Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2001-12-28
2004-03-16
Sanders, Kriellion A. (Department: 1714)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C544S224000, C544S336000, C544S409000, C546S304000, C546S312000, C548S190000, C548S193000, C548S233000, C548S264800, C548S371400
Reexamination Certificate
active
06706920
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to compositions comprising at least one polymer and at least one antistatic agent. This invention further relates to fibers, films, fabrics, coatings, and molded or blown articles comprising the compositions. In other aspects, this invention also relates to novel compounds that are useful as antistatic agents and to processes for imparting antistatic characteristics to substrates.
BACKGROUND OF THE INVENTION
Electrostatic charge buildup is responsible for a variety of problems in the processing and use of many industrial products and materials. Electrostatic charging can cause materials to stick together or to repel one another. This is a particular problem in fiber and textile processing. In addition, static charge buildup can cause objects to attract dirt and dust, which can lead to fabrication or soiling problems and can impair product performance.
Sudden electrostatic discharges from insulating objects can also be a serious problem. With photographic film, such discharges can cause fogging and the appearance of artifacts. When flammable materials are present, a static electric discharge can serve as an ignition source, resulting in fires and/or explosions.
Static is a particular problem in the electronics industry, since modern electronic devices are extremely susceptible to permanent damage by static electric discharges. The buildup of static charge on insulating objects is especially common and problematic under conditions of low humidity and when liquids or solids move in contact with one another (tribocharging).
Static charge buildup can be controlled by increasing the electrical conductivity of a material. This can be accomplished by increasing ionic or electronic conductivity. The most common means of controlling static accumulation today is by increasing electrical conductivity through moisture adsorption. This is commonly achieved by adding moisture to the surrounding air (humidification) or by use of hygroscopic antistatic agents, which are generally referred to as humectants since they rely on the adsorption of atmospheric moisture for their effectiveness. Most antistatic agents operate by dissipating static charge as it builds up; thus, static decay rate and surface conductivity are common measures of the effectiveness of antistatic agents.
Antistatic agents can be applied to the surface (external antistat) or incorporated into the bulk (internal antistat) of an otherwise insulating material. Internal antistats are commonly employed in polymers such as plastics. Generally, internal antistats are mixed directly into a molten polymer during melt processing. (Typical polymer melt processing techniques include molding, melt blowing, melt spinning, and melt extrusion.) Relatively few antistatic agents have the requisite thermal stability to withstand polymer melt processing temperatures, which can be as high as 250 to 400° C. or more. Since static buildup is typically a surface phenomenon, internal antistats that are capable of migrating to and enriching the surface of a material are generally most effective.
Known antistatic agents cover a broad range of chemical classes, including organic amines and amides, esters of fatty acids, organic acids, polyoxyethylene derivatives, polyhydridic alcohols, metals, carbon black, semiconductors, and various organic and inorganic salts. Many are also surfactants and can be neutral or ionic in nature.
Many low molecular weight, neutral antistats have sufficiently high vapor pressures that they are unsuitable for use at high temperatures, as in polymer melt processing, due to material losses that occur via evaporation. Many other neutral antistats have insufficient thermal stability to survive polymer melt processing or other high temperature processing conditions.
Most nonmetallic antistats are humectants that rely on the adsorption and conductivity of water for charge dissipation. Thus, their effectiveness is typically diminished at low atmospheric humidity. Since many of these antistatic agents are also water soluble, they are easily removed by exposure of the material to water (as in washing) and are therefore not very durable. Water associated with hygroscopic antistatic agents can be a particular problem during polymer melt processing, since the water tends to vaporize rapidly at melt processing temperatures. This leads to the undesirable formation of bubbles in the polymer and can cause screw slippage in extrusion equipment.
Quaternary ammonium salts are well known in the art to be useful antistatic agents. They can be solid or liquid, the most common being halide or methanesulfonate salts. The salts provide excellent antistatic performance but suffer from limited thermal stability and are generally hygroscopic. Thus, they are not capable of withstanding the high temperature processing conditions required for many high performance thermoplastic resins.
Metal salts of inorganic, organic, and fluoroorganic anions have also shown proven utility as antistatic agents in certain polymer compositions. Alkali metal salts are most commonly employed, due to cost and toxicity considerations and to the high affinity of alkali metal cations, especially lithium, for water. However, most metal salts provide insufficient thermal stability under high temperature processing conditions and are not compatible with polymers of moderate to low polarity, such as polypropylene, polyester, and polycarbonate. This incompatibility can result in inadequate antistat performance and/or an unacceptable reduction in physical properties or transparency in a finished polymeric article. Consequently, the utility of metal salts as internal antistatic agents is generally limited to highly polar and/or hydrophilic polymer matrices cast from aqueous or organic solution at relatively low temperatures.
Furthermore, since many metal salts are corrosive towards metals and electronic components, they are unsuitable for applications where they may come into contact with such surfaces. Known hydrophilic metal salts and quaternary ammonium salts generally suffer all the disadvantages of other humectant antistatic agents (vide supra).
Thus, there remains a need in the art for antistatic agents that exhibit a superior balance of high thermal stability, hydrophobicity, low volatility, low corrosivity toward metals and electronic components, durability, and polymer compatibility, and that can impart good antistatic performance to a variety of insulating materials over a wide range of humidity levels.
SUMMARY OF THE INVENTION
Briefly, in one aspect, this invention provides an antistatic composition comprising or consisting essentially of a melt blend of (a) at least one ionic salt consisting of a nonpolymeric nitrogen onium cation (for example, a quaternary ammonium ion) and a weakly coordinating fluoroorganic anion, the conjugate acid of the anion being a superacid (for example, a bis(perfluoroalkanesulfonyl)imide ion); and (b) at least one thermoplastic polymer. As used herein, the term “melt blend” means a blend that has been prepared by melt processing technique(s), and the term “onium” means a positively charged ion having at least part of its charge localized on at least one nitrogen atom. Preferably, the Hammett acidity function, H
0
, of the conjugate acid of the anion is less than about −10.
It has been discovered that the above-described ionic salts can be used as additives (internal antistats) or topical treatments (external antistats) to impart antistatic characteristics to polymers or other insulating materials. These ionic salts are surprisingly effective at dissipating the static charge that can accumulate in an otherwise insulating substrate such as a polymer film or fabric. For example, when incorporated as polymer melt additive in polypropylene melt-blown nonwoven fabric, certain preferred salts impart static dissipation rates that are as good or better than those of any known antistatic agents under the same static decay test conditions. The ionic salts used in the composition of the invention are effect
Fanta Alan D.
Hachey Kathleen A.
Klun Thomas P.
Lamanna William M.
3M Innovative Properties Company
Fulton Lisa P.
Sanders Kriellion A.
Weiss Lucy C
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