the composition of the invention has particular application as a buoyant putty suitable for supportably floating in water an object which would otherwise sink in water . the object may be wrapped , embedded or otherwise held in a suitable amount of the putty to render it floatable in water . when the composition is employed as a buoyant putty , the continuous phase is preferably employed in a volume which is sufficient to fill the void volume between the microballoons , but not substantially greater than the void volume ; the purpose of this is to minimize the density of the composition ; employing a volume of the continuous phase greater than that required to fill the void volume has the effect of unnecessarily increasing the density of the putty and thus rendering the putty less - buoyant , and also increases its tendency to undesired sag , flow and exudation . insofar as density may be less critical in other applications of the composition , this maximum volume requirement for the continuous phase will be less important . in general , the liquid continuous phase should comprise at least 98 parts , and in particular 98 to 100 parts , by volume of the polydimethylsiloxane or mixture of polydimethylsiloxanes per 100 parts by volume of the continuous phase . thus there may be up to 2 parts by volume of liquid additives such as dyes in the liquid phase . in general , the solid discontinuous phase comprises at least 65 parts and thus 65 to 100 parts , and preferably at least 98 parts , by volume of microballoons per 100 parts by volume of the continuous phase . thus there may be up to 45 parts by volume of solids other than the microballoons in the discontinuous . the volume of the continuous phase relative to the total volume of the composition is greater than or equal to the minimum that is required for said continuous phase to entirely fill the void volume of the discontinuous phase , but not exceeding 56 % more of said minimum relative volume . either the continuous phase or the discontinuous phase may further comprise up to 2 parts by volume of a dye or pigment , based on 100 parts of the respective phase . the discontinuous phase may further comprise up to 33 parts by volume of particles , fibers , filaments , felts or fabrics , of composition selected from sand , glass , silica , alumina , calcium carbonate , calcium silicate including wollastonite , kaolin , talc , barite , mica , asbestos , fly ash , ceramic , boron carbide , silicon carbide , boron nitride , zirconia , boron , aluminum , copper , bronze , iron , steel , carbon , cellulose , wool , silk , hair , bone , polyimide , polyester , polyethylene , and polyamide including nylon and aramid , based on 100 parts by volume of the discontinuous phase . when the composition is to form a buoyant putty , the composition suitably contains the continuous phase in an amount ranging from 25 to 39 , preferably 26 to 31 parts by volume , per 100 parts by volume , of the composition ; the microballoons forming the discontinuous phase are suitably present in the composition in an amount ranging from 61 to 75 , preferably 69 to 74 parts by volume , per 100 parts by volume , of the composition ; and , with organic polymer microballoons , the composition suitably has a density ranging from 0 . 26 to 0 . 40 , preferably 0 . 27 to 0 . 32 g / ml . the microballoons ( also called hollow microspheres ) in the composition of the invention may be filled with air , or nitrogen or similarly inert gas . they should be as light as possible , yet strong enough so as not to be crushed while blending or using the composition . organic polymer or plastic is therefore generally to be preferred over glass or ceramic as giving acceptable strength for the least mass , and as having a more hydrophobic native surface to adsorb less water . such organic polymer microballoons are also referred to herein as plastic microballoons . the plastic should be one able to withstand environmental conditions of storage or use of the composition . smaller microballoons give a smoother texture to the buoyant putty for a closer fit , and better grip , on the sinkable object being held ; per unit volume used , smaller microballoons have more surface in contact with the intervening viscous liquid , for a more cohesive composition that is less prone to exudation and phase separation . suitable microballoons typically have a true density ( i . e . mass / volume where &# 34 ; volume &# 34 ; does not include the void volume between the individual microballoons ) of less than 0 . 10 g / ml and a diameter of less than 1 mm and typically from 15 - 200 μm ; more especially they may have a mean diameter of about 100 μm . suitable microballoons include those available from pq corporation as pm 6545 plastic microspheres of vinyl chloride - acrylonitrile copolymer , and which are sufficiently strong , light ( 0 . 02 g / ml ), heat - stable ( to 120 ° c . ), and small ( having a mean diameter ca . 