Two-component waterborne polyurethane (2K WB PU) coating technology has been commercialized since 1990, when such products were developed primarily to reduce the problem of VOC content, which was not feasible to solve using solvent-based technology.1 Since the introduction of two-component waterborne polyurethane (2K WB PU) coating technology, progress has been made to address many of the shortcomings inherent in waterborne coatings. Efforts have been made to match the performance requirements and application range of waterborne coatings with those of conventional two-component solvent-borne polyurethane coatings.
However, a difficult deficiency of two-component waterborne polyurethane (2K WB PU) systems to overcome is the drying speed, especially in high humidity conditions. This problem is particularly evident when typical polyester polyols are used as the OH component of the system. Acrylic polyols do not confer the problem of severely slowed drying times under high humidity conditions, but other properties such as flexibility, durability or resistance to chemical media may be affected. It will therefore be interesting to check whether the correct choice of catalyst can improve the drying time problems of polyester-based two-component waterborne polyurethane (2K WB PU) coatings.
The catalytic performance of generic polyurethane catalysts such as dibutyltin laurate (DBTDL) in aqueous systems is diminished, mainly due to incompatibility and hydrolytic instability in aqueous matrices. Two important characteristics of effective waterborne polyurethane catalysts are hydrolytic stability and increased water solubility. In addition to these characteristics, the waterborne polyurethane coating catalyst should be able to provide the required reactivity and assist in the formation of various formulation characteristics properties (chemical structure, functional groups, additives, % solids, etc.). Ideally an effective waterborne polyurethane catalyst should also provide consistent buildability and other performance characteristics under a variety of environmental conditions including temperature and relative humidity.
Reaxis has developed a novel waterborne catalyst with excellent hydrolytic stability compared to typical polyurethane catalysts to provide improved performance in two-component waterborne polyurethane (2K WB PU) formulations under a variety of environmental conditions. This paper focuses on in-service stability, service life, service life, drying time, solvent resistance, and the effect of humidity on cure rate.

Reactivity and Film Formation Properties
Two approaches can be used to prepare stable two-component waterborne polyurethane (2K WB PU) coating formulations.2 One approach is to use hydrophilically modified polyols to provide emulsification capability, which allows the use of typical hydrophobic polyisocyanates. The polyol droplets are typically much smaller and surround the polyisocyanate droplets to help them disperse. Emulsification occurs when the polyol droplets surrounding the larger polyisocyanate droplets form stable polyisocyanate micelles.
In addition, typical two-component waterborne polyurethane (2KWB PU) coatings can be prepared with hydrophobically modified polyisocyanate dispersions mixed with polyols. Polyisocyanates can form micelle structures without the help of polyols (Figure 1). As the formulated product sits for a longer period of time, the polyisocyanate droplets and polyol droplets begin to agglomerate and become larger in particle size. This usually leads to a decrease in starting viscosity. Because of this drop, these systems cannot be measured by measuring the increase in viscosity with time to determine the service life, which is often the case with solvent-based two-component polyurethane systems.

Once the formulated product is coated, the water begins to evaporate and the particles begin to agglomerate and form a paint film.3 The curing curve in Figure 2 was generated by measuring the relative concentrations of water and isocyanate groups (NCO) using Fourier infrared spectroscopy (FT-IR). The curves show that most of the water evaporates within the first 30 minutes and almost all of the water evaporates after 60 minutes. The main reaction that occurs at this point is the reaction of the hydroxyl (OH) group of the polyol with the NCO group of the polyisocyanate. The reactivity and selectivity of the catalyst is very important, as is the competitive reaction of the formulation with water in the mixing tank between the first 30 and 60 minutes after the construction of the paint film. It is desirable that the catalyst preferentially promotes the reaction of the NCO group with the OH group of the polyol over the reaction with water. Too much water reacting with the NCO groups will form bubbles due to the release of carbon dioxide. If the catalyst is too reactive, too much crosslinking will form before all the water evaporates, as carbon dioxide bubbles are entrapped and pinholes form.

