Radiation curable poly (1-alkene) based pressure-sensitive adhesives

18 Pages·2013·1.88 MB·English

US006177190B1
(12) United States Patent (10) Patent No.: US 6,177,190 B1
Gehlsen et al. (45) Date of Patent: Jan. 23, 2001
(54) RADIATION CURABLE POLY(1-ALKENE) 5,427,842 6/1995 Bland et a1. ....................... .. 428/213
BASED PRESSURESENSITIVE ADHESIVES 5,589,122 12/1996 Leonard et a1. ................... .. 264/146
5,599,602 2/1997 Leonard et al. 428/56
(75) Inventors: Mark David Gehlsen, Eagan, MN 5,644,007 7/1997 Davidson et a1. 526/64
(Us); Chad Everett Brown, Chicago, 5,660,922 8/1997 Herndge et a1. ................... .. 428/214
IL (Us); Patrick Darby Hyde, 2:333??? 13/133; 3333?.‘ .............................. .. 525/240
Burnsvrlle, MN (US); Eugene Gregory 578597088 * 1/1999 Peterson _
Joseph, Vadnars Heights, MN (US);
Vasant Venugopal Kolpe, Mendota FOREIGN PATENT DOCUMENTS
Helghts’ MN (Us) 0 620 258 A2 4/1994 (EP) .
. _ . . W0 93 11184 6/1993 (W0).
(73) Assrgnee. lrianotlialtcltiel PIIJ‘EPEI‘UES Company, 96 07674 3/1996 (W0) '
am all, ( ) 96 25469 8/1996 (WO) .
96 37568 11/1996 WO .
( * ) Notice: Under 35 U.S.C. 154(b), the term Of this 97 23577 7/1997 EWOg _
patent shall be extended for 0 days. W0 97 48777 12/1997 (WO) .
W0 98 23699 6/1998 (WO) .
(21) Appl. No.: 09/087,611 OTHER PUBLICATIONS
(22) Filed: May 29’ 1998 Barrett, AB, and Miller, R. A., Extending Styrenic Block
(51) Int. Cl.7 ...................................................... .. B32B 7/ 12 copolymers With Amorphous Polyole?ns, TECHNOWSI Hot
(52) US. Cl. .................................. .. 428/355 EN; 522/112; Melts, AdhesivesAgeAug- 199511925934
522/157; 522/158; 522/160; 522/161 Robe, G. R., Amorphous Polyole?ns As Ingredients in
(58) Field Of Search ................................... .. 428/354, 355, Pressure/“sensitive Adhesives, 1992 TAPPI Hot Melt Sym
428/355 EN; 522/112, 157, 158, 160, 161 P°Sium> PP- 142
(List continued on next page.)
(56) References Cited
Us PATENT DOCUMENTS Primary Examiner—Terrel Morris
ASSLSZLZI’LZ Exammer—Sharm1stha Gupta
3,565,985 2/1971 Schrenk et a1. .................... .. 264/171 ('74) Attorney) Agent) or Firm—Me1anie GOVer
3,630,980 12/1971 Russell et a1. . 260/27
3,850,858 11/1974 Park et a1. 260/27 (57) ABSTRACT
4,022,728 5/1977 Trotter et a1. .. 260/27
260/897 The present invention relates to pressure-sensitive adhesive
44,,017025,,773158 28//11997788 AWredeemmeasg neit a1. 260/889 compositions. The compositions comprise a poly(1-alkene)
.. 427/54.1 pressure-sensitive adhesive component, a non-pressure
44,,128117,,745228 81//11998800 MMacrCtoennnse lelt ae1t. a1
525/191 sensitive adhesive component, and a radiation-activatable
4,259,470 * 3/1981 Trotter ...... .. 428/355 curing agent. The invention further provides pressure
4’329’384 5/1982 veslejy et a1‘ 428/40 sensitive adhesive tapes and methods for making the com
4,332,655 6/1982 Bere]ka ........ .. . 204/1592 Ositions and ta es
5,112,882 5/1992 Babu et a1. 522/158 p p '
5,354,619 10/1994 Babu ............ .. 428/462
5,407,970 4/1995 Peterson et a1. ..................... .. 522/33 20 Claims, 2 Drawing Sheets
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US 6,177,190 B1
Page 2
OTHER PUBLICATIONS Standard Practice for Dilute Solution Viscosity of Polymers,
Designation: D 2857—95, pp. 150—154.
Barrett, A. E. and Miller, R. A., Amorphous Polyole?ns as
Extenders for Styrenic Block Copolymers in Hot Melt
Krishnamurthy, V., Sustic A., Dynamic Mechanical Analysis
Formulations, 1995 TAPPI Hot Melt Symposium, pp.
169—183. of ReXtac® Amorphous Polyalphaole?ns (APAO) and
Clauss, M., Earhart, J. J ., Stabilization Of Amorphous Poly— Blends With Styrene Block Copolymers (SBCs), TAPPI
Alpha Ole?n(Apao) Based Hot Melt Adhesives, 1995 Hot
1992 Hot Melt Symposium, pp. 77—83.
Melt Symposium, pp. 151—159.
Test Methods for Pressure Sensitive adhesives Tapes, Test
Methods, 1994, 11th Edition, pp. 1—37. * cited by examiner
U.S. Patent Jan. 23, 2001 Sheet 1 0f 2 US 6,177,190 B1
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US 6,177,190 B1
1 2
RADIATION CURABLE POLY(1-ALKENE) 50,000, have found uses as hot melt adhesives. These
BASED PRESSURE-SENSITIVE ADHESIVES copolymers also make pressure-sensitive adhesives When
miXed With tacki?ers.
