JPH10166382A - Polyacetal resin molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart excellent dimensional accuracy or weatherabllity and to prevent the generation of a sink or warpage by providing a skin layer with a thickness of a specific value or less to the surface layer part of an outer surface but providing no skin layer to the surface layer part of an inner surface. SOLUTION: A skin layer is a layer constituted of spherulitic material quality noncrystalline and/or low in a degree of crystallization provided in the surface layer part being in contact with a cavity and set to 150μm or less in its thickness. Hollow injection molding is executed by using a polyacetal resin to produce a gear part 10, a roller part 11 and a gear integrated type roller 9 consisting of shaft parts 12a, 12b. The cylinder temp. of a molding machine is set to 190 deg.C and the temp. of a mold is set arbitrarily. The gas injected in order to form a hollow part to a product is set to nitrogen gas and the pressure thereof is set to 120kg/cm<2> . An injection part injecting nitrogen gas into a resin is provided to the runner part of the mold.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a crystalline resin molded article. More specifically, the present invention relates to a polyacetal resin molded product having excellent dimensional accuracy, weather resistance, chemical resistance, and heat aging characteristics, and having less occurrence of sink marks and warpage.

[0002]

2. Description of the Related Art Polyacetal resin molded products are used in automobiles,
It is used for a wide range of applications in various fields such as general machinery, precision machinery, electricity, electronics, and general industrial parts. And
The demand is on the rise because it can be mass-produced, has good moldability, is lightweight and does not rust.
Among them, polyacetal resin is often used mainly for mechanical parts. In recent years, with the expansion of its use, the required accuracy has become higher.

[0003] Many polyacetal resin molded articles are manufactured by an injection molding method. Polyacetal resin molded products manufactured by the injection molding method often have an increased degree of deformation such as warpage, sink mark, and deflection due to the progress of resin shrinkage after molding, and it is difficult to ensure dimensional accuracy. Was.

[0004]

SUMMARY OF THE INVENTION The present invention provides dimensional accuracy,
An object of the present invention is to provide a molded product of a polyacetal resin which is excellent in weather resistance, chemical resistance, and heat aging characteristics, and has less occurrence of sink marks and warpage.

[0005]

That is, the present invention is as follows. A molded article of a polyacetal resin having a hollow portion therein, the outer surface of the molded article having a skin layer having a maximum thickness of 150 μm or less, and the outer surface of the molded article having a skin layer. A polyacetal resin molded product characterized by having no layer.

Hereinafter, the present invention will be described in detail. The polyacetal resin molded article having a hollow portion therein according to the present invention has less deformation of the product due to heat aging after molding as compared with a normal injection molded article, and has a good weight retention rate in chemical resistance. It has the characteristic that it is a molded product. Although the polyacetal resin molded product according to the present invention has a hollow portion inside, the hollow portion is not formed by a cavity (void) or a foaming agent, but is formed by a hollow injection molding method. It is. Further, the hollow portion may not be a closed system, but since the gas trapped inside the molded product expands and the molded product may be broken from the inside, at least one communication port with the outside air is provided. It is preferred to have.

[0007] The polyacetal resin molded product obtained by the present invention has a hollow portion, and a preferable hollow ratio is 2 to 80.
%, And more preferably 2 to 50%. A hollow molded article having a hollow ratio of more than 80% is not preferable because the thickness of the product becomes extremely thin and the strength of the product is reduced. Further, when the hollow ratio is 80% or more, the amount of the resin filled in the cavity is small, so that the pressurized fluid injected to form the hollow portion in the product easily flows out of the product from the thin portion. This is not preferable because it is difficult to obtain a hollow molded product having a desired shape.

A hollow molded article having a hollow ratio of less than 2% is not preferable because the effect of the pressurized fluid is reduced and it is difficult to sufficiently improve the dimensional accuracy, which is the object of the present invention. The hollow ratio is defined by the following equation. Hollow ratio (%) = {(V × ρ−M) / (V × ρ)} × 10
In the above equation, V is the volume when the hollow portion is filled with the same resin, ρ is the specific gravity of the resin used, and M is the mass of the hollow molded product.

