Development and application of super stain-resistant water-based wood paint formula

Wood coatings is one of the first subdivisions that mentions water-based and invests huge resources in research and development

After sorting out the above ideas, we visited customers and found that the stain resistance of the paint film is still very challenging in real-color paint applications such as cabinets, dining tables and chairs, and children's furniture

 Experimental part 

Experimental materials

Coating formula raw materials

Rheovis®PU1250, Joncryl®HPD296-E, Joncryl®9503ap, FoamStar®SI2280, Dispex®X4231, Attagel®50: BASF New Materials Co.

Stain resistance test material

Lipton green tea-bags, Nescafe coffee-alcohol instant coffee, French's yellow mustard, McCormick tomato sauce, Zhenjiang balsamic vinegar (acidity 9), red wine (Jacob's Creek) are all food grade

Test Equipment

A portable gloss meter pendulum hardness tester, wire rod 100 microns: BYK-Gardner; pencil hardness tester: Modern Environmental Engineering Co.

Preparation of water-based paint

The preparation process of water-based white paint is as follows: weigh the components of the white slurry into the container according to the formula in Table 7, grind or disperse to 20~30 microns, add the remaining raw materials in sequence according to the formula under stirring, and choose according to the specific situation after the addition is complete Disperse at a suitable rotation speed for 20 to 30 minutes

Sample paint film preparation

Paint film: Refer to GB/T 9271-1988 to prepare paint film test samples, using black and white cardboard and glass plates, respectively, using 100 micron wire rods for coating, and the dry film thickness of the paint film is 25-30 microns

Performance Testing

As shown in Table 1, refer to the American Cabinet Association standard ANSI/KCMAA161.

Table 1 »Reference standards and experimental test plan for chemical resistance and stain resistance of water-based wood coatings

Remark 

1.
The American Cabinet Association standard ANSI/KCMA A161.
1-2012 requires the ethanol concentration to be 100%.
This experiment uniformly uses a 48% mass concentration of ethanol solution for testing
.

2.
The American Cabinet Association standard ANSI/KCMA A161.
1-2012 requires the coffee concentration to be about 1%.
This experiment uniformly uses a coffee solution with a mass concentration of 4% for testing
.

3.
Although red wine stains are not in the above test standards, they are still common and difficult to handle stains in daily life
.

Table 2 »GB/T 4893.
1-2005 stain marks grading standard evaluation table

Table 3 »Determination of anti-graffiti level in GB/T 33394-2016

Formulation design and discussion of experimental results

Before discussing the formulation design of stain resistance, we might as well understand stains first
.
We just take coffee and yellow mustard, two common stubborn stains, as examples
.
Coffee is derived from green coffee beans, and about 35%-45% of the ingredients are polysaccharides.
After roasting, most of the sugar will be converted into caramel, which makes the coffee brown.
Caramel is a natural coloring agent that is easy to remain On the surface of the coating film, it is relatively stable to light and heat, so coffee stains are more difficult to wipe clean, and the longer the time, the more serious the coffee residue marks
.
Mustard has a bright yellow color and comes from finely ground yellow mustard seeds.
It contains the powerful coloring spice turmeric
.
Curcumin has strong tinting power, bright color and stable properties, but light and heat can promote its oxidative decomposition and lose its color development ability
.
Direct sunlight for 5 hours, the loss rate of curcumin is about 33%
.
Therefore, although yellow mustard has strong coloring ability and obvious initial residual traces, after the test, the mustard traces will fade to a certain extent[1]
.

To fight against these stubborn stains and be efficient, the formulation design of the coating film is very critical
.
The performance of the coating film mainly depends on the emulsion itself as the main resin, and the selection of the emulsion is very important
.
On this basis, according to the needs of specific application scenarios, select the appropriate type of pigments and additives to complement the shortcomings of the emulsion, and then the basic formula can be constructed, and then through detailed optimization, a mature, stable and easy-to-operate formula can be obtained
.

