JP3254808B2 - Polyoxymethylene resin composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyoxymethylene resin composition which can provide a molded article having excellent dimensional accuracy and friction and abrasion resistance and also has excellent thermal stability.

[0002]

2. Description of the Related Art Polyoxymethylene resin is known as an engineering plastic having a good balance of mechanical strength and impact resistance, and is used in a wide range of fields as electronic equipment and automobile parts. It is widely used for mechanical parts such as gears and bearings by utilizing characteristics, fatigue resistance, and friction and wear resistance.

[0003] Some of the mechanical parts requiring such friction and abrasion resistance are sufficiently satisfactory even with a polyoxymethylene resin alone. Those requiring addition are increasing.
Particularly, a component to which a load is applied is a component to which a solid lubricant such as graphite is added.

[0004] For example, Japanese Patent Application Laid-Open Nos. 50-117841, 50-15939 and 57-979
No. 393, JP-A-62-267351, JP-A-3-91556, JP-A-3-217448, and JP-A-3-27564 disclose polyoxymethylene resin and graphite, or polyolefin resin. A polyoxymethylene resin composition using the above lubricant in combination is disclosed. Japanese Patent Publication No. 57-9393 discloses a polyoxymethylene resin composition comprising a polyoxymethylene resin and scale-like graphite having an average particle size of 0.5 to 20 μm. Also, in JP-A-3-27564,
It is described that natural graphite in which graphite crystals having a particle size of 3 to 300 μm are developed is preferable. In addition, Japanese Unexamined Patent Publication
No. 217448 discloses polyoxymethylene resin and 5
A polyoxymethylene resin composition comprising heat-treated expanded graphite impregnated with a lubricating oil at twice or more the amount is disclosed.

[0005]

However, Japanese Patent Application Laid-Open Nos. 50-117841 and 50-1595 describe above.
39, JP-B-57-9393, JP-A-62
-267351, JP-A-3-91556,
JP-A-3-217448, JP-A-3-27576
No. 4, the composition disclosed in the publication, the purity of the graphite,
The particle size, shape, and crystallinity are unsuitable, so that not only satisfactory friction and wear resistance cannot be obtained, but also the problem that the polyoxymethylene resin is decomposed to lower the thermal stability. Therefore, an object of the present invention is to obtain a polyoxymethylene resin composition which can provide a molded article having excellent dimensional accuracy and friction and wear resistance and also has excellent thermal stability.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that a polyoxymethylene resin composition containing specific graphite with respect to the polyoxymethylene resin has a dimensional accuracy. The present invention has been found to provide a molded article having excellent frictional wear resistance and excellent thermal stability.

That is, the present invention relates to (A) 100 parts by weight of a polyoxymethylene resin, (B) 95% or more of fixed carbon, an average particle diameter of 1 to 20 μm, and a crystallinity of 80%. Artificial graphite 0.1-200 in the range of ~ 92%
It is a polyoxymethylene resin composition containing parts by weight.

The polyoxymethylene resin (A) used in the present invention includes oxymethylene homopolymer,
An oxymethylene copolymer mainly composed of oxymethylene units and containing at least one oxyalkylene unit having 2 to 8 carbon atoms in the polymer main chain can be used.

As the oxymethylene homopolymer, oxymethylene homopolymer stabilized by substituting an unstable hydroxyl group at a terminal with an ester group or an ether group or the like can be used. For example, substantially anhydrous formaldehyde is introduced into an organic solvent containing a basic polymerization catalyst such as an organic amine, an organic or inorganic tin compound, or a metal hydroxide, polymerized, and the polymer is separated by filtration. And oxymethylene homopolymer obtained by acetylating the terminal by heating in acetic anhydride in the presence of sodium acetate.

As the oxymethylene copolymer, for example, a substantially anhydrous trioxane or a cyclic oligomer of formaldehyde such as tetraoxane and at least one cyclic ether or cyclic formal as a copolymerization component are combined with cyclohexane or benzene. A copolymer prepared by dissolving or suspending in an organic solvent such as above, polymerizing by adding a Lewis acid catalyst such as boron trifluoride / diethyl etherate, and decomposing and removing unstable terminals. Alternatively, bulk polymerization is carried out by introducing a pre-mixture of trioxane and a copolymerization component / catalyst into a self-cleaning type stirrer without using any solvent. If desired, a copolymer produced by removing the catalyst from the polymer by washing, or deactivating the catalyst by a deactivator, and then decomposing and removing the unstable terminal may be mentioned.

