JP2005522590A - White pitch deposit treatment - Google Patents

Abstract

The present invention relates to inorganic or organic (natural or synthetic) coagulants and particulate materials (synthetic or naturally occurring) for pulps containing white pitch / tackiness, such as bentonite clay, crosslinked polymers, colloidal silica, The present invention relates to a deposit control system made of polysilicate.

Description

Background Organic deposits in papermaking systems can cause lost productivity and degrade the quality of the finished paper product by forming stains, holes and tears. These organic deposits are the result of pitches naturally present in the wood itself, or are from synthetic materials such as adhesives, hot melts or latex found in recycled pulp. These components are hydrophobic and accumulate in process water. These deposits clump together and stick to the paper machine surface or in the paper sheet. Deposits generated from wood are called “wood pitch”, and deposits from man-made materials are called “sticky” or “white pitch”. White pitch is characteristic of coating binder lattices such as styrene butadiene rubber (SBR) and polyvinyl acetate.

  Papermaking, in its simplest sense, involves producing pulp from wood, slurrying the pulp with water, forming a pulp mat, pressing it and drying to form paper. In an important forming step, the pulp / water slurry (finisher) is formed as a mat on the wire web of the paper machine. Excess water and fine (white water) permeate the mat on the wire and are recycled. The formed web goes to the press and drying section of the paper machine where the mat becomes paper.

  Scrap paper is a term used in the paper industry to describe paper that does not conform to standards and therefore cannot be sold. This paper is usually recycled internally at the paper mill to recover the fiber, but may be sold to other paper mills as a fiber source. The waste paper can also be coated, in which case the coating is applied to the paper base sheet during manufacture. The coated waste paper is called coated waste paper. Waste paper is a term used in the paper industry to describe paper used by consumers. Often referred to as “consumed waste paper”. In many cases, the paper is collected and recycled at a paper mill to recover the fibers. Waste paper can also be coated, in which case the coating is applied to the paper base sheet during manufacture. The coated waste paper is called coated waste paper. The recycled coated paper can be waste paper or waste paper. In recent years, many paper mills have problems with the recycling of coated paper. The reason is that the coating introduces substances that would not normally be present in the fiber stock used to make the base paper sheet.

  The coating usually contains various pigments and binders. Typical pigments used include many types of clay, calcium carbonate, titanium dioxide and other special fillers. The white pitch problem is believed to be caused primarily by binders containing latex polymers derived from styrene-butadiene and polyvinyl acetate resins and natural binders such as starch.

  The white pitch problem has been known for some time in the paper industry. White pitch is a sticky, light gray material found as a deposit on a metal surface at the wet end, molding press or drying section of a paper machine. It is called "white" to distinguish it from the brown or black pitch that results from the materials contained in the wood. White pitch is also found in white water systems. Sometimes, the pitch deposits are carbonized to produce black deposits in the drying section of the paper machine. The white pitch problem has been shown to be caused by the relatively high utilization of coated paper in the paper mill furnish that has problems. When the coated paper is repulped, the clay or mineral and latex in the coating do not disperse easily in the pulp and form agglomerates, resulting in white pitch. If the white pitch enters the paper machine together with the pulp, there is a risk of covering the apparatus or forming a defect in the paper. High machine downtime, frequent cleaning, paper sheet defects such as holes and increased sheet breakage are costly problems associated with white pitch deposits. Cleaning of the equipment is essential because deposits are found on foils, table rolls, vacuum boxes, drying cans and drying felts and everywhere in the press felt.

  Various solutions have been proposed to address the white pitch problem. Currently, several deposit control agents are used or evaluated by the paper industry. By confining and dispersing small latex particles in the sheet, the white pitch problem can be suppressed. More specifically, the latex particles should adhere to the fibers just prior to passing through the repulper. At this point the latex particles are small and anionic and can therefore exit the system as part of the sheet. Due to the anionic properties of latex particles and fibers, additives with low molecular weight and high cationic charge are very suitable for this purpose. However, the additive alone may not be sufficient to include latex particles in the paper sheet, and the use of a retention aid that is compatible with the additive may be important in successfully suppressing white pitch.

