US20030127210A1

US20030127210A1 - Sizing paper by wet-end addition of water dispersibility polyester

Info

Publication number: US20030127210A1
Application number: US10/331,577
Authority: US
Inventors: Pierre Pelletier; Timothy Wang
Original assignee: Individual
Current assignee: Nouryon Chemicals LLC
Priority date: 2002-01-04
Filing date: 2002-12-30
Publication date: 2003-07-10

Abstract

Water dispersible polyesters are used to treat and size paper by applying them at the wet-end of the paper process. The water dispersible polyesters can be used alone or with other chemicals typically used to treat or size paper in order to increase the paper's dry strength, wet strength, stiffness, water repellency, water resistance, and sizing properties. The water dispersible polyester is made with recycled polyethylene terephthalate or fresh glycol and polyacid or with virgin polyethylene terephthalate. The polyester sized paper is repulpable and recyclable. If the polyester size is used with traditional wet-strength resins, such as Kymene, the polyester-Kymene mixture will be repulpable and recyclable, whereas Kymene by itself is not easily repulpable nor recyclable in a paper mill process.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from provisional patent application Serial No. 60/345,045, filed Jan. 4, 2002 having the same title and inventors.[0001]

FIELD OF THE INVENTION

This invention relates generally to treating and sizing paper at the wet end of the paper making process. Particularly, this invention relates to the use of recycled, water dispersible polyesters to make an improved, repulpable and recyclable paper product.

BACKGROUND OF THE INVENTION

In the paper industry, paper strength may be improved by sizing with materials, such as starch, modified starch, polyvinyl alcohol, polyacrylamide, alkyl succinic anhydride (ASA), alkyl ketene dimer (AKD) and carboxy methyl cellulose. These materials give the paper better strength, but if the paper is used in high humidity or wet conditions, the paper can still lose from 80 to 98% of its dry strength. Sometimes certain polymers are used to improve the wet or high humidity strength, such as Kymene, (Hercules, Inc.'s brand of poly(aminoamide)-epichlorohydrin)polyacrylate and SBR (styrene-butadiner rubber) but these chemicals make the paper and paperboard non-repulpable and non-recyclable because, when they are repulped according to currently used, standard repulping conditions, they will leave sticky and other undesirable deposits on the dryer felt or screen as the paper is being formed or will keep the treated paper from breaking up into individual fibers so that a new sheet can be formed. These non-recyclable polymers also cause environmental problems since they have to be disposed of in land fills thereby wasting non-renewable resources.

Wax such as paraffin wax is another material which is used to make paper water and humidity resistant. Instead of being added to the wet end of the paper making process, wax is applied to the converted paper product which is then usually folded into a carton or corrugated box. The presence of wax on the paper also makes it non-recyclable and non-repulpable. Accordingly, a general object of the present invention is to provide an improvement in the paper making process that will produce a recyclable water resistant paper product.

In U.S. Pat. No. 4,210,685 granted to Robert B. Login, et al. on Jul. 1, 1980 and in U.S. Pat. No. 4,263,094 granted on Apr. 21, 1981 to the same inventor, paper or paperboard is surface sized with an aqueous dispersion of a combination of degradable starch or a starch derivative and a branched-chain, water dispersible polyester condensation product. However, these patents describe a surface-sized product whereas another object of the present invention is to provide an internally sized product.

In a paper under the topic “Opportunities in Wet-End Chemistry: Feature Essay, Posted October 2001,” an essay entitled “Good Chemistry-Looking Towards the Future of Paper Making Additives” by Martin A. Hubble of North Carolina State University, wet strength agents are noted, particularly, formaldehydes used for acidic papermaking. A problem in biodegradability has been to make biodegradable paper with enough wet strength to withstand repulping. Also, for internal sizing, rosin sizing is mentioned. Another object of the present invention is to not only provide an internally sized product but also one that can withstand repulping.

Another use of polyesters as a size is described in U.S. Pat. No. 3,931,422 which issued on Jan. 6, 1976 to Mark E. Bateman, et al. However, the size in this instance is applied on the surface, not internally, and the size only enhances surface properties whereas an object of this invention is to improve many of the properties of the paper.

