JPH04164978A - Manufacture of color pencil lead - Google Patents

Abstract

PURPOSE:To obtain a good color pencil lead having high strength and high density and excellent in color forming properties by oxidizing a color pencil lead material filled with carbon fibers when it is extruded and baked at high temperature, and filling an ink into the formed pores. CONSTITUTION:In the manufacture of a color pencil lead wherein an ink is filled into the pores of a sinter obtained by kneading and baking a sinterable color pencil lead material, the pencil lead material is filled with carbon fibers and extruded, oxidized to remove the carbon fibers before or after baking at high temperature, and an ink is filled into the obtained pores. This pencil lead has high porosity for its strength and is dense and excellent in color forming properties. Further, since a series of continuous pores can be obtained, the ink can sufficiently penetrate deep into the interior of the pencil lead body to thereby give a color pencil lead having a very high density. Also, in spite of its high porosity, it has high strength. In this manufacturing method, the control of porosity can be facilitated, and the process control is very easy.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a sintered colored lead core, and more specifically, the present invention relates to the use of carbon fiber as a pore-forming material to make it porous. This is a characteristic feature.

[Conventional technology]

So-called sintered colored lead cores conventionally consist of a core made of a bulking material such as boron nitride, a binder such as clay, and heat-resistant pigment added as needed, and a dye contained in the pores of this core. It was impregnated with ink to form a colored lead core. At this time, the important characteristics of the colored lead core are not only strength, but also a dark color with particularly excellent coloring properties. However, conventional colored lead cores do not have sufficient density and color development. Therefore, in order to achieve the above purpose,
Various methods are known for making the core porous, based on the idea that it is sufficient to increase the amount of ink impregnated into the core while maintaining sufficient strength to withstand writing. Examples include: 1) A resin is added to the extender and the binder, and during firing the resin is sublimed or burned in an oxidizing atmosphere to make it porous. (Tokuko Shou 64-4555, Sho 5l-413
76) 2) Use carbon particulate material as a pore-forming material and remove it by oxidation to make it porous. (Unexamined Japanese Patent Publication No. 1986-61- [Problems to be Solved by the Invention]) The core obtained by the method 1) is certainly more porous than the core obtained without adding resin. However, that look,
The density is still not sufficient.

The reason for this seems to be that the diameter of the pores after the resin is removed is extremely small, making it difficult for ink to penetrate deep into the pores, and at the same time, the absolute amount of ink is small. Therefore, if a large amount of resin is used to make the material even more porous, the strength will be significantly degraded, making it unusable.

There are also the following problems. In other words, when a pyrolyzable or sublimable resin is used as a pore-forming material in the colored lead core, before the inorganic binder that is the colored lead core material shrinks,
These resins sublime and decompose at about 200 to 300°C.

In other words, in the case of resin, its molecular shape is linear and two-dimensional bonds, so the molecules easily break together, and the reactivity is high, so decomposition and sublimation begin at a relatively low temperature. Furthermore, thermally decomposable and thermally sublimable resins contain oxygen and hydrogen and are therefore more easily oxidized. Therefore, after the resin is scattered, the binding material shrinks to around 1000 degrees Celsius, and the pores that have already been obtained become smaller, shredded, or crushed, making it difficult for them to exhibit sufficient effects as pores. There is a problem that. Therefore, it is difficult to ensure the desired porosity and control becomes difficult. In addition, the method of making it porous by oxidation treatment takes a long time to sufficiently remove the carbonized components present inside the sintered material.
Furthermore, if the treatment is carried out at a high temperature in order to complete the process in a short time, it may cause cracking or swelling of the sintered body.

Method 2) is a method to solve the above problem, and because pores are obtained according to the diameter of the carbon particulate material, a much larger pore diameter and porosity can be obtained compared to method 1).

Therefore, as the pore size becomes larger, it becomes easier for ink to enter the pores, and a large amount of the pores can be filled, which is a desirable characteristic.

However, even in this method, the powders are dispersed in the core without any relation to each other, so the efficiency of the pores is extremely reduced. Therefore, in order to have efficient pores, the pores must be continuous, but this requires a large amount of particulate matter, which results in a loss of strength and makes it unusable. . Further, for the above-mentioned reasons, there is also the problem that it is difficult to control the porosity and obtain stability of the core diameter. Furthermore, carbon powder is removed by oxidation treatment, but it is difficult to remove all the powder dispersed in the core, and the material itself before being filled with ink becomes ash.
This tends to result in a blackish color, making it difficult to obtain a colored lead core with a vivid color.

In addition, a common problem with 1) and 2) is that when the resin or carbon is diffused, it is diffused from the side of the core, so when these pores are impregnated with ink, the ink solvent evaporates from the side of the core. As a result, stability over time tends to deteriorate.

In short, if you try to improve the density and color development, which are the problems with conventional colored lead cores, the strength will become unusable.
Color development deteriorates.

