Propylene polymer blends, processes of producing the same...

Details Propylene polymer blends, processes of producing the same... Propylene polymer blends, processes of producing the same...

1998-05-20

2001-11-20

Wilson, Donald R. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S216000, C525S322000, C525S323000, C524S451000, C524S394000, C524S399000, C524S108000, C524S132000

Reexamination Certificate

active

06319991

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to propylene polymer blends, processes of producing the same and polypropylene resin compositions comprising said polymer blends as a main component. More particularly, the invention relates to propylene polymer blends, polypropylene resin compositions which are excellent in transparency, stress-whitening resistance and low-temperature impact resistance and processes of producing said propylene polymer blends by a vapor phase polymerization.
BACKGROUND OF THE INVENTION
Polypropylene resins are relatively cheap and have excellent thermal and mechanical properties, and so have been used in a wide variety of the fields. In general, however, a propylene homopolymer has high rigidity, but is inferior in impact resistance, especially low-temperature impact resistance. As a composition containing the propylene homopolymer improved in low-temperature impact resistance, there has been employed in each of industrial fields including automobiles and household appliances, a propylene block copolymer composition wherein the propylene homopolymer is initially produced and subsequently an ethylene-propylene random copolymer component is produced.
Those propylene block copolymer compositions which have been used hitherto are excellent in impact resistance, but inferior in transparency to homopolymer and have a high whitening on impacting. As a method to improve the disadvantage of whitening on impacting in the propylene block copolymer, there have been proposed the method of increasing the ethylene content in the copolymer and the method of adding polyethylene to the propylene block copolymer composition. Both methods are excellent in improving the whitening on impacting, while lowering the transparency of the product.
JP-A-5-331327 discloses a polymer composition comprising a propylene block copolymer composition with the specified ratio of the intrinsic viscosity of a propylene homopolymer component to that of an ethylene propylene random copolymer component.
JP-A-6-145268 discloses a polymer composition with the specified intrinsic viscosity of a propylene homopolymer component, the specified ratio of the intrinsic viscosity of a propylene homopolymer component to that of an ethylene propylene copolymer component and the specified ethylene content in the ethylene propylene random copolymer component.
JP-A-56-72042 discloses a polyolefin resin composition comprising an ethylene-propylene block copolymer and an ethylene polymer.
JP-A-57-63350 discloses a propylene copolymer composition comprising a propylene-ethylene block copolymer and an ethylene-alpha olefin copolymer.
Those polymer compositions have been more improved than conventional propylene polymer blends in respect of the impact-whitening resistance and transparency from the measured result of haze for the injection-molded articles of the polymer compositions, but more improvements have been desired for the polymer compositions. In addition, blending various components may bring about unbalance of the properties due to scattered dispersibility of each component in the final product.
SUMMARY OF THE INVENTION
An object of the invention is to provide a propylene polymer blend having excellent balance of various properties such as transparency, stress-whitening resistance and low-temperature impact resistance, etc., and a process of producing the polymer blend.
Another object of the invention is to provide a polypropylene resin composition comprising said propylene polymer blend as a main component, suitable for the production of the molded articles having excellent balance of various properties such as transparency, stress-whitening resistance and low-temperature impact resistance, etc.
Other objects of the invention will be apparent from the description mentioned later.
As a result of various investigations to attain the above-described objects, we have found that a propylene polymer blend comprising (A) a propylene-&agr;-olefin random copolymer and (B) a propylene-&agr;-olefin random copolymer with different &agr;-olefin contents from the random copolymer (A) has excellent balance of the transparency, stress-whitening resistance and low-temperature impact resistance, when the intrinsic viscosity of the copolymer B, the ratio of the intrinsic viscosities of both copolymers and a product of the intrinsic ratio of both copolymers and the weight ratio of both copolymers are within the the prescribed ranges.
In accordance with the present invention there is provided a propylene polymer blend comprising (A) a propylene-&agr;-olefin random copolymer with a propylene content of 90 to 99% by weight and (B) a propylene-&agr;-olefin random copolymer with a propylene content of 55 to 90% by weight, wherein the intrinsic viscosity ([&eegr;
B
]) of the copolymer B ranges from 1.3 to 3.5 dl/g, the ratio ([&eegr;
A
]/[&eegr;
B
]) of the intrinsic viscosity ([&eegr;
B
]) of the copolymer B to the intrinsic viscosity ([&eegr;
A
]) of the copolymer A ranges from 0.5 to 1.3 and a product (([&eegr;
B
]/[&eegr;
A
])×(W
A
/W
B
)) of the intrinsic ratio ([&eegr;
B
]/[&eegr;
A
]) of both copolymers and the weight ratio (W
A
/W
B
) of both copolymers ranges from 1.0 to 4.5.
The present invention also provides a process of producing the propylene polymer blend which comprises in sequence:
(a) carrying out a first polymerization step wherein propylene and other &agr;-olefins than propylene are copolymerized in a vapor phase in the presence of a catalyst for a stereoregular olefin polymerization which comprises a combination of a titanium-containing solid catalyst component having an average particle size of 20-300 &mgr;m, an organoaluminum compound of the formula AlR
1
m
X
3−m
wherein R
1
is a hydrocarbyl group of 1-20 carbons, X is a halogen atom and m is a positive number of 3≧m≧1.5, and an organosilicon compound of the formula R
2
X
R
3
Y
Si(OR
4
)
Z
wherein R
2
and R
4
is a hydrocarbyl group, R
3
is a hydrocarbyl group or a hydrocarbyl group containing a hetero atom, X, Y and Z have a relationship of 0≦X≦2, 1≦Y≦3, 1≦Z≦3, and X+Y+Z=4, to produce 90 to 50% by weight of a propylene-&agr;-olefin random copolymer (A) based on the total weight of the polymer blend and then
(b) carrying out a second polymerization step wherein propylene and other &agr;-olefins than propylene are copolymerized to produce 10 to 50% by weight of a propylene-&agr;-olefin random copolymer (B) having a propylene content of 55 to 90% by weight, based on the total weight of the polymer blend.
The present invention further provides a polypropylene resin composition which comprises 99 to 99.9999% by weight of the propylene polymer blend and 1 to 0.0001% by weight of an &agr;-crystal nucleating agent.


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