A pencil lead with controllable writing damping and a method of making the same

Abstract

A pencil lead with controllable writing damping and its preparation method. This invention belongs to the field of pencil lead technology. The purpose of this invention is to solve the technical problem that existing pencil leads cannot simultaneously achieve stable pen control, easy application of ink, no paper scratching, and high core strength, making them unsuitable for young children and other writing beginners. The pencil lead of this invention consists of a porous sintered matrix and a damping mixture filled into the pores of the matrix through vacuum impregnation; the porous sintered matrix consists of graphite powder, bentonite, reinforcing filler, temporary binder, and water; the damping mixture consists of base grease, micro-adhesive wax, and friction-regulating particles. This invention provides a pencil lead that, through material selection and proportion control, precisely creates a soft, delayed damping effect through an internal damping mixture, resulting in smooth and easy application of ink, no paper scratching, a controllable coefficient of friction, a uniform and solid damping feel, and high structural strength, making it suitable for children learning to write and writing beginners.

Description

Technical Field

[0001] This invention belongs to the field of pencil lead technology, specifically relating to a pencil lead with controllable writing damping and its preparation method. Background Technology

[0002] The writing feel, coloring effect, and ease of control of pencil leads are core elements of the user experience for children and beginners learning to write. Currently, the two main types of graphite pencil leads on the market have significant shortcomings for toddlers and children just starting to learn to write: The first type is traditional graphite-clay pencil leads that pursue low friction and extreme smoothness. Their development relies solely on adjusting the graphite-clay ratio and impregnating the lead with low-viscosity oils to control the coefficient of friction below 0.20. These products have extremely low writing resistance, completely lacking any lag or damping, resulting in a floaty feel at the tip. Children and beginners have weak hand control, extremely poor fine-grained pen control, and their writing is prone to crookedness and inconsistent line pressure. The depth of the lines fluctuates greatly with the pressure applied while holding the pencil, leading to poor uniformity of the writing. Furthermore, to reduce the coefficient of friction, the strength of the core structure is often weakened, making the lead prone to breakage and crumbling during sharpening and writing. The second type, traditional sintered graphite clay lead cores without oil impregnation optimization, rely solely on high-temperature sintering of graphite and clay. Without dedicated lubricating and buffering components, the overall matrix is ​​rough, with a simple pore structure, resulting in problems such as a high coefficient of friction, dryness when writing, difficulty in applying ink, and exposed hard mineral particles that easily scratch paper. Even with the addition of a small amount of a single wax for improvement, it can only slightly alleviate the dryness and cannot stably control the writing feel. The writing resistance fluctuates greatly, making it difficult for children to accurately control the pen when practicing calligraphy, resulting in uneven line depth.

[0003] Existing improvement solutions mostly involve simply adding wax and a small amount of lubricating oil for surface modification. Another approach in the industry is to directly and significantly increase the particle size of graphite and bentonite powder to improve the friction resistance of the paper surface, attempting to improve the poor pen control of the smooth pen core. However, this method can only drastically increase the friction of the paper surface and cannot form a uniform and gentle hysteresis damping. Large-sized hard mineral particles directly contact the paper surface, ultimately causing problems such as dry and difficult-to-color strokes, obvious scratches on the paper surface, and rough writing feel. It cannot simultaneously achieve the four major advantages of stable pen control, easy-to-color strokes, no paper scratches, and high core strength. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problems of existing pencil leads, which cannot simultaneously achieve stable pen control, easy application of ink, no scratching of paper, and high strength, making them unsuitable for young children and other beginner writers. The invention provides a pencil lead with controllable writing damping and its preparation method.

