WACKER SILICONES: Perfect Toners hide a Secret: HDK ... · ket presence. With the Clariant...

CREATING TOMORROW’S SOLUTIONS

PERFECT TONERS HIDE A SECRET: HDK® – PYROGENIC SILICA

ContentsPerformance and Expertise 3High Performance 5Particle Size 6Hydrophobization and Functionalization 7Fundamental Research 8Registration and Toxicology 9Exact Measurement 10HDK® Product Ranges 16Service 20WACKER at a Glance 21

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HDK® PYROGENIC SILICA: TOTAL CONTROL OVER TONER CHARGE AND FLOW

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Your expectations of an electrophoto-graphic toner are highly specific –HDK® is no less specific in influenc-ing your toner. This pyrogenic silicatunes tribocharging properties andflow selectively, efficiently and reli-ably. And that is the HDK® secret tooptimized toners.

Principle behind the electrophotographic process

Unique product propertiesWACKER has been producing HDK®

pyrogenic silica for more than 30 yearsand, for 20 of those, it has produceddedicated grades for toner use. And wecontinue to specifically enhance theunique properties of the HDK® range.The pay-off: HDK® effectively and selec-tively optimizes the charge and flowproperties of a wide variety of toners,whether made by classic melt/grindingor by new chemical methods.

The electrophotographic process is based on two natural phenomena:materials of opposite charge attract, and certain materials become moreelectrically – conducting when exposed to light.

PERFORMANCE AND EXPERTISE

WACKER and HDK® are registered trademarks of Wacker Chemie AG.

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Processes for toner production

Toner ProductionGenerally, a crude toner consists of abinder resin, a colorant and additionaltechnical ingredients (CCAs, waxes).This crude toner is then coated with asmall quantity of flow improver (HDK®) inthe additive blending process. There arebasically two different ways for makingthe crude toner:

Melt-grind: The main steps are meltmixing, grinding/jetting and classifying.This method makes toner by pulverizingchunks of toner compounds and sievingthem to collect the proper size of tonerparticles. This process leads to irregular-ly – shaped toner particles with meansizes between 6 to 12 micrometers. Theend product is a “conventional” toner.

Chemical: This process follows the path from molecule to solid particle, withthe particles growing under controlledconditions. These may be made eitherby emulsion polymerization of resinmonomers or by controlled growth oflatex particles. This process leads toregularly shaped toner particles (spheres,“potatoes,” etc.) with mean sizesbetween 5 to 7 micrometers. The endproduct is a “chemical” toner.

To satisfy the highest quality demands ofthis market and to accommodate therising diversity of modern toners, wehave developed a unique productmatrix. This matrix enables HDK®

grades to be selected according tostringent key parameters:– HDK® – particle size– HDK® – surface chemistry– HDK® – tribocharging

Concentrated expertiseAn innovative, highly motivated partnerto the non-impact printing industry, wenot only supply products of the utmostquality, but also stay abreast of techno-logical development through our ownscientific contributions. We haveobtained patent protection for our prod-ucts and their use in the field of non-impact printing (NIP). For more than adecade, we have participated actively in international NIP platforms, such asIS&T, Japan Hardcopy and IMI.We are also collaborating closely withClariant, a major international player inthe field of toner pigments and charge-control agents, to boost our global mar-ket presence. With the Clariant partner-ship, we are positioned as an expertsupplier of an impressive portfolio ofpigments, charge-control agents andHDK® pyrogenic silica. Moreover, we provide thoroughlyreliable, personalized advice worldwideand a full package of technical supporton location.

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HIGH PERFORMANCE NEEDS A STRONGFOUNDATION: HDK® PYROGENIC SILICA

Scanning electron micrograph (SEM) of a CPT particles covered with HDK® particles

HDK® pyrogenic silica – the production process

Note: Definitions of primary particles, aggregates and agglomerates are those contained in DIN 53206 page 1 (08/72).

