JPH0952926A - Polyoxymethylene resin material for cutting and processed products - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To provide a material for cutting, such as an extruded rod-shaped article made of polyoxymethylene resin, which has no white spots in the central portion of the cross section and has a uniform appearance in the peripheral portion and the central portion in the cross section, and a high-quality poly. Provide processed products of oxymethylene resin. SOLUTION: The polyoxymethylene resin material for cutting has an isothermal crystallization rate of 200 seconds or more, and a difference in size of spherulites between the peripheral portion and the central portion as viewed from the cross section of the resin material is 10 microns or less, or the same. The difference in latent heat of crystal fusion between the peripheral portion and the central portion is 10 Joules / g or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cutting material such as a polyoxymethylene resin extruded rod which is used as a machine part by cutting with a lathe or a milling machine, and a processed product thereof. .

[0002]

2. Description of the Related Art Conventionally, rod-shaped materials, plate-shaped materials, etc. of resins such as polyamide, polyethylene, polypropylene, ABS, polyoxymethylene and polybutylene terephthalate have been produced as extruded plastic materials for cutting. Above all, a great number of polyoxymethylene resin materials are produced due to their excellent fatigue resistance, moisture absorption, weather resistance, balanced strength, and machinability. Used in parts and others.

However, for example, the central portion of a rod-shaped article such as a round rod made of polyoxymethylene resin is whiter than other portions (peripheral portions) (hereinafter referred to as white spots), and this is in terms of strength. Although there is no problem, the product value is reduced in appearance.

The cause of such white spots is considered as follows. That is, when the polyoxymethylene resin is cooled and solidified from a molten state, abrupt volume contraction occurs due to crystallization. At this time, in the case of extrusion molding of a round bar, it is cooled and solidified from the outer peripheral portion, and finally the central portion is solidified,
A void is generated in the center due to the volume contraction. In order to prevent the generation of the voids, it is conceivable to replenish the central portion with the resin while continuously applying pressure.
Many small holes of about 0.05 mm are generated, which causes diffuse reflection of light and looks white unlike the surrounding area.

The existence of such a small hole can be confirmed by immersing the sample in a dye solution and washing it with water so that the dye penetrates into the small hole, and can be observed by magnifying 50 times or more with an optical microscope. . Such a small hole can be solved by strictly controlling and optimizing the extrusion conditions.

However, even if the presence of fine holes cannot be confirmed by observing with such a dye soaking test or a microscope,
After all, in the center of the bar of polyoxymethylene resin,
White spots that are different from those in the peripheral area have occurred, and the cause has not been clarified until now.

On the other hand, as an extrusion molding grade of a polyoxymethylene resin, a melt index M is generally used.
Although those having an I value of about 2.5 are commercially available, polyoxymethylene resins have a very high crystallization rate when cooled and solidified, and thus are easily affected by crystallization characteristics due to disturbances such as molding conditions. Therefore, it is easy to obtain uniform crystals by decreasing the crystallization rate. However, increasing the crystallization rate can be easily carried out by adding a nucleating agent, but on the contrary, decreasing the crystallization rate requires addition of a large amount of an amorphous crystallization material, and polyoxymethylene. It may sacrifice the original properties of the resin.

[0008]

SUMMARY OF THE INVENTION Accordingly, the present inventors
As a result of diligent research, we succeeded in producing a bar-shaped product in which the crystallization rate was slowed down by increasing the molecular weight to form a polyoxymethylene resin, and there was no difference between the central part and the peripheral part and the white spot phenomenon was not observed. .

That is, an object of the present invention is to solve the above-mentioned problems, extruded rod-shaped article made of polyoxymethylene resin having no white spots in the central portion of the cross section and having a uniform appearance in the peripheral portion and the central portion in the cross section. To provide cutting materials and high-quality polyoxymethylene resin processed products.

[0010]

The present invention is intended to achieve the above object, and the polyoxymethylene resin material for cutting according to the present invention has an isothermal crystallization rate at 150 ° C of 200 seconds or more, It is preferably characterized by comprising a polyoxymethylene resin for 220 seconds or more.

