New lubricants offer higher efficiency in PVC extrusion

Plastics Additives & Compounding September/October 2008

26ISSN1464-391X/08 © 2008 Elsevier Ltd. All rights reserved.

New lubricants offer higher effi ciency in PVC extrusion

HPL’s high performance results in low extrusion torque, reduced melt pressure at the die and a high gloss surface even at very low dosage levels. It allows PVC processors to operate extrusion machinery at peak effi ciency, to extrude PVC compounds at lower melt temperatures, avoid burning and discoloration, reduce plate-out, lower the frequency of maintenance shutdowns and cleaning cycles, reduce power con-sumption, and minimize rejection and scrap rates. The dosage of lubricants can be reduced by 25-50 per cent.These benefits can be reached while maintaining mechanical strength and weathering stability at the same level.

The role of lubricantsLubricants are essential components in rigid PVC formulations. They infl uence the manner in which PVC melts and fl ows during processing. The selection of the right lubricant, the best combination and the optimum lubricant dosage will have a positive effect on several factors, including the energy consumption of the processing machine, melt pressure in the machine, pro-ductivity, dispersion of fi llers and pigments, and gelation of PVC.In addition to the lubricant, several other components in the PVC formu-lation directly or indirectly influence the lubrication of the polymer melt:

• Metal soaps in Ca/Zn or lead stabilizers contribute significantly to the total lubrication conditions, while tin stabilizers or organic-based metal-free stabilizers have only a minor influence.

• Fillers and pigments, as well as co-stabilizers such as zeolites and hydrotalcites, may partly absorb

lubricants and so reduce lubricant effi ciency.

• Processing aids and modifi ers alter melt rheology in the processing of rigid PVC and directly interact with functions provided by lubricants.

All these infl uences make it necessary to adapt the lubricant package uniquely for each PVC formulation.

European polyvinyl chloride (PVC) processors have been seeking a high performance extrusion lubricant to use with calcium/zinc-based (Ca/Zn) stabilizers, which are increasingly being used in place of lead stabilizers. In response, Honeywell has developed the HPL (High Performance Lubricant). Dr. Rolf Spiekermann, technology manager Performance Products at the company’s Seelze plant in Germany explains how they can offer many quality and fi nancial benefi ts.

Figure 1: Time of fusion (Brabender).

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Lubricants for use in rigid PVC processing are generally classed as internal or external. External lubricants influence the conditions between the polymer melt and the metal surface of the processing equipment. Good external lubrication means the melt

glides easily over the screw, barrel and die. This results in lower torque and reduced melt pressure at the die.Due to their more polar structure, internal lubricants have a better compatibility with PVC. They can penetrate into the PVC melt and ease

the movement of a polymer chain with respect to others. Internal lubricants typically lead to faster fusion, resulting in higher torque and increasing melt pressure at the die.The ongoing replacement of lead formu-lations by Ca/Zn stabilized formulations in the European PVC profi le and pipe industry requires readjustment of numer-ous recipes. This is a challenging task. The Ca/Zn stabilizer systems being eval-uated tend to have reduced dynamic heat stability and may form more calibration plate-out. The demand is for additives that help regain formulating fl exibility and reduce plate-out formation.

Extrusion parametersHoneywell conducted a series of trials in its application laboratory in Seelze, Germany. The objective was to find out how typical extrusion parameters are affected by using HPL instead of conventional lubricants.The equipment used consisted of an in-dustry standard torque rheometer, a small scale extruder with fl at profi le die (Krauss-Maffei KMDL 25) and a semi-produc-tion-scale extruder with window profi le tool (Battenfeld MBEX 2-50-16V).The comparison tests were primarily performed with a Ca/Zn stabilized window profile formulation, which is a standard application in the PVC industry. The Ca/Zn core pack is a stabilizer based on Ca-stearate and Zn-stearate, containing co-stabilizers and processing aid but without a lubricant. The lubricant was the only compo-nent which was varied over the tests. All tests were run with the addition of just one lubricant type (no lubricant combinations were tested).For the tests in this report the lubri-cant level was varied between 0.03 phr and 0.5 phr. The following lubricants were compared:• Stearylstearate (ester, internal lubricant)• Di-stearylphthalate (ester, internal

lubricant)• A-C 400 A (PE-EVA copolymeric wax,

external lubricant)• A-C 617 A (LDPE homopolymeric

wax, external lubricant)• Honeywell Rheolub® HPL (High

Performance Lubricant, internal and external)

Figure 2: Melt pressure (Krauss Maffei extruder).

Figure 3: Melt pressure (BEX)



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To determine a ‘baseline’ value, the test formulation was also processed without any additional lubricant.

Time of fusionThe time of fusion results were achieved by using a Brabender torque

rheometer (see Figure 1). It can clearly be seen that the waxes and external lubricants A-C 400 and A-C 617 delay fusion increasingly with dosage as expected. This a normal feature of external lubricants.The esters and internal lubricants Stearylstearate and Di-stearylphthalate

accelerate fusion at typical dosage lev-els (up to 0.3 phr). This effect declines only at higher dosage levels, due to over lubrication.HPL reacts very distinctively. At dos-ages between 0.05 and 0.15 phr, fusion is slightly accelerated, while at higher dosage levels the HPL significantly delays fusion. This gives users more flexibility and the option to determine the time of fusion in accordance to the special application. The dosage of the lubricant can serve as a parameter to control time of fusion.

