US1964862A - Process for the manufacture of moistureproof opaque or transparent paper - Google Patents

Description

Patented July 3, 1934 PATENT OFFICE,

rnooess son THE PARENT PAPER AOTURE or MANUF MOISTUREPROOF OPAQUE -R TRANS- Eugene Sonneni'eld, Paris, France in. Drawing. Application July 20, 1932, Serial No. 623,687. In Germany July so, 1931,

. 8 Claims.

This invention relates to a process for the manufacture of moistureproof opaque or transparent paper.

A simple method of rendering paper moistureproof and transparent which is very frequently employed is to impregnate the same with molten paraflin, .wax or stearine or else oils.

Owing to their resistance to penetration by water, moisture and gases and their adequate de- 10 gree of transparency, such oiled and waxed papers find an extended application, which is limited only by the fact that they cannot easily be glued. Hard parafiln-papers are subject however to the drawback that they crack even when bent to the slightest degree so that transparency is of course, lost at the cracks, whilst flexible paraflin papers on the other hand, easily grease even when touched with warm hands. Paraifined papers are moreover unsuitable for wrapping goods sen- 0 sitive to grease,particularly in tropical climates or during warm seasons.

Another method of imparting the hereinbefore described qualities to paper is to apply a coating of transparent lacquer to one or both surfaces thereof. The transparency of these lacquered papers is greatly superior to that of parafllned papers and by selecting a suitable composition of the lacquer these coated papers can be rendered waterand moisture-proof.

Such lacquered papers are however only superficially waterproof. If water penetrates into the interior via the edges or from the back of paper coated on one side only, the paper becomes softened and the tensile strength is reduced considerably. Moreover moisture penetrates through the cracks or flaws in the waterproof coatingwhich are caused by the excessively great difference between the flexibility and tensile strength of the paper and the coating respectively and which cannot be remedied. The continuity of the waterproof coating is very easily broken on subjecting the coatedpaper to stretching, bend-- ing and other mechanicalstresses during use,. with the result "that impermeability of the paper is lost at these places. Such coated paper 'therefore only aifords an apparent protection against penetration by moisture; the protection being real only when rigid even surfaces are coated! such as for example, maps and blackboards.

The present invention relates to the manufacture of both waterproof and moistureproof paper; opaque or transparent, and aims at combining! the advantageous qualities of the oiled (waxed) and lacquered papers without introducing any of the disadvantages attending same.

According to the process of the present invention, rubber or oils, fats and waxes of mineral, vegetable or animal origin and/or their derivatives are worked up into plastic masses with cellulose esters and/or ethers and plasticizers which 00 are then incorporated in a finely divided condition with the paper-pulp before, during or after grinding it in the beating engine. The finely divided plastic material in the paper-pulp con,- glomerates into a coherent mass when the paper is calendered on hot rolls, the framework of paper fibres being completely embedded therein.

Paper manufactured by the process of the presentinvention is impermeable to water, moisture and gases, is transparent, does not grease and can be readily glued or cemented. Its mechanical strength properties have been modified to such an extent that any coatings applied thereto if desired for improving the'transparency and producing a high lustre do not crack, even when the 76 paper is bent sharply.

The moistureproofing impregnating mass employed according to the present invention can be mixed with dyestuifs'and resins and if opacity is desired, with pigments and other fillers.

Cellulose lacquers containing paraffin have already been recommended for waterproofing purposes, but they are attended with the drawback, in contradistinction to the plastic masses of the present invention, of being suitable only for producing a superficial layer, besides being much more costly. No protection is therefore afforded to the interior of the paper against the action of water.

A proposal has already been made on the other hand, to, add cellulose esters to paper pulp prior to working up the pulp into paper or pasteboard, then to treat the finished paper with solvents adapted to dissolve orgsoft'en the cellulose esters. After the evaporation of the solvent "the fibres 96 are said to be cemented together by the dissolved or softened cellulose ester, so that the paper has become waterproof and stronger.

Comparative experiments have shown that the aforesaidprocess is very diflicult to carry out in 100 practice. Under the conditions required for continuous manufacture the period of contact of the paper with the solvent is too short, hence the cellulose esters contained in the paperare only superficially softened, a coherent protective layer is not produced and the resistance to tearing of the paper is not improved. Prolonged treatment of the paper with solvents extracts the cellulom esters out of the paper to a considerable extent. Moreover, the two surfaces of the paper no ployed makes inevitably become tacky at the same time. The method usedfor recovering the solvents emit difficult to forward the paper, tacky on both sides, with the necessary speed. It is moreover, quite impossible to render paper with which has been incorporated pure cellulose esters waterproof and moistureproof byhot calendering, that is by the simple and economical method of the present invention, because cellulose esters, unless first gelatinized with camphor substitutes, do not behave as plastic masses and consequently cannot be fused under heat and pressure into an elastic coherent mass in which the framework of fibres is embedded.

The impregnating mass of the present invention is produced for example by'kneading cellulose esters or ethers in a jacketted kneading apparatus with suitable quantities of plasticizers and a water repellent substance as hereinbefore described; dyestuffs, resins, pigments and other fillers being incorporated if desired with the ad'- dition of small quantities of a volatile organic solvent or mixture of solvents. It is essential during this operation that the temperature should not rise above the boiling point of the :solvent employed. When the kneaded material is entirely homogeneous the temperature is increased so that the solvent is able to escape, the escaping solvent being replaced'by the same quantity of a precipitant of higher boiling point, such as for example, water. As soon as the mass is free from solvent the temperature is increased again until the whole of the precipitant has been driven off.

