JP5229458B2 - Polyacetal resin composition excellent in slidability - Google Patents

Description

The present invention relates to a polyacetal resin composition having a low content of volatile cyclic siloxane oligomer, and a method for producing the same.

In general, contacted electrical / electronic components such as switches and relays are not only required to have high flame resistance, but also from the perspective of achieving the miniaturization and weight reduction that the contacted electrical / electronic components always aim for. In addition, a resin molding structure that is a part of its constituent elements requires a minute and complicated molding structure. Also, in terms of production and maintenance of mechanical properties, melt stability with little change in melt viscosity over time It is required to have an excellent quality.

As resin molding materials that meet these various requirements, thermoplastic resins called so-called engineering plastics such as polyacetal resins, polyamide resins, polycarbonate resins, etc., which are excellent in mechanical properties and electrical properties, are generally used. ing. The polyacetal resin is particularly excellent in balance of mechanical properties, extremely excellent fatigue resistance, low water absorption, and the like. In order to improve the slidability of this polyacetal resin, it is known to add a silicone compound (see Patent Document 1).
Japanese Patent No. 2970691

However, when a generally available silicone compound is used, there has been a problem of causing electrical contact failure of components such as relays, switches and motors used in electronic and electrical equipment.

In view of such circumstances, an object of the present invention is to provide a polyacetal resin composition that does not cause an electrical contact failure and a method for producing the same.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a polyacetal resin composition having a low content of cyclic siloxane oligomer solves the above-mentioned problems, and has reached the present invention.

That is, the present invention firstly provides a polyacetal resin composition comprising a polyacetal resin (A), wherein the content of a cyclic siloxane oligomer of 10-mer or less is less than 100 ppm. .

The second aspect of the present invention is a polyacetal resin composition comprising a polyacetal resin (A), a polyethylene wax and / or polyethylene resin (B), and a silicone oil (C). Provided is a method for producing a polyacetal resin composition, wherein the content of the cyclic siloxane oligomer is 100 ppm or less.

The polyacetal resin composition of the present invention has excellent mechanical properties and has a low content of a cyclic siloxane oligomer of 10-mer or less that causes electrical contact failure, so that electrical contact failure can be reduced. It is useful for highly reliable electronic parts. Moreover, according to the manufacturing method of this invention, such a polyacetal resin composition can be manufactured easily.

The present invention will be described in detail below.
In the present invention, examples of the cyclic siloxane oligomer of 10-mer or less include the following general formula (Formula 1)
(R ¹ R ² SiO) _m
(In the formula, R ¹ and R ² represent an alkyl group having 1 to 8 carbon atoms or a phenyl group, and examples thereof include a methyl group, an ethyl group, and a propyl group, and these may be the same or different. Represents an integer of -10.)
The compound represented by these is mentioned. The content of these cyclic siloxane oligomers in the polyacetal resin composition is required to be 100 ppm or less in order to develop high reliability. More preferably, it is 50 ppm or less.

The polyacetal resin used in the present invention is a polymer having an acetal structure — (— O—CRH—) _n — (wherein R represents a hydrogen atom or an organic group) in a repeating structure, and usually R is a hydrogen atom. A certain oxymethylene group (—CH ₂ O—) is the main structural unit. The polyacetal resin used in the present invention includes a copolymer (block copolymer) or a terpolymer containing one or more repeating structural units other than the oxymethylene group in addition to the acetal homopolymer consisting only of this repeating structure, and further linear. It may have not only a structure but also a branched or crosslinked structure.
Examples of the structural unit other than the oxymethylene group include an oxyethylene group (—CH ₂ CH ₂ O—), an oxypropylene group (—CH ₂ CH ₂ CH ₂ O—), and an oxybutylene group (—CH ₂ CH ₂ CH). ₂ CH ₂ O—) and the like may be an oxyalkylene group having 2 to 10 carbon atoms which may be branched, and an oxyalkylene group having 2 to 4 carbon atoms which may be branched is particularly preferable. An oxyethylene group is preferred. In addition, the content of such oxyalkylene structural units other than oxymethylene groups is preferably 0.1% by weight or more and 40% by weight or less in the polyacetal resin.

The production method of the polyacetal resin used in the present invention is arbitrary, and may be produced by any conventionally known method. For example, a bulk polymerization method can be mentioned. This is a polymerization method using a monomer in a molten state, and a solid polymer in the form of lumps and powders is obtained as the polymerization proceeds.

