US3642975A

US3642975A - Process for forming a stress-free article containing a depression from a polymer

Info

Publication number: US3642975A
Application number: US840317A
Authority: US
Inventors: Ray B Duggins; Robert J Gross
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1969-07-09
Filing date: 1969-07-09
Publication date: 1972-02-15
Anticipated expiration: 1989-02-15
Also published as: CA917868A

Abstract

A PROCESS FOR FORMING A STRESS-FREE ARTICLE, CONTAINING A DEPRESSION, FROM POLYMER THAT SHRINKS UPON POLYMERIZATION, WHICH COMPRISES: FORMING A MIXTURE FROM TEH POLYMER AND AN INERT FILLER; DEPOSITION THE MIXTURE ONTO A FIRST CASTING SURFACE HAVING A DEFORMABLE PORTION; POSITIONING A SECOND CASTING SURFACE, CONTAINING A CONCAVITY, ABOVE THE FIRST CASTING SURFACE; APPLYING A FORCE TO DEFORM THE DEFORMABLE PORTION OF SAID FIRST CASTING SURFACE TOWARDS THE CONCAVITY WHILE THE MIXTURE IS STILL IN A LIQUID STATE; HARDEING THE MIXTURE; AND DURING HARDENING CAUSING THE DEFORMABLE PORTION OF THE FIRST CASTING SURFACE TO COLLAPSE BY JUST ENOUGH TO ALLOW THE MIXTURE TO HARDEN AND SHRINK FREELY WITHOUT STRAINING TO OVERCOME THE APPLIED FORCE. A STRUCTURE WITH A CONSISTENT SURFACE PATTERN CAN BE FORMED USING THE ABOVE PROCESS, AS CAN A COMPLETELY FORMED LAVATORY UNIT IF THE CONCAVITY SUPPORTS A PROPERTY POSITIONED DEGRADABLE DRAIN CORE THAT CAN BE DISSOLVED AFTER THE MIXTURE HAS HARDENED.

Description

Feb. 15, 1972 R. B; nussms ETAL 3,642,75

PRQCESS FOR FORMING A STRESS-FREE ARTICLE CONTAINING A DEPRESSION FROM A POLYMER Filed July 9, 1969 INVENTORS RAY B. DUGGINS ROBERT J. GROSS AGENT United States Patent US. Cl. 264-314 38 Claims ABSTRACT OF THE DISCLOSURE A process for forming a stress-free article, containing a depression, from a polymer that shrinks upon polymerization, which comprises: forming a mixture from the polymer and an inert filler; depositing the mixture onto a first casting surface having a deformable portion; positioning a second casting surface, containing a concavity, above the first casting surface; applying a force to deform the deformable portion of said first casting surface towards the concavity while the mixture is still in a liquid state; hardening the mixture; and, during hardening, causing the deformable portion of the first casting surface to collapse by just enough to allow the mixture to harden and shrink freely without straining to overcome the applied force. A structure with a consistent surface pattern can be formed using the above process, as can a completely formed lavatory unit if the concavity supports a properly positioned degradable drain core that can be dissolved after the mixture has hardened.

BACKGROUND OF INVENTION This invention relates to a process for forming a stressfree article, containing a depression from a polymer. More particularly it relates to a process for forming a stressfree article, containing a depression, from a polymer that shrinks upon polymerization. Still more particularly it relates to a process for forming a stress-free article, containing a depression, from a mixture comprising a polymer and an inert filler. The process is particularly useful in the formation of a stress-free article, containing a depression, and having a consistent pattern over one entire surface. It is also particularly useful in the formation of a completely formed lavatory unit, with drain structure included, from a polymer that shrinks upon polymerization.

Casting sheet-like structures from thermoplastics is an old art. There are still a number of problems to be solved, however, especially when the structure so cast contains a depression or deformation. The main problem is simply to find a workable process for forming a sheet-like structure containing a deformation from a thermoplastic that shrinks upon polymerization. The simplest process for forming such a structure, that of casting the structure in a solid mold, is completely ineffective. A rigid casting frame will not allow the structure to shrink during polymerization, and as a consequence, it is virtually impossible to form a structure in this manner that doesnt contain stress cracks formed as the structure strains to accommodate the stress produced during polymerization. Even if a structure can beformed without visible stress cracks, the structure so formed will usually be extremely brittle so that a slight blow will cause it to crack. In addition, the structure so formed is usually highly unstable to temperature variations. A hot object, such as a match, placed on the structure will cause the stressed polymer chains within it to relax, producing a distortion or even a hole in What had appeared to be a stable surface. To circumvent these problems, practitioners of the art usually dilute the polymer with inert fillers which tend to inhibit shrinkage of the structure as it hardens. The difliculty with this solution is that massive loading of the polymer with inert fillers, usually at or above by weight, is necessary before shrinkage of the structure can be appreciably decreased.

Another method that has been widely used is to cast a flat structure, allow it to harden completely or at least to a semi-hard or gel state, and then to heat the structure and deform it while warm. This process also produces a structure in which the polymer chains are highly stressed so that most of the problems inherent in the method previously discussed are inherent in this method. With care, however, a mechanically stable structure can be produced, but the structure so formed is not thermally stable. Upon reheating it, has a tendency to return to its original state, that of a fiat structure without a depression.

