JP2002146038A - Method for producing polypropylene-based resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a polypropylene-based resin composition consisting of a polypropylene-based resin and a thermoplastic elastomer obtained by copolymerizing propylene with another α-olefin, having less fisheyes and capable of giving a good product appearance on its molding. SOLUTION: This method for producing the polypropylene-based resin composition is provided by melting and kneading a mixture containing 50-95 wt.% polypropylene-based resin and 5-50 wt.% olefin-based thermoplastic elastomer obtained by copolymerizing propylene with another α-olefin (provided that, the total of both as 100 wt.%) in the presence of a super critical fluid.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for producing a polypropylene resin composition comprising a polypropylene resin and a thermoplastic elastomer obtained by copolymerizing propylene with another α-olefin. Specifically, a polypropylene-based resin composition comprising a polypropylene-based resin and a thermoplastic elastomer obtained by copolymerizing propylene and another α-olefin, which has a low fish eye and can give a good product appearance at the time of molding. And a method for producing the same.

[0001]

2. Description of the Related Art Polypropylene resins have excellent transparency and chemical resistance, and have been widely used for various molded articles including packaging containers. However, since molded products made of polypropylene resin are easily damaged when subjected to impact, in order to impart impact resistance thereto, a polyolefin-based thermoplastic elastomer component obtained by copolymerizing α-olefins is used as a polypropylene resin. Materials designed to improve the impact strength by dispersing the material in the material have been developed.

This elastomer component may be blended with a separately prepared polypropylene resin in a blending, kneading, or granulating step before molding. In addition, a multistage polymerization or the like may be used to convert the polypropylene resin in the previous polymerization. It is produced in a polymerization system, and is produced at the time of polymerization by a method of producing an elastomer component by copolymerization with another α-olefin by the next stage polymerization. In general, the latter method is preferably used because the elastomer component to be produced is easily dispersed finely in the polypropylene resin, and the effect of improving impact resistance is enhanced.

[0003] When polymerizing an olefinic elastomer component by this multi-stage polymerization method, the polymerization reaction may become non-uniform and the polymerization may proceed locally. In such a case, impact strength, appearance, In some cases, “fish eyes”, which are unmelted particles, which significantly deteriorate product properties such as tensile elongation and coatability, may be generated. In order to prevent the generation of such “fish eyes”, see, for example,
In JP-A-49716, it is possible to incorporate a classifier into the process, and in JP-A-61-69821, it is possible to add an alcohol as a deactivator.
Each has been proposed.

[0004] However, as a result of the recent development of catalyst development technology, the activity of the catalyst has been dramatically increased. As a result, the control of fish eyes is insufficient with a conventional classifier alone, and the use of a deactivator results in a subsequent polymerization reaction. However, the activity of the catalyst was significantly reduced, and it could not be said that this was a very effective means from the viewpoint of productivity.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned disadvantages of the prior art and to effectively remove fish eyes in the melt-kneading step performed during molding, thereby adversely affecting productivity during polymerization. An object of the present invention is to provide a method for producing a polypropylene-based resin composition capable of obtaining a molded article of good quality without affecting the composition.

[0006]

Means for Solving the Problems The present inventors have made various studies in order to solve the above problems, and found that when these mixtures are melt-kneaded, good results can be obtained by performing them under specific conditions. Were obtained, and the present invention was completed. That is, the gist of the present invention is that the polypropylene resin 50
Olefinic thermoplastic elastomer obtained by copolymerizing propylene with another α-olefin.
50% by weight (However, the total of both is 100% by weight)
And melt-kneading a mixture containing the following in the presence of a supercritical fluid.

Another object of the present invention is to provide a method for producing the above polypropylene resin composition in which the supercritical fluid used is carbon dioxide or nitrogen, and the above polypropylene series in which melt kneading is carried out using a twin screw extruder. A method for producing a resin composition also exists. Another gist of the present invention is a method for producing the above-mentioned polypropylene-based resin composition, wherein the polypropylene-based resin used is a propylene homopolymer, and the above-mentioned polypropylene, wherein the olefin-based thermoplastic elastomer is a copolymer of propylene and ethylene. Method for producing resin-based composition, and the above-mentioned polypropylene-based resin wherein the composition ratio (mol / mol) of ethylene and propylene in the olefin-based thermoplastic elastomer is in the range of ethylene / propylene = 30/70 to 95/5 A method for producing the composition also exists.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with respect to each of raw materials, kneading equipment, and obtained composition. (1) Raw Materials The main raw materials used in the method of the present invention are a polypropylene resin and an olefin thermoplastic elastomer.

