Cellulose fiber-containing resin composite, cellulose fiber-containing resin molded body, and component or article having hinge constituted from cellulose fiber-containing resin composite

Abstract

Provided are: a cellulose fiber-containing resin composite comprising a polypropylene (PP) resin and cellulose fibers (CF) and satisfying condition 1 or 2 below; and a cellulose fiber-containing resin molded body obtained by molding the same. -Condition 1- The CF average diameter is 5-15 μm, the CF average length is more than 35 μm but not more than 130 μm, and inequality expression A is satisfied where the proportion of CF in the total amount of PP and CF is Xa mass% and the proportion of soft PP in the PP is Ya mass%.　Inequality expression A:　Ya≥Xa×2.5, where Xa>0 and Ya>0 -Condition 2- The CF average diameter is 5-10 μm, the CF average length is not more than 35 μm, and inequality expression B is satisfied where the proportion of CF in the total amount of PP and CF is Xb mass% and the proportion of soft PP in the PP is Yb mass%.　Inequality expression B:　Yb≥Xb×2.5-25, where Xb>0 and Yb>0

Description

Cellulose fiber-containing resin composite, cellulose fiber-containing resin molded body, and parts or articles having a hinge portion made of a cellulose fiber-containing resin composite.

[0001] The present invention relates to a cellulose fiber-containing resin composite, a cellulose fiber-containing resin molded article, and a part or article having a hinge portion composed of a cellulose fiber-containing resin composite.

[0002] Cellulose fibers are an inexhaustible natural resource found in all plants, and because they are lightweight yet high-strength, their application in automotive parts and structural materials by compounding them with resins is being considered. However, in order to put resin composites containing cellulose fibers into practical use, it is necessary to sufficiently improve the integration between the highly hydrophilic cellulose fibers and the highly hydrophobic resin, such as polyolefin resin, and there are limitations to improving the reinforcing effect of resins by cellulose fibers.

[0003] Various proposals have been made to enhance the reinforcing effect of cellulose fibers. For example, Patent Document 1 discloses a resin composite comprising a resin and cellulose fibers, wherein the resin composite is obtained by kneading the resin and cellulose fiber pre-defibration using a uniscrew or multiscrew kneader, the cellulose fiber pre-defibration is obtained by mechanically treating pulp, the cellulose fiber pre-defibration contains 40% to less than 58% of fibers with a fiber length of 0.1 mm or more and less than 0.5 mm, and 5% to less than 10% of fibers with a fiber length of 1.5 mm or more and less than 2.0 mm, and the proportion of cellulose fibers contained in the resin composite having an average fiber width of 1 μm or less is 50 volume% or more. According to this resin composite, it has a high tensile modulus and high tensile strength, and is said to have an excellent balance with tensile elongation. Furthermore, Patent Document 2 discloses a resin composition containing modified cellulose fibers and a resin obtained by a method for producing modified cellulose fibers, in which one or more compounds selected from aromatic ring-containing alkylene oxide compounds and aromatic ring-containing glycidyl ether compounds are introduced to a cellulose-based raw material via ether bonding in the presence of a base, followed by micronization treatment. This resin composition is said to have excellent mechanical strength and toughness.

[0004] In order to realize a sustainable society, in recent years, the momentum for plastic reduction has been increasing globally. As a material that reduces the amount of plastic used as much as possible and realizes a reduction in environmental load, resin composites containing cellulose fibers have attracted attention.

[0005] Japanese Patent Application Laid-Open No. 2022-118772, Japanese Patent Application Laid-Open No. 2018-145571

[0006] Generally, a resin molded body obtained by adding cellulose fibers to a resin has improved mechanical properties such as bending strength, but has a hard and brittle characteristic. When used as a material for a hinge part or the like, there is a problem that cracks and cracks are likely to occur due to bending. An object of the present invention is to provide a cellulose fiber-containing resin molded body having excellent flexural resistance (flexibility that does not cause cracks or cracks even when bent), and a cellulose fiber-containing resin composite suitable for obtaining this resin molded body. Another object of the present invention is to provide a part or article having a hinge portion composed of a cellulose fiber-containing resin composite.

[0007] The present inventors have found that in a resin composite combining a polypropylene resin and cellulose fibers, by containing a specific amount of a soft polypropylene resin in the polypropylene resin and further keeping the average fiber diameter and average fiber length of the cellulose fibers within a specific range, the flexural resistance of the resin molded body obtained using this composite can be effectively enhanced. The present invention has been completed through further studies based on these findings.

