US3019134A

US3019134A - Cellulosic product

Info

Publication number: US3019134A
Application number: US760152A
Authority: US
Inventors: John F Hechtman; Edwin G Greenman
Original assignee: Kimberly Clark Corp
Current assignee: Kimberly Clark Corp
Priority date: 1958-09-10
Filing date: 1958-09-10
Publication date: 1962-01-30
Anticipated expiration: 1979-01-30

Description

Jan. 30, 1962 J. F. HECHTMAN ETAL 3,019,134

CELLULOSIC PRODUCT Filed Sept. 10, 1958 Q 3 a g 2 a c 'Q a 4 U O I o 0 9 3: B m N 3,6l9,l34 Patented .l'an. 30, 1952 3,019,134 CELLUL SIC PRODUCT John F. Hechtman and Edwin G. Greenman, Munising, Mich, assignors to Kimberly-Clark Corporation, Neenah, Wis, a corporation of Delaware Filed Sept. 10, 1958, Ser. No. 760,152 7 Claims. (Cl. 117-155) The present invention is directed to a cellulosic product and more particularly to a cellulosic fiber web impregnated with a composition containing elastomeric material and to methods for its manufacture.

Paper sheets impregnated with elastomers have come into widespread use for many purposes in recent years. Such impregnated sheets are characterized by moderate tensile strength, flexibility, resistance to moisture and chemical attack, dimensional stability and good electrical properties. Such impregnated paper sheets may readily be coated with a variety of resinous materials such as polyvinyl chloride and pyroxylin to produce bright colorful decorative surfaces. The coating may also be functional in that it may be wear and abrasion resistant. Many types of paper, including both creped and flat-back (uncreped) paper have been employed as the base sheet. Natural rubber latices have been the most used saturants although the use of synthetic latices has been increasing. Such impregnated sheets have been highly successful in the fields of tapes, masking materials, surfacing materials, wrapping materials, artificial leather, etc.

Elastomer impregnated papers, however, have been relatively unsuccessful in certain other fields. One such field is that in which cloth has usually been employed because of its high resistance to edge tear and internal tear, in addition to moderate tensile strength. For example, automotive trim panels which are usually applied by means of nails or sharp-edged fasteners must have in addition to considerable tensile strength, great resistance to tearing. Furthermore, such materials usually must have good flexibility, and folding endurance. They should also be compatible with commonly used coating resins, such as the vinyl chloride type and often good wet strength is required.

Another field in which elastomer impregnated papers have been relatively unsuccessful is that wherein a large degree of stretch of the product is required without excessive loss of strength. Efforts have been made to increase the stretch of the impregnated sheet by employing a creped base paper, but the increase in stretch has usually been accompanied by a corresponding loss in strength.

It is an object of the present invention to provide an elastomer impregnated paper sheet having exceptional resistance to edge tear.

It is a further object of the present invention to provide such a sheet having exceptional tensile strength and stretch.

It is a further object to provide an elastomer impregnated paper sheet having good flexibility, folding endurance and wet strength properties. Other objects will be apparent from the following description of the present invention.

In accordance with the process of the present invention a fibrous web comprising a web of loosely bonded cellulosic fibers is impregnated with a composition containing a copolymer of butadiene and acrylonitrile, said copolymer characterized by having a Mooney viscosity (ML 4) in the range 60-85.

More particularly the present invention is concerned with a saturated paper sheet characterized by good tensile strength, exceptional edge tear and internal tear resistance, very high stretch and good flexibility, comprising a web of loosely bonded cellulose fibers, said web having a tensile sum per pound within the range of about 0.04-0.24, an apparent density of from about 1.0 to about 2.6, a time of climb of from about 4 to about 35 seconds and a Frazier porosity of 150 to 8 for a 25 pound sheet, said web impregnated with a composition containing from about 30 to parts by weight on a dry weight basis per 100 parts by weight of fiber of a copolymer formed from 60-75 weight percent of butadiene and 40-25 weight percent of acrylonitrile, said copolymer having a Mooney viscosity (ML 4) in the range 60-85.

