Formulation design of orange powder coating

Abstract: Based on the texturing mechanism of orange peel powder coating, this paper discusses the influence of flocculent, amount of pigment and filler, baking conditions on orange peel, and puts forward the way to solve the problem of film exposure and thick coating flattening With the increasing of the amount of powder coating and its application scope, orange powder coating has covered the defects of the substrate with its special texture effect, and can avoid the defects of coating such as particles, shrinkage cavity, flow adjustment, etc its excellent decorative properties are favored by people Orange peel powder, also known as wrinkle powder, is generally made by adding filler, using different curing agent, adding floating agent, adding orange peel agent, etc At present, the orange peel powder produced by the first two methods in the market is seldom used by the powder manufacturers because of the bad mechanical properties or the poor adjustability of texture size The main method is to add floating agent and orange peel agent to make orange peel powder In this paper, the mechanism and formula design of these two methods are briefly described 2 There are two steps in the process of pulverizing First, the bottom powder of the main material is prepared, and then a certain amount of flocculent is added by dry mixing method The mechanism of the grain formation is that the surface tension of the powder is high because there is no leveling agent in the formula or the amount of leveling agent is very little The flocculent is generally a material with limited compatibility with resin, and its surface tension is small, so it is not mixed and extruded with the main material Therefore, a surface tension gradient is formed on the surface of the whole molten powder coating According to the Bernal swirl flow theory, a shrinkage cavity is formed where the surface tension is small, which makes the coating form a rough orange surface The mechanism of adding orange agent is the same as that of adding floating agent The difference between them is that orange agent and main material are mixed and melted together Orange agent is also a material with limited compatibility with resin Its melting point is higher than that of resin It will not melt during melt extrusion, but it is uniformly dispersed in the main material 3 see Table 1 for the formula used in this test Table 1 test formula of orange peel powder coating 1 23 4 5 6 polyester resin 35 35 30 30 sj-3 × B polyester resin 65 65 SJ-4 × C leveling agent 0.10.1 pv88 epoxy resin 35 35 35 30 30 sj-e12 TGIC 5 5 sj-tgic titanium white powder 20 20 20 20 20 20 barium sulfate 10 10 20 10 10 10 10 10 benzoin 0.30.3 0.3 0.30.30.3 carbon black 0.10.10.10.10.10.1 orange peel agent 0.10.1 floating agent 0.7% 1% 1% 1% note: the curing condition is 180 ℃ / 20min 4 Through the test, we found that the following factors have influence on the performance of orange peel powder 4.1 the effect of the amount of flocculent on the size of orange peel is shown in Table 1 The amount of flocculent in Formula 1 is different from that in formula 2 The orange peel in Formula 1 is larger than that in formula 2, but there is no uniform peel in formula 2 This is due to the small amount of flocculent in Formula 1, the uneven surface tension gradient of the coating when the powder is melted, the uneven distribution of the shrinkage cavity (concave) on the surface of the coating, resulting in large and uneven orange lines, while formula 2 is just the opposite 4.2 effect of the amount of pigments and fillers on the size of orange stripe The dosage of pigment and filler in formula 2 and formula 3 are different From the orange lines of the obtained film, formula 3 has a stronger stereoscopic sense than formula 2 This is because the dosage of pigment and filler in Formula 3 is large, and the surface tension and melting viscosity of the main material are much higher than those in formula with low dosage of pigment and filler during melting Therefore, it forms a larger surface tension gradient with the floating agent with small surface tension after it, and melts at the same time The high viscosity results in the low fluidity of the coating, thus forming a strong three-dimensional orange surface 4.3 the problems of thin coating, exposed bottom and flat thick coating are as mentioned above The orange lines are mainly caused by continuous shrinkage caused by floating agent Therefore, whether the orange lines can be formed by the coating is related to the surface tension gradient and shrinkage caused by adding floating agent and orange line agent when the coating is melted However, the size of orange lines is related to the fluidity of the coating when it is melted The fluidity of paint can be expressed as follows: H 2G = - Δ V 2 η, in which: G - paint fluidity H - wet film thickness η - viscosity Δ V - surface tension gradient of cross section It can be seen from the above formula that the fluidity of paint has a great relationship with film thickness According to Bernal's vortex theory, the coating moves up from the bottom layer under the action of surface tension, and moves down from the top layer under the action of gravity The surface tension of the coating shrinkage cavity is usually small, but the fluidity is large If the coating is too thin, the downward flowing coating is far from enough to supplement the upward flowing coating, and then the phenomenon of bottom shrinkage will occur When the coating is thick, although the fluidity of the shrinkage cavity is large, the thick enough coating will increase the fluidity of the coating, so that the difference between the up and down flowing coating is not big, so that the shrinkage cavity is eliminated , the coating becomes flat Therefore, to solve the problem of thin coating, on the one hand, do not spray too thin when spraying, on the other hand, you can choose the floating agent or orange agent whose surface tension is not much different from that of the main material; the measures to solve the problem of thick coating flattening are just the opposite 4.4 the effect of baking conditions on the size and stereoacuity of orange peel the size and stereoacuity of orange peel discussed above refers to the surface of orange peel obtained by baking and curing at 180 ℃ In practical application, there are many cases in which the parts are sprayed and then put into the oven, rising from normal temperature to 180 ℃, or the oven temperature is higher than 180 ℃ The former is relatively flat compared with the surface of orange grain baked at 180 ℃, while the latter is generally stronger than the surface of orange grain baked at 180 ℃ This is because in the process of rising from normal temperature to 180 ℃, the resin composition in the main material starts to melt and flow at about 100 ℃ In the temperature range of 100 ~ 180 ℃, the viscosity of the main material decreases and the fluidity increases with the rise of temperature At this time, the crosslinking density of the coating increases with the rise of temperature, which makes the viscosity and fluidity increase Compared with the constant temperature baking condition of 180 ℃, the coating When the baking temperature is higher than 180 ℃, the main material crosslinks rapidly and the fluidity drops rapidly, which is very favorable for the coating to produce shrinkage, thus forming a strong three-dimensional orange surface However, when the temperature is too high, the curing speed of the main material is too fast, which can inhibit the possibility that the floating agent (orange agent) causes the surface tension gradient of the film to form shrinkage cavity, so only a flat film surface can be obtained Therefore, under the above two non constant temperature curing conditions, the gelation time of the main material should be properly prolonged and the floating agent (orange agent) with high surface tension should be selected Conclusion the orange grain size and stereoscopic sense of orange grain powder coating are not only related to the amount of flocculent, the amount of pigments and fillers, baking temperature, but also related to the content of effective ingredients, resin viscosity, oil absorption of pigments and fillers In order to produce orange grain powder coating, the above factors must be considered carefully to obtain satisfactory orange grain surface References: 1 Qian Fenglin, Zhu Yushu, paint additives - variety and performance manual, Beijing, chemical industry press, 1990.