Patent Application
20100184902
The invention is in the field of polyamide-epihalohydrin creping adhesives.
In the manufacture of tissue and towel products, a common step is creping the product to provide desired aesthetic and performance properties to the product. Creping is commonly used in both the conventional wet press and through air drying processes. Many of the aesthetic properties of tissue and towel products rely more upon the perceptions of the consumer than on properties that can be measured quantitatively. Such things as softness, and perceived bulk are not easily quantified, but have significant impacts on consumer acceptance. However both softness and bulk are dramatically improved by the creping process. Creping is generally accomplished by mechanically foreshortening or compacting paper in the machine direction with a flexible blade, a so-called doctor blade, against a Yankee dryer in an on-machine operation. This blade is also sometimes referred to as a creping blade or simply a creper. By breaking a significant number of interfiber bonds and slowing down the speeds between the Yankee and the reel, creping increases the basis weight (mass per unit area) of the paper and effects significant changes in many physical properties, particularly when measured in the machine direction. Creping thus enhances bulk and stretch, and increases the perceived softness of the resulting product.
A Yankee dryer is a large diameter, generally 8-20 foot drum which is designed to be pressurized with steam to provide a hot surface for completing the drying of papermaking webs at the end of the papermaking process. The paper web which is first formed on a foraminiferous forming carrier, such as a Fourdrinier wire, where it is freed of the copious water needed to disperse the fibrous slurry, then is usually transferred to a felt or fabric either for dewatering in a press section where de-watering is continued by mechanically compacting the paper or by some other water removal method such as through-drying with hot air, before finally being transferred in the semi-dry condition to the surface of the Yankee for the drying to be completed. Before transferring to the Yankee dryer, an adhesive is applied directly to the Yankee dryer.
Obtaining and maintaining adhesion of tissue and towel products to Yankee dryers is an important factor in determining crepe quality. Re-wetability, doctorability, and the level of adhesion are important properties of a creping adhesive. The ability of the adhesive to be rewet on the surface of the dryer helps to prevent buildup on the drum and on the creping blade. Inadequate adhesion results in poor creping, sheet floating, and poor sheet handling whereas excessive adhesion may result in crepe blade picking, sheet plugging behind the crepe blade, and sheet breaks due to excessive tension. Traditionally, creping adhesives alone or in combination with release agents and/or modifiers have been applied to the surface of the dryer in order to provide the appropriate adhesion to produce the desired crepe. The adhesive coating also serves the purpose of protecting the Yankee dryer and creping blade surfaces from excessive wear. In this role, the coating agents provide improved runnability of the tissue machine. As creping blades wear, they must be replaced with new ones. This replacement process represents a significant source of tissue machine downtime, or lost production.
Various types of creping adhesives have been used to adhere fibrous webs to dryer surfaces such as Yankee dryers. Some examples of prior art creping adhesives rely upon combinations of self-crosslinkable soft polymers with a non-film forming hard polymer emulsion (U.S. Pat. No. 4,886,579). Some others involve thermoset resins (U.S. Pat. Nos. 4,528,316 and 4,501,640). The ability to control the mechanical properties of the polymers, as well as the adhesion and release of the fibrous web from the Yankee dryer, is limited when using these types of creping adhesives. A variety of proposals have been made in an attempt to improve the properties of certain adhesives. For example, U.S. Pat. No. 5,370,773 describes the use of a phosphate surfactant with an adhesive composition that includes a non-self-crosslinkable polymer or oligomer having functional groups that can be ionic crosslinked using a high valence metallic crosslinking agent. U.S. Pat. No. 6,280,571 describes the use of an acid selected from hypophosphorous acid, phosphorous acid, hypodiphosphoric acid, diphosphorous acid, hypophosphoric acid, pyrophosphorous acid, or their salts, to stabilize a polymer selected from polyamidoamine-epichlorohydrin resin, polyamine-epichlorohydrin resin, reaction products of epichlorohydrin with highly branched polyamidoamines and polyvinyl alcohol.
