Antibacterial and antiviral composite resin molded article

Abstract

This composite resin molded body comprises a principal-agent resin, a filler dispersed in the principal-agent resin, and a furan ring compound. The filler includes a fibrous filler and a particulate filler having a smaller aspect ratio than that of the fibrous filler. The aspect ratio of the fibrous filler is 10 or higher, and the aspect ratio of the particulate filler is two or less.

Description

Technical Field

[0001] The present disclosure relates to an antibacterial and antiviral composite resin molded body that can realize a molded body having excellent mechanical properties, designability, and antibacterial properties.

Background Art

[0002] So-called "general-purpose plastics" such as polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC) are not only very inexpensive, but also easy to mold and are several times lighter than metals or ceramics. Therefore, general-purpose plastics are often used as materials for various daily necessities such as bags, various packages, various containers, and sheets, and also as materials for industrial parts such as automotive parts and electrical parts, building supplies, and daily necessities and miscellaneous goods.

[0003] As described above, resins are convenient and are used in many places where people touch. However, it has been pointed out that the growth of bacteria and viruses on the surface of resin products can have an adverse effect on the human body, and it is preferable to impart antibacterial and antiviral properties. As a method of imparting antibacterial properties, there are methods such as kneading an antibacterial agent into a thermoplastic resin or a thermosetting resin, or applying an antibacterial agent to the surface.

[0004] On the other hand, as a filler, a technique for improving the mechanical strength of a general-purpose plastic by dispersing natural fibers, glass fibers, carbon fibers, etc., which are fibrous fillers, into the resin of the general-purpose plastic is known. In addition, a technique for improving the mechanical strength of a general-purpose plastic by dispersing inorganic powders such as talc and silica, and cellulose-based powders such as pulp powder, waste paper powder, and wood chip powder, as particulate fillers into the resin of the general-purpose plastic is also known. Among these, organic fillers such as cellulose are attracting particular attention as reinforcing materials because they are inexpensive and have excellent environmental properties when discarded.

[0005] Companies are working to improve the mechanical strength of general-purpose plastics. For example, Patent Document 1 describes a resin containing up to 75% cellulose fibers and calcium carbonate, which exhibits antibacterial properties due to the cellulose fibers and calcium carbonate, and also increases the strength of the molded article. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 6472604 [Overview of the Initiative]

[0007] A composite resin molded article according to one aspect of the present disclosure comprises a main resin, a filler dispersed in the main resin, and a furan ring compound, wherein the filler includes a fibrous filler and a particulate filler having a smaller aspect ratio than the fibrous filler, the fibrous filler having an aspect ratio of 10 or more, and the particulate filler having an aspect ratio of 2 or less.

[0008] A method for producing a composite resin molded article according to one aspect of the present disclosure includes the steps of: preparing a predetermined amount of a main resin and a filler containing fibrous filler and particulate filler; and melt-kneading the main resin and the filler to obtain a composite resin molded article in which the filler is dispersed in the main resin, wherein the melt-kneading step provides the filler to contain fibrous filler with an aspect ratio of 10 or more and particulate filler with an aspect ratio of 2 or less, and also generates a furan ring compound. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view of a composite resin molded body according to Embodiment 1. [Figure 2] This is a schematic cross-sectional view (enlarged view) of a composite resin molded body according to Embodiment 1. [Figure 3] This is an electron microscope image of the fibrous filler in a composite resin molded article according to Embodiment 1. [Figure 4] This is a schematic diagram of the manufacturing process for a composite resin molded article according to Embodiment 1. [Figure 5] Table 1 shows the measurement results for each of Examples 1-5 and Comparative Examples 1-4. [Modes for carrying out the invention]

[0010] <Background leading to this disclosure> Antimicrobial agents include inorganic and organic antimicrobial agents. However, prolonged contact with these artificial antimicrobial agents can cause adverse effects such as allergic reactions in humans. In particular, contact with products containing artificial antimicrobial agents such as pyridine-based organic antimicrobial agents can cause allergic dermatitis and other skin problems.

[0011] Therefore, by utilizing naturally derived materials and imparting antibacterial properties, it is possible to suppress the impact on the human body. Furthermore, there is a demand for significantly improving the material properties (mechanical strength, etc.) of general-purpose plastics. The inventors of this invention believe that by adding naturally derived materials as fillers to improve strength, and by utilizing the antibacterial properties of these naturally derived materials, it is possible to improve strength and impart antibacterial properties without adding artificial antibacterial agents, leading to this disclosure.

[0012] Furthermore, while Patent Document 1 uses cellulose fibers for antibacterial properties, cellulose itself has little antibacterial activity. Therefore, it is used in combination with calcium carbonate, which presents challenges such as an increased specific gravity when used as a composite resin.

[0013] This disclosure aims to solve the above-mentioned conventional problems and to provide a composite resin molded article that has antibacterial and antiviral properties and high strength due to naturally derived materials, and a composite resin molded article.

[0014] The composite resin molded body according to the first aspect includes a main resin, a filler dispersed in the main resin, and a furan ring compound. The filler includes a fibrous filler and a particulate filler having an aspect ratio smaller than that of the fibrous filler. The fibrous filler has an aspect ratio of 10 or more, and the particulate filler has an aspect ratio of 2 or less.

