PRACTICAL TROUBLE - SHOOTING    ADHESIVES FOR WET LAMINATION   

PRACTICAL TROUBLE - SHOOTING

By

F.J. Gunasingam

SYMPTOM

Wrinkles

Side Gauge Band- uneven film/adjust the dancing roller provided in the machine.

Middle gauge Band-Bow roller to be made use of  which is provided in the machine.

Excessive brake-oil the brakes and give optimum brake.

Rollers-clean oil rollers and powder it (French Talc) and ensure that the bearings are greased properly.

Pinch rollers-The brackets supporting the pinch rollers should be tightened properly and during operation the pinch rollers should be evenly closed.

On dipping the adhesive roller, keep the dip to the optimum level, so that the film just comes into contact with the adhesive roller.

For screen printed jobs, if good quality ink and suitable medium is not used, wrinkles will form after lamination.  

Corona Treatment

The treatment given for the film is 38-42 dynes, but the time it reaches the end user it will drop down to 38 dynes. If the treatment is lower the adhesive will not have proper dispersion on the film. Test, apply a thin coat of ink on the film, if it bubbles the treatment is low, it is not suitable for lamination if it retains for 20 seconds as a line, the treatment is good.

Some film will have 2 sides treatment. Some film will have one side treatment. Check the correct side before lamination.

Blocking

If the film does not unwind smoothly, it tears, then the film is old and blocked. Rewind it very slowly and use it, if possible, preferably use it by slitting and rewinding under moderate tension.

Side Wrinkles

The film used should always be less than the sheet width.

Star Marks

The printers uses non stick powder for solid prints for drying this causes star marks after laminations.

Wipe the sheets properly and then laminate. In case it occurs again, give a coat of varnishing and then laminate. Advise the printers not to use non stick powder but to use drier for lamination job.

Dust Particles

Wipe the surface of the sheets to be laminated properly. The old gum removed from the machine should be kept separately without mixing with the new one. Filter and reuse it.

Variation in Punching

The measurement for making punching dye should be done only with a laminated sheet because there is m.m.difference between ordinary sheet and a laminated sheet.

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ADHESIVES FOR WET LAMINATION

By

Vinay Ghatge

Arofine Polymers Pvt. Ltd.,

Wet Lamination adhesive were developed in India some time in 1980. Films available at that time were polyester and PVC. With the advent of BOPP film in 80's and availability of locality made laminating machines, print lamination industry came of age and grew very rapidly.

With growth, competition for development of cheaper lamination adhesives started. In the beginning there were very few manufacturers who could offer good quality adhesives specifically for wet lamination.

A brief description of adhesive manufacturing, without going into elaborate details will be given here for the benefit of laminators who are not conversant with the chemistry of adhesive manufacturing.

Wet lamination adhesives are based on polymers made by emulsion polymerization technique. These are basically dispersion of polymers in water as a carrier.

Starting with, monomers in liquid form are polymerized in the presence of initiators, surfactants and protective colloids to give film forming polymers in dispersion form. These dispersions when coated on a substrate like PVC, polyester or BOPP film, forms a continuous adhesive film by coalescence of polymer particles and evaporation of water from the dispersion. The adhesive coating thus formed is thermoplastic in nature and bonds the film to board or paper.

In India, the choice of monomers available for emulsion polymers is restricted to following monomers; 

Of these Group I monomers are the main components of formulation and these are copolymerised with Group II or Group III monomers. Sometimes Group I, II & III monomers are used together to give terpolymers.

Depending on the cost of momomers, choice of monomers in India is restricted to few monomers like Vinyl Acetate, Butyl Acrylkate, 2 EHA, DBM and DOM. Besides these monomers, the cost of final product depends on the protective colloid used during polymerization to get stability and desired viscosity. The protective colloids generally used are Hydroxyethyl Cellulose and Polyvinyl alcohol. The protective colloid governs the viscosity of adhesive being the external phase of polymer emulsion. This also contributes to the machinability of the adhesive on laminating machines.

The viscosity of emulsions is normally around 5000 to 10000 cps which is measured by instrument called Brookfield Viscometer. The solid vary from 45 to 55 per cent and PH is 4.5 to 6.5.

Further modification of these basic emulsions can be done by external compounding. Additives to improve flow, adhesion, flexibility are added. Considering the varied atmospheric conditions like temperature and humidity, humactants are incorporated in the adhesive formulation. Due care is taken to check the effects of these additives on the inks, like bleeding of pigments used in the inks.

Some common problems associated with wet lamination will be reviewed here with an attempt to analyze and overcome these recurring hazards of print lamination.

Piping

Commonly called in India as wrinkling. Probability of tunneling when film like PVC, Polyester or BOPP is used occurs due to swelling of the film in the presence of some volatile products when printing ink is drying. Once the film has been bonded to the print, there is always a possibility that residual volatiles will cause a localized expansion of the film into 'Pipes'. It is essential that the strength of the adhesive bond is sufficient to withstand this movement. Adhesive strength must be built up rapidly to avoid this effect.

Expansion or contraction of the paper in the cross grain direction with changes in ambient relatives humidity will alter its dimensions relative to the stable film. Incorrect choice of adhesive or substrate can be a problem in this respect.

Silvering or 'stars'

Silver spots can be the visual  result of non-contact between the film and printed board or paper. This can be directly related to surface roughness. The presence of an antiset off powder commonly used while printing is the most common cause and it is therefore essential to avoid or use minimum amount of fine, well dispersed grade of powder. Apart from this, surface homogeneity and nip consistency are critical.

Shriveling

When using a rough substrate a heavy coat weight of adhesive is some times used to counteract the silvering effect. Uneven drying can be some times result in a wrinkled defect.

Poor Adhesion

The adhesive will form a poor bond to the print when the ink surface is insufficiently wettable. The correct choice of adhesive, substrate and ink is therefore very important.

Drying

Insufficient time allowed between printing and laminating can result in set off on to the film, piping and an increased risk of color change with sensitive pigments used in inks. Drying periods vary immensely depending on the specific ink formulation and several external factors. Fast dispersion of volatiles from the inks is obviously dependent upon optimizing air, temperature, humidity and flow. Factors such as heavy coat weights, high or covered stacks of printed paper board and damp cold conditions can extend critically the drying period, thus creating pressure on commercial lead times for the converter. A faster setting adhesive will have significant benefits in this context.

Color Fading

The problem of ink bleeding has always been prevalent with solvent based adhesives systems but some colors notably blue and magenta, tend to fade in the presence of most water based adhesives. This can be attributed to the alkaline environment generated.

By and large, laminators in India are well conversant with these problems.

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