US2966719A - Manufacture of ceramics - Google Patents

Description

Jan. 3, 1961 J. L.. PARK, JR 2,966,719

MANUFACTURE oF CERAMICS Filed June 15, 1954 L l l MMX ,4%

Unite 2,966,719 MANUFACTURE OF CERAMICS Filed June 15, 1954, Ser. No. 436,850

15 Claims. (Cl. 25-156) This invention relates to a solvent, moldable, flexible, vitriable ceramic-particulate films and masses which remain undeteriorated during storage before further processing; to a process of making the same; and more particularly, to the manufacture of thin ceramic dielectrics therefrom.

In the manufacture of ceramics, the .evaporation of volatile constituents from a slip of inorganic materials has been accomplished to provide, before firing, a bonedry replica of the article to be vitried, i.e., Vformed into a ceramic. This drying to rigidity has been considered a required step inasmuch as it has been thought that the greatest shrinkage of a piece should take place under conditions where it could be observed, i.e., before firing.

In recent years interest has been stimulated in making extremely thin ceramic articles for use in a dielectric function, particularly as insulators, components of capacitors and the like. The manufacture of these thin ceramic sections, however, presents difliculties inasmuch as a thin, bone-dry specimen, being stiff and brittle, which has been considered the nature of all ceramics before firing, is easily broken and cannot be cut or trimmed without accumulating a number of defective forms which must be rejected with a consequent waste of material. Furthermore, known methods of manufacturing thin ceramics have not been reliable in giving uniformly thin, nor extremely thin, products.

This invention provides dry, flexible, cohesive, ceramicparticulate films which may be cut easily to any desired dimensions, and which may lbe coiled or otherwise changed in shape immediately prior to tiring, without giving rise to an untoward incidence of faulty specimens and the waste occasioned thereby. These films remain in a state which may be termed leather-hard even when dry, that is, even after the volatile temporary vehicle has been removed before firing. They may vbe formed as thin as on the order of l mil in thickness, may be manipulated much the same as tapes, and may be fabricated convenientlyto any desired length.

Another advantage of this invention is that these films of dried, flexible, dense, vitriable, ceramic-particulate materials may be stored indefinitely before further processing and still retain their exibility, their moldability and freedom from undesirable cracks, pinholes and particulate disruption. Consequently, these films may be manufactured in excess of any immediate requirements and stored or otherwise handled until needed. They are tough, may be processed in an automatic manner through working machinery such as cutters, stampers, molders, rollers, and thereafter may be tired to vitrication by conventional methods.

The thin films of this invention may be made by a process of extreme simplicity requiring but a few active steps and but few precautions as compared to prior processes of making thin sheets of ceramic-particulate to be fired to a ceramic condition. Yet, by the process herein set forth, thin dielectric ceramics can more easily be made thinner than previously realized.

States Pate f 2,966,719 `'Patented Jan. 3, .1.961

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One form of `apparatus suitable for carrying out the process of my invention is illustrated schematically in the attached drawings forming a part of this specification.

Fig. `l is a side-view, schematic illustration of apparatus which maybe used in carrying out the method of coating and drying a slip of ceramic-particulate. Fig. 2 is a schematic illustration of the method of cutting the tape supported lilms hereof. Fig. 3 is a cross-section of cutting surfaces .taken 'along lines 3 3 of Fig. 2. Fig. 4 is a top-view of a cut lilm of ceramic-particulate material supported by the tape. Fig. 5 is a side-view of the peeling operation to remove the ceramicparticulate yfilm from the tape.

ln carrying out the process of kthis invention, a slip .of finely divided ceramic powder is first compounded by mixing together ,the powder, an organic volatile solvent, a wetting agent, and an organic binder composition to be hereinafter described. Conventional methods of compounding this slip may be employed but it must be thoroughly mixed to a homogeneous suspension in order to avoid undesirable striations, fractures or areas of poor strength in the fired end product. The slip is `deposited on a flexible moving tape support, spread, leveled, and slightly compressed into a thin layer, i.e., a iilrn, and then dried in situ. Drying is accomplished by the evaporation of volatile constituents, i.e., the temporary organic vehicle or solvent. Shrinkage during :drying is limited, by coaction between Ythe tape vcarrier and the iilm, to that which 'takes place perpendicular to the tape carrier; shrinkage of the ceramic-particulate lilm in a -direction parallel to the tape carrier 'or support'either-does not occur or is so negligible that it ldoes not 'impair the quality of the final Atired ceramic, even if the `ceramic is to be used lin a capacitor. Consequently, shrinkage of the film, if any, occurring in a Idirec-tion par-alici to `the tape support may accurately be termed negligible. The flexible dried film remains 'light-ly adherent on the :tape support.

