JP2025168189A - Resin composition, pellets and molded products - Google Patents

Abstract

[Problem] To provide a resin composition, pellets, and molded articles that have improved sliding properties when molded into an environmentally friendly product. [Solution] The resin composition according to the present disclosure contains 1 to 50 parts by mass of plant-derived porous powder particles containing fatty acids, pulverized by freeze-pulverization, per 100 parts by mass of polyacetal resin. [Selected Figures] None

Description

The present invention relates to a resin composition, pellets, and molded articles. In particular, it relates to a resin composition containing polyacetal resin as a primary component.

Polyacetal resin is a plastic having excellent mechanical properties, electrical properties, and chemical properties such as chemical resistance, and is used in a wide range of applications.
One of the known uses of polyacetal resin is as a sliding member. Examples of the use of polyacetal resin as a sliding member include Patent Documents 1 and 2.

JP 2008-214490 A International Publication No. 2018/230389

The resin compositions described in Patent Documents 1 and 2 are materials with excellent sliding properties. However, in recent years, from the viewpoint of environmental conservation, the utilization of biomass materials and the effective utilization of resources have become issues. In other words, resin compositions with sliding properties that take environmental conservation into consideration are also required.
The present invention aims to solve these problems and to provide a resin composition, pellets, and molded articles that have improved sliding properties when formed into a molded article and that are environmentally friendly.

In light of the above-mentioned problems, the present inventors have conducted research and found that high sliding properties can be achieved using biomass materials by using a porous powder derived from a plant containing freeze-pulverized fatty acids in a polyacetal resin.
[1] Per 100 parts by mass of polyacetal resin,
A resin composition comprising 1 to 50 parts by mass of a plant-derived porous powder containing fatty acids pulverized by freeze-pulverization.
[2] The resin composition according to [1], further comprising 0.1 to 3 parts by mass of a fatty acid metal salt per 100 parts by mass of the polyacetal resin.
[3] The resin composition according to [1] or [2], wherein the porous powder is derived from coffee grounds.
[4] Further, the composition contains 0.1 to 3 parts by mass of a fatty acid metal salt relative to 100 parts by mass of the polyacetal resin,
The resin composition according to any one of [1] to [3], wherein the porous powder is derived from coffee grounds.
[5] Pellets of the resin composition according to any one of [1] to [4].
[6] A molded article molded from the resin composition according to any one of [1] to [4].
[7] A molded article molded from the pellets according to [5].
[8] The molded article according to [6] or [7], which is a sliding member.

The present invention provides a resin composition, pellets, and molded articles that have improved sliding properties and are environmentally friendly.

Hereinafter, an embodiment of the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. Note that the present embodiment is an example for explaining the present invention, and the present invention is not limited to only this embodiment.
In this specification, the word "to" is used to mean that the numerical values before and after it are included as the lower limit and upper limit.
In this specification, various physical properties and characteristic values are those at 23° C. unless otherwise specified.
If the measurement methods, etc. described in the standards shown in this specification differ from year to year, they will be based on the standards as of January 1, 2023, unless otherwise stated.

The resin composition of this embodiment is characterized by containing 1 to 50 parts by mass of plant-derived porous powder particles containing fatty acids pulverized by freeze-pulverization, relative to 100 parts by mass of polyacetal resin.
The present inventors have disclosed in the specification of International Application No. PCT/JP2024/011564 that the sliding properties can be improved by blending porous powder particles derived from plants containing fatty acids with polyacetal resin.
Furthermore, the use of porous powders derived from plants makes it an environmentally friendly material. In particular, the use of waste materials such as coffee grounds makes it possible to recycle resources.
Under these circumstances, the present inventors conducted research and found that freeze-drying porous powders such as coffee grounds and then pulverizing them can further improve the sliding properties of the resulting molded product. Porous powders derived from plants such as coffee grounds tend to have improved sliding properties because they contain fatty acids. However, when pulverized, the fatty acids tend to be released onto the blades of the grinder and adhere to the blades. In this embodiment, it is believed that by using a pulverized product that has been frozen and then pulverized, it is possible to prevent the fatty acids from adhering to the blades, thereby further improving the sliding properties.

