CA1307927C - Radio frequency energy sensitized compositions and method for sensitizing compositions to radio frequency energy - Google Patents

Abstract

ABSTRACT

A composition of enhanced radio frequency sensitivity and a method for providing enhanced radio frequency sensitivity to a compo-sition in which a substance suitable for enhancement of radio frequency sensitivity is admixed with a radio frequency sensitizing amount of bentonite clay inorganic radio frequency sensitizer treated essentially to remove absorbed water and/or other volatiles. A process for molding using these compositions and the molded product. The composition, method for enhancing radio frequency sensitivity, process for molding and molded product with a polymeric substance, particularly ultra high molec-ular weight polyethylene, as the substance suitable for enhancement of radio frequency sensitivity.

Description

RADIO FREQUENCY EN~RGY SEN'31TIZED COMPOSITIONS AND
METHOD FOR SENSITIZING CO~POSIT:[ONS TO RADIO FREQUENCY E~ERGY
Background of the Invention This inve~tion relates to the enhancement of sensitivity of compositions to radio frequency eQergy. In one of its aspects it relates to compositions that are transparent to radio frequency energy. In another of its aspects this invention relates to compositions that have low sensitivity to radio frequency energy. In another of its aspects this invention relates to compositions whose sensitivity to radio frequency energy has been e~hanced.
It is k~ow~ that sold hygroscopic fillers ca~ be added to certain polymer compositioQs to provide receptivity to microwave (MW) radiation (See U.S. 4,234,636). It has been noted that the microwave ~eceptivity of these polymer compositions is significantly reduced by drying the filler~ before compounding with the polymers. It has, therefore, been sugg~sted that water associated with the hygroscopic filler is responsible for the MW receptivity.
It is ~lso k~own that polar organic compounds can be admixed with particul~te i~organic materials such as silicas to provide MW
senjitizi~g compositions suitable for blending with polymers to provide MW receptivity to the resulting polymer compositions (See U.S.
20 4,360,607).
It has now been found tha~ certain iuorganic compounds can provide radio frequency (R~) radiation receptivity to a wide variety of co~positions, especially polymers 9 after these inorganic compounds have . ~

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2 ~ 3~9~7 31388CA

been essentially dried and in the absence of added polar organic co~pounds. This invention, therefore, provides many opportunities to utilize RF radiation for heating of compositions containing these certain inorga~i-c compounds so that a multiplicity of products, such as molded objects, can be produced for a multiplicity of purposes.
It is, therefore, an object of this invention to provide a ~ethod for enhancing the radio frequ~ency sensitivity of compounds to which the process is applicable. It is another object of this invention to provide compositions of enhanced radio frequency sensitivity. It is still another object of this invention to provide compositions containing certain inorganic compounds so that these co~positions have enhanced radis frequency sensitivity as compared to the CompOsitiOQs without these inorganic compounds. It is still another object of this invention to produce molded objects by subjecting compositio~s of enhanced radio f~equency sensitivity to radio frequency energy in a molding operation such as transfer, injection or compression ~olding. It is still another object of this invention to enhance the radio frequency sensitivity of suitable polymeric materials, particularly ultra hi8h molecular weight polyethylene.
Other aspects, objects and the various advantages of ~his invention will become apparent upon reading this specification and the appended claims.
Statement of the Invention .
In accordance with this invention there are provided compositions in whi-h ~here is a substance suitable for enhancement of radio frequency sensitivity and a radio frequency sensitizing amount of an inorga~ic radio frequency sensitizer treated essentially to remove absorbed wat~r and/or other volatiles said sensitizer chosen from the ~roup consisting of (1) zinc oxide (A~erican Process~, 12) bentoaite 3Q clay, and (3) crystalline or a~orphous al~ali or alkaline earth metal aluminosilicate.
In an embodimeDt of the invention a method is provided for enhancing the radio frequency sensi~ivity of a substance suitable for such enhancement in which there is ad~ixed with the substance suitable for radio frequency enbance~ent a radio frequency sensitizing amount of

