MXPA98005447A - Methods of application of chemical apprentice agents to make a wet tisu reduc - Google Patents

Abstract

A soft tissue that reduces fluid penetration can be produced by the indirect addition of chemical sizing agents to the tissue by applying the chemical sizing agents to the surface of the Yankee dryer, such as by spraying. More specifically, sizing agents can be included as part of the creping adhesive formula, which is sprayed onto the surface of the Yankee dryer between the creping blade and the pressure roller. Sizing agents are subsequently transferred to the surface of the tisue sheet when the sheet is compressed against the Yankee dryer. The benefit of reduced fluid penetration is that the hands remain dry during the period of

Description

METHODS OF APPLYING CHEMICAL APPRENTICE AGENTS TO MAKE A REDUCED WET TISSUE BACKGROUND OF THE INVENTION The use of sizing agents in the manufacture of tissue, such as facial and bath tissue, is not common practice in the industry. However, it has been shown that the addition of sizing agents similar to those commonly used in fine papers reduces the ability of the fluid to penetrate the tissue and thus keeps the hands of users dry during most uses. Such tissues also have adequate absorbency to make them functionally useful. These tissues typically contain a mixture of relatively long fibers, which are usually hardwood fibers, and relatively short fibers, which are usually hardwood fibers. Preferably, the sizing agent is added to the long fibers before forming the fabric as better chemical retention is achieved than with the addition of short fibers. The long fibers are also treated with reinforcing agents (wet and dry) and refined. Both refining and reinforcing agents are frequently used because the excessive use of any treatment can have an adverse effect on the tissue manufacturing process and / or on the resulting tissue product.

However, the addition of the sizing agents to the fiber supply may have some disadvantages. In one case, the sizing agents added to a supply prior to formation cause internal disunion resulting in the loss of tensile strength and increased dust when the sheet contacts the creping doctor blade. The loss in tensile strength may require an additive of strength or excessive refinement which may have a detrimental effect on the softness of the tissue. Excessive dust can increase the frequency of sheet breaks on the reel, provide a less than desirable environment for the operators of the machine and is detrimental to the consumer's perception of the tissue.

Therefore there is a need for a more efficient method for using the sizing agents in the manufacture of tissues.

Synthesis of the Invention It has now been discovered that soft creped tissue can be produced by the indirect addition of chemical sizing agents to tissue tissue by applying the chemical sizing agents to the surface of the Yankee dryer, such as by spraying. More specifically, the sizing agents can be included as part of the creping adhesive formula, which is sprayed onto the surface of the Yankee dryer between the creping blade and the pressure roller. The sizing agents are subsequently transferred to the surface of the tissue sheet by pressing the sheet against the Yankee dryer.

The sizing agent remains predominantly on the surface of the sheet where it is most beneficial, thereby resulting in a barrier to rapid absorption of the fluid. Some of the sizing agent passes through the sheet while it is at the pressure point of the pressure rolls and recirculates back to the wet end of the tissue machine with the white water. As such, additional quantities are incorporated into the tissue sheet at that point in the process, but these quantities are more evenly distributed throughout the sheet. The net result is a tissue sheet having a greater concentration of sizing agent on the surface of the sheet, thereby reducing the rapid absorption of fluid within the sheet relative to sheets made in a conventional manner.

Thus in one aspect the invention resides in a method for making a creped tissue comprising: (a) forming a wet tissue by depositing a supply for making aqueous paper on a forming fabric; (b) partially draining the tissue tissue; (c) applying a creping adhesive and one or more sizing agents to the surface of a Yankee dryer; (d) adhering the tissue tissue to the surface of the Yankee dryer so that the sizing agent is transferred to the tissue tissue; and (e) creping the tissue.

In another aspect, the invention resides in a tissue product made by the above-mentioned method.

As used herein, a "sizing" agent is any chemical that imparts water repellency to cellulosic fibers. Suitable sizing agents are described in the text entitled "Papermaking and Cardboard Manufacturing" second edition, volume III, edited by R. G. MacDonald, and J. N. Franklin, which is incorporated herein by reference.

