KR19980064083A - Process for preparing stabilized oxymethylene copolymer - Google Patents

Abstract

The present invention relates to a process for economically preparing oxymethylene copolymers having excellent thermal stability. Steric hindered phenol as copolyoxymethylene with labile end portions is added to the monomer mixture in an amount of 0.001 to 2.0% by weight of all monomers, the monomer mixture is polymerized and the resulting crude polyoxymethylene is ground Obtaining a powder having a specific particle size distribution and using a copolymer obtained by deactivating a polymerization catalyst contained in the material; Adding water and a stabilizer to copolyoxymethylene as a raw material; By stabilizing the raw material by evacuating the molten mixture in vacuo, stabilized copolyoxymethylene is obtained from copolyoxymethylene having unstable end portions.

Description

Process for preparing stabilized oxymethylene copolymer

The present invention relates to an economical process for preparing oxymethylene copolymers having excellent thermal stability.

Polyoxymethylene copolymer (hereinafter abbreviated as POM copolymer) has excellent mechanical properties, heat resistance, chemical resistance, electrical properties and sliding properties, as well as excellent moldability or formability. Therefore, they are used as engineering plastics for various applications such as mechanical parts, automobile parts or electric / electronic parts.

Practical stabilized POM copolymers are generally known to be prepared according to the following method.

First, cyclic acetals such as trioxane as main monomers and cyclic acetals or cyclic ethers having adjacent carbon atoms as comonomers are used; Add a chain transfer agent for controlling the degree of polymerization according to the purpose; The resulting mixture is then copolymerized in the presence of a cationic active catalyst to produce a crude POM copolymer. Such crude POM copolymers generally contain large amounts of labile end portions. If heat is applied to the copolymer while the polymerization catalyst contained in the crude copolymer is still active, the copolymer may depolymerize or an unstable end portion may increase.

Thus, the catalyst contained in the copolymer is neutralized or deactivated with organic or inorganic basic compounds such as alkylamines, alkoxyamines or hindered amines or hydroxides of alkali metals or alkaline earth metals, and then the crude POM copolymer, which is a polymerization product, is unstable. For disassembly and removal of the distal end. The copolymer thus treated is then heated in the presence of a basic compound such as the compound exemplified above and water, or a mixture of the basic compound and an alcohol as necessary to remove unstable end portions by decomposition.

Various additives can be added to the POM copolymer from which the unstable end portion is removed by decomposition to impart thermal stability and long term stability to the copolymer, and other additives or reinforcing agents can be added as necessary to the desired properties. Can be imparted and then melt kneaded to produce a practical stabilized POM copolymer.

Various studies have been conducted to make stabilized POM copolymers more economically. Examples of known measures of economical production methods include improvement of the polymerization reactor, improvement of the deactivator such as polymerization catalyst in the polymerization step, deactivation method of the catalyst deactivation step, etc. and improvement of the decomposition accelerator, decomposition of the unstable end portions. And decomposition and removal apparatuses in the removal step.

All of these measures are for specific steps only and the resulting improvements have limitations. Therefore, there is a need to devise a process that can be more economically prepared POM copolymer over the entire stage from the step of polymerizing to stabilizing the POM copolymer. In particular, in the above-described steps, the step of disassembling and removing the unstable end portions requires cumbersome work and requires a lot of energy for processing. If the POM polymer can be provided in the final stabilization step without substantially undergoing decomposition and removal steps, economically advantageous production will be possible. To this end, it is necessary to produce high quality crude POM polymers in the polymerization step and / or catalyst deactivation step.

Applicants of the present invention add 0.001-2.0% sterically hindered phenol to the monomer mixture, based on the weight of all monomers, to polymerize the resulting mixture and heat the POM copolymer and A method of stabilizing the POM copolymer by melting has been proposed (JP-B-87-13369). The addition of sterically hindered phenols in the polymerization step improves the dispersibility of sterically hindered phenols over the dispersibility of sterically hindered phenols added during the melt stabilization treatment, thereby inhibiting oxidative degradation of the POM copolymer during the melt stabilization step, It was found that the degradation products of the appearing POM were not sufficiently removed.

As a method of improving catalyst deactivation, it is known to pulverize the crude POM copolymer which is a polymerization product before the deactivation step in order to enhance the catalyst deactivation efficiency and the decomposition and removal efficiency of unstable end portions. In view of this, pulverized copolymers having smaller particle diameters are considered preferable (JP-A-82-80414 and JP-A-83-34819).

