PROPYLENE POLYMER COMPOSITION

Abstract: Blends of a propylene polymer, an ethylene-vinyl acetate copolymer and optionally a synthetic rubber, with small amounts of a polyterpene resin as a compatabilizer, possess excellent properties for the manufacture of heat-sealable and sterilizable films as well as for the manufacture of molded speciality sealed containers and bottles.

Description: The present invention relates to polymer compositions having remarkable strength and toughness properties, and in particular to blends of a propylene polymer, an ethylene-vinyl acetate polymer, a specific compatabilizer and optionally a synthetic rubber. Parenteral solutions are used in fluid replacement, electrolyte replacement and are vehicles for drug medication. Solutions include blood plasma, platelets, red cells, kidney dialysis solutions, saline solutions and nutritional products. These solutions were initially bottled in glass, but with the introduction of the collapsible parenteral solution bag some years ago airborne contamination was significantly reduced since the flexible bags empty without outside air entering the system. The general requirements of a polymer composition to be used in the manufacture of parenteral solution bags include flexibility, clarity, toughness at low temperatures, heat-sealability, good processability, moisture vapor permeability resistance and ability to be sterilized. The industry is presently employing a highly plasticized polyvinyl chloride (PVC) film for this purpose. Although this resin does meet most of the requirements, a material is preferred that has little or no plasticizer. Also, PVC film is not very resistant to moisture vapor permeability, and consequently a continuing loss of moisture of the parenteral solutions reduces their storage life considerably. Therefore, it is required that the bag be sealed within an overpouch made from a film resin designed to have a low water vapor transmission rate (WVTR). In the manufacture of molded specialty bottles and containers, many of the above-mentioned properties are also desired although other properties might need to be different, e.g. the degree of stiffness might be varied from one application to another. EP-A-41 747 relates to plastic products, e.g. Films, based on polypropylene and an ethylene-vinyl alcohol copolymer. The present invention seeks to provide a polymer composition which is useful e.g. in the manufacture of strong and flexible parenteral solution bag films which are heat sealable and sterilizable, in the manufacture of squeeze bottles and containers, and in the manufacture of containers and of seals for co-called "tear tab" containers. Other aspects of the invention relates to monolayer and coextruded films suitable for manufacture of IV bags. In accordance with the present invention there is provided a polymer composition comprising (a) 10 to 98 wt % of a propylene polymer; (b) 1 to 60 wt % of an ethylene-vinyl acetate copolymer; (c) 0 to 60 wt % of a synthetic rubber; and (d) 0.005 to 1.5 wt %, based on the total weight of (a), (b) and (c), of a polyterpene resin. The propylene polymer component (a) can be a propylene homopolymer, a random copolymer of propylene and ethylene containing from 0.5 to 6 wt % polymerized ethylene and preferably from 1 to 5 wt % of polymerized ethylene, or a mixture of the homopolymer and copolymer. The ethylene-vinyl acetate copolymer (b) should be a high molecular weight resin containing between 3 and 25 wt %, preferably between 4 and 12 wt %, polymerized vinyl acetate groups. The synthetic rubber component (c), if present, is suitably selected from butyl rubber, polybutadiene, polyisobutene, styrene-butadiene rubber, ethylene-propylene rubber and ethylene-propylene-diene terpolymer (EPDM). The polyterpene resin compatabilizer (d) is a thermoplastic polymer produced by the polymerization of terpene hydrocarbons consisting primarily of either beta-pinene or dipentene. These resins are commercially available and have been used as tackifiers and adhesive promoters. For heat sterilizable film applications the preferred composition is a blend comprising: (a) 10 to 50 wt % of the propylene polymer; (b) 10 to 60 wt % of the ethylene-vinyl acetate copolymer; (c) 10 to 60 wt % of the synthetic rubber, and (d) 0.01 to 1.5 wt %, based on the total weight of (a), (b) and (c), of the polyterpene resin. The most preferred ranges for the four components are respectively: (a) 15 to 35 wt %; (b) 30 to 50 wt %; (c) 30 to 50 wt %, and (d) 0.1 to 1 wt % based on the total weight of (a), (b) and (c). One optional component of the resin blend is an agent added in a quantity effective to produce films of improved clarity. Examples of suitable agents are sodium benzoate, dibenzylidene sorbitol and sorbitan monooleate. Usually the agents are added in quantities between 0.1 and 2 wt %, based on the total weight of components (a) to (c). The polymer composition or blend of the present invention is easily processable into blown or cast film products which, in addition to high clarity, exhibit other desirable properties such as flexibility, toughness at low temperatures and heat-sealability. Also, the films have good resistance to moisture vapor permeability and can be steam sterilized at 121°C without significantly affecting their physical properties in a detrimental way. Finally, the films contain no additives, which would prevent their use in food or medical applications, either in direct or indirect contact. The film should usually have a thickness from 76 to 254 µm (3 to 10 mils) for the manufacture of collapsible, flexible parenteral solution bags. In order to improve the read-through clarity of the film prepared from the blend, it is sometimes preferably to coextrude the blend with a propylene polymer, such as the propylene polymer component (a), to produce a composite film of at least two layers. A three-layered composite film with propylene polymer outer layers is within the scope of the invention. For best heat-sealability it is preferred that a two-layered composite film be employed in the manufacture of IV bags with the propylene polymer as the outside film layers. The blend is also useful in the manufacture of flexible containers such as squeeze bottles or tubes. The bottles or tubes can be injection molded or blow molded using any conventional techniques and can be used for containment and dispersion of a variety of viscous materials such as salves, ointments and lotions. Foods and condiments are also packaged with advantage in the squeeze containers. Another embodiment of the present invention relates to resins useful in the manufacture of more rigid bottles and containers having improved tear resistance. Specifically, these resins are particularly desirable for the manufacture of tear tab containers, i.e. containers which are formed, filled and sealed in one manufacturing operation. The seals of the filled containers are broken by manual pulling on the tear tab thereby releasing the container top from the container. It is of real importance that there should be no failures such as breaking or splitting of the tear tab during the opening of the container. The preferred polymer composition for use in the manufacture of containers of improve tear resistance comprises: (a) 90 to 99 wt % of the propylene polymer; (b) 1 to 10 wt % of the ethylene-vinyl acetate copolymer; (c) 0 to 9 wt % of the synthetic rubber; and (d) 0.005 to 1.5 wt %, based on the total weight of (a), (b) and (c), of the polyterpene resin. The most preferred ranges for the four components are respectively: (a) 92 to 98 wt %; (b) 1.5 to 7 wt %; (c) 1.5 to 7 wt %; and (d) 0.01 to 1.0 wt %, based on the total weight of (a), (b) and (c). The present invention will be further described by reference to the following Examples. EXAMPLE 1 A blend was prepared of 18.2 kg (40 pounds) "Polysar"® butyl rubber XC 961, 18.2 kg (40 pounds) of an ethylene/vinyl acetate copolymer (containing about 9.0 wt % vinyl acetate groups), 9.1 kg (20 pounds) of a random copolymer of propylene and ethylene (containing about 2.3 wt % ethylene groups) and 0.23 kg (0.5 pounds) of "Zonarez"® 7115, a polyterpene resin based primarily on dipentene. The blend was used in preparing a blown film of 178 µm (7 mil) thickness. It had excellent toughness, was easily heat-sealable and was flexible. Pouches made from these films were filled with water, heat-sealed and tossed in the air to simulate a 3m (10 foot) drop. All pouches survived at least 6 drops at ambient temperature. EXAMPLE 2 The blend of Example 1 was coextruded with the random propylene/ethylene copolymer component into a 203 µm (8 mil) three-layered film composite with the random copolymer as the outside layers. Table 1 lists the physical properties of the film which also had excellent see-through properties. EXAMPLES 3 - 5 These blends suitable for tear tab bottle production were prepared from the components of Example 1 in the proportions listed in Table 2, which also shows the results of tests performed on the compositions. No failures were observed in tests opening sealed bottles by pulling the tear tabs.

