CN113150618B - Colored pencil lead and preparation method thereof - Google Patents
Colored pencil lead and preparation method thereof Download PDFInfo
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- CN113150618B CN113150618B CN202110218184.9A CN202110218184A CN113150618B CN 113150618 B CN113150618 B CN 113150618B CN 202110218184 A CN202110218184 A CN 202110218184A CN 113150618 B CN113150618 B CN 113150618B
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- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
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Abstract
The invention discloses a colored pencil lead and a preparation method thereof, belonging to the field of lead manufacturing. The method comprises the following steps: blending the polyurethane prepolymer with the terminal isocyanate group, zinc stearate, barium sulfate, magnesium sulfate whisker, calcium carbonate, talcum powder and pigment, and then mixing and reacting to obtain a reaction system; dissolving polyvinyl alcohol in water to prepare polyvinyl alcohol colloid, adding the polyvinyl alcohol colloid into the obtained reaction system, and continuously mixing and reacting to obtain a dough-like blend; processing the obtained blend according to the production process of the pencil lead to obtain a colored resin pencil lead; wherein, polyurethane prepolymer with end group isocyanate group and polyvinyl alcohol are used as adhesive. The colored pencil lead prepared by the method can be subjected to chemical reaction with the filler by using the adhesive, so that the adhesive effect is improved, the interference on the color developing agent is small, and the colored pencil lead has higher flexural strength and writing fluency.
Description
Technical Field
The invention belongs to the field of lead core manufacturing, and particularly relates to a colored pencil core and a preparation method thereof.
Background
The color pencil lead is a stationery widely used in daily life and study. With the continuous development of consumer demands, the market demands more and more for very thin pencil leads used by mechanical pencils. The smaller the diameter of the pencil lead, the poorer the flexural strength, which has an influence on the fluency of use. Different from the traditional black lead core, the color lead core mainly takes toner as a coloring agent, the toner and a filling agent are bonded by an adhesive, and the color lead core is prepared by the processes of mixing, grinding, extrusion molding and the like. The adhesive determines the mechanical properties of the product, and in order not to affect the smoothness of writing and the vividness of color, the adhesive needs to provide the maximum enhancement effect under a small enough adding amount, and the transparency of the adhesive needs to be high so as not to interfere the color development effect of the toner.
The currently used adhesives mainly comprise resin materials such as phenolic resin, epoxy resin, polyvinyl chloride and the like. It is proposed in the patent publication No. CN110387166A to use polystyrene as a binder added to colored pencil leads to enhance the flexural strength of the product. There are also patents that polyurethane resin is used as adhesive to improve the mechanical properties of the product. However, these methods are only simple to mix the resin and the powder together, and although the method has an effect of enhancing the mechanical properties of the pencil lead, since the inorganic filler and the resin do not have a chemical reaction, the compatibility is poor and the dispersion is not uniform, a larger amount of the resin is often required to affect the smoothness of the product when the product is used. Moreover, the performance of the pencil lead can be changed only by changing the addition amount of the resin when a single resin is used, and the pencil lead cannot adapt to ever-changing market demands.
At present, the production performance of the colored thin pencil lead in China still cannot meet the market demand, so that a proper adhesive is selected, and a novel preparation method of the colored pencil lead with adjustable performance is found, so that the method has important practical significance for the current pencil lead market development in China.
Disclosure of Invention
The invention provides a colored pencil lead and a preparation method thereof, aiming at solving the problem that the mechanical property of the colored pencil lead is not good and the performance is not adjustable.
In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:
the invention discloses a preparation method of a colored pencil lead, which comprises the following steps:
a. mixing the polyurethane prepolymer with the terminal isocyanate group, 4-8 parts by mass of zinc stearate, 20-25 parts by mass of barium sulfate, 15-20 parts by mass of magnesium sulfate whiskers, 20-30 parts by mass of calcium carbonate, 5-12 parts by mass of talcum powder and 5-10 parts by mass of pigment, and then mixing and reacting to obtain a reaction system;
b. b, dissolving polyvinyl alcohol in water to obtain polyvinyl alcohol colloid, adding the polyvinyl alcohol colloid into the reaction system obtained in the step a, and continuously mixing and reacting to obtain a dough-shaped blend;
c. c, sequentially carrying out roller refining, rod beating, core extruding, core drying and oil immersion on the blend obtained in the step b to obtain a colored pencil core;
wherein, polyurethane prepolymer with end group isocyanate group and polyvinyl alcohol are used as adhesive.
