Process for slightly pressing double-sided coated paper by adopting multiple coatings

Abstract

The invention discloses a multi-coating soft-pressing double-sided coated paper process, which establishes a foundation for producing high-quality double-sided coated paper by regulating and controlling the ratio of bleached sulfate softwood pulp, bleached sulfate hardwood pulp, bleached chemical thermo-mechanical pulp, ground calcium carbonate and alkenyl succinic anhydride and selecting the model of the bleached chemical thermo-mechanical pulp. According to the invention, a multi-coating light-pressing process of three-section sizing and four-section coating is adopted, the gloss, roughness and smoothness of finished paper are improved by optimizing a coating formula, the physical properties of single-pressed finished paper all accord with grade-A quality, and a brand-new cost-saving and environment-friendly papermaking mode is realized.

Description

Technical Field

[0001] The invention relates to the technical field of papermaking, and in particular to a process for double-sided coated paper using multiple coatings and light pressing. Background Art

[0002] Coated paper is also called printing coated paper. A layer of white coating is applied on the surface of the base paper, and it is processed by super calendering. It is divided into single-sided and double-sided. The paper surface is divided into glossy and cloth-textured. The paper surface is smooth, white, and has good ink absorption and inking performance. It is mainly used for offset printing and gravure fine-line printing, such as high-end picture albums, calendars, books and periodicals. Coated base paper is made of bleached chemical wood pulp or partially bleached chemical straw pulp on a papermaking machine. With base paper as the paper base, white pigment (also called white clay, such as kaolin, talcum powder, calcium carbonate, titanium dioxide, etc.), adhesive (polyvinyl alcohol, casein, modified starch, synthetic latex, etc.), and other auxiliary materials (such as gloss agent, hardener, plasticizer, dispersant, wetting agent, opal, fluorescent whitening agent, toner, etc.) are evenly coated on the coating machine, and then dried and super calendered to make it.

[0003] Coated paper papermaking enterprises are mostly high-speed online sizing and coating paper machines. The coated paper process produced by the paper machine needs to be subjected to offline super calendering to improve gloss, smoothness, reduce roughness, and full-width uniformity to meet the quality requirements of the finished paper. At present, due to the low gloss, high roughness, uneven paper surface, and rough paper surface on both sides of the coated paper base paper in the papermaking process, coated paper needs to be processed in the full-press (8NIP) mode selected by the offline super calender for the later stage, but the full-press mode has large pressure loss. If the full-press mode is required, a high coated paper thickness must be ensured when the paper machine is being produced, which not only causes high paper machine costs, but also affects the increase in vehicle speed, dehydration, etc., which is not conducive to energy saving and consumption reduction. The full-press mode requires a high thickness of coated paper, resulting in a serious excess of basis weight during paper machine production, leading to the risk of customer complaints from publishers, and seriously affecting sales.

[0004] Therefore, a multi-coated light-pressed double-sided coated paper process was developed. By optimizing the whole process control, adjusting the pulp ratio, and optimizing the coating formula, the gloss and roughness of the paper in the coating and calendering sections were controlled to achieve A-level quality control of the finished paper, which is of great significance for achieving energy conservation, environmental protection, and cost reduction. Summary of the invention

[0005] In view of this, the present invention proposes a process of using multi-coating and lightly pressed double-sided coated paper to solve the above problems.

[0006] The technical solution of the present invention is achieved in this way:

[0007] A process for producing double-sided coated paper by multi-coating and light pressing, comprising the following steps:

[0008] S1. Take bleached kraft softwood pulp, bleached kraft hardwood pulp and bleached chemical thermomechanical pulp, and mix them in a weight ratio of 10-15:55-60:30 to form a pulp mixture; the bulk thickness of the bleached chemical thermomechanical pulp is 2.7-3.0 cm 3 / g;

[0009] S2, adding ground calcium carbonate and alkenyl succinic anhydride to the pulp mixture to obtain base paper pulp;

[0010] S3, the base paper pulp enters the head box, is dehydrated, pressed, dried, formed into uncoated base paper, and hard calendered;

