JP2006291001A - Method for producing polyacetal resin composition reduced in formaldehyde content - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently and economically producing polyacetal reduced in formaldehyde content, scarcely causing yellowing and contamination of molds. <P>SOLUTION: The method for producing the polyacetal resin composition reduced in formaldehyde comprises melting a polyoxymethylene copolymer immediately after polymerization in which a catalyst is deactivated in an extruder (A), continuously introducing the melted copolymer into a twin-shaft surface renewal type horizontal kneader in the melted state, devolatilizing the melted copolymer under reduced pressure of 1.01×10<SP>2</SP>to 1.33×10<SP>-2</SP>kPa at 190-240°C internal resin temperature and further kneading a polyacetal copolymer discharged from the twin-shaft surface renewal type horizontal kneader with a formaldehyde scavenger and devolatilizing the kneaded material under reduced pressure in an extruder (B) in which a kneading part having a length not longer than 3D<SB>2</SB>[D<SB>2</SB>is an inner diameter of the extruder (B)] is installed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a low-formaldehyde polyacetal resin composition. More specifically, the present invention relates to an economical and efficient method for producing a low-formaldehyde polyacetal with little yellowing and mold fouling (mold deposit).

Polyacetal copolymers have excellent mechanical properties, thermal properties, electrical properties, slidability, moldability, etc., and are used as structural materials and mechanical components such as electrical equipment, automobile parts, and precision machinery. Widely used for parts.
In recent years, formaldehyde has been generated from the final product, and its influence on sick house syndrome has been pointed out. The Ministry of Health, Labor and Welfare specified 0.08 ppm as a guideline value for indoor formaldehyde concentration as a countermeasure for sick house syndrome, so that it was required to reduce the amount of formaldehyde generated from the final polyacetal product. Therefore, it is required to produce a large amount of low-formaldehyde polyacetal resin with low formaldehyde generation amount from polyacetal resin at low cost.

  This low-formaldehyde polyacetal resin is achieved by melt-kneading a hydrazide compound, which is a formaldehyde scavenger, with an extruder or the like. However, since the hydrazide compound itself gradually deteriorates when it is retained in the molten resin for a long time, it has been necessary to knead it under conditions that suppress shearing in as short a time as possible.

  In addition, since the generation of formaldehyde is newly increased at the stage of plasticizing the pellets, more hydrazide compounds than expected are required, but adding more hydrazide compounds than necessary tends to increase yellowing and mold contamination. There was a problem that occurred.

As a method of adding a hydrazide compound, a resin composition containing various hydrazide compounds (Patent Document 1), a resin composition containing a borate of a nitrogen-containing compound such as hydrazide (Patent Document 2), or formaldehyde As an adsorbent, a resin composition (Patent Document 3) containing 1,2,3,4-butanetetracarboxylic acid hydrazide, which is a novel compound, and a deodorant containing hydrazide and urea or a derivative thereof at a specific ratio ( Patent document 4) etc. are mentioned. However, these have problems such as insufficient suppression of the amount of formaldehyde generated and reduced physical properties of molded articles, and a polyacetal resin composition having a lower amount of formaldehyde generated has been demanded.
JP-A-4-345648 Japanese Unexamined Patent Publication No. 7-109402 JP-A-6-080619 JP 2002-035098 A

  An object of the present invention is to provide an efficient and economical method for producing a low-formaldehyde polyacetal with little yellowing and mold contamination.

