Note: Descriptions are shown in the official language in which they were submitted.
6~
This invention relates to improved m~lded
articles from sintered particulate solids and to methods and
materials for producing articles from particulate materials
which exhibit unusual physical integri~y in the green body
stage and unusual dimensional precision as final products,
i.e., after "burn-out" and sintering~ ln particular, this
invention is concerned with articles produced by mixing
particulate solids with a thermoplastic, sacrificial-binder
- material, molding the article into its green body configura-
tion, burning out the sacrificial-binder material and sinter-
ing ~he particulate solids into a single solid mass, with
methods for making such articles and to uni~ue sacrificial
binders for use in making such articles. This invention is
applicable to all particulate solids which are sinterable,
as that term is hereinater de~ined.
: . ' . .::
:: :~ ~ ::: :
~ 2
` ~: :
~(~6613~
1 The sacrificial binders of this invention are thermo-
2 plastic a~d contain as the principal binder xesin a thermo-
3 plastic, rubber-related, klock polymer having the physical
4 properties hereinafter delineated, and the stxuctural formula
AB ~AB~n A, wherein " n" is o or a positive integer, "A" is . .
6 a linear or branched polymer that is glassy ox crystal~ine
7 at room temperature and has its softening point in the range
8 of about 80~C. to about 250C. and "B~ i5 a polymer different in
9 chemical composition ~rom A that behaves as an elastomer at
processing tempexatures. A detailed description of block polymers,
11 ~heir preparation, composition and physical properties are to be
12 found in "Synthe~is o~ Block Polymers by Homogeneous Anionic
13 Polymerization" by L. J. Fetters, Institute of Polymex Sciencet
14 The University of Akron, Akron, Ohio published in the Journal
of Polymer Science, Part C, Mo. 26, pages 1-35 (1969) and
16 "Rubber-R~lated Polymers, I. Thermoplastic Elastomers'~ by
17 W. R~ ~endricks and R. J. Enders, Elasto~ers Technic~l Center,
18 Shell Development Company, Torxance, Cali~oxnia, publi~hed
19 in Rub~er Technology, Second Edition, Chapter 20, pages
515-533, by Van Nostrand Reinhold Company, New York,
21 Cincinnati, Toronto, London and Melbourne (1973), which
22 are incorporated herein by reference. For the details of
23 vacuum apparatus and method or performing anionic initiated
24 polymerizations which can be used to produce block polymers,
see "Procedures for ~omogeneous Anionic Polymeriza~io~" by
26 Lewis J~ Fetters, ~ournal of Research of the National
27 Burèau of Standards, Vol. 70A, No. 5, September-Oct~ber 1966,
28 pages 4~1-433 and nThe Association of Polystyryllithiu~, -
~6~8~:~
1 Polyisoprenyllithium, and Poly~utadienyllithium in ~ydrocarbon
2 Solvents," by ~aurice ~lorton, Lewis J. Fetters, R, A. Pett, and
3 J. F. Meier, Institute of Polymer Science, published in
4 Macromolecules, Vol. 3, pages 327~332, by the American
Chemical Society (1970) which are herein incorporated ~y
6 xeference.
7 ~asically, the concept here involved provides or
8 makin~ sintered articles fro~ particulate solids employing
g sacrificial binders which behave as thermoplastics during
the processing, i.e., mixing and molding, in that they flow
11 readily at the temperatures used for these operations and
12 yet behave in the nature of thermosets during storage of the
13 green body at room temperature and during firing un-til the
14 sintered body has taken permanent form. This is achieved
with the block polymer elastomers hereinbefore and
16 hereinafter more ~ully described and the oil or wax or
17 oil and wax used as plasticizer. The oil serves to aid
18 in processing by reducing the viscosity of t~e elastomer
19 which is of particular importance during the application
of shear forces at mixing and molding temperatures. Thus,
21 when the tempçrature o~ the material is xaised above the
22 gla~s transition temperature of the block polymer
23 elastomer, l.e., the glas~ transition temperature of the
24 "A" segments of the block polymer, and shear forces are
applied, the material becomes le~s ~iscous and flows like
2Ç a thermoplasticO When the system is cooled to room temperature
~27 after forming, the "A" se~ments, e.g., polystyrene, tend to
28 agglomerate to form "domains" and provide a structure similar
~6~g ;:
in physical behavior to a crosslinked polymer. Subsequent
firing at a higher temperature drives off the oil and/or wax.
As no applied shear forces are presen-t during firing, the "A"
segmen-ts domains remain in their agglomerated form, thus
maintaining the shape of the green body through burn-out and
such shape is maintained through sintering by the integri~y
of the structure of the residual particulate solids.
A. The Principal Binder Resin
The principal binder resin is a thermoplastic
block polymer having the structural formula AB ~ABt~ A
wherein "~" is 0 or a positive integer and "A" and "B" are
different polymers. This block polymer advantageously comprises
in excess of 50 wt. % of polymeric material in the binder
excluding the oil and/or wax of the plasticizer. For purposes
of simplicity, these polymers will be primarily discussed with ~ -
reference to their most simple form wherein "~" is 0, i.e., a
block polymer of the structural formula A-B-~. It is to be
understood that the statements made about khese txiblock polymers
apply equally to those block polymers wherein "~" LS one (1)
or greater even though certain of the "A" segments will not
be terminal and certain of the "B" segments will not be center
segments.
The "A" se~ments of these block p~lymers are
non-crosslinked, linear or branched polymers which are glassy
or crystalline a~ room temperature and have their softening
.
point in the range of about 80C. to about ~50C. When the
D lded article is in the green body stage, i~e.~ after
: .
~ormation and prior to burn-out of the sacrificial binder, and at ro~m
t~ature, i.eO ~ 20-25C:., the "Ai' segments e~hibi~ a mK~us grea~er
~han 100 dynes~cm2 Whexe the block polymers are prepared b~ anlonic
poly~leri-zati~n-, suitable
- 5 -
.
" 3L~66~32~!
