JP6886785B2 - Polyacetal resin and its manufacturing method - Google Patents

Description

The present invention relates to a polyacetal resin and a method for producing the same.

Polyacetal resin is a resin having excellent mechanical strength such as rigidity and toughness, slidability, creepability, etc., and is widely used mainly in automobile parts, electric / electronic devices, and various mechanical parts.
In recent years, it has become important to reduce volatile substances generated from resins, mainly in the fields of automobile parts and the like. The volatile substance is an organic compound that easily volatilizes in the atmosphere at normal temperature and pressure, and formaldehyde is a problem in polyacetal resins. Therefore, there is a need for a technique for reducing the volatilization of formaldehyde from a polyacetal resin.
As a conventional technique for reducing the volatilization of formaldehyde from a polyacetal resin, for example, a technique for adding a hydrazide compound, an imide compound, and a sterically impaired phenol as additives is known (Patent Document 1). Further, a technique for defining a terminal of polyacetal in a specific structure and adding a guanamine compound and an ester compound is disclosed (Patent Document 2).

Japanese Unexamined Patent Publication No. 2005-336304 Japanese Unexamined Patent Publication No. 2007-051205

However, the above-mentioned technique for reducing the volatilization of formaldehyde is based on the addition of a nitrogen compound that reacts with formaldehyde, and many problems due to the additive have occurred. For example, the generation of deposits on the mold during injection molding (mold deposit, which may be abbreviated as MD below), the generation of additive bleeding from the molded piece, and the like can be mentioned. In this way, it is difficult to suppress the generation of MD (hereinafter referred to as "MD property") and reduce the generation of bleeding (hereinafter referred to as "bleed property") while reducing the volatilization of formaldehyde. Met.

As a result of diligent studies to solve the above problems, the present inventors have found that the volatilization of formaldehyde can be reduced by controlling the relaxation time of the intermediate phase in the crystal structure of the polyacetal resin within a specific range. It came to.

That is, the present invention is as follows.
[1] The relaxation time of the intermediate phase in the crystal structure measured by pulse NMR is 0.036 ms or less, the relaxation time of the intermediate phase / the relaxation time of the crystal phase is 1.9 or less, and the melting point is 160 ° C. to 170 ° C. Polyacetal resin.
[2] The relaxation time of the intermediate phase in the crystal structure measured by pulse NMR is 0.035 ms to 0.036 ms, and the relaxation time of the intermediate phase / relaxation time of the crystal phase is 1.6 to 1.9 [. 1] The polyacetal resin according to the above.
[3] The polyacetal resin according to [1] or [2], wherein the amount of fluorine in the polyacetal resin is 10 ppm or less.
[4] A molded product containing the polyacetal resin according to any one of [1] to [3].
[5] In the method for producing the polyacetal resin according to any one of [1] to [3], in the step of premixing the cyclic ether and / or the cyclic formal and the polymerization catalyst, and the step of premixing. It has a step of polymerizing the obtained mixture and other monomers, and in the step of premixing, an aliphatic hydrocarbon having a cyclic structure and a fat having a linear structure are used as a solvent for diluting the polymerization catalyst. In combination with group hydrocarbons,
The amount of the cyclic ether and / or the cyclic formal added is 1.0 × 10 ⁻² mol or more and 7.0 × 10 ⁻² mol or less with respect to 1 mol of the other monomer.
The surface roughness of the inner wall of the instruments used in performing the pre-mixing Ru der than 3.1 .mu.m, the production method of the polyacetal resin.
[6] The method for producing a polyacetal resin according to [5], wherein the temperature of the polymerization catalyst and the cyclic ether and / or cyclic formal is 20 to 60 ° C. in the step of premixing.

According to the present invention, it is possible to provide a polyacetal resin having less volatilization of formaldehyde and excellent MD property and bleeding property.

It is a damping curve fitted by using the equation (1) with respect to the damping curve obtained by the pulse NMR measurement of the polyacetal resin of Example 1.

Hereinafter, embodiments for carrying out the present invention (hereinafter, referred to as “the present embodiment”) will be described in detail.
The present invention is not limited to the following description, and can be implemented with various modifications within the scope of the gist thereof.