A low bonded paper sheet impregnated with a butadiene-acrylonitrile (Buna-N) copolymer of the above characteristics in accordance with the process of the present invention has in addition to great tensile strength, exceptional characteristics of edge tear resistance which make such impregnated paper sheets suitable for many applications in the cloth and elastomer impregnated cloth fields. For example, low bonded flat-back papers impregnated with an elastomer in accordance with the present invention and having a basis weight of 62.5 pounds per ream (17 x 22-500) have upon being tested for tearing strength by the typical cloth testing method of trapezoidal tear (American Society for Testing Materials'-A.S.T.M. D39-49) exhibited a trapezoidal tear strength of 35 pounds for the sum of the machine and cross directions strengths of the sheet. Dry stretch char acteristics of such impregnated sheets have been of the order of 50 percent measured in the machine direction and 75 percent in the cross direction.

The low bonded sheet used in the impregnated fiber product of the invention, prior to saturation, may be characterized by low tensile strength, low apparent den sity, low rseistance to air passage, high porosity, and a low time of climb. All of these properties are partially interdependent. As a useful and convenient primary property describing the low fiber bonding, tensile strength may be used as an index. A tensile sum per pound, as hereinafter defined, within the range from about 0.04 to about 0.24 indicates the range of a low bonded sheet within the scope of the invention. The apparent density is also a good index of low fiber bonding and in the low bonded sheets is within the range from about 1.0 to about 2.6. In low bonded sheets the time of climb is from about 4 to about 35 seconds, and the Frazier porosity from about to about 8 for a 25 pound sheet.

A low degree of fiber bonding may be obtained by the process of sheet manufacture, and selection of the kind of fiber used. The manufacturing process involves forming a sheet of relatively unrefined fibers from an aqueous suspension, and subjecting the sheet to a minimum of Wet pressing before drying. For example, the fibers may be refined by means of a Jordan engine to the desired degree consistent with the formation and degree of fiber bonding desired, and then formed on a Fourdrinier paper machine. The Wet sheet may be subjected to no pressing, or may be pressed with one, or two, presses before drying. The amount of pressing is determined by the inherent tendency of the particular fibers used to bond to each other, and the degree of fiber bonding desired in the final sheet. After drying, the sheet may or may not be calendered depending on the end use of the finished product. The data in Table I indicates the effect of some of these variables. Any fiber having a bonding surface which is activated by an aqueous medium will have a lesser degree of fiber to fiber bonding when formed into a sheet if the fiber refining is at a minimum and wet pressing of the sheet is at a minimum. Special preference is given to cellulose fibers and desirably long fiber wood pulps.

Investigation of specialty wood pulps has shown that alpha treated pulps (pulps treated with caustic) exhibit lower degrees of fiber to fiber bonding than untreated pulps. Long fiber kraft pulps, both bleached and unbleached, treated With a higher concentration of caustic than normally employed in the alpha treatment process exhibit very low degrees of fiber to fiber bonding and are well suited to the production of low bonded papers. Alpha treated pulps produced by the kraft process generally exhibit a lesser degree of bonding than alpha treated sulphite pulps. Satisfactory low bonded sheets may be obtained with a high caustic concentration treated unbleached kraft spruce pulp or an alpha treated bleached kraft spruce pulp.

For the production and subsequent processing of low fiber to fiber bonded sheets it has been found that certain sheet additives act as processing aids without materially detracting from the features of the low bonded sheet. Wet strength agents such as melamine-formaldehyde, dry strength agents such as gums and starches, the combination of wet strength and dry strength agents to produce both wet and dry strength as well as a very modest degree of sizing may be used as processing aids.

Table I below presents the major physical properties of a variety of saturating papers exhibiting various degrees of low fiber bonding within the range contemplated by the invention:

TABLE I Physical properties and fiber identification of unsaturated low bonded base papers Basis Weight 23. 8 23. 9 33. 6 38. 5 25. G Caliper 21. 6 21. 8 21. 16. 3 9. 97 Apparent Density 1.10 1. 09 1. 60 2. 36 2. 57 Tensile, Sum/Lb 0.078 0.066 0. 08 0.120 0.164 Tensile Ratio 1.91 1. 75 2. l 1. 80 2. 26 Porosity:

Gurley 0.25 16 0.8 2. 1 3. 111 mine i ii) l 13) ""015 p 1 o N umDI/JIefr of Presses Used None None None 2 2 m g Relative Degree of Refining Slight Slight Slight Hard Med.

Unbleached. Given strong caustic Conventional alpha treatment- The units, used in the above table, and elsewhere in the specification and claims, are defined as follows:

Basis weight.Weight in pounds of a ream of paper 17 inches 'by 22 inches per 500 sheets, Weighed at percent relative humidity and 72 F. Essentially the same as TAPPI Method T 410 m-45. All subsequent tests are made on like conditioned paper.

