Non-silicon-coated release paper and method for manufacturing the same

Abstract

The application discloses a non-film-coated silicon release paper, which is composed of a base paper layer, a sizing layer and a coating layer; the base paper layer slurry comprises bleached kraft broadleaf wood pulp, bleached kraft coniferous wood pulp, a filler, an alkenyl succinic anhydride, a retention and drainage aid and cationic starch; the sizing layer raw material comprises starch glue and an anionic surface sizing agent; the coating layer comprises a top coating layer and a back coating layer; the coating layer raw material is reasonably proportioned by selecting appropriate specifications of porcelain clay, calcium carbonate with different particle size distribution specifications and latex with different glass transition temperatures, so that the prepared paper has good smoothness and glossiness, and meanwhile, water absorption and oil absorption are controlled, and the paper has good release performance after being coated with silicon.

Description

Technical Field

[0001] The present 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 serve 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 release paper substrate is paper, usually coated paper or base paper. The advantages of paper substrate are low cost and easy processing, but its 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 liner substrates on the market typically require lamination before silicone oil coating is applied. This prevents silicone oil penetration and ensures excellent release properties. However, lamination has certain limitations, such as environmental concerns and high costs. Therefore, developing a non-lamination silicone-coated release liner, and improving its performance after silicone coating by adjusting the coating formula and optimizing the preparation process, is crucial for achieving high-performance, environmentally friendly release liner. Summary of the Invention

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

[0005] The technical solution of the present invention is achieved as follows:

[0006] A non-film-coated silicon release base paper, comprising a base paper layer, a sizing layer and a coating layer; the base paper layer comprises pulp comprising: 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, and defoamer;

[0010] The raw materials of the back coating layer include: second calcium carbonate, second latex, thickener, dispersant, lubricant, and 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 layer, 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 layer, 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: the content of particles with a particle size of 2 μm is 75% to 85%.

[0015] China clay is used as a coating pigment to provide excellent coating uniformity and hiding power. It requires that the content of 2μm particles is 75% to 85%, and the content of heavy metals such as arsenic, chromium, cadmium, copper, and lead are all less than 30ppb.

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

[0017] Latex acts as a binder, providing 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 sulfate hardwood pulp, 5 to 30 parts of bleached sulfate 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 the 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; and the addition amount of the anionic surface sizing agent is 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%, α-amylase is added when the temperature is raised to 75 to 85°C and the reaction is carried out 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 the 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 in parts 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 in parts 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 lauryl 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 can also be replaced by a defoaming agent with similar effects conventionally used in the art.

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

[0030] S1. Preparation of base paper layer: After pulping, descaling, and refining bleached hardwood sulfate pulp and bleached softwood sulfate pulp, filler, alkenyl succinic anhydride, cationic starch, and retention and drainage aid are added in sequence, and the mixture is evenly mixed to obtain a slurry. The slurry is formed on a screen and vacuum dehydrated to obtain base paper;

[0031] S2. sizing: 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 the sizing paper;

[0032] S3. Top coating process: The top coating is done by blade coating, with the same coating 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 the paper is dried after coating.

[0033] S4, back coating process: Back coating adopts doctor blade coating, and the back of the base paper layer is coated once. The coating is evenly applied to 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. 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 perform calendering in four nips 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 release paper before silicone coating.

[0035] S6. Silicon coating: The surface of the release paper is coated with silicone oil, and the release paper is not coated with silicone.

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

[0037] The back coating process is primarily used to improve the post-coating state of paper and prevent warping. During production, moisture levels are controlled to ≤5% before sizing and ≤5% at reel-up. Calendering conditions are used to modify the surface of the finished paper, improving 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-filmed silicon-coated release base paper and its preparation method, which optimizes the raw material formula and preparation method, and improves the processing performance of the base paper. The coating raw materials are rationally proportioned by selecting appropriate specifications of No. 3 porcelain clay, calcium carbonate and latex, so that the finished paper has good smoothness and glossiness, while also controlling water absorption and oil absorption, so that the finished paper has a glossiness greater than 50%, a Cobb value ≤ 20gsm, a smoothness ≥ 1500s, an oil absorption < 1gsm, and a peel force of < 20gf / inch under 0.6-1gsm silicone oil coating. The present invention improves the release performance of paper after silicon coating, ensuring good peeling morphology after the paper is composited with adhesive and face paper, and no delamination occurs 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 examples are provided below to further illustrate the present invention.

