Plastic wrap with cling layer

In order to form a plastic wrap which exhibits little or no cling until such time as the wrap is applied to an article or the like, the adhesive layer, which is formed on one side of a sheet of olefinic polymer, is exposed to a treatment which superficially oxidizes or cross-links the outer layer of adhesive material to form a film which exhibits greatly attenuated adhesion. This film is disruptable as the wrap is applied and is stretched and or deformed in a manner which uncovers the adhesive material and endows cling properties on at least localized areas of the wrap. Techniques for treating the adhesive layer include UV irradiation, exposure to corona and ozonification.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a plastic wrap with a cling layer. More 
specifically, the present invention relates to a plastic wrap having an 
adhesive cling layer wherein the adhesive layer is modified to reduce or 
eliminate the amount of cling produced until the modified surface is 
disrupted by stretching/application of the wrap. 
2. Description of the Related Art 
Olefinic polymers, particularly polymers of ethylene, are employed in a 
variety of end use applications including the preparation of wrapping 
films. In conventional wrapping processes, e.g. spin or rotary stretch 
wrapping techniques, the polymeric film is wound under tension around a 
package by either rotating the package on a turntable or by winding the 
film around a stationary package. In such applications, it is generally 
desirable for the overlapping portions of the film to adhere to each other 
thereby self-sealing the wrap without the need for an external adhesive or 
heat sealing operation. 
To achieve the above, it has been proposed to provide one surface of the 
wrap with cling properties which allow the wrap to cling to itself, and to 
provide the other side with so called "slip" characteristics which endow a 
low coefficient of friction on an outer, non-cling surface. The provision 
of this slip surface prevents adjacent packages which are wrapped 
individually in cling wrap, from sticking to each other and from 
undergoing possible damage when pulled apart. 
In order to impart cling properties or improve the cling of the cling side 
of such films, it has been proposed to add tackifying additives or to use 
acrylates in the (co)polymer. However, the use of tackifiers has 
disadvantages in that, while these enhance the cling properties of the 
wrap they tend to induce a number of drawbacks. For example, they tend to 
have an adverse effect on the optical properties of the film and enhance 
surface migration of the additive(s). This type of migration can induce 
rolls of the wrap to telescope and/or collapse. A further problem is 
encountered in the instance wherein the tackifier is "picked off" onto the 
slip side of the film while the film is rolled due to the slip and cling 
layers being maintained in intimate contact. 
In order to promote the slip characteristics of the slip surface of the 
wrap, it is possible to treat one side (viz., the outer, non-cling side) 
of the film in a manner which promotes a reduction in the coefficient of 
friction. This can be achieved through the use of anti-cling and/or 
antiblock additives including silicas, silicates, diatomaceous earth and 
various lubricants. U.S. Pat. No. 5,225,257 to Brant discloses the use of 
corona discharge for modifying the outer slip surface of the wrap and for 
improving the anti-cling characteristics. 
However, despite the above progress, a drawback is encountered in that the 
very cling characteristics which are vital during application, tend to 
interfere with handling and storage during production, roll release and 
ease of use by the consumer. 
Accordingly, there still exists a need for a plastic cling wrap which is 
easy to handle during production and storage, and which still produces the 
desired amount of "cling" when used to wrap an article or the like. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a cling wrap that 
exhibits limited or no cling characteristics until such time as a consumer 
applies the wrap to an article or the like. 
It is a further object of the present invention to provide a cling wrap 
which is easy to manufacture and which exhibits a thin protective layer 
which is disrupted to expose unmodified adhesive when the wrap is 
stretched and/or applied to an item by a consumer. 
In brief, the above and other objects are achieved by modifying an adhesive 
layer, which is formed on one side of a sheet of olefinic polymer, by 
exposing it to a treatment which superficially oxidizes or cross-links the 
outer layer of adhesive material and forms a thin film which exhibits 
greatly attenuated adhesion. This film is disruptable as the wrap is 
applied and is stretched and or deformed in a manner which uncovers the 
adhesive material and endows cling properties on at least localized areas 
of the wrap. 
