JP2018002983A - Polyacetal resin, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyacetal resin that has low volatility, and also has reduced occurrences of MDs (mold deposits) and bleeding.SOLUTION: In a polyacetal resin, in a crystal structure measured by pulse NMR, the relaxation time of an intermediate phase is 0.037 ms or less, the relaxation time of the intermediate phase/the relaxation time of a crystal phase is 1.9 or less, and a melting point is 160°C-170°C.SELECTED DRAWING: Figure 1

Description

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

Polyacetal resin is a resin excellent in mechanical strength such as rigidity and toughness, slidability, and creep properties, and is widely used mainly in automobile parts, electrical / electronic devices and various mechanical parts.
In recent years, it has become important to reduce volatile substances generated from resins, mainly in the field of automobile parts and the like. Volatile substances are organic compounds that easily volatilize in the atmosphere at normal temperature and pressure, and formaldehyde is a problem in polyacetal resins. Therefore, a technique for reducing volatilization of formaldehyde from the polyacetal resin is required.
As a conventional technique for reducing volatilization of formaldehyde from a polyacetal resin, for example, a technique of adding a hydrazide compound, an imide compound, and a sterically hindered phenol as additives is known (Patent Document 1). Moreover, the technique which prescribes | regulates the terminal of a polyacetal to a specific structure, and adds a guanamine compound and an ester compound is disclosed (patent document 2).

JP-A-2005-336304 JP 2007-051205 A

  However, the technique for reducing volatilization of formaldehyde is based on the addition of a nitrogen compound that reacts with formaldehyde, and there are many problems arising from the additive. For example, generation of deposits (mold deposit, which may be abbreviated as MD hereinafter) on the mold during injection molding, generation of additive bleeding from the molded piece, and the like can be mentioned. Thus, it is difficult to suppress the occurrence of MD while reducing the volatilization of formaldehyde (hereinafter referred to as “MD property”) and to reduce the occurrence of bleed (hereinafter referred to as “bleed property”). Met.

  As a result of intensive investigations 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, and the present invention. 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 0.037 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. A polyacetal resin.
[2] The relaxation time of the intermediate phase in the crystal structure measured by pulse NMR is 0.035 ms to 0.037 ms, and the relaxation time of the intermediate phase / relaxation time of the crystal phase is 1.6 to 1.9 [ 1].
[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 article comprising the polyacetal resin according to any one of [1] to [3].

  According to the present invention, it is possible to provide a polyacetal resin with less formaldehyde volatilization and excellent MD and bleed properties.

FIG. 3 is an attenuation curve fitted using the equation (1) with respect to an attenuation curve obtained by pulse NMR measurement on the polyacetal resin of Example 1. FIG.

Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail.
In addition, this invention is not limited to the following description, In the range of the summary, various deformation | transformation can be implemented.

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

A typical polyacetal copolymer is a polyacetal copolymer obtained by copolymerizing trioxane and 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 that act as chain transfer agents such as water, methanol, formic acid, and methyl formate, 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, relative to 1 mol of trioxane.
By reducing the amount of impurities as indicated above, the polymer produced has excellent thermal stability (less formaldehyde volatilization). Moreover, MD property and bleed property when mixed with additives and the like are excellent.

Cyclic ether and / or cyclic formal is a component copolymerizable with the trioxane, such as ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, epibromohydrin, styrene oxide, oxatan, 1,3-dioxolane, ethylene. Examples include glycol formal, propylene glycol formal, diethylene glycol formal, triethylene glycol formal, 1,4-butanediol formal, 1,5-pentanediol formal, and 1,6-hexanediol formal.
Among 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 addition amount of cyclic ether and / or cyclic formal is preferably 1.0 × 10 ⁻² mol or more and 7.0 × 10 ⁻² mol or less, more preferably 3.0 × 10 ⁻² mol, relative to 1 mol of trioxane. The amount is 6.0 × 10 ⁻² mol or less.
When the copolymerization ratio of the cyclic ether and / or the cyclic formal is within 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 / the relaxation time of the crystal phase to the ranges described later.

Examples of the polymerization catalyst include boric acid typified by Lewis acid, tin, titanium, phosphorus, arsenic and antimonide, especially boron trifluoride, boron trifluoride hydrate, and oxygen atom or sulfur atom. A coordination complex compound of an organic compound containing and boron trifluoride is preferable. For example, boron trifluoride, boron trifluoride diethyl etherate, and boron trifluoride-di-n-butyl etherate are preferable examples.
These may be used alone or in combination of two or more.