Caliper.Thickness of a single sheet of paper expressed in mils or thousandths of an inch, as by TAPPI Method T 411 m-44.

Apparent density.Apparent density is determined by dividing the basis weight by the caliper to yield the ream weight in pounds per mil of thickness.

Dry tensile strength machine and cross direction.-- The breaking strength as determined on a pendulum type tester having a bottom jaw travel of 12 inches per minute. The test is performed on a strip 15 mm. wide, and the tensile strength is reported in kg./ 15 mm. strip width. TAPPI Method T 404 m-50.

Tensile sum per pound of basis weight.This index is obtained by dividing the sum of the machine and cross direction tensiles in kg./ 15 mm. by the basis weight.

Tensile rati0.A dimensionless number which is obtained by dividing the machine direction tensile by the cross machine tensile and is primarily used as a restriction in comparing tensile sums of paper having large differences in tensile ratios. Most Fourdrinier saturating papers in the weight range of 10 lbs. up have ratios of 1.4 to 3.5. Cylinder machine grades mayhave ratios of as high as 10.

P0rosity.--Gurley porosity is of only limited value in evaluating low bonded paper since the porosity is below the useful range of the instrument. On low bonded papers Gurley porosities have been found of 0.3 second per 100 cc. for eight sheets having a basis weight of 35 lbs. A Frazier porosity tester has been found better suited for determining the porosity of low bonded papers. The units of Frazier porosity are cubic feet of air flow through the material per minute per square foot under a. differential head of 0.5 inch of water.

The following Table II presents a heater analysis of various pulps illustrating suitable and unsuitable fibers for the preparation of low bonded cellulose sheets. Fibers characterized by low apparent density, low tensile sum per pound, low time of climb and low Gurley porosity will produce base sheets of the desired low fiber to fiber bonding.

TABLE II identification of pulps not covered in Table l Beating Porosity Pulp No. Time, Basis Appar. Tensile, Tear Time of Min. Weight Dens. Sum/Lb. Climb Gurley Frazier 5 6 TABLE IIContlnued Beating Porosity Time Pulp N 0. Time, Basis Appar. Tensile, Tear of Min. Weight Dens. Sum/Lb. Climb Gurley Frazier 17. 3 2. 97 .146 4. G 70 23.0 (10) 17.6 3. l4 222 0.9 118 41. 9 17. 8 3. 57 536 11. 8 100 74. 0 17. 1 3. 86 S12 34. 9 79 205. 6 0 15. 9 2. 96 .239 6. 9 48 81.2 (n) 5 l0. 6 3. 55 .470 22. 7 46 4 10 17. l 4. 04 G32 56. 0 40 348 (5) Essentially the same as (2) in Table I. (6) Same as (3) of Table I. (7) Same as (4) of Table I. (8) Sulfite pulped spruce fiber. Conventional alpha treatment. Bleached.

(9) Kraft pnlped Norwegian pine.

Bleached. (10) Kraft pulped spruce fiber.

Bleached.

(11) Conventional sulfite pnlped spruce, balsam, and poplar wood mixture.

chlorite bleached.

The units used in the above Table II, and elsewhere in the specification, have been previously defined in connection with Table I, except:

Time of climb.Time in seconds for distilled water to climb 1.0 inch above the water level when the end of a vertically suspended machine direction strip 1.0 inch wide is immersed in the distilled Water.

Tenn-Internal tearing resistance of paper as described by TAPPI Method T 414 m-49.

As a matter of information, attention should be brought to another method of producing low fiber bonded sheets, although it is expensive and impractical. This method involves the replacement of water from a water wet sheet, initially with a water miscible organic liquid, and finally with a non polar organic liquid before dry- 1ng.

As it will be subsequently pointed out, employment of a low bonded paper as a base for the impregnant rather than conventional papers having greater degree of bondings and corresponding increased tensile strengths is of the utmost importance in obtaining saturated papers by the process of the present invention.

The saturant employed for the impregnation of the low bonded fiber sheet is a composition containing a copolymer formed from butadiene and acrylonitrile and characterized by a Mooney viscosity (ML-4) in the range 60-85. Copolymers of butadiene and acrylonitrile are often referred to as Buna-N type copolyrners. The butadiene-acrylonitrile saturant may be obtained by charging butadiene and acrylonitrile to a reactor in an appropriate ratio of 60-75 percent butadiene and 40-25 percent acryloniu'ile. The components are usually charged to the reactor in an appropriate ratio to obtain approximately 34 percent bound acrylonitrile in the copolymer. A ratio of 65 parts of butadiene to 35 parts of acrylonitrile is normai but may vary somewhat de pending on the degree of conversion of the monomers into the copolymer, which can be varied from approximately 80-95 percent. The unreacted monomers upon completion of the reaction may be recovered from the reactor by steam distillation as is conventional in the production of synthetic elastomers.

