CA2131916A1

CA2131916A1 - Thermoplastic syntactic foam pipe insulation

Info

Publication number: CA2131916A1
Application number: CA002131916A
Authority: CA
Inventors: Thomas J. Murray; Noel J. Tessier
Original assignee: Individual
Current assignee: WR Grace and Co Conn
Priority date: 1992-03-31
Filing date: 1993-03-29
Publication date: 1993-10-14
Also published as: JPH07505435A; AU3968993A; EP0637282A4; WO1993019927A1; EP0637282A1; BR9306155A; NO943611D0; NO943611L; RU94045989A

Abstract

Flexible syntactic foam insulation, and methods for making it, are disclosed. A low melt index thermoplastic resin is fluidified to produce a melt stream, and microspheres are metered into the melt stream under low shear conditions. The method allows for faster production of syntactic foams and for the production of higher quality foams because breakage of the microspheres is substantially reduced. An integral insulated pipe section (16) including a pipe (17) and a covering of syntactic foam insulation (18) is produced.

Description

2 1 3 1 9 1 6 ~Cr/US93/02870 ~

THERMOPLASTIC SYNTACTIC FOAM PI~E INSULATION

FIELD OF THE INVENTION
s This invention relates generally to syntactic foam insulation, and n~>re particularly to flexible thermoplastic syntactic foam pi~e insulating materi~l made by fluidifying a thermoplastic resin having a defined melt index to p r-)duce a melt stream; metering a spherical filler int-- the melt stream under lotv shear conditions to form a Is~ixture, and forming the mixture into a final form.
BACKGRQ~ND O~THEINVENTION
Off~hore petroleum prc cluction requires the lse of submanne pipes or conduits to transport oil or gas back to a centralized surface platform or to sllore.
ln some fields, the oil or gas contains paraffins that can precipit?~te out as the temperature of the vil or gas passing through the pipes is lowered due to heat transfer from the pipe contents to the cold ocean. This significantly reduces flow or causes blocka~e of production lines, increasing the cost of production. If blockage occurs costly mechanical or chemical means are necessarv to clear any blockage. Added expenses are the cost of shutting down production and the potential loss of any pipe contents causecl during removal of the blockage.
Several teclmiques are known for alleviating this probiem: 1) adding chemicals to the oil to prevent paraf~ pr~cipitation, 2) heating the production lines, or 3) instllatin~ the pipes. However, adding chemicaLs to the oil or gas is costly because of the effort and money expended in purchase and addition, and the chen~icals must later be lefined out of tl e oil. Heating tlle piF~eline is also costly because it is not energy-ef~icient and requires heating equipn~ t ~aJl1ich must 'L~e installed over kilometers of pipeline, and monitored for }~roper operation. On the vther hand, insulating the production lines is a cost effeetiv~

