Choice of resins for wood coatings: a formula designer's guide

China Coatings Online News Information:
problems faced by wood coatings are the diversity of existing resins and their different applications in the industry. The key to finding the best single-part (
1K
) water-based polyurethane resin for wood coatings is to thoroughly understand two elements: the performance of the resin itself and the evaluation criteria for a particular end market. The two elements are closely linked, so in order to better address this dilemma, they must consider
-
together.
Bayer MaterialScience researchers classified the company's
1K
water-based polyurethane technology and the importance of different uses so that formulators have an overall understanding of resins and their suitability for special-purpose wood coatings. In this paper, the general results are given to make the resin screening process of wood coating more smooth.
polyurethane dispersion (
). PUDs
) type
the main components or building blocks of polyurethane dispersions: polyethers, polyesters, and polycarbonates. In some cases, polyurethane dispersions are prepared together with two main components. It may contain the advantages and disadvantages of each ingredient (table
1
).
there are some self-linked polyurethane dispersions. These dispersions contain chain segments that can be cross-linked when triggered. Some types of self-linking materials contain fatty acid chain segments, which allow them to oxidize and cure over time.
important tests for the wood coatings market
After a preliminary understanding of the performance combinations typically displayed by different types of polyurethane dispersions, it is important to understand what important tests are being performed to determine whether the resin is best suited for the different end wood coatings market. The usual tests are as follows:

drying time;

surface hardness (swing bar hardness);

Taber
wear test to determine scratch resistance and wear performance
(CS-10
grinding wheel,
1,000
-
Weights of 1,000 g
);
.
chemical-resistant media (ethanol
/
water, acetone, formula
409
and water);
.
black heel marks (
BHMR
);

outdoor durability.
solvent-free polyurethane dispersions
, after deciding which tests are important to the wood coatings market,
,
researchers conducted these tests on a variety of solvent-free polyurethane dispersions. Table
2
is a matrix
developed by the
, which lists how these polyurethane dispersions conduct the experiments given above.
these are solvent-free polyurethane dispersants, they need to be valued as solvents that help film at room temperature. Where the resin
UH XP 4
is a unique material that does not require solvent assistance. As a result, the
VOC
content of products made with it is very low (below
50 g/L
), which is very attractive for some end markets. However, it is important to remember that
UH XP4
is an oxidizing curing material and therefore requires a drying agent or catalyst to promote the oxidation curing process. Such catalysts usually contain a specific metal, such as cobalt, and of course can be used to update more environmentally friendly materials, such as iron-containing materials.
end-
Table
2
provides a good overview of the performance of the different polyurethane dispersions used by wood coating manufacturers. However, another important aspect that needs to be evaluated is end-use. For example, wear resistance
-
may be important for flooring, but not for cabinets. With this in mind, researchers are also considering the requirements of several different applications: floors, cabinets, furniture, indoor windows and doors, and outdoor wood, in an effort to help formulators choose the most suitable resin.
wood flooring
researchers conducted a
BHMR
) test to evaluate whether shoe prints can be removed, an important test for wood flooring. For this purpose, it is also important that the coating is resistant to wear (
Test
test for Taber). They should also be hard enough (swing bar hardness), as if the coating is soft, dust will suck in, resulting in unwelcome dirty imprints. Based on these special performance requirements related to use, the researchers again referred to the matrix in table
2
and concluded that
UH3
is the best product in the market.
kitchen
an important performance of the market is chemical resistance media (staining agents). The main test of the market, developed by the
KCMA
, is the exposure of coatings to these media such as mustard, coffee and vinegar. After a period of time, remove the media to see if dyeing occurs. Equally important for kitchen cabinets is excellent wear resistance (
Taber
wear test) and excellent contamination resistance (swing bar hardness).
furniture
excellent contamination resistance (swing bar hardness), wear resistance (
Taber
wear test) and water resistance (water droplets) are the most important properties of furniture coatings. In addition, excellent chemical-resistant media (staining agents) such as shoe polish, nail polish, soft drinks, and other media often seen in the office environment should also be identified as an important standard for judging office furniture coatings.
Indoor Windows and Doors
In addition to excellent water resistance and chemical media resistance, good anti-adhesion time is also an important consideration for coatings for indoor windows and doors.
An outdoor wood
as expected, excellent weather resistance
-
includes good light preservation, non-fragmentation, non-powdering, non-bursting or yellowing
-
is the most important for the outdoor wood coatings market.
Gest polyurethane dispersions required for different market uses
researchers looked at the properties most relevant to important applications and combined them with a solvent-free performance matrix of polyurethane dispersions (Table
2
) to create a chart (Table
3
), which identifies resins that may best match a particular application. The researchers stress that the diagram is the starting point for formulaters' work, as the best material may not be a single material, but a mixture.
Effect of adding crosslinkers
Although single-group water-based dispersants provide some of the required properties, chemical media resistance, adhesion, or other properties may be further improved by adding crosslinkers. Several chemicals are available
-
polyneume heterocyclic propane, polycarbonized glycamines, and water dispersable polycyanates.
polyneume hexapane and polycarbonized diamin provide easy-dispersion and low-viscosity performance, but are sensitive to
pH
values and must be separately associated with acidic hydrodes.
the first generation of polycyanate has under been hydro-modified, thus providing susceptible dispersion. This option is usually low in isocyanate and therefore has a high viscosity.
second generation polycyanate is solvent-free and ion-modified
,
is another patented technology. One advantage of this technique is that isocyanates are high in
(23%)
And the viscosity is very
,
makes it suitable for the preparation of
with
low VOC color.
important to keep this in mind, which helps ensure the best coating formulation, taking into account both the polyurethane dispersion and end-use used when selecting crosslinkers.
conclusion
there are a variety of single-group water-based polyurethane resins available for wood coatings. Finding the best technology requires a thorough understanding not only of resin performance, but also of the end-use of wood coatings, such as flooring, kitchen cabinets, furniture, indoor windows and doors, and outdoor woodware.
While single-group water-based resins provide a good balance between the required properties, it is also important to remember that the performance of water-based coatings can be improved by adding crosslinkers to the formulation. The choice of suitable crosslinker depends on the use of polyurethane dispersions.
and tests carried out in the laboratory can make the resin selection process smooth. For formulat designers, this means saving a lot of time, money and resources. Furthermore, it makes it easier to select the best resin for the required performance of wood coatings for specific applications.
。