Polymer, paper reinforcing agent and preparation method thereof

Abstract

The invention belongs to the field of macromolecules, and discloses a polymer for a paper reinforcing agent, the polymer contains an acrylamide structural unit, a cationic structural unit containing a cationic group, and a functional structural unit for improving the rigidity or crosslinking density of the polymer; the weight-average molecular weight of the polymer is 0.5-1 million, and the dispersion coefficient is less than 3. After the polymer is applied to a paper reinforcing agent, the strength of paper can be improved, and meanwhile, the water filtering performance can be improved. Meanwhile, the invention also provides a preparation method of the polymer, a paper reinforcing agent and a preparation method of the paper reinforcing agent.

Description

Technical Field

[0001] The present invention relates to the field of polymers, and particularly to a polymer, a paper strengthening agent and a preparation method thereof. Background Art

[0002] In the papermaking process, in order to endow the finished paper with dry strength, it is often necessary to add some strength aids. Currently, dry strength agents used include modified starch, chitosan and other natural polymers, acrylamide (PAM) and polyvinyl alcohol (PVA) in synthetic polymers, etc. Among them, according to their charge properties, they can be divided into cationic type (CPAM), anionic type (APAM) and amphoteric dry strength agents (ACPAM).

[0003] Patent technologies CN 116964147 A and CN 113785029 A describe an aqueous aldehyde compound as a paper strengthening agent, which is a glyoxal-modified cationic polyacrylamide-based strengthening agent. However, the strengthening amplitude is not enough. Especially in a system with more short fibers, the strength increase of the obtained finished paper is less, thus limiting the wide use of such strengthening agents.

[0004] The problem to be solved by this solution: how to improve the strengthening amplitude of the paper strengthening agent for paper. Summary of the Invention

[0005] The purpose of the present invention is to provide a polymer. After this polymer is applied to a paper strengthening agent, it can improve the strength of paper and at the same time improve the water filtration performance.

[0006] Meanwhile, the present invention also provides a preparation method of this polymer, a paper strengthening agent and a preparation method thereof.

[0007] To achieve the above purpose, the present application discloses a polymer for a paper strengthening agent. The polymer contains acrylamide structural units, cationic structural units containing cationic groups, and functional structural units for improving the rigidity or crosslinking density of the polymer;

[0008] The weight-average molecular weight of the polymer is 500,000 to 1,000,000, and the dispersion coefficient is 1.5 to 3.

[0009] The strength of paper fibers is generally composed of four factors: 1. The strength of a single fiber; 2. The bonding strength between fibers; 3. The bonding area of fibers; 4. The evenness of the finished paper. And the strengthening agent generally improves the fiber bonding area and strength, makes more fibers more dense, and at the same time improves the overall bonding strength, thereby achieving the improvement of strength.

[0010] To achieve the affinity for fibers, especially the bonding of short fibers, the hydrogen bonds, chemical bonds, and physical entanglements between the polymer network and the fibers are utilized to enhance fiber bonding and strength. At the same time, the molecular weight and dispersity of the polymer are also factors affecting the binding stability with the fibers. If the molecular weight is too small, although it can bind to the fibers faster, due to its low strength, the resulting strength is not significant. Meanwhile, if the molecular weight is too large, the binding speed with the fibers is slow, the evenness of the resulting paper is poor, and the resulting strength will not be too large. Therefore, a moderate molecular weight is emphasized in the present invention.

[0011] The dispersity of the polymer molecular weight represents the molecular weight statistical data. If the dispersity is too large, there will be a lack of strength performance. Obtaining a polymer with a low dispersion coefficient is also one of the objectives of the present invention. Further optimization to obtain an ideal strength, and having a polymer network structure that can react with the fibers is the key to achieving the purpose of this invention.

[0012] Generally speaking, a polymer with a certain network structure can achieve the retention of fine fibers, enabling the fibers to better contact and stack, thereby achieving an increase in strength. Secondly, the strength of the paper is improved by increasing the interaction strength between the polymer and the fibers. Finally, the overall strength of the paper is imparted by increasing the strength of the polymer itself.

