US2039883A - Casting method and apparatus therefor - Google Patents

Description

May 5, 1936. w. H. cHARcH ET AL CASTING METHOD AND APPARATUS THEREFOR Filed Jan. 22, 1932 3 Sheets-Sheet l '1 --11 :1 g i J YII 1 :1 2 J p 53 v F I- G mmuz:

WmHa/e Chara/7 INVENTORS Clarence fCa/eman,

BY THEIR ATTORNEY PK i3 I; I%Z%WWUW y 5, 1936- r w. H. CHARCH El AL CASTING METHOD AND APPARATUS THEREFOR V 5 Shets-Sheet 2 Filed Jan. 22, 1932 w 6 HL :n

m 65 an Wm. Ha/e Chart/7, INvEN'roR:

Clarence f. Co/eman,

95:15:: THEIR ATTORNW y 1 w. H. CHARCH ET AL. 2,039,883

CASTING METHOD AND APPARATUS THEREFOR I Filed Jan. 2 2, '1952 3 Sheets-Sheet 3 Fig.6

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Figli Wm. Hale C h arch Clarence Co/emcm BY Patented May 5, 1936 UNITED STATES PATENT OFFICE CASTING BIETHOD AND APPARATUS THEREFOR of Delaware Application January 22, 1932, Serial No. 588,079

26 Claims.

This invention relates to a process for manufacturing films of regenerated cellulose. More particularly it relates to a method and machine for casting cellulosic solutions into films whereby excessive lateral shrinkage is prevented, and a greater yield and an improved product are secured.

At the present time there are two general methods for the manufacture of films of regenerated cellulose. The first of these is known as the Brandenberger process; the other will be called the Wheel casting method.

In the so-called Brandenberger process a reservoir containing a viscose solution has beneath the surface of a setting bath an orifice through which the. viscose solution is extruded. The bath begins to act on both sides of the extruded viscose film as soon as it issues from the orifice, coagulation proceeding inwardly from all faces of the film. The time required for complete setting is afiected inter alia by the concentration and temperature of the bath, by the thickness of the film, and by the composition of the viscose. The complete setting of an extruded viscose sheet, for example, may require from a few seconds to more than a minute.

In the Brandenberger process the film after issuing from the reservoir passes under a roll or rod, is drawn out of the bath, is transported by a series of rolls in festoon arrangement through tanks filled with various other treating liquids, and is then transported to the drier rolls. Excessive shrinkage in the lateral direction takes place in this process, the sheet at the wind-up being only about half the width of the sheet extruded from the reservoir orifice. The greater part of this contraction occurs during setting but the amount which occurs in the other steps of treating and drying is not small and is accentuated more or less in proportion to the speed of the machine and the consequent pull on the film in the machine direction.

In the wheel casting method the viscose is'extruded through the orifice of a reservoir upon a wheel having a highly polished surface. The lower portion of the wheel is immersed in a setting bath and the wheel is turned at a rate sufiiciently slow to permit the viscose deposit to spread itself uniformly upon the wheel before it is dipped. After or just before leaving the setting bath the sheet is stripped from the wheel and carriedover rollers into more setting liquid and through the other steps of the process substantially as in the Brandenberger method. Initial setting proceeds only from one side of the sheet and is correspondingly slow, but film cast by this method tends to contract less laterally than film cast by the Brandenberger process wherein the film is supported on rollers only at relatively widely spaced intervals, and wherein, as a consequence, setting takes place while the film is substantially laterally unsupported. The Brandenberger process is faster than the wheel casting process but the latter is adapted to the production, from a hopper of given width, of a wider film having lateral strength greater than Brandenberger process film and more nearly equal to its own longitudinal strength.

It is an object of this invention to produce films of regenerated cellulose by a new and improved process which has the advantage of high speed production, good width, superior appearance, and a good ratio of lateral to longitudinal strength. Another object of the invention is the production of a machine for preparing films of regenerated cellulose. Other objects of the invention will be in part apparent and in part set forth as the description proceeds.

