JP2005264102A - Polyacetal resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve compression characteristics of a polyacetal resin, high-temperature creep-resistant characteristics and resistances thereof to corrosion of metal and other resins. <P>SOLUTION: The polyacetal resin has &lt;10 wt.ppm total amount of volatile organic compounds except formaldehyde released when heated at 90&deg;C for 30 min. The polyacetal resin comprises a sterically hindered phenol as an antioxidant, a compound and/or a polymer containing a formaldehyde-reactive nitrogen as a heat stabilizer and a formic acid scavenger. <P>COPYRIGHT: (C)2005,JPO&amp;NCIPI

Description

  The present invention relates to a polyacetal resin having excellent compression characteristics, high temperature creep resistance, metal corrosion resistance, and other resin corrosion resistance.

Polyacetal resin has balanced mechanical properties and is excellent in fatigue resistance, creep resistance, friction wear resistance, and chemical resistance, so it can be used in a wide range of applications such as automobiles, electrical / electronic equipment, and building materials. Is used.
However, as the use of polyacetal resin expands, the demand for quality is becoming increasingly sophisticated. As a required characteristic, it is possible to improve the compression characteristic and the creep characteristic without greatly reducing the molding processability. It is known that the compression property is improved by controlling the spherulite size and heat of fusion of the polyacetal resin (see, for example, Patent Document 1). As for the creep characteristics, it is generally known that the creep rupture life can be increased as the molecular weight is increased. However, this method deteriorates the moldability. Although it has been proposed to use a branched polyoxymethylene copolymer as a method for solving this problem, a reduction in molding processability is inevitable (see, for example, Patent Document 2).

  Moreover, even if the creep characteristics are improved by these methods, the compression characteristics are often deteriorated. Further, the conventional creep property improving methods are mainly intended to improve in a temperature range of 100 ° C. or lower. In recent years, with the increase in the density of electric and electronic devices, polyacetal resins are increasingly used in a temperature range of 100 ° C. or higher. In the temperature range exceeding 100 ° C., the conventional creep improvement method alone is insufficient and a completely new method is required. Another required characteristic is improved metal corrosion resistance and other resin corrosion resistance. In electrical and electronic equipment, polyacetal resin is not used alone. Metals such as magnetic materials applied to various metal parts and magnetic tape, polycarbonate resin, polyphenylene ether resin, polyamide resin, ABS resin, methacrylic resin In general, it is used in the presence of other resins such as polystyrene resin, polyethylene resin, and polypropylene resin.

  When these electrical / electronic devices are used in car audio, for example, metal and other resins corrode under the influence of formaldehyde and other volatile organic compounds released from polyacetal resin in a high temperature and high humidity environment. May cause a drop. As a method of improving the metal corrosion resistance and other resin corrosion resistance of polyacetal resin, the amount of decomposed formaldehyde gas generated at 230 ° C is small, or a polyoxymethylene copolymer is added to a hindered phenol antioxidant or hindered amine light. A method of adding a stabilizer, a fatty acid ester of glycerin, and formaldehyde-reactive nitrogen (for example, see Patent Document 3), an antioxidant and an isocyanate compound and / or Li, Na, K, Mg, Ca, Ba, Zn A method of adding one or more metal hydroxides, carbonates or fatty acid salts having 6 or more carbon atoms has been proposed (for example, see Patent Documents 4 and 5), but the effect of improving corrosion is insufficient. Is needed.

JP 2003-269035 A JP 2003-105048 A JP-A-7-252400 JP-A-6-274854 JP-A-6-271743

  An object of the present invention is to improve the compression property, high temperature creep resistance, metal corrosion resistance, and other resin corrosion resistance of a polyacetal resin.