It is particularly preferred that trioxane and a cyclic ether or cyclic formal are subjected to bulk polymerization in the presence of a Lewis acid catalyst such as boron trifluoride / diethyl etherate and then subjected to steric reaction such as a tetramethylpiperidyl group. A polymer obtained by adding a hindered amine compound having an amino group having a large hindrance to terminate the polymerization reaction, and further decomposing and removing unstable terminals.

The graphite (B) used in the present invention must be artificial graphite. Graphite includes natural graphite and artificial graphite. In natural graphite, flaky graphite, flaky graphite, earthy graphite is generally known, even if these natural graphite is added to polyoxymethylene resin, its purity, particle size,
For reasons such as shape, crystallinity, and affinity for resin, the coefficient of kinetic friction can be reduced, but the amount of wear increases, or even if the amount of wear can be reduced, the coefficient of kinetic friction increases. Problems such as curling or decomposing the polyoxymethylene resin to lower the thermal stability occur.

[0013] The artificial graphite (B) used in the present invention is obtained by using petroleum coke or coal coke as a raw material, adding tar pitch, etc., for example, first calcining at about 800 ° C, and further about 2400-3000. Graphite heated to ℃ can be preferably used.

The fixed carbon of the artificial graphite needs to be 95% or more, preferably 97% or more. If the fixed carbon is less than 95%, sufficient sliding characteristics cannot be obtained.
Further, the average particle size needs to be 1 to 20 μm, and preferably 2 to 10 μm. Average particle size is 1μm
If it is less than 20 μm, coagulation occurs, resulting in poor dispersion.

The degree of crystallinity of the artificial graphite is 80-92.
%, Particularly preferably 8%.
It is in the range of 3 to 90%. If the crystallinity is less than 80%, the dimensional variation becomes large, and the effect of improving the dynamic friction coefficient is small, which is not preferable. On the other hand, when the crystallinity exceeds 92%, not only the amount of wear during sliding increases, but also the impact strength decreases, which is not preferable.

The crystallinity is measured by measuring the average value (C0) of the two interlayers of the graphite crystal by the X-ray diffraction method, finding the average interlayer spacing (d0) as d0 = 1 / 2C0,
The degree of crystal orientation (P1) is calculated from the experimental formula (1) of ARRR, and P1 is expressed as a percentage.

D0 = 3.354 · P1 + 3.44 (1-P1) (1) The amount of the artificial graphite (B) used in the present invention is 1 to 200 parts by weight based on 100 parts by weight of the polyoxymethylene resin. Parts, preferably 3 to 100 parts by weight, particularly preferably 5 to 100 parts by weight.
It is in the range of 80 parts by weight. If the amount is less than 1 part by weight, the effect of improving the wear resistance cannot be expected. If the amount exceeds 200 parts by weight, not only the appearance of the molded product is impaired, but also the mechanical properties deteriorate, which is not preferable.

The artificial graphite used in the present invention may be used by treating its surface with a known coupling agent (for example, a silane coupling agent or a titanate coupling agent).

Further, the polyoxymethylene resin composition of the present invention may contain a reinforcing agent and a filler.
As the reinforcing agent and filler, for example, glass fiber, carbon fiber, aromatic polyamide fiber, potassium titanate fiber, gypsum fiber, brass fiber, stainless steel fiber, steel fiber, ceramic fiber, boron whisker fiber, asbestos fiber, mica, Examples thereof include fibrous, powdery, granular, and plate-like inorganic or organic fillers such as talc, silica, calcium carbonate, glass beads, glass flakes, glass microballoons, clay, wollastenite, titanium oxide, and molybdenum disulfide. Further, as for these fillers and reinforcing agents, those treated with a silane-based or titanate-based coupling agent or other surface treatment agents may be used.

Further, a lubricant can be used in combination with the polyoxymethylene resin composition of the present invention. As the lubricant, for example, various lubricating oils, various polyolefin resins or modified polyolefin resins such as high-density polyethylene resin, various fluorine resins such as tetrafluoroethylene resin, various silicone resins or silicone oils,
Various elastomers such as a polyurethane resin, a polyester resin, a polyester ether resin, and a polyesteramide resin are exemplified.

As a method for producing the polyoxymethylene resin composition of the present invention, generally known methods can be employed. For example, the polyoxymethylene resin and the artificial graphite used in the present invention are pelletized, powdered, or mixed in a granular form, and may be melt-processed as it is, but a Banbury mixer, a roll,
A method of melt-kneading with an extruder or the like can also be adopted. Especially 1
150-250 ° C. using a screw or twin screw extruder
Is preferred.

