CA2212758A1 - Antistatic polymeric articles having a coating comprising an antistatic surfactant and a water soluble ink - Google Patents

Abstract

An article comprised of a polymeric material bearing a coating. The coating comprises a residual layer formed by applying and allowing to dry a mixture containing from about 7.5 to about 23.5 weight percent of a humidity sensitive antistatic surfactant compound and from about 10 to about 30 weight percent of a water soluble ink. The article possesses an electrostatic potential of from about -5 to about +5 kilovolts as measured at one inch from the coating. A process for producing a formed article which is relatively free from the effects of static electricity. The process includes the steps of topically applying a mixture comprising a humidity sensitive antistatic surfactant compound to a stock comprising a foamed polymeric material, conditioning the foam stock in humidity-controlled environment effective to reduce electrostatic potential of the stock to between from about -5 to about +5 kilovolts, and thereafter forming the article from the conditioned foam stock. The polymeric material may comprise polystyrene and the water soluble ink may comprise a mixing white ink. The humidity sensitive surfactant is preferably comprised of a mixture of sodium alkyl sulfonates consisting essentially of sulfonates having the molecular formulas C10-18H21-39SO3Na.

Description

CA 022127~8 1997-08-12 CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application No. 60/023,820, filed August 12, 1996.

5 Field of the Invention This invention relates to articles having improved antistatic plopellies, that are formed at least in part from polymeric materials, as well as to methods and compositions useful for producing those articles.

Back~round of the Invention The use of articles formed at least in part from a polymeric material is widespread.
Foamed polymer m~teri~l.c in particular are used in a wide variety of applications because foamed polymer products possess desirable in~ ting, shock absorbing or strength to weight ratio plu~llies. For example, the food service industry often uses foamed polystyrene conlaillel~ thermoformed from a foamed polymer roll stock because these containers are strong, lightweight and possess good thermal insulating propel lies.
Unfortunately, the presence of static electricity on polymeric articles can limit the usefulness of the containers. Undesired static electricity can hinder separation of individual articles from a stack of nested articles and can cause the articles to collect dust or other fine - 20 particles present in the ellvilollllRnt where the articles are manufactured or used.
Foamed polymer cups typify the foregoing problems. These cups usually are supplied to a food service vendor as a stack of several nested cups wrapped in a plastic sleeve. Static cling may only be a nllis~nl~e when foam cups are manually separated from a nested cup stack. However, when cup stacks are used in automated beverage vending machine applications, static charges can prevent reliable sepalalillg and dispensing of individual cups and cause the cups to collect dust prior to dispensing. While these effects are more pronounced with foam cups, the effects may occur when solid plastic cups are used, and to a lesser extent when paper cups are coated with one or more layers of solid polymeric m~teri~
Reliable cup separation is a critical prerequisite in vending applications. Automated vending machines typically employ vertical stacks of nested cups stored in a multi-position turret. When a drink is vended, a dispensing ring located at the bottom of a cup stack C: 55710(16ZS01!.DOC) CA 022127~8 1997-08-12 disengages the lowest cup from the stack. The disengaged cup traverses a chute or similar path by gravity to a cup fill area of the vending machine. Because gravity is the primary force causing the disengaged cup to travel to the cup fill area, and because a cup is a relatively light object, disengagement and travel of the cup can be substantially affected by electrostatic 5 forces. These electrostatic forces can prevent the timely arrival of the cup in the cup fill area.
If the cup is late to the cup fill area, incomplete cup fills can result. Even worse, electrostatic forces may prevent the cup from reaching the cup fill area, resulting in a customer watching his or her drink ~licpellcing directly into the cup fill area drain. In addition to customer ~licc~ticf~ction, late or non-arrival of cups at the filling station often results in a demand for an 10 unnecessary and expensive service call.
As a result of above ~liccl~cse~l problems, vending service companies typically require that cup vending failures not exceed a failure rate of 1 in 1000 vending a~ L~, with some co~.\rAniec requiring that failure rates not exceed 1 in 100,000 vending aUellll)L~. These very demanding specifications have resulted in cup producers employing various mPch~nic~l and 15 chemical methods in order to produce a reliably vended foam cup.
Mechanical efforts to improve the vendibility of foam cup attempt to minimi7e the contact area between a(ljace-nt nested cups, thereby reducing the chance that cups will fail to drop in a timely manner. For example, the Sweetheart Cup Company produces a TROPHY
brand cup which includes a plurality of indentations in the lower cup sidewall. The 20 in~l~nt~tions prevent the cups from nesting completely within each other, which l~ il.l;7.~S
contact of ~ ent cup surf~çes While this mechanical method reduces friction between çent cups, some sidewall to sidewall contact between cups remains. Because static cling problems can occur when any part of a cup contacts any part of an adjacent cup, minimi~ing the area of sidewall contact does not elimin~te electrostatic attraction between ~(ljacent cups.
2s Furthermore, cups with sidewall in(lçnt~tions increases the vertical stack height for a given number of cups which reduces the cup capacity of a given vending m~chin.o.
Electrostatic problems may also be reduced by applying chemical ~ntict~tic materials to foamed products. ~ food container applications, these Antict~tic agents typically take the form of organic compounds extruded or otherwise contailled in either a typically hydrophobic 30 polymeric foamed m~teri~l layer or contained in solid m~tçri~l adhered to a polymeric foam material layer. In a typical foam cup application, an ~ntict~tic agent is combined with a resin used to fabricate a cup's foamed or solid polymeric material and subsequently migrates or C: 55710(16Z501!.DCIC) CA 022127~8 1997-08-12 "blooms" to the surface of the cup slowly during the perceived useful life of the cup. After blooming to the cup's surface, the antistatic agent interacts with atmospheric moisture to form a conductive surface which can dissipate static charges. In many instances, the use of such extruded antistatic compounds alone is insufficient to produce a reliably vended cup. The use s of ~ntict~tic agents as just described may be inadequate for any of several reasons. For example, because the antictatic agent "blooms" to the surface slowly or at an unpredictable rate, a discontinuous hydrophilic film may be formed that cannot uniformly dissipate a static charge from the object's surface. Alternatively, the foregoing method may fail either because the successful use of these coll~oullds requires the presence of relatively high levels of 10 ambient moisture which frequently are not present in air conditioned environments or under dry winter weather conditions, or because extruded antictatic materi~lc remain predomin~ntly within the polymeric material and therefore are not highly available at the surface of the polymeric material to minimi7ç static accumlllation during the cup production process. In addition, the choice of such antistatic agents is limited in food container applications because 15 of govçrnm~ntal regulations.
Although the ~ntictatic agents ~liccucse-l above may be applied directly to a surface of a cup, this process results in an uncontrolled loss of antistatic agent from the cup and reles with the ability of the cup to durably retain a printed image during manuf~tllring or use. This later consideration is of substantial collmlelcial importance because the sponsors of 20 graphic information printed on a vending cup do not want their information to be displayed in a low quality manner or have the scuffed or smudged ink from the vending cup soil a user clothes or other objects.
Other types of non-blooming chemical antict~tic compounds and methods to producesuch products, such as those disclosed in U.S. Patent No. 4,715,968, claim to function 25 indep~nflently of ambient moisture conditions, and might be useful in products destined for automated vending applications, but these non-blooming compounds are not believed to meet governm.o~t~l requirements for foodstuff-related applications.
Therefore, a need exists for polymeric products, including foamed polymeric products, that are relatively free from the effects of static electricity. The products should ~refelably 30 retain their antict~tic plOpellieS for extended periods of time, have no objectionable odors or taste as perceived by a consumer, and retain a well-defined printed image if a printed image is desirable.

