Pressure-sensitive adhesive based on partially oriented and partially crystallized elastomer

A pressure-sensitive adhesive comprises an elastomer having a partially oriented and partially crystallized elastomer component. Articles comprising the pressure-sensitive adhesive on a backing or substrate are also disclosed, as are methods of preparing the adhesive and the articles.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to pressure-sensitive adhesives, articles comprising 
substrates or backings coated with such adhesives, a hot-melt process for 
preparing such adhesive-coated backings, and the use of such articles. 
More specifically, this invention relates to pressure-sensitive adhesives 
having a partially oriented and partially crystallized elastomer component 
which, in a particularly preferred embodiment, imparts anisotropic peel 
behavior to the adhesive. 
2. Description of the Related Art 
Pressure-sensitive adhesives ("PSAs") are typically provided in the form of 
a tacky adhesive coating that is disposed on a backing (e.g., a tape or a 
sheet made of polymeric film, metal foil, paper, cloth, release liner, 
etc.). Such adhesives are useful for adhesively bonding two surfaces 
together with light finger-pressure, so as to form a relatively weak bond 
that usually can be easily broken by peeling the adhesive-coated tape or 
sheet to remove it from the surface to which it is attached. Preferably 
the adhesive-coated tape or sheet can be removed without damaging the 
surface and without leaving adhesive residue behind. A PSA article 
commonly used today is Scotch.TM. brand masking tape made by the 3M 
Company, which began using rubber-based PSAs for such articles in the late 
1920s. 
A solvent-free, hot-melt process for preparing a PSA from a tackified 
non-thermoplastic elastomer, such as natural rubber, polyisobutylene, and 
other hydrocarbon elastomers, is described in the PCT international patent 
application (of the assignee hereof) published May 26, 1994 as WO 
94/11175. The process uses a continuous compounding device that has a 
sequence of alternating conveying zones and processing zones which 
masticate the elastomer and mix the elastomer, tackifier, and adjuvants to 
form the adhesive. Molten adhesive may be pumped through a coating die in 
the form of a thin film and directly onto a support which preferably 
comprises a moving web that passes around a heated coating roll. 
Japanese kokai patent application no. HEI 71995!-18227, published Jan. 20, 
1995, describes anisotropic adhesive material having an adhesive layer on 
at least one side of a base having anisotropic flexibility and corrugated 
orcord-like structure. 
U.S. Pat. No. 5,156,911 (Stewart), issued Oct. 20, 1992, discloses 
skin-activated, temperature-sensitive adhesive assemblies. In one 
embodiment there is an adhesive that is substantially non-tacky at or 
below room temperature, becomes aggressively tacky at skin temperature, 
but reverts to its substantially non-tacky condition upon cooling (e.g., 
by applying ice or a cold pack). Regardless of the embodiment, the 
adhesive includes a crystallizable polymer that may be crosslinked. 
Similar materials are described by R. Clarke et al. in "Temperature 
Switchable Pressure Sensitive Adhesives," Adhesives Age, September, 1993, 
pp. 39-41. 
There is a desire for adhesives that have anisotropic peel behavior (i.e., 
different adhesion when peeled in different directions). Such adhesives 
would be useful in many applications (e.g., graphic application tapes and 
other uses described more fully below). If an adhesive article having such 
properties could be provided independent of a backing, substantial 
flexibility in backing selection would be possible. It would also be 
desirable if a known adhesive composition could be manufactured in a 
manner to provide such properties. There is also a desire for adhesives 
having heat activatable tack as these would be useful in situations where 
low initial tack is advantageous, especially if known adhesive 
compositions can be manufactured in a manner to provide such properties. 
SUMMARY OF THE INVENTION 
In one aspect, the present invention provides a pressure-sensitive adhesive 
comprising a partially oriented and partially crystallized elastomer. 
Preferably, the molecular repeat units of the elastomer are partially 
directionally oriented and exhibit partial crystallinity. By "partially 
oriented" it is meant that the elastomer is sufficiently oriented that the 
orientation can be revealed by optical birefringence, infrared dichroism, 
or x-ray diffraction. By "partially crystalline" it is meant that the 
elastomer has sufficient crystallinity to be detected by differential 
scanning calorimetry or X-ray diffraction. 
Varying the degrees or extents of orientation and crystallinity in the 
elastomer can advantageously influence the properties of the PSA. For 
example, in one embodiment of this invention, the orientation and 
crystallinity of the elastomer are sufficient to impart anisotropic peel 
forces to a PSA article (e.g., a substrate or backing on which the PSA is 
coated). The anisotropic peel force is an unusual property because the 
force necessary to peel the PSA article from a surface to which it is 
adhered varies when measured along different axes. That is, the PSA 
article displays different adhesion when peeled from the surface in 
different directions. The degrees of orientation and crystallinity of the 
elastomer can be sufficient to cause (1) the peel force measured in the 
direction parallel to the preferred orientation to be substantially less 
than that observed for a PSA of the same formulation but whose elastomer 
is not oriented, and to cause (2) the peel force measured in the direction 
perpendicular to the preferred orientation to be substantially greater 
than that measured in the parallel direction. Generally, the peel force in 
the parallel direction will be less than 90%, preferably less than 50%, 
and most preferably less than 10%, of the higher peel force (i.e., the 
peel force in the perpendicular direction). 
When the PSA article is made by extruding the adhesive, the preferred 
orientation of the elastomer will generally be the "machine direction" (or 
"MD"), that is, parallel to the extrusion coating line. The direction 
perpendicular to the extrusion coating line is generally referred to as 
the "cross direction" (or "CD"). For example, in the case of PSA-coated 
tape made by extruding a hot melt of tackified-natural rubber PSA onto a 
continuously moving web backing, the peel force of the tape is 
substantially different depending on whether the tape is peeled from an 
adhered surface in the direction parallel to the extrusion coating line 
(the machine direction) or the cross direction (i.e., the direction 
perpendicular or transverse to the extrusion coating line). 
Generally, the ratio of the peel force in the machine direction to the peel 
force in the cross direction is less than 1, more preferably about 0.9 to 
0.002. However, heating the anisotropic PSA to a temperature above the 
melting point of oriented, crystalline regions of the elastomer 
irreversibly converts the PSA to an essentially or substantially isotropic 
state, the ratio of the MD peel force to the CD peel force being 
essentially 1. 
The unique anisotropic peel force property enables PSA articles of the 
invention (e.g., PSA-coated tapes or sheets) to be advantageously used in 
graphic arts applications, (e.g., a premask tape, a prespace tape, a 
graphic art film, die-cut products, or dry transfer lettering, such as the 
graphic arts products described by Satas, supra, Chap. 32). The 
anisotropic PSA articles of this invention can also be used as a diaper 
fastening tape, a wall decoration film, or other constructions wherein 
differential peel is desirable. 
As the degrees of orientation and crystallization in the elastomer 
increase, they become sufficient to impart to the PSA tack and peel 
resistance which are relatively low in both the machine and cross 
directions (and much lower than that of a PSA having the same formulation 
but in which the elastomer is non-oriented and non-crystalline). However, 
when such a low-tack embodiment of the PSA is heated above the melting 
point of the oriented, crystalline elastomer the elastomer crystals melt, 
the orientation relaxes, and the adhesive properties (tack and peel 
resistance) irreversibly convert to the higher tack and peel resistance 
typical of conventional PSAs of the same formulation. Where the degrees of 
orientation and crystallinity are sufficient to produce relatively low 
tack and low peel force in both the machine and cross directions, these 
two adhesive properties will increase upon heating and become essentially 
or substantially the same in both the machine and cross direction. That 
is, the PSA layer will become isotropic. 
In another embodiment, a PSA article of this invention with an initially 
low-tack adhesive layer is selectively heated to provide a pattern of 
spatially-varying regions of high and low tack to control the adhesive 
force of the article. 
The invention also relates to various processes, such as a process of 
bonding one or more substrates or objects together by applying the PSA to 
the bonding surfaces. Another aspect of the invention provides a process 
of transferring one or more objects from one location to another location, 
by applying to the surfaces of such objects the PSA, and transferring the 
resulting bonded product to the other location. 
In another aspect of this invention, a PSA article is made by a 
solvent-free, hot-melt process which can use, for example, the compounding 
devices, pumps, dies, and coating rolls which are described in published 
PCT application WO 94/11175, which description is incorporated herein by 
reference. 