Internal sizing of paper with ethylene/acrylic acid copolymer and similar polymers is described in U.S. Pat. No. 3,899,389 which issued on Apr. 17, 1975 to Walter Lee Vaughn et al. but enhanced wet strength and repulpability do not appear to be feature disclosed in the patent.

The development of water repellant and water resistant water-dispersible polyesters is described in U.S. Pat. Nos. 5,858,551 issued on Jan. 12, 1999 and 5,958,601 issued Sep. 28,1999 both to Keith Salsman. The disclosure in these patents is incorporated herein by reference. The resins in the Salsman patents can be made with recycled polyethylene terephthalate (PET), with virgin PET, or with fresh glycol and phthalate acid or anhydride monomers. The resins consist of three different chemical segments: (1) polyethylene terephthalate, at 10-90% by weight of the total resin; (2) organo-functional groups, chemically grafted pendant to the PET backbone or copolymerized as block copolymers, at 2-60% by weight of the total resin; and, (3) a hydrophilic group that makes the polyester water dispersible, at 1-30% by weight of the total resin. Heretofore, commercially, these resins have been used principally as paper coatings for water resistance or water repellency to replace the wax coating on boxes and other paper products that are used in contact with water or under high humidity conditions. A still further object of the invention is to use such polyesters to enhance not only surface moisture resistance but to improve the moisture resistance of the total paper product.

The terms used herein regarding paper making will be well understood by those skilled in the art who will readily appreciate this invention upon reading the Summary of Invention and Detailed Description that follow:

SUMMARY OF THE INVENTION

In paper coating processes, resins are coated onto the paper surface using one of several different methods. The paper strength under dry or wet conditions may or may not be increased since the resin is only present on the paper surface. Also, water or moisture can still be absorbed into paper through the un-coated side of the paper or at pinholes inn the coating. However, it has been surprisingly discovered in this invention that by adding the water-dispersible polyesters of the types mentioned above to the pulp while the paper is being made and ensuring that the polyester is evenly dispersed into the paper mixture, the polyester resin will function as an internal size and/or wet strength additive so that the resulting paper product is re-pulpable. Thus, in one aspect, the present invention is a process for producing an improved, sized recyclable paper product by adding a water dispersible polyester to the pulp mixture at the wet end of a paper making process.

In another aspect, the present invention is a paper product having an internal size comprising a water dispersible polyester and in yet another aspect the invention is a paper product having both internal and external sizing of a water dispersible polyester.

More specifically, in one embodiment of the invention designated the “wet end” process, the water-dispersible polyester may be added to the pulp slurry at the pulper or blend chest, or to the low consistency stock at any location including but not limited to the machine chest and up through the head box before paper formation. These polyester resins can also be used as a surface size, added in the size press or water-box, where the sizing resins penetrate into the formed, but still wet paper sheet. With regard to these two different addition points, the wet end is the preferred addition point since it is a more efficient way to use the polyester resins, because a more even distribution of the resins through the sheet can be obtained at this addition point.

As an internal size, applied at the wet-end, the water-dispersible polyester is deposited on the fibers in the pulp. As the fibers with polyester resin deposited thereon begins to form paper, the polyester resin bonds the fibers together. This bonding is in addition to the weaker hydrogen bonds, which under normal paper formation, are the only forces to hold the fibers together for un-sized or starch-sized paper. With the polyester resin bonds, the paper has improved dry and wet strength, greater stiffness, improved water and high humidity resistance, lower porosity, and non-wicking properties. The paper sized by the polyester resins in this manner is glueable with normal starch or modified starch glues and can be coated with similar water-dispersible polyesters or other coating polymers.

The water dispersible polyesters can be used as described above or with other resins. Alkyl ketene dimer (AKD) and alkyl succinic anhydride (ASA) are resins which are widely used as internal or surface sizing materials. The present invention includes the use of water-dispersible polyesters in conjunction with these sizing materials to give the paper the improved properties described above. Wet strength resins, such as Kymene, an epoxy-based material, are widely used to improve the paper wet strength, but these materials make the paper non-repulpable and non-recyclable. In the present invention, the water-dispersible polyester is used with these other materials, not only to enhance the paper wet strength, but also to make the paper repulpable and recyclable.