Sizing agents are commonly added to control the penetration of aqueous liquids into paper or other fibrous structures. In many cases, some resistance is required for the end use. When the surface treatments are applied with conventional equipment, the sizing of the base sheet is often required to control the intake of the aqueous solution. Paper classes such as butcher wrap, milk carton, liner board, bleached and unbleached bag, fine paper, cylinder board, newsprint and corrugated media are routinely prepared.

The internal dressing agents which are those applied to the fibers within the paper structure, provide a reduced penetration rate by slowing the rate of flow through the capillary vessels of the interfiber. When sizing is achieved, the contact angle on the fiber surface is 90 degrees or greater. Internal sizing agents work through the use of low surface energy hydrophobic chemicals which, when attached to the surface of the cellulose, reduce surface energy of the fiber surface.

Suitable preparation agents particularly are those prepared acid or alkali such as acid rosin, alkenyl ketene dimers, alkenyl succinic anhydride, alkenyl ketone dimers and alkenol ketone dimers of the formula: CH = C CH R, i i 0 C = 0 wherein R, and R2 are based on the C16-C18 aliphatic carbon chains, which may be the same or different. Commercially available prepping agents of this type are Hercon 79 and Precis 3000 from Hercules, Inc., of Wilmington, Delaware. The amount of fiber sizing agent can be from 1 to about 10 pounds per ton of fiber, more specifically from about 1.5 to about 3 pounds per ton of fiber, and even more specifically from about 2 to around 2.5 pounds per ton of fiber.

As used herein, "absorbency rate" is a measure of the water repellency imparted to the tissue by means of the priming agent. The absorbency rate is the time it takes for a product to be completely saturated in the distilled water. To measure the absorbency rate, the samples are prepared as 2 and a half inch squares composed of 20 sheets of finished product using a matrix press (eg TMI DGD from Testing Machines Incorporated, Inc., Amityville, New York 11701) . The layer of a finished product dictates the number of individual sheets: 1-layer: 20 individual sheets; 2-layers: 40 individual sheets; 3-layers: 60 individual sheets. When soft rolls are tested (single layer of tissue coming out of the tissue machine before working on the rewinder), 40 individual soft roll sheets are used per sample (if the finished product tried is two layers).

Samples are stapled at all four corners using Swingline S.F. Samples were tested in a constant temperature water bath at a depth of at least 4 inches (maintained through the test) containing distilled water at 30 +/- Io Celsius. The sample was held about 1 inch above the water (the staples point in the downward position) and then dropped flat on the surface of the water. A stopwatch (which can be read at 0.1 second) It started when the sample hit the water. When the sample was completely saturated, the stopwatch was stopped and the Absorbency Rate was recorded. A minimum of five samples were tested and the results of the test were averaged. All tests were carried out in a laboratory atmosphere of 23 +/- Io Celsius and 50 +/- 2 percent of RH. All samples were stored under these conditions for 4 hours before the test. (The prepping agents distribute themselves and react more quickly to higher temperatures).

The tissues of this invention have an Absorbency Rate, for tissue naturally aged for 5 days, of about 10 seconds or more, more specifically of about 100 seconds or more, even more specifically of about 200 seconds or more, yet more specifically about 300 seconds or more, and even more specifically about 100 to about 400 seconds.

Brief Description of the Drawing Figure 1 is a schematic flow diagram of a wet compressed tissue manufacturing process, illustrating the addition of the prepping agents to the surface of the Yankee dryer. The recycling flow of white water is also shown.

Detailed Drawing Description Figure 1 is a schematic flow diagram of a process for manufacturing conventional wet compressed tissue useful in the practice of this invention, even when other tissue manufacturing processes may also be beneficial to the delivery preparation method of this invention, such such as continuous drying or other non-compressive tissue manufacturing processes. The specific training mode illustrated in Figure 1 is commonly referred to as a crescent former, even though many other well-known formers in the art of papermaking can also be used. A head box 21, a forming fabric 22, a forming roller 23, a papermaking felt 24, a press roller 25, a spray stream 26, a Yankee dryer 27, and a creping blade 28 are shown. are shown, but not numbered, several tension or transmission rolls used to define the cloth runs in a schematic diagram, which may differ in practice. As shown, the head box 21 continuously deposits a supply jet 30 between the forming fabric 22 and a felt 24, which is partially wrapped around the forming roll 23. The water is removed from the aqueous supply suspension through the the forming fabric by centrifugal force when passing through the newly formed fabric the arc of the forming roller. Upon separation of the forming fabric and the felt, the wet fabric 31 remains with the felt and is transported to the Yankee dryer 27.