TECHNICAL FIELD Pressure-sensitive adhesives comprising blends of poly
This invention relates to pressure-sensitive adhesive (1-alkenes) and ?oW-control agents are used to protect
compositions, and, more particularly, to pressure-sensitive surfaces such as automobile paint ?nishes and may be
removed Without leaving residue.
adhesive compositions formed from at least tWo polymeric
materials at least one of Which is a poly(1-alkene) based Radiation crosslinking of poly(1-alkene) homopolymer or
pressure-sensitive adhesive, to methods for making such copolymer compositions (both Ziegler Natta-catalyZed and
pressure-sensitive adhesive compositions, and to tapes and 10 metallocene-catalyZed) has been accomplished.
articles including such pressure-sensitive adhesive compo
SUMMARY OF THE INVENTION
sitions.
The present invention provides a radiation-curable
BACKGROUND OF THE INVENTION pressure-sensitive adhesive composition, comprising:
15 (a) a pressure-sensitive adhesive component comprising
Pressure-sensitive adhesive tapes are used for many
diverse applications including, for example, marking, at least one poly(1-alkene);
holding, protecting, sealing and masking purposes. These (b) about 2 to about 100 parts by Weight, based on 100
tapes comprise a backing, or other substrate, and a pressure parts by Weight of said pressure-sensitive adhesive
sensitive adhesive. Pressure-sensitive adhesives used in component, of a polymer component comprising at least one
pressure-sensitive adhesive tapes generally adhere With no non-pressure-sensitive adhesive polymer having reactive
more than applied ?nger pressure and often stay tacky for sites for crosslinking; and
months or years. Pressure-sensitive adhesives eXert a strong (c) a suf?cient amount of at least one crosslinking agent
holding force and should be removable from a smooth to crosslink (a) and (b) to provide on curing a crosslinked
surface Without leaving a residue. pressure-sensitive adhesive composition With shear
25
In the medical ?eld, pressure-sensitive adhesive tapes strength at least 300% greater than, and peel adhesion not
may be used, for example, to secure a Wound dressing or to less than 80% of, that of a crosslinked composition consist
restrict movement of a joint or limb. It is important that the ing essentially of the reaction product of components (a) and
pressure-sensitive adhesive tape adhere Well to skin Without (c), or With (ii) shear strength and peel adhesion each not less
causing skin damage on removal. than 80% of those of a crosslinked composition consisting
essentially of components (a) and (c) produced under (1) the
Electrical tapes typically comprise a pressure-sensitive
same cure conditions including the same curing energy dose,
adhesive applied to a plasticiZed polyvinyl chloride backing
eXcept at a process speed that is at least 100% faster than the
or a polyethylene or rubber ?lm backing. Electrical tape is
process speed for producing the crosslinked reaction product
used to insulate, hold, reinforce and protect electrical Wires.
consisting essentially of components (a) and (c) or (2) the
Other uses include identifying Wires in electrical circuitry, 35
and protecting terminals during manufacture of electrical same process speed, but With cure conditions comprising a
curing energy dosage that is at least 50% less than the curing
circuit boards.
energy dosage for producing the crosslinked reaction prod
Packaging applications require a large variety of tapes for
uses such as closing packages, protecting labels, sealing uOcptt iocnoanlsliys,t tihneg coesmspeonstiitailloyn moaf y cfoumrtphoenr ecnotmsp ri(as)e taancdk i?ers
packages from moisture, and strapping and bundling loose
and/or other additives such as plasticiZers and ?llers.
parts. Packaging tapes are subjected to continuous shear and
Certain pressure-sensitive adhesive compositions accord
loW angle peel forces. Generally, if the adhesive mass is of
ing to the present invention Will not necessarily have all of
loW cohesive strength, it fails in shear; if the shear resistance
the bene?cial physical properties de?ned in the previous
is improved by adding ?rmness to the adhesive, it has a
paragraph. Such pressure-sensitive adhesive compositions
tendency to be less tacky and fail adhesively. 45
may be further de?ned as radiation curable pressure
Pressure-sensitive adhesives require a delicate balance of sensitive adhesive compositions comprising (a) a pressure
viscous and elastic properties Which result in a four-fold
sensitive adhesive component comprising at least one poly
balance of adhesion, cohesion, stretchiness and elasticity.
(1-alkene) With an inherent viscosity of at least about 0.4
Pressure-sensitive adhesives generally comprise polymers
deciliters/gram (dL/g), (b) from about 2 to about 100 parts
that are inherently tacky or polymers that are tacki?ed by the by Weight, per 100 parts of the pressure-sensitive adhesive
addition of tackifying resins.
component, of a polymer component comprising at least one
Major classes of pressure-sensitive adhesives include non-pressure-sensitive polymer having a G‘ of at least
tacki?ed natural rubbers; synthetic rubbers such as butyl about 5><106 dynes/cm2 at 1 HZ and at the use temperature,
rubber; and tacki?ed linear, radial, star, branched and 55 and (ii) a tertiary carbon content of about 1 to about 50 mole
tapered block copolymers such as styrene-butadiene, percent, based on the total moles of the polymer component,
styrene-ethylene/butylene and styrene-isoprene; polyvinyl provided that if the tertiary carbon content of the polymer
ethers; acrylics, especially those having long chain alkyl
component is about 1 to about 10 mole percent, the shear
groups; poly(1-alkene)s (also referred to as poly-ot-ole?ns); viscosity of the polymer component is greater than about
and silicones. 500 Pa-s at 175° C., and (c) a radiation activatable crosslink
Polyole?n catalyst systems (i.e., Ziegler-Natta (ZN) and ing agent. Optionally, the pressure-sensitive adhesive com
metallocene) have made it possible to synthesiZe high position may further comprise tacki?ers and/or other addi
molecular Weight poly(1-alkene) pressure-sensitive adhe tives.