3 1 3 l3 7 '~ ~ ~ 3l3a8c~

an i~ic radio f~e~cy ænsitizer ~at~d essentially to rem~ve absor~sd water a~or othe~ volatiles wi~ a s~nsiti2er ~en fr~n the group cca~!3ist~r~ of (1) zinc cxide (~ican pr~c~s, (2) ~it~ clay, ar~ (3)- c2ystallin~ or an~rpa~ aL'cali or aLlcal~ne ear~ metal S al~ilicate.
~ ar~ther onbodimer~ oî the ~entiorl oca~o6itio~s in accordanoe with the radio fre~ ~h~c of this ir~re~ion are subjected to ~io fr~ ~nergy in a pI'OCeS8 for pmducing nolded ~j~s. .
Ihe sui'cable ~non3anic RF sensiti2ers in th~ is~s~ ~ver~tion pmc~3s), b~anite clay, and cry~allin~ or amorF~ aL~li o~ aL~line "A~3rican pr~s" zirc ~dde is a w~ll h~n a~rcially 15 available material. A~ t~ frc~ 'che "F~ p~3" nHterial, "Pærican praces~" zinc aKidQ is ~ai~ ~y roasti~ of a ~;ui'cable zinc ore ~ ~ha "F~ proc~fi" empl~ an coridaticn of vaporized zinc mEtal. An ~91~ o~ a suitable zin~ oxide i~ ~55R fr~ P~erican - 20 shown bela~:

TE~ ~II,lES (Ave:~e) specii~ic Gra~ity 5, 6 ~ E~ E3ulks~ Gall~ 0.0214 A~: D~ns~ty (I~a./al. f~.) 32 Particlo Di3m~r (Micro) 0.27 Su~aca A~a (Sg.~./gm. ) 4 . 00 ~ast Oil Ab~ption 14 Finer~ thm 325 Mb~h % 99.95 ~c~ Analysi~ ' Z~ (Z~) 99 . 209~

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4 31~88~

Iead (P~) O . 02%
ca~um (a~) o . 0596 Sul~ur (S) O . 03~6 - H20 Solubl~ Sal~ 0.309~

5. Lnsoluble in HCl 0.15%
I~ss at 105'C 0.1096 Berlb~nite clay, partiallæly the '~ type", ~ dlsclosed in U.S. 4,234,636 as a hy~60cpic filler in the prc~r art prQ~

10 suit~ble in the ill~ inv~tian al~tnr a heatir~ ~ to dri~e off tain~ ap~ciable zu~ts of clay ~iner~ m~morillanite, (M~, Ca) O-A1203-5SiO2-~20. AEI ~ abave ~ clay çbtair~ frc~ tha Wes~ sta~s o~ ~ U~ ~ ~xre~err~d Por u~ ln ~a in~ ~.o~.

11~ aL~li or ~ine ear~ matal al~osilicates ar~ a preferr~d gm~ o~ e~itiz#r~ dC~dlhjr ~o 'chi~ ~er~ic~n. Ih~

25 ex~qplified by ~ ~:cially availabla Zeolex 23R, Zeol~ 7~, or zeoleK 7AR ~m J. M. ~ Corp~, Harva d~ Graoe, ~. Ihe suitable zeolitsE~ which a~ c~tallin~ ~nds oc~ o~ l~ of sili~ ~ide~ in ~ al~ at~ have replaced same of ~ silic~.
30 ~ ze~lites ara well knch~ fo~ tbeir icsn ~ ~havior and ~l~lar withln ~ fD~ o~ A, l~ps D, Type L, ~ps R, ~p~ S, Type T, X, q~pe Y ~ ~ ~5. ~re sp~ ic ~le~ inc~lu~ l~pes 3A, 4A, ~A, lOX, 13X, Z5~8 and ZSM~ll.

