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Modern water-based paint formulations with additives Evaluation and Application

Heistman 2013-1-16 5:46:05 Browse:5437 times


Modern water-based paint formulations with
additives Evaluation and Application





   The 21st century , the
traditional solvent-based coatings paint still occupy most of the market , but
the water-based paint has accounted for more than 20 % share, and especially in
Europe is growing rapidly in some areas , in addition to high- solids coatings
also have a 10% share , powder coating about 8 % share.



  A waterborne paint
system



   
In recent years , water-based paints are favored mainly due to its
greatly reduce the pollution of the environment , and have easy construction,
quick-drying , better performance characteristics. Water-based system has been
used in many fields, such as : ink, architectural coatings, wood and furniture
coatings and general industrial coatings. In Europe
, waterborne coatings in the automotive original paint is also playing an
increasingly important role.



   
1.1 Bubble Control



1.1.1 Bubbles
Control



Aqueous
systems in the production and use of the process , often encounter the problem
of bubbles . Therefore , in an aqueous system and the generation of bubbles in
the bubble characteristics become the subject of many papers . To achieve
special effects , often adding a surfactant in the system . In an aqueous
system , the surfactant typically comprises a hydrophobic base emulsion
emulsifier in water with the pigment dispersion to form a stable dispersion
required for wetting and dispersing additive , and a substrate in order to
achieve good wetting effect of the added substrate wetting agent.
By migrating to the surfactant interface ( gas / liquid,
gas / solid or liquid / solid ) and work, generally reduce the surface tension
of the coating. An undesired side effect is a liquid containing a surface
active agent will be stable bubbles. Whether liquid containing a surface active
agent will produce a spherical bubbles. Of bubbles generated in two ways: when
the surface active agent , is covered with a thin bubble surfactant,
or a surfactant -free liquid , the bubble generation thin
walled and not mere surfactant coating . Containing air bubbles migrate to the
surface of the liquid has a tendency , then, if the liquid contains a surface
active agent on the performance of the air bubbles generated in the interface
is very different effects.   



1.1.2 Causes
Bubbles



As described
above , the air will be mixed into the water bubbles . So in the paint and
coatings production construction , will lead to bubbles. Further, when the
coating curing reaction gas is generated when the construction of the coating
to the porous substrate is also a problem bubbles . Construction prevent
bubbles in the paint is the most difficult thing , because there are a lot of
air because of the construction was brought into the coating system . Bring an
effective way to overcome the construction bubble is to use membrane filtration
or airless spraying, other construction methods such as roll coating or paint
brush will bring a lot of bubbles.
But airless
spray can also cause the bubble problem , not only will air into the paint stirring
and spray pressure , there will be air into the paint. When the coating out of
the nozzle , it will further be saturated atmospheric air . More serious
problem is also found in the bubbles with gas spray method , when the paint
drying and curing , bubbles because they can not come fast enough to escape ,
causing the bubble burst and the pinhole film morbid .



    1.1.3
Bubble Stabilization Mechanism



   
Spherical air bubbles are generated in the liquid dispersion , it is
only in the medium containing a high viscosity or a surface active agent to
stabilize exists. Bubble rising speed and solid ball , as follows Stokes (
Stokes ) laws. However, the larger the bubble rise velocity deviation from the
theoretical model is often , especially when the surface active agent. Only a
spherical bubble of air accumulation ( nearly spherical hexagonal stacking) the
density exists, and if the bulk density is further increased on the basis of
this , so-called spherical bubbles into bubbles polyhedron , such defoaming to
form bubbles speak more important.



  1.1.4
Defoamer Formulations



   
Defoamers must contain bubbles can affect the stability of the mechanism
described above substances. Typical antifoam comprising : the active substance
, surface-active substances and the carrier liquid . Active substances are
those that can be eliminated to prevent bubbles or bubbles of material
existence , effective material choice depends largely on the nature of the kind
of anti-foaming system is the medium , and the complexity of the coating system
itself makes this choice becomes more than pure liquid more complicated.
Reasonable choice of surface-active substances are important factors defoamers
effect , but also affect the surface effect of the film . Surface active
substances in the antifoaming effect of the impact gas interface , i.e., the
introduction of the active substance ( example: hydrophobic silica ) contact
structure and stability of the bubble , but it can not , as some silicone or
fluorocarbon copolymer to stabilize bubbles, in addition , the surface does not
have general drawbacks ( such as craters or pinholes ) surfactants produced The
carrier liquid may be transferred very uniform generally hydrophobic to
hydrophilic active substance in the medium , the surface tension of such liquid
is generally lower than that for defoaming systems , it may help the wetting of
thin-walled bubble . Aliphatic and aromatic mineral oils, a mixed solvent of
water even if it is an oil / water emulsion can be used as the carrier liquid .
All active substances used in defoamer formulations followed the same mechanism
: by absorption and diffusion of the incompatibility of the surfactant . Select
defoamers active substance depends on the system you want to use the above
mineral oil defoamers acrylic emulsions for low- light and half light ,
styrene-acrylic emulsions and vinyl acetate emulsion is very appropriate. For
the semi-gloss paint to a high gloss , the presence of mineral oil will cause
reduced gloss . Generally, the higher the required gloss paint , defoamers
choice for more demanding . For a given coating system , defoamers have a
unique incompatibility, otherwise , it may migrate to the air antifoam
interface , it can not be stabilized to eliminate the bubbles . the substance
may cause incompatibility fish eyes, craters and surface coating unevenness and
other ills. To overcome these side effects , a series of defoamer formulations
must be an effective amount and type of carrier liquid available. Hydrophobic
polyether-modified silicone generally foaming system (water / surfactant
solution ) incompatibility with a very high , but with the base material has a
typical compatibility . This can have a very high defoaming efficiency , and
can reduce the risk of shrinkage cavity as possible . Since the
polyether-modified silicone even without a hydrophobic solid particles can have
a very high defoaming efficiency , Accordingly , silica can be made without
defoamer , it is not easy to produce adverse effects on the coating. Synthesis
of a hydrophobic gas-phase silica has a significant effect on the defoaming
effect . Fumed silica having a defoaming specific surface area of 50 ~ 400m2
/ g, average particle diameter of 0.01 ~ 1.0¦Ìm. If hydrophobic silica ( fumed
silica / carrier solution mixture ) viscosity close to film , will get a
suitable defoaming . Antifoaming agent for
hydrophobic substances can cause various surface defects. Mainly because of the
point defects can be re- wetted. Depending on the type of defoaming agent and
the corresponding requirements , the hydrophobic silicic acid content in the
final mixture should generally not exceed 15% . For example , high pigment
volume concentration (PVC) of the coating surface tends to produce defects
smaller than the low PVC coating , then, defoamer formulations may contain more
fumed silica .