The film, still intimately in contact with the supporting tape surface, may now be rolled ontoa lreel or ymay be subjected immediately to further processing steps such as cutting, molding, stamping, and the like, as hereinafter explained.

A Wide variety of thin ceramics-may be made using the process of this invention. lFer dielectrics, inorganic materials consisting chiefly of alumina, steatite, Zircon, aluminum silicate, zirconium dioxide, titanium dioxide, magnesium silicates, etc., and various combinations thereof, Iare preferred, but are only examples of raw materials which may be employed. vThe `ra-w `material selected for the Yslip is ground to a tine particle Isize, on the order of minus 325 mesh or smaller for extremely thin ceramics, but larger, eg., -on the order of minus 200 mesh, if thicker ceramics are to kbe formed, 'and still larger if it is not important lto obtain thin nonporous fired materials. Smaller par-ticle "sizes on the order of minus 325 mesh or the likefacilitate `the formation of a dense, ceramic-particulate film, and aid in getting a dense fired product, which 'is to be desired when the ceramic is to be used in a capacitor. Larger particles result in a red article of substantially less dielectric strength, frequently of va jporous `or permeable nature, and-even of la fractured orrstriat-ed complexion. By using a ceramic-particulate of a preferred small isize, a finished fired ceramic may Vbe made having --a thickness on the order of l mil.

Depending upon the raw material, the density o'f the product will vary, but for use in a capacitor the-density of the fired ceramic should yapproach :the theoretically possible iigure for the raw material selected. -High dielectric strength vthin rcapacitor fdielectrics lmay lhe 'made by this invention which exhibit a porosity, as measured by water absorption, of less than 0.02%. Of course, the refractory characteristic of a raw material affects the quality of the end product and must also be considered in the manufacture of components for capacitors and the like, as is understood in the art. Reference is here made to two patents teaching high dielectric constant ceramics, Nos. 2,429,588 and 2,626,220 to Hans Thurnauer and lames Deaderick.

Thin, dense and non-porous ceramics may be obtained according to the present invention by forming a slip having a high content of finely divided ceramic-particulate, an organic solvent preferably of low boiling point, a wetting agent, and a minimum of a binder composition of the type herein described. These slips will have varied properties, depending upon the inorganic content, but will usually have a specific gravity of between 2 and 2.6.

The binders of this invention serve to retain the ceramic-particulate in undisrupted position after the organic solvent is evaporated from the slip and, together with the organic solvent and wetting agent, facilitate the formation of dry, flexible films of the particulate material free of pinholes, cracks and other imperfections.

A preferred binder composition and wetting agent is as follows:

Percent Polyvinyl butyral 2.5 Polyalkylene glycol derivative 1.0 Alkyl ether of polyethylene glycol .2

The above percentages are by weight of the nel compounded slip. Accordingly, with toluene by weight present as a solvent, 76.3% ceramic-particulate (e.g. 75% barium titanate and 1.3% calcium phosphate, tribasic) is present in the slip.

Polyvinyl butyral is a thermoplastic organic resin having a comparatively low heat-distortion point of 130 to 140 C. In commerce it may be obtained under the trade name Butvar from the Shawinigan Resin Corporation. Polyvinyl butyral is an example of a soluble, thermoplastic, volatilizable, vinyl type resin which may be employed.

A suitable polyalkylene glycol derivative to employ in this binder composition is triethylene glycol hexoate which has a viscosity of approximately 2,000 centipoises and is a compatible plasticizer for polyvinyl butyral, that is, the triethylene glycol hexoate will not separate out into a separate phase. In the binder, the triethylene glycol hexoate functions to improve the exibility and workability of the solvent-free lrn.

A preferred alkyl ether of polyethylene glycol is the ethyl ether thereof. It functions as a wetting agent, is non-ionic and an excellent penetrant. A commercial product sold under the trade name Tergitol by Carbide and Carbon Chemicals Company contains lower alkyl ethers of polyethylene glycol and may be used as a wetting agent in the above binder composition. Compositions without a wetting agent may give a ilexible and moldable ceramic-particulate film, but require longer mixing periods to obtain the desired uniformity and viscosity in a slip. Use of a wetting agent is preferred as this agent also imparts better spreading and working characteristics to the slip, as well as facilitates the formation of an article free of pinholes.