1 materials for the "A" seg~ents include, but not by way of
2 limitation as one skillecl in the art will recognize
3 from the physical and chemical characteristics of these
4 and similar polymers, polystyrelle, poly(acrylonitrile),
poly (p-bromostyrene), poly~methyl methacrylate), poly(alpha-
6 methylstyrene), poly(2-methyl-5-vinylpyridine~ and poly(4-
7 vinylpyridine). Other ~lock polymers ~3uitable ~or use
8 in this invention are advantag~ously prepared by other
9 synthesis routes, i.e., polycondensation, ree radical
initiated polymerization and cationic polymerization using
11 techniques known to the art. When these other syntheses are
12 employed, ~uitable materials for the "A" segments include,
13 but not by way of limitation as one skilled in the art will
14 recognize from the physi~al and chemical characteristics of
these and similar polymers, polytvinyl acetate~, polyesters,
16 . polyamides, polyurethanes, poly~vinyl chloride),
17 . polypropylene, polysulfone , poly(phenylene sulfide), poly (4-
18 methyl pentene-l~ an~ poly(vinyl alcohol).
.
lg . The "Bn~ ~egment of these ArB-A pol~mers
are either rubbery, flexible t glassy or crystalline
21 polymers, as those terms are hereinafter defined~ and
22 behave as elastomers at processing ~emperatures~ The
23 "B" segment may be linear or branched and in some embodiments
24 is chemically crosslinkable. In such embodiments, a cross-
linking agent therefor is added ~uring mixing and reacted on
26 molding. When the molded article is in the green body
27 s-tage and at room temperatuxe, it exhi~its a modulus of
~8 about 106 - 5 x 107 dynes/cm~ when the "B" segment is a
: ` - 6 -
.
8~
1 rubbery polymer. Where the "B" segment is a flexible
2 polymer,at room ten~perature, this modulus will be in the
3 range of about 107 - 109 dynes/cm2. W~ere the "B" segment
4 i5 a glassy or crystalline pol~ner at room temperature, this
modulus will be above about 109 dynes/cm2. Where the block
6 polymers are prepared by anionic polymerization, suitable
7 materials for ~he "B" segments include, but not by way of
8 limitation as one skilled in the art will recognize from the
9 physical and chemical characteristics of these and si~ilar
polymers, polybutadiene, polyisoprene, polydimethylbutadiene,
11 poly~ethylene oxide~, poly(isopropyl acrylate), poly(octamethyl- -
12 cyclotetrasiloxane), and poly (tetrahydrofuran). As afore-
13 mentioned, block polymers suitable for use in this invention
14 are advantageously prepared by other synthesis routes,
i.e., pGlycondensation, free radical initiated polymerization
1~ and cationic polymeriza~ion. When these other synthese~ are
17 employed, suitable materials for the "B" segments include,
18 but not by way of limitation as one ~killed in the art will
19 recognize from the physical and chemical characteristic~ of
these and similar polymers, polyisobutylene, ethylene propylene
21 rubber, ethylene propylene diene terpolymers, butyl rubber,
22 chlorobutyl rubber, bromobutyl rubber, chlorosulfonated
23 polyethylene, epichlorohydrin rubber, fluorocarbon rubbers,
24 sllicone elastomers, e.g., polydimethylsiloxane, polyurethane
2S elastomers and polypropylene oxide elastomers.
26 The molecular weight~ of the "A~ segmentæ and
27 the ~'B'1 seg~ents of tha block poly~ers suitable for use
28 with this in~ention will vsry with the polymer segLent
- ~066~
1 involved as will be obvious to one skilled in ~he ar~ in
2 that physical characteristics must be ~et as hereinbeore
3 recited. For instance, where the block polymer has polystyrene
4 "A" blocks and polybutadiene "B" blocks, the polystyrene
segments advantageously have molecular weights below about
6 20,000 and at least two of such segments have molecular
7 weights above about 10,000 whereas the polybutadiene
8 segment or segments advantageously hav~ molecular weight
9 or weights below about B0,Q00 and at least one such
segment has molecular weight above about 40,00~. The lower
11 limit of molecular weight for the two "A'/ blocks is g~verned
12 by the minimum "A" block chain length required to insure
13 the formation of a heterogeneous phase while the upper
14 limit of "A" blocks is set by the viscosity of both
"A" and "B" blocks when such viscosity begins to hamper
16 domain formation or processing.
17 To mix the block polymer with either of the other
18 component~ of the sacrificial binder or wi~h the particulate
19 solids~ the block polymer must be heated to the softening point
of the "A" segments or above. On~e the blGck polymer
21 has been mixed with the other components o the sacrificial
22 binder, the oil and/or wax can ser~e as a pl~tici~er and
23 permit subsequent working, e.g., mQlding, etc., at a
24 temperature below the softening point sf the "A" segmentsO
~25 The lower temperature limitations for such working wiLl
26 depend upon the chemical composition o~ the "A" segments, the
27 degree to which they are plasticized and the plasticization
28 ~qualities of the plasticizerr In all cases, however9 the
29 lower limit ~f the working temp ratures for such bi~ders will
be a~ove the temperature at which the 'IB" segments of the
: '
: .
~ 66~2~
l block polymers cease to behave as elastomers. In general,
2 the mixing temperature is advantageously in the range
3 between about 15C. below the softeniIIg point of the "A"
4 segments o~ block polymer use~ and about 70C. above such
S sotening point, except where mixing iLs carried out in
6 the absence of gaseous oxygen in which case the temperature
7 may be increased to about 100C. above such softening point.
8 Thus, the forming te~.peratures which may be used with the
9 various suitable block polymers wi~l ~ary between about
65C. and about 32~C. or 350C. in the absence of air
11 or other gaseous oxygen. Forming, other than embossing,
12 is carried out at temperatures above the softening point of
13 the "A~ segments. Embossing can be carried out at the
14 same temperatures or even below the softening point of ~he
"A" segments.
