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PVDC latex technical information
Coating equipment
   Example of coating machine conformation

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Anchor coating (AC) head: Coats the adhesive (AC agent)
Top coating head: Coats the PVDC latex
Drier: Dries the coated AC agent and PVDC latex

Materials of coating machine
Contact with iron, aluminum, or copper will cause PVDC latex to coagulate; never use these materials where they will contact the PVDC latex.
Materials which can be used in contact with PVDC latex include polyethylene, polyvinyl chloride, epoxy-lined steel, FRP, glass-lined steel, and SUS 316 stainless steel.
Because a small amount of hydrogen chloride is generated during drying, anti-corrosion measures are necessary for materials which will not contact the PVDC latex.

Coating methods

Air knife coating:
Used principally for coating film and paper. Coating weight easily changed. Suitable for small lots with frequent changeover.




Reverse gravure roll coating:
Used principally for coating film and paper. High coating speed possible. Suitable for mass production.




Spray coating:
Used principally for fiber binder and polyurethane foam.




Dip coating:
Used principally for polyurethane foam.




Effect of storage conditions on physical properties
Physical properties of PVDC latex are greatly affected by storage temperature. Improper storage temperature may result in diminished coating performance. Always maintain storage temperature at 3–30°C.

pH and chlorine ion concentration:
The pH and Cl-ion concentration of the latex will increase with higher storage temperature.

Viscosity:
Viscosity of the latex will decrease with higher storage temperature.

Surface tension:
Surface tension generally tends to increase with higher storage temperature.

Coating properties:
Barrier properties of coatings deteriorate with higher storage temperature. Transparency of coatings also deteriorates with higher storage temperature, with color tending to become yellow or reddish.

Latex condition:
Latex which has frozen will not recover its original properties when melted. High temperature may cause coagulation. Even when stored in the proper temperature range of 3–30°C, the quality of the latex is not guaranteed beyond the specified shelf life.


Coating with PVDC latex
For reference, typical coating on film is described here.


Selection of substrate film:
Substrate film must be able to withstand the drying temperature, typically 100°C or higher.
To obtain a uniform coating, select a substrate film grade with good thickness uniformity.
Avoid substrate film containing antistatic agent. Such antistatic agent tends to bleed during coating, resulting in poor adhesion and poor coating uniformity of anchor coat and PVDC latex.

Corona treatment:
Corona treatment is recommended to ensure strong adhesion between substrate film and anchor coat. This is especially vital when OPP or other low-adhesion material is used as substrate film.

Selection of anchor coat (adhesive) agent:
An undercoat of adhesive, usually called anchor coat (AC), is necessary to obtain good adhesion of PVDC latex coating on substrate film. An unsuitable AC agent will cause coloration when coated with PVDC latex. Always perform trial coatings to confirm the suitability of the AC agent. A range of AC agents may be used, both solvent-borne and water-borne. In our experience, excellent results have been obtained with polyurethane AC agents.

Additives:
Additives may be used to improve surface smoothness and anti-blocking. Typical additives include inorganic amorphous silica and organic wax. Caution is required as an excessive additive loading will cause poor barrier performance and hazing. Amorphous silica will not disperse sufficiently if added directly to PVDC latex; first add silica to water and mix until well dispersed, then blend this mixture with the latex.

Adjustment of solids content:
When diluting PVDC latex with water to adjust solids content, never use water with hardness greater than 300 ppm. Higher water hardness will cause coagulation.

Drying:
To prevent skinning, it is generally recommendable to set the temperature a little lower in the front part of the dryer and a little higher in the back part of the dryer.

Wind-up:
Caution is required with respect to the wind-up tension and resulting inter-layer pressure in the wound roll. Excessive pressure may cause blocking.

Aging:
Heat treatment after coating will improve barrier performance. This is generally referred to as aging. It is recommended that aging always be performed to obtain the best barrier performance.


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