[0015] In the composite resin molded body according to the second aspect, in the above first aspect, the concentration of the furan ring compound contained in the composite resin molded body may be 4 ppb or more and 1000 ppb or less.

[0016] In the composite resin molded body according to the third aspect, in the above first or second aspect, the composite resin molded body may have an L* value of 80 or more according to the L*a*b* color system.

[0017] In the composite resin molded body according to the fourth aspect, in any of the above first to third aspects, the proportion of the fibrous filler among the fillers is 1% or more and 10% or less, and the proportion of the particulate filler among the fillers may be 50% or more and 70% or less.

[0018] In the composite resin molded body according to the fifth aspect, in any of the above first to fourth aspects, the fibrous filler has a central portion and an end portion. Only the end portion of the fibrous filler is defibrated. The main resin includes a first portion existing around the central portion of the fibrous filler and a second portion existing around the end portion of the fibrous filler. The second portion may contain more furan ring compound than the first portion.

[0019] In the composite resin molded body according to the sixth aspect, in any of the above first to fifth aspects, in the composite resin molded body, the furan ring compound may be present more in the vicinity of the surface than in the interior of the composite resin molded body.

[0020] In the composite resin molded body according to the seventh aspect, in any of the above first to sixth aspects, the main resin may be an olefin resin.

[0021] The manufacturing method of the composite resin molded body according to the eighth aspect includes a step of preparing a predetermined amount of a main resin, a filler containing a fibrous filler and a particulate filler, and a step of melt-kneading the main resin and the filler to obtain a composite resin molded body in which the filler is dispersed in the main resin. By the melt-kneading step, the filler includes a fibrous filler having an aspect ratio of 10 or more and a particulate filler having an aspect ratio of 2 or less, and a furan ring compound is generated.

[0022] In the composite resin molded body according to the ninth aspect, in the eighth aspect, the furan ring compound may be generated by the decomposition of the filler.

[0023] The manufacturing method of the composite resin molded body according to the tenth aspect is as described in the ninth aspect. In the melt-kneading step, the filler is decomposed by the heat during melt-kneading and molding to generate a thermal decomposition product. The degree of decomposition is greater for the particulate filler than for the fibrous filler. The main resin includes a third portion present around the fibrous filler and a fourth portion present around the particulate filler, and the fourth portion may contain more thermal decomposition products than the third portion.

[0024] A composite resin molded body according to one aspect of the present disclosure can realize a composite resin molded body having antibacterial properties, antiviral properties, and high strength.

[0025] Hereinafter, the composite resin molded body according to the embodiment and its manufacturing method will be described with reference to the drawings. In the following description, the same reference numerals are given to the same components, and the description is appropriately omitted.

[0026] (Embodiment 1) The composite resin molded body according to Embodiment 1 includes a main resin, a fibrous filler, a particulate filler, and a furan ring compound. The composite resin molded body may contain a dispersant. As shown in the cross-sectional schematic views of FIGS. 1 and 2, in the main resin 1, a fibrous filler 2 having a large aspect ratio and a particulate filler 3 having a small aspect ratio are dispersed.

[0027] This composite resin molded article, by containing a furan ring compound and a filler, possesses antibacterial and antiviral properties as well as high strength.

[0028] The following describes each component that makes up this composite resin molded body.

[0029] <Main resin component> In this embodiment 1, the main resin 1 is preferably a thermoplastic resin in order to ensure good moldability. Examples of thermoplastic resins include olefin resins (including cyclic olefin resins), styrene resins, (meth)acrylic resins, organic acid vinyl ester resins or their derivatives, vinyl ether resins, halogen-containing resins, polycarbonate resins, polyester resins, polyamide resins, thermoplastic polyurethane resins, polysulfone resins (polyethersulfone, polysulfone, etc.), polyphenylene ether resins (polymers of 2,6-xylenol, etc.), cellulose derivatives (cellulose esters, cellulose carbamates, cellulose ethers, etc.), lignin resins, modified lignin resins, silicone resins (polydimethylsiloxane, polymethylphenylsiloxane, etc.), rubber or elastomers (diene rubbers such as polybutadiene and polyisoprene, styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, acrylic rubber, urethane rubber, silicone rubber, etc.), engineering plastics, etc. The above resins may be derived from petroleum, plants, or microorganisms. The above resins may be used individually or in combination of two or more. They may also be biodegradable by microorganisms, water, heat, etc. Note that the main resin 1 is not limited to the above materials as long as it is thermoplastic.