C: 55710(16ZSOI !.WC) CA 022127~8 1997-08-12 Sl~nm~ry of the Invenffon A first embodiment of the invention provides a formed article which is relatively free from the effects of static electricity. The article is formed from m~tçri~ls including a 5 polymeric m~teri~l, and the polymeric material bears an ~ntist~tic coating over at least part of its surface. The coating is a residual layer formed by applying and allowing to dry a ll~i~lu comprising from about 7.5 to about 23.5 weight percent of a humidity sensitive ~nti~t~tic surfactant compound and from about 10 to about 30 weight percent of a water soluble ink.
The article possesses an electrostatic potential of from about -5 to about +5 kilovolts as 10 measured at one inch from the coating. The low electrostatic potential of the article provides the article with good ~ntict~ti- plopellies. The articles preferably are m~n~lf~( tured from a polymeric foam stock.
The term "electrostatic potential" as used herein refers to the highest elecllo~lalic potential measured on any surface of an article at a distance of one inch from the surface 15 using an electrostatic field strength meter.
The term "foam stock" as used herein refers to any sheet or roll stock m~t~ri~l having at least one foamed polymeric layer and from which an article is subsequently formed. For example, foam stock incllldes sheets of a single foamed polymer such as poly~lyle.le or llli~l~es of poly~ly~ne and one or more other polymers, and ]~min~ted stocks incol~ol~lillg 20 a foamed polymer layer and a non-foam layer such as an extruded solid polymer or other m~teri~l like paper or cardboard.
The term "humidity sensilive ~nti~t~tic surfactant compound" as used herein refers to any highly polar compound that adheres to a polymeric surface of a foamed polymer stock and which demonstrates an increased propensily for dissipating a static charge as ambient 2s hllmi-lity is increased. The term mcludes by example cationic ~ntist~tic compounds such as q~l~t~rn~ry ammonium salts of organic compounds having alkyl chains of from about 4 to about 20 carbon atoms in length; anionic ~ntict~tic compounds such as alkyl slllf~te~, alkyl sulfonates and alkyl phosphates having alkyl chains of from about 4 to about 20 carbon atoms in length; and nonionic highly polar organic compounds such as polyvinyl alcohol, 30 polyvinylpyrrolidone and polyethers, as well as amines, acids and fatty acid esters having alkyl groups of from about 4 to about 20 carbon atoms in length.

C: 55710(16ZS01!.1)0C) CA 022127~8 1997-08-12 In another embodiment of the invention, a process produces a formed article which is relatively free from the effects of static electricity. The process includes the steps of topically applying a mixture c~ lishlg a humidity sensitive ~ntict~tic surfactant compound to a stock comprising a foamed polymeric material, conditioning the foam stock in a humidity-s controlled environment effective to reduce electloslalic potential of the stock to between from about -5 to about +5 kilovolts, and thereafter forming the article from the conditioned foam stock.
In yet another embodiment of the invention, a process produces a nested stack of at least 10 articles having good ~ntist~tic properties from a polymeric foam stack. This process 10 inclll(les the steps of topically applying a mixture comprising from about 7.5 to about 23.5 weight percent of an ionic hllmi-lity-sensitive ~ntist~tic surfactant and about 10 to about 30 weight percent of a water-soluble ink to the foam stock, thereafter forming at least 10 of the articles from the foam stock, and nestably st~c~ing the formed articles. The resulting nested stack of articles exhibits a measured electrostatic potential from about-5 to about +5 kilovolts.
The term "ionic, humidity-sensitive antistatic surfactant compound" as used herein refers to any highly polar ionic compound that adheres to a polymeric surface of a foamed stock and which demonstrates an increased propensity for dissipating a static charge as ambient humidity is increased. The term includes by example cationic ~ntist~tic compounds such as qn~t~rn~ry ammonium salts of organic compounds having alkyl chains of from about 20 4 to about 20 carbon atoms in length and anionic ~ntist~tic compounds such as alkyl s~ lf~tes, sulfonates and phosphates having alkyl chains of from about 4 to about 20 carbon atoms in length, but not nonionic ~ntist~tic compounds such as polymeric or long alkanols, ethers, arnines, acids or fatty acids.
The term "stack" as used herein refers to a plurality of substantially identically-shaped 2s articles symm-~.tric~lly placed one adjacent another, and includes both nestably stacked articles as defined below and stacks of non-nestable articles such as foam sheets. The term "nested stack" or "nestably stacked" as used herein refers to a plurality of subst~nti~lly identically-shaped articles symmetrically arranged in such a manner that a portion of an article is contained within a portion of one or more ~dj~cent articles, such as the stacks of foam cups or 30 plates commonly available in grocery stores.
In another embodiment of the invention, a printed overcoat co~ water, a water soluble transparent or translucent ink, and an ionic humidity sensitive antist~tic surfactant C: 55710(16ZSOI!.DOC) CA 022127~8 1997-08-12 compound is used effectively in the absence of the humidifying the material to produce foamed articles which, even when stacked or nested, are relatively free from the effects of static electricity and which can durably retain a printed image. This embodiment of the invention which does not require humidity conditioning of the roll stock is preferred wherever s the ambient humidity conditions at the m~nllf~,tllring location are sufficient to activate the ~ntict~tic p~ ies of the topically applied overcoat. Articles produced by this process typically exhibit electrostatic potentials from about -5 to about +5 kilovolts when nestably stacked and, thus, are easily separated by gravimetric forces acting on the formed articles.
These articles are ideally suited for food vending applications such as the dispensing of hot 10 beverages into cups because the cups in.c~ te well, reliably vend and present a high quality durable image useful for advertising or the display of other graphic information.
In still another embodiment of the invention, an ~ntict~tic solution for application to a polymeric surface is provided which includes from about 7.5 to about 23.5 weight percent of an ionic hllmi(lity-sensitive ~ntict~tic surfactant, from about 10 to about 30 weight percent of a water soluble ink, and from about 17.5 to about 46.5 weight percent of water.
~ ;felled embo-lim~nt.c of the foregoing inventions employ a printed overcoat cont~ining water, a water soluble Ll~ spalent or translucent ink, and an ionic humidity sensitive antistatic surfactant compound. In these embodiments, the ink acts as a binder which causes the ~ntict~tic agent to be more effectively bound to the surface of the produced 20 article. Thus, the antistatic agent performance does not rapidly deteriorate as might be expected when an ~ntict~tic agent is topically applied to a surface because the binder prevents the topically applied anti-static agent from being vol~tili~ or abraded during manufacture and from migrating into the foam after application. In addition, the use of the transparent ink as a binder in the ~ntict~tic overcoat protects the underlying graphic images from scuffing or 2s cm~ring during subsequent manuf~ctllring steps and use, problems known to occur when images are present on stock to which ~ntict~tic agents have been topically applied.
Furthermore, the topical application of the ~nti~t~tic agent results in a more continuous, more concellllated hydrophilic film of antistatic agent available during the m~nllf~tllring process on the article's surface than can be obtained by an extruded antistatic agent that slowly 30 blooms to the article's surface.
Plc;fclr~d embodiments of the foregoing inventions are formed from poly~Ly~elle foam/solid poly~lylel1e l~min~te stocks and employ anionic hllmi(lity sensitive surf~rt~nts.

