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An Article on

Approaches to develop waterborne

acrylic binders for low VOC Paints

By:Shasanka Sekhar Borkotoky

Parag Choudhury

(M. Tech. Polymer Science & Technology)

Department of Chemical Sciences

TEZPUR UNIVERSITY

NAPAAM, TEZPUR – 784028

DISTRICT- SONITPUR (ASSAM)

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1. INTRODUCTION

The development of new elastomeric waterborne acrylic resins for use in surface tolerant

maintenance coatings will be described. These coatings are resistant to mud cracking, and form

an excellent barrier coating for the protection of steel. Elastomeric coatings based on

waterborne Acrylics have excellent water and corrosion resistance, adhesion, flexibility (even at

low temperatures), and tolerance to application over both clean and rusty steel surfaces. In

addition, these coatings have very low levels of volatile organic compounds (VOC), and offer an

environmentally-friendly and VOC compliant alternative to traditional solvent borne coatings. The

development of a waterborne acrylic binder that can be formulated into zero VOC paints

requires the tuning of film formation under difficult conditions, hardness, and flexibility properties.

To meet these requirements, a model of the ‗ideal‘ film was developed and polymers were

synthesized to comply with this model. The choice of particle size and glass transition temperature

(Tg) of the polymer phases were the key parameters in producing the desired film morphology.

However, to ensure good mechanical properties, it was also crucial to optimize the interaction

between the polymer phases by varying both the polymer composition and the stabilization of

the latex.

Today, most interior and exterior paints are found to have high levels of VOCs, which help

them to dry faster. But, these VOCs emit smog-forming chemicals into the air and thus. Become

the major contributor to ground-level ozone pollution. These release low-level emissions into the

air for years after the application. And the major source of these toxins is a variety of volatile

organic compounds, which, until recently, were essential to the performance of the paint.

The new environmental regulations have resulted in alternative solutions – Low VOC and

Zero VOC paints. Lower VOC paints preserve both indoor and outdoor air quality and reduce the

incidence of eye or respiratory irritation from exposure to VOC fumes. [1]

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Types of non-VOC paints:

1. Natural Paints and Finishes –

These are paints made from natural raw ingredients such as water, plant oils and

resins, plant dyes and essential oils; natural minerals such as clay, chalk and talcum; milk

casein, natural latex, bees wax, earth and mineral dyes. Water based natural paints

give off almost no smell. The oil based natural paints usually have a pleasant fragrance

of citrus or essential oils. Allergies or sensitivities to these paints are uncommon. These

paints are the safest for one‘s health and also for the environment.

2. Zero VOC paints –

According to the EPA (Environmental Protection Agency) standard, any paint in

the range of 5 grams/litre or less can be called ‗Zero VOC‘ paint. Adding a colour tint

usually brings the VOC level up to 10 grams/litre, which is still quite low.

3. Low VOC paints –

As described above, the level of harmful emissions are lower than solvent-borne

surface coatings, as they carry water as a carrier instead of petroleum base solvents.

These certified coatings also contain no, or very low levels, of heavy metals and

formaldehyde. The amount of VOCs in paints should not exceed 200 grams/litre and in

varnishes, it should not exceed 300 grams/litre. Low VOC paints tend to emit odour until

dry. To avoid this, one should buy paints that contain VOCs less than 25 grams/litre. [7]

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2. Waterborne Acrylic Binders

Acrylics began life early in the 20th century and have gone on to produce a

wide range of products. Long before there was any Acrylic artist's paint Acrylic was

replacing glass in World War 2 fighter planes and acrylic fibers were being woven into

textiles. Acrylic emulsions were first used as house paints which were made famous

artistically when they were used by Jackson Pollock, but it was not until after Pollock's

death that the first artist's acrylics became widely available.

Making Acrylic paints is not so simple as the traditional products like oil and

Tempera. However very serviceable paints can be ground in the prepared Acrylic

mediums. As these come in a wide range of viscosity and other properties it is easy to

vary the mixtures to suit individual needs. Taking this approach makes making Acrylic

paints little more difficult than making Tempera. Unlike Tempera, however, a far wider

range of paints can be made from thick impasto paints to tough thin vehicles for

glazing and iridescent coatings.