FIG. 1 shows an example of the "polyacetal resin molded article having a hollow portion" in the present invention, and FIG.
Shown in In the present invention, the “outer surface of the molded product” refers to a surface of the resin in a molten state, which has been injected into the mold cavity during the molding process, is in contact with the cavity surface of the mold.
In the present invention, the “inner surface of the molded product” refers to a boundary surface between the hollow portion and the resin portion of the molded product.

Usually, after the molding process is completed, a part to be a product and a runner part and a sprue part which are unnecessary as a product are cut off at the gate part. Is not included in “outer surface” and “inner surface”. In the present invention, "skin layer"
In a molded article of a crystalline resin, it refers to a layer formed of amorphous and / or spherulites having a low degree of crystallinity, which is found in a surface layer portion in contact with a cavity. FIG. 3A is a crystal photograph of a portion A in the figure of the cross section of the molded product shown in FIG.
FIG. 3B shows a crystal photograph of a portion B in the figure. In the present invention, the skin layer has a thickness of 150 μm or less. Exceeding this will cause a decrease in dimensional accuracy after heat aging, sink marks, and warpage.

In the present invention, the term "molded article" refers to a minimum unit product formed of a resin. Specifically, mechanical parts for electric and electronic equipment, automotive interior and exterior parts, industrial parts,
Sanitary goods and the like. The mechanical parts in the electrical and electronic fields include computers, printers, copiers, fax machines, and other OA equipment, as well as VTRs, televisions, audio equipment, washing machines, dryers, vacuum cleaners, refrigerators, telephones, and electronic devices. Refers to mechanical components used in home appliances such as microwave ovens, dish dryers, and futon dryers. In general, a mechanical component refers to a component that performs its function by performing a rotary motion or a linear motion, and peripheral components thereof. Specifically, various gears (including pinion, helical, rack, etc.), pulleys, cams, rollers, sliders, clutches,
Drums, reels, trays and related parts, as well as hinges, rollers, arms, shafts and bearings. These can have multiple functions. For example, a multi-stage gear, a cam-integrated gear, a gear-integrated roller, a side plate, a guide roller, and the like found in a loading mechanism of a tape cartridge of a VTR device.

The interior / exterior parts of an automobile include door handles, shift knobs, assist grips, select levers, knobs, buckles, glass window elevating mechanism parts, through anchors, seats and reclining mechanism parts thereof, which are mounted inside and outside the car. . Industrial parts include tanks, tubes, stoppers, caps, pedals, joints,
Shower handle, chain, screw, connector, handle, switch, fastener, key, sash, crescent key, handle, door wheel, pen point, medical equipment, etc.

[0013] Sanitary goods include water around bathrooms, washrooms, toilets, kitchens, washing machines, corridors, stairs, entrances,
It refers to a resin molded product such as a veranda that is installed inside or outside the house or used inside and outside the house and requires hygiene. Specifically, shower head, shower handle,
Faucets, handrails, towel rails, hooks, doors, pipes, etc. and their peripheral parts.

Among them, particularly, in the case of a pipe-shaped molded article requiring chemical resistance, since there is no skin layer on the surface layer on the inner surface of the pipe, the chemical resistance is improved, which is preferable. In the present invention, the polyacetal resin is a polyacetal resin containing a polyacetal resin as a main component, and refers to a polyacetal resin alone or a mixture of a polyacetal resin containing 50% by weight or more of polyacetal and another resin.

The polyacetal resin of the present invention includes:
Commonly used additives, such as antioxidants, flame retardants,
One or more release agents, lubricants, heat stabilizers, weather resistance stabilizers, rust inhibitors, fillers, coloring agents, and the like can be added as necessary. A molded article having a hollow portion made of a polyacetal resin having a melting point of 150 to 161 ° C. is preferable because it has excellent surface appearance and mold transferability.

Examples of a method for obtaining a polyacetal resin having a melting point of 150 to 161 ° C. include a method of increasing the ratio of oxyalkylene units in the copolymer molecular chain and a method of increasing the number of different components of the block copolymer. Among them, a method of increasing the ratio of 1,3-dioxolane-derived oxyethylene units in the copolymer molecular chain is most effective.