  Synthetic polymers are known anti-adhesion additives that are most successful for white pitch. They are highly cationic and can form strong electrostatic bonds between the fibers, latex particles and additives. Once bound, the fibers carry latex particles through a paper machine with the aid of a retention aid, and the particles become part of the finished paper product. Medium molecular weight polyglycols, amine / glycol or polyethyleneimine polymers have been shown to be useful in reducing white pitch.

  Some of the methods for dealing with the white pitch problem are described in the following documents.

  US Pat. No. 5,131,982 (Michael R. St. John) contains polymers and copolymers for treating cellulose fibers recycled from coated waste paper recovery to make it suitable for papermaking. Describes the use of DADMAC.

  US Pat. No. 4,997,523 (Pease et al.) Uses tetrafunctional alkoxylated diamines in combination with phosphoric acid compounds, phosphonic acid compounds or phosphoric acid to minimize white pitch adhesion to papermaking equipment. It is described that.

  U.S. Pat. No. 4,643,800 (Maloney et al.) Discloses that a hydroxyl group at one end is substituted with an aliphatic or alkyl aromatic group, and a hydroxyl group at the other end is substituted with a polyoxypropylene group or a benzyl ether group. Using oxyethylene glycol nonionic surfactant in combination with medium molecular weight (500-50,000) polyelectrolyte dispersant to remove and disperse contaminants from secondary fibers during repulping Is described.

  There are several drawbacks to the use of polymers to suppress white pitch. Polymers are generally not cost effective. For example, the tertiary amine polymer polyethyleneimine (PEI) is an effective white pitch inhibiting additive, but is very expensive to use.

  There are other solutions used for white pitch suppression. In the past, talc has been commonly used and is still sometimes used to control deposits. As a surface active filler, talc acts to reduce deposits by lowering the tackiness of the area around the pitch particles and preventing the pitch particles from sticking to the papermaking machine. However, this only provides a temporary solution to the pitch problem that reappears as the process continues. Talc does not bind latex particles to the fiber, so when exposed to shear, new tacky areas appear and cause deposits. Additives that react with the surface of the pitch particles to reduce its tack (anti-tacking agents) also provide only a temporary solution to suppress white pitch. US Patent Application Publication 2001/0023751 describes a method for reducing sticky contaminants using polyvinyl alcohol and bentonite. Polyvinyl alcohol acts as a particle masking agent. The problem relates to the need to use excess amounts of polyvinyl alcohol. Bentonite absorbs excess polyvinyl alcohol.

SUMMARY OF THE INVENTION The present invention relates to inorganic or organic (natural or synthetic) coagulants and particulate materials (synthetic or naturally occurring) for pulps containing white pitch / tackiness, such as bentonite clays, crosslinked polymers, It is a deposit control system made of colloidal silica, polysilicate or borosilicate. The order of addition of these two components is extremely important to ensure the advantage of reducing white pitch in the papermaking process. The coagulant can be added to the pulper or thick stock chamber, and the particulate material can be added at the exit from the pulper or stock chamber prior to stock dilution.

Detailed Description The results of a number of turbidimeter measurements are shown in FIG. The turbidity of the backwater (filtrate) is an indicator of the colloid retention or cleanliness of the latex emulsion particles. When polyamine is used as a single component, a reduction in turbidity is achieved compared to the case where the coated waste paper is not treated. However, adding particulate material with the coagulant provides a significant reduction in water turbidity. This data indicates that more white pitch / sticky particles stay with the stock rather than recirculating in the papermaking system. These experimental results demonstrate that the coagulant / particulate material system significantly reduces white pitch / sticky buildup in the papermaking system.

  The present invention relates to inorganic or organic (natural or synthetic) coagulants and particulate materials (synthetic or naturally occurring) for pulps containing white pitch / tackiness, such as bentonite clay, crosslinked polymers, colloidal silica, It is a deposit control system made of polysilicate or borosilicate.

  The coagulant can be an inorganic or organic (natural or synthetic) material. Examples of suitable organic coagulants are low molecular weights that are usually homopolymers of cationic repeat groups or copolymers of at least 80% by weight of cationic monomers and 0-20% by weight of acrylamide or other nonionic monomers. High charge density polymer. Cationic groups can be derived from diallyldimethylammonium chloride and dialkylaminoalkyl (meth) -acrylates and -acrylamides (generally as quaternary ammonium or acid addition salts). In many cases, dimethylaminoethyl acrylate or methacrylate quaternary ammonium salts are particularly preferred. Alternatively, the coagulant can be a condensation polymer such as dicyandiamide polymer, polyamine or polyethyleneimine. Inorganic coagulants such as alum, lime, ferric chloride and ferrous sulfate can also be used.

