US3302239A - Die - Google Patents

Description

Feb. 7, 1967 E, SEN A; 3,302,239

DIE

2 Sheets-Sheet 1 INVENTOR VANCE EVAN SENEGAL Filed May 24 1965 ATTORNEY Feb. 7, 1967 v. E. SENEGAL 3,302,239

DIE

Filed May 24, 1965 2 Sheets-Sheet 2 INVENTOR VANCE EVAN SENEGAL ATTORNEY United States Patent 3,302,239 DIE Vance Evan Senecal, Wilmington, Del, assignor to E. I. du Pont de N emours and Company, Wilmington, Del.

Filed May 24, 1963, Ser. No. 283,018 4 Claims. (Cl. 1812) This invention relates to an extrusion coating die for applying a coating to a moving web. More particularly it relates to a low pressure extrusion coating die with a permanently shaped flow distribution channel.

Photographic films and papers usually have a sheet support and a multiplicity of layers. In the case of blackand-white films, not as many layers are required as for multicolor films. In the former films, however, it is common to coat a gelatino-silver halide emulsion onto a film base and then to coat the emulsion layer with a non-photographic aqueous gelatin solution to provide an antiabrasion layer. In color films, there is usually a separate layer for recording each of the primary colors, and yielding a dye image in addition to tfilter and antiabrasion layers. All of the above layers are usually formed by separate coating operations. The various layers in theses multiplayer photographic elements, particularly in the case of color films, should be of uniform thickness and free from defects.

In black-and-white films the variation in coating weight, ideally, should not exceed i2.0%, and in multicolor films, i1.0%. In order to coat a highly viscous photographic emulsion having a low fluid content at high speeds, emulsions are extruded through a die at elevated pressures. Dies suitable for this purpose usual-1y comprise an internal supply chamber and an orifice formed by two lips co-extensive with said chamber. In order to deposit the desired amount of emulsion per unit of surface at coating speeds of 80 to 400 feet per minute, the orifice must be precisely adjusted and the lips rigid so that the width of the orifice throughout its entire length can be maintained within precise narrow limits. This is because for ideal or so-ca-lled Newtonian fluids the coating weight varies as the third power of the width between the lips.

Since fluid photographic emulsions are non-Newtonian in character, the coating weight of the emulsion layer may vary as much as the 4th or th power of the gap or width dimension variation between the die lips. It has been found that, even where the die and lips are rigid, it is difficult to maintain the transverse coating weight uniform within the above limits. This is due in part to the deflecton of the die lips during the high pressure extrusion thereby giving a non-uniform coating weight profile.

Various types of dies have been proposed in order to provide uniform coatings but uniform flow distribution throughout dies of considerable length is difiicult to attain and improper distribution causes defects in the form of streaks.

The use of an internally braced die as disclosed in assignees Senecal US. application Ser. No. 128,775 filed Aug. 2, 1961, now Patent No. 3,151,356, has reduced the non-uniformity of coating weight by reducing the deflection of the die lips, but the braces can cause flow patterns or streaks in the coated web.

An object of this invention is to provide an improved extrusion die. A further object is to provide an extrusion die which will give a uniform coating under conditions of elevated fluid pressures. Another object is to provide such a die which will give smooth, uniform, wide coatings devoid of streaks and other coatings defects. A further object is to provide a simple and dependable extrusion die. A further object is to provide a die hav- 3,302,239 Patented Feb. 7, 1967 ing improved flow distribution. A further object is a die which provides the required fluid distribution at reduced internal pressures, i.e., not more than 40 pounds per square inch. A still further object is to provide a simple die that can be readily assembled and is useful in applying one coating or two coatings simultaneously to a web. Still other objects will be apparent from the following description of the invention.

According to the present invention, there is provided an extrusion die for controlling the flow to fluid along diverging paths from an inlet to and through a narrow slot outlet comprising:

(a) A body member having at least one inlet and an outlet terminating in a side surface of the body member, a portion of said surface defining one surface of the slot outlet,

(b) A fluid control plate on a side surface, the inner surface of which plate has a series of interconnected depressed chamber areas forming with said surface (1) A centrally disposed inlet area,

' (2) A transverse supply chamber,

(3) A transverse real restricted passage, and

(4) A sec-0nd transverse cross-flow chamber that provides another flow control passage adjacent the slot outlet and communicates with said slot outlet.