The process of making a PSA of this invention, in one aspect, comprises (a) 
masticating or milling a normally solid, undeformed, uncured elastomer 
capable of orientation and strain-induced crystallization, such as uncured 
natural rubber or polyisobutylene; (b) optionally, blending such elastomer 
with tack-inducing additives; (c) heating the masticated elastomer or 
elastomer/tackifier blend above room temperature (&gt;23.degree. C.) to form 
a hot, tacky substance; (d) shaping by shearing, elongating, stretching or 
extending the hot substance to induce stress and strain therein, thereby 
partially molecularly orienting the elastomer; and (e) cooling or 
quenching the resulting hot, oriented composition to a temperature below 
the melt temperature of the oriented elastomer and at a cooling rate fast 
enough to induce partial crystallization in the elastomer in its oriented 
state. 
The hot, tacky substance can be stretched or extended by extruding it, for 
example through the slot of an extrusion die. The film-extrudate can be 
coated or deposited on a backing, such as a biaxially-oriented polyester 
film or a release surface, and then cooled, thereby providing a PSA 
article of this invention, such as a PSA tape or sheet. The cooling can be 
carried out, for example, by depositing the PSA extrudate on a web 
(backing) conveyed by a coating roll having chilled water circulating 
through its interior. Alternatively, the hot, tacky elastomer-containing 
substance and a thermoplastic precursor of the backing can be coextruded 
as a laminate. The PSA extrudate coated on the backing or the coextruded 
laminate may be stretched and cooled to induce the partial orientation and 
crystallization. 
The manufacturing process can affect the extents of orientation and, as a 
result, the properties of the PSA. For example, if the cooling rate is 
relatively slow, then the cooled PSA may have high tack and isotropic peel 
force. As the cooling rate is accelerated, the PSA will have less tack and 
the peel force will be more anisotropic. At relatively fast cooling rates, 
the cooled PSA may have quite low pressure-sensitive tack and low or 
imperceptible peel force. The desired rate of cooling (to produce the 
desired orientation, crystallization and, thus, the desired degrees of 
anisotropy, tack, and peel force) will vary and depends on factors such as 
the particular adhesive components used and the amounts thereof, the 
temperature of the shaped adhesive, the thickness of the PSA coating, the 
particular equipment and operating conditions used to make the PSA article 
(e.g., line speed), and the use or application to be made of the article. 
In order that the PSA article have the desired heat or solvent resistance 
for a particular application, the PSA can be cured or crosslinked. For 
example, where the PSA article is a masking tape to be used in paint 
spraying operations and has to undergo the paint stoving process, a 
crosslinked PSA is particularly useful. However, crosslinking processes 
which involve heating may be detrimental to preserving the orientation and 
crystallinity in the PSA.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, and initially to FIG. 1, reference number 20 
generally designates a device or apparatus which can be a single unit or a 
series of units interconnected so as to continuously compound or process 
the elastomer component of the PSA used in this invention. Device 20 can 
be a twin-screw extruder, such as a Werner-Pfleiderer.TM. co-rotating, 
twin-screw extruder, e.g., Model ZSK-30 or ZSK-60. Device 20 can have a 
sequence of alternating and interconnecting conveying and processing 
sections or zones. A plurality of metering hoppers 21, 22, 23, connected 
to a corresponding plurality of inlet openings, are provided to feed the 
PSA components to device 20 at controlled rates. K-Tron.TM. automatic 
loss-in-weight feeders or liquid addition devices, such as heated pail 
unloaders or liquid metering pumps, can be used to obtain these rates. A 
vent 24 can be provided at the downstream or discharge end of device 20 to 
release volatile substances therefrom. A melt pump 26, such as a 
Zenith-Nichols.TM. gear pump, is connected to the discharge end of device 
20 to convey therefrom at a controlled rate a hot melt of the compounded 
PSA (i.e., molten, compounded PSA). A filter 27 can be disposed downstream 
of pump 26 to filter the metered hot melt and remove unwanted contaminants 
therefrom. Alternatively, the filter 27 can be disposed upstream of pump 
26. 
The molten PSA is shaped by extruding it from an opening or slot in a 
direct-contact coating die 32, such as a flexible blade coater with a 
silicone rubber wiping blade affixed to the upper side of the die slot. 
The die can also be a rotary rod contact die. The die deposits, coats, 
smears, or wipes the molten PSA extrudate as a continuous coating or film 
with desired thickness, e.g. 20-75 .mu.m, onto one surface of a moving web 
34. However, the PSA need not be a continuous coating on the web. It can 
also be provided as a longitudinally or transversely discontinuous coating 
or film. Web 34 provides the backing for the PSA article and may be made 
of any material desired, including those commonly employed as backings for 
pressure sensitive adhesive tapes such as biaxially-oriented polyester or 
polypropylene, vinyl, cloth, paper, metal foil, etc. Additionally, the web 
can be a release surface such as a release liner. 
Shaping and straining of the elastomer component of the PSA melt occurs as 
it flows out of die 32 and is wiped onto web 34. Web 34 passes over a 
guide roll 30 and is conveyed to and from the orifice of die 32 by a 
cooled coating roll or drum 35. The relative positions of die 32 and 
coating roll 35 can be such that the PSA extrudate is deposited as shown 
on the surface of the roll. Roll 35 can be a chromed steel coating roll 
(particularly useful with the flexible blade coater) or a rubber-covered 
coating roll (particularly useful with the rotary rod contact die). The 
interior of the roll 35 can be supplied with a temperature-controlled 
cooling medium (e.g., circulating water) to maintain the roll temperature 
to effect rapid cooling or quenching of the molten of PSA extrudate to 
obtain the desired degrees of orientation and crystallization of the 
elastomer component. Cooling of the molten PSA extrudate is caused by the 
transfer of heat from the extrudate to the backing which is cooled by roll 
35. Alternatively, when roll 35 is rubber-covered, an additional cooled 
roll 36 can be used for cooling the surface of roll 35 to provide the 
requisite quick cooling of the PSA extrudate. Alternatively, or in 
addition, cooling can be provided by a spray device 37 mounted or disposed 
above coating die 32 to spray a cooling medium, such as a mist of water or 
a curtain of chilled nitrogen gas, onto the surface of the molten PSA 
extrudate as it exits the die. A further alternative is to precool web 34 
and to coat the PSA onto the cooled web (which acts as a heat sink). 
Another alternative is to cool the PSA-coated web 38. 
The PSA-coated web 38 may be wound up and slit or otherwise cut to the 
desired size or configuration. As shown in FIG. 1 it may first be conveyed 
to a crosslinking station 39 where the PSA layer on the web is exposed to 
radiation from a radiation source 41. Radiation source 41 may be an 
electron beam (e.g., an Electrocurtain.TM. unit) or ultraviolet radiation. 
Radiation provides crosslinking of the elastomer component of the PSA and 
produces a cross-inked PSA-coated web 42 which may be wound up and cut to 
size. A release coating and/or low-adhesion backsize, such as that 
conventionally used on PSA tapes, may also be applied to the web, either 
before or after the molten PSA extrudate is deposited thereon. Other 
details of the compounding and coating equipment illustrated will be 
omitted in the interest of brevity, such details being set forth in the 
aforementioned PCT application WO 94/11175. 
When coating on relatively thin backings (e.g., approximately 25 .mu.m 
thick), an effective quenching rate to produce the PSA elastomer component 
in the desired oriented, crystallized state can be achieved simply by 
controlling the temperature of the coating roll. With thicker backings, 
however, it may be necessary to employ additional cooling means, such as 
pre-chilling the backing prior to coating it with the PSA extrudate or 
applying cooling in the form of a chilled liquid or gas stream directed at 
the surface of the extrudate immediately downstream of the coating die. 
Other means can be employed, however. The important thing is that the 
cooling rate be sufficiently fast that crystallization occurs in the 
elastomer before the orientation induced by the shaping and/or coating 
operation has relaxed. 
FIG. 2 illustrates the design of a screw extruder that can be used for 
compounding device 20 in FIG. 1. Also shown are hoppers 21, 22 and 23 
which dispense the elastomer, tackifying resin, and antioxidant components 
of the PSA, respectively, into different extruder sections 1, 5, and 7, 
respectively, via inlet openings. The elastomer is kneaded or masticated 
in section 2, conveyed and further masticated in section 3, mixed with 
tackifying resin and/or other adjuvants in section 5, and mixed with 
antioxidant in section 7. Further mixing and mastication takes place in 
sections 6 and 8. The extruder screw has appropriate flights or turns to 
convey the PSA components from one section to a succeeding section in the 
direction indicated by the arrows in the upstream and downstream zones 1 
and 9, respectively. The extruder screw also kneads and masticates the 
elastomer. 
