Chalk based on 3D printing and preparation method thereof

Abstract

The invention provides chalk based on 3D printing and a preparation method thereof, and relates to the technical field of chalk preparation. The chalk is prepared from the following raw materials: calcium carbonate, shell powder, calcined gypsum, kaolin, a plasticizer, polyvinyl alcohol and silicone oil, and the chalk with the components can utilize the interaction among the raw materials to improve the strength and toughness of the chalk, reduce the dust amount in the use process of the chalk and endow the chalk with excellent use performance; secondly, the performance of the chalk is regulated and controlled by regulating and controlling the adding amount of all the raw materials, and finally the chalk with the excellent performance is prepared. Furthermore, according to the chalk preparation method provided by the invention, the 3D printing technology is integrated into the chalk preparation process, the characteristics of customizability and batch production of the 3D printing technology can be utilized, a corresponding printing strategy can be specified according to actual application requirements, large-batch production of the chalk is realized, and the production efficiency of the chalk is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of chalk preparation, and in particular to a chalk based on 3D printing and a preparation method thereof. Background Art

[0002] The following problems exist in the traditional chalk manufacturing process. First, in terms of raw materials, current chalk mainly relies on mineral materials such as gypsum, talc, clay, and some chemical synthetic substances. The mining and processing of these raw materials not only have a certain impact on the environment, but also with the continuous consumption of resources, its sustainability also faces severe challenges; secondly, in terms of production efficiency, the traditional chalk manufacturing process is mostly manual or semi-automated production. This method is not only inefficient and difficult to meet large-scale teaching needs, but also increases labor costs and reduces the economic benefits of the enterprise; thirdly, in terms of environmental performance, traditional chalk is prone to generate dust during use, posing a potential threat to the respiratory system of teachers and students. At the same time, discarded chalk is difficult to degrade, causing continuous pollution to the environment.

[0003] In view of this, it is necessary to design an improved 3D printing-based chalk and a preparation method thereof to solve the above problems. Summary of the Invention

[0004] The object of the present invention is to provide a chalk based on 3D printing and a preparation method thereof.

[0005] To achieve the above-mentioned purpose of the invention, on the one hand, the present invention provides a 3D printing-based chalk, whose raw materials include the following components, calculated by mass percentage: 40-50% calcium carbonate, 20-30% shell powder, 10-20% calcined gypsum, 5-10% kaolin, 2-4% plasticizer, 1-3% polyvinyl alcohol and 1-3% silicone oil.

[0006] Preferably, the plasticizer comprises 0.5-2% by mass of polyethylene glycol and 0.5-1.5% by mass of carboxymethyl cellulose.

[0007] Preferably, the raw materials include the following components in percentage by mass: 45% calcium carbonate, 25% shell powder, 15% calcined gypsum, 8% kaolin, 2% plasticizer, 2% polyvinyl alcohol and 1% silicone oil.

[0008] Preferably, the raw materials include the following components in percentage by mass: 50% calcium carbonate, 20% shell powder, 10% calcined gypsum, 5% kaolin, 2% plasticizer, 2% polyvinyl alcohol and 1% silicone oil.

[0009] Preferably, the raw materials include the following components in percentage by mass: 40% calcium carbonate, 30% shell powder, 10% calcined gypsum, 5% kaolin, 2% plasticizer, 2% polyvinyl alcohol and 1% silicone oil.

[0010] Preferably, the raw materials include the following components in percentage by mass: 40% calcium carbonate, 20% shell powder, 20% calcined gypsum, 5% kaolin, 2% plasticizer, 2% polyvinyl alcohol and 1% silicone oil.

[0011] On the other hand, the present invention also provides a method for preparing the chalk based on 3D printing, comprising the following steps:

[0012] Mixing calcium carbonate, shell powder, calcined gypsum, kaolin, plasticizer, polyvinyl alcohol, silicone oil and water to obtain a mixture;

[0013] The mixed material is added into a vacuum 3D printer, and is extruded and printed in a vacuum environment to obtain wet chalk; and the wet chalk is dried and solidified to obtain the chalk.

