JP2013151153A - Ballpoint pen tip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ballpoint pen tip which prevents the following situations: when a radial groove is formed by inserting a cutting tool with cutting blades disposed radially, impact force and pressing force deform a cross sectional shape of a ball holder, an circularity is reduce; and an annular clearance between the ball and a tip opening part differs according to the position of the ballpoint pen tip, an ink discharge amount varies depending on a writing direction, thereby causing gradation of handwriting, an uneven line width and blur of the handwriting.SOLUTION: In a ballpoint pen, a radial ink flowing groove 1 is formed in an inward projecting part which is formed in a through-hole of a ball holder 6 to restrict rearward movement of a ball 7. A ratio of the volume of the radial groove 1 to the volume of the inward projecting part is set to be 0.03-0.12.

Description

  The present invention comprises at least a ball as a writing member and a ball holder that partially protrudes and holds the ball from the tip opening of the through hole, and restricts rearward movement of the ball formed in the through hole of the ball holder. The present invention relates to a ballpoint pen tip in which radial ink passage grooves are formed in an inward projecting portion.

The above-mentioned radial ink passage groove is the narrowest path in the ink path of the ball holder, which restricts the amount of ink supplied and is an important part for ink discharge performance. Therefore, in order to suppress handwriting defects such as blurring, it is known to form a radial groove that communicates with the center hole and penetrates to the rear hole for the purpose of supplying abundant ink around the ball. Also, in the case of a radial groove that communicates with the central hole and does not penetrate the rear hole, it becomes a curved path, so that the outer diameter of the radial groove and the width of the groove are increased, and the ball is the ball transfer surface of the inward protruding portion. It is known that when the seat is seated, the effective radial groove cross-sectional area opened to the outside is increased, but a cutting jig having radially arranged cutting blades called a so-called broach is attached to the front ball. The cross-sectional shape of the ball holding chamber may be deformed by the impact force or the pressing force when forming the radial groove by inserting from the side where the ball is disposed, and the roundness may be impaired.
As a result, the size of the annular gap between the ball and the tip opening varies depending on the position of the opening, so the amount of the gap that is opened differs depending on the writing direction, resulting in a difference in the amount of ink ejected. In some cases, shading of the handwriting, non-uniform line width, blurring of the handwriting, etc. may occur.

  In view of this, JP 2010-221408A (Patent Document 1) provides an impact force such as cutting or pressing between the radial grooves, thereby widening the width of the opening of the radial groove and applying the impact force. A ballpoint pen tip manufacturing method is disclosed in which the side wall portion of the ball holding chamber corresponding to the formed portion is also tilted inward while correcting a deformation of the cross-sectional shape of the ball holding chamber due to the formation of radial grooves. ing.

JP 2010-221408 A

  However, in the invention described in Patent Document 1, it is necessary to apply between the radial grooves an impact force commensurate with the amount of deformation of the ball holding chamber generated by the impact force or pressing force when forming the radial grooves. If the impact force applied between the radial grooves is small, the effect of correcting the deformation of the cross-sectional shape of the ball holding chamber is small, and if the impact force applied between the radial grooves is excessive, the impact force for correction is reduced. The side wall part of the ball holding chamber on the extension line of the received part falls more than necessary, and on the contrary, the deformation increases, resulting in a difference in the amount of ink ejected, the density of the handwriting, and the line width And unevenness of handwriting and scratches of handwriting are difficult to be suppressed.

  The present invention comprises at least a ball as a writing member and a ball holder that partially protrudes and holds the ball from the tip opening of the through hole, and restricts rearward movement of the ball formed in the through hole of the ball holder. A ball-point pen in which a radial ink passage groove is formed in an inward protruding portion formed, and a ball-point pen tip whose ratio of the volume of the radial groove to the volume of the inward protruding portion is 0.03 or more and 0.12 or less To do.

By setting the ratio of the volume of the radial groove to the volume of the inward protruding portion to be 0.12 or less, the amount of distortion proportional to the amount of processing with respect to the volume of the inward protruding portion is relatively reduced, and the portion of the portion where the radial groove is processed It is possible to prevent the inside of the periphery of the side wall portion of the ball holding chamber corresponding to the extension line from falling down.
Also, the smaller the ratio of the volume of the radial groove to the volume of the inward projecting portion, the smaller the amount of distortion proportional to the amount of processing with respect to the volume of the inward projecting portion, but the volume of the radial groove becomes smaller and affects the ink supply. However, when the ratio of the volume of the radial groove to the volume of the inward projecting portion is 0.03 or more, insufficient ink supply to the ball holding chamber can be prevented.

The longitudinal cross-sectional view which showed the dimension location for the volume and volume calculation of this invention. FIG. 2 is a cross-sectional view taken along the line I-I ′ of FIG. 1. The longitudinal cross-sectional view which removed except the internal holding | projection part of this invention. The longitudinal cross-sectional view of an example of the ball-point pen of this invention. The longitudinal cross-sectional view of an example of the ball-point pen tip of this invention. The II section enlarged view of FIG. The longitudinal cross-sectional view which removed except the internal embedding protrusion in the case of the non-penetrating radial groove | channel equivalent to FIG.

