Film-spraying-free silicon-coated release base paper and preparation method thereof

Abstract

The invention discloses film-spraying-free silicon-coated release base paper which is composed of a base paper layer, a sizing layer and a coating. The raw paper layer pulp comprises bleached sulfate hardwood pulp, bleached sulfate softwood pulp, filler, alkenyl succinic anhydride, a retention and drainage aid and cationic starch; the sizing layer is prepared from starch glue and an anionic surface sizing agent; the coating comprises a surface coating and a back coating; the raw materials of the coating are reasonably proportioned by selecting china clay with proper specifications, calcium carbonate with different particle size distribution specifications and latex with different glass transition temperatures, so that the prepared finished paper has better smoothness and glossiness, water absorption and oil absorption are controlled, and the paper has good release performance after being coated with silicon.

Description

Technical Field

[0001] The invention relates to the technical field of papermaking, and in particular to a non-film-coated silicon-coated release base paper and a preparation method thereof. Background Art

[0002] Release liner, also known as label backing paper, is a material widely used in labels, tapes, medical films, electronic products and various other adhesive applications. Its main function is to act as a protective layer for the adhesive, ensuring that the adhesive does not adhere to other surfaces before use. Release paper usually consists of two parts: a substrate and a coating. The substrate is usually paper or plastic film, and the coating is the key component to prevent the adhesive from adhering to the substrate. The traditional substrate for release paper is paper, usually coated paper or base paper. The advantages of paper substrates are low cost and easy processing, but their moisture resistance and strength are relatively low. The coating of release paper is its most important part, which determines its release performance. Silicone oil coating is the most common type of coating. Silicone oil has excellent anti-adhesion properties and can effectively prevent adhesives from adhering to paper substrates.

[0003] Currently, label base paper substrates on the market usually need to be coated before silicone oil components can be applied to block silicone oil penetration to achieve good peeling performance. However, coating has certain limitations, such as being environmentally unfriendly and costly. Therefore, developing a non-coated silicone-coated release paper, adjusting the coating formula and optimizing the preparation process to improve its performance after silicone coating, is crucial to achieving excellent performance and environmentally friendly release paper. Summary of the invention

[0004] In view of this, the present invention proposes a non-film-coated silicon-coated release base paper and a preparation method thereof to solve the above problems.

[0005] The technical solution of the present invention is achieved in this way:

[0006] A non-film-coated silicon release base paper, comprising a base paper layer, a sizing layer and a coating layer; the pulp of the base paper layer comprises: bleached kraft hardwood pulp, bleached kraft softwood pulp, filler, alkenyl succinic anhydride, retention and drainage aids and cationic starch;

[0007] The raw materials of the sizing layer include starch glue and anionic surface sizing agent;

[0008] The coating comprises a top coating and a back coating;

[0009] The raw materials of the topcoat layer include: china clay, first calcium carbonate, first latex, thickener, dispersant, lubricant, defoamer;

[0010] The raw materials of the back coating layer include: second calcium carbonate, second latex, thickener, dispersant, lubricant, defoamer;

[0011] The first calcium carbonate and the second calcium carbonate have different particle size distributions, and the first latex and the second latex have different glass transition temperatures.

[0012] Preferably, among the raw materials of the top coating, the first calcium carbonate is of grade C98, and the content of particles with a particle size of 1 μm is ≥85%; among the raw materials of the back coating, the second calcium carbonate is of grade C65, and the content of particles with a particle size of 2 μm is ≥65%.

[0013] Preferably, among the raw materials for the top coating layer, the glass transition temperature of the first latex is -5 to 5°C, and among the raw materials for the back coating layer, the glass transition temperature of the second latex is 12 to 18°C.

[0014] Preferably, the porcelain clay is No. 3 porcelain clay, and the particle size distribution is as follows: the content of particles with a particle size of 2 μm is 75% to 85%.

[0015] As a pigment for coatings, china clay provides excellent coating uniformity and hiding power, requiring a 2μm particle content of 75% to 85%, with heavy metal contents such as arsenic, chromium, cadmium, copper, and lead all less than 30ppb.