, 1 307~27 The average particle si~e (diameter) of the inorganic RF
se~sitizers of this inv~ntion is generally within the range of about 0.25 micron to about 15 microns, preferably from about 0.5 micron to about 7 micronS. The surface a~ea (BET mechod) can range from about 1 m2/g to S about 1,000 m2/~, preferably from about 200 m2/g to about 500 ~2/g, For best results, if a material with low surface area is chosen the parCicle size should be as small as practicable. Cooversely~ if a material of large particle size is chosen the surface area should be as hi~h as practicable. In some instances it may be desirable to suoject the material to a preliminary size reduction stcp to i~prove its effectiveness as an RF sensiti~er in the application under consideration.
This also may be especially helpful. when the ~F sen~itizers of this inYe~tion are intended for use in polymer composition~. It is generally true that the physical properties of polymer are least affected when the particle size of the added material is a~ the s~allest end of the raQge.
Si2e reduction can be accomplished by conYentional methods such as grinding, ball milling and the like.
As noted above the inorganic RF sensitizers of the instant invention are subjected to a preliminary treating step which effectively removes adsorbed water and/or other volatiles which might be present.
The conditions employed in the treating step can vary widely dependin~ on the amount of adsorbed water and/or o~her volatiles present among other considerations. Usually hea~ing to a constant weight will be adequate to provide an inorganic RF sensitizer of this invention ~ree o~ adsorbed water and/or other volatiles. Generally, the temperature can range from about 100C to ~bout 300C while the time can r3n~e fro~ about O.S hour to about 72 hour~ in ~he heatin~ s~ep of this invention. rhe heating can be carried out at at~ospheric pressure and in a flowin~ gas such as air, ni~rogen, ar~on or helium if desired. The heatin8 also can be conducced under reduced pressure such as achieved by conventional vacuum pumps.
The inorganic RF sensitizers of this invention which have been treated as described above can be mixed wi~h the material to be subjected to RF radiation in a variety of conventional ~ethods.
For polymer compositions it is particularly effective and pr~ferred to dry blend the inorganic RF sensitizer with solid poly~er 1 307`'327

6 31388C~

~icl~ ~i~h may oantaln ~her a~ tional additives su~ as anti-oxida~ts, pi~s, fillers and the like. Ihe pol~ner particles will preferable have an average particle ~ize of fmm ab~ lo mesh- to a~t 40 nesh tha~h smaller or lar~er particles can be ~plc~ed if desired.
S It is also po~sible to u8e a melt blerx~ peration to ~corporate the inorgarlic RF sensitizer into a polym~r ca~o6itic~ uch as by employing a mixing e~ctn~. ISle RF s~nsitizer can bo a~d be~ore, after, or *ur~ng ad~itian of other polymer a~itives .~n the mixir~ extru~ ~peration.
It ~s ~lso poesi3~le l:o pr~pare a di~ersion of a finely divided inorganic ~F sensitizer in a liquid ~ h is ess~tially inert to RF
r~iation e.g., a ~ hav ~ 5-30 ~L~n atcms, and then oontacting the material be mads RF sensitiv~ w.ith s;~id dispersion ~ by spraying.
milling, tumbling or stirring withcut or with ~ubi qyenC re~oval o~ the dispersion vehicle such as by vacuum aæsist~d evapora~ion.
For ~F t~]n3p~rent poly~ers thQ amount o~ lnorganic RF
sensiti~er employ~d acoording to this inwantlon can be broadly from akcut 1 wt. ~ to about 20 wt. % b ~ an th~ w~igh~ o~ ~he tokal ccmpo#itlon.
Preferably, the amcun~ wlll ranga ~ro~ about 4 wt. ~ to abcut 6 wt. ~ on the same basi9 a5 ~bffV~. These ranges are also particularly suited to RF
equipment of abcut 1 XW power at 100 MH2 ~reqyEncy. For RT eqyipment of hiqher power and frequen~y it wculd be expected that the a~cunt3 of RF

n~re, if thQ polym~ emplayed ha~ sa~ R~ re~nsiveness then th~ amount of RF 9en~itiZOE can ~1 SO be reducel S~ the RF
absorption effecbs ~ polym2r and sersitizer ax~ add~tive.

