US3376371A

US3376371A - Continuous casting process

Info

Publication number: US3376371A
Application number: US490945A
Authority: US
Inventors: Charles J Opel; Paul H Bottoms
Original assignee: Swedlow Inc
Current assignee: GKN Aerospace Transparency Systems Inc
Priority date: 1965-09-28
Filing date: 1965-09-28
Publication date: 1968-04-02
Anticipated expiration: 1985-04-02
Also published as: DK124384C; DE1645388A1; NO136399B; GB1168084A; JPS4936944B1; ES341824A1; DK124384B; NL6613600A; ES331636A1; BE687405A; NO136399C; CH463090A; AT310441B; SE312427B; FR1500417A

Description

April 2, 1968 C.J.OPEL ETAL CONTINUOUS CASTING PROCESS 4 Sheets-Sheet l Filed Sept. 28, 1965 5 u, i 5 m f MQW M Nf a E mf WA i MA ff w S am m April 2, 1968 C.J.OPE| ETAL CNTINUOUS CASTING PROCESS 4 Sheets-Sheet 2 Filed Sept. 28, 1965 April 2, 1968 c. J. OPEL ETAL CONTINUOUS CASTING PROCESS 4 Sheets-Sheet 4 Filed Sept. 28, 1965 mam i WW U 3,376,37l Patented Apr. 2, i968 3,376,371 CONTINUUUS CASTiNG PROCESS Charles J. Opel, Huntington Beach, and Paul H. Bottoms, Hollywood, Calif., assignors to Swedlow, Inc., Garden Grove, Calif., a corporation of California Filed Sept. 28, 1965, Ser. No. 490,945 10 Claims. (Cl. 264-216) The present invention relates to the continuous casting of polymeric compositions. There has been substantial interest in casting polymeric compositions for many years and many processes have been proposed and developed for such casting. Much of this development work has concerned the casting of acrylic and other polymerizable unsaturated organic materials. While the present invention is particularly applicable to the polymerization and casting of unsaturated compounds such as monomers, it is understood that it is applicable to a wide range of polymerizable materials such as pre-polymers and the like, all of which materials will be referred to in the specication and claims for convenience as monomers.

In general, the casting processes which have been previously developed comprise subjecting the polymerizable compositions to heat and/or light with or without the application of pressure. A highly successful and widely used process comprises casting liquid monomer between a pair of rigid sheets which sheets are provi-ded with a peripheral gasket of exible material to compensate for the shrinkage which occurs during polymerization, the assembly being immersed in a hot water bath or hot air oven for the length of time required to carry out the thermal polymerization. The hot water bath is, of course, the source of both heat and pressure. This process has come to be known as cell casting. Cell casting is, as is apparent from the foregoing description, a batch process and, although widely used, is subject to all of the deficiencies of any batch process, viz, a substantial amount of down time between casting operations, size limitations, quality control diiculties due to inadvertent changes in pressure, temperature and composition, etc.

Thus, there has long been substantial interest in the development of a continuous casting process, but, prior to the present invention, a commercially practicable continuous casting process has not been developed. In this regard, it should be pointed out that the diiculties involved in continuous casting become increasingly greater as the thickness of the cast sheet is increased.

One proposal with regard to continuous casting is that disclosed in United States Patent No. 2,500,728 wherein it is suggested that a pair of endless belts arranged such that they are vertically spaced from each other with the lower run of the upper belt and the upper run of the lower belt substantially parallel to each other might be used as a continuous casting apparatus. While this proposal appeared to have substantial possibilities from a theoretical standpoint, it was found that the apparatus specifically disclosed in Patent No. 2,500,728 was not suitable for commercial operation because of its short length and the extremely slow speed of travel required to bring the necessary polymerization -to completion such that a final continuous, rigid sheet would be formed. It was then, of course, proposed that an apparatus of the type disclosed in Patent No. 2,500,728 be produced in which the belts were of substantially greater length. However, when the apparatus was designed such that it would be suitable for commercial operation from a size standpoint, e.g., five feet wide and 100 feet long, it was found that the spacing between the belts could not be maintained if used in the manner described in Patent No. 2,500,728. This, of course, resulted in loss of control over the thickness of the final product and caused non-uniformity in this thickness. This problem was found to be particularly acute when stainless steel belts, which are preferred, were used. In general, this inability to maintain proper spacing between the moving belts results from the lack of support for the lower run of the upper belt which tends to bow downwardly toward the upper run of the lower belt.

