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Technical Update provide relevant technologicial information, presented in a lively format, and of particular interest to newcomers to the surface coatings industry.
Updates from previous volume
Updates from next volume
Preparation of pigmented inkjet inks and their characterisation regarding print quality of pretreated cotton fabric
Pigmented inkjet inks form the fastest growing area within textile printing. These coloration systems have significant advantages because only a simple thermal cure is required after printing, and good quality textiles can be obtained without steaming or post-washing. The cost of pigmented ink printing is lower than that of dye-based ink printing.
The most important requirement of pigmented inks is that they should be sufficiently stable to remain in a dispersed state over a wide temperature range and an extended period of time. There are three main processes involved in achieving fine particle-size dispersions of pigments: wetting, fine dispersion and stabilisation.
Use and performance of anti-skinning agents in air-drying paints
Anti-skinning agents are additives which prevent the unintended skinning of coatings, paints or printing inks. These additives are included in formulations and added in small portions during the production of coating materials or while using them.
Skinning leads to a loss in quality of the coating material and therefore should be prevented. It is usually the result of premature film formation on the surface of the liquid coating material.
In practice, skinning is most frequently noticed on oxidatively drying coatings. These coatings contain air-drying oils or macromolecular binders. Examples are air-drying alkyd resins, epoxy esters, urethane alkyds, and other modified oils. Under the influence of oxygen the binder in the paint is polymerised and transformed into a solid material. In principle, the skinning mechanism is identical to the film formation mechanism.
Epoxy resin formulations and ecological requirements
Epoxy resin systems are well known for their high performance properties in various fields of application. Such systems are preferred as the binder components in coatings for the corrosion protection of steel and concrete constructions (for example, bridges, ships, tanks, and equipment for plant and machine construction). Appropriate formulations were originally based on two-component ambient curing, solvent-based epoxy/amine systems.
Growing environmental awareness and EU-guidelines for the reduction of volatile organic compounds (VOCs) impose new and reasonable demands on manufacturers of epoxy resin systems. These demands can be met in several ways:
Solvent-free coatings (high build) are appropriate if the processing viscosity is low enough.
Colour match prediction for paints and inks
The primary function of a computer colour match prediction (CMP) system is to save money. These savings should come in the form of reduced time spent on formulation, reduced corrections in production and/or optimisation of the use of raw materials.
Unfortunately, down the years, CMP has not always been able to deliver in these areas. Its success depends on the ability of the mathematical matching model to handle the application in question, as well as the quality and accuracy of the raw data fed into this model.
Carboxymethylcellulose acetate butyrate in water-based coatings
For over 40 years cellulose acetate butyrates (CABs) have been used to modify the rheology of solvent-based coatings. However, as pressure on VOC releases has increased, the use of higher solids solvent-based and water-based systems has become more important in recent years. In automotive coatings, metallic and mica-based systems rely on the correct solids/viscosity relationship to achieve the desired appearance. It has been found that high solids systems do not allow the paint formulator to achieve the optimum appearance or maximum flop and so, increasingly, the former low solids solvent-based systems are being replaced with low solids aqueous formulations. It has been estimated that around 50% of the OEM automotive basecoats applied in Western Europe use an aqueous coating basecoat formulation. Automotive refinish paints, industrial metal, wood, and plastic coatings are also being forced down the water-based route and much development work is being directed into this area.
Water-based coatings, however, suffer from several disadvantages compared with their solvent-based precursors. Poor substrate wetting arising from water's high surface tension, its slow evaporation rate, and the susceptibility of that evaporation rate to changes in relative humidity all contribute to difficulties in maintaining constant properties in the appearance and application of water-based coatings. In order to improve application properties and the metallic flake orientation in automotive and other flamboyant coatings, manufacturers have used rheology control additives in the formulation. These additives, such as alkali-swellable thickeners, associative thickeners and clays, are used to increase the low shear viscosity to prevent the coating from dripping off vertical surfaces. In addition, they assist in the orientation of the metal flake which occurs with the shrinkage during the drying process of automotive basecoats. However, the elasticity introduced by such additives can be detrimental to flow and levelling, and may need to be overcome by the use of further additives to reduce the surface tension. This balance between good flow and levelling and sag control can be difficult to achieve. Earlier work by Posey Dowty et al1 demonstrated that carboxymethylcellulose acetate butyrate (CMCAB 641-0.5 cellulose ester) can be used to achieve this balance of properties in aqueous paint systems. This paper reports on further advances in the use of CMCAB 641-0.5 cellulose ester in a variety of coating applications.