C: 55710(16ZS01!.DOC) CA 022127~8 1997-08-12 Brief De~ tion of the Drawin~s Other objects and advantages of the invention will become a~palcllt upon reading the following detailed description and upon reference to the drawings in which:
s FIG. 1 is a flow chart of a typical process used to manufacture polystyrene foam cups;
FIGS. 2-5 illustrate various steps in a foam cup production process;
FIG. 6 is a simplified cross-sectional view of a poly~,ly~cne l~min~tor depicting the placement of static elimin~tion equipment useful for reducing static charges induced in a l~min~te(l foam stock during the l~min~tion process; and FIG. 7 is a cutaway pCl~7~;liVC view of a vendible foam cup in accordance with the invention.
While the invention is susceptible to various m~lifications and ~lt~rn~tive forms, a specific embodiment thereof has been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that it is not intended to limit 15 the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and ~ltern~tives falling within the spirit and scope of the invention as defined by the appended claims.

Detailed Des.~ tion of the Invention According to one embodiment of the present invention, processes and articles arelliscll~se~l below with respect to consisterltly man-lf~et lrin~ a reliable vending cup having a durable printed surface and durable ~nti~t~tic pr~,pGllies. Furthermore, while the following description focuses on the production of foam vending cups from poly~,LylGlle, those skilled in the art will recognize that the invention is applicable in other areas. For example, the present 25 invention is useful for producing a wide variety of articles from a stock including at least one layer of m~t~ri~ls having a propensity for generating or collecting static electricity during the articles' production, storage, h~n~lling or use.

Process to Manufacture Foam Cups Referring to FIG. 1, there is a schematic illustration of a process used to manufacture foam cups. This process may be modified as described later herein to produce foam cup C: 55710(16ZS01!.DOC) CA 022127~8 1997-08-12 stacks in accordance with the present invention which are relatively free of the effects of static electricity.
In the process of FIG. 1, an extruder 20 fitted with a annular die produces tubular poly~lylc;ne foam stock. The foam stock is slit in a slitter 22 to produce a polystyrene foam s web about 52 inches wide and about 0.04 inches thick. The foam web runs from the slitter 22 into a l~min~ting extruder 24 which coats the foam sheet stock with a layer of impact polystyrene to form a web of impact poly~Ly~ e and foam having a thickness of about 0.03 inches. A winder 26 rolls l~min~te~l sheet stock produced by the extruder 24, and then a cutter 28 cuts the wound rolls into rolls of sidewall stock and/or bottom stock of the required 10 dhl~ll~ions for use in a cup forming machine.
A coating or graphic art may be applied to cup sidewall stock by feeding cup roll stock through a printer 30 which unwinds the stock, prints one or more impressions on the impact poly~lylelle surface of the roll stock, and rewinds the roll stock. Typically, the printed roll stock is aged for less than about 24 hours to permit the ink to cure substantially prior to 15 cup forming.
Cups are formed from roll stock by proces~ing the roll stock and cut portions thereof through a number of individual work stations within a cup forming machine 32. First, cup forming machine 32 employs separate blanking stations which are fitted with dies to cut the respective roll stocks into sidewall and bottom cup portions 100 and 102, respectively (see 20 FIGS. 2a and 2b). Sidewall cup portions 100 are transferred to a side seam heating station (not shown) where heat is applied to opposite sides 104 and 106 of sidewall cup portion 100 where a sidewall seam will be formed. Simlllt~n~ously, bottom cup portions 102 are mechanically punched and drawn to form a skirt 108 to be used as a sealing surface for joining sidewall portions 100 and bottom up portions 102 (see FIG. 2c). Portions 102 are 25 then heated at a bottom portion preheat station (not shown).
~,he~l~d cup portions 100 and 102 are joined around a forming mandrel 110 as shown in FIG. 3, with heated sides 104 and 106 overlapping to form a cup shell 112 having a sidewall seam 114. Mandrel 110 then is indexed to a bottom heating station, skirt 108 of bottom portion 102 and the inner lower portion of shell 112 are heated, with portion 102 30 being pushed in the direction of arrow A toward the nallo~er end of shell 112.
Heat-sealed sidewall and bottom portions 100 and 102 are then moved to a bottom incurl station where a lowermost portion 116 of the sidewall portion 100 is curled inwardly C: 55710(16ZS01!.DOC) CA 022127~8 1997-08-12 over skirt 108 as depicted in FIG. 4. Heat-sealed sidewall and bottom portions 100 and 102 are subsequently finished, knurled, sealed and squared at a bottom finish station (not shown).
Next, an open edge 118 of cup shell 112 is mech~nic~lly precurled as shown in FIG. Sa, and then a rim 120 is formed by rolling the precurled end as shown in FIG. Sb. After the s foregoing operations have been completed, the formed cups are heat treated to expand the foam, thereby illlp~ ling a wrinkle-free finish and additional strength to the cup.
The use of an adhesive-free heat-sealing process as discussed above is preferred, although a&esives may be used to join cup portions 100 and 102 if desired. Further detail concerning the use of heat sealing in the production of cups and the like is provided in U.S.
lo Patent Nos. 4,490,130 and S,507,640, the disclosures which are incorporated herein by reference.
Static electricity most commonly is generated when two m~tçri~l~ in contact with each another are subsequently separated. Thus, virtually every step in the above-described process has the potential for gellelalillg static charges in the stock m~teri~l or cup parts or for transferring static charges from process equipment to the stock m~teri~l or cup parts, such as when the stock m~teri~l passes over or betweell equipment components such as idler rollers.
These static charges often can cause a stack of finish~l cups to possess an electrostatic charge that renders the cup stack unreliable for use in automated vending applications.FM. 6 provides a simplified view of the l~min~ting extruder 24 and assists in explaining how static charges are generated in the l~min~tin~ step of the above-described cup production process. As depicted in FIG. 6, l~min~ting extruder 24 includes as its principle colllponell~s an idler roll 134, a first polish roll 136, a l~min~te extruder die 138, a second polish roll 140, a second idler roll 142 and static reduction devices 144 and 146. During operation of l~min~ting extruder 24, a polystyrene foam web 148 of the type described in connection with FIG. 1 first passes over idler roll 134 and then over first polish roll 136 imm~di~tely prior to impact polyslylene 148a being extruded onto web 148 through die 138 The foam web 148 then passes belweell polish rolls 136 and 140 which COlll~l~,SS the l~min~tlod web. The ]~min~t~od web 148 next passes over idler roll 142 and through the fields of static reduction devices 144 and 146. Each time the web 148 contacts and then separates from an extruder component such as rolls 136, 140 or 142, a static charge can be ind~l~ed which may remain with the web 148 throughout the web and cup production processes.

