TAGS: Biocides/ Preservatives Architectural Coatings
The most important job of a waterborne coatings formulator is to develop and manufacture paints that meet customer expectations. From opening the container until many years after application this is your promise to your customer.
Protection from biological contamination at any stage is a key performance indicator for meeting these expectations.
Most of this discussion will use decorative coatings as examples but the principles outlined apply to any other markets where waterborne coatings are used as well. One topic beyond the scope of this discussion is anti-fouling coatings for marine environments since waterborne coatings are very limited in this application.
Understand the key features, processing attributes and regulatory requirements to consider while selecting preservatives & biocides in waterborne coatings in detail, but, first let us begin with their definitions.
Definition of Preservatives & Biocides
What are Preservatives?
Preservatives are used to
prevent degradation of a waterborne paint during storage or use. The conditions causing degradation could include:
- Temperature extremes
- Exposure to humidity or air and
- Biological contamination
A biocide is a type of preservative but not all preservatives are biocides. Antioxidants and
thermal stabilizers are also preservatives but since they do not have activity against living organism they are not biocides.
There are certain cases where an antioxidant and/or a thermal stabilizer would be used in combination with biocides to prevent degradation of a waterborne coating.
What are Biocides?
Biocides are agents which
kills living organisms (plant, animal, microorganism). Commonly used biocides in paints kill microorganisms, such as bacteria or fungi and are also known as anti-microbial agents.
Biocides which target larger organisms, such as mollusks are sometimes used in applications like anti-fouling bottom paints on ships. Some of the earliest biocides were based on Mercury or Formaldehyde but these are no longer used because of their toxicity to humans and other non-targeted organisms.
» View All Biocides & Preservatives Suitable for Coatings!
Function of Preservatives and Biocides in Waterborne Coatings
Prevent/Correct Contamination in the Package
Protecting the paint
“in the can” is a primary use of biocides in architectural coatings. Nothing will destroy trust in a brand faster than when a painting contractor or DIYer opens a spoiled container of latex paint. Totally preventing contamination of latex paints before packaging is practically impossible during manufacturing.
Adding anti-microbial compounds to the paint moderates the damage the growth of microbes causes.
Many types of microorganisms can grow in waterborne paints but the most common are bacteria and fungi. While there are broad spectrum additives capable of controlling more than one type of microorganisms, best results are often realized when a biocide or combination tailored to control the specific contaminant is utilized.
Essential common
raw materials used in waterborne coatings provide nutrients for microorganisms. Nutrient sources include:
- Polymers
- Surfactants, and
- Thickeners
Cellulosic thickeners can supply nutrients for many types of microorganisms. The
optimal pH range for the growth of microorganisms is 4 to 9 with bacteria favoring neutral to slightly basic pH and fungi favoring acidic pH. This corresponds to the pH range of many waterborne coatings.
Prevent Damage to the Applied Coating
After paints have been applied, they are still subject to degradation by microorganisms. Decorative coatings constitute the
greatest volume of waterborne coatings sold. Fungi and algae are the most common causes of decorative paint degradation while in use with fungal damage most common over wood substrates.
Decorative paints applied to cementitious materials can suffer from algae growth and in these cases a herbicide which remains in the film should be added to the formula.
Additives which prevent damage from fungal and algal growth in service are called
dry film preservatives.
Criteria for Selection in Waterborne Coatings
Functions Required
When selecting a
preservative and/or biocide for a waterborne coating your first question should be “
what do I want this additive to accomplish?” Suppliers organize offerings into groups according to functions such as long term anti-bacterial agents or dry film preservatives to control mold and mildew.
Accurately anticipating the performance expectations of the coating in both the long and the short term enables selection of the correct combination of biocides and preservative to ensure end-user success.
Current Regulatory Considerations
Regulations are a real constraint upon choice of biocides and preservatives. After finding candidates which should work in your formulation the next step is to check
each component to verify it complies with regulations in all relevant regions where the product will be manufactured and distributed.
Nothing is worse than preparing and testing prototype formulations only to find that a material is not allowed in your target market.
US Regulations
In the United States, the
Environmental Protection Agency is responsible for regulating any biocidal agents since they are considered pesticides under Federal Law. Regulations specify which compounds are allowed for use in coatings as well as maximum use levels.
