JP2024030729A - Eraser and writing instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an eraser capable of erasing ink handwriting without contaminating a paper surface or the like even when used continuously, and a writing instrument provided with such an eraser.

SOLUTION: Provided is an eraser 20 for erasing handwriting written in a target ink 30 containing colored resin particles and blended with binder resin. The difference in SP value between the binder resin and the material of the eraser 20 is 0.1 or more. The eraser 20 rubs and erases the handwriting made of the film of the target ink 30 ejected onto the paper surface.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2024,JPO&INPIT

Description

TECHNICAL FIELD The present invention relates to erasers and writing instruments.

BACKGROUND ART Conventionally, erasing methods have been proposed for erasing ink handwriting written on paper or the like. For example, Patent Document 1 discloses a friction body (letter eraser) that erases or discolors handwriting by frictional heat by rubbing the handwriting made with ink containing particles of metallic luster pigment in thermochromic ink. There is. This friction body contains a viscoelastic body, and by acting as an elastic body, it emits frictional heat, chemically erases and discolors handwriting, and by acting as a viscous body, it emits frictional heat, and by acting as a viscous body, ink containing particles of metallic luster pigment is added. It can be adsorbed and peeled off.

International Publication No. 2018/116767

However, the friction body disclosed in Patent Document 1 is continuously used with the ink to which metallic luster pigment particles that have been adsorbed and peeled off from the paper surface, etc. adhering to it, so that the paper surface, etc. can be reused. There was a risk of contamination with ink.

The present invention has been created in view of the above points, and provides an eraser and an eraser that can erase ink handwriting without contaminating the paper surface even when used continuously. The purpose of the present invention is to provide a writing instrument equipped with the following.

In order to solve the above-mentioned problems, the present inventors conducted intensive research and, as a result, used an erasing method based on a different principle from the conventional one, in which handwriting made of a film formed on the paper surface by ink is rubbed and erased. We have discovered that by doing this, it is possible to suppress the contamination of the paper surface, etc. by ink, and that there is a relationship between ink and eraser to realize eraser, which erases handwriting by rubbing it.

That is, the eraser of the present invention is an eraser for erasing handwriting made with ink containing colored resin particles and blended with a binder resin, wherein the difference in SP value between the binder resin and the material of the eraser is 0. .1 or more, and the handwriting made of the film of the ink ejected onto the paper surface is rubbed and erased.

Further, in the writing instrument of the present invention, the eraser described above is fixed to, attached to, or covered with an exterior member.

According to the present invention, it is possible to provide an eraser capable of erasing ink handwriting without contaminating the paper surface again even when used continuously, and a writing instrument equipped with the eraser.

FIG. 2 is a schematic diagram showing the appearance of a ballpoint pen according to an embodiment, in which (a) shows a state with a cap attached, and (b) shows a state with a cap removed.

The eraser according to the embodiment of the present invention will be described below. The eraser according to the present embodiment erases handwriting by rubbing the ink to be erased, specifically, the ink containing colored resin particles and containing a binder resin (hereinafter referred to as "target ink"). It is an eraser used for The target ink ejected onto the paper surface does not settle on the paper surface (in other words, it does not get between the fibers of the paper), and the handwriting made with the target ink forms a film on the paper surface. The eraser according to this embodiment erases the handwriting from the paper surface by rubbing the handwriting made of the film formed on the paper surface with the target ink in this way and generating eraser debris.

The eraser according to this embodiment is used, for example, by being fixed to the exterior member of a ballpoint pen (writing instrument). The exterior member as used herein refers to a member that is exposed to the outside and can be directly touched. Exterior members of the writing instrument include, for example, a cap, a tip member (nib metal), a cylinder shaft (case), a tail plug, a grip member (grip portion), and an operating member (knock portion). FIGS. 1A and 1B are schematic diagrams showing the appearance of a cap-type ballpoint pen 10 including an eraser 20 according to an embodiment. As shown in FIGS. 1A and 1B, in the ballpoint pen 10, an ink tank of a refill (not shown) housed inside a case (exterior member) 12 is filled with target ink 30. The target ink 30 is ejected from the pen tip 10a housed in the cap 14.