The next problem to be solved is to produce a sheet-like structure from a pigmented or patterned polymer without visible stress lines or appreciable deformation of the pattern. If the polymer is merely poured into a mold cavity, through a pour hole, it is virtually impossible to preserve any pattern present in the mixture. If the polymer containing the pattern is carefully applied to a casting surface that already contains the desired deformation, a process illustrated by US. Pat. No. 3,433,860 issued to Ruggles et al., there will still be visible variations in the pattern because the resultant force exerted on the mixture as it is applied to the surface contains a horizontal component which tends to accentuate any distortion of the pattern caused by the mere deposition of the mixture on an uneven surface. The process that produces the least distortion in pattern is the process, described above, which consists of depositing the mixture on a flat surface, letting it harden and then deforming it. With this process the pattern is only deformed by as much as the article itself is deformed, which is less than the distortion produced by the above procedures, but even this process suffers from a defect. Aside from its thermal instability, an article produced by such a process still contains regions of high stress which Will affect its local coloration. If there is any pigmentation in the structure at all, that pigmentation will appear different in areas of different stress.

Finally, when the structure is intended for use as a lavatory fixture, there is the problem of producing a completely formed lavatory unit, with drainage structure included, in a single casting so that difficult and time consuming alterations to the structure as formed are not needed. The prior art, represented again by the Ruggles patent, accomplishes this by casting a first layer of material, inserting a drain tube, then casting a second layer of material, and finally drilling into the drain tube after the structure has hardened. At best this is a time consuming multistage process.

It is an object of the present invention to provide an improved process for forming a stress-free article, containing a depression, from a material comprising a polymer that shrinks upon polymerization and optionally a small amount of inert filler. It is a further object of the present invention to provide an improved process for forming a stress-free article, containing a depression, which has a consistent surface pattern, from a material comprising a polymer that shrinks upon polymerization. It is a still further object of the present invention to provide an improved process for forming a stress-free article, containing a depression with a well defined contour, from a material that shrinks upon polymerization. It is a still further object of the present invention to provide an improved process for forming a complete lavatory unit, including all necessary drainage and overflow openings, from a material that shrinks upon polymerization. Other objects of the present invention will appear herein.

SUMMARY OF THE INVENTION These objects are accomplished by the process which comprises the steps of: forming a mixture from the polymerizable material and optionally an inert filler; depositing the mixture on a first casting surface, having a deformable portion in the region of the desired depression; positioning above the mixture a second casting surface having a concavity directed away from the mixture; applying a force to the deformable portion of the first casting surface, while the mixture is still in a liquid state; hardening the mixture; and during the hardening, causing or allowing the deformable portion of the first casting surface to collapse just enough to allow the mixture to shrink freely without straining the polymer chains within it. By deforming the mixture while it is still in its liquid state, before substantial polymerization has occurred, the problem of straining bonds that have already been formed is avoided. By using a deformable portion of the casting surface to form the depression and by deforming that deformable portion of the casting surface with a deformation means and adapted to cause or allow that deformed portion to collapse in response to any increased force exerted on it during polymerization, the bonds that are formed during polymerization will not be strained, substantially, as the structure shrinks. The prior art is replete with examples of structures that are formed from sheetlike structures after polymerization has occurred, or after polymerization has proceeded to the stage where substantial hardening has occurred. The prior art also contains examples of articles formed from thermoplastics while the thermoplastic is in a liquid state, but these structures are either heavily loaded with filler to decrease shrinkage, or reinforced with web-like materials to prevent cracking of the structure upon hardening; this latter technique being illustrated by US. Pat. No. 3,140,325 issued to R. Graff. The present invention is directed to the production of a substantially stress-free deformed structure, without the heavy filler loading or reinforcement required by the prior art.

If the mixture is pigmented or contains a predetermined pattern, then, in order to form the above-mentioned structure in a manner such as to insure a consistent surface pattern, the mixture is first deposited on a substantially flat substantially horizontal casting surftce so that the desired pattern is present on the surface of the mixture in contact with the casting surface prior to deformation. When deformation occurs the pattern is distorted just enough to accommodate the deformation of the surface; the shear forces between the mixture and the casting surface being large enough that the surface of the mixture will not flow causing further distortion of the pattern. Flow changes may occur in the body of the mixture, but at the surface of the casting plate, the mixture and the pattern it contains can be thought of as being locked to the casting surface as soon as the two come into contact. It is essential that the mixture be laid down on a substantially flat substantially horizontal surface, otherwise there will be a horizontal component of force exerted on the mixture as it is deposited, and a consistent pattern cannot be formed in the first place; as is the case when the mixture is deposited on a casting surface already deformed to the desired shape. Some distortion will occur, but by the practice of the present invention, distortion is minimized.

The formation of a completely formed lavatory fixture illustrates one important use of the process described above. For this process, prior to the positioning of a second casting surface, containing a concavity defining the limits of the deformation over the mixture, the second casting surface is prepared by forming a drain hole in the apex of the concavity and by positioning a drain structure, in the form of the desired drainage openings, on the inside of the concavity. This drain structure is made from a material that can be degraded at Will. When deformation occurs, the mixture envelopes the drain structure and,

after the mixture hardens, the drain structure is degraded and removed from the structure so that the article so formed contains drain and overflow openings and a channel connecting the two, all completely formed into the structure. The present invention, therefore, provides a process by which an entire lavatory unit can be formed in one casting step.

The versatility and further advantages of the present invention can better be understood by considering the use of the present invention in producing a fully formed lavatory unit and by reference to the following figures wherein:

FIG. 1 is a cross-sectional view of a schematic diagram of one embodiment of an apparatus, which can be used in the process of the present invention, just prior to positioning of the second casting surface over the mixture;

FIG. 2 is a cross-sectional view of a schematic diagram of the same apparatus as that shown in FIG. 1 after deformation has occurred;

FIG. 3 is a diagram of one possible drain structure that can be used in the production of lavatory fixtures by the process of the present invention;

FIG. 4 is an enlarged cross-sectional view of a portion of the apparatus illustrated in FIGS. 1 and 2, illustrating the use of a vacuum and a film liner to control the contours of the depression formed by the process of the present invention; and

FIG. 5 is a partial cross-sectional diagram of one embodiment of a deformation means for use in the process of the present invention.

