JPS6354741B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved polypropylene composition that has good moldability without impairing the excellent properties of crystalline polypropylene and does not cause the trouble of fish eyes. More specifically, by melt-mixing two specific types of crystalline polypropylene, excellent moldability can be achieved while maintaining the excellent mechanical properties of crystalline polypropylene itself such as rigidity and impact resistance, as well as transparency and heat resistance. The present invention relates to a polypropylene composition which is particularly suitable for injection molding, and which avoids the trouble of causing fish eyes. Due to its good properties, injection molded products of polypropylene are used in large quantities in a wide range of applications, but it is currently desired to further improve moldability in order to increase productivity. The stiffness and impact resistance of polypropylene are highly dependent on the average molecular weight when the stereoregularity that influences these properties is approximately the same. For example, increasing the average molecular weight improves impact resistance, and conversely, decreasing the average molecular weight increases crystallinity and increases rigidity. However, if impact resistance is emphasized and the average molecular weight is increased, moldability will deteriorate, whereas if the average molecular weight is decreased, rigidity will increase and moldability will also improve, but impact resistance will decrease. Therefore, it is important to improve moldability without significantly changing the average molecular weight, that is, the intrinsic viscosity. In order to improve injection moldability, it is necessary to lower the melt viscosity, particularly in the high shear rate region of 100 sec ^-1 or higher, as low as possible. In order to lower the melt viscosity, there are methods such as lowering the average molecular weight or increasing the molding temperature. When the average molecular weight is lowered and the molding temperature is increased, the decrease in melt viscosity becomes even more remarkable.
However, lowering the average molecular weight is not necessarily appropriate for the reasons mentioned above, and increasing the injection molding temperature prolongs the cooling solidification time after injection, which is economically disadvantageous as it lengthens the molding cycle. It is necessary to lower the melt viscosity as much as possible in a high shear rate region at a constant temperature without lowering the average molecular weight, that is, the intrinsic viscosity, that is, it is necessary to impart properties that make so-called non-Newtonian viscosity behavior more pronounced. Conventionally proposed methods for obtaining preferred polypropylene compositions with improved moldability include Japanese Patent Publication No. 37696/1983 and Japanese Patent Application Laid-Open No. 1983-1989.
91954 and JP-A-54-74844 disclose a method of mixing two types of polymers with different molecular weights, and JP-A-54-74844.
In JP-A-38389 and JP-A-54-144448, there is a method in which two or more polymers having different molecular weights are polymerized in multiple stages. In Japanese Patent Publication No. 50-37696, the high molecular weight crystalline polypropylene polymer is 60 to 99.5% by weight;
JP-A-54-74844 teaches a mixing ratio of 60 to 95% by weight, and JP-A-53-91954 teaches that the mixing ratio of high molecular weight crystalline propylene should be 2 to 30 parts by weight. ing. Japanese Patent Publication No. 54-38389,
JP-A-54-144448 discloses a multi-stage polymerization method in which the preferred content of high molecular weight polypropylene is 0.05 to 15% by weight or 5 to 30% by weight. However, when the composition was formed by melt mixing at the mixing ratio taught in JP-A-53-91954, the effect of improving moldability was not sufficient. In addition, in the case where a sufficient improvement effect was observed, many fish eyes were generated on the surface of the molded product. When the composition disclosed in Japanese Patent Publication No. 50-37696 was formed by melt-mixing, the occurrence of fish eyes could be prevented, and the effect of improving moldability was also observed, but this was not yet sufficient. The inventors of the present invention have found that the good properties of crystalline polypropylene, such as rigidity, impact resistance, transparency, and heat resistance, are excellent in moldability without impairing them, and the problem of fish eyes is eliminated. A polypropylene composition was investigated. As a result, a desirable polypropylene composition was obtained by melt-mixing two types of crystalline polypropylene having specific properties. The gist of the present invention is to use a crystalline propylene homopolymer or a copolymer of propylene and other α-olefins having an intrinsic viscosity [η] of 0.6 d/g to 1.7 d/g and more than 40% by weight and less than 70% by weight. Intrinsic viscosity [η]
more than 30% by weight of a crystalline propylene homopolymer or a copolymer of propylene and other α-olefin, which has an intrinsic viscosity [η] of 1.5 d/g to 4.5 d/g and 1.5 times or more of the former. less than % by weight, and the overall intrinsic viscosity [η] is 1d/g or more
2d/g. The composition with improved moldability according to the present invention is a composition suitable for injection molding. In other words, because of the pronounced non-Newtonian viscosity behavior, and therefore the melt viscosity is low in the high shear rate region when the average molecular weight is approximately the same, molding is possible even if the injection molding temperature or injection pressure is lowered. . In particular, lowering the injection molding temperature shortens the molding cycle, which is economically advantageous. In addition, molded products with complex shapes and thin products can be easily obtained, and furthermore, molded products with good surface properties can be obtained. To explain the present invention in detail, the crystalline propylene homopolymer or copolymer of propylene and other α-olefin (sometimes abbreviated as low molecular weight component) used as a single component of the present invention is [η] is 0.6d/g to 1.7d/g, preferably 0.7d/g to 1.5d/g, and its isotactic index II (hereinafter sometimes simply abbreviated as II) is 80% or more, preferably is over 90%. The crystalline propylene homopolymer or copolymer of propylene and other α-olefin (sometimes abbreviated as high molecular weight component) used as the second component has [η] of 1.5 d/g to 4.5 d/g. g, preferably 1.7d/g to 4d/g, and the
II is 80% or more, preferably 90% or more. In these, the value of intrinsic viscosity [η] (d/g) is
Measured in tetralin solution at 135℃,
Isotactic index II (%) is the residual amount (% by weight) after extraction with boiling n-heptane for 6 hours in a modified Soxhlet extractor, and indicates the content of crystalline polymer. These components can be obtained by any method, for example, they can be obtained directly by polymerization, or high molecular weight polymers can be obtained by known methods (heat, oxygen-containing compounds, etc.).
