paint_dispersion in ball mills

8/8/2019 PAINT_Dispersion in Ball Mills

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PAINT AND COATINGS APPLICATION GUID

RAVEN BLACKS


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IntroductionColumbian Chemicals Companys Raven carbon blacks can be used in a widevariety of coatings applications. In this brochure, we will summarize theseapplications, document the proper use of carbon black in the various types ofpaint and coating systems, and help you choose the appropriate Columbiancarbon blacks for use in specific paint and coatings applications.

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Using Raven Blacks In Paint and Coatings Application

T a b l e o f C o n t e n t s

Coatings Defined

General Properties of Coatings

Important Coating Features

Color

Gloss

Rheology

DurabilityOther

Applications and Functions

Automotive

Topcoat

Primer

E-Coat

Industrial Coatings

Architectural Coatings

Universal Colorant Applications

Powder Coatings

Carbon Black Basics

Fundamental Properties of Carbon Black and

Their Influence on Performance

Morphology

Particle Size Distribution

Structure

Porosity

Total vs. External Surface Area

Surface Chemistry

Special Features

Ultra Process Raven Carbon Blacks

Physical Properties of Carbon Particles

Transmission Electron Microscopy


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Selection of Raven Carbon Blacks For Paint & Coating Applications

Matching Performance to Applications Needs

Raven Carbon Blacks Typically used in Paint & Coating Applications (Chart)

Dispersing Raven Carbon Blacks

Recommended Dispersion Techniques for Carbon Blacks Used in Coatings Applications (Chart)

PremixingThe Premixing Process

Premixing, Etc.

Dispersion Measurement

Dispersion Rating Method

Dispersion Requirements

Dispersion Quality and Stability

Rheology

Millbase Viscosity

Resin Solids

Vehicle Chemistry

Premixing

Dispersion Equipment and Methods

Attritor DispersionMedia Mill Dispersion

Ball Mill Dispersion

Limits of the Ball Mill

Formulating For Ideal Ball Mill Viscosity

Daniels Flow Point Method

Sample Flow Point Curve (Graph)

Determining The Flow Point

Finding the End Point

Dispersion Checks

Flocculation Tests

Cutback or Reduction of Milled Pastes

Colloidal Shock

Dilution of Aqueous Systems

Taking Advantage of Beaded Blacks

Performance Measures

Appearance

Color

Gloss

Durability

Customer Assistance

The statements, opinions and/or recommendations contained herein are based on information,

data, reports or tests believed to be reliable. HOWEVER, COLUMBIAN MAKES NO WARRANTY OR

GUARANTEE OF ACCURACY OR COMPLETENESS IN CONNECTION THEREWITH, NOR, WITH RESPECTTO ANY COLUMBIAN PRODUCTS INVOLVED, ANY WARRANTY OR MERCHANTABILITY OR FITNESS

FOR A PARTICULAR PURPOSE OR USE. Statements concerning the possible use of Columbian products

are not intended as recommendations to use such products in the infringement of any patent.

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t a b l e o f c o n t e n t s c o n t .


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PAINT & COATINGS DEFINED

General Description

According to Websters New International Dictionary, a coating

is a layer of any substance used as cover, protection,

decoration, or finish. Although its definition is simple, acoating can be very sophisticated in terms of composition,

curing chemistry, and application performance.

Major advances in coating technology have been achieved over

the last two decades. Prior to the 1970s, low solids

solventborne coatings were the market standards. However,

concerns over the impact of solvents on health and the

environment produced a surge of new coating technologies

focused on reducing volatile organic content (VOC). Several

alternative formulation schemes continue to be developed to

address the need for lower VOC.

High solids solventborne coatings were a naturalprogression from low solids coatings to reducing organic

emissions. Although conversion to high solids has been effective

in reducing solvent emissions, there are still regulatory influences

outside the paint and coating industry that have set lofty goals

driving further VOC reduction.

Powder coatings have been particularly attractive for various

applications due to their 100% solids content along with their

cleanliness compared to liquid coatings and ease of application

via fluid bed or electrostatic methodologies. However, their

primary disadvantages have been the capital requirement for

conversion, formulation inflexibility after production, the overall

appearance and performance after application, and waste

management with regard to handling, overspray capture, and

disposal. Despite these shortcomings, powder coatings maintain

a strong presence in the coatings industry and the technology

continues to develop.

Radiation curable coatings have the advantage of having a

physical form similar to conventional coatings. This permits the

coating user to utilize conventional equipment for application

while yielding attractive performance properties commonly

observed with traditional coatings, i.e., good lay, appearance,

and physical properties. In addition, very fast curing with

virtually no organic emissions can be achieved using equipmentavailable at a nominal cost, especially for UV cure. The radiation

curable coatings market continues to grow at a healthy pace

and their use should expand as the technology matures.

Waterborne coatings have experienced substantial growth

over the past few years. Latex and emulsion coatings are the

most popular, with primary uses being in, but not limited to,

architectural and maintenance applications. Waterborne

coatings yield lower VOC than their solventborne counterparts,

but the co-solvents required to establish acceptable properties

contribute to organic emissions. Waterborne coatings also tend

to have lower solids content than conventional solventborne

coatings. Further advances in formulations and applications

along with more stringent VOC regulatory requirements will

undoubtedly increase the popularity of waterborne coatings in

the future.

IMPORTANT PAINT & COATING FEATURES

Color - The color we observe a paint to have is the function of

the optical properties of the pigments used in the coating. Most

pigments are selective in that they absorb and scatter certain

portions of the visible spectrum more completely than others.

Carbon black can be used to increase the amount of light

absorbed by a coating.

The color properties of a coating can be measured

instrumentally. Greatly simplified, instrumental readings can be

used to describe the color by converting the spectral reflectance

data into a position in three dimensional color space. The

Hunter L,a,b color measurement method system positions the

specimens color in a space defined by its position along threeaxes: L axis for lightness/darkness

a axis for redness/greenness

b axis for yellowness/blueness.

