JPH07228748A - Polypropyrene composition for blow molding - Google Patents

Abstract

PURPOSE:To obtain a blow molded article with excellent drawdown properties without causing cleavage by compounding a propylene-ethylene block copolymer with a high-density polyethylene. CONSTITUTION:This compsn. is obtd. by blending 60-90wt.% propylene-ethylene block copolymer having melt flow rate (23 deg.C, 2.16kg) of 0.7g/10-min or lower and an ethylene content of 5wt.% or higher with 10-40wt.% high-density polyethylene (density: 0.935g/cm<3>) having a melt index (190 deg.C, 2.16kg) of 0.07 g/10 min or lower in such a way that the ratio of the melt flow rate of the former resin to the melt index of the latter is 7 or higher, pref. 10-70. The compsn. is pref. prepd. by postreactor blending, i.e., by in-line mixing powders or pellets of the resins, compounding the mixture with various additives if necessary, and kneading and pelletizing the mixture at 170-260 deg.C on a twin-screw extruder, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene composition for blow molding containing a propylene-ethylene block copolymer as a main component, and in particular, delamination of the end surface of a product from which burrs have been removed and delamination of burrs upon burr crushing. The present invention relates to a polypropylene composition suitable for medium- to large-sized blow-molded articles, which is free from the occurrence of scratches and has good drawdown resistance.

[0002]

2. Description of the Related Art Conventional polypropylene is used for molded articles for various purposes because of its light weight, high rigidity, excellent heat resistance, chemical resistance, etc., and its molding method is injection molding or extrusion molding. Various methods such as blow molding are applied. However, polypropylene alone has problems such as low drawdown resistance and poor blow moldability because it has a lower melt tension than high-density polyethylene, which has a relatively similar physical property. There is a drawback that it is difficult to obtain a molded product having a complicated shape. In order to overcome this drawback, a polypropylene composition comprising crystalline polypropylene, ethylene-α-olefin copolymer rubber and a filler (Japanese Patent Publication No. 64-6656).
Alternatively, a polyolefin composition (Japanese Patent Publication No. 6657/1989) comprising a high-density polyethylene, crystalline polypropylene, an ethylene-α-olefin copolymer rubber, and a filler has been proposed.

Further, as a medium to large blow molding material,
A polypropylene composition in which high-density polyethylene is blended in an amount of about 30% by weight with a base material of a propylene-ethylene block copolymer is known. However, it has been found that a blow-molded product made of this polypropylene composition has a problem that delamination is likely to occur at the end surface after removing burrs and at the time of crushing burrs.

Therefore, an object of the present invention is to eliminate the above-mentioned problem of delamination, and to obtain a medium-sized or large-sized blow molding having excellent surface properties, moldability, heat resistance, impact resistance, high rigidity, mechanical strength, hinge characteristics and the like. An object of the present invention is to provide a polypropylene composition suitable for an article.

[0005]

As a result of earnest research in view of the above object, the present inventors have found that the propylene-ethylene block copolymer is blended with high-density polyethylene and the ethylene content of the propylene-ethylene block copolymer is ,
Further, the inventors have found that by defining the melt flow rate / melt index ratio of both in a predetermined range, it is possible to prevent delamination at the end face after removing burrs and delamination at the time of crushing burrs, and conceived the present invention.

That is, the polypropylene composition for blowing of the present invention comprises (a) a melt flow rate (230 ° C., a load of 2.
Measured under the condition of 16 kg, hereinafter referred to as MFR) 0.7 g / 10 min or less and 60 to 90% by weight of propylene-ethylene block copolymer having an ethylene content of 5% by weight or more, and (b) melt index (190 ° C, load) Measured under 2.16 kg condition, below M
High-density polyethylene with an I of 0.07g / 10min or less 10
-40% by weight, and the MFR of the above (a) and the above
It is characterized in that the ratio of (b) to MI is 7 or more.

The present invention will be described in detail below. The blow molding polypropylene composition of the present invention comprises (a) a propylene-ethylene block copolymer and (b) a high density polyethylene.

[1] Composition (1) Component (a) Propylene-Ethylene Block Copolymer The propylene-ethylene block copolymer in the present invention has an ethylene content of 5% by weight or more. When the ethylene content of the propylene-ethylene block copolymer is less than 5% by weight, physical properties such as delamination and impact strength are low, while when it exceeds 15% by weight, the physical properties such as rigidity are deteriorated. The preferred ethylene content is 5-10% by weight.

The MFR (230 ° C., 2.16 kg) of the propylene-ethylene block copolymer is 0.7 g / 10 min or less, preferably 0.2 to 0.7 g / 10 min. If it exceeds 0.7 g / 10 min, the melt tension decreases, the drawdown increases, and the blow moldability decreases. In addition, when the MFR is less than 0.2 g / 10 min, the moldability is deteriorated in terms of plasticization, which is not preferable.

