Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-08-13
2003-09-23
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S303100, C526S308000, C526S310000, C526S318000, C526S319000, C526S346000, C526S348200, C526S348400, C526S913000, C522S149000, C522S150000, C522S153000, C522S178000, C522S182000, C522S181000, C522S184000, C522S185000, C522S186000, C522S188000, C427S508000, C427S516000
Reexamination Certificate
active
06624273
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to acrylate-based adhesives and in particular plasticized acrylate-based pressure sensitive adhesives.
BACKGROUND OF INVENTION
Pressure-sensitive adhesives are typically coated from solvent or water, extruded as hot-melts, or they are bulk polymerized directly on a release liner or a backing. As more environmentally friendly coating techniques are sought, solvent-and water-free processes have become increasingly desirable.
Today, hot-melt coating is used for pressure-sensitive adhesives based on styrene/rubber based block-copolymers, natural rubbers and acrylate polymers. Block copolymers and natural rubbers can be handled as dry polymer beads or crumbs, which are compounded with tackifiers and oils in the extruder to make the pressure-sensitive adhesives.
Typically, acrylic polymers used for pressure-sensitive adhesives are inherently tacky, which can make the polymer handling and feeding to the equipment challenging. Today, acrylic pressure-sensitive adhesives are delivered as remeltable polymers in drums or pails, extrudable adhesives packaged in siliconized boxes or small pillows and pouches of sticky polymer enclosed in a non-tacky polymer shell. All of these formats require special packaging equipment at the adhesive manufacturing site and special equipment for handling/feeding the polymer at the coating site.
Most of the commercial block copolymer and natural rubber pressure sensitive adhesives use combinations of the elastomer and additives, such as tackifiers and plasticizing agents (or oils). Alternatively, acrylic pressure-sensitive adhesives are often free of any of these additives. Proper selection of the (meth)acrylate and copolymerizable comonomers allows the manufacture of acrylic pressure-sensitive adhesive polymers that are inherently tacky. The absence of additives and the saturated backbone of the acrylate polymer are very common reasons for the selection of acrylic pressure-sensitive adhesives for outdoor applications or when durable bonds need to be made.
However, it is not always possible to achieve the desired pressure-sensitive adhesive properties using acrylic polymers without the use of additives. For example, in order to enhance adhesion against low surface energy substrates, acrylic pressure-sensitive adhesives can be formulated with tackifiers. Since acrylic pressure sensitive adhesives have glass transition temperatures (Tg) that are typically below 0° C., tackifiers are commonly used to decrease the shear storage modulus of the acrylic polymer to improve its surface wetting characteristics. The tackifiers typically have softening points that are well above room temperature, so the Tg of the compounded adhesive will also increase over the untackified acrylate polymer. This effect typically limits the useful amount of tackifiers in a tackified acrylate pressure sensitive adhesive formulation to about 60 pph or less relative to the elastomer.
Tackifiers are often colored and oxidatively unstable, thus sacrificing the unique clarity and stability for which acrylics are known. In addition, it has been found that most commercial tackifiers that are compatible with the polar acrylate matrix will also interfere with bulk polymerization, resulting in much lower molecular weights for the resultant polymer.
Plasticizing agents are less commonly used in acrylate pressure-sensitive adhesives, as plasticizing agents typically decrease the Tg of the compounded adhesive, resulting in a loss of peel strength. Actually, plasticizing agent migration into acrylic pressure sensitive adhesives is one of the well-known failure mechanisms in applications against plasticized polyvinyl chloride.
SUMMARY OF INVENTION
Briefly, in one aspect of the present invention essentially non-tacky, polymers are plasticized into pressure-sensitive adhesives. Plasticized polymer based pressure-sensitive adhesives of the present invention comprises:
a. about 100 parts by weight of a base copolymer having a Tg greater than about 0° C., wherein the base copolymer is formed from and comprises:
(1) about 50 to 70% by weight of a high Tg comonomer component, wherein the homopolymer formed from the high Tg comonomer component has a Tg of at least about 20° C.;
(2) optionally, up to about 20% by weight based on the total weight of the base copolymer of an acidic comonomer; and
(3) about 30 to 50% by weight of one or more low Tg (meth)acrylate comonomer, wherein the Tg of the homopolymer of the low Tg comonomer is less than about 20° C., and
b. about 1 to about 100 parts based on the base copolymer of a non-reactive, non-volatile, non-acrylic-based plasticizing agent.
The plasticized pressure-sensitive adhesives of the present invention have several general advantages over conventional acrylate pressure-sensitive adhesive compositions. Since the base copolymer exhibits little or no tack prior to its combination with the plasticizing agent, new means for handling, processing and delivering these compositions can be practiced. The base copolymer can be transported and processed similarly to other elastomeric materials used in pressure-sensitive adhesive compositions, without the special packaging and processing generally required with traditional acrylate pressure-sensitive adhesives. When the base copolymer is in particulate form, such as dried particles prepared using suspension, emulsion or dispersion polymerization methods or cryo-grinding, powder handling and coating techniques can be employed and exploited to create new pressure-sensitive-adhesive materials and new product applications. Furthermore, the pressure-sensitive properties of the composition can be activated when desired by the formulator or when required by the application.
Conventional understanding of the effect of the addition of plasticizing agents to pressure-sensitive adhesives is that adhesive performance degrades following plasticization. However, by combining the plasticizing agent with a high Tg, high shear storage modulus base copolymer, stable and useful pressure-sensitive adhesive materials can readily be formulated.
In addition, it has been found that some specific classes of plasticizing agent show very limited interference with radiation crosslinking and polymerization processes. Since plasticizing agents are typically free of unsaturation, they are as oxidatively stable as the base copolymer. This inertness toward radiation opens some novel opportunities for cured adhesives where the plasticizing agents can be used as an alternative for tackifiers. Tackifiers are known to interfere with UV processing. Plasticizing agents are also generally significantly lower in cost than tackifiers and can be selected to be compatible and non-volatile with respect to the base copolymer.
In addition, with regard to tackifying agents, it has been found that some tackifiers can cause allergenic response in some medical adhesive applications. Use of plasticizing agents along with a base copolymer to form plasticized pressure sensitive adhesives according to the present invention can offer alternative routes towards modification of base copolymer properties to yield non-allergenic compositions for skin and other medical adhesive applications.
Advantageously, the adhesives of the present invention exhibit fluid-like characteristics despite generally high molecular weights of the base copolymer. Fluidity of the plasticized pressure-sensitive adhesive compositions occurs at lower temperatures as compared to the unplasticized base copolymer. Thus, the adhesives of the present invention provide a distinct advantage for applications using heat sensitive substrates because coatable viscosities can be obtained at lower melt temperatures. Furthermore, because the adhesives of the present invention have a low melt viscosity, they tend to retain less orientation and relax more readily during extrusion. Lower melt viscosities also permit faster coating speeds, an important consideration in the production and commercialization of articles coated with the plasticized pressure-sensitive adhesive compos
Everaerts Albert I.
Moonen Eric B. T.
Stark Peter A.
3M Innovative Properties Company
McClendon Sanza L.
Peters Carolyn V.
Seidleck James J.
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