anti static master batches

8/6/2019 Anti Static Master Batches

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Antistatic Masterbatches

Introduction:

By virtue of their insulating nature, polymers of all types allow static charge to build-up on theirsurfaces, particularly in the case of films and fibers, which have large surface area to volumeratio. Such static charge build-up leads to several undesirable consequences in the final product.For instance, built-up static charge can attract dust onto a food package, which is undesirableaesthetically. At times, static charge can damage circuit boards in electronics packaging and maycause hazards of fire or explosion in the vicinity of flammable materials.

The static charge may also cause several processing problems such as difficulty in winding of

films or melt-spun fibers, agglomeration of powders during transport, adhesion of films during

processing, etc. Such undesirable effects of static charge build-up can be avoided by using

masterbatches containing antistatic agents. The most commonly used are those compounded

internally with the polymer and those applied topically.

Migratory Antistats:

The traditional internal antistats aremigratory in nature. Typically thesemigratory antistatic agents have ahydrophobic organic end and ahydrophilic end. The strongly polarhydrophilic end adsorbs water

molecules which eliminate staticcharges by ionic conduction. Thelong hydrocarbon chain lengthconstitutes the hydrophobic groupand controls the rate of diffusion(or migration) of the antistat to thesurface of the polymer product.

There are three major classes of internal, migratory antistatic agents: esters, amines and amides.Glycerol mono-stearate is commonly used as an antistatic agent for PE and PP but is useful foronly short term antistatic performance of about 1-2 months. The amines and amides are usually

ethoxylated products and are more useful for long term antistatic performance. The amine typeantistats tend to react with polycarbonate, which is commonly used in making electronic circuitboards. Hence a plastic packaging containing amine antistat is detrimental to electronic circuitboards. The amine antistats have limited FDA approval. However, the amines are extremelyeffective as antistatic agents. The amides also have limited FDA approval but broader than theamine antistats. The esters, on the other hand, are FDA approved at any level of concentration.

The performance of the migratory antistats depends on various factors such as:



1. Concentration: The higher the concentration of the antistat, the antistat migration is fasterand usually the performance is better.

2. Relative humidity: All migratory antistats depend on water for functioning. Hence theantistatic performance is always better at higher humidity.

3. Conditioning time: The migratory antistats diffuse through the polymer matrix and have tocome to the polymer surface in sufficient concentration to be effective. It requires time for

the antistats to achieve a monolayer surface coverage and to attain4. Equilibrium between the surface and the bulk concentration. Hence the antistatic

performance usually improves with conditioning time. In the case of LDPE & LLDPE, it isconsidered that two days of conditioning time is adequate to get a monolayer of surfacecoverage for all migratory antistats.

5. Antistat chemistry: The size and the shape of an antistat molecule itself dictates its rate ofdiffusion through a given polymer matrix. Hence the rate of diffusion of the antistat isdependent on its chemistry. In addition, certain antistat chemistries tend to crystallize oncethey are on the film surface in sufficient concentration. It is believed that suchcrystallization of the antistat leads to loss of its antistatic properties. This process dependson the unique mixture of chainlengths in a given antistatic additive. Hence certain antistaticadditives lose their antistatic properties more quickly than others and are useful only as

"short term antistats". All of the GMS chemistries are susceptible to such a process.6. Type of polymer: The polymer used for making films (or other extruded parts) has a major

influence on the diffusion of the antistatic additives. The crystallinity and the polarity of thepolymer are the key properties that influence the behavior of the antistatic additives. Apolymer with high crystallinity (such as HDPE or PP) creates a tortuous path for thediffusion of the antistat, thus retarding the rate of diffusion. In general, all migratoryantistats require a very long time to diffuse out of HDPE or PP homopolymer. Similarly, apolymer with polar groups (such as EVA, EMA, Surlyn, Nylon, PET) has chemicalinteractions (mainly hydrogen bonding) with the polar groups of the antistat molecule.Such interactions also decrease the rate of diffusion of the antistat.

7. Presence of other additives: There are three types of influences from other additives onthe behavior of antistats. (1) If the other additives are also migratory, they compete with

the antistats for diffusion through the polymer matrix and also compete with the antistatsfor surface coverage. Slips are a common example of this type of additive, which mayexert adverse influence on antistatic properties. (2) Some additives tend to have chemicalinteractions with certain types of antistat chemistries. Amine and amide type antistats arebasic (alkaline) in nature, which may react with some acidic flame retardants, which canresult in reduction of antistatic properties. (3) Some antiblocks such as synthetic silica tendto adsorb antistatic additives on their surface, due to their high surface area. Suchadsorption will also retard or prevent the migration of the antistats to the surface of a film.

8. Corona treatment: The treatment of a film surface with corona discharge results inoxidation or 'burning' of the surface layer of the film. Such corona treatment usuallyaccelerates the migration of the antistats to that side, by increasing the concentrationgradient and also by making that surface more polar.

9. Lamination: It is very common in the polyolefins industry to laminate antistatic films bymeans of adhesive lamination. The most commonly used adhesives are polar chemicals,which attract antistatic additives and interact with them. Once the antistatic additivesmigrate from the sealant PE side to the adhesive layers, they usually do not come out andantistatic properties on the PE side are lost forever. In some cases, extrusion lamination iscarried out by high temp. processing and cross-linking of the PE layer to a polar substratesuch as nylon or PET. These polar substrates also attract antistatic additives which resultsultimately in loss of antistatic performance in the PE layer.

