A sheet-shaped desiccant and a method for producing the same

Abstract

The application belongs to the technical field of desiccants, and discloses a sheet-shaped desiccant and a preparation method thereof. The preparation method comprises the following steps: mixing anhydrous magnesium chloride, a gel compound and a tabletting auxiliary agent to obtain surface material; mixing the anhydrous magnesium chloride, a metal oxide and a disintegrant to obtain internal material; dividing the surface material into lower surface material and upper surface material; and then adding the lower surface material, the middle internal material and the upper surface material into a mold in sequence to perform tabletting, so as to obtain the sheet-shaped desiccant. The sheet-shaped desiccant prepared by the method can effectively avoid the problem of too fast saturation of the surface under high humidity conditions, and improve the moisture absorption rate.

Description

Technical Field

[0001] This application relates to the field of desiccant technology, and in particular to a sheet desiccant and its preparation method. Background Technology

[0002] Magnesium chloride desiccant is a highly efficient moisture-proof product based on the principle of chemical hygroscopicity. Its core component, anhydrous magnesium chloride, first absorbs moisture through deliquescence to form a surface solution, and then undergoes an irreversible hydration reaction with water to form crystalline compounds. This process not only gives it extremely strong hygroscopic capacity (especially in low-temperature, high-humidity environments), but also causes its form to gradually change from granules to a solution and eventually harden into clumps, clearly indicating its saturation state. Due to its readily available raw materials, low cost, large hygroscopic capacity, and good safety, this desiccant has been widely used in many fields.

[0003] Traditional powder or granular magnesium chloride desiccants possess a large specific surface area, allowing for ample contact with air and exhibiting key advantages such as rapid moisture absorption start-up, high moisture absorption efficiency, and large moisture absorption capacity per unit weight. This characteristic makes them particularly suitable for industrial scenarios with stringent humidity control requirements, such as the storage and packaging of precision electronic components, mildew prevention for optical instruments, rust prevention between processes in metal products, and moisture control within shipping containers. In these environments, the powder can rapidly reduce the humidity inside the packaging and maintain a dry state for an extended period, effectively protecting product quality.

[0004] However, in certain small, enclosed, or precision spaces, such as small pharmaceutical packages, the interiors of small electronic products (e.g., sensor modules), high-end camera lens barrels, and precision instrument compartments, powder form presents challenges such as dust generation, inconvenient filling, and potential leakage that could contaminate sensitive components. To meet the stringent requirements for ease of use, cleanliness, and precise dosage in these scenarios, the industry has developed magnesium chloride desiccant into tablet form. Tablets are easy to handle and hold, better meeting the needs of miniaturized and integrated packaging.

[0005] However, the tablet form also brings significant performance defects, the most prominent of which is the crusting phenomenon. During the moisture absorption process, especially in high humidity environments, the magnesium chloride on the surface of the tablet becomes saturated too quickly, resulting in the surface completing moisture absorption while the inside becomes dry. This causes a significant decrease in the overall moisture absorption rate of the desiccant, shortening its actual effective protection period. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a sheet-like desiccant and its preparation method, which aims to solve the problem that the moisture absorption rate of sheet-like magnesium chloride desiccant decreases due to rapid surface saturation in high humidity environments.

[0007] To address the aforementioned technical problems, this invention proposes a method for preparing a sheet-like desiccant, the method comprising the following steps: S1. Anhydrous magnesium chloride, gelling compound, and tableting aid are mixed to obtain the surface material; S2. Mix anhydrous magnesium chloride, metal oxide and disintegrant to obtain internal material; S3. Divide the surface material into lower surface material and upper surface material, and then add the lower surface material, middle inner material and upper surface material into the mold in the order of lower surface material, middle inner material and upper surface material to compress into tablets to obtain tablet desiccant.

