Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2000-02-08
2003-01-07
Yoon, Tae H. (Department: 1714)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S3550AC, C524S272000, C524S505000, C525S095000
Reexamination Certificate
active
06503621
ABSTRACT:
BACKGROUND
Pressure sensitive adhesives typically include materials (e.g., elastomers) that are either inherently tacky or that are tackified with the addition of tackifying resins. They can be defined by the Dahlquist criteria described in Handbook of Pressure Sensitive Adhesive Technology, D. Satas, 2
nd
ed., page 172 (1989) at use temperatures. This criterion defines a good pressure sensitive adhesive as one having a 1 second creep compliance of greater than 1×10
−6
cm
2
/dyne. Alternatively, since modulus is, to a first approximation, the inverse of compliance, pressure sensitive adhesives may be defined as adhesives having a modulus of less than 1×10
6
dynes/cm
2
.
Another well-known means of identifying a pressure sensitive adhesive is that it is aggressively and permanently tacky at room temperature and firmly adheres to a variety of dissimilar surfaces upon mere contact without the need of more than finger or hand pressure as described in “Glossary of Terms Used in the Pressure Sensitive Tape Industry” provided by the Pressure Sensitive Tape Council, August, 1985.
Another suitable definition of a pressure sensitive adhesive is that it preferably has a room temperature storage modulus within the area defined by the following points as plotted on a graph of modulus versus frequency at 25° C.: a range of moduli from approximately 2×10
5
to 4×10
5
dynes/cm
2
at a frequency of approximately 0.1 radian/second (0.017 Hz), and a range of moduli from approximately 2×10
6
to 8×10
6
dynes/cm
2
at a frequency of approximately 100 radians/second (17 Hz) (for example, see FIGS. 8-16 on p. 173 Handbook of Pressure Sensitive Adhesive Technology, D. Satas, 2
nd
ed., (1989)).
Other methods of identifying a pressure sensitive adhesive are also known. Any of these methods of identifying a pressure sensitive adhesive may be used to identify suitable pressure sensitive adhesives of the present invention.
There is an ongoing need to modify pressure sensitive adhesives to meet the criteria for new applications. In general, additives may be used to modify adhesives; however, when additives are incorporated into pressure sensitive adhesives to modify their properties, care must be taken to avoid a loss in peel adhesion or shear strength.
Major classes of pressure sensitive adhesives include acrylics, polyurethanes, poly-alpha-olefins, silicones, and tackified natural and synthetic rubbers. Some examples of synthetic rubbers include tackified linear, radial (e.g., star), tapered, and branched styrenic block copolymers, such as styrene-butadiene-styrene, styrene-ethylene/butylene-styrene, and styrene-isoprene-styrene. Uncrosslinked acrylics typically have good low temperature adhesion but poor shear strength. Block copolymer adhesives have good shear strength and adhesion at room temperature, but poor adhesion at non-ambient temperatures, and poor shear strength at elevated temperatures.
Generally, when additives are used to alter properties of pressure sensitive adhesives, the additives should be miscible with the pressure sensitive adhesive or form homogeneous blends at the molecular level. Some types of pressure sensitive adhesives have been modified with tackified thermoplastic elastomers (e.g., styrene-isoprene-styrene block copolymers), thermoplastics (e.g., polystyrene, polyethylene, or polypropylene), and elastomers (e.g., polyolefins, natural and synthetic rubbers). For example, thermoplastic materials have been added to acrylic pressure sensitive adhesives. Such materials are described in International Publication Nos. WO 97/23577, WO 95/25469 (all to Minnesota Mining and Manufacturing Co.) as having a substantially continuous domain and a substantially fibrillous to schistose domain. Although such pressure sensitive adhesives are described as having increased peel adhesion relative to the acrylic component or solvent-coated blends of the same components, there is still a need for adhesives exhibiting useful combinations of properties (i.e., peel, shear, clean removal, etc.), particularly at high and low temperatures (i.e., non-ambient temperatures).
SUMMARY OF THE INVENTION
The present invention is directed to pressure sensitive adhesive compositions that include at least one acrylate pressure sensitive adhesive component and at least one thermoplastic elastomer-based pressure sensitive adhesive component. The acrylate pressure sensitive adhesive component includes at least one polymerized monofunctional (meth)acrylic acid ester monomer having a Tg (glass transition temperature) of no greater than about 0° C. when homopolymerized, and 0 to about 10 wt % of at least one copolymerized monofunctional ethylenically unsaturated monomer having a Tg of at least about 10° C. when homopolymerized. The thermoplastic elastomer-based pressure sensitive adhesive component includes a radial block copolymer, and preferably, a tackifying agent. In certain preferred embodiments, the pressure sensitive adhesive composition is crosslinked. This can occur through crosslinking of the individual components or upon crosslinking the composition after combining the individual components.
As used herein, a thermoplastic elastomer (i.e., thermoplastic rubber) is a polymer having at least two homopolymeric blocks or segments, wherein at least one block has a Tg of greater than room temperature (i.e., about 20° C. to about 25° C.) and at least one block has a Tg of less than room temperature. In a thermoplastic elastomer these two blocks are generally phase separated into one thermoplastic glassy phase and one rubbery elastomeric phase. A radial block copolymer is a polymer having more than two arms that radiate from a central core (which can result from the use of a multifunctional coupling agent, for example), wherein each arm has two or more different homopolymeric blocks or segments as discussed above. See, for example, the
Handbook of Pressure Sensitive Adhesive Technology
, D. Satas, 2
nd
ed., Chapter 13 (1989).
Significantly, the present invention provides adhesives with one or more of the following: good low temperature adhesion, high temperature shear strength, clean removal after high temperature applications, and good lifting resistance as measured by low stress peel. Particularly preferred adhesives have all of these properties. In a preferred embodiment, an adhesive tape sample that includes a backing and the pressure sensitive adhesive composition disposed thereon has a peel adhesion value from a glass substrate of at least about 22 Newtons/decimeter (N/dm) at 4° C. and a shear strength value from stainless steel of at least about 100 minutes at 71° C.
In a preferred embodiment, the present invention provides a crosslinked pressure sensitive adhesive composition that includes at least one crosslinked acrylate pressure sensitive adhesive component and at least one thermoplastic elastomer-based pressure sensitive adhesive component. The thermoplastic elastomer-based pressure sensitive adhesive component includes an asymmetric radial block copolymer of the general formula Q
n
Y wherein Q represents an arm of the asymmetric radial block copolymer and has the formula S-B, n preferably represents the number of arms and is a whole number of at least three, Y is the residue of a multifunctional coupling agent, S is a thermoplastic polymer segment, and B is an elastomeric polymer segment.
Adhesive articles are also provided by the present invention. Such articles include a substrate (i.e., backing) having the pressure sensitive adhesive composition described herein disposed thereon.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Pressure sensitive adhesive compositions of the present invention are suitable for use in a variety of applications, preferably over a broad temperature range (e.g., about 4° C. to about 93° C.). These adhesives include a unique combination of an acrylate pressure sensitive adhesive component and a thermoplastic elastomer-based pressure sensitive adhesive component. Each of these components is a pressure sensitive adhesive with adv
Cernohous Jeff J.
Ma Jingjing
Sedgwick Paul
3M Innovative Properties Company
Blank Colene H.
Yoon Tae H.
LandOfFree
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