Preferably, the temperature of the mixing reaction in the step a is 70-80 ℃ and the time is 0.5-4 h.
Preferably, the mixing reaction in step b is continued for 0.5 to 2 hours.
Preferably, the isocyanate-terminated polyurethane prepolymer is prepared by: 1) Uniformly mixing 8-12 parts by mass of isocyanate and 10-15 parts by mass of polyol to obtain a monomer mixture, adding 0.03-0.05 part by mass of catalyst into the monomer mixture, uniformly mixing, and performing polycondensation reaction to obtain a mixed system; 2) Adding 0.5-2 parts of polyhydroxy crosslinking agent into the mixed system obtained in the step 1) to continue reaction to prepare the polyurethane prepolymer with the terminal isocyanate group.
Further preferably, the polycondensation reaction temperature in the step 1) is 70-80 ℃, and the reaction time is 2-4 h.
Further preferably, the reaction is continued in step 2) for a period of 2 to 4 hours.
Further preferably, the isocyanate in step 1) comprises isophorone diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate.
Further preferably, the polyol in step 1) comprises polytetramethylene glycol 1000, polyoxypropylene diol 1000, polyoxypropylene triol 3000.
Further preferably, the polyhydroxy crosslinking agent in step 2) may be pentaerythritol, trimethylolpropane or a blend of pentaerythritol and trimethylolpropane in various ratios.
Preferably, the amount of the terminal isocyanate group-containing polyurethane prepolymer is 5 to 8 parts by mass.
Preferably, the polyvinyl alcohol is added in an amount of 3 to 6 parts by mass.
The invention discloses a colored pencil lead prepared by the preparation method.
Preferably, when the diameter specification of the colored pencil lead is 0.5mm, the bending strength is 364-410 MPa, and the dynamic friction coefficient is 0.256-0.297.
Preferably, when the diameter of the colored pencil lead is 0.7mm, the bending strength is 478-503 MPa, and the dynamic friction coefficient is 0.285-0.298.
Compared with the prior art, the invention has the following beneficial effects:
the invention discloses a preparation method of a colored pencil lead, which comprises the steps of introducing a polyurethane prepolymer with an isocyanate group at the end group and high-molecular-weight polyvinyl alcohol as an adhesive into a mixed filler of zinc stearate, barium sulfate, barium chloride, magnesium sulfate, calcium carbonate, talcum powder and toner, and fully reacting the isocyanate group with the end group, the surface of the solid filler and hydroxyl groups carried by the polyvinyl alcohol to prepare the colored pencil lead with the required diameter. Compared with the traditional preparation method of the colored pencil lead, the method has the advantages that the adopted binder can fully and tightly bond the filler, and the compatibility between the inorganic filler and the binder is improved, so that the function of the filler is fully exerted on the premise of not influencing the writing smoothness and the color vividness, and the mechanical property of the colored pencil lead is enhanced. Meanwhile, the preparation method is simple and convenient to operate, does not need to introduce new equipment, saves the cost and can meet various requirements of the market.
Furthermore, the preparation operation of the polyurethane prepolymer with the end group isocyanate group enables the structure and the performance of the polyurethane prepolymer to be adjustable, and the performance of the produced colored pencil lead can be controllably adjusted by adjusting the synthesis conditions of the polyurethane prepolymer.
The invention takes the polyurethane prepolymer with the end group isocyanate group and the polyvinyl alcohol with high molecular weight as the adhesive of the colored pencil lead, and has the following advantages:
(1) The isocyanate group can react with the hydroxyl group on the surface of the filler and the hydroxyl group of the polyvinyl alcohol, so that the solid filler can be bonded more closely, the compatibility and the interface bonding property between the inorganic filler and the adhesive are enhanced, and the reinforcing effect of the filler and the adhesive is fully exerted, so that the mechanical property of the colored lead core can be obviously improved under the condition of small addition amount, and the writing smoothness of the product is ensured.
(2) The prepared polyurethane prepolymer with the end group isocyanate group and polyvinyl alcohol have high transparency, and can be used as an adhesive to be added into a colored pencil lead without covering the color of a color developing agent, so that the writing trace of the colored pencil lead is more bright.
(3) The polyurethane prepolymer of the terminal isocyanate group has structural adjustability, the structure and the performance of the adhesive can be effectively changed through the change of the preparation raw materials, and the final mechanical property of the pencil lead is determined by the adhesive, so that the prepared colored pencil lead has good performance adjustability and can quickly meet the ever-changing market demand. The method for adjusting the performance of the product is simple, the operability is strong, new equipment and process are not needed, and the production cost can be effectively reduced.
