JPH1095050A - Manufacture of polypropylene resin molded body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve resistance to impact by retaining a molded body formed by melt molding polypropylene resin of specified isotacticity rate and then water cooling the resin in a specified temperature range for a given time. SOLUTION: A molded body formed by melt molding polyprepylene resin of isotacticity rate of 95% or more and then water cooling the resin is retained in a temperature range of 120 deg.C or higher to the melting point or lower for a given time. When the isotacticity rate is less than 95%, the increase of impact absorbing energy is not larger compared with the processes heretofore available. When the retaining temperature is lower than 120 deg.C, the increase of impact absorbing energy is not larger either compared with the processes heretofore available. In that case, it is not necessary to retain the molded body at the given temperature, but the temperature gradient can be generated in the temperature range. As the time of retaining heat treatment is vaired by the thickness and shape of the molded body, the optimum time is determined each time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a molded article of a polypropylene resin, particularly a molded article of a polypropylene resin having excellent impact resistance.

[0002]

2. Description of the Related Art In general, when the molecular weight of a plastic resin is increased, impact resistance is improved, but moldability is poor. Therefore, Japanese Patent Application Laid-Open No. 56-84728,
A method has been proposed in which an elastomer is added to a polypropylene resin having a high molecular weight and excellent in moldability and is heat-treated at a temperature of 80 ° C. or higher and a melting point or lower to improve impact resistance and low-temperature toughness without impairing moldability. .

[0003]

However, the method described in Japanese Patent Application Laid-Open No. 56-84728 has a problem that the rigidity is reduced and the high-temperature characteristics are deteriorated due to the addition of the elastomer.

The present invention has been made to solve such a problem, and has as its object to provide a method for producing a polypropylene resin molded article having excellent impact resistance without deteriorating other characteristics. I do.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is to maintain a molded article produced by melt-molding a polypropylene resin having an isotacticity of 95% or more and then cooling with water for a predetermined time in a temperature range of 120 ° C. or more and less than a melting point. The problem is solved by a method for producing a molded polypropylene resin article.

Here, the isotacticity ratio is described in reference 1 [Macromolecules, 6, 926 (1).
973)], that is, the isotacticity fraction in pentad units of the molecular chain of polypropylene measured using ¹³ C-NMR.

[0007] The reason why the isotacticity ratio is limited to 95% or more is that, as will be shown later in the examples, when the isotacticity ratio is less than 95%, the increase in shock absorption energy is not so large as compared with the conventional method. The reason why the holding temperature is limited to 120 ° C. or higher is that, as shown in the examples, when the holding temperature is lower than 120 ° C., the increase in the impact absorption energy is not so large as compared with the conventional method.

Another object of the present invention is to melt-mold a polypropylene resin having an isotacticity of 95% or more, and then cool the same in a temperature range from a temperature lower than the melting point to 80 ° C. for a predetermined time. The problem is also solved by a method for producing a polypropylene resin molded article.

The reason why the holding temperature is limited to 80 ° C. or higher is that, as shown in the examples, when the holding temperature is lower than 80 ° C., the increase in the impact absorption energy is not so large as compared with the conventional method. Further, in any case, after holding for a predetermined time, 10
Cooling at a cooling rate of not more than ° C./min provides better impact resistance.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A molded body produced by water cooling after melt molding is kept for a predetermined time in a temperature range of 120 ° C. or more and less than a melting point, or a temperature from a temperature lower than the melting point to 80 ° C. upon cooling after melt molding. When the temperature is maintained in the range for a predetermined time, it is not necessary to maintain the temperature at a constant value.

[0011]

EXAMPLES The present inventors conducted the following studies in order to improve the impact resistance of a molded article of a polypropylene resin.

A polypropylene resin having various isotacticity ratios is melt-molded and then water-cooled to a thickness of 5 m.
m sheet-shaped samples were prepared. And at 140 ° C, 24
After the heat treatment for keeping the time, the impact absorption energy at 40 ° C. was measured by the following method.