The polymerization catalyst is preferably used after being diluted, and the solvent for dilution is not particularly limited as long as it does not participate in the polymerization reaction or exert an adverse effect. For example, as a compound having a cyclic structure, aromatic hydrocarbons such as benzene, toluene and xylene; aliphatic hydrocarbons such as cyclobutane, cyclopentane and cyclohexane; diethyl ether, diethylene glycol dimethyl ether and 1,4-dioxane Ethers,
Compounds having a linear structure include aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, n-octane, n-nonane and n-decane; halogens such as chloroform, dichloromethane and carbon tetrachloride And hydrocarbons.
Among these, aliphatic hydrocarbons are preferable from the viewpoint of low cost, and examples of the compound having a cyclic structure include cyclohexane, and examples of the compound having a linear structure include n-heptane and n-hexane. .
In particular, when an aliphatic hydrocarbon having a cyclic structure and an aliphatic hydrocarbon having a straight chain structure are used in combination, the relaxation time of the intermediate phase in the crystal structure of the resulting polycetal resin is reduced, and volatilization of formaldehyde tends to be reduced. It is in.
Moreover, MD property and bleed property when mixed with additives and the like are excellent.

The addition amount of the polymerization catalyst 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, relative to 1 mol of the trioxane. More preferably, it is the range of 5 * 10 < ^-6 > ^-4 * 10 <^-5> mol.
When the addition amount of the polymerization catalyst is within the above range, a long-time polymerization reaction can be carried out stably.

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

Here, pulse NMR is one of solid-state NMR, and is a technique for detecting a ¹ H nuclear magnetic relaxation time (an index representing molecular mobility) of a sample by detecting a response signal to the pulse. In response to the pulse, a free induction decay (FID signal) is obtained. When a sample having a plurality of components having different molecular motility, such as a crystalline resin, is measured, the FID obtained is the sum of the FIDs of the plurality of components having different relaxation times, and this is separated by using the least square 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 0.03 to 0.1 ms, and a component having 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 amounts of these components are different from the crystallinity obtained by analysis of other measuring means such as WAXS and DSC).
The above-mentioned FID (sum of FID of each component) is represented by the following formula (1), and the relaxation time of the crystal phase is represented by Tc and the relaxation time of the intermediate phase is represented by Ta.

Here, M (t) is the magnetization intensity at time t (ms), C _r , C _a , and C _m are the proportions (wt%) of the crystalline phase, intermediate phase, and amorphous phase contained in the polyacetal resin, respectively. Represents. T _c , T _a , and T _m represent relaxation times (ms) of the crystalline phase, the intermediate phase, and the amorphous phase, respectively.
Wa is a fitting parameter for representing the attenuation curve of the intermediate phase. b is a parameter reflecting the order of proton arrangement. The values of Wa and b vary depending on the object to be measured. In this embodiment (polyacetal resin), Wa = 1.2 and b = 170.

If the relaxation time of the intermediate phase in the crystal structure and the relaxation time of the intermediate phase / the relaxation time of the crystal phase are within the above ranges, the volatilization of formaldehyde can be reduced, and the MD property and bleeding property when mixed with an additive, etc. are excellent. It became clear by the present inventors' research.
The reason why the volatilization of formaldehyde can be reduced when the relaxation time of the intermediate phase in the crystal structure and the relaxation time of the intermediate phase / the relaxation time of the crystal phase are within the above ranges is not clear. However, such polyacetal resin has no molecular mobility. It is presumed that decomposition at high temperature is suppressed because of its superiority. However, the mechanism does not depend on this.

The method for obtaining the polyacetal resin of this embodiment is not limited. 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). ). At this time, the cyclic ether and / or cyclic formal may be premixed in the whole amount, or a part thereof may be premixed and the remaining amount may be mixed in another monomer (trioxane).
The material of the instrument (for example, piping or mixing container) used in the pre-mixing preferably has acid resistance and pitting corrosion resistance of SUS304 or higher. And it is preferable that the surface roughness of the inner wall which contacts cyclic ether and / or cyclic formal and a polymerization catalyst of this instrument is 3.1 micrometers or more. Here, the surface roughness is an arithmetic average roughness (Ra) defined in JIS B0601-2013. Specifically, from the roughness curve obtained for the inner wall, a reference length (l) is extracted in the direction of the average line, and the absolute value of the deviation from the average line of the extracted portion to the roughness curve is summed and averaged. When the roughness curve is represented by y = f (x), it is a value represented by the following formula.
When premixing is performed using an instrument having a large inner wall surface roughness, the relaxation time Ta of the intermediate phase tends to decrease, and when the arithmetic average roughness is 3.1 μm or more, Ta should be 0.037 ms or less. Becomes easier.

Further, the temperature of the polymerization catalyst and the cyclic ether and / or the cyclic formal during premixing is preferably 20 to 60 ° C, more preferably 20 to 40 ° C.
By setting the premixing temperature within the above range, it is possible to improve the dispersibility of the polymerization catalyst during premixing and to obtain a polyacetal resin having a short intermediate phase relaxation time.