Furthermore, the reaction degree of the adhesive can be effectively adjusted through the selection of the polyhydroxy crosslinking agent, so that the crosslinking degree can be regulated and controlled, the overall crystallinity of the obtained colored pencil lead can be effectively influenced, and the method can be suitable for processing the lead leads with different diameters.
The invention also discloses a colored pencil lead, which takes the polyurethane prepolymer with the end group isocyanate group and the polyvinyl alcohol as the adhesives, and can chemically react with the filler when the polyurethane prepolymer with the end group isocyanate group is used as the adhesives, so that the adhesive effect is improved, the interference to the color-developing agent is small, and the colored pencil lead has higher flexural strength and writing fluency. Secondly, the polyurethane structure in the polyurethane prepolymer based on the terminal isocyanate group has adjustability, the adjustment of the structure of the polyurethane prepolymer is realized by adjusting the adding amounts of the raw materials and the cross-linking agent during the preparation of the polyurethane prepolymer based on the terminal isocyanate group, and the performance of the colored pencil lead is determined by the performance of the adhesive, so that the adjustment of the performance of the colored pencil lead can be realized.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, the technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It is noted that the terms first, second and the like in the description and in the claims of the present invention are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
A preparation method of colored pencil leads comprises the following steps:
(1) Firstly, adding 8-12 parts by mass of isocyanate monomer and 10-15 parts by mass of polyol monomer into a reaction kettle, controlling the reaction temperature to be 40-50 ℃, uniformly stirring, then adding 0.03-0.05 part by mass of catalyst, stirring for 10-60 min, heating to 70-80 ℃, and continuing to react for 2-4 h. Finally, 0.5 to 2 parts of polyhydroxy crosslinking agent is added into the mixed system to continue to react for 2 to 4 hours, thus preparing the polyurethane prepolymer with the end group isocyanate group.
(2) Firstly, the polyurethane prepolymer with end group isocyanate group is mixed with zinc stearate, barium sulfate, magnesium sulfate whisker, calcium carbonate, talcum powder and pigment, and then stirred and reacted for 0.5 to 4 hours at the temperature of 70 to 80 ℃. Then adding polyvinyl alcohol colloid dissolved in 1-2 parts of water into the reaction system, and continuing to react for 0.5-2 h under the reaction condition to obtain the dough-like blend. And finally, carrying out roller refining, rod beating, core extruding, core drying, oil immersion and the like on the blend according to the production and processing technology of the traditional pencil core to prepare the colored pencil core with excellent comprehensive performance.
The performance of the resin lead core can be adjusted by adjusting the type of the polyhydroxy crosslinking agent in the step (1). Wherein the polyhydroxy crosslinking agent in step (1) may be pentaerythritol, trimethylolpropane or a blend of pentaerythritol and trimethylolpropane in various ratios.
The resin lead core performance can be adjusted by adjusting the type of isocyanate in the step (1). Wherein the isocyanate in the step (1) comprises isophorone diisocyanate, diphenylmethane diisocyanate and toluene diisocyanate.
The performance of the resin lead can be adjusted by adjusting the type of the polyol in the step (1). Wherein the polyol of the step (1) comprises polytetramethylene glycol 1000, polyoxypropylene diol 1000 and polyoxypropylene triol 3000.
Wherein the ratio (R value) of the amount of the substance of the isocyanate to the amount of the substance of the hydroxyl group in the polyol and the hydroxyl crosslinking agent in the step (1) is 1.8 to 2.5.
Wherein the addition amount of the polyurethane prepolymer with the terminal isocyanate group in the step (2) is 5-8 parts by weight.
Wherein in the step (2), the addition amount of the polyvinyl alcohol is 3-6 parts by mass.
Wherein the adding amount of the filler in the step (2) is calculated by mass parts, zinc stearate is 4-8 parts, calcium carbonate is 20-30 parts, talcum powder is 5-12 parts, magnesium sulfate whisker is 15-20 parts, barium sulfate is 20-25 parts, and pigment is 5-10 parts.
A colored pencil lead with a polyurethane colored resin lead with adjustable performance is prepared by the method.
The diameter specification range of the colored pencil lead is 0.2-5.6 mm.
The diameter specifications of the colored pencil lead are 0.5mm and 0.7mm.
When the diameter specification of the colored pencil lead is 0.5mm, the bending strength is 364-410 MPa, and the dynamic friction coefficient is 0.256-0.297.
