A kraft paper for pre-printing and its preparation process

Abstract

The present invention relates to the technical field of pulp and paper making, and specifically relates to a kraft paper for pre-printing and a preparation process thereof. The structure includes the following layers from top to bottom: a surface sizing layer, a face paper layer, a backing paper layer, a base paper layer, and a bottom sizing layer; the kraft paper is manufactured by a three-layer forming technology. The high-grade white face kraft paper for pre-printing manufactured by the present invention has high compressive strength and bursting resistance, good smoothness and water resistance, good printability, can well adapt to the "pre-pressing" process of cartons, improves the printability of the face paper, and solves the problem of "printing white exposure" in large color block and dot printing.

Description

Technical Field

[0001] The present invention relates to the technical field of pulp and paper making, and particularly to a kraft paper for pre-printing and a preparation process thereof. Background Art

[0002] With the increasing requirements of domestic and foreign consumers for carton packaging, more and more carton manufacturers adopt the "pre-printing" process. Compared with the "post-printing" process of traditional corrugated cartons, color pre-printed corrugated cartons are gradually occupying the mass high-grade corrugated carton market with their exquisite printing patterns, rich colors, and superior physical properties. However, the pre-printing process has higher requirements for the quality of the carton facestock. The facestock used not only needs to have higher compressive strength and bursting resistance, but also good printing performance, especially suitable for large-color block dot printing process. Once the printability of the facestock is a little poor, the problem of "printing showing white" will appear on the surface of the facestock. Therefore, we propose a kraft paper for pre-printing and a preparation process thereof. Summary of the Invention

[0003] The purpose of the present invention is to provide a kraft paper for pre-printing and a preparation process thereof, so as to solve the problems raised in the above background art.

[0004] To solve the above technical problems, the present invention provides the following technical solutions: A kraft paper for pre-printing and a preparation process thereof, which successively include the following structures from top to bottom: a surface sizing layer, a facestock layer, a liner layer, a base paper layer, and a bottom sizing layer;

[0005] The kraft paper is made by using a three-layer forming technology.

[0006] Further, the surface sizing layer and the bottom sizing layer have a grammage of 1-4 g / m 2 .

[0007] Further, the surface sizing layer and the bottom sizing layer are made from a sizing agent;

[0008] The sizing agent mainly includes the following preparation components: starch sizing solution, surface sizing agent, and PAC (poly aluminum chloride).

[0009] Further, in the sizing agent, the mass ratio of the starch sizing solution, the surface sizing agent, and PAC is (80-90):(10-15):(1-2).

[0010] Further, the facestock layer mainly includes the following preparation components: hardwood pulp, MOW pulp (mixed office waste paper pulp), and bentonite.

[0011] Further, in the facestock layer, the mass ratio of the hardwood pulp, the MOW pulp (mixed office waste paper pulp), and the bentonite is (40-49.5):(40-49.5):(1-2).

[0012] Furthermore, in the tissue paper layer, the beating degree of hardwood pulp is 35 - 45°SR, and the wet weight is 2.0 - 2.5 g;

[0013] The beating degree of MOW pulp is 40 - 45°SR, and the wet weight is 1.0 - 1.5 g;

[0014] Bentonite: Sodium-based bentonite, with a particle size of 200 mesh and a cation exchange capacity of 110 mmol / 100 g, sourced from Zhejiang Fenghong Clay Chemical Co., Ltd.

[0015] Furthermore, the grammage of the tissue paper layer is 30 - 47 g / m 2 。

[0016] Furthermore, the liner paper layer is made of 100% MOW pulp (mixed office waste paper pulp).

[0017] Furthermore, in the liner paper layer, the beating degree of MOW pulp is 40 - 43°SR, and the wet weight is 11 - 13 g.

[0018] Furthermore, the grammage of the liner paper layer is 30 - 47 g / m 2 。

[0019] Furthermore, the base paper layer is made of 100% OCC pulp (old corrugated container pulp).

[0020] Furthermore, in the base paper layer, the beating degree of OCC pulp is 32 - 36°SR, and the wet weight is 16 - 17 g.

[0021] Furthermore, the grammage of the base paper layer is 60 - 126 g / m 2 。

[0022] Furthermore, the grammage of the kraft paper is 120 - 220 g / m 2 。

[0023] A preparation process for kraft paper for pre-printing, including the following processes:

[0024] Mix hardwood pulp, MOW pulp (mixed office waste paper pulp) and bentonite as the raw material for the tissue paper layer; 100% MOW pulp as the raw material for the liner paper layer; 100% OCC pulp as the raw material for the base paper layer, and use a triple-wire paper machine for papermaking, followed by compounding, pressing and then drying, coating with sizing agent, and calendering to obtain kraft paper.

[0025] Furthermore, the number of pressing passes is 2 - 3, until the dryness reaches 48% - 52%; in the drying process, the moisture content is controlled at 7% - 9%.