The melting point in the present invention is a value measured using a differential scanning calorimeter (DSC7 manufactured by PerkinElmer). The polyacetal resin is cut into 5 mg from a film formed by a press machine heated to 200 ° C. and used for measurement. Measurement conditions are from 30 ° C to 200
To 320 ° C. at a rate of 320 ° C./min.
The temperature was lowered to 10 ° C./10 minutes to 100 ° C., and further increased from 130 ° C. at 2.5 ° C./minute. When the temperature rises last, an endothermic peak accompanying crystallization is observed, and the peak top temperature at this time is defined as the melting point.

The polyacetal resin of the present invention may optionally contain an inorganic and / or organic filler for the purpose of improving heat resistance and mechanical strength. Suitable fillers include glass fiber, carbon fiber, metal fiber, aramid fiber, potassium titanate, asbestos, silicon carbide, ceramic, silicon nitride, barium sulfate, calcium sulfate, kaolin, clay, pyrophyllite, bentonite, cellite Site, zeolite, mica, mica, nepheline sinite, talc, atalpargite, wollastonite, slag fiber, ferrite, silicon, calcium, calcium carbonate, magnesium carbonate, dolomite, zinc oxide, gypsum, glass beads,
Glass powder, glass balloon, quartz, quartz glass,
Filling reinforcements such as alumina can be mentioned, and these may be hollow. In addition, two or more of these reinforcing fillers can be used in combination. Further, if necessary, it can be used after being pre-treated with a coupling agent such as a silane-based or titanium-based coupling agent.

Further, by selecting one or more of carbon fiber, metal fiber, and graphite as the filler, the electric resistance of the crystalline resin can be reduced. Adhesion can be prevented, which is preferable. Other resins that can be used as a mixture with the polyacetal resin are not particularly limited as long as they are compatible with the polyacetal resin. For example, polyethylene, polypropylene, polystyrene, ABS resin,
Polyvinyl chloride, polyamide, polycarbonate, modified polyphenylene ether, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polyimide, polyamideimide, polyetherimide, polyarylate, polysulfone, polyethersulfone, polyetheretherketone, liquid crystal polymer, poly Examples thereof include tetrafluoroethylene, thermoplastic elastomer, polytetrafluoroethylene, and polyvinyl alcohol.

When a mixed composition of a polyacetal resin and another resin is used, the content of the polyacetal resin is 50%.
% By weight or more, preferably 70% by weight.
That is all. If the content of the polyacetal resin is less than 50% by weight, it becomes difficult to obtain the characteristics of the polyacetal resin as an engineering resin, which is not preferable.

In the present invention, "hollow injection molding method" means
This is an injection molding method in which a hollow molded article is obtained by injecting a pressurized fluid into the resin during injection of the crystalline resin into the mold cavity or after injection is completed. As the pressurized fluid used in the “hollow injection molding method” according to the present invention, a gaseous or liquid one at normal temperature is used. Those which do not react or are incompatible are preferred. Further, it is preferable that the resin does not decompose or burn under the temperature and pressure of injection molding. For example, nitrogen, carbon dioxide, air, helium, glycerin, liquid paraffin and the like can be mentioned.

Usually, a pressurized gas is used, and it is particularly preferable to use an inert gas such as nitrogen, helium, neon, or argon. Considering economics, nitrogen gas is industrially preferable. Hereinafter, a general example of a hollow injection molding method using a pressurized gas will be further described. Hollow injection molding using a pressurized gas is performed by a combination of a usual injection molding machine and a gas injection device. The gas injection device is a device that injects a gas into the resin through a pipe after starting the injection of the resin and holds the gas for a set time. For this, the gas to be injected is compressed to a high pressure in advance, stored in an accumulator, and a high-pressure gas is introduced through a pipe at the time of gas injection, or a method in which a certain amount of gas is measured and continuously fed by a pump to pressurize, etc. However, any method is possible as long as a gas can be fed into the resin during and after the injection. At this time, the gas inlet may be provided in the nozzle of the cylinder, the sprue, the runner, or the cavity of the mold. Any method can be used as long as a high-pressure gas can be injected into the resin.

The following method is generally used as a usual hollow injection molding method, and is suitably used in the present invention. A hollow injection molding method in which a molten resin is injected so that no unfilled portion remains in a mold cavity, and then a pressurized fluid for forming a hollow portion in a molded product is injected into the resin. During or after injecting the molten resin in the mold cavity with an amount of the unfilled portion remaining into the cavity, a pressurized fluid for forming a hollow portion in the molded product is injected into the resin, and the pressurization is performed. A hollow injection molding method in which a resin is extruded by a fluid to reach an unfilled portion of a mold cavity while forming a hollow portion.

