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...
Utility Patent
1997-06-25
2001-01-02
Mulcahy, Peter D. (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...
C524S317000
Utility Patent
active
06169133
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to blends of glycerol monostearate and other compounds that improve the antistatic properties of polyolefins.
BACKGROUND OF THE INVENTION
Plastics are excellent insulators and have a tendency to generate and retain static charges. Static charges on bottles and other packaging products charge dust particles in the air by induction. The dust particles acquire a charge of the opposite polarity than the plastic package, and so are attracted to the package. Dust attracted to the packages of consumer products makes them less attractive. Plastic resin powders can explode when they generate a static charge. Static charged sheets of plastic are difficult to separate, and static charged plastic products are an explosion hazard in areas where flammable gases are used. Electronic circuit chips are susceptible to damage from static charged plastic packaging. Thus, there is a clear need in the plastic art for effective antistatic agents.
Antistatic agents may be applied to the surface of the finished article or incorporated in the bulk of the polymer during processing. They function by decreasing the rate of charge generation, by increasing the rate of charge dissipation, or by both mechanisms.
Plastics are rendered static dissipative by either adding a conductive material to the plastic in sufficient quantity that there is a three-dimensional conductive pathway through the plastics, or by adding to the plastic a surfactant-type chemical that will attract moisture to the surface of the plastic. Since water is a conductor, the surface layer of moisture then dissipates a static charge. The source of conductive material can be either an inherently conductive polymer, a metal or metal-containing material, or carbon black. The conductive additive can be added to the plastic at a high enough concentration make it static dissipative, but not completely conductive. Surfactant-type additives are of several different chemical types. They can be applied to the surface of the finished plastic article or incorporated in the bulk of the polymer when the polymer is made.
Conducting polymers are polymers with a pi-electron backbone capable of passing an electrical current. These polymers generally are not sufficiently conductive as neat polymers but require the inclusion of an oxidizing or reducing agent (dopant) to render them conductive.
Common conductive polymers are polyacetylene, polyphenylene, poly (phenylene sulfide), polypyrrole, and polyvinylcarbazole. A static-dissipative polymer based on a polyether copolymer has been announced. In general, electroconductive polymers have proven to be expensive and difficult to process. In most cases they are blended with another polymer to improve the processibility. Conductive polymers have met with limited commercial success.
Metal-containing polymers function simply by adding sufficient quantities of a metal to form a three-dimensional conduction pathway through the plastic. The metal is in the form of a powder, micrometer-sized needles, or as a thin coating on glass spheres, carbon fibers, or mica. The metals normally employed are nickel, zinc, stainless steel, copper, and aluminum. At higher levels these materials make the polymer capable of shielding electromagnetic impulses (EMI). Metals are typically not useful in applications where the plastic product is to be optically clear, i.e., transparent.
Inherently conductive antistats have the advantage of not being dependent on atmospheric moisture to function. Their drawbacks include expense, coloration of the plastic, and alteration of the mechanical properties of the plastic. The added stiffness caused by conductive fillers may not be a problem with a rigid containers, but it can be a problem for a flexible bag.
Surfactant-type antistats find the widest use because of their low cost and minimal effect on the mechanical properties of the plastic. Ease of use is another favorable aspect to surfactants. They can be mixed with the bulk of the plastic prior to processing or can be applied to the surface of the finished plastic article as the need dictates.
Internal surfactant antistats are physically mixed with the plastic resin prior to processing. When the resin is melted, the antistat distributed evenly in the polymer matrix. The antistat usually has some degree of solubility in the molten polymer. However, when the polymer is processed (extruded, molded, etc) into its final form and allowed to cool, the antistat migrates to the surface of the finished article due to its limited solubility in the solidified resin. The molecule of a surface-active agent is composed of a polar hydrophilic portion and a nonpolar hydrophobic portion. The hydrophilic portion of the surfactant at the surface attracts moisture from the atmosphere; it is the moisture that has the static dissipative effect.
Because the antistatic effect only occurs after the surfactant has migrated to the surface, the solubility of the surfactant in the polymer is an important consideration. Surfactants can generally be classified as one of four chemical types: cationic, where the hydrophilic portion has a positive charge; anionic, where the hydrophilic portion has a negative charge, nonionic, where the hydrophile does not have a charge; and amphoteric, where the molecule contains both positive and negative charges.
Cationic, anionic, and amphoteric surfactants derive their water solubility from their ionic charge, whereas the nonionic hydrophile derives its water solubility from highly polar terminal groups such as hydroxyl. Cationic surfactants perform well in polymers like styrenics and polyurethane. Examples of cationic surfactants are quaternary ammonium chlorides, quaternary ammonium methosulfates, and quaternary ammonium nitrates. Anionic surfactants work well in PVC and styrenics. Examples of anionic surfactants are fatty phosphate esters and alkyl sulfonates.
Nonionic surfactants have been found to perform well in nonpolar polymers such as polyethylene and polypropylene. Examples of nonionic surfactants are ethoxylated fatty amines, fatty diethanolamides, and mono- and diglycerides. Amphoteric surfactants find little use in plastics. Currently, the standard antistatic agent used in polyolefins is what is known as HMS, a high glycerol monostearate-containing blend of fatty esterified glycerin. HMS contains glycerol mono-, di-, and tri-stearate, and glycerol; for the composition to be considered “high-monostearate”, it must contain greater than 52% glycerol monostearate, preferably from 52 to 57% glycerol monostearate. However, there is a need in the polyolefin art for compositions which impart even greater antistatic properties than HMS, and which are economical, easy to formulate and incorporate into polyolefins.
SUMMARY OF THE INVENTION
It has now been surprisingly and unexpectedly discovered that excellent antistatic properties can be achieved in polyolefins by the addition of blends of either HMS:benzoic acid:sodium benzoate or of HMS:benzoic acid. The blends are prepared by mixing the ingredients together and heating until a clear, homogeneous solution is obtained. A usable form, which can be either beads or flakes, can then be prepared for end users to incorporate into polyolefins.
The antistatic blends of the invention have the following desirable characteristics:
1. They are equally efficacious antistatic agents and have been shown to do provide greater antistatic activity than the current state of the art product, HMS.
2. The HMS:benzoic acid blend is clear and flowable as a melt, and is almost four times more stable to transesterification mono reversion, than blends of HMS:sodium benzoate:benzoic acid and six times more stable than blends of HMS:sodium stearate.
3. Both blends can be beaded without reducing the mono content of the HMS or losing the performance advantages gained.
The invention also encompasses polyolefins which comprise the antistatic blends of the present invention and polyolefin products formed from the polyolefins and the antistatic blends of the present invent
Darby & Darby
Lonza Inc.
Mulcahy Peter D.
LandOfFree
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