US2141377A - Process and apparatus for the production of sheeting - Google Patents

Description

S. CHYLINSKI Filed July 3l. 1936 4INVENTOR.

Dec. 27, 1938.

PRocBss AND APPARATUS on THE PRODUCTION 0F SHEETING Patented DecQZ'?, 1938 PROCESS AND APPARATUS FOR Tm DUCTIN F SHEETING Stanislas Chylinslxi, Wilmington, Del., assigner to E. l. du Pont de Nemours & Company,

ton, llel., a corporation of Delaware Applicationsuly 31, i936, Serial No. @3,697

d Claims.

This invention relates to web, sheet or hlm contacting surfaces. More particularly, it relates to such contacting, surfaces for the drying of materials in the form of webs, sheets and films.

The invention will be described in terms of the drying o f nonl-brous sheets and lms, such as, regenerated cellulose, although' the invention is not to be limited thereto. l

In the manufacture of regenerated cellulose sheetsY and films, a solution such as viscose is brought intopellicular form which is regenerated and purified, and sometimes subjected to a sizing treatment, by passing the same through various treating tanks. After emerging from' the last `1:15 of these tanks, the lm is dried by leading it over a series of internally heated rollers, after which it is Wound up into mill rolls. In the drying of these films great lateral contraction occurs. A lm after it has been dried is often scarcely half the width of the nim when' it is nrst formed. Although the sheet and nlm producing machine readily prevents the nlm from contracting in the longitudinal direction, by keeping it under a longitudinal tension, special steps must be taken to materially prevent or restrict the lm from shrinking laterally. I

Greatdiiiiculty has'been experienced, heretofore, in satisfactorily` restricting the lateral shrinkage of sheets and lms composed of nonbrous materials. In an effort to overcome this difficulty, the -drying rollers have States Letters Patent to Herndon, No. 2,000,079. The procedure set forth in this patent reduces lateral shrinkage to a -great degree but has several defects which this invention is intended to overcome. In the first. place, the iron rollers usually serving as abase for the coating applied according to the Herndon patent are only fair so conductors of heat, and when a resin, lacquer or varnish coating of the type disclosed by Herndon is applied thereto, the heat conduction of the roller as a Whole is still further reduced, due to the low heat conductivity of the coating itself.

t Molded resin drying rollers, such as disclosed by Herndon, have a still lower heat conductivity -than iron or steel coated rollers. Secondly, the Vcharacter of the surface depends to a'great etztent upon the quality of the coating applied and the method o f application. Variation in coating application technique has resulted in very undesirable film width and quality. Uneven application of coating produces uneven wear which refl vsuits in unsatisfactory fum.. Varnish been provided i with anadhesive surface as disclosed in United.

and the like of the Herndon type are also quite perishable and must be frequently renewed.

Additionaly dimculties have vbeen encountered in the drying of specially treated film, when sub- I jected to drying on drier roll surfaces coated with 5 I varnish or similar composition; Certain types of nlm are provided with a tenuous coating or size in the last treating tank, such as is disclosed in United States Letters Patent Numbers 2,008,815 and 2,011,246. This size sometimes tends to come 10 .oi on the drier roll surfaces to a certain extent, and when this has proceeded for a period of time, the accumulation of size on the drier roller causes haziness in the nlm. When the size is removed from the roller in order to overcomethis vhazi- 15 f ness, some of thecoating is also taken o, resulting in non-uniform drier roll surfaces. Because of this, it is necessary to recoat the drier rollers more :frequently, thus causing production delays and additional expense.

, it is therefore an object of this invention to provide an improved surface for drying materials in web form, and particularly non-fibrous, cellulosic sheets and lms cast from aqueous solutions.

It is another object of this invention to provide an improved method 'for the production of webs, sheets and mms, particularly non-nbrous cellulosic sheets and nlms cast from an aqueous solution.

It is a further object of this invention to provide an improved method for drying webs, sheetsv and nlms involving the restraining of the lateral S l- :s: thereof.. v

. It is still another object of this invention to 35 provide a better heat conducting surface on drier rollers, l

it is still another object of this invention to .provide a ydrier roller surface of the required characteristics which will be more permanent 40 than those known heretofore Yet another object of this invention is to provide a drier roll surface of the required characteristics which can be renewed easily and uniiormly, and can be precisely duplicated.

