The relationship between titanium dioxide and powder coating weather resistance

Abstract: The type, surface treatment and characteristics of titanium dioxide have a great influence on the weather resistance of outdoor powder coatings.
key words: powder; paint; titanium white; surface treatment; coating; weather-resistant
0 introduction
in the context of the deepening of the national green development policy, paint powder has become one of the main topics. According to the statistics of fun coating network, China's 2017-2019 period, the sales of thermo-solid powder coatings were 1.605 million t, 1.7606 million t, 1.942 million t, respectively, an increase of 13.03 percent, 9.7 percent, 10.3 percentAmong them, sales of outdoor powder coatings during this period were 80.41 million t, 93.91 million t and 1.0722 million t, respectively, an increase of 18.97 percent, 16.79 percent and 14.17 percent year-on-year. During this period, sales of in-house powder coatings were 80.09 million t, 82.15 million t and 86.98 million t, respectively, an increase of 7.63 percent, 2.57 percent and 5.88 percent year-on-year.
During this period, outdoor powder coatings accounted for 50.1%, 53.34% and 55.21% of the total powder coatings in the whole year, respectively, from the proportion and sales volume, outdoor powder coatings are basically on the rise year by year, and occupy a very large share.
The weather resistance of outdoor powder coating has always been a concern of the industry, and there are many factors affecting the weather resistance of outdoor powder coating: the external factors affecting the weather resistance of powder coating are mainly sunlight, rain, temperature, oxygen, water, dust, etc.; Weather resistance factors are resin, curing agents, additives, pigments, fillers, etc., and directly lead to the film yellowing, decoloration, powdering, cracking, foaming, surface peeling and other aging phenomena, thereby affecting the performance and appearance of the product. For light-colored products, the choice of titanium dioxide is also one of the important factors for outdoor powder coating weather resistance considerations, the current market of more types of titanium dioxide, surface treatment methods and performance parameters are uneven, so how to choose a suitable titanium dioxide is an important link to measure the weather resistance of light-colored outdoor powder coating. Through the introduction of titanium dioxide and surface treatment, the effect of titanium dioxide on weather resistance of outdoor powder coating is introduced by comparison of experimental data.
1 titanium white powder introduction
titanium white powder is the main component of TiO2, relative molecular mass of 79.9 white inorderable pigment. Because of its high whiteness, good brightness and good cover, it is widely used in rubber, cosmetics, plastics, inks, coatings, papermaking and other industrial fields. It is one of the most widely used white pigments. Titanium white powder according to the crystal type can be divided into sharp titanium type, gold redstone type, plate titanium type. The redstone type and the sharp titanium type belong to the same four-square crystal type, but the lattiest is different. The lattic lattiest of the sharp titanium type is small and tight, so it has a high relative density and stability, and the plate titanium type is very rare because of its unstable crystal type, and can be converted to the gold-redstone type at 650 degrees C, which is described here.
-type titanium white powder is better than the powder resistance and light preservation of the sharp titanium-type titanium white powder, in the visible wavelength range (400 to 700nm), redstone type and sharp Titanium-type reflectivity to light is very high, so there is a good whiteness, but in the range less than visible light (300 to 400nm ultraviolet light), the performance of the two types will be very different (see Figure 2). The reflectivity of UV rays in the band with great lethality (350 to 400nm) is much lower than that of the sharp titanium type, that is to say, the sharp titanium type in the 350 to 400nm band has the function of absorbing ultraviolet light, and the damage of ultraviolet light to the coating film is shared. Therefore, from the coating film weather resistance characteristics and performance, the gold-redstone type titanium white powder has more weather resistance advantages.
2 The production method of titanium dioxide is introduced
the production method of titanium dioxide can be divided into sulfuric acid method, chlorination method, hydrochloric acid method, mixing method, phosphoric acid method, nitric acid method and so on. At present, the process of preparing titanium dioxide is mainly sulfuric acid and chlorination.
sulfuric acid method mainly to titanium iron ore or acid-soluble titanium slag as raw materials, titanium raw materials are dispersed with sulfuric acid into TiOSO4 solution and then de-miscellaneous, separation, and finally the formation of finished titanium dioxide.
through the legal system of sulfuric acid prepared titanium white powder there are three main types: redstone-type titanium white powder, sharp titanium-type titanium white powder, enamel-grade titanium white powder. The preparation stage is divided into four stages: (1) acid solution stage, (2) immersion stage, (3) hydrolytic stage and (4) calcination stage.