[Polyacetal resin]
In the present embodiment, the polyacetal resin refers to a polymer compound having an oxymethylene structure as a unit structure, and a polyacetal copolymer is particularly preferable.

A typical polyacetal copolymer is a polyacetal copolymer obtained by copolymerizing trioxane with cyclic ether and / or cyclic formal in the presence of a polymerization catalyst.
Trioxane is a cyclic trimer of formaldehyde, and is generally obtained by reacting an aqueous formaldehyde solution in the presence of an acidic catalyst.
Since this trioxane may contain impurities such as water, methanol, formic acid, and methyl formic acid that act as chain transfer agents, it is preferable to remove and purify these impurities by a method such as distillation.
In that case, the total amount of impurities acting as a chain transfer agent ^{is preferably 1 × 10 -3} mol or less, more preferably 5 × 10 ^-4 mol or less, with respect to 1 mol of trioxane.
By reducing the amount of impurities as described above, the resulting polymer has excellent thermal stability (less formaldehyde volatilization). Further, the MD property and the bleeding property when mixed with an additive or the like are excellent.

Cyclic ether and / or cyclic formal is a component copolymerizable with the trioxane, for example, ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, epibromohydrin, styrene oxide, oxatan, 1,3-dioxolane, ethylene. Glycolformal, propylene glycol formal, diethylene glycol formal, triethylene glycol formal, 1,4-butanediol formal, 1,5-pentanediol formal, 1,6-hexanediol formal and the like can be mentioned.
Of these, 1,3-dioxolane and 1,4-butanediol formal are particularly preferable.
These may be used alone or in combination of two or more.
The amount of the cyclic ether and / or the cyclic formal added is preferably 1.0 × 10 ⁻² mol or more and 7.0 × 10 ⁻² mol or less, more preferably 3.0 × 10 ⁻² mol, based on 1 mol of the trioxane. It is 6.0 × 10 ⁻² mol or less.
When the copolymerization ratio of the cyclic ether and / or the cyclic formal is set in this range, it becomes easy to adjust the values of the relaxation time of the intermediate phase and the relaxation time of the intermediate phase / relaxation time of the crystalline phase to the ranges described later.

Examples of the polymerization catalyst include boric acid, tin, titanium, phosphorus, arsenic and antimony compounds represented by Lewis acid, and in particular, boron trifluoride, boron trifluoride-based hydrate, and oxygen atom or sulfur atom. A coordination compound compound of an organic compound containing the above and boron trifluoride is preferable. For example, boron trifluoride, boron trifluoride diethyl etherate, and boron trifluoride-di-n-butyl etherate can be mentioned as preferable examples.
These may be used alone or in combination of two or more.

Further, the polymerization catalyst is preferably diluted and used, and the solvent to be diluted is not particularly limited as long as it does not participate in or adversely affect the polymerization reaction. For example, aromatic hydrocarbons such as benzene, toluene, xylene; aliphatic hydrocarbons such as cyclobutane, cyclopentane, cyclohexane; diethyl ether, diethylene glycol dimethyl ether, 1,4-dioxane, etc., as compounds having a cyclic structure. Ethers are mentioned,
Aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane as compounds having a linear structure; halogens such as chloroform, dichloromethane, carbon tetrachloride. Examples include chemical hydrocarbons.
Among these, aliphatic hydrocarbons are preferable from the viewpoint of low cost, cyclohexane can be mentioned as a compound having a cyclic structure, and n-heptane and n-hexane can be mentioned as preferable compounds as a compound having a linear structure. ..
In particular, when an aliphatic hydrocarbon having a cyclic structure and an aliphatic hydrocarbon having a linear structure are used in combination, the relaxation time of the intermediate phase in the crystal structure of the obtained polycetal resin is shortened, and the volatilization of formaldehyde tends to be reduced. It is in.
Further, the MD property and the bleeding property when mixed with an additive or the like are excellent.

