Ink composition for a writing board and a writing instrument containing the same

Abstract

The present invention provides a writing board oil ink composition containing at least a pigment, an organic solvent, a polyvinyl acetal resin having a glass transition temperature of 75°C or higher and 120°C or lower represented by the following general formula (1), and a release agent. In the formula, p, q, r, and s represent the composition ratio, p is optionally 0, q, r, and s each have a value greater than 0, and the sum of p, q, r, and s is 100.

Description

Technical Field

[0001] This disclosure relates to an oil-based ink composition for writing boards and a writing instrument containing the same, and more specifically, to an oil-based ink composition for writing boards with excellent erasability and a writing instrument containing the same. Background Technology

[0002] In the past, in order to enable repeated writing and erasing, oil-based inks for writing boards (so-called whiteboards or blackboards) made of materials such as enamel, metal or plastic, would contain an adhesive resin to give the writing on the writing board adhesion, and a release agent to remove the writing by wiping it with an eraser (an erasing part made of felt or cloth).

[0003] Polyvinyl butyral resin is widely used as the aforementioned adhesive resin from the viewpoint of obtaining excellent adhesion.

[0004] Regarding this resin, the following have been described: a writing board marking ink composition (e.g., Patent Document 1) containing pigment, polyvinyl butyral resin, ethanol, and a compound having a salicylic acid skeleton as an additive; or an oil-based marker ink composition for writing boards (e.g., Patent Document 2) containing pigment, organic solvent, polyvinyl butyral resin, and one or more release agents selected from polyoxyalkylene glycerol ethers and polyoxyalkylene polyglycerol ethers.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2010-144064

[0008] Patent Document 2: Japanese Patent Application Publication No. 2017-214519 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] In the oil-based ink compositions for writing boards described in the aforementioned patent documents, although the adhesion of the ink is improved by adding polyvinyl butyral resin, a highly resilient ink coating is formed that adheres firmly to the writing surface, making it difficult to erase with light force. Furthermore, the physical properties of the ink coating formed on the writing board can change over time and / or due to external factors, resulting in ink adhering to the writing board and causing some ink residue to remain after erasing, or ink spreading and contaminating the writing board.

[0011] Furthermore, some unerased ink residue cannot be removed even with a regular eraser or a damp cloth. Removal requires solvents and / or special cleaning agents, but these are often difficult to obtain and require preparation, which is time-consuming and laborious. Therefore, a preferred method is an oil-based ink composition for writing boards that can completely erase ink residue using a regular eraser without the need for these solvents and special cleaning agents.

[0012] The present disclosure aims to eliminate the aforementioned undesirable conditions and provide an oil-based ink composition for writing boards and a writing instrument containing the same. The oil-based ink composition for writing boards can form a pen mark film with excellent erasability regardless of the type of solvent and stripper, and can always be erased with light force regardless of the time elapsed since the pen mark was formed, the material of the writing board, or even the material and bristle length of the eraser.

[0013] Problem Solving Methods

[0014] Method 1 of the present invention is an oil-based ink composition for writing boards, which contains at least: pigment, organic solvent, polyvinyl acetal resin of the following general formula (1) with a glass transition temperature of 75°C or higher and 120°C or lower, and a release agent.

[0015] [Chemical Formula 1]

[0016]

[0017] In the formula, p, q, r, and s represent the composition ratios, p can be arbitrarily set to 0, q, r, and s all have values ​​greater than 0, and the sum of p, q, r, and s is 100.

[0018] Embodiment 2 of the present invention is the oil-based ink composition for writing boards described in Embodiment 1, wherein,

[0019] The mass ratio of the polyvinyl acetal resin to the pigment is 0.34 or more.

[0020] The third embodiment of the present invention is the oil-based ink composition for writing boards described in embodiment 1 or 2, wherein,

[0021] The content of the above-mentioned polyvinyl acetal resin exceeds 1.0% by mass.

[0022] The fourth embodiment of the present invention is an oil-based ink composition for writing boards as described in any one of embodiments 1 to 3, which further comprises a second resin other than the polyvinyl acetal resin described above.