[0030] Of these thermoplastic resins, the main resin 1 is preferably an olefin-based resin or a polyamide-based resin with a relatively low melting point. Olefin-based resins include homopolymers of olefin-based monomers, copolymers of olefin-based monomers, and copolymers of olefin-based monomers with other copolymerizable monomers. Examples of olefin-based monomers include linear olefins (such as ethylene, propylene, 1-butene, isobutene, 1-pentene, 4-methyl-1-pentene, 1-octene, and other α-C2-20 olefins), and cyclic olefins. These olefin-based monomers may be used individually or in combination of two or more. Among the above olefin-based monomers, linear olefins such as ethylene and propylene are preferred. Other copolymerizable monomers include, for example, vinyl fatty acid esters such as vinyl acetate and vinyl propionate; (meth)acrylic monomers such as (meth)acrylic acid, alkyl (meth)acrylate, and glycidyl (meth)acrylate; unsaturated dicarboxylic acids or their anhydrides such as maleic acid, fumaric acid, and maleic anhydride; vinyl esters of carboxylic acids (e.g., vinyl acetate, vinyl propionate); cyclic olefins such as norbornene and cyclopentadiene; and dienes such as butadiene and isoprene. These copolymerizable monomers may be used alone or in combination of two or more. Specific examples of olefin resins include polyethylene (low-density, medium-density, high-density, or linear low-density polyethylene, etc.), polypropylene, ethylene-propylene copolymers, terpolymers such as ethylene-propylene-butene-1, and copolymers of chain-like olefins (especially α-C2-4 olefins). Examples of polyamide resins, which are polymers formed by the bonding of numerous monomers via amide bonds, include nylon (polyamide) 6, nylon 11, nylon 12, nylon 66, nylon 610, nylon 612, nylon 1010, nylon 1012, and nylon 6T.

[0031] <Dispersant> Next, the dispersant will be described. The composite resin molded article according to this embodiment 1 may contain a dispersant for purposes such as improving the adhesion between the fibrous filler 2 and particulate filler 3 and the main resin 1, or improving the dispersibility of the fibrous filler 2 and particulate filler 3 in the main resin 1. Examples of dispersants include various titanate coupling agents, silane coupling agents, unsaturated carboxylic acids, maleic acid, maleic anhydride, or modified polyolefins grafted with the anhydride thereof, fatty acids, fatty acid metal salts, and fatty acid esters. Among the silane coupling agents, unsaturated hydrocarbon-based or epoxy-based ones are preferred. The surface of the dispersant may be treated and modified with a thermosetting or thermoplastic polymer component without issue. The dispersant content in the composite resin molded article in this embodiment is preferably 0.01% by mass or more and 20% by mass or less, more preferably 0.1% by mass or more and 10% by mass or less, and even more preferably 0.5% by mass or more and 5% by mass or less. If the dispersant content is less than 0.01% by mass, poor dispersion will occur, while if the dispersant content exceeds 20% by mass, the strength of the composite resin molded article will decrease. The dispersant should be appropriately selected based on the combination of the main resin 1, fibrous filler 2, and particulate filler 3, and it may be omitted if the combination does not require a dispersant.

[0032] <Furan ring compounds> The composite resin molded article contains a furan ring compound. This gives it antibacterial and antiviral properties. The concentration of this furan ring compound is, for example, 4 ppb or more and 1000 ppb or less. A composite resin molded article containing 4 ppb or more of the furan ring compound exhibits sufficient antibacterial and antiviral properties. A composite resin molded article containing 1000 ppb or less of the furan ring compound exhibits sufficient whiteness with reduced browning and other discoloration. Furthermore, the furan ring compound only needs to be included in at least one of the main resin, dispersant, fibrous filler, or particulate filler. The furan ring compound may be added or generated by the decomposition of the filler, as described later.

[0033] <Fibrous fillers, particulate fillers> Next, we will describe the fibrous filler 2 and the particulate filler 3. The particulate filler 3 may be essentially the same material as the fibrous filler 2. In this case, the only differences between the fibrous filler and the particulate filler are the filler length and aspect ratio. Therefore, the following description will focus on the fibrous filler 2.

[0034] The fibrous filler 2 (hereinafter sometimes simply referred to as "fiber") contained in the composite resin molded article according to this embodiment 1 is used in resin molded articles formed using the composite resin molded article primarily for the purpose of improving mechanical properties and improving dimensional stability by reducing the coefficient of linear expansion. For this purpose, the fibrous filler 2 preferably has a higher elastic modulus than the main resin 1. Specifically, examples include carbon fiber, carbon nanotube, pulp, cellulose, cellulose nanofiber, lignocellulose, lignocellulose nanofiber, basic magnesium sulfate fiber (magnesium oxysulfate fiber), potassium titanate fiber, aluminum borate fiber, calcium silicate fiber, calcium carbonate fiber, silicon carbide fiber, wollastonite, xonotlite, various metal fibers, natural fibers such as cotton, silk, wool or hemp, jute fiber, regenerated fibers such as rayon or cupro, semi-synthetic fibers such as acetate and promix, synthetic fibers such as polyester, polyacrylonitrile, polyamide, aramid, and polyolefin, and modified fibers with chemical modifications to their surfaces and ends. The material does not have to be fibrous; it may be needle-shaped, and may be wood powder obtained from cedar, cypress, bamboo, etc., or powder from coffee, wheat, tea leaves, etc. Furthermore, among these, carbons and celluloses are particularly preferred from the viewpoint of availability, high elastic modulus, and environmental friendliness. From the viewpoint of antibacterial properties, natural fibers and natural materials such as celluloses and wood powder are preferred.