The above-mentioned propylene-ethylene block copolymer can be synthesized by, for example, a multistage polymerization method.
In the multi-stage polymerization method, propylene is first polymerized in the presence of a Ziegler catalyst or the like to give a crystalline propylene homopolymer portion (may contain a small amount of comonomer component).
And then switched to ethylene + propylene to produce a random copolymerization moiety. In some cases, a crystalline ethylene homopolymer portion may be produced by further supplying ethylene and performing homopolymerization.

The propylene-ethylene block copolymer synthesized by the above-mentioned multi-stage polymerization method has a substantially crystalline homopolypropylene portion, a low crystalline propylene-ethylene random copolymer portion, and a small amount of a crystalline homopolyethylene portion. It consists of and.

Each of the moieties may be present as a single polymer or may be in the state of being bonded to each other. The above-mentioned parts are basically composed of propylene and / or ethylene, but may contain a small amount of other α-olefin, diene-based monomer or the like.

[0013] As (b) high density polyethylene high density polyethylene has a density of 0.935 g / cm ³ or more, preferably to use those 0.940 ~0.970g / cm ^3. When the density is 0.935 g / cm ³ or less, the rigidity of the obtained polypropylene composition is low.

In addition, the high density polyethylene MI (190
℃, 2.16kg) is 0.07g / 10min or less, preferably 0.
It is from 01 to 0.07g / 10min. When the MI value is less than 0.01 g / 10 min, the fluidity of the obtained composition is poor, while 0.07 g / min
If it exceeds, the mechanical strength of the resulting composition will be reduced.

(2) Blending ratio (a) The blending ratio of the propylene-ethylene block copolymer and (b) high density polyethylene is such that (a) is 60 to 90% by weight,
It is preferably 65 to 80% by weight, (b) is 10 to 40% by weight,
It is preferably 20 to 35% by weight. When the propylene-ethylene block copolymer is less than 60% by weight (when the high-density polyethylene exceeds 40% by weight), rigidity, heat resistance and the like are deteriorated. On the other hand, the propylene-ethylene block copolymer
When it exceeds 90% by weight (when the high-density polyethylene is less than 10% by weight), the melt tension is low, the drawdown is large, and the blow moldability is deteriorated.

(3) MFR / MI ratio It is essential that the ratio of MFR of the propylene-ethylene block copolymer to MI of the high density polyethylene is 7 or more. When the MFR / MI ratio is less than 7, delamination occurs in blow molding or burr crushing. On the other hand, MFR /
If the MI ratio exceeds 70, it will be difficult to melt and disperse evenly.
The preferred MFR / MI ratio is 10-70.

(4) MFR of composition The MFR of the composition of propylene-ethylene block copolymer and high-density polyethylene is 0.7 g / 10 min or less,
It is preferably 0.2 to 0.6 g / min. If the MFR exceeds 0.7 g / min, the drop-down resistance is poor and the functional strength is also low.

(5) Other components In the polypropylene composition of the present invention, if necessary, other additives such as a filler such as talc, a heat stabilizer, an antioxidant, a mold release agent, and the like are appropriately added. It can be added.

[2] Production Method The polypropylene composition of the present invention can be obtained by mixing the above-mentioned components by various blending methods. Examples of the blending method include multistage polymerization blending, post-reactor blending, powder blending, pellet blending, dry blending and the like, with post-reactor blending being particularly preferred. In the case of this post-reactor blend, powders or pellets of the components (a) and (b) are mixed in-line at a predetermined ratio, and after mixing the above-mentioned various additives as necessary, an extruder, preferably a twin-screw extruder is used. Used at 170-260 ° C, preferably 180-230 ° C
Dissolve and knead to pelletize. In some cases, the components (a) and (b) may be mixed by a reactor blend.

[0020]

[Function] The blow molding polypropylene composition of the present invention is
(a) Propylene-ethylene block copolymer having MFR of 0.7 g / 10 min or less and ethylene content of 5% by weight or more 60-
90% by weight and (b) 10 to 40% by weight of high-density polyethylene having MI of 0.07 g / 10 min or less.
Since the ratio of FR to MI in the above (b) is 7 or more, it is possible to prevent the occurrence of layered peeling at the end surface of the molded product and at the time of crushing burr. The reason why such an effect is obtained is not necessarily clear, but by setting the MFR / MI ratio to 7 or more, the difference in melt viscosity between the propylene-ethylene block copolymer and the high-density polyethylene is increased, and the high It is considered that by increasing the melt viscosity of the density polyethylene, the layered deformation due to shearing during the molding process can be prevented to prevent the layered peeling.