However, as a result of the study, the present inventors can improve the quality of the resultant POM polymer by pulverizing and inactivating the crude POM copolymer, but following the POM copolymer without decomposing and removing unstable end portions, It has been found that the resultant POM copolymer has significantly lowered operability when provided in a stabilization step and when a stabilizer is added to this copolymer and the resulting mixture is melt-kneaded.

JP-A-95-233230 uses a crude POM copolymer having a finite amount of unstable end portions as a raw material and adds stabilizers and water to the end stabilization zone in an extruder having a melt zone, a terminal stabilization zone and an exhaust zone. Suggest a method. As a result of studying the method, the method allows for smooth production of stabilized POM, but has economic problems, because the extruder must be lengthened to meet the requirements of the end stabilization zone with sufficient length.

It is an object of the present invention to provide an economically advantageous and simple method for producing practical stabilized POM copolymers in order to overcome the above mentioned problems. As will be described in detail, it is an object of the present invention to provide a process for preparing practical stabilized POM copolymers without the need for the decomposition and removal steps of unstable end portions that are commonly used. Another object of the present invention is to provide a practical method by inhibiting the oxidation of the POM copolymer having an unstable end portion as a raw material in the stabilization step when it takes some time until the POM copolymer as a raw material is supplied to the stabilization step due to transportation, storage, and the like. It is to provide a method for preparing a stabilized POM copolymer.

In connection with achieving the above object, the inventors of the present invention have thoroughly studied the process from the polymerization stage to the stabilization stage of the POM copolymer. As a result, in the polymerization step, the unstable end-containing POM copolymer, which is a raw material in the stabilization step, is added together with the hindered phenol; Suitably adjusting the particle size distribution during the grinding of the polymer; By adding a small amount of water to the raw material or adding water after the raw material is melt plasticized in the stabilization step, the oxidation and decomposition of the POM copolymer as the raw material is suppressed and operability problems such as a biting neck in the stabilization step Has been overcome and it has been found that the decomposition products of the POM polymer formed by pyrolysis upon melting can be easily removed by vacuum evacuation and on the basis of this the present invention has been completed.

In addition, when the unstable end-containing POM copolymer, which is a raw material in the stabilization step, has a certain amount of unstable end parts and has a moderately controlled particle size distribution, a small amount of water is added to the raw material or melt plasticized in the stabilization step, followed by water When added, the oxidation and decomposition of the POM copolymer as a raw material can be suppressed, and furthermore, it is possible to overcome operability problems such as biting neck in the stabilization step, so that the decomposition products of the POM polymer formed by pyrolysis at the time of melting can be easily removed by vacuum evacuation. It was found that it could be removed, and the present invention was completed based on this.

In the present invention, the following method is provided:

1. (A) Copolyoxymethylene having unstable end portions, wherein from 0.001 to 2.0% of hindered phenols, based on the weight of all monomers, are added to the monomer mixture, the monomer mixture is polymerized and the resulting crude polyoxy Methylene is pulverized so that (1) an average particle size of 0.3 to 0.7 mm, (2) a particle size of 3 to 20% by weight of particles larger than 1.0 mm, and (3) a particle size of 0.18 mm or more and 1.0 mm or less To obtain a powder having a specific particle size distribution having a content of 50 to 97% by weight and (4) a particle having a particle size of less than 0.18 mm and having a content of 0 to 30% by weight (total amount is 100% by weight), and the crude poly Using a copolymer obtained by deactivating a polymerization catalyst contained in oxymethylene;

(B) Copolyoxymethylene stabilized by stabilizing copolyoxymethylene having unstable end portions, characterized by adding water and a stabilizer to copolyoxymethylene as raw material and evacuating the molten mixture in vacuo. Manufacturing method;

2. (A) Copolymethylene having unstable end portions, containing 0.3 to 0.8% by weight of unstable end portions (based on the copolymer), (1) an average particle diameter of 0.3 to 0.7 mm, and (2) a particle diameter of 1.0 3 to 20% by weight of particles larger than mm, (3) 50 to 97% by weight of particles having a particle diameter of 0.18 mm or more and 1.0 mm or less, and (4) 0 to particles of particle size of less than 0.18 mm. Using a copolymer powder having a specific particle size distribution ranging from 30% by weight to 100% by weight in total;

(B) Copolyoxymethylene stabilized by stabilizing copolyoxymethylene having unstable end portions, characterized by adding water and a stabilizer to copolyoxymethylene as raw material and evacuating the molten mixture in vacuo. Manufacturing method;