The chamber area forming the transverse rear restricted passage can be of lesser or greater depth than the chamber area of the cross-flow chamber.

At least one of the leading and trailing edges of the transverse rear restricted passage is curved from a central point to the lateral edge so that integral units of emulsion passing from the inlet through the supply chamber and traveling the shortest path to the cross-flow chamber must travel a longer distance through the restricted passage to compensate for diiferences in pressure drop. The length of the transverse rear restricted passage in the direction of fluid flow is varied along diverging paths of fluid flow from the centrally disposed fluid opening to the slot outlet to equate total pressure drops along each of said paths.

In the preferred die, shown in the drawings, the die body is wedge-shaped and has a control plate on each surface. If desired, each control plate can be provided with a pressure measuring and controlling device mounted adjacent to and in communication with the fluid supply chamber. Also, if desired, the body and/ or plate can be provide with passages and fittings so that the heat exchange fluid can be circulated therethrough to control the temperature of the body or plate.

The invention will now be described with reference to the accompanying drawings in which:

FIG. 1 is a vertical cross-section of the die taken along the line 11 of 'FIG. 2 except that the pressure transducer and bolts, respectively, are not shown in the lower and upper plates.

FIG. 2 is a plan view of one of the plate members showing the location of the flow distribution chambers or recesses in relation to the lips of the die;

FIG. 3 is an isometric view of the inner surface of the control plate showing the various dimension symbols used in the mathematical computation; and

FIG. 4 is an enlarged, modified vertical sectional view of the left portion of FIG. 1 and showing various dimension symbols.

Referring now to the drawings, wherein the same reference numerals refer to the same parts in the several views, the extrusion die of this invention comprises a In the inner surface of each plate and communicating with a fluid inlet area is a recessed, transverse supply chamber 5. Spaced therefrom is a second recessed transverse cross-flow chamber 6, the bottom wall 7 of which at its trailing edge slopes inwardly toward the coacting slanting surface of the body member until it meets a slot orifice-defining surface 8, which is preferably parallel to said surface for a short distance. Between the supply chamber and the cross-flow chamber formed with the surface of the body and the plate there is a recessed, rear, restricted fluid distribution passage 9 of less depth than supply chamber 5.

Either the trailing edge 10, leading edge 11, or both, of the rear, restrictive fluid distribution passage are shaped according to a mathematical calculation so that the integral units of emulsion passing from the inlet through the supply chamber in traveling the shortest path to the rear restrictive passage must travel a longer length through the restricted distribution passage to compensate for the differences in pressure drop.

The shape of the edge is calculated on an approximate solution of the equations of motion for a Newtonian fluid. Referring to FIGURE 3, P equals the pressure at the inlet to the supply chamber; P(x) equals the pressure at a perpendicular distance x from the center of the die, L equals the length of the supply chamber from the center of the die and equals the pressure gradient in a channel of the same shape as the fluid supply chamber but without distributing fluidallowance being made, however for fluid removal en route. The proper design of the shaped edge, the leading edge 11 in this case, requires that the pressure at the trailing edge of the rear restrictive passage 9 be uniform along the edge. The critical step in the design is the calculation of the supply chamber pressure at various points along the leading edge. It can be shown mathematicaly and experimentaly that as the ratio of the width of the feeding chamber to the length of the chamber becomes small, the pressure in the chamber at position x The shape of the leading edge is determined then by specifying that the pressure at the trailing edge of the rear restrictive passage is constant, thus obtains the length of passage Y in a particular location as where b equals the depth of the rear restrictive passage and C is a function of the geometry of the supply chamber.

Use of this computation is strictly valid only when the fluid is Newtonian in both the supply chamber and the rear restrictive passage and the ratio of the width of the supply chamber to its length tends toward zero, but it has been found experimentally that any deviation is small and can be compensated for by the cross flow chamber.

In a die where the depth of the supply chamber was 0.313 inch, the width of the chamber is 1.000 inch, and the depth of the rear restrictive passage b is 0.120 inch the length of the rear restrictive passage is equal to 0.4 68

Using this die it was found that the coating weight uniformity has variations below i2% over 9095% of the film width and below -:1% over 80-85% of the width.

