JPH1143584A - Polyoxymethylene composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition capable of manifesting characteristics excellent in heat stability and moldability, and hardly causing the shape change under load by introducing an oxyalkylene unit to a polyoxymethylene in a specific amount. SOLUTION: This composition is obtained by compounding (A) a polyoxymethylene copolymer containing 0.30-1.50 pts.wt. 2-6C oxyalkylene unit as a comonomer based on 100 pts.wt. polyoxymethylene unit, with (B) an organic compound [for example, 2,2'-methylenebis(4-methyl-6-t-butylphenol)] as a thermal stabilizer and/or a processing modifier, and has <=0.025 wt.%/min average weight diminution rate after leaving the composition at 230 deg.C in air for 60 minutes, and >=83 Rockwell hardness of the molding product thereof measured by the M scale. Preferably, the component B is compounded with the component A so as to be 0.1-2.0 wt.%. As a result, the very preferable resin composition capable of resisting to a severe condition is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyoxymethylene copolymer composition having excellent heat stability and moldability, and having a characteristic of little change in shape under load.

[0002]

BACKGROUND OF THE INVENTION Polyoxymethylene is polymerized from formaldehyde or its cyclic oligomer, trioxane, or a comonomer such as trioxane and a cyclic ether or cyclic formal,
The terminal is stabilized, and an antioxidant and other heat stabilizers are added to prevent the decomposition. In recent years, such polyoxymethylene resins are very widely used as representative engineering resins having excellent physical properties such as mechanical properties and electrical properties, or chemical properties such as chemical resistance and heat resistance. Used in various fields. However, with the expansion of fields in which polyoxymethylene resins are used, further improvements are required in the properties of the materials. An example of such a requirement is, for example, one of the most demanding uses of a sliding member. ), It is required to have excellent mechanical strength and durability. However, when a polyoxymethylene resin is applied to such an application, the polyoxymethylene homopolymer has a high crystallization rate, which is advantageous for shortening the molding cycle. Insufficient properties (including water resistance) cause a problem that gear teeth are suddenly damaged, and a general polyoxymethylene copolymer has a low melting point, and the gear teeth are deformed by a slight force. There is a problem. In order to solve these problems, it is conceivable to add various additives such as a reinforcing filler to the polyoxymethylene resin, but the effect is limited,
Further, even if one property is improved, the other property is often sacrificed, and the sliding property, moldability and the like are often deteriorated, and it cannot be said that this is an essential solution.

[0003]

Means for Solving the Problems The present inventors have solved the above-mentioned problems and made use of the properties of both polyoxymethylene homopolymers and copolymers, while maintaining the durability of the polyoxymethylene copolymer. As a result of diligent research to obtain a polyoxymethylene resin having the same physical and mechanical properties as oxymethylene homopolymer, it has been found that the specified purpose can be achieved by introducing a specific amount of oxyalkylene units into polyoxymethylene. Headings,
The present invention has been completed. That is, the present invention relates to a polyoxymethylene resin composition obtained by blending a heat stabilizer and / or a processability improver with a polyoxymethylene copolymer. When the weight loss rate is less than 0.025 wt% / min,
And a polyoxymethylene composition having a Rockwell hardness of 83 or more on an M scale and a polyoxymethylene copolymer having 2 to 6 carbon atoms per 100 parts by weight of a polyoxymethylene unit. 0.3 to 1.50 parts by weight of an oxyalkylene unit as a comonomer and a total compounding amount of an organic compound as a heat stabilizer and / or a processability improver of 0.1 to 2.0% by weight (based on polyoxymethylene copolymer). The present invention relates to a polyoxymethylene composition.