These may be used as a mixture of those individually produced as described above, or a mixture produced successively in the polymerization process. The polypropylene resin that can be used in the present invention is a homopolymer of propylene or a copolymer of propylene based on propylene and another copolymerizable monomer, and has a high Young's modulus at room temperature. Which do not exhibit rubber-like elasticity. Also,
In the case of a copolymer, the content of propylene is 80 mol%.
The above is preferable, and 90% or more is more preferable.

As the polypropylene resin used in the present invention, a homopolymer of propylene is most preferred. The α-olefin which is a component of the olefin-based thermoplastic elastomer obtained by copolymerizing propylene and another α-olefin that can be used in the present invention includes ethylene, 1-butene, 1-pentene, Although any α-olefin such as hexene and styrene can be used, preferred are α-olefins having 2 or 4 to 10 carbon atoms such as ethylene and 1-butene. Among them, ethylene having 2 carbon atoms is preferable. Is preferred.

The composition ratio of these copolymer components may be appropriately determined according to the number of carbon atoms of the α-olefin used and the impact resistance and other physical properties required for the final product, but ethylene is used as the copolymer component. In this case, the composition ratio (mole / mole) of ethylene and propylene is in the range of ethylene / propylene = 30/70 to 95/5 to improve the compatibility with the polypropylene resin and the impact resistance. It is preferred in that respect.

As described above, the polypropylene resin and the olefin-based thermoplastic elastomer may be used as a mixture of individually manufactured ones. However, the polypropylene resin may be mixed in the polymerization system in the previous polymerization by multi-stage polymerization or the like. Generated by
It is preferable to use a polymer produced by polymerization, in which an elastomer component is formed by copolymerization with another α-olefin in the next stage of polymerization.

As a polymerization catalyst used for producing a mixture of a polypropylene resin and an olefin thermoplastic elastomer by polymerization, a vanadium type catalyst, a Ziegler-Natta catalyst combining titanium trichloride and organoaluminum, and a catalyst using the same as a carrier. Any catalyst such as a supported catalyst and a metallocene catalyst can be used, but from the viewpoint of productivity, it is preferable to use a catalyst having high polymerization activity.

It is preferable to use a continuous polymerization method having high productivity as the polymerization method, and the polymerization can be carried out by any method such as slurry polymerization, bulk polymerization and gas phase polymerization. At the time of this polymerization, fish eyes may be prevented from occurring as long as the productivity is not impaired, by using the above-described classifier and alcohols as a polymerization deactivator. The mixing ratio of the polypropylene resin and the olefin thermoplastic elastomer used in the present invention is 50 to 95% by weight of the polypropylene resin and 5 to 50% by weight of the olefinic thermoplastic elastomer. If the mixing ratio of the elastomer exceeds 50% by weight, physical properties such as rigidity and heat resistance inherently possessed by the polypropylene resin are significantly reduced, while if the mixing ratio of the elastomer is less than 5% by weight, impact resistance and the like are reduced. Cannot sufficiently obtain the effect of improving the physical properties.

[0015] The melt flow rate of the polypropylene resin composition obtained by the method of the present invention is as follows:
0.5 to 200 g / 10 min (230 ° C., load 21.
18N / JIS-K-7210). When the melt flow rate is less than 0.5 g / 10 min, the fluidity when molding the obtained composition by the injection molding method becomes insufficient. On the other hand, when it is higher than 200 g / 10 min, the melt viscosity is too low. As a result, a sufficient shearing force for finely dispersing the unmelted particles contained in the olefin-based thermoplastic elastomer component cannot be obtained, and both are not preferred. The ratio of the molecular weights of the polypropylene resin component and the olefin thermoplastic elastomer component is M
w (polypropylene resin) / Mw (elastomer) =
The range of 1/20 to 1/1, preferably 1/10 to 1/2 is suitable from the viewpoint of the effect of improving impact resistance. (However, Mw means a weight average molecular weight.)

The supercritical fluid used in the present invention can be used without any particular limitation as long as it is a substance capable of undergoing a phase transition to a supercritical state. In view of this, it is preferable to use carbon dioxide or nitrogen. The supercritical fluid is generated by setting the pressure and temperature to be equal to or higher than the critical pressure and the critical temperature by a supercritical fluid generator that simultaneously performs pressurization and heating.

In the present invention, the melt kneading is performed in the presence of the supercritical fluid. The amount of the supercritical fluid used is adjusted according to the amount of the supercritical fluid saturated and dissolved in the molten resin and the elastomer to be kneaded. do it. For example, when using carbon dioxide as the supercritical fluid, it is preferable to use 0.1 to 11% by weight, preferably 1 to 10% by weight, particularly preferably 2 to 8% by weight based on the molten resin and the elastomer. is there.

