How to choose suitable additives for different kinds of coatings

Coating additives are not "general additives", and the essence of their selection is the dynamic adaptation of the molecular structure of additives, the characteristics of coating system and the final performance goal. The choice of additives that are separated from the type of coating base material, film-forming mode and application scenario will inevitably lead to performance redundancy or function failure. The core logic and key technical points of adjuvant selection are analyzed from the classification of mainstream coating systems. Solvent based coatings: focus on "balance compatibility and functionality"

Solvent based coatings use organic solvent as the dispersion medium, and the system is characterized by sufficient resin dissolution and good molecular fluidity, but it is prone to problems such as uneven solvent volatilization and unbalanced surface tension. The triangular balance of "compatibility volatility functionality" should be given priority in the selection of additives to avoid color bleeding, shrinkage or migration of additives.

1.film forming AIDS: match the glass transition temperature (TG) of resin and solvent evaporation rate

The film-forming additives need to temporarily reduce the Tg of the resin during the film-forming process and assist the diffusion and fusion of molecular chains. The core of their selection is the synergy with the volatilization rhythm of the main solvent.

-For high Tg acrylic resin (TG ＞ 50 ℃): alcohol esters with "high boiling point and slow volatilization" (such as dodecanol ester) are preferred, which can remain in the film after a large amount of solvent volatilization, continue to play a plasticizing role, and avoid film embrittlement; If ether alcohols (such as ethylene glycol ether) are selected, it is easy to cause "insufficient early film formation" due to too fast volatilization. -For low Tg polyurethane resin (TG ＜ 20 ℃): low boiling point esters (such as butyl acetate) can be used to mix with alcohols to reduce the decline of film stain resistance caused by the residue of additives; Aromatic solvents (such as toluene) should be avoided as film-forming additives, which have poor compatibility with PU resin and are easy to cause film shrinkage.

2. leveling agent: control surface tension gradient and avoid "Bernard vortex"

The surface tension gradient is easily formed due to the difference of solvent volatilization rate during the solvent based coating flow, which causes Bernard vortex (manifested as coating orange peel). When selecting leveling agent, it is necessary to distinguish between "resin type" and "construction method":

-Brush coating/roll coating construction: polyether modified polydimethylsiloxane is preferred, which can reduce the surface tension without affecting the wettability and avoid brush marks; It is necessary to avoid the use of acrylic leveling agent, which is prone to foam under high shear construction.

-Spraying construction: fluorine modified acrylate is selected, which has fast surface migration speed and can quickly eliminate the micro shrinkage formed in the atomization process; However, it is necessary to control the addition amount (usually ≤ 0.5%), and excessive amount will lead to the decrease of film adhesion.

3. anti sedimentation agent: give consideration to "suspension stability" and "construction fluidity"

Pigments (such as carbon black and titanium dioxide) in solvent based coatings are easy to settle due to density difference, so the anti settling agent needs to form thixotropic structure during storage, and restore fluidity due to shear stress damage during construction.

-For industrial coatings with high pigment volume concentration (PVC>40%), organic bentonite and polyamide wax are used to form a three-dimensional network through hydrogen bonding, and polyamide wax enhances suspension stability through crystal structure. The combination of the two can avoid "hard precipitation"; The use of organic bentonite alone can easily lead to the decline of film leveling.

-For high-grade wood coatings with low PVC: the modified hydrogenated castor oil is preferred, which forms a fibrous structure after being dispersed in the solvent, has good suspension property and does not affect the gloss of the film; Avoid the use of fumed silica, which is easy to absorb leveling agent, resulting in surface defects.

Water based coatings: focus on "solving interface stability"

Water based coatings take water as the dispersion medium, and the system has three core problems: high surface tension of water, aggregation of resin emulsion particles, and poor wettability of pigments. The selection of additives should focus on the interface function of "water phase oil phase solid phase", focusing on solving the three pain points of dispersion, defoaming and water resistance.

