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Biocide Selection: In-can Preservation, Dry Film Protection, Anti-fouling...

The ever-changing global regulatory landscape for anti-microbial additives makes the selection process daunting.

Are you also hunting for the right biocide for your coating formulation? We will help you!

Explore the detailed knowledge on biocides for paints and coatings and find out:

Biocides for Paints & Coatings

Antimicrobial additives (also called Biocides) are used in formulations to keep bacteria from spoiling paint during storage, or to keep fungi, algae and other micro-organisms from growing on the applied paint.

Biocides for Paints and Coatings

There exixt a criteria for selecting antimicrobial additives depending on the coating type and end-use application of your product. To learn the same, it is important to know about the types of antimicrobial additives available in the market, their chemistries and purpose of addition.

So, let's begin with types of biocides available for paints & coatings...

Major Categories of Biocides

#1. In-Can Preservatives

Paint Spoiled by Algae Growth During StorageAll waterborne paints contain nutrients for bacteria, fungi and yeast.  Microbial attack can therefor happen inside the can, which would affect the quality of the paint. When it happens, you can experience:

  • Foul odor
  • Loss of viscosity
  • Gassing
  • Phase separation
  • Discoloration
  • pH drop

To protect your coating from such issues & extend the storage life of your coating, you have to use In-can Preservatives. They are organic materials. They are used at low levels; < 0.1% by weight typically.

An efficient In-can biocide should have the following properties:

  • A broad-spectrum antimicrobial efficacy
    Measurement of Minimum Inhibitory Concentration (MIC) is a good way to test biocide efficacy. MIC is the lowest preservative concentration at which growth of a test organism is inhibited under laboratory conditions.

  • Long-term protection
    Paints may be kept in storage for long periods and exposed to wide temperature variations. Optimum preservation can only be achieved if the in-can preservative is compatible with coating ingredients and is stable over time.

 » Check Out All available In-can Preservatives Available in the Marlet Today! 

#2. Anti-Fouling Agents

Anti-fouling AgentsThis is specific of marine coatings. The goal is to avoid marine organisms such as algae and molluscs to attach themselves to the ship. They would otherwise impact the ship performance (speed, maneuverability, fuel consumption).

Anti-Fouling Agents include both organic and inorganic chemistries. The use of some chemistries are restricted geographically for their effect on marine wildlife, so ensure to be compliant with regulatory guidelines for chemistry as well as use level.

 » Explore All Anti-foulants Here! 

#3. Mildewcide/Anti-fungal

Mildewcide Mildewcides and antifungal materials are used in all exterior coatings where any moisture will promote the growth of organisms, such as mold, mildew and other fungi. Paints for interior applications where higher moisture levels are encountered, such as kitchens and especially bathrooms, also utilize mildewcides.
Since mold and mildew will grow even on glass in the presence of water, additives to prevent the microorganisms from establishing colonies are essential to keeping the coating looking pristine and free of discoloration due to mildew growth.

Zinc Oxide (ZnO) is by far the most common inorganic material used. There are several processed used to manufacture ZnO and it is important to adjust usage level based on type due to particle size distribution and therefore reactivity with the coating components.

Many organic materials work well alone or better in conjunction with ZnO, assuming the ZnO can be stabilized. The organics are highly-scrutinized and it is imperative that any used to formulate a coating are appropriate for the climate, but most importantly that they are approved geographically from the regulatory agency.

 » Choose the Anti-fungal Biocide for Your Coating Here! 

#4. Other

Nanomaterials are also used to prevent microbial growth; Silver (Ag) more often than others.

Most applications are where there is a concern for microbes (bacteria, viruses) developing resistance to an organic antimicrobial.

Criteria to Consider for Good Biocide Selection

In paints where antimicrobials that are soluble and easily-dispersed during paint processing, the surface is well-protected against biocidal growth.

In systems where the antimicrobial is immiscible or difficult to disperse, a much higher level of biocide may be required to provide the same protection versus an antimicrobial with excellent dispersibility.

Organic versus Inorganic Antimicrobials

   Organic Antimicrobials
 Inorganic Antimicrobials
  • Non-reactive in total paint systems
  • Don't lead to gelation

  • Inert to U-V
  • Do not leach from the film, thanks to their low water solubility

  • Can leach out from a coating over time with   repeated exposure to water (rain, humidity)
  • May be sensitive to sunlight (U-V)

  • Small particle size inorganic antimicrobials are reactive, especially w.r.t binders
  • Can lead to increased viscosity or even gelation

When should you Consider Blends?

A blend of materials may prove to be effective where there is a synergy between using the blended materials for a system, such as the blend providing efficacy over a greater pH range than either of the constituents.

