Antistatic composition, method, and coated antistatic surface

An antistatic composition comprising an admixture of a water soluble polymer of a quaternary ammonium salt and a an amino or sulfonyl titanate or zirconate composition. The titanate or zirconate composition is present in the admixture in an amount sufficient to reduce the moisture sensitivity of the quaternary ammonium salt polymer while retaining its antistatic properties. The antistatic properties of the composition are greater than the additive antistatic properties of the polymer and the titanate or zirconate composition. An associated method and coated antistatic surface are also disclosed.

FIELD OF THE INVENTION 
The present invention relates to antistatic or static dissipative 
compositions and in particular relates to a water soluble composition that 
can be applied from an aqueous solution and coated on various substrates 
to give them desired antistatic properties. 
BACKGROUND OF THE INVENTION 
The rapid growth in the semiconductor electronics industry over a wide 
range of applications, has led to some associated packaging, handling, and 
operating considerations for electronic devices. One consideration for 
many electronic devices is that static electricity be controlled in some 
fashion. For example, because electronic components are becoming smaller 
and smaller, and operating on smaller power and current levels, the 
generation of static electricity, which would be considered no more than a 
nuisance in other circumstances (e.g., getting a shock after walking on a 
synthetic carpet), can become a significant problem with electronic 
components and devices. For example, static electricity can affect the 
memory or performance characteristics of small integrated circuits or 
"chips." From a physical standpoint, static electricity, which has the 
tendency to cause small objects to be attracted to one another, can cause 
handling problems when the small delicate parts used in many electronic 
applications are being physically handled. Static electricity can affect 
memory or programming aspects of a chip either temporarily or permanently 
and can interfere with the operation of electronic devices, or their 
memory components, in a number of ways including loss of data on magnetic 
media, equipment damage, and even fire hazards. 
Accordingly, control of static electricity, whether by shielding, 
grounding, or some other technique is a necessary consideration in the 
manufacture and use of electronic devices. 
One application for which static electricity must be controlled is the 
handling during manufacture of semiconductor chips as they are being 
assembled into larger circuits and electronic devices. One such handling 
technique is set forth in copending application Ser. No. 08/252,177, U.S. 
Pat. No. 5,447,784, filed Jun. 2, 1994, for "STATIC DISSIPATIVE COVER 
TAPE" which is assigned to the assignee of the present invention. As set 
forth therein, in order to be conveniently packaged for automated or 
robotic handling and assembly, integrated circuits are often packaged in 
longitudinal strip packages which consist of molded pockets covered with 
an adhesive tape that completes the package. The adhesive tape is removed 
and the pocketed carrier advanced by mechanical devices. Because the chips 
are sensitive to static electricity, the packaging tape must likewise be 
either antistatic or static dissipating in character. 
As generally used in this field, the terms "antistatic" and "static 
dissipating" both refer to the same property: conductivity. The term 
"static dissipating" generally refers to a higher conductivity than does 
the term "antistatic." For example, antistatic is often used to 
characterize resistivities of 10.sup.9 to 10.sup.14 ohms per square, while 
static dissipative is used to characterize resistivities of 10.sup.5 to 
10.sup.9 ohms per square. It will be understood that these terms are thus 
used descriptively rather than in any absolute or unreasonably limiting 
sense. 
One way to make a cover tape--or indeed any similar surface--static 
dissipating or antistatic in character is to coat it with a composition 
that will both adhere to the tape and provide the necessary conductivity 
properties. Conductive coatings can be formed of a number of different 
materials, all of which have various advantages and disadvantages. For 
example, a thin metal coating will be conductive and therefore antistatic 
or static dissipating, but metal coatings can be expensive and difficult 
to apply. Furthermore, when metals are applied in amounts sufficient to 
provide the necessary conductivity, they may make the surface opaque, or 
otherwise change its appearance, a factor which is undesirable in many 
circumstances. 
Other conductive materials such as carbon black are appropriate in 
different circumstances, but as with metals, carbon black (as indicated by 
its common name) is generally unsuitable for antistatic or static 
dissipating applications where the color or transparency of a given 
substrate are of importance to the finished product. 
Additional choices for conductive materials include monoacyl glycerides, 
monoalkyl phosphates, and various metallocenes. Some of these exhibit 
solubility problems, however, or tend to decompose at lower temperatures 
than are generally convenient for use in certain circumstances. 
