Resin composition and molded article using same

Abstract

A resin composition according to the present disclosure includes cellulose having a surface roughness such that the arithmetic average height at a cutoff value of 5 [mu] m is 0.1 [mu] m or less, a thermoplastic resin, and titanium oxide. The cellulose content is 60 wt% or less. According to the present disclosure, it is possible to provide a resin composition with which it is possible to obtain a light-colored molded article having excellent environmental affinity and suppressed thermal discoloration of cellulose during molding.

Description

Technical Field

[0001] This disclosure relates to resin compositions and molded articles using the same. Background Technology

[0002] In recent years, driven by environmental concerns and the desire to move away from fossil fuels in the materials field, the utilization of biomass has garnered attention. Biomass raw materials are one means of reducing carbon dioxide emissions to achieve carbon neutrality. Specifically, for example, by adding biomass raw materials to resins to obtain resin molded bodies, it is possible to reduce carbon dioxide emissions from fossil fuels during combustion.

[0003] Cellulose, a biomass raw material, has been used as a resin reinforcing material to improve the rigidity of resin molded articles by being added to resins. Compared with other resin reinforcing materials such as glass fiber, carbon fiber, and aramid fiber, cellulose is inexpensive and has excellent environmental friendliness, and is therefore attracting attention.

[0004] However, in order to obtain molded articles using cellulose-containing resin compositions, it is necessary to heat the resin to a temperature at which it melts and then perform molding (injection molding). However, cellulose-containing resin compositions are prone to discoloration upon heating, making it difficult to obtain light-colored resin molded articles.

[0005] To address this problem, for example, Patent Document 1 describes how, in a resin composition comprising an aqueous dispersion of cellulose fibers or a dried cellulose fiber body and a thermoplastic resin, color change during injection molding can be suppressed by covering the surface of the cellulose fibers. It should be noted that the aqueous dispersion of cellulose fibers comprises cellulose fibers, polyurethane, and water, and the dried cellulose fiber body is the dried product of the aqueous dispersion of cellulose fibers.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2020-176157 Summary of the Invention

[0009] However, in order to cover the surface of cellulose, as described in Patent Document 1, for example, a coating process using a surface treatment agent is required after dispersing the cellulose fibers in an aqueous solvent, but this process is complicated.

[0010] Furthermore, in manufacturing processes that use cellulose-containing resin compositions to produce molded articles, for example, if the operation of the manufacturing equipment is temporarily stopped due to some malfunction, the residence time of the cellulose-containing resin composition at high temperatures may sometimes be longer than usual. In this case, it is difficult to suppress the thermal discoloration of cellulose.

[0011] The purpose of this disclosure is to provide a resin composition that produces a light-colored molded article with excellent environmental compatibility and inhibits heat discoloration of cellulose during molding. Furthermore, the purpose of this disclosure is to provide a molded article using the above-described resin composition.

[0012] One aspect of the resin composition disclosed herein comprises: cellulose, a thermoplastic resin, and titanium dioxide having a surface roughness of 0.1 μm or less at a cutoff value of 5 μm. The content of the cellulose is 60% by weight or less.

[0013] According to this disclosure, a resin composition can be provided that yields a light-colored molded article with excellent environmental compatibility, inhibits heat discoloration of cellulose during molding, and produces a light-colored molded article. Furthermore, according to this disclosure, a light-colored molded article using the above-described resin composition can be provided. Detailed Implementation

[0014] The embodiments of this disclosure will now be described.

[0015] <Resin Composition>

[0016] As described above, the resin composition of this embodiment comprises: cellulose, a thermoplastic resin, and titanium dioxide, having a surface roughness of 0.1 μm or less with an arithmetic mean height at a cutoff value of 5 μm. The content of the cellulose is 60% by weight or less. According to the resin composition having this structure, it is possible to obtain a light-colored molded body that exhibits excellent environmental compatibility, suppresses heat discoloration of cellulose during molding, and has light-colored properties.

[0017] In the past, when using a resin composition containing cellulose to manufacture molded articles, it was difficult to obtain light-colored molded articles due to the thermal discoloration of cellulose during melt mixing / injection molding. However, the inventors of this application have discovered that by using cellulose with a surface roughness of 0.1 μm or less with an arithmetic mean height (cutoff value of 5 μm) and setting the content of the cellulose relative to the resin composition to 60% by weight or less, it is possible to suppress the thermal discoloration of cellulose during melt mixing / injection molding and obtain light-colored molded articles.

[0018] According to the resin composition of this embodiment, heat discoloration can be suppressed even if the conventional steps of dispersing cellulose in an aqueous solvent and coating the surface of cellulose to suppress heat discoloration are omitted. Therefore, a light-colored molded article can be obtained in a simple way.

[0019] Furthermore, according to the resin composition of this embodiment, even when the resin composition is kept at high temperature for a long time during melt mixing / injection molding, the thermal discoloration of cellulose can be suppressed.

[0020] In this disclosure, a colorimeter (e.g., "RM200QC", manufactured by X-Rite Inc.) is used to measure the L of the molded body. * a * b * The measurement will be performed, and the result will be L * (From black to white) is +90.0 or higher, a * (From green to red) is above -4.0 and below +4.0, b * Molded bodies with a temperature range of -4.0 to +8.0 (from blue to yellow) are defined as light-colored. In L... * a * b * In color space, use L * To represent brightness, use 'a'. * b * Chromaticity refers to both hue and saturation.