The relative color of two samples can be described by the

differences in their positions along the L, a, and b axis. The total

color difference between two samples is described, in the

Hunter system, by DE or the square root of the sum of the

squares of their L, a, and b differences.

Columbian observes an excellent correlation between visual

color perception and the color values obtained using

spectrophotometers equipped with 0/45 geometry for

measuring jet black colors.

Carbon blacks presence primarily reduces the L value of the

coatings measured color. This property can be to achieve mass

color (jetness) where the carbon black is used as the sole

pigment or to darken a tint. Well dispersed carbon blacks range

from neutral to blue in undertone. Less well dispersed carbon

blacks tend to be brown in undertone.

Gloss - The gloss of a coating is a function of its surface texture.

The surface texture of a cured film is influenced by vehicle type,

solvent choices, wetting agents, pigment choice, the surface

chemistry of the pigment, the pigment concentration, and the

3 Using Raven Carbon Blacks In Paint and Coatings Applications

L=100

L=0black

white

+a red-a green

-b blue

+b yellow


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APPLICATIONS AND FUNCTIONS

Automotive topcoats provide the beauty we see when viewing the surface appearance of an automobile. The topcoat is there

to protect and to provide the desired surface appearance.The 8nm particle size and the surface chemistry of Raven 5000 Ultra IIhave made it widely accepted as the pigment of choice for these masstone applications, which require ultimate jetness, gloss, and

UV protection. Raven 5000 Ultra III is the leading edge product for the automotive market. It provides greatly enhanced purity, low

residual salts and very low sulfur along with previously unattainable jetness.

Automotive Primers are what we do not see, but act as the foundation of the surface that we appreciate. Requirements includedispersibility, purity, and in some cases, electrical properties. Products of choice include the Raven 400 series.

Automotive E-Coatprimers fall into two categories, those that are themselves applied by electrodeposition, and those whichare conductive and applied to non-conductive substrates that facilitate the application of the next paint layer by electrodeposition.

The blacks of choice for the first category again include the Raven 400 series blacks.Conductex 975 Ultra is well suited for the

conductive primers used as a foundation for electrodeposition.

Industrial Coatings appear on the surface of equipment and machinery. They have a very broad range of pigment requirementsThese systems are not limited to a particular vehicle type, application method or color. Columbians Raven carbon blacks products,

ranging from the lampblack replacements to high color carbon blacks, find use in these applications. Carbon Black choices need to

be based on the specific requirements of the individual application.

Architectural coatings use carbon black primarily as a tinting pigment. Coarser, easier to disperse carbon blacks are often thepigment of choice. Where UV protection is required, blacks approaching the 20 nm fineness range are preferred. Requirements for

tinting often include stability, resistance to flooding and floating, and blue undertone properties. These requirements are filled by

the lampblack replacement carbon blacks for the ultimate in blue undertone in tint applications, and by the low to medium color

blacks where cost may be a major factor.

Universal colorants are used to pigment both waterborne and oil based coatings. Universal colorants can consist of a pigment

dispersed in a solvent combined with co-solvents, diluents, and wetting agents. Rarely do they include resin solids. This applicationhas special requirements, including long term shelflife in the form of color stability, flocculation resistance, viscosity stability, and

freedom from settling. Coarse carbon blacks tend to be the easiest to stabilize, therefore have become well accepted in universal

colorants.

Powder coatings have provided a method of application essentially free of VOCs. The basic procedure for preparation is todisperse the pigment in the desired resin system, and then convert the dispersion into powder. Dispersion is carried out using a

continuous process, with a compounding extruder feeding out through a sheet die, granulated, and subjected to post grinding to

convert the dispersion into powder form.

The ability of the black to be fully dispersed by the relatively low shear of the extruder process is key to the success of the product.

Carbon black selections are certainly based on color requirements, but are also based on the dispersion efficiency. Treated blacks

can demonstrate advantages in this application.

Using Raven Carbon Blacks In Paint and Coatings Application

level of dispersion achieved. Carbon black tends to function as

a vehicle absorber. This will typically result in a directional

reduction in gloss. The higher the vehicle demand the black has,

the more significant the reduction in gloss may become.

Choosing a carbon black with good dispersion properties and

low vehicle demand would be methods of maximizing gloss.

Rheology - The viscosity of a paint is designed around the end

use and application method. Typically, increasing pigment surface

area, structure, and concentration will increase the viscosity of a

coating. Carbon blacks particulate nature, and its affinity for the

vehicles it is dispersed, tends to increase the viscosity of the

unpigmented vehicle and make the system less Newtonian.

Surface treatment of the carbon black used can provide

reduction in viscosity and improvement in flow properties.

Durability - The ability of the paint film to stand up to the

ravages of exposure to the elements and physical abuse is a

measure of durability. Carbon blacks excellent absorber of al

wavelengths of light make it a good choice for providing UV

protection for the paint system it is dispersed in. Finer blacks

tend to absorb more UV than coarser ones, thus finer blacks are

preferred where UV protection is required. Increased loadingsalso result in increased UV absorption.

Freedom from pigment impurities is important in maximizing a

paint films durability. Columbians Ultra carbon black

technology results in carbon blacks with impurities(ash, residue,

and residual metals) typically an order of magnitude lower than

their forerunners.


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FUNDAMENTAL PROPERTIES OFCARBON BLACK

Several fundamental carbon black properties that influence

the final paint and coating properties include:

Fineness, or Particle Size Distribution

Structure, or Aggregate Size/Shape Distribution

Porosity, or Pore Size Distribution, and

Surface Chemistry, or Surface Activity Distribution

Carbon Properties Influence Performance.

