CA1169211A - Hollow organic film forming material microspheres - Google Patents

Abstract

ABSTRACT

The invention relates to hollow organic film forming material (preferably plastic) microspheres of substantially uniform diameter of 200 to 10,000 microns and of substantially uniform wall thickness of 0.1 to 1,000 microns. The microspheres are free of latent solid or liquid blowing gas materials or gases and the walls of the microspheres are substantially free of holes, relatively thinned wall portions or sections and bubbles. The microspheres may be filamented and connected to each other by filament portions which are continuous with the microspheres and are of the same organic film forming material.

Description

- ~692~1 This application is a division of Serial No. 334,619, filed August 27, 1979.
The present invention relates ~o hollow microspheres formed from organic film forming materials. Preferably, the organic ~ilm forming material is plastic and the invention is hereinafter described in that context.
The present invention also relates to hollow plastic microsphereshaving a thin t~ansparent metal coating deposited on the inner wall surface of the microsphere.
The present invention also relates to hollow plastic microspheres having a thin re1ective metal coating deposited on the inner wall sur-face of the microsphere.
The present invention furt~er relates to the use o ~he hollow plastic microspheres in the manufacture of improved insulation materials for use in construction of homes, factories and of~ice buildings and in the manufacture o~
products in which heat baxriers are desired or necessary.
The present invention furth~r relates ; to the use o~ the hollow plastic microspheres as filler materials in s~ntactic foam systems.
The hollow plastic microspheres of the pre-sen~ invention, depending on their diame~er anà
the,r wall ~hickness and the particular compo-sition from which they are made, are capable o withstanding rela~ively hign e~ternal pressures and/or weigh~. Hollow plastic microspheres can be made tnat are -esistant to re~tively ~ign tem~eratures and stable to many chemical agents and wea~hering conditions. These characteristics make the microspheres suitable for a wide variety of uses.
~, 3 2 ~ 1 BACKGROUND OF THE INVENTION
_ In recent years the substantial increases in costs of basic materials such as plastics, cement, asphalt and the li'~e has encouraged development and use of filler materials to reduce the amount and cost of the basic materials used and the weight of the finished materials.
The substantial increases in the energy costs of hea~ing and cooling has encouraged the develop-ment of new and be~ter insulation materials andmany new insulation materials and insulating systems usin~ the new materials have been developed in an attempt to satisfy these needs.
One o~ the newly suggested filler materials and insulating materials utilizes hollow plastic microspheres. The known me~hods for producing hollow plastic microspheres, however, have not been.successful in producing microspheres of uniorm size or uniform thin walls which makes it very difficult to produce filler and insu-lation materials of controlled and predictable physical and chemical characteristics and quality. Also, the relatively high cost and the re~latively small size of tne prior art microspheres 25 has limi~ed their use.
One of the existing methods o producing hollow plastic microspheres, for example, as disclosed i~ ~he Veatch et al U.S. Patent

2,797,201, is to disperse a liquid or solid gas-phase precursor material ~n a plastic material~o be blown to form the microspheres. The plastic material containing the solid or liquid gas-phase precursor enclosed therein is then neated to convert the solid or liquid gas-phase precursor material into a gas and is ~urther heated to expand the gas

- 3 and produce the hollow plastic microsphere con-taining therein the e~panded gas. This process is, understandably, difficul~ to control and inherently produces plastic microspheres of random size and wall thickness, microsphPres with walls that have sections or portions of the walls ~ha~ are rela~ively thin, walls that have hole~, small trapped bubbles, trapped or dissolved solvents or gases, any one or more of which will result in a substantial weakening of the microspheres~ and a substantial pro-portion o~ the microspheres which are not suitable for use and must be scrapped or recycled.
. Further, the use o~ conven~ional fiberglass insulation is being ques~ioned in the light of the recently discovered possibili~y that~riber-glass of certain particle size may be carcino-genic in the same or similar manner as asbestos.
The use of polyurethane foams, urea~formaldehyde foams and oolystyrene oams as insulating ma~erials have recently been criticized because of their dimensional and chemical instability, for example, a tendency to shrink and to evolve the biowing gases such as Freon and to evolve unreacted gases such as formaldehyde.

In addition, in some applications, the use of low density microspheres presents a serious problem because they are difficult to handle since they are readily elutriated and tend to blow about. In situations of this type, the filamented microspheres of the presen~ invention provide a convenient and safe method o~ handling the microspheres.

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BRIEF DESCRIPTION OF THE INVENTION

According to the present invention, there are provided hollow organic film forming material microspheres of substantially uniform diameter of 200 to 10,000 microns and of substantially uniform wall thickness of 0.1 to 1,000 microns, wherein said microspheres are free of latent solid or liquid blowing gas materials or gases and the walls of said microspheres are substantially free of holes, relatively thinned wall portions or sections and bubbles.
According to a further aspect of the present invention, there are provided filamented, hollow inorganic film forming material microspheres having a diameter of 200 to 10,000 microns, having a wall thickness of 0.1 to 1,000 microns, wherein said microspheres are connected to each other by filament portions which are continuous with the microspheres and are of the same organic film forming material from which the microspheres are made.
Preferably the organic film forming material is plastic and, as stated above, the invention i5 discussed herein in that context.

~ ~92~ 1 The microspheres can be made ro~ a low heat conductivity plascic composi~lon and can contain a low heat cond~ctivity gas. The micros?heres can also be made to contain a thin metal coating deposited on the inner wall surface of the micro-spheres. The metal coating, depending on i~s thic~ness, can be transparent or reflective. The use of a reflective metal coating i~proves the insulating and heat reflecting characteristies of the microspheres.
The plastic microspheres of tne present inven-tion can be used to form a heat barrier by using them to ill void spaces between existing walls or o~her spaces and by forming them into sheets or other shaped forms ~o be used as insulation barriers. When used to form insulation barriers, the interstices between the microspheres can be filled wi~h a low hea~ conductivity gas, a foam or other material all of which increase the heat ~ 20 insulation characteristics of ~he materials ~ade `~ from the microspheres.
In one embodiment of the invention, the micro-spheres are coated with an adhesîve or Loam filler and flat~ened to an oblate spheroid or a generally cellular shape. The microspheres are held in the ~latt~ned position until the adhesive hardens and/or cures after which the microspheres retain -- their fla~tened shape. The use of the flattened microspheres substan~ially reduces the -volume of the interstices between ~he microspheres and significantly improves the ~hermal insulating characteristics of the microspheres.
ne microspheres can be made from plastic composi~ions selected for their desired optical and chemical properties and for the particular gaseous material to be contained therein.

Where a gas con~aining dispersed metal particles i5 used to blow ~he microspheres, a metal layer is deposited on the inner wall sur-ace of the microsphere as a thin metal coating.
Where a gaseous organo metal compound is used to deposit the me~al layers, a gaseous organo metal compound is used as or wi~h the blowing gas to blow the microspheres. The organo metal com-pound can be decomposed just prior ~o blowing the microspheres or after the microsphe~es are for~ed by, or example, subjecting the blowing gas or the mie~osp~eres to heat and/or an elect~iczl ~ischarge.
The ilamented microspheres are made in a manner such that they are connec~ed or atta~ed to each other by a thin cont;nuous plastic ~ament. ~ne .ilamented microspheres can be flat~ened to produce the oblate spheroids. The filaments interrupt and reduce the area of wall to wall con~act be~een the microspheres and reduce ~he thermal conducti~
vity between the walls of the microspheres. The ~ilamented microspheres also assist in handling and preventing scatterin~ of m:icrospheres, particu-larly whers very small diamete~ microspheres or low density mic~ospheres are produced. The fila-mented microspheres have a distinc~ advancage ~ver th~ simple addition of ilaments in ~nat the continu~us filamen~s do not tend to se~tle in ~e systems in which they are used.
~ E ADVANTAGES
The present invention overcomes many of the problems associated with prior at~empts to produce hollow plastic microspheres- The invention allows the production of hollow plastic microspheres having 1 1~9?,1 1 predetermined characteristics such ~haL improved - filler materials and insulating materials and insulating sys~ems can be designed, manuactured and tailor made to suit a par~icular desired use7 The diameter and wall thickness uniformity, and the ther~al, strength and chemical resistance characteristics of the plastic microspheres can be determined by carefully selecting the plastic and constituents of ~he plastic composition and con~rolling the blowing gas pressure and tempera-: ture, and the temperature, viscosity and thickness of the liquid plastic film from which the micro-spheres are formed. The inner volume of the microspheres may con~ain an inert low heat con-ductivity gas used ~o blow the ~icros~here. The ; hollow plastic microspheres of ~he presen~ inven-tion can have a transparent metal co2ting de~osited : on the inner wall surface ~hereof which allows visual light to pass ~hrougn ~he microspheres but reflects and traps infrared radiations. The holl QW plas~ic microspheres can also h2~e a low :: emissivi~y reflec~ive metal coating depo~ited on : the inner wall surface of ~he microsphere whicn effectively re~l~.cts visual light and radiant : hea~ energy.
The invention ~rovides a practical and economical means by which hollow plastic microspheres having a : high heat insulation eficiency can be utilized to prepare a relatively low cos~ e ficient insu-lating material for common every day uses. The present in~ention also allows the economic pro-. duction of hollow plas~ic microspheres from plas-: ~ic compositions which incor~orates a metallic ra ~ ticn barrier and can be used as an ~sula~lon ~a~erial.

~l ~6(~2 The process and apparatus aspects of the present invention, as compared to the prior art processes of using a latent liquid or .solid blowing agent, can be conducted at higher temperatures sin~e there is no included expandible and/or decom-posable blowing agent used. The ability ~o use higher blowing ~empera~ures resul~s in for particular plastic composi~ions a lower vis-cosity or ~he plastic composition which allows surface tension forces to produce significantly greater uniformi~y in wall thickness, sp~ericity and diameter o the microspheres produced.
The presen~ invent~on also allows the use of a wide variety of blowing gases and/or blowing gas materials. In accordance wiLh the present invention, a wide variety of gaseous material blowing gas can be encapsulated, i.e.
i~ is no longer requir~d to use a latent liquid or solid blowing agent as the blowing gas.
The invention provides for the production of hollow plastic microspheres at economic prices and in : large quantities. The invention allows the production o hollow plastic microspheres having predetermined diameters, wall thicknesses, strength and resistance to chemical agents and weathering and gas permeability such that superior systems can be designed, manufactured and tailor made to suit a particular desired use.

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9~ 92~1 B~IEF DESCRIPTION OF THE DR4WINGS
The attached drawings illustrate exemplary forms of a method and apparatu~ for making microspheres for use in and às filler materials and for use in and as insulating materials.
The Figure 1 o~ the drawings shows in cross-sec~ion an apparatus having mult-iple coa~ial blowing nozzle means for supplying the gaseous material for blowing hollow plastic mierospheres, a ~rans~erse ~et providing an entraining fluid to assist in the form~tion and de~ac~ent OL ~he microspheres from the blowing nozzles, and means for supplying a quench or heating LlUid tc cool or heat ;he microspheres.
T'ne Figure 2 of the drawings is an.enlarged de~ailed c_oss-sec~ion of the nozzle means o apparatus sho~-n in Figure L.

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~ 1~92~ 1 The Figure 3 of the drawings is a detailed cross-section of a modified form o the nozzle means shown in Figure 2 in which the lower end of the nozzle means is ~apered inwardl~.
The Figure 3a of the drawings is a detailed cross-section of a modified transverse jet entraining means having a 1attened ori~ice opening and the Figure 3 nozzle means.
The Figur~ 3b of the drawings is a top plane view of the modified transvexse jet entraining means and the nozæle means illus~rated in Figure 3a o the drawings.
The Figure 3c of the drawings illustrates the use of the apparatus of Figure 3b to make filamented hollow plastic microspheres.
The Figu~e 4 of the drawings is; a detailed cross-section of a modified form of the nozzIe means shown in Figure 2 in which the lower por-tion OL the nozzle i9 enlarge~
~;~ 20 The~Figure 5 of the d~awings shows a cross-section of an en~ view of a flat plate solar energy~collector using the~hollow plastic ~icro-~
spheres of the present in~en~ion.
~ ~ The Figure 6 of the drawings shows a c. oss-;~ section of an end view of a tubular solar energv collector using;the hoilow plastic microspheres of the present invention.
The Figure 7 of the drawings shows a cross-section of spherical shaped hollow plastic micro-spheres ~ade into a ormed panel.
The Figure 7a of the drawings shows a cross-sec~ion of oblate spheroid shaped hollow plastlc microspheres made into a Eormed panel.
The Figure 7b o the drawings shows a cross-section of oblate spheroid shaped hollow plastic 2 1 ~

filamented microspheres made into a formed panel in which the ilaments interrupt the microsphere wall to wall contact.
DETAILED DISCUSSION
OF THE DRAWINGS
The invention will be described with reference to the accompanying Figures of ~he drawings where-in like numbers designate li~e parts throughout the se~eral views.
Referring to Figures 1 and 2 of ~he drawings, there is illustrated a vessel 1, made or suitable container material heated, as necessary, by means not shown for holding a liquid plastic 2. The bot~om floor 3 o~ vessel 1 contains a plurality of openings 4 ~hrough whi~ch liquid plastic 2 is fed to coaxial blowing nozzles 5. T-ne coaxial blowing nozzle 5 can be made sepa~ately or can be formed by a downwa-.d extension o the Dottom 3 of vesseI 1. The coaxial blowing nozzle 5 consists of an inner nozzle 6 having an ori~ice 6a for a blowing gas and an outer nozzle 7 having an ori ice 7a ~or liquid plastic. T'ne inner nozzle 6 is disposed within and coa~ial to outer nozzle 7 to form annular space 8 be~ween nozzles 6 ~nd 7, which annular space provides a flow path for liquid plas~ic. The ori~ice 6a of inner nozzle 6 terminates at or a short distance above ~he plane of orifice 7a of outer nozzle 7 The liquid plas~ic 2 a~ about at~ospheric pressure or a~ elevated pressure flows downwardly through annular space 8 and fllls the area be~ween orifice 6a and 7a. The surface tension orces in the liquid plastic 2 from a thin liquid plas~ic ilm 9 across orifices 6a and 7a.

