CA1308248C - 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 zinc oxide (American process) 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 com-position, method for enhancing radio frequency sensitivity, process for molding and molded product with a polymeric substance, particularly ultra high molecular weight polyethylene, as the substance suitable for en-hancement of radio frequency sensitivity.

Description

3138&CA
8~

- RADIO FREQUENCY ENERGY SENSITIZED COMPOSITIONS AND
~METXOD FOR SENSITIZING SOMPOSITIONS TO RADIO FREQUENCY ENERGY
. .
Back~round of thc Invention ~: This invention relates to ~he enhancement of sensitivity o f compositions to radio frequency energy. I~ one of its aspects it relates to co~positions that are transparent to radio fsequency ene~gy. Iu another of its aspects this invention relates to compositions ~hat 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 enhanced.
It is known that sold hygroscopic fillers can be added to certain polymer compositions to provide receptivity to microwave (MW) radiation (See U.S. 4,234,636). It has been noted that the microwave receptivity of these polymer compositions is significantly reduced by drying the fillers before compounding with the polymers. It h~s, therefore, been suggested tha~ water associated with tbe hygroscopic 15 filler is respon~ible for the MW receptivi~y. ;~It i~ also known that polar organic compou~ds can be admixe~
with particulate inorganic ma~erials such as silicas to provide MW
sensiti2ing compositions suitable for blending with poly~ers to provide MW receptivity to the resulting polymer ~ompositions (See U.S.
4,360,~07).
It has now bee~ found ehat cer~ain inorganic compounds can provide radio frequency (~F) radiation receptivity to a wide variety of co~po~itions, especially polymers, af~er these inorganic compounds have

2 3138~CA

been essentially dried and in the absen~e of added polar organic compounds. This inven~ion, therefore, provides many opportunities to utilize RF radiation for heating of compositions containing these certain inorganic 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 method for enhancing the radio frequency sensitivity of compounds to which the process is applicable. It is another object of this invention to provide co~positions of enhanced radio frequency sensitivity. It is still another object of this invention to provide sompositions containing certain inorganic compounds so that these compositions have eDhanced radio frequency sensitivity as compared to the compositions without these inorganic compounds. It is still another object of this invention to produce molded objects by subjecting compositions of enhanced radio frequency sensitivity to radio frequency energy in a molding operation such as transfer, injection or co~pression molding. It is ~till another object of this invention to enhance the radio frequency sensitivity of suitable polymeric materials, particularly ultra high molecular weight polyethylene.
Other aspects, objects and the various advantages of this 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 which there is a substance suitable for enhancem2nt of radio frequency sensitivity and a radio frequency sensiti2in~ amount of an inorganic radio frequency sensitizer treated essentially to remove absorbed water and/or other vola~iles said sensitizer chosen from the gronp ConSiStiQg of (1) zinc oxide ~American Process), (~) bentonite clay, and (3) crystalline or a~orphou~ al~ali or alkaline earth me~al aluminosilicate.
In an embodiment cf the inve~tion a method is provided for eohancing the radio frequency sensitivity of a substance suitable for such e~hancemPnt in which there is admixed wi~h ~he substance suitable for radio frequency enhancement a radio frequency sensitizing amount of

3 31388C~

an ~r~anic radio fre~er~r sensitizer treated ess~ntially to remave absor~ed water arxVor othar v~latiles~ with a sensitizer cho6~ fr~n ~he gra~ consisting of (1) z~r~c cocide (American proc~s, (2) ~ite clay, and (3) ~ryE;~line or amorp~ous aL~i or aL'caline ear~ m2tal 5 al~ilicate.
~ anoth~ ~i~ of the invention c~ositians ~n accor~anoe with t~he radio Pre~ ~ar~t of this invention are s~ibjected to radio f~y ener3y in a proces~ ~or producing molded clbjects.
The suitablQ ~rganic RF sensitizers in the ins~ i~erltisn are selec~ad ~r~n the gr~ consistir~ of: 2~ cqcida [~ican pr~s), bentonite clay, and crystallin~ or amor~ aLkali or alkaline "An~ican pmc~ss" zinc ~d~ ~s a well kr~ ~cially 15 available ~t~rial. As distl~pl~d fr~n the IIF~ proc~s" naterial, th~ "P~ican pr~cess" z~rx: 0c~de is ~btained by roastir~ of a ~uitable zir~c ore ~ereaE~ t~e "F~ process'~ ~nplays an cxida~ian o~ vaporized zinc metal. An exan~le of a suiWle zinc cocidç~ is AZ0-5~R frcm kn~ican S~ltin~ i~ CoO, Colu~, ~hio, with ~pical pm~erties as 2 0 ~hawr~ h~l aw:

TE~lIC~L VAII~ (Average) l~ysical Bpertie~
cific Gravity 5.6 ~ne P~nd BuL~ Gallc~s 0.0214 A~2~rent Density (:tbs./cu. ft.) 32 Particle Diameter (Mic~ns~ 0~27 Surfaoe Area (Sq,m./s~m. ) 4 . 00 R~ Oil ~6Q~O~ 1 F~3 thn~ 325 ~3sh % 99.95 ~ , _ .
Ctwnical analyE~is zinc Q~ (Zr~) 99.20%

4 31388C~

lead (P~) O . 0296 Ca~ (ad) o. 05%
Sul ~ur (S) o . 03%
H20 Soluble Sal~
Insol~le ~ H~l 0.15%
~ss at 105C 0.10~6 Bentoqnite cla~, ~rtiallarly the ~tW~n ~pe", i~ disclos2d ~n U.S. 4,234,636 as a h~c~pic fill~ in the p~¢r art proc~s 10 suiWle ~n the ~nstant ~ ion a:Eter a hea~ir~ s~ to dri~le off al3sori~d wa~er. ~nite clay ~s a natl~rally cc~rrirJ3 material corltair~ aFpreciable amo~ of clay min~al n~rillo3lite, (~, ~a) O-A1203-5SiO~-~20. As nok0d abovla ~ite clay c~t:ai~l ~ ~e W~ state~ o~ ~e U~ is preferred ~or use in ~ i~ i~rticn.
15 A part larl5r use~ul West~n b~cs~ rial i~ N~el-5 fr~m prefen~d gr~ of ~F sensitiz~ ac~or~lir~ to thi~ i~verIticQ~. These materials can be either amorpa~s or cryst~line in nature and can be 20 ~tair~ l~ etic m~t~. Ih~ aL~li me~al i~ can ba lithium, ic~ can be ma~#si~m or calcium, usllally calciu~n. It is also po~sible for can~ ns o~ the al~e ic~3 to be pr~ in the ~l~nir~silicates 25 ex~lified by ~ o~i~ly ~able Zeolex 23R~ Zeol~x 7~DR, ~r Zeolex 7A~ fr~ J. M. ~ber Corp., E~ de Grace, MD. Ihe suitable zeolite~ which are crystalline ~ ~osed of te~s of sili~ axide in ~ibh alumi~ atc~ hav~ replaced s~ne of ~e silicon.
30 me zeolite~ are well krx~ for ~ i~ e~ e behavior arx~ mol~Llar wi~ ~e f~milies of Type A, Typ~ D, Iype L, Type 2, IYPQ S, I~pe T, Typ~ X, qypa Y and l~ 5. Mb~e sp~::ific e~les ir2clude l~ypes 3A, 4A, 5A, lOX, 13~, Z~8 ar3d ZSM-ll.

~ 31388CA

The average particle size (diameter) of the inorganic RF
se~sitizers of this inv~ntion is generally within ~he ran%e of about 0 25 micron to about 15 microns, p~eferably from about 0.5 micrOn ~o about 7 microns. The surface area (BET method) can range from about 1 m2/g to about 1,000 m2/g, preferably ~rom about 200 m2/g to about 500 m2/g. For best results, if a material with low surface area is chosen the particle size should be as small as practicable. Conversely, if a material of large particle size is chosen the surface area should be as high as practicable. In some instances it may be desirable to subject the material to a preliminary size reduction step eo improve its effectiveness as an RF sensitizer in the application under consideratioQ.
This also may be especially helpful ~hen the RF sensitizers of this invention are intended for use in polymer compositions. It is generally true that the physical properties of polymer are least affected ~hen the particle size of the added material is at the smallest end of the range.
Size reduction can be accomplished by conventional 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 depending on the amount of adsorbed watcr and/or o~her volatiles present among other considerations. Vsually heating to a constant wei~ht will be adequate to provide an inor~anic RF sensitizer of this invention free of adsorbed water and/or other volatiles. Generally, the temperature can range ~rom about 100C to about 300C while the time can ran8e from about 0.5 hour to abou~ 72 hours in the heating step of this invention. The heating can be carried out at atmospheric pressure and in a flowing gas such as air, nitrogen, argon or helium if desired. The heatin8 also can be conducted 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 with the material to be subjected to ~F radiation in a variety of conventional methods.
For polymer composi~ions it is pareicularly effective and preferred to dry blend the inorganic R~ sensitizer with solid polymer %~
6 31388C~