'..' ~' , WO 93/1g927 Pcr/us93/0~870 213191~
solution because the insulation may be hlstalled on the pipeline before it is laid and needs no continuous monitoring.
Submarine oil or gas production pipelines must also be pllysically protected. Steel pipes are most cc~mmonly used hl fabricating off-shore pipelines, and as such require protection from the corrosive sea water. Typically neoprene or epoxy coatings are used for this purpose. However, such coatings are subject to abrasion caused by the installation process, and an additional over :oating is needed, e.g., of polyethylene.
Appropriate syntactic ~oam insulation could insulate the pipe as well as o provide corrosion resistance, abrasion resistance and resistance to hydrostatic F ressures. Syntactic materials are those in which hollow spherical filler material is embedded in a pc-lymeric matrix. The filler material, most often glass or plastic microspheres in the micron size range, imparts thermally-insulative ;
properties to the syntactic material; generally, for a given thickness of syntactic s material, as the concentration of microspheres in the matrix rises, so does the insulative property of the syntactic material.
~ ~ -Additional ~hysical attributes such as increased resilience, low thermal conductivity, low creep, and flexibility or elasticity may be given to tlle syntactic rnaterial through the selection of various polymeric matrices. E;or instance, it has -long been desired to make a flexible syntactic foam insulation whi-h could be -formed directly on the pipe sections, or wrapped around it as a sleeve or a self~
adhesive tape, before the pipe is shipped to a lay barge for pipe laying. This "pre-coating" is desirable because it means the crew laying the pipe now l as one less task to do, namely coating the pipe sections, although tlle joints must still be 2s wrapped and sealed. Also, ~e flexibility is necessary because the pipe sections must flex and bend during installation. Por example, in tl e commonly-used "j-curve" pipe-laying method, pipe sections are welded together on a lay barge moving horizontally, while the pipeline is lowered down to the ocean floor, typically entering the water at an angle of from about 60 to 80- from the horizontal. As the long pipeline reaches the ocean floor, it fvrms a "J" shape as it bends. Conventional syntactic foams, made of thermoset resins, are not flexibl~
enough for such an application. Thus, it would be advantageous to select a polymeric base for the syntactic foam which is flexible enough for such an application, such as several of tl~e thermoplastic resins. `
A drawback with exisling syntactic foam ir~ulating materials, however, is the relative d~ lty of making them easily and quickly in large quantities, such as for coaling long sections of pipe, and also of the desired quality. Currently available syntactic foams are made using thermoset resins such as polyurethane;
these resins are more difficult to work with than lhermoplastic resins because they may only be processed at temper~tures below the ~stage of the resin, i.e., the temperature at which the resin begins to cross-link. Further, such foams do 5 not have tlle desired flexibility to bend with the pipe during installation, and also often absorb water, requiring a separate coating to make the foam water-impermeable.
Synt~ctic foam insulation having a tllermoplastic matrix has been long desired, but hard to make. Particularly, it is difficult to compound glass o microspheres and other hollow spherical fillers into a thermoplastic polymericmatrix at low enough shear ~orces to prevent crushing the spheres during tlle process. The thermal conductivity of an effective submarine pipe insulation ~ -needs to be less than about 0.15 W/m-~C. When about 5% or 8reater of the cpheres in the matrix are crushed, it is difficult to attain this necessary level of s thermal conductivity. Furthermore, the structural properties of the syntactic foam are also adversely affected.
One mëthod towards this en~l is taugllt in European Patent Applicati~n 47~ i A1, wherein rnicrospheres that have been treated with a chain scission agent are added to a fluîd stream of short chain polypropylene or polybutylene 2D to form a crosslinked synhctic foam insulative material. This method is taught as useful for producing rnaterîal of a low thermal conductivity. However, the plastic starting rnaterials taught for use therein are generally not optimum forsubmarine pîpe insulation, because while the short chain polypropylene or polybutylene affords low breakage of the microspheres, the method requires the 2s presence of a chain scissîon a~ent, coated on the mîcrospheres, to cross-link the short-chaîn polymer. Without the presence of this agent, the finished insulationwould be totally unacceptable ~or use as submarine pipe insulatiorl, because it ~ ;
would not be hydrostatic pressure-resistant, abuse-resistant, or creep-resistallt.
Furthermore, the chaill-scission agent stiffens the plastic matrix, decreasing the 30 fle~ability of the material so as to make it impractical for use as submarine pipe insulation, because it will not flex well as the pipe is laid.
E~uoyant therrnoplastic syntactic cable jacketing has been made, but sucl jacketing contains a large amount of entrained air to keep the cable jacketing buoyant. Such materials are inappro~riate for insulating deep sea pipeline, ~ `
35 however; the air pockets in the material will cause the material to collapse at ocean-floor-pressures, leading to absorption of water in the interstices of the material. These materials are also not abrasion c r heat resistant, and cannot be `