[0008] In some embodiments, step S1 includes: S1.1 In an inert atmosphere, anhydrous magnesium chloride is added to anhydrous lower alcohol, the temperature is increased to 60~70℃, the reaction is stirred for 2~3h, and the temperature is reduced to 20~30℃ to obtain an alcoholic magnesium chloride suspension, wherein the mass ratio of anhydrous magnesium chloride to anhydrous lower alcohol is 1:(6~10). S1.2 Add gelling compound and ammonia compound to the magnesium chloride suspension, stir and react at 30~40℃ for 1~2h to obtain a mixed slurry, wherein the mass ratio of anhydrous magnesium chloride: gelling compound: ammonia compound is (20~45):(10~30):(5~15), and the particle size D90 of the ammonia compound is ≤10μm; S1.3. The mixed slurry is distilled under reduced pressure at -0.05~-0.02MPa and 30~40℃ until the content of anhydrous lower alcohol is reduced to 85~90% of the initial content, to obtain a pretreated paste. The pretreated paste is then dried under vacuum at 30~40℃ and 0.01~0.03MPa to constant weight, crushed, and the composite powder is obtained. S1.4 Add the composite powder, tableting aid, and release agent to a mixer and mix at 20-30 rpm for 40-50 min to obtain the material shown in the table. The mass ratio of anhydrous magnesium chloride to tableting aid to release agent is (20-45): (10-35): (0-2.5).

[0009] In some embodiments, step S2 includes: S2.1 Add anhydrous magnesium chloride, metal oxide and disintegrant to a mixer and mix at 20-30 rpm for 15-25 min to obtain a mixture, wherein the mass ratio of anhydrous magnesium chloride, metal oxide and disintegrant is (10-30):(10-30):(0-10); S2.2 Add ammonia reactant and release agent to the premixed material, and continue mixing for 5~15 min to obtain the inner material, wherein the mass ratio of anhydrous magnesium chloride: ammonia reactant: release agent is (10~30):(3~10):(0~2.5).

[0010] In some embodiments, the metal oxide includes at least one of lightly calcined magnesium oxide, active magnesium oxide, active zinc oxide, and active calcium oxide; the disintegrant is magnesium aluminum silicate and / or povidone K30; the ammonia reactant includes at least one of polyacrylic acid, aluminum sulfate, and calcium chloride; and the release agent includes at least one of sodium stearate, magnesium stearate, and polyethylene glycol.

[0011] In some embodiments, step S3 includes: S3.1. Divide the surface material into lower surface material and upper surface material, and then add the lower surface material, middle inner material and upper surface material into the mold in the order of lower surface material, middle inner material and upper surface material. Heat treatment at 80~90℃ for 1~3h to obtain heat-treated material. The mass ratio of anhydrous magnesium chloride in the surface material to anhydrous magnesium chloride in the inner material is (20~45):(10~30). The mass of the lower surface material and the upper surface material is the same. S3.2. Compress the heat-treated material into tablets at a pressure of 5~15 kN / cm. 2 A sheet-like desiccant is obtained.

[0012] In addition, a sheet-like desiccant is also provided, which is prepared by the above-described method for preparing a sheet-like desiccant; The sheet-like dried product, by weight, comprises the following components: 30-75 parts anhydrous magnesium chloride, 10-30 parts metal oxide, 10-30 parts gelling compound, 1-10 parts disintegrant, 10-35 parts tableting aid, and 1-5 parts release agent.

[0013] In some embodiments, the sheet desiccant further contains 3 to 10 parts of ammonia reactant.

[0014] The beneficial effects of this invention are: First, the anhydrous magnesium chloride distributed on the surface, with its strong deliquescence, first captures environmental moisture. The gel compound then rapidly binds water molecules through hydrogen bonds in its hydrophilic chains. However, the polymer network structure restricts the free flow of water, preventing the instantaneous formation of a dense liquid saturation layer on the surface. Simultaneously, the gel phase formed by the absorption and swelling of water creates the initial water penetration channels. Second, the anhydrous magnesium chloride and metal oxides in the inner layer form a chemically fixed core. The highly reactive surface of lightly calcined magnesium oxide reacts with the penetrating magnesium chloride solution to generate basic magnesium chloride solid. This process irreversibly consumes a large amount of water and significantly reduces the chemical potential of the water in the inner layer, thereby establishing a stable concentration gradient between the surface and inner layers. This gradient drives the spontaneous and continuous migration of water from the high potential energy region (surface layer) to the low potential energy region (inner layer). Meanwhile, the outer layer of tableting aids, through its rigid particle support and stacked structure, acts as a skeleton during compression molding, preventing over-compaction of the material. This forms and maintains a permeable pore network within the tablet, allowing moisture penetration and transport. The inner layer of disintegrants acts as a dynamic pore expander; upon contact with water, its interlayer structure expands, generating micro-stress within the tablet. This causes the existing pore network to expand and new micro-cracks to form, synergistically with the channels maintained by the tableting aids, creating a three-dimensional transport channel that accelerates penetration. This system utilizes the continuous consumption of the inner layer's chemical reaction as a power source, with the surface gel network's guidance and the internal pores providing transport assurance. This synergistic effect forces surface moisture to continuously penetrate the inner layer, thereby increasing the moisture absorption rate of the flake magnesium chloride desiccant in high-humidity environments. Attached Figure Description