3. A process for preparing a stabilized copolyoxymethylene as described in 1 or 2, which premixes water with a copolyoxymethylene feedstock having an unstable end portion;

4. Process for preparing stabilized copolyoxymethylene as described in 1 or 2, wherein water is added after melt plasticizing the copolyoxymethylene feedstock with labile end portions;

5. A process for preparing a stabilized copolyoxymethylene as described in any of 1-3, wherein the copolyoxymethylene feedstock having an unstable end portion is premixed with a stabilizer and water;

6. Premixing the copolyoxymethylene feedstock with labile end portions with the stabilizer, followed by melt plasticizing the copolyoxymethylene feedstock with labile end portions and then adding water to A process for preparing stabilized copolyoxymethylene as described;

7. A process for preparing stabilized copolyoxymethylene as described in any one of 1, 2 and 4, after melt plasticizing the copolyoxymethylene feedstock with labile end portions and then adding water and a stabilizer.

According to the invention, stabilized POM copolymers can be economically prepared, which can be seen from the results of the examples which will be described later.

The present invention will now be described in more detail.

The (crude) oxymethylene polymer (POM copolymer) to which the present invention can be applied is obtained by copolymerizing a cyclic acetal such as trioxane as main monomer and a cyclic ether or cyclic formal as comonomer in the presence of a cationic active catalyst. .

As used herein, a cyclic ether or cyclic formal is a cyclic compound containing one or more pairs of coupling carbon atoms and oxygen atoms. Examples are ethylene oxide, 1,3-dioxolane, 1,3,5-trioxetane, diethylene glycol formal, 1,4-butanediol formal, 1,3-dioxane and propylene oxide. Among them, preferred comonomers are ethylene oxide, 1,3-dioxolane, diethylene glycol formal and 1,4-butanediol formal. The comonomer is used in an amount of 0.1 to 20 mol%, preferably 0.2 to 10 mol%, based on trioxane as the main monomer.

When preparing the (crude) POM copolymer by copolymerization of such monomers and comonomers, the cationic catalyst originally used is used as a polymerization catalyst. Examples of cationic catalysts include Lewis acids, such as halides of boron, tin, titanium, phosphorus, arsene and antimony, for example boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentachloride, phosphorus pentafluoride, arsen pentafluoride and OH Esters of positive assets such as antimony fluoride, complexes or salts thereof, positive assets such as trifluoromethanesulfonic acid and perchloric acid, esters of perchloric acid and lower aliphatic alcohols (e.g. tertiary butyl ester of perchloric acid), positive Anhydrides of the assets, in particular mixed acid anhydrides of perchloric acid and lower fatty carboxylic acids (e.g. acetyl perchlorate), isopoly acids, heteropoly acids (e.g. phosphomolybdic acid), triethyloxonium hexafluorophosphate, triphenylmethyl hexa Fluoroarsenate and acetyl hexafluoroborate.

Of these, boron trifluoride and coordination compounds between boron trifluoride and organic compounds (eg ethers) are the most commonly used catalysts. Protic assets such as heteropolyacids or isopolyacids have high activity as catalysts, which readily provide high quality crude POM copolymers in small amounts and are easily deactivated. Therefore, it is preferable to prepare the crude POM copolymer by carrying out the polymerization in the presence of a catalyst selected from the catalyst or a mixture of two or more catalysts. If Lewis acids such as boron trifluoride are used as catalysts, it is preferred to add them in an amount of 15 to 25 ppm based on the monomer feedstock. In order to obtain high quality crude POM copolymers it is preferred to use monomers having a water content of 10 ppm or less.

In order to control the molecular weight of the crude POM copolymer obtainable by copolymerization, the polymerization may also be carried out by adding an appropriate amount of a suitable chain transfer agent, for example, an acetal compound such as methylal or dioxymethylene dimethyl ether.

The crude POM copolymer can be copolymerized by commonly known apparatus and methods, for example batch or continuous methods, or by melt polymerization or melt bulk polymerization. From an industrial point of view, a continuous bulk process is generally used and preferred in which the polymer is obtained as a solid powder mass as liquid monomers are used and as the polymerization proceeds. In this case, the polymerization can be carried out if necessary in the presence of an inert liquid medium. Examples of polymerization apparatus usable in the present invention include co-kneaders, twin-screw continuous extrusion mixers and puddle continuous mixers.

