JP2007246592A - Manufacturing process for high slidability polyacetal resin composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an efficient and economical manufacturing process for a high slidability polyacetal resin having reduced burn, discoloration and mold staining. <P>SOLUTION: The manufacturing process comprises melting a polyacetal copolymer immediately after polymerization with a twin-screw extruder, continuously introducing the copolymer as it is molten into a surface-renewal model horizontal reactor, devolatilizing the melt under reduced pressure at a temperature not lower than the melting point and kneading and devolatilizing the polyacetal copolymer discharged from the reactor after adding additives under reduced pressure in an extruder (B). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a high sliding polyacetal resin composition. More specifically, the present invention relates to a method for producing a highly slidable polyacetal resin composition efficiently and economically with little discoloration, discoloration, and mold contamination.

Polyacetal copolymer has excellent properties in mechanical properties, thermal properties, electrical properties, slidability, and moldability, etc., as structural materials and mechanical parts, etc. Widely used for machine parts.
In recent years, the range of use has further expanded, and further high-sliding polyacetals have been developed to meet higher performance requirements for the resins.

  As an improvement method to high sliding polyacetal, for example, a method of impregnating and mixing oil into a polyacetal resin (see Patent Document 1), a method of mixing polytetrafluoroethylene (see, for example, Patent Document 2), and mixing high density polyethylene A method (for example, refer to Patent Document 3) is known. However, the method of impregnating and mixing oil has the disadvantage of poor oil retention and poor moldability. Further, the method of mixing polytetrafluoroethylene is very expensive and has a drawback that mold deposits are likely to occur during molding. Furthermore, the method of mixing with high-density polyethylene is inferior in dispersibility of the high-density polyethylene in the polyacetal resin, and has a problem in that delamination tends to occur.

  Also, a method of mixing silicone oil and ultrahigh molecular weight polyethylene with a synthetic resin has been shown, but the affinity between ultrahigh molecular weight polyethylene and silicone oil is poor, and oil exudation is severe, resulting in poor moldability. The dimensional accuracy and appearance of the molded product were poor (see, for example, Patent Document 4).

Therefore, the stabilized polyacetal resin pellets were melted and kneaded with silicone oil and polyethylene wax with an extruder to overcome the above-mentioned drawbacks and achieved excellent sliding characteristics (Patent Literature) 5), the extrusion kneading process is performed twice, which is inefficient and increases the cost. Therefore, it is possible to reduce the extrusion process once by kneading silicone oil and polyethylene wax together with an antioxidant and a heat stabilizer in an unstabilized polyacetal resin (hereinafter referred to as crude polyacetal resin). However, since silicone oil and polyethylene wax are sliding agents, slippage occurs even when biting into the screw of the extruder, so that productivity is greatly reduced. In addition, in order to sufficiently disperse the sliding agent, it is necessary to tighten the kneading conditions such as increasing the residence time and shaft rotation speed in the 2-axis surface renewal type horizontal reactor, and it causes burns, yellowing, mold contamination It was regarded as a problem that many were seen.
Japanese Examined Patent Publication No. 46-42217 Japanese Patent Publication No.46-30590 Japanese Patent Publication No.46-41456 Japanese Patent Publication No.47-29374 JP-A-4-224856

  An object of the present invention is to provide an efficient and economical method for producing a high-sliding polyacetal with little discoloration, discoloration, and mold contamination.

As a result of intensive studies in view of the above problems, the present inventors have melted a polyacetal copolymer immediately after polymerization with a twin-screw extruder and continuously introduced it into a biaxial surface-renewed horizontal reactor in a molten state. The high-sliding polyacetal is efficiently obtained by performing vacuum devolatilization at a temperature equal to or higher than the melting point, and further kneading the additive with the polyacetal copolymer discharged therefrom and performing vacuum devolatilization with an extruder (B). And it discovered that it could manufacture economically and came to complete this invention. That is, in the present invention, after the catalyst is deactivated, the polyacetal copolymer is melted by an extruder (A) and continuously introduced into a biaxial surface renewal type horizontal kneader in a molten state, Was vacuum devolatilized at 190 to 240 ° C. and 1.01 × 10 ^{2 to} 1.33 × 10 ⁻² kPa for 15 to 60 minutes, and then discharged from the biaxial surface renewal type horizontal kneader The resin composition is kneaded and devolatilized under reduced pressure in an extruder (B) provided with a kneading part having a length of ₂ to 5D ₂ with respect to the inner diameter D2 of the extruder (B). The manufacturing method of the high sliding polyacetal resin composition characterized by these is provided.

