Overcoming Formulation Challenges for Low-VOC Interior Paints with New Binder Solutions

VOC Emissions – Common Sources, Examples & Formula

Interior wall paints are recognized as a significant source of VOCs in spaces where we occupy 85-90% of our time (e.g., schools, workplaces, leisure areas, etc.). They are the origin of what has been called the 'sick building syndrome' since VOCs can be related to allergies, asthma, carcinogens, and other health issues. New buildings and freshly renovated areas especially contribute to the highest level of VOC emissions because of the abundant concentration of VOCs generated at the same time. 

Common examples of VOCs that can be present are propylene and ethylene glycol, alcohols, aldehydes, butyl propionate, and butoxyethanol among others. In waterborne coatings, the primary source of these VOCs is coalescing agents and additives such as anti-freeze agents, biocides, and amine neutralizers. 

The most widely used approach in determining VOC content in paints and for labeling is to calculate pounds (or grams) of VOC per gallon (or liter) of solution minus exempt solvents (including water and VOC-exempt organic compounds).

 

Regulations, public pressure, and general apprehension regarding the environment have led manufacturers to reduce VOC content from 150-350 g/L to as low as 50 g/L. Concerns with interior air quality have also led to new regulations mandating reduced emission levels.
 

Different Approaches Followed by Countries in Characterizing VOC emissions
 

To determine indoor paint emissions, volatile components are investigated in emission test chambers under controlled applications and climatic conditions. Europe and the US follow different approaches in characterizing emissions although there are some commonalities (See table below).² However, ISO 16000-6 attempts to harmonize emission test methods.
 

Indoor emission test results of a specific VOC per ISO 16000-6 can be compared to various set reference limits.
 

• In Europe, emission concentration limits have been established by French, Italian, and German legislation.
• In the US, the most widely used comparison standard is the Office of Environmental Health Hazard Assessment (OEHHA) reference levels (RELS).
   

Certification criteria (e.g., Greenguard, LEED) have also been developed by independent organizations, and they may even be stricter than legislation requirements. Examples of such indoor emission limits are shown in the table below.
 

Low-VOC paint compositions can have performance issues that challenge formulators in several respects. One of the more promising routes to producing low- or no-VOC paint is to limit volatile coalescing agents and plasticizers by using softer polymer binder compositions. Coalescing agents function by softening the polymer particles in a latex, enabling the formation of a continuous film as the coating cures. Additional functions of a coalescing agent are to improve open time, prevent skinning, and change the rheology of the formulation.

Traditionally acrylic polymers for interior coatings have a relatively high glass transition temperature (Tg) to provide the required performance properties. Elimination of the coalescing agent requires a binder with a lower Tg and minimum film-forming temperature (MFFT) below about 4°C. However, such softer polymers can result in formulations with reduced performance characteristics such as:
 

• Higher odor
• Poor stain resistance
• Poor dirt pick-up resistance and cleanability
• Low wet scrub resistance
• Poor color development and fastness
• Poor adhesion to old paint
• Lack of sufficient hiding power
   

These poor performance factors can result in reduced service life which necessitates repainting and another cycle of indoor emissions.

New proprietary resin binder technologies relieve many of these performance problems. The optimal use of materials and processes produces resins with reduced Tg and MFFT. As a result of these efforts, low-VOC interior paints can be manufactured without coalescent and yet have properties that are equivalent or superior to high-VOC paints.

A secondary approach to formulating low-VOC paint is to consider the contributions of conventional paint additives which include – anti-freeze agents, mildewcides, rheology modifiers, defoamers, and surfactants. In conventional VOC coatings, these contributions are not significant, but in low-VOC formulations, they can be the largest source of VOCs. Newly developed additives allow further reduction in VOC.

Vinavil has recently developed three unique polymers (Crilat 4750, Crilat 4816, and Vinavil 04V) that have less VOC content, reduced emission levels, and performance levels at least equivalent to higher VOC paints. Properties of these resin binders are shown in the table below.
 

With such low VOC levels, the odor of paints made with these resin dispersions is extremely low. The Vinavil products also have the following ideal characteristics for environmentally friendly interior paints:
 

• Low MFFT of 0-5 °C
• VOC content less than 0.15%
• Low residual monomer
• No formaldehyde producing components
• Free of hazardous and toxic substances (CMR, sensitizers)
• No environmental hazardous substances (e.g., APEO)
• Low odor
• Excellent compatibility with pigments, fillers, and other additives

These resin binders offer excellent versatility in formulating many kinds of waterborne coatings at low, medium, and high pigment volume content (PVC) levels for use in indoor applications. These paint systems have stain resistance, low dirt pick-up, and wet-scrub resistance. This results in improved durability allowing greater intervals between repainting and subsequent reintroduction of indoor emissions.

 

Several starting formulations for indoor paints have been suggested for the new Vinavil dispersions. These all have safe and low-VOC additives. Performance properties, as described in the next section, are comparable to premium interior paints with higher VOC content and indoor emission levels.

The formulation shown in the table below is for a low-VOC interior paint with a relatively high 80% pigment volume content (PVC) typically used in flat paint. As PVC increases, density and paint hiding power increase, but performance properties such as durability (e.g., scrub, stain, and dirt pick-up resistance) typically decrease. The Crilat 4750 formulation, however, shows no reduction in these important performance properties. High PVC paints are often less expensive than lower PVC paints when quality is equal.
 