sives including homopolymers of C6 to C10 poly(1-alkenes). Further provided is a method of making a radiation
Another type of poly(1-alkene) material, by-products of 65 crosslinkable pressure-sensitive adhesive composition com
isotactic polypropylene that are described as atactic copoly prising melt miXing a pressure-sensitive adhesive com
mers of C3—C6 and C3—C8 With molecular Weights up to ponent having at least one poly(1-alkene) With an inherent
US 6,177,190 B1
3 4
viscosity greater than about 0.4 dL/g, (ii) about 2 to about “use temperature” means the temperature that a pressure
100 parts by Weight, per 100 parts of said pressure-sensitive sensitive adhesive composition experiences during its use;
adhesive component, of a polymer component comprising at “shear viscosity” or “melt viscosity” means the ratio of
least one non-pressure-sensitive polymer having a G‘ of at shear stress to strain rate, as determined by test methods
least about 5><106 dynes/cm2 at 1 HZ at the use temperature described herein, on a material at a given temperature and
and having a tertiary carbon content of about 1 to about 50 shear rate; it is arbitrarily measured at 175° C. and 100 s-1
mole percent, based on the total moles of the polymer although the actual temperature to Which the material is
component, provided that if the tertiary carbon mole percent exposed during melt-processing may be higher or loWer.
is from about 1 to about 10 mole percent, the polymer The radiation-crosslinked pressure-sensitive adhesives of
the invention provides the advantage of surprisingly high
component has a shear viscosity greater than about 500 Pa-s 10
shear properties (up to over 10,000 minutes) With decreases
at 175° C., and (iii) a radiation activatable crosslinking
agent. Apressure-sensitive adhesive article can be made by in peel adhesion of as little as 10% or less compared to
crosslinked pressure-sensitive adhesives of similar compo
(1) forming said composition into a shaped article, and (2)
sitions (tested at the same shear rate) that do not contain the
cooling, if needed, the shaped article. The shaped article
polymer component of the invention. Shear values of up to
may be a pressure-sensitive adhesive suitable for subsequent 15 ?ve times that of ultraviolet crosslinked poly(1-alkene)
lamination to a surface or may be a pressure-sensitive pressure-sensitive adhesives not containing the polymer
adhesive layer on a substrate. The radiation crosslinkable
component have been observed With no corresponding
pressure-sensitive adhesive may be exposed to radiation to decrease in peel adhesion at room temperature (25° C.). In
create a partially or fully radiation crosslinked pressure addition, the present invention provides the advantage of
sensitive adhesive. 20 having the option of producing pressure-sensitive adhesive
The method may be used to make poly(1-alkene) compositions having peel and shear properties equivalent to
pressure-sensitive adhesives having improved shear proper those of ultraviolet crosslinked poly(1-alkene) pressure
ties and approximately equivalent peel properties, compared sensitive adhesives not containing the polymer component
to poly(1-alkene) pressure-sensitive adhesives not contain by only exposing the pressure-sensitive adhesive composi
ing the polymer component. Alternatively, the method may 25 tions of the invention to approximately 25% of the ultra
violet light irradiation that Would be used to produce the
be used to make, With less radiation exposure, pressure
adhesive not containing the polymer component. If the
sensitive adhesives having peel properties and shear prop
erties equivalent to poly(1-alkene) pressure-sensitive adhe irradiation intensity is not reduced, as much as a four-fold
increase in line speed may be achieved.
sives not containing the polymer component. The reduction
in radiation exposure may be realiZed by loWering the 30 A further advantage of the method of making a pressure
radiation dose to Which the pressure-sensitive adhesive sensitive adhesive composition disclosed in this invention is
composition is exposed, shortening the process line, or that no solvent is required for the process Which, among
increasing the speed of the process line. other things, eliminates the need for a solvent coater. Other
advantages include the small amount of residuals produces
The present invention further provides articles such as
pressure-sensitive adhesive tapes or sheets and double 35 in making the compositions of the invention and the ability
to recycle poly(1-alkene) products.
coated pressure-sensitive adhesive tapes or sheets made by
extrusion or coextrusion methods. BRIEF DESCRIPTION OF THE DRAWINGS
In this description: FIG. 1 is a graph Which plots polymer component elastic
modulus (G‘) in dynes/cm2 against tertiary carbon mole
“crosslinked” means a connection formed Within or 40
betWeen one or more polymer molecules Wherein the con percent (%). The triangles represent pressure sensitive adhe
nection is a covalent bond resulting from a chemical reac sive compositions, containing the polymer components,
tion. Which have static shear performances of less than 10,000
minutes at 25° C. The squares represent pressure sensitive
“elastic shear modulus” or “G‘” means a coefficient of
adhesive compositions, containing the polymer components,
elasticity for a material representing the ratio of shear stress 45
Which have static shear performances of greater than 10,000
to shear strain as the material is deformed under a dynamic
minutes at 25° C.
load as further described herein; it is a measure of the
softness or stiffness of the material; FIG. 2 is a graph Which plots polymer component elastic
modulus (G‘) in dynes/cm2 against tertiary carbon mole
“inherent viscosity” means the viscosity of a material as
percent (%). The triangles represent pressure sensitive adhe
determined by ASTM D2857-93; 50
sive compositions, containing the polymer components,
“polymer component” or “non-pressure-sensitive poly
Which have static shear performances of less than 10,000
mer component” means one or more polymer(s) comprising
minutes at 70° C. The squares represent pressure sensitive
at least one non-pressure sensitive polymer component; adhesive compositions, containing the polymer components,
“shear value” or “shear strength” means the time required Which havestatic shear performances of greater than 10,000
55
for a given doWnWard force to remove a pressure-sensitive minutes at 70° C.