The present invention obviates the foregoing and other diiiculties which have been inherent in the continuous casting processes previously proposed and makes possible, for the rst time, continuous casting of acrylic and other polymerizable monomers in a manner which is suitable for commercial use and which produces a product having acceptable characteristics.

It is a primary object of the present invention to provide a process for the continuous casting of polymerizable organic monomers wherein the liquid organic monomer is cast between a pair of moving endless belts which are so arranged and constructed that the spacing between them is controlled and maintained at a desired predetermined distance.

It is another object of the present invention to provide a process for continuous casting of acrylic and other polymerizable monomers comprising a pair of moving endless belts which are inclined in such a manner that the pressure of the materials between the belts is suflicient to maintain the spacing between them at a desired predetermined distance.

It is a further object of this invention to provide a process for continuous casting of acrylic and other polymerizable monomers which is suitable for commercial use.

`Other objects and advantages of the present invention, it is believed, will be apparent from the following detailed description of specific embodiments thereof.

Broadly, the apparatus used in the method of the present invention comprises a pair of endless belts mounted on rollers in such a manner that the lower run of the upper belt is substantially parallel to the upper run of the lower belt for a substantial portion of their lengths. These belts are arranged such that the lower run of the upper belt and the upper run of the lower belt are inclined at an angle to the horizontal. In operation, each of the belts is caused to move `around its supporting rollers such that ythe lower run of the upper belt and the upper run of the lower belt move in the same direction, and such that there is substantially no relative movement between the lower run of the upper ibelt and the upper run of the lower belt. Liquid polymerizable monomer is fed to the intake ends of these belts and is passed through at least one heating station. In the preferred embodiment of the process of the present invention, a liquid acrylic monomer composition is fed into l'the casting apparatus and is lirst heated -to a sufficient extent to cause the monomer to polymerize (or cure) and is then subjected to a further heating step to postcure the polymerized composition. The initial heating step may be performed by heating with hot air, by causing the moving belts to pass through a zone which is llooded with hot water or, preferably, may be accomplished Iby spraying hot Water on the external surface of the moving belts. In any event, the critical requirement of the apparatus and process of the present invention is that the angle of inclination to the hori zontal of the belts be such that a pressure head of the liquid monomer is developed which is suicient to maintain the spacing ybetween the bel-ts and the desired distance until the liquid has polymerized. As claimed herein, the inclined path of the moving belts may be a str-aight line or, as claimed in copending application Ser. No. 490,897, led on the same date as the present application in the name of Hellsund, and assigned to the assignee of the present application, these belts may follow a curved path which is defined by the natural curvature of the belts.

Referring now to the drawings, FIGURE la illustrates a portion of an embodiment of the present invention 3 wherein the path defined by the moving belts is the natural curvature of these belts.

FIGURE 1b illustrates the remainder of the apparatus illustrated in FIGURE la.

FIGURE 2 is a vertical cross-section taken on line 2-2 of FIGURE 1a which illustrates the spray means used as -a source of heating medium.

FIGURE 3 is a vertical crosssection taken on line 3-3 of FIGURE 2 which illustrates a -side view of the t spray means and moving belts.

FIGURE 4 is a ventical cross-section taken on line 4 4 of FIGURE lb and shows the moving belts passing through the postcuring oven.

FIGURE 5 is a vertical cross-section taken on line 5-5 of FIGURE 4 and illustrates a side view of the moving belt passing through the postcuring oven.

FIGURE 6 illustrates another embodiment of the present invention wherein the path of the moving belt is a straight line which is inclined to the horizontal.

