Wang Lixin，Liu Songjie
Abstract ：A method to improve the hardness of one-component waterborne wood paint was introduced, which could meet the needs of waterborne furniture market within a hardness ≥2H，though reasonably hybridizing the nanometer silica dispersion on the selected aqueous acrylic emulsion and aqueous polyurethane resin dispersion, and using new material and special technology to solve the compatible problem. At the same time, the effects of various factors on the hardness of the coating film were studied and visually demonstrated by single factor experiment and response surface method. The experimental results showed that the hardness of the coating film increased with the increase of the proportion of the aqueous polyurethane resin dispersion in the film-forming material and then decreased. The hardness of the coating film increased with increasing the amount of nanometer-silica dispersion, also increased with increasing the dispersion time of nanometer silica in the film-forming material, but it does not continue rise after increasing to a certain extent.
With the pressure of environmental protection policies and the continuous improvement of consumers’ environmental protection awareness, in particular, provinces and cities across the country have issued VOC (volatile organic compound) emission limits and charging standards to encourage furniture companies to use non-solvent coatings and give water-based environmental protection coatings Development brings opportunities. Although traditional coatings still occupy a large market share, water-based coatings are a green industry and the direction of future development. It is an indisputable fact that the development and market share of water-based coatings are increasing year by year, and there is a tendency to accelerate. Some companies have realized the broad market potential of water-based coatings, and have developed, entered and expanded the water-based coatings market one after another.
Although water-based coatings are superior to solvent-based coatings in terms of environmental protection performance, water-based coatings have defects such as difficulty in construction, poor water resistance, easy peeling, poor fullness, and low hardness. Solvent-based coatings are still the first choice for furniture decoration due to their high hardness, good film fullness, and easy construction. Only when the shortcomings of physical properties and application properties are resolved, even beyond solvent-based coatings, consumers will be more proactive in choosing water-based coatings. Catering to consumers in terms of environmental performance alone, they cannot satisfy consumers in terms of construction technology and decorative effects, and the market for water-based coatings is still difficult to open. At present, the production of single-component waterborne wood lacquers on the market mainly uses self-crosslinking water-based acrylic emulsion synthetic materials as film-forming materials. The main advantages of the products are good environmental protection and low price, but the fatal disadvantage is low hardness and easy Scratches, poor water resistance, easy whitening when exposed to water, poor heat resistance, and easy adhesion when heated, have only been successfully applied in home decoration and ordinary furniture, and are expanding their market share. However, in the high-end furniture market occupied by solvent-based polyurethane coatings, water-based coatings are still difficult to make a difference.
Some studies have shown that adding nano-silica to coatings can improve the coating film properties, such as improving the scratch resistance, wear resistance and hardness of the coating film. The main reason is that nano-silica not only has the characteristics of hydrophilicity and high hardness of inorganic substances, but also its own nano-structure can effectively cover and disperse among the particles of the film-forming material. Degussa has developed anti-scratch acrylic nano coatings using siloxane-embedded nanoparticles. These coatings have good scratch resistance and abrasion resistance that is 10 times that of traditional acrylic coating systems. Wang Ben and other studies found that adding a small amount of nano-SiO2 can significantly enhance the hardness, adhesion, and weather resistance of coatings. Studies by Zhang Ling and others have shown that the addition of nano-SiO2 to epoxy acrylate systems can significantly improve the abrasion resistance, hardness, impact resistance, and flexibility of coating films. Zhang XH modified the nano-SiO2 epoxy coating with silane coupling agents KH560 and KH550, respectively. The impact strength of the coating film was increased by 3 times, and the bending strength and tensile strength were increased by 2 times. Wu Zhongyue and other studies found that adding nano-silica gel to waterborne wood coatings can increase the hardness of the coating film, improve the water resistance, aging resistance, and anti-blocking properties of the coating film. In the closed primer, the nano-silicone body can easily enter the small holes of wood or fiberboard. These holes can be filled or closed, and after drying and forming into a film, they will bond with the substrate to form a water-insoluble coating film, resulting in a good Closure effect. Adding an appropriate amount of nano-silica sol can not only accelerate the release of moisture in the primer, shorten the drying speed, but also increase the hardness of the coating film and reduce the cost of the primer. Adding an appropriate amount of nano-silica sol to the water-based topcoat can improve the water resistance, blocking resistance and hardness of the coating film.
