Double-sided coated white board and preparation process thereof

Abstract

The application discloses a double-side coated white board, wherein the pigment in the front surface coating layer further comprises calcium carbonate; the calcium carbonate comprises precipitated calcium carbonate generated in the slurry during the mixing process and micron-sized calcium carbonate participating in the mixing; the micron-sized calcium carbonate participating in the mixing comprises micron-sized calcium carbonate dispersed in the coating slurry and micron-sized calcium carbonate particles dispersed on the surface of the wet front surface coating layer after the slurry coating; after drying, a micron-sized calcium carbonate particle enrichment area is formed on one side of the superficial layer of the front surface coating layer of the obtained double-side coated white board; and the application further discloses a preparation method of the double-side coated white board; and the application constructs the adding sequence of micron-sized calcium carbonate and nano-sized calcium carbonate particles on the coating surface, simultaneously constructs the regular stacking of the pigment particles in the coating, fills the gaps between the micron-sized particles with the nano-sized calcium carbonate particles, forms a more uniform coating structure, controls the distribution of the styrene-butadiene latex, improves the printing quality and reduces the coating defects.

Description

Technical Field

[0001] This invention relates to the field of double-sided coated whiteboard paper technology, and in particular to a double-sided coated whiteboard paper and its preparation process. Background Technology

[0002] Coated whiteboard paper can be divided into two types: single-sided coating and double-sided coating. Because of the double-sided coating process, the rheological properties of the coating material have a significant impact on the performance of the double-sided coating. Rheological properties include the viscosity, thixotropy, and pseudoplasticity of the coating material. These characteristics determine the flowability and stability of the coating during the coating process, thus affecting the uniformity of the coating and the final quality of the paper.

[0003] Patent application CN101806013A discloses a topcoat for double-sided coated whiteboard paper. This patent addresses the technical problem of a dense, sealed surface coating on double-sided coated whiteboard paper, which hinders the penetration of blister packing oil. The specific composition (by weight) includes: 20 to 50 parts kaolin, 50 to 80 parts calcium carbonate, 10 to 18 parts latex, and 25 to 35 parts water, along with additives including a dispersant. It also adds 0.6 to 3.0 parts of the functional additive PC4200 soy protein. This soy protein, as a substitute for PC4200 paper-making adhesives, has an amphoteric charge; its anions can interact with mineral pigments to give the final coating higher porosity, thereby improving the penetration of blister packing oil. However, the addition of soy protein reduces the surface strength of the paper and increases production costs. Summary of the Invention

[0004] The purpose of this invention is to provide a double-sided coated whiteboard paper. This invention involves adding micron-sized and nano-sized calcium carbonate particles to the coating surface in a stepwise manner between coating and drying / calendering. At the same time, it constructs a regular stacking of pigment particles in the coating. The nano-sized calcium carbonate particles fill the gaps between the micron-sized particles, forming a more uniform coating structure, controlling the distribution of styrene-butadiene latex, improving printing quality, and reducing coating defects.

[0005] To solve this technical problem, the technical solution of the present invention is: a double-sided coated whiteboard paper, comprising coated paper and two-sided coatings, wherein the two-sided coatings include a front base coating, a back coating, and a front surface coating.

[0006] The pigments in the front coating also include calcium carbonate;

[0007] Calcium carbonate includes precipitated calcium carbonate formed in the slurry during the mixing process and calcium carbonate particles of micron size that participate in the mixing process.

[0008] The micron-sized calcium carbonate particles involved in the mixing include micron-sized calcium carbonate dispersed in the coating slurry and micron-sized calcium carbonate particles that are vibrated and dispersed on the wet front surface coating after the slurry is applied.

[0009] After drying, a micron-sized calcium carbonate particle enrichment area is formed on one side of the shallow coating layer on the front side of the double-sided coated whiteboard paper.

