Processing method for recycled resin material and molded article

Abstract

In the present invention, a recycled resin material M, which is obtained by crushing a resin molded article, is added to cellulose nanofiber dispersed water CW that has been injected into a container 1 and is stirred by a crushing member 2 in the container 1. Thus, the recycled resin material M is further finely cut, and the surface of the recycled resin material M is scratched and coated with cellulose nanofibers.

Description

Processing method of recycled resin material and molded body 【0001】 The present invention relates to a processing (preparation) method of a recycled resin material using cellulose nanofibers (hereinafter referred to as CNF) and a molded body. 【0002】 In various products made of resin materials and the like, it is required to contribute to global environmental protection, and various recycling methods (such as the container and packaging recycling method) have also been established. In response to this, for example, due to the demand for recycled products (remanufactured products) using recycled materials instead of virgin materials, various research and developments have been carried out so that the recycled products have desired characteristics. 【0003】 As an example of a recycled material, there is, for example, a recycled resin material obtained by miniaturizing (crushing, pulverizing, etc.) separately collected resin containers, packages, etc. (for example, products with a recycling mark). 【0004】 Although such recycled resin materials have begun to be applied to various recycled products, they often do not obtain desired physical properties (for example, high mechanical strength, etc.), so they have been diverted to products with low added value. For this reason, research and development of processing technologies for reinforcing recycled resin materials and the like have also been carried out, but it is difficult to apply them to actual recycled products, and the fact is that they have not reached industrial production level commercialization. 【0005】In the field of virgin materials, which is different from the field of recycled materials, several techniques are known for improving the physical properties of virgin materials. For example, Patent Document 1 discloses a processing method using CNF obtained by the underwater counter-impact method (Patent Document 3) as a reinforcing filler. In this method, first, the surface of the resin particles is coated with CNF by a coating step in which resin particles are immersed in a dispersion of water in which CNF is dispersed as an example of nanonatural polymer dispersion water and shaken (Patent Document 2). Then, the resin particles that have gone through this coating step are subjected to processing consisting of multiple steps (dehydration step, drying step, pre-molding step, compounding step, molding step, etc.) to obtain a nanocomposite material (a composite material having a honeycomb-like three-dimensional structure) having desired physical properties (mechanical strength, elastic modulus, impact resistance, etc.). 【0006】 Furthermore, CNF is a reinforcing filler that can be obtained from various plants, for example, and is also biodegradable, so it is beginning to attract significant attention and expectations as a renewable (carbon neutral) material. 【0007】 Japanese Patent Publication No. 6979083, Japanese Patent Publication No. 5690387, Japanese Unexamined Patent Publication No. 2005-270891 【0008】 In the method described in Patent Document 1, the material to be coated with CNF is preferably a virgin material with relatively small particle size (for example, particle size at the level of several μm), and its composition and shape are uniform (including substantially uniform) depending on the type of virgin material. 【0009】 On the other hand, recycled resin materials often come in relatively large shapes (for example, flakes, pellets, or powders with an outer diameter of several centimeters), and their composition and shape are often non-uniform. Therefore, even if the method described in Patent Document 1 is applied (as a target for CNF coating), it is not possible to coat the recycled resin material with CNF as desired (especially the amount of CNF coating does not reach the predetermined amount), making it difficult to obtain the desired physical properties. 【0010】For example, in the case of recycled resin materials, if the components are made nearly uniform and / or refined into relatively small particle shapes by strictly carrying out pre-processing steps (separation and collection, removal of foreign matter, etc.) before the CNF coating process, it may be possible to impart the desired physical properties by applying the processing method of Patent Document 1. 【0011】 However, the processing method described in Patent Document 1 requires many processing steps (dehydration, drying, pre-molding, compounding, molding, etc.) after the CNF coating step, which hinders the reduction of time and energy required for the entire processing process. 【0012】 Therefore, even if the processing method described in Patent Document 1 can impart the desired physical properties to the recycled resin material, there is a risk that the manufacturing efficiency of recycled products using the recycled resin material will be low, making it difficult to commercialize at an industrial production level. 【0013】 The present invention has been made in view of the above circumstances, and aims to provide a technology for preparing and processing recycled resin materials that makes it easier to impart desired physical properties to recycled resin materials and improves the manufacturing efficiency of said recycled products. 【0014】 Therefore, one aspect of the present invention is a method for processing recycled resin material, comprising the steps of adding recycled resin material obtained by crushing a molded resin product to CNF dispersed water in a container, and stirring with a crushing member in the container to further cut and scratch the recycled resin material and coat the surface of the recycled resin material with cellulose nanofibers. 【0015】 One aspect of the present invention is a cutting blade that is rotatably mounted at the bottom of the container in the processing method described above. 