Lacquer is a liquid or powdery coating material that is applied thinly to objects and is built up into a continuous, solid film through chemical or physical processes (e.g. evaporation of the solvent ) . Paints usually consist of binders such as resins , dispersions or emulsions , fillers , pigments , solvents , and additives such as biocides (can preservatives).
The three main tasks of paints are:
- Protection (protective effect, such as protective coating with a combination of primer and top coat, protective varnish ),
- Decoration (optical effect, certain color effect) and
- Function (special surface properties, changed electrical conductivity).
It is estimated that in 2007 around 28 billion liters of paint were produced worldwide, valued at 92 billion US dollars .
The origin of the word is not entirely certain. Linguists follow the explanation of Manfred Mayrhofer , who in the 1950s traced the Sanskrit word lākṣā "red varnish" back to the Indo-European root * reg- "color, redden". To this end, the old Indian ráyjati “colors, reddens”.
The philologist Karl Lokotsch , on the other hand, had lākṣā in 1927 as a whole with “Marke, Fleck; one hundred thousand ”translated and lacquer added,“ after the innumerable insects Cocca ilicis , which cause the resinous secretion through their sting on quercus coccifera ”; from this the numeral Lakh "hundred thousand" originated. Clever Etymological Dictionary of the German Language adopted this explanation from the 11th edition (1934) to the 17th edition (1957), but followed Mayrhofer's derivation since the 18th edition (1960). This did not prevent Lokotsch's interpretation from spreading in more recent publications.
Early examples of paint use can be found in China . The discovery of lacquer technology is attributed to the Chinese. More than 7,500 years ago ( Hemudu culture ) they used the bark of the lacquer tree as a binding agent.
The oldest traditional formulation of a paint dates from the 12th century and consisted of linseed oil as a binding agent and cinnabar as a pigment. From the 18th century the so-called lacquer boilers emerged , which quickly conquered a market for the coating of a wide variety of objects. As the name Siederei already suggests, the paint components were usually mixed with one another at high temperatures.
Start of industrial paint production
Until the beginning of the industrial age, lacquer was used to enhance the color of objects. In the industrial age, paints increasingly had a protective function to maintain the value of objects and buildings. Systems were built for industrial painting, which made the tedious manual work with the brush superfluous. Objects could be painted very evenly by pouring, rolling and dipping. In 1882 there were already 1,105 companies in Germany producing paints. At the end of the 19th century, many of the largest German paint manufacturers were founded, for example Herberts Lacke, Axalta, formerly DuPont or the Deutsche Amphibolinwerke . Strong competition from abroad finally led to the founding of the existing association of the German paint and printing ink industry in 1900. The most important industry magazine, Farbe und Lack , was founded in 1893. In 1916 the interest group of German tar paint factories was founded, which from 1925 became IG Farben was renamed.
At the beginning of the 20th century, new binders were developed, such as Laccain (1902) or Bakelite (1905). In 1913 the first synthetic resins, i.e. fully synthesized binders, were produced. These were phenolic resins , which were followed by urea resins in 1918 and alkyd resins in 1927. In 1921, nitrocellulose lacquers were used for the first time in automotive series painting. In 1934 the first emulsion paints were produced on the basis of a binder in the form of a dispersion .
With regard to lacquer-specific training, the foundation stone was laid in Krefeld in 1924 with the establishment of a lacquer department at the local dyeing and finishing school, part of the Niederrhein University of Applied Sciences . The RAL colors still customary on the market were first published in 1924.
Development after the Second World War
The first technological innovation after the Second World War was the development of epoxy resins in 1948. As early as 1949, the first water-based paints were produced. From 1952, paints were made on a plastic dispersion basis.
In 1960, in addition to anodic dip painting (ATL), which was replaced by cathodic dip painting (KTL) in 1976 , the first silicone resins were also brought out and the first applications for coil coating were found. In 1966 the first German powder coating plant was put into operation, followed by various start-ups in this area. In 1975 the first color mixing systems came onto the market.
In the recent past the environmental aspect has become more and more important. In the past (1960–1970), the proportion of organic solvents in paints was around 50% - 70%, sometimes harmful solvents such as chlorinated organic compounds or even benzene were used. In the 1970s and 1980s, the harmful solvents in paint formulations were replaced and the solvent content was reduced. In 1983, German paint manufacturers committed themselves to reducing volatile organic compounds and pigments containing heavy metals such as lead chromate in paint formulations. In 1985 the first emulsion paints with low emissions and low solvents, with up to 10% organic solvents, came onto the market. In comparison, natural resin, synthetic resin and alkyd resin paints have a solvent content of up to 60%.