[0015] Figure 1 This is a schematic flowchart of a method for preparing a sheet-like desiccant according to an embodiment of the present invention. Detailed Implementation

[0016] In the description of this application, it should be noted that, unless specific conditions are specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0017] Please refer to Figure 1 This invention provides a method for preparing a sheet-like desiccant, the method comprising the following steps: S1. Anhydrous magnesium chloride, tableting aid, and gelling compound are mixed to obtain the surface material; By combining the high hygroscopicity of anhydrous magnesium chloride with the network regulation capability of gel compounds, the surface saturation problem in high humidity environments is effectively alleviated: upon contact with water, the gel compounds rapidly form a three-dimensional hydrogel network. This network, on the one hand, quickly captures and binds surface moisture through its hydrophilic groups, preventing magnesium chloride particles from forming a dense, impermeable liquid film due to excessive dissolution; on the other hand, the gel network generates capillary forces and establishes continuous hydrophilic channels during the swelling process, guiding the captured moisture to diffuse into the interior of the tablet, avoiding moisture retention and saturation on the surface, thus creating conditions for the inner desiccant to continuously exert its hygroscopic effect and improving the overall hygroscopic efficiency.

[0018] S1.1 In an inert atmosphere, anhydrous magnesium chloride is added to anhydrous lower alcohol, the temperature is increased to 60~70℃, the mixture is stirred and reacted for 2~3 hours, and then the temperature is lowered to 20~30℃ to obtain an alcoholic magnesium chloride suspension, wherein the mass ratio of anhydrous magnesium chloride to anhydrous lower alcohol is 1:(6~10).

[0019] Lower alcohols (such as ethanol and isopropanol) can undergo a mild and complete alcoholysis reaction with magnesium chloride to generate highly active and uniformly dispersed alcoholysis particles, forming a stable suspension that provides an ideal reactive nucleus for subsequent in-situ encapsulation. At the same time, the moderate polarity and boiling point of lower alcohols ensure the homogeneity and controllability of the reaction system, and their volatility is particularly crucial, allowing excess alcohol solvent after the reaction to be efficiently and energy-efficiently recovered and removed by subsequent low-temperature vacuum distillation, thereby avoiding interference from solvent residues with subsequent encapsulation, drying, and tableting processes.

[0020] S1.2 Add gelling compound and ammonia compound to the magnesium chloride suspension and stir at 30~40℃ for 1~2h to obtain a mixed slurry, wherein the mass ratio of anhydrous magnesium chloride: gelling compound: ammonia compound is (20~45):(10~30):(5~15), and the particle size D90 of the ammonia compound is ≤10μm.

[0021] Under mild conditions of 30~40℃, the gel compound powder and ultrafine ammonia compound (D90≤10μm) are simultaneously added to the alcohol-based magnesium chloride suspension and stirred continuously for 1~2h. This process promotes the gel compound to fully swell and develop adhesion in the alcohol medium. At the same time, the mechanical shear force enables the ammonia compound micro powder, gel network and magnesium chloride particles to achieve uniform dispersion and intercalation in three-dimensional space, thereby directly obtaining a solid-liquid mixture with highly uniform component distribution and excellent stability.

[0022] S1.3. The mixed slurry is distilled under reduced pressure at -0.05~-0.02MPa and 30~40℃ until the content of anhydrous lower alcohol is reduced to 85~90% of the initial content, to obtain a pretreated paste. The pretreated paste is then dried under vacuum at 30~40℃ and 0.01~0.03MPa to constant weight, and then crushed to obtain composite powder.

