WO2002102593A1 - Paper like polymeric material - Google Patents

Abstract

A film is produced from high or medium density polyethylene containing dispersed calcium carbonate between 10 and 50 percent by mass to provide a film having properties the same as or similar to natural paper having regard to parameters such as dead fold, feel and rigidity or stiffness and also with superior strength.

Description

PAPER LIKE POLYMERIC MATERIAL

TECHNICAL FIELD OF THE INVENTION

This invention relates to material with paper-like characteristics made from synthetic polymers.

BACKGROUND ART

It would be advantageous to provide a product from polymeric material in order to combine the look, stiffness, feel and dead fold characteristics of paper with the strength, waterproofing, and other advantages of polymeric sheeting.

It is an object of the present invention to provide a strong polymeric sheet material which has a definite paper feel and which can be used to great advantage in many typical applications of paper, such as bags, wrapping, packaging, stationery, bookbinding material and many others.

In the replacement of paper by the product of the present invention, the environmental advantage will be apparent in that trees may be saved instead of used for paper manufacture. Furthermore, the by-products derived during the paper manufacture process impacts negatively on the environment. In addition, the product of the invention is recyclable and reusable, or may be disposed of without creating an environmentally dangerous or unpleasant waste product. It can also be safely incinerated without forming any noxious or unpleasant gases.

DISCLOSURE OF THE INVENTION

According to the invention in its broadest aspect a polymeric film is produced which contains a polymer, or blend of polymers which provide adequate strength and flexibility for use as a paper substitute and which also contains an extender in finely divided form to provide a product which has a coefficient of friction similar to that of natural paper and which has a dead fold property similar to that of natural paper.

In a preferred form of the invention the extender is calcium carbonate which should be easily dispersible in a molten polymeric medium such as the medium chosen for the present invention. Thus, for example, a calcium carbonate product provided in the form of pellets in a polymeric binder which melts at operating temperatures allowing the calcium carbonate to disperse uniformly into the polymer or polymer blend is preferred.

It will, of course, be appreciated that many possible extenders may be used in the process of the present invention, but calcium carbonate has been found to be best substance for this purpose. The calcium carbonate should be present in an amount of between about 10 percent and 50 percent of the mass of the polymer.

One of the main considerations in the choice of extender is the particle size as this will have a great effect on the feel of the product which should not be too coarse, nor too smooth, otherwise it will not have the characteristic paper like feel.

The invention is preferably in the form of multilayer product which is formed by co-extrusion of two or more different compositions chosen for particular end uses of the product formed.

High density polyethylene has been found to be a suitable polymeric material and when mixed with about 20 percent by mass of calcium carbonate, forms an excellent product which has the properties required. The upper limit of calcium carbonate is about 50 percent.

As mentioned above the invention may be provided in multilayer constructions, one or both of the outer layers having a composition for the required paper like feel while the internal layers may have compositions to provide adhesion between adjacent layers, to provide strength and waterproofing and/or degree of air or vapour permeability. It has been found that the intermediate layer/s should contain the extender to certain degree because this ensures that the product will exhibit the dead fold property which polymer sheeting never does because of the inherent memory of the polymer. It seems that the extender, and in particular calcium carbonate at the correct percentage guarantees that this desirable property is achieved.

It has been found that the outside layers provide the desired properties if extruded from high density or medium density polyethylene (density between 0.94 and 0.96g/cm³) while the interaiediate layers should have a certain amount of low density polyethylene and particularly linear low density polyethylene. The latter has a beneficial effect on the bonding of adjacent layers so that the blown coextrusion of the various layers is effectively carried out.

It has been found that a film or layer having about 60 percent of high density polyethylene and containing above 20 percent of calcium carbonate has a density of about 1.lg/cm³ and is very similar in all respects to paper of the same of similar thickness, except that the layer or film of the invention is infinitely stronger than the paper equivalent.

It will be appreciated that the coextrusion method involved may be predetermined to produce products having different colours front and back, or different feels - for example for certain types of packaging or bags (cement bags, dog food bags and others for example). One product of the invention may have a paper like feel on one side and a perfectly smooth feel on the other.

Ϊ , In a particular example of the invention a three layer product is prepared, the outer layers comprising 60 percent high density polyethylene and 20 to 30 percent calcium carbonate and the core layer comprising a blend of high density polyethylene and linear low density polyethylene with 20 percent of calcium carbonate.

In an example of the invention a film was obtained having the following parameters. TYPICAL VALUES BASED ON 50HΠI FILM

Variations of the coefficent of friction with increasing amounts of calcium carbonate are shown in the following Table

% CaCO3 vs C.O.F

Other parameters of films according to the invention of increasing thickness are shown in the following Table

Paperlike Films Analysis

The films of the invention may be corona treated on either or both sides to a level of 40 Dyne which is ideally suited for printing and laminating. Due to its low water absorbency, solvent based inks are recommended for printing and it has been found that the quality of printing is excellent.

Claims

CLAIMS:

1. A polymeric film characterised in that it contains a polymer, or blend of polymers which provide adequate strength stiffness and flexibility for use as a paper substitute and which also contains an extender in finely divided form to provide a product which has a coefficient of friction similar to that of natural paper and which has a dead fold property similar to that of natural paper.

2. The film according to claim 1 characterised in that the extender is calcium carbonate which is dispersible in the polymer according to claim 1.

3. The film according to claim 2 characterised in that the calcium carbonate is in the form of pellets in a polymeric binder which melts at operating temperatures allowing the calcium carbonate to disperse uniformly into the polymer or polymer blend is preferred.

4. The film according to claim 2 or claim 3 characterised in that the calcium carbonate is present in an amount of between about 10 percent and 50 percent of the mass of the polymer.

Ϊ ,

5. The film according to any of the above claims characterised in that the polymer is high density or medium density having a density between 0.94 and 0.96 without the extender.

6. A multilayer construction Including at least one layer of a film according to any of the above claims.

7. A multilayer construction according to claim 6 characterised in that a core layer comprises a film of low density linear or non-linear polyethylene; or a blend thereof.

8. A multilayer construction according to claim 6 or claim 7 characterised in that a core layer includes between 10 and 50 percent by mass of calcium carbonate.

However, the product is not recommend for processes involving long exposure to temperatures above 60 degrees C. But is it suitable for heat sealing and can be used in most FFS (form, fill, seal) applications. Continuously heated jaws may pose a problem in stop-start operations due to the film overheating and melting. Seals may be formed in a broad spectrum of sealing temperatures (100 to 150 degrees C) provided the dwell time and jaw pressure is minimal. The film may shrink at higher temperatures but the films have proved successful in sealing operations using hot melts and cold contact adhesives.

The films are not recommended for microwave cooking but can be used for defrosting food products in a microwave oven.

No problems have been encountered when the films are used for deep freezing operations.

In view of the great strength characteristics of the films of the invention it may be necessary to make adjustments to cutting apparatus and blades.