Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-02-20
2004-01-13
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S190000, C525S242000, C525S452000, C525S539000, C525S540000
Reexamination Certificate
active
06677402
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to pressure sensitive adhesives and tape articles prepared therefrom. The tapes are characterized by exhibiting an overall balance of adhesive and cohesive characteristics and exceptional load bearing capabilities at elevated temperatures.
BACKGROUND OF THE INVENTION
Pressure sensitive tapes are virtually ubiquitous in the home and workplace. In its simplest configuration, a pressure sensitive tape comprises an adhesive and a backing, and the overall construction is tacky at the use temperature and adheres to a variety of substrates using only moderate pressure to form the bond. In this fashion, pressure sensitive tapes constitute a complete, self-contained bonding system.
According to D. W. Aubrey in “Developments in Adhesives” (ed. W. C. Wake, Vol. 1, Chapter 5, Applied Science Publishers: London, 1977), a good pressure sensitive adhesive (psa) must fulfill three main technical requirements:
1. The adhesive must conform quickly to the surface to which it is applied in order to rapidly form a bond; this relates to tack.
2. The adhesive must display adequate resistance to separation by peeling once the bond is formed; this relates to adhesion.
3. The adhesive must exhibit resistance to shear under the influence of an applied load; this relates to the adhesive's cohesion.
These three requirements are assessed generally by means of tests which are designed to individually measure tack, adhesion (peel strength), and cohesion (shear holding power). These measurements taken together constitute the balance of properties often used to characterize a psa.
With broadened use of pressure sensitive tapes over the years, performance requirements have become more demanding. Shear holding capability, for example, which originally was intended for applications supporting modest loads at room temperature has now increased substantially for many applications in terms of operating temperature and load. So-called high performance pressure sensitive tapes are those capable of essentially permanently supporting loads of >300 grams per square centimeter of adhesive at temperatures of 150° F. (65° C.) or higher. Increased shear holding capability has generally been accomplished by crosslinking the psa, although considerable care must be exercised so that high levels of tack and adhesion are retained in order to retain the aforementioned balance of properties.
SUMMARY OF THE INVENTION
In one aspect this invention provides a novel pre-adhesive syrup polymer composition comprising:
a first component comprising a solute polymer comprising a plurality of polymerized monomer units comprising pendant reactive nucleophilic or electrophilic functional groups;
a second component having a plurality of co-reactive nucleophilic or electrophilic functional groups selected from a second solute polymer comprising a plurality of polymerized monomer units comprising co-reactive functional groups and a polyfunctional compound having co-reactive functional groups; and
a third component comprising at least one free-radically polymerizable solvent monomer.
The novel pre-adhesive syrup polymer compositions of the present invention cure to pressure sensitive adhesives possessing high load bearing capability at elevated temperatures by means of the photopolymerization of the solvent monomer component and crosslinking by means of reactive and co-reactive functional groups. In another aspect the invention provides an adhesive article comprising the polymerized, crosslinked syrup polymer coated on a substrate.
In another aspect this invention provides a process of preparing a novel adhesive composition which comprises the steps of providing the novel syrup polymer composition of this invention further comprising an effective amount of a photoinitiator, and subjecting said composition to sufficient energy to activate said photoinitiator to polymerize the solvent monomer(s) of the syrup polymer composition, and crosslinking the first solute polymer and second component by forming covalent bonds between the reactive and co-reactive functional groups.
For performance, environmental, and economic considerations, photoinitiated polymerization is a particularly desirable method for preparing a psa directly on the tape backing (or release liner in the case of a so-called transfer tape in which the psa is ultimately transferred to a substrate instead of a tape backing to provide for adhesion of the bonded article or adherend). With this bulk polymerization technique, a common practice in order to achieve a coatable viscosity of 500-10,000 centipoises is to partially polymerize, either thermally or photochemically, the monomers to a conversion of 5-10%.
In another aspect this invention provides a process for preparing an adhesive article comprising coating the novel syrup polymer composition on a substrate in the presence of a free-radical initiator, and subjecting the coated substrate to sufficient energy to polymerize the solvent monomer and crosslink the components by forming covalent bonds between the reactive and co-reactive functional groups.
Briefly, the present invention provides novel pressure sensitive photoadhesive compositions prepared from a first solute polymer containing reactive functional groups capable of reaction at effective rates (at normal processing temperatures) with a co-reactive second component possessing functionality that is complementary to that of the first solute polymer. By complementary is meant that if the solute polymer reactive functional groups are electrophilic in nature, the second component should possess co-reactive nucleophilic groups. The converse is also useful; when the solute polymer contains reactive nucleophilic groups then the second component contains co-reactive electrophilic groups. In addition, reactions involving polymeric reactants of the instant invention are controlled and precise in that they result in polymer—polymer coupling reactions only by reaction between the reactive and co-reactive functional groups. The polymerization of the novel syrup polymer composition has been discovered to provide high load holding capability pressure sensitive adhesives, especially at elevated temperatures.
In this application “pre-adhesive” refers to the solution comprising functional solute polymer, a second component and third monomer component which may be polymerized and crosslinked to form a pressure sensitive adhesive. “Syrup polymer” refers to a solution of a solute polymer in one or more solvent monomers, the solution having a viscosity of from 500 to 10,000 cPs at 22° C.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides pressure sensitive adhesives possessing essentially permanent, high load bearing capabilities at temperatures up to 70° C. The pressure sensitive adhesives of the invention are polymers exhibiting a glass transition temperature of less than −15° C. and are formed from 100 parts of ethylenically unsaturated monomers and polymers. The pressure sensitive adhesives comprise a polymerized product of a syrup polymer mixture comprising:
(a) from 2 to 20 parts by weight of a first component comprising a solute polymer having pendant reactive electrophilic or nucleophilic functional groups:
(b) from 0.01 to 10.00 parts by weight of a second component having a plurality of co-reactive electrophilic or nucleophilic functional groups;
(c) from 70.00-97.99 parts by weight of a third component comprising polymerizable, ethylenically-unsaturated monomers selected from acrylic acid esters of non-tertiary alkyl alcohols containing 1-14 carbon atoms (i.e. “acrylate monomers”).
This invention also provides a polymerizable syrup polymer comprising the syrup polymer and photoinitiator.
The first solute polymer, as well as the second solute polymer (if used in lieu of the polyfunctional compound) comprises
(1) from 75.00 to 99.99 parts by weight of polymerized monomer units derived from acrylic acid esters of non-tertiary alkyl alcohols containing 1-14 carbon atoms;
(2) from 0.01 to 5.00 parts by weight
Abuelyaman Ahmed S.
Gaddam Babu N.
Heilmann Steven M.
3M Innovative Properties Company
Kokko Kent S.
Mullis Jeffrey
LandOfFree
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