JP7725945B2 - Polyphenylene sulfide resin composition and molded article thereof - Google Patents

Description

The present invention relates to a polyphenylene sulfide resin composition and a molded article containing the same. More specifically, the present invention relates to a polyphenylene sulfide resin composition and molded article thereof that are suitable for sliding and have high abrasion resistance and excellent strength in dry and liquid environments.

Polyphenylene sulfide resin (hereinafter sometimes abbreviated as PPS resin) is a highly heat-resistant super engineering plastic. Its mechanical strength, rigidity, flame retardancy, chemical resistance, electrical properties, and dimensional stability make it widely used in a variety of applications, primarily for injection molding, including various electrical and electronic components, home appliance components, automotive components, and machine components. Among its various applications, PPS resin's excellent chemical resistance and dimensional stability make it widely used in sliding components used in liquids, such as slide valves, gears, and bearing retainers. Sliding components typically incorporate a lubricant at the sliding interface to improve their sliding properties. However, certain conditions can cause the lubricant to dry up during use, leading to equipment failure due to abnormal wear of the sliding components. To maintain good performance, it is important to increase robustness against the presence or absence of lubricant.

For example, Patent Document 1 proposes a PPS resin composition containing carbon fiber and a sliding property improver in PPS resin as a resin composition with high strength and excellent friction and wear resistance. Patent Document 2 proposes a PPS resin composition containing PAN-based carbon fiber, anisotropic pitch-based carbon fiber, and a fluororesin as a PPS resin composition intended for compressor sealing members. Patent Document 3 proposes a PPS resin composition blended with a fibrous filler and a fluororesin as a PPS resin composition intended for valve slide moldings that can withstand high temperatures and high loads. Patent Document 4 proposes a PPS resin composition blended with a matrix synthetic resin, carbon fiber with a specific specific surface area, and a solid lubricant as a resin composition with excellent wear resistance even under sliding conditions in the absence of lubricating oil.

JP 9-59592 JP 2001-115976 JP 2002-5316 JP 7-268126

In recent years, there has been a demand for better mechanical properties and wear resistance in molded products for sliding components used in liquids. In addition, from the perspective of equipment maintenance, there is a demand for excellent wear resistance in both liquid and dry environments.

However, while Patent Documents 1, 2, and 3 disclose improved abrasion resistance in environments where lubricating oil or refrigerating oil is present, there are issues with abrasion resistance in dry environments. Patent Document 4 discloses improved abrasion resistance in lubricating oil and dry environments, but the abrasion resistance in dry environments is not necessarily excellent, and there is an issue of low part strength due to low material strength. Therefore, the object of the present invention is to solve the above-mentioned issues and provide a PPS resin composition and molded article that can produce molded articles with excellent mechanical properties and abrasion resistance in dry and liquid environments.

As a result of extensive research into resolving the above-mentioned problems, the inventors discovered that the above problems could be resolved by adjusting the content of PPS resin, PAN-based carbon fiber, isotropic pitch-based carbon fiber, and fluororesin in the PPS resin composition to fall within specific ranges, leading to the completion of the present invention.

That is, the present invention provides the following.
(1) A polyphenylene sulfide resin composition comprising a polyphenylene sulfide resin, a PAN-based carbon fiber having a tensile strength of 3000 MPa or more , an isotropic pitch-based carbon fiber , and a fluororesin ,
The content of the PAN-based carbon fiber having a tensile strength of 3000 MPa or more is 10 to 40 parts by weight and the content of the isotropic pitch-based carbon fiber is 5 to 30 parts by weight relative to 100 parts by weight of the polyphenylene sulfide resin,
A polyphenylene sulfide resin composition for sliding applications, characterized in that the content of the fluororesin is 6 parts by weight or more and 30 parts by weight or less per 100 parts by weight of the polyphenylene sulfide resin, and the total content of the isotropic pitch-based carbon fiber and the fluororesin is 15 to 60 parts by weight per 100 parts by weight of the polyphenylene sulfide resin.
(2) The polyphenylene sulfide resin composition for sliding applications according to (1), characterized in that the tensile strength is 120 MPa or more.
(3) A molded article obtained by molding the polyphenylene sulfide resin composition according to (1) or (2).

The present invention makes it possible to provide a PPS resin composition and molded articles thereof that have excellent mechanical properties and excellent abrasion resistance in both dry and submerged environments.

FIG. 1 is a schematic diagram showing a wear resistance test (ball-on-disk wear test).

The following describes in detail the mode for carrying out the present invention (hereinafter sometimes referred to as the "present embodiment"). Note that the present invention is not limited to the following embodiment.