1. dispersant: matching of anchoring group and hydrophilic chain of resin

Pigment dispersion in waterborne coatings depends on the "anchoring stability" of dispersant, and the key to selection is the compatibility between the anchoring group of dispersant and the surface charge of pigment.

-Inorganic pigments (such as titanium white and iron oxide red): the surface is negativelycharged, so the anionic polycarboxylate dispersant is preferred. Its carboxylate (-coo ⁻) can anchor the pigment surface through electrostatic action, and the polyether side chain extends to the aqueous phase to form a steric hindrance; If a non-ionic dispersant (such as polyoxyethylene ether) is selected, it is only anchored by hydrogen bond, which has poor stability and is prone to pigment flocculation.

-Organic pigments (such as phthalocyanine blue and YONGGU yellow): due to low surface polarity, it is necessary to select a dispersant with dual adaptation of "anchoring group+solvation chain" - such as a polymer dispersant containing azo group (-n=n-). The azo group can form π - π conjugation with the aromatic ring of the organic pigment. The solvation chain uses an acrylate chain segment compatible with the emulsion resin to avoid "incompatible flocculation".

2.defoamer: break the "gas liquid solid" three-phase foam to avoid "shrinkage sequelae"

The foam of water-based coatings comes from the residual surfactant in emulsion polymerization and the air brought in by stirring. The defoamer should have both "fast foam breaking" and "long foam inhibition" and do not affect the gloss of the film.

-Emulsion type industrial coatings (such as water-borne emulsion paint): polyether modified siloxane and mineral oil are used as defoamers to enhance the compatibility between polyether segments and aqueous phase, siloxane reduces surface tension and foam breaking, and mineral oil prolongs foam inhibition time; It is necessary to avoid the use of high-purity siloxane defoamer, which has poor compatibility and is easy to cause "fish eye" shrinkage.

Waterborne wood coatings (such as waterborne PU paint): fluoro modified polyether defoamer is preferred. Its surface energy is very low (<20 mN/M), which can quickly break the micro foam on the surface of the film without affecting the hand feel and scratch resistance of the film; If silicone defoamer is used, it is easy to form silicon spots on the surface of the film, affecting the adhesion of subsequent coatings.

3.thickener: control "pseudoplasticity" and "thixotropy", and adapt the construction method

The viscosity of water-based coatings depends on the adjustment of thickeners. Different construction methods have different requirements for viscosity and rheology, and the selection needs to accurately match the "construction shear rate".

-Spraying construction: the paint is required to have low viscosity and easy atomization under high shear (shear rate at the nozzle outlet>1000 s ⁻ ¹), high viscosity and anti sagging when standing. Associating polyurethane thickener (HEUR) is preferred, which forms a reversible network through the association of hydrophobic groups. The network damage viscosity decreases under shear, and re associating after standing; Avoid the use of cellulose ether thickeners, which have poor shear thinning effect and can easily lead to "gun blockage" during spraying.

-Brushing Construction: the coating is required to be easy to brush and free from sagging under low shear (brush shear rate ＜ 100 s ⁻ ¹). Alkali swelling Acrylic Acid Thickener (ASE) is preferred, which expands to form a three-dimensional structure under alkaline conditions, and the viscosity is stably adjusted with pH value; HEUR thickener alone can easily lead to "heavy brush marks", which should be used in combination with ase.

Powder coatings: focusing on the "adaptive melting film forming process"

The powder coating is a 100% solid system without solvent volatilization. Its film-forming process is "heating melting flow leveling crosslinking curing". The selection of additives should focus on three stages: melting fluidity, curing reaction and film surface state, and should meet the "high temperature stability" (baking temperature is usually 160-220 ℃).

1. leveling agent: reduce melt viscosity, eliminate "orange peel" and "pinhole"

When the powder coating melts, the resin viscosity is high, and the leveling agent needs to quickly migrate to the surface at the melting temperature to reduce the surface tension and promote leveling.

