QI Xiang-ye, PEI Yong, LI Xin-cheng
(BATF Industry Co., Ltd., Foshan 528322, Guangdong, China)
Abstract: Multiple crosslinking systems were introduced into the pine emulsion synthesis process, including the metal crosslinking system and the carbonyl/hydrazine crosslinking system. It made the synthesized emulsion dry fast and form a dense network structure after film formation, and thus provided outstanding early rubbing and anti-blocking properties.
0 Foreword With
its unpretentious texture, lifelike texture, and pure and bright color, pine wood decorates the home environment elegant, pure, and integrates into harmony and tranquility with nature. Pine furniture is also a kind of green environment-friendly natural wood with low formaldehyde content, which is especially suitable for children’s furniture. It is also easy to maintain and durable. Therefore, pine furniture has become the pioneer of water-based coating for certain reasons. However, with the continuous expansion of the pine wood coating market, competition is intensifying, leading furniture factories to continuously shorten the pine wood coating cycle, thereby reducing costs and gaining greater competitive advantages. Therefore, pine wood coatings are required to have a shorter time to be sandable and can be used. The properties of anti-adhesion and water resistance, etc., therefore put forward higher requirements for the properties of pine coating emulsions. This paper introduces water-based acrylic emulsions specially used in pine wood coatings. Through metal cross-linking and carbonyl / hydrazine cross-linking technology, the emulsions are made into coatings and formed into films. After drying at room temperature for 4 h, they have excellent sanding and anti-sticking properties. , Can fully meet the requirements of the current pine wood coating emulsion.
1.1 Experimental raw materials
methyl methacrylate (MMA), methacrylic acid (MAA), and butyl acrylate (BA) are all industrial grade, Shenzhen Donggangtian Chemical Group; sodium dodecyl sulfate (SDS), Reactive emulsifiers (SR-10), all analytical grade, Guangzhou Zhuoneng Trading Co., Ltd., zinc oxide (ZnO): analytical grade, Tianjin Best Chemical Co., Ltd .; sodium bicarbonate (NaHCO3), ammonium persulfate (APS) ), Diacetone acrylamide (DAAM), adipic acid dihydrazide (ADH), are industrial grade, Guangzhou Tianyi Chemical Co., Ltd .; ammonia (NH3 · H2O), industrial grade, Guangzhou Nantao Chemical Co., Ltd .; Wetting agent TEGO500, defoaming agent TEGO902W, and defoaming agent TEGO810, Guangzhou Jiazhong Trading Co., Ltd .; film-forming aid DPnB, film-forming aid DPM, Guangzhou Zhuoyue Trading Co., Ltd .; thickener RW8W, Guangzhou Yongyi Trade Company; deionized water, industrial grade, homemade.
1.2 Polymerization process
The monomers MMA, MAA, BA, DAAM, and some emulsifiers and deionized water are stirred in a pre-emulsified bottle at high speed for 30-50 minutes to prepare a pre-emulsion, which is ready for use; in a constant-pressure dropping funnel, reflux condensation Add a part of emulsifier (SDS and SR-10), buffer (NaHCO3), part of initiator (APS) and deionized water to the four-necked flask of tube, thermometer and stirrer; under low speed stirring, warm to (83 ± 1 ) After ℃, take 1% of the pre-emulsion and add it to the reactor, keep it at (83 ± 1) ℃ for 20 minutes, then add the pre-emulsion and the initiator solution dropwise at the same time, add 3 hours dropwise; keep 1 hour, reduce to 60 ± 1) ℃, add a self-made zinc oxide aqueous solution, stir for 30min, neutralize the pH value to 8, add tailings and filter out the material.
In the experimental formula, the ratio of SDS and SR-10 in the bottom of the kettle and pre-emulsification is 1: 1, the theoretical Tg is set to 15 ° C, and the amount of initiator added is 0.5% of the amount of monomer. Variable experiments were performed on ZnO and DAAM under these conditions, as shown in Table 1.
1.3 Formulation of water-based wood coatings
In the emulsion synthesized in the laboratory, an appropriate amount of water-based additives and film-forming additives are added under certain process conditions to prepare water-based wood varnishes. The formula is shown in Table 2.
First, formulate the paint according to the reference formula of the water-based wood coatings in Table 2. Spray paint on the pine boards, dry it for 4 hours at room temperature, polish it flat, and then spray a second coat of paint. After drying at room temperature for 4 hours, check the sandability and resistance. Back to stickiness.
1.4 Testing of basic properties of
emulsions The abrasiveness and anti-stickiness of emulsions are tested in accordance with the requirements of GB / T 23982—2009. The specific test method is as follows:
Sanding test method: spray the sample emulsion evenly on the pine board after painting, dry the coating film at room temperature for 4 h, and then manually polish it with 400 mesh water sandpaper 20 times to observe whether the sandpaper will stick. And the amount of powder, the more powder, the less sticky sandpaper, the better the sandability.