DETAILED DESCRIPTION OF DRAWINGS In FIG. 1, the mixture 11 from which the article is to be made, is deposited onto a first casting surface 12. As illustrated, this first casting surface 12 comprises a fiat support structure 13 with an opening 14 in its center, a thin stretchable film 15 covering the entire support surface, and a ridge 16 at least partially defining the edges of the article and extending above the first support surface to a height which defines the thickness of the mixture deposited on the first casting surface. A deformable diaphragm 17 is attached to support structure 13, covering opening 14. A pressure chamber 18 with a port 19 surrounds diaphragm 17, in a manner such that an increase in pressure within the pressure chamber will deform diaphragm 17 towards the mixture.

The mixture from which the article is made, normally comprises a polymerizable mixture and an inert filler. Any polymerizable mixture can be used, but the process is particularly useful for polymerizable materials that shrink as they polymerize. Polymerizable mixtures containing monomers selected from the group consisting of esters, acrylics, lactams, epoxies and isocyanates are examples of the type of material that can be used. The addition of inert fillers to the material decreases the amount of shrinkage that occurs in the article when the material polymerizes. The process is perhaps most useful when no filler is used because this is the condition under which most shrinkage occurs. The process will work when the mixture contains no filler as long as the deformation means designed to respond to the shrinking of the article is elastic enough to respond to the large changes that will occur. Normally, however, some filler is included to reduce shrinkage and to give some character to the surface of the casting. The present process has been demonstrated at filler levels as low as 40% by weight. The process has not been tested at lower filler levels, not because of any expected difficulty, but because the product of interest has more character and appears more attractive when the amount of filler used is above this value. Prior art deals primarily with heavy loading, above by weight, because at this high loading shrinkage, and the problems caused by it, are minimized. While the present process can also be used when the polymer has been loaded with above 85% by weight of filler, it is most useful at those lower loadings where substantial shrinkage does occur.

The filler used can be any inert filler, which for the purpose of two invention is any filler that does not inhibit the polymerization. Inorganic materials such as calcium carbonate, calcium. sulfate, clay, silica, calcium silicate, alumina, aluminum silicate, granite, titanium dioxide and portland cement are illustrative of the type of filler that can be used. In addition to these inorganic fillers any inert organic filler such as textile fibers, feathers, etc. can be used; these usually for their decorative effect. The shape of the filler is not critical; fibers, chunks, crystals, and the like, all can be employed as long as the materials can be homogeneously mixed. In some cases the fillers are used only for surface effect and are, therefore, contained only on the surface of the mixture so that the mixture is not strictly speaking homogeneous. Such surface anomalies can be tolerated, but for best results the mixture should be as homogeneous as possi- H ble so that hardening takes place uniformly.

While the process of the present invention can be used to produce perfectly white, unpigmented or unpatterned structure, it is particularly useful in the production of articles with some pigmentation or surface pattern. This includes those cases where there is a visible filler content. The reason for this is the fact that when deformation occurs after some hardening of the mixture has occurred, stress lines are visible in all but completely unpigmented articles. This effect is, of course, best visualized in the case of an article which ha a surface pattern, as discussed below, but it is also visible when the mixture is merely pigmented, because a stretching of the hardened materials acts to decrease the pigment concentration in the highly stressed areas of the structure. The same result occurs when a filler such as calcium carbonate is used at a level that is visible.

The advantages of the present invention in the production of pigmented or patterned articles can be illustrated by considering the production of simulated marble articles. There are a number of ways in which the mixture for such an article can be prepared, the details of which will not be discussed here. Suffice it to say that in the most general situation, one material, which is the major constituent and is either pigmented or unpigmented, is mixed with another material of different pigmentation, so that a visible pattern of the second material appears in the first material. Both materials can be identical, except for pigmentation, or different; and either or both materials can be mixtures of polymer and inert filler, as discussed above. Usually if differently pigmented mixtures of polymer and inert filler are used, the initial mixtures are formed in a high speed mixer, and the mixing of the differently pigmented mixtures to form the simulated marble is accomplished in a low speed mixer. In this illustration, the marble pattern exists throughout the mixture, making the structure as homogeneous as possible under the circumstances, but it must be realized that surface pigmentation is also possible. The marbelized mixture, so formed, is deposited directly on a flat casting surface, so that the desired pattern is placed in direct contact with the casting surface. When deformation of the casting surface occurs, changes in the orientation of the pattern within the body of the mixture will occur causing an exaggeration of the distortion, but at the interface between the mixture and the casting surface substantially no change in the pattern occur. The mixture is deformed while it is still in a liquid state, so that flow of the differently pigmented portions relative to one another is to be expected. The reason that it does not occur at the interface is due to the fact that between the mixture and the casting surface the shear force necessary to distort the pattern at this interface is so great that no relative movement of the material occurs other than that caused by the deformation itself. It might be said that the pattern is locked to the surface by its contact with the surface, so that deformation of the casting surface will change the pattern only to the extent that the casting surface itself is deformed. The same result would, of course, occur if deformation occurred after the mixture had hardened and the pattern was completely stabilized, but as indicated above, such a procedure produces a highly stressed structure which exhibits its own pigmentation difficulties.

