Water-based wood coatings: outdoor doors and windows applications and research

With the improvement of people's environmental awareness and high concern for health, as well as the progress of water-based wood coating technology, water-based wood coating has become one of the trends in the development of wood coatings. Water-based wood coatings are due to its low hazard, low pollution characteristics, the future will certainly occupy a very important position in the home decoration and furniture coatings market. The main functions of outdoor water-based wood coatings are: decorative, water-resistant, weather-resistant, tough, environmentally friendly and safe, wood coatings can protect wood, effectively extend the service life of wood .
1 Research purposes and backgrounds
Outdoor doors and windows are not ordinary flat doors in the traditional sense, but products made of profiles such as plastic steel and aluminum alloy, commonly known as aluminum-wrapped wooden doors and windows (see Figure 1). At present, many domestic manufacturers specializing in the production of doors and windows have been in the application of water-based paint coating, some will encounter due to improper process caused by the product's coating shedding, color fading, product color is not equal situation, and the purpose of this study is to make water-based paint more easily seep into the wood layer so as to protect the wood will not be due to long-term water mold and fall off, through the process and color system so that the product no longer fade, as new. At the same time it is just a framework, traditional operating methods will waste a lot of paint, while traditional products will increase operating time, thereby increasing human, time and financial resources and many other costs. We will also apply products in this area in special ways to save energy and reduce consumption.
2 Application
application materials: pine, oak, birch and other solid wood, see Figure 2.
3 Traditional process coating methods and process shortcomings
traditional water-based coating methods in oak, birch and other semi-open coating in doors and windows, usually the process is closed →scrub the background color→ on the primer →painting color→ on the paint. And like pine is basically only closed coating, usually the process is spray-→ and primer→ face-→ paint.
the traditional approach has several disadvantages: (1) waste. Because when the large frame is sprayed, the actual use of the coating is less than 20%, resulting in waste. (2) Poor weather resistance outdoors. Ordinary color repair is the use of color refinement, and color refinement is usually less sun-resistant durability, and thus fade. (3) Pine and other soft materials rise seriously. The effect is fine when spraying the base color, but once the primer is wood-printed protrusion, grinding flat will certainly cause the wood ribs to fade, then the product will flower. Traditional water-based coating film thickness is generally low, and used outdoors to achieve wet film more than 240 m.
4 Comprehensive needs to solve the problem
wood in the outdoor destruction and corruption including bacteria, insects, fungi, viruses on the wood, so wood in possession of a certain aspect of the use of value, can be made up for its defects through artificial efforts, the correct use and protection is the key to the use of wood outdoors. There is damage under natural conditions, including ultraviolet rays, wind, frost, rain and snow, etc. Among them, the destruction of water is reflected in the change of physical properties after fiber absorption of moisture and provides a better breeding environment for insects, germs and so on. Ultraviolet damage is most serious, mainly by breaking down the natural color of wood and destroying the molecular structure of wood fiber cells. In this case, water-based outdoor coatings are widely used for their outdoor durability. The application of water-based coatings must solve the problem of wood ribs, and the use of outdoor doors and windows must also take into account wood coloring, film thickness and color weather resistance.
5 Problem Solution
5.1
Emulsion
5.1.1 Primer With Lotion
Primer Although the solid content can be low, but the emulsion in particle size and polishing must also be considered comprehensively, after repeated exploration, and finally mainly focused on the following two aspects of research. The experimental selection of a strong penetration capacity and Tg suitable (Tg is usually around 45 degrees C) emulsion, and the ability to carry the slurry is strong.
5.1.2 lacquer emulsion
due to the use of outdoor, and according to the traditional Chinese preferences and the particularity of the coating film thickness, and after a lot of screening and experiments, the final selection of Tg at about 25 degrees C and is the nuclear shell structure, water dispersion is very good, that is, very permeable very good emulsion. Of course, weather resistance, powder resistance is also to do experiments to carry out targeted exposure, aging spray, etc. , repeated comparison.
