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Mechanism Resulting Coating Film Blurs and Treatment Methods

Heistman 2013-5-26 12:28:39 Browse:5302 times


Mechanism Resulting Coating Film Blurs
and Treatment Methods





Blurs different density and particle size and the
degree of wetting when used in the production of various pigments , the film
formation process but undetermined settling down in film speed is different.
Small size, low density pigments ( such as carbon black , iron blue,
phthalocyanine blue, etc. ) is relatively slow settling velocity , so that when
the cured film has been completely rendered appearance of color is not needed
even complex color , and Be an unsightly to small particle size , low density
pigment constitutes a significant color to the film.



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Flooding is due to different surface
tension of different pigments , paints have the same affinity for the gap ,
resulting in the emergence of the film surface to produce pigment concentration
distribution is uneven, irregular partial to a higher concentration of pigment
spots.



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Film blurs There are two cases :



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hydrophilic-lipophilic or tank
still floating color imbalance caused by the surface tension



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dried coating film due to the dynamic movement of the pigment
particles floating color difference caused by



1 Static
tank floating color
--- Vertical floating color



After standing for some time
the paint evenly dispersed in the tank , the tank , one or more pigments appear
separated emerge in the surface phenomenon , known static color float tank ,
also called a vertical floating color . Emerging phenomenon such as blue or
black surfaced within black alkyd primer gray nitro tank, phthalocyanine blue
or black with blue or gray tone paint , of course, in some systems may emerge
white .



The reason : the surface
tension is uneven or hydrophilic-lipophilic basic paint palette and paste
imbalance emerges between the surface of the phenomenon



1.1 Static float tank causes color



1.1.1 Hydrophilic -lipophilic balance (HLB):



Use latex, pigments , solvents, co-solvents and additives
in the manufacture of various types of paint . If  HLB values match each material properties of
the coating system is very good, floating color , blur , watershed and other
phenomena will be overcome. As the emulsion used in the future fillers
selected, its HLB value is calm , but you can choose auxiliaries, wetting HLB
value that dispersants, thickeners to adjust the system so that the HLB value
of the balance of the whole system .



We know that the oleophilic substance pro end surface tension of oil
paint in the container storage tank , these lipophilic substances easy to float
up to the surface , from a thermodynamic point of view, the energy of the
system decreases, the system is stable. When the production of latex paint that
is in a container in the static on the floating color , not only ineffective cans
, construction performance is not good , the film state is not good. If the
floating white paint , understand that the slurry HLB value is relatively small
, relatively lipophilic white pulp , so it is imperative the production of
white pulp white pulp as a little too hydrophilic ; If the paint is floating
color paste , pulp understand that HLB value is relatively large , relatively
hydrophilic , when you put on the production of white pulp white pulp for too
lipophilic some paint to prevent floating color .



Match hydrophilic-lipophilic balance (HLB value ) can be produced by
careful selection of a wetting , dispersing agent to complete. Salt dispersant
with an anionic dispersing agent, a hydrophobic group in the ratio of
carboxylic acid to the sodium salt of a lipophilic dispersant , HLB value is
small, with a hydrophobic group and an ammonium salt dispersant floating paint
coating color is also greatly improved. Because when the pigment particles are
wrapped dispersant of this type , not only the pigment particles around the
electrostatic resistance , there is a sterically hindered , and the coating
during the drying process , as the evaporation of water , the ammonium salt is
ammonium volatile , so some of the more hydrophobic such dispersants , the pigment
particles so as to envelop such dispersants and better compatibility with film
material , with such steric structure becomes bulky , so that the coating film
floating color coating drying process , the dynamic process of floating color
has also been suppressed.



Lipophilic substances whose
lipophilic end surface tension , the coating is stored in the container , the
lipophilic substance to the surface float up easily , reduce the energy of the
entire system , the system is stable. When the static floating color , not only
bad effect cans , construction performance is not good , the film state is not
good.



1.1.2 Surface tension
difference affect floating color :



In the process of paint , white pulp production
and the production of paste formulation process is different, making the white
pulp often used anionic or nonionic polyelectrolyte dispersants , and paste is
to use more non-ionic dispersing agent , or with some anionic dispersing agent
and use, and thus the color pigment particles of a white pigment and a
different layer due to the adsorption of a wetting and dispersing agent having
an HLB value is not the same due to its surface tension is not the same .