~ 1 3 1 9 1 PCr/US93~02870 ma~le desiral~ly thin to bend wi~l~ the pipe, wlule providin~s efficien~ insulation for it.
The inventors have thus found no truly satisfactory way to compound spherical ~illers into a thermoplastic polymeric matrix to make an 5 advantAgeously thin, flexible syntactic foam pipe insulating material without 1 ) cruslung a substantial proportion of the spherical filler durin~ processing, 2) being time-consuming and difficult to put into practice on a large scale, or 3) utilizing specialized, or heavily modified standard equipment.
Thus it is an object of the invenLion to provide a method for making o syntactic foam insulation having superior thermal and structural qualities which may be carried out on a large scale, e.g., in sufficient volume for pipe applications, on presently available e~luipment.
It i~ another object of the invention to provide a method for making one-piece pipe units ready for assembly in submarine oil or g~s cs)nduits which 5 comprise a layer of flexible syntactic foam insul~tion on the pipe's outer surface.
It is a further object of the invention tv provide one-piece insulated pipe units ready for assembly in submarine oil or gas conduits made by the above method.
It is yet another object of the invention to provide adhesive flexible 20 'syntactic foam insulating tapes and sleeves made by the method of the invention.
Purther objects of the invention are to provide a syntactic foam insulativn made by a method of the illvention, and t~- pro~ide a method of insulating pipe utilizing a syntactic foam made by a metllod of the invention.
Other objects of the in~ention will he apparent to those of ordinary skill in 25 the art upon reading the spe~vification, claims and drawings.

The present invenlion relates to a metllo~l of makin~ synt~ctic foam insulation, comprising the steps of fluidifying a thermoplastic resin having a melt index of from 3 to 30g/10 min to produce a melt stream; metering ~
~o sF herical filler into the melt stream under low shear conditions to form a rnixture, and forming the mixture into a final form. The invention ~urther relates ~o syntactic foam insulation mAde by the above process.

DESCRIPIION OF THE DRAWINGS
Fi~ure 1 depicts in simplified side view a doubl~-stage extruder carrying 3s out the method of the invention. 4 WO93/19927 2 1 3 1 ~ 1 6 PCI/US93/02870 Figure 2 depicts ~n partial cross-section a ready-to-use pipe section in accordance comprising an outer sleeve of syntactic material superimposed over the outer pipe sur~ace.
Figure 3 depicts in plan view a pipe section wrapped with a self-adhesive syntactic foam tape made in accordance with the invention.

~PTION OF THE INVENTION
The o~jects of the insrention have been substantially accomplished by the use of a method wllich, in a preferred embodiment, uses a two~tage extrusion process, whereby a first stage of an extruder means fluidizes a thermoplastic resin base and conveys it to a second stage of an extruder means where, under low shear conditions, a spherical filler material is introduced into the fluid plastic stream. In this preferred embodiment the thermoplastic and filler rnaterial thereafter mix in the second stage of the extruder barrel and the fluid n ixture is deaerated and extruded into a desired final form. The resulting 1S product contains a substantially h- rnogeneous distribution of spherical fisler material in the polymeric matrix, which, as stated previously, is cruci~l to ~izing the thermal and s~uctural properties of the finished syntactic foam.
'~hermoplastic", as used herein, is intended to mean any plastic, polymeric, or elastomeric base commonly used in the art as feed stock in extrusion or extrusion-related processes which can be heated and softened repeatedly without suffering any basic change in characteristics. Thermoplastics used in this invention must be of a hi~h "melt index," which are defined as t~ose which,tmder test conditions specified by ASI~M standard ~3835, have a low viscosity, i.e., in the ran~se of from about 3.0 to 30g/I0mirl, preferably from Pbout 15 to2s 30~/I()min, an~l more preferably from about 20 to 25g/I0min. Thermosettin~
resins are inappropriate for use in the invention.
Examples of thermop1?stic resins are polyimides, acrylonitrile-butadien~
styrene ("ABS") resins~ acetals, acrylics, cellulosics, chlorinated polyethers, fluorocarbons, nylons (polyamisies), polycarbonates, polyolefins and copolymers thereof including, but not limited to, polyethylenes and copol,vmers thereof, polypropylenes and copolymers thereof, chlorinated or fluorinatecl polyolefins and copolymers thereof; polystyrenes, and vinyls, e.g., polyvinyl chloride. The omission of any specific type of thermoplastic resin should not be construed as a limitati~n on tl e il1vention. It should also be noted that mixtures of one or more thermoplastic resins may be employed.