[0008] In other words, the above problems of the present invention have been solved by the following means. [1] A cellulose fiber-containing resin composite comprising a polypropylene resin and cellulose fibers, which satisfies either of the following conditions 1 or 2. -Condition 1- The average fiber diameter of the cellulose fibers is 5 to 15 μm, and the average fiber length is greater than 35 μm and less than or equal to 130 μm, and when the proportion of the cellulose fibers in the total amount of the polypropylene resin and the cellulose fibers is Xa by mass%, and the proportion of the soft polypropylene resin in the polypropylene resin is Ya by mass%, the following inequality A is satisfied. Inequality A: Ya ≥ Xa × 2.5 Xa > 0, Ya > 0 -Condition 2- The average fiber diameter of the cellulose fibers is 5 to 10 μm, and the average fiber length is 35 μm or less, and when the proportion of the cellulose fibers in the total amount of the polypropylene resin and the cellulose fibers is Xb by mass%, and the proportion of the soft polypropylene resin in the polypropylene resin is Yb by mass%, the following inequality B is satisfied. Inequality B: Yb ≥ Xb × 2.5 - 25 Xb > 0, Yb > 0 [2] A cellulose fiber-containing resin composite according to [1], wherein Xa is 5 to 40% by mass. [3] A cellulose fiber-containing resin composite according to [1], wherein Xb is 5 to 50% by mass. [4] A cellulose fiber-containing resin molded article obtained by molding a cellulose fiber-containing resin composite according to any one of [1] to [3]. [5] A part or article having a hinge portion made of a cellulose fiber-containing resin composite according to any one of [1] to [3].

[0009] In the description of this invention, "~" is used to mean that the numerical values ​​described before and after it are included as the lower limit and upper limit.

[0010] The cellulose fiber-containing resin composite of the present invention can produce a resin molded article with excellent bending resistance. Because the cellulose fiber-containing resin molded article of the present invention has excellent bending resistance, it is suitable as a part or article itself for articles that require various bending processes. A part or article having a hinge portion made of the cellulose fiber-containing resin composite of the present invention has excellent bending resistance.

[0011] Figure 1 is an explanatory diagram showing the shape of the resin molded body (test piece) used in the bending resistance test of the example. Figure 1(a) is a front view of the test piece, and Figure 1(b) is a side view of the test piece when bent at 90°. Figure 2 is a graph summarizing the relationship between composition and bending resistance when cellulose fiber-2 is used. Figure 3 is a graph summarizing the relationship between composition and bending resistance when cellulose fiber-3 is used. Figure 4 is a graph summarizing the relationship between composition and bending resistance when cellulose fiber-4 is used.

[0012] [Cellulose Fiber-Containing Resin Composite] The cellulose fiber-containing resin composite of the present invention (hereinafter also referred to as "the composite of the present invention") contains polypropylene resin and cellulose fibers in a specific ratio. Furthermore, the composite of the present invention uses polypropylene resin as the base resin and contains a specific amount of soft polypropylene resin in the polypropylene resin. In addition, the composite of the present invention satisfies either of the following conditions 1 and 2. That is, the composite of the present invention encompasses two embodiments (the embodiment of condition 1 and the embodiment of condition 2) depending on the average fiber length of the cellulose fibers.

[0013] -Condition 1- The average fiber diameter of the cellulose fibers is 5 to 15 μm, and the average fiber length is greater than 35 μm and less than or equal to 130 μm. When the proportion of cellulose fibers in the total amount of polypropylene resin and cellulose fibers is Xa by mass%, and the proportion of soft polypropylene resin in the polypropylene resin is Ya by mass%, the following inequality A is satisfied. Inequality A: Ya ≥ Xa × 2.5 Xa > 0, Ya > 0

[0014] -Condition 2- The average fiber diameter of the cellulose fibers is 5 to 10 μm, and the average fiber length is 35 μm or less. When the proportion of cellulose fibers in the total amount of polypropylene resin and cellulose fibers is Xb by mass%, and the proportion of soft polypropylene resin in the polypropylene resin is Yb by mass%, the following inequality B is satisfied. Inequality B: Yb ≥ Xb × 2.5 - 25 Xb > 0, Yb > 0

[0015] The composite of the present invention effectively enhances the bending resistance of the composite or the resin molded article obtained using it, while enjoying the reinforcing effect of the cellulose fibers, by controlling the ratio and size of cellulose fibers in the polypropylene resin, as well as the ratio of soft polypropylene resin in the polypropylene resin, within a specific range.

[0016] The embodiment of Condition 1 will now be described. In the embodiment of Condition 1, cellulose fibers with an average fiber diameter of 5 to 15 μm and an average fiber length exceeding 35 μm and not exceeding 130 μm are used. By setting the average fiber diameter and average fiber length within the above range, and by ensuring that the ratio of cellulose fibers to soft polypropylene satisfies inequality A, the flexibility of the composition is increased and its bending resistance is improved. The cellulose fibers preferably have an average fiber length of 40 to 130 μm, and more preferably 50 to 130 μm.

