JP6831634B2 - Polyoxymethylene resin composition - Google Patents

Description

The present invention relates to a polyoxymethylene resin composition.

The polyoxymethylene resin has an excellent balance of mechanical strength, chemical resistance, slidability, and abrasion resistance, and is easy to process. Therefore, polyoxymethylene resin is widely used as a typical engineering plastic in mechanical parts, automobile parts and other mechanical parts of electrical equipment.

When the polyoxymethylene resin is used for various purposes as described above, the good slidability of the polyoxymethylene resin is particularly important. For example, in the gear of a compact disc drive or the autosampler part of a measuring device, under a relatively high load (for example, a load of about 1 to 2N), it may be connected to other parts (own material, other material). Rubbing (friction) occurs. Therefore, high slidability that does not wear at that time is required.

For the purpose of improving the wear resistance against a relatively high load as described above, for example, Patent Document 1 describes a copolymer of ethylene and α-olefin as a sliding agent or a modified polyethylene wax thereof. A technique for adding polyethylene oxide is disclosed, and Patent Document 2 proposes a technique for adding polyethylene oxide wax as a sliding agent.
Further, although the slidability is not mentioned, Patent Document 3 describes a technique of using a modified polyolefin wax in order to suppress shrinkage anisotropy.

The above-mentioned conventional technique is effective in improving shrinkage anisotropy and wear resistance during high-load sliding, but it is effective in improving wear resistance under a very low load (load of 0.05 N or less). Has the problem that the effect of is unknown.
In addition, it is required to reduce the odor during melt processing such as extrusion and molding, and to improve the problem of strand breakage due to peeling due to the use of a sliding agent and adhesion of eye tar to the die (production stability during extrusion). There is.

On the other hand, for example, as described in Patent Document 4, a polyoxymethylene resin has recently been used for a component called a lamp in a hard disk drive.
This component called a lamp is a component for the slider head, which is a read / write part, to evacuate from the hard disk when reading / writing to the hard disk is not in operation. Specifically, when the slider head moves in and out of the lamp, the tab at the tip of the head scratches the inclined portion of the lamp. The load at the time of this scraping is very low (generally, a load of 0.05 N or less), and the material having high slidability under the above-mentioned relatively high load (load of about 1 to 2 N) is used as it is with a very low load. It is often not applicable to materials under (load of 0.05 N or less). Similarly, a material used under a very low load (load of 0.05 N or less) is often not applicable as a material having high slidability under the above-mentioned high load (load of about 1 to 2 N).
For example, a material having excellent slidability such as a gear driven under a high load (load of about 1 to 2N) described above is applied under a very low load (load of 0.05N or less) such as a lamp component. In some cases, it does not always give parts with good performance. From this point of view, there is a demand for a material for hard disk lamp parts and the like under a very low load (load of 0.05 N or less), completely different from the sliding agents used under a high load so far.

Recently, the main applications of hard disks are shifting from those installed in personal computers to those installed in large-capacity servers compatible with cloud computing and mobile type hard disk drives (HDD) cassettes (iVDR).
Therefore, new characteristics are required from the viewpoint of ensuring high reliability such as an increase in the amount of data stored, an increase in the number of accesses to the hard disk, and prevention of vibration, shock, and malfunction due to a high temperature environment.
Specifically, the resin constituting the lamp component has further wear resistance, for example, slidability that can withstand more than 1 million scratches, which is to improve the wear resistance to more than twice that of the conventional technology. It has been requested.

In view of such a requirement, Patent Document 4 discloses a polyoxymethylene composition containing a polyoxymethylene copolymer, an inorganic filler, a lubricant and the like.
Further, as a lubricant, a modified polyolefin such as a maleic anhydride-modified polyolefin is disclosed.
This Patent Document 4 also shows the effect of wear resistance under a very low load.

Japanese Patent No. 6-49320 Japanese Patent No. 4906984 Japanese Unexamined Patent Publication No. 2000-7884 Japanese Unexamined Patent Publication No. 2011-208114

However, in the above-mentioned conventional technique, there is room for improvement in wear resistance, and further reduction in wear resistance is desired.
Furthermore, there is an increasing demand for reducing odor during melt processing such as extrusion and molding, and further, in order to cope with the occurrence of peeling due to the use of a large amount of conventional sliding agents, production stability during extrusion ( It is also required to improve (suppressing strand breakage and adhesion to the dice).

Therefore, in the present invention, the amount of wear during long-term micro-load sliding is dramatically reduced as compared with the prior art, and excellent sliding characteristics are exhibited in a high temperature environment, and odor during melt processing such as extrusion and molding is reduced. Another object of the present invention is to provide a polyoxymethylene resin composition having excellent production stability during extrusion (suppressing strand breakage and adhesion of eyelids to dies).

As a result of diligent studies to solve the above problems, the present inventors have found that a polyoxymethylene resin composition containing a specific amount of an acid-modified polyolefin having a specific acid value can solve the above problems. , The present invention has been completed.
That is, the present invention is as follows.

[1]
(A) 100 parts by mass of polyoxymethylene resin and
(B) 0.1 to 5 parts by mass of acid-modified polyolefin having an acid value of 40 to 63 mg-KOH / g.
, Contains
A lamp molded product for a hard disk, which is a molded product of a polyoxymethylene resin composition.
[2]
A lamp molded product for a hard disk, which is a molded product of the polyoxymethylene resin composition according to the above [1], further containing 0.01 to 3 parts by mass of a (C) colorant having a Mohs hardness of 6 or less.
[3]
The acid-modified polyolefin (B)
A lamp molded product for a hard disk, which is a molded product of the polyoxymethylene resin composition according to the above [1] or [2], which is a modified wax containing acid-modified polyethylene and / or acid-modified polypropylene.
[4]
A lamp molded product for a hard disk, which is a molded product of the polyoxymethylene resin composition according to any one of the above [1] to [3], wherein the acid-modified polyolefin (B) has a weight average molecular weight of 100 to 100,000. ..
[5]
A lamp molded product for a hard disk, which is a molded product of the polyoxymethylene resin composition according to any one of the above [1] to [4] , wherein the acid-modified polyolefin (B) has a weight average molecular weight of 100 to 30,000. ..
[6]
A lamp molded product for a hard disk, which is a molded product of the polyoxymethylene resin composition according to any one of the above [1] to [5] , wherein the acid-modified polyolefin (B) has a weight average molecular weight of 300 to 3000. ..
[7]
The hard disk, which is a molded product of the polyoxymethylene resin composition according to any one of [1] to [6] , wherein the acid-modified polyolefin (B) has a melt viscosity of 1 to 1000 mPa · s at 140 ° C. Lamp molded body.
[8]
The colorant (C) is zinc sulfide, zinc oxide, iron oxide, zinc yellow 1 type, zinc yellow 2 types, zinc white, titanium white, alumina white, talc, white carbon, silver white, carbon black, acetylene black, The colorant containing at least one of the above-mentioned [2] to [7] , which is selected from the group consisting of lamp black, furnas black, calcium carbonate, and an inorganic pigment selected from the group consisting of organic dyeing pigments. A lamp molded body for a hard disk, which is a molded body of the polyoxymethylene resin composition according to any one.
[9]
A lamp molded product for a hard disk, which is a molded product of the polyoxymethylene resin composition according to any one of [1] to [8] above, wherein the polyoxymethylene resin (A) contains a block copolymer.
[10]
A lamp molded product for a hard disk, wherein the block copolymer is an ABA type block copolymer, which is a molded product of the polyoxymethylene resin composition according to the above [9] .
[11]
A hard disk lamp molded product, which is a molded product of the polyoxymethylene resin composition according to any one of the above [1] to [10] , and has a relative element concentration ratio of carbon and oxygen on the surface [C / O] (atomic%) is 1.01 to 2.50, which is a hard disk lamp molded product.
[12]
A lamp molded product for a hard disk, which is a molded product of the polyoxymethylene resin composition according to any one of the above [1] to [10] .
The surface of the hard disk lamp molded body has a peak intensity ratio (CO / C = O) of 10 to 200 between the CO expansion and contraction vibration peak obtained by infrared spectroscopy and the C = O expansion and contraction vibration peak. , Lamp molded body for hard disk.