It is also possible to obtain the desired polymer [η] by decomposition. II can also be extracted in advance with a solvent to suit the purpose of the present invention. The composition of the present invention comprises more than 40% by weight and less than 70% by weight of low molecular weight components and more than 30% by weight and less than 60% by weight of high molecular weight components, preferably 45% to 65% by weight of low molecular weight components. It is composed of a high molecular weight component of 35% to 55% by weight, and the ratio of [η] between the high molecular weight component and the low molecular weight component is 1.5 or more,
It is preferably 2.0 or more, and [η] of the entire composition
is 1d/g or more and less than 2d/g. Naturally, a small amount of a polymer having a different [η] may be added as the third component, as long as the purpose of the present invention is not impaired. When using a copolymer of propylene and other α-olefin as one or both of the high molecular weight component and the low molecular weight component, it is possible to improve moldability without substantially impairing the properties of the crystalline propylene random copolymer. It is an object of the present invention to obtain a composition which has good properties and which does not cause the problem of burning eyes.
Therefore, copolymers of propylene and other α-olefins are crystalline propylene random copolymers and do not include so-called amorphous copolymers. The amount of α-olefin other than propylene contained in the crystalline copolymer is 10% by weight or less, preferably 8% by weight or less. If [η] of the high molecular weight component is smaller than 1.5 d/g, the effect of improving non-Newtonian viscosity behavior is small and undesirable. Moreover, if [η] is larger than 4.5 d/g, fish eyes will occur due to poor dispersion of high molecular weight components, which is not preferable. High molecular weight components
If the amount is less than 30% by weight, especially less than 10% by weight, the non-Newtonian viscosity behavior will not be improved that much, and therefore the moldability will not be improved sufficiently, and if the moldability improvement effect is significant, there will be a large number of fibers on the surface of the molded product.・Ai is recognized and is not desirable. When the high molecular weight component exceeds 60% by weight, particularly when it exceeds 80% by weight, almost no formation of fish eyes is observed, but the effect of improving moldability is still insufficient. The ratio of [η] of high molecular weight components and low molecular weight components is
If it is less than 1.5, the improvement in non-Newtonian viscosity behavior is small and the improvement in moldability is also insufficient. Hereinafter, the present invention will be explained in more detail with reference to Examples, and the composition of the present invention can be prepared using a known mixer, such as a ribbon blender, a V-type blender, a Henschel mixer, a conventional screw extruder, a Banbury mixer, a roll mixer, etc. It can be prepared by combining with a kneading machine such as Furthermore, heat stabilizers,
It goes without saying that in addition to stabilizers such as antioxidants and ultraviolet absorbers, various additives such as lubricants and nucleating agents may be added as necessary. Further, the present invention is not limited to the following examples unless it exceeds the gist thereof. The evaluation methods for various physical properties, moldability, etc. of the composition are as follows. First yield point strength (Kg/cm ² ); ASTM D638-72
It was determined by a tensile test of a dumbbell piece punched out from a press sheet in accordance with . unless otherwise specified
This is a measurement value at 20℃. Izotsu impact strength (Kg・cm/cm); ASTM
Measurements were made on strips punched out from press sheets with notches in accordance with D256. Tensile impact strength (Kg・cm/cm ² ); ASTM D1822
Measurements were made on test pieces made by punching dumbbell pieces from press sheets in accordance with . These are all measured values at 20°C. Outflow ratio: Melt ratio according to ASTM D1238-70
The flow rate and shear stress at 230℃ and shear stress of 5 x 10 ⁵ dyne/cm ² were measured using a flow index measuring device.