The basic structure of a ballpoint pen tip consists of a ball that becomes a writing member that contacts the writing surface such as paper and transfers the ink, and a ball holder that rotatably holds the ball. Ink is applied to the writing surface through the through hole of the ball holder.
The ink passage, which is a through hole of the ball holder, communicates with the inner hole of the ink tank by connecting the ball holder to a member that becomes an ink tank directly or via a connecting member. In addition, the ball holder forms an inward protruding portion in the middle of the ink passage to serve as a ball retraction restricting portion, and the tip opening portion is a crimped portion processed to have a smaller diameter than the ball diameter. Holds the ball and prevents it from slipping out.
In the inward projecting portion, a radial groove communicated with the center hole is divided substantially evenly and arranged circumferentially.
The radial groove communicates with the central hole and does not penetrate to the rear hole (hereinafter referred to as a non-through radial groove) and the radial groove communicates with the central hole and penetrates to the rear hole (hereinafter referred to as a through radial groove). ), But the inward protruding portion is formed by shearing with a cutting jig having cutting blades arranged radially, so that the non-through radial formed by stopping the cutting jig in the middle of the inward protruding portion In the groove, all the processed surfaces become shear surfaces, and the processing resistance increases in proportion to the processing amount, that is, the volume of the radial groove, and the amount of distortion increases.
On the other hand, in the through radial groove formed by penetrating the cutting jig through the rear hole, when the cutting jig penetrates the rear hole, the flesh of the inward projecting portion is broken to have a shear surface and a fracture surface. During shearing, the machining resistance increases in proportion to the machining amount, as in the case of non-penetrating radial grooves, but the processing resistance increases rapidly when fractured, so the ratio of the volume of the radial groove to the volume of the inward protrusion is non-penetrating. In the case of the same as the radial groove, the through radial groove tends to have a larger amount of distortion, and the non-through radial groove can be said to be advantageous for distortion, but the non-through radial groove has a curved path. Therefore, the ink flow is hindered. Increasing the depth of the radial groove, increasing the outer diameter, increasing the width of the radial groove, widening toward the outer shape and widening the opening part as a way to improve ink flow, The volume of the radial groove is increased, the ratio of the volume of the radial groove to the volume of the inward protruding portion is increased, and the amount of distortion is increased.
The radial grooves serve as a path for the ink to flow into the ball holding chamber. If only the ink flow rate is taken into consideration, a large number and a wider width are preferable. The cross-sectional area of the ink passage is preferably 35% or more, but the ratio of the volume of the radial groove to the volume of the inward protruding portion is increased, and the amount of distortion proportional to the processing amount with respect to the volume of the inward protruding portion is increased. .

When not in use, a coil spring is placed in the ink path of the ball holder in order to keep the ball in contact with the tip opening of the ball holder in a circumferential manner and to prevent ink leakage especially when low-viscosity ink is used. And the ball can be urged forward at the tip thereof directly or through a member. The rearward movement of the coil spring can be restricted by caulking the rear end of the ball holder or by applying the rear end of the coil spring to a step formed on the ink tank or the connecting member with the ink tank.
When the coil spring is inserted as described above, the above-described ink passage cross-sectional area is an effective ink passage cross-sectional area obtained by subtracting the cross-sectional area of the tip portion of the coil spring.

The ballpoint pen tip of the present invention is such that the ratio of the volume of the radial groove to the volume of the inward protruding portion is 0.03 or more and 0.12 or less for such a ballpoint pen tip. In the case of a through-radiating groove, the volume is a volume of a portion that is in contact with the outermost part of each of the opening portions before and after the radial groove and is sandwiched by a cross section perpendicular to the axis. Similarly, in the case of a non-penetrating radial groove, the volume of the portion that is in contact with the outermost portion of the front opening portion of the radial groove and the rear opening portion to the center hole of the radial groove and is sandwiched by the transverse section perpendicular to the axis is taken.
The volume (V1) of the part is a non-circularity corresponding to FIG. 1 which is a through radial groove in FIG. 1 and FIG. 2 which is a cross section taken along line II ′ of FIG. As shown in FIG. 7 except for the inward projecting portion that is a through radial groove, the foremost opening of the front opening of the radial grooves 1 and 1 ′ and the rearmost opening of the rear opening of the through radial groove or The volume of the ball holder in the portion sandwiched by the virtual cross section including the rear opening to the center hole of the non-through radial groove.
In the case of the through radial groove, the volume of the center hole (V3) and the volume of the radial groove (V4), and the ball holding chamber side bottom portion, from the volume (V2) of the truncated cone forming the outer shape of the sandwiched portion, It can be calculated as a volume obtained by subtracting the volume (V5) of the front frustoconical recess portion formed at the front end portion of the rear hole and the volume (V6) of the rear frustoconical recess portion.
That is, V1 = V2-V3-V4-V5-V6.
In the case of a non-penetrating radial groove, the volume (V3) of the center hole, the volume of the radial groove (V4), and the ball holding chamber side bottom part from the volume (V2) of the truncated cone forming the outer shape of the sandwiched part Can be calculated as a volume obtained by subtracting the volume (V5) of the concave portion of the front frustoconical shape formed in the above.
That is, V1 = V2-V3-V4-V5.

