JPH08231822A - Polyoxymethylene composition and its molded item - Google Patents

Abstract

PURPOSE: To obtain a polyoxymethylene compsn. which has been improved in thermal stability, esp. the appearance of mold deposit during molding, and in overcoming functional troubles (e.g. staining due to exuded matters from a rubber or corrosion of a magnetic metal) due to formic acid occurring from the compsn. CONSTITUTION: 100 pts.wt. polyoxymethylene is compounded with 0.01-5.0 pts.wt. antioxidant, 0.01-5.0 pts.wt. at least one nitrogen compd. selected from among melamine cyanurate, melam, and melem, and 0.001-10 pts.wt. at least one metal- contg. compd. selected from among oxides and carbonates of magnesium and calcium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has an improved thermal stability, in particular, the generation of mold deposits during molding, and the functional disorder due to formic acid generated from the composition (for example, contamination from rubber exudates and The present invention relates to a polyoxymethylene composition having improved corrosion of a metal magnetic material) and a molded article thereof.

[0002]

BACKGROUND OF THE INVENTION Polyoxymethylene is polymerized or copolymerized from formaldehyde or its cyclic oligomer trioxane or a comonomer such as trioxane and cyclic ether or cyclic formal to stabilize the terminal. Treated and antioxidants and other heat stabilizers added to prevent decomposition. The antioxidant added to polyoxymethylene is a sterically hindered phenol compound or a sterically hindered amine compound, and other heat stabilizers include polyamide, urea derivatives, amidine compounds, water of alkali or alkaline earth metals. Oxides have been proposed, but polyoxymethylene resin compositions containing these compounds are subject to the action of heat and oxygen in the cylinder of the molding machine at the time of molding, and formaldehyde odor is easily generated, which causes labor loss. (Hygiene) If the environment is deteriorated or if molding is performed for a long time, fine powdery substances and tar-like substances (MD) will adhere to the surface of the mold, resulting in deterioration of the appearance of the molded product. In spite of the fact that various innovations and proposals have been made so far, satisfactory results have not always been obtained. For example, melamine-formaldehyde polycondensate is known as a useful additive, and in West German Patent Application Publication No. 1694097, a combination of an antioxidant and a water-soluble melamine-formaldehyde polycondensate is disclosed in Japanese Patent Laid-Open No. No. 33943 proposes a combination of an antioxidant and a water-insoluble melamine-formaldehyde polycondensate. Although the thermal stability of the polyoxymethylene composition is improved by these proposals, further improvement in the properties as a material is required depending on the field in which the polyoxymethylene is used. An example of such a demand is improvement of functional failures in mechanical parts used in electric / electronic devices such as audio and video. That is, audio and video mechanism parts manufactured and assembled in a highly clean environment such as a dust-free room to prevent pollution from the environment will also be contaminated from the environment such as dust when exposed to a high temperature and high humidity atmosphere. Despite the absence, it often hinders practical operation. This is because the additive in the rubber roller used for audio and video mechanical parts bleeds to the rubber surface and contaminates the magnetic head through the magnetic tape. As a temporary countermeasure against this problem, the rubber surfaces in the audio and video mechanical parts exposed to the high temperature and high humidity atmosphere are cleaned, and some effects are obtained. However, this measure is not only permanent, it also requires a huge labor force. Also, if the polyoxymethylene molded product is used in a state where it is relatively sealed with a magnetic magnetic material such as a magneto-optical disk or a metal evaporated tape, the magnetic material may be corroded, and the fundamental problem can be solved. Was wanted.

[0003]