[0013] In summary, in this case, the strength of the polymer is enhanced by using functional structural units, the retention and fixation of fine fibers are improved, and the paper strength is increased. At the same time, by optimizing the molecular weight and molecular weight distribution, the retention and fixation of fine fibers are improved, and a suitable binding speed with the fibers is maintained. Through the above optimizations, a significant increase in paper strength is achieved.

[0014] In the above polymer, the weight-average molecular weight of the polymer is 140,000 - 280,000, and the dispersion coefficient is 2.3 - 2.8. Particularly preferably, the weight-average molecular weight of the polymer is 142,000 - 262,000.

[0015] The cationic monomer generally refers to a compound containing an ammonium salt or other compounds containing a tertiary amine, which ionizes into the corresponding N+ ions in an aqueous solution. More specifically, the acrylamide structural unit is acrylamide or methacrylamide; the cationic structural unit is one or a combination of dimethyldiallylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, and tetraallylammonium chloride.

[0016] The functional structural unit refers to a chemical substance that can bring a specific morphological structure to the polymer, especially some monomers that can increase the rigidity of the polymer or monomers that can increase the density of the polymer network structure.

[0017] Some monomers that can enhance the rigidity of polymers refer to those that can make the polymers more rigid, which can generally be characterized by the glass transition temperature (Tg) of the polymer or by the polymer rigidity index. Among them, the glass transition temperature (Tg) can be pre-estimated by the Fox formula and can also be measured by differential scanning calorimetry. The rigidity index of the polymer can also be represented by the mean square end-to-end distance of the polymer and can be measured by light scattering. Specifically, the functional structural unit is one or a combination of N-isopropylacrylamide, N-hydroxymethylacrylamide, glycidyl methacrylate, and β-acryloyloxypropionic acid.

[0018] In addition, the present invention can also additionally use other functional monomers, which are formed by some polymer post-modification methods and refer to introducing reactive functional groups on the side of the polymer chain.

[0019] In the above polymer, the weight ratio of the acrylamide structural unit, cationic structural unit, and functional structural unit is 70-95:1-30:1-10. Preferably, the weight ratio of the acrylamide structural unit, cationic structural unit, and functional structural unit is 77-84:10-14:5-9; more preferably, the weight ratio of the acrylamide structural unit, cationic structural unit, and functional structural unit is 77.6-83.8:10.4-13.8:5.6-8.4.

[0020] Meanwhile, the present invention also discloses a preparation method of a polymer for a paper strengthening agent as described in any one of the above, characterized in that: it is prepared by a free radical solution polymerization method. Specifically: the method is specifically as follows: dispersing the acrylamide structural unit, cationic structural unit, functional structural unit, and structural regulator in water and carrying out a polymerization reaction under the action of an initiator; the structural regulator is used to adjust the molecular weight and / or molecular weight distribution of the polymer.

[0021] The structural regulator mentioned above is a chemical substance that brings a specific structure to the polymer. Here, the structure refers to a relatively small polymer molecular weight distribution coefficient, which can generally be constructed through a chain reaction during the chain radical growth process. The construction through the chain reaction during the chain radical growth process means that it is completed by controlling the conversion and linking form of the active chain and the inactivated polymer chain during the polymerization chain growth stage. Preferably, it is to capture one or more active polymer chains to inactivate the polymer chain to form a certain structure for the final product. Preferably, the structural regulator is one or a combination of sodium hypophosphite, organic acid, and thiol compounds; the amount of the structural regulator is 0.01 - 0.2 wt% based on the total weight of the monomers; the amount of water used is 4 - 5 times the total weight of the monomers; the initiator is a water-soluble initiator; the initiator is 0.1 - 0.3 wt% based on the total weight of the monomers. The water-soluble initiator is a water-soluble redox initiator system, which includes a water-soluble oxidant and a water-soluble reductant; the water-soluble oxidant includes persulfate, hydrogen peroxide, bromate, etc., and the water-soluble reductant includes sulfite, metabisulfite, thiosulfate, etc.; the water-soluble initiator also includes a water-soluble thermal initiator, including but not limited to water-soluble azo compounds; the water-soluble azo compounds include at least 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, azodiisobutylamidine hydrochloride, etc.