[Means to solve the problem]

The present invention solves the above problem by filling carbon fibers into a colored lead core material, removing the carbon fibers by oxidation treatment during firing after extrusion, and impregnating ink into the resulting pores. By doing so, it is possible to obtain a colored lead core with high strength, high concentration, excellent color development, and good change over time.
This provides a manufacturing method with easy process control.

Next, the method for manufacturing the colored lead core of the present invention will be specifically explained.

The colored lead core material used in the present invention includes all conventionally known materials used for colored lead cores, including white materials such as titanium oxide, mica, talc, boron nitride, silica, alumina, and calcium carbonate. Depending on the hue, colored materials such as molybdenum disulfide and tungsten disulfide can also be used, and these can be used alone or in combination depending on the purpose of use. Furthermore, a heat-resistant pigment may be added as necessary. Further, as the inorganic binder for baking the structural material, for example, clays such as kaolinite, sericite, montmorite, bentonite, zeolite, diatomaceous earth, activated clay,
Examples include silica, aluminum phosphate, silicone resin, silicone rubber, etc., and these can be used alone or in combination. Furthermore, a colored lead core material may be used, for example, using boron oxide as an inorganic binder, molded and then fired in a nitrogen atmosphere. Note that these inorganic structural materials and inorganic binding materials may overlap each other depending on the usage situation, and there are also substances that are the same that are classified into both of the above.

Furthermore, an organic polymer compound may be added in addition to the above-mentioned extender and inorganic binder. By adding it, the bonding strength during extrusion is improved. Examples of the organic polymer compound include waxes, synthetic resins, natural resins, natural and synthetic rubbers, depolymerized resins, pitch, asphalt, and the like.

Next, when kneading and extruding the colored lead core material and the inorganic binder, carbon fibers are filled. At this time, carbon fibers include not only so-called carbonaceous fibers, but also graphite fibers, as well as carbon whiskers, graphite whiskers, and the like.

In particular, since the whiskers are thin, there is very little breakage due to shear stress during kneading and molding, so the shape stability in the longitudinal direction is good, the strength is improved, and the pores can be controlled more easily.

The method for filling carbon fibers is to add short fibers when kneading with one three-roll kneader and then knead and extrude, or to fill carbon fibers by using a crosshead method to fill carbon fibers with a filler material and an inorganic binder. When extruding the mixed wire material, there is a method in which long fibers are simultaneously extruded while being contained in the mixed wire material, and any method may be used.

The outer diameter of the carbon fiber is arbitrary, and may be set appropriately depending on the purpose or the properties of the ink so that a large amount of ink can be impregnated with the balance with strength. In other words, when impregnating highly viscous dye ink, resin-added ink, or ink whose main component is pigment with large particle size, use carbon fiber with a large outer diameter to facilitate impregnation. good. By using this ink,
A colored lead core with superior color density and color development can be obtained, and its durability can also be improved. In this case, the outer diameter is preferably 0.05 μm or more, for example. Of course, in the case of ordinary ink or ink with low viscosity, there is no problem even if the thickness is 0.05 μm or less.

Further, there is no set limit for the outer diameter, and it needs to be set appropriately depending on the viscosity of the ink. If the ink has a high viscosity, a relatively large outer diameter is required. The outer diameter at that time is, for example, 100 μm or less, particularly 50 μm.
m or less is preferable in relation to strength.

The amount of carbon fiber added is also arbitrary and may be set appropriately depending on the strength and diameter of the fiber, but preferably 10 to 80% by weight based on the total components in order to provide efficient continuous pores.
, particularly preferably 10 to 60% by weight. If it is less than 10% by weight, single pores are likely to form and it becomes difficult to remove by oxidation treatment, and if it is more than 80% by weight, it becomes easy to break due to strength.

After extruding a colored lead core material containing carbon fiber, it is fired at a high temperature. When firing, oxidation treatment is performed to remove carbon fibers.The firing method is to sinter the inorganic binder in an inert gas and then oxidize it, or to oxidize it and then oxidize it. The inorganic binder may be sintered in an inert gas. Furthermore, it is also possible to remove the fibers and sinter the inorganic binder at the same time by performing oxidation treatment alone. The oxidation treatment temperature in the above firing method is preferably approximately 500°C or higher. Carbon fiber is an aggregate of microcrystals made of three-dimensionally bonded carbon, so it does not decompose when heated. Furthermore, it is resistant to oxidation. That is, since the carbon fibers are oxidized after the inorganic binder has shrunk to a considerable extent, pores having approximately the same shape as the carbon fibers are obtained.

The higher the porosity of the core obtained by the above method, the better, and it is necessary to set it appropriately from the viewpoint of strength and density.
In particular, 30 to 80% is good.