Means for Solving the Problems As a result of detailed investigations on the bleeding of rubber and the corrosion of metallic magnetic materials in order to solve the above problems, the present inventors have found that Found that the constituent materials of the audio and video mechanical parts are closely related. That is, conventionally, as audio and video mechanical parts, chassis (base),
Reel, tape cassette parts such as gears and bearings
As disk cartridge parts such as guide rollers,
It has become clear that the polyoxymethylene molded products that have been used mainly for shutters and cartridge bodies cause corrosion of bleeding of rubber parts such as rollers and belts and corrosion of metal magnetic materials in relatively high temperature and high humidity. As a result, the formic acid contained in the polyoxymethylene molded product was released by using water in high humidity as a medium, and it adhered to and penetrated into the rubber and the metal magnetic material. It reacts with the water-insoluble magnesium oxide in water to form magnesium easily-soluble magnesium formate, which bleeds onto the rubber surface and contaminates the magnetic head with the tape as a medium. In the case of the body, it was revealed that formic acid itself corrodes metals. Although the thermal stability of polyoxymethylene has been improved by the addition of antioxidants and various stabilizers as described above, it is unavoidable that some thermal decomposition will occur during the molding process. It contains the products formaldehyde and formic acid. Formaldehyde is released to the surroundings as a gas when the molded product is heated to several tens of degrees Celsius or higher, so it can be greatly reduced by subjecting the molded product to high-temperature heat treatment or vacuum degassing. Formic acid cannot be reduced so much by heat treatment at a high temperature of hundreds of tens of degrees Celsius or by treatment in hot water. As a result of further study on this point, the present inventors have found that the amount of formic acid generated can be significantly reduced by blending polyoxymethylene with an antioxidant, melamine cyanurate and a specific metal compound. The present invention has been completed and the present invention has been completed. That is, the present invention is based on 100 parts by weight of polyoxymethylene, (a) 0.01 to 5.0 parts by weight of an antioxidant, (b) containing at least one nitrogen selected from melamine cyanurate, melam and / or melem. A polyoxymethylene composition comprising 0.01 to 5.0 parts by weight of a compound, 0.001 to 10 parts by weight of (c) one or more metal-containing compounds selected from oxides or carbonates of magnesium or calcium, and the composition. Made by molding,
The polyoxymethylene molded article is characterized in that the amount of formic acid generated from the molded article of the polyoxymethylene composition is 1.0 microgram or less per cm ^{2 of the} surface area of the molded article.

The present invention will be described in detail below.
The polyoxymethylene used in the present invention is a polymer compound having an oxymethylene group (—CH ₂ O—) as a main constituent unit, and contains a small amount of other constituent units in addition to the polyoxymethylene homopolymer and the oxymethylene group. It may be a copolymer, a terpolymer or a block copolymer, and
The molecule may have not only a linear structure but also a branched or crosslinked structure. Further, there is no particular limitation on the degree of polymerization or the like.

The (a) antioxidant used in the present invention is 2,2'-methylenebis (4methyl-6-t).
-Butylphenol), 1,6-hexanediol-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], pentaerythritol tetrakis [3- (3,5-di-t-butyl) -4-Hydroxy-phenyl) 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-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), di-stearyl-3,5-di-t-butyl-4-hydroxybenzylphosphonate, 2-t-butyl-6- (3-t-butyl-5) -Methyl-2-hydroxybenzyl) -4-methylphenyl acrylate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) are hindered phenolic antioxidants Examples of the agent include triphenylphosphite, trisnonylphenylphosphite, tris (2,4-di-t-butylphenyl) phosphite, tris (2-t-butyl-4-).
Methylphenyl) phosphite, tris (2,4-di-t-
Amylphenyl) phosphite, tris (2-t-butylphenyl) phosphite, tris (2-t-phenylphenyl) phosphite, tris (2- (1,1-dimethylpropyl) -phenyl) phosphite, tris ( 2,4- (1,1-dimethylpropyl) -phenyl) phosphite, tris (2
-Cyclohexylphenyl) phosphite, tris (2-
Examples of the phosphorus-based antioxidant include t-butyl-4-phenylphenyl) phosphite. In addition, hindered amine-based antioxidants can also be used, and at least one kind or two or more kinds thereof can be used. Among these, 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-hydroxy) Phenyl) propionate], N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) are particularly preferred substances.

The melamine cyanuric acid salt (b) used in the present invention is produced by a known method. That is, the reaction is carried out at a charged mole number of cyanuric acid with respect to melamine of 0.5 to 2.0, preferably 0.9 to 1.1, and then purified by washing and removing excess components that have not become salts, and preferably
It is pulverized and classified to 50 micrometers or less, particularly preferably 10 micrometers or less. It is also possible to use a commercially available product. Melam and melem are also produced by known methods. For example, it can be produced by heating melamine for deammonification or by thermally decomposing ammonium thiocyanate.

