Faster drying and more efficient polyurethane coating - non-isocyanate polyurethane technology that extends the applicable period and reduces the drying time at the same time

China Coatings Online News Information: In the need to improve efficiency and/or shorten the maintenance cycle, end-users have higher requirements for the drying speed of industrial coatings. However, when using traditional two-part (2K) polyurethane coatings, the drying time is subject to the need for a balanced applicable period and cannot be significantly improved. Slowing the reaction between the base resin (part A) and isocyanate crosslinker (part B) extends the much-needed applicability period, but also prolongs the drying time. Dow Chemical's business unit, Dow Coatings, has developed PARALOID™ non-isocyanate polyurethane technology, which uses an interlinking system of urethane, so that there is no longer a contradiction between the applicable period of the system and the rate of curing at room temperature, so that formula designers can optimize both characteristics at the same time.
drying speed requires
in the field of industrial coatings, faster drying speed is an important competitive advantage. Faster drying and shorter process times increase productivity, reduce labor costs and increase customer satisfaction. In the overall good economic situation, the number of car users increased rapidly, industry mergers also reduced the number of garages, so car repair paint more need to improve the speed of operation2. Although there are many factors that affect the construction cycle of car repair paint, speeding up the drying speed of polyurethane coatings is undoubtedly one of the most effective measures.
car repair paint practitioners use approximately 60 million pounds of polyurethane per year. 3 Most of them are two-part coatings based on adipose isocyanates and acrylic polyols. 4 These ingredients have excellent weather resistance, including UV exposure and yellowing resistance, excellent color and light protection (even after very long exposure times), excellent water, oil and chemical resistance, and excellent hardness and scratch resistance. However, in the absence of two-component spray equipment or thermally assisted curing, these high-performance properties require an extended polishing drying time after coating primers and polishing drying time after coating. In addition, there is a limited applicable period. Once the two parts are mixed, the sprayable time is reduced to several hours.
unlike the traditional room temperature curing of polyurethanes with isocyanate as an crosslinker, paraLOID™ Edge non-isocyanate polyurethane technology is used without having to trade off the contradiction between curing speed/applicability. As shown in Figure 1, this innovative technique uses an active group based on amino acid, a formaldehyde crosslinker and an acid catalyst. In addition to reducing room temperature drying time and extending the active life, the technology also enables formulation and application engineers to use a crosslinking system free of isocyanate, thereby improving the environmental protection, health and safety of coatings.
1 PARALOID™ Edge non-isocyanate polyurethane technology uses the reaction of polyurethane and dialdehyde to create a cross-linked polyurethane film.
photo caption At the Dow Coating Materials Research Laboratory in Midland, Michigan, a car fender was coated with primer in polyurethane made using PARALOID™ Edge non-isocyanate polyurethane technology.
the primer process
the car repair process requires multiple coatings, and each layer of coating requires a certain drying time. After filling and polishing the refurbishment area, the primer is applied in multiple channels by spraying. After the primer has dried, polish and clean it before the final coating process. If the drying time of the primer is shortened, the cycle time of the overall paint repair operation is significantly shortened, thus improving the efficiency of the repair shop5. Table 1 provides a reference formula for a two™-component polyurethane car repair primer based on PARALOID™ Edge non-isocyanate polyurethane technology.
1 is based on the formulation details and coating characteristics of the two-component polyurethane automotive repair primer based on PARAALOID™ Edge 1100 alicylate resin and PARALOID™ Edge XL-195 crosslinker.
。 Recipe detailsAgroup
pointspoundsgallonspulp grinding PARALOID™ Edge 1100
Resin 305.89 36.99xylene
18.88 2.60toluene 136.85 18.85methyl ethyl ketone 66.97 9.91 Disbyk 110
Dispersant 10.33 1.39 Tiona 585
Titanium Dioxide 64.69 1.89 Nicron 665
Talc powder 64.69 2.77
Optiwhite
calcined aluminum silicate 45.00 2.25 Miti-wite
sulphate 73.12 1.99 Letdown ethanol 88.08 13.37 diproptonol 17.80 2.27
B lb gallons PARALOID Edge XL-195
Crosslinker 3 7.72 4.39 Catalyst DNNDSA
(
55%
solid) 11.24 1.35 Totals total 941.24 100.00 coating
characteristics volume solid containing 28.8% weight
solid containing 49.8% PVC pigment volume concentration 25.0% Density (lb
/
gallons) 9.41 VOC (g/L) 564 In order to verify room temperature curing, spray two layers of primer on a cold-rolled steel plate (polished with Sandpaper No. 80) with 10 minutes of solvent evaporation time after coating each layer. Store the coated steel plate in a constant temperature and humidity tank for drying. Sanding is done by hand using Sandpaper No. 320, e.g. sandpaper is not bonded when polished, and any residual material on the paper can be easily dropped or touched to be considered polishable.
as shown in
table
2 , the polishing time (
40
minutes) of primers using PARALOID™ Edge
technology is very short. By contrast, a commercially available isocyanate-containing polyurethane takes more than four times as long to polish, requiring
180
minutes of drying time before grinding.
Table
2 the grinding time required to apply primers using PARALOID™ Edge
technology compared to commercially available isocyanate coatings.
。 Medium primer Volatility time minutes Volatility conditions Drying conditions Grinding time (minutes) PARAL Edge 10 23 C 50% RH 22 3

C 50 % RH 40 isocyanate comparison 10 23

C50% RH 23

C 50 % RH 180
RH - Relative humidity.
typical features should not be considered product specifications.
excellent adhesion
adhesion and solvent resistance are important features required to apply primers in automotive repair. Table 3 summarizes the solvent resistance and ™ test results for primers applied using PARALOID and Edge technology. After 24 hours, methyl ethyl ketone wipes more than 100, after 7 days more than 200. The adhesion test follows the TEST method of ASTM 3359 and uses a 3mm blade for the adhesion test using the adhesion method. The tests were carried out on two systems: steel plates coated only with medium primer, and the same medium-coated and commercially available black paint and transparent cover. After seven days, only the system of medium primer and the steel plate coated with medium primer/black paint/transparent cover surface show and maintain good adhesion.
3 is solvent-resistant and adhesive for automotive repair primers made with PARALOID™ Edge non-isocyanate polyurethane technology. 。 PARALOID™ Edge
Isocyanate Polyurethane Coated Primer Film Thickness (microns) 85 77.5 150 157.5 Steel Plate Type Primer only Primer Primer
/
Color paint
/
transparent cover primer
/
color paint
/
transparent cover methyl ethyl ketone wipe (double friction) 24
hours (
25%
film loss) 175

175 。
7
days (
25%
film loss) >200 >200 adhesion to the 24
hours 4B 4B 5B 5B 7
days 3B 3B 4B 5B
typical features should not be considered product specifications.
The overnight applicable period
In shown above, an important feature of PARALOID™ Edge's non-isocyanate polyurethane technology is the ability to eliminate the correlation between the applicable period and curing speed and coating performance. To demonstrate this characteristic, the primer is sprayed within one hour of preparation and then sprayed at room temperature for 6, 16 and 24 hours, respectively, to determine the impact of applicable time on curing speed and coating performance. In addition to polishing, solvent resistance was tested after one and seven days of coating curing, respectively. All coatings are well polished after 40 minutes of drying, proving that formula aging of up to 24 hours does not affect rapid grinding. Place the coating for 16 and 24 hours before spraying