This is the pure acrylic resin without modification so it is a thin milky liquid that

dries to a tough flexible film that is the strongest and most durable of the Acrylic paint

films. Pigment can be ground directly into Binder Medium, or the binder can be freely

mixed with other mediums to increase resin content. On its own this makes fabulous

glue that is perfect for gluing canvas to panels because it is nice and thick, and is great

as general purpose glue as well as a medium for making paints. Gel Medium Thick,

transparent, and glossy makes a good strong paint film with maximum brilliance of

colors. The addition of spreader medium will increase flow property.

Impasto Medium The base for thicker paints

Impasto medium does not dry perfectly clear as it has a solid content already. So

it is the starting point for making acrylic gouaches with the addition of precipitated

chalk or for adding calcite to make thick modeling style pastes.

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Iridescent Medium For special effects

Iridescence can be added to any pigment by using Iridescent medium. It is

basically Acrylic binder with Mica Titanate added that gives the iridescent sparkle to

any color ground in this medium. Transparent pigments will have a greater iridescence

and opaque pigments less so.

Modifiers Retard, spread, break surface tension etc

Retarder

Retarder mediums adjust drying speed by replacing water with a liquid that drys

more slowly than water. Useful up to a point but too much can create a paint that

won't dry properly.

Spreader or Thickener

This adjusts the flow and leveling qualities of the paint (technically called

rheology). Thickeners are available with both short and long rheology.

Defoaming agents

These are silicones that combat the surficants within the Acrylic which have a

tendency to foam during dispersal by popping bubbles as they form. Overuse causes

'cratering'.

Matting agents

This is silica and in the case of making Acrylic paint the naturally derived crystaline

version is better than the synthetic 'amorphous' type.

Wetting agent

Often called Surface Tension Breaker's these are valuable for wetting the

synthetic organic pigments during predispersal of the pigments.

Calcite

Calcite can be freely mixed with the acrylic to make a modeling paste or paint

that holds brushstrokes easily.

Ammonia

This can be just the Cloudy Ammonia from the supermarket. As you make paint

the pH level may fall. Acrylic paint exhibits ideal paint qualities between pH levels of 8

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and 9 (water is 7) and if the pH gets too low the paint goes funny and can be ruined. A

little Ammonia helps return the alkalinity the paint needs.[2]

These are some industrially used Acrylic Binders.

Chemical

Nature

pH

(±0.05)

Dry Cont.

(±2%)

Cold

Crac 0C

Film Properties

General properties

and uses

Acrylic Emulsion

6.5

35%

-

Hard Clear

Transparent Glossy

General used as a topcoat for resin as

well as glazed finishes. It produces a bright, lustrous and a radiant gloss with a pleasant touch. It can be used as an intermediate binder

for plate release.

Acrylic Emulsion

7.0

38%

12 0C

Med-Soft Glossy Elastic Non-Tack

Self-crosslinking binder used for general plated resin finishes. It has excellent surface

build up and surface smoothness.

Acrylic Emulsion

6.0

35%

-15 0C

Med-Soft Elastic Glossy

Self cross Linking general-purpose med-soft binder used as a major binder for bottom as well as intermediate coats...It has moderate surface build up.

Acrylic Emulsion

6.5

38%

-12 0C

Soft Good Filling Glossy

Soft binders with low tackiness, good gloss, filling, anchorage and possesses good fastness properties.

Acrylic Emulsion

6.5

38%

-12 0C

Med. Soft, Good Filling, Glossy

Non-Tack Med. Soft, elastic resin with low tack, good flow and embossing properties. Excellent fastness to light.

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Acrylic Emulsion

7.0

35%

-25 0C

Very-soft Strongly Filling Glossy

Slight Tack

Soft binder with fine particle size used for sealing coat in finishing splits.

Acrylic Emulsion

4.5

35%

-18 0C

Soft, Fine Glossy,

Soft, fine elastic binder with low tackiness for full grain/garment leather. Improve adhesion without overloading the

grain.

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3. Low VOC Paints

Volatile organic compounds are substances that evaporate from paint

allowing it to dry and are very toxic to humans. Even after the paint has dried,

VOCs can continue to be released from the paint for years, thus, harming the

occupants. The easiest solution is to use paints that do not contain VOCs and

instead contain a non-harmful drying agent.

