JPH07178750A - Forming method for polypropylene - Google Patents

Abstract

PURPOSE:To improve the smoothness of the surface of a molded article, and draw forth the mechanical characteristics of the polypropylene to the maximum by injection-forming a polypropylene of which the limiting viscosity being measured in tetralin at a specified temperature is a specified value, by a specified expansion ratio. CONSTITUTION:A polypropyrene, having a limiting viscosity of 2.0-12.0l/g measured in a tetralin at 135 deg.C, is formed by injection molding at an expansion ratio of 1.005-1.200 times. In this case, if the limiting viscosity is less than 2.0dl/g, although the smoothness of the surface of a molded article is generally favorable, remarkably excellent mechanical characteristics do not present, compared with a general polypropylene. In the limiting viscosity exceeds 12.0dl/g, the injection molding is difficult even when a foaming agent is added, and since an expansion is insufficient, the smoothness is unsatisfactory. Also, the expansion ratio is especially important in order to obtain favorable smoothness and mechanical characteristics, and if the expansion ratio is less than 1.005, a favorable smoothness cannot be obtained, and if the expansion ratio is 1.200 or higher, it is nit preferable because the mechanical characteristics are spoiled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene molding method which is excellent in dimensional accuracy and surface smoothness of a molded product and is excellent in mechanical properties such as rigidity, surface impact resistance and surface hardness. .

[0002]

2. Description of the Related Art Polypropylene having an intrinsic viscosity of 2.0 to 12.0 dl / g measured in 135 ° C. tetralin has a rigidity, impact resistance, surface hardness, etc., which are higher than those of polypropylene commercially available. It is a polymer with outstanding remarkably excellent properties. However, since these polypropylenes have extremely high viscosity when melted and have poor fluidity,
The smoothness of the surface of the molded product obtained by injection molding was inferior to that of polypropylene which is generally commercially available.

Conventionally, as a means for improving the smoothness of the surface of an injection-molded product of a resin having a high melt viscosity, a method of increasing the molding temperature of the resin and lowering the melt viscosity to perform injection molding has been used. However, when polypropylene having an intrinsic viscosity of 2.0 to 12.0 dl / g is injection-molded at a high temperature, the smoothness of the surface of the injection-molded product is improved, but the molecular chain is broken, resulting in excellent mechanical properties. There was a problem of being damaged.

[0004]

Therefore, an object of the present invention is to improve the smoothness of the surface of an injection-molded product of polypropylene having an intrinsic viscosity of 2.0 to 12.0 dl / g, and to improve the mechanical properties of this polypropylene. It is to propose an injection molding method that maximizes the characteristics.

[0005]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have found that the dimensional accuracy of molded products is good, the surface smoothness is good, and the mechanical properties such as rigidity and surface hardness are excellent. Moreover, it was surprisingly found that a molded product having a significantly improved surface impact strength was obtained, and the present invention was completed.

That is, the present invention is characterized in that polypropylene having an intrinsic viscosity measured in tetralin at 135 ° C. of 2.0 to 12.0 dl / g is injection molded at a foaming ratio of 1.005 to 1.200. Is a polypropylene molding method.

The polypropylene used in the present invention is 1
Intrinsic viscosity measured in 35 ° C. tetralin 2.0-1
2.0 dl / g, more preferable range is 2.2-8.0
dl / g. When the intrinsic viscosity is less than 2.0 dl / g, the smoothness of the surface of the molded product is generally good, but mechanical properties which are remarkably superior to those of polypropylene commercially available are not exhibited, which is not preferable. Further, polypropylene having an intrinsic viscosity of more than 12.0 dl / g is difficult to injection-mold even if a foaming agent is added, and since foaming is insufficient, the surface smoothness of the obtained molded product is I'm not satisfied.

The polypropylene used in the present invention includes homopolymers of propylene, propylene, ethylene and 1
-Random with other α-olefins such as butene, 1-hexene, 1-octene, and 4-methyl-1pentene,
Alternatively, it contains a block copolymer. When the copolymer is a random copolymer, the amount of other α-olefin to be copolymerized is preferably 5 mol% or less, and when the copolymer is a block copolymer, the amount of other α-olefin is preferably 20 mol% or less.