[0004]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the polyoxymethylene copolymer composition of the present invention will be described in detail. The polyoxymethylene copolymer used in the present invention is a copolymer containing 0.3 to 1.50 parts by weight of an oxyalkylene unit having 2 to 6 carbon atoms as a comonomer with respect to 100 parts by weight of a polyoxymethylene unit. The main monomer is formaldehyde or its cyclic oligomer trioxane, ethylene oxide, 1,3-dioxolan,
1,3,5-trioxepane, oxetane, 1,3-dioxane, 4-methyl-1,3-dioxolan, 6-methyl-1,
3,5-trioxepane, 1,4-butanediol formal, 4-ethyl-1,3-dioxolan, 6-ethyl-1,
3,5-trioxepane, 4-methyl-1,3-dioxane, 5-methyl-1,3-dioxane, 1,5-pentenediol formal, 4-propyl-1,3-dioxolan, 6-propyl-1, 3,5-trioxepane, 4-ethyl-1,3-dioxane, 5-ethyl-1,3-dioxane, 1,6-hexanediol formal, 4-butyl-
At least one selected from 1,3-dioxolane, 6-butyl-1,3,5-trioxepane, 4-propyl-1,3-dioxane, and 5-propyl-1,3-dioxane as a cationic monomer It is obtained by copolymerization in the presence of a catalyst, is subjected to a terminal stabilization treatment by a well-known method, and is added with an antioxidant, other stabilizers, and a processability improver to prevent decomposition. As a raw material comonomer for introducing an oxyalkylene unit, 1,3-dioxolan, 1,3, which has a small adverse effect on the crystal formation of polyoxymethylene, obtains a good comonomer dispersion state, does not form a comonomer chain in the polymer, , 5 −
It is particularly preferred to use trioxepane, 1,3-dioxane, 1,4-butanediol formal. The preferred content of the comonomer in the polyoxymethylene copolymer used in the present invention is 0.30 to 1.50 parts by weight, particularly preferably 0.50 to 1.50 parts by weight. If the content of the comonomer is too low, the stability of the copolymer to heat or chemicals is insufficient, and if it is too high, the strength and the rigidity tend to decrease, and the object of the present invention cannot be satisfied. Absent. In order to control the molecular weight of the polyoxymethylene copolymer in the present invention, if necessary, an appropriate chain transfer agent is added. As such a chain transfer agent,
Methylal, ethylal, butyral and the like are exemplified.

[0005] The polymerization catalyst in the present invention includes:
Common cationically active catalysts are used. Such cationically active catalysts include Lewis acids, especially boron, tin,
Titanium, phosphorus, arsenic, and halides such as antimony, such as boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentachloride, phosphorus pentafluoride, arsenic pentafluoride, and antimony pentafluoride, and the like. Compounds such as complex compounds or salts, protic acids such as trifluoromethanesulfonic acid, perchloric acid, esters of protic acids, especially esters of perchloric acid with lower aliphatic alcohols (eg perchloric acid tertiary butyl ester), protic acids Anhydrides, especially mixed anhydrides of perchloric acid and lower aliphatic carboxylic acids (especially acetyl perchlorate), or isopolyacids, heteropolyacids (for example, phosphomolybdic acid), or triethyloxonium hexafluorophosphate, Phenylmethylhexafluoroarsenate,
Acetyl hexafluoroborate and the like can be mentioned. Among them, boron trifluoride or a coordination compound of boron trifluoride and an organic compound (for example, ethers) is the most general and suitable.