[0016] Calcium carbonate is used as a pigment for the coating to give the coating an appropriate gloss. The particle size requirements are two specifications: 2μm particle content ≥65% and 1μm particle content ≥85%.

[0017] As a binder, latex provides adhesion and flexibility to the coating, ensuring stable adhesion of the coating to the substrate. The glass transition temperature (Tg) is available in two specifications: -5 to 5°C and 12 to 18°C.

[0018] Preferably, the pulp of the base paper layer comprises, by weight: 70 to 95 parts of bleached kraft hardwood pulp, 5 to 30 parts of bleached kraft coniferous pulp, and 5 to 15 parts of filler. The amount of alkenyl succinic anhydride is 0.5 to 1.5 kg / ton, the concentration of retention and drainage aid is 100 to 150 ppm, and the amount of cationic starch is 5 to 10 kg / ton.

[0019] Preferably, the filler is one or more of ground calcium carbonate and porcelain clay.

[0020] Preferably, the retention and drainage aid is one or more of nonionic polyacrylamide, cationic polyacrylamide, and anionic polyacrylamide, including but not limited to the nonionic polyacrylamide listed in the embodiments of the present invention, and can also be replaced by other conventional cationic polyacrylamide and anionic polyacrylamide retention and drainage aids in the papermaking field.

[0021] Preferably, the starch glue is an oxidized starch solution or an enzyme-converted starch solution prepared using starch as raw material; the anionic surface sizing agent is one of a styrene-acrylate anionic sizing agent and an anionic surface sizing agent compounded with a styrene-acrylate anionic sizing agent and an alkyl ketene dimer; the anionic surface sizing agent is added in an amount of 150 to 250 kg per ton of starch.

[0022] Preferably, the preparation method of the enzyme-converted starch solution is: corn starch is added to water and stirred to prepare a starch solution with a mass concentration of 20wt% to 30wt%, a-amylase is added when the temperature is raised to 75 to 85°C to react for 30 to 60 minutes, the enzyme is inactivated, and the pH value is adjusted to 10 to 11 with sodium hydroxide buffer to obtain an enzyme-converted starch solution.

[0023] Preferably, the addition amount of the α-amylase is 0.1 to 0.2 vol % of the corn starch aqueous solution.

[0024] Preferably, the formula of the top coating layer comprises the following components by weight: 40-60 parts of china clay, 40-60 parts of calcium carbonate, 25-35 parts of latex, 0.1-1 parts of thickener, 0.1-0.5 parts of dispersant, 0.1-0.5 parts of lubricant, and 0.05-0.2 parts of defoamer; the formula of the back coating layer comprises the following components by weight: 100 parts of calcium carbonate, 8-15 parts of latex, 0.1-1 parts of thickener, 0.1-0.5 parts of dispersant, 0.1-0.5 parts of lubricant, and 0.05-0.2 parts of defoamer.

[0025] Preferably, the thickener is one or more of sodium carboxymethyl cellulose, sodium carboxymethyl starch, and methyl cellulose, including but not limited to those listed in the embodiments of the present invention, and may also be replaced by other thickeners conventionally used in the art.

[0026] Preferably, the dispersant is one or more of sodium polyacrylate and sodium dodecyl sulfate, including but not limited to those listed in the embodiments of the present invention, and may also be replaced by other dispersants conventionally used in the art.

[0027] Preferably, the lubricant is one or more of sodium stearate and calcium stearate, including but not limited to those listed in the embodiments of the present invention, and may also be replaced by other lubricants conventionally used in the art.

[0028] Preferably, the defoaming agent is a polyol defoaming agent, including but not limited to those listed in the embodiments of the present invention, and may also be replaced by a defoaming agent with similar effect conventionally used in the art.