【0016】 In one aspect of the present invention, in the processing method, the cellulose nanofiber dispersion water has a cellulose nanofiber concentration of less than 1 wt%. 【0017】 One aspect of the present invention is the processing method wherein the cellulose nanofiber dispersion water has a concentration of 1 × 10⁻¹⁶ cellulose nanofibers.－４ wt% ~ 1 × 10 －１ It is within the wt% range. 【0018】 In one aspect of the present invention, in the processing method, the recycled resin material has a maximum outer diameter of 50 mm or less. 【0019】 In one aspect of the present invention, in the processing method, the molded article is made of an olefin resin. 【0020】 One aspect of the present invention further comprises the following steps in the processing method: separating the recycled resin material from the cellulose nanofiber dispersion water after the coating step; drying the recycled resin material after the separation step; and molding the recycled resin material after the drying step. 【0021】 One aspect of the present invention is a molded article made of a recycled resin material coated with cellulose nanofibers by the processing method described above. 【0022】 According to the present invention, it is possible to easily impart desired physical properties to recycled resin materials and improve the manufacturing efficiency of the recycled products. 【0023】 A schematic diagram of a container related to the coating process of recycled resin material of the present invention. 【0024】 In this invention, a recycled resin material M, which is obtained by crushing a molded resin product, is added to a CNF-dispersed water CW, which is obtained by dispersing CNF in water W in a container 1 as shown in Figure 1, and the mixture is stirred by a crushing member 2 in the container 1, thereby cutting and scratching the recycled resin material M and coating the surface of the recycled resin material M with CNF. 【0025】 According to the coating process of the present invention, even if the recycled resin material M is relatively large in size (for example, with an average diameter of several tens of mm) and has non-uniform composition and shape, the cutting and scratching process further refines it and increases its surface area. As a result, the surface of the recycled resin material M is coated to the maximum extent with CNF, and desired physical properties can be easily obtained in the recycled resin material M after molding. 【0026】For example, olefin resins such as polypropylene and polyethylene tend to be nonpolar and relatively hydrophobic. However, according to this embodiment, CNF can be similarly attached to and coated on recycled resin material M containing such olefin resins, making it possible to obtain desired physical properties. 【0027】 The processing method of the present invention does not require many steps such as pre-molding, compounding, and molding after the coating process, as in conventional processing methods (Patent Document 1), and allows for the production of molded articles (recycled products) with desired properties (impact resistance). Therefore, the manufacturing efficiency of molded articles of recycled resin material M is improved (reduced man-hours, lower costs, etc.), and the commercialization of CNF at an industrial production level is promoted. 【0028】 The following describes specific embodiments of the processing method of the present invention. 【0029】 The processing method for the recycled resin material M of this embodiment includes a coating step P1, a sieving step P2, a drying step P3, and an injection step P4. 【0030】 In coating step P1, as shown in Figure 1, recycled resin material M is added to the CNF dispersed water CW placed in container 1 and stirred by the crushing member 2 inside container 1. As a result, the recycled resin material M is further finely cut, and the surface of the recycled resin material M is appropriately scratched and coated with CNF. 【0031】 CNF-dispersed water (CW) is water in which CNF is dispersed. In CNF, only the interactions between natural cellulose fibers are broken down into nanoparticles, and there is no structural change in the cellulose molecules. It forms rod-shaped or spindle-shaped structures with a diameter of 4 nm to 50 nm and a length of 100 nm to 500 nm or less, exhibiting amphiphilicity with both hydrophilic and hydrophobic sites coexisting. 【0032】 Examples of CNF include CNF derived from polysaccharides, such as wood fiber, bamboo fiber, sugarcane fiber, seed hair fiber, and leaf fiber, and the CNF may be used alone or in mixtures of two or more types. 【0033】CNF can be obtained by appropriately defibrating the aforementioned polysaccharides by applying a defibration method such as the underwater counter-collision method (Aqueous Counter Collision method; hereinafter simply referred to as the ACC method) disclosed in Patent Documents 1 to 3, for example. 【0034】 The CNF dispersion water CW placed in container 1 is diluted with water W to a CNF concentration of, for example, less than 1 wt%, preferably 1 × 10⁻⁶. －１ wt% or less (for example, 1 x 10) －２ wt% ~ 1 × 10 －４ The CNF is prepared (within the wt%) range and redispersed by stirring for about 1 minute. The amount of CNF dispersion water CW added to container 1 is determined based on the weight ratio to the recycled resin material M. For example, 10 L to 40 L is used for 10 kg of recycled resin material M. 【0035】 The recycled resin material M is not limited in shape or particle size as long as it can be cut and scratched by the crushing member 2. Specific forms of the recycled resin material M include, for example, flakes, pellets, or granules with a maximum outer diameter of 50 mm or less, obtained by crushing the molded product. The amount of CNF coating is proportional to the particle size of the recycled resin material M. 