Metal coil stock hanging in a workshop, the strip surface bright and clean
The coating paste for synthetic leather holds a layer of microfoam that shows nothing at all during embossing, yet the moment the release paper is peeled back the surface is covered with fine pitting and bright spots, and the whole roll of base fabric can only be downgraded, with the loss counted by the metre.
Chemi Tech makes defoamers for synthetic leather coating, artificial leather surface treatment and coating systems, from the defoamer KM-680 series. Which grade is added depends on whether the coating is solvent-borne or water-based, whether the coating process is roller or curtain, and whether an embossing step follows. In water-based coating systems, KM-680 is the general-purpose water-based grade and tolerates high salt, so it is used widely; where the film appearance has to be high and silicone spots must be avoided, the silicone-free KM-192 is the closer fit and also works in silicone-free processes. Send over the paste system and the coating parameters, and we will look at these items together and recommend the right option for you.
Advantages of Chemi Tech Defoamers
The Chemi Tech defoamer KM-680 series disperses readily in the paste and does not form local high-concentration pockets, so craters and pinholes do not appear on the coated face. It also knocks down microfoam properly, bringing out the fine invisible bubbles in the paste so that no pitting shows once the paper is lifted. Its compatibility is good as well, so it does not separate or precipitate when placed together with a water-based resin system. It does not interfere with the forming effect of subsequent embossing either, and the definition of the grain is retained. On top of that, the effect on gloss is small, so the haze value of the finished leather stays stable.
A note from Chemi Tech: the behaviour above comes from a typical water-based synthetic leather coating condition. Change the paste system or the coating method and the results move. Confirm on a small sample before scaling up.
Industry Pain Points and Solutions
Foam in synthetic leather is hard to treat because it hides inside the coating and only shows itself at the step where the release paper is peeled.
Watching the dosage and not the point of addition is the easiest one to get wrong. Pour the whole drum into the mixing tank and the additive never disperses, dragging in a field of craters instead. Chemi Tech splits the addition point into two, at the mixing stage and before coating, with the mixing stage pressing down mechanical foam and the pre-coating point taking out the fine bubbles.
What follows is the compatibility between the defoamer and the system. Pick the wrong type and the paste throws a layer to the surface overnight, with bright spots across the coated face. Chemi Tech's approach is to validate compatibility in both the standing and the heated state first, and to scale up only once both pass.
One more point is easily missed: it holds in the laboratory and fails on the line. Stirrer speed and coating line speed are far apart, and the dynamic foam generation is a different matter altogether. Chemi Tech's approach is to run the dynamic foaming comparison against the customer's actual coating line speed and roller pressure conditions.
The compatibility and dynamic foaming comparison data come from us, and the dosage and the addition points are calibrated together, so two more lines on the batch record are all it takes.
Typical Conditions and Verification
Customer: a synthetic leather manufacturer in Zhejiang, applying it to the mixing and coating sections of a water-based coating line.
This mill's water-based coating had been running heavy on fine pitting, the surface after embossing needed spot inspection for bright spots, and every batch ended with several hundred metres downgraded. The solution offered by Chemi Tech defoamers was: against the paste system and the coating parameters, KM-680 was selected from the KM-680 series, the addition point was split into the mixing stage and the pre-coating point, and the dosage was recalibrated to the coating line speed. After the change the fine pitting after the paper was lifted largely disappeared, the metres lost to downgrading came down very low, and the haze value of the finished leather held steady. The turbidity meter in the quality room is now brought out only when the paste is changed.
Frequently Asked Questions
Will the defoamer leave silicone spots on the coating surface?
That risk does exist: once the dosage of a silicone-bearing type runs high, the surface tension difference shows up and the coated face looks uneven. The KM-192 Chemi Tech supplies to synthetic leather plants is silicone-free and has been compared on systems with high appearance requirements, and at normal dosage it leaves no silicone spots. Give the paste system, the coating method and the appearance acceptance standard to the Chemi Tech technical department, and we will run the compatibility and surface appearance comparison for you, with the dosage settled once the data is out.