[0029] The present invention also provides a method for preparing a non-film-coated silicon-coated release paper, comprising the following steps:

[0030] S1. Preparation of base paper layer: after pulping, deslurrying and refining bleached kraft hardwood pulp and bleached kraft softwood pulp, filler, alkenyl succinic anhydride, cationic starch and retention and drainage aid are added in sequence, the mixture is mixed evenly to obtain slurry, the slurry is put on a screen for forming, and vacuum dehydration is performed to obtain base paper;

[0031] S2. Gluing: After mixing the raw materials for the sizing layer, the surface sizing is applied on both sides of the base paper layer by film transfer, and the coating amount is controlled between 2 and 3 gsm to obtain sizing paper;

[0032] S3, top coating process: top coating adopts scraper coating, the same coating is applied twice on one side, the coating is evenly applied on the surface of the base paper after sizing, the coating amount is controlled between 8 and 10 gsm each time, and drying is carried out after coating;

[0033] S4, back coating process: Back coating adopts doctor blade coating, and the back of the base paper layer is coated once, and the coating is evenly coated on the back of the base paper after sizing and top coating. The coating amount of a single coating is controlled between 9 and 11 gsm, and drying is carried out after coating;

[0034] S5. Super calendering process: After coating, the paper is calendered using a super calender. The calendering method is to calender the front side in four nipping zones. The calendering line pressure is controlled at 40-60 kN / m, and the calendering temperature is controlled at 40-60°C to obtain the pre-silicon coated release base paper.

[0035] S6. Silicon coating: The surface of the release paper is coated with silicone oil to obtain a non-silicon coated release paper.

[0036] Preferably, the drying includes infrared radiation and hot air drying processes.

[0037] The back coating process is mainly used to improve the state of the paper after coating and avoid warping. The moisture content before sizing is controlled to be ≤5% and the moisture content after winding is ≤5% during the production process. The surface of the finished paper is modified through the above calendering conditions to improve its roughness, smoothness and flatness.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The present invention provides a non-film-coated silicon-coated release base paper and a preparation method thereof, optimizes the raw material formula and preparation method, and improves the processing performance of the base paper, wherein the coating raw materials are reasonably proportioned by selecting No. 3 porcelain clay, calcium carbonate and latex of appropriate specifications, so that the finished paper has good smoothness and glossiness, while controlling the water absorption and oil absorption, so that the finished paper has a glossiness>50%, Cobb value≤20gsm, smoothness≥1500s, oil absorption<1gsm, and a peeling force<20gf / inch under 0.6-1gsm silicone oil coating. The present invention improves the release performance of paper after silicon coating, ensures that the paper has a good peeling morphology when laminated with adhesive and face paper in the rear composite section, and there is no stratification during the peeling process. It has been verified that the paper produced by the present invention can reach the domestic advanced level through the current domestic silicon coating and lamination process. DETAILED DESCRIPTION

[0040] In order to better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention.

[0041] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0042] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial sources.

[0043] No. 3 porcelain clay was purchased from IMERYS.

[0044] Bleached hardwood kraft pulp and bleached softwood kraft pulp were purchased from Metsä Fibre, Finland.

[0045] The main component of the polyol defoamer used in the examples and comparative examples of the present invention is a high-carbon alcohol emulsion purchased from Zhucheng Tongshun Rubber Industry Co., Ltd.

[0046] The starch glue used in Examples 1-2 of the present invention is an enzyme-converted starch solution. The preparation method of the enzyme-converted starch solution is as follows: an appropriate amount of corn starch is added to water and stirred to prepare a starch solution with a mass concentration of 20 wt%, and α-amylase (the addition amount is 0.2 vol% of the corn starch aqueous solution, and the α-amylase activity is 40000 u·mL -1 ), heated to 85°C for 45 min, inactivated the enzyme, and adjusted the pH value to 11 with sodium hydroxide buffer to obtain an enzyme-converted starch solution.

