US 3821068 A
Description (OCR text may contain errors)
United States Patent [191 Field Inventor:
David L Shaw, Philadelphia, Pa.
Scott Paper Company, Philadelphia, Pa.
Oct. 17, 1972 US. Cl 162/111, 156/183, 161/128,
Int. Cl. D211 9/02, B31f l/14 of Search 162/111, 112, 158, 113,
References Cited UNITED STATES PATENTS 4/1971 Parrish.... 162/111 5/1934 Alden 16 2/112 1/1962 Hechtman et a1 117/155 UA 8/1965 McCarty 162/113 1/1967 Cooper et a1. 162/113 1/1967 Sanford et al. 162/113 U11 3,821,068 [45 June 28, 1974 8/1970 lhrman 162/111 l/197l Herveyetal. ..162/158 5 7 ABSTRACT A soft, absorbent, creped paper web formed by deposition from an aqueous slurry of principally lignocellulosic fibers and dried to at least 80 percent fiber consistency or dryness without being subjected to mechanical compression of the web to substantially reduce formation of papermaking bonds which would form upon compression of the web while wet. The resultant uniform density web is adhered to a dryer through the use of a creping adhesive (which does not add significant strength to the web) and is creped therefrom. The fibers in the web are bonded together almost exclusively by conventional papermaking bonds formed upon drying of the web. The uniform density web product has a dry basis weight of from about 10 to 30 lbs/ 2,880 feet a TEA-to-stiffness ratio greater than 0.5 X 10 and an average calculated density throughout it thickness under no load of less than 0.3 grams per cubic centimeter.
12 Claims, 1 Drawing Figure BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an absorbent, creped, sanitary paper product with improved softness and to a method for making it.
2. Description of the Prior Art In the field of sanitary paper products, which includes bathroom tissues and other tissue products, softness is probably the most desired property. Use of these products requires intimate contact with the consumer, and it is well known that a harsh-feeling product will not often be purchased by the consumer.
While the difference between a soft product and a harsh one is perceived by a consumer as a single property, softness is actually a combination of several physical properties. Softness has been described as the subjective property of paper exhibited by the feeling of softness when a sheet is crumpled in the hand. This feeling depends in large measure on the ease of crumpling, or flexibility of the sheet, together with the absence of sharp edges in the crumpled sheet. Therefore, softness is not only a function of the stiffness of the sheet, but also the thickness of the sheet. For example, if two sheets have the same stiffness, the thicker of the two feels softer. Further adding to a feeling of softness is the ability of the sheet to be compressed between the fingers, a factor determined in large measure by the density of the sheet. Thus, a low density sheet formed with, little compaction will be easily compressed between the fingers.
In the conventional process for manufacturing sanitary paper products, an aqueous slurry of papermaking fibers is deposited upon a foraminous member, such as a Fourdrinier wire, and water is removed to form a coherent web of the fibers. Upon drying, the fibers interbond where they contact each other by the hydrate bonding process associated with papermaking. Because conventional, papermaking fibers are short, less than. V4 inch, there is little or no physical entanglement of the fibers, and almost all of the webs strength comes from the papermaking bonds. To a large extent, the interfiber bonding strength of the papermaking bonds formed, and thus the strength of the web, is dependent upon the closeness of the fibers to each other when the bonds are formed. Accordingly, it is customary in a papermaking operation to compact the paper web before it is dry to increase the strength of the web. Accompanyin g this increase of strength is an increase in stiffness.
Furthermore, when the wet-compacted web dries it remains in its compacted condition, resulting in a high density web. Thus, the softness of the conventionally formed web is reduced not only because its stiffness is increased as a result of increased interfiber bonding by papermaking bonds, but also because the compressibility of the web is decreased as a result of the increased density of the web.
It has long been recognized that a reductionin interfiber bonding by papermaking bonds in a paper web will result in a reduction of stifi'ness. Probably the most commonly employed method for reducing papermaking bonds is creping of the dried web from a drying surface with a doctor blade, an action which disrupts and breaks many of the interfiber bonds already formed in the paper web.