In the drawings: Figure 1 is a side view of our new machine; Figure 2 is a plan view of the new machine; Figure 3 is a view from the head or casting end of the machine; Figure 4 is a side view of a modified form of the machine; Figure 5 is a plan view of the machine shown in Figure 4; Figure 6 is a cross section on the line VIVI of Figure 1; Figure 7 is a longitudinal section on line VIIVII showing the drum structure; Figure 8 is a similar section showing a difierent construction of drum; Figure 9 is a similar section showing a further drum modification; Figure 10 is a similar section showing yet another form of drum; Figure 11 shows a support in the form of a. moving belt to replace the wheel of the other figures. I

l is a reservoir or hopper for holding viscose; II is an orifice in the hopper through which viscose is extruded; I2 is a mechanism for varying the angle at which the orifice directs the viscose into the regenerating bath; I5 is the film proceeding through the various stages of manufacture; 2 is a well for holding a setting bath; 2| is a wheel or rod for guiding the extruded film through the bath; 22 indicates generally the driving means for wheel 2|; 23 is a line showing the approximate level of the setting fluid in the machine; 3 is a supporting wheel upon which the partially set film is supported during the setting; 3|3| are bearings which support the wheel 3; 32 is a well in which the wheel 3 rotates; 33 represents a driving mechanism of any convenient type; 4 are sprays for showering the film with setting fluid; 5 are supporting rollers for carrying and directing the sheet through further setting fluid and or the other steps in the process; 5| is a section of the well through which the film is transported by rolls 5.

The nature of the drum surface is highly important, since its character will to a large extent determine the transverse tenacity of the film and the amount of film contraction in the setting portions of the process. In Figures '7 through 10 are shown several drums with various surfaces.

In Figure 7 a drum 3 having a plane surface is covered with a corrugated sheet of metal or composition 355 which in turn supports a perforated metal or composition sheet and/or a wire screen, and/or cloth covering 314'. If 3 is, or contains, a Wire screen the screen is preferably, but not necessarily, rolled to remove surface inequalities before application to the wheel. If. a cloth is used, it may advantageously be of open or meshelike weave.

In Figure 8 the wheel 3, has a solid or forminous plane surface covered with a heavy wire screen and/or fine screen or a cloth covering 314.

In Figure 9 the wheel itself has a perforated or foraminous surface 3l6, which may be bare, but ispreferably covered with a fine screen or'a cloth.

In Figure 10 a wheel 3 having a plane surface carries slat-like cross members 3l'l which are preferably low and which in turn support a wire screen or similar surface 3H8.v

In all cases the wheel foraminations are arranged to allow the escape of gases from the underside of the film, and are preferably of a size which will permit them to carry quantities of regenerating fluid into contact with the under surface ofv the-film. It will be understood that the process will function without drum foraminations to allow the escapeof gases, but that, their absence will result in the entrapment of liquid in pools between the film and the drum, which is objectionable.

In Figures 4 and 5 is illustrated a modified form of our invention. In these figures l' is a reservoir hopper; l I is a reservoir orifice; I2 is a mechanism for adjusting the angle at which the viscose solution is injected into the setting bath; 2 is a tank containing all or a part of the setting system; 2! is a roller for transporting the film through the settingliquid; 23 is a line indicating a satisfactory liquid level; 3 is a wheel similar to wheel 3 heretofore described; 36 is a second wheel similar to the wheel 3; 32I indicates a false bottom in the tank; 35 and 38 are rollers; 3 are drain pipes for emptying the tank; 32 andxs 'l indicate the sections of the tank, or the separate tanks as the case may be, in which the wheels 3 and 36 revolve; 4 are showers for applying liquid to the film; 5| is a tank containing setting fluid or other treating fluid; 5 are rollers for transporting the film through tank 5|; 52 is a roller for carrying the film from tank 3'! to, tank 5|.

It might be suggested that the film be carried under rather than'over the rollers, but experience has shown that that expedient renders the process to all practical purposes inoperative.

Our invention functions as follows:-

Viscose, cuprammonium cellulose, or any similar regenerable cellulosic composition is extruded from the reservoir or hopper into a, setting bath through which it passes for only a short distance in a substantially laterally unsupported condition and from which it is drawn onto the surface of the supporting wheel which resists: any

further tendency of the film to contract laterally and whereon the setting is continued. There is thus afforded to the film an initial period of setting, wherein the film just after extrusion is substantially unsupported and contracts freely under the influences of the setting bath, and a second period of setting which takes place while the film is on-the contraction-resisting drum surface. It is one function of the initial step to form a surface skin on the film which will serve to prevent the film from taking marks from the drum surface during the second step of the process. Because of the substantially free lateral contraction while the film is unsupported this initial, unsupported period of setting is continued only long enough to form a surface skin on the film which will prevent the marking of the film by the drum. In the second period of setting, which occurs while the film is on the drum, the setting may or may not be fully completed. The more nearly it is completed while the film is in the supported state, the better will be the results in the finished product. In practice, hoWever,-it has been found unnecessary to fully complete the entire action of the bath on the film in order to achieve satisfactory results. There may be, consequently, a third setting step conducted, in the usual manner, after the film has left the drum. During this third step, if used, the film will be substantially set and will, consequently, not shrink to a great extent.