The present invention provides a powder having a specific particle size distribution by pulverizing the crude POM copolymer obtained by adding sterically hindered phenol, which is used as a raw material; Deactivating the polymerization catalyst contained in the powder copolymer; Adding water and a stabilizer to the feedstock of the POM copolymer; Provided is a process for preparing a stabilized POM copolymer characterized by evacuating the molten mixture in vacuo without substantially stabilizing and removing steps by decomposition of the end portions.

It is necessary to prepare the crude POM copolymer obtained by copolymerization in the presence of a hindered phenol (hindered phenol compound) which is an antioxidant. The hindered phenols prevent the resulting POM copolymer from being degraded by oxidation during polymerization and from being degraded by oxidation at high temperatures in subsequent steps to provide a high quality POM copolymer to the final stabilization step. The crude POM copolymer obtained by is suitable for applying the present invention.

The hindered phenol usable in the present invention preferably has a structure represented by the following general formula (1):

Wherein R ₁ and R ₂ are the same or different from each other and each has at least 4 carbon atoms.

Examples include 2,2'-methylenebis (4-methyl-6-t-butylphenol), hexamethylene glycol-bis (3,5-di-t-butyl-4-hydroxyhydrocinnamate), tetrakis [Methylene (3,5-di-t-butyl-4-hydroxyhydrocinnamate)] methane, triethylene glycol-bis-3- (3-t-butyl-4-hydroxy-5-methylphenyl) propio Nate, 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxy-benzyl) benzene, n-octadecyl-3- (4'-hydroxy -3 ', 5'-di-t-butylphenol) propionate, 4,4'-methylenebis (2,6-di-t-butylphenol), 4,4'-butylidene-bis- ( 6-t-butyl-3-methyl-phenol), 2,2'-thiodiethyl-bis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, di- Stearyl-3,5-di-t-butyl-4-hydroxybenzylphosphonate, 2-t-butyl-6- (3-t-butyl-5-methyl-2-hydroxybenzyl) -4- Methylphenylacrylate is included. The hindered phenols exemplified above may be used alone or as a mixture. Examples are not limiting and all sterically hindered phenols of the same type are available. Hexamethylene glycol-bis (3,5-di-t-butyl-4-hydroxyhydrocinnamate), such as Irganox 259 (trade name, manufactured by Ciba Geigy), Iganox 1010 A tree such as Tetrakis [methylene (3,5-di-t-butyl-4-hydroxyhydrocinnamate)] methane and Iganox 245 (trade name, manufactured by Ciba-Geigy) Ethylene glycol-bis-3- (3-t-butyl-4-hydroxy-5-methylphenyl) propionate is particularly effective. On the other hand, if any substance other than sterically hindered phenol is added to the monomer, which is generally used as a stabilizer for amines, amidines and polyacetals, the polymerization does not occur.

It is effective to add even minor traces of sterically hindered phenol to the monomer prior to the polymerization step. Phenol is used at 0.001 to 2.0% by weight, particularly preferably 0.005 to 1.0% by weight, based on all monomers. Adding an amount less than the above range is less effective for preventing oxidation and decomposition, while adding more than the above range is not economical because it tends to decrease the polymerization reaction rate. Therefore, it is not preferable to use an amount other than the above range.

In the process of adding sterically hindered phenol to the monomer, sterically hindered phenol is added to the liquid monomer to dissolve the hindered phenol in the monomer, or the hindered phenol is added in the form of a solution dissolved in a small amount of solvent inert to the polymerization reaction. . In the case of continuous polymerization, a certain amount of sterically hindered phenol is fed to the monomer line fed to the polymerizer and then mixed and dissolved in the monomer to supply the resulting solution to the polymerizer or added or dissolved in advance in the monomer layer upon storage. .

The crude POM copolymer thus polymerized was then pulverized to (1) an average particle diameter of 0.3 to 0.7 mm, (2) a particle size of 3 to 20% by weight of particles larger than 1.0 mm, and (3) a particle diameter of 0.18 mm. Powder having a specific particle size distribution of 50 to 97% by weight of particles having a particle size of 1.0 mm or less, and having a particle size of 0 to 30% by weight (total amount of 100% by weight) of particles having a particle size of less than 0.18 mm. To obtain.

The inventors of the present invention find that the quality of the POM copolymer obtained by grinding and deactivation of the catalyst, in particular the amount of unstable end portions; And extensive particle size distribution have been found in connection with satisfying both the operability in the step of stabilizing the ground POM copolymer in a molten state with water and a stabilizer followed by evacuation in vacuum.

