JP2006076040A - Manufacturing method of lead for pencil, colored pencil and mechanical pencil by multiscrew multilayer extrusion method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve relations of inverse correlation that density decreases when flexural strength is enhanced and that the flexural strength lessens when the density is increased, in the manufacture of a lead for a pencil, a colored pencil and a mechanical pencil. <P>SOLUTION: By using a multiscrew extruder having a multilayer die, the lead constituted of a multiple layer of two or more layers is manufactured with the materials or constituents of individual layers or the composition rates thereof varied. While making the best use of the features of physical properties of each layer, balances between the layers are held, and the lead excellent in the overall characteristics of the whole lead is obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a method of manufacturing a pencil core, a color pencil core, and a mechanical pencil core by a multiaxial extrusion method having a multilayer die.

Conventional pencil, colored pencil and mechanical pencil core manufacturing methods include solid writing materials made of carbon, such as graphite, and binders such as organic polymers and clays. In general, after kneading raw materials composed of oil / fat / wax, extender, binder, etc., it is formed into a wire by extrusion molding and dried or fired, or impregnated with fats / oils in a subsequent process to obtain a product. The extruder used here is usually a single screw extruder with a circular head.

Patent No. 3203040

This is a method of manufacturing a pencil for writing or coloring by adopting a three-layer extrusion method for each material of a shaft having a core material, an intermediate protective layer, and a woody material. This is highly productive, in which the core material and the shaft are simultaneously and continuously formed, which is completely different from the conventional manufacturing method.

However, this production method has the purpose of proposing a new method for producing a pencil for writing by simultaneously extruding a core material and a shaft, and is not intended to improve or improve the core itself.

51-38067

We have proposed a method for manufacturing a pencil in which a core is coated with a foamable resin by an extruder equipped with a double-capable crosshead die. However, like the above patent, no modification or improvement of the pencil lead body is proposed.

According to the conventional manufacturing method for a pencil, a colored pencil or a mechanical pencil lead, in order to increase the bending strength of the lead, mainly the method of increasing the strength of the binding material and the density of the drawn line is increased. For this purpose, it has been dealt with by a method such as making the binding material easy to collapse. However, when the bending strength is increased, the concentration decreases, and when the concentration is increased, the bending strength decreases. So-called inverse correlation is generally observed. It has become a big problem to be solved.

In order to solve the above-mentioned problems, a new substance is mainly used for the material constituting the binder mainly for the purpose of improving the physical properties of the core, and the mixing ratio thereof is changed. Or the method of changing the adjustment conditions of an ingredient has been taken.

However, even with the various methods described above, it is very difficult to maintain mechanical strength such as bending strength, tensile strength, and impact strength above a certain level while maintaining a sufficient line density. there were.

In the present invention, in order to solve the above problems, a multi-core multilayer extrusion method is used to manufacture a core for pencils, colored pencils, or mechanical pencils, thereby obtaining a multilayer core. is there.

In each layer constituting the core, by changing the kind and mixing ratio of the raw materials, the physical properties of each layer are adjusted to be different from those of the other layers, and then the core is manufactured by a multilayer extruder.

By adopting this method, each layer can have at least one superior property that other layers do not have. As a result, it is possible to provide a core material having excellent contents of physical properties as a whole core by complementing the defects that the other layers do not have.

In determining the selection of materials, mixing ratio, etc., it is only necessary to consider at least one physical property for only one layer, so that the degree of freedom in design increases.

As described above, by forming a core with multiple layers, in order to manufacture a core having excellent physical properties, which has a high concentration and a high bending strength, which were difficult to achieve with the conventional manufacturing method, For example, the following contents are devised.

Consider the case where the core is composed of two layers. The physical property of the first layer, which is the innermost layer of the core, is a property that focuses on increasing the density of drawn lines. The outer second layer has a property that focuses on physical strength such as bending strength and tensile strength. As a result, a core having the characteristics of two layers, that is, a core having high concentration and high bending strength can be obtained.

According to the production method of the present invention, each layer may individually determine conditions such as selection of materials and composition ratios for the purpose of enhancing individual physical properties. Therefore, there is an advantage that the selection range of each element can be widened from their physical and chemical viewpoints.

However, in actual use, since both the first layer and the second layer are simultaneously transferred onto the paper surface, there is a concern whether a stable and uniform writing feel and handwriting density can be achieved.

In order to avoid the above problems, it is necessary to consider the layer thickness ratio of each layer with respect to the radial direction of the core.

Consider the case of a core composed of two layers as described above. The thickness of the second layer is made thinner than that of the first layer. That is, the drawn line density on the paper surface expressed as the entire core mainly reflects the density of the first layer, while the strength is mainly maintained by the second layer. If the layer thickness of the first layer is increased as shown in this layer thickness ratio, the writing feel when writing on the paper is that the layer thickness of the second layer is thin. It is felt that it dominates the whole. The transfer density on the paper surface reflects the density of the first layer in which the layer thickness dominates.