particle~3 ~ich may contain other c~nventic~al additives su~ as ar~
ox~dants, pig~, fillers an~ the like. The poly~[~r particles will preferable h~e an average particle size of fr~n abaut 10 mesh t~ ut 40 me~ thaugh smaller or lar~er particles can be ~nploye~ if desired.
It i5 al~;o poss~ble to use a malt blendi~3g cperatic~ to incorporate the ino~3anic RF sensitizer irr~o a polymer ca[~osition such as by e~ployi~ a addition of ~ther polymer ac~1itive~; ~n ~e mixi~ exl:n~ ~eration~
It l.c also possible to pr~pare a di~er~ion o~ a finely divided inorl3anic ~YF sensi~izer in a liquid which is esserltiall~,r ir~c to RF
radiation e.g., alkanes hav~ 5-30 car~on at~, and th~ co~tacting ~e ma~erial be mad~ RF sensitive wi'ch s,aid dispersion as by ~rayi~.
milling, t~lir~ or st~rr~rq wi~t or with s~s~ent remaval of the dispersian v~hicle such as }~y vacuu~ assisted ~vaporatic~.
For RP trar~r~r~ poly~rs the a~t o~ inor~3~c ~
sensitizer employed accordir~ to thi~ i~ian can be broadly fL~u abalt 1 wt. % l:o aba;rt 20 wt. % basad cn the wzi~ of ~e ~tal ca~o~ition.
~referably, the ama~ ~ill ran~ fmm abaut 4 wt. % to a~ 6 wt. % on the sam~ basis as above. Ihese ranges are also partia~larly suited 'co RF
e~iF~t of abaut 11~ paler at 100 ~Iz ~. For RF equipnent of higher pawer arx~ fre~en~y it w~uld be expected that the a~sts of RF
sensitizer can ba r~d.

t~ the amcunt o~ RF sensitizer can ~lso be r~ed s~ the RF
absorpticql effects of pol~ and s~itizer are additiv~.
In th~ 1~ the Federal oc~cation3 C~mnissicn (F~C) has 2450 MHz, 5800 MHz an~ 22000 ~z for ir~trial hl3atin~ ~mits tc mini~ize sensitized acccrdir~ to ~ instar~ inv~ti~ can be treat~ wi~h elec~na~ne~:ic radiatiall o~ pref~bly fr~su abaII: 1~ ~o ~t 2500 ~Iz, more preferably fr~ abaIt 20 ~IZ to a~ lûO0 MHz.
Several ma~fa~s pravide e~i~t sui~able for generating ~3Q~8 7 3138~A

Electronic Heating Equipment with 1.25 kW power at 100 ~Hz made by '~. T.
La20se & Associates Troy, NY.
Power absorption is governed by the equation P = 1.41 (E/D)2 x f x E" where P is in watt/in3, E is the electrode

5 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 product 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 equipment to the compositions being treated with 10 RF energy.
Broadly speaking, the inorganic RF sensitizers of the instant i~vention are useful in 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 i~organic RE sensitizers of 15 this invention provide opportunities to use RE radiation for heating in a multitude of applications.
One area of application that is especially important involves polymer processing. In operations such as injection molding, transfer molding, blow molding, vacuum forming, extrusion, softening, foaming, 20 shaping, curing and the like the RF sensitized polymer compositions can be subjected to RF radiation to efficiently provide the needed heat to accomplish the desired operation. The inorganic RF sensitizers can be used in presence of other polymer compounding ingredients such as carbon black which are also RF sensitive to some extent to enhance the level of 25 RF sensitivity of the composition. This enhancement can also be obtained with the us~ of the inventive inorganic RF sensitizers in certain polar polymers which are io themselves ~F sensitive. One particular area r withi~ the field of polymer processing that is especially aided by the inorganic RF sensitizers of this invention is that of handling ultra high 30 molecular weight polyethylene (UHnWPE). .It is recognized that this material has many desirable properties but the ultra high molecular weight which is apparently responsible for the desirable proper~ies also makes this material extre~ely difficul~ to process. RF heating has been utilized with carbon black as the RF sensitizer but this has not been 35 entirely satisfactory especially if articles having color other than black are desired. ~ccordin~ to the instant invention the ~n~PE
material can be intensively mixed with an inorganic RF sensitizer of this invention and then subjected to RE radiation during the molding, e.g transfer,- injection, or compression molding, of various articles therefrom.
The following are processes and compositions suitable in processes illustrative of the present invention. These examples should be taken as illustrative and should not be considered to be restrictive.