adhesive tape from a vertical substrate at a given FIG. 3 is a graph of the elastic modulus (G‘) in dynes/cm2
temperature, as determined by methods described herein;
versus temperature in ° C. for ENGAGETM EG8200, a
“peel adhesion” or “peel strength” means the given force poly(ethylene-octene) copolymer. It also shoWs the lines
to remove a pressure-sensitive adhesive tape from a sub tangential to the melting transition section of the elastic
60
strate at a given temperature, angle, rate, and tape Width, as modulus data Which lines are used to determine Tom”, and
determined by methods described herein; T?nal, Which in turn are averaged to determine the melting
“poly(1-alkene)” or “poly-ot-ole?n” means a polymer temperature, Tm, of the polymer.
prepared by polymeriZation of at least one 1-alkene mono FIG. 4 is a graph of the elastic modulus (G‘) in dynes/cm2
mer; a 1-alkene, or alpha-ole?n monomer, is a hydrocarbon 65 versus temperature in ° C. for ESCORENETM 1024, a
having a double bond betWeen the ?rst and second carbon propylene polymer. It also shoWs the melting temperature of
atoms; the polymer.
US 6,177,190 B1
5 6
DETAILED DESCRIPTION 5,112,882 (Babu, et al), incorporated herein by reference, or
The present invention relates to radiation crosslinkable through chemical modi?cation, as described in US. Pat. No.
pressure-sensitive adhesive compositions generally com 5,407,970 (Babu, et al), incorporated herein by reference.
prising a poly(1-alkene) pressure-sensitive adhesive Useful poly(1-alkene)s are generally self-tacky or made
component, a non-pressure-sensitive adhesive polymer tacky by adding a tacki?er miscible in the poly(1-alkene).
component able to crosslink With the pressure-sensitive Tacki?er may also be added to a self-tacky polymer to
adhesive component, and radiation-activatable crosslinking augment pressure-sensitive adhesive properties such as peel
agent(s).
adhesion and tack. Tacki?ers often loWer the viscosity of a
The pressure-sensitive adhesive composition is generally polymer and thus may be used to make the polymer more
made in a melt-mix process Wherein the poly(1-alkene) 10 suitable for hot melt processing.
component is mixed With the polymer component in a Hydrocarbon tacki?ers are preferred for use in the
molten or softened state along With a crosslinking agent and pressure-sensitive adhesive compositions of the present
any additional additives such as tacki?er. Mixing may be invention. Useful tackifying resins include resins derived by
done by any method that results in a substantially homoge polymeriZation of the folloWing: C5 to C9 unsaturated
neous distribution of the components. After mixing, the 15 hydrocarbon monomers, polyterpenes, synthetic
pressure-sensitive adhesive composition may be formed into polyterpenes, and the like. Examples of useful commercially
coatings or layers by extrusion methods using batch or available tackifying resins are those available under the
continuous process methods. The coatings may be solidi?ed trade names WINGTACKTM 95 and WINGTACKTM 115
by quenching using direct methods such as chill rolls or from Goodyear Tire and Rubber Co., Akron, Ohio. Other
Water baths and indirect methods such as air or gas impinge 20 useful hydrocarbon tacki?er resins are available under the
ment. The pressure-sensitive adhesive composition may trade names REGALREZTM 1078 and REGALREZTM 1126
alternatively be formed into other shapes. The composition from Hercules Chemical Co., Wilmington, Del., and under
may remain uncured or may be partially or completely cured the trade names ARKONTM P90 and ARKONTM P115 from
by exposure to radiation. The composition may be partially ArakaWa Chemical Co. (USA), Chicago, Ill.
or totally cured before or after it is formed into its ?nal 25 The tacki?er may be ethylenically unsaturated; hoWever,
shape. saturated tacki?ers are preferred for those applications
Poly(1-alkene) Pressure-Sensitive Adhesive Component Where oxidation resistance is important. The total amount of
(“Poly(1-alkene) Component”) tackifying resin in the poly(1-alkene) component preferably
One component of the radiation crosslinkable pressure is from 0 to 150 parts by Weight, more preferably 5 to 50
sensitive adhesive composition of the invention is itself a 30 parts by Weight, and most preferably 25 to 35 parts by
pressure-sensitive adhesive comprising one or more poly(1 Weight, per 100 parts of the poly(1-alkene) component.
alkene)s. Non-Pressure-Sensitive Adhesive Polymer Component
A suitable poly(1 -alkene) has a glass transition tempera (“Polymer Component”)
ture (Tg) preferably in the range of —70° C. to 0° C., more A second component of the radiation crosslinkable
preferably in the range of —60° C. to —20° C., and an average 35 pressure-sensitive adhesive compositions of the present
inherent viscosity in the range of 0.4 dL/g to 9.0 dL/g, invention is a non-pressure-sensitive adhesive polymer com
preferably in the range of 0.5 dL/g to 6.0 dL/g, and more ponent that may be crosslinked With the pressure-sensitive
preferably in the range of 1.5 dL/g to 4.0 dL/g as determined adhesive component. That is, this component contains at
using a Number 50 Cannon-Fenske Viscometer tube, With a least one polymer that lacks one or more physical charac
0.1 g/dL solution of polymer in toluene, at 27° C. The ranges 40 teristics Which a pressure-sensitive adhesive requires to be
of inherent viscosity should provide a poly(1-alkene) poly so designated. Typically this polymer component is a melt
mer that is soft enough to be melt processed. processable organic polymeric material. The polymer com
An inherent viscosity above these values may result in a ponent preferably has a G‘ of at least about 5><106 dynes/cm2
polymer that is dif?cult to melt process. An inherent vis at 1 HZ at the use temperature and a multiplicity of reaction
cosity beloW the above-stated values may cause the 45 sites for crosslinking.