[0023] Embodiment 5 of the present invention is the oil-based ink composition for writing boards described in Embodiment 4, wherein,

[0024] The second resin mentioned above is polyvinyl butyral resin.

[0025] Embodiment 6 of the present invention is the oil-based ink composition for writing boards described in any one of Embodiments 1 to 5, wherein,

[0026] The stripping agent described above comprises any one or more selected from carboxylic acid esters, silicone surfactants, anionic surfactants, nonionic surfactants, polyoxyalkylene glycerol ethers, polyoxyalkylene polyglycerol ethers, sulfates of polyoxyalkylene alkyl ethers, sulfates of polyoxyethylene alkylene alkyl ethers, sulfates of polyoxyalkylene alkyl aryl ethers, phosphates of polyoxyethylene alkyl ethers or their salts, and polyalkylene glycol esters.

[0027] Embodiment 7 of the present invention is the oil-based ink composition for writing boards described in Embodiment 6, wherein,

[0028] The above-mentioned carboxylic acid esters include compounds represented by the following general formula (3).

[0029] [Chemical Formula 2]

[0030]

[0031] Where R in the formula 1 ~R 2 They are either alkyl groups with 6 to 18 carbon atoms or alkoxy polyethylene glycol groups with 2 to 18 carbon atoms and 2 to 10 oxygen atoms.

[0032] Embodiment 8 of the present invention is an oil-based ink composition for writing boards according to any one of Embodiments 1 to 7, wherein,

[0033] The glass transition temperature mentioned above is below 109°C.

[0034] Embodiment 9 of the present invention is a writing instrument containing an oil-based ink composition for a writing board as described in any one of embodiments 1 to 8.

[0035] The effects of the invention

[0036] According to embodiments of the present invention, an oil-based ink composition for writing boards, which is unaffected by the type of solvent and stripping agent and exhibits excellent erasability of ink marks formed on the writing board, and a writing instrument containing the composition can be provided. Detailed Implementation

[0037] The embodiments of the present invention will now be described in detail.

[0038] It should be noted that, unless otherwise specified, the terms "parts," "%," and "ratio" used to indicate the combination in this specification are used as quality standards. Specifically, the "composition ratio" in general formulas (1) and (2) is a percentage of the number of repeating units and is not a quality standard.

[0039] The writing board oil-based ink composition (hereinafter, as appropriate, also referred to as "oil-based ink composition" or "oil-based ink") in the embodiments of the present invention contains at least: pigment, organic solvent, polyvinyl acetal resin of general formula (1) with a glass transition temperature of 75°C or higher and 120°C or lower, and a release agent (or also referred to as an erasable agent).

[0040] Polyvinyl acetal resin

[0041] The polyvinyl acetal resin in the embodiments of the present invention is represented by the following general formula (1).

[0042] [Chemical Formula 3]

[0043]

[0044] In general formula (1), p, q, r, and s represent composition ratios, where p can be arbitrarily set to 0, and q, r, and s all have values ​​greater than 0. The sum of p, q, r, and s is 100. Here, the "composition ratio" in general formula (1) is the percentage of the number of repeating units.

[0045] In general formula (1), polyvinyl alcohol acetal resin with p = 0 is represented by the following general formula (2).

[0046] [Chemical Formula 4]

[0047]

[0048] In general formula (2), q, r, and s represent composition ratios, all of which have values ​​greater than 0, and the sum of q, r, and s is 100. Here, the "composition ratio" in general formula (2) is the percentage of the number of repeating units.

[0049] From the viewpoint of obtaining excellent erasability, the glass transition temperature of the polyvinyl acetal resin represented by general formulas (1) and (2) used in the embodiments of the present invention is set to 75°C or higher, preferably 77°C or higher, more preferably 80°C or higher, even more preferably 83°C or higher, even more preferably 84°C or higher, even more preferably 92°C or higher, particularly preferably 100°C or higher, with an upper limit of 120°C or lower, preferably 110°C or lower, more preferably 109°C or lower, and even more preferably 108°C or lower. It should be noted that the glass transition temperature is determined by the method described in the embodiments below.