【0036】The resin constituting the molded product can be any resin that can be coated with CNF by adhering CNF using CNF dispersed water, and various embodiments can be applied (Patent Document 2). For example, a common example in the recycling field is one obtained by micronizing (coarse crushing, crushing, pulverizing, etc.) molded products such as containers and packaging made of resin that have been collected separately (for example, products with a recycling mark). Examples of resin molded articles include those made using one or more resins from the group of resins such as siloxane, polytetrafluoroethylene (PTFE), polypropylene (PP), polyethylene (PE), polyvinylidene fluoride (PVDF), low-density polyethylene (LDPE), high-density polyethylene (HDPE), polyvinyl acetate (PVAc), polyvinyl alcohol (PVA), polyhydroxyethyl methacrylate (PHEMA), polyvinyl fluoride (PVF), polyimide (PI), polystyrene (PS), methyl polyacrylate (PMA), acrylic resin (PMMA), polyvinyl chloride (PVC), polybutadiene (PB), polyethylene glycol (PEG), polyethylene terephthalate (PET), polycarbonate (PC), polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), polyacrylamide (PAAM), and polylactic acid (PLA), as well as those made by appropriately adding various additives to the resin. 【0037】 As described above, the shape of the micronized recycled resin material M can be, for example, flakes, pellets, or powders with an outer diameter of several centimeters. However, considering the handling properties of the recycled resin material, the adhesion of CNF when a CNF dispersion is sprayed, and the moldability of molded articles using the recycled resin material, it is preferable to appropriately micronize the recycled resin material so that its outer diameter is approximately 5 cm or less. 【0038】 Furthermore, recycled resin materials may have contaminated surfaces or contain foreign matter. In such cases, washing and sorting processes (for example, sorting using a vibrating separator, air separator, optical separator, magnetic separator, etc.) may be carried out as needed. 【0039】Furthermore, various additives may be appropriately blended into the CNF-dispersed water, in addition to CNF, according to the purpose. For example, additives for enhancing the functionality of recycled resin materials include known dyes, pigments, fillers, flame retardants that make flammable resins less flammable, mold release agents, stabilizers for polymers typified by antioxidants for improving durability, clarifying agents, plasticizers for imparting flexibility, antistatic agents for removing the adverse effects caused by electrostatic charging, lubricants for improving lubricity, weather resistance improvements for suppressing ultraviolet absorption, metal deactivators for preventing oxidation deterioration by metals, additives for improving stability during processing, and the like. 【0040】 In addition, additives for enhancing the functionality of the CNF skeleton include compounds having a carboxyl group. Specifically, known cellulose derivatives having a carboxyl group such as carboxymethyl cellulose (CMC) can be exemplified. 【0041】 In addition, known wet strength agents such as polyamide polyamine - epichlorohydrin type, melamine - formalin type, and urea - formalin type can also be mentioned. 【0042】 And the CNF-dispersed water may be redispersed (for example, defibrated by the ACC method) as necessary before being used in the coating step P1. 【0043】 As the crushing member 2, a well-known cutter blade rotatably provided at the bottom inside the container 1 is applied. As the cutter blade, a flat blade type or a saw blade type is arbitrarily adopted, and a plurality of them, for example, 2 to 4 pieces, are appropriately installed. 【0044】 The rotational speed of the cutter blade is desirably set to a rotational speed at which CNF does not aggregate in the liquid phase inside the container 1. For example, it is adjusted to 3,000 revolutions per minute or less, and more specifically, 2,000 to 3,000 revolutions per minute. 【0045】By the above rotation, a downward water flow is generated in the container 1, efficiently stirring the plastic, enabling the cutting and scratching of the recycled resin material M by the crushing member 2. As an example of the processing time, about 15 to 20 minutes is illustrated, but it is appropriately adjusted according to the specifications of the rotating machine of the crushing member 2 and the crushing state of the recycled resin material M. 【0046】 In the sieving step P2, the recycled resin material M is separated from the CNF-dispersed water CW. The separation means applied to the sieving step P2 is not particularly limited as long as it can separate the recycled resin material M coated with CNF after passing through the coating step P1 from the CNF-dispersed water CW. As the separation means, for example, the self-weight dropping method using a plain-woven stainless steel or PET mesh can be applied at a low cost. The mesh of the said mesh is not particularly limited, but by adopting a mesh with a smaller diameter than the particle size of the recycled resin material M, the recycled resin material M can be efficiently recovered. 【0047】 In the drying step P3, the coated recycled resin material M separated by the sieving step P2 is dried. As the drying means, as long as it can be carried out under a temperature not exceeding the melting point of the resin, it is not particularly limited, and well-known and inexpensive drying methods such as natural drying, blow drying, and oven drying at 50 °C are applied. 【0048】 In the injection step P4, it is appropriately molded according to the target recycled product. The molding method is not particularly limited. As an example, for the purpose of facilitating the molding of a desired recycled product using the recycled resin material, the recycled resin material is preliminarily molded into pellets, powders, etc. in advance. And then, the preliminarily molded recycled resin material is molded into a desired recycled product by injection molding, press molding, or extrusion molding. Also, the molding conditions (molding temperature, molding pressure, etc.) in the case of molding as described above can be appropriately set and are not particularly limited. As an example of the kneading speed and injection speed in the injection step P4, the kneading speed is about 65% of the upper limit speed (220 rpm), and the injection speed is about 30% of the upper limit speed (175 MPa), but it is appropriately adjusted according to the specifications of the injection molding apparatus. 