[0021] [Cellulose]

[0022] The cellulose contained in the resin composition of this embodiment will be described in detail below.

[0023] As described above, the arithmetic mean height (cutoff value of 5 μm) of the surface roughness of the cellulose in this embodiment is 0.1 μm or less. With this configuration, thermal discoloration of the cellulose during molding can be suppressed, resulting in a light-colored molded body. More preferably, the arithmetic mean height (cutoff value of 5 μm) is 0.08 μm or less.

[0024] In this embodiment, in order to eliminate the large-wavelength surface irregularities caused by undulations in cellulose, a phase-compensated filter is used to cut off the measurement data (cutoff value of 5 μm) to calculate the arithmetic mean height.

[0025] In this disclosure, the arithmetic mean height refers to the arithmetic mean height (Sa) calculated based on the surface roughness of the cellulose surface measured with a cutoff value of 5 μm according to the methods of JIS B 0601:1994 and JIS B 0031:1994. The aforementioned arithmetic mean height can be measured, for example, by the method described in the embodiments described later.

[0026] In this embodiment, the cellulose content is 60% by weight or less relative to the above-described resin composition. When the cellulose content is 60% by weight or less relative to the above-described resin composition, the resin composition exhibits good fluidity. Therefore, by suppressing the thermal discoloration of cellulose during melt mixing / injection molding, a light-colored molded article can be obtained.

[0027] If the cellulose content is 60% by weight or less relative to the resin composition, large parts can be molded without excessively increasing the temperature during melt mixing / injection molding. Therefore, when molding large parts, heat discoloration of cellulose during melt mixing / injection molding can be suppressed, resulting in a light-colored molded body.

[0028] If the cellulose content is 60% by weight or less relative to the resin composition, a molded article with a good appearance can be obtained that suppresses the formation of aggregates during melt mixing / injection molding.

[0029] When the thermoplastic resin is a polyolefin and the molded body formed from the resin composition is a handheld hair dryer or a vacuum cleaner, the cellulose content relative to the resin composition is 60% by weight or less. This reduces the specific gravity, achieving lightweighting and thus reducing the burden during use.

[0030] The content of cellulose in the above-mentioned resin composition is preferably 50% by weight or less. Furthermore, the content of cellulose is more preferably 45% by weight or less, even more preferably 30% by weight or less, and most preferably 15% by weight or less.

[0031] The cellulose content is preferably 10% by weight or more relative to the resin composition. If the cellulose content is 10% by weight or more relative to the resin composition, a molded article with excellent environmental compatibility can be obtained more reliably. If the cellulose content is 10% by weight or more relative to the resin composition, the rigidity of the molded article using the resin composition can be improved.

[0032] In this embodiment, the average particle size of the cellulose is preferably 100 μm or less. If the average particle size is 100 μm or less, in addition to obtaining a light-colored molded article, the formation of cellulose aggregates during the mixing / molding of the resin composition can be suppressed. Therefore, a molded article with a good appearance can be obtained. The average particle size is more preferably 80 μm or less, and even more preferably 60 μm or less.

[0033] The average particle size of the cellulose is preferably 5 μm or more. If the average particle size is 5 μm or more, in addition to obtaining a light-colored molded article, the rigidity of the molded article using the above-mentioned resin composition can also be improved. The average particle size is more preferably 10 μm or more, and even more preferably 15 μm or more.

[0034] The maximum particle size of the cellulose is not particularly limited, but is preferably 200 μm or more and 400 μm or less. If the maximum particle size is 200 μm or more, the rigidity of the molded article using the above resin composition can be improved. If the maximum particle size is 400 μm or less, a molded article with a good appearance can be obtained.

[0035] The minimum particle size of the cellulose is preferably 0.1 μm or more and 4 μm or less. If the minimum particle size is 0.1 μm or more, the rigidity of the molded article using the above resin composition can be improved. If the minimum particle size is 4 μm or less, a molded article with a good appearance can be obtained.

[0036] The aspect ratio of the cellulose is preferably 2 to 10. If the aspect ratio is within this range, the rigidity of the molded article using the resin composition can be improved.

[0037] The average particle size, minimum particle size, maximum particle size, and aspect ratio of the cellulose can be determined, for example, by the following methods.

[0038] A portion of the cellulose sample was dispersed on a glass slide and magnified photographs were taken. During photographing, the total number of individual cellulose samples was set to several dozen. Image processing was performed on the captured images using image analysis software (Image-Pro PLUS, manufactured by Nippon Roper KK). The obtained digital microscopy images (data) were binarized using a contrast threshold, extracting only the cellulose image.

[0039] The minor axis length, major axis length, and aspect ratio (the ratio of the major axis length to the minor axis length) of cellulose are determined using the extracted images. The minor axis length is the smallest diameter (minimum diameter) among two points connecting the center of gravity of the object to its outer perimeter. The major axis length can be calculated as (perimeter of the object) / (2 - minor axis length). The major axis length refers to the particle size of cellulose. The lower limit for the major axis length that can be determined using this method is 3 μm.

[0040] In the distribution of major axis length, the average particle size is the average value of the major axis length, the minimum particle size is the minimum value of the major axis length, and the maximum particle size is the maximum value of the major axis length.