According to the present invention, it has extremely high sliding characteristics that reduce wear during long-term micro-load sliding, and in particular, it has excellent sliding characteristics in a high temperature environment, and further, extrusion, molding, etc. It is possible to provide a polyoxymethylene resin composition having an effect of reducing odor during melt processing and further improving production stability during extrusion (suppressing strand breakage and adhesion to eyes and eyes on dies).

Hereinafter, a mode for carrying out the present invention (hereinafter, referred to as “the present embodiment”) will be described in detail.
The following embodiments are examples for explaining the present invention, and are not intended to limit the present invention to the following contents. The present invention can be appropriately modified and implemented within the scope of the gist thereof.

[Polyoxymethylene resin composition]
The polyoxymethylene resin composition of the present embodiment is
(A) 100 parts by mass of polyoxymethylene resin and
(B) 0.1 to 5 parts by mass of acid-modified polyolefin having an acid value of 38 to 80 mg-KOH / g.
, Contain.

The polyoxymethylene resin composition of the present embodiment has extremely high sliding characteristics that the amount of wear is small under a very small load (for example, a load of 0.05 N or less).
As described above, it is difficult to achieve both slidability under a high load (for example, a load of about 1 to 2N) and slidability under a very low load because of sliding. It is considered that the difference in load and the difference in sliding speed are the factors.
When sliding under a very low load, sliding is often performed at a relatively high sliding speed, up to a very surface layer (for example, a depth of several μm) of a molded product made of a polyoxymethylene resin composition. However, wear damage does not occur. This is a wear that is completely different from the conventional sliding under high load.
Unlike the conventionally known resin compositions, the polyoxymethylene resin composition of the present embodiment specifically exerts an effect on improving wear of the polar surface layer under a very low load.
The polyoxymethylene resin composition of the present embodiment has the effect of suppressing abrasion damage of only the polar surface layer as described above, and the effect can be maintained until after 1 million times of rubbing.
Each component constituting the polyoxymethylene resin composition of the present embodiment will be described in detail.

((A) Polyoxymethylene resin)
Here, the (A) polyoxymethylene resin contained in the polyoxymethylene resin composition of the present embodiment (in this specification, the component (A) and (A) may be described in detail) will be described in detail. To do.
Examples of the (A) polyoxymethylene resin that can be used in the present embodiment include polyoxymethylene homopolymers and polyoxymethylene copolymers.
Specifically, a polyoxymethylene homopolymer consisting substantially only of oximethylene units obtained by homopolymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde such as a trimeric (trioxane) or tetramer (tetraoxane) thereof. Or, a cyclic oligomer of formaldehyde such as formaldehyde monomer or its trimer (trioxane) or tetramer (tetraoxane), ethylene oxide, propylene oxide, epichlorohydrin, 1,3-dioxolane or 1,4-butanediolformal. Examples thereof include a polyoxymethylene copolymer obtained by copolymerizing cyclic ether or cyclic formaldehyde such as cyclic formal of glycol or diglycol.
Further, as the polyoxymethylene copolymer, a polyoxymethylene copolymer having a branch obtained by copolymerizing a formaldehyde monomer and / or a cyclic oligomer of formaldehyde and a monofunctional glycidyl ether, and a formaldehyde monomer. And / or a polyoxymethylene copolymer having a crosslinked structure obtained by copolymerizing a cyclic oligomer of formaldehyde and a polyfunctional glycidyl ether can also be used.
Furthermore, the (A) polyoxymethylene resin may contain a block copolymer having a different type of block different from the repeating structural unit of polyoxymethylene.
When the polyoxymethylene resin (A) contains a block copolymer, the acid-modified polyolefin (B) constituting the polyoxymethylene resin composition of the present embodiment is selectively and stably present in the different block portion thereof. Can be made to. This makes it possible to develop more stable wear resistance after sliding more than 1 million times.

The block copolymer referred to here is an acetal homopolymer having at least one block portion represented by any of the following general formulas (1), (2), (3) or (4), or an acetal copolymer (both). In addition, it is also referred to as "block copolymer" below).

In the above general formulas (1), (2) and (3), R ₁ and R ₂ are independently selected from the group consisting of a hydrogen atom, an alkyl group, a substituted alkyl group, an aryl group and a substituted aryl group1 When the chemical species of the species are indicated and R ₁ and R ₂ are plural, they may be the same or different.
Further, R ₃ represents one chemical species selected from the group consisting of an alkyl group, a substituted alkyl group, an aryl group, and a substituted aryl group.
m represents an integer of 2 to 6, and an integer of 2 to 4 is preferable.
n represents an integer of 1 to 1000, and an integer of 10 to 250 is preferable.

The group represented by the general formula (1) is a residue obtained by desorbing a hydrogen atom from the (poly) alkylene oxide adduct of alcohol, and the group represented by the general formula (2) is a carboxylic acid. It is a residue obtained by desorbing a hydrogen atom from the (poly) alkylene oxide adduct, and the group represented by the above general formula (3) is a residue obtained by desorbing a hydrogen atom from the (poly) alkylene oxide.
The polyoxymethylene polymer having the block component can be prepared by referring to, for example, the methods described in JP-A-57-31918 and JP-A-60-170652.

In the general formula (4), R ₄ is a hydrogen atom, an alkyl group, a substituted alkyl group, represents one species selected from the group consisting of aryl and substituted aryl groups, R ₄ is more, They may be the same or different.
Further, p represents an integer of 2 to 6, and the two ps may be the same or different.
q and r represent positive numbers, respectively, and q is 2 to 100 mol% and r is 0 to 98 mol% with respect to a total of 100 mol% of q and r, and − (CH (CH ₂ CH ₃ )). CH ₂ ) -units and-(CH ₂ CH ₂ CH ₂ CH ₂ ) -units exist randomly or in blocks, respectively.

The block portion of the block copolymer represented by these formulas (1) to (4) is a compound constituting a block having a functional group such as a hydroxyl group at both ends or one end in the terminal portion in the polymerization process of the polyoxymethylene resin. It is obtained by reacting with.

The amount of the block component represented by the formulas (1), (2), (3) or (4) in the block copolymer is not particularly limited, but 0.001 mass when the block copolymer is 100% by mass. It is preferably% to 30% by mass.
A more preferable upper limit of the insertion amount of the block component is 15% by mass, further preferably 10% by mass, and even more preferably 8% by mass.
The lower limit of the insertion amount of the block component is 0.01% by mass, more preferably 0.1% by mass, and even more preferably 1% by mass.

From the viewpoint of not reducing the rigidity of the molded product containing the polyoxymethylene resin composition of the present embodiment, it is preferable that the upper limit of the insertion amount of the block component is 30% by mass or less, and stable slidability is maintained. From the viewpoint, the insertion amount of the block component is preferably 0.001% by mass or more.

The molecular weight of the block component in the block copolymer is preferably 10,000 or less from the viewpoint of not reducing the rigidity of the molded product containing the polyoxymethylene resin composition of the present embodiment, more preferably 8,000 or less, still more preferably. Is less than 5000.
The lower limit of the molecular weight of the block component is not particularly limited, but it is preferably 100 or more from the viewpoint of maintaining stable slidability.

The compound forming the block component in the block copolymer is not particularly limited, but for example, C ₁₈ H ₃₇ O (CH ₂ CH ₂ O) ₄₀ C ₁₈ H ₃₇ , C ₁₁ H ₂₃ CO ₂ (CH ₂ CH ₂ O). ) ₃₀ H, C ₁₈ H ₃₇ O (CH ₂ CH ₂ O) ₇₀ H, C ₁₈ H ₃₇ O (CH ₂ CH ₂ O) ₄₀ H, polyethylene glycol with hydroxyl groups at both ends, hydroxyl groups at both ends Examples thereof include polypropylene glycol, hydrogenated polybutadiene having hydroxyl groups at both ends, hydroxyalkylated polyethylene glycol at both ends, hydroxyalkylated polypropylene glycol at both ends, and hydroxyalkylated hydrogenated polybutadiene at both ends.

