Research on the preparation and performance of UV-cured hydro-water coatings

China Coatings Online NewsEugene Liu Yakang Jia Chunhua (Beijing University of Chemical Engineering School of Materials Science and Engineering, Beijing 100029)
Abstract: The introduction of photo-sensitive monolithyl acrylic shrink glyceride (GMA) on acrylic hydrophobic resins, so that the coating film can be temperature-cured and has good hydrophobic and water resistance. The effects of trigger and chain transfer agent molar fractions on acrylic co-polymer molecular weight and molecular weight dispersion, as well as the effects of thinners, monomer ratios and GMA molar fractions on coating hydrophobicity and water resistance were studied. The experimental results showed that when the trigger molar score was 1. 2%, chain transfer agent molar fraction of 2%, can be made molecular weight of about 1300, molecular weight dispersion 1. 85 acrylic co-polymers; When the GMA Moore score is 15% ( Compared to the amount of AA substance), the thinner is acrylic hydroxypropyl (HPA) and the mass score is 30%, AA and HPA quality ratio is 6:4, the film hydrophobic and water-resistant comprehensive performance is the best, hydrophobic angle is 14. 2 degrees, weight loss rate of 1. 61%。
key words: hydro-hydro; UV curing; Acrylic; Methyl acrylic shrinkage glycerides
in the figure classification number: TQ630. 6
Introduction
light curing coating has the advantages of fast curing speed, environment-friendly, energy saving, low cost, etc. , in paper, rubber, plastic and other coating fields are widely used. In general, light-sensitive liquid resins can be converted directly into curing resins at room temperature under UV lamps, and generally do not contain volatile organic matter. With the attention to environmental issues, the research and development and application of this environmentally friendly "green" process is becoming more and more in-depth and popular.
hydro-hydropluable coating is a functional coating that has developed rapidly in recent years and is mainly used in aluminum and aluminum alloy products, such as aluminum fins for air conditioning heat exchangers. Traditional hydro-water coatings are usually hydro-water resins baked at a high temperature of 200 degrees C for tens of seconds, and thermo-cured cross-linked film is made. Although the preparation method has mature process and good hydro-water performance, it has high energy consumption, high volatility of organic solvents and poor construction environment. The use of photo-curing cross-linking to prepare pure organic hydrophoresic coatings, not only the advantages of UV curing can meet the requirements of hydrophobility, but at present has not been reported in this regard. In this paper, a new synthesis idea is adopted, based on low molecular weight acrylate co-polymer, the introduction of photosensitive monomer, and then photo-curing cross-linked film to make hydrophobic coatings, the introduction of GMA and monomer ratio, active thinner type and content and other factors on the paint hydrophobic and water resistance effects.
1. The experimental part
1. 1 Experimental raw materials
acrylic acid (AA), acrylic hydroxypropyl (HPA), butyl acetate, ethylene glycol monomethyl ether, acetone diobutylene (AIBN), xylitol, ammonium tetbutyl bromide, methyl propylene acid shrink glycerides (GMA), N-vinyl pyridine (NVP), all analyzed, Beijing Chemical Testing Company; Light trigger 1173,1,6-hethyl glycol diacrylate (HDDA), industrial grade, Dibixie Chemical Trading Co., Ltd.
1. 2 Photosensitive hydrophobic acrylic synthetic
added a certain amount of butyl acetate and ethylene glycol monomethyl ether mixture solvent to the four-mouth bottle, heating up to about 70 degrees C; Dissolve the metered trigger azithroid, decthionyl alcohol in a mixture of monopropylene and acrylic hydroxypropylate, and then add the mixture to a four-mouth bottle within 4 to 5 h to polymerized and keep warm at 2 h. After the polymerization is complete, the temperature of the system is raised to 105 to 110 degrees C, and a certain amount of GMA, catalyst ammonium tetyl bromide, polymer inhibitor to phenol, reaction 2. 5 h, obtain photosensitive hydro-hydropholding prejudes. A diagram of the specific reaction process is shown in Figure 1.
1. 3 UV photo-curing coating preparation
the photosensitive hydro-hydroploric prejudging decompression distillation, add light trigger, active thinner, stirring and dispersing evenly. Then the wire rod coater (XB type, Shanghai Standard Instrument Co., Ltd.) is coated on the surface of the treated aluminum foil, exposed to 2 min under the high-pressure mercury lamp, to make hydro-water coating.