[0022] In the above preparation method, the reaction temperature of the free radical solution polymerization is 30 - 95 °C, and the reaction time is 2 - 6 h; the initiator is added to the reaction system in a dropwise manner; preferably, the reaction temperature of the free radical solution polymerization is 65 °C - 90 °C, and the reaction time is 3 - 5 h.

[0023] Finally, the present invention also discloses a paper strength enhancer, which is obtained by reacting a polymer as described above with an aldehyde agent. Preferably, the mass ratio of the polymer to the aldehyde agent is 3:1 - 14:1; preferably 4:1 - 8:1, and particularly preferably 4.4:1 - 7:1; the pH value of the reaction system is 8 - 12; more preferably, the pH is 9.5 - 10.5; the weight average molecular weight of the paper strength enhancer is 50 - 5 million, and the distribution coefficient is 3 - 8; preferably, the weight average molecular weight of the paper strength enhancer is 84.3 - 111.2 million, and the distribution coefficient is 5.1 - 5.7. The aldehyde agent is a compound containing 2 or more aldehyde group structures, preferably a dialdehyde substance, and particularly preferably glyoxal or glutaraldehyde.

[0024] The present invention has the following advantages and effects compared with the prior art:

[0025] (1) The strength enhancer provided by the present invention is a composition with a moderate molecular weight, a smaller dispersion coefficient, a higher network density, and a stiffer molecular chain.

[0026] (2) In the wet end chemistry of paper, since fines are easily lost with white water, the strength of the resulting product is lower due to less bonding; at the same time, how quickly, stably, and effectively the polymer used as a strengthening agent binds to the fibers is also the key to the effectiveness of strengthening. If the molecular weight is too large or too small, it cannot bind well to the fibers. First, as the water drains away, the fibers quickly bind together due to capillary action. The small molecule part of the polymer can bind to the fibers relatively quickly. Due to the limited contact sites, the larger molecules in the polymer are excluded, resulting in impaired final strengthening effect. However, if the polymer has a large molecular weight, it cannot act on the interior of the fibers before the capillary action disappears, and the bonding between the fibers is only composed of corresponding hydrogen bonds, also leading to impaired final strengthening effect. Therefore, appropriate molecular weight and distribution are one of the important factors for strengthening effect. Finally, since the polymer is finally incorporated into the finished fibers, the strength of its interaction with the fibers, i.e., the bond energy of the bond, is important, and the strength of the polymer itself is also one of the important factors.

[0027] After the strengthening agent provided by the present invention is added among the fibers, the special polymer network structure of the present invention can provide excellent ability to retain fines, so that more fibers are retained, forming more fiber bonds. Compared with the blank, the retention of the product of the present invention reaches more than 30%.

[0028] At the same time, the molecular weight and distribution of the present invention are more suitable, between 800,000 and 1.6 million, and the distribution coefficient is between 4 and 6. Finally, some reaction sites of the product form a relatively strong covalent bonding system with the fibers or itself during the paper drying process, and the strength of the resulting product is greatly improved. Detailed implementation mode

[0029] The following will describe the present invention clearly and completely in combination with the embodiments of the present invention. In the description of the present invention, it should be noted that for those not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0030] Example 1

[0031] The following ratio is carried out (parts are by mass):

[0032] 3000 parts of acrylamide;

[0033] 1200 parts of methacrylamide;

[0034] 290 parts of N-methylolacrylamide;

[0035] 720 parts of diallyldimethylammonium chloride;

[0036] 8 parts of sodium hypophosphite

[0037] 4.3 parts of ammonium persulfate;

[0038] 1.8 parts of sodium metabisulfite;

[0039] Water is adjusted to an effective content of about 17.5%.

[0040] Weigh each component except ammonium persulfate and sodium metabisulfite, mix them, and then conduct nitrogen purging and deoxidation for half an hour. At 60 °C, add ammonium persulfate and sodium metabisulfite dropwise, react for 3 hours while adding dropwise, and keep the temperature for 1 hour to obtain the first polymerized polymer.

[0041] Take 200 parts by mass of the solid content of the effective component of the above-mentioned first polymerized polymer, continue to add 50 parts by mass of glyoxal and mix. React at pH 10 and a temperature of 30 °C for 20 minutes to obtain Composition 1.