16 In the thermoplastic block polymers having the
17 A-B-A struc~ure, the end segmen~s, "~", which are rigid at
18 room temperature associate with each other to give ~arge
I9 aggre~ates which are referred to in the literature as "domains" 4
At normal handling temperature ~or the molded article after
21 final forming of the green body sta~e, e.g., room temperature
22 or slightly above, these domains are hard and im~.obilize the
23 ends of the ~B" segments. This end segment immobilization in
24 conjunction with chain entanglements creates physical
crosslinks which helps to protect the green body from dis-
26 ~iguration as the result of handling. At hi~her temperatures,
27 the terminal, "A" se~ments soften and may be disrupted
28 by applied stress, allowing the polymer to flowO The latter
~ _ g _
i,
~al66~312~
1 cor.dition makes possi~le the mixing, molding, etc. which
2 are necessary o.r optional steps in preparing the green body.
3 Cooling will then provide a green bo~y having unusual
~ resistance to physical change pri.or to the heating associated
with burn-out and sintering.
6 B. The Plasticiæer
7 The ~acrificial binder also includes a plasticizer
8 which is either an oil or a wax or both. The oils and waxes
9 used for this purpose are naphthenic, paraffinic or a mixture
10 . of paraffinic and naphtherlic co~stituen~s. They are sufficiently
11 volati~e to be removed easily and rapidly in the ~urn-out
12 process but insuficiently volatile to be substantially removed
13 during mixing and/or molding. ~he loss due to volatilization
14 during mixing and/or molding is advantageously below 20
and preferably below lO weight percent.
16 Functionally, the oil.s and/or waxes must be
17 compatible with the rubbery phase of the principal binder
18 resin when it becomes ru~bery on plasticization at a
19 temp~rature ~omewhat below the ~oftening point of the "A"
segments of th0 principal rQsin. This gives the binder a
2~ capability of accepting high filler loadings while remaining
22 strong and flexible.
23 At least 75~ ~y weight of the oils used as
24 plasticizers boil in the range o~ about 550~F.
to about 1038~.~ prefexably in the range of ab~ut 55GF.
26 to about 86$F. They have viscosit e~ at 210F. in the
~7 : range of about 30 to abou~ 22G Saykol~ Uni~ersal S~conds,
28 herainafter ref~rred to as S~ advantageously in the
~9 rang~of about 35 to about 155 S~U.S., and preferahly
:
:
-- 10 --
:'
66~2~
in the range of about 35 to about 80 S.U.S. These
~ oils have their Aniline Point in the range o~ about 17~F.
3 to about 255~F. The oils may be a product of petroleum
4 refinin~ operations or ve~etable or a.nimal oils and they
may include or be low molecular weiht synthetic polymers
6 such as polystyrene, poly(alpha-methyl styrene), or a
7 polyolefin.
8 The waxes used have melting points in the range
g of about 130F. to about 170F. At lleast about 75~ by weight
of such wax boils at temperatures in the range of about 600 GF.
11 to about 900F. These may be a product of petroleum
12 refining operations, vegetable or animal waxes or synthetic
13 polymers such as low molecular weight polyolefins.
14 C. Optional Constituents
The sacrificial binders of this invention ~ay
16 and in c~rtain embodiments aavantageousl~ do contain additional
17 materials such as supplementary resins, supplementary
18 elastomers and antioxidants.
19 Supplementary resins are use~ul in em~odiments
where there is a desire to increase the stiffness of the green
21 ~dy while still providing fluidity at processing temperatures.
22 Suitable secondary xesins include any o the aforementioned
23 polymers suitable for use as l'A" segments in block polymers,
24 resirs similar to resins suitable for use as "A" segments and
having affinity for the "A" segments of the block polymer
~6 used, e.g., cumarone-indene resins and polyindene with block
27 ~polymer having polystyr~ne "A" blocks, and resins which
2~ have a~ af~inity for the "B" seyment or segments in the
29 block polymers, e.g., polyterpenes with polybutadi~ne nBI'
blocks. It is to be understood that resins having an affinity
.
- ~6~
1 for the "A" or "B" segment~ of the block polymer may also
2 be polymers suitable for use as "~" or "B" respectively
in other embodiments when they meet the limitations set
4 forth herein for "A" or "B'~.
Supple~entary elastomers are useful in embodiments
6 where there is a desire to improve tear strength in the ~reen
7 body~ Suitable secondary elasto~.ers inclu~e natural rubber
8 and synthetic slastom~ers , e . g ., polybutad iene , polyisoprene ,
9 etc.
Antioxidants are useful to retard oxidative degrada-
11 tion of the block polymer during mixing thus minimizin~ loss
12 of strength in the green body. The antioxidant also
13 allows more rapid removal of binder during burn-off by
14 minimizin~ surface oxidation which may tend to seal off
the surface. Suitahle antioxid2nts include, but not by
16 way of li~ltation, 2,6-ditert-butyl-ph~nol, a polymerized
17 1,2-dihydro-2,2,4-trimethyl ~uinoline, 2-mercapto~,enzimidaæole~
18 tetrakis~methylene-3-t3',5'-ditert-butyl-4'-hydroxyphenyl~
19 propionate] methane, etc~
. Process aids which are conventional tc molding
21 and forming operations with polymeric matexials are likewise
22 u~e~ul in the practise of this invention to improve the
23 relea~e characteristic~ of the green body from any type o
24 moiding or forming ap~,aratus with which the green body comes in
contac~ and to improve the flow charac~eristics of ~he ~inder-
26 ~iller mix~ure during such operations as ex~rusion molding,
27 ~ injection molding, transfer molding, e~c. Process aids which
28 may be of assistance include methylacetylricinoleate r stearic
9 acid~ poIyethylene, polyethyle~e wax, mi~tures of ~atural
~30 ~axes and wax deri~atives~ ve~etable fats~ partiaIly oxidized
31 polyethylene, etc.
.
