JP5129109B2 - Polyacetal resin composition and molded product formed by molding the same - Google Patents

Description

The present invention relates to a polyacetal resin composition and a molded article comprising the same. The polyacetal resin composition provided by the present invention is excellent in rigidity and heat resistance, and gives a molded product excellent in surface appearance.

Polyacetal resins have well-balanced mechanical properties and good self-lubricating properties and electrical properties, and are widely used as engineering plastics for various mechanical and electrical components. For applications that require a high degree of rigidity and heat resistance, reinforced compositions in which glass fibers or carbon fibers are blended with polyacetal resins are widely used, as with other thermoplastic resins.
On the other hand, in recent years, those derived from plants have attracted attention as renewable resources in relation to global warming. The use of cellulosic materials has also been studied as a reinforcing material for thermoplastic resins.

For example, Patent Documents 1 to 3 propose a resin composition composed of a polyolefin resin such as a polypropylene resin and a cellulose material.
Patent Documents 4 to 5 propose resin compositions comprising a styrene resin and a cellulose material.
Patent Documents 6 to 7 propose resin compositions comprising a polyamide resin and a cellulosic material.

Patent Document 8 proposes a resin composition comprising a cellulose material and a methacrylic resin, a polycarbonate resin, a rubber-reinforced acrylonitrile-styrene resin, a saturated polyester resin, and the like.
Patent Documents 9 to 11 propose a resin composition comprising an aliphatic polyester resin such as polylactic acid and a cellulosic material.

However, the effect of improving heat resistance in these resin compositions is still insufficient. Also, in general, when a resin composition in which a cellulose-based material is blended with a thermoplastic resin is molded by a conventional method, a unique pattern often referred to as wood grain may be formed on the molded product, which is molded in terms of design. There is a problem that the use of the product is limited.

Patent Document 12 proposes a resin composition composed of a polyacetal resin and a cellulosic material, but the description of what should be used as the cellulosic material is also based on the properties of the cellulosic material. There is no description of how it changes, and there is no description of heat resistance.

JP-A-11-12041 JP-A-11-43562 JP 2003-559728 A Japanese Patent Application Laid-Open No. 8-231895 Japanese Patent Laid-Open No. 10-147689 JP 2004-204104 A JP 2004-339505 A JP 2003-165909 A Japanese Patent Laid-Open No. 11-241009 JP 2004-315577 A JP 2004-359939 A JP-A-5-17664

An object of the present invention is to provide a polyacetal resin composition that uses a fibrous cellulosic material, which is a renewable resource, as a reinforcing material, and gives a molded product having excellent rigidity and heat resistance and a good surface appearance. is there. Another object of the present invention is to provide a polyacetal resin molded article excellent in all of rigidity, heat resistance and surface appearance formed by molding this resin composition.

As a result of studying the cellulosic material used as the reinforcing material, the present inventor has learned that the bulk density of the cellulosic material greatly affects the properties of the resulting resin composition, and has completed the present invention. .

That is, the gist of the present invention resides in a polyacetal resin composition comprising 5 to 100 parts by weight of a fibrous cellulosic material having a bulk density of 0.1 to 0.5 g / ml in 100 parts by weight of a polyacetal resin. . Moreover, the other summary of this invention exists in the molded article which consists of this resin composition.

The polyacetal resin composition of the present invention is excellent in rigidity and heat resistance, and gives a molded product excellent in surface appearance in addition to these characteristics. Therefore, this molded product is used for automobile interior parts, interior parts for houses (hot water mixing taps, etc.), clothing parts (fasteners, belt buckles, etc.) and building materials (piping / pump parts, etc.), electrical parts (printers, copying machines, etc.) It can be suitably used for office equipment such as facsimiles, resin parts such as precision parts such as watch parts, and gears.

Hereinafter, the present invention will be described in detail.
As is well known, a polyacetal resin is a polymer having an acetal represented by — (— O—CRH—) n— (wherein R represents a hydrogen atom or an organic group) as a structural unit, and has various grades. Things are available on the market. The polyacetal resin usually has an oxymethylene group (—CH ₂ O—) in which R is a hydrogen atom as a main structural unit. However, the polyacetal resin used in the present invention has an oxymethylene group other than a homopolymer consisting of only this structural unit. It may be a copolymer (block copolymer) or a terpolymer containing a repeating unit other than the above, and may have not only a linear structure but also a branched or crosslinked structure.