Particle formation of HDK® pyrogenic silica

Primary particles 5 .......... 50 nm 300 – 50 m2/g BET surface area

Aggregates 0.1 ...... 0.5 µm Actual particle size on the toner surface

Agglomerates 1 ........ 250 µm A narrow distribution ensures evenreduction in the mixing process to thefinal aggregate size.

HDK® enables toner flow and chargeproperties to be formulated especiallyefficiently and economically. We havecreated a comprehensive, dedicatedrange of HDK® grades that areextremely effective at the smallest ofloadings. An overview of this range ispresented on pages 16 – 18.

HDK® particle sizesParticle size is inextricably linked to theunique process by which the pyrogenicsilica is made. The aggregates are formed by the colli-sion of primary particles during particlegrowth. The aggregates represent thesmallest, most stable, non-dispersibleparticle unit of three-dimensional struc-ture. Nevertheless, the freely – availableBET surface area ensures that the silica adheres extensively on the tonerparticles, and that even applies to the aggregates.

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WACKER SILICONES deploys thelatest manufacturing technologiesand integrated production workflows.These safeguard HDK®’s extraordi-nary versatility and guarantee thatquality remains consistently high.

Targeted particle size controlUnder common conditions of technicalhandling (filling, shipping, storage etc.)the agglomerate is the relevant particlesize. During the critical additive-blendingprocess for making toner, these arereduced to the size of aggregates. Thisensures optimum coverage of the tonersurface with HDK® particles. It is highlyadvantageous to the additive-blendingprocess to have a narrow agglomeratesize distribution and for agglomerates to be as small as possible. To this end,a grinding-classifying stage is incorpo-rated into the process line.

PARTICLE SIZE

Process control station: HDK® for toneruse is produced on our own specially-developed process lines.

The advantages:– Easy dispersing– Shorter mixing times– Homogeneous distribution of HDK®

aggregates on the toner surface– Fast, stable charging of the toner

Agglomerate size distributions, volume density distribution (q3) and volume cumulativedistribution (Q3) of toner HDK® vs. a commercial standard silica for toner use.

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Special surface treatmentHDK® with an unmodified surface has 2 silanol groups per square nanometer(nm2) and so is hydrophilic. This leads tohigh surface energy and high levels ofwater absorption.

Toners must continue to possess freeflow and a stable charge at high atmos-pheric humidity and elevated tempera-tures. That is where hydrophobic HDK®

comes in, with its much reduced densityof silanol groups (<0.5 per nm2). Itssurface energy is significantly lower andit absorbs noticeably less moisture.

As leading producer of silanes, siliconesand HDK® pyrogenic silica, WACKERSILICONES deploys the latest knowledgefrom organosilicon research to optimizeand further advance the surface chem-istry of HDK®. Our development goals are: – Chemical immobilization of the

organosilicon component on the HDK® surface

– Even distribution of the organosiliconcomponent over the HDK® surface

The surface energy of hydrophobicHDK® can be determined by Stevens’method, which measures the miscibilityof a powder in water/alcohol mixtures.The variable here is the volume ofalcohol needed for wetting the powder.A high alcohol consumption means thatthe solid has a low surface energy.

The methanol wetting test can be usedto grade the levels of hydrophobization. Functionalization of the HDK® surfacewith certain chemical groups not only isuseful for imparting hydrophobic proper-ties, but also affords a way of obtainingthe desired level of tribocharging.

Results of the methanol wetting test

The HDK® product portfolio for toneruse comprises:– Surface-modified HDK® ranging

from low specific BET surface area(large particles) to a high specific BETsurface area (small particles)

– HDK® surface-treated with dimethyl-dichlorosilane, hexamethyldisilazane,PDMS for negative tribocharging

– HDK® functionalized with amino/ammonium end groups for positivetribocharging

– Development of customized productsfor specialty requirements (minimumorder quantity required)

Using HDK® to formulate toners is highlyeconomical because it is so efficient and processing is simple. The specialmechanical de-agglomeration pretreat-ment step makes the HDK® easy to dis-perse so that it distributes itself evenlyover the entire toner surface. Excellentresults are obtained at minimum loadingwith 0.2 to 2 %.