[0011] S4, after hard calendering, the uncoated base paper is subjected to a three-stage surface sizing process, wherein the first stage of sizing SP1 is to apply sizing liquid to the front and back sides of the base paper, the second stage of sizing SP2 is to open the bypass and not apply sizing; the third stage of sizing SP3 is to apply the first layer of primer coating on the upper and lower mesh surfaces by film transfer of a sizing machine;

[0012] S5, then four coating processes are performed, the first coating CT1 / the second coating CT2 is to coat the second middle coating coating on the upper / lower mesh surface, the third coating CT3 / the fourth coating CT4 is to coat the third layer coating coating on the upper / lower mesh surface, and the coated paper is obtained;

[0013] S6. Use 2-NIP calendering mode to calender the coated paper, and apply more lightly pressed double-sided coated paper;

[0014] The primer coating of SP3 in step S4 has the same composition as the mid-coat coating of CT1 / CT2 in step S5.

[0015] Preferably, in step S2, the specific operation is: adding 8.0-10.0% ground calcium carbonate relative to the absolute dry fiber mass to the slurry mixture, and adding 1.5-1.7 kg / t alkenyl succinic anhydride.

[0016] Preferably, in step S3, the pressing is performed by a shoe pressing method with a line pressure of 950-1050 kN / m; the line pressure of hard calendering is controlled to be 30-35 kN / m, and the hard calendering temperature is set to 70 degrees.

[0017] Preferably, the glue applied by SP1 is obtained by mixing enzyme-cut starch and styrene acrylate surface sizing agent in a mass ratio of 70-80:20-30.

[0018] Preferably, the SP1 gluing temperature is 60 degrees and the mass concentration of starch glue is 9%.

[0019] Preferably, the first layer of primer is made of ground calcium carbonate and styrene-butadiene latex in an absolute dry weight ratio of 89-91:9-11, and the coating amount on the upper / lower mesh surface is 10±0.5gsm.

[0020] Preferably, the coating temperature is 50 degrees, and the solid content of the first layer of primer is 60%.

[0021] Preferably, the second intermediate coating is made of ground calcium carbonate and styrene-butadiene latex in an absolute dry weight ratio of 89-91:9-11, and the second layer coating amount of CT1 / CT2 on the upper / lower mesh surface is 10±0.5gsm.

[0022] Preferably, the third layer coating is made of calcium carbonate, china clay and styrene-butadiene latex in an absolute dry weight ratio of 70-80:10-20:9-11; the third layer coating amount of CT3 / CT4 on the upper and lower meshes is 10±0.5gsm.

[0023] Preferably, the second middle coating has a solid content of 63%-65%; the third layer of top coating has a solid content of 65%-68%.

[0024] In order to improve the surface feel, the coating method of CT1, CT2, CT3, and CT4 in step S5 is blade coating, using a new alloy knife with a 35-degree blade edge, and controlling the paper roughness to be ≤2.2 and the gloss of the coated base paper to be ≥56.

[0025] Preferably, the calendering conditions of the 2-NIP calendering mode are as follows: the oil temperature setting temperature of the steel roller is 160-180°C, the operating line pressure is 90KN / m, the vehicle speed is 1500m / min, the lower paper line pressure is 55KN / m, the vehicle speed is 100m / min, the machine tension unwinding is 790KN / m, the 2nd pressure zone is 730KN / m, the cold cylinder is 680KN / m, and the winding is 730N / cm, and more lightly pressed double-sided coated paper should be coated.

[0026] The invention also provides a double-sided coated paper, which is made by the above-mentioned multi-coating and light-pressing double-sided coated paper process.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention provides a double-sided coated paper process using multiple coatings and light pressing. The gloss, roughness, and smoothness of the coated paper are regulated by optimizing the whole process control, adjusting the pulp ratio, and optimizing the coating formula. The physical properties of the single-pressed paper all meet the A-level quality, realizing a new cost-saving green and environmentally friendly papermaking mode. The 2-NIP single-pressing mode is used for papermaking, which uses less pressing area than the full-pressing mode, and reduces the cost of NIPCO roller grinding and rubber coating: about 69,800 yuan / year. The calendering 2-NIP mode is used for papermaking, and the basis weight of the coated paper is reduced, and the thickness of the coated paper can be reduced, which not only improves the speed efficiency and time efficiency of the paper machine equipment, but also reduces the thickness of the coated paper and reduces costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a papermaking flow chart of the three-stage sizing and four-stage coating coated paper machine of the present invention.