- Other objects of the invention will appear here- 'fter. t

The objects of the invention are accomplished, in general, by passing wet webs, sheets or mms over a drying surface, for example, a drying 50 roller, composed essentially of aluminum on which a layer of aluminum oxide has been' formed by means of an electric current. f

The detalls of the invention will Abe more clearly apparent by'vreference to the following de- 55 panying illustration, in which:

operation.` It is also preferably further smoothed by a grinding, burnishing or bufhng operation. However, in someA cases it may be desired to form a slightly roughened surface on the machined body. Desirable roughened surfaces may be obtained by sand blasting with sand of various de grees of flneness or by etching with an etching solution, for example, by subjecting the aluminum body to an aqueous solution containing caustic soda and 4% sodium chloride at a temperature of 77 C. Any other method of uniformly roughing the body may be equally applicable.

After the aluminum body has been suitably smoothed or Toughened, as the case may be,l it is placed into an electrolytic bath through which .an electric current isl passed, and in which the aluminum body serves as the anode of an electrolytic cell. This treatment causes the surface of the body to be changed to an aluminum oxide, the depth of the oxide surface being dependent upon the specific procedure employed and length oftime of the operation. 'I'his treatment will be referred to hereinafter as "anodizing".

Referring to Figure 1 .of the drawing, reference to character il, designates a drying roller of thetype commonly used in the production of transparent regenerated cellulose pellicles. The

drying roller i I may be suitably mounted in bearings i3 and i5 and is provided with an open end il through which a liquid heating medium may be circulated within the roller II. The heating medium may be introduced into the interior of the roller il by means of conduit I9 which is preferably provided with a plurality of apertures 2l for the even distribution of the' liquid. The heating liquid ows from the roller il through the open end li and is withdrawn through the funnel-shaped conduit v23 to be reheated and again re-circulated through the roller Ii in a known manner. The heating liquid is ordinarily water, although any other liquid or gaseous heating medium may be utilized. The roller I i is provided at the external surface thereof with an aluminum oxide coating 25' preparedA thereon by anodization through means'of an electric current. This external surface 25 readily conducts the heat from the aluminum roller il, which in turn is heated by the heating medium passed against the internal surface thereof. Due to the high heat conductivity of aluminum, the heat is rapidly and efilciently conducted to the anodized aluminum oxide surface 25, and wet webs, films or sheets placed in contact with the hot roller surface 25 are eectively dried in a minimum period of time by contact withV a relatively small number of such drier roller surfaces.

Figure 2 diagrammatically illustrates the extrusion of a non-fibrous cellulosic material into a coagulating bath 50 by means of an extrusion device generally indicated by 52. The l111111 as it scription taken in connection with the accompasses from the extrusion device 52 is coagulated in the bath 50 and is thence passedthrough a series of washing and purifying baths (not shown) ,`and in some cases through a sizing bath 7 54 from 'which it is removed to be passed into drier 56 in which are positioned a series of drier rollers Il. The drier 5B may be provided with a covering 58 to form a chamber from which the moist air may be removed through outlet 60. It may, in some cases, however, be desired to dispense with the cover 58 and merely-allow the moist atmosphere driven oi from the film to pass into the surrounding atmosphere. After passing through the drier or rather over'the drier rolls i I, the web, sheet or filml I0 is wound into a mill roll 62'in a known manner.

The following specific example is given to illustrate in detail one method in which the anodizing of an aluminum body may be carried out. lI-low'- ever, theinvention is not to be limited thereto.

An aluminum body, drawn into hollow cylindrical roller form and suitablymachined and buffed, is placed in a lead lined tank containing a 15% solution of sulphuric acid at a temperature of 68 to '12 F. The aluminum roll is made to constitute the anode, and the lead lining in the tank the cathode of an electrolyzing circuit, through which a current of about 18 amperes per square` foot of aluminum is passed. 'I'he aluminum roll is electrolyzed in this manner for a period of about 50 minutes, at the end of which time the surface of the aluminum is converted to an oxide approximatey 0.001 inch deep. The body is then washed and is ready for any further treatment to which it is desired to subject the same.

In recent years, there has been developed an improved method for after-treating anodized aluminum surfaces. This method is known as "sealing", and consists in placingy the anodized aluminum, after washing, in boiling water, where it remains for a suitable perio'd of time, for example, thirty minutes. The sealing operation has the eifectof giving to the oxide surface a high polish and making it denser, more impervious to certain liquids and less sticky in character. It is thought that this is due to the fact that, before sealing, the surface apparently consists of pointed serrations, 'the points of which are quite widely separated, and that, after sealing, these points appear to be drawn closer together. This may have some distinct bearing on the stickiness of the unsealed anodized surfaces above referred to.