[0005] The technical solution of the present invention is as follows: One of the objectives of this invention is to provide a pencil lead with controllable writing damping, the pencil lead being composed of a porous sintered matrix and a damping mixture filled in the pores of the matrix by vacuum impregnation; The porous sintered matrix is ​​prepared by weight of 45-65 parts graphite powder, 15-28 parts bentonite, 3-10 parts reinforcing filler, 4-12 parts temporary binder, and 10-25 parts water; the reinforcing filler is selected from at least one of mica powder, boron nitride, and diatomaceous earth. The damping mixture, by weight, consists of 10-30 parts of base grease, 5-20 parts of micro-adhesive wax, and 1-8 parts of friction-regulating particles; the friction-regulating particles are selected from at least one of diamond micro powder, silicon carbide micro powder, and spherical zirconia micro powder. The porosity of the porous sintered matrix is ​​25-45%; the damping mixture accounts for 8-22% of the total weight of the pencil lead.

[0006] Further specified, the average particle size of graphite powder is 12~25μm, and the average particle size of bentonite powder is 8~18μm.

[0007] Further specified, the base oil is selected from one or two of silicone oil, mineral oil, and synthetic ester oil; its kinematic viscosity is 100~800 mm. 2 / s.

[0008] Further specifying, the temporary binder is selected from at least one of starch, polyvinyl alcohol, sodium carboxymethyl cellulose, and dextrin.

[0009] Further specifying, the micro-adhesive wax is selected from at least one of paraffin wax, microcrystalline wax, and polyethylene wax.

[0010] Further, the average particle size of the friction-controlled particles is 0.5~5μm.

[0011] The second objective of this invention is to provide a method for preparing a pencil lead with controllable writing damping, the method comprising the following steps: (1) Mixing and paste preparation: Graphite powder, bentonite, reinforcing filler, temporary binder and water are ball-milled and mixed to obtain a uniform paste; (2) Molding and sintering: The paste is extruded into slender green core strips through a mold, dried at low temperature, and then sintered at high temperature in an inert atmosphere to obtain a porous sintered matrix with a porosity of 25~45%; (3) Preparation of damping mixture impregnation liquid: Add micro-sticky wax to the base oil, heat and stir continuously until the micro-sticky wax is completely melted to form a uniform oil-wax mixture. Keep the temperature constant and stir, and add friction control particles at a feeding rate of 0.1~0.5 g / min. After the feeding is completed, continue stirring for 30~60 min until the particles are uniformly suspended to obtain a stable damping mixture impregnation liquid. (4) Vacuum impregnation: The porous sintered matrix is ​​immersed in the damping mixture impregnation liquid for vacuum impregnation. After impregnation, it is naturally cooled to room temperature to obtain pencil lead.

[0012] Further, the high-temperature sintering temperature in step (2) is 850~1050℃ and the time is 1.5~3h.

[0013] Further specified, in step (3), the temperature is heated to 50~90℃.

[0014] Further specifying, the vacuum impregnation conditions in step (4) are: temperature of 50~90℃, vacuum degree of -0.06 ~ -0.09MPa, and time of 30~90min.

[0015] The advantages of this invention compared to existing technologies are: This invention provides a pencil lead and its preparation method that utilizes material selection and proportion control to precisely create a soft, delayed damping effect through an internal damping mixture, rather than simply increasing the powder particle size to improve the coefficient of friction. This results in a pencil lead that is smooth to apply, easy to color, does not scratch the paper, has a controllable coefficient of friction, provides a uniform and solid damping feel, and has high structural strength, making it less prone to breakage and crumbling. It is suitable for children learning to write and beginners. This invention addresses the problem that current pencil leads on the market cannot simultaneously achieve smooth color application, soft damping, no paper scratching, and less breakage, thus failing to meet the needs of children learning to write and beginners. Specific advantages are as follows: (1) The damping feel is soft and controllable, suitable for beginner children to control the pen. It does not rely on the high friction of ultra-large particle size powder to achieve damping: This invention abandons the two extreme designs of traditional pencil leads (extreme low friction and no damping, and enlarging graphite / bentonite to more than 50μm to form a hard high friction and scratch the paper). Instead, it uses a three-component compound damping mixture system of base oil with limited viscosity, micro-adhesive wax, and 0.5~5μm ultra-fine friction control particles. When writing, the main material graphite has excellent coloring ability. With the continuous release of oil and wax lubricating medium in the pore damping mixture, graphite fragments can be transferred to the paper surface smoothly and continuously, effectively preventing problems such as ink breakage, whitening, and dryness and difficulty in coloring when writing, and ensuring that the writing lines are continuous and uniform in depth. The base grease provides basic lubrication for easy color application, the micro-adhesive wax stabilizes the system and creates gentle, delayed damping, and the ultra-fine coated friction-regulating particles form uniform, micro-convex buffer friction contacts. The three work together to stably control the dynamic friction coefficient of writing within the range of 0.25 to 0.45. The damping comes from the pore-filling components rather than the ultra-large particle size hard powder of the matrix, resulting in a solid and stable stroke. Young children and beginners can easily control the direction and pressure of their strokes, while also ensuring smooth and easy color application.