As a result of intensive studies to solve the above problems, the present inventors have determined that the polyacetal resin powder has a total amount of volatile organic compounds excluding formaldehyde that is released when heated at 90 ° C. for 30 minutes less than 10 ppm by weight. Alternatively, the inventors have found that the object can be achieved by using pellets or molded bodies, and have reached the present invention based on this finding.
That is, the present invention
1. A polyacetal resin characterized in that the total amount of volatile organic compounds excluding formaldehyde released when heated at 90 ° C. for 30 minutes is less than 10 ppm by weight,
2. The polyacetal resin according to the above 1, wherein the amount of formaldehyde released when heated at 60 ° C. for 3 hours is 10 ppm by weight or less,
3. The polyacetal resin contains at least one sterically hindered phenol as an antioxidant, at least one compound and / or polymer containing formaldehyde-reactive nitrogen as a heat stabilizer, and at least one formic acid scavenger, respectively. The polyacetal resin according to the above 1 or 2, characterized in that
4). The polyacetal resin according to 3 above, wherein the formic acid scavenger is an alkaline earth metal carboxylate,
5). The polyacetal resin according to any one of 1 to 4 above, wherein the polyacetal resin is a polyoxymethylene copolymer,
6). A molded body obtained from the polyacetal resin according to any one of 1 to 5,
7). The molded product according to 6 above, wherein the total amount of volatile organic compounds excluding formaldehyde released when the molded product is heated at 90 ° C. for 30 minutes is less than 10 ppm by weight,
8). The molded body according to 6 or 7 above, wherein the molded body is a part for an electric / electronic device,
9. The molded product according to 6 or 7 above, wherein the molded product is a door or an automobile part,
About.

  The polyacetal resin powder, pellets and molded product of the present invention have improved compression characteristics and high temperature creep resistance characteristics. Therefore, it is suitable for door pulleys and automobile-related parts that are particularly required for these performances, particularly for fuel parts such as a fuel tank flange, and seat belt parts such as a seat belt retracting mechanism. Furthermore, since the polyacetal resin powder, pellets, and molded products of the present invention are excellent in corrosion resistance against metals and other resins, they are also suitable for electrical and electronic equipment used in the presence of metals and other resins. is there.

Hereinafter, the present invention will be specifically described.
The polyacetal resin of the present invention is a polyoxygen comprising substantially repeating oxymethylene units produced using a formaldehyde monomer or a cyclic oligomer such as a trimer (trioxane) or tetramer (tetraoxane) as a raw material. A methylene homopolymer or an oxyalkylene unit having 2 to 8 carbon atoms produced from the above raw material and a cyclic ether such as ethylene oxide, propylene oxide, epichlorohydrin, 1,3-dioxolane, glycol formal, diglycol formal, etc. Oxymethylene copolymer containing 0.1 to 20% by weight, preferably 0.2 to 10% by weight, further having a crosslinked or branched molecular chain, oxymethylene unit, oxyethylene unit, oxypropylene unit, methylene unit, Propylene unit, etc. It encompasses such polyoxymethylene block copolymer having a repeating unit different from the oxymethylene units. Moreover, the mixture of various polyacetal resin mentioned above may be sufficient.

  The polyacetal resin of the present invention may be in the form of powder or pellet. In the present invention, the total amount of volatile organic compounds excluding formaldehyde released when the polyacetal resin of these shapes is heated at 90 ° C. for 30 minutes is less than 10 ppm by weight, preferably less than 5 ppm by weight based on the polyacetal resin. It is essential. The total amount of volatile organic compounds released can be determined by GC (Gas Chromatography) -MS (Mass Spectrometer) analysis (separated by gas chromatography and then quantified with toluene as a standard substance by a mass spectrometer). When the total amount of volatile organic compounds is 10 ppm by weight or more, the effect of the present invention cannot be exhibited. In the present invention, the amount of formaldehyde released when heated at 60 ° C. for 30 minutes is preferably 10 ppm by weight or less with respect to the polyacetal resin from the viewpoint of improving metal corrosion resistance and other resin corrosion resistance. The amount of formaldehyde released can be determined by absorbing formaldehyde released from the polyacetal resin in water in a closed container and quantitatively analyzing it by the acetylacetone method.

Moreover, the molded object obtained from the polyacetal resin of this invention also has the effect of this invention. That is, in the molded article of the present invention, the total amount of volatile organic compounds excluding formaldehyde released when heated at 90 ° C. for 30 minutes is 10 to 100 ppm by weight with respect to the molded article obtained from the polyacetal resin.
A polyoxymethylene copolymer is preferred as the polyacetal resin of the present invention, and a method for obtaining the polyacetal resin powder, pellets, or molded product of the present invention will be described below using the polyoxymethylene copolymer as an example. In order to obtain a polyoxymethylene copolymer for practical use, first, typically, a trioxane and a cyclic ether such as 1,3-dioxolane or a cyclic formal are mixed with a Lewis acid such as boron trifluoride di-n-butyl ether. And a protonic acid such as trifluoromethanesulfonic acid as a catalyst.