E~I
A lar~e rnm~ of ~n~r~anic pa~lers was tested for RP
~iveness before arxl after drying (heat~ng~ at 138C (280F) for 18 haurs. Ihe tests we~ c~nduct~3d by plac~r~ a wel~d portic~ of ~e 5 ~no~ganic pa~ler in a l~flar~R Di~ s~le holder of 3 3/32 irrh caYity dia~[eter and 1/2 ir~h dee~ whi~ ~uld be c~vered with a 1/4 in~ ~ick Teflc~ lid. Ihe san~le h~lder wa~ placed betwe~ 6 ir~ x 6 ir~
electrode pla~ens set 1 V2 ir~ a~art in T~ermall #9R, 1.25 k~, 100 ~ heat~ ~a~e ~ W. T. I~æe and As~ociates, 1~, NY. Eac~ sa~le 10 w~ e3~ to ~e RF ra~iatian for ~e ir~icated time while the c~
flc~w in mill~ ~mA) and te~erature rsached (F) ~y the sa~le were no~d. q~ bachgr~d or "r~load" a~t readir~ was 167 m~.
I~t~re ~asu~t wa~ a~in~ with a r~dle E~eter inser~d 15 ~er~b2res greater than aba~t 600~F w~re est~nated. q~ble Ia pres~
result~ ~btain~ for a rn~ex of inc~ c pa~s ~ich ai~ter dry~

re~ults for cartain am~ trea~6d or ^ilane tr~ 3d c~ays ~i~h were 20 that t~e clay traating agent~3 ~ a:3 amir~ ~ w~uld be expe~d to add polæit~ ~o the clay~ t~s pr~vide salle degree of RF
s~nsitivity. ~ e mat~rials in Table~ Ia and Ib ar~ tside the ~ e of the instant invention. Tahle Ic presents results on ino ~ ic pcw~ers which after drying show "Good" to "Excellent" ~T response and ~hese illustrate the RT sensitizers of the ins~ant inventicn.
It is surpr~ing that the A~erican process zinc oxide was '~ery good'~ in RF xespcnsa (Table Ic) after ~rylng while the French pGccess zinc oKide is essentlally "nonreqponiive" even befor~ drylng. In addl~icn, it 1 surpri~in~ ~ha~ the o~h~r materials in Table Ic w~re 30 71good" to "ex~lent" in RF r~ a~ dryir~.

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Example II
. Other tests were conducted with the same apparatus employed in Example I in ~hich amorphous sodium aluminum silicates (Table [c, Example I) were admixed with several RF transparent polymers to provi-le polymer compositions with RF sensitivity. The results shown in Table II below clearly demonstrate the effectiveness of the dried amorphous sodium aluminum silicates in providing RF sensitivity to otherwise RF
transparent polymers.

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EXAMPLE III
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.
Reci~e Parts. bv wt Rubber(a) 100 Oil and stabilizers 11.5 Sulfur 0.5 Zinc dimethyldiehiocarbamate 3 Zinc dibutyldithiocarbamate 3 Carbon black, N-390 11 ~arbon black, N-550 30 Calcium oxide in oil 10 4,4'-Dithiodimorpholine 2 Sodium Alu~inum silicate 0 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 continuous manner to a vacuum extruder and the extrudate fed to a microwave curing oven (10 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 air then through a water bath 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 IIIa Run IIIb (Control)(Invention) Zeolex 23~, phr 0 9 Linear speed, 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 temperature durin~ 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 promoting effect for the Zeolex 23~ additive.
X

This is 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 in the compound. Carbon blacks are known to promote microwave responsiveness in rubber compositions.
Example IV
The RF responsiveness of both amorphous and crystalline sodium aluminum silicate according to this invention was utilized to prepare sintered polymer compositions useful as filters the the like.
These compositions 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 22~ or 27) and RF sensitizir,g additive were ballmilled for 45 minutes in a glass jar with steel balls. The resulting mixture (about 18 g) was placed in the Teflon sample holder of the RF hearing apparatus described in Example I which served as the mold. In these runs the electrode platen distance was 1 S/8 inch. Each mixture was subjected to very llght 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. The runs in Table IVa were made with an amorphous sodium aluminum silicate, Zeolex 7 ~D~ from J.
M. Huber Corp. as the RF sensitizer while the runs in Table IVb were made with a crystalline sodium aluminum silicate, 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 temperature, i.e., no mold preheating.

