US1944907A - Impregnated paper product - Google Patents

Description

Patented Jan. 30, 1934 ILUNITED STATES PATENT OFFICE mrnnona'rnn PAPER rnonuc'r poration of Delaware No Drawing. Application April 1, 1933 I Serial No. 664,043

19 Claims.

This invention relates to impregnated sheet material and more particularly to an impregnated cellulose fabric which exhibits to an-exceptional degree those properties most desired in artificial leather products.

This case is a continuation in part of application Serial No. 599,808 filed March 18, 1932, which is a continuation in part of Patent No. 1,857,100.

Among the various methods suggested for making absorbent paper and impregnated products therefrom is one which consists of manufacturing a puffed paper by immersing a sheet of paper in strong caustic solution 'and'drying the sat- 16 urated sheet in air. The absorption of carbon dioxide causes the formation of sodium carbonate crystals which are subsequently washed out. The pufling efl'ect is due to the formation of the cystals in the sheet. The long contact of 20 the fibers with the strong caustic prevents any appreciable crinkling of the fibers. Furthermore, the restricted movement of the fibers when treated in sheet form prevents the formation of a base having the high degreeof crinkle, high freeness and capability of uniform impregnation which characterizes the product of the present invention. Prior treatments of paper pulp with caustic have been chiefly concerned with the manufacture of high alpha cellulose through solution of the non-alpha celluloses by the caustic. The solution of the non-alpha cellulose bonding materials, which is the object of the process, causes the original fiber to separate into the finer component fibers. The fibers are also shortened because the end portions, which are thinner than the middle portions, are dissolved off. This shortening and thinning of the fiber is evidenced by the slowness of the treated pulp and the decrease in the freeness value from that of the original pulp. High alpha cellulose papers now known are too expensive for general use as an impregnating base and the impregnated products possess certain deficiencies.

This invention has as an object an improved method of making artificial leather and 'sheet impregnated products in general. A further object is new and improved impregnated material products having-a base of felted paper making fibers. Other objects will appear hereinafter.

These objects are accomplished by preparing a fabric base in the special manner disclosed in the patent mentioned above and impregnating it with certain colloidal impregnating materials as will more fully appear in the following specification.

(c1. s2-4o) The fabric base is a paper or felt made of artificially crinkled cellulose fibers having a high freeness. The'method of making the base, as disclosed in the mentioned cases, is briefly as follows: Paper pulp is treated with a solution of 80 caustic soda of mercerizing activity under conditions which cause only a superficial reaction between the pulp and the caustic. To this end the reaction is stopped short of gelatinizatlon, and the mercerizing action of the caustic is not allowed to proceed appreciably beyond a superficial or skin eifect. The method of treating the pulp to bring about these conditions consists in dispersing the pulp with the caustic at high pulp consistencies (a low ratio of liquor to pulp) and diluting the caustic below mercerizing activity promptly after the fibers have been dispersed from the pulp mass and wet with the solution. By high pulp consistencies we mean consistencies above 10%,i. e., more than 10 parts by weight 7 of pulp per 90 parts by weight of liquor. For most purposes, however, we prefer to use consistencies from 15 to 20%. The maximum usable consistency corresponds to the minimum volume of liquor that will thoroughly wet the fibers in a time short enough so that the concentration of the liquor is not materially lowered by reaction with the fibers before all of the fibers are wet. Simultaneously with the wetting of the fibers by the mercerizing solution the crinkle and freeness of the pulp is at a maximum and these values decrease with increasing time of treatment. The use of high pulp consistencies has the efiect of retarding the time action of the caustic on the fibers. Even with these high pulp consistencies, however, the solution should, for the best results, be removed promptly, a time as long as thirty minutes being usually undesirable except for certain highly resistant pulp such as rope. When using mechanism specially designed for swift dispersion of the fibers and prompt dilution of the caustic in contact therewith, it is not, except for economic reasons. essential that a low ratio of liquor to pulp be used.

The initial material is preferably kraft paper pulp. Unlike the process for treating pulp to make high alpha cellulose, the action of the caustic in the present process is stopped before a major portion of non-alpha cellulose constituents are removed from the fibers and before the ultimate fibers have been liberated by solution of the ligneous bonding materials and the non-alpha. cellulose constituents.

