Chemically recycled pet fiber, tire cord, and tire

Abstract

Provided are a chemically recycled PET fiber that exhibits less degradation and has excellent strength and durability, and a rubber-fiber composite product such as a tire or the like in which said chemically recycled PET fiber is used.　This chemically recycled PET fiber is obtained by chemically recycling PET products and spinning the same. The chemically recycled PET fiber is characterized in that: the chemically recycled PET fiber has a weight average molecular weight of 21000-27000 and a polydispersity index (weight average molecular weight / number average molecular weight) of 1.8-2.3; and, in the chemically recycled PET fiber, the content of isophthalic acid (IPA), the terminal carboxyl group (CEG) concentration, and the diethylene glycol (DEG) content satisfy the formula 101.57-0.67×CEG concentration-4.24×IPA content-21.74×DEG content≥54.4.

Description

Chemical recycled PET fiber, tire cord, and tire

[0001] The present invention relates to chemical recycled PET fiber, tire cord, and tire.

[0002] Currently, polyester is used in many products consumed by humans, and among the most widely known ones is polyethylene terephthalate, more widely known as PET, which is a saturated polyester obtained from the reaction of terephthalic acid and ethylene glycol. In recent years, the consumption of PET has grown rapidly, and this compound is particularly used in large quantities for manufacturing containers for various liquid products such as bottled beverages.

[0003] PET is widely used in the manufacture of beverage bottles in particular because of its light weight, high durability, low gas permeability, and especially the characteristic of not having a harmful effect on human health. However, PET has a high resistance to the atmosphere and organisms and decomposes very slowly, so there is a problem of causing environmental problems with mass production.

[0004] Therefore, from the perspectives of environmental problems and economic advantages, recycling of PET products using various technologies and methods has been carried out. For example, there is a method known as "material recycling" in which waste polymers are collected, purified, pulverized, made into particles, and used as materials for products that do not need to meet high standards regarding quality and purity. However, the recycling in this form has limited fields of use.

[0005] In addition, as a recycling technology for PET products, there is also a method called "chemical recycling" in which PET products are depolymerized and then polymerized again. Among the chemical methods for depolymerizing PET, for example, there are hydrolysis method, methanolysis method, glycolysis method, etc. For example, Patent Document 1 discloses a technology for manufacturing chemical recycled PET by depolymerizing PET waste into monomers and polymerizing the depolymerized monomers, and using it as a reinforcing material for tires.

[0006] However, PET recycled using technologies such as those described in Patent Document 1 had a problem in that components (impurities) contained in the PET products used as recycled material inhibited crystallization and facilitated degradation. Therefore, it was not sufficiently suitable for applications requiring strength and durability, such as tire cords, and further improvements were desired.

[0007] Therefore, Patent Documents 2 and 3 disclose technologies for providing chemically recycled PET fibers in which crystallization degradation is suppressed by reducing impurity components and functional groups that promote degradation contained in PET products.

[0008] European Patent Application Publication No. 3753965, Specification International Publication No. 2023 / 013330, International Publication No. 2023 / 013331

[0009] Chemically recycled PET fibers obtained by the technologies described in Patent Documents 2 and 3 exhibit suppressed degradation and possess a certain level of strength and durability. However, from the perspective of application to uses requiring extremely high strength and durability, such as cords incorporated into tires, further improvements were desired.

[0010] Therefore, an object of the present invention is to provide chemically recycled PET fibers that can suppress deterioration and have excellent strength and durability. Another object of the present invention is to provide tire cords and tires that have excellent strength and durability.

[0011] The inventors of the present invention conducted research on chemically recycled PET fibers to solve the above problems and found that by controlling the weight-average molecular weight and polydispersity index (PDI: weight-average molecular weight (Mw) / number-average molecular weight (Mn)) of chemically recycled PET fibers within a specific range, and by ensuring that the isophthalic acid (IPA) content, terminal carboxyl group (CEG) concentration, and diethylene glycol (DEG) content in the chemically recycled PET fibers satisfy a specific relationship obtained from multiple regression analysis so as to maintain high cord strength after degradation, it is possible to reliably spin fibers with superior strength, as well as suppress the degradation reaction of PET fibers and improve durability.

