US3535416A - Preparation of amylose molds and of castings made therewith - Google Patents

Description

1970 M. D. MELNICK ETAL 3,535,416

PREPARATION OF AMYLOSE MOLDS AND OF CASTINGS MADE THEREWITH Filed March 14, 1968 FIG, 2

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INVENTORS M/(A AH 0. MfL/V/C/r WILL/AM ymesr United States Patent 3,535,416 PREPARATION OF AMYLOSE MOLDS AND OF CASTINGS MADE THEREWITH Michael D. Melnick, Highland Park, and William Herbst, Watchung, N.J., assignors to National Starch and Chemical Corporation, New York, N.Y., a corporation of Delaware Filed Mar. 14, 1968, Ser. No. 713,200 Int. Cl. B29c 1/02 US. Cl. 264-220 2 Claims ABSTRACT OF THE DISCLOSURE The preparation of amylose molds and of castings made therewith characterized by (a) the making of negative molds of an original model or specimen which molds congeal into tough, strong matrices exhibiting exceptional dimensional stability used (b) for casting a large number of casting materials which as a result faithfully reproduce in great detail the configuration of the original model or specimen. Such molds are also readily disposable without leaving a residual ash by the application of heat such as is used to speed up or complete the setting or solidification of the cast product.

Negative or female molds may be defined as matrices or hollow forms in which castings of fluid materials are made. Among the structural materials which are presently being used for the preparation of such molds are included concrete, plaster, and and reinforced plastics. The basic disadvantage of molds prepared from these conventional materials is their lack of dimensional stability. Thus, there is a tendency for such molds to shrink during the setting stage, i.e. the stage when they assume their ultimate rigid configuration. Needless to say, such variations in size and shape cannot be tolerated in applications where it is desired to prepare highly precise reproductions or in mass production operations wherein unvarying uniformity of the final product is of extreme importance.

Furthermore, Where ashing techniques are utilized in order to destroy the mold structure and to thereby expose the cast object, the conventional mold forming materials are again less than satisfactory inasmuch as they do not ash completely and thus leave an undesirable residue. This residual ash may serve as a contaminant for the cast object. In addition, it poses problems with respect to waste removal and the purging of the firing kiln.

It is, thus, the object of this invention to prepare molds that exhibit a high degree of strength and dimensonal stability. It is a further object to prepare molds that can be readily ashed so as to permit their disposal without leaving an undesirable ash residue. Various other objects and advantages of this invention will be apparent to the practitioner from the following detailed description thereof.

We have now found that by utilizing amylose products, as hereinafter described, in the preparation of negative mold structures, it is possible to overcome the difiiculties which were heretofore inherent in the preparation of such molds. Thus, the novel molds which are derived from these amylose products are characterized by their ability to congeal into tough, strong matrices which do not require reinforcement with external structural braces. Furthermore, these molds exhibit exceptional dimensional stability inasmuch as they retain both their size and shape during the setting stage of the mold forming operation. This may be contrasted with the performance of conventional, low amylose starches wherein weak, unstable, sagging molds are frequently produced. Of particular importance is the fact that these molds are capable of Patented Oct. 20, 1970 being ashed without the formation of an ash residue, thereby eliminating the possibility of contamination and the need for disposing of such residue. Furthermore, the use of these amylose products in the preparation of molds enables the practitioner to cast a vast number of materials into an infinite variety of shapes and configurations with excellent faithful reproducibility of even the most minute details which are present on the original model.

It should be noted that it has been known to utilize amylose for the preparation of certain articles which are essentially fiat or uni-dimensional in their configuration, such as films, filaments and tubes; such procedures usually requiring the presence of various reagents, in addition to amylose, in order to effect their preparation. Our invention, on the other hand, enables the practitioner to prepare three-dimensional products, namely, consumable, dimensionally precise molds, which may consist solely of amylose.

To the accomplishment of the foregoing objects, and such other objects as may hereinafter appear, our invention relates to the mold, a method of producing the same, and of producing castings made therewith, as more particularly defined in the appended claims taken together with the following description and the accompanying drawings thereof, in which:

FIG. 1 is a cross-sectional view illustrating a typical mold assembly obtained in the preparation of the novel amylose negative molds of this invention;

FIG. 2 is a cross-sectional view of a typical amylose negative mold obtained by employing the assembly of FIG. 1;

FIG. 3 is a cross-sectional view illustrating a method for utilizing an amylose negative mold in the preparation of cast reproductions; and,

FIG. 4 is a cross-sectional view of a typical cast reproduction obtained by employing our novel amylose molds in the method of FIG. 3.