100 μm , with 15 - 200 μm range ). the composition exhibits self - adhesion , in other words it is co - adhesive , but is non - tacky and displays low adhesion to surfaces . thus , when employed as a buoyant putty , an object is embedded in the composition or encased or enwrapped , at least in part , by the composition so that reliance is made on the cohesive nature of the composition to engagingly hold the object . it is not necessary that the object being completely enclosed by the composition and indeed this will not normally be desirable ; thus , for example , a band of the composition may surround a portion of a fountain pen . for the composition of the invention to be sufficiently stiff , cohesive and non - exuding , it has been found that the viscosity of the continuous liquid phase must exceed 100 , 000 cs ( centistokes ), and preferably exceed 200 , 000 cs . this eliminates from consideration such hydrophobic liquids that are &# 34 ; oils &# 34 ; including peanut oil and other vegetable oils , epoxidized soybean oil , even &# 34 ; heavy &# 34 ; paraffin or mineral oils , and silicone oil or fluid of viscosity of 100 , 000 cs or less . of the more viscous hydrophobic oligomers and polymers that are liquids to - 40 ° c ., polyisobutylenes such as the indopol ( trade - mark ) series h - 40 , h - 300 , h - 1500 and h - 1900 of increasing viscosity , from amoco inc ., even and particularly when more viscous than 100 , 000 cs , are unacceptably sticky to hands and other surfaces ; so too are polyisoprenes that also contain reactive alkene groups that make them subject to viscosity change through autoxidation , while fluorocarbons are relatively dense and expensive , and polysulphides dense and typically smelly . polydimethylsiloxanes are well - known for their antistick properties , which make them useful as mould - release agents . they are also used to coat textiles and other solid articles to confer water repellence , and as ingredients in cosmetics and polishes . the higher atomic number of silicon makes them slightly denser ( 0 . 98 g / ml ) than saturated hydrocarbon polymers , but still less dense than even fresh water . these polymers are inert towards and repel water , though they will wet organic surfaces such as the surface of plastic microballoons ; they are odourless , non - toxic , nonflammable , and very stable to air and light . the viscosity of mixtures of polydimethylsiloxanes increases with their weight - average molecular weight : low - molecular weight mixtures are called silicone fluids or silicone oils , while higher molecular weight mixtures of barely discernible flow are called silicone gums . the industry commonly mixes polydimethylsiloxanes of higher and lower weight - average molecular weights to produce polydimethylsiloxanes of intermediate weight - average molecular weights . polydimethylsiloxanes do not become glassy solids until temperatures below - 123 ° c ., and are used as heating media to over + 150 ° c . though they can be chemically crosslinked with peroxides or by other means to form non - flowable soft or hard gels , in the absence of such curing agents they remain liquids with flow properties that do not greatly change with time , light , moderate heat , or contact with air or water . general electric inc . supplies the viscasil ® series of polydimethylsiloxane liquids of 30 , 000 cs ( visc - 30m ) , 60 , 000 cs ( visc - 60m ) and 100 , 000 cs ( visc - 100m ), and others of viscosities below 100 , 000 cs . however , it has been found that even the visc - 100m by itself was not viscous enough to give a composition with microballoons at any ratio that was sufficiently stiff , cohesive and non - exuding for use as in a buoyant putty . the same company once supplied a 600 , 000 cs silicone fluid , but this has been discontinued in recent years . wacker inc . also supplies a series of polydimethylsiloxanes , of which their wacker silicone fluid ak 500000 , of 500 , 000 cs viscosity , was found suitable as the polydimethylsiloxane component of the invention . polydimethylsiloxane fluids of sufficiently high viscosity may also be achieved by blending a silicone fluid of 100 , 000 cs or less , with a high viscosity silicone gum such as se30 of general electric ; se30 is a polydimethylsiloxane having , according to the manufacturer , a viscosity well exceeding 2 , 000 , 000 cs ( i . e . beyond the upper range of apparatus normally used to generate viscosity values in centistokes ), and a penetration number of 500 to 1500 . the penetration number is used for describing the hardness or viscosity of asphalt or bitumen and other highly viscous liquid ( i . e . flowable ) substances , as the distance that a standard needle penetrates in a fixed time under standard conditions , with higher values therefore denoting softness or lower viscosity ( corbett , l . w . and r . urban ( 1985 ). &# 34 ; asphalt and bitumen .