[0041] Various properties of cellulose contained in the resin composition or molded body, such as arithmetic mean height and particle size, are determined after cellulose is extracted from the resin composition or molded body. To extract cellulose from the resin composition or molded body, for example, a sample (resin composition or molded body) of about 0.2 g is prepared, and the thermoplastic resin is removed using any chemical in an automated high-speed solvent extraction apparatus. The resulting insoluble components are then dried under reduced pressure.

[0042] Regarding the removal of thermoplastic resins, specifically, for example, to remove polypropylene from a sample, o-xylene with added butylated hydroxytoluene (BHT) can be used at a high temperature (135°C). For example, to remove polystyrene (PS), polycarbonate (PC), acrylonitrile styrene (AS), etc., chloroform, toluene, tetrahydrofuran (THF), etc., can be used.

[0043] In this embodiment, the amount of hemicellulose in the cellulose is preferably 10% by weight or less. The hemicellulose present in the cellulose is one of the causes of heat discoloration during molding. Therefore, by making the amount of hemicellulose in the cellulose 10% by weight or less, heat discoloration during molding can be suppressed, and a lighter-colored molded body can be obtained more reliably.

[0044] The cellulose in this embodiment can be unmodified cellulose derived from cellulose whose OH groups have not been modified by any substituents, or it can be modified cellulose derived from cellulose whose OH groups (especially a portion thereof) have been modified (or substituted). However, the cellulose described above is preferably unmodified cellulose without chemical modification.

[0045] Chemical modification of cellulose requires a dehydration / drying process, which increases environmental impact and cost. On the other hand, chemical modification improves heat resistance. However, according to the cellulose of this embodiment with the above-described structure, even without chemical modification, heat discoloration of the cellulose during molding can be suppressed, resulting in a more reliable light-colored molded body.

[0046] The shape of the cellulose in this embodiment is not particularly limited; for example, it can be in powder form or in fibrous form.

[0047] [Methods for manufacturing cellulose]

[0048] The cellulose contained in the resin composition of this embodiment is manufactured from cellulose raw materials using various manufacturing methods. There are no particular limitations on the raw materials and manufacturing methods of cellulose. Hereinafter, an example of a cellulose manufacturing method will be described.

[0049] Cellulose can be derived from natural sources or from recycled materials. However, from an environmental perspective, recycled materials are preferred for cellulose. Naturally derived cellulose includes, for example, wood pulp and non-wood pulps such as rice, cotton, kenaf, bagasse, abaca, hemp, and bamboo. Recycled cellulose may include, for example, paper pulp made by finely pulverizing materials that have already been used to make paper.

[0050] The paper in this case can be new paper or recycled waste paper. Regenerated cellulose may also include, for example, cellulose obtained from a molded body containing the cellulose of this embodiment. The cellulose raw material may contain only one material or may contain two or more materials.

[0051] The preferred raw material for cellulose is bleached pulp. Bleaching the pulp reduces its hemicellulose content. Wood and other materials used as raw materials for pulp typically contain hemicellulose, lignin, and other components in addition to cellulose.

[0052] However, if hemicellulose is present in the pulp used as the raw material for the aforementioned cellulose, as described above, it becomes a cause of heat discoloration during hemicellulose molding. Therefore, if bleached pulp is used in the raw material for the aforementioned cellulose, heat discoloration can be suppressed, and lighter-colored molded articles can be obtained more reliably.

[0053] It can be assumed that even after bleaching, hemicellulose remains in the pulp. In the resin composition of this embodiment, even if the pulp containing hemicellulose is included in the cellulose raw material, it is possible to suppress the thermal discoloration of cellulose during molding and obtain a light-colored molded article.

[0054] There are no particular limitations on the chemicals used in bleaching processes, including, for example, sodium hypochlorite (NaClO), hydrogen peroxide (H2O2), ozone (O3), oxygen (O2), sodium hydroxide (NaOH), and mixtures thereof.

[0055] There are no particular limitations on the methods for manufacturing cellulose, including methods such as mechanically pulverizing (micro-grinding) the cellulose raw materials and acid hydrolysis of the cellulose raw materials. However, it is preferred to manufacture cellulose by mechanically pulverizing the cellulose raw materials.

[0056] Compared to micronization based on acid hydrolysis, micronization based on mechanical processing causes less damage to the cellulose surface. Micronization based on acid hydrolysis involves more steps and generates more carbon dioxide emissions. Therefore, micronization based on mechanical processing is less costly and more environmentally friendly.

[0057] There are no particular limitations on the cellulose mills that can be used for mechanical processing, including, for example, the Opposed Jet Mill, Micron Jet (registered trademark), Innomizer (registered trademark) (all manufactured by HOSOKAWAMICRON CORPORATION), and impact jet mills. The conditions for mechanical processing can be appropriately set to obtain the desired cellulose.

[0058] By applying a classifier and sieving process to the micronized cellulose, cellulose with the desired particle size can be obtained. There are no particular limitations on the classifier; examples include Micron Separator (registered trademark), Turboplex (registered trademark) (centrifugal air classifier), coarse powder classifier (manufactured by HOSOKAWA MICRON CORPORATION), and Elbow-jet (registered trademark) (manufactured by Nittetsu Mining CO., Ltd.).

[0059] There are no particular limitations on the screening devices used for screening coarse particles, including ultrasonic screens (manufactured by Koei Sangyo Co., Ltd.), Rezona Sieve, Gyro-Sifter (manufactured by Tokuju Corporation), VibraSonic System (manufactured by DALTON Corporation), and circular screens.

[0060] [Thermoplastic resin]

[0061] The thermoplastic resin contained in the resin composition of this embodiment will be described in detail below.

