PVA Film Cast Film Production Process: Complete Guide for Water Soluble Film Manufacturing

PVA film cast production is currently the most widely adopted and most stable process for manufacturing water soluble film. The entire process can be summarized as: dissolution and defoaming → casting and film formation → drying and setting → post-treatment. This guide breaks down each stage with the key parameters—solids content, temperature, air velocity, and moisture content—used in PVA film and water soluble film production.

1. Preparation of the Stock Solution and Defoaming

PVA powder, plasticizers, surfactants, and other additives are added to water and stirred for dissolution at 80–100°C (at atmospheric pressure) or 90–120°C (under pressure). Complete dissolution typically requires 3–10 hours.

Key control points for PVA film stock solution:

• Solids content:usually controlled between 15% and 35%
• Defoaming method:vacuum defoaming or static defoaming
• Defoaming conditions:50–100°C for 2–30 hours

The solution must undergo defoaming; otherwise, residual bubbles will remain in the water soluble film and cause defects.

2. Casting and Primary Drying

After defoaming, the temperature of the stock solution must be controlled at 60–98°C (preferably 70–95°C). If the temperature is too low, the viscosity becomes too high; if too high, foaming tends to occur during casting.

The stock solution is cast through a T-shaped die onto a support. For water soluble film, the support may be:

• A metal roll (surface temperature 50–110°C)
• A PET release film
• A steel belt

On the support, the film must be dried until the volatile content drops to 5–50% (i.e., it still retains some moisture, sufficient to maintain its own strength without being sticky to the touch) before it is peeled off.

The drying method typically involves blowing hot air onto the non-contact side of the film: 70–120°C, air velocity 1–10 m/s.

3. Post-Drying and Heat Treatment

After peeling, the film usually passes through a set of drying rolls, allowing the two sides of the film to alternately contact the roll surfaces. This makes the crystallinity of both sides more uniform.

Drying roll temperature control:

• Range:40–110°C
• Preferred:50–85°C

Avoid excessively high temperatures, which cause excessive crystallization and affect the water solubility of the PVA film.

4. Embossing and Winding

This is a step unique to water soluble film. To prevent blocking, the film usually needs to pass through embossing rolls before winding, impressing fine concave-convex patterns on the surface.

Embossing parameters:

• Temperature:60–150°C
• Pressure:2–8 MPa

Finally, the moisture content of the finished PVA film must be controlled at 3–15 wt% (preferably 5–13 wt%). If the moisture content is too low, the film becomes brittle; if too high, it tends to block.

5. FAQ: PVA Film & Water Soluble Film Production

Q1: What are the core steps of the PVA film cast production process?
A: The core steps are dissolution and defoaming, casting and film formation, drying and setting, and post-treatment (including embossing and winding).

Q2: What solids content is used for PVA film stock solution?
A: Typically 15–35%.

Q3: Why must the stock solution temperature be controlled during casting?
A: If too low, viscosity becomes too high; if too high, foaming occurs during casting.

Q4: Why does water soluble film need embossing?
A: Embossing prevents blocking after winding and improves handling.

Q5: What is the ideal moisture content for finished PVA film?
A: 3–15 wt%, preferably 5–13 wt%.

6. Conclusion

The PVA film cast production process depends on stock solution stability, casting temperature window, drying gradient, and final moisture control. By controlling the four stages—dissolution and defoaming, casting and drying, post-drying and heat treatment, and embossing and winding—you can consistently produce water soluble film with fewer bubbles, uniform crystallinity on both sides, and consistent water solubility.