Green offset paper and preparation method thereof

Abstract

The present application relates to the technical field of papermaking, and provides a green offset paper and a preparation method thereof. The method comprises: mixing coniferous wood pulp, hardwood wood pulp, dry damaged pulp, and wet damaged pulp to obtain a first mixed pulp; adding auxiliary materials to the first mixed pulp for mixing to obtain a second mixed pulp; adding a part of the formula amount of dye to the second mixed pulp for a primary dyeing treatment to obtain a third mixed pulp; adding the remaining formula amount of dye to the third mixed pulp for a secondary dyeing treatment to obtain a fourth mixed pulp; using the fourth mixed pulp for papermaking to obtain a wet paper sheet; using a surface sizing agent to perform a surface sizing treatment on the wet paper sheet to obtain a green offset paper. The present application can reduce the problems of color spots, color streaks, and uneven dyeing during the production, use, or storage of paper, and can reduce the tensile index loss rate and yellowing rate of paper after aging, improve the durability of paper, and enable the paper to be stored for a long time.

Description

Technical Field

[0001] The present application relates to the technical field of papermaking, and in particular to a green offset paper and a preparation method thereof. Background Art

[0002] Green offset paper is widely used in all kinds of books and teaching materials because of its soft color and ability to reduce reading visual fatigue. For example, the Harry Potter series has been using green offset paper since 2004.

[0003] However, the quality of green offset paper on the market varies greatly. Some green offset papers are prone to color spots, color streaks, and poor paper dyeing uniformity during production, use, or storage. In addition, these green offset papers have a large loss rate of tensile index and a high yellowing value after aging, and the durability of the paper is poor, making it difficult to store for a long time. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present application is to provide a green offset paper and a preparation method thereof. The preparation method of the present application dyes the slurry in stages by adding dye twice, so that it is not easy to have color spots and color streaks during production, use or storage, and the paper has good dyeing uniformity; by using a specific surface sizing agent to perform surface sizing treatment on wet paper sheets, the tensile index loss rate of the paper after aging can be effectively reduced, and the yellowing rate can be reduced, thereby improving the durability of the paper and allowing the paper to be preserved for a long time.

[0005] In order to achieve the above invention objectives, the technical solutions adopted in this application are as follows:

[0006] In a first aspect, an embodiment of the present application provides a method for preparing green offset paper, comprising:

[0007] Adding coniferous wood pulp, hardwood pulp, dry damaged pulp and wet damaged pulp into a pulp preparation tank for mixing to obtain a first mixed pulp; wherein the mass ratio of coniferous wood pulp, hardwood pulp, dry damaged pulp and wet damaged pulp is 20-30:25-40:0-15:0-15;

[0008] The first mixed slurry is conveyed to a slurry mixing box, and auxiliary materials are added for mixing to obtain a second mixed slurry;

[0009] The second mixed slurry is conveyed to a pulping tank and dyes are added to perform a dyeing treatment to obtain a third mixed slurry; the dyes include blue dyes and yellow dyes, and the amount of the dyes added is 70% to 80% of the formula amount;

[0010] The third mixed slurry is conveyed to a headbox and the remaining amount of dye is added to perform secondary dyeing treatment to obtain a fourth mixed slurry;

[0011] Using the fourth mixed slurry to papermake to obtain a wet paper sheet;

[0012] After the wet paper sheet is subjected to a primary drying and dehydration treatment, a surface sizing agent is used to perform surface sizing treatment on the wet paper sheet, and then a secondary drying and dehydration treatment and a calendering treatment are performed to obtain green offset paper; wherein the surface sizing agent is nano cross-linked modified starch, the sizing concentration is 12% to 25%, the sizing temperature is 70 to 80°C, and the sizing amount is 6 to 8g / m 2 .

[0013] In a second aspect, an embodiment of the present application further provides a green offset paper, which is prepared by the preparation method of the green offset paper of the first aspect.

[0014] The beneficial effects of this application include at least:

[0015] The preparation method provided in the embodiment of the present application dyes the slurry in stages by adding dye twice, so that problems such as color spots and color streaks are not likely to occur during production, use or storage, and the paper has good dyeing uniformity; by using a specific surface sizing agent to perform surface sizing treatment on the wet paper sheets, the tensile index loss rate of the paper after aging can be effectively reduced, and the yellowing rate can be reduced, thereby improving the durability of the paper and allowing the paper to be preserved for a long time. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 It is a schematic diagram of a process flow of preparing green offset paper provided in an embodiment of the present application. DETAILED DESCRIPTION

[0018] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail in conjunction with the embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present application, but the implementation methods of the present application are not limited thereto.

[0019] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which this application belongs. The experimental reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents, which can be obtained through commercial channels; the amounts of experimental reagents, unless otherwise specified, are the amounts of reagents used in conventional experimental operations; and the experimental methods, unless otherwise specified, are all conventional methods.