[0010] Preferably, the coating material of the front surface layer comprises the following substances in parts by weight:

[0011] The coating material of the front surface layer comprises the following substances in parts by weight:

[0012]

[0013] The preferred pigments are in parts by weight of 100, including 30 parts kaolin and 70 parts calcium carbonate;

[0014] The 70 parts of calcium carbonate comprise 10 to 15 parts of precipitated calcium carbonate particles and 15 to 20 parts of micron-sized calcium carbonate particles that are vibrated and dispersed on the wet front surface of the coating after the slurry is applied. The remainder consists of micron-sized calcium carbonate particles directly dispersed in the coating slurry. In this invention, the precipitated calcium carbonate particles include spherical nano-calcium carbonate particles and spherical micron-sized calcium carbonate particles. The spherical nano-calcium carbonate particles not only effectively promote the dispersion of calcium carbonate in the coating, but also, especially, effectively disperse between the micron-sized calcium carbonate nano-particles and kaolin particles, thus promoting the dispersion of the ink. In this invention, spherical calcium carbonate particles generated in situ in the slurry and micron-sized calcium carbonate particles distributed on the shallow surface of the coating layer form an orderly distribution, improving the regular rather than random distribution of pigment particles in the resulting coating layer. In particular, the uniform and controllable distribution of micron-sized calcium carbonate particles on the shallow surface of the resulting coated white cardboard paper results in a uniform and consistent surface. The shallow surface of the front coating obtained by this invention has large pores that facilitate ink absorption and penetration due to the uniform dispersion of micron-sized calcium carbonate particles, thereby accelerating the ink absorption performance.

[0015] The preferred method for preparing the front surface coating includes the following steps:

[0016] S11. Dissolve sodium tripolyphosphate and sodium carboxymethyl cellulose in a 0.2 mol / L calcium chloride aqueous solution and stir until homogeneous;

[0017] S12. Add sodium carbonate solution of equal molar amount to calcium chloride aqueous solution to the mixture obtained in S11 to obtain spherical calcium carbonate particles, wherein the precipitated calcium carbonate includes micron-sized precipitated calcium carbonate particles and nano-sized precipitated calcium carbonate particles.

[0018] S13. Mix polyvinyl alcohol, kaolin, and defoamer evenly according to the stated mass fractions;

[0019] S14. Add deionized water to adjust the solid content of the resulting coating to obtain the target coating.

[0020] This invention controls the amount of sodium carboxymethyl cellulose and sodium tripolyphosphate, wherein sodium carboxymethyl cellulose chelates calcium ions to form uniform micron-sized spherical particles; sodium tripolyphosphate promotes the precipitation of calcium carbonate into spherical nano-calcium carbonate particles, thereby achieving a gradation of micron-sized and nano-sized particles and introducing nano-sized spherical calcium carbonate particles into the slurry.

[0021] The preferred process conditions for constant-speed stirring in S11 are 800 r / min to 1000 r / min and stirring time is 45 min to 65 min.

[0022] Preferably, the concentration of sodium carboxymethyl cellulose in S11 is 0.5 g / L to 0.75 g / L, and the concentration of sodium tripolyphosphate is 0.75 g / L to 1.0 g / L. This invention controls the gradation of spherical calcium carbonate and the viscosity of the resulting slurry by controlling the amounts of sodium carboxymethyl cellulose and sodium tripolyphosphate.

[0023] Preferably, the solid content of the coating on the front surface is 40% to 45%.

[0024] Preferably, the coating of the front undercoat comprises the following substances in parts by weight:

[0025]

[0026] In this invention, the dispersant is stearamide, the hydration resistant agent is polyamide resin, and the lubricant is polyethylene oxide.

[0027] This invention uses a waterproof topcoat layer, which effectively complements the effect of the relatively low solids content topcoat layer on the coated paper before it dries, making it suitable for coating topcoats with low solids content but suitable viscosity.

[0028] Another objective of this invention is to provide a method for preparing double-sided coated whiteboard paper. This invention utilizes coating combined with vibration to disperse micron-sized calcium carbonate particles to form a gradation of nano-calcium carbonate particles and micron-sized calcium carbonate particles, thereby constructing a regular stacking of pigment particles in the coating, improving coating efficiency and the smoothness of the coating on the resulting double-sided coated whiteboard paper, and increasing the ink absorption rate.