In the polyoxymethylene resin material for cutting according to the present invention, the difference in size of spherulites between the peripheral portion and the central portion as viewed from the cross section of the resin material is 10 μm or less,
More preferably, it is characterized by being 5 microns or less.

Further, the polyoxymethylene resin material for cutting according to the present invention is characterized in that the difference in latent heat of crystal fusion between the peripheral portion and the central portion as viewed from the cross section of the resin material is 10 Joule / g or less. Is.

A preferred embodiment of the present invention further includes the following contents. (1) A resin material for cutting, which is made of polyoxymethylene resin, has an isothermal crystallization rate of 200 seconds or more at 150 ° C., and has a spherulite content in the peripheral portion and the central portion as viewed from its cross section. A polyoxymethylene resin material for cutting, which has a size difference of 5 microns or less.

(2) A resin material for cutting, which is made of polyoxymethylene resin and has a temperature of 150 ° C.
In the polyoxymethylene resin material for cutting, the isothermal crystallization rate in (1) is 200 seconds or more, and the difference in latent heat of crystal fusion between the peripheral portion and the central portion as viewed from the cross section is 10 Joule / g or less.

(3) A resin material for cutting, which is made of polyoxymethylene resin, and the difference in size of spherulites between the peripheral portion and the central portion as viewed from the cross section of the resin material is 5 μm or less, and A polyoxymethylene resin material for cutting, characterized in that the difference in latent heat of crystal fusion between the peripheral portion and the central portion is 10 Joule / g or less.

(4) A resin material for cutting, which is made of polyoxymethylene resin and has a temperature of 150 ° C.
Is 200 seconds or more, the difference in size of spherulites between the peripheral portion and the central portion as viewed from its cross section is 5 microns or less, and the difference in latent heat of crystal fusion between the peripheral portion and the central portion is A polyoxymethylene resin material for cutting, which is 10 joules / g or less.

(5) A polyoxymethylene resin material for cutting, wherein the resin material is a rod-shaped material such as a round bar.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described specifically. The polyoxymethylene resin used in the present invention may be a homopolymer or a copolymer, and may be a composition containing them. Copolymers are preferably used, and as comonomers, ethylene oxide, propylene oxide, diethylene glycol formal,
1,3-dioxolane, 1,4-butanediol formal, trioxeban and the like can be mentioned. These comonomers are preferably incorporated in the polymer at 0.5 to 6.0% by weight.

Further, in the present invention, it can be used as a composition, and in this case, an antioxidant, a heat stabilizer and the like are also added.

According to the studies by the present inventors, one cause of the white spots of the polyoxymethylene resin rod-like material is considered as follows. In other words, the central part of the rod-shaped material is cooled very slowly and the degree of crystallinity becomes high.Because it crystallizes under pressure, the spherulites are smaller than those in the peripheral parts, and not only ordinary spherulites but also trans-crystals. It has been confirmed with a microscope that the crystal morphology occurs. This can also be confirmed from the fact that the latent heat of crystal dissolution in the white spot is larger than that in the peripheral portion when the latent heat of crystal dissolution is measured by a differential scanning calorimeter. Therefore, it is considered that the light has a different refractive index and appears white as a white spot. The vitiligo part due to such a cause has a high crystallinity and thus has a higher density than the peripheral part,
Although there is no strength problem, it gives an impression that there is a defect in appearance, which is also not preferable. The present invention has been accomplished in view of this point.

The polyoxymethylene resin used in the practice of this invention has a melt flow index (MI).
Value (190 ° C, load 2,160g) is 1.5-2.0g
/ 10 min is preferable, and more preferably,
It is 1.7 to 1.9 g / 10 min.

If the MI value is less than 1.5, the viscosity is too high, the pressure loss is large, and small holes are liable to be formed at the beginning of the occurrence of white spots. If the MI value exceeds 2.0, the crystallization rate is increased. Becomes faster and white spots tend to occur, which is not preferable.

The polyoxymethylene resin of the present invention has an isothermal crystallization rate of 20 at 150 ° C. according to the measuring method described later.
One feature is that it is 0 seconds or more. It is more preferably 220 seconds or more, for example, 220 to 270 seconds. If the isothermal crystallization rate at 150 ° C. is shorter than 200 seconds, the crystallization rate will be too fast and the crystallization characteristics will be affected by disturbances such as changes in molding conditions, and white spots will appear at the center of the resin material.