The binder constituents, wetting agent, solvent and ceramic-particulate are thoroughly mixed in apparatus such as a pebble mill to gain a smooth, uniformly dispersed or suspended slip. This procedure may be varied, if desired, by first compounding the non-vetriiiable formulation, that is, the binder, ingredients and wetting agent, with the organic volatile solvent, and then adding the ceramic-particulate. The resulting slip has a consistency of thick cream or molasses.

To attain the proper strength and liexibility in a solvent-free film according to this invention, a variety of compatibly plasticized thermoplastic binder systems may be used. For example, polymethyl methacrylate resin compatibly plasticized with methyl abietate has been found to be a successful plasticized resin combination to gain the desired effects. Ethyl alcohol is a preferred solvent for this combination.

Cellulose acetate butyrate resin compatibly plasticized with dimethyl phthalate, or tricresyl phosphate, and dissolved in acetone as a Solvent, has also been found to form the desired uniform films of this invention.

The above specific examples of suitable binders are not meant to be limitative. Other soluble, thermoplastic, volatizable, organic resins may be employed satisfactorily as binder components to give a solvent-free, flexible, moldable and workable ceramic-particulate material. The thermoplastic resin selected may be hard or soft, high or low in viscosity, but must be volatizable during tiring of the molded article to a rigid ceramic. in the case of extremely soft, viscous-liquid polyacrylate esters, that is, those of long chain alcohols, a binder composition may be formed without the need for an added plasticizer, as long as the viscosity in the resulting slip at a high ceramic-particulate content, at least above 70%, and preferably above 75% by weight, and a solvent content by weight on the order of 20%, remains at the consistency of molasses or thick cream. These resins of low viscosity may be said to be internally plasticized and, therefore, are considered to fall within the scope of the term compatibly plasticized resins. In the case of extremely hard thermoplastic resins, such as soluble petroleum derivative resins, a higher plasticizer content is necessary in the binder composition to obtain a slip of suitable viscosity and workable characteristics and which Will give a iilm or cohesive mass having moldable and workable properties once the organic volatile solvent is volatilized therefrom. As would be expected, the amount of plasticizer required decreases with the decrease in hardness of the resin. It may be observed here that a resin and plasticizer combination is selected to gain a viscous-liquid mass of resin and plasticizer, that is, a viscous-liquid plasticized resin mass at room temperature.

Using a plasticizing agent in my binder composition serves to enhance the lm forming characteristics of the resulting slip as well as lower the temperature at which the asolvent, flexible, ceramic-particulate material will remain permanently flexible, moldable and workable. In each case, the plasticizer selected must have a specificity, a compatibility, for the particular organic resin with which it is to be employed in a binder composition and must also be soluble in the organic vehicle chosen. For example, alkyl phthalates, abietates and glycolates are all compatible plasticizers for polyvinyl butyral, and are soluble in common volatile organic solvents for the polyvinyl butyral.

The wetting `agent in the binder composition facilitates the formation lof homogeneously uniform slips having desirable spreadability. Additional examples of wetting agents are ethyl phenyl glycol, or other alkylarylpolyether alcohols, polyoxyethylene acetate, or other polyoxyethylene ester, and the like. Without such an agent, excessive mixing is required and uniform films free of imperfections are extremely diicult to form. With it, the process becomes surprisingly simple. The wetting agent selected must, of course, be soluble in the organic solvent used for the plasticized resin, be compatible therewith, and preferably is of an organic nature so that it is volatilized during tiring. While ionic inorganic wetting agents may be used, better results are obtained with volatilizable organic wetting agents which are compatible with other components of the slip. By compatible it is meant that the agent will not separate out from the other components,

The total amount of non-vitriiiable components, that is, plasticized resin, wetting agent and the like, which may be present in an asolvent, ceramic-particulate film 'having properties as desired may vary from approximately 3% to approximately 15%, but preferably is between 3 and for capacitor dielectrics. The amount of wetting agent employed is only a relatively small proportion of the total of the non-Vitriiable components, and in most films does not exceed approximately 2 or 3% of the dry weight of the film.