Another method of reducing the papermaking bonds is to prevent their formation either by chemical treatment of the fibers to reduce their interfiber bonding capacity or by the use of little or no pressing of the web while it is wet. However, it has always been thought that practice of this method to the degree which would significantly increase softness would make the web too weak to be suitable for commercial products. Accordingly, where this method has been practiced in the past, bonding materials have been added to the web to restore the strength lost by reduction. of the papermaking bonds. These bonding materials were selected to add strength to the web to a greater degree than they add stiffness. This method is disclosed in US. Pat. application Ser. Nos. 156,327 and 156,282, where it is also suggested that further softening of the web can be accomplished by combining creping with the other steps.
Another method of reducing the number of papermaking bonds formed in a web is disclosed in US. Pat. No. 3,301,746 to Sanford et al. In that method, the paper web is formed under little or no pressing; but while still wet enough to allow an increase in bonding by compaction (stated as being between 30 and percent dry), the web is heavily compacted in a knuckle pattern against a dryer drum. The pattern compaction of the web leaves the majority of the web uncompacted, and presumed weak, while at the same time adding strength to the web as a whole with the numerous papermaking bonds present in the compacted'areas. Further softening of. the web is accomplished by creping the web from the dryer drum. The resulting product is alleged to be softer, although weaker than a comparable product formed by a conventional papermaking process. However, the patent indicates that the loss of strength is not so great as to render the product unsuitable for commercial use.
All of these described methods to reduce papermaking bonds can be successfully used to soften paper webs. However, the methods employing the addition of bonding materials have the disadvantages of increased material costs as well as process complications. And the method of the Sanford patent, as well as the creping method, produces a degree of softness which is less than ideally desired. In view of these shortcomings, it is easily appreciated that methods have been sought for a long time to produce a softer web, especially methods which are less expensive than the prior art methods.
In view of the clear teachings of the prior art, it was very surprising to discover that a very soft paper web could be produced with adequate strength for commercially useful products by elimination of a process step which has long been believed necessary in the prior art.
SUMMARY OF THE INVENTION The product of the invention is a soft, absorbent, creped, fibrous web formed by deposition from an aqueous slurry of principally lignocellulosic fibers. The web is formed and dried to a predetermined dryness level withoutbeing subjected to mechanical compression. Atdryness levels beyond this predetermined dryness level, further interbonding of the fibers by papermaking bonds to a significant extent will not occur upon mechanical compression of the web. The predetermined dryness level is chosen to produce a very soft, low density web.
Further reduction of papermaking bonds, and thus softening of the web is accomplished by creping the web from a dryer surface. The web is adhered to the dryer surface through the use of a creping adhesive, chosen to adhere the web to the dryer surface without adding significant interfiber bonding to the web. The fibers in the web are bonded together almost exclusively by papermaking bonds formed upon drying of the web. The web thus formed has exceptional softness and surprisingly adequate strength when compared to products in the prior art relying upon papermaking bonds for their strength.
The predetermined dryness level is preferably at least 80% fiber consistency, that is, containing no more than 20 percent moisture by weight, but the web may be rewet to as low as 70 percent fiber consistency upon application of the creping adhesive to the web. The web is subjected to a modest pressure when it is applied to the creping surface, increasing web density and formation of papermaking bonds to a slight extent when web has been rewet to 70 percent dryness, and much less so when web has been rewet to no wetter than 80 percent fiber consistency.
BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic side view of a preferred form of apparatus for carrying out the method of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS As illustrated in the drawing, the papermaking machine has a stock distribution means, indicated generally by reference numeral 10, for delivering an aqueous papermaking slurry or fiber furnish to a Fourdrinier wire 16. The stock distribution means includes a tapered manifold or header 11 which is connected to a source (not shown) of an aqueous papermaking slurry or fiber furnish. A number of branch tubes or laterals l2 connect the tapered manifold 11 to blending chamber 13 defined by generally parallel, upper and lower walls 14 and 15. The stock distribution system may be similar to that disclosed in US. Pat. No. 3,298,905.