[0042] Example 2

[0043] Conduct according to the following ratio (parts are by mass):

[0044] 3000 parts of acrylamide;

[0045] 1200 parts of methacrylamide;

[0046] 450 parts of glycidyl methacrylate;

[0047] 720 parts of diallyldimethylammonium chloride;

[0048] 8 parts of sodium hypophosphite

[0049] 4.3 parts of ammonium persulfate;

[0050] 1.8 parts of sodium metabisulfite;

[0051] Water is adjusted to an effective content of about 17.5%.

[0052] Weigh each component except ammonium persulfate and sodium metabisulfite, mix them, and then conduct nitrogen purging and deoxidation for half an hour. At 60 °C, add ammonium persulfate and sodium metabisulfite dropwise, react for 3 hours while adding dropwise, and keep the temperature for 1 hour to obtain the first polymerized polymer.

[0053] Take 200 parts by mass of the solid content of the effective component of the above-mentioned first polymerized polymer, continue to add 50 parts by mass of glyoxal and mix. React at pH 10 and a temperature of 30 °C for 20 minutes to obtain Composition 2.

[0054] Example 3

[0055] Conduct according to the following ratio (parts are by mass):

[0056] 3000 parts of acrylamide;

[0057] 1200 parts of methacrylamide;

[0058] 150 parts of N - hydroxymethylacrylamide

[0059] 220 parts of glycidyl methacrylate;

[0060] 720 parts of diallyldimethylammonium chloride;

[0061] 8 parts of sodium hypophosphite

[0062] 4.3 parts of ammonium persulfate;

[0063] 1.8 parts of sodium metabisulfite;

[0064] Adjust water to an effective content of about 17.5%.

[0065] Weigh each component except ammonium persulfate and sodium metabisulfite, mix them, and conduct nitrogen purging for deoxygenation for half an hour. At 60 °C, add ammonium persulfate and sodium metabisulfite dropwise, react for 3 hours while adding dropwise, and keep warm for 1 hour to obtain the first - polymerized polymer.

[0066] Take 200 mass parts of the solid content of the effective component of the above - mentioned first - polymerized polymer, continue to add 50 mass parts of glyoxal and mix. React at pH 10 and a temperature of 30 °C for 30 minutes to obtain Composition 3.

[0067] Example 4

[0068] Proceed according to the following ratio (parts are by mass):

[0069] 3000 parts of acrylamide;

[0070] 1200 parts of methacrylamide;

[0071] 450 parts of β - carboxyethyl acrylate;

[0072] 720 parts of diallyldimethylammonium chloride;

[0073] 8 parts of sodium hypophosphite

[0074] 4.3 parts of ammonium persulfate;

[0075] 1.8 parts of sodium metabisulfite;

[0076] Adjust water to an effective content of about 17.5%.

[0077] Weigh each component except ammonium persulfate and sodium metabisulfite, mix them, and conduct nitrogen purging for deoxygenation for half an hour. At 60 °C, add ammonium persulfate and sodium metabisulfite dropwise, react for 3 hours while adding dropwise, and keep warm for 1 hour to obtain the first - polymerized polymer.

[0078] 200 parts by mass of the effective solid content of the polymer obtained by the first polymerization was taken, 50 parts by mass of glyoxal was added and mixed, and the mixture was reacted at a pH of 10 and a temperature of 30° C. for 20 minutes to obtain Composition 4.

[0079] Example 5

[0080] Proceed according to the following ratio (parts are by mass):

[0081] 2000 parts of acrylamide;

[0082] 2200 parts of methacrylamide;

[0083] 290 parts of N-hydroxymethyl acrylamide;

[0084] 520 parts of diallyldimethylammonium chloride;

[0085] 8 parts of sodium hypophosphite

[0086] 4.3 parts of ammonium persulfate;

[0087] 1.8 parts of sodium metabisulfite;

[0088] The water content is adjusted to about 17.5% effective content.

[0089] Weigh all ingredients except ammonium persulfate and sodium metabisulfite, mix them, and then deoxygenate them by nitrogen for half an hour. Add ammonium persulfate and sodium metabisulfite dropwise at 60° C., react while adding dropwise for 3 hours, and keep warm for 1 hour to obtain a first polymer.