The term "sealed as used throughout the present specification and claims refers to surfaces which have been treated as outlined in the preceding paragraph. Contrarywise, the term unsealed refers to surfaces which have not been so treated. t

Although an anodizedv and sealed aluminum surface may in some cases be very desirable due to its smoothness and highly efncient conduction of heat, it offers no substantial improvement over previously known drying rollers in preventing or reducing transverse shrinkage of sheets and films. This may possibly be due to the fact that the sealing treatment apparentlysaturates the surface with water of hydration; When it is not saturated, the water contained in the lm being dried may have sufcient chemical affinity for the aluminum oxide 'to restrain shrinkage of the film.

The remarkable discovery has been made, however, that by omitting the sealing treatment, anodized aluminum surfaces are extremely eilicient in preventing transverse shrinkage of webs, sheets and lms during the drying thereof. Drying rollers provided with an anodized, unsealed surface, therefore, are found to have great utility, not only in reducing the shrinkage of sheets or lms to one-half or less than one-half as previously obtainable, but also vin procuring accurate control of the lateral shrinkage of such sheets and films.

In view of the eflicacy` of unsealed anodized aluminum surfaces in the prevention or restriction of lateral shrinkage in non-brous cellulosic sheets and films, it might be expected that this characteristic of anodized aluminum surfaces might be enhanced by submitting such surfaces prior to the anodization thereof to a roughening treatment such as by sand blasting, rough grinding or the like. It has been found, however, contrary to expectations, that the elmcacy of the special aluminum oxide surface in preventing shrinkage of film dried thereon is materially improved by making the surface as smooth as possible .before forming the oxide surface thereon. Ihis is possibly'due to the fact Athat the particular aluminum oxide surface is the effective means for preventing shrinkage, and the greatest conversion tothe oxide and the greatest contact of the oxide ywith the film being dried will be effected by leveling o of the high points of the rough surface prior to its conversion to the oxide. This is preferably edected by machining, and further enhanced by bung.

Another peculiar characteristic of this anodized and unsealed surface and its effectiveness in preventing shrinkage is its. greater emciency' or effectiveness when in contact'with wet film'. Tests have been made to determine the behaviour of regenerated cellulose films of Varying moisture content, dried on such a surface.` It has been found that this surface although very -eective when the film is wet, becomesvl much less effective as it approaches dryness. example,A a film containing less than approximately water, based on the Weight of the cellulose, is not prevented from, shrinking during the drying'thereof to-any greater extent than by a surface of the type disclosed in U. S. Patent Number 2,000,079. This characteristic of unsealed anodized surfaces is very desirable. The greatest amount of shrinkage of non-fibrous cellulosic sheets and films occurs above the 70% moisture content of sheets and films, and it is this shrinkage Whichit is usually'desired to prevent, in vorder to secure a film of maximum width. The shrinkage occurring below the 70% moisture content is known as "permanent shrinkage and it is usually desired to permit this shrinkage to take place.'

Itis not definitely known why an unsealed anodized aluminum surface will have a greater efficiency to prevent shrinkage of films' when' they are wet, however, it is'l believed -thatthis may be due to the great aninity of aluminum oxide for water. Since water is intimately bound in the structure of a gel regenerated cellulose film, it is possible that as the film is brought into contact with the aluminum oxide surface of the roller, the water in the film will form a physico-- chemical union with the aluminum oxide roller surface, thus restraining the lm from shrink'- ing. As the drying proceeds, less water is availf able for forming the union between the. nlm and the roller surface and the restraining force thus becomes weaker. 1 In view of the -above described unusual-but .column is shown the amount 'of claims is intended to ed by adding to aluminum one desirable characteristics of unsealed, anodized aluminum surfaces, it is ordinarily preferred that the aluminum body is not subjected` to a sealing treatment afteranodization. Nevertheless, in certain cases, where shrinkage of sheets and films is unimportant, or in cases where suon shrinkage is desirable, it may be desired to use a. sealed anodized aluminum surface in view of its greater smoothness and high heat conductivity. The type of anodized roll surface may be varied in different parts of the same machine, or for the production of different types of film in differentmachines according to the shrinkage eects desired.

Various other finishing treatments may be applied to anodized aluminum surfaces. Anodized drying roller surfaces for use in drying certain special types of film may require the application of certain finishing materials to the roller surface. In some cases it has been found desirable, for example, that rosi or silica be aplied to an anodized aluminum surface which is to be used as a drying surface. ARosin may, for example, be applied thereto from solution or in molten or powdered form, The silica may be applied tosuch a surface by dipping the surface for ten minutes in a 10%.solution of sodium silicate.