Poly(aminoamide)-epihalohydrin type creping adhesives (also referred to as PAE resins), exemplified by poly(aminoamide)-epichlorohydrin, provide a class of resins distinct from the above polymers. Resins of this type have been used for many years in paper making and are described in U.S. Pat. Nos. 2,926,116 and 3,058,873, the disclosure of which are incorporated herein by reference. They are generally prepared by reacting an epihalohydrin and a polyamide containing secondary or tertiary amine groups, followed by stabilizing the reaction products by acidification with sulfuric or hydrochloric acid. They have very useful properties when freshly applied in runnability and initial re-wetability and doctorability. However, a problem with the poly(aminoamide)-epihalohydrin type creping adhesives is the phenomenon of coating buildup. This problem is evidenced by high spots in the coating on the Yankee and/or build up on the rear surface of the blade, particularly along the edges or corners of the creping blade, which can cause chattering, or bouncing of the blade. Ultimately, portions of the sheet may travel underneath the creping blade, causing picks or holes in the sheet leading to sheet breaks and machine downtime. Commonly water sprays have been used to remove or minimize adhesive buildup, but eventually may prove inadequate.
In order to produce a bulky and soft tissue with conventional wet press paper machines, the paper sheet is preferably dried to very low moisture levels (e.g., less than 3%), thus economic considerations often require an adhesive that will perform at very high sheet temperatures. But the foregoing problems with the poly(aminoamide)-epihalohydrin type creping adhesives can be particularly severe at higher temperatures.
Another difficulty with PAE resins is the adverse effect of sizing agents such as alkyl ketene dimer (AKD), alkylene ketene dimers and alkylene succinic anhydride (ASA) on the creping process. These sizing agents, particularly AKD, are sometimes added to paper webs to impart moisture resistance properties for some special grades of paper. However, AKD performs as a strong release on the Yankee. When AKD is added to the furnish in the wet end, most of the PAE adhesives have issues in generating sufficient adhesion between the Yankee surface and the sheet often resulting in poor creping and sheet handling issues or limiting the amount of these sizing agents that can be incorporated into the sheet if good creping is desired.
The present invention provides an improved method for manufacturing tissue using an improved poly(aminoamide)-epihalohydrin creping adhesive that is re-wetable, and that reduces buildup, or facilitates its removal, with attendant significant decrease in downtime and maintenance. Moreover, we have discovered that, in one particularly demanding application, the creping adhesive of the present invention provides a particularly impressive improvement. When tissue substrates, such as might be used in napkin basestock, are treated with sizing agents such as AKD, they can become particularly difficult to crepe. We have found that the creping adhesives of the present invention provide dramatically improved creping performance when used with AKD treated base sheets, such as are disclosed in U.S. application Ser. No. 10/995,457 filed Nov. 22, 2004 entitled “Multi-Ply Paper Product With Moisture Strike Through Resistance And Method Of Making The Same.”
The adhesive is prepared in the usual manner of preparing poly(aminoamide)-epihalohydrin creping adhesives with a change in one step, a change that appears to be simple, yet which, very surprisingly, results in essentially substantial alleviation of the problems of adhesive buildup. This is accomplished at the end of the polymerization reaction, at the quenching step, by replacing the usual sulfuric acid or hydrochloric acid with phosphoric acid.
More particularly, a poly(aminoamide)-epihalohydrin creping adhesive is prepared by first reacting a dibasic carboxylic acid, or its ester, half-ester, or anhydride derivative, with a polyalkylene polyamine, preferably in aqueous solution, under conditions suitable to produce a water soluble polyamide. The water-soluble polyamide is then reacted with an epihalohydrin until substantially fully cross-linked, and stabilized by acidification with phosphoric acid at the end of the polymerization reaction to form the water-soluble cationic polyamide-epihalohydrin resin of this invention. The epihalohydrin used in preparing the phosphoric acid stabilized poly(aminoamide)-epihalohydrin resin is preferably epichlorohydrin, to prepare a phosphoric acid stabilized poly(aminoamide)-epichlorohydrin resin.
