US2921345A - Production of matte finish sheeting in dope casting procedure by use of air blast - Google Patents

Description

Jan. 19, 1960 w. J

PRODUCTION OF MATTE F BENNES 2,921,345

IN ISH SHEEITING IN DOPE CASTING PROCEDURE BY USE OF AIR BLAST Filed Dec. 15, 1954 INVENTOR. 14 d. Ben/v55 States William J. Bennes, Union, N.J., assignor to Celanese Corporation of America, New York, N.Y., a corporation of Delaware Application December 15, 1954, Serial No. 475,442

4 Claims. (Cl. 18-57) This invention relates to matte finish sheeting and relates more particularly to an improved process for the production of matte-finish sheeting.

An important object of this invention is to provide an improved process for the production of matte-finish sheeting by the solvent casting process.

A further object of this invention is to provide an improved process for the production of matte-finish sheeting by the solvent casting process wherein a stream of air or other gas is directed onto the sheeting as it is stripped from the casting surface.

Other objects of this invention will be apparent from the following detailed description and claims.

In the manufacture of film or sheeting, hereinafter referred to as sheeting, by the solvent casting process, a layer of a solution of a film-forming material in a volatile sol vent, known as dope, is deposited on a smooth casting surface, which may be a wheel or belt, by any suitable means, such as a casting hopper. A portion of the volatile solvent is evaporated from the dope by passing a stream of air or other evaporative medium over the layer of dope, generally while heating the casting surface, the evaporative medium, or both. After a sufficient amount of solvent has been removed from the dope so that the layer of film-forming material is self-sustaining, it is stripped from the casting surface and is then passed through a drying chamber wherein the bulk of the solvent remaining therein is removed. Finally, the sheeting is drawn from the casting apparatus and may be wound into a roll or otherwise packed. Sheeting prepared in this manner has a smooth, highly polished finish, accurately reproducing the finish of the casting surface.-

According to the present invention, it has been found that a matte surface may be developed on sheeting prepared by the solvent casting process by directing a stream of air or other gas onto the surface of the sheeting that has been in contact with the casting surface as the sheeting is stripped from the casting surface and while it still contains a considerable amount of solvent. Through the use of this invention, it is possible to employ a single casting apparatus for the production of both highly polished and matte sheeting, simply by providing means such as a conduit positioned so that a stream of air or other gas may be directed thereby onto the sheeting as it leaves the casting surface. It is also possible to direct the stream of air or other gas against portions only of the sheeting whereby only the said portions will develop a matte finish, thereby producing an attractive decorative effect. In this way, the flexibility of the casting apparatus may be increased and products of several different types may be. prepared thereon without the need for making expensive alterations or additions thereto.

In carrying out the process of this invention, a layer of dope is applied to the casting surface by any suitable means, such as a casting hopper, in a manner Well known in the art. Thereafter, a portion of the solvent is removed Patented Jan. 19, 1960 'ice from the dope by passing a stream of evaporative medium over the layer of dope, again in a manner well known in the art. After a sufiicient amount of solvent is removed from the layer of the dope so that the resultant sheeting is self-sustaining, it is stripped from the casting surface. At this point, the sheeting should contain a relatively high proportion of solvent, it having been found that when the drying of the sheeting on the casting surface is carried too far, it is not possible to produce a matte surface on the said sheeting. The exact proportion of solvent that should remain in the sheeting at the stripping point will vary depending on the exact nature of the filmforming material, the volatile solvent, etc. However, for any given set of conditions, the proportion of solvent needed to produce a matte surface may be readily determined, for example, by reducing the degree of drying during the casting of the sheeting and while treating it in accordance with this invention to develop the matte surface thereon.