Screening of emulsion

In order to understand the occurrence of stains more clearly, we simulated the penetration of stains through fluorescent solutions, and observed the penetration of stains in the longitudinal section of the paint film using an electron microscope (as shown in Figure 1)
.
The black part in the picture is air, the gray part is the paint film layer, and the white part is the fluorescent solution, which shows a brightening effect under the microscope for easy observation
.
We found that competing emulsions, which are known to have good stain resistance, have loose microscopic film formation, and stains can easily penetrate through the surface into the fine pores of the paint film and become whitish, allowing us to see the enriched honeycomb structure on a microscopic scale (Figure 1) On the left), it is difficult for the stain to escape from the paint film after it dries, so obvious marks or even complete marks are formed on the macroscopic view
.
Joncryl®9503 ap is the latest acrylic antifouling emulsion developed by BASF’s dispersions and resins business unit in the Asia-Pacific region.
No red continuous image is found, it can be seen that the interior is very dense, and it is difficult for stains to penetrate into the deep paint film, and only a small amount of stains stay on the surface of the paint film.
It is especially suitable for water-based wood coating applications with high stain resistance requirements
.

Figure 1 »Comparison of the microstructure of competing emulsion and Joncryl® 9503 ap paint film

The solid content of Joncryl®9503 ap is 39%~40%, and the minimum film forming temperature is about 35℃.
With its high film density, it reduces the staining power of the paint film surface and the solvent swelling ability of the paint film.
, Helps to improve the stain resistance of the paint film, and can make the furniture last forever
.
In addition to regular green tea, coffee, and red wine, its resistance to yellow mustard is also very outstanding.
If the formula is adjusted properly, it can even be resistant to yellow mustard for up to 6 hours
.

Screening of dispersing aids

The dispersant adsorbs on the pigment surface to form a charge effect or steric hindrance effect, so that the pigment is in a stable state, while the wetting agent can reduce the tension between the liquid-solid interface, enhance the lyophilicity of the pigment, and improve the efficiency of mechanical grinding
.
The structure of commercially available wetting and dispersing agents is similar to that of surfactants, and their effects are very similar to those of dispersing agents.
It is often difficult to distinguish between the two, especially polymer dispersing agents, which have both wetting and dispersing effects [2]
.

For the dispersion of titanium dioxide, this experiment uses Joncryl® HPD 296-E water-based styrene-acrylic emulsion to compare with the polymer-based dispersant to investigate its impact on stain resistance
.
The emulsion can be regarded as a water-based grinding resin and has excellent wetting and dispersing properties for pigments, without the use of wetting and dispersing agents, and can also maintain good color development and storage stability of the color paste
.
Competitor dispersants belong to the type of block copolymerized polymer and have excellent pigment stability.
Its A and B blocks contain anchoring segments on the surface of pigment particles and system compatible segments respectively, which are suitable for most organic and inorganic pigments
.

Table 4 »Technical data of dispersing additives

Table 5 »Technical data of dispersing additives

We choose room temperature water, 48% ethanol solution, and difficult to pass coffee and yellow mustard for rapid screening tests
.
From the test results in Table 5, it can be found that the water resistance and ethanol resistance of the two are similar, but the polymer wetting and dispersing agent has a certain negative effect on the stain resistance.
This may be related to the wetting and dispersing of the stain after penetrating the surface of the coating film.
The group of the agent is anchored, so that stains remain on the coating film, which is difficult to wipe clean
.
The molecular weight of Joncryl® HPD 296-E is higher than that of wetting and dispersing additives, and only a lower addition amount (as shown in Table 4) can help improve the stain resistance of the paint film and is more suitable for use in formulations
.

Screening of pigments and fillers

Titanium dioxide has high refractive index, ideal particle size distribution, good hiding power and tinting power, and is a white pigment with excellent performance
.
In the post-treatment process of titanium dioxide production, inorganic coating modification is often carried out to form a barrier between the surface and the medium, which can reduce the photocatalytic activity and enhance the weather resistance, dispersibility, and pulverization resistance of the titanium dioxide.
Application performance [3]
.

