Low temperature impact and puncture resistant thermoplastic films and bags therefrom.

DESCRIPTION

This invention relates to thermoplastic films and bag structures made therefrom that have improved impact and perforation resistance properties at low temperature, and high heat resistance. The invention also relates to films and bag structures comprising two layers of films that are formed from different thermoplastic resins. The bag structures are particularly suitable for use as storage containers for frozen foods, and for subsequent heating and / or cooking of food therein such as in hot water or in a microwave oven. The bag structures may include a locking device for a closure with a mutatic interlocking.

In the past, thermoplastic films and bag structures made from them for the storage of food in its refrigerated or frozen state, have used polyethylene as the building material. This type of container or bag is particularly suitable for storing food and surplus food that is intended for subsequent reheating or cooking. The storage bags have been formed based on comparatively low density polyethylene resin, for example polyethylene having a density of about 0.910 to about 0.930 grams per quantum centimeter. However, bags made of said low density polyethylene have no utility for preserving food or surplus food during heating or cooking, since the polyethylene film cannot withstand high temperatures of approximately 101.6 C or higher. Even at temperatures above said aforementioned range, the polyethylene film has a tendency to melt at least partially and stick to the surface of the heating medium or the container.

In order to overcome the above-mentioned disadvantages when using polyethylene films, attempts have been made to use other resins such as polyesters in high temperature environments. However, these films have been found to suffer from hermetic closure problems, such as providing a narrow heat sealing margin, a limitation in manufacturing processes, and are also expensive for disposable bags. In addition, to compensate for the thermal weakness, other thermoplastic resins such as polypropylene, which has a melting point between approximately 156.7 ° C and 162.8 ° C, and where the film structure is relatively thick, can be used at temperatures high cooking, replacing polyethylene. However, although the melting temperature and the suitability properties for use in microwave ovens of thermoplastic resins, such as polypropylene, are higher than those of polyethylene, the main weakness of resins such as those of polypropylene is their lack of properties of low temperature mechanical resistance. That is, at or around freezing temperatures, polypropylene films are fragile, the impact resistance and perforation resistance of the films is low, and the films are likely to develop cracks and stings within them. This last deficiency of polypropylene makes it unsatisfactory for use in the cold storage of food and in the handling of said food containers in the frozen state. That is, when the containers are removed and stirred in a freezer, such manipulation causes the development of tension cracks in the walls of the containers and, after all, leaks and leaks from spills develop from them when the containers They are thawed.

It is also well known that films for food packaging can be formed from a multilayer film such as a laminate of a polyamide and polyethylene, in which an adhesive binder material or layer is disposed between the layers of polyethylene film and of polyamide film. However, said multilayer film materials are generally deficient when used as a container that can withstand overheating or cooking temperatures due to the fact that the thermal resistance of the polyethylene pipe is less than desired.

Thus, it would be desirable to create thermoplastic films and bag structures that could be used as a food storage bag that had improved impact and perforation resistance properties at low temperatures. It would also be desirable to obtain thermoplastic multilayer films and bag structures that will provide improved resistance properties when the films and containers are used at elevated temperatures, such as when a variety of foods are cooked or heated.

The preceding criteria for thermoplastic films and bag structures that have a variety of uses, but which are particularly well adapted over a wide range of temperatures to contain food during storage and handling in freezers, and also during reheating or cooking of food within them, are fulfilled by the present invention.

In one embodiment, the thermoplastic film and the bag structure of this invention comprise a

002 139 inner film layer comprising a mixture of a polypropylene copolymer with a percentage between about 5 percent and about 30 percent by weight of a resin material selected from the group consisting of (a) very low density polyethylene, (b ) polybutylene, (c) an ethylene-methyl acrylate copolymer, and (d) polyisobutylene, based on the weight of the mixture; and an outer film layer of a resin material having a melting temperature that is higher than that of the inner film layer.

In a further embodiment, the thermoplastic film and the bag structure of this invention comprises an inner film layer comprising a mixture of a polypropylene copolymer with a percentage between about 5 percent and about 30 percent by weight of a mixture of resin materials, selected from the group consisting of (a) very low density polyethylene and polybutylene, (b) very low density polyethylene and an ethylene-methyl acrylate copolymer, (c) very low density polyethylene and polyisobutylene, (d) polybutylene and an ethylene-methyl acrylate copolymer, (e) polybutylene and polyisobutylene, and (f) an ethylene-methyl acrylate and polyisobutylene copolymer, based on the weight of the mixture; and an outer film layer of a resin material having a melting temperature that is higher than that of the inner film layer.

As indicated from the foregoing, the inner film layer of the multilayer film and the bag structure of this invention provides the same mechanical resistance properties at low temperatures, such as impact resistance and strength. drilling, while also having the ability to withstand high temperatures such as those that occur during cooking or reheating food. The outer film layer of the multilayer film and the pouch structure of this invention serves to keep the inner layer of film of mine thermally susceptible, in contact with food, out of contact with the surfaces of the cooking vessel or heating, and consequently improves the ability of the film and the bag structure to withstand high temperatures.

In yet another embodiment the thermoplastic film and the bag structure of this invention comprises a single layer film comprising a mixture of a polypropylene copolymer with a percentage between about 5 percent and about 30 percent by weight of a material of resin selected from the group consisting of (a) very low density polyethylene, (b) polybutylene, (c) an ethylene-methyl acrylate copolymer, and (d) polyisobutylene, based on the weight of the mixture.