[0006] The polyoxymethylene copolymer used in the present invention can be produced by the same equipment and method as in the conventional trioxane polymerization method. That is, any of a batch type and a continuous type can be used, and any of a solution polymerization, a melt bulk polymerization, and the like may be used. However, a continuous bulk polymerization using a liquid monomer and obtaining a solid powder bulk polymer as the polymerization proceeds. The method is industrially common and preferred. In this case, an inert liquid medium can coexist as necessary. As the polymerization apparatus used in the present invention, a co-kneader, a twin-screw continuous extrusion mixer, a twin-screw paddle-type continuous mixer, and other continuous polymerization apparatuses for trioxane proposed in the present invention can be used. If so, it may be divided into two or more stages. Particularly, those having a crushing function such that a solid polymer produced by a polymerization reaction can be obtained in a fine form are preferable. After the completion of the polymerization, the crude polymer discharged from the polymerization machine must be immediately mixed and contacted with a deactivator to deactivate the polymerization catalyst. Examples of the deactivator include a solution in which amines such as triethylamine and triethanolamine and inorganic alkaline substances such as sodium fluoride and potassium fluoride are mixed. As the solution, an aqueous solution is particularly preferable. The deactivated copolymer of the polymerization catalyst is
Further, if necessary, washing, separation and recovery of unreacted monomers, drying, etc., and further, if necessary, further stabilization step, and additives such as various stabilizers are added, melt-kneaded and pelletized to obtain a product. .

In the present invention, a stabilizer and / or a processability improver are blended for the purpose of suppressing the decomposition of the polyoxymethylene copolymer. Examples of the organic compound used as a stabilizer and / or a processability improver include 2,2′-methylenebis (4-methyl-6-t-butylphenol) and 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], 1,3,5-trimethyl-2,4,6-
Tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, n-octadecyl-3- (4'-hydroxy-3 ', 5'-di-t-butylphenyl) propionate, 4,4' -Methylenebis (2,6-di-t-butylphenol), 4,4'-butylidenebis- (6-t-butyl-3
-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, di-stearyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonate, 2-tert-butyl-6- (3-tert-butyl-5-methyl Hindered phenols such as -2-hydroxybenzyl) -4-methylphenyl acrylate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide), 4-acetoxy-2,2,6,6-tetramethylpiperidine, bis (2,
Antioxidants represented by hindered amines such as 2,6,6-tetramethyl-4-piperidyl) adipate, polyamides such as nylon 6,10, nylon 6,66,610, polyacrylamide, melamine, dicyandiamide, and formaldehyde Metal-containing compounds such as nitrogen-containing compounds typified by polycondensates with higher fatty acids such as stearic acid such as sodium, potassium, magnesium, calcium and barium and salts of substituted higher fatty acids having a substituent such as a hydroxyl group; -[2-hydroxy-3,5-bis- (α,
α-dimethylbenzyl) phenyl] benzotriazoles such as benzotriazole, ultraviolet absorbers represented by benzophenones such as 2-hydroxy-4-methoxybenzophenone, and higher fatty acid esters such as glycerin monostearate and pentaerythritol tristearate , Lubricants represented by higher fatty acid amides such as ethylene bis (stearylamide), plasticizers such as polyethylene glycol and polyoxyethylene polyoxypropylene copolymers, and slidability improvers such as polyolefins and silicone oils. More than one kind. Of these, pentaerythritol tetrakis [3-
(3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol bis [3-
(3,5-di-t-butyl-4-hydroxyphenyl) propionate], 3,9-bis {2- [3- (3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy]- Hindered phenols such as 1,1-dimethylethyl-2,4,8,10-tetraoxaspiro [5,5] undecane, as nitrogen-containing compounds, melamine, dicyandiamide, etc. and polycondensates with formaldehyde, metals As the contained compounds, salts of higher fatty acids of magnesium and calcium and salts of substituted higher fatty acids are preferred compounds. The total amount of organic compounds added as a heat stabilizer and / or a processability improver to the polyoxymethylene resin composition of the present invention is 0.1 to 2.0% by weight, preferably 0.1 to 0.8% by weight, based on polyoxymethylene. It is. If the amount of these additives is too small, a sufficient effect cannot be obtained. If the amount is too large, the strength and rigidity of the composition tend to be significantly reduced, which is not preferable.