<Polyphenylene sulfide resin>
Typical examples of the polyphenylene sulfide resin (PPS resin) used in the present invention include polyarylene sulfide, polyarylene sulfide sulfone, polyarylene sulfide ketone, their random copolymers, block copolymers, and mixtures thereof, among which polyarylene sulfide is particularly preferably used. Such polyarylene sulfide is a polymer containing preferably 70 mol % or more, more preferably 90 mol % or more, of a repeating unit represented by the following structural formula, and when the repeating unit is 70 mol % or more, it is preferred in terms of excellent heat resistance.

Furthermore, such polyarylene sulfide resins may be composed of 30 mol % or less of repeating units having the following structural formula, and may be random copolymers, block copolymers, or mixtures thereof.

Such polyarylene sulfide resins can be produced by commonly known methods, such as the method for obtaining a polymer with a relatively low molecular weight described in Japanese Patent Publication No. 45-3368, or the method for obtaining a polymer with a relatively high molecular weight described in Japanese Patent Publication No. 52-12240 and Japanese Patent Laid-Open Publication No. 61-7332.

In the method for producing the polyarylene sulfide resin used in the present invention, after polymerization is completed, solid matter is recovered from the polymerization reaction product containing the polymer, solvent, etc. Any known recovery method may be used for the polyarylene sulfide resin used in the present invention.

For example, after the polymerization reaction is complete, the mixture may be slowly cooled to recover the particulate polymer. There are no particular restrictions on the cooling rate, but it is typically about 0.1°C/min to 3°C/min. It is not necessary to cool at the same rate throughout the entire cooling process; instead, it is possible to cool at a rate of 0.1 to 1°C/min until the polymer particles crystallize and precipitate, and then at a rate of 1°C/min or faster.

Another preferred method is to carry out the recovery under rapid cooling conditions, and a preferred example of this recovery method is the flash method. The flash method is a method in which the polymerization reaction product is flashed from a high-temperature, high-pressure state (usually 250°C or higher, 8 kg/cm2 or ^higher ) into an atmosphere of normal pressure or reduced pressure, and the polymer is recovered in powder form at the same time as the solvent is recovered; flashing here means that the polymerization reaction product is ejected from a nozzle. Specific examples of the flashing atmosphere include nitrogen or water vapor at normal pressure, and the temperature is usually selected in the range of 150 to 250°C.

In the present invention, the polyarylene sulfide resin obtained as described above can, of course, also be used after undergoing various treatments, such as crosslinking/polymerization by heating in air, heat treatment in an inert gas atmosphere such as nitrogen or under reduced pressure, washing with an organic solvent, hot water, or an acid aqueous solution, or activation with a functional group-containing compound such as an acid anhydride, amine, isocyanate, or functional group-containing disulfide compound. However, since crosslinking/polymerization by heating in air can cause oxidative discoloration of the polyarylene sulfide resin, a substantially linear polyarylene sulfide resin that is not crosslinked/polymerized by heating is preferred in order to achieve the target whiteness.

When washing polyarylene sulfide resin with an organic solvent, any organic solvent can be used for washing, as long as it does not decompose the polyarylene sulfide resin. Examples of suitable organic solvents include nitrogen-containing polar solvents such as N-methylpyrrolidone, dimethylformamide, and dimethylacetamide; sulfoxide/sulfone solvents such as dimethyl sulfoxide and dimethyl sulfone; ketone solvents such as acetone, methyl ethyl ketone, diethyl ketone, and acetophenone; ketone solvents such as dimethyl ether, dipropyl ether, and tetrahydrofuran; halogenated solvents such as chloroform, tetrachloroethane, and chlorobenzene; alcohol/phenol solvents such as methanol, ethanol, propanol, butanol, pentanol, ethylene glycol, propylene glycol, phenol, cresol, and polyethylene glycol; and aromatic hydrocarbon solvents such as benzene, toluene, and xylene. These organic solvents can be used alone or in combination.

Specific methods for washing with such organic solvents include immersing the polyarylene sulfide resin in the organic solvent, which can be stirred or heated as needed. There are no particular restrictions on the washing temperature when washing the polyarylene sulfide resin with an organic solvent, and any temperature between room temperature and approximately 300°C can be selected. While higher washing temperatures tend to improve cleaning efficiency, a washing temperature between room temperature and 150°C typically provides sufficient results. It is preferable to wash the polyarylene sulfide resin that has been washed with an organic solvent several times with water or warm water to remove any remaining organic solvent. The temperature for the water wash is preferably 50 to 90°C, and more preferably 60 to 80°C.

Specific examples of methods for treating polyarylene sulfide resin with hot water include the following. Specifically, to achieve the desired chemical modification effect of the polyarylene sulfide resin by hot water washing, it is preferable to use distilled or deionized water. Hot water treatment is usually carried out by adding a predetermined amount of polyarylene sulfide resin to a predetermined amount of water, and then heating and stirring at normal pressure or in a pressure vessel. The ratio of polyarylene sulfide resin to water is preferably higher, and a bath ratio of 200 g or less of polyarylene sulfide resin per 1 liter of water is preferably used.