  According to the present invention, a highly slidable polyacetal with little burn, discoloration, and mold contamination can be produced efficiently and economically.

  The polymerization method of the polyacetal copolymer in the present invention includes a bulk polymerization method. 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 in the present invention is trioxane, which is a cyclic trimer of formaldehyde, and cyclic formal and / or ether is used as a 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.

The addition amount of the comonomer is preferably 0.5 to 40.0 mol%, more preferably 1.1 to 20.0 mol% with respect to trioxane. When the amount of the comonomer used is larger than this, the polymerization yield decreases, and when it is small, the thermal stability decreases.
Moreover, you may add 0.001-0.2 weight part of polyfunctional epoxy compounds, such as 1, 4- butanediol diglycidyl ether and polyethyleneglycol diglycidyl ether, as a crosslinking and branching agent.

As the polymerization catalyst of the present invention, a general cationically 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 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 polymerization method of the present invention, an appropriate molecular weight regulator may be used as necessary to adjust the molecular weight of the polyacetal copolymer. 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.
In general, the amount of these molecular weight modifiers is adjusted in the range of 0 to 1.0 part by weight based on the monomer, depending on 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 of the present invention, 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 a deactivator, primary, secondary, and tertiary aliphatic amines, aromatic amines, heterocyclic amines, and the like can be used. 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 need not 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 within 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 copolymer is preferably a fine powder, 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 copolymer is separately pulverized using a pulverizer, or pulverization and stirring may be simultaneously performed in the presence of the deactivator. When the crude polyacetal copolymer 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 the deactivation of the catalyst is not sufficient and the molecular weight of the final product is low, the molecular weight regulator should be adjusted in advance to increase the molecular weight of the crude polyacetal copolymer in consideration of the decrease in molecular weight. A method of adjusting the molecular weight is taken.

  The deactivated crude polyacetal copolymer is melted in the extruder (A), degassed under reduced pressure in a biaxial surface renewal type horizontal reactor, introduced into the extruder (B), and melted with the additive. Knead. The main purpose of the extruder (A) is to melt the solid crude polyacetal copolymer, and the auxiliary purpose is to assist the vacuum devolatilization of the biaxial surface renewal type horizontal reactor and the extruder (B). It is an additive melt kneading aid. The main purpose of the biaxial surface renewal type horizontal reactor is to thermally decompose and remove the thermally unstable structure contained in the crude polyacetal copolymer by decompression. The main purpose of the extruder (B) is melt mixing of the additive and the polyacetal copolymer, and the auxiliary purpose is to assist the vacuum devolatilization of the biaxial surface renewal type horizontal reactor. Details of the optimum device configuration and the like are shown below.

The crude polyacetal copolymer subjected to the deactivation treatment is melted in an extruder (A) in which a kneading portion having a length of 2D _{1 to} 10D ₁ (D ₁ is an inner diameter of the extruder (A)) is installed. 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 (A), 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 copolymer becomes insufficient, or the rough When the polyacetal copolymer is mixed with the stabilizer in advance, the mixing of the crude polyacetal copolymer and the stabilizer becomes insufficient, and the target effect cannot be obtained unless the stabilizer is added excessively. If the kneading part is longer than the range, the polyacetal copolymer will be decomposed due to excessive shear stress in the kneading part, resulting in the formation of a new unstable structure due to coloring or viscosity (or molecular weight) reduction. . 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.

In the present invention, the kneading part is provided with a kneading part at a position 5D ₁ or more away from the position where the crude polyacetal copolymer is introduced in powder with respect to the flow direction, and further at a position 8D ₁ or more away. It is suitable for this. When installing a kneading part in the position near this, the transfer capability of the rough polyacetal copolymer in an extruder (A) will fall, and productivity will fall. Moreover, it is preferable to install a flight part in a screw until it installs a kneading part from the position where a rough polyacetal copolymer is introduce | transduced with a 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 (A).

