NO140830B - PROCEDURE FOR PREPARING A CARBOXYMETHYLELLELLOSE-CONTAINING FIBER SHEET PRODUCT - Google Patents

Description

The present invention relates to a method for the production of a carboxymethyl cellulose-containing fiber sheet product with good shredding properties, and the distinctive feature of the method according to the invention is the following steps: a) forming a fiber slurry of said carboxymethyl cellulose fibers with a fiber consistency of 0.5 - 3% by weight, preferably approx. 2% by weight, in an aqueous organic solvent slurry containing 32 - 50% by weight, preferably approx. 40% by weight water, b) forming a fiber sheet from the slurry on a filter medium, c) washing the fiber sheet in 2 - 5, preferably 3-4 steps of displacement washing with alcohol, using

10 - 50 parts by weight, preferably approx. 30 parts by weight of alcohol

per part by weight of carboxymethyl cellulose fibers in the fiber sheet in each washing step to gradually reduce the water content in the fiber sheet to 0.02 - 0.5 parts by weight, preferably 0.02 - 0.3 parts by weight of water per weight part carboxymethyl cellulose fibers, and

d) drying the washed fiber sheet to provide a sheet consisting of fibers which are at least partially water-soluble and partially water-swellable and such that when the sheet is subjected to disintegration in a Waring-Blender at a rate of

16,500 revolutions per minute for 15 seconds, 0.1 - 30% by weight, preferably 0.1 - 20% by weight, of the resulting fiber particles are returned to a sieve with 1.4 mm mesh openings

when the disintegrated particles are classified in an air stream with a pressure difference through the screen of 52 mm Hg.

At least partially water-soluble and water-swellable cellulose derivatives such as sodium carboxymethylcellulose, moist crosslinked epichlorohydrin sodium carboxymethylcellulose, and self-wetting crosslinked sodium carboxymethylcellulose are available in fibrous form. Such at least partially water soluble and water swellable sodium carboxymethyl cellulose fibers are described in U.S. Patent No. 3,347,855. Processes for making moist crosslinked epichlorohydrin cellulose derivative fibers and the products and uses thereof are described in U.S. Patent No. 3,589,364. Cellulose derivatives produced and used in accordance with this patent document are highly absorbent and liquid-retaining for use in special products where these absorbent properties contribute to either improved product efficiency or hitherto unattainable results. Further examples of water-soluble or partially water-soluble fibers usable for web production and products according to the invention are the self-moistening cross-linked carboxymethyl cellulose fibers produced according to the method described in U.S. Patent No. 3,678,031.

Although cellulose derivative fibers have been available in loose powder form and to a certain extent in loose fiber form, it has been observed that these physical forms present problems where precision distribution and application of the cellulose derivatives is desired. For example, continuous precision weighing of a loose powder or a loose fiber mass has proven difficult to achieve due to caking, suspension in silos and weighing difficulties. These handling and weighing problems make it difficult to precisely disperse and also apply precise amounts of cellulose derivative fibers on desired surfaces or in fiber combinations in the manufacture of products for hygienic, surgical and personal use, such as baby diapers, surgical tampons, bandages and menstrual articles.

In order to ease the dispersion and handling problems that accompany the placement of the aforementioned cellulose derivatives in the described applications, various devices have been proposed and used in which different steps and increasing mechanical complexity are used. Although such weighing devices and handling equipment have helped to solve the problem, their use is costly in terms of acquisition and they generally require careful maintenance to ensure continued accuracy.

In contrast, the fiber sheet products provided by the present invention are able to be stored in roll form or flat and due to the accurate surface weights they enable accurate weight supply at web or calibrated roll unwinding speed. Such area feed ensures excellent precision when fed to a process or comminution device whose resulting production is either distributed on or combined with a product.

Cellulose derivative fibers with special physical properties, for example methyl cellulose fibers, have been produced in web form by the method described in U.S. Patent No. 2,364,028. Furthermore, cellulose derivative fibers have been slurried in alcoholic solutions and formed into web structures according to the method of U.S. Patent No. 2,648,635. However, it has been found that these previously known methods are not generally applicable and fail when it comes to providing cellulose derivative products in web form which exhibit both physical handling properties and comminution quality.

