Resin molding

Abstract

To improve the impact resistance of a resin molding that is formed from a cellulose-fiber composite resin composition.SOLUTION: A resin molding (10) is composed of a resin composition including polypropylene (PP) and cellulose fibers such as cellulose nanofibers (CNF). The resin composition constituting a resin molding further contains dispersed particulate post-added rubber.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a resin molded article made of a cellulose fiber composite resin composition. [Background technology]

[0002] Materials made by combining polypropylene with a reinforcing material are commonly used in resin molded products that form interior and exterior parts of automobiles. Because of their environmentally friendly nature, the use of cellulose fibers, such as cellulose nanofibers, which are naturally derived materials, as reinforcing materials is being considered. A cellulose fiber composite resin composition made by combining polypropylene with cellulose fiber is disclosed, for example, in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-156073 Summary of the Invention [Problem to be solved by the invention]

[0004] One way to increase the impact resistance of resin molded products is to add a rubber component to the resin composition. Due to its compatibility with polypropylene and its cost advantages, the rubber component is added by mixing ethylene or other rubber components into the polypropylene during the manufacturing stage (polymerization process) and chemically bonding the rubber component to the polypropylene to form a polymerized rubber.

[0005] The addition of such polymerized rubber is effective in increasing impact resistance when inorganic materials other than cellulose fiber, such as talc, are used as reinforcing materials. However, the inventors of the present application have found that adding polymerized rubber to cellulose fiber composite resin compositions does not adequately increase the impact resistance of resin molded articles.

[0006] An object of the present disclosure is to improve the impact resistance of a resin molded article made of a cellulose fiber composite resin composition. [Means for solving the problem]

[0007] The present inventors have confirmed through extensive research that adding a post-added rubber is effective in improving the impact resistance of resin molded articles made from cellulose fiber composite resin compositions. Therefore, in order to achieve the above object, the present disclosure employs the technique of adding a post-added rubber to a cellulose fiber composite resin composition.

[0008] Specifically, a first aspect of the present disclosure relates to a resin molded article made of a resin composition containing polypropylene and cellulose fibers, wherein the resin composition further contains dispersed particulate post-added rubber.

[0009] A second aspect of the present disclosure is the resin molded article of the first aspect, wherein the content of the post-added rubber is more than 0% by weight and 30% by weight or less.

[0010] A third aspect of the present disclosure is the resin molded article of the first or second aspect, wherein the post-added rubber has an average aspect ratio of 1 / 2 or more and 1 / 20 or less.

[0011] A fourth aspect of the present disclosure is the resin molded article of any one of the first to third aspects, wherein the post-added rubber is one or more types of rubber selected from the group consisting of ethylene-butene rubber, ethylene-octene rubber, and styrene-ethylene-butylene-styrene rubber.

[0012] A fifth aspect of the present disclosure is the resin molded article of any one of the first to fourth aspects, wherein the resin molded article has an Izod impact strength of 5.0 kJ / m 2 The resin molded article has a flexural modulus of 1800 MPa or more and a flexural modulus of 1800 MPa or more. This resin molded article is used for interior or exterior parts of automobiles. [Effects of the Invention]

[0013] According to a first aspect, a resin molded article is made of a cellulose fiber composite resin composition and contains dispersed particulate post-added rubber. The post-added rubber is a rubber component simply mixed with polypropylene. When the post-added rubber is dispersed in the resin composition, the impact resistance of the resin molded article made of the cellulose fiber composite resin composition can be improved.

[0014] According to a second aspect, the content of the post-added rubber is 30% by weight or less. The greater the amount of post-added rubber, the lower the flexural modulus of the resin molded product. If the content of the post-added rubber is greater than 30% by weight, the flexural modulus of the resin molded product may be significantly impaired. In contrast, if the content of the post-added rubber is 30% by weight or less, the impact resistance of the resin molded product can be improved while preventing the flexural modulus of the resin molded product from decreasing too much.

[0015] According to a third aspect, the average aspect ratio of the post-added rubber is 1 / 2 or more and 1 / 20 or less. The surface area of ​​a post-added rubber that satisfies such an average aspect ratio is larger than the surface area of ​​a post-added rubber that is a perfect sphere or a nearly perfect sphere. In other words, the interface of the post-added rubber in the resin composition is relatively large. When a resin molded product is destroyed by impact, the destruction begins at the interface peeling of the post-added rubber. Therefore, the relatively large interface of the post-added rubber allows the post-added rubber to effectively absorb impact energy. This is advantageous for improving the impact resistance of the resin molded product.