[0090] 200 parts by mass of the effective solid content of the polymer obtained by the first polymerization was taken, 50 parts by mass of glyoxal was added and mixed, and the mixture was reacted at a pH of 10 and a temperature of 30° C. for 20 minutes to obtain a composition 5.

[0091] Example 6

[0092] Proceed according to the following ratio (parts are by mass):

[0093] 3500 parts of acrylamide;

[0094] 700 parts of methacrylamide;

[0095] 290 parts of N-hydroxymethyl acrylamide;

[0096] 920 parts of diallyldimethylammonium chloride;

[0097] 8 parts of 2-propanethiol

[0098] 4.3 parts of ammonium persulfate;

[0099] 1.8 parts of sodium metabisulfite;

[0100] The water is adjusted to an effective content of about 17.5%.

[0101] Weigh each component except ammonium persulfate and sodium metabisulfite, mix them, and then conduct nitrogen deoxidation for half an hour. At 60 °C, add ammonium persulfate and sodium metabisulfite dropwise, and react for 3 hours while dropping, and keep warm for 1 hour to obtain the first polymerized polymer.

[0102] Take 200 parts by mass of the solid content of the effective component of the above first polymerized polymer, continue to add 50 parts by mass of glyoxal and mix. At pH 10 and a temperature of 30 °C, react for 20 minutes to obtain Composition 6.

[0103] Comparative Example 1

[0104] Conduct according to the following ratio (parts are by mass):

[0105] 3200 parts of acrylamide;

[0106] 1200 parts of methacrylamide;

[0107] 720 parts of diallyldimethylammonium chloride;

[0108] 8 parts of sodium hypophosphite

[0109] 4.3 parts of ammonium persulfate;

[0110] 1.8 parts of sodium metabisulfite;

[0111] The water is adjusted to an effective content of about 17.5%.

[0112] Weigh each component except ammonium persulfate and sodium metabisulfite, mix them, and then conduct nitrogen deoxidation for half an hour. At 60 °C, add ammonium persulfate and sodium metabisulfite dropwise, and react for 3 hours while dropping, and keep warm for 1 hour to obtain the first polymerized polymer.

[0113] Take 200 parts by mass of the solid content of the effective component of the above first polymerized polymer, continue to add 50 parts by mass of glyoxal and mix. At pH 10 and a temperature of 30 °C, react for 20 minutes to obtain Composition 7.

[0114] Comparative Example 2

[0115] Conduct according to the following ratio (parts are by mass):

[0116] 3200 parts of acrylamide;

[0117] 1200 parts of methacrylamide;

[0118] 720 parts of diallyldimethylammonium chloride;

[0119] 6.3 parts of ammonium persulfate;

[0120] 2.6 parts of sodium metabisulfite;

[0121] Adjust the water to an effective content of about 17.5%.

[0122] Weigh each component except ammonium persulfate and sodium metabisulfite, mix them, and then conduct nitrogen purging for deoxygenation for half an hour. At 60°C, add ammonium persulfate and sodium metabisulfite dropwise, react while adding for 3 hours, and keep warm for 1 hour to obtain the first polymerized polymer.

[0123] Take 200 parts by mass of the effective solid content of the above-mentioned first polymerized polymer, continue to add 50 parts by mass of glyoxal and mix. React at a pH of 10 and a temperature of 30°C for 20 minutes to obtain Composition 8.

[0124] Comparative Example 3

[0125] Conduct according to the following ratio (parts are by mass):

[0126] 4400 parts of acrylamide;

[0127] 290 parts of N-methylolacrylamide;

[0128] 720 parts of diallyldimethylammonium chloride;

[0129] 8 parts of sodium hypophosphite

[0130] 4.3 parts of ammonium persulfate;

[0131] 1.8 parts of sodium metabisulfite;

[0132] Adjust the water to an effective content of about 17.5%.

[0133] Weigh each component except ammonium persulfate and sodium metabisulfite, mix them, and then conduct nitrogen purging for deoxygenation for half an hour. At 60°C, add ammonium persulfate and sodium metabisulfite dropwise, react while adding for 3 hours, and keep warm for 1 hour to obtain the first polymerized polymer.