A suitable emulsifying system such as a resin soap emulsifying agent dissolved in Water is employed to disperse the butadiene and acrylonitrile. Conventional rosin soap emulsifying agents such as the derivatives of abietic acid are preferably employed. Buna-N copolymers made with rosin emulsifying agents are substantially better for the purpose of the present invention than those made with the conventional fatty acid soaps as evidenced by the trapezoidal tear characteristics of papers impregnated with copolymers made with rosin soaps. Five to 10 parts of soap in 150 parts of water per 100 parts of monomers is suflicient to provide a stable emulsion.

The standard peroxidic catalyst may be used to initiate the polymerization, for example a catalyst such as potassium persulfate may be used in amounts of approximately Hypo- 0.25 parts to 0.75 parts per 100 parts of monomers. A modifier of the mercaptan or other similar types is employed to control the viscosity of the resultant product in COHjUIlCfiOIl with the time and temperature conditions of the polymerization reaction. The mercaptans and similar modifiers such as alkyl-ated hydrocarbons and other sulfur derivatives, act as chain transfer agents and thereby reduces branching and cross linking. Conventional modifier agents such as described by Schneider and others, J. Am. Chem. Soc. 68 1422 (1946) and Wall et al., J. Am. Chem. Soc. 68 1429 (1946) may be employed. A modifier of the mercaptan type might vary from 0.30 part to 0.70 parts per 100 parts of monomers in order to obtain a Mooney viscosity of the resultant copolymer in the 60-85 range. The polymerization reaction is preferably carried out at a temperature of from about 90 F., to 150 F., and copolymers having the desired Mooney viscosities can be obtained at this temperature in reaction times of the order of 12 to 30 hours.

When the desired Mooney viscosity has been obtained, polymerization may be stopped by the addition to the reaction mixture of a small amount, for example 0.1 part, of a short stop such as the hydroquinone or bydroxylamine type. A suitable short stop is 2,5 di-tertamyl hydroquinone. Unreacted monomers are then removed from the reaction vessel by steam distillation and an anti-oxidant of the non-staining class, such as those sold commercially as Naugawhite by the Naugatnck Chemical Division, U.S. Rubber Co., or Santowhite by the Monsanto Chemical Company is added. A typical anti-oxidant may consist essentially of 4-4'-*hiobis (6-tert butyl-m-cresol). In this way it is possible to prepare dispersions which may contain between about 20 and percent solids of the resinous copolymers on a weight basis. An emulsion having about 40 percent solids is, however, preferred.

The Mooney viscosity of the elastomer refers to a viscosity measure of the material obtained by means of a shearing disc viscometer. A method for determining the viscosity of rubber and rubberlike materials is described by Mooney, industrial and Engineering Chemistry, Analytical Edition, volume 6, No. 2, March 1934,

page 147 and has been adopted by the American Society tain desirable features.

of Testing Materials, ASTM volume 6, D927-52T. All Mooney viscosity tests mentioned in the present specification were carried out in accordance with the ASTM specification with a large rotor, a one minute warmup period and a four minute test interval at 212 F. Throughout the present specification and claims these conditions are indicated by the notation MlL-4.

While the copolymer described imm diately above may be employed alone as the saturant of the iow bonded paper and such produces a resultant product having an excellent edge tear resistance and neutral color char acteristics, the copolymer may also be blended with other copolymers to produce impregnated papers having cer- A particularly desirable blend of the above described copolymer is obtained by blending the copolymer with a sulfomethylated phenol formaldehyde resin in the A or resol stage in a quantity of about 100 parts of the above described copolymer with from about 0.5 to 8 parts of the phenolic resol and preferably about parts. Low bonded paper impregnated with this polymer blend in accordance with the process of the present invention, is characterized by having an improved trapezoidal tear strength which indicates a synergistic elTect of the combination of phenolic and butadieneacrylonitn'le polymers. In addition to the improved tear strength obtained by this combination a phenomenal increase in wet strength is also obtained over what would be expected. It has been found that wet tensile strengths of cured impregnated low bonded papers of the order of 125 percent of the dry tensile strength may be obtained by the impregnation of low bonded paper with this combination. Other similar resins such as the melamines, and resorcinol formaldehydes may be substituted for the phenol formaldehyde resin. Other compatible polymers (such as styrene and vinyl resins) may also be blended with the Buna-N copolymer.