[0014] Preferably, the drying and curing treatment conditions are: temperature 60-80° C., humidity 30-50%, and time 12-24 hours.

[0015] Preferably, the raw materials other than water in the mixture are composed as follows by mass percentage: 40-50% calcium carbonate, 20-30% shell powder, 10-20% calcined gypsum, 5-10% kaolin, 2-4% plasticizer, 1-3% polyvinyl alcohol, and 1-3% silicone oil.

[0016] The beneficial effects of the present invention are:

[0017] 1. The present invention provides a method for preparing chalk based on 3D printing. This method realizes customizable production of chalk by means of 3D printing technology. The corresponding printing strategy can be specified according to the needs of actual applications, thereby realizing mass production of chalk and improving chalk production efficiency.

[0018] 2. The 3D printing-based chalk provided by the present invention uses calcium carbonate, shell powder, calcined gypsum, kaolin, plasticizer, polyvinyl alcohol and silicone oil as raw materials. Combined with the regulation of each component in the raw materials, it can not only improve the environmental adaptability (writing fluency and durability) of the prepared chalk during use, but also improve the strength and toughness of the chalk, giving the chalk excellent performance.

[0019] 3. The 3D printing-based chalk provided by the present invention, by adding plasticizers, polyvinyl alcohol, and silicone oil, can utilize the interaction between the polyethylene glycol and carboxymethyl cellulose in the plasticizer and the polyvinyl alcohol and silicone oil to jointly improve the strength and flexibility of the chalk.

[0020] 4. The 3D printing-based chalk provided by the present invention, by adding shell powder, not only realizes the recycling of waste, but also improves the environmental performance of the chalk. By regulating the amount of shell powder added, it can ensure that the raw materials are evenly mixed and have appropriate viscosity, which facilitates the extrusion and molding of the chalk. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to specific embodiments.

[0022] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the solutions of the present invention are shown in the text, while other details that are not closely related to the present invention are omitted.

[0023] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0024] The invention provides a 3D printing-based chalk. The raw materials of the chalk include the following components, calculated by mass percentage: 40-50% calcium carbonate, 20-30% shell powder, 10-20% calcined gypsum, 5-10% kaolin, 2-4% plasticizer, 1-3% polyvinyl alcohol and 1-3% silicone oil.

[0025] In some embodiments, the plasticizer is used to improve the plasticity and fluidity of the chalk, enhance its crack resistance, increase the cohesiveness and strength of the chalk, improve the smoothness of writing, and make the printed chalk less likely to break during use. The plasticizer includes 0.5-2% polyethylene glycol and 0.5-1.5% carboxymethyl cellulose.

[0026] By adding the above-mentioned plasticizer, it can be used together with polyvinyl alcohol and silicone oil to enhance the strength and flexibility of chalk. In this process, the polyethylene glycol in the plasticizer has strong hydrophilicity and can be inserted between the chalk matrix (gypsum / calcium carbonate) particles, combining with the particle surface through hydrogen bonds, reducing the friction resistance between the particles and reducing the risk of brittle fracture. During subsequent drying and curing, part of the polyethylene glycol in the chalk volatilizes to form a micron-scale pore structure, releasing internal stress and avoiding crack expansion caused by stress concentration. The carboxymethyl group of carboxymethyl cellulose can undergo ionic cross-linking with the calcium ions in the matrix to form a three-dimensional network structure, thereby enhancing the bonding force between the particles. At the same time, the high water holding capacity of carboxymethyl cellulose can slow the solidification speed of the chalk slurry, promote uniform arrangement of particles, and reduce internal defects. After drying, polyvinyl alcohol can form a continuous flexible film that wraps the gypsum particles and bridges cracks, thereby improving the toughness of the chalk as a whole. Through the bonding enhancement of polyvinyl alcohol and carboxymethyl cellulose, the plasticization and buffering of polyethylene glycol, and the interfacial lubrication of silicone oil, the strength and flexibility of the chalk are simultaneously improved.