The resin composition of the present invention may contain an antioxidant such as a hindered phenol compound, a formaldehyde scavenger such as a triazine compound, a polyamide compound, or a polyacrylamide compound, or a coloring agent, as long as the effects of the present invention are not impaired. Agents (pigments, dyes), nucleating agents, plasticizers, release agents such as fatty acid esters, ethylenebisstearamide, polyethylene wax, conductive agents such as carbon black, thioether compounds, phosphite compounds Optional additives such as secondary antioxidants, benzophenone-based compounds, benzotriazole-based compounds, light stabilizers such as hindered amine compounds, adhesives, lubricants such as metal soaps, hydrolysis resistance improvers, adhesion aids, etc. It can be contained.

The polyoxymethylene resin obtained by the present invention includes a sensor, an LED lamp, a connector, a socket, a resistor, a relay case, a switch, a coil hobbin,
Condenser, variable condenser case, optical pickup, oscillator, various terminal boards, transformer, plug, printed board, tuner, speaker, microphone, headphone,
Small motor, magnetic head base, power module,
It is suitably used for electric and electronic parts such as semiconductors, liquid crystal, FDD carriages, FDD chassis, magnetic tape cassette reels, tape guide devices, motor brush holders, parabolic antennas, computer-related parts, etc. VTR parts, VTR camera parts, TV parts, irons, hair dryers,
Shaver, electric fan, juicer, rice cooker parts, microwave parts, audio equipment parts such as headphone stereo, boombox, audio / laser disk, compact disk, lighting parts, refrigerator parts, air conditioner parts, typewriter parts, calculators, word processor parts, etc. Home, office electrical product parts, office computer related parts, telephone related parts, facsimile related parts,
Copier related parts, cleaning jigs, motor parts, machine related parts represented by lighters, typewriters, etc., optical equipment represented by microscopes, binoculars, cameras, clocks, etc.
Parts related to precision machinery, alternator terminal, alternator connector, IC regulator, potentiometer base for light deer, various valves such as exhaust gas valve, fuel related, exhaust system, intake system various pipes, air intake nozzle snorkel, intake manifold, fuel Pump, engine cooling water joint, carburetor main body, carburetor spacer, exhaust gas sensor, cooling water sensor, hot water sensor, brake pad wear sensor, throttle position sensor, crankshaft position sensor, air flow meter, brake pad wear sensor, air conditioner Thermostat base, heating hot air flow control valve, brush holder for radiator motor, water pump Peller, turbine vane, wiper motor related parts, distributor, starter switch, starter relay, transmission wire harness, air conditioner panel switch base, fuel related electromagnetic valve coil, fuse connector, horn terminal, electrical component insulating plate, step Motor rotor, lamp socket, lamp reflector, lamp housing, brake piston, solenoid hobbin, engine oil filter, radiator drain cock, in-tank fuel pump, diaphragm valve, auto antenna gear case, door lock, turn signal switch, wiper gear, wiper pivot Bearing, speedometer gear, parts, housing, window glass bottom channel, seat belt housing , Seat belt retractor parts, heater control lever, inside door handle, regulator handle, outer door handle, sun visor bracket, collapsible room mirror stay, seat hook, fender mirror case, fuel cap, window washer nozzle, ignition device, etc. Automotive / vehicle-related parts, bicycles, lawn mowers, partition corner pieces, curtain liners, blind gears, door wheels, office furniture parts, various fasteners, piping systems, hose joints, valves, bindings, adjustments, various fasteners, meters, shoe parts Beauty parts such as toys, music boxes, combs, caster brackets, rollers, caps, major parts, lighters, aerosol bottles, sports equipment, etc. It can also be used for various other general equipment parts.

Hereinafter, the present invention will be described by way of examples, but the present invention is not limited to these examples.

[0025]

The present invention will be described below with reference to examples. All percentages and parts in the examples are on a weight basis.

The friction and wear test, dimensional accuracy, and thermal stability of the resin composition of the molded articles shown in the examples and comparative examples were performed as follows.

Molding: Using an injection molding machine having a mold clamping force of 60 t, a cylinder temperature of 190 ° C., a mold temperature of 60 ° C., and a molding cycle of 30 seconds are set to 30 × 30 × 3 t (m
m) was injection molded.

Abrasion resistance test: A test was performed under the following conditions using a sliding ring made of steel (S45C) of φ22.8 × 2t (mm) as a mating material and a mating material, and a dynamic friction coefficient and a specific wear amount were measured. Was measured.