It is well known that starch is generally composed of two fractions, one a linear fraction known as amylose, and the other a branched fraction known as amylopectin. Each starch type, e.g. corn, potato, tapioca, etc., contains these two fractions in a specific ratio characteristic of that particular starch; typical amylose concentrations ranging from about 18 to 30%, by weight. Since the amylose molecules are linear and contain hydroxyl groups, they have a tendency to be attracted to each other and to align themselves by the association, as for example, by hydrogen bonding, through the hydroxyl groups of neighboring molecules.

This phenomenon of molecular association through by drogen bonding is commonly referred to as retrogradation and is generally manifested by crystallization from aqueous dispersions and the formation of rigid gels. On the other hand, the highly branched structure of amylopectin prevents its molecules from approaching each other closely enough to permit the extensive hydrogen bonding which is necessary for retrogradation to occur. As a result, aqueous dispersions of amylopectin exhibit good solution stability and do not gel.

The ability of amylose products to provide the superior negative molds of this invention is believed to result from the presence therein of this increased concentration of linear molecules and the corresponding increase and alignment thereof in the resulting molds. Thus, as a result of such increased association, these amylose products exhibit excellent setting and congealing characteristics as well as the ability to provide strong, dimensionally stable mold structures.

It is to be noted that when we use the term amylose product for the purposes of this invention, we refer to the amylose resulting from the fractionation of whole starch into its respective amylose and amylopectin components; or, to whole, high amylose starch which is composed of at least about 40%, by weight, of amylase; or, to mixtures of high amylose starches or amylose fractions with conventional, low amylose starches wherein the total amylose content of the resulting mixture is at least about 40%, by weight. In each instance, the amylose or high amylose starch may be further treated as with heat and/or acids or with oxidizing agents so as to form so-called dextrins or thin boiling products; the latter products being especially preferred in the process of this invention because of the decided linearity of the amylose molecules therein and their ability to be cooked at higher solids concentrations, thereby yielding dispersions with higher gel strengths. In addition, the amylose product may be mildly chemically derivatized, i.e. derivatized to the extent that the degree of substitution of the resulting derivative does not exceed about 0.07, as by means of an esterification procedure which would thus yield amylose esters such, for example, as the acetate, propionate and butyrate esters; or, by means of an etherification reaction which would thus yield amylose ethers such, for example, as the hydroxyethyl, hydroxypropyl and carboxymethyl ethers. It is necessary that the above stated limitation on the maximum degree of substitution in such ester and ether derivatives be observed in order to maintain the desired gel formation properties of these derivatized amylose products.

In using the above described amylose products for the preparation of the disposable molds of this invention, it is first necessary to slurry them in water at a solids content of from about to 70%, and preferably from about to 40%, by weight. The resulting slurries are then cooked for a period of about 2 to 5 minutes at temperatures of from about 225 to 350 F. and at the corresponding elevated pressures of from about 4 to 120 p.s.i. The precise extent of the cooking operation will be dependent upon the particular amylose product which has been selected. Upon completion of the cooking operation, the hot amylose slurry is pumped directly into a positive or male mold, e.g. a container which contains or houses the model that is to be reproduced, where the slurry is allowed to cool and thereby retrograde so as to form a rigid gel structure.

It should be noted that it is preferable to maintain the amylose slurry at a temperature above about 190 F. during its transfer to the positive mold or container in order to prevent the possibility of premature retrogradation of the amylose product.

Alternatively, such premature retrogradation may be prevented by the presence, in the system, of a stabilizer or by the use of an amylose derivative such as an acetate ester or a hydroxypropyl ether. The viscosity of the slurry during the transfer step will, needless to say, be dependent upon the temperature at which it is maintained; it being preferable to maintain the slurry at a low viscosity, e.g. at about 500 centipoises, in order to facilitate the formation of a uniform, strong mold having a minimum of air bubbles entrapped in its walls.

Furthermore, although the transferred amylose slurry is preferably maintained at ambient temperatures and thus is cooled at a comparatively slow rate, it may also be rapidly cooled by circulating a current of cool air around the positive mold or container or by storing the positive mold containing the slurry at reduced temperatures. In addition, it is preferable to keep the entire mold system covered while the amylose slurry is retrograding in order to prevent excessive loss of water by evaporation and the resultant weakening of its walls.

It should also be noted that various inert bulking agents may be optionally present as fillers or extenders in the amylose slurries. Included among such bulking agents are: clay; sand; non-cookable starches; inorganic salts such as sodium sulfate; inert organic materials such as cellulosic fibers; and, organic polymers such as polyvinyl alcohol. These bulking agents may be added to the amylose slurry either prior to or immediately after it is subjected to the cooking procedure. It is essential that these additives be present at concentration levels which do not adversely affect the gel strength of the resulting amylose mold. Furthermore, where these amylose molds are to be disposed of by means of an ashing procedure, as hereinafter described, it is best to avoid the use of materials, such as clay, sand or salts, which are prone to leave a substantial amount of residual ash.

