WO2025053044A1 - Resin composition, pellets, and molded article - Google Patents

Abstract

Provided are a resin composition, pellets, and a molded article. The resin composition includes a polyacetal resin (A), a silicone resin (B) having a weight-average molecular weight of 800,000 or more, and a silicone oil (C) having a weight-average molecular weight of less than 100,000, wherein the mass ratio (B)/(C) of the silicone resin (B) to the silicone oil (C) is 10/90 to 90/10.

Description

Resin composition, pellets, and molded products

The present invention relates to a resin composition, pellets, and molded products. In particular, the present invention relates to a resin composition whose main component is polyacetal resin.

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. As an example of using polyacetal resin as a sliding member, Patent Document 1 discloses a polyacetal resin composition obtained by blending 99.8 to 80 parts by weight of polyacetal, 0.1 to 20 parts by weight of polyethylene wax, and 0.1 to 5 parts by weight of silicone oil.

Japanese Patent Application Publication No. 04-224856

The resin composition described in the above Patent Document 1 is a material with excellent sliding properties. However, in recent years, there has been a demand for even better sliding properties. However, if the amount of the sliding agent blended is large, metal mold contamination during molding becomes a problem.
The present invention aims to solve such problems, and to provide a resin composition that can provide a molded article with excellent sliding properties and causes little mold contamination, as well as pellets and a molded article.

In view of the above problems, the present inventors have conducted research and found that the above problems can be solved by using a silicone resin having a predetermined molecular weight in combination with a silicone oil for a polyacetal resin.
Specifically, the above problems were solved by the following means.
<1> A composition comprising a polyacetal resin (A), a silicone resin (B) having a weight-average molecular weight of 800,000 or more, and a silicone oil (C) having a weight-average molecular weight of less than 100,000;
A resin composition, wherein the mass ratio of the silicone resin (B) to the silicone oil (C), (B)/(C), is 10/90 to 90/10.
<2> The resin composition according to <1>, in which the total content of the silicone resin (B) and the silicone oil (C) is 0.5 parts by mass or more and less than 10 parts by mass per 100 parts by mass of the polyacetal resin (A).
<3> The resin composition according to <1>, wherein the total content of the silicone resin (B) and the silicone oil (C) is 0.5 parts by mass or more and less than 2 parts by mass per 100 parts by mass of the polyacetal resin (A).
<4> Pellets of the resin composition according to any one of <1> to <3>.
<5> A molded article formed from the resin composition according to any one of <1> to <3>.
<6> A molded article formed from the pellets according to <4>.

The present invention makes it possible to provide molded articles with excellent sliding properties, and resin compositions, as well as pellets and molded articles with minimal mold contamination.

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 the present embodiment.
In this specification, the use of "to" means 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 vary from year to year, they will be based on the standards as of January 1, 2023, unless otherwise specified.

The resin composition of the present embodiment is characterized in that it contains a polyacetal resin (A), a silicone resin (B) having a weight average molecular weight of 800,000 or more, and a silicone oil (C) having a weight average molecular weight of less than 100,000, and the mass ratio of the silicone resin (B) to the silicone oil (C), (B)/(C), is 10/90 to 90/10. By adopting such a configuration, it is possible to provide a molded product with excellent sliding properties with little mold contamination during molding.
By blending a silicone resin (B) having a weight-average molecular weight of 800,000 or more, the sliding properties of the resulting molded article can be improved. This is presumably because a silicone resin with a large molecular weight has a large dispersion diameter in the polyacetal resin, which makes the silicone resin more likely to appear on the surface of the molded article.
However, it has been found that when using silicone resin with large molecular weight, mold contamination is likely to occur during molding.In this embodiment, in order to solve this problem, silicone oil (C) with weight-average molecular weight of less than 100,000 is blended.That is, silicone oil (C) with weight-average molecular weight of less than 100,000 alone cannot achieve sufficient sliding properties, but by blending two kinds of silicone resins, it is possible to maintain excellent sliding properties and suppress mold contamination at the same time.
Furthermore, when a high molecular weight silicone resin is used, the resulting molded product tends to have poor delamination, but this aspect can also be suppressed by using the silicone oil (C) having a weight average molecular weight of less than 100,000 in combination.
The details of this embodiment will be described below.

