GB1568194A - Process for making creped sheets - Google Patents

Description

(54) PROCESS FOR MAKING CREPED SHEETS (71) We, CROWN ZELLERBACH CORPORATION, a Corporation organized and existing under the laws of the State of Nevada, United States of America, of One Bush Street, San Francisco, California 94119, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention generally relates to a process for making soft, high-bulk, lowdensity, finely creped paper sheets from an aqueous fiber furnish containing cellulosic fibers, which includes (a) nonthermal dewatering of a wet web including a bonding inhibitor; (b) controlled spraying of an adhesive, in the form of uniform, discrete droplets, onto one surface of the wet web; (c) adhering the sprayed web to a thermaldrying surface; (d) drying the sprayed web on the thermal-drying surface; and (e) creping the dried sheet from the thermaldrying surface.

The prior art describes various papermaking processes which employ nonthermal dewatering, adhesive application, and thermal-drying operations.

However, the sheets produced by these known processes exhibit relatively high density and/or a high degree of stiffness, and are generally neither soft nor highly bulky in nature. Examples of these processes include U.S. Patent 962,501 to Funke et al. and U.S.

Patent 2,635,972 to Azorlosa. More specifically, these processes employ various adhesive substances, such as starch, glycerine, and carboxymethyl cellulose salts, which are applied to conventionally formed webs to promote bonding of the web to a drying cylinder. Other prior art methods, such as U.S. Patent 2,940,890 to Braun and U.S. Patent 3,014,832 to Donnelly, set forth improved methods of creping by the addition of a release agent, such as mineral oil or fatty acid compounds, so that the tissue web may be more easily removed from a thermal-drying surface on creping. Finally, U.S. Patent 3,640,841 to Winslow provides a process directed to adding a water-dispersible pumpable polyamide polyamine compound which is incorporated into the web prior to drying same on a Yankee dryer so that uniform adhesion and release from the dryer surface is obtained during creping.

In another prior art method, additional subsequent drying of a wet web following the initial thermal-drying step on a Yankee dryer is employed. This method is known as "wet-creping". To illustrate this, U.S.

Patent 3,018,214 to Waldie, Jr., et al., sets forth a process which includes the introduction of a small amount of watersoluble soap added to the pulp furnish, or, after formation of the web, to provide a uniform wet-crepe which, after leaving the Yankee dryer, is subsequently thermally dried.

Conventional sheet-making can be modified for purposes of improving softness by the introduction of chemical modifiers, such as polymeric latices, and the like, into the aqueous fiber furnish. However, the use of these materials as "wet-end" additives is generally detrimental to the runnability of the paper-making equipment since these materials cause problems including precipitation of solids and the attendant build-up on the equipment, coating of the paper web with the precipitated solids, and prevention of the foraminous conveying means from properly draining. These processes include, for example, U.S. Patent 3,844,880 to Meisel, Jr., in which cellulose paper sheets are prepared by modifying the furnish through the sequential introduction of a cationic surface-active agent, a resinous latex, and a deposition aid for the resin, and U.S. Patent 3,812,000 to Salvucci in which an elastomeric bonding material, such as polyvinyl alcohol (PVA) or carboxymethyl cellulose (CMC), is added to the fiber furnish along with a cationic debonding agent. The debonding material is added to reduce interfiber bonding between adjacent fibers.

A method has been recently developed for producing soft, bulky sheets known as "through-drying". Typically, the throughdrying operation includes thermal dewatering of an uncompacted web until the consistency reaches a minimum of about 7es00, followed by creping of the dry, uncompacted web from a thermal-drying surface. In through-drying, the thermaldrying surface, using a Yankee drying cylinder, acts only minimally as a means for thermally drying the web (removes only about 15% water). Through-drying equipment requires a substantial capital investment and, once the equipment is in place, requires the use of large quantities of heat energy in order to thermally dry the uncompacted web to the minimum 7080% consistency level. An adhesive is used to bond the web to the creping surface during the through-drying operation. Throughdrying processes include U.S. Patent 3,301,746 to Sanford in which a small amount of adhesive solution, such as animal glue, is sprayed on the surface of the Yankee dryer (See Figure 1, sprayer 29); U.S. Patent 3,812,000 to Salvucci in which an adhesive is sprayed on the web or creping drum; U.S. Patent 3,821,068 to Shaw, in which an adhesive is applied to the web or to the Yankee cylinder, by either spraying or printing with a rotogravure roll so that the adhesive does not add significant strength to the web; and U.S. Patent 3,926,716 to Bates, in which a partially hydrolyzed PVA composition is sprayed on the surface of a Yankee drying cylinder, the details of the spraying operation being described in Figure 3 of that patent.

In British Patent Specification 1,294,794, a water-soluble resinous bonding material, such as PVA or CMC, is applied to a dry web, using a patterned printing roll. However, a print bonding operation can only be conducted at relatively low machine speeds, thereby minimizing productivity of a given high speed machine.