Conventional rubber anti-oxidants have been found to enhance the heat and light stability of sheets impregnated with the copolymer composition where extreme resistance to these conditions is required. A typical anti-oxidant is 2,2-methylene-bis (4 methyl-6 tertiary-butyl phenol).

Sensitizing agents to prevent migration of the wet saturant during drying may be employed. Among the conventional sensitizing agents, sodium silico fluoride may be used. Migration may also be controlled by agents which reach a very high viscosity during the drying process.

Clay has been employed as a loading or extending agent. Calcium carbonate, blanc fixe, talc and the like, may also be used. Such agents may be employed in proportion to the weight of the copolymer on a dry solids basis as great as about 6 to 10.

Titanium dioxide may also be employed for increasing opacity and improving whiteness in the finished product. As much as 60 parts of titanium dioxide per 100 parts by weight of the dry copolymer may be used.

Many of the conventional colored pigment have been employed. Metal powders and dyes may also be incorporated in the copolymer composition to impart color thereto.

In order to give greater flexibility to the saturated sheet a fiber plasticizer such as glycerine or a rubber plasticizer such as dioctyl phthalate may be compounded into the saturant. The cellulosic type of plasticizer is preferred. As much as 60 parts of plasticizer per 100 parts by weight of polymer may be incorporated.

The saturation with the copolymer composition of a dry sheet of paper maybe accomplished in the following manner.

Roll stock of unsaturated base paper is fed into a saturating head. The saturating head may be a float type head, prior to the squeeze rolls, in which the paper is floated on the surface of the saturant and becomes impregnated by capillary forces carrying the saturant into the sheet. Another type of saturating head is a shower type at the squeeze roll. The sheet is passed into the squeeze roll nip at a downward angle and the saturant is supplied by means of a shower pipe to the trough formed by the paper and top squeeze roll. Excess saturant is removed by the squeeze roll and the saturant vehicle is evaporated by passing the sheet over a heated can drier. The dried sheet is then wound up in a roll. As alternate drying methods, festoon or tunnel driers may be used. The ratio of dry saturant polymer to fiber for a given base sheet is controlled primarily by the dry solids of the saturant. A secondary but minor control is effected by the nip pressure on the squeeze rolls.

The preferred range of saturant solids in the saturant suspension is about 30 to 60 percent. A 40 percent saturant solids emulsion is commonly employed. A majority of products are made within the range of from about 40 to about 150 parts of dry saturant per parts by weight of fiber although it is possible to produce useful products having a much greater range of saturant content.

Heat treating of the dried sheet following its impregnation is of the utmost importance in developing certain properties of the impregnated sheet particularly such propertim as wet tensile strength and edge tear. A customary method of heat treating saturated sheets comprises winding the dry saturated sheet in a roll at a predetermined temperature. This may be accomplished by passing the sheet as it is wound onto the roll under infra red or other standard types of heaters. The roll is then stored at a like temperature for a predetermined time. The reaction during heat treatment is stopped by rewinding the roll to reduce the temperature. Heat treatment of 0.5 to 20 hours at temperatures above 100 C., may be employed, although about 1 to about 7 hours at about C., are most generally used. It is to be understood, of course, that practical equivalent time, temperature relationships may be employed.

Now that the process of the present invention has been generally described the important variable of the process may be further illustrated by the following tables.

The great importance of employing low bonded papers as the base for impregnants of the present invention is demonstrated by the Table III.

TABLE III Comparison of trapezoidal tear at equal basis weight of saturated low and medium bonded base sheets M.D.Machine direction of base paper. C.D.Cross direction of base paper.

