WO1997015630A1 - High thermal conductivity waxes and polymers - Google Patents

High thermal conductivity waxes and polymers Download PDF

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Publication number
WO1997015630A1
WO1997015630A1 PCT/US1996/015868 US9615868W WO9715630A1 WO 1997015630 A1 WO1997015630 A1 WO 1997015630A1 US 9615868 W US9615868 W US 9615868W WO 9715630 A1 WO9715630 A1 WO 9715630A1
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WO
WIPO (PCT)
Prior art keywords
wax
composition
thermally expandable
thermal conductivity
actuators
Prior art date
Application number
PCT/US1996/015868
Other languages
French (fr)
Inventor
M. Ishaq Haider
James B. Stamatoff
Joseph D. Menhczel
Barbara J. Long
David S. Rademacher
Original Assignee
Hoechst Celanese Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to US54664995A priority Critical
Priority to US08/546,649 priority
Application filed by Hoechst Celanese Corporation filed Critical Hoechst Celanese Corporation
Publication of WO1997015630A1 publication Critical patent/WO1997015630A1/en

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    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08KUse of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00Use of inorganic substances as compounding ingredients
    • C08K3/02Elements
    • C08K3/04Carbon

Abstract

This invention discloses a thermally expandable composition for use in actuators having a high thermal conductivity. This composition contains about 10-50 weight percent graphite particles dispersed in a wax or polymer. The high thermal conductivity of the composition increases the operating speed of the thermally-operated actuator.