The polypropylene used in the present invention is 13
The intrinsic viscosity measured in 5 ° C. tetralin is 2.0-12.
If it is 0 dl / g, it may be produced by any method, and it can be produced by any known method using a Ziegler type polymerization catalyst and its improved catalyst without any limitation. For example, a titanium compound conventionally known as a catalyst and an organoaluminum compound can be used in combination, and if necessary, various electron donors such as ester and ether can be combined. The polymerization mode may be either continuous or batch type, and may be solution polymerization carried out in a solution of heptane or the like, slurry polymerization using propylene itself as a solvent, or gas phase polymerization. Polymerization is usually carried out by supplying propylene and, if necessary, hydrogen in the temperature range of 0 ° C. to 100 ° C., and after the predetermined polymerization is completed, the polymerization is stopped with a terminating agent such as isopropyl alcohol. In the polymerization of polypropylene, the polypropylene used in the present invention can be obtained by, for example, reducing the amount of hydrogen, which is a molecular weight modifier, to a very small amount, or performing the polymerization without using hydrogen.

In the present invention, it is preferable to use a mixture of high molecular weight polypropylene and low molecular weight polypropylene in order to improve the fluidity at the time of molding and, in turn, the moldability. Of course, when using these mixtures, the intrinsic viscosity of the mixture, measured in tetralin at 135 ° C., must be 2.0-12.0 dl / g.

As the high molecular weight polypropylene constituting such a mixture, the intrinsic viscosity measured in tetralin at 135 ° C. is 4.5 to 12.0 dl / g, and further 5.
It is preferably from 5 to 8.0 dl / g. On the other hand, as the low molecular weight polypropylene, the intrinsic viscosity measured in tetralin at 135 ° C. is measured in order to prevent miscibility with high molecular weight polypropylene and bleed out and to prevent the mechanical properties of the high molecular weight polypropylene from being impaired. 0.03 to 3.5 dl / g, further 0.05 to 3.0
It is preferably in the range of dl / g. Further, the low-molecular-weight polypropylene in the present invention has an isotactic pentad fraction determined by ¹³ C-NMR of 0.960 or more, more preferably, in order to improve mechanical properties.
It is preferable to use 0.965 or more.

The high molecular weight polypropylene in this method can be produced by the method described above. The low-molecular-weight polypropylene may be produced by a known method using a Ziegler-type polymerization catalyst or a modified catalyst thereof, as in the case of high-molecular-weight polypropylene, but polymerization for increasing the isotactic pentad fraction is possible. As a method, use of a prepolymerization catalyst obtained by prepolymerizing a small amount of propylene in the presence of a titanium compound, an organoaluminum compound, an organosilicon compound and an iodine compound as disclosed in JP-A-2-170802. Is preferred. The polymerization mode may be either continuous or batch type, and may be solution polymerization carried out in a solution of heptane or the like, slurry polymerization using propylene itself as a solvent, or gas phase polymerization. Polymerization is usually performed in the temperature range of 0 ° C to 100 ° C.
Polymerization is carried out by supplying propylene and hydrogen, and after the predetermined polymerization is completed, the polymerization is stopped with a terminating agent such as isopropyl alcohol. In addition, this low molecular weight polypropylene
It may be obtained by decomposing polypropylene having an intrinsic viscosity of more than 3.5 dl / g by a known method such as decomposition with a peroxide.

When a mixture of high molecular weight polypropylene and low molecular weight polypropylene is used in the present invention, the above low molecular weight polypropylene is in the range of 5 to 100 parts by weight, more preferably 10 parts by weight, based on 100 parts by weight of high molecular weight polypropylene. Mixing in the range of ˜80 parts by weight is preferred for obtaining good moldability and mechanical properties. The intrinsic viscosity of the mixture obtained by mixing is 2.0 to 4.5 dl in order to obtain good moldability and mechanical properties.
/ G, and more preferably in the range of 2.2 to 4.3 dl / g.

The method of mixing the high molecular weight polypropylene and the low molecular weight polypropylene is not particularly limited, but a method of dry blending both components using a Henschel mixer or the like, or a method of producing both components in multiple stages during polymerization, etc. Can be used.