The elastomer can be supplied to device 20 as a warm mass from an external 
processing device. Alternatively, it can be fed in a pelletized or ground 
form and coated or dusted with powdered talc or other common parting 
agents to prevent or minimize the sticking of the elastomer to the screw 
or interior wall of the extruder. If aerobic processing is desired, an 
oxygen-containing gas, such as compressed air, can be injected (e.g., at a 
pressure of 5-100 psig, 30-700 kPa) into the extruder, for example, in 
section 3, to aid in the controlled reduction of the elastomer molecular 
weight and to ease processing of the PSA. During processing of the PSA and 
its components in the extruder, the various extruder sections are heated, 
e.g., to 160.degree. C., and, optionally, other adjuvants can be added to 
the extruder and compounded with the elastomer and tackifying resin. 
FIG. 3 illustrates the cross-section of a PSA article 43 of this invention, 
such as that cut from web 38 or 42 of FIG. 1. Article 43 comprises the PSA 
coating 44 derived from the hot PSA extrudate, and web or backing 46 such 
as biaxially-oriented polyester or polypropylene. 
As mentioned above, in one embodiment of the PSA article of this invention, 
the degrees of orientation and crystallinity of the PSA elastomer are 
sufficient to impart anisotropic peel force to the article. An article 
having anisotropic peel force may be used as a graphics application tape 
(including both premask and prespace tapes), which is useful in graphic 
arts work. For example, die-cut graphics often take the form of such vinyl 
decals. Typically, the decal is formed by cutting it from a sheet of 
colored, adhesive-coated vinyl film which has been laminated to a release 
liner. The waste or weed is peeled away and then a graphics application 
tape is applied to the top of the die-cut decals to lift them from the 
release liner while keeping them in register. The decals are then 
transferred to the desired target substrate and the graphics application 
tape is peeled away. Such graphics application tapes need to be aggressive 
enough to reliably lift all of the components of the graphic (i.e., the 
decals in this example) from the release liner, but still should be easily 
removed after transferring the graphic to the target substrate and should 
not pull any of the graphic off the target. This is often a difficult 
balance to achieve. Using the PSA tape of the present invention as the 
graphics application tape, one could pull in the high adhesion direction 
to remove the graphic from the liner, apply it to the target substrate, 
and then remove the graphics application tape by pulling in the low 
adhesion direction. Other graphics application tapes do not involve 
die-cut components but there would still be an advantage to having 
graphics application tapes with a very easy removal direction because the 
graphics can be very wide and difficult to pull off with conventional 
adhesives. When a conventional adhesive is formulated to have a low 
removal force, the ability to hold onto the graphic is impaired. The 
anisotropic PSA tapes of the present invention can have high holding 
ability but still have a low removal force. 
An embodiment of a graphics application article of this invention is 
illustrated in FIGS. 4-7. It comprises a tape or sheet generally 
designated 43 (a cross-sectional portion of which is also shown in FIG. 3) 
comprising a PSA coating 44 with anisotropic peel force on a backing 46. 
In FIG. 4, graphics application article 43 is shown placed on top of a 
release liner 51 which functioned as a substrate for PSA-coated die-cut 
letter 52 in the form of "E". The lower surface of graphic application 
article 43 is defined by the exposed surface of the PSA coating 44. By 
placing the article over the release liner 51 and then peeling or lifting 
the tape up in the direction shown in FIG. 4 by the vertical arrow (that 
is, the high adhesion direction or the cross direction shown by the 
horizontal arrow designated "CD"), the die-cut letter 52 is removed from 
the substrate because it adheres to PSA coating 44. This use of the 
graphic application article 43 is further illustrated in FIG. 6, where 
release liner 51 has removably mounted thereon in a desired pattern an 
array of PSA-coated die-cut letters 52a, 52b, 52c, 52d, 52e, and 52f, each 
comprising a backing 53 coated with a conventional isotropic PSA 54. FIGS. 
5 and 7 illustrate how the die-cut letters 52a, etc., loaded on 
anisotropic graphic application article 43 of FIGS. 4 and 6, respectively, 
can be removed therefrom and transferred to a target substrate 56. The 
letter-loaded graphic application article is placed on the target 
substrate and the graphic application article is peeled therefrom in the 
direction shown in FIG. 5 by the vertical arrow, (the machine direction 
shown by the arrow designated "MD"). The letter 52, "E", is thus 
transferred to the target substrate 56, as shown in FIG. 5, and the array 
of letters 52a, etc., are transferred in a desired pattern to the target 
substrate 56 as shown in FIG. 7. 
Another application in which the anisotropic peeling properties of the 
invention can be used is in the manufacture of diaper fastening tape. The 
low peel force of such a tape in the machine direction would allow a large 
stock roll of the tape to be unwound for converting without the aid of a 
release material. In the process of converting the stock roll to 
individual tapes, the tape could be cut so the cross direction of the 
stock roll, which is the high adhesion direction, becomes the direction of 
peel on the finished diaper product. 
Yet another application of the PSA article would be in wall decoration 
films. One can produce a graphic wall decoration with the anisotropic PSA 
article in such a way that the high adhesion direction is vertical or down 
the wall to prevent failure due to gravity, while the low adhesion 
direction is horizontal to provide an easy removal direction avoiding any 
damage to the wall. 
Another use for an anisotropic PSA article of the invention is in masking 
applications that use a maskant sheet or drape adhesively fixed to a 
substrate in order to mask a large area of the substrate. Maskant sheets 
or drapes are used in automotive painting or refinishing and in commercial 
and residential wall painting wherein a paper or plastic film is taped to 
the autobody part or the wall in order to prevent overspraying of a 
coating onto the area that is masked. If the maskant sheet is relatively 
long and heavy it will induce a constant peel force in the direction of 
the drape that may cause the tape to pull away from the substrate. The 
adhesive can be formulated to be more aggressive and overcome the stress 
induced by the weight of the drape, but the tape may then be difficult to 
remove completely from the substrate after the painting operation is 
completed. An anisotropic PSA tape of the present invention that exhibits 
low peel force in the machine direction and high peel force in the cross 
direction is useful in such masking applications. The tape can be made to 
have high peel resistance or holding ability in the cross direction to 
overcome the peel stress induced by the weight of the drape, but have only 
a very low peel or removal force in the lengthwise direction to remove the 
tape without damage to the substrate. Since heating the PSA tape could 
detrimentally affect its anisotropic characteristics, it is not 
recommended to pass the tape through a paint baking oven. 
Another use for an anisotropic PSA article of this invention is as an 
adhesively bonded wall hook or wall hanger, e.g., for a picture frame. 
Such an article would have its anisotropic PSA layer positioned such that 
its high adhesion direction would be down the wall to prevent adhesion 
failure due to gravity or the weight of the picture frame. The wall hanger 
can be easily repositioned if desired by removing it from the wall by 
pulling it therefrom in the horizontal direction (in which adhesion of the 
PSA layer is low), and then, when the hanger is in the new, desired 
position, heating it, for example, with a hot air gun or dryer, to fix the 
hanger in position. 
Another embodiment of this invention is a PSA article comprising a PSA 
layer of a partially oriented and partially crystalline elastomer, where 
the degrees of orientation and crystallinity of the elastomer are 
sufficient to impart tack and peel resistance which are relatively low in 
both directions (and much lower than that of a product of the same 
formulation in which the elastomer in the adhesive layer was non-oriented 
and non-crystalline). 