The resin material for cutting, which is made of the polyoxymethylene resin of the present invention, has a difference in the size of spherulites (according to the measuring method described later) between the peripheral portion and the central portion as viewed from the cross section of 10 μm or less. , And more preferably 5 microns or less.

The size of the spherulites varies in a considerable range depending on molding conditions such as resin temperature, cooling temperature, molding rate, pressure, and presence / absence of nucleating agent. In the present invention, it is several tens of microns, for example, about 30 to about 60 microns. If there is too much difference in the size of the spherulites between the central part and the peripheral part, there will be a difference in the refractive index of light, and so white spots will also appear in the central part of the resin material.

Further, in the resin material for cutting processing comprising the polyoxymethylene resin of the present invention, the difference in latent heat of crystal fusion (according to the measuring method described later) between the peripheral portion and the central portion as viewed from the cross section is 10 Joule / g. It is the following. The higher the crystallinity, the larger the latent heat becomes. Therefore, the difference in latent heat between the peripheral portion and the central portion means that the both are not in a uniform crystal state, which is one of the causes of the generation of spots.

The resin material for cutting processing comprising the polyoxymethylene resin of the present invention can be produced by extruding such a polyoxymethylene resin.

Generally, in extrusion molding, the resin is extruded in a molten state from a die and then cooled while maintaining its shape by a roll or a sizing die, which is a little away from the die, so that there is little drawdown when pulled out from the die. It is desirable to use a high viscosity type resin. However, in the case of a thick product, voids are generated inside or shrinkage is generated on the surface due to volume contraction when cooled and solidified.

A typical example of the resin material for cutting according to the present invention is
This is a round bar having an outer diameter of 10 mm or more, and such a thick round bar cannot be molded because voids are generated in a general melt extrusion and it becomes a very large ellipse. Therefore,
A solidification extrusion method is adopted in which such a rod-shaped material is continuously extruded while being cooled and solidified in a die attached to an extruder. Also, in solidification extrusion, the resin is not pulled out from the die in a molten state, so there is no worry of drawdown,
Molding is possible regardless of viscosity.

Therefore, thick-walled molded products such as round bars can be molded by the solidification extrusion method even in the generally commercially available injection molding and extrusion molding grades having an MI value of 2.1 to 12.0. However, when the MI value is 2.1 or more, the crystallization rate is too fast, and white spots occur in the central part.

The resin material for cutting according to the present invention has a diameter of 1
A round bar of 0 mm or more, a plate material of 5 t or more, and a deformed section with a wall thickness of 10 mm or more are included, which are mechanically processed by ordinary means such as cutting with a lathe or a milling machine, mechanical parts,
Processed into automobile parts, etc. Specific main processed products include screws, bearings, nozzle parts, sensor parts, gears, rollers, axles, pallets and the like.

The isothermal crystallization rate, the size of spherulites and the latent heat of fusion of crystallization in the present invention are determined according to the following measuring methods, respectively.

Isothermal crystallization rate: Differential scanning calorimeter (Diff
erense Scanning Caloriemeter), the sample was once heated to 210 ° C and held for 5 minutes, then the temperature was lowered to 150 ° C at 80 ° C / min, and the maximum exothermic peak of the crystal when starting to hold at 150 ° C Measure time.

Size of spherulites: A sample is sliced into thin pieces and observed with a polarizing microscope at a magnification of 300 times or more.

Latent heat of fusion of crystal: Using a differential scanning calorimeter, the latent heat of fusion of crystal is measured according to JIS K7122.

[0036]

The present invention will be described below with reference to examples. (Example 1) A polyoxymethylene copolymer having an isothermal crystallization rate of 222 seconds and a melt index (MI) value of 1.9 g / 10 min was used to mold a round bar having an outer diameter of 160 mm under the following conditions. Extruder used Screw diameter: 50 mm Cylinder temperature 185 to 195 ° C. Die temperature 190 to 200 ° C. Molding pressure 80 to 100 Kg / cm ² Die cooling temperature 20 to 30 ° C. There is no white spots in the center, and the difference in appearance and the peripheral part. Did not occur.