Current developments are due to the further reduced VOC limit values in accordance with EU legislation from 2007 and 2010 and the requirements of REACH and GHS . So that the customer can see whether the product he has bought complies with the Decopaint directive , the solvent content - expressed as a VOC value in grams per liter - must be declared on the container. The maximum permissible limit value is also listed on the container and varies for water-based and solvent-based coating materials.
In 2007 around 28 billion liters of paint were produced worldwide. Compared to 2002 there is a production increase of 4.8%.
The largest areas of application are building paints (51% by quantity, 43% by value), industrial paints (10% by quantity, 11% by value) and powder coatings (9% by quantity, 7% by value). The important sector of automotive coatings, together with aircraft and other means of transport coatings, achieves 6% in terms of quantity and 8% in terms of value and is thus roughly on a par with anti-corrosion coatings and wood coatings. The segment with the strongest growth in the years 2002 to 2007 is the powder coating area with approx. 13% growth.
Regionally, around 35% of all coatings are sold in Europe , 30% in Asia and 25% in North America . The rest is divided equally between South America and Africa . Europe and North America recorded a growing share, while paint consumption declined in other parts of the world. This can also be seen in the per capita consumption , where in North America with around 10 liters of paint per inhabitant and year and in Europe with 8 liters around twice to four times as much paint is used as in other parts of the world.
Paint production in Germany
In 2010, the production volume of paints and varnishes in Germany was 2.04 million tons, which corresponds to a production value of 4.26 billion €. This corresponds to an increase of 4% in terms of quantity or 7% in terms of value compared to 2009. In addition to varnishes, this information also includes emulsion paints . In 2010, solvent-based paints in Germany accounted for 24% in terms of quantity (45% in terms of value). Solvent-free paints, together with powder paints and emulsion paints, have a share of 77% by quantity and 55% by value. There are around 250 small and medium-sized paint manufacturers in Germany. Some of them are highly specialized and many of them work regionally.
The following table shows the production of paints and varnishes in Germany in 2010.
|Substance class||Annual production in tons||Sales in million euros||class|
|Alkyd resin paints (air-drying)||65.103||220||solvent-based|
|Alkyd resin paints (heat-drying)||12,929||47||solvent-based|
|Oil paints, oil varnishes||7.179||60||solvent-based|
|Cellulose nitrate varnishes||16,720||54||solvent-based|
|Bituminous and tar-based paints||7.157||21st||solvent-based|
|Colors based on shellac or similar||3,320||8th||solvent-based|
|Phenolic, urea and melamine resin varnishes||20,231||40||solvent-based|
|Epoxy resin paints||66,563||219||solvent-based|
|Polyurethane resin paints||59,270||320||solvent-based|
|Polystyrene and polyvinyl resin paints||21,906||78||solvent-based|
|Acrylic polymer based paints and varnishes||41,357||176||solvent-based|
|Other colors based on synthetic polymers||45,236||207||solvent-based|
|High solid paints||41,407||144||solvent-based|
|Powder coatings||63,658||246||solvent and water free|
|Emulsion paints (inside)||614.784||572||aqueous|
|Emulsion paints (outside)||133,898||196||aqueous|
|Primers and coatings||75,068||138||aqueous|
|Glue paints and watercolors||24,397||88||aqueous|
|Electrophoresis and other water-based paints||13,656||31||aqueous|
|Aqueous phenolic, urea and melamine resins||778||4th||aqueous|
|Paint and other fillers||176,968||128||aqueous|
|Silicone resin paints||6,815||25th||aqueous|
|Silicone resin plasters||28,201||34||aqueous|
|Other colors based on synthetic polymers||77,841||334||aqueous|
|Other colors based on natural polymers||2,295||11||aqueous|
In 2010, 484,620 tons of solvent-based and 1,488,720 tons of water-based paints and varnishes were produced. These had a total value of 1.909 and 2.101 billion euros, respectively.
With the variety of varnishes, different ways of classification are common.
Paints are classified according to formulation or processing aspects, such as the type of binder (example: oil paint ), type of solvent (example: spirit paints ), drying method (air-drying, heat-drying or as stoving paint ) or area of application (example: car paint ).