FIGURE 7 is a vertical cross-section taken on line 7 7 of FIGURE 6 and illustrates the water looding heating means which may be used in the present invention.

As shown in FIGURE 1a and FIGURE lb, one embodiment of the apparatus used in the method of the present invention comprises an upper belt 11 which is positioned above a lower belt 12. Upper belt 11 is supported on rollers 13 and 14 while lower belt 12 is supponted on rollers 15, 16, 17. As is seen most clearly `in FIGURE la, lower belt 12 is somewhat longer than upper belt 11 so as to provide exposed area 18 which serves as a convenient means for feeding liquid monomer between rollers 13 and 16. Support posts 19' which are provided with rollers and rollers 21 provide additional support for the belts 11 and 12. Roller 14 is mounted on movable support 22 and support 22 is in turn connected to piston 23. Thus, the tension exerted by the rollers on belt 11 may be adjusted by actuating piston 23 so as to move support 22 and roller 14. Roller 15 is similarly mounted on movable support 24 which support is connected to piston 25 so that the tension exerted by the rollers on belt 12 may also be adjusted. Rollers 14 and 17 are driven by motor 26 .through chains 27 and 28.

Also illustrated in FIGURES la and lb are the housing 29 for the spray means which are used to provide lthe heat for polymerization of the monomer and housing 30 of the postcuring oven. These heating means are illustrated in more detail in FIGURES 2-5.

As shown in FIGUR-

ES

2 and 3, housing 29 encloses a series of spray means some of which are positioned above the lower run of the upper belt as indicated generally by numeral 31 and some of which are positioned below the upper run of the lower belt and are indicated generally by numeral 32. Preferably, -spray nozzles 33 are so constructed such that a square pattern is sprayed by each nozzle on belts 11 and 12 in the manner indicated by the broken lines emanating from each nozzle 33. Each of the nozzles 33 is mounted on one of pipes 34 and the pipes 34 are connected to conduits 35. Conduits 35 are connected to a source of hot water or other suitable liquid (not shown). As shown in FIGURE 2, housing 29 is provided with a supporting gusset 36. Gaskets 50 and y51 are also provided between belts 11 Aand 12 to prevent leakage of the polymerizable composition.

As further shown in FIGURES 2 and 3, a series of rollers 37 are provided above the lower run of belt 11 and a desired inclined path which is generally parallel to belt 12. Furthermore, since shrinkage generally occurs during polymerization, this shrinkage must be compensated for by causing belts 11 and 12 to assume a path which converges to the same extent as the decrease in thickness caused by polymerization shrinkage. Preferably, this may be accomplished by providing spring-loaded mountings for rollers 37, such as those shown in FIGURE 7 for rollers 77, or any other suitable means may be used such las adjustable mountings.

Rollers

37 and 38 are preferably arranged such that they form a square pattern, i.e., such that each roller is equidistant from its adjacent rollers in both the lateral and longitudinal direction.

Preferably, housing 29 is constructed in sections, two of which are indicated generally by

numerals

39 and 40 in FIGURE 3. Each of these sections is supported at one end by support member 19 and at the other end by support member 41 as seen most clearly in FIGURE la. As shown in FIGURE 3, the exit end of each section is provided t with wiper means 42 and 43 which substantially prevent the water or other liquid on the surfaces of belts 11 and 12 from leaving section 39.`

Refering now to FIGURES 4 and 5, We find the postcuring section which is surrounded by housing `30. AsA

shown in FIGURE 5, housing 30 is adjacent to the last section of housing 29 and wiper means 44 and `45 are provided to substantially prevent the water or other liquid on the surfaces of belts 11 and 12 from entering housing 1 30. A series of upper rollers 46 and a series of lower rollers 47 are also provided in housing 30 to supportfbelts 11 and 12 in much the sarne manner as

rollers

37 and 38 in housing 29. However,

rollers

46 and 47 are so arranged i that the belts 11 and 12 assume a converging path in order product. Preferably, rollers 46 are spring mounted in order to compensate yfor the shrinkage which might occur during post-curing. If the product shrinks away from the belts,