[0020] In a first aspect, an embodiment of the present application provides a method for preparing green offset paper, comprising the following steps:

[0021] S1. Adding coniferous pulp, hardwood pulp, dry damaged pulp and wet damaged pulp into a pulp preparation tank for mixing to obtain a first mixed pulp; wherein the mass ratio of coniferous pulp, hardwood pulp, dry damaged pulp and wet damaged pulp is 20-30:25-40:0-15:0-15;

[0022] S2, conveying the first mixed slurry to a slurry mixing box, adding auxiliary materials for mixing, and obtaining a second mixed slurry;

[0023] S3, conveying the second mixed slurry to a slurry flushing tank and adding dyes for dyeing to obtain a third mixed slurry; the dyes include blue dyes and yellow dyes, and the amount of dyes added is 70% to 80% of the formula amount;

[0024] S4, conveying the third mixed slurry to a headbox and adding the remaining amount of dye for secondary dyeing to obtain a fourth mixed slurry;

[0025] S5, using the fourth mixed slurry to carry out papermaking to obtain a wet paper sheet;

[0026] S6. After the wet paper sheet is subjected to a primary drying and dehydration treatment, a surface sizing agent is used to perform surface sizing treatment on the wet paper sheet, and then a secondary drying and dehydration treatment and calendering treatment are performed to obtain green offset paper; wherein the surface sizing agent is nano cross-linked modified starch, the sizing concentration is 12% to 25%, the sizing temperature is 70 to 80°C, and the sizing amount is 6 to 8 g / m 2 .

[0027] In some embodiments, in the above step S1, the coniferous wood pulp may be bleached sulfite coniferous wood pulp; and the broadleaf wood pulp may be bleached sulfite broadleaf wood pulp.

[0028] Dry damaged pulp generally refers to some dry damaged scraps or unqualified products produced in the process of producing offset paper, which are obtained by beating with a pulper (such as a double-disc refiner).

[0029] Wet-damaged pulp generally refers to some wet-damaged scraps or unqualified products produced in the process of producing offset paper, which are obtained by beating with a pulping machine.

[0030] Optionally, the coniferous wood pulp may be Canadian "Continental" or "Lion" coniferous chemical pulp.

[0031] Optionally, the hardwood pulp may be Brazilian "Goldfish" or Canadian "Knight" hardwood chemical mechanical pulp.

[0032] Furthermore, the beating degree of coniferous pulp is 40-50°SR; the beating degree of hardwood pulp is 30-40°SR; the beating degree of dry-damaged pulp is 35-45°SR; and the beating degree of wet-damaged pulp is 35-45°SR.

[0033] The beating degree of pulp will affect the dyeing quality of paper. Appropriate beating degree can ensure the uniformity of paper dyeing and reduce the probability of problems such as color spots, color streaks or uneven dyeing during paper production, use or storage.

[0034] In some embodiments, in the above step S2, the auxiliary materials include fillers and retention and drainage aids. Among them, the filler includes light calcium carbonate (particle size is 1.2 to 1.9 μm). The retention and drainage aids include tertiary amine type amphoteric polyacrylamide and dimethyl sulfate. The amount of filler used is 20% to 30% (as a percentage of the total mass of the first mixed slurry); the amount of retention and drainage aid used is 0.2% to 0.4% (as a percentage of the total mass of the first mixed slurry). The mass ratio of tertiary amine type amphoteric polyacrylamide and dimethyl sulfate is 1:0.4 to 0.6 (for example, it can be 1:0.4, 1:0.5 or 1:0.6, etc.).

[0035] By using a combination of tertiary amine type amphoteric polyacrylamide and dimethyl sulfate as a retention and drainage aid, the first-pass retention rate of the filler can be increased, which is beneficial to improving the opacity of the paper.

[0036] In some embodiments, in the above step S3, the blue dye is direct lake blue or basic royal blue; the yellow dye is basic light yellow; the usage of the blue dye is 1.0-1.2 kg / t pulp; the usage of the yellow dye is 0.18-0.22 kg / t pulp.

[0037] Optionally, the usage amount of blue dye is 1.1 kg / t pulp (for the second mixed pulp); the usage amount of yellow dye is 0.2 kg / t pulp (for the second mixed pulp).

[0038] By dyeing the pulp with a specific ratio of blue dye and yellow dye, the paper can be made greener, thereby producing green offset paper, which can be used to print various books, teaching materials, etc., for example, it can be used to print the Harry Potter series of books, etc. This type of green offset has the advantages of soft color, which is conducive to reducing reading eyestrain.

[0039] In some embodiments, in the above step S3, specifically, dispersed rosin glue and polyaluminium chloride can be added to the second mixed slurry in the slurry flushing tank in sequence, and dyes are added after being evenly mixed, and the temperature is raised to 60°C to 70°C, and the pH value of the mixed material is adjusted to 4.5 to 6.5, and stirred and mixed for 1 to 2 minutes to obtain a third mixed slurry. Among them, the amount of dispersed rosin glue is 0.4% to 0.5% (accounting for the mass percentage of the second mixed slurry), and the amount of polyaluminium chloride is 4% to 5% (accounting for the mass percentage of the second mixed slurry).

[0040] By adding dispersed rosin glue and polyaluminium chloride to the second mixed slurry in sequence, and then adding dye, and controlling the temperature to be 60°C to 70°C and the pH value to be 4.5 to 6.5 for dyeing, the pulp can be dyed more evenly and is conducive to reducing problems such as colour spots and streaks during subsequent paper production, use or storage.