As the sheeting is drawn from the casting surface, there is directed onto the surface of the sheeting that has been in contact with the casting surface a stream of air or other gas. The stream of air should impinge upon the sheeting at the stripping point, it having been found that the im pingment of the stream of air on the sheeting that has already been stripped will not produce a matte surface. In actual practice, the stream of air will spread as it moves from its source to the stripping point so that it will impinge on the stripped sheeting and also on the casting surface, as well as upon the sheeting at the stripping point. It is also important in developing a matte surface, to strip the sheeting from the casting surface in such a manner that the angle between the sheeting and a tangent to the casting surface at the stripping point is approximately a right angle, varying between about and degrees. When the angle between the sheeting and the casting surface is altered appreciably outside this range, for example, to a value of 30 degrees a matte surface will not develop.

The air or other gas that is directed onto the sheeting as it is stripped from the casting surface need not be heated or cooled or otherwise treated, except to insure that no droplets of oil, liquid water or other materials are present therein so as to avoid the marking or spotting of the sheeting. The air or other gas may be delivered to the desired point in any suitable manner. For example, there may be provided a conduit having a slit or a series of perforations extending the length thereof and positioned so that the air emerging therefrom will impinge on the sheeting at the desired point. It is preferred, however, particularly where a relatively wide sheeting is being treated, to deliver the air to the sheeting through means, such as nozzles, each equipped with valve or other regulating mechanism to permit the distribution of air to be controlled accurately whereby a uniform matte finish or a d ecorative pattern may be more readily achieved.

' After the sheeting has been stripped from the casting surface, it is passed through a drying chamber where the bulk of the residual solvent is removed therefrom in a manner well known in the art. The sheeting is then wound into a roll or otherwise taken up in package form. The sheeting prepared in this manner has an attractive, uniform, matte surface that takes pencil writing, ink, typing and printing inks well.

A preferred embodiment of the apparatus used in the process of this invention is shown in the accompanying drawing wherein Fig. 1 is a diagrammatic side elevation of the casting apparatus, and

Fig. 2 is a fragmentary detail view showing the arrangement of the gas delivery means.

Referring now to the drawing, the reference numeral 11 designates a casting wheel onto which there is deposited from a casting hopper 12 a layer of dope 13. The casting wheel 11 is rotated by any suitable means (not shown) and carries the layer of dope into a chamber 14 into which a stream of evaporative medium is entered through a condu it 16 and from which the evaporative medium leaves throught a conduit after having passed over the layer 13 and removed a portion of the solvent therefrom. When the layer 13 reaches the stripping point 17 it is a self-sustaining sheeting and it is pulled from the surface of the casting wheel 11 by means of a pair of positively driven stripping rollers 18.

A stream of air or other gas is directed at the stripping point 17 by means of a gas delivery means, indicated generally by reference numeral 19. The gas delivery means comprises a supply conduit 21. provided with a regulating valve 22 which delivers a stream of compressed air to a conduit 23 that extends across the full width of the casting wheel 11. A series of conduits 24 are tapped into the conduit 23 and are provided with flared discharge tips 25 that discharge a flat, wide stream of air to the stripping point 17. Each of the conduits 24 is equipped with a regulating valve 26 which permits the flow of the air through said conduits 24 to be adjusted so as to obtain a uniform matte surface or a patterned surface, if desired.

This invention will now be described specifically in connection with the production of a matte surface on sheeting prepared from a dope of secondary cellulose acetate in acetone, since this is commercially one of the most important solvent cast sheetings at the present time. In this case, the sheeting should have a residual solvent content of at least about 16% by weight at the stripping point. It should be understood however, that it is also applicable to the production of a matte surface on other solvent cast sheetings. Examples of such other solvent cast sheeting material include those prepared from other esters of cellulose such as cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose nitrate and the like dissolved in acetone, methylene chloride, and mixtures of methylene chloride and alcohols such as methanol, ethanol, propanol, and butanol. In addition, the invention may be employed for the development of a matte surface on solvent cast sheeting materials from vinyl chloride dissolved in ethylmethyl ketone; ethyl cellulose dissolved in a mixture of benzene and ethyl alcohol; and other high polymers dissolved in appropriate solvents.

The following examples are given to illustrate this invention further.