[0027] Among the above components, calcium carbonate serves as the chalk matrix, providing the chalk with the necessary hardness and stability. The higher its purity and the finer its particle size, the finer the texture of the chalk produced, the smoother the writing, and the better the wear resistance. Its particle size can be adjusted as needed, but is not limited to this, as long as it can meet the chalk's requirements for hardness, writing smoothness, and durability.

[0028] Shell powder is the discarded shells of oysters, mussels, clams, and snails, after the flesh has been removed. The powder is obtained through cleaning and grinding. It is 95% calcium carbonate, with small amounts of calcium oxide, calcium hydroxide, and other calcified substances, making it a mineral supplement. Using it as a chalk raw material not only recycles waste but also improves the chalk's environmental performance. This solution, by adjusting the amount of shell powder added, ensures a uniform mixing of the raw materials and an appropriate viscosity, making it easier to extrude and shape the chalk.

[0029] Calcined gypsum, another chalk base, is a hygroscopic material that helps maintain proper humidity during the chalk manufacturing process. It helps regulate the chalk's drying speed and hardness, improving its texture and durability, making the printed chalk more comfortable to use and less prone to breakage. It also helps the chalk be easily erased after use, preventing marks from leaving behind. The main function of using kaolin is to improve the chalk's plasticity and printability. It allows the raw materials to mix more evenly with water and creates a fine, uniform texture during the printing process. The finer the kaolin particle size, the finer the texture. The addition of kaolin improves the chalk's plasticity and printability, and together with calcined gypsum, improves the chalk's drying speed, hardness, writing fluidity, and erasability.

[0030] Silicone oil mainly acts as a lubricant, which can reduce frictional resistance during the printing process, making the printed chalk smoother and easier to write with. Together with plasticizers and polyvinyl alcohol, it improves the strength, flexibility, writing fluency and surface smoothness of the chalk, giving the chalk excellent performance.

[0031] Furthermore, the present invention also provides a method for preparing the above chalk, comprising the following steps:

[0032] Customize the chalk design using 3D modeling software;

[0033] By mass percentage, 40-50% calcium carbonate, 20-30% shell powder, 10-20% calcined gypsum, 5-10% kaolin, 2-4% plasticizer, 1-3% polyvinyl alcohol, 1-3% silicone oil and an appropriate amount of water are mixed evenly to obtain a mixture;

[0034] The mixed material is added into a vacuum 3D printer and extruded and printed in a vacuum environment to obtain wet chalk; the wet chalk is dried and solidified to remove moisture therein to obtain chalk.

[0035] In the above preparation method, by introducing 3D printing technology into the production process of chalk, the customizability and mass production characteristics of 3D printing technology can be utilized, and corresponding printing strategies can be specified according to actual application requirements to efficiently produce chalk products with excellent performance.

[0036] In some embodiments, the plasticizer is used to improve the plasticity and fluidity of the chalk, enhance its crack resistance, increase the cohesiveness and strength of the chalk, improve the smoothness of writing, and make the printed chalk less likely to break during use. The plasticizer includes 0.5-2% polyethylene glycol and 0.5-1.5% carboxymethyl cellulose.

[0037] In some embodiments, the process parameters for printing and molding are as follows: printing speed 20-30 mm / s, extrusion pressure 0.3-0.6 MPa, layer height 0.4-0.8 mm, nozzle diameter 0.8-1.2 mm, and printing temperature 25-40°C. By controlling the printing parameters within the above range, it is possible to ensure that the chalk has a regular shape and a uniform internal composition without defects, thereby avoiding cracks in the chalk during subsequent drying. For example, if the printing speed is too slow, although it can ensure that the chalk mixture is extruded evenly and the interlayers are firmly bonded, it will also cause the mixture to accumulate, easily causing the chalk to deform, and at the same time affecting the preparation efficiency. If the printing speed is too fast, it will result in loose interlayer bonding or uneven extrusion, which will in turn affect the quality of the chalk.

