Special reinforcing agent for coated paper and production method thereof

Abstract

The invention provides a special reinforcing agent for coated paper, which is prepared from the following raw materials in parts by mass: 10 parts of polyvinyl alcohol; 1 to 3 parts of cationic polyacrylamide; 1-5 parts of a bactericide; 1 to 5 parts of a defoaming agent; 5 to 10 parts of a VAE emulsion; 5 to 10 parts of paraffin emulsion; 1 to 3 parts of redispersible latex powder; 2 to 4 parts of borax; 1-3 parts of a filler; 0.5 to 1.5 parts of cellulose; and 43.5 to 73.5 parts of deionized water. The special reinforcing agent for the coated paper is used as a prime coat paint and is used for prime coat of common fiber papermaking to form a prime coat layer, so that the obtained coated base paper has higher surface strength and better moisture resistance and smoothness, and can be used for preparing high-quality coated paper.

Description

Technical Field

[0001] The present application belongs to the technical field of papermaking additives, and specifically relates to a special reinforcing agent for coated paper and a production method thereof. Background Art

[0002] Coated paper is also called coated printing paper. Coated paper is a common name and is one of the main papers used by printing houses. It is a high-grade printing paper made of base paper coated with white coating. The surface is smooth and delicate. The coating can be double-sided or single-sided. The paper can be glossy or matte (matte) coated paper. Coated paper is widely used in real life. It is mainly used for printing covers and illustrations of high-grade books and periodicals, color pictures, various exquisite product advertisements, samples, product packaging, trademarks, etc. It has a good development prospect.

[0003] Affected by the national environmental protection policy and the management of imported waste paper, the raw materials used by domestic papermaking enterprises have gradually turned to domestic waste paper. Wood pulp is mostly based on fast-growing poplar pulp, which has the advantage of low cost compared with coniferous and hardwood pulp, but the fiber microstructure of fast-growing poplar pulp is short and thick, and its strength is far worse than that of thin and long coniferous and hardwood pulp. Due to many drawbacks in the recycling process of domestic waste paper, the quality of secondary fiber raw materials used by enterprises has dropped significantly. Regardless of whether the paper mill uses secondary fiber papermaking, fast-growing poplar pulp papermaking or secondary fiber accelerated poplar pulp papermaking, the quality of the finished paper does not meet the standards, especially the strength indicator. The substandard strength of the base paper has a great impact on the subsequent coating process, and may even affect the printing performance of the paper in the later stage. Therefore, it is necessary to strengthen the base paper used to prepare coated paper so that it is suitable for coating to obtain high-quality coated paper.

[0004] Patent CN102277784A discloses a paper folding enhancer and its preparation method. The weight parts of the raw material components are: polyvinyl alcohol 37.5-38: carboxymethyl cellulose 40-42: chitosan 2.0-2.5: starch 10-12: dry strength agent 4-5: phosphoric acid 5-6; its preparation method is as follows: 1. Prepare polyvinyl alcohol aqueous solution: 2. Prepare carboxymethyl cellulose aqueous solution: 3. Mix the above: aqueous solution made of polyvinyl alcohol and aqueous solution made of carboxymethyl cellulose; 4. Add chitosan and starch, stir to form a mixed solution; 5. After diluting the dry strength agent, add the above mixed solution and stir; 6. Add clean water; 7. Adjust the pH value. The paper surface enhancer of this patent is composed of a variety of polymer compounds, which are compounded according to a certain proportion and process. When used, it is diluted and evenly applied to the surface of the paper. The fiber enhancer has excellent affinity and extremely strong film-forming properties, and can be used for sizing and coating the surface of white paper, kraft liner board, coated paper, etc. But the problem is that when the enhancer is used on coated paper, the coating is highly hydrophilic, which will cause the subsequent coating to absorb too much water in the coating, and the adhesive will migrate to the coating, resulting in weak binding force of the pigment in the coating, affecting the performance of the coated paper.