Low VOC paints are the ones which use water as a carrier and it contain

reduced levels of volatile organic compounds (VOCs), which emit smog

producing pollutants into the air.

Formulation of a zero VOC polymer

Choice of thickener

When formulating the zero VOC binders, the careful choice of the thickener

was considered to be crucial. The stability of the formulation during film

formation is important to obtain the optimal balance in properties. Since the

binder was optimized in its stabilization mechanism, certain thickeners can have

a detrimental effect on the film-formation and application properties.

Two thickeners that were found to be suitable were next to the Rheolate 350

from Elementis Coapur 3025 from Coatex. Both can act as the basis for further

formulation.

Choice of defoamer

Defoamers are known for their strong effect on film properties and always

have to be optimized according to the final formulation. Important in this

specific formulation was the fact that they should not contain any organic

solvent. Two defoamers which showed the best properties in the screening

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formulations were Foamex 805 from Tego and Drewplus S4386 from Ashland. BYK

022 was only used in the pigment paste.[8]

Addition of solvent

Although the intention of the binders is based on a completely zero VOC

formulation, it is feasible to add some additional cosolvent. The binders are

compatible with standard organic solvents such as butylene diglycol

(BDG), ethylene diglycol (EDG), dipropylene glycol methyl ether (DPM) and

dipropylene glycol butyl ether (DPNB). In these cases, the cosolvents did

not have an additional function as a coalescent aid, but had an effect on the

paint viscosity. One has to be careful that the solvents have no negative impact

on other properties such as the hardness and the blocking tendencies, mainly

due to retention in the film. Increasingly demanding environmental regulations

for industrial maintenance coatings have put pressure on manufacturers and

users of both solvent borne and waterborne coating systems. The lowering of

volatile organic compound (VOC) levels to below 100 g/L is being considered

for industrial maintenance coatings in many regions of the world. This article

discusses the development of Waterborne acrylic latex polymers for use in high

performance,VOC-compliant coatings applied to steel and concrete structures.

Formulation and coating properties of these polymers are described, with an

emphasis on comparisons of performance to traditional, higher VOC

waterborne and solvent borne coatings. Environmental regulations have put

increasing pressure on all members of the coatings industry to develop and use

coatings that have lower impact on our environment. Raw material suppliers are

constantly working to develop new resins and additives that allow paint

manufacturers to produce coatings with favorable health, safety, and

environmental profiles. In addition, painting contractors and end-users such as

home owners and facility owners are constantly asking for higher performing

products. Those two desires are often difficult to bring together in a new

product, especially when it comes to lowering volatile organic compound

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(VOC) levels. Waterborne latex coatings are one technology which provides an

opportunity to reduce VOC levels relative to traditional solvent borne

technologies. However, technical challenges still exist, considering the low-VOC

targets posed by many existing and proposed regulations. In particular,

properties such as hardness, dirt pickup resistance, block and print resistance,

and the ability to withstand freeze-thaw cycles, can be difficult to achieve.

Using latex polymers with lower glass transition temperatures is an obvious route

to coatings that require less coalescing solvents and have lower VOC demands.

Industrial maintenance painting of steel and concrete structures is still

done mainly with solvent borne coating technologies. It is estimated that about

80% or more of the coatings used in these applications are solvent borne, with

epoxies, polyurethanes, and alkyds making up the bulk. Only about 16% by

volume of industrial painting relies on waterborne acrylic latex coatings, while

architectural applications today overwhelmingly utilize latex-based coatings.

However, the use of waterborne coatings for industrial maintenance has grown

considerably since the 1970s, when they were virtually non-existent. Waterborne

acrylics now find use in a variety of light and medium duty industrial

applications. Overall, the phenomenal growth of waterborne acrylic has been

driven by a number of factors, including compliance with VOC regulations, ease

of clean-up, less hazardous waste disposal and its associated costs, lower risk of

health hazards due to exposure to solvents, less concerns with flammability and

the impact on insurance costs, their one-component ease of use, and, finally,

their proven performance capabilities in real world settings. As with architectural

coatings, industrial maintenance (IM) coatings are coming under increasingly

stringent VOC regulations in many areas of the world. Standard VOC levels for

industrial maintenance coatings to 100 g/L. Such regulatory pressures will

continue to move IM coatings towards waterborne, high-solids solvent borne,

and other technologies that are able to comply with these strict limits. At the

same time, end-users are unwilling to sacrifice coatings performance for these

often high-performance coatings.[4]

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The major paint properties, which include an excellent film formation of

zero VOC paints under difficult circumstances (e.g., drying at 4degreeC on a

porous substrate), combined with a good hardness, blocking, and sufficient

flexibility to follow dimensional changes of the wood, put a high demand on the

design of the acrylic binder.