The raw material monomer of the polyacetal resin is trioxane, which is a cyclic trimer of formaldehyde, and cyclic formal and / or ether is used as the comonomer.
Examples of the cyclic formal and / or ether which is a comonomer include 1,3-dioxolane, 2-ethyl-1,3-dioxolane, 2-propyl-1,3-dioxolane, 2-butyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2-phenyl-2-methyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, 2,4-dimethyl-1,3-dioxolane, 2- Ethyl-4-methyl-1,3-dioxolane, 4,4-dimethyl-1,3-dioxolane, 4,5-dimethyl-1,3-dioxolane, 2,2,4-trimethyl-1,3-dioxolane, 4-hydroxymethyl-1,3-dioxolane, 4-butyloxymethyl-1,3-dioxolane, 4-phenoxymethyl-1,3-dioxolane, 4 Chloromethyl-1,3-dioxolane, 1,3-dioxabicyclo [3,4,0] nonane, ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, styrene oxide, oxytane, 3,3-bis (chloromethyl) oxetane, tetrahydrofuran, And oxepane. Of these, 1,3-dioxolane is particularly preferred.

（式中、RO，RO‘ は同一または異なって水素原子、アルキル基もしくはアルキル基を有する有機基、フェニル基またはフェニル基を有する有機基を示す。mは2〜6の整数を示す。）
また、１，４−ブタンジオールジグリシジルエーテル、ポリエチレングリコールジグリシジルエーテル等の多官能エポキシ化合物を架橋・分岐剤として添加しても良い。 The addition amount of the comonomer is preferably 0.3 to 50 parts by weight, more preferably 1.1 to 20.0 parts by weight with respect to 100 parts by weight of trioxane. When the amount of the comonomer used is more than 50 parts by weight, the polymerization yield decreases, and when it is less than 0.3 parts by weight, the thermal stability decreases.
The oxymethylene copolymer is obtained by copolymerizing 0.3 to 50 parts by weight of one or more comonomers with respect to 100 parts by weight of trioxane having the structure represented by the following general formula (1). It is a thing.

(In the formula, RO and RO ′ are the same or different and each represents a hydrogen atom, an alkyl group or an organic group having an alkyl group, a phenyl group or an organic group having a phenyl group. M represents an integer of 2 to 6.)
Further, a polyfunctional epoxy compound such as 1,4-butanediol diglycidyl ether or polyethylene glycol diglycidyl ether may be added as a crosslinking / branching agent.

As the polymerization catalyst, a general cationic active catalyst is used. Such cationically active catalysts include Lewis acids, particularly halides such as boron, tin, titanium, phosphorus, arsenic and antimony, such as boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentachloride, pentafluoride. Compounds such as phosphorus, arsenic pentafluoride and antimony pentafluoride, and complex compounds or salts thereof, protic acids such as trifluoromethanesulfonic acid, perchloric acid, esters of protic acids, especially perchloric acid and lower aliphatic alcohols Esters, protonic acid anhydrides, especially mixed anhydrides of perchloric acid and lower aliphatic carboxylic acids, or triethyloxonium hexafluorophosphate, triphenylmethylhexafluoroarsenate, acetylhexafluoroborate, heteropolyacid or Its acid salt, isopolyacid or its Such as gender salts. In particular, a compound containing boron trifluoride, or boron trifluoride hydrate and a coordination complex compound are suitable, and boron trifluoride diethyl etherate, trifluoride which is a coordination complex with ethers. Boron dibutyl etherate is particularly preferred.
The amount of the catalyst used is usually 1 × 10 ⁻⁷ to 1 × 10 ⁻³ mol, preferably 1 × 10 ⁻⁷ to 1 × 10 ⁻⁴ mol, relative to 1 mol of trioxane. When the amount of the catalyst used is larger than this, the thermal stability is lowered, and when it is less, the polymerization yield is lowered.

In the above polymerization method, an appropriate molecular weight regulator may be used as necessary to adjust the molecular weight of the polyacetal resin. Examples of the molecular weight regulator include carboxylic acid, carboxylic anhydride, ester, amide, imide, phenols, acetal compound and the like. In particular, phenol, 2,6-dimethylphenol, methylal, and polyacetal dimethoxide are preferably used, and most preferred is methylal. The molecular weight regulator is used alone or in the form of a solution. When used in a solution, examples of the solvent include aliphatic hydrocarbons such as hexane, heptane, and cyclohexane, aromatic hydrocarbons such as benzene, toluene, and xylene, and halogenated hydrocarbons such as methylene dichloride and ethylene dichloride.
Generally, the addition amount of these molecular weight modifiers is adjusted in the range of 0 to 1.0 part by weight with respect to 100 parts by weight of the monomer according to the target molecular weight.
These molecular weight regulators are usually supplied to a mixed raw material liquid of trioxane and a comonomer. Although there is no restriction | limiting in particular in an addition position, It is preferable to supply before supplying a cation active catalyst to this mixed raw material liquid.