When the extruder (A) is biaxial, it may be either the same direction rotating type or the different direction rotating type, but preferably the same direction rotating type with excellent productivity is used. For the purpose of assisting in the process of removing the thermal decomposition component in the biaxial surface renewal type horizontal reactor described later, one or more vent portions are provided in the extruder and vacuum devolatilization is performed at 1.01 × 10 ^{2 to} 1.33. It is preferable to carry out at a pressure of × 10 ⁻² kPa (reduced pressure indicates 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. If it is lower than 190 ° C, an unmelted polyacetal copolymer may remain or the molten polyacetal copolymer may solidify. If it is higher than 240 ° C, it may be yellowed or decomposed by the main chain of the polymer due to heat. This results in a decrease in thermal stability, which is not preferable.

The size of the extruder (A) varies depending on the feed amount (production amount) of the crude polyacetal copolymer, but in the range of the feed amount of the crude polyacetal copolymer of 100 to 4000 kg / hour, the inner diameter is usually 50 mm to 250 mm, L / D20-50 (L is the length of the screw) is selected, and can be operated in the range of screw rotation speed 400-50rpm.
When the crude polyacetal copolymer is melted in the extruder (A), a known additive such as an antioxidant or a heat stabilizer is added to the deactivated crude polyacetal copolymer in advance or in a divided manner. I can keep it.

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 adding an additive, one kind or two or more kinds can be added, and the addition amount must be appropriately selected according to the various additives. Each additive is added to 100 parts by weight of the polyacetal copolymer. On the other hand, 0.001 to 5.0 parts by weight is added.

  The method for mixing the crude polyacetal and various additives is not particularly limited as long as the additive and the powder of the crude polyacetal copolymer 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 copolymer melted in the extruder (A) is subsequently introduced into a biaxial surface renewal type horizontal reactor and evacuated under reduced pressure. The vacuum devolatilization is performed while melt kneading under a pressure of 1.01 × 10 ^{2 to} 1.33 × 10 ⁻² kPa. 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 generated when the crude polyacetal is melted cannot be sufficiently devolatilized. In addition, even in a biaxial surface-renewed horizontal reactor where the shear stress is much weaker than that of an extruder, if the residence time exceeds 60 minutes, the polyacetal copolymer will turn yellow or the thermal stability will deteriorate due to main chain decomposition. It is not preferable. It is also preferable to introduce an inert gas such as nitrogen gas or alcohol or water vaporized under devolatilization decompression conditions during decompression devolatilization to avoid the entry of air from the outside, or to control the degree of decompression. 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.

Polyacetal copolymer subjected to decompression treatment in a biaxial surface renewal type horizontal reactor is an extruder provided with a kneading section having a length of 3D _{2 to} 10D ₂ (D ₂ is the inner diameter of the extruder (B)). Introduced in (B). In this case, it is preferable to continuously introduce the polyacetal copolymer into the extruder (B) in a molten state after the pressure reduction treatment. Although it is possible to introduce into the extruder (B) after cooling and solidifying once after the pressure reduction treatment, it is necessary to melt the solidified polyacetal copolymer again in the extruder, which is disadvantageous in terms of energy, and The L / D of the extruder becomes longer and the apparatus becomes larger.

The length of the kneading part of the extruder (B) is 2D _{2 to} 5D ₂ , preferably 2.5D _{2 to} 4.5D ₂ , and more preferably 3D _{2 to} 4D ₂ . If the kneading part is shorter than this range, the kneading property with the molten polyacetal copolymer becomes insufficient, and the target slidability cannot be obtained or causes variation. If the kneading part is longer than this range, the polyacetal copolymer is decomposed due to excessive shearing stress in the kneading part, resulting in the formation of a new unstable structure due to coloring or molecular weight reduction. It is desirable to install a flight part that does not generate excessive shear stress in the screws other than the kneading part.