[0023] The above preparation process removes most of the lower alcohols through vacuum distillation under mild conditions of -0.05 to -0.02 MPa and 30 to 40°C, concentrating and solidifying the mixed slurry into a pre-treated paste with a pre-fixed structure, effectively preventing component separation. Subsequently, it is dried at a low temperature of 0.01 to 0.03 MPa and 30 to 40°C to constant weight, completely removing residual solvents. Finally, it is crushed to obtain a composite powder with good flowability. This segmented low-temperature desolventizing process strictly controls the temperature below the thermal decomposition temperature of the ammonia compound throughout, preserving the integrity of the ammonia compound. The resulting composite powder ultimately contains magnesium chloride (alcoholized) as the core active component, a gel compound as a binder and molding framework, and intact ammonia compound solid particles as a pore-forming template.

[0024] S1.4 Add the composite powder, tableting aid, and release agent to a mixer and mix at 20-30 rpm for 40-50 min to obtain the material shown in the table. The mass ratio of anhydrous magnesium chloride to tableting aid to release agent is (20-45): (10-35): (0-2.5).

[0025] By mixing the composite powder with tableting aids and release agents at low speeds, it is ensured that the tableting aids such as nano-silica and microcrystalline cellulose, as well as the release agents such as magnesium stearate, can uniformly and completely coat or disperse on the particle surface and in the gaps without damaging the original core-shell precursor structure of the composite powder. This significantly improves the flowability, filling properties and compressibility of the powder. At the same time, the external lubrication provides the necessary process performance guarantee for subsequent tableting, ultimately resulting in a surface material with highly uniform composition and function.

[0026] In step S1, the anhydrous lower alcohol includes at least one of methanol, ethanol, propanol, and isopropanol; the gelling compound includes at least one of carboxyethyl cellulose, sodium carboxymethyl cellulose, and guar gum; the ammonia compound is ammonium bicarbonate and / or ammonium carbonate; the tableting aid includes at least one of nano silica, microcrystalline cellulose, and mannitol; and the release agent includes at least one of sodium stearate, magnesium stearate, and polyethylene glycol.

[0027] S2. Mix anhydrous magnesium chloride, metal oxide and disintegrant to obtain internal material.

[0028] The anhydrous magnesium chloride and metal oxides in the inner layer form a chemical fixation core. The highly active surface of the lightly burned magnesium oxide reacts with the infiltrated magnesium chloride solution to generate basic magnesium chloride solid. This process irreversibly consumes a large amount of water and significantly reduces the chemical potential of the water in the inner layer, thereby establishing a stable concentration gradient between the surface and inner layers. This gradient drives water to spontaneously and continuously migrate from the high potential energy region (surface layer) to the low potential energy region (inner layer).

[0029] Step S2 includes: S2.1 Add anhydrous magnesium chloride, metal oxide and disintegrant to a mixer and mix at 20-30 rpm for 15-25 min to obtain a mixture, wherein the mass ratio of anhydrous magnesium chloride, metal oxide and disintegrant is (10-30):(10-30):(0-10).

[0030] By thoroughly mixing anhydrous magnesium chloride, metal oxides, and disintegrants at low speeds, highly uniform dispersion of each component in a dry state is achieved. Gentle stirring effectively avoids dust dispersion or particle agglomeration of anhydrous magnesium chloride and light metal oxides caused by violent shearing. This ensures that the anhydrous magnesium chloride, metal oxides, and disintegrants that guarantee the disintegration performance of tablets in water can be in close contact and uniformly compounded, laying a precise formulation foundation for the subsequent formation of a structurally stable and uniformly performing inner layer material.

[0031] S2.2 Add ammonia reactant and release agent to the premixed material, and continue mixing for 5~15 min to obtain the inner material, wherein the mass ratio of anhydrous magnesium chloride: ammonia reactant: release agent is (10~30):(3~10):(0~2.5).

[0032] Adding the ammonia reactant in the later stages of mixing avoids unnecessary pre-reactions or hygroscopic deactivation with metal oxides during dry mixing, ensuring its existence as independent, highly reactive particles. When desiccant tablets containing this material are heat-treated, the ammonia gas released from the decomposition of the outer ammonia compound (such as ammonium bicarbonate) diffuses into the inner layer and undergoes a specific chemical reaction with these dispersed ammonia reactant particles, generating highly hygroscopic salts (such as ammonium chloride), hydrophilic gels (such as aluminum hydroxide), or strongly hydrophilic polymers (such as ammonium polyacrylate). These products can construct strongly hydrophilic microdomains and a high osmotic pressure environment in situ within the inner layer, establishing a stable chemical potential gradient and efficient transport channels for moisture migration from the surface to the inner layer.