The above method is called "full shot method". Since the hollow portion is obtained with the pressurized fluid in an amount that compensates for the molding shrinkage of the molten resin, the hollow ratio becomes substantially equal to the molding shrinkage of the molten resin, and the effect of the pressurized fluid is small. Therefore, a method of providing an auxiliary cavity (also referred to as an auxiliary chamber or a discard cavity) in a mold has been devised for the purpose of improving the effect of the pressurized fluid. This auxiliary cavity is a cavity for allowing a part of the resin in the cavity to escape when the pressurized fluid is injected, and is disclosed in Japanese Patent Application Laid-Open No. 3-121820. By adjusting the volume of the auxiliary cavity, the hollow ratio of the product can be adjusted.

The auxiliary cavities and the communication passages between the cavities and the auxiliary cavities are often cut off from the parts to be products after molding. The cut surface on the side to be the product is not included in the “outer surface” and the “inner surface” in the present invention. The above method is called "short shot method". Adjustment of the hollow ratio in the short shot method is possible by adjusting the injection amount of the resin.

In the hollow injection molding according to the present invention, the pressure of the gas to be pressurized is preferably ²⁰ to 300 kg / cm ² , more preferably 50 to 200 kg / cm ² . In order to effectively form a hollow portion inside a molded article, a gas pressure of 20 kg / cm ² or more is required. In the hollow injection molding according to the present invention, a hollow portion is obtained by injecting a pressurized fluid into the resin during or after injection of the resin, and this pressurized gas is injected during injection of the molten resin by the injection operation of the molding machine. It is necessary to start the injection into the resin within 10 seconds after the completion of the injection, preferably within 5 seconds after the completion of the injection. This is because when 10 seconds or more elapse after the completion of injection of the molten resin, the resin in the cavity is gradually cooled, solidification proceeds from the surface in contact with the mold cavity surface, and a hollow portion is formed in the molded product. This is because it becomes difficult.

In the hollow injection molding of the present invention, a hollow portion is obtained by injecting a pressurized fluid into the resin during or after the injection of the resin. However, the hollow portion is kept in the hollow portion until the resin in the cavity is cooled. It is necessary to maintain the pressure of the injected gas for a certain time. The holding time of the pressurized gas necessary for effectively forming the hollow portion is 0 to 90 seconds, and more preferably 10 to 60 seconds.

Further, by adjusting the pressure of the pressurized gas to be injected and the pressure holding time of the pressurized fluid, the size of the molded product can be easily adjusted.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to examples. When carrying out each example and comparative example, a polyacetal resin (Tenac 4010, 7010, Tenac-C 4520, 7 manufactured by Asahi Kasei Corporation)
520), hollow injection molding and injection molding were performed.

[0030]

Examples 1 to 3 In Examples 1 to 3, polyacetal resin, Tenac-C 752 manufactured by Asahi Kasei Kogyo Co., Ltd.
0, hollow injection molding is performed, and as shown in FIG. 4, the gear unit 10, the roller unit 11, and the shaft units 12a and 12b.
Was obtained by hollow injection molding.

The cylinder temperature of the molding machine was set at 190 ° C. and the mold temperature was set arbitrarily. The gas injected to form a hollow portion in the product is nitrogen gas, and the pressure of the nitrogen gas is 120.
kg / cm ² . The injection portion for injecting nitrogen gas into the resin was provided in the runner portion of the mold. FIG. 5 shows a cross-sectional view of the obtained molded product.

The obtained molded article was observed for its crystal state, and the thickness of the skin layer was measured. The dimensional accuracy of the molded product was obtained by measuring the sink amount at point A and the gear meshing error in the gear portion 10 shown in FIG. The measurement was performed by placing the molded article in an atmosphere at 23 ° C. and a humidity of 50% for 24 hours.
This was carried out after storage for a time and conditioning.