[0005] Patent CN118727505A discloses a kind of coated paper and its pre-coating and topcoating; the pre-coating includes: 100 parts of ground calcium carbonate C65, 0-2 parts of synthetic latex, 10-16 parts of starch adhesive, 0-0.5 parts of coupling agent, 0.1-0.5 parts of alkali solution and 0.1-0.5 parts of dispersant. The pre-coating of coated paper provided by the patent can make the coating more environmentally friendly and reduce costs by using bio-based (starch) adhesive. However, the problem is that the coating uses inorganic filler calcium carbonate as the main material, and its coating enhancement effect is easily affected by the coated paper. For coated paper with low strength and high absorbency, the pre-coating cannot effectively enhance the surface strength of the coated paper.

[0006] Therefore, it is necessary to provide a special reinforcing agent for coated paper to enhance the surface strength of coated paper. Summary of the invention

[0007] In view of this, the present application provides a special enhancer for coated paper, which can effectively enhance the surface strength of coated paper and is used for preparing high-performance coated paper.

[0008] In the first aspect, the present application provides a special enhancer for coated paper, comprising the following raw materials in parts by weight: polyvinyl alcohol: 10 parts; cationic polyacrylamide: 1 to 3 parts; bactericide: 1 to 5 parts; defoamer: 1 to 5 parts; VAE emulsion: 5 to 10 parts; paraffin emulsion: 5 to 10 parts; redispersible latex powder: 1 to 3 parts; borax: 2 to 4 parts; filler: 1 to 3 parts; cellulose: 0.5 to 1.5 parts; deionized water: 43.5 to 73.5 parts.

[0009] Based on the present application, by using the above-mentioned special reinforcer for coated paper as a primer coating, it is used for the primer coating of general fiber papermaking to form a primer layer, and the obtained coated paper has a higher surface strength, and at the same time has good moisture resistance and smoothness, and can be used to prepare high-quality coated paper.

[0010] In some embodiments, the following raw materials are included in parts by mass: polyvinyl alcohol: 10 parts; cationic polyacrylamide: 2 to 3 parts; bactericide: 1 to 2 parts; defoamer: 1 to 3 parts; VAE emulsion: 8 to 10 parts; paraffin emulsion: 5 to 8 parts; redispersible latex powder: 2 to 3 parts; borax: 2 to 4 parts; filler: 2 to 3 parts; cellulose: 0.5 to 1.5 parts; deionized water: 43.5 to 73.5 parts.

[0011] In some embodiments, the filler includes modified silica, and the modified silica is silica modified by a hydroxy silane coupling agent.

[0012] In some embodiments, the method for preparing the modified silicon dioxide comprises:

[0013] 1-3 parts of porous silica are ultrasonically dispersed in 50-100 parts of ethanol, 0.1-1 parts of hydroxy silane coupling agent are added, reacted at 50-70° C. for 2-4 hours, centrifuged and dried to obtain modified silica.

[0014] In some embodiments, the porous silica has an average particle size of 200 to 500 nm and an average pore size of 10 to 50 nm.

[0015] In some embodiments, the average polymerization degree of the polyvinyl alcohol is 450-600, and the alcoholysis degree is 95%-99%.

[0016] In some embodiments, the cationic polyacrylamide has a weight average molecular weight of 5 million to 10 million.

[0017] In some embodiments, the cellulose is hydroxypropyl methylcellulose having a weight average molecular weight of 80,000 to 150,000.

[0018] In some embodiments, the coated paper-specific enhancer satisfies at least one of the following conditions: (1) the pH of the paraffin emulsion is 7 to 9, and the solid content is 40% to 60%; (2) the viscosity of the VAE emulsion is 500 to 1000 mPa·s, and the solid content is 50% to 60%; (3) the defoaming agent includes at least one of polyether, silicone oil, and octadecyl alcohol; (4) the bactericide includes at least one of hypochlorite, chlorine dioxide, and chloramine.

[0019] In a second aspect, the present application provides a method for preparing the special enhancing agent for coated paper according to any embodiment of the first aspect, comprising the following steps:

[0020] Step S1: ultrasonically dispersing the filler in water to obtain a filler dispersion;

[0021] Step S2: adding polyvinyl alcohol to the filler dispersion and swelling for 60 to 120 minutes to obtain a first mixture;

[0022] Step S3: adding cationic polyacrylamide, redispersible latex powder and cellulose to the first mixture, and heating at 70-100° C. for 90-120 min to obtain a second mixture;

[0023] Step S4: adding the borax aqueous solution to the second mixture to obtain a third mixture;

[0024] Step S5: adding VAE emulsion, paraffin emulsion, bactericide and defoamer into the third mixture to obtain a special reinforcing agent for coated paper. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present application more clear, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

[0026] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the implementation or examples are included in at least one implementation or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same implementation or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more implementations or examples in a suitable manner.