The eraser 20 is made of a viscoelastic body that has ink erasing properties for the target ink 30. As shown in FIGS. 1(a) and 1(b), the eraser 20 is fixed to the case 12 at the pen end 10b of the ballpoint pen 10, which is opposite to the pen tip 10a. It is designed not to deviate from 12. The eraser 20 may not only be fixed to the case 12, but may also be attached to or covered with the case 12. Further, the part of the ballpoint pen 10 to which the eraser 20 is attached is not limited to the case 12, but may be any exterior member that is exposed to the outside of the ballpoint pen 10.

The target ink 30 is required to form a film having a predetermined thickness when it is ejected onto a paper surface. The colored resin particles contained in the target ink 30 are preferably acrylic resin particles or urethane resin particles in which a pigment such as carbon black is encapsulated. Further, it is preferable that the difference in specific gravity between the colored resin particles and the solvent of the target ink 30 is small (specifically, 0.7 or less). The colored resin particles are, for example, acrylic copolymer fine particles.

The average particle diameter of the colored resin particles contained in the target ink 30 is preferably 5 μm to 15 μm. A more preferable average particle diameter of the colored resin particles is 6 μm. If the average particle diameter of the colored resin particles is smaller than 5 μm, the target ink 30 ejected onto the paper surface tends to settle on the paper surface and easily enters between the fibers of the paper. On the other hand, if the average particle diameter of the colored resin particles is larger than 15 μm, the density of handwriting decreases. When the average particle size of the colored resin particles is within the above range, the target ink 30 forms handwriting on the paper surface with an appropriate handwriting density and a film in which the ink does not settle on the paper surface.

The binder resin contained in the target ink 30 is preferably acrylonitrile butadiene rubber (NBR). This is because when the binder resin is acrylonitrile butadiene rubber, it has excellent adhesion to the paper surface. Preferred binder resins other than acrylonitrile butadiene rubber include styrene butadiene rubber (SBR) and the like.

In addition to the above colored resin particles and binder resin, the target ink 30 contains a dispersant such as a nonionic surfactant for dispersing the colored resin particles, and a high boiling point solvent for imparting so-called cap-off properties to the target ink 30. , a thickener for suppressing sedimentation of the colored resin particles on the paper surface, water, etc. may be included.

When the target ink 30 configured as described above is ejected from the nib 10a of the ballpoint pen 10 onto the paper surface, solvent components such as water are absorbed by the paper surface and volatilize into the atmosphere, causing colored resin to be deposited on the paper surface. A skin-like film made of particles and binder resin is formed with a thickness of, for example, 1 to 100 μm. The eraser 20 described below erases handwriting made of such a film by rubbing it from the surface of the paper.

Next, the eraser 20 according to this embodiment will be described in detail. The eraser 20 is made of a material such that the difference in SP (Solubility Parameter) value ((cal/cm ³ ) ^1/2 ) with the binder resin contained in the target ink 30 is 0.1 or more. has been done. The SP value in this embodiment is calculated from the square root of the heat of evaporation required to evaporate 1 cm ³ of liquid.

If the difference in the above SP values is smaller than 0.1, the affinity between the eraser 20 and the binder resin blended in the target ink 30 will be high (easier to dissolve), and the handwriting will be reduced during the scratching operation. The binder resin contained in the film adheres to the eraser 20 and becomes easy to stretch. Therefore, the paper surface is likely to be contaminated during the scratching operation. By setting the difference between the above SP values to 0.1 or more, the binder resin is prevented from spreading on the paper surface, so the Eraser 20 can erase handwriting on the paper surface without contaminating the paper surface. . In this way, the difference in SP value affects the difficulty of contamination when erasing handwriting.

Moreover, it is preferable that the eraser 20 is formed of a material that has a contact angle of less than 60° when the target ink 30 is dropped onto its surface. The contact angle in this specification refers to a static contact angle, and is measured, for example, by the θ/2 method. If the above-mentioned contact angle is 60° or more (difficult to wet), when erasing handwriting, there will be slippage between the eraser 20 and the film that makes up the handwriting made of the target ink 30 (slipping on the handwriting). , the film is difficult to adhere to the eraser 20. This makes it difficult to rub the film that makes up the handwriting, making it difficult to erase the handwriting. On the other hand, if the contact angle is less than 60°, the film constituting the handwriting will easily adhere to the eraser 20 when erasing the handwriting, making it easier to erase the handwriting. In this way, the contact angle influences the degree of erasure when handwriting is erased.