Consolidation at the supplier level: Coloured organic pigments
'Why should I be concerned about consolidation in the organic pigments industry?' is the first question that most people will ask when they come into professional contact with the use of colour in their work. This paper will seek to present an overview of that consolidation and also sound some warnings to the colour-using industries as to why they should take care in their choice of supplier.
A new approach to intumescent clear varnish in wood fire protection
If we look around us we can see that wood is part of our daily life. Mankind has taken this material from nature to take advantage of its properties and characteristics, and therefore to achieve a better quality of life by using it as a structural or decorative element in housing, as furniture, or as art (sculpture). In other words, wood provides us with comfort and benefits.
We should therefore preserve it from everything that could damage and destroy it by using barriers that stop moisture, prevent mildew, insect attack, and the like.
Great advances have been achieved in the wood coating field (paints and varnish). But fire is an element which should be taken into account. As wood is a combustible material, it will burn under certain conditions (heat energy + oxygen + combustible material), causing not only material loss but also the loss of human life.
Levelling agents for water-borne coating systems
In order to reduce volatile organic compound (VOC) emissions, waterborne coatings systems have been developed for many application areas. Protective and decorative properties are key factors in coatings, with examples easily found in the coating of metal, plastics or wood substrates. Defects in the paint film deviate from the evenness of the surface and are judged to be an indication of an imperfect coating process. To prevent such defects, for example poor levelling, orange peel or cratering, leveling agents are used.
The most important coating defects to be caused by surface tension gradients are referred to as craters, fisheyes, crawling, orange peel, Benard cells and flotation (which is the visible consequence of Benard cell formation in a pigmented coating).
Nano-talc pigment-based barrier coatings
Paper is a fibrous, hydrophilic substrate; it absorbs materials such as water, grease and oil. Additionally, uncoated paper allows the easy passage of moisture. The main reason for this is the space that consists of countless air voids between the interlinked fibres of paper. It is these air voids and the micropores within the cell walls of fibres that determine the porosity of the paper.
Fibre refining, the preparation process prior to actual paper formation in which fibres are crushed and broken, influences porosity. Extensive refining results in fibre shortening and collapsing of the fibre cell walls, producing a more closed-up sheet surface. Surface sizing agents such as starch, applied to the surface of the paper, further decrease the porosity of the paper by filling the air voids between the fibres and coating the micropores on the fibre walls. As a result of these treatments, many of the pores in the base paper become inaccessible to fluid flow.
Even after physical and chemical treatment, there remain some micropores on the surface of the paper that will allow some fluid flow. In this situation, the use of nano-pigments with an appropriate binder in the coating formulation will help plug the micropores and offer better barrier properties.
To study how nano-talc improves the barrier properties of paper, coatings of nano-talc and a binder at different pigment-to-binder ratios were prepared and applied to paper samples. The barrier properties were analysed and compared with the properties given by conventional talc with the same binder in the same pigment-to-binder ratios. Fluorochemically-treated samples were also prepared as a basis for comparison.
UV-reactive Elvacite acrylic resins for property differentiation
Coatings are conventionally applied using organic solvents, but these are under ever increasing environmental pressure, especially with respect to legislative control of volatile organic compounds (VOC). Environmentally friendly alternatives to solvent-based coatings include water-based UV-curable coatings and powder coatings. The first UV-curable coatings were developed over 20 years ago. They represent up to 10% of the overall coatings market and the consumption of UV-curable materials continues to grow at an average rate of approximately 10% per annum. UV-curable coatings represent a 100% solids (zero VOC) technology since the entirety of the liquid film applied to a substrate becomes an integral part of the coating after exposure to UV light. In addition to this advantage, UV curing is very rapid compared to thermal curing enabling high rates of production. Excellent properties can be achieved in this time. UV curing falls into two main classes, the free-radical curing of acrylate groups and the cationic curing of cycloaliphatic epoxides. The curing of acrylates is most popular and represents 85% of materials' usage.
Water-borne urethane-acrylic copolymers offer best of both worlds
In a demanding business like the surface coatings industry, new urethane-acrylic copolymer technology sets a standard for the future whilst offering good economics, environmental compliance and high performance; all combined in one product.
In today’s highly competitive surface coating market , the proper balance between cost and performance is an increasingly important factor. At the same time, the pressure of ever increasing legislative restrictions on solvent emissions, and with it the demand for alternative coatings like eg waterborne systems.