[0027] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0028] In the first aspect, the present application provides a special enhancer for coated paper, comprising the following raw materials in parts by weight: polyvinyl alcohol: 10 parts; cationic polyacrylamide: 1 to 3 parts; bactericide: 1 to 5 parts; defoamer: 1 to 5 parts; VAE emulsion: 5 to 10 parts; paraffin emulsion: 5 to 10 parts; redispersible latex powder: 1 to 3 parts; borax: 2 to 4 parts; filler: 1 to 3 parts; cellulose: 0.5 to 1.5 parts; deionized water: 43.5 to 73.5 parts.

[0029] Based on the present application, by using the above-mentioned special reinforcer for coated paper as a primer coating, it is used for the primer coating of general fiber papermaking to form a primer layer, and the obtained coated paper has a higher surface strength, and at the same time has good moisture resistance and smoothness, and can be used to prepare high-quality coated paper.

[0030] Specifically, coated paper is the basis of coated paper and is also an important factor affecting the coating quality. Factors such as the surface strength, absorbency and surface smoothness of coated paper have a great influence on the quality of coated paper. The special enhancer for coated paper provided in this application is prepared by forming a base coating suitable for coating on general fiber papermaking, thereby preparing high-quality coated paper.

[0031] After the base paper is coated with the coating, the moisture and adhesive in the coating will be partially transferred to the paper as the base paper absorbs it. If the absorption rate is too high, the adhesive will migrate too much to the base paper, which will reduce the binding force of the pigment particles in the coating and cause the problem of powder loss. If the absorption rate is too low, the force between the coating and the base paper will be weak, the peeling strength will be low, and the coating will peel off. In the reinforcing agent provided in the present application, the absorbency of the base coating is mainly adjusted by polyvinyl alcohol and paraffin emulsion, so that the coated base paper has suitable absorbency. In addition, polyvinyl alcohol has good adhesion and film-forming properties, and can form a tough base coating on the surface of fiber papermaking, thereby improving the surface strength of the coated base paper. The use of paraffin emulsion will affect the surface strength of the coating to a certain extent. By further adding borax, the effect of the paraffin emulsion on the surface strength of the coating can be reduced by cross-linking.

[0032] Cationic polyacrylamide in the special reinforcing agent for coated paper can be used as a dry strength agent and retention agent to penetrate into the fiber papermaking to increase the bonding force between fibers, thereby helping the fiber papermaking to maintain strength during coating drying, reducing the deformation of the fiber papermaking, and improving the performance of the coated base paper.

[0033] VAE emulsion (ethylene-vinyl acetate copolymer emulsion) and redispersible latex powder are used to improve the flexibility, wear resistance and adhesion of the coating, and can synergistically cross-link polyvinyl alcohol to give the base coating higher strength.

[0034] By adding a small amount of filler to the reinforcing agent, the filler generally has the characteristics of high hardness and wear resistance, which can improve the wear resistance and strength of the base coating, thereby reducing the damage to the base coating surface due to friction and mechanical impact, and can also improve the smoothness and flatness of the base coating surface, making the coated paper more suitable for coating.

[0035] In addition, the bactericide in the enhancer can inhibit the growth of microorganisms, prevent the coated paper from mildewing during storage and use, and improve the durability of the coated paper; the role of the defoamer is to reduce the foam formed during the production process, reduce the formation of bubbles during the coating process, ensure the uniformity of the base coating, and avoid the foam affecting the flatness of the paper surface; cellulose can be used to adjust the viscosity of the enhancer, so that the enhancer is more suitable for coating to form a base coating.

[0036] Therefore, by using the above-mentioned components of the special reinforcer for coated paper, it can be applied to general fiber papermaking, and a base coating with good moisture resistance and smoothness and high surface strength is formed on its surface, which can be used to further obtain high-quality coated paper by coating pigments.