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A blowing gas 10 and/or blowing gas containing dispersed metal particles, which is a~ or below ambient temperature or which is heated by means not shown to about the temperature o~ the liquid plastic and which is at a pressure above the liquid plastic pressure at the blowing nozzle, is fed through distribution condui~ 11 and inner coaxial nozzle 6 and brought into contact with the inner surace of the liquid plastic film 9.
The blowing.gzs exerts a positive pressure on the liquid ~lastic film to blow and distend the ~: film outwardly to orm an elongated cylinder shaped liquid film 12 of plastic filled with the : blowing gas. The elonga~ed cylinder 12 is closed at its outer end and is connected at its ;~ inner end to outer nozzle 7 at the peripheral edge of orifice 7a. A balancing pressure of a gas or of an inert gas, i.eO a slightly lower : pressure, is provided in the area of the blowing nozzle into which the elongated cylinder shaped liquid ilm is blown. The il~ustrated coaxial nozzle can be used to produce~microspheres naving ~: : diameters three to :five times the size o~ the : inside diameter of orifice 7a and is useful in biowing low viscosity plastic materials.
: A transverse jet 13 is used to direc~ an iner~ entraining fluid 14, which is at about, below or above the temperature of the liquid plastic 2. The entraining fluid 14 is fed through distribution conduit 15, nozzle 13 and transverse jet nozzle orifice 13a and directed at the coaxial blowing nozæle 5. The transverse jet 13 is aligned to direct the flow of entraining fluid 14 over and around blowing nozzle 7 in the ~ ~921 1 microsphere forming region at and behind the orifice 7a. The entraining fluid 14 as it passes over and around blowing nozzle 5 fluid dynamically induces a pulsating or fluctuating pressure field in the entraining 1uid 14 at ~he opposite or lee side of blowing nozzle 5 in its wake or shadow.
The entraining fluid 14 envelops and acts on ~he elongated cylinder 12 in such a manner as ~o and causes ~he cylinder ~o flap, fold, pinch and close-of at its inner end at a point 16 proximate to the ori~ice 7a of outer nozzle 7.
The continued movement of the entraining fluid 14 over the elongated cylinder 12 produces fluid drag forces on the cylinder 12 and detaches it rom the orifice 7a o the outer nozzle 7 to 2110w the cylinder to ~all. The surface tension forces of the liquid plastic act on the entrained, ralling elongated cylinder L2 and cause ~he cylinder to seeX a minimum surace area and ~o form a spherical shape hollow plastic microsphere : . 17.
Quench or heating nozzles 18 having oriices 18a are disposed below and on bo~h sides of coaxial blowing nozzle 5 and direct cooling or heating'fluid l9 at and in~o contact wi~h the liquid plastic microsphere 17 ~.o rapidly cool or ; heat and cure and solidify the liquid plas~ic and form a smooth, hardened, hollow plastic micro-.
sphere. The quench or heating fluid 19 also serves ~o carry the hollow plastic microspheres away from the coaxial blowin~ nozzle 5, Su~icient heating and curing time can be provided by using a heated fluidized bed, heated liquid carrier ~ ~g2~ 1 or belt carrier system for the thermosetting hollow plastic micro-spheres to cure and harden ~he microspheres with substantially little or no distortion or effect on the size or shape of the microspheres. Where the plastic is thermosetting, the heated and cured plastic microsphexes can be subsequently cooled. The solidified and harden~d hollow plastic microspheres are collected by suitable ~eans not shown.
. In Fi~ure 3 of the drawings, the lower portion of the outer coaxial nozzle 7 is tapered downwardly and inwardly at 21.
This embodiment as in ~he previous embodiment comprises coaxial blowing nozzle 5 which consists of inner nozzle 6 wi~h orifice 6a and outer nozzle 6 with orifice 7a'. The figure of the draw-ings also shows elonga~ed cylinder shaped liquid film 12 with a pinched portion 16.
The use of ~he tapered nozzle 21 construction was found to substantially assist in the formation of a thin plas~ic film 9' in the area between ori~ice 6a of inner nozzle 6 and orifice : 7a' of outer nozzle 7~ The inner wall surface 22 of the taper portion 21 of the outer nozzle 7 when pressure is applied to liquid plastic 2 orces the liquid p:Lastic 2 to squeeze through a fine gap formed between the outer edge of orifice 6a, i.e., the ou~ex edge of inner nozzle 6, and the inner surface 22 to form the thin liquid plastic film 9' across orifices 6a and 7a'.
The ormation of the liquid plastic film 9' ~oes not in this embodiment rely solely on the surface tension properties of the liquid plas~icO The illustrated coaxial nozzle can be used to produce - 15 - 1~9211 microspheres having diameters three to five times the size of the diameter of oriice 7a of coaxial nozzle 7 and allows making microspheres of s~aller diameter than thosR made using the Figure 2 apparatus and is particularly useful in blowing high viscosity plastic materials.
. The diame~er of the microsphere is determined by the diameter of orifice 7a'. This apparatus allows the use of larger inner diameters of outer nozzle 7 and larger inner diame~ers Oc inner nozzle 6, bo~h of which reduce the possibility o~ plugging of the coaxial nozzles when in use.
These ~eatures are particularl~ advantageous when the blowing gas contains dispersed metal particles andlor the plastic compositions contain additive material par~icles.
In Figures 3a and 3b of the drawings the outer portion of the transvers~
jet 13 is flattened to form a ~enerally rectangular or oval shaped orifice opening 13a. The ori~ice opening 13a can be disposed at an angle relative ~:o a line dra~n ~hrough ~he central axis o~
coa~ial nozzle 5. The preferred angie, however, is that as illustrated in the drawing. Thac is, at an angle of about 90 to the central a~is of the coa-.~ial nozzle 5.
The use of the flattened transverse jet entraining fluid was found, at a given velocity, to concentrate the ef~ect of the fluctuating pressure field and to increase the ampl~ude of tne pressure fluctuations induced in the region o the ~ormation of the hollow microspheres at the opposite or lee side of the blowing nozz7 e 5.

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By the use of ~he fla~tened transverse je~ and increasing ~he amplitude oE the pressure fluc-tuations, the pinching action exerted on the cylinder 12 is increased. This action facili-tates the closing of of the cylinder 12 at i~s inner pinched end 1~ and detaching o the cylinder 13 from ~he oriice 7a o the cent~er nozzle 7.
The Figure 3c of the drawings illustra~es apparatus in which a hi~h viscosity plastic material is used to blow 'nollow olas~ic filamented micro-spheres. In this Figure, the eiong~ted shaped cyLinder 12 and plastic microspheres 17a, 17b and 17c are connec~ed to each other by thin plastic filaments 17d. As can be seen in the drawin~, as ~he micros?heres 17a, i7b and 17c progress zway from blowing nozzle ~ surace tension forces act on the elonga~ed cylinder 12 to effect the gradual change of the elongated shaped cylinder 12 to t~e generally spherical shape 17a, more spherical~shape 17b and finally the spheri~al shape microsphere 17c. The same surface tension ~orces cause a gradual reduction - in the diameter Oc the connecting filaments L7d, as the distance between the microspheres and filaments and the blowing nozzle 5 increases.
The hollow plastic microspheres 17a, 17b and 17c that are obtai~ed are con~ected by thln filament portions 17d that are substantially of ~qual length and that are continuous wi~h the plastic microsphere.
The operation of the apparatus illustra~ed in Figures 3, 3a, 3b and 3c otnerwise ;han dis-cussed above is similar to that discussed ~ h 17 ~ 921~

regard to Figures 1 and 2 o ~he drawings.
The Figure 4 of the draw~ngs illustrates apparatus in which the lower portion of the coaxial nozzle 7 is provided with a bulbous member 23 which imparts to the outer nozzle 7 an expanded spherical shape. This embo-diment as in the previous embodiments comprises coaxial blowing nozzle 5 which consists of inner nozzle 6 with orifice 6a and outer nozzle 7 wi~h orifice 7a. The Figure of ~he drawings also shows elonga~ed cylinder shaped liquid film 1~ with the pinched ~ortion 16.
The use of the bulbous spherical shaped member 23 is found ror a given veloeity o ent~aining fluid 14 (Figure 2) to subs~antially increase the amplitude of ~ne pressure 1uctuations included in the region of the formation of ~he hollow micro-sPneres 2t the opposi~e or lee side of the blowing ~ozzle ~. By the use of the bulbous member 23 and increasing ~he amplitude of the pressure fluc-~uations, the pinching action exerted on ~he elongated cylinder 12 is increased. This action ~acilitates ~he closing of of the cylinder 12 at its inner pinched end 16 and detaching the cylinder 12 from the orifice 7a of ~he outer noz~le 7.
Referring again to Fi~ure 4 of the drawings, a beater bar 24 can be used to assist in detaching the c~Jlinder 12 from ori~ice 7a. The beater bar 24 is attached to a spindle, not shown, which is caused to ro~a~e in a manner such that the beater bar 24 is brought to bear upon the pinched portion 16 of the elongated cylinder 12 and to thus facilitate ~he closing off of the 92~ 1 cylinder 12 at its inner pinched end 16 and detaching the cylinder 12 from the orifice 7a o outer nozzle 7.
The ~p~aratus illustrated in the Figures 2 to 4 can be used singly or in various eombinations as the situation may rea,uire.
The en~ire apparatus can be enclosed in a high pressure containment vessel, no~ shown, which allows the process to be carried out at elevated 10 pressures.
The Figure ; of the drawings illustrates Lhe use of the hollo~ plastic microspheres of the present invention in the cons~ruc~ion of a fla~
pla~e solar energy collector 29. The drawing shows a cross-section taken ,rom an end view OL
the solar collector. The ~uter cover member 30 rotects the solar collector from the weather elements. The cover 30 can be made ,rom cle~r giass or plastic. The cover member 30 can also be made ~rom several layers of light ~ransparent hollow plastic microspheres of this inventian ; bonded together with a transparen~ polyacrylate or polymethyl acrylate resin to ~orm a trans-parent co~er. There is disposed below and ?arallel ~: tO cover 30 a black coated fla~ metal plate absorber 31 to which there is bonded ~o the bottom surface thereof a mul~iplicitY or eYenly spaced heat exchanae medium 32 containin~ tubes 33. The heat exchange medium can, .or example, be water and the tubes 33 are in~erconnected by conven~ional means not shown ~o allow for the flow of ;he heat exchange medium 32 ~hrough ~hn tubes 33. ~n order to minimize heat loss from the solar collector and increase its eficiency, ~he space between ~he outer cover 30 and ~'ne rlat 11~92~1 plate absorber 31 can also be filled with a bed o li~ht transparent hollow plastic microspheres 34 of the present invention. The solar coll~ctor 29 has an inner cover member 35 by means of which the collector can be at~ached to a roof 36 of a home. To ~urther decrease the heat loss o~ the solar collector and increase its efficiency, the space between the lower surace of the flat plate absorber 31 and the inner cover member 35 can be ~illed with reflective hollow plast~c microspheres 39 containing on the inner wall surface thereof a visible light and infrared radiation reflective metal coating. The end members 37 and 38 of the solar collec~or 29 close-off the top and bottom edges of the collector.
The construc~ion and operation of the flat plate solar collector are other~-ise essentially the same as the know flat plate solar collector.
~; ~ The Figure 6 or the drawings illustrates the ; 20 use of the hollow plastic microspheres of the prese~t invention in the construction of a tubular solar energy collector 43. The drawing shows a c~oss~section taken ~rom an end view of the solar collector. The outer cover member 44 can be made rom clea~ gl~ss or plastic. The cover member 44 can als,o be made from several layers of light transparent hollow plastic microspheres o~ this invention bonded toge~her wi~h a trans~parent polyester or polyolefin resin to form a trans-parent cover. There is disposed below and paralleIto cover 30 a double pipe tubular member 45.
The tubular member 45 consists of an inner feed tube 46 and an outer return ~ube 47. The heat exchange medium 48, for example water, is fed through inner feed tube 46, passes to one end of 2 ~ ~

the tube where it reverses its direction of flow, by means not shown, and ~he heat exchange medium 49 (return) passes back through the return tube 47. The inner feed tube 46 is coaxial to ~he outer return tube 47. The outer return tube 47 has on its outer surface a black heat absorbing coating. The heat exchange medium in passing through feed tube 46 and return tube 47 is heated.
The tubular collector 43 has outer parallel side covers 50 and a lower outer curved cover portion 51. The lower curved cover portion 5L
is concentric with the inner tube 46 and outer tube 47. The inner surface of the lower portion 51 is coated with a reflecting material 52 such that ~he sun's rays are re~lec~ed and~concentrated in the direction of the~black heat absorbing surface coating of return tube 47. In order to minimiæe heat loss from the solar collector and increase its erficiency, the entire area between the outer covers 44, 50 and 51 and the return tube 47 can be filled with a bed of the visible ligh~ transparent hollow~plas~ic microspheres 54 of the present invention.
The tubular solar collector 43 is normally mounted in groups in a manner such tha~ they intercept the movement of the sun across the sky.
The sun's rays pass through the tra~sparent micro-spneres 54 and impinged directly on the outer side of the return tube 47 and are reflected by reflector 52 and impin~ed on the lower side of ; return tube 47.
The construction and operation of the tubular solar collector are othe~ise essentially the same as the known tubular solar collectors.