Yet another category of antistatic compositions includes the quaternary 
ammonium salts; i.e., organic nitrogen compounds that include a central 
nitrogen atom joined to four organic groups (the cation) and a negatively 
charged acid radical (the anion). Lewis, HAWLEY'S CONDENSED CHEMICAL 
DICTIONARY, 12th Ed. (1993) p. 986. These salt compositions are 
well-known, predictable in their antistatic characteristics, and soluble 
in water and in certain organic solvents. They tend, however, to be quite 
sensitive to relative humidity and in particular their conductive 
properties tend to fade or disappear at lower relative humidities; i.e., 
relative humidities of about 20% or less. Therefore, they are either 
undesirable or simply unusable for particular applications. 
Therefore, there exists the need for compositions that can produce 
antistatic or static dissipating properties on substrates that can be 
easily coated on those substrates, will adhere to them properly, and will 
provide antistatic properties even under varying conditions of relative 
humidity. 
OBJECT AND SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide 
compositions that produce antistatic or static dissipating properties on 
substrates that are independent of conditions of varying humidity, and 
that can be coated onto substrates in a straightforward manner. 
The invention meets this object with an antistatic composition that 
comprises an admixture of a water soluble polymer of a quaternary ammonium 
salt and an amino or sulfonyl titanate or zirconate composition. The 
titanate or zirconate composition is present in the admixture in an amount 
sufficient to reduce the moisture sensitivity of the quaternary ammonium 
salt polymer while retaining its antistatic properties, and wherein the 
antistatic properties of the composition are greater than the additive 
antistatic properties of the polymer in the titanate or zirconate 
compound. 
In another aspect, the invention is an aqueous solution of the water 
soluble polymer of the quaternary ammonium salt and the titanate or 
zirconate composition. 
In a further aspect, the invention is a method of coating a substrate with 
the solution of the admixture of the quaternary ammonium salt and the 
titanate or zirconate composition. 
In yet another aspect, the invention comprises a surface coated with the 
admixture of the water soluble water polymer of the quaternary ammonium 
salt and the titanate or zirconate composition to give that surface 
antistatic properties. 
The foregoing and other objects, advantages and features of the invention, 
and the manner in which the same are accomplished, will become more 
readily apparent upon consideration of the following detailed description 
of the invention which illustrates preferred and exemplary embodiments.

DETAILED DESCRIPTION 
The invention is an antistatic composition comprising an admixture of a 
water soluble polymer of a quaternary ammonium salt and an amino or 
sulfonyl titanate or zirconate composition. The titanate or zirconate 
composition is present in the admixture in an amount sufficient to reduce 
the moisture sensitivity of the quaternary ammonium salt polymer while 
retaining antistatic properties so that the antistatic properties of the 
composition are unexpectedly and apparently synergistically greater than 
the additive antistatic properties of the polymer and the titanate or 
zirconate composition. 
As noted above, quaternary ammonium salts are well-known chemical 
formulations that are of ionic character. In preferred embodiments of the 
present invention, the quaternary ammonium salt polymers are linear higher 
molecular weight water soluble polymers that have the formulas described 
in U.S. Pat. No. 3,288,770, to Butler, issued Nov. 29, 1966 for "Water 
Soluble Quaternary Ammonium Polymers", the contents of which are 
incorporated entirely herein by reference. These quaternary ammonium salt 
polymers are also described in U.S. Pat. No. 5,268,407 to Hayashi et al., 
which is also incorporated entirely herein by reference. 
Exemplary commercial embodiments of these quaternary ammonium salt polymers 
are available from the Specialties Group of Calgon Corporation under the 
designations "Conductive Polymer 261.RTM.RV" and "Conductive Polymer 
261.RTM.LV". Generally speaking, the 261.RTM. conductive polymers are used 
for controlling and increasing the electrical conductivity of sensitized 
papers in various electrographic and photographic reproduction techniques. 
According to the Calgon Corporation, the 261.RTM. polymers promote better 
copy contrast and prevent toner pickup in non-imaged areas. 
As is the case with most quaternary ammonium salts, however, the polymers 
described herein, including the 261.RTM. polymers, vary greatly in their 
conductivity depending upon relative humidity. In particular, the 
quaternary ammonium salt polymers that are most preferred in the present 
invention have conductivities about 1.times.10.sup.12 ohms per square at 
about 5% relative humidity and about 5.times.10.sup.5 ohms per square at 
about 90% relative humidity. Thus, although these compounds are useful in 
some circumstances, they are less desirable in others. 
As set forth above, the compositions of the present invention further 
comprise an amino or sulfonyl titanate or zirconate. In preferred 
embodiments, the titanate or zirconate composition is one of those 
described and claimed in U.S. Pat. No. 4,715,968 to Sugarman, et al., 
issued Dec. 29, 1987, and the contents of which are incorporated entirely 
herein by reference. In more preferred embodiments the composition 
comprises an amino titanate or zirconate and a sulfonyl titanate or 
zirconate, including titanium (IV) neoalkoxy titanates. In the most 
preferred embodiments the titanate or zirconate composition comprises a 
mixture of an amino titanate and a sulfonyl titanate. 