[0026] Furthermore, the temperature of the sizing agent is 60 - 70°C; the calendering temperature is 90 - 105°C.

[0027] Furthermore, the sizing agent is prepared by the following process:

[0028] Take the starch sizing solution, heat it to 78 - 82 °C, stir at a speed of 2800 - 3000 r / min, and simultaneously add the surface sizing agent, stir and emulsify for 8 - 12 min, and homogenize; add polyaluminum chloride PAC to obtain the sizing agent.

[0029] Furthermore, the surface sizing agent is molten alkyl ketene dimer, which is obtained by melting alkyl ketene dimer at 65 - 70 °C, and the surface sizing agent is sourced from Kemira Tiancheng Chemical Reagent Company.

[0030] Furthermore, the process conditions for homogenization are: the first - stage homogenization, low pressure 9.8 - 10.5 MPa, high pressure 19.8 - 20.2 MPa; the second - stage homogenization, low pressure 9.8 - 10.5 MPa, high pressure 29.8 - 30.2 MPa.

[0031] Furthermore, the starch sizing solution is prepared by the following process:

[0032] Mix starch with deionized water, stir to obtain a suspension; heat to 40 - 45 °C, keep warm for 27 - 35 min, slowly add sodium hydroxide, and finish adding within 30 min, and carry out a constant - temperature reaction for 27 - 35 min;

[0033] Slowly add the etherifying agent, and finish adding within 30 min, raise the temperature to 75 - 85 °C, keep warm for 180 - 300 min; add sodium lignosulfonate, raise the temperature to 85 - 95 °C, keep warm for 150 - 200 min;

[0034] Slowly add the initiator and unsaturated monomer, and finish adding within 60 min, keep warm at 80 - 90 °C for 50 - 70 min; cool down to below 40 °C, add phenolic resin and hexamethylenetetramine, and adjust the pH of the system to 4 - 6 to obtain the starch sizing solution.

[0035] Furthermore, the ratio of starch to deionized water is 1 g / 2 mL; the mass concentration of the suspension is about 33%.

[0036] Furthermore, sodium hydroxide is added in the form of an aqueous solution, and the mass concentration of the aqueous solution is 30% - 35%;

[0037] The etherifying agent is 3 - chloro - 2 - hydroxypropyltrimethylammonium chloride, which is added in the form of an aqueous solution with a mass concentration of 69%, and is sourced from Zibo Aolte Chemical Company;

[0038] The initiator is potassium persulfate, which is added in the form of an aqueous solution with a mass concentration of 10%;

[0039] The unsaturated monomer is added in the form of an aqueous solution with a mass concentration of 10%.

[0040] Furthermore, the mass ratio of the suspension to the sodium hydroxide aqueous solution is 100:(6.3 - 10.4).

[0041] Furthermore, the mass ratio of starch, etherifying agent, sodium lignosulfonate, initiator, and unsaturated monomer is 100:(25.9 - 37.5):(4.5 - 6.0):(0.025 - 0.125):(2.5 - 12.5).

[0042] The phenolic resin is added in the form of an ethanol solution with a mass concentration of 30% - 40%, and the addition amount of the phenolic resin solution is 3% - 8% of the mass of the starch;

[0043] The addition amount of hexamethylenetetramine is 0.20% - 0.32% of the mass of the starch;

[0044] Starch: Industrial - grade cassava starch, sourced from Yanzhou Xilai Fine Chemical Co., Ltd.;

[0045] Phenolic resin: 411, sourced from Dongzhi Guangquan New Materials Co., Ltd.

[0046] Furthermore, the unsaturated monomer is prepared by the following process:

[0047] Take epichlorohydrin, slowly add concentrated hydrochloric acid, stir and mix, heat up to 43 - 47 °C, slowly add N,N - dimethyldodecylamine, add it all within 30 min, keep warm for 27 - 35 min, heat up to 48 - 54 °C, add sodium hydroxide aqueous solution to adjust the pH of the system to 8 - 9, and react for 150 - 200 min to obtain alkyl ammonium chloride;

[0048] Take ethanol as the solvent, add p - allylphenol, add sodium hydroxide aqueous solution to adjust the pH of the system to 10 - 12, heat up to 48 - 54 °C, slowly add alkyl ammonium chloride, add it all within 30 min, stir and reflux for 150 - 200 min; distill and recover the solvent, filter, wash, and dry to obtain the unsaturated monomer.

[0049] Furthermore, the mass ratio of epichlorohydrin to N,N - dimethyldodecylamine is 1.0:1.6;

[0050] The mass concentration of concentrated hydrochloric acid is 36% - 38%, and the ratio of epichlorohydrin to concentrated hydrochloric acid is (9 - 10) g / 100 mL.