&# 34 ; ullmann &# 39 ; s encyclopedia of industrial chemistry . w . gerhartz ed ., vch publishers , deerfield beach fla . usa y1985 va . 3 p169 - 188 ). a fluid of too high a viscosity , such as from too much of the high viscosity silicone gum in a polydimethylsiloxane mixture , is difficult to mix with the microballoons , and gives a buoyant putty with properties not improved enough to warrant the extra cost ( silicone gum or other more viscous polydimethylsiloxane being a relatively more expensive component ), and effort of mixing . a single silicone fluid of 500 , 000 cs , or a mixture of substantially equal parts of a silicone fluid of 30 , 000 cs and a silicone gum having a penetration number of 500 to 1500 , have been found especially suitable as the polydimethylsiloxane of the continuous phase of the invention , however , it is within the skill of the art to formulate different polydimethylsiloxanes having the required viscosity of the invention , so as to provide other embodiments of the composition of the invention . the liquid continuous phase in the composition of the invention has a viscosity of less than 2 , 000 , 000 cs . the viscosity of the continuous phase is also less than a viscosity corresponding to a penetration number of 500 . among the substances that can be added to a liquid to increase its apparent viscosity , those that do so by forming a microcrystalline suspension without dissolving in the liquid , such as wax , fatty amide or colloidal silica in polydimethylsiloxane fluid , are less able to retain them against undesired exudation or phase - separation , than higher - molecular weight analogs of the liquid &# 39 ; s molecules , such as silicone gum in silicone fluid . however , should the polydimethylsiloxane of the continuous phase already be viscous enough to prevent such exudation , additional particulate or fibrous filler can further increase the strength and stiffness of the composition , for applications where such qualities are useful . however , the composition would entirely lose its buoyant quality on substituting microballoons ( density ca . 0 g / ml ) with non - hollow particles or fibers of , for example , glass ( density ca . 3 g / ml ), in more than ca . 33 % of the volume of the discontinuous phase . for a typical embodiment of the invention having the discontinuous phase occupying 70 % of the total volume , this would thus impose a maximum glass content of 23 % of the total volume , which is also in the range of glass content for typical fiberglass formulations ( j . wiley &# 34 ; the fiberglass repair and construction handbook &# 34 ; e2 mcgraw - hill , new york n . y . usa p59 - 65 ). a gentle stretching and folding action , as is done for preparing bread or other dough , is suitable for preparing the composition of the invention by mixing together the components of its continuous and discontinuous phases without rupturing the microballoons of the discontinuous phase . though this can be done by hand , a machine capable of such action , such as the planetary hobart type of doughmaker , or the horizontal - spindle model from ross inc ., is more suited for preparation of the composition of the invention on a larger scale . it would help protect a portion of the composition of the invention , and the underlying object it may hold or enclose , against sudden crushing , scratching , gouging , tearing , piercing or cutting damage , to employ an embodiment that is stronger and stiffer , or to enclose the portion with a strong flexible envelope that is either impermeable to liquids , or that is a woven or knitted fabric that is permeable to liquids . portions of the composition of the invention may also be contained as layers between other layers of other materials , or held within holes or pockets formed by other materials . the composition of the invention also has other useful qualities of softness , lightness , flexibility , stiffness , non - toxicity , and thermal , electrical , shock , vibration and acoustic insulation , that would also make it useful as a sealant , packaging material , or as an insulating component within supports for engines or other machinery , or in the floors , ceilings or walls of studios , theatres , engine rooms , or other rooms or buildings , or of freezers , refrigerators , coolers , incubators , ovens or other temperature - controlled areas or devices , or of aircraft , boats , cars and other vehicles , or of speakers , microphones or other acoustic devices , or as a filler for lining or padding in boots , jackets , suits , lifejackets , armour , and other articles of regular , sports , work , recreational , police , combat or emergency clothing , or in seats , cushions , pads , beds , grips and other cushioning or vibration - damping devices or furniture , or in medical or veterinary prostheses . a typical formulation of the invention consists of , by volume , 13 . 5 parts of se30 silicone gum , 13 . 