[0035] Wood powders such as cedar, cypress, and bamboo, as well as powders of coffee, wheat, and tea leaves, contain antibacterial substances such as hinokitiol, caffeine, and catechin in their original components, respectively. As a result, molded products made from these powders also exhibit antibacterial properties. However, cellulose itself, such as pulp, does not possess antibacterial properties. Through diligent research, the inventors have confirmed that furan ring compounds, such as furfural and furfuryl alcohol, which are decomposition products of cellulose, possess antibacterial and antiviral properties. Other major furan ring compounds include 5-hydroxymethyl-2-furfural, 2,5-franzicarboxyaldehyde, and 2-furaldehyde. In order to generate furan ring compounds, it is necessary to apply heat to the resin composition containing cellulose or the resin molded product. However, applying heat decomposes the cellulose, resulting in the loss of the reinforcing effect of the molded product and the discoloration of the molded product. Therefore, after diligent research, it has been determined that the concentration of furan ring compounds that can achieve a balance between strength, antibacterial properties, and appearance of the molded product is preferably, for example, 4 ppb or more and 1000 ppb or less. The concentration of this furan ring compound can be calculated using a gas chromatograph-mass spectrometer or the like. A more preferable concentration of the furan ring compound is 4 ppb or more and 100 ppb or less, and even more preferably 4 ppb or more and 50 ppb or less.

[0036] The shapes of the fibrous filler 2 and the particulate filler 3 will be described. In the case of natural fibers and natural materials, the starting materials for the fibrous filler 2 and the particulate filler may be the same, in which case the fibrous filler becomes particulate by being finely ground. The symbol L is the length of the fibrous filler 2 or particulate filler 3 (hereinafter sometimes referred to as "fiber length"), and the symbol d is the width of the fibrous filler 2 or particulate filler 3 (hereinafter sometimes referred to as "fiber diameter"). With respect to the fibrous filler 2 and particulate filler 3, if there are many fibers with a large aspect ratio (L / d), that is, if there is many fibrous filler 2, the elastic modulus improves. The aspect ratio of the fibrous filler 2 is preferably 10 or more. However, if there are many fibers with a large aspect ratio, the impact resistance deteriorates, and the amount of fiber aggregates increases, resulting in poor appearance. On the other hand, if there are many fibers with a small aspect ratio, that is, if there is many particulate filler 2, the impact resistance improves, there are fewer fiber aggregates, and the appearance is good. The aspect ratio of the particulate filler 3 is preferably 2 or less. However, if there are many fibers with a small aspect ratio, the elastic modulus decreases.

[0037] By including fibrous filler 2 and particulate filler 3 in a composite resin molded body, the heat generated during the kneading of the resin composition and during the molding of the resin molded body is more easily applied to the finely pulverized and damaged particulate filler 3, making it easier for furan ring compounds to be generated through decomposition. On the other hand, the presence of fibrous filler improves the strength of the molded body. The relationship between the mixing ratios of each fiber that allows for both antibacterial properties and strength is calculated through experiments and simulations. For example, it is preferable that the proportion of fibers with an aspect ratio of 10 or more is 1% to 15%, and the proportion of fibers with an aspect ratio of 2 or less is 40% to 60%. In other words, it is preferable that the proportion of fibrous filler in the filler is 1% to 15%, and the proportion of particulate filler in the filler is 40% to 60%. Furthermore, the proportion of other fibers with an aspect ratio higher than 2 and less than 10 is 25% to 49%. The above proportions refer to the ratio of fibrous fillers, particulate fillers, and other fillers to the total number of fillers.

[0038] As described above, by applying little heat to the fibrous filler 2 to prevent the generation of furan ring compounds, and applying a relatively large amount of heat to the particulate filler 3, a molded article that achieves both antibacterial properties and strength can be realized. The main resin 1 includes a portion surrounding the fibrous filler 2 (third portion) and a portion surrounding the particulate filler 3 (fourth portion). The fourth portion contains more thermal decomposition products (i.e., furan ring compounds) than the third portion. Figure 2 shows an enlarged schematic cross-sectional view of a composite resin molded article according to Embodiment 1. As shown in Figure 2, a high-concentration area 4 (fourth portion) of furan ring compounds exists around the particulate filler 3. Furthermore, by controlling the concentration of the furan ring compounds in the molded article, both appearance and properties can be achieved.

[0039] This section describes the relationship between aspect ratio and elastic modulus as factors affecting the strength of a composite resin molded article. When stress is applied to a composite resin molded article, if there are fibers with a large aspect ratio, the resin may stretch, but the rigid fibers will not stretch easily, preventing the composite resin from deforming. Therefore, the elastic modulus improves. On the other hand, if there are fibers with a small aspect ratio, the strain-suppressing effect of the fibers is diminished when stress is applied, causing the composite resin to deform and the elastic modulus to decrease.

[0040] This section describes the relationship between aspect ratio and impact resistance. When a composite resin molded product is subjected to impact load, if there are fibers with a large aspect ratio, the fibers cannot follow the expansion of the resin, causing cracks to form between the resin and fibers, which then propagate into fractures. On the other hand, if there are fibers with a small aspect ratio, the fibers are finer, so they can follow the expansion of the resin during impact loads, making it less likely for cracks to form and thus less likely for the product to fracture.

