Progress in the single-part moisture-cured polyurethane primer process

A class of important isocyanate products is a single-part system that can be cured with moisture. Single-pack polyurethane systems are prone to foaming on the surface and therefore require special surface treatment. Since the construction of a single-part primer system is more convenient than a two-part primer system,
Huntsman
has studied a wet-cured
MDI,
called
SUPRASEC
®
9611
, which is
MDI
has low viscosity, less foaming and does not contain
VOC
. This paper describes the physical properties, reactivity and treatment conditions of this new type of
MDI
primer, and compares its performance with the existing primer system.
Introduction
Two-component spray coatings based on polycetamol, hybridization and polyurethane elastomer processes still have successful sales performance in civilian infrastructure, processing plants and more
1,2
. Treating the substrate surface in the right way is the key to the successful application of these coatings
3
. For concrete surfaces, treatment may include chemical erosion or blasting. However, surface treatment does not always guarantee good adhesion or a defect-free coating. Sometimes, incorrect surface treatment can produce unwanted surface stress, or damp substrates can cause excessive degassing. All of these problems can cause foaming or pinholes in the coating surface and may even cause the coating to disengage from the substrate. It will be time-saving to solve the problem after it has arisen.
when faced with a hard-to-handle substrate or surface, sprayers can reduce this problem by applying the right primer. The primer system increases the adhesion of the overall coating system.
when the primer penetrates into the porous surface, a physical bond is formed, thus achieving this. In this case, the construction of the primer increases the overall strength of the substrate. In addition, the paint also has the opportunity to form a chemical bond with the primer. These co-priced keys also increase the overall attachment strength. Finally, the primer acts as a barrier to prevent moisture from releasing from the substrate surface, thus suppressing surface defects that may be encountered if the primer is not applied.
of two-part polyurethane systems over the years have been thought to act as primers, something that has recently
Camargo
and
Skok
discussed
4
. They describe the advantages of a two-component coating by applying durable primers to a damp concrete surface before coating the finish. For formulaters, the main advantage is that the performance of the coating can be adjusted by selecting polyols and mixing ratios, and the curing speed can be adjusted by selecting catalysts.
addition to the above advantages, it is much more convenient to use a single-part system in the field than a two-part system. The use of a single-part system does not have problems such as incorrect mixing ratios, incorrect or incorrect mixing of parts that have limited post-mixing adaptation periods. Single-group moisture-cured polyurethanes are usually made by reacting excess isocyanate with high relative molecular mass polyester or polyether polyols. The amount of free
NCO
remaining in these prejudes is usually
16%
or lower. Once the moisture-cured prejudging is applied to the substrate with a film, the value of the relative humidity controls the curing speed. In pre-polymers,
NCO
reactions in the icing group with active hydrogen in water molecules to produce amines and carbon dioxide. In addition
NCO
the amine group began to react with the amine to produce
until all
NCO groups were reacted off. The
co2
out of the membrane and evaporates into the air. If the film is too thick or the moisture content is too high,
CO2
may be intercepted in the paint film, will produce undesirable foaming phenomenon. If the viscosity of the prejudes is too high, the effect will be further expanded. The higher the viscosity of the prejudging, the slower the
CO2
gas is removed from the paint film, increasing the likelihood that the gas will be intercepted. For this reason, it has become the industry consensus to add solvents to prejudes to reduce viscosity. In addition to reducing the foaming effect, the overall viscosity decrease also helps to penetrate into the substrate, thus increasing the bonding strength. Unfortunately, the addition of solvents in coating systems can significantly increase the
of
VOC. There has been a practice in the industry of not adopting this consensus as much as possible. For this reason,
Huntsman
has developed
SUPRASEC 9611
, a preconjudge that does not contain
VOC
, low viscosity,
MDI
wet curing to be used as a primer on a porous substrate.
six
paint
were evaluated in this study. Most of the primers available on the market are water-based acrylic, water-based acrylic without body pigments, two-part isocyanate
/
castor oil system, single-group solvent-based isocyanate,
VOC
-free single-group isocyanate, emulsified isocyanate
/
water system. The product names and descriptions of the six primers used for comparison are listed in table
1
.
is
the drying process of various systems with
Gardco
's
B-K
film drying recorder at
23
degrees C and a relative humidity of
50%
. Apply each system
20
thick film to a clean glass plate and let it cure for a week. Remove the film from the glass and test the stretch strength, elongation, and
C
mold tearing according to the
ASTM
method standard,
ASTM D 882
and
ASTM D 624
, respectively.