As a result of intensive studies in view of the above problems, the present inventors have melted a catalyst-deactivated polyacetal copolymer immediately after polymerization (hereinafter referred to as a crude polyacetal copolymer) with a twin-screw extruder (A). And continuously introduced into a biaxial surface renewal type horizontal kneader in a molten state, subjected to vacuum devolatilization at a temperature equal to or higher than the melting point, and the molten polyacetal copolymer discharged therefrom is extruded with an extruder (B). The inventors have found that a low-formaldehyde polyacetal can be produced stably and efficiently at low cost by kneading the additive and devolatilization under reduced pressure, and have completed the present invention. That is, in the present invention, a crude polyacetal copolymer 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. In addition, devolatilization under reduced pressure was performed at 1.01 × 10 ^{2 to} 1.33 × 10 ⁻² kPa, and the polyacetal copolymer discharged from the biaxial surface renewal type horizontal kneader was converted into 3D ₂ (D ₂ is In the method for producing a low-formaldehyde polyacetal resin composition by kneading a formaldehyde scavenger and performing devolatilization under reduced pressure in an extruder (B) provided with a kneading section having a length equal to or less than the inner diameter of the extruder (B) is there.

  According to the method of the present invention, a low-formaldehyde polyacetal resin composition with little yellowing and mold contamination can be produced efficiently and stably at low cost.

  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, per 1 mol of the total amount of all monomers (trioxane + comonomer). ^-4 mol. 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 parts by weight with respect to the total amount of all monomers 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 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 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 thereof include mono-n-butylamine, di-n-butylamine, tripropylamine, tri-n-butylamine, 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 dimethylbutylamine.
The deactivator does not need to be added in an amount that completely deactivates the catalyst, and the molecular weight reduction of the crude polyacetal copolymer may be suppressed within the allowable range of the product. 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. Further, a deactivator may be added after pulverizing the polyacetal copolymer immediately after polymerization using another pulverizer, or pulverization and stirring may be simultaneously performed in the presence of the deactivator. If the polyacetal copolymer at the time of mixing with the deactivator is not a fine particle, the catalyst contained in the resin is not sufficiently deactivated, and therefore depolymerization gradually proceeds with the remaining active catalyst. The molecular weight is reduced. 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), depressurized by a biaxial surface renewal type horizontal kneader, introduced into the extruder (B), and melted with the additive. Knead. The main purpose of the extruder (A) is to melt the crude polyacetal copolymer in a granular form, and the auxiliary purpose is to assist the vacuum devolatilization of the biaxial surface renewal type horizontal kneader. The main purpose of the biaxial surface renewal type horizontal kneader 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 formaldehyde scavenger, and the auxiliary purpose is to assist the vacuum devolatilization of the biaxial surface renewal type horizontal kneader. 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), 2D _{1 to} 10D ₁ need to be installed as the total length of the kneading part, and if the kneading part is shorter than this range, the melting of the crude polyacetal copolymer becomes insufficient, Alternatively, when the crude polyacetal copolymer is mixed with a 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 this range, the polyacetal copolymer will be decomposed by 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. Will occur. 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 the removal process of the thermal decomposition component in the biaxial surface renewal type horizontal kneader 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. If the temperature is low, unmelted polyacetal copolymer may remain or the melted polyacetal copolymer may solidify. If the temperature is high, heat stability is achieved by yellowing or decomposition of the main chain of the polymer by heat. As a result, it leads to a decrease in performance.

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.

Antioxidants that can be used include, for example, 1,6-hexanediol-bis [3- (3,5-di-tert-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-hydride Kishifeniru) propionamide], 3,5-bis (1,1-dimethylethyl) -4-sterically hindered phenols such as hydroxy benzenepropanoic acid 1,6-hexanediyl ester.
Usable 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 Examples thereof include inorganic acid salts, hydroxides, organic acid salts of magnesium and barium.
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.

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

  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, mixing at the same time as the quenching agent during the deactivation treatment is preferable because it is not necessary to use other mixing equipment, but after the deactivation process, a method of mixing continuously or batchwise with a normal powder mixer is used. You can also.

The crude polyacetal copolymer melted in the extruder (A) is subsequently introduced into a biaxial surface renewal type horizontal kneader 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. Even in a biaxial surface renewal type horizontal kneader 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 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.