In order to facilitate and, so far as is practicable, to complete the setting of the film while it is on the drum, the film may be sprayed with setting liquid of the same or of different concen-- tration and temperature than the initial bath. With the proper choice of factors, for instance, by theme of a hotter and more concentrated solution in the second step; the setting may be substantially completed upon the wheel with, due to the lateral resistance offered to contraction by the surface of the wheel, a minimum of lateral contraction.

The tank in which the wheel runs may be separate from the tank in which initial setting occurs or it may bea part of it. In usual cases it is filled with fluid to a level which will permit the film to be applied to and stripped from the drum beneath the surface of the liquid. Since the drum foraminations will carry liquid into contact with the underside of the film, and since the'film itself carries considerable quantities of setting liquid with it, setting takes place from. both sides of thefilm while the film is supported.

The foraminations or channels in the supporting wheel permit the escape of the gases which are given off by the film during setting and also permit the escape of excess quantities of liquid which may be carried up by the wheel or by the film and which would otherwise form small blankets with tendencies to lift the film off the surface;

After: passing over the wheel the film will be transferred'to'a roller at least partially submerged in the bath and will thence be drawn by rollers or other means to further setting baths and/ or to the other steps of the process, the nature of which will be understood by persons skilled in the art.

In our process the wheels and rollers with which the film comes in contact are preferably driven.

It will be apparent that many modifications can be made in our invention. For instance, any type of viscose reservoir and any means of supplying it can be used; the film after leaving the orifice of the hopper may be carried through the solution by a roller orit mayproceed directlyto the surface of the supporting wheel withoutthe intermediation of a roller; the showers which-project setting liquid upon the surface of the filmon the wheel may be arranged in number and location to suit the particular needs of a process; the surface of the wheel may be made foraminous in many ways, a number of which have heretofore been described; an endless belt provided with an equivalent surface or surface coveringmay be substituted for the wheel; the setting system may be contained in one tank, in several tanks, or in one tank which is. divided into several compartments, each compartment containing one step in the process; the concentration-of the solutions used in different compartments and in the sprays may be advantageously varied to suit individual conditions as, for instance, by using a stronger setting solution at a higher temperature in the later stages of setting. The invention may be used with a two-step treatment such as that in which viscose, is first precipitated by treatment with a material, such as ammonium sulphate, and is subsequently regenerated in an acid bath. In this adaptation of the invention it will be advisable to treat with ammonium sulfate in a substantially unsupported condition in a first tank, to transfer the film from the ammonium sulfate step to a tank containing the acid bath Where the setting will be completed, or substantially completed, upon a drum, in the manner hereinbefore disclosed.

The device or wheel which is used may be varied to suit varying conditions and the number of the wheels may be increased to any satisfactory extent. In general it will be found thatone twelvefoot wheel will be more satisfactory than two six-foot wheels because where two six-foot wheels are used the sheet is partially unsupported between the wheels and will shrink at the unsupported point. However, in some cases it will be more advantageous to use a number of small wheels than a single large one, or to use an endless belt instead of a wheel. In all such cases satisfactory results will be obtained.

Beneficial results may be obtained under certain circumstances by the use of auxiliary means having a tendency to prevent lateral contraction of the film. For instance, an endless web-of about the width of the supporting drum may be suspended .on rollers above the supporting drum in a position such that it Will contact with the film on the drum surface and press it against the drum. The pressure exerted by the web can be regulated by any suitable means such as by passing it over at least one springpulled roller, or by making the web of material sufficiently heavy alone or when wet with setting fluid to have suffi cient weight to resist the tendency of the film to contract. This Web may advantageously be made of, or surfaced with, a. material which, of its own nature or because of its form, resists the tendency of the film to contract. Such materials and surfaces are described herein in connection with the supporting drum. It is advisable that a web, if used, should cover the entire width of the film since they use of belts of less width than the film (applied, for instance, to the edges of the film) tends to produce a sheet in which the portions near the belts are more thinned by contraction than the portions away from the belts. In other words films held only at the edges tend to contract unequally and produce a sheet of non-uniform thickness.

The cloth covering for the drum or belt may be impregnated with a phenol-aldehyde condensation product or a similar product, the superficial surface being ground down to expose the cloth.

The principles of the invention may be applied to other steps in the process, for instance to desulphuring wherein lateral shrinkage is known to occur.