C: 5571~X16Zsol~.Doc) CA 022127~8 1997-08-12 To mitigate the effects of static electricity, various types of static reduction equipment can be added to process equipment, such as extruder 24, once an equipment component has been identified as a source of static charge. For example, static reduction devices 144 and 146 were added to the l~min~ting extruder 24 when it was discovered that the l~min~tion process in~ ced charges in the l~min~tçd stock that generally remained in the l~min~t~d stock throughout the cup production process.
According to one embodiment of the present invention, static reduction device 144 employs a very thin film of radioactive, alpha particle emitting Polonium 210. The alpha particles emitted by the device 144 ionize the air between the web 148 and the device 144, 10 thereby allowing static charges generated in the l~min~tion process to dissipate through the ionized air to a grounded surface. While the device 144 can be effective at distances up to about three inches from web 148, it is preferred that device 144 be within about one inch of web 148 to m~imi7e its effectiveness. To further reduce static present on l~min~te~l web 148, web 148 passes through the web bar static reduction device 146. Device 146 employs a 15 several thousand volt ~lt~rn~tin~ current source to ionize the air around web 148. Devices 146 and 148 typically reduce electrostatic potential as measured one inch above web 148 from about +/-10 to lS kilovolts to about +/- 1 to 2 kilovolts as the web 148 leaves the device 146.
Good engineering practice suggests that all significant sources of static electricity in 20 foam product production equipment such as extruder 24 be identified and that static reduction equipment such as devices 146 and 148 be installed to reduce the inflllce~l static throughout the production process. For example, in some cases, it may be desirable to place additional static elimin~tion equipment imm.o~ tely before and after an idler roll such as idler roll 134 at locations A and B in FIG. 6 on opposite sides of the web to minimi7e the chance that a 25 static charge may become trapped within web 148 by the phenomena typically known to those skilled in the art as Maxwell-Wagner pol~ri7~tion. In this regard, it should be noted that while l~min~te layers applied to foam substrates at tem~el~Lul~s above the l~min~te's glass transition te~ lule typically do not accllm~ te or contribute to static charges, the l~min~te layer can entrap a static charge already present on the foamed layer.
Additional techniques may be employed wherever possible, such as the use of corona treatment in the printing process. Corona treatment employs relatively high voltages to roughen the web surface prior to printing. The improved surface provides greater adhesion of C: 55710(16Z501!.DCC) CA 022127~8 1997-08-12 topical agents and is believed to provide an effective means to alter and randomize accumnl~tçd charges on the cup stock, thereby potentially minimi7ing the effect of the charges.
Unfortunately, experience has shown that while the static reduction techniques s described above are nPcess~ry to produce foamed articles which are relatively free from the effects of static electricity, application of those techniques alone is insufficient to produce nested stacks of reliably vendible foam cups. Foam cup stacks produced on foam production lines incorporating the static reduction techniques discussed above at times often exhibit a high electrostatic potential. Cups from stacks exhibiting high electrostatic potential will not 10 reliably separate from the stack when used in automatic vending applications. Generally, a stack of S0 or more foam cups has been found to vend successfully when the electrostatic potential measured at one inch from the cup stack was less than about +/- 7.5 kilovolts and the potential measured at one inch from all surfaces of a cup separated from the stack was less than about +/- S kilovolts.
Examples In an effort to reduce static levels on thermoformed foam cups, several e~.hllents were performed in which commercially available antistatic agents were either topically applied to the cup exterior surfaces or extruded into the foam or solid poly~lylcne layers of 20 the l~ d layer of the cup stock. These experiments are sllmm~ri7ed in the following Examples. The foam stock used in all of the following Examples to prepare cups was a solid poly~lyl~ne/polystyrene foam roll stock prepared as described above. Formed cups were conditioned as described below and their vendibility tested by dispensing the cups in either an Automatic Vending Products Tn~ern~tional, Ltd. Model 213 20 beverage vending machine, or 2s in a Crane National Vendors Model 625D beverage vending m~hin~. The results of these tests are sllmm~ri7ed as Examples 1-26 in Tables 1, 2 and 3. These Examples demonstrated the ability of ~nti~t~tic coatings in accordance with the present invention to dissipate and relax electrostatic potential induced in the cup or cup stock by the cup m~nllfactllring process.
Examples 1-13 Referring to Table 1, Example 1 is representative of a cup manufactured in accordance with the above described process, but without the use of an ~ntist~tic chemical. The cups in Example 1 were stored at a temperature of about 18~C and 15% relative humidity for 10 days C: 55710(16ZS01!.DOC) CA 022127~8 1997-08-12 prior to testing in a commercial vending machine. Immediately prior to testing, five stacks of 72 cups (360 total cups) were removed from the storage chamber and loaded into a vending machine. Cup stack potentials were measured before placing the cup stacks in the vending m~rhine using a SIMCO HAND-E-STAT portable field strength meter held one inch from s the cup stack surface. The field strength meter was swept along the length of the cup stack to ~letçrmine the m~ximllm positive and negative potential values reported herein. The ambient environm~nt~l condition during the testing was 19~C and 48% relative humidity. The time required for each cup vend was measured for deterrnination of a "good vend" or a "failed vend". A "good vend" occurred when a cup arrived at the cup fill station in 5 seconds or less 10 after being dispensed from the cup stack by the dispenser ring, and a "failed vend" occurred when a cup took longer than 5 seconds to arrive at the cup fill station or never arrived at the fill station.
As shown in Table 1, Co~ ~ativ~; Example 1 had a failed vend 2 of the 360 cups.
While this failure rate may appear to be relatively low, the ~ lly acceptable vending failure rate of 1 in 1000. The results are not surprising since the cup stacks exhibited cup stack potentials ranging from 4.8 to +8.2 kilovolts.
Inventive Examples 2-6 demonstrate the effectiveness of cups produced in accordance with the present invention. Each cup in Inventive Examples 2-6 was formed from cup stock that was ovel~lint~d with about a one micron thick layer of a solution comprised of 12 wt.%
20 of the commercially available ~ntict~tic agent HOSTASTAT HS-l, 20 wt.% of #7210 mixing white ink available from Lewis O. Werneke Co., of Plymouth Minnesota, and 68 wt.%
deionized water. (referred to in Table 1 as "12 % HS-l"). HS-l is an anionic surfactant ~nti~t~tic agent availaUe as a water soluble powder from Hoechst Celanese Corporation of Charlotte, North Carolina, and is a mixture of sodium alkyl sulfonates having the formula C
25 18 H2l 39 SO3Na. Inventive Examples 3 and 6 included an additional 4 wt.% of HS-l extruded into the impact poly~lylelle outer cup stock layer to ~letermine if the presence of extruded ~nti~tic agent improved vending performance. The storage and test procedures for Inventive Examples 2-6 mirrored those of Colllpa~ative Example 1, with the specific storage, test and vending conditions indicated in Table 1.
Unlike Colll~alalive Example 1, every cup tested in Inventive Examples 2-6 resulted in a good vend. In addition, the printed image on each cup in Inventive Examples 2-6 was sufficiently durable in that no scuffing of the cups appeared from the cup forming, st~c~ing or C: 55710(16ZW1!.DOC) CA 022127~8 1997-08-12 subsequent h~n~lling. Furthermore, the measured cupstack potentials were substantially lower than in Colllp~live Example 1, with no measured potential excee-ling +/-4 kilovolts, thereby verifying the correlation between good vends and low cup stack electrostatic potential. The presence of extruded antistatic agent in the foam layer of the stock in Inventive Examples 3 s and 6 did not appear to produce superior vending performance since all of the cups vended successfully. This was surprising since the manufacturer recommended extruding HS- 1 into a polymer foam. Lastly, the cups with the antistatic coating in Inventive Examples 2-6 did not have detect~ble odors or taste ~ltering effects when qualitatively tested.
Colll~lalive Examples 7-13 did not use an alkyl salt surfactant as an ~nti~t~tic agent (like in Examples 2-6). However, Examples 7-10 and 13 used the same mixing white ink as used in Examples 2-6. The storage and test procedures for Examples 7- 13 mirrored those of Example 1, with the specific storage, test and vending conditions and vending test results in-lic~t~cl in Table 1.
Specifically, Examples 7 and 8 comprised a printed overcoat consisting of 6 wt.% of polyvinyl alcohol, 20 wt.% of mixing white ink, and 74 wt.% of deionized water. (referred to as "PVA" in Table 1). Examples 9 and 10 comprised a printed overcoat of 10 wt.% polyvinyl pyrrolidone, 20 wt.% of mixing white ink, and 70 wt.% of deionized water. (referred to as "PVP" in Table 1). Examples 11 and 12 comprised a printed overcoat of 100 wt.% of Adcote 61X102 ll~ls~alent coating available from Morton International of Chicago, Illinois.
(referred to as "Morton" in Table 1). Finally, Example 13 comprised a printed overcoat of 67 wt.% of the #7210 mixing white ink and 33 wt.% of the proprietary polyether antistatic ink FDA-3 m~rkPte~l by Amstat Tnl1llctries, Inc. of Glenview, Illinois. (referred to as "FDA-3" in Table 1).
The results showed that Colllpra~ive Examples 7-13 had much lower vending rates 2s and much higher cllpstack electronic potentials as compared to Inventive Examples 2-6.
Thus, the topically applied alkyl salt/mixing white ink ~nti.ct~tic coating (Examples 2-6) had much better results than using commercially available ~nti~t~tic agents with the mixing white ink (Examples 7-10 and 13) or using only a commercially available ~nti~t~tic agent ink (Examples 11 and 12).