The amount of the (a) antioxidant added and blended in the present invention is 0.1 with respect to 100 parts by weight of polyoxymethylene.
01 to 5 parts by weight, preferably 0.1 to 3 parts by weight, (b) the amount of one or more nitrogen-containing compounds selected from melamine cyanurate, melam and / or melem is 0.01 to 5 parts by weight,
It is preferably 0.01 to 1 part by weight. If the added amount of these substances is too small, a sufficient effect cannot be obtained, and if the added amount is too large, the effect of thermal stability reaches saturation, rather causing a discoloration tendency, which is not preferable.

The (c) metal-containing compound used in the present invention is an oxide or carbonate of magnesium or calcium, specifically, magnesium oxide, calcium oxide,
Magnesium carbonate and calcium carbonate. The compounding amount of these compounds is 0.001 to 10 parts by weight, preferably 0.001 to 5 parts by weight, more preferably 0.001 to 2 parts by weight, and particularly preferably 100 parts by weight of polyoxymethylene.
0.003 to 0.5 parts by weight. When the amount is less than 0.001 part by weight, the desired effect can hardly be obtained, and when the amount is more than 10 parts by weight, the effect of suppressing the generation of formic acid reaches saturation,
Rather, discoloration tends to occur, which is not preferable.

The (c) metal-containing compound and (a) antioxidant, which are compounded in the composition of the present invention, may be added to the monomer in the polymerization stage of the polymer, or added in the stabilization process of the polymer. Is also good.

Further, for the purpose of suppressing the amount of deposits on the mold during molding to a minute amount, it is preferable to further add a fatty acid ester compound having 10 or more carbon atoms, and an ester compound with a polyhydric alcohol is particularly desirable. Examples of such compounds include glycerin monopalmitate, glycerin monostearate, glycerin monoisostearate, glycerin monobehenate and pentaerythritol tristearate. The compounding amount of the fatty acid ester compound having 10 or more carbon atoms is 0.01 with respect to 100 parts by weight of polyoxymethylene.
To 2.0 parts by weight, preferably 0.05 to 1.0 parts by weight.

The method for measuring the amount of formic acid generated will be explained. After molding the above composition, cutting the molded product as the case may be, and measuring the surface area thereof, an appropriate amount of the molded product (surface area of 30 to 60 cm ² Approximately) is placed in a closed container (capacity 100 ml) so as not to be soaked in 1 ml of pure water, and left at 60 ° C for 168 hours. The water in this closed container was diluted to 100 ml, and the formic acid concentration (μg) of this solution was measured with an ion chromatograph (Yokogawa Hewlett Packard IC500, organic acid column, 0.1 mM perchloric acid aqueous solution as a carrier). The amount of formic acid generated per surface area of the molded product (μg / cm ² ) was determined by measurement. The polyoxymethylene moldings preferred in the present invention have a formic acid generation rate of 1.0 microgram or less per 1 cm ^{2 of the} surface area of the molding, particularly preferably a formic acid generation rate of 1.0 microgram or less per 1 cm ^{2 of the} surface area of the molding, and a resin content of 1 Not more than 5.0 micrograms per gram. The numerical regulation of the amount of formic acid generated in the present invention is not limited to a molded article using a polyoxymethylene composition containing a known stabilizer and a known additive such as a release agent, as well as containing an inorganic filler or another polymer. The present invention is also applicable to a molded article of the composition as long as the majority of the surface of the molded article is polyoxymethylene.

Although not essential to the polyoxymethylene composition of the present invention, the polyoxymethylene composition of the present invention may further be selected according to the purpose (b).
One or more melamine / cyanuric acid salts, nitrogen-containing compounds other than melam and / or melem, and (c) one or more organic or inorganic metal-containing compounds other than magnesium or calcium oxides or carbonates may be used in combination. The polyoxymethylene composition of the present invention may further contain various known additives.
For example, various colorants, slidability improvers, release agents, nucleating agents,
Antistatic agents, weathering (light) stabilizers, other surfactants,
Various polymers and the like. Further, as long as it is within a range that does not significantly reduce the performance of the molded article targeted by the present invention, one or two known fillers such as fibrous, plate-like, and granular materials such as inorganic, organic, and metallic materials can be used. It is also possible to mix and blend more than one species. Examples of such inorganic fillers include glass fiber, potassium titanate fiber, glass beads, talc,
Examples thereof include mica, white mica, wollastonite, and the like, but are not limited to these. The polyacetal resin molded article of the present invention can be easily prepared by a known method generally used as a conventional resin molded article preparation method. For example, after mixing each component, uniaxially, or
Any method such as a method of kneading and extruding with a twin-screw extruder to prepare pellets, mixing (diluting) a predetermined amount of the pellets and subjecting to molding, and obtaining a molded product of the target composition after molding, can be used. Further, in the preparation of the composition used for such a molded article, it is necessary to pulverize a part or all of the polyacetal resin which is the substrate, mix this with other components, and then carry out extrusion or the like to improve the dispersibility of the additive. This is a preferable method for improving the quality.

