JP2016145278A - Polyacetal resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyacetal resin composition having reduced formaldehyde generation amount while having high rigidity and high toughness.SOLUTION: The polyacetal resin composition contains 100 pts.wt. of a linear polyacetal copolymer having an oxymethylene unit as a main constitutional component and containing an oxyalkylene unit of 0.4 mol% to 0.9 mol% as a percentage in the constitutional composition of the linear polyacetal copolymer as a comonomer unit and 0.1 pts.wt. to 2 pts.wt. of a polyacetal copolymer having a branched or crosslinked structure, which is a copolymer of (b1) trioxane, (b2) a compound having 3 to 4 cyclic ether units in a molecule and (b3) a compound having a cyclic ether unit in a molecule and has Charpy impact strength (notched, 23°C) of 6 kJ/mor more.SELECTED DRAWING: None

Description

  The present invention relates to a polyacetal resin composition.

  Polyacetal resin is also referred to as POM resin, and has excellent properties in mechanical properties, thermal properties, electrical properties, slidability, moldability, etc. Widely used in automobile parts, precision machine parts, etc. However, with the expansion of the field where polyacetal resins are used, the required characteristics tend to become more sophisticated, complex and specialized.

  As an example, there is a demand for a material that further improves the rigidity, surface hardness, sliding characteristics, and the like while maintaining the excellent moldability, surface condition, and the like inherent in polyacetal resin. In response to such demands, as a means for improving rigidity, a method of filling a fibrous filler into a polyacetal resin is common, but this method has problems such as poor appearance of the molded product and deterioration of sliding characteristics. There is.

To increase rigidity, 99.5 to 97.5% by weight of trioxane (a) and 0.5 to 2.5% by weight of a compound (b) selected from a monofunctional cyclic ether compound and a monofunctional cyclic formal compound are copolymerized. To 99.9 to 90 parts by weight of a linear polyacetal resin (A) having a melt index of 1 to 50 g / min, 99.49 to 95.0% by weight of trioxane (a), a monofunctional cyclic ether compound, and Copolymerization of 0.5 to 4.0% by weight of the compound (b) selected from monofunctional cyclic formal compounds and 0.01 to 1.0% by weight of the polyfunctional glycidyl ether compound (c) having 3 to 4 functional groups Obtained by blending 0.1 to 10 parts by weight of a branched or cross-linked polyacetal resin (B) having a melt index of 0.1 to 10 g / min. Index and melt index of branched or crosslinked polyacetal resin ratio of the melt index of (B) is _{0.02 ≦ MI B / MI A ≦} 1.5 (MI A linear polyacetal resin (A), MI _B is a branched or There has been proposed a polyacetal resin composition in which a linear polyacetal resin (A) and a branched or cross-linked polyacetal resin (B) are selected so as to satisfy the relationship of the melt index of the cross-linked polyacetal resin (B) (for example, a patent Reference 1). The polyacetal resin composition described in Patent Document 1 is excellent in high rigidity, dimensional stability, and creep characteristics.

  Further, in order to improve sliding properties, 100 parts by weight of trioxane (a) with respect to 100 parts by weight of polyacetal resin (A), compound (b) 0.0005-2 having two or more cyclic ether units in one molecule Polyacetal copolymer (B) obtained by copolymerizing 0 to 20 parts by weight of compound (c) having one cyclic ether unit in one part by weight and a molecule, and having a total terminal group content of 15 to 150 mmol / kg A polyacetal resin composition containing 0.01 to 100 parts by weight has been proposed (see, for example, Patent Document 2). The polyacetal resin composition described in Patent Document 2 is excellent in rigidity, surface hardness, and sliding characteristics. Moreover, since the polyacetal resin composition of patent document 2 has suppressed the total terminal group amount of (B) component to below a fixed amount, it has suitable toughness.

JP 2003-342442 A JP 2002-003694 A

  In recent years, there has been a demand for a high-quality polyacetal copolymer that has particularly excellent thermal stability and generates very little formaldehyde. Therefore, further improvement is required to keep the amount of formaldehyde generated lower while having high rigidity and high toughness.