1. 4 The infrared spectrum of
acrylic pre-polymers tested and masted is indicated using the Nexus 670 Fourier infrared spectrometer of Nigoli Corporation of the United States; The coating hydro-water angle was measured using the OCA20 contact angle measuring instrument of the German company dataphysics; The viscosity of the coating was measured by the DV-III. ULTRA viscosity meter of Shanghai Quiyuan Scientific Instruments Co., Ltd.
weight loss rate is indicated by the water resistance of the coating. The weight loss rate test is: soak the coating in flowing water, 24 h after removal, room temperature dry to constant weight, in order to cycle 3 times, weighing the quality of the coating before and after soaking. Weight loss rate s is calculated as s ( m0 - m1) / m0 (1)
(1) m0 as the pre-coating immersion mass and m1 as the coating post-soaked mass.
2. Results and discussions
2. 1 Molecular weight and molecular weight dispersion of acrylic co-polymers
co- polymericity with 20 g acrylic and 13.4 g acrylic hydroxypropylate, the relationship between co-polymer molecular weight and molecular weight dispersion and the content of triggers and chain transfer agents is shown in Table 1.
free-form polymerization system, the polymer polymerization Xn can be expressed as a(2) medium chain throw rate constant kp, chain growth rate constant kd, chain termination rate constant kt, chain transfer constant Ks, polymerization efficiency f are fixed values, so when the concentration of the monosome cM fixed, the polymerization Xn is only related to the trigger concentration cI and chain transfer agent concentration cS.
as can be seen from Table 1, when the mass of the monomer is constant and the molar fraction of the chain transfer agent is fixed at 1%, the molecular weight of the co-polymer decreases from 4300 to about 1000 with the increase of the amount of the trigger. Because the molar fraction of the trigger increases, the density of free fundamentals increases, i.e. the center of activity increases, resulting in a decrease in polymerization, a decrease in molecular weight, and a decrease in molecular weight dispersion. However, the content of the trigger can not be increased indefinitely, because acrylic polymerization is a strong heat release reaction, if the content of the trigger is too large, the reaction is too fast, will lead to local overheating and make the polymer hydroxyl and carboxyl cross-linked, resulting in white insoluble. The fixed trigger molar score is 1. 2%, the polymer molecular weight decreases with the concentration of chain transfer agent. When the chain transfer agent molar fraction is 2%, the polymer molecular weight dispersion is minimal. Theoretically, an acetylene decomposes two free-agents, and a chain transfer agent terminates a free-agent, so the chain transfer agent has the lowest dispersion when the concentration of the trigger is 2 times. However, the efficiency of the trigger can not reach 1, and free-form also has the possibility of transfer to solvents and so on, so the chain transfer agent and the amount of the trigger material ratio is slightly less than 2 when the least dispersion. As can be seen in Table 1, the trigger molar score is 1. 2%, the chain transfer agent molar fraction of 2%, the resulting co-polymer molecular weight of about 1300, molecular weight dispersion of 1. 85。
2. Infrared spectral analysis of acrylics and photosensitive acrylics
Figure 2 is an infrared spectral map of acrylates co-polymers (a) and photosensitive acrylates lysates (b).
figure 2, spectral line a is in 1731. Feature peaks of C O on acrylic base appear at 4 cm - 1 place, feature absorption peaks of  CO on acrylic hydroxylate appear at 1170. 1 cm - 1 place, and wide and strong hydroxyl feature peaks appear at 3340. 2 cm - 1 indicate the presence of hydroxyl and hydroxyl, AA and HPA. b The curve is in 1635. 9cm - 1 and 812. C C dual-bond characteristic absorption peak appears at 8 cm - 1 and the characteristic absorption peak of no epoxy group at 908 cm - 1 indicates that the epoxy group and acrylates on the GMA have a ester reaction, acrylic bonding on the GMA, the preparation of a double-bonded acrylic resin.
2. 3 Factors that affect coating performance
2. 3. 1 Diluent
Because acrylic copolymers contain a large amount of hydroxyl and carboxyl, the hydrogen bond between polymers is very strong, the system viscosity is high, a certain amount of thinner must be added to regulate the viscosity. The active thinners given in Table 2 are single-function group active diluent HPA, NVP, and dual-function group active diluent HDDA.
of the three thinners in Table 2 are the same, and the mass score is 30% of the coating formula. As can be seen from Table 2, HDDA does not contain hydroporic groups in itself, so the coating film hydroporic angle is larger. Although NVP has good hydropyurism, but does not have water resistance, weight loss rate is too large, at the same time added with low-lying content compatible is not good, the film color is too dark. Therefore, HPA is the best active thinner in the system in terms of film hydro hydroffin and water resistance, film color and pre-coating system viscosity.