When the diameter of the colored pencil lead is 0.7mm, the bending strength is 478-503 MPa, and the dynamic friction coefficient is 0.285-0.298.
In order to make the technical means, the creation features and the achieved effects of the present invention more intuitive, the present invention is further described below with reference to the specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes and modifications can be made by one skilled in the art after reading the disclosure set forth herein, and equivalents may fall within the scope of the invention as defined by the claims appended hereto.
Example 1
(1) Firstly, 12 parts by mass of isophorone diisocyanate and 10 parts by mass of vacuum-dried polytetramethylene glycol 1000 are added into a reaction kettle. And controlling the reaction temperature to be at 50 ℃, uniformly stirring, then adding a proper amount of 0.03 part of dibutyltin dilaurate serving as a catalyst, stirring for 30min, heating to 75 ℃, and continuing to react for 3h. And finally, cooling to 70 ℃, adding 0.5 part of pentaerythritol into the mixed system, and continuously reacting for 2 hours to prepare the polyurethane prepolymer of the terminal group isocyanate.
(2) Firstly, 6 parts by weight of the prepared polyurethane prepolymer with the end group isocyanate group, 5 parts of zinc stearate, 25 parts of calcium carbonate, 5 parts of talcum powder, 20 parts of magnesium sulfate, 25 parts of barium sulfate and 8 parts of red toner are blended, and then stirred and reacted for 0.5 hour at the temperature of 75 ℃. Then, 5 parts of polyvinyl alcohol colloid dissolved in 2 parts of water was added to the above reaction system, and the reaction was continued for 1 hour under the above reaction conditions to obtain a batter-like mixture. And finally, carrying out roller refining, rod beating, core extruding, core drying, oil immersion and other treatments on the blend according to the traditional lead core production process to prepare the colored pencil core with excellent comprehensive performance.
Tests show that the resin pencil lead prepared by the embodiment has very good mechanical property and lubricating property, and is bright in color and not easy to fade. When the diameter of the pencil lead is 0.528mm, the flexural strength is 410MPa, and the dynamic friction coefficient is 0.289. When the diameter of the pencil lead is 0.721mm, the flexural strength is 503MPa, and the dynamic friction coefficient is 0.298. Since this example adds only a tetrafunctional crosslinker, the pencil lead of this example has greater strength and lower toughness, and the method is suitable for use with finer pencil leads.
Example 2
(1) Firstly, adding 12 parts by mass of isophorone diisocyanate and 11 parts by mass of vacuum-dried polytetramethylene glycol 1000 into a reaction kettle, controlling the reaction temperature, uniformly stirring at 50 ℃, then adding a proper amount of 0.05 part of dibutyltin dilaurate serving as a catalyst, stirring for 30min, and heating to 75 ℃ to continue to react for 3h. And finally, cooling to 70 ℃, adding 1.5 parts of trimethylolpropane into the mixed system, and continuing to react for 2 hours to obtain the polyurethane prepolymer with the end group isocyanate group.
(2) Firstly, 8 parts by weight of the prepared polyurethane prepolymer with the terminal isocyanate, 6 parts by weight of zinc stearate, 24 parts by weight of calcium carbonate, 8 parts by weight of talcum powder, 20 parts by weight of magnesium sulfate, 24 parts by weight of barium sulfate and 7 parts by weight of pigment are blended, and then stirred and reacted for 0.5 hour at the temperature of 75 ℃. Then, 6 parts of a polyvinyl alcohol colloid dissolved in 1.5 parts of water was added to the above reaction system. And continuously reacting for 1h under the reaction conditions to obtain a pasty mixture. And finally, carrying out roller refining, rod beating, core extruding, core drying, oil immersion and other treatments on the blend according to the traditional lead core production process to prepare the colored pencil core with excellent comprehensive performance.
Tests show that the resin pencil lead prepared by the embodiment has very good mechanical property and lubricity, the diameter of the pencil lead is 0.536mm, the bending strength is 364MPa, and the dynamic friction coefficient is 0.269. When the diameter of the pencil lead is 0.719mm, the flexural strength is 478MPa, and the coefficient of dynamic friction is 0.285. The pencil lead of this example has greater toughness and lower strength due to the addition of only a trifunctional crosslinking agent, and is suitable for use with thicker pencil leads and wood pencil leads.
