CN117629699A

CN117629699A - Papermaking method for improving paper strength

Info

Publication number: CN117629699A
Application number: CN202210952595.5A
Authority: CN
Inventors: 张福山; 覃朝颖; 刘波; 王祥槐
Original assignee: Risingstar Biotech Guangzhou Co ltd
Current assignee: Risingstar Biotech Guangzhou Co ltd
Priority date: 2022-08-09
Filing date: 2022-08-09
Publication date: 2024-03-01

Abstract

The invention relates to a papermaking method for improving the strength of finished paper, which comprises the following steps: and adding a composite cationic polymer into the papermaking slurry to react, and preparing the reacted papermaking slurry into a paper product. Among them, the composite cationic polymer has a dual reinforcing mechanism, and besides the composite cationic polymer itself can enhance the paper strength by forming hydrogen bonds with fibers, the composite cationic polymer molecule can also fix the starch to the fiber surface if the eluted starch exists in the pulp, and the starch is retained in the finally prepared paper, thereby further playing a role in enhancing the paper strength. For the papermaking process using recycled fibers as raw materials, because the pulp always contains unequal amounts of free starch, the papermaking method can synergistically improve the strength of the finished paper through two different mechanisms, so that the reinforcing effect on the finished paper is obviously better than that of the common polyacrylamide dry strengthening agent.

Description

Papermaking method for improving paper strength

Technical Field

The invention relates to the field of papermaking, in particular to a papermaking method for improving the strength of finished paper.

Background

In the paper making process, various papermaking aids are widely used to improve the yield and quality of the product in order to produce the best quality product with the highest efficiency. These adjuvants can be largely divided into two main categories: one type is to improve the performance and quality of the paper product and is therefore called a functional auxiliary. The other is to improve the running efficiency of the papermaking process, reduce the loss of fibers and fillers, and is called a process aid. Common papermaking functional aids are mainly dry reinforcing agents, wet reinforcing agents, internal sizing agents, surface sizing agents, brighteners, softeners, flame retardants, water repellents, and the like. Common papermaking process aids are mainly: retention aids, drainage aids, fibrous dispersants, stickies control agents, anionic trash traps, defoamers, preservatives, bactericides, clothing cleaners, dryer strippers, and the like.

Dry strength agents refer to chemical adjuvants capable of improving the strength of paper, also known as "dry strength agents" or "reinforcing agents". Paper strength is one of the most important properties of paper. In general, paper strength refers to the strength properties of air-dried paper, so-called dry strength. The main dry strength properties of paper include: tensile strength, fracture length, burst strength, folding strength, interlayer bonding force, tear strength, stiffness, loop compression, and the like. The factors influencing the dry strength of paper are, above all, the morphology and properties of the papermaking fibers themselves. For example, the fiber length, the length-width ratio and the softness are high, and the dry paper strength is high. The mixed cells and lignin in the papermaking fibers influence the flexibility of the fibers, so that the strength of the dry paper is reduced; the hydroxyl groups of hemicellulose can increase hydrogen bonding, improving dry paper strength. As another example, chemical pulp is stronger than mechanical pulp and virgin pulp is better than recycled waste pulp. The chemical pulp is the same, the softwood pulp is better than the hardwood pulp, and the hardwood pulp is better than the wheat straw pulp.

Second, the bonding forces between papermaking fibers are another important factor affecting the dry strength of the paper. The bonding forces between the fibers in the sheet are mainly derived from hydrogen bonding. The more hydrogen bonds between the fibers, the greater the bonding force between the fibers and the higher the dry paper strength of the paper. And the fiber is fibrillated by a pulping method, so that the specific surface area of the fiber is increased. The larger the surface area of the fibers, the more hydroxyl groups (-OH) on the surface and thus the greater the number of hydrogen bonding between the fibers, and the greater the dry strength of the paper. Generally, the higher the beating degree, the higher the strength of the paper is within a certain range. However, there is a limit to improving the strength of paper by beating. This is because beating is a double blade sword, which promotes the fibrillation of the fibers, and is advantageous for improving the strength of paper making, and which shortens the fibers, and has a negative effect on the strength of paper. In addition, as the freeness increases, not only is the power consumption increased, but also the dewatering of the pulp in the wire section of the machine becomes poor and drying becomes difficult.

In addition to the method of beating, the addition of dry strength agents for paper manufacture to increase the strength of paper is also a common method in the paper industry. The papermaking dry strength agent refers to an auxiliary agent added to paper pulp in the papermaking process. The dry strength agent is added into the paper pulp, so that the following economic benefits can be obtained: 1) On the premise of ensuring that the original strength index is not reduced, the secondary fiber raw material with lower price can be used for replacing the high-priced high-quality fiber, thereby saving the production cost; 2) On the premise of ensuring that the original strength index is not reduced, the quantitative paper is reduced, so that raw materials are saved, and the cost is reduced; 3) The paper strength is improved, the quality of the product can be improved, the grade of the product is improved, and the value of the product is improved; 4) Under the condition of obtaining the same paper strength, the pulping energy consumption can be reduced, meanwhile, the water filtering can be improved, the vehicle speed can be increased, and the yield can be increased.

Dry strength agents for papermaking can be largely divided into two main classes, one class being natural polymers and their modified derivatives, and the other class being synthetic polymers. The most fundamental feature of these dry strength agents, whether natural or synthetic, is the high content of hydroxyl (-OH), or amine groups (e.g., -NH) ₂ -NHR, etc., R is alkyl), or an amide group (e.g., -C (O) -NH) ₂ ) So as to form hydrogen bonds with hydroxyl groups on the surface of the fiber, thereby achieving the effect of improving the strength of the paper sheet. Dry strength agents are typically added to the pulp of the papermaking process. In order to make a dry strength agentBeing able to remain on the fibers without losing with the paper making waste water, the dry strength agent molecules typically need to be charged to a certain amount. Since the fibre surface is negatively charged, the dry strength agents are usually positively charged, and sometimes only positively charged, so-called "cationic dry strength agents"; some have a negative charge in addition to a positive charge, so-called "ampholytic dry strength agents". There are few dry strength agents that are negatively charged only, i.e. "anionic dry strength agents". Anionic dry strength agents are usually used in combination with cationic adjuvants to achieve the enhancement effect.

The natural polymer dry strength agent mainly comprises starch, guar gum, chitosan, water-soluble cellulose, etc. Among these, modified starches are most commonly used and used in the greatest amounts. Raw starch (native starch) is a type of starch produced without any chemical treatment and without changing the inherent physical and chemical properties of starch, and is mainly composed of: cereal starches, potato starches, legume starches and other starches. The raw starch is substantially electrically neutral. If raw starch is added directly to the pulp, it will be difficult to leave it on the papermaking fibers. Thus, raw starch is often required to be chemically modified to impart charge properties to the starch before it can be suitable as a papermaking dry strength agent. Modified starches used as dry strength agents for papermaking are mostly cationic or amphoteric starches, with anionic starches being less useful. The amount of starch-based dry strength agent is generally from 5kg/T to 20kg/T of absolute dry weight of paper.