The low bonded sheet was one having an apparent density of 2.0, a tensile sum of 0.087 and a Gurley porosity of 1.5 seconds per 100 cc. 8 sheets made from unbleached alpha spruce kraft. The medium bonded sheet was one having an apparent density of 3.01, and a tensile sum of 0.330, made from a bleached kraft spruce pulp. All sheets were impregnated with a saturant of a copolymer of 34 percent bound acrylonitrile and 66 parts bound butadiene containing 29 percent solids and emulsified with a rosin acid type emulsifier, and having an average particle size of 0.07 microns diameter. The gel content of the saturant was less than 40 percent. The Mooney viscosity of the butadiene-acrylonitrile copolymer is in dicated in the table. The copolymer was blended with a snlfomethylated phenolic resin in the proportion of 5 parts of phenolic solids per 100 parts of copolymer solids. The phenolic resin (Durez 14798) was characterized by ASTM solids of 63-67 percent, specific gravity at 25 C., of 1.260-1.270, viscosity at 25 C., of 4000-5500 centipoises, pH of 6.8-7.2 and infinite water solubility, The paper was saturated with 60 parts of dry saturant per 100 parts of fiber and then cured 8 hours at C. Now it will be noted from the table that the sum of the trapezoidal tear strengths of saturated low bonded paper is at least 94 percent greater than the strength of saturated medium bonded paper. However, when a saturant having a butadieneacrylonitrile copolymer of the correct Mooney viscosity is employed in accordance with the process of this invention, the improvement in strength is 622 percent. Thus the table not only illustrates the importance of employing a low bonded saturating paper but 9 also illustrates the importance of the Mooney viscosity of the butadiene-acrylonitrile copolymer.

The importance of employing a copolymer having the Mooney viscosity within the preferred range of the present invention is further illustrated by the following Table IV. In the series of examples illustrated by this table, identical sheets of low bonded papers such as were described in connection with Table III were impregnated with butadiene-acrylonitrile copolymer compositions containing a phenolic resin and differing only in the Mooney viscosity of the butadiene-acrylonitrile component. The paper impregnated was a low bonded sheet having an apparent density of 2.00. The apparent density is obtained by dividing the basis weight of the sheet by its caliper. In the present instance the basis Weight was 62.5 pounds per ream of 500 sheets of 17" X 22." paper (17 x 22 -500) and the caliper was 0.018 inch. Samples of the low bonded base paper were impregnated with an impregnant composition consisting of 100 part of 65 percent butadiene-35 percent acrylonitrile copolymer, parts of a sulfomethylatedv phenolic resin, 0.4 parts of ammonia and 2.0 parts of a sodium salt of a disproportionated rosin acid which acted as a dispersing agent. The butadiene-acrylonitrile copolymer had been prepared in such a manner that the Mooney viscosity of the various samples varied as shown in the table. The paper sheets were impregnated with the resin to an impregnant content of 60 parts of impregnant solids per 100 parts of fiber by dry weight. The impregnated sheets were then cured for 8 hours at 115 C. Upon completion of the curing operation the physical characteristics of the sheet were determined and are tabulated in Table IV.

TABLE IV The trapezoidal tear characteristics of the foregoing sheets illustrates the great importance of employing a butadiene-acrylonitrile copolymer composition in which the butadiene-acrylonitrile component has an appropriate Mooney viscosity. The importance of this feature is further illustrated by the figure in which the sum in pounds of the trapezoidal tear in the machine direction and the cross direction, is plotted against the Mooney viscosity of the butadiene-acrylonitrile component of the impregnant employed.

The foregoing table also illustrates the very large degree of stretch which is obtained in the product of the present invention. The dry stretch of the order of percent in machine direction and 65-75 percent in the cross direction is contrasted with the stretch of a typical unsaturated paper of 1 /2 percent. It is believed that it is this stretch which strongly contributes to the outstanding tear strength which is characteristic of the saturated papers of the present invention.

The greatly improved wet tensile strength and trapezoidal tear which may be obtained by incorporating a small amount of phenolic resin in the copolymer composition may be illustrated by the following table. Similar sheets of low bonded paper were impregnated with F a copolymer composition such as described above in connection with Table IV and with an identical copolymer composition except with the phenol resin component omitted. The resulting impregnated sheets were then cured for 6 hours at 115 C., and the physical characteristics of the sheet determined as shown by the accompanying table:

Efiect of the Mooney viscosily of Bztna-N component of physical properties of saturated low bonded base paper Mooney ViseosityML 4 52 62 76 8O 36 88 96 116 Dry Tensile, kg./15 mm.:

M.D 6.6 7.7 7.8 7.9 8.3 9.3 9.4 9.2 C.D 4.9 4.3 4.2 4.2 4.5 4.9 5.0 4.9 Dry Stretch, Percent:

MD 49.1 44.0 40.0 44.0 43.0 40.0 39.2 37.0 C.D 54.8 73.0 76.0 75.0 00.0 60.6 56.8 54.2 Wet: (Water) Tensile, Kg./l5 IIIHLZ M.D 5.5 5.3 7.4 7.2 7.0 7.3 8.2 7.9 56 iiifitffifff. I: 5' 07:4 30:4 550 500 5 34:0 Trapezoidal Tear, Lb.:

M.D 9.0 15.4 18.7 20.5 11.7 6.4 5.6 5.7 O.D 10.7 12.7 14.3 15.0 11.4 5.3 4.8 4.9 Sum 10.7 28.1 33. 30.1 23.1 11.7 10.4 10.0

0 TABLE V a 0 l I e f i i m the above i i eiswhere Efiect 0f plsenolzc additive to Elma-N copolymerimpregm we spefsmcdtlod been Prevmusly dang-r except mm on physical properties of saturated low handed the following: sheet Dry tensile strength-Essentially the same as Covered in Table I; however, it is necessary to introduce the con- Impregnaut cept of loading rate. Because of the rheological char- B \I acteristics of resins and elastomers their tensile strength iii Bump}; and stretch properties vary under different rates of stress Phenolic application. The tensile data reported here were ob- 2 a .tained under an average loading rate of 1.8 kilograms "j 9 $535 1 a e 1 1 e, '1; v A parent; Densi y 3.54 3.46 pcrlsccono pe1l15 1lllflei6f stiip Wrota on a Strlfd 100 {2% g mil/15 FD D 42 3; 3 mil m ters in agtl "tween tie l'l 111 ws. -i-y trctcl percent Iv. .7

g WetTensi1e:kg./15Ii1m.,h D. 7.7 2.2 Dry szretcl7.- This data is obtained in conjunction with 1 the tensile strength, and is expressed as the percentage 45 increase in strip length where the increase in strip length .r 1 J, a a 1 l the dlflerence 0591mm ouemal 5:11P f' l The outstanding wet tensile strength and the substantial lfictfid to stress and U16 filial stfessfii P iefigtfi improvement in trapezoidal tear characteristics or the time of rupture. 7 phenolic modified resin are clearly illustrated by the table. v I q 1 Wet and i Tflebe e obtamed'm Subsequent mechanical treatment of the saturated sheet tile 3mm mannsl' me dry Propemes i eifsepnofi is often used to produce a variety of effects. Calenderllhai the strips p l Wet Wlth i116 llqmd 1T1 B ing and supercalendering have been used to increase the tion, and the average loading rate is 0.6 kg./sec. apparent density and soften the saturated sheet as well as to improve the surface for coating. For a number of end uses it is desirable ot emboss the saturated sheet with a variety of patterns and pattern depths. Saturated products made from low bonded, as contrasted to medium. or high bonded sheets, are outstanding in their resistance to degradation of physical properties by any of the above mechanical treatments. An important change in physical characteristics of the product of this invention brought about by mechanical treatment is an increase in flexibility, without degradation of other desirable properties.

Saturated sheets described herein may be used for abrasive papers, glue coated tape stocks, pressure sensitive tape stocks, protective masking sheets, artificial leather stocks, artificial chamois, pennant and banner stock, labels, book cover stock, automobile trim panel base stock, projection screens, printing press top cover sheets, gaskets, cloth replacements, window shades, and the like.

It should be noted that nearly all of the ultimate products require subsequent coating, spreading, or laminating operations on the saturated base sheet. Herein lies a distinctly advantageous feature of the disclosed saturated sheets. The same forces which promote adhesion of the polymers to fibers also promote adhesion of a variety of widely used coating materials. Good adhesion be tween saturated sheets of the invention and plasticized vinyl chloride, pyroxylin, acrylates, abrasive paper varnishes, animal glues, and the like is obtained.

Other modes of applying the principles of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

We, therefore, particularly point out and distinctly claim as our invention:

1. A cellulosic product comprising a sheet of loosely bonded cellulose fibers having prior to saturation an apparent density of about 1.0 to about 2.6, said sheet being saturated with from about 30 to 120 parts by weight on a solids weight basis per 100 parts by weight of dry fibers of a composition containing a copolymer of butadiene and acrylonitrile, said copolymer formed from 60-75 weight percent of butadiene and 40-25 weight percent of acrylonitrile and said copolymer characterized by having a Mooney viscosity (ML 4) of about 60-85, said product characterized by a high trapezoidal tear.