<Polyacetal resin (A)>
The resin composition of the present embodiment contains a polyacetal resin.
The polyacetal resin is not particularly limited in terms of its type, 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 usually used as the main raw material. To introduce an oxyalkylene group having 2 to 6 carbon atoms into the polyacetal resin, a cyclic formal or a cyclic ether can be used. Specific examples of the cyclic formal include 1,3-dioxolane, 1,3-dioxane, 1,3-dioxepane, 1,3-dioxocane, 1,3,5-trioxepane, and 1,3,6-trioxocane, and specific examples of the cyclic ether include ethylene oxide, propylene oxide, and butylene oxide. To introduce an oxyethylene group into the polyacetal resin, 1,3-dioxolane can be used as the main raw material. To introduce an oxypropylene group, 1,3-dioxane can be used as the main raw material. To introduce an oxybutylene group, 1,3-dioxepane can be used as the main raw material. In addition, in a polyacetal resin, it is preferable that the amount of hemiformal end groups, formyl end groups, and end groups unstable to heat, acid, or base is small. Here, the hemiformal end group is represented by -OCH ₂ OH, and the formyl end group is represented by -CHO.

The polyacetal resin used in this embodiment has a melt volume rate (MVR) measured according to ISO1133 at a temperature of 190°C and a load of 2.16 kg of preferably 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, even more preferably 1 ^cm3 /10 min or more, and even more preferably 5 ^cm3 /10 min or more. By setting the MVR to the lower limit or more, the productivity of the resin composition tends to be further improved. In addition, 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, even more preferably 10 ^cm3 /10 min or less, and even more preferably 8 ^cm3 /10 min or less.

In addition to the above, the polyacetal resins described in paragraphs 0018 to 0043 of JP-A-2015-074724 can be used as the polyacetal resin, the contents of which are incorporated herein by reference.
The polyacetal resin used in this embodiment may be a recycled product (including recovered products, material recycled products, chemical recycled products, etc.), a rejected product, or a scrap from thermoplastic resin molding.

The resin composition of the present embodiment preferably contains polyacetal resin in a proportion of 80 mass % or more of the resin composition, more preferably contains 85 mass % or more, even more preferably contains 90 mass % or more, still more preferably contains 93 mass % or more, even more preferably contains 95 mass % or more, and still more preferably contains 97 mass % or more. In addition, all components other than the silicone resin (B) and the silicone oil (C) may be 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.

<Silicone resin (B) having a weight average molecular weight of 800,000 or more>
The resin composition of the present embodiment contains a silicone resin (B) having a weight average molecular weight of 800,000 or more. By containing a silicone resin (B) having a weight average molecular weight of 800,000 or more, the sliding properties can be improved. In particular, the limit PV value can be improved and the dynamic friction coefficient can be reduced.

The weight average molecular weight of the silicone resin (B) is preferably 850,000 or more, more preferably 900,000 or more, even more preferably 950,000 or more, and still more preferably 980,000 or more, and is preferably 2,000,000 or less, more preferably 1,800,000 or less, and even more preferably 1,500,000 or less, and may be 1,200,000 or less.
By setting the content to be equal to or more than the lower limit, the sliding properties tend to be improved, whereas by setting the content to be equal to or less than the upper limit, the effect of suppressing mold contamination and delamination of molded pieces tends to be improved.

In this embodiment, the molecular weight of the silicone resin (B) is measured according to the following method.
Silicone in silicone resin is extracted with dichloromethane. The extracted silicone is adjusted with 0.2% by mass of toluene eluent and left at room temperature for 12 hours. Then, it is filtered with a 0.45 μm membrane filter, and the filtrate is subjected to gel permeation chromatography (GPC) measurement. When performing GPC measurement, AQCUITY APC manufactured by Waters can be used.
When the resin composition of the present embodiment contains two or more types of silicone resin (B), the Mw of the silicone resin (B) is the Mw of the mixture.
The same applies to the silicone oil (C).