[0051] Furthermore, the mass ratio of p - allylphenol to alkyl ammonium chloride is 10:(18.0 - 19.8);

[0052] The ratio of p - allylphenol to ethanol is (9 - 10) g / 100 mL;

[0053] The concentration of the aqueous sodium hydroxide solution is 0.1 mol / L.

[0054] In the above technical solution, under the promotion of sodium hydroxide, the hydroxyl groups in starch are exposed, come into contact with and react with the etherifying agent, catalyzing the etherification reaction of starch, thereby obtaining cationic starch. Then sodium lignosulfonate is added, and grafting occurs between the hydroxyl groups in its molecular structure and starch to obtain modified starch. Finally, potassium persulfate is used as an initiator to initiate the grafting between the obtained modified starch and the unsaturated monomer, and chain growth continues with the unsaturated monomer for graft copolymerization to obtain a starch sizing solution, which can be used as an emulsifier to promote the emulsification of the surface sizing agent and prepare the required sizing agent.

[0055] The unsaturated monomer is obtained by the reaction of epichlorohydrin, N,N-dimethyldodecylamine, and p-allylphenol to form an unsaturated quaternary ammonium salt with an alkyl long chain, which can enhance the hydrophobic and lipophilic ability of the prepared sizing agent, improve the water resistance and printing adaptability of the prepared kraft paper to ink, and improve its color rendering ability to ink. At the same time, the introduction of the alkyl long chain quaternary ammonium salt can also make the prepared sizing agent have good surface activity, solubility, and antibacterial ability, promote the coating of the starch sizing solution on the surface sizing agent, and facilitate the application of the prepared sizing agent in the sizing process.

[0056] In the sizing process, the cationic sizing agent undergoes electrostatic adsorption with the surface cellulose (negatively charged) of the kraft paper, causing the sizing agent to adhere to the surface of the kraft paper and fill the surface pores, which can enhance the binding strength between cellulose and the sizing agent, and between cellulose and cellulose, improving the folding resistance and tear resistance of the kraft paper; the coating has hydrophobicity, significantly reducing the water absorption performance of the coated kraft paper and enhancing its water resistance; it has good leveling and film-forming properties, which can improve the smoothness and gloss of the kraft paper and increase the printing density of the printed pattern.

[0057] The molecular structure of alkyl ketene dimer contains a hydrophilic group lactone ring and a hydrophobic group long chain alkyl. Among them, the hydrophobic group long chain alkyl can play a hydrophobic role in the sizing process, and the hydrophilic group lactone ring can react with the surface cellulose hydroxyl groups of the kraft paper to form an ester, forming a ketone ester combined with cellulose, reducing the surface hydroxyl groups of the kraft paper and weakening the wetting ability of its surface cellulose; at this time, the hydrophobic group of the alkyl ketene dimer faces outward, which can further improve the hydrophobic and water resistance of the prepared kraft paper and increase the adhesion between the printing ink and the kraft paper.

[0058] The starch sizing solution introduces sodium lignosulfonate into the sizing agent system, which can be well adsorbed on the cellulose of the paper surface, complex with metal ions contained in the paper, generate ionic cross-linking, and enhance the surface strength of the produced kraft paper. Hexamethylenetetramine hydrolyzes to produce active formaldehyde, which can undergo dehydration condensation and double bond addition with hydroxyl groups, cross-link the starch and phenolic resin in the sizing agent system, form a three-dimensional network structure on the surface of the kraft paper, further improve the strength of the kraft paper, play a synergistic strengthening role of the starch sizing solution components, and improve the water resistance of the produced kraft paper and the permeability of printing ink on the kraft paper. Detailed implementation manners

[0059] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0060] In the following embodiments,

[0061] In the face paper layer, the beating degree of hardwood pulp is 40°SR, and the wet weight is 2.2 g;

[0062] The beating degree of MOW pulp is 42°SR, and the wet weight is 1.2 g;

[0063] Bentonite: Sodium-based bentonite, with a particle size of 200 mesh and a cation exchange capacity of 110 mmol / 100 g, sourced from Zhejiang Fenghong Clay Chemical Co., Ltd.;

[0064] In the liner paper layer, the beating degree of MOW pulp is 41°SR, and the wet weight is 12 g;

[0065] In the base paper layer, the beating degree of OCC pulp is 34°SR, and the wet weight is 16 g;

[0066] The surface sizing agent is alkyl ketene dimer (AKD wax powder), sourced from Kemira Tiancheng Wanfeng Chemical Co., Ltd.;

[0067] The etherifying agent is 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, sourced from Zibo Aolte Chemical Co., Ltd.;

[0068] Starch: Industrial grade cassava starch, sourced from Yanzhou Xilai Fine Chemical Co., Ltd.;

[0069] Phenolic resin: 411, sourced from Dongzhi Guangquan New Materials Co., Ltd.