pressure-sensitive adhesive composition to cohesively frac The improved peel and shear properties of the pressure
ture and leave a residue When removed. Crosslinking the sensitive adhesive composition of this invention are a direct
pressure-sensitive adhesive composition may extend the result of the addition of the polymer component When added
loWer range of acceptable inherent viscosity for the poly(1 in an appropriate amount. If the Weight ratio of the polymer
alkene) component beyond that Which is acceptable for an 50 component to the poly(1-alkene) component is substantially
uncrosslinked poly(1-alkene). Number average molecular greater than 1:1, the peel and shear strengths of the com
Weights of the uncrosslinked poly(1-alkene) polymers are position are typically detrimentally effected. The tolerated
preferably in the range of 5,000 to 50,000,000, more pref concentration of the polymer component may be increased
erably 50,000 to 5,000,000. by adding plasticiZers and/or tackifying materials to the
Useful poly(1-alkene)s include, for example, non 55 pressure-sensitive adhesive composition. The effective con
crystalline polymers such as C5 to C12 poly(1-alkene) centration of the polymer component depends on the speci?c
homopolymers and copolymers, including copolymers With types, concentrations, and characteristics of the polymer(s)
C3; more preferably C6 to C10 poly(1-alkene) homopoly in the polymer component and of each of the other compo
mers and copolymers, including copolymers With C3; most nents used in the pressure-sensitive adhesive composition.
preferably C6 to C8 poly(1-alkene) homopolymers and 60 The amount of polymer component in the pressure-sensitive
copolymers, including copolymers With C3. Particularly adhesive composition may vary from about 2 to about 100
useful poly(1-alkene)s are poly(1-hexene) and poly(1 parts by Weight, and preferably from about 8 to about 60
octene), described in US. Pat. No. 5,644,007 (Davidson, et parts, per 100 parts of the poly(1-alkene) component.
al), incorporated herein by reference. Another group of The polymer component preferably has sufficient vis
useful poly(1-alkene)s is those that have pendent groups 65 coelastic characteristics to impart in the pressure-sensitive
susceptible to crosslinking and have been obtained either adhesive composition satisfactory cohesive strength to avoid
through copolymeriZation, as described in US. Pat. No. splitting of the adhesive mass upon removal. That is, the
US 6,177,190 B1
7 8
cohesive strength of the resultant adhesive mass preferably mately 50 mole percent of the total moles of the polymer
is higher than the bond strength betWeen the adhesive and component, preferably from about 10 to about 50 mole
the adherend. Generally, the desirable visco-elastic charac percent. Radiation-crosslinked pressure-sensitive adhesives
teristics may be achieved by using polymers having a shear containing a polymer component With a tertiary carbon
elastic modulus, i.e., G‘, of greater than about 5><106 dynes/ content of as little as 1 mole percent have crosslinked to
cm2 measured at 1 HZ at the use temperature. Polymers With provide an adhesive composition that exhibits an increase in
a G‘ less than this value tend to form a radiation crosslinked room temperature shear performance With little or no
decrease in peel adhesion When compared to similar com
pressure-sensitive adhesive shoWing little or no improve
positions not containing the polymer component of this
ment in shear performance over a crosslinked pressure
invention. HoWever, beloW a tertiary carbon content of
sensitive adhesive not containing the polymer component. 10 approximately 10 mole percent, the characteristics of the
It should be further noted that if the use temperature
pressure-sensitive adhesive composition appear to be in?u
approaches the melting temperature, Tm, of the polymer
enced by additional factors.
component, the polymer component may begin to melt,
For some pressure-sensitive adhesive compositions hav
causing the pressure-sensitive adhesive to fail cohesively. It
ing a tertiary carbon content of less than about 10 mole
is recommended that the polymer component be chosen so 15 percent, the G‘ and the amount of crosslinkable sites do not
the use temperature does not come Within 10° C. of the appear to fully account for the behavior of the resulting
polymer component’s melting temperature. The melting pressure-sensitive adhesive. For some pressure-sensitive
temperature of a polymeric material may be determined by adhesives With a polymer component having a G‘ of 5><10°
dynamic analysis, at a given frequency, in conjunction With dynes/cm2 at 1 HZ and a tertiary carbon content of less than
the determination of G‘. In the present case, Tm of the 20 about 10 mole percent, the performance of the pressure
polymer component Was characteriZed using mechanical sensitive adhesives may not be improved over a pressure
spectroscopy under the same conditions as those described sensitive adhesive not containing the polymer component
herein for the determination of G‘. The melting temperature unless the shear viscosity of the polymer component is
Was determined, from the data collected for the G‘ greater than about 500 Pa-s at 175° C. When the tertiary
determination, by using a graph of G‘ versus ° C. for a 25 carbon content of the polymer component is above approxi
polymer component. A tangential line Was extended from mately 10 atomic percent, and its G‘ is at least 5><106
the elastic modulus data line both above and beloW the dynes/cm2, a shear viscosity beloW about 500 Pa-s at 175°
melting transition portion of the elastic modulus (G‘) data. C. appears to have little or no detrimental effect on perfor
The points at Which the data deviates from the tangent are mance of the resulting pressure-sensitive adhesive.
