JPH0739453B2 - Method for stabilizing oxymethylene copolymer - Google Patents

Description

The present invention relates to a method for stabilizing an end-unstabilized oxymethylene copolymer.

(Prior Art) It is known that an end-unstabilized oxymethylene copolymer having a thermolabile moiety consisting of an oxymethylene unit at the main chain terminal is obtained by copolymerization of formaldehyde or a cyclic oligomer thereof and cyclic formal. Is. The heat-unstable portion of this terminal-unstabilized oxymethylene copolymer is
Must be disassembled and removed prior to use.

Several methods have been proposed as methods for decomposing and removing the heat-unstable portion. In Japanese Patent Publication No. Sho 53-36876,
A method of heating an end-unstabilized oxymethylene copolymer in the presence of a metal salt of ethylenediaminetetraacetic acid in a water-alcohol mixed solvent is described. In addition, Japanese Examined Japanese Patent Sho 55-45
Japanese Patent No. 087 discloses a method of heating an end-unstabilized oxymethylene copolymer in the presence of a trivalent organic phosphorus compound, a phenolic antioxidant and a metal hydroxide.

(Problems to be Solved) The method described in Japanese Patent Publication No. Sho 53-36876 stabilizes the oxymethylene copolymer in a large amount of solvent. Therefore, in an industrial process, recovery and purification of the solvent should be performed after stabilization. It needs to be done and requires equipment and expense for it.

The method disclosed in Japanese Examined Patent Publication No. 55-45087 is suitable as an industrial process because it does not use a solvent and thus does not cause the inconvenience as in the above method. However, in this method, it is necessary to heat the unmodified unstabilized oxymethylene copolymer in the vicinity of its melting point, and in order to prevent the decrease in the molecular weight of the copolymer due to the breaking of the main chain, the heat treatment time should be as short as possible. Although it is desired to impart sufficient thermal stability while shortening it, it is difficult to satisfy both at the same time.

(Object of the invention) The object of the present invention is that the thermal decomposition stabilization can be carried out in a short time, in other words, the reduction of the molecular weight can be prevented,
Another object of the present invention is to provide a method for stabilizing an oxymethylene copolymer having an unterminated end that can impart sufficient thermal stability.

(Summary of the Invention) According to the present invention, a composition of an end-unstabilized oxymethylene copolymer and a thermal decomposition stabilizer is heated to a temperature equal to or higher than the melting point of the copolymer to give a composition of the copolymer. When decomposing and removing the terminal unstable portion, the decomposition removal by heating is performed by 10 to 100 parts by weight of water and / or an aliphatic alcohol having 1 to 4 carbon atoms per 100 parts by weight of the terminal unstabilized oxymethylene copolymer (hereinafter A method for stabilizing an oxymethylene copolymer is provided, which is characterized by being carried out in the presence of "alcohol").

DETAILED DESCRIPTION OF THE INVENTION The end-unstabilized oxymethylene copolymer used in the present invention is derived from 0.1 to 10 mol%, preferably 1 to 4 mol% of cyclic formal in the oxymethylene repeating unit. It is a copolymer having a unit and a thermolabile moiety composed of a repeating unit of oxymethylene at its molecular end.

Examples of the above cyclic formal include the general formula The compound represented by In the above formula, R ₁ ,
_{R 2, R 3, R 4} , R 5 and R ₆ are each a hydrogen atom, an alkyl group, an allyl group and a cycloalkyl group, 1, m and n is an integer from 1 to 6 respectively and 1, At least one of m and n is an integer of 2 or more, and a, b and c
Are 0 or 1, respectively.

Specific examples of the cyclic formal include ethylene oxide, propylene oxide, butene-1-oxide,
1,3-Butadiene-1-oxide, styrene oxide, α-methylstyrene oxide, oxetane, tetrahydrofuran, 1,3-dioxolane, 4-phenyl-
1,3-dioxolane, 2-methyl-1,3-dioxolane,
1,3-dioxepane, 2-butyl-1,3-dioxepane,
Included are 1,3,6-trioxocane, 1,3,5-trioxepane and polyethylene glycol formal.

The terminal unstabilized oxymethylene copolymer is a known method,
For example, a method of copolymerizing formaldehyde or trioxane and cyclic formal in the presence of a Lewis acid such as boron trifluoride or its ether complex, and reacting an oxymethylene homopolymer with a cyclic formal in the presence of a Lewis acid. Can be prepared by any method.

Examples of the thermal decomposition stabilizer used in the present invention include alkali metal salts or alkaline earth metal salts of nitrilotriacetic acid or ethylenediaminetetraacetic acid (referred to as stabilizer (1)), hydroxides of alkaline earth metal (stabilizer). (Referred to as (2)), a phenolic antioxidant (referred to as stabilizer (3)), an amine-substituted triazine compound and / or a cyanoguanidine compound (referred to as stabilizer (4)), and the like.