  The polymerization method is not particularly limited, but bulk polymerization can be given as a representative example. As the polymerization apparatus, a self-cleaning reactor such as a kneader is generally used. In the bulk polymerization, the monomer in a molten state changes to a solid bulk as the polymerization proceeds, and this is pulverized by a kneader to obtain a powdery polymer. Next, the polymer obtained by copolymerization is brought into contact with a triethylamine aqueous solution or the like to neutralize and deactivate the polymerization catalyst, and is washed and dried as necessary. Thereafter, the thermally unstable terminal portion present in the polymer is removed by melt hydrolysis with an extruder or the like in the presence of a basic compound such as triethylamine or a quaternary ammonium salt, and an antioxidant as necessary. And put to practical use after adding heat stabilizers.

  Components detected when the polyacetal resin thus obtained is heated at 90 ° C. for 30 minutes include residual monomers such as trioxane and 1,3-dioxolane, reaction intermediates such as tetraoxane and trioxepane, Examples thereof include linear or cyclic low molecular weight formaldehyde polymers and amine compounds having an average molecular weight of 500 or less, mainly 300 or less. In particular, since amine compounds are likely to cause malodor, they are preferably 50 ppm or less, more preferably 20 ppm or less, relative to the polyacetal resin. These components do not have strong corrosiveness to metals and other resins as they are, but as a result of investigations by the inventors, these components decompose when they come into contact with metals and other resins, particularly in a high temperature and high humidity environment. Formaldehyde was generated, and it was found that this formaldehyde was changed to formic acid by the oxidation reaction and the cannizzaro reaction with water, and corroded metals and other resins.

As a method of making these components less than 10 ppm by weight of the present invention, a method of reducing the residual monomers by making the polymerization yield close to 100%, a method of washing or drying the polymer obtained by polymerization, A method of devolatilizing and removing from a vent at the time of melt hydrolysis or additive kneading using an extruder with a vent, a method of drying or washing the obtained pellets or powder obtained by pulverizing them, injection molding , Methods for heating or washing molded bodies obtained by gas injection molding, extrusion molding, compression molding, etc., and combinations of these methods.
In the present invention, there is no particular limitation on the method for reducing the volatile organic compound, and any method may be selected. However, it is released when the polyacetal resin powder, pellets, or molded product to be used is heated at 90 ° C. for 30 minutes. The volatile organic compound excluding formaldehyde may be less than 10 ppm by weight. More specifically, the amount of volatile organic compounds when heated at 90 ° C. for 30 minutes under various conditions such as washing and drying temperature and time, melting temperature, number of times of melting and devolatilization, and vent pressure is measured and complicated. The optimum condition that falls within the scope of the present invention is selected from the various combination conditions.

  As the antioxidant, hindered phenol antioxidants are preferable. For example, n-octadecyl-3- (3′5′-di-t-butyl-4′-hydroxyphenyl) -propionate, n-octadecyl-3- (3′-methyl-5′-t-butyl-4′- Hydroxyphenyl) -propionate, n-tetradecyl-3- (3'5'-di-t-hydroxyphenyl) -propionate, 1,6-hexanediol-bis- (3- (3,5-di-t-butyl) -4-hydroxyphenyl) -propionate, 1,4-butanediol-bis- (3- (3,5-di-t-butyl-4-hydroxyphenyl) -propionate, triethylene glycol-bis- (3- ( 3-t-butyl-5-methyl-4-hydroxyphenyl) -propionate).

  Tetrakis- (methylene-3- (3′5′-di-t-butyl-4′-hydroxyphenyl) -propionate methane, 3,9-bis (2- (3- (3-t-butyl) -4-hydroxy-5-methylphenyl) propionyloxy) 1,1-dimethylethyl) 2,4,8,10-tetraoxaspiro (5,5 ') undecane, N, N'-bis-3- (3 '5'-di-t-butyl-4-hydroxyphenol) priionyl hexamethylenediamine, N, N'-tetramethylenebis-3- (3'-methyl-5'-t-butyl-4-hydroxy Phenol) pripionyldiamine, N, N′-bis-3- (3 ′, 5′-di-t-butyl-4-hydroxyphenol) prepionyl) hydrazine, N-salicyloyl-N′-salicylidenehydrazine, 3- (N-salicyloyl) amine-1,2,4-triazole, N, N′-bis- (2- (3- (3,5-di-butyl-4-hydroxyphenyl) propionyloxy) ethyl) oxyamide Etc.