The following describes in detail an embodiment of the present invention. However, the following description of the components is an example of an embodiment of the present invention and is not intended to limit the scope of the present invention.

<Polyacetal resin>
The resin composition of the present embodiment contains a polyacetal resin.
The polyacetal resin is not particularly limited in terms of its type, etc., and may be a homopolymer containing only divalent oxymethylene groups as constituent units, or a copolymer containing divalent oxymethylene groups and divalent oxyalkylene groups having 2 to 6 carbon atoms as constituent units.

Examples of oxyalkylene groups having 2 to 6 carbon atoms include oxyethylene groups, oxypropylene groups, and oxybutylene groups.

In polyacetal resins, the proportion of oxyalkylene groups having 2 to 6 carbon atoms in the total number of moles of oxymethylene groups and oxyalkylene groups having 2 to 6 carbon atoms is not particularly limited, but may be 0.5 to 10 mol %.

To produce the polyacetal resin, trioxane is typically used as the main raw material. Furthermore, to introduce oxyalkylene groups having 2 to 6 carbon atoms into the polyacetal resin, cyclic formals or cyclic ethers can be used. Specific examples of cyclic formals include 1,3-dioxolane, 1,3-dioxane, 1,3-dioxepane, 1,3-dioxocane, 1,3,5-trioxepane, and 1,3,6-trioxocane. Specific examples of cyclic ethers include ethylene oxide, propylene oxide, and butylene oxide. To introduce oxyethylene groups into the polyacetal resin, 1,3-dioxolane can be used as the main raw material. To introduce oxypropylene groups, 1,3-dioxane can be used as the main raw material. To introduce oxybutylene groups, 1,3-dioxepane can be used as the main raw material. In addition, it is preferable that the polyacetal resin has a small amount of hemiformal terminal groups, formyl terminal groups, and terminal groups that are unstable to heat, acid, or base. Here, the hemiformal terminal groups are represented by —OCH ₂ OH, and the formyl terminal groups are represented by —CHO.

The polyacetal resin used in this embodiment preferably has a melt volume rate (MVR) measured in accordance with ISO 1133 at a temperature of 190°C and a load of 2.16 kg of 0.5 ^cm3 /10 min or more, more preferably 0.6 ^cm3 /10 min or more, even more preferably 0.8 ^cm3 /10 min or more, still more preferably 1 ^cm3 /10 min or more, and even more preferably 5 ^cm3 /10 min or more. By setting the MVR at or above the lower limit, the productivity of the resin composition tends to be further improved. Furthermore, the MVR of the polyacetal resin is preferably 20 ^cm3 /10 min or less, more preferably 18 ^cm3 /10 min or less, even more preferably 14 ^cm3 /10 min or less, still more preferably 10 ^cm3 /10 min or less, and even more preferably 8 ^cm3 /10 min or less.

In addition to the polyacetal resins described above, the polyacetal resins described in paragraphs 0018 to 0043 of JP 2015-074724 A can also be used, the contents of which are incorporated herein by reference.

The resin composition of this embodiment preferably contains polyacetal resin in a proportion of 50% by mass or more of the resin composition, more preferably 55% by mass or more, and even more preferably 60% by mass or more, with the upper limit being the amount at which the total amount of the resin composition other than the plant-derived porous powder or granule containing fatty acid becomes polyacetal resin.
The resin composition of the present embodiment may contain only one type of polyacetal resin, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