Ionic surfactants generally larger than the
surface tension of the non -ionic surfactant . Are nonionic surfactants ,
hydrophobic end of its molecular structure is not the same, the surface tension
is not the same , but the molecular structure of the outermost end of the
hydrophobic chain sections maximum contribution of the surface tension .



Low surface tension of the pigment particles
adsorbed easily transferred to the surface, leaving the system is stable , due
to surface tension is reduced to weaken the surface and the droplet , and the
liquid polymerization shrinkage tendency , the additional pressure differential
curved lower surface , which is conducive to the dispersion liquid , and system
stability.



If the surface tension
between the white pulp or paste the difference between the surface tension and
the system is large, you can use wetting and dispersing agent to adjust the
white pulp or paste surface tension , reduce the surface tension of the
difference between its and coating systems to eliminate paint floating color ,
blur .



2 The film dynamic floating color -
horizontal blur



Paint coating pigment
particles during the drying process occurs separation phenomenon called dynamic
floating color , dynamic floating color pigments isolated two cases : one is
the color of the paint coating uneven surface flooding , the other is a
floating color coating good surface color uniformity , but there are
differences in the surface layer and the underlying color , usually refers to
the color development to identify rubbing floating color ; If the presence of
floating color paint , not rubbing grinding surfaces after grinding and rubbing
differences in hue , rubbing grinding process easy separation of the pigment
appears filamentous stripes, rub the surface after grinding dried paint film
edges vortex pattern ( Bénard cells ) .



Dynamic
floating color film processing



Film appears Bénard cells : the surface tension is too
large , the choice of a strong reduction of surface tension of a surfactant ,
such as silicone surfactants , to migrate to the surface of the single
molecular film formed on the paint film during drying , equilibrium surface
tension reduction of the drying process to control flooding vortex action , the
pigment can be separated to reduce the power .



Thixotropic paint additives may be added to the
structure , the network structure formed in the film , form flocs , rapid
recovery coating viscosity , reduced exercise, reducing Bernardo vortex action
to reduce power pigment isolated , or floating color blur can be reduced .



Flooding occurs filamentous stripes coating : coating
compatibility is poor , base paint on the paste color development is poor,
recommend suitable wetting and dispersing agent to improve .



3Paint film blurs the
mechanism and treatment methods



3.1 Floating color pigment affinity
flocculation



Paint pigment dispersion can be divided into
steps :



pigment surface air and
moisture is expelled , and replaced by a wetting and dispersing agent and a
resin solution , the solid / gas interface into the solid / liquid interface ;



over mechanical energy
shock and shear forces , pigment agglomerates rupture, smaller particle size ;



material dispersion must be
stable in order to prevent the formation of uncontrolled flocculation .
Small particle
size, large specific surface area of organic pigments , the particle size is
smaller than the larger surface area of the inorganic pigment flocculation
easier , such as phthalocyanine blue , toluidine red and black is easy to
flocculate . The small size pigment particles move faster particles collide
with the adjacent high frequency , there is more chance of finding low energy ,
high interfacial affinity for the pigment . Color developing agents, wetting
agents or other materials may be such surfaces. Well-dispersed pigments in deflocculation state , a good flow and
leveling , sag resistance and anti- settling . Paint protection is not enough,
there will be a pigment affinity flocculation.



Cause flocculation of the pigment with a
movement of the pigment particles is deteriorated , and the particle size
increased due to flocculation , slow motion , and easily separated from the
precipitate at the bottom .
After the
pigment dispersion , such as thin layer of pigment particles adsorbed on the
surface wetting and dispersing agent or resin , due to the adsorption layer is
too thin , entropy repulsion is not enough, for some reason ( such as freezing
and thawing , the addition of electrolytes ) or compressed adsorbed layer
desorption , adsorption layer off, resulting in contact with the pigment
particles to reduce the surface area , the lower energy state recovery ,
reducing the energy system , the occurrence of flocculation affinity . Floc
produced , will reduce the tinctorial strength , gloss , rheology changes ,
increased thixotropy.



3.2 Floating color affinity flocculation prevention and treatment



Flocs and agglomerates are very similar
structure , the difference between the flocs is a dispersant of the pigment , a
resin solution , instead of air . Between the role of weak floc particle phase
, the general mechanical dispersion can open floc ; agglomerates into smaller
particles , the need to increase the interface and the interfacial energy ,
higher energy system . Such systems are trying to get rid of high-energy state
, revert to the original low-energy state , the need to strengthen the
protection of the pigment particles , increasing protection agents ( dispersing
agent or resin ) . Should be tested before use paste the stability of the paste
before poor stability , increased use of wetting and dispersing agents, pigment
thin protective layer thickness of the protective layer can be added to improve
resistance to flocculation, preventing floating color .