The block copolymer is preferably an ABA type block copolymer as its bonding form.
Here, the ABA-type block copolymer contains, for example, a polyoxymethylene segment A and a compound (segment B (hereinafter, also referred to as “B”)) constituting a block having a functional group such as a hydroxyl group (hydroxyl group) at both ends. , Obtained by reacting with the terminal portion in the polymerization process of the polyoxymethylene resin.
As a compound constituting a block having a functional group such as a hydroxyl group at both ends, for example, a polyalkylene oxide such as polyethylene glycol having a hydroxyl group at both ends and a hydrogenated polybutadiene having a hydroxy group at both ends are used. Then, an ABA type block copolymer having a block represented by the above formulas (3) and (4) as B can be obtained.

The above equation (1), equation (2), the block component represented by formula (3) or Formula (4) may have the following unsaturated bond iodine value 20g-I ₂ / 100g.
The unsaturated bond is not particularly limited, and examples thereof include a carbon-carbon double bond.
Examples of the polyoxymethylene block copolymer having the block component include the polyoxymethylene block copolymer disclosed in Japanese Patent Application Laid-Open No. 60-170652 and International Publication No. 01/09213, and the methods described in the publication. Can be prepared with reference to.

By using the ABA type block copolymer as the block copolymer, in the molded product containing the polyoxymethylene resin composition of the present embodiment, a polymer that functions as a sliding agent constituting the polyoxymethylene resin composition of the present embodiment can be obtained. There is a tendency that fine dispersion can be performed more stably, and there is a tendency that a dispersed phase containing a polymer that functions as a large number of sliding agents can be present near the surface layer, and in sliding exceeding 1 million times. There is a tendency that it becomes possible to further develop stable wear resistance until the end.

The (A) polyoxymethylene resin constituting the molded product of the polyoxymethylene resin composition of the present embodiment includes a polyoxymethylene homopolymer, a polyoxymethylene copolymer, a polyoxymethylene copolymer having a crosslinked structure, and a block portion. Both homopolymer-based block copolymers and copolymer-based block copolymers having block components can be used, and these can be used in combination.

Further, as the (A) polyoxymethylene resin, for example, a combination having a different molecular weight, a combination of polyoxymethylene copolymers having different comonomer amounts, and the like can be appropriately used.

Among these, in the present embodiment, the polyoxymethylene resin (A) preferably contains a block copolymer.
(A) By including the block copolymer as the polyoxymethylene resin, it tends to be possible to further achieve both the rigidity of the resin molded product and the stable wear resistance after sliding more than 1 million times. ..

The ratio of the block copolymer in the (A) polyoxymethylene resin is preferably 5% by mass to 95% by mass when the total amount of the (A) polyoxymethylene resin is 100% by mass.
A more preferable upper limit of the ratio of the block copolymer is 90% by mass, further preferably 75% by mass, even more preferably 65% by mass, and most preferably 60% by mass.
The lower limit of the ratio of the block copolymer is 10% by mass, more preferably 25% by mass, even more preferably 35% by mass, and even more preferably 40% by mass.
The ratio of the block copolymer in the molded product containing the polyoxymethylene resin composition of the present embodiment can be measured by ¹ H-NMR, ¹³ C-NMR or the like.

((B) Acid-modified polyolefin having an acid value of 38 to 80)
Next, the (B) acid-modified polyolefin having an acid value of 38 to 80 mg-KOH / g contained in the polyoxymethylene resin composition of the present embodiment is described as the component (B) and (B) in the present specification. In some cases) will be described in detail.

The acid-modified polyolefin (B) used in the present embodiment is not particularly limited, but an acidic group can be introduced by an oxidation reaction of the polyolefin wax, the polyolefin can be oxidatively decomposed, or an inorganic acid, an organic acid or an unsaturated carboxylic acid can be added to the polyolefin wax. It can be obtained by reacting an acid or the like to introduce a polar group such as a carboxyl group or a sulfonic acid group, or by introducing a monomer having an acidic group during polymerization of polyolefin wax.
These are commercially available under the names such as oxidation-modified type or acid-modified type polyolefin wax, and can be easily obtained.

The polyolefin wax is not limited to the following, but includes, for example, paraffin wax, microcrystalline wax, Montan wax, Fishertropch wax, polyethylene wax, polypropylene wax, and high-density polymerization type and low-density polymerization type thereof. Examples include a modified monomer modified type.
Examples of polyolefins include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-octene copolymer, polypropylene-butene copolymer, polybutene, polybutadiene hydrogenated product, and ethylene-acrylic acid. Examples thereof include ester copolymers, ethylene-methacrylic acid ester copolymers, ethylene-acrylic acid copolymers, ethylene-vinyl acetate copolymers and the like.

As the component (B), only one kind may be used alone, or two or more kinds may be used in combination.
The components (B) include paraffin wax, polyethylene wax, acid-modified product of polypropylene wax, polyethylene (high-pressure method low-density polyethylene, linear low-density polyethylene, ultra-low-density polyethylene), polypropylene, from the viewpoint of improving slidability. Acid-modified products of polyethylene-propylene copolymer and polyethylene-butene copolymer are preferable.
The component (B) is particularly preferably a modified wax containing acid-modified polyethylene and / or acid-modified polypropylene.

The component (B) used in the polyoxymethylene resin composition of the present embodiment is an acid-modified polyolefin having an acid value of 38 to 80 mg-KOH / g.
By setting the acid value in the above range, the odorability is suppressed, and the wear resistance at the time of high-temperature sliding with a minute load tends to be good.
The preferred lower limit of the acid value is 40 mg-KOH / g, more preferably 46 mg-KOH / g, and even more preferably 50 mg-KOH / g.
The upper limit of the acid value is 78 mg-KOH / g, more preferably 75 mg-KOH / g, still more preferably 70 mg-KOH / g, and even more preferably 65 mg-KOH / g. is there.
The acid value of the component (B) can be measured by a method conforming to JIS K0070.
The acid value of the component (B) can be controlled by adjusting the introduction amount of the acidic group and the introduction amount of the polar group described above.

In the polyoxymethylene resin composition of the present embodiment, the component (B) is contained in an amount of 0.1 to 5 parts by mass with respect to 100 parts by mass of the component (A).
By setting the content of the component (B) to 0.1 part by mass or more with respect to 100 parts by mass of the component (A), the slidability of the molded product of the polyoxymethylene resin composition of the present embodiment tends to be improved. It is in.
Further, by setting the content of the component (B) to 5 parts by mass or less with respect to 100 parts by mass of the component (A), it is possible to suppress layer peeling in the molded product of the polyoxymethylene resin composition of the present embodiment. it can.

The preferable lower limit of the content of the component (B) is 0.3 parts by mass, more preferably 0.5 parts by mass, and further preferably 1.0 with respect to 100 parts by mass of the component (A). It is a mass part.
The upper limit of the content of the component (B) is 4.4 parts by mass, more preferably 4 parts by mass, and further preferably 2.9 parts by mass with respect to 100 parts by mass of the component (A). Is.

The component (B) used in the present embodiment preferably has a weight average molecular weight of 100,000 or less. In the polyoxymethylene resin composition of the present embodiment and its molded product, the presence state of the (B) acid-modified polyolefin in the vicinity of the surface layer has a great influence on the sliding characteristics, and therefore, the weight average molecular weight of the component (B) Is an important factor. That is, the polyoxymethylene resin composition of the present embodiment achieves maintenance of wear resistance over 1 million sliding times by using the component (B) as an acid-modified polyolefin having a weight average molecular weight of 100,000 or less. It will be possible.
The lower limit of the weight average molecular weight of the component (B) used in the present embodiment is not particularly limited, but it is preferably 100 or more from the viewpoint of ease of handling. It is preferably 200, more preferably 250, even more preferably 300, and even more preferably 350.
Within the above range, aggregation of the component (B) between molecules can be suppressed and good dispersion can be achieved.
The preferable upper limit of the weight average molecular weight of the component (B) is 90,000, more preferably 30,000, still more preferably 20,000, even more preferably 15,000, still more preferably 4000, and particularly. It is preferably 3000.

The lower limit of the molecular weight distribution of the component (B) used in the polyoxymethylene resin composition of the present embodiment is not particularly limited, but 1.0 is set from the viewpoint of the stability of the friction coefficient during sliding. It is a guide.
The preferable upper limit of the molecular weight distribution of the component (B) is 4.0, more preferably 3.5, still more preferably 3.0, and even more preferably 2.5.
The weight average molecular weight and the molecular weight distribution of the component (B) used in the present embodiment are calculated in terms of standard polystyrene measured by gel permeation chromatography.