  Cationic coagulant materials that may find use in this aspect of the invention are well known commercially available low to low, including those prepared by reaction of alkylene polyamines with difunctional alkyl halides. Contains medium molecular weight water-soluble polyalkylene polyamines. This type of material is derived from reactions of ethylene dichloride and ammonia ethylene dichloride, ammonia and secondary amines such as dimethylamine, epichlorohydrin-dimethylamine, epichlorohydrin-dimethylamine-ammonia, polyethyleneimine, etc. Contains the condensation polymer to be prepared. In certain cases, cationic starch may be used as a coagulant. Inorganic coagulants such as alum and polyaluminum chloride may also be used in the present invention. The usage rate of the inorganic coagulant is generally 0.005 to 1% by weight based on the dry weight of the fibers in the furnish.

  A preferred coagulant is a cationic polyelectrolyte that is a poly (diallyldi (hydrogen or lower alkyl) ammonium salt having a number average molecular weight of greater than 300,000 and less than 2,000,000.

  The particulate material can be synthetic or naturally occurring. Examples of suitable particulate materials are granules selected from swellable clays, crosslinked polymers, colloidal silica, borosilicate or bentonite, colloidal silica, polysilicate microgels, polysilicate microgels and crosslinked microemulsions of water soluble monomeric materials. A suspension of the anionic substance.

  Particulate matter is widely used in the paper industry, especially as a retention aid for the production of fine paper. One such system for providing an improved combination of retention and watering using swellable clay is disclosed in US Pat. No. 4,753,710, the disclosure of which is incorporated herein by reference. And 4,913,775. In the method disclosed in Langley et al., A high molecular weight linear cationic polymer is added to an aqueous cellulose paper suspension, then the suspension is sheared, followed by the addition of a swellable clay such as bentonite. Yes. Shear is generally provided by one or more of the cleaning, mixing and pumping steps of the papermaking process, breaking down large floc masses formed by high molecular weight polymers into micro flocs. Thereafter, further agglomeration occurs as a result of the addition of bentonite clay particles.

  Other particulate programs include colloidal silica and particulates as particulates as described in US Pat. Nos. 4,388,150 and 4,385,961, the disclosures of which are incorporated herein by reference. Cationic starch, agglomerates based on combinations with starch or as described in US Pat. Nos. 5,098,520 and 5,185,062, which are also incorporated herein by reference. Based on combined use of agent and silica sol. U.S. Pat. No. 4,643,801 claims a papermaking process using high molecular weight anionic water soluble polymers, dispersed silica and cationic starch.

  Additional microparticles are derived from an aqueous solution of borosilicate colloidal particles having a borosilicate, preferably a boron: silicon molar ratio of 1: 1000 to 100: 1, generally 1: 100 to 2: 5. The particulate retention aid can be a borosilicate colloid having similar chemical properties as borosilicate glass. This colloid is generally prepared by reacting an alkali metal salt of a boron-containing compound with silicic acid under conditions that result in the formation of a colloid. The borosilicate particles can have a wide range of particle sizes, for example, 1 nm (nanometers) to 2 microns (2000 nm), preferably 1 nm to 1 micron.

  The fine particles can be inorganic, such as colloidal silica (eg, as described in US Pat. No. 4,643,801), polysilicate microgel (eg, as described in EP-A-359,552), polysilicic acid. Microgels (such as those described in EP-A-348,366), an aluminum modified form thereof, may be used. In particular, U.S. Pat. Nos. 4,927,498, 4,954,220, 5,176,891 and 5,279,807 are listed under the trade name Particol by Ciba Specialty Chemicals and DuPont. Commercially available systems can be used.