The silicone resin (B) used in this embodiment is preferably a polyorganosiloxane, and is preferably a compound represented by -(Si(R) ₂ -O)-, where R is each independently a hydrogen atom, a hydrocarbon group, an -O-hydrocarbon group, or a hydroxyl group (with the proviso that at least one of R is a hydrocarbon group or an -O-hydrocarbon group). Each R is preferably independently a hydrogen atom, a hydrocarbon group having 1 to 6 carbon atoms, an -O-hydrocarbon group having 1 to 6 carbon atoms, or a hydroxyl group, and is preferably a hydrogen atom, a methyl group, an ethyl group, a phenyl group, a methoxy group, an ethoxy group, a phenoxy group, or a hydroxyl group, more preferably a hydrogen atom, a methyl group, or a methoxy group, and even more preferably a hydrogen atom or a methyl group.
The silicone resin (B) may contain one type of —(Si(R) ₂ —O)—, or two or more types of —(Si(R) 2 —O)—.

The silicone resin (B) used in this embodiment is preferably a non-crosslinked silicone. Non-crosslinked silicones are exemplified by silicones represented by -(Si(R) ₂ -O)-, where each R is independently a silicone that does not contain a structure represented by -(Si(R') ₂ -O)- (each R' independently forms a crosslinked structure with another moiety). R is the same as above, and the preferred range is also the same.

The silicone resin (B) used in this embodiment is preferably a linear silicone. An example of a linear silicone is a compound represented by -(Si(R) ₂ -O)-, where each R is independently an atomic group having 12 or less carbon atoms and not containing a silicon atom. R here is the same as above, and the preferred range is also the same.

When compounding the silicone resin (B), it may be made into a masterbatch. The resin used in the masterbatch is preferably a polyacetal resin. The proportion of silicone resin (B) in the masterbatch is preferably 10% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, and is preferably 80% by mass or less, preferably 70% by mass or less, and more preferably 60% by mass or less.

The content of the silicone resin (B) in the resin composition of this embodiment is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, even more preferably 0.3 parts by mass or more, and even more preferably 0.4 parts by mass or more, relative to 100 parts by mass of the polyacetal resin (A), and may be 0.6 parts by mass or more depending on the application, and may be 9 parts by mass or less, more preferably 7 parts by mass or less, even more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, even more preferably 1 part by mass or less, and even more preferably 0.9 parts by mass or less, and may be 0.7 parts by mass or less depending on the application. By making it equal to or more than the lower limit, the sliding property tends to be further improved. Also, by making it equal to or less than the upper limit, the effect of suppressing mold contamination and delamination of molded pieces tends to be further improved.
The resin composition of the present embodiment may contain only one type of silicone resin (B), or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

<Silicone Oil (C) with Weight Average Molecular Weight of Less than 100,000>
The resin composition of the present embodiment contains a silicone oil (C) having a weight-average molecular weight of less than 100,000. By using the silicone oil (C) having a weight-average molecular weight of less than 100,000 in combination with the silicone resin (B), it is possible to effectively suppress mold contamination and delamination while maintaining high slidability (particularly, the limit PV value).

The weight average molecular weight of the silicone oil (C) is preferably 95,000 or less, more preferably 90,000 or less, and even more preferably 85,000 or less, and is preferably 10,000 or more, more preferably 20,000 or more, and even more preferably 35,000 or more.
By setting the content to be equal to or more than the lower limit, the sliding properties tend to be improved, whereas by setting the content to be equal to or less than the upper limit, the effect of suppressing mold contamination and delamination of molded pieces tends to be improved.

The silicone oil (C) used in this embodiment is preferably an organosiloxane, and is preferably a compound represented by -(Si(R) ₂ -O)-, where each R is independently a hydrogen atom, a hydrocarbon group, an -O-hydrocarbon group, or a hydroxyl group (with the proviso that at least one of R is a hydrocarbon group or an -O-hydrocarbon group). Each R is preferably independently a hydrogen atom, a hydrocarbon group having 1 to 6 carbon atoms, an -O-hydrocarbon group having 1 to 6 carbon atoms, or a hydroxyl group, and is preferably a hydrogen atom, a methyl group, an ethyl group, a phenyl group, a methoxy group, an ethoxy group, a phenoxy group, or a hydroxyl group, more preferably a hydrogen atom, a methyl group, or a methoxy group, and even more preferably a hydrogen atom or a methyl group.
The —(Si(R) ₂ —O)— in the silicone oil (C) may be of one type or of two or more types.