In this study, silane-modified nano-silica dispersion was selected as a special additive, hybridized with organic polymers, and compatibility issues were solved through some new materials, new additives, and special processes, thereby developing a market for high-end furniture paints. Waterborne wood paint products with high hardness and excellent scratch resistance.
1 Test Section
1.1 Materials and Instruments
Water-based acrylic emulsion, water-based polyurethane dispersion, AMP-95 (pH adjuster), nano-silica dispersion, BYK-024 (polysiloxane-based defoamer), dipropylene glycol methyl ether (film-forming aid), Glide450 (polysiloxane polyether copolymer type leveling agent), WetKL270 (polysiloxane polyether copolymer type wetting agent), TSW-100W (fumed silica type matting agent), AR8959 (associative type Polyurethane thickener), the above are all industrial grade.
JSF400 multi-purpose agitator sander, SZQ wet film preparation device.
1.2 Formulation and Process
Raw material w /%
acrylic emulsion 46
Aqueous polyurethane dispersion 40
nanometer silica dispersion 3
Dipropylene glycol methyl ether 5
Glide 450 0.5
Pure water 2.3
process flow: first put the acrylic emulsion and water-based polyurethane dispersion into the paint tank, add the pH adjuster and nano-silica dispersion, stir evenly, add the same amount of sand beads, and disperse at a high speed for a certain time and filter Remove the sand beads and add the film-forming aid while stirring. Dilute BYK-024 defoamer with deionized water and slowly add it to the system. Disperse at high speed (2 500 r / min) to the fineness plate. After the squeegee has no shrinkage phenomenon, wetting agent, dispersant, TSW-100W matting agent are put in order, and then the viscosity is adjusted with thickener, and the preservative is added, and the mixture is stirred, filtered and packed.
1.3 Prototype production
Prepare the template according to the method in 6.3 of HG / T 3828-2006. On the glass plate (200 mm × 100 mm × 4 mm), a wet coating film with a thickness of 100 μm was applied with a paint film applicator and left for 7 days.
1.4 Performance test
According to GB / T 6739—1996, use the coated portable pencil hardness tester to test the pencil hardness of the coating.
According to GB / T 9279-1988, use the coating film scratch tester to test the scratch resistance and scratch resistance of the coating film.
2 Results and discussion
2.1 Effects of different film-forming substances on the coating film performance
The effects of the mixing ratio of acrylic emulsion and water-based polyurethane resin dispersion on the performance of water-based wood coating film are shown in Table 1.
It can be seen from Table 1 that as the amount of the aqueous polyurethane resin dispersion increases, the hardness of the coating film increases, but after increasing to a certain extent, the hardness of the coating film decreases again. This is because the polyurethane coating film has a certain elasticity and toughness. When the amount of the aqueous polyurethane resin dispersion is too large, the coating film elasticity increases, and the hardness decreases.
2.2 Effect of the addition amount of nano-silica dispersion on the coating film performance
The effect of the addition amount of nano-silica dispersion on the coating film performance of water-based woodware is shown in Table 2.
It can be seen from Table 2 that as the addition amount of the nano-silica dispersion increases, the hardness of the coating film increases, but after increasing to a certain extent, the hardness of the coating film no longer changes. This is because with the increase of the amount of addition, the nano-silica continues to penetrate the three-dimensional network coating film formed by the hybridization and cross-linking of the polymer material, resulting in an increase in the hardness of the coating film, but after reaching a certain level, the crosslinking effect weakens. The strength of silicon oxide cannot be further reflected in the coating film, so the hardness of the coating film does not change.