The resin composition of the present invention can be used in any application where formic acid is considered to cause harmful effects.
It is preferably used in a field (application) where a rubber material or a metal magnetic material and a polyoxymethylene molded product are used for at least a part of components of electric / electronic equipment, particularly audio equipment, video equipment and the like. Specific molded products are exemplified below. As the electric / electronic device at least a part of which is composed of a polyoxymethylene molded product and a rubber part, or which has a large number of metal contacts, an audio device such as a cassette tape recorder, a video device such as a VTR, 8 mm video and a video camera. Or an OA device such as a copying machine, a facsimile, a printer, a word processor, etc., and further applicable to a motor, a toy that is driven by a driving force such as a spring, a telephone, a keyboard attached to a computer, and the like. Specific components include a chassis (base), gears, levers, cam pulleys, bearings, and the like. Further, the optical and magnetic media software, at least a part of which is made of a polyoxymethylene molded product, is, for example, a metal thin film magnetic tape cassette, a magnetic disk cartridge, a magneto-optical disk cartridge, an optical disk cartridge, or the like. , Metal tape cassettes for music, digital audio tape cassettes, 8mm video tape cassettes, floppy disk cartridges, and mini disk cartridges. Specific parts include tape cassette bodies, reels, hubs, guides, rollers, stoppers, and lids. Etc., disk cartridge body (case), shutter, hub,
A clamping plate etc. are mentioned. In addition, the polyoxymethylene molded product of the present invention is a component that comes into contact with a metal such as a carrier plate of a window regulator, an automobile component such as a fuel system or an electrical system component, a medical-related component such as a needle holder, and water purification. Vessel, spray nozzle,
It is preferably used for household items such as spray containers.

[0014]