[0050] Generally, the ink coating formed on a writing surface through solvent evaporation is prone to changes in physical properties due to various factors such as temperature and sunlight. This is especially true for ink coatings that have been in use for a long time, where changes in physical properties are more likely to occur, resulting in a noticeable decrease in erasability.

[0051] Previously, the ink coating of oil-based inks using polyvinyl butyral resin had a low glass transition temperature. Therefore, the ink coating was easily affected by external temperature and / or sunlight, causing the physical properties of the polyvinyl butyral resin in the ink coating to change, resulting in so-called deterioration where part of the ink remained on the writing surface.

[0052] In the pen ink coating film formed by the oil-based ink according to the embodiments of the present invention, the glass transition temperature of the polyvinyl acetal resin is as high as 75°C or above, so it is not easy for its physical properties to change due to external factors, and its erasability will not decrease even after a long time.

[0053] The ink coating of oil-based inks using the aforementioned polyvinyl acetal resin has higher brittleness, so the ink does not adhere firmly to the writing surface and can be easily erased with light force.

[0054] The reason is not yet determined, but the following can be considered.

[0055] Compared to previously widely used polyvinyl butyral resins, the polyvinyl butyral resin of the above general formula exhibits a steric hindrance effect due to its acetal structure containing methyl groups with fewer carbon atoms than butyl groups, and a smaller proportion of butyl acetal structures. This results in the formation of a highly brittle pen-writing coating. Consequently, the formed pen-writing coating adheres gently to the writing board and can be easily erased with light force without leaving any pen marks on the writing board.

[0056] Furthermore, by adding the aforementioned polyvinyl acetal resin to oil-based inks containing pigments, the polyvinyl acetal resin is gently adsorbed onto the pigment surface, thereby improving the pigment dispersion stability in the oil-based ink. With the improved pigment dispersion in the oil-based ink, pigment aggregation and sedimentation in the ink or at the tip of the writing instrument can be suppressed, eliminating writing defects such as broken lines and poor ink flow.

[0057] In addition, the aforementioned polyvinyl acetal resin also functions as a resin for improving the adhesion of handwriting and inhibiting ink bleeding (i.e., it has the same function as the second resin described later).

[0058] From the viewpoint of improving adhesion, the weight-average molecular weight (hereinafter, sometimes referred to as "molecular weight") of the above-mentioned polyvinyl acetal resin can be 150,000 or less, or 110,000 or less, or 100,000 or less. There is no particular limitation on the lower limit of the weight-average molecular weight, but from the viewpoint of the dispersion stability of the above-mentioned polyvinyl acetal resin, it can be 10,000 or more.

[0059] In addition, from the viewpoint of obtaining excellent discharge stability of ink, the content of hydroxyl groups in the above-mentioned polyvinyl acetal resin (i.e., "s" in general formulas (1) and (2), hereinafter referred to as "hydroxyl content" as appropriate) only needs to be 5 or more, and can be 10 or more or 14 or more, and the upper limit only needs to be 36 or less, and can be 32 or less or 27 or less.

[0060] The aforementioned polyvinyl alcohol acetal resin can be synthesized appropriately or commercially available products can be used. There are no particular limitations on the synthesis method of the aforementioned polyvinyl alcohol acetal resin; for example, the following method can be used: polyvinyl acetate, which is a polymer formed by polymerizing vinyl acetate, is saponified to replace the acetic acid groups with hydroxyl groups, thereby synthesizing polyvinyl alcohol; acetaldehyde (and, if necessary, butyraldehyde) or other aldehydes are used to perform an acetalization reaction with the synthesized polyvinyl alcohol.