It is therefore an object of the present invention to avoid the above-mentioned problems, by providing a method for the production of cellulose derivative fibers that are at least partially mobile and swellable in water in a continuous web form with an even distribution of the fibers and which have the necessary physical properties for handling and comminution.

The invention provides web forms of at least water-soluble and water-swellable carboxymethyl cellulose fibers by slurping these up in preferred aqueous methyl and isopropyl alcohol solutions and combinations thereof containing approx. 32 - 50 wt% water to preserve fiber integrity and then form the fibers into a web from said slurry. Other organic slurry media commonly used in the manufacture of such fibers, including acetone, may be used for preparation of the slurries. In order to obtain a flexible rollable and divisible web having the necessary strength for handling, the water content of the formed fiber web is reduced after web forming so that the web is finally dried to a state in which it contains 0.02 - 0.5, preferably 0.02 - 0.3 parts by weight of water per weight fraction fibres. In general, the fibers are displacement washed in several steps after web forming with alcoholic solutions containing smaller amounts of water in subsequent steps before the final drying. Fiber webs dried directly after web forming and not subjected to alcoholic washing according to the present invention have been found to exhibit a comminution quality of only 50 to 80 as defined below. When carrying out the present web forming process, it has been found advantageous to gradually reduce the water content in the cellulose derivative fiber webs in subsequent stages of displacement washing with alcoholic solutions in that the first alcoholic displacement washing should contain at least 10% by weight of water so that the free water content in the fiber webs is gradually reduced.

After alcohol counter-current washing to regulate the water content

in the web to 0.02 - 0.5, preferably 0.02 - 0.3 parts by weight of water in the fibers in free contact with water-swollen fibers, as a means of regulating the physical properties of the web product, the washed web is dried. In another way of reducing the free water in contact with the fibers, additional isopropyl alcohol can be added in the final step of the countercurrent washing so that the free water is taken up in azeotropic solution with the isopropyl alcohol.

When producing a slurry of partially water-soluble and water-swellable fibers as mentioned above, the fibers are generally obtained in moist fiber cake form. In processes where the slurry reaction for the production of the fibers is carried out in isopropyl alcohol medium to prevent dissolution of the fiber sheet in water present during forming, the moist fiber cake generally contains 30-60% by weight of soft, flexible water-swollen fibers. The percentage is dependent on the efficiency of the centrifuge operation or of other devices used to drive the reaction medium out of the fiber product. The remaining approx. 40 - 70 percent by weight in the moist fiber cake is isopropyl alcohol and water. In the 30-60% by weight solids in the moist fiber cake, 50-70% by weight consist of the partially water-soluble and water-swellable fibers from which excellent fiber sheet products are produced using the method according to the present invention. The remaining solids content of the moist fiber cake is by-product salts from the cellulose derivative fiber formation reactions, usually sodium chloride, since carboxymethyl cellulose derivative fibers are usually prepared in the form of their sodium salts. The method according to the present invention is further advantageous in that it ensures complete removal of these by-product salts from the cellulose derivative fibers during the displacement washing which is carried out after web forming.

For advantageous performance of the web forming process according to the present invention, the preferably moist cake of fibers or fibers in other available forms, including dried fibers, should be separated and dispersed in slurry form. IN

an embodiment of the present invention in which the slurrying takes place from the moist cake state and reaction salts, normally sodium chloride, are present, it is advantageous that the reaction salts are washed out during the slurrying operation and removed from the fibres.

Organic slurrying agents that are usually used in the production of potentially water-soluble and water-swellable cellulose derivative fibres, including acetone, can be used in aqueous solutions to carry out the slurrying.

Both methyl and isopropyl alcohol and combinations thereof are preferably used in aqueous solutions for carrying out the dispersion slurry of the fibers in the present invention and the present method will be further described in connection with their use. Methyl alcohol is the preferred suspension medium for salt removal, as the usual reaction salt, sodium chloride, is more soluble in aqueous solutions of methyl alcohol. As described in more detail below, however, isopropyl alcohol used alone or in combination with methyl alcohol has an advantage in that it produces a soft and crumbly web product where such properties are desirable.