<Plant-derived porous powder containing fatty acids>
The resin composition of this embodiment includes a plant-derived porous powder containing fatty acids, which has been pulverized by freeze-pulverization. By using a plant-derived porous powder, an environmentally friendly resin composition can be obtained. Furthermore, by using a porous powder containing fatty acids, the sliding properties of the resin composition can be improved. In particular, the use of the porous powder achieves an oil absorption effect and provides a sustained release effect, allowing the sliding properties to be maintained for a long time.
Furthermore, by using porous powder particles that have been pulverized by freeze-pulverization, the sliding properties are further improved.
Freeze-pulverization means that the material is frozen and then pulverized. Known freezing methods can be used, but freezing with liquid nitrogen is preferred. Freeze-pulverization allows the material to be pulverized without the fatty acids adhering to the blades during pulverization. It is also believed that the cell walls of the porous powder are destroyed during pulverization, making it easier for the fatty acids inside to be exposed. As a result, it is believed that the use of freeze-pulverized porous powder improves the sliding properties of the resulting molded product.

Examples of plant-derived porous powders containing fatty acids include coffee grounds (residue after coffee extraction), soybean pulp, and residues (grounds) left after extracting oils such as rapeseed oil, sesame oil, and camellia oil. Because these substances contain fatty acids and have a porous structure, they can achieve oil absorption and maintain long-lasting sliding properties while taking environmental conservation into consideration. In this embodiment, the use of coffee grounds allows a marble-like pattern to be formed on the molded product, thereby achieving designability.
Furthermore, the porous powder particles derived from plants containing fatty acids are porous, and therefore effectively function as a filler.
Such a porous structure is formed by, for example, including cellulose.

The plant-derived porous powder containing fatty acids of this embodiment is preferably heated before use. When the porous powder is a dried product, it functions better as a filler.
The drying temperature of the porous powder or granule is preferably less than 150° C., more preferably 140° C. or less, more preferably 125° C. or less, even more preferably 105° C. or less, still more preferably 90° C. or less, even more preferably 75° C. or less, and may further be 70° C. or less, 65° C. or less, 60° C. or less, or 55° C. The lower limit of the drying temperature of the porous powder or granule is, for example, 45° C. or more.
By heating under such low temperature conditions, the sliding properties of the resulting molded product can be further improved, presumably because the deterioration and carbonization of the fatty acids contained in the porous powder or granules can be more effectively suppressed.
The drying time for drying the porous powder or granule is preferably 30 minutes or more, more preferably 1 hour or more, more preferably 5 hours or more, or may be 10 hours or more, and is preferably 1 week or less, more preferably 3 days or less.
Moreover, the porous powder is usually water-insoluble.

The average particle diameter D50 of the porous powder or granule is preferably 1 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, even more preferably 15 μm or more, even more preferably 20 μm or more, and preferably 400 μm or less, more preferably 300 μm or less, even more preferably 200 μm or less, even more preferably 150 μm or less, and even more preferably 70 μm or less. By setting it to the upper limit or less, the tensile elongation of the obtained molded product tends to be further improved. Furthermore, by setting it to the lower limit or more, the effect of (improving the handleability of the powder) tends to be further improved.
The average particle size D50 of the porous powder is measured according to the description in the Examples section below.

The type of fatty acid contained in the porous powder or granule depends on the type of plant used, but when the porous powder or granule is heated at 280°C for 10 minutes and the gas generated by heating is analyzed by GC-MS, the fatty acids detected include unsaturated fatty acids and/or saturated fatty acids, and preferably at least unsaturated fatty acids.
The unsaturated fatty acid may be a monounsaturated fatty acid or a polyunsaturated fatty acid, and preferably contains at least a polyunsaturated fatty acid.
Specific examples of unsaturated fatty acids include linoleic acid, oleic acid, linolenic acid, eicosapentaenoic acid, docosapentaenoic acid, docosahexaenoic acid, and arachidonic acid.
Examples of saturated fatty acids include myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, heneicosylic acid, behenic acid, lignoceric acid, cerotic acid, and montanic acid.

