Note: Descriptions are shown in the official language in which they were submitted.
2~
ACKGROUND OF THE INVENTION
Field of the Invention
,
The present invention is directed to adhesive coated sheet
materials and especially those in the for~ of tapes, strips or
the like. In paxticular, the invention is directed to such of
those sheet materials as are intended generally for one-time
use wherein they are bonded to themselves by contact between
the adhesive surface and the opposite surface or back side.
Such adhesive coated sheet materials are well known, and
provide means for restraining coiled, stacked or gathered
items. Familiar examples include tape seal closures for rolls
of postage stamps, banders for stacks of currency, skeins of
yarn or shoestrings and the like. Due to the high value of
many of these items, it is extremely important that the
adhesive aggressively maintain the closure. On the other hand,
the single use of such strips demands a cost consistent with
disposability.
Description of the Prior Art
- Published patents and literature descriptions of adhesive
coated sheet materials are legion. It is also well known to
use adhesive coated strips for the specific application of
banding rolls of stamps, stacks of currency and the like. As
above stated, this application demands a delicate balance
between the strength and tack properties required to prevent
premature release and the cost of the banders, themselves. The
use of strips of conventional masking tape or a tape comprised
of an uncoated Kraft base sheet having a conventional gum
3. `
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coating applied thereto have both proven unsatisfactory because
the aggressive nature of the adhesive frequently resulted in
the tape base sheet, itself, prematurely tearing or
delaminating all axound the strip, thus leaving the contents
still banded. Attempts to modify such materials by providing
selective coating of the adhesive to reduce the peel strength
have proven costly. Other attempts to reduce the bonding by
applying release coating to the back side have also been
expensive. The use of an adhesive with less tack or bond
strength is subject to premature adhesive failure. An
alternative approach has been ~o increase the integrity of the
base sheet to prevent delamination, but such stronger base
sheets also increase costs and nonwoven base sheets require
specially formulated adhesives or extended drying times. To
merely illustrate this discussion of prior art adhesive coated
materials, the following patents may be identified: U.S.
Patent 3,425,968 to Reiling dated 4 February 1969 directed to
non-curling gummed products, U.S. Patent 4,377,433 to Merz et
al. dated 22 March 1983, U.S. Patent 2,978,343 to Russo et al.
dated 4 April 1961, U~S. Patent 3,574,153 to Sirota dated
6 April 1971, and U.S. Patent 4,192,783 to Bomball et al. dated
11 March 1980. These patents and conventional practice,
however, reflect a standard procedure of applying the adhesive
coating to uncoated base stock or to the uncoated side of
coated base stock, thus leaving the coated side free for
accepting printing. Both structures fail to satisfy the
adhesive property requirements with ready release. U.S. Patent
3,076,588 to Conway et al. dated 5 February 1963 is directed to
an adhesive construc~ion requiring a smooth, film layer
component.
SUM~ARY
The present invention provides a unique and cost effective
adhesive coated sheet material particularly adapted for the
bander applications above described. In accordance with the
invention, it has been found that by selection of a particular
coated base sheet web and applying the adhesive coating to a
coated side of the base web or otherwise so that in use it will
contact the coating, the resulting combination, while
aggressively bonded upon contact between the adhesive coated
side and the opposite side and activation of the adhesive, may
be readily separated without delamination of the base sheet
web, itself. Rather, the coating remains with the adhesive and
separates from the base sheet web and releases the banded
contents. In this manner, use may be made of conventionally
available water moistenable, solvent activated, or heat
sensitive adhesives as well as readily available coated webs as
the base sheet. In contrast to prior attempts, however, it is
not necessary to utilize separate release coatings or resort to
selective adhesive application. Also contrary to conventional
practice, the application of the adhesive to the coated side of
the base sheet is preferred to achieve the benefits described.
Examples of preferred embodiments include a clay coated Xraft
stock base sheet to which is applied on the coated side a water
moistenable adhesive formulation. Others include the use of a
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coated latex saturated base sheet or a coated Kraft base sheet
as well as other conventional coated base sheets such as
60 lbs./3300 ft2 coated litho webs. In use as a bander, the
strips of the present invention produce a strong seal since an
aggressive adhesive may be used in combination with a smooth
backing and yet are readily and quickly releasable when
desired. In general, the peel strength under such conditions
will be at least in the range of about 0.Ql to 10.0 lbs./inch
width and, preferably, 0.2 to 3.0 lbs./inch width. The coating
will have an affinity for the adhesive that is greater than its
affinity for the base sheet web or itself as measured by
microscopic examination of separated bands in the previously
bonded area. The clay coa-ting originally on the stock will be
found predominantly adhered on the surface of the adhesive. A
useful independent measure with moistenable adhesives involves
moistening the adhesive coat on a one-inch strip and bonding it
to a 99 lbs./3300 fta Kraft paper. After drying for 1/2 to 1
minute, the strip is slowly hand peeled from the paper at an
ang1e of abotu 120 at a rate of about 20 inches/minute.