(Example 2) The isothermal crystallization rate was 260.8.
A round bar having an outer diameter of 90 mm was molded under the following conditions using a polyoxymethylene copolymer having an MI value of 1.7 g / 10 min. Extruder used Screw diameter: 40 mm Cylinder temperature 185 to 195 ° C. Die temperature 190 to 200 ° C. Molding pressure 80 to 100 Kg / cm ² Die cooling temperature 20 to 30 ° C. There is no white spots in the center, and there is no difference in appearance and peripheral parts. Did not occur.

Comparative Example 1 The isothermal crystallization rate was 142.7.
A round bar having an outer diameter of 160 mm was molded under the following conditions using a polyoxymethylene copolymer having an MI value of 2.7 g / 10 min. Extruder used Screw diameter: 50 mm Cylinder temperature 175 to 185 ° C. Die temperature 180 to 190 ° C. Molding pressure 80 to 100 Kg / cm ² Die cooling temperature 20 to 30 ° C. A white spot with an outer diameter of 11 mm was generated at the center.

(Comparative Example 2) Molding pressure of 50 to 80 kg /
except that the cm ² had an outer diameter of 160 under the same conditions as Comparative Example 1
mm round bar was formed. A white spot having an outer diameter of 6 mm was generated in the center, dyeing was found in the dye-dyeing test, and a small void was generated in the center.

(Comparative Example 3) The isothermal crystallization rate was 174.5.
A round bar having an outer diameter of 90 mm was molded under the following conditions using a polyoxymethylene copolymer having an MI value of 2.4 g / 10 min. Extruder used Screw diameter: 40 mm Cylinder temperature 175 to 185 ° C. Die temperature 180 to 190 ° C. Molding pressure 80 to 100 Kg / cm ² Die cooling temperature 20 to 30 ° C. White spots having an outer diameter of 8 mm were generated at the center.

The above results are summarized in Table 1. The polyoxymethylene copolymers used above are of the same composition but different in molecular weight.

[0042]

[Table 1]

In Table 1, (Note 1), the numerical value after the presence of white spots indicates the size of white spots. (Note 2) The center part is sampled from within 5 mm of the center of the round bar. (Note 3) The peripheral part is sampled from the 1/2 radius part of the round bar. (Note 4) Appearance is uniform except for the central white spot. (Note 5) The dye soak test is to inspect whether a small hole (0.5 mm or less) appears in the center and whether it looks white. Methyl alcohol 100 cc dye (MIKE
TON FAST YELLOW) 0.5g soaked in a solution of the solution for 3 minutes, then washed with water to check if the dye is soaked.

[0044]

According to the present invention, a material for cutting such as extruded round bar made of polyoxymethylene, which has a uniform appearance and has no white spots in the central portion in its cross section and no difference between the peripheral portion and the central portion. Can be obtained, and various processed products of high quality can be obtained by machining this.

Claims (6)

[Claims] 1. The isothermal crystallization rate at 150 ° C. is 20.
A polyoxymethylene resin material for cutting, characterized by comprising a polyoxymethylene resin having a time of 0 seconds or more. 2. A resin material for cutting, comprising a polyoxymethylene resin, characterized in that the difference in size of spherulites between the peripheral portion and the central portion as viewed from the cross section of the resin material is 10 μm or less. Polyoxymethylene resin material for cutting. 3. A resin material for cutting, comprising a polyoxymethylene resin, wherein the difference in latent heat of crystal fusion between the peripheral portion and the central portion of the resin material in cross section is 10 Joule / g or less. Polyoxymethylene resin material for cutting. 4. A resin material for cutting, comprising a polyoxymethylene resin, wherein the resin material has an isothermal crystallization rate of 200 seconds or more at 150 ° C., and a sphere in a peripheral portion and a central portion viewed from its cross section. A polyoxymethylene resin material for cutting, wherein the difference in crystal size is 10 microns or less, and the difference in latent heat of crystal fusion between the peripheral portion and the central portion is 10 joules / g or less. 5. The polyoxymethylene resin material for cutting according to claim 1, wherein the resin material is a rod-shaped material. 6. A processed polyoxymethylene resin product obtained by cutting the polyoxymethylene resin material for cutting according to claim 1.