When the porous powder used in this embodiment is heated at 280°C for 10 minutes and the gas generated is analyzed by GC-MS, the amount of fatty acids, in decane equivalent, is preferably 500 μg/g or more, more preferably 700 μg/g or more, even more preferably 1000 μg/g or more, even more preferably 1500 μg/g or more, and even more preferably 2500 μg/g or more. By setting the amount above the lower limit, the sliding properties of the resin composition tend to be further improved. Furthermore, when the porous powder used in this embodiment is analyzed by GC-MS, the amount of fatty acids, in decane equivalent, is preferably 10,000 μg/g or less, more preferably 8,000 μg/g or less, even more preferably 7,000 μg/g or less, even more preferably 6,000 μg/g or less, and even more preferably 5,000 μg/g or less. By setting the amount below the upper limit, moldability tends to be further improved.

The porous powder or granule used in this embodiment may contain only one type of fatty acid, but typically contains two or more types. Furthermore, when the porous powder or granule contains two or more types of fatty acids, it is preferable that the total amount be within the above range.

The content of the porous powder or granules in the resin composition of this embodiment is 1 part by mass or more, preferably 3 parts by mass or more, more preferably 8 parts by mass or more, even more preferably 10 parts by mass or more, even more preferably 18 parts by mass or more, and even more preferably 25 parts by mass or more, per 100 parts by mass of polyacetal resin. By setting the content at or above the lower limit, the sliding properties of the resulting molded product tend to be further improved. Furthermore, the upper limit of the content of the porous powder or granules is 50 parts by mass or less, preferably 40 parts by mass or less, per 100 parts by mass of polyacetal resin. By setting the content at or below the upper limit, mechanical properties tend to be maintained at a high level.
The resin composition of the present embodiment may contain only one type of porous powder or particle, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

<Fatty acid metal salts>
The resin composition of the present embodiment preferably contains a fatty acid metal salt, which effectively prevents fatty acids derived from the porous powder or granule from appearing on the surface of the molded body, thereby shortening the molding time.
In this embodiment, it is particularly preferred that the fatty acid of the plant-derived porous powder or grain containing fatty acid contains an unsaturated fatty acid, and the fatty acid constituting the fatty acid metal salt contains a saturated fatty acid. By adopting such a configuration, the effects of the present invention tend to be more effectively exhibited.

The fatty acid metal salt used in this embodiment is preferably a calcium salt and/or a magnesium salt, and preferably contains at least a calcium salt.
The fatty acid metal salt used in this embodiment preferably has an aliphatic group having 10 to 50 carbon atoms. The number of carbon atoms in the fatty acid metal salt is preferably 12 or more, more preferably 14 or more, and is preferably 36 or less, more preferably 28 or less, even more preferably 25 or less, and even more preferably 20 or less.
The aliphatic group is preferably a straight-chain aliphatic group.
The aliphatic group may have a hydroxyl group as a substituent. By having a hydroxyl group as a substituent, the weighing time during molding of the resulting resin composition tends to be shorter. The aliphatic group may be a saturated aliphatic group or an unsaturated aliphatic group, but a saturated aliphatic group is preferred.
More specifically, examples of fatty acids that constitute fatty acid metal salts include myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, heneicosylic acid, behenic acid, lignoceric acid, cerotic acid, and montanic acid, as well as fatty acids in which one of the hydrogen atoms in the aliphatic chain of these fatty acids has been substituted with a hydroxyl group, with stearic acid and hydroxystearic acid being preferred.
In this embodiment, the fatty acid metal salt is preferably calcium stearate, magnesium stearate, calcium hydroxystearate, or magnesium hydroxystearate, more preferably calcium hydroxystearate or calcium stearate.

The content of the fatty acid metal salt in the resin composition of this embodiment is typically 0.1 parts by mass or more, preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, and may be 0.6 parts by mass or more, or even 0.9 parts by mass or more, or even 1.1 parts by mass or more, per 100 parts by mass of the polyacetal resin. By setting the content at or above the lower limit, the effect of suppressing slipping during molding tends to be further improved. Furthermore, the content of the fatty acid metal salt is typically 3 parts by mass or less, per 100 parts by mass of the polyacetal resin. By setting the content at or below the upper limit, the effect of suppressing discoloration when the molded product is heated tends to be further improved.
The resin composition of the present embodiment may contain only one fatty acid metal salt, or may contain two or more fatty acid metal salts. When two or more fatty acid metal salts are contained, the total amount is preferably in the above range.

