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I. Preface

In the system of industrial water-based coatings, water-based lotion, water-based adhesives, water-based slurries, and water-based additives for building materials, microbial corruption is one of the most hidden quality problems that cause product scrap, customer complaints, and most. The vast majority of formula engineers are prone to the biggest misconception: they believe that “adding a preservative can solve both storage odor and paint film mold at the same time”.

In fact, the antibacterial agent (liquid anti-corrosion) and the dry film antifungal agent (solid paint film antifungal) in the tank belong to two completely different chemical systems, mechanisms of action, dissolution characteristics, applicable stages, and killing targets. The two are not interchangeable, irreplaceable, and indispensable.

Only add antibacterial agent in the tank: stored without odor, but it is prone to mold, algae growth, and black spots outdoors.

Only add dry film anti mold agent: The paint film does not mold, but it is prone to bloating, odor, emulsion breaking, and viscosity drop inside the barrel.

This article comprehensively and deeply disassembles the micro mechanism, physical and chemical properties, production drawbacks, compatibility taboos, working condition selection, and compounding schemes, and establishes a standardized antibacterial and anti mold selection system for industrial water-based systems.

2、 The real causes of microbial decay in industrial water-based systems

The water-based system is rich in water, lotion polymers, polyols, wetting dispersants, cellulose, modification additives and other organic nutrients. The production and storage environment with temperature of 20 – 45 ℃ and pH of 7 – 9 is just the best breeding hotbed for bacteria, yeast, mold and algae.

Bacteria and yeast: mainly destroy liquid coatings (inside the tank), quickly decompose thickeners and surfactants, causing viscosity decrease, water separation, bloating, and odor.

Mold and algae: cannot reproduce in large quantities in a closed liquid system, mainly growing on surfaces that come into contact with air and moisture after the film is formed, causing blackening, spotting, powdering, peeling, and water seepage of the paint film.

Due to the completely different types, growth stages, and growth environments of microorganisms, it is necessary to divide the protection into a dual system of in tank antibacterial system and dry film anti mold system.

3、 Deep analysis of antibacterial agents in tanks: mechanism, category, and characteristics

1. Core definition and functional stages

In tank bacteriostatic agents, also known as water-based preservatives and in tank bactericides, are specially designed for liquid uncured water-based paint/lotion systems. Action cycle: End of production – Storage and transportation – Before customer opens and uses.

Core task: Kill bacteria, inhibit yeast, prevent system biodegradation, and ensure stable shelf life of coatings.

2. Sterilization mechanism

Mainstream isothiazolinones (BIT, CMIT/MIT) penetrate microbial cell membranes, bind to intracellular protein thiol groups (- SH), disrupt enzyme system activity, block microbial respiration and metabolism, rapidly kill bacteria, inhibit yeast reproduction, and fundamentally prevent system decay.

3. Mainstream product categories and industrial adaptability

(1) BIT Benzoisothiazolinone

Physical and chemical advantages: high temperature resistance (able to withstand processes above 80 ℃), strong alkali resistance, pH stability range of 2-14, chlorine free, non allergenic, long-lasting stability, and not easily hydrolyzed.

Shortcoming: The speed of killing yeast is relatively weak, and long-term use alone can easily lead to mild drug resistance.

Adaptation system: high pH emulsion paint, industrial water-based paint, water-based epoxy, water-based lotion, high-temperature feeding process.

(2) CMIT/MIT compound Carcassone

Physical and chemical advantages: extremely fast sterilization speed, broad-spectrum killing of bacteria and yeast, low cost, fast onset of action.

Shortcomings: Not resistant to high temperatures, rapid deactivation at pH>9.0, easy decomposition at high temperatures, risk of skin sensitization, average storage stability.

Adaptation system: room temperature paint adjustment and later addition, civilian coatings, medium low pH system.

4. Common characteristics of antibacterial agents in the tank

1. Highly water-soluble, completely soluble in aqueous phase;

2. After film formation, a large amount of residue remains on the surface of the paint film, which is easily washed away by rainwater and moisture when in contact with water;

3. Unable to retain the interior of the paint film, completely lacking long-term dry film anti mold ability;

4. Extremely low addition amount: Conventional 0.1% -0.3% can meet the anti-corrosion requirements;

5. Only targeting bacteria and yeast, with extremely weak inhibitory ability against mold and algae.

5. Typical drawbacks caused by failure

In tank distension drum, sour smell, steep drop of viscosity, layered water separation, lotion demulsification, color paste thickening and storage blackening.

4、 Deep analysis of dry film mold inhibitor (anti mold and anti algae coating)

1. Core definition and functional stages

Dry film mold inhibitor is specifically designed for solid paint films that have been cured and dried. Action cycle: After the coating is applied and forms a film, it is in the long-term outdoor/high humidity environment service stage.

Core task: Inhibit the implantation, growth, and spread of mold, fungi, and algae on the surface of the paint film, prevent wall blackening, green moss growth, paint film mold, powdering, water seepage, and peeling.

