Test Bench EXTRA-FINE ACRYLIC STUDIO ACRYLIC AND AUXILIARY ACRYLIC PRODUCTS With their extremely tactile texture, - When acrylic is used in watercolour extremely complex physical and physi- which reacts to the artist’s tool and techniques, washes remain stable when cochemical transformations. keeps the mark of the movement, and a second coat is applied. In addition, the their concentrated high-quality pig- pigments are lightfast and there is no The film is formed in three stages: ments, EXTRA-FINE ACRYLIC and STU- risk of fading. DIO ACRYLIC are pleasant to use and - In the first stage, the water evaporates easy to mix; all the colours in each of 2-DRYING : at a speed which depends entirely on the two ranges can be mixed with one THE PHENOMENON OF COALESCENCE the temperature, humidity and ventila- another. tion. Matte or gloss effects can be obtained Our paints are formulated with resins, by mixing the paint with the appro- resulting from the polymerization in - In the second stage, known as coales- priate medium. emulsion of acrylic monomers in cence, the particles are in contact with water. one another and interpenetrate. 1-THE ADVANTAGES OF ACRYLIC When the emulsion changes from the liquid to the solid state, it undergoes a - In the third (film-forming) stage, the Acrylic paint has many advantages: series of transformations involving characteristics of the film are defined. - Artists who dislike the strong smell of oil paint and turpentine will be plea- santly surprised by these almost odour- less products (which contain very little ammonia). The binder used is synthesized as an emulsion in water, using no aliphatic or aromatic solvents, which are respon- sible for the odour. This means that when the paint is still wet, it can be washed off the tools with water after use. - It dries quickly and is ideal when a painting, even unfinished, has to be transported. Successive coats can be applied easily with no risk of cracking or streaks. - Mistakes are easily corrected by cove- ring with acrylic gesso and painting over. After the film-forming stage, the film is dry state, which may affect colour APPENDIX insensitive to water (but sensitive to intensity after drying. The particle size the solvents in the resin). The physico - grading of the resins used for EXTRA- AGEING OF THE FILM: chemical properties of the film are FINE ACRYLIC, STUDIO ACRYLIC and When a film appears dry, it continues irreversible under the action of water their auxiliary products has been selec- to evolve, forming a three-dimensional molecules and another coat of colour ted so as to limit this phenomenon and network. When the network index (the can be applied instantly as soon as the to ensure colour fidelity after the film number of intermolecular covalent first is dry. is dry. Acrylic colours in general tend to bonds) is high, the film is hard and change and become less bright as they insoluble in certain solvents. This har- Drying : dry. dening is however moderated by the EXTRA-FINE ACRYLIC simultaneous formation of small mole- Drying time : 40 minutes The action of ultra-violet rays : cules resulting from the degradation of + 10% of RETARDER : 55 minutes This type of polymer is very lightfast. macromolecules and acting as a plasti- (drying time increased by 35%) Ultraviolet action causes little or no cizer. This degradation is due to a num- photo-oxidation or photo-degradation ber of secondary reactions controlled of the film (conclusions of a study by by oxygen, moisture in the air and STUDIO ACRYLIC the CNEP). ultraviolet rays. These reactions gene- Drying time : 25 minutes rate organic substances, such as hydro- + 10% of RETARDER : 30 minutes The film: ketones, diketones, diols, aldehydes and After the film has coalesced, it is acids, which cause yellowing phenome- 3-THE PHYSICOCHEMICAL ASPECT pliable and the canvas can be rolled up na due to unsaturated ketones (diace- once it is dry with no risk of cracking. tyl and dibenzalketone), phenomena of Acrylic thus has many qualities: very acidification of the film, resulting, for quick drying time, water as a thinner, 4-TOXICOLOGICAL ASPECTS example, in changes in certain pig- good adherence to any non-greasy sup- ments, and hydrolysis phenomena port, the colour does not dull or change The resins in acrylic paints contain no resulting in powdering. when dry. free monomers such as acrylamide, In the wet state, acrylic emulsions are acrylonitrile, ethyl acrylate or n-butyl During crosslinking, the mesh of the milky, varying with the fineness of the acrylate, which can cause contact der- network shrinks and fluids are expel- polymer particles in the resin. When matitis and other skin allergies. led towards the surface of the film or the film is dry, this milkiness disap- The paints are pleasant to use because towards lower levels. This phenomenon pears. they contain very little ammonia, is known as syneresis. The film sweats The colour of paint formulated with which irritates the nose and eyes. They and this plays an important role in sur- this type of emulsion may vary accor- are practically odourless. face flatness and optical qualities: dull- ding to the diameter of the particles in ness or gloss. the resin. In addition, the light refrac- tion coefficient of these polymer par- NB: Further information will be publi- ticles is different in the wet and in the shed as current studies progress. GLOSSARY THIXOTROPY: UNSATURATION: MILKINESS: The property of certain very viscous A double bond on oil molecules allo- The whitish colour of a film of acrylic gels which liquefy when stirred, but wing the phenomenon of siccativation. resin in emulsion before it dries. become viscous again at rest. In other words, thixotropic paint may have the following characteristics: Reactive functions Covalent bonds -its viscosity decreases when stirring increases, -its viscosity decreases when the dura- Monomers with 2 tion of stirring increases, reactive functions -when it is stirred violently for a long 1-Diagram of a straight-chain macromolecule time, the viscosity approaches a final viscosity, -when it is left to rest after stirring, it returns to its initial state fairly quickly. WASH: Strongly diluted paint, used for the Monomers with 2 first sketches. The first coats should be reactive functions the thinnest. THINNER: Monomers with 3 What is the difference between a sol- reactive functions 2-Diagram of a three-dimensional network based on two monomers, vent and a thinner? one of which has three reactive functions A solvent dissolves a product, in prin- ciple in any proportions. A thinner does not dissolve a product, CHROMOPHORS: but can be added to a solution of the lat- A chemical group responsible for the ter in significant quantities. For colour of a molecule in a given example, water dissolves sugar; it is a medium. solvent. Syrup is obtained, to which alcohol can be added, as a thinner. It RHEOLOGY makes the syrup more liquid. Alcohol The science of the behaviour of fluids alone would have no effect on the sugar. subjected to chemical and physical stresses. SICCATIVATION: Chemical transformation of certain oils APPARENT WETTABILITY: by fixing oxygen from the air, so that a The tendency of fillers and pigments in very strong three-dimensional net- paint to absorb the binder (oil) and be work is formed. This phenomenon coated with it. takes the form of an increase in the weight of the film of oil used in paint OIL ABSORPTION: as it dries. This reaction is activated by The quantity (by volume) of binder temperature and ultraviolet rays. required to wet 100 g of pigment com- pletely. Oil absorption depends on the POLYCONDENSATES: diameter (the specific surface area) of Film-forming substances are polymers the pigment and filler particles. consisting of macromolecules. The lat- ter are produced from chains of small STREAKINESS: reactive molecules known as monomer The result of redilution, caused by the units. A polycondensate (or polymer) application of a second coat of paint is a macromolecule obtained through containing a thinning solvent of the condensation of monomer units, by a first coat. chemical reaction.