Conformable and die-cuttable biaxially oriented films and labelstocks

Abstract

This invention relates to die-cuttable stretch oriented films wherein the tensile modulus of the film in the machine direction is greater than the tensile modulus in the cross direction and the tensile modulus in the cross direction is about 150,000 psi or less. The oriented films are useful in particular for preparing adhesive containing labelstock for use in adhesive labels.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is a division of copending U.S. application Ser. No. 10 / 236,769 filed on Sep. 6, 2002 which is a division of copending U.S. application Ser. No. 09 / 531,978 filed on Mar. 20, 2002.FIELD OF THE INVENTION [0002] This invention relates to conformable and die-cuttable biaxially oriented films, and more particularly to biaxially stretch-oriented monolayer and multilayer films. BACKGROUND OF THE INVENTION [0003] It has long been known to manufacture and distribute pressure-sensitive adhesive stock for labels by providing a layer of face or facestock material for the label or sign backed by a layer of pressure-sensitive adhesive which in turn is covered by a release liner or carrier. The liner or carrier protects the adhesive during shipment and storage and allows for efficient handling of an array of individual labels after the labels are die-cut and the matrix is stripped from the layer of facestock material and up to the poi...

AI Technical Summary

Benefits of technology

"This patent describes a type of film that can be used for making adhesive labels. The film is made up of polyethylene and propylene polymers or copolymers, and it has a specific mechanical properties that make it suitable for use in adhesive labels. The film can be made by a process called biaxial stretch-oriented, which involves stretching the film in both the machine direction (the direction in which it moves) and the cross direction (perpendicular to the machine direction). The resulting film has a specific tensile modulus in the machine direction and a much lower tensile modulus in the cross direction, which makes it easier to cut and use in adhesive labels."

Problems solved by technology

Such failure to dispense is believed to be associated with excessive release values between the label facestock material and the liner.

Failure to dispense may also be characterized by the wrinkling of the label due to lack of label stiffness at the dispensing speed as it is transferred from the carrier to the substrate.

However, the migration of the plasticizers used in PVC films to convert the normally rigid films to flexible films was recognized as a major problem area for these types of films resulting in loss of desirable properties such as adhesion, color buildup, shrinkage, and flexibility.

Eventually, migration of the plasticizer results in wrinkling, cracking and visual deterioration of the facestock and / or label.

Such reduction in facestock thickness often has resulted in reduced stiffness and the inability to die-cut and dispense the labels in a reliable commercially acceptable manner using automatic machinery.

There also was pressure for environmental reasons to prepare labels from polymer facestocks other than polyvinyl chloride.

However, these materials also have relatively high tensile modulus values in both machine-direction (MD) and cross direction (CD) which results in labels which are not very conformable.

Related conformability problems have been encountered in respect to rigid surfaces such as glass.

For example, when biaxially-oriented films are applied to rigid substrates such as glass bottles, the application is not completely successful.

The relatively stiff labels have a tendency to bridge surface depressions and the mold seams resulting from bottle-forming processes resulting in an undesirable surface appearance of the applied label simulating trapped air bubbles.

This has somewhat impeded the use of pressure-sensitive adhesive labels to replace priorglass bottle labeling techniques such as ceramic ink directly bonded to the bottle surface during glass bottle manufacturing processes as customers find the appearance unattractive.

Such ceramic ink techniques are environmentally undesirable due to objectionable ink components and the contamination of the ink in the crushed bottle glass in recycling processes.

Attempts to use the relatively stiff oriented polypropylene films on flexible substrates such as plastic bottles also have not been completely successful because the labels do not have the flexibility required to conform to the flexible plastic containers.

Oriented polypropylene films are also more difficult to print than PVC or polyethylene films.

However, both of these films are difficult to die-cut and do not dispense well at low calipers.

Attempts to reduce the gauge of the polyethylene facestock to reduce costs has not yet met with any degree of success because the thinner polyethylene facestock is not readily die-cuttable with the die leaving a mark on the liner and stringers on the cut label.

Additionally, the thinner facestock becomes difficult to dispense at higher speeds over a peel plate because of reduced stiffness.