In the dispersion slurry step, it is advantageous for the production of smooth webs that the alcohol solution used has a sufficiently high water concentration to cause the fibers to swell and reduce fiber entanglement and a sufficiently low water concentration to prevent fiber dissolution. To achieve these double results, the aqueous alcohol solution for dispersing is adjusted to contain 32 - 50, preferably approx. 40% water by weight before the fibers are suspended in it.

The amount by weight of the alcoholic solution used as slurry medium is regulated in relation to the amount of fibers that are dispersed and suspended therein, so that a fiber concentration of 0.5 - 3, preferably approx. 2 percent by weight in the aqueous alcoholic slurry medium. The above fiber concentrations in the slurry medium result in a stirred and mixed fiber slurry in which the fibers are swollen and separated for subsequent web forming. As a further aid to fiber dispersion in the slurry medium, it has been found that moderate increases in the slurry temperature lead to better dispersion in the presently used aqueous alcoholic slurry media. Temperatures of approx. 20°C to 50°C, preferably 50°C, has been found to be particularly beneficial in promoting the desired fiber dispersion.

After the preparation of the dispersed fiber slurries in the aqueous alcoholic slurry media, the fibers are formed into webs on a flat belt filter. A 60 x 40 mesh woven filter medium made from polypropylene monofilaments has been found effective in the present process. Other filter media suitable for forming fiber webs and which are in a reasonable relationship to the drainage rate of the present cellulose derivative fiber dispersions may be found suitable for use in the method.

When forming the fiber webs, the previously produced fiber dispersions can be regulated to fiber consistencies of approx. 0.5-2% by weight with aqueous alcoholic solutions, preferably from the recycled alcoholic washing solutions described below, and then introduced into the feed box of a regular paper machine. The fiber slurry then flows from the feed box onto the filter medium which has speeds such as for paper production of from 1.2 - 30, preferably 7.5 - 15 meters per hour. minute. Higher speeds when forming paper webs are possible. As an example, filter medium movement rates of 1.2 - 30, preferably 7.5 - 15 meters per minute and higher advantageous in the production of fiber webs having a dry basis weight of 50 -

112 kg, preferably approx. 95 kg based on the weight of 500 rice sheets of dimension 48 x 60 cm. Fiber webs that have other basis weights can be produced by the method according to the present invention.

Although the present invention has been described in connection with the use of a flat belt filter similar to the common Fourdrinier wire used in papermaking, the fiber sheet products can be advantageously produced on other types of common papermaking equipment, for example laboratory equipment for the production of handmade paper, cylinder machines and inclined wire Fourdrinier machines.In particular, care must be taken that any web forming equipment selected for use in the practice of the present process must be operated at speeds consistent with the drainage characteristics of the dispersed slurries, as will be readily appreciated by one skilled in the art .

After the web forming, the formed filter web moves forward on the filter medium and is displacement washed with aqueous alcoholic solutions with decreasing water content which are applied by spraying devices or other common distribution equipment. When performing the displacement washing step, which is critical for the present method and product, the purpose is to displace and gradually reduce the remaining water in the shaped web. Displacement washing serves to ensure that the fiber web before drying contains 0.02 - 0.5, preferably 0.02 - 0.3 parts by weight of free water in relation to the fibres. Vacuum pressure difference of e.g. about. 127 mm Hg applied through the web and filter media has been found useful in promoting thorough displacement of the wash step.

In the most preferred embodiment of the invention, the displacement washing is carried out according to the countercurrent principle using 10 - 50, preferably 30 parts by weight of methyl alcohol per weight fraction fibres.

In other embodiments of the invention, an ultra-soft and finely divisible web is produced by adding at least 6.9 parts by weight of isopropyl alcohol per part free water, which is water between the fibers, which remains in the fiber web in the last displacement washing to form an azeotropic solution with said water. Such use of isopropyl alcohol can be carried out either in a separate final washing step or in combination with the final methyl alcohol washing step. Although the mechanism of the formation of such an ultra-soft web is not fully understood, it is believed that the use of such an amount of isopropyl alcohol in the final counter-current displacement washing step binds any remaining free water in an azeotropic solution. The fibers in the web are then bound together by the water in the swollen fibers.

