www.rechargermagazine.com November 2008 57

Technical

Various low molecularweight (LMW) polyolefinshave been widely used inconventional imaging toner to pro-vide a low energy surface, abrasionand scratch resistance, and releaseproperties. LMW polyethylene waxis a nonfunctionalized wax that is akey additive in digital processes suchas electrophotographic, thermal andinkjet printing. Polyethylene releasewax (hereafter referred to as releasewax) provides release and lubrica-tion, while also improving imagesharpness.

Despite the vital role it plays, thedispersion of release wax in polartoner resins remains a challenge.Baker Petrolite, a Baker Hughes com-

pany, evaluated the effect of combin-ing specialty performance LMWpolymers (hereafter referred to asspecialty polymers) with release waxto enhance compatibility with polartoner resins. The compatibility wasassessed in both polyester andstyrene acrylic resins by using a scan-ning electron microscope (SEM),light microscope and differentialscanning calorimetry (DSC).

Background Xerographic printing is a process

that generates and develops electro-static toner images onto recordingmedia, typically by the process of hot-roll fusing. Toners are used to producethe printed images. A typical toner

consists of resins, colorants, charge-control agents, and functional addi-tives.

The basic steps for hot-roll fusingof xerographic engines include: 1)charging of the photoreceptor, 2) gen-erating electrostatic images onto thephotoreceptor, 3) developing electro-static images with toner, 4) transfer-ring toner onto the recording media,5) fusing toned images onto therecording media to form final images,and 6) releasing the recording mediafrom the fuser roll.

In this study, specialty polymerswere introduced into a conventionalmelt pulverized toner formulation.The objective was to improve the dis-persion of release wax in the poly-

Improving the Compatibility of Nonfunctionalized Wax inPolyester and Styrene Acrylic Toner Resins

The Chemistryof Toner Polymers

by Elizabeth Yuan Baker Hughes Incorporated

Technical

58 November 2008 www.rechargermagazine.com

ester and styrene acrylic toner resinsand reduce the domain size of therelease wax, thereby improving tonerrelease and allowing toner to be usedin an oil-less fusing print engine.

Experimental ProcedureSpecimens were prepared by com-

pounding polyester or styrene acrylicresin, release wax, and specialtypolymers in a batch mixer.1 Fracturesurfaces of the compounded speci-mens were generated and inspectedunder a scanning electron micro-scope (SEM) or light microscope toreveal the size of dispersed waxdomains and their uniformity.

The thermal behavior of the spec-imens was evaluated by differentialscanning calorimetry to assess theeffect of compatibilizers on the glasstransition temperature of the tonerresin.

Materials used in thisstudy.

Polyester resin: cross-linkedpolyester2 and linear polyester (pro-prietary material).

Styrene acrylic resin3: cross-linked and linear

LMW polyethylene4: a non-functionalized LMW polyethylenetypically used as a release wax(abbreviated here as PW 850).

Specialty polymers: (fromBaker Petrolite studied as compatibi-lizers.

Table 1 summarizes the relevantproperties of these materials.

Base formulations for the samplesconsisted of 90-95 percent polyester

resin or styrene acrylic resin, 0-5 per-cent release wax, and 0-5 percent spe-cialty polymers. Reference specimensfor the polyester resin were preparedby mixing 95percent cross-linkedpolyester resin and 5 percent PW 850.Reference samples for the styreneacrylic resins were prepared by mix-ing 95percent of each styrene acrylicresin (i.e., cross-linked or linear) with5percent PW 850.

Results and DiscussionSEM and light microscope photo-

graphs were used to qualitativelycompare the various specialty poly-mers ability to compatibilize therelease wax in cross-linked polyesterand styrene acrylic resin.

Polyethylene EthoxylatesFigure 1 shows light microscope

comparisons of wax dispersion inpolyester resin with different levelsof HLB polyethylene ethoxylates.

Light microscope photographsdemonstrate that both the U750 andU720 appear to improve release waxdispersion in the polyester tonerresin. However, the high HLB U750improves release wax dispersionmore than the low HLB U720. It isalso clear that release wax can be dis-persed uniformly in the base resin

Figure 1. Photo A shows 5 percent PW 850; photo B has 2.5 percent PW 850 with2.5 percent U720; and photo C shows a 2.5 percent PW 850 with 2.5 percent U750,all at 1000x.