  In the case of a through radial groove in which the radial groove 1 penetrates the rear hole 13, the transverse sectional diameter at the foremost end position 1ap of the front opening 1a of the radial groove 1 is d1, and the rear end 1b of the rear opening 1b is at the rearmost position 1bp. The cross-sectional diameter is d2, the distance of the cross-section including the front and rear end openings of the front and rear openings of the radial groove 1 is L1, the maximum outer diameter of the radial groove 1 is d3, and the width of the radial groove 1 is W. The number of the radial grooves 1 is N, the diameter of the central hole 2 is d4, the height from the foremost end 1ap of the front opening 1a of the radial groove 1 to the front opening 2a of the central hole 2 is L2, and the radial groove 1 When the height from the rearmost end 1bp of the rear opening 1b to the rear opening 2b of the center hole 2 is L3, and the height of the center hole 2 is L4, the following calculation is performed.

The volume V2 of the truncated cone forming the outer shape of the portion sandwiched by the virtual cross section including the foremost end and the rearmost end opening of each of the openings before and after the radial groove 1 is obtained as follows.
Area of a circle having a cross-sectional diameter d1 at the foremost end position 1ap of the front opening 1a of the radial groove 1 as a diameter (S1) = (d1 / 2) ² × circumference ratio)
Area of a circle having a cross-sectional diameter d2 at the rearmost end position 1bp of the rear opening 1b of the radial groove 1 as a diameter (S2) = (d2 / 2) ² × circumferential ratio)
From the height of the truncated cone L1,
Apply the formula for calculating the volume of the truncated cone 3,
V2 = (S1 + S2 + √S1 × S2) × L1 × 1/3
The volume (V3) of the center hole 2 is
V3 = (d4 / 2) ² × circumference × L4
(L4 = L1-L2-L3)
The volume (V5) of the concave portion 4 of the front frustoconical shape is
Opening area of center hole 2 (S4) = (d4 / 2) ² × circumference ratio)
The inscribed circle area whose diameter is the maximum outer diameter of the radial groove 1 is
(S3) = (d3 / 2) ² × circumference ratio)
Than,
V5 = (S3 + S4 + √S3 × S4) × L2 × 1/3
The volume (V6) of the recessed part 5 of the rear frustoconical shape is
Opening area of center hole 2 (S4) = (d4 / 2) ² × circumference ratio)
Inscribed circle area (S3) = (d3 / 2) ² × circumference ratio) where the maximum outer diameter of the radial groove 1 is the diameter.
Than,
V6 = (S3 + S4 + √S3 × S4) × L3 × 1/3
The volume (V4) of the radial groove 1 is approximately approximate to the volume of a four-column pillar in the vertical cross section of the ball holder 6 with the vertical cross section of the radial groove 1 as the bottom and the groove width as the height.
Therefore, it can be calculated by multiplying the longitudinal sectional area (S5) occupied by the radial groove by the groove width (W) and the number of grooves (N).
That is,
Longitudinal sectional area of radial groove (S5) = (L1 + L4) / 2 × (d3-d4) / 2
V4 = S5 × W × N
based on the above results,
The volume of the inward protruding portion can be calculated by substituting each value into the volume of the inward protruding portion (V1) = V2-V3-V4-V5-V6.

  Further, in the case of a non-penetrating radial groove in which the radial groove 1 ′ is not penetrated through the rear hole 13, the transverse sectional diameter at the foremost end position 1ap of the front opening 1a of the radial groove 1 ′ is d1, and the radial groove 1 ′ The transverse sectional diameter of the rear opening 2b ′ to the center hole 2 of the bottom surface 1b ′ is d2, the frontmost end position 1ap of the front opening 1a of the radial groove 1 ′ and the center hole 2 of the bottom surface 1b ′ of the radial groove 1 ′. The distance of the cross section including the rear opening 2b ′ is L1, the maximum outer diameter of the radial groove 1 ′ is d3, the width of the radial groove 1 ′ is W, the number of the radial grooves 1 ′ is N, and the diameter of the central hole 2 is d4, the height from the foremost end 1ap of the front opening 1a of the radial groove 1 ′ to the front opening 2a of the center hole 2 is L2, and the radial groove from the rear end position 1bp ′ of the bottom surface 1b ′ of the radial groove 1 ′ The rear opening 2b ′ to the center hole 2 of the bottom surface 1b ′ of 1 ′ is L3, in front of the center hole 2 of the radial groove 1 ′. When the height of the rear end position 1bp 'of the bottom surface 1b' of the radial groove 1 'from the opening 2a is L4, the following calculation is performed.

