As the core film-forming matrix of waterborne coatings, waterborne acrylic lotion’s monomer ratio, polymerization process, core-shell structure, emulsification system and crosslinking mode directly determine the film-forming performance, weather resistance, storage stability and construction suitability of coatings. At the paint production and construction site, most of the paint film defects (low-temperature cracking, high-temperature backtacking, water resistance and whitening, storage layering, outdoor yellowing, abnormal curing, etc.), we habitually give priority to the investigation of additives, pigments and fillers, and construction technology, but in fact, more than 70% of the stubborn systemic defects are rooted in the wrong selection of lotion or the quality defects of lotion itself.
Additive and process problems can be quickly rectified through small test adjustment, while the structural defect of lotion itself is a systematic problem. Only minor adjustment of additives can only cure the symptoms rather than the root causes, and long-term repeated quality hazards occur. This article aims at the eight high frequency disadvantages in the process of coating production, construction and service, traces the source from the polymerization mechanism of lotion, structural characteristics, selection errors, complete rectification scheme and lotion upgrading optimization standard, and adapts to the whole system of products such as architectural latex paint, elastic paint, water-based industrial paint, two-component polyurethane paint, etc.
2、 Disadvantage 1: Cracking, powdering, and lack of continuous paint film in low-temperature construction paint film
1. On site phenomena
Construction in low temperature environments (below 5 ℃) during autumn and winter, the paint film becomes rough, white and powdery after drying, with network cracks and turtle cracks appearing on the surface. The paint film has no toughness, and the powder will fall off when rubbed by hand, resulting in ineffective coverage and inability to form a continuous and dense paint film; Construction at room temperature is normal and belongs to the typical problem of low-temperature film formation failure.
2. Traceability mechanism of core lotion
The root cause is that the minimum film forming temperature MFFT of lotion is too high, which does not match the construction temperature. The glass transition temperature (Tg) of lotion is too high, the proportion of hard monomer (MMA, styrene) is too large, the content of soft monomer is insufficient, and the latex particles are extremely rigid. At low temperatures, latex particles cannot undergo plastic deformation, and cannot be tightly squeezed, fused, or overlapped between particles. They can only accumulate on the surface of the substrate and cannot form a continuous polymer film structure, ultimately resulting in loose particles, powdering, and cracking.
At the same time, the common homogeneous lotion has inherent shortcomings: if the overall Tg is reduced in order to accommodate the low temperature film formation, the high temperature film in summer will become soft and dusty; If the Tg is increased to ensure hardness, it will also lead to poor film formation in winter, which cannot balance the construction performance in all seasons. In addition, some low-end lotion have many residual monomers and uneven particle size distribution, which will further aggravate the low temperature film forming defects.
3. Precise rectification and optimization plan
Short term formula adjustment (emergency rectification): Replace high boiling point and low volatility film-forming aids with DPnB and alcohol ester dodecane instead of ordinary BCS and PMA to improve low-temperature plasticizing effect; Properly increase the amount of film forming additives (to 8% -12% of the solid content of lotion), and temporarily reduce the MFFT of the system; Strictly control the temperature of the construction environment and stop construction below 5 ℃.
Long term lotion upgrading (radical solution): eliminate ordinary homogeneous high Tg lotion and replace soft core and hard shell core-shell structure self crosslinking acrylic lotion. Using ultra soft monomers in the core to ensure low-temperature deformation fusion, and hard monomers in the shell to lock in the hardness of the paint film, solving the contradiction between film-forming properties and hardness from a molecular structure perspective; The low MFFT lotion prepared by reactive emulsifier is preferred, and the MFFT of ex factory is ≤ 5 ℃, which is suitable for the whole low-temperature construction scenario.
4. Key points for avoiding pitfalls
It is prohibited to improve film formation by adding too much antifreeze. Antifreeze can only prevent coating from freezing during storage, but cannot reduce the MFFT of lotion. It does not help film formation. Excessive addition will reduce the water resistance of the film.
3、 Disadvantage 2: High temperature paint film sticking in summer, wall dust sticking, poor stain resistance
1. On site phenomena
The paint film for construction at room temperature is normal. After exposure to high temperatures in summer, the paint film becomes soft and sticky, and the wall surface is prone to dust and mosquitoes. After long-term service, the wall surface turns black and accumulates severe dirt. It cannot be cleaned by rainwater erosion, and the hardness of the paint film is extremely low. Scratches can occur with slight friction.