Melt pressureThe trials were conducted by using both the Krauss-Maffei small scale extruder with conical screws (KMDL 25) (see Figure 2) and the Battenfeld semi-production-scale parallel screw extruder (MBEX) (see Figure 3). The results were similar. In both cases, HPL showed the lowest pressure, by far, during the extrusion process. While the baseline (without lubricant) in the KMDL 25 trial was at 256 bar, HPL showed at a dosage of 0.3 phr at a pressure of 186 bar only. The waxes ranked second with 193 and 202 bar respectively. The esters showed 255 and 260 bar respectively at the 0.3 phr dosage.The only difference was that in the small scale extruder the results with ester lubricants were at low dosages up to 0.3 phr higher than the baseline. In this machine, HPL created a slightly higher die pressure at 0.1 phr as well (clear evidence of fusion acceleration), but the pressure went immediately down at slightly higher dosages, due to the effect of external lubrication.

TorqueThe torque results (see Figures 4 and 5) were quite similar to those measuring melt pressure. The higher the dosage, the lower was the torque when using HPL. While the baseline (without any lubricant) in the KMDL 25 trials was at 63 per cent, HPL showed 41 per cent at a dosage of 0.3 phr. The waxes were at 44 per cent and 48 per cent respec-tively, the esters were at 61 per cent and 66 per cent respectively.

Figure 4: Torque (KMD)

Figure 5: Torque (BEX)



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GlossHomopolymeric PE-waxes are well known as gloss improvers. This was confi rmed by the tests. The A-C 617 A delivered the best gloss with a maximum at about 0.3 phr. The copolymeric wax A-C 400 A and HPL also showed similar effects with a slightly lower gloss value. Ester lubricants at application lev-els of 0.2 phr to 0.3 phr do not signifi cantly improve gloss (Stearylstearate) or even reduce gloss (Di-stearylphthalate) by showing results below baseline (see Figure 6).

Industrial applicationsThese results from scientifi c tests can be verifi ed by using HPL in typical PVC for-mulations for the industry. This is intended to show how HPL meets industry require-ments. PVC compounds to be processed on industrial extrusion lines, for production of PVC profi les or PVC pipes, need to be op-timized with respect to the output rate and properties of the fi nal product (the product appearance, such as its gloss, and mechani-cal data such as weather stability).Based on the results of the comparison tests outlines above, lower dosages of HPL lubricants are necessary to achieve the required lubrication effects. This was dem-onstrated in three examples (see Figure 7).

Test run 1The fi rst example describes three versions of a basic profi le formulation. Version 1 includes a commercial Ca/Zn one-pack stabilizer containing 0.55 phr conventional lubricants. Version 2 uses a Ca/Zn core pack as a stabilizer (without lubricant) plus the commercial grade Honeywell Rheolub®HPL6001 at a lower dosage of 0.4 phr. Version 3 is similar to version 2 but uses an experimen-tal lubricant, Honeywell Rheolub®HPLX, at the same low dosage as version 2.The reduction of melt temperature, melt pressure and extrusion torque when using HPL formulations is signifi cant. The experi-mental (and not yet commercially available) HPLX showed the best results. By using the Rheolub®HPL 6001, power consumption could be reduced by 6.0 per cent and by using the experimental HPLX the reduc-tion was even greater at 10.5 per cent. This is an excellent contribution to improved profi tability.

Test run 2Example 2 used a higher fi lled profi le formulation requiring more lubricant. A commercial stabilizer one-pack with con-ventional lubricants (version 1) was com-pared against the corresponding core-pack.

Core-pack formulation was lubricated either with a conventional lubricant system (version 2, dosage 1.2 phr) or with a HPL lubricant pack Rheolub®RL 805 (version 3, dosage 0.6 phr).In this formulation HPL at 0.6 phr provides better lubrication than conven-tional lubricants at 1.2 phr. Melt pres-sure and extrusion torque are remarkably lower. Gloss was signifi cantly better with HPL. Mechanical data of the extrudate produced with HPL were equivalent to standard and fulfi lled all requirements.

Test run 3This used a profi le formulation stabilized with a heavy metal-free organic stabilizer.The target was to match production conditions of a formulation with con-ventional lubricants by replacing them with HPL. In this case, too, all results were better: melt temperature, melt pressure, extrusion torque and power consumption were all lower, while gloss was signifi cantly improved. These results were achieved at a dosage which was reduced by 32 per cent.

ResultsThe evaluation of these tests clearly demon-strates the extremely high lubricant effi ciency of the HPL component in Ca/Zn stabilized rigid PVC extrusion. The use of HPL leads to low torque and low die pressure even at very low dosages. Although these data indicate a strong external lubricant activity of HPL at dosages of 0.1 to 0.15 phr we can identify signs for fusion acceleration as well. Additionally, HPL acts as a strong gloss improver similar to the most effi cient homopolymeric LDPE waxes. It is the very special combination of features - saving energy and reducing dosages of lubricants - which makes HPL a very profi table solution for many applications.

Contact:Dr. Rolf SpiekermannHoneywellWunstorfer Strasse 4030926 SeelzeGermanyTel: +49 5137 999 570Fax: +49 5137 999 186Email: [email protected]: www.honeywell.com/sm

Figure 6: Gloss (BEX)


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http://www.honeywell.com/sm



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Figure 7: Use of High Performance Lubricants.


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New lubricants offer higher efficiency in PVC extrusion