C: 5571~X 16ZS01 !.DOC) TABLE lA

Cup Storage Conditions Antistatic Agent Antistatic Agent Antistatic Agent Te.. l~.alulG (~C) Relative Cup Stack Extruded Into Extruded Into Topically Applied Humidity (%) Potential (kV) Foam Layer Foam Layerto Laminate (wt.%) (wt.%) Layer Examp' e ' 0 0 Nor e 1 '' ' ' -'.8 to + ' .', Examp .e ~ O C 1'"7~- l 1 ' '. ' -2.1 to +3.' Examp e ~ ' -1 1 ' r _''.0 to +' .:
E%amp e ~ r +3. ~ to -O.h Examp e ' ~ C '.2~. - -: 66 :. o.r to +1.-.
Examp'e6 C' ~ .'-' 6r~ : +1. to-1."
Examp'e7 0 ;~ ''VA '. :' +l''to=>20 Examp' e ~~~ 'VA : :~ >+''0 Examp e ~ V ' : :r +1' .7 to -16.1 Examp e ' O ~ V ' : '.' >+20 Exarnp.e :' l~ .V'orton .. ~ ' ' +1'.8 to -14.8 Examp.e ' ~ C (I V orton - r +lr to > -20 Exarnp.e J C F~A-3 ' :' >+20 TABLE lB

Vending Test Conditions and Results Te~ dtulG Relative Total Cups Good Vends Failed Vends Print Durability (~C) Hurmidity Examp: c ~ ~r 6~ ~ : 58 " ~ -ooc Exampe" .~i ~r ~o- ~oo ~ C'OOc Exarnp.e: '.'~ ~n ~5 ' 50 J COOc Exatnp e~ ,o 15 "OC! ' 00 0 C'-ooc Exampe ' ' " ~r ' 00 200 0 COOc Examp e ;~ "" ' ' 200 "00 0 ~-ooc Examp e ~ :.' ~ to 15 : 00 ~"0 20 C'-ooc Examp'e r ~j '8 :.00 '.~ 74 C-ooc Examp e u u '8 :00 74 '' 1 C'ooc Exampe '.0 '.' ~ to 15 :50 1~9 ' 1 C'-ooc Examp e :: :'~ ~8 100 5~ ooc Examp'e ' '' 1 ' ' to 15 300 26 "74 Gooc Examp e 1, 19 '8 500 223 ''77 Cooc C: 55710(16ZSOI !.DOC) CA 022127~8 1997-08-12 Example 14-20 Examples 14-20 in Table 2 comprised different concentrations of an alkyl salt useable in a mixing white ink and deionized water mixture topically applied to cup stock.
Specifically, Examples 14-16 comprised a one micron thick printed overcoat of an ~nti~t~tic s agent consisting of 23.5 wt.% of HS-l, 20 wt.% of mixing white ink, and 56.5 wt.% of deionized water. (referred to as "23.5% HS-l" in Table 2). Examples 17-20 comprised a one micron thick printed overcoat of an antistatic agent consisting of 7.5 wt.% of HS- 1, 20 wt.%
of mixing white ink, and 72.5 wt.% of deionized water. (referred to "7.5% HS-l" in Table 2).
Referring to Table 2, Examples 14-16 with the 23.5% HS-l mixture resulted in no 10 failed vends. However, the printed image on the cups in Examples 14-16 was not durable because the images on the fini~hP-l cups were scuffed. The poor durability of the printed image is believed to result from the relatively high levels of HS- 1 in the printed overcoat inlel~;Lillg with ink in images already printed on the cup. This h~t~l~clillg may occur because of the overcoat rewetted the printing image or the overcoat prevented the image from drying.
Examples 17-20 with the 7.5% HS-l solution resulted in printed images that were durable. However, the vending performance of the cups in Examples 17-20 was nnc~ti~f~ctory. This is clearly shown when all of the Examples 17-20 failed to satisfy the minim~l standard of 1 vending failure per 1000 cups vended.