[0041] In some embodiments, in the above step S6, the preparation step of the nano cross-linked modified starch includes:

[0042] Dispersing plant starch in water to prepare a starch suspension with a mass concentration of 1% to 2%;

[0043] The starch suspension is subjected to ultrasonic treatment for 60 to 80 minutes at an ultrasonic frequency of 21 to 23 kHz, an ultrasonic power of 175 to 180 W, and a temperature of 5 to 7° C. to obtain nano starch particles;

[0044] Nano starch particles are dispersed in an emulsion and a cross-linking agent is added to obtain nano cross-linked modified starch.

[0045] Among them, the plant starch can be tapioca starch, corn starch or potato starch.

[0046] Optionally, the vegetable starch is waxy corn starch.

[0047] By dispersing plant starch in water to prepare a starch suspension with a mass concentration of 1% to 2%, and then performing ultrasonic treatment, and controlling the ultrasonic frequency to be 21 to 23kHz, the ultrasonic power to be 175 to 180W, the temperature to be 5 to 7°C, and the ultrasonic treatment time to be 60 to 80 minutes, nano starch particles with a particle size of 30nm to 100nm can be obtained. The whole process does not require the addition of any chemical reagents, and the product yield can be close to 100%.

[0048] In some embodiments, the emulsifier is 1-hexadecyl 1-3-methylimidazolium bromide; and the cross-linking agent is epichlorohydrin.

[0049] In some embodiments, when the ultrasonic treatment is performed for 75 min under the ultrasonic conditions of an ultrasonic frequency of 23 kHz, an ultrasonic power of 175 W, and a temperature of 7° C., the yield of nano starch particles is the highest, close to 100%.

[0050] In some embodiments, in the above step S6, in the surface sizing treatment, the sizing pH value is 7-8.

[0051] By controlling the pH value of the surface sizing treatment to 7-8, it is helpful to reduce the yellowing degree of paper during use and storage.

[0052] In a second aspect, an embodiment of the present application further provides a green offset paper, which is prepared by the preparation method of the green offset paper of the first aspect.

[0053] The green offset paper prepared by the preparation method of the embodiment of the present application has soft color, is not prone to color spots, color streaks and other problems during use and storage, and can effectively reduce the loss rate of the tensile index after paper aging and reduce the yellowing rate. The durability of the paper is good, allowing the paper to be stored for a long time.

[0054] Figure 1 It is a schematic diagram of a process flow of preparing green offset paper provided in an embodiment of the present application.

[0055] See also Figure 1 The process system for implementing the preparation method of the green offset paper of the embodiment of the present application includes a pulp preparation pool 101, a pulp mixing box 102, a pulp flushing pool 103, a stock flow box 104, a fourdrinier section 105, a pressing section 106, a first drying section 107, a surface sizing machine 108, a second drying section 109, a calender 110 and a paper reel 111, which are connected in sequence through pipelines (pipes) or connecting components (such as conveyor belts, etc.).

[0056] The method for preparing green offset paper provided in the embodiment of the present application comprises the following steps:

[0057] Step 1, pulping: adding coniferous wood pulp, hardwood pulp, dry damaged pulp and wet damaged pulp into the pulping tank 101 in a mass ratio of 20-30:25-40:0-15:0-15 for mixing to obtain a first mixed pulp, and conveying the first mixed pulp to the pulp mixing box 102.

[0058] Step 2, slurry preparation: auxiliary materials (including fillers and retention and drainage aids) are added into the slurry preparation box 102 for mixing to obtain a second mixed slurry, and the second mixed slurry is transported to the slurry flushing tank 103 .

[0059] Step three, primary dyeing treatment: in the slurry tank 103, the second mixed slurry is fully mixed with the concentrated white water in the slurry tank 103, and dispersed rosin glue (the added amount is 0.4% to 0.5% of the mass of the second mixed slurry) and polyaluminum chloride (the added amount is 4% to 5% of the mass of the second mixed slurry) are added to the slurry tank 103 in sequence, and then 70% to 80% of the formula amount of dye is added, and the temperature is controlled at 60°C to 70°C and the pH value is 4.5 to 6.5. The slurry is dyed once to obtain a third mixed slurry, and the third mixed slurry is pumped to the headbox 104.

[0060] Step 4: Secondary dyeing treatment: Add the remaining amount of dye into the headbox 104 to perform secondary dyeing treatment on the slurry to obtain a fourth mixed slurry.

[0061] Step 5, papermaking, forming, pressing, and primary drying: the fourth mixed slurry flowing out from the headbox 104 is papermade and formed through the fourdrinier wire section 105 to obtain a wet paper sheet, which is then sequentially passed through the pressing section 106 for pressing and dehydration, and through the first drying section 107 for primary drying.

[0062] Process 7: Surface sizing treatment: After the first drying section

[0063] After the first drying, the paper sheet enters the surface sizing machine 108 for surface sizing. In the surface sizing process, nano cross-linked modified starch is used as the surface sizing agent, and the sizing process conditions are controlled to be 12% to 25%, 70 to 80°C, and 6 to 8 g / m 2 .