characteriZed as the “onset” (Tome) and “?nal” (T?nal) 30 It should be noted, hoWever, that if the shear viscosity of
temperatures. The Tm is de?ned as the average of Tom” and the polymer component (or the pressure sensitive adhesive
T?nal. FIG. 3 graphically depicts this technique. FIGS. 3 and composition) is high enough to prevent the polymer com
4, respectively, shoW a Tm close to, and distant from, the use ponent from mixing With the poly(1-a1kene) under the given
temperature of 70° C. mixing conditions, the pressure sensitive adhesive properties
The polymer component is characteriZed by having 35 of the resulting composition may be poor regardless of the
crosslinking sites suf?cient to provide crosslinking With the G‘ and tertiary carbon content. It is preferable to have the
poly(1-alkene). These crosslinking sites may be provided by viscosity ratio, 11R, betWeen about 0.4 and about 2. The
tertiary carbon atoms in the polymer component molecule. viscosity ratio is calculated as 11 D/n M Where 11D is the melt
They may also be provided by, eg., unsaturated carbon viscosity of the dispersed phase (usually the polymer
bonds. HoWever, it should be noted that unsaturated bonds, 40 component) and 11M is the melt viscosity of the matrix phase
i.e., alkenyl and aromatic bonds, tend to absorb ultraviolet (usually the poly(1-alkene)). As 11R approaches 3, it appears
(UV) radiation Which may interfere With crosslinking When that poor dispersion of the dispersed phase component in the
UV radiation is used for crosslinking. HoWever, the presence matrix component may occur and poor peel values may
of unsaturated bonds need not hamper the curing process. result.
Radiation-activated crosslinking agents activated by means 45 Plots of G‘ against ° C. for polymer components are
other than UV radiation in the absorption range of the shoWn in FIG. 1 and FIG. 2. FIG. 1 also shoWs Whether the
unsaturated bonds of the polymer component may be used. pressure sensitive adhesives containing the polymer com
Examples of such agents include those that may be activated ponents have a static shear performance greater, or less, than
by exposure to heat or visible irradiation, such as dicumyl 10,000 minutes at a use temperature of 25° C. FIG. 2 shoWs
peroxide subjected to thermal radiation. Determination of 50 the same information for a use temperature of 70° C. As seen
the most favorable activation means depends on the initia in FIG. 1, the shear performance of the pressure-sensitive
tors used and on the characteristics of the speci?c adhesive compositions containing a polymer component
polymer(s) used. having a tertiary carbon content betWeen 1 and 35 atomic
The experiments conducted in the present invention used percent is generally over 10,000 minutes at 25° C. if the G‘
a free radical initiation process to promote crosslinking. 55 of the polymer component is greater than about 5><10°
BenZophenone Was used to initiate hydrogen abstraction of dynes/cm2 at 1 HZ at 25° C. In FIG. 2, the shear strength of
primary (1°), secondary (2°), or tertiary (3°) hydrogens to the pressure-sensitive adhesive composition containing a
create free radicals. Because the bond dissociation energies polymer component With a tertiary carbon content betWeen
and ease of abstraction are loWest for tertiary hydrogens, 1 and 35 atomic percent is generally over 10,000 minutes at
Which are bonded to tertiary carbons, the propensity of a 60 70° C. if the G‘ of the polymer component is greater than
polymer to have crosslinking sites Was estimated based on about 5><106 dynes/cm2 at 1 HZ at 70° C. In most cases in
the concentration of tertiary carbons in the polymer. Other Which the shear property Was less than 10,000 minutes, the
methods may also be used to estimate the concentration of G‘ value at the use temperature Was Within approximately
crosslinkable sites. 10° C. of the melting temperature of the polymer compo
For this invention, the desired amount of crosslinking 65 nent.
may be achieved With a concentration of tertiary carbons The polymer component may be a homopolymer or a
ranging from approximately 1 mole percent to approxi copolymer, may be linear or branched, and may also be a
US 6,177,190 B1
9 10
mixture thereof. Suitable homopolymers include, for silica. Pigments and ?llers may be incorporated into the
example, propylene, available under the trade name EAST adhesive composition to manipulate the properties of the
OFLEXTM P1023 from Eastman Chemical Co., Kingsport, adhesive. For instance, very ?ne pigments may increase
Tenn., and under the trade names ESCORENETM 3505, cohesive strength and stiffness, reduce cold ?oW, and reduce
ESCORENETM 3445, ESCORENETM 1024 and tack. Plate-like pigments such as mica, graphite, and talc
ACHIEVETM 3825 from Exxon Chemical Co., Houston, may provide acid and chemical resistance and loW gas
Tex. Suitable copolymers include, for example, poly permeability. Clays, hydrated silicas, calcium silicates,
(ethylene-butene) available under the trade name EXACTTM silico-aluminates, and carbon blacks may increase cohesive
4011 from Exxon Chemical Co., Houston, Tex.; poly strength and stiffness. PlasticiZers may modify the physical
(ethylene-octene) available under the trade names 10 properties of polymer components and make them easier to
ENGAGETM EG8200 and AFFINITYTM PL1845 from DoW process. Finally, antioxidants and ultraviolet stabiliZers may
Chemical Co., Midland, Mich., poly(propylene-ethylene) be used to protect against severe environmental aging
available under the trade name EASTOFLEXTM 1060 from caused by ultraviolet light or heat. Antioxidants and ultra
Eastman Chemical Co., Houston, Tex.; and linear loW den violet stabiliZers include, for example, hindered phenols,
sity polyethylene available under the trade name 15 amines, and sulfur and phosphorous hydroxide decompos
DOWLEXTM 2045 from DoW Chemical Co.; polystyrene ers.