Useful materials will exhibit a substantial amount of clay
coating deposited on the surface of the adhesive layer on the
paper.
BRIEF DESCRIPTION OF T~E DRAWINGS
FIG. 1 illustrates in schematic form one process for
producing an improved releasable adhesive sheet of the present
invention;
6.
FIG. 2 illustrates, in cross section, one form of the
improved releasable adhesive sheet of the invention;
FIG. 3 illustrates a similar view of a second form of the
releasable adhesive sheet material of the present invention;
FIG. 4 illustrates the adhesive sheet material of the
present invention illustrated in FIG. 2 in use as a bander;
FIG. 5 illustrates the bander of FIG. 4 peeled away with
certain portions greatly exaggerated for clarity; and
FIG. 6 is an enlarged view similar to that of FIG. 5
showing the embodiment of FIG. 3.
DESCRIPTION OF T~E PREFERRED EMBODIMENTS
While the invention will be described in connection with
preferred embodiments, it will be understood that it is not
intended to limit the invention to those embodiments. On the
contrary, it is intended to cover all alternatives,
modifications and equivalents as may be included within the
spirit and scope of the invention as defined by the appended
claims.
In accordance with the present invention, the base sheet
material may be selected from a wide variety of available
coated webs. These webs include tho~e that have been
previously employed as adhesive backings by applying the
adhesive coating to the uncoated side. While not wishing to
limit the present invention to specific base materials,
examples include clay coated bleached Kraft stock
t35-60 lbs./3300 ft2) such as is available from Watervliet
Paper Company, smudgeproof coated latex saturated sheet as is
available from Kimberly-Clark Corporation under the designation
Munising Division Grade C~32714, and treated synthetic nonwoven
webs such as spunbonded polyolefin as is available from duPont
under the trademark Tyvek~ designation 1073D. Other base web
materials will suggest themselves to thosle skilled in the art.
It is only essential that the base web material have a coating
or a treatment resulting in the fibers or at least one side of
the web having a substantially continuous film formed thereon
on at least one side thereof. Such coatings or treatments as
are contemplated are those which are normally employed for
improved printability, generally clay and other pigment
coatings. These are low cost coatings and may be applied
directly on the paper making machine or as an off machine
coating step. For most purposes, a clay coating of about 10 to
25 lbs./3300 ft2 and, preferably lS to 20 lbs./3300 ft2 will be
suitable for purposes of the present invention while falling
within the range of commercial paper production. Examples of
other coatings or treatments which may be used include sizing
or holdout coatings conventionally employed to reduce
requirements for subsequent pxint or other coatings as well as
antistatic and others which form a film on the web or fibers.
Any of a wide variety of adhesives may be employed in the
present invention. These include, without limitation, water
moistenable adhesives such as are described in the above
mentioned U.S. Patent 3,425~968 to Reiling dated 4 February
1969, for example, heat seal coatings such as are taught in
U.S. Patent 2,625,287 to Holt, Jr., et. al., dated 13 January
8.
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1953 and solvent activatable adhesive coatings such as are
described in U.S. Patent 3,531~316 to Sternasty dated
29 September 1970. Selection of a particular coating for the
purposes of the present invention will depend upon the desired
end use as well as the nature of the coated base sheet web.