[0012] In other words, the chemically recycled PET fiber of the present invention is a chemically recycled PET fiber obtained by chemically recycling PET products and then spinning them, wherein the weight-average molecular weight of the chemically recycled PET fiber is 21,000 to 27,000, the polydispersity index (weight-average molecular weight / number-average molecular weight) is 1.8 to 2.3, and the isophthalic acid (IPA) content, terminal carboxyl group (CEG) concentration, and diethylene glycol (DEG) content in the chemically recycled PET fiber satisfy the following formula: 101.57 - 0.67 × CEG concentration - 4.24 × IPA content - 21.74 × DEG content ≥ 54.4. By having the above configuration, the deterioration of the chemically recycled PET fiber is suppressed, and excellent strength and durability can be achieved.

[0013] The tire cord of the present invention is characterized by using the chemically recycled PET fibers of the present invention as described above. By having the above configuration, deterioration can be suppressed and excellent strength and durability can be achieved.

[0014] The tire of the present invention is characterized by using the chemically recycled PET fibers of the present invention as described above. By having the above configuration, deterioration can be suppressed and excellent strength and durability can be achieved.

[0015] According to the present invention, it is possible to provide chemically recycled PET fibers that can suppress deterioration and have excellent strength and durability. Furthermore, according to the present invention, it is possible to provide tire cords and tires with excellent strength and durability.

[0016] Embodiments of the present invention are described below in detail. <Recycled PET Fiber> The chemically recycled polyethylene terephthalate fiber of the present invention (hereinafter referred to as "chemically recycled PET fiber") is a chemically recycled PET fiber obtained by polymerizing a raw material containing monomers such as terephthalic acid (TPA) and dimethyl terephthalate (DMT), and intermediates such as bis(2-hydroxyethyl) terephthalate (BHET) (including BHET oligomers), which are obtained by depolymerizing PET products, and then spinning the resulting recycled PET.

[0017] Here, the PET products to be recycled refer to plastic products whose main component is polyethylene terephthalate, such as PET bottles, food packaging films, optical sheets, clothing fibers, and tire cords. Among these, it is preferable to use PET bottles because they are readily available in large quantities and easy to process. The PET products are not particularly limited, but it is preferable that they be crushed (flaked) prior to the depolymerization process into monomers or BHET, etc.

[0018] Furthermore, as a depolymerization method in the aforementioned chemical recycling, for example, when obtaining TPA as a monomer, the hydrolysis method can be used. Also, as a depolymerization method in the aforementioned chemical recycling, for example, when obtaining DMT as a monomer, the methanolysis method can be used. In addition, as a depolymerization method in the aforementioned chemical recycling, for example, when obtaining intermediates such as BHET, the glycolysis method can be used. When using the glycolysis method, compared to depolymerizing to monomers such as TPA and DMT, it is possible to shorten the recycling process and reduce the costs required for recycling.

[0019] Furthermore, it is preferable that intermediates such as BHET obtained by the depolymerization of the PET product do not contain residual components such as polymerization catalysts or dyes. These residual components may adversely affect the degradation of the resulting chemically recycled PET fibers, and if there is a large amount of residual polymerization catalyst, it may become difficult to control the polymerization reaction when repolymerizing. By removing these residual components from intermediates such as BHET, the strength and durability of the chemically recycled PET fibers can be more reliably improved.

[0020] The polymerization of the raw material obtained by the depolymerization of the aforementioned PET product is carried out by melt polymerization followed by solid-phase polymerization. The detailed polymerization conditions (catalyst, reaction temperature, polymerization time, etc.) are not particularly limited and can be appropriately selected according to the application and required performance of the chemically recycled PET fiber.

[0021] The chemically recycled PET fibers of the present invention are obtained by spinning PET obtained through the polymerization process into fibers. The spinning and fiber conditions are not particularly limited and can be appropriately selected according to the application and required performance of the chemically recycled PET fibers.