[0029] To solve this technical problem, the technical solution of the present invention is: a preparation process for the double-sided coated whiteboard paper proposed in this invention, comprising the following steps:

[0030] S1. Apply the front base coating to the coated paper with a humidity of less than 90%;

[0031] S2, Apply a back coating layer to the coated paper that has passed through S2;

[0032] S3. Apply a topcoat layer to the surface of the base coating layer on the front side of the coated paper;

[0033] S4. After coating, the micron-sized calcium carbonate particles are vibrated and dispersed in the moist coating of the front coating layer, dried, and calendered to obtain the target double-sided coated whiteboard paper.

[0034] The preferred coating process parameters in step S3 are as follows:

[0035] Coating amount is 20g / m 2 Up to 35g / m 2 ;

[0036] The drying process parameters in step S4 are: drying temperature 50℃.

[0037] By adopting the above technical solution, the beneficial effects of the present invention are:

[0038] This invention, by combining vibrating and dispersing micron-sized calcium carbonate particles on the surface of the wet front-side coating after coating, forms a gradation of nano-calcium carbonate particles and micron-sized calcium carbonate particles. This creates a regular stacking of pigment particles in the coating, with the nano-calcium carbonate particles filling the gaps between the micron-sized particles, resulting in a more uniform coating structure. By changing the order of addition and combining the gradation of calcium carbonate particles of different sizes, this invention achieves the surface of the coating with micron-sized calcium carbonate particles, effectively changing the aggregated structure of styrene-butadiene latex in the front-side coating. Simultaneously, the nano-calcium carbonate particles generated in situ in the slurry effectively inhibit the migration and aggregation of styrene-butadiene latex during the drying process. The spherical nano-calcium carbonate particles increase the viscosity of the coating, thereby slowing down the movement of latex particles and helping to prevent their migration and aggregation during drying. Furthermore, the addition of spherical nano-calcium carbonate particles may also improve the stability of the coating, reducing potential problems during drying, such as orange peel effect or uneven coating. This invention, by grading the pigment particles, affects the formation of porosity, adjusts ink absorption properties, helps to form a smooth paper surface, improves printing quality, and reduces coating defects.

[0039] This invention incorporates calcium carbonate particles in batches during the coating process. After coating, the addition of micron-sized calcium carbonate introduces an interface between the micron-sized calcium carbonate particles and the coating slurry on the coating surface. During the drying process, the accumulation of micron-sized calcium carbonate particles in the shallow layer of the front coating has more large pores compared to other areas distributed along the thickness direction towards the surface of the coated paper. This facilitates the rapid absorption and penetration of ink into the front coating, which is beneficial for subsequent printing. Furthermore, the enrichment of micron-sized calcium carbonate particles in the shallow layer increases the porosity of the shallow layer, improving the ink absorption performance. It also inhibits the aggregation of styrene-butadiene latex on the coating surface, regulates the distribution as an adhesive, and effectively improves the surface strength of the resulting coated white board paper.

[0040] The preparation process of this invention also improves coating efficiency and the smoothness of the coating on the resulting double-sided coated whiteboard paper. Attached Figure Description

[0041] Figure 1 This is a particle size analysis diagram of the precipitated calcium carbonate particles in Example 1 of the present invention. Detailed Implementation

[0042] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0043] This invention, by combining vibrating and dispersing micron-sized calcium carbonate particles on the surface of the wet front-side coating after coating, forms a gradation of nano-calcium carbonate particles and micron-sized calcium carbonate particles. This creates a regular stacking of pigment particles in the coating, with the nano-calcium carbonate particles filling the gaps between the micron-sized particles, resulting in a more uniform coating structure. By changing the order of addition and combining the gradation of calcium carbonate particles of different sizes, this invention achieves the surface of the coating with micron-sized calcium carbonate particles, effectively changing the aggregated structure of styrene-butadiene latex in the front-side coating. Simultaneously, the nano-calcium carbonate particles generated in situ in the slurry effectively inhibit the migration and aggregation of styrene-butadiene latex during the drying process. The spherical nano-calcium carbonate particles increase the viscosity of the coating, thereby slowing down the movement of latex particles and helping to prevent their migration and aggregation during drying. Furthermore, the addition of spherical nano-calcium carbonate particles may also improve the stability of the coating, reducing potential problems during drying, such as orange peel effect or uneven coating. This invention, by grading the pigment particles, affects the formation of porosity, adjusts ink absorption properties, helps to form a smooth paper surface, improves printing quality, and reduces coating defects.