The volume V2 of the truncated cone forming the outer shape of the portion sandwiched by the virtual cross section including the frontmost opening of the front opening of the radial groove 1 ′ and the rear opening to the center hole at the bottom of the radial groove 1 ′ is It is required as follows.
Area of a circle having a cross-sectional diameter d1 at the foremost end position 1ap of the front opening 1a of the radial groove 1 ′ (S1) = (d1 / 2) ² × circumferential ratio)
The area of a circle whose diameter is the cross-sectional diameter d2 in the rear opening 2b ′ to the center hole 2 of the bottom surface 1b ′ of the radial groove 1 ′ (S2) = (d2 / 2) ² × circumference ratio)
From the height L1 of the truncated cone 3,
Apply the formula for calculating the volume of the truncated cone,
V2 = (S1 + S2 + √S1 × S2) × L1 × 1/3 is obtained in the same manner as the above-described through-radiating groove.
The volume (V3) of the center hole 2 is
From the height L5 = L4 + L3 of the center hole 2,
V3 = (d4 / 2) ² × circumferential ratio × L5
The volume (V5) of the concave portion 4 of the front frustoconical shape is
Opening area of center hole 2 (S4) = (d4 / 2) ² × circumference ratio)
The inscribed circle area whose diameter is the maximum outer diameter of the radial groove 1 is
(S3) = (d3 / 2) ² × circumference ratio)
Than,
V5 = (S3 + S4 + √S3 × S4) × L2 × 1/3 is obtained in the same manner as the above-described through-radiation groove.
Note that the volume (V6) of the rear frustoconical recessed portion 5 is not formed because the radial groove 1 ′ is not penetrating into the rear hole 13.
The volume (V4) of the radial groove 1 ′ is approximately similar to the volume of the four-column pillar in the vertical cross section of the ball holder 6 with the vertical cross section of the radial groove 1 ′ as the bottom surface and the groove width as in the vertical cross section of the ball holder 6.
Therefore, it can be calculated by multiplying the longitudinal sectional area (S5) occupied by the radial groove by the groove width (W) and the number of grooves (N).
That is,
Longitudinal sectional area of radial groove (S5) = (L1 + L4) / 2 × (d3-d4) / 2
V4 = S5 × W × N
based on the above results,
The volume of the inward protruding portion can be calculated by substituting each value into the volume of the inward protruding portion (V1) = V2-V3-V4-V5.

In addition to the method of measuring and calculating the dimensions of each part as described above, in the case of a through-radiating groove, the outermost part of each of the openings before and after the radial groove, which is the volume of the inward protruding part, is provided. It can be calculated from the specific gravity of the material obtained by cutting and removing unnecessary portions other than the portion sandwiched by the cross section perpendicular to the axis of contact, and the measured value of the weight of the material. Similarly, in the case of a non-penetrating radial groove, an unnecessary portion other than the portion sandwiched by the transverse section perpendicular to the shaft center is in contact with the outermost portion of the front opening portion of the radial groove and the rear opening portion to the center hole of the bottom surface of the radial groove. It can be calculated from the specific gravity of the material from which the material has been cut off and the measured value of the weight of the material.
In addition, the volume of the liquid that increases when the material is submerged in a liquid such as water or silicone oil can be measured.
As a method for cutting and removing unnecessary portions, the ball pen tip sample is infiltrated into a transparent synthetic resin such as an unsaturated polyester resin, which will be described later in the method of measuring the size of each part of the test ball pen tip sample, and then gradually solidified with sand paper or the like. Unnecessary portions are removed by shaving, and then the resin solidified by a high temperature of 200 ° C. or higher, for example, a gas burner is oxidized and decomposed to be removed.
Note that the volume of the inward projecting portion is very small, and several tens of samples are required to improve measurement accuracy.

The volume of the inward protruding portion described above is a portion that is subjected to machining resistance when forming the radial groove, so that the volume of the inward protruding portion is large and the volume of the radial groove is preferably small. Considering the ink supply to the holding chamber, there is a limit to the adjustment to be a small value, and the effective ink passage cross-sectional area including the central hole and the radial groove needs to be 35% or more with respect to the ball projected cross-sectional area.
In order to increase the volume of the inward projecting portion, it is only necessary to increase the cross-sectional area of the corresponding portion of the material, and as one element thereof, it is only necessary to increase the front outer diameter and rear outer diameter of the ball holder in the corresponding portion, This can be done by adjusting the taper angle that decreases toward the tip of the ball holder. However, if the taper angle that decreases toward the tip is too acute with respect to the axial center, the tip of the ball holder becomes too thick and the tip of the ball holder hits the paper surface during writing, resulting in poor writing feeling and handwriting. Scratching may occur. Further, if the tip wall thickness of the ball holder is made constant and the taper angle is made obtuse with respect to the axis, the taper portion is shortened and visibility is lowered.
In addition, by reducing the center hole diameter, which is another factor, the volume of the center hole can be reduced and the volume of the inward protruding portion can be increased, but as described above, the ink supply to the ball holding chamber Therefore, the size setting is focused on ink supply, and there is a limit to adjustment. In addition, by increasing the length of the central hole, the height of the truncated cone including the inward protruding portion can be increased, the volume of the truncated cone can be increased, and the volume of the inward protruding portion can be increased. The reduction of the center hole diameter and the extension of the length of the radial groove increase the volume of the radial groove with the increase of the volume of the inward projecting portion. Therefore, the volume of the radial groove with respect to the volume of the inward projecting portion is increased. By adjusting each dimension so that the ratio is 0.03 or more and 0.12 or less, deformation of the ball holding chamber at the time of radial groove processing can be suppressed, and insufficient ink supply to the ball holding chamber can be prevented. .