  An object of the present invention is to provide a polyacetal resin composition that has high rigidity and high toughness and suppresses the amount of formaldehyde generated as low as possible.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventor has found that a linear polyacetal copolymer containing oxyalkylene units at a certain ratio as comonomer units and a trifunctional or tetrafunctional polyacetal copolymer having a branched or crosslinked structure. It has been found that the above object can be achieved by including coalescence in a predetermined weight ratio, and the present invention has been completed. More specifically, the present invention provides the following.

(1) The present invention contains an oxymethylene unit as a main constituent component and an oxyalkylene unit as a comonomer unit as a proportion of a constituent unit of the linear polyacetal copolymer of 0.4 mol% or more and 0.9 mol% or less. 100 parts by weight of a linear polyacetal copolymer, (b1) trioxane, (b2) a compound having 3 to 4 cyclic ether units in one molecule, and (b3) a compound having one cyclic ether unit in one molecule ( c) 0.1 to 2 parts by weight of a polyacetal copolymer having a branched or crosslinked structure, which is a copolymer, and Charpy impact strength (notched, 23 ° C.) is 6 kJ / m ² or more It is a polyacetal resin composition.

  According to the present invention, it is possible to provide a polyacetal resin composition that has high rigidity and high toughness while keeping the amount of formaldehyde generated low.

  Hereinafter, specific embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and may be implemented with appropriate modifications within the scope of the object of the present invention. can do.

<Polyacetal resin composition>
The polyacetal resin composition according to the present invention includes a linear polyacetal copolymer that contains an oxyalkylene unit as a comonomer unit at a certain ratio, and is copolymerized using a heteropolyacid as a polymerization catalyst, and a trifunctional or 4-functional branched or crosslinked structure. And a functional polyacetal copolymer in a predetermined weight ratio.

[(A) linear polyacetal copolymer]
The (A) linear polyacetal copolymer has an oxymethylene unit as a main constituent component, and the oxyalkylene unit as a comonomer unit as a proportion of the constituent unit of the (A) linear polyacetal copolymer is 0.4 mol% or more. .9 mol% or less. In the present embodiment, the linear polyacetal copolymer refers to a linear polymer in which oxyalkylene monomer units are randomly inserted into a polymer chain composed of oxymethylene monomer units. Hereinafter, the (A) linear polyacetal copolymer is also referred to as “component (A)”.

The component (A) is positioned as a base resin. The component (A) is a polyacetal copolymer having an oxymethylene unit (—CH ₂ O—) as a main constituent unit and other comonomer units in addition to the oxymethylene group.

  (A1) Trioxane is widely used as the main raw material for the component (A). Trioxane refers to a cyclic trimer of formaldehyde, which is generally obtained by reacting an aqueous formaldehyde solution in the presence of an acidic catalyst, and is used after being purified by a method such as distillation. (A1) Trioxane is preferably one containing as little impurities as possible, such as water, methanol, formic acid and the like.

In the component (A), the comonomer unit includes an oxyalkylene unit (for example, an oxyethylene group (—CH ₂ CH ₂ O—), an oxybutylene group (—CH ₂ CH ₂ CH ₂ CH ₂ O—), etc.). .

  The proportion of the comonomer unit is 0.4 mol% or more and 0.9 mol% or less as a proportion of the constituent units of the linear polyacetal copolymer. If the proportion of comonomer units is too low, the amount of formaldehyde released may increase, which is not preferable. Moreover, when the ratio of a comonomer unit is too high, even if it mixes with (B) component in a suitable ratio, since sufficient rigidity may not be obtained, it is unpreferable. Specifically, when the ratio of the comonomer unit is too high, the bending elastic modulus of the test piece based on ISO178 may be less than 2700 MPa.

  The number of carbon atoms of the oxyalkylene unit is not particularly limited, but is preferably 2 or more and 4 or less.