copolymers such as poly(styrene-ethylene/butylene-styrene) Method of Making Pressure-Sensitive Adhesive Composi
available under the trade name KRATONTM G1657 from tions and Articles
Shell Chemical Co., Houston, Tex. and poly(styrene A pressure-sensitive adhesive composition of this inven
isoprenbe-styrene) available under the trade name KRA tion is made by mixing a pressure-sensitive adhesive com
TONTM D1107 from Shell Chemical Co.; polystyrene; poly ponent comprising at least one poly(1-alkene) pressure
methacrylate; and polymethylmethacrylate. The preferred sensitive adhesive, a non-pressure-sensitive-adhesive
homopolymers are propylene, such as that available under polymer component having reactive sites for crosslinking,
the trade names EASTOFLEXTM P1023 and ESCORENETM and a radiation activatable crosslinking agent. Solvent is not
3505, 3445, or 1024, and copolymers such as poly(ethylene 25 required but may be added as a carrier ?uid to introduce
butene) available under the trade name EXACTTM 4011; additive components. The mixture is hot melt coated, usu
poly(ethylene-octene), available under the trade names ally onto a substrate, and may be irradiated to cause
ENGAGETM EG8200 and AFFINITYTM PL1845, and linear crosslinking. More than one poly(1-alkene) component,
loW density polyethylene, available under the trade name polymer component and/or crosslinking agent may be used
DOWLEXTM 2045. The more preferred polymer compo depending on the desired properties and ultimate use of the
nents are the homopolymers ESCORENETM 3445 and 1024, pressure-sensitive adhesive.
and copolymers such as, for example, EXACTTM 4011 and Mixing may be done by any method that produces a
AFFINITYTM PL1845. substantially uniform distribution of the components. A
Crosslinking Agent substantially uniform distribution is generally indicated
Athird component of the radiation crosslinkable pressure 35 When any discrete phase of any one of the components has
sensitive adhesive composition is a radiation-activatable a shorter pro?le than a layer of the pressure-sensitive
crosslinking agent. These agents are compounds Which, adhesive composition, for example When the pressure
under the in?uence of activating radiation, connect polymer sensitive adhesive composition is coated onto a substrate. A
chains and may become incorporated therein. The activating discrete phase of any one component is preferably l/io”1 the
radiation may comprise actinic (electromagnetic) or thermal thickness of the pressure-sensitive adhesive composition
radiation, including exposing dicumyl peroxide to thermal layer, and more preferably l/ioo?1 the thickness.
radiation to generate free radicals. The components are melt mixed in a molten or softened
Crosslinking the components of a composition may state using devices that provide dispersive mixing, distribu
increase the molecular Weight of the individual polymer tive mixing, or a combination of dispersive and distributive
molecules in a pressure-sensitive adhesive composition and 45 mixing. The speci?c temperature used depends on the mate
concurrently increase the composition’s cohesive strength. rials being mixed. Mixing methods are explained in
Suitable radiation activatable crosslinking agents include, RauWendaal, C., Polymer Extrusion (3’d ed. 1994), Hanser
but are not limited to: aldehydes, such as benZaldehyde, Publishers, Cincinnati, Ohio. Both batch and continuous
acetaldehyde, and their substituted derivatives; ketones, methods of blending may be used. Examples of batch
such as acetophenone, benZophenone, and their substituted machines include internal mixing apparatus available under
derivatives; quinones such as the benZoquinones, the trade names BRABENDERTM or BANBURYTM, or roll
anthraquinone, and their substituted derivatives; thioxantho mixers. Examples of continuous methods include single
nes such as 2-isopropylthioxanthone and screW extruding, tWin screW extruding, disk extruding,
2-dodecylthioxanthone; and certain chromophore reciprocating single screW extruding, and pin barrel single
substituted vinyl halomethyl-sym-triaZines such as 2,4-bis 55 screW extruding. The continuous methods may include dis
(trichloromethyl)-6-(3‘,4‘-dimethoxyphenyl)-sym-triaZine. tributive elements such as cavity transfer elements available,
The concentration of radiation activatable crosslinking agent e.g., under the trade name CTMTM from RAPRA
may be in the range of 0.05 to 6.0 percent by Weight of the Technology, Ltd., ShreWsbury, England, pin mixing
poly(1-alkene) component, preferably 0.1 to 2.0 percent by elements, and static mixing elements as Well as dispersive
Weight, and more preferably 0.15 to 0.5 percent by Weight. elements, e.g., mixing elements available under the trade
Other Additives names MADDOCKTM and SAXTONTM.
In addition, other additives such as pigments, ?llers, After the hot melt mixing step, the softened or molten
Waxes, extenders, oils, plasticiZers, ultraviolet stabiliZers, pressure-sensitive adhesive composition may be formed into
and antioxidants may be used in the pressure-sensitive coatings by Well knoWn batch or continuous hot melt coating
adhesive composition. Examples of ?llers include, but are 65 techniques. An example of a batch coating process is the
not limited to, inorganic ?llers such as Zinc oxide, alumina placement of a portion of the blended mixture betWeen a
trihydrate, talc, titanium dioxide, aluminum oxide, and substrate desired to be coated and a release liner, pressing
US 6,177,190 B1
11 12
this composite structure in a heated platen press, at a The composition coating or article may be exposed to
controlled temperature and pressure, to form a pressure activating radiation to crosslink the poly(1-alkene) and
sensitive adhesive coating of a desired thickness on the polymer components. This exposure usually occurs after the
substrate, and cooling the resultant coating. Continuous crosslinkable pressure-sensitive adhesive is applied to a
coating methods include, for example, extrusion and coex substrate or release liner or after it has been transferred from
trusion. a release liner to another substrate, and is usually done at
The pressure-sensitive adhesive composition may be room temperature. HoWever, the pressure-sensitive adhesive
extruded onto a preformed backing to form an adhesive may be exposed to radiation before application to the
article. This may be done by draWing the pressure-sensitive substrate if the composition is already formed into its ?nal
adhesive composition out of a ?lm die and contacting it With 1O shape or if the crosslinked composition could still be pro
a moving plastic Web or other suitable substrate. These cessed into a ?nal shape.