~ ~692~ 1 The Figure 7 o~ the drawings illustrates the use of the hollow plastic microspheres of the present invention in the construction of a formed panel 61. The panel contains mul~iple layers of uniform sized plastic microspheres 62. The micro-spheres can have a thin deposi~ed layer 63 o~ a re1ecting me~al deposited on their inner wall surface. The internal volume of the microspheres can be filled with a low heat conductivity gas 64 and the interstices 65 between the microspheres can be filled with the same gas or 2 low heat conductivity foam containing a low heat conductivi~y gas. The acing surface 66 can be coated with a thin layer of plaster suitable for subsequent sizing and painting and/or covering wi~h wall paper. The backing surface 67 can be coated ~ith the same or different plastic from wh~ch the microspheres are made ~o form a vapor barrier or with plaster or with both materials.
The Figure 7a of the drawings illustrates the use o~ the hollow plastic microspheres OL- the present invention in the construction of a for~ed panel 71. The panel contains multiple layers of uniform sized 1at~ened obla~e spheroid or rec-tangular shaped microspheres 72. The oblate spheroid shaped microspheres can have an inner thin deposi~ed layer 73 of a re~lective me~al.
The internal volume of the microsphere can be filled with a low heat conductivity ~as 74. The Llattened coni~uration of the microspheres sub-stantially reduces ~he volume o the inters~ices ~etween the microspheres which can be filled with a low hea~ conductivi~y foam 75. The facing 76 can be coated with a thin Layer of plaster suitable for subsequent sizing and painting ~ ~6921 ~

and/or covering with wall paper. The backing sur-face 77 can be coated with the same or different plastic from which the microspheres are made to ; ~orm a vapor barrier or with plaster or with both ; materials.
The Figure 7b of the drawings illustrates an e~bodiment of the formed wall panel of Figure 7a in which fil~ted hollow plastic microspheres connected by very thin plastic filamen~s 78 are used. The thi.n plastic filaments 78 are formed bet-~een adjacent microspheres when and as the microspheres are blown and jo~n the microspheres together. T'ne connecting il~ments 78 in ~he formed panel interrupt the wall tQ wall contact, i.e. ~he contact between ~he microspheres and serve to substantially reduce the conduction heat transfer between adja-; cent microspheres. The use of filamented micro-spheres to provide the interrupting filaments is particularly ad~antageous and preferred becausa the filaments are posl~ivel-r evenly dist~ibuted, cannot settle, are supplied in the desired con~rolled amountJ and in the formed panel provide an interloc~ing structure which serves to strengthen the formed panel. The ~acing 76, as before, can be coated with a thin layer o~ plaster suitable ror subsequent sizing znd painting and/or covering with wall ~ paper. The backing surface 77 can be coa~ed ; ~ith the same or diferent plas~ic fro~ which 30 the microspheres are made to form a vapor barrier or with plaster or with both materials.

:~692:L1 ORGANIC FILM FO~MING ~ATERIAL
AND PLASTIC COMPOSITIONS
The organic film forming material and compositions and particularly the plastic composi~ions rom which the hollow plastic microspheres of ~he present invention are made can be widely varied to obtain the desired physical characteristics for blowing and forming, cooling or heating and curing the microspheres and the desired neat ins~la~ing, strength, gas permeability and light trasmission characteristics o~ the plastic microspheres ~roduced.
The plastic composi~ions can be selected to have a low heat conductivity and sufficient strength when hardened, solidified and cured to support a substantial amount of external pressure or weight.
The constituents of the plastic compositions c2n vary widely, depending on their intended use and can inolude naturally occu~ring resins as well as synthetically produced plas~ic materials.
The cons~ituents of the plastic com~ositions can be selected and blended to have 'nigh resis-tance to orrosive gaseous materlals, hign resistance to gaseous chemical agen~s,~ high resistance to alkali and weather, low suscepti-bility to diffusion of gaseous materials into ; ~nd out of the plastic microspheres, and to be substantially free of trapped gas bubbIes or dissolved gases in the walls or the microspheres which can form bubbles and to have suficient strength when cured, hardened and solidified to withstand external ?ressure and/or weight.
The microspheres of the present invention are capable of contacting adjacent microspheres with-out signi~icant wear or deterioration at the points of contact and are resistant to deterior-ation from e.~posure to moisture, heat 11692~ 1 and/or weathering.
The plastic compositions that can be used to form microspheres of the present invention include thermosetting and thermoplastic materials such as polyethylene, polypropylene, polystyrene, poly-es~ers, polyurethanes, plychloro-trifluoro ethylene, polyvinyl fluoride, polyvinylidene, polymethyl me~hacrylate acetyl, phenol-formaldehyde resins and silicone and polycarbonate resins.
The plastic compositions also inclu~e organic materials such as cellulose ace~ate, cellulose ace~ate-butyra~e, and cellulose acetate-propiona~e.
The plastic compositions may consist essentially of the plas~ic material or may contain the plasti~ material dissolved or dispersed in a suitable solvent.
Thermoplastic synthetic resins that can ~e used are polyvinyl resins, i.e. polyvinyl alcohol (wa~er- or organic solvent-soluble)~ polyvinyl chloride, copolymers of vinyl chloride and vinyl acetate, polyvinyl b~tyral, pol.ystyrene, poly-~inylidene chloride, acrylic resins such as polymethyl methacrylate, polyallyL, polye~hylene, and polyamide (nylon~ resins.
Ther~osetting resins ~hat can be used are those in ~he thermoplastic water- or organic solven~-soluble stage of partial polymerization, the resins being converted after or during formation of the microspheres into a more or less fully polymeri7ed solvent-insoluble sLage.
O~her useful resins are alkyd, polysilo~ane, phenol-~ormaldehyde, urea-formaldehyde and melamine-~ormaldehyde resins.

~ ~9~ 1 Natural ilm forming materials are also included within the scope of the form, including soybean pro~ein, zein protein, alginates, and cel~.ulose in solution as cellulose Xanthate or cuprammonium cellulose.
The plastic compositions disclosed in Veatch et al U~S. Patent 2,797,201 and the Morehouse, Jr. U.S. Patent 3,615,972 can also ba used in carrying out the present invention.
There may be added to ~he plastic compositions chemical agents or addi~ives which effect the viscosity o the compositions or of the surface film of the microsphere in ordex to obtain the desired viscosities needed to obtain a s~ahle film for blowing the microspheres. Suitable chemical agents are materials that act as sol~ents for the plastic compositions. The solvents that are used will, of course, depend on the solubility in the solvent of the plastic composition used. Water, al~ohols, ethers, esters, organlc acids, hydrocarbons and chlorinated hydrocarbons can be used as solvents. To assist in the blowing and formation of the plastic microspheres, surface active agents, such as colloidal particles of insoluble substances and viscQsity stabilizers can be added to the plastic composition as additives. These additives can afPect the viscosity of the surface film of the microsphere to stabilize the film during film formation.
A distinct and advantageous feature o the present invention is that latent solid or latent liquid blowing gases are not used or required and that the microspheres that 2 1 ~

are produced are Xree of latent solid or latent liquid blowing gas materials or gases.
Additlonal plastic compositions suitable for use in the present inven~ion are:
Thermoplastic resins: Epoxy resins, phenol~ormaldehyde resins, and ~elmac;
Other resin compositions are: Elvanol, silicones, and Te10n.
For a more speaific description of ~he above plastic and resin compositions see Zimmerman and Lavine, "Handbook of Material Trade Names", Vols. I-IV, 1953-1965.
The plastic compositions of the present invention are formulated to have a relatively narrow temperature difference between ~he liquid ~emperature and the plastic hardening tempera-ture (thenmoplastic) or a relatively narrow temperature difference betwe~n the liquid temperature and the ~hermosetting and cuxing temperature. The plastic compositions are formulated such that they have a high rate of viscosity increase with the haxdening temperature or the *hermosetting emperature such that the micro-sphere walls will solidify, harden and strengthen before theblowing gas within the sphere decreases in volume and pressure a sufficient amount to cause the microsphere to collapse. Where it is desirous to maintain a positive pressure in the contained vo~ume of the microspheres, the permeabili~y of the contained gases can be decreased in the manner discussed below.
The use o~ Saran plastic compositions is found to pro-duce microspheres ~hat are useful as filler materials. The poly-s~yrene plastic compositions can be used to make microspheres for .

* Trademark 2 1 :1 use as improved insulating materials. The poly-ethylene plastic compositions can be advantageously used to make microspheres for use as filler materials in plasti~ molding compositions. The polypropylene plastic compositions can be used to make microspheres for use as aggregate in concrete.
The plas~ic compositions from which the hollow plastic microsphere can~be made are, depending on the particular plastic materials used, to some degree permeable to the gas materials used to blow the microspheres and/or to the gases prese~t in the medium surrounding the microspheres. The gas permeability of the plastic compositions can be reduced and~or substantially eliminated by the addition, prior to blowing ~he ~icrospheres, to the plas~ic composition of very small inert lam;nar plane-orientable additive material parti-cles. Suitable additive partlcles are mica, graphite and aluminum leaf powders. When any one or more OL these laminar plane orientable additive material particles are added to a plastic composir.ion prior to the blowing and formation of the hollol~ plastic microspheres, the process of making the microsphere aligns the laminar particles, as the plastic film is stretched in passing, i.e. extruded, through the conical blowing nozzle, with the walls of the hollo~ plastic microsphere and normal to the gas diffusion direction. The presence of the laminar plane particles in ~he mic-osphere walls substan-tiallv diminishes the gas permeability of the plastic f~lm. The sizes of .he additive particles are 92~ ~

advantageously selected to be less than one-half the thickness of the wall of the microspheres. The gas permeability of certain plastics may be further diminished or reduced by subjecting the microspheres to ionization radiation to promote cross-linking of the plastic molecules.
BL~WING ~S
The hollow plastic microspheres used to make insulating materials can ~e blown with an inert gas or gas containing dis-persed me~al particles or a mixture ~hereof. The ya~es that are used to blow the microspheres are selected to have a low heat conductivity and generally involve heavy molecules which do not transfer heat readily. Suitable blowing gases can be argon, xenon, Freon yases, nitrogen, sulfur and sulfur dioxide. The ~lowing gas is selected to have the desired internal pressure when cooled to ambient ~emperatures. Blowing gases can also be selected that react with the plastic microspheres, e.g. to assist in the hardening and/or curing of the microspheres or to make the microsphere less permeable to the contained blowing gases~
For certain uses, oxygen or air can be used as or added to the blowing gas.
A blowing gas containing di~persed metal par~icles can be used to obtain in ~he contained volume of the microsphere a deposit of a ~hin metal coating on the inner wall surface of the hollow p~astic microsphexe. The thickness of metal coating deposited will determine whe~her the metal coating is trans-parent or reflective ~ ~&92~:1 _ 29 _ of visible light. The blowing gases can also be selected to react with ~he deposited thin metal layer to obtain desired characteristics in the me~al layer. For example, to reduce the thermal conductivi~y of the metal layer.
The rnetal used to coat the inner wall surface of the hollow plastic microspheres is.selected to have the desired emissivity, low heat conduc-~ion characteristics, and ~o adhere to the inner wall surface of the plastic microspheres. The thickness and the nature of the deposited metal coating will depend to some extent upon ~.he metal, the particle size o~ the metal used, the size of the microsp~ere and the amount of dispersed metal particles used.
The dispersed metal particle size can be 25A
O O O
to lO,OOOA, preferably 50A to 5,000A and more pre-ferably lOOA to l,OOOA. A suf~icient amount of the metal is dispersed in the blowing gas to ob-~0 tain the desired ~hickness of the deposited metal.The dispersed metal particles can advantageously be p~ovided with an electrost~tic char~e to assist in depositing them on the inner wall surface of the microsp~eres.
Metal particXes such as aluminum, silver, nickel, zinc, antimony, barium, cadmium, cesîum, bismuth, selenium, lithium, magnesium, potassium, and gold can be used. Aluminum, zinc and nickel, however, are preferred. Dispersed me~al oxide particles can in a similar manner be used to obtain similar effects to that or the metals.
In addition, ~he metal oxide particles can be used to produce a deposited film of lower heat conductivity characteristics.