Examples of the repeating unit other than the oxymethylene group include an oxyethylene group (—CH ₂ CH ₂ O—), an oxypropylene group (—CH ₂ CH ₂ CH ₂ O—), and an oxybutylene group (—CH ₂ CH ₂ CH). _{And an} oxyalkylene group having 2 to 10 carbon atoms such as ₂ CH ₂ O—). These oxyalkylene groups may be branched instead of linear. Of these, an oxyalkylene group having 2 to 4 carbon atoms which may be branched is preferable, and an oxyethylene group is most preferable. The content of oxyalkylene groups other than oxymethylene groups in the polyacetal resin is preferably 0.1% by weight to 20% by weight. The melt index of the polyacetal resin is usually 1 to 60 g / 10 minutes as measured under the conditions of 190 ° C. and 2.16 kg according to ISO 1133, but in the present invention, it is 2 to 30 g / 10 minutes, particularly 3 to 20 g / minute. It is preferred to use a 10 minute one.

A number of methods for producing a polyacetal resin are known, but those obtained by any method can be used in the present invention. For example, if it is a polyacetal resin which has an oxymethylene group and a C2-C4 oxyalkylene group as a structural unit, cyclic oligomers of oxymethylene groups such as formaldehyde trimer (trioxane) and tetramer (tetraoxane) And a cyclic oligomer containing an oxyalkylene group having 2 to 4 carbon atoms such as ethylene oxide, 1,3-dioxolane, 1,3,6-trioxocane and 1,3-dioxepane. Can be used. The polyacetal resin used in the present invention is preferably a copolymer of a cyclic oligomer such as trioxane or tetraoxane and ethylene oxide or 1,3-dioxolane, and particularly preferably a copolymer of trioxane and 1,3-dioxolane.

The fibrous cellulosic material used in the present invention is a fibrous material mainly composed of cellulose, and is typically a so-called cellulose pulp (hereinafter sometimes referred to as pulp). It is known that pulp can be produced from various plants including wood, but in the present invention, any pulp made from any plant can be used. Various methods for producing pulp are also known, and the quality of the pulp differs depending on the production method, but any method may be used. For example, pulp obtained by digesting wood with various chemicals to dissolve and remove lignin, which is a contaminant, and then treating with a bleaching agent can be used.

In the present invention, among these pulps, those having a bulk density of 0.1 to 0.5 g / ml are used. Of these, those having a bulk density of 0.2 to 0.4 g / ml are preferred. In the case of papermaking pulp that is produced in large quantities using wood as a raw material, it is said that the longer the fiber, the stronger the paper will be obtained.For example, the average fiber length of pulp made from softwood suitable for papermaking Is about 4 mm. On the other hand, the pulp having the above-described bulk density used in the present invention has an average fiber length of about several tens to several hundreds of μm, and the average fiber length is significantly shorter than that of paper pulp. It is obtained by further pulverizing and refining the pulp obtained by the method.

If a material having a bulk density of less than 0.1 g / ml is used, it is difficult to obtain a resin composition having desired rigidity and heat resistance. This is probably because the fiber length is too short and the reinforcing effect is small. Moreover, it is easy to aggregate at the time of melt-kneading with a polyacetal resin, As a result, the surface appearance of the molded product obtained from a resin composition tends to be inferior. On the other hand, it is difficult to obtain a resin composition having desired rigidity and heat resistance even if a bulk density exceeding 0.5 g / ml is used. The reason is considered to be that the pulp is not sufficiently dispersed. That is, in the pulp, single fibers aggregate to form an aggregate, but when this is melt kneaded with a polyacetal resin, the aggregate is dissociated into single fibers or small aggregates by shearing force and dispersed in the resin. By the way, since a large bulk density has a large aggregate, dissociation into single fibers or small aggregates does not proceed sufficiently, and therefore, it is considered that the pulp is difficult to uniformly disperse in the polyacetal resin. In addition, it is considered that the high bulk density is likely to cause entanglement because the fiber is long, which is also a factor hindering uniform dispersion.

