Note: Descriptions are shown in the official language in which they were submitted.
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, FIELD OF TECHNOLOGY
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The present invention relates to a polypropylene composition,
3 and more particularly to a polypropylene composition which is superior
in clarity and low-temperature impact resistance.
BACKGROUND OF_TEC~NOLOGY
O Polypropylene is in use in many fields because of its
7 superior mechanical properties, clarity, chemical resistance and
processability. However, polypropylene has a disadvantage of being
~ poor in impact resistance at low temperatures. Several methods have
lo been proposed in order to overcome this disadvantage, such as incor
11 porating polypropylene with polyethylene (~apane~e Patent Publication
12 No. 6975/1962), incorporating polypropylene with a solid propylene
13 ethylene copolymer con~aining 30 to 70 wt% of ethylene (Japanese
14 Pat~ent Publication No. 7088/1960), incorporating polypropylene wi~h
15 polybutene (Japanese Patent Publication No. 2245/1959), and incorpor-
16 ating polypropylene with polyi`sobutene (Japanese Patent Publication
1~ No. 10640/1960). - .
18 The above-mentioned methods are effective at improving the
79 low-temperature impact re~istance of polypropylene, but only at the
~0 sacrifice of polypropylene's inherent clarity, Therefore, the polymer
21 products cannot be applied to the production of film or sheet or
22 blowmoldings for food-packaging that requires clarity,
~3 On the other hand, there is disclosed in Japanese Patent
24 .Publication No. 256g3/1983 a composition composed of polypropylene,
25 low-density polyethy1ene~ and an amorphous ethylene-l-butene polymer
26 or amorphous ethylene-propylene copolymer resulting from polymeriza-
27 tion by a catalyst system consisting of a soluble vanadium compound
28 and an organoaluminum compound This composition is good in clarity
29 but is decreased in .stiffness and is not necessarily satisfactory in
impact resistance.
31 SUMMARY OF THE INVENTION
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32 It is an object of this invention to provide a polypropylene
33 composition which has improved low-temperature impact resistance and
34 yet preserves polypropylene's inherent clarity. This invention is a
3~ result of the present inventors' intensive studies on clarity.
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1 Two methods were conceived for producing a polypropylene
2 composition having the same degree of clarity as that of polypro-
3 pylene. According to the first method, the component to be dispersed
4 in polypropylene (referred to as the disperse phase) is divided into
fine particles having a diameter smaller than the wavelength of
6 light. According to the second method, polypropylene is incorporated
7 with the disperse phase having the same refractive in~ex as that of
polypropylene. The first method requires that the disperse phase
3 should have a considerably lower viscosity (molecular weight); but
this leads to poor impact resistance. In addition, it is impossible
11 to divide the disperse phase into fine particles having a diameter
12 smaller than the wavelength of light.
13 As the result of intensive studies on the second method, it
14 was found that an ethylene-propylene random copolymer containing a`
- ` 15 specific amount of ethylene produced by the polymerization with a
16 polymerization catalyst composed of a titanium trichloride catalyst-
17 co~ponent, organoaluminum compound, and a Lewis base has the same
18 refractive index as that of polypropylene. It was also found that
19 this ethylene-propylene random copolymer improves the impact resis-
tance of polypropylene when incorporated at a certain ratio into
21 polypropylene, whiiè preserving the clarity of polypropylene. The
22 present invention was completed based on these findings.
23 DETAILED DESCRIPTION OF THE INVENTI~N
24 The gist of this invention resides in a polypropylene compo-
2~5 sition which comprises:
~6 A. 65 to 95 wt~ of crystalline polypropylene, and
?7 ` B. 5 to 35 wt~ of ethylene-propylene random copolymer
28 containing higher than 70 wt% to 85 wt% of ethylene,` said copolymer
29 being one which is produced by copolymerizing ethylene with propylene
in the presence of a polymerization catalyst composed of a catalyst
31 component whose principal ingredient is titanium trichloride, an
32 organoaluminum compound and a Lewis base selected from carboxylic acid
33 ester, ether and ketone.
34 Polypropylene
The crystalline polypropylene used in this invention is a
36 propylene homopolymer.
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1 If the polypropylene composition is to have high stiffness,
2 it is necessary that the crystalline polypropylene should contain more
3 than 90 wt%, preferably more than 95 wt%, of boiling n-heptane insolu-
4 ble matter (referred to as HI hereinafter). In addition, it should
preferably have a melt flow rate (MFR) of 0.1 to 30 g/10 min (accord-
6 ing to ASTM D-1238-659 load:2160 9, temperature: 230C). The one
7 having a MFR lower than 0.1 results in a composition which is poor in
8 moldability, and the one having a MFR in excess of 30 provides a
9 composition which is poor in stiffness.
