U.S. patent number 3,719,548 [Application Number 05/169,653] was granted by the patent office on 1973-03-06 for fracturable adhesive backing.
This patent grant is currently assigned to Ludlow Corporation. Invention is credited to Jerry L. Keck, James Robert Rowley.
United States Patent |
3,719,548 |
Keck , et al. |
March 6, 1973 |
FRACTURABLE ADHESIVE BACKING
Abstract
A process and apparatus for selectively compressing paper stock
of the type which is used as a protective backing sheet for
adhesive-coated systems. The process comprises use of a novel
compression tool, the precise characteristics of which depend on
the paper stock being utilized. The compression tool comprises a
blunt, rotatable, circular, working edge which has a radius of at
least 0.02, but preferably at least 0.04 inches in diameter and at
least one half of the thickness of the paper being weakened. This
tool advantageously comprises the compressing edge, being mounted
integrally with a bearing surface which makes pressure control
easier and limits penetration of the tool. In the preferred
embodiments of the invention, the bearing surface is faced with
elastomeric material. Disclosure is also made of a novel release
sheet and adhesive sheet assembly which is manufactured utilizing
the process and apparatus of the invention.
Inventors: |
Keck; Jerry L. (Chicago,
IL), Rowley; James Robert (Calumet Park, IL) |
Assignee: |
Ludlow Corporation (Needham
Heights, MA)
|
Family
ID: |
22616600 |
Appl.
No.: |
05/169,653 |
Filed: |
August 6, 1971 |
Current U.S.
Class: |
428/41.7; 83/886;
428/43; 428/161; 428/452; 156/257; 156/268; 428/155; 428/332 |
Current CPC
Class: |
C09J
7/401 (20180101); G09F 3/0286 (20130101); C09J
7/403 (20180101); Y10T 428/24471 (20150115); Y10T
428/1471 (20150115); Y10T 428/15 (20150115); Y10T
83/0385 (20150401); Y10T 428/24521 (20150115); Y10T
428/26 (20150115); C09J 2483/005 (20130101); Y10T
156/1082 (20150115); Y10T 156/1064 (20150115) |
Current International
Class: |
G09F
3/02 (20060101); C09J 7/02 (20060101); B32b
003/30 () |
Field of
Search: |
;161/117,119,121,123,124,209,270,406,411,165 ;156/257,268
;83/7,11,12 ;93/58,58.1 ;117/8,11 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Fritsch; Daniel J.
Claims
What is claimed is:
1. In an adhesive-sheet assembly of the type consisting essentially
of (a) an adhesive-bearing sheet material and (b) a protective,
peelable, backing sheet having a surface coated with a release
agent, said surface in contact with said adhesive, the improvement
wherein said backing sheet comprises at least one linear
compression-embrittled path therealong of relatively low resistance
to bending stress and wherein said path is of embrittled paper
compressed to less than 50% of its original thickness and less than
20% of its original tensile strength along said linear path, and
wherein the non-compressed portion of the backing sheet is at least
0.004 inches thick and wherein said compressed path is indented
into that side of said sheet coated with said release coating.
2. A release-sheet backed adhesive-sheet assembly of the type
defined in claim 1 wherein said release coating is a silicone-based
coating.
3. A release-sheet-backed adhesive-sheet assembly of the type
defined in claim 1 wherein said release sheet is formed of paper
about 0.007 inches thick and wherein said linear path has a tensile
strength of from 5 to 18 psi.
Description
BACKGROUND OF THE INVENTION
There have always been a number of problems associated with the use
of adhesive-backed papers such as those used as labels, etc. These
problems, largely related to avoiding premature contact of the
adhesive with other objects, have been largely overcome by the use
of releasable backing sheets. The need for convenient removal of
labels or other adhesive papers from these release-coated backing
sheets raised new problems and a considerable amount of inventive
effort has been undertaken in solving such problems.
For example, U.S. Pat. No. 3,035,957 to Morgan disclosed a
"chemical embrittlement" process which is used to provide
embrittled lines along a backing sheet and thereby facilitate the
breaking of the backing sheet and the mechanical removal of the
sheet from the adhesive. Such a process avoids the need to
mechanically score and cut through the release-coated sheet. The
avoidance of cut-through eliminates the problem associated with the
seepage of adhesive through the cuts. On the other hand, use of
chemical compositions present handling problems in the plant, leave
an unsightly marking on the sheet, and have a tendency to result in
a product that will flake and lint in use.
U.S. Pat. No. 2,319,272 to Starr includes a disclosure of other
methods such as knife-scoring, scorching and abrasion of a sheet,
to selectively weaken linear portions therealong, on an
adhesive-coated rubber patch. Starr's rubber patch may provide an
especially high degree of cushioning for the backing sheet being
processed; the Starr patent does teach the utility of such support,
however.
Thus it is seen that the prior art has utilized various linear
weakening techniques such as applying thin lines of acid to
chemically weaken selected linear portions of the backing sheet,
abrading the sheet to selectively weaken it along the abraded line,
cutting through part of the sheet along predetermined lines,
etc.