6~
1 D. Paxticulate Material
2 This inventio~ is applicable to all particulate
3 material that i~ "sinterable;' as that term is hereinafter
4 defined. Specific examples .include9 ceramic powders such
as cordierite powders, alumina, B-spodumene, crystalline
6 or fused silica, mullite, k~anite, æirconia, beryllia, masne~iar
7 titania, chromium oxide~ iron oxide and complex oxides
B comprising two or more of these oxide~, metal powders suc~
~ as iron, iron alloys, cop~er, copper alloys, aluminum,
alumin~ alloys, silicon, silicon alloys, nickel ba~e super
11 alloys, cobalt ba~e super alloys and stainless steals t
12 inter~etallics such as nickel aluminides and molybdenum
13 silicide, carbides such as silicon carbide, tungsten car~ide,
14 and iron carbide, nitrides uch as silicon nitride and boron
nitride, and co~posites of metal-ceramic~, metal carbides
16 and metal nitriæes.
17 One o the advantages of these binders is that
18 they are amenable to high flllings of p~rticulate solids.
19 The molding mixture advantageously comprises about 30 to
:20 about 70, preferably about 50 to about 65, volume percent
21 particulat~ solid~ with the balance being made up of the
22 sacrlficial binders.
Z~ ~. Propor~ions of Binder Constituents
.
24 The proportions of:the principal binder resin
or ~lastomex, i.e., the block polymer, and the pla~ticizer,
;2~ i.e~., the oil~ wax or Qil and wax, may vary widely. In
~ 27: ::a binder consisting 501ely of the block pol~mer and plastici.zer~
;~ 28 the block pol~mer will comprise between 10 and 90, pxeferably
2~ : ~etween about 30 and about ~5, and most preferably be~ween
:
about 45 and about 65~ weight percent of th~ ~otal b.inder
31 with the plasticize.r co~prising the balance~ i.e.,
.
.
- 13 -
~L~66~32~3 :
between 90 and 10, preferably between about 70 and
_ about 15, and. most preferably between about 55 and about 35
3 weight percent, provided, however, that the wax constitue~lt
4 ~hen used, advanta~eously does not exceed a~out 70 weight
percent of the binde.r.
6 It will be understood that one may replace any
7 fraction less than 50 weight percent, :i.e., a to between
8 49 and 50, more commonly between about 0.1 and about 30r
g weight percent of the block polymer aforedefined ~-ith
an e~uivalent amount by weight of another polymer that
11 is within the limitatio.ns of "A" in the aforementioned
12 formula.
13 It will also be understood that one may replace
14 any fraction less than S0 weight percent, i.e., 0 to between
49 and 50, more commonly between about 0.1 and akout 3n,
16 weight percent of the aforedefine~ block polymer with an
17 equivale~t amount by weight of another polymer that i~
18 within the limitations of "E'l in the a~orementioned formula.
1~ It will be ~urther understood that one may repla~e
any fraction less than 50 weight percent, i.e., 0 to between
21 45 and 50, more commonly between about ~.1 and about 40
2Z weight percent o~ the block polymer aforede~ined with an
23 equivalent amount by weight of a block pol~.er havin~
24 the structural formula X ~B (~B) n A] n ~ wherein "X" is a
multiunctional halogen functional linking agent, A or B
26 :~ "n" is 0 or a positive integer, "n~' is a positive integer greater
27 ~ than 2 and A and B have the same limitations as A and
28 in t~e hereinbafor~ described block polymer haviny the
~29 ~ structural formula AB ~AB~n A. The linking ag~nt, when the
~ block polymer has a linking ~gent, is a multi~unctional
~:31 ~ ~2) ~ompound consisting essentially of elements selected
.,
~ : ~
.
-
` ~66~3Z~
1 from the ~roup consisting of car~on, hydrogen, oxy~en,
2 halogens, nitrogen, silicon, phosphorous and sulfur.
3 When anionic polymerization is used, this iS a halogen functional
4 coupling species. The following are illustrative
S but not exhaustive: silicon tetrachloride, 1,2,4-tri
6 (chloromethyl)benzene, 1,2y4,5-tetra(chloromethyl) benzene,
7 Bis(trichlorosilyl)ethane, cyclic trimer of phosphonitrilic
8 chloride, ben~ene, chloromethylated polystyrene,
9 trichloromethylsilane, and silicon tetrachloride.
The use of these linking agents is discussed in the aore-
11 mentioned article ~Synthesis of Block Polymers by Homogeneous
12 Anionic Polymerizationn by L. J. Fetters. When the block
13 polymers are prepared by other synthesis routes as aforementioned,
14 one would use other linking agents. In the case of ~ree
radical polymerization, one may us~ a multifunctional co~pound
16 that will initiate polymerization of the "B" block, as when
17 the "B'l block is poly(ethyl acrylate~, and react with ~he
18 "B" block~ e.g., a branched azonitrile such as one pxepared
19 by reacting tri~lathylolpropane with a diisocyanate such
a~ toluene diisocyanate and a glycol suoh as poly(oxypropylene
21 glycol~ In the case of polycondensationt one may use a
22 multifunctional compound tha~ will react with the ~B" block,
2~ e.g., ~rimelliti~ anhydride. In the case of c:ationic polyn~.eri-
24 zation, one may react poly(vinyl cbloxide) with trimethyl
aluminum which will initiate polymeri~ation of the "B"
26 blo~k, as when the "B'~ block is polyisobutylene, and reaot
27 ~ with the "B" bIock. A~ afoxementioned, '~X" may be polymer
2E~ 91p~ polymer "B" or a linking agent. For purposes o:E this
~ lnvention and the use of such block polymers in sacrificial
binders for a ~olding mixture, the subs~i~ution of a linking
. .
15 -
~66~3Z9
1 agent for polymer "A" or polymer "s" as the "x'1 component
2 does no~ materially a~fect the physical prnperties of the
3 block polymer. Linking agents are conventionally u~ed in
4 such klock polymers and are well known to those skilled in
the art as shown in the hereinbefore citecl literature.
6 With such teachings, selection of a specific lin~ing agent
7 for a specific block polymer is quite within the skill o
8 those skilled in the artO
9 In combination the substitutions of such "~ ype
polymers, such "B" type polymers and such other type of
11 block polymers should constitute less than 50 weight percent
12 o the principal bind~r resin, block polymer previously
13 described.
14 In the following table there is set forth advantageous
ranges for cons~ituents when optional ma~erials are
16 included.