The ~hin metal coating can also be deposited on the inner wall surface of the microsphere by using as or with blowing gas organo metal compounds tha~ are gases at ambient temperatures or that become gases on heating. 0~ the organo metal compounds available, the organo carbonyl compounds are pre~erred. Suitable organo metal carbonyl compounds are nickel and iron.
The organo metal compounds can be decomposed by heating just prior to blowing the microspheres to obtain finelv dis~ersed me~al particles and a decomposi~ion gas or product. The deccmposition gas, if present, can be used to assist in blowing the micro-spheres. The dispersed metal particles from decomposition of the organo me~al compound, as before, deposit to form the thin me~al layer.
Alternatively, the microsphere, a~ter being formed and containing the gaseous organo metal compound blowing gas, can be subjected to "electrlcal dischar~e" means which deco~poses the organo metai compound to form the rinely dispersed metal particles and the decomposition ga~s or product.
The thickness of the deposited metal layer will depend primarily on the partial pressure of the gaseous organo metal blowing gas and the inside dia~eter o~ the microsphere.
An auxiliar~ blowing gas, e.g. an inert blowing gas, can be used to dilute the gaseous organo metal compound blowing gas in order to control ~he thickness o~ the deposi~ed metal layer. There can also be used as an auxiliarv blowing gas~a gas that acts as a catalyst or 1~;92 hardening agent for the plastic compositions. The addition of the catalyst or hardening agent to the blowing gas prevents contact of the catalyst or hardening agent with the plastic composition until a time just before the microsphere is formed.
The entraining fluid, e.g. an inert entraining fluid, can be a Oas a~ a high or low temperature and can be selected to react wi~h or be inert to the plastic compo~ition. Suitable entraining fluids are nitrogen, air, steam and argon. A
gaseous catalyst for the plastic can also be included in the entrainin~ fluid.
The quench or heating fluid can be a llquid, a liquid dispersion or a gas. Suitable quencn or heating fluids are steam, a fine water spray, air, nitrogen or mixtures thereof. The selection of a specific quench or heating fluid and quench or 'neating temperature depends to some e~tent on the plastic composition ~rom which the microspheres are made and the blowing gas temperature and pressure.
PROCESS CONDITIONS
__ _ The orga~ic film forming materials and/or plastic compositions o the presen~ invention are in 2 liquid-fluid form at the desired blowing temper-ature and during the blowing operation. The liquid plastic composition can be at a temperature of about 0C. to about 400C., preferably 10C.
to 300C. and more preferably 20C. to 200C., depending on the constituents and state of poly-merization of, for example, the plastic composition.
The plas~ic composition at the blowing temperature is liquid, fluid and flows easily. The liauid : 3.692~ ~ -plastic just prior to the blowing operation can have a viscosity 5f 0 . 10 to 600 poises, usually 10 to 350 poises and more usually 30 to 200 poises.
Where the process is used to make non-fila-mented microspheres, the liquid plastic just prior to the blowing operation can ha~e a viscosity of ~.1 to 200 poises, preferably 0.5 to 100 poises, and more preferably S.0 ~o 50 poises.
Where the process is used to make filamented microspheres, the liquid plastic just prior to the blowing operation can have a viscosity of 50 to 600 poises, preferably 100 to 400 poises, and more preferably 150 to 300 poises. The viscosity can be measured by conventional means, e.g. using a Broofield viscometer.
A critical feature of ~he present invention is ~hat the formation of the hollow plastic micro-spheres can be carried out at low viscosities relative to the viscosities her?tofore used in the prior art processes that utilized latent liquid or solid blowing agents dispersed throughout or contained in the plastic compositions used to blow the microspheres. Because of the abili~y ~o utilize comparatively low viscosities, applicant is able to obtain hollow plastic microspheres, the walls o which are ~ree of any entrapped or dissolved gases or bubbles. With the low vis-cosities used by appIicant, any entrapped or dissolved gases diffuse out and escape from the plastic film surface during the btbble formation.
With the high viscosities required to be used in the prior are processes, any dissolved gaseous bubbles are trapped in the ~alls of the plastic microspheres as they are formed because of the high viscosities required to be used.

2 1 ~

The liquid plastic fed to the coaxial blowing nozzle can be at about ambient pressure or can be at an elevated pressure. The liquid plastic feed can be at a pressure of 1 to 20,000 p.s.i~g., usually 3 to 10,000 p.s.i.g. and more usually 5 to 5,000 p.s.i.g.
Where the process is used to make microspheres for use as insulating materials and in insulating systems, for use in syntactic foam `systems and as filler materials in general, the li~uid plastic fed to the coaxial blowing nozzle can be at a pressure of 1 to' 1,000 p.s.i.g., preerabl~ at 3 to 100 p.s.i.g., and more preferably at 5 to 50 p . s . i . g .
The liquid plastic is continuously fed to the coa~ial blowing nozzle during the blowing operation to prevent ?remature breaking and detaching of tne elonga~ed cylinder shaped liquid plastic film as it is being formed by the blowing gas.
20 The blowing gas or gaseous material blowing gas will be at about the same temperature as the liquid plastic being blown. T'ne blowing gas or gaseous ma~erial blowing gas te~perature can, however, be at a hioher temperature than the liquid plastic to assist in maintaining the fluidity of the hollow liquid plastic ~icrosphere : durin~ the blowing operation or can be at a lower temperature than the liquid plastic to assist in the solidiication and hardening of the hollow liquid plastic microsphere as it is formed. The pressure of the blowing gas or gaseous material blowing gas is sufficient to - 1 ~692 1 1 ) - ~4 -blow the microsphere and will be slightly above the pressure of liquid plastic film at the oriice 7a of the outer nozzle 7. The blowing gas pres-sure will also depend on and be slightly above the ambient pressure external to the blowing nozzle.
The temperatures of the gaseous material blowing gases will depend on the blowing gas used and ~he viscosity-temperature-shear relationship f~r the plastic materials used to make the micro-spheres.
The pressure of the blowing gas or gaseous material blowing gas is sufricient to blow the microsphere and will be sligh~ly above ~he pres-sure of liquid plastic at the orifice 7a of the ou~er nozzle 7. Depending on the gaseous materiai to be encapsulated within the hollow plastic microspheres, the blowing gas or the gaseous material can be at a pressure of 1 to 20,000 p.s.i.g.j usually 3 to 10,000 p.s.i.g. and more usually 5 to 5,000 p.s.i.g.
The blowing gas or gaseo~s material blowing gas can also be at a pressure of 1 to 1,000 p.s.i.g., prefer~bly 3 to 100 p.s.i.g. and more preferably 5 to 50 p.s.i.g.

~1692 Where the process is used to make microspheres for use as insula~ing materials and in insulating systems, for use in syntactic foam systems and as filler materials in general, the blowing gas or gaseous material blowing gas can be at a pres-sure of 1 to 125 p.s.i.g., preferably at 2 to lOO p.s.i.g. and more preferably at 5 .to 30 p . s . i . g .
The pressure of the blowing gas containing dispersed mecal particles alone and/or in combi-nation with the principle blowing gas is sufficient ~o blow the microsphere and the combined gas pres-sure will be slightly above the pressure of the liq~id plastic at the oriflce 7a of the outer 2 1 ~

_36 nozzle 7. The pressure o the combined mixture of the blo~ing gases will also depend on and be slightly above the ambient pressure external to the blowing nozzle.
The ambient pressure external to the blowing nozzle can be at about atmospheric pressure or can be a~ suba~mospheric or super-~mospheric pressure. The ambient pressure external to the blowing nozzle will be such that it substantially balances, but is slightly less than ~he blowing gas pressure.
The transverse jet ~ntraining fluid which is ~ directed over and around the coaxial blowing ;~ nozzle to assist in ~he formation and detaching of the hoIlow liquid plastic microsphere rrom the coaxial blowing nozzle can have a linear velocity in the region of microsphere formation of 1 to 120 ft/sec, usually 5 to 80 ,~/sec and more usually 10 to 60 ft/sec.
Where the process if~used to make non-fila-~ented~microspheres, ~he linea~ velocity o the transverse j.et fluid in the region of microsphere formation c~n be 30 to 120 ft/sec, preer~ablv 40 to 100 ft/sec and more preferably 50 to 80 ft/sec.
Where the process is used to make filamented microspheres, the linear velocity of the trans-verse je~ fluid in the region o microspher2 rormation can be I to 50 ~/sec, preferably~5 to 40 ft/sec and more preferably 10 to 30 ft/sec.
Further, it is found (Figures 2 to 4) ~hat pulsing the transverse jet entraining fluid at a ra~e of 2 to lS00 pulses/sec, preferably 50 ~o 1000 pulses/sec and more preferably 100 ~o S00 6921 ~

pulses/sec assists in controlling the diameter of the microspheres and detaching the micro-spheres ~rom.the coaxial blowing nozzle.
The distance between filamented microspheres depends to some extent on the viscosity of the plastic and the linear velocity of the transverse jet entraining fluid.
The entraining fluid can be at the same temperature as the liquid plastic being blown.
The entraining fluid can, however, be at a higher ~empexa~ure ~han the liquid plastic to assis~
in maintaining ~he fluidity of the hollow liquid plas~ic microsphere during ~he blowing operation or can be at a lower tempera~ure than the liquid plastic to assist in the stabilization of the forming film and the solidification and hardening o the hollow liquid plastic microsphere as -it is formed.
The quench or heating 1uid:is at a tempera-ture such that i~ rapidly cools or heats the~micro- ~
spheres to solidify, harden and streng~hen t~e ~ :
liquid plastic before the inner gas pressure decreases to a value at which the plastic micro-sphere would collapse or Durst the microsphere The quench cooling fluid can be at a tem~erature of 0 to 200F., ~sually 40 to 200F. and more usually 50 ~o 100F. The heating fluid can be at a temperature OL 100 to 800F., usually 200 to 600F. and more usually 300 to 500F,, depending on the plastic composition.
The quench cooling fluid very rapidly cools the outer liquid plastic surface of the micro-sphere with which it is in direct contact and more slowly cools the blowing gas enclosed within ~6~21 ~

the microsphere because of ~he lower thermal conductivity of the gas. This cooling process allows sufficient ~ime for the plastic walls of the microspheres to strengthen before the gas is cooled and ~he pressùre within the plastic microsphere is substantially reduced.
The time elapsed from commencement of the blowing of the plastic microspheres to the cooling and ~nitial hardening o the ~icrospheres can be .0001 to 60.0 seconds, preferably .0010 to 30.0 seconds and more preferably 0.10 to 10.0 seconds.
Where a ther~osetting plastic com~osition is used to ~orm the microsphere, the time elapsed from co~mencement o the blowing of the plas~ic ~icrosphere to the heating and curing of the microsphere for i~ to have suf~icient strength to maintain its size and shape can be 0.10 second to 30 minutes, preferably 1 second to 20 minutes and more preferably 10 seconds to 10 minutes.
The filamented microspnere embodiment of the~in~ention provides a means by which the mi-crospheres may be suspended and allowed to harden and/or cure without being brought into contact with any surface. The ilamented microspheres are simply drawn on a blanket or drum and are suspended between the blowing nozzle and ~he blanket or drum for a sufficien~
period or time for them to harden andlor cure.

~ g21~

APPARATUS
Referring to Figures 1 and 2 o the drawings, the vessel 1 is constructed to maintain the liquid plastic at thP desired operating tempera-tures. The liquid plas~ic 2 is fed to coaxial blowing nozzle S. The coaxial blowing nozzle 5 consists o an inner nozzle 6 having an outside diameter of 0.32 ~o 0.010 inch, preferably 0.20 to 0.015 inch and more preferably 0.10 to 0.020 inch and an outer nozzle 7 having an inside diameter of 0.420 to 3.020 inch, preferablv 0.260 to 0.025 and more preferably 0.130 to 0.030 inch. The inner nozzle 5 and outer nozzle 7 form annular space 8 which provides a 1OW path ~hrough-~hi~h the liqu:i~ piastic 2 is ex~n~ed. The ois- ;
~nce be~Jee~ ~he ~ner nozzle 6 and outer nozzle 7 can be 0.050 to 0.004, preferably 0.030 to 0.005 and more preerably 0.015 to 0.008;inch.
The orlfice 6a of inner nozzle 6 ter~inates a short distance above the plane of orifice 7a of outer nozzle 7. The orifice 6a can be spaced above oriice 7a at a dis~ance of 0.001 to 0.125 inch, prefe~ably 0.00~ to 0.050 incn and more preferably 0.003 to 0.025 inch. The liquid plas~ic 2 ~lows ~nwardly and is ~x~ed ~rough arnular space 8 and fills the area between orifice 6a and 7a. The orifices 6a and 7a can be made from ~ stainless steel, pla~tinum allo~s, glass or ; fused aiumina. S~ainless steel, however, is preferred. The surface tension forces in the liquid plastic 2 form a thin liquid plastic .ilm 9 across orifices 6a and 7a which has about the same or a smaller thickness as the distance of orifice 6a is spaced above orifice 7a.

