MXPA98000637A - Method to treat a supply to make paper to manufacture tisu su - Google Patents

Abstract

The present invention relates to an efficient and effective method for treating the supply to make tissue to make soft tissue involves adding a softening agent to a first supply to make paper of short fibers, such as eucalyptus fibers. A second supply for making long fiber paper, such as softwood fibers, is mixed with the supply of short fibers. Then, the wet strength agents and / or the dry strength agents with aggregates to the mixed supply. The treated supply is then fed to the head box and processed in a tissue in any suitable manner.

Description

METHOD FOR TREATING A SUPPLY TO MAKE PAPER TO MANUFACTURE SOFT TISSUE Background of the Invention The use of softening and strengthening agents in the manufacture of tissues such as facial and bath tissue is a common practice in the industry. These tissues typically contain a mixture of relatively long fibers, which are usually softwood fibers, and relatively short fibers, which are usually hardwood fibers. The softening and strengthening agents can be added separately to these different fiber species before mixing the fibers together and forming the tissue. The softening agent is added to the short fibers since the short fibers primarily contribute to the softness of the tissue. The long fibers are treated separately with reinforcing agents (dry and wet) and refined. Both refining and reinforcing agents are used because excessive use of any treatment can have an adverse effect on the manufacturing process of the tissue and / or the resulting tissue product.

However, the conventional method for adding reinforcing agents to the long fibers may have some disadvantages. In one case, the combination of reinforcement agents with refinement on the same scale can cause poor efficiency. If the reinforcing agents are added before refining, the cutting forces can remove the reinforcing agent attached from the fiber. If the reinforcing agents are added directly after refining, the reinforcing agents are preferably subjected to fines generated by the refinement, thereby reducing the chemical efficiency.

Furthermore, adding the reinforcing agents to the long fiber in the conventional manner results in a long residence time for the reinforcing agent to reach the headbox. Very often changes in addition rates are necessary to maintain the specifications of the base sheet. By adding the reinforcing agents too far back into the system, there is a greater likelihood that the product is out of target specifications for a longer period of time resulting in a greater waste and delay on the tissue machine.

Thus there is a need for a more efficient method for using softening agents and reinforcing agents in the manufacture of tissues.

Synthesis of the Invention It has now been discovered that a particularly soft tissue can be produced by the selective and sequential addition of the softening and tissue strengthening agents. More specifically, one or more softening agents are added to the short fiber supply prior to the mixing of the short fibers with the long fibers. Once mixed, the entire supply is treated with dry strength and wet strength additives, formed, drained, and dried to produce a tissue product with adequate strength, absorbency and superior softness. The refinement of the long fiber can be minimized to maximize volume development. The process, involving relatively low capital costs, is easily incorporated into conventional wet and continuous drying facilities to make tissue products from a single stratum or from multiple strata.

Therefore, in one aspect, the invention resides in a method for treating a papermaking supply comprising: (a) adding a softening agent to a first papermaking supply comprising primarily short papermaking fibers; (b) mixing the first paper supply with a second paper supply comprising primarily long papermaking fibers; and (c) adding one or more dry strength agents and / or one or more wet strength agents to the mixed supply.

The dry strength agent or agents and the wet strength agent or agents can be added in any order, even when first adding the reinforcing agent having the lowest loading density is preferred to improve its substantivity to the fibers. The charge density correlates with the ability of the reinforcing agent to adhere to the fibers. The determination of the charge density is mentioned in "Systems of Auxilio-Retention of Microparticles" of A. Swerin and others, Technology of the Paper, Volume 33, No. 12, pages 28-29, December of 1992, which is incorporated here for reference.

As used herein, "short" papermaking fibers are fibers for making paper having an average length of about 1 millimeter or less. Short paper fibers include most hardwood species, such as eucalyptus, maple, birch, and aspen, and the like. The "long" papermaking fibers are those papermaking fibers having an average length greater than about 1 millimeter, which include softwood species such as northern and southern pine. It is preferred that the first paper supply comprises at least 75 percent by weight of short fibers and, more specifically, essentially all short fibers. Similarly, it is preferred that the second paper furnish comprises at least 75 percent by weight of long fibers and, more specifically, essentially all of the long fibers.

