded product X may be humidified before being pulverized, so that the pulverized product has a predetermined moisture content. For example, in some embodiments, a step of pulverizing the molded article X to obtain a pulverized product may be provided before step 1. Also, for example, in some embodiments, step 1 may include a step of conditioning the humidity of the molded article X and a step of pulverizing the humidity-conditioned molded article X. In step 1, the pulverized product of the molded product X is conditioned so that the moisture content of the pulverized product is a predetermined amount.

[0019] For example, polyethylene terephthalate resin generally tends to have low hydrolysis resistance and its physical properties are easily deteriorated by moisture absorption, so a drying process may be carried out before repelletization or solid-state polymerization may be carried out after repelletization to increase the molecular weight. PBT resin generally tends to have better hydrolysis resistance than polyethylene terephthalate resin, so drying is not usually carried out before repelletization.

[0020] The moisture content of molded products containing PBT resin typically ranges from several tens to several thousand ppm depending on the environment. Molded products using PBT resin are typically dried to a moisture content of 200 ppm or less to prevent hydrolysis, and then injection molded. Therefore, when used in a dry environment, the moisture content is only several tens of ppm. Furthermore, because PBT resin is a polymer with ester bonds, it is generally not actively used in water to avoid strength loss due to hydrolysis. However, for example, if a molded product containing PBT resin is immersed in water at 20°C for one month, the moisture content can reach approximately 4,000 ppm relative to the total mass of the molded product.

[0021] From the viewpoint of the stability of the color tone of the resulting recycled material, in step 1A, the pulverized product of molded product X is preferably conditioned so that the moisture content of the pulverized product is 400 ppm or less, and more preferably 200 ppm or less, relative to the total mass of the pulverized product. From the viewpoint of the color stability of the resulting recycled material, in step 1B, the pulverized product of molded article X is preferably conditioned so that the moisture content of the pulverized product is 1000 ppm or more, and more preferably 1100 ppm or more, relative to the total mass of the pulverized product. On the other hand, from the viewpoint of the color stability of the resulting recycled material, in step 1B, the pulverized product of molded article X is preferably conditioned so that the moisture content of the pulverized product is 1500 ppm or less, and more preferably 1400 ppm or less, relative to the total mass of the pulverized product. In step 1B, the pulverized product of molded article X is preferably conditioned so that the moisture content of the pulverized product is 1000 ppm to 1500 ppm, and more preferably 1100 ppm to 1400 ppm, relative to the total mass of the pulverized product. The color tone of the pulverized molded product X may differ between when the moisture content of the pulverized material is 400 ppm or less relative to the total mass of the pulverized material and when it is 1000 ppm to 1500 ppm, even if the resin composition is the same. Therefore, it is preferable to knead the two materials separately and make them into recycled materials separately.

[0022] There are no particular limitations on the method for adjusting the moisture content of the pulverized product of the molded article X so that the moisture content of the pulverized product is 400 ppm or less, or 1000 ppm to 1500 ppm, relative to the total mass of the pulverized product. The moisture content of the pulverized material of the molded product X can be adjusted by, for example, using a dryer, storing in a constant temperature and humidity environment, adding moisture, etc. These methods may be applied to the pulverized material or to the molded product before pulverization.

[0023] For example, a dryer or the like can be used to adjust the moisture content of the pulverized material of molded product X to 400 ppm or less relative to the total mass of the pulverized material. To achieve a moisture content of 400 ppm or less relative to the total mass of the pulverized material, drying is preferably performed at 80°C or higher, and more preferably at 100°C or higher. If the sprue and runners generated during injection molding are crushed and repelletized immediately after injection molding, the moisture content is typically 200 ppm or less. Therefore, sprues and runners can usually be used for repelletization without drying. However, sprues and runners are not usually available on the market. It is more energy-efficient to crush and then use the sprues and runners directly in injection molding without repelletization, as this eliminates thermal degradation due to repelletization. There is also less risk of contamination.

[0024] When the pulverized product of molded article X is conditioned so that the moisture content of the pulverized product is 400 ppm or less relative to the total mass of the pulverized product, from the viewpoint of avoiding discoloration of the PBT resin, the drying temperature during the humidification is preferably 150° C. or less, and more preferably 140° C. or less. When the pulverized product is conditioned so that the moisture content of the pulverized product is 400 ppm or less relative to the total mass of the pulverized product, the drying temperature during the humidification may be, for example, 80 to 150° C., and preferably 80 to 140° C. The drying time can be appropriately selected depending on the drying temperature, etc. For example, in some embodiments, the moisture content can be adjusted to 400 ppm or less by processing for 20 hours when the drying temperature is 80°C, 2 hours when it is 100°C, 1 hour when it is 120°C, and about 30 minutes when it is 140°C.

