Long-lasting easy-to-wipe, anti-graffiti powder coating development.

Abstract
The reaction mechanism of long-acting easy-to-wipe and anti-graffiti powder is expounded, and the formulation design of long-acting anti-graffiti powder is discussed through experiments, and the mechanical and easy-to-wipe properties of the product are indicated.
keywords: easy-to-wipe; anti-graffiti; powder paint; surface free energy; polyurethane;
1, introduction
The word graffiti originated in Italy and means "draw a line on a hard surface", an expression of an art form that has existed for thousands of years. However, while some graffiti is a real work of art, over time graffiti is now mostly considered an act of vandalism, with graffiti often linked to profiteering and crime, and graffiti not only affects appearance, but also irreversibly damages objectsThe removal of graffiti is also very expensive, with The Portuguese Railways reportedly spending 304,000 euros a year cleaning graffiti in train carriages.
The so-called anti-graffiti, easy-to-wipe powder coating is the powder coating static spray on the work piece, according to the set temperature, time curing, the coating film not only has the decoration of conventional powder coating, protection, weather resistance, etc. , the coating surface graffiti can be easily removed, in addition, the coating film gloss, color will not change significantly.
2, application areas and standards, testing methods
easy to wipe, anti-graffiti powder coating is widely used in municipal public facilities, furniture, hospitals, electronics, instrumentation, metal decoration, automotive and other fields, such as: automotive wheels, lying machines, outdoor guardrails, home aluminum furniture, schools, hospitals, public tables and chairs.
The American Materials Association issued a standard for anti-graffiti testing methods in 2000, ASTM D6578-00 Standard for determined of graffiti Resistance, based on the application of graffiti materials to the coating surface, after a certain period of time according to the prescribed cleaning method to clean the graffiti surface, with a washable level to represent the anti-graffiti properties of the coating. The cleaning methods in the standard include manual method and scrub machine method.
The Ministry of Housing and Construction in 2011 issued the construction industry product standard JG/T 304-2011 "building anti-graffiti anti-paste paint", the standard applies to the building outdoor, urban public facilities, such as the use of anti-graffiti function of the paint, the standard selected three representative graffiti materials: ink, oil marker pen and spray paint, respectively coated on the coating surface, 24h after the graffiti manual cleaning. Cleaning materials according to the cleaning capacity is weak -medium-strong in order of row: no suede cloth, 1% water-based cleaning agent, citrus-based cleaning agent (effectively become refined for citrus, grapefruit, lemon fruit hydrocarbon solvents) and alcohol. If the weak cleaning material can not remove graffiti, then choose a strong cleaning material test, and according to the cleaning material to assess the anti-graffiti rating as follows: table
1 JG/T 304-2011 anti-graffiti rating
3, easy to erase, Anti-graffiti reaction mechanism
The main difference between anti-graffiti powder coating and other products is that the surface coated by it can form a dense low-surface energy structure, making it difficult for contaminants to adhere to the surface of the paint film and difficult to penetrate, so as to obtain a better anti-graffiti effect. Easy-to-erase powder coatings not only reduce their own adhesion, but also consider how to remove contaminants from the interface of the substrate. These factors include the moistness of the substrate, the attraction between atoms, and the diffusion of molecules.
easy-to-clean, anti-graffiti powder coatings are divided into sacrificial anti-graffiti coatings, semi-permanent anti-graffiti coatings and permanent anti-graffiti coatings according to their protective characteristics. Sacrificing, semi-permanent graffiti-resistant coatings are usually made of wax, which is removed along with contaminants, and the biggest problem with this method is that the cleaning effect varies with the number of removals. Permanent, long-lasting powder coating, long coating life, the use of safe neutral cleaning agent can be used multiple times to remove graffiti, postings or other contaminants on the coating surface without losing the performance of the coating itself.
permanent easy to erase, anti-graffiti powder coating has the following common characteristics:
(1) coating surface can be low,
shown as hydrophobic, oil- and graffiti difficult to adhere to;
(3) coating has a certain anti-corrosion, anti-aging properties, can be applied in the outdoor area

4, experimental part
experimental raw materials and tests
experimental extruder: 35 machine, screw line cloth: medium displacement, extrusion temperature, set according to different systems; testing equipment: Espresso brand low temperature oven (0-250 degrees C), Shanghai Chemical Research Institute, Resin A: Hydroxy 35-45mg KOH/g, Resin B: Hydroxy 75-85mg KOH/g, Resin C: Hydroxy 120-150mg KOH/g, resin D: hydroxy value 250-300mg KOH/g, curing agent for Degussa B1530, NCO content 14.8-15.7%, leveling agent, resting fragrance, filler, Titanium white powder and other commonly used mature materials for the market, the test results are as follows: table
Table 2 different hydroxy resin film performance comparison
A prominent advantage of polyurethane powder coating is super level, high smooth and smooth surface can prevent the infiltration of contaminants, residue on the surface of the coating paint or similar paste can be easily removed by cleaning agent. Obviously for this performance, coatings require high smoothness and high crosslink density.
From the above results can be seen that the mechanical performance of low hydroxy resin is better, but the anti-graffiti performance is poor, with the increase of hydroxy, anti-graffiti performance gradually improved, when the use of hydroxyl value of 300 polyester resin design formula, ink juice, oil marker pen can be easily removed, but mechanical performance deterioration, impact can only reach 30cm positive punch, because high hydroxy resin film cross-link density is too large, hard film caused by.
Using hydroxy 35mgKOH/g resin A and hydroxy 300mg KOH/g resin D mash-up design formulation, film-forming performance comparison is as follows: table
Table 3 high/low hydroxy resin mash-up film performance comparison
- Half-light - no light downward trend, when the dosage is higher than 3:1, mechanical performance decreased, anti-graffiti performance did not improve with the increase of cross-link density, because the low-light coating surface has many microscopic unevenness, contaminants can seep into the coating film, anti-graffiti performance is reduced, from the test results, the best ratio A:D=4:1.
Application of anti-graffiti additives
When the use of polyurethane system high and low hydroxy value matching, and add different content of anti-graffiti additives, the results of the coating test results are> as follows:
Table 4 different anti-graffiti additives added performance comparison
However, the amount added was more than 1%, the mechanical properties of the coating decreased significantly, as the impact performance decreased, and the best recommended addition for anti-graffiti additives was 1%.
The application of anti-graffiti additives is derived from the functions of natural organisms, such as the lotus leaf effect, which mainly benefits from the special shape and hydrophobicity of the lotus leaf surface, the special surface appearance prevents the dirt from touching the lotus leaf surface closely, and the hydrophobicity makes the lotus leaf hydrophobic, so the water droplets will roll off its surface and carry dirt down.
Figure 1 Yang formula
Figure 2 contact angle and hydrophobic, hydrophobic
from Yang's formula can be seen, when the contact angle >90 degrees, the coating film presents a better hydrophobic, anti-graffiti additives applied in powder coating, can reduce the surface pressure of the coating, its contact angle with water droplets is about 160 degrees, the coating surface is smooth, and can be applied to the paint anti-graffiti properties. When oily pens or spray paint graffiti on the surface of the coating film, the handwriting shrinks and can be easily erased by lint-free cotton cloth.
5, conclusion
graffiti is a global problem, while the paint industry has brought great challenges. Although graffiti is not completely stopped, the use of anti-graffiti powder not only protects the substrate, but also makes graffiti much easier to clean up.
from the experimental results, the use of polyurethane system high and low hydroxy value matching, and add 1% anti-graffiti additives, the resulting coating film has excellent long-lasting easy to wipe, anti-graffiti performance.
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