It has been found that displacement washing of the formed fiber web to regulate the water content before the final drying should be carried out in 2 to 5, preferably 3 to 4 steps. It has further been found advantageous in the production of present web products with the desired physical properties and pulverization quality that the water content in the formed web is gradually reduced, i.e. it has been found to be harmful to the web quality to wash the newly formed web with approximately non-aqueous methyl alcohol in the first washing step after the web formation, and that aqueous alcoholic solutions containing at least 10% water by weight are preferred in this step.

The preferred countercurrent displacement washing steps are arranged in countercurrent order along the forward moving filter medium so that the aqueous alcoholic washing liquid containing the smallest amount of water is used in the washing step closest to the subsequent drying step. In a preferred embodiment, three stages of aqueous alcoholic displacement washing are arranged, with 20 - 40, preferably 30 parts by weight of alcohol per weight fraction of fibers in the fiber web. In the displacement washing step before the drying step, the aqueous alcoholic washing liquid is approximately anhydrous methyl alcohol. In the second step of displacement washing, the recycled washing liquid from the first washing step is used and this contains approx. 10% by weight of water taken up by displacement washing in the first stage. IN

the third displacement washing step, the step immediately after web forming, uses the recycled aqueous methyl alcohol washing liquid from the second displacement washing step and this contains 20% by weight of water.

Two, four and five stage displacement wash operations are also advantageous and are carried out in a similar manner with the resulting balanced differences in water content of the alcoholic wash liquids in the individual stages of the displacement wash.

In all methods of preferred displacement washing operations, the result is achieved that one avoids initial washing of the formed web immediately after web formation with alcoholic washing liquid containing less than approx. 10% water by weight to ensure that the track does not become satin. It should be noted that close physical placement of the wash nozzles or other distribution devices is preferred to avoid the passage of air through the web between the displacement wash stages, as such air has been found to re-introduce water from the atmosphere into the web.

It is necessary that the physical and comminution properties of the fiber sheet product be controlled by regulating the displacement washing speed or adding water to the displacement washing step closest to the drying step to ensure that the water content of the fiber web before drying is 0.02 - 0.5, preferably 0.02 - 0.3 parts by weight . weight fraction fibres. Higher final water content in the fiber web immediately before drying

tends to harden the web product and reduce the comminution quality. Lower final water content in the fiber web immediately before drying tends to reduce the strength properties of the fiber web product and to increase the comminution quality.

It is essential that special attention is paid to the aforementioned low areas for the water content in the fibres. Without being bound by any theory, it is believed that the displacement washing in the present method greatly affects the free water between the water-swollen fibers and not the water retained in the fibers themselves. As mentioned above, it is advantageous that isopropyl alcohol is added to the displacement washing liquid in the methyl alcohol displacement washing step closest to the drying step in quantities necessary to form an azeotropic solution with the remaining water. Such isopropyl alcohol can also be added to the fiber web in a separate washing step immediately before drying. These additions of isopropyl alcohol result in a softer fiber web product that has increased comminution quality.

After the final water content regulation in the fiber web to achieve the desired precise web properties, the fiber web is dried. The drying can be carried out on ordinary drying equipment in which it is provided

for precautions for flammable solvents. Drum dryers, tunnel dryers and air dryers in which heated air or inert gas passes through the fiber web can all be used to carry out the drying. In a preferred embodiment of the method, the web is dried by passing inert gas, e.g. nitrogen, at approx. 125°C through the fiber path at a speed of approx. 24 to 36 m / /min/m 2 web to be dried. Under such drying conditions, a drying time of approx. 4 minutes found effective. The dried fiber web product can be sliced, cut into lengths, layered or rolled up as desired, on standard equipment for storage and handling.