[0022] One example of a PET manufacturing process involves purifying TPA and / or DMT obtained by depolymerizing PET products, melt-polymerizing them with monoethylene glycol (MEG) to obtain chemically recycled PET resin, and then solid-phase polymerizing and spinning that resin to obtain chemically recycled PET fibers. In another PET manufacturing process, BHET, an intermediate obtained by depolymerizing the aforementioned PET products, is purified and melt-polymerized to obtain chemically recycled PET resin, and then solid-phase polymerizing and spinning that resin to obtain chemically recycled PET fibers.

[0023] Here, the polyethylene terephthalate (PET) constituting the PET fiber typically has the structure shown below.

[0024] Furthermore, in the chemically recycled PET fiber of the present invention, it is preferable that the polydispersity index (PDI) is 1.8 to 2.3, the isophthalic acid (IPA) content is 0.1 to 0.4 mol%, the terminal carboxyl group (CEG) concentration is 17.0 eq / t or less, and the chemically recycled PET fiber has a diethylene glycol (DEG) content of 0.5 to 1.5% by weight.

[0025] PET products used as raw materials for chemical recycling contain impurities such as isophthalic acid (IPA) and diethylene glycol (DEG) randomly, as shown in the following formula. Such impurities can inhibit the crystallization of PET during chemical recycling, leading to a decrease in the strength of chemically recycled PET fibers. Therefore, in the chemically recycled PET fibers of the present invention, it is preferable to specify the content of IPA, one of the impurities, to 0.1 to 0.4 mol%. If the IPA content exceeds 0.4 mol%, the amount of IPA contained in the PET raw material will be large, and there is a risk that the crystallization of the recycled PET may not have progressed sufficiently. On the other hand, reducing the IPA content requires the selection of the PET product to be used as the raw material and purification to remove IPA from the raw material. Considering the cost and effect, it is thought that the lower limit of the IPA content of the obtained chemically recycled PET fibers is about 0.1 mol%. The IPA content in the PET fibers is determined according to the method described in Polym. Degrad. Stab., 94, 1849-1859 (2009). １ It can be quantified by 1H-NMR measurement.

[0026] Furthermore, diethylene glycol (DEG) contained in PET products used as raw materials for chemical recycling, similar to IPA mentioned above, can inhibit the crystallization of PET during chemical recycling, potentially leading to a decrease in the strength of the chemically recycled PET fibers. Therefore, in the chemically recycled PET fibers of the present invention, the diethylene glycol (DEG) content is preferably 0.5 to 1.5% by weight. If the DEG content exceeds 1.5% by weight, it is likely that the crystallization of the recycled PET is insufficient because the amount of DEG in the PET raw material is high. On the other hand, reducing the DEG content requires moderating the polymerization conditions (generally lowering the temperature or considering the type and amount of catalyst). Therefore, considering cost and effectiveness, the lower limit of the DEG content in the resulting chemically recycled PET fibers is preferably around 0.5% by weight. The DEG content in the PET fibers is similar to that of IPA. １ It can be quantified by 1H-NMR measurement.

[0027] Furthermore, recycled PET obtained as a result of chemical recycling may contain terminal carboxyl groups (CEGs), as shown in the following formula. These CEGs can act as catalysts and accelerate degradation reactions, leading to a decrease in the physical properties (strength, durability, etc.) of chemically recycled PET fibers after degradation. Therefore, in the chemically recycled PET fibers of the present invention, by lowering the CEG concentration to 17.0 eq / t or less, the deterioration of the chemically recycled PET fibers can be suppressed, and strength and durability can be maintained at a high level. The CEG in the chemically recycled PET fibers is determined in accordance with the method described in Polymer, 44, 4429-4434 (2003). １９ It can be quantified by F-NMR measurement.

[0028] Furthermore, while it is preferable to reduce the CEG concentration of the chemically recycled PET fibers of the present invention by making the polymerization conditions milder, it can also be controlled by reacting the obtained recycled PET with carbodiimide to encapsulate the carboxyl groups at the molecular chain ends of the recycled PET. By encapsulating the CEG concentration of the chemically recycled PET using the carbodiimide, the CEG concentration can be reduced more reliably.

[0029] One way to seal the carboxyl groups at the end of the molecular chains of the recycled PET is, for example, to mix an end-sealing agent such as carbodiimide with the recycled PET powder in a predetermined ratio during kneading, and then feed it into an extruder to react with the CEG.