HYDROPHOBIZATION ANDFUNCTIONALIZATION

The benefits:– Significant improvement in toner flow– Better toner transfer from the

developer unit to the organic photo-conductor (OPC)

– Precise control over tribocharge– High charge stability– Selective functionalization, i.e., high

positive or negative charge on thehighly hydrophobic HDK® over all BET surface areas

– Easier cleaning of the OPC– Better transfer of toner to the

substrate

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A critical parameter is how strongly the HDK® particles adhere on the tonersurface. If the adhesive forces are tooweak, the HDK® will be lost. Further-more, the toner loses its ability to flowand its electrostatic charge also changes.

In the end, print quality suffers. We workclosely with external research institutions(e.g., Ulm University) to quantify theadhesive forces involved. Our researchinvolves a scanning force microscope.

Scanning force microscopes use a tinycantilever to scan the sample – here, a toner particle – line by line. Aside from revealing the topography, contactbetween the tip and the sample’ssurface enables additional properties,such as hardness and adhesion, to be determined due to a phenomenonknown as phase displacement.

Free cantilever vs. cantilever in contact

Scanning force micrograph (SFM) inphase displacement of a conventionally– produced polyester toner containing0.5 wt% HDK® H30TD

Phase displacement“Harder” HDK® particles show up clearly in phase-displacement images as “bright” particles. A loading of0.5 wt% of a 50 m2/g HDK® is notenough to completely envelop thetoner’s surface. But a 300 m2/g HDK®

(HDK® H30TD) at 0.5 wt% producesalmost total coverage.

References: Heinemann et al, Organosilicon Chemistry VI, N. Auner,J. Weis, Silica Adhesion on Toner Surfaces Studied byScanning Force Microscopy, Wiley-VCH, 2005, p. 910 – 919.Heinemann et al: 2002 International Conference onDigital Printing Technologies, Silica Adhesion on TonerSurfaces studied by Scanning Force Microscopy,Proceedings, p. 651 – 656. Heinemann et al, IS&T’s NIP19: 2003 InternationalConference on Digital Printing Technologies, Adhesion ofSilica Particles and Silylated Silicon Tips on Model TonerSurfaces – a SFM Study, Proceedings, p. 155 – 160.

2 µm

FUNDAMENTAL RESEARCH

HDK® pyrogenic silica registrationAll HDK® grades for toner applicationhave been chemically – registered with the relevant national and inter-national authorities.

HDK® pyrogenic silica toxicology and safetyLike all synthetic, amorphous silicas,HDK® is classified as non-toxic whenused as intended. Details are providedin the relevant safety data sheets.

REGISTRATION AND TOXICOLOGY

Inherent powder flow properties

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EFFICIENCY IS THE RESULT OF EXACTMEASUREMENT

Intensive, fundamental scientificresearch by WACKER SILICONES isused to continually develop specialtyHDK® grades of very narrow particlesize distribution (agglomerates),different tribocharge and higher flowthat make your products successfulin your market.

Flow propertiesTo measure the flow performance ofHDK® or toner/HDK® systems we areusing a commercial Shear Scan PowderFlowability Analyzer which enables us to quantify cohesion, flow index values,angle of internal friction and other flowcharacteristics.

HDK® H30TD has less strength thanHDK® H05TD under all loads (kPa).HDK® H30TD flows better. Toner/HDK® system based on BET300 m2/g will flow the best.

Toner HDK® fundamentally improvestoner flow. The cohesion forces betweenthe toner particles are significantlyreduced by the “surface layer” HDK®.

Flow functions of HDK® H05TD and HDK® H30TD; equipment: Sci-Tec; Shear Scan TS12

The best tool for comparing powderbehavior is the flow function. This is aplot of a material´s strength versusconsolidation stress. The powder withthe lowest strength at any given stresswill flow the best.