British Patent Specification No. 1,426,694 also describes creping from a dry web. This specification discloses a method of making crepe paper which comprises the steps of forming a wet web from a fibrous furnish (which may include small amounts of materials which reduce inter fiber bonding capacity), removing water from the web until it is at least 80% dry, so that the fibers are bonded substantially by paper-making bonds, and then creping the web. Since the web is applied to the creping drum in substantially dry condition, it may be necessary to apply a creping adhesive and the more dry the web is, the more necessary the adhesive is because there is little natural adhesion of the web to the creping drum.

The adhesive is applied in such a way as to re-wet the web evenly all over its surface.

In the process of the present invention, a web is dewatered to a consistency of up to 60% by weight, i.e. a maximum dry matter content of 60% and a minimum water content of 40%. To this partly wet web there is applied a limited amount of adhesive, insufficient to cover the surface uniformly.

According to the present invention there is provided a process for producing a soft, high-bulk, low-density, finely creped sheet, which comprises: (a) forming an aqueous fiber furnish including cellulosic papermaking fibers, and a bonding inhibitor which minimizes the formation of papermaking bonds between respective cellulosic fibers during sheet formation; (b) forming a wet web from said aqueous fiber furnish; (c) dewatering said wet web, employing non-thermal dewatering means, to a consistency of up to 60% by weight, based on the total weight of fibers in said wet web; (d) applying an adhesive in the form of discrete droplets onto one surface of said wet web before, during, or after said nonthermal dewatering step, the adhesive spray being controlled so that said droplets have an average droplet size of from 10 microns to 75 microns, and the coverage of said web surface by said droplets is from 10% up to 60%; the amount of adhesive being sufficient to cause the web to adhere to the thermal-drying surface in the next step but insufficient to prevent creping; (e) adhering the sprayed surface of the web to a thermal-drying surface for thermally drying said web; (f) drying said sprayed web on said thermal-drying surface; and (g) creping said dried web from the thermal-drying surface.

The process of the present invention produces a sheet which is extremely soft, highly bulky, has a low density, is finely creped, all at up to relatively high basis weights, while maintaining strength properties in both the machine- and crossmachine directions without having to maintain a low machine speed. All of the above is accomplished without requiring the use of costly and unnecessary thermal dewatering (through-drying) or post-drying (wet-crepe process) operations, respectively.

Sheets produced by the subject process are formed by first incorporating a bonding inhibitor into an aqueous pulp furnish of predominantly cellulose papermaking fibers to minimize the formation of hydrogen bonds between adjacent fibers during sheet formation. Prior to drying a web formed from the above aqueous furnish on a thermal-drying surface, the web is dewatered by nonthermal dewatering means to a consistency up to 60%, and an adhesive in the form of discrete, fine droplets is sprayed in a controlled manner onto one of the surfaces of the wet web prior to, during, or subsequent to dewatering the web by nonthermal dewatering means so that optimum coverage of the sprayed surface is provided with a minimum build-up of adhesive on the thermal-drying surface.

Thus, by applying the adhesive to the web in the manner prescribed above, the sprayed surface of the web uniformly adheres to the thermal-drying surface, resulting in the formation of a sheet on creping having a fine creped pattern and having excellent bulk, softness, and strength properties. This is in contrast to the high-density, minimumsoftness sheets typically produced by prior art processes using conventional papermaking technology without requiring a thermal-dewatering step.

It should be particularly noted that postdrying, or thermal drying of the web to a high consistency (at least 70 x) in an uncompacted state, as practiced in the through-drying processes of the prior art, are not required herein. In fact, quite unexpectedly, the process of the present invention contemplated dewatering the wet web by nonthermal dewatering means to a consistency of up to 60% by weight, based on the total weight of pulp in the web, prior to drying the web on thermal-drying surface, thereby eliminating the need for expensive through-drying equipment and attendant high energy consumption problems associated therewith.

("Consistency" of the percentage by weight of dry matter in the web.) More particularly, the adhesive composition sprayed directly onto one surface of the web is controlled so as to be in the form of small, discrete droplets having an average droplet size of from 10 microns to 75 microns, and covering from 10a/", preferably from 15%, to 60% of the web surface. By employing this controlled spraying technique, stiffness and density are minimized and softness and bulk are maximized. And, in spite of the fact that nonthermal dewatering means is employed, the sheet is preferably maintained at a density of not more than 0.2 gram per cc, and at a bulk softness level of not more than 1.25 HOM/(caliper)2xlOS.

In a preferred embodiment of this invention, a creped sheet of the type previously described, having a basis weight in an uncreped state of at least 12 pounds per 3,000 square feet, up to 25 pounds per 3,000 square feet, can be produced without employing a thermal dewatering step.