[0064] Process eight, secondary drying, calendering, and winding: After surface sizing treatment by the surface sizing machine 108, the paper sheets enter the second drying section 109, the calender 110, and the paper winder 111 in sequence, and undergo secondary drying, calendering, finishing, and winding treatment to obtain finished paper.

[0065] The present application has been subjected to multiple tests, and part of the test results are now cited as references to further describe the invention in detail, which is described in detail below in conjunction with specific embodiments.

[0066] Example 1

[0067] See also Figure 1 The preparation method of the green offset paper provided in this embodiment is as follows:

[0068] Step 1, pulping: adding coniferous wood pulp, hardwood wood pulp, dry damaged pulp and wet damaged pulp into the pulping tank 101 in a mass ratio of 20:25:15:5 for mixing to obtain a first mixed pulp, and conveying the first mixed pulp to the pulp mixing box 102.

[0069] Step 2: Slurry preparation: Light calcium carbonate (particle size of 1.2 μm), tertiary amine type amphoteric polyacrylamide and dimethyl sulfate are added to the slurry preparation box 102 for mixing to obtain a second mixed slurry, and the second mixed slurry is transported to the slurry flushing tank 103. The total mass of tertiary amine type amphoteric polyacrylamide and dimethyl sulfate accounts for 0.2% of the mass of the second mixed slurry; the mass ratio of tertiary amine type amphoteric polyacrylamide and dimethyl sulfate is 1:0.4. The amount of light calcium carbonate added accounts for 20% of the mass of the second mixed slurry.

[0070] Step 3, primary dyeing treatment: In the slurry tank 103, the second mixed slurry is fully mixed with the concentrated white water in the slurry tank 103, and dispersed rosin glue (the addition amount is 0.4% of the mass of the second mixed slurry) and polyaluminum chloride (the addition amount is 4% of the mass of the second mixed slurry) are added to the slurry tank 103 in sequence, and then 80% of the formula amount of dye (including direct turquoise and alkaline yellow) is added, and the temperature is controlled at 60°C and the pH value is 4.5. The slurry is dyed once to obtain a third mixed slurry, and the third mixed slurry is pumped to the headbox 104. Among them, the use amount of direct turquoise is 1.1kg / t slurry (for the third mixed slurry); the use amount of alkaline yellow is 0.18kg / t slurry (for the third mixed slurry).

[0071] Step 4: Secondary dyeing treatment: Add the remaining amount of dye (including direct lake blue and alkaline light yellow) into the headbox 104 to perform secondary dyeing treatment on the slurry to obtain a fourth mixed slurry.

[0072] Step 5, papermaking, forming, pressing, and primary drying: the fourth mixed slurry flowing out from the headbox 104 is papermade and formed through the fourdrinier wire section 105 to obtain a wet paper sheet, which is then sequentially passed through the pressing section 106 for pressing and dehydration, and through the first drying section 107 for primary drying.

[0073] Step 7: Surface sizing treatment: Surface sizing treatment is performed on the paper sheet that has been dried once in the first drying section 107 and then enters the surface sizing machine 108. In the surface sizing process, nano cross-linked modified starch is used as the surface sizing agent, and the sizing process conditions are controlled to be 12% sizing concentration, 80°C sizing temperature, and 6g / m 2 , the sizing pH value is 7.

[0074] Process eight, secondary drying, calendering, and winding: After surface sizing treatment by the surface sizing machine 108, the paper sheets enter the second drying section 109, the calender 110, and the paper winder 111 in sequence, and undergo secondary drying, calendering, finishing, and winding treatment to obtain finished paper.

[0075] Example 2

[0076] See also Figure 1 The preparation method of the green offset paper provided in this embodiment is as follows:

[0077] Step 1, pulping: adding coniferous wood pulp, hardwood wood pulp, dry damaged pulp and wet damaged pulp into the pulping tank 101 in a mass ratio of 25:25:10:5 for mixing to obtain a first mixed pulp, and conveying the first mixed pulp to the pulp mixing box 102.

[0078] Step 2: Slurry preparation: Light calcium carbonate (particle size of 1.5 μm), tertiary amine type amphoteric polyacrylamide and dimethyl sulfate are added to the slurry preparation box 102 for mixing to obtain a second mixed slurry, and the second mixed slurry is transported to the slurry flushing tank 103. The total mass of tertiary amine type amphoteric polyacrylamide and dimethyl sulfate accounts for 0.3% of the mass of the second mixed slurry; the mass ratio of tertiary amine type amphoteric polyacrylamide and dimethyl sulfate is 1:0.5. The amount of light calcium carbonate added accounts for 25% of the mass of the second mixed slurry.