  The internal resin temperature of the biaxial surface renewal type horizontal kneader during the vacuum devolatilization treatment is preferably 190 to 240 ° C, and if the temperature is low, the molten polyacetal copolymer may crystallize (solidify), On the other hand, a high temperature is not preferable because it causes yellowing or a decrease in thermal stability due to main chain decomposition of the polymer due to heat.

  The biaxial surface renewal type horizontal kneader 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 copolymer that has been decompressed with a biaxial surface renewal type horizontal kneader is an extruder having a kneading section having a length equal to or less than 3D ₂ (D ₂ is the inner diameter of the extruder (B)). 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 cool and solidify once after the pressure reduction treatment, it is possible to introduce into the extruder (B), but it is necessary to melt the solidified polyacetal copolymer again in the extruder, which is disadvantageous in terms of energy and extrusion. The L / D of the machine becomes long and the apparatus becomes large.

The kneading part with a length of 3D ₂ or less in the extruder (B) is one in which the effect of adding the formaldehyde scavenger is hindered mainly by high shear, or the effect of applying a thermal history to the formaldehyde scavenger itself It is suitable for kneading what deteriorates or changes. The length of the kneading part is preferably 2.5D ₂ or less, more preferably 2D ₂ or less. It is preferred length of kneading portion in the case of 0D ₂ for installing the seal ring before devolatilization vent. If the kneading part is longer than this range, an excessive reaction due to the additive occurs, or the additive effect is significantly reduced due to the modification of the additive itself. It is desirable to install a flight part that does not generate excessive shear stress in the screws other than the kneading part.

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 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 of a type in which one or more vent portions are installed, and more preferably, a polyacetal copolymer decomposition product or additive that could not be devolatilized by a biaxial surface renewal type horizontal kneader. From the standpoint of removing volatile components from the above, a type in which two or more vent portions are installed is preferable. 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 residence time in the extruder (B) is 3 minutes or less. Further, the internal resin temperature is preferably 190 to 240 ° C. If the temperature is low, the molten polyacetal copolymer may crystallize (solidify). This is not preferable because it results in deterioration of thermal stability due to chain decomposition, and further deterioration of the effect of the formaldehyde scavenger itself or structural change.

  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.

  As the hydrazide compound added and blended as a formaldehyde scavenger in the present invention, any aliphatic or aromatic hydrazide compound can be used. Examples of the aliphatic hydrazide compounds include monohydrazide compounds such as propionic acid hydrazide and thiocarbohydrazide, and dihydrazide compounds include oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, sebacic acid dihydride Examples include diacid dihydrazide, 1,18-octadecanedicarbohydrazide, maleic acid dihydrazide, fumaric acid dihydrazide, 7,11-octadecandiene-1,18-dicarbohydrazide, and the like.

  Examples of the aromatic hydrazide compound include salicylic acid hydrazide, terephthalic acid dihydrazide, 3-hydroxy-2-naphthoic acid hydrazide, p-toluenesulfonyl hydrazide, aminobenzhydrazide, 4-pyridinecarboxylic acid hydrazide, 1,5-naphthalenedicarbohydrazide, Examples include dihydrazides such as 1,8-naphthalenedicarbohydrazide, 2,6-naphthalenedicarbohydrazide, 4,4′-oxybisbenzenesulfonylhydrazide, 1,5-diphenylcarbonohydrazide. Polyhydrazides such as aminopolyacrylamide and 1,3,5-tris (2-hydrazinocarbonylethyl) isocyanurate can also be used.

Of these hydrazide compounds, dihydrazide compounds are preferred.
Further, the dihydrazide compound used in the present invention includes adipic acid dihydrazide, sebacic acid dihydrazide, dodecanedioic acid dihydrazide, 1,18-octadecanedicarbohydrazide, terephthalic acid dihydrazide, 1,8-naphthalenedicarbohydrazide, 2,6 -Naphthalenedicarbohydrazide and the like are particularly preferable.