Wet-end chemical modifiers such as emulsifiers or polymeric latices are not employed in the present process scheme, thereby eliminating any of the previously described detrimental effects posed by these materials during web formation and mechanical dewatering. Thus, since the addition to the aqueous furnish of materials such as disclosed by Meisel et al., etc., are not used in conducting the subject process, the build-up, coating and drainage problems associated with their use are not manifested herein.

In accordance with the present invention, a process is provided for producing soft, bulky, low-density, creped sheets in which an aqueous furnish is first formed including cellulosic papermaking fibers. The cellulosic fibers employed have typically undergone some degree of lignin modification, such as at least partial chemical treatment, to produce materials such as chemimechanical pulp, semichemical pulp, chemical pulp, or the like. Suitable materials from which the above cellulose fibers can be derived include the usual species of coniferous pulp wood such as spruce, hemlock, fir and pine as well as deciduous pulp wood such as oak, poplar, birch, cottonwood, alder.

Preferably, the cellulosic component of the above aqueous furnish will predominantly include softwood fibers because of their greater fiber length as compared with their hardwood counterparts.

The consistency of the aqueous furnish is maintained at a level sufficient to permit the formation of a substantially dry web upon completion of the hereinafter described nonthermal-dewatering and thermal-drying steps, respectively, without requiring further drying of the sheet subsequent to creping. As a practical matter, however, the consistency of the aqueous furnish used in forming the subject wet web is desirably maintained at a level from 0.1% by weight, based on the total weight of the aqueous furnish, up to 1.0 , by weight.

In order to enhance the softness and bulk properties of the final creped sheet product, a bonding inhibitor is added to the aqueous furnish for minimizing the formation of papermaking bonds between respective cellulosic fibers during sheet formation. The cellulosic fibers may, for example, be separated by the incorporation of pulps having a low affinity for forming papermaking bonds, such as thermomechanical pulp, solvent-dried pulp, and the like, or convoluted, fiberized, cellulosic fibers described in our co-pending application No. 53725/76 (Serial No.

1550880). However, the bonding inhibitor generally utilized is a chemical debonding agent. The chemical debonding agent is normally added directly to the aqueous furnish where it combines with the cellulosic papermaking fibers, thereby reducing the degree of dissipation which that material undergoes during sheet formation. Debonding agents which are substantially cationic in nature are preferably employed. Examples of suitable debonding agents include Quaker 2001 (Quaker Chemical), Ceranine HCS (Sandoz), Leomin KP (Hoechst AG), and Amasoft 16-7 (American Color and Chemical). A "bonding inhibitor" is a material which when added to the aqueous furnish reduces hydrogen bonding between fibers. Typically, a long-chain fatty acid chemical debonding agent is employed for this purpose. The preferred debonding agents are long-chain cationic surfactants, preferably with at least 12 carbon atoms and at least 1 alkyl group. Typical examples of these compounds are fatty dialkyl quaternary amine salts, mono fatty alkyl tertiary amine salts, primary amine salts, and unsaturated alkyl amine salts.

When a chemical debonder is used, an amount is added to the aqueous furnish which is sufficient to minimize the formation of papermaking bonds, but less than an amount which would cause significant runnability and sheet strength problems. Ordinarily, the amount of chemical debonding agent used, on a 100% active basis, is from 0.25 pound per ton pulp to 10 pounds per ton, of pulp (based on the weight of cellulose in the pulp, i.e. per ADT). However, the addition of from one pound of chemical debonding agent per ton of cellulose pulp to 5 pounds per ton, is preferred.

A wet web is then formed from the aqueous furnish on a wet-web forming means, typically a conventional papermaking system including a foraminous conveying means such as a Fourdrinier, or a Stevens former. First, substantial dewatering of the wet web is provided prior to the thermal-drying operation employing nonthermal dewatering means. The nonthermal dewatering is usually accomplished using various means for imparting mechanical compression to the web, such as a series of coacting press rolls.

This is in complete contradistinction to the previously described through-drying operation in which substantially no mechanical compression is applied to an uncompacted web until the sheet is at least 7080% dry. The mechanical compression step normally increases the compaction of the sheet at this point in the process to a level which is detrimental to the throughdrying operation. For purposes of illustration of the process of this invention, a wet web formed from an aqueous fiber furnish can be initially formed on a foraminous conveying means. The wet web can then be dewatered by subjecting the web to the compressive forces exerted by nonthermal dewatering means such as, for example, a pair of press rolls followed by a roll coacting with a thermal-drying cylinder.

One of the first pair of rolls can be a vacuum or dewatering roll, or the rolls may also be provided without vacuum. The other roll may be a resilient press roll fabricated of hard rubber, metal, or other like material.

The wet web is carried by the foraminous conveying means through the nonthermal dewatering means where it is preferably dewatered to a consistency of at least 10%, and preferably at least 15%, up to a consistency of most 60%, and preferably up to a consistency of 40%.