Various other reagents may be used instead of caustic soda. These reagents are those which at 0 iii? suitable concentration and temperature are capable dissolving or dispersing cellulose, the concentra ion of the reagent being within the range known as mercerizing strength, that is the concentration commonly used in mercerizing cotton goods. For a given concentration of these reagents the mercerizing activity of the solution is dependent upon the temperature. In the case of caustic soda, which is our preferred reagent, the activity increases as the temperature is lowered.

Inasmuch as the strength of a particular solution required to show a mercerizing effect may vary somewhat depending upon whether the fiber is more or less resistant than cotton fibers, we desire it to be understood that by solutions of mercerizing activity we mean solutions of such strengths which will produce the characteristic effects of mercerization in the particular fiber treated. The caustic content of a solution that may be designated as being of mercerizing activity at any given temperature is well understood by those skilled in the fiber art. A caustic solution of this strength improves the luster oi fabric and also improves the dyeing properties and tensile strength. The dye absorbency of the fibers of paper pulp is also increased, the X-ray pattern changed, the ease of the hydration reduced, and the fiber changed from a fiat ribbon form to a rod-like form.

The concentration of solution required to give the necessary mercerizing activity may, for practically all purposes, be defined as a solution having a mercerizing activity equivalent to that of an aqueous sodium hydroxide solution of 8% to concentration at 25 0.

While the process may be operated between the freezing point of the caustic solution and the temperature at which degradation of the fibers begin (from i0 C. to about +104 0'. for sodium hydroxide) it is not desirable to operate at the lower and the higher temperatures because the gelatinizing action at the lower temperatures and the degrading action at the higher temperatures takes place with such rapidity that it is difficult-to effect distribution of the caustic throughout the pulp and to wash out the caustic to stop the reaction in time required to prevent the mentioned gelatinizing and degrading action from decreasing the amount of crinkle in the fibers below the desired value. It is preferred, therefore, to operate at temperatures not far removed from room temperatures. The best commercial operating conditions are between 20 C. and C. with a concentration above 10%. We prefer to use an 18% concentration at room temperature.

The fibers must be in pulp form during the caustic treatment, and by pulp it is to be understood that we mean-cellulosic fibrous material consisting of fibers not arranged into sheets and short enough and sufiiciently low in diameter to he made into a uniform felt from a water suspension. The fibers must be of paper-making length, and long fibers, such as those separated from the raw materials by some form of degumming process, will not give the kind of product with which the present invention is concerned. Fibers that may be designated as paper making length have a minimum mean length of about mm. and a maximum mean length of about d mm. Because of the fact that fibers having a mean length of less than 1 mm, such as the fibers of non-coniferous wood pulp, do not crinkle as intensely as the longer fibers within the paper= making range, we prefer, especially when wag-lg ing with the weaker solutions within the mercerizing range to use fibers having a mean length of 1%; to e In preparing the pulp for the paper base the non-fluid high consistency mixture of pulp and caustic solution may be dispersed into the free fibers by means of the ordinary Hollander heater having the beater roll raised from the bed plate so that the pulp is squeezed without abrasive action. The pulp may be forced under the roll with paddles. After substantially all of the fibers have been separated from the mass and individually wetted with the caustic, a stream of water is run into the heater in order to stop the reaction.

For dispersing the pulp with the caustic, we prefer, however, to use a swifter dispersing mechanism such as the disc refiner described and illus= trated in detail in our mentioned patent.

The following examples in which the parts are by weight, are illustrative of the method for carrying out the invention:

Example I Kraft pulp, 90% bone dry (freeness on special tester seconds) 1000 lbs. Sodium hydroxide (aqueous solution 18.5% at 21 C.) @000 lbs.