When silicone oil (C) is blended, it may be made into a masterbatch. The resin used in the masterbatch is preferably polyacetal resin. The proportion of silicone oil (C) in the masterbatch is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, and is preferably 60% by mass or less, preferably 55% by mass or less, and more preferably 45% by mass or less.

The content of silicone oil (C) in the resin composition of this embodiment is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.2 parts by mass or more, relative to 100 parts by mass of polyacetal resin (A), and may be 0.3 parts by mass or more depending on the application, and may be 9 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, even more preferably 1 part by mass or less, and even more preferably 0.6 parts by mass or less, and may be 0.4 parts by mass or less depending on the application. By making it equal to or more than the lower limit, the sliding property tends to be further improved. Also, by making it equal to or less than the upper limit, the delamination suppression effect tends to be further improved.
The resin composition of the present embodiment may contain only one type of silicone oil (C), or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

<Blend of Silicone Resin (B) and Silicone Oil (C)>
In the resin composition of the present embodiment, the mass ratio of the silicone resin (B) to the silicone oil (C), that is, (B)/(C), is 10/90 to 90/10. By adopting such a configuration, it is possible to improve the sliding properties and suppress the mold contamination in a well-balanced manner.
The blend ratio of the silicone resin (B) and the silicone oil (C) is preferably 15 parts by mass or more of the silicone resin (B) per 100 parts by mass of the total of the silicone resin (B) and the silicone oil (C), more preferably 20 parts by mass or more, even more preferably 30 parts by mass or more, and preferably 40 parts by mass or more. Depending on the application, etc., it may be 51 parts by mass or more, or even 55 parts by mass or more, and is preferably 85 parts by mass or less, more preferably 80 parts by mass or less, and may be 75 parts by mass or less, or even 70 parts by mass or less, depending on the application, etc.

When the weight average molecular weights of the silicone resin (B) and the silicone oil (C) are _MwB and _MwC , respectively, the ratio of the weight average molecular weights of the silicone resin (B) and the silicone oil (C), _MwB / _MwC , is preferably 10 or more, and may be 20 or more, or even 40 or more, and is preferably 100 or less, and may be 50 or less, 30 or less, or even 15 or less. By being in the above range, the effects of the present invention tend to be more effectively exhibited.

In the resin composition of the present embodiment, the total content of the silicone resin (B) and the silicone oil (C) is preferably more than 0.1 parts by mass and less than 10 parts by mass with respect to 100 parts by mass of the polyacetal resin (A). By making it equal to or more than the lower limit, the sliding property tends to be improved. Also, by making it equal to or less than the upper limit, the effect of suppressing mold contamination and delamination of molded pieces tends to be improved.
The total content of the silicone resin (B) and the silicone oil (C) is, relative to 100 parts by mass of the polyacetal resin (A), more preferably 0.1 parts by mass or more, even more preferably 0.11 parts by mass or more, even more preferably 0.2 parts by mass or more, even more preferably 0.3 parts by mass or more, even more preferably 0.5 parts by mass or more, even more preferably 0.8 parts by mass or more, and preferably 9 parts by mass or less, more preferably 8 parts by mass or less, even more preferably 7 parts by mass or less, even more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, even more preferably 2 parts by mass or less, and even more preferably 1.5 parts by mass or less.

The resin composition of this embodiment may or may not contain a silicone compound having a weight average molecular weight of 100,000 or more and less than 800,000. One example of this embodiment is one that is substantially free of silicone compounds having a weight average molecular weight of 100,000 or more and less than 800,000. "Substantially free" means that the content of silicone compounds having a weight average molecular weight of 100,000 or more and less than 800,000 contained in the resin composition is less than 10% by mass of the total content of the silicone resin (B) and the silicone oil (C), preferably less than 5% by mass, more preferably less than 3% by mass, and may be less than 1% by mass.

