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.

Abstract

Provided are a cellulose fiber-containing resin molded body excellent in flexural fatigue resistance and a cellulose fiber-containing resin composite suitable for obtaining this molded body. 【Solution means】A cellulose fiber-containing resin composite and a cellulose fiber-containing resin molded body, which contain polypropylene resin (PP) and cellulose fiber (CF) and satisfy the following condition 1 or 2. - Condition 1 - The average fiber diameter of CF is 5 to 15 μm, the average fiber length is more than 35 μm and 130 μm or less, and when the ratio of CF in the total amount of PP and CF is Xa mass% and the ratio of soft PP in PP is Ya mass%, inequality A is satisfied. Inequality A: Ya ≥ Xa × 2.5 Xa > 0, Ya > 0 - Condition 2 - The average fiber diameter of CF is 5 to 10 μm, the average fiber length is 35 μm or less, and when the ratio of CF in the total amount of PP and CF is Xb mass% and the ratio of soft PP in PP is Yb mass%, inequality B is satisfied. Inequality B: Yb ≥ Xb × 2.5 - 25 Xb > 0, Yb > 0

Description

Technical Field

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

Background Art

[0002] Cellulose fibers are a natural resource that can be said to be an inexhaustible resource contained in all plants, and since they are lightweight and have high strength, their application to automotive parts and structural materials by being compounded with resins has been studied. However, in the practical application of a resin composite containing cellulose fibers, it is necessary to sufficiently enhance the integrality between highly hydrophilic cellulose fibers and a highly hydrophobic resin such as a polyolefin resin, and there are restrictions on improving the strengthening (reinforcement) effect of the resin by cellulose fibers.

[0003] Various proposals have been made to enhance the strengthening effect by cellulose fibers. For example, Patent Document 1 discloses a resin composite containing a resin and cellulose fibers, wherein the resin composite is obtained by kneading the resin and a pre-disintegrated cellulose fiber product using a uniaxial or multi-axial kneader, the pre-disintegrated cellulose fiber product is obtained by mechanically treating pulp, the pre-disintegrated cellulose fiber product has a fiber length of 0.1 mm or more and less than 0.5 mm in a proportion of 40% or more and less than 58%, and a fiber length of 1.5 mm or more and less than 2.0 mm in a proportion of 5% or more and 10% or less, and the cellulose fibers contained in the resin composite have an average fiber width of 1 μm or less in a proportion of 50% by volume or more. According to this resin composite, it has a high tensile elastic modulus and high tensile strength, and is further 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 recent years, there has been a growing global movement to reduce plastic use in order to realize a sustainable society. Cellulose fiber-containing resin composites are attracting attention as a material that can minimize plastic use and reduce environmental impact. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-118772 (Publication of 7108727) [Patent Document 2] Japanese Patent Publication No. 2018-145571 (Publication of Patent No. 6779158) [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Generally, resin molded products obtained by adding cellulose fibers to resin have improved mechanical properties such as bending strength, but they also become hard and brittle. When used as a material for hinges and other parts, they are prone to cracking and splitting when bent. The present invention aims to provide a cellulose fiber-containing resin molded article with excellent bending resistance (flexibility that does not cause cracks or fractures when bent), and a cellulose fiber-containing resin composite suitable for obtaining this resin molded article. The present invention further aims to provide a part or article having a hinge portion made of a cellulose fiber-containing resin composite. [Means for solving the problem]

[0007] The inventors have discovered that in a resin composite combining polypropylene resin and cellulose fibers, by incorporating a specific amount of soft polypropylene resin into the polypropylene resin, and further keeping the average fiber diameter and average fiber length of the cellulose fibers within a specific range, the bending resistance of the resin molded article obtained using this composite can be effectively improved. The present invention was completed after further investigation based on these findings.

[0008] In other words, the above-mentioned problems of the present invention were solved by the following means. [1] A cellulose fiber-containing resin composite comprising polypropylene resin and cellulose fibers, wherein the cellulose fiber-containing resin composite satisfies either of the following conditions 1 and 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 cellulose fibers in the total amount of the 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 -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 the 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 [2] A cellulose fiber-containing resin composite according to [1], wherein Xa is 5 to 40% by mass. [3] The cellulose fiber-containing resin composite according to [1] wherein Xb is 5 to 50% by mass. [4] A cellulose fiber-containing resin molded article formed by molding the cellulose fiber-containing resin composite according to any one of [1] to [3]. [4] A part or article having a hinge portion composed of the cellulose fiber-containing resin composite according to any one of [1] to [3].