Table 1. Specialty Polymers as Compatibilizers

ChemistryCategory

SampleAbbreviation Functional Groups

Polyethylene EthoxylateLong hydrocarbon

chain ethylene oxide5

U720 Low (HLB*=4)

U750 High (HLB=10)

Maleic graftedpolyolefin5

C67 Low (Acid No.** = 48)

C1608 High (Acid No. = 160)

Polyalphaolefin5Amorphous hyperbranched

polyolefinV103 None, but highlybranched

* HLB = hydrophilic-lipophilic balance. An HLB of 0 corresponds to a completely hydrophobic molecule, and a value of20 corresponds to a molecule of completely hydrophilic components.

** Acid number unit is mgKOH/g

A B C

1 Plasti-Corder, C. W. Brabender Instruments, Inc. So. Hackensack, N.J.2 Diacron ER-508, Dianal America, Pasadena, Texas3 Bayton C-300 and Bayton T493, Sybron Chemicals Inc., Birmingham, N.J. 4 POLYWAX 850 Polyethylene, Baker Petrolite Corporation, Sugar Land, Texas.5 UNITHOX 720 Ethoxylate, UNITHOX 750 Ethoxylate, CERAMER 67 Maleic Grafted Poly-ethylene, CERAMER1608 Maleic Grafted Polymer, and VYBAR 103 Polyalphaolefin are prod-ucts of Baker Petrolite Corporation, Sugar Land, Texas

Technical

www.rechargermagazine.com November 2008 59

and its domain size can be reducedby incorporating the polyethyleneethoxylates. These results suggestpolyethylene with ethylene oxidefunctional groups may create abridge between the polar polyesterresin and the release wax to improvethe dispersion of the release wax inthe polyester resin.

Our experiments also indicatedthat polyethylene ethoxylates weregood compatibilizers for PW 850 inboth types of styrene acrylic resins,but they were more effective compat-ibilizers for the linear nonfunctional-ized styrene acrylic resin than for theslightly functionalized cross-linkedstyrene acrylic resin.

Maleic Grafted Materials Light microscope results indicated

that both the high-functionalitymaleic grafted polymer C1608 andlow- functionality C67 polyethyleneimproved wax dispersion in thecross-linked polyester base resin.This would indicate that acid func-tionality in the polyethylene can alsoact as bridge between polar resin andrelease wax.

The SEMs in Figure 2 illustratedispersion of wax in the cross-linkedstyrene acrylic resin.

The results showed that C67improved PW 850 dispersion in thecross-linked styrene acrylic resin, butC1608 had the opposite effect.

For the linear styrene acrylic resin,the C67 Polymer improved PW 850dispersion, but as with the cross-linked resin, the C 1608 Polymer hada negative effect on PW 850 disper-sion.

PolyalphaolefinThe light microscope photographs

in Figure 3 demonstrate the ability ofhyperbranched V103 to compatibi-

lize release wax in the cross-linkedpolyester base resin.

This highly-branched polymerwith wide polydispersity appearedto improve wax dispersion andreduce the wax domain size in thepolyester resin.

We also studied the effect of V103on release wax dispersion in styreneacrylic resin. Based on SEM photos,V103 did not demonstrate a positiveeffect on PW850 dispersion in eitherthe cross-linked or linear styreneacrylic resins.

Resin Chemistry Effect The study also evaluated the

effect of cross-linked or linear resinstructures on the dispersion of therelease wax (Figure 4).

Our data indicated that releasewax dispersion in the linear poly-ester resin was better than in thecross-linked polyester resin. Itappears that release wax dispersionin this type of polyester resinstrongly depends on resin chemistry.

Differential ScanningCalorimetry Evaluations

In this study, DSC was used as atool to understand the effect ofadding release wax and specialtypolymers on toner polymer glass

Figure 2. Cross-linked styrene resin + 5 percent PW 850 (A), cross-linked styreneresin/PW 850 with C67, 1:1 (B), and cross-linked styrene resin/PW 850 with C1608,1:1 (C), all at 500x.

A B C

B C

Figure 3. Control (A) and with 2.5 percent V103 (B), both at 1000x.

Figure 4. Comparison of wax domains in two types of polyester resins: cross-linked polyester resin (A, 50x) and linear polyester resin (B, 100x).

A B

A B

Technical

60 November 2008 www.rechargermagazine.com

transition temperature (Tg). Speci-mens were prepared with the cross-linked polyester resin.

As Table 2 indicates, DSC showeda small decrease in the Tg of the poly-ester resin when the release wax wasadded. However, incorporating spe-cialty polymers in the formula didnot further shift the Tg of the poly-ester resin.