The advantages of using a catalyst can be illustrated by a simple FT-IR experiment. Cured lacquer films with and without catalyst were analyzed to show the difference in cure completion. After two days, no isocyanate peaks were found in the cured paint film with the new REAXIS C333 catalyst. In contrast, the isocyanate peak (2265 cm-1) was still visible in the paint film prepared without the catalyst, as shown in Figure 3.

Experiment
Two polyester/hexamethyl diisocyanate (HDI) formulations with different reactivities were used in this study. Throughout this article, the two formulations are defined in the following way: Formulation 1 is composed of Bayer Bayhydrol® 2591 urethane modified polyol and Bayhydur® 2487/1 isocyanate. Formulation 2 is composed of W2K® 2002 polyester polyol and Bayhydur 302 isocyanate from American Polymers.
We further defined the formulation as high performance and standard performance based on the hydroxyl functional groups and the main chain structure of the polyol. Thus, formulation 1 (tetrafunctional carbamate functional polyol with an OH equivalent of 436) is defined as high performance, while formulation 2 (polyester polyol with an OH equivalent of 252) is defined as standard performance. bayhydrol 2591 has an equivalent of 436 at 100% solids, while W2K 2002 is 252. these formulations are shown in tables 1 and 2. based on resin solids, the The amount of catalyst used is 0.2%.

In preparing the coatings, Component A (polyol, catalyst, water, wetting additive) was mixed with Component B (isocyanate) for 1 minute. Using a Binks siphon gun, set the gun pressure to 50 psi and spray each coating onto the aluminum substrate with a dry film thickness of 1.5-2.0 mils. The coatings were allowed to dry in air for the specified time as required by the test method used. Finger touch dry time, non-dusting dry time, dry hard time, number of butanone reciprocal wipes and pencil hardness were determined in the determination of physical properties as specified by ASTM.

Results
Physical properties
The results of the comparison of physical properties illustrate the short drying time from finger touch to solid dry for the coatings on the formulated plates using Reaxis C333. They also obtained the same final physical properties as any other catalyst. Of course, the final physical properties are determined by the nature of the raw material selected and REAXIS C333 helps to obtain these final properties in a short period of time. Catalysts can reduce the time needed to obtain these end properties, but they may also degrade the end physical properties if they promote undesired side reactions. Thus, selectivity is an important property.
Table 3 illustrates that for reactive polyols all catalysts act similarly, but the solid dry time is good with REAXIS C333. We define the reactivity of a polyol as the ability to give the formulation better final film properties, all else being equal. Table 4 shows that the use of REAXIS C333 in a sub-reactive polyol system resulted in a more rapid formation of final film properties.

An important advantage of the REAXIS C333 catalyst is that it is soluble in both the organic and aqueous phases. This makes the catalyst compatible with most systems and ensures uniform distribution in the formulated product. This helps to ensure uniform curing of the coating.

Storage period stability
For practical reasons, it is important to determine the appropriate shelf life stability of the A and B components of a two-component waterborne polyurethane (2K WB PU) system. The best stability is usually seen when a catalyst is added to the A component. The use of catalysts in the B component (NCO) can lead to the formation of by-products such as diurea, urea formate, isocyanate and urea under certain conditions. Similarly the use of catalysts in component A avoids catalytic effects on the water/NCO reaction because the mixture absorbs water as it sits.

Tables 5 and 6 illustrate that the drying time and pencil hardness of the formulated products were largely unaffected by the addition of C333 to the polyol matrix (component A) after 2 weeks at 60°C. Further testing is needed to confirm the stability of the polyol matrix, but these preliminary results are very encouraging.

Certain catalysts are designed to be used in polyisocyanate matrices (B component); however, this is not the norm. As mentioned earlier, if traces of moisture get into the polyisocyanate component, it can lead to many problems. We did not find any difference in the performance of the aged and unaged formulations of the B component, except for the good pencil hardness of the REAXIS C333 system. REAXIS C333 showed good versatility in that it can be used in either component A and B as long as the B component is kept free of moisture.

Service life
With waterborne coatings, the service life is usually not measured by an increase in viscosity, since a decrease in viscosity is usually encountered when the coating is left to age. The typical method of measuring the service life of waterborne coatings is to measure the physical properties after a specified period of time.
Although REAXIS C333 promotes rapid attainment of final properties, a reasonable action time (at least 2 hours) is required after mixing the A and B components. The drying time was shortened due to certain reactions occurring in the tank, but the final properties did not change. Then, as shown in Tables 8 and 10, the difference in pencil hardness after aging placement was more significant for the system based on REAXIS C333 compared to the use of other catalysts.