In the Yankee dryer, the creping chemicals are applied continuously in the form of an aqueous solution to the surface of the Yankee dryer on top of the residual adhesive remaining after creping. In accordance with this invention, creping chemicals may include one or more prepping agents. The solution is applied by any conventional means preferably using a spray stream 26 which evenly sprays the surface of the dryer with the creping adhesive solution. The application point on the surface of the dryer is immediately below the creping doctor blade 28, thereby allowing sufficient time for the spreading and drying of the fresh adhesive film before it contacts the fabric at the pressure point of the roller of the press The wet fabric 31 is applied to the surface of the dryer by means of the press roll 25 with an application force typically of about 200 pounds per square inch (psi). The incoming fabric is nominally about 10 percent consistency (range from about 8 to about 20 percent) by the time it reaches the press roll. After the compression and drainage step, the consistency of the fabric is or is above 40 percent. Sufficient Yankee dryer steam strength and a drying capacity of cover are applied to this cloth to achieve a final moisture content of about 2.5 percent or less.

Also illustrated in Figure 1 is the white water recycling system. At the pressure point of the press roll, the white water effluent squeezed out of the woven fabric is collected in a tray 36. The collected white water 37 is drained into the wire hole 38. The thick supply 40 having a consistency of about 3 percent is diluted with white water in the fan pump 39 to a consistency of about 0.1 percent. The diluted supply 41 is subsequently injected into the head box 21 to form the wet tissue.

Examples Example 1. (Control) A soft tissue product was made using the general process of Figure 1. More specifically, a papermaking supply was prepared consisting of 35 percent northern softwood kraft (NS K), 15 percent High Maple Quinnesec and 50 percent eucalyptus fibers. Quinnesec and eucalyptus pulps were struck together at a consistency of 3.5 percent. The NSWK was hit separately around a 3.5 percent consistency. The two pulp streams were mixed together before dilution.

The blended feed was then further diluted to about 0.1 weight percent based on the dry fiber, fed to a head box and deposited from the head box on a multi-layer polyester forming fabric to form the fabric. tissue. The fabric was then transferred from the forming fabric to a conventional wet compressed carrier felt. The water content of the sheet and the felt just before the transfer to the Yankee dryer was about 88 percent. The sheet was transferred to the Yankee dryer with a vacuum pressure roller. The clamping point pressure was around 230 pounds per square inch. The moisture of the sheet after the compression roll was around 42 percent. The adhesive mixture sprayed onto the surface of the Yankee just before the pressure roll consisted of 28 percent polyvinyl alcohol, 58 percent polyamide resin (Ky eneLX) and 14 percent release agent (Quaker 2008). The spray application rate was about 4.2 pounds of dry chemical per metric ton of fiber. A cover heated with natural gas partially enclosing the Yankee had a supply air temperature of 626 degrees F to aid in drying. The moisture of the blade after the creping blade was around 2.0 percent. The speed of the machine was around 4100 feet per minute. The crepe ratio was 1.30 or 30 percent. The resulting tissue was folded together and calendered with two steel rolls at around 70 pounds per linear inch. The two-layer product had the side of the dryer folded to the outside. When it was converted, the finished basis weight of the two-layer facial tissue at a standard TAPPI temperature and humidity was around 17 pounds per 2880 square feet.