The amount of the polymerization catalyst added ^{is preferably in the range of 1 × 10 -6} to 1 × 10 ^-4 mol, more preferably in the range of 3 × 10 ^{-6 to} 5 × 10 ^-5 mol, based on 1 mol of the trioxane. More preferably, it is in the range of ^{5 × 10 -6} to 4 × 10 ^{-5 mol.}
When the amount of the polymerization catalyst added is within the above range, the polymerization reaction can be stably carried out for a long time.

The polyacetal resin of the present embodiment has a relaxation time of the intermediate phase of 0.037 ms or less, a relaxation time of the intermediate phase / relaxation time of the crystal phase of 1.9 or less, and a melting point in the crystal structure measured by pulse NMR. It is 160 to 170 ° C. The relaxation time of the intermediate phase is preferably 0.035 ms to 0.037 ms, and the relaxation time of the intermediate phase / relaxation time of the crystalline phase is preferably 1.6 to 1.9.

Here, the pulse NMR is one of the solid NMR, and detecting a response signal to the pulse, a technique for obtaining ¹ H nuclear magnetic relaxation time of the sample (index indicating the molecular mobility). As a response to the pulse, a free induction decay signal (FID signal) is obtained. When a sample having a plurality of components having different molecular motility such as a crystalline resin is measured, the obtained FID is the sum of the FIDs of the multiple components having different relaxation times, and this is separated by using the least squares method. , The relaxation time of each component can be detected.
In general, the crystalline resin is often separated into three components, a component having a relaxation time of 0.01 to 0.02 ms, a component having a relaxation time of 0.03 to 0.1 ms, and a component having a relaxation time of 0.1 ms or more. A component having a relaxation time of 0.01 to 0.02 ms corresponds to a crystalline phase, a component having a relaxation time of 100 ms or more corresponds to an amorphous phase, and a component having a relaxation time of 0.03 to 0.1 ms is an intermediate phase. (However, the amount of these components is different from the crystallinity obtained by analysis of other measuring means such as WAXS and DSC).
The above-mentioned FID (sum of FIDs of each component) is represented by the following formula (1), the relaxation time of the crystal phase is represented by Tc, and the relaxation time of the intermediate phase is represented by Ta.

ここで、Ｍ（ｔ）は、時間ｔ（ｍｓ）における磁化強度、Ｃ_r、Ｃ_a、Ｃ_mは、それぞれ、ポリアセタール樹脂に含まれる結晶相、中間相及び非晶相の割合（ｗｔ％）を表す。Ｔ_c、Ｔ_a、Ｔ_mは、それぞれ結晶相、中間相、非晶相の緩和時間（ｍｓ）を表す。
また、Ｗａは中間相の減衰曲線を表すためのフィッティングパラメータである。ｂはプロトン配置の秩序性を反映するパラメータである。Ｗａおよびｂの値は測定対象によって異なり、本実施態様（ポリアセタール樹脂）においてはＷａ＝１．２、ｂ＝１７０とする。

Here, M (t) is the magnetization strength at time t (ms), and C _r , C _a , and C _m are the ratios (wt%) of the crystalline phase, intermediate phase, and amorphous phase contained in the polyacetal resin, respectively. Represents. T _c, T _a, T _m are each crystalline phase, it represents an intermediate phase, an amorphous phase relaxation time (ms).
Wa is a fitting parameter for expressing the attenuation curve of the intermediate phase. b is a parameter that reflects the order of the proton arrangement. The values of Wa and b differ depending on the measurement target, and in this embodiment (polyacetal resin), Wa = 1.2 and b = 170.

When the relaxation time of the intermediate phase and the relaxation time of the intermediate phase / relaxation time of the crystal phase in the crystal structure are within the above ranges, the volatilization of formaldehyde can be reduced, and the MD property and bleeding property when mixed with additives or the like are excellent. It was found by the research of the present inventors.
Although it is not clear why the relaxation time of the intermediate phase and the relaxation time of the intermediate phase / relaxation time of the crystal phase in the crystal structure can reduce the volatilization of formaldehyde, such a polyacetal resin has molecular motility. It is presumed that this is because it is excellent and decomposition at high temperatures is suppressed. However, the mechanism does not depend on this.