EXAMPLES The present invention will now be specifically described with reference to examples, but the present invention is not limited thereto. still,
The evaluation method shown in the following examples is as follows. 1) Amount of formic acid generated from the molded product The amount of formic acid generated is 10 g of the cut polyoxymethylene molded product having a total surface area of about 10 cm ² in a closed container (capacity 100 ml) so as not to be directly immersed in 1 ml of pure water. 16 at 60 ℃ / 90% RH
After leaving it for 8 hours, dilute the water in this closed container to 100 ml,
The formic acid concentration of this solution was determined by measuring with an ion chromatograph (IC500 manufactured by Yokogawa Hewlett-Packard Co., a column for organic acid, 0.1 mM perchloric acid aqueous solution as a carrier). The amount of formic acid generated was expressed by converting the value obtained by this ion chromatography into a unit surface area. 2) Rubber blooming A rubber blooming test was conducted in the following procedure in high temperature and high humidity using a polyethylene bag with a sound / image reproduction mechanism part in which rubber parts were incorporated on a base on which a polyoxymethylene molded product was mounted. The table below shows the relationship between the amount of leaching on the surface of rubber parts (ranked in 10 stages by observing the rubber surface under a microscope) and the amount of formic acid generated on the molding substrate in the case of aging. For the rubber parts, use a roller made of chloroprene rubber in a cylindrical shape, and incorporate it into the sound image playback mechanism base made of polyacetal resin, and package it in a polyethylene bag at 60 ° C / 90% RH atmosphere. After leaving it for one week,
The exudates on the rubber surface were observed under a microscope, and the degree was visually ranked in 10 levels (1 for none, 10 for very high). This test was performed 3 times, and the average value is shown in the table. 3) Moldability (amount of mold deposit) The sample polyacetal resin composition was continuously molded (24 hours) into a molded product of a specific shape under the following conditions using an injection molding machine, and the amount of mold deposit was evaluated. . That is, stains on the mold during continuous molding were evaluated by visual observation in the following 5 grades. (Molding conditions) Injection molding machine; Toshiba IS30EPN (manufactured by Toshiba Machine Co., Ltd.) Cylinder temperature: 210 ° C. Injection pressure: 750 kg / cm ² Injection time: 4 sec Cooling time: 3sec Mold temperature; 30 ℃ A B C D E ← ──────────────── → Extremely large amount (there are deposits on the entire surface) Examples 1 to 11 Polyoxymethylene copolymers (DURACON manufactured by Polyplastics Co., Ltd.) The antioxidants, melamine cyanuric acid salts, melam and / or melem and magnesium and calcium oxides and carbonates shown in Table 1, and fatty acid ester compounds in the proportions shown in Table 1 (based on 100 parts by weight of polyoxymethylene) Part) was added and mixed, and a pelletized composition was obtained by an extruder, and the above evaluation was performed. The results are shown in Table 1. Comparative Examples 1 to 8 In addition, for comparison, as shown in Table 1, in the case where no metal oxide or carbonate is added, the case where another metal oxide other than the definition of the present invention is added, or the like, A pellet-shaped composition was prepared in the same manner as in, and the above evaluation was performed. The results are shown in Table 1. The antioxidants, melamine cyanuric acid salts, metal oxides and carbonates used are as follows. 1. Antioxidant a-1) Triethylene glycol-bis- [3- (3-t
-Butyl-5-methyl-4-hydroxyphenyl) propionate] a-2) pentaerythritol tetrakis [3- (3,5-
Di-t-butyl-4-hydroxyphenyl) propionate] 1. Melamine cyanuric acid salt, melam and / or melem b-1) A mixture prepared by mixing 1 mol of melamine and 1 mol of cyanuric acid was heated at 300 ° C. and then pulverized,
Melamine / cyanuric acid salt fine powder obtained by washing with pure water 3 times, once with acetone, and drying b-2) A mixture of melam and melem obtained as follows: Melamine is heated to 350 ° C. Then, the generated ammonia gas was absorbed outside the reaction system in pure water to which phenolphthalein had been dropped. The end point of the reaction was determined while titrating this with hydrochloric acid. The reaction product was cooled, pulverized, and then purified with pure water.
The mixture was washed once with acetone and then dried to obtain a mixture of melam and melem. 3. Metal oxides and carbonates c-1) Magnesium oxide c-2) Calcium oxide c-3) Magnesium carbonate c'-1) Barium oxide c'-2) Zinc oxide 4. Fatty acid ester compound d-1) Glycerin monostearate d-2) Glycerin monoisostearate 5. Other compounds e-1) Melamine e-2) Dicyandiamide

[0015]

[Table 1]

[0016]

As is clear from the above description and the examples, the amount of formic acid generated in the molded article made of the resin composition of the present invention is
It is clear that at 1.0 μg / cm ² or less, the polyacetal resin molded product has little effect on the blooming of rubber. According to the present invention, as described above, the amount of formic acid generated from a molded product can be suppressed to 1.0 μg / cm ² or less, so that it is possible to fundamentally solve the blooming problem of rubber parts. It is preferably used for.

Claims (5)

[Claims] Claims: 1. To 100 parts by weight of polyoxymethylene, (a) 0.01 to 5.0 parts by weight of an antioxidant, (b) melamine.
1 selected from cyanurate, melam and / or melem
A polyoxymethylene composition comprising 0.01 to 5.0 parts by weight of one or more nitrogen-containing compounds and (c) 0.001 to 10 parts by weight of one or more metal-containing compounds selected from magnesium or calcium oxides or carbonates. 2. A fatty acid ester compound having 10 or more carbon atoms is added in an amount of 0.01 to 2.0 per 100 parts by weight of polyoxymethylene.
The polyoxymethylene composition according to claim 1, which is blended by weight. 3. A composition obtained by molding the composition according to claim 1 or 2, wherein the amount of formic acid generated from the molded product of the polyoxymethylene composition is 1.0 microgram or less per 1 cm ^{2 of the} surface area of the molded product. Characterized polyoxymethylene moldings. 4. The polyoxymethylene molded product according to claim 3, wherein the molded product is an electric / electronic device part. 5. An electric / electronic device comprising the polyoxymethylene molded article according to claim 4 and a rubber part as a part of the constitution.