In still another embodiment, the thermoplastic film and the bag structure of this invention comprise a single layer film comprising a mixture of a polypropylene copolymer with a percentage between about 5 percent and about 30 percent by weight of a mixture of resin materials selected from the group consisting of (a) very low density polyethylene and polybutylene, (b) very low density polyethylene and an ethylene-methyl acrylate copolymer, (c) very low density polyethylene and polyisobutylene, (d) polybutylene and an ethylene-methyl acrylate copolymer,

002 139 (e) polybutylene and polyisobutylene, and (f) a copolymer of ethylene-methyl acrylate and polyisobutylene, based on the weight of the mixture.

The polypropylene copolymer material, present in the film and in the bag structure of this invention, is preferably a random polypropylene-ethylene copolymer resin, having a melt flow rate or melt index between about 3 decigram per minute and approximately 10 decigram per minute, and a density of approximately 0.90 g / cm³, as commercially available from Himont, Inc., Wilmington, Delaware, under the trade names PRO-FAX® SA-861 and PRO-FAX® SA-752, or from Exxon Chemical Americas, Houston, Texas, under the designation PD - 9012, since said polypropylene copolymer material has desirable extrusion characteristics and physical properties to be used in this case. In addition, the poly (propylene-ethylene) copolymer material preferably contains up to about 5 percent by weight of a standard batch material (mother mix) of slip agent selected from the group consisting of (a) about 95 percent in polypropylene weight having a melt flow rate of about 12 decimals per minute, and about 5 percent by weight of a sliding agent of the erucamide type, as available from Ampacet, Mount Vernon, New York, under the designation Product 40254, and (b) about 95 percent by weight of a polyethylene-methyl acrylate copolymer having a melt index of about 2 tenths per minute and approximately 5 percent by weight of a sliding agent of the erucamide type, such as is available from Ampacet, Mount Vernon, New York, under the designation Product 10110.

In the best way of carrying out this invention, the polyisobutylene material, present in the inner film layer of the multilayer film structures, comprises a polyisobutylene material having a melt flow rate between about 0.3 and about 10.0 decigrams per minute, and a specific density between approximately 0.90 g / cm³ and about 0.92 g / cm³. Such polyisobutylene materials are available from Exxon Chemicals, Linden, New Jersey, under the designation of Exxon PA-30 and VISTANEX3 polyisobutylene. Very low density polyethylene comprises a material that has a density between approximately 0.88 g / cm³ and about 0.90 g / cm³, and a melt index between about 0.3 and about 2.0 decimals per minute, as available from Union Carbide Corporation, Danbury, Connecticut, under the designation UCAR FLX DFDA-1137. The polybutylene material may comprise one that have a melt index between about 2 and about 8 grams per 10 minutes, and a density of about 0.91 g / cm³ as available from Shell Chemical Company, Dakbrool, Illinois, under the designation Shell 8340. The ethylene-methyl acrylate copolymer material may be one having a melt index between about 1 and about 10 grams per 10 minutes, and a density of about 0.94 g / cm³, as available from Gulf Oil Chemicals Company, Orange, Texas, under the designation Gulf PE 2207.

It has been found that polypropylene homopolymers generally have lower impact resistance properties at low temperature, as compared to polypropylene copolymers. For example, copolymerization of propylene with ethylene would improve the low temperature impact resistance properties of those. However, as the ethylene content in propylene-ethylene copolymers is increased, this also undesirably decreases its melting point, and the film, or the film structure made from it, loses its physical stability at elevated temperatures, due to For example, at temperatures that can be found during cooking conditions in microwave ovens, this is between about 121.1 ° C and about 148.9 ° C.

In accordance with the present invention, it has been found that the polypropylene copolymer material, when mixed with a percentage between about 5 percent and about 30 percent by weight, preferably between about 5 percent and about 20 percent by weight, of a material selected from the group consisting of (a) very low density polyethylene, (b) polybutylene, (c) an ethylene-methyl acrylate copolymer, (d) and polyisobutylene, and

002 139 (e) mixtures thereof, provides a multilayer film and a multilayer film structure, which have improved impact and puncture resistance properties at low temperature and which are also stable at temperatures up to about 148.9 ° C.

Also, when very low density polyethylene, polybutylene, or a copolymer of ethylene methyl acrylate are used, in combination with approximately similar amounts of isobutylene to a total concentration of approximately 20 percent by weight, based on the weight of the film, the film and film structure, based on polypropylene, you have better impact and puncture resistance properties at low temperature than when either very low density polyethylene, polybutylene, an ethylene-methyl acrylate copolymer, or polyisobutylene is mixed alone with polypropylene in equivalent concentrations.

In addition, the resin compositions described above can be used to produce a single layer film suitable for freezer and microwave oven applications, preferably in the form of an appropriate container such as a bag or a sack. In that case, the single layer film comprises the polypropylene copolymer material described above, mixed with a percentage between about 5 percent and about 30 percent by weight, preferably between about 5 percent and about 20 percent by weight of a resin material selected from the group consisting of (a) very low density polyethylene, (b) polybutylene, (c) an ethylene-methyl acrylate copolymer, (d) polyisobutylene, and (e) mixtures thereof, based on the weight of the mixture.