Description

HIGH THERMAL CONDUCTIVITY WAXES AND POLYMERS
Background of the Invention
This invention relates to the field of thermally expandable materials for actuators, especially to thermally expandable compositions containing an additive to increase thermal conductivity.
Actuators are generally devices that produce some motion. While actuators are of many types, certain types of actuators such as ceramic actuators, piezoelectric actuators and the like are described in some detail by K. Uchino, The Encyclopedia of Advanced Materials, Vol. 1 , pp. 30-35, Pergamon Press, Elsevier Science Inc., Tarrytown, New York (1994). Many actuators use a thermally expandable material as part of their motion-producing action. A commonly used thermally expandable material is a type of wax, although plastics and metals have also been employed in actuators and similar devices that use thermally expandable materials. Waxes have the advantage of a low melting point, so that the large expansion that occurs when the solid melts into liquid occurs at relatively low operating temperatures. The term wax refers to a substance that is a plastic solid at room temperature and melts at a relatively moderate temperature to form a relatively low viscosity liquid. Waxes are generally a complex combination of organic compounds, especially long-chained organic acids, esters and hydrocarbons. Waxes include beeswax, waxes taken from plants (e.g., carnauba wax, bayberry wax, and the like), and mineral waxes derived from petroleum or coal. Montan wax is an example of the latter, being derived by solvent extraction of lignite. Paraffin is a well- known type of petroleum wax, obtained by crude oil distillation/separation. Low molecular weight (about 10,000 g/mole or less) hydrocarbon polymers also form waxes, especially polyethylene and polypropylene waxes; these waxes may be made by polymerization or obtained by thermally degrading higher molecular weight polymers. Unlike other waxes, these polymers tend to contain molecules that are of the same type, although as in all waxes the molecular weights of the molecules vary.
The exact composition of any type of wax varies based on the origin of the wax and the treatment it has undergone. Waxes of the same type may vary in purity, color, melting point, hardness, and other properties and characteristics. Operating temperature and degree of expansion are significant factors in actuator performance, but in many applications the speed of expansion and contraction is also important. The speed depends on how rapidly heat can be transferred into and out of the thermally expandable material, which depends in large part on the thermal conductivity of the material, as well as the technique used to heat the material.
Schneider (U.S. Patent No. 5,177,969) recognized the need for rapid heat transfer, and addressed this problem by designing the actuator so that the material was contained in thin passages, increasing the surface area exposed to heating or cooling. However, this may not be a practical design in all actuators, and does not improve the thermal conductivity of the material itself.
Several other workers have used metal powders or carbon black to increase thermal conductivity in thermally expandable materials. U.S. Patent Nos. 3,186,230, 3,187,577, 3,234,793, and 3,403,560 teach combining metal powders with thermally expandable materials for use in thermo-actuators. U.S. Patent No. 3,688,582 teaches adding carbon black to the thermally expandable material in a thermometer to improve visibility and/or heat conductivity. A study of thermally expandable polymers is reported by Z. Jang and Z. J. Zhang in "Thermally- and Phase Transformation-Induced
Volume Changes of Polymers for Actuator Applications", Joumal of
Intelligent Material Svstems and Structures. Vol. 5, Nov.1994, pp. 758- 763.
It is an object of the present invention to provide a highly thermally conductive expandable composition for actuators.
It is another object of the present invention to provide a thermally- activated actuator having a rapid response time. It is yet another object of the present invention to provide materials for substantially matching the density of an expanding ingredient in actuator when the expanding ingredient is in a molten or semi-molten state or during the actuating process.
It is still another object of the present invention to provide an actuator which comprises a uniformly blended mixture of an expanding ingredient and a conducting ingredient whose densities are substantially matched during the actuating process.
It is a further object of the present invention to provide means for increasing the speed of thermally induced solid-liquid phase changes in expandable materials for actuators.
Other objects and advantages of the present invention will be apparent to those skilled in the art from the following description and the appended claims.
Summary Of The Invention
The present invention is a thermally expandable composition for use in actuators comprising about 10-50 weight percent graphite particles dispersed in a wax or polymer. The composition has a thermal conductivity of at least 0.2 watts/(meter°C) at ambient temperatures. Ambient temperatures refer to temperatures in the range 22-28°C. The graphite particles in the defined ratio provide an unique and substantial match of the density of the wax or polymer when such wax or polymer is in a molten or semi-molten state or during the actuating process.
Detailed Description Of The Preferred Embodiments
In one preferred embodiment of the present invention, 50% by weight graphite particles, preferably powder, are melt blended with a suitable wax to substantially uniformly disperse the powder in the wax.
The resulting composition has a much higher thermal conductivity than does the wax alone, typically 0.4-0.5 watts/(meter°C) at ambient temperatures.
This composition can be used in an actuator that requires a thermally expandable material such as a wax or other material. The composition of the present invention produces a much faster response time for the actuator because the wax can be heated or cooled much more rapidly due to its enhanced thermal transfer rate compared to wax without graphite particles. The composition further provides a unique method of matching substantially the density of the wax or polymer by the graphite particles when the wax or polymer (the expanding/contracting ingredient) is in the molten or semi-molten state or during the actuating process.
Although graphite powder is the most preferred form of graphite in the practice of the present invention, other graphite particles may be employed, including fibers or fibrils.
Any type of wax or polymer material that is suitable for use as the thermally expandable material in an actuator may be used in the present invention. Many such waxes are commercially available as montan wax, polyethylene wax, polypropylene wax, wax emulsifiers and the like. Some typical trademarked names for useful waxes are, for example, Hoechst Wachs S, LP, E, HP, PE, NE, Ceridust and many such others (available from Hoechst AG, Frankfurt, Germany).
The temperature and technique for blending the graphite particles into the wax material may vary depending upon the material used, but the selection of the blending method is well within the ordinary skill in the art.
It is not necessary that the blending be done by melt blending. Any method that disperses the graphite in the material uniformly is suitable in the practice of this invention. It is important that the graphite is well- dispersed throughout the material so that the conductivity of the entire material is enhanced.
It is preferred that the composition contains about 10-50% by weight of graphite particles. In compositions containing less than 10% graphite the thermal conductivity may not be increased sufficiently, whereas compositions having more than 50% will have such a low proportion of expandable material that the composition may not expand sufficiently to be useful in the actuator. The skilled practitioner can tailor the composition to achieve a desired combination of thermal conductivity and expansion by thoughtfully selecting the proportion of graphite particles to be blended with a given material.
Typically, in those compositions of the present invention which consist essentially of a wax and graphite, the thermal conductivities are about 0.2-0.5 watts/(meter°C) at 23°C, as measured by the flux method described by M. R. Kamal et al, Advances in Polymer Technology, Vol. 3 (No. 2), 89 (1983). It is preferred that the thermal conductivity of these 6 compositions be at least about 0.3 watts/(meter°C), more preferably at least about 0.4 watts/(meter°C), at ambient temperatures.
Matching of the density of the wax or polymer by the graphite particles when the wax or polymer is in its molten or semi-molten state or during the actuating process is an important and unique advantage of the present inventive compositions. If the densities are not substantially matched, then there is the danger of phase separation of the ingredients during the actuating process. The inventive compositions offer an advantage of such density matching. The following Examples are presented to illustrate the present invention, but should not be construed as limiting the scope of this invention.
EXAMPLES AND COMPARATIVE EXAMPLES A wax made by Hoechst AG., known as Hoechst Wachs E™, was used to prepare compositions for thermal conductivity tests. Approximately 200 grams of each composition were prepared with the additives indicated in Table 1 , including a control containing only the wax. The wax and additive for each composition were melt blended for about 30 minutes at 100 rpm and about 120°C. After cooling, these compositions were ground into a course powder and then compression molded into plaques 3" x 3" x 1/8" using a hot press at about 170°C for 1.5-2.0 minutes, followed by rapid cooling under pressure.
The thermal conductivity of each sample was measured at 23 °C using an apparatus set-up similar to the one described by M. R. Kamal ef al, referred to above. The results are presented in Table 1 ; the examples illustrating the present invention (i.e. graphite particles) are in bold typeface. Table 1
Composition Additive Thermal Conductivity in warts/(meter°C)
None (Control; only wax) 0.120
25% Diamond Powder 0.134
50% Diamond Powder 0.161
25% Silicon Nitride Powder 0.143
25% Silicon Nitride Mesh 0.147
10% Graphite Fibers 0.216
50% Graphite Powder 0.433
50% Tungsten Powder 0.146
25% Copper Powder 0.162
50% Copper Powder 0.177
The data in Table 1 indicate that graphite produces a surprisingly high thermal conductivity compared to metal powders, silicon nitride, and diamond powder (non-graphitic carbon). Although none of the other materials produced a thermal conductivity of 0.2 watts/(meter°C) even at a 50% level, a mere 10% graphite fiber produced a thermal conductivity greater than 0.2 watts/(meter°C). At comparable loading levels, the graphite appears to produce 2-3 times greater conductivity, demonstrating the advantageous aspects of the graphite-containing wax compositions of the present invention.
Many variations of the present invention not illustrated herein will occur to those skilled in the art. The present invention is not limited to the embodiments illustrated and described herein, but encompasses all the subject matter within the scope of the appended claims.