-wo 93/l99272 1 3 1 9 1 6 PCl`/US93/02870 Speci~ic types of resins witl~ill each class named above that are suitahle for use in the invention are well-knowll to those of ordinary skill in the art and need not be mentioned here. Hc>wever, the inventors have found that thermoplastic polyolefins (' TPO") such as those manufactured under the trademarks HIFAX
s (~imont) and E;L~(OMER (Union Carbide) are particularly suitable for use inthe invention, as are SURLYN (E. I. Du Pont de ~emours Co.) ionically cross-linked thermoplastic polymers derived from ethyiene/methacrylic acid copolymers, and thermoplastic elastomers ~'`TPE") such as PEl~AX (Atochem), which is a polvether blocked polynmide ~BA"). However, the invention o should not be limite~l to the use of these resins. These thermoplastic resins provide the necessary flexibility to the finished syntactic foam insulation, which is al~o very desirable from the stalldpoint of producing such articles as syntactic foam insulatin~ tapes and sleeves, wluch by their nahtre need to be flexible and/~r pliable for easy installation. Although these resins are flexible, they are also resistant to creep, elon~tion, abrasion and corrosion, making their use in pipeline applications even more desirable. Fttrther, such resins are very resistant to the high temperatures of the pipelines (as high as 125- C). These resins have a characteristic chain length tl at distinguishes them from other thermoplastic resins that have been used in this art. Specifically, these resins have longer ch-~ins and low melt indices, which makes th~m very flexible and strong.
~luidification of such resins and addition of spherical filler under low shear conditions to make a syntactic foam havin~ a high proportion of intact microspheres, as described herein, makes the use of short chain polymers with a chain-scission agent, as taught in U. S. Patent No. 5,158,727, ~mnecessary. `
~ .
The spherical filler used in the invention may be any type of hollow spheres which are typically used in making syntactic foams. (Por brevity and convenience the term "microspheres" will be used hereinafter to describe spherical filler used in the invention.) The rnicrospheres are preferably made of glassJ but may also be made of plastic or otl er materials well-known to those skilled in the art, provided that they will not melt under the conditions necessary for fluidifica~ion of the thermoplastic resin to produce the melt stream. The size range of the spheres ~ill depend on the particular demands to be made c-n tl~e syntactic foam to be produced. Generally, the spheres will range in diameter from about 3 to 100~, preferably from about 5 to 80~L, more preferably from abvut 3~ 20 to 8011, even more preferably from about 20 to 70~1, and most preferably from about 50 to 7011. Microspheres of rnore tllan one size, or a range of sizes, may be used, e.g., a~blend of spheres ranging in diameter from about 1 to 20,u and s~heres ranging in diameter from about 50 to 100~1. Thus in some applications a WO 93/19927 21 3 I 91 6 Pcr/uss3/o287o such a size distribution may allow denser packing of the rnicrospheres in the fir~ished syntactic foam. The strength of the microspheres is critic~l; the puremicrospheres should be able to withstand pressures of from 6.89 x103 to 27.6 x103 MpA under conditions according to ASI~ D3102 while sustaining no more s than 20~ breakage. The density of the m~icrospheres is preferably in the range of from about 0.1 to 1.1g/cc, and more preferably from about 0.20 to 0.4~g/cc.
The method is generally carried out using extrusion apparatus, as such apparatus are widely available. Typicallyr a two-stage extruder like the double-screw unit depicted (in greatly simplified form) in FIG. 1 may be employed.
o Such extruders are advantage~us because they allow addition and fluidificationof the resin in the first stage, and addition of the spherical filler in the second stage, thus making separate apparatus for carrying out the flwdification and filler addition steps unnecessary. However, we think that there may be some cases where separ~tion of the fluidification and filler addition functions are 5 desirable or necessary, and is thus within the scope of the invention. Extruders that may be used in the method of the mvention are well-known in the art; -conventional double-screw extruders or double-stage Buss Kneader double-screw extruders may be used, with a corotatin~ design being preferable.
Referrin~ now to FIG. 1, such a two-stage extruder comprises a feed hopper - :
20 1 into which thermoplastic feed mateAal is placed for extrusion. A feeder such as an auger feeder (not shown) may be used if more precise feed stock addithm is desired. The feed n aterial passes from hvpper 1 through feed throat 2 onto screw ~ which is dri~en by a motor UlUt 6b coupled by a belt 6a to a gear reducer 5 to a thrust bearing 4 connected to screw 3. The design of screw 3 25 within first-stage barrel 7 is of a geometry to effectively plasticate, shear and meter the thermoplastic resin in the first-stage barrel Z into a melt stream of the desired viscosity. Those skilled in ~e art will know how to fabIicate such a screw.
As screw 3 rotates, the thennoplastic is pumped into first sta~e barrel Z
30 which is heated by heaters 8 monitored by thermoco~ples 2. The heat produced by heaters 8 and the frictional action of screw 3 against the feed material ~nd first stage barrel 7 liq~lefies the the~noplastic, forming a melt stream which is metered into second stage barrel 10.
As the melt stream is metered into second stage barrel ~Q microspheres 12 35 (which have been pre~ iously placed into rnicrosphere hopper 11) are metered into the melt stream in second sta~e b~rrel lQ under low shear conditions; it ispreferred to meter microspheres using a feeder such as a weight belt side feeder.