[0062] The thermoplastic resin of this embodiment preferably has a content of 1×10⁻⁶ at 200°C. 6 Viscosities below Pa·s. If the viscosity at 200℃ is 1×10⁻⁶ Pa·s... 6 Below Pa·s, the temperature rise of the resin caused by shear heating during melt mixing and injection molding can be suppressed. Therefore, the thermal discoloration of cellulose during melt mixing / injection molding can be suppressed, and lighter-colored molded parts can be obtained more reliably.

[0063] Furthermore, if the above viscosity is 1×10 6 A viscosity below Pa·s can suppress the temperature rise of the resin caused by shear heating during melt mixing / injection molding. Therefore, it is easy to mold large components for home appliances, automobiles, building materials, etc. A viscosity of 5 × 10⁻⁶ is more preferably preferred. 5 Pa·s and below.

[0064] Furthermore, the viscosity mentioned above is preferably 1×10⁻⁶. 3 Pa·s or higher. Therefore, when using the resin composition for molding, it is possible to maintain the fluidity during molding to a certain extent and ensure the rigidity of the molded body. The above viscosity is more preferably 5 × 10⁻⁶. 3 Pa·s or higher, more preferably 1×10 4 Pa·s and above.

[0065] The viscosity described above can be determined according to the methods of JIS K 7210 and JIS K 7311. Specifically, the viscosity can be measured, for example, using a constant test force extrusion capillary rheometer flow tester (manufactured by Shimadzu Corporation).

[0066] The thermoplastic resin of this embodiment preferably has a melting point (melting temperature) of 200°C or lower. If the melting temperature is 200°C or lower, the resin temperature during melt mixing can be kept below 200°C. Therefore, heat discoloration and decomposition of cellulose can be suppressed, thereby enabling the more reliable acquisition of light-colored molded articles.

[0067] In this embodiment, the melt flow rate (MFR) of the thermoplastic resin at a temperature of 230°C and a load of 2.16 kgf is preferably 2.5 g / 10 min or more. When the MFR is 2.5 g / 10 min or more, the resin composition exhibits good flowability. Therefore, the injection pressure during melt mixing / injection molding can be suppressed, and heat generation due to shear is less likely to occur.

[0068] When molding large parts, molding can be carried out without excessively raising the molding temperature. Therefore, if the above MFR is 2.5g / 10min or higher, the thermal discoloration of cellulose during melt mixing / injection molding can be suppressed, and lighter-colored molded parts can be obtained more reliably.

[0069] If the MFR is 2.5 g / 10 min or higher, even when molding relatively large parts, it is possible to use an injection molding machine with a relatively low clamping force. Therefore, molded parts can be obtained using relatively inexpensive equipment. In this disclosure, the MFR of the thermoplastic resin is determined using a method based on JIS K 7210.

[0070] The flexural modulus of the thermoplastic resin in this embodiment is not particularly limited, but is preferably 1200 MPa or more, and more preferably 1400 MPa or more. In this disclosure, the flexural modulus of the thermoplastic resin is measured by a method based on JIS K 7171.

[0071] As the thermoplastic resin in this embodiment, unused resin, recycled resin (recycled material) obtained from waste, or both unused resin and recycled material can be used. From the viewpoint of environmental friendliness, it is preferable to include recycled material in the above-mentioned thermoplastic resin.

[0072] The aforementioned thermoplastic resins include, for example, polyolefins, polystyrene, acrylonitrile-butadiene-styrene (ABS), polycarbonate, polyamide, and acrylic resins. Polyolefins are preferred. Examples of polyolefins include polyethylene, polypropylene, polybutene, and polymethylpentene. Polypropylene is preferred.

[0073] The aforementioned thermoplastic resin may consist of only one type of resin or may consist of two or more types of resin.

[0074] According to the resin composition of this embodiment, even when the aforementioned thermoplastic resin is incompatible with cellulose, a light-colored molded article with a good appearance can be obtained using the resin composition. Examples of thermoplastic resins incompatible with cellulose include polypropylene, polyethylene, polystyrene, and ABS.

[0075] The content of thermoplastic resin in the resin composition of this embodiment is preferably 40% by weight or more, more preferably 60% by weight or more, relative to the above-described resin composition. The content of the thermoplastic resin is preferably 90% by weight or less, more preferably 88% by weight or less, relative to the above-described resin composition.

[0076] If the content of the above-mentioned thermoplastic resin is 88% by weight or less relative to the above-mentioned resin composition, it is possible to ensure the rigidity of the molded article obtained by using the above-mentioned resin composition and its excellent environmental friendliness.

[0077] If the content of the aforementioned thermoplastic resin is 60% by weight or more relative to the aforementioned resin composition, the concentration of cellulose becomes thinner, and the flowability improves. This makes molding easier and allows for the molding of larger parts. If the content of the aforementioned thermoplastic resin is 60% by weight or more relative to the aforementioned resin composition, and if the specific gravity of the thermoplastic resin is lower than that of cellulose, weight reduction can also be expected.

[0078] Titanium oxide

[0079] The titanium dioxide contained in the resin composition of this embodiment will be described in detail below.

[0080] In this embodiment, the titanium dioxide is a white pigment. If the resin composition contains titanium dioxide, the light color of the molded article using the resin composition can be ensured.