[0016] (2) Smooth writing and easy coloring, without scratching the paper: The graphite and bentonite matrix of this invention are constructed with medium particle sizes of 12~25μm and 8~18μm to form a high-porosity matrix, storing sufficient damping lubricating components. During writing, the lubricating medium is continuously released, and the graphite debris is transferred smoothly, which completely solves the problem of dryness and difficulty in coloring and paper scratching caused by the industry increasing the particle size of graphite and bentonite to more than 50μm. All friction control particles are coated with oil and wax, with no sharp edges exposed, so they will not scratch the exercise book or calligraphy paper, and there is no rough scratching feel.

[0017] (3) Stable and durable structure: Relying on medium-sized graphite and bentonite combined with reinforcing fillers to build a high-strength matrix skeleton, combined with the pore filling auxiliary reinforcement effect of the impregnation damping composition, the overall structure of the pencil lead has good stability, which greatly reduces the probability of the lead breaking and falling off during children's pencil sharpening and writing process.

[0018] (4) Excellent writing quality: The vacuum impregnation process ensures that the damping mixture is evenly distributed inside the pen core. Combined with the continuous ink guiding effect of the oil and wax system, the writing lines are continuous and uniform, without ink breaks or white spots; the damping feel is stable throughout the process and there will be no sudden change in resistance as the writing time increases, so that the lines of children practicing writing are uniform in thickness.

[0019] (5) Strong process compatibility and easy mass production: The entire preparation process can be realized by modifying the existing sintered pencil lead production line without major equipment replacement. Raw materials are readily available and the production threshold is low, making it suitable for large-scale industrial production of children's beginner pencils. Attached Figure Description

[0020] Figure 1 The images are actual colored photographs of the pencil leads obtained in Comparative Examples 1-2 and Example 1 of the present invention; wherein a) - Comparative Example 1, b) - Comparative Example 2, c) - Example 1. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0023] All performance data described below were obtained under standard conditions of 23°C room temperature and 60% relative humidity; the arithmetic mean of 10 lead cores randomly selected from each sample was taken after testing. Writing and appearance performance were in accordance with GB / T26704-2011 "Pencils".

[0024] Example 1: Standard damping pencil lead for beginners practicing calligraphy and its preparation method: Pencil lead formula: The pencil lead consists of a porous sintered matrix and a damping mixture that is filled into the pores of the matrix by vacuum impregnation; The porous sintered matrix is ​​prepared by weight of 55 parts graphite powder (average particle size 20 μm), 22 parts bentonite (average particle size 15 μm), 5 parts mica powder, 7 parts sodium carboxymethyl cellulose (Ashland Bonvi, model C1592), and 11 parts water. The medium-sized graphite and bentonite are only used to construct highly interconnected pores to store damping components, without relying on powder to increase paper surface friction, thus ensuring continuous lubrication and easy color removal. The damping mixture, by weight, consists of a base oil (mineral oil, kinematic viscosity 350 mm). 2 The composition consists of 18 parts of polyethylene wax, 12 parts of diamond micro powder (average particle size 3μm), and 3 parts of diamond micro powder (average particle size 3μm). The porosity of the porous sintered matrix is ​​40%; the damping mixture accounts for 18% of the total weight of the pencil lead.