[0070] Example 1: A preparation process of kraft paper for pre-printing, including the following processes:

[0071] S1. Mix hardwood pulp, MOW pulp (mixed office waste paper pulp) and bentonite in a mass ratio of 40:40:1 as the raw material for the face paper layer; 100% MOW pulp as the raw material for the liner paper layer; 100% OCC pulp as the raw material for the bottom paper layer;

[0072] S2. (1) Take 10 g of epichlorohydrin, slowly add it to 100 mL of 37% concentrated hydrochloric acid, stir and mix, heat up to 43 °C, slowly add 16 g of N,N-dimethyldodecylamine, add it within 30 min, keep warm for 27 min, heat up to 48 °C, add 0.1 mol / L sodium hydroxide aqueous solution to adjust the pH of the system to 8, react for 150 min to obtain alkyl ammonium chloride;

[0073] Take 100 mL of ethanol as the solvent, add 10 g of p-allylphenol, add sodium hydroxide aqueous solution to adjust the pH of the system to 10, heat up to 48 °C, slowly add 18.0 g of alkyl ammonium chloride, add it within 30 min, stir and reflux for 150 min; Distill and recover the solvent, filter by suction, wash, and dry to obtain unsaturated monomer;

[0074] (2) Mix 100 g of starch with 200 mL of deionized water, stir to obtain a suspension; Heat to 40 °C, keep warm for 27 min, slowly add 18.9 g of sodium hydroxide (added in the form of an aqueous solution, the mass concentration of the aqueous solution is 30%), add it within 30 min, and react at a constant temperature for 27 min;

[0075] Slowly add 25.9 g of etherifying agent (added in the form of an aqueous solution, the mass concentration is 69%), add it within 30 min, heat up to 75 °C, keep warm for 180 min; Add 4.5 g of sodium lignosulfonate, heat up to 85 °C, keep warm for 150 min;

[0076] Slowly add 0.025 g of initiator potassium persulfate (added in the form of an aqueous solution, the mass concentration is 10%), 2.5 g of unsaturated monomer (added in the form of an aqueous solution, the mass concentration is 10%), add it within 60 min, at a temperature of 80 °C, keep warm for 50 min; Cool down to below 40 °C, add 3 g of phenolic resin (added in the form of an ethanol solution, the mass concentration is 30%), 0.20 g of hexamethylenetetramine, and adjust the pH of the system to 6 to obtain starch sizing solution;

[0077] (3) Take the starch sizing solution, heat it to 78 °C, stir at a speed of 2800 r / min, and at the same time add a surface sizing agent, stir and emulsify for 8 min, homogenize, and the homogenization process conditions are: the first homogenization, low pressure 9.8 MPa, high pressure 19.8 MPa; the second homogenization, low pressure 9.8 MPa, high pressure 29.8 MPa; Add polyaluminum chloride PAC to obtain a sizing agent; The surface sizing agent is molten alkyl ketene dimer, and the alkyl ketene dimer is melted by heating to 65 °C;

[0078] S3. It is made by a triple - wire paper machine, compounded, pressed, with 2 pressing passes until the dryness reaches 48%; dried, with the moisture controlled at 7%; coated with a sizing agent, the temperature of the sizing agent is 60°C, dried at 105°C for 10 min; calendered, the calendering conditions are 2 MPa and 90°C, and the following structure is formed from top to bottom: surface sizing layer, face paper layer, liner paper layer, base paper layer and bottom sizing layer to obtain kraft paper;

[0079] The grammage of the face paper layer is 40 g / m 2 ; The grammage of the liner paper layer is 40 g / m 2 ; The grammage of the base paper layer is 80 g / m 2 ; For the surface sizing layer and the bottom sizing layer, the grammage is 1 g / m 2 .

[0080] Example 2: A preparation process of kraft paper for pre - printing, including the following processes:

[0081] S1. Hardwood pulp, MOW pulp (mixed office waste paper pulp) and bentonite are mixed in a mass ratio of 45:45:1.5 as the raw material for the face paper layer; 100% MOW pulp as the raw material for the liner paper layer; 100% OCC pulp as the raw material for the base paper layer;

[0082] S2. (1) Take 10 g of epichlorohydrin, slowly add 100 mL of 37% concentrated hydrochloric acid, stir and mix, heat up to 45°C, slowly add 16 g of N,N - dimethyldodecylamine, add it within 30 min, keep warm for 30 min, heat up to 52°C, add 0.1 mol / L sodium hydroxide aqueous solution to adjust the pH of the system to 8.5, react for 180 min to obtain alkyl ammonium chloride;

[0083] Take 100 mL of ethanol as the solvent, add 10 g of p - allylphenol, add sodium hydroxide aqueous solution to adjust the pH of the system to 11, heat up to 50°C, slowly add 18.9 g of alkyl ammonium chloride, add it within 30 min, stir and reflux for 180 min; Distill and recover the solvent, filter by suction, wash, and dry to obtain the unsaturated monomer;