Upon molding, the polypropylene used in the present invention may be added with additives such as heat stabilizers, weather resistance stabilizers, nucleating agents, fillers, pigments and lubricants which have been conventionally used.

The foaming agent used in the present invention is not particularly limited, such as a physical foaming agent such as air and nitrogen, a chemical foaming agent which decomposes by heat to generate a gas, but since the gas is rapidly generated, Organic thermal decomposition type chemical foaming agents are preferred. As this foaming agent, azodicarbonamide (A
DCA), azobisisobutyronitrile (AIBN),
p, p-Oxybisbenzelsulfonyl hydrazide (O
BSH), N, N′-dinitrosopentamethylenetetramine (DPT), p-toluenesulfonyl semicarbazide (TSSC), trihydrazotriazine (THT) and the like can be used.

The amount of the foaming agent added may be such an amount that the above expansion ratio is achieved, but in consideration of the smoothness of the surface of the molded product, it is generally 0.2 to 2 with respect to 100 parts by weight of polypropylene. The range of parts by weight is preferable, and 0.3 to 1.
It is more preferably 5 parts by weight.

As a method for adding the foaming agent, a method in which the foaming agent is directly dry-blended with polypropylene, or a method in which a masterbatch pellet containing 10 to 80% by weight of the foaming agent in a resin is first prepared and then dry-blended with polypropylene is prepared. There is no particular limitation.

The injection molding machine used in the present invention is not particularly limited, and the nozzle shape is an open nozzle type,
The shut-off nozzle type is not particularly limited.

The molding temperature during injection molding is 180 ° C. to 260 ° C.
It is preferable to mold at a temperature of 90 ° C, more preferably 190 ° C to 240 ° C. If the temperature is lower than 180 ° C., the injection molding machine is insufficient in capacity, so that filling becomes difficult, and if the temperature is 260 ° C. or higher, foaming on the surface is increased, and good smoothness and surface gloss are not obtained.

The filling amount of polypropylene at the time of injection molding is
In order to obtain good surface smoothness and mechanical properties, it is preferable that the filling amount of polypropylene is about 0 to 20% smaller than that in the case of molding without adding a foaming agent.

The mold used in the present invention is not particularly limited, and a mold used in general injection molding may be used, or a mold having a function of vacuuming the inside of the cavity may be used. Polypropylene may be filled in the depressurized cavity. The mold temperature is preferably 20 to 120 ° C, more preferably 30 to 100 ° C.

The expansion ratio of the molded product of the present invention is 1.005 in order to obtain a molded product having good smoothness and mechanical properties.
It is particularly important that it is ˜1.200 times, preferably 1.010 to 1.100 times. If it is less than 1.005 times, good smoothness cannot be obtained, and if it is 1.200 times or more, mechanical properties such as rigidity are deteriorated, which is not preferable. The expansion ratio of the molded product in the present invention is a value obtained by dividing the specific gravity of the polypropylene molded product injection-molded without foaming by the specific gravity of the foamed injection-molded product. Such a method of controlling the expansion ratio can be performed by adjusting the amount of the foaming agent added, the molding temperature which is the injection molding condition, the polypropylene filling amount, and the mold temperature within the ranges described above.

[0024]

The polypropylene molding method of the present invention comprises:
It is possible to obtain a polypropylene molded product having excellent smoothness on the surface of the molded product and excellent mechanical properties. Therefore, the polypropylene molding method of the present invention can be used as a molding method for gears that require mechanical strength, mechanical parts such as packing, radiator tanks, automobile parts such as pillars, and various lining materials.

[0025]

EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples. Prior to the examples, the injection molding machine, the mold, and the measuring method used in the examples will be described.

(1) Injection molding machine An injection molding machine having a mold clamping force of 150 tons and a heating cylinder diameter of 46 mm was used. The heating cylinder temperature was set to 210 ° C. and the injection rate was set to 260 cm ³ / sec.

(2) Mold A flat plate was molded using a mold having a cavity of 260 mm in length × 60 mm in width × 5 mm in thickness. The gate style is direct sprue gate, and the mold set temperature is 80 ℃.
And

(3) Intrinsic viscosity Measured in tetralin at 135 ° C.