Specifically, the material of the eraser 20 is preferably one of natural rubber, synthetic rubber, and synthetic resin, which are used as materials for general erasers. Examples of the synthetic rubber include styrene-butadiene rubber, chloroprene rubber, butyl rubber, acrylonitrile-butadiene rubber, acrylic rubber, urethane rubber, silicone rubber, and fluorine rubber. Examples of synthetic resins include polyvinyl chloride and polypropylene. By comparing the difference in SP value with the binder resin blended in the target ink 30, an appropriate material can be selected from the above materials.

Further, when the material of the eraser 20 is synthetic rubber, it is preferably urethane rubber. For example, for the target ink 30, if the average particle diameter of the colored resin particles to be blended is within the range of 5 to 15 μm and the binder resin to be blended is acrylonitrile butadiene rubber, the SP value of the acrylonitrile butadiene rubber and the urethane rubber is This is because the difference is 0.1 or more and the contact angle when the target ink 30 is dropped onto urethane rubber is less than 60°. Furthermore, since urethane rubber has excellent abrasion resistance, when the film forming the handwriting is rubbed and erased, the urethane rubber does not easily disintegrate, and the film can be rubbed effectively.

Note that the eraser 20 is preferably made of a material with excellent wear resistance. If the abrasion resistance of the eraser 20 is low, the eraser 20 itself will easily disintegrate when the film forming the handwriting is rubbed and erased with the target ink 30 on the paper surface, and eraser debris will The amount of will increase. On the other hand, if the eraser 20 is made of a material with excellent wear resistance, the eraser 20 will not easily collapse when erasing handwriting. Therefore, only the handwriting can be sufficiently erased, and the amount of erased waste produced by the eraser 20 can be reduced. In this way, abrasion resistance affects the amount of eraser waste when erasing handwriting.

Further, it is preferable that the eraser 20 is made of a material having a high critical surface tension (easily wetted). If the critical surface tension of the letter eraser 20 is small (if it is difficult to get wet), it will be difficult for the film to adhere to the surface of the letter eraser when the film that makes up the handwriting is rubbed and erased, similar to the contact angle mentioned above. The eraser slides easily over the handwriting, making it difficult to erase the handwriting. In this way, the critical surface tension affects the degree of erasure when handwriting is erased.

The eraser 20 according to the present embodiment configured as described above is used for erasing handwriting created by the target ink 30 containing colored resin particles and blended with a binder resin. The difference in SP value between the binder resin and the material of the eraser 20 is 0.1 or more, and the handwriting made of the film formed by the target ink 30 is erased by rubbing. That is, by satisfying the above relationship with the target ink 30, the eraser 20 of this embodiment reduces the amount of eraser waste by rubbing the handwriting made of the skin-like film formed by the target ink 30. It is possible to irreversibly erase only the handwriting by physically stripping it off while suppressing it as much as possible.

Furthermore, the eraser 20 of this embodiment prevents eraser debris from adhering to the eraser 20 due to the target ink 30 adsorbed and peeled off from the paper surface by peeling off the skin-like film. When erasing handwriting with an eraser, graphite does not adhere to the eraser and contaminate the paper surface again. From the above, even when the eraser 20 of this embodiment is used continuously, it is possible to erase the handwriting made by the target ink 30 without contaminating the paper surface or the like.

Further, the eraser 20 of the present embodiment is different from conventional erasers for chemically erasing handwriting using thermochromic ink, and the erased handwriting does not recover due to changes in environmental temperature. Therefore, it is possible to realize a novel eraser 20 that can physically erase handwriting made with the target ink 30 without contaminating the paper surface or the like, regardless of changes in the environmental temperature.

Further, in the ballpoint pen 10 according to the present embodiment, the eraser 20 described above is fixed to the case 12. Thereby, the eraser 20 can be made easier to use. Furthermore, in the ballpoint pen 10 according to this embodiment, the inside of the case 12 is filled with the target ink 30. Thereby, a writing instrument using the target ink 30 and the eraser 20 can be provided as a set.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various changes can be made without departing from the gist thereof. For example, in the present embodiment, a ballpoint pen with an eraser is illustrated, but the writing instrument is not limited to a writing instrument with an eraser. For example, it may be a fountain pen, a marker, or a knock-type writing instrument equipped with an eraser.

Hereinafter, the present invention will be explained in detail with reference to Examples. In this example, a test was conducted to select the most suitable material for the eraser to erase the target ink. Specifically, for each of the 11 types of materials (elastomers) to be selected, the difference in SP value with the target ink, abrasion resistance, critical surface tension, erasability, and contact angle with the target ink were examined.