  The hydrazide compounds may be used alone or in combination of two or more. The compounding quantity of the hydrazide compound in this invention composition is 0.01-0.5 weight part with respect to 100 weight part of polyacetal copolymers, Preferably it is 0.02-0.4 weight part, More preferably, it is 0.00. 03 to 0.3 parts by weight. When the amount is less than 0.01 part by weight, the formaldehyde scavenging effect is not sufficient. When the amount exceeds 0.5 part by weight, not only the formaldehyde scavenging effect is decreased, but also the mold deposit is greatly increased.

  Furthermore, other additives that can be kneaded in the extruder (B) include antioxidants, heat stabilizers, colorants, nucleating agents, plasticizers, fluorescent whitening agents, and the like that are added in the extruder (A) described above. Or a release agent such as a fatty acid ester or silicon compound such as pentaerythritol tetrastearate, an antistatic agent such as polyethylene glycol or glycerin, a higher fatty acid salt, an ultraviolet absorber such as a benzotriazole or benzophenone compound, Alternatively, light stabilizers such as hindered amines, various elastomers, organic / inorganic fillers, and the like can be added depending on the intended use.

  The introduction position of the additive such as formaldehyde scavenger is preferably installed between the biaxial surface renewal type horizontal kneader and the kneading part of the extruder (B). One or more additives can be added from the same addition position and / or different addition positions, and the remainder of the additive divided and mixed in the extruder (A) can be added here. it can.

  The method of adding the additive in the extruder (B) is not particularly limited, but the method of directly introducing the additive into the extruder or the master batch method (high concentration additive mixed polyacetal copolymer is powdered, pelletized Introduced into the extruder in the form of a molten or molten state, one or a combination of two or more additives can be added, and the additive concentration is increased to about 10 to 10,000 times the additive concentration of the final polyacetal copolymer Is possible). 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.

[Polymerization of crude polyacetal copolymer]
With respect to 100 parts by weight of trioxane, 4.5 parts by weight of 1,3-dioxolane, and boron trifluoride diethyl etherate as a catalyst as a benzene solution (0.62 mol / Kg-benzene) is 0.05 mmol with respect to 1 mol of all monomers. In a biaxial kneader with a self-cleaning paddle having a jacket in which methylal as a molecular weight regulator is continuously added as a benzene solution (25% by weight) at 500 ppm with respect to all monomers and the temperature is set to 65 ° C., Polymerization was continuously performed 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 was obtained. The MI value was 8.3.

[Processing Example of Extruder (A)]
After polymerization, 100 parts by weight of a polyacetal copolymer was mixed with triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate] (trade name: Irganox, manufactured by Ciba Geigy Co., Ltd.) as a stabilizer. 245) 0.3 parts by weight and 0.05 parts by weight of melamine 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, the vent is installed in a position of 24.50~28.0D _1, same direction vented installed sealing (0.5 D ₁₎ to vent the front lower part of the 24.5～28.0D ₁ The product was introduced into a rotary twin screw extruder (inner diameter 69 mm, L / D = 31.5) at 60 kg / hour, and the crude polyacetal copolymer was melted at 220 ° C. with a reduced pressure of 20 kPa at the vent, and continuously twined. Were introduced into a surface renewal type horizontal kneader.

[Example of reduced pressure devolatilization of a biaxial surface renewal type horizontal kneader]
The polyacetal copolymer introduced in a molten state from the above-mentioned co-rotating twin screw extruder is a biaxial surface renewal type horizontal kneader (effective internal volume 60 L: volume excluding the volume occupied by the stirring blades) The liquid level was adjusted so that the residence time at 25 minutes was 25 minutes, and continuously extracted with a gear pump while performing vacuum devolatilization at 220 ° C. under a reduced pressure of 20 kPa.

[Processing Example of Extruder (B)]
1D ₂ kneading part is installed at the position of 7.0-10.5D ₂ from the feed port while the sample continuously extracted with the gear pump is in the molten state, and vented at the position of 10.5-14.0D ₂ Was installed in a co-rotating twin screw extruder (inner diameter 58.0 mm, L / D = 17.5). At the same time, the hydrazide compound as a formaldehyde scavenger was supplied from the position 3.5 to 7.0 D ₂ from the feed port with the side feeder as powder. 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 80 ° C. for 3 hours to obtain a final sample.