3.3 Flocculation floating bridge
color



Thickening or dispersing agents certain groups
(e.g., hydrophobic end groups ) of a strong affinity for the pigment particles
, adsorption of the pigment particle flocculation bridge formation , resulting
in the floating paint color . Strong hydrophobic associative thickener ( eg PU
class ) due to adsorption of hydrophobic groups on the particles caused paste
bridge flocculation, poor color development . Alkali swellable thickeners ,
because the number of different charges carried by ions , salt cause thickening
film after film drying materials with different charges in the quantity of
titanium dioxide particles in the strong affinity of different polarity ,
floating color different severity there are differences in terms of color
development .
On the one hand can be controlled by the viscosity pigment
thickener to improve flocculation , sedimentation and Bernard whirlpool flow ,
reduce flooding and floating phenomenon, but under certain conditions
exacerbate the paint film blurs . Some strong pseudoplastic associative
thickener with an HLB value greater surfactants have great affinity for the
pigment surface to desorption , causing aggregation and flocculation of the
pigment , and then the system was lowered and coloring power produced film
blurs . Organic and inorganic pigments in the mixed system, in particular
titanium dioxide and phthalocyanine blue , phthalocyanine green , and carbon
black paste when sharing using weak pseudoplastic associative thickeners ( such
as Heistman 620 , Corning 2000 , Luo Haas 2020 , etc. ) get satisfactory color
paint and a good leveling.



3.4
Pigments and color development agent ( polymer ) flocculation floating color



Flocculation of pigment particles and between developing toner ,
resulting in paint floating color , associated with the structural properties
of pigments, polymers, solvents between . Drying the coating process, the main
film-forming material ( polymer ) is similar to one or both of a pigment paste
structure , good compatibility , a large affinity , and other pigment particles
with a large difference due to the molecular structure , low affinity , slight
repulsion or , in the drying process , the vortex action Bernardo , small
pigment particles tend to affinity from the bottom through the coating film was
composed of mesh networks, and other raw materials , up to the conveying
surface of the coating . Affinity of the polymer and the pigment particles is
large enough , these pigment particles are hard to be transported to the
surface , sink or remain stagnant in the bottom . Since the pigment and the
polymer flocculation in Bernardo vortex continue to rise , sink , the tumbling
action , the pigment particle separation occurs , and thus floating color .



In conventional latex -based paint palette , acrylic emulsion presents
the most common floating blue, black, purple -colored paste , Chin white
particles flocculation ; styrene-acrylic , fluorocarbon emulsion paint palette
-based organic pigments and carbon black flocculation , floating white is a
common phenomenon , the data in Table 1 illustrates this regularity : in weakly
polar polymers , carbon black and phthalocyanine blue flocculation, such as
styrene-acrylic emulsion B-96, 296D , the floating white. According to the
different hydrophobic emulsion , floating color also regularly : hydrophobic
emulsion with iron oxide inorganic pigment color is good, Promise carbon black
, easy and weakly polar organic pigments floating white polymer flocculation ;
emulsion system using hydrophilic Promise of carbon black, weakly polar organic
pigment color is good, easy to iron oxide pigments and polar polymer
flocculation floating white. Acrylic emulsion system (AC-261, PA-237), titanium
dioxide flocculation , floating carbon black or phthalocyanine blue, purple,
red and so on. These are typical floating color pigment and polymer
flocculation phenomenon .