Various carbon properties that can have an important influence

on the performance of paint and coatings applications include:

Smaller Particle Size (Higher Surface Area) Increases Blackness Increases Tint Strength Increases UV Protection and Absorption Increases Electrical Conductivity Increases Vehicle Demand and Viscosity Lowers Dispersibility

Higher Structure (Increasing DBPA) Reduces Blackness and Tint Strength Improves Dispersibility Increases Vehicle Demand and Viscosity Increases Electrical Conductivity

Higher Porosity (Larger differences between NSA and

STSA) (Note: NSA and STSA measure total surface area and externalsurface area respectively)

Increases Vehicle Demand and Viscosity Increases Electrical Conductivity Enables Reduced Loadings in Conductive Applications

Increased Surface Oxides (Higher Volatile Content ) Improves Vehicle Wetting Reduces Viscosity of Liquid Systems Lowers Electrical Conductivity

Additional carbon black properties that may affect the

performance of an paint and coating include other constituents

of the carbon black such as sulfur, ash, residue, etc. and its

physical form i.e. : powder or beads.

Carbon black fundamental properties are distributional. A givengrade of carbon black, for example, cannot be produced at asingle particle size but is made up of a range of particle sizes. Ingeneral, we refer to the mean particle size, but the breadth andshape of the distribution are also important factors in theperformance of the paint and coating.

ULTRA PROCESS RAVEN CARBON BLACKS

Ultra technology is a commercial development of theColumbian Chemicals Company directed at manufacturingcarbon black with extremely high purity. Carbon blackgrades produced using this innovative technology typically haveash and 325 mesh residue levels one-tenth that of gradesmanufactured with conventional technology. The inclusion ofUltra in a Raven name indicates a product for paint andcoatings that can be relied on to demonstrate improvements inease of dispersion, gloss, stability, and consistency.

PHYSICAL PROPERTIES OFCARBON PARTICLES

Transmission electron microscopy with automated imageanalysis (TEM/AIA) is routinely used by Columbian ChemicalsCompany to determine particle and aggregate size and shapedistributional properties of carbon blacks. An advanced TEM

technique utilizing multiple images of aggregates has recentlybeen employed to gain more insight into three-dimensionalaggregate structure. As aggregates are rotated using thegoniometer in the electron microscope, different aspects of theirstructure are ascertained at different angles. Three dimensionalmodels of the aggregates can be constructed from multipleaggregate images. On average, highly structured, complexaggregates exhibit larger changes in projected image propertieswith rotation than aggregates of low DBPA (low structure)grades.

The figure below depicts an electron micrograph of anaggregate (left)and a projected image of a three dimensionalcomputer model of the same aggregate (right) at identicalmagnifications. Although the pictures themselves are two-dimensional, the model image (right) clearly conveys a sense ofaggregate three-dimensionality and helps the observer gaininformation about the spatial relationships between particles inaggregates. In addition, these computer models may be rotatedto any desired orientation for viewing and measurement.Continued development of three-dimensional analysistechniques will enable further understanding of how aggregatestructure influences applications properties.

High Structure Carbon BlackTEM Image 3D Model

~50,000 X magnification



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Columbian makes more than 20 different Raven carbon blacks for paint and coating applications. The range of applications is broad,

covering basic primers, universal colorants, conductive coatings, industrial finishes, and automotive topcoats, to name a few.

There is a Raven carbon black to fill any coating application need

The following section discusses the dispersion methods available to take full advantage of the properties available in the carbon blacks used.

MAKING THE SELECTION DECISION

Columbians Raven carbon blacks have set a benchmark of quality and performance, featuring a range of carbon black products

for paint and coating applications that meet or exceed the expectations of their users. We are proud of the Raven reputation for

outstanding quality and service.

There is a Raven carbon black for every paint and coating application. However, should you find an application that requires specia

properties, Columbians Technical Service, Product Technology and Laboratory Support personnel will be there to find a solution to

meet these requirements.

This section provided you with the background and information needed to select the appropriate Raven carbon black for your

paint and coating application need. The table below is a guide to aid in the selection of carbon blacks for specific applications and

only serves as an indicator of the blacks typically used and/or designed for the paint and coating types shown.

Using Raven Carbon Blacks In Paint and Coatings Applicatio

GradeHigh Color

Automotive, Furniture

Medium ColorIndustrial, Equipment

Low ColorUniversal Colorants, Tints

Lampblack Types

Blue Undertone

TintsLow energy dispersion

Conductive

Special

Raven 5000 Ultra III1

Raven 5000 Ultra II

1

Raven 70001

Raven 35001

Raven 2500 Ultra

Raven 1500

Raven 12551

Raven 1200

Raven 1170

Raven 1100 Ultra1

Raven 1060 Ultra1

Raven 10401

Raven 10351

Raven 1020

Raven L

Raven 1000Raven 890

Raven 850

Raven 460

Raven 450

Raven 420

Raven 410

Raven 22

Raven 16

Raven 141

Raven H2O1

Conductex 975 Ultra

Raven Carbon Blacks Typically used in Paint & Coatings Applications

1post treated


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DISPERSING RAVEN CARBON BLACKS

This section describes the various methods and techniques used toproperly disperse the Raven carbon blacks for your paint andcoating applications. The previous section showed how to selectthe right Raven carbon black for the needed application, whilethis section details ways to optimize the use of Raven carbonblacks.

The chart below provides a quick overview of the recommendeddispersing techniques for Raven carbon blacks used in paint andcoating applications.


Dispersion Techniques Recommended For Carbon Blacks Used In Paint and Coating Applications

Dispersion

Equipment

Premix

Requirement

Dispersion

Classification

Recommended Raven

Carbon Black Form

Media Mills

Two Roll Mills

Ball Mills

Attritors

Rotor Stator

High Speed Impeller

Medium Shear

High Shear

Medium Shear

Medium Shear

Low Shear

Low Shear

Required

Desirable

Not Needed

Not Needed

Not Needed

Used Primarily as a Premixer

Powder preferred,Beads can be used with good premix

Beads

Beads

Beads

Powder

Powder

The following section describes recommended carbon black

dispersing techniques and milling requirements. This informationwill assist you in fully utilizing all the advantages of the full array of

Raven carbon blacks for your paint and coating application needs.