For an excellent film formation at a temperature of 4degreeC, one would

need a very soft polymer to ensure optimal polymer flow, even at higher

pigment loadings. This implies that the polymer will need a glass transition

temperature (Tg) that is well below 4degreeC. This will result in insufficient

hardness and extremely poor block resistance. To achieve the required hardness

and blocking, a high Tg is required. This will result in a poor film formation,

because of the contradictory requirements for this low VOC application.

Through the years, researchers have sought the ultimate balance in these

properties by combining hard and soft polymers in a variety of ways.

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4. Structure and Formation of low VOC

Paints

Film Formation

Film formation using acrylic binders is a process that has been studied by

many people over the years. When homogeneous latex is applied, the ultimate

film should eventually result in a homogeneous polymer film.

When one considers the contradictory application requirements, this

homogeneous film would hardly ever be able to deliver the desired properties.

Thus, for many years, attempts were made to synthesize acrylic dispersions that

would give a heterogeneous film on drying, by combining hard and soft

polymers. The most common way of obtaining a structured film was to apply a

blend of hard and soft particles and/or to change the particle morphology of

the single particles.

By using this method; several film structures can be obtained. In the rest of

the article, the terms ‗hard‘ and ‗soft‘ polymer will be used. The term ‗soft‘

refers to a polymer with a Tg < 0degreeC; the term ‗hard‘ refers to a polymer

with a Tg > 50degreeC.

A model is proposed that is believed to give the most desirable film

morphology for a zero- VOC paint. It is thought that in an ideal case, the hard

polymer builds an internal film structure along the edges of the particles of the

soft polymer. The soft polymer is able to form a coherent film under ambient

conditions, and the internal structure of a limited amount of hard polymeric

material provides the required hardness.

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An additional requirement is to obtain a flexibility of at least 100%.

Flexibility, in this case, was measured using the percentage elongation of the

film up to the point of failure due to the propagation of fractures in the film.

For good elongation, the most flexible (i.e., soft) phase should form the

continuous phase, in which case failure will occur in this soft, continuous matrix.

The case where the fracture occurs along the interface of soft and hard

material is undesirable, because this points to a weak interface between hard

and soft particles and, therefore, reduced elongation. This all leads to the

conclusion that the interface between the polymers has to be tougher than the

soft polymer matrices.

Another important parameter that has to be taken into account is the

fact that the polymer dispersions are being used as binders in paints. In other

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words, the pigment ability of these formulations containing the polymers plays a

major role in the overall performance of the material. This implies that the

desired hardness/ flexibility balance has to occur in a pigmented formulation

where the pigment binder interaction plays an important role. Therefore, in

addition to the interaction between the different polymers, the interaction of

the polymer with the pigment will also determine the properties of the final

paint.

Considering all these factors, it is clear that such systems require a careful

balancing of parameters in the polymer binder.[5]

Structure of the polymer film

The first target was to obtain a film that had an internal structure, which

resembled that shown in Fig. The most logical route to obtaining such a structure

was through the use of a blend of two polymers. For this purpose, a range of

polymers was synthesized, varying in both particle size and Tg. These polymers

were blended in several ratios and evaluated. More experimental details

regarding the polymers are clarified in reference. To clarify the internal film

structure, atomic force microscopy (AFM) experiments were conducted on the

films of the blends not only exhibiting the surface of the film (as is normally the

case when applying AFM), but also studying the interior of the film. This latter set

of experiments was performed by applying AFM on cryo-microtome crosscuts of

the films. Since the AFM method that was applied was sensitive to the hardness

of the surface, a picture could be obtained of the internal morphology of the

film, where the dark regions indicated soft material (low Tg) and light regions

indicated hard material (high Tg). By applying this technique, it became clear

that the film morphology could be modified by varying particle sizes, hard/soft

ratios, as well as particle morphologies. Table displays the three key parameters

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that were chosen to judge the applicability of the binder. AFM internal

morphology images of these four samples are also displayed in Fig.