[0030] Figure 2 This is a diagram of the super calender 2-NIP single pressure mode of the present invention. DETAILED DESCRIPTION

[0031] In order to better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention.

[0032] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0033] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial sources.

[0034] Table 1

[0035]

[0036]

[0037] The papermaking process flow chart of the 3-stage sizing and 4-stage coated coated paper machine of the present invention is as follows: Figure 1 The super calender 2-NIP single pressure mode diagram of the present invention is shown in FIG. Figure 2 shown.

[0038] Example 1

[0039] A process for producing double-sided coated paper by multi-coating and light pressing, comprising the following steps:

[0040] S1. Mixing bleached kraft softwood pulp, bleached kraft hardwood pulp and bleached chemical thermomechanical pulp in a weight ratio of 10:60:30 to form a pulp mixture;

[0041] Before mixing, the bleached softwood kraft pulp was pulped and refined to obtain a freeness of 410 ml and a bulk of 1.2 cm. 3 / g pulp; bleached kraft hardwood pulp is pulped and refined to obtain a freeness of 410ml and a bulk thickness of 1.2cm 3 / g pulp; bleached chemical thermomechanical pulp was dispersed and refined to obtain a freeness of 280ml and a bulk thickness of 2.8cm 3 / g pulp, the refining energy consumption is ≤35kwh / t;

[0042] S2, adding 10% ground calcium carbonate relative to the absolute dry fiber mass to the pulp mixture of step S1, and adding 1.6 kg / t alkenyl succinic anhydride sizing agent to obtain base paper pulp;

[0043] S3, the base paper pulp obtained in step S2 enters the single-layer head box, is formed by net dehydration, the wire speed is 1450m / min, the pulp-net speed ratio is 1.045, and then is subjected to shoe pressing, the line pressure is 1000kN / m, and the front-stage drying cylinder is dried to form uncoated base paper, the base paper basis weight is 106gsm; then hard calendering is performed, the hard calendering temperature is set to 70 degrees, and the hard calendering line pressure is 35KN / m, so as to reduce the roughness and modify the flatness;

[0044] S4. A three-stage surface sizing process is used for the uncoated base paper. In the first stage of sizing, SP1, the sizing amount of the front and back sides of the base paper is 0.9±0.1gsm (a total of 2g). The glue solution is obtained by mixing enzyme-cut starch and styrene acrylate surface sizing agent in a mass ratio of 80:20, the mass concentration of the glue solution is 9%, the sizing temperature is 60 degrees, and the back-stage drying cylinder is carried out after the first sizing; the second stage of sizing, SP2, is to open the bypass and not apply glue; the third stage of sizing, SP3, is to apply 10±0.5gsm of primer coating on the upper and lower mesh surfaces by film transfer of the sizing machine (the primer coating is made of ground calcium carbonate and styrene-butadiene latex in a 90:10 absolute dry mass ratio, the coating solid content is 60%, the coating temperature is 50 degrees, and attention is paid to no missing coating on the sizing roller surface. Missing coating will increase the wear of the coating scraper and easily lead to uneven coating or other paper defects;

[0045] S5, after the sizing process is completed, four coating processes are carried out, the first coating CT1 / the second coating CT2 is to apply the second middle coating coating on the upper / lower mesh surface (the second coating is made of ground calcium carbonate and styrene butadiene latex in a ratio of 90:10, the coating solid content is 65%, and the coating temperature is 50 degrees), and the coating amount of the upper / lower mesh surface is 10±0.5gsm; the third coating CT3 / the fourth coating CT4 is to apply the third layer coating coating on the upper and lower mesh surfaces (the third layer coating is made of calcium carbonate, china clay, and styrene butadiene latex in a ratio of 75:15:10 in terms of absolute dry mass, the coating solid content is 68%, and the coating temperature is 50 degrees), and the coating amount of the upper / lower mesh surface is 10±0.5gsm, and the coated paper is obtained;