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Raven carbon blacks provide the state-of-the-art blacks for

paint and coating applications. But in order to take full

advantage of the potential of any carbon black, several steps

must be taken, including:

Incorporating the carbon black into the vehicle system Displacing the air entrained in the carbon black with the

vehicle (wetting out the pigment) Reducing carbon black macroagglomerates to

microagglomerates or aggregates through grinding

Raven carbon blacks will provide optimum performance in

jetness, undertone, tint, gloss, stability, and rheology when

these steps are successfully carried out

DISPERSION MEASUREMENT

The paint and coating industry uses a variety of tools, such asthe Hegman and PC grind gages, to characterize the dispersionlevel achieved. Different groups can utilize and interpret these

tools in many different ways.

Grind gages rely on a simple principle. When a dispersionsample is drawn down from the deep end of the gage towardthe shallow end, the undispersed agglomerates will protrudefrom the surface of the paint and coating in the channel if theagglomerates are larger than the depth of the gage. Theseprotrusions are seen as specks on the surface of the paint andcoating path on the gage.

A Hegman gage, with a channel ranging from 100 to 0 deep,is used to determine the grind or the point at which nofurther increase in the frequency of specks can be observed. Thedepth of the channel at the grind, measured in microns, is

noted. The Hegman gage scale ranges from 0 at the 100 depthto 8 at the 0 depth. An 8 Hegman grind rating is ideal. A 0Hegman grind rating is poor.

The grind gage is only a basic tool for describing the relativedispersion performance of a paint while still in liquid form.Columbian uses gloss measurements, light microscopy andelectron microscopy combined with automated image analysisto complement the grind gage ratings and to evaluatedispersion.

DISPERSION REQUIREMENTS

CARBON BLACK LOADING

For efficient and economical paint and coating production, thequantity of black used in the dispersion process should be ashigh as possible, yet consistent with good mill performance andthe type and quality of product being produced.

Different paints and coatings require different levels ofdispersion. In many cases, poor performance of a black paintcan be directly attributed to insufficient pigment dispersion. Thisexemplifies the importance of developing and maintaining gooddispersion levels.

Excellent dispersion is necessary for coatings with stringentrequirements for appearance properties. For instance, ultimatecarbon black dispersion is usually not necessary for primerapplications. However, better control over paint and coatingproperties such as color, undertone, viscosity, gloss, durabilityetc., can be accomplished by attaining a good grind level (


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PROBLEMS AND LIMITATIONSOF HIGH LOADING

Numerous problems can occur when using a high loading(>20%) to manufacture a carbon black dispersion. While highcarbon black loading is desirable, imitations on the amount that

can be used must be considered. The following describes theselimitations:

Millbase ViscosityThere are many types of milling equipment on the market whichvary in their effectiveness to provide adequate dispersion levelswith carbon black. The single most important factor in thisvariation is the viscosity of the millbase. Dispersion equipment,such as a three-roll mill, is designed to accommodate highmillbase viscosity. Media mills, attritors and ball/pebble millsrequire lower viscosity or elevated temperature to handleconcentrates.

Resin Solids

The amount of resin solids present in the grind will influence thefinal stability of the millbase. Reduction of resin solids tends toreduce stability due to less resin available to establish a stericbarrier between carbon black agglomerates. Over time,millbases will exhibit increased thixotropic characteristics (falsebody), along with progressive stiffening, as vehicle solids arereduced.

Vehicle ChemistryCompatibility between the vehicle and the carbon black candramatically affect dispersion time and the final stability of thepaint and coating. Good interaction between the vehicle andcarbon black will facilitate wetting and accelerate the dispersionprocess. In other words, better carbon black/resin interaction

means better paint and coating stability.

In any situation requiring high loadings, vehicles capable ofhandling such loadings should be used.

The proper choice of effective wetting and dispersing agents canprovide vast improvements in paint and coating performance.Also, paint and coating manufacturers should evaluate thedispersion and rheological advantages associated with post-treated blacks in their applications.

PREMIXING

As can be seen by the chart at the beginning of this section, notall dispersion equipment requires premixing of the carbon blackwith the vehicle. To ensure best operation on media mills andtwo-roll mills, however, we recommend that premixing be doneto ensure the best operation on the mill.

Proper pre-wetting and removal of entrained air on the blackduring the premixing stage can save appreciable working timeon the dispersing mill and can improve the stability of the paintand coating.

Practicing good premixing with the vehicle and a high qualityRaven carbon black provides a great number of advantages,such as: Better pre-wetting of black. Removal of the bulk of entrained air. Initiation of the dispersion process. Earlier effective usage of additives such as dispersing and

wetting agents, extra driers, etc. Sufficient time for partial equilibrium to take place between

vehicle components and the Raven carbon black surface. More uniform initial viscosities which provide for optimum

shearing. Faster and more complete dispersion on the mill. Less puffiness of mill paste due to entrained air and

reduced degradation of vehicles oversensitive to oxidationand polymerization.

The Premixing Process

Premixing should begin with small quantities of the vehicle inthe premixer while adding just enough Raven carbon black tocreate a fairly stiff but mobile paste. More vehicle is then addedand thoroughly blended, followed by the addition of moreRaven carbon black. This cycle is repeated until the charge inthe mixer is completed. Mixing time should continue as long aspossible for a more thorough premix.

Choosing a Premixer

Todays paint and coating makers use a variety of premixers, theCowles-type high speed mixer is a typical example. Coatingmanufactures can select from two basic dispersion methods.They can choose to produce their end products in one step oruse a base dispersion method where the pigment concentration

in the dispersion phase is well above that of the finished paintand coating. The individual manufacturer will make this decisionbased on his equipment capabilities and needs.

Paint bases typically have fairly high viscosity, which is cut backwith the appropriate vehicles to a proper consistency afterprocessing. In this type of premixing process, a considerableamount of carbon black dispersion may be accomplished.When very high black concentrations are used, paint bases candemand high temperatures to maintain workable viscosities.

Premixing, Etc.

