Application and research of water-based wood coatings in outdoor doors and windows!

With the improvement of people's awareness of environmental protection and a high degree of concern for health, as well as the advancement of water-based wood coating technology, water-based wood coatings have become one of the development trends of wood coatings

Research purpose and background

Outdoor doors and windows are not ordinary flat doors in the traditional sense, but are inlaid with profiles, such as plastic steel and aluminum alloy, commonly known as aluminum-clad wooden doors and windows (see Figure 1)

Application material

Application materials: pure solid wood such as pine, oak, oak, etc.

Traditional process coating method and process shortcomings

In traditional water-based paint coating methods, oak, oak wood, etc.

Comprehensive problems to be solved by various needs

Outdoor destruction and corruption of wood include bacteria, insects, ants, fungi, and viruses.

Problem solution

5.

5.

Although the solid content of the primer can be lower, the particle size and sandability of the emulsion must also be considered comprehensively.

5.

Because it is used outdoors, and according to the preferences of traditional Chinese people and the particularity of the thickness of the coating film, and after a lot of screening and experimentation, the final selection of Tg is about 25 ℃ and has a core-shell structure with very good water dispersibility, that is, permeability Very good lotion

5.
2 Selection of additives and colorants

5.
2.
1 Defoaming and wetting

Defoaming mainly considers the defoaming ability of high-viscosity and high-shearing systems; for wetting, it must be considered that it cannot have foam stabilization, strong permeability, and strong anti-porosity
.

5.
2.
2 Thickening system

The main problem is the high viscosity of the topcoat
.
First of all, the spraying viscosity is high, so it is necessary to consider the effect of false thickening, and the anti-sagging property is strong
.
Secondly, due to the problem of the thickness of the wet film, a thickener that does not affect the permeability must be selected, that is, a suitable polyurethane thickener that has good compatibility with the resin
.

5.
2.
3 Screening of colorants

Use inorganic iron oxide pigments to prepare color pastes and grind them to a level that is almost as transparent as color concentrates
.
Organic pigments are much worse in light fastness, and are easy to float and become too bright
.
In addition, the compatibility of color paste and emulsion must be considered comprehensively
.

5.
2.
4 Antifungal agent

Since the applied products often experience sun and rain, and may be partially immersed in water, although the water-based emulsions currently produced have anti-corrosion and anti-mildew properties, it is necessary to add strong anti-corrosion and anti-mildew additives when preparing this coating.

.

Production process formulation

6.
1 Research direction of primer

Since it is necessary to make a product with good permeability and good color paste, the defoamer and wetting agent must be added to the emulsion in advance and dispersed directly until there is no pores, and then water and some solvents are added
.
For permeability, thickening is not required, and dipping is required, so the viscosity and resin content cannot be too high
.

6.
2 Research direction of topcoat

The topcoat viscosity system is completely different from normal decoration water-based paints, and many large factories use high-pressure spraying, so defoaming is very important
.
Therefore, during production, every step must be monitored to prevent pores from appearing on the scraper, and it is best to overnight before the final thickening, so as to ensure that the high-viscosity topcoat is free of bubbles
.

Construction technology

After combining product characteristics and various methods of testing, the most suitable process combination is summarized as follows: material polishing and smoothing → dip coating primer → primer coloring → top coat spraying → second top coat spraying
.
The specific construction process is as follows:

7.
1 Primer process

The first dip coating is to make the emulsion particles enter the brown eyes and the wood tendons to swell, and after it is dry, it is polished and smooth.
Therefore, the dip coating operation is used for this time
.
For the second time, use the same primer plus the adjusted transparent color paste, then dip or wipe
.
Due to its extremely small molecular structure, the dipping primer provides a special penetration effect for the resin and oily substances contained
.
As shown in Figure 3, the general primer cannot connect the gaps or small holes in the wood
.
The dip primer is used to penetrate deep into the wood in two steps
.
This infiltration makes the adhesion of the back coating better, so as to protect the corners of the frame fan from being excessively polished, and make the adhesion performance of the topcoat on the corners of the frame fan better
.

The special topcoat for outdoor doors and windows slowly flows into the small holes, and the air squeezes the topcoat film out, causing uneven cracks in the topcoat.
The surface layer of the coating film has condensed, and the cracks generated when the non-flowable air escapes will remain to avoid The appearance of bubbles and uneven marks in the coating film
.

Solution: Use water-based dip coating primer with impregnating material
.

Result: The dipping primer penetrates into the small holes, and the wall of the small holes is covered by the impregnating material.
At the same time, the air in the small holes is directly discharged, so that the door and window finishes immediately flow into the small holes, and the residual air is immediately discharged, avoiding air bubbles and The formation of the gap is shown in Figure 5
.

7.
2 Top coat construction

Due to the spraying thickness of the topcoat, only about 5% of water can be added during operation, and a large-caliber spray gun should be used for spraying
.
In order to have a stronger sense of layering, a small amount of transparent paint can be added to the topcoat and sprayed twice, each time the wet film thickness reaches about 240 μm
.
The dipping primer has an excellent dipping effect in the end profile and V-groove
.
Nevertheless, the topcoat may be absorbed by the wood too much, and cracks may occur due to the thin film
.
The second top coat is in the "area no longer absorbed".
If the top coat has good elasticity, it will seal the cracks, as shown in Figure 6
.

At present, the domestic outdoor door and window coating uses 100 million liters or more of paint per year, but the water-based coatings of foreign brands account for more than 70%, and outdoor doors and windows are the first water-based industries in China.
We hope that our research can help peers Our joint entry into this field has enabled our water-based coatings to grow rapidly, keeping up with or even catching up with the pace of the international water-based coatings industry
.