advantages of producing titanium dioxide by sulfuric acid are; With titanium iron ore or acid-soluble titanium slag and sulfuric acid as raw materials, raw materials are cheap and easy to obtain, production costs are lower than chlorination method, the technology is mature, the equipment is simple, the production process is easy to replicate, with the improvement of the particle size control of hydrolysis and calcination section and the progress of coating technology, narrowing the difference with the quality of chlorinated products. The disadvantages are: long process, mainly intermittent operation, compared with titanium dioxide products chlorinated method, the quality of titanium dioxide by sulfate method is relatively poor, sulfuric acid and water consumption is high, waste and by-products, environmental pollution is greater.
of titanium dioxide preparation for chlorination is divided into three parts: first, the ore and high purity coke are mixed, react with chlorine gas at high temperatures, and a titanium chlorine compound containing a variety of impurities is prepared (rough TiCl4). The coarse TiCl4 is removed by distillation or chemical treatment machine, and the pure fine TiCl4 is obtained, and gas phase oxidation is carried out. Finally, the coarse TiCl4 after gas phase oxidation is reprocessed, further dechlorinated, and then ball grinding and surface treatment are carried out.
the main advantages of the production of titanium dioxide process by chlorination method are: short process, fewer process control points, continuous production, easy to achieve automated control;
3 Introduction to weather-resistant titanium dioxide
the main factors affecting the weather resistance index of titanium white powder: chemical composition, chemical form of envelope substances, crystal structure, application formula, etc. Due to the defects of its lattice, ti4 plus in titanium white powder can easily be reduced to Ti3 plus, releasing primary ecological oxygen. Due to the strong reaction activity of primary ecological oxygen, organic matter can be oxidized, molecular chain broken or degraded, which destroys the continuity of coating, resulting in film powdering and decreased weather resistance. The surface treatment of titanium dioxide can avoid the direct contact between titanium dioxide and ultraviolet light and improve the surface chemistry of titanium white powder. Figure 3 shows a diagram of the surface treatment of titanium dioxide.
inorderable treatment is mainly to eliminate the photochemical activity of titanium dioxide, improve the weather resistance of titanium white powder. Currently commonly used surface treatment agents are SiO2, Al2O3, ZrO2. The different surface treatment methods are divided into unit type, dual type, triple type (less of this type on the market), through the type of surface treatment and the percentage of treatment agent in titanium dioxide, to give titanium dioxide higher weather resistance.
Usually the method of testing the weather resistance of titanium dioxide is the relationship between the amount of surface treatment agent and acid solubility, and the amount of general surface treatment agent is inversely inversely related to acid solubility (acid solubility of weather-resistant products<1.0, ultra-weather-resistant products <0.5), as shown in Figure 4.
ferable from figure 4 data, the addition of surface treatment agents can meet the general weather resistance standards at ≥4%, and the addition of surface treatment agents ≥5%, can meet the ultra-weathering standards of titanium dioxide.
redstone titanium dioxide can be divided into: R1, R2, R3 three categories (GB/T1706-2006 and the international standard ISO591-1:2000 (E)). Among them, R2 type is the most widely used, the international application volume accounts for 80% of the total production of redstone. The most used in powder coatings is also R2 type titanium white powder. The advantages are as follows: (1) good masking, (2) good gloss, (3) low oil absorption, (4) good weather resistance, (5) the titanium content of R2 type titanium dioxide can be as low as 90%.
treatment is mainly to improve the dispersion and wetting properties of titanium white in various media. There are two main ways to connect an organic treatment agent to the surface of titanium dioxide particles, one is physical adsorption and the other is chemical adsorption, i.e. it is connected to hydroxyl reaction on the titanium white surface, which makes titanium white powder water-repulsive and pro-oil.
4 Titanium white powder film after weather-resistant data introduction
4.1 experimental instrument
extruder: Haiyang, Shandong Province; coffee grinding, electrostation spray gun (MAOS Jinma four generations manual spray gun): Swiss Jinma; curing oven: Beijing Cowei Yongxing Instrument Co., Ltd.; particle size analyzer (BT-9) 300H): Dandong Bait Instrument; Chroma Meter (CR-10Plus): Melanda, Japan; Glossy Meter (BK1568S): Stronpico; Membrane Thick meter (4500): Nix, Germany; Xenon Aging Box (XD-21-866): Shanghai Hyundai.
4.2 Experimental raw materials
non-branched end pyrethroid polyester, isocyanuric acid triglycerides, polyethylene waxes, acrylates leveling agents, benzene marriage, acrylates and methyl acrylates co-polygons, inorganic pigments, titanium dioxide, precipitation of sulfuric acid: commercially available industrial products.
4.3 Aging Test Method
(1) Instrument Detection: Xenon light test conditions refer to GB/T23443-2009 in 7.12.2;
natural exposure location: Northwest China.
