Coating processes – Electrical product produced – Welding electrode
Reexamination Certificate
2002-07-30
2004-07-06
Seidleck, James J. (Department: 1711)
Coating processes
Electrical product produced
Welding electrode
C521S050000, C521S063000, C521S064000, C521S065000, C521S072000, C521S082000, C521S142000, C521S150000, C521S149000, C521S915000, C522S084000, C522S113000, C522S114000, C522S120000, C522S121000, C522S149000, C522S150000, C427S243000, C427S244000, C427S508000
Reexamination Certificate
active
06759080
ABSTRACT:
TECHNICAL FIELD
This invention relates to foams made by photopolymerizing emulsions. The emulsions comprise a reactive phase and an immiscible phase wherein the reactive phase or both phases are continuous. The resulting foams may be closed or open cell, depending on the initial emulsion microstructure.
BACKGROUND
In the past, thermal polymerization has been used as a technique to polymerize high internal phase emulsions (HIPE)s. Typically these HIPEs contain styrene and divinylbenzene as well as other monomers. The thermal polymerization technique is very time intensive, usually requiring more than 10 hours for polymerization, and prohibits continuous production of foams. For thermal polymerization, emulsions are made and poured into a sealed container in which they are heated for many hours. After polymerization, the solid foams (still containing water) are removed and dried in an oven.
The emulsions used in thermal polymerization must remain stable for many hours until the polymerization process is complete, otherwise inhomogeneous foam materials would be formed. The requirement for a stable emulsion limits the types of monomers and surfactants that may be used in a thermal polymerization process.
SUMMARY OF INVENTION
The present invention features a novel method for creating foams, including open cell foams, from water-in-oil emulsions. The applicants found, surprisingly, that they could make foams from high internal phase emulsions (HIPEs) and other water-in-oil emulsions using a photopolymerization process. This is unexpected because emulsions typically have an opaque appearance and would not be expected to transmit enough light to conduct a photopolymerization reaction. Applicants found that they could cure an emulsion as thick as 8 millimeters.
The foams may be made by a batch process, or a continuous process in which the emulsion may be coated on a moving support. In either case, the foam is polymerized and crosslinked by exposure to actinic radiation. Some embodiments of the foams may be polymerized and crosslinked within one second or less of radiation illumination time. The fast polymerization process of the present invention allows a broad range of materials to be used because the emulsion needs to be stable for only a short time (seconds to minutes).
One aspect of the present invention provides a process for making a crosslinked polymeric foam comprising: a) mixing a reactive phase comprising at least one polymerizable material, at least one crosslinking agent, and at least one emulsifier with at least one photoinitiator and a liquid fluid immiscible with the reactive phase to form an emulsion wherein the immiscible fluid forms a discontinuous or co-continuous phase with the continuous reactive phase; b) shaping the emulsion; and c) exposing the emulsion to actinic radiation to form a crosslinked polymeric foam containing residual immiscible fluid.
The process may comprise further steps of exposing the emulsion to heat and/or removing residual immiscible fluid from the foam.
The polymerizable material may be ethylenically- or acetylenically-unsaturated, such as an acrylate, and free-radically or cationically-curable. The polymerizable material may be the same as the crosslinking agent or the emulsifier.
The immiscible phase is typically water, but may comprise other liquids such as fluorocarbons or organic liquids. The immiscible fluid may comprise 74 volume percent, or more, of the emulsion.
The reactive phase may include, e.g., non-polymerizable materials and materials that can incorporate functional groups into the foam.
The structure of the foam of the present invention may be controlled by aging the emulsion prior to polymerization or by selection of a particular agitation method for making the emulsion.
The emulsion may include photoinitiators in the reactive or immiscible phase. Preferably, the photoinitiators are activated by ultraviolet or visible radiation of 300 to 800 nanometers.
Polymerization and crosslinking of the emulsion may occur in as little as 10 minutes or even 10 seconds.
A further aspect of the invention is an emulsion having a continuous reactive phase comprising at least one polymerizable material and at least one crosslinking agent, a discontinuous or co-continuous phase comprising a liquid fluid immiscible with the reactive phase, and at least one photoinitiator.
A further aspect of the invention is an open cell cross-linked foam comprising no thermal initiator residue. Another aspect of the invention is an open cell cross-linked foam comprising residue of a photoinitiator that absorbs at a wavelength of 300 to 800 nanometers.
A further aspect of the invention is a closed cell cross-linked foam comprising no thermal initiator residue. Another aspect of the invention is a closed cell cross-linked foam comprising residue of a photoinitiator that absorbs at a wavelength of 300 to 800 nanometers.
The foams may be crosslinked within the voids of a material selected from the group consisting of polymeric, woven, nonwoven, and metals. Alternatively, the foam may contain non-polymerizable materials selected from the group consisting of polymers, metals, particles, and fibers.
Some foams of the present invention can absorb at least two and one-half times their weight in fluid. Some of the foams collapse when fluid is removed.
Another aspect of the present invention is articles made using the foams of the present invention.
Foams of the present invention made from HIPEs have relatively homogeneous structures and may possess cell sizes between 1 and 200 microns and densities of at least 0.01 g/cc. Cells are typically joined by open “windows” or holes connecting adjacent cells. Some of the resulting foam materials may be capable of absorbing 25 or more times, typically 4 to 16 times, their weight in fluid (water or organic fluids). Some of the foams are extremely porous, having Gurley values (at 50 cc of air) of 2 to 70 seconds for a 0.2 cm (80 mil) thick specimen.
Foams of the present invention made from non-HIPE emulsions typically have interconnecting channel structures rather than a well-defined cellular structure.
Closed cell foams may also be made using the photopolymerization process of the present invention.
As used in this invention:
“HIPE” or “high internal phase emulsion” means an emulsion comprising a continuous reactive phase, typically an oil phase, and a discontinuous or co-continuous phase immiscible with the oil phase, typically a water phase, wherein the immiscible phase comprises at least 74 volume percent of the the emulsion;
“water-in-oil emulsion” means an emulsion containing a continuous oil phase and a discontinuous water phase; the oil and water phases may be co-continuous in some cases;
“reactive phase” means the continuous phase which contains the monomer or reactive species that are sensitive to reactive propagating species (e.g., those having free radical or cationic centers) and can be polymerized or crosslinked;
“immiscible phase” means a phase in which the reactive components have limited solubility; the immiscible phase may be discontinuous, or co-continuous with the reactive phase;
“stable” means the composition and microstructure of the emulsion is not changing over time;
“functional group” means a chemical entity capable of undergoing a non-polymerization reaction;
“monomer” means chemical species capable of polymerizing, it includes monomers and oligomers;
“reactive surfactant” means a surfactant (i.e., emulsifier) having sufficient reactivity to undergo polymerization reactions such that it becomes part of a polymer backbone;
“open cell” means a foam wherein the majority of adjoining cells are in open communication with each other; an open cell foam includes foams made from co-continuous emulsions in which the cell structure is not clearly defined, but there are interconnected channels creating at least one open pathway through the foam;
“window” means an intercellular opening;
“shaping” means forming into a shape and includes pouring, coating, and dispensing;
“polymerize” or “cure” are used interchangeably i
Gehlsen Mark David
Gold Douglas
Koecher Steven Dean
Nelson Eric Wayne
Thunhorst Kristin La Velle
3M Innovative Properties Company
Edman Sean J.
McClendon Sanza L.
Seidleck James J.
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