Among the above requirements, the upper limit of the average particle diameter in (1) (0.7 mm) and the upper limit of the ratio of particles having a particle diameter larger than 1.0 mm in (2) are the main requirements for determining the quality of the POM copolymer. On the other hand, the lower limit of the average particle diameter (0.3 mm) in (1), the lower limit of the ratio of particles having a particle size larger than 1.0 mm in (2) and the upper limit of the ratio of particles having a particle size smaller than 0.18 mm in (4) It is a major requirement for determining the operability in the stabilization stage with a stabilizer.

When the particle diameter is larger than the particle size distribution, for example, when the average particle diameter is larger than its upper limit or the ratio of particles having a particle size larger than 1.0 mm is larger than its upper limit, the quality of the pulverized POM copolymer is deteriorated, in particular. The amount of unstable end portions increases, making it difficult to produce POM copolymers with sufficient stability to be commercially available only by stabilization with stabilizers without undergoing stabilization of the end portions by decomposition and removal of the unstable end portions. When the particle diameter is smaller than the particle size distribution, for example, the ratio of particles having a particle size whose average particle diameter is smaller than its lower limit or larger than 1.0 mm is smaller than its lower limit or that the particle ratio having a particle size smaller than 0.18 mm is larger than its upper limit. In this case, since the operability in the stabilization step of kneading with a stabilizer instead of satisfactory quality of the POM copolymer is significantly lowered, it becomes difficult to economically prepare a stabilized POM copolymer.

In view of the foregoing, the preferred particle size distribution that can satisfy both the better quality of the POM copolymer and the operability in the stabilization step is (1) 'average particle size is 0.4 to 0.7 mm, and (2)' particle size is 1.0 mm (3) the particle size is larger than 5 to 15% by weight, the particle size is greater than or equal to 0.18 mm and the particle size is less than or equal to 1.0 mm, and the particle size is less than 0.18 mm. 0 to 25% by weight (total amount is 100% by weight).

In the case of grinding as described above, the grinder to be used is not particularly limited. For example, rotary mills, hammer mills, jaw crushers, feather mills, rotary cutter mills, turbo mills and classified impacts Classifying type impact pulverizer. The specific particle size distribution can be adjusted by rotational speed or by the clearance of the grinder, or by a screen mesh attached to the grinder and / or an individually attached shift as required.

Conventionally known methods can be used to deactivate the catalyst contained in the crude POM copolymer. In the present invention, deactivation is performed by grinding the crude POM copolymer into a powder having the above-described particle size distribution by wet grinding using an aqueous solution of an organic or inorganic basic compound such as triethylamine, triethanolamine, sodium carbonate or calcium hydroxide. It is preferable. Among them, it is preferred to add a deactivator in the path from the point just before the exit of the polymer to the inlet of the mill (in this case a high quality POM copolymer can be obtained). After deactivation and pulverization of the catalyst, the POM copolymer is washed, dried and other processes as required. The crude POM copolymer thus treated can be used as raw material for the stabilization step.

The present invention uses, as a raw material, a POM copolymer having an unstable end portion of 0.3 to 0.8% by weight based on the copolymer and having a specific particle size distribution; Water and a stabilizer are added to the resulting POM copolymer; Another method of preparing a stabilized polyoxymethylene copolymer in the stabilization step of a polyoxymethylene copolymer having unstable end portions is characterized by evacuating the mixture in a molten state in vacuo.

Incidentally, the amount of unstable end portions of the POM copolymer as used herein refers to the amount of formaldehyde based on the copolymer (% by weight), which is a 50% methanol aqueous solution containing 1 g of POM copolymer and 0.5% of ammonium hydroxide. 100 ml was filled into a closed pressure vessel, the resulting mixture was heated at 180 ° C. for 45 minutes, cooled, the liquid was removed from the vessel and the amount was analyzed by analyzing the amount of decomposed formaldehyde and eluted formaldehyde into the liquid. Measure

The polymerization product comprises an organic or inorganic basic such as triethylamine, triethanolamine, sodium carbonate or calcium hydroxide, either by a polymerization process comprising the addition of sterically hindered phenol, or in the case of deactivation after polymerization if no sterically hindered phenol is added. The compound is dissolved in a methanol solution and the POM copolymer is then precipitated again to adjust the amount of unstable end portions to fall within the range of 0.3 to 0.8 weight percent. The crude POM copolymer thus obtained has (1) an average particle diameter of 0.3 to 0.7 mm, (2) a particle size of 3 to 20% by weight of particles larger than 1.0 mm, (3) a particle diameter of 0.18 mm or more and 1.0 50 to 97% by weight of particles having a thickness of less than or equal to (4) formed of a powder capable of satisfying the particle size distribution having a content of 0 to 30% by weight (total amount of 100% by weight) of particles having a particle diameter of less than 0.18 mm To provide it as a raw material.