As indicated herein, the improved low temperature mechaonic resistance properties of the films of this invention are provided by incorporating between about 5 percent and about 30 percent by weight, based on the weight of the films, of a resin material selected from (a) very low density polyethylene, (b) polybutene, (c) an ethylene-methylacrylate copolymer, (d) polyisobutylene, (e) mixtures thereof.

It is desired that the films contain at least about 5 percent by weight of said resin materials so that the films are provided with said improved low temperature mechanical resistance properties, and up to about 30 percent by weight of said materials of resin since higher amounts generally undesirably reduced the melting point of the films, making them less resistant to heat. Preferably, the amount of said resin materials present in the films of this invention should not be greater than about 20 percent by weight, based on the weight of the films as high as possible while obtaining the improved properties of low temperature mechanical resistance of the films.

In addition, in the best mode of this invention, the multilayer film comprises an outer film layer of a resin material that contains a melting temperature that is higher than that of the inner film layer. Suitable resin materials for the outer film layer include polyesters such as (ethylene terephthalate) and poly (butylene terephthalate), polyamides such as niloon-6, niloon-6/6, nylon-12, polysulfones, polyaryl sulfones, and mixtures thereof.

However, it is preferred that the outer film layer comprises a polyamide and, more preferably, that the polyamide comprises nylon-6 such as was commercially available under the product designations Capron-8207 and Capron 8209 of the Allied Chemical Company, The polyamide material considered here includes nylon prepared by condensation of a dibaic acid and a diamine, and those formed by polymerization by means of addition reactions of ammonium compounds

002 139 containing as many acid groups as amino groups in the monomer. Examples of the first type of polyamide are nylon-6/6, nylon-6/9, nylon-6/10 and nylon-6/12. An example of a polymerized nylon by the reaction of adding ring compounds and, which is particularly preferred, the nylon-6, polymerized from ε-caprolactam to form polycaproamide. In addition, the copolymers of the aforementioned polyamide materials are also suitable for the outer film layer of the present case.

In the best mode, the multilayer film structure of this invention comprises the inner film layer described above and the external film layer described above, joined together by a tie layer. The bonding layer preferably comprises a polypropylene based bonding resin, such as that available from Chemplex Company, Rolling Meadows, Illinois, under the designation Plexar 2511, or from Mitsui Petrochemical Industries, Ltd., Houston, Texas, under the designation Admer 500 However, other binding materials such as adhesive resins selected from copolymers of ionomers, modified polyolefins, copolymers, ethylene vinyl acetate, ethylene-acrylic acid copolymers, polyolefins grafted with acrylic acid and other multi-methylene compositions can be used. The chemically modified polyolefin can be obtained from a certain number of polyolefin resins, such as high, intermediate and low density polyethylenes, polypropylenes, ethylene-vinyl acetate copolymers, and ethylene-acrylic acid copolymers, which are modified by the provision of functional groups in the polymer, which have a strong affinity for the nylon molecule, and that they form strong bonds with nylon under the heat and pressure that are involved in the coextrusion process. These binding materials are generally commercially available, for example, ionomer copolymers can be obtained from EI. Du Pont de Nemours and Company under the trade name SURLYN® resin Similarly, modified polyolefins are available from the Chemplex Company of Rolling Meadows, Illinois, under the trade name PLEXAR® resins, such as Plexar - 3 which is an ethylene copolymer - Modified vinyl acetate, intended and adapted for coextrusion of cast films. Other suitable multi-polymer compositions include commercially available ones, such as CXA-3101, from EI Du Pont de Nemours and Company. The bonding layer material should comprise an adhesive resin having a high melting point and high heat resistance, and the bonding layer should be sufficient to provide a bond strength, between the inner film layer and the coating layer. external film, at least about 7,874 grams / millimeters of film.

The total thickness of the multilayer film films and structures of this invention preferably ranges between about 0.0127 millimeters and about 0.254 millimeters, more preferably between about 0.0254 and about 0.127 millimeters, and even more preferably between about 0.0381 and about 0.0762 millimeters. The thickness of the inner film layer may vary between about 0.01016 millimeters and about 0.2032 millimeters, and preferably between about 0.0127 millimeters and about 0.0508 millimeters. The thickness of the outer film layer may vary between about 0.00254 and about 0.0254 millimeters, preferably between about 0.00381 millimeters and about 0.02032 millimeters. The bonding layer between the inner film layer and the outer film layer of the multilayer films of this invention can have any appropriate thickness. Typically, the thickness of the bonding layer may be between about 0.00254 millimeters and about 0.0127 millimeters, preferably about 0.00381 millimeters, or the thickness of the bonding layer may vary between about 10 percent and about 20 percent of the total thickness of the multiple films are used to produce food bags or containers, the total thickness of the films was preferably between about 0.01905 and about 0.1016 millimeters.

The multilayer films of this invention can have a ratio of thicknesses of the outer film layer to the inner film layer between about 1: 2 and about 1:20, but the preferred ratio of thicknesses of the outer film layer to The inner film layer was between about 1: 3 and about 1: 8.