Eth~lene-propylene Random Copolymer
11 The ethylene-propylene random copolymer used in this inven-
12 tion is one coniaining higher than 70 wt% to 85 wt% of ethylene which
13 is produced by copolymeri~zinq ethylene with propylene in the presence
14 of a polymerization catalyst composed of a catalyst component whose
principal ingredient is titanium trichloride, an organoa1uminum ~om-
16 pound and a Lewis base se'lected'from carboxylic acid ester, ether, and
17 ketone.
18 ` The catalyst component constituting the polymerization cata-
19 lyst is titanium trichl'oride obtained by reducing titanium tetra-
chloride by the known methodO The titanium trichloride may be used as
21 ~uch or may be used after activation. Activation may be accomplished
22 by bringing titanium trichloride into contact with an electron donor
23 compound (such as alcohol, ether, ester, lactone, amine, acid halide,
24 and acid anhydride) and/or an activator (such as a halogen-containing
compound ~e.g., titanium tetrachloride, silicon tetrachloride, hydro-
26 gen halides, ànd halogenated hydrocarbons] and a halogen [e.g., iodine
2i and'chlorine]). Activation of titanium chlorides is well known in the
28 art.
~29 Preferred catalyst components are titanium trichloride, which
is obtained by reducing titanium tetrachloride with an organoaluminum
31 compound, and titanium trichloride-aluminum chloride eutectic crystal,
32 which is obtained by reducing titanium tetrachloride with aluminum
33 metal. Both of them are treated with one of the above-mentioned
34 activators.
The organoaluminum compound 'to be used in combination with
36 the catalyst component includes, for example, methylaluminum dichlo-
37 ride, ethylaluminum dichloride, diethylaluminum chloride, dibutyl-
38 aluminum c~loride, diethylaluminum bromide, ethylaluminum sesqui-
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1 chloride, butylaluminum sesquichloride, triethylaluminum, and
2 triisobutylaluminum. Preferably, among them are alkylaluminum chlo-
3 ride such as diethylaluminum chloride and ethylaluminum sesqui-
4 chloride. Usually, the organoaluminum compound is used in an amount
of l to 500 mol for l mol of titanium trichloride in the catalyst
b component.
7 The Lewis base, which is the remaining component of the
8 polymeri~ation catalyst, is selected from a carboxylic acid esterl
9 ether, and ketone. Examples of the carboxylic acid ester include
methyl ben20ate, ethyl benzoate, methyl p^toluate, ethyl p-toluate,
11 methyl methacrylate, methyl p-anisateS and ethyl p-anisate Examples
12 of the ether compoùnd include diethyl ether, dibutyl ether, diisobutyl
13 ether, diphenyl ether, anisole, and phenetole. Examples of the ketone
14 compound i-nclude methyl phenyl ketone and ethyl phenyl ketone.
lS Preferred ones among them are methyl p-anisate and ethyl p-ani~ate
16 which have bo~h the ester linkage and the ether linkaye. Usually, the
I7 Lewis base is used in an amount of 2 to 60 mol%, preferably lO to 30
18 mol%, based on the organoaluminum compound.
19 The ethylene-propylene random copolymer is produced by random
copolymeri2ation of ethylene and propylene in the gas phase or in an
21 inert hydrocarboni in the presence of a polymerization catalyst.
22 Examples of the inert hydrocarbon include propane, butane, pentane,
23 hexane, heptane, octane, decane, cyclohexane, benzene, toluene, and
24 xylene Usually, polymerization is performed at 0 to 120C and, if
necessary, in the presence of a molecular weight modifier such as
26 gaseous hydrogen.
` ` 27 According to this invention, it is necessary to use a copoly
28 mer containing higher than 70 wt% to 85 wt% of ethylene. If the
.~ 29 ethylene content is 70 wt% or lower than 70 wt%, the resulting compo-
s;tion is poor in clarity and stiffness. If the ethylene content is
31 higher than 85 wtX, the resulting composition is poor in clarity and
32 impact resistance. In either case, the resulting composition lacks
33 the balance between stiffness and impact resistance.
34 The ethylene-propylene copolymer desirably will have a
density of 0.875 to 0.915 g/cm3, preferably 0.885 to 0.903 g/cm3,
36 depending on ethylene content. In addition, the ethylene-propylene
37 copolymer will desirably have an MFR of O.OOl to lO g/lO min, prefer-
38 ably O.Ol to 5 g/lO min.
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1 Preparation of the Composition
2 The composition of this invention is prepared by mixing 65 to
3 95 wt%, preferably 75 to 90 wt%, of crystalline polypropylene and S to
4 35 wt%, preferably 10 to 25 wt%, of the ethylene-propylenP random
copolymer. If the amounts are outside the broad limits, the object of
6 this invention is not achieved. The two components may be mixed by
methods well known such as, for example, by using a mixing apparatus
8 such as V-blender, ribbon blender, and Henschel mixer, or a kneader
~ such as extruder, calender roll, and Banbury mixer. The composition
of this invention may be incorporated with a variety of additives
11 accordin~ to the intended use, such as antioxidants, UV stabilizers,
12 anti-slip agents, and anti-block agents.