2450 MXz, 5800 MHz and 22000 MHz ~or ln~o3trLal hatiny unit~ to minimize confiict wi~h oo~unicat$on systems. The cç~positions whlch are RF
sensiti~ed 3cccrding to ~ha ins~ant inven~l~n can be treated ~ th elactromagnetic raliation og pre~erably fr3~ akou~ LMH2 to about 2500 MHz, more preferably ~rom about 20 ~H~ to ~ 1000 M~z.
Sevexal m2nu~ac ~ providQ equlpment sui~able for generatLng the RF radiati~l withln tha needed ran~es. An exampl~ LS Ihrmall #gR

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1 307~27

7 31388GA

Electronic Heating Equipment with 1.25 kW power at 100 ;~Hz made by W. T.
La~ose & Associates Troy, NY.
Power absorption is governed by the equation P = 1.4l (E/D)2 x f x E" where P is in watt/in3, E is the electrode voltage in kV, D is the electrode distance in inches, f is frequency in MHz and E" is the dielectric loss factor which is the pr~duct of the dielectric constant, E', and dissipation factor, tan ~. This equation is well known to those skilled in the art of RF or MW heating and can be used to adjust availabLe equip~ent to the compositions being treated with RF energy.
Broadly speaking, the inorganic RF sensitizers of the instant invention are useful Ln essentially any composition wherein the inorganic compound is not materially detrimental and which is to be subjected to RF
radiation for heating purposes. Thus, the inorganic ~F sensitizers of this invention provide opportunities to use RF radiation for heatin8 in a multitude of applications.
One area of application that is especially i~portant involves polymer processing. In operations such as injection ~olding, transfer molding, blow molding, vacuum formin~, extrusion, softenin~, foaming, shaping, curi~g and the like the RF se~sitized polymer compositions can be subjected to RF radiation to efficiently provide the needed heat to accomplish the desired operation. The inorganic RF sensitizers ca~ be used in presence of other poly~er compounding iQgredients such as carbon black which are also RF sensitive to so~e extent to eDhance the level of RF sensitivity of the composition. This ~nhance~ent can also be obtained with the use of the iuventive inorganic RF sensitizers in certain pDlar poly~ers which are in t~sel~es RF sensitive. One particular area within the field of poly~or processing that is especially aided by the inorgauic RF sensieizers of this invention is that of handling ultra high 3~ molecular weight polyethylene (UH~WPE). .It is recogni2ed that this material has many desirable properties but the ultra high molecular weight ~hich is Ippar~ntly responsible for the desirabl~ properties also makes this material extre~ely difficult to proces~. RF heatin8 has been utilized with carbon black as the RF se~sitizer but this has not been entirely satisfactory especially if articles havin~ color other than ''~

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8 1 3~7927 31388CA

black are desired. Accordin~ to the instant invention ~he ~ PE
material can be intensively mixed with an inorganic RE sensi~izer of this invention and then subjected to RF radiation during the molding, e.g.
transfer,- injection, or compression molding, of various articles therefrom.
The following are processes and COmpOSitiODs suitable in processes illustrative of the present invention. These examples should be taken as illustrative and shouid not be considered to be restrictive.

~" 9 1 3rJ7q27 Ex2Qnple~;
A li~ ~er of ~organic pa~ers wa~ tested ~or RF
~ive~ ~f.Qre i~d af~ dryim;J (heatin~:J) at 13~C (280F) for 18 h~. Ihe tests ~ere ~ by placir~ a waighed porticql of the 5 inorganic pa~er in a IeflanR Disl~ sampl~ holder of 3 3/32 in~ cavity diameter i~ 1/2 in*~ ~ich calld b~ covered Wit~l a 1/4 inch thick Teflc~ lid. me sa~le hol~er was pli~ced bet~ 6 ir~h x 6 inch electr~de pla~ set 1 1/2 in~ i~art in l~er~l #9R, 1.25 ~, 100 MHz heater made by W. T. IaR~6e and A;scciates, 1~, NY. Each san~le 10 wa~ ex~ed ~o the RF ras~ icn for th~ in~cated ti~De ~ile t~e a~t zx~d. ~e b~ch3r~ or "rx~ a~rr&-Tt ~ wa~ 167 m~.