The continuous polymerization apparatus used in the present invention is equipped with a rapid solidification during polymerization, a powerful stirring ability capable of coping with heat generation, precise temperature control, and a self-cleaning function that prevents scale adhesion. Two or more types of polymerization can be used, such as a kneader, a twin screw continuous extrusion kneader, a twin screw paddle type continuous mixer, and other trioxane continuous polymerization apparatuses proposed so far. A combination of machines can also be used. Among these, a continuous horizontal reactor provided with a pair of shafts rotating in the same direction and in which a large number of convex lens type or pseudo triangle type paddles engaged with each other is fitted is preferable.

In the practice of the present invention, the polymerization time is selected from 3 to 120 minutes, and preferably 5 to 60 minutes. When the polymerization time is shorter than this, the polymerization yield or the thermal stability is lowered, and when it is longer, the productivity is deteriorated.
The polymerization time has a preferable lower limit depending on the comonomer ratio in terms of polymerization yield or thermal stability, and it is necessary to increase the polymerization time as the comonomer ratio increases. For example, when 11 to 20 mol of 1,3-dioxolane is copolymerized with respect to 100 mol of trioxane, 5 to 120 minutes, preferably 6 to 60 minutes is appropriate.

As the catalyst deactivator, trivalent organic phosphorus compounds, organic amine compounds, alkali metal or alkaline earth metal hydroxides, and the like can be used.
As the organic amine compound used as the deactivator, primary, secondary and tertiary aliphatic amines, aromatic amines, heterocyclic amines and the like can be used, and specifically, for example, ethylamine, diethylamine, triethylamine, Examples include mono-n-butylamine, di-n-butylamine, tripropylamine, tri-n-butylamine, N, N-dimethylbutylamine, aniline, diphenylamine, pyridine, piperidine, morpholine, melamine, and methylolmelamine.
Of these exemplified catalyst deactivators, trivalent organic phosphorus compounds and tertiary amines are preferred. Of the trivalent organophosphorus compounds, a particularly preferred compound is triphenylphosphine, which is thermally stable and does not adversely affect the coloration of the molded product by heat. Of the tertiary amines, particularly preferred compounds are triethylamine and N, N-dimethylbutylamine.
The deactivator does not need to be added in an amount that completely deactivates the catalyst, and it is sufficient that the decrease in the molecular weight of the crude polyacetal copolymer is suppressed to the allowable range of the product when the organic amine is added and held as described below. The amount of the deactivator used is usually 0.01 to 500 times, preferably 0.05 to 100 times, based on the number of moles of the catalyst used.
When the quencher is used in the form of a solution or suspension, the solvent used is not particularly limited. Examples thereof include various aliphatic or aromatic organic solvents such as water, alcohols, raw material monomers, comonomers, acetone, methyl ethyl ketone, hexane, cyclohexane, heptane, benzene, toluene, xylene, methylene dichloride, and ethylene dichloride. These can also be used as a mixture.

In the deactivation treatment in the present invention, the crude polyacetal resin is preferably a fine particle, and the polymerization reactor preferably has a function of sufficiently pulverizing the bulk polymer. In addition, a deactivator may be added after the polymerized crude polyacetal resin is separately pulverized using a pulverizer, or may be pulverized and stirred simultaneously in the presence of the deactivator. When the crude polyacetal resin is not a fine particle, the catalyst contained in the resin is not sufficiently deactivated, and therefore depolymerization proceeds gradually with the remaining active catalyst, resulting in a decrease in molecular weight. If catalyst deactivation is not sufficient and the final product has a low molecular weight, the molecular weight regulator should be adjusted in advance to increase the molecular weight of the crude polyacetal resin, and the molecular weight of the final product should be increased. A way to adjust is taken.

The crude polyacetal resin subjected to the deactivation treatment can be melted with an extruder and melt kneaded with an additive to obtain pellets having excellent thermal stability. It is also an effective means to perform vacuum devolatilization by combining an extruder and a biaxial surface renewal type horizontal reactor.