The pulp was passed into the disc refiner with a fixed rate of feeding the solution and pulp so as to give a uniform consistency. The strength of the solution in contact with the fibers during the treatment was 18% and the time of treatment with this solution was 3.5 seconds. The freeness after completing the treatment was 21.2 seconds. The treated pulp gave a dark blue color with zinc chloriodine reagent. '1

A sheet of felt was formed from this pulp by the following process: The pulp was dispersed in Hollander heaters with the rolls in a light brushing position for a half hour to disperse the fibers. The pulp was then let down into a preparation chest and after the pulp was diluted with some water and stirred just enough to keep it in suspension it was pumped through a Jordan in which the cone was backed oi? the bars to prevent cutting. Following dilution with more water in a machine chest the pulp was pumped to a flow box above plate screens where it was diluted to a consistency of 0.4%, screened and passed onto a Fourdrinier provided with three slices and having an up-hill pitch of one inch for six feet of length. The shake was thirty per minute at an amplitude of three eighths inch. The first press roll was felt covered. After drying on regular papermachine driers the sheet was passed between two calendar rolls to soften. The final sheet was .060 inches thick and weighed. 0.68 pounds for an area of 36x40 inches.

The felt thus produced was impregnated with a composition consisting of:

, Parts Asphalt (M. P. 170 C.) 100 Naphtha (boiling at 137-l40 C.) 100 Heat bodied linseed oil with drier so Naphtha (boiling at l95-2l0 C.) 40

This impregnating mixture was prepared as follows: 97.5 parts of raw alkali refined linseed oil was heated at 310 C. to a viscosity of T+8.5 by the Gardner-Holdt scale. It was then cooled to 213 C. when 2.5 parts of solid lead-manganese resinate was added with stirring until the resinate was completely dissolved. The ratio of lead to to 1.50 parts of manganese.

'of a mat or sheet provided the'individual fibers manganese in the resinate was 6.42 parts of lead One hundred parts of asphalt (M. P. 170 CT) "was heated to 246 C. and was then cooled to 211 C. when 100 parts of the lower boiling naphtha was added with stirring. As soon as the asphalt was entirely dissolved, parts of the '50%' solution of the heat bodied oil containing drier was added with stirring until a homogeneous mixture was obtained.

The impregnated sheet contained 48% saturant based on the total weight of product. It had a Mullen strength of 305 pounds, an Elmendorf tear of 890 grams and a porosity of 1.4 seconds for 100 cc. displacement on the Gurley Densometer. Itdid not stifien to a sufficient extent at -6 C. to cause cracking when bent quickly in a complete fold. There was no surface exudation or stickiness when exposed to intense direct summer sunlight for extended periods.

Valuable products are also obtained by using drying oil or asphalt alone as the impregnating agent.

Example If The paper base of Example I was impregnated with a mixture consisting of:

Heat bodied linseed oil with drier 140 parts Naphtha (boiling at 137-140 C.) 100 parts The completely oxidized product obtained after squeezing out the excess solution with rolls contained 54% saturant based on the total weight of product. This sheet had a Mullen strength of 290 pounds, an Elrnendorf tear of 920 grams, and a porosity of 1.5 seconds for 100 cc. displacement on'the Gurley Densometer.

Example III The felt of Example Iwasimpregnated with a composition consisting of:

Blown asphalt (M. P. 180 c.) 50 parts Toluol 50 parts The Elmendorf tearing strength was 1450 grams and the solids absorption based on the total weight of the product was 58%. Although the amount of asphalt absorbed in the sheet. is unusually high the product was flexible and did not have an asphalt-like appearance.

Our preferred method of impregnating the felt base consists in passing the sheet from a roll through an impregnating tank, containing 40% to 60% solutions or dispersions of the drying oil, at a speed-regulated to give thorough impregnation. The impregnated sheet is first passed between two knivesto scrape off excess dispersion and thence into a heated drying chamber. The

dried product, on emerging from the chamber.

may be wound into a roll immediately or it may be passed between embossing or calendaring rolls to smooth the surface.

In order to obtain the maximum increase'in freeness and crinkle by our caustic treatment, a,

have sufiicient freedom of movement and are not compacted or felted as in a finished sheet of paper. be formed on a Fourdrinier or cylinder machine from a. water suspension or from a caustic soda dispersion below mercerizing activity and while the mat is still in a loose uncompacted condition,

before heat drying, the caustic soda solution of mercerizing activity may be applied to the surface of the sheet. The force of gravity will carry the mercerizing solution through the sheet and For example, a mat of untreated fibers may all of the fibers will be crinkled in situ, though i not to the samedegree as when they are dispersed in the form of pulp. Or when still further crinkling is required, the fibers treated in pulp form may be dried as loose pulp, or as loose sheets, and then redispersed to form sheets, thus adding still more bulk to the finished sheet.