illtO th~ sanple at several poirrts and th~ highest r~adin~ r~x orded.
15 l~tun~ grea~er than a~aut 600'F we~ es~mated. ~bl~ Ia presen~
rasult~ ~ for a ~ o~ inorganic pc~er~ wh~s::h i~r dryi~

re~t~3 for ~rtain aminQ treat~d or silar~ trea~ cla~ ~iC~ WerQ
rated a8 having '~derat~ ~r dryi~. It ~hauld ~Q noted 20 ~at th0 clay treating a~sts su~ a8 i~ ~ ~ld b~ ex~cted to i~ polarity to the clays and ~ ~vide SOE~ degr~ of RF
sensitivil~. Ihe naterialq in Tables Ia i~d Ib i~ ~ altside the 25 ff~a illustral:~ t~ RF ser~i~izers of ths in~a~ ~enticQ.

~ n, it i3 ~$r~ that th~ at~r ~a~rials in ~ Ic were 30 "~" to "~lle~t" in RF ra~3e ~ÇE drying.

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` 1 307927 EXAMPLE I I I
Tests were conducted which examined the effect of added amorphous sodium aluminum silicate on the microwave curing of a rubber composition containing carbon black. The compounding receipt is shown below.
Recipe Parts. bv wt Rubber(a) 100 Oil and stabilizers 11.5 Sulfur 0 5 Zinc dimethyldithiocarbamate 3 Zinc dibutyldithiocarbamate 3 Carbon black, N-390 ll Carbon black, N-550 30 Calcium oxide in oil 10 4,4'-~ithiodimorpholine 2 Sodium Aluminum silicate O or 9 (a) Oil extended (50 phr oil) ethylene/propylene/diene monomer (EPDM) rubber.
(b) Zeolex 23 from J. M. Huber Corp.
The compounds were mixed then fed in a contJnuous mam-er to a vacuum extrudar and the extrudate fed to a microwave curing oven (lO
KW Despatch oven made by Despatch Oven Co.) with surrounding air kept at 500F to prevent heat loss then to a hot air oven with 500F hot 25 air then through a water ba~h for cooling before take off on a turntable. At an extrudate cross section of about 0.4 square inch the results shown below were obtained.
Run IIIaRun IIIb (Control)(Invention) Zeolex 230, phr O 9 Linear spe~d, ft/min 20 27 Microwave power setting, KW 8 4 At an extrudate cross section of about 0.1 square inch the invention compound gave blistered product which indicated excessive 35 temperature during curing which in turn indicated that 9 phr at the amorphous sodium aluminum silicate was too much for the conditions used. However, the results shown for the thicker extrudate demonstrate a strong microwave cure promo~in~ effect for the Zeolex 23~ additive.

~r .~ . .

1 3079~7 This ls seen by increased oven throughput and a reduced microwave power output requirement. It should also be noted that the cure promoting effect was evident even though large amounts of carbon black were present ln tha compound. Carbon blacks are known to promote S microwave responsiveness in rubber compositions.
Example IV
The RF responsiveness of both amorphous and crystalline sodium aluminum silicate according to this inventlon was utllized to prepare sintered polymer compositions useful as filters the the like.
These ~ompositions are especially useful as filters and the like.
These compositions have excellent strength properties even though they are porous.
In these tests the polymer (Hercules UHMWPE 1900 IV 220 or 27) and RF sensitizing additive were ballmillsd for 45 minutes in a glass ~ar with steel balls. The resulting mixture (about 18 g) was placed ln the Teflon sample holder of the RF hearlng apparatus descrlbed ln Example I which served as the mold. In these runs the electrode platen distance was 1 5/8 inch. Each mlxture was sub;ected to very light mold pressure of 5.5 g/cm2 (none in Run 7 of Table IVa) during the RF radiation treatment. The results obtained in these runs are presented in Table IVa and IVb below. Ihe runs in Table IVa were made with an amorphous sodium aluminum sili~ate, Zeolex 7 UD~ from J.
M. Huber Corp. as the RF sensitizer whlle the runs in Table IVb were made with a crystalllne sodium aluminum silic~te, Arogen 3001 also from J. M. Huber Corp. as the RF sensitizer. Except as indicated for Runs 8 and 11-13 of Table IVb the mold was exposed to RF radiation as ambient temp~rature, i.e., no mold preheating.