[0017] The average fiber diameter and average fiber length of cellulose fibers are measured using a scanning electron microscope (SEM) if the fiber length is 200 μm or less, and using a fiber analyzer if the fiber length exceeds 200 μm. Specifically, the measurements can be taken as follows: When using an SEM, observe an image at a magnification of 200 to 1000x, randomly select 20 fibers from the observation surface for which both the short side (fiber diameter) and long side (fiber length) can be measured, and take the average fiber diameter (arithmetic mean) of the 20 fiber diameters as the average fiber diameter, and the average fiber length (arithmetic mean) of the 20 fiber lengths as the average fiber length. The magnification should be the maximum magnification that allows at least 5 measurable fibers to fit within one field of view. A "measurable fiber" means a fiber that fits from end to end within the field of view and is not bent. "Not bent" means that the fiber is not bent in the depth direction of the image. If there are not 20 "measurable fibers" in one field of view, observe using multiple fields of view and measure a total of 20 fibers. Furthermore, when using a fiber analyzer, the mean fiber width (arithmetic mean) obtained by measurement with MORFI COMPACT (TECKPAP) is used as the average fiber diameter, and the mean length-weighted fiber length (Σ(Li*Li) / ΣLi) is used as the average fiber length. Six 50 mg / L fiber suspensions are used for measuring each fiber. MORFI COMPACT considers objects with a length of 200 μm to 10,000 μm and a width of 5 μm to 75 μm as fibers, and automatically analyzes fibers within an 11 × 13 mm field of view.

[0018] The proportion Xa of cellulose fibers in the total amount of polypropylene resin and cellulose fibers is not particularly limited as long as the above inequality A is satisfied. Xa is preferably 5 to 40% by mass, more preferably 10 to 38% by mass, and even more preferably 15 to 35% by mass. From the viewpoint of reducing environmental impact, a higher proportion Xa of cellulose fibers is preferable.

[0019] The proportion Ya of soft polypropylene resin in the polypropylene resin is not particularly limited as long as the above inequality A is satisfied. Ya is preferably 10 to 100% by mass, more preferably 20 to 80% by mass, and even more preferably 40 to 60% by mass. From the viewpoint of increasing the bending strength of the resin molded article and from the viewpoint of forming the resin molded article by extrusion molding, a smaller proportion of soft polypropylene resin is preferable. From the viewpoint of achieving a good balance between bending resistance and bending strength in the resin molded article, Ya is preferably 20 to 80% by mass, and more preferably 40 to 60% by mass.

[0020] The embodiment of Condition 2 will now be described. In the embodiment of Condition 2, cellulose fibers with an average fiber diameter of 5 to 10 μm and an average fiber length of 35 μm or less are used. By keeping the average fiber diameter within the above range and the average fiber length below the above upper limit, and by satisfying inequality B with respect to the ratio of cellulose fibers and soft polypropylene, the flexibility of the composition is increased and its bending resistance is improved. The cellulose fibers preferably have an average fiber length of 10 to 35 μm, and more preferably 10 to 30 μm.

[0021] The proportion Xb of cellulose fibers in the total amount of polypropylene resin and cellulose fibers is not particularly limited as long as it satisfies the above inequality B. Xb is preferably 5 to 50% by mass, more preferably 10 to 48% by mass, and even more preferably 15 to 45% by mass. From the viewpoint of reducing environmental impact, a higher proportion Xb of cellulose fibers is preferable.

[0022] The proportion Yb of soft polypropylene resin in the polypropylene resin is not particularly limited as long as the above inequality B is satisfied. Yb is preferably 10 to 100% by mass, more preferably 20 to 80% by mass, and even more preferably 40 to 60% by mass. From the viewpoint of increasing the bending strength of the resin molded article and from the viewpoint of forming the resin molded article by extrusion molding, a smaller proportion of soft polypropylene resin is preferable. From the viewpoint of achieving a good balance between bending resistance and bending strength in the resin molded article, Yb is preferably 20 to 80% by mass, and more preferably 40 to 60% by mass.

[0023] Furthermore, matters common to both the aspects of Condition 1 and Condition 2 will be explained.

[0024] In the composite of the present invention, the base resin preferably contains 90% by mass or more of polypropylene resin, more preferably 95% by mass or more, and even more preferably 98% by mass or more. The base resin can be 100% by mass of polypropylene resin.

[0025] Each component constituting the complex of the present invention will be described in more detail.

[0026] (Polypropylene Resin) Examples of polypropylene resins include propylene homopolymers, propylene-ethylene random copolymers, propylene-α-olefin random copolymers, propylene-ethylene-α-olefin copolymers, propylene block copolymers (polymers consisting of a propylene homopolymer component or a copolymer component mainly composed of propylene, and a copolymer component obtained by copolymerizing at least one monomer selected from ethylene and α-olefin with propylene), copolymers of the above copolymers with ethylene-propylene rubber or ethylene-propylene diene rubber, and resins or rubbers of mixtures or composites. These polypropylene resins may be used alone or in combination of two or more. In this invention, resins containing both ethylene and propylene components are classified as polypropylene resins.

[0027] The α-olefin used in polypropylene resin is preferably at least one of 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, and 1-decene, and more preferably at least one of 1-butene, 1-hexene, and 1-octene.

[0028] Examples of propylene-α-olefin random copolymers include propylene-1-butene random copolymer, propylene-1-hexene random copolymer, and propylene-1-octene random copolymer.