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

[0042] Unless otherwise specified, the materials, reagents, etc. used in the examples 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 higher 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 form 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) is added. -1 ), heated to 85°C for 45 min, inactivated the enzyme, and adjusted the pH to 11 with sodium hydroxide buffer to obtain an enzyme-converted starch solution.

[0047] Example 1

[0048] A finished product of a non-laminated silicone release paper consists of a base paper layer, a sizing layer and a coating layer. 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, the amount of alkenyl succinic anhydride is 0.5 kg / ton of paper, the concentration of retention and drainage aid (non-ionic polyacrylamide) is 100 ppm, and the amount of cationic starch is 5 kg / ton; among which porcelain 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 addition amount being 250kg / ton of starch.

[0051] The topcoat 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: content of particles with a particle size of 2 μm ≥ 65%), 15 parts of latex (glass transition temperature of 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 product of a non-laminated silicone release paper consists of a base paper layer, a sizing layer and a coating layer. 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 addition 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: content of particles with a particle size of 2 μm ≥ 65%), 9 parts of latex (glass transition temperature of 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 product of a non-laminated silicone release paper consists 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: starch glue is an oxidized starch solution (mass concentration is 20wt%), and an anionic surface sizing agent prepared by compounding 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, with an addition amount of 150kg / ton of 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: the content of particles with a particle size of 2 μm is ≥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: After pulping, deslurrying, and refining bleached kraft hardwood pulp and bleached kraft softwood pulp according to the recipe, filler, alkenyl succinic anhydride, cationic starch, and retention and drainage aid are added in sequence, and the mixture is evenly mixed to obtain a slurry. The slurry is formed on a screen and vacuum dehydrated to obtain base paper;

[0067] S2. Sizing: After mixing the raw materials for the sizing layer, apply sizing to both sides of the base paper layer using a film transfer method. The coating amount is controlled between 2 and 3 gsm to produce sizing paper. The moisture content before sizing is controlled to be ≤5% during the production process.

[0068] S3. Topcoating process: The coating materials are mixed according to the formula to prepare the coating. The topcoat is applied by doctor blade coating. The same coating is applied twice on each side. The coating is evenly applied to the surface of the base paper after sizing. The coating amount is controlled at 9gsm each time, totaling 18gsm. The coated substrate is dried by infrared radiation and hot air drying process to make the coating uniformly cured and 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. The coating is evenly applied to 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 and 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 nips. The calendering line pressure is controlled at 60kN / 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 release paper before silicone coating is obtained.

[0071] S6. Silicon coating: The surface of the release paper is coated with silicone oil, and the release paper is not coated with silicone.

[0072] Comparative Example 1

[0073] The difference between this comparative example and Example 2 is that the topcoat raw materials do not contain porcelain clay, that is, the topcoat 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 of -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-laminated silicon-coated release 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-laminated silicon-coated release 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 the calcium carbonate in the top coating are interchanged.

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

[0081] Experimental example

[0082] The performance of the pre-siliconized release papers and the non-siliconized release papers 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) s: Depending on the formulation of topcoat calcium carbonate and china clay, the smoothness is controlled between 800 and 3000s.

[0086] IGT (Printability Tester) (front) cm / s: After coating, the topcoat 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 a mixture of hydrogenated silicone oil and vinyl silicone oil, the following values ​​are measured:

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

[0092] Peel force (60℃ x 7 days) gf / inch: Peel force test after seven days in a 60℃ oven <30gf / inch.