[0030] Furthermore, the IPA content, CEG concentration, and DEG content contained in the chemically recycled PET fiber of the present invention satisfy the following equation, obtained by multiple regression analysis based on the strength values ​​of the degraded cord and the new cord: 101.57 - 0.67 × CEG concentration - 4.24 × IPA content - 21.74 × DEG content ≥ 54.4 By adjusting the IPA content, CEG concentration, and DEG content so that all of them satisfy the above relationship, the obtained chemically recycled PET fiber has a good balance of strength and durability after degradation. For example, regarding the above equation, after measuring the degraded strength A of multiple PET fiber cords, the average strength B of new cords derived from petroleum (the average value of multiple samples measured separately) can be obtained, the index of A with B set to 100 can be calculated, and then the relationship between the index of A (the right side of the equation) and the IPA content, CEG concentration, and DEG content can be derived through multiple regression analysis. The reason why the exponent of A (the right-hand side of the equation) is set to 54.4 here is that if it is 54.4 or higher, the deteriorated PET fiber cord can have sufficient strength.

[0031] Furthermore, the chemically recycled PET fibers of the present invention have a weight-average molecular weight (Mw) of 21,000 to 27,000. If the weight-average molecular weight is less than 21,000, sufficient strength cannot be obtained, and if it exceeds 27,000, extrusion during spinning becomes difficult, and it does not contribute to improving the strength of the resulting chemically recycled PET fibers.

[0032] Furthermore, the chemically recycled PET fibers of the present invention preferably have a polydispersity index (PDI) of 1.8 to 2.3. This is because if the PDI value is less than 1.8, it becomes difficult to control the molecular weight in the production of recycled PET, and the production efficiency decreases. If it exceeds 2.3, the molecular weight distribution of the obtained recycled PET becomes broad, making spinning difficult.

[0033] Furthermore, the weight-average molecular weight (Mw), number-average molecular weight (Mn), and polydispersity index (PDI) can be measured by size exclusion chromatography (SEC). Examples of measurement conditions include the following: Eluent: Hexafluoroisopropanol Pretreatment: Filtration using a membrane filter (Myshor Disk H-25-2, manufactured by Tosoh Corporation), 0.2 μm. Additive: Sodium trifluoroacetate (10 mmol / L) Standard: Poly(methacrylic acid) standard ReadyCal set Mp 500 - 2,200,00 Product number 81506 Methyl methacrylate (manufactured by Sigma-Aldrich) Concentration: 0.003 g / 5 mL Injection volume: 10 μL Flow rate: (Sample) 0.2 mL / min, (Reference) 0.1 mL / min Column temperature: 40°C Equipment used: HLC-8320GPC (with RI detector) (manufactured by Tosoh Corporation) Column: TSKgel Super AWM-H (Tosoh) x 2

[0034] Furthermore, the chemically recycled fibers of the present invention may also include biomass-derived PET. This further reduces the environmental burden. Examples of biomass-derived PET include PET products obtained by polymerizing ethylene glycol or terephthalic acid using non-petroleum-derived materials such as plants as raw materials. Chemically recycled PET can be obtained by depolymerizing and then repolymerizing such biomass-derived PET. Mechanically recycled PET can also be obtained by melting and then remolding biomass-derived PET. In addition, the biomass-derived PET may also include those that have isophthalic acid or terminal carboxyl groups (CEGs) during the manufacturing process.

[0035] <Rubber-Fiber Composite, Tire Cord> The rubber-fiber composite of the present invention is characterized by using the chemically recycled PET fibers of the present invention as described above. By using the chemically recycled PET fibers of the present invention, excellent strength and durability can be achieved even in a rubber-fiber composite made from recycled materials.

[0036] In addition, in the rubber-fiber composite of the present invention, it is only necessary to contain the chemical recycling PET fiber, and it can be used in mixture with other organic fibers. Further, other conditions of the chemical recycling PET fiber can be appropriately selected according to the required performance.

[0037] In addition, among various applications, the rubber-fiber composite of the present invention is preferably used as a tire cord. Even when a tire cord using a recycled material is included, excellent strength and durability can be achieved. Further, for a tire cord, since a high level of deterioration suppression, strength, and durability are required, the effects of the present invention can be more significantly exhibited.