Any volatile, low boiling point (e.g., preferably approximately on the order of the boiling point of toluene or below), organic solvent in which all non-vitrifable components of the slipare soluble is suitable to employ. Examples of solvents are toluene, ethanol, butanol, acetone, methyl isobutyl ketone, isopropanol, diacetone alcohol, benzene and the like, but the specific temporary organic vehicle selected for use as the solvent must be one in which the resin, plasticizer and wetting agent of the slip formulation are allsoluble.

After gaining a slip of a viseocity which may vary from approximately 400 to approximately 1200 centipoise seconds, and which may be characterized as of the consistency of molasses or thick cream, the mass is deaired by means well known in the ceramic art. At this point the slip is still maintained at the consistency of molasses or thick cream. Deairng accomplished, the slip is transferred to a slip reservoir where it is suitably maintained in a uniform homogeneous state -by an agitating arm. The agitation effected by any agitating arm is never allowed to proceed to the point where air is entrained in the body of the slip.

From the reservoir the `slip is discharged through a small orifice in a pool onto a substantially-horizontal, flexible, supporting tape. The flexible supporting tape may be of any impervious, non-porous material, such as polytetrafluoroethylene (Teflon), glycol terephthalic acid polyester (Mylar), cellulose acetate, cellophane (regenerated cellulose) and the like. A cellulose derivative is preferred. 'Ille advantage of using materials of this type lies in the fact that great uninterrupted lengths of a uniform supporting surface may be passed beneath the discharge orifice. Interruptions o-f the process are, therefore, less frequent than with other processes, and irregularities in the flexible ceramic-particulate film are avoided. However, any suitable impervious, non-porous, smooth, insoluble, flexible materials may be employed as the supporting tape.

The slip, e.g., one formulated with the preferred binder and wetting agent as set forth above, deposited in a pool on the supporting tape, is then slightly compressed, spread and leveled. While I use a method of depositing the slip on the tape which amounts to fundamentally a pouring action, other methods of placing the slip on the tape may be employed, methods such as extrusion included. After being spread on the supporting tape surface, volatile constituents of the slip--in the preferred embodiment, the tolueneare removed by evaporation. Removal of the volatile constituents from the film of slip is accomplished at a raised temperature and at a rate depending upon the thickness of the film. The temperature should not exceed the boiling point of the particular solvent employed, temperatures slightly below 80 C. being preferred since at higher temperatures the film of ceramic-particulate material has a tendency to bubble up and form cracks and pinholes. The factors of temperature and rate of drying are controlled by passing heated air in a countercurrent direction to the movement of the coated supporting tape through a drying chamber. This operation may be accomplished in as short a period as two minutes for extremely thin coats and in progressively longer periods as the thickness of the film of ceramic-particulate material is increased. It is preferred to dry thick coats at substantially lower temperatures, on the order of 30 to 50 C., than those employed when dealing with thin coats, which can be dried suitably at temperatures as high as 80 C., inasmuch as with thick coats of slips there is a tendency at higher temperatures `toward drying-crust formation before all volatile constituents of the temporary vehicle have escaped from the center of the slab. If a thick film or coat of ceramic is desired, a highly volatile solvent such vas acetone, depending also upon the nonvitrifiable components, may be employed advantageously. In the usual case, rdrying is suitably accomplished by merely passing a two inch wide, tape-supported slip-film at approximately '3 linear feet per minute through an approximately 8 foot long drying chamber.

After volatile constituents have been removed, the tapesupported dried film may be wound upon a reel. The,

/dried film is an intimate blend of inorganic materials in a matrix comprising binder and wetting agent, and remains flexible even after an extended period of storage. in most cases, however, this storage period is short, the film usually being immediately subjected to further processing. Using a thin flexible film of ceramic-particulate such as herein disclosed permits the manufacture of highly dense ceramic dielectrics, on the order of l mil in thickness, by rapid, automatic processes.