[0047] Example 1

[0048] A finished paper of non-film-coated silicon release base paper consists of a base paper layer, a sizing layer and a coating layer, and the formula of each part is as follows:

[0049] The base paper layer pulp includes the following raw materials in parts by weight: 70 parts of bleached sulfate hardwood pulp, 30 parts of bleached sulfate softwood pulp, 15 parts of filler, 0.5 kg / ton of alkenyl succinic anhydride, 100 ppm concentration of retention and filtration aid (non-ionic polyacrylamide), and 5 kg / ton of cationic starch; among which china clay is selected as the filler.

[0050] Raw materials for the sizing layer: Starch glue is an enzyme-converted starch solution, to which a styrene-acrylate anionic sizing agent is added, with the added amount being 250kg / ton of starch.

[0051] The top coating formula includes the following components by weight: 40 parts of No. 3 porcelain clay (the content of particles with a particle size of 2 μm is 75% to 85%), 60 parts of ground calcium carbonate (C98 grade, particle size distribution: the content of particles with a particle size of 1 μm is ≥85%), 25 parts of latex (glass transition temperature is -5°C), 1 part of thickener (methyl cellulose), 0.1 part of dispersant (sodium polyacrylate), 0.2 part of lubricant (sodium stearate), and 0.2 part of polyol defoaming agent.

[0052] The back coating formula includes the following components by weight: 100 parts of calcium carbonate (C65 grade, particle size distribution: 2 μm particle size particle content ≥ 65%), 15 parts of latex (glass transition temperature is 15°C), 1 part of thickener (methyl cellulose), 0.1 part of dispersant (sodium polyacrylate), 0.1 part of lubricant (sodium stearate), and 0.2 part of polyol defoaming agent.

[0053] Example 2

[0054] A finished paper of non-film-coated silicon release base paper consists of a base paper layer, a sizing layer and a coating layer, and the formula of each part is as follows:

[0055] The base paper layer pulp includes the following raw materials in parts by weight: 85 parts of bleached sulfate hardwood pulp, 15 parts of bleached sulfate softwood pulp, 10 parts of filler, the amount of alkenyl succinic anhydride is 1 kg / ton of paper, the concentration of retention and drainage aid (non-ionic polyacrylamide) is 120 ppm, and the amount of cationic starch is 8 kg / ton; the filler is 100% ground calcium carbonate.

[0056] Raw materials for the sizing layer: Starch glue is an enzyme-converted starch solution, to which a styrene-acrylate anionic sizing agent is added, with the added amount being 200 kg / ton of starch.

[0057] The topcoat formula includes the following components by weight: 50 parts of No. 3 porcelain clay (the content of particles with a particle size of 2 μm is 75% to 85%), 50 parts of ground calcium carbonate (C98 grade, particle size distribution: the content of particles with a particle size of 1 μm is ≥85%), 30 parts of latex (glass transition temperature is -5°C), 0.5 parts of thickener (sodium carboxymethyl cellulose), 0.2 parts of dispersant (sodium polyacrylate), 0.2 parts of lubricant (sodium stearate), and 0.07 parts of polyol defoaming agent.

[0058] The back coating formula includes the following components by weight: 100 parts of calcium carbonate (C65 grade, particle size distribution: 2 μm particle size particle content ≥ 65%), 9 parts of latex (glass transition temperature is 15°C), 0.5 parts of thickener (carboxymethyl cellulose), 0.2 parts of dispersant (sodium polyacrylate), 0.2 parts of lubricant (sodium stearate), and 0.07 parts of polyol defoaming agent.

[0059] Example 3

[0060] A finished paper of non-film coated silicon release base paper is composed of a base paper layer, a sizing layer and a coating layer. The formula of each part is as follows:

[0061] The base paper layer pulp includes the following raw materials in parts by weight: 95 parts of bleached sulfate hardwood pulp, 5 parts of bleached sulfate softwood pulp, 5 parts of filler, the amount of alkenyl succinic anhydride is 1.5 kg / ton of paper, the concentration of retention and drainage aid (non-ionic polyacrylamide) is 150 ppm, and the amount of cationic starch is 10 kg / ton; the filler is 100% ground calcium carbonate.