A stabilizer and water are added to the raw crude POM copolymer thus prepared and the resulting mixture is evacuated in vacuo in a molten state to obtain a stabilized POM copolymer.

The present invention uses the POM copolymer thus prepared as a raw material; Water is added to the raw material during the stabilization step to obtain a stabilized POM copolymer, and then the resulting mixture is mixed with a stabilizer or the like, remaining in the raw material or volatile compounds such as decomposition products of the POM polymer produced during the stabilization step (form Aldehyde gas).

It is preferred to add 0.05% to 5.0% by weight, preferably 0.5 to 3.0% by weight of water, based on the weight of the raw material. It is not desirable to remove volatile components in an amount below this range, whereas using an amount larger than this range is undesirable because the water will remain in the kneaded mixture. Water may be added after premixing with the raw material or after melt plasticizing the raw material. In the former method, water can be dispersed in advance, and sufficient water can be dispersed after melt plasticization. It is not desirable to add water during melt plasticization because there is a risk that large amounts of water are present locally to inhibit plasticization of the raw material or that there is an unplasticized portion mixed with the raw material.

Useful stabilizers herein are not particularly limited and any known stabilizer may be used. However, antioxidants and heat stabilizers are generally used in mixtures.

Examples of antioxidants include 1,6-hexanediol-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], pentaerythritol tetrakis [3- (3,5 -Di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] and N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-cinnamate).

Examples of heat stabilizers include triazine compounds such as melamine and melamine-formaldehyde concentrates, polyamides such as nylon 12 and nylon 6.10; Hydroxides, carbonates, phosphates, acetates and oxalates of alkali or alkaline earth metals; And metal salts of higher fatty acids with substituents such as hydroxyl or higher fatty acids such as stearic acid.

Various additives may be added to the POM copolymer of the present invention depending on the purpose. For example, weather resistant (photo) stabilizers, lubricants, nucleators, mold release agents, antistatic agents, dyes, pigments, other organic polymeric materials, and inorganic and organic fibrous, plate or powder fillers.

Examples of devices usable in the stabilization step of the present invention include continuous extruders such as twin-screw extruders equipped with vents and single screw extruders equipped with vents. Volatile components are removed from the exhaust port under reduced pressure.

The present invention will now be described with reference to Examples and Comparative Examples, but it should be understood that the present invention is not limited by the following Examples.

Assessment Methods

Extrudeability (biting characteristics of raw materials)

When the stabilizer is incorporated into the powder POM copolymer and the mixture is melt-kneaded in the extruder, the state of raw material biting into the extruder and the state of stabilized POM exiting the extruder are observed. These are evaluated in three grades A to C below.

A: Both the biting state and the discharged strand are stable.

B: The biting condition is sometimes poor and the thickness of the strands fluctuates.

C: Variation in biting condition is slightly severe, fluctuation in strand thickness is large and the strand sometimes breaks

The amount of unstable end portions of the POM copolymer

100 ml of 50% aqueous methanol solution containing 0.5% ammonium hydroxide and 1 g of POM copolymer were charged into a closed pressure vessel and heated at 180 ° C. for 45 minutes. The reaction mixture is cooled down and taken out of the vessel. The amount of formaldehyde dissolved and dissolved in the solution is determined by analysis and expressed as weight percent based on the copolymer.

Content of monomers (formaldehyde) in the polymer (amount of formaldehyde extracted)

2 g of POM copolymer was charged to 40 ml of distilled water and then refluxed while boiling for 1.5 hours. The amount of formaldehyde extracted in water is then determined by analysis and expressed as parts by weight based on the polymerized product.

Examples 1-5, Comparative Examples 1-5

Preparation of Crude POM Copolymer (POM Copolymer with Unstable End) Feedstock

In each example, trioxane and 2.5% by weight (based on total monomers) of 1,3-dioxolane are continuously fed to a pair-puddle continuous polymerizer and the polymerization is carried out in the presence of boron trifluoride or phosphomolybdic acid as a catalyst. Was performed. In some embodiments, tetrakis [methylene (3,5-di-t-butyl-4-hydroxycinnamate)] methane (Irganox 1010, trade name, Ciba-Geigy) is 0.05% (all monomers) In an amount, based on the amount of, and not added in other examples (shown in Tables 1 and 2). The crude POM copolymer discharged from the outlet of the polymerizer terminal was dehydrated and dried, wet pulverized and the catalyst was deactivated to obtain a powdery POM copolymer having a particle size distribution shown in Table 1 or Table 2.