The fact that the patterned mixture is deposited on a flat casting surface which is later deformed rather than a casting surface which has already been deformed is important. If the casting surface has already been deformed, as the mixture is being deposited on the surface it has a tendency torun down the surface distorting the pattern before it becomes locked to the surface. If a very viscous material were being deposited on the deformed casting surface, it is conceivable that the pattern achieved by this process would 'be the same as the pattern achieved by later deforming a flat surface, but when the mixture is in the liquid state enough flow occurs, as the mixture is deposited, to cause a visible distortion in the pattern which is greater than the distortion which occurs when the surface itself is later distorted. In part this can be understood by realizing that when the casting surface is flat, the resulting force which the casting surface exerts on the mixture as it is deposited on the casting surface is a vertical force. When there is a deformation, the resulting force has a vertical component and a horizontal component. The horizontal component causes the additional distortion of the surface. The same would, of course, be true if the flat surface were tilted at an angle from the horizontal, so that for best results the first casting surface should be substantially horizontal, as well as substantially flat.

The process of the present invention is useful regardless of the length of time over which polymerization occurs. The more rapid the polymerization, however, the more efficient the process. For this reason, the rapid polymerization mixtures described in U.'S. Pat. No. 3,405,088, issued to Slocum, and in copending U.'S. application Ser. No. 838,688, filed on July 2, 1969 by R. B. Duggins and assigned to the assignee of the present application are most useful. The mixtures described in Slocum comprise: a sirup containing 10-35% by weight of methyl methacrylate polymer, selected from the group consisting of methyl methacrylate homopolymers and copolymers of methyl methacrylate with a,B-ethylenically unsaturated compounds in which the copolymers contain more than 50% methyl methacrylate and in which the polymer has an inherent viscosity of 0.25-l.0 in monomeric methyl methacrylate; 40-85% by weight of inert additives, such as the inert additives discussed above; and 0.2-6% by weight of a peroxy compound, preferably a hemiperester of maleic acid or a metal salt thereof, having the formula when R is a saturated tertiary alkyl radical. This mixture polymerizes in a few hours. The improvement described in Duggins reduces the polymerization time to between 15 and 30 minutes, and comprises the addition to the above mixture of between 0.05 to 5 parts per hundred, based on the Weight of the syrup, of a solvent for the peroxy compound. This solvent is defined as a fluid in which the peroxy compound is substantially completely soluble, at a temperature of F. and which is inert to the reactants. Water is a preferred solvent. Other such solvents would be methyl alcohol, ethyl alcohol, glycerol and in general alcohols, diols and triols having 1 to 6 carbon atoms.

Having deposited one of the mixtures described above on the first casting surface, a second casting surface 20, having a flat portion 21 and a concavity 22 extending away from the mixture, is prepared and positioned over the mixture. Normally, it is supported on the ridge 16 which is part of the first casting surface. This second casting surface can be made from any rigid material, but Teflon fluorocarbon is a particularly useful material because of its nonstick properties. In this particular example the article being formed is a vanity top with a sink integrally formed into it, so the second casting surface must be prepared by fitting it with a drain structure 23. This drain structure is illustrated in detail in FIG. 3 and shown in position within the concavity in FIG. 1. The drain structure comprises a drain plug 24 which is in the general shape of the desired drain hole, a connecting portion 25 which connects the drain plug 24 to a single or a series of overflow plugs 26 which will be used to form the overflow openings in the sink. The structure is positioned within the concavity of the first casting surface by inserting the drain plug 24 into an opening which has been formed in the apex of the concavity, and securing it there by some means 27. Means 27 can be adapted merely to retain the core in the concavity, or it can be further adapted to define the actual dimensions of the drain core. As such it can be made from wax, plastic, metal or any other suitable material. The connecting portion 23 is shaped so that it will fit near the surface of the concavity as shown, but it is displaced from the concavity so that it can be enveloped by the mixture.

The whole drain structure 23 is made from a material which can be caused to degrade, either thermally, chemically or by some other means. One such structure is made by casting drain structure 23 from polystyrene foam and then coating the polystyrene foam with a thin coating of wax. Polystyrene foam will dissolve in the monomer of methyl methacrylatc, so that if the mixture from which the article is to be made contains methyl methacrylate, the wax coating will protect the core only until the heat of polymerization increases to the point where the wax melts, at which point the monomer vapor will dissolve the polystyrene foam and the whole drain structure 23 will dissolve. So long as enough polymerization has occurred so that the mixture does not flow into the region previously occupied by the drain structure, when the structure has finally hardened, there will be a drain hole in the region previously occupied by drain plug 24, overflow openings in the region previously occupied by overflow plugs 26 and an overflow channel connecting the drain hole and overflow openings in the region previously occupied by connecting portion 25. The particular drain structure described above is useful when the mixture contains the monomer of methyl methacrylate, but any drain structure which will degrade or dissolve by the addition of heat, chemicals or some other process can be used as the circumstances demand.

The second casting surface 20 is disposed above the first casting surface 12 so that concavity 22 is just above opening 14. The diameter of the concavity at its largest portion should be greater than the diameter of the opening and the concavity should be positioned so that the projection of the perimeter of the concavity on the first casting surface will completely enclose the perimeter of the deformable portion of said first casting surface. Under these conditions, when the deformable portion of the first casting surface is deformed towards the concavity there will be a separation between that deformed portion of the first casting surface and the concavity, providing a thickness to the article at that point which is about equal to the average thickness of the rest of the article. The actual difference in diameter is not critical, but it should be large enough to impart a reasonable thickness to the bowl. Actually the concavity and hole need not be circular. Oval shapes, or practically any smoothly varying shape will suflice. Even sharp edged openings such as one in the shape of a star or a rectangle can be used.