[0061] Commercially available products of the above-mentioned general type of polyvinyl alcohol acetal resin include those manufactured by Sekisui Chemicals Co., Ltd. under the trade names "S-LEC BX-L", "S-LEC BX-1", "S-LEC BX-5(Z)", "S-LEC KS-1", "S-LEC KS-10", "S-LEC KS-5Z", and "S-LEC KS-6Z"; and those manufactured by Kuraray Co., Ltd. under the trade name "Mowital BA20S".

[0062] These polyvinyl acetal resins can be used alone or in combination of two or more.

[0063] The mass ratio of polyvinyl acetal resin to pigment in the oil-based ink composition for writing boards is preferably 0.34 or more, more preferably more than 0.50, and even more preferably 0.60 or more. This further improves the erasability of ink marks formed on the writing board. There is no particular upper limit to the mass ratio of polyvinyl acetal resin to pigment; for example, it can be 20.00 or less, or 10.00 or less.

[0064] The content of the polyvinyl acetal resin relative to the total amount of the oil-based ink composition can be, for example, 0.01 to 10% by mass, or 0.1 to 5% by mass. The content of the polyvinyl acetal resin is preferably more than 1.0% by mass, more preferably more than 1.5% by mass, and even more preferably 1.7% by mass or more. This further improves the erasability of the ink marks formed on the writing board and increases the density of the ink marks.

[0065] It should be noted that polyvinyl acetal resin can be added in the form of the processed pigments described later. It should also be noted that the content of polyvinyl acetal resin in processed pigments is not included in the "pigment content," but rather in the "polyvinyl acetal resin content."

[0066] <Organic solvents>

[0067] As an organic solvent in embodiments of the present invention, it can be used without particular limitation, and volatile (low boiling point) organic solvents can be used appropriately. Oil-based ink compositions using volatile organic solvents exhibit excellent ink drying properties even when writing on whiteboards or other writing surfaces. Therefore, when the hand touches freshly written ink, there will be no undried ink adhering to the hand or contaminating blank areas of the writing surface where no ink has formed, resulting in good ink marks.

[0068] Examples of volatile organic solvents include lower aliphatic alcohols or glycol ethers, which are preferably used as the main solvent (accounting for more than 50% by weight of all solvents).

[0069] Examples of lower aliphatic alcohol solvents include methanol, ethanol, n-propanol, and isopropanol, which have 2 to 4 carbon atoms. Examples of glycol ether solvents include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether, which have 4 to 6 carbon atoms. More preferably, the lower aliphatic alcohol solvents are aliphatic alcohol solvents with 2 to 4 carbon atoms, and the glycol ether solvents are glycol ether solvents with 3 to 5 carbon atoms. These organic solvents can be used alone or in combination of two or more.

[0070] In addition, other solvents can be used in combination as needed. Examples of other solvents that can be used in combination include: hydrocarbon organic solvents such as n-heptane, n-octane, isooctane, methylcyclohexane, ethylcyclohexane, toluene, xylene, and ethylbenzene; ketone organic solvents such as methyl isobutyl ketone, methyl n-propyl ketone, methyl n-butyl ketone, and di n-propyl ketone; ester organic solvents such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, n-butyl formate, isobutyl formate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, ethyl propionate, n-butyl propionate, methyl butyrate, ethyl butyrate, methyl lactate, and ethyl lactate; diol solvents such as ethylene glycol, diethylene glycol, propylene glycol, and benzyl ethylene glycol; and benzyl alcohol and γ-butyrolactone.

[0071] <Release agent (or "erasing agent")>

[0072] As the stripping agent in the embodiments of the present invention, there are no particular limitations, and known stripping agents can be used. Specifically, one or more selected from carboxylic acid esters, silicone surfactants, anionic surfactants, nonionic surfactants, polyoxyalkylene glycerol ethers and polyoxyalkylene polyglycerol ethers, sulfates of polyoxyalkylene alkyl ethers, sulfates of polyoxyethylene alkylene alkyl ethers, sulfates of polyoxyalkylene alkyl aryl ethers, phosphates of polyoxyethylene alkyl ethers or their salts, and polyalkylene glycol esters can be used. Preferably, one or more selected from carboxylic acid esters, polyoxyalkylene glycerol ethers, and polyoxyalkylene polyglycerol ethers can be used, and more preferably, carboxylic acid esters can be used. This further improves the erasability of handwriting formed on the writing board.