From the AFM pictures and the application results, it can be concluded

that the control of the internal film morphology clearly influences the final

properties of the film.

When a homogeneous film is obtained with a limited internal structure

(sample A), the properties are quite poor. The hardness and elongation

properties are inadequate and film formation at 4degreeC is not optimal.

Introducing a separation in hard and soft material, where both hard and soft

components are present in equal amounts, results in a sort of bi-continuous

phase (sample B). This has a positive effect on both the hardness and the

elongation. When the particle-size ratio between the soft and hard particles is

increased (sample C), an internal structure starts to develop and appear,

resembling the model presented in Figure. The elongation immediately

increases. However, film formation at 4degreeC is still not optimal, because of a

relatively large amount of hard material. Decreasing the amount of hard

material (sample D) surprisingly did not influence the measured hardness much

and had a very positive effect on the film formation at 4degreeC. A closer

inspection of the AFM picture of the interior of the film still revealed an internal

structure in the film,

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where the hard material was present at the outside of the soft particles.[6]

Interaction between the different polymers

Although there is a clear relation between the film morphology and

application properties, it was immediately clear that the internal film structure

was not the only parameter determining the properties. The elongation

properties and the ability to formulate the binder are determined by the

chemical buildup of the polymer and the stabilization mechanism of the

polymer emulsions. Changing the composition of the polymer backbone and

changing the stabilization mechanism can have a dramatic effect on the

mechanical properties of the film. Where scanning electron microscope (SEM)

images of the fracture surfaces, after failure in the elongation experiments, are

presented. Here, three blends of polymers with the same ratio hard/soft material

were investigated. The particle sizes of both the hard particles and the soft

particles were identical, so no effect of the film structure was expected. The only

differences between the three samples were the composition of the soft

material (Tg was kept identical) and the stabilization mechanism. The hard

polymer was kept the same in all cases. What can be seen in the first

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sample is that there has been very poor interaction between the hard and soft

polymer phases. It appeared that the hard particles and the soft matrix

material were completely separate from each other. Furthermore, due to poor

stability during film formation, the hard polymer particles exhibited clustering,

resulting in large hard domains. This resulted in a brittle fracture over the

interfaces between the two polymer phases.

The second sample contained the same soft polymers and hard polymers,

only with an improved stabilization of the polymer particles. The system also

showed typical surface features associated with a brittle fracture. It appears

that this system also failed at the interface between the hard and soft particles.

However, no large clustering of hard polymer particles was observed, indicating

better stability during film formation. The third sample contained a soft polymer

with similar stabilization to that of polymer. However, this polymer was designed

to have better compatibility with the hard polymer phase. The fracture surface

was more ductile in nature. The failure appears to have occurred through the

main, soft, polymer matrix because fewer hard particles were visible. This

indicates a better interaction between the soft and hard phases. As a result,

there was a significant improvement in the hardness-flexibility balance, as

shown in Table 1.

When the results in Table are compared, it is clear that good interaction

and good stability during film formation are very beneficial for the overall

performance of the system. It is also evident that when the hard and the soft

polymers exhibit excellent interaction, the hard polymer strengthens the soft

polymer phase. When this is combined with the positive effect that one can

obtain with an internal structure in the polymer film, the result can be that

relatively small amounts of hard polymer have a very positive effect on the

mechanical properties of the polymer film.

It is clear that the complete domination of the polymer film by the hard

phase resulted in a decrease of the measured elongation. The balance

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between hardness and elongation was clearly very sensitive. It is usual to add as

much hard material as possible to obtain the highest possible hardness.