certain defects including surface irregularities will occur in the product. Preferably, rollers 46 are spring mounted in order to urge belt 11 toward Ibelt 12 and thereby compensate for the shrinkage. It is also preferred to provide

rollers

38 and 47 with fixed mountings. Housing 30 may might remain on the surface of belts 11 and 12 and may comprise any conventional means such as spray means, rotating brushes, solvent solution, etc. It is, of course, desirable to remove any deposits which may be present on the surfaces of belts 11 and 12 since such deposits would otherwise result in the formation of irregularities on the surface of the cast sheet.

Referring now to FIGURES 6 and 7, another embodiment of the present invention is illustrated in which endless belts 50 and 51 are arranged such that the path of the lower run of belt 50 and the upper lun of 51 is a substantially straight line which is inclined to the horizontal.

As shown in FIGURE 6, belt 50 is mounted on

rollers

52 and 53 while belt 51 is mounted on rollers 54 and 55. Roller 52 is preferably adjustably mounted as illustrated in FIGURE 6 such that screw 56 may be used to adjust the position of axle 57 in mounting 58 to thereby adjust the tension exerted by

rollers

52 and 53 on belt 50. Roller 54 is similarly preferably `adjustably mounted such that screw 59 `may be used to adjust the position of axle 60 in mounting 61 to adjust the tension exerted on belt 51. Rollers 53 and 55 are driven by motor 62 through chains 63 and 64.

It is to be understood that the spraying means illustrated in FIGURES 2 and 3 may be used with the embodiment of the present invention illustrated in FIGURE 6. However, for the purpose of completeness, a water flooding means which may be used as an alternative heating means is illustrated in FIGURES 6 and 7. This water flooding heating means comprises an upper water inlet pipe 65 which branches into feeder pipe 66 which feeder pipe in turn branches into a pair of delivery pipes 68. As shown in FIGURE 6, delivery pipes 68 deliver hot water to the inlet end of the upper portion of the heating means. Similarly, hot water is supplied to the inlet end of the lower portion of the water flooding means by pipe 70. Pipe 70 is surrounded by housing 72 which is provided with front and back walls 73 and 74. A slight clearance is maintained between belt 51 and the upper edges of Walls 73 and 74 such that the water in housing 72 may overiiow into drainage tank '75 and from tank 75 into pipe 76 which conveys the -water to a recirculating pump and heating unit (not shown).

Rollers 77 are provided above the lower run of belt 50 and rollers 78 are provided below the upper run of belt 51. As explained with regard to

rollers

37 and 38, rollers 77 function to support belt 51 while rollers 77 maintain belt 51 in the desired position and exert pressure on the material being cast. Rollers 77 are illustrated as being spring loaded in FIGURE 7 such that springs 79 urge these rollers toward belt 50. However, rollers 77 may also be provided with a fixed mounting.

A postcuring means which is indicated generally by numeral 80 is also illustrated in FIGURE 6. The postcuring means comprises a conventional forced air heating system. As in the case of

rollers

46 and 47, rollers 86 and 81 are mounted such that the shrinkage which occurs during postcuring is compensated for by causing the belts 50 and 51 to assume a converging path. Preferably, this is accomplished by providing rollers 86 with a spring loaded mounting while providing rollers 81 with a fixed mounting. IRollers 7 S are preferably provided with a fixed mounting as illustrated in FIGURE 7.

In order to prevent the escape of fluid materials froml between belts 50 and 51, a pair of gaskets 82 and 83 may be provided. Gaskets 82 and 83 may travel at substantially the same speed as belts 50 and 51 and thus provide a dynamic side seal for the material being cast.