The subdivision according to surface properties divides paints according to the appearance of the surface. The type of formulation can produce dull matt (as soft-feel surfaces in vehicle interiors) to high-gloss (for piano lacquers ) surfaces. Likewise, depending on the type of formulation, varnishes can be produced that are smooth to highly structured, that is, hammer finish varnish and cracked markings or varnishes that cause shrinkage.
Traditional paints are made from plants, from resins such as copal and rosin . Shellac from the secretions of an Asian type of lice. In Asian lacquer is Chinese lacquer , the Chinese lacquer and the Japanese lacquer art , from the wound juice of lacquer tree with addition of vermilion or carbon black produced in the classical paint colors red and black.
Paints are sometimes classified according to special properties (more or less arbitrarily). A clear lacquer is a transparent lacquer that does not contain any coloring pigments . Tensioning varnish tensions paper and fabric as it dries, strengthens and impregnates them. A dip paint is a paint that is applied by dipping the workpiece into the paint (see anodic and cathodic dip painting ). Effect lacquers show a so-called flop , i.e. a change in brightness or color , depending on the direction of view and lighting .
More special coatings provide for example, acrylic paint , alkyd resin paint , violin varnish , Japanese lacquer , wine paint , conductive ink , UV-hardening photoresist for printed circuit board manufacture, nail varnish , nitrocellulose lacquer , powder coating, sealing wax , varnish (piano), protective varnish, silicone resin paint , heat-resistant Alulack for furnace tubes, release agents and spray represent.
A paint consists of volatile solvents and non-volatile components. The solvent (the volatile component) evaporates during the drying process, while the non-volatile components adhere to the painted object as a smooth film. The non-volatile components are binders , pigments, oils, resins, fillers and additives. The binder ensures a good, uniform suspension of pigments and solvents in the paint, is responsible for an optimal drying process (no blistering) and for the gloss after drying. The essential basis of a paint is the binder and solvent. Pigments are not a necessary component of a paint. There are also pigment-free clear coats and solvent-free powder coatings. A paint should be durable and not peel off from the surface. The paint forms a solid layer on the substrate. If the surface is contaminated, there is no good bond between the substrate and the paint in the event of mechanical loads or environmental influences. In many cases, the peeling of a paint is due to poor cleaning, degreasing or rust removal from the painted materials.
The term binder is often only used for the film-forming part (film-forming agent ); strictly speaking, the non-volatile part of the additives must also be included, as this is not part of the integrated phase (pigments and fillers).
Modern binders ( polymers ) are offered as a dispersion in aqueous solution or dissolved in a solvent as a one-component system (1K paints). In two-component systems (2K paints), the binder consists of synthetic resin and hardener. These are stored separately. The two components are mixed shortly before processing. They react chemically and harden (without drying) if they do not contain any solvents. Most 2K systems have both hardening and drying processes. Traditional binders in oil varnishes include natural resins as well as oils ( oil paint ) and plant components ( Chinese varnish, Japanese varnish). If the binder is not in liquid form, a solvent that is able to dissolve the binder is required as an additional component. Solvents in physically drying paints should be colorless, should not have a negative impact on the binding agent and should evaporate without leaving any residue. Since most of the solvents for paints are organic solvents, some of which are toxic or flammable, there is an increasing tendency towards solvent-free systems, i.e. powder paints or suspensions of paint particles in water. Another way to work solvent-free (emission-free) is to use radiation-curing paint systems ( radiation curing ). With this technology, a monomer acts as a "solvent" that polymerizes into the paint film during curing. It is a low-molecular binder with low vapor pressure, which cures chemically via UV-induced processes (within fractions of a second). A UV high-performance lamp is usually used as the radiation source.
After the paint has been applied and dried, film formers form a cohesive layer (the film) with good chemical and mechanical (hardness) properties. The film formers change into high molecular weight compounds during the curing process. Low molecular weight film formers are, for example, nitrocellulose , vinyl chloride-vinyl acetate copolymers, high molecular weight film formers are, for example, unsaturated polyester resins and epoxy resins. Film formers of physically drying paints (e.g. chlorinated rubber, vinyl polymers, styrene-butadiene copolymers, silicones) do not show any chemical reaction between the macromolecular substances during the drying process ( evaporation of the solvent). These coatings can be swollen again and partially dissolved by a solvent. Crosslinking film formers (unsaturated polyester resins , acrylic acid esters , epoxy resins , alkyd resins or polyester resins) can, for example, crosslink with phenolic or melamine resins and cannot be dissolved by a solvent after the paint has dried. The lacquer coatings show only a very weak swelling capacity under the influence of solvents. A distinction is made between natural resins ( colophony , dammar ) and synthetic resins. Resins are important for better adhesion to the substrate and the gloss of paintwork.