The ball can be a sintered ball mainly composed of tungsten carbide or silicon carbide, and the metal columnar member used as a ball holder is made by cutting a wire made of an alloy such as stainless steel, brass, or white. Although it can be used, it is mainly made of stainless steel material that has high wear resistance at the contact portion between the tip holder and the ball due to corrosion resistance with ink and ball rotation during writing. Austenitic stainless steel with a higher elongation rate than ferritic stainless steel when using a manufacturing method mainly for plastic working that pushes the pin from the side and forms a radial ink passage simultaneously with the formation of the internal protrusion SUS303 and SUS304, which are suitable, are manufactured mainly for cutting such as processing radial grooves with a cutting blade. When employing the method, SUS430 is suitable is a high machinability ferritic stainless steel.
Furthermore, free-cutting stainless steel SF20Т (Shimomura Special Seiko Co., Ltd.), which has improved corrosion resistance to the same extent as SUS303 and improved machinability, is preferable.
Further, a free-cutting stainless steel material that is environmentally friendly while maintaining machinability by replacing lead, which is a component affecting the machinability, with bismuth, is more preferable.
In order to suppress the fall of the bottom of the ball holding chamber to the rear hole side when machining the radial groove that is the ink flow path, and the inside of the periphery of the side wall of the ball holding chamber, processing should be performed. Materials that are easy to handle are desirable, and brass and white that have a shear resistance of about 1/2 that of stainless steel are preferred, but the hardness near the outer periphery is Hv 220 to 280 due to the corrosiveness with ink and the wear of the contact portion with the ball during writing. It is common to use a stainless steel material of a degree, but on the other hand, if the hardness is high, the durability of the cutting jig having cutting blades arranged radially decreases, the shearing force decreases, and the shearing of the work surface decreases. The cutting force is increased and the deformation of the ball holding chamber is facilitated by shortening the surface and increasing the fracture surface. Further, since the processing of the radial groove is formed by cutting the vicinity of the center of the ball holder, it is preferable that the hardness near the outer periphery is about Hv 240 to 270 and the hardness near the center is about Hv 220 to 250.

The through hole of the ball holder is an ink flow path and is formed by a drill or the like.
First, a portion that becomes a central hole is formed in a columnar member with a relatively small-diameter drill, and then a large-diameter portion in front of the ball holding chamber is dug up to a predetermined size from the center hole side with a large-diameter drill. . The length of the center hole is determined by adjusting the cutting depth when forming a large-diameter rear hole with a large-diameter drill from the end of the ball holder opposite to the ball holding chamber. The diameter of the center hole is preferably about 50% of the ball diameter, and the diameter of the ball holding chamber is an inner diameter obtained by adding 0.01 mm to 0.04 mm to the ball diameter, and is appropriately set depending on the viscosity of the ink. In addition, when using a long full-length ball holder, etc., when it is necessary to dig deeper in the rear hole, which is the rear part of the inward protruding part, a large force is required to dig deeper to the end with a large diameter drill. Since the burden on the drill is also large, it is about 0.01 to 0.05 mm except for the formation of a step necessary for function after digging about 3 times or less of the drill diameter with a large diameter drill at first. It is preferable to gradually change the drill so that the diameter becomes smaller as the drill is changed to a smaller diameter, and gradually dig deeper. The cutting depth of each drill is to prevent clogging of the chip into the twisted groove of the chip and to process it. In order to improve the discharge of chips from the object, the drill diameter is preferably 3 times or less the drill diameter. As a method of deep hole machining, there is a process called stepping. For example, after drilling up to 3 times the diameter with a drill of the same diameter, remove the drill from the work piece and insert the drill again up to 0.6 times the machining depth before The operation of machining, further removing the drill from the workpiece, and re-inserting the drill again up to 0.6 times the machining depth before is repeated to obtain a predetermined hole depth.
In order to form a through radial groove that penetrates the radial groove through the rear hole, it is necessary that the cutting jig having the radially arranged cutting blades penetrate the rear hole inclined surface of the inward projecting portion, and the outer diameter of the cutting blade is below With the rear hole diameter, the cutting blade collides with the meat part of the ball holder and cannot penetrate, so the outer diameter of the foremost end of the rear hole is larger than the outer diameter of the cutting blade forming the radial groove, that is, the outer diameter of the radial groove. There is a need to.
The inward projecting portion formed in this way also serves as a part for receiving the processing resistance when forming the radial groove, and therefore it is necessary to set the dimension in consideration of the ratio of the volume of the radial groove to the volume of the inward projecting portion. .
In addition, even when machining is performed by rotating a cutting jig having a cutting blade such as a center hole and a rear hole or rotating a workpiece as a ball holder, the machining resistance may be reduced depending on the machining conditions, although it is not as great as the radial groove forming process. Since it may increase and the workpiece may be deformed, it is desirable to process at a cutting speed and a cutting feed in accordance with the cutting jig material and the workpiece material.