The preferred dried continuous fiber web product has

as mentioned above, a surface weight of 50 - 112 kg, preferably 95 kg based on the weight of 500 rice sheets of dimension 48 x 60 cm. Such product webs will have a thickness of from 1.3 to 3.0 mm, preferably 1.5 mm to 2.0 mm, depending on the roll pressure applied to the web during forming and drying. As previously mentioned, fiber webs with other basis weights can be produced by the method according to the present invention. Such fiber sheet products will have comparable thicknesses and exhibit the existing fine-cutting quality. In addition to the foregoing physical advantages, the fiber webs exhibit a fineness quality as defined in the following paragraph, of as much as 0.1 to 30, preferably 0.1

to 20. The achievement of such excellent comminution quality in a

continuous fiber web has been found to be very surprising and quality-improving, as such webs, formed and dried directly from fiber slurries, exhibit fineness qualities of 80 and more.

The above test results of f division qualities: and the results given in the following examples were obtained by the "Quick Disintegration" test method which is carried out as follows. Dried fiber web samples are conditioned overnight at 50% relative humidity and 22.2°C. The conditioned dried fiber web samples are then cut into 25.4 x 25.4 mm square pieces. A whole number of square samples weighing 10 - 12 grams are weighed and the weight is noted and constitutes a sample. The weighed sample of said squares is placed in a "Waring Blender" (Model No. CB-5) with blunt blades and spun around at the lowest speed (16,500 rpm) for 15 seconds. The resulting fibers are placed without compacting on top of a standard 14 mesh sieve with mesh openings 1.4 mm, placed between two airtight chambers. Compressed air is introduced into the top chamber to violently agitate, but not further shred, the fibers while the lower chamber is provided with a vacuum system for removing fibers that pass through the sieve. The compressed air and vacuum system working together provide a pressure differential across the screen of 52 mm Hg, which pressure differential is maintained for 2 minutes. The fraction of fibers remaining on top of the 14 mesh sieve and the fraction falling through the sieve are then weighed. The percentage of the total weight of fibers remaining on the 14 mesh sieve is noted. At least two and preferably ten such tests are made and their mathematical average is noted as the test result. Higher numbers indicate a lower shredding quality, while lower numbers mean easier shredding and higher shredding quality. The Mullen and tensile strength test results given in the examples were obtained by test methods commonly used in

. the paper industry.

After having described the method and the product according to the invention, the following examples are intended to illustrate advantageous modes of operation within the method for producing the relevant fiber products with desired physical properties.

Examples I - IV

Handmade sheets were prepared in the laboratory by slurrying liquid absorbent fibers prepared according to the method described in U.S. Patent No. 3,589,364 and which will be referred to hereinafter as CMC fibers, in an alcoholic solution containing 60 percent by weight methyl alcohol and 4 0% water by weight. The fiber slurry was prepared at 50°c and contained 0.5% by weight of fibres. After dispersing the fibers in the slurry by stirring, bee handmade sheets with a basis weight of 99

kg per 500 rice sheets of size approx. 48 x 60 cm shaped on standard laboratory equipment for the production of handmade sheets.

The formed fiber sheets were washed in a three-stage displacement wash with aqueous methyl alcohol solutions, where in each washing step 20 parts by weight of aqueous methyl alcohol solution were used per weight fraction of fibers in the formed fiber sheets.

The first washing step after the sheet forming was carried out with the fixed amount of aqueous methyl alcohol solution containing such an amount of water that the aqueous alcohol solution contained 80 weight percent methyl alcohol and 20 weight percent water.

The second washing step was carried out with the same fixed amount of aqueous methyl alcohol solution per weight fraction of fibers in the fiber sheet. The aqueous methyl alcohol solution in the second washing step contained such an amount of water that the alcoholic solution contained 90 weight percent methyl alcohol and 10 weight percent water.