  Examples of the comonomer include (a2) one or more compounds selected from a monofunctional cyclic ether compound and a monofunctional cyclic formal compound. In the present embodiment, the monofunctional cyclic ether compound refers to a compound having one cyclic ether unit in one molecule, and the monofunctional cyclic formal compound refers to a compound having one cyclic formal unit in one molecule. . Specifically, ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, epibromohydrin, styrene oxide, oxetane, 3,3-bis (chloromethyl) oxetane, tetrahydrofuran, trioxepane, 1,3-dioxolane, ethylene glycol Examples include formal, propylene glycol formal, diethylene glycol formal, triethylene glycol formal, 1,4-butanediol formal, 1,5-pentanediol formal, 1,6-hexanediol formal, and the like.

  The melt index (also referred to as “MI”) of the component (A) is not particularly limited, but is preferably 7 g / 10 min or more and 20 g / 10 min or less in view of strength and moldability, More preferably, it is / 10 min or more and 15 g / 10 min or less. In this embodiment, the melt index is a characteristic value corresponding to the molecular weight. A lower MI indicates a higher molecular weight, and a higher MI indicates a lower molecular weight. When the melt index is too small, the fluidity is lowered, and there is a possibility that a problem occurs in moldability. On the other hand, if the melt index is too large, the strength may be reduced. In the present embodiment, the melt index refers to a value measured under conditions of 190 ° C. and a load of 2160 g according to ASTM D-1238.

  The component (A) may be a terpolymer composed of three components. The polyacetal copolymer may be a random copolymer, a block copolymer, or the like.

[Production method of component (A)]
In producing the component (A), the polymerization apparatus is not particularly limited, and a known apparatus can be used, and any method such as a batch system or a continuous system can be used.

  The component (A) is generally obtained by a method of adding a suitable amount of molecular weight regulator and performing bulk polymerization using a cationic polymerization catalyst. Examples of the molecular weight modifier include low molecular weight acetal compounds having alkoxy groups such as methylal, methoxymethylal, dimethoxymethylal, trimethoxymethylal, oxymethylene di-n-butyl ether, alcohols such as methanol, ethanol, and butanol. Illustrated.

  In this embodiment, a heteropolyacid, an isopolyacid, or an acid salt thereof is used as a polymerization catalyst. They can also be used after diluting with an organic solvent or the like. In the present embodiment, by using a heteropolyacid, an isopolyacid or an acidic salt thereof as a polymerization catalyst, by using together with the component (B) described later, the amount of formaldehyde generated is reduced while having high rigidity and high toughness. A polyacetal resin composition kept as low as possible can be provided.

In particular, in toughness, a high Charpy impact strength (notched, 23 ° C.) of 6 kJ / m ² or more can be realized. In the present embodiment, the Charpy impact strength refers to a Charpy impact test value at 23 ° C. in a notched Charpy test piece prepared by injection molding in accordance with ISO 179 / 1eA.

  In addition, the amount of formaldehyde generated can be suppressed lower than that of other polymerization catalysts.

  Examples of the polymerization catalyst include compounds containing at least one selected from heteropolyacids, isopolyacids, or acidic salts thereof. Heteropolyacid is a polyacid produced by dehydration condensation of dissimilar oxygen acids, and a mononuclear or dinuclear nucleus formed by condensation of condensed acid groups sharing a oxygen atom with a specific dissimilar element at the center. Has complex ions. The isopolyacid is also referred to as an isopolyacid, a homonuclear condensed acid, or a homopolyacid, and refers to a high molecular weight inorganic oxygen acid comprising a condensate of inorganic oxygen acids having a single V-valent or VI-valent metal. .

(Heteropolyacid or its acid salt)
First, the heteropolyacid or its acid salt will be described in detail. The heteropolyacid or its acid salt can be represented by the general formula (1).
_{H x [M m · M '} n O l] · yH 2 O ··· (1)

  The heteropolyacid particularly effective as the polymerization catalyst of the present invention is at least one element selected from P and / or Si as the central element M in the above composition formula, and the coordination element M ′ is W, Mo, V This is a case of one or more elements selected from the above. From the viewpoint of polymerization activity, the coordination element M ′ is more preferably W or Mo. Moreover, in General formula (1), l is 10-100, m is 1-10, n is 6-40, x is 1 or more, y is 0-50.

