WO1984002682A1

WO1984002682A1 - Method and apparatus for molding

Info

Publication number: WO1984002682A1
Application number: PCT/US1983/002057
Authority: WO
Inventors: Sherwood Glenn Benfield
Original assignee: POLYCAST CORP
Current assignee: POLYCAST CORP
Priority date: 1983-01-10
Filing date: 1983-12-27
Publication date: 1984-07-19
Anticipated expiration: 1986-06-27
Also published as: ES8504013A1; KR840007379A; EP0131037A1; FI840074A0; DK421884D0; IL70613A0; PT77935B; ES528686A0; DK421884A; JPS60500409A; ES8605181A1; ES539896A0; PT77935A; NO843546L

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 This invention relates to the molding of foam articles using reactant chemicals which form foamed plastics, such as poIyurethanes.

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 while also obtaining easy release of the molded article from the mold. Particularly with respect to certain foam materials, of which thermosetting chemically blown foams, isocyanurates and polyurethane are examples, the unavailability of controlled surface finishes and freely releasing molds has severely restricted the usefulness of t hose materials.

Attempts have been made heretofore to attack certain of such problems through the use of molds spray coated with release agents. Such release agents have been found to have very limited life, 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 life of the mold quIckIy ends.

Brief Description of Invention

With the problems and difficulties heretofore encountered particularly in mind, It Is an object of this invention to accomplish molding of three dimensional objects of chemical foams in accordance with methods which make controlled surface finishes available. in realizing this object of the present invention, a mold in which a foam material object Is to be formed Is lined with a liner 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 life of a mold in accordance with this invention Is more fully realized.

A further object of the present invention Is to accomplish ready release of a molded foam object from the mold in which the foam Is formed into a desired shape. in realizing this object of the present invention, the fluorocarbon polymer liner 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 as brought out more fully hereinafter, stripping of the moided article or object from the mold is accomplished by distending the liner 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 liner has been vacuum formed into the configuration and position required for proper functioning of the apparatus. in realizing this object of the present invention, a mold form is provided, a l iner film of the type described Is provided, and the liner is formed to the configuration of the mold. in accordance with certain embodiments of this invention as pointed out more fuIIy hereinafter, the liner may be dlstendable by fluid pressure. in accordance with other embodiments, the liner 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 essentially 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 will appear as the description proceeds, when taken in connection with the accompanying drawings, in which:

Figure 1 Is a perspective view of a molding apparatus in accordance with this invention, illustrating one step in a process of this invention; Figure 2 is a schematic elevation view, partly in section, through the apparatus of Figure 1 and Illustrating another step in a process of this invention;

Figure 3 is a view similar to Figure 2 illustrating 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 will be described more fully here inafter 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 follows that persons of skill in the appropriate arts may modify the invention here described while still achieving the favorable results of this invention. Accordingly, the description which follows Is to be understood as being a broad, teaching disclosure directed to persons of skill in the appropriate arts, and not as limiting upon the present invention .

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 will be described in connection with that apparatus showing. Alternate embodiments for the apparatus and methods will become more clear hereinafter, as they are mentioned. The specific apparatus illustrated has a mold box generally indicated at 10, within which Is located a mold member 11. in the form illustrated, the box 10 Is generally 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 will 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 will be descrjbed.

The mold box 10 has provision for vacuum forming a fluorocarbon film liner, which in the illustrated embodiment includes an air handling device generally indicated at 12. The mold box 10 and the member 11 therewithin have passageways formed therein for air flow, as is known generally to persons skilled in the arts of vacuum forming polymer films. ln accordance with the present invention, a fluorocarbon polymer film generally indicated at 14 is used as a liner for the mold cavity defined within the box 10. The polymer film Is formed, in accordance with this invention, from a polymer selected from among the class consisting of polychIortrIfluoroethyIene, polytetrafIuoroethyIene, fluoropIastic, polyvinylidene fluoride, and a co-polymer having a carbon-fluorine main chain and polyfluoroalkoxy side chains. Such films have in common the characteristics of being the slipperiest of all solids, essentially chemically inert, and of good mechanical strength. The mechanical strength of the films allows significant resistance to repetitive bending or folding stress, thereby aiding in avoiding microcracking as mentioned above. Such films may be etched where appropriate, and vacuum formed using technology which is essentially known to persons of appropriate skill in the applicable 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 will 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 accomplished by a convectlve air heater 16 blowing hot air against the film, or by a radiant heat source as Is known to skilled 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 slick, highly finished surface for the cavity.