Examples of the alkali metal or alkaline earth metal in the stabilizer (1) include sodium, potassium, magnesium, calcium and barium. Specific examples of the stabilizer (1) include trisodium nitrilotriacetate, tripotassium nitrilotriacetate, sodium calcium nitrilotriacetate, potassium barium nitrilotriacetate, tetrasodium ethylenediaminetetraacetate, tetrapotassium ethylenediaminetetraacetate, ethylenediamine. Examples thereof include disodium tetraacetate-calcium, disodium ethylenediaminetetraacetate-magnesium, dicalcium ethylenediaminetetraacetate, and dibarium ethylenediaminetetraacetate.

Specific examples of the stabilizer (2) include magnesium hydroxide,
Included are calcium hydroxide and barium hydroxide.

Specific examples of the stabilizer (3) include 2,2'-methylenebis (4-methyl-6-t-butylphenol) and 4,4'-
Methylenebis (2,6-di-t-butylphenol), 2,6
-Di-t-butyl-4-hydroxymethylphenol,
Triethylene glycol-bis-3- (3'-t-butyl-4'-hydroxy-5'-methylphenyl) propionate, 1,6-hexanediol-bis-3- (3 ',
5'-di-t-butyl-4'-hydroxyphenyl) propionate, pentaerythrityl-tetrakis-3-
(3 ', 5'-di-t-butyl-4'-hydroxyphenyl) propionate, 1,3,5-trimethyl-2,4,6-tris (3', 5'-di-t-butyl-4) '-Hydroxybenzyl) benzene, distearyl-3,5-di-t-butyl-hydroxybenzylphosphonate, 2,6,7-trioxa-1-phosphobicyclo [2.2.2] -oct-4-
Iyl-methyl-3 ', 5'-di-t-butyl-4'-hydroxyphenyl-propionate, 3,5-di-t-butyl-4-hydroxybenzyldimethylamine, and 3,5
-Di-t-butyl-4-hydroxyphenyl-3 ', 5'
-Distearyl-thiotriazylamine.

Specific examples of the amine-substituted triazine compound in the stabilizer (4) include melamine, N-butylmelamine, N-phenylmelamine, N, N'-diphenylmelamine, N, N ',
Examples thereof include N ″ -triphenylmelamine, ethylene dimelamine, melam, melem, guanamine, and benzoguanamine. Specific examples of the cyanoguanidine compound in the stabilizer (4) include dicyandiamide and 1-cyano-3-methylguanidine. , 1-cyano-3-ethylguanidine, and 1-cyano-3-isopropylguanidine.

These stabilizers can be used alone, but it is preferable to use at least one of the stabilizer (2), the stabilizer (3) and the stabilizer (4) together with the stabilizer (1).
Best results can be obtained when the above stabilizers are used simultaneously. The amount of the stabilizers (1) to (4) used is preferably 0.001 to 2 parts by weight, and particularly preferably 0.01 to 1 part by weight, per 100 parts by weight of the terminal-unstabilized oxymethylene copolymer.

If the amount of the stabilizer (1) used is too small, it takes a long time to decompose the terminal heat-labile portion of the terminal-unstabilized oxymethylene copolymer, and as a result, the main chain of the copolymer is cleaved. Like If the amount of the stabilizer (2), the stabilizer (3) or the stabilizer (4) used is too small, the thermal stability of the oxymethylene copolymer after the stabilization treatment will be insufficient.
Even if the amount of the thermal decomposition stabilizer used is excessively increased, no further effect is exhibited, which is economically disadvantageous.

There is no particular limitation on the method for preparing the composition of the terminal-unstabilized oxymethylene copolymer and the thermal decomposition stabilizer, a method of dry-blending the two, and adding the copolymer to the solution of the thermal decomposition stabilizer. A method known per se such as a method of removing the solvent after mixing can be appropriately adopted.

In the present invention, the composition of the terminal-unstabilized oxymethylene copolymer and the thermal decomposition stabilizer is heated to a temperature equal to or higher than the melting point of the copolymer in the presence of water and / or alcohol to obtain a copolymer. The thermally unstable portion consisting of oxymethylene unit at the terminal of the main chain of the polymer is decomposed and removed.

Water and / or alcohol may be supplied in gaseous form,
It may be supplied in liquid form. Examples of the former mode include a method of supplying gaseous water and / or alcohol to the gas phase part of the thermal decomposition reactor, and the latter mode includes thermal decomposition stability impregnated with water and / or alcohol. There is a method in which the agent is mixed with an end-unstabilized oxymethylene copolymer, and this mixture is supplied to a thermal decomposition reactor.

Specific examples of alcohol include methanol, ethanol,
Isopropanol may be mentioned.