As illustrated in FIG. 2, diaphragm 17 is forced upward into the concavity, forcing the stretchable film 15 to deform with it. Actually both the diaphragm and the film together are not necessary. The film itself, will suflice. The force exerted to deform the diaphragm in the case illustrated will then be exerted on the film alone to achieve the same result. Likewise, film 15 is not really necessary. If opening 14 is filled with diaphragm 17 in a manner such that the upper surface of the structure formed by support structure 13 and diaphragm 17 is reasonably continuous and flat, it will form the flat casting surface itself. In the situation illustrated in the figures, however, it is the film 15 that is the actual deformable portion of the casting surface, and to cause the deformation, diaphragm 17 must coact with it. The film provides a good fiat surface and also provides a way to release the hardened article from the support structure. For this reason, a second film, not shown, is often provided on top of the mixture between the mixture and the second casting surface.

Diaphragm 17 is forced upward until it touches the bottom of drain plug 24 and the projecting points of plugs 26. The liquid mixture flows to fill the region between the two casting surfaces, as illustrated. So that there is no empty space left at the top of the concavity, the volume of the region between the concavity and the deformable portion of the first casting surface should be approximately equal to the volume of the mixture over opening 14; otherwise, either too much or too little of the mixture will be available to fill the space. An air hole, not shown, is provided either in drain plug 24, or around it, so that air will not be trapped in the region between the concavity and the deformable portion of the first casting surface. This hole allows the mixture to displace the air and completely fill the region of the depression. In some cases, when the amount of mixture present is not enough to accomplish this, the structure can be topped off by adding more material at the top through the air hole, to fill the space between the concavity and the deformable portion of the first casting surface.

As it flows, the mixture will completely envelop the drain structure 23 except at those places, specifically at the extremities of the drain plug 24 and the plug 26, when the drain structure 23 contacts either the concavity or the deformable portion of the first casting surface.

The force to deform the deformable portion of the first casting surface can be supplied in a number of ways. The only criterion is that the deformation means for exerting the force must be adapted so that as the mixture hardens and shrinks in the process, the deformable portion of the first casting surface will be caused or allowed to collapse so that said polymerizable material under-goes substantially unrestrained shrinkage. As illustrated, in FIGS. 1 and 2 the force is applied by building up the pressure in chamber 18. This is accomplished by introducing a fluid, usually air under pressure, into the chamber through opening 19. The increased pressure deforms the diaphragm 17, which is made from some deformable material such as neoprene, which in turn deforms film 15, until the proper shape is achieved. At this point the chamber is sealed off and the pressure within it remains constant. As the material begins to harden and shrink it will increase the downward force on the diaphragm and tend to cause the diaphragm to retract, causing the pressure inside the chamber to increase to the point when it can withstand the force created by the shrinking mixture. The system can be designed so that the pressure, both before and after it changes, is suflicient to maintain the deformation over the force of gravity but not enough to keep the diaphragm from responding freely to the force developed as the mixture hardens. If the pressure is too high to react properly to the shrinking polymer, which might happen if the diaphragm is too stiff to deform easily, then the pressure inside the chamber may have to be relieved, from time to time during hardening or in some systematic way, to allow the diaphragm to collapse in response to the increasing force.

Film which covers the support structure can be made from any material which will stretch under a reasonable force. A thin film of polyvinyl alcohol is a suitable film. If the only force that acts on the film is the force exerted by the diaphragm, the resulting structure will have a very thin wall at the base of the concavity. The film will not adhere to the diaphragm so that there will be a region in which the film pulls away from the support structure and the diaphragm, in a way which affects the contour of the depression. This can best be seen by reference to FIG. 4 where the dotted lines illustrate the configuration that film 15 would normally assume in relation to diaphragm 17. The separation between film 15 and the concavity narrows at the point Where the concavity flares away from the flat portion of the second casting surface 20. so that the whole structure is weakened at that point. To avert this, and in a larger sense, to gain some control over the shape of the depression (bowl) at the point where it flares away from fiat portion (top) in the finished structure, the support structure 13 is provided with a series of channels leading to vacuum ports 31 located all around opening 14. By applying a vacuum in the region between the film and the support structure, the film can be pulled down into a configuration, such as the one illustrated by the solid lines 15, or any other desired configuration.

If fluid pressure is used to deform diaphragm 17, then the diaphragm itself can be designed so as to impart various designs to the inner surface of the depression in the finished article. For example a flared contour for the bowl can be achieved by using a diaphragm shaped like an inflated parachute or one that is reinforced in various regions so that when it is inflated it will take on the appearance of an inflated parachute. Various other designs, or surface depressions can be used, either with or without the use of the film as discussed above. Since these variations are limited only by the imagination of the designer no further discussion of them will be pursued.

Another means for deforming the diaphragm is illustrated in FIG. 5. Here a solid plug 35 raised either mechanically or pneumatically is used to form diaphragm 17. To allow retraction of the diaphragm as the mixture hardens, the plug is spring loaded with spring 36 so that as the force exerted by the hardening mixture increases the plug will retract. To insure that the diaphragm conforms to the contours of the plug, the plug contains a vacuum chamber connected to number of vacuum ports 38 on the surface of the plug. A vacuum applied through these ports, to the diaphragm, insures that the diaphragm will conform to the contours of the plug. Alternately, the plug itself could be made from a deformable material which would respond to the increased force by collapsing under it.

The two deforming means discussed above are merely illustrative. Any other means that will allow the deformable portion of the first casting surface to collapse under the increasing force of the shrinking polymer can be used.

After the mixture has hardened the structure is cooled and removed from the mold. The degradable core is de graded and removed from the structure, unless this has already occurred automatically as described above. The resulting structure is a completely formed vanity top and bowl which needs little if any finishing to remove rough edges.