1 307q27 Table IVa Hercules UHMWPE 1900 IV 22 Run Sensitizer, Exposure Max-Min Calculated No. php time, sec mA ~ Porosity (b) Observations 1 5 240 35-35 - Much loose powder 2 5 330 40-35 - Some loose powder, marginal 3 10 120 60-40 49 Good, but some loose powder on surface.
4 15 90 68-65 41 Very good. No loose powder 70-65 42 Very good. No loose powder.
6 25 70 100-90 48 Fair. Loose powder (a) on surface.
7 20 90 68-62 43 Fair. Some loose powder on surface.
(a) No pressure applied to mold.
(b) Ratio of product specific gravity over polymer specific gravity X 100.

Table IVb Hercules UHMWPE 1900 IV 22(a) Run Sensltizer, Exposure Max-Min Calculated b No. php time. sec mA ~ Porosit~ ( ) Observations 1 5 180 42-42 49 Good, but some loose powder on surface.
2 5 240 43-43 47 Excellent 3 10 120 90-70 50 Excellent 4 15 90 112-105 52 Excellent 150-140 50 Very Good 6 25 20 200- 50 Poor, much loose b powder on surface.
7 lO(b) 90 96-47 51 Excellent 8(C) 10( ) 60 100-50 54 Excellent 9( 10 120 90-72 51 Excellent ~O(a) lo(d) 120 90-70 - Poor, not sintered.
ll(c) 15 60 135-125 50 Excellent 12(C) 15( ) 30 135-125 49 Very good 13 15 45 137-72 51 Excellent (a) Runs 9 and 10 employed IV 27 type polymer.
(b) Added 1 php of N-ethyl-o and p-toluene-sulfonamide.
(c) Mold temperature increased to 320F before RF exposure.
(d) Added 1 php of glycerine.
(e) added 2 php of an azodicarbonamide blowing agent (Porofor ADC/M~ from Mobay Chemicals) and 0.5 php of American process type zinc oxide/.
X

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-'~ l9 1 307927 ~1388CA

The results in Tables IVa ~nd I~b dbove show that sintered polymer compositionS of suitable porosity and sCrensth for use as ~ilters can be readily made from ~ PE and amorphous or crystalline sodium alumin~ silicates employing RE heating. It was further sho~n that such filter materials have a very high absorption capacity ~or ordinary tobacco smoke in ~hat 20 mouthfuls of cigarette s00ke blown chrough the same filter area left only a small depth discolored.
It can also be seen that at about 25 php of inorganic RF
sensitizer there is interference with sintering of the U~PE polymer particles. In these tests about 10-15 php of sensitizer seemed co give best results.
Comparison o~ Runs 7 and 8 and Runs 4 and l1 of Table IVb show that preheating the mold to about 300-350F can reduce RF exposure time and improve surface sintering.
There is also indication that cslculated porosity of the material ca~ be controlled by mold pressurc, sensitizer level, exposure time and polymer particle si~e. Porosity appears to reach a maximum just before polymer starts to melt and mechanical strength also appears to peak near this same point. This point is observed whe~ the current just starts to increase from a minimum after first having passed a maximum.
It is also seen that organic additives (Run lO Table I~b), even in small amounts, seem to interfere with the sintering though Runs 7 and B of Table IVb show an exception to this effect.
It was also found that the RF sintering of polycarbonate or poly(phenylene sulfide) polymer powders to form porous materials was not successful because the sa~ples melted. It is believed that the sharp melting poi~ts of these poLy~ers was responsible for this behavior.
Example V
The effect of prehea~i~g conditions on the RF sensitivity of various i~organic materials W25 examined. These tests were conducted in the apparatus previou ly described in Example I. These tests measured weight (moisture) loss as well as RF responsiveness of ~he inorganic material after the preheating treatment. The results are presented in Table Y below. In each test about 18 g of sa~ple was employed for a 2 minute preheat at the indicated te~perature.

