Research and application of crack paint in construction machinery industry
Introduction to crack paint
Crack Paint is an art paint, it is distinctly different colors with primer paint spraying cracks formed on the surface to be painted pattern uniform texture, varied, well-proportioned, very three-dimensional effect with a crack beauty named.
Crack paint forming principle
In the crack topcoat film forming process, since the rapid evaporation of the solvent, resulting in internal topcoat film cracks due to uneven force, showing a gap irregular crack, the crack so that a different color basecoat topcoats It revealed gaps in the crack, forming a good, uniform crack pattern. General crack primer and paint both color contrast, the more three-dimensional sense, the better.
Studies have shown that crack formation depends on the interaction strength paint, coating layer. When the coating in an isolated state, even contraction in all directions; when the coating on the substrate, the film except by their own shrink tension and tensile strength, but also by the fluidity of the primer, resulting in uneven shrinkage finish produce stress concentration, when this stress is greater than the tensile strength of the coating film will crack, the crack is formed. On the contrary, when there is no flexibility primer, topcoat will not produce stress concentration, will not crack; and when the top coat large stress is less than the tensile strength of the film, it will not crack.
The effect of the formation of cracks in the coating composition is largely related to weak links in the paint when fewer molecular chain, combining the strength of an hour, when the crack crack will be relatively flat; on the contrary, when the molecular chain binding strength, cracking point are more curved and jagged sticks forming effect. Case to ensure uniformity of size and crack spray, paint cracks in the production of small parts generally used in spray, such as panels, cover and other decorative plane.
Crack paint workability
1. Substrate Select: spray paint cracks to select a wide range of substrates, steel, wood, glass, steel and plastic products can be.
2. Paint choices: To ensure the construction machinery products better corrosion resistance, decorative appearance and environmental protection, is generally used in two-component epoxy primer sticks, water-based resin paint and curing time longer flexible curing agent , paints and coatings matching system. Because if the curing time is too short, it will be difficult to control the coating process finish, film cracking difficult and poor, environmental and safety considerations, the aqueous paint become more and more choices.
3. The coating process: crack paint spraying and paint spraying same ordinary, generally: the substrate before treatment – Spraying crack primer – drying – spray paint cracks – Dry – Spray varnish – dried. Because crack paint itself loose, and the underlying lack of proper paint adhesion, so the surface must also be spray paint crack varnish, lacquer crack to increase bond strength and adhesion to the primer.
4. The process of spraying process requirements and precautions: cracks in the surface paint can exhibit a uniform, beautiful patterns, in addition to the performance of the crack paint itself related, more closely related to the corresponding coating technology and the environment. The production process, the following factors must be taken to ensure that normal paint cracks efficient implementation process.
1) pre-construction must have spray paint spray style demo board, according to the size of the effect of crack and choose paint application viscosity good crack, the thickness of the film, adjusting the shape of a good gun, air pressure, the amount of paint ( stereotypes), walking speed gun control, distance, spraying techniques, atomized condition, paint mixing color scale.
2) be leveling primer spray-drying, the film reaches dry state after a wet-on-wet coating can crack finish. The difference between conventional products that can not be dried to crack primer hard work state, otherwise it will affect the adhesion between the primer and topcoat, not crack effect.
3) When the paint coating thickness to completely cover the primer colors prevail, concrete can crack the size you want to get control film thickness. When the crack initiation generally began to spread from the edge to the middle, the initial stages of crack lines shallow and thin, with time, the crack grew gradually deepen bold. General crack big thick film, thin film small crack, crack faster, uniform film thickness, the crack size is consistent, uniform appearance. If you need a large crack effect, the primer film thickness should be thicker, but also should be more crack paint spray 2-3 times, and the volume is not very big; to small cracks on the contrary.
4) After the spray varnish, in order to obtain good film hardness, typically for drying. 150 ℃ high temperature drying, the film maximum hardness, temperature 80 ℃ drying film hardness Secondly, at room temperature from the dry film hardness worst.
5) temperature and humidity of choice: paint cracks due to temperature and humidity are more sensitive to environmental humidity, temperature is too high, too low, are not suitable for construction, in order to avoid adverse effects, generally at a temperature of 25 degrees Celsius, relative humidity 75% better. At higher temperatures the scene, faster solvent evaporation, spray paint needs as quickly as possible, otherwise the primer too dry, less prone to cracking. Water-based paint cracks cracking is usually in the topcoat 20min-40min after the start, according to the ambient temperature, humidity and coating thickness will vary. General spraying ambient temperature is high, cracking faster. Even confined poorly ventilated environment, but also can be formed cracks.
6) Further oil paint and water-based paint spray gun should be used separately, or likely to cause secondary pollution of the film.