Example I A dope containing 25% by weight of secondary cellulose acetate dissolved in acetone and also containing 5% by weight of a plasticizer is deposited from a casting hopper onto a rotating casting wheel. The layer of dope is carried, in an apparatus as shown in the drawing, by the rotation of the casting wheel from the casting point to the stripping point where it has a residual acetone content of 23.79%. The sheeting is then stripped from the casting wheel in such a manner that the angle between the sheeting and a tangent to the casting wheel at the stripping point is approximately 90 degrees. A stream of air having a pressure of 10 pounds per square inch gage, a temperature of 90 F. and a dew point of 50 F. is directed at the sheeting as it is stripped from the casting wheel through a series of fiat discharge tips 7 inch wide and 0.02 inch high spaced 5 inches from the stripping point and located on 2 inch centers. The stripped sheeting is then dried. The product obtained has an attractive, uniform matte finish.

When the stripping tension is changed so that the angle between the sheeting and a tangent to the wheel at the stripping point is 30 degrees, a stream of air directed at the stripping point does not produce a matte finish.

When a similar run is made, but the degree of drying on the casting wheel is increased so that the sheeting reaches the stripping point with an acetone content of only 14.71% by weight, no matte finish is obtained.

Example II The process of Example I is repeated, but the degree of drying is reduced so that the sheeting reaches the stripping point with an acetone content of 24.21% by weight. There is obtained a somewhat denser matte finish than is obtained in Example I.

It is to be understood that the foregoing detailed description is merely given by way of illustration and that many variations may be made therein without departing from the spirit of my invention.

Having described my invention what I desire to secure by Letters Patent is:

i. Frocess for the production of matte finish sheeting, which comprises depositing a layer of dope containing a film-forming material dissolved in a volatile solvent onto a casting surface, said dope being one which forms a self-sustaining film on deposition on said casting surface followed by evaporation of said solvent, drying said dope to remove a portion only of the solvent therefrom so that said layer is self-sustaining but still retains a considerable portion of solvent, stripping the sheeting so formed from the casting surface so that the angle between the sheeting and a tangent to the casting surface at the stripping point is between about 80 and 120 degrees, directing a stream of gas at the stripping point as said sheeting is stripped from the casting surface and maintaining the solvent content of the sheeting being stripped at a level such that the directing of said stream of gas at said stripping point produces a matte finish on said sheeting.

2. Process for the production of matte finish sheeting, which comprises depositing a layer of dope containing a film-forming material dissolved in a volatile solvent onto a casting surface, said dope being one which forms a self-sustaining film on deposition on said casting surface followed by evaporation of said solvent, drying said dope to remove a portion only of the solvent therefrom so that said layer is self-sustaining but still retains a considerable portion of solvent, stripping the sheeting so formed from the casting surface so that the angle between the sheeting and a tangent to the casting surface at the stripping point is about degrees, directing a stream of gas at the stripping point against the surface of the sheeting that has been in contact with the casting surface and maintaining the solvent content of the sheeting being stripped at a level such that the directing of said stream of gas at said stripping point produces a matte finish on said sheeting.

3. Process for the production of matte finish cellulose acetate sheeting, which comprises depositing a layer of dope containing cellulose acetate dissolved in acetone onto a casting surface, said dope being one which forms a self-sustaining film on deposition on said casting surface followed by evaporation of said solvent, drying said dope to remove a portion only of the solvent therefrom so that said layer is self-sustaining but still retains at least about 16% by weight of acetone, stripping the cellulose acetate sheeting so formed from the casting surface so that the angle between the sheeting and a tangent to the casting surface at the stripping point is between about 80 and degrees, and producing a matte finish on said sheeting by directing a stream of gas against said sheeting as it is stripped from the casting surface.

4. The process according to claim 1, wherein said filmforming material and said volatile solvent of said dope are cellulose acetate and acetone, respectively. 1

References Cited in the file of this patent UNITED STATES PATENTS 6 Mosler Oct. 14, 1941 Dalin Oct. 28, 1941 Derby et a1. May 4, 1943 Harcourt et a1 June 27, 1944 Overton June 27, 1944 FOREIGN PATENTS Great Britain Mar. 15, 1938

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