Anti-sticking test method: Take two pine boards of the same size, spray them at 80 ～ 120 g / m3, and dry them at room temperature for 2 h. Then stack the two boards side by side at 1.5 t / m3. Press the weight on it, and leave it at room temperature for 12-16 hours. Then separate the two plates and observe whether the coating film will fall off. If it does not appear, it will pass.
2 Results and analysis
2.1 Effect of metal cross-linking system on emulsion performance
Metal ion cross-linking emulsion refers to a class of polymers formed by complexing some metal cations with acid radicals suspended on the molecular chain of the copolymer. It is relatively easy to introduce carboxyl groups in the emulsion polymerization process. Therefore, carboxylic acid type ion-crosslinked emulsions are the most common. Carboxylic acid ion-crosslinking emulsion introduces unsaturated carboxylic acid (such as acrylic acid, methacrylic acid and other monomers) or monomers containing chelating groups into the emulsion, and obtains carboxyl groups or chelating groups on the molecular chain by copolymerization. The polymer emulsion is then introduced with metal ions and crosslinked during the film formation of the emulsion, thereby achieving the complexation of metal cations and carboxyl groups of the emulsion. This paper uses a cross-linking system formed by methacrylic acid and zinc oxide. The reaction mechanism is shown in Figure 1.
First, after zinc oxide enters the interior of the emulsion, it will react with carboxyl groups to form zinc ions. Zinc ions first form a complex with the free ammonia in the emulsion and exist in the emulsion. When the emulsion forms a film, as the ammonia volatilizes, zinc ions are gradually released. It further complexes with the carboxyl group to form a stable chelate compound, so that the crosslinking reaction occurs when the emulsion is formed into a film, thereby improving the early drying speed and hardness of the coating film, so the coating sanding and anti-blocking properties are further improved.
It can be known from Table 3 that as the content of zinc oxide increases, the abrasiveness and anti-sticking resistance of the emulsion increase significantly. This is because with the increase of zinc oxide, the emulsion has more carboxyl groups during film formation. Cross-linking with zinc ions, thereby weakening the hydrogen bonding force of carboxyl group with water, allowing water to volatilize quickly, increasing the drying speed of the emulsion, thereby obtaining better sanding and stacking resistance. When the mass fraction of zinc oxide reaches 1.5%, the crosslink density of zinc ions and carboxyl groups is in an optimal state. When the amount of zinc oxide is increased, the abrasiveness and anti-sticking resistance of the emulsion do not change significantly, and when a certain amount is reached Zinc oxide will precipitate from the emulsion system and affect the stability of the emulsion. Therefore, considering the effect of zinc oxide on the performance of the emulsion, the mass fraction of zinc oxide is selected to be 1.5%.
2.2 Effect of carbonyl / hydrazine cross-linking system on emulsion performance
The carbonyl / diamine cross-linking system described herein is a diacetone acrylamide provided with a carbonyl group and crosslinked with an adipic acid dihydrazide provided by a diamine. Diacetone acrylamide is a special functional monomer. It contains both vinyl and ketocarbonyl groups in the molecule and can be copolymerized with other vinyl monomers to form polymers with reactive ketocarbonyl groups. Ketone carbonyl can react with adipic acid dihydrazide to form hydrazone and water at room temperature, and a reversible reaction occurs. Therefore, as the water volatilizes during the film formation of the emulsion, the polymer with the active group keto carbonyl can react with The adipic acid dihydrazide free in the interior of the emulsion reacts to achieve self-crosslinking. Greatly improve the denseness of the coating film, thereby improving the early drying speed and hardness of the coating film, so that it has good early sanding and anti-blocking properties . The amount of DAAM was changed, and its effect on the sandability and anti-sticking properties of the emulsion was studied. The results are shown in Table 4.
It can be seen from Table 4 that due to the reversible reaction of the cross-linking of DAAM and ADH, the emulsion was formed during the film formation process. With the volatilization of water, the polymer with active ketone carbonyl group can react with adipic acid dihydrazide free in the emulsion to achieve self-crosslinking. As the content of DAAM increases, the Increasing the degree of self-crosslinking can promote the volatilization of water, and at the same time greatly improve the denseness of the coating film, thereby increasing the early drying speed and hardness of the coating film, making it have good early sanding and anti-sticking properties. Therefore, considering the effect of DAAM on the performance of the emulsion, the DAAM mass fraction was selected to be 3%.
Through the above research and testing, it can be concluded that through the cross-linking of zinc oxide with carboxyl groups, carbonyl groups and polyamines, a pine emulsion with excellent drying speed, abrasiveness and anti-sticking resistance is synthesized, and when zinc oxide When the content is 1.5% (mass fraction) and DAAM content is 3% (mass fraction), the obtained emulsion has the best early sanding and anti-blocking properties, which meets the requirements for rapid application of pine furniture coatings.