Chemical and commercial aspects of Florstab UV in-can stabilisers for UV-inks and coatings
Free radicals are essential for successful UV-curing, but also they can give UV formulators some serious problems if they are not controlled. The author will consider the present knowledge and outline the major precautions the UV formulator has to consider in the endeavour to continuously improve the performance of UV systems, especially to improve the in-can stability.
Radiation-curable coatings: A variety of technologies for a variety of applications
Since the early seventies, radiation curing technology has enjoyed an uninterrupted growth in the field of coatings, printing inks and adhesives, and this trend is expected to continue into the first decade of this century. The major factors fuelling the growth of radiation-cured formulations include the outstanding performance of coatings (gloss, durability, adhesion to substrate), very fast curing (within seconds or fractions of seconds) without the need for heating, low process costs per square metre of surface, product stability on the application machines, and the low space requirements of the application lines.
In 1985, radiation-curable coatings constituted 1% of all original equipment manufacturers' (OEM) product coatings. By the year 2000, their share had grown to 2.3% on a volume basis, 5 to 6% by value. In the area of graphic arts, radiation-cured products accounted for 1% volume, but as much as 7 to 8% of value.
The largest areas of application for UV coatings are currently furniture and buildings, where these products are used mainly on wooden furniture, parquet, and other resilient and laminated flooring surfaces. This is closely followed by the graphic arts industries including inks and overprinting varnishes (OPV). Breakdown of the European market into end-use industries (2000) is given in Figure 1.1
In markets where UV curing is the industry norm, growth will be limited to the growth of the market for coated products. Conversely, in markets where penetration of UV technology is currently very low, growth potential is high. The development of new chemistries and/or the development of new application technologies should help to sustain this growth.
On 11th March 1999, the European Union adopted Directive 1999/13/CE which targeted a fall in VOC emissions of 67% compared with the levels recorded in the nineties. This has to be achieved by 2007 and is valid for both new and existing lines. This directive is expected to stimulate even more the expansion of low or no VOC-emitting technologies like liquid UV coatings, water-borne UV coatings and UV powder coatings. This paper will focus on these areas.
Hydrophobic and hydrophilic silicone-containing systems for external antisoiling protection of porous building materials
Architectural objects, especially when situated in highly-polluted urban or industrial regions, are exposed to staining due to environmental pollution. The aggressive air-pollutants are formed as gases, dust and aerosols, and some can be transported by winds even for long distances. The most corrosive substances widely present in the atmosphere are dusts suspensions and gaseous products such as SO2, NO, F- and products of their transformations occurring in air. These pollutants are increasing the salt content in building materials. The crystallisation processes (connected with high changes in salt volume) are leading to micro-cracks in building materials. The deposition of nitrogen compounds take part in the biological corrosion by increasing the growth of fungi and algae. The presence of dust particles in the atmosphere is connected with urban or industrial smoke (soot from combustion processes, partially-fumed organic particles, heavy metal particles from industrial processes) and natural processes such as volcanic eruptions, sand storms, and oil erosion. The most dangerous are soot particles from smoke measuring <1µm. Dust particles, gases and water act as aggressive agents contributing to the destruction of building materials by the formation of soiling and hard, non-porous patina. Non-porous patina is a non-permeable barrier to salts and water vapour, moving through building material. The crystallisation of salts under the layer of patina can lead to delamination of this layer, along with the surface layer of building materials.
Recently, anti-staining coatings, especially self-cleaning ones, have become a focus of interest in the field of architectural coatings. However, there are several published papers concerning staining of architectural coatings where there is little description of their development, especially for unpainted surfaces (eg sandstone, limestone, bricks and clinker).
Mathematical calculations for adhesion with emphasis on polysulfide-modified coatings
You will have heard how contact angle measurements can be used to predict adhesion - or lack of it - in coatings. For many formulators the task of establishing whether a new or modified product will adhere to a specific surface is a matter of trial and error, commonly called product development. However, if you are faced with a variety of surfaces and a number of modifications, this can lead to a large-scale programme of work. For many the possibility of establishing the potential for adhesion by calculation would prevent the unnecessary time consumption used in a large screening test. It is the aim of this paper to give an overview of the mathematics involved to aid this work.
In order to avoid using commercial products as the basis of discussion, the paper deals with the properties of polysulfide polymers and their contribution to adhesion. Thus, no account is taken of the contribution of copolymers or adhesion promoters that may be used in a specific formulation.