HPA single-function group active thinner contains only 1 C C dual bond per molecule that can participate in curing reaction, which generally has the characteristics of high conversion rate, low curing speed and low cross-link density. Since the active thinner is directly involved in the curing reaction, the amount of diluent will also have a significant impact on the overall performance of the coating. The relationship between HPA thinner dosage and coating viscosity, coating hydroffinity, and water resistance is shown in Table 3.
can be found in Table 3, the smaller the thinner content, the smaller the hydrotherm angle. When the HPA mass score is 20%, the hydropable angle is reduced to 13. 1°。 Because the amount of diluent is small, the corresponding proportion of hydro-water resin is large, and the density of hydro-hydro-energy group increases, especially the increase of nirbic base, so that the hydro-water angle becomes smaller. However, when the HPA mass score is 20%, the coating mucus is too high to operate, and the film after light curing is difficult to be uniform. When the HPA mass score is greater than 30%, the film weight loss rate increases significantly, and when the thinner mass fraction increases to 50%, the weight loss rate can reach 5. 93%。 This is due to the increase in the amount of single-nel thinner, the decrease in cross-link density, water resistance performance decreased. In combination, the quality score of HPA was 30%.
2. 3. 2 Monosome ratio
The hydro-performance of the coating film is mainly affected by hydro-water-dependent resins, which rely on the content of hydro-based groups on the molecular chain and the synergy of several hydro-based groups. The hydro-hydropitable properties of the two co-polysexual monomers are different, and the hydro-hydropitability of the co-polymers is also different. Table 4 lists the effects of different mass ratios of hydro-water monosomes on coating hydro-hydro?
from Table 4, it can be found that the GMA content, with the increase of AA content, the coating film hydroploric angle decreased, which is due to the reason that the hydromassin-based hydroploride is stronger than hydroxyl. When the mass ratio of AA to HPA is 6:4, the minimum is 15. 7 degrees, and when the AA content increases again, the hydro-water angle increases slightly. This is because the AA content continues to increase, the carboxyl is too dense, the hydrogen bond between the carboxyl and hydroxyl action is strong, affecting the extension of the molecular chain, resulting in the resin photo-curing into a membrane after exposed hydrophobia group decreased, hydrophobia decreased. As can be seen from Table 4, the synergy between AA and HPA of this system is best when the mass ratio is 6:4, and the hydropability is the best.
2. 3. 3 GMA
hydrophobrium acrylic pre-polymer containing unsaturated double bonds becomes an interlinked body structure when cured. GMA in this system plays the role of the equivalent of crosslinking agent. After the introduction of GMA, a certain amount of hydroxyl is consumed on the polymer chain to produce the same amount of the same substance. Different GMA dosing will have a critical impact on the hydromassiveness and water resistance of the coating film. Figures 3 and 4 show the effect of the mass ratio of monosome AA to HPA, the thinner HPA content unchanged, and the effect of GMA molar fraction xGMA (as opposed to the amount of AA substance) on coating hydromassiveness and water resistance when changing the GMA addition.
can be seen from Figure 3, with the increase of GMA content, hydro-water angle gradually increased. When the molar fraction of GMA increases from 10% to 30%, the hydro-water angle increases from 12. 6 degrees increased to 34. 5°。 This is due to the fact that the hydromassiveness of the carboxyl is stronger than that of hydroxyl, while the GMA content increases and the consumption of the carboxyl increases. At the same time, the GMA content increases, the film density increases, and the freeness of the hydromassive group becomes worse, resulting in the poor hydromassivity of the photo-curing film.
but not the lower the GMA content, the better the coating performance, Figure 4 shows the relationship between the GMA content and the coating weight loss rate. With the increase of GMA content, the cross-linking degree of film increases, the water resistance increases, and the weight loss rate decreases. The molecular weight of the co-polymer is about 1300, with an average of about 0. 6Mn /72 s 11 acrylic molecules. When the GMA mole score exceeds 15%, the average GMA on each chain is greater than 1. 6, the co-cluster can almost all participate in cross-link curing reaction, thus reducing the weight loss rate slowly. Considering the combination of hydromassiveness and water resistance, when the GMA thing volume (molar fraction) of synthetic resin is 15%, the coating composite performance is the best, and the hydro-water angle is 14. 2 degrees, weight loss rate of 1. 61%。
3. Conclusions
(1) The synthesis conditions for AAHPA co-polymers with low molecular weight (1300) and narrow distribution (1.85) are: the molar fraction of the trigger AIBN is 1.2%, and the molar fraction of the chain transfer agent tesulol is 2%.
(2) the best process parameters for UV-cured hydrophobic coatings with a hydrophobic angle of 14.2 degrees and a weight loss rate of 1.61% are: GMA accounts for 15% of the AA molar score, HPA is used as the active thinner and the mass fraction is 30% of the coating fluid, and the mass ratio between AA and HPA is 6:4.
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