The third washing step before the sheet drying was carried out with the same amount of aqueous methyl alcohol solution in which the water content was varied for examples I - IV. The water contents of the aqueous alcoholic solutions used in the preceding washing steps were equal to the water contents of aqueous alcoholic washing solutions used in the continuous practice of the present invention. In Example I, the third washing step contained 0% by weight of water, while the third washing step in Example II contained 2.5% by weight of water. Example III had 5% water by weight in the final wash step and Example IV had 10% water by weight. Examples I - IV illustrate the production of the present fiber webs in the form of handmade sheets produced by laboratory methods and the preferred method of operation in which the formed fiber sheets are subjected to stepwise displacement washing with aqueous alcoholic solutions with gradually reduced water content.

After the third washing step, the sheets in Examples I - IV were dried on a laboratory tumble drier and examined for shredding quality. The results of the comminution quality tests together with parts by weight of water per weight fraction of fibers in the fiber sheets before drying is given in table I below.

The fiber web products in Examples I - IV were continuous and had excellent comminution quality well suited for precision weight dispersion when comminuting into fiber combinations for use in hygienic, surgical and personal consumable products. The methods in examples I - IV have been used for the production of similar fiber web products from sodium carboxymethyl cellulose fibres.

Examples V - VII

Additional hand-made sheets were produced in the laboratory according to the procedure in example I, with the exception that in examples V - VII the water content present in the aqueous alcoholic solutions used to slurry the liquid-absorbing fibers prior to sheet forming was varied. In example V in-

the alcoholic slurry solution contained 36% water by weight, while the alcoholic slurry solution in Example VII contained 44% water by weight. The alcoholic slurry solution used in Example VI contained 40% water by weight as in Example I.

Examples V - VII were carried out to show how the varying water content in the alcoholic slurry solutions affected the sheet forming quality. The dried fiber web products in examples V - VII were examined visually for forming quality, i.e. evenness of the fiber distribution in the sheets, and further tested for comminution quality. The results are set out in Table II below.

The continuous fiber web products in Examples V-VII are useful for precision weight distribution when dividing the surface of baby diapers. Similar fiber web products can be prepared according to the method of Example I with the exception that the initial fiber slurry dispersion is carried out at 20°C.

Examples VIII and IX

Coherent fiber webs were produced in a continuous web forming operation from self-wetting cross-linked carboxymethyl cellulose fibers. The fibers were first slurried and dispersed by stirring in an alcoholic solution containing 57% by weight methyl alcohol and 4.3% by weight water. The slurry dispersion contained 3% by weight of fibers and had a temperature of 50°C. Before introduction into a regular feed box for continuous web forming, sufficient aqueous methyl alcohol was added to the slurry so that the fiber consistency in the feed box was reduced to 2 percent by weight.

The fiber slurry was then allowed to flow out through the feed case slot onto a moving continuous filter belt consisting of 60 x 40

mesh woven fabric filter made from polypropylene monofilaments,

for forming a continuous web with a dry basis weight of 94.5 kg per 500 rice sheets of dimension 48 x 60 cm.

The moving web was counter-current displacement washed in example VIII by four-stage displacement washing, in which an alcoholic solution containing 30 parts by weight of methyl alcohol per weight fraction of fibers in the web. The procedure for countercurrent washing was such that the moving web was displacement washed with the fixed amount of methyl alcohol containing 0% water by weight immediately before drying. The other three washing steps were carried out successively and in countercurrent to the continuous advance of the fiber web in the direction of the feed box. Taken in the direction upstream of the advance of the fiber web, each displacement washing step was carried out with the fixed amount of methyl alcohol together with water taken from the fiber web in the previous displacement washing. In the four successive countercurrent displacement washing steps, the water content of the alcoholic washing solutions was 0%, 3-7% and 7-12% and 19-24%, determined by individual samples during the continuous operation. Similar continuous web forming operation can be performed using 2 and 5 stage countercurrent displacement washing, although with 2 stage countercurrent washing special attention must be paid to achieving effective displacement in the limited number of washing stages.

After the countercurrent displacement washing, the fiber web was dried

by passing through it nitrogen at 150°c at a rate of 30 m 3 /min/m 2 of continuously advanced fiber web for four minutes. Similar drying operations can be carried out at different temperatures and rates of nitrogen passage through the web, as the time for drying will naturally vary.