Suitable softening agents for treating the first supply of (short) fibers, include a variety of chemicals that contribute to the feeling of softness, silky, soft, velvety, raised, lotion, cushioned, cushioned, delicate, satiny and comforting. tissue. These agents include, but are not limited to, imidazoline quaternaries; ester quaternaries, phospholipids; silicone phospholipids; silicone quaternaries; quaternized lanolin derivatives; wheat protein / hydrolyzed polydimethyl siloxane; wheat protein / hydropolyzed dimethicone phosphocopolyol copolymer; organoreactive polysiloxanes; nonionic surfactants, such as alkylphenol ethoxylates, aliphatic alcohol ethoxylates, fatty acid alkoxylates, fatty alcohol alkoxylates, and block copolymers of ethylene oxide and propylene oxide; condensation products of ethylene oxide with the product resulting from the reaction of propylene oxide and ethylene diamine; condensation products of propylene oxide with the reaction product of ethylene oxide and ethylene diamine; semi-polar nonionic surfactants, such as water-soluble amine oxides; alkylpolysaccharides, such as alkyl polyglycosides; fatty acid amide surfactants; polyhydroxy compounds, including glycerol, polyethylene glycols, and polypropylene glycols having a weight average molecular weight of from 200 to 4000; quaternized protein compounds; silicone emulsions and silicone glycols.

The amount of softening agent added to the first supply can be any amount that is effective to increase the softness of the resulting tissue and will depend on the particular softening agent selected and the desired softness effect. Notwithstanding this, adequate amounts of softening agent, based on the dry weight of the fiber, can be about 0.005 percent by weight or greater, more specifically from about 0.1 to about 1.0 percent by weight, and even more specifically from around 0.3 to about 0.7 percent by weight.

Dry strength agents that can be used include, without limitation, any type of starch, starch derivatives, gums, polyacrylamide resins, and carboxymethyl celluloses.

The amount of dry strength agent added to the mixed supply can be any amount that is effective to increase the dry strength of the resulting tissue and will depend on the particular dry strength agent selected and the desired strength effect. Notwithstanding this, suitable amounts of the dry strength agent can be, based on the dry weight of the fiber, of about 0.05 percent by weight or greater, more specifically from about 0.1 to about 1.0 percent by weight, and even more specifically from around 0.3 to about 0.5 percent by weight.

Suitable wet strength agents include both temporary and permanent wet strength additives. Such wet strength agents include without limitation, the polyamine amide epichlorohydrin, the urea formaldehyde resins, the melamine-formaldehyde resins, the glyoxalated polyacrylamide resins, the polyethyleneimine resins, dialdehyde starch, cationic aldehyde starch, cellulose xanthate, Synthetic latexes, glyoxal, acrylic emulsions, and amphoteric starch siloxanes.

The amount of wet strength agent added to the mixed supply can be any amount that is effective to increase the softness of the resulting tissue and will depend in particular on the smoothing agent selected and the desired strength effect. Notwithstanding this, suitable amounts of wet strength agent, based on the dry weight of the fiber, may be about 0.05 weight percent or more, more specifically from about 0.1 to about 3.0 weight percent. weight, and even more specifically from around 0.3 to about 1.0 percent by weight.

Brief Description of the Drawings Figure 1 is a schematic flow diagram of a preparatory system useful for the purposes of this invention.

Figure 2 is a schematic diagram of a tissue manufacturing process useful for carrying out the method of this invention.