WO 93/19927 2 1 3 1 9 1 6 Pcr/US93/0287û

The precise addition rate will depen~l on the desired concentration of rnicrospheres 12 in the syntactic foam, and the extrusion rate. The geometry of the section of screw 3 under micros~here hopper 11 must be chosen so the microspheres are fol~ed gently into the melt stream; such "low shear" ~rofile 5 screw designs will be apparent to tl~ose skilled in;the art, and such screw profiles ~rovide the necessa~y low shear c~nditions f~ r addition of microspheres withoutbreakage. Tl~us, providing "low shear conditions" in accordance with tlle invention means using "1OW shear" designs to gently fold spherical ffller into the melt stream containing the low melt index thermoplastic resins of the invention.
The microspheres 12 are thus c~rried intv the melt stream and mixed into it with little or no breakage; less lhan 5~ breakage is important. Preferably less than 3% of the microspheres in t~e thermoplastic are broken. More preferably, substantially all of the microsyheres present are unbroken. The mixture is transported down second stage barrel ;lQ, heated by heaters 13 and regulated by 5 thermocouples ;~. A venting zone 16 to allc w the removal of any air entrainedinto the melt stream caused by the mixture of the microsF~heres into the melt stream is preferably installed in second sta~e barrel lQ. It is hi~hly desirable to have the venting zone su~ stantially remove any unreinforced air ~i.e., air not contained within microspheres) from the extrudate, because the presence of 20 unreinforced air in the matrix of the syntactic foam insu1ation makes the ~sulation hi~hly susceptible to water incursion and collapse at high hydrostaticpressures, resultin~ in a significant reduction in the insulative efficiency of the insulation.
Higher microsrhere loadings impart greater insulative capacity to lhe 25 syntactic foam insulativn. If higher loa~ings of microspheres in the syntactic foam are desired, i.e., about 30-50~ by volume of the foam insulation, we have found it advrtntageous to meter a proportion of the spherical filler into a first point of the melt stream under low shear conditions, and the remainder at a second pOillt of the melt stream, located downstream of the first, uncler low shear 30 conditic ns. Generally, the proportion of filler metered into the first pOillt ranges from 10 lo 90%, with 30 to 80% bein~ preferred, and 50 to 70% particul?.rl~
preferred.
Other additives may be added to the melt strean~ along witll the spherical filler if desired, such as silanes, adhesivn promoters, or coupling ageltts.
The mixture exits at the screw tip i~ at which point is connected a die of some kind, s~lch as a flat sheet die, a pro~iled sheet die, a h~llow mandrel die, etc. The mixture is then pulled, rolled, cas~, chopped, etc. into the desired final WO 93/19927 2 1 3 1 9 1 6 PCr/US93/02870 form. The final form may be spheres, pellets, tapes or ribbons, etc. We have also found pellets of the syntactic foam to b~ !seful ~ts a masterbatch from which other insulative articl~s m~y be made. For instance, syntactic foam pellets may be blended with, e.g., EPDM rubber or extender resin and extruded to form an insulated pipe wrap that is more elastomeric and abuse-resistant.