Although there is no particular lower limit of the melting point of the component (B) used in the present embodiment, 100 ° C. is preferable from the viewpoint of ease of handling during melt-kneading of the polyoxymethylene resin composition of the present embodiment.
The more preferable upper limit of the melting point of the component (B) is 145 ° C, still more preferably 140 ° C, even more preferably 135 ° C, and even more preferably 133 ° C.
The melting point of the component (B) can be measured by a method (DSC method) based on JIS K 7121.

The lower limit of the 140 ° C. melt viscosity of the component (B) used in the present embodiment is not particularly limited, but from the viewpoint of processability during melt-kneading of the polyoxymethylene resin composition of the present embodiment, 1 mPa. s is preferable, 20 mPa · s is more preferable, 25 mPa · s is more preferable, 30 mPa · s is even more preferable, and 50 mPa · s is even more preferable.
The preferable upper limit of the 140 ° C. melt viscosity of the component (B) is 10000 mPa · s, more preferably 9000 mPa · s, further preferably 3500 mPa · s, and even more preferably 3000 mPa · s. Even more preferably, it is 1000 mPa · s.
By setting the content within the above range, the polyoxymethylene resin composition of the present embodiment is more preferably within the above range because the polyoxymethylene resin pellets are completely melted during melt-kneading and the kneading is sufficiently performed.
The melt viscosity of the component (B) at 140 ° C. can be measured with a Brookfield viscometer.

((C) Colorant)
The polyoxymethylene resin composition of the present embodiment may contain (C) a colorant as an additional component (optional component).
(C) The colorant will be described in detail.
(C) Colorant refers to a substance that changes its appearance by the action of absorption, scattering, reflection, etc. of visible light.
In the polyoxymethylene resin composition of the present embodiment, (C) a colorant (in this specification, it may be referred to as (C) component and (C)) is added to (A) 100 mass of polyoxymethylene resin. It is preferable to contain 0.01 to 3 parts by mass with respect to parts.

In the present embodiment, the (C) colorant present in the molded product of the polyoxymethylene resin composition is said to further improve the wear resistance by combining with the component (B) in addition to the original purpose of coloring. Has an important role.
From the viewpoint of obtaining excellent wear resistance, it is important to include the colorant in the polyoxymethylene resin composition of the present embodiment in an amount within the above range.
The reason for the improvement in wear resistance due to the presence of (C) the colorant is not clear, but (C) the surface hardness of the molded product is improved by the colorant to improve the wear resistance, and (C) coloring. It is conceivable that the agent retains the (B) acid-modified polyolefin and is unevenly distributed near the surface layer.

The colorant (C) is not limited to the following, and examples thereof include inorganic pigments and organic dyes.
Examples of the inorganic pigment include an inorganic pigment generally used for coloring a resin.
The inorganic pigment is not limited to the following, but is, for example, an oxide of at least one metal selected from the group consisting of iron, zinc and titanium; at least selected from the group consisting of iron, zinc and titanium. Carbon carbonate of one metal; zinc sulfide, titanium oxide, zinc oxide, iron oxide, barium sulfate, titanium dioxide, barium sulfate, chromium hydroxide-containing, chromium oxide, cobalt aluminate, barite powder, zinc yellow 1 type, zinc yellow 2 types, ferrosian iron potassium, kaolin, titanium yellow, cobalt blue, ultramarine blue, cadmium, nickel titanium, lithopon, strontium, umber, shenna, azurite, malakite, azuro malakite, opiment, realger, dragon sand, Turkish stone, Ryomanganese ore, yellow ocher, tail belt, low shenna, low amber, Cassel earth, white, gypsum, burnt shenna, burnt amber, lapis lazuli, azurite, malakite, coral powder, white mica, cobalt blue, cerulean blue, cobalt violet, cobalt Green, Zinc White, Titanium White, Light Red, Chrome Oxide Green, Mars Black, Villijan, Yellow Ocher, Alumina White, Cadmium Yellow, Cadmium Red, Vermilion, Tarku, White Carbon, Clay, Mineral Violet, Rose Cobalt Violet, Silver white, gold powder, bronze powder, aluminum powder, Prussian blue, aureolin, talc, wollastonite, mica titanium, carbon black, acetylene black, lamp black, furnas black, vegetable black, bone charcoal, calcium carbonate, navy blue, etc. Be done.
The "metal oxide" also includes a "composite metal oxide" composed of two or more kinds of metals selected from iron, zinc or titanium.
(C) As the colorant, an oxide of at least one metal selected from the group consisting of iron, zinc and titanium, a carbonate of at least one metal selected from the group consisting of iron, zinc and titanium, and zinc sulfide. , Zinc oxide, iron oxide, zinc yellow 1 type, zinc yellow 2 types, zinc white, titanium white, alumina white, talc, white carbon, silver white, carbon black, acetylene black, lamp black, funus black, calcium carbonate, It is mentioned as preferable.
Among these, a colorant having a Mohs hardness of 8 or less is preferable from the viewpoint of abrasion resistance of the polyoxymethylene resin composition of the present embodiment. More preferably, the Mohs hardness is 7 or less, and even more preferably, the Mohs hardness is 6 or less.
The Mohs hardness of the colorant (C) can be measured with a Mohs hardness meter.

The organic dyeing pigment is not limited to the following, but for example, condensed azo type, quinone type, phthalocyanine type, monoazo type, diazo type, polyazo type, anthraquinone type, heterocyclic type, pennon type, quinacridone. Examples thereof include organic dyes such as thioindic, berylene, dioxazine, and phthalocyanine.
From the viewpoint of the thermal stability of the polyoxymethylene resin composition of the present embodiment, the organic dyes include condensed azo, quinone, phthalocyanine, anthracinone, heterocyclic, pennon, quinacridone, and thioindico. Preferables are based, berylene-based, dioxazine-based, or phthalocyanine-based organic dyes. More preferably, it is a condensed azo-based, quinone-based, flotasianin-based, anthracinone-based, heterocyclic, pennon-based, quinacridone-based, verylene-based, or phthalocyanine-based organic dye pigment. More preferably, it is a quinone-based, flotasianin-based, anthracinone-based, heterocyclic, quinacridone-based, berylene-based, or phthalocyanine-based organic dye pigment.

A more preferable upper limit amount of the (C) colorant contained in the polyoxymethylene resin composition of the present embodiment is 2.5 parts by mass with respect to 100 parts by mass of the (A) polyoxymethylene resin, which is even more preferable. Is 2.0 parts by mass, and even more preferably 1.8 parts by mass.
The lower limit of the (C) colorant is 0.03 parts by mass, more preferably 0.05 parts by mass, and even more preferably 0 with respect to 100 parts by mass of the (A) polyoxymethylene resin. .1 part by mass.

As described above, by setting the content of the colorant (C) to 3 parts by mass or less, the polyoxymethylene resin composition of the present embodiment has a sufficient effect of improving the wear characteristics when sliding with a small load. Be done.
On the other hand, by setting the content of the colorant (C) to 0.01 parts by mass or more, the polyoxymethylene resin composition of the present embodiment can ensure sufficient colorability.

(Other additives)
The polyoxymethylene resin composition of the present embodiment can contain various conventionally known stabilizers as long as the object of the present invention is not impaired.
Stabilizers include, but are not limited to, the following antioxidants, formaldehyde and formic acid scavengers.
Only one of these may be used alone, or two or more thereof may be used in combination.
As the antioxidant, a hindered phenolic antioxidant is preferable from the viewpoint of improving the thermal stability of the polyoxymethylene resin composition of the present embodiment.
The hindered phenolic antioxidant is not particularly limited, and known ones can be appropriately used.
The trapping agent for formaldehyde and formic acid is not limited to the following, but for example, compounds containing formaldehyde-reactive nitrogen such as melamine and polyamide resins and their polymers, alkali metals or alkali earth metal hydroxides. , Inorganic acid salts, and carboxylates. Specific examples include calcium hydroxide, calcium carbonate, calcium phosphate, calcium silicate, calcium borate, and calcium fatty acid salts (calcium stearate, calcium myristate, etc.). The fatty acid may be substituted with a hydroxyl group.
The amount of each of the above-mentioned stabilizers added is 0.1 to 2 parts by mass of an antioxidant, for example, a hindered phenolic antioxidant, and formaldehyde or formic acid with respect to 100 parts by mass of the (A) polymer resin. It is preferable that the polymer containing a trapping agent such as formaldehyde-reactive nitrogen is in the range of 0.1 to 3 parts by mass, and the fatty acid salt of the alkaline earth metal is in the range of 0.1 to 1 part by mass.