  The residence time in the extruder (B) is 5 minutes or less. Moreover, 190-240 degreeC is preferable and internal resin temperature is 200-230 degreeC more preferably. If it is lower than 190 ° C, the melted polyacetal copolymer may be crystallized (solidified), and if it is higher than 240 ° C, the heat stability is reduced due to yellowing or decomposition of the main chain of the polymer due to heat. As a result, the effect of the agent itself is deteriorated or the structure is changed.

  The additive used here is a sliding agent, and examples of the sliding agent include silicone oil and polyethylene wax.

  The silicone oil 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 a methyl group of a dimethylsiloxane unit is 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 of the total composition weight. 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 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 oxidizing or acid-modifying them. 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.

The blending amount of the polyethylene wax is 0.1 to 20 parts by weight, preferably 0.5 to 5 parts by weight. 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 to polyethylene wax is preferably in the range of 0.01 to 4, more preferably in the range of 0.05 to 2.

  Additives kneaded in the extruder (B) are antioxidants, heat stabilizers, colorants, nucleating agents, plasticizers, fluorescent brighteners, pentaerythritol tetrastearate, etc., which are added in the extruder (A). Release agents such as fatty acid esters or silicon compounds, antistatic agents such as polyethylene glycol and glycerin, higher fatty acid salts, UV absorbers such as benzotriazole or benzophenone compounds, or light such as hindered amines Stabilizers, various elastomers, organic / inorganic fillers, and the like can also be added depending on the purpose of use.

Here, the kneading portion refers to a portion of the extruder screw in which a disk-shaped screw 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 _{2 to} 1.0D ₂ 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.
The kneading part does not need to be continuously installed with a length of L / D = 1.0 to 0.5 or 2.0 to 10.0 with respect to the screw length direction. As a configuration in which the flight section is introduced between the ding sections, the kneading section can be divided into three zones or four zones or more and installed on the screw of the extruder (B).
It is preferable to install a flight part where excessive shear stress is not easily applied to the screw other than the kneading part.

The extruder (B) is preferably a single-screw or twin-screw or more extruder, and is preferably a co-rotating twin-screw extruder having excellent productivity. The extruder (B) is preferably a type in which one or more vent portions are installed. The pressure at the vent is 1.01 × 10 ² kPa or less. Combined with a method of improving the devolatilization efficiency or a method of controlling the degree of decompression by introducing an inert gas such as nitrogen gas at the time of extrusion devolatilization or by introducing alcohol or water vaporized under devolatilization decompression conditions into the vent part or directly into the molten resin It is also suitable.

  The size of the extruder (B) may be the same as or different from that of the extruder (A), but it depends on the feed amount (production amount) of the crude polyacetal copolymer, and the crude polyacetal In the range of the copolymer feed amount of 100 to 4000 kg / hour, an extruder having an inner diameter of 50 mm to 250 mm and L / D of 5 to 40 (L is the length of the screw) is usually selected, and the screw rotation speed is in the range of 50 to 400 rpm. You can drive.

  The introduction position of the additive is preferably provided between the biaxial surface renewal type horizontal reactor and the kneading part of the extruder (B). In this case, the additive is the above-mentioned additive, for example, a sliding agent or a plasticizer. One or more additives can be added from the same addition position and / or different addition positions, and the additive divided and mixed in the extruder (A) can be added again here. .

  The method for adding the additive in the extruder (B) is not particularly limited, but the method of introducing the additive directly into the extruder or the masterbatch method (high concentration additive mixed polyacetal copolymer in the form of powder or pellet Alternatively, it can be introduced into the extruder in a molten state, and one or a combination of two or more additives can be used, and the additive concentration can be increased to about 10 to 10,000 times the additive concentration of the final polyacetal copolymer. Is preferred). As the apparatus for introducing the additive, it is preferable to select one or more kinds of the best apparatus depending on the properties of the additive from a press-fitting pump, a screw feeder, a single screw extruder, a twin screw extruder or the like. is there.

  Examples and Comparative Examples of the present invention are shown below, but the present invention is not limited to these.