[0044] This invention incorporates calcium carbonate particles in batches during the coating process. After coating, the addition of micron-sized calcium carbonate introduces an interface between the micron-sized calcium carbonate particles and the coating slurry on the coating surface. During the drying process, the accumulation of micron-sized calcium carbonate particles in the shallow layer of the front coating has more large pores compared to other areas distributed along the thickness direction towards the surface of the coated paper. This facilitates the rapid absorption and penetration of ink into the front coating, which is beneficial for subsequent printing. Furthermore, the enrichment of micron-sized calcium carbonate particles in the shallow layer increases the porosity of the shallow layer, improving the ink absorption performance. It also inhibits the aggregation of styrene-butadiene latex on the coating surface, regulates the distribution as an adhesive, and effectively improves the surface strength of the resulting coated white board paper.

[0045] The preparation process of this invention also improves coating efficiency and the smoothness of the coating on the resulting double-sided coated whiteboard paper.

[0046] Example 1

[0047] This embodiment discloses a double-sided coated whiteboard paper, including coated paper and two-sided coatings, the two-sided coatings including a front base coating, a back coating and a front surface coating;

[0048] The pigments in the front coating also include calcium carbonate;

[0049] Calcium carbonate includes precipitated calcium carbonate formed in the slurry during the mixing process and calcium carbonate particles of micron size that participate in the mixing process.

[0050] The micron-sized calcium carbonate particles involved in the mixing include micron-sized calcium carbonate dispersed in the coating slurry and micron-sized calcium carbonate particles that are vibrated and dispersed on the surface of the wet front coating after the slurry is coated. After drying, a micron-sized calcium carbonate particle enrichment area is formed on one side of the shallow layer of the front coating of the double-sided coated whiteboard paper.

[0051] The coating material for the front surface layer described in this embodiment, in parts by weight, is shown in Table 1. It includes the following substances:

[0052] The coating material of the front surface layer comprises the following substances in parts by weight:

[0053]

[0054]

[0055] In this embodiment, the pigment is calculated in parts by weight of 100, including 30 parts kaolin and 70 parts calcium carbonate. The calcium carbonate comprises precipitated calcium carbonate particles (D-CaCO3) and micron-sized calcium carbonate particles (F-CaCO3) dispersed by vibration on the wet front surface coating after slurry application. The remaining amount is micron-sized calcium carbonate particles (H-CaCO3) directly dispersed in the coating slurry, as shown in Table 1. The precipitated calcium carbonate particles in this invention include spherical nano-calcium carbonate particles and spherical micron-sized calcium carbonate particles, such as... Figure 1As shown, the spherical nano-calcium carbonate particles not only effectively promote the dispersion of calcium carbonate in the coating, but also effectively disperse between the micron-sized calcium carbonate nanoparticles and kaolin particles, thus promoting ink dispersion. The spherical calcium carbonate particles generated in situ in the slurry and the micron-sized calcium carbonate particles distributed on the shallow surface of the coating layer form an orderly distribution, improving the regularity of pigment particle distribution in the resulting coating layer, rather than randomness. In particular, the uniform and controllable distribution of the micron-sized calcium carbonate particles on the shallow surface of the resulting coated white cardboard paper results in a uniform surface. Simultaneously, the concentration of the micron-sized calcium carbonate particles maintains a uniform roughness on the coating surface, increasing the contact area between the ink and the paper, promoting the formation of larger voids, and improving ink absorption efficiency. In this embodiment, the micron-sized calcium carbonate particles (F-CaCO3) used for vibration dispersion on the wet front coating surface are calcium carbonate particles soaked in deionized water for 2 hours, avoiding the formation of pinholes due to changes in surface tension of the wet film layer caused by the distribution of micron-sized calcium carbonate particles (F-CaCO3) on the wet slurry coating surface.

[0056] The method for preparing the front surface coating in this embodiment includes the following steps:

[0057] S11. Dissolve sodium tripolyphosphate and sodium carboxymethyl cellulose in a 0.2 mol / L calcium chloride aqueous solution and stir until homogeneous;

[0058] In this embodiment, the concentrations of sodium carboxymethyl cellulose and sodium tripolyphosphate in S11 are detailed in Table 2. This invention controls the gradation of spherical calcium carbonate and the viscosity of the resulting slurry by controlling the amounts of sodium carboxymethyl cellulose and sodium tripolyphosphate.