The determining factors will be the compatibility of the base
web sheet and the adhesive; for example, the adhesive must not
unduly deteriorate the base web sheet nor can the coating of
the base web sheet interfere unduly with the adhesive action of
the adhesive composition. A second important factor will be
the degree of bonding obtained when the adhesive side is placed
in contact with the opposite side and the adhesive activated by
solvent, water, heat, or the like, the requirement being that
the coating bond more aggressively to the adhesive than to its
web substrate or to itself such that the coating will
delaminate when peel stress is applied. This may be readily
determined by weighing samples before and after peeling and
comparing the amount of coating adhering to the peeled
components. Examples of adhesives which may be used include
water moistenable adhesives as described in the above mentioned
U.S. Pa$ent 3,425,968 to Reiling dated 4 February 1969, heat
seal adhesives such as homopolymers and copolymers of ethylene
and vinyl acetate, solvent activatable adhesives such as
acrylic and styrene polymers and copolymers and nitrile or
chloraprene elastomers. The amount of adhesive required will
also depend upon the nature of the base web and the desired end
use. In general, the amount will be sufficient to provide a
peel strength of at least about 0.01 to 10 lbs./inch width, and
preferably abou~ 0.2 to 3.0 lbs./inch width. For example, for
the application as a bander for coiled stamps and using a base
sheet of a 62 lbs./3300 ft~ latex saturated paper web having
one side clay coated, the amount of dry gum water moistenable
adhesive will be generally in the range of from about 6 to
14 lbs./3300 ft2, and preferably about 10 to 12 lbs./3300 ft2.
Turning to FIG. 1, a method for preparing a preferred
embodiment of the lnvention will be described. As shown, base
sheet 10 having coated side 12 is unwound from roll 14
supported by stand 15 and directed over idler and guide rolls
17 to adhesive coating station 16 where adhesive 18 is applied
by means of roll 20 or other suitable means such as a rod,
blade, or the like. The adhesive coated sheet 22 is then dried
by passing through forced air dryer 24 over guide rolls 25,
cooled and rewound by means of chilled rolls 27 or the like
into roll 26 over idler rolls 29. The resultant stock may be
slit into desired widths by slitting, wound into rolls or
sheeted as desired. Various support means required (only
partially illustrated) will be apparent to those skilled in
this art.
Turning to FIG. 2, coated sheet 22 is shown in
cross-section. As illustrated, it shows the combination of
base sheet 10 with adhesive 18 applied to the coating 12 on one
side thereof.
Turning to FIG. 3, a similar view is shown wherein a
different base sheet 30 is employed and the coating and
adhesive are on opposite sides.
10 . ...
Turning to FIGS. 4 and 5, the adhesive sheet of the
invention in tape form is illustrated in cross-section as a
bander for a coil of po~tage stamps. As shown, tape 32
encircles stamp coil 34 and is bonded to itself by means of
contact between activated adhesive 18 and the opposite side 36
at overlap area 38. Thus, stamp coil 34 is retained in a
compact, rolled condition. As shown in FIG. 5, when it is
desired to open the coil of stamps, the adhesive tab 35 is
pulled away, and coating 40 delaminates as shown in exaggerated
detail. Thus, the stamp package may be conveniently and
quickly opened without premature tearing and without
delamination of bander web 10.
Turning to FIG. 6, there is shown an enlarged and
exaggerated cross-sectional view of the embodiment of F'IG. 3 in
use. In this case, bander 42 comprises base sheet 30 having
adhesive 44 on one side and a surface sizing 46 on the other.
Such a composite may utilize webs as disclosed in Louden U.S.
Patent 4,058,648 dated 15 November 1977, for example. As shown
in FIG. 6, in use, the adhesive layer 44 will contact sizing
46. When peeled away, although the sizing 46 may not totally
and cleanly adhere to adhesive layer 44, the preferentlal
adhesion is sufficient to result in pulling away at areas 47
and opening the band without delamination of base sheet 30.
EXAMPLES
Example 1
Using the process described with respect to FIG. 1, a
77 lb. per 3300 sq.ft. Kraft stock coated with about
11 . ',
15 lbs./3300 ft~ of a clay coating (the composite being
available from Watervliet Paper Co. under designation "Envelope
Kraft-coated one side") was coated on the clay coated side with
about 10 lbs. per 3300 sq.ft. of a water moistenable adhesive
formulation dispersed in a water-organic solvent system of the
type described in the above mentioned Reiling U.S. Patent
3,425,968 dated 4 February 1969 and offered commercially by
Kimberly-Clark Corporation as the adhesive on its Pancake~ dry
gum label and business form paper. The coated web was then
dried free of solvent, the adhesive coating moistened with
water over a 1 in. 2 area and the web bonded to its reverse
side. Quick tack ranged about 23 sec. This was determlned by
separating the moistened stock immediately after application to
its reverse side. Separation was obtained by hand pulling at
an angle of about 120 and a rate of about 20 ln./min. ~he end
point was defined as the time at which coating separation
occurred.