13 Effect of the Invention
14 The composition of this invention is superior in clarity as
well as mechanical properties, particularly impact resistance at low
16 temperatures. Especia11y, a good effect is produced when the compo-
17 sition contains an ethylene-propylene copolymer which is polymerized
18 with a carboxylic aeid ester having both ester linkage and ether
19 linkage. The invention is now described in more detail with reference
to the following examples, in which % means wt% unless otherwise
21~ noted.
2? Example 1
23 Sythesis of Ethylene-Propylene Copolymer
24 Preparation of Catalyst Component
~5 Into a steel ball mill, with the atmosphere replaced with
26 argon, was charged 240 9 of commercial titanium trichloride of type
2i AA. Then a reaction product of diethyl ether (12 9) and titanium
28 tetrachloride (2.5 9) was added. The components were pulverized for
29 10 hours to give the catalyst component.
Copolymerization of Ethylene and Propylene
31 Into an autoclave were charged 250 mg of the catalyst compo-
32 nent obtained as mentioned above, diethylaluminum chloride in an
33 amount corresponding to 3 gram mol for 1 gram atom of titanium in the
34 catalyst comPonent~ ethyl p-anisate (abbreviated as EPA) in an amount
of 20 molX based on the diethylaluminum chloride, 600 ml of n-heptane,
36 and 100 ml of hydrogen. Reaction was carried out at 70C for 1 hour
37 while feeding to the autoclave an ethylene-propylene mixture gas
3~ (molar ratio ~ 1.1). The resulting polymer slurry ws placed in
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1 methanol, and the polymer precipitates were washed thoroughly with hot
2 n-hexane, followed by drying under vacuum. Thus, there was obtained
3 an ethylene-propylene random copolymer having a density of 0.895
4 g/cm3 and an MFR of 0.02 g/lO min.
Preparation of Composition
6 The ethylene-propylene copolymer obtained as mentioned above
7 was mixed with crystalline polypropylene (Y203, a product of Tonen
8 Sekiyu Kagaku Co., Ltd.) having a MFR of 3 g/lO min and an Hl of 95.5%
9 at a ratio of l5% to 85%. Mixing was carried out for 5 minutes by
using a Brabender Plastometer at 200C and lO0 rpm. Thus there was
11 obtained a composition of this invention.
12 The composition was made into test specimens by melt pressing
13 (heating at 2l0~C for 3 minutes, and compressing under lO0 kg/cm2
14 for l minute, followed by water cooling). The test specimens were
used to determine the physical properties of the composition. The
16 results are shown in Table l. Flexural moqulus was measured according
17 to ASTM D790-66, and Izod impact strength was measured according to
18 AST~l D256-56 (at 23~C and -20C,- with a notch). Haze was measured
19 with a hazemeter (HGM-2 ~ a product of Suga Shikenki Co., Ltd.) using
a 0.5 mm thick speeimen formed by pressing.
21 Example 2 and Comparative Examples l to 3
22 Several kinds of ethylene-propylene copolymers which are
23 different in ethylene content were synthesized in the same way as in
24 Example l, except that the ratio of ethylene to propylene in the
mixture gas was changed. Compositions were prepared from these
26 copolymers in the same way as in Example l, and test specimens were
?7` prepared from the compositions for measurements of physical proper-
28 ties. The results are shown in Table l.
29 Comparative Example 4
An ethylene-propylene copolymer containing 75% of ethylene
31 was produced in the same way as in Example l, except that the polymer-
32 ization catalyst lacked EPA. A composition was prepared from this
33 copolymer in the same way as in Example l and test specimens were
34 prepared from the composition for measurements of physical proper-
ties. The results are shown in Table l.
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1 Examples 3 and 4 and Comparative Examples 5 and 6
2 Polypropylene compositions were prepared in the same way as
3 in Example l, except that a change was made in the mixing ratio of
4 cry~talline propylene and ethylene-propylene copolymer. ~he physical
properties of the compositions were measured. The results are shown
6 in Table 2.
7 Comparative Examples 7 to lO and Re~erential Example
8 Polypropylene compositions were prepared in the same way as
9 in Example l, except that the ethylene-propylene copolymer was
replaced by ethylene-propylene rubber (EPR), low-density polyethylene
11 (LDPE), or high-density polyethylene (HDPE). Their physical proper~
12 ties were measured. The results are shown in Table 3. Referential
13 example in Table 3 indicates the physical properties of the crystal-
14 line polypropylene (PP) used in Example l.
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Description of the polymers used:
16 EPR : EP07P~ a product of Japan Synthetic Rubber Co.~ Ltd.
17 (polymerized with a vanadium catalyst), MFR (230C):
18 0.7, density: 0.86 g/cm3, ethylene content: 72%.
19 LDPE : 8012, a product of Nippon Unicar Co., Ltd., MI (l90C):~0 0.25, density: 0.924 9/cm3.
21 HDPE : B601 ~ a product of Tonen Sekiyu Kagaku Co., Ltd., MI
22 (l90C~: 0.25, density: 0.954 g/cm3.
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