The common synthetic dry strength agent is mainly a copolymer of polyacrylamide, and is synthesized by polymerizing an acrylamide monomer with other monomers with charges. Wherein the amide group of the acrylamide monomer is [ -C (=O) -NH ₂ ]Can form hydrogen bond with paper fiber to provide reinforcement; and the monomer with charge can assist the adsorption of the dry strength agent molecules on the papermaking fibers through electrostatic attraction. The polyacrylamide dry strength agents can be classified into cationic, anionic and amphoteric types according to their charge. The most commonly used are cationic and amphoteric. Anionic polyacrylamide dry strength agents are less useful. Nonionic polyacrylamides are generally rarely used because of their difficulty in retaining on papermaking fibers. Commonly used polyacrylamide The dry strength agent is typically an aqueous cationic or amphoteric polyacrylamide solution at a concentration of 10% to 20% absolute dry weight, a molecular weight of between 100,000g/mol and 1,000,000g/mol, and a net charge density (ph=7) typically below 0.2meq/g.

Although dry strength agents have been widely used to increase the strength of paper, they have several problems: first, a relatively high amount of starch-based dry strength agent, or an artificially synthesized dry strength agent, is generally required to achieve the strength-enhancing effect. For example, starch-based dry strength agents are typically used in amounts of 5kg/T to 20kg/T and polyacrylamide-based dry strength agents are typically used in amounts of 1.5kg/T to 10kg/T paper on a dry weight basis. The excessive dosage of the dry strength agent not only can increase the production cost, but also can influence the chemical balance of the paper machine system, thereby negatively affecting the operation of the paper machine. Secondly, the dry strength of paper can be improved along with the increase of the dosage of the dry strength agent only in a certain dosage range no matter the starch dry strength agent or the artificially synthesized dry strength agent is used. When the dosage of the dry strength agent is increased to a certain degree, the enhancement effect is weakened or even completely disappeared by continuously increasing the dosage of the dry strength agent. For this reason, it is sometimes necessary to use two or more different dry strength agents in combination with each other to achieve the desired reinforcing effect. Furthermore, starch based dry strength agents, which are basically powders, require investment in specialized equipment to gelatinize, dissolve and dilute the starch, which not only increases equipment investment costs, but also is inconvenient to use. The polyacrylamide dry strength agent is an aqueous solution, so that the use is convenient, but the concentration of the polyacrylamide dry strength agent is usually only 15%, and the transportation cost is high, so that the application of the polyacrylamide dry strength agent is limited to a certain extent. In addition, if the starch dry strength agent is excessively used, the starch is easy to accumulate in a white water system of the paper machine, and the microbial activity is bred, so that the problems of acidification of the paper machine system, air odor of a paper making workshop, rising of waste water discharge COD and the like are caused. The excessive consumption of the polyacrylamide dry strength agent can also cause the discharge and the rise of COD pollution of the wastewater and cause the deposition of adhesive matters.

In addition to this, the chemical composition of the pulp during the paper making process is rather complex, with some detrimental impurities in addition to the paper making fibers and other necessary raw materials. These deleterious impurities are typically dissolved and colloidal substances (Dissolved and Colloidal Substance, DCS for short) and are negatively charged and are sometimes referred to as anionic trash. These anionic trash, some from substances released during pulping, such as lignin, hemicellulose, extractives, etc., or from the sticky substances from recycled waste paper; some from papermaking aids remaining in the system, such as dispersants, dyes, sizing agents, and the like; and in some cases, the product of microbial activity in papermaking systems. In recent years, due to various reasons, more and more anionic trash in a papermaking white water circulation system affects not only the smooth running of a papermaking machine, but also the quality of finished paper products, and meanwhile, the use efficiency of cationic papermaking auxiliary agents is reduced.

In order to reduce the hazard of anionic trash in papermaking systems, a common approach is to pretreat the slurry with an anionic trash catcher (sometimes also referred to as a fixative). The most effective anionic trash traps are typically high charge density low molecular weight cationic polymers such as polydiallyl dimethyl ammonium chloride (PDADMAC), polyamines, polyethylenimine (PEI), polyvinylamine (PVAm), and the like. These materials can neutralize the charge of a portion of the anionic trash in the papermaking system and anchor the anionic trash on the papermaking fibers as the sheet leaves the machine system, thereby reducing the accumulation of anionic trash within the machine system.

In summary, the dry strength agent is a commonly used papermaking functional auxiliary agent, and is used for improving the strength property of paper and improving and enhancing the quality of the paper; the anionic trash catcher is a common papermaking process auxiliary agent and is used for inhibiting and eliminating the harm of anionic trash in a papermaking system, and improving and enhancing the operation efficiency of a paper machine. In order to improve the production efficiency and the product quality of paper, for a papermaking process, both a dry strength agent and an anionic trash catcher are often used. However, to date, polyacrylamide dry strength agents and anionic trash catchers have been applied separately to the papermaking process as two separate products. In practice, it is almost impossible to pre-mix the dry strength agent and the anionic trash catcher into a single product. First, this is because, as previously described, the amount of polyacrylamide dry strength agent used is considerable during the paper making process, and the product concentration is relatively low and the transportation cost is high. If the polyacrylamide dry strength agent and the anionic trash catcher are pre-mixed into a single product, the polyacrylamide dry strength agent is further diluted, and the transportation cost is further increased. Secondly, the polyacrylamide dry strength agent and the anionic trash catcher are both water-soluble polymers. When two water-soluble polymers are mixed in the water phase, because each polymer molecule chain occupies a certain "excluded volume", this reduces the solubility of the polymers in the mixed solution, limiting the concentration of the two polymers in the mixed solution.

It is therefore an object of the present invention to provide a papermaking aid which combines the functions of both a papermaking dry strength agent and an anionic trash catcher. It is another object of the present invention to provide a method for preparing a dry strength agent for papermaking having a polyacrylamide component concentration of greater than 15 wt%. It is yet another object of the present invention to provide a method of combining a papermaking polyacrylamide dry strength agent and an anionic trash catcher together to form a high consistency product. It is a further object of the present invention to provide a papermaking process employing the composite cationic polymer of the present invention to increase the strength of paper.

Disclosure of Invention

Based on the above, the invention provides a papermaking method for improving the paper forming strength, which comprises the steps of adding the composite cationic polymer into papermaking slurry, and preparing the papermaking slurry after reaction into a paper product. The composite cationic polymer in the method has a dual reinforcing mechanism, and the reinforcing effect on the finished paper is obviously better than that of the common papermaking dry strength agent.

The specific technical scheme comprises the following steps of.

A method of making paper to increase the strength of the formed paper, comprising the steps of:

adding a composite cationic polymer into papermaking slurry to react, and preparing the reacted papermaking slurry into a paper product;

The composite cationic polymer comprises a cationic polymer a and a cationic polymer B different from cationic polymer a, which are bonded together to form a composite;

the composite cationic polymer is prepared by a water-dispersion polymerization method of a nonionic monomer and a cationic monomer for synthesizing the cationic polymer A in a reaction medium containing the cationic polymer B as a dispersion stabilizer.