Additional items that should be considered in the premixing

process include:

1) Cutting back of heavy paint base should be carried out withgreat care. The vehicle and thinners must be added slowly in smallincrements with constant stirring to ensure homogeneous mixtures.

2) Aging of the premixed base paint before mill dispersion is veryhelpful since it allows further pre-wetting. In this process, however,heat losses must be considered. Upon aging, the surface of the

carbon black can absorb the dispersing agents and other

ingredients from the vehicle, thus establishing an equilibrium.



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High Plasticity DispersionThe use of two-roll mills involves the principle of high plasticitymilling. These mills consist of two closely-spaced rollers that

frequently differ in surface speed. The distance between therollers is often being less than ~1-2mm.

Two-roll mills are occasionally used to achieve ultimatedispersion when compounding carbon black in such products asnitrocellulose lacquers for automotive coatings.

High plasticity dispersion of carbon blacks has been used bypaint and coating makers for many years and provides manyadvantages, such as:

Better wetting

High degree of carbon black dispersion High gloss

High pigment loading in base dispersion Better development of color and undertone Production results that would be difficult by other means Improved effectiveness in the use of dispersing agents

Many resins and vehicle solids can be used for high plasticity

dispersion paint and coating products. Warning: Care must be

taken to avoid a fire or explosion when employingnitrocellulose.

The high plasticity process is a reliable dispersion method forinducing good color values, gloss, and other desirablerequirements. However, as in all types of dispersion, requisitesinclude the use of the proper dispersion media, dispersingagents, solvents, and ratios of carbon black to vehicle solidscombined with sufficient time to achieve the desired level ofdispersion.

Automotive topcoats and other types of coatings such asnitrocellulose lacquer furniture finishes can employ the end

products of such high plasticity dispersion techniques. The useof the two-roll mill is not a requirement for this process; otherequipment, such as a heavy duty sand/shot mills, or ball mills canbe employed to attain very satisfactory results.

EXAMPLE - High Plasticity Dispersions For Liquid Paint & Coatings

Several basic methods are available for making automotive, furniture and similar black paint and coatings. These dispersions canbe carried out directly as a liquid in ball mills, attritors, or any variation of shot mill or in a solid or plastic phase, followed by dilutionwith large amounts of solvent.

In two-roll mill usage, high plasticity compounds are handled with resins, such as acrylics, nitrocellulose, cellulose acetate, andalcohol soluble resins. All Raven carbon blacks, from the finest through the coarsest grades, can be employed.

In this process, the proportions of ingredients used and the temperature of the mill should allow the batch to be soft enough toband around the two-roll mill at the beginning of the milling process. As the temperature increases and the black disperses, thebatch stiffens due to the surface area of the black becoming available for vehicle adsorption. Temperature controls are required toregulate the stiffness of the batch and to prevent excess loss of solvent and decomposition of the vehicle.

Depending on the product, the batch can be sheeted off the two-roll mill, either as a flexible or brittle sheet, and cut back furtherwith reducing vehicles and solvents in a suitable mixer. The products that are sheeted off the two-roll mill can be broken up intosmall pieces and stored for future use.

Higher gloss will prevail in paint and coatings when the carbon black has been well dispersed in this manner. A superior degree of

dispersion also results in blacker masstone and bluer undertone.

DISPERSIONNow that we have discussed premixing requirements, we can address the dispersion process.



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Attritor Dispersion

An attritor is essentially a ball mill set on end that replaces therotation of the vessel with a rotating vertical shaft having pinsarranged perpendicular to the shaft. The pins serve to agitate aball charge as they pass through the batch. The attritor has beenshown to reduce the time required to achieve full dispersion

considerably as compared to a ball mill. Attritors have similarrheological requirements to ball mills. Due to this, formulationsthat work well in a ball mill will require little adjustment to workin an attritor.

Media Mill Dispersion

In a broad sense, media mills can be considered as an extension

of ball mill technology using smaller media. The dispersion

process of a media mill is similar to a ball mill in that dispersion

is achieved through forces imparted by the media upon the

pigment. However, a media mill depends on centrifugal forces

applied to the media by flat disk impellers rotating at high

velocity to achieve dispersion, whereas a ball mill relies ongravitational forces to provide the cascading action of the

media.

Advantages offered by the media mill include speed of reaching

a finished dispersion (minutes as opposed to days for the ball

mill), being a continuous process, the ability to work successfully

with high viscosity systems, and its small size relative to the

formulation quantity being dispersed. A disadvantage of the

media mill is that it usually requires premixing of the ingredients

in the formula to be efficient.

Steel shot, glass beads, and ceramic beads are among the broad

variety of media being used in media milling.

Typically, dispersion in media mills can be enhanced by using

smaller media to increase the number of potential points of

impact and maintaining the volume of media corresponding to

80-90% of the internal mill volume. When a media mill is

operated, the media tend to become evenly distributed in the

mill. A reduction of the volume percentage of media charged in

the mill will result in the media becoming too separated to

disperse the pigment efficiently. Using too much media in the

mill will result in excessive media wear.

With experience, the paint manufacturer can achieve excellent

results with a media mill.

Ball Mill Dispersion

The ball mill has attained important status among the paint and

coating makers production techniques. This mill disperses

pigment as a result of the cascading action of the media within

the closed mill. As the mill is rotated, the viscosity of the

formulation causes the media to be lifted around the perimeter

of the mill. When the forces of gravity overcome the lifting

action of the formulation, the media cascades down upon itself,

creating compression and shearing forces on the pigment,

which result in the eventual dispersion of the pigment. The

beaded form of carbon black, pioneered by Columbian

Chemicals Company, has helped to made the ball mill popular

for dispersing carbon blacks.

Our studies of carbon black dispersion in a steel ball mill showedthat a careful balance of resin or vehicle solids, carbon black,

and solvent permits increased loadings of black with greateroutput of dispersed black.

The use of the beaded form of carbon black generally results inbetter dispersion quality in a ball mill. This improved dispersionquality appears to be due to the controlled wetting allowed bythe bead as compared to the high initial viscosity encounteredwhen a powdered black is added to a liquid vehicle system.Such viscosity can actually hinder the tumbling action in the ballmill and thus hinder dispersion.