An application of the above-described low-tack PSA article of the invention 
is as a pressure sensitive tape that does not need a low adhesion backsize 
(LAB) on the back side of the adhesive-coated tape backing. Such a tape is 
useful, for example, where it is desirable to print directly on the back 
side of the tape. Printing on many commercially available tapes currently 
involves a multi-step process wherein the LAB coating is partially or 
completely removed, the printing is applied to the back side of the tape 
using standard flexographic methods, and then an LAB is again applied over 
the printed surface. Since the PSA tape of the present invention can be 
made to have very low tack, the LAB can be eliminated and indicia can be 
printed directly on the tape backing. The tape can then be wound up again 
into a roll having low tack, or an LAB can be applied over the printed 
backing and the tape heated up to provide a printed tape having normal 
tack and peel. Similarly, the low-tack PSA tape of this invention may be 
used to produce linerless labels that can be printed in the low-tack state 
and then heated immediately before application to restore the tack and 
peel resistance. For example, a tape or label stock having low tack could 
be (1) fed to a station that would print the desired indicia on the 
backing by any conventional printing technique, (2) advanced past a heated 
roller or wire to increase the tack of the adhesive, (3) be cut off to 
form a label of the desired length, and (4) be directly applied to a 
substrate. If the printing in this process is accomplished by thermal 
printing, and it is desired to store the resulting product before use, 
then one must be sure that the temperature needed for printing should be 
less than that needed to melt the crystalline regions of the elastomer 
component of the PSA and relax orientation in the adhesive. 
Another application of the low-tack PSA of the invention is in the 
manufacture of a PSA tape having tack so low that the surface of its 
adhesive layer will not stick to most other surfaces, but wherein the 
surfaces of the tape stick to each other. Surprisingly, the low-tack 
adhesive surface of this embodiment of the invention adheres aggressively 
to itself or another similar low-tack adhesive surface even though the 
adhesive surfaces are not tacky to the touch. Such a tape would be useful 
for a variety of fastening and sealing applications, such as, for example, 
diaper closures, sealing strips on envelopes and packages, clothing 
fasteners, and other applications where hook and loop fasteners are 
commonly used. 
Another application of the low-tack PSA of the invention is in bundling 
operations where a number of elements are bound together by wrapping with 
adhesive tape, but wherein the bundling tape initially has low tack to 
allow some slip during the bundling, and the bundle is then heated to 
increase the holding ability so that slip is eliminated. Such a tape would 
be useful in wrapping cables, filaments, reinforcing fibers, and other 
elongate members. 
The PSA article having low-tack oriented adhesive may also be treated by a 
zone heating technique to modify the PSA layer and impart a desired 
pattern thereto of spatially-variable tacky and nontacky regions or to 
impart different adhesive properties to different regions such as varying 
regular, random, or patterned zones of high and low tack. This 
modification (illustrated in FIGS. 9-11, described hereinafter) can be 
accomplished, for example, by placing a mask, such as clear polyethylene 
terephthalate film, on the exposed adhesive surface of a PSA article of 
this invention having low anisotropic peel force in the machine direction 
and directing infrared (IR) radiation toward the exposed face of the 
so-placed mask. The mask will have a desired array or pattern of 
laser-printed blackened features or zones which absorb the IR radiation, 
and transmit or reflect IR radiation through the non-blackened zones of 
the mask. The temperature of that portion of the PSA layer that lies 
beneath and in registry with the blackened zones of the mask is raised, 
e.g., to temperatures of 50.degree. to 150.degree. C. This causes thermal 
relaxation of the oriented, crystallized PSA elastomer component with a 
consequent increase in the tack of the so-heated portions of the PSA 
layer. The unwind noise of a PSA tape can be altered by spatially varying 
the tack of the adhesive. A PSA tape having such a patterned adhesive may 
also be used in security and tamper-evident applications wherein a 
predetermined pattern of adhesive could be left on the substrate when the 
tape is removed. 
Additionally, selectively heating regions of the PSA layer to increase the 
tack could be an alternative to pattern coating an adhesive or selectively 
detackifying areas of an adhesive with varnishes or cover films. For 
example, "pouch tapes" used to form pockets that contain invoices or other 
documents on shipping cartons are currently made by coating the entire 
surface of the backing with adhesive, and then coating the center section 
with a varnish to deaden the adhesive everywhere except at the periphery 
of the pouch. Documents can then be placed in the center region, so that 
they do not contact the active adhesive at the periphery, and then the 
pouch is pressure-sealed to the shipping container by the exposed tacky 
adhesive at the edges of the pouch. 
Alternatively, a pouch may be made from a low-tack PSA tape of the present 
invention. Documents can be placed directly against the low tack adhesive 
surface of the tape and positioned as desired on the shipping carton. The 
periphery of the pouch can then be heated, for example by a heated iron 
that limits heating to the peripheral edge where it is desired to increase 
the tack and peel of the adhesive. 
Similarly, the low-tack PSA article of the present invention may be used as 
an alternative to pattern coating an adhesive, which often requires 
precise registration of the adhesive application. This is used, for 
example, in cover tapes for surface-mount component carrier tapes wherein 
it is desired that adhesive be present only at the outer edges of the 
cover tape so that it contacts only the side rails of the carrier tape and 
not the components which are held in the pockets of the carrier tape by 
the cover tape. It is difficult to obtain the precise registration of 
adhesive needed for this application, and often a blocker film is used 
down the center of the adhesive coated cover tape to ensure that the tacky 
surface of the adhesive does not contact electronic components that are 
held in the pockets of the carrier tape by the cover tape. Alternatively, 
the low-tack PSA of the present invention can be used on the entire 
surface of the cover tape, but then activated only at the edges by 
heat-sealing the cover tape to the side rails of the carrier tape. 
Similarly, a low-tack PSA of the present invention can be used in 
applications where pattern coating of the adhesive is needed by simply 
heat activating only those areas of the adhesive where sealing is desired. 
Any of the natural rubbers which have heretofore been used or proposed for 
use as the elastomer component of natural rubber-based PSAs can be used to 
make the PSAs used in the practice of this invention. Uncured natural 
rubber is chemically unsaturated and an amorphous material in the 
unstressed or unstretched state and is subject to strain-induced 
orientation and crystallization (at least partially) of its molecules upon 
stretching. Natural rubber hydrocarbon is a 1,4-polyisoprene having 
essentially 100% cis structure and has little inherent tack (thus, it is 
preferably compounded with tackifying resin for PSA use). Commercial 
natural rubber products which can be used in making the PSAs of this 
invention are the visually graded rubbers known as ribbed smoked sheets 
and pale crepes, the technically specified rubbers, such as the SIR or 
SMR, and the controlled viscosity grades such as the CV60 version (which 
are described in Kirk-Othmer, Encyclopedia of Polymer Sci. and Eng., Vol. 
14, p. 692, John Wiley E. Sons, Inc., 1988, which description is 
incorporated herein by reference). 
Polyisobutylene, also useful as the non-thermoplastic elastomer component 
of the PSAs of this invention, has little tendency to crystallize in the 
unoriented state but likewise is subject to orientation and strain-induced 
crystallization upon stretching. This elastomer has only terminal 
unsaturation. It has inherent tack at low molecular weight, though it is 
often compounded with tackifying resins to obtain the balanced PSA 
properties. Commercially available polyisobutylene products which can be 
used in this invention include those high molecular weight, normally solid 
products, such as Vistanex.TM. MM L-80. Low molecular weight 
polyisobutylene, such as Vistanex.TM. LMMS, can be used along with the 
high molecular weight version to contribute tack (see the description of 
Vistanex.RTM. Polyisobutylene in product bulletin SYN-76-1434 published by 
Exxon Chem. Co. U.S.A., which description is incorporated herein by 
reference). 
Tackifying resins useful as components of the PSAs of this invention 
include those normally liquid or solid resins known to tackify natural 
rubber- and polyisobutylene-based PSAs. Those resins preferably have 
molecular weights that are relatively lower than the elastomer component 
and glass transition temperatures higher that the elastomer component. The 
main classes of tackifying resins useful herein include the known classes: 
wood rosin and its derivatives; petroleum based resins; and terpenes. The 
amount of the tackifying resin to be used will be that sufficient to 
impart the desired tack to the PSA, and that amount generally will be 10 
to 400 parts, preferably 20 to 150 parts, by weight, per 100 parts by 
weight of elastomer. Particularly useful commercially available tackifying 
resins for tackifying natural rubber are Piccolyte.TM. S-115 terpene and 
Escorez.TM. 1310. Particularly useful commercial petroleum-based resins 
useful in tackifying polyisobutylene-based PSAs are Escorez.TM. 1310 
tackifiers. 
Other adjuvants commonly used in rubber-based PSAs can also be included in 
the PSAs of this invention, such as antioxidants, e.g., Irganox.TM. 1010 
tetrakismethylene-3-(3', 
5'-di-tert-butyl-4'-hydroxyphenyl)-propionate!methane, plasticizer oils, 
e.g., white mineral oil, elastomer oligomers, waxes, and inorganic 
fillers, e.g., talc, zinc oxide, titanium dioxide, aluminum oxide, and 
silica (see Satas, supra, Chap. II for a description of such adjuvants). 