Crude polyacetal copolymer (1) Polymerization example To 100 parts by weight of trioxane, 4.5 parts by weight of 1,3-dioxolane, and boron trifluoride diethyl etherate as a catalyst in a benzene solution (0.62 mol / Kg-benzene) Self-cleaning type having a jacket in which 2000 ppm is continuously added to all monomers as a benzene solution (25% by weight) as a molecular weight regulator and 0.06 mmol to 1 mol of all monomers as a molecular weight regulator. Polymerization was continuously carried out in a biaxial kneader with paddles 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 copolymer (1) was obtained. The MI value was 48.0.
Crude polyacetal copolymer (2) Polymerization example To 100 parts by weight of trioxane, 4.5 parts by weight of 1,3-dioxolane, and boron trifluoride diethyl etherate as a catalyst in a benzene solution (0.62 mol / Kg-benzene) As a benzene solution (25% by weight) as a molecular weight regulator, and 500 ppm of all monomers are continuously added, and a self-cleaning type having a jacket whose temperature is set to 65 ° C. Polymerization was continuously carried out in a biaxial kneader with paddles 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. In this way, a crude polyacetal copolymer (2) was obtained. The MI value was 8.3.

Extruder (A) Treatment Example After polymerization, 100 parts by weight of polyacetal copolymer was mixed with triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate] (Ciba Geigy) as a stabilizer. A product name, Irganox 245) 0.3 part by weight, 0.1 part by weight of melamine, and 0.05 part by weight of magnesium hydroxide were premixed using a Henschel mixer. A kneading part having a length of 3D ₁ is installed at a position of 10.5 to 14.0D ₁ from the feed port of the crude polyacetal copolymer that has been premixed from a hopper equipped with an automatic quantitative feed function. -17.5D ₁ , 24.5-28.0D ₁ The same direction rotation type 2 in which a vent is installed and a seal ring (0.5D) is introduced in the lower front part of the vent of 24.5-28.0D ₁ It is introduced into a shaft extruder (inner diameter 69 mm, L / D 31.5) at 60 kg / hour, and the crude polyacetal copolymer is melted at 220 ° C. under a reduced pressure of 20 kPa at the vent, and continuously biaxial surface renewal type horizontal type It was introduced into a kneader.

Example of devolatilization and decompression of a biaxial surface renewal horizontal reactor A polyacetal copolymer introduced in a molten state from the above-mentioned co-rotating biaxial extruder was converted into a biaxial surface renewal horizontal reactor (effective internal volume 60 L: all Adjust the liquid level so that the residence time in the internal volume (excluding the volume occupied by the stirring blades) is 25 minutes, and continuously pull out with a gear pump while performing vacuum devolatilization at 220 ° C under a reduced pressure of 20 kPa. It was.

Example of Extruder (B) Processing A 3D ₂ kneading section is installed at a position of 7.0 to 10.5 D ₂ from the feed port while the sample continuously extracted by the gear pump is in a molten state, and 10.5 to 14 vent the position of .0D ₂ the installed co-rotating twin-screw extruder (inner diameter 58.0mm, L / D17.5) was introduced into. At the same time, polyethylene wax (made by Mitsui Chemicals, trade name: high wax 405MP, molecular weight 4000, low acid value type, acid value 1) 0.9 kg / hour, silicone oil (manufactured by Shin-Etsu Silicone Co., Ltd .: polydimethylsiloxane; KF) -96-1000000CS, viscosity 1 million cSt) master pellets (silicone oil content 40 parts by weight), base resin: Mitsubishi engineering plastics polyacetal resin F30-01) 3.5-7 with a side feeder It was fed from the position of .0D _2. The polyacetal copolymer was cooled in water and pelletized while devolatilizing at an internal resin temperature of 220 ° C. under a reduced pressure of 20 kPa. The obtained pellets were dried with a hot air dryer at 120 ° C. for 12 hours to obtain a final sample.

Examples 1-5
Crude polyacetal copolymer polymerization examples 1 and 2, extruder (A) treatment example, biaxial surface renewal type horizontal reactor devolatilization decompression example and extruder (B) treatment example, pellets of polyacetal resin composition were obtained. . Sample preparation conditions and physical property values are shown in the table.

