Polyolefin polymers compositions have gained wide acceptance and usage in numerous commercial applications because of the relatively low cost of the polymers and the desirable properties they exhibit. Such commercial applications include plastic film, such as cast and oriented films. The plastic film can be used for food and commercial product packaging, containers for food, and medical devices such as syringes. It is very important for materials used as packaging for foods, medical devices, and other commercial products, that the presence or absence of impurities or foreign substances such as refuse or the like in the contents of a container can be externally confirmed. It is not desirable that the color tint of the contents be changed when it is observed through the container. For this reason, it is desired to use a polymer composition of high transparency, high gloss and good color, in these fields. Moreover, in recent years, the film industry is requesting polymer compositions with improved tensile properties in order to facilitate processability.
In an attempt to provide homopolymer products capable of withstanding commercial stretching ratios, it is known to adjust the amorphous or solubles content of the homopolymer from about 4.2% weight (% wt) to about 6.0% wt. The tensile strength of these increased amorphous containing polymers is still low relative to ethylene random copolymers. Ethylene randoms containing 0.3% to 0.7% by weight of ethylene are typically used to obtain a good balance between processability and mechanical properties for oriented propylene film. Incorporation of ethylene in amounts greater than 0.5% weight tends to result in a softer product having a low tensile modulus. Further, ethylene random films tend to show visible signs of aging such as a "grease" or "bloom" layer developing on the surface of the film which adversely effects the clarity of the film.
Antiblock agents have been typically used in polymer films to prevent the blocking (or sticking together) of the polymer film. However, these antiblock agents have an adverse effect on the optical properties such as haze and gloss of the polymer film.
Low hexane extractables content copolymer is very desirable because the U.S. Food and Drug Administration ("FDA") has specific solubles requirements that polyolefin copolymers must satisfy in order to be used for food or medical applications. As noted previously, ethylene random copolymers are typically used for food and medical packaging. However, ethylene randoms may require an additional washing step during manufacture to meet the FDA hexane extractables limits.
It would be of advantage to provide improved random copolymers, and films thereof including a process for producing the improved copolymers, having an improved balance of good optical properties such as low haze, low blooming, good color, low yellowing, and low hexane extractables, low xylene solubles levels, improved tensile strength and high stiffness.