WO2000061677A1

WO2000061677A1 - Film wrap composition and method

Info

Publication number: WO2000061677A1
Application number: PCT/US2000/008298
Authority: WO
Inventors: Cheol Yong Cha; Young Bae Park
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 1999-04-14
Filing date: 2000-03-28
Publication date: 2000-10-19
Anticipated expiration: 2001-10-14
Also published as: KR20000066184A; AU4180300A; KR100324295B1

Abstract

The present invention relates to a film-wrap composition comprising (A) 96-99 wt % of a mixture consisting of 35-40 wt % of a linear low density polyethylene, 35-40 wt % of a low density polyethylene, 20-25 wt % of an ethylene butene polymeric resin modifier and 1-4 wt % of a processing aid; (B) 1-4 wt % of a mixture consisting of 10-20 wt % of an anti-dewing agent, 20-30 wt % of an antistatic agent, 10-20 wt % of a soybean oil and 45-55 wt % of polybutene; and (C) 3-5 wt % of EPDM based on the total weight of a blend of (A) with (B). The invention also relates to a process for forming film-wrap by extrusion of the film-wrap composition, obtained by mixing components (A), (B) and (C), through a T-die. The resulting film-wrap is suitable for use with microwave ovens.

Description

FILM WRAP COMPOSITION AND METHOD

Background of the Invention

Film-wrap materials, suitable for packaging fresh or processed foods, are very thin with a thickness range of from 8μm to 20μm (0.08-0.02mm). Preferably, for food packaging, film-wrap should exhibit the following properties: Protection of Packaged Food

1. Physical properties - strength, tear-resistance, dispensability and shrinkage.

2. Barrier properties - moisture-proof, waterproof, and air resistant. 3. Stability - resistant to water, acid, oil, heat and cold.

4. Environmental - non-toxic. Convenience for Use

1. Suitable cling characteristics for packaging.

2. Easy dispensability in terms of cutting and unwind. Product Quality

1. Suitable transparency to observe the contents of the package.

2. Moisture repellant.

3. Glossy, smooth, clean looking appearance. Material Cost 1 Since it is used as a consumable material, film-wrap should be inexpensive.

Film wrap with these properties represents a suitable material for packaging food. Materials used for conventional film-wrap include polyvinyl chloride (PVC), polyvinyhdene chloride, polybutadiene, ethylvinylacetate (EVA), low density polyethylene (LD-PE), etc. Low cost film-wrap for domestic use include those made from LD-PE, PVC, polyvinyhdene chloride and polybutadiene. Polyvinyl chloride film-wrap is commonly used for commercial applications.

Film-wrap made from PVC has good transparency, but such wrap is known to generate hydrogen chloride and chlorine gas at a high temperature. These gases and other PVC decomposition products, are harmful to humans and represent potential carcinogens. While film-wrap made from LD-PE is harmless to humans, it is not particularly convenient for use due to low strength and insufficient transparency. Korean Patent Publication No. 90-414 addressed these problems using a blend (A) of linear low density polyethylene ("LLD-PE", an additive approved by FDA in the U.S.), which is safe, strong and inexpensive, low density polyethylene ("LD-PE") and a polyolefin-based resin modifier, with an additive (B) comprising a surfactant, a corn oil, a stearic acid, polybutene and a petroleum resin. The resulting formulation was processed using conventional extrusion methods.

Though LLD-PE has good strength, is non-polluting and inexpensive, it is unsuitable for preparing film-wrap due to its poor transparency, inadequate cling, reduced anti-fogging and other properties. However, publication KR 90-414 provides a LLD-PE wrap film with transparency by minimizing crystallization of LLD-PE using an appropriate amount of a petroleum resin. Further improvement in transparency occurs with addition of polybutene which normally acts to provide tackiness. The method for preparing film-wrap from this material is expensive and subject to moisture condensation because of difficulties in uniformly distributing surfactant throughout the composition. This problem may be solved according to Korean Patent Publication No. 97-65599 using an alternative film wrap made by mixing (A) a blend comprising LLD-PE, LD-PE, a polyolefin-based resin modifier and a processing aid in a proper ratio with (B) an additive comprising a surfactant, liquid oil (e.g., soybean oil, vegetable oil, sesame oil, or corn oil), polybutene and an antistatic agent in a proper ratio; adequately kneading the mixture in an extruder; and extruding a film using a T-die. Film-wrap, prepared by this method, needs no additive to improve transparency. It is highly flexible and impact-resistant. Since a large amount of the mixture can be extruded with a T-die, costs can be reduced. Also, uniform dispersion of surfactant, using T-die extrusion, can prevent moisture condensation and improve the smoothness of the film. The initial use of film-wrap was mainly for sealing and packaging food at room temperature or below. Recently, however, there has been increasing use of film- wrap in homes and restaurants to retain the moisture and flavor of food prepared by boiling or heating in a microwave oven. This application requires a film-wrap preferably possessing heat-resistance, along with the desirable properties mentioned previously. Although conventional film-wraps perform satisfactorily for simple sealing or packaging use, they often tear under the pressure of vapor generated during boiling of greasy food in high temperature ovens. Moreover, after removal from the oven, the expanded film-wrap does not recover to its original state, but tends to sag into contact with the warmed food as the water vapor pressure decreases. This raises concerns about potential for food contamination and leads to the need for previously undisclosed improvement in heat-resistance of a film- wrap packaging films.

Summary of the Invention The present invention overcomes the drawbacks discussed above by providing a film-wrap having heat-resistance, suitable shrinkage, flexibility and cling characteristics as well as the benefits associated with conventional film-wraps. More particularly, the present invention provides a safe, microwave-compatible, film- wrap which has desired strength, shrinkage, transparency, with suitable barrier properties including moisture and oil repellency.