On the other hand, the nature of the second layer, that is, the hardness in this case, is harder than that of the first layer, but since the layer thickness is thin, a different texture is hardly felt during writing.

In particular, in the case of a lead for a mechanical pencil, generally, it is often a thin lead having a diameter of 1 mm or less. Therefore, in actual writing, all the surfaces of the cross section perpendicular to the length direction come into contact with the target paper surface. In this case, the writing feeling is almost indistinguishable from that of the core using the first layer component alone.

The reason for this is that both the first layer and the second layer are in contact with the paper surface at the same time, so that the component of the first layer acts as an anti-friction material and the component of the second layer contacts the paper surface. It is thought that it works to relieve the feeling of hardness when doing.

On the other hand, in the case of a pencil lead, in the normal usage method of shaving the wood part and putting out the lead, when writing is reduced by about 50% from the tip part of the shaved lead, the writing is stopped and a new shaving is made. Is common. Therefore, the first layer is first transferred to the paper surface, and the second layer is not directly related to the drawn line.

For the above reasons, the second layer mainly serves as a reinforcement for the first layer of the shaved core. It is very rare to use up to the exposed core. Therefore, there is no sense of discomfort in writing due to the difference in physical properties between the first layer and the second layer.

In the above-described example, since the physical properties of the first layer and the second layer are changed, the difference between the apparent expansion and contraction ratios is the main cause after drying or heat-treating the extruded core. Deformation such as bending or twisting may occur.

As a means for solving this problem, an intermediate layer may be inserted between the first layer and the second layer. That is, the difference in elongation between the first layer and the second layer is absorbed by causing the intermediate layer to have a sliding action. This is a relaxation layer.

Since the purpose of the intermediate layer is only to cause a sliding action, it is not necessary to have physical properties related to concentration and strength. This layer thickness may be considerably thinner than either the first layer or the second layer.

The raw material component is preferably a soft substance that retains a sliding action even after molding and heating. For example, it is suitable to use natural rubber, butyl rubber, polystyrene, nylon or the like as a main component and to add talc to this.

Further, as a role of the intermediate layer different from the above, in order to prevent the mutual adhesion due to the difference in the properties of the first layer and the second layer, adhesion may be imparted.

The ratio of the thickness of each layer (distance on the center line in the cut plane perpendicular to the length direction of the core) is 50 to 80% for the first layer and 10 to 30% for the second layer. Is suitably in the range of about 5 to 10%.

Further, consider the case where the core is formed in multiple layers. When writing, it is common to use the axis of a pencil or mechanical pencil slightly inclined with respect to the paper surface. For this reason, the touch of the hand reflects the nature of the outermost layer of the core in No. 1.

Therefore, in order to obtain a smooth feel, the outermost layer of the core may be made of a smooth material having a relatively small hardness as a physical property. In the center layer of the core, a material having properties that govern the apparent density of the core as a whole is placed. The intermediate layer between them is made of a material having the property of maintaining the strength of the core.

Since the intermediate layer is sandwiched between the central layer and the outermost layer having different physical properties, the entire core is likely to be distorted due to the difference in expansion / contraction rate. In order to alleviate this, a relaxation layer is inserted in the layers on both sides in the same manner as described above. As a result, the entire core is composed of five layers.

In the case of five layers, the ratio of the thickness of each layer to the diameter of the core is 30 to 50% for the first layer, 5 to 10% for the second layer, 10 to 30% for the third layer, Suitably the layer is 5 to 10% and the fifth layer is 5 to 20%.

Taking advantage of the feature of the core being composed of multiple layers, the following usage examples can be considered. When writing with a mechanical pencil, especially when a force is applied, the lead may slip through the chuck and enter. In order to prevent this, in order to increase the gripping force of the lead chuck, conventionally, improvement of physical properties on the surface of the lead or application of a substance that easily causes friction has been taken.

In the present invention, in order to improve the gripping property, a fine powder of a frictional inorganic substance is mixed with other constitutional materials in the outermost layer constituent material in which the core contacts the chuck, taking advantage of the multilayer characteristics. The purpose is achieved by molding.

Examples of the inorganic substance include alumina and silica. Unlike the case where these are simply applied to the surface of the core, it is advantageous that these substances do not fall off and the gripping effect can be maintained.

Since this effect is only on the surface where the core contacts the chuck, the layer thickness may be negligible. Usually, 10% or less of the core diameter is sufficient. If this layer is made too thick, it will feel rough during writing and should be avoided.

In the production of the core of the present invention, an extruder is used as in the conventional production method. However, in order to extrude different components in multiple layers at the same time, the die is a multilayer die and the extrusion part uses a multi-screw. In the case of two-layer extrusion, there is a cross-head die or a double-head die, and in the case of three-layer extrusion, there is a cross-head die or a triple-head die.

In the die of the multilayer extrusion molding machine, the thickness of each layer is very small and the layers are close to each other. Therefore, in order to avoid troubles during extrusion, the raw material to be supplied is required to have a higher grade of particle fineness than that supplied to a conventional extruder. In addition, it is necessary to pay sufficient attention to avoid mixing foreign substances as much as possible.