This invention has broad utility with cellulosic fibers generally and across all types of fiber formed paper, including, but not limited to, bleached and unbleached Kraft fibers, recycled fibers, hard wood and soft wood fibers, cotton fiber, and non-wood fibers.

DESCRIPTION OF THE DRAWINGS

In the drawings which are appended hereto and made a part of this disclosure by way of illustration and not by way of limitation, [0017]
FIG. 1 is a flow diagram for one embodiment of the present invention showing the steps for a neutral or basic process; and, [0018]
FIG. 2 is a flow diagram for another embodiment of the present invention showing the steps for an acid or rosin based process. [0019]

DETAILED DESCRIPTION

The preferred polyester resins are made as described in the above mentioned U.S. Pat. Nos. 5,858,551 and 5,958,601. The water-dispersible polyester resin comprises three different constituents: (1) polyethylene terephthalate backbone; (2) short or long chain hydrophilic or hydrophobic alkyl or aromatic groups; and, (3) hydrophilic end groups. The resin molecular weight may be between 1,000 and 100,000, but 2,000 to 10,000 is preferred. The polyethylene terephthalate backbone is 10% to 90% of the final polymer, the functional hydrophilic or hydrophobic alkyl or aromatic section is 2% to 60%, and hydrophilic groups are at 1% to 30%. The selection of either hydrophobic or hydrophilic resin depends upon the characteristics to be imparted to the paper, e.g., the hydrophobic polyester is used to make the paper water repellant, water resistant, and to increase paper strength whereas the hydrophillic polyester is used only to increase paper strength. [0020]
The resin can be a solid powder or liquid. The solid powder is dispersed into hot water with the aid of a dispersion chemical. The liquid resin is directly dispersed into water with agitation. The dispersed polyester solution may be between 5% and 45% solids, but 20%-35% is preferred. The dispersed solution may vary from a transparent solution to a slightly, white emulsion, depending on the solids level and the dispersion conditions. [0021]
As mentioned above, the water-dispersible polyester products can size paper by either wet end addition or by adding it later in the paper making process at the size press or water box, though the wet end process is more efficient and is preferred. Both FIGS. 1 and 2 attached hereto illustrate the wet end addition processes. References to “pulper”, “machine chest”, “stuff box”, “head box”, etc. may be made hereinafter and are shown in the flow diagrams of FIGS. 1 and 2. The two flow diagrams also show the difference in an acid/rosin system (FIG. 1) and in a neutral or basic system (FIG. 2). Both flow diagrams illustrate steps in the paper making process prior to the formation of paper. In the acid system, FIG. 1, when using EvCote® PWR-25 water dispersible polyester (see Example 1) on the wet end of an acid system, typically rosin size is used as the setting resin. First, the rosin should be pure rosin, modified rosin or neutral rosin. Alum is generally chosen to set the size to the fiber, and then the mixture is thermo set in the dryer section of the machine. [0022]
The ideal pH for maximum charge value of alum is 4.8, and the ideal total acidity should be at 50 ppm or less, but greater than 10 ppm. As the total acidity of the wet end rises, there is less disassociation of the alumina ions with the sulfate ions, resulting in lessening charge value on the alumina ions. As the total acidity of the system gets closer to zero (0), the alumina ions associate with the OH groups to form aluminum hydroxide, resulting again in the loss of positive charge. Less alumina charge results in less water dispersible polyester and rosin size being attached to the fiber and less sizing efficiency. [0023]
If PWR-25 polyester is added to the thick stock (at a rate of from 25 to 30 wet pounds/ton), with normal rosin size added to an acid paper making process, non-wicking and water hold out will happen, as opposed to hold out alone with rosin size. To determine how much the size should be reduced to achieve non-wicking, machine trial runs must be performed, preferably starting with about half of the sizing. [0024]
The PWR-25 should be added to the pulper, the alum added after refining, size to the stuff box, and retention aid after the selectifier screen. Care should be taken to monitor the calcium level of the water, as high calcium levels (over 200 ppm of calcium hardness) interfere with sizing efficiency. For maximum performance, the sheet should get to at least 225° F. in the dryer section of the machine. [0025]
In the neutral system of FIG. 2, a pH of 6.5 to 6.8 is preferred though pH's as high as 7.5-8.0 can be used with less efficiency. Typically AKD is used as the setting resin, not rosin. PAC (polyaluminum chloride) or PASS (polyaluminum sodium sulphate) is the product to use for best alumina charge values instead of alum. Otherwise, the application and use is similar to the Acid System above. [0026]
In the wet-end addition process, called internal sizing, the polyester solution is pumped into the cellulosic pulp slurry at the pulper (Batch Pulper of FIGS. 1 and 2) or blend chest, or to the low consistency stock at any location including but not limited to the machine chest and up through the head box before the paper formation. However, the preferred addition point is at the pulper. The pulp solids level at the pulper can be 0.1% to 15%, but 4% to 6% is preferred. The pH in the pulp can be 2 to 10, but 4 to 7 is preferred. If the pH is not within the desired range, it can be adjusted either before or after the polyester solution addition, but adjusting pH first is preferred. Charge leveling agents, such as poly-aluminum chloride, alum, polyethylene imines, or other such agents, can be added to adjust the charge level as is needed. The charge level can be from −3 to +3, but −0.5 to +0.5 is preferred. [0027]