The caustic alkali may be replaced by solutions of other mercerizing reagents of equivalent activity as for instance solutions of zinc chloride, ferric chloride hexahydrate, cuprammonium, calcium thiocyanate, sulfuric acid, etc.

Among pulps other than krait which may be used in the practice of the present invention are sulfite and soda jpulp, bleached or unbleached. Pulps from sources other than wood may also be used by first subjecting the fibers to treatment which will reduce them to paper making length. Sheets made from pulps that have been bleached after the alkali treatment are especially soft and porous.

In order to obtain various degrees of absorbency and strength in the impregnating base, we may treatmixtures consisting of reactive fibers and fibers such as rope, which are less reactive to the treatment disclosed herein. Likewise, we may make the base material from various mixtures of the treated or crinkled fibers with untreated fibers. The treated fibers should preferably constitute at least 23% of the mixture.

The absolute freeness values referred to herein are the values obtained by using the special freeness tester described in our patent previously referred to and are expressed as the time in seconds for the water level of a dispersion of the pulp, at 25 C. containing 5 grams of bone dry pulp in sufficient water to make 1000 cc. of .pulp suspension, to drop 30 centimeters when the suspension is contained in a vertical glass tube 1 13/16 inches in diameter closed at the bottom with a circular brass wire screen 1 inches in diameter, 0.006 inch thick and having a mesh of 50 70.

Pulp such as treated in accordance with the present invention with a solution at the minimum strength within the mercerizing range, about 8% caustic soda at room temperature, is increased in freeness about 14%. The percent increase in freeness becomes rapidly greater as the caustic concentration rises to about 18%. Above this concentration a very slight additional increase in freeness takes place until'the concentration reaches about 24%, above which it is not desirable to go because the slight additional increase in crinkle doesnot justify the expense of higher caustic concentrations, and the wetting properties of the solution become poorer, requiring at a 35% concentration a too large excess of the strong solution for complete wetting. The felts which give the most outstanding results in the present process are those which have been -made with pulps treated with mercerizing soluabove 10.5% at 25 C. which causes an increase in freeness of from 35% to as high as 60%.

The absolute freeness values of the pulps used in the presentprocess are unusually high and serve to identify the pulp. The absolute freeness may be as high as 15 seconds for a pulp having a freeness increase of 60%. In our process for producing improved impregnated fabric products the best results are obtained with pulps having a freeness between 15 and 28 seconds which corresponds to a freeness increase of 35% to 60% for pulps such as kraft pulp. Pulps of this freeness are obtainable by using caustic soda solutions of 10.5% to 18% concentration and above room temperature in accordance with the procedure outlined above. Pulps having a final ireeness of 20 to 40 seconds corresponding to a rreeness increase of 15% to 35%, obtainable with 8% to 10.5% caustic soda at room temperature, also felt into products capable of absorbing large quantities of asphalt and drying oils.

The impregnated products of the above examples are still relatively porous after impregnation, and coating films are therefore readily anchored to them. This makes possible the production of artificial leather of a highly pleasing appearance which is very limp and flexible and which at the same time is exceptionally strong.

The finishing coat for the impregnated products may be of the type known to be useful in the manufacture of artificial leather products. We usually prefer pigmented rubber and pyroxylin compositions such as the following:

Example I V Parts Pyroxylin 1.00 Castor oil 1.90 Pigment 0.60 Ethyl alcohol (denatured) 5.00 Ethyl acetate 4.50 Butyl acetate 0.50

Example V Parts Rubber (smoked sheet) 57.50 Zinc oxide 30.00 Litharge 8.50 Lamp black 3.00 Sulphur 0.75 Palm oil 0.25 Naphtha 200.00

when a sizing coat is desired for securing good anchorage, the following composition is suitable:

Parts Pyroxylin 4.00 Orange shellac 4.00 Ethyl alcohol (denatured) 25.00 Ethyl acetate 22.50 Butyl acetate 2.50

Our improved artificial leather and impregnated products in general may be identified by separating the base from the impregnating and coating materials with suitable solvents and noting the freeness of the pulp of the base and its response to the test for mercerizecl fibers. If the pulp has been crinkled with caustic soda of mercerizing strength the fibers are not only changed as viewed through the microscope, from the ribbon-like to rod-like form, but they also respond to the test with zinc chloriodine which distinguishes pulps or papers treated with sodium hydroxide solutions of mercerizing activity. While pulps treated with this strength of caustic for periods longer than those which characterize g essee? the present invention also respond to the zinc chloriodine test, they are dliferentiated by their freeness, since they seldom have a ireeness as determined by the method described herein faster than 60 scconds. Pulps that have been manufactored by the soda process in which wood chips are cooked with 8% to 11% of sodium hydroxide at high temperature and pressure show only a slight coloration easily distinguished from that obtained when this pulp is further treated with caustic as described herein.