  Among these hindered phenolic antioxidants, triethylene glycol-bis- (3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) -propionate), tetrakis- (methylene-3- ( 3'5'-di-t-butyl-4'-hydroxyphenyl) -propionate methane is preferred. These antioxidants are 0.01-3 parts by weight, preferably 100 parts by weight of polyacetal resin. It is used in the range of 0.05 to 2 parts by weight, more preferably 0.1 to 1 part by weight.

  Thermal stabilizers include compounds and polymers containing formaldehyde-reactive nitrogen such as dicyanamide, melamine, melamine and formaldehyde compounds, polyamide resins (eg, nylon 46, 6, 66, 610, 612, 12 66-6, 66-66-10, 66-12, etc.), poly-β-alanine, polyacrylamide, urea derivatives such as urea and hydantoin, allantoin, acid imides such as succinimide, hydrazide compounds and the like. Among these, a cocondensate of melamine and formaldehyde, a polyamide resin, poly-β-alanine, and polyacrylamide are preferable, and a polyamide resin and poly-β-alanine are more preferable. These are 0.001-5 weight part with respect to 100 weight part of polyacetal resin, Preferably it is 0.005-3 weight part, More preferably, it is 0.01-2 weight part.

Examples of formic acid supplements include alkali metal or alkaline earth metal hydroxides, inorganic acid salts and carboxylate salts, such as hydroxides such as sodium, potassium, magnesium, calcium or barium, and carbonic acid of the above metals. Examples include salts, phosphates, silicates, and borates. Specifically, calcium salts are most preferred, and are calcium hydroxide, calcium carbonate, calcium phosphate, calcium silicate, calcium borate, and fatty acid calcium (calcium stearate, calcium myristate, etc.), and these fatty acids are substituted with hydroxyl groups. It may be. Of these, fatty acid calcium salts (calcium stearate, calcium myristate) are preferred. These alkali metal or alkaline earth metal hydroxides, inorganic acid salts and carboxylates are used in an amount of 0.01 to 3 parts by weight, preferably 0.03 to 1 part by weight, more preferably 100 parts by weight of the polyacetal resin. Is 0.03 to 0.5 parts by weight.
The composition of the present invention includes known heat stabilizers, antioxidants, formic acid scavengers, weathering (light) stabilizers, and crystals of lubricants, talc, boron nitride, etc., as long as the effects of the present invention are not impaired. Nucleating agents, pigments, reinforcing materials, conductive materials, thermoplastic resins, thermoplastic elastomers and the like can be added.

The present invention will be described based on examples and comparative examples.
First, the evaluation methods used in Examples and Comparative Examples are shown below.
(1) Compression characteristics (distortion amount: mm)
Using an SH-75 injection molding machine manufactured by Sumitomo Heavy Industries, Ltd., cylinder temperature 200 ° C., injection pressure 30 MPa, injection speed 30%, injection time 25 seconds, cooling time 15 seconds, mold temperature 70 ° C., length 4 mm × A rectangular parallelepiped having a width of 4 mm and a height of 6 mm was formed, and the amount of strain was measured when compressed for 1000 minutes with a force of 400 N from the height direction at 70 ° C. The smaller the amount of distortion, the better the compression characteristics.

(2) High temperature creep resistance (destruction time)
Using an IS-80A injection molding machine manufactured by Toshiba Corporation, cylinder temperature 200 ° C., injection pressure 50 MPa, injection speed 30%, injection time 15 seconds, cooling time 25 seconds, mold temperature 70 ° C., dimensions 110 mm × 6. A strip-shaped test piece of 5 mm × 3 mm was prepared, and a tensile stress of 8 MPa was applied to the test piece and left in air at 130 ° C., and the time until the test piece was broken was measured. The longer the time until destruction, the better the creep resistance.