The polyester addition can be from 0.2 dry pounds per dry ton of cellulosic fiber to 600 dry pounds per ton of fiber. Depending on the final requirements of the paper, 5 to 200 pounds per ton of fiber is the preferred range. Other chemicals, such as AKD, ASA, Kymene, dye or pigment, filler, wetting agent, and polymer, can be added before, after or with the water-dispersible polyester solution. The polyester resin does not have a negative effect on the other constituent's function, but promotes their functionality, such as wet and dry strength, water adsorption resistance, sizing properties, chemical retention, and dye hold out. [0028]
If the polyester resins of this invention are to be used in a standard sizing process, the water-dispersible polyester solution is directly pumped into the size press or water box as a solution of 1% to 30% solids, though 4%-15% solids is preferred. The sizing process disclosed herein includes the prior art size press on the paper machine, the water box before the final drying cans, a hydro-sizer located between the head box and the dry end of the drying table, and any other equipment that will apply the polyester chemicals used in this invention intimately onto the fibers of the sheet, but the size press is preferred. All of these sizing processes are referred to as surface sizing in this disclosure. The size press can operate in the range of 0 to 100 psi. The polyester solution may be used as a sizing solution by itself or mixed with other constituents, such as starch, latex, and fillers. [0029]
This invention has broad utility across all types of fiber formed paper, including, but not limited to, bleached and unbleached Kraft fibers, recycled fibers, hard wood and soft wood fibers, cotton fiber, and non-wood fibers. [0030]
When paper undergoes sizing treatment with the water-dispersible polyester by the internal or the surface sizing process, its strength properties are characterized by increased tensile strength (both wet and dry), burst strength, and short span compression test (SCT). The dry tensile strength can be increased from 1% to 50% of its original tensile strength as compared to an untreated control without the polyester resins described in this invention. The wet tensile strength can be increased 1 to 12 times as compared to a control without the polyester resins described in this invention. The dry burst strength is increased from zero (0)% to 100% as compared to the control without the polyester described in this invention. The wet burst strength of paper made with the water dispersible polyester is 1 to 15 times greater as compared to the control without the polyester described in this invention. The dry SCT of paper sized with this polyester is increased from zero (0)% to 120% as compared to the control without the polyester described in this invention. The high humidity SCT, tested at 80%-95% relative humidity, is increased from 20% to 250% as compared to the control without the polyester described in this invention. The water resistant and water repellent properties of the paper sized with this polyester are shown by its 30 minute wicking, its 30 minute Cobb value, tested at TAPPI standard, and water contact angle tested at TAPPI standard. The wicking of paper made with the water-dispersible polyester is from 0 to 30 millimeters compared with 40 to 120 millimeters by the control without the polyester described in this disclosure. The 30 minute Cobb number of paper sized with water-dispersible polyester is from 2 to 250 grams per decimeter, but most fall between 20 and 100 grams per decimeter depending on the fiber source. A control will typically have a Cobb number in excess of 450 grams per decimeter. The water contact-angle on the paper sized with the polyester, tested as a TAPPI method, is at 50 to 110 degree. An untreated control will typically absorb the water and not show a contact angle. [0031]
The paper sized according to the invention is glueable with normal starch or modified starch glues or synthetic glues and can be coated with the water-dispersible polyester or other coatings typically used in the paper industry. Paper sized with AKD alone has water repellent properties, but it also has low water adsorption which makes it very difficult to glue. The water-dispersible polyester sized paper in this invention not only has improved water repellency and water resistance properties, but also is easily glued under normal conditions with starch glue, such as the glue typically used in corrugated paperboard. This invention contemplates the use of water-based polyesters as both internal and external size, makes the paper or paperboard repulpable, recyclable, glueable, water repellent and water resistant, increases the sizing properties, and imparts increased dry and wet strength. For internal sizing, the water-dispersible polyester size also increases the retention of the fiber, fines and fillers in the stock, giving greater yield in the paper making process. The water-dispersible polyester is compatible with other wet-strength and sizing agents. The wet-end size not only increases the paper's dry and wet strength, but also makes the sized paper repulpable and recyclable. [0032]
The examples below are further illustrations of the invention. The “control” referred to in the examples is paper made according to composition and process in the respective example but without the water dispensible polyesters. [0033]