[0059] S12. Add sodium carbonate solution of equal molar amount to calcium chloride aqueous solution to the mixture obtained in S11 to obtain spherical calcium carbonate particles, wherein the precipitated calcium carbonate includes micron-sized precipitated calcium carbonate particles and nano-sized precipitated calcium carbonate particles.

[0060] The process conditions and stirring time for constant speed stirring in S11 in this embodiment are detailed in Table 2.

[0061] S13. Mix polyvinyl alcohol, kaolin, and defoamer evenly according to the stated mass fractions;

[0062] S14. Add deionized water to adjust the solid content of the resulting coating to obtain the target coating.

[0063] The solid content and viscosity of the coating on the front surface in this embodiment are detailed in Table 2.

[0064] This invention controls the amount of sodium carboxymethyl cellulose and sodium tripolyphosphate, wherein sodium carboxymethyl cellulose chelates calcium ions to form uniform micron-sized spherical particles; sodium tripolyphosphate promotes the precipitation of calcium carbonate into spherical nano-calcium carbonate particles, thereby achieving a gradation of micron-sized and nano-sized particles and introducing nano-sized spherical calcium carbonate particles into the slurry.

[0065] The coating material of the front undercoat in this embodiment includes the following substances in parts by weight:

[0066]

[0067] In this embodiment, the water-resistant agent is polyamide resin, and the lubricant is modified oxidized polyethylene polymer.

[0068] In this embodiment, a waterproof top coat is used, which effectively complements the effect of the relatively low solids content top coat on the coated paper before it dries, making it suitable for coating top coats with low solids content but appropriate viscosity.

[0069] This embodiment also discloses a preparation process for the double-sided coated whiteboard paper proposed in this invention, including the following steps:

[0070] S1. Apply a top coat to the coated paper with a moisture content below 90%; the top coat coating amount is 10 g / m². 2 ;

[0071] S2. Apply a back coating layer to the coated paper that has passed through S2; the coating amount of the back coating layer is 1.5 g / m². 2 ;

[0072] S3. Apply a topcoat layer to the surface of the base coating layer on the front side of the coated paper. The topcoat layer coating amount is 25 g / m². 2 ;

[0073] S4. After coating, the micron-sized calcium carbonate particles are vibrated and dispersed in the moist coating of the front coating layer, dried, and calendered to obtain the target double-sided coated whiteboard paper.

[0074] The drying process parameters in step S4 are: drying temperature 50℃.

[0075] Example 2

[0076] The main difference between this embodiment and Embodiment 1 lies in the composition of the front coating layer and the preparation process parameters, as detailed in Tables 1 and 2.

[0077] Example 3

[0078] The main difference between this embodiment and Embodiment 1 lies in the composition of the front coating layer and the preparation process parameters, as detailed in Tables 1 and 2.

[0079] Example 4

[0080] The main difference between this embodiment and Embodiment 1 lies in the composition of the front coating layer and the preparation process parameters, as detailed in Tables 1 and 2.

[0081] Example 5

[0082] The main difference between this embodiment and Embodiment 1 lies in the composition of the front coating layer and the preparation process parameters, as detailed in Tables 1 and 2.

[0083] Comparative Example

[0084] This comparative example proposes a double-sided coated whiteboard paper, including coated paper and two-sided coatings, the two-sided coatings including a front base coating, a back coating and a front surface coating;

[0085] The pigments in the front coating also include calcium carbonate. The mass ratio of kaolin and calcium carbonate is 30:70, with 100 parts by mass. The micron-sized calcium carbonate particles in this comparative example are commercially available calcium carbonate with specific parameters of D50≤12μm and purity≥98%.

[0086] The coating material of the front surface layer comprises the following substances in parts by weight:

[0087]

[0088] The method for preparing the front surface coating in this embodiment includes the following steps:

[0089] The above components were stirred at a constant speed of 800 r / min for 45 min. Deionized water was added to adjust the solid content of the resulting coating to 60% and the viscosity to 11670 mPa·s, thus obtaining the target coating.

