US2214845A - Improving color of iron stained material - Google Patents

Description

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Patented Sept. 17, 1940 UNITED STATES IMPROVING COLOR OF IRON STAINED MATERIAL Sidney D. Wells, Combined Locks, Wis., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Michigan No Drawing. Application May 6, 1939, Serial No. 272,142

8 Claims.

This invention relates to the color lightening and brightening of materials occurring naturally and contaminated with iron, manufactured in contact with iron, or otherwise subject to contamination with iron whereby the material contains iron compounds discoloring the material. As such materials are mentioned paper pulps, clay, kaolin, fine sand, bauxite, and the like, old newspapers, and in fact any material which can be formed into an aqueous suspension and treated in the presence of water, such as paper stock, straw, and other materials.

The invention will be particularly described as it relates to the treatment of a paper pulp, but this is only by way of example, and not by way of limitation as to broad features of the invention. However, because of the presence of tannin in paper pulp, the invention is peculiarly applicable to color lightening of such pulps.

Paper made from pulp containing small amounts of iron compounds derived from the vegetable materials of which the pulp is comprised, from the water or from chemicals used in the production thereof, has a dull shade which is objectionable in many kinds of paper. This dull shade I have found is imparted to the paper by the iron compounds and may be of an orange or reddish cast. Where tannic acid is present in even a slight amount and comes into contact with the pulp, the color imparted to the pulp is grey and produces a marked lowering of the brightness of the finished product.

In accordance with the present invention, the color of the pulp can be brightened materially even though compounds of iron may be present in amounts sufficient to seriously dull the color of the pulp if made by the usual processes. This is obtained by changing the iron compounds to ferrous ferricyanide, commonly known as Turnbulls Blue. When this is accomplished, the color characteristics of the paper is materially improved, for the grey compounds and other compounds which would otherwise absorb the blue components of the light reflected from the surface of the fibers are converted into compounds which do not absorb the blue components, whereby the paper appears to be whiter in color. Since the reflected light is usually more deficient in blue than in yellow and red, the general effect is to raise the whiteness of the reflected light, and consequently the brightness of the color. In ordinary practice the excess of red and green is corrected by adding blue dye or pigment and the degree of whiteness is usually brought somewhat lower than the parts blue in the pulp mixture as furnished. By changing the iron compounds over to Turnbulls Blue they are changed from compounds which absorb the blue components of white light to one which reflects them very effectively and the result is an increase in the amount of blue reflected. By the control of the amount of Turnbulls Blue produced, the red and yellow components of the light reflected are only absorbed to the extent to which they exceed the blue. As a consequence, the general effect produced is an increase in whiteness.

In practicing this invention, the pulp is first subject to a treatment whereby the iron compounds present are reduced to the ferrous state, after which the pulp is reacted with a small amount of a ferricyanide. Any one of the usual reducing agents can be employed, such as sodium, potassium, and ammonium hydrosulfites. I can also employ successfully sodium, potassium and ammonium addition products of a hydrosullite and an aldehyde, or a ketone, such as is disclosed in the Hirschkind Patent 2,071,305 of February 16, 1937. I can also successfully employ the sodium, potassium, and ammonium sulfoxylates and other sulfoxylates, such as those disclosed in the Hirschkind Patent 2,071,306 of February 16, 1937. I can also successfully employ any of the above compounds manufactured in situ, and I have operated with particular success by employing zinc dust in connection with sulfurous acid or bisulfites of sulfuric acid present in the pulp or other suspension. Zinc hydrosulfite can be manufactured in situ, or added, or any reducing agent can be used which is sufficiently rapid in reducing action to permit the process to be practiced without any extensive change in the procedure and equipment of the industry in which the color brightening is being practiced. For the purposes of illustrating the process, the following examples are given on paper pulps.

Time of reaction: Three hours at room temperature.

Brightness: Raised from 63 to 70%.

The brightened pulp was used with sulphite pulp in the manufacture of print papers.