The particle size was adjusted by varying the number of revolutions of the size or shape of the screen mesh.

Stabilization treatment

0.45% by weight of tetrakis [methylene (3,5-di-t-butyl-4-hydroxycinnamate)] methane (Irganox 1010, trade name, Ciba-Geigy Products) ) And 0.1% by weight calcium stearate and melt kneaded in a single or twin screw extruder equipped with vents. At this time, (1) water is added after premixing with the feedstock, (2) melt-plasticizing the feedstock, and then water is added, or (3) water is not added.

The results are shown in Table 1 and Table 2.

In the table below, the abbreviations have the following meanings.

Particle size distribution

Within range: Within the range of particle size distribution as described in claim 1

Out of range 1: Outside the range of particle size distribution described in claim 1 (content of particles having a particle diameter of less than 0.18 mm exceeds 30% by weight)

Out of range 2: Outside the particle size distribution range described in claim 1 (content of particles having a particle size of 1.00 mm or more exceeds 20% by weight)

How to add

Injection: add water to the extruder after melt plasticization of feedstock

Premix: Add water after mixing water with raw material

Type of catalyst

BF ₃ : boron trifluoride

HPA: Phosphomolybdic Acid

Example 1 Example 2 Example 3 Example 4 Example 5 Manufacture of raw materials Addition of Iganox 1010 adding adding adding adding adding Type of catalyst BF ₃ BF ₃ BF ₃ BF ₃ HPA Amount of catalyst added (ppm) 20 20 20 20 5 Particle size distribution In range In range In range In range In range Stabilization stage Extruder shorten shorten Biaxial Biaxial Biaxial % Of water added 2 2 2 2 2 How to add Injection Premix Injection Premix Injection Extrudability A A A A A Evaluation (after extrusion) % Of unstable distal end 0.41 0.49 0.40 0.45 0.50 Amount of formaldehyde extracted (ppm) 65 78 63 70 80

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Manufacture of raw materials Addition of Iganox 1010 No addition adding adding adding adding Type of catalyst BF ₃ BF ₃ BF ₃ BF ₃ BF ₃ Amount of catalyst added (ppm) 20 20 20 20 20 Particle size distribution In range 1 out of range 2 out of range In range In range Stabilization stage Extruder shorten shorten shorten shorten shorten % Of water added 2 2 2 - 5.5 How to add Injection Premix Injection - Injection Extrudability A C A A B Evaluation (after extrusion) % Of unstable distal end 0.59 0.50 0.92 0.61 0.83 Amount of formaldehyde extracted (ppm) 152 96 182 253 70

Examples 6-8, Comparative Examples 6-9

Preparation of Crude POM Copolymer (POM Copolymer with Unstable End) Feedstock

In each example, the tri-puddle continuous polymerizer was continuously fed trioxane and 2.5% by weight (based on total monomers) of 1,3-dioxolane and polymerization was carried out in the presence of 20 ppm boron trifluoride as catalyst. The crude POM copolymer discharged from the outlet at the end of the polymerizer was dissolved in a methanol solution containing 0.25% by weight of triethylamine while heating at 180 ° C., and cooled to precipitate the POM copolymer. The solvent was removed from the resulting precipitate, dried and dried to give a powdered POM polymer having a predetermined particle size distribution. The amount of unstable end portion of the POM copolymer raw material was controlled by changing the residence time in methanol solution at 180 ° C.

Stabilization treatment

The powdered POM copolymer thus obtained was prepared by mixing 0.5 wt% of tetrakis [methylene (3,5-di-t-butyl-4-hydroxycinnamate)] methane (Iganox 1010, trade name, manufactured by Ciba-Geigy) and 0.1 It is mixed with wt% calcium stearate and melt kneaded in an exhaust or single screw or twin screw extruder. At this time, water is added after (1) premixing the water with the feedstock, or (2) water is added after melt plasticizing the feedstock, or (3) no water is added.

The results are shown in Tables 3 and 4.