[Method for producing polyoxymethylene resin composition of the present embodiment]
The polyoxymethylene resin composition of the present embodiment is obtained by melt-kneading, for example, (A) polyoxymethylene resin, (B) acid-modified polyolefin, and if necessary, (C) a colorant and other additives. Obtainable.
Here, the polyoxymethylene resin composition of the present embodiment contains (A) an acid-modified polyolefin having an acid value of 38 to 80 mg-KOH / g with respect to 100 parts by mass of the polyoxymethylene resin. Contains 1 to 5 parts by mass.
A known method is used as a method for obtaining the polyoxymethylene resin composition of the present embodiment.
For example, a single-screw or multi-screw kneading extruder, a roll, a Banbury mixer and the like can be mentioned, and among them, a twin-screw extruder equipped with a decompression device, a side feeder facility and the like can be particularly preferably used.
The method of mixing and melt-kneading the raw material components is not particularly limited, and a method well known to those skilled in the art can be used.
For example, a method in which the components (A) and (B) are all mixed in advance with a super mixer, tumbler, V-shaped blender, etc. and collectively melt-kneaded with a twin-screw extruder, and the component (A) is mixed with a twin-screw extruder. Etc., and the method of melting the component (B) from the middle of the extruder and adding it in a liquid state while melting and kneading can be mentioned, but any of these can be used without any problem.
The polyoxymethylene resin composition of the present embodiment is obtained in the form of pellets when produced by the above extruder.

[Molded product]
The molded product of the present embodiment contains the polyoxymethylene resin composition of the present embodiment.
The method for obtaining the molded product is not particularly limited, and a known molding method can be applied.
For example, extrusion molding, injection molding, vacuum molding, blow molding, injection compression molding, decorative molding, molding of other materials, gas-assisted injection molding, foam injection molding, low-pressure molding, ultra-thin injection molding (ultra-high-speed injection molding), Any molding method such as in-mold composite molding (insert molding, outsert molding) can be applied.
The shape of the molded product is not particularly limited, and examples thereof include gears, cams, rollers, lamps, and seats.

The molded product of the polyoxymethylene resin composition of the present embodiment has the effect of suppressing abrasion damage of only the surface layer described above, and the effect can be maintained until after rubbing 1 million times.

It is considered that the molded product of the polyoxymethylene resin composition of the present embodiment exerts such an effect by having a special surface layer.

The special surface layer referred to in the present embodiment is a relative element concentration ratio [C / O] (atomic%) of carbon and oxygen on the surface of the molded product (hereinafter, may be abbreviated as "C / O ratio"). Is a surface layer of 1.01 to 2.50. The relative element concentration ratio [C / O] can be measured by the method described later.

Generally, if the polyacetal resin is used alone, the C / O ratio is 1.00 based on the constituent element ratio. When various sliding agents are added to this, the C / O ratio of the surface layer changes. The commonly used sliding agent is a relatively low molecular weight ester compound, an amide compound, or a polymer sliding agent such as polyolefin. The C / O ratio cannot be controlled in the range of 1.01 to 2.50 only by blending such a sliding agent by a usual method.

Specifically, when a relatively low molecular weight ester compound or amide compound is simply blended into the polyacetal resin as a sliding agent without any special ingenuity, these ester compounds or amide compounds are formed on the surface layer of the molded body. It bleeds out in large quantities, and the C / O ratio of the surface layer greatly exceeds 2.5. In this case, the wear resistance of the obtained molded product under a very small load (hereinafter, may be abbreviated as "micro load wear") is improved by the bleed-out sliding agent at the initial stage. When the bleed-out material is removed by sliding, it tends to deteriorate rapidly.

Further, for example, when a polymer sliding agent such as polyolefin is used alone instead of a low molecular weight ester compound or amide compound as the sliding agent, the C / O ratio of the surface layer is the same as that of the polyacetal resin1. It becomes .00. It is considered that this is because the polymer sliding agent is present only at a depth of several μm to 10 μm from the surface layer. This indicates that the polymer sliding agent is not exposed on the surface. In this case, the minute load wear deteriorates from the initial stage of sliding, and cannot meet the new requirement of scratch resistance exceeding 1 million times.

The method for measuring the value of the C / O ratio referred to in this embodiment will be illustrated below.

The C / O ratio on the surface of the molded product can be easily obtained by measuring the surface of the molded product of the resin composition using a high-performance X-ray photoelectron spectrometer (generally referred to as XPS). Can be done. These analytical instruments are common, and examples thereof include ESCALAB250 manufactured by Fisher Scientific Co., Ltd.

It is preferable to use monoAlKα or the like as an excitation source at the time of measurement.

Further, in order to remove the influence of the adherent contaminants adhering to the surface of the molded body, the surface of the molded body is ultrasonically cleaned with a cleaning agent (for example, an aqueous solution of VALTRON DP97031), washed with pure water, and dried in an oven or the like.

The C concentration in the XPS measurement has a peak area in the range of 284 eV to 288 eV at the peak top, and the O concentration has a peak area in the range of 530 eV to 536 eV at the peak top, and the relative element concentration can be calculated from the ratio of each peak area.

The C / O ratio on the surface of the molded product of the polyoxymethylene resin composition of the present embodiment is the acid-modified polyolefin (B) that functions as a sliding agent that constitutes the molded product of the polyoxymethylene resin composition described later. It is an index of the amount of bleed-out. The upper limit of the C / O ratio on the surface of the molded product of the polyoxymethylene resin composition of the present embodiment is preferably 2.50 and the lower limit is preferably 1.01.

For example, if a large amount of (B) acid-modified polyolefin bleeds out on the surface of the lamp molded product, bleed-out substances adhere to, accumulate, and fall off on the tabs that slide on the surface, which causes reading problems of the hard disk, which is not preferable. .. By setting the upper limit of the C / O ratio on the surface of the resin molded product to 2.50, it is possible to obtain a good resin molded product in which the above-mentioned problems are suppressed.

The upper limit of the C / O ratio on the surface of the resin molded product is more preferably 2.30, still more preferably 2.00, even more preferably 1.90, and even more preferably 1.80.

The lower limit of the C / O ratio on the surface of the resin molded product is preferably 1.01, which indicates that the bleed-out is extremely small, that is, it is very close to the surface layer of the polyacetal itself. The lower limit of the more preferable C / O ratio is 1.03, still more preferably 1.05, even more preferably 1.08, and even more preferably 1.10.

As a more preferable surface layer for forming a molded product having a special surface layer according to the present embodiment, for example, a CO expansion / contraction vibration peak and a C = O expansion / contraction vibration peak on the surface of the molded product obtained by infrared spectroscopy are used. The peak intensity ratio (C—O / C = O) is 10 to 200.

The peak intensity ratio of the CO expansion / contraction vibration peak and the C = O expansion / contraction vibration peak on the surface of the molded body obtained by the infrared spectroscopy according to the present embodiment (hereinafter, simply the peak intensity ratio (CO / C = O)). ) May be abbreviated as).

The peak intensity ratio (C—O / C = O) of the surface of the resin molded product can be easily obtained by measuring and analyzing the surface of the resin molded product using the total reflection method (ATR method) of an infrared spectrophotometer. be able to. As these measuring instruments, for example, a commercially available Spectrum One manufactured by Perkin-Elmer can be used.

The ATR method is used to obtain information on the surface state by utilizing the fact that infrared light incident on a crystal in contact with a resin molded product is absorbed by the surface of the resin molded product while being reflected in the crystal multiple times. It is a measurement method of. At this time, a phenomenon called evanescent wave, in which infrared rays permeate into the molded product, occurs on the surface of the molded product. The depth varies slightly depending on the wavelength and the type of crystal, but is approximately several μm. That is, the peak intensity ratio (CO / C = O) of the surface of the resin molded product measured and analyzed using the total reflection method (ATR method) of the infrared spectrophotometer is several μm from the surface layer of the molded product. Depth information. As the crystal used in the ATR method in the present embodiment, it is preferable to use diamond / ZnSe from the viewpoint of the penetration depth.