It is desired that the multilayer films of this invention have the thicknesses and thickness ratios of the film layers, as mentioned above, since the cost of the material of the outer film layer is topically expensive, but this should be thick enough to protect the inner film layer at elevated temperatures, and the thickness of the inner film layer should be sufficient to obtain a good moisture barrier and high temperature resistance properties, while providing a film that has a toughness throughout its length.

The total thickness of the single layer films of this invention may vary between approximately 6

002 139 0.0127 millimeters and approximately 0.127 millimeters, preferably between about 0.0254 millimeters and about 0.1016 millimeters, and more preferably between about 0.0254 millimeters and about 0.0762 millimeters.

The multilayer films of this invention can be produced by any one of several well known methods. Preferably, the films can be produced by what is commonly known as the slot casting extrusion method. Films can also be produced by what is commonly known as the air blown film extrusion method, but this last method is less preferred. The slot casting method produces a film with better clarity than the other methods known in the technical sector. The multi-layered film can be cast in groove with extrusion equipment using a multi-hole groove casting matrix or a multi-layer adapter for a single-layer groove casting matrix.

In addition, the film structures of this invention can be shaped to give containers such as bags or sacks for food with or without portions reinforced with bevels. For example, the containers may have a reinforcement of bevels or side edges of the side walls of the containers, and / or a portion reinforced with bevel in the bottom portion of the containers. In addition, when the film structures are shaped as containers, the containers may be provided with a closing device such as a simple rope or twisted tie, or the closing device may comprise a locking device with muted interlocking that has any desired structural configuration. Typically, in said case, the closure device is placed next to the mouth portions of the container to facilitate opening and closing of the container.

As indicated above, the film structures of this invention are particularly idyllic for their manufacture in the form of useful bags to contain food that is to be heated to a preparation temperature. These bags are generally defined by a structure that results from folding the film to form a generally U-shaped breast and then closing both ends of the breast hermetically to form a simple bag or sac. In use, the consumer would place the food to be prepared, or reheated, inside the bag and close the upper part by some appropriate means, as indicated above. To form such a bag, the outer layer will be the resin material having a melting temperature that is higher than that of the inner film layer, for example a niloin film for the surface that comes into direct contact with the cooking or reheating vessel. The outer film layer keeps the inner layer of mine thermally susceptible, which is in contact with the food, out of contact with the surfaces of the cooking vessel and, consequently, improves the ability of the bag to withstand high temperatures. Niloin-6, for example, has a melting or adhesion temperature of the order of temperature greater than 21 ° C, is heat stable, and would not adhere or stick to the side walls of the container while food is being reheated or cooked inside him. The bag containing food was intended to be submerged in a fluid, such as water, or used in a microwave to reheat and / or cook.

The invention will be clear and manifest when considered in conjunction with the following examples, which are set forth as merely illustrative of the invention and which are not intended in any way to be limiting thereof. Unless otherwise indicated, all parts and percentages are by weight.

In the following Examples, the films and film structures of this invention were prepared by a groove casting and cpn groove coextrusion process. The materials were dry mixed in a drum type dump mixer and fed to conventional type extruders. The melt existing in the extruder was fed through a coextrusion feed block and a conventional "T" or hanger type die. The extruded material from the die was cast on a typical casting system with deep cooling roller.

In addition, in the following Examples, the impact resistance and puncture resistance of the thermoplastic films of this invention were evaluated as follows. The impact resistance of plastics films was determined by measuring the residual energy of a dart in free fall after passing through the film sample. The instrument, by Kayeness, Inc. Model D - 2090, with cryogenic system (option C), actually measures the dart speed differences, caused by the resistance of the test sample. A dart, of sufficient weight to pass through the film, is dropped from a height, and the energy of the dart in free fall, absorbed by the test sample, is determined from velocity readings obtained by means of Photo - activated digital chronographs, located below the test sample. This test procedure follows the

002 139 ASTM D-4272-83.

The puncture resistance of plastic films was determined using an Instron Tensile - Compressian Tester model No. 1122 test device with an Environmental Chamber part No. 3111-541. In this test, a probe is passed to through a test film at a constant speed of 500 millimeters / minute. The load force required to elastically deform and, finally, drill the test sample, together with the magnitude of the elongation that occurs with a deformation, is recorded. Perforation resistance is defined as the force required to break a test sample and the energy absorbed by the film during breakage.

Example I

To evaluate the low temperature physical properties and suitability for application to food freezers of the film compositions of this invention, energy tests of total impact and peforacian tenacity were performed, as described above, in a structure single-layer polypropylene copolymer film layer, and compared with single layer film structures of modified polypropopylene copolymer. These measurements were made at 0 ° C and at - 17.8 ° C.

The polypropylene copolymer material was a random poly (propylene-ethylene) copolymer resin, which had a melt flow rate of approximately 7 decimals per minute and a density of approximately 0.90 g / cm.³, commercially available from Himont, Inc., Wilmington, Delaware, under the designation PRO - FAX®SA - 861.