[0062] Raw materials for the sizing layer: The starch glue is an oxidized starch solution (mass concentration is 20wt%), and an anionic surface sizing agent prepared by mixing a styrene-acrylate anionic sizing agent and an alkyl ketene dimer in a mass ratio of 1:1 is added to the oxidized starch solution, and the added amount is 150kg / ton starch.

[0063] The topcoat formula includes the following components by weight: 60 parts of No. 3 porcelain clay (the content of particles with a particle size of 2 μm is 75% to 85%), 40 parts of ground calcium carbonate (C98 grade, particle size distribution: the content of particles with a particle size of 1 μm is ≥85%), 35 parts of latex (glass transition temperature is -5°C), 0.1 part of thickener (a mixture of sodium carboxymethyl cellulose and sodium carboxymethyl starch in a mass ratio of 1:1), 0.5 part of dispersant (sodium polyacrylate), 0.5 part of lubricant (sodium stearate), and 0.05 part of polyol defoaming agent.

[0064] The back coating formula includes the following components by weight: 100 parts of calcium carbonate (C65 grade, particle size distribution: 2μm particle size particle content ≥65%), 8 parts of latex (glass transition temperature is 15°C), 0.1 parts of thickener (a mixture of sodium carboxymethyl cellulose and sodium carboxymethyl starch in a mass ratio of 1:1), 0.5 parts of dispersant (sodium polyacrylate), 0.5 parts of lubricant (sodium stearate), and 0.05 parts of polyol defoaming agent.

[0065] The method for preparing the non-film-coated silicon release paper described in Examples 1 to 3 comprises the following steps:

[0066] S1. Preparation of base paper layer: according to the formula, filler, alkenyl succinic anhydride, cationic starch and retention and drainage aid are added to bleached kraft hardwood pulp and bleached kraft softwood pulp after pulping, deslurrying and refining, and the mixture is evenly mixed to obtain slurry, and the slurry is put on a screen for forming and vacuum dehydration to obtain base paper;

[0067] S2. Gluing: After mixing the raw materials for the sizing layer, the surface sizing is applied on both sides of the base paper layer by film transfer, and the coating amount is controlled between 2 and 3 gsm to obtain sizing paper; the moisture content before sizing is controlled to be ≤5% during the production process;

[0068] S3, top coating process: the coating raw materials are mixed according to the formula to prepare the coating, the top coating is applied by scraper coating, the same coating is applied twice on one side, the coating is evenly applied on the surface of the base paper after sizing, the coating amount is controlled at 9gsm each time, and the total is 18gsm. The coated substrate is dried by infrared radiation and hot air drying process to make the coating uniformly cured to ensure the adhesion and stability of the coating;

[0069] S4, back coating process: Back coating adopts doctor blade coating, and the back of the base paper layer is coated once, and the coating is evenly coated on the back of the base paper after sizing and top coating. The coating amount of a single coating is controlled at 10gsm. The coated substrate is dried by infrared radiation and hot air drying process to make the coating uniformly cured to ensure the adhesion and stability of the coating;

[0070] S5. Super calendering process: After coating, the finished paper is calendered using a super calender. The calendering method is to perform calendering on the front side in four nipping zones. The calendering line pressure is controlled at 60 kN / m, and the calendering temperature is controlled at 50°C. The surface of the finished paper is modified by calendering to improve its roughness, smoothness and flatness, and the pre-silicon coated release base paper is obtained.

[0071] S6. Silicon coating: The surface of the release paper is coated with silicone oil to obtain a non-silicon coated release paper.

[0072] Comparative Example 1

[0073] The difference between this comparative example and Example 2 is that the top coating raw materials do not contain porcelain clay, that is, the top coating formula includes the following components by weight: 100 parts of ground calcium carbonate (C98 grade, particle size distribution: 1 μm particle size particle content ≥ 85%), 30 parts of latex (glass transition temperature is -5°C), 0.5 parts of thickener (sodium carboxymethyl cellulose), 0.2 parts of dispersant (sodium polyacrylate), 0.2 parts of lubricant (sodium stearate), and 0.07 parts of polyol defoaming agent.