C: 55710(16ZS01!.DOC) Vending Test Results Antistatic Antistatic Antistatic Corona Total Good Failed Print Agent Agent Agent Tre~ttn.. nt Cups Vends Vends Durability Extruded Into Extruded Into Typically Foam Layer T ~min~te Applied to (wt.%) Layer T ~min~te (wt.%) Layer Example 14 0 2 23.5% HS-l Yes 700 700 0 Poor Example 15 0 2 23.5% HS-l Yes 700 700 0 Poor O
Example 16 0 2 23.5% HS-l Yes 700 700 0 Poor ~, Example 17 0 4 7% HS-l Yes 450 447 3 Good Example 18 0 2 7% HS-l Yes 450 334 116 Good O
Example 19 0 2 7% HS-l Yes 450 419 31 Good Example 20 0 2 7% HS-l Yes 450 444 6 Good C: 55710(16ZS01!.DOC) CA 022127~8 1997-08-12 Examples 21-26 Cups prepared in accordance with Inventive Examples 2-6 provided outst~n-ling print durability and vendibility under most manufacturing conditions. However, isolated production runs of cups produced in accordance with Inventive Fx~mples 2-6 sporadically s exhibited poor vendibility. These cups typically were not reliably vended when the relative hllmi(lity in the m~nllf~cturing facility was 30% or less, with more extreme vending difficulties occllrrin~ when the relative humidity was less than 20%.
Referring to Table 3, Examples 21 -24 tested four batches of cups produced underextremely low humidity m~nllf~ctllring conditions. Examples 21-24 all comprised 12 wt.%
10 HS-l, but Examples 22 and 24 had corona treatment of the web imm~ tely prior to printing and Examples 23 and 24 had additional antistatic agent incorporated into the polymeric material used to create the cup's outer l~min~te layer. The vending results in Table 3 inrlic~t~cl that neither the corona treatment and the additional ~nti~t~tic agent incorporated in to the polymeric material had a sigtlific~nt effect on the failed vends. However, the corona 15 treatment is still important because the ink more effectively adheres to the polymeric surface.
The cup stacks typically exhibited electrostatic potentials in excess of +/- 7.5 kilovolts in Examples 21-24. Similarly high electrostatic potentials were present on the cup roll stock as the stock was unwound and fed to the cup forming machine. F.x~mples 25 and 26 were performed to see of the topically applied ~ntist~tic mixture could further enhance its 20 performance prior to cup forming. Because the ~ntist~tic agent was hllmi~lity-sensitive, the roll stock was conditioned in a relatively higher humidity envilolll.lelll so that the roll stock might better dissipate unwanted static before being exposed to charges generated by cup forming e ~
Specifically, the printed rolls of cup stock in Examples 25 and 26 were treated with 2s ~nti~t~tic coatings of the present invention and placed in a storage area where the relative hllmi-lity was m~int~in~.-1 at about 50%. The roll stock was preconditioned in the storage area for a period of 72 hours prior to cup forrning. The cups were then m lnllf~tured from the preconditioned roll stock under the same adverse, low humidity conditions already noted. As shown in Table 3, all of the cups in Fx~mples 25 and 26 resulted in good vends. The 30 preconditioning of the roll stocks used under the extremely low hllmi~lity conditions reduced the electrostatic potential on cup stock fed to the cup forming machine to levels below +/-5 kilovolts.

C: 55710(16ZSOI !.DOC) CA 022127~8 1997-08-12 While not wishing to be bound by the theory, it appears that humi~lity preconditioning a treated roll stock prior to cup forming increases the effectiveness of the ~ntict~tic overcoat so that the overcoat can dissipate static charges intl~lce-l in the cup stock, cups or cup stacks in the cup manufacturing process. While it was also noted that it was possible to exploit the effects of topically applied ~ntict~tic mixtures in accordance with the present invention by hllmi(lity conditioning foamed articles after the forming step, such conditioning is relatively inefficient when compared to preconditioning roll stock and in some instances proved ineffective in dissipating static charges acc-lm~ t~l during the forming process.

C: 55710(16ZS01!.DOC) Vending Test Results Antistatic Agent Antistatic Agent Antistatic Corona Total Cups Good Vends Failed Vends ExtrudedInto ExtrudedInto Coating Treatment Foam Layer T "tnin ~e Layer (wt.%) (wt.%) Example 21 0 0 12% HS-1 No 250 236 14 Exarnple 22 0 0 12% HS-1 Yes 250 230 20 Exarnple 23 0 4 12% HS-1 No 250 219 31 O
Example 24 0 4 12% HS-1 Yes 250 232 18 ~, vl Example 25 0 0 12% HS-1 Yes 400 400 0 x Exarnple 26 0 0 12% HS-1 Yes 400 400 0 ~' -C: 55710(16ZS01!.DOC) CA 022127~8 1997-08-12 A fini~h~cl cup 150 represen~alive of the cups used in the above Examples is shown in more detail in FIG. 7. The cup 150 includes a generally circular bottom 152 which typically is cut and formed from the same foam stock as cup frustoconical sidewall 154. The sidewall 154 typically has a trun~e~l frustoconical shape as shown in FIG. 7 to facilitate cup nesting.
s The sidewall 154 includes a generally circular, upper open end portion 156 and a lower base portion 158, and is formed from the foamed poly~yl~ne/solid poly~Lyl~lle l~min~te described above. The sidewall 154 has a foamed poly~lylelle inner sidewall surface 154a and a solid poly~lylene outer surface 154b. Bottom 152 is circurnferentially attached at or near the lower base portion 158 by any of a number of attachment means known in the art, such as gluing or lo heat expansion of the bottom-sidewall interface. Typically, cup bottom 152 is fastened to lower base portion 158 slightly above the bottom edge of lower base portion 158 to prevent bottom nesting of stacked cups and to allow a section 158' of lower base portion 158 to be folded upwardly and inwardly to provide additional support for bottom 152 as already discussed herein. To assist in reinforcing, sidewall 154 includes a rim 160 around the upper Is periphery thereof.
In most cases, outer surface 154b of the cup 150 will bear a printed image (not shown) which has been printed on uncut cup roll stock by a flexographic printing process. Chemical coating 164 cont~ining antistatic agent and a transparent or translucent water-soluble ink is printed over the desired graphic image prior to the roll stock being rewound and transferred to a cup forming m~hinç
Typically, chemical coating 164 will cover all outer surfaces of cup 150. However, it is believed that the advantages of the invention can be realized if at least 75 percent of the outer sidewall of cup lS0 is ovel~lillted with the chemical coating. Less than complete coating of an article's surface area may limit the ability of the web or the article to dissipate 2s accllmlll~tçd static charge. Therefore, it is desired to cover all the outer surfaces of the cup 150.
The first process is typically for low relative humidity manuf~hlrin~ envilolllllents.
This process generally in~ des the steps of topically applying a mixture comprising a hllmi-lity-sensiliv~ ~nti~t~tic surfactant compound to a foam stock from which the article is to 30 be formed, conditioning the foam stock in a humidity-controlled environment effective to reduce electrostatic potential of the stock to between -S and +S kilovolts, and thereafter, thermoforming the article from the conditioned foam stock.