Specific examples of acid-treating polyarylene sulfide resin include the following methods. Specifically, the polyarylene sulfide resin can be immersed in an acid or an aqueous solution of an acid, with stirring or heating as necessary. The acid used is not particularly limited as long as it does not decompose the polyarylene sulfide resin. Examples include saturated aromatic monocarboxylic acids such as formic acid, acetic acid, propionic acid, and butyric acid; halo-substituted saturated aliphatic carboxylic acids such as chloroacetic acid and dichloroacetic acid; unsaturated aliphatic monocarboxylic acids such as acrylic acid and crotonic acid; aromatic carboxylic acids such as benzoic acid and salicylic acid; dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, phthalic acid, and fumaric acid; and inorganic acidic compounds such as sulfuric acid, phosphoric acid, hydrochloric acid, carbonic acid, and silicic acid. Among these acids, acetic acid and hydrochloric acid are particularly preferred. The acid-treated polyarylene sulfide resin is preferably washed several times with water to remove any remaining acid or salt. The temperature for the water washing is preferably 50 to 90°C, and more preferably 60 to 80°C. Furthermore, the water used for washing is preferably distilled water or deionized water, so as not to impair the desired chemical modification effect of the polyarylene sulfide resin by the acid treatment.

The melt flow rate (hereinafter sometimes abbreviated as MFR) of the polyarylene sulfide resin used in the present invention is preferably 1000 g/10 min or less, 700 g/10 min or less, and more preferably 500 g/10 min or less. If the MFR exceeds 1000 g/10 min, the degree of polymerization will be too low, resulting in reduced mechanical strength. The lower limit is preferably greater than 80 g/10 min, and more preferably 100 g/10 min or more. Here, MFR is a value measured in accordance with ASTM-D1238-70 at 315.5°C under a 5000 g load.

<PAN-based carbon fiber>
PAN-based carbon fibers are primarily composed of filament fibers consisting essentially of carbon, which are produced by insolubilizing and carbonizing fibers made of polyacrylonitrile resin polymerized with acrylonitrile as the primary component. Spinning methods for such PAN-based carbon fibers include wet spinning and dry-wet spinning, and any spinning method can be selected depending on the desired properties.

The PAN-based carbon fiber used in the present invention must have a tensile strength of 3000 MPa or more. A tensile strength of 3000 MPa or more prevents the PAN-based carbon fiber from breaking and falling off at the sliding interface, and does not impair wear resistance. As PAN-based carbon fibers with a tensile strength of 3000 MPa or more, known PAN-based carbon fibers or commercially available PAN-based carbon fibers with a tensile strength of 3000 MPa or more can be used. Examples include Toray Industries, Inc.'s Torayca® T300 (tensile strength 3530 MPa), Torayca® T700SC (tensile strength 4900 MPa), Torayca® T800SC (tensile strength 5880 MPa), and Torayca® T1100GC (tensile strength 7000 MPa), and Teijin Limited's Tenax® Filament HTA40 (tensile strength 4100 MPa) and Tenax® Filament HTS40 (tensile strength 4400 MPa). There is no particular upper limit to the tensile strength of the PAN-based carbon fiber used in the present invention, but a value of 8000 MPa or less is preferred.

The PAN-based carbon fiber used in the present invention is preferably one with a tensile breaking elongation of 1.3% or more. Using PAN-based carbon fiber with a tensile breaking elongation of 1.3% or more suppresses fiber breakage during the PPS resin composition manufacturing process and injection process, and allows the fibers to be maintained for a long time in the resin composition and molded article, resulting in a PPS resin composition and molded article with excellent mechanical properties. The tensile breaking elongation of the PAN-based carbon fiber is preferably 1.5% or more.

The average fiber diameter of the PAN-based carbon fiber used in the present invention is preferably 1 to 20 μm, and more preferably 3 to 17 μm. If the average fiber diameter is 1 μm or less, it becomes difficult to disperse the carbon fiber in the PPS resin, making it difficult to obtain a sufficient reinforcing effect from the carbon fiber. If the average fiber diameter is 20 μm or more, the number of fibers contained in the PPS resin composition becomes too small, making it difficult to obtain a sufficient reinforcing effect.

In this embodiment, the PAN-based carbon fiber content is 10 to 40 parts by weight per 100 parts by weight of PPS resin. When the PAN-based carbon fiber content is in the range of 10 to 40 parts by weight per 100 parts by weight of PPS resin, molded articles containing it will have an excellent balance of abrasion resistance and strength in dry and submerged environments, which is required.