The manufacturing method includes applying a creping adhesive to the surface of a Yankee dryer, while using a felt or carrier fabric to apply a preformed nascent fibrous paper web to the creping adhesive on the surface of the dryer, thereafter removing the paper web from the Yankee dryer by use of a creping blade and winding the dried paper onto a roll. The method may optionally also include applying water or a modifier, e.g., by spraying, to the exposed edges of the Yankee drum directed principally against the drum surfaces not contacted by the felt or carrier fabric, to control buildup.
In this particular arrangement, transfer and impression felt carrier fabric designated at 1 carries the nascent, dewatered paper web 2 around turning pressure roll 3 to the nip between the pressure roll 3 and Yankee dryer drum 4. The fabric, web and dryer move in the directions indicated by the arrows. The entry of the web to the dryer is well around the drum 4 from a creping doctor blade 5 which, as schematically indicated at 6, crepes the traveling web from the dryer. Creped web 7 exiting from the dryer is wound into a soft creped tissue reel 8. To adhere nascent web 2 to the surface of the dryer, spray boom 9 sprays adhesive 10 directly onto the outer surface of the internally heated Yankee drum 4. Additionally, hot air flow is applied to the adhered paper web by a hood 11. Suitable apparatus for use with the present invention are disclosed in U.S. Pat. Nos. 4,304,625 and 4,064,213, which are hereby incorporated by reference.
The apparatus can be configured so that the felt or carrier fabric 1 is of a dimension sufficient to entirely cover the surface of the drum 4 contacted by the doctor blade 5. If it not so dimensioned, which is typically the case, then in accordance with a preferred embodiment of the invention, possible in substantial part by the superior re-wetability of the adhesive obtained by the use of a phosphoric acid quenching step, water or modifier is applied to the exposed edge(s). An edge spray 12 can be used to apply a water spray 13 to the exposed side edge or edges of the drum, i.e., on the drive side and/or operator side of the adhesive coated Yankee drum, as the case may be.
This illustration does not incorporate all the possible configurations used in presenting a nascent web to a Yankee dryer. It is used only to describe how the adhesive of the present invention can be used to promote adhesion and thereby influence the crepe of the product. The present invention can be used with all other known processes that rely upon creping the web from a creping surface. In the same manner, the method of application of the adhesive to the surface of the dryer or the web is not restricted to spray applications, although these are generally the most expedient for adhesive application.
The present invention is useful for the preparation of fibrous webs which are creped to increase the thickness of the web and to provide texture to the web. The invention is particularly useful in the preparation of final products such as facial tissue, napkins, bath tissue, paper towels and the like. The fibrous web can be formed from various types of wood pulp based fibers which are used to make the above products such as hardwood kraft fibers, softwood kraft fibers, hardwood sulfite fibers, softwood sulfite fibers, high yield fibers such as chemi-thermo-mechanical pulps, thermomechanical pulps, or refiner mechanical pulps and the like. Furnishes used may also contain or be totally comprised of recycled fibers (i.e., secondary fibers). The fibrous web, prior to application to the Yankee dryer, usually has a water content of 40 to 80 wt. %, more preferably 50 to 70 wt. %. At the creping stage, the fibrous web usually has a water content of less than 7 wt. %, preferably less than 5 wt. %. The final product, after creping and drying, has a basis weight of 7 to 80 pounds per ream.
The creping operation itself can be conducted under conventional conditions except that the creping adhesive of the present invention is substituted for a conventional creping adhesive.
In accordance with this invention, an improved poly(aminoamide)-epihalohydrin creping adhesive that is re-wetable and facilitates water spray removal of buildup so as to lengthen the life of the creping blades, with attendant significant decrease in downtime and maintenance. The adhesive is prepared in the usual manner of preparing poly(aminoamide)-epihalohydrin creping adhesives with a change in one step, a change that appears to be simple, yet which, very surprisingly, results in substantial alleviation of the problems of adhesive buildup; and, in many cases, makes it possible for the creping package to provide an increased level of adhesion producing a softer more flexible creped sheet as reflected by a decreased tensile modulus. This change is accomplished at the end of the polymerization reaction, at the quenching step, by replacing the usual sulfuric acid or hydrochloric acid with phosphoric acid.