内壁の表面粗さが大きい器具を用いてプレ混合を行うと中間相の緩和時間Ｔａが小さくなる傾向にあり、算術平均粗さを３．１μｍ以上とすると、Ｔａを０．０３７ｍｓ以下にすることが容易になる。 The method for obtaining the polyacetal resin of the present embodiment is not limited, but for example, at least a part of the cyclic ether and / or cyclic formal is premixed with the polymerization catalyst in advance, and then another monomer (for example, trioxane) is obtained. ) Is effective. At this time, the total amount of the cyclic ether and / or the cyclic formal may be premixed, or a part of the cyclic ether and / or the cyclic formal may be premixed and the remaining amount may be mixed with another monomer (trioxane).
The material of the equipment (for example, piping or mixing container) used at the time of this pre-mixing is preferably one having SUS304 or more acid resistance and pitting corrosion resistance. The surface roughness of the inner wall of this instrument in contact with the cyclic ether and / or the cyclic formal and the polymerization catalyst is preferably 3.1 μm or more. Here, the surface roughness is the arithmetic mean roughness (Ra) defined by JIS B0601-2013. Specifically, from the roughness curve obtained for the inner wall, only the reference length (l) is extracted in the direction of the average line, and the absolute values of the deviations from the average line of the extracted portion to the roughness curve are summed and averaged. It is a value expressed by the following formula when the roughness curve is expressed by y = f (x).

Pre-mixing using an instrument with a large inner wall surface roughness tends to reduce the relaxation time Ta of the intermediate phase. If the arithmetic mean roughness is 3.1 μm or more, Ta should be 0.037 ms or less. Becomes easier.

The temperature of the polymerization catalyst and the cyclic ether and / or cyclic formal during premixing is preferably 20 to 60 ° C, more preferably 20 to 40 ° C.
By setting the pre-mixing temperature in the above range, the dispersibility of the polymerization catalyst at the time of pre-mixing is improved, and a polyacetal resin having a short relaxation time of the intermediate phase can be obtained.

After the above pre-mixing step, the polyacetal resin of the present embodiment is obtained through conventionally known polymerization steps and, if necessary, steps such as deactivation, drying, terminal stabilization, and stabilizer compounding.

The melt index (MI) (ASTM-D-1238-57T, 190 ° C., 2.16 kg) of the polyacetal resin of the present embodiment is preferably 0.5 g / 10 min or more and less than 120.0 g / 10 min, more preferably 1.0 g. It is / 10 min or more and 80.0 g / 10 min, more preferably 2.0 g / 10 min or more and 60.0 g / 10 min.
When MI is in the above range, the conventional characteristics of the polyacetal resin such as mechanical strength and abrasion resistance are sufficiently exhibited.

The melting point of the polyacetal resin of the present embodiment is 160 ° C to 170 ° C. By setting the melting point to 160 ° C to 170 ° C, the volatile components can be further reduced.
The polyacetal resin of the present embodiment preferably has a fluorine content of 10 ppm or less. Fluorine is generally due to the residue of the polymerization catalyst, and the amount of fluorine can be reduced by sufficiently deactivating the catalyst and kneading after the polymerization. The smaller the amount of fluorine, the better, and there is no lower limit, but for example, if the amount of fluorine is 5 ppm or more, it is less likely to cause a problem. Within such a range, the amounts of the crystal phase and the intermediate phase can be appropriately controlled.

The polyacetal resin of the present embodiment is an additive used in combination with a conventional polyacetal resin, for example, an antioxidant, a heat stabilizer, a light-resistant stabilizer, a mold release agent, as long as the effect of the present invention is not impaired. Colorants and the like may be added.
These may be used alone or in combination of two or more.

The molded body of the polyacetal resin of the present embodiment is not particularly limited, and examples thereof include molded bodies molded by injection molding, extrusion molding, etc., for example, the automobile field, the home appliance OA field, the medical field, and the industry. It can be used in the material field, and can be particularly suitably used in the automobile field, home appliance OA field, and medical field.

Hereinafter, the present invention will be described in detail with reference to specific examples and comparative examples, but the present invention is not limited to the following examples.
The terms and characteristic measurement methods in Examples and Comparative Examples are as follows.