adhesion model is a moist or dry concrete block, the substrate is previously coated with
5
of thick primer by brushing. Dry concrete blocks are placed
for
week at a relative humidity of
50%
23 degrees Celsius. Wet concrete blocks are immersed in water for 3
hours
hours. Once removed from the water, apply primer as soon as it is wet. To spray standard polylycryse formulations based on commercially available
MDI
prejudes at different intervals, the primer spray is constructed using a
GusmerH20/35
rationing unit and a
Graco Fusion
air spray gun modeled
AR2020
. Details of the polyp system can be found in table
2
. A week later, prepare a test post with a diameter of
1
inches on the test adhesion model and use the
Elcometer 106
adhesion tester to conduct a pull-out test to measure the adhesion strength and damage.
results and discussion
physical properties
scraping paint film (
20
mils) on a glass plate to form a bubble-free, defect-free coating that we can use to evaluate each base The physical properties of lacquer chemicals, except emulsified systems (
SUPRASEC 9259
and water by
75
to
25
mass ratio mix). The membrane formed by this system is very brittle and cannot be tested. The physical performance of the remaining systems is listed
table
. The chemicals in the polyurethane structure have the highest overall physical strength.
the RUBINATE 9511
and xylene single-group systems have the highest stretch values, followed by the
SUPRASEC 9611
. This can be expected because the combination of
RUBINATE 9511
and xylene has the highest content of the free
NCO
group, which reacts with water to produce a hard chain segment of radon, which provides strength to the coating. Acrylic emulsions are softer materials with low stretch strength. Acrylic emulsions
#2
without body pigments have physical properties, such as stretching and tear strength, over acrylic emulsions containing body pigments.
reaction
reaction curve for each primer chemical is shown in figure 1
1
. Open time is the time value at which the primer remains liquid. The viscosity of the liquid increases until the glue becomes
,
"glue time" shown in Figure 1. The material loses its adhesive properties, expressed as "finger drying time", which also means that the material is completely cured. Both acrylic emulsions
fastest
at a relative humidity of 50% of the total. The final curing is completed
2
hours. Single-pack moisture cured isocyanate
SUPRASEC 9611
and
RUBINATE 9511
with xylene, which is finally cured within
3
hours
.
these curing curves illustrate typical curing behavior, with increased temperature and humidity and less time required to achieve full curing. Previous studies have indicated that polysaccharide paint can be sprayed before the primer reaches final curing
3
. The adhesion of the polyurethane system was found to increase, even if the polyurethane was applied in a wet or sticky state of the primer. In these examples, it is assumed that the unresponsive
NCO
group in the primer has the opportunity to bond
to the polyyurea substrate co-price, so
so adhesion is increased.
Adhesion
apply six primers to
5
thick brushes of the eardrums on wet or dry concrete. Spray the polysaccharid paint on the primer after
1
hours,
3
hours,
6
hours and
24
hours of primer. The adhesion value between the entire primer and polyp system and wet and dry concrete was measured (figure
2
). For dry concrete,
SUPRASEC9611
,
the RUBINATE9511
and xylene,
SUPRASEC9584
and castor oil system adhesion were found to be improved. The adhesion averages of the two acrylic systems are below
300psi
, slightly lower than the adhesion values of unpainted primers. The average adhesion of the unpasted polyp system on concrete is
400 psi
.
the adhesion value on wet concrete is generally lower than the adhesion value on dry concrete (figure
3
). Before the primer was applied, the concrete was completely saturated with water, and the test conditions represented an absolutely bad condition with water in the substrate on site. The adhesion value of the concrete polyp on concrete without any primer is
100psi
. When the primer is used before spraying polypropyl paint, the adhesion is improved overall. The highest adhesion is the use of
SUPRASEC 9611
or
SUPRASEC 9259
water systems. For both single-group systems, there is a trend for
adhesion
24 hours after 24 hours. Data
more than
24 hours is not assessed in this article, but previous data show a higher adhesion
5
. We believe that
than 24
hours, the chances of staining solidified primers in an industrial environment are also greater.
visual inspection
the visual inspection test post after the adhesion test is completed can provide very important information about the adhesion properties of primers and paints. The adhesion tester and the test post pulled from the concrete block are shown in
photo
figure 4. In addition, photographs were taken of the test post pulled from dry and wet concrete after applying primer
1
hours and
24
hours after applying polysalt paint (Figures
5
,
6
). The dark part of the post is actually a piece of concrete pulled from the concrete block. This type of concrete damage is very promising
,
because it means that the primer has successfully penetrated into the substrate. The columns in the photo appear white to indicate that no concrete has been taken off. We can clearly see that the white color of the polyp coating indicates that the primer is not very effective.
5
5
, the post on the left side of the photo is much more damaged by concrete than by the column on the right. As expected, the adhesion value measured on wet concrete blocks is usually lower than on dry concrete blocks. Figure
5
,
SUPRASEC9611
,
SUPRASEC 9584
and castor oil systems experienced the most concrete damage. Acrylic system is
#1