More particularly, a poly(aminoamide)-epihalohydrin creping adhesive is prepared by first reacting a dibasic carboxylic acid, or its ester, half-ester, or anhydride derivative, with a polyalkylene polyamine, preferably in aqueous solution, under conditions suitable to produce a water soluble polyamide. To form the water-soluble cationic polyamide-epihalohydrin resin of this invention, the water-soluble polyamide is then reacted with an epihalohydrin, and stabilized by acidification with phosphoric acid at the end of the polymerization reaction, preferably with 85% ortho-phosphoric acid, 0.1-2.0 molar equivalent based on polymer content to a pH of 3.5-7.0, most preferably to 7.0. Acidification quenches the epihalohydrin cross-linking reaction, in which molecular weight is built, to prevent gelation. The acid salts of the remaining amine groups in the polymer backbone are less reactive toward the azetidinium rings than were the free amines at the higher pH before quenching.
The extent of cross-linking, whether partial or fully cross-linked, can be controlled with reaction conditions. For fully cross-linked polymer, epihalohydrin is added in aliquots to base polymer and reacted at high temperature at each stage until there is viscosity “burn-out”, with no more advancement. The polymer is then acidified, ensuring that the difunctional epihalohydrin has reacted completely with prepolymer. The correct viscosity end point is determined by carefully controlling the amount of epihalohydrin added. For partial cross-linking, a small excess of epihalohydrin is added (compared to fully cross-linked, either in aliquots or at once) and reacted to a pre-determined viscosity end point before the reaction burns out. The viscosity advancement is halted at the determined end point by addition of acid. This ensures that the epihalohydrin is not completely cross-linked and that some residual pendant chlorohydrin remains.
We can distinguish differences in the degree of cross-linking with total and ionic chloride titrations. C-13 NMR can detect pendant chlorohydrin present in partially cross-linked resins. Also, the viscosity of the partially cross-linked material can be made to advance with heat, and can change during storage while fully cross-linked materials are far more stable over time.
The polyalkylene polyamine preferably has the repeating units
—NH(CnHnHN)x—CORCO—
where n and x are each 2 or more and R is the divalent hydrocarbon radical of the dibasic carboxylic acid or its derivative containing from about 3-10 carbon atoms. The polyamide secondary amine groups are preferably derived from a polyalkylene polyamine for example polyethylene polyamides, polypropylene polyamines or polybutylene polyamines and the like, with diethylenetriamine being preferred.
Poly(aminoamide)-epihalohydrin resins undergo at least two types of reactions that contribute to wet strength. One reaction involves the reaction of an azetidinium group in one molecule with an unreacted secondary amine group in another molecule to produce a cross-link between the two molecules. In the second reaction at least two azetidinium groups on a single resin molecule react with carboxyl groups on two different fibers to produce an interfiber cross-link. It is also known to utilize promoters such as carboxymethyl cellulose to enhance the performance of these materials in paper products.
The dicarboxylic acid is one of the saturated aliphatic dibasic carboxylic acids containing from about 3 to about 10 carbon atoms. Examples are malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic, and sebacic dicarboxylic acids, and mixtures thereof. Examples of ester, half-ester, or anhydride derivatives of adipoc acid are dimethyl adipate, diethyl adipate, adipic acid monomethyl ester, adipic acid monoethyl ester, and adipic acid anhydride. Corresponding esters, half esters, and anhydrides of each of the listed dibasic acids are further examples. Blends of two or more of derivatives of dibasic carboxylic acids may also be used, as well as blends of one or more derivatives of dibasic carboxylic acids with dibasic acids. Dicarboxylic acids containing from 4 to 8 carbon atoms, and their derivatives, are preferred, with adipic acid (hexanedioic acid) being most preferred. Preferably the mole ratio of polyalkylene to dibasic carboxylic acid, or equivalent amount of its derivative, is from about 0.8 to 1 to about 1.5 to 1. The mole ratio of epihalohydrin to secondary amine groups in the polyamide is preferably from about 0.01 to 1 to about 2 to 1.