[0021]

The present invention will be described in more detail by the following examples. The propylene-ethylene block copolymer and high density polyethylene used in the following examples are as follows.

(1) Propylene-ethylene block copolymer BPP-1, ethylene content 5.7% by weight, MFR (230 ° C,
2.16kg) 0.7g / 10min. BPP-2, ethylene content 4.7% by weight, MFR (230 ℃,
2.16kg) 0.6g / 10min. BPP-3, ethylene content 2.9% by weight, MFR (230 ℃,
2.16kg) 0.6g / 10min. BPP-4, ethylene content 1.6% by weight, MFR (230 ℃,
2.16kg) 0.5g / 10min. BPP-5, ethylene content 5.9% by weight, MFR (230 ℃,
2.16kg) 0.6g / 10min. BPP-6, ethylene content 6.1% by weight, MFR (230 ℃,
2.16kg) 0.4g / 10min.

(2) High-density polyethylene HDPE-1, MI (190 ° C, 2.16kg) 0.02g / 10min, density 0.
945 g / cm ³ . HDPE-2, MI (190 ° C, 2.16kg) 0.3 g / 10min, density 0.
949 g / cm ³ . HDPE-3, MI (190 ° C, 2.16kg) 0.25g / 10min, density 0.
954 g / cm ³ . HDPE-4, MI (190 ℃, 2.16kg) 0.15g / 10min, density 0.
951 g / cm ³ . HDPE-5, MI (190 ° C, 2.16kg) 0.07g / 10min, density 0.
948 g / cm ³ . HDPE-6, MI (190 ℃, 2.16kg) 1.2 g / 10min, density 0.
952 g / cm ³ .

Examples 1 to 3 and Comparative Examples 1 to 3 In order to examine the influence of the ethylene content of the propylene-ethylene block copolymer (BPP) on the peeling state of blow molded products, propylene-ethylene shown in Table 1 was used. A block copolymer and high density polyethylene (HDPE) were used. Dry blend both with a super mixer,
Extrusion from blow molding machine (BEKUM BA-2) at 200 ℃, MF
R and drawdown properties were evaluated, and extrusion blow molded products (300 cc bottles) were prepared. At that time, observe the delamination of the burr end face and remove the test piece (10
(0 mm × 15 mm × 1 mm) was cut out and the peeling state of the test piece was observed by a tensile test according to JIS 6760.

The drawdown evaluation criteria are as follows. ○: No drawdown △: Slight drawdown ×: Significant drawdown

The evaluation criteria for the layered peeling are as follows. ○: No peeling △: Slight peeling ×: Marked peeling

Table 1 Unit of composition (% by weight) BPP HDPE No. Type MFR Ethylene content Type MI Example 1 BPP-1 0.7 5.7 HDPE-1 0.02 2 BPP-6 0.4 6.1 HDPE-1 0.02 3 BPP-5 0.6 5.9 HDPE-1 0.02 Comparative Example 1 BPP-2 0.6 4.7 HDPE-1 0.02 2 BPP-3 0.6 2.9 HDPE-1 0.02 3 BPP-4 0.5 1.6 HDPE-1 0.02

Table 1 (continued) Molded product Blow molded bottle No. BPP / HDPE MFR / MI MFR Drawdown peeling state Example 1 70/30 35 0.37 ○ ○ 2 70/30 20 0.26 ○ ○ 3 70/30 30 0.32 ○ ○ Comparative example 1 70/30 30 0.34 ○ △ 2 70 / 30 30 0.28 ○ × 3 70/30 25 0.28 ○ ×

From the above results, it is understood that when the ethylene content of the propylene-ethylene block copolymer is less than 5% by weight, the blow-molded product obtained has a poor peeling state.

Examples 4 to 7 and Comparative Examples 4 to 8 In order to investigate the effect of the ratio of MFR of propylene-ethylene block copolymer and MI of high density polyethylene on drawdown property and delamination during blow molding. A polypropylene composition having the compounding ratio shown in Table 2 was prepared in the same manner as in Example 1. In the same manner as in Example 1, the MFR of the molten composition, the drawdown property during blow molding, and the peeled state were observed. The results are shown in Table 2.