The fibrous cellulosic material used in the present invention can be prepared by pulverizing paper pulp, but can also be obtained on the market. For example, “ARBOCEL” and [LIGNOCEL] of Rettenmeier, which are sold for foods, etc., [KC Flock] of Nippon Paper Industries Co., Ltd., “Avicel RC” of Asahi Kasei Corporation and the like can be used. The bulk density is measured according to JIS R3105 by placing a sample and measuring the weight while tapping lightly on a 100 ml measuring cylinder. The measurement is performed 5 times, and the average value of the 3 measured values excluding the maximum value and the minimum value is taken as the bulk density.

The blending amount of the fibrous cellulosic material is 5 to 100 parts by weight with respect to 100 parts by weight of the polyacetal resin. If the blending amount is less than 5 parts by weight, it is difficult for the resin composition to exhibit desired rigidity and heat resistance. If the blending amount exceeds 100 parts by weight, it is difficult to uniformly disperse it in the polyacetal resin by melt kneading. As a result, the molded product obtained by molding the resulting resin composition has poor mechanical properties and surface appearance. It will be. The blending amount of the fibrous cellulose substance with respect to 100 parts by weight of the polyacetal resin is preferably 10 to 80 parts by weight, particularly preferably 10 to 50 parts by weight.

The polyacetal resin composition of the present invention may further contain various known thermoplastic resins, additives and the like within a range not impairing the effects of the present invention. Examples of the additive include a heat stabilizer, a lubricant, a mold release agent, an antistatic agent, an ultraviolet absorber, a light stabilizer, a sliding property improver, a flow modifier, and a formaldehyde scavenger. Further, pigments and dyes may be added to achieve a desired color.

The polyacetal resin composition of the present invention can be produced by adding a predetermined amount of fibrous cellulosic material to polyacetal and melt-kneading. The melt-kneading may be performed at 180 to 250 ° C. using a conventional kneading apparatus such as a single-screw or multi-screw extruder. The time required for kneading varies depending on the kneading conditions, but is usually 1 to 5 minutes. Since the fibrous cellulosic material is flexible, it does not break under normal kneading conditions unlike glass fibers.

EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to these Examples, unless the summary is exceeded. “Part” means “part by weight”.

<Manufacture of resin composition>
Each component described in Table 1 was blended at the ratio (weight ratio) described in Table 2 and Table 3, and mixed for 20 minutes with a tumbler. The obtained mixture was melt-kneaded at a cylinder temperature of 190 ° C. and a discharge rate of 20 kg / hr using a 40 mmφ single screw extruder (manufactured by Tanabe Plastics Co., Ltd., model: VS-40) to produce polyacetal resin composition pellets. Manufactured.

<Manufacture of test pieces>
Using the obtained pellets, an ISO dumbbell specimen having a thickness of 3 mm was molded by injection molding under the conditions of a cylinder temperature of 190 ° C. and a mold temperature of 80 ° C.

<Surface appearance>
The surface appearance of the ISO dumbbell test piece obtained above was visually observed, and “○” indicates that almost no agglomerates (lumps or clumps) of fibrous cellulosic material were observed. What was obtained was evaluated as “Δ”, and what was clearly recognized over the entire molded product was evaluated as “x”.

<Elastic modulus>
The flexural modulus was measured according to ISO178. The unit is GPa.

<Load deflection temperature>
The load deflection temperature at a load of 1.80 MPa was measured in accordance with ISO75-1,2. The unit is ° C.

（平均繊維長はカタログ値）

(Average fiber length is catalog value)

Examples 5 and 6 are reference examples.

（比較例２及び３は、樹脂組成物のペレットを製造するに際し、ストランドを安定して押し出すことができなかった（押出加工性が×だった）ので、外観・弾性率・荷重撓み温度の試験は行わなかった。）

(Comparative Examples 2 and 3 were not able to stably extrude strands when producing pellets of the resin composition (extrudability was x), so the appearance, elastic modulus, and load deflection temperature were tested. Did not.)

Claims (4)

A polyacetal resin composition characterized by melting and kneading 100 parts by weight of a polyacetal resin and 5 to 50 parts by weight of a fibrous cellulosic material having a bulk density of 0.2 to 0.293 g / ml using an extruder. Production method. The manufacturing method of Claim 1 whose average fiber length of a fibrous cellulosic substance is 30 micrometers or more. A molded article produced by the method according to claim 1 or 2. The molded article according to claim 3, wherein the fibrous cellulose material has an average fiber length of 30 µm or more.