In the resin composition of this embodiment, the total content of the polyacetal resin (A), silicone resin (B), and silicone oil (C) in the resin composition is preferably 90% by mass or more, 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 may be 100% by mass or less.

<Other ingredients>
The resin composition of the present embodiment may contain known additives and fillers within the scope of the present invention. Examples of additives and fillers that can be used in the present embodiment include known thermoplastic polymers other than polyacetal resins, acid-modified polymers, weathering agents, formaldehyde scavengers, inorganic particles, antioxidants (hindered amines, hindered phenols, etc.), heat stabilizers, colorants, nucleating agents, plasticizers, fluorescent brighteners, release agents, antistatic agents, ultraviolet absorbers, flame retardants, and flame retardant assistants, etc., which may be added as necessary.
The resin composition of the present embodiment is prepared so that the total of the polyacetal resin, the silicone resin (B), and the silicone oil (C), as well as other components that are blended as necessary, is 100 mass %.

<Physical Properties of Resin Composition>
The resin composition of the present embodiment preferably has excellent slidability.
The resin composition of the present embodiment preferably has a dynamic friction coefficient of 0.25 or less when molded into a cylindrical thrust test piece. The lower limit is, for example, 0.01 or more, which is practical. Such a small dynamic friction coefficient is achieved mainly by blending the silicone oil (C) with the polyacetal resin (A).
The dynamic friction coefficient is measured as described in the Examples section below.

The resin composition of this embodiment is molded into a cylindrical thrust test piece, and when measured according to the thrust ring friction and wear test specified in JIS K7218 Method A at a contact area of 2 ^cm2 and a temperature of 23°C, the limit PV value (MPa cm/s) is preferably 16.0 MPa cm/s or more. There is no particular upper limit, but 50.0 MPa cm/s or less is practical. Such a high limit PV value is mainly achieved by blending the silicone resin (B) with the polyacetal resin (A).
The limit PV value is measured as described in the Examples section below.

<Method of producing resin composition>
The resin composition of the present embodiment can be easily prepared by a known method generally used for preparing conventional thermoplastic resin compositions. For example, (1) a method of mixing all the components constituting the resin composition, feeding the mixture into an extruder and melt-kneading the mixture to obtain a pellet-shaped resin composition, (2) a method of feeding a part of the components constituting the resin composition from the main feed port of an extruder and the remaining components from the side feed port, melt-kneading the mixture to obtain a pellet-shaped resin composition, (3) a method of preparing pellets with different compositions by extrusion or the like, mixing the pellets to prepare a resin composition having a predetermined composition, etc. can be adopted.
In this embodiment, it is preferable that the silicone resin (B) and/or the silicone oil (C) (preferably the silicone resin (B)) is made into a master batch in advance, and then melt-kneaded with the remaining components.
Examples of the kneading machine include a kneader, a Banbury mixer, and an extruder. There are no particular limitations on the various conditions and devices for mixing and kneading, and they may be appropriately selected from any conventionally known conditions. Kneading is preferably performed 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 products>
The molded article of the present embodiment is formed from the resin composition or pellets of the present embodiment. The pellets obtained by pelletizing the resin composition of the present embodiment are molded into a molded article by various molding methods. Alternatively, the resin composition melt-kneaded in an extruder can be directly molded into a molded article without going through pellets.
The shape of the molded product is not particularly limited and can be appropriately selected depending on the application and purpose of the molded product, and examples thereof 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, panel-like, etc. The molded product of this embodiment may be a finished product or a part.

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

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 described in more detail below with reference to examples. The materials, amounts, ratios, processing contents, 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 following raw materials were used:

2. Examples 1 to 6 and Comparative Examples 1 to 6
<Production of Resin Composition (Pellets)>
The components shown in Table 1 were mixed uniformly in the ratios shown in Table 2 (the ratios of each component are parts by mass) using a Super Mixer manufactured by Kawada Manufacturing Co., Ltd. The resulting mixture was melt shear mixed using a vented twin-screw extruder with a screw diameter of 30 mm ("PCM30" manufactured by Ikegai Corporation) at a cylinder temperature of 190°C, a screw rotation speed of 120 rpm, and a discharge rate of 10 kg/hour to produce pellets of the resin composition.

