METHOD AND APPARATUS FOR MOLDING

Abstract: Methods and apparatus for molding foam materials in which smooth surface finishes and easy release of molded objects or articles (20) from the molds (10) in which they are formed are accomplished by the provision of fluorocarbon polymer mold liners (14) movable relative to supporting mold structures.

Description: METHOD AND APPARATUS FOR HOLDING Field and Background of Invention T is Invention relates to the molding of foam articles using reactant chemicals which form foamed plastics, such as po I yurethanes. It has been proposed heretofore that foam plastic articles be formed by molding processes using both open and closed molds, and capable of producing three dimensional objects used for packaging, for decorative effect, and for structural purposes among others. One consistent problem throughout such molding processes and apparatus used In practicing such methods Is that of obtaining a s.mooth surface finish on a molded article whi le also obtaining easy release of the molded article froπrt ' he mold. Particularly with respect to certain foam materials, of which thermosettI ng chemical ly blown foams, Isocyanurates and polyurethane are examples, the unavai labi l ity of control led surface finishes and freely releasing molds has severely restricted the usefulness of those materials. Attempts have been made heretofore to attack cer¬ tain of such problems through the use of molds spray coated with release agents. Such release agents have been found to have very l imited l ife, resulting from the formation In the spray coatings of microscopic cracks Into which the materials being molded penetrate. With the formation of such cracks and the penetration of the material being molded, the. free release of molded articles Is no longer possible and useful l ife of the mol d qu Ic I y ends . Brief Description of Invention With the problems and difficulties heretofore encountered particularly In mind, It Is an object of this Invention to accompl ish molding of three dimensional objects of chemical foams in accordance with methods which make control led surface finishes available. In real izing this object of the present Invention, a mold In which a foam material object Is to be formed Is l ined with a l iner formed of a fluorocarbon polymer film. Films of the type specified have very smooth surfaces, . making possible the attainment of high surface finishes on foam formed against such a mold surface. When used In accordance with this Invention as described hereinafter, the mlcrocrack i ng encountered with prior spray coatings is entirely avoided, and the useful l ife of a mold in accordance with this Invention Is more ful ly real ized. A further object of the present invention Is to accompl ish ready release of a molded foam object from the mold In which the foam Is formed Into a desired shape. In real izing this object of the present Invention, the fluorocarbon polymer l iner used prevents adhesion of the molded foam to the mold form, thereby permitting the finished article to be easily released. In accordance with certain embodiments of this Invention - 3 - as brought out more ful ly hereinafter, stripping of the molded article or object from the mold is accompl ished by distending the l iner with fluid pressure. Yet a further object of this Invention Is to provide molding apparatus for use In practicing the methods described above and In which a fluorocarbon polymer l iner has been vacuum formed into the configuration and position required for proper functioning of the apparatus. In real izing this object of the present Invention, a mold form Is provided, a l iner fi lm of the type described Is provided, and the l iner Is formed to the configuration of the mold. In accordance with certain embodiments of this Invention as pointed out more fu I I y .hereinafter, _ the l iner may be dlstendable by fluid pressure. In accordance with other embodiments, the l iner may be adhered In use position and renewable as required to maintain efficiency of the molding apparatus. Further, the mold forms used may be open, with essential ly unconflned foam formation, or closed, with confined and pressurized foam formation. Brief Description of Drawings Some of the objects of the Invention having been stated, other objects wi l l appear as the description proceeds, when taken In connection with the accompanying draw I ngs, In which: Figure 1 Is a perspective view of a molding apparatus In accordance ..with this Invention, I l lustrating one step fn a process of this Invention; OMPI Figure 2 Is a schematic elevation view, partly In section, through the apparatus of Figure 1 and Il lustrating another step In a process of this InventIon; Figure 3 Is a view similar to Figure 2 Il lustrating another step in a process In accordance with this Invention; and Figure 4 Is an exploded perspective view of the apparatus of Figures 1 through 3, showing another step In accordance with a process In accordance with this InventIon . Detailed Description of Invention While the present Invention wil l be described more ful ly hereinafter with reference to the accompanying drawings, In which a preferred embodiment of the present Invention Is shown, it Is to be understood at the outset of the description which fol lows that persons of skil l In the appropriate arts may modify the Invention here described while stil l achieving the favorable results of this Invention. Accordingly, the description which fol lows Is to be understood as being a broad, teaching disclosure directed to persons of skil l In the appropriate arts, and not as l imiting upon the present I nventIon . Referring now more particularly to the accompanying drawing, an apparatus showing one embodiment of the present Invention Is there shown, and a method In accordance with the present Invention wil l OMPI be described In connection with that apparatus showing. Alternate embodiments for the apparatus and methods wi l l become more clear hereinafter, as they are mentioned. The specific apparatus Il lustrated has a mold box general ly Indicated at 