[0079] Step 3, primary dyeing treatment: In the slurry tank 103, the second mixed slurry is fully mixed with the concentrated white water in the slurry tank 103, and dispersed rosin glue (the addition amount is 0.45% of the mass of the second mixed slurry) and polyaluminum chloride (the addition amount is 5% of the mass of the second mixed slurry) are added to the slurry tank 103 in sequence, and then 70% of the formula amount of dye (including direct turquoise and alkaline yellow) is added, and the temperature is controlled at 65°C and the pH value is 5.5. The slurry is dyed once to obtain a third mixed slurry, and the third mixed slurry is pumped to the headbox 104. Among them, the use amount of direct turquoise is 1.1kg / t slurry (for the third mixed slurry); the use amount of alkaline yellow is 0.19kg / t slurry (for the third mixed slurry).

[0080] Step 4: Secondary dyeing treatment: Add the remaining amount of dye (including direct lake blue and alkaline light yellow) into the headbox 104 to perform secondary dyeing treatment on the slurry to obtain a fourth mixed slurry.

[0081] Step 5, papermaking, forming, pressing, and primary drying: the fourth mixed slurry flowing out from the headbox 104 is papermade and formed through the fourdrinier wire section 105 to obtain a wet paper sheet, which is then sequentially passed through the pressing section 106 for pressing and dehydration, and through the first drying section 107 for primary drying.

[0082] Step 7: Surface sizing treatment: Surface sizing treatment is performed on the paper sheet that has been dried once in the first drying section 107 and then enters the surface sizing machine 108. In the surface sizing process, nano cross-linked modified starch is used as the surface sizing agent, and the sizing process conditions are controlled to be 15% sizing concentration, 70°C sizing temperature, and 6g / m 2, the sizing pH value is 7.5.

[0083] Process eight, secondary drying, calendering, and winding: After surface sizing treatment by the surface sizing machine 108, the paper sheets enter the second drying section 109, the calender 110, and the paper winder 111 in sequence, and undergo secondary drying, calendering, finishing, and winding treatment to obtain finished paper.

[0084] Example 3

[0085] See also Figure 1 The preparation method of the green offset paper provided in this embodiment is as follows:

[0086] Step 1, pulping: adding coniferous wood pulp, hardwood wood pulp, dry damaged pulp and wet damaged pulp into the pulping tank 101 in a mass ratio of 30:35:10:15 for mixing to obtain a first mixed pulp, and conveying the first mixed pulp to the pulp mixing box 102.

[0087] Step 2: Slurry preparation: Light calcium carbonate (particle size of 1.9 μm), tertiary amine type amphoteric polyacrylamide and dimethyl sulfate are added to the slurry preparation box 102 for mixing to obtain a second mixed slurry, and the second mixed slurry is transported to the slurry flushing tank 103. The total mass of tertiary amine type amphoteric polyacrylamide and dimethyl sulfate accounts for 0.4% of the mass of the second mixed slurry; the mass ratio of tertiary amine type amphoteric polyacrylamide and dimethyl sulfate is 1:0.6. The amount of light calcium carbonate added accounts for 30% of the mass of the second mixed slurry.

[0088] Step 3, primary dyeing treatment: In the slurry tank 103, the second mixed slurry is fully mixed with the concentrated white water in the slurry tank 103, and dispersed rosin glue (the addition amount is 0.5% of the mass of the second mixed slurry) and polyaluminum chloride (the addition amount is 5% of the mass of the second mixed slurry) are added to the slurry tank 103 in sequence, and then 75% of the formula amount of dye (including direct turquoise and alkaline yellow) is added, and the temperature is controlled at 70°C and the pH value is 6.5. The slurry is dyed once to obtain a third mixed slurry, and the third mixed slurry is pumped to the headbox 104. Among them, the use amount of direct turquoise is 1.2kg / t slurry (for the third mixed slurry); the use amount of alkaline yellow is 0.2kg / t slurry (for the third mixed slurry).

[0089] Step 4: Secondary dyeing treatment: Add the remaining amount of dye (including direct lake blue and alkaline light yellow) into the headbox 104 to perform secondary dyeing treatment on the slurry to obtain a fourth mixed slurry.

[0090] Step 5, papermaking, forming, pressing, and primary drying: the fourth mixed slurry flowing out from the headbox 104 is papermade and formed through the fourdrinier wire section 105 to obtain a wet paper sheet, which is then sequentially passed through the pressing section 106 for pressing and dehydration, and through the first drying section 107 for primary drying.

[0091] Step 7: Surface sizing treatment: Surface sizing treatment is performed on the paper sheet that has been dried once in the first drying section 107 and then enters the surface sizing machine 108. In the surface sizing process, nano cross-linked modified starch is used as the surface sizing agent, and the sizing process conditions are controlled to be 15% sizing concentration, 70°C sizing temperature, and 8g / m 2 , the sizing pH value is 8.

[0092] Process eight, secondary drying, calendering, and winding: After surface sizing treatment by the surface sizing machine 108, the paper sheets enter the second drying section 109, the calender 110, and the paper winder 111 in sequence, and undergo secondary drying, calendering, finishing, and winding treatment to obtain finished paper.

[0093] Example 4

[0094] See also Figure 1 The preparation method of the green offset paper provided in this embodiment is as follows:

[0095] Step 1, pulping: adding coniferous wood pulp, hardwood wood pulp, dry damaged pulp and wet damaged pulp into the pulping tank 101 in a mass ratio of 30:40:5:5 for mixing to obtain a first mixed pulp, and conveying the first mixed pulp to the pulp mixing box 102.