The hardening is based on a chemical reaction between the oxygen in the air and the unsaturated fatty acids , which leads to cross-linking of the molecules; in the case of linseed oil, linoxin is produced . So-called siccatives (often cobalt naphthenate) promote radical networking. Occasionally natural ( turpentine , orange peel oil ) or synthetic solvents (1,4 – polybutadiene oils) are added. The solidification of the paint only takes place when a solvent is used, also partially by drying . Depending on the vegetable oil used, oil paints tend to yellow. Frequent contact with water leads to hydrolysis of the ester bonds, which reduces the durability especially of oil paints with water-based solvents and leads to a washout effect on painted surfaces. The drying time is usually longer than with conventional paints. Linseed oil paint is also used for priming of structural steel used.
Oil paints with admixture of resins are known as varnish . If pigments are added in addition to resins , an oil varnish or natural resin varnish is obtained . Oil varnishes have been known in China for over 2000 years and are still used (sometimes with synthetic binders). The proportion of solvents can be up to 60 percent, but paints emulsified with water are now also produced.
The cellulose esters should be mentioned in the first place . Cellulose nitrates ( nitrocellulose ) have been known for painting purposes since 1855 (Parkes). It was not until around 1880 that it was recognized that solvents such as ethyl acetate were well suited that larger quantities were produced. The technical breakthrough came around 1920 for cellulose nitrates in painting in automobile production. In contrast to oil varnishes, which required a long drying time due to the oxygen in the air, nitrocellulose varnishes set quickly. From 1930 on, nitrocellulose lacquers were mixed with alkyd resins. With this lacquer binder, metal, wood and fabric could now be lacquered. Today's areas of application for nitrocellulose lacquers are: furniture lacquers, metal lacquers, foil lacquers, textile and leather lacquers, nail lacquers. In 2007, 27,000 tons of nitrocellulose paints were produced in Germany. Cellulose acetate , which is used in solutions, for example as an electrical insulating varnish, is also gaining in importance.
Sugar as mono- or disaccharides are suitable as polyhydroxy compounds as starting materials for the production of paints. By reacting saccharides with ethylene oxide or propylene oxide , polyols are obtained which can be condensed with other components such as urea or formaldehyde . Organic acids can be obtained through the oxidation of saccharides, which in turn can be converted into polyesters . Of particular importance are compounds formed by attaching vinyl - acrylate or - methyl acrylate groups are formed to the saccharides. This is used to produce dispersions as binders for lacquers such as wood lacquers, the proportion of renewable raw materials in these lacquers being over 60%. Water-based alkyd resins based on sucrose and fatty acid methyl esters can now also be successfully synthesized. Isosorbide can be synthesized from glucose via sorbitol , which serves as a component for powder coatings.
The drying time of oil paints had become an important criterion in the industrial mass production of kitchen appliances and small parts. Quick-drying paints were also required in residential construction. With the development of alkyd resin paints around 1930, a very good film former was found.
At that time, alkyd resins mostly consisted of a dicarboxylic acid ( phthalic acid ), a polyalcohol (mostly glycerine ) as well as linseed oil and soybean oil. From 1945 mixed alkyd resins with styrene were also produced. These copolymers showed faster drying, higher weather resistance, greater surface hardness and less yellowing. Alkyd resins can be combined with many other film-forming agents, such as phenolic resins, nitrocellulose or epoxy resins. Another modification are acrylated alkyd resins, i.e. copolymers with acrylic acid esters, and urethane-modified alkyd resins, which are characterized by greater hardness and greater resistance to chemicals.
Alkyd resin lacquers contain synthetic synthetic resins as binders, which is why they are also known as synthetic resin lacquers. Due to their relatively high solvent content, they also have a negative impact on the environment and health. Alkyd resin paints are suitable for wood and metal, both indoors and outdoors.
Dispersion varnishes (acrylic or water-based varnishes) consist of water-dilutable plastic dispersions based on polymerized acrylic acid esters . The proportion of organic solvents of up to ten percent is very low. Dispersion paints are suitable for coating a wide variety of surfaces, both indoors and outdoors.