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

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. / 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 characteristics of polyacetal resin, such as mechanical strength and abrasion resistance, are sufficiently developed.

The melting point of the polyacetal resin of this embodiment is 160 ° C to 170 ° C. By setting the melting point to 160 ° C. to 170 ° C., volatile components can be further reduced.
The polyacetal resin of this 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 performing catalyst deactivation and kneading after polymerization. A smaller amount of fluorine is better and there is no lower limit. For example, if the amount of fluorine is 5 ppm or more, there is little problem. By setting it as such a range, the quantity of a crystal phase and an intermediate phase can be controlled moderately.

The polyacetal resin of the present embodiment is an additive used in combination with a conventional polyacetal resin within a range not impairing the effects of the present invention, for example, an antioxidant, a heat stabilizer, a light stabilizer, a release agent, A colorant or the like may be added.
These may be used alone or in combination.

  Although it does not specifically limit as a molded object of the polyacetal resin of this embodiment, The molded object shape | molded by injection molding, extrusion molding etc. is mentioned, For example, a motor vehicle field, household appliances OA field | area, a medical field, industrial It can be used in the material field, and can be suitably used particularly in the automobile field, home appliance OA field, and medical field.

Hereinafter, the present invention will be described in detail with specific examples and comparative examples, but the present invention is not limited to the following examples.
In addition, the measurement method of the term and characteristic in an Example and a comparative example was as follows.

<Measurement of relaxation time of intermediate phase and crystal phase in crystal structure by pulse NMR>
Apparatus: Minispec MQ20 (Bruker Biospin Co., Ltd.)
Nuclide: ¹ H
Measurement: T ₂
Measurement method: Solid echo method Integration count: 256 times Repeat time: 1.0 sec
Measurement temperature: 30 ° C
Using the above apparatus and conditions, about 900 mg of sample pellets were filled in a 10 mmφ sample tube, and pulse NMR was measured to obtain an attenuation curve.
The obtained attenuation curve was fitted and analyzed using the following formula (1) to obtain relaxation times of the crystal phase and the intermediate phase in the polyacetal resin. For fitting and analysis, software attached to the measurement apparatus was used.
C _r , C _a , and C _m represent the proportions (wt%) of the crystalline phase, the intermediate phase, and the amorphous phase, respectively.
T _c , T _a , and T _m represent relaxation times (ms) of the crystalline phase, the intermediate phase, and the amorphous phase, respectively.
W _a is a fitting parameter for representing the attenuation curve of the intermediate phase, and Wa = 1.2. b is a parameter reflecting the order of proton arrangement, and b = 170.

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

<Evaluation of MD>
Using a 100GN injection molding machine manufactured by Toshiba Machine Co., Ltd., a test piece of 40 mm × 100 mm and a thickness of 3 mm was continuously molded from a polyacetal resin pellet 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 five stages.
Here, “cavity” refers to a molding frame on the mold surface.
5. No deposit was observed.
4. A small amount of deposit 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 deposit was observed in the cabinet.
1. A large amount of deposits were observed in the cabinet.

<Evaluation of bleeding>
Using a 100GN injection molding machine manufactured by Toshiba Machine Co., Ltd., a test piece of 40 mm × 100 mm and a thickness of 3 mm was molded from the polyacetal resin pellets at a molding temperature of 220 ° C. and a mold temperature of 80 ° C. The test piece was allowed 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 results were evaluated in the following five stages.
Here, “bleed” means that an additive or the like is raised on the surface of the test piece.
5. No bleed occurred.
4. Bleed occurred on less than 10% of the test piece surface.
3. Bleeding occurred on 10% or more and less than 30% of the test piece surface.
2. Bleed occurred on 30% or more and less than 60% of the test piece surface.
1. Bleed occurred in 60% or more of the test pieces.

<Measurement of polymerization yield (wt%)>
The mass of the obtained polyacetal resin was determined by dividing 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 / 10 min)>
According to ASTM D1238, measurement was performed at 190 ° C. and a load of 2.16 kg using a MELT INDEXER manufactured by Toyo Seiki Seisakusho.

<Measurement of fluorine content>
The measurement was performed with a fluorine ion meter.
Ion meter: HORIBA's ion meter Fluorine electrode: HORIBA's fluorine ion electrode a) Preparation of measurement sample Polyacetal resin pellets 3g, 1N HCl 15g were charged in a pressure-resistant bottle, thermally decomposed at 130 ° C for 3 hours, cooled and then decomposed 8g A sample solution was prepared by adding 32 g of pure water and 60 g of Buffer solution.
b) Preparation of Buffer liquid 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. Thereafter, the total amount was adjusted to 1 L with pure water.
c) Preparation of standard solutions Three types of commercially available fluorine standard solutions with known concentrations are prepared, and each of 2 g is prepared by adding 60 g of the above Buffer solution and 38 g of pure water to prepare three types of standard solutions. A calibration curve was created.