The ball mill is widely used in the manufacture of a broad rangeof paints and coatings.

Limits of Ball Mill

The viscosity of the pigmented vehicle limits the effectiveness ofthe ball mill (or similar type of mill). In this type of mill, a verysatisfactory dispersion of carbon black can be obtained onlywhen the proper viscosity is used in the millbase. The beadedform of carbon black is available in practically all of theColumbian Raven paint and coating grades.

Some of the factors that must be considered in using a steel ballmill of this type are:

The best physical form of carbon black beads The best type of carbon black for the paint and coating The speed of mill and interior design The proper size ball and the quantity to be used

for best results The volume of paint and coating or paint and coating

base to be dispersed The consistency or viscosity of paint and coating to

be dispersed The temperature controls The cleanliness of the mill from one batch to another The timing of addition of formula components

Viscosity and yield values of the batch being dispersed are themost important items to be considered in ball and pebble milloperations. This is assuming that the proper design of lining,baffles, size of charge with the proper balls or pebbles selected,and control of the temperature and speed are used. If the paintor coating base is too thick, the media will not make propercontact, they will not cascade properly, and the carbon black willnot be dispersed. Conversely, if the batch is too thin, the balls orpebbles will grind against each other with minimum efficiency ofdispersion. In addition, contamination from the media mayoccur.

Laboratory work at Columbian Chemicals on steel ball mills hasshown that, in a normal steel ball mill dispersion, a good startingpoint would be a viscosity between 1600 and 2400 cps atmoderate shear (10-100 sec -1).



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Determining The Flow Point- The Daniel method requires modification for carbon black due to the significant change in exposedsurface area as the carbon black is dispersed. When determining the flow point for carbon blacks, the test should be carried outin a small, open top media mill, using a pint can, sand or shot, and a high speed mixer equipped with a 50 mm disk.

The media and pigment should be gently mixed together. The vehicles should then be slowly added with sufficient disk speed tocreate a vortex in the mini sand mill. When a flowing condition is achieved, the mixing should be allowed to proceed to ensure thatthe blacks surface area has been exposed to the vehicle. Small additions of the vehicle will be required as the black disperses tocompensate for the additional surface area being wetted. The flow properties of the mixture should be determined after dispersionhas been achieved.

The modified Daniels method can be used to quickly develop a mill base formulation with sufficient vehicle for good mill flow.However, this flow point formulation does not provide good colloidal stability. It is therefore recommended that the vehiclecomponent be increased by 5% to 10% at the end of the dispersion cycle to provide colloidal stability and to reduce the potentialfor flocculation during storage or letdown.

Temperature control is another important consideration in finding the proper formulation. If the formulation requires reduction inviscosity by heat, which is true in many important cases, then the temperature controls must be adequate. If the temperature is notkept uniformly high, a batch may thicken up, which would cause dispersion to be minimized.

Despite all these factors and precautions, ball and pebble mill dispersions are relatively easy to attain with normal care. This methodis also an efficient and clean operation requiring minimum attention once the various controls are set.


This starting point, however, must be adjusted locally to a higher or lower level depending on the many factors involved, i.e., type ovehicle, behavior under various temperature conditions, type of black in relation to vehicle, and many other considerations.

Formulating for Ideal Ball Mill Viscosity

Daniels Flow Point Method- F.K. Daniel developed a method to optimize both pigment concentration and vehicle solids for bal

milling. For pigments such as TiO2, the method applies simple stirring to incorporate the pigment into a vehicle using a range ovehicle solids. The test calls for the slow addition of vehicle until flow is achieved.

The following illustration can be used to detect desirable flow properties :

The spatula is dipped into a pigment/vehicle mixture and is withdrawn. The mixture will flow off the spatula and terminate with anelastic snap back towards the spatula once an ideal flow is attained. When the viscosity is too high, the mixture will exhibit, at best,limited flow. If too much vehicle is added, the elastic snap will be lost.

This effect can also be shown using a flow point curve (sample curve right). The amount of vehicle per unit of pigment used isplotted against the vehicle solids.

The points on the plot are then connected to determine the minimum point on the flow point curve. The minimum point on the

curve indicates both the pigment concentration and the vehicle solids best suited for dispersion in a ball mill.

70

60

50

40

30

20

100

10 15 20 25 30 35 40 45 50% Vehicle Solids

Vehicle

Demand,

gvehicle/10gC

Flow Point


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Fine particle size Carbon Black

Fully Dispersed Micro -Flocculated

TEM @ 25,000 X magnification

EXAMPLE - Primer Preparation in Steel Ball Mills

Primer can be made in a steel ball without undue precautions. However, there are a few simple everyday rules that should be followed.

A superb dispersion is not required in this situation, since high gloss is not a factor in primers. The primary function of a primer isto provide adhesion of the next layer of paint and the primers substrate. In order to maintain low production costs, the minimumtime should be employed to disperse the bead black.

Beaded carbon blacks such as Raven 450 and Raven 410 are recommended for primers for the following reasons:

Freedom from dust Ease of handling Fast incorporation of the black by the vehicle Less air involved Controlled surface area development in the early stages

of milling resulting in faster dispersion of the black. Ease of Dispersion

In producing primer coatings, a combination of vehicle and surfactant should be chosen to benefit from the advantages of thedispersing effect, as well as the lowered viscosity and increased flow which are so important in this operation.

The time involved for dispersion depends on mill efficiency, vehicles, etc. Typically, eight hours or less is required for ball milling a primer.

Finding The End Point - The end point of the dispersion cycle is indicated by the black being dispersed to a grind finenessdemanded by the customers requirements. For those new at this type of operation, samples should be taken from the ball mill atvarious intervals, starting after four hours of grinding. Additional dispersion checks should be made periodically until the desireddispersion quality has been attained, guaranteeing a reasonable uniformity of product. The grind can be determined with the useof grind gages and/or filtration to determine if a specific residue level has been achieved.