Epoxy resin lacquers often consist of 2-component (2K) systems that are mixed before painting. The lacquer must be applied quickly after the components have been mixed, as the application period (“pot life”) is short. Epoxy resins are polyadducts of epichlorohydrin with bisphenol A . These are crosslinked with a hardener. At room temperature, the curing times are around twelve hours, at 120 ° C around 30 minutes. In combination with amino resins, epoxy resins can also be used as stoving enamels . In this process, the binder consists of only one component. Temperatures around 160 to 200 ° C are used here.
Single or multi-component paints (reaction paints) consist of one or more components that react with the air after application or with one another after mixing. This includes polyurethane (PUR) paints. Since they have a very high content of solvents and isocyanates , they are harmful to the environment and health. Because of their high resistance, they are used in the commercial sector for sealing parquet floors and furniture.
Pigments cover the coated material and are decisive for the color impression. Pigments also ensure that the paint is more resistant to corrosion from UV radiation. The mean grain size of the particles is decisive for the color impression and color strength. The smaller the grain size, the higher the color strength. The particle diameter should preferably be between 0.1 and 2.0 μm.
The most important pigment for paints is the white pigment titanium dioxide . Around 2.4 million tons of this pigment were used for coatings worldwide in 2008. The paint industry (including emulsion paints ) is the main area of application for titanium dioxide. Very important colored inorganic pigments are the iron oxides (185,000 tons for the paint industry, 1989): Fe 2 O 3 (red), Fe 3 O 4 (black), FeOOH (yellow).
Another important class of inorganic pigments for the paint industry are lead-molybdate pigments, with a changing composition of Pb (Cr, S, Mo) O 4 . The yellow lead chromate PbCrO 4 (harmful to health, poisonous, possibly carcinogenic without lacquer binding) with high opacity and color strength, good thermal stability belonged to this category and was still used in the lacquer industry in the nineties. Lead molybdate pigments are poisonous, but there is no danger in the dried paint. The annual consumption of this substance class in 1988 was 130,000 tons.
Other important inorganic pigments are Cr 2 O 3 (green color, 20,000 tons for the paint industry in 1988), ultramarine pigments (blue, red and green color, 30,000 tons per year for the paint industry in 1988), iron blue pigments (composition : M (I) Fe (III) (CN) 6 , 50,000 tons for the paint industry in 1988), pearlescent pigments (thin interference layers, for example made of TiO 2 on mica or other platelet-shaped substrates, with other oxides, colors: black, gold, blue-gray , silver).
Many organic pigments are also used in the paint industry. Organic pigments often have a higher light absorption, a greater color strength and a lower hiding power than inorganic pigments. Mixtures of inorganic and organic pigments are used to balance out the effects. The most important organic pigment groups are azo pigments and copper phthalocyanine pigments. Important representatives of yellow shades are, for example, CI Pigment Yellow 1 (Hansa-Gelb G, a very old organic pigment used in paints, 1910) and CI Pigment Yellow 74. Important blue and green pigments are the variants of copper phthalocyanine (blue: CI Pigment Blue 15: 1 to 15: 6, green: CI Pigment Green 7 and 36).
Frequently used fillers are calcium carbonate (chalk), barium sulfate (heavy spar) and kaolin . You lower the formulation costs through the partial replacement of pigments. In addition, they serve to set the degree of gloss, a defined surface structure and the improvement of the mechanical properties.
Additives or auxiliaries change the properties of the paint film, such as its shelf life (biocides, antimicrobial additives that control the growth of microorganisms in aqueous liquids or the destruction of dry films) or the processability (wetting and dispersing aids, siccative , antioxidants). Curing accelerators lead to faster curing of the paint film. Plasticizers reduce the softening range of the binder and ensure better elasticity of the paint films. An example of an important plasticizer is dioctyl phthalate . Biocidal substances (formaldehyde releasers or isothiazolinones) prevent paints from becoming unusable by microorganisms.
Additives increase the shelf life and make processing easier. They preserve, ensure film formation or a certain elasticity or softness, prevent "skin formation" in the container (can, pot) and cause a certain viscosity that makes the paint drip-free, or accelerate drying (siccatives). Preservatives (in-can preservatives), required for water-thinnable paints and glazes, are biocidal substances that are intended to prevent the paint in the container from becoming unusable due to microorganisms. Usually formaldehyde releasers or isothiazolinones are used. There are labeling requirements for preservatives both under the CLP regulation (concentration-dependent) and under the regulation on biocidal products ( independent of concentration). There are also guidelines within the industry.