The cover plates are fastened to the wedge-shaped member by a plurality of machine screws 12 which extend through the control plates and have threaded engagement with threaded holes (not numbered) in the body member. If desired, as shown in FIG. 1, the heads of these screws can fit in recesses 13 in the plates.

Each plate is preferably provided with a lateral socket 14 opposite the fluid supply chamber and having communication therewith through passages 15. A pressuresensitive device, e.g., a pressure transducer 16, is placed in the socket and is fixed in place by a suitale guide sleeve 17 and held in place by suitable flanges 18, which are held in place by means of screws 19. A lateral pipe 20 extends through the cap and is connected to the transducer. The pipe connects with a suitable control device so that the fluid pressure in the fluid supply chamber can be controlled and determined.

Coacting with each fluid inlet passage 3 there is a pipe sealing flange 21 which is fastened to the upper surface of the body member. Pipe 22 fitted into the flange connects to a source of fluid material to be extruded. The source for one supply chamber can be different from that of the other chamber. The body member and/or each plate or both plates can be provided with channels or passages 23 for circulation of a heat-exchange liquid.

As shown in FIG. 1 of the drawing, the bottom edges of each plate preferably converge at or near the apex of the body member so that the sheets of material being extruded meet at or near the orifice. In this way a composite sheet can be formed from the two extruded layers as they come into surface contact. The bottom of each of the plates can be of the same pointed shape or they can be different, as shown in FIG. 1 of the drawings.

The wedge shaped body may come to a knife-edge or sharp point or it may be truncated slightly to form, for example, a narrow, fiat edge, e.g., about 0.002 inch in width.

Referring to FIG. 4, the use of low internal pressure provides for better coating geometry. With very little deflection problem the lip tip angles Q can be reduced to approximately 30 in both the plates and the wedge piece. These small angles permit closer access to the coating roller 24 and shorten the distance between the end of the orifice and the surface of the web being coated, thereby minimizing susceptibility to coating disturbances. The use of a coating roller with a small diameter, i.e., /2 inch in conjunction with the low lip tip angle also permits said distance or extrudate length to be described.

The extrudate angle A or the angle formed between the die slot from which the emulsion emerges and a line drawn from the die lips to the coating roll tangent also has an effect on the uniformity of the coating. An angle of or greater with as short an extrudate 2: as possible is the ideal condition. It was found that with an angle of and an extrudate of 0.150 inch the uniformity of the coated emulsion was within the desired limits.

In assembling the device the plate members are put in place and fastened down with the screws 12. A gasket (not shown) should be inserted around the periphery or outside edges of the plates to seal the chambers.

The control plates and wedge-shaped member can be made of any strong metal or metal alloy. The plates and wedge-shaped member, for example, can be made of cast iron, stainless steel, die steel, including vanadium steel, titanium, brass or bronze. For example, when coating a photographic emulsion with an 0.012-inch lip opening to control coating weights within 10.5 to 1% across the web, all interior surfaces including mating surfaces and the die lips must be highly polished to within a dimensional accuracy :20 micro-inches. The particular metal used will depend on the corrosive characteristics of the material being coated. The various screws, bolts, etc. can be made of steel, stainless steel, titanium or other suitable metal or metal alloy.

In operation, when coating, for example, a viscous, aqueous photographic silver halide gelatin emulsion and an aqueous gelatin solution to form an antiabrasion layer, the extrusion coating die is placed in position for coating a suitable web. In FIG. 1, the extrusion coating die is shown in position relative to the coating roll supporting the web to be coated. In normal coating position, the center line of the emulsion flow path should be directed up at an angle of 35 to the horizontal and approximately tangent to the coating roll surface. The length of the unsupported region of flow for the composite sheet of silver halide emulsion layer and antiabrasion layer where it is being drawn down from the plane of the tips of the lips on the control plates 4 to the point of contact with the web on the coating roll should not exceed 0.300 inch in the direction of web travel. In the arrangement, a continuous sheet of film or paper 25 from a source (not shown) passes around coating roller 24 and to a suitable drying Zone and thence to a windup apparatus (all not shown).