Example 3
(1) Firstly, adding 12 parts by mass of isophorone diisocyanate and 11 parts by mass of polybutylene glycol 1000 subjected to vacuum drying into a reaction kettle, controlling the reaction temperature to be uniformly stirred at 50 ℃, then adding a proper amount of 0.03 part of dibutyltin dilaurate serving as a catalyst, and stirring for 30 min. The temperature is increased to 75 ℃ and the reaction is continued for 3h. And finally, cooling to 70 ℃, adding 1.2 parts of trimethylolpropane and 0.2 part of pentaerythritol into the mixed system, and continuously reacting for 2 hours to obtain the polyurethane prepolymer with the end group isocyanate group.
(2) Firstly, 8 parts by weight of the polyurethane prepolymer of the terminal isocyanate, 6 parts by weight of zinc stearate, 25 parts by weight of calcium carbonate, 10 parts by weight of talcum powder, 15 parts by weight of magnesium sulfate, 24 parts by weight of barium sulfate and 10 parts by weight of red toner are mixed together and stirred to react for 0.5 hour at the temperature of 75 ℃. Then, 6 parts of a polyvinyl alcohol colloid dissolved in 2 parts of water was added to the above reaction system. And continuously reacting for 1h under the reaction conditions to obtain a pasty mixture. And finally, carrying out roller refining, rod beating, core extruding, core drying, oil immersion and other treatments on the blend according to the traditional lead core production process to prepare the colored pencil core with excellent comprehensive performance.
Tests show that the resin pencil lead prepared by the embodiment has very good mechanical property and lubricating property, and when the diameter of the pencil lead is 0.517mm, the bending strength is 396MPa, and the dynamic friction coefficient is 0.297. When the diameter of the pencil lead is 0.709mm, the flexural strength is 495MPa, and the dynamic friction coefficient is 0.287. The pencil lead of this example has greater toughness and lower strength due to the addition of only a trifunctional cross-linking agent, and the method is suitable for various specifications of mechanical pencil leads and wood pencil leads.
Example 4
(1) Firstly, 11 parts of diphenylmethane diisocyanate and 12 parts of vacuum-dried polytetramethylene glycol 1000 are added into a reaction kettle in parts by mass, and the temperature is controlled to be 50 ℃ and the mixture is uniformly stirred. Then, an appropriate amount of 0.04 parts of dibutyltin dilaurate as a catalyst was added thereto and the mixture was stirred for 30 min. The temperature is increased to 75 ℃ and the reaction is continued for 3h. And finally, cooling to 70 ℃, adding 1.1 part of trimethylolpropane and 0.4 part of pentaerythritol into the mixed system, and continuously reacting for 2 hours to obtain the polyurethane prepolymer with the end group isocyanate group.
(2) And (2) blending 7 parts of the prepared polyurethane prepolymer of the terminal isocyanate, 7 parts of zinc stearate, 23 parts of calcium carbonate, 9 parts of talcum powder, 15 parts of magnesium sulfate, 23 parts of barium sulfate and 8 parts of red toner in parts by mass. The reaction was stirred at 75 ℃ for 0.5h. Then, 5 parts of a polyvinyl alcohol colloid dissolved in 1.7 parts of water was added to the above reaction system. And continuously reacting for 1 hour under the reaction condition to obtain a pasty mixture. And finally, carrying out roller refining, rod beating, core extruding, core drying, oil immersion and other treatments on the blend according to the traditional lead core production process to prepare the colored pencil core with excellent comprehensive performance.
Tests show that the resin pencil lead prepared by the embodiment has very good mechanical property and lubricity, the bending strength is 403MPa and the dynamic friction coefficient is 0.287 when the diameter of the pencil lead is 0.522 mm. When the diameter of the pencil lead is 0.726mm, the flexural strength is 487MPa, and the dynamic friction coefficient is 0.295. In the embodiment, diphenylmethane diisocyanate is used as a raw material to prepare the polyurethane prepolymer with the terminal isocyanate group, and the prepared prepolymer has high crystallinity due to more regular raw materials, so that the prepared prepolymer has better transparency and relatively better mechanical property. The prepared pencil lead is bright in color and good in mechanical property, and is suitable for producing thinner automatic pencil leads.
Example 5
(1) First, 11 parts by mass of diphenylmethane diisocyanate and 12 parts by mass of vacuum-dried polyoxypropylene glycol 1000 were added to a reaction kettle, and the mixture was stirred uniformly at a controlled temperature of 50 ℃. Then, an appropriate amount of 0.04 parts of dibutyltin dilaurate as a catalyst was added thereto and the mixture was stirred for 30 min. The temperature is increased to 75 ℃ and the reaction is continued for 3h. And finally, cooling to 70 ℃, adding 1.1 part of trimethylolpropane and 0.4 part of pentaerythritol into the mixed system, and continuously reacting for 2 hours to obtain the polyurethane prepolymer with the end group isocyanate group.