[0134] Take 200 parts by mass of the effective solid content of the above-mentioned first polymerized polymer, continue to add 50 parts by mass of glyoxal and mix. React at a pH of 10 and a temperature of 30°C for 20 minutes to obtain Composition 9.

[0135] The performance and formulation data of all compositions are shown in Table 1.

[0136] Table 1 Formulation and Performance Table

[0137]

[0138]

[0139]

[0140] The determination of solid content described in the above table refers to GB / T 12005.2-1989 "Determination Method for Solid Content of Polyacrylamide";

[0141] The viscosity was measured using a Brookfield rotational viscometer with a No. 1 rotor at a speed of 60 RPM;

[0142] The molecular weight and distribution were tested using dynamic light scattering method;

[0143] In order to evaluate the effect of the compositions obtained in the examples, the obtained compositions were added to the paper furnish as reinforcing agents.

[0144] The paper furnish described above can have various compositions. Here, it is distinguished according to the ratio of hardwood fibers and softwood fibers. In order to distinguish the reinforcement differences of the compositions from commercially available products (aqueous solution with a solid content of 2%, a molecular weight of 580 kD, a distribution coefficient of 7.4, and a light blue transparency), the following Table 2 scheme was selected.

[0145] Compositions 1-9 were respectively added to pulps A-C, and the retention rate % of short fiber, the tensile index and burst index of the paper products were respectively tested. The results in Table 2 compared the properties obtained from the compositions of the present invention and commercially available products.

[0146] Table 2 Information Table of Pulps with Different Softwood Contents

[0147]

[0148]

[0149] The specific operation is as follows: According to the ratio of pulps A / B / C in Table 2, select a mixture of softwood and hardwood pulps, add water at a certain concentration to prepare a 10% fiber slurry, use an MJ01-RFI type refiner from Guangdong Interson Instruments Co., Ltd. to grind for 5000 revolutions; after the grinding is completed, further dilute the pulp concentration to 1% concentration, use a CBJ-A type fiber standard disintegrator from Changchun Mingyue Small Test Machine Co., Ltd. to disintegrate for 15000 revolutions; then add a reinforcing agent dosage of 0.12% of the absolute solid content and disintegrate for another 5000 revolutions; use a pta group RK-2A type sheet former to form sheets, with the precise weight of each sheet being 80 g ± 1 g for testing strength; at the same time, test the retention of the 1% concentration sheet-forming slurry on a mütek TM .

[0150] DFR-05 type dynamic retention and drainage instrument for retention testing. The pulp without the reinforcing agent was used as a blank sample, and the data of the increase in the performance of the sample with the reinforcing agent compared to the blank sample were listed in the following Table 3.

[0151] The finished paper sheets are cut into certain sizes. The tensile strength is tested using the WZL-C horizontal computerized tensile tester of China National Building Materials Intelligent Automation Research Institute Co., Ltd.; the bursting strength is tested using the PN-BSM160F paper bursting strength tester of Hangzhou Pinxiang Technology Co., Ltd.

[0152] The values in the list are the improvement rates of performance indices, which are defined as the performance increase rate divided by the paper grammage; where the performance increase rate is the number of performance increases divided by the performance base number of the blank sample. The specific formula is as follows

[0153] Performance index increase rate % = (T1 - T0) / (T0 * W)

[0154] T1: Performance after adding the strengthening agent;

[0155] T0: Performance of the blank sample;

[0156] W: Grammage of the paper

[0157] Table 3 Performance of different compositions

[0158]

[0159]

[0160] Result analysis:

[0161] From Compositions 1 to 6, it can be seen that the retention rates, tensile index increase rates, and bursting index increase rates of different papers are significantly better than those of Compositions 7 to 9 and commercial products; and it is found that as the pulp changes from A to C, the tensile and bursting index increase rates of Composition 3 are still over 20%, while those of Compositions 7 to 9 and commercial products decrease significantly with the increase of short fibers, thus limiting their application scope.