[0038] In some embodiments, the drying and curing process is performed at a temperature of 60-80°C, a humidity of 30-50%, and a time of 12-24 hours. Specifically, the drying and curing process is performed using a step-by-step temperature increase, with the following specific steps: placing the chalk in a 60°C environment, spraying an appropriate amount of water on the surface of the chalk, and drying the chalk at 60°C for 0-4 hours to perform primary shaping. During the first 0-2 hours, the chalk is turned every 30 minutes to ensure uniform heating. During the 4th to 12th hours, the temperature is increased to 70°C to dehydrate and strengthen the chalk. During the 12th to 24th hours, the temperature is increased to 80°C to complete the drying and curing of the chalk.

[0039] In the above process, the purpose of spraying an appropriate amount of water on the surface of the chalk is to provide an appropriate amount of moisture to the surface of the chalk, preventing the chalk from cracking or deforming due to rapid dehydration during the heating process. In particular, the initial turning operation can avoid uneven local drying. After spraying water, the surface of the chalk as a whole is slightly moistened but no water droplets are formed; through step-by-step heating and segmented drying, the chalk can be ensured to be heated evenly during the drying process, prompting the moisture inside the chalk to gradually evaporate, which is beneficial to improving the hardness of the chalk and avoiding problems such as cracking or deformation of the chalk during the drying process; by regulating the drying temperature, humidity, and time, the chalk is fully dried, effectively reducing the amount of dust generated by the chalk during use and improving the writing experience. Secondly, under a certain humidity environment, the chalk can be maintained during the drying process to reduce cracks and defects on the chalk surface, which is beneficial to improving the smoothness of the chalk. It should be noted that the humidity of the drying process can be achieved by setting a humidifier or other equipment that can change the humidity of the drying environment. The specific operation process can be selected as needed, as long as it can meet the required humidity requirements, and this is not limited here.

[0040] The 3D printing-based chalk and its preparation method proposed by the present invention are further described below with reference to specific embodiments:

[0041] Examples 1 to 4

[0042] Examples 1 to 4 prepared a 3D printing-based chalk, and the preparation method thereof is as follows:

[0043] A hexagonal chalk was custom-designed using 3D modeling software. The chalk dimensions were as follows: 80 mm in length, 5 mm in hexagonal side length, 10 mm in diameter, and a 20° tip taper. The customization process was completed using Blender software, following a common method in the field.

[0044] Calcium carbonate, shell powder, calcined gypsum, kaolin, plasticizer, polyvinyl alcohol, silicone oil and an appropriate amount of water are uniformly mixed to obtain a mixture, wherein the plasticizer is composed of 1% by mass of polyethylene glycol and 1% by mass of carboxymethyl cellulose, and the mass percentages of polyethylene glycol and carboxymethyl cellulose are the ratios of their masses to the sum of the masses of all raw materials (e.g., the mass percentage of polyethylene glycol is the ratio of the mass of polyethylene glycol to the sum of the masses of all raw materials), and the shell powder is the discarded shells of oysters after meat removal, and is obtained by washing, grinding and other treatment methods. It should be noted that the particle size of the above-mentioned powder raw materials can be adjusted according to actual design requirements, as long as it can meet the actual application requirements, and this is not limited here;

[0045] The mixture was added to a vacuum 3D printer and extruded and printed under vacuum to produce wet chalk. The wet chalk was then dried and solidified to remove moisture, resulting in the finished chalk. The drying and solidification process was performed at a temperature of 70°C, a humidity of 40%, and a time of 15 hours. The printing parameters were as follows: a printing speed of 20 mm / s, an extrusion pressure of 0.5 MPa, a layer height of 0.6 mm, a nozzle diameter of 1 mm, and a printing temperature of 25°C.

[0046] The raw material compositions of Examples 1 to 4 are shown in Table 1. The amount of water added in each example can be adjusted as needed and is therefore not provided herein. The properties of the chalks obtained under the corresponding conditions are shown in Table 2. The hardness and dust content were measured according to the method specified in QB / T2223-2010 "Chalk". The dust content indicates the amount of dust on the chalk path during writing (the amount of chalk residue dropped during chalk writing). This scheme uses a relative hardness scale to assess the hardness of chalk writing, with grades 1-5 indicating a gradual increase in hardness. The flexural strength of chalk refers to the ability of the chalk to resist breakage or fragmentation during writing, which is measured using a three-point bending method.