The acidic salts H _x in the general formula (1) is substituted by a variety of metals it can also be used as catalysts of the present invention.

  Specific examples of heteropolyacids include phosphomolybdic acid, phosphotungstic acid, phosphomolybdotungstic acid, phosphomolybdovanadic acid, phosphomolybdotungstovanadic acid, phosphotungstovanadic acid, silicotungstic acid, silicomolybdic acid, and cimomolybdo Examples include tungstic acid and silicoribed tungsten tovanadate. In particular, from the viewpoint of polymerization activity, the heteropolyacid is preferably selected from silicomolybdic acid, silicotungstic acid, phosphomolybdic acid, and phosphotungstic acid.

(Isopolyacid or its acid salt)
Subsequently, the isopolyacid or the acid salt thereof will be described in detail. The isopolyacid or its acid salt can be represented by the general formula (2) or the general formula (3).
xM ^I ₂ O · pM ^V ₂ O ₆ · yH ₂ O (2)
xM ^I ₂ O · pM ^VI ₂ O ₆ · yH ₂ O (3)

In the general formulas (2) and (3), M ^I is hydrogen, but a part thereof may be substituted with a metal. MV represents one or more elements selected from V, Nb, and Ta of Group ^V of the periodic table. M ^VI represents one or more elements selected from Cr, Mo, W, and U of the VI group of the periodic table. p and x are 1 or more, and y is 0-50.

  The isopolyacid is prepared by various methods such as a method of treating an isopolyacid salt solution with an ion exchange resin and a method of adding a mineral acid to a concentrated solution of an isopolyacid salt and extracting with ether. In the present invention, not only isopolyacids but also acid salts of isopolyacids can be used as the polymerization catalyst. The isopolyacid salt may be any of the above general formulas (2) and (3), but is preferably an isopolyacid of the general formula (3) or an acid salt thereof from the viewpoint of polymerization activity.

  Specific examples of suitable isopolyacids include isopolytungstic acid exemplified by paratungstic acid, metatungstic acid, etc., isopolymolybdic acid exemplified by paramolybdic acid, metamolybdic acid, etc. Examples thereof include vanadium acid. Of these, isopolytungstic acid is preferable from the viewpoint of polymerization activity.

(solvent)
In order to carry out the polymerization reaction uniformly, the non-volatile protonic acid is preferably diluted with an inert solvent that does not adversely affect the polymerization and added to trioxane and / or a comonomer. Examples of inert solvents include low molecular weight carboxylic acids having 1 to 10 carbon atoms such as formic acid, acetic acid, propionic acid, butyric acid, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2- Esters obtained by condensation of low molecular weight alcohols having 1 to 10 carbon atoms such as methyl-1-propanol, 2-methyl-2-propanol, 1-pentanol, 3-methyl-1-butanol and 1-hexanol Preferred are low molecular weight ketones having 1 to 10 carbon atoms such as acetone, 2-butanone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, methyl isobutyl ketone, and methyl-t-butyl ketone. However, it is not limited to these. Considering industrial availability, methyl formate, ethyl formate, methyl acetate, ethyl acetate, butyl acetate, acetone, 2-butanone, methyl isobutyl ketone and the like are most suitable. The polymerization catalyst is preferably dissolved in the inert solvent at a concentration of 1 to 30% by weight / weight, but is not limited thereto. In addition, a predetermined amount of a non-volatile protonic acid is mixed in advance with a part or all of one or more of trioxane, comonomer, molecular weight regulator, etc., and this solution is added to the polymerization system for polymerization. A method is also preferred.

  The amount of the polymerization catalyst is not particularly limited, but is preferably 0.1 ppm or more and 50 ppm or less, more preferably 0.1 ppm or more and 10 ppm or less with respect to the total of all monomers.

  The polymerization temperature is preferably maintained at 65 ° C or higher and 135 ° C or lower.

  Subsequently, the deactivation of the polymerization catalyst due to the addition of the basic compound will be described.