As used herein, the term neoalkoxy refers to the presence of four (4) 
alkoxy groups joined to the titanium. In turn, the term alkoxy refers to 
the ester-like structure of the organic groups joined to the titanium (IV) 
ion. 
Exemplary formulations for the titanium (IV) neoalkoxy compounds are 
available under the Ken-Stat.TM. designation from Kenrich Petrochemicals, 
Inc., 140 East 22nd Street, P. O. Box 32, Bayonne, N.J. 07002. Typical 
formulations include Ken-Stat.TM. KS Q100P which is a mixture of about 55% 
by weight bis(dodecyl)benzenesulfonato-o bis(2-ethylenediamino)ethylato 
titanium (IV) and about 45% by weight of a polyethylene glycol 
(a-hydro-w-hydroxy poly(oxy-1,2-ethanediyl)); and Ken-Stat.TM. N100 which 
is a mixture of 2,2-(bis-2-propenolatomethyl) butanolato 
tris(dodecyl)benzenesulfonato-o titanium (IV) (about 54% by weight), a 
proprietary amino alkoxy titanium compound designated "Ken-React Lica 44B" 
(about 22% by weight), and dodecylbenzene (about 18% by weight). It will 
be understood, however, that similar compositions can be incorporated into 
the present invention provided that they give the desired antistatic 
properties, but without deleteriously affecting the antistatic properties 
of the compositions of the present invention. 
As described in the Sugarman patent, these titanate or zirconate 
compositions are mixed with polyethylene glycol or a structurally very 
similar compound. Then, the titanate or zirconate compounds are mixed or 
otherwise blended with polymers in a manner other than surface application 
and before the polymers are finally set to thereby produce polymers with 
reduced static buildup tendencies. 
It has been unexpectedly found according to the present invention, however, 
that if the titanate or zirconate composition is mixed with the quaternary 
ammonium salt polymers in a mixture of about ten parts of the quaternary 
ammonium salt polymer with about one part of the titanate or zirconate 
composition, a combined synergistic antistatic property results in which 
the antistatic properties of the admixture are greater than those of the 
quaternary ammonium salt and the titanium (IV) composition added together. 
Such a synergistic result from the addition of approximately ten percent 
(10%) by weight of the titanate or zirconate is particularly unexpected 
because of the ionic and molecular mechanisms through which antistatic or 
static dissipating compositions tend to work. 
For example, as noted above the quaternary ammonium salt polymer has a 
conductivity of about 1.times.10.sup.12 ohms per square at about 5% 
relative humidity and about 5.times.10.sup.5 ohms per square at about 90% 
relative humidity. The titanate or zirconate composition has a 
conductivity of between about 1.times.10.sup.8 and 1.times.10.sup.9 ohms 
per square at relative humidities of between about 20% and 50%. When these 
are mixed together in accordance with the present invention, however, the 
admixture has conductivity of about 1.times.10.sup.5 ohms per square at 
relative humidities of between about 20% and 50%. The conductivities 
herein were measured according to ASTM-258 using a Kiethley electrometer 
with a 100 volt power supply, and with both concentric circle and 
two-point probes. 
In other words, the overall conductivity of compositions according to the 
present invention appears to be better than the best conductivity of the 
quaternary ammonium salt standing alone at the most favorable conditions 
of relative humidity, and yet will exhibit this greater conductivity of 
all levels of relative humidity. 
In another aspect and because both the quaternary ammonium salt polymer and 
the titanate or zirconate composition are water soluble, the invention 
comprises an aqueous solution of the quaternary ammonium salt polymer and 
the titanate or zirconate composition in which the titanate or zirconate 
composition is present in the solution in an amount sufficient, when the 
solution is deposited on a substrate and water substantially removed, to 
reduce the moisture sensitivity of the quaternary ammonium salt polymer 
while retaining its antistatic properties. As in the other embodiments, 
the antistatic properties of the composition of the invention are greater 
than the additive antistatic properties of the polymer and the titanate or 
zirconate compound. As noted above, the quaternary ammonium salt and the 
titanate or zirconate composition are preferably present in a ratio of 
about ten to one (10:1) by weight, quaternary ammonium salt polymer to 
titanate or zirconate composition. 
In preferred embodiments of this aspect of the invention, the aqueous 
solution comprises at least about 60% by weight water; i.e., about 40% by 
weight of the composition. It will be understood, however, that the 
preferred concentration can be diluted to produce various other 
concentrations suitable for various coating techniques or applications. As 
in the earlier embodiments, the titanate or zirconate composition can 
comprise one or more an amino or sulfonyl titanate or zirconate compounds. 
