Pressed Candy OEM Film Coating: Weight Gain, Inlet Temperature and Spray Atomisation Settings
Film coating is usually treated as the cosmetic last step in pressed candy production. On the shop floor it is closer to a full audit of the tablet core: if the core is soft, friable or burred, the coating pan will amplify every one of those faults into picking, rough surfaces and edge chipping. Brands running pressed candy OEM programmes routinely spend weeks on the core formula and say almost nothing about coating parameters, then discover at first-article stage that the appearance fails and reworking costs more than the formulation work did. Coating is not one set point but the balance of inlet air, exhaust, atomisation and pan speed.
1. Decide what the coating is actually for
Weight gain and material system follow the objective. When taste masking is the goal, the film has to be continuous and dense, which usually means 2 to 3 percent of tablet weight; less leaves the off-note uncovered, more starts pushing out disintegration time. When moisture barrier is the goal, the emphasis shifts to the barrier properties of the polymer and to coverage at the tablet edges, because moisture almost always enters through the corners rather than the faces, and the weight gain has to be a little higher with an explicit edge-coverage check. When colour is the goal, weight gain can be lower and the difficulty moves to pigment dispersion and batch-to-batch shade consistency. Problems start when a single layer is asked to do all three. The cleaner approach is to split the job: a functional subcoat for barrier or taste, then a coloured topcoat for appearance.
2. Weight gain: calculate it, then correct for real losses
The theory is simple. Multiply core weight by the target gain, divide by the solids content of the suspension, and you have the volume to spray. Reality diverges through overspray, droplets lost to the exhaust, and uneven uptake while cores build their first film. In a 30 to 50 kg pan, actual consumption typically runs 8 to 15 percent above theory; larger pans lose less but distribute less evenly. That is why sampling should not be charged with a single calculated batch. Make the suspension in portions, weigh the bed as you go, and use the measured weight-gain curve to derive the charging factor for production. One more variable deserves attention: core weight variation. If tablet weight drifts beyond plus or minus 3 percent, the same sprayed volume produces visibly uneven gain and the batch comes out in two shades.
3. Inlet temperature, exhaust and pan pressure
For aqueous film coating the inlet usually sits between 55 and 75 C, with a bed temperature of 40 to 45 C as a safe working band. The classic mistake is to raise inlet air the moment the bed looks cool. Hotter inlet dries the droplets before they ever reach the tablets - spray drying inside the pan - and the coating polymer leaves as dust through the exhaust, leaving a rough, sandy surface. The correct sequence is to read bed temperature first, then check that exhaust volume matches inlet volume, and only then touch inlet temperature. A slight negative pressure in the pan, typically minus 10 to minus 30 Pa, is what you want; too much pulls in untreated air and undermines the cleanroom envelope, while positive pressure pushes suspension mist out of every seal. Pan speed should move with the process: slower at the start while cores are slick, faster once the film has built and the tablets can tumble evenly, then slower again during final drying to stop tablets abrading each other.
4. Atomisation and gun layout: droplet size sets the finish
Atomising pressure sets droplet size. Too large and the droplet lands and dries before it can level, giving orange peel or visible speckle. Too small and the airflow carries the droplets away, coating efficiency collapses and the pan walls collect the material instead of the tablets. The usual method is to set atomisation until the spray cone is crisp with no dripping, then use pattern air to adjust coverage. Gun-to-bed distance is typically 20 to 30 cm: closer risks local overwetting and picking, further increases overspray loss. With multiple guns, adjacent cones should overlap slightly but never fire directly at each other, because colliding droplets merge into large ones mid-air. Suspension viscosity has to match the guns as well - higher solids means higher viscosity and coarser atomisation, so it often has to be diluted to a sprayable range at the cost of longer application time. Change one variable per trial. It is the single discipline that most shortens a sampling programme.
5. Coating defects: cause and the order to fix them
Bridging, where the film pulls away from the debossed lettering, usually means the surface energy of the core and the wetting of the suspension are mismatched, or that drying is fast enough to build shrinkage stress in the film. Lower inlet temperature first, then raise spray rate. Orange peel and rough surfaces point at insufficient atomisation pressure or excessive gun distance. Picking and twinning mean the bed is too wet: cut spray rate or raise pan speed before reaching for more heat. Shade variation has to be diagnosed before it is treated - speckled dark spots indicate poor pigment dispersion and belong back in the mixing tank, while whole-tablet light and dark indicates uneven spray and belongs at gun distance and pattern. Worn edges are nearly always a core friability problem that coating can only soften by slowing the pan; the root cause is upstream at the press. Change one variable at a time; adjust three together and the next trial starts from nowhere.
6. What to lock down before scale-up
Coating is not a process to keep re-tuning once production starts, so sampling has to produce a signed parameter set covering six items: coating system and supplier; target weight gain with tolerance; bed and inlet temperature ranges; atomisation and pattern pressures; spray rate and total application time; and an appearance acceptance standard that specifies the light source for shade comparison and the sealed reference photos. Three pilot batches at intermediate scale are worth insisting on, because a single sampling pan behaves differently from a production run where the pan body retains heat and the suspension sits for hours. Written into a process instruction, those numbers turn coating from a cosmetic afterthought into a genuinely controlled unit operation.
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About Guangzhou Mesen Health Biotechnology Co., Ltd
Guangzhou Mesen Health Biotechnology Co., Ltd is located in the Huashan Science and Technology Park, Huadu District, Guangzhou. The company has focused on OEM and ODM services for the big health industry for nearly 20 years, operating dedicated research, production, sales and management centres, and maintaining long-term strategic partnerships with well-known Chinese medicine colleges and research institutions. Capabilities span pressed candy, gummies, capsules, solid beverages, herbal teas, plant beverages, protein powders, dietary supplements and enzyme jelly - from formulation development through contract manufacturing. For details on minimum order quantities, sampling lead times and quotations, see our manufacturing advantages and product range, or contact us for a tailored proposal.
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