10, within which Is located a mold member 11. In the form I l lustrated, the box 10 Is general ly square, defining a mold cavity of that configuration, and the member 11 Is convex or what may be referred to as a male mold member. As wi l l be pointed out hereinafter, the three dimensional article or object produced in the moid box 10 has a concavity for receiving some object to be packaged. It is contemplated that the Invention here described Is useful with other types of mold forms, as wil l be descrjbed. The mold box 10 has provision for vacuum forming a fluorocarbon fi lm l iner, which In the I l lustrated embodiment includes an air handl ing device general ly indicated at 12. The mold box 10 and the member 11 therewithln have passageways formed therein for air flow, as Is known general ly to persons ski l led In the arts of vacuum forming polymer fi lms. In accordance with the present Invention, a fluorocarbon polymer film general ly Indicated at 14 Is used as a l iner for the mold cavity defined within the box 10. The polymer fi lm Is formed, In accordance with this Invention, from a polymer select-ed from among the class consisting of pol ych I ortrI f I uoroethy I ene, po I ytetraf I uoroethy I ene, f I uorop I ast I c, po I yv I . ny I 1 dene fluoride, and a co-polymer having a carbon-fluorine main chain and polyf 1 uoroa I koxy side chains. Such films have In common the characteristics of being the sl ipperiest of al l sol ids, essential ly chemical ly Inert, and of good mechanical strength. The mechanical strength of the fi lms al lows significant resistance to repetitive bending or folding stress, thereby aiding In avoiding microcrack ing as mentioned above. Such films may be etched where appropriate, and vacuum formed using technology which is essential ly known to persons of appropriate skil l In the appl icable vacuum forming art. In practicing the present Invention, the film 14 Is positioned over an open side of the box 10 and retained In place by appropriate means . such as edge clamps 15. Other forms of clamps may be used, and wil l be known to vacuuming forming technicians. The film 14 Is then heated and drawn Into the cavity provided by the box 10 by the removal of air therefrom by the device 12. Heating may be accompl ished by a convectlve air heater 16 blowing hot air against the film, or by a radiant heat source as Is known to skil led vacuum forming technicians. With the liner being vacuum formed to the mold, the film takes on the configuration of the mold cavity and provides a sl ick, highly finished surface for the cavity. The mold Is thus prepared for the introduction of foam reactants, which Is accomplished by del ivering such chemicals through an appropriate nozzle or gun -18. The -^tJRE_C nature of the chemicals used, and their del ivery In such a way as to mix and begin a foaming reaction, Is wel l known within the chemical Industry and wi l l not here be described In detai l . It Is contemplated that the apparatus and methods of the present Invention may be used with any such foam forming chemical system. However, ft Is known that the present Invention has particular value with chemical systems which have heretofore been Impossible to adapt to molding techniques as here described. In particular, one foam system which has heretofore found usefulness In certain appl ications is urethane based. Urethane foams, whi le economical ly attractive, have not been used In certain paekaging and structural appl ications because of difficulty In obtaining suitable surface finishes and In obtaining release of the molded products from the molds used. The present Invention solves both of these problems, thereby significantly broadening the usefulness of urethane foams. In certain such foaming systems, It Is desirable to control the pressure under which foaming occurs. With such a system, the mold apparatus in accordance with this Invention may have a cover 19 (Figure 3) which may, In any appropriate manner, control the pressure during reaction and thus the density of the foam. As Indicated In Figure 3, the reactants Introduced Into the mold wil l form therewithin a molded article or object 20. In the apparatus I l lustrated, the object 20 may be - 8 - stripped or ejected from the mold by distending the film liner 14, as Indicated In Figure 4. There, the air handl ing device 12 has been used to Inflate the l iner 14 by applying fluid pressure between the l iner and the mold box 10. As the film Is distended, the object 20 formed by the molding process is removed from the mold. The mold is thus prepared for a repetition of the steps of drawing the l iner Into position by vacuum, Introducing reactants for forming foam, molding an object, and ejecting the object from the mold. A succession of objects may thus be formed, al l with the desired high surface finish. While the fluorocarbon polymer films used have good mechanical strength, the liner wI i I- u 111-mateI y fail by bending stress as cycles of molding continue. Upon failure, the l iner Is readily replaced In accordance with the methods described to this point, and molding operations may continue. In accordance with other embodiments of the Inventions described above, molding In an open sided mold may be acompl lshed both with and without distending the film l iner to strip the molded article from the mold. The mold employed may be either a male mold or a female mold, imparting either concave, convex, or compound shapes to the molded objects. Where an open sided mold Is to be used without distending of the liner, the l iner may be etched on one surface and adhered In place for use, then later stripped -from the OMH mold should replacement be necessary. By such methods, the useful l ife of molds Is significantly extended, and molds made be made from less expensive materials. Further, such methods permit the l iner, which Is separate from or non-Integral with the mold structure, to adjust to variations In thermal expansion and contraction between the l iner and the mold structure which supports the l iner during molding. This adjustment is bel