[0037] In some embodiments, the following raw materials are included in parts by mass: polyvinyl alcohol: 10 parts; cationic polyacrylamide: 2 to 3 parts; bactericide: 1 to 2 parts; defoamer: 1 to 3 parts; VAE emulsion: 8 to 10 parts; paraffin emulsion: 5 to 8 parts; redispersible latex powder: 2 to 3 parts; borax: 2 to 4 parts; filler: 2 to 3 parts; cellulose: 0.5 to 1.5 parts; deionized water: 43.5 to 73.5 parts.

[0038] Based on the above implementation, the components of the special reinforcing agent for coated paper are further optimized. Under the above conditions, the surface strength and smoothness of the base coating layer can be further improved.

[0039] In some embodiments, the filler includes modified silica, which is silica modified by a hydroxy silane coupling agent.

[0040] In some of the above embodiments, the filler includes modified silica. Generally, silica has poor dispersibility in the above-mentioned coated paper-specific reinforcing agent, which will affect the surface strength and smoothness of the base coating. By using a hydroxy silane coupling agent to improve silica, the dispersibility of silica can be significantly improved. At the same time, the hydroxyl groups grafted on the surface have better cross-linking activity than the hydroxyl groups on the surface of silica, and can be further cross-linked with polyvinyl alcohol in the reinforcing agent under the action of borax. It can be understood that the solid phase modified silica can make the cross-linked structure formed by the base coating more stable through the nucleation effect, thereby further improving the strength of the base coating and obtaining higher quality coated paper.

[0041] In some embodiments, the method for preparing modified silica comprises:

[0042] 1-3 parts of porous silica are ultrasonically dispersed in 50-100 parts of ethanol, 0.1-1 parts of hydroxy silane coupling agent are added, reacted at 50-70° C. for 2-4 hours, centrifuged and dried to obtain modified silica.

[0043] In some of the above embodiments, the modified silica has a porous structure. The modified silica with a porous structure has a larger specific surface area and thus has more reaction sites, which can further increase the crosslinking density with polyethylene glycol, thereby further increasing the surface strength of the primer layer. On the other hand, the porous structure is more conducive to the uniform dispersion of the modified silica in the reinforcing agent, and interacts with other components in the reinforcing agent (such as redispersible latex powder, VAE, paraffin, etc.) through a larger specific surface area, such as polymer chain segments interpenetrating with each other in the pores, thereby further improving the uniformity of the components in the reinforcing agent, and further improving the stability and strength of the primer layer.

[0044] As a preferred embodiment, in one embodiment of the present application, γ-aminopropyltriethoxysilane is used as a hydroxysilane coupling agent.

[0045] In some embodiments, the porous silica has an average particle size of 200 to 500 nm and an average pore size of 10 to 50 nm.

[0046] In some of the above embodiments, porous silica with appropriate particle size has better dispersibility, and the appropriate pore size also takes advantage of the interaction with the components in the reinforcing agent. In this case, the base coating formed by the dedicated reinforcing agent has higher strength.

[0047] In some embodiments, the average polymerization degree of polyvinyl alcohol is 450-600, and the alcoholysis degree is 95%-99%.

[0048] In some of the above embodiments, the polyvinyl alcohol with the above polymerization degree has better film-forming properties, and the higher alcoholysis degree makes it have higher reactivity, which can further increase the crosslinking density in the primer layer and make the primer layer have higher strength. As an example, one embodiment of the present application uses polyvinyl alcohol with an average polymerization degree of 550 and an alcoholysis degree of 99%.

[0049] In some embodiments, the weight average molecular weight of the cationic polyacrylamide is 5 million to 10 million. As an example, an embodiment of the present application uses a cationic polyacrylamide with a weight average molecular weight of 8 million.

[0050] In some embodiments, the cellulose is hydroxypropyl methylcellulose with a weight average molecular weight of 80,000 to 150,000. As an example, an embodiment of the present application uses hydroxypropyl methylcellulose with a weight average molecular weight of 100,000.

[0051] In some embodiments, the pH of the paraffin emulsion is 7 to 9, and the solid content is 40% to 60%. As an example, an embodiment of the present application uses a paraffin emulsion with a pH of 8 and a solid content of 50%.

[0052] In some embodiments, the viscosity of the VAE emulsion is 500-1000 mPa·s, and the solid content is 50%-60%. As an example, an embodiment of the present application uses a VAE emulsion with a viscosity of 800 mPa·s and a solid content of 54.5%.