Pigment different varieties , different molecular structure , crystal
structure, the geometry is different . Same type pigments ( eg titanium dioxide
) , different companies , different brands of products , the type of surface
treatment agent , the amount of the surface treatment agent is different .
Surface treatment is different, different surface charge , hydrophilic
lipophilic , weather and other aspects of the performance of the differences ,
in which the charge distribution, the impact of the movement of the hydrophilic
lipophilic pigment particles. From the molecular polarity perspective, strong
polar inorganic pigments , organic pigments weakly polar or non-polar .
Titanium and titanium atoms between the oxygen atom electronegativity
difference is large , for the strong polar molecules ; phthalocyanine molecule
atomic electronegativity difference between small , weak polarity ; carbon
atoms of the same species , electronegativity difference is zero , polarity .
From the structure , the surface of the polar surface of the titanium dioxide ;
benzene with most organic pigment , azo , such as phthalocyanine blue (PB15:
3), violet (PV23), red (PR254) having a plurality of benzene , etc. ring , the
carbon black pigment hexagonal layered rings. Since the hexagonal rings of
carbon black layered structure , in preparation of carbon black pigment
grinding paste formulations to control the amount of benzene solvent , because
it takes precedence over structural similarity dispersant adsorbed on the
surface of the pigment resin, etc. , affect the dispersion stabilizing effect
and paste blackness .



Different polymer emulsion particles ,
the use of different monomers , the choice of different kinds and amounts of
emulsifier , the final surface properties of the emulsion particles are not the
same, different structures, different polarity of the strength , the
distribution of the emulsion in the emulsifier molecules different from the
particle surface . Weakly polar polymeric emulsifiers lipophilic end and good
compatibility with the polymer , the polymer can be inserted inside the person
; strongly polar polymeric emulsifier lipophilic polymer phase ends with the
exclusion, emulsifiers reclined polymer surface .
Typically, the polymer
coating carried by a carboxyl group , a light group and the application of an
anionic additive , coating with a negative charge . Styrene- styrene-acrylic
emulsion is added by the coating film weakening the polarity of the inorganic
titanium dioxide attract weakened, and having a cyclic structure carbon black,
phthalocyanine pigments attract increased, there rubbing the coating film
drying means floating phenomenon is the result of the white pigment and the
polymer flocculation .
Through the analysis of the pigment , the polymer
molecular structure discovery , phenylpropyl , fluorocarbon systems are more
prone to carbon black, phthalocyanine blue, flocculation , white floating
phenomena ; the acrylic system , the polarity of the , titanium dioxide and the
polymer coagulated ( Titanium easy stagnant or sinking ) , appeared floating in
blue , red, purple, black and so on.



3.5 Pigments
and color development agent flocculation floating color solutions



Coagulation factors are floating color polymers, pigments
, fillers, solvents types , thickeners, wetting and dispersing agents. Use
wetting and dispersing agents floating color adjustment most effective, and
with less impact on small paint other properties . By selecting compatibility
or matching between the polymer and pigment to solve floating color , so
formulation subject to certain restrictions , and is not fundamentally solve
the floating color .
Selection of suitable
wetting and dispersing agents , adjust the particle surface properties ,
regulate their movement balance, floating color is the best way to control .
Wetting and dispersing agent adsorbed on the surface of the pigment particles ,
has the following features: a stable dispersion of pigment particles , stable
hue, to improve the surface properties of the pigment particles ; improve color
development ; improve or control the floating color phenomenon . Wetting and
dispersing agents are commonly used ionic ( anionic, cationic, amphoteric ) ,
non-ionic , multi-functional type . Pigment wetting and dispersing agent is
adsorbed on the particle surface , changing the polarity of the surface of the
pigment , the pigment portion of the surface configuration changes , forming
the primary regulator affinity substance ( polymer ) between the pigment
particles .



Whatever the
cause of self- colored pigment flocculation floating color , or white pigment
flocculation floating paste color, wetting and dispersing agent can be used to
solve flocculation, improving the surface properties of particles , preventing
or controlling floating color . Floating color process control , two floating
color phenomenon can be converted to each other , to control excessive floating
white additive white excessive flocculation, appeared floating paste
circumstances . Water paint systems , coating paste flocculation occurs
floating white base paint prepared by adding a low-polarity additive -modified
titanium dioxide particles oleophilic , dispersing or wetting agent is added to
the paste in the modified pigment particles in the paste . Anti- Floating
Additives can be anti- white film floating in some systems but also anti- film
floating paste colors. Add in the finished paint anionic wetting and dispersing
agent adsorbed on carbon or organic purple pigment particle surface , improving
the surface properties of the pigment particles , enhances the polarity so that
these non-polar , weakly polar particles of titanium dioxide particles having
the same polarity , and polymer adsorption and flocculation with the same
degree of force , thus drying the coating is quite athletic , restrained the
floating color ( using two floating color pigments are anti- flocculation
principle ) .