methods are explained in, for example, Michaeli, W., Extru To achieve crosslinking, the radiation activatable
sion Dies, (2nd ed. 1992), Hanser Publishers, Munich, Ger crosslinking agent in the pressure-sensitive adhesive com
many. The extruded adhesive and the preformed backing position may be exposed to actinic (electromagnetic) radia
may be nipped together. In the case of heat sensitive 15 tion thereby generating free radicals Which promote the
backings, the extruded adhesive should be alloWed to cool crosslinking process. Commercially available actinic radia
before contacting the backing. Alternatively, adhesive tion sources include infrared, visible, and ultraviolet radia
articles may be prepared by laminating a preformed ?lm of tion. The use of UV radiation is explained in Hoyle and
the pressure-sensitive adhesive composition to a preformed Kinstle, Radiation Curing 0f Polymeric Materials,
backing using heat and pressure to ensure that the adhesive (American Chemical Society, 1990). The preferable Wave
and the backing bond together. length range to activate the radiation activatable crosslinking
The most preferred approach is coextrusion of the layers agents disclosed herein is 250 to 400 nm. The dose of radiant
of an adhesive article. A pressure-sensitive adhesive com energy applied in this Wavelength range is preferably less
position extruded from a ?lm die may be joined With a than 1500 millijoules/cm2 and more preferably less than 800
backing material extruded from another ?lm die With the 25 millijoules/cm2. Details of a radiation crosslinking process
composite material being cooled to form a pressure-sensitive are disclosed in US. Pat. Nos. 4,181,752 and 4,329,384.
adhesive tape. In this method, the pressure-sensitive adhe Because the pressure-sensitive adhesive component of the
sive composition may be applied to a moving Web using a present invention already contains polymers, the pre
die having ?exible die lips, such as a reverse ori?ce coating polymeriZation step disclosed in ’752 and ’384 is not
die. A source of contact dies is Extrusion Dies, Inc., required in the radiation crosslinking process of the present
ChippeWa Falls, Wis. A variation of this method involves invention.
coextruding the pressure-sensitive adhesive composition, It is also possible to initiate crosslinking during the
the backing, and a loW adhesion backsiZe through either a extrusion process by using a crosslinker that may be acti
feedblock die or a multimanifold die, such as those vated by heat, for example, a triaZine compound. The heat
described in Us. Pat. No. 3,565,985 (Schrenk); US. Pat. 35 generated to melt the polymer mixture in the extrusion
No. 5,427,842 (Bland); US. Pat. No. 5,589,122 (Leonard); process may initiate thermal crosslinking. HoWever, condi
US. Pat. No. 5,599,602 (Leonard); and Us. Pat. No. tions must be carefully controlled to ensure that the
5,660,922 (Herridge). Combinations of these different crosslinking takes place only as the material exits the
manufacturing techniques may also be used such as coex extruder and not While it is still in the extruder.
truding the backing and the loW adhesion backsiZe, then Pressure-sensitive adhesive articles of the invention may
laminating the pressure-sensitive adhesive onto the backing. comprise a layer of the pressure-sensitive adhesive compo
Any suitable substrates may be used, including, but not sition coated on a backing Which may have a releasable
limited to, natural and synthetic cloth including ?ber-glass surface on the side opposite that coated With the pressure
cloth, metaliZed ?lms and foils, polymeric ?lms, nonWoven sensitive adhesive. The articles may be in the form of rolls,
materials, paper and polymer coated paper, foam backings, 45 sheets or other shapes determined by the speci?c use
and micro-porous articles. Polymeric ?lms include, but are requirements. The exposed surface of the pressure-sensitive
not limited to, polyole?ns such as polypropylene, adhesive coating may subsequently be applied to a surface
polyethylene, loW density polyethylene, linear loW density from Which it could be later released, i.e., a release liner, or
polyethylene and high density polyethylene; polyesters such directly to the desired substrate.
as polyethylene terephthalate; polycarbonates; cellulose Transfer articles may also be made. These articles com
acetates; polyimides available under the trade name KAP prise the pressure-sensitive adhesive composition betWeen
TONTM from E. I. du Pont de Nemours and Company, tWo release liners. The release liners often comprise a clear
Wilmington, Del. NonWoven materials, generally made polymeric material such as polyole?n or polyester that is
from randomly oriented ?bers, include, but are not limited transparent to ultraviolet radiation. Preferably, each release
to, nylon, polypropylene, ethylene-vinyl acetate copolymer, 55 liner is ?rst coated With a release material, such as silicone,
polyurethane, rayon and the like. Foam backings include, to obtain easier release from the pressure-sensitive adhesive
but are not limited to acrylic, silicone, polyurethane, of the invention.
polyethylene, neoprene rubber, and polypropylene, and may The process of making the radiation-crosslinked poly(1
be ?lled or un?lled. Micro-porous articles include, for alkene) pressure-sensitive adhesives of this invention has
example, microvoided polymers and thermally-induced several advantages over processes knoWn to the art. Not only
phase separated polymeric constructions. Backings that are may one make pressure-sensitive adhesives that have excel
layered, such as polyethylene-aluminum membrane lent room temperature and elevated temperature shear
composites, are also suitable. properties, but one may also make radiation-crosslinked
After forming, the pressure-sensitive adhesive coatings pressure-sensitive adhesives having shear and peel adhesion
are typically solidi?ed by quenching, using direct methods, 65 performance similar to knoWn crosslinked pressure
such as chill rolls or Water baths, or indirect methods, such sensitive adhesives but requiring much less radiation expo
as air or gas impingement. sure during the curing process.