[0033] In step S2, the metal oxide includes at least one of lightly calcined magnesium oxide, active magnesium oxide, active zinc oxide, and active calcium oxide; the disintegrant is magnesium aluminum silicate and / or povidone K30; the ammonia reactant includes at least one of polyacrylic acid, aluminum sulfate, and calcium chloride; and the release agent includes at least one of sodium stearate, magnesium stearate, and polyethylene glycol.

[0034] In one embodiment, when aluminum sulfate is used as the ammonia reactant, the hardness of the expanded sheet desiccant can be improved. This is because it reacts with ammonia and moisture during heat treatment to generate amorphous aluminum hydroxide gel. During the subsequent moisture absorption, expansion, and heat release of the desiccant, this gel gradually dehydrates and undergoes a phase transition, transforming into aluminum hydroxyl oxides or oxides such as boehmite or γ-alumina, which have higher crystallinity. These newly formed nanoscale inorganic rigid particles are uniformly dispersed and embedded in the magnesium chloride and magnesium oxide matrix. Through strong surface Al-O-Al bonding or hydrogen bonding, a robust ceramic bond bridge network is formed between the particles and between the particles and the matrix. This in-situ generated inorganic reinforcing phase significantly strengthens the bonding force between particles and the mechanical strength of the pore walls. Thus, when the tablet expands as a whole due to moisture absorption, it can effectively resist structural softening or collapse caused by internal stress, ultimately resulting in a significant improvement in the macroscopic hardness of the expanded sheet desiccant.

[0035] The ammonium chloride produced by the reaction of calcium chloride with ammonia is a highly soluble hygroscopic salt that exists in ionic form in humid environments and has no structural support capabilities. Its byproduct, calcium hydroxide, although solid, is relatively soft and does not transform into a high-hardness ceramic phase. After ammoniation, polyacrylic acid forms a strongly hydrophilic organic polymer gel, which functions to swell, increase pores, and conduct water. However, the gel phase itself has a low modulus and a soft texture, and cannot further enhance the mechanical framework.

[0036] S3. Divide the surface material into lower surface material and upper surface material, and then add the lower surface material, middle inner material and upper surface material into the mold in the order of lower surface material, middle inner material and upper surface material to compress the desiccant into tablets.

[0037] Step S3 includes: S3.1. Divide the surface material into lower surface material and upper surface material, and then add the lower surface material, middle inner material and upper surface material into the mold in the order of lower surface material, middle inner material and upper surface material. Heat treatment at 80~90℃ for 1~3h to obtain heat-treated material. The mass ratio of anhydrous magnesium chloride in the surface material to anhydrous magnesium chloride in the inner material is (20~45):(10~30). The mass of the lower surface material and the upper surface material is the same. Heat treatment of the laminated material (bottom-inner-top layer) at 80-90℃ for 1-3 hours within a mold produces several key beneficial effects: First, the heat treatment causes the bound alcohol in the magnesium chloride in the surface layer to be removed, transforming it back into highly active anhydrous magnesium chloride, restoring its core hygroscopic capacity. Second, the temperature is sufficient to trigger the decomposition of ammonia compounds in the surface layer, and the resulting ammonia diffuses into the inner layer and reacts with the ammonia reactants therein, becoming fixed. This process not only leaves a rich microporous structure in situ on the surface layer but also eliminates the risk of ammonia escape. Finally, dividing the surface material into two equal layers is crucial. The ammonia produced by the decomposition of the upper surface material during heating diffuses outwards, and its downward diffusion synergizes with the ammonia produced in the lower layer, ensuring that the ammonia reactants on the upper surface of the inner layer are also fully reacted. This compensates for the insufficient reaction on the upper surface of the inner layer that might result from unidirectional gas supply from the lower layer. At the same time, the symmetrical structure ensures the uniformity of heat and mass transfer during heat treatment, ultimately resulting in a heat-treated material with a complete structure and balanced function.

[0038] S3.2. Compress the heat-treated material into tablets at a pressure of 5~15 kN / cm. 2 A sheet-like desiccant is obtained.