  Anionic fine particulate materials can also be used. For example, an anionic organic polymer emulsion is suitable. The emulsified polymer particles can also be insoluble thanks to being formed from a copolymer of a water-soluble anionic monomer and one or more insoluble monomers, such as ethyl acrylate, but preferably the polymer emulsion is, for example, US Patent Cross-linked microemulsions of water-soluble monomeric materials described in US Pat. Nos. 5,167,766 and 5,274,055 and marketed by Ciba Specialty Chemicals under the trade name Polyflex.

  The particle size of the finely divided material is generally less than 2 m, preferably less than 1 m, most preferably less than 0.1 m.

  The amount of particulate material (dry weight based on the dry weight of the cellulose suspension) is generally at least 0.03%, usually at least 0.1%. For example, it can reach 1.6 or 2%, but is generally less than 1%.

  Preferred particulate materials are swellable clays, particularly smectite group swellable clays. Preferred smectite group clays include bentonite, montmorillonite, saponite, hectorite, beidilite, nontronite, fuller's earth and mixtures thereof. A swellable clay component mainly containing bentonite is particularly preferred. Bentonite should be in a highly swelled activated form, which in practice means that it should be in the form of a monovalent salt of bentonite, such as sodium bentonite. Although there are several naturally occurring sources of sodium bentonite, most natural bentonites are alkaline earth bentonites, generally calcium or magnesium bentonites. The usual practice is to activate alkaline earth bentonite by ion exchange of calcium or magnesium ions with sodium ions or other alkali metal ions or ammonium ions. Generally this is done by exposing the bentonite to an aqueous solution of sodium carbonate, although several other activators are known. Swellable clay is a naturally occurring substance and is commercially available.

  Suitable fibers for the production of pulp are all qualities conventionally used for this purpose, such as mechanical pulp, bleached and unbleached chemical pulp and paper stock from all annual plants. Mechanical pulp is, for example, groundwood pulp, thermomechanical pulp (TMP), chemothermomechanical pulp (CTMP), pressurized groundwood pulp, semi-chemical pulp, high yield chemical pulp and refiner mechanical pulp (RMP). Examples of suitable chemical pulps include sulfate, sulfite and soda pulp. It is preferred to use unbleached chemical pulp, also called unbleached kraft carrier pulp. Suitable annual plants for the production of stock are, for example, rice, wheat, sugar cane and kenaf. Pulp is produced using only waste paper or as a mixture with other fibers. Waste paper includes coated waste paper that produces a white pitch due to the inclusion of a binder for the coating and printing ink. The aforementioned fibers and pulp can be used alone or as a mixture with each other. Adhesives from pressure sensitive adhesive labels and wrapping materials as well as adhesives from the back of the book and hot melt result in the formation of stickiness.

  The present invention is particularly suitable for papermaking systems that utilize pulp from significant amounts of recycled or spoiled paper. The definition of a significant amount depends on the system and the type of recycled paper or waste paper utilized, but is characterized by the presence of a white pitch in the process stream sufficient to substantially achieve operating conditions. In general, at least 10% of the pulp must come from recycled or spoiled paper to produce a substantial amount of white pitch.

  The deposit control system is introduced into the papermaking system by addition to the rich or dilute stock system in the papermaking process. An important aspect of this method is the timing of each component addition. This method requires the addition of a cationic coagulant followed by the addition of anionic particulates. Without being bound by theory, it is believed that prior addition of cationic coagulant improves white pitch adsorption by anionic microparticles. Furthermore, it is believed that the cationic coagulant is absorbed by pitches (wood, white and sticky) that are predominantly anionic or nonionic, making it at least partially cationic. Bentonite adsorbing the increased amount of pitch is then retained in the paper being formed. As a result, the amount of white pitch in the effluent is reduced. In a preferred embodiment, the coagulant is added to the pulper or thick stock chamber and the particulate material is added at the outlet of the pulper or stock chamber prior to stock dilution.

  The invention is further illustrated by the following non-limiting examples. The examples illustrate the invention defined only by the claims.

Example 1
The coated paper sheet was repulped with a laboratory disintegrator. A 400 ml aliquot of 1% consistency stock was mixed at 1000 rpm. During mixing, polyamine coagulant and bentonite particulates were added at 1 minute intervals. 1,1.5 or 2 pounds per ton were added with the polyamine as received, followed by 4, 6 or 8 pounds of bentonite. After the treatment, the stock was filtered through a 100 mesh screen, and the turbidity of the filtrate was measured. Each filtrate sample was prepared at a 1:14 dilution with deionized water. A portable turbidimeter Hach 2100P was used for the test and the results were recorded in NTU (turbidimetric turbidity units). The results are shown in FIG.