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q/m-mono device; Epping GmbH; Germany

Charge spectrometers

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Toner flow results determined with “aged” toner

References: Heinemann et al: IS&T’s NIP12: 1996 InternationalConference on Digital Printing Technologies, The Surface Modification of Silicas on the Free Flow andCharging Properties of Monocomponent MagneticToners, Proceedings, p. 511 – 516.

How the q/m-mono instrument works

By using the same amount of HDK® the flow of the tonerimproves with increasing BET surface of the correspon-ding HDK®.

In use, each toner/HDK® system is sub-ject to extensive shearing, sometimesunder critical environmental conditions.We estimate the flow of such “aged”toner/HDK® systems using a specialcharge/flow tester (q/m-mono device; Epping GmbH; Germany).

The toner collected inside the cell (iso-lated faraday cage) is used not only fordetermining the charge, but also formeasuring the flow of the toner/HDK®

system. Prior to the measurement, thetoner system is aged by moving it past a doctor blade for a defined period,equivalent to several thousand photo-copies. The more toner that ends up inthe measuring cell, the better the flow.

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Charge propertiesThe intrinsic charge of the silica ismeasured by blowing silica off iron carri-er particles. Most HDK® toner gradeshave a high negative tribocharge. HDK®

grades with a high BET surface areaundergo the most charging. The HDK®

surface charge can be changed to posi-tive by functionalizing the HDK® withamino/ammonium groups.

We use a Q-Test charge spectrometerprovided by Epping, Germany, to con-duct detailed studies.

In addition to the charge mean value, it is possible to measure the charge ofeach individual toner particle.

Q-Test, Fa. Epping, Germany

q/m Meter, Fa. Epping, Germany

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Charge/size distribution of a model toner – 0.5 wt% HDK® H05TD

HDK® particle size expressed in BET surface vs. toner charge

For example, in a negative toner systemopposite charged toner particles maylead to inferior photocopy images. Theirproportion in the toner can be reducedthrough judicious choice of HDK®.

Consistent with accepted theory, smallHDK® particles (larger BET surface area)prove to be more effective at chargingthe toner/HDK® system. In all cases, a full charge is quickly attained and itremains stable for the duration of thestudy.

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HDK® surface chemistry vs. toner charge

Triboelectric charge stability of toner/HDK® systems at low/high atmospheric humidityand low/elevated temperature and increasing stress time – 0.8 wt% HDK®

The surface chemistry of HDK® influ-ences the system’s charge (positive or negative), the level and its stability. Silica/toner systems are renowned fortheir unstable charges, especially at

high atmospheric humidity and elevatedtemperatures. Assuming that the tonerand silica are blended under optimumconditions, the cause of the instabilitymay be related to poor or uneven

hydrophobization of the silica. This is why WACKER SILICONES focuses on optimized processes for hydro-phobizing HDK®.

With HDK® a higher charge level of the toner is achieved; the highest levelwith the toner/HDK® developmentcombination. In the standard HDK®/toner system a slight decrease of thecharge over time occurs. The toner/HDK® development system shows anearly stable charge over time evenunder H/H conditions.

HDK® with negative tribocharge

HDK® H1303VP H2000/4 H2000T H3004

Surface area (BET)hydrophobic1) [m2/g] 120 ± 30 120 ± 20 140 ± 30 210 ± 40

pH2) 6 – 8.5 7 – 9 6 – 8 6 – 8

Tamped density3) [g/l] approx. 180 approx. 220 approx. 200 approx. 120

Carbon content [wt %] approx. 2.5 approx. 2.8 approx. 2.8 approx. 4.0

Primary particle size distribution d50

(mean)4)