2. Traceability mechanism of core lotion
The core problem is that the overall glass transition temperature Tg of the lotion is too low, and the soft monomer is excessively enriched. Some manufacturers, in pursuit of extreme low temperature film-forming property, have significantly increased the proportion of soft monomers such as butyl acrylate and isooctyl acrylate, and reduced the overall Tg of lotion (Tg<15 ℃). Excellent film formation at low temperatures, but in high temperature environments, the mobility of polymer chains is enhanced, causing the paint film to transition from a glassy state to a highly elastic or even viscous state, resulting in a significant rebound phenomenon.
At the same time, the molecular chain of ordinary non crosslinked lotion is linear structure, and there is no chemical bond cross-linking after film formation. The molecular gap is large, the film compactness is poor, the surface hardness and anti adhesion performance are extremely low, and the defects are continuously amplified under high temperature, and finally there are problems of ash and tackiness.
3. Precise rectification and optimization plan
Short term formula adjustment: appropriately reduce the amount of film-forming additives added to reduce the temporary plasticizing effect of the paint film; Paired with a small amount of high hardness hydrophobic additives to enhance surface density; Control the thickness of the paint film to avoid increased sticking caused by thick coating.
Long term lotion upgrading (radical solution): replace it with high Tg self crosslinking pure acrylic lotion, and select Tg 25 ℃ -30 ℃ core-shell lotion for exterior wall coating to ensure rigidity and stability of paint film under high temperature; The DAAM/ADH room temperature self crosslinking system is selected, and after film formation, the molecular chains undergo crosslinking reactions to form a three-dimensional network structure, greatly improving the hardness, density, and anti adhesion of the paint film, fundamentally solving the problem of high temperature adhesion and dust sticking.
4. Key points for avoiding pitfalls
It is not allowed to increase the hardness of the paint film blindly through thickeners and fillers. Too many inorganic fillers will reduce the flexibility of the paint film and cause cracking in the later stage. The problem of back sticking can only be solved through the upgrading of lotion structure.
4、 Disadvantage 3: After soaking in water, the paint film turns white, milky white, extremely poor water resistance, and local foaming and peeling
1. On site phenomena
After the drying and curing of the paint film is completed, if it is washed away by rainwater, soaked in water, or in a high humidity environment, the paint film will quickly turn white, lose its luster, and become cloudy. In severe cases, the paint film may bubble, hollow, or peel off from the substrate. After drying, the whitening phenomenon cannot be restored, and the protective performance will be completely lost.
2. Traceability mechanism of core lotion
First, the selection of lotion is at the low end, and there are too many hydrophilic groups: acetate acrylic and ordinary styrene acrylic lotion contain a large number of vinyl acetate hydrophilic groups, and the proportion of acrylic acid hydrophilic monomer is high. After the curing of the paint film, a large number of hydrophilic points remain in the molecular chain, which is very easy to absorb water molecules. Water molecules penetrate into the paint film to cause changes in the light refractive index, leading to the whitening of the paint film.
Second, the crosslinking density is insufficient: the non crosslinked linear lotion has large molecular gap after film formation, and water molecules are easy to penetrate; The low-end lotion uses ordinary small molecule emulsifier, and the system has a large amount of free emulsifier left, which remains in the paint film after film formation, forming a hydrophilic channel and continuously absorbing water and whitening.
The third is the non hydrophobic modified structure, which has a high surface energy of the paint film and cannot form a hydrophobic barrier. The continuous penetration of moisture can damage the adhesion between the paint film and the substrate.
3. Precise rectification and optimization plan
Short term formula adjustment: Strictly control the amount of wetting agents and dispersants added to avoid surface active agent residue exacerbating hydrophilic problems; Add hydrophobic additives and silane coupling agents in moderation to enhance the density of the paint film; Extend the curing time of the paint film to ensure that the additives are fully evaporated and the paint film is completely cured.
Long term lotion upgrading (radical solution): eliminate acetate acrylic lotion in indoor water resistant scenes and replace ordinary styrene acrylic self crosslinking lotion; The exterior wall, waterproof and high humidity scenes are comprehensively upgraded with silicone acrylic lotion or high water resistant pure acrylic self crosslinking lotion. The silicone acrylic lotion is grafted with silicone hydrophobic group, which greatly reduces the surface energy of the paint film and has extremely low water absorption; The self crosslinking system forms a dense network structure, closing molecular gaps and blocking water molecule permeation. At the same time, soap free lotion (reactive emulsifier system) is optimized to completely eliminate the hidden trouble of residual free emulsifier.
5、 Disadvantage 4: Short term storage delamination, water discharge, viscosity attenuation, and system instability of coatings
1. On site phenomena
When the paint is stored at room temperature for 7-15 days, a large amount of water will precipitate on the upper layer of the tank, causing the paint to layer and become thinner. The KU viscosity will continue to decrease without obvious precipitation; Under the condition of thermal storage at 50 ℃, the problem of layered water discharge intensifies sharply. After stirring, it can be temporarily restored, but after standing still, it recurs again, which is a typical system stability defect.