[0084] (2) Mix 100 g of starch with 200 mL of deionized water, stir to obtain a suspension; Heat to 42°C, keep warm for 30 min, slowly add 25.0 g of sodium hydroxide (added in the form of an aqueous solution, the mass concentration of the aqueous solution is 32%), add it within 30 min, and react at a constant temperature for 30 min;

[0085] Slowly add 31.7 g of etherifying agent (3 - chloro - 2 - hydroxypropyltrimethylammonium chloride added in the form of an aqueous solution, the mass concentration is 69%), add it within 30 min, heat up to 80°C, keep warm for 240 min; Add 5.3 g of sodium lignosulfonate, heat up to 90°C, keep warm for 180 min;

[0086] Slowly add 0.075 g of initiator potassium persulfate (added in the form of an aqueous solution with a mass concentration of 10%) and 7.5 g of unsaturated monomer (added in the form of an aqueous solution with a mass concentration of 10%), and add them all within 60 min. Keep the temperature at 85 °C for 60 min; cool down to below 40 °C, add 6 g of phenolic resin (added in the form of an ethanol solution with a mass concentration of 35%) and 0.26 g of hexamethylenetetramine, and adjust the pH of the system to 5 to obtain a starch sizing solution;

[0087] (3) Take the starch sizing solution, heat it to 80 °C, stir at a speed of 2900 r / min, and at the same time add a surface sizing agent, stir and emulsify for 10 min, and homogenize. The homogenization process conditions are: the first homogenization, low pressure 10.0 MPa, high pressure 20.0 MPa; the second homogenization, low pressure 10.0 MPa, high pressure 30.0 MPa; add polyaluminum chloride PAC to obtain a sizing agent; the surface sizing agent is molten alkyl ketene dimer, and the alkyl ketene dimer is melted by heating to 68 °C;

[0088] S3. Use a triple-wire paper machine for papermaking, composite, press, with 3 press passes until the dryness reaches 50%; dry, control the moisture content at 8%; coat with the sizing agent, the temperature of the sizing agent is 65 °C, and dry at 105 °C for 10 min; calender, the calendering conditions are 2 MPa and 98 °C, and the following structure is formed from top to bottom in sequence: surface sizing layer, face paper layer, backing paper layer, base paper layer, and bottom sizing layer to obtain kraft paper.

[0089] The grammage of the face paper layer is 40 g / m 2 ; The grammage of the backing paper layer is 40 g / m 2 ; The grammage of the base paper layer is 80 g / m 2 ; The surface sizing layer and the bottom sizing layer have a grammage of 2.5 g / m 2 .

[0090] Example 3: A preparation process for pre-printed kraft paper, including the following processes:

[0091] S1. Mix hardwood pulp, MOW pulp (mixed office waste paper pulp) and bentonite in a mass ratio of 49.5:49.5:2 as the raw material for the face paper layer; 100% MOW pulp as the raw material for the backing paper layer; 100% OCC pulp as the raw material for the base paper layer;

[0092] S2. (1) Take 10 g of epichlorohydrin, slowly add 100 mL of 37% concentrated hydrochloric acid, stir and mix, heat up to 47 °C, slowly add 16 g of N,N-dimethyldodecylamine, add it all within 30 min, keep the temperature for 35 min, heat up to 54 °C, add 0.1 mol / L sodium hydroxide aqueous solution to adjust the pH of the system to 9, and react for 200 min to obtain alkyl ammonium chloride;

[0093] Take 100 mL of ethanol as the solvent, add 10 g of p-allylphenol, and adjust the pH of the system to 12 with an aqueous sodium hydroxide solution. Heat the mixture to 54 °C, and slowly add 19.8 g of alkyl ammonium chloride within 30 min. After adding, stir and reflux for 200 min; distill and recover the solvent, then filter, wash, and dry to obtain the unsaturated monomer;

[0094] (2) Mix 100 g of starch with 200 mL of deionized water and stir to obtain a suspension; heat to 45 °C, keep warm for 35 min, and slowly add 31.2 g of sodium hydroxide (added in the form of an aqueous solution with a mass concentration of 35%) within 30 min. After adding, react at a constant temperature for 35 min;

[0095] Slowly add 37.5 g of etherifying agent (3-chloro-2-hydroxypropyltrimethylammonium chloride added in the form of an aqueous solution with a mass concentration of 69%) within 30 min. After adding, heat to 85 °C and keep warm for 300 min; add 6.0 g of sodium lignosulfonate, then heat to 95 °C and keep warm for 200 min;