17 Sacri~icial ~i-dtr- With ~tional Constituents
: 18 Material Range, W*.~ Preferred Range 2~Iost Preferred
I9 ~ o Binders Wto % of Binder_ Ran~e, Wt.% o~
- Binaer _ _ .
21 block polymer10-90 30-g5 45-65
22 plasticizer Y0-10 70-15 35-55
23 oil 0 90 0 70 0 55
24 wax 0-70 0-30 0-10
secondary resin 0-40 0-25 Q-15
26 secondary
27 ela~tomer 0-40 0-15 0~10
~::28 antioxidants 0-7 ~: 0-5 0-3
29 proce3s aids 0 15 0~10 . 0-7
:
F. Definitions
,.
31 The term "sintering" is used herein to mean
32 the coalescence by heat o~ crystalline or amorphous particles
, .
16 -
,:
~L~66~Z9
1 into a solid mass.
2 The term "moldin~" is used herein to mean any
3 of the methods of forming known in the art as extrusion
4 molding, inieetion molding, compression molding, laminating
which includes compression molding, tr,ansfer molding~
6 pressure molding, displacement molding, blo~ molding,
7 calendering, and e~,bossingq
8 ~he term l'processing" is used herein to mean
9 mixing, forming, and mixing and forming.
The term "green body" is used herein to mean
11 a molded arti~le comprising an intin~ate mixture of 3interable
12 particulate solids and a thermoplastic, organic binder.
13 The term "molecular weight" is used herein
14 to mean average molecular weight (Mn)~
The term "room temperature" is used herein
16 to mean a temperature in the range of 2C-25C.
17 ~he term "softening point" is used herein to
18 mean the gl~s~ transition temperature when used with
19 reRpect to glassy polymers and the crystalline melting
poin~ when used with respect to crystalline polymers.
21 The term "glass transition temperaturel' is
22 signified herein by the sym~ol IITg" and is used herein
23 to mean that temperature below which a non-crystallizing
polymer becomes a supercooled liquid~ i~e., a gla~s.
The term "crystalline melting point" is
26 ~ig~ified herein by the symbol l'Tml' and is used herein
27 to mean that temperatuxe at which a crystalline polymer
28 melts and becomes non-cry~talline.
2g Both "~lass transition temperature" and
'lcrystalline mel~ing pointl' represent areas of transition
:
.
~C~66~Z~31
` but are practical terms ~hich are sufficiently de~initive
2 and exact for ~he full and complete practice of this
3 invention by one skilled in the art without experimentation
4 beyond normal routine.
The term "glassy polymer" is used herein to mean
6 a non-crystalliziny polymer which at room temperature
7 i9 below its glas~ transition temperatureO
8 The term "rubbery polymer" is used herein to
g mean a non-crystalline polymer that is akove its Tg
at room temperature.
11 ~he term l'cystalline polymer~ is used herein
12 to mean a crystallizins polymer which is below its Tm
13 at xoom temperature.
14 ~he term "flexi~le polymer" is used herein
to mean a polymer which at room temperature is in
16 transition from glass or crystalline material to an
17 ela~tomeric state, i3e~ ~ to a ru~ber.
lB It will be understood by those sk.illed in
13 the axt that it is possible for portions o~ a particular
poly~.eri~ mas~ to exist in more than one state at room
21 temperature and not be in a state of transition from one
22 to the other, e.g., a polymeric mass in which one
23 portion is a "rubbery polymer" as defined above
24 and a ~econd portion is a "crystalline polymer" as
~25 defined above. Thus~ ~he defined term concerned shall
26 be understood to mean that the largest fraction of such
27 polymeric ma~s meets the li~i~ations of ~he term used.
28 The following are illustrative examples
29 : wherein, unl~ss otherwise specified, the materials
used are within the limitations hereinbeforP set forth
31 or su~h materials in the practice of this invention.
z~
l An A-B-A block polymer elastomer, hereinafter
2 called "khe elastomer", is prepared by an anionic initiated
3 polymerization using the ~asic high vacuum apparatus and
4 general procedures for anionic poly~eri~ation described
in section 2 ~Experimental Techniques~ of the aorecited
6 artiele "Procedures for Homogeneous Anionic Polymerization",
7 by L~ J. Fetters. In addition, all attachments of
8 the ve~sels to the vacuum line are accomplished through
g a grease trap as shown in the aforecited article "The
lo Association of Polystyryllithium, Polyisoprenyllithium,
11 and Polybutadienyllithium in ~ydrocarbon Solvents" by M.
12 Morton et al.
13 The reactor is first flamed while under vacuum.
14 The reactor is cooled, sealed off from the vacuum line, and
then rinsed ~ith a solution of ethyllithium in n-hexane
16 to reaGt with any residual materials that could terminate
17 the growin~ polymer chains. The monomers and solvent~ to be
18 . used in praparing the elastomer are purified according to
19 the article by L. J. Fetters last mentioned above.
~o The reactor is reattached to the vacuum line~
21 A solu~ion containing O . 036 grams of ethyllithium in 3 ml .
22 benzene is added to the reactor. To the reactor is charged
23 370 ml. of ~enzene. Styrene monomer in the amount of 15
24 gramæ is distilled into the reactor throu~h a breakseal
~25 ~ onto the top of the benzene. ~he contents are cooled to
:
26 dry-ice/alcoh~l t~mperatures e.g., ~65~. to -7~ac. The
:
27: reactor i9 ~ealed of~ from the vacuum llne and the contents
allowed to warm-up from a dry/ice alcohol temperature.
2:9 A~ SOOD as the contents have ~hawed 0.65 gram~ of anisole
: : 30 in 4 ml. of benzene is added and shaken wi~h ~he benzene
31 and styrene in the reactorO The polymerization of the styrene
;
:
. - l
.