Typically, the amount (on a weight basis, per 100 parts by weight of 
elastomer) of antioxidant to be used will be up to 5 parts, the amount of 
plasticizer will be up to 50 parts, preferably up to 20 parts, and the 
amount of filler will be up to 50 parts. 
The materials which can be used as a backing or substrate for the PSA 
articles of this invention include those heretofore used for rubber-based 
PSA articles, including polymeric films, e.g., flexible polypropylene and 
polyester films, metallic foils, paper, ceramic films, and the like. Such 
backings can also comprise a plurality of fibers in a woven or nonwoven 
mat-like construction. The other side of the backing can be coated with a 
release coating or low adhesion backsize and the PSA layer can be covered 
with a release liner. Backings and release coatings or liners are 
described in Satas, supra pp. 208-211, 585-600, which description is 
incorporated herein by reference. 
EXAMPLES 
The invention is illustrated in the following examples, but the particular 
materials and forms and amounts thereof, and the equipment and process 
conditions which are set forth in these examples, should not be construed 
to unduly limit this invention. In preparing the PSA articles of these 
examples, equipment like that illustrated in FIG. 1 was used. In these 
examples, the orientation and crystallization of the elastomer PSA 
components were measured at room temperature with a combination of 
techniques. The molecular weight of the natural rubber after processing in 
the mastication section of the extruder was measured in terms of inherent 
viscosity (IV). The tack and peel force of the PSA products were also 
measured. The techniques or methods of these measurements are as follows. 
The optical birefringence measurements of the PSA showed evidence of 
orientation in that the PSA had different refractive indices for light 
polarized parallel to the machine direction compared to that for light 
polarized perpendicular to the machine direction. 
The crystallinity of the elastomer in the PSA was detected by x-ray 
diffraction analysis. The degree of crystallinity was estimated from 
differential scanning calorimetry analysis and was determined to be low in 
these samples, viz., on the order of a few percent by weight of the 
elastomer. 
Direct measurement of the PSA orientation was made using samples of PSA 
which were coated on the release side of a film which had been previously 
treated with a silicone release coating. Multiple layers of the adhesive 
were transferred from the release film to a clean glass slide (of 
microscope quality but larger in dimension) by applying the glass slide to 
the adhesive surface, trimming the adhesive around the edge of the slide 
with a razor blade, and lifting the slide. This process was repeated as 
many times as necessary to obtain the desired number of adhesive layers, 
maintaining the relative orientation of the slide and the coated adhesive 
each time. The slide was mounted on a sample holder on an optical bench. 
The birefringence of the PSA samples was determined by adjusting the 
Babinet compensator so that its birefringence was equal and opposite to 
that of the sample, as indicated by the black line appearing in the center 
of the crosshairs of the compensator eyepiece. The birefringence of the 
sample was determined by the compensator setting, the wavelength of the 
light (546 nm), and the sample thickness following standard methods, such 
as described by White, J. L. et al. in Encyclopedia of Polymer Science, 
John Wiley & Sons, Vol. 10, p. 605, 1987. The definition of birefringence 
is the difference in refractive index of the sample for light polarized in 
two mutually perpendicular directions. In this patent specification, the 
birefringence value is the refractive index difference for light polarized 
parallel and perpendicular to the direction of preferred orientation. 
Fourier transform attenuated total reflectance infrared (FT AIR-IR) 
dichroism measurements were performed on some of the PSA articles of this 
invention to measure the molecular orientation in the plane of the 
coating. The method is more fully described by F. Mirabella in J. Applied 
Spectroscopy 42(7), 1258-1265 (1988), and J. Polymer Science, Polymer 
Physics Edition 22, 1283-1304 (1984). The Nicollet 10-DX Fourier Transform 
infrared spectrometer that was used was fitted with an ATR attachment and 
a germanium (Ge) single diamond polarizer (Harrick, PSD-J1R). A Ge 
internal reflection element cut for a 45.degree. incidence angle was 
placed at 22.degree. from the normal to the beam after the polarizing 
element and before the detector. The crystal measured 50 mm.times.20 
mm.times.3 mm thick. The actual incidence angle into the Ge crystal was 
calculated to be 39.degree. due to refraction, corresponding to a 1 micron 
thick penetration depth of the infrared energy into the pressure-sensitive 
adhesive coating. We found that an absorption at 1130 cm.sup.-1 was 
sensitive to orientation in the sample such that its absorption intensity 
was higher when the IR beam was polarized along the machine (or web) 
direction compared to when the beam was polarized along the transverse 
direction for samples having anisotropic peel adhesion and molecular 
orientation. The tape samples were directly adhered to both sides of the 
Ge crystal. The polarization of the incident IR beam was selected to be 
parallel to the plane of the adhesive coating. When a PSA sample was 
mounted with the electric field vector of the radiation parallel to the 
machine direction, the machine direction absorption spectrum was obtained. 
Conversely, when a sample was mounted with the electric field vector 
parallel to the cross-web direction, the cross-web absorption spectrum was 
obtained. The intensity of the 1130 cm.sup.-1 band was measured as the 
peak height minus the baseline signal. This value was normalized by 
dividing this intensity by the intensity of the 1095 cm.sup.-1 absorption 
(also having baseline signal subtracted) which is independent of 
orientation so that sample contact area artifacts for the MD and CD 
spectra could be factored out. For each spectrum, 50 scans for both 
background and sample were averaged. For each sample, the relative 
absorptance of the 1130 cm.sup.-1 band for both machine and cross-web 
directions was measured. The "IR anisotropy" is defined as the ratio of 
the normalized absorptance of the 1130 cm.sup.-1 band for IR radiation 
polarized in the machine direction to the absorptance for radiation 
polarized in the cross direction. 
The resistance of a PSA tape to peeling under a constant load was measured 
by the test referred to as adhesion at constant angle and stress (ACAS) 
which is a variation of PSTC 14 (Pressure Sensitive Tape Council, 
Glenview, Ill.). The static load peel resistance of the tapes was tested 
in the following manner. A strip of tape 0.75 inch (1.9 cm) wide was cut 
with a razor cutter and applied to a polished stainless steel panel. For 
some of the testing, a quartz substrate was used instead of stainless 
steel. The panels were cleaned between uses by washing once with diacetone 
alcohol and then three times with heptane, wiping with Kimwipe.TM. sheets 
each time. The tape was rolled down onto the panel with a 4.5 lb (2 kg) 
rubber-coated roller 4 inches (10 cm) in diameter using two passes at 
approximately 12 in/min(30.5 cm/min). A wire hook was affixed to one end 
of the tape strip. The panel was mounted horizontally with the tape on the 
bottom side. A 200 g weight was hung from the hook and the peel rate was 
determined by measuring the time to peel the 3-inch (7.6 cm) length of the 
panel. The peel resistance was calculated as the inverse peel rate in 
min/in. Replicate measurements were made and the peel resistance values 
averaged. The results using this test method are referred to herein as 
ACAS1. Alternatively, the aforementioned test was run using quartz plate 
as a substrate instead of stainless steel and the alternative test results 
are referred to herein as ACAS2. 
The peel strength at fixed peeling speed was also measured using an 
Instron.TM. universal test machine. A 1-inch (2.54 cm) wide strip of tape 
was cut and applied to a flat glass plate. The strip was rolled down with 
two passes of a 4 5 lb (2 kg) rubber covered roller as in the holding 
power measurements described above. The glass plate with attached sample 
was mounted horizontally in a sliding jig on the Instron machine. A cord 
attached to the front edge of the sliding plate was threaded through a 
pulley and attached to the crosshead. The tape tab was clamped in the 
grips attached to the force transducer in the moving crosshead. The tape 
was peeled by moving the crosshead up at a constant speed of 12 in/min 
(3.5 cm/min). This arrangement allowed for 90.degree. peel of the tape 
while maintaining the peel front directly below the crosshead. The average 
peel force during the peeling was determined. The peel strength is 
expressed as the force divided by the width of the tape. The results of 
this test are referred to herein as PL1. 