The epihalohydrin used in preparing the poly(aminoamide)-epihalohydrin resin is preferably epichlorohydrin, to prepare a phosphoric acid stabilized poly(aminoamide)-epichlorohydrin resin.
Finally, as a last step, the poly(aminoamide)-epihalohydrin resin is stabilized by acidification to a pH of 3.5-7.0, preferably to 7.0, at the end of the polymerization reaction. In accordance with this invention, in place of the usual acidification with sulfuric acid, or in some cases with hydrochloric acid, the poly(aminoamide)-epihalohydrin resin is stabilized with phoshoric acid. Preferably, it is stabilized with 85% ortho-phosphoric acid, 0.1-2.0 molar equivalent based on polymer content phosphoric acid, to a pH of 3.5-7.0, most preferably to 7.0.
The following Examples are illustrative of, but are not to be construed as limiting, the invention embodied therein.
A 2.5 l (2.5 liter) reactor equipped with hot oil bath, stainless steel stirring shaft, agitator, thermometer and a reflux condenser with nitrogen inlet. The reactor condenser was configured for reflux. 990.2242 grams of liquid DETA (diethylenetriamine) were loaded to the reactor at 25° C. and atmospheric pressure. To this was added 1446.0327 grams of solid adipic acid over a 30 minute period in six equal portions with agitation and at atmospheric pressure. The reaction was exothermal, raising the temperature from 40° C. to about 147° C. during the course of adipic acid additions. After the adipic acid load was complete, the reactor condenser was switched from reflux to distillation and heat was applied to raise the reaction temperature to a maximum of 165° C. Water began to distill from the reaction mixture at about 160° C., and heat was supplied to slowly ramp-up the reaction temperature to a maximum temperature of 165° C. Once the desired degree of polymerization was obtained as determined by check-cut viscosity tests (i.e., comparing the viscosity of small samples taken during this polymerization to the viscosity of a sample having a known degree of polymerization obtained during a previous synthesis) the condenser was then switched back to reflux, and fresh water was gradually loaded to the molten prepolymer at 158° C. and atmospheric pressure. The addition of water brought the prepolymer to about 66% concentration and reduced the reaction temperature to about 100° C. The prepolymer was then diluted to 45% non-volatiles, and the viscosity was 290 cP by Brookfield.
To a 5 l glass reactor equipped with stirring shaft, stainless steel cooling coils, heating mantle, reflux condenser, pH/temperature probe, and equal pressure addition funnel was added 3295.71 grams of polyamide prepolymer from Example 1. To this was added 1372.32 grams of water. The mixture was then heated to 40° C. 23.24 grams of epichlorohydrin was added via addition funnel to the heated mixture in 2 aliquots over a 2 hour period. After addition of the first aliquot of epichlorohydrin the reaction was heated to 90° C. The viscosity of the mixture was monitored with Gardner-Holdt bubble tubes every ten minutes over the 2 hour period. The reaction mixture advanced to a maximum of GH Gardner-Holdt bubble tube viscosity. When the viscosity ceased to advance further with continuous heating at 90° C., the reaction mixture was cooled to 25° C. and 407 grams of 85% phosphoric acid was slowly added to adjust the pH of the mixture to 7.0. Water was added to dilute the finished polymer mixture to 35% non-volatile content, with a Brookfield viscosity of 150 cP and pH 7.0
To a 2.5 l glass reactor equipped with stirring shaft, stainless steel cooling coils, heating mantle, reflux condenser, pH/temperature probe, and equal pressure addition funnel was added 1647.86 grams of polyamide prepolymer from Example 1. To this was added 686.16 grams of water. The mixture was then heated to 40° C. 14.32 grams of epichlorohydrin, was added via addition funnel to the heated mixture in 3 aliquots over a 2 hour period. After addition of the first aliquot of epichlorohydrin the reaction was heated to 90° C. The viscosity of the mixture was monitored with Gardner-Holdt bubble tubes every ten minutes over the 2 hour period. The reaction mixture advanced to a maximum of GGH Gardner-Holdt bubble tube viscosity. When the viscosity ceased to advance further with continuous heating at 90° C., the reaction mixture was cooled to 25° C. and 116.52 grams of 93% sulfuric acid was slowly added to adjust the pH of the mixture to 7.0. Water was added to dilute the finished polymer mixture to 35% non-volatile content, with a Brookfield viscosity of 130 cP and pH 7.0.