The mass remaining is fritted together, de-' pending on the quantity of plasticizers and water repellent substances employed, until it forms a soft paste, which cannot be converted into the fine state of subdivision required for further treatment by the usual grinding ina mill. i

It has been ascertained in. accordance with the present invention that the required state of subdivision can be obtained in a very simple manner by cooling the mass after the precipitant has been expelled-Imeading it constantly the while-down to the temperature of ordinary water, this temperature being maintained until the mass has fallen to powder. The powder thus obtained is sifted and dried at room temperature. Any cellulose ester and ether can be employed for the manufacture of the impregnating mass, but it is preferable to employ cellulose esters and ethers of high viscosity, in contradistinction to the low viscosity esters and ethers used for cellulose lacquers, since the former produce more plastic masses which can more readily be worked into the pores of the fibres when the paper is hot calendered. Moreover cellulose esters and ethers of high viscosity produce finished products of improved mechanical. strength properties as regards stresses due to binding or tension. A particularly suitable cellulose ether is ethyl cellulose, due to its elasticity and softness.

Suitable plasticizers for the purpose of the present invention comprise all the substances and mixtures usually employed for cellulose ethers and esters, nevertheless the plasticizer mixture is advantageously of suchconstitution that it contains a preponderance of true gelatinizing agents for the cellulose esters and ethers employed, that is to say agents which form with the latter so-called solid solutions which'do not tend to segregate under the action-of heat and pressure during the hot calendering. It has moreover proved to be of advantage to select a plasticizing agent which simultaneously acts'as a solvent for various other constituents of the impregnating mass, and especially for the water repellent substances employed. Dibutyl phthalate, for example, fulfills. the aforesaid conditions if ethyl cellulose be employed for the manufacture of the impregnating mass and if oils be employed for repelling water. Highly satisfactory results accrue from the employment of water soluble plasticizers of low volatility. Rubber, oils, fats and waxes of mineral, vegetable or animal origin and derivatives thereof,

insoluble plasticizers may function simultaneously as water repellent agents.

The proportions in which the various ingredients are employed may vary within wide limits depending on the requirements which the finished product has to fulfill in respect of suppleness,

impermeability to moisture and transparency.

- The following composition of an impregnating mass of proved utility is given purely by way of example and is not intended to be limitative:

Percent Ethyl cellulose 65 Dibutyl phthalate 25 Castor oil 10 thereof. The mixture thus obtained is then precipitated as hereinbefore described, finely divided and mixed up alone or with the addition of further quantities of cellulose in the beating engine and worked up'into paper as in the case of ordinary paper pulp.

Owing to the ready fusibility of this mass it is also possible to impregnate the finished paperweb with sameusing small quantities of high boiling solvents if desired-similar to the method of impregnatingwith paraifin, for example.

It is advantageous in all cases to subject the impregnated paper web to hot calendering.

The proportion of impregnating mass to paper stock canbe varied' within wide limits depending on the qualities desired in the finished product. Adequate impermeability to water is obtained, in the case of thin'paper, for example, by adding from 5 to -15% of the impregnating mass thereto.

I claimz-ie j '1. A proc: fss for the manufacture of moistureproof paper-which comprises first gelatinizing a mixture of ulose derivatives, plasticizers, and water repellen ubstances, comminuting the plastic mass so formed, and incorporating said plastic mass with paper pulp during the manufacture of paper therefrom.

2. A process for the manufacture of moistureproof paper which comprises first gelatinizing a mixture of cellulose esters, plasticizers and water repellent substances, comminuting .the plastic mass so formed, and incorporating said plastic 4. A process for the manufacture of moistureproof paper which comprises kneading together cellulose derivatives, plasticizers and water repellent substances in the presence of volatile organic solvents, at a temperature not in excess of the boiling point of said solvent, raising the temperature to expel the solvent, precipitating the mass, cooling it to ordinary temperature whilst kneading continuously until the mass falls to powder, drying said powder and adding it to paper pulp mixing in a beating engine and working the mixture up into paper.

to form a plastic mass, finely dividing said plastic mass and incorporatingit with paper pulp during the manufacture of paper therefrom.

6. A process for the manufacture of moistureproof paper which comprises kneading together cellulose derivatives, plasticizers, water repellent substances and tinctorial substances to form a plastic mass, finely dividing said plastic mass and incorporating it with paper pulp during the manufacture of paper therefrom.

7. A process for the manufacture of moistureproof paper which comprises kneading together cellulose derivatives, plasticizers, water repellent substances and pigments and other fillers to form a plastic mass, finely dividing said plastic mass and incorporating it with paper pulp during the manufacture of paper therefrom.

8. A process for the manufacture of moistureproof paper which comprises kneading together cellulose derivatives, plasticizers, and a wax-like mass to form a plastic mass, finely dividing said plastic mass and incorporating it with paper pulp during the manufacture of paper therefrom.

EUGENE SONNENFELD.