[0096] Step 2: Slurry preparation: Light calcium carbonate (particle size of 1.7 μm), tertiary amine type amphoteric polyacrylamide and dimethyl sulfate are added to the slurry preparation box 102 for mixing to obtain a second mixed slurry, and the second mixed slurry is transported to the slurry flushing tank 103. The total mass of tertiary amine type amphoteric polyacrylamide and dimethyl sulfate accounts for 0.4% of the mass of the second mixed slurry; the mass ratio of tertiary amine type amphoteric polyacrylamide and dimethyl sulfate is 1:0.6. The amount of light calcium carbonate added accounts for 25% of the mass of the second mixed slurry.

[0097] Step 3, primary dyeing treatment: In the slurry tank 103, the second mixed slurry is fully mixed with the concentrated white water in the slurry tank 103, and dispersed rosin glue (the addition amount is 0.45% of the mass of the second mixed slurry) and polyaluminum chloride (the addition amount is 4% of the mass of the second mixed slurry) are added to the slurry tank 103 in sequence, and then 70% of the formula amount of dye (including direct turquoise and alkaline yellow) is added, and the temperature is controlled at 60°C and the pH value is 6. The slurry is dyed once to obtain a third mixed slurry, and the third mixed slurry is pumped to the headbox 104. Among them, the use amount of direct turquoise is 1.1kg / t slurry (for the third mixed slurry); the use amount of alkaline yellow is 0.2kg / t slurry (for the third mixed slurry).

[0098] Step 4: Secondary dyeing treatment: Add the remaining amount of dye (including direct lake blue and alkaline light yellow) into the headbox 104 to perform secondary dyeing treatment on the slurry to obtain a fourth mixed slurry.

[0099] Step 5, papermaking, forming, pressing, and primary drying: the fourth mixed slurry flowing out from the headbox 104 is papermade and formed through the fourdrinier wire section 105 to obtain a wet paper sheet, which is then sequentially passed through the pressing section 106 for pressing and dehydration, and through the first drying section 107 for primary drying.

[0100] Step 7: Surface sizing treatment: Surface sizing treatment is performed on the paper sheet that has been dried once in the first drying section 107 and then enters the surface sizing machine 108. In the surface sizing process, nano cross-linked modified starch is used as the surface sizing agent, and the sizing process conditions are controlled to be 12% sizing concentration, 70°C sizing temperature, and 8g / m 2 , the sizing pH value is 7.5.

[0101] Process eight, secondary drying, calendering, and winding: After surface sizing treatment by the surface sizing machine 108, the paper sheets enter the second drying section 109, the calender 110, and the paper winder 111 in sequence, and undergo secondary drying, calendering, finishing, and winding treatment to obtain finished paper.

[0102] Comparative Example 1

[0103] This comparative example provides a green offset paper, and its preparation method is basically the same as that of the above-mentioned embodiment 4, except that: step 4 is omitted, and step 3 is replaced by: in the slurry tank 103, the second mixed slurry is fully mixed with the concentrated white water in the slurry tank 103, and 100% of the formula amount of dye (including direct turquoise and alkaline yellow) is added to the slurry tank 103 to dye the slurry to obtain a third mixed slurry, and the third mixed slurry is pumped to the headbox 104. Among them, the amount of direct turquoise is 1.1 kg / t slurry (for the third mixed slurry); the amount of alkaline yellow is 0.2 kg / t slurry (for the third mixed slurry).

[0104] Comparative Example 2

[0105] This comparative example provides a green offset paper, and its preparation method is basically the same as that of the above-mentioned Example 4, except that: the process three is replaced by: in the pulping tank 103, the second mixed pulp is fully mixed with the concentrated white water in the pulping tank 103 to obtain a third mixed pulp, and the third mixed pulp is pumped to the headbox 104. The process four is replaced by: adding the remaining formula amount of dye (including direct lake blue and alkaline tender yellow) to the headbox 104 to perform secondary dyeing treatment on the pulp to obtain a fourth mixed pulp. Among them, the amount of direct lake blue used is 1.1kg / t pulp (for the fourth mixed pulp); the amount of alkaline tender yellow used is 0.2kg / t pulp (for the fourth mixed pulp).

[0106] Comparative Example 3

[0107] This comparative example provides a green offset paper, and its preparation method is basically the same as that of the above-mentioned embodiment 4, and the only difference is that: the step 7 is replaced by: the paper sheet that is dried once in the first drying section 107 and enters the surface sizing machine 108 is subjected to surface sizing treatment. In the surface sizing treatment process, ordinary corn starch (unmodified) is used as the surface sizing agent, and the sizing process conditions are controlled to be 12% sizing concentration, 70°C sizing temperature, and 8g / m 2 , the sizing pH value is 7.5.

[0108] The green offset papers prepared in the above-mentioned Examples 1 to 4 and Comparative Examples 1 to 3 were tested for the following performance indicators, and the test results are shown in Table 1. All indicators were tested in accordance with relevant national standards.

