1. The Three Core Issues of Coating Sedimentation: Phenomena, Diagnosis and Root Causes
In the paint, ink, and chemical color-matching industries, sedimentation of materials within raw material tanks has long been a key issue affecting production efficiency and product quality. Materials such as pigments and color pastes are highly prone to separation and settling when left to stand, due to differences in the specific gravity of their components. Sedimentation not only leads to color deviations and equipment blockages, but also results in material wastage and increased production costs. As a critical supporting process for paint dosing machines, anti-sedimentation in raw material drums directly determines color-matching accuracy and production stability.
This article will systematically analyse how to resolve sedimentation issues in water-based, UV, and solvent-based materials, focusing on paint dosing machines such as the DF-M, DM Series, lab dosing machine, and D2-INK.
The phenomenon whereby the solid components of a coating (primarily fillers and pigments) sink to the bottom of the container during storage is known as coating sedimentation, also referred to as settling.
When sedimentation is severe, and particles such as pigments and fillers in the coating have settled at the bottom and agglomerated, they become difficult to redisperse by stirring alone, forming dense lumps; this is referred to as caking.
It should be noted that most types of coatings exhibit varying degrees of sedimentation, which is normal; however, if caking occurs and the material is difficult to disperse, this constitutes a quality issue.
Upon opening the paint bucket, first observe whether there is a layer of clear liquid on the surface of the paint; if so, settlement is highly likely. Next, insert a stirring rod into the bucket and quickly lift it out after approximately 30 seconds. If the color and consistency of the paint adhering to the stirring rod are uniform throughout, there is no settlement. If the paint is thinner at the top and thicker at the bottom, and there is a sensation of resistance when stirring the bottom, settlement has occurred. If the stirring rod cannot reach the bottom of the container, and the sediment at the bottom has hardened, making it impossible to stir the paint evenly, this indicates the presence of clumping.
(1) Pigments and fillers that have not been ground finely enough, poor dispersion, and subsequent agglomeration of pigments with the resin;
(2) Factors such as an excessively high pigment-to-binder ratio in the formulation and high density of pigments and fillers can easily lead to sedimentation;
(3) Excessive addition of thinner results in excessively low viscosity, causing the coating to lose its normal surface suspension state, leading to the settling of pigments and fillers;
(4) Prolonged storage beyond the coating’s shelf life causes the coating to deteriorate, particularly when left undisturbed for extended periods. If colored paints are stored for too long, the high density of pigments and fillers causes them to settle at the bottom of the container, eventually forming a hardened mass. Some resins may also deteriorate.
(5) Storage temperature is too high; generally, the optimal storage temperature for paints is between 15 and 25 °C. At temperatures exceeding 30 °C, the suspension properties of certain pigments and resins in the paint are compromised, causing the paint’s viscosity to decrease and leading to sedimentation and caking.
Water-based materials possess unique physicochemical properties. Pigment dispersion in water-based systems is relatively stable; however, due to the high surface tension of water, pigment particles will still settle slowly.
For water-based materials, large-scale paint dosing machines such as the DF-M, DM Series, and lab dosing machines employ a highly efficient recirculation system. Two hoses are fitted to the raw material drum:
Discharge hose: one hose draws the material out of the drum to complete the dispensing process
Return hose: after dispensing, any excess material passes through a diaphragm pump and returns to the drum via this hose
The cycle repeats as follows: “from the tank → discharge pipe → diaphragm pump → return pipe → back to the tank”. This not only prevents material wastage but also keeps the material in constant motion, thereby preventing sedimentation.
UV materials (ultraviolet-curing inks/coatings) and solvent-based materials have higher viscosities, and the difference in specific gravity between the pigments and the resin system is more pronounced. Such materials are more prone to separation and sedimentation when left to stand. To address this characteristic, our large-scale paint dosing machines are fitted with a stirring device on the drum lid to resolve this issue.
Our drum lid stirring device is mounted directly above the lid of the raw material drum. It is extremely simple to operate and features two main control systems:
There is a button on the drum lid; pressing this button activates the lifting system to lower the stirring blades precisely into the drum or raise them out of it. The lifting height can reach up to 1 metre. If the raw material drum is too large, we can also supply a longer lifting mechanism.