Claims

ClaimsWhat is claimed is:
1. A thermally expandable composition for use in actuators comprising up to about 10-50 weight percent graphite particles dispersed in a thermally expandable material.
2. The composition of claim 1 wherein said material comprises a wax.
3. The composition of claim 1 wherein said material comprises a polymer.
4. An actuator comprising the thermally expandable composition of claim 1.
5. A thermally expandable composition for use in actuators having a thermal conductivity of at least about 0.2 watts/(meter°C) at 23°C comprising approximately 10-50 weight percent graphite particles dispersed in a wax.
6. An actuator comprising the thermally expandable composition of claim 5.
7. A composition according to claim 5 wherein said conductivity is at least about 0.3 watts/(meter°C) at 23° C.
8. A composition according to claim 5 wherein said conductivity is at least about 0.4 watts/(meter°C) at 23° C.
9. An actuator comprising the thermally expandable composition of claim 8.
10. A device comprising said actuator of claim 1 .
1 1 . A thermally expandable composition for use in actuators comprising up to about 10-50 weight percent graphite particles dispersed in a thermally expandable material, wherein said graphite particles substantially match the density of said material during actuation.
12. A process to substantially match density in the melt of a thermally expandable material by blending said material with about 10-50 weight percent graphite particles prior to melting of said material such that said particles are uniformly dispersed in said material.
13. The process of claim 11 , wherein said material is a wax or polymer.
PCT/US1996/015868 1995-10-23 1996-10-03 High thermal conductivity waxes and polymers WO1997015630A1 (en)

Priority Applications (2)

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US54664995A true 1995-10-23 1995-10-23
US08/546,649 1995-10-23

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1997031081A1 (en) * 1996-02-23 1997-08-28 Hoechst Celanese Corporation Thermally expandable, viscosity modified wax compositions and method of use in actuators
US6552472B1 (en) * 1998-12-05 2003-04-22 Robert Bosch Gmbh Piezoelectric actuator
DE102014208355A1 (en) * 2014-05-05 2015-11-05 Behr Thermot-Tronik Gmbh Wachsdehnstoff

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4206102A (en) * 1976-09-15 1980-06-03 Mobay Chemical Corporation Method of producing polyurethanes with increased resistance to abrasion
WO1994021452A1 (en) * 1993-03-24 1994-09-29 E.I. Du Pont De Nemours And Company Wet-laid sheet material and composites thereof

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4206102A (en) * 1976-09-15 1980-06-03 Mobay Chemical Corporation Method of producing polyurethanes with increased resistance to abrasion
WO1994021452A1 (en) * 1993-03-24 1994-09-29 E.I. Du Pont De Nemours And Company Wet-laid sheet material and composites thereof

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
DATABASE WPI Derwent World Patents Index; *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1997031081A1 (en) * 1996-02-23 1997-08-28 Hoechst Celanese Corporation Thermally expandable, viscosity modified wax compositions and method of use in actuators
US5772949A (en) * 1996-02-23 1998-06-30 Hoechst Celanese Corp. Thermally expandable, viscosity modified wax compositions and method of use in actuators
US6552472B1 (en) * 1998-12-05 2003-04-22 Robert Bosch Gmbh Piezoelectric actuator
DE102014208355A1 (en) * 2014-05-05 2015-11-05 Behr Thermot-Tronik Gmbh Wachsdehnstoff
EP2942371A1 (en) * 2014-05-05 2015-11-11 Behr Thermot-tronik GmbH Wax expansion material

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