In using the extrusion die of this invention, two thin wide layers of viscous materials are simultaneously extruded under pressure and brought into surface contact at or near the orifice, then applied to the surface of a continuous web moving at a speed greater than the speed of extrusion. The layers, as they leave the orifice, can be about .00025 to .014 inch in thickness and when one layer is used as a sublayer or protective layer for the main layer, in general, it will be to /2 the thickness of the former. By having the web moving at a rate of speed faster than the speed of extrusion, one can obtain a drawdown of the extruded film 1 to 2.00 times in thickness at coating speeds greater than 80 feet per minute, particularly with viscous liquids having a viscosity of 2000 to 50,000 centipoises. Pressures of to 40 pounds per square inch can be used. If desired, a single layer of a desired coating material may also be coated by using only one side of the novel coating die.

In an exemplary procedure of coating a single layer, a silver halide emulsion was made, extruded, and coated onto a cellulose acetate film base as follows:

A dilute aqueous photographic emulsion containing about 5.98% silver halide and about 10% gelatin by weight was concentrated by heating it in a climbing film evaporator and the temperature adjusted to about 107 P. where the viscosity was about 5 000 centipoises. The silver halide emulsion coating solution was fed from a pressurized chamber into one inlet passage 3 of the dual extrusion coating die of this invention. The flow rate was adjusted so that the emulsion was applied at the rate of approximately 60 mg. silver halide per square decimeter.

The die lips were placed above a 4 inch diameter coating roller so that the draw-down span between the web and the bottom edge of the plate on the left side was 0.150 inch. The pressure in the coating chamber was held at 45 mm. mercury absolute and the coating speed was 252 feet per minute. After coating, the emulsion was dried, and had satisfactory photographic quality. The layer of emulsion had good adherence to the base and the layer was uniform in thickness throughout its area indicating a uniform transverse coating weight profile across the width of the web.

The extrusion die of the invention is particularly useful in simultaneously extruding (a) a thin layer of an aqueous dispersion of light-sensitive silver halide in a natural or synthetic water-permeable colloid and (b) a thin protective layer of a water-permeable colloid containing an antistatic agent, or (c) an antihalation layer from an aqueous dipsersion or solution of an antihalation pigment or dye in a water-permeable colloid binding agent and then applying the composite layer to the surface of a moving web of film or paper. Alternatively, two different aqueous dispersions of silver halides in a water-permeable macromolecular organic colloid can be extruded simultaneously and the composite layer coated onto a continuous moving web. The above two different dispersions may contain color formers or filter dyes and may be two of the record and/orauxiliary layers of a multilayer film for color photography. An important feature of the invention is that the novel coating die can just as easily be used to coat single layer products.

Various kinds of liquid or liquefied materials can be extruded by the apparatus of this invention. Among such materials are film-forming polymers including polyethylene, polyvinyl chloride, poly(vinylchloride 00 vinyl acetate), polymethyl methacrylate, polystyrene, polyethylene terephthalate; regenerated cellulose, cellulose acetate, cellulose propionate, cellulose acetate butyrate and ethyl cellulose; rubber hydrochloride, etc. These materials can be extruded in the form of an aqueous dispersion, solution in a solvent, or in molten or liquefied form. The apparatus is especially useful in coating gelatine-silver halide emulsions, and other dispersions of finely divided materials in water-permeable colloids.

When the material being extruded has to be held at a certain temperature, a heat-exchange fluid, e.g., water, diphenyl oxide, chlorinated biphenyl, chlorinated naphthalene and parafiin hydrocarbon oils, maintained at the requisite temperature, is passed through the circulation passages in the wedge-shaped member and the plate members.

Antiabrasion coatings, such as those used to coat X-ray sensitive silver halide emulsions are effective in thicknesses as low as thirty millionths of an inch. Yet, such exceedingly thin layers are diflicult to extrude or coat in the form of uniform wide layers. By using the extrusion die of this invention, such exceedingly thin layers can be readily extruded and coated onto webs over long periods of time. By extruding one extremely thin silver halide emulsion layer in contact with a thick emulsion layer, the composite films or layers can be stretched during the coating operation, whereas the extremely thin layer would be too fragile to be stretched or drawn down separately.

The apparatus of this invention has the advantage that it is simple in design but dependable in operation. It enables one to extrude a composition onto a rapidly moving web with uniform distribution throughout the thickness and width of the layer and without coating streaks. A further advantage of the invention is that the apparatus enables one to provide an extruded composite film having a uniform coating weight profile across the width of the coating or layer. A still further advantage of the die of this invention is that it has a few simple parts which can be readily assembled and quickly adjusted to give a coating of uniform profile.