One problem which has interfered with obtaining the maximum project
advantage from these processes has been the requirement to leave a
rather high safety margin to avoid cutting a slit through the paper
during each process. Such cut-through, of course, tends to allow
adhesive to seep through the backing sheet and stick to adjacent
sheets, thereby completely obviating the advantage sought by using
a non-perforating process to selectively weaken the paper.
While it is undesirable to have such adhesive-penetrable weak-spots
in the backing sheet, it is equally undesirable to have tear lines
which are supposed to crack open when deliberately flexed by the
user but which do not do so because the line is not weak enough.
Therefore, it will be understood that a selectively weakened line
must be deep enough to allow easy splitting but also must be strong
enough so that it will not split when it is not supposed to split
(for example, by tearing at split points not subjected to
deliberate flexing. Such secondary split lines are often provided
on release sheets of the co-called "universal-split" type and which
are particularly described in U.S. Pat. No. 3,006,793 to
Wheeler.)
In many prior art backing sheets, the extra lines were so weak that
the sheet would tear at the extra lines and greatly slow down the
stripping of the backing sheet and consequently, delay the
label-applying process. The compressed paper lines of the instant
invention have a relatively high residual strength when compared to
the low resistance to breakage when flexed along a score line. As
has been indicated above, this strength is a consequence of the
uniformity with which weakening may be achieved by use of the
present method and apparatus.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide an
improved process for controllably weakening a protective,
release-coated backing sheet for use in backing of an
adhesive-coated label stock or the like.
Another object of the invention is to provide improved apparatus
for selectively weakening paper along linear portions thereof.
Another object of the invention is to provide a superior process
for making a release-sheet-backed label display assembly.
A further object of the invention is to provide an improved
apparatus for selectively weakening linear section of paper
sheet.
Another object of the invention is to provide such apparatus which
performs well when applied to resin-coated paper surfaces.
Other objects of the invention will be obvious to those skilled in
the art on reading the instant application.
The above objects have been substantially achieved by a process
utilizing a novel tool having a working edge of a relatively large
radius with respect to the paper to be compressed, and
simultaneously weakened by use of the tool. The use of such an edge
has been found to allow a compressing depth of up to 70 percent or
more of the paper thickness without danger of excessively
weakening, or cutting through, the paper being processed. The
compression of paper caused by use of this tool results in a
weakened path which parts easily along a sheet when one bends the
sheet along the line of the compressed path. However, the processed
sheet also provides a suitable shield against seepage of adhesive.
The invention when used with relatively heavy paper, such as
clay-coated kraft tag stock of 78 lbs. per ream, does not have any
significant tendency to part at embrittled and compressed linear
paths along which splitting is required during removal of the
backing from an adhesive sheet. This is a consequence of the
relative uniformity with which the linear paths can be formed:
enough compression can be achieved to give an easy-snapping line
but the residual tensile strength is great enough to prevent
accidental tearing.
The radius of the edge of the embrittling tool of the invention is
from about 0.020 inches to 0.100 inches depending on the thickness
of the paper. It has been determined that there should be a bearing
surface mounted with compression edge to assure maximum ease of
control over the line of compression when light paper stock is
being processed. In such cases the cutting edge protrudes a
distance from the bearing surface of about 75 percent of the
paper's thickness. By light paper stock is meant paper of about 80
lbs per ream or heavier and particularly paper of 100 lbs or more
per ream. With heavier paper bearing surfaces are not needed to
moderate compression, but they are helpful for carrying traction
rings and for moderating the rate of compression.
ILLUSTRATIVE EMBODIMENT OF THE INVENTION
In this application and accompanying drawings are shown and
described a preferred embodiment of the invention. Various
alternatives and modifications thereof, are suggested, but it is to
be understood that these are not intended to be exhaustive and that
other changes and modifications can be made within the scope of the
invention. The suggestions herein are selected and included for
purposes of illustration in order that others skilled in the art
will more fully understand the invention and the principles
thereof, and will be able to modify it and embody it in a variety
of forms, each as may be best suited in the condition of a
particular case.
In the drawings:
FIG. 1 is a plan view of a segment of a typical backing sheet of
the "universal-split type" mounted over an adhesive-coated
sheet.
FIG. 2 shows a cross-sectioned, somewhat schematic view of the
backed adhesive sheet of FIG. 1.
FIG. 3 is a side view of one compression wheel constructed
according to the invention.
FIG. 4 is an elevation taken normal to the axial direction of the
compression wheel of FIG. 3.
FIG. 5 is an elevation of another compression wheel constructed
according to the invention and taken normal to the axial direction
thereof.
FIGS. 6 and 7 show a particularly advantageous tool formed
according to the process of the invention.
Referring to FIGS. 1 and 2, it is seen that an adhesive-sheet
assembly 10 comprises an adhesive-bearing sheet 12, a coating of
adhesive 14 firmly attached thereto, and an adhesive-backing sheet
16. Backing sheet 16 is only moderately adherent to adhesive 14 and
may be conveniently peeled therefrom. Such peeling is facilitated
by bending sheet assembly 10 toward the label-bearing side and
thereby causing it to crack along a line 18 as shown in FIG. 2. The
bending causes cracking along the compressed paper 20 of lines 18.
