Theory of Corona Treatment

The physical phenomenon of wrappings isn't sufficiently high to allow sensible adhesion of print ink with plastic film . just in case of lamination , it prevents higher bonding between 2 or a lot of materials. Hence, for higher quality of printing, lamination and coating processes , physical phenomenon of the plastic films ought to be hyperbolic. The Corona Treatment technique is wide used these days to extend the physical phenomenon of the films.

The Corona Treatment of wrapping is completed by passing the film through the Saint Ulmo's light created between conductor and nonconductor lined ( ususally synthetic rubber Sleeve) earthed roller as shown in Fig. 1. The air gap between conductor & roller is 2-3 metric linear unit. The conductor is connected to electrical offer having high voltage & high frequency. As film passes through the Saint Ulmo's light, molecules of surface gets oxidises that has a lot of physical phenomenon. The Saint Ulmo's light between conductor and roller is visible by violet color flame bet'n them.

Corona Treating Printing

To improve the wettability and adherence of inks, coatings, and adhesives, corona treatment systems are created to boost the surface energy of plastic films, foils, and paper. The materials treated as a result will have better printing and coating quality as well as higher lamination strength.

Treatment Terms

SPECIFIC ENERGY

This mensuration identifies the Corona Treatment dose to that a movie is subjected. enclosed in it area unit the operating speed, breadth and applied power.

POWER DENSITY

This specifies the facility per cm of discharge line. This data is vital so as to assess the saturation result of the discharge and, in my opinion, as Associate in Nursing assessment criterion regarding the degree of thermal shock applied to the foil by the corona treatment.

CORONA TREATMENT DOSE

The is that the specific amount of power applied to the online material. victimisation this parameter, it's attainable to calculate the rise within the surface energy or to dimension a corona treatment system for a selected application.

POWER DENSITY

This is the precise power applied to a 10mm length of a private corona section. victimisation this parameter, the effectiveness of a discharge are often assessed or a treatment station are often properly dimensioned for a selected treatment application.

TREATABILITY

Not all film materials are often equally well treated. PP is extremely arduous to treat and needs a lot of treatment power. alphabetic character is a smaller amount troublesome to treat compared to PP. PVC and PET doesn't need treatment for printing as their initial physical phenomenon is high.

Unit of physical phenomenon : Dynes/Cm.

GENERATOR POWER

The required generator power is set by the subsequent

Treat breadth x line speed x # of sides x the watt density needed to extend the surface energy of the substrate to the required level. The watt density is set by the sort of substrate and therefore the quantity of additives within the substrate. Having calculated the proper kW rating, it's vital to see the proper discharge space (size and # of electrodes) so as to match the electric resistance of the system properly and not over stress the electrodes. Having an honest match can optimize the potency of the discharge space or conductor

It should be unbroken in mind that if you have got a segmental conductor, it's presumably that not all segments are going to be engaged at identical time. this is often done by moving bound sections of the conductor out of the treat position. This will increase the quantity of power on the market to the remaining electrodes that area unit still engaged for treatment.

SEGMENTED conductor

There area unit variety of things deciding the type and elegance of conductor that will best suit Associate in Nursing application. within the Blown/Cast screenland, a typical application needs the fabric be strip or lane treated. during this case a segmental conductor would be best on a lined roll communicator, which suggests the bottom roll would have Associate in Nursing insulated covering like siloxane sleeve, vulcanised or ceramic nonconductor. segmental electrodes created of chrome steel or metal area unit wide used.

How To Check Corona Treatment

1. For wrapping

QUALITATIVE technique

This is the straightforward and wide used technique to examine the treatment on the film. This technique solely provides indication of excellent or weak Corona treatment however it doesn’t offer any figure of dynes level achieved. during this technique, tiny piece of treated film is taken and skinny layer of ink is applied across the film. permit time to dry the ink. Stick cellotape over the ink space firmly and so peel it off in one stroke. Observe for any ink jutting on the cellotape and treatment are often classified as follows:

• GOOD CORONA TREATMENT : If in the raw out ink isn't quite five you look after ink space over that cellotape is applied.
• WEAK TREATMENT : : If in the raw out ink is between five-hitter and half-hour of ink over that cellotape is applied.
• POOR TREATMENT : If in the raw out ink is quite half-hour of ink overwhich cellotape is applied.