(4) Foaming Ratio The specific gravity of a polypropylene injection-molded product containing no foaming agent is
It was determined by dividing by the specific gravity of the foam injection molded product.

(5) Smoothness of the surface of the molded product The surface of the molded product was visually observed and the above three-stage evaluation was performed.

◯: Smoothness is good.

Δ: The smoothness is slightly inferior.

X: The smoothness is poor.

(6) Sink of molded product A value obtained by dividing the difference between the maximum thickness and the minimum thickness of the molded product by the maximum thickness.

(7) Flexural Modulus The flexural modulus was measured according to ASTM: D790.

(8) Surface impact strength According to JIS: K7211, tip radius 7 mm, weight 30
The 50% breaking height with a 0 g weight was measured. The occurrence of cracks was judged to be destruction.

Example 1 1 polymerized according to the method described in JP-A-3-7704
The intrinsic viscosity measured in 35 ° C. tetralin is 9.2 dl /
100 parts by weight of homopolypropylene (g) and a concentration of azodicarbonamide (hereinafter referred to as ADCA) 50 wt
% Masterbatch pellets 2 parts by weight were dry blended and then injection molded. The expansion ratio of the surface of the obtained molded product, the smoothness of the surface, the sink of the molded product, the flexural modulus, and the surface impact strength were measured. The results are shown in Table 1.

Examples 2 to 3 Injection molding was carried out in the same manner as in Example 1 except that polypropylene having the intrinsic viscosity shown in Table 1 was used and the addition amount of ADCA was changed to the amount shown in Table 1. . The results are shown in Table 1.
It was shown to.

Comparative Examples 1 to 3 Injection molding was performed in the same manner as in Examples 1 to 3 except that ADCA masterbatch pellets were not used. The results are shown in Table 1.

Example 4 100 parts by weight of high molecular weight homopolypropylene having an intrinsic viscosity of 6.0 dl / g and 25 parts by weight of low molecular weight homopolypropylene having an intrinsic viscosity of 1.1 dl / g were mixed with a Henschel mixer to obtain an intrinsic viscosity of 4.2 dl. / G polypropylene composition was obtained. 100 parts by weight of this polypropylene composition and 0.5 part by weight of the same master batch pellets of ADCA as used in Example 1 were dry-blended and injection-molded. The results are shown in Table 1.

Examples 5 to 7 Injection molding was carried out in the same manner as in Example 4 except that ADCA master batch pellets were added so that the amount of ADCA added was as shown in Table 1. The results are shown in Table 1.

Comparative Examples 4 to 6 Injection molding was carried out in the same manner as in Example 4 except that ADCA masterbatch pellets were added so that the amount of ADCA added was as shown in Table 1. The results are shown in Table 1.

Example 8 100 parts by weight of high molecular weight homopolypropylene having an intrinsic viscosity of 6.0 dl / g and 40 parts by weight of low molecular weight homopolypropylene having an intrinsic viscosity of 0.46 dl / g were mixed with a Henschel mixer to obtain an intrinsic viscosity of 2.6 dl. / G polypropylene composition was obtained. After 100 parts by weight of this polypropylene composition and 1 part by weight of the same master batch pellets of ADCA used in Example 1 were dry blended, injection molding was performed.
The results are shown in Table 1.

Comparative Example 7 Injection molding was carried out in the same manner as in Example 8 except that the ADCA masterbatch pellets were not used. The results are shown in Table 1.
It was shown to.

Comparative Examples 8 to 10 Homopolypropylene with an intrinsic viscosity of 1.6 dl / g and ADC
The amount of ADCA added to the masterbatch pellet of A is shown in Table 1.
Injection molding was carried out in the same manner as in Example 1 except that the amount was added as shown in. The results are shown in Table 1.

Example 9 The same polypropylene composition 100 used in Example 4
After 1 part by weight of N, N'-dinitrosopentamethylenetetramine (abbreviated as DPT) was dry blended, injection molding was performed. The results are shown in Table 1.

[0047]

[Table 1]

Claims (1)

[Claims] 1. A polypropylene characterized in that polypropylene having an intrinsic viscosity of 2.0 to 12.0 dl / g measured in tetralin at 135 ° C. is injection molded at a foaming ratio of 1.005 to 1.200 times. Molding method.