Coating performance under different humidity conditions
REAXIS C333 catalyst provides excellent curing in a wide range of humidity conditions. High humidity often results in slower drying of aqueous coatings. Drying time and final physical properties of the coating remain relatively unchanged with REAXIS C333. This is advantageous to the end-user because it allows the coating to be applied under a variety of conditions. For example, consistent performance can be obtained in high humidity conditions and/or hot outdoor environments (where temperature and humidity cannot be controlled).

Selectivity of the isocyanate/water reaction and isocyanate/hydroxyl reaction
FT-IR was used to investigate the relative selectivity of C333 for promoting the reactions of isocyanates with hydroxyl groups and water. Polyisocyanate (concentration of 0.8 molar concentration) and co-reactants were mixed in dipropylene glycol dimethyl ether. The catalyst was used at a metal concentration of 200 ppm relative to the reactant solid. The negative natural logarithm of the height of the absorbance peak of NCO (-Ln) was plotted against time in minutes. The slope of the straight line was compared to determine the relative rate. Figure 4 shows that n-butanol reacts 6.7 times faster with the aliphatic NCO group in the primary position than water reacts with the NCO group. This is very advantageous for formulating two-component waterborne polyurethane coatings as it helps prevent poor film appearance due to blistering. seneker and Potter reported a selectivity of about 24 for DBTDL. figure 5 shows that the reaction of water with NCO catalyzed by DBTDL is 1.45 times faster than the reaction catalyzed by REAXIS C333.

Overview and Conclusion
Reaxis C333 is a water-soluble, hydrolytically stable catalyst that provides fast drying times and good physical properties for two-component aqueous polyurethane (2K WB PU) formulations at a variety of temperatures and humidity conditions. Many two-component waterborne polyurethane (2K WB PU) systems suffer from slow drying times and reduced physical properties at higher humidity levels, so the use of C333 provides a wider range of applications.
REAXIS C333 is unique in that it is soluble in both aqueous and organic media, thus providing a very wide formulation range that allows it to be uniformly distributed in liquid coatings, resulting in uniform curing of the entire paint film.

The activity of REAXIS C333 can be illustrated by the fact that two-component waterborne polyurethane (2K WB PU) formulations containing this catalyst retain their original physical properties and drying time after aging. Likewise, the service life and in-service stability of these formulations is excellent.
The excellent selectivity of REAXIS C333 (compared to DBTDL) promotes the reaction of isocyanates with hydroxyl groups over water, as confirmed by FT-IR tests. This is a very important advantage over typical catalysts used in other two-component waterborne polyurethane (2K WBPU) coating formulations, as it helps prevent blistering and thus optimizes the appearance of the film.
Further testing is needed to better determine and understand the benefits of using C333 in two-component waterborne polyurethane (2K WBPU) systems and related coating technologies. Preliminary studies have provided promising data that require further research

Polyethylene (PE) is one of the most important types of plastics today. It is used in a variety of everyday products, from plastic bottles, pipes and skiing to paints and toys. In the form of PE dispersions, it forms the basis for different coatings and adhesives.

The basic structural unit of PE is ethylene, a gaseous hydrocarbon. A suitable chemical catalyst is used to facilitate and accelerate the polymerization process. During the polymerization process, the individual structural units are linked together to form large polymer molecules. In the production of PE dispersions for coatings, polymerization usually takes place in organic solvents, requiring additional steps that are both technically complex and energy-consuming.

Therefore, researchers are looking for ways to produce PE directly in the form of aqueous dispersions during the polymerization process. However, polymerizing PE directly in water is challenging. Study author Stefan Mecking explains, “This requires catalysts that are active in water but at the same time are not destroyed by water, whereas most conventional catalysts break down once they come into contact with water.”

After several experiments, Stefan Mecking’s team finally developed a new type of catalyst. Although it comes into direct contact with water during the chemical reaction, it remains highly stable.