2. A paper product comprising a sheet of loosely bonded cellulose fibers having prior to saturation an apparent density of from about 1.0 to about 2.6, said sheet being saturated with from about 30-120 parts by weight on a solid weight basis per 100 parts by weight of fibers of a composition containing a copolymer of butadiene and acrylonitrile, and 0.5-8 parts by Weight per 100 parts by weight of the copolymer, both on a solids weight basis, of a resin of the group consisting of phenol formaldehyde resin, melamine resins and urea formaldehyde resins, said copolymer formed from 60-75 weight percent of butadiene and 40-25 weight percent of acrylonitrile and said copolymer characterized by having a Mooney viscosity (ML 4) of about 60-85, said product characterized by high trapezoidal tear and a dry stretch of at least 40% in the machine direction of the sheet and at least 65% in the cross direction of the sheet.

3. A paper product comprising a sheet of loosely bonded cellulose fibers having prior to saturation an apparent density from about 1.0 to about 2.6 and a tensile sum per pound of about 0.04 to about 0.24, said sheet being saturated with a composition containing from about 30-120 parts by weight on a dry weight basis per 100 parts by weight of fiber, of a copolymer formed from 60-75 weight percent butadiene and 40-25 weight percent of acrylonitrile, said copolymer characterized by having a Mooney viscosity (ML 4) of 60-85, and 0.5-8 parts by solids weight of copolymer of a sulfomethylated phenol resin, said product characterized by a trapezoidal tear value of at least 26 and a dry stretch of at least 40% in the machine direction of the sheet and at least 65% in the cross direction of the sheet.

4. A paper product comprising a sheet of loosely bonded cellulose fibers having prior to saturation an apparent density from about 1.0 to about 2.6, saturated with a composition containing a butadiene-acrylonitrile copolymer having a. Mooney viscosity (ML 4) of about 60-85 and 0.5-8 parts by solids weight of copolymer of a sulfomethylated phenol resin, said product characterized by a high trapezoidal tear value.

5. A paper product characterized by large edge tear resistance and high stretch comprising a sheet of loosely bonded cellulose fibers having prior to saturation an apparent density of 1.0-2.6, said sheet saturated with from about 50 to parts by weight on a solids weight basis per parts of dry fiber of a composition consisting essentially of about 100 parts of a copolymer of butadiene and acrylonitrile, and about 5 parts of a sulfomethylated phenol resin, said copolymer containing on a solids basis about 65 weight percent butadiene and 35 weight percent acrylonitrile, and characterized by having a Mooney viscosity (ML 4) of about 60-85, said product characterized by a trapezoidal tear value of at least 26 and a dry stretch of at least 40% in the machine direction of the sheet and at least 65 in the cross direction of the sheet.

6. The process of manufacturing an impregnated fiber sheet characterized by large edge tear resistance and high stretch which comprises forming a sheet of loosely bonded cellulose fibers having an apparent density of 1.0-2.6 impregnating said sheet with a composition containing a copolymer of 60-75 weight percent on a solids basis of butadiene and 40-25 weight percent of acrylonitrile, and characterized by having a Mooney viscosity (ML 4) of about 60-85, and subjecting said impregnated sheet to elevated temperatures.

7. The process of claim 6 in which the sheet of fibers is impregnated with an impregnant consisting essentially of 100 parts of a butadiene-acrylonitrile copolymer characterized by a Mooney viscosity (ML 4) of about 60-85 and about 5 parts of a sulfomethylated phenol formaldehyde resin.

References Cited in the file of this patent UNITED STATES PATENTS 30-48), The Ettect of Certain Latex Variables in Beater Addition of Nitrile Rubber Latices.

Claims

1. A CELLULOSIC PRODUCT COMPRISING A SHEET OF LOOSELY BONDED CELLULOSE FIBERS HAVING PRIOR TO SATURATION AN APPARENT DENSITY OF ABOUT 1.0 TO ABOUT 2.6, SAID SHEET BEING SATURATED WITH FROM ABOUT 30 TO 120 PARTS BY WEIGHT ON A SOLIDS WEIGHT BASIS PER 100 PARTS BY WEIGHT OF DRY FIBERS OF A COMPOSITION CONTAINING A COPOLYMER OF BUTADIENE AND ACRYLONITRILE, SAID COPOLYMER FORMED FROM 60-75 WEIGHT PERCENT OF BUTADIENE AND 40-25 WEIGHT PERCENT OF ACRYLONITRILE AND SAID COPOLYMER CHARATERIZED BY HAVING A MOONEY VISCOSITY (ML 4) OF ABOUT 60-85, SAID PRODUCT CHARACTERIZED BY A HIGH TRAPEZOIDAL TEAR.