C: 55710(16ZS01!.DOC) CA 022127~8 1997-08-12 As discussed earlier, this process maximally exploits the antistatic effects of the topically applied ~ntict~tic agent during the manufacturing process by using humidity to condition a foam stock just before the stock is processed in a thermoforming apparatus. The conditioning renders the topically applied antistatic mixture highly effective for dissipating static charges s that otherwise would readily ~ec-lm~ tP, during the cup production and handling processes under the low relative humidity conditions. This result is not possible when using only an extruded ~ntict~tic agent that "blooms" to the surface over the life of the cup because the concentration of antistatic agent available to be effected by the hllmillifieation step during cup m~nllf~eture is insufficient to effectively dissipate static electricity generated in the cup's 10 production and h~n(lling process.
A second process in accordance with the present invention is better suited to m~nnf~cturing under conditions where the relative hllmi-lity typically exceeds 30%. This process elimin~tPs the need for a humidity conditioning step and relies instead on ambient hnmi~lity to render the topically applied ~ntict~tic mixture effective during the manufacturing 5 process.
~ llmiclity sensitive ~ntict~tic surfactant compounds useful in either of the above-described processes are highly polar compounds that adhere to a surface of a foamed polymer stock and demonstrate an increased propensity for dissipating a static charge as ambient hllmi-lity is increased. Such highly polar compounds include cationic ~ntict~tic compounds 20 such as quaternary ammonium salts of organic compounds having alkyl chains of from about 4 to about 20 carbon atoms in length; anionic ~ntict~tic compounds such alkyl sulf~tes, alkyl sulfonates and alkyl phosphates having alkyl chains of from about 4 to about 20 carbon atoms in length; and nonionic highly polar organic compounds such as polyvinyl alcohol, poly~ yl~ olidone and polyethers, as well as ~minPs, acids and fatty acid esters. The 25 amines, acids and fatty acid esters have alkyl groups of from about 4 to about 20 carbon atoms in length.
The use of the anionic and cationic eompounds is preferred, with the use of anionic compounds most preferred. The anionic compounds including alkyl sulfates, sulfonates and phosphates having alkyl chains of from about 4 to about 20 carbon atoms are believed to be 30 the most ~l~felled compounds, with a mixture of sodium alkyl sulfonates having the formula Cl~lg H2l 39 SO3Na being partieularly effective as demonstrated by the foregoing Examples.

C: 55710(16ZS01!.DOC) CA 022127~8 1997-08-12 The data from Table 2 suggested that the amount of an ionic surfactant used in the printed overcoat should be from about 7.5 wt.% to about 23.5 wt.%. The preferred amount of ionic surf~t~nt in the applied mixture should be from about 10 to about 15 wt.%.
It is contemplated that the foregoing compounds can be applied in any manner known s in the art such as printing, dipping, spraying and the like. However, the durability of graphic images and the ~nti~t~tic compound is çnh~nced by pr~ g an aqueous solution of the ~nti~t~tic mixture and a translucent or transparent ink (often referred to as a "mixing white ink") which is printed over a graphic image already printed onto the foam stock during a flexographic printing process. The overcoat thickness should be from about 0.5 to about 3 10 microns, since thinner layers may not impart sufficient ~nti~t~tic agent to be effective, while thicker layers may interfere with drying of the underlying image or soften an already dry image. The overcoat thickness is preferably about 1 micron.
While most water soluble inks are suitable for use in this application, some inks perform better than others, and should be empirically evaluated with the selected ~ntict~tic 5 agent or agents. For example, in some instances, the Werneke #7210 mixing white ink and the MW1 mixing white ink available from Mead Ink Products of Anniston, Alabama, provided superior print durability and vending results when compared to other similar inks used with the HS-1 anti~t~tic agent. The preferred amount of mixing white ink in the overcoat mixture ranges from about 10 to about 30 percent, and preferably from about 15 to 20 about 25 percent.
Foam stocks useful in the present invention can be any sheet or roll stock material suitable for forming which has at least one foamed polymeric layer. Examples of preferred sheet stocks include sheets of a single foamed polymer such as poly~lylelle as well as multi-layered l~min~ted stocks incorporating a foamed polymer layer and a non-foamed polymer 2s layer such as a solid polymer or other m~teri~l such as paper or cardboard. A most preferred stock for forrning cups intended for vending machine use is a roll stock that has an inner foamed poly~lylene layer and an outer impact polystyrene layer.
The foregoing applications and Examples are merely representative of processes and articles in accordance with the present invention. Those skilled in the art will readily 30 recognize other applications for the invention. While the invention has been disclosed in connection with a web-fed flexographic foam cup process, the invention can be used with other processes such as blank-fed machines, pneumatic part transfer or f1lm production C: 55711X16ZSOI!.WC) CA 022127~8 1997-08-12 processes. Other potential applications include the m~nllf~cture of containers suitable for p~ ging static-sensitive electronic devices or other products where the presence of static electricity can damage the product or cause dust or other fine particles to undesirably ~ccllmlll~te in or on the package or packaged product. Alternatively, processes and articles in s accordance with the invention may be used in any application where the reliable separation of stacked polymeric a~rticles is required. The invention, therefore is not limited to the foregoing Examples, but only by the scope of the following claims.

C: 5nlO(16ZSOl!.DOC)

Claims (38)

1. An article comprising a polymeric material bearing a coating, said coating comprising a residual layer formed by applying and allowing to dry a mixture containing from about 7.5 to about 23.5 weight percent of a humidity sensitive antistatic surfactant and from about 10 to about 30 weight percent of a water soluble ink, said article further having an electrostatic potential from about -5 to about +5 kilovolts as measured at one inch from said coating.

2. The article of claim 1 wherein said coating is from about 0.5 to about 3.0 microns thick.

3. The article of claim 1 wherein said article has an outer surface, and whereinsaid coating covers at least 75 percent of said outer surface.

4. The article of claim 1 wherein the article is a cup comprising a generally circular bottom and a truncated frustoconical cup sidewall, said sidewall comprising a polymeric material and having inner and outer surfaces, said inner surface and said circular bottom circumferentially cooperate to form a liquid tight seal between the bottom and the sidewall, and wherein the coated surface covers at least about 75 percent of said sidewall outer surface of the cup.