(Basic compound)
The type and method of addition of the basic compound are not particularly limited, but the basic compound can be added to the crude polyacetal copolymer as it is without washing the crude polyacetal copolymer and melt kneaded. The basic compound can be used for deactivation of the polymerization catalyst and stabilization of the unstable terminal of the crude polyacetal copolymer. It is preferable to include at least one selected from acid salts or hydrates thereof, triazine ring-containing compounds having an amino group or a substituted amino group.
Furthermore, when a carbonate, hydrogen carbonate, carboxylate or hydrate of an alkali metal element or alkaline earth metal element or a hydrate thereof is used, in a composition containing a branched polymer finally obtained, the formaldehyde The generated amount is particularly low and is more preferable. Specifically, it is more preferable to include at least one selected from sodium formate, sodium acetate, sodium carbonate, sodium bicarbonate, disodium succinate, sodium laurate, sodium palmitate, sodium stearate or calcium stearate.

  In the present invention, the above basic compound may be one kind, a plurality may be used in combination, or a hydrate, mixture, double salt or the like thereof.

  After the polymerization method and the deactivation method, separation and recovery of unreacted monomers, drying, and the like are performed by a conventionally known method as necessary.

[(B) polyacetal copolymer having a branched or crosslinked structure]
(B) A polyacetal copolymer having a branched or crosslinked structure comprises (b1) trioxane, (b2) a compound having 3 or more and 4 or less cyclic ether units in one molecule, and (b3) a cyclic ether unit in one molecule. It is a copolymer with a compound having one. Hereinafter, the polyacetal copolymer (B) having a branched or crosslinked structure is also referred to as “component (B)”.

[(B1) trioxane]
(B1) Trioxane is the same as the trioxane described in the component (A) and is a cyclic trimer of formaldehyde. (B1) Trioxane is also preferably free of impurities as much as possible.

[(B2) Compound having 3 or more and 4 or less cyclic ether units in one molecule]
(B2) A compound having 3 or more and 4 or less cyclic ether units in one molecule is an epoxy unit, a glycidyl unit, a 1,3-dioxolane unit, a 1,4-butanediol formal unit, or a diethylene glycol formal unit in one molecule. And a general term for compounds having 3 to 4 cyclic ether units selected from the group consisting of 1,3,6-trioxepane units and the like. If the number of cyclic ether units is 2, sufficient rigidity may not be obtained. Specifically, the bending elastic modulus of the test piece based on ISO178 may be less than 2700 MPa. On the other hand, when there are too many cyclic ether units, toughness may fall.

  Moreover, as a cyclic ether unit, a glycidyl unit is preferable and a triglycidyl ether compound and a tetraglycidyl ether compound are mentioned as a preferable compound. Examples thereof include glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, and the like. These compounds can be used alone or in combination of two or more for copolymerization with (a) trioxane.

  (B2) The amount of copolymerization of the compound having 3 or more and 4 or less cyclic ether units in one molecule is not particularly limited. However, in view of suitably obtaining a polyacetal resin composition having the desired characteristics, The polymerization amount is preferably 0.01 parts by weight or more and 1 part by weight or less, more preferably 0.05 parts by weight or more and 0.5 parts by weight or less, with respect to 100 parts by weight of (b1) trioxane. More preferably, it is 1 part by weight or more and 0.3 part by weight or less.

[(B3) Compound having one cyclic ether unit in one molecule]
(B3) A compound having one cyclic ether unit in one molecule is suitable in that it can stabilize the polymerization reaction when producing the component (B) and increase the thermal stability of the component (B) produced. It is.

  (B3) As a compound having one cyclic ether unit in one molecule, ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, epibromohydrin, styrene oxide, oxetane, 3,3-bis (chloromethyl) oxetane , Tetrahydrofuran, trioxepane, 1,3-dioxolane, ethylene glycol formal, propylene glycol formal, diethylene glycol formal, triethylene glycol formal, 1,4-butanediol formal, 1,5-pentanediol formal, 1,6-hexanediol formal Etc. Of these, ethylene oxide, 1,3-dioxolane, 1,4-butanediol formal, and diethylene glycol formal are preferable.