The Fourdrinier wire 16 is carried over a suction breast roll 17 and over a plurality of table rolls 18, after which it passes around a wire turning roll 20 and is threaded past three guide rolls 2], 22 and 23 and back to the suction breast roll 17. The Fourdrinier wire 16 and its supporting rolls is driven by drive means (not shown) connected to the wire turning roll 20.
One or more vacuum boxes, hydrofoils or other dewatering or formation assisting devices (none of which are shown in the drawing) may be employed in conjunction with the Fourdrinier wire 16. In addition, the configuration of the papennaking machine may vary widely from that described above without having any effect upon the present invention. It is essential, however, that the web thus formed on the Fourdrinier wire 16 or other foraminous surface be maintained virtually free from any mechanical compression or compaction until it is at least 80 percent dry.
After the slurry is deposited on the Fourdrinier wire 16 and dewatered sufficiently to form a web, the web is transferred, substantially free from any compaction or mechanical compression, from the upper surface of the Fourdrinier wire 16 to the surface of aforaminous drying fabric 24. The drying fabric 24 may comprise a woven sheet material, such as made from wire or other filamentary materials, or a perforated or foraminous base. The drying fabric 24 is advanced past the position closely adjacent the portion of the Fourdrinier wire 16 running between the wire turning roll 20 and the first guide roll 22. In doing so, it passes over a rotating suction pickup roll 25 or a stationary suction pickup shoe, and transfer of the web to the drying fabric 24 at this location may be assisted, if desired, by steam or air jet, such as might issue from a header 26 (shown in phantom line in the drawing) disposed opposite the Fourdrinier wire 16 and the suction pickup roll 25.
The drying fabric 24 carrying the web moves from the suction pickup roll 25 into the drying means, indicated generally by reference numeral 27, and then is carried about guide rolls 28 and 30, and about transfer roll 31 which lightly presses the web into contact with the surface of the creping drum 32. One or more vacuum boxes (not shown) may be disposed behind drying fabric 24 following the suction pickup roll 25 to remove additional entrained water from the web without compression. The drying fabric 24 continues on about a'further guide roll 33 and then returns to the transfer point adjacent the suction pickup roll 25.
The drying means 27 may comprise any means for preferably drying, without compressing, a web to a point where it has a moisture content of preferably less than 20 percent by weight, that is, so that it is more than percent dry. Various techniques for drying the web may be employed, such as radiant heat lamps, tunnel dryers, or transpiration dryers wherein air, preferably heated, is passed through the web. The drawing illustrates a typical fonn of transpiration dryerin which air from a hood 34 is passed through the web, through the drying fabric 24, and through the drum 35 which supports both the web and the drying fabric 24. The air is then removed from the interior of the drum 35 by another hood 36. A typical form of such drying apparatus is shown in US. Pat. No- 3,432,936. I
Since the web is applied to the surface of the creping drum 32, which preferably is a Yankee dryer, in a dry condition, it is usually necessary to apply a creping adhesive to the web surface or to the creping drum 32. This is particularly true where the sheet is dried to a level of percent or above, since there is insufficient moisture remaining in the web at this point to adhere it to the creping drum 32 tightly enough to permit it to be creped therefrom. Furthermore, because of the de sirability of avoiding heavy pressure being applied to the web when it is brought into contact with the creping drum 32, there is little natural adhesion of the web to the drum, even at the higher wetness levels.
The creping adhesive may be applied by an elongate sprayer 37, such as that shown in phantom line in the drawing. Alternative methods for applying adhesive to the web in order to adhere to the creping drum 32 may be employed. For example, a glue application roll which picks up adhesive from a reservoir and transmits it to the surface of a web immediately prior to the web contacting the creping drum 32 can be used. Also, a glue application roll which picks up adhesive from a reservoir and applies it directly to the creping drum 32 after which the web is pressed into contact with and adhered to the creping drum 32 can be employed.