This design offers significant advantages:
When staff are replacing the material drum, the stirring device is simply raised, and the drum lid removed
It is compatible with drums of various specifications (different heights and diameters)
Operation is simple; all steps can be completed with a single button press
A single computer can control the agitation speed, duration, and mode. Workshop staff simply need to set the most suitable agitation parameters based on the characteristics of the material (viscosity, specific gravity, sedimentation, etc.) to complete the process.
The advantages of computer control are:
Precision: Computer control eliminates the risk of inadequate agitation that can occur with manual operation
Timed operation: Stirring can be scheduled (for example, to occur automatically several times a day) without the need for manual intervention
Traceability: Stirring records can be archived, facilitating quality traceability
The D2-INK is an exceptionally convenient piece of equipment. It does not require you to consider whether your material is water-based or solvent-based, as it is equipped with internal stirring blades.
The impeller blades are arranged on a single shaft; when the machine is running, the shaft rotates in unison with the machine, and the blades rotate via their shaft, thereby ensuring comprehensive mixing of the entire batch.
Axial flow: The material moves up and down along the axis.
Radial flow: The material moves from the centre of the shaft towards the tank walls.
Shear dispersion: The edges of the impeller blades exert shear forces on the material, breaking up agglomerated pigment particles.
The agitator blades within the raw material drum also operate during mixing, ensuring that the material inside the drum remains uniformly dispersed at all times.
Integrated design: The agitator is integrated within the raw material drum, eliminating the need for external equipment.
Space-saving: It does not occupy any additional space outside the drum.
Ease of operation: Simply start the machine to begin mixing; no lifting, installation or other operations are required.
It is crucial to select the appropriate anti-sedimentation solution based on the type of material and the severity of sedimentation:
| Material Type | Severity of Sedimentation | Recommended Solution |
| Water-Based Materials | Minor sedimentation | Dual Hose + Diaphragm Pump |
| Water-Based Materials | Severe sedimentation | Drum Lid Agitator |
| UV Materials | Minor Sedimentation | Dual Hose + Diaphragm Pump |
| UV Materials (especially white) | Severe Sedimentation | Drum Lid Agitator |
| Solvent-Based Materials | Any Degree | Drum Lid Agitator |
In addition to installing agitators in the equipment, there are steps you can take when mixing pigments to prevent sedimentation.
(1) When formulating coatings, consider an appropriate pigment-to-binder ratio; generally, this should not exceed 2:1, except for special grades. Where possible, select pigments and fillers with lower density. Certain pigments, such as red lead powder, chrome yellow, mica iron oxide, iron red and precipitated barium sulphate, have relatively high densities; these should be used sparingly or, where appropriate, replaced with lower-density alternatives.
(2) The viscosity of the coating should not be too low, and the selected pigments and fillers must not react with one another. As zinc powder, aluminium powder and zinc oxide are relatively reactive, they should be avoided where possible in coatings with poor storage stability, or packaged separately.
(3) Add anti-settling agents to the coating; by utilising the specific properties of small amounts of additives, thixotropic coatings can be formulated to alter the suspension state of the coating. Commonly used anti-settling agents include the stearic acid series, fumed silica, modified bentonite and hydrogenated castor oil. There are now many varieties of imported anti-settling agents available; generally, an addition of 0.1%–0.5% is sufficient to prevent settling, whilst an addition of 2%–3% can produce a thixotropic coating capable of forming a thicker film.
(4) Coatings should be stored in a cool, well-ventilated place. Attention must be paid to the storage life of the coatings, and the first to be received should be the first to be used. Particular care must be taken with coatings that have a short storage life, such as chlorinated rubber, vinyl chloride and polyurethane-based coatings.
(5) For coatings that have settled, they may be used after thorough stirring. In the event of caking, first pour out the free-flowing portion, then use a scraper to dislodge the sediment from the bottom of the container. Once broken up, pour the free-flowing medium back into the original container and mix thoroughly. If this method fails to achieve a homogeneous mixture and dry, caked sediment remains, the coating must be scrapped or downgraded for use.
Managing anti-sedimentation in raw material drums is a critical aspect of color-matching production. The correct selection and standardised use of anti-sedimentation devices not only ensure color-matching accuracy and product quality but also extend equipment lifespan, reduce material wastage and deliver long-term, stable benefits for production.
Should you require further details regarding anti-sedimentation devices for paint dosing machines, please feel free to contact us at any time for professional technical support and product selection advice.