The stability of dispersion and viscosity of the concentrated base should be examined after it has cooled to typical storage temperaturesand/or it has cooled to the lower temperatures possibly encountered in a cold storage room, or those found if it is shipped to a distantblending point. The stability should also be examined at intervals of days, weeks, or months, depending on how soon the concentratedbase will be used before dilution or cutback.

EXAMPLE - Automotive Topcoat Preparation in Ball MillsDispersion of an automotive topcoat requires close attention to all facets of formulation and dispersion to provide optimum coatingperformance. Dispersion assessment is critical to obtaining performance. The coating manufacturer cannot rely on a grind gagealone to determine when the dispersion level needed has been attained. The electron micrograph below compares two dispersionthat were off scale on a grind gage. On the right is a micro-flocculated carbon black. On the left is the same black when fullydispersed. These dispersions would both be rated as complete with either a grind gage or light microscope.

The effects of the micro-flocculation demonstrated to the rightinclude drastically reduced jetness and extremely brownundertone. The fully dispersed black in this case was 50 shades jetter in masstone (50 distinguishable colors could be placedbetween these two) and developed very blue undertone. The

root cause of these differences was a reduction of ball mill timeto only 8 hours less than optimum. This demonstrates that grindgage dispersion measurements alone are insufficient to predictperformance.

Labs equipped with electron microscopy should consider usingthis resource for critical applications. When an electronmicroscope is not available, assessment of final performancecan be relied on to determine if specifications have been met. Inthis case, measuring the color development indicates the poorperformance of the micro-flocculated paint. In other cases glossor haze can indicate a poor dispersion level.



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Flocculation Tests - There are several easy-to-use tests that can detect flocculation. A drawdown of the paint can be rubbed upwith a finger prior to completion of the drying process. If flocculation is present, the color of the rubbed area will not match theun-rubbed area. This indicates that the shear imparted by rubbing the paint was sufficient to de-flocculate the pigment. A secondmethod that can detect flocculation is to place a drop of the paint between two glass slides and apply sufficient pressure to theslides to cause the paint to spread out thin enough to see through. Allow the slides to rest undisturbed for a few minutes, thenshear one slide over the other while looking through the slides at a light source. A paint that is not flocculated will not change intransparency when sheared. A flocculated sample will become more opaque upon being sheared. The increase in opacity observedwhen shear is applied to a flocculated sample is due to the pigment being redispersed.

The selection of a post treated carbon black, increased dispersion energy and dispersingagents suited for the vehicle system are the potential means to alleviate flocculation.

Place drop of painton slide, then coverwith second slide.

Apply enoughpressure to makesample transparent,then allow itto rest.

Shear one slide overthe other and checkfor any changes intransparency.No change indicatesno flocculation.

Darkening of thesample uponshearing one slideover the otherindicates thatflocculation ispresent.



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CUTBACK OR REDUCTION OF MILLED PASTES

Since so much time has been spent explaining how to obtain the maximum in blackness, hiding power, and gloss from a Raven

carbon black paste, we would be remiss if we did not discuss the method of cutback from paste to the final paint and coating. Eachof the areas previously discussed contributes to the end result, i.e., the best paint and coating film. Still, it must be recalled that weare working with colloidal dispersions of carbon black.

Even if, in the processing up to this point, the best techniques have been employed, it is quite possible to completely ruin all of thegood work by a poorly-handled cutback of the base to the final paint and coating. The following describes ways to avoid this trouble:

1) If the base paste is viscous, the cutback should be made slowly, adding the reducingvehicle in small increments. Otherwise, formation of large lumps or very small gel-like specksof paste that are difficult to break down might be encountered. The latter results in a roughsurface, dirty paint or a seedy appearance.

2) Whether using a thin paste or a heavy paste, the reducing vehicle should never beadded too rapidly. Colloidal shock can occur and result in either flocculation of the pigment,loss of color, brownness of shade, or a combination of the three.

3) The normal paste should be stirred or milled continuously to keep it soft, whilesimultaneously, slowly adding the reducing vehicle.

4) Attention should be given to the temperature of the paste or the reducing vehicle.A cold-reducing vehicle should not be added to a hot or warm paste. Flocculation, loss ofcolor, etc., due to colloidal shock will occur. This situation is particularly true in cold weather,when the operator brings in the reducing vehicle from the warehouse or outside storage at atemperature potentially much lower than the batch to be reduced.

5) Heavily-pigmented millbases should not be stored for too long an interval, since, in

some cases, the vehicle used is not a good colloidal stabilizer due to performancerequirements. Setting up or gelling of the grind base can occur, plus flocculation oragglomeration of the black. In these cases, it is safer to cut back as soon as possible aftermilling. The same is true for a good dispersing vehicle if over-pigmented.

6) The choice of reducing resin or vehicle should be made carefully, keeping thespecification requirements of the final product in mind. The best vehicle to do the job shouldbe employed, and should be clean and free of fine gel particles, or any other contamination.Contamination can sometimes induce seeding, dirtiness, grit, etc., which will providepoor surface appearance.

7) In some paint systems where solvents and diluents are used, a combination thatdoes not hold the vehicle in solution should not be used; otherwise, a throw-out orflocculation of the vehicle solids can occur, carrying the pigment along with it. While notnoticed in production, the throw-out may develop while standing in the customerswarehouse or factory.

During warm weather, it might not be noticed at either the producers or users factory, but incold weather, the flocculation will occur during shipment or at the customers cold warehouse.This situation should be monitored closely in low viscosity coatings. Such throw-out of thepigment can also be caused by excess solvent.



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COLLOIDAL SHOCK

The loss of stability during dilution or cutback of the paste is dueto colloidal shock.

The addition of the clear vehicle, particularly if the introductionis too rapid, can cause an upset in the equilibrium of the two

main millbase components black and vehicle solids. It takestime for the millbase phase to blend with the new liquid phaseand reach equilibrium or maximum stability of the final paint. Inthis interval of reorientation, a drop in color and a change ofshade can occur due to a temporary flocculation of pigmentalone, or pigment and paste solids. The dilution effect alone canbe destructive.