[0081] The crystal structures of the aforementioned titanium oxide include, for example, rutile and anatase. There are no particular limitations, but the rutile crystal structure is preferred. The rutile crystal structure has a higher refractive index than other crystal structures, which allows for light scattering and improves the concealment of foreign objects such as black spots.

[0082] The particle size of the titanium dioxide is preferably 1 μm or less. If the particle size of the titanium dioxide is 0.5 μm or less, the dispersibility of the titanium dioxide in the molded body is improved compared to adding the same weight percentage of titanium dioxide with a larger particle size. Therefore, the concealment of foreign matter is improved, and the appearance of the molded body is improved. The titanium dioxide may or may not be surface-treated.

[0083] The content of titanium dioxide is preferably 5% by weight or less relative to the resin composition. If the content of titanium dioxide is 5% by weight or less, it is possible to control costs while ensuring the light color of the molded article using the resin composition. Furthermore, it is possible to maintain the rigidity and impact resistance of the molded article.

[0084] If the above resin composition contains titanium dioxide, the specific gravity becomes higher, and the lightweight properties are compromised. Therefore, it is preferable to minimize the content as much as possible. There is no particular limitation on the lower limit of the titanium dioxide content, but it is preferably 1.5% by weight or more relative to the above resin composition.

[0085] [Other ingredients]

[0086] In addition to the components described above, the resin composition of this embodiment may also appropriately include at least one of maleic acid-modified polypropylene, antioxidants, ultraviolet absorbers, light stabilizers, antistatic agents, metal passivators, plasticizers, nucleating agents, flame retardants, and lubricants to enable the thermoplastic resin to bond with cellulose. Furthermore, in addition to the components described above, the resin composition of this embodiment may also appropriately include additives for coating the surface of the cellulose.

[0087] <Molded Body>

[0088] The molded body in this embodiment is light-colored. Specifically, in this embodiment, a colorimeter (RM200QC, manufactured by X-Rite Inc.) is used to measure the L color of the molded body. * a * b * The measurement will be performed, and the result will be L * (From black to white) is +90.0 or higher, a * (From green to red) is above -4.0 and below +4.0, b * Molded bodies with a value between -4.0 and +8.0 (ranging from blue to yellow) are defined as light-colored.

[0089] The following example illustrates a method for manufacturing the molded article of this embodiment. However, there are no particular limitations on various conditions, as long as the molded article can be obtained by injection molding the above-described resin composition.

[0090] First, the aforementioned components, such as cellulose, thermoplastic resin, and titanium dioxide, are premixed at the desired formulation amounts, and then melt-mixed using a twin-screw compounding extruder. For example, a mixer can be used to premix the components. The aforementioned twin-screw compounding extruder is, for example, a twin-screw compounding extruder manufactured by TECHNOVEL CORPORATION (Technovel).

[0091] The temperature during the melt mixing process is preferably below 200°C. Setting the melt mixing temperature to below 200°C prevents the resin temperature from becoming excessively high, thus suppressing heat generation caused by shear. Therefore, heat discoloration of cellulose can be suppressed, resulting in a more reliable light-colored molded body.

[0092] To suppress heat generated by shearing, the screw configuration can be adjusted to reduce the rotational speed. However, this reduces the dispersibility of cellulose, which can sometimes affect the appearance; therefore, a balanced adjustment is preferable. If the dispersibility of cellulose is reduced, resin deterioration may accumulate in the die at the extrusion section. In this case, the strand is prone to breakage, potentially affecting the compounding productivity.

[0093] During the melt blending process described above, cellulose readily absorbs water and generates steam due to the heat of the blender. Therefore, the blender preferably has an exhaust port (Vent) for releasing the steam.

[0094] The resulting compound is dried to produce pellets, which are then fed into an injection molding machine to form molded parts. The barrel temperature during molding is preferably below 200°C. Setting the barrel temperature below 200°C suppresses heat discoloration of the cellulose, resulting in more reliably lighter-colored molded parts.

[0095] This disclosure discloses various techniques as described above, and the main techniques are summarized below.

[0096] The resin composition of the first embodiment comprises: cellulose, a thermoplastic resin, and titanium dioxide having a surface roughness of 0.1 μm or less at a cutoff value of 5 μm. The content of the cellulose is 60% by weight or less.

[0097] In the resin composition of the second embodiment, the content of the cellulose is 10% by weight or more, based on the first embodiment.

[0098] In the resin composition of the third embodiment, based on the first or second embodiment, the cellulose comprises recycled material.

[0099] In the resin composition of the fourth embodiment, based on any one of the first to third embodiments, the amount of hemicellulose in the cellulose is 10% by weight or less.

[0100] In the resin composition of the fifth embodiment, the cellulose is not chemically modified based on any of the first to fourth embodiments.

[0101] In the resin composition of the sixth embodiment, based on any one of the embodiments from the first to the fifth, the average particle size of the cellulose is 100 μm or less.

[0102] In the resin composition of the seventh embodiment, based on any one of the embodiments from the first to the sixth, the viscosity of the aforementioned thermoplastic resin at 200°C is 1 × 10⁻⁶. 6 Pa·s and below.

[0103] In the resin composition of the eighth embodiment, based on any one of the first to seventh embodiments, the melting temperature of the aforementioned thermoplastic resin is 200°C or less.

[0104] In the resin composition of the 9th embodiment, based on any one of the 1st to 8th embodiments, the melt flow rate (MFR) of the above-mentioned thermoplastic resin at a temperature of 230°C and a load of 2.16 kgf is 2.5 g / 10 min or more.