The mold is thus prepared for the introduction of foam reactants, which Is accomplished by delivering such chemicals through an appropriate nozzle or gun 18. The nature of the chemicals used, and their delivery in such a way as to mix and begin a foaming reaction, Is well known within the chemical industry and will not here be described in detail. 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 applications is urethane based. Urethane foams, while economically attractive, have not been used in certain paekaging and structural applications 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 will form therewithin a molded article or object 20. In the apparatus il lustrated, the object 20 may be stripped or ejected from the mold by distending the film liner 14, as indicated in Figure 4. There, the air handling device 12 has been used to inflate the liner 14 by applying fluid pressure between the liner 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 liner 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, all with the desired high surface finish.

While the fluorocarbon polymer films used have good mechanical strength, the liner will ultimateIy fail by bending stress as cycles of molding continue. Upon failure, the liner 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 acompllshed both with and without distending the film liner 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 liner may be etched on one surface and adhered in place for use, then later stripped from the mold should replacement be necessary. By such methods, the useful life of molds Is significantly extended, and molds made be made from less expensive materials. Further, such methods permit the liner, which Is separate from or non-integral with the mold structure, to adjust to variations in thermal expansion and contraction between the liner and the mold structure which supports the liner during molding. This adjustment is believed to contribute to the avoidance of microcracking which Is known to be a characteristic of this invention. in accordance with still other embodiments of this invention, the liner may be formed to the desired configuration by techniques other than vacuum forming. By way of example, the liner 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 while the liner is free to move separately from or be removed from the mold structure. Thus, while vacuum forming may well be a preferred process for forming the liner, it Is recognized as being only one of the available 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 limitation.

Claims

That which Is claimed is

1. A method of manufacturing molded foam articles comprising the steps of: positioning a flurocarbon polymer film mold liner formed into a configuration so as to fit closely with a mold member in engagement with the mold member, then depositing onto the lined 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 Iiner.

2. A method of according to Claim 1 further comprising the steps of: forming the flurocarbon polymer film mold liner into a configuration so as to fit closely with the mold member, and thereafter repeatedly depositing onto the lined mold member reactants for forming foam and molding a successive plurality of foam articles configured to the mold member, and thereafter stripping the liner from the mold member and repeating the steps of forming and positioning a flurocarbon mold liner in engagement with the mold member in preparation for continuing the step of molding a successive plurality of foam articles.

3. A method of according to Claim 2 wherein the step of forming the mold liner comprises vacuum forming a flurocarbon polymer film over a mold member, and further wherein the step of stripping the article from the mold member and liner 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 liner comprises applying fluid pressure to the l iner for distending the liner and stripping the article from the mold form and liner, and further comprising the steps of vacuuming the liner into position on the male mold member, and repeating the steps of depositing foam reactants, applying fluid pressure and vacuuming the liner into position.

5. A method according to one of Claim 3 or Claim 4 wherein the step of forming a liner comprises mounting a film adjacent the mold member, heating the film to an elevated temperature for pliability, and drawing a vacuum between the film and the mold member so as to conform the film closely to the mold member.

6. A method according to Claim 5 wherein the step of heating the film comprises directing a flow of heated air against the film.

7. A method according to Claim 5 wherein the step of heating the film comprises directing radiant energy against the film.

8. A method accordino 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 mold 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 configurat i on of said mold form means, and upon moving to said distended release position effecting separation of molded products from said mold form means.

11. Apparatus according to Claim 10 wherein said mold form means comprises a mold member having a special configuration and further wherein said mold liner means comprises a film 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 film mold liner means Is formed by a film selected from among the class consisting of polychlortrifluoroethyIene, poIytetrafIuoroethylene, fluoroplastic, poIyvinyIidene fluoride, and a co-polymer having a carbon-fluorine main chain and poIyfluoroalkoxy side chains.

13. Apparatus according to Claim 10 wherein said mold form means and said mold liner 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 liner means for directing fluid flowing from said volume and to said volume for thereby vacuum forming said mold liner means to said mold form means and also for thereby moving said mold liner means between said molding and release positions.

14. Apparatus according to Claim 9 wherein said mold liner means Is temporarily adhered to said mold form means.