[0025] Preparation method: (1) Mixing and paste preparation: Graphite powder, bentonite, mica powder, sodium carboxymethyl cellulose and water are ball-milled and mixed to obtain a uniform paste; (2) Molding and sintering: The paste is extruded into slender green core strips through a mold, and after being dried at low temperature to remove most of the free water, it is sintered at high temperature in an inert atmosphere at 920℃ for 2 hours to obtain a porous sintered matrix with a porosity of 40%. (3) Preparation of damping mixture impregnation liquid: Add polyethylene wax to mineral oil, heat and stir continuously until the polyethylene wax is completely melted to form a uniform oil-wax mixture. Keep the temperature constant and stir, and add diamond micro powder at a feeding rate of 0.3 g / min. After the feeding is completed, continue stirring until the particles are completely suspended to obtain a stable damping mixture impregnation liquid. (4) Vacuum impregnation: The porous sintered matrix is ​​immersed in the damping mixture impregnation liquid and vacuum impregnated for 60 min at a temperature of 70℃ and a vacuum degree of -0.08MPa. After impregnation, it is naturally cooled to room temperature to obtain pencil lead.

[0026] Performance testing: The finished product has a coefficient of friction of 0.32. The damping is moderate and gentle, resulting in smooth application and easy color application (see...). Figure 1 c. Easy to apply color, does not scratch the paper, high concentration), excellent pen control for beginners, writing lines that are even and solid, without flaking, broken cores, or scratching the paper. See Table 1 for details.

[0027] Example 2: Strong Damping Beginner Pencil Lead and its Preparation Method Pencil lead formula: The pencil lead consists of a porous sintered matrix and a damping mixture that is filled into the pores of the matrix by vacuum impregnation; The porous sintered matrix is ​​prepared by weight of 55 parts graphite powder (average particle size 20 μm), 22 parts bentonite (average particle size 15 μm), 5 parts mica powder, 7 parts sodium carboxymethyl cellulose (Ashland Bonvi, model C1592), and 11 parts water. The medium-sized graphite and bentonite are only used to construct highly interconnected pores to store damping components, without relying on powder to increase paper surface friction, thus ensuring continuous lubrication and easy color removal. The damping mixture, by weight, consists of a base grease (silicone oil, kinematic viscosity 500 mm). 2 The composition consists of 18 parts of polyethylene wax, 12 parts of silicon carbide micro powder (average particle size 4μm), and 5 parts of silicon carbide micro powder (average particle size 4μm). The porosity of the porous sintered matrix is ​​40%; the damping mixture accounts for 18% of the total weight of the pencil lead.

[0028] Preparation method: Same as in Example 1.

[0029] Performance testing: The finished product has a coefficient of friction of 0.41, stronger damping and lag, sufficient oil and wax lubrication, and rich coloring when writing. It is suitable for young children who are not yet stable in their hand strength and are just beginning to write. It does not scratch the paper or damage the notebook. See Table 1 for details.

[0030] Example 3: Lightly damped everyday beginner writing pencil lead and its preparation method: Pencil lead formula: The pencil lead consists of a porous sintered matrix and a damping mixture that is filled into the pores of the matrix by vacuum impregnation; The porous sintered matrix is ​​prepared by weight of 55 parts graphite powder (average particle size 20 μm), 22 parts bentonite (average particle size 15 μm), 5 parts mica powder, 7 parts polyvinyl alcohol (1788, Wanwei High-Tech), and 11 parts water. The medium-sized graphite and bentonite are only used to construct highly interconnected pores to store damping components, without relying on powder to increase paper surface friction, thus ensuring continuous lubrication and easy color removal. The damping mixture, by weight, consists of a base oil (polyol synthetic ester oil (PriEco 3026 polyol ester, Shanghai Nake Lubrication Technology Co., Ltd.), with a kinematic viscosity of 200 mmHg). 2 The composition consists of 18 parts of zirconia powder (average particle size 1 μm), 12 parts of microcrystalline wax, and 2 parts of spherical zirconia micro powder (average particle size 1 μm). The porosity of the porous sintered matrix is ​​42%; the damping mixture accounts for 20% of the total weight of the pencil lead.