[0053] In some embodiments, the defoaming agent includes at least one of polyether, silicone oil, and octadecanol. As an example, one embodiment of the present application uses polydimethylsiloxane as the defoaming agent.

[0054] In some embodiments, the bactericide includes at least one of hypochlorite, chlorine dioxide, and chloramine. As an example, an embodiment of the present application uses hypochlorite as a bactericide.

[0055] In a second aspect, the present application provides a method for preparing a special reinforcing agent for coated paper according to any embodiment of the first aspect, comprising the following steps:

[0056] Step S1: ultrasonically dispersing the filler in water to obtain a filler dispersion;

[0057] Step S2: adding polyvinyl alcohol to the filler dispersion and swelling for 60 to 120 minutes to obtain a first mixture;

[0058] Step S3: adding cationic polyacrylamide, redispersible latex powder and cellulose to the first mixture, and heating at 70-100° C. for 90-120 min to obtain a second mixture;

[0059] Step S4: adding the borax aqueous solution to the second mixture to obtain a third mixture;

[0060] Step S5: adding VAE emulsion, paraffin emulsion, bactericide and defoamer into the third mixture to obtain a special reinforcing agent for coated paper.

[0061] According to the present application, the coated paper-specific reinforcing agent of any embodiment of the first aspect can be obtained by the above method, which has the beneficial effects of the first aspect.

[0062] It is understood that the types and weight proportions of the above-mentioned fillers, polyvinyl alcohol, cationic polyacrylamide, redispersible latex powder, cellulose, VAE emulsion, paraffin emulsion, bactericide and defoamer can be selected according to the implementation of the first aspect.

[0063] The scheme of the present application is described below in conjunction with the following specific examples. Unless otherwise specified, the raw materials used in the following examples are all from common commercial products, and the devices or equipment used are all purchased from conventional market sales channels.

[0064] The present application example uses polyvinyl alcohol with an average degree of polymerization of 550 and a degree of alcoholysis of 99%; cationic polyacrylamide with a weight average molecular weight of 8 million; hydroxypropyl methylcellulose with a weight average molecular weight of 100,000 as cellulose; paraffin emulsion with a pH of 8 and a solid content of 50%; VAE emulsion with a viscosity of 800 mPa·s and a solid content of 54.5%; polydimethylsiloxane as a defoamer; hypochlorite as a bactericide; and the redispersible latex powder model is 7850A.

[0065] Example 1

[0066] Preparation of special enhancer for coated paper:

[0067] The following raw materials are provided in parts by mass: polyvinyl alcohol: 10 parts; cationic polyacrylamide: 2 parts; bactericide: 2 parts; defoamer: 2 parts; VAE emulsion: 8 parts; paraffin emulsion: 7 parts; redispersible latex powder: 2 parts; borax: 3 parts; filler: 2.5 parts; cellulose: 1 part; and deionized water: 60 parts.

[0068] Ultrasonic dispersion of fillers in water to obtain a filler dispersion;

[0069] Adding polyvinyl alcohol to the filler dispersion and swelling for 120 minutes to obtain a first mixture;

[0070] Adding cationic polyacrylamide, redispersible latex powder and cellulose to the first mixture, and heating at 90° C. for 100 minutes to obtain a second mixture;

[0071] adding the borax aqueous solution to the second mixture to obtain a third mixture;

[0072] VAE emulsion, paraffin emulsion, bactericide and defoamer are added into the third mixture to obtain a special reinforcing agent for coated paper.

[0073] The filler is modified silica, which is prepared by the following method: ultrasonically dispersing 2 parts of porous silica in 80 parts of ethanol, adding 0.5 parts of γ-aminopropyltriethoxysilane, reacting at 70°C for 4 hours, centrifuging and drying to obtain modified silica; the average particle size of the porous silica is 400nm, and the average pore size is 20nm.

[0074] Example 2

[0075] Preparation of special enhancer for coated paper:

[0076] The following raw materials are provided in parts by mass: polyvinyl alcohol: 10 parts; cationic polyacrylamide: 2 parts; bactericide: 2 parts; defoamer: 2 parts; VAE emulsion: 8 parts; paraffin emulsion: 7 parts; redispersible latex powder: 2 parts; borax: 3 parts; filler: 2.5 parts; cellulose: 1 part; and deionized water: 60 parts.