-Epoxy polyester mixed powder: acrylate leveling agent is preferred, which has good compatibility with resin, can effectively reduce the viscosity of the system after melting, and does not affect the chemical resistance of the film; Avoid the use of silicone leveling agent, which is easy to migrate to the film surface at high temperature, resulting in the decrease of adhesion of subsequent coatings.

2.curing accelerator: control the crosslinking reaction rate to avoid "over curing" or "under curing"

The curing reaction of powder coatings depends on the curing accelerator (such as imidazole and tertiary amine). The core of selection is the matching of the active temperature of accelerator and baking process.

-Low temperature rapid curing powder (baking at 160 ℃/15min): select highly active imidazole derivatives (such as 2-methylimidazole), which can initiate the curing reaction at 120 ℃ and shorten the baking time; However, attention should be paid to the storage stability - high activity accelerator is easy to cause powder "caking", which needs to be mixed with anti caking agent (such as fumed silica).

-High temperature curing powder (baking at 200 ℃/30min): low active tertiary amine accelerator (such as triethanolamine) is selected, which slowly releases active groups at high temperature to avoid the increase of internal stress and cracking of the film caused by too fast curing; Avoid using imidazole accelerators, which are easy to decompose at high temperature, resulting in yellowing of the film.

3. degassing agent: eliminate "volatile bubbles" in the melting process

The residual resin monomer and water adsorbed by pigment in powder coatings will volatilize and form bubbles during melting, and the degassing agent needs to be released rapidly at the initial stage of melting to break the bubbles.

Four functional coatings: focusing on "additives - precise coordination of functional objectives"

The selection of additives for functional coatings (such as anticorrosive, fireproof and conductive coatings) needs to jump out of the "general performance optimization", focus on the enhancement or empowerment of additives to core functions, and even need "customized additive system".

1.anti corrosion coatings: additives need to enhance the synergy of "shielding passivation corrosion inhibition"

The core of anti-corrosion coatings is to prevent the penetration of water, oxygen and ions. The selection of additives needs to assist the resin to form a dense coating and enhance the protection of metal substrates.

-Epoxy zinc rich primer (cathodic protection type): it is necessary to add zinc powder directional alignment agent (such as organic amines), which can guide the zinc powder in the film parallel to the substrate to form a continuous "zinc powder conductive network" and improve the cathodic protection effect; At the same time, phosphate passivator is added, which reacts with the metal substrate to form a passivation film to avoid excessive corrosion of zinc powder.

-Polyurea anticorrosive coating (rapid curing type): silane coupling agent is selected as the adhesion promoter. The amino group at one end reacts with polyurea resin, and the siloxane at the other end forms a covalent bond with the metal substrate to enhance the adhesion between the coating and the substrate; At the same time, fumed silica is added as thixotropic agent to prevent "sagging" during construction and ensure uniform coating thickness, which is the key factor leading to local corrosion.

2. fire retardant coatings: additives should match the "flame retardant mechanism" to avoid "functional conflict"

The flame retardant mechanism of fire retardant coatings can be divided into "intumescent" and "non intumescent". The selection of additives should be coordinated with the flame retardant system and should not be blindly added.

-Intumescent fire retardant coating: carbon forming catalyst (such as ammonium polyphosphate), foaming agent (such as melamine) and carbon forming agent (such as pentaerythritol) need to be added, and the proportion of the three needs to be strictly controlled (usually 4:1:1). At the same time, acrylate leveling agent needs to be added - it needs to be melted at high temperature, assist the three to be evenly dispersed, and then form a dense expansion layer through carbonization; Avoid using silicone leveling agent, which is easy to decompose into silicon dioxide at high temperature, hindering the formation of expansion layer.

-Non intumescent fire retardant coatings (such as fire retardant latex paint): aluminum hydroxide and magnesium hydroxide are selected as flame retardants, and polycarboxylate dispersants (rather than anionic surfactants) need to be added, which can avoid agglomeration of flame retardant particles and ensure uniform release of crystalline water for cooling in case of fire; At the same time, thickening agent is added to adjust the viscosity to avoid "local flame retardant failure" caused by the settlement of flame retardant.