[0162] Combined with the data in Table 1, it can be seen that the changes in the above performances are related to the polymer performances; for example, Compositions 2 and 7 have extremely strong similarities in the relevant indices of the paper strengthening agent such as molecular weight and molecular weight distribution, but there are significant differences in performance, which indicates that the performance of the product is not solely determined by the molecular weight and molecular weight distribution of the paper strengthening agent, but more by the polymer performance. For example, in the polymers involved in Compositions 2 and 7, functional structural units are not used; in addition, the polymers involved in Composition 2 and Composition 8 are relatively close in molecular weight, but the polymer involved in Composition 8 not only does not use functional structural units, but also has an overly large molecular weight distribution, which further shows that the functional structural units and molecular weight distribution of the polymer have a direct impact on the product performance.

[0163] Therefore, we can clearly draw the conclusion that the possible factors causing the above effects are as follows: 1. The introduction of functional structural units; 2. The ingenious control of molecular weight and molecular weight distribution; In order to achieve the affinity for fibers, especially the binding of short fibers, by means of hydrogen bonds, chemical bonds and physical entanglements between the polymer network and the fibers, the fiber binding and strength are improved; In addition, as can be seen from the polymer of Composition 9, the combined use of amide monomers is a strong guarantee for improving performance.

Claims

1. A polymer for paper strengthening agent, characterized in that, The polymer contains acrylamide structural units, cationic structural units containing cationic groups, and functional structural units for improving the rigidity or crosslinking density of the polymer; The polymer has a weight-average molecular weight of 50,000 to 1,000,000 and a dispersion coefficient of less than 3.

2. The polymer according to claim 1, wherein The polymer has a weight-average molecular weight of 140,000 to 280,000 and a dispersion coefficient of 2.3 to 2.

8.

3. The polymer according to claim 1, wherein The acrylamide structural units are acrylamide or methacrylamide; the cationic structural units are one or more combinations of dimethyldiallylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, and tetraallylammonium chloride; the functional structural units are one or more combinations of N-isopropylacrylamide, N-hydroxymethylacrylamide, glycidyl methacrylate, and β-acryloyloxypropionic acid.

4. The polymer according to claim 1, characterized in that The weight ratio of the acrylamide structural units, cationic structural units, and functional structural units is 70 to 95: 1 to 30: 1 to 10.

5. A method for preparing a polymer for a paper strengthening agent according to any one of claims 1 to 4, characterized in that: It is prepared by a method of free radical solution polymerization or free radical suspension polymerization.

6. The preparation method according to claim 5, wherein: Specifically, the method is as follows: the acrylamide structural units, cationic structural units, functional structural units, and structural regulators are dispersed in water, and a polymerization reaction is carried out under the action of an initiator; the structural regulator is used to adjust the molecular weight and / or molecular weight distribution of the polymer.

7. The preparation method according to claim 6, characterized in that: The structural regulator is one or more combinations of sodium hypophosphite, organic acids, and thiol compounds; the structural regulator is equivalent to 0.01 to 0.2 wt% of the total weight of the monomers; The amount of water used is equivalent to 4 to 5 times the total weight of the monomers; The initiator is a water-soluble initiator; the initiator is equivalent to 0.1 to 0.3 wt% of the total weight of the monomers.

8. The preparation method according to claim 6, characterized in that: The reaction temperature of the free radical solution polymerization is 30 to 95 °C, and the reaction time is 2 to 6 h; the initiator is added to the reaction system in a dropwise manner; Preferably, the reaction temperature of the free radical solution polymerization is 65 °C - 90 °C, and the reaction time is 3 to 5 h.

9. A paper strengthening agent, characterized in that, It is obtained by reacting the polymer as described in any one of claims 1 to 4 with an aldehyde agent.

10. The paper strengthening agent according to claim 9, characterized in that, The mass ratio of the aldehyde agent to the polymer is 3:1 to 14:1; preferably 4:1 to 8:1, and particularly preferably 4.5:1 to 7:1; The pH value of the reaction system is 8 to 12; more preferably, the pH is 9.5 to 10.5; The aldehyde agent is a compound containing 2 or more aldehyde group structures, preferably a dialdehyde substance, and particularly preferably glyoxal or glutaraldehyde; The weight-average molecular weight of the paper strengthening agent is 500,000 to 5,000,000, and the distribution coefficient is 3 to 8; preferably, the weight-average molecular weight of the paper strengthening agent is 800,000 to 1,200,000, and the distribution coefficient is 5.1 to 5.7.

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