Example 1
The coated paper sheet was repulped with a laboratory disintegrator. A 400 ml aliquot of 2.5% consistency stock was mixed at 1000 rpm. During mixing, a coagulant of either polyamine, polyDADMAC or polyaluminum chloride (PAC) and bentonite particulates were added at 1 minute intervals. One pound per ton was added as received with coagulant, followed by 4, 6 or 8 pounds of bentonite. Also, the coagulant was added 1 or 2 pounds per ton as a single component, as received. After the treatment, the stock was filtered through a 100 mesh screen, and the turbidity of the filtrate was measured. Each filtrate sample was prepared at a 1:14 dilution with deionized water. A portable turbidimeter was used for the test and the results were recorded in NTU (turbidimetric turbidity units).

Results The results of turbidimeter measurements for each treatment are shown in FIG. The turbidity of the backwater (filtrate) can be an indicator of the colloid retention or cleanliness of the latex emulsion. By using 1 or 2 pounds per ton of polyamine or polyDADMAC as a single component, a reduction in turbidity is achieved compared to not treating the coated waste paper. However, adding bentonite with various coagulants provides a reduction in water turbidity. A significant decrease in turbidity is noted when comparing 1 lb polyamine or PAC coagulant plus bentonite as received to 2 lb per tonne as received. .

It is a figure which shows the influence of the quantity of the coagulant | flocculant with respect to turbidity in a coated waste paper process. It is a figure which shows the turbidimeter measurement result of each process.

Claims (17)

  A papermaking method comprising adding an effective amount of at least one cationic coagulant polymer or inorganic coagulant to the stock and then adding particulate matter to reduce white pitch adhesion, A process wherein the stock contains pulp derived at least in part from recycled paper products.   The particulate material is a particulate anionic property selected from swellable clays, crosslinked polymers, colloidal silica, borosilicate or bentonite, colloidal silica, polysilicate microgels, polysilicate microgels and crosslinked microemulsions of water soluble monomeric materials. The method of claim 1, wherein the method is selected from the group consisting of suspensions of substances as well as mixtures thereof.   The method of claim 2, wherein the particulate material is an anionic material.   The method according to claim 2 or 3, wherein the particulate material is a smectite group swelling clay.   The method according to any one of claims 2 to 4, wherein the particulate material is a mineral consisting essentially of bentonite, montmorillonite, saponite, hectorite, baidylite, nontronite, fuller's earth, and mixtures thereof.   The method according to claim 1, wherein the particulate material is a mineral mainly composed of bentonite.   The cationic coagulant polymer is a homopolymer containing cationic repeat groups or a copolymer of at least 80% by weight cationic monomer and 0-20% by weight acrylamide or other nonionic monomer. 6. The method according to any one of 6.   8. The method of claim 7, wherein the cationic group is derived from diallyldimethylammonium chloride and dialkylaminoalkyl (meth) -acrylate and -acrylamide or a quaternary ammonium salt thereof.   9. The method of claim 8, wherein the cationic group is dimethylaminoethyl acrylate or methacrylate quaternary ammonium salt.   The method according to claim 1, wherein the coagulant is a dicyandiamide polymer, a polyamine or polyethyleneimine.   The method according to any of claims 1 to 6, wherein the coagulant is selected from the group consisting of alum, lime, ferric chloride, polyaluminum chloride, ferrous sulfate and mixtures thereof.   The method according to any one of claims 1 to 7, wherein the coagulant is a polyalkylene polyamine prepared by reaction of an alkylene polyamine with a difunctional alkyl halide.   2. The cationic polyelectrolyte, wherein the coagulant is a poly (diallyldi (hydrogen or lower alkyl) ammonium salt having a number average molecular weight of greater than 300,000 and less than 2,000,000. 8. The method according to any one of 7.   14. The method of claim 13, wherein the particulate material is a mineral composed primarily of bentonite.   A paper product produced by the method according to any one of claims 1 to 5 or 7 to 13.   A paper product produced by the method of claim 6.   A paper product made by the method of claim 14.

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