In the present invention, a pencil, a colored pencil, and a mechanical pencil core are manufactured using a multi-layered multi-screw extruder. By using multiple layers, the material / component of each layer and the composition ratio thereof can be selected independently, and the degree of freedom of preparation increases. As a result, it has become possible to change the physical properties of each layer into characteristic ones, and to make the overall characteristics of the entire core excellent as never before. For example, it is possible to obtain a core having both the properties of high bending strength and high concentration.

The best mode for carrying out the invention will be described below.

The example implemented about the core for mechanical pencils comprised by two layers is described below.

The components of the first layer (the inner layer of the core) and the mixing ratio thereof were as follows: 46% by weight of polyvinyl chloride (hereinafter referred to as “% by weight”) as a binder, 40% of graphite, 7% of talc, The material was stearic acid 3%, and the plastic material was dioctyl phthalate 4%.

The components of the second layer (the outer layer of the core) are almost the same as those of the first layer, but the strength is increased by changing the proportion of each component. As binder, 25% by weight of polyvinyl chloride (hereinafter all weight percent), as extender, graphite 35%, talc 9%, clay 15%, as lubricant, stearic acid 3%, as plasticizer, dioctyl phthalate 13%.

The above materials for the first layer and the second layer are adjusted separately. After sufficiently kneading with a three-roll kneader, extrusion molding was performed with a twin-screw extruder having a two-layer extrusion die. After firing at 1000 ° C. in a nitrogen atmosphere, the spindle oil was impregnated.

The diameter of the obtained core is 0.70 mm. The diameter of the first layer is 0.58 mm, and the second layer has an inner diameter of 0.58 mm and an outer diameter of 0.70 mm.

On the other hand, as a comparative example, a core composed of the same components as the first layer and the same mixing ratio was obtained. After kneading and extrusion molding under the same conditions as described above, heat treatment was performed to obtain a core having a diameter of 0.70 mm.

With respect to the above two types of cores, the bending strength and concentration were measured according to the measuring method described in JIS S6005. The results are shown in the following table. All are average values of 15 test results.

Table 1

A comparative test when actually used was conducted. I wrote on the paper and saw how many times the core broke. Seven students were selected for the exam, consisting of 2 junior high school students, 1 high school student, 1 university student, and 3 adults. The length of the lead protruding from the tip of the mechanical pencil was 3 mm longer than that during normal use.

The written characters are “pencil” in Chinese characters, “pencil” in hiragana, and “PENCIL” in English blocks, with a little more emphasis than normal writing. I got it. I wrote 12 times each. The results obtained are shown in the following table. Numbers indicate the number of broken cores.

Table 2

As is apparent from the results in Table 2, the first layer and the second layer shown in the examples are more effective than the case where the core manufactured with the same components and mixing ratio as the first layer shown in the comparative example is used. The wick was harder to break in the case of the wick.

In this example, the lead for a mechanical pencil for firing was shown. However, the present invention is not limited to this, and the invention is not limited to a black lead for firing, a lead for a soft coloring pencil, and a lead for a mechanical pencil. It can also be applied to the manufacture of

Sectional drawing of the core comprised by a 1st layer and a 2nd layer. Sectional drawing of the core comprised by a 1st layer, a 2nd layer, and an intermediate | middle layer. The external view at the time of shaving the pencil with the core comprised by the 1st layer and the 2nd layer.

Explanation of symbols

1 1st layer 2 2nd layer 3 Intermediate layer 4 Wood part

Claims (4)

  Using a multi-axis extrusion molding machine with a multi-layer die, cores for pencils, colored pencils and mechanical pencils consisting of two or more multilayers are manufactured, and the materials and components of each layer and their composition ratios are the same or different. A method for producing a core, wherein each layer after production has the same or different physical properties.   It is a manufacturing method of the core for pencils, colored pencils, and mechanical pencils described in Claim 1, Comprising: A layer is comprised from 2 layers, A 1st layer (inner layer) is a 2nd layer (outside) The second layer has a physical property that is higher in concentration and lower in bending strength than that of the first layer, and that the second layer has a physical property that is lower in concentration and higher in bending strength than the first layer. The manufacturing method of the core characterized by the above.   It is a manufacturing method of the lead for pencils, colored pencils, and a mechanical pencil as described in Claim 2, Comprising: An intermediate | middle layer is provided between the 1st layer and the 2nd layer, and this layer is the 1st layer and the 2nd layer. A core manufacturing method comprising: a component having a function of absorbing a difference in shrinkage ratio between the first layer and the second layer, having a softer physical property and having a buffering function. A method for producing a pencil lead, a colored pencil lead and a mechanical pencil lead according to claim 1, wherein the outermost layer is blended with a fine powder of a frictional inorganic substance to improve the gripping performance of the mechanical pencil lead. A method for producing a lead for a mechanical pencil.

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