[0029] Examples of propylene-ethylene-α-olefin copolymers include propylene-ethylene-1-butene copolymer, propylene-ethylene-1-hexene copolymer, and propylene-ethylene-1-octene copolymer. Random copolymers are preferred. Examples of propylene block copolymers include (propylene)-(propylene-ethylene) copolymer, (propylene)-(propylene-ethylene-1-butene) copolymer, (propylene)-(propylene-ethylene-1-hexene) copolymer, (propylene)-(propylene-1-butene) copolymer, (propylene)-(propylene-1-hexene) copolymer, (propylene-ethylene)-(propylene-ethylene) copolymer, (propylene-ethylene)-(propylene-ethylene-1-butene) copolymer, (propylene-ethylene)-(propylene-ethylene- Examples include 1-hexene copolymer, (propylene-ethylene)-(propylene-1-butene) copolymer, (propylene-ethylene)-(propylene-1-hexene) copolymer, (propylene-1-butene)-(propylene-ethylene) copolymer, (propylene-1-butene)-(propylene-ethylene-1-butene) copolymer, (propylene-1-butene)-(propylene-ethylene-1-butene) copolymer, (propylene-1-butene)-(propylene-ethylene-1-hexene) copolymer, (propylene-1-butene)-(propylene-1-butene) copolymer, and (propylene-1-butene)-(propylene-1-hexene) copolymer.

[0030] Of these polypropylene resins, propylene homopolymer, propylene-ethylene random copolymer, propylene-1-butene random copolymer, propylene-ethylene-1-butene random copolymer, and propylene block copolymer are preferred, and one or more of these can be used as the polypropylene resin.

[0031] The melt flow rate (MFR) of the polypropylene resin is preferably 0.1 to 100 g / 10 min, and more preferably 10 to 30 g / 10 min. For the polypropylene resin, the value is obtained in accordance with JIS K7210-1:2014, at 230°C and under a load of 2.16 kg.

[0032] The density of polypropylene resin is 0.90–0.91 g / cm³. ３ It is preferable.

[0033] Preferably, the polypropylene resin is one in which at least a portion of the polypropylene resin forms a crystalline structure at room temperature (25°C) within the molded resin. When differential scanning calorimetry (DSC measurement) is performed on a molded resin containing such polypropylene resin, a melting peak associated with the melting of polypropylene crystals is observed at 164±5°C.

[0034] In this invention, the polypropylene resin includes flexible polypropylene resin. In this invention, flexible polypropylene resin means a polypropylene resin in which the tanδ peak at -40°C ± 10°C, described later, is higher than 0.05 and lower than 0.30. The flexible polypropylene resin can be selected from the above-mentioned polypropylene resins and exhibit the above-mentioned tanδ peak, and a polypropylene resin containing both hard and soft components is preferred. Generally, polypropylene resins have a tanδ (loss tangent) peak at least at 0°C ± 10°C in dynamic viscoelasticity measurements performed in accordance with JIS K7244-4:1999, and may also have a tanδ peak at -40°C ± 10°C. For polypropylene resins other than the flexible polypropylene resin in this invention, if the tanδ peak is at -40°C ± 10°C, the peak height is 0.03 to 0.05. On the other hand, the flexible polypropylene resin in this invention has a tanδ peak at -40°C ± 10°C that is higher than 0.05 and lower than 0.30. Therefore, in this invention, the intensity of the tanδ peak at -40°C ± 10°C in the dynamic viscoelasticity measurement described above is used as an indicator, and among polypropylene resins, those in which the tanδ peak at -40°C ± 10°C is higher than 0.05 and lower than 0.30 are defined as soft polypropylene resins. Hereafter, polypropylene resins other than soft polypropylene resins may be referred to as "hard polypropylene resins." Furthermore, the term "polypropylene resin" is used without distinguishing between soft polypropylene resins and hard polypropylene resins.

[0035] The rigid polypropylene resin may be modified. For example, the rigid polypropylene resin may be modified with an unsaturated carboxylic acid compound or its anhydride. Alternatively, the rigid polypropylene resin may be modified with an alkoxysilane compound (for example, a silane coupling agent having an alkoxysilyl group). The proportion of the modified polypropylene resin in the polypropylene resin is preferably 10% by mass or less, and more preferably 5% by mass or less.

[0036] (Cellulose Fibers) Cellulose fibers have higher strength and rigidity compared to the base resin. Therefore, cellulose fibers reinforce the base resin and increase the rigidity of the resin molded product. The cellulose fibers used in this invention are preferably fine plant-derived cellulose fibers (powdered pulp). Pulp is also a raw material for paper and is mainly composed of tracheids extracted from plants. Chemically, the main component is polysaccharides, and the main component of those is cellulose. Plant-derived cellulose fibers are not particularly limited, but examples include those derived from plants such as wood, bamboo, hemp, jute, kenaf, agricultural waste (e.g., straw from wheat and rice, stalks from corn and cotton, sugarcane), cloth, recycled pulp, waste paper, and wood powder. In this invention, wood or wood-derived materials are preferred, and kraft pulp is more preferred. Kraft pulp is a general term for pulp obtained by removing lignin and hemicellulose from wood or plant materials through chemical treatment with caustic soda, thereby extracting nearly pure cellulose. It is composed mainly of cellulose molecules, with hemicellulose and lignin. The size of the cellulose fibers used in this invention is one that satisfies the size specified in condition 1 or condition 2 among the above-mentioned cellulose fibers.