:~ 16~2 ~ ~

The liquid plastic film 9 can be 25 ~o 3175 microns, prefe~abiy 50 to 1270 microns, and mo~e preferably 76 to 635 microns thick.
The Figure 2 blowing nozzle can be used to blow liquid plastic at relatively low viscosities, for example, of 10 to 60 poises and to blow hollow plastic micropsheres of relatively thick wall size, for example, o 20 to 100 microns or more.
A blowing gas or gaseous material blowing gas is fed ~hrough inner coaxial nozzle 6 and brought into COtltaC L with the inner su~face of liquid plastic film 9. The blowing gas or gaseous material blowing gas e~erts a positive pressure on the li~ui.d plastic film to blow and distend the film outwardly and downwardly to form-an elo~gated cylinder shaped liquid film 12 of liquid plastic filled with the inert blowing gas or gaseous material blowing gas 10. T'ne elongated cylinder 12 is closed at its outer end and is connected to outer nozzle 7 at the peripheral edge of orifice 7a.
; The transverse jet 13 is used to direct an inert entraini~g fluid 14 through nozzle 13 and transverse jet nozzle orifice 13a at the coaxial blowing nozzle 5. The coaxial blowing nozzle 5 , has an outer diameter OL 0.52 to 0.030 inch, preferabl,y 0.36 to 0.035 inch and more preferably 0.140 to 0.040 inch.
The process wa~ found to be very sensitive to the distance of the trans~
verse jet 13 ~rom the orifice 7a of ou~er nozzle 7, the angle at which the transverse jet was directed at coaxial blowing nozzle ; and the g21~

point at which a line drawn through the center axis of trans~erse jet 13 intersected with a line drawn through the center a~is of coaxial nozzle 5. The transverse jet 13 is aligned to direct the flow of entraining fluid 14 over and around outer nozzle 7 in the microsphere forming region o the orifice 7a. The oriice 13a o transverse jet 13 is located a distance of 0.5 to 14 times, preferably 1 to 10 times and more preferably 1.5 to 8 times and s~ill more preferably 1.5 to 4 times the outside dizmeter oL coaxial blowing nozzl~ 5 away from the poin~ of intersect of a line drawn along the center axis o~ transverse jet 13 and a line drawn along the center axis o~ coaxial blowing nozzle S. The center axis of transverse jet 13 is aligned at an angle of 15 to 85, pre~erably 25 to 75 and more preferably 35 to 55 relative to the center axi~s o~ the coaxial blowing nozzle 5. The orifice 13a can be circular in shape and have an inside diameter of 0.32 to 0.010 inch, preferably 0.20 to 0.015 inch and more preferably 0.10 to 0.020 inch.
The line dra~n through the center axis of : trans~erse jet 13 intersects the line drawn through the center axis of coaxial blowing noæzle S at a point above the oririce 7a of outer nozzle 7 which is .5 to 4 ti~es, preferably 1.0 to 3.5 times and more pre~erably 2 to 3 times the outside diameter of the coaxial blowing nozzle 5. The transverse jet entraining fluid acts on the elongated shaped cylinder 12 to flap and pinch i~ closed and to detach it rom the orifice 7a o~ the outer nozzle 7 to allow the cvlinder to fall, i.e. be trànsported away from the outer nozzle 7 by the entraining fluid.

~ ~g2~ ~ ~

The transverse jet entraining fluid as it passes over and around the blowing nozzle 1uid dynamically induces a periodic pulsating or fluctuating pressure field at ~he opposite or lee side of the blowing nozzle in the wake or shadow of the coaxial blowing nozzle. A similar periodic pulsating or fluctuating pressure field can be produced by a pulsating sonic pressure field directed at the coaxial blowing nozzle.
The entraining fluid assists in ~he ormation - and detaching of the hollow plastic microsphere from tke coaxial blowing nozzle. The use of the transverse jet and entraining 1uid in the manner described also discourages wetting of the ou~er wall surface of the coaxi.al blowing nozzle S by the fluid plastic being blow~. The wetting of the outer wall disrupts and in~erfers with blowing the microspheres.
The quench or heating nozzles 18 are dis-posed below and on both sides of the coaxial blowing nozzle 5 a su~licient distance apart, o allow the microspheres 17 to fall between the quench nozzles 18. The inside diameter of quench nozzlP orifice 18a can be 0.1 to 0.75 inch, prefe~ably 0.2 to 0.6 inch and more preferably 0.3 to 0.5 inch. The quench nozzles 18 direct cooling or hea~ing fluid 19 at and into contact with the liquid plastic microspheres 17 at a velocity of 2 to 14, preferably 3 to 10 and more preferably 4 to 8 ft/sec to rapidly cool o. heat and solldi~y the liquid plastic and form a nerd, smooth hollow plastic microsphere.

- 43 - ~ 9 2 ~ ~

Referrin~ to Figure 3 of the ~raw-n~s, it is found that in blowing high viscosity liquid plastic compositions that it is advantageous to immediately prior to blowing the liquid plastic to provide : by extrllsion a very thin Liquid plastic film for blowing into ~he elongated cylinder shape liquid film 12. The thin liquid film 9' is provided by having the lower portion of the outer coaxial nozzle 7 tapered downwardly and inwardly a~ 21.
: 10 The tapered portion 21 a~d inner wall surace 22 : thereof can be at an angle o 15 to 75, 30 to 60 and pref erably abou~ 45~ relative to the center axis or coaxial blowing nozzle 5. The oriice 7a' can be 0.19 to l.S times, preerably 0.20 to 1.1 times and more preferably 0.25 to .8 times the inner diameter of orifice 6a of inner nozzle : 6.
: The thickness of the liqtlid plas~ic film 9' :
i ~ can be varied by adjusti.ng the distance of or fice 2~0 6a of inner nozzle 6 above orifice 7a o~ o~ter ~ :
: nozzle 7 such that:the distance between the ~ : periDheral edge of orifice~68 and the~inner wall :~ ~ surface 22 of tapered nozzle 21 can be varied.
By control~ing the distance bet~een the peripheral edge of orifice 6a and the inner wall surface 22 of the tapered nozzle to form a very fine~gap and~by controlling the pressure applied to feed : ~he liauid plastic 2 through annula~space 8 tne liquid plastic 2 can be squeezed or extruded through the very fine gap to form a relatively thin liquid plastic fil~ 9'.

.

_ 44 ~ 9~1~

The proper gap can best be determined by pressing ~he inner coaxial nozzle 6 downward with sufficien~ pressure to completely block-of the ~low of plastic, and to then very slowly raise the inne~ coaxial nozzle 6 until a stable system is obtained, i.e. un~il the microspheres are being ~ormed.
When blowing high or low viscosity plastic compositions, it was found to be advantageous to obtain the very ~hin liquid plastic film and to continue durlng the blowing operation to supply liquid plastic to the elongated cylinder shaped liquid film as it was formed. Where a high pres-sure is used ~o squeeze, i.e. ex~rude, the liquid plasLic thr,ough the very thin gap, the pressure of the inert blowing gas or gaseous material blowing ~as is gene~ally less than the liquid plastic feed pressure, but slightly abcve che pressure of ~he liquid plastic at ~he coaxial blowing nozzle.
T'ne tapered nozzle coniguration of Figure 3 is also par~icularly useful in aligning the~
la~inar pl ane orientable plastic addtivie materials .
The passage of the plastic material through the fine or narrow gap se:rves ~o align the additive materials wi~h the walls of the microspheres as the microspheres are being formed.

_ 45 ~ g211 In Figures 3a and 3b of the drawings, the transverse jet 13 can be flattened to form a generally rectangular or oval shape. The orifice 13a can also be flattened to form a generally oval or rectangular shape. The width of the orifice can be 0.96 too.030 inch, preferably 0. 60 to 0. 045 inch and more preferably 0.030 to 0.060 inch. The height of the orifice can be 0.32 to 0.010 inch, preferably 0.020 to 0.015 inch and more preferably 0.10 to 0.20 inch.
With reference to Figure 3c of the drawings, there is shown the formation of the uniform diameter filamented microspheres spaced about equal distances apart. The numbered items in this drawing have the same means as discussed above with reference ~o Figures 1, 2, 3, 3a and 3b.
With reference to Figure 4 of the drawings, it was found that in blowing the liquid plastic to form the elongated cylinder shaped liquid film 12 that it was advantageous to increase the .

,

- 4~ 9211 outer diame~er of the lower portion coa~ial blowing nozzle 5. One me~hod of increasing the outer diameter of coaxial blowing nozzle 5 is by pro-~iding the lower portion of outer nozzle 7 with a bulbous member 23 which imparts to the lower portion of outer nozzle 7 a spherical shape. The use o ~he bulbous spherical shaped member 23 is found for a given velocity of the entraining fluid to substantially increase the amplitude o~ the ~ pressure f~uctuations induced in the region or the formation of the hollow microspheres. The diame~er of the bulbous member 23 can be l.25 to 4 times, pre~erably 1.5 to 3 times and more preferably l.75 ~o 2.75 times ~he diameter of the outer diameter of coaxial blowing nozzle 5. When using a hulbous member 23, the transverse jet 13 is generally aligned such that a line drawn through the center axis of trans~erse je~ i3 will pass through the cen~er of bulbous member 23.
- Referriny again to Figure 4, a beater bar 24 is used to facilitate detaching of ~he elongated cylinder shaped liquid fiLm 12 from the ori,ice 7a of outer nozzle 7. The ~eater ~ar 24 is attached to a spindle, no~ sho~n, which is caused to rotate in a manner such that the beater bar 24 is brought to bear upon the pinched portion 16 of che elonga~ed c~linder 12. The beater bar 24 is set ; to spin at about the same rzte as tne for~ation of hollow microspheres and can be 2 to 1500, preferably 10 to 800 and more preferably 20 to 400 revolutions per second. The bea~er bar 24 can thus be used to facilitate the closing o~
of t~e cylinder 12 at i~s inner pinched end 16 and to detacn the cylinder 12 from the oririce 7a o outer nozzle 7.

~ 16921~

~ 47 DESCRIPTIO~ OF THE M_ ROSPHERES
The hollow microspheres made in accordance with the present invention can be made from a wide variety of organic film forming materials and co~-positions particularly plastic compositions.
The hollow plastic microspheres made in accordance with the presen~ invention can be made from suitable organic film forming compositions which are resistant to high temperatures and ohemical attack and resistant to weathering as the situation may require.
The organic film forming composi~ions that can be used are those that have the necessary ~is-cosities, as mentioned above, when being blown to form stable ~ilms and ~hich have a rapid change from the molten or liquid state to the solid or hard state with a relatively narrow temperature change or within a rela~ively short cure time.
That is, they change from liquid to solid within a relative narrowly defined temperature range and/or cure in a rela.ively short time.
The hollow plastic microspheres are sub-stant ally uniform ln diameter and wall thickness, and depending on their composi~ion and the blowing conditions are light transparent, trans-lucent or opaque, sof~ or hard, and smooth or rough. The walls of the microspheres are free or substantially free of any holes, rela~ively thinned wall portions or sections, trapped gas bubbles, or suficient amounts of dissolved gases or solvents to form bubbles. The micro-spheres are 2190 free of any latent solid or 9~

liquid blowing gas materials or gases. The pre-ferred plastic compositions are those that are resistant to chemical attack, elevated temperatures, weatherlng and diffusion of gases into and/or out of the microspheres. Where the blowing gases may decompose at elevated temperatures, plastic compositions th~t are liquid below the decompositlon temperatures of the gases can be used.
The plastic microspheres can be made in various diameters and wall thickness, depending upon the desired end use of the microspheres. The microspheres can have an outer diameter of 200 to 10,000 microns, preferably 500 to 6,000 microns and more preferably 1,000 to 4,000 microns. The microspheres can have a wall thickness of 0.1 to 1,000 microns, preferably 0.5 to 400 microns and more preferably 1 to 100 microns.
The diameter and wall thic'~ness of the hollow microspheres will of course affect the average bulk density of the microspheres. The microspheres can have an average bulk density of 0.2 to 15 lblft3, usually 0.5 to 12 lb/ft3 and more usually 0.75 to 9 lb/ft3. For use in a preferred embodiment to ma~e low density insulating materials, the hollow plastic microspheres can have an average bul:~ density as low as 0.5 to 1.5, for example, about 1.0 lb/ft3.