1066BZ9
is allowed to proceed for 4 hours at 30C. The reactor
2 i.s then reattached to the vacuum line and 60 ~rams of
3 butadiene is distilled in~ ~fter the contents have keen
4 cooled with liquid nitrogen, the reactor is sealed off from
the vacuum line. The mixture is allowed to tha~ and after
6 ~tirring the polymerization of butadiene is allowed to proceed
7 at 30C. for 16 hours. The mixtuxe is cooled to a
8 dry-ice/alcohol temperature and 15 gram~ of styrene are
9 distilled in after the reactor has been attached to the
vacuum lineO ~he reactor is once again sealed off from the
11 ~acuum line, the contents thawed and mixed, and polymeri-
12 zation of the styrene allowed to continue for 4 hours at
13 30C. The elastomer in the reactor is then coagulated ~y
14 slowly pouring the benzene solution into methanol containing
a small amount of phenylbetanaphthylamine to stabilize
16 the elastomer. The elastomer is dried and is then ready for :
17 use as the principal binder resin.
18 This polystyrene-polybutadiene-polystyrene
19 elastomer containing about 33.3 wt. ~ poly~tyrene in the
amount of 14.5 grams is banded on a tight mill which has
21 been preheated ~o 300F. About 10 grams, of 100 total grams,
22 of ~lassy cordierite frit are then added on the mill to
23 stabili~e the band. The oil, 12.5 grams of a commercially
24 available, paraffinic petroleum oilS Flexon 845 a tradename
~f Exxon Company, ~S.A. is ætirred with 50 gx~ms of the
26 : cordierite ~rit. ~his oil has the following properties:
27 speci~ic gravity (6~/~0~.) o~ 0.8~49-0.8811; colox ~ASTM~
28 ~of 1-4; vi~cosity (210F~) of 43~4-61.5 S.U.~; aniline
29: point of 219-2409F~ and silica gel aromatics o~ 14.9-16.1
wt. %O About half of the oil/cordierite mixture is added
31 to the mill and mixed in~ As the viscosity of the mixture
32 decr2ases~ the mill temperature is reduced to 290F~ to
33 minimize volatilization of the oil. The remainder of the
- 20
2~1
~? dry cordierite and the remainder of the cordierite/oil
2 mixture are mixed by alternately adding a few grams of
3 one and then of ~he other to the materi.al on the mill.
4 When the mixing is complete in about 20-30 minutes, the
composition is sheeted from the mill and allowed to cool.
6 Ri~bed sheets of the mixture are prepared by
7 compression molding. The sheet obtainled from the above recited
8 mixing is banded on a 2gOF. mill and the nip width is decreased
9 so that a sheet 0.030 inch thick is obtained. A preform
3 1/2 inch square is cut from the 0.03lD inch thick sheet,
11 the same providing an excess o~ material for the ribbed mold
12 being used. A pres~ with a 3 5/8 inch diameter ram and th~
13 bottom half of the mold are preheated to 250F. The preform
14 is then placed on the preheated bottom half of the mold for -
lS 15 seconds. The unheated top half of the mold is then placed
16 upon the preform and the bottom hal~. Both halves of the
17 mold are coated with polytetrafluoroethylene. The press
18 i~ closed and a pressure of 2,000 psiy is applied, Th;.s
19 pres3ure is maintained ~or 15 seconds. The pressure is
then released and the ribbed sheet removed from the mol
21 The ribbed sheet i5 then heated in accordance
: ,
22 with the following cyc}e:
23 Table I
: 24 ~ _re, F. Time, Hrs.
:25 1 :160 4
, .
. 26 2 260
~-27 3 400O~50 4
28 The~resulting~body is then fired in accordance
:~ :2g with the following cycle:
::; :
: ~ - 21 -
~ Table I:[
__
2 S~Rate of Temp~rature Temperature Range
3 Ri.se/=_F ~ F. ~ ___
4 1 600-$00 room 2200
2 100 2200 - 2500
6 This result~ in a strong, densat cordierite
7 ri~bed she~t.
8 The procedures of Example 1 are repeated with
9 the single difference that the block polymer elastomer
used is a commer~ially-available triblock (ABA) polymer
ll having a polybutadiene center block and polystyrene end
12 blocks. This ~lock polymer contains 30 weight pexcent
13 polystyrene, i.e., Kraton 1101. Kraton is a tradename
14 of Shell Oil Company. This block polymer has specific
gravity of about 0.95 ~nd intrinsic viscosity of a~out
16 1.00 dl/g ~30C. in toluene).
17 This results in a strong, dense, cordierite ri~bed
l8 sheet
; ~ . . '
~,
The procedures of Example 2 are repeated except
~ or the difference that the elastomer, the oil and the frit are
21 ~irst ~tirred together and then mixed in a Banbury mixer which
~ 22 is prehe~ted to 310 to 320F. for 15 minutes. The resulting
: ~ 23: : mixture is then banded on a two roll:mill which has been
Z4 preheated: to 290F. After tw~ to five minute~ o~ mill mixing,
.
~he composition is ~heeted and allowed to cool. It is now
~26 ~ ready for compression molding and is molded in accordance
27 :: with the previous examples. This results in a strong, dense~
28 cordiexlte sheet.
:
' .
- 22 -
3~668~:~
Exampl~ 4
l The procedures of Example 3 are repeat~d except
2 for the following differences: twenty-nine (29,0) parts
3 by weight of the polystyrene-polybutadiene-polystyrene
4 triblock polymer elastomer are mixed with 27.3 parts
S by weight of parafin wax (m.p. 130F,), and 200 parts by
6 wei~ht of glassy cordierite fri~. This xesults in a
7 strong, dense, cordierite sheet. The paraf~in wax ac~s
8 as a process aid and plasticiæer and provides smoother
9 extrusions. It also increases the stiffness of t~e green
body.
Exxmple 5
11 The procedures of Example 3 are repeated
12 except for the following differences: test bars are
13 molded using a ram type injection molding machine.