Next, a cutting jig having cutting blades arranged radially is inserted from the ball holding chamber side, and the inward protruding portion is partially peeled off from the step side between the ball holding chamber and the center hole, The portion communicates with the central hole, and a non-penetrating radial groove in which the cutting jig is stopped in the middle of the central hole and is not penetrated through the hole or a through radial groove in which the cutting jig is penetrated through the rear hole is formed.
The cutting blade to be used has a shape in which the cutting blade is formed radially from the central portion, but the overall outer shape is a shape in which a cone of the bottom surface of the same diameter is connected to the tip of a cylinder. If the part corresponding to the cylindrical part forms a so-called back taper that has a slightly smaller diameter in the rear, the resistance during cutting can be reduced, and the ratio of the shear surface length to the radial groove length can be increased, It becomes a so-called cut state, and deformation of the ball holding chamber can be suppressed.
The material of the cutting blade includes die steel, cemented carbide, ultrafine particle cemented carbide, etc., and the balance between hardness and toughness is made appropriate according to the amount of processing. It is better to have a coating of TiC, TiCN, etc. to improve durability and slipperiness with the workpiece, but if the coating film is too thick, the cutting edge becomes rounded and the sharpness is reduced. About a thin film is preferred.
When the opening angle of the tip of the cutting blade forming the radial groove is sharper than the ball holding chamber inclined surface angle, the cutting blade forming the radial groove contacts the ball holding chamber inclined surface from the center hole. As a result, the force that pushes the ball holding chamber radially outward increases, leading to an increase in cutting resistance, which promotes deformation of the ball holding chamber.
By making the opening angle of the tip portion of the cutting blade forming the radial groove an obtuse angle of 10 ° to 20 ° from the ball holding chamber inclined surface angle, the outer shape of the cutting blade forming the radial groove is changed to the ball holding chamber inclined surface. It is preferable that the contact force is suppressed, and the force that pushes the ball holding chamber outward in the radial direction is suppressed, and the cutting force that forms the radial groove increases in the component force that advances in the direction of the inclined surface of the rear hole, thereby reducing the cutting resistance. .

Next, the ball to be a writing member is placed in the ball holding chamber, and the edge portion of the tip opening of the ball holder is subjected to plastic deformation processing called caulking with a pressure welding tool to reduce the diameter to a smaller diameter than the ball diameter. The ball is prevented from coming off.
Subsequently, a so-called hammer process is performed to apply an impact force to the ball with a hammer tool, the ball is shot against the step between the ball holding chamber and the center hole, and is plastically deformed into the shape of the ball to form a concave ball. A space in which the ball can move back and forth is formed simultaneously with the formation of the transfer portion. As a result, when writing, the ball comes into contact with the paper and moves backward, thereby forming a gap through which ink is ejected. Therefore, by adjusting the size of the concave ball transfer portion, the space in which the ball can move back and forth is adjusted, and the ink discharge can be made to an appropriate amount.
Also, by pressing the ball deeply, the size of the concave ball transfer portion is widened, so that the concave ball transfer portion wears due to the rotation of the ball at the time of writing, and an opening is formed at the outer edge of the concave ball transfer portion of the radial groove. Although the decrease in the ink discharge amount due to the decrease in the ink passage to be suppressed can be suppressed, the ratio of the volume of the concave ball transfer portion to the volume of the inward protruding portion is increased similarly to the relationship of the volume of the radial groove to the volume of the inward protruding portion. Since the amount of distortion proportional to the amount of processing with respect to the volume of the side projection increases, and the ball holding chamber is deformed, it is necessary to adjust the size of the concave ball transfer portion as appropriate.
If the caulking process is performed after the step of forming the concave ball transfer portion, a pin is inserted through the rear hole and the ball is pushed up to slightly expand the caulked ball holder tip. It is also possible to form a space that can move back and forth.

As the ink applied to the ballpoint pen using the ballpoint pen tip obtained in the present invention, either water-based ink using water as a main medium or oil-based ink using an organic solvent such as alcohol as a main medium can be used. Pigments and dyes that are coloring components, high-boiling organic solvents for preventing freezing, resin components that provide fixability to the writing surface, surfactants that adjust surface tension, viscoelasticity, lubricity, etc. Saccharides, rust preventives, and antifungal agents are blended, and may be blended with a white hiding component such as titanium oxide for the purpose of correcting typographical errors.
Also, if necessary, such as checking the viscosity or remaining amount of the ink, contact the ink interface to remove gelled products such as α-olefin and polybutene, high viscosity fluids such as silicone oil, etc. that are incompatible with the ink. It is also possible to fill and arrange in layers so as to follow the movement. This high-viscosity fluid can also serve to suppress the backflow of ink.

Hereinafter, an example will be described based on the drawings.
In FIG. 4, the ink holder 8 is joined to the ball holder 6 that rotatably holds the ball 7 as a writing member in a state in which the ball 7 protrudes partially from the tip opening 6 a of the ball holder 6. It is a ballpoint pen body. Although shown as what is called a refill that is housed and used in an exterior body, illustration and description of the exterior are omitted.
The small-diameter portion at the rear end is fixed by being press-fitted into the front end of the ink containing portion 8 which is an extruded pipe such as polypropylene resin.
An ink 9 is accommodated in the ink accommodating portion 8, and a backflow preventing body composition 10, which is a high-viscosity fluid that is incompatible with the ink, is disposed in contact with the rear end interface of the ink 9.