[0077] Ultrasonic dispersion of fillers in water to obtain a filler dispersion;

[0078] Adding polyvinyl alcohol to the filler dispersion and swelling for 120 minutes to obtain a first mixture;

[0079] Adding cationic polyacrylamide, redispersible latex powder and cellulose to the first mixture, and heating at 90° C. for 100 minutes to obtain a second mixture;

[0080] adding the borax aqueous solution to the second mixture to obtain a third mixture;

[0081] VAE emulsion, paraffin emulsion, bactericide and defoamer are added into the third mixture to obtain a special reinforcing agent for coated paper.

[0082] The filler is silicon dioxide, and the average particle size of the silicon dioxide is 400 nm.

[0083] Example 3

[0084] Preparation of special enhancer for coated paper:

[0085] The following raw materials are provided in parts by mass: polyvinyl alcohol: 10 parts; cationic polyacrylamide: 2 parts; bactericide: 2 parts; defoamer: 2 parts; VAE emulsion: 8 parts; paraffin emulsion: 7 parts; redispersible latex powder: 2 parts; borax: 3 parts; filler: 2.5 parts; cellulose: 1 part; and deionized water: 60 parts.

[0086] Ultrasonic dispersion of fillers in water to obtain a filler dispersion;

[0087] Adding polyvinyl alcohol to the filler dispersion and swelling for 120 minutes to obtain a first mixture;

[0088] Adding cationic polyacrylamide, redispersible latex powder and cellulose to the first mixture, and heating at 90° C. for 100 minutes to obtain a second mixture;

[0089] adding the borax aqueous solution to the second mixture to obtain a third mixture;

[0090] VAE emulsion, paraffin emulsion, bactericide and defoamer are added into the third mixture to obtain a special reinforcing agent for coated paper.

[0091] The filler is modified silica, which is prepared by the following method: ultrasonically dispersing 2 parts of silica in 80 parts of ethanol, adding 0.5 parts of γ-aminopropyltriethoxysilane, reacting at 70°C for 4 hours, centrifuging and drying to obtain modified silica; wherein the average particle size of the silica is 400nm.

[0092] Example 4

[0093] The following raw materials are provided in parts by mass: polyvinyl alcohol: 10 parts; cationic polyacrylamide: 2 parts; bactericide: 2 parts; defoamer: 2 parts; VAE emulsion: 8 parts; paraffin emulsion: 7 parts; redispersible latex powder: 2 parts; borax: 3 parts; filler: 2.5 parts; cellulose: 1 part; and deionized water: 60 parts.

[0094] Ultrasonic dispersion of fillers in water to obtain a filler dispersion;

[0095] Adding polyvinyl alcohol to the filler dispersion and swelling for 120 minutes to obtain a first mixture;

[0096] Adding cationic polyacrylamide, redispersible latex powder and cellulose to the first mixture, and heating at 90° C. for 100 minutes to obtain a second mixture;

[0097] adding the borax aqueous solution to the second mixture to obtain a third mixture;

[0098] VAE emulsion, paraffin emulsion, bactericide and defoamer are added into the third mixture to obtain a special reinforcing agent for coated paper.

[0099] The filler is porous silica, and the average particle size of the porous silica is 400 nm and the average pore size is 20 nm.

[0100] Set the blank group as base paper, the base paper has a basis weight of 100±1g / m 2 Fiber papermaking, one-side coating, coating amount is 5g / m2 The coated paper was obtained by drying and calendering. The printing surface strength of the coated paper and the blank group was tested according to GB / T22365-2008. The roughness of the coated paper and the blank group was tested according to GB / T 22881-2008. The results are shown in Table 1.

[0101] Table 1

[0102] Roughness(mL / min) Printing surface strength (m / s) Example 1 61.2 0.463 Example 2 86.6 0.402 Example 3 75.3 0.428 Example 4 72.9 0.421 Blank Group 150.6 0.359

[0103] According to Table 1, the roughness of each embodiment is significantly reduced compared with the blank group, and the printed surface strength is significantly improved, indicating that the reinforcing agent obtained in each embodiment can effectively improve the flatness and surface strength of the base paper surface as a primer coating.