5.2 additives, color paste selection
5.2.1 de-foaming wetting
de-foaming mainly considers high viscosity, high shear force system de-foaming capacity;
5.2.2 thickening system
mainly the high viscosity of paint. First of all, spraying high viscosity, we must consider to make a false thickening effect, and strong anti-flow hanging. Secondly, due to the wet film thickness problem, it is necessary to choose a thickener that does not affect permeability, that is, a good solubility and suitable polyurethane thickener with resin.
5.2.3 color paste screening
using inorganic iron oxide pigments to prepare the color paste, and to grind to almost as permeable as color essence level. Organic pigments are much less resistant to sun exposure, and can be prone to floating colors and too bright. In addition, the solubility of color paste and emulsion should be considered.
5.2.4 Anti-mold agent
Because the products used often experience sun and rain, and local may be immersed in water, although the current production of water-based lotions have anti-corrosion and mold resistance, but the preparation of this coating must be added a strong ability of anti-corrosion anti-mold additives.
6 The development of the production process
6.1 primer research direction
because to make a good permeability, carrying good color paste products, so in the production of deblisters and moisturizers must be pre-added to the emulsion directly dispersed to no holes, and then add water and part of the solvent. Permeability does not require thickening. Also to be immersed so the viscosity and resin content should not be too high.
6.2 paint research direction
paint viscosity system and normal decoration of water-based paint is completely different, and many large factories choose high-pressure spraying, so de-foaming is very important. Therefore, every step of the production, to monitor the scraper plate can not have dredging appearance, and the last thickening before the best overnight, so as to ensure that high viscosity paint bubble-free.
7 Construction process
by combining product characteristics and a variety of methods to test the following most suitable process combination: material polishing smoothing→ immersion primer→ primer coloring→ paint spraying→ the second paint spray. The specific construction process is as follows:
7.1 primer process
the first dip is to make emulsion particles into the brown eye and wood ribs bulging, to dry after grinding flat, so this time the use of immersion operation. The second time you choose the same primer plus a well-tuned transparent paste, dip or wipe it.
coating primer because of its very small molecular structure, for the resin and oily substances contained in the special penetration effect.
as shown in Figure 3, the general primer does not connect gaps or holes in the wood. The immersion primer is used to penetrate deep into the wood in two steps. This penetration makes the back coating adhesion better so as to protect the frame fan corners from excessive polishing, so that the paint in the frame fan corners of the attachment performance is better.
Outdoor doors and windows special paint slowly into small holes, air squeeze open paint coating film scattered, so that the paint uneven gap, coating surface has condensed, non-flowable air scattered when the cracks will be retained, to avoid the film bubbles and uneven marks appear.
solution: Apply a primer with a water-immersed material.
Results: immersion primer seeps into small holes, the hole walls of small holes are covered by impregnated material, while the air in small holes is discharged directly, so that the door and window paint immediately flows into the small holes, while the residual air is also immediately discharged, avoiding the formation of bubbles and gaps, see Figure 5.
7.2 paint construction
paint due to spray thickness requirements, so in operation, can only add about 5% of the water, and to choose a large-caliber spray gun spray. In order to be more layered, a small amount of transparent paint can be added to the paint, sprayed twice, each wet film thickness of about 240 m. Immersion primers have excellent impregnation effects in end profiles and V-slots. Nevertheless, the paint may also be absorbed too much wood, resulting in cracks due to the thin coating. The second level of paint in the "no longer absorbed area", if the paint elasticity is good, it will seal the crack, see Figure 6.
8 Conclusion
At present, the annual paint volume of outdoor doors and windows in China is 100 million L or more, but foreign brands of water-based paint accounted for more than 70%. And outdoor doors and windows are the first water-based industry in China, hope that through our research can help peers to enter the field together, so that our rapid growth of water-based coatings, keep up with or even catch up with the pace of the international water-based coatings industry.