Prior to, during or subsequent to dewatering the wet web with the nonthermal dewatering means but, in any case, prior to drying on the thermal-drying surface (e.g. a Yankee dryer), and adhesive composition in the form of small, discrete droplets is applied, in a controlled manner, onto one side of the wet web; this serves subsequently, to uniformly bond the web to the thermal-drying surface. Optimum coverage of the web surface by the droplets is provided. Typically, the application is conducted using a spray nozzle system, such as a plurality of spray nozzles capable of spraying a given amount of adhesive onto the web in the form of discrete, small droplets. Preferably, the small, discrete droplets are sprayed on the web employing sonic spray nozzle means. For example, sonic spray nozzles such as manufactured by the Sonic Development Corporation of Upper Saddle River, New Jersey, can be employed in the process of the present invention. By employing the controlled spray means of this invention, the web surface having adhesive droplets thereon will uniformly adhere to the thermal-drying surface. With optimum coverage there is applied an amount of adhesive sufficient to adhere the sheet to the yankee so that on creping minimum adhesive build-up means that the thermal-drying surface (yankee) does not become coated with an amount of adhesive over a period of time which would prevent effective creping.

The average size of the adhesive droplets is maintained small in order to circumvent the sheet stiffness problems associated with the uncontrolled spraying of the sheet with a larger particle-size spray.

The average droplet size of the adhesive spray employed herein is maintained from 10 microns, and preferably from 30 microns to 75 microns, to 50 microns.

The average droplet size of the adhesive spray, for purposes of this invention, was determined experimentally by placing a glass slide in the path of the spray droplets containing a fluorescent chemical agent and measuring the size of the droplets, in the wet state, using a microscope equipped with a calibrated micrometer eye piece. The droplet size was then determined visually and the average size calculated. For purposes of making this calculation, it is assumed that the droplet size on the slide is twice the size of the actual droplet being sprayed.

In addition to maintaining the spray directed onto one surface of the sheet in the form of small, discrete droplets, an optimum level of coverage of the sheet surface by the spray droplets is provided in order to effect uniform adhesion of the sheet to the thermal-drying surface while maintaining the strength properties of the sheet but less than a level which would cause substantial sheet stiffness, excess adhesion of the sheet to the thermal-drying surface, and excessive build-up of the adhesive on the thermaldrying surface. "Coverage" is defined as the percentage of the area of the total sheet surface which is covered by the adhesive droplets which have been sprayed thereon. The coverage of a given sheet surface was determined for purposes of this invention by spraying the sheet with an adhesive, including a color dye or with a fluorescent dye, and measuring the droplet coverage by the integrated reading of color intensity on a Zizz Spectrophotometer, Model DMC 25.

By comparing respective sprayed and unsprayed samples, using the same parent paper, in a range of 253 nm to 400 nm for fluorescent dye and 380 nm to 720 nm for colored dye, the percent coverage of the sheet by the adhesive can be determined.

The percent coverage of the sheet by the adhesive spray droplets will be from 10, and more preferably from 20%, up to 60%, and more preferably up to 40%.

In carrying out the present invention, the adhesive employed is preferably anionic or nonionic in nature although other types of compounds may be employed. Example of typical adhesive compositions which can be used include carboxymethyl cellulose, polyvinyl alcohol, anionic starch, various soluble natural polymers such as gums, and sythetic resins such as polyamide resins.

In order to minimize build-up of the adhesive on the thermal-drying surface, a small amount of a lubricating agent can be added to the adhesive composition prior to spraying same on the web surface. Anionictype lubricants are preferably employed such as long-chain fatty acid compounds.

To further minimize adhesive build-up, mechanical cleaning of the thermal-drying surface may optionally be employed.

Devices known in the papermaking art such as cleaning doctors, steam showers, and other like equipment, can be used.

The amount of adhesive sprayed onto the sheet is adjusted to provide the requisite degree of bonding between the sprayed surface of the web and the thermal-drying surface. This amount will vary depending on the adhesive, the conditions employed in the sheet formation process, and the specific type of creped sheet being produced. For example, in making creped tissue sheets by the process of this invention, the amount of adhesive employed will typically be from 0.25 pound of adhesive per ton of pulp, and preferably from 0.5 pound of adhesive per ton of pulp, to 2.0 pounds of adhesive per ton of pulp, and preferably 1.25 pounds of adhesive per ton of pulp.

The wet web surface which has been sprayed with adhesive is then adhered to a thermal-drying surface, generally a thermaldrying cylinder. Preferably, a Yankee drying cylinder is employed and the sprayed surface is adhered thereto by the mechanical, compressive action exerted thereon, generally using one or more mechanical press rolls which form a nip in combination with the Yankee drying cylinder, and brings the adhesive-containing surface of the web into uniform contact with the thermal-drying surface.

The web is then dried on the thermaldrying surface, preferably to a consistency of at least 92%, and more preferably to a consistency of at least 97%.