The materials used to modify the single layer film structures of polypropylene copolymers will be selected from (a) polybutylene having a melt index of approximately 4 grams per 10 minutes, and a density of approximately 0.91 g / cm³, available from Shell Chemical Company, Oakbrook, Illinois, under the designation Shell 8340, (b) an ethylene-methyl acrylate copolymer having a melt index approximately 6 grams per 10 minutes and a density approximately 0.94 g / cm³, available from Gulf Oil Chemicals Company, Orange, Texas, under the designation Gulf PE 2207;

(c) polyisobutylene having a melt flow rate of approximately 0.50 decimals per minute and a specific density of approximately 0.91 g / cm³, which is a polyisobutylene concentrate per 1 part of polypropylene, available from Exxon Chemicals, Linden, New Jersey, under the designation Exxon PA-30, and (d) very low density polyethylene having a density of approximately 0.8 decigrams per minute, available from Union Carbide Corporation, Danbury, Connecticut, under the designation UCAR FLX DFDA-1137.

The modifying materials were mixed with the polypropylene copolymer material at a concentration of 10 percent, 20 percent, and 30 percent by weight, based on the weight of the combined polypropylene copolymer and modifier materials; the mixtures were then cast into the film forms, each of which was approximately 0.0508 millimeters thick.

The results of the tests for energy of total impact and perforation toughness in the films containing up to 30 percent by weight of the modifying materials, based on the weight of the film of a single layer of modified polypropylene copolymer, are shown graphically in figures 1 4. In Figures 1-4, PB represents polybutylene, EMA represents the ethylene-methyl acrylate copolymer, PIB represents polyisobutylene, and VLDPE represents very low density polyethylene.

From Figures 1-4, it can be seen that all modifier components have some effect on the low temperature properties of the film at concentrations up to 30 percent. Although the use of modified polyisobutylene shows a significant improvement in impact resistance properties (Figure 1 and Figure 2), it is less effective as a modifier of low temperature drilling energy (Figure 3 and Figure 4). Conversely, polybutylene is not such an effective impact modifier, but it provides a significant improvement in perforation toughness to the films. Figures 1-4 illustrate, therefore, how single layer films can be formulated

002 139 according to this invention to provide the most favorable balance of physical properties at low temperature for a particular end use.

Example II

In this Example, it is shown that when very low density polyethylene, polybutylene or an ethylene-methyl acrylate copolymer are used in combination with similar amounts of polyisobutylene to a total concentration of about 10 percent by weight, based on the weight of the film, the single layer film based on polypropylene has better impact properties at low temperature and puncture resistance than when any of these components, or the polyisobutylene, is mixed alone with the polypropylene material of Example I at equivalent concentrations. This synergistic effect on the properties of the films at -17.8 ° C and 0 ° C is shown in Tables I and II. Table I of the impact resistance properties of the films, and Table II shows the improvement in the puncture resistance of the films, as indicated by the increase in perforation energy values. All the films tested had a thickness of approximately 0.0508 millimeters.

TABLE I

Effect of a modifier on the impact resistance of a polypropylene film

<td>Modifier</td><td colspan="2">Impact Energy (Joules)</td>

<td></td><td>- 17.8 ° C</td><td>0 ° C</td>

<td>None</td><td> 0,0854</td><td> 0,0800</td>

<td>10% GDP</td><td> 0,1464</td><td> 0,1587</td>

<td>10% PB</td><td> 0,0800</td><td> 0,1519</td>

<td>5% PB, 5% GDP</td><td> 0,1505</td><td> 0,2956</td>

<td>10% EMA</td><td> 0,1258</td><td> 0,1681</td>

<td>5% EMA, 5% GDP</td><td> 0,1437</td><td> 0,3173</td>

<td>10% VLDPE</td><td> 0,0895</td><td> 0,1248</td>

<td>5% VLDPE, 5% GDP</td><td> 0,1709</td><td> 0,2088</td>

Being:

GDP. - polyisobutylene as in Example I.

PB. - polybutylene as in Example I.

EMA. - an ethylene-methyl acrylate copolymer as in Example I. VLDPE. - Very low density polyethylene as in Example I.

(See Table II on next page)

002 139

TABLE II

Effect of a modifier on the puncture resistance of a polypropylene film

<td>Modifier</td><td colspan="2">Drilling energy (joules / mm)</td>

<td></td><td>- 17.8 ° C</td><td>0 ° C</td>

<td>None</td><td> 5,6055</td><td> 48,3587</td>

<td>10% GDP</td><td> 26,1591</td><td> 41,8634</td>

<td>10% PB</td><td> 16,5496</td><td> 61,3047</td>

<td>5% PB, 5% GDP</td><td> 37,2366</td><td> 76,4307</td>

<td>10% EMA</td><td> 26,2035</td><td> 55,2988</td>

<td>5% EMA, 5% GDP</td><td> 28,7839</td><td> 81,0575</td>

<td>10% VLDPE</td><td> 15,4374</td><td> 56,1441</td>

<td>5% VLDPE, 5% GDP</td><td> 37,5035</td><td> 80.4791</td>

Being:

GDP - polyisobutylene as in Example I.

PB. - polybutylene as in Example I.

EMA. - an ethylene methyl acrylate copolymer as in Example I. VLDPE. - Very low density polyethylene as in Example I.