[0096] Slowly add 0.125 g of initiator potassium persulfate (added in the form of an aqueous solution with a mass concentration of 10%) and 12.5 g of unsaturated monomer (added in the form of an aqueous solution with a mass concentration of 10%) within 60 min. After adding, keep warm at 90 °C for 70 min; cool down to below 40 °C, add 8 g of phenolic resin (added in the form of an ethanol solution with a mass concentration of 40%) and 0.32 g of hexamethylenetetramine, and adjust the pH of the system to 4 to obtain the starch sizing solution;

[0097] (3) Take the starch sizing solution, heat to 82 °C, stir at a speed of 3000 r / min, and simultaneously add the surface sizing agent, then stir and emulsify for 12 min and homogenize. The homogenization process conditions are: the first homogenization, low pressure 10.5 MPa, high pressure 20.2 MPa; the second homogenization, low pressure 10.5 MPa, high pressure 30.2 MPa; add polyaluminum chloride PAC to obtain the sizing agent; the surface sizing agent is molten alkyl ketene dimer, which is obtained by melting alkyl ketene dimer at 70 °C;

[0098] S3. Use a triple wire paper machine for papermaking, composite, press, with 3 press passes until the dryness reaches 52%; dry, control the moisture content at 9%; coat with the sizing agent, the temperature of the sizing agent is 70 °C, dry at 105 °C for 10 min; calender, the calendering conditions are 2 MPa, 105 °C, and form the following structure from top to bottom in sequence: surface sizing layer, top paper layer, liner paper layer, bottom paper layer, and bottom sizing layer to obtain kraft paper.

[0099] The grammage of the top paper layer is 40 g / m 2 ; The grammage of the liner paper layer is 40 g / m 2; The basis weight of the base paper layer is 80 g / m² 2 ; The surface sizing layer and the base sizing layer, with a basis weight of 4 g / m² 2 .

[0100] Comparative Example 1: A preparation process of pre-printed kraft paper, including the following processes:

[0101] S2. (1) Take 10 g of epichlorohydrin, slowly add it to 100 mL of 37% concentrated hydrochloric acid, stir and mix, heat up to 43 °C, slowly add 16 g of N,N-dimethyldodecylamine, add it within 30 min, keep warm for 27 min, heat up to 48 °C, add 0.1 mol / L sodium hydroxide aqueous solution to adjust the pH of the system to 8, react for 150 min to obtain alkyl ammonium chloride;

[0102] Take 100 mL of ethanol as a solvent, add 10 g of p-allylphenol, add sodium hydroxide aqueous solution to adjust the pH of the system to 10, heat up to 48 °C, slowly add 18.0 g of alkyl ammonium chloride, add it within 30 min, stir and reflux for 150 min; Distill and recover the solvent, filter by suction, wash, and dry to obtain unsaturated monomer;

[0103] (2) Mix 100 g of starch with 200 mL of deionized water, stir to obtain a suspension; Heat to 40 °C, keep warm for 27 min, slowly add 18.9 g of sodium hydroxide (added in the form of an aqueous solution, the mass concentration of the aqueous solution is 30%), add it within 30 min, and react at a constant temperature for 27 min;

[0104] Slowly add 25.9 g of etherifying agent (3-chloro-2-hydroxypropyltrimethylammonium chloride added in the form of an aqueous solution, with a mass concentration of 69%), add it within 30 min, heat up to 75 °C, keep warm for 180 min; Add 4.5 g of sodium lignosulfonate, heat up to 85 °C, keep warm for 150 min;

[0105] Slowly add 0.025 g of initiator potassium persulfate (added in the form of an aqueous solution, with a mass concentration of 10%), 2.5 g of unsaturated monomer (added in the form of an aqueous solution, with a mass concentration of 10%), add it within 60 min, and keep warm at 80 °C for 50 min; Cool down to below 40 °C to obtain starch sizing solution;

[0106] (3) Take the starch sizing solution, heat it to 78 °C, stir at a speed of 2800 r / min, and at the same time add a surface sizing agent, stir and emulsify for 8 min, homogenize, and the homogenization process conditions are: the first homogenization, low pressure 9.8 MPa, high pressure 19.8 MPa; the second homogenization, low pressure 9.8 MPa, high pressure 29.8 MPa; Add polyaluminum chloride PAC to obtain a sizing agent; The surface sizing agent is molten alkyl ketene dimer, and the alkyl ketene dimer is melted by heating to 65 °C;

[0107] Steps S1 and S2 are the same as those in Example 1 to obtain kraft paper.