: 14: The barrel and nozzle of the injection molding machine
are preheated and controLled to 320F. A mold for molding
16 ~wo ~es~t bars is preheuted to 100F. und clamped with a
;~; 17 prassure of 15,000 psi. Twenty ~20) grams of pieces eut
: 18 from the above sheet are introduced into the barrel and
~19 allowed to heat ~0 5 minutes~ The material is then in-
jec~ed into the mold with ~he ram pressure (800 psi) being
: ~ 21 maintained for one m~nute. Ram pressure is released followed
22~ ~ ~: by selease of clump pres~ure from the mold and the test bars
:23~ ~ are removed ~rom the mold. T~e test bars are first heated
~24 : ~ and then fired using the same cycles used ~or the sheet
~5~ material in the preceding examples. This results in strong,
26~: dense, cor~ierite ~ars.
'::
.
- 23 - .
,
.
~L~6~2g
1 The procedures of ~xample 2 are repeated except
2 for the following differences: A flat sheet is prepared by
3 use of a screw type extruder havina a 2-inch bore. The
4 binder cordierite mixture is pelletiæed and the pellets
are fed into the hopper of the e~truder. It is then
6 conveyed through the extruder and passed through a thin slit
7 die ~0.020 inch thick, 4 inches wide~, The temperature
8 settings on the extruder are: ~eed section 175F~,
g tran~ition ~ection 250F., and die ~ec~ion 300F8 The
5heet is then cooled to room temperature and stored. ~he
11 cooled sheet is flexible and suitable for subsequent handling
12 such as ~litting, rewinding and e~bos~in~ and when ~ired
13 yields a stron~, dense, cordierite sheet.
.
Ex~ le 7 .
14 The procedure~ of Example 2 are repeated with
the exception that a different, commercially available,
16 polystyrene-~olybutadiene-polystyrene, triblock polymer
17 is used a~ the elastomer, i.e., ~rato~ 1102. This
;~ ~18 elastomer contains about 28% by weight polystyrene and has
19 a lower viscosit~, i.e.~ intrinsic viscosity of 0.84,
dl/g (30QC~ in toluene), than the one pre~iously exemplified
21 and identified by containing 30~ by weight polystyrene.
~2 : As a result Q~ the lower viscosity of: he elas~omer, the
.
:3 :~ ~inder composition has a lower viscosity and is moxe ea ily :.
24 processed. The product obtained is not as ~tiff in the
:
~25 : ~ green state but still resul~s in a StrOD~, dense, co~dierite
26 ribbed sheet when firedO
. :
:: .
~ 4 -
. .
6~329
Example 8
__
1 The procedures o~ Example 2 are repeated with
2 the single difference ~hat a com~ercial:Ly-available, polystyrene-
3 polyisoprene-polystyrene triblock polymer elastomer, i.e.,
4 Kraton 1107 containing about 14 wei~ht percen~ polystyrene
: 5 is used as the elastomer. When mixed w:ith oil and frit,
6 this elastomer yields a composition of ]Lower modulus but
7 of inferior strength in the green body state to those of
the preceding examples. It still yields, however, a strong,
g dense, cordierite ribbed sheet after fixing.
The procedures of Example 2 are repeated
11 except for the differences: ~ commercially-available,
12 triblock polymer ela~tomer having polystyrene end blocks
13 and a poly ~ethylene-butylene) rubber center and
14 contalning 12-14 weight percent polystyrene, i.e., Kraton GX-
7820, is used as the elastomer and a paraffinic oil, i.e.,
16 Shellflex 790, is ~ubstituted for the oil used in ~xample 2
17 Shellflex is a tradename of Shell Chemical Company. This
18 change of oils is made to reduce the volatilization which
19 would otherwise occur because of the higher mill temperatures
be9t suited to work this plasticized ela~tomer, i.e.,
21 about 350UF. The green body is stiffer than that o~ Example
: 22 2 and a poorer dispersion of filler is obtained. The ribbed
sheet obtained after firing is less dense and of lesser
~24 streng~h than those produced in ~he preceding examples.
25 : Th~ procedures of Example 2 are repeated ex~ept
26 for the difference that the parts ~y weight of th~ elastomer,
, ~ :
- 25 -
~L~6~9
- oil and cordierite frit are as follows: elastomer 2.75,
~ oil 22.77 and frit 100.00. This example illustrates
3 approaching toward minimum elastomer and maximum oil content
4 in the binder. The green body is soft and lacking in
strength and integrity. The rib~ed sheet obtained after
6 firing is less dense and of lesser strength than those
7 produced in the preceding examples.
8 The procedures of Example 2 are repeated except
9 for the difference that the parts by wei~ht of the elastomer,
oil and cordierite frit are as follows: elastomer 24.78,
11 oil 2.53 and frit 100.00. This example illustrates approaching
12 toward maximum elastomer and minimum oil content in
13 the binder. This composition is stiffer and more difficul~
14 to process than those produced in the preceding examples.
15 ~ The procedures of Examp}e 2 are repeated except
1~ for the difference that para~fin wax (m.p. 130F.) i9
17 substituted fo~ the oil in the binder and the parts by weight o
18 the elastomer, wax and ~rit are as ~ollows: elastomer 8~26,
19 wax 19.07, and frit 100Ø This compo~ition results in
a sti~fer ~reen body with les tendency to crack during
21 burn-ou~ and firing.
22 A commercially-available polystyrene in
23~ the amount of 12.17 grams is banded on a tight mill
24 ~ which has been preheated to 320F. ~his polystyrene has
~5 specific gravity o about 1.05, a Vicat softening point
::: ;: :
: ':
~ - 26 -
:~ :
~L~61~ 9
of about 97C., and a melt flow of about 3.5 grams~lO
2 minutes (ASTM-D1~3 8 condition G). The polystyrene-
3 polybutadiene-polystyrene elastomer of Example 2 in the
~ amount of 12.39 grams (30 weight percent polystyrene) is
then combined on the mill with the polystyrene
6 a~er the temperature is reduced to 310F. for the
7 remainder of the mixing. Two grams. of the lO0 grams of
8 glassy cordierite frit to be used, are then added on the
9 mill to stabilize the band. The paraffinic petrolaum oil of
Example 2 in the amount of 3.80 gram~ is stixred with sn grams
ll o the cordierite frit. About hal~ of the oil~cordierite
12 mixture is added to the mill and mixed in. T~e remainder
13 of the dry cordierite and the cordierite/oil mixture
14 are mixed in by a~ternating a ~ew grams of one and then
the other. When mixing i~ complete in about 20 to 25
16 minutes, the composition iS sheeted from th~ mill and
17 allowed to cool. The remainder of the processing is
18 - the same as in ~xample 2. Thi~ also results in a stiff
l9 green body but with improved green strength and better
re~ention of shape during burn-out. The proces~ability
21 of the mix improved as mixing proceeded.