In the preferred method of the invention, the web is essentially dried by the creping drum 32, that is, to a fiber consistency of about 95 percent or above. A creping blade 38 disposed on the opposite side of the creping drum32 from the roll 31 is usedto remove the web from the drum while creping it. In the alternative, the web can be creped from the creping drum 32 at a dryness less than 95 percent, in which case the web will be further dried by other, conventional drying means.
In practicing the invention, it would be ideal to avoid all mechanical pressing on the web until it is dry enough to not form significantly more papermaking bonds upon being compressed. However, it is impracticable to avoid small amounts of pressure at some locations in the apparatus, such as where the Fourdrinier wire 16 comes together with the drying fabric 24. But, in accordance with the practice of the invention, the pressure applied at such locations in the apparatus is so small as to be insignificant in the compacting effect it has on the web. As an illustration, the pressure applied to the web at all locations in the apparatus preceding adherence of the web to the creping surface is usually less than 3 psi. In comparison, a conventional press operation, as used in the prior art, applies a pressure to the web of up to several hundred psi, and the knuckle pressure applied to the web in the method disclosed in the Sanford patent ranges from about 1,000 psi up to 11,000 psi, depending upon basis weight of the web. For purposes of interpreting the term without mechanical compression as it is used herein, it shall be considered to be less than 5 psi.
in the preferred method of the invention, the web is dried to at least 80percent dry without mechanical compression of the web more preferably to 90 percent or more, then an adhesive is applied to the web to enable it to be adhered to the dryer drum. The adhesive can be applied to the web directly or to the drum first, by either spraying or printing with a rotogravure roll. The adhesive is selected for its ability to adhere the web to the drum and not for adding strength to the web.ln practice,,the adhesive is a material which because of its nature or the amount used adds no significant strength to the web, less than percent of the total web strength, for example. Examples of suitable adhesives are Accostrength 95 and Accostrength 86, both from American Cyanimid, Creptrol 190 from Hercules Corporation, and animal glues from Peter Cooper Corporation.
The most common adhesives suitable for this purpose are in aqueous solutions, and therefore, the web is rewet somewhat upon application of the adhesive. In the most preferred practice of the invention, the web is more than 90 percent dry upon application of the adhesive, and it is rewet to a degree which reduces the web dryness to no less than 80 percent. The invention may be practiced with beneficial results, however, by applying the adhesive to a web of only about 80 percent dryness, reducing its dryness to as little as 70 percent dry. in all cases, the web is rewet generally evenly all over its surface to avoid excessively wet areas. This is true even though the adhesive is applied in a pattern, because the wet adhesive spreads over' the surface by capillary action. I
Another variation which may be employed in practicing the invention is the addition into the slurry of small amounts of materials which reduce interfiber bonding capacity of the fibers. Examples of such materials are Quaker 2000 and Quaker 2003, both from Quaker Chemical Corporation, and Rycofox 618 from Ryco Corporation. Another variation includes the addition into the slurry of small amounts of fibers other than papermaking fibers, such as cotton, wool, rayon and others.