116921~

The microspheres, because the walls are free or substantially free of any holes, thinned sections, trapped gas bubbles, and/or suficient amo~nts of dissol~ed gases or solve~ts to form bubbles and are substantially stronger than the microspheres heretofore produced.
The microspheres made from thermoplastic compositions ater being formed can be reheated to soften the plastic and enlarge .he microspheres andlor to impro~e the surface smoo~hness of the microspheres. On reheating, ~he internal gas pressure will increase and cause tne microspnere to increase in size. After reheating to the des,ired size~ for example, in a "shot tower", the microspheres are rapidly cooled to -eeai~

.

1 l6921 ~

the increase in size.
Where the microspheres are formed in a manner such that they are ccnnected by continuous ~in plastic ilaments, that is they are made in the form of filamented microspheres, the length of the con-necting filaments can be 1 to 40, usually 2 to 20 and more usually 3 to 15 times the diameter of ~he microspheres. The diame~er~ that is the thickness o~ the connecting filaments, can be 1/~000 to 1/10, usually 1/2500 to 1/20 and more usually 1/1000 to l/30 of the diameter of the microspheres.
The microspheres can contain a gas a~ super-atmospheric pressure, about ambient pressure or at par~ial vacuum.
Where the microspheres are used as insu-lating materials and in insulating sys~ems, or in syntactic foam systems, or 2S filler material in general, the microspheres can have an outer diameter o~ ~00 to 5,000, preferably 500 to 3,000 and more preferably 7~ to 2000 microns. These micro-spheres can have a wall thickness o~ 0.1 to 500 microns, preferably 0.5 to 200 microns and more preferably 1 to 50 microns. These microspheres can have an average bulk density of 0. 3 to 15 : 1~D/ft3~ preferably l~.5 to 1~ lb/C~ and more preferably ~.75 LO 5.0 lbJ~3. These microspheres can have a contained gas pressure of 12 tO 100 p.s.i.a., preferably 15,o 75 p.s.i.a. and more preferably 18 to 25 p.s.i.a.
In a preferred embodiment of the invention, the ratio of the diameter to the wall thickness OL the microspheres is selected such that the microspheres are fle~ible, i.e. can be deformed under pressure without breaking.

The microspheres can contain a thin metal layer deposited on the inner wall surface of ~he microsphere where the blowing gas contains dis-persed metal particles. The thickness of the thin metal coa~ing deposited on the inner wall surface of the microsphere will depend on the amount and particle size of the dispers~d metal particles or partial ~ressure of organo metal blowing gas that are used and the diameter of the microsphere.
The thickness of the thin metal coating can be 25 to lO,OOOA, preferably 50 to 5,000A and more pre-ferably 109 to l,OOOA.
When it is desired that the deposited metal coa~ing be transparent to light, the coating should be less than lOOA and preerably less than 80A.
The transparent metal coated microspheres can have a deposi~ed me~al coating 25 to 95A and ?referably 50 to 80A thick. These microspheres, though trans-paren~ to visible light, are substantially reflec-tive of infrared radlation.
~ en it is desired that the deposited metalcoating be reflective to light, the coating can De more than lOOA and preferably more than 150A thick.
The reflective metal coated microspheres can have a depositea metal coating 105 to 600A, preferably 150 to 400A.and more preferably 150 to 250A thick.
The thermal heat conductivity characteristics o~ heat barriers made rrom the microspheres can be further lmproved by partially flattening the microspheres into an oblate spheroid or generaily rectangular shape. The ~hermal conductivi~y o~ the ~ 16g21 '~

oblate spheroids is further improved by mixing with the obla~e spheroids thin plastic filaments.
The filaments are preferably provided in ~he form of the filamented microspheres.
The filamented microspheres can as they are formed be drawn and laid on a conveyor belt or drum.
A sufficient amount of tension can be maintained on the filamented microspheres as they are drawn to stretch them into the oblate spheroid shape.
The filamented microspheres are maintained in that shape for a sufficient period of time to harden and cure. A~er hardening of the filamen~ed oblate spheroids, they can be laid in a bed, an adhesive and/or foam can be added and the filamented microspheres can be made into, e.g. a fou- by eigh~ formed panel. The panel can be 1/4 to 3 inches in thickness, ~or example, 1/2, 1, 1 l/2 or 2 inches in thickness.
The thermal properties of the microspheres : can also be improved by filling the interstices between the microspheres with a low thermal con-ductlvity gas, finely divided inert particles, e.g. lamp black, a low conductivity foam, e.g.
polyurethane, or polyolefin resin foam.

~ ~6921 ~

The hollow plastic microspheres of the present invention can be used to design systems having improved insulating characteristics. Where hollow microspheres are used in which the contained volume has a low hea~ conductivity gas, systems can be designed in which the thermal conductivity can be R5 to R9, for example, R8 per inch.
Where hollow plastic microspheres are used ~aving a low heat conductivity gas and a low emissivity, reflective metal coating deposited on the inner wall suriace thereof are used, systems can be designed in which the ther~al conductivi~y c2n ~e R7 to R12, for example, R10 per inch .
Where an insula~ing system containing fila-mented oblate spheroids and a reflective metal coating deposited on the inner wall surface or the microsphere are used, systems can ~e designed in which ~he thermal conductivity can be R9 to R16,~for e~ample R14 ?er inch.
The microspheres can also be used as heat barriers by Lilling spaces between e~isting walls or other void spaces or can be m2de in,o sheets or other shaped forms b~ cementinO the micro-spheres toge~her with a suitable resin or other a &esive or by fusing the microspheres together and can be used in new construction.
When the hollow plastic microspheres are massed together to form a 'neat b~rrier, there is reduced heat ~ransfer by solid conduction because o the point to point contact be~ween adjacent spheres and the low conductivity of the plastic material used to form the spheres. There is little heat transer hy convectior. because the characteristic di~,ensions of the voids between ~g21 1 _ 54 -the packed spheres are below that necessary to initiate convection. There is little heat trans-fer by gas conduction within the spheres when there is a low heat conductivity gas in the enclosed volume. Where there is a low emissivity, highly reflective metal layer deposited on the inner wall surace of the microspheres, ~here is substantialiy llt~le radiant heat trans~er because of the highly rerlective metal layer on the inner ; 10 wall surface of the spheres. A primary mode of heat transfer remainlng, therefore, is by gas conduction ln the interstices or voids be~een the microspheres. The overall conductivi~y of the system is lo~-er than that of the volds gas because t'ne voids gas occuples only ~ frac~ion o the volume of ~he total sys~em, and because conductlon paths through the voids gas are attentuated by ~he presence of the low conductivity microspheres and the filaments. The use of a low heat conductivity gas and/or a foam containing a low heat conductivity gas to fill the interstices bet~een the microspheres fur~her reduces the then~al conductivity of a bed of the mic~ospheres.
The hollow plastlc microspheres Oc the ~resent inve~ion have a distinct adv~ntage o$ being s~rong and capabie of su?porting a substanLial amount of weight. They can thus be used to make simple inexpensive self-suppor~ing or load bearing systems.
The following e~amples are used to illustrate the invention.

.~692~ ~

EXAMPLES
The ~amples 1-7 are illus~rative of the use of the present invention to make insulating materials and~or systems.
Example 1 A thermoplastic composition comprising the . following constituents is used to make hollow plastic microspheres:
Polyethylene polymer.
rne plastic composition is heated to ~; form a fluid ?lastic having a viscosity of 10 to 20 poises at the blowing nozzle.
The liquid plastic is fed to the aDparatus of Figures 1 and 2 of the drawings. The liquid lastic passes through annular space 8 o~ blowing nozzle 5 and rorms a thin liquid plastic fil~
across the orlfices 6a and 7a. The blowing nozzle i has an outside diameter of 0.040 incn anâ
orifice 7a has an inside diameter o~ 0.030 inch.
The thin liquid molten plastic Lilm has a diameter or 9. a30 inch and a thickness of a . 005;inch.
A heated blowing gas consisting of argon or a low heat conductivity.gas 2t a positive pressure is applied to ~he inner surface of the liquid plastic film causing the film ~o distend do~-n~.~ardlt into a elongated cylinder shape with its outer end closed and its inner end attached LO the outer edge of orifice 7a, The transverse jet is used ~o direct an entraining fluid which consists of heated nitrogen over and around the blowing nozzle 5. The transverse je~ is aligned at an angle of 35 to 50 relative to ~he blowin~ nozzle ~ ~92~ ~

5~

and a line drawn through the center axis of the transverse jet intersects a line drawn through the center axis of the blowing nozzle 5 at a point 2 to 3 times the outside diameter of the coaxial blowing nozzle 5 above the orifice 7a.
. The entrained falling elonga~ed cylinders assume a spherical shape, are cooled to about zmbient temperature by a cool quench fluid consisting o~ a fine -~ater spray which quic~ly cools, solidifies and hardens the plastic microspheres.
Uniform sized, smoo~h, hollow plastic microspheres having a 2000 to 3000 mlcron aiameter, a 20 ~o 40 micron wall thickness znd filled with arCon or a low hea~ conductivitv gas are obtained. The mic.ospheres are closely e~amined and the walls are .ound to be free of any trapped gas bubbles.
ExamPle 2 A thermose~ting plas~ic composition comprisinG
a mi~ture of 50% by weight acrylonitrile and 50%
by weight vinylidene chloride and a suitable catalyst is used to ~ake hollow plas~ic microspheres.
The plas~ic composition mixture at the blowing nozzle has a viscosity of ten poises.
The liquid plastic mixture is hezted and is fed to the apparatus of Fi~ures 1 and 3 o the drawlngs. The liquid plastic is passed through annular space 3 of blowing nozzle S and into tapered ?ortion 21 or outer nozzle 7. The liquid plastic under ?ressure is squeezed and extruded through a fine gap formed between ~he outer edge of orifice 6a and the inner surace 22 of the tapered po ~ion 21 of outer nozzle 7 and forms a thin liquid p7astiC film across ~he ~ :16~21 ~

orifices 6a and 7a'. The blowing nozzle 5 has an outside diameter of 0.04 inch and orifice 7a' has an inside diameter of 0.01 inch. The thin liquid plastic film has a diameter of 0.01 inch and thickness of 0.003 inch. A heated blowing gas con-sisting of argon or a low heat conductivity gas at a positive pressure is applied to the inner surface of the liquid plastic film causlng the film to distend outwardly into an elonga~ed cylinder shape with its outer end closed and its inner end attached to the outer edge of orifice 7a'.
The transverse jet is used to direct an entraining fluid which consists of heated nitrogen over and around the blowing nozzle. The transverse jet is aligned at an angle OL 35 ot 50 relative to the blowing noz le and a line dr2wn th_ough the center axls of the transverse jet intersects a line drawn through the center axis of the blowin~
nozzle ~ at a point 2 to 3 times the outside diameter of the~coaxial blowing noz21e 5 above ; or~fic~ 7a'.
The e~trained falling elongated cylinders filled with .he blowing gas quickly assume a spherical shape. The micros~heres are contacted with a 'neating rluid consisting of heated nitrogen whlch solidifies, harder.s and begins ~o cure the liquid plastic.
Unifor~ sized, smooth, hollow plastic micro-spheres having an about 800 to 900 micron diamete~, a 8 to 20 micron wall thickness and an lnternal pressure Oc 12 p.s.i.a. are obtained. The micro-spheres are examined and are found to be fLee of ~ ~92:~ 1 any trapped gas bubbles.
Exam~
A ther~osetting composition comprising a mi~-ture o 90% by wei~ht methyl methacrylate and 10%
by weight styrene and a suitable catalyst is used to make low emissivity, reflective hollow plastic microspheres.
The plastic composition mix~ure has a visco-sity of ten poises at the blowing nozzle.
The liquid plastic mixture is fed to the appara-tus of Figures 1 and 3 of the drawings. The liquid plastic is heated to and is passed through annular ; space 8 of the blowing nozzle 5 and into tapered : portion 21 of outer nozzle 7. The liquid plastic ; under pressure is squeezed through a fine gap formed bet~reen the outer edge of oriice 6a and the inner surace 22 of the tapered portion 21 of outer nozzle 7 and orms a thin liquid plastic : fil~ across the orifices 6a and 7a'. The blowing nozzle S has an out~side diameter o:E O.OS inch and orifice 7a' has an inside diameter of 0.03 inch.
: rne thin li~uid plastic film has a diameter of 0.03 ,nch and a thickness of 0.01 inch. A heated blowing gas consisting of argon or a low heat conductivit.~ gas and containing finely dispersed aluminum particles 0.03 to 0.05 micron size and at a positive pressure is applied to the inner surface of the liquid plastic film causing the film to distend outwardly into an elongated c~linder shape with its outer end closed and its inner end attached to the outer edge of orifice 7a'.
The transverse jet is used to direct an inert entraining fluid which consists or 'neated nitrogen gas over and around the biowing ~ozzle.
The t~ansverse jet is aligned at an angle Oc 35 to 50 relative to the b!.owing nozzle and a 2 :~ 1 line drawn ~hrough the center axis of the trans-verse jet intersects a line drawn through the center axis of the blowing nozzle 5 at a point 2 to 3 times the outside diameter of the coaxial blowing nozzle 5 above orifice 7a'.
The entrained falling elongated cylinders filled with the blowing gas containing ~he dis-persed aluminum par~icles quickly ass~me a spheri-cal shape. The microspheres are contacted with a heating fluid consisting of heated nitrogen which quickly solidifies, hardens and begins to cure the liquid plastic. The dispersed aluminum particles are deposited on and adhere to ~he inner wall surface o the plastic microsphere.
Uniform sized, smooth, hollow plas~lc micro-spheres having an about 3000 to 4000 micLon diameter7 a 30 to 40 micron wall thicl~ness and having a low emissivity, reflective aluminum metal coating 600A
to lOOOA thick and an internal contained pressure of 12 p.s.i.a. are obtained. The ~icros~heres - are examined and are found to be free of any ~rapped ga5 bubbles.
Example 4 An efficient flat plate solar energy collector, as illustrated in Figure 5 of the drawings, is constructed using the plastic microspnere of the present invention as an improved insulating material.
In accordance with the present invention, the area between the outer cover and the upper sur~ace of the black coated metal absorber plate is filled to a dep~h of about one inch with transparent plastic microspheres made by the method of Example 2 of about 800 ~icron diameter, 10 micron wall thickness and having an internal contained ~ressure of iO