In test studies, the scientists demonstrated that their new catalyst polymerizes ethylene, forming a large number of small PE particles with high molecular weight and linearity, the so-called high-density polyethylene (HDPE). This is decisive for the production of coatings based on PE dispersions and opens up the prospect of producing zero-pollution coatings.

The research paper, entitled “Hydrophilic Catalysts with High Activity and Stability in Aqueous Polymerization to High Molecular Weight Polyethylene “has been published in Angewandte Chemie International Edition.

Forward-looking Economist App Information Group

Original paper: https://onlinelibrary.wiley.com/doi/10.1002/anie.202203923

From academia to industry, for more relevant data, please refer to the Foresight Industrial Research Institute’s “China Catalyst Industry Market Foresight and Investment Strategic Planning Analysis Report, 2022-2027”. Meanwhile, Foresight Industrial Research Institute also provides solutions such as industrial big data, industrial research, industrial chain consulting, industrial mapping, industrial planning, park planning, industrial investment attraction, IPO fundraising feasibility study, IPO business and technical writing, and IPO working draft consulting.

Coating auxiliaries, also known as paint auxiliaries, are auxiliary materials for the preparation of coatings, which can improve the performance of coatings and promote the formation of coating films. There are many types, including catalysts, toughening agents, emulsifiers, thickeners, pigment dispersants, defoamers, leveling agents, anti-crusting agents, matting agents, light stabilizers, anti-mildew agents, anti-static agents (see plastic additives), etc., of which a large amount is catalysts and toughening agents. At present, the research of coating additives to water emulsion paint additives for the focus.

Chinese name: coating additives

Foreign name: Paintadditives

Also known as: paint additives

Used for: Auxiliaries for water emulsion paints

Contents

1 Introduction

2Types

3Details

Drying agents

Toughening agent

Thickening agent

Pigment dispersant

Introduction

Coating additives are those ingredients that are added in small quantities to a coating formulation to control or enhance the performance of the coating. In total, there are about 40 different functional types of coating additives (emulsifiers, dispersants, defoamers, thickeners, anti-cratering agents, drying accelerators, fungicides, etc.), as well as additives composed of different chemical components. Usually the formulation of a coating will contain a variety of additives, and in general the total amount of additives used is less than 5% of the total formulation, but in some cases it may be as high as 10% or more. Due to the relatively high value of additives, the formulation will be designed to minimize the amount of additives used as much as possible.

Types

After years of development, there are many types of coating additives, and they play different roles in each stage of coating production. In the manufacturing stage, there are: initiators, dispersants, ester exchange catalysts; in the reaction process, there are: defoamers, emulsifiers, filtering additives; in the storage stage, there are: anti-crusting agents, anti-sedimentation agents, thickeners, thixotropic agents, anti-floating coloring agents, anti-gelling agents; in the construction stage, there are: leveling agents, anti-cratering agents, anti-sagging agents, hammering additives, flow control agents, plasticizers, defoamers, etc.; in the film-forming stage, there are: agglomeration additives, adhesion promoters (also called adhesion promoters), adhesion promoters, etc. adhesion promoter (also called adhesion enhancer), photoinitiator, light stabilizer, drying, light, slip, matting, curing, cross-linking, catalyst and other additives; to give special features are: flame retardant, biocide, anti-algae, anti-static, conductive, corrosion inhibition, rust prevention and other additives.

In general, according to its use, including adhesion enhancers, anti-adhesive agents, anti-cratering agents, anti-flowering agents, anti-floating agents, defoamers, foam inhibitors, anti-gelling agents, viscosity stabilizers, antioxidants, anti-crusting agents, anti-sagging agents, anti-sedimentation agents, antistatic agents, conductive control agents, anti-mold agents, anticorrosion agents, agglomeration additives, corrosion inhibitors, rust inhibitors, dispersants, wetting agents, drying agents, flame retardants, flow control agents, hammering agents, corrosion inhibitors, rust inhibitors, anti-corrosion agents. flow control agents, hammering additives, drying agents, matting agents, light stabilizers, photosensitizers, optical brightening agents, plasticizers, slip enhancers, anti-scratch agents, thickeners, thixotropic agents, anti-mouse bite agents, other additives.