The crude polyacetal resin that has been subjected to the deactivation treatment is melted in an extruder provided with a kneading portion having a length of 2D _{1 to} 10D ₁ (D ₁ is the inner diameter of the extruder). Here, the kneading part refers to a part of the extruder screw in which a disk-shaped segment having a surface perpendicular to the resin flow direction is installed. As an example of a disk-shaped screw segment, a plurality of elliptical disks having a thickness of 0.1D _{1 to} 1.0D ₁ with a notch at the tip are arranged side by side in the resin flow direction. Adjacent disk-shaped screw segments are offset by −90 to 90 ° in the rotational direction, and the type is perpendicular to the adjacent disk installed on the other screw.
In the extruder, the kneading part needs to be installed in a total length of 2D _{1 to} 10D _1, and if the kneading part is shorter than this range, the melting of the crude polyacetal resin becomes insufficient, or the crude polyacetal resin is stabilized in advance. When mixing with the agent, the mixing of the crude polyacetal resin and the stabilizer becomes insufficient, and unless the stabilizer is added excessively, the desired effect cannot be obtained. The polyacetal resin is decomposed due to excessive shearing stress in the ding part, resulting in adverse effects such as coloration or the formation of a new unstable structure due to a decrease in viscosity (or molecular weight). It is desirable to install a flight part (screw-like segment) in which excessive shear stress is not generated in the screw other than the kneading part.

For the present invention, the kneading part may be installed at a position 5D ₁ or more away from the position where the coarse polyacetal resin is introduced in powder with respect to the flow direction, and further at a position 8D ₁ or more apart. Is preferred. When the kneading part is installed at a position closer to this, the transfer capability of the crude polyacetal resin in the extruder is lowered, and the productivity is lowered. Moreover, it is preferable to install a flight part in a screw until it installs a kneading part from the position where coarse polyacetal resin is introduce | transduced with powder.
The kneading part does not need to be continuously installed in the length of 2D _{1 to} 10D ₁ with respect to the screw length direction, and the kneading part is configured to introduce the flight part between the kneading part and the kneading part. Can be divided into two zones or more than two zones and installed on the screw of the extruder.

In the case of a twin screw extruder, the same direction rotating type or the different direction rotating type may be used, but the same direction rotating type having excellent productivity is preferably used. The extruder is preferably provided with one or more vent portions, and vacuum devolatilization is preferably performed under a reduced pressure of 50 kPa or more (a reduced pressure indicates an absolute pressure; the same applies hereinafter). The temperature range of the extruder is preferably set to a temperature range of 190 to 240 ° C, more preferably 200 to 230 ° C. When the temperature is lower than 190 ° C., (1) the unmelted polyacetal resin remains, (2) the unstable portion contained in the crude polyacetal resin cannot be sufficiently decomposed and the thermal stability is poor, and the cyclic siloxane oligomer is sufficiently devolatilized. It is not preferable because it cannot be done. On the other hand, a temperature higher than 240 ° C. is not preferable because it results in yellowing or a decrease in thermal stability due to main chain decomposition of the polymer due to heat.

The size of the extruder varies depending on the feed amount (production amount) of the crude polyacetal resin, but in the range of the feed amount of the crude polyacetal resin of 100 to 4000 kg / hour, the inner diameter is usually 50 mm to 250 mm, and L / D 20 to 50 (L is The screw length) extruder is selected and can be operated in the range of screw rotation speeds of 500-50 rpm.
When melting the crude polyacetal resin with an extruder, additives such as an antioxidant, a heat stabilizer, a sliding agent, etc. may be added to the deactivated crude polyacetal resin in advance or in portions. it can.

As additives that can be used, antioxidants include, for example, 1,6-hexanediol-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis-3- (3-t-butyl-4-hydroxy-5-methylphenyl) propionate, pentaerythrityl-tetrakis-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2,2′-methylenebis (6-t-butyl-4-methylphenol), 3,9-bis {2- [3- (3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl } -2,4,8,10-tetraoxaspiro [5,5] undecane, N, N′-hexane-1,6-diylbis [3- (3,5-di-t-butyl) 4-hydroxyphenyl) propionamide], 3,5-bis (1,1-dimethylethyl) -4-sterically hindered phenols such as hydroxy benzenepropanoic acid 1,6-hexanediyl ester.
Heat stabilizers include amine-substituted triazines such as melamine, methylol melamine, benzoguanamine, cyanoguanidine, N, N-diarylmelamine, polyamides, urea derivatives, hydrazine derivatives, urethanes, and sodium, potassium, calcium, magnesium , Barium inorganic acid salt, hydroxide, organic acid salt and the like.
Examples of other additives include colorants, nucleating agents, optical brighteners, mold release agents such as fatty acid esters or silicon compounds such as pentaerythritol tetrastearate, and antistatic agents such as polyethylene glycol and glycerin. Examples thereof include ultraviolet absorbers such as higher fatty acid salts, benzotriazole compounds or benzophenone compounds, and light stabilizers such as hindered amine compounds.
When these additives are added, one or two or more kinds can be added, and the addition amount must be appropriately selected according to the various additives, but each additive is based on 100 parts by weight of the polyacetal resin. 0.001 to 5.0 parts by weight are added.