In contrast to other paint components, solvents are not part of the paint layer produced. They are primarily used to adjust the properties of the paint during the coating process and the film formation. Organic solvents are being displaced more and more by water as a solvent. Conventionally formulated paint systems contain 45 to 65% solvents. The more modern high-solids paints contain 3 to 25% organic solvents, depending on the application. Even water-based paints contain around 10% organic solvents, which are used there as so-called co-solvents. Since 2010, the maximum permissible values for solvents in paints have been regulated in the ChemVOCFarb regulation and must be declared. It is subject to paints and varnishes that are used in the construction sector, with the exception of bridges and swimming pools, or in the vehicle sector, except for rail vehicles and aircraft. Solvent-free systems are, for example, powder coatings or systems that only contain reactive thinners . This refers to substances that act as solvents, but crosslink with the binders. So they are not released into the environment when the paint is hardened.
Solvents improve the wetting behavior by lowering the surface tension of the paint. By lowering the viscosity , the paint material can be adjusted to the flow properties required for processing, such as spraying or brushing . Since solvent mixtures are mostly used, it is possible to control the behavior during film formation by selecting the individual solvents according to their evaporation behavior .
Paint solvents are divided into active solvents (dissolve the film former without auxiliary agents), latent solvents (dissolve the film former only in combination with active solvents or non-solvents) and non-solvents. This division is made separately for each binding agent. A distinction is also made according to the evaporation behavior, whereby the classic classification into low, medium and high boilers is mostly replaced by the evaporation number VZ. This indicates the evaporation time based on diethyl ether (VZ = 1). A distinction is made between volatile (<10), medium volatile (10 to 35), low volatility (35 to 50) and very low volatility (> 50) solvents.
When formulating paints, combinations of low, medium and low volatility solvents are used. The highly volatile solvents are used for quick drying, the medium-volatile solvents for better degassing, the low-volatility solvents improve the flow and gloss of the coating. The least volatile solvent must be a real solvent for the binder used, otherwise there is a risk of craters and specks forming .
The most important paint solvents belong to the substance groups aliphatic , cycloaliphatic and aromatic hydrocarbons , alcohols , glycols , glycol ethers , ketones and esters . Outside of Europe, terpene hydrocarbons and chlorinated hydrocarbons are still used. The use of natural solvents, citrus terpenes, turpentine oil and larch balm is mostly limited to natural resin and oil varnishes.
As individual substances are n-hexane , white spirit and cyclohexane in the aliphatic, and xylene , and solvent naphtha may be mentioned the aromatic hydrocarbons. The most important alcohols are propanol , n-butanol and isobutanol . Important glycol ethers are butyl glycol , butyl diglycol , ethylene glycol and diethylglycol important esters are butyl acetate , ethyl acetate and 2-butoxyethanol acetate . Butanone and acetone are frequently used ketones.
Large paint companies often produce the raw materials such as alkyd and acrylic resins themselves. Paint factories also need pigments with the appropriate grain size, color fastness and other products from the chemical industry. The production of varnish includes the uniform introduction and wetting of the pigments in the binder system. A simple dispersion by stirring is not sufficient for many applications. Many pigments can only be used in certain binder systems. Many devices are used by paint manufacturers to mix pigments and paint binders well. The following are important: high-speed stirrers, dissolvers, kneaders, hopper mills, rolling machines, ball mills, agitator mills.
According to DIN EN 971-1: 1996-09, an application consisting of several layers of paint should fulfill several tasks:
- The first layer to be applied (base coat) should be an adhesion promoter that enables properties such as protection against corrosion in metals and / or covering the unsightly surface.
- The middle layer is called the filler, it contains a higher number of pigments and can therefore be applied in a thicker layer to even out minor unevenness.
- The coloring layer (water-based paint, solid-color paint or metallic paint (solvent paint))
- The top layer, the top coat, should be a clear coat that provides gloss, hardness, weather resistance, light resistance and color fastness of the coloring layer.
Swipe and roll
In household use, the paint is applied with a brush, the acrylic resin dispersion for wall paint with a roller.