[0025] On the other hand, when the pulverized product of molded article X is to be conditioned so that the moisture content of the pulverized product is 1000 ppm to 1500 ppm relative to the total mass of the pulverized product, methods such as storing the pulverized product in a constant temperature and humidity environment, immersing the pulverized product in water, or mixing the pulverized product or the pulverized product with water can be used. These methods can be performed on the pulverized product or on the pulverized product before pulverization. The constant temperature and humidity conditions can be, for example, a humidity of 60 RH% or less, preferably 55 RH% or less, and more preferably 50 RH% or less. For example, at 23°C and 50 RH%, the storage time can be approximately 250 hours. When immersing the pulverized product in water, the immersion time can be several hours or less. For example, when the pulverized product of molded article X is mixed with water, such a mixture can be kneaded in step 2.

[0026] In step 2, the pulverized material whose humidity has been adjusted as described above is kneaded. There are no particular limitations on the kneading method. For example, the pulverized material whose humidity has been adjusted is fed into an extruder, melted and kneaded, and pelletized. There are no particular limitations on the equipment and conditions of the extruder used.

[0027] In order to suppress variations in the color of the resulting recycled material, a master batch of carbon black or the like may be added to color the recycled material. [Example]

[0028] Specific examples are given below, but the present invention is not limited to these examples.

[0029] The materials listed below were melt-mixed and extruded using a 30 mm diameter twin-screw extruder (TEX-30 manufactured by The Japan Steel Works, Ltd.) at a cylinder temperature of 250°C and a screw rotation speed of 130 rpm to obtain pellets for producing molded products A and B. These pellets were dried at 140°C for 3 hours and then injection-molded at a cylinder temperature of 260°C and a mold temperature of 80°C to produce molded products A and B. Materials of molded item A (total 100% by mass): Polybutylene terephthalate resin 70% by mass, glass fiber 30% by mass Materials of molded item B (total 100% by mass): Polybutylene terephthalate resin 80% by mass, glass fiber 20% by mass

[0030] Molded products A and B were each pulverized in a Willey pulverizer, and the resulting pulverized products were dried at 140°C for 3 hours, and then conditioned at 23°C and 50% RH for 0 hours to 30 days.

[0031] The moisture content of the conditioned pulverized material was measured using a Karl Fischer moisture measuring device CA-200 Moisture Meter manufactured by Nitto Seiko Analytec and a moisture vaporizer VA-200 Vaprizer, with Aquamicron AS as the anolyte and Aquamicron CXU as the catholyte. Tables 1 and 2 show the moisture content (moisture content (ppm) relative to the total mass of the pulverized material) of molded products A and B, respectively, after conditioned moisture.

[0032] The moisture-controlled pulverized material was melt-kneaded and extruded using a twin-screw extruder (TEX30 manufactured by Japan Steel Works) at a cylinder temperature of 260°C and a screw rotation of 130 rpm to obtain a recycled material containing polybutylene terephthalate resin in the form of pellets (hereinafter also referred to as "recycled pellets").

[0033] The hue of the recycled pellets was measured using a Suga Test Instruments SM-P color computer (measurement hole: φ=15 mm). The results (L* value and b* value) are shown in Tables 1 and 2. The L* value is an index of CIE 1976 lightness. The b* value is an index of blue / yellow color. Figure 1 shows the relationship between the moisture content of the pulverized material after humidity conditioning (moisture content (ppm) relative to the total mass of the pulverized material) and the b* value of the resulting recycled pellets for each of molded products A and B. In Figure 1, the horizontal axis represents the moisture content of the pulverized material after humidity conditioning (moisture content (ppm) relative to the total mass of the pulverized material), and the vertical axis represents the b* value of the resulting recycled pellets.

[0034] [Table 1]

[0035] [Table 2]

[0036] For recycled pellets obtained using molded product A, the b* value was stable at approximately 12 when the moisture content of the ground material was 400 ppm or less, while for recycled pellets obtained using molded product B, the b* value was stable at approximately 10 when the moisture content of the ground material was 400 ppm or less. When the moisture content of the ground material was 1000 to 1500 ppm, the b* value tended to stabilize at 7 to 8.

Claims

1. A method for producing a recycled material containing polybutylene terephthalate resin, comprising: adjusting the moisture content of crushed molded products containing polybutylene terephthalate resin recovered from the market so that the moisture content of the crushed product is 400 ppm or less relative to the total mass of the crushed product; and kneading the crushed product after adjusting the moisture content.

2. A method for producing a recycled material containing polybutylene terephthalate resin, comprising: adjusting the moisture content of pulverized molded products containing polybutylene terephthalate resin recovered from the market so that the moisture content of the pulverized product is 1000 ppm or more and 1500 ppm or less relative to the total mass of the pulverized product; and kneading the pulverized product having the adjusted moisture content.

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