5. The cup of claim 4 wherein said sidewall comprises an inner layer of foamed polystyrene and an outer layer of solid polystyrene, and wherein said coating resides on said outer solid polystyrene sidewall surface and is from about 0.5 to about 3.0 microns thick.

6. The cup of claim 5 wherein said outer polystyrene sidewall surface bears a printed image, wherein said coating has been applied over said printed image, and wherein said printed image is visible through the residual layer.

7. The cup of claim 6 wherein said humidity-sensitive antistatic surfactant is an anionic humidity sensitive surfactant and wherein said water soluble ink is a mixing white ink.

8. The article of claim 7 wherein said anionic humidity sensitive surfactant is chosen from the group consisting of alkyl sulfates, alkyl sulfonates, and alkyl phosphates, said surfactants containing alkyl chains of from about 4 to about 20 carbon atoms in length.

9. The cup of claim 8 wherein said anionic humidity surfactant comprises a mixture of sodium alkyl sulfonates consisting essentially of sulfonates having the molecular formulas C10-18H21 39SO3Na.

10. A nested stack of at least 10 cups of claim 8 wherein said nested cup stack has an electrostatic potential from about -5 to about +5 kilovolts as measured at one inch from any cup stack surface.

11. The article of claim 1 wherein said polymeric material comprises polystyrene, wherein said article has been thermoformed, said humidity-sensitive antistatic surfactant is an anionic humidity sensitive surfactant and said water soluble ink is a mixing white ink.

12. The cup of claim 11 wherein said anionic humidity sensitive surfactant is chosen from the group consisting of alkyl sulfates, alkyl sulfonates, and alkyl phosphates, said surfactants containing alkyl chains of from about 4 to about 20 carbon atoms in length.

13. The article of claim 12 wherein said surfactant comprises a mixture of sodium alkyl sulfonates consisting essentially of sulfonates having the molecular formulas C10-18H21-39 SO3Na.

14. A stack of at least 10 articles of claim 11 wherein said stack has an electrostatic potential from about -5 to about +5 kilovolts as measured at one inch from any stack surface.

15. A process for producing a formed article which is relatively free from the effects of static electricity, said process comprising the steps of:
topically applying a mixture comprising a humidity-sensitive antistatic surfactant compound to a stock comprising a foamed polymeric material;

conditioning the stock in a humidity-controlled environment effective to reduce the stock's electrostatic potential from about -5 to about +5 kilovolts; and thereafter forming said article from said conditioned foam stock.

16. The process of claim 15 wherein said mixture comprises anionic humidity-sensitive antistatic surfactant compound and wherein the article is thermoformed from a polymeric material comprising polystyrene foam.

17. The process of claim 16 wherein said mixture includes volatile compounds, wherein the applying step comprises printing the mixture containing said antistatic compound to the stock, said process further comprising the step of thereafter allowing the volatile compounds to evaporate to deposit a coating on the article having a thickness from about 0.5 to about 3.0 microns.

18. The process of claim 16 wherein said mixture comprises from about 7.5 to about 23.5 weight percent of said anionic humidity-sensitive antistatic surfactant compound and from about 10 to about 30 weight percent of a water-soluble ink.

19. The process of claim 17 wherein said mixture comprises from about 7.5 to about 23.5 weight percent of said anionic humidity-sensitive antistatic surfactant compound and from about 10 to about 30 weight percent of a water-soluble ink.

20. The process of claim 18 wherein said foam stock comprises a layer of foamed polystyrene adhered to a layer of a non-foamed polymer, and wherein said mixture is applied to the layer of non-foamed polymer.

21. The process of claim 19 wherein said foam stock comprises a layer of foamed polystyrene adhered to a layer of a non-foamed polymer, and wherein said mixture is applied to the layer of non-foamed polymer.

22. The formed article produced by the process of claim 15.

23. A stack of at least 10 nested articles produced by the process of claim 15, said stack exhibiting a measured electrostatic potential from about -5 to about +5 kilovolts.

24. A stack of at least 10 nested articles produced by the process of claim 21, said stack exhibiting a measured electrostatic potential from about -5 to about +5 kilovolts.

25. The stack of articles of claim 24 wherein said nested articles are cups.

26. A process for producing a nested stack of at least 10 articles from a polymeric foam stock comprising the steps of:
topically applying a mixture comprising from about 7.5 to about 23.5 weight percent of an ionic humidity-sensitive antistatic surfactant and from about 10 to about 30 weight percent of a water-soluble ink to said foam stock;
thereafter forming at least 10 of the articles from the foam stock; and nestably stacking the formed articles, said nested stack of formed articles exhibiting a measured electrostatic potential from about -5 to about +5 kilovolts.

27. The process of claim 26 further comprising the steps of printing a graphic image on said foam stock prior to topically applying said mixture, allowing said mixture to dry, and wherein said graphic image thereafter remains visible through said topically applied mixture.

28. The process of claim 27 wherein said mixture is topically applied by printing the mixture over the printed image and allowing the mixture to dry, thereby depositing from the mixture a coating having a thickness from about 0.5 to about 3.0 microns.

29. The process of claim 28 wherein the surfactant comprises at least one anionic surfactants selected from the group consisting of alkyl sulfates, alkyl sulfonates and alkyl phosphates, said surfactants containing alkyl chains of from about 4 to about 20 carbon atoms in length.

30. The process of claim 29 wherein the surfactant comprises a mixture of sodiumalkyl sulfonates consisting essentially of sulfonates having the molecular formulas C10-18H21-39 SO3Na.

31. The process of claim 29 wherein the forming step comprises the steps of cutting a cup sidewall portion from the foam stock; wrapping the cup sidewall portion around a cup bottom portion to form a truncated frustoconical sidewall around said cup sidewall portion; and circumferentially sealing said cup sidewall portion around the cup bottom portion.

32. The process of claim 31 further comprising the step of forming the foam stock by adhering a layer of solid polystyrene to a layer of foamed polystyrene, and wherein the mixture is applied to the adhered layer of solid polystyrene.

33. An antistatic solution for application to a polymeric surface comprising:
7.5 to 23.5 weight percent of an ionic humidity-sensitive antistatic surfactant; 10 to 30 weight percent of a water soluble ink; and 46.5 to 87.5 weight percent water.

34. The solution of claim 33 wherein said water-soluble ink is a mixing white ink.

35. The solution of claim 34 wherein said surfactant comprises at least one anionic surfactants chosen from the group consisting of alkyl sulfates, alkyl sulfonates and alkyl phosphates, said surfactants containing alkyl chains of from about 4 to about 20 carbon atoms in length.

36. The solution of claim 34 wherein said surfactant comprises a mixture of sodium alkyl sulfates having the molecular formulas C10-18H21-39SO3Na.

37. The solution of claim 36 consisting essentially of said water, said mixing white ink, and said surfactant.

38. The solution of claim 36 wherein said surfactant is present in the amount offrom about 10 to about 15 weight percent.