1 3~7927 Table V
Run Inorganic Molsture Time sec/to No. Material Loss~ wt ~ Reach Temp F
1 A 7.1 310/600~ b 2 B l.9 240/250 ( 3 C 9.6 150/Glow (b) 4 D 12.2 20/Glow (b E 13.9 70/Glow (b) 6 F 0 50/Glow 400C Preheat 8 A 9.1 360/400 9 b 31.8 240/400 b C 11.8 130/Glow (b) 11 D 21.1 40/Clow (b) 12 E 15.3 58/Glow (b) 13 F 0 30/Glow (b 14 G 20.4 60/Glow 600C Preheat A 9.9 360/270 17 C 16.8 500;Glow 18 D 22.2 40/Glow b 19 E 16.2 58/Glow ( ) F 0 30/Glow (b) 21 G 21.~ 60/Glow ( ) (a) A is precipitated hydrated amorphous silica, Hi Sil 233~.
B is a hydrated alumina, Hydral 705~.
C is a Western bentonite clay, Nygel.
D is a crystalline sodiu~ silicate (zeolite), Arogen 3001 E is an amorphous sodium aluminum silicate, ~eolex 7 UD~.
F is an American process zinc oxide, Type B, lead free.
G is a crystalline sodium aluminum silicate, Zeolite ZLD 1000 (b) Material glowed on e~posure to RF energy.
It is seen from Table V that RF responsiveness actually increased for materials B, E and F after preheating at 200, 400 and 600C while material A decreased in RF responsiveness as the preheat temperature increased, apparently due to the increasing mo1sture loss.
Material C and G firs5 showed an increase in RF responsiveness on increasing preheat: temperature from 200 to 400C but then decreased .~ in RF responsiveness as the temperature was raised from 400 to 600C.

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This decrease may have been due to a collapse of crystalline structure in these materials at sbout 530C. Material D appeared relatively insensitive to preheat temperature in terms of RF
responsiveness even though significant moisture loss occurred at each temperature which indicates that the RF responsiveness of this material was not significantly dep,endent on its water content.
EXAMPLE VI
Tests were conducted using the RF heating apparatus described in Example I at 1.5 inch electrode distance to exAmine the effect of polymer particle size on RF responsiveness of polymer particles (20 g) admixed (ballmilled 30 minutes) with 5 php of crystalline sodium aluminum silicate, Arogen 2001~, Type 4A zeolite, particle size >1 micron, surface area >200 m /g (BET/method) from J. M. Huber Corp. (The zeolite was not preheated.) Exposure time in each run was 45 seconds and the recorded temperature was obtsined by use of a needle pyrometer.
The results obtained in these runs are presented below in Table VI.

'~~ 22 1 3n79~7 31388CA

Table VI
A. _ ly(e~_nvlene Sulfide~ (a) Run No. Parll~ahæ_~la~L Lmeshl m~e F
1 > 12 18-3S 360 2 12 < 20 20-36 395 3 20 < 40 20-34 345 4 40 < 50 20-32 315 6 Unfractionated 20-33 340 B. Hig~ D P~lyethylene ( ) 7 > 20 17-32 220 8 20 < 40 17-32 210 9 40 < S0 16-30 192 < 50 16-30 189 11 Unfractionated 18-31 200 C. Ul~rahioh M~ Polyethylene ( ) 12 > 50 17-37 267 13 < 50 18-36 264 (a) Ryto ~ MR-03 (b) Marle ~ HXM 50100 (c) Hercules 1900 rv 22 As seen in Table VI above tha larger polymer particles appear to be more responsiva to RF heating. This may be due to a greater concentration of RF sensitizer on the surfac~ of said particles cauSLng greater en~n~y avsorption on the sur~a oe of the larger particles. If surface cverheating is exFxx~ted to be very dete~IL~ental then it will be preferable tc use a smaller particle size for the polymer and with a naumow particle size distribution if possible. If CrxLr~er polymer particle~ have to be used i~ wculd be preferable that they ba mixed with smaller polymer particles if possi~le.
Exa~ele VI~
Okher tests wore conducted with crystall m e or amorphcus sodium aliminum s.ilicates o~ varicus particle sizes used ~s RF
sensitizers in ultrahigh molecular weight polyethylene (~ercules UT~PE 1900 rv 22 , '^ ' 23 31,~8CA