The ratio of the outflow amount at 10 ⁴ dyne/cm ² was determined. When the intrinsic viscosity [η] is the same, the larger the flow rate ratio, the higher the melt viscosity in the low shear rate region, and the lower the melt viscosity in the high shear rate region, that is, the non-Newtonian viscosity behavior is more pronounced. shows. Comb type flow length (mm); using a 1 oz injection molding machine, thickness 0.2, 0.4, 0.6 mm, width 5.0 mm, length 70.0 mm
Using a comb flow mold, the flow length at an injection pressure of 480 kg/cm ² was determined, and the results are shown for a thickness of 0.4 mm. Surface quality: A flat plate with a thickness of 1 mm, width of 80 mm, and length of 80 mm was produced using a 1-ounce injection molding machine, and visually judged. Here, we have ranked Fuitsyu Ai as follows.

[Table] Examples 1 to 3, Comparative Examples 1 to 2 Propylene homopolymers or propylene-ethylene random copolymers having the properties shown in Table 1 were mixed in a Henschel mixer at the mixing ratio shown in the table, Next, the mixtures were melt-mixed using a screw extruder and granulated using a pelletizer to obtain compositions of Examples 1 to 3. The ethylene content in the propylene-ethylene random copolymer was measured by infrared absorption spectrum. In Comparative Examples 1 and 2, the intrinsic viscosity [η] was that of Examples 1 and 3.
Comparative Example 1 is a random copolymer. The results are shown in Table 1. Examples 1 to 3 are Comparative Example 1
Compared to ~2, the outflow ratio is larger and the comb-shaped flow is greatly improved. The balance between the first yield point strength, the Izot impact strength, and the tensile impact strength of Examples 1 to 2 and Example 3 is the same as that of Comparative Example 1 and Comparative Example 2. In addition, there were almost no visible fish eyes on the injection flat plate, and the surface quality was good. Comparative Examples 3 to 13 In Comparative Examples 3 to 13, the propylene homopolymer or propylene-ethylene random copolymer shown in Table 2 was mixed at the mixing ratio shown in the table, and Examples 1 to 13 were mixed.
It was obtained by the same method as 3. The results are shown in Table 2. Comparative Examples 6 to 8 are cases in which the mixing ratio of high molecular weight components is high, and the occurrence of fish eyes is not observed. However, compared to Comparative Example 3 or Comparative Example 2, which have substantially the same intrinsic viscosity, the outflow ratio is larger and the comb flow is improved, but this is not necessarily sufficient. Comparative Examples 9 to 11 are cases where the mixing ratio of high molecular weight components is small. In Comparative Example 9, the fish eye was good, but the outflow ratio was small, and the improvement effect in the comb flow was not satisfactory. Comparative Example 10 has a large outflow ratio and a comb-shaped flow that is better than, for example, Comparative Example 6 with the same [η], but fish eyes occur, which is not preferable. Comparative Example 11 is a case where [η] of the high molecular weight component is even larger, but many fish eyes occurred due to poor dispersion of the high molecular weight component. The flow rate ratio is small, and the Izot impact strength and tensile impact strength are lower than Comparative Example 2, which has almost the same [η], and the impact resistance is also inferior, which is not preferable. Comparative Examples 12 and 13 each have a high molecular weight component [η]
In the case where the ratio of [η] between the high molecular weight component and the low molecular weight component is small, the outflow ratio is small in both cases, and the comb-shaped flow is sufficiently improved, although the occurrence of fish eyes is not observed. Not. Examples 4 to 8 Examples 4 to 8 are compositions obtained from the polymers and mixing ratios of the polymers shown in Table 3 by the same method as Examples 1 to 3. The results are shown in Table 3. Examples 4 to 8 have almost the same [η] as Comparative Example 3
The outflow rate ratio is larger than that of No. 5, and the comb-like flow is good. Izot impact strength and tensile impact strength are comparable to those of Comparative Examples 3 to 5, and therefore Examples 4 to 8 are compositions with improved moldability without impairing impact resistance. Further, no occurrence of burning eyes was observed, and an injection flat plate with good surface quality was obtained.

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Claims (1)

[Claims] 1. Intrinsic viscosity [η] is 0.6 d/g to 1.7 d/
g of crystalline propylene homopolymer or copolymer of propylene and other α-olefin exceeding 40% by weight and less than 70% by weight and having an intrinsic viscosity [η] of 1.5d/g
or more than 30% by weight and less than 60% by weight of a crystalline propylene homopolymer or a copolymer of propylene and other α-olefin, which has an intrinsic viscosity [η] of 4.5 d/g and 1.5 times or more of the former. A polypropylene composition having a total intrinsic viscosity [η] of 1 d/g or more and less than 2 d/g.