Referring now to the figure inconporated in and made a part of this specification, it is seen that a slip reservoir 10 is placed immediately above a supporting conveyor tape 11. A stirrer (not shown) may be employed within the slip reservoir to agita-te the slip, that is, the suspension of ceramic-particulate, without entrainin-g air. The slip reservoir terminates in la small nozzle 12 with an orifice in its end of approximately 1/16 of an inch in diameter. While I prefer a discharge nozzle with an orifice 0f approximately 1/16 of an inch in diameter, other discharge slot shapes may be employed. A pay-out roll of flexible "supporting tape 13 is mounted with a friction clutch (not shown) to allow the flexible tape to be peeled therefrom vonly under a slight tension, thereby to prevent the tape from unwinding in excess. The tape moves over a suppont iron 14 where slip is received, and then passes beneath -a doctor blade or bar 15 where the slip is spread, leveled and slightly compressed against the tape. Guide panels may be used on each side of the doctor blade to prevent waste of slip by any action spreading it off the tape. The flexible supporting tape 11, coated to each edge with slip, then passes between two baffles 16 and 17, one below and one above the tape, into a drying chamber 18. The drying chamber is preferably approximately 8 feet long and is fitted with a plurality of spindles 19 to support Ithe flexible tape as it passes therethrough. These spindles 19 are spaced at different levels so as to form somewhat of an arc the length of the drying chamber. This is required when heating extremely thin fil-ms of ceramic-particulate on flexible tapes inasmuch as the tape itself undergoes some warping when subjected to heat. Heated air is passed in a counter-current direction to that direction taken by the passage of the flexible supporting tape through the drying chamber. A-t the end of the drying chamber the Ebaffles serve to deflect the air from that tape which has just been coated with slip and prevent premature drying action at the point of spreading and leveling of the slip on the tape. The coated tape vpasses between rollers 20 and 21 and is drawn through the apparatus by these rollers, roller 20 being supplied with low geared power and roller 21 pressing resiliently thereagainst. The coated tape is then wound on a reel 22.

The solvent-free, flexible, ceramic-particulate film may now be subjected conveniently to any necessary process before =being fired to vitrification. It has the property of being slightly elastic when subjected to stress and may be fired under stresses, e.g., fin arcuate form, without untoward-development of areas of poor dielectric strength due to strain in the product. ln 'the flexible dried state, the amount of ceramic-particulate in the film formed with the preferred binder composition and wetting agent in amounts as set forth above is around 96%. In the usual case, the amount of ceramic-particulate in the film to be used as a dielectric shold lbe above 90%, and, preferably should approach 96 or 97%. As low as 85% may be employed, but this renders the film undesirable for use in the manufacture of components for capacitors. Generally speaking, it is the high ceramic-particulate content of my flexible films which makes them so desirable for use in the manufacture of dielectrics. With such a high content of non-film forming ceramic-particulate constituents, it is surprising that an asolvent, flexible, tough, slightly elastic film as disclosed herein can be formed.

A solvent-free film having a high content of barium titanate, or the like, as disclosed in the above referenced patents, may be used in the manufacture of capacitor plates. Referring to Figure 2, the tape supported ceramicparticulate, eg., barium titanate, film 23 is drawn from a reel 24 beneath stationary cutting surfaces 25 which act to slice the film longitudinally. Figure 3 is an enlarged cross section of these cutting surfaces taken along line 3 3 in Figure 2, and shows an enlarged View of the cutting knives 25 penetrating only the ceramic-particulate coating 26 on the tape 38. The tape supported lm is pulled in a taut manner beneath these cutting surfaces by rollers 2.7 and 2S, roller 27 being powered and roller 28 pressing resiliently thereagainst. The tape supported lm is then allowed a compensating lag 29 before it is advanced intermittently, by `and between resiliently opposed rollers 30 and 31, beneath a synchronized transverse cutting edge 32, which acts against surface 33, with :a tolerance within approximately 0.()02

' of an inch, to cut the film without cutting the supporting tape. At this stage the ceramic-particulate film has been cut into a plurality of small square or rectangular units supported on the flexible tape. The tape supported units then `are wound on a roll 34. From the roll 34, the units are transferred to refractory plates by an unusually unique step in this art. A strip of tape holding the cut film, as illustrated `in Figure 4, is pulled off the reel, inverted, that is, placed film side down on a refractorysetter plate 35, as illustrated in Figure 5, and stripped from Ithe ceramic-particulate units 36, leaving them in position for firing. The small square or rectangular units of ceramic-particulate remain loosely adherent to the supporting tape and, therefore, the inversion of the tape need not be accompanied by any special precautions. To accomplish the removal of the tape from the small units 36 of ceramic-particulate in a swift manner, a rod 37 is placed on top of the inverted tape 38 and the tape peeled from the cu-t units by pulling it around this rod. In order to do this in a manner to prevent adherence of the small cut units to the withdrawn tape and consequent distortion of the units, particularly arcuate distortion, the rod must be of a small diameter, preferably on the order of approximately 1/s of an inch. It will be seen that a `great number of thin capacitors may be made continually by my process in a short period of ltime and in ya substantially automatic manner. While I show particularly cutting of the fiexible film, other methods of forming the film into articles, methods such as scoring, stamping and the like, may be employed. Ceiling and arching of the film separated from the supporting tape, and firing it in a coiled or arched state, is also possible without untoward occurrence of areas of poor dielectric strength due to strains in the fired product.