[0047] According to the data in the analysis table, the chalk obtained in Example 1 has the best comprehensive performance, because: the components act synergistically, the ratio is optimized, and hardness, toughness and environmental protection are balanced. The excessive calcium carbonate in the formula of Example 2, due to its higher hardness, can affect the toughness of the internal structure of the chalk to a certain extent. When the chalk is subjected to an external force (such as writing), the internal lacks enough flexibility to buffer these external forces, and brittle cracking occurs easily. The high proportion of shell powder in Example 3 can increase the friction between the chalk particles, absorb more water or other additives, and affect extrusion fluidity. The high proportion of calcined gypsum in Example 4 can form too much rigid gypsum structure inside the chalk, lacking enough elasticity and toughness to withstand external force. After drying, it can become harder and more brittle, affecting the comprehensive performance of the chalk.

[0048] Table 1 Raw material composition of Examples 1 to 4

[0049]

[0050] Table 2 Chalk performance comparison obtained in Examples 1 to 4

[0051]

[0052] Examples 5 to 6

[0053] The only difference between Examples 5 and 6 and Example 1 is that the process parameters of the printing and molding process are different from those of Example 1, and the other process conditions are the same as those of Example 1 and will not be repeated here. The printing and molding process parameters of Examples 1 and Examples 5 to 6 and the chalk properties obtained under the corresponding conditions are shown in Table 3. The results show that the extrusion speed and the mold aperture need to be controlled in a coordinated manner to ensure the best overall performance of the chalk and effectively avoid pores and structural defects. In addition, during the printing process, the chalk obtained in Example 1 is smooth, uniform, and complete as a whole, while in Example 5, due to the slow printing speed, the chalk is delaminated internally during extrusion and is prone to local breakage. The chalk obtained in Example 6 has an uneven diameter because the excessively large aperture affects the structural density of the chalk.

[0054] Table 3 Printing process parameters of Example 1 and Examples 5 to 6 and chalk properties obtained under corresponding conditions

[0055]

[0056] Comparative Examples 1 to 3

[0057] The difference between Comparative Examples 1 to 3 and Example 1 is only that: the formula of chalk raw material is different from Example 1, the processing parameter of preparation process is the same as Example 1, and will not be repeated here, raw material composition is as shown in Table 4, and the chalk performance obtained under corresponding conditions is as shown in Table 5, and result shows that the chalk comprehensive performance of Example 1 is obviously better than Comparative Examples 1-3, this is because the effect of each raw material can be maximized under the formula of Example 1, and the mutual synergy between raw materials can be effectively utilized. And Comparative Example 1 reduces the consumption of calcium carbonate relative to Example 1, and when calcium carbonate ratio is too low, the calcium carbonate content that plays support and filling effect in chalk is reduced, and it is impossible to form sufficiently firm skeleton structure, so that chalk overall texture softens, and hardness does not reach ideal state. When writing, due to the insufficient hardness of the chalk, it is not possible to leave clear and deep marks on the blackboard, and it is easily erased or blurred, affecting the writing effect; Comparative Example 2 reduces the amount of shell powder relative to Example 1. When the shell powder ratio is too low, the environmentally friendly components from shell powder in the chalk are reduced, and the proportion of other components that may contain harmful substances or are not easily degraded is relatively increased, thereby reducing the overall environmental performance of the chalk; Comparative Example 3 reduces the amount of burnt gypsum relative to Example 1. When the burnt gypsum ratio is too low, its ability to absorb water and solidify is weakened, resulting in a slower drying speed of the chalk. The hardened structure formed by burnt gypsum plays an important role in maintaining the shape and strength of the chalk. When the ratio is too low, cracks are more likely to occur, and crack resistance deteriorates.

[0058] Table 4 Raw material composition of Comparative Examples 1 to 3

[0059]

[0060] Table 5 Chalk properties obtained from Example 1 and Comparative Examples 1 to 3

[0061]

[0062] Note: The symbols ▲ / ▼ indicate performance improvement (compared with Example 1).