The obtained spectrum is analyzed as an absorbance ratio. Specifically, as a signal C-O (derived repeating structure of polyacetal), the peak intensity is between 1160 cm ^-1 from 1040 cm ^-1 (peak height), as a signal C = O is, 1600 cm ^-1 The peak intensities between the two and 1750 cm ^-1 are calculated, and the peak intensity ratio (CO / C = O) is defined as the peak intensity ratio (CO / C = O) on the surface of the resin molded product. At this time, to eliminate the error, for obtaining the peak intensity, the baseline is subtracted from each 1040 cm ^-1 1160 cm ^-1, the straight line from the 1590 cm ^-1 to 1760 cm ^-1, the peak intensity the height from the baseline Read as.

The peak intensity ratio (C—O / C = O) of the surface of the molded product of the polyoxymethylene resin composition of the present embodiment is defined as the acid-modified polyolefin (B) constituting the resin molded product of the present embodiment described later. , It is an index of the amount existing in the vicinity of the surface layer (within a depth of several μm).
The peak intensity ratio (C—O / C = O) is preferably 10 to 200. When this value exceeds 200, it means that the acid-modified polyolefin (B) constituting the resin molded product of the present embodiment described later is hardly present in the vicinity of the surface layer, and is less than 10. Indicates that an extremely large amount of (B) acid-modified polyolefin is unevenly distributed near the surface layer. Peak strength ratio (CO / C = O) of the surface of the resin molded product from the viewpoint of maintaining high slidability with more than 1 million scrapes and suppressing deterioration of wear resistance due to surface layer peeling on the surface layer. Is preferably between 10 and 200.

The upper limit of the peak intensity ratio (CO / C = O) on the surface of the resin molded product, which is more preferable in the present embodiment, is 180, more preferably 150, and even more preferably 140. Further, the lower limit of the peak intensity ratio (CO / C = O) on the surface of the resin molded product is more preferably 15, still more preferably 20, and even more preferably 25.

[Use]
The polyoxymethylene resin composition of the present embodiment and the molded product containing the resin composition can be suitably used for applications requiring repeated sliding under a minute load.
Specific examples include hard disk internal parts (lamps, latch materials), watch internal parts (gears, balances, ankles, escape wheel, etc.).
In addition to these, since the molded product containing the polyoxymethylene resin composition of the present embodiment has high slidability, it can be applied to known applications as polyoxymethylene. Not limited to, for example, cams, sliders, levers, arms, clutches, felt clutches, idler gears, pulleys, rollers, rollers, key stems, key tops, shutters, reels, shafts, joints, shafts, bearings. , And mechanical parts such as guides; resin parts for outsert molding, resin parts for insert molding, chassis, trays, side plates, printers, and parts for office automation equipment such as copiers; digital video cameras, and Parts for video equipment such as digital cameras; CD, DVD, Blu-ray (registered trademark) Disc, and other optical disk drives; for music, video or information equipment such as navigation systems and mobile personal computers, mobile phones and facsimiles. Typical examples include parts for communication equipment; parts for electrical equipment; parts for electronic equipment and the like.
In addition, as automobile parts, for example, fuel parts such as gasoline tanks, fuel pump modules, valves, and gasoline tank flanges; door parts such as door locks, door handles, window regulators, and speaker grills. ; Seatbelt peripheral parts typified by seatbelt slip rings, press buttons, etc .; Applicable to parts such as combination switch parts, switches, clips, etc.
Furthermore, as other supplies, the pen tip of the writing tool, mechanical parts for inserting and removing the core; washstand, drain port, and drain plug opening and closing mechanical parts; cord stopper for clothing, adjuster, button; nozzle for sprinkling, sprinkling hose connection Joints; building supplies that support stair railings and flooring materials; toys, fasteners, chains, conveyors, buckles, sporting goods, vending machines (opening / closing lock mechanism, product discharge mechanism parts), furniture, musical instruments, housing It can also be suitably used as an equipment component.

Hereinafter, the present embodiment will be described with reference to specific examples and comparative examples, but the present embodiment is not limited to the examples described later.
The production conditions and characteristic evaluation items of the polyoxymethylene resin compositions of Examples and Comparative Examples and their molded articles are shown below.

[Manufacturing of polyoxymethylene resin composition and molded article]
(1) Extrusion of resin composition A cylinder using a twin-screw extruder (TEM-26SS extruder manufactured by Toshiba Machine Co., Ltd. (L (effective screw length) / D (screw diameter) = 48, with vent) All the temperatures are set to 200 ° C., the component (A), the component (B), and the component (C), which will be described later, are mixed together and supplied from the main throat section of the extruder from the quantitative feeder, and the extrusion speed is 15 kg. The resin kneaded product was extruded into a strand shape under the condition of / hour and a screw rotation speed of 150 rpm, rapidly cooled in a strand bath, and cut with a strand cutter to obtain a pellet-shaped resin composition.

(2) Molding (manufacturing of multipurpose test piece-shaped molded body by injection molding machine)
Using an injection molding machine (EC-75NII, manufactured by Toshiba Machine Co., Ltd.), the cylinder temperature is set to 205 ° C., and molding is performed under injection conditions with an injection time of 35 seconds and a cooling time of 15 seconds to achieve ISO 294-1. A compliant multipurpose test piece-shaped molded product was obtained.
The mold temperature at this time was 80 ° C.

(3) Cleaning of the molded body In order to remove the deposits on the surface layer of the molded body obtained in (2) above, a 1.5% aqueous solution of a commercially available cleaning agent for precision equipment (VALTRON DP97031 (registered trademark)) was used. After removing organic substances on the surface by ultrasonic cleaning at 50 ° C. for 3 minutes, ultrasonic treatment was performed for 15 minutes under room temperature conditions using distilled water for high performance liquid chromatography to carry out the cleaning.
Next, the washed sample was dried in a drying oven at 80 ° C. for 1 hour to obtain a molded product (multipurpose test piece-shaped molded product) of the polyoxymethylene resin composition for measurement.

[Characteristic evaluation]
(1) Sliding test under minute load (wear resistance)
Using a ball-on-disk type friction and wear tester (Nano tribometer2 (registered trademark), TTX-NTR2 type, manufactured by CSM Instruments Co., Ltd.), load 0.1N, sliding speed 200mm / sec, reciprocating distance 10000μm, number of reciprocations A sliding test of the multipurpose test piece-shaped molded product obtained in (3) of the above [Production of polyoxymethylene resin composition and molded product] was carried out under the condition of 1.2 million times.
As the ball material, a SUJ2 ball (a ball having a diameter of 1.5 mm) was used.
The test environment was 23 ° C. and 50% humidity (sliding test-1) and 80 ° C. and 50% humidity (sliding test-2), respectively.

(2) Evaluation method of wear resistance characteristics The amount of wear (wear cross-sectional area) of the molded body after the "sliding test of (1)" in the above [characteristic evaluation] is measured with a confocal microscope (OPTELICS (registered trademark) H1200). , Lasertec Co., Ltd.).
The wear cross-sectional area was taken as the average value of the numerical values measured at n = 4, and rounded off to the first decimal place.
The measurement points were measured at equal intervals of 2000 μm from the edges of the wear marks.
In addition, it was evaluated that the lower the value of the wear cross-sectional area, the better the wear resistance characteristics.

(3) Odorability 1 kg of pellets immediately after the strand cutter during the above [Manufacturing of polyoxymethylene resin composition and molded product] is captured in a paper bag having a length of 50 cm and a width of 25 cm. After gathering, five people sniffed and judged this odor.
The judgment value was the average value of 5 people, and was rounded off to the first decimal place.
The judgment criteria were as follows.
1: I didn't smell it.
2: I felt a little smell.
3: I felt a smell.
4: I strongly felt the smell.
5: I felt the smell quite strongly.