In order to compare the aging characteristics,
After measurement 24 hours after molding, heat aging was performed in an oven at 80 ° C. The aging time was 24 hours, 48 hours, and 72 hours. After the molded article was taken out of the oven, the state was adjusted for 24 hours in an atmosphere at 23 ° C. and a humidity of 50%, and then measured. For measuring the sink mark amount at point A, a surface roughness profile measuring machine Surfcom 575A manufactured by Tokyo Seimitsu Co., Ltd. was used. The measurement distance was 30 mm, which is the same value as the pitch circle diameter of the gear portion 10, and the measurement was performed in the diameter direction. Table 1 shows the measurement results.

The measurement of the meshing error of the gears was performed using a JGM using a double-tooth flank meshing tester manufactured by Osaka Seimitsu Kikai Co., Ltd.
A standard 116-02 (1983) was performed. Table 2 shows the measurement results.

[0035]

Comparative Examples 1-2 The gear-integrated roller 9 shown in FIG. 4 was obtained by hollow injection molding and injection molding in the same manner as in Examples 1-3. The evaluation of the obtained molded articles was performed in Examples 1 to 3.
The same was done. Table 1 shows the measurement results of the sink mark amount, and Table 2 shows the measurement results of the engagement error between the both tooth surfaces.

[0036]

Examples 4 to 7 In Examples 4 to 7, polyacetal resin, Tenac 4010 manufactured by Asahi Kasei Corporation,
Hollow injection molding was performed using Tenac-C 4520, and the roller portion 11 and the shaft portion 12 as shown in FIG.
A shaft-integrated roller composed of a and 12b was obtained by hollow injection molding.

The cylinder temperature of the molding machine was set at 200 ° C. during molding of the polyacetal resin, and the mold temperature was arbitrarily set. The gas injected to form the hollow portion in the product was nitrogen gas, and the pressure of the nitrogen gas was 150 kg / cm ² .
The injection part for injecting nitrogen gas into the resin was provided at the nozzle of the molding machine. FIG. 7 shows a cross-sectional view of the obtained molded product.

The crystal state of the obtained molded article was observed, and the thickness of the skin layer was measured. The evaluation of the obtained molded product is shown in FIG.
The results were obtained by measuring the amount of deflection in the roller portion 11 shown in FIG. In FIG. 6, the points A and C were fixed, and the amount of deflection at the point B was measured. The measurement of the deflection is
After molding the molded product in a constant temperature and humidity room at 23 ° C and 50% humidity, 2
It was stored for 4 hours, and the condition was adjusted, and then the test was performed. Also,
In order to compare the aging characteristics, after measuring the amount of deflection 24 hours after molding, heat aging was performed in an oven at 80 ° C. The aging time is 24 hours, 48 hours, and 72 hours, and is 2 hours in a constant temperature and humidity room at 23 ° C. and 50% humidity.
After conditioning for 4 hours, the deflection was measured again.

Table 3 shows the measurement results. When measuring the amount of deflection, use the roundness measuring instrument RA-Mitutoyo Co., Ltd.
424. Those having a deflection value of about 300 μm or more exceeded the measurement range of the measuring instrument and could not be measured. For this reason, remeasurement was performed using a dial gauge.

[0040]

Comparative Examples 3 to 4 In the same manner as in Examples 4 to 7, the shaft-integrated roller 13 shown in FIG. 6 was obtained by injection molding. The evaluation of the obtained molded article was performed in the same manner as in Examples 4 to 7 by confirming the crystal state, measuring the amount of deflection, and evaluating the aging characteristics. Table 3 shows the measurement results.

[0041]

Examples 8 and 9 In Examples 8 and 9, polyacetal resin, Tenac-C 401 manufactured by Asahi Kasei Kogyo Co., Ltd.
Hollow injection molding was performed using 0, 4520, and a flat plate 14 having a length of 60 mm, a width of 60 mm, and a thickness of 5 mm as shown in FIG. 8 was obtained by the hollow injection molding.

The cylinder temperature of the molding machine was set at 190 ° C., and the mold temperature was set arbitrarily. The gas injected to form a hollow portion in the product is nitrogen gas, and the pressure of the nitrogen gas is 120.
kg / cm ² . Further, a gas injection part for injecting nitrogen gas into the resin was provided at a nozzle part of the molding machine. FIG. 9 shows a cross-sectional view of the obtained flat plate 14.