Example 2. (Invention) A soft tissue product with reduced moisture penetration can be made in accordance with this invention using the general process of Figure 1. More specifically, a papermaking supply consisting of 35 percent kraft of northern softwood was prepared ( NSWK), 15 percent of High Maple Quinnesec and 50 percent of eucalyptus fibers. Quinnesec and eucalyptus pulps are beaten together at a consistency of about 3.5 percent. The NSWK is hit separately at a consistency of about 3.5 percent. The two pulp streams are mixed together before dilution. The mixed supply can further be diluted to about 0.1 percent by weight based on the dry fiber, supplied to a headbox and deposited from the headbox on a multi-layered polyester forming fabric to form the tissue of the tissue. The fabric is then transferred from the forming fabric to a conventional wet-compressed carrier felt. The water content of the sheet on the felt just before the transfer to the Yankee dryer can be about 88 percent. The sheet is transferred to the Yankee dryer with a pressure roller with vacuum. The clamping point pressure can be around 230 pounds per square inch. The moisture of the sheet after the pressure roll can be about 42 percent. The spray mixture sprayed onto the Yankee surface just before the pressure roller can consist of about 20 percent polyvinyl alcohol, 35 percent polyamide resin (KymeneLX) and 45 percent primer (PTD-M-1332 or PTD-M-1331 available from Hercules, Inc.). The spray application rate was about 8 pounds of dry chemical per metric ton of fiber. A cover heated with natural gas partially enclosing the Yankee can have a supply air temperature of 626 degrees F to aid in drying. The moisture of the blade after the creping blade can be around 2.0 percent. The speed of the machine can be around 4100 feet per minute. The crepe ratio can be around 1.27 or 27 percent. The resulting tissue is folded together and calendered with two steel rolls at about 70 pounds per linear inch. The two-layer product can be folded with the side of the dryer to the outside. When converted, the finished basis weight of the two-layer facial tissue at the standard TAPPI temperature and humidity can be around 17 pounds by 2880 square feet. The resulting facial tissue can resist penetration of moisture thereby providing the benefit of keeping the user's hands dry during normal use. This tissue can have an Absorbance Rate of 10 to 400 seconds compared to 3 seconds for the control (Example 1).

It will be appreciated from the foregoing Examples, given for purposes of illustration, that they should not be considered as limiting the scope of the invention, which is defined by the following clauses and all equivalents thereof.

Claims (10)

R E I V I N D I C A C I O N S

1. A method for making a creped tissue comprising: (a) forming a wet tissue by depositing a supply for making aqueous paper on a forming fabric; (b) partially draining the tissue tissue; (c) applying a creping adhesive and one or more prepping agents to the surface of a Yankee dryer; (d) adhering the tissue tissue to the surface of the Yankee dryer so that the sizing agent is transferred to the tissue tissue; and (e) creping the tissue.

2. The method as claimed in clause 1 characterized in that the amount of appressing agent added to the Yankee dryer surface is from about 1 to about 10 pounds per ton of fiber.

3. The method as claimed in clause 1 characterized in that the amount of sizing agent added to the surface of the Yankee dryer is from about 1.5 to about 3 pounds per ton of fiber.

4. The method as claimed in clause 1 characterized in that the amount of sizing agent added to the surface of the Yankee dryer is from about 2 to about 2.5 pounds per ton of fiber.

5. The method as claimed in clause 1 characterized in that the Absorbency Rate of the creped tissue is about 10 seconds or greater.

6. The method as claimed in clause 1 characterized in that the Absorbency Rate of the creped tissue is around 100 seconds or greater.

7. The method as claimed in clause 1 characterized in that the Absorbency Rate of the creped tissue is around 200 seconds or greater.

8. The method as claimed in clause 1 characterized in that the Absorbency Rate of the creped tissue is around 300 seconds or greater.

. The method as claimed in clause 1 characterized in that the Absorbency Rate of the creped fabric is from about 100 to about 400 seconds.

10. A creped tissue produced by the method as claimed in clause 1. SUMMARY A soft creped tissue that reduces fluid penetration can be produced by the indirect addition of chemical sizing agents to the tissue by applying the chemical sizing agents to the surface of the Yankee dryer, such as by spraying. More specifically, sizing agents can be included as part of the creping adhesive formula, which is sprayed onto the surface of the Yankee dryer between the creping blade and the pressure roller. Sizing agents are subsequently transferred to the surface of the tisue sheet when the sheet is pressed against the Yankee dryer. The benefit of reduced fluid penetration is that the hands remain dry during use.