3. conductive coatings: additives should ensure "continuity of conductive path" and reduce "contact resistance"

Conductive coatings rely on conductive fillers (such as carbon black and silver powder) to form a conductive path. The selection of additives should avoid damaging the path by "insulating additives" and enhance the dispersion of fillers.

-Carbon black based conductive coating: non ionic polymer dispersant (such as polyoxyethylene polyoxypropylene ether) is selected, which will not form an insulating layer on the surface of carbon black, and can prevent the agglomeration of carbon black through steric hindrance to ensure the continuity of conductive path; Avoid the use of anionic dispersants, whose carboxylate will form a charge layer on the surface of carbon black and increase the contact resistance.

-Silver powder based conductive coating: add fatty acid amide leveling agent, which can reduce the surface tension of the film, promote the directional arrangement of silver powder on the film surface (forming a "Silver Powder Mirror"), and improve the conductivity; At the same time, anti oxidants (such as benzotriazole) are added to prevent the oxidation of silver powder to form insulating silver oxide, leading to the decline of conductivity.

Five "three golden rules" for selection of coating additives

1. system priority: first clarify the type of coating base material (solvent/water-based/powder), film-forming method (physical drying/chemical curing), and then screen the structure of additives that match the compatibility of the system (e.g. avoid using oil-soluble additives for water-based systems).

2. function focus: avoid the "superposition of multiple additives", and select the main additives according to the core requirements (such as leveling/defoaming/anti-corrosion). The auxiliary additives are only used to make up for the performance shortcomings of the main additives (such as leveling agent+degassing agent to solve surface defects).

3. coating additives are not "general additives", and the essence of their selection is the dynamic adaptation of the molecular structure of additives, the characteristics of coating system and the final performance goal. The choice of additives that are separated from the type of coating base material, film-forming mode and application scenario will inevitably lead to performance redundancy or function failure. The core logic and key technical points of adjuvant selection are analyzed from the classification of mainstream coating systems.

Solvent based coatings: focus on "balance compatibility and functionality"

Solvent based coatings use organic solvent as the dispersion medium, and the system is characterized by sufficient resin dissolution and good molecular fluidity, but it is prone to problems such as uneven solvent volatilization and unbalanced surface tension. The triangular balance of "compatibility volatility functionality" should be given priority in the selection of additives to avoid color bleeding, shrinkage or migration of additives.

1. film forming AIDS: match the glass transition temperature (TG) of resin and solvent evaporation rate

The film-forming additives need to temporarily reduce the Tg of the resin during the film-forming process and assist the diffusion and fusion of molecular chains. The core of their selection is the synergy with the volatilization rhythm of the main solvent.

-For high Tg acrylic resin (TG ＞ 50 ℃): alcohol esters with "high boiling point and slow volatilization" (such as dodecanol ester) are preferred, which can remain in the film after a large amount of solvent volatilization, continue to play a plasticizing role, and avoid film embrittlement; If ether alcohols (such as ethylene glycol ether) are selected, it is easy to cause "insufficient early film formation" due to too fast volatilization.

-For low Tg polyurethane resin (TG ＜ 20 ℃): low boiling point esters (such as butyl acetate) can be used to mix with alcohols to reduce the decline of film stain resistance caused by the residue of additives; Aromatic solvents (such as toluene) should be avoided as film-forming additives, which have poor compatibility with PU resin and are easy to cause film shrinkage.

2.leveling agent: control surface tension gradient and avoid "Bernard vortex"

The surface tension gradient is easily formed due to the difference of solvent volatilization rate during the solvent based coating flow, which causes Bernard vortex (manifested as coating orange peel). When selecting leveling agent, it is necessary to distinguish between "resin type" and "construction method":

-Brush coating/roll coating construction: polyether modified polydimethylsiloxane is preferred, which can reduce the surface tension without affecting the wettability and avoid brush marks; It is necessary to avoid the use of acrylic leveling agent, which is prone to foam under high shear construction.