Splash and spray
The most common types of application in the paint industry are spraying and spraying. Pressure atomizers are used for spraying, which apply the paint by means of a compressor in the low pressure (0.5–0.7 bar), high pressure (1–8 bar) or airless process (60–250 bar).
A workpiece is dipped into the paint. In electrodeposition painting, an electric field of 50–300 V is applied in a paint solution with suitable film formers and the workpiece is connected as grounding . The electrodeposition coating was developed by Ford as an anodic dip coating for the production of a protective coating for cars and is used as a cathodic dip coating in the entire automotive industry.
Electrostatic spray processes
This process uses an electrostatic high-voltage field of 80 to 150 kV. Rotating paint atomizers (high-speed rotary atomizers) are often used.
Pigmented binder powders are used for solvent-free powder coatings. The process was introduced in the paint industry in 1965. In powder paints and other paints, ionic substances ( sodium dodecyl sulfate ) are introduced into the film former (often epoxy resin) with an electrical charge.
Powder coatings can be electrically charged using a high-voltage electrode. Applying an electrostatic primer to materials such as plastic or metals significantly reduces the amount of paint used when spraying paint. This process takes place fully automatically with robots.
In coil coating, a metal strip is continuously coated with paint between rollers. The painted metal strip then runs over an oven zone, whereby the paint hardens. It has been used in the US since 1957 and in Germany since 1960. The coil coating process has become established for the coating of all white household appliances (washing machines, refrigerators, tumble dryers) in a very short time . The paint consumption has been reduced considerably through modern processes.
Numerous tests are carried out on wet paints and finished paint layers. The following is a list of paint-relevant test procedures / tests.
Tests on wet paint (delivery form)
- Rub-out test
- Minimum film forming temperature
- Pot life and gel time
- Viscosity / rheology
- Flash point
- Solids content
- PH value
- Particle size
- Molar mass distribution
Tests on finished paint layers
- Hiding power
- Coloristic (hue)
- Water vapor permeability
- Pigment volume concentration
- Chemical resistance
- Rockfall test
- Layer thickness
Paints are used wherever surfaces are permanently exposed to external influences such as weathering, mechanical use and others and must be protected from them. In many cases, lacquer was also used in arts and crafts for the color design of surfaces, i.e. in painting , lacquer carving and lacquer painting . The starting point for this development was China . The world's only museum for lacquer art is in Münster .
If wood is coated with lacquer, moisture that has penetrated the wood due to possible injuries or stress cracks can no longer evaporate through the otherwise water (vapor) tight film. The wood swells up and leads to further stress cracks and to the decomposition of the wood. Wood for outdoor use is therefore more likely to be oiled, which also creates a water-repellent surface that is not water-vapor-proof. In addition, constructive wood protection (avoidance of irrigation, sloping surfaces from which water can run off) tries to divert the water away from the wood.
In the area of metal coating, the main area of application of paint systems is corrosion protection. Without a sufficient coating (for example with anti-rust primer and topcoat) the most common metals (carbon steel) would be attacked (oxidized) in humid climates and thus restricted in their properties due to corrosion phenomena.
Plastic painting is generally a 1- or 2-layer paint system with a primer and top coat or just a top coat (either colored or transparent). A 3-layer structure is required as soon as the intermediate coat (colored basecoat) alone cannot ensure adhesion to the substrate or the color or the effect requires a colored primer layer.
Also in the paint clothes such coating processes take place.
The paint manufacturer industry employs many people and the companies are spread all over Germany. Nevertheless, the companies that are active in the field of paint production are hardly noticed by the public. The following is a list of paint manufacturers from Germany and abroad.
Paint manufacturer from Germany
- Axalta Coating Systems
- BASF Coatings
- Grebe Holding (with Weilburger )
- Hesse Lignal
- Mipa SE
- Novatic group ,
- Sika AG
- Sto AG
- SW color paint factory
Paint manufacturers from abroad
- Akzo Nobel
- IGP powder technology
- PPG Industries
- Rohm & Haas
- Tiger Coatings
- H. Kittel: Textbook of paints and coatings , Vol. 6 (- 10), S. Hirzel Verlag, Stuttgart 2008; ISBN 978-3-7776-1016-0 .
- Paolo Nanetti: varnish for beginners ; Vincentz Publishing House; Hanover 2008; ISBN 3866308477 .
- Paolo Nanetti: Lacquer raw materials science ; Vincentz Publishing House; Hanover 2000; ISBN 3-87870-560-3 .
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