[0039] This moderate pressure range allows for the tight compaction of heat-treated materials that already possess a preliminary pore structure and active components. While ensuring a strong mechanical bond between layers and obtaining high-strength tablets, it also avoids excessive pressure that could completely crush the microporous structure generated in situ during the heat treatment stage. This successfully locks in and preserves a continuous and stable pore network within the final sheet-like desiccant. These pores provide efficient channels for the rapid diffusion of moisture, significantly improving the dynamic moisture absorption capacity and absorption rate of the desiccant.

[0040] The present invention also provides a sheet desiccant, which is prepared by the above-described method for preparing a sheet desiccant; The sheet-like dried product, by weight, comprises the following components: 30-75 parts anhydrous magnesium chloride, 10-30 parts metal oxide, 10-30 parts gelling compound, 1-10 parts disintegrant, 10-35 parts tableting aid, and 1-5 parts release agent.

[0041] In some embodiments, the sheet desiccant further contains 3 to 10 parts of ammonia reactant.

[0042] For example, the present invention provides the following specific embodiments to illustrate specific preparation methods.

[0043] Example 1: S1.1 In an inert atmosphere, anhydrous magnesium chloride is added to anhydrous ethanol, the temperature is increased to 65°C, the mixture is stirred and reacted for 2.5 h, and then the temperature is lowered to 25°C to obtain an alcoholic magnesium chloride suspension, wherein the mass ratio of anhydrous magnesium chloride to anhydrous ethanol is 1:8. S1.2 Add carboxyethyl cellulose and ammonium bicarbonate to the magnesium chloride suspension and stir at 35°C for 1.5 h to obtain a mixed slurry, wherein the mass ratio of anhydrous magnesium chloride: carboxyethyl cellulose: ammonium bicarbonate is 20:20:10, and the particle size of ammonium bicarbonate D90≤10μm. S1.3. The mixed slurry is distilled under reduced pressure at -0.04MPa and 35℃ until the anhydrous ethanol content reaches 90% of the initial content to obtain a pretreated paste. The pretreated paste is then dried under vacuum at 35℃ and 0.00MPa to constant weight, crushed, and the composite powder is obtained. S1.4 Add the composite powder, mannitol, and sodium stearate to a mixer and mix at 20-30 rpm for 40-50 min to obtain the surface material, wherein the mass ratio of anhydrous magnesium chloride: mannitol: sodium stearate is 20:20:1. S2.1 Add anhydrous magnesium chloride, active magnesium oxide and magnesium aluminum silicate to a mixer and mix at 25 rpm for 20 min to obtain a mixture, wherein the mass ratio of anhydrous magnesium chloride, active magnesium oxide and magnesium aluminum silicate is 10:20:5. S2.2 Add sodium stearate to the premixed material and continue mixing for 10 minutes to obtain the inner material, wherein the mass ratio of anhydrous magnesium chloride to sodium stearate is 10:1; S3.1 Divide the surface material into lower surface material and upper surface material, and then add the lower surface material, middle inner material and upper surface material into the mold in the order of lower surface material, middle inner material and upper surface material. Heat treatment at 85℃ for 2 hours to obtain heat-treated material. The mass ratio of anhydrous magnesium chloride in the surface material to anhydrous magnesium chloride in the inner material is 20:10. The mass of the lower surface material and the upper surface material is the same. S3.2. Compress the heat-treated material into tablets at a pressure of 10 kN / cm². 2 A sheet-like desiccant is obtained; The sheet-like desiccant contains 30 parts anhydrous magnesium chloride, 20 parts active magnesium oxide, 20 parts carboxyethyl cellulose, 5 parts magnesium aluminum silicate, 20 parts mannitol, and 2 parts sodium stearate.

[0044] Example 2:

[0045] The process is basically the same as in Example 1, except that aluminum sulfate, an ammonia reactant, is added in step S2.2. The specific steps are as follows: S2.2 Add aluminum sulfate and sodium stearate to the premixed material and continue mixing for 10 minutes to obtain the inner material, wherein the mass ratio of anhydrous magnesium chloride: aluminum sulfate: sodium stearate is 10:6:1; The sheet desiccant contains 30 parts anhydrous magnesium chloride, 20 parts active magnesium oxide, 20 parts carboxyethyl cellulose, 5 parts magnesium aluminum silicate, 20 parts mannitol, 2 parts sodium stearate, and 6 parts aluminum sulfate.