-Spraying construction: fluorine modified acrylate is selected, which has fast surface migration speed and can quickly eliminate the micro shrinkage formed in the atomization process; However, it is necessary to control the addition amount (usually ≤ 0.5%), and excessive amount will lead to the decrease of film adhesion.

3. anti sedimentation agent: give consideration to "suspension stability" and "construction fluidity"

Pigments (such as carbon black and titanium dioxide) in solvent based coatings are easy to settle due to density difference, so the anti settling agent needs to form thixotropic structure during storage, and restore fluidity due to shear stress damage during construction.

-For industrial coatings with high pigment volume concentration (PVC>40%), organic bentonite and polyamide wax are used to form a three-dimensional network through hydrogen bonding, and polyamide wax enhances suspension stability through crystal structure. The combination of the two can avoid "hard precipitation"; The use of organic bentonite alone can easily lead to the decline of film leveling.

-For high-grade wood coatings with low PVC: the modified hydrogenated castor oil is preferred, which forms a fibrous structure after being dispersed in the solvent, has good suspension property and does not affect the gloss of the film; Avoid the use of fumed silica, which is easy to absorb leveling agent, resulting in surface defects.

Aqueous coatings: focus on "solving interface stability"

Water based coatings take water as the dispersion medium, and the system has three core problems: high surface tension of water, aggregation of resin emulsion particles, and poor wettability of pigments. The selection of additives should focus on the interface function of "water phase oil phase solid phase", focusing on solving the three pain points of dispersion, defoaming and water resistance.

1. dispersant: matching of anchoring group and hydrophilic chain of resin

Pigment dispersion in waterborne coatings depends on the "anchoring stability" of dispersant, and the key to selection is the compatibility between the anchoring group of dispersant and the surface charge of pigment.

-Inorganic pigments (such as titanium white and iron oxide red): the surface is negatively charged, so the anionic polycarboxylate dispersant is preferred. Its carboxylate (-coo ⁻) can anchor the pigment surface through electrostatic action, and the polyether side chain extends to the aqueous phase to form a steric hindrance; If a non-ionic dispersant (such as polyoxyethylene ether) is selected, it is only anchored by hydrogen bond, which has poor stability and is prone to pigment flocculation.

-Organic pigments (such as phthalocyanine blue and YONGGU yellow): due to low surface polarity, it is necessary to select a dispersant with dual adaptation of "anchoring group+solvation chain" - such as a polymer dispersant containing azo group (-n=n-). The azo group can form π - π conjugation with the aromatic ring of the organic pigment. The solvation chain uses an acrylate chain segment compatible with the emulsion resin to avoid "incompatible flocculation".

2. defoamer: break the "gas liquid solid" three-phase foam to avoid "shrinkage sequelae"

The foam of water-based coatings comes from the residual surfactant in emulsion polymerization and the air brought in by stirring. The defoamer should have both "fast foam breaking" and "long foam inhibition" and do not affect the gloss of the film.

-Emulsion type industrial coatings (such as water-borne emulsion paint): polyether modified siloxane and mineral oil are used as defoamers to enhance the compatibility between polyether segments and aqueous phase, siloxane reduces surface tension and foam breaking, and mineral oil prolongs foam inhibition time; It is necessary to avoid the use of high-purity siloxane defoamer, which has poor compatibility and is easy to cause "fish eye" shrinkage.

-Waterborne wood coatings (such as waterborne PU paint): fluoro modified polyether defoamer is preferred. Its surface energy is very low (<20 mN/M), which can quickly break the micro foam on the surface of the film without affecting the hand feel and scratch resistance of the film; If silicone defoamer is used, it is easy to form silicon spots on the surface of the film, affecting the adhesion of subsequent coatings.

3. thickener: control "pseudoplasticity" and "thixotropy", and adapt the construction method

The viscosity of water-based coatings depends on the adjustment of thickeners. Different construction methods have different requirements for viscosity and rheology, and the selection needs to accurately match the "construction shear rate".