Examples of the sliding agent include silicone oil, polyethylene wax, and polyethylene resin.

The silicone oil (C) used in the present invention can be arbitrarily selected from those generally known. For example, silicone oil made of polydimethylsiloxane, silicone oil in which a part of methyl group of polydimethylsiloxane is substituted with phenyl group, silicone oil in which part of methyl group of polydimethylsiloxane is substituted with halogenated phenyl group, Silicone oil in which a part of methyl group of polydimethylsiloxane is substituted with fluoroester group, epoxy-modified silicone oil such as polydimethylsiloxane having epoxy group, amino-modified silicone oil such as polydimethylsiloxane having amino group, Alcohol-modified silicone oils such as polydimethylsiloxane having alcohol groups, alkylaralkyl silicone oils such as dimethylsiloxane and phenylmethylsiloxane, methyl dimethylsiloxane units A polyether-modified silicone oil such as polydimethylsiloxane having a structure in which a part of the dimethylsiloxane unit is substituted with a polyether, a siloxane having a structure in which some of the methyl groups of the dimethylsiloxane unit are substituted with a polyether, and phenylmethylsiloxane Alkyria aralkyl polyether-modified silicone oil such as These silicone oils preferably have a viscosity at 25 ° C. of 0.65 to 1 million St, more preferably 100 to 100,000 St, and particularly preferably 5000 to 100,000 St.

These silicone oils can be used alone or in combination of two or more. The addition amount is 0.1 to 5 parts by weight, preferably 0.2 to 2 parts by weight with respect to 100 parts by weight of the polyacetal resin (A). If it is lower than this, sufficient sliding characteristics cannot be obtained. Moreover, if it is more than this, the moldability of the composition is inferior and the appearance is also deteriorated.

The polyethylene wax (B) in the present invention means a low molecular weight polyethylene, a low molecular weight polyethylene copolymer, or a modified polyethylene wax having a polar group introduced by oxidative modification or acid modification thereof. The number average molecular weight is preferably 500 to 15000, more preferably 1000 to 10,000. Polyethylene wax of low molecular weight polyethylene and low molecular weight polyethylene copolymer is manufactured by a method of directly polymerizing ethylene or ethylene and α-olefin using a Ziegler catalyst, a method of thermally decomposing high molecular weight polyethylene or copolymer, etc. Can do. Among these, a copolymer-type polyethylene wax of 50 to 99 mol% ethylene and 1 to 50 mol% α-olefin is preferable. Particularly preferably, the α-olefin is propylene. The modified polyethylene wax means the above-mentioned low molecular weight polyethylene, low molecular weight polyethylene copolymer or modified polyethylene wax obtained by oxidizing or acid-modifying them. The oxidative modification is performed by treating the wax with peroxide or oxygen and introducing polar groups such as carboxyl groups and hydroxyl groups. In addition, if necessary, acid modification treatment is performed by introducing a polar group such as a carboxyl group or a sulfone group by treating the wax with an inorganic acid, an organic acid, or an unsaturated carboxylic acid in the presence of peroxide or oxygen. Is done. These polyethylene waxes are marketed under the names of general type high density polyethylene wax, general type low density polyethylene wax, high oxidation type polyethylene wax, low oxidation type polyethylene wax, acid-modified polyethylene wax or special monomer modified type, etc. It can be easily obtained.