[0046] In order to improve the surface feel, the coating method is blade coating, using a new alloy knife with a 35-degree blade edge, and controlling the roughness of the finished paper to be ≤2.2 and the gloss of the coated base paper to be ≥56; SP3 coating and blade coating CT1 / 2 / 3 / 4 are applied on the upper / lower screen with a cumulative coating of 30 / 30g to obtain the coated paper, with a coated paper base of 175gsm, and the moisture content of the finished paper is controlled at 5.2%;

[0047] S6. Calender the coated paper. Super calendering adopts 2-NIP calendering mode. The calendering conditions are steel roller oil temperature setting temperature 180℃, operating line pressure 90KN / m, machine speed 1500m / min, lower paper line pressure 55KN / m, machine speed 100m / min, machine tension unwinding 790KN / m, 2nd pressure zone 730KN / m, cold cylinder 680KN / m, winding 730N / cm, and more lightly pressed double-sided coated paper should be coated.

[0048] Example 2

[0049] A process for producing double-sided coated paper by multi-coating and light pressing, comprising the following steps:

[0050] S1. Mixing bleached kraft softwood pulp, bleached kraft hardwood pulp and bleached chemical thermomechanical pulp in a weight ratio of 15:55:30 to form a pulp mixture;

[0051] Before mixing, the bleached softwood kraft pulp was pulped and refined to obtain a freeness of 420 ml and a bulk of 1.4 cm. 3 / g pulp; bleached kraft hardwood pulp is pulped and refined to obtain a freeness of 420ml and a bulk thickness of 1.3cm 3 / g pulp; bleached chemical thermomechanical pulp was dispersed and refined to obtain a freeness of 290ml and a bulk thickness of 3.0cm 3 / g pulp, the refining energy consumption is ≤35kwh / t;

[0052] S2, adding 10% ground calcium carbonate relative to the absolute dry fiber mass to the pulp mixture of step S1, and adding 1.6 kg / t alkenyl succinic anhydride sizing agent to obtain base paper pulp;

[0053] S3, the base paper pulp obtained in step S2 enters the single-layer head box, is formed by dehydration through a clamping wire, the wire speed is 1450m / min, the pulp-to-wire speed ratio is 1.045, and then is subjected to shoe pressing with a line pressure of 1000kN / m, and is dried in a front-stage drying cylinder to form an uncoated base paper with a base paper basis weight of 108gsm; and then is subjected to hard calendering with a hard calendering temperature set at 70 degrees and a line pressure of 35KN / m to reduce roughness and modify flatness;

[0054] S4. A three-stage surface sizing process is used for uncoated base paper. In the first stage of sizing, SP1, the amount of sizing applied to the front and back sides of the base paper is 0.9±0.1gsm (a total of 2g). The glue solution is obtained by mixing enzyme-cut starch and styrene acrylate surface sizing agent in a mass ratio of 80:20. The glue solution is diluted to a mass concentration of 9%, and the sizing temperature is 60 degrees. After the first sizing, the back-stage drying cylinder is carried out; the second stage of sizing, SP2, is to open the bypass and not apply sizing; the third stage of sizing, SP3, is to apply 10±0.5gsm of primer coating on the upper and lower mesh surfaces by film transfer of the sizing machine (the primer coating is made of ground calcium carbonate and styrene-butadiene latex in a 90:10 absolute dry mass ratio, the coating solid content is 60%, and the coating temperature is 50 degrees). Pay attention to the glue roller surface without missing coating. Missing coating will increase the wear of the coating scraper and easily lead to uneven coating or other paper defects.