ieved to contribute to the avoidance of microcrack 1 ng which Is known to be a characteristic of this I nvent Ion . In accordance with sti l l other embodiments of this Invention, the l iner may be formed to the desired configuration by techniques other than vacuum forming. By way of example, the l iner may be form by die casting, blow molding, pressing, Injection molding, or extruding, so long as the desired configuration matching the supporting mold structure Is achieved whi le the l iner Is free to move separately from or be removed from the mold structure. Thus, whi le vacuum forming may wel l be a preferred process for forming the l iner, it Is recognized as being only one of the avai lable means. In the drawings and specifications there has been set forth a preferred embodiment of the Invention and, although specific terms are used, the description thus given uses terminology In a generic and descriptive sense only and not for purposes of l imitation. OMH

Claims: That which Is claimed is 1. A method of manufacturing molded foam articles comprising the steps of: positioning a flurocarbon polymer fi lm mold l iner formed Into a configuration so as to fit closely with a mold member in engagement with the mold member, then depositing onto the l ined mold member reactants for forming foam and molding a foam article configured to the mold member, and then stripping the article from the mold member and I I ner. 2. A method o ' f . according to Claim 1 further comprising the steps of: forming the flurocarbon polymer fi lm mold l iner Into a configuration so as to fit closely with the mold member, and thereafter repeatedly depositing onto the l ined mold member reactants for forming foam and molding a successive plural ity of foam articles configured to the mold member, and thereafter stripping the l iner from the mold member and repeating the steps of forming and " positioning a fluro¬ carbon mold l iner in engagement with the mold member In preparation for continuing the step of molding a successive plural ity of foam articles. OMPI - 1 1 - 3. A method of according to Claim 2 wherein the step of forming the mold l iner comprises vacuum forming a flurocarbon polymer fi lm over a mold member, and further wherein the step of stripping the article from the mold member and l iner comprises distending the l iner. 4. A method of according to Claim 2 wherein the step of stripping the article from the mold member and l iner comprises applying fluid pressure to the l iner for distending the l iner and stripping the article from the mold form and l iner, and further comprising the steps of vacuuming the l iner into position on the male mold member, and repeating the steps of depositing foam re¬ actants, applying fluid pressure and vacuuming the l iner i nto pos Ition . 5. A method according to one of Claim 3 or Claim 4 wherein the step of forming a l iner comprises mounting a fi lm adjacent the mold member, heating the fi lm to an elevated temperature for pl iabi l ity, and drawing a vacuum between the fi lm and the mold member so as to conform the fi lm closely to the mold member. 6. A method according to Claim 5 wherein the step of heating the fi lm comprises directing a flow of heated al r aga 1 nst the fi lm. 7. A method according to Claim 5 wherein the step of heating the fi lm comprises directing radiant energy agal nst the fi lm. OMP- , - 12 - 8. A method accordlno to one of Claim 3 or Claim 4 wherein the step of dlstendlnα the liner comprises delivering pressurized fluid Into a volume defined between the mold member and the film liner. 9. An apparatus for molding foam materials and comprIsIng: mold form means defining a mold volume for receiving and confining foam reactants, and flurocarbon polymer film mold liner means formed Into a configuration so as to fit closely with said mold form means when In engagement with said mold form means and cooperating with said mold form means for effecting ready release of molded foam articles from said mold form means, said mold liner means Imparting to foam products molded within said apparatus the configuration of said moid form means. 10. An apparatus according to Claim 9 wherein said mold liner means Is movable between a molding position closely engaging said mold form means and a release position distended from said mold form means, said mold liner means when in said molding position Imparting to foam products molded within said apparatus the configu¬ ration of said mold form means, and upon moving to said distended release position- effecting separation of molded products from said mold form means. ^ . Apparatus according to Claim 10 wherein said mold form means comprises a mold member having a special - 1 3 - configuration and further wherein said mold l iner means comprises a fi lm vacuum formed In situ to the special configuration of said mold member. 12. Apparatus according to one of Claim 9 or Claim 10 wherein said fi lm mold l iner means Is formed by a fi lm selected from among the class consisting of polychlor- tr I f I uoroethy I ene, po I ytetraf I uoroethy I ene, fluoro- plastic, po I yv I ny I 1 dene fluoride, and a co-polymer having a carbon-fluorine main chain and po I yf I uoroa I koxy s i de cha I ns . 13. Apparatus according to Claim 10 wherein said mold form means and said mold l iner means are sealed one with respect to the other and further comprising fluid flow communicating means operatlvely communicating with a' volume confined between said mold form means and said mold l iner means for directing fluid flowing from said volume and to said volume for thereby vacuum forming said mold l iner means to said mold form means and also for thereby moving said mold l iner means between said molding and release positions. 14. Apparatus according to Claim 9 wherein said mold l iner means Is temporari ly adhered to said mold form means . OMPI ?NftT-θr

Inventors: BENFIELD SHERWOOD GLENN, BENFIELD, SHERWOOD, GLENN
Applicants: POLYCAST CORP, POLYCAST CORPORATION
Application year: 1983
Main classification: B29D27
IPC codes: B29C33, B29C37, B29C39, B29C51, B29K105