A creping means then removes the dried sheet from the thermal-drying surface, the creping action disrupting bonds between respective fibers and causing a softening effect on the sheet. In general, the creping means is a doctor blade which crepes and removes the sheet from the thermal-drying surface. If desired, subsequent embossing of the sheet can be provided employing conventional embossing techniques known to the prior art or pneumatic embossing as, for example, described in U.S. Patent 4,000,242 to Hartbauer.

By producing a creped sheet in accordance with the teachings of this invention, a high-bulk softness is achieved, as measured by conducting a Handle-O Meter test (HOM). The HOM test is described in TAPPI T-498. The bulk softness (reciprocal of stiffness) of a given sheet is then calculated by dividing the HOM value by the square of the caliper of a given single sheet being tested, the quotient thereof being multiplied by 105. For example, in high basis weight, single-ply tissue and towel applications, depending on the type of furnish employed, bulk softness, expressed as HOM/(caliper)2x 105, is desirably not more than 1.25, and preferably not more than 1.0, and more preferably not more than 0.75. Furthermore, in lower basis weight sheets employed in two-ply tissue applications, the bulk softness of each sheet is generally not nore than 0.75, and preferably not more than 0.6, and more preferably not more than 0.4.

An important aspect of this invention is the ability of the process to produce soft, bulky, low-density sheets in an extremely broad basis weight range. The basis weight of a given sheet is determined according to TAPPI test No. T-410. As opposed to the prior art sheets formed on conventional papermaking equipment, the basis weights of the sheets produced by the process of the invention, in an uncreped state, can range from 7 pounds per 3,000 square feet, and preferably from 8 pounds per 3,000 square feet to 25 pounds per 3,000 square feet, and preferably to 20 pounds per 3,000 square feet. More specifically, the basis weight of a typical tissue sheet for use in a two-ply-sheet construction is from 7 pounds per 3,000 square feet, and preferably from 8 pounds per 3,000 square feet, 12 pounds per 3,000 square feet, and preferably from 10 pounds per 3,000 square feet. Moreover, a singleply tissue can be produced having a basis weight range of from 12 pounds per 3,000 square feet, and preferably from 14 pounds per 3,000 square feet, to 18 pounds per 3,000 square feet, and preferably to 17 pounds per 3,000 square feet.

A critical measure of the sheet quality is consumer-perceived softness at a given, acceptable, bulk and sheet strength level.

Although softness is difficult to quantify, it can be closely correlated to the manner in which the sheet is creped from the thermaldrying surface. Thus, if the sheet is not bonded to the thermal-drying surface by the spray adhesive in a uniform manner, or if the bonding effect is too strong between the sheet and the thermal-drying surface, the crepe quality imparted to the sheet in the machine direction will be coarse, and a consumer-perceived feel of the sheet will be unacceptable. It is therefore important to have a fine degree of creping in the machine direction. Generally, it has been found that for applications such as tissue and toweling when a number of crepes in the machine direction (CM) is at least 50 creped lines per inch, and preferably at least 60 creped lines per inch, excellent consumer-perceived softness is obtained. the number of creped lines per inch is analytically determined using a Nikon 6C Profile Projector with a 10x magnification lens and a high intensity surface illuminator. The paper specimens are mounted so that the surface light beam is parallel to the machine direction of the sheet. The transmitted and surface illumination are employed at an intensity level which maximizes visibility of the crepe lines. A photograph is taken at 10x magnification and the crepe count per linear inch determined using a ruler.

It has been found that when comparing the number of crepe lines per inch of a sheet made by the process of the present invention with a creped sheet which has not been sprayed with adhesive, both sheets having been made from the same parent paper, the subject sheet has at least 10% more creped lines per inch, and preferably at least 25% more creped lines per inch, than its nonsprayed counterpart.

One method of defining bulkiness of a sheet is by determining its density. Prior sheets produced on conventional equipment generally exhibit a density which falls above acceptable limits for high-bulk applications at the requisite softness and strength levels.

Thus, it is preferred that the creped sheets produced by the process of this invention have a density of not more than 0.2 gram per cc, and preferably not more than a density of 0.18 gram per cc. The density of a given sheet is calculated by determining the Lobb caliper of the sheet and dividing by the previously described basis weight thereof.

Lobb caliper is determined by placing 24 sheets between a set of matching cylinders four inches in diameter, under a load of 1.35 pounds per square inch, and measuring the thickness of the sheet to the nearest 0.001 of an inch. The caliper of a single sheet is then determined by dividing the Lobb caliper reading by 24.

Each sheet must have enough structural integrity so that it will be capable of being processed according to the subject system without tearing. A measure of the structural integrity is the breaking length of the sheet.

This procedure is run according to TAPPI test No. T-222, except that instead of a 15 mm wide sample strip, a one-inch (25.4 mm) wide strip is used. Average breaking length <RTI unacceptable to the consumer. Thus, it is preferred that the By,,, not be greater than 450 meters, and more preferably not greater than 400 meters.