Referring now more in detail to the drawings and first to FIG. 1 thereof, which illustrates the preparation of an amylose negative mold of the invention, the prepared hot amylose slurry 10 is poured, as by being pumped, into a container or positive mold 12 which contains a model or specimen 14 that is to be reproduced, which latter for simplicity is shown as a threaded male pipe. The amylose slurry 10 is allowed to cool and thereby retrograde so as to form a rigid gel structure.

After the amylose slurry 10 has been completely formed and solidified, it is removed from the positive mold or container 12, split into two sections, and the model or specimen 14 removed therefrom. The result is a twopart amylose mold 16 shown in FIG. 2, having an upper section 16 and a lower section 16 produced by splitting the mold along its mid-line 18 and having a mold cavity 20 which is a faithful negative of the model or specimen 14. These two sections 16 and 16 are, thus, the negative mold sections which are to be used in producing the final positive cast product. The thickness of the molds of this invention may vary according to the overall size thereof. Thus, as larger molds aremade it is preferable to correspondingly increase their wall thickness in order to maintain the necessary high degree of strength in the resulting mold.

A large number of materials may be cast in the amylose molds 16 of this invention; it being merely required that these materials be able to assume a fluid state which can be maintained, without solidification, for a period of time sufficient to permit it to be poured into the molds 16 so as to completely occupy the mold cavity 20. However, inasmuch as exposing the molds 16 to excessive tempera- .tures may cause them to experience a moisture loss and a concurrent dimensional change, it is preferred that the casting materials be able to assume the desired fluid state at temperatures below about 100 F.

Among the materials that meet these requirements are included: plaster, epoxy resins, and waxes and salts having melting points in the range of from about -100 F., etc.

As depicted in FIG. 3, the method utilized for molding or casting the casting materials in our amylose molds 16 involves the step of first physicaly joining the upper and lower mold sections of the mold, as by the exertion of pressure thereon or by returning them to their former position in the retaining vessel of the positive mold 12 and then pouring the fluid casting material 22 through a channel 24 which has been formed in the upper section 16 of the mold. The casting material 22 is then allowed to set. Where the resulting casting does not require the application of heat in order to complete its solidification, e.g. plaster castings, the two sections 16 and 16 may be removed, intact, at the conclusion of the setting period so as to thereby expose and remove the resulting cast product 26 shown in FIG. 4. In these instances, the amylose molds may be used for the preparation of an indeterminate number of castings.

Where, however, heat is required to set and cure the casting or where it is utilized to speed the setting process, e.g. when epoxy resins are used as the casting material, the entire assembly comprising the mold 16 and the gelled casting material 22 may be subjected to temperatures of from about 400 to 700 C. At the latter temperatures, the entire amylose mold 16 is completely transformed into carbon dioxide and water vapor and thereby disposed of without the formation of a contaminating ash residue.

Simultaneously therewith, the heat which has been applied serves to complete the solidification of the cast product 26 so that when the amylose mold 16 is burned off, a solid, rigid casting 26 has been produced.

It should be noted that regardless of the method by which the amylose molds of this invention are utilized, the resulting cast products are always found to be uniform and dimensionally precise. In addition, they faithfully reflect each minute detail that was present on the original model.

The following examples will further illustrate the embodiment of this invention.

EXAMPLE I This example illustrates the use of the novel amylose molds of this invention in a typical casting operation.

Thus, 600 grams of a high amylose corn starch containing 70%, by weight, of amylose were dispersed in Water so as to obtain an amylose slurry having a solids content of 20%, by Weight. The resulting slurry was cooked at a temperature of 300 F. for a period of three minutes and then maintained at a temperature of 200 F. whereupon it was poured into a vessel containing a 3" section of a threaded male pipe. The system was then covered and allowed to slowly cool by being maintained at ambient temperatures for a period of about 20 hours.

The thus formed rigid negative mold was then split into two sections and the pipe removed therefrom. These sections were then reunited, by being returned to their former position in the vessel which housed the pipe model, and a channel cut in the upper section so as to enable the epoxy resin casting material to be introduced into the mold. The cast epoxy resin Was allowed to set by maintaining the mold system at room temperature for a period of 24 hours, whereupon the mold was removed revealing an exact duplicate of the threaded pipe section.