[0037] (Other Components) The composite of the present invention may consist of the polypropylene resin and cellulose fibers described above, and may also contain resins other than polypropylene resin as long as it does not impair the effects of the present invention. For example, the physical properties of the resin composite may be modified by adding an elastomer such as an ethylene-α-olefin copolymer. Furthermore, the composite of the present invention may appropriately contain antioxidants, light stabilizers, radical scavengers, ultraviolet absorbers, colorants (dyes, organic pigments, inorganic pigments), fillers, lubricants, plasticizers, processing aids such as acrylic processing aids, foaming agents, lubricants such as paraffin wax, surface treatment agents, crystal nucleating agents, mold release agents, hydrolysis inhibitors, antiblocking agents, antistatic agents, antifogging agents, anti-fogging agents, ion trapping agents, flame retardants, flame retardant aids, etc., as long as it does not impair the above objectives.

[0038] The composite of the present invention can be preferably used as a material for cellulose fiber-containing resin molded articles, as described later. The shape of the composite of the present invention is not particularly limited and can be molded into any desired shape. For example, it can be in the shape of pellets, strands, sheets / films, balls, or molded articles having a three-dimensional shape. Furthermore, the composite of the present invention may be in a molten state.

[0039] [Cellulose Fiber-Containing Resin Molded Article] The cellulose fiber-containing resin molded article of the present invention (also referred to as the molded article of the present invention) is obtained by molding the composite of the present invention into a desired shape. Therefore, the molded article of the present invention contains polypropylene resin and cellulose fibers and satisfies the above conditions 1 and 2. Thus, the composition of the molded article of the present invention is the same as that of the composite of the present invention. The molded article of the present invention can be a molded product (part or article) as shown in the [Applications] section below. The molded article of the present invention may have a hinge portion. The molded article of the present invention is less prone to cracking or splitting even after repeated bending; in other words, the composite of the present invention is suitable for forming parts or articles having a hinge portion. Therefore, a preferred form of the cellulose fiber-containing resin molded article of the present invention is a part or article having a hinge portion composed of the composite of the present invention.

[0040] [Method for producing a cellulose fiber-containing resin composite (composite formation method) and method for producing a resin molded article] The composite of the present invention can be obtained by melt-mixing a polypropylene resin (containing a specific amount of soft polypropylene resin) and cellulose fibers of a specific size in a specific ratio defined in the present invention. The resin molded article of the present invention can be obtained by molding the obtained molten mixture (cellulose fiber-containing resin composite) into a desired shape. The melt-mixing temperature is not particularly limited as long as it is above the melting point of the resin. For example, it can be 160 to 230°C, and more preferably 170 to 210°C. From the viewpoint of reducing thermal decomposition of cellulose fibers, the melt-mixing temperature is preferably 250°C or lower, more preferably 230°C or lower, and even more preferably 200°C or lower. When the melt-mixing step is performed at a high temperature, for example, an antioxidant or the like may be added during melt-mixing to suppress thermal degradation or oxidative degradation. The melt-mixing time is not particularly limited and can be set as appropriate. The apparatus used for the melt mixing described above is not particularly limited as long as it is capable of melt mixing at a temperature above the melting point of the resin components. Examples include blenders, kneaders, mixing rolls, Banbury mixers, and single-screw or twin-screw extruders, with twin-screw extruders being preferred. From the viewpoint of ease of handling in the subsequent molding process, it is preferable to process the obtained molten mixture into pellets (hereinafter, the obtained pellets will also be simply referred to as "pellets"). The conditions for pellet processing are not particularly limited and can be carried out by conventional methods. For example, one method is to cool the molten mixture with water and then process it into pellets using a strand cutter or the like. Prior to melt mixing, each component may be dry-blended (pre-mixed). Dry blending is not particularly limited and can be carried out by conventional methods.

[0041] The molded article of the present invention can be obtained by moltening the composite of the present invention (e.g., in pellet form) and using injection molding, extrusion molding, press molding, blow molding, etc. Molding can be performed simultaneously with or immediately following the preparation of the composite of the present invention (the molten mixture described above). For example, a series of steps can be employed in which each component constituting the composite of the present invention is molten and mixed in a molding apparatus during or immediately before injection molding, and then injected to form a desired shape.