-Spraying construction: the paint is required to have low viscosity and easy atomization under high shear (shear rate at the nozzle outlet>1000 s ⁻ ¹), high viscosity and anti sagging when standing. Associating polyurethane thickener (HEUR) is preferred, which forms a reversible network through the association of hydrophobic groups. The network damage viscosity decreases under shear, and re associating after standing; Avoid the use of cellulose ether thickeners, which have poor shear thinning effect and can easily lead to "gun blockage" during spraying.

-Brushing Construction: the coating is required to be easy to brush and free from sagging under low shear (brush shear rate ＜ 100 s ⁻ ¹). Alkali swelling Acrylic Acid Thickener (ASE) is preferred, which expands to form a three-dimensional structure under alkaline conditions, and the viscosity is stably adjusted with pH value; HEUR thickener alone can easily lead to "heavy brush marks", which should be used in combination with ase.

Three powder coatings: with the core of "adaptive melting film forming process"

The powder coating is a 100% solid system without solvent volatilization. Its film forming process is "heating melting flow leveling crosslinking curing". The selection of additives should focus on three stages: melting fluidity, curing reaction and film surface state, and should meet the "high temperature stability" (baking temperature is usually 160-220 ℃).

1. leveling agent: reduce melt viscosity, eliminate "orange peel" and "pinhole"

When the powder coating melts, the resin viscosity is high, and the leveling agent needs to quickly migrate to the surface at the melting temperature to reduce the surface tension and promote leveling.

-Epoxy polyester mixed powder: acrylate leveling agent is preferred, which has good compatibility with resin, can effectively reduce the viscosity of the system after melting, and does not affect the chemical resistance of the film; Avoid the use of silicone leveling agent, which is easy to migrate to the film surface at high temperature, resulting in the decrease of adhesion of subsequent coatings.

2. curing accelerator: control the crosslinking reaction rate to avoid "over curing" or "under curing"

The curing reaction of powder coatings depends on the curing accelerator (such as imidazole and tertiary amine). The core of selection is the matching of the active temperature of accelerator and baking process.

-Low temperature rapid curing powder (baking at 160 ℃/15min): select highly active imidazole derivatives (such as 2-methylimidazole), which can initiate the curing reaction at 120 ℃ and shorten the baking time; However, attention should be paid to the storage stability - high activity accelerator is easy to cause powder "caking", which needs to be mixed with anti caking agent (such as fumed silica).

-High temperature curing powder (baking at 200 ℃/30min): low active tertiary amine accelerator (such as triethanolamine) is selected, which slowly releases active groups at high temperature to avoid the increase of internal stress and cracking of the film caused by too fast curing; Avoid using imidazole accelerators, which are easy to decompose at high temperature, resulting in yellowing of the film.

3. degassing agent: eliminate "volatile bubbles" in the melting process

The residual resin monomer and water adsorbed by pigment in powder coatings will volatilize and form bubbles during melting, and the degassing agent needs to be released rapidly at the initial stage of melting to break the bubbles.

Four functional coatings: focusing on "additives - precise coordination of functional objectives"

The selection of additives for functional coatings (such as anticorrosive, fireproof and conductive coatings) needs to jump out of the "general performance optimization", focus on the enhancement or empowerment of additives to core functions, and even need "customized additive system".

1. anti corrosion coatings: additives need to enhance the synergy of "shielding passivation corrosion inhibition"

The core of anti-corrosion coatings is to prevent the penetration of water, oxygen and ions. The selection of additives needs to assist the resin to form a dense coating and enhance the protection of metal substrates.

-Epoxy zinc rich primer (cathodic protection type): it is necessary to add zinc powder directional alignment agent (such as organic amines), which can guide the zinc powder in the film parallel to the substrate to form a continuous "zinc powder conductive network" and improve the cathodic protection effect; At the same time, phosphate passivator is added, which reacts with the metal substrate to form a passivation film to avoid excessive corrosion of zinc powder.