Ｃ_r、Ｃ_a、Ｃ_mは、それぞれ結晶相、中間相、非晶相の割合（ｗｔ％）を表す。
Ｔ_c、Ｔ_a、Ｔ_mは、それぞれ結晶相、中間相、非晶相の緩和時間（ｍｓ）を表す。
Ｗ_aは中間相の減衰曲線を表すためのフィッティングパラメータであり、Ｗａ＝１．２とした。ｂはプロトン配置の秩序性を反映するパラメータであり、ｂ＝１７０とした。 <Measurement of relaxation time of intermediate phase and crystal phase in crystal structure by pulse NMR>
Equipment: Minispec MQ20 (manufactured by Bruker Biospin Co., Ltd.)
Nuclide: ¹ H
Measurement: T ₂
Measurement method: Solid echo method Number of integrations: 256 times Repeat time: 1.0 sec
Measurement temperature: 30 ° C
Attenuation curves were obtained by filling a 10 mmφ sample tube with about 900 mg of sample pellets under the above equipment and conditions and measuring pulse NMR.
The obtained attenuation curve was fitted and analyzed using the following formula (1) to obtain relaxation times for the crystal phase and the intermediate phase in the polyacetal resin. For fitting and analysis, the software attached to the above measuring device was used.

C _r , C _a , and C _m represent the ratios (wt%) of the crystalline phase, the intermediate phase, and the amorphous phase, respectively.
T _c, T _a, T _m are each crystalline phase, it represents an intermediate phase, an amorphous phase relaxation time (ms).
W _a is a fitting parameter for representing the decay curve of the intermediate phase, and the Wa = 1.2. b is a parameter that reflects the order of the proton arrangement, and b = 170.

<Measurement of formaldehyde volatilization amount (mg / kg)>
Using a 100GN injection molding machine manufactured by Toshiba Machine Co., Ltd., a test piece having a thickness of 40 mm × 100 mm and a thickness of 3 mm was molded from a polyacetal resin pellet at a molding temperature of 220 ° C. and a mold temperature of 80 ° C. The obtained test piece was left to stand in an environment of a temperature of 23 ° C. and a humidity of 50% for 1 day. Then, according to the VDA275 test of the German Association of the Automotive Industry (VDA), the amount of formaldehyde generated at 60 ° C. × 3 hr was measured.

<Evaluation of MD property>
Using a 100GN injection molding machine manufactured by Toshiba Machine Co., Ltd., a test piece having a thickness of 40 mm × 100 mm and a thickness of 3 mm was continuously molded from polyacetal resin pellets at a molding temperature of 200 ° C. and a mold temperature of 30 ° C. for 2000 shots. The state of the mold surface after 2000 shot molding was observed, and the results were evaluated in the following 5 stages.
Here, the "cavity" refers to a molding frame on the surface of the mold.
5 ... No deposits were observed.
4. A small amount of deposits was observed outside the cabinet. No deposits were observed in the cabinet.
3. A large amount of deposits were observed outside the cabinet. No deposits were observed in the cabinet.
2. A small amount of deposits was observed in the cabinet.
1. A large amount of deposits were observed in the cabinet.

<Evaluation of bleeding property>
Using a 100GN injection molding machine manufactured by Toshiba Machine Co., Ltd., a test piece having a thickness of 40 mm × 100 mm and a thickness of 3 mm was molded from a polyacetal resin pellet at a molding temperature of 220 ° C. and a mold temperature of 80 ° C. This test piece was left to stand for 300 hours in an environment of a temperature of 80 ° C. and a humidity of 90%, the state of the surface of the test piece was observed, and the result was evaluated in the following five stages.
Here, "bleed" means the embossment of an additive or the like on the surface of a test piece.
5. No bleeding occurred.
4. Bleed occurred on less than 10% of the surface of the test piece.
3 ... Bleed occurred on 10% or more and less than 30% of the surface of the test piece.
2. Bleed occurred on 30% or more and less than 60% of the surface of the test piece.
1. Bleed occurred in more than 60% of the test pieces.