The most important feature of the invention is the avoidance of significant mechanical pressure being applied to the web until the web is too dry to form significant additional papermaking bonds upon being compressed. It has been known in the prior art that dry paper webs will not be subject to a significant increase in papermaking bonds upon being pressed. However, it was not known in the prior art that acceptable strength can be obtained without wet pressing or some other form of strengthening step, such as those previously described. But, surprisingly, practice of the invention enables production of an exceptionally soft web with adequate strength for commercially useful products. When compared to other paper products relying almost ex clusively upon papermaking bonds for their strength, the product of the invention is remarkably softer than such prior art products of equivalent strength. The product of the invention has been found to have particularly desirable properties when made in the basis weight range from about 10 to about 30 lbs/2,880 ft and is very desirable for a bathroom tissue when made in the basis weight range from about 15 to about 22 lbs/2,880 ft To illustrate the unexpected properties discovered in the product of the invention, examples of the product of the invention and of the prior art and their properties are disclosed herein. Full appreciation of these products and their properties requires a description of the procedures employed to measure them. For purposes of measuring the acceptability of these sheet materials of the present invention from a general standpoint of softness, two different properties have been found which in combination provide a basis for accurately distinguishing such materials from. those of the prior art, as well as providing a reliable indicator of the comparable softness and strength. These properties are: (1) TEA-to-stiffness ratio of the sheet material and (2) the average calculated density throughout the thickness of the sheet material under no load. These properties and the procedures and techniques for determining them are described in detail hereinso as to explain the invention and to permit others to clearly ascertain its scope with regard to such sheet materials.
The TEA-to-stiffness ratio is obtained by first measuring the TEA (tensile energy absorbtion) of a given specimen of sheet material in accordance with the TAPPI'Test, T494 SU-64, in both the machine direction (MD) and the cross-machine direction (CD), in kilogram-meters per square meter, with the exception that a jaw spacing of 2 inches rather than the 8 inches recommended by TAPPI is used because of the particular nature of the product, some of which have lines of perforation which must be avoided. This test method is not a TAPPI standard, but is suggested by TAPPI as the most suitable method to date. The stiffness of the product is then measured by subjecting the specimen to the test set forth in TAPPI standard test, T451 M-60, in
both the machine direction and the cross-machine direction, to determine its effective overhanging length (critical length) denoted as L in centimeters. The stiffness of the product is proportional to the cube of the effective overhanging length and is therefore expressed herein as L Briefly described, the TEA of a product is obtained by clamping a 1.000 i 0.005 in. (2.54 i 0.01 cm) wide specimen in two spaced sets of jaws when they are 2 in. (5.08 cm) apart, with any noticeable slack being pulled out of the strip before clamping. Strain is applied to the specimen by moving the jaws farther apart at a constant rate of 1.00 i 0.01 in./min. (2.54 t 0.02 cm./min.) while recording the elongation with an accuracy of i 2 percent of the actual value and the load, in either pounds or kilograms, with an accuracy of $0.5 percent until breakage of the specimen. The area under the load-elongation curve is then measured by planimeter or integrator with an accuracy of i 2 percent. The TEA is then calculated using the equation:
TEA lA/LW with units of kilogram-meters per square meter where:
A area under load elongation curve in kilogramcentimeters L initial span between clamp lines in centimeters W initial width of specimen in centimeters.
The stiffness of a product is obtained with a Clark Softness Tester by placing the end of a to 50 mm. (%'to 2 inches) wide specimen with parallel edges and of convenient length between the jaws or rollers comprising a clamp mounted on a rotatable spindle. The spindle can be rotated about a horizontal axis parallel to the long axis of the jaws or rollers and perpendicular to the long axis of the paper strip. The overhanging length of the specimen is adjusted by resetting the jaws or turning the rollers until, when the spindle is slowly rotated back and forth through 90, the specimen just falls over at each of the end points of rotation. The overhanging or critical length L is then measured from the line where the edges of the jaws or rollers grip the specimen to the end of the strip. For purposes of defining the product of the present invention, the stiffness is indicated by the cube of L.
In using the above tests for TEA and stiffness to form a ratio which defines a desired property of a fibrous product of the invention, specimens for each test are taken in both the machine direction (M.D.) and the cross-machine direction (C.D.). Preferably, several tests are made with each and the results averaged in order to eliminate errors due to measurement or to formation. The resulting values are then combined in ratio form as follows:
The TEA-to-stiffness ratio TEA (M.D.) X TEA (C.D.)/L (M.D.) X L (C.D.)