[0093] Residual adhesion (immediate) %: The residual adhesion test is performed using a standard steel plate, 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-coated silicone-coated release paper produced by this invention exhibits excellent smoothness and glossiness while also controlling water and oil absorption. The silicone-coated paper exhibits excellent release properties, ensuring excellent peeling properties after lamination with adhesive and face paper, without 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 principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a non-film-coated silicon release paper, characterized in that: The following steps are involved: S1. Preparation of base paper layer: After pulping, descaling, and refining bleached hardwood sulfate pulp and bleached softwood sulfate pulp, filler, alkenyl succinic anhydride, cationic starch, and retention and drainage aid are added in sequence, and the mixture is evenly mixed to obtain a slurry. The slurry is formed on a screen and vacuum dehydrated to obtain base paper; S2. Sizing: After mixing the raw materials for the sizing layer, surface sizing is performed on both sides of the base paper layer by film transfer, with the coating amount controlled between 2 and 3 gsm to produce sized paper; the raw materials for the sizing layer include starch glue and anionic surface sizing agent; S3. Top coating process: The top coating is done by blade coating, with the same coating 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 the paper is dried after coating. The topcoat comprises the following components by weight: 40-60 parts of china clay, 40-60 parts of first calcium carbonate, 25-35 parts of first 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. In the coating formulation of the topcoat, the first calcium carbonate is of grade C98, and the content of particles with a particle size of 1 μm is ≥ 85%; In the coating formulation of the topcoat, the glass transition temperature of the first latex is -5 to 5°C; 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%; S4, back coating process: Back coating adopts doctor blade coating, and the back of the base paper layer is coated once. The coating is evenly applied to the back of the base paper after sizing and top coating. The coating amount of a single coating is controlled between 9~11gsm, and the coating is dried after coating; The back coating comprises the following components by weight: 100 parts of a second calcium carbonate, 8-15 parts of a second latex, 0.1-1 parts of a thickener, 0.1-0.5 parts of a dispersant, 0.1-0.5 parts of a lubricant, and 0.05-0.2 parts of a defoaming agent; In the back coating formulation, the second calcium carbonate is of grade C65, and the content of particles with a particle size of 2 μm is ≥ 65%; In the back coating formulation, the glass transition temperature of the second latex is 12-18°C; S5. Super calendering process: After coating, use a super calender to calender. The calendering method is to perform calendering in four nip 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 release paper before silicone coating. S6. Silicon coating: The surface of the release paper is coated with silicone oil, and the release paper is not coated with silicone.

2. The method for preparing a non-coated silicon-coated release paper according to claim 1, characterized in that: The pulp of the base paper layer comprises, by weight, 70 to 95 parts of bleached sulfate hardwood pulp, 5 to 30 parts of bleached sulfate 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 the retention and drainage aid is 100 to 150 ppm, and the amount of cationic starch is 5 to 10 kg / ton.

3. The method for preparing a non-coated silicon-coated release paper according to claim 1, characterized in that: 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 a styrene-acrylate anionic sizing agent or a compound of a styrene-acrylate anionic sizing agent and an alkyl ketene dimer; and the addition amount of the anionic surface sizing agent is 150-250 kg / ton of starch.

4. The method for preparing a non-coated silicon-coated release paper according to claim 3, characterized in that: The preparation method of the enzyme-converted starch solution comprises the following steps: adding corn starch to water and stirring evenly to prepare a starch solution with a mass concentration of 20wt% to 30wt%, adding α-amylase when the temperature is raised to 75°C to 85°C, reacting for 30 to 60 minutes, inactivating the enzyme, and adjusting the pH value to 10 to 11 with a sodium hydroxide buffer to obtain the enzyme-converted starch solution.

5. The method for preparing a non-coated silicon-coated release paper according to claim 4, characterized in that: The addition amount of the α-amylase is 0.1-0.2 vol% of the corn starch aqueous solution.

6. Non-film-coated silicon release paper prepared by the preparation method according to any one of claims 1 to 5.

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