EXAMPLE1

A composition of 677.58 grams of un-bleached brown kraft virgin pulp at 17.71% solids was diluted to 6% consistency and mixed with 20 grams of polyester solution, EvCote® PGLR-30[0034] ¹, at 30% solids, then mixed with 3.6 grams of poly-aluminum chloride, PAC-70². The pulp is diluted to 0.2% paper solids. The paper sheets were made and tested according to TAPPI standard procedure. The paper made in this example with polyester does not wick after 30 minutes in water as compared with 120 millimeters of wicking in the control of the same brown kraft made without the polyester of this invention. Water adsorption (30 minute Cobb value) is 79 grams per decimeter for a basic weight of 55 pounds per thousand square feet compared with 700 grams per decimeter for the control; and, wet tensile is increased four times that of the control.

EXAMPLE 2

A bleached pulp composed of 70% hardwood fiber and 30% softwood fiber at 4% to 6% consistency was mixed with EvCote® PWR-25[0035] ³polyester solution, at a dosage of 10 dry pounds per ton of dry fiber. Poly-aluminum chloride was added at 20 wet pounds per ton of dry fiber; alkyl kotene dimer was added at 1.2 pounds per ton of dry fiber, and cationic starch was added at 15 pounds per ton of dry fiber. The sheets were made as described in Example 1, and the sized sheet properties were 986.7 seconds of HST (Hercules Sizing Test), no wicking, and 28.4 grams per decimeter (30 minute Cobb).

EXAMPLE 3

On a production paper machine, the bleached pulp with fillers was mixed with EvCote® PWR-25 water-dispersible polyester, and poly-aluminum chloride at the pulper at 6.75 dry pounds per ton of fiber for the polyester and 15 wet pounds per ton for the PAC. Next, 600 centiliters of alkyl ketene dimer per minute and 0.5 pound of polyacrylamide per ton of fiber were added at the machine chest. Paper was made on the paper machine. The resulting paper tensile strength was increased 17% in the cross machine (transverse) direction and 19% in the machine direction compared to the control without the polyester. The sizing of the sheet increased from 200 seconds HST without polyester to greater than 1200 seconds HST with the water-dispersible polyester and showed improved water repellency of the paper. The solids retention increased from 89% without polyester to 97% with polyester. The paper did not wick after being soaked in water for more than one month. [0036]

EXAMPLE 4

Recycled gold envelope stock paper was repulped at 6% solids. The water-dispersible polyester, EvCote® PWR-25, was added into the recycled pulp at 40 dry pounds per ton of fiber. Next, 160 wet pounds of poly-aluminum chloride (as a 17% solids solution) and 20 wet pounds of alkyl ketene dimer were added to the pulp following the polyester addition. The envelope stock paper sheets were formed from the pulp, which was at a 0.1% consistency. The paper sheet had three times the wet strength of the sheet without the polyester addition and had 30 grams of water adsorption (30 minute Cobb test) compared with 161 grams of water adsorption for the sheet without polyester. The sheet containing the polyester did not wick water. [0037]