The average calculated density throughout the thickness of the sheet material under no load is determined by the following procedure'An approximately 1 inch long specimen of the product is oven-dried to eliminate moisture therein. The dried specimen is inserted in a small container and is slowly immersed at atmospheric pressure in a solution of butyl methacrylate monomer therein containing a small amount of benzoyl peroxide as a catalyst. The container and the immersed specimen are placed in an oven having an interior temperature of 55 C for a period of about 16 hours to cause polymerization of the monomer. A small amount of volumetric shrinkage occurs which is insignificant because it is constant for each sample. Cross-sections are cut from the resulting embedded sample using a microtome, the sections having a thickness of 10 to 12 microns.
Each section is placed on a glass slide, and covered with mineral oil and a glass cover slip. The section of the specimen is now photographed by transmitted light through a microscope adjusted to give a linear magnification of 80, and the magnified picture is printed in a 5 inches by 7 inches format.
The resulting photomicrograph is mounted on a board, and transparent paper is placed over the photomicrograph. The outline of the resulting cross-section shown in the photomicrograph is now traced onto the transparent paper, care being taken to follow the basic curves and undulations of the cross-sectional outline to an extent sufficient to get inside the outline at least percent or more of the cross-sectional area including any stray fibers. Certain stray fibers deviating from the outline of the cross-section should be left outside the area in order to obtain truer density values. A planimeter is then used to measure the area within the inside edge of the line defining the cross-sectional outline in square inches. Several photographs of each specimen are preferably used and several cross-sectional area measurements are taken, the results being averaged to obtain a reliable cross-sectional area.
The actual thickness of the sample is obtained by dividing the area by the length of the cross-section outlined and by the linear magnification of 80. The calculated density under no load in grams per cubic centimeter was obtained by the equation:
Calculated Density g/cc [basis weight (g/m )/Actual thickness (in.)] X
(2.54 cm/in.) X (10,000 cm /m where the basis weight is that of the original sheet materialfrom which the specimen was taken as determined by TAPPl'standard T410 OS-61.
Other tests were made in accordance with the following standard tests: Tensile measurements were made using TAPPI standard T404 TS-66; and Stretch measurements were made using TAPPI standard T457 M-46.
The following examples comparatively illustrate the difference between the sheet materials of the present invention and. the conventional sheet materials of the prior art.
' EXAMPLE 1 As an illustration of the prior art, a web was formed from a fiber furnish consisting of the following conventional papermaking pulps in water:
20 percent soft wood bleached kraft 20 percent soft wood bleached sulfite 40 percent hardwood bleached kraft 20 percent mechanical fiber.
The web was formed on a conventional Fourdriniertype papermaking machine which included wet pressing to remove water and add strength to the web and was transferred onto the surface of the Yankee dryer at about 30 percent dryness. The web was creped from the Yankee dryer when it was about 65 percent dry, that is, when it contained about 35 percent moisture by weight. The web was further dried in an afterdryer in the form of heated drums until it was more than about 92 percent dry. The resulting sheet material was one which was typically used in sanitary paper products, such as wet creped bathroom tissue, and possessed the following general properties:
basis weight 12.3 lbs/2880 ft bulk 0.081 in/24 sheets As another illustration of the prior art, a web was formed from a fiber furnish consisting of water and the following papermaking pulps:
30 percent softwood bleached kraft 25 percent softwood bleached sulfite 35 percent hardwood bleached kraft 10 percent mechanical fiber The web was formed in a conventional Fourdriniertype paper-making machine which included wet pressing to remove water and add strength to the web and was transferred onto the surface of the Yankee dryer at about 30 percent dryness. The web was creped from the Yankee dryer when it was about 94 percent dry, that is, when it contained only about 6 percent moisture by weight. The resulting sheet material was one which was typically used in sanitary paper products such as dry creped bathroom tissue, and possessed the following general properties:
basis weight 9.5 lbs/2880 ft bulk 0.074 in/24 sheets tensile (M.D.) 8.8 oz/in. stretch (M.D.) 14.271 TEA (M.D.) .875 kg M/M tensile (C.D.) 2.5 oz/in stretch (C.D.) 5.4% TEA (C.D.) 0.173 kg M/M L (M.D.) 3.9 cm. L (C.D.) 4.0 cm.