[0041] Next, we will explain the appearance. When a composite resin composition is applied to parts of home appliances and other devices that require coloring in multiple colors, including white, the composite resin molded article must have colorability. In order for a composite resin molded article to have colorability, the whiteness of the composite resin molded article must be maintained, and the whiteness of the added fibers must also be maintained. For example, whiteness can be expressed by the L* value (also called lightness or L value) in the L*a*b* color system. This whiteness is inversely proportional to the amount of the furan ring compound mentioned above, and a higher L* value obtained by measuring the color difference of the fibers is preferable. The L* value of the fibers that improves the colorability of the composite resin molded article has been calculated experimentally, and it is preferable that the L* value exceeds 80, and even more preferable that the L* value is 85 or higher.

[0042] To further improve mechanical properties, a larger specific surface area of ​​the fibers is preferable, as a greater number of bonding interfaces between the fibers and the main resin leads to an improvement in the elastic modulus. To increase the specific surface area of ​​the fibers, the most preferable structure is one in which at least one end A in the fiber length direction is partially defibrated, as shown in Figure 3.

[0043] As described above, by defibrating only the tip of the fiber, the antibacterial properties of the composite resin molded body can be further enhanced. The defibrated portion at the tip of the fiber of the fibrous filler is relatively more damaged than the undefibrated portion in the center and is more easily decomposed by heat. Therefore, the heat generated during kneading and molding makes it easier to generate furan ring compounds, making it possible to further enhance the antibacterial properties while maintaining the strength of the composite resin molded body. In other words, the fibrous filler 2 has an undefibrated central portion and defibrated ends. The main resin 1 includes a portion surrounding the central portion of the fibrous filler 2 (first portion) and a portion surrounding the ends of the fibrous filler 2 (second portion). The second portion contains more furan ring compounds than the first portion. Figure 3 shows an electron microscope image of the defibrated portion. The optimal fiber shape has been calculated from experimental and simulation results as follows: The defibrated portion is preferably 5% or more and 30% or less of the total fiber length L of the fibrous filler 2. If the defibration portion accounts for 5% or more of the total fiber length L, furan ring compounds are more easily generated by heat, resulting in improved antibacterial properties. If it is 30% or less, fiber decomposition is suppressed, leading to the maintenance of good strength and reducing discoloration of the molded product, thus achieving a good appearance.

[0044] During the molding of the resin body, a slow cooling thermal process allows the tips of the fibers, which have been defibrated only at the ends, to remain inside the molded body, while the central portion remains outside. This reduces the exposure of the areas with a high concentration of furan ring compounds at the ends to the surface of the molded body, minimizing the loss of furan ring compounds due to volatilization or solvent washing, and thus enabling the maintenance of antibacterial and antiviral properties for a longer period.

[0045] Next, the properties of fibrous filler 2 will be explained. The types of main resin 1 and fibrous filler 2 are as described above. If fibrous filler 2 is too soft relative to main resin 1, i.e., has a low modulus of elasticity, the composite resin molded article will have a low modulus of elasticity overall, resulting in reduced strength. On the other hand, if fibrous filler 2 is too hard relative to main resin 1, i.e., has a high modulus of elasticity, the shock wave generated during impact will not propagate but will be absorbed at the interface between main resin 1 and fibrous filler 2. As a result, cracks and crazing are more likely to occur near that interface, resulting in reduced impact strength. Therefore, it is preferable that the modulus of elasticity of fibrous filler 2 is higher than that of main resin 1, and that the difference is as small as possible. The optimal relationship is calculated from simulation results, and it is preferable that the difference in modulus of elasticity between main resin 1 and fibrous filler 2 is within 20 GPa.

[0046] Furthermore, these fibrous fillers 2 may be surface-treated with various titanate-based coupling agents, silane coupling agents, unsaturated carboxylic acids, maleic acid, maleic anhydride, or modified polyolefins grafted with the anhydride, fatty acids, fatty acid metal salts, fatty acid esters, etc., for purposes such as improving adhesion to the main resin 1 or dispersibility in the composite resin molded product. Alternatively, those surface-treated with thermosetting or thermoplastic polymer components are also acceptable.

[0047] <Method for manufacturing a composite resin molded product> Next, the method for manufacturing the composite resin molded article will be described. Figure 4 is a flowchart illustrating the manufacturing process of the composite resin molded article in this embodiment 1.

[0048] (1) The main resin, fibrous fillers including particulate fillers, and a dispersant as needed are introduced into the melt-kneading apparatus and melt-kneaded within the apparatus. As a result, the main resin melts, and the fibrous fillers and dispersant are dispersed in the molten main resin. At the same time, the shearing action of the apparatus promotes the defibrillation of aggregates of fibrous fillers, allowing the fibrous fillers to be finely dispersed in the main resin.

[0049] Conventionally, fibrous and particulate fillers were used after pre-treatment such as wet dispersion to defibrate the fibers. However, when fibrous fillers are pre-defibrated in the solvent used in wet dispersion, they defibrate more easily than when defibrated in the molten main resin, making it difficult to defibrate only the ends, resulting in the entire fibrous filler being defibrated. In addition, the pre-treatment process increases the number of steps and reduces productivity.

