foam coating process review

7/29/2019 Foam Coating Process Review

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Review of foam applications and research since 1980sFoam typesStable foam -mainly used in gap coating or screen coating e.g. back coating, black out,laminating, flocking etc. Appearance: cream like ,half life above 5 hoursSemi-stable foam -mainly used to a certain penetration surface coating Appearance:Shampoo foam like , half life around 30 minutesUnstable foam -Used for deeply penetrated chemical application Appearance: Beer foamlike, half life less than 6 minutes

Notes Half life means the time it will take for half of the total weight foam collapseinto liquidConventional foam application mainly use blade coating or screen printing use stablefoam

Advantages of foam coating Reduce weight and economize yarn consumption of the substrate

Insulation against heat and cold

Sound-deafening

Shock-absorbing (packaging material)

Handle effects

Very good embossing properties


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Water vapor permeability

Reduce coating strokes

Comparison stable foam coating / paste coatinguntreated fabric

foam coating with

knife-over-roller

foam coating

calendered

fine coating doctor

knife

Conventional foam coating use aerated coating paste to coat onto fabrics by blade or screen

- Soft handle- Low specific gravity, therefore less penetration into

the fabric,- Coating of open fabrics possible,

-Less adhesion-Difficult to have high solid add-on

- High technical knowledgenecessary

Conventional paste or foam coating methodsKnife over air

Blade selective, must be sharp Solid add on 5-50 g/m2

Fabric selective , cannot operate on coarse structure fabrics

Knife over roller Suitable for paste and foam coating, Solid add on 25-250 g/m2

Coating thickness rely on blade and fabric gap


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Screen coating Solid add on 5-120 g/m2

Only suitable for water based coating foam or paste

Can do foam finishing for its higher penetration

Can do color coating

Blade typesConventional method to control application of foam/paste by options of blades and

angle of the blade


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Other foam application methods

Why semi/un-stable foam is not used from 1980sReasonsFoam collapse all the time affect foam concentration esp. semi-stable and unstable

foam. Even the collapsing time is in seconds, collapsed foams chemical concentration ismuch high than fresh foam.ResultsUnevenness across the width and tailing

Problems must be solved to use semi/un-stable foamFoam must collapse the same across the whole width.

Foam must collapse the same to the fabric from start to end.

Conventional foam application control Holland methodHolland Method: Two pipes with outlet holes inside screen for mixing fresh and collapsedfoamsSince foam is not linear collapsing ,fresh foam and collapsed foam mixing do

not give the same chemical concentration across the width.


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Suitable for stable and nearly semi-stable foam ,but still have strips ( dyestuff indicator in foam)

Conventional foam application controlMoving pipe methodMoving pipe method: Foam pipe moving across the fabric width before coating bladeFoam rolls collapsed and fresh as pipe moves leading to chemicals concentrationvariation across the width.

Suitable for stable foam ,but in case of semi/un-stable foam it has zig-zag unevenness

Conventional foam application controlEnglish divided pipe control methodBy dividing the main foam inlet pipe into 3 pipes ,control the pipe valves to control foam

flow across the width Still have stripes since foam is always fresh in the middle( lesschemical concentration) less fresh near the sides(high chemical concentration)whatever adjustment of the pipe valves


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Suitable for stable foam ,but in case of semi/un-stable foam shade is always lighter in the middle than

edges

Conventional foam application control German multi divided pipe method Main pipe isdivided into two , then each divided into two again..,50%/50% dividing is very difficult

to control. Foam near outlet pipe exits are fresher (chemical concentration is low) .

Suitable for stable foam ,but for semi/un-stable foam applicated foam layer has divided strips

Conventional foam application controlUS parabolic box methodFoam goes through a parabolic box with a parabolic plate in the middle, then pressed

out through a slot. Foam collapse the same across the fabric width , leads to an even

application of foam across the width.


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Distances of foam moving from inlet to slot are all equal

Suitable for stable and unstable foam , even application if dyestuff put into chemical asan indicator.

Disadvantage: Parabolic box have large space to fill and drain leading to difficulty incleaning and slow response of production lines. Fabric width is limited to parabolic box

width, will have high chemical concentration at edges if fabric is narrower than boxwidth.

foam coating process review

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