The resulting syntactic foam may be installed on pipe in a number of ways.
An integral insulated pipe section like that depicted in partial cross-section in ~ ~ ~
FIG. 2 may be made by placing a section of pipe to be insulated within a ~ ~ -cylindrical form; the syntactic foam insulation may then be extruded into the o space between the form and the pipe's outer surface to form the outer coating.
Referring to FIG. 2, the resulting integral insulated pipe section 16 comprises a pipe ;~ and a c~vering of syntactic foam insulation 18. After removal of the form the integral insulated pipe section is ready to ship to the laybarge where it may be inserted into a pipeline without any further preparation.
Por covering the pint sections of pipe, an insulative tape may be wrapped ` `
around tlle jOillt. However, time is of the essence when laying pipeline, and wrappin~ tape over a pint is time consuming. Preferably, therefore, a custom ~ ~
molded clamshell-type insulative enclosure may be made by compression ~ -molding or casting the fluidified syntactic foam insulation into the desired configuration. The insulative enclosure could be attached in a matter of seconds, `~
simplifying operations on the laybarge. ; ~
Alternately the insulation may be a syntactic foam insulative tape which ~ `
may wrapped around the pipe and/or joints. The flexible syntactic foam described herein may be extruded into a tape or ribbon fom~, to one side of 2s which may be applied a self-adl esive coating and/or a release layer which will :
be removed before installation of the tape. Alternately the tape may be left ~ -~
uncoated, with adhesive being applied to either tl e tape or the pipe at a latertime. An insulated pipe 27 having such a flexi~le insulative syntactic foam tape28 wrapped ar~und it is shown in plan view in FIG. 3.
Syntactic foam of the inven~ion made with thermoplastics s-lch as the ~FAX type mentioned is desirably abrasion-resistant, but there mav be instances where an outer protective coating is desirable or necessaIy. Outer abrasion-resistant coatings which could be applied are, e.g., neoprene;
polyethylene; polypropylene; polyurethane; polyvinyl chloride; glass; and abrasion-resistant fabrics such as KEVLAR aromatic nylons. Other coatings, in~partin~ a-dvantageous properties to tl e syntactic foam, can also be ap~lied if desired. -~

W093/19927 21319 16 PCr/US93/028~0 Tlle thermal conductivity of syntactic foam produced according to the invention is generally no higller than about 0.14W/m- K. Another property of the inventive syntactic foam i.s its flexibility, which, when installed on a pipe, enables it to bend with the pipe during laying operations. Syntactic foam made 5 in accordance with the invention generally has a flexural modulus of about 3000 to 4000psi, and preferably 3500 to 4000psi.