[0055] S5, after the sizing process is completed, four coating processes are carried out, the first coating CT1 / the second coating CT2 is to apply the second middle coating coating on the upper / lower mesh surface (the second coating is made of ground calcium carbonate and styrene butadiene latex in a ratio of 90:10, the coating solid content is 65%, and the coating temperature is 50 degrees), and the coating amount of the upper / lower mesh surface is 10±0.5gsm; the third coating CT3 / the fourth coating CT4 is to apply the third layer coating coating on the upper and lower mesh surfaces (the third layer coating is made of calcium carbonate, china clay, and styrene butadiene latex in a ratio of 70:20:10 in terms of absolute dry mass, the coating solid content is 68%, and the coating temperature is 50 degrees), and the coating amount of the upper / lower mesh surface is 10±0.5gsm, and the coated paper is obtained;

[0056] In order to improve the surface feel, the coating method is blade coating, using a new alloy knife with a 35-degree blade edge, and controlling the roughness of the finished paper to be within ≤2.2 and the gloss of the coated base paper to be ≥56; SP3 coating and blade coating CT1 / 2 / 3 / 4 are applied on the upper / lower screen with a cumulative coating of 30 / 30g to obtain coated paper;

[0057] S6. Calender the coated paper. Super calendering adopts 2-NIP calendering mode. The calendering conditions are steel roller oil temperature setting temperature 160℃, operating line pressure 90KN / m, machine speed 1500m / min, lower paper line pressure 55KN / m, machine speed 100m / min, machine tension unwinding 790KN / m, 2nd pressure zone 730KN / m, cold cylinder 680KN / m, winding 730N / cm, and more lightly pressed double-sided coated paper should be coated.

[0058] Example 3

[0059] A process for producing double-sided coated paper by multi-coating and light pressing, comprising the following steps:

[0060] S1. Mixing bleached kraft softwood pulp, bleached kraft hardwood pulp and bleached chemical thermomechanical pulp in a weight ratio of 12:58:30 to form a pulp mixture;

[0061] Before mixing, the bleached softwood kraft pulp was pulped and refined to obtain a freeness of 410 ml and a bulk of 1.2 cm. 3 / g pulp; bleached kraft hardwood pulp is pulped and refined to obtain a freeness of 410ml and a bulk thickness of 1.2cm 3 / g pulp; bleached chemical thermomechanical pulp was dispersed and refined to obtain a freeness of 290ml and a bulk thickness of 2.7cm 3 / g pulp, the refining energy consumption is ≤35kwh / t;

[0062] S2, adding 8% ground calcium carbonate relative to the absolute dry fiber mass to the pulp mixture of step S1, and adding 1.7 kg / t alkenyl succinic anhydride sizing agent to obtain base paper pulp;

[0063] S3, the base paper pulp obtained in step S2 enters the single-layer head box, is formed by net dehydration, the wire speed is 1450m / min, the pulp-net speed ratio is 1.045, and then is subjected to shoe pressing, the line pressure is 1000kN / m, and the front-stage drying cylinder is dried to form uncoated base paper, the base paper basis weight is 103gsm; then hard calendering is performed, the hard calendering temperature is set to 70 degrees, and the hard calendering line pressure is 35KN / m, so as to reduce the roughness and modify the flatness;

[0064] S4. A three-stage surface sizing process is used for uncoated base paper. In the first stage of sizing SP1, the amount of sizing applied to the front and back sides of the base paper is 0.9±0.1gsm (a total of 2g). The glue solution is obtained by mixing enzyme-cut starch and styrene acrylate surface sizing agent in a mass ratio of 70:30, the mass concentration of the glue solution is 9%, and the sizing temperature is 60 degrees. After the first sizing, the back-stage drying cylinder is carried out; the second stage of sizing SP2 is to open the bypass and not apply sizing; the third stage of sizing SP3 is to apply 10±0.5gsm of primer coating on the upper and lower mesh surfaces by film transfer of the sizing machine (the primer coating is made of ground calcium carbonate and styrene-butadiene latex in a 90:10 absolute dry mass ratio), and pay attention to no missing coating on the sizing roller surface. Missing coating will increase the wear of the coating scraper and easily lead to uneven coating or other paper defects.