Similarly, the unexpected synergistic improvement in conductivity and 
resulting antistatic properties occurs when the invention is expressed as 
a solution as well. 
In other embodiments, the antistatic composition according to the present 
invention can be incorporated into a water-based polymer binder such as 
acrylic, urethane, or ethylene vinyl acetate polymers. 
As an unexpected further benefit, the quaternary ammonium salts, which 
tends to exhibit poor wetting properties on certain surfaces, wets those 
surfaces quite well when mixed in this fashion with the organotitanate. 
In yet another aspect the invention can further comprise a method of 
producing a surface with antistatic properties by applying the composition 
to the surface and then drying the surface to remove water while leaving 
the antistatic composition in place. Preferably, when the composition is 
applied in water solution in which water is present by at least 60% by 
weight of this solution, the solution is applied in an amount of between 
about 0.5 and 1.5 pounds per ream. Because a ream represents three 
thousand square feet (3,000 ft.sup.2), this is about the same as adding 
between about 0.8 and 2.4 grams per square meter. 
Accordingly, the invention can further comprise a substrate surface coated 
with the solution of the invention. In this aspect, the invention 
comprises a substrate, and an antistatic composition on the substrate. The 
antistatic composition comprises the admixture of the water soluble 
polymer of the quaternary ammonium salt and the titanate or zirconate 
composition, and with the titanate or zirconate composition present in the 
admixture in an amount sufficient to reduce the moisture sensitivity of 
the quaternary ammonium salt polymer while retaining its antistatic 
properties. As in the other embodiments, the antistatic properties of the 
composition are greater than the additive antistatic properties of the 
polymer and the titanate or zirconate composition. 
In preferred embodiments, the antistatic surface can comprise a transparent 
polymer, examples of which are well-known to those familiar with this art. 
For example, polyester, polyethylene, polypropylene, other polyolefins, 
saran, polyurethanes, polyvinyl chloride (PVC), and numerous other 
polymers are appropriate substrates. It will be understood that these 
specific polymer types are given here by way of example and not by way of 
limitation. 
When the composition of the invention is applied as previously described 
and the surface then dried, the composition will be present on the surface 
in an amount of between 0.3 and 0.9 pounds per ream (about 0.48 and 1.44 
grams per square meter). As in the earlier described embodiments, the 
titanate or zirconate composition can comprise either a single an amino or 
sulfonyl titanate or zirconate compound or a combination of two or more an 
amino or sulfonyl titanate or zirconate compounds. Similarly, the 
quaternary ammonium salt polymer has a conductivity of about 
1.times.10.sup.12 ohms per square at about 5% relative humidity increasing 
to about 5.times.10.sup.5 ohms per square at about 90% relative humidity, 
while the titanate or zirconate composition has a conductivity of between 
about 1.times.10.sup.8 and 1.times.10.sup.9 ohms per square at 
substantially all relative humidities. The resulting composition on the 
surface, however, has conductivity of about 1.times.10.sup.5 ohms per 
square at substantially all relative humidities. 
As in the earlier embodiments, the preferred admixture comprises about ten 
parts of quaternary ammonium salt polymer and about one part of the an 
amino or sulfonyl titanate or zirconate composition. Furthermore, in 
preferred embodiments the titanate or zirconate composition further 
comprises a mixture of the composition with a polymer, and the most 
preferred embodiments comprises a mixture of about 55% by weight of a 
titanium (IV) neoalkoxy composition and about 45% by weight of a 
polyethylene polymer. 
EXAMPLE 
Ten parts by weight of a quaternary ammonium salt provided from Calgon 
Corporation, under the designation Calgon Conductive Polymer 261LV are 
admixed with approximately one part by weight of a titanate composition 
under the designation KEN-STAT.TM. KS Q 100P. The composition is then 
mixed with about 60 percent by weight water (i.e., 40% by weight 
composition and 60% by weight water). This solution is applied to a 
surface of a transparent polyolefin polymer to produce a surface coated 
with between about 0.8 and 2,4 grams per square meter which is then dried. 
The conductivity of the resulting surface is measured according to 
ASTM-258 using a Kiethley electrometer with a 100 volt power supply, and 
with both concentric circle and two point probes. In all cases, the 
resulting conductivity is approximately 1.times.10.sup.5 ohms per square 
at all relative humidities between 20 and 50%. 
In the drawings and specification, there have been disclosed typical 
preferred embodiments of the invention and, although specific terms have 
been employed, they have been used in a generic and descriptive sense only 
and not for purposes of limitation, the scope of the invention being set 
forth in the following claims.