2.3 Effect of dispersion time of nano-silica dispersion in film-forming material on coating film properties
Table 3 shows the effect of dispersion time of nano-silica dispersion in film-forming material on coating film properties.
It can be seen from Table 3 that as the dispersion time of the nano-silica dispersion in the film-forming substance increases, the hardness of the coating film increases, but after the dispersion time is extended to a certain extent, the hardness of the coating film no longer changes. This is because the process of hybrid cross-linking to form a three-dimensional network structure is slow at room temperature. With the extension of the dispersion time, the degree of cross-linking of the coating film gradually increases, and the hardness of the coating film continues to increase, but after reaching a certain level, the cross-linking The joint effect is reduced, and the hardness of the coating film is no longer changed.
3 factorial experimental design
In order to optimize the formula of water-based wood varnish and improve the coating film performance of water-based wood varnish, the above factors affecting the hardness of the coating film are tested by factors to find the optimal parameters. Considering the complex interaction and continuity of hybridization, the BBD (Box-Benhnken) method in response surface optimization was used to design the experiments, and the best results were optimized and verified. Specific factors and levels are shown in Table 4.
3.1 Factor test design results
In order to facilitate data calculations, statistical optimization analysis is performed to convert the pencil hardness mark grades into numerical grades [ie: 6B, 5B, 4B, 3B, 2B (5), B (6), HB (7), F (8), H (9), 2H (10), 3H, 4H, 5H, 6H, 7H, 8H, 9H, 10H and other 18 hardness levels are defined in order as 1 ~ 18, the larger the number indicates the higher hardness] The test results shown in Table 5 were obtained.
Polynomial fitting regression was performed on the test data, with hardness as the dependent variable (Y), film-forming material ratio (A), dispersion addition (B), and sanding dispersion time (C) as independent variables. The regression equation was established as follows :
R2 = 0.9314, indicating that 93.14% of the experimental data can be explained by this model. According to the equation, a response surface analysis map (3D map) and a contour map are drawn, as shown in Figure 1. The response surface and contour plots are used to visualize the ratio of the film-forming material, the amount of nano-silica dispersion, and the time for sand-dispersion of the nano-silica dispersion in the film-forming material. (Min) The effect on the hardness of water-based wood paint coating film.
3.2 Validation of the equation
When the process conditions, that is, the dispersion time of the nano-silica dispersion in the film-forming substance is limited to 60 min, in order to obtain a coating film hardness of 2H, the film-forming substance ratio and nano-dioxide are predicted by the equation. The amount of silicon dispersion was verified by experiments. This fully shows that it is feasible to use the response surface technology to optimize the dosage and process conditions.
(1) Inorganic-organic hybrid technology is applied to the preparation of waterborne wood lacquer. Based on the compounding of water-based acrylic emulsion and water-based polyurethane resin dispersion, the nano-silica dispersion is reasonably hybridized, and new materials and The special process solves the compatibility problem, so as to produce a high hardness (2H) waterborne wood paint product.
(2) The effects of the ratio of film-forming materials, the amount of silica dispersion and sanding dispersion time on the hardness of water-borne wood paint coatings were investigated through a single factor test. The test results show that as the proportion of the aqueous polyurethane resin dispersion in the film-forming material increases, the hardness of the coating film first increases and then decreases; as the amount of nano-silica dispersion added increases, the hardness of the coating film increases, but increases to a certain level After the degree, the hardness of the coating film no longer changes; as the dispersion time of the nano-silica dispersion in the film-forming substance increases, the hardness of the coating film increases, but after increasing to a certain degree, the hardness of the coating film no longer changes.
(3) Perform regression equation analysis through factor experiment design to find suitable formula (balanced) dosage and process conditions. When the process conditions, that is, the dispersion time of the nano-silica dispersion in the film-forming substance is limited to 60 min, in order to obtain a coating film hardness of 2H, the formula of the film-forming substance and the nano-silica dispersion are successfully predicted by the equation. The addition amount is consistent with the experimental verification results.