As shown in FIG. 5, which is an enlarged view of the ballpoint pen tip of FIG. 4, a coil spring 11 is disposed inside the ball holder 6 to push the ball 7 from the back and urge it forward. The coil spring 11 is inserted into the ball holder 6, and then pushed into the rear end opening 6 b of the ball holder 6 in a state in which the coil spring 11 is pressed to compress the entire length of the coil spring 11. It is fixed with the end biased.
The coil spring 11 includes a winding portion 11 a that expands and contracts, and a tip straight portion 11 b that rises linearly at the tip, and the tip straight portion 11 b passes through a through hole that is an ink passage of the ball holder 6 and passes through the ball 7. The rear end of the ball holder 6 is directly pressed to bring the ball 7 into contact with the inner edge of the tip opening 6 a of the ball holder 6.

FIG. 6 is an enlarged view of the II part of only the ballpoint pen tip. For convenience of explanation, the outer shape of the ball 7 is indicated by a broken line and shown in a transparent manner.
The ball holder 6 has a ball holding chamber 12, a center hole 2, and a rear hole 13 from the front end side as an ink passage penetrating the cylindrical metal member. An inward protruding portion 14 is formed between the ball holding chamber 12 and the rear hole 13.
The front end opening 6 a of the ball holding chamber 12 is reduced in diameter by caulking, and the reduced diameter front end opening 6 a and the inward projecting portion 14 move the ball 7 in the front-rear direction. The range that can be moved is specified, and when forming the radial groove, it becomes a portion that receives the processing resistance.
Further, the radial grooves 1 are formed in the inward projecting portion 14 in an annular manner at equal intervals. This radial groove 1 is shown as a through radial groove that communicates with the center hole 2 and penetrates the rear hole 13. However, the radial groove 1 communicates with the center hole 2 and is not penetrated into the rear hole 13. It may be a groove.

The inward projecting portion 14 is formed with a concave ball transfer portion 15 by pressing the ball 7, and the concave ball transfer portion 15 is in contact with the paper surface or the like when writing and the ball 7 is retracted. It is intended to stabilize the position of the ball and to ensure smooth rotation with little unnecessary vibration, etc., and has a shape in which the ball 7 and the concave ball transfer portion 15 are in contact with each other in a substantially planar shape. It is also possible to make use of the ink 9 intervening as a lubricant against the rotation of the ball 7.
Further, the aforementioned radial groove 1 has an opening 1 a outside the concave ball transfer portion 15 of the inward projecting portion 14, and ensures ink supply to the ball holding chamber 12.

  Test ballpoint pen samples with different dimensions were prepared (see Table 1), and the following tests were performed. In addition, each part dimension was directly measured by 200 times with Olympus digital microscope VHX-900, with the ball-point pen tip vertically divided in half. The vertically divided state means a state as shown in FIG. 3 or FIG. 7, but a transparent synthetic resin such as an unsaturated polyester resin, specifically, a cold embedding resin manufactured by Marumoto Struers Co., Ltd. No. No. 105 is a cold embedding resin no. A sample to be measured is prepared by adding about 2% of a curing agent for 105 and kneading well into a gap to solidify and then gradually scraping with sandpaper or the like.

  Each of the ballpoint pen tips shown in Table 1 is attached to an ink containing pipe of a 0.7 mm ballpoint pen “Dot Eball 0.7” (product code: BK127-A) manufactured by Pentel Co., Ltd. Then, the centrifugal force works in the direction of the nib, centrifuge with a centrifuge (manufactured by Japan Centrifuge Co., Ltd .: tabletop centrifuge H-103N) to remove the gas present in the writing instrument. A test ballpoint pen sample was used.

The composition of the ink used in the test is as follows. Note that “parts” in the composition simply means “parts by weight”.
Water black # 108-L (14% aqueous solution of CI DIRECT BLACK19, manufactured by Orient Chemical Industry Co., Ltd.) 40.0 parts Kelzan AR (xanthan gum, shear thinning resin, manufactured by Sanki Co., Ltd.) 0.2 Parts ethylene glycol 10.0 parts glycerin 10.0 parts benzotriazole 0.5 part potassium hydroquinone sulfonate 0.5 part proxel GXL (1,2-benzisothiazolin-3-one, preservative, manufactured by ICI)
0.3 part ion-exchanged water 38.5 parts Among the above components, the whole amount of Kelzan AR and 5.0 parts of water were stirred for 30 minutes with a laboratory mixer and uniformly dissolved to prepare a Kelzan aqueous solution. The remaining components were mixed, mixed and stirred for 1 hour, then added with an aqueous Kelzan AR solution, and further stirred for 2 hours to obtain a black ink having a viscosity of 70 mPa · s at a shear rate of 10 sec-1.

(Writing test 1)
Each test ballpoint pen sample was rotated at 0 °, which is an arbitrary direction with respect to the outer periphery of the ballpoint pen, and 120 ° with respect to the outer circumference of the ballpoint pen under the conditions of a writing load of 100 g, a writing angle of 70 ° and a writing speed of 7 cm / s. In each of the two directions rotated by 240 °, the ballpoint pen is not rotated, but each 3 m is written in a straight line, the respective discharge amounts are measured, and the following items are evaluated.
(1) Discharge difference The difference obtained by subtracting the minimum value from the maximum value is calculated for the discharge amount in each of the three directions.
(2) Difference in writing width Each writing width in three directions is measured, and a difference obtained by subtracting the minimum value from the maximum value is calculated.