Comparative Examples 1-5
In the same manner as in the examples, the residence time and the resin temperature in the biaxial surface renewal type horizontal kneader, the resin temperature of the extruder (A), the conditions regarding the kneading length in the extruder (B) and the physical property values are tabulated. Show.

Comparative Example 6
According to a crude polyacetal copolymer polymerization example 1, an extruder (A) treatment example, and a biaxial surface renewal type horizontal reactor devolatilization decompression example, pellets of a polyacetal resin composition were obtained. The sliding agent was added together with the crude polyacetal polymer and the stabilizer by an extruder (A). Sample preparation conditions and physical property values are shown in the table.

<Evaluation method>
(A) Thrust-type frictional wear test (specific wear)
Using an orientec thrust friction wear test (contact area 2.0 cm ² ), at a temperature of 23 ° C. and a humidity of 50%, with the same kind of materials at a linear velocity of 0.3 m / s and a surface pressure of 0.15 MPa. The amount of wear after the 20-hour test was measured (unit: × 10 ⁻⁶ mm ³ / N · m). Three test pieces of each sample were randomly extracted and measured.

(B) Burn: The number of pellets containing burn in 25 kg of the resin composition obtained in the examples or comparative examples was evaluated.

(C) Yellow discoloration: The resin composition obtained in Examples or Comparative Examples was molded using a IS90B molding machine manufactured by Toshiba Machine Co., Ltd. at a molding temperature of 240 ° C. and a mold temperature of 80 ° C. Yellow discoloration was observed and evaluated according to the following 6 levels.

（d） 金型汚染性：実施例または比較例で得られた樹脂組成物を、住友重機械工業（株）製ミニマットＭ８／７Ａ成形機を用い、しずく型金型を用いて、成形温度２３０℃、金型温度３５℃で５００ショット連続成形し、終了後、金型の付着物（モールドデポジット）の状態を観察し、以下の６段階の基準で評価した。

(D) Mold fouling property: Molding temperature of resin composition obtained in Examples or Comparative Examples using Sumitomo Heavy Industries, Ltd. mini mat M8 / 7A molding machine, using a drop mold. 500 shots were continuously molded at 230 ° C. and a mold temperature of 35 ° C. After completion, the state of the deposit (mold deposit) on the mold was observed and evaluated according to the following six criteria.

（e）溶融指数（ＭＩ値）：重合により得られた粗ポリアセタール重合体１００重量部に対し、トリエチレングリコール−ビス〔３−（３−ｔ−ブチル−５−メチル−４−ヒドロキシフェニル）プロピオネート〕（チバガイギー社製、商品名イルガノックス２４５）０．３重量部、メラミン０．１重量部、水酸化マグネシウム０．０５重量部を各々添加し、均一にブレンドした後、ラボプラストミルを用いて安定化し、ＡＳＴＭ−Ｄ１２３８（１９０℃、２．１６ｋｇ荷重下）に従って測定を行った。

(E) Melt index (MI value): Triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate with respect to 100 parts by weight of the crude polyacetal polymer obtained by polymerization. ] (Ciba Geigy Co., Ltd., trade name: Irganox 245) 0.3 parts by weight, 0.1 part by weight of melamine, 0.05 part by weight of magnesium hydroxide were added and blended uniformly, and then using a lab plast mill. Stabilized and measured according to ASTM-D1238 (190 ° C., 2.16 kg load).

Claims (2)

The polyacetal copolymer whose catalyst has been deactivated is melted by an extruder (A) and continuously introduced into a biaxial surface renewal type horizontal kneader in a molten state, and the internal resin temperature is 190 to 240 ° C. and 1 The polyacetal resin composition discharged from the biaxial surface renewal type horizontal kneader was subjected to vacuum devolatilization at 0.01 × 10 ^{2 to} 1.33 × 10 ⁻² kPa for 15 to 60 minutes. B) Sliding agent kneading and devolatilization under reduced pressure in an extruder (B) provided with a kneading part having a length of ₂ to 5D ₂ with respect to the inner diameter D2 of B). A method for producing a resin composition. The temperature in an extruder (B) is 190-240 degreeC, The manufacturing method of the polyacetal resin composition of Claim 1 characterized by the above-mentioned.