  The amount of copolymerization of the compound (b3) having one cyclic ether unit in one molecule in the component (B) is not particularly limited, but it is 20 parts by weight or less with respect to 100 parts by weight of (b1) trioxane. Is preferably 0.05 parts by weight or more and 15 parts by weight or less, and more preferably 0.1 parts by weight or more and 10 parts by weight or less.

[Melt index]
The melt index of the component (B) is not particularly limited, but considering the strength, it is preferably 0.2 g / 10 min or more and 3 g / 10 min or less, and 0.5 g / 10 min or more and 1.5 g / min. More preferably, it is 10 min or less. If the melt index is too small, the toughness may decrease. Moreover, if the melt index is too large, the rigidity may decrease.

[Method for producing component (B)]
In producing the component (B), the polymerization apparatus is not particularly limited, and a known apparatus can be used, and any method such as a batch system or a continuous system can be used. The polymerization temperature is preferably maintained at 65 ° C. or higher and 135 ° C. or lower.

  Unlike the production of the component (A), the type of the polymerization catalyst is not particularly limited in the production of the component (B). A cationic polymerization catalyst is mentioned as a polymerization catalyst, A conventionally well-known thing is enough for a cationic polymerization catalyst. The cationic polymerization catalyst can be used after diluting with an organic solvent or the like.

  Deactivation after polymerization is carried out by a conventionally known method. For example, after the polymerization reaction, a basic reaction product or an aqueous solution thereof may be added to the product reaction product discharged from the polymerization machine and the reaction product in the polymerization machine.

  The basic compound for neutralizing and deactivating the polymerization catalyst is not particularly limited. After the polymerization method and the deactivation method, washing, separation and recovery of unreacted monomers, drying, and the like are further performed by a conventionally known method as necessary.

[Other ingredients]
The polyacetal resin composition may contain other components as necessary. For example, the stabilizer may include any one or more of hindered phenol compounds, nitrogen-containing compounds, alkali or alkaline earth metal hydroxides, inorganic salts, carboxylates, and the like.

  In addition, as long as the purpose and effect of the present invention are not impaired, general additives for thermoplastic resins, for example, coloring agents such as dyes and pigments, lubricants, mold release agents, antistatic agents, surfactants, if necessary. Alternatively, one or more organic polymer materials, inorganic or organic fibrous, powdery, and plate-like fillers can be added.

[Preparation of polyacetal resin composition]
The polyacetal resin composition is easily prepared by a known method generally used as a conventional resin composition preparation method. For example, after mixing each component, it kneads and extrudes with an extruder, and a pellet is obtained.

  (B) Content of a component is 0.1 to 2 weight part with respect to 100 weight part of (A) component. If the content of the component (B) is too small, there is a possibility that a polyacetal resin composition having sufficient rigidity may not be obtained, which is not preferable. If the content of the component (B) is too large, there is a possibility that a polyacetal resin composition having sufficient toughness may not be obtained.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

メルトインデックス測定装置：Ｍｅｌｔ Ｉｎｄｅｘｅｒ Ｌ２０２型（タカラサーミスタ社製）を用い、荷重２．１６ｋｇ、温度１９０℃でのメルトインデックスを測定した。 <Preparation of (A) Linear Polyacetal Copolymer>

Melt index measuring apparatus: Melt Index L202 type (manufactured by Takara Thermistor) was used to measure the melt index at a load of 2.16 kg and a temperature of 190 ° C.