[0074] The preparation method of the non-film-coated silicon release base paper is basically the same as that of Example 2.

[0075] Comparative Example 2

[0076] The difference between this comparative example and Example 2 is that the specifications of the latex in the back coating formula and the latex in the top coating are interchanged.

[0077] The preparation method of the non-film-coated silicon release base paper is basically the same as that of Example 2.

[0078] Comparative Example 3

[0079] The difference between this comparative example and Example 2 is that the specifications of calcium carbonate in the back coating formula and calcium carbonate in the top coating are interchanged.

[0080] The preparation method of the non-film-coated silicon release base paper is basically the same as that of Example 2.

[0081] Experimental example

[0082] The performance of the pre-siliconized release paper and the non-siliconized release paper prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was evaluated.

[0083] Technical indicators of paper before silicon coating:

[0084] Glossiness (front) %: Depending on the formulation of calcium carbonate and porcelain clay in the topcoat, the glossiness is controlled between 30% and 55%.

[0085] BEKK smoothness (front side) s: Depending on the different formulations of calcium carbonate and china clay in the topcoat, the smoothness is controlled between 800 and 3000s.

[0086] IGT (Printability Tester) (front) cm / s: After coating, the top coating IGT>300cm / s is required.

[0087] Oil absorption value (front) gsm: Use castor oil for COBB60 test, the value is required to be <1gsm.

[0088] Water absorption value COBB (front) gsm: Use treated water for COBB60 test, the value is required to be <20gsm.

[0089] Technical indicators of paper after silicon coating:

[0090] After coating the finished paper with 0.6-1.2gsm of hydrogenated silicone oil and vinyl silicone oil, the following values ​​are tested:

[0091] Peel force (immediate) gf / inch: <30 gf / inch tested immediately after silicone coating.

[0092] Peel force (60℃x7 days) gf / inch: Peel force test after seven days in 60℃ oven <30gf / inch.

[0093] Residual adhesion (immediate) %: Use standard steel plate to test the residual adhesion, and the residual adhesion is required to be >70%.

[0094] The test results are shown in Table 1.

[0095] Table 1

[0096]

[0097]

[0098] The non-film-coated silicon-coated release base paper prepared by the present invention has good smoothness and glossiness, while controlling water absorption and oil absorption. The paper has good release performance after silicon coating, ensuring that the paper has a good peeling morphology after being laminated with the adhesive and the surface paper, and there is no delamination during the peeling process.

[0099] 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 non-film-coated silicon release paper, characterized in that: Including base paper layer, sizing layer and coating layer; The pulp of the base paper layer comprises: bleached kraft hardwood pulp, bleached kraft softwood pulp, filler, alkenyl succinic anhydride, retention and drainage aids and cationic starch; The raw materials of the sizing layer include starch glue and anionic surface sizing agent; The coating comprises a top coating and a back coating; The raw materials of the topcoat layer include: china clay, first calcium carbonate, first latex, thickener, dispersant, lubricant, defoamer; The raw materials of the back coating layer include: second calcium carbonate, second latex, thickener, dispersant, lubricant, defoamer; The first calcium carbonate and the second calcium carbonate have different particle size distributions, and the first latex and the second latex have different glass transition temperatures.

2. The non-film-coated silicon release paper according to claim 1, characterized in that: Among the raw materials of the top coating, the first calcium carbonate is of grade C98, and the content of particles with a particle size of 1 μm is ≥85%; among the raw materials of the back coating, the second calcium carbonate is of grade C65, and the content of particles with a particle size of 2 μm is ≥65%.

3. The non-film-coated silicon release paper according to claim 1, characterized in that: Among the raw materials of the top coating layer, the glass transition temperature of the first latex is -5 to 5°C, and among the raw materials of the back coating layer, the glass transition temperature of the second latex is 12 to 18°C.