Claims: A polymer composition comprising (a) 10 to 98 wt % of a propylene polymer; (b) 1 to 60 wt % of an ethylene-vinyl acetate copolymer; (c) 0 to 60 wt % of a synthetic rubber; and (d) 0.005 to 1.5 wt %, based on the total weight of (a), (b) and (c), of a polyterpene resin. A composition according to claim 1 wherein the propylene polymer is propylene homopolymer, a random copolymer of propylene and ethylene containing from 0.5 to 6 wt % polymerized ethylene, or a mixture of said homopolymer and copolymer. A composition according to claim 1 or 2 wherein the ethylene-vinyl acetate copolymer contains between 3 and 25 wt % polymerised vinyl acetate groups. A composition according to claim 1, 2 or 3 for use in the manufacture of sterilizable, heat-sealable film comprising 10 to 50 wt % of component (a), 10 to 60 wt % of component (b), 10 to 60 wt % of component (c) and 0.01 to 1.5 wt %, based on the total weight of (a), (b) and (c), of component (d). A composition according to claim 4 comprising 15 to 35 wt % of component (a), 30 to 50 wt % of component (b), 30 to 50 wt % of component (c), and from 0.1 to 1 wt % of component (d) based on the total weight of (a), (b) and (c). A composition according to claim 1, 2 or 3 for use in the manufacture of tear tab bottles comprising 90 to 99 wt % of component (a), 1 to 10 wt % of component (b), 0 to 9 wt % of component (c), and 0.005 to 1.5 wt %, based on the total weight of (a), (b) and (c), of component (d). A composition according to claim 6, comprising 1.5 to 7 wt % of component (b), 1.5 to 7 wt % of component (c), and 0.01 to 1 wt % of component (d) the amount of component (d) being based on the total weight of (a), (b) and (c). A composition according to any one of the preceding claims wherein the synthetic rubber is butyl rubber. A composition according to any one of the preceding claims wherein the polyterpene resin is polymerized primarily from dipentene. A sterilizable, heat-sealable film or flexible container produced from a composition as claimed in claim 4 or 5. A composite film comprising a first layer produced from a composition as claimed in claim 4 or 5 and a second layer coextruded with the first layer and comprised of the propylene polymer of component (a). A composition film according to claim 11 further comprising a third layer of the propylene polymer of component (a) coextruded with the first and second layers and positioned to enclose the first layer between said second and third layers. A tear tab container produced from a composition as claimed in claim 6 or 7.

Inventors: LUCAS, BENNIE M.
Applicants: REXENE PRODUCTS COMPANY (A DELAWARE CORPORATION)
Application year: 1986
Main classification: C08L23
IPC codes: C08J5, C08L23, C08L21, B32B27, C08L101, C08L45, C08L87, C08L31, C08L7