[Copolymer No. A1-1 to A1-5]
A continuous biaxial polymerization machine was used as the polymerization reactor. This polymerization machine has a jacket for passing a heating or cooling medium on the outside, and two rotating shafts with a large number of paddles for stirring and propulsion are provided in the longitudinal direction in the inside. ing. While passing a 80 ° C. heating medium through the jacket of this biaxial polymerization machine and rotating the two rotating shafts at a constant speed, 1200 ppm of methylal as a chain transfer agent was continuously supplied to one end thereof, and trioxane and A mixed solution of 1,3-dioxolane as a comonomer was continuously added in an amount shown in Table 1, and a methyl formate solution containing 0.3 parts by weight of a polymerization catalyst shown in Table 1 was added to the mixed solution. Copolymerization was carried out by continuously adding the monomers in the amounts shown in Table 1. In Table 1, the addition amount of the polymerization catalyst is a weight ratio (unit: ppm) to the total of all monomers. Thereafter, the crude polyacetal copolymer was discharged from a discharge port provided at the other end of the polymerization machine, and a deactivator shown in Table 1 was added to deactivate the polymerization catalyst. In Table 1, the amount of the quenching agent is a weight ratio (unit: ppm) to the crude polyacetal copolymer. Next, 0.3 parts by weight of triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyfehl) propionate] is added as an antioxidant and a twin screw extruder with a vent is used. The mixture was melt-kneaded and extruded at a temperature of 220 ° C. and a degree of vacuum of 5 mmHg at the vent. A linear polyacetal copolymer was obtained through the above steps.

[Copolymer No. 2A-1]
No. 3 is used until the crude polyacetal copolymer is discharged from a discharge port provided at the other end of the polymerization machine using boron trifluoride as a catalyst. It carried out similarly to A1-1 to A1-5. While the discharged reaction product was immediately passed through a crusher, it was added to a 60 ° C. aqueous solution containing 0.05% by weight of triethylamine to deactivate the catalyst. Further, a crude polyacetal copolymer was obtained by separation, washing and drying. Next, 3 wt% of a triethylamine 5 wt% aqueous solution and pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate with respect to 100 parts by weight of the crude polyacetal copolymer. 0.3 wt% was added and melt kneaded at 210 ° C. with a twin screw extruder to remove unstable parts. A linear polyacetal copolymer according to A2-1 was obtained.

<(B) Preparation of branched / crosslinked polyacetal copolymer>
[Copolymer No. B1 (Trifunctional)]
The composition of the raw materials is (b1) 98.9 parts by weight of trioxane, (b2) 0.2 parts by weight of trimethylolpropane triglycidyl ether (TMPTGE) and (b3) 1.1 parts by weight of 1,3-dioxolane Copolymer No. In the same manner as in A2-1, the copolymer No. A branched / crosslinked polyacetal copolymer according to B1 was obtained. At this time, the copolymer No. The melt index of the branched / crosslinked polyacetal copolymer according to B1 was 1.1 g / 10 min.

[Copolymer No. B2 (tetrafunctional)]
(B2) Copolymer No. 1 was used except that the component was not pentamethylerythritol tetraglycidyl ether (PETGE) but trimethylolpropane triglycidyl ether (TMPTGE). In the same manner as in B1, the copolymer No. A branched / crosslinked polyacetal copolymer according to B2 was obtained. At this time, the copolymer No. The melt index of the branched / crosslinked polyacetal copolymer according to B2 was 1.3 g / 10 min.

[Copolymer No. B3 (bifunctional)]
(B2) Copolymer No. 1 was used except that the component was not trimethylolpropane triglycidyl ether (TMPTGE) but butanediol diglycidyl ether (BDGE). In the same manner as in B1, the copolymer No. A branched / crosslinked polyacetal copolymer according to B3 was obtained. At this time, the copolymer No. The melt index of the branched / crosslinked polyacetal copolymer according to B3 was 1.2 g / 10 min.

<Examples and Comparative Examples>

<Examples and Comparative Examples>
[Preparation of polyacetal resin composition]
<(A) Preparation of linear polyacetal copolymer> and <(B) Preparation of branched / crosslinked polyacetal copolymer> (A) component and (b) component blended in proportions shown in Table 2 And it knead | mixed and kneaded at 210 degreeC with the twin-screw extruder, and obtained the pellet-shaped polyacetal resin composition which concerns on an Example and a comparative example.

[Evaluation]
In order to evaluate the pellet-like polyacetal resin compositions according to Examples and Comparative Examples, bending elastic modulus, Charpy impact strength and formaldehyde generation amount were measured.