If the amount of PAN-based carbon fiber is less than 10 parts by weight, the mechanical strength of the molded product will be poor. On the other hand, if the amount of PAN-based carbon fiber exceeds 40 parts by weight, the mechanical strength will be high, but the PAN-based carbon fiber that falls off during wear will be present at the sliding interface, resulting in poor wear resistance in dry and liquid environments.

<Isotropic pitch-based carbon fiber>
Isotropic pitch-based carbon fibers are carbon fibers made from isotropic pitch as a carbon precursor. Isotropy refers to optical isotropy, which indicates that molecules or molecular clusters are randomly oriented. Carbon precursors refer to a series of carbonization intermediates that precede the desired final carbon product.

Pitch, a carbon precursor, is a solid at room temperature obtained by heat-treating and polymerizing liquid tar obtained during the carbonization of wood or coal, bitumen obtained from oil sands, oil obtained by carbonization of oil shale, residual oil from crude oil distillation, and tar produced by cracking petroleum fractions. Specific examples include coal-based pitch, petroleum-based pitch, and synthetic pitch obtained by polymerizing aromatic compounds such as naphthalene. Chemically, pitch is a mixture of countless condensed polycyclic aromatic compounds. An example of coal-based pitch obtained from coal is pitch obtained by heat-treating coal tar from coke ovens.

In the present invention, the isotropic pitch used as a raw material is not particularly limited, but coal-based isotropic pitch is preferred.

The method for producing isotropic pitch-based carbon fiber consists of the steps of spinning molten pitch, insolubilizing it, and carbonizing it. In the spinning process, a vortex method can be used to first impart a swirling flow to the molten pitch, and then the molten pitch is discharged from an outlet nozzle. The pitch is spun and deposited on a table to form a pitch fiber mat.

The insolubilization process involves introducing oxygen to the surface of pitch fibers to oxidize them. The atmosphere used in the insolubilization process can be air or NOx, and the insolubilization process produces a mat-like isotropic pitch-based carbon fiber.

Mat-like isotropic pitch-based carbon fibers can be cut and crushed to the desired length and then kneaded with PPS resin to obtain a PPS resin composition. Methods for cutting and crushing the mat fibers include, for example, crushing using a jet mill, hammer mill, or pin mill, or cutting using a roving cutter, guillotine cutter, cross cutter, or low-speed shear screen crusher.

There are no particular restrictions on the average fiber diameter of isotropic pitch-based carbon fiber, but fibers of around 10 to 20 μm are generally available. Most commercially available products are 13 to 18 μm, and of these, fibers with a smaller fiber diameter are preferred as they provide better dispersibility in PPS resin.

Isotropic pitch-based carbon fibers have a crystalline structure in which the carbon hexagonal mesh planes are arranged randomly along the fiber axis, making them susceptible to shear and exhibiting cleavage properties when subjected to sliding. Therefore, resin compositions containing isotropic pitch-based carbon fibers have good abrasion resistance in dry environments.

Isotropic pitch-based carbon fibers are capable of absorbing liquids such as moisture, so resin compositions containing isotropic pitch-based carbon fibers can retain the liquid that acts as a lubricant during sliding in liquid at the sliding interface without expelling it, providing good wear resistance even in liquid environments.

In this embodiment, the isotropic pitch-based carbon fiber content is 5 to 30 parts by weight per 100 parts by weight of PPS resin. When the isotropic pitch-based carbon fiber content is in the range of 5 to 30 parts by weight per 100 parts by weight of PPS resin, molded articles containing it will exhibit excellent abrasion resistance in dry and liquid environments.

If the amount of isotropic pitch-based carbon fiber is less than 5 parts by weight, the cleavage of the crystalline structure of the isotropic pitch-based carbon fiber will not have a sufficient effect on abrasion resistance, and the molded product will have poor abrasion resistance in a liquid environment. On the other hand, if the amount of isotropic pitch-based carbon fiber exceeds 30 parts by weight, the mechanical properties of the PPS resin composition will deteriorate and the PPS resin composition will become significantly embrittled, resulting in poor abrasion resistance in both dry and liquid environments.

<Fluoropolymer>
In this embodiment, the content of the fluororesin is 6 parts by weight or more and 30 parts by weight or less with respect to 100 parts by weight of the PPS resin .