. ..
X

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Table IVa Hercules UHMWPE 1900 IV 22 Run Sensitizer, Exposure Max-Min CalCulated (b) Obser~ations No, php time~ sec mA ~ PorositY
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 (a) Hercules UHMWPE 1900 IV 22 Run Sensitizer, Exposure Max-Min Calculated (b) php time. sec mA ~ PorositY _ _ 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 10( ) 90 96-47 51 Excellent

8(C) lo(b) 60 100-50 54 Excellent S( ) 10 d 120 90-72 51 Excellent 10( ) 10( ) 120 90-70 - Poor, not sintered.
ll(c) 15 60 135-125 50 Excellent 12( ) 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.
- 40 (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~.

19 ~l3~8CA

The results in Tables IVa and l~b above show ~hat sintered polymer compositions of suitable porosity and str~ng~h for use as filters can be r~adily made from ~ E and amorphous or crystalline sodium aluminw~ silicates employing RF heating. It was further sho~n that such filter materials have a very high absorption capacity for ordinary tobacco smoke in that 20 mouthfuls of cigarette smoke blown through 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 UXMWPE polymer particles. In these tests about 10-15 php of sensitizer seemed to give best results.
Comparison of Runs 7 and 8 and Runs 4 and 11 of Table IVb show that preheating the mold to about 300-35GF can reduce RF exposure time and improve surface sintering.
There is also indication that calculated porosity of the material can be controlled by mold pressure, sensitizer level, exposure time and polymer particle size. 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 when the current just starts to increase from a minimum after first having passed a maximum.
It is also seen that organic additives (Run 10 Table IVb), even in small amounts, seem to interfere with the sintering though Runs 7 and 8 of Table IVb show an exception to this effect.
It was also fou~d that the RF sintering of polycarbonate or ~5 poly(phenylene sulfide) polymer powders to form porous materials ~as not successful because the samples melted. It is believed that the sharp melting points of these polymers was responsible for this behavior.
Example V
The effect of preheating conditions on the RF sensitivity of various inorganic materials was examined. These tests were conducted in the apparatus previously described in Example I. These tests measured weight (moisture) loss as well as RF responsiveness of the inorganic material after the preheating treatme~t. The results are presented in - Table V below. In each test about 18 g of sample was employed for a 2 minute preheat at the indica~ed ~emperature.

Table V
Run InorganicMoisture Time sec/~o No, MaterialLoss, wt_~ Reach Temp_F
1 A 7.1 310/600~ b 2 B 1.9 240/250 (b) 3 C 9.6 150/Glow ( ) 4 D 12.2 20/Glow (b) E 13.9 70/Glow ( ) 6 F 0 50/Glow (b) ; 10 7 G 11 7/450 400C Preheat .
8 A 9.1 360/400

9 b 31.8 240/400 b C 11.8 130/Glow ( ) 11 D 21.1 40/Glow (bb) 12 E 16.3 58/Glow (b 13 F 0 30/Glow b 14 G 20.4 60/Glow ( ) 600C Preheat A 9.9 360/270 16 B ~ b 17 C 16.8 500/Glow (b 18 D 22.2 40/Glow b 19 E 16.2 58/Glow (b) F 0 30/Glow 21 G 21.8 60/Glow (b) (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 sodium silieate (zeolite), Arogen 3001 E is an amorphous sodium aluminum silicate, Zeolex 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 exposure 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 moisture 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.

X
. .

~3~ 8 This decrease may have been due to a collapse of crystalline structure in these materials at about 500C. Material D appeared relatively insensitive to preheat temperature in terms of RF
responsiveness even though significant moisture loss occurred at each temperature which indicate~ that the RF responsiveness of this material was not significantly dependent 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 ths 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 20010, Type 4A zeolite, particle size >1 micron, surface area >200 m /g (BET/method) from J. M. ~uber Corp. (The zeolite was not preheated,) Exposure time in each run was 45 seconds and the recorded temperature was obtained by use of a needle pyrometer.
The results obtained in these runs are presented below in Table VI.