Detailed Description of the Invention The present invention satisfies the need for a film-wrap with superior heat- resistance and shrinkage, using ethylene propylene diene monomer (EPDM, an additive approved by the FDA) to provide film-wrap packaging with physical properties suitable for use in a microwave oven.

The film- wrap composition comprises (A) 96-99 wt % of a mixture consisting of 35-40 wt % of a linear low density polyethylene (LLD-PE), 35-40 wt % of a low density polyethylene, 20-25 wt % of an ethylene butene polymer resin modifier and 1-4 wt % of a processing aid; (B) 1 -4 wt % of a mixture consisting of 10-20 wt % of an anti-dewing agent, 20-30 wt % of an antistatic agent, 10-20 wt % of a soybean oil and 45-55 wt % of polybutene; and (C) 3-5 wt % of EPDM based on the total weight of a blend of (A) with (B).

A film-wrap, particularly suitable for use in a microwave ovens, may be formed after mixing the components (A), (B) and (C), using extrusion equipment that includes a T-die.

The wrap film according to the invention comprises conventional components of a wrap film such as an ethylene butene polymer resin modifier for improving low temperature impact-resistance, a processing aid for improving surface roughness, a soybean oil for improving release characteristics, and polybutene for improved cling. The film further comprises EPDM for superior heat-resistance and shrinkage. Accordingly, the film- wrap of the present invention has superior heat -resistance, as well as the advantages, previously discussed, of prior art film- wrap packaging films.

The following examples are representative of the present invention but should not be construed as limiting in scope.

Examples 1-3

Films having a thickness of 11 μm were extruded through a T-die at a temperature of 270°C, using resin compositions comprising (A) 98.3 wt % of a mixture consisting of 37.5 wt % of LLD-PE, 37.5 wt % of LD-PE, 23 wt % of a resin modifier and 2 wt % of a processing aid; (B) 1.7 wt. % of another mixture consisting of 48.13 wt % of polybutene, 15.09 wt % of a soybean oil, 14.15 wt % of an anti-dewing agent and 22.62 wt % of an antistatic agent; (C) 3 wt % (Example 1), 4 wt % (Example 2) and 5 v . % (Example 3) of EPDM based on the total weight of a blend of (A) with (B).

Comparative Examples 1-4

A commercial film-wrap, "FRESH WRAP" available from Minnesota Mining and Manufacturing Company (3M) (Comparative Example 1) which contains no EPDM, and three films, extruded as described for the previous examples, respectively containing 1 wt % (Comparative Example 2), 7 wt % (Comparative Example 3) and 9 wt % (Comparative

Example 4) of EPDM based on the total amount of a blend of components (A) and (B), were provided as comparative examples.

Heat Resistance Test The film- wraps of Examples 1-3 and Comparative Examples 1-4 were cut into strips 20mm wide and 100mm long to provide three samples for each wrap film. Weights of 30g were hung at the ends of these samples in a Dispatch™ oven at a temperature of 100°C. The increased length of the samples were measured after 30 minutes. The results are shown in Table 1 below. Also, the same test was performed with air flow blocked from both sides in the oven. The results are shown in Table 2. Table 1

The results clearly show that film-wrap samples of the present invention, prepared by adding a specific amount, i.e., 3-5 wt. %, of EPDM show less extension and increase in length at a high temperature than conventional film- wrap, which do not contain EPDM or which contains EPDM in an amount outside of the range required for the present invention. This proves that the wrap films of the present invention have stability at a high temperature, i.e., superior heat-resistance.

Dimensional Stability Test

Bowls containing food were covered and sealed with wrap films of Examples 1-3 and Comparative Examples 1-4, and heated in a microwave oven for a determined period of time. The condition of the film-wrap was observed after the bowls were taken from the oven. Conventional film- wrap of Comparative Example 1 sank, i.e. sagged towards the food, without recovering to the original state. In contrast, the films of Examples 1-3 of the present invention recovered substantially to their original state without touching the food.

As stated above, the film- wrap of the present invention has superior heat-resistance when compared to the conventional films, thereby solving the problem of film rupture at high temperature. Even after being expanded by the pressure of water vapor, films of the present invention quickly recover to their original state by elastic shrinkage. Thus, they retain a relatively stretched condition when removed and allowed to cool after being heated in a microwave oven. Films according to the present invention also have superior flexibility and cling suitable for use in a microwave oven.

The examples set forth above are merely to illustrate the invention. Various modifications and alterations that do not depart from the scope and spirit of the invention will become apparent to those skilled in the art. Any modified and altered examples are also considered to be included within the scope of the following claims.

Claims

ClaimsWhat is claimed is:

1. A film-wrap composition, comprising: (A) 96-99 wt % of a mixture of 35-40 wt % of a linear low density polyethylene,

35-40 wt % of a low density polyethylene, 20-25 wt % ofan ethylene butene polymer resin modifier and 1-4 wt % of a processing aid;

(B) 1 -4 wt % of a mixture consisting of 10-20 wt % of an anti-dewing agent, 20-30 wt % ofan antistatic agent, 10-20 wt % of a soybean oil and 45-55 wt % of polybutene; and

(C) 3-5 wt % of EPDM based on the total weight of a blend of (A) with (B).

2. A method of making a film, comprising the steps of: providing a film-wrap composition comprising: (A) 96-99 wt % of a mixture of 35-40 wt % of a linear low density polyethylene,

(B) 1-4 wt % of a mixture consisting of 10-20 wt % of an anti-dewing agent, 20-30 wt % ofan antistatic agent, 10-20 wt % of a soybean oil and 45-55 wt % of polybutene; and

(C) 3-5 wt % of EPDM based on the total weight of a blend of (A) with (B); and extruding film through a T-die.