4.4 Test method
the assessment of the preservation rate by GB/T9754-2007;
to assess the degree of color change by GB/T1766-2008;
by reference to GB/T1766-2008.
5 Experiments
5.1 Formula
Table 2.
2 titanium dioxide 1 and cell 2 titanium dioxide are used in different surface treatment agents.
two-meta titanium white powder 1 and two-meta titanium white powder 2 respectively using different surface treatment agents.
5.2 powdering
process: (1) weighing; (2) mixing; (3) extrusion (4) cooling, crushing; (5) particle size screening (smashing).
5.3 Model preparation
(1) electrostectrulation spraying;
condition: 200 degrees C×15min.
5.4 Test Results
Under the same polyester formula, different surface-treated titanium dioxide, the photon preservation rate comparison (natural sun exposure) test results are shown in Figure 6, with reference to GB/T9754-2007 to assess the preservation rate.
the results of the light preservation rate from good to poor were 1> dual 2> unit type 1> unit type 2>R1.
can be seen from Figure 6, the surface treatment of titanium dioxide is very different to the coating film preservation rate is very different. With the exception of the R1 product gloss reduction situation is serious, the rest of the products are in the 6th month gloss showed an overall downward trend. And during the period of 6 to 18 months, the degree of UV damage to the coating film is different. Membrane loss is most severe between 18 and 24 months.
: Titanium white powder surface treatment technology weather-resistant sorting is better than the unit type is better than unsopersed titanium dioxide, and the data of the previous group show the basic match. However, it can be seen that there are also differences between two different dual and unit types. In other words, the weather resistance of titanium dioxide treated with different surface treatment agents varies. This is mainly due to the different properties given to titanium dioxide by different surface treatment agents.
Under the same polyester formula, the degree of powdering under different surface treatment of titanium dioxide (natural sun exposure in northern China) is seen in Table 3, and the detection method is used to assess the degree of powdering by reference to GB/T1766-2008.
can be seen from Table 3, different surface treatment of titanium dioxide has a great impact on the powder resistance of the coating film. Double-meta-titanium white powder after 24 months found no signs of powdering, while unit-type titanium white powder in the 18th and 24th months, respectively, appeared very slight powdering phenomenon, R1 products performance is not good.
analysis: Titanium dioxide surface treatment technology weather-resistant sorting is better than the unit type is better than unsalted titanium dioxide, and the data of the previous group show the basic match. Since dual-meta-surface treatments are generally weather-resistant, no further explanation is given (due to the long detection time, it is not possible to further compared dual 1 and double-2). The difference in cell titanium dioxide is due to differences in powder resistance due to differences in surface treatment agents or different coating rates of surface treatment.
in the same polyester formula, prepare a model with a coating film thickness of (85±5) sm, measure it with a color difference meter, and assess the degree of color change with reference to GB/T1766-2008.
test conditions for xenon lamp aging are as follows:
test conditions refer to GB/T23443-2009 in 7.12.2.
irradiance: 550W/m2, lighting time: 102min, blackboard temperature: (63±3) degrees C, relative humidity: (65±55),, spray_e_r_I time: 18min, filter: Daylight, exposure time: 1000h.
the degree of color change under different surface treatments of titanium dioxide can be found in Table 5. Xue Feng: The relationship between titanium dioxide powder and powder coating weather resistance aging test after color difference results from good to poor are 1> dual type 2> unit type 1> unit type 2>R1.
can be seen from the upper group of experiments, the different surface treatment of titanium dioxide has a great effect on the color preservation of the coating film. Under the same test conditions, the surface treatment process of titanium dioxide directly affects the weather-resistant color of the coating film, as can be seen from the above decomposition chart, the numerical difference of a is not obvious, but because the red and green phase in the white coating film has a greater impact, so this set of data can not be judged by the numerical difference size. It is clear from the decomposition diagram b that the degree to which different surface-treated titanium dioxide inhibits yellow change is basically the same as that of the yellowing. The comprehensive color difference is basically similar to the curve trend of L, a and b.
: Titanium white powder surface treatment technology weather-resistant sorting is better than the unit type is better than unsopersed titanium dioxide, and the data of the previous group show the basic match. As mentioned above, due to the lattice defects of titanium dioxide, the photochemical properties are very strong, the surface treatment of titanium dioxide can effectively avoid the direct contact between titanium dioxide and ultraviolet light, so the color preservation of the product has also been significantly improved. In addition, in the relationship between the dosage of surface treatment agents mentioned above and acid solubility, the relationship between the dosage of surface treatment agents and the weather resistance of titanium dioxide also needs to be taken into account.
the above 3 groups of comparative experiments, targeted to no