The fluororesin may be a monomer represented by tetrafluoroethylene (TFE), vinylidene fluoride, chlorotrifluoroethylene, vinyl fluoride, hexafluoropropylene, hexafluoroisobutene, CH ₂ ═CX ¹ (CF ₂ ) _n X ² (wherein X ¹ is H or F, X ² is H, F or Cl, and n is an integer of 1 to 10), a perfluoro(alkyl vinyl ether) represented by CF ₂ ═CF-ORf ¹ (wherein Rf ¹ represents a perfluoroalkyl group having 1 to 8 carbon atoms), or a perfluoro(alkyl vinyl ether) represented by CF ₂ ═CF-OCH ₂ -Rf ² (wherein Rf Preferably, the fluororesin has polymerization units based on at least one fluorine-containing monomer selected from the group consisting of alkyl perfluorovinyl ether derivatives represented by the formula ⁽² ) (a perfluoroalkyl group having 1 to 5 carbon atoms), trifluoroethylene, trifluoropropylene, tetrafluoropropylene, pentafluoropropylene, trifluorobutene, tetrafluoroisobutene, and iodine-containing fluorinated vinyl ethers. The fluororesin may be a homopolymer of the fluorine-containing monomer, or may be a modified fluororesin (produced by copolymerizing the fluorine-containing monomer with a comonomer to an extent that does not impair the effects of the present invention) . The fluororesin is preferably a homopolymer of a fluorine-containing monomer.

In a dry environment, when fluororesin falls off from a PPS resin composition (sliding member) due to sliding, it can remain on the surface of the sliding member and can also be transferred to the surface of the mating sliding member, resulting in the fluororesin being present at the sliding interface and potentially providing good wear resistance. However, as will be described later, in the present invention, by controlling the content of PAN-based carbon fiber or isotropic pitch-based carbon fiber (particularly the content of isotropic pitch-based carbon fiber) within a specified range, good wear resistance can be achieved without incorporating fluororesin into the PPS resin composition.

In addition, the fluororesin content in this embodiment must be 30 parts by weight or less per 100 parts by weight of PPS resin. If the fluororesin content is greater than 30 parts by weight, the fluororesin will inhibit the lubricating action of the liquid at the sliding interface in a liquid environment, or the fluororesin will flow out of the sliding surface due to the liquid, resulting in poor wear resistance in liquid.

From the perspective of the appearance of the resulting molded article, the melting point of the fluororesin is preferably 140 to 340°C, and more preferably 150 to 330°C. The melting point is the temperature corresponding to the maximum value on the heat of melting curve when heated at a rate of 10°C/min using a differential scanning calorimeter (DSC).

The fluororesin preferably has a melt flow rate (MFR) of 0.3 to 300 g/10 min at 372°C. If the MFR is too low, low friction and non-stick properties may be poor, while if the MFR is too high, abrasion resistance may be poor. The above MFR is a value obtained in accordance with ASTM D 1238 at a temperature of 372°C and a load of 5 kg.

<Relationship between the content of isotropic pitch-based carbon fiber and fluororesin>
The present inventors have found that when the total content of the isotropic pitch-based carbon fiber and the fluororesin is within a certain range, the resulting molded article has particularly excellent abrasion resistance in dry and submerged environments.

That is, in the present invention, it is important that the total content of the isotropic pitch-based carbon fiber and the fluororesin is 15 to 60 parts by weight per 100 parts by weight of the PPS resin.
The reason why the wear resistance of the resulting molded article in dry and liquid environments is improved by setting the total content of the isotropic pitch-based carbon fiber and the fluororesin within the above range is not clear, but is presumed to be as follows.

When a sliding member slides against a mating member (e.g., a metal part) in a dry environment, the sliding member wears, causing the isotropic pitch-based carbon fiber and fluororesin to fall off. Isotropic pitch-based carbon fiber easily falls off due to shear stress. Furthermore, because isotropic pitch-based carbon fiber has cleavage properties, it significantly reduces the amount of wear at the sliding interface between the sliding member and the mating member. Wear at the sliding interface between the sliding member and the mating member is reduced by the cleavage properties of the isotropic pitch-based carbon fiber, and this performance correlates with the amount of isotropic pitch-based carbon fiber blended. Therefore, the amount (content) of isotropic pitch-based carbon fiber has the aforementioned lower limit. Furthermore, when a PPS resin composition contains a fluororesin, the fluororesin may also fall off the sliding member and transfer to the mating member, forming a fluororesin layer at the sliding interface. This lubricating effect may reduce wear, similar to that of isotropic pitch-based carbon fiber. Furthermore, when the PPS resin composition contains an appropriate amount of isotropic pitch-based carbon fiber and fluororesin, the above effects combine to produce a synergistic effect.