Regarding the SP value, wear resistance, and critical surface tension of each material to be selected (hereinafter referred to as "selected material"), literature values were investigated. The documents to be investigated are: 1. “Rubber material application (ketech.in.coocan.jp/r-17.pdf)”, 2. Reference was made to ``Journal of the Japan Rubber Association, Vol. 51, No. 8 (1978), Introductory course for rubber engineers, Compound design (1) Types and properties of raw rubber, Moriichi Maeda.'' On the other hand, regarding the erasability of the selected materials, a sensory evaluation was performed on the erasability of handwriting with the target ink. Regarding the contact angle of the selected material, the contact angle when the target ink was dropped onto the selected material was measured. Based on these results, we selected the most suitable eraser material for erasing the target ink.

(1) Selected materials The following 11 types of materials (elastomers) were extracted for selection (symbols are shown in parentheses). 1. Natural rubber (NR), 2. Styrene butadiene rubber (SBR), 3. Chloroprene rubber (CR), 4. Butyl rubber (IIR), 5. Acrylonitrile butadiene rubber (NBR: nitrile content 30%), 6. Low nitrile content acrylonitrile butadiene rubber (NBR18: nitrile content 18%) (described as "low nitrile" in Table 2), 7. Acrylonitrile butadiene rubber with medium-high nitrile content (NBR30: nitrile content 30%) (described as "medium-high nitrile" in Table 2), 8. Urethane rubber (U), 9. Silicone rubber (Q), 10. Fluorine rubber (FKM), 11. PVC eraser (PVA).

(2) Composition of target ink The composition of the ink composition used as the target ink is shown in Table 1 below. The compounding units indicated by numbers in Table 1 are % by weight, and the total amount is 100% by weight. The acrylic dispersion shown in Table 1 is obtained by dispersing acrylic colored resin particles with an average particle diameter of 6 μm in an acrylic dispersant and water (compounding ratio: 60% by weight of colored resin particles, acrylic dispersant 10% by weight, 30% by weight of water). The NBR emulsion shown in Table 1 is an emulsion in which acrylonitrile butadiene rubber is dispersed as a binder resin (solid content 48.5%). Regarding the composition other than the colored resin particles and the binder resin, ethylene glycol was blended as a high boiling point solvent, and a 3% aqueous xanthan gum solution and water were blended as thickeners. Note that the difference in specific gravity between the colored resin particles and the solvent in the ink composition used as the target ink was 0.11. Moreover, the average particle diameter here is the value of D50 calculated on a volume basis in a laser diffraction method.

(3) Investigation of literature values regarding SP values The SP values ((cal/cm ³ ) ^1/2 ) shown in literature for the selected materials were investigated. Note that the SP value of acrylonitrile butadiene rubber (NBR), which is a binder resin contained in the target ink, was 9.4 to 9.9 ((cal/cm ³ ) ^1/2 ) based on literature values. Regarding the selected materials, for those for which both the upper and lower limits of the SP value are indicated in the literature, the numerical range between the upper and lower limits and the SP value of the above acrylonitrile butadiene rubber from 9.4 to The difference with the numerical range of 9.9 ((cal/cm ³ ) ^1/2 ) was compared. The optimal eraser material is required to have a difference in SP value of 0.1 or more from the acrylonitrile butadiene rubber contained in the target ink.

(4) Investigation of literature values regarding abrasion resistance and surface tension Regarding the abrasion resistance of the selected materials, we investigated the abrasion resistance based on the literature values of the wear loss test conducted in accordance with the JIS standard (JIS S6004-1994). Those with excellent abrasion resistance were rated ◎, those with good abrasion resistance were rated ○, and those with poor abrasion resistance were rated △. The optimal eraser material is required to have excellent or good wear resistance. In addition, for the selected materials, literature values of critical surface tension (dyne/cm) with respect to water were investigated. The optimal eraser material is required to have a high critical surface tension (easy wettability).

(5) Sensory evaluation of erasability For each material to be selected, the handwriting written in the target ink on the surface of high-quality paper was manually rubbed several times, and the erasability was visually evaluated. Papers for which no unerased material was visually confirmed are evaluated as ◎, and papers whose paper surface was contaminated by rubbing (conspicuous contamination) and paper for which unerased material was visually confirmed are evaluated as △. Those that were noticeable and those that could hardly be erased were rated as ×.