(2) Firstly, 8 parts by mass of the polyurethane prepolymer of the terminal isocyanate prepared above is blended with 8 parts by mass of zinc stearate, 25 parts by mass of calcium carbonate, 10 parts by mass of talcum powder, 17 parts by mass of magnesium sulfate, 24 parts by mass of barium sulfate and 8 parts by mass of red toner. The reaction was stirred at 75 ℃ for 0.5h. Then, 5 parts of a polyvinyl alcohol colloid dissolved in 1 part of water was added to the above reaction system. And continuously reacting for 1h under the reaction conditions to obtain a pasty mixture. And finally, carrying out roller refining, rod beating, core extruding, core drying, oil immersion and other treatments on the blend according to the traditional lead core production process to prepare the colored pencil core with excellent comprehensive performance.
Tests show that the resin pencil lead prepared by the embodiment has very good mechanical property and lubricating property, the bending strength is 394MPa and the dynamic friction coefficient is 0.256 when the diameter of the pencil lead is 0.509 mm. When the diameter of the pencil lead is 0.705mm, the flexural strength is 471MPa, and the dynamic friction coefficient is 0.278. In the embodiment, diphenylmethane diisocyanate and polyoxypropylene diol are used as raw materials to prepare the polyurethane prepolymer with the terminal isocyanate group, and the polyoxypropylene diol 1000 has a long chain segment, so that the prepared prepolymer has more soft segments, and has good transparency and relatively good flexibility. The pencil lead is bright and soft in color, and is suitable for producing thick automatic pencil leads and wooden pencil leads.
Example 6
(1) First, 12 parts by mass of diphenylmethane diisocyanate and 15 parts by mass of vacuum-dried polyoxypropylene triol 3000 are added to a reaction kettle, and the temperature is controlled to be 50 ℃ and the mixture is stirred uniformly. Then, an appropriate amount of 0.04 part of dibutyltin dilaurate was added as a catalyst and stirred for 30 min. The temperature is increased to 75 ℃ and the reaction is continued for 3h. And finally, cooling to 70 ℃, adding 0.5 part of pentaerythritol into the mixed system, and continuously reacting for 2 hours to obtain the polyurethane prepolymer with the end group isocyanate group.
(2) Firstly, 7 parts by mass of the polyurethane prepolymer of the terminal isocyanate prepared above is blended with 8 parts by mass of zinc stearate, 25 parts by mass of calcium carbonate, 10 parts by mass of talcum powder, 17 parts by mass of magnesium sulfate, 24 parts by mass of barium sulfate and 8 parts by mass of red toner. The reaction was stirred at 75 ℃ for 0.5h. Then, 4 parts of a polyvinyl alcohol colloid dissolved in 1 part of water was added to the above reaction system. And continuously reacting for 1h under the reaction conditions to obtain a pasty mixture. And finally, carrying out roller refining, rod beating, core extruding, core drying, oil immersion and other treatments on the blend according to the traditional lead core production process to prepare the colored pencil core with excellent comprehensive performance.
Tests show that the resin pencil lead prepared by the embodiment has very good mechanical property and lubricity, when the diameter of the pencil lead is 0.533mm, the bending strength is 400MPa, and the dynamic friction coefficient is 0.290. When the diameter of the pencil lead is 0.721mm, the flexural strength is 499MPa, and the dynamic friction coefficient is 0.289. In the embodiment, diphenylmethane diisocyanate and polyoxypropylene triol 3000 are used as raw materials to prepare the polyurethane prepolymer with the terminal isocyanate group, and the polyoxypropylene triol 3000 has high molecular weight and provides a certain crosslinking degree, so that the prepared prepolymer has high molecular weight and high crosslinking degree, and has good mechanical properties. The manufactured pencil lead has high color flexural strength and is suitable for producing various specifications of automatic pencil leads and wooden pencil leads.
Example 7
(1) First, 8 parts by mass of toluene diisocyanate and 15 parts by mass of vacuum-dried polyoxypropylene glycol 1000 were added to a reaction kettle, and the temperature was controlled to be 45 ℃ and stirred uniformly. Then, an appropriate amount of 0.04 parts of dibutyltin dilaurate as a catalyst was added thereto and the mixture was stirred for 60 min. The temperature is increased to 80 ℃ and the reaction is continued for 2h. And finally, cooling to 70 ℃, adding 1 part of trimethylolpropane and 1 part of pentaerythritol into the mixed system, and continuing to react for 3 hours to obtain the polyurethane prepolymer with the end group isocyanate group.