[0009] In the description of the present invention, "~" is used in the sense of including the numerical values described before and after as the lower limit value and the upper limit value. [Advantages of the Invention]

[0010] The cellulose fiber-containing resin composite of the present invention can obtain a resin molded article excellent in flexural fatigue resistance. Since the cellulose fiber-containing resin molded article of the present invention is excellent in flexural fatigue resistance, it is suitable as a part or the article itself of an article that requires various foldings. A part or article having a hinge portion composed of the cellulose fiber-containing resin composite of the present invention is excellent in flexural fatigue resistance. [Brief Description of the Drawings]

[0011] [Figure 1] FIG. 1 is an explanatory view showing the shape of a resin molded article (test piece) used in the bending resistance test of the example. FIG. 1(a) is a front view of the test piece, and FIG. 1(b) is a side view of the state where the test piece is bent at 90°. [Figure 2] FIG. 2 is a graph showing the relationship between the composition and the flexural fatigue resistance when using cellulose fiber-2. [Figure 3] FIG. 3 is a graph showing the relationship between the composition and the flexural fatigue resistance when using cellulose fiber-3. [Figure 4] FIG. 4 is a graph showing the relationship between the composition and the flexural fatigue resistance when using cellulose fiber-4. [Modes for Carrying Out the Invention]

[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 fiber at a specific ratio. Further, the composite of the present invention has a polypropylene resin as a base resin and contains a specific amount of soft polypropylene resin in the polypropylene resin. Furthermore, the composite of the present invention satisfies either of the following Condition 1 and Condition 2. That is, the composite of the present invention includes two modes (the mode of Condition 1 and the mode of Condition 2) according to the average fiber length of the cellulose fiber.

[0013] - Condition 1 - The average fiber diameter of the cellulose fiber is 5 to 15 μm, and the average fiber length is more than 35 μm and 130 μm or less. When the ratio of the cellulose fiber in the total amount of the polypropylene resin and the cellulose fiber is Xa mass% and the ratio of the soft polypropylene resin in the polypropylene resin is Ya 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 fiber is 5 to 10 μm, and the average fiber length is 35 μm or less. When the ratio of the cellulose fiber in the total amount of the polypropylene resin and the cellulose fiber is Xb mass% and the ratio of the soft polypropylene resin in the polypropylene resin is Yb mass%, the following Inequality B is satisfied. Inequality B: Yb ≥ Xb × 2.5 - 25 Xb > 0, Yb > 0

[0015] ​

[0016] The manner of Condition 1 will be explained. 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 keeping 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, they can be measured as follows. When using a SEM, observe images 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 define the average fiber diameter as the average (arithmetic mean) of the diameters of the 20 fibers, and the average fiber length as the average (arithmetic mean) of the lengths of the 20 fibers. 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 the measurement of each fiber. With MORFI COMPACT, objects with a length of 200 μm to 10,000 μm and a width of 5 μm to 75 μm are considered fibers, and fibers within an 11 × 13 mm field of view are automatically analyzed.

[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 flexural strength of the resin molded article and from the viewpoint of forming the resin molded article by extrusion molding, a lower proportion of soft polypropylene resin is preferable. From the viewpoint of achieving a good balance between bending resistance and flexural strength in the resin molded article, Ya is preferably 20 to 80% by mass, and more preferably 40 to 60% by mass.

[0020] The characteristics of Condition 2 will be explained. 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 upper limit, and by ensuring that the ratio of cellulose fibers to soft polypropylene satisfies inequality B, 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 flexural strength of the resin molded article and from the viewpoint of forming the resin molded article by extrusion molding, a lower proportion of soft polypropylene resin is preferable. From the viewpoint of achieving a good balance between bending resistance and flexural 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 individually 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-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 values ​​are based on JIS K7210-1:2014, at 230°C and under a 2.16 kg load.