~, . ... . .

22 ~ 31388CA

TablP. Vl A. Poly(phenylene Sulfide) (a) Run No. Particle size (mesh~ ~mAmp F
1 ~ 12 1~-35 360 2 12 < 20 20 36 395 3 20 < 40 20-34 345 4 40 < 50 20-32 315 6 Unfractionated 20-33 340 Hiqh MW HD Polyethylene_(b) 7 > 20 17-32 220 8 20 < 40 17-32 210 9 40 < 50 16-30 192 < 50 16-30 189 11 Unfractionated 18-31 200 C. Ultrahi~h MW Pol~ethylen~ (C_ 12 > ~0 17 37 267 13 < 50 18-36 264 (a) Ryto ~ MR-03 (b) Marle ~ HXM 50100 (c) Hercules 1900 IV 22 As s~en in Table Vl above the larger polymer particles appear to be more responsive to RF heating. ~his may be due to a greater concentration of RF sensitizer on the surface of said particles causing greater energy avsorp~ion on the sur~ace of the langer particles. If surface overheating is expected to be very determinental then it will be preferable to use a smaller particle size for the polymer and with a narrow particle size distrikution if possible. If ~ r polymer particles h~ve to be used it w~uld be preferable that they be mlxed with smaller polymer particles if possible.
Example VII
Okher tests were ~onducked with cxystalline or amorphous sodium alimlnum silicat~s of various particle sizes used as RF
sensitizers in ultrahigh molecul æ weight polyethylene (Hercules 23 ~ CA

powder). All of the sodium 31uminum sllicates were supplipd b~ J.:l.
Huber Corp. The tests here made using the RF e4uipment ~reviously described in Example I.
In each test 50 g of ~PE powder was ball milled for ~0 min.
S with 2.5 g of the sodium aluminum silicate. A 20 g portion of the blend 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 the material exposed to RF cross-field at an electrode distallce of 1.5 inch for 30 and 60 seconds. As before, the temperature was measured with a needle pyrometer. The ~mAmp value is the difference between the actuzl mAmp reading with sample in place a~d the mAmp reading for RF exposure of the empty sample holder. The sample holder was cooled to room temperature before each test was run.
The results obtained in these tests are presented in Table VII
lS below.
' ~ 1~
a ~ ~1 n ~ L~ Ln :
-I la -- ___L~__ ~Jl Ll I
O
X l ~ O -- -- ~ ~ ~ 1-- ~ ~ O O
:~," ~ _ ~ L~ n ~o .. o ~ L~ L~J _ ~ L~
~J

~,q ~i 3 IIIII~ IIIIIII ~IJ
e r~ nL~ L~ c <I
L~
"
_ U~ ~ , O ~ U ~ t,l 'J ~ J J ~J
~ ~ L~ , . . ¢j .~1 ~ ~ L ~ O L~ L--l ~
3 . _ _-~ L~ ~ L~ ~ ~ ~
_ L~
:~ oo ~-- OJ N '~
u E L~ o E- ~ ~ - o o L~ LL~l ~ _ 00 ~ O
O o o o ~ L~1 o o :r~ Ln L~
O ~O ~q ~ L~ O O
.~

-~ C o ~ u ~ U~ I~ ~~ O O t~l O O O
N ~J

;~
ta ~ ~ O
_ ~ ~ ~ ~~I oa '`
~ U,,,,,, ,,,, .,,, ~ O --2 _1 ec ~:
._1 U~ U~
1~ ~ O
a. ~n e ~ 4~
0, ~ ~ ~ ~ u ~: Z ~
U~ o ~J

g5 ~ CA

The results sho~n in Table ~II demonstrate that ~or the amorphouS or crystalline sodium aluminum silicates a signL~icant improvement in RF sensitizing efficiency is seen in using those materials which ha-ve high surface area and small particle size. It is also expected that the RF sensitizer materials of smaller particle s-ze will have less effect on polymer physical properties than similar materials 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 zinc oxide (American process) 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 frequence sensitizing amount of zinc oxide (American process) 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 zinc oxide (American process) inorganic radio frequency sensitizer treated essentially to remove absorbed water and/or other volatiles wherein said sensitizer is present in an amount in a 27 31388CAl 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 zinc oxide (American process) 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 1 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.