2. Traceability mechanism of core lotion
90% of this problem stems from the stability defect of lotion itself, rather than the problem of rheological additives: first, a large number of free small molecular emulsifiers remain in the low-end lotion, which belong to strong surfactants, and will continue to destroy the molecular network of polyurethane HEUR association thickening, leading to the collapse of the system’s low shear viscosity and rapid precipitation of water; Second, the outgoing pH of lotion is low (pH<7.5), the carboxyl group dissociation is insufficient, the charge stability is insufficient, and it cannot work together with HASE alkali swelling thickener, so the rheological structure of the system is fragile; Third, the particle size distribution of lotion is too wide, the coarse and fine particles are uneven, the settling potential of the system is unbalanced, and the phase separation is accelerated; Fourth, the stability of lotion against electrolyte is poor, and the colloidal stability of the system decreases when it is compatible with pigment and filler metal ions.
3. Precise rectification and optimization plan
Short term formula fine-tuning: AMP-95 buffer neutralizer is used to stabilize the pH of the paint system at 8.0-8.8, strengthening the charge stability of lotion; Composite water-based bentonite and cellulose reinforced low shear viscosity to compensate for rheological network defects; Strictly control the amount of wetting and dispersing agents added to avoid surface active agent stacking and damaging the system.
Long term lotion upgrading (radical solution): replace reactive emulsifier soap free acrylic lotion to eliminate interference of free emulsifier from the source; The pH, calcium ion stability and thermal storage stability of lotion shall be strictly tested when entering the factory, and low-end lotion with wide particle size distribution and unstable system shall be eliminated; For products with high storage stability requirements, core shell structure lotion is preferred. Its rigid shell can greatly improve the anti flocculation and anti stratification capabilities.
6、 Disadvantage 5: Incomplete curing of two-component waterborne polyurethane topcoat, fogging, whitening, sticking and non drying of paint film
1. On site phenomena
After the application of water-based acrylic lotion with HDI water-based isocyanate curing agent, the paint film will not dry for a long time, and the surface will become sticky. After drying, the paint film will become turbid and foggy, with poor transparency, low gloss, poor water resistance and friction resistance, which completely fails to meet the industrial paint standards.
2. Traceability mechanism of core lotion
It is a serious type selection error of lotion, which is a problem of high frequency trampling of industrial coatings. The common anionic acrylic acid lotion for construction has no effective hydroxyl functional group in the molecular chain, so it cannot cross link with isocyanate curing agent; At the same time, the residual hydrophilic carboxyl groups, free emulsifiers and small molecule additives in the lotion will have side reactions with the curing agent, consume the effective ingredients of the curing agent, and lead to incomplete crosslinking reaction.
In addition, the stability of building lotion against amine and electrolyte is poor, and the system is micro flocculated after mixing with curing agent, resulting in tiny particles inside the paint film, which is finally shown as foggy, turbid, non dry and sticky paint film.
3. Precise rectification and optimization plan
Urgent rectification: building grade acrylic lotion is completely prohibited for two-component waterborne PU system, and mixing is prohibited.
Standard upgrading scheme: special supporting industrial grade hydroxyacrylic acid aqueous dispersion. The molecular chain of this kind of lotion is precisely designed with hydroxyl functional groups, which can efficiently cross link with HDI curing agent. The film is dense, with high gloss, strong adhesion and excellent medium resistance; Simultaneously possessing strong resistance to electrolytes and amines, and compatible with curing agents without flocculation or side reactions.
7、 Disadvantage 6: Short term yellowing, powdering, loss of gloss, and poor weather resistance of outdoor coatings
1. On site phenomena
After the construction of exterior latex paint and outdoor topcoat, the paint film will turn yellow and the gloss will continue to decrease after short-term exposure to sunlight. In the later stage, the paint film will powder, peel off, and peel off, and the color and light retention performance will be extremely poor, which cannot meet the requirements of outdoor weather resistance.
2. Traceability mechanism of core lotion
The core root is the misuse of styrene acrylic lotion containing benzene ring. Styrene monomers contain conjugated structures with benzene rings, which have extremely poor UV resistance. Under long-term outdoor exposure, the benzene rings are prone to photodegradation reactions, causing molecular chain breakage and resulting in yellowing, powdering, and loss of gloss in the paint film. In order to reduce costs, some manufacturers use styrene acrylic lotion instead of pure acrylic lotion to make exterior wall coatings. Even if ultraviolet absorbers and antioxidants are added, it can only temporarily delay aging, and cannot fundamentally prevent the photodegradation of benzene ring, so long-term service will inevitably fail.