In contrast to many prior art processes, such as print bonding, the process of the present invention can be employed on high speed commercial equipment such as machines having speeds of at least 2,000 feet per minute, and preferably at least 3,000 feet per minute.

Example 1 Experiments were conducted to demonstrate that a soft, high-bulk, lowdensity, finely creped sheet can be produced employing a bonding inhibitor and controlled adhesive spraying, as described by the process of the present invention.

Thus, an aqueous fiber furnish was formed containing 65% softwood kraft fibers (spruce/pine) and 35% kraft broke (75% softwood and 25% hardwood) on a commercial paper machine, including a Stevens former wet-end system. In the first experiment, no bonding inhibitor was added to the fiber furnish. In the second experiment, 6 pounds per ton of a chemical debonding agent (Ceranine HCS) was added, and in the third instance, 10 pounds per ton of Ceranine HCS was employed.

Only 6 pounds per ton of chemical debonder was employed in the second experimental run because more than that amount caused intermittent, as opposed to, uniform bonding of the sheet to the Yankee drying cylinder. Therefore, the sheet could not be properly dried, resulting in sheet breakage and the inability of the sheet to be finely creped.

A 0.05% consistency aqueous fiber furnish was fed to the wet-end of the Stevens former foraminous wire and a wet web formed. The wet web was picked up from the forming wire by a vacuum felt pick-up and conveyed in the first and second experiments directly to the Yankee drying cylinder. However, in run 3, small, discrete droplets of carboxymethyl cellulose (CMC) adhesive were sprayed onto the underside of the wet web at a point downstream from the Yankee cylinder sufficient to preclude significant build-up on the thermal-drying surface. This controlled spraying was done employing a bank of 22 Sonicore Atomizing Nozzles, Type 125H.

The CMC was a 0.5% solution of Hercules 7LT containing about 0.21 cc of calcium stearate/gallon H2O. The sonic nozzles were manufactured by Sonic Development Corporation of Upper Saddle River, New Jersey. The small, discrete particles were controlled so that their average size was maintained in a range of between 50--75 microns, and the spray rate adjusted so that the coverage of the web was about 20%. In all three cases, the wet web was adhered to a Yankee drying cylinder by the action of a vacuum press roll interacting with the thermal-drying surface. The consistency of the wet web after nonthermal dewatering was about 30 in all three runs.

The Yankee drying cylinder was equipped with a doctor blade to crepe the dried sheet from the Yankee cylinder drying surface and, in the case of Run No. 3, a cleaning doctor, located after the creping doctor blade, was employed to remove any excess adhesive which might build up on the Yankee drying cylinder surface. About 0.85 pound of adhesive per ton of pulp was employed in Run No. 3. The creped sheets from each of the three runs are tabulated in Table I.

TABLE I Run 1 Run 2 Run 3 Basis Weight pounds/3,000 ft2 14.5 14.4 14.7 Lobb Caliper per Sheet 102 106 120 Density, g/cc 0.218 0.209 0.188 BL,, meters 742 459 324 Bulk Softness HOM/(Cal)2x 106 1.59 1.34 0.75 Crepe Lines per Inch (CM) 45 45 65 From an examination of the data outlined in Table I, it is clear that only when the process of the present invention was employed was a sheet produced which was soft, highly bulky, low density, and finely creped.

Example 2 Experiments were conducted in a similar manner to the procedure described in Example 1 to produce a soft, high-bulk, lowdensity, finely creped sheet having a high basis weight, i.e., about 17.5 pounds per 3,000 square feet.

When the process of the present invention was employed, the dried sheet exhibited a fine crepe pattern, was soft, bulky, and had the physical properties outlined in Table II, Run No. 1.

The above experiment was repeated without the use of the Ceranine HCS debonding agent or the carboxymethyl cellulose adhesive. The results of that experiment are also in Table II, Run No. 2.

A third experiment was conducted in a similar manner to Run No. 1, except that 10 pounds per ton of Ceranine HCS and 4.6 pounds per ton of carboxymethyl cellulose were added directly to the aqueous fiber furnish prior to forming the wet web. The results of that run were also shown in Table II.

TABLE II Runl Run2 Run3 Basis Weight pounds/3,000 ft2 17.5 17.7 16.5 Lobb Caliper per Sheet 6.32 5.08 4.84 Density, g/cc 0.177 0.223 0.218 BLaV9, meters 323 621 631 Bulk Softness HOM/(Cal)2x 105 0.93 2.00 2.14 It is clear from comparing the results of the respective experiments that only when a debonding agent was added to the fiber furnish followed by subsequent spraying of the wet web, as described by the process of this invention, can a high basis weight (17.5 pounds per 3,000 square feet), low density (0.117 gram per cc), soft (0.93 HOM/(caliper)2x 105), finely creped sheet be provided.