Specialty Polymers asCompatibilizers

The first portion of the studydemonstrated how incorporation ofspecialty polymers improved releasewax dispersion in polyester resin. Inthis portion, the effect of specialtypolymers on polypropylene (PP) waxdispersion in polyester resin wasevaluated. Samples were preparedby mixing cross-linked polyesterresin, PP wax, and specialty poly-mers (Table 3).

To understand wax dispersion inpolyester resin, DSC data comparedthe heat of fusion of wax in classifiedtoner and in fine powder. The ratio offine powder to classified toner (F/C)

indicates the amount of wax remain-ing in the classified toner to thatremaining in the fine powder. If F/C =1, the wax is well dispersed in thetoner materials. If the F/C ratio ishigh, the wax is not well dispersed inthe toner. Clearly, the data showedthat toners containing the U750 hadF/C ratios very close to 1, which indi-cated U750 materials were the mosteffective compatibilizers for PP waxamong the materials studied here.

This study illustrates that a com-patibilizer assists wax incorporationand dispersion, thereby reducing freewax. With reduced free wax and bet-ter dispersion of wax within the tonerparticle, more wax can be available toprovide the release function duringthe toner fusing step.

ConclusionsThe polyethylene ethoxylates

(U720 and U 750) and low functional-

ized maleic grafted polymer (C67),improved the dispersion of both non-functionalized LMW polyethyleneand polypropylene in polyester andstyrene toner resin. The polyalp-holefin (V103) and the high function-alized maleic grafted polymer(C1608) improved wax dispersion inpolyester resin but not in styreneacrylic toner resins.

The U750 polyethylene ethoxylateproved to be the best compatibilizingagent among the materials studiedfor both polyethylene wax andpolypropylene wax in polyester andstyrene acrylic resin.

Resin chemistry had a strongeffect on wax dispersion. LMW poly-olefins could be dispersed into linearpolyester resin and low functional-ized cross-linked styrene acrylic resinmore uniformly than into the cross-linked polyester and nonfunctional-ized linear styrene acrylic resins. R

Table 2. Compatibilizer Effect onPolyester Resin Tg Compound

Compound Tg (degrees Celsius)

Polyester resin 66.0

With 5 percentPW 850 63.7

With 5 percent PW850/C67 (1:1) 63.7

With 5 percent PW850/U720 (1:1) 63.7

With 5 percent PW850/U750 (1:1) 63.4

With 5 percent PW850/V103 (1:1) 63.5

Elizabeth Yuan is a senior application research chemist in the polymer groupof Baker Petrolite. She can be reached at Elizabeth.Yuan@bakerpetrolite.com.

Table 3. Compatibilizer Effect on PP Wax in Polyester Resin

CompatibilizerDSC(J/g) H After Pulverizing

Classified Fine Powder Fine/Classified(F/C)

Control (polyester resin + 4% PP wax) 0.88 3.84 4.36

Replace 2% PP with 2% U720 1.13 1.63 1.44

Replace 2% PP with 2% U750 1.34 1.40 1.04

Replace 2% PP with 2% C67 0.80 2.67 3.33

Replace 2% PP with 2% V103 1.18 2.37 2.00

2009 Baker Hughes Incorporated. All rights reserved. PET-09-25438 (4/09)

12645 West Airport BoulevardSugar Land, Texas 77478Tel +1 800 331 5516Fax +1 281 276 5669

www.bakerhughes.com/polymers

For more specific information, please contact your Baker Hughes representative.

Because it has become common for purchasers of our products to file patents for specific end uses of our polymer products, Baker Petrolite Polymers advises its customers to research their particular end use for possible intellectual property issues with respect to third party patents.

Disclaimer of Liability:Baker Petrolite Corporation and its affiliates (BPC) disclaim all warranties or representations express or implied, including any implied warranties of merchantability or fitness for a particular purpose or to the accuracy, correctness or completeness of such information herein or that reliance on such information will accomplish any particular result. All such information is furnished as is and by using such information the user is assuming all liabilities for the use or reliance on such information. BPC SHALL NOT BE LIABLE FOR ANY INDIRECT, SPECIAL, PUNITIVE, EXEMPLARY OR CONSEQUENTIAL DAMAGES OR LOSSES FROM ANY CAUSE WHATSOEVER INCLUDING BUT NOT LIMITED TO ITS NEGLIGENCE.