[0105] In the resin composition of the 10th embodiment, based on any one of the 1st to 9th embodiments, the thermoplastic resin comprises a polyolefin.

[0106] In the resin composition of the 11th embodiment, based on any one of the 1st to 10th embodiments, the aforementioned thermoplastic resin comprises recycled material.

[0107] In the resin composition of the 12th embodiment, based on any one of the 1st to 11th embodiments, the content of the titanium oxide is 5% by weight or less relative to 100% by weight of the resin composition.

[0108] In the light-colored molded body of the 13th embodiment, the resin composition of any one of the 1st to 12th embodiments is injection molded.

[0109] The present disclosure will be described in more detail below through embodiments, but the present disclosure is not limited to the embodiments.

[0110] Example

[0111] [Methods for determining cellulose]

[0112] The method for determining the arithmetic mean height (Sa) and particle size of cellulose surface in the following examples is described.

[0113] (Methods for determining the arithmetic mean height)

[0114] The surface roughness of cellulose was measured using a non-contact laser microscope (LEXT OLS4100, manufactured by Olympus Corporation) with a cutoff value of 5 μm, according to the methods of JIS B 0601:1994 and JIS B 0031:1994, and the arithmetic mean height (Sa) was calculated. Specifically, the surface roughness of the fiber sample was measured, and the obtained height data (arithmetic mean height (Sa)) was calculated. It should be noted that the objective lens of the laser microscope was set to 100x and the optical zoom was set to 3x.

[0115] (Methods for determining particle size (average particle size, maximum particle size, minimum particle size))

[0116] The methods for determining the average particle size, minimum particle size, and maximum particle size of cellulose are as described above.

[0117] Next, the components used to prepare the resin compositions in Examples 1-9 and Comparative Example 1 will be described.

[0118] [Cellulose]

[0119] Cellulose A

[0120] The bleached pulp was milled and then subjected to classifying and sieving processes to obtain cellulose A with an average particle size of 15 μm and a surface roughness of 0.05 μm with an arithmetic mean height (Sa) (cutoff value of 5 μm). It should be noted that the maximum particle size was 121 μm and the minimum particle size was 3 μm.

[0121] Cellulose B

[0122] The bleached pulp was milled and then subjected to classifying and sieving processes to obtain cellulose B with an average particle size of 47 μm and a surface roughness of 0.06 μm with an arithmetic mean height (Sa) (cutoff value of 5 μm). It should be noted that the maximum particle size was 279 μm and the minimum particle size was 4 μm.

[0123] ·Cellulose C

[0124] The bleached pulp was milled and then subjected to classifying and sieving processes to obtain cellulose C with an average particle size of 140 μm and a surface roughness of 0.05 μm with an arithmetic mean height (Sa) (cutoff value of 5 μm). It should be noted that the maximum particle size was 500 μm and the minimum particle size was 60 μm.

[0125] ·Cellulose P

[0126] After bleaching, the pulp was acid-hydrolyzed, filtered / washed, and dewatered / dried. The pulp was then subjected to classifying and sieving to obtain cellulose P with an average particle size of 23 μm and an arithmetic mean height (Sa) (cutoff value of 5 μm) of 0.11 μm. It should be noted that the maximum particle size was 130 μm and the minimum particle size was 4 μm.

[0127] [Thermoplastic resin]

[0128] • Resin 1: Polypropylene (PP) (block PP, MFR: 30g / 10min, flexural modulus: 1800MPa)

[0129] • Resin 2: Polypropylene (PP) (block PP, MFR: 2.5 g / 10 min, flexural modulus: 1650 MPa)

[0130] • Resin 3: Polypropylene (PP) (block PP, MFR: 60g / 10min, flexural modulus: 1300MPa)

[0131] Titanium oxide

[0132] Model "R-FC-5", manufactured by Venator Materials (Venator Materials PLC)

[0133] <Evaluation Experiment 1>

[0134] [Example 1]

[0135] As Example 1, a molded article was prepared using a resin composition obtained by mixing the above-mentioned components in the mixing ratios (contents) shown in Table 1. That is, granules were manufactured using resin 1, cellulose, and titanium dioxide as thermoplastic resins. Specifically, the above-mentioned raw materials were weighed in such a way that the content in the resin composition was as shown in Table 1 (weight %), and then dry-mixed.

[0136] Next, the dry-mixed raw materials were melt-mixed in a twin-screw compounding extruder (KZW15TW-45MG-NH(-700), manufactured by TECHNOVELCORPORATION) at a temperature of 170°C and a discharge rate of 2 kg / h. The compounded raw materials were cooled with water to produce granules, which were then molded at 185°C to obtain molded bodies. The light color and heat resistance color change of the obtained molded bodies were investigated using the following methods. These results are shown in Table 1.

[0137] [Examples 2-9, Comparative Examples 1-2]

[0138] As Examples 2-9 and Comparative Examples 1-2, molded articles were prepared using resin compositions obtained by mixing the above-mentioned components in the mixing ratios (contents) described in Table 1 using the same method as in Example 1. The light color and heat resistance color change of the obtained molded articles were investigated by the following methods. These results are shown in Table 1.

[0139] (Light color, heat resistance to discoloration)

[0140] The above components were mixed in the proportions (contents) listed in Table 1, and then melt-blended at 190°C using a twin-screw compounding extruder (KZW15TW-45MG-NH(-700), manufactured by TECHNOVEL CORPORATION). The resulting compound was dried to obtain granules.