<Other ingredients>
The resin composition of this embodiment may contain known additives and fillers within the scope of the present invention. Examples of the additives and fillers that can be used in this embodiment include known thermoplastic polymers other than polyacetal resins (such as acid-modified polymers), weathering agents, formaldehyde scavengers, inorganic particles, antioxidants (hindered amines, hindered phenols), heat stabilizers, colorants, nucleating agents, plasticizers, fluorescent brighteners, mold release agents (such as silicon compounds), antistatic agents, ultraviolet absorbers (such as benzotriazoles or benzophenones), flame retardants, and flame retardant assistants, which may be added as needed.
The resin composition of this embodiment is prepared so that the total of the polyacetal resin, the plant-derived porous powder containing a fatty acid, and other components blended as necessary is 100% by mass. In the resin composition of this embodiment, the total of the polyacetal resin and the plant-derived porous powder containing a fatty acid preferably accounts for 85% by mass or more of the resin composition, more preferably 90% by mass or more, even more preferably 95% by mass or more, and may even account for 98% by mass or more.
In the resin composition of the present embodiment, the plant-derived porous powder or granule containing the polyacetal resin and the fatty acid, and the thermoplastic polymer other than the polyacetal resin, the weathering agent, the formaldehyde scavenger, the inorganic particles, the antioxidant, the heat stabilizer, the colorant, the nucleating agent, the plasticizer, the fluorescent brightener, the release agent, the antistatic agent, the ultraviolet absorber, the flame retardant, and the flame retardant aid, which are blended as necessary, preferably account for 90% by mass or more of the resin composition, more preferably 95% by mass or more, even more preferably 97% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and even more preferably 100% by mass.
More preferably, in the resin composition of the present embodiment, the polyacetal resin, the plant-derived porous powder or granule containing a fatty acid, and the weathering agent, formaldehyde scavenger, antioxidant, heat stabilizer, colorant, nucleating agent, plasticizer, fluorescent brightener, release agent, antistatic agent, ultraviolet absorber, flame retardant, and flame retardant aid, which are blended as necessary, together account for preferably 95% by mass or more of the resin composition, more preferably 90% by mass or more, even more preferably 97% by mass or more, still more preferably 98% by mass or more, even more preferably 99% by mass or more, and still more preferably 100% by mass.

The resin composition of the present embodiment may be substantially free of lubricating oil, meaning that the lubricating oil content is less than 1% by mass of the resin composition, preferably less than 0.1% by mass, more preferably less than 0.01% by mass, and even more preferably less than 0.001% by mass.
The resin composition in this embodiment may be configured to be substantially free of glass. "Substantially free of glass" means that the glass content in the resin composition is less than 15% by mass, preferably less than 10% by mass, more preferably less than 7% by mass, even more preferably less than 5% by mass, even more preferably less than 3% by mass, and even more preferably less than 1% by mass.
The resin composition of this embodiment preferably does not substantially contain any filler other than the porous powder or granule derived from a plant containing a fatty acid. Specifically, the content of fillers other than the porous powder or granule derived from a plant containing a fatty acid in the resin composition is preferably less than 10% by mass of the content of the porous powder or granule derived from a plant containing a fatty acid, more preferably less than 7% by mass, even more preferably less than 5% by mass, even more preferably less than 3% by mass, and even more preferably less than 1% by mass.