In some of these embodiments, the cationic polymer a is a cationic copolymer produced by free radical polymerization of a nonionic monomer and a cationic monomer in a reaction medium containing the cationic polymer B as a dispersion stabilizer; wherein the cationic monomer is selected from at least one of acryloyloxyethyl trimethyl ammonium chloride, methacryloyloxyethyl trimethyl ammonium chloride, acryloyloxypropyl trimethyl ammonium chloride, methacryloyloxypropyl trimethyl ammonium chloride, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, dimethylaminopropyl acrylate, dimethylaminopropyl methacrylate, acryloyloxyethyl dimethylbenzyl ammonium chloride, methacryloyloxyethyl dimethylbenzyl ammonium chloride, acryloyloxypropyl dimethyl benzyl ammonium chloride, methacryloyloxypropyl dimethylbenzyl ammonium chloride, acrylamide propyl trimethyl ammonium chloride, methacrylamidoethyl trimethyl ammonium chloride, N- (3-dimethylaminopropyl) acrylamide, N- (3-dimethylaminopropyl) methacrylamide, N- (2-dimethylaminoethyl) acrylamide, N- (2-dimethylaminoethyl) methacrylamide and dimethyldiallyl ammonium chloride; the nonionic monomer is at least one selected from the group consisting of acrylamide, methacrylamide, N-methylacrylamide, N-methyl (meth) acrylamide, N-isopropylacrylamide, N-dimethylacrylamide, N-dimethyl (meth) acrylamide, N-diethylacrylamide, N-diethyl (meth) acrylamide, N-methyl-N-ethylacrylamide, N-methyl-N-ethyl (meth) acrylamide, N-hydroxyethyl acrylamide and N-hydroxyethyl (meth) acrylamide.

In some of these embodiments, the cationic polymer a has a cationicity of 10mol% to 90mol%.

In some of these embodiments, the cationic polymer A has a cationicity of 30mol% to 70mol%,

in some of these embodiments, the cationic polymer a has a cationicity of 40mol% to 60mol%.

In some of these embodiments, the nonionic monomer in the cationic polymer a is acrylamide and the cationic monomer is acryloyloxyethyl trimethyl ammonium chloride.

In some of these embodiments, the molar ratio of acrylamide to acryloyloxyethyl trimethyl ammonium chloride is 1:0.1-4.

In some of these embodiments, the molar ratio of acrylamide to acryloyloxyethyl trimethyl ammonium chloride is 1:0.25-2.

In some of these embodiments, the molar ratio of acrylamide to acryloyloxyethyl trimethyl ammonium chloride is 1:0.75-1.25.

In some embodiments, the cationic polymer B is a cationic homopolymer selected from the group consisting of polyacrylamide propyl trimethyl ammonium chloride, polymethacrylamide propyl trimethyl ammonium chloride, polyacrylamide ethyl trimethyl ammonium chloride, polymethacrylamide ethyl trimethyl ammonium chloride, polydimethylaminopropyl acrylamide, polydimethylaminopropyl methacrylamide, polydimethylaminoethyl acrylamide, polydimethylaminoethyl methacrylamide, polyacrylamidoethyl trimethyl ammonium chloride, polymethacryloxyethyl trimethyl ammonium chloride, polyacrylamidoethyl trimethyl ammonium chloride, polyacrylamidopropyl trimethyl ammonium chloride, polymethacryloxypropyl trimethyl ammonium chloride, polyacrylic acid dimethylaminoethyl ester, polymethacrylate dimethylaminoethyl ester, polyacrylic acid dimethylaminopropyl ester, polymethacrylate dimethylaminopropyl ester, polyacrylamidoethyl dimethylbenzyl ammonium chloride, polymethacryloxyethyl dimethylbenzyl ammonium chloride, polyacrylamidoethyl dimethyl benzyl ammonium chloride, polydimethyl diallyl ammonium chloride, epoxychloropropane-dimethylamine polycondensate, polyethylene imine, dicyandiamide, and at least one quaternary ammonium salt of Dicyandiamide.

In some of these embodiments, the composite cationic polymer has an apparent intrinsic viscosity of 100mL/g to 800mL/g.

In some of these embodiments, the composite cationic polymer has an apparent intrinsic viscosity of 150mL/g to 550mL/g.

In some of these embodiments, the composite cationic polymer has an apparent intrinsic viscosity of 380mL/g to 520mL/g.

In some of these embodiments, the composite cationic polymer has an apparent intrinsic viscosity of 480mL/g to 510mL/g.

In some of these embodiments, the composite cationic polymer has an apparent molecular weight of 1,000,000 to 5,000,000g/mol.

In some of these embodiments, the composite cationic polymer has an apparent molecular weight of 1,000,000 to 3,000,000g/mol.

In some of these embodiments, the composite cationic polymer has an apparent molecular weight of 1,700,000g/mol to 2,500,000g/mol.

In some of these embodiments, the composite cationic polymer has an apparent charge density of 0.2 to 5meq/g on a dry weight basis.

In some of these embodiments, the composite cationic polymer has an apparent charge density of 0.5 to 4meq/g on a dry weight basis.

In some of these embodiments, the composite cationic polymer has an apparent charge density of 3 to 3.6meq/g on a dry weight basis.

In some of these embodiments, the complex cationic polymer is added to the papermaking slurry as a complex cationic polymer suspension having a solids content of 25% to 60%.

In some of these embodiments, the complex cationic polymer suspension has a solids content of 35% to 50%.

In some of these embodiments, the complex cationic polymer suspension has a solids content of 40-45%.

In some of these embodiments, the mass ratio of cationic polymer a to cationic polymer B is 1:0.1-2.

In some of these embodiments, the mass ratio of cationic polymer a to cationic polymer B is from 1:0.5 to 1.5.

In some of these embodiments, the method of preparing the composite cationic polymer comprises the steps of:

a) Preparing an aqueous solution of said cationic polymer B;

b) Adding a cationic monomer and a nonionic monomer required for synthesizing the cationic polymer A into the aqueous solution of the cationic polymer B, and synthesizing the cationic polymer A through free radical polymerization;

c) During the reaction to form the cationic polymer a, the cationic polymer a and the cationic polymer B are bonded together to form the composite cationic polymer.

In some of these embodiments, the aqueous solution of cationic polymer B has a solids content of 30% to 50%.

In some of these embodiments, the aqueous solution of cationic polymer B has a solids content of 38-42%.

In some of these embodiments, the composite cationic polymer is used in an amount of 0.1kg/t to 4kg/t of paper on an oven dry weight basis.

In some of these embodiments, the composite cationic polymer is used in an amount of 0.5kg/t to 3.5kg/t of paper on an oven dry weight basis.

In some of these embodiments, the composite cationic polymer is used in an amount of 1kg/t to 3kg/t of paper on an oven dry weight basis.

In some of these embodiments, the composite cationic polymer is used in an amount of 1.5kg/t to 3kg/t paper on an oven dry weight basis.

In some of these embodiments, the composite cationic polymer is used in an amount of 2.0kg/t to 2.8kg/t paper on an oven dry weight basis.

In some of these embodiments, the reaction time is 10s to 60min.

In some of these embodiments, the papermaking slurry contains free starch.

In some of these embodiments, the free starch is present in the papermaking slurry in an amount of from 1 to 100kg/t paper on an oven dry weight basis.

In some of these embodiments, the free starch content of the papermaking slurry is from 1 to 50kg/t paper on an oven dry weight basis.

In some embodiments, the papermaking pulp is selected from at least one of OCC pulp, deinked pulp, mechanical pulp, chemi-mechanical pulp, semi-chemical pulp and chemical pulp, such as bleached broadleaf pulp and bleached needle-leaf pulp.

In some of these embodiments, one or more of the following adjuvants may be added to the papermaking slurry prior to its preparation into a paper product: dry strength agent, wet strength agent, retention and drainage aid, sizing agent, adhesive control agent and defoaming agent.

