US2011156A - Process for the manufacture of paper - Google Patents

Description

Patented Aug. 13, 1935 raocsss Foa THE MANUFACTURE or mean Harry Huet Nelson, Paris,

and Guillaume Becker,

Versailles, France No Drawing. Application April 14, 1933, Serial N0. 666,224. In France April 19, 1932 -2 Claims.

The present invention relates to a process of manufacture of a waterproof paper or cloth having a high mechanical resistance especially in the wet state, and likewise possessing a very high 5 chemical resistance, said paper being particularly suitable as packing paper and for the manufacture of paper bags of the type used for example for carrying plaster or other materials.

Said process is essentially characterized by the fact that the paper pulp, that is to say, the cellulose fibres, previously obtained by any of the usual known means, but preferably by a chemical method and superficially hydrated, are impregnated with an alkaline solution offreshly prepared cellulose thiosulfocarbonate, which is then subjected to the action of a suitable coagulant producing a precipitation of hydrocellulose which constitutes the binder of the cellulose fibres.

Such coagulated hydrocellulose exists in the paper according to the invention in a form similar to that in which it exists in artificial silk. As such hydrocellulose has a very high tensile strength, the paper thus obtained is likewise very resistant.

If such a solution is permitted to age, its viscosity increases and its colloidal micellae polymerize, giving rise in the space of six to eight days to the product used in the artificial silk trade under the name of viscose. Numerous tests have shown that it is just as impossible to obtain the desired effect with this product, when a previously formed paper web is impregnated with it as when the paper is prepared directly by adding the product in the pulping machine.

It would seem from the above and from observations of the phenomena of coagulation and regeneration of the cellulose oi the solution that in the course of manufacture the condensation of the thiosulfocarbonate is considerably accelerated under the influence of the contact ot the excess cellulose.

Coagulation may be effected by means of any of the numerous coagulants used for viscose, subject, however, to the proviso that its acidity shall be considerably diminished as otherwise it has been found that the sudden change from the alkaline state of the thiosulfocarbonate solution has a harmful eil'ect on account oi the acid condition of the coagulant bath,'and destroys the homogeneousness of the fibre-binder mixture of thepaper. It is therefore necessary to arrange matters so that .the changes about the neutral point will be as small as possible, that is to say that the solution to coagulate shall have the minimum of alkalinity and the coagulant the minimum of acidity necessary to render the operation successful.

The use of coagulants having the same composition and concentration as those used in the preparation of viscose silk would result in valueless products completelyfilled with gas bubbles. A good quality of the product according to the present invention can only be obtained by diminishing the quantity of bi-sulfate, or sulfuric or M hydrochloric acid etc. contained side by side with the neutral salts in the coagulants of viscose to reduce it to or 1/20 of the usual concentrations. Better and more reliable results are obtained if the strong acids are replaced by weak 15 acids, as for example sulfurous acidor bi-sulfites. Another method consists in providing two 00- agulant baths: a first saline bath having a neutral or alkaline chemical reaction, and a second slightly acidulated bath which promotes coagula- 20 tion. By slightly heating the coagulation baths their reagent concentration may be diminished, and the qualities of the paper obtained improved.

The cellulose thiosulfocarbonate may be impregnated by soaking the already formed paper in a solution of thiosulfocarbonate, it being possible to facilitate penetration by previously moistening the paper with a very dilute alkaline solution of thiosulfocarbonate as also by the vacuum producedunder the paper web if a paper couchso ing machine is used.

After coagulation, the paper is washed to rid it of impurities and then dried. To eliminate all traces of sulfur, hyposulfate or an alkaline sulfide may be added to the wash water.

There is thus obtained a translucent and homogeneous sheet of paper having the aspect of green leather and which, under the influence of formaldehyde, undergoes a change of appearance and quantity like leather during tanning. 40 Such paper is highly resistant and is particularly suitable for the manufacture of packing sacks for building materials or similar applications.

The invention is likewise concerned with a process for preparing in the cold the alkaline cellulose from which the solution of cellulose thiosulfocarbonate is derived.