[0109] Table 1

[0110]

[0111] Table 2

[0112]

[0113]

[0114] It can be seen from Table 1 and Table 2 that the green offset paper prepared in Examples 1 to 4 of the present application has a soft tone, a high opacity, a tensile index loss rate after aging of less than 5%, a yellowing value of less than 0.5%, and a pH value of the water extract between 7.8 and 8.5. The paper has good durability and can be stored for a long time.

[0115] From the comparison results of Example 4 and Comparative Examples 1-2, it can be seen that by adding dyes in batches to dye the slurry once or twice, or directly adding all the dyes at once in process three, or adding all the dyes at once in process four, the effect on the loss rate of tensile index after aging, yellowing value and pH value of water extract of green offset paper is not obvious. However, the green offset paper prepared in Comparative Examples 1-2 will have different degrees of color spots, color lines and uneven dyeing during production, use and storage. It can be seen that by adding dyes in batches to dye the slurry once or twice, it is beneficial to reduce the problems of color spots, color lines and uneven dyeing on paper during production, use or storage.

[0116] From the comparison results of Example 4 and Comparative Example 3, it can be seen that by using the nano-cross-linked modified starch provided in the examples of the present application as a surface sizing agent, it is beneficial to reduce the tensile index loss rate of paper after aging.

[0117] In addition, a large number of experiments have found that the sizing concentration, sizing temperature, sizing amount and sizing pH value of the surface sizing agent have a great influence on the tensile index loss rate and yellowing rate of paper after aging.

[0118] Experiment 1: Effect of different sizing concentrations of surface sizing agents on paper quality

[0119] On the basis of Example 4, other raw materials and process conditions were kept unchanged, and only the sizing concentration of the surface sizing agent in step 7 was changed to 10%, 12%, 15%, 18%, 22%, 25% and 27%, respectively, and green offset paper was prepared under the above conditions. The performance of the green offset paper (flat paper) prepared in each test group was tested, and the test results are shown in Table 3.

[0120] Table 3 Effect of different sizing concentrations on paper quality

[0121]

[0122]

[0123] It can be seen from Table 3 above that when the sizing concentration is lower than 12%, the tensile index loss rate and yellowing rate of the green offset paper (flat paper) after aging are high; when the sizing concentration is in the range of 12% to 25%, the tensile index loss rate and yellowing rate of the green offset paper (flat paper) after aging do not change much; when the sizing concentration exceeds 25%, the tensile index loss rate and yellowing rate of the green offset paper (flat paper) after aging have an upward trend. Therefore, the preferred sizing concentration of the embodiment of the present application is 12% to 25%. Since a low concentration is conducive to the flow of the glue solution and is convenient for controlling the amount of sizing, the most preferred sizing concentration is 12%.

[0124] Experiment 2: Effect of different sizing temperatures of surface sizing agent on paper quality

[0125] On the basis of Example 4, other raw materials and process conditions were kept unchanged, and only the sizing temperature of the surface sizing agent in step 7 was changed to 60°C, 70°C, 80°C and 90°C, respectively, and green offset paper was prepared under the above conditions. The performance of the green offset paper (flat paper) prepared in each test group was tested, and the test results are shown in Table 4.

[0126] Table 4 Effect of different sizing temperatures on paper quality

[0127] Gluing temperature (℃) 60 70 80 90 Tensile index loss rate after aging (%) 3.0 2.7 3.1 3.2 Yellowing rate (%) 0.32 0.18 0.23 0.25

[0128] It can be seen from Table 4 that when the sizing temperature is in the range of 60℃~90℃, the tensile index loss rate and yellowing rate of the green offset paper (flat paper) after aging do not change much. During the test, it was found that when the sizing temperature is 70℃~80℃, the surface sizing agent is more evenly distributed on the paper, so the preferred sizing temperature is 70℃~80℃.

[0129] Experiment 3: Effect of different amounts of surface sizing agent on paper quality

[0130] On the basis of Example 4, other raw materials and process conditions were kept unchanged, and only the sizing amount of the surface sizing agent in step 7 was changed to 5, 6, 7, 8, and 9 g / m 2 , green offset paper was prepared under the above conditions. The performance of the green offset paper (flat paper) prepared in each test group was tested, and the test results are shown in Table 5.

[0131] Table 5 Effect of different sizing amounts on paper quality

[0132] <![CDATA[施胶量(g / m 2 )]]> 5 6 7 8 9 Tensile index loss rate after aging (%) 4.5 3.2 3.0 2.7 2.6 Yellowing rate (%) 0.21 0.22 0.20 0.18 0.30

[0133] It can be seen from Table 5 that with the increase of sizing amount, the tensile index loss rate of the green offset paper (flat paper) after aging shows a downward trend. 2When the sizing amount exceeds 8g / m 2 When the yellowing rate of the green offset paper (flat paper) is increased significantly, therefore, the preferred sizing amount in the present embodiment is 6 to 8 g / m 2 .

[0134] Experiment 4: Effect of different pH values ​​of surface sizing agent on paper quality

[0135] On the basis of Example 4, other raw materials and process conditions were kept unchanged, and only the sizing pH value of the surface sizing agent in step 7 was changed to 6, 6.5, 7, 7.5, 8, and 8.5, respectively, and green offset paper was prepared under the above conditions. The performance of the green offset paper (flat paper) prepared in each test group was tested, and the test results are shown in Table 6.