The operation of the apparatus illustrated in FIG- URES 1-5 and the apparatus illustrated in FIGURES 6 and 7 are similar in many respects. In each case, a fluid composition comprising a polymerizable organic monomer is fed to the inlet end of the casting apparatus and is polymerized while being carried between the moving belts which are substantially parallel for a large portion of the time during which they are in contact with the composition being polymerized and cast. These belts have substantially no relative motion during the time they are in contact with the composition being polymerized and cast and are inclined at an angle to the horizontal. When the path of the moving belts is substantially a straight line as illustrated in FIGURE 6, this angle of inclination will depend upon the viscosity of the composition being polymerized, the polymerization conditions, the length of the belts and other factors. However, given the principles of the present invention, only routine experimentation is required to determine that angle of inclination which will be sufficient to maintain the desired spacing between the moving belts by means of the uid pressure being exerted by the material being polymerized. In general, it has been found that this angle may vary from about 0.5 to about 5.0.

When the embodiment illustrated in FIGURES la and 1b is used, the configuration of the curved path defined by the lower belt will be the natural sag or natural curvature of these belts. As used herein, natural curvature means that curvature which a given belt would assume when the ends thereof are supported at a given height under a given tension. It has been found preferable to calculate the natural curvature for a given tension and to arrange

support rollers

37 and 38 such that they assume the path of this natural curvature and then to hold the upper belt under greater tension than the given tension and the lower belt under less tension than the given tension such that the tension on the upper belt tends to` pull the lower run thereof against rollers 37 and the upper run of the lower belt can relax against rollers 38. Thus, in a preferred embodiment, the stainless steel belts which are held under a tension of about 5100 p.s.i. for the lower belt and 7000 p.s.i. for the upper belt, these being somewhat less than maximum tension, maximum tension being defined as the greatest tension to which the belts may be subjected without reaching the yield point. The concept of natural curvature and the methods of calculating this curvature are known to those skilled in the art and, as such, do not form a part of the present invention. For example, these considerations are discussed in The Sandvik Steel Band Conveyor Handbook published in 1956 by The Sandvik Steel Works Co. Ltd., which is incorporated by reference herein.

In a preferred embodiment, the curved incline of the belts extends over only a portion of their path between the rollers. Thus, as shown in FIGURE 1b, the path of the belts is substantially horizontal from a point shortly before they enter the postcuring unit housing 30 until they reach rollers 14 and 17 and the curved path extends between the last section of the housing 29 and rollers 13 and 16. The curved portion of this path is tangent to the horizontal portion and this relationship taken with the length of the path between rollers 13 and 16 and the horizontal portion plus the natural curvature of the belts under a given tension will determine the vertical distance above rollers 14 and 17 to which rollers 13 and 16 must be raised.

It is to be understood that the word inclined as used in the present specification and claims is intended to include straight, curved, angular or other paths which may be defined by a belt moving between a rst roller and a second roller wherein the Vfirst roller is at a height greater than that of the second roller.

The compositions which may be cast according to the present invention may be various types of liquids including monomeric compounds in the liquid state, preferably when at normal atmospheric pressure, partially polymerized monomeric compounds and solutions of soluble polymeric resins in monomeric compounds. In addition, pastes may be employed including mixtures of liquid monomeric and solid polymeric organic compounds which are at least partially soluble in the monomeric compounds.

Monomeric compounds which are in the liquid state at normal atmospheric pressure may contain one CH2=C group per molecule, eg., methyl rnethacrylate, butyl methacrylate, styrene and vinyl acetate, or more than one CH2=C group per molecule, eg., glycol dimethacrylate, allyl methacrylate, diallyl oxalate, etc. Monomeric compounds which contain more than one CII2=C group per molecule when polymerized alone, or in the presence of a compound containing more than one CH2=C group per molecule and which is not an overwhelmingly major component of the mixture, e.g., not more than about first form viscous liquids, then gels which have only a small solubility in monomers and then insoluble solid polymeric resins. Thus, not all partially polymerized or fully polymerized monomeric compounds are suitable for use in the present invention particularly when the monomers contain more than one CH2=C group per molecule.

The liquids and pastes used in the present invention may `contain plasticizers such as tricresyl phosphate or dibutyl phthalate; fillers such as iinely divided inorganic materials; reinforcing materials such as fabrics, glass fibers, wire, etc.; dyes and pigments, providing that these materials do not prevent the polymerization of the monomeric compounds contained in these mixtures. The monomeric material may also contain a parting agent to facilitate separation of the belts from the cast product and polymerization catalyst such as benzoyl peroxide or acetyl peroxide.