[0050] In contrast, the manufacturing process for the composite resin molded article in this embodiment does not involve pretreatment by wet dispersion for the purpose of defibration and modification of fibrous fillers and particulate fillers, but instead performs melt-kneading treatment (all-dry method) together with the main resin and dispersant. In this method, by not performing wet dispersion treatment of the fibrous fillers, the fibrous fillers can be partially defibrated only at the ends as described above, and the number of steps is reduced, improving productivity.

[0051] To produce the fibers of this embodiment using a completely dry process, it is preferable to apply high shear stress during mixing. Specific mixing methods include single-screw mixers, twin-screw mixers, roll mixers, Banbury mixers, and combinations thereof. Continuous twin-screw mixers and continuous roll mixers are particularly preferred from the viewpoint of easily applying high shear stress and having high mass production capabilities. Any mixing method other than those mentioned above is acceptable as long as it can apply high shear stress.

[0052] (2) The composite resin molded body extruded from the melting and mixing device is processed into pellets through a cutting process such as a pelletizer. Methods of pelletization include methods performed immediately after resin melting, such as the air hot cutting method, the underwater hot cutting method, and the strand cutting method. Alternatively, there are also crushing methods, which involve crushing and cutting the molded body or sheet after it has been formed.

[0053] By injection molding these pellets, injection-molded products can be produced as composite resin molded bodies. As described above, the mixing of fibrous fillers and particulate fillers in the pellets allows for the creation of injection-molded products with excellent antibacterial properties, strength, and appearance. The inventors will now describe various examples and comparative examples from their experiments.

[0054] (Example 1) A pulp-dispersed polypropylene composite resin molded article was produced by the following manufacturing method.

[0055] Coniferous pulp (manufactured by Mitsubishi Paper Mills Ltd., product name: NBKP Celgar) was used as the starting material for the fibrous filler and particulate filler. This coniferous pulp was crushed in a pulverizer to obtain a mixture of fibrous filler and particulate filler. The aspect ratio of each was adjusted during the crushing process. Polypropylene (manufactured by Prime Polymer Co., Ltd., product name: J108M) as the main resin, the mixture of the fibrous and particulate filler, and maleic anhydride (manufactured by Sanyo Chemical Industries, Ltd., product name: Yumex) were weighed in a weight ratio of 43:55:2 and dry blended. Then, the mixture was melt-kneaded and dispersed in a twin-screw kneader (manufactured by Kurimoto Iron Works Co., Ltd., KRC Kneader). The shear force could be changed by changing the screw configuration of the twin-screw kneader, and in Example 1, a medium shear type specification was used. The molten resin was hot-cut to produce pulp-dispersed polypropylene pellets.

[0056] Test specimens of composite resin molded products were prepared using the fabricated pulp-dispersed polypropylene pellets and an injection molding machine (Japan Steel Works 180AD). The conditions for preparing the test specimens were a resin temperature of 210°C, a mold temperature of 60°C, an injection speed of 60 mm / s, and a holding pressure of 80 MPa. The shape of the test specimens was changed according to the evaluation items described below, and a No. 1 size dumbbell was prepared for elastic modulus measurement. The obtained pulp-dispersed polypropylene composite resin molded product test specimens were evaluated using the following method.

[0057] (Fiber aspect ratio, end defibrillation degree) The obtained pulp-dispersed polypropylene pellets were immersed in xylene solvent to dissolve the polypropylene, and the shape of the remaining pulp fibers was observed using a scanning electron microscope (SEM). Approximately 50 representative fibers were measured at 5 locations. The results showed that an average percentage of fibers with an aspect ratio of 10 or greater was 7.5%, an average percentage of fibers with an aspect ratio of 2 or less was 55%, and the remainder were fibers with an aspect ratio greater than 2 but less than 10. Fillers with an aspect ratio of 10 or greater were classified as fibrous fillers, and fillers with an aspect ratio of 2 or less were classified as particulate fillers. The ends of the fibers were defibrated, and the average percentage of the length of a single fiber that was defibrated was 25%.

[0058] (Furan ring compound concentration and location) The concentration and location of furan ring compounds in composite resin molded articles were measured using gas chromatography-mass spectrometry (GC / MS). The sample to be measured was extracted from the composite resin molded article, freeze-dried, immersed in distilled chloroform, refluxed, and then filtered to separate chloroform-soluble and insoluble materials. The chloroform-soluble material was evaporated and dried, then dissolved again in distilled chloroform for GC / MS analysis. The concentration of furan ring compounds in a sample taken from the entire composite resin molded article was 7 ppb. When the concentration of furan ring compounds was measured from the resin surrounding particulate and fibrous fillers, the concentration around the particulate fillers was higher.

[0059] (Whiteness of molded product) To measure the whiteness of the molded product, a colorimeter (Konica Minolta Japan, Inc., Colorimeter CR-400) was used. The L* value in the L*a*b* color system was used as the scale for whiteness. The L* value was 90.