However, too much hard material will have a negative effect on the film

formation properties and on the elongation characteristics of the film.[7]

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5. New developments and technologies in

Water based Polymers

A Driving force in the development of water based binders has been, and

still is, the introduction of legislation to protect the environment and increasing

legislation to protect our safety and health. Acceptance of new technology

depends much on such practical factors as the ease of coating production, the

ease and speed of application, drying methods and the final properties of the

finished material. But such, new technologies should not lead to a decrease in

the capability of the finish to beautify wood or furniture. The development of

water based binders has always concentrated on this aspect, but so far, the

trouble-free replacement of solvent based coatings by water based systems has

not been too easy. Recent developments in acrylic emulsion and polyurethane

dispersion technology give coating manufacturers the possibility of formulating

paints and lacquers which perform very near to the quality furniture producers

are used to. With the introduction of surfactant-free emulsions, a new

generation of urethane/acrylic copolymers, fatty acid modified polymers, water

based UV curing technology and the increasing know how in controlling

emulsion particle size and shape, formulators can now develop coatings fit for

the new age.[8]

Development need

Intensive discussions and co-operation with paint producers and end users

made visible what the shortcomings of the water based technology are and

which coating aspects should be

improved making a higher penetration of the market share of water based

technology possible. The following table lists these aspects or points of

improvement:

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It Improves

· Wood wetting

· Stain resistance

· Scratch resistance

· Block- and imprint resistance

. Transparency

· Filling properties

· De-foaming properties

· Grain-raising resistance

· Flow- or stretch of the applied coating

Technologies

The various technologies used are

Self cross linking one component acrylic emulsions;

Fatty acid modified urethane dispersions;

Controlled particle size morphology and distribution emulsions;

Surfactant free acrylic technology;

New urethane acrylic polymerization technology

Various coatings used in the industrial wood coating sector, such as those for

tables, kitchen cabinets, office furniture, etc. require a high level of resistance. A

resistance level that preferably is obtained by using one-component coating

systems, since the use of polyaziridine nor the addition of cross linking

formaldehyde releasing urea resins is no longer wished and the addition of poly

isocyanates is possible only under strict conditions and some application

methods, such as curtain coating, do not allow their use, due to the relatively

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short pot life. Improved resistance of one-component systems can be obtained

by various techniques.

Self Cross Linking Resins

By incorporating self cross linking capability into an acrylic copolymer it is

possible to improve the chemical resistance. Self cross linking is obtained at

room temperature but optimal cross linking is reached at elevated temperatures

of 50 to 60 Centigrade. The temperature increase improves the molecular

mobility and furthermore leads to a faster optimal acidity of the emulsion system,

enabling quicker and more intense cross linking. These systems, now in use for

many years, have caused wider and easier acceptance of water based

systems due to the higher resistance level .

Fatty Acid Modification

Fatty acid modification of waterborne polyurethanes or acrylic/urethane

copolymers is yet another way of increasing resistance to chemicals, stains and

solvents. By building in fatty acid, auto-oxidation is introduced, leading to

increased resistance, but also offering improved scuff resistance, comparable to

that of a water borne polyurethane cross linked with an aziridine or solvent

based oil modified urethane. Interesting side effects of this fatty acid

modification is offered towards the improvement of filling properties,

transparency, gloss, wood wetting, hardness and flow. In some European areas,

where deep gloss, excellent wood wetting and flow are desired, the use of this

material can replace solvent based products in furniture and flooring

application.

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Novel Morphology

The performance properties of acrylic copolymer emulsions can be

drastically improved by altering the shape of the polymer. Acrylic emulsions

synthesised by conventional free radical polymerisation have usually lacked the

clarity, block resistance and durability necessary for end users such as furniture

and kitchen cabinets.

The use of new polymerization techniques, such as sequential polymerization,

offers acrylic emulsions with improved clarity, sand ability and better block

resistance.

The segregation of the different monomers into distinct phases by sequential

polymerization can produce a polymer with glassy or rubbery regions. Reduced

film former demand, improved block resistance and improved adhesion is

obtainable depending on the sequence in which the monomers are

polymerised.Copolymers designed with a hard, glass like core and a soft

rubbery shell will show a lower minimum film forming temperature at a

comparable coalescent level than a physical blend of the same composition.

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Reversing the structure will lead to improved block resistance. Sequential

polymerization can mask a particular monomers weakness while playing to its

strength.

Water based UV curing

Industrial wood finishing is an application area where water based UV curing

coatings are used in increasing quantities. Application methods vary from

conventional air spraying, airless spraying, air mix spraying, curtain coating

application and even roller coating application.

The advantages are numerous:

No- to very low - coalescing solvent need,

Ease of obtaining low gloss levels,

Ease of application and physical drying properties.