~ . .
22 Natural rubber ~#l rib~ed smoke sheet~ in the
23 amount of 10.67 gra~s is banded on a tight mill which has been
~24 preheated to 30GF. It is ~hen removed from the mill and set
.
aside7 The ela~tomer of Example 2 in the amount o 13.77
26 grams is then banded on the 300F. mill. Half of the natural
27 rubber is then added to the mixture on the mill. ~he remainder
28 of the dry cordierlte and the natural rubber axe then mixed in
- 27
~ .
:~L0668~9
1 by alternating a few grams of one and then of the other.
2 When mixing is complete in abou~ 20-25 minutes, the
3 composition is sheeted from the mill ancl allowed to cool.
A The remainder of the proce~sing is the C;ame as that o
Example 2. The use of tlle natuxal rubber gives Lmproved
6 tear strength in the green body and gives a modulus
7 lower than that in Example 2.
~ ,.
8 The procedures of Example 2 are repeated wi.th the
9 following changes: all of the cordierite is added in the
first addition and none is mixed separately with the oil.
11 In addition,. the parts by weight of elastomer, oil and
12 cordierite are as follows: elastomer 27.54, oil 25.30
13 and frit 2.72. This provides an extremely soft
14 co~position with a tendency to provide a porous ceramic
I5 par~. .
.
~ . ~ .
16 The procedures of Example 2 ar2 repeated with
17 the following changes: the parts by weight of elastomer,
18 oil and frit are elastomer 12.39, oil 13092 and frit 123.81.
19 At this high loading of ~rit, the green hody is very stiff
bu~ very weak a~d difficult to process.
::
:
21 The proaedure of Example 2 is repeated with the
22 ~ollowing changes: the parts ~y weight of elast~mer, oil
:23 and frit are elastomer 13.77, oil 12.53 and fri~ 100.00
: ~ :
~ - 28 w
~ .
il29
` In addition, the mixture also contains 0.14 parts by
2 weight of an antioxidant, i.e., 4,4' methylene bis(2,6-di-
3 tert-butyl-phenol). ~se of the antio~iclant results ~n
4 ~etter retention of stren~th durin~ mixing and improved
resistance to slumping durin~ binder burn-off.
Example 18
6 The procedure of Example 2 is repeated
7 with the following changes: the proportions by weight
8 of the binder inyredients and frit are elastomer 13.77,
9 oil 11.39, fri~ 100.00 and methylacetylricinoleate, a
prvcess aid, 1.36. Use of the process aid results in
11 better processability during calendering and extrusion.
~ .
12 Sintered, modified, beta-alumina tubes are
13 produced by extrusion molding using the elastomer and oil of
14 Example 2, wax~ an antioxidant and particulate beta~-alumlna.
The composition mixed for molding is as follows:
16 ; Ta~le I
17 Material P~ y~ ght
18 ~ Ela~tomer o~ Example 2 4.7
19 ~ Oil of Example 2 3~2
~ Para~fic wax ~m.p. 135Fo) 3~5
~ :: ,
21 ~n~ioxidant, poly 1,2 dihydro-
~22 ~ ;2~24-trime~hylquinoline 0.5
23 Powder li~hium-modified beta~
24 alumina (9.0~ Na, 0.8% Li 0
~25 ~ and 90.2% A12Q3~ 2 50.0
~ .
~ 29
' ~
.
, .,
661329
The above-listed materials are mixed at 310F.
2 (154C.) on a two roll mill After bain~ extruded into
3 tube shape using a 310F. (154C.) nozzle temperature
4 with a barrel tenperature of 340~. (171C.), the tubes
are then burned-out and sintered using ~he following
6 schedule:
7 Tahle II
8 Step Rate of Temp. Rise Temperature
r ~; C.~Hr. Ran~, C~
1 50 100 700
11 2 Hold for 15 hrs. 700
12 3 Cool to room temperature
13 over 3 hours
14 Each such tube is placed in a platinum tu~e
which is mechanically sealed. The sealed sample is then
1~ placed in a furnace. The ~urnace is heated to 1100C.
17 over 15 hours. From 1100C., the furnace is heated to
18 1570C~ over 4 hours and 45 minutes where it is held
lg for 15 minutes and then cooled to 1~20C. over 15 minutes.
The sample is held at 1420C. for 8 hours and then cooled
21 to 360(:., over 7 hours at which point the sample is allowed
22 to cool to ambient emperature in air.
,
23 The procedures of the previous examples are
24 repeated with the single difference that particulate alumina
:25 : is substituted ~or the cordierite and sintering is carried
26~ out at temperatures of 1600 - 1700C.
:
~ 30 -
-
: ~ :
~66~
1 The procedures of the previcus exa~ples are
2 repeated with the single difference that particulate
3 silicon carbiae is substituted for the cordierite, and
4 sintering is carried out at te~peratures of 2000 - 2200C.
The procedures of the previous examples are
6 repeated except that particulate aluminum is substituted
7 for the cordierite and sintering is carried out at
8 temperatures of 550 - 650C.
Example 23
9 The procedures of the previous examples are
lC repeated except that particulate tainless steel is
11 substituted for the cordierite and sintering is carried
12 out at temperatures of 1400 - 1500Co
.
13 . The foregoing ~xamples are merely illustrati~e
14 of the practice o~ thi~ in~ention and those skilled in
the art will readily recognize that modifications and
16 variations may be made in these examples without departing
17 from the scnpe o~ this lnvention as set forth in the
18 ~ appended claims.
9 . _ :
'~
: ~ .
~ 31 -
~ .
. . .