The invention also provides application of the composite cationic polymer.

The specific technical scheme comprises the following steps of.

The application of the composite cationic polymer as a paper reinforcing agent in papermaking production.

The composite cationic polymer is applied to papermaking production as an anionic trash catcher.

The use of the above-described complex cationic polymers as free starch retaining agents for the immobilized retention of starch molecules on the resulting fibers during the papermaking process.

The application of the composite cationic polymer in recovering free starch in papermaking wastewater.

The application of the composite cationic polymer in reducing the COD concentration of papermaking wastewater.

The papermaking method for improving the paper strength has the following beneficial effects:

First, the composite cationic polymer of the present invention contains two cationic polymers of different properties, wherein cationic polymer a has the function of a papermaking dry strength agent, and cationic polymer B has the function of an anionic trash catcher. The dry strength agent is the most commonly used functional auxiliary agent for papermaking, and the anionic trash catcher is the commonly used process auxiliary agent for papermaking. The papermaking process often requires the co-use of these two auxiliaries, especially for the production of packaging paper and board paper from recycled waste paper as the main raw material, or for the production of mechanical pulp as the main raw material, because the pulp and white water of these two types of papermaking processes contain more anionic trash, while the strength of both recycled fibers and mechanical pulp fibers is relatively weak. The papermaking dry strength agent and the anionic trash catcher are combined into a product, so that the papermaking dry strength agent is convenient to use, and the cost of transportation, storage and operation is saved. In addition, the composite cationic polymer provided by the invention has a dual reinforcing mechanism as a papermaking dry strength agent, besides the composite cationic polymer can be used for improving the paper forming strength by forming hydrogen bonds with papermaking fibers, if free starch exists in paper pulp, the composite cationic polymer can be used for fixing the free starch on the surfaces of the fibers, so that the paper forming strength can be further improved. This is because the papermaking process using recycled fibers as the starting material can increase the strength of the finished paper by two different mechanisms due to the often unequal amounts of free starch present in the slurry. Therefore, the enhancement effect of the composite cationic polymer on the paper strength is obviously superior to that of the common papermaking dry strength agent.

Secondly, compared with the common polyacrylamide dry strength agent for papermaking, the composite cationic polymer disclosed by the invention has the advantages of high content of active ingredients and transportation cost saving. The solids content of the composite cationic polymer of the present invention is typically between 30% and 50% absolute dry, in contrast to polyacrylamide which is used as a dry strength agent in papermaking, which is typically an aqueous solution having a concentration of 10% to 20%.

Thirdly, the composite cationic polymer of the invention is used for recycling the free starch in the paper pulp, thereby not only improving the strength of the paper, but also reducing the environmental pollution. For the papermaking process using recycled fibers as raw materials, because the pulp is always provided with the free starch with different amounts, the starch not only can increase the activity of microorganisms in a papermaking system, so that the pulp generates peculiar smell due to the activity of the microorganisms and pollutes the air in a papermaking workshop, but also can increase the COD discharge of papermaking wastewater, and is unfavorable for environmental protection. In addition, in some cases, microbial activity of the pulp can also cause spoilage of the pulp, forming a pulp, affecting the quality of the finished paper product. The composite cationic polymer can be applied to the papermaking production process, and the part of free starch can be reserved on papermaking fibers again, so that the free starch plays a role in improving the strength of paper sheets, meanwhile, the circulation of the free starch in a paper machine system is reduced, the COD emission of waste water is reduced, the peculiar smell in the air is lightened, and the environment is protected.

Fourthly, the composite cationic polymer can fix and retain the basic neutral raw starch molecules on the fiber, so that the direct application of the raw starch as a papermaking dry strength agent is possible. The raw starch is not chemically modified, is basically electrically neutral, and is not easy to be fixedly reserved on papermaking fibers. Thus, raw starch cannot generally be added directly to pulp as a dry strength agent for papermaking. However, by using the composite cationic polymer of the invention, the basic neutral raw starch molecules can be fixedly remained on the fiber, thereby achieving the purpose of further improving the strength of paper. Thus, the raw starch can be directly used as the papermaking dry strength agent, which is more cost-effective than the modified starch, such as cationic starch or amphoteric starch, used as the papermaking dry strength agent.

Detailed Description

In order that the invention may be understood more fully, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended claims. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.

Term interpretation:

composite cationic polymer: two or more cationic polymers of different properties are combined together by a physical chemical process, not simple mechanical mixing, to form a uniform and stable product, wherein the individual cationic polymer molecules are not independently present but are combined with each other by non-covalent forces.

Apparent molecular weight of the composite cationic polymer: the molecular weight of the composite cationic polymer as a whole.

Apparent intrinsic viscosity of the composite cationic polymer: the intrinsic viscosity of the composite cationic polymer as a whole was measured.

Apparent charge density of the composite cationic polymer: the charge density measured for the composite cationic polymer as a whole.

Cationic degree of cationic copolymer: the cationic monomer comprises mole percent of all monomers of the copolymer.

Pulp free starch: the starch molecules present in the aqueous phase of the pulp, either from recycled fibers or from the starch from which the broke is dissolved during the pulping process, or from additional raw or non-ionic starches, are characterized by being essentially uncharged, electrically neutral or near electrically neutral, and are difficult to fix and retain on the papermaking fibers by electrostatic interactions and thus are present in the aqueous phase of the pulp primarily in the form of free molecules.

The invention relates to application of a composite cationic polymer in a papermaking process to improve paper strength and control anionic trash in a papermaking system. The composite cationic polymer is in fact a suspension of particles of cationic polymer a with cationic polymer B as dispersant. Can be prepared by water-dispersible polymerization techniques. Specifically, in an aqueous dispersion containing a cationic polymer B, a cationic monomer and a nonionic monomer required for synthesizing the cationic polymer A are added, and then the monomers are initiated to undergo free radical polymerization under the condition of no oxygen to produce cationic polymer A particles. Since the cationic polymer B has a protective and dispersing effect on the cationic polymer A particles, the polymerization reaction finally forms a homogeneous and stable particle suspension, also known as a double aqueous emulsion or a water-in-water emulsion. If necessary, adjuvants may be added to give the particle suspension of the composite cationic polymer better stability and flowability.

From the perspective of papermaking, the composite cationic polymer has the greatest characteristics that two common papermaking aids, namely a dry strength agent and an anionic trash catcher, are combined into one product, so that the operation is simplified, and the time and the labor are saved. In addition, the composite cationic polymer disclosed by the invention does not contain an organic solvent and has the characteristics of environment friendliness.

The inventor of the present invention unexpectedly found in the experimental process that the addition of the composite cationic polymer of the present invention to pulp can replace the common polyacrylamide aqueous solution dry strength agent to improve the binding force between the paper-forming fibers; in addition, for the papermaking process using recycled fibers as raw materials, the composite cationic polymer can fix the dissolved free starch on the surface of the fibers due to the existence of the free starch dissolved from the recycled fibers in the slurry, thereby further playing a role in reinforcement. That is, for the paper making process using recycled fiber as raw material, the composite cationic polymer can raise the strength of the paper to make the strength of the paper better than that of common polyacrylamide water solution dry strength agent.

