US2228320A - Method of making filter paper - Google Patents

Description

Patented Jan. 14, 1941 UNITED STATES PATENT OFFICE METHOD OF MAKING FILTER PAPER tion of Delaware No Drawing. Application October 8, 1937, Serial No. 168,082

4 Claims. (01. 210-204 This invention relates to filter paper and more particularly to filter paper for use under conditions where it is necessary to combine a high rate of flow of filtrate per square inch of area with substantial tensile strength and stiffness.

An object of the invention is to produce a paper combining large capacity per unit of area, high tensile strength, and good capacity for removing fine particles of solid matter.

A further object of the invention is to produce a filter paper of the above character which is capable of being operated at high fiuid pressure without having the fibres of the paper matted together by the pressure in such a way as to retard the flow of filtrate.

A further object of the invention is to produce a filter paper which is capable of retaining the above described characteristics in the presence of water or dampness in the filter and which will, go in fact, be capable of filtering water Without loss of tensile strength or any of the other qualities above described.

In making filter paper-according to our invention, we may use ordinary wood pulp paper or paper made from cotton rags or paper made from wool fibre. We may also use any paper containing these or similar ingredients or mixtures thereof. These papers are well known on the market and no specified description is necessary. The thickness of the paper may be selected according to the purpose for which it is intended, but an approximate thickness of has been found to be satisfactory for most purposes.

In preparing filter paper according to our invention, we first take the dried and rolled porous paper stock as furnished by the paper mills and soak it in a solution of caustic soda (NaOH) in water. Any desired strength of solution may be used, but a 5% solution is suggested. Stronger 40 solutions may also be used, particularly in cases where it is desired to use the same solution a second time after it has been washed out of the paper. The washing process naturally dilutes the solution, and by starting out with a strong solution, it is possible to use it several times before it falls below its strength sufficient to give satisfactory results. When the solution becomes too Weak, it may, in most instances, be brought up to strength by boiling as long as the chemical composition of the caustic soda has not been destroyed.

The temperature of the soda bath need not be held within accurate limits and ordinary room temperature F.) is satisfactory. The time controlled by the operator who observes the paper in the soaking and swelling process. From one to five minutes in the soaking bath is usually sufficient. After soaking, the paper will be found to be swelled to approximately twice its normal thickness and the length and width of the sheet will be shrunk. The paper is now in a very much weakened condition, not being much more than a mush, so that it is necessary to handle it on or between screens to keep it from falling apart. After the soaking process, the caustic soda solution is washed out with water, the first part of the Wash water being saved for reuse. 'As soon as the caustic is removed from the paper, its strength is substantially increased, but it is still not strong enough to stand rough handling until it is dried. The drying is preferably in the presence of heat.

When the paper has been thoroughly dried, its thickness will be found to be substantially increased, although the length and width of the sheet will be smaller than the original. The paper is now in condition for use as a filter, and the fiow capacity per square inch will be substantially increased over the original. We do not, however, consider that either this product or the original paper is entirely suitable for filtering fluids containing Water or dampness because of the great loss of tensile strength in the presence of water. In order to make the paper thoroughly satisfactory, we give it a further treatment with a 10% lacquer solution as described in the, United States patents to G. R. Ericson #1,944,550, issued January 23, 1934, and #2,007,753, issued July 9, 1935. After this treatment, the paper will be found to have its increased flow capacity and will have greater tensile strength and resistance to moisture. The lacquer solution may be made weaker or stronger as'desired, but a mixture of 10% of ordinary brushing lacquer and thinner gives highly satisfactory results. For use in filtering liquids containing gasoline, we prefer to use a lacquer containing glyptal gum or other substance similarly insoluble in gasoline.

The operation above described first has the effect of loosening, distorting or rearranging, and swelling the fibres to at least twice their normal size which shrinks the paper in the plane of the sheet and substantially thickens it. This operation also expands the interstices between the fibres whereby a relatively hard paper may be used and the filtering capacity of the paper is thereby increased. After the caustic treatment, the interstices will be more tortuous which results in better filtering properties than would be the case if a more loosely matted or softer paper were used in the first place. The lacquer coating has the effect of strengthening, bonding, :and fixing the distorted fibres and rendering the paper resistant to gasoline and moisture. The resultant product is an eflicient, durable filter paper adapted for use, particularly, in the fuel supply lines of internal combustion engines.

The exclusive use of all modifications as come within the scope of the appended claims is contemplated.

We claim:

1. The method of conditioning a sheet of porous paper stock for use as filter paper which comprises loosening and distorting the fibres to increase the filtering capacity of the stock and applying a thin solution of glyptal lacquer to simul taneously water-proof fibres and cause them to adhere to each other.

2. A filter paper comprising a sheet of porous, paper stock in which the fibres are loosened and distorted and provided with a bonding and liquid resistant coating.

3. The method of conditioning filter paper which comprises first swelling the fibres by soaking the paper in a solution of caustic soda, washing out the caustic solution after the fibres have been sufliciently swelled, drying the paper, applying a thin solution of lacquer, and again drying.

4. A filter paper comprising a mat of fibres, said fibres having been loosened and distorted by a swelling and reshrinking, and being cemented together at their points of contact and provided with a water resistant coating.

W. C. MAGRUDER, JR. A. C. KORTE.