[0042] In the injection molding described above, the injection temperature is not particularly limited as long as it is above the melting point of the polypropylene resin, and can be, for example, 160 to 230°C, with 170 to 210°C being preferred. From the viewpoint of reducing the thermal decomposition of cellulose fibers, the injection temperature is preferably 250°C or lower, more preferably 230°C or lower, and even more preferably 200°C or lower. The conditions such as injection speed, mold temperature, holding pressure, and holding pressure time in the injection molding described above can be appropriately adjusted according to the purpose.

[0043] [Use] Using the composite of the present invention, a foldable part (hinge part) can be formed. A molded product having a foldable part can be used as a part for imparting a hinge part to an article (finished product), or the molded product can be the article itself. The hinge part may be a so-called living hinge (flexible hinge). A living hinge means a hinge part integrally formed of the same material as two constituent parts (for example, a resin container and a lid part) connected by the hinge part. A living hinge can usually be bent 180 degrees. Also, depending on the use of the molded product, it can be designed to be bent only once or designed to be bent multiple times. The living hinge may be a flat hinge, a double hinge, a butterfly hinge, or a bistable hinge, or a combination thereof. Examples of molded products having a living hinge include a cap; a container with a lid; a screw cover; a handle with a screw cover; a cover for an electric wire, an optical fiber, etc. Further, the resin molded body of the present invention can be made into a molded product that is not bent but requires flexibility. Examples of such molded products include a binding band, a snap fit, a hole hiding cover, a case with a battery box, etc.

[0044] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

[0045] [Materials Used] The materials used are listed below. (1) Cellulose fiber-1: Rheocrysta I-2SX (product name), manufactured by Daiichi Kogyo Seiyaku Co., Ltd., average fiber diameter approximately 3 nm (2) Cellulose fiber-2: KC Floc W-200Y (product name), manufactured by Nippon Paper Industries Ltd., average fiber diameter 12 μm, average fiber length 100 μm (3) Cellulose fiber-3: ARBOCEL UFC100 (product name), manufactured by Rettenmeyer AG, average fiber diameter 7 μm, average fiber length 25 μm (4) Cellulose fiber-4: ARBOCEL B400 (product name), manufactured by Rettenmeyer AG, average fiber diameter 20 μm, average fiber length 900 μm In (1) to (4) above, the average fiber diameter and average fiber length of cellulose fiber-2 and cellulose fiber-3 are measured values ​​determined by the method using the SEM described above. On the other hand, the average fiber diameter of cellulose fiber-1 is the value listed in the catalog. This is because cellulose fiber-1 was too small to be measured using the SEM method described above. Also, although the average fiber diameter and average fiber length of cellulose fiber-4 are the values ​​listed in the catalog, even when measured using the SEM method described above, the average fiber diameter was clearly greater than 15 μm and the average fiber length was longer than 500 μm. (5) Polypropylene resin-1: J783HV (product name), manufactured by Prime Polymer Co., Ltd., tanδ peak height of 0.03 at -40℃±10℃ in dynamic viscoelasticity measurement (rigid polypropylene) (6) Polypropylene resin-2: NBX8HR (product name), manufactured by Nippon Polypropylene Co., Ltd., tanδ peak height of 0.13 at -40℃±10℃ in dynamic viscoelasticity measurement (flexible polypropylene resin) The above tanδ peak heights at -40℃±10℃ for polypropylene resin-1 and polypropylene resin-2 were measured according to the dynamic viscoelasticity measurement method described above.

[0046] [Compounding Method] We attempted to prepare a complex with the component composition shown in the table below. In the "Composition" column of the table below, a blank space indicates that the component is not present.

[0047] {Example using Cellulose Fiber-1 (average fiber length: 3 nm)} (Comparative Example 1) An attempt was made to produce a cellulose fiber-containing resin composite with 10% by mass of Cellulose Fiber-1, 45% by mass of Polypropylene Resin-1, and 45% by mass of Polypropylene Resin-2. The above raw materials were charged into a co-rotating twin-screw extruder with a screw diameter of 15 mm and L / D = 45 (KZW15TW-45MG-NH (trade name), manufactured by Technovel Corporation) from the hopper and melt-mixed under the conditions of 170 to 190 °C and 300 rpm. However, uniform mixing could not be achieved, and a cellulose fiber-containing resin composite could not be obtained.

[0048] {Example using Cellulose Fiber-2 (average fiber diameter: 12 μm, average fiber length: 100 μm)} (Example 1) 40% by mass of Cellulose Fiber-2 and 60% by mass of Polypropylene Resin-2 as the base resin were charged into a co-rotating twin-screw extruder with a screw diameter of 15 mm and L / D = 45 (KZW15TW-45MG-NH (trade name), manufactured by Technovel Corporation) from the hopper, mixed under the conditions of 170 to 190 °C and 300 rpm, and extruded into strands. After cooling and cutting, a pelletized cellulose fiber-containing resin composite was obtained.

[0049] (Examples 2 to 7 and Comparative Examples 2 to 7) Cellulose fiber-containing resin composites of Examples 2 to 7 and Comparative Examples 2 to 7 were obtained in the same manner as in Example 1, except that the blending amount of Cellulose Fiber-2, the type and blending amount of the base resin were as shown in Table 1.