(6) Measurement of contact angle For each material to be selected, the target ink was dropped onto its flat surface, and the contact angle (°) was measured. Specifically, the static contact angle was measured by the θ/2 method. The contact angle was measured using a digital microscope (manufactured by Keyence Corporation: VHX series) under an environment of a temperature of 25° C. and a humidity of 50%. The optimal eraser material is required to have a small contact angle (easy wettability).

(7) Selection of optimal material Regarding the selected materials, the results of the investigation of each literature value and the evaluation and measurement results of each test are summarized in Table 2 below. Note that blank columns in Table 2 indicate those that were not described in the literature.

Comparing the SP value investigation results and the eraseability sensory evaluation results, it was found that among the selected materials, the difference in SP value was similar to that of the acrylonitrile butadiene rubber of the target ink, specifically, the difference in SP value was less than 0.1. Regarding chloroprene rubber, acrylonitrile butadiene rubber, and medium-high nitrile, the erasability sensory evaluation was △ or ×, confirming that they tend to stain the paper surface or that handwriting cannot be erased. Furthermore, among the selected materials that have a difference in SP value of 0.1 or more from the target ink's acrylonitrile butadiene rubber, butyl rubber was confirmed to have good performance (◎ rating) in the sensory evaluation of erasability. .

In addition, when comparing the results of the abrasion resistance investigation and the sensory evaluation results for erasability, it was found that among the materials with excellent abrasion resistance (those evaluated as ◎), natural rubber, styrene-butadiene rubber, and urethane rubber were evaluated for sensory erasability evaluation. It was confirmed that the results were also good (rating ◎). Regarding fluororubber, the reason why the eraser sensory evaluation is △ even though it has excellent abrasion resistance is because it has a low critical surface tension, so it slides over the handwriting when erasing. It is assumed that there is.

Furthermore, when comparing the critical surface tension survey results and the sensory evaluation results for erasability, among those with critical surface tensions of 30 (dyne/cm) or higher, styrene-butadiene rubber and urethane rubber also showed good performance in the sensory evaluation for erasability. It was confirmed that (◎ evaluation).

Furthermore, regarding the sensory evaluation of erasability, it was confirmed that natural rubber, styrene-butadiene rubber, butyl rubber, low nitrile rubber, and urethane rubber were all good (rated ◎).

In addition, when comparing the contact angle measurement results and the eraseability sensory evaluation results, silicone rubber and fluorine rubber with a contact angle of 60° or more and PVC eraser with a contact angle of less than 60° show that The evaluation was △ or ×, and it was confirmed that the paper surface was easily contaminated or handwriting could not be erased. Furthermore, among the selected materials, it was confirmed that urethane rubber, which had the smallest contact angle with respect to the target ink (13.0°), was also good (rated ◎) in the sensory evaluation of erasability.

From the above study results, among the selected materials, those that were good in the erasability sensory evaluation (◎ evaluation) had a difference in SP value of 0.1 or more, had the smallest contact angle, and had excellent wear resistance. It was also confirmed that urethane rubber, which had the highest critical surface tension, was most suitable for erasing handwriting created by the target ink.

10 Ballpoint pen 10a Pen tip 10b Pen end 12 Case 14 Cap 20 Character eraser 30 Target ink

Claims (8)

An eraser for erasing handwriting made with ink containing colored resin particles and blended with a binder resin,
The difference in SP value between the binder resin and the eraser material is 0.1 or more,
Scratching and erasing the handwriting made of the ink film ejected onto the paper surface;
Erase characters. The eraser according to claim 1, which erases handwriting made with the ink, in which the colored resin particles have an average particle diameter of 5 μm or more and 15 μm or less. The eraser according to claim 1, wherein when the ink is dropped onto the surface of the eraser, a contact angle is less than 60°. The eraser according to claim 1, wherein the binder resin is acrylonitrile butadiene rubber for erasing handwriting made with the ink. The eraser according to claim 1, which is made of natural rubber, synthetic rubber, or synthetic resin. The eraser according to claim 5, wherein the material is urethane rubber. A writing instrument, wherein the eraser according to any one of claims 1 to 6 is fixed to, attached to, or covered with an exterior member. A writing instrument according to claim 7, filled with the ink.

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