<Dynamic friction coefficient>
The pellets obtained above were molded into cylindrical thrust test pieces using a SE-30DUZ with a screw diameter of 32 mm manufactured by Sumitomo Heavy Industries, Ltd. under conditions of a cylinder temperature of 195°C and a mold temperature of 80°C.
The cylindrical thrust test pieces thus obtained were subjected to a thrust type friction and wear test to measure the dynamic friction coefficient.
The thrust test was carried out using EFM-3-G manufactured by A&D Co., Ltd.
For cylindrical thrust test pieces, in a thrust friction wear test conducted on a polyacetal resin test piece at a linear velocity of 10 cm/s, the surface pressure was increased by 5 kg every 3 minutes, from 3 kg, 5 kg, and 10 kg, and thereafter. Focusing on the kinetic friction coefficient under low surface pressure (load 3 kg, surface pressure 0.15 MPa) where differences in the kinetic friction coefficient due to the formulation tend to occur, the average value of the kinetic friction coefficient over 3 minutes was recorded and evaluated.

<Limit PV value>
The pellets obtained above were injection molded using an SE30DUZ (manufactured by Sumitomo Heavy Industries, Ltd.) with a screw diameter of 32 mm under conditions of a cylinder temperature of 195°C and a mold temperature of 80°C, and a thrust wear test was performed using the cylindrical thrust test pieces.
A thrust friction and wear test was conducted on the cylindrical thrust test pieces at a linear velocity of 10 cm/s, with the surface pressure being increased every 3 minutes to 3 kg, 5 kg, and 10 kg, with the surface pressure increasing by 5 kg from 5 kg onwards. The product of the surface pressure and the speed one step below at which the test pieces were fused due to frictional heat was defined as the limit PV value (unit: MPa cm/s).

<Delamination>
The resin composition obtained above was molded using SE-30DUZ manufactured by Sumitomo Heavy Industries, Ltd. at a cylinder temperature of 215°C, a mold temperature of 80°C, and an injection speed of 30 mm/s to prepare test pieces of 40 mm x 100 mm x 2 mm.
Delamination was evaluated as follows, with A and B being at practical levels.
A: 3cm or less, less than 5cm from the gate B: 5cm or more, less than 7cm from the gate C: 7cm or more from the gate

<Mold contamination>
The resin composition obtained above was molded continuously for 500 shots using a molding machine, SE7MII, manufactured by Sumitomo Heavy Industries, Ltd., with a cylinder temperature of 230°C and a teardrop-shaped mold set at a mold temperature of 40°C. The state of the mold was then confirmed. The evaluation was carried out by five experts, who decided by majority vote. A and B are practical levels.
A: No deposits on the mold at all, and the mold contamination suppression effect is extremely good. B: There is a small amount of deposits on the mold, but the mold contamination suppression effect is good (inferior to A above).
C: There is a lot of mold adhesion, and the mold contamination suppression effect is poor (inferior to B above)

As is clear from the above results, the molded article obtained from the resin composition of this embodiment had excellent sliding properties. Furthermore, mold contamination was also suppressed.

Claims (6)

The composition comprises a polyacetal resin (A), a silicone resin (B) having a weight-average molecular weight of 800,000 or more, and a silicone oil (C) having a weight-average molecular weight of less than 100,000,
A resin composition, wherein the mass ratio of the silicone resin (B) to the silicone oil (C), (B)/(C), is 10/90 to 90/10. The resin composition according to claim 1, wherein the total content of the silicone resin (B) and the silicone oil (C) is 0.5 parts by mass or more and less than 10 parts by mass per 100 parts by mass of the polyacetal resin (A). The resin composition according to claim 1, wherein the total content of the silicone resin (B) and the silicone oil (C) is 0.5 parts by mass or more and less than 2 parts by mass per 100 parts by mass of the polyacetal resin (A). Pellets of the resin composition according to any one of claims 1 to 3. A molded article formed from the resin composition according to any one of claims 1 to 3. A molded article formed from the pellets according to claim 4.