-Polyurea anticorrosive coating (rapid curing type): silane coupling agent is selected as the adhesion promoter. The amino group at one end reacts with polyurea resin, and the siloxane at the other end forms a covalent bond with the metal substrate to enhance the adhesion between the coating and the substrate; At the same time, fumed silica is added as thixotropic agent to prevent "sagging" during construction and ensure uniform coating thickness, which is the key factor leading to local corrosion.

2. fire retardant coatings: additives should match the "flame retardant mechanism" to avoid "functional conflict"

The flame retardant mechanism of fire retardant coatings can be divided into "intumescent" and "non intumescent". The selection of additives should be coordinated with the flame retardant system and should not be blindly added.

-Intumescent fire retardant coating: carbon forming catalyst (such as ammonium polyphosphate), foaming agent (such as melamine) and carbon forming agent (such as pentaerythritol) need to be added, and the proportion of the three needs to be strictly controlled (usually 4:1:1). At the same time, acrylate leveling agent needs to be added - it needs to be melted at high temperature, assist the three to be evenly dispersed, and then form a dense expansion layer through carbonization; Avoid using silicone leveling agent, which is easy to decompose into silicon dioxide at high temperature, hindering the formation of expansion layer.

-Non intumescent fire retardant coatings (such as fire retardant latex paint): aluminum hydroxide and magnesium hydroxide are selected as flame retardants, and polycarboxylate dispersants (rather than anionic surfactants) need to be added, which can avoid agglomeration of flame retardant particles and ensure uniform release of crystalline water for cooling in case of fire; At the same time, thickening agent is added to adjust the viscosity to avoid "local flame retardant failure" caused by the settlement of flame retardant.

3. conductive coatings: additives should ensure "continuity of conductive path" and reduce "contact resistance"

Conductive coatings rely on conductive fillers (such as carbon black and silver powder) to form a conductive path. The selection of additives should avoid damaging the path by "insulating additives" and enhance the dispersion of fillers.

-Carbon black based conductive coating: non ionic polymer dispersant (such as polyoxyethylene polyoxypropylene ether) is selected, which will not form an insulating layer on the surface of carbon black, and can prevent the agglomeration of carbon black through steric hindrance to ensure the continuity of conductive path; Avoid the use of anionic dispersants, whose carboxylate will form a charge layer on the surface of carbon black and increase the contact resistance.

-Silver powder based conductive coating: add fatty acid amide leveling agent, which can reduce the surface tension of the film, promote the directional arrangement of silver powder on the film surface (forming a "Silver Powder Mirror"), and improve the conductivity; At the same time, anti oxidants (such as benzotriazole) are added to prevent the oxidation of silver powder to form insulating silver oxide, leading to the decline of conductivity.

Five "three golden rules" for selection of coating additives

1. system priority: first clarify the type of coating base material (solvent/water-based/powder), film-forming method (physical drying/chemical curing), and then screen the structure of additives that match the compatibility of the system (e.g. avoid using oil-soluble additives for water-based systems).

2. function focus: avoid the "superposition of multiple additives", and select the main additives according to the core requirements (such as leveling/defoaming/anti-corrosion). The auxiliary additives are only used to make up for the performance shortcomings of the main additives (such as leveling agent+degassing agent to solve surface defects).

3. process adaptation: the construction method (spraying/brushing) and baking temperature (low/high temperature) directly determine the active temperature and shear stability of the additives, and separation from the process selection will inevitably lead to "excellent laboratory performance and failure of industrial application".

The value of coating additives does not lie in "addition", but in "accurate matching" -- through the coordination of molecular structure and system characteristics, the coating performance can be "customized on demand".

Eric

• Vice Chairman of the Coatings and Adhesives Association

• Senior New Materials R&D Engineer

• Bachelor of Engineering

• General Manager

• Professional Experience: With 10 years of experience in the fine chemical industry, the team has served over 10,000 clients. Committed to providing one-stop fine chemical services for global clients and helping them optimize the selection of chemical materials.