When a sliding member slides against a mating member (e.g., a metal part) in a liquid environment, the liquid generally remains at the sliding interface and acts as a lubricant. However, in areas with large irregularities, the sliding member comes into contact with the mating member and wears, just as in a dry environment. Isotropic pitch-based carbon fibers are prone to shear shear and fall off at the contact points, but their liquid absorption properties allow them to retain the liquid acting as a lubricant at the sliding interface between the sliding member and the mating member without expelling it, resulting in good wear resistance. The liquid absorption properties of isotropic pitch-based carbon fibers can reduce wear at the sliding interface between the sliding member and the mating member, and this performance correlates with the amount of isotropic pitch-based carbon fiber blended. Therefore, there is a lower limit, as mentioned above, for the amount (content) of isotropic pitch-based carbon fiber blended. Furthermore, when the PPS resin composition contains a fluororesin, the fluororesin may fall off the sliding member and transfer to the mating member, forming a fluororesin layer at the sliding interface, which may reduce the amount of wear. Furthermore, when the PPS resin composition contains an appropriate amount of isotropic pitch-based carbon fiber and fluororesin, the above effects may combine to produce a synergistic effect.

In the present invention, it is important that the total content of isotropic pitch-based carbon fiber and fluororesin is 15 to 60 parts by weight per 100 parts by weight of PPS resin. If the total amount of isotropic pitch-based carbon fiber and fluororesin is less than 15 parts by weight, the lubricating effect of the cleavage of the isotropic pitch-based carbon fiber at the sliding interface between the sliding member and the mating member in a dry environment will be insufficient, and wear will increase even with the synergistic effect of the fluororesin.

On the other hand, if the total amount of pitch-based carbon fiber and fluororesin is greater than 60 parts by weight, the fluororesin will inhibit the lubricating effect of the liquid at the sliding interface in a liquid environment, resulting in increased wear.

<PPS resin composition>
In addition to the above-mentioned components, the PPS resin composition of the present invention may further contain other additives that are commonly used during the production (mixing) and molding of a resin composition, provided that the additives do not impair the physical properties of the resin composition.

<Characteristics of PPS resin composition>
In the present invention, the tensile strength of the PPS resin composition is preferably 120 MPa or more. A tensile strength of 120 MPa or more prevents localized breakdown due to stress generated by relative movement in contact with a mating member due to the sliding member, and thus may reduce the amount of wear. For example, the tensile strength of the PPS resin composition can be increased to 120 MPa or more by incorporating 10 parts by weight or more of PAN-based carbon fiber per 100 parts by weight of PPS resin.

<Method of producing PPS resin composition>
The PPS resin composition of the present embodiment can be produced by blending PPS resin, PAN-based carbon fiber, isotropic pitch-based carbon fiber, and fluororesin, and optionally other additives. Known techniques can be used as the blending method.

For example, one method involves melt-kneading the raw materials. There are no particular restrictions on the order in which the components are mixed. Taking the example of melt-kneading using a twin-screw extruder, one method involves feeding PPS resin and fluororesin from the main feeder, and feeding PAN-based carbon fiber and isotropic pitch-based carbon fiber from the side feeder of the twin-screw extruder.

<Method of manufacturing molded products>
The molded article of the present invention can be obtained by molding the PPS resin composition. The molding method is not particularly limited, and known methods such as injection molding, injection compression molding, extrusion molding, profile extrusion, transfer molding, blow molding, gas-assisted blow molding, blow molding, extrusion blow molding, multilayer molding, two-color molding, insert molding, foam molding, and pressure molding can be used. In terms of shape freedom and productivity, injection molding and injection compression molding are preferred.

<Uses of PPS resin compositions and molded products>
The PPS resin composition of this embodiment and molded articles obtained by molding it have good mechanical properties and good abrasion resistance in dry and liquid environments, and therefore can be suitably used in a variety of applications, such as various electronic and electrical parts, home appliance parts, building parts, sanitary goods, automobile parts, etc. In particular, the PPS resin composition of this embodiment can be particularly suitably used in sliding applications, and molded articles can be suitably used as various sliding members.

Sliding parts used in electrical and electronic components, home appliance components, building components, and sanitary products include, but are not limited to, gears, cams, bearing retainers, bearings, pulleys, end face materials for mechanical seals, valve seats, V-rings, impellers, vanes, pump casings, pipe joints, water control valves, hot water temperature sensors, and water volume sensors.

Sliding components for automotive parts include, but are not limited to, gears, actuators, bearing retainers, bearings, chain guides, chain tensioners, switches, pistons, packings, rollers, and belts, and can be used effectively in components that slide in dry and submerged environments.

The present invention will be described in detail below using examples, but the gist of the present invention is not limited to the following examples.

(PPS resin (A))
A 70-liter autoclave equipped with a stirrer and a bottom stop valve was charged with 8.27 kg (70.00 mol) of 47.5% sodium hydrosulfide, 2.96 kg (71.1 mol) of 96% sodium hydroxide, 11.43 kg (115.50 mol) of N-methyl-2-pyrrolidone (NMP), 1.72 kg (21.00 mol) of sodium acetate, and 10.5 kg of ion-exchanged water. The mixture was gradually heated to 230°C over approximately 3 hours under atmospheric pressure while passing nitrogen through it. After distilling off 14.78 kg of water and 0.28 kg of NMP, the reaction vessel was cooled to 160°C. The amount of water remaining in the system per mole of charged alkali metal sulfide was 1.06 mol, including the water consumed in the hydrolysis of NMP. The amount of hydrogen sulfide released was 0.017 mol per mole of charged alkali metal sulfide.