Below 30%, the strength is strong but the concentration is poor, and 80%
If the concentration is higher than that, the concentration will become higher, but the strength will deteriorate.

Next, ink is impregnated into the pores obtained by the above method. The impregnation method involves immersing the sintered body in ink and allowing it to penetrate into the pores under conditions such as heating, reduced pressure, and pressurization.

Further, the ink used in the present invention may be any ink that easily penetrates into pores by the above-mentioned impregnation method and has the property of filling most pores, such as colorants such as dyes and pigments. Commonly used printing ink manufactured by dissolving or dispersing in animal and vegetable oils, synthetic oils, alcohols, hydrocarbon oils, water, etc., or by further adding resins, surfactants, etc. as necessary. , stamp ink, ballpoint pen ink, water-based writing ink, etc. are used. In particular, by selecting the diameter of the carbon fibers, the pores obtained in the present invention can be used for inks containing high viscosity dyes or high molecular weight dyes, inks containing pigments, etc., which were previously difficult to fill. Can be easily filled. By filling these inks, colored lead cores with little change over time and excellent density and color development can be obtained.

〔Example〕

Example 1 30 parts of boron nitride as a structural material, 30 parts of clay as an inorganic binder, and carbon fiber (outer diameter 12 μm 1 length 3 mm) 3
0 parts and 1 in which 10 parts of polyvinyl alcohol was dissolved.
In addition to 0.00 parts of water, the mixture was kneaded using three rolls of a kneader to adjust the moisture content. This was extruded into a thin wire shape to produce an extruded material with a colored lead core. Next, 10 pieces of this colored lead core extruded material
After drying at 0°C for 24 hours or more, the temperature was increased to 900°C at a temperature increase rate of 50°C/hr in an inert atmosphere, and the temperature was increased to 900°C for 1
The clay was sintered and the polyvinyl alcohol was carbonized by firing for an hour. Next, the heating rate was 100°C/hr in air.
The temperature was raised to 700°C, and the carbon content was removed by firing at 700°C for 5 hours to obtain a white porous sintered body. According to SEM observation, this porous sintered body had continuous pores with a diameter comparable to that of the filled carbon fibers.

Next, the porous sintered body was immersed in red ballpoint pen ink and left at 70° C. under reduced pressure for 24 hours. The porous sintered body impregnated with this ink was washed with alcohol to complete a red colored lead core with a nominal size of 0.9 nonΦ.

Comparative Example 1 Instead of the carbon fiber in Example 1, graphite with a particle size of 5 μm was added, a porous sintered body was formed in the same process as in Example 1, and it was impregnated with red ink to form a red colored lead core. was created.

〔Effect of the invention〕

The results of comparing the performance of Example 1 and Comparative Example 1 are shown in the following table.

Color development of handwriting: Comparison of samples drawn with a 30og load.

Light resistance of handwriting + A sample marked with a 300 g load was placed under a fluorescent lamp at a distance of 30 cm and exposed for one month.

As shown in the table above, the colored lead core of the present invention has a high porosity in relation to its strength, is dark, and has excellent color development. Furthermore, it has the following various features.

1. Since one continuous hole is obtained, the ink can sufficiently penetrate deep into the core, resulting in a colored lead core with extremely high concentration.

2. Despite the high porosity, the colored lead core of the present invention has high strength. The reason for this is not clear, but for example, when fine powder such as conventional graphite is added, the fine powder is uniformly dispersed in the core, so when the fine powder is removed after firing, voids are created between the core materials. Therefore, it is thought that a strong bond cannot be obtained.On the other hand, in the case of the present invention, only the fiber portion is hollow, so the core body has a cellular structure, which makes it a strong skeleton. .

3. Since the diameter of the pores can be made larger than that of conventional pores, it can be easily impregnated with inks containing high viscosity dyes, high molecular weight dyes, and pigment inks, which were difficult to impregnate until now. An excellent colored lead core can be obtained.

4. If there are pores on the side of the core, as with conventional colored lead cores, the ink solvent will change and easily evaporate, resulting in poor stability over time. On the other hand, since the pores of the colored lead core of the present invention are along the orientation axis of extrusion, evaporation of the solvent from the side surface is less likely to occur, resulting in good stability over time.

55 With the colored lead core of the present invention, it is easy to ensure the desired substantial porosity that is approximately the same shape as that of the carbon fiber, and moreover, pores with less variation in shape and diameter can be obtained.

Therefore, the pores can be easily controlled, and the manufacturing method is extremely simple and easy in terms of process control.

Claims (1)

[Claims] 1. In a method for manufacturing a colored lead core, which is obtained by kneading and firing a sintered colored lead core material and filling the pores of the sintered body with ink, carbon fibers are added to the colored lead core material. A method for producing a colored lead core, which is characterized by filling, extruding, oxidizing to remove carbon fibers before or after firing at a high temperature, and filling the resulting pores with ink.