US2219781A - Process for demkmg imprinted - Google Patents

Description

Patented Oct. 29, 1940 PATENT oFrIcE PROCESS FOR DEINKING HWPRINTED PAPER Richard H. Lowe, Salt Lake City, Utah, assignor to The General Engineering Company, Salt Lake City, Utah, a corporation of Utah No Drawing. Application September 8, 1937,

-Serial No. 162,886

1 Claim.

My invention relates to the recovery, forreuse, of imprinted papers made principally from chemical pulps and substantially free from ground wood or mechanical pulps, by removing the ink therefrom by a flotation process, and my invention resides in my discovery that by control of 'the temperature in the cooking preparation of the stock before entering the flotation step, more complete saponification is obtained and the soaps formed are readily precipitated or flocculated by simple means and do not retard the selective flocculation of the carbon particles in the pulp.

The carbon particles constituent of printing inks are of such size that they exhibit colloidal properties. This does not infer that these particles are true colloid, and they may actually be suspensoids, but I mean that they exhibit true colloidal properties with respect to flotation treatment. To be successfully treated by the froth flotation method, asubstance must act as a finite particle and not as a colloid. To provide colloidal substances with finite particle characteristics they must be grouped together, or

flocculated in order that a large number of colloidal particles will have the physical characteristics of a single particle when grouped together. Therefore, the successful removal of carbon particles from a pulp is dependent on obtaining a proper state of flocculation of the carbon particles, so that their colloidal properties will be lost and they will acquire the properties of a finite particle.

In the deinking of waste papers the paper is usually given a cooking treatment with an alkali for the purpose of disintegrating or deflberizing the paper stock, and facilitating the separation of the carbon particles from the paper fibers and fillers. In this treatment certain substances, contained in the paper, such as free rosin in the sizing of the paper, and certain .oils used in the imprinting inks react with the alkali of said treatment to form soaps, and these soaps, together with the soaps already present in the sizing, cause a dispersion of the pulp and of the carbon particles in the .pulp. The subsequent flocculation of the pulp and of the carbon particles in the pulp is dependent upon the proper control, or the removal of these soaps. The present practice is to increase the speed of the saponification step by effecting the cooking at high temperatures. But, high temperatures cause the formation of substances which retard the action of the flocculation agents, later added to flocculate the carbon particles, and the pulp, thus making it necessary=to remove these substances by washing before proceeding to the flotation step in the process. This washing step is expensive in cost of time and equipment necessarily em-' ployed.

I have discovered that if-the temperature in the cooking treatment with alkali is controlled within certain limits, only such soaps and substances are formed which are readily flocculated by simple means, and further their presence is beneficial in the later flotation treatment or step.

I have, furthermore, discovered certain combinations of reagents that will successfully flocculate the pulp and selectively flocculate or collect the carbon particles in the presence of' such soaps,, and thus allow the carbon particles to become attached to the froth bubbles produced in the pulp, and thus rise to the surface of the pulp for removal. p

I carry out my invention in the following manner:

Waste paper, preferably shredded, is added to a water solution containing about 0.5% to 1.0% caustic soda (sodium hydroxide), soda ash (sodium carbonate) or any similar proportion of the two mixed as convenient. This solution is maintained preferably at about 140 F. and must not exceed 174 F. for 20 to minutes, or until disintegration of the paper manifests itself.

The liquor or solution is then drained from the paper, and the paper is squeezed reasonably free of the liquor, but it is not to be washed, as retention of some of the soaps formed in the cooking liquor is desirable for later treatment of the pulp by flotation. The stock is then diluted with water to a suitable consistency, usually about 6%, and beaten or agitated until the stock is defiberized. Approximately 80 lb. of lime per ton dry weight of paper is then added, and the stock is agitated several minutes prior to flotation treatment. The lime may be added during the defiberizing step, but preferably it should not be in contact with the pulp over 45 minutes prior to flotation, as its effectiveness gradually diminishes after a period of 30 minutes. The pulp is then further diluted with water to a suitable consistency, usually between 1% and 2%. One of the lighter distillates of the hydrocarbon group, such as kerosene, is then introduced into the pulp to cause selective flocculation and collection of the carbon particles, and also to prevent excessive froth volume being produced. Air is then introduced into the pulp so as to cause froth to form and rise to the surface of the pulp. This froth, which contains the deleterious substances.

is removed from the surface of the pulp in the same manner as is practiced in mineral flota tion. The pulp remaining in the flotation machine is then a clean pulp, devoid of deleterious" lection desired. A short time should elapse between the addition of lime and the addition'of kerosene or similar reagent to obtain the maximum results. The volume of froth can be regulated by the later addition of either lime or kerosene or similar reagent, lime producing a more voluminous froth,- and the kerosene diminishing it, and thus controlling its volume; and excess of kerosene will kill the froth completely. I have found by experimentation that about 80 lb. lime and about 5 lb. kerosene per ton of paper dry weight is satisfactory for most, types of papers. I have furthermore discovered that if the temperature used in cooking the paper is permitted to rise above -174 F. the efiectiveness of the flotation agents is-destroyed. In other words, at the inhibited higher temperatures the pulp remains in a semi-dispersed condition even in the presence of flocculating agents, and suiiicient collection and removal of the carbon particles is im- P ssible.

I have also discovered that complete removal of the carbon particles is not practicalif either a general pulp flocculent, such as lime, or a selecti-ve flocculent or collector such as kerosene is used alone; these two agents must be used together and approximately in the proportions stated.

I claim:

The process of delnking printed paper which consists in cooking the stock inan alkaline solution of a strength equal to .5 to 1.0% of caustic soda at a temperature between 140 F. and 174 F. for a period of between twenty and thirty minutes, removing in part the cooking liquor by draining, and without washing, deflberizing the stock, diluting the stock to a consistency of approximately 1% to 2%, adding lime, adding a reagent having collective properties toward carbon particles and froth modifying characteristics, producing frothing in said stock by the aid of the soapy liquor retained in, the pulp, and removing the resulting froth from the surface of RICHARD H. LOWE.

. the pulp.