After aging for 24 hours, the shear bond strength of the
construction prepared was greater than the tensile strength of
the stock ~about 30-38 lbs./in. width), however, the bond
readily separated as desired upon application of a peel force
of about 0.27 to 0.78 lb./inch width with the stock remaining
sssentially intact. This and other data contained in the
Examples were obtained using an Instron Model 1130 tester with
a jaw separation speed of 12 in.~min.
Example 2
Example 1 was repeated with a base sheet of 62 lbs. per
3300 sq.ft. of a clay coated latex saturated sheet (available
12.
from Kimberly-Clark Corporation under the designation Munising
Grade C-32714), and the result was a shear bond strength
exceeding the tensile strength of the base stock (about 29 to
37 lbs./in. width) and a web band that was also readily
separated when a peel force of about 0.35 to 0.65 lb./in. width
was applied. The quick tack results were 90 to 120 sec.
Example 3
Example 1 was repeated using a 112 lb~/3300 fta latex
saturated base sheet with a clay coating on both sides
(available from Kimberly Clark Corporation under designation
Munising Grade M31415). The result was a shear bond strength
exceeding the tensile strength of the stock (about 42 to 49
lbs./inch width). The bond, however, was readily separated
when a peel force of about 0.6 to 1.1 lb./inch width was
applied. The quick tack of this construction was about
300 sec.
Example 1 was repeated using a base sheet of 47 lbs. per
3300 sq.ft. of a densified Kra~t coated with 8 lbs.~3300 ft~ of
polyvinyl alcohol resin (Gelva grade 20-30 from Monsanto)
applied by Meyer rod rom a 72% aqueous methanol mixture. For
this Example, the moistenable adhesive was applied to the side
opposite the polyvinyl alcohol resin coating. In this case,
the shear bond strength of the construction was about
7.5 lbs./inch width and the bond readily separated by applying
a peel force of about 0.14 to 14 lbs./inch width.
Example 5
The base stock of Example 2 was coated on the clay coated
side with 12 lbs./3300 ftl of a blend of polymers and
copol~mers of ethylene and vinyl acetate (offered by
Kimberly-Clark Corporation, Brown-Bridge Division on coated
stock as adhesive 808-PP). The coated web was dried free of
water and the adhesive activated at 320F for 5 seconds with a
heating iron applied over a 1 in. 2 area in contact with the
reverse side. After 24 hours, the shear bond strength exceeded
the tensile strength of the stock ~about 26 to 32 lbs./inch
width). ~owever, the bond readily separated as desired upon
application of a peel force of about 0.45 to 0.8 lb./inch width
with the stock remaining essentially intact.
Example 6
The base stock of Example 2 was coated on the clay coated
side with about 12 lhs./3300 ft2 of a blend of styrene and
acrylic ester polymers and copolymers applied from a water
dispersion (offered by Kimberly-Clark Corporation, Brown-Bridge
Division on coated stock as adhesive SA-354). The coated stock
was dried free of water, and the adhesive activated over a
1 in.~ area by treating with toluene and bonded to its reverse
side. After 24 hours, the shear bond strength was between 14
and 32 lbs./inch width. However, the bond readily separated as
desired upon application of a peel force of about 0.1 to
0.3 lb./inch width with the stock essentially intact. The
quick tack after solvent activation with toluene, averaged
150 sec.
14.
For comparison, two samples of coiled stamps obtained from
a U.S. Post Ofice banded by a web of 38.5 lbs./3300 ft2
bleached Kraft coated ~ith 16 lbs./3300 ft2 of a vegetable
based water moistenable adhesive were also tested. These bands
had a shear bond strength in excess of the tensile strength of
the paper (about 20 to 23 lbs./inch width) and both delaminated
within the base
web, itself, upon hand peeling by grasping the finger tab, thus
hindering unwrapping of the coil stamps. The same result
occurred upon mechanical testing of laboratory prepared samples
using a peel force of 0.25 to 0.45 lb./inch width.
While the invention has been demonstrated with respect to
specific adhesives, it will be apparent that by following the
criteria defined above, suitable adhesive coated sheets in
accordance with the invention may be made with other types of
adhesives as well.
; Thus, it is apparent ihat there has been provided, in
accordance with the invention, a releasable adhesive sheet
material that fully satisfies the objects, aims, and advantages
set forth above. While the invention has been described in
coniunction with specific embodiments thereof, it is evident
that many alternatives, modifications, and variations will be
apparent to those skilled in the art in light of the foregoing
description. Accordingly, it is intended to embrace all such
alternatives, modifications, and variations as fall within the
spirit and broad scope of the appended claimsO
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