[nm] 20 18 12 8

Agglomerate particle size d50 (mean)5) [µm] <20 <20 <20 <20

Residual SiOH6) [%] 18 30 18 20

q/m7) [µC/g] approx. –350 approx. –200 approx. –380 approx. –410

Surface modification HMDS HMDS HMDS HMDS

HDK® H15 H20 H30

Surface area (BET)hydrophobic1) [m2/g] 120 ± 20 170 ± 30 250 ± 20

pH2) 3.8 – 4.8 3.8 – 4.8 3.8 – 4.5

Tamped density3) [g/l] approx. 40 approx. 40 approx. 40

Carbon content [wt %] approx. 0.9 approx. 1.1 approx. 1.8


(mean)4)

[nm] 18 14 12

Agglomerate particle size d50 (mean)5) [µm] >50 >50 >50

Residual SiOH6) [%] 48 50 54

q/m7) [µC/g] approx. –500 approx. –600 approx. –650

Surface modification DMDS DMDS DMDS

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THE RIGHT HDK® PYROGENIC SILICAGRADE FOR EVERY TONER

The comprehensive HDK® rangesatisfies all charge stability and flowrequirements. The following tablesprovide an overview of the offerings.Please contact WACKER SILICONESfor detailed information.

1) DIN ISO 9277; DIN66131; Hydrophobic BET surface areasdo not lend themselves to determinations of particle size

2) DIN EN ISO 787-9; 4% in methanol / water 50:503) DIN EN ISO 787-114) Primary particles of silica do not occur as individual units 5) Laser diffraction; easily dispersed to submicron sized

aggregates in the additive blending step 6) Relative silanol content with respect to hydrophilic pyro-

genic silica (containing 2 SiOH/nm2)7) Blow off vs. ferrite; WACKER method

Note: These figures are intended as a guide and should notbe used in preparing specifications.

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HDK® H05TD H13TD H20TD H30TD

Surface area (BET) hydrophilic1) [m2/g] 50 ± 20 125 ± 15 200 ± 30 300 ± 30

pH2) 4 – 7 4 – 7 4 – 7 4 – 7



Primary particle size d50 (mean)4)

[nm] 50 20 12 8


Residual SiOH6) [%] <20 <20 <20 <20


Surface modification PDMS PDMS PDMS PDMS

HDK® H05TM H13TM H20TM H30TM


pH2) 5 – 8 5 – 8 5– 8 5 – 8



Primary particle size d50 (mean)4) [nm] 50 20 12 8


Residual SiOH6) [%] <20 <20 <20 <20


Surface modification HMDS HMDS HMDS HMDS

HDK® H05TX H13TX H20TX H30TX


pH2) 5 – 8 5 – 8 5– 8 5 – 8



Primary particle size d50 (mean)4) [nm] 50 20 12 8


Residual SiOH6) [%] <20 <20 <20 <20


Surface modification HMDS/PDMS HMDS/PDMS HMDS/PDMS HMDS/PDMS

1) DIN ISO 9277; DIN661312) DIN EN ISO 787-9; 4% in methanol / water 50:503) DIN EN ISO 787-114) Primary particles of silica do not occur as individual units 5) Laser diffraction; easily dispersed to submicron sized




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HDK® with positive tribocharge

1) DIN ISO 9277; DIN661312) DIN EN ISO 787-9; 4% in methanol / water 50:503) DIN EN ISO 787-114) Primary particles of silica do not occur as individual units 5) Laser diffraction; easily dispersed to submicron sized




Abbreviations:HMDS = Hexamethyldisilazane Si–O–Si(CH3)3DMDS = Dimethyldichlorosilane Si–O–[Si(CH3)2–O–]x=1-3

PDMS = Polydimethylsiloxane Si–O–[Si(CH3)2–O–]x=3-6(10)

1) DIN ISO 9277; DIN66131; Hydrophobic BET surface areasdo not lend themselves to determinations of particle size

2) DIN EN ISO 787-9; 4% in methanol / water 50:503) DIN EN ISO 787-114) Primary particles of silica do not occur as individual units 5) Laser diffraction; easily dispersed to submicron sized