The prompt occurrence of blue color indicates that the pulp has been treated with about 8% to 35% sodium hydroxide. H the color is very deep, it indicates that the concentration of the solution (at room temperature) was above 13% and graduations of lighter shades indicate concentrations down to the point where mercerizing activity begins. Mixtures of treated and untreated fibers are recognized under the microscope after staining with zinc chloride solution. The 'color persists several days with bleached sulfite pulps treated by the present process. Unbleached kraft pulps treated likewise give a color almost black due to the brown color of the pulp and it fades within a few hours.

In the practice of our invention, any ofthe fatty oils of a drying nature, such as blown, heat bodied or raw China wood oil; fish oil and soya bean oil, may be used, either alone or in con junction with asphalt. Pigments in various amounts may be added to the drying oil before saturation in order to give color or hardness.

The asphalts suitable in producing our improved impregnated products include the blown asphalts, steam refined asphalts, and stearin pitches. The asphalt used may be in the form of an organic or aqueous dispersion or the felt base may be impregnated with the melted asphalt. Although asphaltic materials such as asphalts and pitches have been cited herein specifically, other bituminous materials having satisfactory melting ranges and adhesive properties are applicable to the purposes of the present invention.

The residual porosity which enables our impregnated products to take finishing coats is a valuable feature of our invention. The prior art materials which have sufiicient residual porosity for the anchorage of top coatings are usually deficient in tearing strength. Known high alpha cellulose base material is not only too expensive for the purposes of the present invention, but the impregnated products seldom possess satisfactory residual porosity except when the solids content is low and certain impregnating media are used.

By means of the present invention, we obtain highly advantageous results without resorting to the usual processes of making highly purified pulp with attendant costs and further defibering into finer fibers.

Asphalt is valuable as an impregnating agent for our felt because of its permanence and water resistance. However, asphalt does not produce such resilient impregnated products as the drying=oi1 compositions, so it is desirable to utilize the properties of both drying oils and asphalts. When drying oils are prepared by heat bodying or by combination of heat bodying and blowing, they are miscible with asphalts such as those cited herein and they form saturating compositions that are of more value than compositions from. either the drying oil or asphalt alone. These advantages are mainly that the temperature is lowered at which the impregnated felt becomes stifi enough to crack on bending, the impregnated sheet is drier on the surface at high temperatures of service such as the temperature obtained on an oxidized linseed oil prevents the asphalt from flowing evenwhen heated above the melting point of the asphalt.

Our products obtained by impregnation with drying oil are particularly valuable inasmuch as they possess the combination of properties .most desired for the purposes of the present invention and not completely obtained with other impregnating media. Our drying oil impregnated prodnot is a tough material resistant to abrasion, re-z silient, water proof, and non-plastic and contrasts markedly with the dense appearing drying oil impregnated paper heretofore produced which have a low tear resistance and are susceptible to cracking at moderately low temperature. The blown drying oil impregnated products described herein retain their resilience and freedom from creasing for a great many years. They have unusual aging properties and we have found them to be just as pliable after five years as when first prepared. They also have the advantage of low cost, ease in compounding and low solvent requirements for making compositions low enough in fluidity for impregnation.

Our impregnated products have the saturant uniformly distributed throughout the sheet. This makes possible the production of extremely flexible products because the impregnating medium is not concentrated at the surface of the sheet due to the filtering effect of conventional absorbent papers on colloidal particles. The artificial leather products have the finishing coat firmly'anchored because of the high residual porosity of the impregnated sheet. The product may contain large ratios of water resistant materials, such as asphalts, and yet retain felt-like characteristics. The impregnating material is distributed uniformly throughout the sheet and does not have an un-impregnated core because of the straining or filtering of the impregnating media at the surface of the sheet or because of a denser formation in the center of the sheet Our products are usefulnot only as decorative limp artificial leather for book binding, etc., but are also particularly useful in shoe parts because the breathing properties (residual porosity) are comparable to leather; Our products are also usefi'l for gasket materials, floor coverings, electrical insulation, wall coverings, and roofing materials.