These variables should be watched with special regard tomatching standards of blackness, working properties, control ofblack purchased, and deliveries of finished paint to the all-important customers. A factory batch may be passed by thelaboratory on a freshly-made paint and coating but may notpass if it is tested after aging overnight.

Stability can be enhanced by a thorough, long, blending timeunder the proper conditions.

Protective agents (those that help give greater stability ofdispersion, i.e., dispersing agents, synthetic or natural) can helpto keep borderline stability in check. However, it is a dangeroushabit to depend on.

It is good practice to use some of the protective agents in thediluting vehicle. These agents will act as colloidal stabilizers bothin organic and aqueous systems.

DILUTION OF AQUEOUS SYSTEMSIn aqueous systems, care should be taken to use sufficientdispersing and wetting agents in the base paint and coating towithstand the later dilution with the reducing vehicle, the wateralone, or water containing vehicle solids.

Guidelines for Diluting Aqueous Systems

In aqueous systems, the same general rules apply, i.e., stirring inthe reducing vehicle slowly. The incorporation of a portion of thecolloidal stabilizers in the reducing vehicle is also recommended.The pH behavior must be controlled throughout the dispersingand cutback cycle. If optimum stability of the water baserequires a pH close to 7, as in some paint and coatings systems,

then the pH should not be allowed to decrease in the freshly-made paint and coating or on aging in the customers plant.

With certain systems, if the pH is allowed to go too high,reduction in the viscosity can occur. This, in turn, may result insettling of the pigment. However, other paint and coatingsystems may maintain their stability at higher pH levels. Thiscould be due to the particular ingredients used in theformulation, such as a suspending agent in the form of athickener.

It is quite obvious that the cutback step, or dilution, is just asimportant as any preceding processing step. A good job ofdispersion can be deteriorated or made commercially

unacceptable by not exercising care when making the letdownProduction rate versus quality should always be kept in mind.

Dispersion techniques properly applied result in the optimumquality attainable with a given pigment/vehicle combination.

BEADED BLACKS

Powder blacks are very popular in paint and coatings productiondue to the ease in which they can be dispersed. However, bulkhandling, economics, freight, cleanliness or a particular requiredproperty may mandate the use of a beaded black.

When using beaded blacks, wetting/premix times should beextended as much as possible to ensure that the beads havebeen broken down. The paint maker can anticipate dispersion torequire more work when using a beaded black. However, thisadditional work can be offset by faster incorporation of thebeaded black into the vehicle and significant improvements inhandling and housekeeping.

Columbians North Bend plant is equipped with specializedequipment to produce beaded blacks which are particularly easyto disperse. The paint and coating grade carbons listed beloware produced at the North Bend plant.

NORTH BEND RAVEN CARBON BLACKS

Raven 5000 Ultra III Raven 5000 Ultra II

Raven 7000 Raven 3500

Raven 2500 Ultra Raven 1500


Raven 1170 Raven 1100 Ultra

Raven

1060 Ultra

Raven

1040Raven 1035 Raven 1020


Raven 850 Raven 450

In some special cases, the customer may choose to pulverize thecarbon black beads prior to incorporation into the vehiclesystem. Proper air handling/ventilation equipment is required fordust containment if pulverization is to be practical.

EXAMPLE - Bead use in Liquid Paint & Coatings-Presoaking

If solvents are used in the paint system, soaking the beads in thesolvent will soften them and make them more readilydispersible. The following experiment, which is carried out on aglass plate, will support this statement.

Take a small amount of beads and add just enough solvent tosoak them. Work the beads with a spatula until a creamy massis obtained. Blend the mass into a heavy varnish vehicle andnote the ease of incorporation. Contrast this with the use of thedry, unsoaked bead. This method is only practicable with paintand coatings where solvent in a sufficient quantity can be usedThe addition of dispersing agents in this solvent soaking/wettingcycle is very helpful.

Using Raven Carbon Blacks In Paint and Coatings Applications


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PERFORMANCE MEASURES

Matching the appearance of the finished coating to the desired

color, gloss, and durability targets are key elements in

customer satisfaction.

The color of the final coating can be evaluated subjectively byeye or with the aid of instrumentation. As has been stated

previously, color measurements taken with instruments

equipped with 0/45o geometry offer the highest probability of

success in achieving a good correlation with visually observed

color.

Gloss properties of a finished paint can be easily and accurately

characterized with any number of gloss meters. The selection of

measurement angle of incidence is somewhat dictated by the

general gloss level of the coating to be measured. Low gloss

paints can be more easily distinguished by using an 85o or 60o

angle of incidence. High gloss coatings are easier to distinguish

by using a 20o angle of incidence.

The durability of a coating can be measured by its surface

hardness, resistance to chemical attack, or its ability to resist

fading upon exposure to the elements of time and weather.

The mechanical and chemical tests for durability are relatively

straight forward. Accelerated weatherability testing used to

predict the effects time, however, is much more challenging.

Great care should be exercised in selecting test conditions and

developing a correlation with natural exposure.

The use of properly selected, high quality carbon blacks

combined with sound formulating practices and good dispersion

techniques, will result in the expectations established for the

coating being achieved.



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Customer Assistance

At Columbian Chemicals Company, we are proud to provide you with the informa-

tion and assistance to help you use our Raven carbon blacks. We are committed to

providing our customers with the finest in service, information, and support, while

manufacturing the finest carbon blacks available anywhere.

We understand that you may have questions or need assistance with the processes

and products mentioned in this brochure. Please feel free to call us and let us know

how we can help you.


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-a green

whiteL=100

blackL=0

+a red

-b blue

+b yellow

C O L U M B I A N C H E M I C A L S C O M P A N YWorld Headquarters Marietta, Georgia USA

A subsidiary of

paint_dispersion in ball mills

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