[0031] Preparation method: Same as in Example 1.

[0032] Performance testing: The finished product has a coefficient of friction of 0.28, with gentle damping and a thin profile. It has sufficient lubricating components and is not prone to drying out after long periods of writing. It is suitable for primary school students in the lower grades to practice writing and write new characters in class. See Table 1 for details.

[0033] Comparative Example 1 (Common Improvement Solution on the Market: Significantly Increased Powder Particle Size, No Lead Core Impregnation, No Reinforcing Filler, and No Damping Mixture Impregnation Process) The porous sintered matrix raw materials, by weight, consist of: 55 parts graphite powder (average particle size 50 μm), 22 parts bentonite (average particle size 50 μm), 7 parts sodium carboxymethyl cellulose (Ashland Bonvi, model C1592), and 11 parts water; impregnation process without reinforcing fillers or damping mixture. This formulation attempts to improve the poor pen control of smooth pen leads by increasing the particle size of graphite and bentonite to 50 μm and relying on the contact of ultra-large hard powders with the paper surface to increase friction. Sintering process: Sintering at 920℃ for 2 hours, without vacuum impregnation step; Performance testing: Dynamic friction coefficient 0.45; writing is dry and choppy, with very little graphite transfer, resulting in light lines that are difficult to color; 50μm ultra-large hard mineral particles are directly exposed, severely scratching the paper and roughening the practice paper during writing (see...). Figure 1 a. Scratching paper, low concentration); it is very easy to shed crumbs when cutting, and the core breaks frequently. The writing resistance is stiff and lacks softness and lag, making it difficult for beginners to control the pen, and the handwriting is crooked and out of control. See Table 1 for details.

[0034] Comparative Example 2 (Low-oil single-layer impregnation smooth children's pencil, low friction and no damping) Porous sintered matrix raw materials by weight: 55 parts graphite powder (average particle size 12μm), 22 parts bentonite (average particle size 10μm), 7 parts sodium carboxymethyl cellulose (Ashland Bonvi, model C1592), 11 parts water; no reinforcing filler. Sintering process: sintering at 920℃ for 2 days; Only impregnated with low-viscosity mineral oil (kinematic viscosity 30 mm). 2 / s), free of micro-adhesive wax and friction-controlled particles.

[0035] Performance testing: Dynamic friction coefficient 0.17; excessively slippery with no damping, making it extremely easy for young children to slip and veer off course (see...). Figure 1 b) Smooth and undamped; the oil is easily separated and lost, and it dries quickly after a short period of writing, with obvious fluctuations in line depth; without a buffer damping layer, it is completely unsuitable for children learning to write. See Table 1 for details.

[0036] Comparative Example 3: Non-impregnated ultra-large particle size sintered lead core (industry-widened powder friction enhancement solution) The raw material ratio of the porous sintered matrix (parts by weight) is as follows: 55 parts graphite powder (average particle size 50 μm), 22 parts bentonite (average particle size 50 μm), 5 parts mica powder, 7 parts sodium carboxymethyl cellulose (Ashland Bonvi, model C1592), and 11 parts water; the sintering process is sintering at 920℃ for 2 hours without any vacuum impregnation treatment with damping mixture impregnation liquid. This comparative example deliberately enlarges the particle size of graphite and bentonite to 50 μm, relying on ultra-large hard powder to enhance paper surface friction, without an internal oil and wax damping buffer system.

[0037] Performance testing: The coefficient of friction is 0.55, the writing resistance is stiff and dry, it is difficult to apply ink, there are many obvious scratches on the paper, the pen control stability of beginner children is extremely poor, the sharpening of the pen produces slight shavings, and the lines are uneven in thickness. See Table 1 for details.