[0050] {Example using Cellulose Fiber-3 (average fiber diameter: 7 μm, average fiber length: 25 μm)} (Examples 8 to 13 and Comparative Examples 8 to 13) Cellulose fiber-containing resin composites of Examples 8 to 13 and Comparative Examples 8 to 13 were obtained in the same manner as in Example 1, except that Cellulose Fiber-3 was used and the blending amount of Cellulose Fiber-3, the type and blending amount of the base resin were as shown in Table 1.

[0051] {Example using cellulose fiber-4 (average fiber diameter 20 μm, average fiber length 900 μm)} (Comparative Examples 14-17) Except for using cellulose fiber-4, and the amount of cellulose fiber-4 and the type and amount of base resin as shown in Table 1, comparative examples 14-17 containing cellulose fiber were obtained in the same manner as in Example 1.

[0052] {Example without using cellulose fibers} (Reference Example 1) The above polypropylene resin-1 was used as the resin in Reference Example 1.

[0053] Using each of the obtained resin composites (or resin in the case of Reference Example 1), molded articles having hinge portions were prepared as described below, and the following tests were conducted. The results are shown in Table 1. Note that Comparative Example 1 could not be evaluated because a cellulose fiber-containing resin composite could not be obtained, so it is marked with "-" in Table 1.

[0054] -Bending Resistance Test- Pellets of each cellulose fiber-containing resin composite were placed in an injection molding machine (ROBOSHOT S-2000i50A (product name), manufactured by FANUC Corporation), and the resin molded body 10 shown in Figure 1 was injection molded under conditions of 170-190°C and 100 mm / s. As shown in Figures 1(a) and 1(b), the resin molded body 10 has a structure in which two rectangular body parts 1 and 2 are connected by a hinge part 3, with a resin reservoir part 5 at the end of body part 1 for injection molding and a body part 4 at the end of body part 2. Body part 1 is 15 mm long, 10 mm wide, and 2 mm thick, body part 2 is 15 mm long, 10 mm wide, and 2 mm thick, and the hinge part 3 is 10 mm long, 10 mm wide, and 0.7 mm thick. The resin reservoir part 5 and body part 4 are thicker than body parts 1 and 2, respectively. The resin molded body 10, holding its main body portion 1 and main body portion 2, was bent 180 degrees in the direction shown in Figure 1(b) at the central part of the length of the hinge portion 3. The result was evaluated as follows: × if a crack occurred, △ if no crack occurred but a fissure appeared, and ○ if neither a crack nor a fissure appeared. Figure 1(b) shows the state during the bending process during the above test (the resin molded body 10 bent at approximately 90 degrees).

[0055] Figures 2-4 show graphs summarizing the relationship between composition and bending resistance for each cellulose fiber. In Figures 2-4, the horizontal axis (X-axis) represents the proportion of cellulose fibers in the total amount of polypropylene resin and cellulose fibers (labeled "cellulose concentration" in the figures). The vertical axis (Y-axis) represents the proportion of soft polypropylene resin contained in the polypropylene resin (labeled "proportion of soft PP in resin" in the figures). ○, △, and × are as described above and represent the results of the bending resistance test. In Figure 2, the cellulose fiber size is defined by condition 1, and the range satisfying inequality A: Ya ≥ Xa × 2.5 is shown in light gray. In Figure 3, the cellulose fiber size is defined by condition 2, and the range satisfying inequality B: Yb ≥ Xb × 2.5 - 25 is shown in light gray.

[0056] - Bending Strength Test - Pellets of each cellulose fiber-containing resin composite (resin in the case of Reference Example 1) were fed into an injection molding machine (ROBOSHOT S-2000i50A, manufactured by FANUC Corporation) and molded into strip-shaped test pieces measuring 80 mm × 10 mm × 4 mm at 170-190°C and 100 mm / s. Using these test pieces, the bending strength (MPa) was measured by a three-point bending test at room temperature (25°C) with a support distance of 64 mm and a test speed of 2 mm / min, in accordance with JIS K7171:2022. Five test pieces were prepared for each cellulose fiber-containing resin composite, and the above test was performed on each piece. The average of the obtained measurements was taken as the bending strength.

[0057] Table 1 shows the composition and evaluation results for each example, comparative example, and reference example 1.