(4) Extruding production stability The stability of the strand immediately after the die of the extruder was determined when (1) in the above [Production of polyoxymethylene resin composition and molded product] was carried out.
The judgment value was the average value of the numerical values obtained by visually judging for 1 minute at n = 5, and rounded off to the first decimal place.
The judgment criteria were as follows.
1: No eye rash was observed and there was no pulsation.
2: A slight eye tar was observed.
3: A slight eye shaving was observed, and there was a slight pulsation.
4: A pulsation was observed, and the thickness of the strand fluctuated over time.
5: There were a lot of eye boogers, and the beats were repeated.

(5) Relative element concentration ratio [C / O]
(2) Molding (manufacturing of multipurpose test piece-shaped molded product by injection molding machine) in the above [Production of polyoxymethylene resin composition and molded product], the above [Production of polyoxymethylene resin composition and molded product] The relative element concentration ratio [C / O] (atomic%) of carbon and oxygen on the surface of the multipurpose test piece obtained by (3) washing the molded product in [Manufacturing] was measured as follows.
ESCALAB250 manufactured by Fisher Scientific Co., Ltd. was used as a measuring device, and monoAlKα (15 kV × 10 mA) was used as an excitation source. The sample at the time of measurement is cut out to a size of about 1 mm (shape is elliptical), and then a 1.5% aqueous solution of a commercially available cleaning agent for precision equipment (VALTRON DP97031) is used to remove deposits on the surface layer of the molded body. After removing organic substances on the surface by ultrasonic cleaning at 50 ° C. for 3 minutes, ultrasonic treatment was performed with distilled water for high performance liquid chromatography for 15 minutes at room temperature to carry out the cleaning. Next, the washed sample was dried in a drying oven at 80 ° C. for 1 hour and subjected to measurement. In the measurement, the photoelectron capture angle was set to 0 ° (the axis of the spectroscope and the sample plane were perpendicular to each other), and the capture region was a region of 0 to 1100 eV for the Survey scan and C 1s, O 1s, and N 1s for the Narrow scan. In addition, Pass Energy was carried out at 100 eV for Survey scan and 20 eV for Now scan. The C concentration at this time was defined as a peak area ratio in the range of 284 eV to 288 eV for each peak top. The O concentration was defined as a peak area ratio in the range of 530 eV to 536 eV for each peak top. The relative element concentration was calculated from the area ratio of each peak, and rounded off to 1 significant digit or more with 2 significant figures, and less than 1 atomic% with 1 significant digit. The ratio of each of these element concentrations was defined as the "relative element concentration ratio of carbon and oxygen on the surface".

(5) Peak intensity ratio (CO / C = O)
(2) Molding (manufacturing of multipurpose test piece-shaped molded product by injection molding machine) in the above [Production of polyoxymethylene resin composition and molded product], the above [Production of polyoxymethylene resin composition and molded product] (Manufacturing) (3) Peak intensity ratio (C-O / C = O) of the C-O expansion and contraction vibration peak and the C = O expansion and contraction vibration peak on the surface of the multipurpose test piece-shaped molded product obtained by cleaning the molded product. ) Was obtained by analysis by infrared spectroscopy as follows.
The measuring instrument was a Spectrum One manufactured by Perkin-Elmer, and the measurement was performed by the ATR method (crystal: diamond / ZnSe). 4000 cm ^-1 Measurement range 500 cm ^-1, wave number resolution and 4 cm ^-1, and the number of integration and 16 times. Signal as 1090 cm ^-1 peak intensity during measurement of C-O (derived repeating structure of polyacetal) (peak height), C = O of the signal peak strength of 1750 cm ^-1 from 1600 cm ^-1 as the respectively calculated, " The peak intensity ratio (CO / C = O) of the CO expansion / contraction vibration peak and the C = O expansion / contraction vibration peak on the surface of the molded body was determined. Incidentally, when obtaining the peak intensity, the linear baseline, 1160 cm ^-1 from 1040 cm ^-1, respectively, after subtracting from 1590 cm ^-1 to 1760 cm ^-1, it was read positive height as the peak intensity from baseline ..

[Ingredients of polyoxymethylene resin composition]
The raw material components of the polyoxymethylene resin composition used in Examples and Comparative Examples described later will be described below.
((A) Production example of polyoxymethylene resin)
<(A1) Polyoxymethylene copolymer>
A twin-screw self-cleaning type polymerization machine with a jacket that allows a heat medium to pass through (L / D = 8 (L: distance (m) from the raw material supply port to the discharge port of the polymerization machine, D: inner diameter of the polymerization machine ( m).) Was adjusted to 80 ° C.
To the polymerization machine, 4 kg / hour of trioxane, 128.3 g / hour of 1,3-dioxolane as a comonomer, and 0.25 × 10 ^-3 mol of methylal as a chain transfer agent were continuously added to 1 mol of trioxane. did.
Further, a boron trifluoride di-n-butyl etherate was continuously added to the polymerization machine in an amount of 1.5 × 10 ^-5 mol with respect to 1 mol of trioxane to carry out the polymerization.
The polyoxymethylene copolymer discharged from the polymerization machine was put into a 0.1% aqueous solution of triethylamine to deactivate the polymerization catalyst.
After filtering the inactivated polyoxymethylene copolymer with a centrifuge, 1 part by mass of an aqueous solution containing a quaternary ammonium compound was added to 100 parts by mass of the polyoxymethylene copolymer and mixed uniformly. It is supplied to a twin-screw extruder with a vent, and 0.5 part by mass of water is added to 100 parts by mass of the molten polyoxymethylene copolymer in the extruder, and the set temperature of the extruder is 200 ° C. With a residence time of 7 minutes, the unstable end portion of the polyoxymethylene copolymer was decomposed and removed.
At this time, the amount of the quaternary ammonium compound added was 20 mass ppm in terms of the amount of nitrogen.
Triethylene glycol-bis- [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) -propionate] 0.3% by mass as an antioxidant on the decomposed polyoxymethylene copolymer at the unstable end. The part was added and extruded as a strand from the die part of the extruder while being devolatile under the condition of a vacuum degree of 20 Torr in an extruder with a vent, and pelletized.
The polyoxymethylene copolymer thus obtained was designated as a polyoxymethylene resin (A1).
The melt flow rate of the polyoxymethylene resin (A1) was 9 g / 10 minutes (ISO-1133 condition D).

<(A2) Polyoxymethylene block copolymer>
A twin-screw paddle type continuous polymerization machine with a jacket capable of passing a heat medium was adjusted to 80 ° C.
40 mol / hr of trioxane, 1,3-dioxolane as a cyclic formal 2 mol / hour, trioxane boron trifluoride di -n- butyl etherate dissolved in cyclohexane as a polymerization catalyst relative to 1 mol 5 × 10 ^{- The} amount of polybutadiene (number average molecular weight Mn = 2330) represented by the following formula (5) as a chain transfer agent is 1 × 10 ^-3 mol per 1 mol of trioxane. , The polymer was continuously supplied to the polymerization machine to carry out polymerization.

Next, the polymer discharged from the polymerization machine is put into a 1% aqueous solution of triethylamine to completely deactivate the polymerization catalyst, and then the polymer is filtered and washed to obtain a crude polyoxymethylene block copolymer. Obtained.
To 100 parts by mass of the crude polyoxymethylene block copolymer, 1 part by mass of an aqueous solution containing a quaternary ammonium compound was added, mixed uniformly, and supplied to a twin-screw screw extruder with a vent. 0.5 parts by mass of water was added to 100 parts by mass of the molten polyoxymethylene block copolymer, and the polyoxymethylene block copolymer was unstable at an extruder set temperature of 200 ° C. and a residence time of 7 minutes in the extruder. The end part was decomposed and removed.
At this time, the amount of the quaternary ammonium compound added was 20 mass ppm in terms of the amount of nitrogen.
Triethylene glycol-bis- [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) -propionate] 0.3 as an antioxidant in the decomposed polyoxymethylene block copolymer at the unstable end. A part by mass was added, and the mixture was extruded as a strand from the die part of the extruder while being devolatile under the condition of a vacuum degree of 20 Torr in an extruder with a vent, and pelletized.
The polyoxymethylene block copolymer thus obtained was designated as (A2) polyoxymethylene block copolymer.
This block copolymer was an ABA type block copolymer and had a melt flow rate of 10.0 g / 10 min (ISO-1133 Condition D).