In addition, with varying regulations globally limiting the use levels of A-M, a blend or a blended material may meet the performance requirements as well as the regulatory requirements.

Factors to Consider during Biocide Selection

Biocide selection criteria

FAQs on Using Biocides Depending on the Type / Application of Coating

Will it be used for a Waterborne or Solventborne Coating?

When a paint is formulated, there are several aspects to be taken care of. First of course, is performance of the paint as formulated. The other is the stability of the paint, which includes maintaining viscosity as well as minimum or no phase-separation.

If an antimicrobial is at least not miscible, it will separate and may form a thin layer at the surface of the paint in the container. Unless well-stirred, the paint applied to the substrate may not be uniform in the protection by the antimicrobial. Resistance to mildew and fungus may be poor as a result.

  1. Antimicrobial suppliers aren’t always specific about applications, as they want customers to use their products in as many applications (and therefore greater volumes) as possible. Many TDS’ show antimicrobial to be slightly miscible in water and only soluble or miscible in certain solvents.
  2. This becomes a key area for testing – compatibility. A good screening method is to make a very simple mixture of resin and solvent proportional to the coating and place in a small bottle or vial and shake vigorously. Incorporate the antimicrobial to determine if it is:
    • Compatible
    • Can be dispersed
    • Stays dispersed over time, or
    • Incompatible and cannot be dispersed or/and forms seeds.
  3. Try adding and shaking in, and if that doesn’t work, use a table/bath sonicator for 10 minutes.

Will it be used for Interior / Exterior Paints & Inks?


SB / WB Antimicrobial Type Chemistry
In-Can Anti-fouling Mildewcide / antifungal Other Organic Inorganic Blend O Blend
SB - Interior


SB - Exterior




WB - Interior







WB - Exterior








Paper Coating


Antimicrobials for Other Applications


SB / WB Antimicrobial Type Chemistry
In-Can Anti-fouling Mildewcide / antifungal Other Organic Inorganic Blend O Blend






Construction Products





Paper as raw material


The greatest application concerns are related to the regulatory environment and solubility. In the former, a paint using a specific level of an antimicrobial in one geography of the world, may not be in compliance in another geography due to use level or local regulations.

It also has to be known how the antimicrobial will be used. For example, there are FDA regulations that dictate use levels and chemistries with respect to indirect or direct food contact and others for adhesives, etc. In each case, the material has to be approved for use in that application, along with the maximum level of usage.

Solubility dictates toxicity which can affect humans on exposure to leachates present in water and plants due to solubility and runoff.

In which Geographies will it be used?

There has been a move to deregulate some products, so ensure that you use the most current MSDS from the supplier’s website and not rely on a document that your company may have filed.

Effects of Environment

  • Damp, humid, overcast environment / weather will be more harsh on an antimicrobial
  • Sunlight can dry out the surface on a regular basis
  • UV can itself kill bacteria (think southern vs northern exposure; mold and mildew vs. nearly none)

What Range of Microorganisms are Present?

In general, you won’t know specifically what microorganisms are present, but the environment in which the coating is applied dictates this. In an institutional setting, such as a hospital, doctor’s office, veterinarian, etc., there will be bacteria and viruses. In an interior room with humidity >75% regularly, the conditions are prime for mold and mildew, although bacteria and viruses will also exist.

Outside in humid climates and particularly on the northern exposure of a building, mold and mildew and algae will readily grow. Other microbials are not of interest.

  • Some newer blends of materials may be more effective over a broader pH range

    • Companies have extensive test data. They are more reluctant to publish some data so you may need to ask for the information.

  • If an Institution (hospital, etc.) are there any restrictions on products due to the development of methicillin-resistance microbes?

    • Some state hospitals in the U.S. are restricting use of organic biocides due to the concern that MRSA strains will develop.

If in the US and related to food, what FDA regulations are required?

Ensure you are using the most current MSDS. Secure a letter certifying compliance and level usage from the antimicrobial supplier if in doubt.

Does your company currently have an inventory on anything that meets your criteria?

Most companies will not allow a new product to be added to their extensive inventory unless you can exhibit a cost/performance benefit that is inclusive in many other applications as well. When you are developing a finished product, certainly evaluate new products as the volume of data over time is the only way to have a new product approved. But don’t rely of products that your company doesn’t use unless you are provided with a large development window.

Does your company have historical data on the performance of any of the materials?

Most companies have more than a handful of antimicrobial products for different applications. The larger companies who merge and acquire, usually acquire more choices of antimicrobial as well, which may be pared down as dictated by the company to achieve the continued benefit of favorable pricing based on volume.

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