The amount of water and / or alcohol used is 10 to 100 parts by weight per 100 parts by weight of the terminal-unstabilized oxymethylene copolymer. When the amount of water and / or alcohol used is less than the above lower limit, when a stabilized oxymethylene copolymer having practically sufficient thermal stability is to be obtained, the main chain of the copolymer is cleaved to cause The molecular weight of the polymer is reduced. That is, it takes a long time to decompose and remove the thermally unstable portion at the end of the main chain of the terminal-unstabilized oxymethylene copolymer, so that the main chain is cleaved by heat. Even if water and / or alcohol is used in excess of the above upper limit, the thermal decomposition time does not become shorter.

If the heating temperature is lower than the above lower limit, an oxymethylene copolymer having practically sufficient thermal stability cannot be obtained. The preferred heating temperature is in the range of melting point to a temperature 80 ° C. higher than the melting point. The upper limit of heating temperature is usually 245 ° C. If the heating temperature is excessively high, the main chain of the oxymethylene copolymer will be cleaved. The heating time varies depending on the heating temperature, but is usually 5 to 60 minutes.

As the thermal decomposition apparatus, an apparatus capable of sufficiently renewing the surface of the melt is preferably used in order to efficiently remove gases such as formaldehyde generated by thermal decomposition. Such an apparatus is described, for example, in Japanese Examined Patent Publication No. 50-21514. As described above, water and / or alcohol can be supplied to the thermal decomposition apparatus in the form of gas or liquid, but when supplied in the form of gas, this can be used as a carrier gas for the decomposition gas, and in the form of liquid. When supplied, it is desirable to circulate nitrogen gas or the like for carrying the decomposition gas.

(Example) An example and a comparative example are shown below.

The intrinsic viscosity of the oxymethylene copolymer was measured at 60 ° C. using p-chlorophenol containing 2% α-pinene as a solvent. A ₂₂₂ is the weight loss rate (% / min) of the stabilized oxymethylene copolymer in an air atmosphere at 222 ° C. In the following, all "parts" indicate "parts by weight".

Examples 1 and 2 100 parts of terminally unstabilized oxymethylene copolymers containing 1.58 mol% of units derived from 1,3,6-trioxocane and an intrinsic viscosity of 1.43 dl / g and described in Table 1. The thermal decomposition stabilizer of was mixed in a powder state, and the mixed powder was charged into a biaxial stirring reactor. The mixture was heated to 200 ° C. while flowing water vapor from the inlet side of the reactor, and was decompressed on the outlet side of the reactor to forcibly discharge the decomposition gas for a predetermined time.

The color tone of each of the obtained stabilized oxymethylene copolymers was white. The physical properties of the stabilized copolymer are shown in Table 1.

Example 3 The thermal decomposition stabilizer described in Table 1 was immersed in water and stirred, and the resulting mixture was blended with the same terminal-unstabilized oxymethylene copolymer as in Example 1 and then depressurized. Dried. The mixture was charged into the reactor used in Example 1, heated to 200 ° C. while flowing nitrogen gas from the inlet side, decompressed at the outlet side of the reactor and forcibly exhausted decomposition gas, and treated for a predetermined time. .

The color tone of the obtained stabilized oxymethylene copolymer was white. The physical properties of the stabilized copolymer are shown in Table 1.

Example 4 The same method as in Example 3 was repeated except that ethanol was used instead of water. The color tone of the obtained stabilized oxymethylene copolymer was white. The physical properties of the stabilized copolymer are shown in Table 1.

Comparative Example 1 The same method as in Example 1 was repeated except that nitrogen gas was used instead of steam. The color tone of the obtained stabilized oxymethylene copolymer was white. The physical properties of the stabilized copolymer are shown in Table 1.

Comparative Example 2 The same method as in Comparative Example 1 was repeated except that the heating time was changed to 60 minutes. The color tone of the obtained stabilized oxymethylene copolymer was white. The physical properties of the stabilized copolymer are shown in Table 1.

(Effects of the invention) As can be seen from Table 1, according to the present invention, the thermally unstable terminal portion of the terminally unstabilized oxymethylene copolymer is decomposed and removed in a short time, and the obtained stabilized oxymethylene copolymer is obtained. Has excellent thermal stability. On the other hand, according to the known method, it takes a long time to decompose and remove the heat labile portion, and the molecular weight of the obtained stabilizing copolymer is lowered and the thermal stability is insufficient.

Claims (1)

[Claims] 1. A composition comprising an end-unstabilized oxymethylene copolymer and a thermal decomposition stabilizer is heated to a temperature equal to or higher than the melting point of the copolymer to decompose the end-unstable portion of the copolymer. When removing, decomposition and removal by heating are performed in the presence of 10 to 100 parts by weight of water and / or an aliphatic alcohol having 1 to 4 carbon atoms per 100 parts by weight of the terminal-unstabilized oxymethylene copolymer. A method for stabilizing an oxymethylene copolymer.