[0013] The shock absorption energy is 2 mm deep with a 0.5 mm deep cut at the tip by a laser and an angle of 45 mm.
This is the absorbed energy per unit area determined by the Charpy test using a test piece having a length of 55 mm and a width of 10 mm provided with a V notch at an impact speed of 3.8 m / sec over a span of 40 mm.

FIG. 1 shows that after melt-molding, water-cooling is performed,
4 shows the relationship between the impact absorption energy at 40 ° C. and the isotacticity of a sample that has been heat treated at 24 ° C. for 24 hours.

A resin having an isotacticity of 95% or more and having a temperature in the range of 120 ° C. or higher and lower than the melting point is used.
It can be seen that when the sample is kept at 0 ° C. for a predetermined time, the impact resistance is greatly improved as compared with a conventional sample, that is, a sample which is still water-cooled after melt molding.

Next, when the polypropylene resin having various isotacticity rates is melt-molded and then cooled,
The sheet was heat-treated at 60 ° C. and 120 ° C. for 2 hours to prepare a 5 mm thick sheet sample. Then, the impact absorption energy at 40 ° C. was measured by the above method.

FIG. 2 shows that during the cooling process after the melt molding,
4 shows the relationship between the impact absorption energy at 40 ° C. and the isotacticity of the sample subjected to heat treatment at 120 ° C. for 2 hours.

If a resin having an isotacticity of 95% or more is used and held for a predetermined time at 120 ° C. in a temperature range from a temperature lower than the melting point to 80 ° C., the conventional method, that is, when water-cooled after melt molding, is used. In comparison, it can be seen that the impact resistance is greatly improved.

On the other hand, even if the heat treatment is performed at a temperature of 60 ° C., the impact resistance is not improved as compared with the conventional case.

The reason why the impact resistance is improved by such a heat treatment is not necessarily clear, but it is considered that the entanglement (entanglement) of the polymer is optimized by the heat treatment in this temperature range.

In each case, since no special additives such as elastomers were added, deterioration of rigidity and high temperature characteristics was not recognized.

Since the holding time of the heat treatment varies depending on the thickness and shape of the compact, it is necessary to determine the optimum time each time.

Next, a more detailed experiment was conducted to examine the relationship between the isotacticity ratio and the heat treatment conditions and the impact absorption energy.

First, a homopolymer extrusion grade manufactured by Mitsui Petrochemical Co., Ltd. having an isotacticity of 9
Using 8.5%, 95.0%, and 92.0% polypropylene resin, the conventional method was simulated, that is, melt molding was performed at 200 ° C. for 5 minutes by a hot press, and then the water was cooled to 20 ° C. A sheet-like sample having a thickness of 5 mm was prepared under the condition of cooling with a press at a pressure of 10 MPa for 5 minutes.

This sheet sample was heat-treated under the conditions shown in Table 1 to prepare Samples 1 to 6. Then, the impact absorption energy at 40 ° C. was measured by the above method.

The melt flow rate MFR of the polypropylene resin used was measured at a temperature of 230 ° C. and a load of 2.16 kg according to JIS K6758.
It was 0 g / 10 minutes.

Sample 1 has an isotacticity ratio of 9
After 8.5% heat treatment at 140 ° C for 24 hours, 10 ° C /
5 is a sample according to the method of the present invention cooled in min.

Sample 2 has an isotacticity ratio of 9
After 8.5% heat treatment at 120 ° C. for 24 hours, 10 ° C. /
5 is a sample according to the method of the present invention cooled in min.

Sample 3 has an isotacticity ratio of 9
After 8.5% heat treatment at 100 ° C for 24 hours, 10 ° C /
It is a sample outside the present invention cooled in min. (The heat treatment temperature is lower than the lower limit of 120 ° C. of the present invention.) Sample 4
Has an isotacticity of 95.0% and a temperature of 140 ° C.
This is a sample according to the method of the present invention cooled at 10 ° C./min after a heat treatment of × 24 hours.