<Measurement of polymerization yield (wt%)>
It was determined by dividing the mass of the obtained polyacetal resin by the total mass of trioxane, cyclic ether and cyclic formal used in the polymerization.
<Measurement of melting point (° C)>
5 mg of resin was collected from the polyacetal resin pellets, and the melting point was measured under the following conditions.
-Device: DSC-7 manufactured by PerkinElmer Co., Ltd.
-Conditions: The temperature was raised to 200 ° C. at 80 ° C./min, held for 2 min, then lowered to 50 ° C. at 80 ° C./min, raised to 200 ° C. at 2.5 ° C./min, and the melting point was measured.
<Measurement of MI (g / 10min)>
According to ASTM D1238, the measurement was carried out at 190 ° C. and a load of 2.16 kg using MELT INDEXER manufactured by Toyo Seiki Seisakusho Co., Ltd.

<Measurement of fluorine amount>
The measurement was performed with a fluoride ion meter.
Ion meter: HORIBA ion meter Fluoride electrode: HORIBA fluorine ion electrode a) Preparation of measurement sample 3 g of polyacetal resin pellets and 15 g of 1N HCL are placed in a pressure-resistant bottle, heated and decomposed at 130 ° C. for 3 hours, and after cooling, 8 g of decomposition liquid To this, 32 g of pure water and 60 g of Buffer solution were added to prepare a sample solution.
b) Preparation of Buffer solution To 500 ml of pure water, 121 g of tris (hydroxymethyl) aminomethane, 158 g of tris (hydroxymethyl) aminomethane hydrochloride, and 230 g of sodium tartrate dihydrate are added and dissolved. Then, the total amount was adjusted to 1 L with pure water.
c) Preparation of standard solution Three types of commercially available fluorine standard solutions with known concentrations were prepared, and 60 g of the above Buffer solution and 38 g of pure water were added to 2 g of each to prepare three types of standard solutions, and these were used. A calibration curve was created.

[Example 1]
A biaxial paddle type continuous polymerization reactor with a jacket (Kurimoto, Ltd., diameter 2B, L / D = 14.8) capable of passing a heat medium was adjusted to 80 ° C.
As a premix, the polymerization catalyst and the cyclic ether and / or the cyclic formal were mixed using a T-shaped pipe (arithmetic mean roughness of the inner wall of the pipe was 4 μm) so that they would collide from the front. Specifically, as a polymerization catalyst, 0.18 g / hr of boron trifluoride-di-n-butyl etherate, 5.5 g / hr of cyclohexane and 1.0 g / hr of n-hexane were continuously mixed. , Cyclic ether and / or cyclic formal, 1,3-dioxolane 120.9 g / hr was continuously introduced from each sleeve of the above-mentioned T-shaped pipe, and both were collided head-on to obtain a premixed solution. The temperature of the polymerization catalyst and the cyclic ether and / or cyclic formal during premix was 30 ° C.
The premixed solution obtained in this manner, 127.58 g / hr, and the mixed solution, which is a mixture of trioxane 3500 g / hr and methylal 2.1 g / hr as a molecular weight modifier continuously in a pipe, are mixed from separate pipes. It was continuously supplied to the polymerization reactor, and polymerization was carried out under the conditions of the polymerization reactor set temperature of 80 ° C., the polymerization peak temperature of 110 ° C., and the polymerization time (retention time) of 5 minutes. The amount of impurities in the trioxane was 7 × 10 ^-4 mol / mol-trioxane.
What was discharged from the polymerization reactor was put into an aqueous triethylamine solution (0.5% by mass) to completely deactivate the polymerization catalyst, and then filtered, washed, and dried to obtain a crude polyacetal copolymer. .. To the obtained crude polyacetal copolymer, triethyl (2-hydroxyethyl) ammonium hydrochloride as a quaternary ammonium compound was added so as to be 10 ppm in terms of the amount of nitrogen. After mixing uniformly, it was dried at 120 ° C.
The obtained polyacetal resin (polyacetal copolymer) had a polymerization yield of 80% and a melting point of 164 ° C.
Next, 0.35 parts by mass of triethylene glycol-bis- [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] was added and mixed with 100 parts by mass of the dried polyacetal resin, and the temperature was adjusted to 200 ° C. It was supplied to a set twin-screw extruder (L / D = 40) with a vent together with 2 parts by mass of a 0.8 mass% triethylamine aqueous solution, decomposed and stabilized while degassing under reduced pressure at 21 KPa, and pelletized with a pelletizer. did. Then, it was dried for 2 hours at 100 ° C. to obtain stable polyacetal resin pellets. The results are shown in Table 1.