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Pounds action of a reducing agent effective toreduce sub- 2. Unbleached sulphite pulp %0 stantially all iron therein to the ferrous state, Spruce groundwood 800 and adding a ferricyanide to said suspension after Clay 300 said reduction to react with the ferrous iron and Rosin size 5 form Turnbulls Blue in said solid. Paper blue R .007 3. A process for improving the color of a finely Rhodamine .047 divided material darkened by the presence of Alum 10 iron or iron compounds, the process comprising Zinc hydrosulphite 7 subjecting an aqueous suspension of said mate- Potassium ferricyanide 2 rial to the reducing action of a reducing agent The ingredients listed were added to the beater in the order indicated and no more time was taken with each beater so charged than was taken by the same treatment prior to the use of the brightening agents. The color of the paper made by this process was as bright as paper made with 250 pounds of bleached sulphite and 750 pounds spruce groundwood with a considerable saving in cost.

Groundwood pulps, unbleached hemlock sulphite, and bleached soda pulps are all considerably improved in brightness by this process of treatment. Unbleached spruce sulphite and. bleached kraft pulps are also improved as well as unbleached kraft pulps when made into paper in which blue dye is ordinarily used as part of the color.

The conditions described in the foregoing description and examples are typical but the present process is not limited to the particular cases cited and can be extended or modified to: suit numerous conditions.

In the treatment of other materials such as those previously mentioned, the material to be treated is disintegrated and then treated with the reducing agent in an amount sufiicient to reduce the iron to the ferrous state. Thereafter the material is treated with the ferricyanide, all the while in a water suspension or in the presence of water. The pH of the aqueous suspension is adjusted and maintained at that most favorable to action of the reducing agent employed. The temperature of the suspension can also be raised by heating to- F. and as high as 212 F. if desired.

This is a continuation in part of my application Serial Number 163,857 filed September 14, 1937 and allowed November 7, 1938 but now forfeited.

I claim:

1. A process for improving color of a material darkened by presence of iron or iron compounds comprising subjecting the material in an aqueous suspension to the reducing action of a reducing agent to reduce substantially all iron present to the ferrous state and reacting the reduced iron with a ferricyanide.

2. A process for improving color of a finely divided solid contaminated with iron or iron compounds comprising forming a suspension of said solid in water, subjecting said suspension to the effective to reduce substantially all iron present to the ferrous state and reacting the so reduced iron with a ferricyanide to form Turnbulls Blue in said suspension.

4. A process for improving the color of a mineral material darkened by the presence of iron or iron compounds, the process comprising reducing substantially all iron in said material while said material is in finely divided form and in an aqueous suspension with a reducing agent and then reacting said reduced iron with a ferricyanide to'forrn Turnbulls Blue in said material.

5. A process for improving the color of a cellulose pulp darkened by the presence of iron or iron compounds, the process comp-rising reducing substantially all iron in said pulp in aqueous suspension with a hydrosulfite and then reacting said reduced iron with a ferricyanide to form- Turnbulls Blue in said pulp, said hydrosulfite being employed .in an amount of about 1% on the Weight of the pulp present, said ferricyanide being present in an amount of about 0.25% on the weight of pulp present.

6- A process for improving the color of a cellulose pulp darkened by the presence of iron or iron compounds, the process comprising subjecting an aqueous suspension of said pulp to the reducing action of a reducing agent effective to reduce substantially all iron present to the ferrous state and reacting the so reduced iron with a ferricyanide.

7. A process for improving the color of a cellulose pulp darkened by the presence of iron or iron compounds, the process comprising subjecting an aqueous suspension of said pulp to the reducing action of a hydrosulfite for about half an hour to reduce substantially all iron present to the ferrous state and reacting the so reduced iron with an alkali metal salt including, upon hydrolysis, the ion Fe(CN)e.

. 8. A process for improving the color of a cellulose pulp darkened by the presence of iron or iron compounds, the process comprising subjecting an aqueous suspension of said pulp to the reducing action of a hydrosulfite for about half an hour to reduce substantially all iron present to the ferrous state and reacting the so reduced iron with a material providing the ion Fe(CN)c to react with said ferrous iron.

SIDNEY D. WELLS.