【0049】While the molding temperature in injection process P4 is generally around 230°C, molding at a relatively low temperature, for example, below 170°C (e.g., around 160°C or 170°C), can yield molded articles with superior impact resistance. This reduces the energy consumption in injection process P4 and improves the manufacturing efficiency of the molded articles. 【0050】 According to the above processing method for recycled resin material M, in the coating step P1, stirring by the crushing member 2 inside the container 1 suppresses the aggregation of CNF inside the container 1 and increases the contact efficiency between CNF and recycled resin material M. Furthermore, the recycled resin material M is uniformly finely divided by being cut by the crushing member 2. In addition, the surface of the recycled resin material M is scratched by the crushing member 2, which increases the contact surface area between the recycled resin material M and other recycled resin material M. 【0051】 Therefore, according to the processing method for recycled resin material M of this embodiment, the surface of the recycled resin material RM can be coated with CNF to the maximum extent possible, and the CNF can be effectively utilized. As a result, the impact resistance of the molded article recycled by the injection molding process P5 can be improved without requiring the steps of honeycomb structuring and the melt crystallization described above. In addition, it is possible to easily impart desired physical properties to the recycled resin material and improve the manufacturing efficiency of the recycled product. 【0052】 The following describes embodiments of the present invention. 【0053】 The following verification was performed using commercially available recycled resin materials in "crushed" and "pellet" forms, respectively, as "Sample S1" and "Sample S2". The aforementioned commercially available recycled resin material mainly consists of polypropylene, contains a small amount of polyethylene, and contains about 9% residue (estimated to be talc). Its shape is that of flakes, with a thickness of about 2 mm and an outer diameter of about 5 mm to 10 mm. 【0054】Then, samples S1 and S2 were subjected to a coating process P1, a sieving process P2, and a drying process P3 to coat samples S1 and S2 with CNF. Specifically, first, 84 g of approximately 1% CNF was measured and diluted with 20 L of water to prepare CNF dispersion water CW, which was then added to container 1 for the coating process P1. Next, the crushing member 2 in container 1 was stirred at 3,000 revolutions per minute for more than 1 minute to redisperse the CNF in the CNF dispersion water CW. Next, 5 kg of samples S1 and S2 were added to this CNF dispersion water CW in which the CNF had been redispersed. Then, samples S1 and S2 and the CNF dispersion water CW were stirred by operating the crushing member 2 at 3,000 revolutions per minute for 15 minutes. Finally, samples S1 and S2 that had gone through the coating process P1 were recovered by sieving in process P2 using a plain weave stainless steel sieve, and then dried in drying process P3 by oven drying at 50°C. 【0055】 When the amount of CNF adsorbed onto samples S1 and S2 after coating with CNF was measured using the phenol-sulfuric acid method, the CNF concentration in each sample was 0.022 wt% or higher, confirming that a sufficient amount of CNF could be used to coat samples S1 and S2. 【0056】 Furthermore, when the melt flow rate (g / 10min) of samples S1 and S2 after coating was measured at a temperature of 190°C (three measurements were taken and the average median was calculated), it was approximately 4.27. On the other hand, as a comparative example, when the melt flow rate of a commercially available pulverized product (Neat PP) that had not undergone the aforementioned coating was similarly measured, it was approximately 3.70. From this, it was confirmed that the melt flow rate of samples S1 and S2 improved by about 15% when coated with CNF. 【0057】Next, samples S11, S21-S25, consisting of Charpy impact test specimens (with notches) conforming to JIS K 7111-1:2012, were prepared by injection molding the coated samples S1 and S2. The Charpy impact values ​​of samples S11, S21-S25 were then measured, and the results shown in Table 1 below were obtained. The injection molding conditions were as follows: an injection molding machine (model number: HM7-C) manufactured by Nissei Plastic Industrial Co., Ltd. was used, with the injection molding temperature set to 170-190°C, the mixing speed set to 65% of the upper limit mixing speed (220 rpm), and the injection speed set to 30% of the upper limit injection speed (175 MPa). The impact values ​​of samples S11, S21-S25 shown in Table 1 are converted values ​​when the Charpy impact value of the injection-molded Charpy impact test specimen (with notches) of the pulverized product not coated with CNF is set to 1. 【0058】 【0059】 As is clear from the results in Table 1, it was confirmed that samples S11, S21-S15, after the example processing, showed an impact resistance of approximately 10% or more compared to the pulverized product that had not undergone the example processing. In particular, it was confirmed that impact resistance could be ensured by molding at a relatively low temperature of 160-170°C. 【0060】 Conventional processing methods required honeycomb structuring of the CNF layer coating the recycled resin and melt crystallization of the resin at 180-200°C to ensure the impact resistance of the molded article. In contrast, as is clear from the results of the above examples, the processing method of the present invention allows for improved impact resistance of the molded article by molding at relatively low temperatures without requiring the honeycomb structuring and melt crystallization described above. Thus, the present invention demonstrates that it is possible to reduce the time and energy required for the entire processing of recycled resin materials. 【0061】 Although the present invention has been described in detail only with respect to the specific examples described above, it will be obvious to those skilled in the art that a wide variety of modifications are possible within the scope of the technical concept of the present invention, and it is natural that such modifications fall within the scope of the claims. 【0062】1...Container 2...Crushing material W...Water CNF...Cellulose nanofiber CW...CNF dispersed water M...Recycled resin material