[0073] Examples of carboxylic acid esters include monocarboxylic acid esters and dicarboxylic acid esters. Examples of dicarboxylic acid esters include aliphatic dicarboxylic acid esters and aromatic dicarboxylic acid esters such as cyclohexane-1,2-dicarboxylic acid diisononyl ester. In addition to diglycerides of isostearate, other monocarboxylic acid esters include: cetyl octanoate, cetyl isoctanoate, isopropyl myristate, butyl myristate, isocetyl myristate, octyl dodecyl myristate, 2-hexyl decyl myristate, isopropyl isostearate, butyl isostearate, isocetyl isostearate, 2-hexyl decyl isostearate, isopropyl palmitate, 2-ethylhexyl palmitate, isooctyl palmitate, isooctadecyl palmitate, isocetyl palmitate, cetyl palmitate, isostearyl palmitate, isooctyl palmitate, isooctyl stearate, isooctyl stearate, butyl stearate, isotridecyl stearate, 2-hexyl decyl stearate, 2-ethylhexyl stearate, isooctadecyl stearate, and oil. Ethyl linoleate, cetyl 2-ethylhexanoate, stearyl 2-ethylhexanoate, isostearyl 2-ethylhexanoate, oleic acid ester, ethyl linoleate, isopropyl linoleate, isobutyl oleate, lauryl oleate, myristyl hexanoate, isostearyl hexanoate, oleic acid ester, isostearyl caprylate, oleic acid ester, isooctadecyl decanoate, oleic acid ester, butoxyethyl palmitate, triisostearate, propylene glycol didecanoate, propylene glycol dioctanoate, pentaerythritol tetraethylhexanoate, trimethylolpropane triethylhexanoate, trimethylolpropane triisostearate, tri-2-ethylhexanoate, tri(octanoic acid / decanoic acid) glyceride, propylene glycol monooctanoate, 2-butyl-2-ethyl-1,3-propane 2-ethylhexanoate, etc. Examples of aliphatic diester esters include: dibutyl adipate, diisobutyl adipate, dioctyl adipate, diisononyl adipate, diisodecyl adipate, di(2-ethylhexyl) adipate, di(tetrazyl) adipate, dibutyl sebacate, dioctyl sebacate, di(2-ethylhexyl) sebacate, dioctyl azelate, di(2-ethylhexyl) azelate, di(2-ethylhexyl) decanoate, dioctyl dodecanoate, di(2-ethylhexyl) dodecanoate, bis(2-butoxyethyl) adipate, bis(2-butoxyethyl) sebacate, bis[2-(2-butoxyethoxy)ethyl] adipate, etc.

[0074] As a carboxylic acid ester, it is preferable to include a compound represented by the following general formula (3), thereby further improving the erasability of the writing formed on the writing board.

[0075] [Chemical Formula 5]

[0076]

[0077] Here, R in the formula 1 ~R 2They are either alkyl groups with 6 to 18 carbon atoms or alkoxy polyethylene glycol groups with 2 to 18 carbon atoms and 2 to 10 oxygen atoms.

[0078] The compound represented by the above general formula (3) is a cyclohexanedicarboxylic acid ester obtained by bonding a cyclohexanedicarboxylic acid with a carboxylic acid group at any of the ortho, meta, or para positions with an alkyl alcohol having 6 to 18 carbon atoms or an alkoxy polyethylene glycol having 2 to 18 carbon atoms and 2 to 10 oxygen atoms via ester bonds. Because it can exist uniformly in the handwriting, it exhibits a high peeling effect. Furthermore, it can be inferred that the compound of the above general formula (3), due to its cyclohexane backbone and two carboxylic acid ester structures, readily forms a weak bond with the methyl acetal structure in polyvinyl alcohol acetal resin based on intermolecular forces, resulting in high compatibility. Therefore, compared to higher fatty acids such as cetyl isooctanoate, the compound of the above general formula (3) has high compatibility with polyvinyl alcohol acetal resin, and thus, even if the solvent evaporates, the components will not precipitate. Therefore, by using the compound of the above general formula (3), even when the concentration of the ink increases due to solvent evaporation at the tip of the marker pen with a large ink exposure area, it is not easy to hinder the dispersion of the pigment by the polyvinyl acetal resin. Therefore, it is easy to impart anti-caking properties, and even when the state of the exposed pen tip continues for a long time, it is possible to form the pen marks without breaking the lines when writing.