Detailed Description of the Drawings Figure 1 is a schematic flow diagram of a preparatory system useful in the practice of this invention. A first supply of short fibers and a second supply of long fibers are shown which are fed to low consistency pulper hydro-reducers which disperse the dry overlap pulp and break it into individual fibers. Fiber reduction typically occurs between 4-5% consistency. Both pulp reducers run continuously in a loading format to supply short and long fiber to the tissue machine. Once a fiber charge is complete, it is pumped into a chest and diluted to 3-4% consistency. The short fiber supply is not refined and is transferred directly to a clean supply box and diluted to a consistency of about 2-3%. The clean supply chest is maintained at a constant level allowing a continuous supply of softening agent as shown to improve the touch properties of the finished product. The long fiber supply, after having been completely dispersed in the pulp, is pumped into a discharge chest and diluted to a consistency of 3-4%. The long fiber feed is then transferred to a refiner where a low level of refinement (typically no load) is applied to the long fiber to impart some sheet strength without deteriorating the volume and stiffness of the tissue.

Both supplies of long fiber and short fiber are blended in the chest of the machine at a predetermined short fiber / long fiber ratio, typically around 60% short fiber and about 40% long fiber. The consistency in the chest of the machine is around 2-3%. The break in the machine can also be dosed inside the machine chest. The breakage ratio is dictated by current performance specifications and breakage storage levels.

Once the two fiber supplies are mixed, the pumped supply from the machine chest to a low density cleaner which decreases the consistency of the supply to 0.6 percent. At any convenient point after two supplies have been mixed, such as between the machine chest and the low density cleaner, wet and dry strength agents can be added in sequence to improve the integrity of the sheet. The sequence of addition will often depend on the polymer loading densities of each material. If the loading densities are significantly different, it is preferable to first add the material having the lowest charge density.

The mixed supply is further diluted to about 0.1% in the fan pump before entering the headbox.

Figure 2 is a matic flow diagram of a conventional wet press tissue manufacturing process useful in the practice of this invention, even though other tissue manufacturing processes may also benefit from the preparative delivery method of this invention, such as continuous drying or other non-compressive papermaking processes. The specific training mode illustrated in Figure 2 is commonly mentioned as a decreasing former, even though many other well-known formers in the papermaking art can also be used. A head box 21, a forming fabric 22, a forming roll 23, a papermaking felt 24, a compression roller 25, a Yankee dryer 26 and a creping blade 27 are shown. Also shown, but not listed , several loose or tension rolls used to define the fabric runs in the matic diagram, which may differ in practice. As shown, the head box 21 continuously deposits a mixed supply jet between the forming fabric 22 and the filter 24, which is partially wrapped around the forming roller 23. The water is removed from the aqueous supply suspension through of the forming fabric by centrifugal force when passing through the newly formed fabric the arc of the forming roller. When the forming fabric and the felt are separated, the wet cloth remains with the felt and is transported to the Yankee drying 26.

In the Yankee dryer, the creping chemicals are applied continuously on top of the adhesive that remains after creping in the form of an aqueous solution. The solutions are applied by any conventional means, preferably using a spray duct which evenly sprays the surface of the dryer with the creping adhesive solution. The point of application on the surface of the dryer is immediately followed by the creping doctor 27, allowing sufficient time for the spreading and drying of the fresh adhesive film.

The wet fabric is applied to the surface of the dryer by means of a compression roller with an application force typically of about 200 pounds per square inch (psi). The incoming fabric is nominally at a consistency of about 10% (varying from 8 to about 20%) by the time it reaches the pressure roller. After the compression and the drain step, the consistency of the fabric is at or above about 30%. Sufficient drying capacity and drying capacity of Yankee dryer are applied to this cloth to achieve a final moisture content of about 2.5% or less.

Examples Example 1 An absorbent and soft bath tissue product was made in accordance with this invention using the general process of Figure 2. More specifically, a first papermaking supply consisting of eucalyptus hardwood fiber (short fibers) was treated with an imidazoline softening agent (methyl-1-oleyl amidoethyl-2-oleyl imidazolinium methylisulfate, identified as C-6027, commercially available from Witco Corporation). The softening agent was added in the form of an aqueous mixture having about 1% solids. The addition rate was 0.11 percent by weight based on the dry fiber in the final tissue. At the point of addition, the thick supply of eucalyptus was around 2.5 percent solids. In the machine chest, a second supply was mixed to make paper consisting of kraft fiber from soft northern wood together with the first supply treated to the same consistency. The resulting mixed feed contained about 60 percent by dry weight of eucalyptus fibers and about 40 percent by dry weight of northern softwood kraft fibers.