[0090] The front undercoat used in this comparative example is the same as in Example 1.

[0091] The preparation process of double-sided coated whiteboard paper in this embodiment uses the same coating and drying process parameters as in Example 1.

[0092] Table 1. Coating composition of the front surface coating in Examples 1 to 5

[0093]

[0094]

[0095] Table 2. Preparation process parameters of the front-side coating slurry used in Examples 1 to 5.

[0096] CMC-Na 0.5g / L 0.6g / L 0.75g / L 0.7g / L 0.8g / L Sodium tripolyphosphate 1.0g / L 0.75g / L 0.5g / L 0.75g / L 0.5g / L Stirring speed 800r / min 800r / min 1000r / min 1000r / min 1000r / min Stirring time 45min 45min 50min 60min 60min Solid content 40％ 45％ 38％ 48％ 42％ Viscosity (mPa·s) 514 591 487 638 549

[0097] Performance tests were conducted on the double-sided coated whiteboard paper obtained in Examples 1 to 5 and the comparative examples. The specific performance tests and reference standards are detailed in Table 3.

[0098] Table 3 shows the performance data of double-sided coated whiteboard paper obtained in Examples 1 to 5 and comparative examples.

[0099]

[0100]

[0101] The porosity determination methods in Table 3 are as follows:

[0102] The porosity of the coating was determined using the silicone oil penetration method. Silicone oil penetrated into the coating pores, and excess silicone oil on the surface was wiped off after 2 minutes. The mass of the samples before and after penetration was measured to determine the mass of silicone oil absorbed by the coating. Then, based on the content and density of each component in the coating, the volume of absorbed silicone oil and the total volume of the coating were calculated. The calculation method for the coating porosity is shown below:

[0103] φ = Vimb / Vb * 100%; where φ is the coating porosity, Vimb is the volume of silicone oil absorbed, and m 3 Vb is the volume of the coating, in meters. 3 .

[0104] As can be seen from Tables 1, 2 and 3, compared with the comparative example, the present invention effectively improves the ink absorption performance and porosity by controlling the gradation and distribution of calcium carbonate particles, and also affects the distribution of styrene-butadiene latex as an adhesive, thereby improving the surface strength of the resulting coated whiteboard paper.

Claims

1. A double-sided coated whiteboard paper, characterized in that: It includes coated paper and two-sided coating, the two-sided coating including a front base coating, a back coating and a front top coating; The pigment in the front coating includes calcium carbonate; the calcium carbonate includes precipitated calcium carbonate generated in the coating slurry during the mixing process, micron-sized calcium carbonate particles directly dispersed in the coating slurry, and micron-sized calcium carbonate particles vibrated and dispersed on the wet front coating surface after the coating slurry is applied. After drying, a micron-sized calcium carbonate particle enrichment area is formed on one side of the shallow layer of the coating on the front side of the double-sided coated whiteboard paper. The coating material of the front surface layer comprises the following substances in parts by weight: 100 parts pigment; 15 to 20 parts of styrene-butadiene latex; 2 to 4 parts polyvinyl alcohol; 0.1 to 0.5 parts of defoamer; The pigment, in parts by weight of 100, comprises 30 parts kaolin and 70 parts calcium carbonate; wherein the 70 parts calcium carbonate includes 10 to 15 parts precipitated calcium carbonate and 15 to 20 parts micron-sized calcium carbonate particles that are vibrated and dispersed on the wet front surface of the coating after the paint slurry is applied, and the remainder consists of micron-sized calcium carbonate particles directly dispersed in the paint slurry; wherein the precipitated calcium carbonate includes spherical micron-sized precipitated calcium carbonate particles and spherical nano-sized precipitated calcium carbonate particles.

2. The double-sided coated whiteboard paper as described in claim 1, characterized in that: The coating of the front undercoat comprises the following substances in parts by weight: 100 parts of calcium carbonate; 12 to 15 parts of styrene-butadiene latex; 0.1 to 0.2 parts of dispersant; 0.2 to 0.4 parts of water-resistant agent; Lubricant 0.1 to 0.3 parts; Sodium hydroxide 0.1 to 0.2 parts; Sodium carboxymethyl cellulose, 0.3 to 0.6 parts.

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