Another peel strength test was used for some of the testing. In this 
further test, a piece of biaxially-oriented polypropylene (BOPP) film was 
applied to a stainless steel test panel with double-sided PSA tape. The 
PSA tape product of this invention to be tested was slit to a 1-inch (2.54 
cm) width and then applied to the BOPP film and rolled down as described 
in the above-described PL1 test. The tape was peeled by the Instron 
machine with a 180.degree. peel angle with a crosshead speed of 12 in/min 
(30.5 cm/min). The average peel force was measured and the peel strength 
calculated as the peel force divided by the tape width. The results of 
this test are referred to herein as PL2. 
A third type of peel test was conducted by applying a 1 inch (2.54 cm) wide 
strip of the PSA tape of this invention to a glass substrate, rolling and 
peeling at a peel angle of 180.degree. and a peeling speed of 90 
inches/min (228.6 cm/min). The results of the test are referred to herein 
as PL3. The same test method was run at a peel rate of 12 inches/min 
(30.48 cm/min) and the results are referred to herein as PL4. 
Tack was measured by the rolling ball test method described in PSTC 6. A 
strip of adhesive tape was mounted, adhesive side up, at the base of an 
inclined plane. A stainless steel ball was released from the top of the 
inclined plane and the distance it traveled on the adhesive surface before 
stopping was measured. Results are averages of two measurements. The 
results of this test are referred to herein as RBT. 
The molecular weight of the natural rubber after processing in the 
mastication zone of the extruder was sometimes characterized using 
inherent viscosity (IV) measurements. This technique is well known in the 
polymer science art. A sample of the rubber was removed from the extruder 
at the tackifier addition port with the tackifier addition turned off. 
This sample was dissolved in toluene and diluted to a concentration of 
0.15 g/dl.+-.0.02 g/dl. The diluted solution was centrifuged to remove 
insoluble components. A 10 ml portion of the solution was transferred to a 
Cannon-Fenske glass capillary viscometer. The viscometer and solution were 
equilibrated for 5 min in a water bath maintained at 25.degree. C. The 
solution was then drawn up in the viscometer to the indicated mark with a 
squeeze bulb and allowed to flow through the capillary of the viscometer. 
The time for the solution to flow through was measured with a stopwatch. 
This procedure was repeated for a sample of the pure solvent in the same 
viscometer. The precise polymer concentration was determined by delivering 
20 ml of solution with a pipette to a preweighed aluminum drying dish. The 
solution was placed in an oven at 100.degree. C. for 2 hours. The 
remaining polymer weight was then determined. All weights were determined 
using an analytical balance with 0.1 mg resolution. The IV (inherent 
viscosity) was calculated by the following relation: 
##EQU1## 
wherein: t.sub.solution is efflux time for the polymer solution 
t.sub.solvent is efflux time for the solvent 
c is polymer concentration (g/dl) 
1n is natural logarithm. 
Examples 1-4 and Comparison Example A 
All of these examples were produced with a single adhesive formulation and 
fixed extruder conditions. The formulation consisted of the following 
components: 
______________________________________ 
Component Parts by weight 
______________________________________ 
Natural rubber (ribbed smoked sheet) 
100 
Piccolyte .TM. S-115 tackifier 
65 
Irganox .TM. 1010 antioxidant 
1 
______________________________________ 
The natural rubber, supplied by Goodyear Chemical Plantation Division, was 
ground and fed to the extruder at a rate of 68.4 g/min. The Piccolyte.TM. 
S-115 tackifier was ground and dry blended with Irganox.TM. 1010 
antioxidant at a weight ratio of 65/1 Piccolyte.TM. S-115/Irganox.TM. 
1010, and this blend was fed at a rate of 45.1 g/min to the extruder at a 
second addition port downstream of the rubber addition. The extruder screw 
configuration shown in FIG. 2 was used along with air injection to the 
rubber mastication zone. The screw speed was 475 rpm and temperature in 
the mastication zone was 172.degree. C. Under these conditions, the rubber 
IV was 2.0 dl/g. The line speed was 60 ft/min (18.3 m/min) and the 
adhesive melt temperature at the die was 100.degree. C. A contact type die 
was used with a rubber lip in conjunction with a chromed steel backup roll 
as shown in FIG. 1. 
The quick cooling of the PSA extrudate was effected with a backup roll 
having a diameter of 30 cm and a circumference of 94 cm. The roll interior 
was maintained in Examples 1-4 at temperatures of 15.degree. to 50.degree. 
C. using circulating water. In Comparison Example A, the backup roll 
interior temperature was 70.degree. C. In all examples, a biaxially 
oriented polyethylene terephthalate film (30 .mu.m in thickness) was used 
as a backing and was coated with the PSA extrudate at a thickness of 40 
.mu.m. For each example the same conditions were also used to make a 
second sample by coating the same PSA extrudate on a backing of 50 .mu.m 
thick polyester film having a silicone release coating on the side to 
which the adhesive was applied. This second sample was produced so that 
the adhesive could be transferred to a glass slide for measurements of the 
elastomer orientation by bireflingence. Test results on the adhesive and 
tape prepared in this way are shown below in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Coating 
Bire- 
Rolling 
ASCAS1 ACAS2 PL2 
roll 
frig- 
ball sec/cm sec/cm N/cm Anise- 
Ex. 
temp., 
ence 
tack, RBT, 
(min/in) 
(min/in) 
(lb/in) tropy 
No. 
.degree.C. 
.DELTA.nx10.sup.3 
cm MD CD MD CD MD CD IR 
__________________________________________________________________________ 
1 15 1.4 6.2 0.7 43 0.2 66 0.11 
1.05 
2.3 
(0.03) 
(1.8) 
(0.01) 
(2.8) 
(0.06) 
(0.60) 
2 30 1.9 2.2 0.7 83 --* -- -- -- 2.2 
(0.03) 
(3.5) 
3 40 0.32 
2.1 1.9 40 1.4 54 0.12 
2.50 
1.8 
(0.08) 
(1.7) 
(0.06) 
(2.3) 
(0.07) 
(1.43) 
4 50 0.22 
1.5 28 52 -- -- -- -- 1.1 
(1.2) 
(2.2) 
A 70 0.02 
1.4 99 135 118 139 2.50 
2.45 
1.0 
(4.2) 
(5.7) 
(5.0) 
(5.9) 
(1.43) 
(1.40) 
__________________________________________________________________________ 
*The dashes in Table 1 mean the values were not measured. 
Both the birefringence and infra-red dichroism data of Table 1 show that 
there is significant molecular orientation of the elastomer in the PSAs of 
this invention, Examples 1-4, which were prepared by cooling the PSA 
extrudate at 15.degree.-50.degree. C. The peel resistance data of Table 1 
(under the headings ACAS1, ACAS2, and PL2) for the PSA articles of 
Examples 1-4 are values that are greater by significant amounts in the 
cross direction (CD) than in the machine direction (MD), the higher 
anisotropy correlating with greater orientation. In contrast, in preparing 
the PSA of Comparison Example A, using a higher backup roll temperature, 
70.degree. C., the consequent, relatively slow cooling of the PSA 
extrudate resulted in little or no orientation and crystallization of the 
elastomer, as shown by the birefringence and infra-red dichroism data of 
Table 1. The peel resistance values for the machine and cross directions 
for the Comparative Example A do not appreciably differ or are nearly the 
same, indicating very low or essentially no adhesion anisotropy. The 
rolling ball tack data demonstrate that, at high degrees of orientation, 
the tack is reduced substantially. 
The PSA prepared under the conditions for Example 2 was coated on a release 
liner and transferred to glass for x-ray diffraction analysis. The results 
showed two diffraction peaks (which were not present in the spectrum from 
Comparative Example A) which were at diffraction angles matching those 
reported in the literature for crystallized natural rubber. Differential 
scanning calorimetry (DSC) analysis of this adhesive showed an endothermic 
peak at 52.degree. C. with a heat of fusion of 0.2 cal/g of adhesive. With 
the literature value of the heat of melting of rubber crystals given as 
16.1 cal/g crystals, approximately 2% of the elastomer in the PSA of 
Example 2 was calculated to be crystalline. 
Example 5 
A sample of the PSA article prepared in Example 1, affixed to a glass 
slide, was mounted in the birefringence setup described earlier. The PSA 
layer of the article was heated with a heat gun to a temperature of about 
80.degree. C. for 1 minute and the birefringence fell to less than 
0.01.times.103. The sample felt substantially tackier to the touch after 
heat treatment than it did before heating, demonstrating that the 
oriented, crystallized state of the elastomer of the PSA can be eliminated 
by heating to a temperature above the melting point of the oriented, 
crystalline phase of the elastomer. 