In the following table, the abbreviations have the following meanings:

Particle size distribution

Within range: Within the range of particle size distribution as described in claim 1

Out of range 1: Outside the range of particle size distribution described in claim 1 (content of particles having a particle size of less than 0.18 mm exceeds 30% by weight)

Out of range 2: Outside the particle size distribution range described in claim 1 (content of particles having a particle diameter of 1.00 mm or more exceeds 20% by weight)

How to add

Injection: add water to the extruder after melt plasticization of feedstock

Premix: Add water after mixing water with raw material

Example 6 Example 7 Example 8 Manufacture of raw materials % Of unstable distal end 0.45 0.45 0.45 Particle size distribution In range In range In range Stabilization stage Extruder shorten shorten Biaxial % Of water added 2 2 2 How to add Injection Premix Injection Extrudability A A A Evaluation (after extrusion) % Of unstable distal end 0.25 0.31 0.20 Amount of formaldehyde extracted (ppm) 63 75 50

Example 6 Example 7 Example 8 Example 9 Manufacture of raw materials % Of unstable distal end 0.45 0.44 0.46 0.70 Particle size distribution In range 1 out of range 2 out of range In range Stabilization stage Extruder shorten shorten shorten shorten % Of water added - 2 2 2 How to add - Injection Injection Injection Extrudability A C A A Evaluation (after extrusion) % Of unstable distal end 0.38 0.35 0.50 0.61 Amount of formaldehyde extracted (ppm) 110 76 110 300

The present invention provides an economically advantageous and simple method for producing a practical stabilized POM copolymer that can overcome the problems arising in the prior art. Specifically, there is provided a process for preparing a practical stabilized POM copolymer without the need for the decomposition and removal steps of commonly used unstable ends. Also provided is a method of producing a practical stabilized POM copolymer by inhibiting oxidation of the POM copolymer having unstable end portions as a raw material in the stabilization step.

Claims (7)

(A) Copolyoxymethylene with unstable end portions, wherein from 0.001 to 2.0% of hindered phenols, based on the weight of all monomers, are added to the monomer mixture, the monomer mixture is polymerized and the crude polyoxymethylene obtained as a result of Pulverization, (1) the average particle size is 0.3 to 0.7mm, (2) the particle content is 3 to 20% by weight of the particle size larger than 1.0mm, and (3) the particle size is 0.18mm or more and 1.0mm or less 50 to 97% by weight, and (4) a powder having a specific particle size distribution having a particle size of 0 to 30% by weight (with a total of 100% by weight) in a particle size of less than 0.18 mm, wherein the crude polyoxymethylene Using a copolymer obtained by deactivating the polymerization catalyst contained in the; (B) Copolyoxymethylene stabilized by stabilizing copolyoxymethylene having unstable end portions, characterized by adding water and a stabilizer to copolyoxymethylene as raw material and evacuating the molten mixture in vacuo. How to manufacture. (A) Copolyoxymethylene having unstable end portions, containing 0.3 to 0.8% by weight of unstable end portions (based on copolymer), (1) an average particle diameter of 0.3 to 0.7 mm, and (2) a particle diameter of 1.0 mm 3 to 20% by weight of large particles, (3) 50 to 97% by weight of particles having a particle diameter of 0.18 mm or more and 1.0 mm or less, and (4) 0 to 30 of particles having a particle size of less than 0.18 mm. Using a copolymer powder having a specific particle size distribution that is weight percent (total weight is 100 weight percent); (B) Copolyoxymethylene stabilized by stabilizing copolyoxymethylene having unstable end portions, characterized by adding water and a stabilizer to copolyoxymethylene as raw material and evacuating the molten mixture in vacuo. How to manufacture. The method according to claim 1 or 2, A process for preparing stabilized copolyoxymethylene, wherein the copolyoxymethylene feedstock having labile end portions is premixed with water. The method according to claim 1 or 2, A process for producing a stabilized copolyoxymethylene, wherein water is added after melt plasticizing the copolyoxymethylene feedstock with labile end portions. The method according to any one of claims 1 to 3, A process for preparing stabilized copolyoxymethylene, wherein the copolyoxymethylene feedstock having labile end portions is premixed with the stabilizer and water. The method according to any one of claims 1, 2 and 4, A method of making a stabilized copolyoxymethylene, wherein the copolyoxymethylene feedstock with labile end portions is premixed with a stabilizer and water is added after melt plasticizing the copolyoxymethylene feedstock with labile end portions. The method according to any one of claims 1, 2 and 4, A process for preparing stabilized copolyoxymethylene, wherein water and a stabilizer are added after melt plasticizing the copolyoxymethylene feedstock with labile end portions.