The fiber web in Example IX was prepared in the same manner as it

in example VIII with the exception that immediately before drying and after the displacement washing with methyl alcohol containing 0% by weight of water, the fiber web was applied with isopropyl alcohol in an amount equal to 6.9 parts by weight of isopropyl alcohol per weight fraction remaining water in the fiber web. It should be noted that a similar

path product will result if the isopropyl alcohol is used together with the pure methyl alcohol used in the previous step of the countercurrent displacement wash.

The dried continuous fiber webs in Examples VIII and IX

was tested for comminution quality with the result that Example VIII had a comminution quality of 5.5 while the comminution quality in Example IX was 0.5. These results illustrate the improvement achieved in comminution quality by introducing isopropyl alcohol into the fiber web immediately before drying according to the method according to the invention.

In the continuous web forming process of Example VIII, inefficient displacement in the washing steps can produce a co-suspended fiber web product with a comminution quality of 30. Comminution qualities of 0.1 can be achieved by using 15 parts by weight of isopropyl alcohol instead of 6.9 parts in the process of Example IX . The continuous fiber web products are well suited for rolling and subsequent finely divided dispersion in hygienic and surgical products.

Examples X - XVII

To further illustrate the trajectory property effects achieved

by variation of parts by weight of water per weight fraction of fibers in the fiber webs according to the present invention immediately before drying, examples X - XVII were carried out according to the procedures in examples I - IV with the exception that the water content in the third stage of alcoholic washing immediately before web drying was varied as indicated in table III below. The weight parts water per weight fraction of fibers in the fiber webs before the final drying is indicated in the table in relation to the fiber web properties as illustrated by Mullen tests, for web elasticity and breaking properties, and tensile strength tests.

The fiber web products in examples X - XVII had comminution quali-

teters of 5 to 30 and their physical properties were suitable for handling and comminution according to the present invention.

PATENT CLAIMS

Claims (4)

PATENT REQUIREMENTS 1. Process for the production of a carboxymethylcellulose-containing fiber sheet product with good fine-cutting properties, characterized by the following steps: a) forming a fiber slurry of said carboxymethyl cellulose fibers with a fiber consistency of 0.5-3% by weight, preferably approx. 2 percent by weight, in an aqueous organic solvent slurry containing 32 - 50 percent by weight, preferred approx. 40 weight percent water, b) forming a fiber sheet from the slurry on a filter medium, c) washing the fiber sheet in 2 - 5, preferably 3-4 steps of displacement washing with alcohol, using 10 - 50 parts by weight, preferably approx. 30 parts by weight of alcohol per part by weight of carboxymethyl cellulose fibers in the fiber sheet in each washing step to gradually reduce the water content in the fiber sheet to 0.02 - 0.5 parts by weight, preferably 0.02 - 0.3 parts by weight of water per weight part carboxymethyl cellulose fibers, and d) drying the washed fiber sheet to give a sheet consisting of fibers which are at least partially water-soluble and partially swellable in water and such that when the sheet is subjected to disintegration in a Waring-Blender with a speed of 16,500 revolutions per minute for 15 seconds, 0.1 - 30% by weight, preferably 0.1 - 20% by weight, of the fiber particles thus formed are returned to a sieve with 1.4 mm mesh openings when the disintegrated particles are classified in an air stream with a pressure difference through the 52 mm sieve Hg. 2. Method as stated in claim 1, characterized in that the formation of the fiber slurry in step a) takes place at a temperature of 20 - 50°C, and the formation of the fiber sheet in step b) takes place on a filter medium which moves at a speed of 1 - 30 m/min., preferably 75 - 15 m/min. 3. Method as stated in claim 1 or 2, characterized in that at least 6.9 parts by weight, preferably less than 15 parts by weight isopropyl alcohol per weight part of water present in the washed fiber sheet is applied to the washed fiber sheet in the final step by displacement washing with methyl alcohol in step c) before drying. 4. Method as stated in claims 1-3, characterized in that the drying step d) is carried out by passing inert gas at a temperature of approximately 121°C through the washed fiber sheet at a volume rate of 80 - 120 cm 3 /min/cm2 of the sheet which should be dried for about 4 minutes.