[Example 2]
The same operation as in Example 1 was carried out except that the temperature of the polymerization catalyst and the cyclic ether and / or the cyclic formal during the premix was set to 45 ° C. At this time, the polymerization yield was 81%. The results are shown in Table 1.
[ Reference Example 3]
The same operation as in Example 1 was carried out except that the amount of 1,3-dioxolane was set to 43.2 g / hr. At this time, the polymerization yield was 81%. The results are shown in Table 1.
[ Reference Example 4]
The same operation as in Example 1 was carried out except that cyclohexane was the only diluting solvent for the polymerization catalyst (6.5 g / hr). At this time, the polymerization yield was 80%. The results are shown in Table 1.

[Comparative Example 1]
The same operation as in Example 1 was carried out except that the temperature of the premixed polymerization catalyst and the cyclic ether and / or cyclic formal was set to 10 ° C. At this time, the polymerization yield was 80%. The results are shown in Table 1.
[Comparative Example 2]
The same operation as in Example 1 was carried out except that 1,3-dioxolane was continuously mixed with trioxane and supplied without premixing, and the amount of polymerization catalyst was 0.18 g / hr. At this time, the polymerization yield was 79%. The results are shown in Table 1.
[Comparative Example 3]
The same operation as in Example 1 was carried out except that the supply amount of 1,3-dioxolane was set to 14.4 g / hr. At this time, the polymerization yield was 79%. The results are shown in Table 1.
[Comparative Example 4]
The same operation as in Example 1 was performed except that the arithmetic mean roughness of the inner wall of the T-shaped pipe used for pre-mixing was set to 2.9 μm. At this time, the polymerization yield was 80%. The results are shown in Table 1.

Compared with those of Comparative Examples, the polyacetal resins of Examples 1 and 2 and Reference Examples 3 and 4 had less formaldehyde volatilization and were excellent in MD property and bleeding property .

The polyacetal resin of the present invention has less volatilization of formaldehyde and is excellent in MD property and bleeding property, so that it can be used for various purposes. In particular, the polyacetal resin of the present invention can be suitably used for automobile parts, electric / electronic devices, and the like.

Claims (6)

The relaxation time of the intermediate phase in the crystal structure measured by pulse NMR is 0.036 ms or less, the relaxation time of the intermediate phase / the relaxation time of the crystal phase is 1.9 or less, and the melting point is 160 ° C. to 170 ° C. resin. According to claim 1, the relaxation time of the intermediate phase in the crystal structure measured by pulse NMR is 0.035 ms to 0.036 ms, and the relaxation time of the intermediate phase / relaxation time of the crystal phase is 1.6 to 1.9. The polyacetal resin described. The polyacetal resin according to claim 1 or 2, wherein the amount of fluorine in the polyacetal resin is 10 ppm or less. A molded product containing the polyacetal resin according to any one of claims 1 to 3. The method for producing a polyacetal resin according to any one of claims 1 to 3.
It comprises a step of premixing the cyclic ether and / or cyclic formal and the polymerization catalyst, and a step of polymerizing the mixture obtained in the premixing step with other monomers.
In the pre-mixing step, an aliphatic hydrocarbon having a cyclic structure and an aliphatic hydrocarbon having a linear structure are used in combination as a solvent for diluting the polymerization catalyst.
The amount of the cyclic ether and / or the cyclic formal added is 1.0 × 10 ⁻² mol or more and 7.0 × 10 ⁻² mol or less with respect to 1 mol of the other monomer.
The surface roughness of the inner wall of the instruments used in performing the pre-mixing Ru der than 3.1 .mu.m, the production method of the polyacetal resin. The method for producing a polyacetal resin according to claim 5, wherein in the pre-mixing step, the temperature of the polymerization catalyst and the cyclic ether and / or the cyclic formal is 20 to 60 ° C.

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