The photographic films and papers obtainable by use of the extrusion die of this invention, moreover, have improved characteristics. Multilayer col-or films having extremely thin filter, light-absorbing barrier and other layers contiguous with or adjacent to a silver halide emulsion layer or layers, antihalation layers, etc., have improved resolution over films having thicker layers obtainable by conventional ooating methods.

I claim:

1. An extrusion die for controlling the flow of fluid along diverging paths from an inlet to and through a narrow slot outlet comprising:

(a) a body member having at least one inlet and an outlet terminating in a side surface of the body member, a portion of said surface defining one surface of the slot out-let,

(b) a fluid control plate on a side surface, the inner surface of which plate has a series of interconnected depressed chamber areas forming with said side surface (1) a centrally disposed inlet area, (2) an unobstructed transverse supply chamber,

7 8 (3) a transverse unobstructed rear restricted pas- 3. An extrusion die according to claim 1 where the sage, and chamber are-a forming the restricted passage is of greater (4) an unobstructed second transverse cross-flow depth than the chamber area of the cross-flow chamber. chamber that provides another flow control pas- 4. An extrusion die according to claim 1 wherein said sage adjacent the slot outlet and communicates 5 body member is wedge shaped and the side surface of the with said slot outlet, the length of the transverse body member is a slanting surface. rear restricted passage in the direction of fluid flow from said centrally disposed inlet area to References Cited y the Examine! the slot outlet being varied along diverging paths UNITED STATES PATENTS of fluid flow from said inlet area to said slot outlet 10 to equate total pressure drops along each of said at paths, the shape of the curved leading edge of 2932855 4/1960 Bartlett-e121 18-15 X said restricted passage being determined by 10/1962 Reifenhauser' 18 12v maintaining the pressure at the trailing edge of 3118179 1/1964 Bonner 18 12 the rear restricted passage at all points so that 15 3151356 10/1964 Senecal 1812 at a par icular poin in the leading edge of the 3197815 8/1965 V 18-12 passage the said length Y equals an lper 531,201 X X 2 References Cited by the Applicant 3 Z (Z 1 UNITED STATES PATENTS 2,734,224 2/1956 Winstead. where b equals the depth of the rear restrictive 2 813 301 11/1957 Underwooi passage, L is one-half the total transverse width 2 901 9/1959 Beck of the passage and C is a constant function of the geometry of the supply chamber. OTHER REFERENCES 2. An extrusion die according to claim 1 Where the 25 M d Pl ti page 112, July 1960, chamber area forming the restricted passage is of lesser depth than the chamber area of the cross-flow chamber. WILLIAM J. STEPHENSON, Primary Examiner.

Claims (1)

1. AN EXTRUSION DIE FOR CONTROLLING THE FLOW OF FLUID ALONG DIVERGING PATHS FROM AN INLET TO AN THROUGH A NARROW SLOT OUTLET COMPRISING: (A) A BODY MEMBER HAVING AT LEAST ONE INLET AND AN OUTLET TERMINATING IN A SIDE SURFACE OF THE BODY MEMBER, A PORTION OF SAID SURFACE DEFINING ONE SURFACE OF THE SLOT OUTET. (B) A FLUID CONTROL PLATE ON A SIDE SURFACE, THE INNER SURFACE OF WHICH PLATE HAS A SERIES OF INTERCONNECTED DEPRESSED CHAMBER AREAS FORMING WITH SAID SIDE SURFACE (1) A CENTRALLY DISPOSED INLET AREA, (2) AN NOBSTRUCTED TRANSVERSE SUPPLY CHAMBER, (3) A TRANSVERSE UNOBSTRUCTRED REAR PASSAGE, AND (4) AN UNOBSTRUCTED SECOND TRANSVERSE CROSS-FLOW CHAMBER THAT PROVIDES ANOTHER FLOW CONTROL PASSAGE ADJACENT THE SLOT OUTLET AND COMMUNICATES WITH SAID SLOT OUTLET, THE LENGTH OF THE TRANSVERSE REAR RESTRICTED PASSAGE IN THE DIRECTION OF FLUID FLOW FROM SAID CENTRALLY DISPOSED INLET AREA TO THE SLOT OUTLET BEING VARIED ALONG DIVERGING PATHS

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