<Method of producing resin composition>
The resin composition of this embodiment can be easily prepared by a known method commonly used for preparing conventional thermoplastic resin compositions. For example, (1) a method in which all components constituting the resin composition are mixed, fed into an extruder, and melt-kneaded to obtain a pellet-shaped resin composition, (2) a method in which some of the components constituting the resin composition are fed through a main feed port of an extruder and the remaining components are fed through a side feed port, and melt-kneaded to obtain a pellet-shaped resin composition, or (3) a method in which pellets of different compositions are prepared by extrusion or the like, and the pellets are mixed to obtain a resin composition having a predetermined composition, etc., can be employed.
Examples of the kneading machine include a kneader, a Banbury mixer, an extruder, etc. The various conditions and devices for mixing and kneading are not particularly limited and may be appropriately selected from any conventionally known conditions. Kneading is preferably carried out at a temperature at which the polyacetal resin melts or higher, specifically at the melting temperature of the polyacetal resin or higher (generally 180°C or higher).

<Molded product>
The molded article of this embodiment is formed from the resin composition or pellets of this embodiment. The pellets obtained by pelletizing the resin composition of this embodiment can be molded into a molded article using various molding methods. Alternatively, a resin composition melt-kneaded in an extruder can be directly molded into a molded article without going through pelletization. An example of a molded article formed from the resin composition of this embodiment is an injection-molded article. Since injection-molded articles are formed in a mold, welds are formed. That is, an example of a molded article of this embodiment is a molded article having welds. The shape of the molded article is not particularly limited and can be appropriately selected depending on the application and purpose of the molded article. Examples include plate-like, plate-like, rod-like, sheet-like, film-like, cylindrical, annular, circular, elliptical, gear-like, polygonal, irregularly shaped, hollow, frame-like, box-like, and panel-like shapes. The molded article of this embodiment may be a finished product or a part.

The method for molding the molded article is not particularly limited, and any conventionally known molding method can be used, such as injection molding, injection compression molding, extrusion molding, profile extrusion, transfer molding, blow molding, gas-assisted blow molding, blow molding, extrusion blow molding, IMC (in-mold coating molding), rotational molding, multi-layer molding, two-color molding, insert molding, sandwich molding, foam molding, and pressure molding.

The resin composition of this embodiment is preferably used for forming a sliding member, and therefore, a molded article formed from the resin composition of this embodiment is preferably used as a sliding member (sliding part).
Specific examples of sliding members include gears, rotating shafts, bearings, various gears, cams, end face materials for mechanical seals, valve seats for valves and the like, sealing members such as V-rings, rod packings, piston rings, and rider rings, as well as sliding members such as rotating shafts, rotating sleeves, pistons, impellers, and rollers of compressors, which are intended to meet the high quality demands of electric and electronic equipment, office equipment, vehicles (automobiles), industrial equipment, and the like.

The sliding member of this embodiment can be used not only with other sliding members of this embodiment, but also with other resin sliding members, fiber-reinforced resin sliding members, and ceramic or metal sliding members.

The present invention will be explained in more detail below with reference to examples. The materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.
If the measuring instruments used in the examples are difficult to obtain due to discontinuation or the like, measurements can be made using other instruments with equivalent performance.

1. Raw materials The raw materials shown in Table 1 were used.

Coffee grounds A were frozen with liquid nitrogen and then pulverized in a grinder.
Coffee grounds B were not pretreated and were ground in a grinder.
Coffee grounds C were not ground.

The average particle size D50 of the coffee grounds was measured using a laser diffraction particle size distribution analyzer, and the particle size at 50% cumulative volume was defined as the average particle size D50 in this specification. The laser diffraction particle size distribution analyzer used was the MT3000II (product name, manufactured by Microtrac Bell Co., Ltd.).

In Table 1 above, 1 g of coffee grounds was heated at 280°C for 10 minutes using a thermal desorption-gas chromatograph/mass spectrometer, and the gas evolved from the heating was analyzed by GC-MS. The fatty acids detected were, in descending order of abundance, palmitic acid, a mixture of linoleic acid and oleic acid, stearic acid, and arachidic acid.
The coffee grounds were heated at 280°C for 10 minutes, and the amount of fatty acids generated was analyzed by GC-MS, in decane equivalent, in the range of 500 μg/g to 10,000 μg/g.

