In the production of sports shoes, leather shoes and other footwear products, consumers often pay attention to the gloss,
wear resistance or color brightness of the upper, but rarely pay attention to the tiny but far-reaching "invisible killer" on the
surface of the coating - foam. When bubbles are generated during the mixing, spraying or drying process of the coating,
the upper may leave defects such as pinholes, orange peels or even delamination, which directly reduces the product yield.
The shoe coating defoamer is the key technology to solve this problem. It provides full-process protection for shoe coatings
from production to film formation through precise chemical reactions.
1. The "destructive power" of foam: from production defects to cost crisis
On the production line of shoe coatings, the harm of foam is far more than surface defects. Taking water-based polyurethane
coatings as an example, the emulsifiers, thickeners and other ingredients contained in its formula are very easy to generate
bubbles when stirred or sprayed at high speed. If these bubbles are not eliminated in time, they will lead to:
Coating defects: pinholes and shrinkage holes will form after drying, reducing water resistance and wear resistance;
Equipment loss: foam overflows the mixing tank, polluting the production line and increasing cleaning costs;
Raw material waste: repeated spraying is required to cover up defects, resulting in an increase in paint consumption of 15%-30%;
Delivery delays: the increase in rework rate extends the production cycle and affects order delivery efficiency.
A sports brand once scrapped a batch of shoe upper coatings worth 5 million yuan due to foam problems. Finally, the rework
rate was reduced from 12% to less than 2% by introducing silicone defoamers, saving more than 2 million yuan in annual costs.
2. The "double defense" of defoamers: the chemical game between foam breaking and foam suppression
The core mechanism of defoamers for shoe coatings is to achieve a "foam breaking-foam suppression" cycle by reducing the
surface tension of the liquid:
Quick foam breaking:
hydrophobic particles (such as fumed silica) in the defoamer migrate to the surface of the foam liquid film, forming a local
surface tension difference, causing the liquid film to break from the weak point;
Persistent foam suppression:
polyether-modified silicone oil and other ingredients form a monomolecular film in the coating to prevent the stable formation
of new bubbles, and the foam suppression time can reach more than 48 hours;
Directed migration technology:
By regulating the hydrophilic-hydrophobic balance of the molecular chain segment, the defoamer is accurately positioned at
the gas-liquid interface in the coating system, improving efficiency while reducing the risk of shrinkage.
Take the block polyether-modified silicone oil defoamer developed by an international chemical company as an example.
Through technical cooperation with Tsinghua University, it has increased the defoaming speed to 3 times that of traditional
products, and remains stable under extreme environments of pH 2-14.
3. "Customized solutions" in the field of footwear materials
Different footwear materials have significant differences in their performance requirements for defoamers, and targeted
formulas need to be selected:
Sports shoe uppers:
Scenario: High-elastic polyurethane coating spraying
Pain point: High-speed spraying is prone to microbubbles, affecting air permeability
Solution: Use polyether/fatty alcohol composite defoamer, which can achieve rapid defoaming at an addition amount of
0.01%-0.1% without affecting the flexibility of the coating. After a domestic sports brand applied it, the pass rate of the
upper air permeability test increased from 78% to 95%.
Leather shoe finishing:
Scenario: Solvent-based acrylic resin coating
Pain point: Traditional silicone defoamers easily cause the coating to become cloudy
Solution: Use a silicone-free polyether defoamer to achieve perfect compatibility with the resin by adjusting the HLB value
(hydrophilic-lipophilic balance value). After a high-end leather shoe brand applied it, the glossiness of the coating increased
by 10 units (60° angle detection).
Safety shoe protective layer:
Scenario: Epoxy resin thick coating process
Pain point: High viscosity system (>15000cps) defoaming is difficult
Solution: Use two-addition method - add 70% mineral oil defoamer in the premixing stage, and add 30% silicone defoamer
in the paint mixing stage, so that the 10mm thick coating will not produce bubbles when baked at 120℃.
4. Technology iteration: from "defoaming" to "intelligent protection"
As shoe materials develop towards lightweight and functionalization, defoamer technology presents three major trends:
Nano-level dispersion technology: control the defoamer particle size to D90<10μm through microencapsulation, and improve
the dispersibility in ultra-fine pigment systems;
Multifunctional composite: develop defoaming-leveling-hardening three-in-one additives to reduce process steps;
Biological-based substitution: use renewable raw materials such as castor oil derivatives to meet the EU REACH regulations
on VOC restrictions.
The AGITAN® 206E defoamer launched by a German company has achieved 100% replacement of bio-based raw materials.
The application test in a certain outdoor brand shoe material shows that its defoaming efficiency is on par with petrochemical
products, but the carbon footprint is reduced by 65%.
5. Future Outlook: "Symbiotic Evolution" of Defoamers and Shoe Materials
With the emergence of new technologies such as 3D printing shoe materials and intelligent temperature control coatings,
defoamers are upgrading from single functional additives to "material solutions". For example, the supercritical CO2 defoaming
system developed for liquid metal spraying process can achieve instant defoaming at a low temperature of -50℃; while the
conductive coating defoamer used for electronic shoe materials needs to meet the triple requirements of defoaming,
conductivity, and bending resistance at the same time.
In this micro-revolution of materials science, shoe coating defoamers are playing the role of "invisible guardians" to promote
the footwear industry towards higher quality and more sustainable directions.