Flat panels as well as three dimensional surfaces, in the case of e.g. the

coating of chairs, are coated with water based UV curing coatings, replacing

two-component solvent based systems, Obtaining high quality coatings with

superior properties is not difficult by the use of the available Water- based UV

curing chemistry. Combining aliphatic- or aromatic, acrylic terminated,

polyurethane technology with polyester and/or acrylic materials offers

advantages such as quick water release, wood wetting, physical drying, surface

hardness and resistance. Blending with acrylic emulsions leads to improved

leveling. Water based UV curing dispersions can be formulated into transparent

and pigmented low and high gloss coatings.

Surfactant-free Polymers

Polymerization of polymers without the use of surfactants or emulsifying

agents, offers various interesting features as e.g. lower polymer particle size, less

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foam formation during coating production, increased wood wetting properties,

coating transparency and improved water resistance.

Formulating surfactant free materials into coatings does not differ much in

comparison with formulating with conventional acrylic copolymers. As we are

used to with our standard emulsion programme the choice of film forming agent

needs attention, not only because of compatibility but also because of the, by

legislation, limited choice of coalescing agents in various countries. The

following table shows the compatibility results of a surfactant free copolymer

with various coalescing agents.

Recent development in surfactant-free polymerization has shown that

combining the advantages of low molecular weight binder solutions (offering

improved wood wetting, ease of film formation and better flow properties), with

higher molecular weight free radical polymerization technology will offer us the

best of both systems.

This new method of producing acrylic emulsions enables the formulator to

produce water based furniture coatings offering high transparency, wood

wetting, superior pore wetting and touch, excellent de- foaming properties and

application properties.

New Urethane Acrylic Polymers

Again economics and the wish for increased properties, as resistance to

butyl acetate and acetone as required in the British Standard BS-6250 Severe,

excellent block resistance and hand cream resistance, made a search for new

polymerization techniques necessary. A new generation of urethane acrylic

copolymers was developed and is now used by formulators to create water-

borne clear and pigmented coatings for kitchen cabinets, table tops, chairs

and panels, replacing conventional solvent-based coatings such as acid curing

coatings and in some cases even 2 component coatings.

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Wood & Grain Raising

Grain raising caused by water contact is a well known, but not much desired

effect by the wood processing industry. The swelling of the wood fiber results in a

rough surface which requires extra sanding will it not lead to visible defects in

the topcoat. A subjective method was determined to assess grain raising.

Factors influencing grain raising were listed and literature study was done. Grain

raising is not a very well described nor understood phenomenon.

It depends on the following :

Grain Raising Influence

Wood Type

Co solvent use , type and quantity

pH level

Solids content

Coating thickness

Surface tension

Solubility of the polymer

Emulsifier type used for polymerization ( cationic/anionic)

Tg, MFT(Melt Flow temperature)

Drying speed and method

Surface preparation

Particle size

Viscosity

Application method

It is cleared that grain raising made clear that the type of grain raising will

be different by the selected wood type. The grain raising of oak, mahogany,

pine, beech, etc, is not equal. There are no standard test surfaces nor special

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laboratory equipment known which can be used to qualify grain raising. The

wood quality and type of grain raising differs too much in wood panels to make

use of equipment which measures the roughness of the coated wood by means

of laser technique/digital surf, inter-ferometry or con-vocal microscopy. [3]

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6. Advantages of Low VOC Paints for Water

borne Acrylic Binders

Major advantages of low VOC paints using water borne Acrylic Binders are

Environment friendly, as there are lower levels of ozone pollution

Fewer emissions of smog-forming chemicals.

Better indoor and outdoor air quality

Allergies or sensitivities to these paints is uncommon

Ideal for commercial applications, and offer excellent scrub ability

Quick Drying

Low Odour

Non-yellowing

Increased UV resistance, flexibility

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7. Conclusions

A high-performance, zero-VOC acrylic topcoat has been formulated

based on a new innovative acrylic resin that has a fine particle size and a

proper Tg without adding solvent or additives that contain VOCs or HAPs

materials. The new development offers excellent corrosion resistance,

weathering durability, early moisture resistance, freeze-thaw resistance and dirt

pick-up resistance that is suitable for protective coating applications. The

performance properties of the new zero-VOC acrylic topcoat are comparable

to the commercial high-VOC, high-performance acrylic.