2. Examples 1 to 3 and Comparative Examples 1 to 6
<Compound>
The components shown in Table 1 were compounded as shown in Tables 2 to 4 (the units for each component in Tables 2 to 4 are parts by mass), preblended in a Henschel mixer, and then charged into the main feed port of a 30 mm diameter twin-screw extruder equipped with one vent port for melt mixing (extrusion conditions: L/D=35, extrusion temperature=190°C, screw rotation speed=120 rpm, vent vacuum pressure=−0.08 MPa, discharge rate=10 kg/hr) to prepare a pelletized resin composition.
The resulting resin compositions were evaluated as follows.

<Sliding properties>
Cylindrical thrust test specimens were prepared using the resin composition obtained above by injection molding at a cylinder temperature of 200°C and a mold temperature of 80°C.
The cylindrical thrust test piece thus obtained was subjected to a thrust friction and wear test against carbon steel S45C, and the dynamic friction coefficient was measured under a load of 3 kgf, a surface pressure of 0.15 MPa, and a linear velocity of 0.1 m/sec.
The measurement was carried out using a thrust type friction and wear tester manufactured by Orientec Co., Ltd. in an atmosphere at a temperature of 23° C. and a humidity of 50%.

By freeze-drying and then pulverizing coffee grounds, the resin composition of the present invention exhibited improved sliding properties compared to grinding by other methods or when the grounds were not pulverized (Compare Example 1 with Comparative Examples 2 and 3, Example 2 with Comparative Examples 4 and 5, and Example 3 with Comparative Examples 5 and 6).

3. Reference examples A to D
Coffee grounds C were dried under the conditions shown in Table 5. After drying, the components were not pulverized but were compounded as shown in Table 5 (the units for each component in Table 5 are parts by mass), preblended in a Henschel mixer, and then charged into the main feed port of a 30 mm diameter twin-screw extruder equipped with one vent port for melt mixing (extrusion conditions: L/D = 35, extrusion temperature = 190°C, screw rotation speed = 120 rpm, vent vacuum pressure = -0.08 MPa, discharge rate = 10 kg/hr) to prepare a resin composition in pellet form.
The resulting resin compositions were evaluated as follows.

<Dynamic friction coefficient>
The resin composition obtained above was dried at 80°C for 3 hours, and then molded into a cylindrical thrust test piece using an injection molding machine (Sumitomo Heavy Industries, Ltd., "SE-30DUZ") under conditions of a cylinder temperature of 195°C and a mold temperature of 90°C.
The obtained cylindrical thrust test pieces were subjected to a thrust friction and wear test against carbon steel S45C at a linear velocity of 10 cm/s, with the surface pressure increased every 3 minutes by 3 kg, 5 kg, and 10 kg, with the surface pressure increasing by 5 kg from 5 kg onwards. Focusing on the dynamic friction coefficient under high surface pressure (load 50 kg, surface pressure 4.9 MPa), where differences in the dynamic friction coefficient due to formulation are likely to occur, the average value of the dynamic friction coefficient over 3 minutes was recorded.

Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention.

Claims (8)

For 100 parts by mass of polyacetal resin,
A resin composition comprising 1 to 50 parts by mass of a plant-derived porous powder containing fatty acids pulverized by freeze-pulverization. The resin composition according to claim 1 further contains 0.1 to 3 parts by mass of a fatty acid metal salt per 100 parts by mass of the polyacetal resin. The resin composition according to claim 1, wherein the porous powder is derived from coffee grounds. Further, the composition contains 0.1 to 3 parts by mass of a fatty acid metal salt relative to 100 parts by mass of the polyacetal resin,
The resin composition according to claim 1 , wherein the porous powder is derived from coffee grounds. Pellets of the resin composition described in any one of claims 1 to 4. A molded article molded from the resin composition described in any one of claims 1 to 4. A molded article molded from the pellets described in claim 5. The molded article according to claim 6, which is a sliding member.