If desired, cakes lof moldable, cohesive, ceramic-particulate masses may be formed by a variation of the process above, such a process comprising extruding a highly viscous slip of ceramic-particulate in a layer onto a conveyor, and drying it as set forth above with respect to the drying of thick films at lower temperatures and at a slow rate. The solvent-free, cohesive aggregate or mass of inorganic materials may be molded by impact, injection or other means as desired. It remains workable until red to a rigid ceramic.

Asolvent, flexible strips of extruded or coated ceramic- 'particulate material hereof may also be employed in the manufacture 4of a number of like parts by an unusual simultaneous stamping and molding process, the parts, thereafter, being fired to vitrification.

The simultaneous stamping and molding of these strips or thick films, preferably after they have been separated from a supporting surface, may be accomplished to only a partial state, i.e., the stamping operation may be used to mold in the strip an article which still clings to the body of the strip. In effect, the molded article is merely scored in the strip. In this condition, the strip is fired and the molded article or articles later separated from the strip.

I do not wish to be limited in the scope of my invention defined above except as set forth in the appended claims.

I claim:

LA process of making ceramics comprising formulating a slip of a homogeneous character and adapted for use in forming dense ceramics, said slip comprising a high content of ceramic-particulate, a volatile organic temporary vehicle, and a compatibly plasticized thermoplastic binder resin which promotes the formation of fiexible films and which is soluble in said vehicle, spreading and coating said slip in a film on a smooth flexible movable supporting tape, removing the volatile temporary vehicle from the film while simultaneously retaining the remaining coated constituents of said slip in adherent relation to the flexible supporting tape and supported thereby, and firing the vehicle-free flexible film to a rigid ceramic.

2. A process as in claim l in which the film comprising ceramic-particulate is formed, after removing the volatile temporary vehicle, into articles while supported by the supporting tape.

3. A process for making thin ceramics comprising formulating a slip of a homogeneous character and adapted for use in forming dense ceramics, said slip comprising sufficient ceramic-particulate to account for at least o-f the solids material of said slip, a volatile organic temporary vehicle, a compatibly plasticized thermoplastic binder resin, and a wetting agent compatible with the plasticized resin, said plasticized resin and wetting agent Ibeing soluble in the temporary organic vehicle, spreading said slip in a film on a smooth flexible movable supporting tape, removing the volatile organic temporary Vehicle from said slip while simultaneously retaining the remaining film constituents of said slip in adherent relation to the flexible supporting tape and supported thereby, forming the flexible, vehicle-free film of ceramic-particulate into articles, and firing the formed articles to a rigid ceramic.

4. A process as in claim 3 in which articles formed from the vehicle-free film of ceramic-particulate material are thereafter arched and fired in arcuate form.

5. A process as in claim 3 in which the resin is a polyvinyl type compatibly plasticized with a polyalkylene glycol derivative.

6. A process as in claim 3 in which the vehicle-free, flexible film of ceramic-particulate, while supported on the tape, is cut by drawing said tape-supported film in a taut manner and at a uniform rate of movement beneath longitudinal cutting means, and by advancing said tapesupported film intermittently through synchronized lateral cutting means.

7. A process for making thin ceramics comprising formulating a slip of a homogeneous character and adapted for use in forming dense ceramics, said slip comprising sufficient ceramic-particulate to account for at least 85% of the solids material of said slip, a Volatile organic temporary vehicle, and a compatibly plasticized organic binder resin, spreading and leveling said slip in a film on a substantially horizontal, smooth flexible movable supporting tape, removing volatile constituents 'from said slip at a raised temperature up to approximately 9 80 C. to leave it in a solvent-free condition while simultaneously retaining the solvent-free, tiexible lm of ceramic-particulate in intimate adherent relation to the supporting tape and supported thereby, cutting the iiexible film While adherently supported on the tape, resting said cut iilm in contact with a refractory surface, removing the cut lm from the flexible supporting tape Without arcuate distortion of the film by peeling the tape over itself from the lm, and tiring the said iilm to a rigid ceramic.