Among the advantagesof our invention are the production from a given hopper width of a wider sheet of regenerated cellulose than is possible with the so-called Brandenberger process; the production of a sheet of regenerated cellulose of better quality than that produced by the Brandenberger process; the production of a sheet of regenerated cellulose whose lateral and longitudinal physical properties are more nearly equal than that which is produced by the Brandenberger process; the production of a sheet of regenerated cellulose of high quality compared to the wheel casting method at a higher speed than is possible with the wheel casting method and without the necessity of using expensive, highly polished casting wheels; a method of carrying on the setting of a film from both sides while the film is supported against lateral contraction; and the use of solutions of different activity in conjunction with the other features as a means of preventing excessive lateral contraction. Other advantages of the invention will be apparent from a reading of the specification.

As many apparently Widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiments thereof except as defined in the appended claims.

We claim:

1. The method of preparing a film of regenerated cellulose which comprises extruding a film of viscose into a setting bath, transferring the film in apartially set condition to a moving support which is provided with means for allowing the escape of fiuid from the film, spraying the support,- ed film with setting liquid, and restraining the lateral contraction of the film.

2. The method of preparing a film of regenerated cellulose which comprises extruding a film of viscose into and beneath the surface of a setting bath, transferring the film in partially set condition to a moving support which is only pa tially immersed in a setting liquid while allowing the escape of excess fluids from beneath the film, spraying the supported film with setting liquid more active than that of the bath, and restraining the film-from contraction laterally of the sup port.

3. The method of preparing a film of regenerated cellulose which comprises extruding a film of viscoseinto and beneath the surface of a setting bath, transferring the film in a partially set condition to a moving support which is only partially immersed in a regenerating liquid while allowing the escape of excess fluids from beneath the film, spraying the supported film with setting liquid more active than that of the bath, and restraining the lateral contraction of the filrn on the support by restraining portions of the film from motion laterally of the support.

4. The method of preparing a film of regenerated cellulose which comprises extruding a film cf viscose into and beneath the surface of a setting bath, transferring the film in a partially set condition to a surface which is only partially immersed in a setting liquid while applying setting liquid to both sides of the film and allowing the escape of excess fluids from beneath the film, spraying the supported film with a setting liquid more active than that of the bath, restraining the lateral contraction of the film by restraining portions of the film from motion laterally of the support, and removing the film from the support.

5. The method of preparing a film of regenerated cellulose which comprises extruding a film of viscose into and beneath the surface of a setting bath, transferring the film in a partially set condition to a surface which is only partially immersed in a setting liquid while applying setting liquidto the film and allowing the escape of excess fluids from beneath the film, spraying the supported film with setting liquid at a higher temperature than that of the bath, restraining the lateral contraction of the film on the support, and removing the film from the support.

6.'The method of preparing a film of regenerated cellulose which comprises extruding a film of viscose into and beneath the surface of a setting bath, transferring the film in a partially set condition to a surface which is only partially immersed in a setting liquid while applying setting liquid to the film and allowing the escape of excess fluids from beneath the film, spraying the supported film with setting liquid more concentrated than that of the initial bath, restraining the lateral contraction of the film on the support, and removing the film from the support.

'7 A machine for preparing films of regenerated cellulose comprising, means for injecting a film of regenerable cellulosic solution into a setting bath to partially set the same, means for supporting the partially set cellulosic film against lateral contraction, and means on said supporting means for permitting the escape of fluids from beneath the film.

8. A machine for preparing films of regenerated cellulose comprising means for injecting a viscose solution in a setting bath, a rotatable wheel for withdrawing the cellulosic film from the bath and for supporting it against lateral contraction, means on said Wheel for permitting the escape of fluids from beneath the film, means for maintaining setting fluid in contact with the film on said wheel.

9. A machine for preparing films of regenerated cellulose comprising a reservoir for containing a viscose solution, an orifice in the reservoir beneath the surface of a setting bath, a rotatable wheel for withdrawing the cellulosic film from the bath and for supporting it against lateral contraction, means on said wheel for retaining quantities of setting liquid and for permitting the escape of fiuids from beneath the film, means for maintaining setting liquid in contact with a portion of said wheel, means for restraining lateral shrinkage of the film on the Wheel, and means for spraying the film on the wheel with setting fluid.

10. A machine for preparing films of regenerated cellulose comprising a reservoir for containing a viscose solution, an orifice in the reservoir beneath the surface of a setting bath, a rotatable wheel for withdrawing the cellulosic film from the bath and for supporting it against lateral contraction, the surface of the said wheel having channels for permitting the escape of fluids from beneath the film, means for maintaining setting liquid in contact with a portion of said wheel, and means for spraying the film on the wheel with setting fiuid.