The solid content of the composite cationic polymer is 25-60% of absolute dryness, the apparent molecular weight is 1,000,000g/mol to 5,000,000g/mol, the charge type is cationic, and the apparent charge density is 0.2-5 meq/g. In contrast, polyacrylamides conventionally used in the art as dry strength agents for papermaking are typically aqueous solutions having a concentration of 10% to 20%, a molecular weight of between 100,000g/mol and 1,000,000g/mol, charge types being cationic, anionic, amphoteric and nonionic, and the net charge density (ph=7) typically being below 0.2meq/g. The inventors have found that molecular weight (or intrinsic viscosity) and charge characteristics are key factors affecting the reinforcing effect of the polyacrylamide dry strength agent. Too low or too high molecular weight (or intrinsic viscosity) is detrimental to improving the strength of the paper, and if too low molecular weight (or intrinsic viscosity) results in a low adsorption efficiency of the polyacrylamide molecules on the fiber surface, which is detrimental to improving the strength of the paper; conversely, if the molecular weight (or intrinsic viscosity) is too high, excessive flocculation of the fibers is liable to occur, affecting the uniformity of the paper, but adversely affecting the strength of the paper. Likewise, if the cationic degree of polyacrylamide is too low, adsorption of the polyacrylamide molecules on the fiber surface is not favored, whereas if the cationic degree is too high, localized excessive flocculation of the pulp is caused, which is detrimental to improving the paper strength.

While cationic polyacrylamide water-in-water emulsions are commercially available, these commercial cationic polyacrylamide water-in-water emulsions are commonly used as flocculants for the treatment of sewage and sludge, as retention and drainage aids in papermaking, to improve retention and drainage properties of the stock, rather than as a dry strength agent to improve the strength of the finished paper, such products typically employ polydimethyl diallyl ammonium chloride homopolymer as a dispersant, and cationic polyacrylamide copolymers as flocculants and papermaking retention and drainage aids typically have a cationic degree of no more than 30mol%. The composite cationic polymer is synthesized by adopting a water-dispersible polymerization method. Water-dispersion polymerization processes are also known as two-aqueous phase polymerization, or water-in-water emulsion polymerization. Such synthetic methods are known to those familiar with the art. According to the method disclosed in U.S. Pat. No. 3,137, soluble polymer composition, cationic polyacrylamide is polymerized by reacting monomers (including acrylamide monomers and cationic monomers) in aqueous solutions containing different cationic polymers as dispersion stabilizers. In the early stage of dispersion polymerization, the monomer, the initiator, the dispersion stabilizer and other auxiliary agents are completely dissolved in a reaction medium and are a homogeneous system; when the reaction is carried out to a certain extent, as the cationic polyacrylamide copolymer molecules are generated, and the chain length of the molecular chains reaches a critical point, granular precipitate is formed as the cationic polyacrylamide copolymer molecules become insoluble in the reaction medium, and precipitation from the reaction medium begins; these particles continue to grow while the adsorption dispersion stabilizer is uniformly and stably dispersed in the system to form a stable particle suspension, otherwise known as a two-aqueous phase emulsion, a water-in-water emulsion, in which the cationic polyacrylamide copolymer preferably has a cationicity of 40 to 60mol%.

Suitable cationic polymers B for use in the composite cationic polymers of the present invention are cationic homopolymers selected from the group consisting of polyacrylamide propyl trimethyl ammonium chloride, polymethacrylamide propyl trimethyl ammonium chloride, polyacrylamide ethyl trimethyl ammonium chloride, polymethacrylamide ethyl trimethyl ammonium chloride, polydimethylaminopropyl acrylamide, polydimethylaminopropyl methacrylamide, polydimethylaminoethyl acrylamide, polydimethylaminoethyl methacrylamide, polyacrylamidoethyl trimethyl ammonium chloride, polymethacryloyloxyethyl trimethyl ammonium chloride, polyacrylamidoethyl trimethyl ammonium chloride, polyacrylamidopropyl trimethyl ammonium chloride, polymethacryloyloxypropyl trimethyl ammonium chloride, polyacrylic acid dimethylaminoethyl ester, polydimethylaminoethyl methacrylate, polydimethylaminopropyl acrylate, polydimethylaminopropyl methacrylate, polyacrylamidoethyl dimethylbenzyl ammonium chloride, polydiacryloyloxyethyl dimethylbenzyl ammonium chloride, polyacrylamidoethyl dimethyl benzyl ammonium chloride, polydimethyl diallyl ammonium chloride, epichlorohydrin-dimethylamine, polyethylene imine, polyamide quaternary ammonium salts and polyamide quaternary ammonium salts.

Cationic polymer a suitable as the composite cationic polymer in the present invention is a cationic copolymer produced by free radical polymerization of a nonionic monomer and a cationic monomer in a reaction medium containing cationic polymer B as a dispersion stabilizer. Wherein the cationic monomer is selected from at least one of acryloyloxyethyl trimethyl ammonium chloride, methacryloyloxyethyl trimethyl ammonium chloride, acryloyloxypropyl trimethyl ammonium chloride, methacryloyloxypropyl trimethyl ammonium chloride, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, dimethylaminopropyl acrylate, dimethylaminopropyl methacrylate, acryloyloxyethyl dimethylbenzyl ammonium chloride, methacryloyloxyethyl dimethylbenzyl ammonium chloride, acryloyloxypropyl dimethylbenzyl ammonium chloride, methacryloyloxypropyl dimethylbenzyl ammonium chloride, acrylamide propyl trimethyl ammonium chloride, methacrylamidopropyl trimethyl ammonium chloride, acrylamide ethyl trimethyl ammonium chloride, methacrylamidoethyl trimethyl ammonium chloride, N- (3-dimethylaminopropyl) acrylamide, N- (3-dimethylaminopropyl) methacrylamide, N- (2-dimethylaminoethyl) acrylamide, N- (2-dimethylaminoethyl) methacrylamide and dimethyl diallyl ammonium chloride.

The nonionic monomer of the cationic polymer A is at least one selected from the group consisting of acrylamide, methacrylamide, N-methylacrylamide, N-methyl (meth) acrylamide, N-isopropylacrylamide, N-isopropyl (meth) acrylamide, N-dimethylacrylamide, N-diethylacrylamide, N-methyl-N-ethylacrylamide, N-hydroxyethyl (meth) acrylamide and N-hydroxyethyl (meth) acrylamide.

The nonionic monomer of the cationic polymer A and the cationic monomer are subjected to free radical polymerization in a reaction medium containing the cationic polymer B as a dispersion stabilizer to form the cationic polymer A, and the composite cationic polymer is formed in the process of forming the cationic polymer A. The apparent molecular weight of the composite cationic polymer is 1,000,000g/mol to 5,000,000g/mol, preferably 1,000,000g/mol to 3,000,000g/mol, preferably 1,700,000g/mol to 2,500,000g/mol.

The mass ratio of the cationic polymer A to the cationic polymer B in the composite cationic polymer is 1:0.1-2, preferably 1:0.5-1.5.

The samples used in the examples below, wherein C is the comparative sample and E1-E4 are the samples described according to the invention, have the main characteristics listed in Table 1.

TABLE 1

Sample C: comparative sample, "paper dry strength agent-1971", amphoteric polyacrylamide dry strength agent, product of paper research institute, guangdong province.