Example III

This Example shows the synergistic effect of modifying the inner layer of a polypropylene-based film, which has the same composition as the single layer of Example I, with very low density polyethylene, polybutylene, ethylene-methyl acrylate copolymer, and polyisobutylene , alone or in combination. The inner layer based on polypropylene had a thickness of approximately 0.0394 millimeters. The outer layer of the multilayer film was composed of nylon-6, available as Capron 8209 from Allied Chemical Company, and had a film thickness of approximately 0.00762 millimeters. The inner layer and the outer layer had between them a unioin layer composed of a polypropylene-based unioin resin, available from Mitsui Petrochemical Industries, Inc., Houston Texas, under the designation Admer 500, and which was present in a thickness approximately 0.00381 mm.

The films were prepared by coextrusioin to form multilayer films. Apart from the multilayer control film, all films contained a total of 20 percent by weight of one or more modifier (s).

Table III shows the total impact energy values ​​at low temperature obtained in the multilayer films. It can be seen from Table III that all multilayer film compositions containing either polybutylene, an ethylene-methyl acrylate copolymer, or very low density polyethylene, combined with approximately an equivalent amount of polyisobutylene, had higher heats of total impact energy at low temperature than those obtained for

002 139 the films containing the components of individual modifiers mixed with the polypropylene copolymer. Table III is as follows.

TABLE III

Effect of low temperature imapct modifiers on coextruded multilayer film.

<td>Modification of the polypropylene layer</td><td colspan="2">Impact Energy (Joules)</td>

<td></td><td>- 17.8 ° C</td><td>0 ° C</td>

<td>no modifier</td><td> 0,1736</td><td> 0,3919</td>

<td>20% PB</td><td> 0,1600</td><td> 0,3159</td>

<td>20% EMA</td><td> 0,1695</td><td> 0,4529</td>

<td>20% VLDPE</td><td> 0,2671</td><td> 0,4705</td>

<td>20% GDP</td><td> 0,2495</td><td> 0,1478</td>

<td>10% PB + 10 GDP</td><td> 0,2834</td><td> 0,6075</td>

<td>10% EMA + 10% GDP</td><td> 0,3485</td><td> 0,5221</td>

<td>10% VLDPE + 10% GDP</td><td> 0,3159</td><td> 0,4963</td>

Being:

PB. - polybutylene as in Example I.

EMA. - an ethylene-methyl acrylate co-polymer as in Example I. VLDPE. - Very low density polyethylene as in Example I.

GDP - polyisobutylene as in Example I.

Example IV

In order to evaluate the low temperature impact resistance properties of the film compositions of the film structures of this invention, real end use tests were carried out on bags with a size of 1.1 liters of capacity having a width dimension approximately

177.8 millimeters and a length dimension of approximately 203.2 millimeters. The bags were constructed from the test films shown in Table IV below and filled with water, sealed tightly, and placed in a freezer maintained at a temperature of approximately -20.5 C. After freezing the contents, the bags were systematically manipulated, simulating normal treatment by a consumer in the freezer, defrosted, and examined for holes and cracks in the film, caused by impact stresses. The results are summarized in Table IV.

In Table IV, PP-861 represents a random polypropylene copolymer available from Hercules, Inc. Wilmington, Delaware, under the product designation PRO-FAX®SA-861. The designation 7042 represents a low density polyethylene material. , linear, which has a density of approximately 0.918 g / cm³, available from Union Carbide Corporation, Danbury, Connecticut, under product code 7042. The designation 7047 designates a linear, low density polyethylene material having a density of approximately 0.918 g / cm³, available from Union Carbide Corporation, Danbury, Connecticut, under the product name UCAR FLX DFDA - 1137. The designation Plexar

002 139

2511 represents a polypropylene-based bonding resin, available from Chemplex Company, Rolling Meadows, Illinois, under the product name Plexar 2511. Nylon material - 6 represents a polyamide material available from Allied Chemical Company under the product name Capron - 8209 and that has a density of approximately 1.13 grams per cubic centimeter, and an elóastico limit to the traction of approximately 826 kg / cm² by the ASTM P-638 method.

TABLE IV

Freezer tests of a multi-layer modified polypropylene film

<td colspan="5">Film compositions (millimeters thick)</td>

<td>Movie from test</td><td>Inner layer (0,0292)</td><td>Bonding layer (0.00381)</td><td>External layer (0.00762)</td><td>Handling in freezer, % of failure</td>

<td> 1</td><td>PP - 861</td><td>Plexar 2511</td><td>Nilon - 6</td><td> 58</td>

<td> 2</td><td>PP - 861 + 10% 7042</td><td>Plexar 2511</td><td>Nilon - 6</td><td> 43</td>

<td> 3</td><td>PP - 861 + 10% 7047</td><td>Plexar 2511</td><td>Nylon - 6</td><td> 75</td>

<td> 4</td><td>PP - 861 + 10% 1137</td><td>Plexar 2511</td><td>Nylon - 6</td><td> 26</td>

Being:

PP - 861. - a polypropylene copolymer

7042 . - low density polyethylene

7047 . - low density polyethylene

1137 . - Very low density polyethylene.

It can be seen in Table IV that modifying the composition of the polypropylene inner layer film (film 1) with a very low density polyethylene (film 4) significantly improves the low temperature impact resistance properties of the film of multiple layers, as reflected by the much lower percentage of bag failures in the freezer handling test. It can also be seen from the test results, shown in Table IV, that modifying the composition of the polypropylene inner layer film (film 1) with a very low density polyethylene (film 4) provides greater Improved properties of low temperature impact resistance of a polypropylene than a polypropylene mixed with a low density polyethylene material (films 2 and 3).