The process for forming the vanity top and bowl discussed above is a very specialized process. Depending on the circumstances, simpler or more complicated structures can be formed in the same way. For example instead of using the two distinctly different casting surfaces described above, two identical casting surfaces, each with a deformable portion, can be used. The mixture is placed on one and covered by the other in a manner such that one deformable portion is directly over the other. Then one or the other of the two deformable surfaces is deformed toward the other, either up or down, by any of the methods described above. Deformation of one coacts with the mixture to deform the other, and a depression is formed in an essentially flat structure by again allowing the mixture to harden and, as the mixture shrinks, causing or allowing the deformable portion of the casting surface that was directly deformed to collapse under the increasing force. Care must be exercised in the use of this process so that the structure so formed will be formed without a thin spot at its center due to the tendency of the diaphragms to come together at that spot. This is done by designing the two deformable portions of the casting plates so that they will preferentially draw to the desired shape and so that the article thickness will be maintained reasonably constant. One way to accomplish this is to use diaphragms reinforced in the appropriate areas.

The above discussion describes the manufacture of a simple depression and of a more complicated vanity top and bowl. Other structures of varying simplicity can also be produced using the above technique.

What is claimed is:

1. A process for forming a substantially stress-free article containing a depression from a polymerizable material, which comprises:

(a) depositing said polymerizable material onto a substantially flat first casting surface, said first casting surface having a deformable portion;

(b) positioning a second casting surface above said polymerizable material, said second casting surface having a concavity directed away from said polymerizable material, said concavity being disposed above the deformable portion of said first casting surface in a manner such that the projection of its perimeter on said first casting surface completely encloses the perimeter of the deformable portion of said first casting surface;

(c) applying a force to the deformable portion of said first casting surface, while said polymerizable material is still in a liquid state, said force being sufficient to deform the deformable portion of said first casting surface until said polymerizable material fills the region between said first and second casting surfaces, said force being applied by a deformation means adapted to allow said polymerizable material to undergo substantially unrestrained shrinkage;

(d) polymerizing said polymerizable material; and

(e) during the polymerization, collapsing the deformable portion of said first casting surface in a manner such that said polymerizable material undergoes substantially unrestrained shrinkage, whereby said polymerizable material hardens into a substantially stress-free article.

2. A process for forming a substantially stress-free article, containing a depression, from a polymerizable material that shrinks upon polymerization, which comprises:

(a) forming a mixture comprising said polymerizable material and an inert filler;

(b) depositing said mixture onto a substantially flat first casting surface, said first casting surface having a deformable portion;

(c) positioning a second casting surface above said mixture, said second casting surface having a concavity, directed away from said mixture, said concavity being disposed above the deformable portion of said first casting surface in a manner such that the projection of its perimeter on said first casting surface completely encloses the deformable portion of said first casting surface;

(d) applying a force to the deformable portion of said first casting surface while said mixture is still in a liquid state, said force being sufficient to deform the deformable portion of said first casting surface until said mixture substantially fills the region between said first and second casting surfaces, said force being applied by a deformation means adapted to allow said polymerizable material to undergo substantially unrestrained shrinkage;

(e) polymerizing said polymerizable material; and

(f) during the polymerization, collapsing the deformable portion of said first casting surface in a manner such that the polymerizable material undergoes substantially unrestrained shrinkage, whereby said mixture hardens into a substantially stress-free article.

3. The process of claim 2 wherein said mixture comprises less than 85% by weight of an inert filler.

4. The process of claim 2 wherein said mixture comprises between 40 and 85% by weight of an inert filler.

5. The process of claim 4 wherein said polymerizable material comprises monomers selected from the group consisting of esters, acrylics, lactam-s, epoxies and isocyanates.

6. The process of claim 4 wherein said inert filler is an inert filler chosen from the group consisting of: calcium carbonate, calcium sulfate, silica, calcium silicate, alumina, aluminum silicate, and titanium dioxide.

7. The process of claim 4 wherein the step of depositing said mixture onto a substantially flat first casting surface comprises: first preparing a substantially flat first casting surface by laying a stretchable film on top of a substantially fiat support structure, said substantially flat support structure having an opening in the region of the desired depression; and then depositing said mixture onto said substantially fiat first casting surface, whereby said stretchable film constitutes the deformable portion of said first casting surface.

8. The process of claim 7 further comprising the steps of: applying a vacuum between said fiat support structure and said film in the region of the periphery of said opening and varying the vacuum applied, as the deformable portion of said first casting surface is deformed, to control the radius of curvature of the deformable portion of said first casting surface at the point where it joins the nondeformable portion of said first casting surface.

9. The process of claim 4 wherein the step of applying a force to the deformable portion of said first casting surface is accomplished by applying an increasing fluid pressure to the deformable portion of said first casting surface, inflating it until said mixture substantially fills the region between said first and second casting surfaces, and maintaining the pressure substantially contant, whereby the de formable portion of said first casting surface automatically responds to the increased forces exterted on it by shrinkage of the polymerizing material by deflating until those forces are dissipated.

10. The process of claim 4 wherein the step of applying a force to the deformable portion of said first casting surface is accomplised by raising a plug under the deformable portion of said first casting surface to deform it until said mixture substantially fills the region between said first and second casting surfaces, said plug being itself made from a deformable material which will respond to the increased forces exerted on it by shrinkage of the polymerizing material by collapsing under those forces until they are dissipated.

11. The process of claim 4 wherein the step of applying a force to the deformable portion of said first casting surface is accomplished by raising a plug under the deformable portion of said first casting surface to deform it until said mixture substantially fills the region between said first and second casting surfaces, said plug being raised by means adapted in a manner such that said plug will respond to the forces exerted on it by shrinking of the poly- 12 merizing material by retracting under those forces until they are dissipated.

12. The process of claim 11 wherein a vacuum is applied to the deformable portion of said first casting surface, through said plug, to control the radius of curvature of the deformable portion of said first casting surface at the point where it joins the non-deformable portion of said first casting surface.

