Development and influence factors of vacuum coating UV prime

Because of the green environmental protection and high efficiency of radiation curing coatings, the technology has been paid more and more attention and rapid growth in the world, and its application field is more and more extensive. The UV coating has excellent surface finish and is suitable for use as a primer in the vacuum metal coating technology, and a very bright metallic appearance can be obtained on the plastic base material. With the development of automobile industry, many metal replacement technology has been applied, the application in the field of automotive lamp reflection cover, has been fully used to improve the reflection effect by vacuum film in PC, BMC and other plastic surface, for this field along with excellent leveling property, high temperature resistance (for PC substrate for more than 120 DEG C, the BMC substrate is up to 180 DEG C).

In this paper, some formulation principles of UV primer applied on automobile reflector of PC substrate are studied and discussed. Various factors influencing the properties of primer are analyzed.

1 、 experimental part

1.1 raw materials

Desmolux 2265 (aliphatic polyurethane acrylate oligomer, Bayer), CN965 (aliphatic polyurethane acrylate oligomer, Sartomer), epoxy acrylate (homemade), amino acrylate (homemade), three trihydroxymethylenepropane three acrylate (TMPTA), butyl acrylate (BA), ethylene glycol (HDDA) two, two acrylate three glycol reduction two acrylate (TPGDA), RUNTECURE1103, RUNTECURE1107 (light initiator, Changzhou Huatai Co. Ltd), Irgacure184, methyl isobutyl ketone, toluene, isopropyl alcohol, butyl acetate.

1.2 experimental instruments

Type UV-102 light curing unit (Ou Shi man Technology Development Co., Ltd.), UV-INTEGRATOR UV energy meter (Germany), 730 Fu Liye infrared spectrometer (Nicolet), differential scanning calorimetry Q-100 differential (TA Instruments), 1800 * 1950 automatic evaporation vacuum coating machine (Foshan City AIT Manchester vacuum machine factory).

Preparation of 1.3 UV coatings

Mix the amount of active oligomer, active diluent, photoinitiator, diluent and so on into the container.

1.4 experimental method

The UV coating sprayed on the PC substrate, the curing in the curing machine, then vacuum aluminum, determination of physical mechanical properties of the coating and the substrate, coating and plating layer by GB method. The change of double bond before and after solidification of coating was tested by Fu Liye infrared spectrometer and KBr tabletting method. Differential scanning calorimetry (DSC) was used to test the thermal flux change of the coating at elevated temperature, and to determine the thermal stability of the coating.

2, results and discussion

2.1 vacuum coating requirements for UV primers

The main reason for vacuum coating prior to UV coating on a plastic substrate surface has the following two points: first, through the UV coating to prevent volatile impurities from closed substrate, substrate in vacuum coating or workpiece is used, affects the coating quality. When the lamp cover is used, the temperature of the utility model can be increased to more than 100 DEG C in the process of using, and if the volatile impurities are released in the base material, the aluminized layer can be colored, discolor and influence the reflection effect. Figure 1 (omitted) curve of PC plastic DSC, this figure shows the PC substrate at a temperature of 90 DEG C when the heat flux changes, can be considered to have material release, the glass transition temperature of Tg is about 140 degrees Celsius, the use temperature of the material should be lower than the temperature. Second, to improve the smoothness of substrate surface, to ensure that the mirror coating effect. General plastic surface itself has about 0.51nn roughness, vacuum coating thickness of not more than 0.2 mu m, unable to fill the surface of the substrate is uneven, not the ideal mirror effect, UV coating thickness reached 10-20 mu m, the surface roughness is below 0.1 mu m, coating material defects and Tian Pingji effect can get ideal.

Applicable to PC lamp reflector materials of UV curing coatings must have the following basic characteristics: (1) flow condition is good, so you can ensure that the paint is full of light, vacuum coating has a complete reflection film. (2) the coating has a sealing effect, and it can ensure that the PC substrate does not affect the coating when it is 120 degrees centigrade. (3) the coating itself has a certain heat resistance, at 120 DEG C will not have the material decomposition and release, and have an impact on the coating.

Effect of 2.2 active oligomer on properties of vacuum coating UV primer

The fixed formula is 47% active oligomer, 20%TPGDA30% methyl isobutyl ketone and 3%1103. The difference of coating properties of various active oligomers cured by UV and the feasibility of applying them to vacuum coating primer are investigated. The results are shown in table 1.