[0046] Example 3:

[0047] This is basically the same as Example 2, except that calcium chloride is used instead of aluminum sulfate, i.e., the ammonia reactant is calcium chloride.

[0048] Example 4:

[0049] This is essentially the same as Example 2, except that polyacrylic acid is used instead of aluminum sulfate, i.e., the ammonia reactant is polyacrylic acid.

[0050] Comparative Example 1: It is basically the same as Example 1, except that carboxyethyl cellulose is not used in step S1, that is, the sheet desiccant does not contain gel compounds.

[0051] Comparative Example 2: It is basically the same as Example 1, except that active magnesium oxide is not used in step S2, that is, the sheet desiccant does not contain metal oxides.

[0052] Comparative Example 3: The process is basically the same as in Example 1, except that step S3 is as follows: S3. Mix the surface material and the inner material and add them to the mold. Heat at 85℃ for 2 hours to obtain the heat-treated material. Then, compress the material into tablets at a pressure of 10 kN / cm. 2 A sheet-like desiccant was obtained, wherein the mass ratio of anhydrous magnesium chloride in the surface material to anhydrous magnesium chloride in the inner material was 20:10.

[0053] Comparative Example 4: The preparation method of sheet desiccant is as follows: A mixture of 30 parts anhydrous magnesium chloride, 5 parts magnesium aluminum silicate, 20 parts mannitol, 2 parts sodium stearate, and 6 parts aluminum sulfate was added to a mold and compressed into tablets at a pressure of 10 kN / cm². 2 A sheet-like desiccant is obtained.

[0054] Performance testing: Moisture absorption rate test: The sample was made into a circular sheet with a diameter of 12 mm and a mass of 0.4 g. It was placed in an environment with a temperature of 25℃ and a relative humidity of 90%. The moisture absorption was measured for 24 hours, and the moisture absorption rate was calculated as follows: Moisture absorption rate = (mass after moisture absorption - initial mass) / initial mass × 100%. The test results are shown in Table 1.

[0055] Hardness test: The hardness of the tablet desiccant prepared in Examples 1-4 before and after moisture absorption was tested using a tablet hardness tester. The test results are shown in Table 2.

[0056] As shown in Table 1, in Examples 1-4, compared with Comparative Example 4, the sheet desiccant prepared in this application can effectively improve its moisture absorption rate in a high humidity environment, with the optimal moisture absorption rate reaching 179%. Furthermore, observations of Examples 1 and 2 show that when aluminum sulfate is used as an ammonia reactant, it can effectively improve the hardness of the sheet desiccant after moisture absorption. This effect is not present in polyacrylic acid and calcium chloride, two ammonia reactants. Further observation of Example 1 and Comparative Examples 1-2 shows that when the sheet desiccant lacks a gelling compound or metal oxide, it will have a significant impact on the final moisture absorption rate of the sheet desiccant. Finally, observing Example 1 and Comparative Example 3, it can be seen that when the surface material and the inner material are not placed in the mold in the order of lower surface material, middle inner material, and upper surface material, but are directly mixed and then put in, it will also affect the final moisture absorption rate. This is because when absorbing moisture, all magnesium chloride deliquesces at the same time. Although the metal oxide can react locally, it cannot form a stable water chemical potential gradient from the surface to the inside of the tablet, thus causing the final moisture absorption rate to decrease compared to Example 1.

[0057] The above embodiments are preferred embodiments of this application, but the implementation of this application is not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of this application shall be considered equivalent substitutions and shall be included within the protection scope of this application.

Claims

1. A method for preparing a sheet-like desiccant, characterized in that, The preparation method includes the following steps: S1. Anhydrous magnesium chloride, gelling compound and tableting aid are mixed to obtain the surface material; S2. Mix anhydrous magnesium chloride, metal oxide and disintegrant to obtain internal material; S3. Divide the surface material into lower surface material and upper surface material, and then add the lower surface material, middle inner material and upper surface material into the mold in the order of lower surface material, middle inner material and upper surface material to compress the desiccant into tablets. The gelling compound includes at least one of carboxyethyl cellulose, sodium carboxymethyl cellulose, and guar gum; Metal oxides include at least one of active magnesium oxide, active zinc oxide, and active calcium oxide.