[0016] According to a fourth aspect, ethylene-butene rubber (EBR), ethylene-octene rubber (EOR), or styrene-ethylene-butylene-styrene rubber (SEBS) is used as the post-added rubber. These rubbers are effective in improving the impact resistance of resin molded articles made from a cellulose fiber composite resin composition.

[0017] According to the fifth aspect, the resin molded article has an Izod impact strength of 5.0 kJ / m or more and a flexural modulus of 1800 MPa or more. Resin molded articles having such mechanical properties can be suitably used for interior and exterior parts of automobiles. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a perspective view illustrating a rear spoiler included in a back door of an automobile. [Figure 2] Figure 2 is a photomicrograph of the fracture cross section of a resin molded product taken with an electron microscope. [Figure 3] FIG. 3 is a diagram illustrating a pellet forming step in the production of a resin molded product. [Figure 4] FIG. 4 is a diagram illustrating a molded product forming step in the manufacture of a resin molded product. [Figure 5] FIG. 5 is a graph showing the relationship between the amount of rubber component and Izod impact strength in Examples and Comparative Examples. [Figure 6] FIG. 6 is a graph showing the relationship between the amount of rubber component and the flexural modulus in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0019] Exemplary embodiments will now be described in detail with reference to the accompanying drawings.

[0020] The resin molded article 10 of this embodiment is made of a cellulose fiber composite resin composition, and has excellent mechanical properties such as good balance between impact resistance and bending strength.

[0021] The Izod impact strength of the resin molded product 10 is 5.0 kJ / m 2 The flexural modulus of the resin molded article 10 is 1800 MPa or more. The Izod impact strength is measured in accordance with ASTM D256 using a commercially available Izod impact tester. The flexural modulus is measured in accordance with ASTM D790 using a commercially available flexural modulus tester.

[0022] The resin molded product 10 is used as an interior or exterior part for an automobile. Specifically, the resin molded product 10 is a panel member 22 constituting a rear spoiler 20 shown in FIG. 1. The rear spoiler 20 is an example of an exterior part, and is an aerodynamic part attached to the rear of a vehicle. The rear spoiler 20 is provided above a hatchback-type back door 1 so as to protrude rearward from the vehicle body and form a canopy-like shape above the rear window 30.

[0023] -Resin composition- The resin molded article 10 is made of a resin composition containing polypropylene (PP) and cellulose fibers. The resin composition further contains dispersed particulate post-added rubber.

[0024] <Polypropylene> The polypropylene (PP) is not particularly limited, but examples thereof include homopropylene obtained by polymerizing only propylene, and block polypropylene obtained by copolymerizing propylene with ethylene, etc. The content of polypropylene (PP) in the resin composition is not particularly limited, but is 20% by weight to 80% by weight.

[0025] <Cellulose fiber> Cellulose fibers are plant-derived fibers obtained by defibrating wood pulp or the like. Cellulose fibers have an excellent reinforcing effect that improves the strength of the resin molded article 10. Examples of cellulose fibers include, but are not limited to, cellulose nanofibers (CNF). Cellulose fibers in the resin composition exist as microfibrils or microfibril bundles.

[0026] The cellulose fibers may be commercially available or may be produced by a known production method. The cellulose fibers have a fiber length of, for example, 5 μm to 150 μm. The cellulose fibers have a fiber diameter of 3 nm to 100 nm. The content of the cellulose fibers in the resin composition is not particularly limited, but is 20 wt % to 40 wt %. The cellulose fibers may contain cellulose microfibers (CMF) in addition to or instead of cellulose nanofibers (CNF).

[0027] <Post-added rubber> Post-added rubber is a rubber component simply mixed with polypropylene (PP). Post-added rubber is not chemically bonded to polypropylene (PP), and is distinguished from polymerized rubber, in which a rubber component is chemically bonded to polypropylene (PP). Post-added rubber is a component added to enhance the impact resistance of the mechanical properties of the resin molded product 10.

[0028] The content of the post-added rubber in the resin composition is, for example, more than 0% by weight and not more than 30% by weight. The greater the content of the post-added rubber, the lower the flexural modulus of the resin molded article 10. For this reason, from the viewpoint of balancing the impact resistance and flexural modulus of the resin molded article 10, the content of the post-added rubber is preferably 10% by weight to 25% by weight, and even more preferably 15% by weight to 20% by weight.