[0058]

[0059]

[0060] (Table Notes) "Amount of cellulose in the total amount of PP and cellulose (X)" indicates the proportion of cellulose fibers in the total amount of polypropylene resin and cellulose fibers. "Amount of soft PP in PP (Y)" indicates the proportion of soft polypropylene resin in the polypropylene resin. In "Inequality A: Ya ≥ Xa × 2.5", "○" is shown if inequality A is satisfied, and "×" is shown if it is not satisfied. In "Inequality B: Yb ≥ Xb × 2.5 - 25", "○" is shown if inequality B is satisfied, and "×" is shown if it is not satisfied. Furthermore, in "Inequality A: Ya ≥ Xa × 2.5" and "Inequality B: Yb ≥ Xb × 2.5 - 25", the satisfaction of "Inequality A: Ya ≥ Xa × 2.5" was evaluated as ○ or × if the cellulose fibers used satisfy the average fiber diameter and average fiber length of cellulose fibers specified in Condition 1, and the satisfaction of "Inequality B: Yb ≥ Xb × 2.5 - 25" was evaluated as ○ or × as described above if the cellulose fibers used satisfy the average fiber diameter and average fiber length of cellulose fibers specified in Condition 2. In addition, if the cellulose fibers used do not satisfy the average fiber diameter and average fiber length of cellulose fibers specified in Condition 1, and also do not satisfy the average fiber diameter and average fiber length of cellulose fibers specified in Condition 2, the judgment results for both inequality A and B are shown.

[0061] The composite of Reference Example 1 does not contain soft polypropylene resin in the polypropylene resin. The molded article formed using the composite of Reference Example 1 passed the bending resistance test. It also had a high bending strength of 35.5 MPa. Comparative Example 1 is a comparative example in which cellulose fibers smaller than the size specified in the present invention were used as cellulose fibers. In Comparative Example 1, uniform mixing could not be achieved, and a composite could not be obtained, so the bending resistance test and bending strength test could not be performed. The composites of Comparative Examples 2 to 7 use cellulose fibers that satisfy the average fiber diameter and average fiber length of the cellulose fibers shown in Condition 1, but do not satisfy inequality A. The composites of Comparative Examples 8 to 13 also use cellulose fibers that satisfy the average fiber diameter and average fiber length of the cellulose fibers shown in Condition 2, but do not satisfy inequality B. Comparative Examples 14 to 17 use cellulose fibers having an average fiber diameter and average fiber length larger than the average fiber diameter and average fiber length of the cellulose fibers shown in Conditions 1 and 2. The molded articles formed using these composites cracked or fractured in the bending resistance test. In contrast, the composites of Examples 1 to 7 use cellulose fibers that satisfy the average fiber diameter and average fiber length specified in Condition 1, thus satisfying inequality A. Furthermore, the composites of Examples 8 to 13 use cellulose fibers that satisfy the average fiber diameter and average fiber length specified in Condition 2, thus satisfying inequality B. Molded articles formed using these composites showed no cracks or fissures in the bending resistance test, demonstrating excellent bending resistance. In addition, the bending strength was relatively high, although lower than that of Reference Example 1. In particular, the bending strength was high when a certain amount of hard polypropylene resin was included in addition to soft polypropylene resin.Therefore, it can be seen that a molded article with excellent bending resistance can be obtained by using the composite of the present invention, and that a good balance between bending resistance and bending strength can be achieved by including both soft and hard polypropylene resin. Furthermore, the molded articles using the composites of Examples 1 to 13 did not crack or fissure even after repeating the above 180-degree bending 10 times.

[0062] Although we have described the present invention along with its embodiments, we do not intend to limit our invention in any detail of the description unless specifically designated, and we believe that it should be interpreted broadly without contradicting the spirit and scope of the invention as set forth in the appended claims.

[0063] This application claims priority based on Japanese Patent Application No. 2024-227742, filed in Japan on 24 December 2024, the contents of which are incorporated herein by reference as part of this specification.

[0064] 10 Resin molded body 1 Main body 2 Main body 3 Hinge 4 Main body 5 Resin reservoir

Claims

1. A cellulose fiber-containing resin composite comprising a polypropylene resin and cellulose fibers, satisfying either of the following conditions 1 or 2. -Condition 1- The average fiber diameter of the cellulose fibers is 5 to 15 μm, and the average fiber length is greater than 35 μm and less than or equal to 130 μm. When the proportion of the cellulose fibers in the total amount of the polypropylene resin and the cellulose fibers is Xa by mass%, and the proportion of the soft polypropylene resin in the polypropylene resin is Ya by mass%, the following inequality A is satisfied. Inequality A: Ya ≥ Xa × 2.5 Xa > 0, Ya > 0 -Condition 2- The average fiber diameter of the cellulose fibers is 5 to 10 μm, and the average fiber length is 35 μm or less. When the proportion of the cellulose fibers in the total amount of the polypropylene resin and the cellulose fibers is Xb by mass%, and the proportion of the soft polypropylene resin in the polypropylene resin is Yb by mass%, the following inequality B is satisfied. Inequality B: Yb≧Xb×2.5-25 Xb>0, Yb>0 2. The cellulose fiber-containing resin composite according to claim 1, wherein Xa is 5 to 40% by mass.

3. The cellulose fiber-containing resin composite according to claim 1, wherein Xb is 5 to 50% by mass.

4. A cellulose fiber-containing resin molded article obtained by molding a cellulose fiber-containing resin composite according to any one of claims 1 to 3.

5. A part or article having a hinge portion made of a cellulose fiber-containing resin composite as described in any one of claims 1 to 3.

Images