CA1272829A - Clearer blends of polypropylene and ethylene/ propylene copolymer - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A polypropylene composition having superior clarity and good low-temperature impact resistance, said composition comprising 65 wt% to 95 wt% crystalline polypropylene and 5 wt% to 35 wt% of ethylene-propylene random copolymer containing higher than 70 wt% to 85 wt% of ethylene. Such compositions can be used for example in the production of film, sheet or blowmoldings for food packaging.

Description

, FIELD OF TECHNOLOGY
-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.

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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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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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- 5 -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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Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A polypropylene composition which comprises 65 wt% to 95 wt% crystalline polypropylene and 5 wt% to 35 wt% of an ethylene-propylene random copolymer containing higher than 70 wt%
to 85 wt% ethylene wherein said ethylene-propylene random copolymer is produced by copolymerizing ethylene with propylene in the presence of a polymerization catalyst comprising a titanium trichloride containing catalyst component, an organoaluminum cocatalyst and a Lewis base.

2. The polypropylene composition of claim 2 wherein the Lewis base is selected from a carboxylic acid ester, an ether or a ketone.

3. The polypropylene composition of claim 2 wherein the catalyst comprises titanium trichloride, diethylaluminum chloride, and ethyl p-anisate.