[0038] Comparative Example 4: Pencil lead impregnated only with base oils Porous sintered matrix raw material ratio (parts by weight): graphite powder 55 parts (average particle size 20 μm), bentonite 22 parts (average particle size 15 μm), mica powder 5 parts, sodium carboxymethyl cellulose (Ashland Bonvi, model C1592) 7 parts, water 11 parts; sintering process is the same as in Example 1; only base mineral oil (kinematic viscosity 350 mmHg) is impregnated. 2 / s), without the addition of micro-adhesive wax and friction-modifying particles.

[0039] Performance testing: The coefficient of friction is 0.18, the damping effect is lacking, the hand feel is slippery and floaty, and it is very easy for young children to slip when writing. After a long time of writing, the oil is consumed and it dries quickly, which cannot meet the needs of beginners to practice writing. See Table 1 for details.

[0040] Comparative Example 5: Base oil + slightly sticky wax combination pencil lead Porous sintered matrix raw material ratio (parts by weight): 55 parts graphite powder (average particle size 20μm), 22 parts bentonite (Average particle size 15μm), 5 parts mica powder, 7 parts sodium carboxymethyl cellulose (Ashland Bonvi, model C1592), 11 parts water; sintering process is the same as in Example 1; the damping mixture impregnation liquid contains only 18 parts base oil (Kunlun No. 5 industrial white oil, kinematic viscosity 350 mmHg). 2 / s), 12 parts microcrystalline wax, without added friction-regulating particles.

[0041] Performance testing: The coefficient of friction is 0.21, which does not reach the target soft damping range. The writing resistance is inconsistent, and the damping uniformity is poor. The thickness of the lines written by children fluctuates significantly. See Table 1 for details.

[0042] Example 1: The pencil leads from the above examples and comparative examples were tested under a standard environment of 23°C and 60% relative humidity. Ten leads were randomly selected from each sample group for testing, and the arithmetic mean was taken. Writing and appearance performance were performed in accordance with GB / T 26704-2011 "Pencils". The results are shown in Table 1.

[0043] Table 1

[0044] The test results in the table above show that: Examples 1, 2, and 3, and Comparative Examples 4 and 5 use medium-sized (20μm / 15μm) graphite and bentonite matrix formulations, only changing the composition of the damping mixture impregnation liquid; Comparative Examples 3 and 1 deliberately enlarged the graphite and bentonite particle size to 50μm, without an impregnation damping system, relying on the direct friction of ultra-large hard powders to increase resistance on the paper surface; Comparative Example 2 uses a commercially available small-particle-size smooth matrix. The particle sizes of the matrix powders in each group are clearly distinguishable, and the performance differences are determined solely by the damping mixture system and the powder particle size, which proves two points: 1. Simply enlarging the graphite and bentonite particle size to 50μm can only rigidly increase paper surface friction, failing to form gentle damping, and also bringing defects such as severe paper scratching, color difference, and difficulty in pen control; 2. The gentle and controllable damping and easy coloring characteristics come from the ternary damping mixture filling the pores, rather than the graphite and bentonite matrix powder itself. Using kinematic viscosity 100~800 mm 2 The pencil lead, made by vacuum impregnation and filling a damping mixture composed of a base oil, micro-adhesive wax, and 0.5~5μm ultrafine friction-regulating particles, can stably achieve a target soft damping range of 0.25~0.45. This perfectly solves the defects of the industry that result from scaling up graphite and bentonite to 50μm, such as high frictional resistance, dryness, and paper scratching. It is specially designed for children learning to write, and its overall writing performance is far superior to existing conventional children's pencils and single-component modified products.

[0045] Example 2: Customer test and evaluation (only for children learning to write) The standard damping pencil lead prepared by this invention (Example 1) was subjected to a 30-day multi-dimensional test and evaluation on young beginners learning to write.

[0046] Assessment of lower elementary school children (60 students aged 5-8 who have just started writing): After practicing writing for 30 minutes every day, feedback showed that the writing was smooth and without any sticking, and the characters were clearly colored; the damping force was moderate, and the writing did not slip or become crooked like ordinary smooth pencils; the hand did not need to be deliberately controlled, and there was no soreness or fatigue in the wrist during long periods of writing practice; the pencil did not break or shed any lead during sharpening, and the writing notebook was free of scratches and lint; parents reported that their children's enthusiasm for writing practice had significantly increased.