EXAMPLE 5

In this example, 573.2 grams of medium pulp at 20.96% consistency was diluted to 5%. Next, 10 grams of water-dispersed polyester, EvCote® PGLR-30[0038] ⁴, at 30% solids was added into the pulp with agitation, and, then, 1.52 grams of poly-aluminum chloride, PAC-70, was added following the addition of the polyester solution. The above mixture was diluted to a 0.2% consistency and paper was formed. The resulting paper showed 13 millimeter wicking in 30 minutes compared to 48 mm of wicking without polyester. The paper absorbs 230 grams of water per square decimeter (30 minute Cobb test) compared to 358 grams adsorption without polyester. Wet tensile was increased 200% compared to the control without polyester sizing.

EXAMPLE 6

The procedure and dosage of polyester was the same as in Example 5, but 30 wet pounds per thousand pounds of solution of polyethylene imine was added in the head box of the sheet former. The sheet showed 18 mm wicking in 30 minutes and the wet tensile strength was increased 3.8 times that of the control. [0039]

EXAMPLE 7

Paper was saturated with a 6 percent solution of the water-dispersed polyester, EvCote® P56-20[0040] ⁵, in a size press and pressed with a press roll at 30 psi. The paper picked up 2 to 3 pounds of P56 per thousand square feet. The sized paper was 1 to 3 times stiffer than the original unsized paper. Its dry SCT strength was increased from 43 to 97%, compared to the original paper. The short span compression strength at high humidity is increased from 37 to 87 percent, compared to the original paper.

EXAMPLE 8

As described in Example 7, 6 to 15 percent of EvCote® P56-20 polyester was added to the size box on a paper machine. The paper picked up 1 to 3 pounds of polyester per thousand square feet of paper. The paper stiffness increased 1 to 2 times that of the control. The sized paper was corrugated under standard corrugating conditions, utilizing a hot starch glue. The performance of the corrugated sheet is equivalent to that of the control. [0041]

EXAMPLE 9

In this example, 881.7 grams of pulp at 13.61 % consistency was diluted with 1600 grams of water. To this, 40 grams of water-dispersed polyester, EvCote® PGLR-30, at 30% solids, 8.4 grams of poly aluminum chloride, 0.18 grams of defoamer, and 0.03 grams of surfactant were added into the pulp, sequentially, with agitation. Paper sheets were made from this pulp from a 0.1% consistency mixture. The paper made with the polyester wicked only slightly; the 30 minute Cobb number was 102 grams per square decimeter paper at a basis weight of 40 pounds per thousand square feet compared with 419 grams per square decimeter for the control. The dry tensile strength was 15.83 kgs compared with 12 kgs without polyester. The wet tensile strength, tested after immersing the sample in 2 centimeters of water for 90 minutes, was 6.09 kgs compared with 0.4 kgs without polyester. The compression strength was increased 100% compared with the control. [0042]

EXAMPLE 10

As in the procedure in Example 9, the EvCote® PGLR-30 polyester was added into a mix of both recycled and virgin fiber. The rate of addition was 100 pounds per ton of dry fiber. The dry tensile strength was increased 17 percent; the wet tensile strength was increased 630 percent; the Cobb number was down 53 percent; and, the 30 minute wicking decreased 16 percent. All tests results are in comparison to the control. [0043]

EXAMPLE 11

Paper sheets were sized with Kymene at 30 wet pounds per ton of fiber, with a Kymene-polyester mixture at 15 wet pounds of Kymene and 24 dry pounds of water-dispersible polyester per ton of fiber, and with the water-dispersible polyester at 50 dry pounds per ton of fiber. The sheets with the different chemicals were repulped in a pulper for 20,000 revolutions at 55 degrees Centigrade. The resulting pulp was screened with a shives separator. Shives are fibers that lump and do not separate cleanly into individual fibers. The shives caused by the various chemical treatments are determined and compared with a control. The results are shown in the table. [0044]