Certain US States, such as California, have increased restrictions on biocide use in addition to Federal Law. Registering a new pesticide for use can take up to 5 years with associated costs of an estimated 3 million US dollars.
EU Regulations
The
Biocidal Products Regulation (BPR) determines what biocides can be used for defined applications within EU countries. Implementation of the BPR has:
Changing Regulatory Landscape and Regulatory Trends
Regulation of biocides is sure to become stricter in the future with most regions following the global lead of the EU and the USA. Increased restrictions of
isothiazolinone biocides are expected due to their potential as allergens.
Get tips to select the right biocide or anti-foulant for your paints and coatings.
Practical Processing Attributes of Preservatives and Biocides
Ease of Incorporation Into Your Formulation
Identical anti-microbial agents are often sold in various forms. Packaging similar
active compounds in these different forms enable incorporation into a wide range of waterborne coatings. Choosing the delivery form best suited to your coating will allow easier incorporation while reducing processing time.
A biocide dissolved in a compatible solvent would be a good choice for a waterborne alkyd
DTM coating while the same active ingredient delivered as a
VOC-free dispersion in water would be the best option for a latex architectural paint.
Stability in Your Formulation
Both active ingredient type and the delivery form can affect the stability of a biocide in a specific formulation. Negative interactions between the biocide and other raw materials must be avoided.
Most biocides are mobile, reactive molecules which can
interact with formulation components, such as:
These interactions might lead to problems like gelation, pH drift and changes in
viscosity.
Persistence of Action or Longevity
How long a biocide remains active in a waterborne coating depends on several factors which must be considered during the formulation process. Half-life is one way to measure the persistence of an anti-microbial agent. Defined as the time required for the measured concentration to fall to half of the initial concentration, half-life can be used to estimate the approximate time the agent will remain active in the formulation.
Based on the
length of time a biocide is active they can be classified into groups, such as:
- “Quick kill” compounds
- Package stabilizers, and
- Dry film preservatives
Putting it All Together – Preservative and Biocide Selection for Success
How to Fit the Preservative/Biocide Package to Your Customers Needs
When trying to decide
what preservative and biocide package to use for your formulation the following must be considered:
- What is the expected shelf life and storage conditions of the paint?
- Could the paint become contaminated with microorganisms before packaging or during use?
- Once the waterborne coating is applied, will it be subject to conditions which promote microbial growth?
Proven Solutions for Common Waterborne Coatings Requirements
There are hundreds of registered preservatives and biocides to choose from to protect waterborne coatings from spoilage and damage due to microbiological attack. The time and capital investments required to certify new biocides for use means that predominantly large,
global suppliers have comprehensive offerings. Such suppliers include:
Other suppliers produce more limited ranges of products based on compounds which have been previously registered and have well established reputations for efficacy. Smaller suppliers may offer cost advantages for these established biocides.
Here are several common scenarios and suggested biocide solutions to meet your customers’ expectations:
- Latex based interior latex flat wall paints: This scenario calls for protection on two fronts. The first is a quick kill biocide to eliminate contamination introduced during manufacturing processes & a longer acting component like BIT to prevent growth of any remaining microbes during the products shelf life.
- Latex based exterior paints: Adding a dry film preservative, such as Zinc Pyrithione to prevent fungal or algal growth to the required components from the scenario above should provide adequate protection for most exterior architectural applications. An interior paint recommended for use in high humidity areas, such as bathrooms should also contain a dry film preservative to prevent mold and mildew damage.
- Waterborne acrylic industrial coatings: Storage conditions are generally more controlled for industrial controls and the expected shelf life is often shorter. Longer acting biocides may not be needed or lower levels required. Industrial coatings for exterior application to wood or fiber-cement substrates should include a dry film preservative to prevent algal and/or fungal growth.
Conclusion
Careful consideration is required when choosing preservatives and biocides for your waterborne coating formulations. Start by thoroughly reviewing the customers’ expectations, then confirm that your choices are compliant in your targeted regions and finally conduct relevant tests to confirm that your formulation performs as expected.
There are many sources of information and advice to help you make good choices for your formulation. Consulting suppliers’ websites and technical service personnel, reading technical journals and conference proceedings as well as utilizing material selectors such as SpecialChem provide valuable guidance to formulate successful products.
Commercially Available Biocides & Preservatives Suitable for Paints & Coatings