[0060] (Antibacterial properties of composite resin molded products) An antimicrobial test was conducted using the obtained dumbbell-shaped test piece No. 1. The antimicrobial test was conducted in accordance with JIS Z 2801, using Escherichia coli (NBRC 3972) and Staphylococcus aureus (NBRC 12732) as test bacteria, with an initial bacterial count of approximately 104 The bacterial count was measured after 24 hours, with a concentration of cfu / mL. The bacterial count is expressed as a common logarithm. In the case of polypropylene resin alone without pulp, the bacterial count after 24 hours was 5 for both E. coli and Staphylococcus aureus, compared to an initial count of 4. In this example, the bacterial count after 24 hours was 0 for both E. coli and Staphylococcus aureus in the sample.

[0061] (Antiviral properties of composite resin molded products) An antiviral test was conducted using the obtained dumbbell-shaped test specimen No. 1. The antiviral test was conducted in accordance with JIS R 1706:2013, using bacteriophage Qβ as the virus species, and the initial infectivity titer was set to approximately 10. 6 The CFU / test specimen was used, and the viral infectivity titer was measured after 24 hours. The viral count is expressed as a common logarithm; while the initial count was 6, the viral count after 24 hours for polypropylene resin alone (without pulp) was 5. The viral count of the sample in this example after 24 hours was 1.

[0062] (Elastic modulus of composite resin molded articles) A bending test was conducted using the obtained dumbbell-shaped specimen (No. 1). The bending modulus was 4.3 GPa, indicating a reinforcement effect from the filler.

[0063] (Appearance of composite resin molded products) The appearance of the composite resin molded body was evaluated at a visual level. A uniform appearance without color unevenness or browning was considered OK, while an appearance with color unevenness or browning was considered NG. This sample passed the appearance evaluation.

[0064] (Example 2) In Example 2, the pulp concentration was changed to 70%, and pulp-dispersed polypropylene pellets and composite resin molded articles were produced using the same material and process conditions as in Example 1. The evaluation was also performed in the same manner as in Example 1.

[0065] (Example 3) In Example 3, the resin temperature during molding was set to 240 degrees Celsius, and pulp-dispersed polypropylene pellets and composite resin molded articles were produced using the same material and process conditions as in Example 1. The evaluation was also carried out in the same manner as in Example 1.

[0066] (Example 4) In Example 4, heat was applied during pulp grinding to damage the entire filler. Other material and process conditions were the same as in Example 1 to produce pulp-dispersed polypropylene pellets and composite resin molded articles. The evaluation was also the same as in Example 1.

[0067] (Example 5) In Example 5, the number of passes through the kneader was increased to seven times the normal number to promote fiber defibration. Other material and process conditions were the same as in Example 1 to produce pulp-dispersed polypropylene pellets and composite resin molded articles. The evaluation was also the same as in Example 1.

[0068] (Comparative Example 1) In Comparative Example 1, the pulp concentration was changed to 20%, and pulp-dispersed polypropylene pellets and composite resin molded articles were produced using the same material and process conditions as in Example 1. The evaluation was also performed in the same manner as in Example 1.

[0069] (Comparative Example 2) In Comparative Example 2, pulp-dispersed polypropylene pellets and composite resin molded articles were produced without pulverizing the pulp, using the same material and process conditions as in Example 1. The evaluation was also carried out in the same manner as in Example 1.

[0070] (Comparative Example 3) In Comparative Example 3, a low-shear type kneader was used to prevent fiber defibration. Other material and process conditions were the same as in Example 1 to produce pulp-dispersed polypropylene pellets and composite resin molded articles. The evaluation was also the same as in Example 1.

[0071] (Comparative Example 4) In Comparative Example 4, powdered cellulose was used as the starting material for the pulp, and pulp-dispersed polypropylene pellets and composite resin molded articles were produced using the same material and process conditions as in Example 1. The evaluation was also carried out in the same manner as in Example 1.

[0072] Figure 5 is Table 1, which shows the measurement results for each of Examples 1 to 5 and each of Comparative Examples 1 to 4.

[0073] As is clear from Table 1 in Figure 5, in Example 2, where the pulp concentration was changed to a high concentration of 70%, the furan ring compound concentration increased to 300 ppb. Consequently, the L* value, which indicates whiteness, decreased slightly to 82, but the modulus of elasticity increased. Since the furan ring compound was present at the predetermined concentration, it was confirmed that it had antibacterial properties against both E. coli and Staphylococcus aureus, as well as antiviral properties. Furthermore, in Examples 1, 2, and 5, the molded article contained fibrous filler and particulate filler with a smaller aspect ratio than the fibrous filler. The fibrous filler had an aspect ratio of 10 or more, and the particulate filler had an aspect ratio of 2 or less. The molded article contained a furan ring compound, with a concentration between 4 ppb and 1000 ppb, and the furan ring compound was present in greater quantities in the resin surrounding the particulate filler than in the resin surrounding the fibrous filler. In such cases, it was confirmed that a molded article could be obtained that achieved a balance of antibacterial properties, antiviral properties, high modulus of elasticity, and good appearance.

[0074] In Example 3, where the resin temperature during molding was 240°C, thermal decomposition of the pulp progressed, and the furan ring compound increased considerably to 90,000 ppb. However, the molded product turned brown, resulting in an unacceptable appearance, and the elastic modulus was also somewhat low.