Weatherable topcoats
There have been times when high-performance coatings in the heavy-duty industry have been used to protect capital investments, giving little attention to their long-term gloss and colour performance, and with little consideration to pollution or potential effects to the environment.
In those days, it was considered that chlorinated rubber and vinyl coatings provided acceptable gloss and colour retention, while the chalking of epoxy coatings was regarded positively as a self-cleaning property.
With the development and introduction of vinyl acrylic, polyurethane and epoxy acrylic topcoats, a gradual change in the protective coatings industry, putting more emphasis on colour and gloss retention of topcoats, has taken place.
Polyurethanes entered the protective coatings industry 20 to 25 years ago to improve the cosmetic appearance of epoxies, used as intermediates in multi-coat high-performance coating systems, being described as weatherable topcoats.
As an alternative to the polyurethanes, epoxy acrylics were developed to overcome health hazards related to these isocyanate-based coatings. However, epoxy acrylics did not provide the same level of weatherability to improve the cosmetic appearance of high-performance coatings like polyurethanes.
After years of extensive research and development work on inorganic hybrid coatings, in 1994 Ameron introduced their patented polysiloxane coatings, which revolutionised protective coatings technology, combining unprecedented protection from harsh atmospheric corrosive conditions with weatherability characteristics, giving performance exceeding the best polyurethanes.
The drive towards high solids, low VOC coatings, initiated and fostered by the environmental regulations, has also caused a change in the types of coatings. The physical drying coatings, such as the chlorinated rubbers, vinyls and vinyl acrylics have gradually been replaced by the chemical drying two component epoxies, polyurethanes and epoxy acrylics. The ultimate on the reduction of volatile organic compounds in topcoats has been achieved with the polysiloxane coatings.
Selecting TiO2 pigments for optimum performance in water-borne industrial coatings
Water-borne resins have long since dominated the decorative coatings market. Their use for industrial coatings has been far more restricted, as they have not been able to compete so well with their solvent-borne equivalents to give the level of performance demanded of many industrial coatings.
However, with legislation on VOC limits forever intensifying, resin manufacturers are gradually improving the performance of water-borne industrial resins. It is therefore becoming increasingly important for the TiO2 manufacturer to be aware of this growing water-borne market and to be able to recommend suitable TiO2 pigments for water-borne industrial coatings.
This paper describes work undertaken with water-borne general industrial systems: to learn about the performance of TiO2 pigments in these systems, and to aid pigment selection.
Basic principles of particle-size analysis
What is a particle?
This may seem a fairly stupid question to ask! However, it is fundamental in order to understand the results which come from various particle-size analysis techniques. Dispersion processes and the shape of materials makes particle-size analysis a more complex matter than it first appears.
Imagine that I give you a matchbox and a ruler and ask you to tell me the size of it. You may reply saying that the matchbox is 20 x 10 x 5mm. You cannot correctly say 'the matchbox is 20mm' as this is only one aspect of its size. So it is not possible for you to describe the three-dimensional matchbox with one unique number. Obviously the situation is more difficult for a complex shape like a grain of sand or a pigment particle in a can of paint. If I am a QA Manager, I will want one number only to describe my particles - I will need to know if the average size has increased or decreased since the last production run, for example. This is the basic problem of particle-size analysis - how do we describe a three-dimensional object with only one number?
CEPE Annual Press Conference 2002
I will give you an overview of the economic development of the paint and printing ink industry in 2001, and update you on the main activities of CEPE (European Council of the Paint, Printing Ink and Artists' Colours Industry).
An alternative look at gloss housepaints: Problems associated with their use by 20th century artists
Twenty four members and guests attended the fourth technical meeting of the London Section 2002/03 programme. This was held on Thursday 28th November 2002 at the Naval Club. The guest speaker was Harriet Standeven, who is a PhD Research Student at the Victoria and Albert Museum and the Royal College of Art.
After a brief introduction to the Conservation Programme run by the Royal College of Art / Victoria and Albert Museum, Harriet continued by describing the nature of the research that she had been involved in during the last three years. The conservation programme run by the organisations is designed to train conservators in fields as diverse as furniture, metal, ethnographic objects and paper conservation. This includes research studentships which are based around several areas: the application of computers in conservation, ethics, risk and modern materials. The research falls into the latter category, and investigates the historical and technical development of gloss housepaints, with reference to their use by 20th century artists. The period of interest is from the late 1920s, when artists first began to experiment with non-traditional paints, until the early 1960s. She continued by pointing out that two distinct areas were covered and these were: