Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-11-17
2003-09-16
Egwim, Kelechi (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S433000, C524S458000, C524S533000, C524S535000, C524S547000, C524S609000
Reexamination Certificate
active
06620874
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method of making ionomeric particulate compositions that are useful for modifying the rheology, functionality, and physical properties of a polymer matrix so as to render the matrix more useful in applications that require adhesive properties.
BACKGROUND
Suspension polymerization has been used to make polymer beads. For example, U.S. Pat. Nos. 4,833,179 (Young et al.) and 4,952,650 (Young et al.) describe methods of aqueous suspension polymerization to form pressure sensitive acrylate copolymer beads. The methods generally comprise making a monomer premix comprising acrylic acid esters of a non-tertiary alcohol, an acid monomer co-polymerizable with the a acrylic acid ester, a chain transfer agent, a free radical initiator, and a modifier moiety. The monomer premix is combined with a water phase, which contains a sufficient amount of suspending agent, to form a suspension. Polymerization occurs by mixing the premix phase with the water phase until the polymer beads are formed. The polymer beads may remain in the water prior to coating, during which time the beads are preferably storage-stable so as not to coalesce or agglomerate together. When coalescence is present, the beads tend to migrate towards one another and can form large masses. Coalescence of the beads hampers their handling and transportation and is undesirable.
U.S. Pat. No. 5,952,420 (Senkus et al.) discloses permeable, self-supporting, shaped structures that can be used in applications such as filters, masks, or respirators. The structure comprises a mass of active particulate (e.g., sorbents such as activated carbon, silica gel, or alumina granules) bonded together with pressure sensitive adhesive polymer particulates (also referred to as “PSA suspension beads”) distributed in the mass of active particulate. PSA suspension beads from about 10 to 100 micrometers can be prepared using a combination of surfactants and using, as another comonomer, a styrene sulfonate salt, such as sodium salt, to control particle size in the suspension polymerization. PSA suspension beads from about 1 to 10 micrometer can be achieved by homogenizing the polymerization reaction mixture comprising (1) the styrene sulfonate salt and (2) an amount of surfactant above the critical micelle concentration added to the water phase before suspension polymerization. See Column 9, lines 39-44 and lines 57-61. Senkus also discloses that the PSA polymer is essentially any polymer, copolymer, or blend of copolymer that has pressure sensitive adhesive properties. A related case is U.S. Pat. No. 5,696,199 (Senkus et al.) The polymeric particulate and beads discussed thus far typically use added chain transfer agents. Chain transfer refers to the termination of a growing polymer chain and the start of a new one thus controlling the molecular weight of the polymer. The process can be affected by use of a chain transfer agent, which, in most cases, is some species that has been added to the polymerization process to effect chain transfer (referred to as an “added chain transfer agent”). Chain transfer agents are used widely in polymerization processing to decrease the molecular weight of the polymer thereby imparting to the polymer one of the features necessary for pressure sensitive tack. In suspension polymerization, chain transfer agents are typically added to the oil phase, which contains the monomers. When the monomers are acrylate esters of a non-tertiary alcohol having 1 to 14 carbon atoms, common chain transfer agents include mercaptans, alcohols, and carbon tetrabromide, with isooctyl thioglycolate being a preferred one. See U.S. Pat. No. 4,833,179, Column 4, lines 37-42. The beads discussed thus far typically possess room temperature tackiness and thus are well suited as a pressure sensitive adhesive.
To control the beads' particle size, surfactants in a certain amount, surfactants in combination with another comonomer, and homogenization techniques have been used. Homogenization, which generally refers to reducing a material to particles and dispersing the particles throughout a liquid, can be achieved by using the appropriate agitation. Typically, for laboratory size batches (i.e., on the order of a few liters), a Waring™ blender is used for homogenization. It is well known in the suspension polymerization art that agitation can be important to achieving the desired particle-size distribution in the final product.
While the foregoing methods of aqueous suspension polymerization and the resulting acrylate pressure sensitive adhesive beads have been proven useful, other suspension polymerization methods and compositions therefrom are sought.
SUMMARY
This invention provides a novel method of making ionomeric particulate compositions where the method does not rely on the use of an added chain transfer agent to control the molecular weight of the resulting particulate. Because the inventive method does not use an added chain transfer agent, the resulting particles tend to have high molecular weight and also tend to have little to no pressure sensitive tack. The inventive method produces ionomeric particulates that can readily act as a reinforcing agent for and thereby strengthening a polymer matrix. Also, the invention does not rely on the practice of homogenization to control the particle size. Instead, the ionomeric particulates' particle size can be controlled through the use of surfactants, one of which is a monomer surfactant.
In brief summary, the method of making an ionomeric particulate of the invention comprises or consists essentially of: (a) forming an aqueous phase comprising an acid monomer, a metal oxide, and at least a first and a second surfactant, the first being a monomer surfactant; (b) forming an oil phase comprising at least one vinyl monomer; and (c) suspension polymerizing the oil phase.
The present inventive method provides novel ionomeric particulates that can be dispersed into a polymer matrix to modify the rheology, functionality, and physical properties (e.g., cohesive strength, adhesion, toughness, elasticity, flexibility) of the polymer matrix so as to yield a useful organic particulate-filled adhesive. A key advantage of the present invention lies in the ability to tailor the ionomeric particulate so that when combined with a polymer matrix, the resulting organic particulate-filled adhesive exhibits the desired properties.
The ionomeric particulates can be used to modify any polymer matrix that is compatible with it to yield an organic particulate-filled adhesive useful for a variety of diverse applications. The adhesive can be formulated to have pressure sensitive adhesive properties by choosing the appropriate ionomeric particulate composition polymer matrix, and various other components, such as plasticizers and tackifiers. For example, it has been discovered that the inventive ionomeric particulates are useful as part of a repulpable adhesive. Repulpability requires that the adhesive components be water-soluble or water-dispersible. When the components are water-dispersible, they are preferably of a sufficiently small particle size to pass through the repulping equipments. The inventive ionomeric particulates are also useful as a part of an adhesive that is applied to mammalian skin to remove undesirable materials (e.g., comedomes, unwanted hair follicles, dirt, oil, debris, dead skin). These particular adhesives (repulpable and skin cleansing) are disclosed in Assignee's copending U.S. application Ser. No. 09/441,580, which is hereby incorporated by reference, the application being filed on the same day as this application.
The present invention provides several processing advantages for controlling the ionomeric particulate properties, such as molecular weight and average diameter. First, there is no reliance on the use of an added chain transfer agent for controlling molecular weight. Second, the inventive method eliminates a homogenization step as a means of controlling the particle size. Homogenization on a production size scale, i.e. for batch s
Engel Michael R.
Tseng Chi-Ming
Young Chung I.
Egwim Kelechi
Pribnow Scott R
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