11. A machine for preparing films of regenerated cellulose comprising a reservoir for containing a viscose solution, an orifice in thereservoir for-injecting a viscose film into a setting bath, a rotatable foraminous wheel for withdrawing the cellulosic film from the bath andfor supporting it against lateral contraction, means for maintaining setting fluid in contact with a portion of said wheel, and means for spraying the film on the wheel with setting fluid.

12. A machine for preparing films of regenerated cellulose comprising a reservoir for containing a viscose solution, an orifice in the reservoir for injecting a viscose film into a setting bath, a rotatable wire mesh surfaced wheel for withdrawing the cellulosic film from the bath and for supporting it against lateral contraction, means for maintaining setting fluid in contact with a portion of said wheel, and means for spraying the film on the wheel with setting fluid.

13. A machine for preparing films of regenerated cellulose comprising a reservoir for containing a viscose solution, an orifice in the reservoir beneath the surface of a setting bath, a rotatable, cloth covered wheel for withdrawing the cellulosic film from the bath and for supporting it against lateral contraction, and for maintaining setting liquid in contact with the film on the said wheel.

14. In a machine for preparing films of regenated cellulose means for extruding a film of cellulosic solution into a setting bath to partially set the same, and a Wheel having an irregular surface for supporting the film while the setting is continued.

15. In a machine for preparing films of regenerated cellulose means for extruding a film of cellulosic solution into a setting bath to partially set the same, and a supporting wheel having a perforated surface 'for supporting the film while the setting is continued.

16. In a machine for preparing films of regenerated cellulose means for extruding a film of cellulosic solution into a setting bath to partially set the same, and a wheel having a foraminous surface for continuing the setting.

17. In a machine for preparing films of regenerated cellulose means for extruding a film of cellulosic solution into a setting bath to partially set the same, and a wheel having a wire screen surface for supporting the film while the setting is continued.

18. In a machine for preparing films of regenerated cellulose means for extruding a film of cellulosic solution into a setting bath to partially set the same, and a supporting wheel having a cloth surface for supporting the film while the setting is continued.

19. The method of preparing a film of regenerated cellulose which comprises the steps of extruding a film of a regenerable cellulosic solution into a setting bath to partially regenerate the same While freely contractible in a lateral direction, continuing the setting while restraining the contraction thereof in the lateral direction, and applying a setting fluid more concentrated than the fluid of said setting bath to the film during the step of continuing said setting.

20. The method of preparing a film of regenerated cellulose which comprises the steps of extruding a film of a regenerable cellulosic solution into a setting bath to partially regenerate the same While freely contractible in a lateral direction,-

continuing the setting while restraining the contraction thereof in the lateral direction, and applying a setting fluid having a higher temperature than the fluid of said setting bath to the film during the step of continuing said setting.

21. The method of preparing a film of regenerated cellulose which comprises the steps of extruding a film of a regenerable cellulosic solution into a setting bath to partially regenerate the same while freely contractible in a lateral direction, continuing the setting while restraining the contraction thereof in the lateral direction, and applying a setting fluid more concentrated and having a higher temperature than the fluid of said setting bath to the film during the step of continuing said setting.

22. The method of preparing a film of regenerated cellulose which comprises the steps of extruding a film of a regenerable cellulosic solution into a setting bath to partially regenerate the same while freely contractible in a lateral direction, continuing the setting while restraining the contraction thereof in the lateral direction, and applying a setting fluid more active than the setting fluid of said setting bath to the film during the step of continuing said setting.

23. In a machine for preparing films of nonfibrous cellulosic materials, means for extruding a film of a regenerable cellulosic solution into a setting bath, means for conducting said film through a section of said bath in a laterally unsupported condition, and means for continuing the conduction of said film on a support,'and

means associated with said support for resisting a tendency of the film to contract laterally.

24. A machine for preparing films of regenerated cellulose comprising means for injecting a film of regenerable cellulosic solution into a setting bath to partially set the same, means for supporting the partially set cellulosic film against lateral contraction, said last named means including means for retaining quantities of setting liquid in contact with said film and for permitting escape of fluids from beneath the film.

25. A machine for preparing films of regenerated cellulose comprising a reservoir for containing a, viscose solution, an orifice in the reservoir beneath the surface of a setting bath, a rotatable wheel for withdrawing the cellulosic film from the bath and for supporting it against lateral contraction, and means for spraying the film on the wheel with setting fluid.

26. In the method of making a film of regenerated cellulose the steps comprising extruding a pellicular film of viscose into a setting bath, partially regenerating said film while permitting the same to freely contract in a lateral direction, and continuing the regeneration of said film on a support while restraining the contraction of said film in a lateral direction by removing a substantial amount of the setting bath liquid from between the film and said support.

WILLIAM HALE CHARCH. CLARENCE E. COLEMAN.

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