JPH072893B2 - Method for stabilizing oxymethylene copolymer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for stabilizing an oxymethylene copolymer.

(Prior art and its problems) By copolymerization of formaldehyde or a cyclic oligomer thereof and cyclic formal, an end-unstable oxymethylene copolymer having a heat labile part composed of an oxymethylene unit at the main chain end is obtained. It is known that this is done. The heat labile portion of this unstabilized oxymethylene copolymer must be removed prior to use. As the removal method, for example, in a water-alcohol mixed solvent, in the presence of a metal salt of ethylenediaminetetraacetic acid, a method of heating the terminal unstabilized oxymethylene copolymer (Japanese Patent Publication No. Sho 36-36876), trivalent A method (Japanese Patent Publication No. 55-45087) of heating an end-unstabilized oxymethylene copolymer in the presence of an organic phosphorus compound, a phenolic antioxidant and a metal hydroxide has been proposed.

Since the former method stabilizes the oxymethylene copolymer in a large amount of solvent, it is necessary to recover and purify the solvent after stabilization in an industrial process, which requires equipment and cost.

In the latter method, since no solvent is used, the inconvenience as in the former method does not occur, and it is suitable as an industrial process. In this method, it is necessary to heat the unstabilized copolymer in the vicinity of its melting point, and it is desirable to shorten the heat treatment time as much as possible in order to prevent the reduction of the molecular weight due to the breakage of the main chain. It is hard to say that the proposed method is still sufficient from the viewpoint of shortening the heat treatment time.

(Object of the Invention) An object of the present invention is to provide a method for stabilizing an oxymethylene copolymer capable of completing thermal decomposition stabilization in a short time.

(Summary of the Invention) According to the present invention, (1) an alkali metal salt or an alkaline earth metal salt of nitrilotriacetic acid (hereinafter referred to as compound (1)), (2) phenol -Based antioxidant (hereinafter referred to as compound (2)), (3) hydroxide of alkaline earth metal (hereinafter referred to as compound (3)), and (4) trivalent organic phosphorus compound (hereinafter referred to as compound (4)) A method for stabilizing an oxymethylene copolymer is provided, which comprises heating the composition containing the above) to a temperature equal to or higher than the melting point of the above copolymer.

(Detailed Description of the Invention) The terminal unstabilized oxymethylene copolymer in the present invention is 0.1 to 10 mol% in the oxymethylene repeating unit,
It is preferably a copolymer having 1 to 4 mol% of units derived from cyclic formal and having a thermolabile moiety composed of repeating units of oxymethylene at its molecular end.

Examples of the cyclic formal include the formula A compound represented by The compound represented by In both formulas above,
R ₁ , R ₂ , R ₃ and R ₄ represent a hydrogen atom, an alkyl group, an allyl group and a cycloalkyl group, respectively, and m is 1 to 3.
And n is an integer of 2 to 6.

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 alkali metal or alkaline earth metal in the compound (1) include sodium, potassium, magnesium, calcium and barium. Specific examples of compound (1) include trisodium nitrilotriacetate, tripotassium nitrilotriacetate, sodium calcium nitrilotriacetate, and potassium barium nitrilotriacetate.

Specific examples of the compound (2) include 2,2-methylenebis (4-methyl-6-t-butylphenol), 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-phospha-bicyclo [2,2,2] -oct-4-yl-methyl-3,5-di-t-
Butyl-4-hydroxyphenylpropionate, 3,5
-Di-t-butyl-4-hydroxybenzyldimethylamine, 3,5-di-t-butyl-4-hydroxyphenyl-3,5-distearyl-thiotriazylamine and the like can be mentioned.

Specific examples of the compound (3) include magnesium hydroxide,
Included are calcium hydroxide and barium hydroxide.

Specific examples of the compound (4) include tri-n-butylphosphite, triphenylphosphite, tribenzylphosphite, tritolylphosphite and tris (2,4-
Di-t-butylphenyl) phosphite, tri-n-butylphosphine, n-butyldiphenylphosphine, di-n-butylbenzylphosphine, triphenylphosphine, tribenzylphosphine, tritolylphosphine, tris (2,4-diphenylphosphine -T-butylphenyl) phosphine and the like.

The amount of the compounds (1) to (4) used is 0.0 per 100 parts by weight of the terminal-unstabilized oxymethylene copolymer.
It is preferably from 1 to 2 parts by weight, particularly from 0.1 to 1 part by weight.

When the amount of the compound (1) used is too small, it takes a long time to decompose the terminal thermally unstable portion of the terminal-unstabilized oxymethylene copolymer, and as a result, the main chain is cleaved. If the amounts of the compounds (2) and (3) used are too small, the thermal stability of the oxymethylene copolymer after the stabilization treatment will be insufficient. Further, if the amount of the compound (4) used is too small, the oxymethylene copolymer after the stabilization treatment becomes colored when heated at a high temperature for a long time. Even if the amount of the compounds (1) to (4) used is excessively large, no particular effect is obtained and it is not economical.

These compounds can be blended with the unstabilized oxymethylene copolymer as a powder or as a solution.

In the present invention, the terminal-unstabilized oxymethylene copolymer compounded with the compounds (1) to (4) is heated to a temperature equal to or higher than its melting point, and formaldehyde gas generated by decomposition is discharged to the outside of the system. , To produce a stabilized oxymethylene copolymer.

If the heating temperature is lower than the lower limit, it is not possible to obtain a sufficiently stabilized oxymethylene copolymer. 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 preferred heating temperature is in the range of melting point to a temperature 80 ° C. higher than the melting point. The heating time varies depending on the heating temperature, but is usually 1 to 60 minutes.

There is no particular limitation on the method of heating the terminal-unstabilized oxymethylene copolymer containing the compounds (1) to (4), and examples thereof include a Henschel mixer heated to a predetermined temperature and an inert gas in a twin-screw kneader. A method of stirring while circulating gas can be adopted.

(Example) An example is 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 are parts by weight.

Examples 1 to 3 and Comparative Examples 1 and 2 To 100 parts of an end-unstabilized oxymethylene copolymer (intrinsic viscosity: 1.51 dl / g) containing 2.05 mol% of a unit derived from 1,3,6-trioxocane. The additives shown in Table 1 were blended, the blend was put into a Brabender, and heat-treated at 210 ° C. under a nitrogen flow for a predetermined time. The color tone of each of the stabilized copolymers was white. Table 1 shows the decomposition rate of the terminally heat-labile portion and the physical properties of the obtained stabilized oxymethylene copolymer.

(Effects of the Invention) As is clear from Table 1, according to the present invention, the thermally unstable terminal portion of the unstabilized oxymethylene copolymer is decomposed and removed in a short period of time without lowering the molecular weight. . On the other hand, according to the known method, it takes a long time to decompose and remove the heat labile portion, and if the decomposition rate is increased to the same level as that of the present invention, the molecular weight of the stabilized oxymethylene copolymer decreases. To do.

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area // C08G 2/18 NAP

Claims (1)

[Claims] 1. An end-unstabilized oxymethylene copolymer, (1) nitrilotriacetic acid alkali metal salt or alkaline earth metal salt, (2) phenolic antioxidant, (3) alkaline earth metal water A method for stabilizing an oxymethylene copolymer, which comprises heating a mixture containing an oxide and (4) a trivalent organic phosphorus compound to a temperature equal to or higher than the melting point of the copolymer.