Examples 1-3
Example 1 Polymerization of Crude Polyacetal Copolymer, Example of Extruder (A) Treatment Example, Biaxial Surface Renewable Horizontal Kneader Example of Depressurization and Extruder (B) Example of Polyacetal Resin Composition of Example 1 Product pellets were obtained. In Examples 2 to 3, the sample preparation conditions were changed as shown in Table 1. The results are shown in Table 1.

Comparative Examples 1-4
In the same manner as in Example 1, the residence time and resin temperature in the biaxial surface renewal type horizontal kneader and the kneading length in the extruder (B) were changed as shown in Table 1. The obtained results are shown in Table 1.

Comparative Example 5
Example of polymerization of crude polyacetal copolymer, processing example of extruder (A), polyacetal copolymer pellets obtained according to vacuum devolatilization example of biaxial surface renewal type horizontal kneader (however, in extruder (B) The amount of hydrazide compound shown in Table 1 was mixed with 100 parts by weight of a tumbler type blender. Next, the obtained mixture was melt-kneaded and pelletized by a single screw extruder with a vent (inner diameter 40 mm, L / D = 28) at an internal resin temperature of 220 ° C. and a discharge rate of 13 kg / h to form a polyacetal resin composition. Product pellets were obtained. The results are shown in Table 1.

<Evaluation method>
(a) Generated formaldehyde amount: 100 mm × 40 mm × 2 mm thickness of the resin composition obtained in the example or the comparative example was molded at a cylinder temperature of 215 ° C. using a PS-40E5ASE molding machine manufactured by Nissei Corporation. Using a flat plate as a test piece, measurement was performed on the day after molding in accordance with the method described in German Automobile Manufacturers Association Standard VDA275 (automobile interior parts-quantitative determination of formaldehyde emission by revised flask method).
(I) Put 50 ml of distilled water in a polyethylene container, close the lid with the test piece suspended, and keep it in a sealed state at 60 ° C. for 3 hours.
(Ii) Then, after leaving at room temperature for 60 minutes, a test piece is taken out.
(Iii) The formaldehyde concentration absorbed in distilled water in the polyethylene container is measured by an acetylacetone colorimetric method using a UV spectrometer.
(B) Mold fouling property: Molding temperature of resin compositions obtained in Examples or Comparative Examples using a drop mold using a mini mat M8 / 7A molding machine manufactured by Sumitomo Heavy Industries, Ltd. 500 shots are continuously formed at 230 ° C and mold temperature 35 ° C, and after completion, the state of mold deposits (mold deposits) is observed, and there are 6 levels, from those with less mold contamination to those with more mold contamination. Evaluation was made according to the criteria (1, 2, 3, 4, 5, 6).

Claims (4)

The polyacetal copolymer immediately after the polymerization in which the catalyst is 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. The polyacetal copolymer was vacuum devolatilized at 1.0 ° C. and 1.01 × 10 ^{2 to} 1.33 × 10 ⁻² kPa, and the polyacetal copolymer discharged from the biaxial surface renewal horizontal kneader was converted into 3D ₂ (D ₂ Is a formaldehyde scavenger kneading and devolatilization under reduced pressure in an extruder (B) provided with a kneading section having a length equal to or less than the inner diameter of the extruder (B), and a low-formaldehyde polyacetal resin composition Manufacturing method. The process for producing a polyacetal resin composition according to claim 1, wherein the temperature in the extruder (B) is 190 to 240 ° C. The method for producing a polyacetal resin composition according to claim 1, wherein the formaldehyde scavenger is a hydrazide compound. The method for producing a polyacetal resin composition according to claim 1, wherein the formaldehyde scavenger is a dihydrazide compound.