[0104] By comparing Examples 1 to 4, it can be seen that the coated paper obtained in Example 1 has the best flatness and surface strength, indicating that by using modified porous silica with appropriate particle size and pore size as filler, the reason may be that: the appropriate pore size is more conducive to the uniform dispersion of each component, thereby further improving the surface flatness of the base paper, and the surface active hydroxyl groups can be cross-linked with polyvinyl alcohol through borax, and the strength of the base coating can be improved through the solid phase nucleation effect. The larger specific surface area can also further increase the cross-linking density, and the compatibility of each component can be further improved by synergizing the components to penetrate in the pores of silica. Therefore, the coated paper obtained in this example has the best flatness and surface strength.

[0105] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the principles of the present application should be included in the protection scope of the present application.

Claims

1. A special enhancer for coated paper, characterized in that: The invention comprises the following raw materials in parts by weight: Polyvinyl alcohol: 10 parts; Cationic polyacrylamide: 1-3 parts; Fungicide: 1 to 5 parts; Defoaming agent: 1-5 parts; VAE emulsion: 5-10 parts; Paraffin emulsion: 5-10 parts; Redispersible latex powder: 1 to 3 parts; Borax: 2-4 parts; Filler: 1-3 parts; Cellulose: 0.5-1.5 parts; Deionized water: 43.5 to 73.5 parts.

2. The special strengthening agent for coated paper according to claim 1, characterized in that: The invention comprises the following raw materials in parts by weight: Polyvinyl alcohol: 10 parts; Cationic polyacrylamide: 2-3 parts; Fungicide: 1-2 parts; Defoaming agent: 1 to 3 parts; VAE emulsion: 8-10 parts; Paraffin emulsion: 5-8 parts; Redispersible latex powder: 2-3 parts; Borax: 2-4 parts; Filler: 2-3 parts; Cellulose: 0.5-1.5 parts; Deionized water: 43.5 to 73.5 parts.

3. The special strengthening agent for coated paper according to claim 1 or 2, characterized in that: The filler comprises modified silica, and the modified silica is silica modified by a hydroxy silane coupling agent.

4. The special strengthening agent for coated paper according to claim 3, characterized in that: The preparation method of the modified silicon dioxide comprises: 1-3 parts of porous silica are ultrasonically dispersed in 50-100 parts of ethanol, 0.1-1 parts of hydroxy silane coupling agent are added, reacted at 50-70° C. for 2-4 hours, centrifuged and dried to obtain modified silica.

5. The special strengthening agent for coated paper according to claim 4, characterized in that: The average particle size of the porous silica is 200-500 nm, and the average pore size is 10-50 nm.

6. The special strengthening agent for coated paper according to claim 1 or 2, characterized in that: The average polymerization degree of the polyvinyl alcohol is 450-600, and the alcoholysis degree is 95%-99%.

7. The special strengthening agent for coated paper according to claim 1 or 2, characterized in that: The weight average molecular weight of the cationic polyacrylamide is 5 million to 10 million.

8. The special strengthening agent for coated paper according to claim 1 or 2, characterized in that: The cellulose is hydroxypropyl methylcellulose with a weight average molecular weight of 80,000 to 150,000.

9. The special strengthening agent for coated paper according to claim 1 or 2, characterized in that: The coated paper-specific enhancer satisfies at least one of the following conditions: (1) The pH of the paraffin emulsion is 7 to 9, and the solid content is 40% to 60%; (2) The viscosity of the VAE emulsion is 500-1000 mPa·s, and the solid content is 50%-60%; (3) The defoaming agent includes at least one of polyether, silicone oil and octadecyl alcohol; (4) The bactericide includes at least one of hypochlorite, chlorine dioxide and chloramine.

10. A method for preparing the special strengthening agent for coated paper according to any one of claims 1 to 9, characterized in that: The following steps are involved: Step S1: ultrasonically dispersing the filler in water to obtain a filler dispersion; Step S2: adding polyvinyl alcohol to the filler dispersion and swelling for 60 to 120 minutes to obtain a first mixture; Step S3: adding cationic polyacrylamide, redispersible latex powder and cellulose to the first mixture, and heating at 70-100° C. for 90-120 min to obtain a second mixture; Step S4: adding the borax aqueous solution to the second mixture to obtain a third mixture; Step S5: adding VAE emulsion, paraffin emulsion, bactericide and defoamer into the third mixture to obtain a special reinforcing agent for coated paper.