QUANTATIVE technique

This technique provides figure of treatment level in terms of dynes/cms. during this technique answer is ready by combination ethyl radical Cellosolve and Formamide by volume proportion as shown in table one. The victoria blue dye (in powder form) is intercalary to create the answer visible on the surface of the wrapping. to begin with take an answer of forty five Dynes/cm. Take a cotton bud and dip it within the answer . Apply it over the wrapping whose treatment level is to be checked. If answer film breaks down into droplets inside 2 seconds , then opt for lower dynes answer. the proper force unit are going to be {the answer|the answer} that solution film will breakdown into droplets in 2 seconds

2. Paper

There is no technique to examine treatment on paper.Corona Treatment of paper burns fine tissues on paper surface which can hinder to LD Extrusion/Coating on paper.

3. semiconductive Film. Al. Foil

Basically corona treatment cleans and activates the surface of semiconductive film by nothing however atmospherical Plasma improvement

Corona Treatment v/s. Time

Surface Tension (i.e Level of Treatment ) bit by bit reduces with time. this is often thanks to intermigration of polymers at Surface of the film. As time passes treated compound molecules goes within the film and untreated compound molecules involves the surface. the speed of decay of treatment level depends upon initial treatment level. i.e forty eight dynes/cm involves forty four dynes/cm among a pair of days whereas it takes fifteen days from forty four dynes/cm to forty dynes/cm.

Static Electricity & issues

STATIC ELECTRICITY

Denoting or referring to electricity at rest. however easy and inadequate this definition is of a development that makes issues that value business legion greenbacks annually.

Static electricity is generated by unbalancing the molecular construction of comparatively non-conductive insulators like plastics and paper. All matter consists of atoms. A balanced atom contains positive charges that square measure gift within the nucleus of the atom. associate degree equal quantity of negative charges orbits this nucleus within the style of electrons. each charges square measure equal and, therefore, the charge of a balanced atom is zero. However, ought to this configuration be disturbed and a number of other electrons faraway from this atom, we have a tendency to find yourself with a bigger charge within the nucleus and a deficiency of electrons, which supplies you associate degree overall charge within the positive direction. Conversely, ought to we have a tendency to add a couple of additional electrons, we've associate degree overall charge of negative, thanks to the very fact that we have a tendency to currently have associate degree more than electrons and therefore the internet charge is currently within the negative direction.

STATIC ELECTRICITY PROBLEMS?

Static Electricity may be outlined as associate degree electrical charge on a cloth thanks to a surplus or deficit of electrons. the issues caused by electricity break down into 5 main areas

PRODUCTION issues AND SLOW DOWNS

A static charge generates associate degree electrical field that acts sort of a magnet-repelling similar charges and attracting opposite or neutral charges. This accounts for the attraction between charged materials and machine frames or rollers inflicting machine jams. In several cases the machine operator are forced to run at slow speeds to avoid the issues caused by static.

DUST ATTRACTION

Many merchandise, like plastic molding materials and film, develop high static charges on their surfaces. This high charged surface can attract mobile dirt, typically from over three feet away, and hold it tightly to the surface. ulterior operations (such as molding, printing or laminating) and their finish merchandise may be seriously stricken by such difficult-to-remove contamination.

SHOCKS TO PERSONNEL

When handling highly-charged materials, individuals receive unpleasant shocks either directly from material, or indirectly. associate degree example of indirect shock is once someone slides out of associate degree automobile seat and so touches the door handle.

FIRES AND EXPLOSIONS

Static is typically found on non-conductive materials wherever high ohmic resistance prevents the movement of the charge. There square measure a minimum of 2 things wherever the static charge will move quickly and be dangerous in a very flamable atmosphere. the primary is wherever a grounded object intensifies the static field till it overcomes the material strength of the air and permits current to flow within the style of a spark. The second case is wherever the charge is on a floating conductor like associate degree isolated metal plate. Here the charge is incredibly mobile and can flash to a proximity ground at the primary chance.

DAMAGE AND INTERFERENCE IN ELECTRONIC parts

Strong static fields and static discharges will cause interference with equipment. However, even bigger issues square measure caused by electricity within the physics producing business. E.O.S . (Electrical Overstress) and E.S.D. (Electro-static Discharge) became areas of significant concern in dominant the standard of static sensitive MOS and junction transistor devices wherever it's believed that fifty volts or less will cause element failure.

Corona Treatater counseled Treatment Level (dynes)

Different material needs totally different dynes level betting on the applying and coating on that. Below table offers the widely counseled dynes demand for materials: PP, PE, PVC, PET, PS, PVDC, Pu and PTFE for various processes printing applications like Flexo/Gravure, Litho, Offset/Letterpress, Screen/Pad and lamination and coating application.

All knowledge in dynes/cm

Use this chart as a general guideline solely. every operation has slightly totally different necessities.