2. Mainstream categories and mechanisms

(1) OIT octylisothiazolinone

Oil based, extremely low water solubility, excellent compatibility with paint film resin, firmly locked inside the paint film after film formation, will not be washed away by rainwater, and can effectively inhibit mold and algae for a long time. It is the first choice for exterior wall coatings and industrial outdoor paints.

(2) IPBC iodopropynyl butyl carbamate

Super anti mold ability, targeting stubborn black mold and Aspergillus, often compounded with OIT to enhance the anti mold level.

3. Common characteristics of dry film mold inhibitors

1. Almost insoluble in water, with strong resin affinity;

2. After film formation, it is fixed in the cross-linked structure of the paint film, resistant to rainwater erosion and long-lasting weather resistance;

3. Extremely weak ability to kill bacteria, unable to solve the problem of odor and bloating inside the tank;

4. Higher addition amount: conventional 0.3% -0.8%;

5. Only targeting molds, fungi, and algae, not bacteria or yeast.

4. Typical drawbacks caused by failure

Black spots, mold spots, green algae, localized powdering, sticky paint film on the exterior wall paint film, and widespread mold and blackening on the wall surface during the rainy season.

5、 Comprehensive comparison of core dimensions between in tank antibacterial agents and dry film antifungal agents

Comparison dimension: Tank antibacterial agent (preservative), dry film antifungal agent (anti mold and anti algae agent)

Target bacteria, yeast, mold, fungi, algae

Functional state: Liquid coating, uncured system solid dry film, cured paint film

High water solubility, low water solubility, lipophilic

After film formation, residues are easily lost, with no residual effect and firm fixation, and long-lasting residue

Core solutions include preventing odor, bloating, viscosity decay, mold growth, algae growth, and black spots

Typical components include BIT, CMIT/MIT OIT, IPBC, and compound anti mold system

Conventional addition amount: 0.1% -0.3%, 0.3% -0.8%

High temperature resistance BIT is resistant to high temperatures, while CMIT is generally resistant to high temperatures and has excellent weather resistance

Substitutes cannot replace mold inhibitors and preservatives

6、 Precision selection logic for industrial water-based systems

1. Interior wall latex paint, indoor water-based paint (indoor dry environment)

Requirement: Just ensure that the storage does not spoil and there is almost no mold growing indoors.

Selection: BIT+a small amount of CMIT compound tank antibacterial agent, no need to add dry film antifungal agent.

2. Exterior latex paint, outdoor industrial water-based topcoat, and topcoat varnish

Requirement: Dual requirements for storage odor prevention and outdoor high humidity mold and algae resistance.

Selection: Dual system protection of BIT compound in the tank and OIT/IPBC dry film mold inhibitor.

3. Water based industrial anti-corrosion paint, steel structure water-based paint

The system has a high pH, a lot of powder, and is prone to decay. It is also prone to mold growth when exposed to high humidity outdoors.

Selection: High temperature and alkali resistant BIT as the main preservative+outdoor specific mold inhibitor. It is strictly prohibited to use CMIT alone, as it quickly fails in alkaline environments.

4. Water based epoxy system, two-component industrial paint

Taboo: Amine curing agents can neutralize and inactivate isothiazolinone.

Selection rules: All antibacterial and anti mold additives are added to component A (resin phase), and component B is absolutely not mixed in; Choose an amine resistant stable anti mold system.

5. Waterborne size, color paste, lotion raw material system

High nutrient system, highly perishable, no need for dry film for mold prevention.

Selection: Long term BIT antibacterial system to ensure the stability of raw material storage.

7、 The 4 most common selection errors in the industry

Error 1: Only adding preservatives, not adding mold inhibitors

Consequence: The factory is in good condition, but after six months of construction, there is widespread mold and blackening on the walls, leading to a large number of customer complaints for outdoor projects.

Error 2: Only adding mold inhibitor, not preservatives

Consequence: The paint film does not mold, but the coating will swell, smell, and be scrapped after 1-2 months of storage.

Error 3: High alkali system using CMIT single anti-corrosion

Consequence: After pH>9.2, CMIT rapidly hydrolyzes and fails, and the entire barrel of paint deteriorates in the later stage.

Error 4: Two component epoxy adds antibacterial agent to B-amine component

Consequence: The antibacterial activity instantly fails, and the paint film turns yellow, loses luster, and hardens abnormally.

8、 Optimal industrial compounding solution

1. Universal indoor system (cost-effectiveness)

BIT 0.15% + CMIT/MIT 0.05%， Total addition 0.2%

2. Outdoor weather and mold resistant system (standard engineering payment)

BIT compound preservative 0.2%+OIT dry film mold inhibitor 0.4% -0.6%

3. Exclusive solution for high temperature and high alkali industrial paint

Pure BIT long-lasting anti-corrosion+alkali resistant mold inhibitor, abandoning non alkali resistant CMIT