2 ~ 1 p.s.i.a. These microspheres are transparent to visible light.
The area between the lower surface of the black coated metal absorber plate and the inner cover member is filled to a depth of about 1 1/2 inches with the reflective plastic microspheres made by the method of Example 3 of about 3000 micron diameter, 30 micron wall thickness and having a thin low emissivity, reflective aluminum metal coating 700A thick and an internal contained pressure of 12 p.s.i.a.
E~amPle 5 --An efficient tubular solar energy collector, as illus~rated in Figure 6 or the drawings, is constructed using the ?las~ic microspheres OL
the present inven~ion as an improved insulating material.
In accordance with the present invention, the vol~lme between the outer cover, the sides and the lower curved portion and the double ?ipÇ tubular member is filled with transparent plastic micro-spheres made by the me~hod o Example 2 tO provide an about one inch layer of transparent p}astic microsphe~es completely around ~he double p~?e tubular member. The transparent plastic micro-spheres are 800 microns in diameter, have a -.~all thickness of 10 microns and an internal contained pressure of 12 p.s.i.a. These microspheres are transparent to visible light.

~ ~92~

E~ample 6 The Figure 7 OLC the drawings illustrates the use of the hollow plastic microspheres of the pre-sent invention in the construction of a one-inch thick formed wall panel. The wall panel contains multiple layers o uniform size plastic micro-spheres made by the method OLC Example 3 of the invention. The microspheres have an about 3000 micron diame~er~ 30 micron wali thickness and a thin, low emissivity aluminum metal coating 700A
thic~ deposi~ed on the inner wall surface o~ the microsphere. The internal volume of ~he micro-spheres is ~illed with a low heat conductivity gas, e.g. Freon-ll, 2nd the interstices between ~e micro-spheres is filled wit~ a low heat conductivit~ f~oam con~ain~ng Fre~n-ll gas. The microspheres are treated with a thin adnesl~e coating of a similar composition to that 'ro~
which the pl2stic microspheres were made and ~ -for~ed into a 7/8 inch~thick layer. The ad'nesi~-e is aliowed~to cure to form a semi-rigid wallboard.
The ~2cing surface of the wall~joard is co2ted with an~about 1/8 i~ch~hick plaster which i-s suitable for subsequent~ sizir.g and painting and/or co-~éring with wall DaDer. The backing surace of the panel is coated with an 2bout 1/~1~ inch coating OL ~he s~ame plastic composition rro~ which ~he microspneres are made. The final panels are allowed to cure. The cured panel.s form strong wall panels which can be sawed and nailed ar.d readily used in construction of new homes.
Several sections of the panels are ,ested and found to have a R value of 12 per inch.

~ 1~921 ~

Example 7 -The Figure 7b of the drawings illustrates the use of the hollow plastic microspheres of the ~resent inven~ion in the construction of a formed wall panel one-inch thick. The wall panel con-tains hoLlow plastic microspheres made by the method of Example 3. The microspheres have a diame~er of about 3000 micron, 30 micron wall thickness and a low emissivity aluminum met~l coating 700A thick deposi~ed on the inner wall surface of the microsphere. The microspheres are coated with an adhesive of si~ilar composition to that from whlch the microspheres are made.
A layer of microspheres about two inches thick is pressed and flattened between two flat pl2tes to form the microspheres into an oblate spheroid or a general rec~angular shape in which the ra~io oS the height to length of the flattened micro-sprteres is 1:3. The Llattened microsprteres for~t a layer :about 7l~8 inch thick and a~e neld in th:is~position until ~he adhesive coating on the mic.ospheres cure after which micros?heres retain their flattened~shape. The in~ernal volume o the microspheres.is filled with a low hezt con-ductivitY gas, e.g. Freon-ll. The flattened configur2tion of the microspheres subs.antially reduces the volume of the interstices between the ~ic~ospheres and any-~l~me that rema;ns is r-ill2d~ h a low neat concu tivitv ~02m contai~ing Freon-ll gas. The ~2cing surface of the -~allboard is about 1/8 inch plaster which is suitable for subsequent sizing and painting and/or covering with wall paper. The backing of the wall panel is about 2 1/16 inch coating of the plastic from which the microspneres 2 ~ 1 are made. The panels are cured and form s~rong wall panels which can be sawed and nailed and readily used in construction of new homes. One of the important effects of compressing the microspheres is to significantly reduce the volume of the interstices between the microspheres to sub-stantially reduce the heat loss by convection.
Several sections of the pa~el are tested and found to have a R value of 1~- per inch.
The formed panel of E~amples 6 and 7 can also be made to have a density gradient in the di~ec-tion of t'ne front to bac~ o~ the panel. Where the panel is used indoors the surface .acing the room can be made to have a relatively high densiLy and high stre~gth, by increasing the ?rO-por~ion of resin or otner binder to microspneres.
The sur~ace Lacinc the outside can ~e made to have relatively low density and a high insulation barrier efect by having a high proportion of mlcrospheres to résin or binder. For e~m?le, the front one ~hird of the panel can 'nave an average density o about two to three Limes that OL the average density of the center Lhird OL the panel.
The density of the back one ~hird of the panel ~; ~ can be about one-hal to one-third tha~ of the center third of the panel. r~here ~he panels are used on the outside of a house,~ the sides of the panel can be reversed, i.e. the high density side can face ou~ard.
.

~ ~6g~ ~
~ 64 UTILITY
The hol~ow plastlc microspheres of the present inven~ion have many uses including the manu acture of improved insulating materials and the use of the microspheres as a filler or aggregate in cement, plaster and asphalt and synthetic construc-tion board materials. The microspheres czn also be used in the manuacture of insulated louvers and molded objects or forms.
The microsphere can be used to form thermal insulation barriers merely by filling spaces between the walls of refrigera~or ~rucks or train cars, household refrigera~crs, cold storage building facilities, homes, factories and office buildings.
The hollow microsph res can be produced lrom high melting temperature and/or ire resistant plas.ic comoositions and whe~ used as~ a component in building construction retard the development and eYpansion o fires. The hollow plastic ~icro-spheres, depending on the plastic co~position, are stable ~o many chemical~agen~s and -~ea~hering condit~ons. ~
The microspheres can be bonded together by sintering o~ resin adhesives and molded into sheets or other forms and used in new constructions which requlre thermal insulation including homes, factories and office buildings. Th~-~ constr~uction ~aterials made from the microspheres can oe pre-formed or made at the construction si~e.
The ~icrospneres may be adhered together withknown adhesives or binders to produce semi- or rigi.d cellular type materials or use in manu-facturing various products or in construction.
T:~e microspheres, becauce they can be ~ade from ~1~92~.~

very stable plastic compositions, are not subject to degradation by outgassing, aging, moisture, weathering or biological at~ack. The hollow plas-tic microspheres when uscd in manurac~ure of improved insulating materials can advantageously be used alone or in combina~ion with fiberglass, styrooam, polyu~e~hane ~pam, phenol-formaldehyde foam, organic and inorganic binders.
The ~icrospheres of the present invention can be used to make insulating ma~erial tapes and insu-la~ing, ~allboard and ceiling tiles. The micro-spheres can also 2dvantageously be used in ?lastic o~ resin boat construction to produce high strength hulls and/or hulls which ~hemselves ~re buoyant.
The plastic compositions can also De selected to produce microspheres that will be selecti-vely permeaDle to speciic gases andjor organic mole-cules. These micros?heres can then be used as semi-pe~meable ~embranes to separate gaseous or liquid mi~tures.
The ~lastic composition.~ can be ~ransparent, translucent or opaque. A suitable coloring material can be added to the pl.astic co~posi~ions ~o aid in identifica~ion of microspheres of specified size andlor ~all thickness.
These and other uses of the present invention will become apparent to those skilled in the art and from the foregoing description and the following appended claims.
It will be understood that various changes and modifications may be made in the invention and that the scope thereof is not to be limited except as set forth in the claims

Claims (115)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Hollow organic film forming material microspheres having a diameter of 200 to 10,000 microns and having a wall thickness of 0.1 to 1,000 microns, wherein said microspheres are free of latent solid or liquid blowing gas materials or gases and the walls of said microspheres are substantially free of holes, relatively thinned wall portions or sections and bubbles.

2. Hollow organic film forming material microspheres of substantially uniform diameter of 500 to 6,000 microns and of substantially uniform wall thickness of 0.5 to 400 microns, wherein said microspheres are free of latent solid or liquid blowing gas materials or gases and the walls of said mcirospheres are substantially free of holes, relatively thinned wall portions or sections and bubbles.

3. The hollow microspheres of claim 2 having a contained gas pressure of 15 to 75 psia.

4. The hollow microspheres of claim 2 having deposited on the inner wall surface thereof a thin metal coating 50 to 500°A
thick.

5. The hollow microspheres of claim 2 having a diameter of 500 to 3,000 microns and a wall thickness of 0.5 to 200 microns.

6. The hollow microspheres of claim 2 wherein the microspheres have an average bulk density of 0.5 to 12 lb/ft3.

7. A mass of the microspheres of claim 1.

8. The hollow microspheres of claim 2 having an oblate spheroid shape.

9. Filamented, hollow organic film forming material microspheres having a diameter of 200 to 10,000 microns and having a wall thickness of 0.1 to 1000 microns, wherein said microspheres are connected to each other by filament portions which are continuous with the microspheres and are of the same organic film forming material from which the microspheres are made.

10. Filamented, hollow organic film forming material microspheres having a diameter of 500 to 6000 microns and having a wall thickness of 0.5 to 400 microns, wherein said microspheres are connected to each other by filament portions which are continuous with the microspheres and are of the same organic film forming material from which the microspheres are made.

11. The hollow microspheres of claim 10 wherein the length of the connecting filaments is substantially equal and is 2 to 20 times the diameter of the microspheres.

12. The hollow microspheres of claim 10 wherein the length of the connecting filaments is substantially equal and the diameter of the connecting filaments is 1/2500 to 1/20 the diameter of the microspheres.

13. Hollow plastic microspheres having a diameter of 200 to 10,000 microns and having a wall thickness of 0.1 to 1,000 microns, wherein said microspheres are free of latent solid or liquid blowing gas materials or gases and the walls of said microspheres are substantially free of holes, relatively thinned wall portions or sections and bubbles.

14. Hollow plastic micropsheres of substantially uniform diameter of 500 to 6,000 microns and of substantially uniform wall thickness of 0.5 to 400 microns, wherein said microspheres are free of latent solid or liquid blowing gas materials or gases and the walls of said microspheres are substantially free of holes, relatively thinned wall portions or sections and bubbles.

15. The hollow microspheres of claim 14 having a contained gas pressure of 5 to 75 psia.

16. The hollow microspheres of claim 14 having a thin metal coating deposited on the inner wall surfaces of the microspheres consisting of a layer of dispersed metal particles 50 to 500°A
thick.

17. The hollow mcirospheres of claim 14 having deposited on the inner wall surfaces thereof a thin metal coating 100 to 1000°A thick.

18. The hollow microspheres of claim 17 wherein the deposited metal is less than 100°A thick and is transparent to visible light.

19. The hollow microspheres of claim 17 wherein the deposited metal is more than 100°A thick and is reflective of visible light.

20. The hollow microspheres of claim 14 having a diameter of 500 to 3000 microns and a wall thickness of 0.5 to 200 microns.

21. The hollow microspheres of claim 14 having an average bulk density of 0.5 to 12 lb/ft3.

22. A mass of the microspheres of claim 14.

23. The hollow microspheres of claim 14 having an oblate spheroid shape.

24. The hollow plastic microspheres of claim 14 wherein there is deposited on the inner wall surfaces a thin metal transparent coating 25 to 90°A thick.