Sample E1: the preparation method of the composite cationic polymer sample prepared by the invention is as follows:

step 1: preparation of cationic Polymer B, acryloxypropyl trimethylammonium chloride homopolymer solution (40 wt.%)

352g of purified water, 770g of acrylamide propyl trimethyl ammonium chloride monomer (acrylic acid amide propyl-trimethyl ammonium chloride) having a concentration of 60% by weight and 5.6g of sulfuric acid having a concentration of 50% by weight were charged into a 2L glass reaction vessel equipped with a paddle stirrer and a thermometer. After deoxygenation by nitrogen for 30 minutes, the temperature was raised to 65℃and then 200ppm of the initiator azobisis Ding Mi hydrochloride (VA-044) and the chain transfer agent mercaptoethanol were added. When the temperature reached 85℃150ppm of initiator VA-044 were added and stirred at this temperature for 2 hours. Finally, the obtained product (polyacrylamide propyl trimethyl ammonium chloride homopolymer solution, solid content of which is 40 wt%) was cooled to room temperature and used for the next reaction.

Step 2: polymerization of cationic Polymer A and preparation of composite cationic Polymer suspension

292.5g of the aqueous cationic polymer B prepared above, 70.2g of a 50% strength by weight acrylamide solution, 102.7g of the cationic monomer acryloyloxyethyl trimethyl ammonium chloride (acryloyloxyyethyl-trimethyl ammonium chloride) having a concentration of 80% by weight, 100g of purified water, 6.4g of ammonium sulfate, 1.3g of a chelating agent 5% diethylenetriamine pentasodium pentaacetate solution (Versenex 80) were charged into a 2L glass reaction vessel equipped with a paddle stirrer and a thermometer. After heating to an initial temperature of 35℃and deoxygenation by passing nitrogen, 50ppm sodium metabisulfite, 50ppm sodium persulfate and 5ppm t-butyl hydroperoxide (TBHP) were added to initiate polymerization. Once the temperature reached 60 ℃, 400ppm of initiator 2,2' -azobisisobutylamidine dihydrochloride (ABAH) was added and the reaction was allowed to react at this temperature for an additional 15 minutes. Then 5g of citric acid was added and the final product was cooled to room temperature, 573g of a composite cationic polymer product having a solids content of 42.8% were obtained, wherein the cationic degree of cationic polymer A was 50mol% (i.e., the molar ratio of acrylamide monomer to acryloyloxyethyl trimethyl ammonium chloride cationic monomer was 1:1), and the mass ratio of cationic polymer A to cationic polymer B was 1:1.

Sample E2: water-in-water type polyacrylamide emulsion, a product of Jiangsu wood forest environmental protection technology Co., ltd.

Sample E3: performance K8442, water-in-Water Polyacrylamide emulsion, sorism chemical Co., ltd.

Sample E4: CE6520, water-in-water polyacrylamide emulsion, no tin city Tian Xin chemical company, inc.

The basic test methods used in the examples are as follows:

1. determination of the solid content of the test sample: about 2g of the sample was taken, placed in a weighing bottle which had been dried to constant weight, placed in an oven, dried at 105℃for 4 hours, taken out, placed in a desiccator for cooling for 30min, weighed and calculated.

2. Apparent characteristic viscosity measurement of the composite cationic polymer: according to a point method in national standard GB12005.1-1989 "method for measuring the intrinsic viscosity of polyacrylamide", a certain amount of a complex cationic polymer sample stock solution is diluted to a proper concentration, and then measured by an Ubbelohde viscometer.

3. Determination of apparent molecular weight of the composite cationic Polymer: after the apparent intrinsic viscosity of the composite cationic polymer is measured by the method, the formula [ eta ] is applied according to national standard GB/T12005.10-92 "viscosity method for polyacrylamide molecular weight determination method ]]＝0.0183M ^0.72 The apparent molecular weight of the composite cationic polymer was calculated.

4. Apparent charge density of the composite cationic polymer: diluting a certain amount of complex cationic polymer sample stock solution to a proper concentration, taking 0.001N PVSK solution as titration solution, and using BTG-The PCD-05 particle charge meter titrates to the endpoint and calculates the absolute sample charge.

5. Sheet making experiment: according to the method of the conventional paper sheet former method for preparing laboratory paper sheets of paper pulp of the light industry standard QB/T3703-1999 of China, unless otherwise specified, 320g of a 1% concentration pulp sample is taken, 100g of sheet is made into a sheet with a quantitative quantity of 100g by an IMT-CP01A-3 paper sheet former of an Dongguan Ind Toosen precision instrument, and then the sheet is put into a dryer for drying at 105 ℃ for 5min.

6. Tensile index: according to national standard GB/T22898-2008 "constant speed tensile method for measuring tensile Strength of paper and paper Board", a sheet paper sample is balanced for 24 hours under standard conditions, then cut into 15mm×150mm specifications, and the tensile Strength F is measured by a Runfu computer tensile tester RH-KZY, and the tensile index is calculated as follows:

tensile index = F/sample basis weight

7. Burst index: according to national standard GB/T1539-2007 "determination of paper board bursting strength", balancing a sheet paper sample for 24 hours under standard conditions, and then determining the bursting strength P of the paper sample by using an IMT-201B paper bursting strength determinator of an Dongguan Enginsen precision instrument, wherein the bursting strength index is calculated as follows:

Burst index = P/sample quantification

8. Folding endurance: according to national standard GB/T457-2008 'determination of paper and paperboard folding endurance', the sheet paper sample is balanced for 24 hours under standard conditions, and then is determined by an IMT-205AMIT paper folding endurance determinator of an Dongguan Enginsen precision instrument.

9. Preparation of raw starch solution: taking a certain amount of corn starch, adding water to prepare a starch solution with the concentration of 6%, stirring in a water bath with the temperature of 95 ℃ for 1h, and preserving the temperature of 65 ℃ for later use.

10. Preparation of OCC pulp white water: taking a certain amount of Wanlida OCC, adding 80 ℃ warm water to 13% pulp concentration, pulping for 30min by using an IMT-BSJ high-concentration hydraulic pulper of an Dongguan English Ten-Neisserian precision instrument, taking a pulp sample, filtering and dehydrating, collecting filtrate, and adding 1:3 clear water for dilution to obtain OCC pulp white water.

11. Determination of white water free starch: and (3) centrifuging a certain volume of OCC slurry white water at 4000rpm for 2min, then transferring a certain amount of centrifugal supernatant into a colorimetric tube, adding 0.01N I2/IK dilute iodine solution for color development, measuring absorbance at 600nm, and converting according to a starch absorbance-concentration standard curve to obtain the free starch concentration.

12. Pulp: vanda boxboard OCC pulp, goldfish bleached hardwood pulp, iridescent float Bai Zhenshe pulp.

The following are specific examples.

Example 1

Mixing bleached chemical pulp of goldfish with bleached hardwood pulp of iridescent float Bai Zhenshe pulp in a ratio of 9:1, diluting with clear water to about 1.3% pulp concentration, defibering and pulping with a tile Li Dajiang machine to a beating degree of 29oSR, and supplementing clear water to 1% for later use. 2200g of a prepared slurry sample (1% slurry concentration) was taken, and an aqueous solution of the test sample diluted to 1% concentration was added to each of the sample amounts shown in Table 2 under stirring at 1200rpm, and the reaction was fluffed in a standard fluffer for 4 minutes, and then water was added to a total of 2250g. Taking 320g of the treated slurry, and making into 100g/m by using IMT-CP01A-3 paper sheet former ² The sheet was subjected to total 6 sheets and dried at 105℃for 5 minutes, and the water was equilibrated in a constant humidity chamber for 24 hours, to thereby examine physical properties.