To show even more the advantages of very low density polyethylene (VLDPE) as a low temperature impact modifier for a polypropylene film, low temperature impact resistance (0^°C) was determined on single layer polypropylene films modified with very low density polyethylene or with low density polyethylene in concentrations of 10 percent, 20 percent, and 30 percent by weight of the films. In the very low density it is significantly more effective than a low density polyethylene, and especially at concentrations of 20 percent and 30 percent. All the films tested in this Example were approximately 0.0508 millimeters thick.

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TABLE V

Low temperature impact tests of modified polypropylene film

<td>Film composer</td><td>Impact energy at 0 ° C (joules)</td>

<td>PP - 861</td><td> 0,0800</td>

<td>PP - 861 + 10% 1137</td><td> 0,1248</td>

<td>PP - 861 + 20% 1137</td><td> 0,5180</td>

<td>PP - 861 + 30% 1137</td><td> 0,8204</td>

<td>PP - 861 +10% 7042</td><td> 0,2373</td>

<td>PP - 861 +20% 7042</td><td> 0,3431</td>

<td>PP - 861 +30% 7042</td><td> 0,3132</td>

Example V

In a separate series of evaluations, multilayer films were extruded, the films were shaped into the form of bags, and actual end-use tests were performed with the bags constructed from the test films described in Example IV . The results are summarized in Table VI below.

(see TABLE VI on next page)

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TABLE VI

Testing in multi-layer film freezer of modified polypropylene

<td colspan="5">Film compositions (millimeters thick)</td>

<td>Movie from test</td><td>Inner layer (0,02921)</td><td>Joint layer (0.00381)</td><td>Cap external (0.00762)</td><td>Freezer handling,% failure</td>

<td> 1</td><td>PP - 861</td><td>Admer 500</td><td>Nilon - 6</td><td> 71</td>

<td> 2</td><td>PP - 861 +10% 8340</td><td>Admer 500</td><td>Nilín - 6</td><td> 58</td>

<td> 3</td><td>PP - 861 +20% 8340</td><td>Admer 500</td><td>Nilín - 6</td><td> 54</td>

<td> 4</td><td>PP - 861 +10% 2207</td><td>Admer 500</td><td>Nilon - 6</td><td> 33</td>

<td> 5</td><td>PP - 861 +20% 2207</td><td>Admer 500</td><td>Nilín - 6</td><td> 25</td>

<td> 6</td><td>PP - 861 +15% PA30</td><td>Admer 500</td><td>Nilín - 6</td><td> 25</td>

<td> 7</td><td>PP - 861 +30% PA30</td><td>Admer 500</td><td>Nilín - 6</td><td> 25</td>

<td> 8</td><td>PP - 861 +10% 1137</td><td>Admer 500</td><td>Nilon - 6</td><td> 38</td>

<td> 9</td><td>PP - 861 +20% 1137</td><td>Admer 500</td><td>Nilín - 6</td><td> 29</td>

<td> 10</td><td>PP - 861 +10% 8340</td><td></td><td></td><td></td>

<td></td><td>+15% PA30</td><td>Admer 500</td><td>Nilon - 6</td><td> 13</td>

<td> 11</td><td>PP - 861 +10% 2207</td><td></td><td></td><td></td>

<td></td><td>+15% PA30</td><td>Admer 500</td><td>Nilon - 6</td><td> 25</td>

<td> 12</td><td>PP - 861 +10% 1137</td><td></td><td></td><td></td>

<td></td><td>+15% PA30</td><td>Admer 500</td><td>Nilon - 6</td><td> 9</td>

Being:

PP - 861. - a random polypropylene copolymer.

8340 . - polybutylene.

2207 . - an ethylene-methyl acrylate copolymer.

PA30. - a polyisobutylene concentrate (GDP: pp 2: 1)

1137 . - very low density polyethylene

Admer 500 - a polypropylene based bonding resin

Table VI shows an improvement in reduced freezer handling failures for all test films 2 through 12, compared to control test film 1. In addition, the preferred structures, test films 10 and 12, show mine low percentage of freezer handling failure, and proportional also a favorable synergistic effect of using polybutene or very low density polyethylene, in combination with polyisobutylene, in comparison with a mixture of polyisobutylene and any of the other components, or any of the components of solo modifiers, with the polypropylene copolymer material.

Example VI

This Example compares, on a qualitative basis, the performance reduction of the containers

002 139 commercially available for use as food storage containers placed in a freezer and / or as food cooking containers. The commercial container products that were evaluated were

one. Ziploc Microfreez Microwave Cooking Bages microwave cooking bags sold by Dow Chemical Company, Midland, Michigan;

two. Seal - A - Meal Boilable Cooking Pouches cooking bags sold by Dazey Products Company, Industrial Aiport, Kansas;

3. Hefty Baggies Extra Protection Freezer Bags Extra Protection Freezer Bags sold by Mobil Oil Corporation, Pittsford, New York;

Four. Reynolds Oven Cookings Bags oven cooking bags sold by Reynolds Metals Company, Richmond, Virginia; Y

5. 1.1-liter Ziploc Heavy Duty Bags hard service bags, sold by Dow Chemical Company, Indianapolis, Indiana.