The polyoxymethylene composition of the present invention has 2 to 6 carbon atoms per 100 parts by weight of polyoxymethylene unit.
0.30 to 1.50 of the oxyalkylene unit as a comonomer
A composition containing, by weight, 0.1 to 2.0% by weight (based on polyoxymethylene copolymer) of an organic compound as a heat stabilizer and / or a processability improver.
The average weight loss rate when left for 60 minutes in air is 0.
It is characterized in that the molded product has a Rockwell hardness of 83 or more on an M scale of not more than 83% by weight / min, and is suitably used for various gears, pulleys, bearings, guides, rollers and the like. Particularly preferred is a composition wherein the average weight loss rate is 0.015% by weight / min or less and the Rockwell hardness of the molded product is 85 or more on an M scale. If the above average weight loss rate is higher than 0.025% by weight / min, the heat-resistant life of the composition tends to be short, which is not preferable. If the Rockwell hardness of the molded product is smaller than 83 on the M scale, the gear tooth It is not preferable because the fracture behavior approaches that of the conventional polyoxymethylene copolymer.

Although not essential to the polyoxymethylene composition of the present invention, a nucleating agent, a filler and a reinforcing agent can be blended according to the purpose. Examples of the nucleating agent include, in addition to the main monomers such as trioxane and comonomers such as 1,3-dioxolane, as the third component, glycerol formal and 1,4-butanediol diglycidyl ether such as
A polyoxymethylene terpolymer obtained by adding and copolymerizing a functional and / or tetrafunctional compound, or a fine powder having an internal particle diameter of inorganic particles such as boron nitride or talc of 5 μm or less is preferably used. used. In addition, fillers and reinforcing agents include magnesium oxide, calcium oxide, zinc oxide, magnesium hydroxide, magnesium carbonate, calcium carbonate, talc, mica, clay, kaolin, bentonite, dolomite, silica, alumina, hydrotalcite, and the like. Amorphous, plate-like or spherical powders mainly composed of inorganic acid salts such as oxides, hydroxides, carbonic acid, phosphoric acid, boric acid, silicic acid and the like or silicon dioxide of Group II or III metal of the periodic table. Fibers such as body, glass fiber, carbon fiber, and aramid fiber and their crushed products, and whiskers such as calcium carbonate, titanium oxide, potassium titanate, wollastonite, and graphite are exemplified, and one or more of them are preferable. Used for

The polyoxymethylene composition of the present invention can be easily prepared by a known method generally used as a conventional method for preparing a resin composition. For example, after mixing each component, a single-screw or twin-screw extruder kneads and extrudes to prepare pellets. Pellets having a different composition are prepared once, and the pellets are mixed (diluted) in a predetermined amount and molded. Any method can be used, such as a method for obtaining a molded article having a desired composition after molding. In the preparation of such a composition, pulverizing part or all of the polyoxymethylene as a substrate, mixing this with other components, and then performing extrusion or the like may improve the dispersibility of the additive. Is a preferred method.

[0011]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples. still,
The evaluation method described below is as follows. 1) Average heating weight reduction rate 10 g of pellets of the polyoxymethylene resin composition from which volatile components have been removed in advance by a vacuum dryer at 100 ° C. are weighed on an aluminum dish, and the weight after standing in a 230 ° C. oven for 60 minutes is measured. Measure. By dividing this difference by the initial weight, the heating weight reduction rate is obtained, and further converted per unit time to obtain the average heating weight reduction rate. 2) Shortest molding cycle When the rib-shaped test piece shown in FIG. 1 is injection molded under the following injection molding machine and injection molding conditions, the shortest molding cycle time at which the molded product can be protruded without plastic deformation is shown. In addition,
The molding cycle was changed by changing the cooling time. Molding machine: FANUC, AUTOSHOT MODEL-50 (screw diameter 2
8mm) Molding conditions Cylinder temperature Nozzle 190-190-170-150 ℃ Mold temperature setting 60 ℃ Injection speed 20mm / sec Holding pressure 50MPa Holding pressure 3sec Screw rotation speed 120rpm Back pressure 4.9MPa Sack pack 3mm Ejector speed 20mm / sec 3 ) Load deformation resistance (surface hardness) Using a 6.3 mm thick test piece (ASTM D-790, bending test piece), a Rockwell hardness tester (manufactured by Toyo Seiki Co., Ltd., ROCKWELL H)
ARDNESS TESTER) was used to measure the surface hardness at 23 ° C. 4) Durability (lifetime of physical properties) After keeping the same test specimen at 140 ° C in a gear oven and taking it out for a predetermined time, the test specimen is placed at 23 ° C and 50% RH.
For more than 24 hours. The tensile strength of this test piece was measured using a tensile tester in the same manner. From the graph of the high temperature holding time and the strength, the time at which the strength is reduced to 80% based on the initial tensile strength is determined as the life of the material.