EXAMPLE Ill As yet another illustration of the prior art, a commercial bathroom tissue made using the process described in US. Pat. No. 3,301,746, was tested and possessed the following general properties:
basis weight 1 1.1 lbs/2880 ft hulk 0.135 in/24 sheets tensile (M.D.) 11.20 oz/in.
stretch (M.D.) 13.3%
TEA (M.D.) 0.806 kg M/M tensile (C.D.) 5.7 oz/in.
stretch (C.D.) 5.192
TEA (C.D.) 0.306 kg M/M" L (M.D.) 4.5 cm.
L (C.D.) 5.3 cm.
EXAMPLE IV As an illustration of the present invention, the web was formed from an aqueous slurry of 80 percent kraft softwood pulp and percent kraft hardwood pulp, which was passed through an open gap and formed into tion of mechanical compression to 98 percent fiber consistency by passing heated air through the web. The sheet was then adhered to a Yankee dryer drum with a transfer roll exerting about 150 psi pressure to the web and with the aid of an adhesive applied to the web by gravure printing in a repeating hexagonal pattern, 40 mils in length, 7.5 mils wide, and microns deep, from a copper roll with a 0.002 inch thick chrome outer layer. The adhesive was an aqueous solution of 3 percent Accostrength 95, obtainable from American Cyanamid Corporation, 1 percent National Starch latex 5329, obtainable from National Starch Corporation, and 0.34 percent Rycofax 618, obtainable from the Ryco Corporation. The dryness of the web after printing was 76 percent, and the web had pickedup 0.7 percent adhesive solids. The sheet was then creped and lightly calendered for bulk control. The creped sheet was converted into tissue rolls. The converted paper had the following general properties:
basis weight 16.8 lbs/2880 ft bulk 0.197 in/24 sheets tensile (MD 16.1 oz/in;
stretch (M.D) 16.6%
TEA (M.D.) 0.955 kg M/M tensile (C.D 4.6 oz/in.
stretch (C.D 8.4%
TEA (C.D.) 0.370 kg M/M L (M.D.) 4.0 cm.
L (C.D.) 4.65 cm.
EXAMPLE V As a further illustration of the invention, a web was formed from an aqueous slurry of 80 percent kraft softa h e hashss we.tbrq ishrisqwithsm sas es:
wood fibers and 20 percent kraft hardwood fibers refined to a freeness of 560 mlLTo the aqueous fibrous slurry, 0.2 percent Quaker 2000, obtainable from Quaker Chemical Company, (based on bond dry fiber weight) was added to reduce the interfiber bonding capacity of the fibers. The fiber suspension was formed into a sheet on a Fourdrinier wire and through-dried without application of mechanical compression with hot air to percent fiber consistency. The sheet was then adhered to a Yankee dryer drum by spraying an aqueous solution of 1 percent Accostrength 86 obtainable from American Cyanamid Corporation, in the manner illustrated in the drawing. The amount of chemical pickup to the web from the application of the creping adhesive was less than 1 percent. The amount of pressure exerted on the web by the transfer roll was about psi. The sheet was then creped and converted into bathroom tissue rolls, and had the following general properties:
basis weight 17.4 lbs/2880 i't bulk 188 tn/24 sheets tensile (M.D.) 23.6 oz/in. stretch (M.D.) 19.3% TEA (M.D.) 2.20 kg M/M tensile (C.D.) 5.9 oz/in. stretch (C.D 6.8% TEA (C.D.) .364 kg M/M L (M.D.) I 4.4 cm.
1 l ties for these five examples are set forth below in Table TABLE I 3. Method according to claim 1, wherein application of the creping adhesive causes the web to be rewet to Average Calculated Density TEA-to-Stiffness Table I clearly illustrates the superior softness properties of the product of the invention in comparison with the products of the prior art. For example, the examples of the prior art products all have average calculated densities under no load greater than 0.4 gms/cc. In contrast, the examples of the product of the invention all had average calculated densities under no load of less than 0.3 gms/cc.