Initially, the containers were examined for defects such as cracks, tears or holes. The number of defects was totaled and recorded. The Ziploc Microfreez container is generally considered suitable for the aforementioned uses since the multi-layer sidewall construction comprises an inner layer of high density polyethylene having a thickness of approximately 0.0508 millimeters that provides good properties of Impec at low temperature and is thick enough to be abrasion resistant, and also comprises an outer layer of niloin that increases the impact toughness of the walls of the container.

The Seal-A-Meal vessel was also generally considered acceptable for the aforementioned uses since the construction of multi-layer side walls comprises an inner layer of polyethylene having a thickness of approximately 0.0381 millimeters, providing good impact properties. at low temperature and is thick enough to be resistant to abrasion, and also comprises a tough outer layer of polyethylene terephthalate.

The Hefty Baggies container was generally considered as bad for the aforementioned uses since the film material of the side walls was so thin that it made it very fragile, even though it is believed that the composition of the film is very similar to that of the container Ziploc Microfreez.

The Reynolds Oven Cooking vessel was generally considered as bad for the aforementioned uses since it was found that the sidewall film material contained numerous holes.

The 1.1-liter Heavy Duty Ziploc bags were considered extremely bad for the aforementioned uses since the polyethylene film material of the side walls does not have satisfactory abrasion resistance to resist wear by rubbing on a freezer

In comparison, the modified polypropylene films of this invention have a melting point of approximately 156.7^°C, which makes them useful at elevated temperatures to cook or reheat various foods. In addition, Table VII summarizes the performance of these containers in real-time end-use tests at low temperature. As shown there, the modified polypropylene film structures of this invention are superior to the commercial vessels tested.

(See Table VII on next page)

002 139

TABLE VII

Commercial products in freezer trials

<td>Product</td><td>Inner layer (millimeters thick)</td><td>Outer layer (millimeters thick)</td><td>Freezer handling,% of failures</td>

<td>Dow Ziploc Microfeez Microwave Cooking Bagss</td><td>HDPE (0.04318)</td><td>Nilon - 6 (0.0127)</td><td> 27</td>

<td>Dazey Seal - A - Meal</td><td></td><td></td><td></td>

<td>Boilable Cooking</td><td></td><td></td><td></td>

<td>Pouche</td><td>PE (0.0381)</td><td>PET (0.0127)</td><td> 40</td>

<td>Hefty Baggies Extra</td><td></td><td></td><td></td>

<td>Protection Freezer</td><td>HDPE (0.02794)</td><td>Nilín - 6 (0.00254)</td><td> 50</td>

<td>Bags</td><td></td><td></td><td></td>

<td>Dow Ziploc Heavy</td><td></td><td></td><td></td>

<td>Duty bags</td><td>PE (0.06858)</td><td> -</td><td> 75</td>

<td>Reynolds Oven</td><td>Nylon - 6 / 6.6</td><td></td><td></td>

<td>Cooking Bags</td><td>CO (0.0254)</td><td> -</td><td> 100</td>

<td>This invention,</td><td>PP - 861 + 10%</td><td>Nilon - 6</td><td></td>

<td>movie A</td><td>2207 + 15% PA30 (0.03937)</td><td> (0,00762)</td><td> 25</td>

<td>This invention,</td><td>PP - 861 +10%</td><td>Nilín - 6</td><td></td>

<td>movie B</td><td>8340 + 15% PA30 (0.03937)</td><td> (0,00762)</td><td> 13</td>

<td>This invention,</td><td>PP - 861 + 10%</td><td>Nilín - 6</td><td></td>

<td>movie C</td><td>1137 + 15% PA30 (0.03937)</td><td> (0,00762)</td><td> 9</td>

Being:

HDPE - high density polyethylene;

PE. - polyethylene,

PP - 861. - a random polypropylene copolymer;

2207 . - an ethylene-methyl acrylate copolymer;

PA30. - a polyisobutylene concentrate having a ratio of 2 parts of polyisobutylene to 1 part of polypropylene;

8340 . - polybutylene;

1137 . - very low density polyethylene; and PET represents poly (ethylene terephthalate).

002 139

In summary, even though certain embodiments of the present invention have been described and described in detail, it should be understood that other embodiments of the invention are considered by way of changes, modifications and variations in the description, without departing from the scope and spirit of the invention, as It is set forth in the appended claims. Such changes, modifications and variations were within the scope of this invention.

Additional explanations about the drawings.

Figure 1

This figure illustrates the effect on the impact modification of polypropylene films of PB, EMA, PIB, VLDPE at 0^°C, showing impact resistance in orderly order (joules and the percentage of modifier in jars).

Figure 2

This figure illustrates the effect on the impact modification of polypropylene films of PB, ema, pib, VLDPE at 17.8^° C, the impact resistance (joules) being shown in ordinates and the modifier percentage in abscissa.

Figure 3

This figure illustrates the effect on the modification of the perforation of polypropylene films from PB, EMA, PIB, VLDPE to 0^°C, the perforation energy (joules / mm) being displayed in ordinates and the modifier percentage in abcisses.

Figure 4

This figure illustrates the effect on the modification of the perforation of polypropylene films from PB, EMA, PIB, VILDPE to 18.7^°C, the perforation energy (joules / mm) being shown in ordinates and the percentage of modifier in abscissa

002 139