[Bending elastic modulus]
Using an injection molding machine (“SE100DU” manufactured by Sumitomo Heavy Industries, Ltd.), test pieces (4 mm × 10 mm × 80 mm) from pellets in Examples and Comparative Examples under the conditions of cylinder temperature: 205 ° C. and mold temperature: 90 ° C. ). Thereafter, the flexural modulus of the test piece was measured in accordance with ISO178. The results are shown in Table 3.

[Charpy impact strength]
Using the injection molding machine, a notched Charpy test piece according to ISO 179 / IeA was molded from the pellets in the examples and comparative examples. And according to ISO179 / IeA, the Charpy impact test value in 23 degreeC was measured. The results are shown in Table 3.

[Evaluation of the amount of formaldehyde generated]
The pellets in Examples and Comparative Examples were filled in a cylinder maintained at 200 ° C., melted in 5 minutes, and then the melt was extruded from the cylinder into a sealed container. Nitrogen gas was allowed to flow through this sealed container, and formaldehyde contained in the nitrogen gas that had come out was dissolved and collected in water, and the formaldehyde concentration in the water was measured to determine the weight of formaldehyde released from the melt. The formaldehyde weight was divided by the weight of the melt to obtain the formaldehyde generation amount (unit: ppm). The results are shown in Table 3.

  When a polyacetal resin composition containing the component (A) and the component (B) at a suitable ratio is used, both the rigidity and toughness are excellent, and the amount of formaldehyde generated can be suppressed to a low level (Example).

On the other hand, when the component (B) is produced, if the polymerization catalyst is not a heteropolyacid, the Charpy impact strength (notched, 23 ° C.) is less than 6 kJ / m ² even when mixed with the component (A) at a suitable ratio. In addition to being unable to obtain sufficient toughness, it was confirmed that more formaldehyde was generated than in the case where the polymerization catalyst was a heteropolyacid (Comparative Example 1).

  In addition, regarding (b2) a compound having 3 or more and 4 or less cyclic ether units in one molecule contained in component (B), if the number of cyclic ether units contained in the compound is 2 in one molecule, component (A) Even when mixed at a suitable ratio, it was confirmed that the flexural modulus of the test piece according to ISO 178 was less than 2700 MPa, and sufficient rigidity could not be obtained (Comparative Example 2).

  Further, when the proportion of the comonomer unit (oxyalkylene unit) contained in the component (A) exceeds 0.9 mol% as the proportion of the structural units of the linear polyacetal copolymer, the component (B) is in a suitable ratio. Even if mixed, the bending elastic modulus of the test piece based on ISO178 was less than 2700 MPa, and it was confirmed that sufficient rigidity could not be obtained (Comparative Example 3).

Further, when the content of the component (B) exceeds 2 parts by weight with respect to 100 parts by weight of the component (A), the structure of the copolymer relating to the component (A) and the component (B) is suitable. The Charpy impact strength (notched, 23 ° C.) was less than 6 kJ / m ² , and it was confirmed that sufficient toughness could not be obtained (Comparative Example 4).

  Further, when the content of the component (B) is less than 0.1 parts by weight with respect to 100 parts by weight of the component (A), the structure of the copolymer according to the component (A) and the component (B) is suitable. In addition, it was confirmed that the flexural modulus of the test piece conforming to ISO178 was less than 2700 MPa, and sufficient rigidity could not be obtained (Comparative Example 5).

Claims (1)

A linear polyacetal copolymer 100 containing an oxymethylene unit as a main component and an oxyalkylene unit as a comonomer unit in a proportion of 0.4 mol% or more and 0.9 mol% or less as a proportion of the structural unit of the linear polyacetal copolymer. Parts by weight,
(B1) trioxane, (b2) a copolymer of a compound having 3 to 4 cyclic ether units in one molecule and (b3) a compound (c) having one cyclic ether unit in one molecule, branched or Including 0.1 to 2 parts by weight of a polyacetal copolymer having a crosslinked structure,
A polyacetal resin composition having a Charpy impact strength (notched, 23 ° C.) of 6 kJ / m ² or more.