powder). All of the sodium ~luminum silicates were SUpplied by J.~l.
Huber Corp. The tests here made using the R~ equipment previously described in Example I.
- In each test 50 g of ~H~PE powder was ball milled for ~0 min.
with 2.5 g of the sodium aluminum silicate. A 20 g ~ortion o~ che Dlend was placed in the sample holder cavity taking care that the bed thickness was uniform. The lid was placed on top of the sample holder and che material exposed to RF cross-field at an electrode distance of 1.5 inch for 30 and 60 seconds. As before, the temperature wa~ measured with a needle pyrometer. The ~mA~p value is the difference between the actual mA~p reading with sample in place and the mA~p reading for RF exposure of the empty sample holder. The sampLe holder was cooled to room temperature before each rest was run.
The results obtained in these tests a~e presented in Table VII
below.

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The results sho~n in TabLe ~II demonstrate that ~or the amorphous or crystalline sodium aluminum silicates a si~nlfic3nt improvement in RF sensitizing efficiency is seen in using those materials which ha-ve high surface area and small particle sizc. It is also S expected that the RF sensitlzer materlals of smaller particle s~ze will have less effect on polymer physical properties than similar ma~erials of larger particle size.

Claims (18)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for molding wherein a substance suitable for radio frequency enhancement is treated by the method comprising admixing with said substance suitable for radio frequency enhancement a radio frequency sensitizing amount of bentonite clay inorganic radio frequency sensitizer treated essentially to remove absorbed and/or other volatiles and then subjected to radio frequency energy in a molding process.

2. A method of claim 1 wherein said substance suitable for enhancement of radio frequency sensitivity is a polymer.

3. A method of claim 2 wherein said polymer is ultra-high molecular weight polyethylene.

4. A method of claim 3 wherein said sensitizer has been heat treated.

5. A method of claim 4 wherein said sensitizer is present in an amount in a range of about 1 weight percent to about 20 weight percent based on total composition.

6. A method of molding wherein a composition comprising a substance suitable for enhancement of radio frequency sensitivity and a radio frequency sensitizing amount of bentonite clay inorganic radio frequency sensitizer treated essentially to remove absorbed water and/or other volatiles is subjected to radio frequency energy in a molding process.

7. A method of claim 6 wherein said substance suitable for enhancement of radio frequency sensitivity is a polymer.

8. A method of claim 7 wherein said polymer is ultra-high molecular weight polyethylene.

9. A method of claim 8 wherein said sensitizer has been heat treated.

10. A method of claim 9 wherein said sensitizer is admixed in an amount in a range of about 1 weight percent to about 20 weight percent based on total composition.

11. A composition comprising a substance suitable for enhancement of radio frequency sensitivity and a radio frequency sensitizing amount of bentonite clay inorganic radio frequency sensitizer treated essentially to remove absorbed water and/or other volatiles wherein said sensitizer is present in an amount in a range of about 1 weight percent to about 20 weight percent based on total composition.

12. A composition of claim 11 wherein said substance suitable for enhancement of radio frequency sensitivity is a polymer.

13. A composition of claim 12 wherein said polymer is ultra-high molecular weight polyethylene.

14. A composition of claim 13 wherein said sensitizer has been heat treated.

15. A method for enhancing the radio frequency sensitivity of a substance suitable for radio frequency enhancement comprising admixing with said substance suitable for radio frequency enhancement a radio frequency sensitizing amount of bentonite clay radio frequency sensitizer treated essentially to remove absorbed water and/or other volatiles wherein said sensitizer is admixed in an amount in a range of about l weight percent to about 20 weight percent based on total composition.

16. A method of claim 15 wherein said substance suitable for enhancement of radio frequency sensitivity is a polymer.

17. A method of claim 16 wherein said polymer is ultra-high molecular weight polyethylene.

18. A method of claim 17 wherein said sensitizer has been heat treated.