3.6 Particle size differences lead to floating color



Particle settling velocity is proportional to the
square of the particle size , but with a square is proportional to the density
difference , a big impact on the size of the pigment athletic ability.
According to calculations, the settling velocity of titanium dioxide is roughly
20 times the settling velocity of red iron oxide , red iron oxide density
greater than titanium dioxide , mixing these two pigments , iron oxide red
float will be concentrated in the surface oxide red. Pigment particle size
differences caused differences in particle motion , color separation occurs in
the paint drying process is not difficult to understand .



3.7 Particle
size differences in floating color solutions



Control condition is floating color pigment particle
size uniform, consistent exercise capacity , but the actual size of the pigment
particles , the density differences . Pigment particle size leads to poor
movement differences , the choice of a suitable wetting and dispersing agent (
some multi- point adsorption polymeric dispersant ) can even choose
hyperdispersant for fine particle size pigment particles in a controlled
flocculation, increased pigment particle size , adjust the movement of
ultrafine particles , slowing the movement of small particles. Large particle
size of the pigment particles can be used small molecules ( such as oligomers )
deflocculate wetting and dispersing agents .



In summary, the paint film blurs the internal and
external factors are:



Internal factors : the degree of difference is the
pigment particle size is too large , causing pigment flocculation , while there
is affinity flocculation , bridge of flocculation. Flocculation of pigment and
color development agent pigment particle motion can cause poor .



External: Paint drying process Bénard cells , or a
variety of flocculation such that the pigment particle size difference between
the differences between the exercise capacity , the coating film was dried with
the difference in movement of the pigment particles have a tendency to separate
in the movement caused by the .



4Summary



4.1 The main
factors of the paint film blurs



1( 1 ) Effect of
pigment sedimentation and flocculation : floating color pigments in the coating
surface flooding is caused by the uneven distribution . The reasons are many,
but the dispersion stability of the pigment is one of very important factors.
Dispersing the pigment in a variety of systems , a pigment flocculation or
settling over the pigment dispersion is isolated , which is the main cause
blurs . Also different pigment particle size and density , moisture or high
moisture content is also not one of the factors to produce the film blurs .



2The influence of
surface tension gradients or uneven HLB values : surface tension gradient is
also one of the factors causing flooding of . Solvent evaporation the film
surface , causing the upper and lower surface tension difference , which will
form a vortex Benard generate blur. Wet coating surface is heated unevenly ,
causing the surface tension difference , the coating will produce a parallel
move , the phenomenon appears blur .



3Solvent evaporation rate and the amount of solvent effects:
solvents on the solubility of the polymer resin for paint rheology of coating
process adaptability , speed and form a coating on the drying of paints are of
great significance. In order to give full play to the role of the solvent ,
preferably using a mixture of several solvents , the solvent to the mixture of
solvent and diluent true .



4Binder ( polymer resin ) effects : different types of paint
base , each resin of different molecular weight and molecular weight
distribution , and the size and distribution of the polar active groups are
different , and polar active groups size and distribution are different, these
differences cause different pigment wetting ability . For mixed pigments , the
pigments on the adsorption capacity of the resin is also different, is not
prone to wet paint coagulation phenomenon, which is the cause of floating color
.



5Affect the
solubility of the polymer resin : This is also one of the causes of flooding
and floating . There are two cases : First, the use of several of the resin not
miscible ; another case is optional solvents and good solubility . If several
resin miscible bad, coupled with different affinity for pigments , solvents and
timely role in eliminating the muddy, but after solvent evaporation , flooding
and floating inevitable phenomenon .



6Pigment to binder
ratio, film thickness : the pigment to binder ratio is small, the thicker the
film more easily blurs .



4.2 Paint
film blurs solution



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Polymer resin having a maximum dissolving power , to make the
solubility parameter of the solvent and a resin similar



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Solvent density should be close to the density of the resin



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As close as possible so that the surface tension of the
solvent and the resin



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Mixed solvent evaporation rate of pay attention to balance ,
true solvent and paint thinner to maintain proper proportions needed



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Increase the viscosity of liquid paint , controlling the film
thickness , the solvent to evaporate slowly evaporate faster alternative
solvent coatings



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Adhere to good initial grinding fineness , the choice does
not blur ( surface treated ) pigments



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More effective approach is to use agents to prevent flooding
and floating



Heistman Functional Chemical(Singapore)Co.,Ltd



Shenzhen Heistman New Material Technology Co., Ltd.



Technical Director  
Junqiang Xu