This bending will cause an edge of the sheet 16 to become exposed
and readily grippable for pulling the remaining part of 16 from the
assembly 10.
As indicated in FIG. 1, a backing sheet normally contains a number
of weakened lines 18 so that there will be at least one present on
the smallest item likely to be cut from the sheet by a manufacture.
In practice, this means that most users will be peeling backing
sheet 16 from items containing a plurality of lines 18, some of
which are not intended to be ruptured by that particular user.
Their remaining intact allows a quick removal of the backing sheet
by the user.
FIGS. 3 and 4 illustrate a compression wheel 30 particularly useful
in embrittling a relatively light backing sheet. This wheel is
mounted on an axis 32 and comprises, in addition to a semi-circular
compressing edge 34 having a radius R1 of 0.04 inches, a pair of
integrally mounted shoulders 36 which provide means to limit the
degree of compression along linear portions of a backing-sheet
being treated.
FIG. 5 illustrates a compression wheel which has a radius R.sub.2
of 0.05 inches. Wheels of such radii do not absolutely require
limiting shoulders when used to selectively embrittle backing
sheets of 8 mils or more in thickness, although use of such
shoulders to moderate compression or to hold traction rings is most
often desirable.
It is desirable to operate with 78 lb per ream paper. It is less
troublesome to make "universal-split" type assemblies with such
paper than with paper of a smaller weight basis. Such 78-lb paper
is about 0.004 inches in thickness when clay-coated to provide a
suitable surface for receiving a release coating, e.g. a silicone
coating. With such paper, a radius of about 0.025 inches on the
compressing edge of the tool is about optimum.
The process can be run most smoothly, however, when "coated tag"
papers of 7 to 8 mil caliper are used with a scoring wheel of 0.05
mils in radius and it is such a paper that is most advantageous for
use in the process of the invention. When such papers are properly
compacted, they beak with a sharp snap on being bent about
60.degree. to 90.degree. toward the side which was contacted by the
scoring wheel. The compressing is advantageously done by applying
the scoring tool to the release-coated side of the paper. This
tends to be less stressful on the release coating; strain applied
from the opposite side from the release coating often ruptures
otherwise suitable release coatings. The pressure is such that the
paper is weakened to have a tensile strength of between about 5.0
and about 18 lbs per when tested on an Instron-type tensile-testing
instrument Model No. TM 481, an instrument commonly known to the
art and sold by Instron Corporation. Most advantageously, the
strength of compression line ranges between about 6 to 12 pounds.
And this is less than about 8 to 15 percent of the tensile strength
of the paper before it is embrittled by compression.
The test procedure is as follows:
Sample Size: 1-inch wide; 1 inch between clamp-jaws
Crosshead Speed: 1 inch per minute
Chart Speed: 10 inches per minute
In general, paper should be weakened to less than about 20 percent
of its original strength by the process of invention.
FIGS. 6 and 7 show a particularly advantageous embodiment of the
invention. In this embodiment of the invention, a compression wheel
assembly 40 comprises set into a groove 45 on each side of wheel
30, a resilient wheel such as an O-ring 42. The wheels 42 help to
assure a relatively uniform compression rate and are of particular
value in maintaining traction of the wheel on the paper and this
assuring its continuous rotation. As seen in FIG. 8, they are
compressed when engaged with paper sheet 44 against a firm backing
support member 50. Normally these wheels are formed of an
elastomeric material such as a silicone rubber elastomer, or N type
of synthetic rubber. An O-ring about 0.103 in thickness is
appropriate; an H2-149 O-ring is particularly suitable, and may be
spaced conveniently about 0.15 inch or so from the compressing
wheel itself.
The total width 46 of assembly 40 is about 0.75 inches. Wheels 42
and 30 extend about 0.125 inches outwardly from the main body 48 of
the wheel.
Production speeds of well over 200 feet per minute are easily
attained using the scoring process of the invention because it does
not involve a mechanical engagement with the paper as is required
in conventional scoring or abrading processes, and it does not
require controlled application of a chemical reagent as is required
by use of chemical etchants. Indeed the process is not at all
limiting of line speed in most cases, that being more limited by
drying times. However, when the process is applied to weakening
paper in operations not limited by such factors as drying time, it
allows excellent improvements in line speeds while maintaining a
relatively more uniform weakening of the paper along the line of
compression.
It has been discovered that the most satisfactory procedure to use
is to compress the paper being treated by application of
compression from the release side. This has the special advantage
of eliminating disruptions in the release coating which were
noticed to occur with some frequency when the coating was extended
by strain caused by the scoring tool applied to the non-coated
surface of the release paper. Such disruptions, of course, result
in an undesirable sticking of adhesive coating labels to the paper
substrate and interfere with the convenience with which the mounted
labels can be used.
It has also been found that the rupture of the release paper is
more uniformly controllable when the paper is bent toward the
grooved side rather than away from it.
It is also to be understood that the following claims are intended
to cover all of the generic and specific features of the invention
herein described and all statements of the scope of the invention
which might be said to fall therebetween.
* * * * *