4. The non-film-coated silicon release paper according to claim 1, characterized in that: The porcelain clay is No. 3 porcelain clay, and the particle size distribution is as follows: the content of particles with a particle size of 2 μm is 75% to 85%.

5. The non-film-coated silicon release paper according to claim 1, characterized in that: The pulp of the base paper layer includes, by weight, 70 to 95 parts of bleached kraft hardwood pulp, 5 to 30 parts of bleached kraft softwood pulp, and 5 to 15 parts of filler. The amount of alkenyl succinic anhydride is 0.5 to 1.5 kg / ton, the concentration of retention and drainage aid is 100 to 150 ppm, and the amount of cationic starch is 5 to 10 kg / ton.

6. The non-film-coated silicon release paper according to claim 1, characterized in that: The starch glue is an oxidized starch solution or an enzyme-converted starch solution prepared from starch as raw material; the anionic surface sizing agent is one of a styrene-acrylate anionic sizing agent and an anionic surface sizing agent compounded with a styrene-acrylate anionic sizing agent and an alkyl ketene dimer; the anionic surface sizing agent is added in an amount of 150 to 250 kg per ton of starch.

7. The non-film-coated silicon release paper according to claim 6, characterized in that: The preparation method of the enzyme-converted starch solution comprises the following steps: adding corn starch into water and stirring evenly to prepare a starch solution with a mass concentration of 20wt% to 30wt%, adding a-amylase to react for 30 to 60 minutes when the temperature is raised to 75 to 85°C, killing the enzyme, and adjusting the pH value to 10 to 11 with a sodium hydroxide buffer to obtain the enzyme-converted starch solution.

8. The non-film-coated silicon-coated release paper according to claim 7, characterized in that: The addition amount of the a-amylase is 0.1-0.2 vol% of the corn starch aqueous solution.

9. The non-film-coated silicon-coated release paper according to claim 1, characterized in that: The topcoat coating comprises the following components by weight: 40-60 parts of china clay, 40-60 parts of calcium carbonate, 25-35 parts of latex, 0.1-1 parts of thickener, 0.1-0.5 parts of dispersant, 0.1-0.5 parts of lubricant, and 0.05-0.2 parts of defoamer; The formula of the back coating layer includes the following components by weight: 100 parts of calcium carbonate, 8-15 parts of latex, 0.1-1 parts of thickener, 0.1-0.5 parts of dispersant, 0.1-0.5 parts of lubricant, and 0.05-0.2 parts of defoamer.

10. The method for preparing the non-film-coated silicon release paper according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1. Preparation of base paper layer: after pulping, deslurrying and refining bleached kraft hardwood pulp and bleached kraft softwood pulp, filler, alkenyl succinic anhydride, cationic starch and retention and drainage aid are added in sequence, the mixture is mixed evenly to obtain slurry, the slurry is put on a screen for forming, and vacuum dehydration is performed to obtain base paper; S2. Gluing: After mixing the raw materials for the sizing layer, the surface sizing is applied on both sides of the base paper layer by film transfer, and the coating amount is controlled between 2 and 3 gsm to obtain sizing paper; S3, top coating process: top coating adopts scraper coating, the same coating is applied twice on one side, the coating is evenly applied on the surface of the base paper after sizing, the coating amount is controlled between 8 and 10 gsm each time, and drying is carried out after coating; S4, back coating process: Back coating adopts doctor blade coating, and the back of the base paper layer is coated once, and the coating is evenly coated on the back of the base paper after sizing and top coating. The coating amount of a single coating is controlled between 9 and 11 gsm, and drying is carried out after coating; S5. Super calendering process: After coating, super calendering is used for calendering. The calendering method is to perform calendering in four nipping zones on the front side. The calendering line pressure is controlled at 40-60 kN / m, and the calendering temperature is controlled at 40-60°C to obtain the pre-silicon coated release base paper. S6. Silicon coating: The surface of the release paper is coated with silicone oil to obtain a non-silicon coated release paper.

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