Patterned or contoured surfaces may be produced on the cast sheet by providing a matrix having a surface which is the negative of that desired on the surface of the cast sheet between one or both of the moving belts and the composition being cast. This matrix may be attached to the surface of the moving belt or may be mounted on separate rollers operated at such a speed so as to move the matrix material at substantially the same linear speed as that ofthe moving belts.

The present invention is further illustrated by the following examples in which all proportions are by weight.

Example I A viscous syrup comprising 98% methyl methacrylate, 0.5% laurcyl peroxide (catalyst), .000l% Zelec (parting agent), 0.5% ethylene glycol dimethacrylate and 0.05% Tinuvin P (ultraviolet absorber) is fed to the inlet end of an apparatus of the type illustrated in FIGURES 1a and lb. The length of the curved portion of the path of these belts is approximately 135 feet while the length of the horizontal portion of these belts is approximately 30 feet. The vertical distance between the top and bottom of the curved portion is 6 feet. The belts are 54 inches wide. The temperature in housing 29 is maintained at 160 F. by hot water spray means of the type illustrated in

FTGURES

2 and 3 and 'the temperature in housing 30 is maintained at 225 F. by electric heating means to postcure the cast sheet. The speed of the belts is 3 feet per minute. The belts are set 1A; inch apart to produce a cast sheet having a thickness of approximately Ms inch. These sheets are transparent, have extremely smooth surfaces, are free from internal voids or bubbles and are substantially free from internal strain.

The belts used were fabricated from `highly polished stainless steel.

Example -II the upper belt in such a manner as to maintain a constant spacing of 1/s inch between the belt. The monomeric material was first exposed to a temperature of 150 F. in the water flooding zone to cure the monomeric syrup and was then subjected to a temperature of 250 F. in the hot air oven to postcure the cast sheet.

It is to be expected that certain variations of the specific embodiments disclosed herein will `be devised by those skilled in the art. Thus, the present invention is of the scope of the appended claims.

We claim:

1. A process for preparing substantially rigid sheets and the like which comprises passing a tiuid composition comprising a polymerizable organic monomer between and in contact with two moving surfaces, providing a pair of seals between said surfaces such that said uid composition is confined in a space bounded on -two oppoing sides by said seals, allowing said uid to lill the cavity defined by said surfaces and said seals, passing said composition and moving surfaces through at least one zone in which said composition is subjected to conditions which cause said monomer to polymerize, one of said surfaces being disposed above the other of said surfaces in said zone, said upper surface being of such a size and weight that it would bow downwardly into said uid and toward said second surface if said surfaces were 8 horizontal in said zone, maintaining the path of said surfaces through said zone at anincline to the horizontal to cause a uid head to be developed by said fluid composition, said incline being sufficient for the fluid -pres sure between said surfaces to maintain said surfaces substantially parallel to each other and the spacing between said surfaces at a predetermined distance, bringing said surfaces together to an extent sufficient to compensate for i any shrinkage of the composition during polymerization such that said surfaces are maintained in contact with said lcomposition during polymerization, and removing the resultant polymerized sheet from both of said surfaces.

2. The process of claim 1 wherein said incline comprises a substantially straight line.

3. The process of claim 1 in which said monomer contains at least one CH2==C group.

4. The process of claim` 1 in which the moving surfaces are metal and the monomer is polymerized by heat.

5. The process of claim 4 in which said moving surfaces com-prise stainless steel.

6. The process of claim 1 in which said surfaces are heated by spraying hot liquid thereon.

7. The process of claim 1 wherein said surfaces are heated by applying hot liquid thereto.

8. The process of claim 1 wherein said polymerized` sheet is postcured by passing said sheet :through a postcuring oven before said sheet is removed from said surfaces.