[0108] Comparative Example 2: A preparation process of kraft paper for pre-printing, including the following processes:

[0109] S2.(1) Mix 100 g of starch with 200 mL of deionized water, stir to obtain a suspension; heat to 40 °C, keep warm for 27 min, slowly add 18.9 g of sodium hydroxide (added in the form of an aqueous solution with a mass concentration of 30%), add it within 30 min, and carry out a constant-temperature reaction for 27 min;

[0110] Slowly add 25.9 g of etherifying agent (3-chloro-2-hydroxypropyltrimethylammonium chloride added in the form of an aqueous solution with a mass concentration of 69%), add it within 30 min, raise the temperature to 75 °C, and keep warm for 180 min; add 4.5 g of sodium lignosulfonate, raise the temperature to 85 °C, and keep warm for 150 min;

[0111] Slowly add 0.025 g of initiator potassium persulfate (added in the form of an aqueous solution with a mass concentration of 10%) and 2.5 g of acrylamide (added in the form of an aqueous solution with a mass concentration of 10%), add it within 60 min, and keep warm at 80 °C for 50 min; cool down to below 40 °C to obtain a starch sizing solution;

[0112] (2) Take the starch sizing solution, heat to 78 °C, stir at a speed of 2800 r / min, and at the same time add a surface sizing agent, stir and emulsify for 8 min, and homogenize. The homogenization process conditions are: the first homogenization, low pressure 9.8 MPa, high pressure 19.8 MPa; the second homogenization, low pressure 9.8 MPa, high pressure 29.8 MPa; add polyaluminum chloride PAC to obtain a sizing agent; the surface sizing agent is molten alkyl ketene dimer, and the alkyl ketene dimer is melted by heating to 65 °C;

[0113] Steps S1 and S2 are the same as those in Example 1 to obtain kraft paper.

[0114] Comparative Example 3: A preparation process of kraft paper for pre-printing, including the following processes:

[0115] S2.(1) Mix 100 g of starch with 200 mL of deionized water, stir to obtain a suspension; heat to 40 °C, keep warm for 27 min, slowly add 18.9 g of sodium hydroxide (added in the form of an aqueous solution with a mass concentration of 30%), add it within 30 min, and carry out a constant-temperature reaction for 27 min;

[0116] Slowly add 25.9 g of etherifying agent (3-chloro-2-hydroxypropyltrimethylammonium chloride is added in the form of an aqueous solution with a mass concentration of 69%), and finish adding it within 30 min. Heat up to 75 °C and keep the temperature for 180 min; cool down to below 40 °C to obtain a starch sizing solution;

[0117] (2) Take the starch sizing solution, heat it to 78 °C, stir at a speed of 2800 r / min, and simultaneously add a surface sizing agent. Stir and emulsify for 8 min, and then homogenize. The homogenization process conditions are: the first homogenization, low pressure 9.8 MPa, high pressure 19.8 MPa; the second homogenization, low pressure 9.8 MPa, high pressure 29.8 MPa; add polyaluminum chloride PAC to obtain a sizing agent; the surface sizing agent is molten alkyl ketene dimer, which is obtained by melting alkyl ketene dimer at 65 °C;

[0118] Steps S1 and S2 are the same as those in Example 1 to obtain kraft paper.

[0119] Experiment

[0120] Take the kraft paper obtained in Examples 1-3 and Comparative Examples 1-3, prepare specimens, and detect and record the test results of their properties respectively:

[0121] Bursting strength index test: Referring to GB / T 1539-2007, test the bursting strength index of the kraft paper specimens;

[0122] Ring crush strength index test: Referring to GB / T 2679.8-2016, test the transverse ring crush strength of the kraft paper specimens;

[0123] Smoothness test: Referring to GB / T 456-2002, use an electric smoothness tester to measure the smoothness of the specimens;

[0124] Hot air permeability test: Take 2.5 μL of ink (black water-based ink, viscosity 15 s, coloring power 98%, fineness 10 μm, fluidity ≥ 20 mm, sourced from Guangdong Yingke Group Co., Ltd.) and drop it on the surface of the specimen. Under the condition that the hot air temperature is 56 °C, detect the time (unit: second) when the ink volume reduces to less than 0.1 μL.

[0125] <![CDATA[Bursting strength index (Kpa.m 2 / g)]]> Ring crush index (N.m / g) Smoothness (s) Hot air permeability (s) Example 1 2.72 9.2 22.6 17.5 Example 2 2.90 9.7 24.4 16.3 Example 3 3.07 10.0 25.9 15.4 Comparative Example 1 2.63 8.8 19.7 18.7 Comparative Example 2 2.54 8.5 17.5 20.8 Comparative Example 3 2.42 8.1 15.9 22.8

[0126] According to the data in the above table, the following conclusions can be clearly obtained:

[0127] The kraft paper obtained in Examples 1-3 is compared with the kraft paper obtained in Comparative Examples 1-3. From the test results, it can be seen that

[0128] Compared with the comparative examples, the kraft paper obtained in Examples 1-3 has higher burst index, ring crush index, smoothness data and lower hot air permeability data, which fully demonstrates that the kraft paper prepared by the present invention has achieved improvements in strength, burst resistance, smoothness, printability, etc.