It is known that the viscosity of the thiosulfocarbonate solution is reduced if the alkaline cellulose serving for its manufacture is prepared 50 in the cold. This fact has not been made use of on an industrial scale on account of the dimculties in cooling by refrigeration a 17.5% solution of caustic soda to temperatures at which there is advantage in applying it. I

It has been observed that such cooling may be readily performed if a solution of caustic soda which is more concentrated than that serving for the manufacture of alkaline cellulose is first prepared and if it is then brought back to the desired percentage by addition of crushed ice. By mixing six parts of a lye of 30% sodium hydrate with four parts of ice, it is possible to obtain a 18% lye, the temperature of which is approximately 25 C. lower than that of the original lye. This solution enables the alkaline cellulose to be easily prepared industrially at temperatures below 0 C.

Another advantage of the process is that it avoids the formation of hemicelluloses which are produced when the temperature of the reaction exceeds a certain value and which result in unusable products.

The products based on regenerated cellulose are generally softened after coagulation with glycerine or gluclose. Such softening effect disappears in the wash and leaves a brittle product which has undergone considerable contraction.

Such drawbacks are avoided by adding a small proportion of soap to the solution of cellulose thiosulfocarbonate, before coagulation, soap is preferably added in the form of a solution of soft soap, and more particularly in the form of resinous soap which possesses the property of not precipitating with hydrated lime, and as castor oil soap, which prevents the regenerated cellulose from contracting. The soap micella:

which are too big to pass through the micellae A network of the regenerated cellulose, remain after coagulation trapped in the cellulose and leave it in its initial qualities even after a. lengthy exposure in water. There is advantage in using mixtures of such soaps to combine their qualities.

Certain techincal points are involved in the impregnation of the paper due to the colloidal nature of the cellulose thiosulfocarbonate solution.

For the impregnation to be satisfactory, it is first of all necessary to wait a few minutes between the moment when the product is applied and the leaf coagulates. In the case of continuous manufacture, such waiting period is obtained by causingthe leaf to zig-zag through two rows of rolls placed in front of the coagulation tanks. To avoid tear, the paper web may be transported on conveyor cloths, or it may be passed round lightly constructed drums of large diameter.

The product is applied by means of rubbercoated cylinders. There is advantage in providing two systems of coating rollers, the first of which, located forward of the impregnation track, deposits more product than necessary, while the second removes excess after the impregnation and evens up the thickness of the leaf. In spite of all precautions, it is often impossible Such to obtain a uniform web on account of the air included in the starting paper web which prevents the cellulose solution from penetrating. The web obtained then reveals opaque patches having irregular forms, This may be avoided if the web of paper is slightly moistened with water on one side, and if the moistened web is then applied against a heated cylinder. The contact with the cylinder causes the water to be converted into steam, which can only escape by passing through the web, driving before it the air contained therein and taking its place.

If now the cold cellulosic solution be applied on both sides of the hot steam-laden web, the sudden condensation of the steam creates a vacuum in the paper web whereby the viscose solution is drawn in and a homogeneous impregnation is obtained.

Another means of obtaining a homogeneous impregnation consists in the use of a perforated cylinder provided internally with cells, some of which are in communication with a suction device, similarly to cellular filters, while the cells at the points at which the paper engages with and leaves the cylinder are open to the atmosphere. The product is then applied by means of a coating roller to one side of the paper before it reaches the suction cylinder. While the paper passes on this cylinder, the product is drawn through all its pores and when the strip is taken ofl, the other side is likewise printed and the whole equalized and the excess removed by means of two straining rolls.

It is of course understood that the processes described herein are likewise applicable in the same conditions and procuring the same advantages in order to obtain any highly resistant waterproof 'cloth or textile material.

We claim:

1. Process of manufacture of a waterproof and highly resistant paper or cloth consisting in moistening the formed paper web with a dilute solution of thiosulfocarbonate, in then impregnating the web with a solution offreshly prepared cellulose thiosulfocarbonate, and in precipitating hydrocellulose constituting the binder of the cellulose fibers by means of a coagulant of viscose of weak acidity.

2. A process for the manufacture of a water proof and highly resistant paper and the like comprising refrigerating an alkali solution, treating cellulose with said solution to form alkaline cellulose, preparing cellulose thiosulphocarbonate from said alkaline cellulose, impregnating the material to be treated with a freshly prepared solution of said cellulose thiosulphocarbonate and precipitating hydrocellulose in the material by means of a coagulant.

' HARRY HUET NELSON.

GUILLAUME BECKER.