In addition to the main film-forming substances, color fillers, solvents, a component added to the coating, which can make the coating or coating film of a specific performance to play a significant improvement of the substance. The amount in the coating formula is very small. It is mainly a variety of inorganic compounds and organic compounds, including polymers.

Their names are mostly based on their properties. Those that improve the production process of coatings include wetting agents, dispersants, emulsifiers, defoamers, etc. For improving the storage performance and transportation of coatings, there are anti-sinker, anti-crusting agent, preservative, freeze-thaw stabilizer, etc. To improve coating construction performance and prevent paint film disease, there are anti-sagging agent, leveling agent, floating color and flower prevention agent, defoaming agent, thickening agent, etc. Improve the performance of the coating film and give special performance of ultraviolet absorbers, light stabilizers, flame retardants, anti-static agents, anti-mold agents, etc..

Coating additives can be divided into oil-based coating additives and water-based coating additives. In line with the increasing global attention to environmental protection, the development of water-based coating additives has developed by leaps and bounds. There are more and more new environmentally friendly types of additives. The application is also becoming more and more extensive. It is the mainstream direction of the future development of coating additives.

Detailed introduction

Drying agent

It is a kind of substance that can accelerate the drying of the coating film, and it can promote the absorption of oxygen and the polymerization of double bonds in the dry oil film. It can shorten the drying time of oil film from several days to several hours, facilitate the construction and prevent the staining and damage of the undried film.

Many metal oxides, salts and soaps have a drying effect, but the practical value of lead oxide (red Dan, yellow Dan), manganese dioxide, lead acetate, lead nitrate, manganese sulfate, manganese chloride, manganese borate, manganese acetate, cobalt acetate, cobalt chloride, as well as lead, cobalt, manganese naphthenic soap, linoleic acid soap and rosin acid soap.

As a result of soap drying agent oil solubility is good, so the drying effect is high. Modern paint industry more naphthenic soap for drying agent. Naphthenic acid soap is usually produced by the complex decomposition method.

The amount of drying agent in oil-based coatings depends on the amount of dry oil or semi-dry oil. In dry linseed oil, for example, the amount of lead catalyst (in terms of lead) is 0.4-0.5% of the oil mass; cobalt and manganese are stronger than lead, and the ratio of cobalt, manganese and lead is about 8:1:40. Two or three kinds of metal soaps are used with synergistic effect. In the resin coating, the amount of catalyst must be increased.

Toughening agent

That is, plasticizers (see plastic additives). Coating industry commonly used varieties are diethyl phthalate, dibutyl phthalate, dioctyl phthalate, tributyl phosphate, triphenyl phosphate, trimethylene phosphate and some special varieties.

Thickening agent

A substance that can increase the viscosity of a coating and reduce its fluidity. The important purpose of using thickeners is to reduce the flowing phenomenon during finishing. The thickeners for coatings are mainly the following: ① silica; ② bentonite and organic bentonite (bentonite treated with cationic organic matter); ③ active calcium carbonate particles by surface treatment; ④ hydrogenated castor oil; ⑤ metal soap, such as calcium stearate, aluminum stearate, zinc stearate, etc.; ⑥ polymerized vegetable oil and fatty acid dimer and polyol esters.

Pigment dispersant

Used to prevent pigments from settling or floating. Bentonite and organic bentonite, metal soap, hydrogenated castor oil and other thickening agents can play the role of pigment dispersant. Various surfactants, low molecular weight polyethylene oxide (polyethylene oxide), low viscosity methyl silicone oil, lecithin and its derivatives are also often used.

Levelling agent

Substances that contribute to the formation of a smooth finish. Substances that can reduce the surface tension of coatings generally have the role of leveling agents. Industrial leveling agents have been used fluorinated surfactants, polyacrylates and polyvinyl butyral and other series. General silicone leveling agent is to control the short-wave leveling, reduce surface tension is more obvious; acrylate is to control the long-wave leveling, reduce surface tension amplitude is small.

Anti-crusting agent

The substances that prevent the surface crusting of oil-based coatings in use, such as methyl ethyl ketone oxime and cyclohexanone oxime.