Claims

1. A method for processing recycled resin material, characterized by the steps of adding recycled resin material obtained by crushing a molded resin product to a cellulose nanofiber dispersion in a container, and stirring the recycled resin material with a crushing member in the container, thereby further cutting and scratching the recycled resin material and coating the surface of the recycled resin material with cellulose nanofibers.

2. The method for processing recycled resin material according to claim 1, characterized in that the crushing member is a cutter blade rotatably provided at the bottom of the container.

3. The method for processing recycled resin materials according to claim 1, characterized in that the cellulose nanofiber dispersion water has a concentration of less than 1 wt% of cellulose nanofibers.

4. The concentration of the cellulose nanofiber is 1 × 10⁻⁶ －４ ~1 x 10 －１ The method for processing recycled resin material according to claim 3, characterized in that it is in the range of wt%.

5. The method for processing a recycled resin material according to claim 1, characterized in that the recycled resin material has a maximum outer diameter of 50 mm or less.

6. The method for processing recycled resin material according to claim 1, characterized in that the molded article is made of olefin resin.

7. The method for processing a recycled resin material according to claim 1, further comprising: a step of separating the recycled resin material from the cellulose nanofiber dispersion water after the coating step; a step of drying the recycled resin material after the separation step; and a step of molding the recycled resin material after the drying step.

8. A molded article characterized by being made of the recycled resin material coated with cellulose nanofibers by the processing method described in claim 1.

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