[0065] S5, after the sizing process is completed, four coating processes are carried out, the first coating CT1 / the second coating CT2 is to apply the second middle coating coating on the upper / lower mesh surface (the second coating is made of ground calcium carbonate and styrene butadiene latex in a ratio of 90:10, the coating solid content is 65%, and the coating temperature is 50 degrees), and the coating amount of the upper / lower mesh surface is 10±0.5gsm; the third coating CT3 / the fourth coating CT4 is to apply the third layer coating coating on the upper and lower mesh surfaces (the third layer coating is made of calcium carbonate, china clay, and styrene butadiene latex in an absolute dry mass ratio of 80:10:10, the coating solid content is 68%, and the coating temperature is 50 degrees), and the coating amount of the upper / lower mesh surface is 10±0.5gsm, and the coated paper is obtained;

[0066] In order to improve the surface feel, the coating method is blade coating, using a new alloy knife with a 35-degree blade edge, and controlling the roughness of the finished paper to be within ≤2.2 and the gloss of the coated base paper to be ≥56; SP3 coating and blade coating CT1 / 2 / 3 / 4 are applied on the upper / lower screen with a cumulative coating of 30 / 30g to obtain coated paper;

[0067] S6. Calender the coated paper. Super calendering adopts 2-NIP calendering mode. The calendering conditions are steel roller oil temperature setting temperature 180℃, operating line pressure 90KN / m, machine speed 1500m / min, lower paper line pressure 55KN / m, machine speed 100m / min, machine tension unwinding 790KN / m, 2nd pressure zone 730KN / m, cold cylinder 680KN / m, winding 730N / cm, and more lightly pressed double-sided coated paper should be coated.

[0068] Comparative Example 1

[0069] The difference between this comparative example and Example 1 is that the double-sided coated paper is prepared by calendering in the conventional full-pressing mode 8NIP.

[0070] Comparative Example 2

[0071] The difference between this comparative example and Example 1 is that the weight ratio of the bleached kraft softwood pulp, the bleached kraft hardwood pulp and the bleached chemical thermomechanical pulp in step S1 is 30:40:40.

[0072] Comparative Example 3

[0073] The difference between this comparative example and Example 1 is that the bleached chemical thermomechanical pulp in step S1 is pulped and refined to obtain a freeness of 280 ml and a bulk of 3.2 cm. 3 / g of slurry.

[0074] Comparative Example 4

[0075] The difference between this comparative example and Example 1 is that the third layer of surface coating in step S5 is prepared from calcium carbonate, china clay, and styrene-butadiene latex in an absolute dry weight ratio of 85:5:10.

[0076] Test example

[0077] The pressure loss of the double-sided coated paper obtained in the above Example 1 and Comparative Example 1 was compared, and the results were as follows:

[0078] Table 2

[0079]

[0080] The above results show that the coated paper thickness required for the full-pressing mode is 186 μm. Compared with the traditional full-pressing mode of Comparative Example 1, the coated paper thickness required for the single-pressing mode using the process of the present invention is 177 μm, which is reduced by 9 μm. This not only improves the speed efficiency and time efficiency of the paper machine equipment, but also reduces the thickness of the coated paper, reduces costs, and reduces the pressure loss rate, which can meet the A-level standard.

[0081] The double-sided coated papers obtained in the above Examples 1 to 3 and Comparative Examples 2 to 5 were subjected to performance tests, and the results are shown in Table 3.

[0082] Table 3

[0083]

