Wrapping films

Details Wrapping films Wrapping films

2001-03-30

2003-04-22

Watkins, III, William P. (Department: 1772)

Stock material or miscellaneous articles

Structurally defined web or sheet

Continuous and nonuniform or irregular surface on layer or...

C428S343000, C428S212000, C428S523000

Reexamination Certificate

active

06551687

ABSTRACT:

TECHNICAL FIELD
This invention relates to wrapping films permitting easy handling, and specifically to wrapping films each of which does not cling to itself before wrapping, can exhibit good clinging properties to a wrapped item upon wrapping, and can be peeled off with ease after wrapping.
BACKGROUND ART
As wrapping films for domestic or commercial use, films made primarily of polyvinylidene chloride, polyvinyl chloride, polyethylene, polypropylene, polymethylpentene or the like are used. They are all available in a form such that they are wound on paper-made cores and upon use, are rolled out and cut for use. In the case of a wrapping film with high clinging properties, however, it is often observed irrespective of its material that, after cutting the wrapping film and until wrapping an item with the wrapping film, the wrapping film clings to itself and the wrapping operation is hence inconvenienced. Further, the clinging of the wrapping film to itself usually leads to a reduction in the usable part of the film, resulting in a waste.
In view of the purpose of use of wrapping films, they are also required to have sufficient clinging properties and easy peelability because they are primarily employed to wrap food items for storage and subsequent to the storage, are peeled off to use the food items.
In the case of a wrapping film disclosed in Japanese Patent Publication (Kokai) No. SHO 58-1030, a non-self-clinging portion comprising a number of extremely fine, linear or nonlinear scuff marks is formed on a surface layer of the wrapping film at a peripheral edge portion or one of side edge portions thereof by an abrasive means with a view to improving the peelability of the wrapping film from itself. No clinging properties is therefore exhibited at this non-self-clinging portion. Although no clinging of the film to itself takes place at the non-self-clinging portion, the problem of clinging still remains unsolved because the wrapping film is tacky at the remaining portions. In addition, the non-self-clinging portion may prevent thorough wrapping as items to be wrapped, such as containers and food items, are diverse in size.
To improve both handling ease and airtight sealing performance, WO 97/25256 proposes as a wrapping film a roughened film with a pressure-sensitive adhesive, which shows minimum adhesive or cling properties until activated by a user but exhibits sufficient adhesive or cling properties after activation. The pressure-sensitive adhesive is arranged such that it surrounds non-adhesive protrusions and has a thickness less than the height of the non-adhesive protrusions. Upon application of an external force (compressive force or tensile force), a region where the pressure-sensitive adhesive is arranged is caused to adhere to a target surface to be wrapped, whereby sufficient adhesive properties can be exhibited. This publication describes the roughened film as an improved storage wrap material characterized in that an active side exhibits, as the sufficient adhesive properties, an adhesion peel force of at least one ounce per inch width after activation by a user and also in that the active side includes the pressure-sensitive adhesive. Adhesive properties to a target surface to be wrapped are sufficient insofar as an adhesion peel force of at least one ounce per inch width is provided. Upon peeling off the wrapping film from the target surface after use, however, the adhesion force is so strong that the peelability is insufficient. The wrapping film is therefore very difficult to use. Further, the arrangement of the adhesive results in migration of the adhesive to plates or the like or to food items, and is therefore not preferred from standpoint of safety.
According to the above-publication, the active side is described to be activated under a compressive force of at least 0.1 pound per square inch. If the film is wound into a roll by a conventional method, the active side is prematurely activated in the course of its winding, thereby making it impossible to dispense the film from the roll. To permit rolling-out of the film by a light force, the film has to be formed into a roll by an extremely weak force so that the active side is not activated. This however results in a loose roll and hence in a large dispensing carton, leading to practical inconvenience in that it is not easy to hold the film in hand and to use the same and further in that the film is quickly used up as the rolled length is short. In addition, the film is accompanied by a further drawback that its productivity is not high because it is wound up by an extremely weak force.
The present invention therefore has an object the provision of a wrapping film, preferably a rolled wrapping film having good handling properties, which features minimized migrants to foods, does not cling to itself before wrapping, exhibits good clinging properties to a target item upon wrapping, and has good peelability to permit easy removal after wrapping.
DISCLOSURE OF THE INVENTION
The present inventors proceeded with a detailed study on wrapping operations by wrapping films. It was revealed that a pressure under which a film clings to itself after the film is cut and until a target item such as a container or a food item is wrapped is at least about 4 Pa and also that a pressure required to hold the target item such as the container or the food item in the wrapped state subsequent to its wrapping is at least about 4 kPa. The present inventors have proceeded with a further investigation, and as a result, have found that the above-described object can be achieved when a film is provided with clinging properties such that the film does not exhibit clinging properties to itself when a pressure is about 4 Pa or lower, exhibits clinging properties sufficient for wrapping for the first time when a pressure reaches about 4 kPa or higher which is a pressure applied upon using the film, and is easy to be peeled off.
Another investigation has also been made as to the ease in peeling off wrapping films after wrapping target items such as containers or food items. As a result, it has been found that clinging properties of certain level or higher make it difficult to peel off a wrapping film and hence lead to very difficult handling.
The present invention therefore provides a wrapping film (which may hereinafter be called “the first invention”) having a sticky surface on at least one of sides thereof, characterized in that a shear adhesion strength as measured subsequent to bringing the sticky surface into contact under a pressure of 4 Pa with a glass surface having a surface roughness of from 0.7 to 1.5 nm is at most 400 cN/25 cm
2
, and a shear adhesion strength as measured subsequent to bringing the sticky surface into contact under a pressure of 4 kPa with the glass surface is at least 700 cN/25 cm
2
.
In addition, the present inventors have also proceed with a further investigation as to relationships between surface characteristics of films and properties as wrapping films. As a result, it has been found that a film does not cling to itself when its surface roughness and waviness (Ra′) is 40 nm or greater but clings to itself when its surface roughness and waviness (Ra′) is smaller than 40 nm. As a consequence, it has been found that a surface roughness and waviness (Ra′) of at least 40 nm makes it possible to provide a wrapping film having good handling properties such that it does not cling to itself before wrapping, exhibits good clinging properties to a target item when wrapping, and has good peelability to permit easy removal after wrapping. In other words, it has been found that, when a wrapping film has a surface roughness and waviness (Ra′) of at least 40 nm, the film does not show sufficient clinging properties due to its poor surface smoothness and does not cling to itself even when brought into an overlapped relation with itself. It has also been found that, when a user stretches the film and wraps a target item with it, convexities on the surface are eliminated and the inherent clinging pro

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