[0141] • Lightness test

[0142] The obtained granules were fed into an injection molding machine (J50ADS-60U, manufactured by Nippon Steel Corporation), and the barrel temperature was set to 185°C to produce test piece I, measuring 60mm × 70mm × 1.6mm. The L-value of test piece II, obtained after 10 injection shots, was measured using a colorimeter (RM200QC, manufactured by X-Rite Inc.). * a * b * The measurements were taken.

[0143] As a result, L * (From black to white) is +90.0 or higher, a * (From green to red) is above -4.0 and below +4.0, b * (From blue to yellow) A score between -4.0 and +8.0 is considered acceptable; all other scores are considered unacceptable. These results are shown in Table 1.

[0144] • Heat resistance and color change

[0145] Next, test piece II, made after 10 injections, was taken out, and the granules from the 11th injection were filled into the barrel, with the barrel temperature set to 185°C. After 15 minutes, molding was performed to produce test piece III. The L-value of test piece III was measured using a colorimeter (RM200QC, manufactured by X-Rite Inc.). * a * b * The measurements were taken.

[0146] Calculate the color difference ΔE between test piece III (11th injection) and test piece II (10th injection). ΔE is the value shown in equation (1) below. A value of ΔE below 2.5 is considered acceptable, and a value of ΔE above 2.5 is considered unacceptable. These results are shown in Table 1.

[0147] ΔE=[(ΔL ＊ ) 2 +(Δa) ＊ ) 2 +(Δb) ＊ ) 2 ] 1 / 2 (1)

[0148] [Example 10]

[0149] One hundred molded bodies obtained using the resin composition of Example 1 were pulverized using a coarse crusher to produce sheets. These molded bodies correspond to test sheet I. The resulting sheets were melt-blended at 190°C using a twin-screw compounding extruder (KZW15TW-45MG-NH(-700), manufactured by TECHNOVEL CORPORATION). The resulting compound was dried to obtain granules. Using the obtained granules, the light color and heat discoloration resistance of the molded bodies were evaluated using the same method as in Example 1. These results are shown in Table 1.

[0150] Cellulose D extracted from the granules of Example 10 was subjected to morphological analysis using the methods described above. The results showed an average particle size of 14 μm, a maximum particle size of 114 μm, a minimum particle size of 3 μm, and an arithmetic mean height (Sa) of surface roughness (cutoff value of 5 μm) of 0.08 μm. The thermoplastic resin contained in the granules of Example 10 was the same resin 1 used in Example 1, designated as resin 4 in Table 1.

[0151] [Table 1]

[0152]

[0153] [Inspection]

[0154] As shown in Table 1, in Examples 1-10, where the arithmetic mean height (cutoff value of 5 μm) of the cellulose surface and the cellulose content were appropriately adjusted, the yellow tint of the molded body was suppressed, and the molded body was light-colored. The results of the heat resistance color change test above indicate that the resin compositions of Examples 1-10 can suppress the heat discoloration of cellulose even with a long residence time during injection molding.

[0155] In Example 2, which used a resin with a relatively low MFR and low flowability, the thermal discoloration of cellulose during injection molding was also suppressed, resulting in a light-colored molded body.

[0156] In Example 10, cellulose (recycled material) obtained from the molded body of Example 1 was used as cellulose. In Example 10, the arithmetic mean height of the cellulose surface (cutoff value of 5 μm) was also appropriately adjusted, so that discoloration could be suppressed even if the heat load generated by mixing / molding was applied again, and a light-colored molded body could be achieved.

[0157] In contrast, in the case of Comparative Example 1, which used a resin composition having 65% by weight of cellulose relative to the resin composition, the evaluation of light color and heat resistance color change was unsatisfactory. For the molded body of Comparative Example 2, which used cellulose with a surface roughness of 0.11 μm having an arithmetic mean height (cutoff value of 5 μm), the yellow tint was enhanced, and the light color was unsatisfactory. In Comparative Example 2, regarding the evaluation of heat resistance color change, the yellow tint was also enhanced, resulting in an unsatisfactory result.

[0158] <Evaluation Experiment 2>

[0159] For the resin compositions of Examples 1-9 and Comparative Example 1, tests were further conducted on the appearance quality of the molded articles using the resin compositions using the methods shown below. These results are shown in Table 2.

[0160] [Appearance Quality: Number of Aggregates]

[0161] Cut 1g of the above test piece I and sheet it by hot pressing at 180°C and approximately 5MPa. Using a digital microscope (VHX-6000, manufactured by KEYENCE CORPORATION), count the number of aggregates smaller than 300μm. If the number of aggregates is 0–10, it is rated as “excellent”; if it is 10–30, it is rated as “acceptable”; and if it is more than 30, it is rated as “unacceptable”.

[0162] <Evaluation Experiment 3>

[0163] For the resin compositions of Examples 1-9 and Comparative Example 1, tests were further conducted on the flexural modulus of the molded articles using the resin compositions by the method shown below. These results are shown in Table 2.

[0164] Flexural modulus

[0165] The granules obtained using the above-mentioned mixing mill were fed into an injection molding machine (J50ADS-60U, manufactured by Nippon Steel Corporation). The barrel temperature was set to 185°C, dumbbell test pieces were made, and the flexural modulus was determined using a method based on JIS 7171.