In the method of the present invention, in addition to the above-described polypropylene-based resin, olefin-based thermoplastic elastomer, and supercritical fluid as raw materials, other optional components may be used as long as the effects of the present invention are not significantly impaired. If necessary, kneading may be performed. Such optional components include, for example, antioxidants, ultraviolet absorbers, light stabilizers,
Heat stabilizer, lubricant, antistatic agent, coloring agent, conductive agent, dispersant, printability-imparting agent, filler, flame retardant, flame retardant auxiliary, foaming agent, processing aid, neutralizing agent, heavy metal inert Agents, nucleating agents, antifogging agents and the like. (2) Kneading equipment The equipment for kneading in the method of the present invention is not particularly limited as long as it can handle a supercritical fluid, but a range of kneading conditions, ease of handling the supercritical fluid, and productivity. From the viewpoint, it is preferable to use a twin-screw extruder.

The screw rotating direction, the meshing ratio, the screw length, and the screw diameter of the twin-screw extruder can be arbitrary depending on the resin to be kneaded and the kneading conditions. The screw of this extruder is preferably provided with a kneading element such as a kneading disk or a rotor from the viewpoint of melt kneading performance. Since the supercritical fluid is supplied into the extruder and kneading is performed in that state, it is necessary to maintain the inside of the system of the extruder above the critical pressure and critical temperature of the supercritical substance used. For this reason, the extruder is equipped with a gear pump at its tip, controls the resin pressure at the suction part of the gear pump, or arranges a reverse screw with high pressure boosting ability at the supercritical kneading tip, and rotates the screw. It is preferable to use a material that takes into consideration that the pressure in the supercritical kneading section is increased to a critical pressure or higher by utilizing the pressure increase due to the pressure.

After melt-kneading by the method of the present invention in the presence of a supercritical fluid, the pressure is reduced or cooled to
The supercritical substance is released from the supercritical state. At this time, in order to discharge the vaporized gas, a method of providing a devolatilizing hole in the cylinder of the extruder and sucking the gas with a vacuum pump may be used. Further, in the method of the present invention, since the resin and the elastomer component are kneaded in a state of being dissolved in a supercritical fluid, the viscosity of the melt in the system is reduced and the kneading torque of the extruder is reduced,
Power consumption is reduced, and an energy saving effect can be obtained. (3) Composition Obtained The polypropylene resin composition obtained by kneading according to the method of the present invention can be used in a case where unmelted particles causing fish eyes are generated by local polymerization of an elastomer.
This is finely dispersed by kneading, resulting in a polypropylene resin composition excellent in impact strength, appearance, tensile elongation, coatability, and the like, and capable of giving a molded product of good quality.

The reason why the unmelted particles formed by the local polymerization of the elastomer are finely dispersed by the method of the present invention is not clear, but is presumed to be due to the following reasons. That is, the supercritical fluid has a characteristic that when it comes into contact with a molten resin or the like, it is easily dissolved therein, but the solubility differs depending on the type of the fluid and the resin. In the system of the present invention, the solubility of the supercritical fluid is generally higher for olefin-based elastomers than for polypropylene,
The degree of decrease in the melt viscosity of the olefin-based elastomer is larger than that of the olefin-based elastomer. Therefore, the difference in the melt viscosity between the olefin-based elastomer and the polypropylene-based resin is smaller than that of the ordinary melt-kneading, and the mixing of the two can be performed more uniformly. Therefore, fine dispersion of the olefin elastomer in the polypropylene resin serving as the matrix is achieved. As a result, it is considered that unmelted particles that cause fish eyes existing in the olefin-based elastomer are also finely dispersed and become inconspicuous when formed into a molded product.

[0022]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto without departing from the scope of the present invention. (Example 1) Using a multi-stage polymerization vessel, homopolymerization of propylene in the first stage, and ethylene-propylene copolymerization (ethylene / propylene = 50/50 (molar ratio)) in the second stage with Mg Performed using a catalyst, and a propylene homopolymer: an ethylene-propylene copolymer = 73: 27 (% by weight)
Of a propylene homopolymer and an ethylene-propylene copolymer elastomer.

This mixture was charged together with an antioxidant from a hopper of an extruder (TEX30 co-rotating twin-screw extruder manufactured by Nippon Steel Works Ltd.) of a melt-kneading apparatus having the apparatus configuration shown in FIG. 1 and a screw rotation speed of 200 rpm. Extrusion 15kg /
Under the condition of h, melt kneading was performed using carbon dioxide in a supercritical state. At this time, a gear pump is attached to the extruder tip in order to raise the pressure inside the extruder system to above the critical pressure, and the resin pressure from the supercritical fluid injection section to the gear pump (gear pump) suction section becomes higher than the critical pressure. Thus, the rotation speed of the gear pump was automatically controlled.