More specifically, a first aspect of the present invention resides in a 
plastic wrap comprising: a plastic sheet; an adhesive layer formed on a 
side of the sheet; an adhesive attenuating film formed on an outer surface 
of the adhesive layer, the adhesive attenuating film being disrupted on 
stretching/deformation of the sheet in a manner which exposes portions of 
the adhesive layer formerly covered with the adhesive attenuating film. 
A second aspect of the invention resides in a method of forming a plastic 
wrap having cling properties, comprising the steps of: coating a first 
side of a plastic sheet with a layer of adhesive; and modifying the 
surface of the adhesive layer to form a film having attenuated adhesion. 
In accordance with this aspect of the invention the step of modifying the 
surface of the adhesive layer include one or more of: exposing the 
adhesive layer to UV radiation; exposing the adhesive layer to a corona; 
inducing cross-linking in the surface of the adhesive layer; and oxidizing 
the surface of the adhesive layer such, as by ozonification, to form the 
requisite film. 
A third aspect of the invention resides in a plastic wrap having cling 
characteristics which is formed by: coating a first side of a plastic 
sheet with a layer of adhesive; and modifying the surface of the adhesive 
layer to form a film having attenuated adhesion. 
It is to be appreciated that treatment of the adhesive layer in accordance 
with the present invention differs from that disclosed in the above 
mentioned U.S. Pat. No. 5,225,257 in that the latter seeks to provide a 
permanent reduction in the cling properties of a non-cling surface, while 
the invention provides a temporary cling inhibition to the cling surface 
per se. Thus, the invention is founded on the discovery that the cling 
surface can be temporarily modified in a manner which promotes handling 
and storage, yet uniquely permits the return of adequate cling properties 
during the actual application of the wrap.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In accordance with the present invention, a suitable substrate film or 
sheet 10 made of an olefinic polymer, for example, is coated with a 
suitable adhesive or tackifier layer 12. The coated film 10 is then, as 
shown in FIG. 1, transported past a suitable UV and/or corona discharge 
source 14 in the direction indicated by the bold arrow (A) so as to modify 
the outer surface of the adhesive layer 12 and form a thin oxide film 16 
which is essentially devoid of adhesive characteristics. In this 
embodiment, the oxide film 16 is formed essentially over the entire 
surface of the adhesive layer 12. 
This process produces a plastic wrap which exhibits greatly attenuated or 
totally inhibited adhesion characteristics without the need for external 
agents or the like. In this condition, the plastic wrap is, because of the 
attenuated adhesion characteristics, much easier to handle, roll and store 
than conventional wraps. It also permits the consumer to remove a length 
of the wrap from a roll with less resistance and tendency to fold up and 
stick to itself than possible with conventional products. 
When the wrap according to the present invention is applied to an article 
or the like, the wrap stretches and the areas of the wrap which undergo 
distortion are such that the film oxide 16 is broken and unmodified areas 
of the adhesive layer 12 are exposed in the manner illustrated in FIG. 2. 
This provides these portions of the wrap with the desired cling 
characteristics which adhere to the surface or surfaces against which it 
is brought into contact. 
In summary, the present invention provides a wrap which overcomes the above 
mentioned drawbacks with the prior art in that it provides a thin adhesive 
characteristics attenuating film over the adhesive layer. This thin film 
facilitates the rolling and handling of the film during production, tends 
to inhibit the "pick off" problem wherein the adhesive layer tends to, at 
least in part, become attached to the slip surface of the wrap, and 
further facilitates the unrolling and application of the wrap. The unique 
property wherein the adhesive layer becomes selectively uncovered when the 
wrap is stretched during application greatly enhances the utility of the 
wrap. 
It will be appreciated that the techniques via which the surface of the 
adhesive layer can be treated, are not limited to UV and/or corona 
exposure and that a number of other techniques, such as exposure to ozone 
(ozonification) which induce either oxidation or cross-linking of the 
surface of the adhesive layer in a manner to form a thin disruptable film, 
can be used without departing from the scope of the invention which is 
limited only by the appended claims. 
For examples of the type of polymer and adhesive which can be used in 
accordance with the present invention, reference can be had to U.S. Pat. 
No. 4,542,188 issued on Sep. 17, 1985 in the name of van der Heijden. 
Reference can also be had to U.S. Pat. No. 4,425,268 issued on Jan. 10, 
1984 in the name of Cooper. The content of these two patents is hereby 
incorporated by reference thereto.