[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 a flexible polypropylene resin. In this invention, the flexible polypropylene resin means a polypropylene resin in which the tanδ peak at -40℃±10℃, 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 that exhibit the above-mentioned tanδ peak, and a polypropylene resin containing both a hard component and a soft component is preferred. Generally, polypropylene resins exhibit a tanδ (loss tangent) peak at least at 0°C ± 10°C in dynamic viscoelasticity measurements conducted in accordance with JIS K7244-4:1999, and may also exhibit a tanδ peak at -40°C ± 10°C. For polypropylene resins other than the flexible polypropylene resin in this invention, the peak height at -40°C ± 10°C is 0.03 to 0.05. On the other hand, for the flexible polypropylene resin in this invention, the tanδ peak at -40°C ± 10°C 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 above dynamic viscoelasticity measurement is used as an indicator, and among polypropylene resins, those with a tanδ peak at -40°C ± 10°C higher than 0.05 and lower than 0.30 are defined as flexible polypropylene resins. From now on, polypropylene resins other than flexible polypropylene resins may be referred to as "rigid polypropylene resins." Furthermore, the term "polypropylene resin" will be used without distinguishing between flexible and rigid 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 modified polypropylene resin in the polypropylene resin is preferably 10% by mass or less, and more preferably 5% by mass or less.

[0036] (Cellulose fiber) 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, its 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 flour. 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 also present. The size of the cellulose fibers used in this invention is such that the cellulose fibers described above satisfy the size specified in either condition 1 or condition 2.

[0037] (Other ingredients) The composite of the present invention may consist of the polypropylene resin and cellulose fibers described above, or it may contain resins other than polypropylene resin as long as the effects of the present invention are not impaired. 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., to the extent that the above objectives are not impaired.

[0038] The composite of the present invention can preferably be used as a material for a cellulose fiber-containing resin molded article, 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 form 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 product] 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 conditions 1 and 2 above. 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 described 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 made of a cellulose resin composite.

[0040] [Method for producing cellulose fiber-containing resin composites (composite formation method) and method for producing resin molded articles] 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. Furthermore, 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 temperature at which the above melting and mixing takes place 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 170 to 210°C is more preferred. From the viewpoint of reducing the thermal decomposition of cellulose fibers, the above melting and mixing temperature is preferably 250°C or lower, more preferably 230°C or lower, and even more preferably 200°C or lower. When the above melting and mixing process is carried out at high temperatures, antioxidants or the like may be added during the melting and mixing process, for example, to suppress thermal degradation or oxidative degradation. The above melting and mixing time is not particularly limited and can be set as appropriate. The apparatus used for the above melting and mixing is not particularly limited as long as it is capable of melting and 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 melting and mixing, the components may be dry-blended (pre-mixed). Dry blending is not particularly limited and can be carried out according to conventional methods.

[0041] The molded article of the present invention can be obtained by moltening the composite material of the present invention (for example, in pellet form) and performing 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 melt-mixing described above). For example, a series of steps can be employed in which each component constituting the composite of the present invention is melt-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 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 in the above injection molding process, such as injection speed, mold temperature, holding pressure, and holding pressure time, can be adjusted as appropriate depending on the purpose.

[0043] [Application] The composite material of the present invention can be used to form a foldable portion (hinge portion). The molded product having a foldable portion can be used as a component for attaching a hinge portion to an article (finished product), or the molded product can be the article itself. The hinge portion may be a so-called living hinge (flexible hinge). A living hinge refers to a hinge portion that is integrally formed from the same material as the two components connected by the hinge portion (for example, a resin container and a lid). Living hinges can usually be bent 180 degrees. Depending on the application of the molded product, they can also be designed to bend only once or to bend multiple times. Living hinges may be flat hinges, double hinges, butterfly hinges, bistable hinges, or combinations thereof. Examples of molded products having living hinges include caps, containers with lids, screw covers, handles with screw covers, and covers for wires, optical fibers, etc. Furthermore, the resin molded articles of the present invention can also be molded products that are not bendable but require flexibility. Examples of such molded products include cable ties, snap-fit ​​accessories, hole covers, and battery box cases. [Examples]