13. The process of claim 2 wherein said mixture comprises:

(a) a sirup containing 10-35% by weight of methyl methacrylate polymer selected from the group consisting of methyl methacrylate homopolymer and copolymers of methyl methacrylate with a,}9-ethylenically unsaturated compounds, said copolymers containing more than 50% methyl methacrylate, said polymer having an inherent viscosity of 0.25-l.0, in monomeric methyl methacrylate;

(b) 40-85% by weight of inert additive selected from the group consisting of calcium carbonate, calcium sulfate, silica, calcium silicate, alumina, aluminum silicate and titanium dioxide, and

(c) 0.2-6% by weight of peroxy compound having the wherein R is a saturated tertiary alkyl radical.

14. The process of claim 13 wherein said mixture further comprises a small amount of a solvent for said peroxy compound.

15. A process for forming a substantially stress-free article, containing a depression, from a polymerizable material, which comprises:

(a) depositing said polymerizable material onto a substantially flat first casting surface, said first casting surface having a first deformable portion;

(b) positioning a second casting surface above said polymerizable material, said second casting surface having a second deformable portion disposed above Ehe first deformable portion of said first casting surace;

(c) applying a force directly to one of the deformable portions, while said mixture is still in a liquid state, said force being sufiicient to deform both deformable portions of said first and second casting surfaces and the polymerizable material between them to the desired configuration, both deformable portions of said casting surfaces being adapted such that upon deformation they will preferentially draw into the desired shape and so that the thickness of the article so formed will be reasonably constant throughout, said force being applied by a deformation means adapted to allow said polymerizable material to undergo substantially unrestrained shrinkage;

(d) polymerizing said polymerizable material; and

(e) during the polymerization, collapsing the deformable portion of whichever casting surface has been directly deformed in a manner such that said polymerizable material undergoes substantially unrestrained shrinkage, whereby said polymerizable material hardens into a substantially stress-free article.

16. A process for forming a patterned article comprising the steps of:

(a) forming a liquid mixture containing a first polymerizable material and a second material of visibly different characteristics than said first polymerizable material;

(b) depositing said liquid mixture onto a substantially fiat, substantially horizontal, first casting surface to fix the pattern of said mixture relative to said first casting surface, said first casting surface having a 13 deformable portion occupying less than the total surface area of said first casting surface;

(c) covering said liquid mixture with a second casting surface having a concavity directed away from said liquid mixture, said concavity being disposed direct- 1y above the deformable portion of said first casting surface with the projection of its perimeter on said first casting surface completely enclosing the perimeter of the deformable portion of said first casting surface;

(d) thereafter, forcing said liquid mixture into said concavity by applying a force to the deformable portion of said first casting surface suflicient to deform the deformable portion of said first casting surface until said liquid mixture substantially fills the region between said first and second casting surfaces; and

(e) polymerizing the polymerizable material within said mixture, thereby forming an article containing a depression and having at least one surface on which the pattern of said second material in said first material is substantially consistent over the entire surfface of said article including both the deformed and undeformed portions of the surface.

17. The process of claim 16 wherein said second material is an inert filler.

18. The process of claim 16 wherein said second material is a polymerizable material pigmented differently than said first polymerizable material.

19. The process of claim 18 wherein at least one of said polymerizable materials is a polymerizable material that shrinks during polymerization, and wherein said force is applied by a deformation means adapted to allow said polymerizable material to undergo substantially unrestrained shrinkage, whereby in addition to having at least one surface with a substantially consistent pattern throughout said article is substantially stress free.

20. The process of claim 19 wherein said mixture further comprises between 40 and 85% by weight of an inert filler.

21. The process of claim 19 wherein:

(a) said first polymerizable material is a sirup containing methyl methacrylate polymer selected from the group consisting of methyl methacrylate homopolymer and copolymers of methyl methacrylate with a, 8-ethylenically unsaturated compounds, said copolymers containing more than 50% methyl methacrylate and said polymer having an inherent viscosity of 0.25-1.0, in monomeric methyl methacrylate;

(b) said second polymerizable material is said first polymerizable material pigmented differently than said first polymerizable material, both said first and second polymerizable materials constituting 10- 35 by weight of said mixture; and wherein said mixture further comprises (c) 40-85% by weight of inert additive selected from the group consisting of calcium carbonate, calcium sulfate, silica, calcium silicate, alumina, aluminum silicate and titanium dioxide, and

(d) 0.2-6% by weight of a peroxy compound having the formula 0 Hoii0H Hi100o-R,

wherein R is a saturated tertiary alkyl radical,

22. The process of claim 21 wherein said mixture further comprises a small amount of a solvent for said peroxy compound.

23. The process of claim 19 wherein the step of depositing said mixture onto a substantially flat first casting surface comprises: first preparing a substantially flat first casting surface by laying a stretchable film on top of a sub- 14 stantially flat support structure, said substantially flat support structure having an opening in the region of the desired depression; and then pouring said mixture onto said substantially flat first casting surface, whereby said stretchable film constitutes the deformable portion of said first casting surface.

24. The process of claim 19 wherein the step of forcing said liquid mixture into said concavity by applying a force to the deformable portion of the said first casting surface is accomplished by applying an increasing fiuid pressure to the deformable portion of said first casting surface, inflating it until said mixture substantially fills the region between said first and second casting surfaces, and maintaining the pressure substantially constant, whereby the deformable portion of said first casting surfaces automatically responds to the increased forces exerted on it by the shrinkage of the polymerizing mixture by deflating until those forces are dissipated.

25. The process of claim 19 wherein the step of forcing said liquid mixture into said concavity by applying a force to the deformable portion of said first casting surface is accomplished by raising a plug under the deformable portion of said first casting surface to deform it until said mixture substantially fills the region between said first and second casting surfaces, said plug being itself made from a deformable material which will respond to the increased forces exerted on it by shrinkage of the polymerizing mixture by collapsing under those forces until they are dissipated.