The table below describes low-VOC starting formulations with Vinavil 04V or Crilat 4816 having a PVC of 37%. This is a typical PVC level for satin and egg-shell finishes. In high traffic areas, such as hallways, low PVC paint may be preferred for better durability. 
 

Characteristics of Crilat 4750 vs Styrene Acrylic Copolymers

Crilat 4750 is a styrene acrylic copolymer waterborne dispersion. It is free of APEO, coalescent, plasticizers, formaldehyde, and ammonia. Styrene acrylic copolymers are used as binders for medium and high PVC paints due to their outstanding pigment binding properties.

Crilat 4750 dispersion has lower in-can VOC content and emission levels when compared to conventional styrene acrylic binders. The low indoor emission levels meet Classification A+ according to the Grenelle de l'environnement French legislation (See table below). In comparison to conventional styrene-acrylic copolymers, Crilat 4750 has good flexibility. It is suitable for interior and exterior waterborne paint formulations.
 

In addition to its exceptional environmental profile, the main features of Crilat 4750 paint formulations are: 
 

• Water resistance and wet scrub resistance even in high PVC paints
• High binding power with fillers and pigments, even at high PVC paints
• Good stain resistance
• Excellent alkali resistance that allows the formulation of both exterior paint and textured coating
• Low dirt pick-up and good cleanability
• Odorless
   

The properties of Crilat 4750 satin paint with 37% PVC are provided in the table below. Its versatility and excellent compatibility with cement and mineral binders make it a good solution for medium to high VOC interior paints and wall texture coatings.
 

Characteristics & Emission Results of Vinavil 04V vs Vinyl Acetate Copolymers

Vinavil 04V is a new generation waterborne dispersion of vinyl acetate – Veova copolymer. The copolymer has a unique, highly branched aliphatic structure which contributes to key polymer performance properties. It shows a lower VOC content than conventional vinyl acetate copolymers, and it is free of APEO, coalescent, plasticizers, and formaldehyde.

Waterborne formulations manufactured with Vinavil 04V dispersion have an in-can VOC content of less than 0.1% and emission levels significantly below strictly set environmental limits. The table below shows the results of chamber tests according to ISO 16000-6. As a result, Vinavil 04V can be classified Class A+ according to the Grenelle de l'environnement French legislation, and it also passes the Italian minimum environmental criteria (CAM). 
 

In addition to being low-odor and low-VOC, Vinavil 04V paint is characterized by a combination of features that rival interior paint systems with high VOC levels:
 

• Good color development and hiding power
• Good wet / dry scrub resistance and adhesion
• Low odor
• Good rheological behavior
• Low water resistance
• Good stain and alkali resistance
• Very good compatibility with fillers, pigments, and other additives

The excellent performance properties of Vinavil 04V 37% PVC interior paint are shown in the table below. Vinavil 04V offers great versatility in the preparation of any kind of water-based paints with medium and high PVC.
 

Characteristics & Emission Results of Crilat 4816

Crilat 4816 is a pure acrylic water dispersion, free from coalescing agents, plasticizers, and APEO. It has a low in-can VOC level of less than 0.1% and emission levels significantly below strictly set environmental limits. The table below shows the results of chamber tests according to ISO 16000-6. As a result, Crilat 4816 can be classified Class A+ according to the Grenelle de l'environnement French legislation, and it also passes the Italian minimum environmental criteria (CAM).
 

In addition to being environmentally friendly, Crilat 4816 paints are characterized by a combination of features that rival interior paint systems with high VOC levels:
 

The excellent performance properties of Crilat 4816 37% PVC interior paint are shown in the table below. Paints formulated with Crilat 4816 are also noted for their excellent weathering resistance and durability. They can be used in interior and exterior applications.
 

Architects and builders view indoor air quality as one of the most important attributes when considering interior paint. Indoor air quality is assessed by international certifications, regulatory standards, and third-party agencies. Paint manufacturers are responding to this challenge by formulating products that have low VOC content and provide safe, low levels of emissions when tested according to ISO 16000-6.

The major source of indoor emissions are coalescents or co-solvents and certain formulation additives. To eliminate these environmentally harmful elements, one must use binder resins with a low Tg and MFFT. This can be done with softer resins so that they self-coalesce. However, these softer resins can adversely affect drying times, dirt pickup, scrub ability, and other durability and appearance factors.

Vinavil has developed three unique binder resins (Crilat 4750, Crilat 4816, and Vinavil 04V) that provide ultra-low levels of VOCs and indoor air emissions without compromising the performance of the paint. These resins have the requisite low Tg and MFFT to reduce VOC content to less than 0.15% and still provide excellent film formation without the need for coalescing agents or plasticizers. These resins also have low odor, no APEO, no formaldehyde producing elements, and both Crilat 4750 and Vinavil 04V are free of ammonia.

A series of starting formulations have been provided for formulators to take advantage of these eco-friendly resins and to provide indoor emission levels that are within the limits mandated by legislation. In addition to being environmentally responsible, these paint systems also provide fast drying times, low dirt pick-up, stain resistance, and good wet scrubability. Their performance and durability are comparable to or surpass conventional indoor paint systems having high VOC content and emission levels.