2. The method for preparing a sheet-like desiccant according to claim 1, characterized in that, Step S1 includes: S1.1 In an inert atmosphere, anhydrous magnesium chloride is added to anhydrous lower alcohol, heated to 60~70℃, stirred for 2~3h, and cooled to 20~30℃ to obtain an alcoholic magnesium chloride suspension, wherein the mass ratio of anhydrous magnesium chloride to anhydrous lower alcohol is 1:(6~10). S1.2 Add gelling compound and ammonia compound to the magnesium chloride suspension and stir at 30~40℃ for 1~2h to obtain a mixed slurry. In S1.1, the mass ratio of anhydrous magnesium chloride: gelling compound: ammonia compound is (20~45):(10~30):(5~15), the particle size of ammonia compound D90≤10μm, and the ammonia compound is ammonium bicarbonate and / or ammonium carbonate. S1.

3. The mixed slurry is distilled under reduced pressure at -0.05~-0.02MPa and 30~40℃ to reduce the content of anhydrous lower alcohol to 85~90% of the initial content of anhydrous lower alcohol, to obtain a pretreated paste. The pretreated paste is then dried to constant weight under vacuum at 30~40℃ and 0.01~0.03MPa, and crushed to obtain composite powder. S1.4 Add the composite powder, tableting aid, and release agent to a mixer and mix at 20-30 rpm for 40-50 min to obtain the material shown in the table. The mass ratio of anhydrous magnesium chloride, tableting aid, and release agent in S1.1 is (20-45):(10-35):(0-2.5).

3. The method for preparing a sheet-like desiccant according to claim 2, characterized in that, The anhydrous lower alcohol includes at least one of methanol, ethanol, propanol, and isopropanol; the tableting aid includes at least one of nano-silica, microcrystalline cellulose, and mannitol; and the release agent includes at least one of sodium stearate, magnesium stearate, and polyethylene glycol.

4. The method for preparing a sheet-like desiccant according to claim 1, characterized in that, Step S2 includes: S2.1 Add anhydrous magnesium chloride, metal oxide and disintegrant to a mixer and mix at 20-30 rpm for 15-25 min to obtain a mixture, wherein the mass ratio of anhydrous magnesium chloride, metal oxide and disintegrant is (10-30):(10-30):(0-10) and the mass of disintegrant is not 0. S2.2 Add ammonia reactant and release agent to the mixture and continue mixing for 5~15 min to obtain the inner material. In S2.1, the mass ratio of anhydrous magnesium chloride: ammonia reactant: release agent is (10~30):(3~10):(0~2.5). The ammonia reactant includes at least one of polyacrylic acid, aluminum sulfate and calcium chloride.

5. The method for preparing a sheet-like desiccant according to claim 4, characterized in that, The disintegrant is magnesium aluminum silicate and / or povidone K30, and the release agent includes at least one of sodium stearate, magnesium stearate, and polyethylene glycol.

6. The method for preparing a sheet-like desiccant according to claim 1, characterized in that, Step S3 includes: S3.

1. Divide the surface material into lower surface material and upper surface material, and then add the lower surface material, middle inner material and upper surface material into the mold in the order of lower surface material, middle inner material and upper surface material. Heat treatment at 80~90℃ for 1~3h to obtain heat-treated material. The mass ratio of anhydrous magnesium chloride in the surface material to anhydrous magnesium chloride in the inner material is (20~45):(10~30). The mass of the lower surface material and the upper surface material is the same. S3.

2. Compress the heat-treated material into tablets at a pressure of 5~15 kN / cm. 2 A sheet-like desiccant is obtained.

7. A sheet-like desiccant, characterized in that, The sheet-like desiccant is prepared by any one of the preparation methods described in claims 1-6; The sheet-like desiccant comprises, by weight, the following components: 30-75 parts anhydrous magnesium chloride, 10-30 parts metal oxide, 10-30 parts gelling compound, 1-10 parts disintegrant, 10-35 parts tableting aid, and 1-5 parts release agent; The gelling compound includes at least one of carboxyethyl cellulose, sodium carboxymethyl cellulose, and guar gum; Metal oxides include at least one of active magnesium oxide, active zinc oxide, and active calcium oxide.

8. The sheet-like desiccant according to claim 7, characterized in that, The sheet-like desiccant also contains 3 to 10 parts of an ammonia reactant, which includes at least one of polyacrylic acid, aluminum sulfate, and calcium chloride.

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