As the polyethylene resin (B) of the present invention, those having a number average molecular weight of 2 × 10 ⁴ to 50 × 10 ⁴ are preferably used. Examples of the polyethylene resin include low-density polyethylene, linear low-density polyethylene composed of a copolymer of ethylene and α-olefin, and ultra-low-density polyethylene. Among them, low-density polyethylene is preferably used. (Including linear low-density polyethylene resin and copolymers thereof) indicates a density of 0.910 to 0.940 g / cm ³ , and ultra-low density polyethylene resin has a density of 0.875 g / cm 3. ³ or more and less than 0.910 g / cm ³ . Low-density polyethylene is preferable because it has lower crystallinity than high-density polyethylene and is therefore mixed to some extent with polyacetal to further improve friction and wear characteristics. The polyethylene resin may be polymerized using a conventional multi-site catalyst or polymerized using a single-site catalyst. Further, it may be a polyethylene resin modified with an epoxy such as glycidyl methacrylate or an acid anhydride such as maleic anhydride. The melt viscosity of the polyethylene resin used in the present invention is preferably a melt index (MI) based on ASTM-D1238 (measurement conditions: 190 ° C., under a 2.16 kg load), preferably 0.01 to 150 g / 10 min. More preferably, it is 0.1 to 100 g / 10 min. When the melt index of the polyethylene resin is less than 0.01 g / 10 min, the dispersibility in the polyacetal resin is lowered, and the friction and wear characteristics are reduced. Degradation of physical properties may occur. On the other hand, if it exceeds 150 g / 10 min, the friction and wear characteristics may deteriorate.

The total blending amount of the polyethylene wax and the polyethylene resin is 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight with respect to 100 parts by weight of the polyacetal resin. If it is more than this, the mechanical performance of the polyoxymethylene resin composition is lowered, and if it is less than this, the effect is small. Polyethylene wax may be used alone or in combination of two or more.
The weight ratio of silicone oil (C), polyethylene wax and polyethylene resin (B) is preferably in the range of 0.01 to 4, more preferably in the range of 0.05 to 2.

The method of mixing the crude polyacetal resin and various additives is not particularly limited as long as the additive and the powder of the crude polyacetal resin are uniformly mixed. For example, it is preferable not to use other mixing equipment at the time of the deactivation treatment because it is not necessary to use other mixing equipment, but it is also possible to use a method of mixing continuously or batchwise with a normal powder mixer after the deactivation process. it can.

The crude polyacetal resin melted in the extruder may be subsequently introduced into a biaxial surface renewal horizontal reactor and devolatilized under reduced pressure. When the main purpose of the extruder is designed to assist the plasticization of the crude polyacetal resin and the removal of thermal decomposition components, the pressure reduction degree of the vent portion of the extruder is 1.01 × 10 ^{2 to} 1.33. It is preferably carried out while melt-kneading under a pressure of × 10 ⁻² kPa, and is preferably carried out at a reduced pressure of 50 kPa or more inside the south concentrated air. When the pressure is higher than this range, a sufficient devolatilizing effect cannot be obtained, and when the pressure is lower than this range, the decompression equipment becomes large, which causes a cost increase when the apparatus is installed.
The vacuum devolatilization time is preferably 15 to 60 minutes. If the vacuum devolatilization time is shorter than 15 minutes, the formaldehyde gas and cyclic siloxane oligomer generated when the crude polyacetal is melted cannot be sufficiently devolatilized. Further, even in a biaxial surface renewal type horizontal reactor where the shear stress is much weaker than that of an extruder, if the residence time exceeds 60 minutes, the polyacetal resin will be yellowed or the thermal stability will be lowered due to main chain decomposition, which is not preferable. . It is also preferable to introduce an inert gas such as nitrogen gas at the time of vacuum devolatilization, or to introduce alcohol or water vaporized under devolatilization pressure reduction conditions into the vacuum processing facility to avoid mixing in air from the outside, or to control the degree of vacuum It is.

190-240 degreeC is preferable and the temperature at the time of a vacuum devolatilization process, More preferably, it is 200-230 degreeC. If it is lower than 190 ° C, the melted polyacetal copolymer may be crystallized (solidified), and if it is higher than 240 ° C, it may cause yellowing or thermal stability degradation due to main chain decomposition of the polymer due to heat. It is not preferable.

The biaxial surface renewal type horizontal reactor has a sufficiently wide clearance between the stirring blade and the inner diameter of the kneader, and the space volume in the kneader (the space portion excluding the volume occupied by the molten polyacetal copolymer) is 20% of the total volume. A kneader excellent in surface renewal of the type that can be taken as described above is suitable. For example, Hitachi, Ltd. spectacle blade, lattice wing reactor, Mitsubishi Heavy Industries, Ltd. SCR, NSCR reactor, Examples include KRC kneaders and SC processors manufactured by Kurimoto Steel.