Table 2 Unit of composition (wt%) BPP HDPE No. Type MFR Ethylene content Type MI Example 4 BPP-1 0.7 5.7 HDPE-1 0.02 5 BPP-1 0.7 5.7 HDPE-5 0.07 6 BPP-6 0.4 6.1 HDPE-1 0.02 7 BPP-5 0.6 5.9 HDPE-1 0.02 Comparative Example 4 BPP-1 0.7 5.7 HDPE-2 0.3 5 BPP-1 0.7 5.7 HDPE-6 1.2 6 BPP-6 0.4 6.1 HDPE-3 0.25 7 BPP-6 0.4 6.1 HDPE-2 0.3 8 BPP-6 0.4 6.1 HDPE-4 0.15

Table 2 (continued) Molded product Blow molded bottle No. BPP / HDPE MFR / MI MFR Drawdown property Peeling state Example 4 70/30 35 0.37 ○ ○ 5 70/30 10 0.51 ○ ○ 6 70/30 20 0.26 ○ ○ 7 70/30 30 0.32 ○ ○ Comparative example 4 70 / 30 2.3 0.58 ○ × 5 70/30 0.6 0.83 × × 6 70/30 1.6 − ○ × 7 70/30 1.3 − ○ × 8 70/30 2.7 − ○ ×

From the above results, it is understood that when the MFR / MI ratio is less than 7, the peeled state of the obtained blow-molded product becomes poor.

Examples 8 to 11 and Comparative Examples 9 to 12 To investigate the effect of the ratio of MFR of propylene-ethylene block copolymer and MI of high density polyethylene on drawdown property and delamination during blow molding. A polypropylene composition having the compounding ratio shown in Table 3 was prepared in the same manner as in Example 1. In the same manner as in Example 1, the MFR of the molten composition, the drawdown property during blow molding, and the peeled state were observed. The results are shown in Table 3.

Table 3 Unit of composition (% by weight) BPP HDPE No. Type MFR Ethylene content Type MI Example 8 BPP-1 0.7 5.7 HDPE-1 0.02 9 BPP-1 0.7 5.7 HDPE-1 0.02 10 BPP-1 0.7 5.7 HDPE-1 0.02 11 BPP-1 0.7 5.7 HDPE-1 0.02 Comparative Example 9 BPP-1 0.7 5.7 HDPE-2 0.3 10 BPP-1 0.7 5.7 HDPE-2 0.3 11 BPP-1 0.7 5.7 HDPE-2 0.3 12 BPP-1 0.7 5.7 HDPE-2 0.3 13 BPP-6 0.4 6.1 HDPE-5 0.07

Table 3 (continued) Molded Products Blow Molded Bottle No. BPP / HDPE MFR / MI MFR Drawdown property Peeling state Example 8 90/10 35 0.56 ○ ○ 9 80/20 35 0.52 ○ ○ 10 70/30 35 0.37 ○ ○ 11 60/40 35 0.30 ○ ○ Comparative example 9 90 / 10 2.3 0.66 △ △ 10 80/20 2.3 0.56 ○ △ 11 70/30 2.3 0.58 ○ × 12 60/40 2.3 0.59 ○ × 13 70/30 5.7 0.35 ○ ×

From the above results, it can be seen that when the MFR / MI ratio is less than 10, the blow-molded product obtained has a poor peeling state.

Comparative Examples 14 and 15 The same propylene-ethylene as in Example 8 was used in order to investigate the influence of the blending ratio of the propylene-ethylene block copolymer and the high-density polyethylene on the drawdown property and the delamination during blow molding. A polypropylene composition was prepared in the same manner as in Example 8 except that the block copolymer and the high-density polyethylene were used in the compounding ratios shown in Table 4. In the same manner as in Example 8, the MFR of the molten composition, the drawdown property during blow molding, and the peeled state were observed. The fourth result
Shown in the table.

Table 4 Molded Products Blow Molded Bottle No. BPP / HDPE MFR / MI MFR Drawdown property Peeling state comparative example 14 100/0 − 0.7 × − 15 50/50 35 0.27 ○ ×

As is apparent from Table 4, when the compounding ratio is out of the range of the present invention, the drawdown property and the peeling state at the time of blow molding obtained are inferior.

[0041]

As described above in detail, in the present invention, the ethylene content and MFR of the propylene-ethylene block copolymer and the MI of the high density polyethylene are specified, and the MFR / MI ratio is within a predetermined range. As described above, it is possible to provide a blow-molded article which has excellent drawdown properties and is free from delamination. The blow-molded polypropylene composition of the present invention having such properties is suitable as a material for medium-sized or large-sized blow-molded articles such as various industrial parts and double wall cases.

Claims (2)

[Claims] 1. A melt flow rate (230 ° C., 2.16)
60) to 90% by weight of propylene-ethylene block copolymer with an ethylene content of 0.7% / 10 min or less and an ethylene content of 5% by weight or more.
And (b) the melt index (190 ℃, 2.16kg) is 0.07
g / 10 min or less of high density polyethylene 10 to 40% by weight, and the melt flow rate of the above (a) and the above (b)
The blown polypropylene composition is characterized by having a ratio (MFR / MI) to the melt index of 7 or more. 2. The ratio (MFR / M) of the melt flow rate of (a) and the melt index of (b) according to claim 1.
A polypropylene composition for blow molding, characterized in that I) is 10 to 70.