IL35927A - Alkali removable pressure sensitive adhesive label - Google Patents

Description

if Alkali removable pressure sensitive adhesive label ALKALI REMOVABLE PRESSURE SENSITIVE ADHESIVE LABEL ABSTRACT OF THE INVENTION A substrate designed for use as base stock for labels, tapes, bumper stickers, posters, etc. The substrate is coated with a water soluble pressure sensitive adhesive composition and a barrier layer is placed between the substrate and the adhesive, the barrier layer being chosen from a material which dissolves in water having a pH above 8. The barrier prevents water from migrating through the stock into the adhesive under normal conditions of use thereby preventing the stock from self removing when subjected to rain or highly humid conditions. The stock may be readily removed when such is desired by subjecting it to an alkaline bath so as to dissolve the barrier layer.

BACKGROUND OF THE INVENTION As is known in the art, pressure sensitive adhesives comprise a class of adhesive compositions which share the common characteristic of being able to adhere to a surface by the application of nothing more than manual pressure.

In the past, no one had successfully provided a water permeable substrate capable of being combined with a water soluble pressure sensitive adhesive offering the advantage of being readily removable by washing with water and yet being capable of staying adhered under rain or high humidity conditions. As described in copending application SN. 856,710, system was proposed wherein the assembly is protected from rain but is removable by application of hot water. This is satisfactory for many reasons but is still not suitable when one must remove with cold water.

BRIEF SUMMARY OF THE INVENTION The present invention comprises a special barrier coat which is placed between a substrate and a water soluble pressure sensitive adhesive which functions to prevent self removal due to the migration of water through the substrate into the adhesive.

The barrier coat is chosen from a material which dissolve o in an alkaline bath, e.g., in the range above 90 F. Accordingly, under conditions of high humidity or normal rain fall, the barrier coat remains intact and prevents water from migrating through the stock into the adhesive. However, when one desires to remove the substrate from a surface to which it is adhered, it is only necessary to subject the same to an alkaline bath spray.

In the case of automobile bumper stickers, e.g. , when the car is subjected to soapy water, the bumper sticker will readily remove. The same applied to labels when subjected to automatic washing systems.

DRAWINGS FIGURE 1 illustrates an enlarged cross-section view of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGURE 1, a pressure sensitive label 1 comprising paper base stock 3, barrier layer 5 and a water soluble, pressure sensitive adhesive coating 7. It is to be understood while assembly 1 is to be referred to as a label, it is meant to represent any substrate to which pressure sensitive adhesives are convent onally applied such as tapes, posters, labels, bumper stickers, etc.

The exposed surface of the water soluble pressure sensitive adhesive 7 is protected by a release sheet 9 comprising a substrate 11 having a release coating 13 thereon.

Base stock 3 may comprise cloth or any grade of a er comprise any of those well known in the art such as those described, for example, in U. S. Patent 3,249,572 and U. S. Patent 2,985,609.

The release sheet 9 is comprised of a paper substrate 11, preferably of the kraft type. Release coating 13, which is in contact with the pressure sensitive adhesive, may comprise any conventional material such as nitrocellulose, cellulose triacetate, silicone and any other conventicunal material which is compatible with the adhesive.

THE BARRIER LAYER As hereinbefore described, the barrier layer 5 is chosen so as to dissolve in water having a pH above 8 so a label which is not affected by rain or high humidity yet readily washes off in soapy water. Under normal conditions of use, the barrier layer remains intact and functions to prevent migration of water from the front face of the label stock into the adhesive thereby preventing inadvertent self removal.

The barrier layer is chosen from any film forming material which dissolves only in an alkaline bath. Examples of materials include casein, isolated soy protein, and sodium poly-acrylate. There are also some polyvinyl acetates and starches which are only alkali soluble.

The thickness of the barrier coating can be anywhere in a range greater than .1 mils. The greater the thickness, the greater the resistance to water penetration and thus, the selected thickness will depend upon the time requirements for removal.

The thickness is rarely greater than 5 mils and more generally it is in the range of 1 mil. The barrier coat is applied by simply mixing with solvents and applied by any conventional coating techniques such as by reverse roll, doctor blade, knife, gra-vure , etc .

EXAMPLE I A 36% solid sodium polyacrylate alkaline solution (pH9) was applied with a Myer rod to matte litho label stock and dried at 220°F. for two minutes to provide a .3 mil thick coating. The sodium polyacrylate used is sold by Rohm and Hass under the trademark Acrypol WS-24.

A water soluble pressure sensitive adhesive was applied to a conventional release backing and the adhesive coated backing was laminated to the barrier coated label stock. The adhesive preferentially adheres to the barrier thus permitting the backing to be removed when desired.

A label 2 4 inches with backing removed was adhered to a aluminum panel 3 x 6 inches and placed in an Atlas Weather-ometer going through a cycle of rainfall and sunlight at 80°F.

The label adhered to the panel for 1000+ hours .

A second panel having a label, prepared as above described, was placed under a spray of water having a detergent having a pH above 8 and the label removed in 60 seconds.

A third panel having a label , prepared as above described, except the barrier coat was eliminated, was placed in an Atlas eatherometer under the same conditions above described. The label removed from the panel in 50 hours .

The foregoing is considered illustrative only of the , principles of the invention. Since numerous changes and modifications will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modif cations and equivalents may be resorted to as falls within the scope of the invention.

Claims (1)

1. 5 combination comprising a a water soluble barrier layer on said substrate capable of dissolving in an alkaline having a pH above 8 and being only alkaline a water soluble sensitive adhesive on said barrier layer capable of adhering to a substrate solely by application of manual insufficientOCRQuality