EXAMPLE
A insulative syntactic foam tape was made in the following manner. The polymer used was a HIFAX (Himont) thermoplastic olefirl similar to grade 10 CAl()A. Glass microspheres having an average density of 0.28g/cc, an average size o~ and an average strength of no more than 20% breakage at 6.89MpA
were used.
A tw~ -stage corotating twin scr~w extruder was used to produce the syntactic foam insulation. The twin screw was assembled of various elements to accomplish e~ch extrusion processing requirement. The barrel temperature was set at l90 C~ and the twin screw speed was set at 150 RI~M. Polymer was fed So the feed section at 45kg/hr. As a homogenec us polymer melt stream was established, microspheres were fed int~ the second stage at a rate of 6kg/hr. A
venting zone built into the sec~>nd stage was used to effectively remove entrained 20 air from t~e extrudate. The extrudate reaching the twin-screw tip passed through a die having a rect~ngular cros~s-section, resulting in a 25mm wide tapeabout 6mm thick.
The tape wluch was pr~duced had a thermal conductivity of 0.135W/m-~K, which is adequate for submarine pipe insulation, and wa~s fle~able, abrasion and25 impact resistant.
It should be noted that the above example and description of the preferred embodiment of the invention are intended to illuskate tlle inventivn and not meant to lirnit on it. It is intended that modifications, variations and changes tv the invention may be made within the scope of the append~d claims without 30 departing from the spirit and scope of the present invention.

Claims

What Is Claimed Is:

1. A method for making syntactic foam insulation, comprising the steps of:
a) fluidifying a thermoplastic resin to produce a melt stream, said thermoplastic resin having a melt index of from 3 to 30g/10 min;
b) metering a spherical filler into said melt stream under low shear conditions to form a mixture; and c) forming said mixture into a final form, said final form being substantially free of chain scission agents, and said final form having a thermal conductivity of less than about 0.14 W/m-K.

2. The method of claim 1 wherein said thermoplastic resin is selected from the group consisting of thermoplastic polyolefins; ionically cross-linked thermoplastic polymers derived from ethylene/methacrylic acid copolymers; polyether blocked polyamide thermoplastic elastomers;
polyimides; acrylonitrile-butadiene-styrene resins; acetals; acrylics;
cellulosics; chlorinated polyethers; fluorocarbons; nylons;
polycarbonates; polyolefins and copolymers thereof; and mixtures thereof.

3. The method of claim 1 wherein the size of said spherical filler is in the range of from about 3 to 100µ in diameter.

4. The method of claim 1 wherein the size of said spherical filler is in the range of from about 5 to 80µ in diameter.

5. The method of claim 1 wherein the size of said spherical filler is in the range of from about 20 to 70µ in diameter.

6. The method of claim 1 wherein the density of said spherical filler is in the range of from about 0.1 to 1.1g/cc.

7. The method of claim 1 wherein the density of said spherical filler is in the range of from about 0.2 to 0 40g/cc.

8. The method of claim 1 wherein unreinforced air is substantially removed from said mixture after said spherical filler is metered into said melt stream under low shear conditions.

????????/02???

9. The method of claim 1 wherein said second stage of said extruder further comprises a venting zone means for substantially removing unreinforced air from said mixture.

10. The method of claim 1 wherein said final form consists of pellets or spheres.

11. The method of claim 10 further comprising the steps of adding said pellets or spheres, as a masterbatch, to an extruder; fluidifying said masterbatch to produce a melt stream; and forming said melt stream into a final form.

12. The method of claim 11 further comprising the step of blending a filler into said masterbatch.

13. The method of claim 12 wherein said filler is selected from the group consisting of rubber and extender resin.

14. The method of claim 1 wherein said final form is a ribbon or tape.

15. The method of claim 1 wherein said melt stream is produced using an extruder.

16. The method of claim 15 wherein said extruder is selected from the group consisting of twin-screw extruders; two-stage extruders; and Buss kneaders.