[0129] Compared with Example 1, in the kraft paper obtained in Comparative Example 1, the sizing agent components phenolic resin and hexamethylenetetramine were deleted; in the kraft paper obtained in Comparative Example 2, on the basis of Comparative Example 1, the unsaturated monomer in the sizing agent components was replaced with acrylamide; in the kraft paper obtained in Comparative Example 3, the sizing agent was cationic starch sizing solution; while for the kraft paper obtained in Comparative Examples 1-3, the burst index, ring crush index, smoothness and hot air permeability data deteriorated. It can be seen that the setting of the sizing agent components and their processes in the present invention can promote the improvement of the comprehensive properties such as the strength, burst resistance, smoothness and printability of the prepared kraft paper.

[0130] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device.

[0131] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation process of kraft paper for pre-printing, which is characterized in that: It includes the following processes: Mix hardwood pulp, MOW pulp and bentonite as the raw material for the face paper layer; 100% MOW pulp as the raw material for the liner paper layer; 100% OCC pulp as the raw material for the base paper layer, and use a triple-wire paper machine for papermaking, compounding, pressing and then drying, coating sizing agent, and calendering to obtain kraft paper; The sizing agent is prepared by the following process: Take starch sizing solution, heat it to 78 - 82 °C, stir at a speed of 2800 - 3000 r / min, and at the same time add surface sizing agent, stir and emulsify for 8 - 12 min, and homogenize; add polyaluminum chloride PAC to obtain the sizing agent; The starch sizing solution is prepared by the following process: Mix starch and deionized water, stir to obtain a suspension; heat to 40 - 45 °C, keep warm for 27 - 35 min, slowly add sodium hydroxide, and add it within 30 min, and carry out constant-temperature reaction for 27 - 35 min; Slowly add etherifying agent, and add it within 30 min, raise the temperature to 75 - 85 °C, keep warm for 180 - 300 min; add sodium lignosulfonate, raise the temperature to 85 - 95 °C, keep warm for 150 - 200 min; Slowly add initiator and unsaturated monomer, and add them within 60 min. At a temperature of 80 - 90 °C, keep warm for 50 - 70 min; cool down to below 40 °C, add phenolic resin and hexamethylenetetramine, and adjust the pH of the system to 4 - 6 to obtain the starch sizing solution.

2. The preparation process of kraft paper for pre-printing according to claim 1, which is characterized in that: The mass ratio of the starch, etherifying agent, sodium lignosulfonate, initiator, and unsaturated monomer is 100:(25.9 - 37.5):(4.5 - 6.0):(0.025 - 0.125):(2.5 - 12.5).

3. The preparation process of kraft paper for pre-printing according to claim 2, which is characterized in that: The unsaturated monomer is prepared by the following process: Take epichlorohydrin, slowly add concentrated hydrochloric acid, stir and mix, raise the temperature to 43 - 47 °C, slowly add N,N-dimethyldodecylamine, and add it within 30 min, keep warm for 27 - 35 min, raise the temperature to 48 - 54 °C, add sodium hydroxide aqueous solution to adjust the pH of the system to 8 - 9, and react for 150 - 200 min to obtain alkyl ammonium chloride; Take ethanol as the solvent, add p-allylphenol and sodium hydroxide aqueous solution to adjust the pH of the system to 10 - 12, raise the temperature to 48 - 54 °C, slowly add alkyl ammonium chloride, and add it within 30 min, stir and reflux for 150 - 200 min; distill and recover the solvent, filter, wash, and dry to obtain the unsaturated monomer.

4. The preparation process of kraft paper for pre-printing according to claim 3, which is characterized in that: The mass ratio of epichlorohydrin to N,N-dimethyldodecylamine is 1:1.6; the mass ratio of p-allylphenol to alkyl ammonium chloride is 10:(18.0 - 19.8).

5. The preparation process of kraft paper for pre-printing according to any one of claims 1 - 4, which is characterized in that: It successively includes the following structures from top to bottom: a surface sizing layer, a face paper layer, a backing paper layer, a base paper layer, and a base sizing layer; the kraft paper is manufactured by using a three - layer forming technology.

6. A preparation process of kraft paper for pre - printing according to claim 5, characterized in that: the surface sizing layer and the base sizing layer are made of a sizing agent; the sizing agent mainly includes the following preparation components: starch sizing solution, surface sizing agent, and PAC; in the sizing agent, the mass ratio of the starch sizing solution, the surface sizing agent, and PAC is (80 - 90):(10 - 15):(1 - 2).

7. A preparation process of kraft paper for pre - printing according to claim 5, characterized in that: the face paper layer mainly includes the following preparation components: hardwood pulp, MOW pulp, and bentonite; in the face paper layer, the mass ratio of the hardwood pulp, the MOW pulp, and the bentonite is (40 - 49.5):(40 - 49.5):(1 - 2).