5 parts of visc - 30m silicone fluid , and 73 parts of pm6545 plastic microspheres . these ingredients may suitably be combined in a sealed plastic bag , and blended together by manipulating the outside of the sealed bag by hand so that the contents are subjected to a stretching and folding action . the result is a white , stiff , malleable white mass , that is a composition of the invention and a buoyant putty . the density of the product was measured at 0 . 28 g / ml , by pressing a portion into a measuring spoon of known volume , scraping off the excess and weighing . another portion of this product felt dry , and did not stick nor leave visible liquid or solid residue when briefly pressed onto hands , leather , wood , linoleum , or woven or knitted cotton , rayon or nylon fabrics or other opaque non - reflecting surfaces ; the slightly visible greasy spot left after pressing on clear or reflective glass or plastic could easily be removed by wiping or washing with soap and water . even after prolonged handling of another portion , only a slight and not unpleasant oiliness , and no stickiness , were felt on the hands . another portion that was wrapped in finely woven cotton fabric remained contained even after extensive manipulation , the exterior of the fabric only acquiring a slightly more oily feel , and a quality of water - repellence . another portion retained its approximately spherical shape without sagging for over four months while resting on a solid surface . a hen &# 39 ; s egg , wrapped in another portion to a thickness of 1 cm , did not crack on being dropped 1 m onto smooth concrete , whereas an unprotected egg was thoroughly smashed , thus demonstrating ability to insulate against shock . increasing quantities of sand or cotton batting can be gradually worked into other portions to give product compositions that are increasingly harder and stiffer . another portion that was rolled into a cylinder 1 cm wide by 1 - 3 cm long could be folded 180 ° without large breaks appearing in its surface , thus establishing its cohesiveness . over a wide range of viscosities for the continuous phase , samples prepared with relatively more of the microballoons were not cohesive by this last test , even crumbling into several pieces during moulding efforts , probably due to the amount of continuous phase fluid component not being sufficient to fill the void volume between the microballoons . other samples with less of the microballoons component and more silicone fluid or gum components were denser and no stiffer or stronger . many other combinations of silicone gum and fluid , including less of the gum with a greater portion of more viscous fluid such as visc - 60m or visc - 100m , or use of wacker silicone fluid ak 500000 alone , as the polydimethylsiloxane of the continuous phase , gave putties of similar consistency when mixed with the same proportion of the microballoons . exclusive or too high a proportion of lower - viscosity silicone fluids visc - 30m or visc - 60m , or exclusive visc - 100m , gave putties that were very soft and easy to pull apart ; exclusive or too high a proportion of the se30 gum gave putties that were very stiff and hard , that were difficult to mix during their preparation , and to flex and shape once formed ; wacker silicone fluid ak 1000000 , of 1 , 000 , 000 cs viscosity , proved just barely manageable to mix . formulations similarly prepared using mixtures of silicone fluid or gum with even small quantities of polyisobutylene were noticeably and unpleasantly sticky . substituting the polydimethylsilicone of the continuous phase with borasilicone - based silly putty ® gave a composition whose strength and stiffness greatly decreased after prolonged contact with water , behaving like unsuitable putties prepared from polydimethylsiloxanes less viscous than 100 , 000 cs . the ability of the composition to be coloured was demonstrated by mixing in 1 wt % of &# 34 ; cadmium red &# 34 ; fine pigment . the putty was coloured uniformly red throughout without substantial change in its density or consistency .
a composition suitable as a buoyant putty is disclosed , which is a mixture of a discontinuous solid phase of microballoons , and a viscous liquid continuous phase comprising a polydimethylsiloxane ; the polydimethylsiloxane of the continuous phase has a viscosity between 100 , 000 cs and 2 , 000 , 000 cs ; the viscosity of the polydimethylsiloxane of the continuous phase is achieved by incorporating polydimethylsiloxane molecules of sufficiently high molecular weight ; containment within other materials is optional ; additional dyes , pigments , particles , fibers , felts or fabrics can confer additional visibility , strength , stiffness , dryness or friction ; accompanying properties of malleability , and thermal , electrical , vibratory , shock and acoustical insulation , also make this composition useful for other applications that require such qualities .