((B) component acid-modified polyolefin)
B1 in [Table 1] below was obtained by thermally decomposing commercially available polyethylene, and B2 was obtained by thermally decomposing commercially available polypropylene in an oxygen atmosphere.
The acid-modified polyolefins B3 to B7 shown in [Table 1] below were obtained by the method of "Example 1 or 2" described in JP-A-2004-75749.
B8 in [Table 1] below was obtained by the method of "Example 1" described in JP-A-62-167308.
B9 in [Table 1] below was purchased and used on the market.

The weight average molecular weight and the molecular weight distribution of the component (B) were calculated in terms of standard polystyrene measured by gel permeation chromatography.
The melting point of component (B) was measured by a method (DSC method) based on JIS K 7121.
Further, the viscosity of the component (B) was assumed to be 140 ° C. melt viscosity, and the viscosity was measured with a Brookfield viscometer.

((C) component colorant)
<(C1)>
Zinc sulfide: Mohs hardness 4
<(C2)>
Zinc oxide: Mohs hardness 5
<(C3)>
Zinc / iron composite oxide: Mohs hardness 5
<(C4)>
Iron oxide: Mohs hardness 6
<(C5)>
Titanium oxide: Mohs hardness 7
In this embodiment, the Mohs hardness was measured by a Mohs hardness meter.

[Examples 1 to 5]
Each component is mixed at the ratio shown in the following [Table 2], and the procedure described in "(1) Extrusion processing of the resin composition" of the above-mentioned [Production of polyoxymethylene resin composition for evaluation and molded product]. The molded product is manufactured in the manner of "(2) Molding (manufacturing of multipurpose test piece-shaped molded product by injection molding machine)", and in the sliding test, "(3) Cleaning of the molded product" is further performed. And evaluated various performances.

The contrast of [Examples 1 to 5] is a comparison in which the molecular structure of the acid-modified polyolefin is changed.
From these results, the acid-modified polyolefin having an acid value within a predetermined numerical range is excellent in all of the sliding test-1, the sliding test-2, the odor property, and the production stability. I found out.

[Examples 6 to 7, Comparative Example 1]
A molded product was produced in the same manner as in [Example 1] above, except that each component was mixed at the ratio shown in [Table 3] below, and various performances were evaluated.

In [Examples 6 and 7] and [Comparative Example 1], the amount of the acid-modified polyolefin of [Example 4] added to the polyoxymethylene resin is changed.
In Comparative Example 1 in which 6 phr of acid-modified polyolefin was added to the polyoxymethylene resin, the strands from the biaxial extruder die pulsated, and stable pellets could not be obtained.
Further, by adding the acid-modified polyolefin in an amount of less than 6 parts by mass as in [Examples 6 and 7], the sliding test-1 and the odor property and the production stability were improved.

[Examples 8 to 10]
A molded product was produced in the same manner as in [Example 1] above, except that each component was mixed at the ratio shown in [Table 4] below, and each performance was evaluated.

[Examples 8, 9, and 10] are comparisons of polyoxymethylene resin compositions in which different polyoxymethylene resin components from the polyoxymethylene resin components of [Examples 2, 4, and 5] are mixed.
From these results, it was found that the evaluation of each performance was good even if the (A) polyoxymethylene resin was changed.

[Comparative Examples 2 to 5]
A molded product was produced in the same manner as in [Example 1] above, except that each component was mixed at the ratio shown in [Table 5], and each performance was evaluated.

[Comparative Examples 2 to 5] are a comparison of polyoxymethylene resin compositions using different acid-modified polyolefins having different molecular structures and different acid values as compared with [Examples 4 and 5].
From these results, the resin composition using the acid-modified polyolefin having an acid value within a predetermined numerical range has excellent properties in sliding test-1 and sliding test-2, odorability, and production stability. Was found to be obtained.
Further, in [Comparative Example 5], in the polyoxymethylene resin composition using (B9) ethylene bisstearic acid amide, the strands from the biaxial extruder die beat in the same manner as in [Comparative Examples 3 and 4]. It moved and could not obtain stable pellets.

[Examples 11 to 15]
A molded product was produced in the same manner as in [Example 1] above except that each component was mixed at the ratio shown in [Table 6] below, and each performance was evaluated.

The above [Examples 11 to 15] are a comparison in which the component (C) is added to the above [Example 4].
From these results, it was found that the wear resistance of the sliding test-1 and the sliding test-2 was good even when the pigment was added.

[Examples 16 to 19]
A molded product was produced in the same manner as in [Example 1] above, except that each component was mixed at the ratio shown in [Table 7] below, and each performance was evaluated.

[Examples 16 to 19] are comparisons of colorants with [Example 12].
From these results, it was found that even if various colorants were used, excellent evaluations were obtained in the sliding test-1 and the sliding test-2, and the odor and production stability were also good.

The polyoxymethylene resin composition of the present invention includes hard disk lamp parts that require abrasion resistance under a very small load, internal parts such as wristwatches, and various polyoxymethylene resins for which polyoxymethylene resin has been preferably used. It has industrial applicability as a component application.

Claims (12)

(A) 100 parts by mass of polyoxymethylene resin and
(B) 0.1 to 5 parts by mass of acid-modified polyolefin having an acid value of 40 to 63 mg-KOH / g.
, Contains
A lamp molded product for a hard disk, which is a molded product of a polyoxymethylene resin composition. A lamp molded product for a hard disk, which is a molded product of the polyoxymethylene resin composition according to claim 1, further containing 0.01 to 3 parts by mass of a (C) colorant having a Mohs hardness of 6 or less. The acid-modified polyolefin (B)
A lamp molded article for a hard disk, which is a molded article of the polyoxymethylene resin composition according to claim 1 or 2, which is a modified wax containing acid-modified polyethylene and / or acid-modified polypropylene. A lamp molded product for a hard disk, which is a molded product of the polyoxymethylene resin composition according to any one of claims 1 to 3, wherein the acid-modified polyolefin (B) has a weight average molecular weight of 100 to 100,000. A lamp molded product for a hard disk, which is a molded product of the polyoxymethylene resin composition according to any one of claims 1 to 4 , wherein the acid-modified polyolefin (B) has a weight average molecular weight of 100 to 30,000. A lamp molded product for a hard disk, which is a molded product of the polyoxymethylene resin composition according to any one of claims 1 to 5 , wherein the acid-modified polyolefin (B) has a weight average molecular weight of 300 to 3000. A lamp for a hard disk, which is a molded product of the polyoxymethylene resin composition according to any one of claims 1 to 6 , wherein the acid-modified polyolefin (B) has a melt viscosity of 1 to 1000 mPa · s at 140 ° C. Molded body. The colorant (C) is zinc sulfide, zinc oxide, iron oxide, zinc yellow 1 type, zinc yellow 2 types, zinc white, titanium white, alumina white, talc, white carbon, silver white, carbon black, acetylene black, Any one of claims 2 to 7 , which is a colorant containing at least one selected from the group consisting of lamp black, furnas black, calcium carbonate, and an inorganic pigment selected from the group consisting of organic dyeing pigments. A lamp molded body for a hard disk, which is a molded body of the polyoxymethylene resin composition according to the section. A lamp molded product for a hard disk, which is a molded product of the polyoxymethylene resin composition according to any one of claims 1 to 8 , wherein the polyoxymethylene resin (A) contains a block copolymer. A lamp molded product for a hard disk, wherein the block copolymer is an ABA type block copolymer, which is a molded product of the polyoxymethylene resin composition according to claim 9 . A hard disk lamp molded product, which is a molded product of the polyoxymethylene resin composition according to any one of claims 1 to 10 , and has a relative element concentration ratio of carbon and oxygen on the surface [C / O]. A lamp molded product for a hard disk having (atomic%) of 1.01 to 2.50. A lamp molded product for a hard disk, which is a molded product of the polyoxymethylene resin composition according to any one of claims 1 to 10 .
The surface of the hard disk lamp molded body has a peak intensity ratio (CO / C = O) of 10 to 200 between the CO expansion and contraction vibration peak obtained by infrared spectroscopy and the C = O expansion and contraction vibration peak. , Lamp molded body for hard disk.