The polyacetal resin, polyethylene wax, polyethylene resin, and silicone oil used in the examples and comparative examples are shown below.
(A) Polyacetal resin Trioxane and oxymethylene copolymer of 1,3-dioxolane, a polyacetal resin (melting index (MI): 45 g / 10 min) manufactured by Mitsubishi Engineering Plastics Co., Ltd. was used.
Polyacetal resin; trade name Iupital F40-03
The MI was measured based on ASTM-D1238 (190 ° C., under 2.16 kg load) (A) 100 parts by weight of crude polyacetal resin trioxane, 4.5 parts by weight of 1,3-dioxolane, and 3 parts as a catalyst. Boron fluoride diethyl etherate as a benzene solution (0.62 mol / Kg-benzene) is 0.06 mmol with respect to 1 mol of all monomers, and methylal as a molecular weight regulator as a benzene solution (25% by weight) with respect to all monomers. Polymerization was continuously carried out in a biaxial kneader having a self-cleaning paddle having a jacket with a 2000 ppm continuous addition and a temperature set at 65 ° C. so that the residence time of the polymerization machine was 15 minutes.
Triphenylphosphine is added as a benzene solution (25% by weight) to the resulting polymer so that the amount is 2 mol with respect to 1 mol of boron trifluoride diethyl etherate, and the catalyst is deactivated and then pulverized. Thus, a crude polyacetal resin was obtained. The MI value was 48.0.

(B) Polyethylene wax, manufactured by Mitsui Chemicals, Inc., trade name: high wax 405MP, molecular weight 4000, acid value 1

(B) Polyethylene resin low density polyethylene (density 0.916 g / cm ³ , number average molecular weight 22000) (manufactured by Nippon Unicar Co., Ltd., trade name: NUC-8350, MI: 18 g / 10 min) Based on JIS K6922-2.

(C) Kinematic viscosity at 25 ° C. of silicone oil 100 × 10 ⁴ cSt (manufactured by Shin-Etsu Chemical Co., Ltd., polydimethylsiloxane, trade name: KF-96-1000000CS)

[Measurement of dynamic friction coefficient]
(I) Molding of Specimen A polyacetal resin composition for evaluation was subjected to injection molding under conditions of a cylinder temperature of 200 ° C. and a mold temperature of 80 ° C. (size: outer diameter 25.6 mm × inner diameter 20. 0 mm × height 15.0 mm).
(Ii) Friction and wear tester A thrust type friction and wear tester manufactured by Orientec Co., Ltd. was used.
(Iii) Evaluation Method The above-mentioned injection molded test piece having the same cylindrical shape was used as a thrust test piece for the own material and the counterpart material. The end surfaces of the own material and the mating material are arranged such that the abutting surface is a horizontal plane with the upper side being the own material and the lower side being the mating material. The dynamic friction coefficient (μ) was obtained by fixing the upper side self-material and rotating the lower side counterpart material in the circumferential direction.
The measurement conditions were a temperature of 23 ° C., an atmosphere of 50% humidity, a surface pressure of 0.25 MPa, and a linear velocity of the average inner diameter of the rotary motion of 0.1 m / second.

(2) Specific wear amount Using the same cylindrical thrust test piece and test machine as in (1) above, at a temperature of 23 ° C. and a humidity of 50%, the surface pressure is 0.05 MPa, and the average inner diameter is 0.3 m. The specific wear amount was determined by running for 20 hours per second.
The unit of specific wear was [× 10 ⁻² mm ³ / kg · km].

[Measurement method of cyclic siloxane oligomer]
Measurements were made using a purge and trap-gas chromatograph. The calibration curve was performed using a reagent manufactured by Tokyo Chemical Industry Co., Ltd. Since it was confirmed that the detection sensitivity did not depend on the quantity, a hexamer was used as a calibration curve.
<Device conditions>
GC; HP-6890
Column; HP-5 (φ0.32 mm × 30 m × t 0.5 μm)
Even Temp; 50 ° C (2 minutes)-20 ° C / minute-320 ° C (5 minutes)
Inj Temp; 300 ° C
Detector; FID
Carrier; 2.0 ml / min (He)
Purging Time; 10 minutes Purging Temp; 210 ° C

[ Reference Example 1 and Comparative Example 1]
For 100 parts by weight of polyacetal resin (A), 1.5 parts by weight of polyethylene wax (B), 1 part by weight of silicone oil (C), and 1 part by weight of polyethylene resin (B) After that, a resin composition (pellet shaped product) was obtained using a twin screw extruder (Ikegai Iron Works Co., Ltd., model: PCM-30) under the conditions shown in Table 1. Subsequently, each of the resin compositions was molded into a cylindrical thrust test piece using an injection molding machine, and subjected to evaluation of the dynamic friction coefficient and specific wear amount, and the content of the cyclic siloxane oligomer in the pellet was measured.