[0038] <Tire, Tire Cord> Further, the tire of the present invention is characterized by using the chemical recycling PET fiber of the present invention described above. By including the chemical recycling PET fiber of the present invention in the member, excellent strength and durability can be achieved even when a recycled material is used.

[0039] When the rubber-fiber composite is used for a tire, it is preferably used as a carcass or a belt reinforcing layer of a pneumatic tire, but is not limited thereto. For example, it can also be suitably used for a member for reinforcing the side of a tire or other members.

[0040] <Hose> The hose of the present invention is characterized by using the chemical recycling PET fiber of the present invention described above. By using the chemical recycling PET fiber of the present invention for these articles, excellent strength and durability can be achieved even when a recycled material is used.

[0041] Regarding the configuration of the chemical recycling PET fiber, it is the same as the content described in the chemical recycling PET fiber of the present invention described above.

[0042] The fibers shown in Test Examples 1 to 10 of Table 1 were prepared, and for each of them, the CEG concentration, IPA content, DEG content, number average molecular weight, weight average molecular weight, and polydispersity index were measured. Using the calculation software "JMP" manufactured by JMP Statistical Discovery LLC, the relational expression A (101.57 - 0.67 × CEG concentration - 4.24 × IPA content - 21.74 × DEG content) was calculated. The measurement and calculation results are shown in Table 1. Also, the measurement of the crystallinity of the fiber was carried out by a method conforming to JIS K 7112 D method using a density gradient tube manufactured by Shibayama Scientific Instruments Co., Ltd.

[0043] Then, a cord having the structure shown in Table 1 was produced, coated with rubber, and a rubber-fiber composite was created. After each composite was deteriorated in an environment of 160 °C for 180 minutes, the cord was pulled out, cut into a sample length of 250 mm, and the residual strength of the cord was measured at a tensile speed of 300 mm / min. Table 1 shows the index when the average value of the strength of the non-recycled PET fiber before deterioration was taken as 100 for the measured residual strength. It was evaluated that 54.4 or more was good and less than 54.4 was bad, and the results are shown in Table 1.

[0044] From Table 1, it can be seen that for the chemical recycled PET fiber (Test Example 8) within the scope of the present invention, a cord with high strength was obtained even after deterioration. As can also be seen from the relational expression, by controlling CEG, IPA, and DEG as the main factors, it is possible to control the deterioration property. This tendency is the same for non-recycled PET fibers.

[0045] According to the present invention, it is possible to provide a chemically recycled PET fiber capable of suppressing deterioration and having excellent strength and durability. Also, according to the present invention, it is possible to provide a cord for a tire and a tire having excellent strength and durability.

Claims

1. Chemically recycled PET fiber obtained by chemically recycling PET products and then spinning them, wherein the weight-average molecular weight of the chemically recycled PET fiber is 21,000 to 27,000, the polydispersity index (weight-average molecular weight / number-average molecular weight) is 1.8 to 2.3, and the isophthalic acid (IPA) content, terminal carboxyl group (CEG) concentration, and diethylene glycol (DEG) content in the chemically recycled PET fiber satisfy the following formula: 101.57 - 0.67 × CEG concentration - 4.24 × IPA content - 21.74 × DEG content ≥ 54.

4.

2. The chemically recycled PET fiber according to claim 1, characterized in that the concentration of terminal carboxyl groups (CEGs) is 17.0 eq / t or less.

3. The chemically recycled PET fiber according to claim 1, characterized in that the isophthalic acid (IPA) content is 0.1 to 0.4 mol%.

4. The chemically recycled PET fiber according to claim 1, characterized in that the diethylene glycol (DEG) content is 0.5 to 1.5% by weight.

5. The chemically recycled PET fiber according to claim 1 or 2, characterized in that the CEG concentration is controlled by reacting recycled PET with carbodiimide and encapsulating the carboxyl groups at the ends of the molecular chain.

6. A tire cord characterized by using chemically recycled PET fibers as described in any one of claims 1 to 4.

7. A tire characterized by using chemically recycled PET fibers as described in any one of claims 1 to 4.

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