Examples 1 to 5 and Comparative Examples 1 to 4 A fixed amount of trioxane was placed in a closed autoclave having a jacket through which a heat medium could pass and a stirring blade.
3-dioxolane to trioxane each 0.3
4, 0.68, 0.88 mol% and 0.44 mol% of 1,4-butanediol formal were added in the same manner, and the mixture was stirred.
After maintaining the internal temperature at about 70 ° C. through hot water of 0 ° C., a cyclohexane solution of boron trifluoride butyl etherate (40 ppm as boron trifluoride per trioxane) was added, and oxyethylene was used as a comonomer for 100 parts by weight of oxymethylene. The unit quantity is about 0.5, 1.0,
The copolymerization was carried out so that 1.3 parts by weight and the oxybutylene unit became about 1.0 part by weight. After 5 minutes, the reaction was stopped, the contents were taken out, pulverized to 20 mesh or less, washed with acetone, and dried. Organic compounds such as stabilizers shown in Table 1 were added to the obtained copolymers in the proportions shown in Table 1 (based on 100 parts by weight of polyoxymethylene copolymer), and the mixture was pelletized with an extruder. Were obtained and molded into test pieces by injection molding, and the above evaluation was performed. For comparison, as shown in Table 1, 1,3-dioxolan was 0.20 and
When using 1.37 mol%, 1,3-dioxolane 0.68 mol%
2.0 of processing improver other than heat stabilizer
The above-mentioned evaluation was carried out in the same manner as in the examples, for example, in the case of adding by weight, when using Delrin 500P manufactured by DuPont as a homopolymer, and the like. The results are shown in Table 1. The organic compounds used are as follows.

1. 1. Comonomers a: 1,3-dioxolane b: 1,4-butanediol formal Organic compound c: antioxidant (triethylene glycol bis [3-
(3-t-butyl-5-methyl-4-hydroxyphenyl) propionate]) d: nitrogen-containing compound (melamine) e: processability improver (polyethylene glycol)

[0014]

[Table 1]

[0015]

As is clear from the above description and the examples, the resin composition of the present invention according to the present invention is excellent in shortening the molding cycle, slightly stops the shape change under load, and has a low By maintaining the thermal stability and durability of the oxymethylene copolymer, a highly preferable resin composition that can withstand more severe use conditions can be obtained.

[Brief description of the drawings]

FIG. 1 is a view showing a rib-shaped test piece used in a measurement test of a shortest molding cycle in Examples.

Claims (2)

[Claims] 1. A polyoxymethylene resin composition comprising a polyoxymethylene copolymer and a heat stabilizer and / or a processability improver, wherein the composition is obtained at 230 ° C. in air.
Average weight loss rate when left for 60 minutes is 0.025% by weight / mi
n, and the Rockwell hardness of the molded product is 83 or more on an M scale. 2. The polyoxymethylene copolymer contains 0.30 to 1.50 parts by weight of a oxyalkylene unit having 2 to 6 carbon atoms as a comonomer with respect to 100 parts by weight of the polyoxymethylene unit, and contains a heat stabilizer and / or processability. The polyoxymethylene composition according to claim 1, wherein the total amount of the organic compound as the modifier is 0.1 to 2.0% by weight (based on the polyoxymethylene copolymer).