US1933810A - Process of decorating plastic material - Google Patents

Description

Nov. 7, 1933- W. 0. KENYON El AL 1,933,810

PROCESS OF DECORATING PLASTIC MATERIAL Filed July 9, 1932 MWZGIIJJOR&@TZZJSILZZZCL,

Md M Patented Nov. 7, 1933 1,933,810 rnocnss or DECORATING rms'no MATERIAL William 0. Kenyon and Cyril J. Stand, Rochester,

Rochester, N. Y

on to Eastman Kodak Company,

a corporation of New York Application my 9, 1932. Serial No. 621,742 3 Claims. (01. 204-31) This invention relates to the production of decorative efiects in plastic materials and more particularly to a method of producing colored designs in cellulose ester sheeting.

Plastic products are usually colored by incorporating a pigment, dye, or other coloring matter into the material while still in a flowable condition and then allowing the plastic to set to the desired form. Cellulose ester sheeting, for example, may be colored by incorporating a dye in the dope or solution from which the sheet is formed, but it is practically impossible to form sharply defined designs of different colors and yet havethe dye evenly distributed throughout the sheet. Such sheeting may also be colored by printing the design on the surface by means of an appropriate ink, but this method is not all that is to be desired since the design may be rubbed 01f.

The present invention is designed to overcome the above mentioned dimculties and its principal object is to provide a method whereby cellulose ester plastic products may be decorated with permanent and sharply defined multi- 25 colored designs. A further object is to provide a method for decorating cellulose ester sheeting with a multicolored design which may not be removed by friction. A still further object is to provide a cellulose ester sheeting having a design produced within the body of the material itself and in which the coloring matter is uniformly distributed throughout. Other objects will hereinafter appear.

These objects are accomplished by the following invention which, in its broadest aspects,

comprises the incorporation in a cellulose ester plastic of a dyestufi or indicator whose color changes with a change in the concentration of free hydrogen or hydroxyl ions in its environment, and subsequently subjecting the cellulose ester material to the influence of an electrical" disturbance to produce the desired change in the concentration of these ions. In the case of an indicator responding to production of acids, the 15 ester is decomposed thereby providing the free hydrogen ions necessary for the production of the color change.

Taking the production of colored designs in cellulose acetate sheeting as an example, an 30 indicator such as brom thymol blue is incorporated in the dope from which a cellulose acetate sheet is to be produced. The sheet is coated on an appropriate surface in the usual manner,

dried, stripped from the coating surface, andplaced between two fiat electrodes in which the figure of the design is cut out similar to a stencil. When a relative high electric potential is applied to the electrodes an electrical disturbonce is produced at the exposed edges thereof.

0 The exact nature of this disturbance is not fully understood but it has been found inpractice to act upon the cellulose acetate in such manner as to give rise to the production of free acetic acid in very low concentration. This acid, which need not be more than 1/100,000 N under the conditions just described, causes a change in the color of the indicator,the area of the sheeting exposed to the disturbance becoming yellow in the case of brom thymol blue. The sheet, upon removal from between the electrodes, is found to have a yellow design upon a blue blackground.

In the accompanying drawing in which like reference numerals are applied to like parts, and in the following description, we have set forth one of the preferred embodiments of our invention, but it is included merely for purposes of illustration and not as a limitation thereof.

Fig. 1 is a perspective view showing a simple form of apparatus in which the process may be carried out.

Fig. 2 is a sectional view of the electrode plates and sheeting shown in Fig. 1, the relative thickness of the plates and the sheeting being somewhat exaggerated in the interest of clearness of illustration.

Fig. 3 is a plan view showing the sheeting after the design has been produced therein by means of the present invention.

Referring to Fig. 1, the numeral 1 designates a sheet of cellulose acetate having dispersed therethrough a well-known indicator such as brom thymol blue. The sheet 1 is placed between the electrodes 2 and 3 at least one of which has initials or other form of design cut therefrom.

The electrodes 2 and 3 are adapted to be connected through leads 4 and 5 to a suitable source (not shown) of alternating potential of relatively high magnitude. We have found that with a potential of the order of 5,000 to 10,000 volts and a current of the order of 50 milliamperes satisfactory results may be obtained.

In Fig. 2 showing the relative positions of the electrodes and sheeting, the location of the areas of electrical disturbance are indicated as being the most pronounced in the vicinity of the cut out portions of the electrode. Lines of force 6, '7, 8 and 9 indicate the disturbance produced when a high potential is applied to the electrodes 2 and 3 but are not to be considered as indicating the nature of the disturbance.

It will be apparent that only those portions of the sheeting in the immediate vicinity of the cutout portions and the edges of the electrodes will be afiected. The disturbance causes the development of a very low concentration of acetic acid in the sheeting 1 at the aifected areas. This slight amount of acid is, however, sufiicient to cause the indicator to change from blue to yellow. In treating cellulose acetate sheeting it has been found that a brom thymol blue indicator will change in 1 to 5 minutes when a potential of 10,000 volts at 60 cycles is applied to the electrodes 2 and 3, thus producing in the sheeting a sharply defined design of the stencil in yellow on a blue background.