[0029] The post-added rubber in the resin composition exists in the form of particles of elliptical, oval, or other irregular shapes having a longitudinal direction and an average diameter size on the scale of 1 / 10 to several micrometers. As will be described later, such shapes of the post-added rubber are formed as a result of being stretched in one direction due to shear force, such as when the resin composition is injected into the cavity 88a in the mold 88 when the resin molded article 10 is formed by injection molding. The longitudinal direction of the post-added rubber is oriented in the longitudinal direction (vehicle width direction) of the resin molded article 10 (in this example, the rear spoiler 20).

[0030] The average aspect ratio of the post-added rubber is, for example, 1 / 2 or more and 1 / 20 or less. Here, "average aspect ratio" means the average value of the aspect ratios of multiple post-added rubbers. "Aspect ratio" refers to the ratio of the longitudinal dimension La to the transverse dimension Lb of the post-added rubber (longitudinal dimension La / transverse dimension Lb) (see Figure 2). The longitudinal dimension La is the longest dimension of the post-added rubber (the rubber phase in the resin composition), i.e., the distance between the two furthest points on the contour of the post-added rubber. The transverse dimension Lb is the longest distance between the intersection points that intersect with the contour of the post-added rubber in a direction perpendicular to the direction corresponding to the longitudinal dimension La.

[0031] The post-added rubber is not particularly limited, but is at least one rubber selected from the group consisting of ethylene-butene rubber (EBR), ethylene-octene rubber (EOR), and styrene-ethylene-butylene-styrene rubber (SEBS). The post-added rubber may include other types of rubber in addition to or instead of ethylene-butene rubber (EBR), ethylene-octene rubber (EOR), and styrene-ethylene-butylene-styrene rubber (SEBS).

[0032] <Other additives> The resin composition may contain other additives as needed. Examples of the other additives include, but are not limited to, a compatibilizer that enhances the compatibility between polypropylene (PP) and cellulose fibers, and a filler that improves the properties of the resin molded article 10, such as the sliding properties. The compatibilizer may include maleic acid-modified polypropylene. The filler may include talc.

[0033] -Manufacturing method for resin molded products- The resin molded article 10 can be manufactured by injection molding. The manufacturing method of the resin molded article 10 includes a pellet molding step and a molded article molding step.

[0034] <Pellet molding process> In the pellet forming process, as shown in Fig. 3, polypropylene (PP) pellets P1 and cellulose fibers SF are fed into a hopper 52 of a twin-screw extruder 50, along with post-added rubber granular solid material PR having an average particle size of several µm or less. At this time, other additives (not shown) may also be fed into the hopper 52 as needed. The various raw materials fed into the hopper 52 are then supplied into a heating cylinder 54.

[0035] A twin screw 56 is rotated within the heating cylinder 54 to melt and knead the polypropylene (PP) and cellulose fiber, and to uniformly disperse the granular solid material PR in the molten resin. The molten resin thus obtained is extruded from the heating cylinder 54 into a cooling tank 60 and hardened to form strands. The strands formed in the cooling tank 60 are then introduced into a cutter device 70 and cut into small pieces of a predetermined size. This produces fiber-containing pellets P2 containing dispersed cellulose fiber and post-added rubber.

[0036] <Molded product molding process> Next, as shown in FIG. 4, fiber-containing pellets P2 are charged into a hopper 82 of an injection molding machine 80. The fiber-containing pellets P2 introduced into the hopper 82 are supplied into a heating cylinder 84. A screw 86 is rotated within the heating cylinder 84 to melt and knead the fiber-containing pellets P2. The molten resin thus obtained is injected into a cavity 88a of a mold 88 to fill it. At this time, the post-added rubber contained in the molten resin is stretched by shear force during injection into the cavity 88a of the mold 88, and assumes a shape with a longitudinal direction, which is oriented so as to follow the flow direction of the molten resin within the cavity 88a. The molten resin filled in the cavity 88a is then cooled and solidified to form a resin molded product 10.

[0037] Thereafter, the mold 88 is opened and the resin molded product 10 is taken out, and post-processing is performed to remove unnecessary parts such as gate residues and burrs. In this manner, the resin molded product 10 can be manufactured.

[0038] -Features of the embodiment- The resin molded article 10 of this embodiment is made of a cellulose fiber composite resin composition and contains dispersed particulate post-added rubber. The post-added rubber is a rubber component simply mixed with polypropylene (PP). When the post-added rubber is dispersed in the resin composition, the impact resistance of the resin molded article 10 made of the cellulose fiber composite resin composition can be improved.