10. Winding tension: The rate of diffusion of an antistat in a film wound on a roll is much



slower than an unwound film. The unwound film offers a large surface for the antistat todiffuse and such surface area is not available on a tightly wound roll. Hence the higher thewinding tension, the slower the antistat diffusion.

11. Gauge of film: Higher gauge or thicker films will require more time to achieveequilibrium between the surface and the bulk concentration of the antistat. Butthicker films also have more mass of an antistat than thinner films. Therefore,thicker films usually require slightly lower quantity of an antistatic additive thanthinner films, to achieve the same antistatic performance. However, among all thefactors listed above, the gauge of a film seems to exert the least influence on theantistatic properties.

Non-Migratory Antistats:Recently Ampacet has developedunique, nontraditional antistaticproducts based on a nonmigratoryantistat which have been designed foruse only in skin layers of multilayer

films. These are clear products basedon polymeric antistatic chemistry,which does not depend onatmospheric humidity for functioning.The antistatic additive forms aninterconnecting or percolating network(similar to conductive carbon black)and dissipation of the static. Percolating Network

Charge occurs by an ionic conduction mechanism. As a result, much higher loadings of thisproduct are required, as compared to the traditional migratory antistats, to achieve good antistatic

performance. Hence these products are recommended to be used only in skin layers of multilayerfilms.

The major benefits of non-migratory antistatic masterbatches are as follows:

• No conditioning required .. the antistatic properties obtained immediately off-line

• Useful in multilayer films, which require no migration to the other side.

• No migration into adhesive layer or nylon/PET layer in case of laminated films.

• No adverse effect on heat sealing and printing (in contrast with migratory antistats)

• Antistat properties last theoretically for the life of the film.

• Used only in a skin layer for a multilayer film (not needed in the core, like migratory additives).

• Clear product

•

Able to meet NFPA-99 and Mil-B-81705C criteria.• High thermal stability hence can be used in blown and cast films



Measurement of antistatic properties:Antistatic performance of a product is measured by means of two properties-static decay time andsurface resistivity, which are defined as follows:

Static decay time (or charge decay time): It is the time required to dissipate a certain fraction of

an applied 5 kV static charge and is measured in seconds. Most commonly, static decay times aremeasured for 90% dissipation or 99% dissipation of the applied 5 kV charge. Thesemeasurements are referred to as 10% cutoff (90% dissipation, from 5 kV to 0.5 kV) and 0% cutoff(99% dissipation, from 5 kV to 0.05 kV). If a sample does not pick up the applied 5 kV staticcharge then it has no antistatic performance. In case of migratory antistats, the static decay timesare not dependent on the direction of testing. However, in the case of non-migratory antistats, ithas been found that the static decay times are dependent on the direction of testing. In the caseof blown films, the non-migratory antistats yield much lower static decay times in machinedirection (MD) than transverse direction (TD).

Surface resistivity: It is simply the resistance of a product at its surface and is measured inOhms. The measurement of surface resistivity is somewhat related to the geometry of the probe.If a product has surface resistivity in the range of 109 to 1013 Ohms, it is considered antistatic. Asample having surface resistivity > 1014 Ohms is considered insulative. Typically, PE and PPhave surfaceresistivities in the range of 1015 to 1016 Ohms. The surface resistivity is not direction dependentfor migratory as well as non-migratory antistats. In films containing non-migratory antistats, wehave observed that the surface resistivity values at very low humidity such as 12% RH are verysimilar to those at 50% RH.

Specifications:The antistatic performance of a product is usually compared to a standard specification, set up bysome agency. These specifications dictate the test conditions for measuring antistatic propertiesand set upper limits on the acceptable values of static decay time and surface resistivity. The

most commonly used specifications are "NFPA-99" and "Mil-PRF-81705D" (commonly known as"Mil spec."), which are described below:

NFPA-99:Test conditions: 50% RH, 730F Static decay time for 10% cutoff (90% dissipation of 5 kV) < 0.5sec. OR Surface resistivity < 1011 Ohms

Mil-PRF-81705D:

Test conditions: 12% RH, 730F Static decay time for 0% cutoff (99% dissipation of 5 kV) < 2.0

sec. AND Surface resistivity < 1012 Ohms



Ampacet ' s Migra to ry Ant i s ta t Mas terba tc hes

Electronics Packaging - Migratory antistat masterbatch 101140:

• Antistatic properties of the films last for several months depending on storage & handling

conditions• Meets mil spec. Mil-B-81705C at 12% RH for packaging of electronics and explosives.

• Meets NFPA-99 at 50% RH for medical packaging applications

• For LDPE and LLDPE blown films; LDPE cast films at maximum 500F temps

• FDA approved up to > 10%

• Recommended in the core and skin layer of multilayer films



Masterbatch 101140

Static decay times (sec.) for 1 mil LLDPE blown films: 8.33%

50 % RH 12%RH

Non-migratory Antistat Masterbatches for Non-FDA applications.

Antistat Performance For Masterbatch 101710Static decay times (sec.) for 1 mil LLDPE films (MD) w/ 40% 101710

50 % RH 12%RH



710 50% RH 12% RH

50 % RH 12%RH

Surface Resistivity (Ohms) for 1 mil LLDPE films (MD) w/ 40% 101

For more information please contact Ampacet's technical support team

d to be correct. However, no warranty fitness for use or any other guarantees or warranty of anynd, expressed or implied, is made to the information conta d herein, and Ampacet assumes no responsibility for thesult of the use of the products and processes described herein. This is an uncontrolled document and information

may be out of date.

at 888-822-7546 or 812-466-9828

Disclaimer: The information and recommendations contained in this document are based upon data collected byAmpacet and believe of

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anti static master batches

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