9. The process of claim 1 wherein said fluid composition comprises an acrylic monomer.

10. A process for preparing substantially rigid` sheets and the like which comprises passing a fluid composition comprising a polymerizable organic monomer between and in contact with two moving surfaces, providing a pair of seals between said surfaces such that said fluid composition is confined in a space bounded on two opposing sidesby said seals, allowing said uid to fill the cavity de-` fined by said surfaces and said seals, passing said moving surfaces and said composition through a first heating zone, heating said monomer to an extent sufficient to cause polymerization thereof in said, first heating zone, one of said surfaces being disposed above the other of said surfaces in said zone, said `upper surface being of such a size and weight that it would bow downwardly into said uid and toward said second surface if said surfaces were horizontal in said zone, `maintaining the path of said surfaces through said first zone `being at an incline to the horizontal to cause a fluid head to be developed by said fluid composition, said incline being sufficient for the fluid pressure exerted by said fluid composition between said surfaces to maintain said surfaces substantially parallel to each other and the spacing between said sur-` faces at a predeterrnineddistance, passing said moving surfaces and composition through a second heating zone,

subjecting `said polymerized monomer ito heat to cause postcuring thereof in said second heating zone, bringing said moving surfaces closer together as they pass through said rst heating zone whereby shrinkage of said composition during polymerization is compensated for and said composition `is maintained in contact with both of said surfaces until polymerization and postcuring have been completed, and removing the resultant polymer-ized sheet from both of saidy surfaces.

References Cited UNITED STATES PATENTS ll/l960 `Hunt z 18--6 3/1950 Williams 264-22 ROBERT F. WHTTE, Primary Examiner.

Claims

1. A PROCESS FOR PREPARING SUBSTANTIALLY RIGID SHEETS AND THE LIKE COMPRISES PASSING A FLUID COMPOSITION COMPRISING A POLYMERIZABLE ORGANIC MONOMER BETWEEN AND IN CONTACT WITH TWO MOVING SURFACES, PROVIDING A PAIR OF SEALS BETWEEN SAID SURFACES SUCH THAT SAID FLUID COMPOSITION IN CONFINED IN A SPACE BOUNDED ON TWO OPPOING SIDES BY SAID SEALS, ASLLOWING SAID FLUID TO FILL THE CAVITY DEFINED BY SAID SURFACES AND SAID SEALS, PASSING SAID COMPOSITION AND MOVING SURFACES THROUGH AT LEAST ONE ZONE IN WHICH SAID COMPOSITION IS SUBJECTED TO CONDITIONS WHICH CAUSE SAID MONOMER TO POLYMERIZE, ONE OF SAID SURFACES BEING DISPOSED ABOVE THE OTHER OF SAID SURFACES IN SAID ZONE, SAID UPPER SURFACE BEING OF SUCH A SIZE AND WEIGHT THAT IT WOULD BOW DOWNWARDLY INTO SAID FLUID AND TOWARD SAID SECOND SURFACE IF SAID SURFACES WERE HORIZONTAL IN SAID ZONE, MAINTINING THE PATH OF SAID SURFACES THROUGH SAID ZONE AT AN INCLINE TO THE HORIZONTAL TO CAUSE A FLUID HEAD TO BE DEVELOPED BY SAID FLUID COMPOSITION, SAID INCLINE BEING SUFFICIENT FOR THE FLUID PRESSURE BETWEEN SAID SURFACES TO MAINTAIN SAID SURFACES SUBSTANTIALLY PARALLEL TO EACH OTHER AND THE SPACING BETWEEN SAID SURFACES AT A PREDETERMINED DISTANCE, BRINGING SAID SURFACES TOGETHER TO AN EXTENT SUFFICIENT TO COMPENSATE FOR ANY SHRINKAGE OF THE COMPOSITION DURING POLYMERIZATION SUCH THAT SAID SURFACES ARE MAINTAINED IN CONTACT WITH SAID COMPOSITION DURING POLYMERIZATION, AND REMOVING THE RESULTANT POLYMERIZED SHEET FROM BOTH OF SAID SURFACES.