[Example 1]
A jacketed biaxial paddle type continuous polymerization reactor (Kurimoto Corporation, diameter 2B, L / D = 14.8) capable of passing a heat medium was adjusted to 80 ° C.
As premixing, the polymerization catalyst and cyclic ether and / or cyclic formal were mixed using a T-shaped pipe (arithmetic mean roughness of the inner wall of the pipe of 4 μm) so that both collided from the front. Specifically, boron trifluoride-di-n-butyl etherate 0.18 g / hr, cyclohexane 5.5 g / hr and n-hexane 1.0 g / hr continuously mixed as a polymerization catalyst 1,3-dioxolane 120.9 g / hr as a cyclic ether and / or cyclic formal was continuously introduced from each sleeve of the above-mentioned T-shaped pipe, and both were collided front to obtain a pre-mixed solution. The temperature of the polymerization catalyst and cyclic ether and / or cyclic formal during premixing was 30 ° C.
From the separate pipes, 127.58 g / hr of the pre-mixed liquid obtained in this way and a mixed liquid in which methylal 2.1 g / hr as a molecular weight regulator was continuously mixed with 3500 g / hr of trioxane in a pipe. The polymerization was continuously supplied to the polymerization reactor, and polymerization was carried out under the conditions of a polymerization reactor set temperature of 80 ° C., a polymerization peak temperature of 110 ° C., and a polymerization time (residence time) of 5 minutes. The amount of impurities in trioxane was 7 × 10 ⁻⁴ mol / mol-trioxane.
What was discharged from the polymerization reactor was put into a triethylamine aqueous solution (0.5% by mass) to completely deactivate the polymerization catalyst, followed by filtration, washing and drying to obtain a crude polyacetal copolymer. . Triethyl (2-hydroxyethyl) ammonium formate as a quaternary ammonium compound was added to the obtained crude polyacetal copolymer so as to be 10 ppm in terms of the amount of nitrogen. After uniformly mixing, it was dried at 120 ° C.
The resulting 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-tert-butyl-5-methyl-4-hydroxyphenyl) propionate] is added to and mixed with 100 parts by mass of the dried polyacetal resin, and the mixture is heated to 200 ° C. It is supplied to a set twin-screw extruder with a vent (L / D = 40) together with 2 parts by weight of 0.8% by weight triethylamine aqueous solution, decomposed and stabilized while degassing under reduced pressure at 21 KPa, and pelletized by a pelletizer did. Thereafter, drying was performed at 100 ° C. for 2 hours to obtain stable polyacetal resin pellets. The results are shown in Table 1.

[Example 2]
The same operation as in Example 1 was performed except that the temperature of the polymerization catalyst and cyclic ether and / or cyclic formal at the time of premixing was 45 ° C. At this time, the polymerization yield was 81%. The results are shown in Table 1.
Example 3
The same operation as in Example 1 was performed except that the amount of 1,3-dioxolane was changed to 43.2 g / hr. At this time, the polymerization yield was 81%. The results are shown in Table 1.
Example 4
The diluting solvent for the polymerization catalyst is cyclohexane only (6.5 g / hr)
The same operation as in Example 1 was performed except that. 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 performed except that the temperature of the premixed polymerization catalyst and cyclic ether and / or cyclic formal was 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 performed, except that 1,3-dioxolane was continuously mixed and supplied to trioxane without performing premixing, and the amount of the 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 performed except that the supply amount of 1,3-dioxolane was changed 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 average roughness of the inner wall of the T-shaped pipe used for premixing was 2.9 μm. At this time, the polymerization yield was 80%. The results are shown in Table 1.

  The polyacetal resins of Examples 1 to 4 had less formaldehyde volatilization and excellent MD and bleeding properties than those of the comparative examples.

  Since the polyacetal resin of the present invention has little volatilization of formaldehyde and is excellent in MD property and bleeding property, it can be used for various applications. In particular, the polyacetal resin of the present invention can be suitably used for automobile parts, electrical / electronic devices and the like.

Claims (4)

  Polyacetal having an intermediate phase relaxation time of 0.037 ms or less, an intermediate phase relaxation time / crystal phase relaxation time of 1.9 or less, and a melting point of 160 ° C. to 170 ° C. measured by pulse NMR resin.   The intermediate phase relaxation time in the crystal structure measured by pulsed NMR is 0.035 ms to 0.037 ms, and the intermediate phase relaxation time / crystal phase relaxation time 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.   The molded object containing the polyacetal resin in any one of Claims 1-3.