[0084] The above results show that the double-sided coated paper prepared by the multi-coated light-pressed double-sided coated paper process of the present invention can all meet the A-level standard. Comparative Examples 2 and 3 show that too high a proportion of bleached chemical thermomechanical pulp (BCTMP) will cause problems such as poor paper strength, increased roughness, and decreased glossiness. The selection of BCTMP is very critical in the research process. The above results show that by adjusting the pulp ratio, the selection of BCTMP, and the proportion of coating calcium carbonate, latex, and porcelain clay, the gloss and smoothness of double-sided coated paper can be improved and the roughness can be reduced.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A double-sided coated paper process using multiple coatings and light pressure, characterized in that: The following steps are involved: S1. Take bleached kraft softwood pulp, bleached kraft hardwood pulp and bleached chemical thermomechanical pulp, and mix them in a weight ratio of 10-15:55-60:30 to form a pulp mixture; the bulk thickness of the bleached chemical thermomechanical pulp is 2.7-3.0 cm 3 / g; S2, adding ground calcium carbonate and alkenyl succinic anhydride to the pulp mixture to obtain base paper pulp; S3, the base paper pulp enters the head box, is dehydrated, pressed, dried, formed into uncoated base paper, and hard calendered; S4, after hard calendering, the uncoated base paper is subjected to a three-stage surface sizing process, wherein the first stage of sizing SP1 is to apply sizing liquid to the front and back sides of the base paper, the second stage of sizing SP2 is to open the bypass and not apply sizing; the third stage of sizing SP3 is to apply the first layer of primer coating on the upper and lower mesh surfaces by film transfer of a sizing machine; S5, then four coating processes are performed, the first coating CT1 / the second coating CT2 is to coat the second middle coating coating on the upper / lower mesh surface, the third coating CT3 / the fourth coating CT4 is to coat the third layer coating coating on the upper / lower mesh surface, and the paper is coated; the coating method of CT1, CT2, CT3, and CT4 is doctor blade coating; S6. Use 2-NIP calendering mode to calender the coated paper, and apply more lightly pressed double-sided coated paper; The primer coating of SP3 in step S4 has the same composition as the mid-coat coating of CT1 / CT2 in step S5.

2. The process of using multi-coating and lightly pressed double-sided coated paper according to claim 1, characterized in that: The specific operation of step S2 is: adding 8.0-10.0% ground calcium carbonate relative to the absolute dry fiber mass to the slurry mixture, and adding 1.5-1.7 kg / t alkenyl succinic anhydride.

3. The process of double-sided coated paper with multiple coatings and light pressure according to claim 1, characterized in that: In step S3, the pressing is performed by a shoe pressing method with a line pressure of 950-1050 kN / m; the line pressure of hard calendering is controlled to be 30-35 kN / m, and the hard calendering temperature is set to 70 degrees.

4. The process of using multi-coating and lightly pressed double-sided coated paper according to claim 1, characterized in that: The glue solution applied by SP1 is obtained by mixing enzyme-cut starch and styrene acrylate surface sizing agent in a mass ratio of 70-80:20-30.

5. The process of double-sided coated paper with multiple coatings and light pressure according to claim 1, characterized in that: The first layer of primer is made of ground calcium carbonate and styrene-butadiene latex in an absolute dry weight ratio of 89-91:9-11, and the coating amount of the upper / lower mesh surface is 10±0.5gsm.

6. The process of double-sided coated paper with multiple coatings and light pressure according to claim 1, characterized in that: The second layer of mid-coat is made of ground calcium carbonate and styrene-butadiene latex in an absolute dry weight ratio of 89-91:9-11; the second layer coating amount of CT1 / CT2 on the upper / lower mesh surface is 10±0.5gsm.

7. The process of double-sided coated paper with multiple coatings and light pressure according to claim 1, characterized in that: The third layer coating is made of calcium carbonate, porcelain clay and styrene-butadiene latex in an absolute dry weight ratio of 70-80:10-20:9-11; the third layer coating amount of CT3 / CT4 on the upper and lower nets is 10±0.5gsm.

8. The process of double-sided coated paper with multiple coatings and light pressure according to claim 1, characterized in that: The calendering conditions of the 2-NIP calendering mode are as follows: steel roller oil temperature setting temperature 160-180°C, operating line pressure 90KN / m, machine speed 1500m / min, lower paper line pressure 55KN / m, machine speed 100m / min, machine tension unwinding 790KN / m, 2nd pressure zone 730KN / m, cold cylinder 680KN / m, winding 730N / cm, and more lightly pressed double-sided coated paper should be coated.

9. A double-sided coated paper, made by the double-sided coated paper process using multiple coating and light pressing as described in any one of claims 1 to 8.

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