Next, 10.36 kg (70.5 mol) of p-dichlorobenzene and 9.08 kg (91.7 mol) of NMP were added, the reaction vessel was sealed under nitrogen gas, and the temperature was raised to 270°C at a rate of 0.6°C/min while stirring at 240 rpm, and maintained at 270°C for 140 minutes. 2.52 kg (140 mol) of ion-exchanged water was then pressure-fed into the autoclave while the temperature was cooled to 250°C at a rate of 1.3°C/min. The mixture was then cooled to 200°C at a rate of 1.0°C/min, and then rapidly cooled to near room temperature.

The contents were removed and diluted with 26.3 kg of NMP. The solvent and solids were separated using a sieve (80 mesh). The resulting particles were washed with 31.9 kg of NMP and filtered. These were washed several times with 56 kg of ion-exchanged water and filtered, and then washed with 70 kg of a 0.05 wt% aqueous acetic acid solution and filtered. After washing with 70 kg of ion-exchanged water and filtering, the resulting hydrous PPS particles were dried with hot air at 80°C and then dried under reduced pressure at 120°C to obtain dried PPS resin (A). The MFR of the resulting polymer was 210 g/10 min.

(PAN-based carbon fiber (B))
Toray Industries, Inc.'s Torayca(R) T700SC.

(Isotropic pitch-based carbon fiber (C))
DonaCarbo S-242 manufactured by Osaka Gas Chemicals Co., Ltd.

(Fluororesin (D))
Polytetrafluoroethylene (Lubron L-5 manufactured by Daikin Industries, Ltd.), melting point: 328°C.

[Measurement and evaluation method]
The measurement and evaluation methods in the present examples and comparative examples are as follows.

(Tensile strength of PPS resin composition)
The pellets obtained in each example and comparative example were injection molded using an injection molding machine (SE50DUZ-C160 manufactured by Sumitomo Heavy Industries, Ltd.) under the conditions specified in JIS K7315 to prepare 4.0 mm thick ISO dumbbell test pieces, type 1A. These test pieces were conditioned for 16 hours at 23°C and 50% relative humidity, and then subjected to a tensile test at a crosshead speed of 5 mm/min using an Instron 5581 tensile tester (manufactured by Instron) in accordance with ISO 527. Five measurements were taken, and the average value was calculated as the tensile strength.

(Tensile strength of PAN-based carbon fiber)
The tensile strength of PAN-based carbon fibers can be determined in accordance with the resin-impregnated strand test method of JIS-R-7608 (2004). The resin formulation used is Celloxide (registered trademark: 2021P, manufactured by Daicel Chemical Industries, Ltd.) / boron trifluoride monoethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) / acetone = 100/3/4 (parts by weight), and the curing conditions are 130°C and 30 minutes.

(Wear resistance in dry environments, wear resistance in liquid environments (ball-on-disk wear test))
The pellets obtained in each of the Examples and Comparative Examples were molded into test pieces using an injection molding machine (SE50DUZ-C160 manufactured by Sumitomo Heavy Industries, Ltd.) in accordance with the ball-on-disk wear test method specified in JIS R 1613. Each of the test pieces thus prepared was subjected to a ball-on-disk friction and wear test.

Figure 1 shows a schematic diagram of the ball-on-disk test equipment used to evaluate wear depth. First, a ball (φ6 mm) 1 made of SUJ-2 chrome steel was prepared and fixed to a holder 2. Then, ball 1 fixed to holder 2 was brought into contact with the upper surface of test specimen 3. A load of 20 N was applied from the ball side toward the test specimen side from direction B in Figure 1, while the test specimen was rotated in a circular direction at a speed of 0.3 m/s (A in Figure 1: test specimen rotation direction). Tests were conducted under two conditions: dry conditions at room temperature and atmospheric pressure, and submerged conditions at room temperature and in water. After rotating the test specimens of each example and comparative example for 3 hours, the wear depth of the test specimens was measured using a laser microscope (Keyence VK-X100). Wear depth indicates the amount of wear due to sliding, with shallower wear depth indicating better wear resistance.