Physical properties of the formulations of Example 2 (denoted 378G55) and Example 3 (denoted 315D54), are shown in Table 1. The materials were analyzed for molecular weight based on poly(vinyl pyridine) standards. To determine weight % solids, weighed portions of each sample were dried for 4 hours at 105° C. in a weighed aluminum pan. The dried samples were cooled and weighed again to determine water loss. For C-13 NMR analysis, 2.8 ml of the adhesive was combined with 0.4 ml of D2O and TSP in an NMR tube. Quantitative C-13 and P-31 NMR spectra were taken at 25° C. on a Varian UNITY® 300 MHz NMR using standard suppressed nuclear Overhauser conditions. For P-31 NMR analysis, the samples were first screened for the presence of phosphorus by obtaining a broad band spectrum, the samples that contained phosphorus were then quantitatively analyzed after they were spiked with a known amount of trimethyl phosphate. Corresponding properties of four typical commercial poly(aminoamide)-epichlorohydrin adhesives designated in Table 1 as PAE H, PAE CT, PAE R, AND PAE C are included for comparison.
In addition to the advantages in re-wetability provided by phosphoric acid stabilization, the data in Table 1 demonstrates that because 378G55 is fully cross-linked, it has developed quite a bit of both dry and wet adhesion. Moreover, it has relatively lower molecular weight than the typical commercial PAE adhesives (i.e., ⅙ or less in Mz), it has minimal or no charge density, and nondetectable residual azetidinium. As a result, it is not subject to thermosetting and therefore is much softer than commercial PAE adhesives when the creping temperature is high. The beneficial effect of cross-linking on dry and wet adhesion of the is shown by the dry and wet tack results in Table 2, in which the formulations of Examples 2 (378G55) and 3 (315D54) are compared to partially cross-linked adhesives. It is evident that both high and low molecular weight partially cross-linked adhesives did not perform as well as the fully cross-linked adhesives.
While both low molecular weight fully cross-linked phosphoric acid quenched adhesive had good wet tack values, the phosphoric acid based adhesive displayed significantly better dry tack values.
The formulations of Examples 2 and 3 were used in runs preparing tissue on a Yankee drum with apparatus in which the carrier fabric did not extend to the entire drive and operator sides, leaving drive and operator edges exposed. Referring to
Differences between the two adhesives on key physical properties are also seen in the table of
Referring to Samples 18-1 through 21-1 of
To demonstrate the superior performance obtained with the creping adhesives of the present invention (Unicrepe PAE), a series of creping trials were performed using four different commercially available conventional creping adhesives based on PAE or PVOH at an add on rate of 4 lbs. of creping adhesive per ton of paper passed over Yankee. Creping was attempted with two base sheets: a conventional wet strength base sheet for napkin stock which was substantially free of any release/barrier material, and a barrier napkin base sheets comprising alkenyl ketene dimer in the amounts indicated. All of the creping adhesives were satisfactory with a conventional base sheet. Only the creping adhesive of the present invention was suitable for use with base sheets containing 3.25 lbs of alkenyl ketene dimer per ton of tissue. Referring to Table 3, as indicated in the comments column, the conventional creping adhesives resulted in poor creping and unstable sheets. It is believed that this result can be attributed to the very low creping force observed with each of conventional adhesives. Throughout these examples, a 5° blade bevel was used.
This application is a division of prior U.S. patent application Ser. No. 11/081,387, filed Mar. 15, 2005, the priority of which is hereby claimed and its disclosure incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11081387 | Mar 2005 | US |
| Child | 12749586 | US |