25. The hollow plastic microspheres of claim 14 wherein there is deposited on the inner wall surfaces thereof a thin metal reflective coating 105 to 600°A thick.

26. The hollow microspheres of claim 14 wherein the microspheres have deposited on the inner wall surfaces thereof a thin metal coating 150 to 250°A thick.

27. The hollow microspheres of claim 14 wherein the microspheres have deposited on the inner wall surfaces thereof a thin metal coating 150 to 400°A thick.

28. Filamented, hollow plastic microspheres having a diameter of 200 to 10,000 microns and having a wall thickness of 0.1 to 1,000 microns, wherein said microspheres are connected to each other by filament portions which are continuous with the microspheres and are of the same organic film forming material from which the microspheres are made.

29. Filamented, hollow plastic microspheres having a diameter of 500 to 6000 microns and having a wall thickness o 0.5 to 400 microns, wherein said microspheres are connected to each other by filament portions which are continuous with the microspheres and are of the same organic film forming material from which the microspheres are made.

30. The hollow microspheres of claim 29 having a contained gas pressure of 5 to 75 psia.

31. The hollow microspheres of claim 29 having deposited on the inner wall surfaces thereof a thin metal coating 100 to 1000°A thick.

32. The hollow microspheres of claim 31 wherein the deposited metal is less than 100°A thick and is transparent to visible light.

33. The hollow microspheres of claim 31 wherein the deposited metal is more than 100°A thick and is reflective of visible light.

34. A mass of the microspheres of claim 29.

35. The hollow micrpspheres of claim 29 having an oblate spheroid shape.

36. The hollow microspheres of claim 29 wherein the length of the connecting filaments is substantially equal and is 2 to 20 times the diameter of the microspheres.

37. The hollow microspheres of claim 29 wherein the length of the connecting filaments is substantially equal and the diameter of the connecting filament is 1/2500 to 1/20 the diameter of the microspheres.

38. A shaped form or formed mass of cemented or bonded together hollow organic film forming material microspheres as defined in claim 10.

39. A shaped form or formed mass of cemented or bonded together hollow organic film forming material microspheres as defined in claim 2.

40. The shaped form or formed mass of microspheres of claim 39 wherein the microspheres are cemented together by fusion or sintering or are bonded together with an organic or inorganic bonding agent or adhesive.

41. The shaped form or formed mass of microspheres of claim 39 wherein the micropsheres comprise a filler material.

42. The shaped form or formed mass of microspheres of claim 41 wherein said microspheres have a contained gas pressure of 15 to 75 psia.

43, The shaped form or formed mass of microspheres of claim 40 formed into a thin sheet or panel.

44. The shaped form or formed mass of microspheres of claim 43 wherein said micropsheres have deposited on the inner wall surfaces thereof a thin metal coating 50 to 5000°A thick.

45. A shaped form or formed mass of cemented or bonded together filamented, hollow organic film forming material microspheres as defined by claim 9.

46. A shaped form or formed mass of cemented or bonded together filamented, hollow organic film forming material microspheres as defined in claim 10.

47. The shaped form or formed mass of microspheres of claim 46 wherein the microspheres are cemented together by fusion or sintering or are bonded together with an organic or inorganic bonding agent or adhesive.

48. The shaped form or formed mass of microspheres of claim 47 wherein the length of the connecting filaments is substantially equal and is 2 to 20 times the diameter of the microspheres.

49. The shaped form or formed mass of microspheres of claim 47 wherein the length of the connecting filaments is substantially equal and the diameter of the connecting filaments is 1/2500 to 1/20 the diameter of the microspheres.

50. The shaped form or formed mass of microspheres of claim 46 wherein the microspheres comprise a filler material.

51. The shaped form or formed mass of microspheres of claim 47 formed into a thin sheet or panel.

52. A shaped form or formed mass of cemented or bonded together hollow plastic microspheres as defined in claim 13.

53. A shaped form or formed mass of cemented or bonded together hollow plastic microspheres as defined in claim 14

54. The shaped form or formed mass of microspheres of claim 53 wherein the microspheres are cemented together by fusion or sintering or are bonded together with an organic or inorganic bonding agent or adhesive.

55. The shaped form or formed mass of microspheres of claim 54 said microspheres having a thin metal coating deposited on the inner wall surfaces of the microspheres consisting of a layer of dispersed metal particles 50 to 5000°A thick.

56. The shaped form or formed mass of microspheres of claim 54 said microspheres having a diameter of 500 to 3000 microns and a wall thickness of 0.5 to 200 microns.

57. The shaped form or formed mass of microspheres of claim 54 said microspheres having an average bulk density of 0.5 to 12 lb/ft3.

58. The shaped form or formed mass of microspheres of claim 53 wherein the microspheres comprise a filler material.

59. The shaped form or formed mass of microspheres of claim 58 said microspheres having a contained gas pressure of 15 to 75 psia.

60. The shaped form or formed mass of microspheres of claim 58 wherein the shaped form or formed mass comprises said microspheres and a member selected from the group consisting of plastics, resins, concrete and asphalt.

61. The shaped form or formed mass of microspheres of claim 54 formed into a thin sheet or panel.

62. The shaped form or formed mass of microspheres of claim 61 said microspheres having deposited on the inner wall surfaces thereof a thin metal coating 100 to 1000°A thick.

63. The shaped form or formed mass of microspheres of claim 62 wherein the deposited metal is less than 100°A thick and is transparent to visible light.

64. The shaped form or formed mass of microspheres of claim 62 wherein the deposited metal is more than 100°A thick and is reflective of visible light.

65. The shaped form or formed mass of microspheres of claim 61 said microspheres having an oblate spheroid shape.

66. The shaped form or formed mass of plastic micropsheres of claim 61 wherein there is deposited on the inner wall surfaces of said microspheres a thin metal transparent coating 25 to 90°A
thick.

67. The shaped form or formed mass of plastic microspheres of claim 61 wherein there is deposited on the inner wall surfaces of said microspheres a thin metal reflective coating 105 to 600°A
thick.

68. The shaped form or formed mass of microspheres of claim 61 wherein the microspheres have deposited on the inner wall surfaces thereof a thin metal coating 150 to 250°A thick.

69. The shaped form or formed mass of microspheres of claim 24 wherein the microspheres have deposited on the inner wall surfaces thereof a thin metal coating 150 to 400°A thick.

70. A shaped form or formed mass of cemented or bonded together filamented, hollow plastic microspheres as defined by claim 28.

71. A shaped form or formed mass of cemented or bonded together filamented, hollow plastic microspheres as defined by claim 29.

72. The shaped form or formed mass of microspheres of claim 71 wherein the microspheres are cemented together by fusion or sintering or are bonded together with an organic or inorganic bonding agent or adhesive.

73. The shaped form or formed mass of microspheres of claim 71 wherein the microspheres comprise a filler material.

74. The shaped form or formed mass of microspheres of claim 73 said microspheres having a contained gas pressure of 15 to 75 psia.

75. The shaped form or formed mass of microspheres of claim 73 wherein the shaped form or formed mass comprises said microspheres and a member selected from the group consisting of plastics, resins, concrete and asphalt.

76. The shaped form or formed mass of microspheres of claim 72 formed into a thin sheet or panel.

77. The shaped form or formed mass of microspheres of claim 76 said microspheres having deposited on the inner wall surfaces thereof a thin metal coating 50 to 5000°A thick.

78. The shaped form or formed mass of microspheres of claim 77 wherein the deposited metal is less than 100°A thick and is transparent to visible light.

79. The shaped form or formed mass of microspheres of claim 77 wherein the deposited metal is more than 100°A thick and is reflective of visible light.

800 The shaped form or formed mass of microspheres of claim 76 having an oblate spheroid shape.

81. The shaped form or formed mass of microspheres of claim 72 wherein the length of the connecting filaments is substantially equal and is 2 to 20 times the diameter of the microspheres.

82. The shaped form or formed mass of microspheres of claim 72 wherein the length of the connecting filaments is substantially equal and the diameter of the connecting filament is 1/2500 to 1/20 the diameter of the microspheres.

83. A formed panel comprising a mass of filamented hollow, organic film forming material microspheres as defined by claim 29.

84. A tape comprising a mass of filamented hollow, organic film forming material microspheres as defined by claim 29 an adhesive binder for said microspheres, a backing for said microspheres and an adhesive for said tape.

85. A composition comprising asphalt and a mass of filamented hollow, organic film forming material microspheres as defined by claim 29.

86. A solar energy collector comprising an outer transparent cover and an inner cover, and having disposed therebetween a black coated heat absorber and at least one heat exchange medium tube, wherein said outer cover consists of a transparent sheet or panel comprising a mass of hollow plastic microspheres as defined in claim 13 cemented together by fusion or sintering or bonded together with an organic or inorganic bonding agent or adhesive.

87. The solar energy collector of claim 86 said microspheres having deposited on the inner wall surfaces thereof a thin metal coating.

88. The solar energy collector of claim 86 said microspheres containing a low heat conductivity gas.

89. The solar energy collector of claim 87 wherein the deposited metal is less than 100°A thick and is transparent to visible light.

90. The solar energy collector of claim 86 said microspheres having an oblate spheroid shape.

91. The solar energy collector of claim 86 wherein there is deposited on the inner wall surfaces a thin metal transparent coating 25 to 90°A thick.

92. A solar energy collctor comprising an outer transparent cover and an inner cover, and having disposed therebetween a black coated heat absorber and at least one heat exchange medium tube, wherein said outer cover consists of a transparent sheet or panel comprising a mass of hollow plastic microspheres as defined by claim 29 cemented together by fusion or sintering or bonded together with an organic or inorganic bonding agent or adhesive.

93. The solar energy collector of claim 92 said microspheres having deposited on the inner wall surfaces thereof a thin metal coating.

94. The solar energy collector of claim 92 said microspheres containing a low heat conductivity gas.

95. The solar energy collector of claim 93 wherein the deposited metal is less than 100°A thick and transparent to visible light.

96. The solar energy collector of claim 55 said microspheres having an oblate spheroid shape.

97. The solar energy collector of claim 55 wherein the length of the connecting filaments is substantially equal and is 2 to 20 times the diameter of the microspheres.

98. The solar energy collector of claim 55 wherein the length of the connecting filaments is substantially equal and the diameter of the connecting filament is 1/2500 to 1/20 the diameter of the microspheres.

99. A solar energy collector comprising an outer transparent cover and an inner cover, and having disposed therebetween a black coated heat absorber and at least one heat exchange medium tube, wherein there is disposed between said outer cover and said black coated heat absorber a first mass of hollow plastic microspheres, and there is disposed between said black coated heat absorber tubes and said inner cover a second mass of hollow plastic microspheres, said first and second masses of hollow plastic microspheres being as defined in claim 14.

100. The solar energy collector of claim 99 said microspheres having deposited on the inner wall surfaces thereof a thin metal coating.

101. The solar energy collector of claim 99 said microspheres containing a low heat conductivity gas.

102. The solar energy collector of claim 99 wherein there is deposited on the inner wall surfaces of said first mass of microspheres metal less than 100°A thick and transparent to visible light.

103. The solar energy collector of claim 99 wherein there is deposited on the inner wall surfaces of said second mass of microspheres metal more than 100°A thick and reflective of visible light.

104. The solar energy collector of claim 99 said microspheres having an oblate spheroid shape.

105. The solar energy collector of claim 99 wherein there is deposited on the inner wall surfaces of said first and second masses of microspheres a thin metal transparent coating 25 to 90°A thick.

106. The solar energy collector of microspheres of claim 99 wherein there is deposited on the inner wall surfaces of said second mass microspheres a thin metal reflective coating 105 to 600°A thick.

107. A solar energy collector comprising an outer transparent cover and an inner cover and having disposed therebetween a black coated heat absorber and at least one heat exchange medium tube wherein there is disposed between said outer cover and said black coated heat absorber a first mass of hollow plastic microspheres, and there is disposed between said black coated heat absorber tubes and said inner cover a second mass of hollow plastic microspheres said first and second masses of hollow plastic microspheres being as defined by claim 29.

108. The solar energy collector of claim 107 said microspheres having deposited on the inner wall surfaces thereof a thin metal coating.

109. The solar energy collector of claim 107 said microspheres containing a low heat conductivity gas.

110. The solar energy collector of claim 107 wherein there is deposited on the inner wall surfaces of said first mass of microspheres metal less than 100°A thick and transparent to visible light.

111. The solar energy collector of claim 107 wherein there is deposited on the inner wall surfaces of said second mass of microspheres metal more than 100°A thick and reflective of visible light.

112. The solar energy collector of claim 107 said microspheres having an oblate spheroid shape.

113. The solar energy collector of claim 107 wherein there is deposited on the inner wall surfaces of said first and second masses of microspheres a thin metal transparent coating 25 to 90°A thick.

114. The solar energy collector of claim 107 wherein the length of the connecting filaments is substantially equal and is 2 to 20 times the diameter of the microspheres.

115. The solar energy collector of claim 107 wherein the length of the connecting filaments is substantially equal and the diameter of the connecting filament is 1/2500 to 1/20 the diameter of the microspheres.