8. A solvent-free, moldable, cohesive flexible lm in the form of a length of tape, said film Lbeing reable to a rigid ceramic state and comprising an intimate blend of more than 90% vitriiable inorganic materials in particulate form, an organic-solvent-soluble compatibly plasticized thermoplastic `organic binder resin, and a non-ionic organic wetting agent compatible with said plasticized binder resin.

9. A solvent-free, cohesive Ilayer in the form of a length of tape, said layer being fireable to a rigid ceramic state and comprising an intimate blend of more than 85% inorganic materials in particulate form, an organic-solvent-soluble thermoplastic organic binder resin, a compatible plasticizer for said resin, and a non-ionic organic wetting agent compatible with the plasticized resin, said layer being characterized by a flexibility at room temperature.

10. A solvent-free flexible cohesive layer in the form of a eXible length of tape, said layer comprising an intimate blend of more than 85% ceramic particulate, an organic-solvent-soluble thermoplastic polyvinyl butyral binder resin, and a compatible organicsolvent-soluble polyalkylene glycol plasticizer for said resin, said layer being characterized by being flexible at room temperature as well as by being fireable to a rigid ceramic state.

11. As an article of manufacture: a thin strip of flexible solvent-free green ceramic supported in adherent relation upon a removable smooth flexible supporting tape, said green ceramic strip being solvent-free and comprising an intimate blend of at least 85% ceramic particulate, an organic-solvent-soluble thermoplastic organic binder resin, and an organic-solvent-Soluble cornpatible plasticizer for said resin,

12. A process of making ceramics comprising formulating a slip of a homogeneous character and adapted for use in forming dense ceramics, said slip comprising suficient ceramic particulate to account for at least 85% of the solids material of said slip, a volatile organic temporary vehicle, and a compatibly plasticized organic binder resin which promotes the formation of exible ilms and which is soluble in said volatile organic temporary vehicle, coating said slip in a ilm upon a smooth liexible moving supporting tape, evaporating the volatile temporary vehicle from the coated film While simultaneously retaining the remaining coated constituents of said slip in adherent relation to the flexible supporting tape and supported thereby, then stamping articles out of said resulting vehicle-free exible iilrn, yand ring the articles to a rigid ceramic.

13. A process as in claim 12 in which the vehicle-free exible film is stripped from the supporting tape prior to stamping the articles therefrom.

14. A process for making a exble, vehicle-free cohesive layer comprising at least inorganic materials which may be red to a rigid state, said process compris ing formulating a slip of a homogeneous character and adapted for use in forming dense ceramics, said slip comprising sufficient vitriable inorganic materials in particle form to account for at least 85% of the solids material or" said slip, a volatile organic temporary vehicle, and a compatibly plasticized organic binder resin which promotes lthe formation of flexible layers and which is soluble in said organic vehicle, coating said slip on a smooth flexible moving supporting tape, evaporating the organic temporary vehicle from said layer of coated slip While simultaneously retaining the remaining coated constituents of said layer in adherent relation to the flexible supporting tape and supported thereby, and then forming said vehicle-free iiexible cohesive layer into articles prior to firing the same.

15. A process as in claim 14 in which the vehicle-free exible cohesive layer is Wound into a storage roll before forming articles therefrom.

References Cited in the tile of this patent UNITED STATES PATENTS 2,082,486 Frenkel July l, 1937 2,122,960 Schwartzwalder July 5, 1938 2,266,636 Hauser Dec. 16, 1941 2,358,211 Christensen et al. Sept. l2, 1944 2,371,353 Parsons Mar. 13, 1945 2,382,136 Crowley Aug. 14, 1945 2,425,626 Light Aug. 12, 1947 2,486,410 Howatt Nov. 1, 1949 2,519,280 Potter et al Aug. 15, 1950 2,542,827 Minter Feb. 20, 1951 2,582,993 Howatt Jan. 22, 1952 2,624,683 Bezman Ian. 6, 1953 2,670,339 Edmunds Feb. 23, 1954 2,736,080 Walker et al Feb. 28, 1956

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