As can be seen from the experimental results shown in Table 2, for bleached chemical pulps containing no free starch, the composite cationic polymer samples E1-E4 of the present invention are comparable to the conventional polyacrylamide dry strength agent used as comparative sample C in terms of improving the tensile index and burst index of the sheet, wherein E1 is better than E2-E4, at the same absolute dry dosage.

TABLE 2

Example 2

Taking Wanli finished product OCC cardboard paper, soaking the cardboard paper in clear water, and then fluffing and pulping the cardboard paper by using a tile Li Dajiang machine to prepare the slurry with the concentration of 1.3%. 2200g of the prepared slurry was stirred at 1200rpm for each of the test samples shown in Table 3 The test sample aqueous solution diluted to 1% concentration was added in an amount, stirred for 2 minutes, and water was added to 2250g in total. 355g of the treated slurry was sampled and formed into a sheet having a basis weight of 120g/m by an IMT-CP01A-3 sheet former ² The sheet was subjected to total 6 sheets and dried at 105℃for 5 minutes, and the water was equilibrated in a constant humidity chamber for 24 hours, to thereby examine physical properties.

From the experimental results shown in table 3, it can be seen that under the condition of the same absolute dry dosage, the composite cationic polymer E1 of the present invention has an effect of improving the tensile index, the folding endurance and the burst index of the OCC pulp recycled fiber sheet, but the effect of E1 is more obvious and is obviously better than that of the comparative sample C. This is probably due to the dual reinforcement mechanism of the composite cationic polymer E1 described in this invention for OCC slurries, whereas the common polyacrylamide dry strength agent C has only a single reinforcement mechanism.

TABLE 3 Table 3

Example 3

The bleached chemical pulp goldfish bleached hardwood pulp and the dried pulp of the iridescent float Bai Zhenshe pulp are mixed according to the proportion of 9:1 to prepare 1.3% concentration pulp. The tile Li Dajiang machine is used to first defiberize and pulp to a degree of beating of 30oSR. 2200g of prepared slurry sample is taken, 14.7g of prepared 6% raw starch solution (equivalent to the starch dosage of 40kg/t paper) is added, after the fluffing reaction is carried out for 1min in a standard fluffer, the dosage of each test sample listed in table 4 is calculated, the test sample aqueous solution diluted to 1% concentration is added, then the fluffing reaction is carried out for 3min in the standard fluffer, and water is added to 2250g in total. Taking 320g of the treated slurry, and making into 100g/m by using IMT-CP01A-3 paper sheet former ² The sheet was totally 6 sheets, dried at 105℃for 5 minutes, and the sheet was kept in a constant humidity chamber for balancing the water content for 24 hours to measure the physical properties. Another 10g of the treated pulp was taken and the content of dissolved starch (i.e. white water starch) in the pulp after the reaction was determined.

From the experimental results shown in table 4, it can be seen that the composite cationic polymer E1 of the present invention has more remarkable effect of improving the tensile index and burst index of paper in the presence of the additional raw starch, and is significantly better than that of the conventional polyacrylamide dry strength agent comparative sample C. Furthermore, it can be seen from the results of Table 4 that the free starch concentration in the pulp is reduced after the addition of the complex cationic polymer E1. This means that the free starch molecules in the pulp are fixed to the sheet, thereby further increasing the strength of the sheet. In contrast, sample C had little to no fixed retention of free starch in the pulp.

TABLE 4 Table 4

Example 4

Mixing bleached chemical pulp of goldfish with dried pulp of iridescent float Bai Zhenshe in a ratio of 9:1, adding white water of OCC pulp to 1.3% pulp concentration, fluffing and pulping to beating degree of 29oSR by using a tile Li Dajiang machine, and then supplementing water to 1% pulp concentration for standby. 2200g of prepared slurry was taken, and an aqueous solution of the test sample diluted to a concentration of 1% was added in the amounts of the respective test samples shown in Table 5, followed by a fluffing reaction in a standard fluffer for 4 minutes, and water was added to a total of 2250g. Taking 320g of the treated slurry, and making into 100g/m by using IMT-CP01A-3 paper sheet former ² The sheet was subjected to total 6 sheets and dried at 105℃for 5 minutes, and the water was equilibrated in a constant humidity chamber for 24 hours, to thereby examine physical properties. Another 10g of the treated pulp was taken and the content of dissolved starch (i.e. white water starch) in the pulp after the reaction was determined.

As can be seen from the experimental results in Table 5, for the bleached chemical pulp containing OCC white water free starch, the composite cationic polymers E1-E4 have the effect of improving the tensile index and the burst index of the finished paper, in particular E1, and the effect is more obvious and obviously better than that of a conventional polyacrylamide dry strength agent comparative sample C. Furthermore, it can be seen from the results of Table 5 that the free starch concentration in the pulp is significantly reduced after the addition of the complex cationic polymer E1. This means that the free starch molecules in the pulp are fixed to the sheet, thereby further increasing the strength of the sheet. In contrast, control C had little retention of any fixation to the free starch in the pulp. This demonstrates that samples E1-E4 have better enhancement on paper formation than sample C, since the composite cationic polymer of the present invention has a dual enhancement mechanism for pulp containing free starch, whereas the conventional polyacrylamide dry strength agent C has only a single enhancement mechanism. In addition, sample E1 performed better than samples E2-E4, probably because samples E2-E4, although being cationic polyacrylamide water-in-water emulsions of the same genus as sample E1, were used as flocculants, and were not designed specifically to increase paper strength, and their polymerized monomers and cationicity were different from that of sample E1.

TABLE 5

Example 5

To illustrate the effectiveness of the composite cationic polymers of the present invention as an anionic trash catcher (or fixative as well) in a papermaking process, the sludge from the paper mill is selected to represent anionic trash in the papermaking slurry system. 28.7g of paper sludge (solid content 4.28%) was taken in a 250ml plastic beaker, and the solution of the complex cationic polymer E1 or E4 diluted to 0.1% was added under stirring, and stirring was continued for 10s. Then, the reacted sludge was added to 2328g of vanda boxboard OCC slurry having a slurry concentration of 1%, so that the mixed pulp contained 5wt% of sludge on a dry weight basis, and was stirred at 1800rpm with a propeller type stirrer, and a dry strength agent for paper making of 1.5kg/t of paper was added on a dry weight basis (comparative sample C). After continuing to stir 30, 75g of the mixed slurry was diluted to 250g with deionized water to make the slurry concentrated to be diluted to 0.3%, then the diluted slurry was poured into a 250ml PALL magnetic funnel for vacuum filtration, and the collected filtrate was used as simulated white water for papermaking, and the turbidity of the filtrate was measured with a WZS180 Lei Ci nephelometer (Shanghai electric scientific instruments). The turbidity reflects the amount of anionic trash in the simulated white water. The lower turbidity indicates less anionic trash in the simulated white water and vice versa. The results of the experiment are shown in Table 6.