After two supplies were mixed together, a dry strength agent of amphoteric starch (Redi-Bond 2038, commercially available from National Starch and Chemical Company) and a temporary wet strength agent of glyoxalated polyacrylamide were added in sequence.

(Parez 631-NC, commercially available from Cytec Industries, Inc.) to the mixed supply. Parez 631-NC was added to a 6 percent aqueous mixture. The addition rate was 0. 16 percent by weight based on dry weight. The Redi-Bond 2038 was added as a 1 percent mixture with water and the addition rate was 0.16 percent by weight based on dry fiber. The resulting supply was diluted to a consistency of about 0.6 percent by dry weight.

The mixed feed was then further diluted to about 0.1 percent by weight based on the dry fiber, fed to a headbox and deposited from the headbox on a multi-layer polyester forming fabric to form the tissue. The fabric was then transferred from the forming fabric to a conventional wet compressed carrier felt. The water content of the sheet on the felt just prior to transfer to the Yankee dryer was about 88 percent. The sheet was transferred to the Yankee dryer with a vacuum pressure roller. The pressure of the clamping point was around 230 pounds per square inch. The leaf moisture after the pressure roller was around 45 percent. The adhesive mixture sprayed onto the Yankee surface just before the compression roll consisted of 40 percent polyvinyl alcohol, 40 percent polyamide resin and 20 percent quaternized amine polyamide. The spray application rate was around 5.5 pounds of dry adhesive per ton of dry fiber. A deck heated with natural gas partially around the Yanqui supplied air at a temperature of 533 degrees Fahrenheit to aid in drying. The moisture of the sheet after the creping blade was about 1.5 percent by weight. The speed of the 200-inch-wide blade machine was 4500 feet per minute. The crepe ratio was 1.27 or 27 percent. The resulting tissue was folded together and calendared lightly with two steel rolls at 10 pounds per linear inch. The product of two strata had the driest side folded to the outside. When it was converted, the finished basis weight of the two-layer bath tissue at the standard TAPPI temperature and humidity was 22.0 pounds per 2880 square feet.

Claims (9)

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

1. A method for treating a papermaking supply comprising: (a) adding a softening agent to a first papermaking supply comprising primarily short papermaking fibers; (b) mixing the first paper supply with a second paper supply comprising primarily long papermaking fibers; and (c) adding to the mixed feed one or more reinforcing agents selected from the group consisting of dry strength agents and wet strength agents.

2. The method as claimed in clause 1, characterized in that the smoothing agent is a quaternary imidazoline compound.

3. The method as claimed in clause 1, characterized in that the first supply for making paper consists essentially of short papermaking fibers.

4. The method as claimed in clause 1, characterized in that the second supply for making paper consists essentially of soft wood fibers.

5. The method as claimed in clause 1, characterized in that a wet strength agent and a dry strength agent are added in sequence to the mixed supply.

6. The method as claimed in clause 5, characterized in that the strength agent having a lower charge density is added to the first mixture.

7. The method as claimed in clause 6, characterized in that the dry strength agent is added to the mixed supply before the wet strength agent is added to the mixed supply.

8. The method as claimed in clause 7, characterized in that the dry strength agent is an amphoteric starch.

9. The method as claimed in clause 8, characterized in that the wet strength agent is glyoxalated polyacrylamide. SUMMARY An efficient and effective method for treating tissue supply to make soft tissues involves adding a smoothing agent to a first supply to make paper of short fibers, such as eucalyptus fibers. A second supply for making long fiber paper, such as softwood fibers, is mixed with the supply of short fibers. Then, wet strength agents and / or dry strength agents are added to the mixed supply. The treated supply is then fed to the head box and processed into a soft tissue in any suitable manner.