[0039] In the resin molded article 10 of this embodiment, the content of post-added rubber is 30% by weight or less. If the content of post-added rubber is greater than 30% by weight, there is a risk of significant loss of the flexural modulus of the resin molded article 10. In contrast, if the content of post-added rubber is 30% by weight or less, the impact resistance of the resin molded article 10 can be improved while preventing the flexural modulus of the resin molded article 10 from decreasing too much.

[0040] In the resin molded article 10 of this embodiment, the average aspect ratio of the post-added rubber is 1 / 2 or more and 1 / 20 or less. The surface area of ​​a post-added rubber that satisfies such an average aspect ratio is larger than the surface area of ​​a post-added rubber that is a perfect sphere or a nearly perfect sphere. In other words, the interface of the post-added rubber in the resin composition is relatively large. When the resin molded article 10 is subjected to impact and is destroyed, the destruction begins at the interface peeling of the post-added rubber. Therefore, the relatively large interface of the post-added rubber allows the post-added rubber to effectively absorb impact energy. This is advantageous for increasing the impact resistance of the resin molded article 10.

[0041] In the resin molded article 10 of this embodiment, ethylene-butene rubber (EBR), ethylene-octene rubber (EOR), or styrene-ethylene-butylene-styrene rubber (SEBS) is used as the post-added rubber. These rubbers are effective in increasing the impact resistance of the resin molded article 10 made of a cellulose fiber composite resin composition.

[0042] The resin molded article 10 of this embodiment has an Izod impact strength of 5.0 kJ / m or more and a flexural modulus of elasticity of 1800 MPa or more. The resin molded article 10 having such mechanical properties can be suitably used for interior and exterior parts of automobiles. [Example]

[0043] The resin compositions of Examples 1 to 5 and Comparative Examples 1 to 6 shown in Table 1 below were blended and kneaded, and test pieces were injection molded using each resin composition. The molded test pieces were evaluated for impact resistance and bending strength.

[0044] [Table 1]

[0045] Example 1 52.7 wt% polypropylene (PP), 30 wt% cellulose fiber, 3 wt% maleic acid-modified propylene, 7.7 wt% additives such as talc, and 6.6 wt% post-added rubber were charged into a twin-screw extruder and continuously mixed at 180°C to 200°C to form fiber-containing pellets. These fiber-containing pellets were charged into an injection molding machine as a raw material, and a test piece for Example 1 was obtained by injection molding.

[0046] <Example 2> A test piece for Example 2 was obtained in the same manner as in Example 1, except that the blending amount of polypropylene (PP) was changed to 49.7% by weight and the blending amount of post-added rubber was changed to 9.6% by weight.

[0047] Example 3 A test piece for Example 3 was obtained in the same manner as in Example 1, except that the blending amount of polypropylene (PP) was changed to 48.7% by weight and the blending amount of post-added rubber was changed to 10.6% by weight.

[0048] Example 4 A test piece for Example 4 was obtained in the same manner as in Example 1, except that the blending amount of polypropylene (PP) was changed to 40.9% by weight and the blending amount of post-added rubber was changed to 18.4% by weight.

[0049] <Example 5> A test piece for Example 5 was obtained in the same manner as in Example 1, except that the blending amount of polypropylene (PP) was changed to 29.3% by weight and the blending amount of post-added rubber was changed to 30% by weight.

[0050] <Comparative Example 1> A test piece for Comparative Example 1 was obtained in the same manner as in Example 1, except that the amount of polypropylene (PP) compounded was changed to 59.3% by weight and no post-added rubber was compounded.

[0051] <Comparative Example 2> A test piece for Comparative Example 2 was obtained in the same manner as in Example 1, except that 6.6% by weight of polymerized rubber was compounded in place of the post-added rubber.

[0052] <Comparative Example 3> A test piece for Comparative Example 3 was obtained in the same manner as in Example 2, except that 9.6% by weight of polymerized rubber was compounded in place of the post-added rubber.

[0053] <Comparative Example 4> A test piece for Comparative Example 4 was obtained in the same manner as in Example 3, except that 10.6% by weight of polymerized rubber was compounded in place of the post-added rubber.

[0054] <Comparative Example 5> A test piece for Comparative Example 5 was obtained in the same manner as in Example 4, except that 18.4% by weight of polymerized rubber was compounded in place of the post-added rubber.

[0055] <Comparative Example 6> A test piece for Comparative Example 6 was obtained in the same manner as in Example 5, except that 30% by weight of polymerized rubber was compounded in place of the post-added rubber.