The supercritical carbon dioxide was made supercritical by a supercritical generator and injected into the extruder at a source pressure of 20 MPa via a heating pipe fitted with a flow control valve on the way. The injection amount was controlled by a flow control valve so as to be 3% by weight based on the total amount of the resin components. The polypropylene-based resin composition obtained by melt-kneading is pulverized and formed into a film having a thickness of 30 μm by a T-die forming machine, and an agglomerate having a diameter of 50 μm or more is observed in the film (250 cm ² ). Was measured and fish eyes were evaluated.

Table 1 summarizes the number of fish eyes in the film and the power consumption of the extruder. (Example 2) Melt kneading was performed in the same manner as in Example 1 except that the injection amount of the supercritical fluid was adjusted to 6% by weight based on the total amount of the resin components.

Table 1 shows the number of fish eyes of the obtained polypropylene resin composition and the power consumption of the extruder. (Example 3) The screw rotation speed of the extruder was set to 400 rpm.
Melt kneading was performed in the same manner as in Example 1 except that

Table 1 shows the number of fish eyes of the obtained polypropylene resin composition and the power consumption of the extruder. (Example 4) Melt kneading was performed in the same manner as in Example 3, except that the injection amount of the supercritical fluid was adjusted to 6% by weight based on the total amount of the resin components.

Table 1 shows the number of fish eyes of the obtained polypropylene resin composition and the power consumption of the extruder. (Comparative Example 1) Melt kneading was performed in the same manner as in Example 1 except that kneading was performed without injecting a supercritical fluid.

Table 1 shows the number of fish eyes and the power consumption of the extruder of the obtained polypropylene resin composition. (Comparative Example 2) Melt kneading was performed in the same manner as in Example 3 except that kneading was performed without injecting a supercritical fluid.

Table 1 shows the number of fish eyes of the obtained polypropylene resin composition and the power consumption of the extruder.

[0031]

[Table 1]

<Evaluation of Results> Examples 1 and 2 and Comparative Example 1
Comparing Example 3 and Examples 3 and 4 with Comparative Example 2, it can be seen that in each case the power consumption of the extruder motor is smaller and the number of fish eyes is smaller in Example. In particular, the effects are large in Examples 2 and 4 in which the addition amount of the supercritical fluid is 6% by weight based on the total resin components.

[0033]

EFFECT OF THE INVENTION By using the method of the present invention, it is possible to obtain a good product appearance at the time of molding, having a small fish eye, comprising a polypropylene resin and a thermoplastic elastomer obtained by copolymerizing propylene and another α-olefin. It has become possible to produce a polypropylene-based resin composition capable of giving a low energy cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing a device configuration used in an embodiment of a method of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Twin-screw extruder 2 Raw material resin / elastomer supply device 3 Hopper 4 Supercritical fluid generator 5 Supercritical kneading unit 6 Resin pressure sensor (a injection unit sensor b gear pump front sensor c die unit sensor) 7 gear pump (gear pump) 8 Die connecting pipe 9 Die connecting block 10 Slit die

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B29K 23:00 B29K 23:00 F term (Reference) 4F070 AA15 AA16 AB09 AB11 AB16 FA04 FA17 FB10 FC06 4F201 AA11 AA11E AA45 AM30 AM32 BA01 BC01 BC13 BC15 BK13 BK26 BK75 BN36 BN37 BQ50 BQ57 4J002 BB11W BB12W BB14X BB15X GT00

Claims (6)

[Claims] 1. 50 to 95% by weight of a polypropylene resin
And an olefin-based thermoplastic elastomer obtained by copolymerizing propylene and another α-olefin at 5 to 50% by weight.
(However, the total of both is 100% by weight) is melt-kneaded in the presence of a supercritical fluid. 2. The method for producing a polypropylene resin composition according to claim 1, wherein the supercritical fluid is carbon dioxide or nitrogen. 3. The method for producing a polypropylene resin composition according to claim 1, wherein the melt-kneading is performed using a twin-screw extruder. 4. The method for producing a polypropylene resin composition according to claim 1, wherein the polypropylene resin is a propylene homopolymer. 5. The method for producing a polypropylene resin composition according to claim 1, wherein the olefin thermoplastic elastomer is a copolymer of propylene and ethylene. 6. The polypropylene resin composition according to claim 5, wherein the composition ratio (mole / mole) of ethylene and propylene in the olefin-based thermoplastic elastomer is in the range of ethylene / propylene = 30/70 to 95/5. Method of manufacturing a product.