[0136] Table 6 Effect of different sizing pH values ​​on paper quality

[0137] Sizing pH 6 6.5 7 7.5 8 8.5 Tensile index loss rate after aging (%) 2.8 2.8 2.9 2.7 2.7 2.8 Yellowing rate (%) 1.3 1.0 0.22 0.18 0.26 0.45

[0138] As shown in Table 6, different sizing pH values ​​have little effect on the tensile index loss rate of green offset paper (flat paper) after aging. When the sizing pH value is lower than 7 or higher than 8, the yellowing rate of green offset paper (flat paper) increases significantly. Therefore, the preferred sizing pH value in the present application embodiment is 7 to 8.

[0139] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for preparing green offset paper, characterized in that: include: Adding coniferous wood pulp, hardwood pulp, dry damaged pulp and wet damaged pulp into a pulp preparation tank for mixing to obtain a first mixed pulp; wherein the mass ratio of the coniferous wood pulp, hardwood pulp, dry damaged pulp and wet damaged pulp is 20-30:25-40:0-15:0-15; The first mixed slurry is transported to a slurry mixing box, and auxiliary materials are added for mixing to obtain a second mixed slurry; The second mixed slurry is conveyed to a pulping tank and dyes are added to perform a dyeing treatment to obtain a third mixed slurry; the dyes include blue dyes and yellow dyes, and the amount of the dyes added is 70% to 80% of the formula amount; The third mixed slurry is conveyed to a headbox and the remaining amount of dye is added to perform secondary dyeing treatment to obtain a fourth mixed slurry; Using the fourth mixed slurry to carry out papermaking to obtain a wet paper sheet; After the wet paper sheet is subjected to a primary drying and dehydration treatment, a surface sizing agent is used to perform surface sizing treatment on the wet paper sheet, and then a secondary drying and dehydration treatment and a calendering treatment are performed to obtain green offset paper; wherein the surface sizing agent is nano cross-linked modified starch, the sizing concentration is 12% to 25%, the sizing temperature is 70 to 80°C, and the sizing amount is 6 to 8 g / m 2 .

2. The method for preparing green offset paper according to claim 1, characterized in that: The blue dye is direct lake blue or basic royal blue; the yellow dye is basic tender yellow; The usage of the blue dye is 1.0-1.2 kg / t pulp; The usage of the yellow dye is 0.18-0.22 kg / t pulp.

3. The method for preparing green offset paper according to claim 2, characterized in that: The usage amount of the blue dye is 1.1 kg / t pulp; the usage amount of the yellow dye is 0.2 kg / t pulp.

4. The method for preparing green offset paper according to claim 1, characterized in that: The second mixed slurry is conveyed to a pulping tank and dye is added to perform a dyeing treatment to obtain a third mixed slurry, comprising: To the second mixed slurry in the slurry flushing tank, dispersed rosin glue and polyaluminium chloride are added in sequence, and after being evenly mixed, the dye is added, the temperature is raised to 60° C. to 70° C., the pH value of the mixed material is adjusted to 4.5 to 6.5, and the mixture is stirred for 1 to 2 minutes to obtain a third mixed slurry.

5. The method for preparing green offset paper according to claim 1, characterized in that: The preparation steps of the nano cross-linked modified starch include: Dispersing plant starch in water to prepare a starch suspension with a mass concentration of 1% to 2%; The starch suspension is subjected to ultrasonic treatment for 60 to 80 minutes at an ultrasonic frequency of 21 to 23 kHz, an ultrasonic power of 175 to 180 W, and a temperature of 5 to 7° C. to obtain nano starch particles; The nano starch particles are dispersed in an emulsion, and a cross-linking agent is added to prepare nano cross-linked modified starch.

6. The method for preparing green offset paper according to claim 5, characterized in that: The emulsion is 1-hexadecyl 1-3-methylimidazolium bromide; The cross-linking agent is epichlorohydrin.

7. The method for preparing green offset paper according to claim 5, characterized in that: The starch suspension is subjected to ultrasonic treatment for 60 to 80 minutes at an ultrasonic frequency of 21 to 23 kHz, an ultrasonic power of 175 to 180 W, and a temperature of 5 to 7° C. to obtain nano starch particles, comprising: The starch suspension was ultrasonically treated for 75 minutes at an ultrasonic frequency of 23 kHz, an ultrasonic power of 175 W and a temperature of 7° C. to obtain nano starch particles.

8. The method for preparing green offset paper according to claim 1, characterized in that: In the surface sizing treatment, the sizing pH value is 7-8.

9. The method for preparing green offset paper according to claim 1, characterized in that: The beating degree of the coniferous wood pulp is 40-50°SR; the beating degree of the broadleaf wood pulp is 30-40°SR; the beating degree of the dry-damaged pulp is 35-45°SR; and the beating degree of the wet-damaged pulp is 35-45°SR.

10. A green offset paper, characterized in that: The green offset paper is prepared by the method for preparing green offset paper according to any one of claims 1 to 9.

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