We have described the development of a new waterborne acrylic latex

polymer designed for both low-VOC and high performing industrial

maintenance coatings. The improved performance relative to currently

available binders and commercial coatings is based on the use of a novel

technology which enhances the pigment distribution in both the wet paint and

dry film. The formation of latex polymer-pigment composite particles in the wet

state leads to better pigment dispersion in the dry film, and results in significantly

improved gloss, durability, hiding, and corrosion resistance. In addition, self cross

linking via an oxidative cure mechanism leads to improvements in dirt pickup

and solvent resistance, and also contributes towards the excellent durability.

Direct evidence for the formation of polymer-pigment composites and

improved pigment dispersion in the dry film comes from centrifugation and

microscopy (FE-SEM, AFM) techniques, and correlates with the observed

properties. The technology exploited in this work represents a new method for

controlling the wet paint and dry film structure of waterborne acrylic latex

coatings, and the demonstrated benefits suggest potentially broad utility and

value in both industrial and architectural coating applications.

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New developments in elastomeric waterborne acrylic polymer technology

provide coatings for industrial applications that possess a number of desirable

attributes. Benefits over solvent borne coatings include the user-friendliness, low

VOC levels, low toxicity, and easy cleanup that are already key properties of

waterborne coatings. This study has also shown that the performance of the

elastomeric waterborne acrylic coatings can equal or exceed that of

commercial solvent borne and waterborne coatings.

Maintenance coatings for steel based on the elastomeric technology exhibit

excellent performance properties, including corrosion resistance over clean and

marginally prepared steel, adhesion to difficult substrates such as galvanized

and rusty steel, flexibility, and dirt pick-up resistance. In addition to the

protection of steel, the same coatings have shown promise as coatings for the

protection of industrial concrete. Good adhesion properties and protection of

the concrete from freeze/thaw cycling, water and deicing chemicals suggest

that the elastomeric waterborne acrylics could find utility in the maintenance of

our transportation infrastructure, as well as for other industrial maintenance of

concrete. The ability of the same coating to perform well over both concrete

and steel surfaces is a key benefit, and would allow the use of a single coating

system for both of these very different substrates. It was found that the

combination of zero VOC, flexibility and sufficient hardness could be reached

by designing a polymer film that contained a specific internal film structure. In

addition to this, the interaction between the different hard and soft polymer

phases must be optimized to obtain the required balance of properties.

The internal film structure could be regulated by using a combination of

particle types with different glass transition temperatures and particle sizes. The

interaction between the polymer phases can be optimized by choosing both

the right polymer backbones and an optimal stabilization mechanism for the

polymer latex.[9]

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BIBLIOGRAPHY

(1) ―U.S Paint & Coatings Market Analysis (2000–2005),‖ National

Paint and Coatings Association, Washington, D.C., October

2001.

(2) Rosano, W.R., Bleuzen, M.N., Garzon, A., Gebhard, M.S., Larson,

G.L., and Procopio, L.J., ―Improved Performance of Waterborne

Coatings through Polymer-Pigment Composite Particle

Formation,‖ Proc. of the 28th FATIPEC Congress, 2006.

(3) Braun, Juergen H., ―Titanium Dioxide —A Review,‖ J. COAT.

TECHNOL., 69, No. 868, p. 59 (1997), and references therein.

(4) Hegedus, C.R. and Kamel, I.L., ―Polymer-Filler Interaction

Effects on Coating Properties,‖ J. COATING. TECHNOLOGY., 65, No. 822, p.

37 (1993).

(5) Richey, B. and Wood, T., ―Use of Ambient Temperature

Crosslinking to Improve the Performance of Architectural Latexes and Enamels,‖

JOCCA—Surf. Coat. Int., Vol. 77, No. 1,p. 26 (1994).

(6) Speece, D., Monaghan, G., and Richey, B.,

―Acrylic Ambient Temperature Crosslinking Technology in VOC

Compliant Gloss Paints,‖ Proc. of the 2004 International Coatings

Expo, Chicago, IL, October 2004.

(7) www.wikipedia.org

(8)www.google.com

(9) From various Internet Sources