[0047] Evaluation of children's penmanship beginners (15 teachers from children's calligraphy training institutions): Compared with 50μm large-diameter high-friction pencils and ordinary smooth children's pencils on the market, this product has uniform and stable lag damping, making it easier for young children to control the beginning and end of strokes. The transition between horizontal, vertical, left-falling, and right-falling strokes is natural, and the lines are uniform in thickness. It does not have the problems of traditional 50μm large-diameter lead pencils, such as difficulty in writing, scratching the paper, and dryness and whitening after writing for a long time. It is suitable for toddlers and lower grade children to learn penmanship.

[0048] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A pencil lead with controllable writing damping, characterized in that, The pencil lead consists of a porous sintered matrix and a damping mixture that is filled into the pores of the matrix by vacuum impregnation; The porous sintered matrix is ​​prepared by weight of 45-65 parts graphite powder, 15-28 parts bentonite, 3-10 parts reinforcing filler, 4-12 parts temporary binder, and 10-25 parts water; the reinforcing filler is selected from at least one of mica powder, boron nitride, and diatomaceous earth. The damping mixture, by weight, consists of 10-30 parts of base grease, 5-20 parts of micro-adhesive wax, and 1-8 parts of friction-regulating particles; the friction-regulating particles are selected from at least one of diamond micro powder, silicon carbide micro powder, and spherical zirconia micro powder. The porosity of the porous sintered matrix is ​​25-45%; the damping mixture accounts for 8-22% of the total weight of the pencil lead.

2. The pencil lead according to claim 1, characterized in that, The average particle size of graphite powder is 12~25μm, and the average particle size of bentonite powder is 8~18μm.

3. The pencil lead according to claim 1, characterized in that, The base oil is selected from one or two of silicone oil, mineral oil, and synthetic ester oil; its kinematic viscosity is 100~800 mm. 2 / s.

4. The pencil lead according to claim 1, characterized in that, The temporary binder is selected from at least one of starch, polyvinyl alcohol, sodium carboxymethyl cellulose, and dextrin.

5. The pencil lead according to claim 1, characterized in that, The micro-adhesive wax is selected from at least one of paraffin wax, microcrystalline wax, and polyethylene wax.

6. The pencil lead according to claim 1, characterized in that, The average particle size of the friction-controlled particles is 0.5~5μm.

7. The method for preparing pencil lead according to any one of claims 1-6, characterized in that, The method is performed according to the following steps: (1) Mixing and paste preparation: Graphite powder, bentonite, reinforcing filler, temporary binder and water are ball-milled and mixed to obtain a uniform paste; (2) Molding and sintering: The paste is extruded into slender green core strips through a mold, dried at low temperature, and then sintered at high temperature in an inert atmosphere to obtain a porous sintered matrix with a porosity of 25~45%; (3) Preparation of damping mixture impregnation liquid: Add micro-sticky wax to the base oil, heat and stir continuously until the micro-sticky wax is completely melted to form a uniform oil-wax mixture. Keep the temperature constant and stir, and add friction control particles at a feeding rate of 0.1~0.5 g / min. After the feeding is completed, continue stirring for 30~60 min until the particles are uniformly suspended to obtain a stable damping mixture impregnation liquid. (4) Vacuum impregnation: The porous sintered matrix is ​​immersed in the damping mixture impregnation liquid for vacuum impregnation. After impregnation, it is naturally cooled to room temperature to obtain pencil lead.

8. The method according to claim 7, characterized in that, In step (2), the high-temperature sintering temperature is 850~1050℃ and the time is 1.5~3h.

9. The method according to claim 7, characterized in that, In step (3), heat to 50~90℃.

10. The method according to claim 7, characterized in that, The vacuum impregnation conditions in step (4) are: temperature of 50~90℃, vacuum degree of -0.06 ~ -0.09MPa, and time of 30~90min.

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