The dimensional accuracy inherent in the products cast in the novel molds of this invention was further substantiated by inserting the cast pipe into a comparable section of female threaded pipe. The ease with which the pieces were joined as well as the perfect alignment of the threads were thus indicative of the precise reproducsolidification of the epoxy resin. Thereafter, the filled EXAMPLE II This example illustrates the significant advantages attained by the use of our designated amylose products in the preparation of the novel molds of this invention.

A variety of conventional, i.e. low amylose, and high amylose starch products were subjected to the following gel strength procedure in order to determine their applicability for use in preparing the novel molds of this invention. Gel strength was selected as the distinguishing characteristic because of the criticality of this factor with respect to the formation of satisfactory molds.

Thus, each starch product was slurried in water at a designated solids content and the resulting slurry thereupon cooked at a designated temperature. Thereafter, 30 cubic centimeters of each of the cooked slurries were placed in a series of containers, which Were covered, and allowed to solidify at ambient temperatures for a period of 24 hours. The strength of the resulting rigid gels was then determined by means of an Instron Tensile Tester which had been fitted with a plunger 0.5" in diameter and weighing 6.7 grams. This plunger was then pressed, with increasing pressure, against the upper surface of each gel structure; the pressure which was required in order to fracture the gel structure being noted as the gel strength thereof. For purposes of this invention, starches which exhibited gel strengths in excess of about 10 pounds/ square inch were viewed as being capable of producing satisfactory mold structures.

The complete data for each of the starch samples that was subjected to the above described test procedure are presented in the following table:

Solids content Total of amylose aqueous content, slurry, Cooking percent percent temper- Gel by by attire, strength, Starch product or blend weight weight F. p.s.i.

A high amylose corn starch 70 20 325 26 Do 20 325 28 Amylase resulting from the tract nat n of potato starch 100 14 325 81 A 1:1 mixture of amylose resulting from the iractionation of potato starch and a conventional corn starch 20 325 29 A 1:1 mixture of a high amylose corn starch and a conventional corn starch 50 20 325 11. 8 A high amylose corn starch which had been oxidized with 5%, by weight, of chlorine 35 275 378 A high amylose corn starch which had been acid converted with 2%, by weight, of 98% sulfuric acid 70 35 325 92. 8 An acetate ester of a 70 high amylose corn starch having a degree of substitution of 0.03 70 20 290 17. 6 Corn starch 27 20 325 3. 8 An acetate ester of a high amylose corn starch having a degree of substitution of 0.1 70 20 300 0. 77

tions that can be obtained from the novel casting process of this invention.

The above described procedure was then repeated with the exception that heat was applied to the epoxy-filled amylose mold in order to speed up the setting process as well as to simultaneously dispose of the mold structure. Thus, after introducing the epoxy resin into the amylose mold, the entire assembly was maintained at room tem- The results summarized above thus clearly indicate the criticality inherent in utilizing only the above designated amylose products in preparing the novel amylose 70 molds of this invention.

Summarizing, it is thus seen that this invention provides for the preparation of strong, uniform, dimensionally precise, readily disposable mold structures.

Variations may be made in procedures, proportions and perature for a period of 3-4 hours in order to initiate the 7 materials without departing from the scope of this invention which is defined by the following claims.

We claim:

1. A negative mold structure adapted for receiving and casting a fluid material comprising a three dimensional, shaped mold structure having walls and a hollow, substantially enclosed mold cavity within said walls, the walls of said mold structure serving to substantially enclose said hollow mold cavity; said mold walls comprising a rigid, solidified gel of an amylose product selected from the group consisting of: (1) the amylose fraction of whole starch; (2) whole starch containing at least about 40%, by Weight, of amylose; and, (3) mixtures of whole starches and starch fractions wherein the total amylose content of the resulting mixture is at least about 40%, by weight.

2. A negative mold structure adapted for receiving and casting a fluid material comprising a three dimensional, shaped mold structure having walls and a hollow, substantially enclosed mold cavity within said walls, the

References Cited UNITED STATES PATENTS 1,074,600 10/1913 Breyer .l 106--38.5 X 2,513,638 7/1950 Glabe 106-38.5 X 2,515,017 7/ 1950 Nicholson 264 227 3,226,239 12/1965 Schoch et al. 106-38.5 3,243,308 3/1966 Barger et al. 106--213 3,351,489 11/1967 Battista 106213 X ALLAN LIEBERMAN, Primary Examiner walls of said mold structure serving to substantially en- 20 MORRIS, Assistant Examiner close said hollow mold cavity; said mold walls comprising the rigid, solidified gel of an aqueous slurry of an amylose product containing at least about 40%, by

U.S. Cl. X.R. 106-213

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