We selected commercially available products with different surface modifications and compared the test results (as shown in Table 6).
Titanium dioxide modified with SiO₂ has varying degrees of water resistance, long-term ethanol resistance, and stain resistance.
However, the titanium dioxide modified with Al₂O₃ alone performs best, and the second modified with Al₂O₃-ZrO₂
.
Therefore, if you want to achieve a better degree of stain resistance, the selection of titanium dioxide is also very important
.

*Note: The above comparison tests of titanium dioxide are based on the paint formula with Joncryl® 9503 ap as the main resin, and the weight percentage of titanium dioxide is 19%
.

Table 6» The effect of titanium dioxide on stain resistance test results

Engineers familiar with the formulation know that the white matte finish is the most challenging to test stain resistance, so the selection of matting powder cannot be ignored
.
The commonly used SiO₂ matting powder can effectively reduce the gloss of the paint film, but after all, it has a porous structure and is arranged on the surface of the paint film.
The stains are easy to penetrate and irreversibly.
Therefore, it is recommended to use a micronized wax or wax emulsion with a suitable particle size instead.
It can not only reduce gloss, but also improve scratch resistance at the same time
.

Table 7 »Starting formula of matte white paint based on Joncryl® 9503 ap

Table 8 »Comparison of the main performance of competing emulsion and Joncryl® 9503 ap paint film

In addition to the screening of the above key raw materials, other additives will also affect the stain resistance
.
Choosing relatively hydrophobic surface additives or increasing the use of cross-linking agents will help to improve the ultimate effect of stain resistance
.
Foamstar®SI 2280 is a modified siloxane defoamer with excellent compatibility with the system.
It can be added at any stage of the production process and is safe to use and easy to operate
.
Rheovis®PU 1250 is a hydrophobically modified polyurethane type medium shear rheology additive, which can effectively increase the viscosity of the system
.
EFKA®FL3034 is a modified polysiloxane additive, which takes into account substrate wetting and surface leveling control
.
Attagel®50 is attapulgite with excellent anti-settling properties
.
We list the starting formula of matte white paint based on Joncryl®9503 ap (shown in Table 7), and the corresponding performance comparison results (shown in Table 8), and visually show the results of the stain resistance test (Figure 2) Shown) to facilitate readers to compare
.

Figure 2 »Physical image of the stain resistance test results of competing emulsion and Joncryl® 9503 ap paint film

It can be seen from the above experimental results that Joncryl® 9503 ap has better stain resistance than traditional emulsions due to its higher film-forming density, combined with the dispersion resin Joncryl® HPD 296-E and appropriate types of pigments and fillers, the overall The stain resistance can be further optimized and is highly efficient and durable, especially in the anti-fouling test against red wine, coffee, yellow mustard and markers
.
At the same time, we also found in the experiment that different matching primers will also have an impact on the stain resistance of the topcoat.
Choose UV primer or a base-in-one formula based on Joncryl®9503 ap.
Sexual effects can be guaranteed
.

Concluding remarks 

With the rapid economic development and the gradual improvement of people's environmental awareness, the water-based wood coatings will surely develop and mature together with other types of environmentally friendly green coatings
.
After nearly 20 years of development, water-based wood coatings have gradually entered the deep water area of ​​technological innovation.
Research and development sub-topics such as low toxicity and clean odor, high permeability warm wood, scratch resistance, water resistance and stain resistance will definitely be re-exposed.
In order to develop more distinctive products, further shorten the gap with solvent-based two-component PU, and meet the requirements of the furniture industry to reduce costs and increase efficiency
.
The spring of water-based wood coatings is not far away, what is needed is the joint efforts of you and me!

references

[1] Xiang Bin, Gao Jianrong.
Natural Pigment: Handbook of Practical Natural Products[M].
Beijing: Chemical Industry Press, 2004: 52-76.

[2] Geng Xing.
Handbook of modern water-based industrial additives [M].
Beijing: Sinopec Publishing, 2007 (06): 50-51.

[3] Dong Xiongbo, Yang Chongqing, Sun Zhiming, Zheng Shuilin.
Status and development trend of inorganic coating modification of titanium dioxide[J].
Inorganic Salt Industry, 2017, 49 (05): 5-8.