How To Choose Lubricant For PVC Foam Board

In the production of PVC foam board, the selection of lubricating wax is crucial, which directly affects the processing performance, foaming quality, surface effect and physical properties of the final product. Excellent lubricating wax needs to meet the following key requirements:

1. Excellent lubrication performance, balanced internal and external lubrication

Internal lubrication effect: reduce the friction between PVC molecular chains, promote plasticization, make the melt flow better, and avoid poor cell structure due to uneven plasticization.

External lubrication effect: reduce the adhesion of melt to equipment (such as screws, molds), prevent thermal decomposition, and ensure that the surface of the board is smooth and does not stick to the mold.

Balance: Excessive external lubrication will cause delayed plasticization and affect foaming; excessive internal lubrication may make the melt viscosity too low and the cells easy to break.

Recommended wax types:

Polyethylene wax (PE wax): strong external lubricity, suitable for rigid PVC foam board.
Oxidized polyethylene wax (OPE wax): contains polar groups, has better compatibility with PVC, and has both internal and external lubrication.

Compound lubricating wax (such as ester-modified PE wax): balances internal and external lubrication and improves processing stability.

2. Appropriate melting point and thermal stability

Melting point requirements: Generally, waxes with a temperature of 100–140°C are selected to adapt to the PVC processing temperature (160–220°C).

Waxes with a melting point that is too low (such as stone wax) are easy to volatilize, affecting the long-term lubrication effect.

Waxes with a melting point that is too high (such as PTFE wax) may be unevenly dispersed, affecting the surface quality.

Thermal stability: It does not decompose or volatilize at the PVC processing temperature, avoiding the generation of odor or affecting the effect of the foaming agent (such as AC foaming agent). Recommended wax:

High density polyethylene wax (HDPE wax): high melting point (110–140℃), good thermal stability.

Fischer-Tropsch wax: narrow molecular weight distribution, controllable melting point, stable lubrication effect.

3. Good dispersibility and compatibility

Dispersibility: wax powder needs to be evenly dispersed in the PVC melt to avoid agglomeration and surface defects (such as pitting and streaks).

Particle size recommendation: 5–20μm (too fine is easy to agglomerate, too coarse affects the surface finish).

Compatibility: no adverse reaction with PVC resin, stabilizer, foaming agent and other formulation components.

For example, oxidized polyethylene wax (OPE wax) is more compatible with PVC than ordinary PE wax.

4. No influence on foaming structure

Cellular uniformity: Lubricating wax should not interfere with the decomposition of foaming agent or the growth of bubbles, otherwise it will lead to uneven cell size, collapse or excessive closed cell rate.

Melt strength: Proper lubrication can improve melt elasticity, make bubbles grow stably, and avoid merging or rupture.

Optimization method:

Internal lubricant (such as GMS) is used with foaming agent to promote uniform foaming.

The amount of external lubricant (such as PE wax) needs to be controlled to prevent excessive delay in plasticization.

5. Low migration, prevent precipitation (“frost spraying”)

Problem: Inferior lubricating wax is easy to precipitate on the surface of the board to form white powder, affecting the appearance and subsequent processing (such as printing, lamination).

Solution:

Use high molecular weight wax (such as PE wax with high polymerization degree).
Oxidized modified wax (OPE wax) is preferred because it is more compatible with PVC.

6. Environmental protection and regulatory compliance
No heavy metals: Avoid lubricants containing harmful substances such as lead and cadmium (such as lead stearate).
Low VOC: Meets environmental protection requirements such as RoHS and REACH, and is suitable for applications such as food packaging and building materials.
Recommended environmentally friendly wax:
Calcium zinc stabilizer matching wax (such as TS-5208 product of Tianshi wax powder).
Biological-based lubricants (such as erucic acid amide, used for special environmental protection needs).

7. Practical application suggestions
Small-scale optimization: Test the plasticizing time through a torque rheometer and adjust the lubricant ratio (usually 0.3–1.5phr).
Observe the foaming structure: Analyze the uniformity of the foam cells with a microscope and adjust the internal and external lubrication ratio.
Surface inspection: Check the gloss and precipitation of the board, and optimize the type and amount of wax.

Summary: Core standards of excellent lubricating wax
✅ Lubrication balance (internal/external lubrication coordination)
✅ Thermal stability (no decomposition, no volatility)
✅ Uniform dispersion (no agglomeration, no surface defects)
✅ Cell-friendly (does not affect foaming structure)
✅ Low migration (no precipitation, no frosting)
✅ Environmental compliance (no heavy metals, low VOC)

When selecting, it is necessary to combine the specific formula, foaming process and terminal needs, and cooperate with suppliers for customized adjustments.