While we have illustrated our method by reference to a cellulose acetate plastic, it will be readily seen that the invention is not thus limited, but may be applied equally well to the decoration of any cellulose ester material with which an indicator may be incorporated and in which the desired low concentration of acid may be obtained. It is equally appliable to production of designs in cellulose organic and inorganic ester plastics, mixed cellulose organic ester materials such as cellulose acetate propionate, cellulose acetate butyrate and the like. The particular conditions of operation will, of course, vary with the particular plastic dealt with, and with the particular indicator employed for the different color effects. It is well known that some acids ionize more readily than others and it will accordingly be easier to produce the concentration of acid necessary to eifect a color change with a given indicator with some cellulose esters than with others. For instance, it will require a shorter period or a less pronounced disturbance to produce the necessary concentration of acid in a cellulose formate or cellulose acetate sheet thanit will in the case of a cellulose propionate sheet containing the same indicator. The period or magnitude of the disturbance necessary to produce the desired change will also vary with the thickness of the sheet.

Assuming a particular cellulose ester sheeting is subjected to the process, the conditions of operation will vary in accordance with the particular indicator employed. For example, with indicators whose color changes with pH values, the lower the pH, the greater will be the concentration of acid necessary to be developed in the sheet by the electrical disturbance before the desired effect is obtained.

As examples of various dyestuffs and indicators suitable for use in the process herein described may be mentioned methyl red, lacmoid, propyl red, dichlorophenolsulfonphthalein (chlor phenol red) methyl violet, p-nitrophenol, dibromo-o-sulfonphthalein (brom cresol purple), dibromothymolsulfonphthalein (brom thymol blue). The list of suitable indicators is not intended to include all substanceswhich maybe successfullyemployed, but only those in which color changes occur with an acid concentration of approximately 1/ 100,000 N. Numerous other indicators may be employed for various types of cellulose ester sheeting and may be selected on the basis of their sensitiveness to varying concentrations of acid.

As is well known, each indicator has its characteristic range of pH within which it changes color. For example, some indicators show no color change whatever below a pH of '7, while they may have one or more characteristic color changes as the pH value increases. Conversely, other indicators show no color change with a pH of above '7, but one or more characteristic changes with a .pH below '7. It will thus be seen that the present invention is based upon the broad principle of a change of color occasioned by a change of pH, whether it be upon the side of alkalinity or of acidity.

Many modifications may be made within the scope of our invention. For example, if it is desired to use an indicator changing color at a very low pH value, it will be desirable to employ in the formulation of the sheeting an additional agent which, upon being subjected to the above mentioned electrical disturbance, will give rise to the production of the desired concentration of acid more readily than would be the case with sheeting not thus treated. For example, a plasticizer such as triacetin may be incorporated in the sheeting which, when treated in accordance with our invention, will produce the desired higher concentration of acid much more readily than would be the case with a sheeting from which this material was omitted. Other typical plasticizers which may be employed for this purpose are diethyl tartrate, triphenyl phosphate, epichlorhydrin, and ethyl paratoluene sulfonate.

If desired, an indicator which is colorless at neutrality but which is colored in the presence of a small amount of acid may be employed, thus making possible the production of colored designs upon transparent or colorless backgrounds.

It will be seen that the present invention is distinguished from all known processes of coloring cellulose ester products by the fact that the coloring material is completely dispersed throughout the body of the plastic. Due to this fact it is possible to produce in sheeting a design having a sharply defined outline which extends through the material and which cannot be removed by frictional means. The invention finds particular application to the manufacture of a wide variety of plastic cellulose ester products such as sheeting, material for. the manufacture of lamp shades, desk pads, and, in fact, for the manufacture of any articles in which there is desired a durable, decorative surface.

-What we claim and desire to secure by Letters Patent of the United States is:

1. In the art of producing color changes in cellulose ester material containing an organic indicator, the method of inducing the color change which comprises subjecting the material to the influence of the electrostatic field set up by an alternating current of high potential.

2. The method of producing a permanent, sharply defined, decorative design in a cellulose ester sheeting having incorporated therein an organic indicator which comprises placing the sheet between duplicate metallic stencils carrying the design and impressing a high alternating electrical potential across the stencils, whereby the cellulose ester is slightly de-esterified at those portions corresponding to the cut-out portions of the stencil and whereby suflicient free acid is produced in the body of the sheet to occasion a change of color in the indicator.

3. The method of producing a permanent, sharply defined, decorative design in a cellulose acetate sheet having incorporated therein brom thymol blue indicator which comprises placing the sheet between duplicate metallic stencils carrying the design and impressing a high alternating electrical potential across the stencils, whereby the cellulose acetate is de-esterified at those portions corresponding to the cut-out portions of the stencil and whereby suflicient free acetic acid is produced in the body of the sheet to cause the color of the indicator to change from blue to yellow.

WILLIAM O. KENYON. CYRIL J. STAUD.

CERTIFICATE oi corruption. 5

Patent No. 1,933,810 November 7, 1933.

WILLIAMVO. KENYON, ET AL it is hereby certified that error appears in theprintedspecificetionof'the above numberedpatent requiring correction as follows: ?age 2, iines fl-Q, for "riibromo-o-sulfonphthalein" read dibromo-o-cresolsulfonphthalein; and that the eaid Letter: Patent-should be read with thiscorrection therein that the age may eonform to the record of the case in the Patent @iiiee,

Signed and sealed this 12th do of December; A. D e i933.

i iii Hopkins (Seal) Acting Cmfiaaimer-ofyfitenee,

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