Sample 5 has an isotacticity ratio of 9
2.0%, heat treatment at 120 ° C. × 24 hours, 10 ° C. /
It is a sample outside the present invention cooled in min. (The isotacticity ratio is lower than 95%, which is the lower limit of the present invention.) Sample 6 is a sample with an isotacticity ratio of 98.5% and a water-cooled conventional method that has not been subjected to heat treatment.

The results are shown in Table 1. It can be seen that all of the samples produced by the method of the present invention have greatly improved impact absorption energy as compared with the conventional method. On the other hand, in the samples other than the present invention, only the impact absorption energy equivalent to that of the samples obtained by the conventional method can be obtained.

[0032]

[Table 1]

Next, the same polypropylene resin as above was melt-molded at 200 ° C. for 5 minutes by a hot press, and then heat-treated during cooling under the conditions shown in Table 2 to a thickness of 5 m.
m sheet-shaped samples 7 to 12 were prepared. Then, the impact absorption energy at 40 ° C. was measured by the above method.

Sample 7 has an isotacticity ratio of 9
8.5%, after heat treatment at 120 ° C. for 2 hours, 20 ° C./m
It is a sample according to the method of the present invention cooled in.

Sample 8 has an isotacticity ratio of 9
8.5%, heat treatment at 120 ° C x 2 hours, 10 ° C / m
It is a sample according to the method of the present invention cooled in.

Sample 9 has an isotacticity ratio of 9
8.5%, heat treatment at 80 ° C. × 0.5 hour, 10 ° C. /
5 is a sample according to the method of the present invention cooled in min.

Sample 10 has an isotacticity ratio of 9
After 8.5% heat treatment at 70 ° C. × 0.5 hour, 10 ° C. /
It is a sample outside the present invention cooled in min. (The heat treatment temperature is lower than the lower limit of 80 ° C. of the present invention.)

Sample 11 has an isotacticity ratio of 9
After heat treatment at 5.0% at 120 ° C. for 2 hours, 10 ° C./m
5 is a sample according to the invention cooled in.

Sample 12 has an isotacticity ratio of 9
After heat treatment at 2.0% at 120 ° C for 2 hours, 10 ° C / m
It is a sample outside the present invention cooled in. (The isotacticity ratio is lower than 95%, which is the range of the present invention.) The results are shown in Table 2.

It can be seen that all of the samples prepared by the method of the present invention have greatly improved impact absorption energy as compared with the conventional method. As can be seen from a comparison between Sample 7 and Sample 8, the cooling rate was 10 at the same heat treatment temperature and time.
Higher impact absorption energy can be obtained by slowing down to ° C./min. For samples other than the present invention, only the impact absorption energy equivalent to the sample obtained by the conventional method can be obtained.

[0041]

[Table 2]

[0042]

Since the present invention is constituted as described above, it is possible to provide a method for producing a polypropylene resin molded article having excellent impact resistance without deteriorating other characteristics.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the impact absorption energy at 40 ° C. and the isotacticity ratio of a sample that has been subjected to heat treatment at 140 ° C. for 24 hours after water cooling after melt molding.

FIG. 2 is a diagram showing the relationship between the impact absorption energy at 40 ° C. and the isotacticity of a sample that has been subjected to a heat treatment at 60 ° C. and 120 ° C. for 2 hours in a cooling process after melt molding.

Claims (3)

[Claims] The present invention is characterized in that a molded product produced by melt-molding a polypropylene resin having an isotacticity of 95% or more and then cooling is reheated, and is maintained in a temperature range of 120 ° C. or more and less than a melting point for a predetermined time. Of producing a molded polypropylene resin article. 2. A polypropylene resin molded body characterized in that a polypropylene resin having an isotacticity of 95% or more is maintained for a predetermined time in a temperature range from a temperature lower than the melting point to 80 ° C. when cooling after melt molding. Manufacturing method. 3. After the holding for the predetermined time, 10 ° C./min.
The method for producing a polypropylene resin molded product according to claim 1 or 2, wherein cooling is performed at the following cooling rate.