[0063] Comparative Examples 4 to 9

[0064] The difference between Comparative Examples 4 to 9 and Example 1 is only that: the composition of the chalk raw materials is different from that in Example 1, the processing parameters of the preparation process are the same as those in Example 1, which will not be repeated here. The raw material formula is shown in Table 6, and the chalk performance obtained under the corresponding conditions is shown in Table 7. The results show that the chalk comprehensive performance of Example 1 is the best. The results show that there is a synergistic effect between the raw materials in the chalk formula proposed by the present invention. Calcium carbonate can provide basic hardness, and shell powder can improve toughness and extrusion fluidity. The two can balance the hardness and environmental protection of the chalk together (Comparative Example 4); calcined gypsum can be beneficial to the rapid solidification of the chalk after extrusion, and kaolin can improve the plasticity of the chalk. The two together regulate the drying speed and molding quality of the chalk (Comparative Examples 5-6), and jointly ensure molding efficiency and surface smoothness; plasticizer, polyvinyl alcohol and silicone oil, the three jointly promote the strength, toughness and surface properties of the chalk (Comparative Examples 7-9), which is beneficial to optimizing the strength, flexibility and surface lubricity of the chalk.

[0065] Table 6 Raw material composition of Example 1 and Comparative Examples 4 to 9

[0066]

[0067] Table 7 Chalk properties obtained from Example 1 and Comparative Examples 4 to 9

[0068]

[0069] Note: The symbols ▲ / ▼ indicate performance improvement (compared with Example 1).

[0070] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A chalk based on 3D printing, characterized in that, Calculated by mass percentage, the raw materials include the following components: 40-50% of calcium carbonate, 20-30% of shell powder, 10-20% of calcined gypsum, 5-10% of kaolin, 2-4% of plasticizer, 1-3% of polyvinyl alcohol and 1-3% of silicone oil.

2. The chalk according to claim 1, characterized in that The plasticizer comprises 0.5-2% by mass of polyethylene glycol and 0.5-1.5% by mass of carboxymethyl cellulose.

3. The chalk according to claim 1, characterized in that Calculated by mass percentage, the raw materials include the following components: 45% calcium carbonate, 25% shell powder, 15% calcined gypsum, 8% kaolin, 2% plasticizer, 2% polyvinyl alcohol and 1% silicone oil.

4. The chalk according to claim 1, characterized in that The raw materials include the following components in percentage by mass: 50% calcium carbonate, 20% shell powder, 10% calcined gypsum, 5% kaolin, 2% plasticizer, 2% polyvinyl alcohol and 1% silicone oil.

5. The chalk according to claim 1, characterized in that The raw materials include the following components in percentage by mass: 40% calcium carbonate, 30% shell powder, 10% calcined gypsum, 5% kaolin, 2% plasticizer, 2% polyvinyl alcohol and 1% silicone oil.

6. The chalk according to claim 1, characterized in that Calculated by mass percentage, the raw materials include the following components: 40% calcium carbonate, 20% shell powder, 20% calcined gypsum, 5% kaolin, 2% plasticizer, 2% polyvinyl alcohol and 1% silicone oil.

7. A method for preparing chalk based on 3D printing according to any one of claims 1 to 6, characterized in that: The steps include: Mixing calcium carbonate, shell powder, calcined gypsum, kaolin, plasticizer, polyvinyl alcohol, silicone oil and water to obtain a mixture; The mixed material is added into a vacuum 3D printer, and is extruded and printed in a vacuum environment to obtain wet chalk; and the wet chalk is dried and solidified to obtain the chalk.

8. The preparation method according to claim 7, characterized in that The drying and curing treatment conditions are: temperature 60-80° C., humidity 30-50%, and time 12-24 hours.

9. The preparation method according to claim 7, characterized in that The raw materials other than water in the mixture are composed as follows by mass percentage: 40-50% calcium carbonate, 20-30% shell powder, 10-20% calcined gypsum, 5-10% kaolin, 2-4% plasticizer, 1-3% polyvinyl alcohol, and 1-3% silicone oil.

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