(3) Metal Corrosion Resistance As a typical example of metal, it was molded by the above (2) on a magnetic material that is likely to cause corrosion and its effect can be easily confirmed, specifically on an 8 mm VTR tape (trade name: Hi8ME120 manufactured by TDK). The molded body was placed and allowed to stand for 2 weeks under conditions of 60 ° C. and 90% relative humidity, and evaluated according to the following criteria based on the degree of discoloration of the tape surface.
○ Almost no discoloration on the tape surface △ Slight discoloration on the tape surface × Discoloration on the tape surface

(4) Corrosion resistance to other resins As a representative example of other resins, a polycarbonate resin that often coexists with a polyacetal resin in a magneto-optical disk device or the like was selected. Specifically, CD-R650MB manufactured by Hitachi Maxell Co., Ltd. and the molded body molded in the above (2) were allowed to coexist in a petri dish in a non-contact state, and the condition was 60 ° C. and 90% relative humidity for 2 weeks. After being allowed to stand, the degree of microcracks on the surface of the CD-R was observed with a microscope, and the degree of evaluation was evaluated according to the following criteria.
○: No crack △: Slight cracks are observed ×: Cracks are observed

(5) Total amount of volatile organic compounds excluding formaldehyde released when heated at 90 ° C. for 30 minutes (weight ppm)
Several tens mg of polyacetal resin is heated in a sealed container at 90 ° C. for 30 minutes, and then the gas in the container is introduced into GC (Gas Chromatography) -MS (Mass Spectrometer), and each detected component is quantified using toluene as a standard substance. And the sum was calculated | required about components other than formaldehyde. The lower limit of detection was 1 ppm by weight.
(6) Amount of formaldehyde released when heated at 60 ° C. for 3 hours (weight ppm)
About 20 g of polyacetal resin was suspended in a sealed container filled with 50 g of water so as not to be immersed in water, heated at 60 ° C. for 3 hours to absorb the released formaldehyde, and this water was analyzed by the acetylacetone method.

[Example 1, Comparative Examples 1-2]
First, 0.1% by weight of nylon 6-6 as a heat stabilizer and ethylene bis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate as an antioxidant] Obtained by copolymerization of 0.045 mol of 1,3-dioxolane as a comonomer with respect to 1 mol of trioxane, with 0.3 wt% of 0.1 wt% of calcium distearate as a formic acid scavenger. = 9.8 g / 10 min of polyacetal copolymer pellets (produced according to a known method described in Example 1 of Patent Document 7). The amount of formaldehyde released when heated at 60 ° C. for 3 hours and the total amount of volatile organic compounds excluding formaldehyde released when heated at 90 ° C. for 30 minutes were 15 ppm by weight and 120 wt. ppm. (Comparative Example 1) This polyoxymethylene copolymer was melted and devolatilized with a vented twin screw extruder under 700 Pa vent pressure (Comparative Example 2), and further vacuum dried and devolatilized at 130 ° C and 500 Pa for 48 hours. Thus, the polyacetal resin pellet of the present invention was obtained. The evaluation results are summarized in Table 1.

  The polyacetal resin of the present invention is a vehicle-related part that requires good compression characteristics and high-temperature creep characteristics, particularly fuel-related parts such as a fuel tank flange, seat-belt parts such as a seat belt retracting mechanism, and a door wheel. It is suitable as a building material part. Furthermore, since it is excellent in metal corrosion resistance and other resin corrosion resistance, it is also suitable for electrical and electronic equipment used in the presence of metals and other resins.

Claims (9)

A polyacetal resin, wherein the total amount of volatile organic compounds excluding formaldehyde released when heated at 90 ° C. for 30 minutes is less than 10 ppm by weight. The polyacetal resin according to claim 1, wherein the amount of formaldehyde released when further heated at 60 ° C for 3 hours is 10 ppm by weight or less. The polyacetal resin contains at least one sterically hindered phenol as an antioxidant, at least one compound and / or polymer containing formaldehyde-reactive nitrogen as a heat stabilizer, and at least one formic acid scavenger, respectively. The polyacetal resin according to claim 1 or 2, wherein The polyacetal resin according to claim 3, wherein the formic acid scavenger is an alkaline earth metal carboxylate. The polyacetal resin according to any one of claims 1 to 4, wherein the polyacetal resin is a polyoxymethylene copolymer. The molded object obtained from the polyacetal resin in any one of Claims 1-5. The molded article according to claim 6, wherein the total quantity of volatile organic compounds excluding formaldehyde released when the molded article is heated at 90 ° C for 30 minutes is less than 10 ppm by weight. The molded body according to claim 6 or 7, wherein the molded body is a part for an electric / electronic device. The molded body according to claim 6 or 7, wherein the molded body is a door roller or an automobile part.