P = 10 kgf / cm ² V = 30 m / min Dynamic friction coefficient: friction force (kg) / load (kg) Specific wear: wear (mm ³ ) / (load (kg) × distance (km)) Dimensional accuracy: Using an injection molding machine having a mold clamping force of 40 t, a gear having an outer diameter of 60 mm and a hole diameter of 4 mm was molded at a cylinder temperature of 200 ° C., a mold temperature of 60 ° C., and a molding cycle of 20 seconds. Gear hole diameter is 4.02mm or more and 4.0
Non-defective products of 3 mm or less were regarded as non-defective products, and 50 shots were discarded in conformity with the standard. After that, 500 samples were taken and the defective product ratio was determined.

Thermal stability: 20.0 g of pellets were placed in an aluminum foil container and melted and retained in a 240 ° C. oven for 1 hour. After the test, the weight of the sample solidified at room temperature was measured.

In the examples and comparative examples, the oxymethylene copolymer (P-1) produced by the following method was used as the polyoxymethylene resin (A).

Production method of oxymethylene copolymer (P-1) Trioxane (30 kg / h) was placed in a twin-screw extruder type polymerization machine (100 mmφ, cylinder length (L) / cylinder diameter (D) = 10.2). , 1,3-dioxolane (1150
g / h) and 12 as a catalyst for trioxane.
0 ppm boron trifluoride / dibutyl etherate (2.5% benzene solution), 733 as a molecular weight regulator
ppm of methylal was supplied, and continuous polymerization was performed. The polymerization controlled the outer jacket to 58 ° C,
The rotation was performed at 40 rpm. Methylal dissolved in trioxane. Further, a premixing zone was provided so that 1,3-dioxolane and the catalyst solution were premixed immediately before being supplied to the polymerization machine. The polymer was 28. as a white fine powder.
It was obtained at 3 kg / h.

To 5 kg of the fine powder thus obtained, 50 ml of 9.0 g of "Sanol" LS765 [Sankyo, bis (1,2,2,6,6-pentamethyl-4-piperidyl) sebacate] was added. Was dissolved in benzene and stirred for 3 minutes in a Henschel mixer to deactivate the catalyst. Further, “Irganox” 245 [Ciba Geigy, triethylene glycol-bis {3- (3-
t-butyl-5-methyl-4-hydroxyphenyl) propionate}], 25 g of calcium 12-hydroxystearate and 5 g of melamine, and then 230 ° C./10 mm using a vented 40 mm φ twin screw extruder.
The mixture was heated and melted at torr to obtain P-1.

Examples 1 to 17 and Comparative Examples 1 to 8 Dry blending of various kinds of graphite shown in Table 1 at a ratio shown in Table 1 with respect to the polyoxymethylene resin P-1 was carried out, and a biaxial with a vent manufactured by Ikegai Iron Works was used. 200 ~ using a 30mmφ extruder
It was melt-extruded and kneaded at 210 ° C. In addition, various persons shown in Table 1
The trade names of graphite are as follows. Artificial graphite A: Showa Denko's UFG-30 artificial graphite B: Lonza's T15 artificial graphite C: Lonza's KS-10 artificial graphite D: Nippon Graphite Trading's PAG-15 .

The resulting composition was extruded as a strand and pelletized by a cutter. The pellets were dried in a hot air circulating oven at 80 ° C. for 3 hours, molded, and subjected to a friction and wear test and a measurement of dimensional accuracy.
The thermal stability was evaluated using the dried pellets. These results are summarized in Table 1.

[0036]

[Table 1]

From these results, it is clear that the polyoxymethylene resin composition of the present invention can provide a molded article having excellent dimensional accuracy and friction and wear resistance, and also has excellent thermal stability.

[0038]

EFFECT OF THE INVENTION The polyoxymethylene resin composition of the present invention can provide a molded article having excellent dimensional accuracy and friction and abrasion resistance and has excellent thermal stability. Since it is suitable for mass production, it can be widely used as a mechanical mechanism component in the electric / electronic field, automobile field, etc., which requires high dimensional accuracy and excellent friction and wear resistance.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C08L 59/00-59/04

Claims (2)

(57) [Claims] 1. (A) 100% by weight of polyoxymethylene resin, (B) fixed carbon is 95% or more, average particle size is 1 to 20 μm, and crystallinity is 80 to 92.
% Of artificial graphite in the range of 0.1 to 200 parts by weight. 2. The synthetic graphite (B) has a crystallinity of 83 to 90.
%. The polyoxymethylene resin composition according to claim 1, wherein