From the experimental results in Table 6, it can be seen that both the complex cationic polymers E1 and E4 described in the present invention reduce the turbidity of the simulated papermaking white water, indicating that E1 and E4 capture and fix a portion of the anionic trash in the slurry. It can also be seen from the experimental results of Table 6 that sample E1 captured and immobilized anionic trash more effectively than sample E4. This is probably because, although both belong to the same cationic polyacrylamide water-in-water emulsion, sample E4 is a commercially available product that is designed to act as a flocculant, rather than being designed to capture and immobilize anionic trash in the papermaking system, and its polymerized monomer and cationicity are different from sample E1.

TABLE 6

The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.

The above examples illustrate only a few embodiments of the invention, which are described in detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.

Claims

1. A method of making paper having improved paper strength comprising the steps of:

2. The method for improving the paper-forming strength of paper according to claim 1, wherein the cationic polymer a is a cationic copolymer produced by radical polymerization of a nonionic monomer and a cationic monomer in a reaction medium containing the cationic polymer B as a dispersion stabilizer; wherein the cationic monomer is selected from at least one of acryloyloxyethyl trimethyl ammonium chloride, methacryloyloxyethyl trimethyl ammonium chloride, acryloyloxypropyl trimethyl ammonium chloride, methacryloyloxypropyl trimethyl ammonium chloride, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, dimethylaminopropyl acrylate, dimethylaminopropyl methacrylate, acryloyloxyethyl dimethylbenzyl ammonium chloride, methacryloyloxyethyl dimethylbenzyl ammonium chloride, acryloyloxypropyl dimethyl benzyl ammonium chloride, methacryloyloxypropyl dimethylbenzyl ammonium chloride, acrylamide propyl trimethyl ammonium chloride, methacrylamidoethyl trimethyl ammonium chloride, N- (3-dimethylaminopropyl) acrylamide, N- (3-dimethylaminopropyl) methacrylamide, N- (2-dimethylaminoethyl) acrylamide, N- (2-dimethylaminoethyl) methacrylamide and dimethyldiallyl ammonium chloride; the nonionic monomer is at least one selected from the group consisting of acrylamide, methacrylamide, N-methylacrylamide, N-methyl (meth) acrylamide, N-isopropylacrylamide, N-dimethylacrylamide, N-dimethyl (meth) acrylamide, N-diethylacrylamide, N-diethyl (meth) acrylamide, N-methyl-N-ethylacrylamide, N-methyl-N-ethyl (meth) acrylamide, N-hydroxyethyl acrylamide and N-hydroxyethyl (meth) acrylamide.

3. Papermaking process with improved paper strength according to claim 2, characterised in that the cationic polymer a has a cationicity of 10 to 90mol%, preferably 30 to 70mol%, more preferably 40 to 60mol%.

4. The method for making paper with improved paper forming strength according to claim 2, wherein the nonionic monomer in the cationic polymer a is acrylamide and the cationic monomer is acryloyloxyethyl trimethyl ammonium chloride.

5. The method of claim 4, wherein the molar ratio of acrylamide to acryloyloxyethyl trimethyl ammonium chloride is 1:0.1-4, preferably 1:0.25-2, more preferably 1:0.75-1.25.

6. The method of making paper having improved paper forming strength according to claim 1, wherein the cationic polymer B is a cationic homopolymer selected from the group consisting of polyacrylamide propyl trimethyl ammonium chloride, polymethacrylamide propyl trimethyl ammonium chloride, polyacrylamide ethyl trimethyl ammonium chloride, polymethacrylamide ethyl trimethyl ammonium chloride, polydimethyl amino propyl acrylamide, polydimethyl amino propyl methacrylamide, polydimethyl amino ethyl acrylamide, polydimethyl amino ethyl methacrylamide, polyacrylamidoethyl trimethyl ammonium chloride, polymethacryloyloxyethyl trimethyl ammonium chloride, polyacrylamidopropyl trimethyl ammonium chloride, polymethacryloyloxypropyl trimethyl ammonium chloride, polydimethyl amino ethyl polyacrylate, polydimethyl amino ethyl methacrylate, polydimethyl amino propyl polyacrylate, polydimethyl amino propyl methacrylate, polyacrylamidoethyl dimethylbenzyl ammonium chloride, polymethyl acryloxyethyl dimethylbenzyl ammonium chloride, polydimethyl propyl ammonium chloride, polydimethyl diallyl ammonium chloride, epoxypropane-diamine, and poly (quaternary ammonium salts).

7. The method of claim 1, wherein the composite cationic polymer has an apparent intrinsic viscosity of 100-800 mL/g, preferably 150-550 mL/g, more preferably 380-520 mL/g, more preferably 480-510 mL/g.

8. The paper making process for improving the paper forming strength according to claim 1, wherein the apparent charge density of the complex cationic polymer is 0.2 to 5meq/g, preferably 0.5 to 4meq/g, more preferably 3 to 3.6meq/g, on a dry weight basis.

9. A method of making paper having improved paper forming strength according to claim 1, wherein the complex cationic polymer is added to the papermaking slurry in the form of a complex cationic polymer suspension having a solids content of 25% to 60%, preferably 35% to 50%, more preferably 40% to 45%.

10. Papermaking process with improved paper strength according to claim 1, characterised in that the mass ratio of cationic polymer a to cationic polymer B is 1:0.1-2, preferably 1:0.5-1.5.

11. The method of making paper having improved paper forming strength according to claim 1, wherein the method of preparing the composite cationic polymer comprises the steps of:

a) Preparing an aqueous solution of the cationic polymer B;

12. Papermaking process for increasing the paper-forming strength according to any one of claims 1-11, characterised in that the amount of said complex cationic polymer is 0.1kg/t-4kg/t paper, preferably 0.5kg/t-3.5kg/t paper, more preferably 1kg/t-3kg/t paper, more preferably 1.5kg/t-3kg/t paper, more preferably 2.0kg/t-2.8kg/t paper, on an absolute dry basis.

13. A method of making paper with increased paper strength according to any of claims 1-11, characterized in that the reaction time is 10s-60min.

14. A method of making paper having improved paper strength according to any of claims 1-11, characterized in that the papermaking stock contains free starch.

15. Papermaking process for improving the paper-forming strength according to claim 14, characterised in that the free starch content of the papermaking stock is 1-100kg/t paper, preferably 1-50kg/t paper, on an oven dry weight basis.

16. The method of making paper having improved paper strength according to any one of claims 1 to 11, wherein the papermaking stock is selected from one or more of OCC stock, deinking stock, mechanical stock, chemi-mechanical stock, semi-chemical stock and chemical stock.

17. The method of making paper having improved paper strength according to any one of claims 1 to 11, wherein one or more of the following adjuvants are added to the papermaking slurry prior to preparing the papermaking slurry into a paper product: dry strength agent, wet strength agent, retention and drainage aid, sizing agent, adhesive control agent and defoaming agent.

18. Use of a complex cationic polymer as claimed in any one of claims 1 to 11 as a paper reinforcing agent in the production of paper.

19. Use of a complex cationic polymer as claimed in any one of claims 1 to 11 as an anionic trash catcher in papermaking production.

20. Use of a complex cationic polymer as defined in any one of claims 1-11 as a free starch retention agent in pulp to fixedly retain starch molecules on the resulting fibers during the papermaking process.

21. Use of a complex cationic polymer as claimed in any one of claims 1 to 11 for the recovery of free starch in papermaking wastewater.

22. Use of a complex cationic polymer as claimed in any one of claims 1 to 11 for reducing the COD concentration of papermaking wastewater.