(Examples 3 to 13, Comparative Examples 1 to 17)
The (A) PPS resin and (D) fluororesin shown in the table were fed into a TEX-44αII twin-screw extruder manufactured by Japan Steel Works, Ltd., with a cylinder temperature set at the melting point of the PPS resin + 15°C, and were melted. The raw material feed port was connected to a position 0 when viewed from the upstream side, where the total length of the screw was taken as 1.0, that is, the upstream end of the screw segment. Next, the (B) PAN-based carbon fiber and (C) isotropic pitch-based carbon fiber shown in the table were fed into the twin-screw extruder from a side feeder and melt-kneaded at a discharge rate of 60 kg/hour. The guts discharged from the die were immediately cooled in a water bath and processed into pellets using a strand cutter.

Using the resulting pellets, tensile strength and wear depth after ball-on-disk wear tests in dry and liquid environments were evaluated using the method described in the Reference Example. The evaluation results are shown in the table. Examples 1 to 13 contained 10 to 40 parts by weight of PAN-based carbon fiber, 5 to 30 parts by weight of isotropic pitch-based carbon fiber, and 6 to 30 parts by weight of fluororesin per 100 parts by weight of PPS resin. Since the total amount of isotropic pitch-based carbon fiber and fluororesin was 15 to 60 parts by weight per 100 parts by weight of PPS resin, wear depth was small in dry and liquid environments, demonstrating excellent robustness against environmental conditions. Furthermore, due to their high tensile strength, they are suitable for various sliding parts.

[Comparative Examples 1 and 3]
It can be seen that Comparative Example 1 shown in the table does not contain isotropic pitch-based carbon fibers, which inhibits the lubricating effect due to the cleavage of the isotropic pitch-based carbon fibers in a dry environment, resulting in poor wear resistance.

[Comparative Examples 2, 4, 6, and 9]
In Comparative Examples 2, 4, 6 and 9 shown in the table, the sum of the blending amounts of isotropic pitch-based carbon fiber and fluororesin was low, so no lubricant effect was obtained and the wear resistance in a dry environment was poor.

[Comparative Examples 5, 7, and 11]
In Comparative Examples 5, 7, and 11 shown in the table, the amount of isotropic pitch-based carbon fiber blended was low, which inhibited the lubricating effect of the isotropic pitch-based carbon fiber cleavage in a liquid environment and repelled the liquid acting as a lubricant from the sliding interface, resulting in poor wear resistance.

Comparative Example 8
In Comparative Example 8 shown in the table, the blending amount of PAN-based carbon fiber is high, and therefore, due to its stiffness, it is understood that the abrasion resistance is poor in both dry and submerged environments.

Comparative Example 10
In Comparative Example 10 shown in the table, the blending amount of PAN-based carbon fiber is low, so localized destruction occurs due to stress generated at the sliding interface, and it is clear that the wear resistance in a dry environment is poor.

[Comparative Examples 12, 13, and 15]
Comparative Examples 12, 13, and 15 shown in the table contain a high amount of fluororesin, which inhibits the lubricating action of the liquid at the sliding interface and causes the fluororesin to flow out of the sliding surface due to the liquid, resulting in poor wear resistance in a liquid environment.

[Comparative Examples 14 and 16]
Comparative Examples 14 and 16 shown in the table contain a high amount of isotropic pitch-based carbon fiber, which reduces the tensile strength of the PPS resin composition, and therefore the abrasion resistance is poor in dry and liquid environments.

Comparative Example 17
Comparative Example 17 shown in the table does not contain PAN-based carbon fiber, which reduces the tensile strength of the PPS resin composition, and therefore it is clear that the abrasion resistance in a dry environment is poor.

The polyphenylene sulfide resin composition of the present invention and its molded articles are applicable to any sliding applications requiring high friction resistance and strength in dry and liquid environments.

Ball Holder Test piece A. Rotation direction of test piece B. Load

Claims (3)

A polyphenylene sulfide resin composition comprising a polyphenylene sulfide resin, a PAN-based carbon fiber having a tensile strength of 3000 MPa or more , an isotropic pitch-based carbon fiber , and a fluororesin ,
The content of the PAN-based carbon fiber having a tensile strength of 3000 MPa or more is 10 to 40 parts by weight and the content of the isotropic pitch-based carbon fiber is 5 to 30 parts by weight relative to 100 parts by weight of the polyphenylene sulfide resin,
A polyphenylene sulfide resin composition for sliding applications, characterized in that the content of the fluororesin is 6 parts by weight or more and 30 parts by weight or less per 100 parts by weight of the polyphenylene sulfide resin, and the total content of the isotropic pitch-based carbon fiber and the fluororesin is 15 to 60 parts by weight per 100 parts by weight of the polyphenylene sulfide resin. The polyphenylene sulfide resin composition for sliding applications described in claim 1, characterized in that it has a tensile strength of 120 MPa or more. A molded article obtained by molding the polyphenylene sulfide resin composition described in claim 1 or 2.