In addition, ordinary non crosslinked pure acrylic lotion has low crosslinking density, insufficient film compactness, and continuous penetration of rain, ultraviolet light and oxygen will accelerate the aging and failure of the film.
3. Precise rectification and optimization plan
The formula is rigid: all outdoor, exterior wall, weather resistant and covering products are prohibited to use styrene acrylic lotion, and low-cost replacement is prohibited.
Lotion upgrading plan: the conventional exterior wall products use weather resistant pure acrylic self crosslinking lotion, which has no benzene ring structure, excellent UV resistance, light degradation resistance, and strong color and light retention; In high-end outdoor, self-cleaning, high weather resistant scenes, the silicone acrylic modified acrylic lotion is upgraded. The silicone structure further improves the weather resistance, hydrophobic, anti-aging performance, and significantly extends the service life of the paint film.
8、 Disadvantage 7: Insufficient stretch rate and poor cracking bridging ability of elastic coatings
1. On site phenomena
Elastic latex paint and roof waterproof coating cannot bridge micro cracks in the substrate. After thermal expansion and contraction of the substrate, the paint film is torn, resulting in through cracks; The paint film has low elongation and poor toughness, and is prone to fracture after bending, losing its elastic waterproof protection function.
2. Traceability mechanism of core lotion
The core of elastic system depends on the low Tg characteristic of lotion. The Tg of ordinary exterior wall lotion is too high (>20 ℃), the rigidity of molecular chain is large, the flexibility is extremely poor, and there is no elastic deformation ability. Some low-end elastic lotion are in pursuit of low cost, with insufficient soft monomer ratio, no elastic core shell structure, and inherently deficient tensile ratio; Excessive cross-linking at the same time can cause the paint film to harden and lose elasticity, making it unable to adapt to substrate deformation.
3. Precise rectification and optimization plan
Replace the ultra soft core shell elastic acrylic lotion, control the Tg of the lotion at -20 ℃~-10 ℃, ensure the tensile rate of the ultra high elastic monomer in the core (elongation at break ≥ 500%), and ensure the surface abrasion resistance of the shell by proper crosslinking; Paired with a flexible film-forming system, without the addition of hard fillers or excessive crosslinking agents, it preserves the elastic deformation ability of the paint film and achieves micro crack bridging protection.
9、 Disadvantage 8: Poor adhesion of paint film, peeling, peeling, poor wetting of substrate
1. On site phenomena
After the paint film dries, slight bumps will cause the entire piece to peel off, and the scratch test adhesion does not meet the standard; Cement, metal, and glass substrates all have poor adhesion problems, especially in humid environments where detachment is more severe.
2. Traceability mechanism of core lotion
Ordinary acrylic acid lotion has no active functional group and is attached to the substrate only by physical adsorption, without chemical bonding; The molecular chain of lotion has strong rigidity and poor wettability, so it cannot fit the pores of rough substrate; The low-end lotion has residual hydrophilic groups, and the interface between the paint film and the substrate is easy to absorb water, leading to interface debonding, peeling and falling off.
3. Precise rectification and optimization plan
Upgrading silane modified acrylic lotion, epoxy modified acrylic lotion, and grafting of active functional groups onto lotion molecules can form chemical bonding with inorganic and metal substrates to fundamentally improve adhesion; Paired with silane coupling agent to assist in thickening, optimize interfacial adhesion, and completely solve the problem of peeling off.
10、 Summary: core principles of acrylic lotion selection
1. Indoor general scenario: give priority to styrene acrylic self crosslinking lotion, balance cost and performance, and prohibit acetate acrylic lotion as water resistant and scrub resistant products;
2. Weather resistant scene of exterior wall: force pure acrylic/silicone acrylic lotion, eliminate styrene acrylic lotion, and ensure long-term yellowing resistance, light and color preservation;
3. Low temperature construction scenario: select soft core and hard shell core and shell lotion, reduce MFFT, and give consideration to film forming property and hardness;
4. High temperature anti adhesion scenario: high Tg self crosslinking lotion, which improves the film compactness and anti adhesion by relying on the cross-linking structure;
5. Two component industrial paint scene: special hydroxy acrylic acid dispersion, it is strictly prohibited to substitute building lotion;
6. Waterproof elastic scene: ultra-low Tg elastic core shell lotion to ensure high tensile ratio and crack bridging ability.
Most of the stubborn quality problems of coatings can only be remedied temporarily by adjusting additives. Choosing the right acrylic lotion is the core to solve the film defects and stabilize the product quality.
Post time: Aug-10-2026