The obtained molded article was evaluated by a test for evaluating the weather resistance of the molded article. Specifically, the molded article was subjected to a weather resistance acceleration test using Sunshine Super Long Life Weather Meter manufactured by Suga Test Instruments Co., Ltd.
The accelerated test is performed by irradiating a molded article with ultraviolet rays in an environment of 63 ° C. In addition, the irradiation time of 20
%, And water is sprayed on the molded article at a time corresponding to the percentage.

The molded product was placed in a sunshine super long life weather meter, and the surface of the sample irradiated with ultraviolet rays was observed every 50 hours. The observation results are shown in Table 4.

[0045]

Comparative Examples 5 and 6 In the same manner as in Examples 8 and 9, a flat plate 14 shown in FIG. 8 was obtained by ordinary injection molding. The evaluation method of the obtained molded article is the same as in Examples 8 and 9. The observation results are shown in Table 4.

[0046]

Examples 10 to 11 In Examples 10 to 11, polyacetal resin, Tenac-C manufactured by Asahi Kasei Corporation
Using 4520 and 7520, hollow injection molding was performed to obtain a tube-shaped molded product as shown in FIG. The molded product was observed in a crystalline state. The thickness of the skin layer on the outer surface was measured, and the presence or absence of the skin layer on the inner surface was confirmed.

In the chemical resistance test, a test piece whose weight was measured was put into a solution, taken out at appropriate times, and the weight retention was calculated from the result of weight measurement of each test piece, and evaluated. Example 8-
In No. 9, a chemical resistance test was performed. The solution used was a sodium hypochlorite solution. 100cc per molded product
% Of the solution. The solution was changed once a week.
The molded articles were arbitrarily taken out, and the weight retention was calculated from the weight measurement results of each molded article. Table 5 shows the results.

[0048]

Comparative Examples 7 to 8 In the same manner as in Examples 10 to 11, a tube-shaped molded article having the same shape as in Examples 10 to 11 was obtained by ordinary injection molding. The crystalline state of the molded article was observed, and the thickness of the skin layer on the outer surface and the inner surface was measured. Example 10
A chemical resistance test was performed under the same conditions as in Nos. 1 to 11. Table 5 shows the calculated weight retention.

[0049]

[Table 1]

[0050]

[Table 2]

[0051]

[Table 3]

[0052]

[Table 4]

[0053]

[Table 5]

[0054]

The crystalline resin molded article according to the present invention is a crystalline resin molded article having improved dimensional accuracy and excellent dimensional stability after heat aging, excellent weather resistance and chemical resistance. . For this reason, a crystalline resin molded product that can integrate products composed of a plurality of parts, improve the overall dimensional accuracy of a molded product having a complicated shape, and improve weather resistance and chemical resistance And industrially,
It can be said that this is a very useful crystalline resin molded product.

[Brief description of the drawings]

FIG. 1 shows an example of an external view of a molded article of the present invention.

FIG. 2 is a sectional view of the molded article shown in FIG.

FIG. 3 shows an example of a crystal photograph of the molded article of the present invention.

FIG. 4 is an external view of a molded product obtained in Examples 1 to 3 and Examples 1 and 2.

FIG. 5 is a sectional view of the hollow molded article obtained in Examples 1 to 3.

FIG. 6 is an external view of the hollow molded products obtained in Examples 4 to 7 and Comparative Examples 3 and 4.

FIG. 7 is a cross-sectional view of the hollow molded product obtained in Examples 4 to 7.

FIG. 8 is an external view of molded articles obtained in Examples 8 to 9 and Comparative Examples 5 to 6.

FIG. 9 is a sectional view of a molded product obtained in Examples 8 and 9.

FIG. 10 is an external view of a molded product obtained in Examples 10 to 11 and Comparative Examples 7 and 8.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Molded product 2 Hollow part 3 Outer surface 4 Inner surface 5 Gate 6 Communication port 7 Skin layer 8 Crystal layer 9 Gear integrated roller 10 Gear part 11 Roller part 12a Shaft part a 12b Shaft part b 13 Shaft integrated roller 14 Flat plate

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI B29L 22:00

Claims (2)

[Claims] 1. A molded article of a polyacetal resin having a hollow portion therein, wherein a surface layer on the outer surface of the molded article has a skin layer having a maximum thickness of 150 μm or less. A polyacetal resin molded product having no skin layer on the surface layer. 2. The polyacetal resin molded article according to claim 1, which is produced by a hollow injection molding method.