(Writing test 2)
Each test ballpoint pen sample was rotated under the conditions of a writing load of 100 g, a writing angle of 70 °, and a writing speed of 7 cm / s, 100 m spiral writing, and a discharge amount of 0 to 50 m and a discharge amount of 50 to 100 m were measured. Evaluate the following items.
(1) Discharge increase / decrease rate A ratio obtained by dividing the discharge amount of 50 m to 100 m by the discharge amount of 0 m to 50 m is calculated.
(2) Written width difference A difference is calculated by subtracting the handwriting width near 100 m from the handwriting width near 1 m.
The test results are listed in (Table 2).

In each embodiment in which the ratio of the volume of the radial groove to the volume of the inward protruding portion is 0.03 or more and 0.12 or less, the amount of distortion proportional to the processing amount with respect to the volume of the inward protruding portion is relatively small. The deformation of the ball holding chamber is suppressed, the difference in the discharge amount in each of the three directions according to the writing test 1 is 0.0015 g or less, and the difference in the writing width in each of the three directions is within 0.05 mm. The difference in the shade of the handwriting resulting from the difference in the amount of ink ejected due to the ink and the unevenness of the writing width are not worrisome.
Moreover, since the volume of the radial groove is prevented from being too small and the writing increase / decrease rate in writing test 2 is 90% or more, there is no large difference in the amount of discharge from the initial writing, so the difference in writing width is 0.05 mm or less compared to the initial. Insufficient ink supply can be prevented, and ink followability can be ensured.
In particular, in Examples 3 to 9 in which the ratio of the volume of the radial groove to the volume of the inward projecting portion is 0.05 or more and 0.11 or less, the difference in the discharge amount in each of the three directions by the writing test 1 is 0.0010 g. Hereinafter, the difference in writing width in each of the three directions is also within 0.04 mm, the writing increase / decrease rate by writing test 2 is 95% or more, the difference in writing width is also within 0.02 mm, the density of the handwriting, and the line width Non-uniformity, almost no blurring of handwriting, and better.
On the other hand, in Comparative Example 1, the volume ratio is less than 0.03, and in the writing test 1, the difference in the discharge amount in each of the three directions is 0.0003 g, and the difference in the writing width in each of the three directions is also 0.1. Good results were obtained at 02 mm, but as a result of the volume of the radial groove being reduced too much, the rate of increase / decrease in ejection was 85% or less in writing test 2, and the difference in handwriting width was 0.09 mm, which is a large difference compared to the initial value. Occurred, and the ink writing was faintly thin and the ink was awkward.
On the contrary, in comparison 2, the volume ratio exceeds 0.12 and becomes 0.13, and in writing test 2, the discharge increase / decrease rate is 90% and the difference in handwriting width is 0.01 mm. However, the deformation of the ball holding chamber increased, and in the writing test 1, the difference in the discharge amount in each of the three directions was as large as 0.0020 g, and the difference in the writing width in each of the three directions was as large as 0.08 mm. The difference in density and the unevenness of the writing width are remarkable.
Moreover, in Example 8 which is a non-penetrating radial groove, the ratio of the volume of the radial groove to the volume of the inward protruding portion is three directions according to the writing test 1 as compared with Example 9 which is a through radial groove similar to 0.11. The difference between the discharge amounts is a little as low as 0.0008g, indicating that the distortion in the radial grooving tends to be small.

DESCRIPTION OF SYMBOLS 1 Radial groove 1 'Radial groove 1a Front opening part of radial groove 1ap Foremost position of front opening part of radial groove 1b Rear opening part of radial groove 1b' Bottom face of radial groove 1bp End of rear opening part of radial groove End position 1 bp 'Rear end position of bottom surface of radial groove 2 Center hole 2a Front opening portion of center hole 2b Rear opening portion of center hole 2b' Rear opening portion to center hole of bottom surface of radial groove 3 Frustum of height L1 4 Front frustoconical recessed portion 5 Rear frustoconical recessed portion 6 Ball holder 6a Front end opening 6b Rear end opening 7 Ball 8 Ink receiving portion 9 Ink 10 Backflow prevention body composition 11 Coil spring 11a Winding portion 11b Direct end Shaped part 12 Ball holding chamber 13 Rear hole 14 Inwardly projecting part 15 Ball transfer part d1 Cross sectional diameter d2 Cross sectional diameter d3 Maximum outer diameter of radial groove d4 Center hole diameter L1 Cross sectional distance L2 It is L3 height L4 height L5 height N radial grooves the number W radial groove width

Claims (1)

An inward projection that restricts the rearward movement of the ball formed in the through hole of the ball holder, comprising at least a ball as a writing member and a ball holder that partially holds the ball by projecting from the tip opening of the through hole A ballpoint pen tip in which a radial ink passage groove is formed in a portion, and a ratio of a volume of the radial groove to a volume of the inward protruding portion is 0.03 or more and 0.12 or less.

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