Example 3 An experiment was conducted at high machine speeds (3,000 ft/min at Yankee dryer) to produce a sheet for use in a twoply tissue construction.

Accordingly, an aqueous fiber furnish was prepared using 60% softwood kraft fibers (hemlock and fir), 20% hardwood kraft fibers (alder) and 20% broke (hardwood and softwood kraft fibers). The pH of the furnish was adjusted to 5.6 with alum and 3.5 pounds per ton of a chemical debonding agent (Quaker 2001) was added thereto. The pH of the furnish was adjusted to about 77.5 with soda ash and a wet web was then formed on Fourdrinier wet-end system. The web was first partially de-watered on a Fourdrinier wire employing a vacuum pickup roll followed by a series of vacuum boxes. The wet web was then transferred to a vacuum pickup felt and .6 pound per ton of carboxymethyl cellulose (Hercules 77 LT) was sprayed on the underside of the wet web employing a series of 38 Sonicore Atomizing Nozzles, Type 125H, as previously described in Example 1, except that the average droplet size of the spray droplets was about 30--50 microns and the percent coverage was about 30%. The sprayed web was then further dewatered between a resilient rubber roll and a vacuum press roll and the sprayed surface of the web adhered to the thermal-drying surface of a Yankee cylinder dryer in a uniform manner via a pair of consecutively spaced press rolls. The Yankee cylinder was equippped with a creping doctor blade and a cleaning doctor.

The web was dried on the surface of the Yankee cylinder, the dry sheet creped therefrom, and the physical properties of the sheet measured. The sheet had a basis weight of 9.57 pounds per 3,000 ft2, a Handle-O-Meter of 0.57 HOM/ (caliper)2xl05, a density of 0.155 g/cc, and a BLavg of 336 meters.

The words "Hercules", "Leomin" and "Nikon" used in this specification are Registered Trade Marks.

WHAT WE CLAIM IS: 1. A process for producing a soft, highbulk, low-density, finely creped sheet, which comprises: (a) forming an aqueous fiber furnish including cellulosic papermaking fibers, and a bonding inhibitor which minimizes the formation of papermaking bonds between respective cellulosic fibers during sheet formation; (b) forming a wet web from said aqueous fiber furnish; (c) dewatering said wet web, employing non-thermal dewatering means, to a consistency of up to 60% by weight, based on the total weight of fibers in said wet web; (d) applying an adhesive in the form of discrete droplets onto one surface of said wet web before, during, or after said nonthermal-dewatering step, the adhesive spray being controlled so that said droplets have an average droplet size of from 10 microns to 75 microns, and the coverage of said web surface by said droplets is from 10% up to 60%; the amount of adhesive being sufficient to cause the web to adhere to the thermal-drying surface in the next step but insufficient to prevent creping; (e) adhering the sprayed surface of the web to a thermal-drying surface for thermally drying said web; (f) drying said sprayed web on said thermal-drying surface; and (g) creping said dried web from the thermal-drying surface.

2. A process according to claim 1 wherein the creping is such as to produce finely creped sheet having a bulk softness of not more than 1.25 HOM/(caliper)2x 105 as hereinafter defined, and BLaV9 of from 150 meters, to 500 meters.

3. A process according to claim 1 or 2, wherein the consistency of said

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (20)

**WARNING** start of CLMS field may overlap end of DESC **. A third experiment was conducted in a similar manner to Run No. 1, except that 10 pounds per ton of Ceranine HCS and 4.6 pounds per ton of carboxymethyl cellulose were added directly to the aqueous fiber furnish prior to forming the wet web. The results of that run were also shown in Table II. TABLE II Runl Run2 Run3 Basis Weight pounds/3,000 ft2 17.5 17.7 16.5 Lobb Caliper per Sheet 6.32 5.08 4.84 Density, g/cc 0.177 0.223 0.218 BLaV9, meters 323 621 631 Bulk Softness HOM/(Cal)2x 105 0.93 2.00 2.14 It is clear from comparing the results of the respective experiments that only when a debonding agent was added to the fiber furnish followed by subsequent spraying of the wet web, as described by the process of this invention, can a high basis weight (17.5 pounds per 3,000 square feet), low density (0.117 gram per cc), soft (0.93 HOM/(caliper)2x 105), finely creped sheet be provided. Example 3 An experiment was conducted at high machine speeds (3,000 ft/min at Yankee dryer) to produce a sheet for use in a twoply tissue construction. Accordingly, an aqueous fiber furnish was prepared using 60% softwood kraft fibers (hemlock and fir), 20% hardwood kraft fibers (alder) and 20% broke (hardwood and softwood kraft fibers). The pH of the furnish was adjusted to 5.6 with alum and 3.5 pounds per ton of a chemical debonding agent (Quaker 2001) was added thereto. The pH of the furnish was adjusted to about 77.5 with soda ash and a wet web was then formed on Fourdrinier wet-end system. The web was first partially de-watered on a Fourdrinier wire employing a vacuum pickup roll followed by a series of vacuum boxes. The wet web was then transferred to a vacuum pickup felt and .6 pound per ton of carboxymethyl cellulose (Hercules 77 LT) was sprayed on the underside of the wet web employing a series of 38 Sonicore Atomizing Nozzles, Type 125H, as previously described in Example 1, except that the average droplet size of the spray droplets was about 30--50 microns and the percent coverage was about 30%. The sprayed web was then further dewatered between a resilient rubber roll and a vacuum press roll and the sprayed surface of the web adhered to the thermal-drying surface of a Yankee cylinder dryer in a uniform manner via a pair of consecutively spaced press rolls. The Yankee cylinder was equippped with a creping doctor blade and a cleaning doctor. The web was dried on the surface of the Yankee cylinder, the dry sheet creped therefrom, and the physical properties of the sheet measured. The sheet had a basis weight of 9.57 pounds per 3,000 ft2, a Handle-O-Meter of 0.57 HOM/ (caliper)2xl05, a density of 0.155 g/cc, and a BLavg of 336 meters. The words "Hercules", "Leomin" and "Nikon" used in this specification are Registered Trade Marks. WHAT WE CLAIM IS:

1. A process for producing a soft, highbulk, low-density, finely creped sheet, which comprises: (a) forming an aqueous fiber furnish including cellulosic papermaking fibers, and a bonding inhibitor which minimizes the formation of papermaking bonds between respective cellulosic fibers during sheet formation; (b) forming a wet web from said aqueous fiber furnish; (c) dewatering said wet web, employing non-thermal dewatering means, to a consistency of up to 60% by weight, based on the total weight of fibers in said wet web; (d) applying an adhesive in the form of discrete droplets onto one surface of said wet web before, during, or after said nonthermal-dewatering step, the adhesive spray being controlled so that said droplets have an average droplet size of from 10 microns to 75 microns, and the coverage of said web surface by said droplets is from 10% up to 60%; the amount of adhesive being sufficient to cause the web to adhere to the thermal-drying surface in the next step but insufficient to prevent creping; (e) adhering the sprayed surface of the web to a thermal-drying surface for thermally drying said web; (f) drying said sprayed web on said thermal-drying surface; and (g) creping said dried web from the thermal-drying surface.

2. A process according to claim 1 wherein the creping is such as to produce finely creped sheet having a bulk softness of not more than 1.25 HOM/(caliper)2x 105 as hereinafter defined, and BLaV9 of from 150 meters, to 500 meters.

3. A process according to claim 1 or 2, wherein the consistency of said

nonthermally-dewatered web is up to 40% by weight.

4. A process according to claim 1, 2 or 3 wherein the average droplet size of said discrete droplets is from 30 microns to 50 microns.

5. A process according to any preceding claim, wherein the coverage of adhesive on the surface of the web is from 20% to 40% by weight.

6. A process according to any preceding claim, wherein the amount of adhesive employed is frdm 0.25 pound to 2.0 pound of adhesive per ton of pulp.

7. A process according to any preceding claim, wherein the bulk softness of the crepe product is not more than 1.0 HOM/(caliper)2x 105 as hereinbefore defined.

8. A process according to claim 7, wherein the bulk softness is not more than 0.75 HOM/(caliper)2xlOS.

9. A process according to any preceding claim, wherein the basis weight of said soft, high-bulk, low-density, finely creped sheet, in the uncreped state, is from 7 to 25 pounds per 3,000 square feet.

10. A process according to claim 9, wherein the basis weight is from 8 pounds to 12 pounds per 3,000 square feet.

11. A process according to any preceding claim operated so that the number of creped lines in the machine direction of the product is at least 50 creped lines per inch.

12. A process according to any preceding claim, wherein there is produced a soft, high-bulk, low-density, finely creped sheet which has at least 10% more creped lines per inch than a comparable sheet which has not undergone said controlled spraying.

13. A process according to any preceding claim, wherein the density of the product sheet is not more than 0.2 gram per cc.

14. A process according to any preceding claim, wherein the product has BLayg from 250 meters to 400 meters.

15. A process according to any preceding claim, wherein the web is formed on a continuous papermaking machine of which the machine speed measured as the sprayed surface of the web is being uniformly adhered to the thermal-drying surface, is at least 2,000 feet per minute.

16. A process according to any preceding claim, wherein the adhesive is sprayed from sonic spray nozzles.

17. A process according to claim 16, wherein said spray droplets have an average droplet size of from 10 microns to 75 microns.

18. A process according to claim 17, wherein the coverage of said web surface by said small, discrete droplets of adhesive is from 10% to 60%.

19. A process according to claim 1, substantially as herein described.

20. Crepe paper when made by a process according to any preceding claim.