26. The process of claim 19 wherein the step of forcing said liquid mixture into said concavity by applying a force to the deformable portion of said first casting surface is accomplished by raising a plug under the deformable portion of said first casting surface to deform it until said mixture substantially fills the region between said first and second casting surfaces, said plug being raised by means adapted in a manner such that said plug will respond to the forces exerted on it by shrinkage of the polymerizing mixture by retracting under those forces until they are dissipated.

27. A process for forming a lavatory fixture from a polymerizable material that shrinks upon polymerization which comprises:

(a) forming a mixture comprising said polymerizable material and between 40 and by weight of an inert filler;

(b) depositing said mixture onto a substantially fiat first casting surface, said first casting surface having a deformable portion;

(c) preparing a substantially flat second casting surface having a concavity by positioning a drain structure within said concavity, said drain structure having a drain plug positioned at the apex of said concavity and supporting said drain structure in said concavity, at least one overflow plug positioned near the base of said concavity, and a connecting structure connecting said drain plug and said overflow plug, said drain structure being made from a material that can be degraded to allow its removal from the finished article;

(d) positioning said second casting surface above said mixture in a manner such that said concavity is disposed above the deformable portion of said first casting surface, directed away from said mixture, in a manner such that said drain structure is located between said mixture and the surface of said second casting surface;

(e) applying a force to the deformable portion of said first casting surface, while said mixture is still in a liquid state, said force being sufficient to deform the deformable portion of said first casting surface until the deformable portion of said first casting surface contacts the drain plug and the overflow plug of said drain structure and until said mixture substantially fills the region between said first and second casting surfaces, completely enveloping said drain structure except for that portion of said drain structure contacting said concavity or the deformable portion of said first casting surface, said force being applied by a deformation means adapted to allow said polymerizable material to undergo substantially unrestrained shrinkage;

(f) polymerizing said polymerizable material;

'( g) during the polymerization, collapsing the deformable portion of said first casting surface in a manner such that said polymerizable material undergoes substantially unrestrained shrinkage, whereby said mixture hardens into a substantially stress-free article; and

(h) removing said article from the mold formed by said casting surfaces and degrading said drain structure, whereby a completely formed lavatory unit, including drain and overflow opens and channels, is produced.

28. The process of claim 27 wherein: said drain structure is made from a chemically degradable material coated with wax; and wherein degradation of said drain structure comprises heating said drain structure to melt the wax and then chemically degrading said degradable material.

29. The process of claim 27 wherein: said drain structure is made from a material degradable in the monomer of said polymerizable material coated with wax to initially protect it from said monomer; and wherein degradation of said drain structure proceeds automatically during polymerization, the wax being melted by the heat of polymerization and the degradable material being degraded by the monomer once the wax has been removed.

30. The process of claim 27 wherein said polymerizable material comprises methyl methacrylate, and wherein said drain structure is made from polystyrene foam coated with wax.

31. The process of claim 7 wherein said opening contains a deformable diaphragm and wherein said stretchable film coacting with said deformable diaphragm comprises the deformable portion of said first casting surface.

32. The process of claim 31 further comprising the steps of: applying a vacuum between said flat support structure and said film in the region of said deformable diaphragm; and varying the vacuum applied, as the deformable portion of said first casting surface is deformed, to control the radius of curvature of the deformable portion of said first casting surface at the point where it 16 joins the nondeformable portion of said first casting surface.

33. The process of claim 4 wherein the step of applying a force to the deformable portion of said first casting surface is accomplished by raising a plug under the deformable portion of said first casting surface to deform it until said mixture substantially fills the region between said first and second casting surfaces, said plug being raised by means adapted to allow said polymerizable material to undergo substantially unrestrained shrinkage.

34. The process of claim 23 wherein said opening contains a deformable diaphragm and wherein said stretchable film coacting with said deformable diaphragm comprises the deformable portion of said first casting surface.

35. The process of claim 34 further comprising the steps of: applying a vacuum between said flat support structure and said film in the region of said deformable diaphragm; and varying the vacuum applied, as the deformable portion of said first casting surface is deformed, to control the radius of curvature of the deformable portion of said first casting surface at the point where it joins the non deformable portion of said first casting surface.

36-. The process of claim 19 wherein the step of applying a force to the deformable portion of said first casting surface is accomplished by raising a plug under the de formable portion of said first casting surface to deform it until said mixture substantially fills the region between said first and second casting surfaces, said plug being raised by means adapted to allow said polymerizable material to undergo substantially unrestrained shrinkage.

37. The process of claim 3 wherein said inert filler is granite.

38. The process of claim 16 wherein said mixture further comprises less than by weight of granite.

References Cited UNITED STATES PATENTS 3,230,284 1/1966 Iverson et al. 264-73 3,251,908 5/1966 Wilenius et al 264--89 X 3,315,019 4/1967 Fischler 264--73 ROBERT F. WHITE, Primary Examiner J. H. SILBAUGH, Assistant Examiner US. Cl. X.R.

18-Dig. 19; 24965, 82; 26473, 89, 90, 93, 316, 317, Dig. 50, Dig. 78

EDWARD MJILETCHERJR.

Attesting Officer fig 3 UIIITIED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 6 +2,975 Dated February 15, 1972v Invencofls) Ray B; Dugg iris 80 Robert T Gross It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In Column 10, Claim 1, line 16, after the word material insert the word "substantially- Signed and sealed this- 13th day of March 1973..

(SEAL) Attest:

' ROBERTYGOTTSCHALK Commissioner of Patents