[0075] In Example 4, where heat was applied during pulp grinding to damage the entire filler, the proportion of furan ring compounds in the molded product became approximately equal between particulate and fibrous fillers. This resulted in a slight decrease in whiteness, color unevenness, and an unacceptable appearance.

[0076] In Example 5, where the number of passes through the kneader was increased to seven times the normal number to promote fiber defibration, the fibers in the composite resin molded body were considerably defibrated, with an end defibration degree of 60%. As a result, the concentration of furan ring compounds in the molded body increased, resulting in good antibacterial and antiviral properties, but the reinforcing effect of the fibers was reduced, resulting in a slightly lower elastic modulus.

[0077] In Comparative Example 1, where the pulp concentration was changed to 20%, the furan ring compound concentration was below the detection limit of 2 ppb. As a result, it exhibited poor antibacterial activity against both E. coli and Staphylococcus aureus, poor antiviral activity, and a low modulus of elasticity.

[0078] In Comparative Example 2, where the pulp was not crushed, the fibrous filler ratio was 100% and the particulate filler ratio was 0%. As a result, the elastic modulus was slightly higher, but the antibacterial activity against both E. coli and Staphylococcus aureus was poor, and the antiviral activity was also poor.

[0079] In Comparative Example 3, where a low-shear type kneader was used to prevent fiber defibration, the fibers in the composite resin molded body did not defibrate much, and there were no fibers that defibrated at the ends. As a result, the concentration of furan ring compounds in the molded body was low, leading to poor antibacterial activity against both E. coli and Staphylococcus aureus, as well as poor antiviral activity.

[0080] In Comparative Example 4, where powdered cellulose was used as the starting material for the pulp, the fibrous filler ratio was 0% and the particulate filler ratio was 100%. As a result, a large amount of furan ring compounds were generated, and antibacterial and antiviral properties were observed, but the molded article showed uneven coloring and an undesirable appearance, as well as a low elastic modulus.

[0081] Based on the above evaluation, the composite resin molded article contains fibrous filler and particulate filler with a smaller aspect ratio than the fibrous filler, the fibrous filler has an aspect ratio of 10 or more, the particulate filler has an aspect ratio of 2 or less, the molded article contains a furan ring compound, the concentration of the furan ring compound is 4 ppb or more and 1000 ppb or less, the whiteness of the composite resin molded article is 80 or more, the proportion of fibrous filler among the fillers is 1% or more and 10% or less, and the proportion of particulate filler among the fillers is It was found that when the decomposition rate is between 50% and 70%, the degree of decomposition is greater for particulate fillers than for fibrous fillers, the resin surrounding particulate fillers contains more thermal decomposition products of the fillers than the resin surrounding fibrous fillers, and only the ends of the fibrous fillers are defibrated, and the resin surrounding the ends of the fibrous fillers contains more thermal decomposition products of the fillers than the resin surrounding the central part of the fibrous fillers, it is possible to achieve a balance between antibacterial properties, antiviral properties, mechanical strength, and appearance.

[0082] Furthermore, this disclosure includes appropriately combining any of the various embodiments and / or examples described above, and the effects of each embodiment and / or example can be achieved. [Industrial applicability]

[0083] The composite resin molded articles described herein can be provided with antibacterial and antiviral properties, and offer superior mechanical strength compared to conventional general-purpose resins. Because the properties of the main resin can be improved by the composite resin molded articles described herein, they can be used as substitutes for engineering plastics or metal materials. Therefore, the manufacturing costs of various industrial products or household goods made of engineering plastics or metals can be significantly reduced. Furthermore, they can be used in home appliance casings, building materials, and automotive components. [Explanation of Symbols]

[0084] 1. Main resin 2. Fibrous filler (filler) 3. Particulate fillers (fillers) 4. Regions with high concentrations of furan ring compounds

Claims

1. Main resin and The filler dispersed in the main resin, Furan ring compounds and, A composite resin molded article comprising, The filler comprises a fibrous filler and a particulate filler having a smaller aspect ratio than the fibrous filler. The fibrous filler has an aspect ratio of 10 or more, and the particulate filler has an aspect ratio of 2 or less, The concentration of the furan ring compound contained in the composite resin molded body is 4 ppb or more and 1000 ppb or less, Of the fillers, the proportion of the fibrous filler is 1% or more and 10% or less. Of the fillers, the proportion of particulate fillers is 50% or more and 70% or less. The fibrous filler includes a central portion and an end portion, The fibrous filler is defibrated only at its ends. The main resin comprises a first portion located around the central part of the fibrous filler and a second portion located around the ends of the fibrous filler. The second portion contains more of the furan ring compound than the first portion, The filler is present in an amount of 55 to 70% by weight relative to the total weight of the composite resin molded body. The composite resin molded article has an L* value of 80 or more according to the L*a*b* color system, The filler includes celluloses that decompose to generate furan ring compounds. Composite resin molded body.

2. The composite resin molded article according to claim 1, wherein the furan ring compound is present in greater quantities near the surface than inside the composite resin molded article.

3. The composite resin molded article according to claim 1 or 2, wherein the main resin is an olefin resin.

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