[0166] [Table 2]

[0167]

[0168] [Inspection]

[0169] As shown in Table 2, in Examples 1-8, where the cellulose content and shape were appropriately adjusted, molded articles with fewer aggregates and a better appearance were obtained. In contrast, according to the results in Table 2, in Example 9, which used cellulose with an average particle size of 140 μm, the number of aggregates was high, and a poor appearance was observed.

[0170] In Comparative Example 1, which used cellulose at a content of 65% by weight relative to the resin composition, the number of aggregates was greater than that in Examples 1-8.

[0171] As shown in Table 2, the molded article of Example 4, which used cellulose at a content of 5% by weight relative to the resin composition, had a poor flexural modulus. In contrast, as shown in Table 2, the molded articles with superior flexural modulus could be obtained by using the resin compositions of Examples 1-3 and 5-9, which contained cellulose in appropriate amounts.

[0172] <Evaluation Experiment 4>

[0173] For the resin compositions of Examples 1, 6, and 7, further impact resistance tests were conducted on the molded articles using the resin compositions using the methods shown below. These results are shown in Table 3.

[0174] [Impact resistance]

[0175] The granules obtained using the above-mentioned mixing mill are fed into an injection molding machine. The barrel temperature is set to 185°C, and dumbbell test pieces are made. Using the method based on JIS 7111, notches are added to the dumbbell test pieces, and the Charpy impact value is measured at 23°C.

[0176] [Table 3]

[0177]

[0178] [Inspection]

[0179] As shown in Table 3, by using the resin compositions of Examples 1 and 6 containing titanium oxide in appropriate amounts, molded articles with superior impact resistance can be obtained. In contrast, as shown in Table 3, the molded article of Example 7, with a titanium oxide content of 7.5% by weight, exhibits poor impact resistance.

[0180] <Experimental Example 5>

[0181] For the resin compositions of Examples 1, 10, Comparative Example 1, and 2, weather resistance tests were further conducted on the molded articles using the resin compositions using the methods shown below. These results are shown in Table 4.

[0182] [Weather resistance test]

[0183] The granules obtained in Examples 1, 10, and Comparative Examples 1 and 2 were fed into an injection molding machine, and the barrel temperature was set to 185°C to produce test pieces X measuring 60mm × 70mm × 2mm. Test pieces Y obtained after 10 injection cycles were then used for accelerated weathering testing (carbon arc lamp aging test). Specifically, 12 hours of light adjustment was performed in a sunlight weathering chamber (S80, manufactured by Suga Test Instruments Co., Ltd.) with a cycle of 120 minutes. The initial 18 minutes of light adjustment were performed under conditions of sprayed ion-exchange water.

[0184] The color difference of test piece Y before and after color adjustment was measured using a colorimeter (RM200QC, manufactured by X-Rite Inc.). Based on the color difference measurement results, the following judgments were made. These results are shown in Table 4.

[0185] [Table 4]

[0186]

[0187] [Inspection]

[0188] As shown in Table 4, the resin composition of Example 1, which contains 13.5% by weight of cellulose with an arithmetic mean height (Sa) of 0.05 μm (cutoff value of 5 μm), inhibited discoloration of the molded article even after weathering tests. Furthermore, the resin composition of Example 10, which contains 13.5% by weight of cellulose with an arithmetic mean height (Sa) of 0.08 μm (cutoff value of 5 μm), also inhibited discoloration of the molded article even after weathering tests.

[0189] In contrast, as shown in Table 4, the resin composition of Comparative Example 1, which contains 65% by weight of cellulose with an arithmetic mean height (Sa) of 0.05 μm (cutoff value of 5 μm), failed the weather resistance test and exhibited poorer weather resistance compared to the resin composition of Example 1. Furthermore, the resin composition of Comparative Example 2, which contains 13.5% by weight of cellulose with an arithmetic mean height (Sa) of 0.11 μm (cutoff value of 5 μm), also showed poorer weather resistance compared to the resin composition of Example 10.

Claims

1. A resin composition comprising: cellulose, a thermoplastic resin, and titanium dioxide having a surface roughness of less than 0.1 μm with an arithmetic mean height at a cutoff value of 5 μm. The cellulose content is less than 60% by weight.

2. The resin composition according to claim 1, wherein, The cellulose content is 10% by weight or more.

3. The resin composition according to claim 1, wherein, The cellulose contains recycled materials.

4. The resin composition according to claim 1, wherein, The amount of hemicellulose in the cellulose is less than 10% by weight.

5. The resin composition according to claim 1, wherein, The cellulose was not chemically modified.

6. The resin composition according to claim 1, wherein, The average particle size of the cellulose is less than 100 μm.

7. The resin composition according to claim 1, wherein, The viscosity of the thermoplastic resin at 200°C is 1×10⁻⁶. 6 Pa·s and below.

8. The resin composition according to claim 1, wherein, The melting temperature of the thermoplastic resin is below 200°C.

9. The resin composition according to claim 1, wherein, The thermoplastic resin has a melt flow rate (MFR) of 2.5 g / 10 min or more at a temperature of 230°C and a load of 2.16 kgf.

10. The resin composition according to claim 1, wherein, The thermoplastic resin comprises a polyolefin.

11. The resin composition according to claim 1, wherein, The thermoplastic resin contains recycled materials.

12. The resin composition according to claim 1, wherein, The content of titanium oxide is less than 5% by weight relative to the resin composition.

13. A molded article formed by injection molding the resin composition according to any one of claims 1 to 12.

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