As many apparently widely different embodiments of this invention may be made Without departing from the spirit and scope thereof, it

is to be understood that we do not limit ourselves to the specific embodiments thereof except as defined in the appended claims.

We claim:

1. As an article of manufacture, a sheet of felted artificially crinkled cellulose fibers impregnated with a mixture of drying oil and bituminous material, said fibers having a freeness of 15 to 40 seconds and having the substantially circular form in cross section which characterizes cellulose fibers treated with solutions of mercerizing activity. a

2. As an article of manufacture, a sheet of felted artificially crinkled cellulose fibers impregnated with a mixture of drying oil and bituminous material, said fibers having a freeness of 15 to 28 seconds and having the substantially circular form in cross section which characterizes cellulose fibers treated with solutions of mercerizing activity.

3. The article set forth in claim 1 wherein the bituminous material is asphalt.

4. The article set forth in claim 2 wherein the bituminous material is asphalt.

5. As an article of manufacture, a sheet of artificially crinkled paper making fibers impregnated with drying oil, said fibers having a freeness of 15 to 40 seconds and having the substantially circular form in cross section which characterizes cellulose fibers treated with solutions of mercerizing activity.

6. As an article of manufacture, a sheet of artificially crinkled paper making fibers impregnated with drying .oil, said fibers having a freeness of 15 to 28 seconds and having the substantially circular form in cross section which characterizes cellulose fibers treated with solutions of mercerizing activity.

'7. As an article of manufacture, a sheet of artificially crinkled paper making fibers impregnated with drying oil, said fibers having a freeness of 15 to 40 seconds and exhibiting a blue stain when treated with zinc chloriodine solution.

8. As an article of manufacture, a sheet of artificially crinkled paper making fibers impregnated with drying. oil, said fibers having a freeness of 15' to 28 seconds and exhibiting a blue stain when treated with zinc chlorodine solution.

9. As an article of manufacture, a sheet of artificially crinkled paper making fibers impregnated with bituminous material, said fibers having a freeness of 15 to 40 seconds and having the substantially circular form in cross section which characterizes cellulose fibers treated with solutions of mercerizing activity.

10. As an article of manufacture, a sheet of artificially crinkled paper making fibers impregnated with bituminous material, said fibers having a freeness of 15 to 28 seconds and having the substantially circular form in cross section which characterizes cellulose fibers treated with solutions of mercerizing activity.

11. As an article of manufacture, a sheet of artificially crinkled paper making fibers impregnated with bituminous material, said fibers having a freeness of 15 to 4.0 seconds and exhibiting a blue stain when treated with zinc chloriodine solution.

12. As an article of manufacture, a sheet of artificially crinkled paper making fibers impregnated with bituminous material, said fibers havduced, and impregnating the sheet' with a mix- I ture of drying oil and bituminous material.

15. A process of manufacturing impregnated products which comprises dispersing paper pulp with a solution of mercerizing activity, stopping the reaction before it proceeds substantially beyond a superficial mercerization of the fibers, depositing a sheet of the crinkled fibers thus produced, and impregnating the sheet with drying oil.

16. A process of manufacturing impregnated products which comprises dispersing paper pulp with a-solution of mercerizing activity, stopping the reaction before it proceeds substantially beyond a. superficial mercerizationof the fibers,

depositing a sheet of the crinkled fibers thus' produced, and impregnating the sheet with bituminous material.

17. The process set forth in claim 14 in which said solution has a mercerizing activity equivalent to that of an aqueous sodium hydroxide solution between 10.5 and 35% concentration.

18. The process set forth in'claim 15 in which said solution has a mercerizing activity equivalent to that of an aqueous sodium hydroxide solution between 10.5 and 35% concentration.

19. The process set forth in claim 16' in which said solution has a mercerizing activity equivalent to that of an aqueous sodium hydroxide so lution between 10.5 and 35% concentration.

FRANK H. MCCORMICK. GEORGE L. SCHWARTZ.