(2) Firstly, 8 parts by mass of the polyurethane prepolymer of the terminal isocyanate prepared above is blended with 4 parts by mass of zinc stearate, 20 parts by mass of calcium carbonate, 12 parts by mass of talcum powder, 17 parts by mass of magnesium sulfate, 20 parts by mass of barium sulfate and 10 parts by mass of red toner. The reaction was stirred at 80 ℃ for 2h. Then, 3 parts of a polyvinyl alcohol colloid dissolved in 1 part of water was added to the above reaction system. And continuously reacting for 0.5h under the reaction conditions to obtain a pasty mixture. And finally, carrying out roller refining, rod beating, core extruding, core drying, oil immersion and other treatments on the blend according to the traditional lead core production process to prepare the colored pencil core with excellent comprehensive performance.
Tests show that the resin pencil lead prepared by the embodiment has very good mechanical property and lubricating property, the diameter of the pencil lead is 0.710mm, the bending strength is 493MPa, and the dynamic friction coefficient is 0.286. Because the embodiment simultaneously uses the cross-linking agent with three functionality and four functionality, the pencil lead has certain flexural strength and toughness, the toluene diisocyanate has good regularity, the prepared polyurethane prepolymer has high transparency, the pencil lead has bright color and strong writing flexibility, and the pencil lead is suitable for producing thicker automatic pencil leads and wooden pencil leads.
Example 8
(1) Firstly, 10 parts by mass of toluene diisocyanate and 15 parts by mass of vacuum-dried polyoxypropylene triol 3000 are added into a reaction kettle, and the temperature is controlled to be 40 ℃ and the mixture is stirred uniformly. Then, an appropriate amount of 0.05 part of dibutyltin dilaurate as a catalyst was added thereto and stirred for 10 min. The temperature is increased to 70 ℃ and the reaction is continued for 4h. And maintaining the temperature at 70 ℃, adding 0.5 part of trimethylolpropane and 1.5 parts of pentaerythritol into the mixed system, and continuously reacting for 4 hours to obtain the polyurethane prepolymer with the end group isocyanate group.
(2) Firstly, 5 parts by mass of the polyurethane prepolymer of the terminal isocyanate prepared above is blended with 4 parts by mass of zinc stearate, 30 parts by mass of calcium carbonate, 12 parts by mass of talcum powder, 17 parts by mass of magnesium sulfate, 20 parts by mass of barium sulfate and 5 parts by mass of red toner. The reaction was stirred at 70 ℃ for 4h. Then, 3 parts of a polyvinyl alcohol colloid dissolved in 1 part of water was added to the above reaction system. And continuously reacting for 2 hours under the reaction conditions to obtain a pasty mixture. And finally, carrying out roller refining, rod beating, core extruding, core drying, oil immersion and other treatments on the blend according to the traditional lead core production process to prepare the colored pencil core with excellent comprehensive performance.
Tests show that the resin pencil lead prepared by the embodiment has very good mechanical property and lubricating property, the diameter of the pencil lead is 0.753mm, the bending strength is 494MPa, and the dynamic friction coefficient is 0.288. In this embodiment, since the trifunctional and tetrafunctional cross-linking agents are used, and the tetrafunctional cross-linking agents are more, the hardness and toughness of the lead core are higher, and the flexural strength is higher. The prepared polyurethane prepolymer has high transparency, bright lead color and strong writing flexibility, and is suitable for producing thick automatic pencil leads and wooden pencil leads.
Although the above examples only give the results of studies on 0.5 and 0.7mm thin lead cores, experiments prove that the method is also suitable for preparing pencil cores with diameters of 0.2mm, 0.3mm, 0.7mm, 0.9mm, 1.0mm, 1.3mm, 1.8mm, 2.0mm, 2.2mm, 2.6mm, 2.8mm, 3.0mm, 3.4mm, 4.0mm, 5.6mm and other specifications, and the enhancement effect is also obvious.
In terms of product performance, the resin pencil lead prepared by the invention has the advantages of excellent mechanical property, good writing lubricity and bright coloring. Meanwhile, the performance of the resin pencil lead can be changed according to requirements by changing the structure of the introduced polyurethane prepolymer. The method has the characteristics of simple operation, good product performance, environmental friendliness and the like, and is suitable for future large-scale production.