HDK® H2015EP H2050EP H2150VP H3050VP

Surface area (BET) hydrophobic1) [m2/g] 105 ± 25 110 ± 20 110 ± 20 115 ± 35

pH2) 7 – 9 8 – 9 8 – 9 7.5 – 9


Carbon content [wt %] approx. 5 approx. 7 approx. 7 approx. 7


(mean)4)

[nm] 12 10 10 8


Residual SiOH6) [%] 20 16 16 18

q/m7) [µC/g] approx. 25 approx. 50 approx. 110 approx. 90

Surface modification PDMS/ PDMS/ PDMS/ PDMS/–NR2/–NR3

+ –NR2/–NR3+ –NR2/–NR3

+ –NR2/–NR3+

HDK® H05TA H13TA H30TA

Surface area (BET) hydrophilic1) [m2/g] 50 ± 20 125 ± 15 300 ± 30

pH2) 7 – 9 7 – 9 7 – 9

Tamped density3) [g/l] approx. 100 approx. 70 approx. 50

Carbon content [wt %] approx. 2.0 approx. 4.0 approx. 7.0

Primary particle size d50 (mean)4) [nm] 50 20 8

Agglomerate particle size d50 (mean)5) [µm] <20 <20 <20

Residual SiOH6) [%] <20 <20 <20

q/m7) [µC/g] approx. +50 approx. +100 approx. +200

Surface modification PDMS/ PDMS/ PDMS/–NR2/–NR3

+ –NR2/–NR3+ –NR2/–NR3

+

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CUSTOM SERVICE FOR YOURAPPLICATIONS

Compelling performanceThis brochure shows you what HDK®

can do for toners. Obtainable on requestare detailed product leaflets expandingon the overview information of pages16/17/18. Alternatively, drop by ourinternet site at www.wacker.com/HDK.We use technology platforms such asIS&T and Japan Hardcopy to presentour innovations. The NIP industry is a strategic targetmarket for WACKER SILICONES.Intensified research and developmentand a growing range of new productsare evidence of our commitment.

Local customer service Our local experts see to it that yourinnovations are conducted by our ownproduct developments. Our technicalcore team coordinates all activities and provides assistance ranging fromclassical technical support to funda-mental research through to supply chain support. If you are seeking solutions for conven-tional black or color toners or for chemi-

cal toners in any color category, ourHDK® range offers the right grade for all your needs – hydrophobic or func-tionalized, and customized to yourrequirements. Our specialists will gladlyassist you with choosing the right HDK®

grade. They will also tell you more aboutthe technical support we offer. Our salespartners Clariant Japan K.K. in Japanand Clariant Corporation in the NAFTAare always on hand as well to providefurther information(www.nip.clariant.com).

Our service program– Personalized advice– Custom development of modified

HDK®

– Comprehensive analyticalcharacterization of the silicas

– Determination of the hydrophobic levelof modified silicas (methanol test).

– Determination of the triboelectricproperties of silicas and toner/silicasystems

– Determination of the morphology oftoner/silica systems

– Determination of the flow properties of toner/silica systems

– Global chemical registration of HDK®

– Use of the latest technology in theproduction of HDK® for ensuring safe,ecologically sound manufacture

– We are committed to the principle ofsustainable development

Global PresenceThe NIP industry is a global one. Andthat is how we have aligned ourselves.One face to the customer.

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Wacker Chemie AGHanns-Seidel-Platz 481737 München, [email protected]

www.wacker.com/hdk

Wacker Chemical Corporation3301 Sutton RoadAdrian, MI 49221-9397USATel. +1 517 264-8500Fax +1 517 [email protected]

www.wacker.com/hdk

Wacker Chemicals Trading(Shanghai) Co. Ltd.31 F., Bank of China Tower200 Yin Cheng Road CentralPudongShanghai 200 120ChinaTel. +86 21 6100-3400Fax +86 21 [email protected]

www.wacker.com

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