2.3 effect of reactive diluent on properties of vacuum coating UV primer

Change the kind and proportion of active diluents, and investigate their influence on adhesion between UV coating and substrate, between coating and coating, and on heat resistance of coating. The results are shown in table 2.

As can be seen from table 2, when the addition of TMPTA and HDDA accounts for more than 40% of the total amount of the formula, the coating has a good adhesion to the substrate. On the influencing factors of UV curable coatings on plastic adhesion, reactive diluent mainly reflected in them to the base erosion, active diluents and the plastic base slight swelling or softening, interpenetrating network formed between this interface can improve the adhesion after curing. TMPTA and HDDA have good erosion of PC, BA also has this ability to them is the main active diluent component can ensure the adhesion, comparison, poor erosion ability of PC TPGDA, the adhesion is not good.

Effect of 2.3.2 active diluent on adhesion of coating

As shown in Table 2, the adhesion between coating and coating has been greatly affected with the decrease in the amount of multifunctional reactive diluents. In the process of vacuum deposition, aluminum in evaporation state is easy to form high-energy particles. These particles can be easily embedded in the shallow surface layer of coatings, blurring the boundary, so that the coating and coating are closely integrated. When the UV coatings of bifunctional and monofunctional diluent degree increases, crosslinking density decreased, the vacuum coating process of some substances in the substrate, the unreacted coating composition will reach the surface of the coating under the action of vacuum, weakened the role of energetic particles in the coating film without material will not have the attachment is very good, so the coating adhesion decreased.

Effect of 2.3.3 active diluent on heat resistance of coating

From table 2 shows: the influence on the heat resistance of the coating is an active diluent of functionality, the main reason is because the determination in the other group under the condition of reactive diluent functionality of higher coating crosslinking density is high, close to the substrate is also better, when heated, escaping from the substrate in a hard coating by contact reaction, leading to changes in the appearance of coating. From this point of view, in order to obtain better sealing effect, it is necessary to increase the crosslink density of the coating as long as the other properties of the coating are guaranteed.

2.4 effects of curing degree on coating performance

The curing process of the double bond conversion rate may reach 100%, through infrared spectrum analysis before and after curing can see the changes in the content of double bond. The stretching vibration absorption peaks of carbon and carbon double bonds are obvious at 1635cm-1 and 809.2cm-1. In the cured spectra, the absorption peaks of these two carbon carbon double bonds are greatly reduced, but they do not disappear. We have increased the exposure of the coating from 350mJ/cm2 to 2100mJ/cm2, and this absorption peak still exists. Therefore, we must know to what extent the coating is cured will have minimal impact on the coating properties.

With the continuous improvement of the curing, the hardness of the coating will be getting better and better, figure 2 is along with the change of the situation of coating increased the pendulum hardness UV irradiation dose, the formula for the aforementioned formula 2, formula 5 and formula 6. From Figure 2 (omitted) can be seen: with the curing time of crosslinking continuously, the hardness of the coating has obvious inflection point in curing under the condition of certain, increase the irradiation energy after this point, the hardness of the coating is not improved. Figure 3 (omitted) is the DSC diagram of the coating before and after the inflection point. In Figure 3, A is the result of coating DSC test on formula 5 after receiving UV irradiation amount of 230mJ/cm2, and B is the result of irradiation amount of 260mJ/cm2. Figure 3 shows that when the UV coating is not fully cured, the coating releases low molecular mass at high temperatures, which results in changes in the coating. The experimental results also verify this. Under the curing condition of primer such as A, when the film is heated up to about 110 DEG C, the coating appears. Through the above experiments, we can draw a conclusion that only when the bottom coating of UV is cured completely can a good coating effect be obtained. The so-called solidification here is exactly the hardness of the coating, which appears at the inflection point shown in figure 3.

Effect of 2.5 photoinitiator on coating performance

In the experiment, we found that the coating obtained by the mixed photoinitiator system exhibited better heat resistance after vacuum coating. The experimental results are shown in table 3.

3, Epilogue

In the design of PC light reflector with UV primer, should increase the cross-linking density of the coating to ensure the coating has good sealing performance, by adjusting the formula of the ratio of reactive diluent to the coating and the substrate, coating and the adhesion of the coating to achieve the best, the structure is complex, pay special attention to ensure the full site UV irradiation can be completely cured.

Note: 1 - filtered advertising leveling to 5 for the best, 1 for the worst; 2-DSC test substances coating temperature; 3 - curable coating work required to accept the UV radiation as a unit, the greater the value, that is more difficult to cure.