In further comparison, the TEA-to-stiffness ratios for the examples of the prior art were all 0.40 X or less, in most cases, far less. In contrast, the same ratios for examples of the invention were higher than 0.5 X 10*, and in one case almost twice as high.
It is believed that lower density adds to the subjective feeling of softness in a paper web, and therefore, the above measurement is important in distinguishing the product of the invention over the prior art products. Also, it is believed that the TEA-to-stiffness ratio is an important measurement in comparing flexibility (as exhibited by the length overhang test) of webs on a basis of equal strength, or to state the same in other words, to compare the strength of webs of equal stiffness. Thus, it can be seen from Table I, that the product of the invention is superior to the prior art in this respect also.
Having described the preferred embodiments of the invention, 1 claim:
. 1. Method for making a soft, absorbent, creped, sanitary paper product, comprising the steps of:
forming a web of principally lignocellulosic fibers by deposition of an aqueous slurry of the fibers onto a foraminous surface;
removing water from the web without mechanical compression until the web is at least 80 percent dry to form a web having uniform density;
bonding the fibers together almost exclusively by papermaking bonds formed upon drying of the web;
applying a creping adhesive to one surface of the web, the adhesive not adding significant strength to 1 the web; adhering the web to a creping surface; drying the web on the creping surface to about 95 percent dry; and removing the dried web from the creping surface with a creping blade. 2. Method according to claim 1, wherein the web is at least 90 percent dry prior to application of the crepanew? t swqhra degree which is no wetter than percent dry when adhered to the creping surface.
4. Method according to claim 3, wherein the web is at least percent dry when adhered to the creping surface.
5. Method according to claim 4, wherein the web is at least percent dry when adhered to the creping surface.
6. Method according to claim 5, wherein the web has a dry basis weight of from about .15 to about 22 lbs/2,880 feet 7. Method according to claim 4, wherein the web has a dry basis weight of from about 10 to about 30 lbs/2,880 feet 8. Method according to claim 1, wherein water is removed from the web by passing air through the web. 9. Method according to claim 1, wherein the fibers are treated with a debonding agent before drying of the web to reduce their inter-fiber bonding capacity.
10. Method for making a soft, absorbent, creped, sanitary paper product, comprising the steps of:
forming a web of principally lignocellulosic fibers by deposition of an aqueous slurry of the fibers onto a foraminous surface;
removing water from the web without mechanical compression while the web is less than 80 percent dry to form a web having uniform density;
bonding the fibers together almost exclusively by pa-' permaking bonds formed upon drying of the web; and
creping the web from a creping surface.
11. A soft, absorbent, creped, sanitary paper web product formed by deposition from an aqueous slurry, the web comprising:
randomly arranged, contacting lignocellulosicfibers bonded together almost exclusively by papermaking bonds;
the web being of uniform density and having a dry basis weight of from about 10 to 30 lbs/2,880 feet a TEA-to-stiffness ratio greater than 0.5 X 10 and an average calculated density throughout its thickness under no load of less than 0.3 grams per cubic centimeter.
12. A web according to claim 11, wherein the web is a bathroom tissue having a basis weight of from about 15 to about 22 lbs/2,880 feet UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION patent No. 3,821,068 Dated June 28, 1974 Inventor) DAVID L. SHAW It is certified that error appears in the above-identified patent fend that said Letters Patent are hereby corrected as shown below:
n In co umn 11, in Table I, in the lTEA-to-Stiffness Ratio X 10 column, the "10 should read 10 also that portion of the Ratio column of Table I reading-".98" should read .55-, and that portion of the same column reading ".58" should read .80.
Signed and Scaled this [SEAL] I sixteenth Day Of December 1975 A ttest:
RUTH C. MASON Arresting Officer C. MARSHALL DANN ummissimzer ofPatents and Trademarks