The following table illustrates the effectiveness of drying roller surfaces in restraining the transverse or lateral shrinkage of regenerated cellulose pellicles. The table gives the result of tests performed on sealed and unsealed, roughened and smoothed anodized drying roller surfaces as well as previously known drying roller surfaces. in the first column is listed the various types of drying roller surfaces tested. In the second column is shown the averageamount of shrinkage occurring during therirying step, in percentage of the width of the pellicle emerging from the `final liquid treating hat1 In the third,

variation' "in shrinkage that would occur in films dried on the various surfaces (probable error or reliability tolerance). It will be noted that in all cases the anodized aluminum surfaces show much greater controllability of shrinkage than previously known surfaces. e

. Table Description of surface Shtinkage Tolerance Aluminum Percent Percent Machined, buiied, anodized, not sealed.. 5. 89 5:0. Machined, anodized, not scale 7. 34 5:0. 38

Machined, anodized. impregnated with silica l2. 42 5:0. 46 Etched 5 minutes, anodized, sea1ed 21. 55 :i:1. 03 Etched 3 minutes, anodizednsealed 23. 90 :l:0. 64

Very fine sand blast, anodized, impregnated with silica 3l- 08 :l:0. 18 Very fine sand blast, anodized, sealed- 33. 83 :i:0. 36 Etched 10 minutes, anodized, sealed 35. 40 :i:0. 74 Fine sand blast, anodized, sealed 37. 39 :l:O. 06

Non-aluminum Lacquer-sd, rubber covered cast iron 15. 3:3. Z8 Y Varnished steel (U. S. Patent 2,000,079)..-. 15. 53 :l:l. 12

The term aluminum in this specification and include alloys where aluminum is, the essential alloying element, normally comprising at least r15% to 90%- of the alloy.

,Generally speaking, the qualities sought for in an alloy are hardness and ease and effectiveness ofy anodization. The former, as is known,

or more of certain chromium, silicon,

elements, such as magnesium,

It is true,

copper, zinc, manganese and nickel.

1s effect.

vantageous for use in the preparation of webs,

sheets and lms in which it is desired to prevent or restrain lateral shrinkage thereof. Drier rollers constructed of aluminum and provided with an anodized aluminum surface are found to be light in welght, easy to handle and provide greatly improved heat transfer. When the surface becomes worn down, it can be reproduced easily, cheaply, efficiently and accurately. Undesirable variations in reproducing the anodized surfaces .can be easily avoided, and thus uniform surfaces will exist throughout the various sheet and lm producing machines. The accurate reproducibility of the anodized surfaces and the close controllability of shrinkage effects in lni dried ony such surfaces may make 4it desirable to use this invention whether or not shrinkage is allowed to' take place.

The wearing qualities of the anodized aluminum surfaces are such that they will need to be` renewed much less often than those produced in accordance with U. S. Patent No. 2,000,079. Due to the hardness of anodized aluminum lsurface it has been found to be particularly desirable in resisting abrasion by knife cuts which are frequently made on sheets and filmsy traveling over the rolls. If, by drawing a knife over a drier roller surface, it were abraded to the extent that a burr was raised thereon, it would be entirely unsatisfactory for the further production of cellulose film. Anodized aluminum surfaceshave the property of resisting abrasion by knife cuts to the extent that no burr-will be raised 'on the surfaces thereby.

Another advantage of anodized aluminum drying rolls comprises the ease with which sizing materials may be removed therefrom. When a sizing solution accumulates upon the rollers to such an objectionable extent that it causes haze in the lm, it can be easily and quickly removed bymeans of solvents without injuring the roll surface. Finally, in the preferred embodiment of this invention, in which the anodized aluminum surfaces have not been subjected to a sealing treatment, lateral or transverse shrinkage inl the iilm is removed to one-half or one-third of that known heretofore. I

While the invention has been described in terms of the drying of illms of regenerated cellulose, it is to be understood that it is. equally applicable to the drying of other materials in pellicular form, such as other non-fibrous materials, including cellulose esters and ethers, gelatin and casein as well as fibrous sheet material such as paper and the like. It is also applicable to the prevention of shrinkage in sheets and films during other steps in the manufacture thereof which involve contact with a moist or wet sheet or lm.

It is obvious that various changes and modifications may` be made in the process and apparatus hereinabove described without departing from the nature and spirit of the invention. It is therefore,`to be understood that the invention is not to be limited except as set forth in the following appended claims.

I claim:

1. In the production of non-fibrous cellulosic pellicles, the step which comprises drying said pellicles by passing the same over a heated unsealed anodized aluminum surface.

2. In the production of non-fibrous celluiosic pellicles, the step which comprises dryingl said pellicles by passing the same over a heated smoothed and unsealed anodized aluminum surface. l

3. The method of claim 1 characterized inthat the pellicles are regenerated cellulose pellicles.

4. The method of claim 2 characterized in that the pellicles are regenerated cellulose pellicles.

sTANIsLAs oHYmNsKI.

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