[ Reference Example 2 and Comparative Example 2]
Triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] (trade name: IRGA, manufactured by Ciba Geigy Co., Ltd.) as a stabilizer with respect to 100 parts by weight of the crude polyacetal resin (A) Knox 245) 0.3 parts by weight, melamine 0.1 parts by weight, magnesium hydroxide 0.05 parts by weight, polyethylene wax (B) 1.5 parts by weight, silicone oil (C) 1 part by weight, and polyethylene After mixing 1 part by weight of resin (B) using a super mixer (manufactured by Kawata Co., Ltd.), a twin screw extruder (Ikegai Iron Works Co., Ltd., model: PCM-30) under the conditions described in Table 1 Was used to obtain a resin composition (pellet shape). Subsequently, a cylindrical thrust test piece was molded from each of the resin compositions using an injection molding machine, and used for evaluation of the dynamic friction coefficient and specific wear amount, and the content of the cyclic siloxane oligomer in the pellet was measured.

[Example 3]
Triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate] as a stabilizer (trade name: Irganox 245, manufactured by Ciba Geigy Co., Ltd.) was added to 100 parts by weight of the crude polyacetal copolymer. 0.3 parts by weight, 0.1 parts by weight of melamine, 0.05 parts by weight of magnesium hydroxide, 1.5 parts by weight of polyethylene wax (B), 1 part by weight of silicone oil (C), and polyethylene resin (B ) After mixing 1 part by weight using a super mixer (manufactured by Kawata Co., Ltd.), from a hopper with an automatic quantitative feed function, a length of 3D ₁ at a position of 10.5 to 14.0D ₁ from the feed port kneading portion is disposed _{of, 14.0~17.5D 1,} the vent is installed in a position of 24.5~28.0D _1, 24.5~28.0 It was introduced at 60 kg / time to introduce a sealing ring (0.5 D) to the _first vent front lower co-rotating twin-screw extruder (inner diameter 69mm, L / D31.5), a crude polyacetal copolymer vent Then, it was melted at 220 ° C. under a reduced pressure of 20 kPa, and continuously introduced into a biaxial surface renewal type horizontal kneader. The liquid level was adjusted so that the residence time in the biaxial surface renewal type horizontal reactor (effective internal volume 60 L: volume excluding the volume occupied by the stirring blades from the total internal volume) was 25 minutes, and the pressure was reduced to 20 kPa. Under reduced pressure devolatilization at 220 ° C., it was continuously extracted with a gear pump to obtain a resin composition (pellet shape). Subsequently, a cylindrical thrust test piece was molded from each of the resin compositions using an injection molding machine, and used for evaluation of the dynamic friction coefficient and specific wear amount, and the content of the cyclic siloxane oligomer in the pellet was measured.

Claims (4)

0.1 to 10 parts by weight of polyethylene wax having a number average molecular weight of 500 to 15000 and / or polyethylene resin (B) 0 having a number average molecular weight of 2 * 10 ⁴ to 50 * 10 ⁴ per 100 parts by weight of the crude polyacetal resin (A) 0.1 to 10 parts by weight, and after adding 0.1 to 5 parts by weight of a silicone oil (C) having a kinematic viscosity at 25 ° C. of 50 * 10 ⁴ cSt or more, melt in a twin-screw extruder and remain in a molten state A polyacetal resin that is continuously introduced into a biaxial surface renewal type horizontal kneader and is devolatilized under reduced pressure at an internal resin temperature of 190 to 240 ° C. and −50 kPa or more for 15 to 60 minutes. A method for producing the composition. Deactivate the catalyst in the polyacetal resin (A), then add the silicone oil (C), then add an antioxidant or heat stabilizer and heat to melt to decompose the thermally unstable structure method for producing a polyacetal resin composition according to claim 1, characterized in that removal. The method for producing a polyacetal resin composition according to claim 2 , wherein the catalyst deactivator is triphenylphosphine. The method for producing a polyacetal resin composition according to claim 2 , wherein the antioxidant is a hindered phenol antioxidant and the heat stabilizer is a basic heat stabilizer.