In summary, the invention introduces a preparation method of a colored pencil lead. Which comprises the following steps: firstly, a polyurethane prepolymer with isocyanate groups at the terminal groups is prepared. And then blending the polyurethane prepolymer with a certain mass part of zinc stearate, barium sulfate, magnesium sulfate whisker, calcium carbonate, talcum powder and pigment at 70-80 ℃ for reaction for 0.5-4 h, adding polyvinyl alcohol colloid dissolved in a small amount of water, and continuing the reaction for 0.5-2 h to obtain the dough-like blend. Then the treatments of roller refining, rod beating, core extruding, core drying, oil soaking and the like are carried out according to the traditional lead core production process to prepare the color lead core. The end group isocyanate group polyurethane prepolymer adopted by the invention can be used as an adhesive to perform chemical reaction with the filler, and has excellent adhesive effect and small interference on a color developing agent. Compared with the traditional method, the colored pencil lead product has higher flexural strength and writing fluency. Meanwhile, the performance of the product can be adjusted by adjusting the structure of the polyurethane prepolymer, the operation is simple and convenient, new equipment is not required to be introduced, the cost is saved, and the polyurethane prepolymer can meet various requirements of the market.
The above examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention. Further, it should be understood that various changes and modifications can be made by one skilled in the art after reading the disclosure set forth herein, and equivalents may fall within the scope of the invention as defined by the claims appended hereto.
The above contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention should not be limited thereby, and any modification made on the basis of the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.
Claims (8)
1. A preparation method of a colored pencil lead is characterized by comprising the following steps:
a. blending the polyurethane prepolymer with the terminal isocyanate group, zinc stearate, barium sulfate, magnesium sulfate whisker, calcium carbonate, talcum powder and pigment, and then mixing and reacting to obtain a reaction system;
b. b, dissolving polyvinyl alcohol in water to obtain polyvinyl alcohol colloid, adding the polyvinyl alcohol colloid into the reaction system obtained in the step a, and continuously mixing and reacting to obtain a dough-shaped blend;
c. c, processing the blend obtained in the step b according to the production process of the pencil lead to obtain a colored pencil lead;
wherein, polyurethane prepolymer of end group isocyanate group and polyvinyl alcohol are used as adhesive; the additive amount of each component is as follows according to the mass portion: 5-8 parts by mass of polyurethane prepolymer with end group isocyanate group, 3-6 parts by mass of polyvinyl alcohol, 4-8 parts by mass of zinc stearate, 20-25 parts by mass of barium sulfate, 15-20 parts by mass of magnesium sulfate whisker, 20-30 parts by mass of calcium carbonate, 5-12 parts by mass of talcum powder and 5-10 parts by mass of pigment;
the polyurethane prepolymer with the terminal isocyanate group is prepared by the following steps:
1) Uniformly mixing 8-12 parts of isocyanate and 10-15 parts of polyol by mass to obtain a monomer mixture, adding 0.03-0.05 part of catalyst into the monomer mixture, uniformly mixing, and carrying out polycondensation reaction to obtain a mixed system;
2) Adding 0.5-2 parts of polyhydroxy crosslinking agent into the mixed system obtained in the step 1) to continue reacting to prepare the polyurethane prepolymer with the terminal isocyanate group.
2. The method for preparing a colored pencil lead according to claim 1, wherein the isocyanate in step 1) comprises isophorone diisocyanate, diphenylmethane diisocyanate, and toluene diisocyanate.
3. The method for preparing a colored pencil lead according to claim 2, wherein the polyol in step 1) comprises polytetramethylene glycol 1000, polyoxypropylene triol 3000.
4. The method for preparing a colored pencil lead according to claim 2, wherein the polyhydroxy crosslinking agent in step 2) is pentaerythritol, trimethylolpropane or a blend of pentaerythritol and trimethylolpropane.
5. The method for preparing a colored pencil lead according to claim 2, wherein the polycondensation reaction is carried out at a temperature of 70 ℃ to 80 ℃ for 2 to 4 hours.
6. A colored pencil lead obtained by the production method according to any one of claims 1 to 5.
7. The colored pencil lead according to claim 6, wherein the colored pencil lead has a bending strength of 364-410 MPa and a dynamic friction coefficient of 0.256-0.297 at a diameter of 0.5 mm.
8. A colored pencil lead according to claim 6, characterized in that the bending strength is 478-503 MPa and the coefficient of dynamic friction is 0.285-0.298 when the diameter of the colored pencil lead is 0.7mm.
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