Example 6 
A portion of the PSA tape of Example 2 was applied to a release liner and 
aged in an oven at 65.degree. C. for 5 min. Another portion of the same 
tape was applied to the same release liner and kept at room temperature 
(ca 20.degree. C.). The two portions were then tested for peel resistance 
by the ACAS1 method. The two portions of so-treated tapes were then tested 
and the results are shown in Table 2. 
TABLE 2 
______________________________________ 
ACAS1, sec/cm (min/in) 
Treatment MD CD 
______________________________________ 
Kept at room temperature, ca 23.degree. C. 
0.7 (0.03) 83 (3.5) 
Heated at 65.degree. C. 
1800 (75)* 1800 (75)* 
______________________________________ 
*tape cohesively split 
The data of Table 2 show that the oriented, crystallized state of the 
elastomer of the anisotropic PSA of this invention can be eliminated by 
heat treatment, resulting in an increase in peel resistance and loss of 
the anisotropic peel properties. 
Examples 7 and 8 
For these examples, the extruder screw configuration used was the same as 
illustrated in FIG. 2. The screw speed was 400 rpm and the air injection 
port was closed. For these examples a controlled viscosity grade of 
natural rubber, SMR CV60, available from Goodyear Chemical Plantation 
Division, was used. Piccolyte.TM. S-115 tackifying resin was fed to 
extruder zones 5 and 7 and, in Example 7, white mineral oil was added to 
the vent port in zone 9. The rubber IV under the operating conditions of 
this experiment was measured to be 3.5 dl/g. 
For Example 7, natural rubber CV-60 was pelletized with a Moriyama 
extrusion pelletizer and dusted with talc. The rubber pellets were fed to 
zone 1 of the twin screw extruder at a rate of 68.4 g/min. Ground 
Piccolyte.TM. S-115 tackifying resin which had been preblended with 
Irganox.TM. 1010 antioxidant at a ratio of 15/1 Piccolyte.TM./Irganox.TM. 
was added at a rate of 10.9 g/min to zone 5. Undiluted Piccolyte.TM.S-115 
was added at a rate of 44.5 g/min to zone 7. White mineral oil was added 
at a rate of 13.7 g/min to zone 9. The resulting formulation was as 
follows. 
______________________________________ 
Component Parts by weight 
______________________________________ 
Natural rubber CV-60 
100 
Piccolyte .TM. S-115 tackifier 
80 
Mineral Oil 20 
Irganox .TM. 1010 antioxidant 
1 
______________________________________ 
The PSA temperature at the coating die was 100.degree. C. The same coating 
die and roll were used as in Examples 1-4. The fluid circulating through 
the backup roll was controlled at 40.degree. C. The line speed was 60 
ft/min. (18.3 m/min). The adhesive was coated at a thickness of 50 .mu.m 
onto the same polyester film as used in Examples 1-4. The properties of 
the tape are shown in Table 3. 
For Example 8, the same conditions were used as in Example 7 except that 
the feed rate of Piccolyte.TM. S-115 to zone 7 was 34.2 g/min and no oil 
was added in zone 9. The formula for the PSA of Example 8 was as follows. 
______________________________________ 
Component Parts 
______________________________________ 
Natural Rubber CV-60 
100 
Piccolyte .TM. S-115 tackifier 
65 
Irganox .TM. 1010 antioxidant 
1 
______________________________________ 
The line speed was 30 ft/min. (9.1 m/min). The fluid circulating to the 
backup roll was controlled at 40.degree. C. The adhesive was coated at 50 
.mu.m onto a crepe paper masking tape backing approximately 100 .mu.m 
thick. The tape test results are shown in Table 3. 
TABLE 3 
______________________________________ 
PL1 (MD), PL1 (CD), ACAS1 (MD), 
ACAS1 (CD), 
N/cm N/cm sec/cm sec/cm 
Example 
(lb/in) (lb/in) (min/in) (min/in) 
______________________________________ 
7 0.5 2.8 2 45 
(0.3) (1.6) (0.1) (1.9) 
8 0.9 2.1 0.7 4.2 
(0.5) (1.2) (0.03) (0.18) 
______________________________________ 
The data of Table 3 show that the anisotropic peel properties can be 
achieved with these alternate formulations and backings. 
Examples 9-13 
For these examples, the extruder configuration shown in FIG. 2 was used 
along with a rotary rod die and a rubber-covered backup roll. The air 
injection port of the extruder was closed and the screw speed was 300 rpm. 
The rubber surface of the backup roll was cooled by contact with a chill 
roll and the surface of the adhesive was further cooled using either a 
water spray or a stream of cold nitrogen gas and liquid as shown in FIG. 
1. The nitrogen cooling was provided by supplying liquid nitrogen to a 
copper manifold with holes drilled in it. The liquid nitrogen partially 
evaporated in the transfer hose and the manifold, producing a stream of 
cold nitrogen gas accompanied by a slow drip of liquid nitrogen onto the 
contact point between the die and the web. The water spray was produced by 
supplying water at a metered rate to a set of needles arranged in line 
approximately 0.25 in. (0.67 cm) apart. Compressed air was used to direct 
two impinging air streams from a manifold such that they met at the line 
of needle tips, atomizing the water and carrying the spray toward the web 
immediately downstream of the die. The adhesive was coated at a thickness 
of 40 .mu.m on polyester film backings of various thicknesses. The line 
speed was 30 ft/min. (9.1 m/min). The adhesive temperature at the die was 
150.degree. C. 
For Example 9, the adhesive formulation was as follows. 
______________________________________ 
Component Parts by weight 
______________________________________ 
Natural rubber CV-60 
100 
Piccolyte .TM. S-115 tackifier 
65 
Irganox .TM. 1010 antioxidant 
1 
______________________________________ 
The natural rubber was added at 68.4 g/min to extruder zone 1, undiluted 
Piccolyte.TM.S-115 was added at 13.7 g/min to zone 5, and a blend 
consisting of 45/1 Piccolyte.TM. S-115/Irganox.TM. 1010 was added at 31.5 
g/min to zone 7. Chilled water at a temperature of 15.degree. C. was 
circulated to the chilled nip roll. The water circulating through the 
rubber covered backup roll was at 25.degree. C. No chilled nitrogen gas or 
water spray was used for this example. The adhesive was coated onto a 100 
.mu.m thick biaxially-oriented polyethylene terephthalate (PET) film. 
For Example 10, the same conditions were used as for Example 9 except that 
the liquid nitrogen cooling system was used for quickly cooling the PSA 
extrudate. 
For Example 11 the same conditions were used as for Example 9 except that 
Escorez.TM. 1310 tackifying resin was substituted for Piccolyte.TM. S-115 
product and the adhesive was coated on 50 .mu.m thick PET film. 
For Example 12 the same conditions were used as for Example 11 except that 
the liquid nitrogen cooling system was used to effect the quick cooling. 
For Example 13 the same conditions were used as for Example 11 except that 
the water spray cooling system was used to effect the quick cooling. 
The tape properties of Examples 9-13 are set forth in Table 4. 
TABLE 4 
______________________________________ 
Example No. 
PL3 (MD), N/cm (lb/in) 
PL3 (CD), N/cm (lb/in) 
______________________________________ 
9 1.42 (0.81) 2.05 (1.17) 
10 0.26 (0.15) 1.56 (0.89) 
11 2.40 (1.37) 3.12 (1.78) 
12 0.19 (0.11) 3.59 (2.05) 
13 0.18 (0.10) 3.01 (1.72) 
______________________________________ 
The data of Table 4 show that in making PSA tapes with relatively thick 
backings on the rubber-covered backup roll, cooling from the backup roll 
alone did not provide a high degree of anisotropy. However, the use of 
liquid nitrogen or water cooling can provide the desired degree of 
orientation and anisotropy. 
Example 14 
For Example 14 and Comparative Example B, the extruder and coating station 
setups of Examples 9-13 were used. The fluid circulating through the 
rubber-covered backup roll was controlled at 20.degree. C. The chilled 
roll cooling the surface of the backup roll was cooled with water at 
15.degree. C. The liquid nitrogen cooling system was used with the 
addition of a second manifold to cool the web prior to coating. The 
adhesive had the following formulation. 