Size A B C D

Shives, kg 0.13 0.46 0.43 4.3

Fiber, kg 12.3 11.7 11.8 8.5

Shives/Fiber, % 1.1% 3.9 3.6 37.2
In the table, A is the control paper without additional chemicals; B is the paper made with 50 dry pounds/ton (#/T) of polyester, EvCote® PGLR-30; C is the paper made with 15 wet #/T of Kymene and 24 dry #/T of EvCote® PGLR-30 polyester; and, D is the paper made with 30 wet #/T of Kymene. The addition of water-dispersible polyester to compositions B and C made the resulting paper repulpable whereas internal sizing without the polyester as in composition D produced an unsatisfactory high percentage of shives. [0045]
It will be apparent from the foregoing that many other variations and modifications may be made regarding internal sizing with the water dispersible polyester resins described herein without departing substantially from the essential features and concepts of the present invention. For example, as used in the claims all numbers defining ranges, percentages, ratios or quantities should be read as having the word “about” expressed before the number, e.g., expressed as “about” 5 pounds. Accordingly, it should be clearly understood that the forms of the invention described herein are exemplary only and are not intended as limitations on the scope of the present invention as defined in the appended claims. [0046]

Claims

We claim:

1. In a paper making process wherein dry paper is formed from a wet pulp slurry, the improvement comprising the steps of:

a) providing a water-dispersible polyester resin comprising a polyethylene terephthalate backbone, alkyl or aromatic group, and hydrophillic end groups; and

b) adding said polyester during the paper making process prior to the formation of the dry paper thereby enhancing the wet strength and repulpablity of the resulting paper product.

2. The improved process of claim 1 wherein said polyester is added to the pulp slurry at the wet end of the paper making process to provide internal sizing.

3. The improved process of claim 1 including the steps of:

c) providing an additional quantity of water-dispersible polyester and

d) applying said additional polyester as a surface size to wet paper formed during the paper making process.

4. The improved process of claim 1 wherein said water-dispersible polyester is made from a glycol and polyacid monomer.

5. The improved process of claim 3 whereas said water-dispersible polyester used as a surface size is made from a glycol and polyacid monomer.

6. The improved process of claim 1 wherein said water-dispersible polyester resin is made from recycled or virgin polyethylene terephthalate for the polyester portion of the polymer.

7. The product of the process of claim 1.

8. The paper making process of claim 1 including the step of repulping a paper product made by said process.

9. As an article of manufacture, a paper product having internal sizing which comprises a water dispersible polyester resin having a polyethylene terephthalate backbone, alkyl or aromatic groups, and hydrophilic end groups, said paper product exhibiting improved dry and wet strength properties.

10. A paper product comprising:

a) cellulosic fibers and

b) an internal sizing comprising a water dispersible polyester.

11. The product of claim 10 wherein said cellulosic fibers are wood derived fibers. Cotton fiber and/or other non-wood fibers.

12. The paper product of claim 10 having an external sizing of a water dispersible polyester.

13. The paper product of claim 10 wherein the internal size of water dispersible polyester was present before dry paper formation in the range of 5 to 200 pounds of dry polyester per ton of dry fiber and the external size is present in the range of 163 pounds per thousand square feet of paper.

14. An improvement of the paper making process comprising the steps of:

a) providing a cellulosic pulp fiber slurry prepared for forming paper;

b) providing a water dispersible polyester comprising the reaction production of 30%-70% by weight of a terephthalate polymer; 5%-40% by weight of a hydroxy functional compound having at least two hydroxyl groups; 1%-20% by weight of a carboxyl functional compound having at least two carboxyl groups and 10%-60% by weight of a hydrophic compound selected from the group consisting of C₆-C₂₄straight chain or branched fafty acid or treglyceride thereof; and,

c) adding said polyester in the ratio of 0.2 dry pound to 600 dry pounds of polyester per dry ton of fiber in the pulp slurry at the wet end of the paper making process.

15. The improved process of claim 14 wherein said polyester is added in the ratio of 5 to 200 dry pounds per dry ton of fiber.

16. The improved process of claim 14 including the additional step of applying said polyester resin to wet paper as a surface size.

17. The improved process of claim 14 including the step of adding alkyl ketone dimer or alkyl succinic anhydride to said polyester resin at the wet end as an internal size.

18. The improved process of claim 14 including the step of adding Kymene (or equivalent) to said polyester resin at the wet end as an internal size.

19. The process of claim 14 wherein said polyester size is added at more than one point in the paper making process.