[0044] The present invention will be described in more detail below 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 (trade 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 Co., Ltd., average fiber diameter 12 μm, average fiber length 100 μm (3) Cellulose fiber-3: ARBOCEL UFC100 (trade name), manufactured by Rettenmeyer, average fiber diameter 7 μm, average fiber length 25 μm (4) Cellulose fiber-4: ARBOCEL B400 (trade name), manufactured by Rettenmeyer, 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. Furthermore, while the average fiber diameter and average fiber length of cellulose fiber-4 are the values ​​listed in the catalog, measurements using the above-mentioned SEM method clearly showed that the average fiber diameter exceeded 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 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 (soft polypropylene resin) The tanδ peak heights for polypropylene resin-1 and polypropylene resin-2 at -40°C ± 10°C were measured according to the dynamic viscoelasticity measurement method described above.

[0046] [Combining 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 using 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 fed from a hopper into a co-direction twin-screw extruder with a screw diameter of 15 mm and L / D = 45 (product name: KZW15TW-45MG-NH, manufactured by Technovel Co., Ltd.), and melted and mixed at 170-190°C and 300 rpm. However, uniform mixing was not 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 fed from a hopper into a co-screw twin-screw extruder (product name KZW15TW-45MG-NH, manufactured by Technovel Co., Ltd.) with a screw diameter of 15 mm and an L / D ratio of 45. The mixture was mixed at 170-190°C and 300 rpm and extruded into strands. After cooling and cutting, a pellet-shaped cellulose fiber-containing resin composite was obtained.

[0049] (Examples 2-7 and Comparative Examples 2-7) Cellulose fiber-containing resin composites of Examples 2-7 and Comparative Examples 2-7 were obtained in the same manner as in Example 1, except that the amount of cellulose fiber-2 and the type and amount of 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 8-13 and Comparative Examples 8-13) Cellulose fiber-containing resin composites for Examples 8-13 and Comparative Examples 8-13 were obtained in the same manner as in Example 1, except that cellulose fiber-3 was used, and the amount of cellulose fiber-3 and the type and amount of 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) Comparative Examples 14 to 17 were obtained in the same manner as in Example 1, except that cellulose fiber-4 was used, and the amount of cellulose fiber-4 and the type and amount of base resin were as shown in Table 1.

[0052] {Examples that do not use 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 fed into 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 at 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 1 and main body 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 approximately 90 degrees).

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

[0056] -Bending strength test- Pellets of each cellulose fiber-containing resin composite (or 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 used as the bending strength.

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

[0058] [Table 1-1]

[0059] [Table 1-2]

[0060] (Notes in the table) "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 flexible PP in PP (Y)" indicates the proportion of flexible polypropylene resin in the total polypropylene resin. In the case of "Inequality A: Ya≧Xa×2.5", we indicate "〇" if inequality A is satisfied and "×" if it is not satisfied. In the inequality "Yb≧Xb×2.5-25", we indicate "○" if inequality B is satisfied and "×" 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 × 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 material in Reference Example 1 does not contain soft polypropylene resin in the polypropylene resin. Molded articles formed using the composite material in Reference Example 1 passed the bending resistance test. Furthermore, the bending strength was also high at 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 bending resistance tests and bending strength tests could not be performed. The composites of Comparative Examples 2-7 use cellulose fibers that satisfy the average fiber diameter and average fiber length specified in Condition 1, but do not satisfy inequality A. Similarly, the composites of Comparative Examples 8-13 use cellulose fibers that satisfy the average fiber diameter and average fiber length specified in Condition 2, but do not satisfy inequality B. Comparative Examples 14-17 use cellulose fibers with an average fiber diameter and average fiber length larger than those specified in Conditions 1 and 2. Molded articles formed using these composites showed cracking or fissures in bending resistance tests. 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 using a composition that includes both soft and hard polypropylene resin. Furthermore, the molded products using the composites of Examples 1 to 13 showed no cracks or fissures even after repeating the 180-degree bending process 10 times. [Explanation of symbols]

[0062] 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, wherein the cellulose fiber-containing resin composite satisfies either of the following conditions 1 and 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 cellulose fibers in the total amount of the 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

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.

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