______________________________________ 
Component Parts by weight 
______________________________________ 
Vistanex .TM. MM L-80 polyisobutylene 
62.8 
Vistanex .TM. LMMS polyisobutylene 
20.0 
Escorez .TM. 1310 tackifying resin 
33.7 
White mineral oil 10.0 
Irganox .TM. 1010 antioxidant 
0.6 
______________________________________ 
The Vistanex.TM. MM L-80 polyisobutylene was pelletized in the same way as 
the CV60 natural rubber for the earlier examples and fed to extruder zone 
1. The Vistanex.TM. LMMS polyisobutylene is a low molecular weight product 
which is a very viscous liquid. This material was heated and pumped to 
zone 5 of the compounding device using and heated pail unloader. The 
Escorez.TM. 1310 resin was fed to zone 7 and the mineral oil was metered 
into zone 9 using a gear pump. The antioxidant was preblended with the 
tackifying resin and fed along with it. The adhesive was coated at a 
thickness of 40 .mu.m onto a PET backing 50 .mu.m in thickness. The line 
speed was 30 ft/min. (9.1 m/min). The resulting tape properties are listed 
in Table 5. 
Comparative Example B 
The same conditions were used as in Example 14 except that Exxon Butyl 077 
rubber was substituted in the adhesive formulation for Vistanex.TM. MM L80 
polyisobutylene. The tape properties of this comparative example are also 
set forth in Table 5. 
TABLE 5 
______________________________________ 
Example No. 
PL4 (MD), N/cm (lb/in) 
PL4 (CD), N/cm (lb/in) 
______________________________________ 
14 0.18 (0.10) 4.89 (2.79) 
Comparative B 
6.78 (3.87) 6.31 (3.60) 
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The data of Table 5 show that the polyisobutylene-based adhesive had strong 
peel anisotropy in that the MD peel force was less than 4% of the CD peel 
force, but the butyl rubber-based material produced under identical 
conditions did not. The CD peel force is slightly lower than the MD peel 
force in this case at 93% of the MD value. The difference between Example 
14 and Comparative Example B may be attributed to the fact that the small 
amount of isoprene comonomer in the Butyl 077 rubber prevents 
crystallization of the rubber. 
Example 15 
A tape made according to Example 10 was cut to approximately six inches 
(15.2 cm) in length. Approximately one-half of the width of the tape was 
masked to allow heating of only a portion of the adhesive so as to 
selectively melt the crystallinity and relax the orientation of the 
elastomer and thereby selectively alter the tack of the adhesive. The 
rolling ball tack (RBT) of the tape sample prior to any masking or 
selective heating was 68 mm. 
A mask was then prepared. More specifically, a pattern was laser printed on 
paper such that one-half of the paper was printed black and one-half 
remained unprinted. The paper was then fed through a Thermofax.TM. 
photocopying machine with an infrared transparency film, which darkens by 
absorbing infrared energy in the machine selectively in those areas which 
are dark on the paper. This resulted in a patterned transparency film mask 
which was half dark and half transparent. 
The PSA tape (comprising an elastomer having a partially oriented and 
partially crystalline component) was than applied to the patterned 
transparency film mask so that one-half of the tape in the longitudinal 
direction overlapped the dark patterned region of the transparency, and 
one-half overlapped the clear unpatterned region. In order to further 
protect the unmasked area of the PSA tape from the effects of infrared 
absorption, a white tape that did not significantly absorb infrared energy 
was laminated over the clear unpatterned area of the transparency film 
mask and to the back of the PSA tape in the area which overlapped the 
clear unpatterned region of the transparency film mask. The laminate was 
fed through the Thermofax.TM. machine again, with the machine at a setting 
of 6, causing local heating of the adhesive in the area that overlapped 
the dark pattern on the transparency film. 
The rolling ball tack (RBT) of each side of the tape sample was measured 
and found to be 38 mm for the unmasked side, and 11 mm for the masked, 
heated side of the tape. From these data, it appears that some heating and 
concurrent melting of the oriented crystalline component of the elastomer 
occurs even in the unpatterned regions due to generalized heating within 
the Thermofax.TM. machine. 
Example 16 
A second six inch (15.2 cm) tape sample made according to Example 10 was 
masked to allow heating in a spatially varying pattern to give a pattern 
of alternating high and low tack. Prior to any masking or selective 
heating, the rolling ball tack (RBT) of the tape sample was measured at 68 
mm. A pattern as shown in FIG. 10 was produced using a computer drawing 
program and printed on paper with a laser printer. The paper was then fed 
through a Thermofax.TM. photocopying machine with an infrared transparency 
film as described in Example 15 to form a transparency film mask patterned 
with alternating dark and transparent lines as shown in FIG. 10. The PSA 
tape (comprising an elastomer having a partially oriented and partially 
crystalline component) was than applied to the patterned transparency film 
mask with the maskant lines perpendicular to the longitudinal direction of 
the tape. The laminate was fed through the Thermofax.TM. machine again, 
with the machine at a setting of 4, causing local heating of the adhesive 
in the areas that overlapped the dark lines on the transparency film. The 
rolling ball tack (RBT) of the selectively heated tape sample was measured 
at 10 mm, with the tack measured across (perpendicular to) the alternating 
heated and unheated regions of the elastomer. 
Examples 17-20 
A PSA tape was prepared using the same extruder screw configuration, 
coating roll, and die setup used in Examples 1-4. The rubber used was SMR 
CV60 natural rubber, and the PSA formulation of Examples 17-20 was as 
follows: 
______________________________________ 
Component Parts by weight 
______________________________________ 
Natural rubber 100 
Piccolyte .TM. S-115 
50 
Irganox .TM. 1010 
1 
______________________________________ 
The coating roll temperature was controlled at 30.degree. C., and the tape 
produced had relatively low tack and high peel anisotropy. 
The PSA tapes of Examples 17-20 were exposed to heat in a spatially-varying 
pattern to selectively melt the crystallinity and relax the orientation of 
the elastomer. By varying the shape of the heating pattern, the unwind 
characteristics of the tape could be varied. To accomplish the heating, 
the desired pattern was produced as described in Example 16, except using 
the patterns shown in FIGS. 9-11 and in Table 6 below. FIG. 9 shows a tape 
sample made from a maskant having alternating dark and transparent regions 
which run parallel to the machine direction of the tape, and FIG. 10 shows 
a tape sample made from a maskant having alternating dark and transparent 
regions which run perpendicular to the machine direction of the tape. FIG. 
8 is a control sample which corresponds to an unpatterned, relatively low 
tack tape sample that was not selectively heated to vary its unwind 
characteristics. 
The tapes were peeled at a speed of 100 in/min (254 cm/min) to characterize 
the noise levels of the tapes during unwind. The characteristics are shown 
in Table 6. 
TABLE 6 
______________________________________ 
Example No. Pattern Noise characteristics 
______________________________________ 
17 FIG. 8 low peel adhesion, raspy 
18 FIG. 9 smooth peel, quiet 
19 FIG. 10 shocky peel, raspy 
20 FIG. 11 smooth peel, quiet 
______________________________________ 
From these data, it is apparent that the peel characteristics and unwind 
noise levels can be altered by spatially varying the tack of the adhesive. 
Example 21 
An anisotropic PSA tape was made by the same conditions as in Example 10 
with the exception that the PSA was coated on 50 .mu.m thick polyester 
film. The adhesion of the PSA tape measured by the PL3 method was found to 
be 0.15N/cm when peeled in the machine direction and 4.40N/cm in the cross 
direction. A sheet of this tape was used as an application tape to 
transfer die cut letters from a silicone release liner, similar to that 
illustrated in FIGS. 4-7. Letters approximately 1.2 cm in height were die 
cut from a vinyl graphic Controltac.RTM. film and the waste vinyl material 
removed from the space between the letters. The tape was applied to the 
surface of the die cut letters on the release liner and rubbed down. The 
application tape was then peeled in the cross direction (the high-adhesion 
direction). The high adhesion exhibited by the application tape in this 
direction ensured that all of the letters would be lifted from the release 
liner and held securely to the application tape. The application tape and 
its attached die cut letters were then applied to the target substrate and 
rubbed down. The application tape was then removed by peeling in the 
machine direction (the low-adhesion direction). The low peel force of the 
tape when peeling in this direction ensured that all of the letters 
remained bonded to the target substrate and the application tape was easy 
to remove. 
Various modifications and alterations of this invention will become 
apparent to those skilled in the art without departing from the scope and 
spirit of this invention.