[0056] <Impact resistance evaluation> The Izod impact strength of the test pieces of Examples 1 to 5 and Comparative Examples 1 to 6 was measured by a method conforming to ASTM D256 in a room temperature environment of 23° C. The results of the Izod impact strength measurements are summarized in Table 1 and shown as a graph in FIG.

[0057] As shown in FIG. 5, there is not much difference in Izod impact strength among the test pieces of Comparative Examples 1 to 6. That is, there is no change in Izod impact strength depending on whether or not polymerized rubber is compounded and the amount of polymerized rubber compounded. This shows that adding polymerized rubber does not suitably improve the impact resistance of the resin molded product. In contrast, the test pieces of Examples 1 to 5 have higher Izod impact strengths than the test pieces of Comparative Examples 1 to 6. Furthermore, the Izod impact strength increases in the order of Examples 1 to 5, and it can be seen that the impact resistance of the resin molded product is improved more effectively as the amount of post-added rubber increases.

[0058] <Bending strength evaluation> The flexural modulus of the test pieces of Examples 1 to 5 and Comparative Examples 1 to 6 was measured by a method conforming to ASTM D790 in a room temperature environment of 23° C. The measurement results of the flexural modulus are summarized in Table 1 and shown as a graph in FIG.

[0059] As shown in FIG. 6, the flexural modulus of the test pieces of Comparative Examples 1 to 6 decreases in the order of Comparative Examples 1 to 6, indicating that the flexural strength of the resin molded product decreases with the presence or absence of polymerized rubber and the amount of polymerized rubber added. This tendency for the flexural strength of the test piece to decrease depending on the amount of rubber component added is also observed in the test pieces of Examples 1 to 5, which use post-added rubber. However, the degree of decrease in flexural modulus depending on the amount of post-added rubber seen in Examples 1 to 5 is smaller than the degree of decrease in flexural modulus depending on the amount of polymerized rubber added seen in Comparative Examples 1 to 6. From this, it can be said that adding a post-added rubber is advantageous in that it can suppress the decrease in flexural strength compared to adding a polymerized rubber.

[0060] The results of the above evaluation tests revealed that blending polymerized rubber into a cellulose fiber composite resin composition is not effective in improving the impact resistance of a resin molded article, and in fact reduces the flexural strength of the resin molded article. Furthermore, blending post-added rubber into a cellulose fiber composite resin composition is effective in improving the impact resistance of the resin molded article. Furthermore, as shown in Figures 5 and 6, there is a trade-off between the impact resistance and flexural strength of a resin molded article, which change depending on the blending amount of post-added rubber. Therefore, for applications in automotive interior or exterior parts, the blending amount of post-added rubber (content in the resin molded article) is found to be 30 wt% or less, and from the viewpoint of balancing the impact resistance and flexural strength of the resin molded article, a blending amount of 10 wt% to 25 wt% is preferable, and a blending amount of 15 wt% to 20 wt% is even more preferable.

[0061] In the above embodiment, the resin molded product is used as an interior or exterior part for an automobile, but this is not limiting. The resin molded product according to the present disclosure may be used for purposes other than automobiles.

[0062] In addition, the notation "to" in the above-mentioned numerical ranges means a range that includes the numerical values ​​before and after it. In other words, if X and Y are used as substitutes for numerical values, then "X to Y" indicates a range of "greater than or equal to X and less than or equal to Y." [Industrial Applicability]

[0063] INDUSTRIAL APPLICABILITY As described above, the present disclosure is useful for a resin molded article made of a cellulose fiber composite resin composition. [Explanation of symbols]

[0064] 10 Resin molded products 20 Rear spoiler (exterior part)

Claims

1. A resin molded article made of a resin composition containing polypropylene and cellulose fibers, The resin composition further contains dispersed particulate post-added rubber. A resin molded product characterized by:

2. The resin molded product according to claim 1, The content of the post-added rubber is greater than 0% by weight and less than or equal to 30% by weight. A resin molded product characterized by:

3. The resin molded product according to claim 1, The average aspect ratio of the post-added rubber is 1 / 2 or more and 1 / 20 or less. A resin molded product characterized by:

4. The resin molded product according to claim 1, The post-added rubber is one or more rubbers selected from the group consisting of ethylene-butene rubber, ethylene-octene rubber, and styrene-ethylene-butylene-styrene rubber. A resin molded product characterized by:

5. The resin molded product according to any one of claims 1 to 4, Izod impact strength is 5.0 kJ / m ２ That's all, The flexural modulus is 1800 MPa or more, Used for interior or exterior parts of automobiles, A resin molded product characterized by:

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