17. The method of claim 1 wherein a proportion of said spherical filler is metered into a first point of said melt stream under low shear conditions; and the remainder of said spherical filler is metered into a second point of said melt stream, located downstream of said first point, under low shear conditions.

18. The method of claim 1 comprising the additional step of applying an outer coating to said final form.

PCT/US??/028??

19. The method of claim 17 wherein said outer coating is selected from the group consisting of neoprene; polyethylene; polypropylene;
polyurethane; glass; and aromatic nylons.

20. A method for making an insulated pipe unit comprising superimposing, over the outer surface of a pipe, a covering of syntactic foam pipe insulation made by a process comprising the steps of:
a) fluidifying a thermoplastic resin to produce a melt stream, said thermoplastic resin having a melt index of from 3 to 30g/10 min;
b) metering a spherical filler into said melt stream under low shear conditions to form a mixture; and c) forming said covering from said mixture, said covering being substantially free of chain scission agents, and said covering having a thermal conductivity of less than about 0.14 W/m-K.

21. A syntactic foam insulation made by the process comprising the steps of:
a) fluidifying a thermoplastic resin to produce a melt stream, said thermoplastic resin having a melt index of from 3 to 30g/10 min;
b) metering a spherical filler into said melt stream under low shear conditions to form a mixture; and c) forming said mixture into a final form;
wherein said insulation is substantially free of chain scission agents, and said insulation has a thermal conductivity of less than about 0.14 W/m-K.

22. The syntactic foam insulation of claim 21 wherein said insulation has a thermal conductivity of no higher than about 0.14 W/m-K.

23. The syntactic foam insulation of claim 21 wherein said insulation has a flexural modulus of at least about 3000 to 4000psi.

24. A syntactic foam insulation comprising:
a) a thermoplastic resin having a melt index of from 3 to 30g/10 min and being selected from the group consisting of polyolefins and ionically cross-linked thermoplastic polymers derived from ethylene/methacrylic acid copolymers; and ???????????

b) a spherical filler of reinforced air present in an amount of from 10 to 50% by volume of the insulation; and wherein the insulation is substantially free of chain scission agents, has a modulus of elasticity form 3000 to 4000 psi and a thermal conductivity of less than 0.14W/m-°K.

25. The insulation of claim 24 further comprising a second filler selected from the group consisting of rubber and extender resin.

26. The insulation of claim 24 further comprising an outer coating formed on a major surface of the insulation and wherein the coating is selected from the group consisting of neoprene; polyethylene; polypropylene;
polyurethane; polyvinyl chloride; glass; and nylon.

27. The syntactic foam insulation of claim 24 wherein the spherical filler is formed of glass microspheres and the size of said spherical filler is in the range of from about 3 to 100µ in diameter.

28. The syntactic foam insulation of claim 24 wherein the density of said spherical filler is in the range of from about 0.1 to 1.1 g/cc.

29. An integral insulated pipe section comprising a section of pipe and an outer covering of a syntactic foam pipe insulation comprising: an uncrosslinked thermoplastic resin and from 10 to 50% by volume of the insulation of reinforced air in the form of glass microspheres; wherein the insulation has a thermal conductivity of less than 0.14W/m-°K, a modulus of elasticity from 3000 to 4000 psi, is substantially free of unreinforced air and is substantially free of chain scission agents, and has less than 5% of the microspheres broken or damaged.

30. The insulated pipe of claim 29 wherein the insulation is applied to the pipe as a tape.

31. The insulated pipe of claim 29 wherein the insulation is applied to the pipe as a molten coating.

32. The insulated pipe of claim 29 wherein the insulation is applied to the pipe as a sleeve.

33. The insulated pipe of claim 29 further comprising a filler selected from the group consisting of rubber and extender resin.

34. The insulated pipe of claim 29 wherein said thermoplastic resin is selected from the group consisting of polyolefins and ionically cross-linked thermoplastic polymers derived from ethylene/methacrylic acid copolymers.