[0079] Examples of alkyl groups with 6 to 18 carbon atoms include 2-ethylhexyl, lauryl, and isononyl. Alkyl groups with 6 to 16 carbon atoms are preferred, and those with 8 to 14 carbon atoms are more preferred. Furthermore, the alkyl group with 6 to 18 carbon atoms is preferably liquid at room temperature and can be either branched or straight-chain alkyl.

[0080] Alkoxylated polyethylene glycol groups with 2-18 carbon atoms and 2-10 oxygen atoms are R-(O-(CH2)). n1 ) n2 The group represented by -O- [where R represents an alkyl group, n1 is 1 to 4, and n2 is 1 to 9] is an alkoxy polyethylene glycol group with 2 to 18 carbon atoms and 2 to 10 oxygen atoms. Examples of alkoxy polyethylene glycol groups include methoxypropanol, methoxydipropanol, and ethoxydiethylene glycol. Preferably, the alkoxy polyethylene glycol group has 2 to 16 carbon atoms and 2 to 10 oxygen atoms, and more preferably, it has 2 to 12 carbon atoms and 2 to 6 oxygen atoms. In addition, the alkoxy polyethylene glycol group with 2 to 18 carbon atoms and 2 to 10 oxygen atoms is preferably liquid at room temperature, and its alkoxy group can be a branched alkoxy or a straight-chain alkoxy.

[0081] The aforementioned release agent can be used alone or in combination of two or more. There are no particular limitations on the content of the release agent; for example, relative to the total amount of the oil-based ink composition, it can be 1.0% by mass or more and less than 15.0% by mass, or 1.0% by mass or more and less than 14.0% by mass.

[0082] Pigments

[0083] As pigments used in embodiments of the present invention, conventional pigments suitable for oil-based inks can be appropriately used. Specifically, examples include: inorganic pigments such as carbon black, ultramarine, and titanium dioxide pigments; organic pigments such as azo pigments, phthalocyanine pigments, indigo pigments, thiocyanate pigments, threne pigments, quinacridone pigments, anthraquinone pigments, threne pigments, diketopyrrolopyrrole pigments, dioxazine pigments, perylene pigments, perylene ketone pigments, and isoindolinone pigments; metallic pigments such as aluminum powder and products obtained by treating the surface of aluminum powder with coloring resin; and pigments that are transparent or colored. Metallic pigments obtained by forming a metal vapor-deposited film such as aluminum on a transparent film; metallic pigments with a thickness of 0.01 to 0.1 μm obtained by peeling off a metal vapor-deposited film such as aluminum formed on a substrate such as a film; colloidal particles selected from gold, silver, platinum, and copper with an average particle size of 5 to 30 nm; fluorescent pigments, phosphorescent pigments, and thermochromic pigments; pearlescent pigments obtained by coating the surface of natural mica, synthetic mica, glass sheets, alumina, or transparent films as core materials with metal oxides such as titanium dioxide. In addition, pigments that have undergone surface modification with resins and / or surfactants (i.e., processed pigments) can also be used. The above-mentioned pigments can be used alone or in combination of two or more. For example, in pigments that have undergone surface modification with resins, the mass ratio of resin to pigment is not particularly limited, and can be, for example, 20:1 to 1:4.

[0084] The content of the pigment described above is preferably 1 to 40% by mass, more preferably 3 to 40% by mass, relative to the total amount of the ink composition. Furthermore, common dyes, such as organic solvent-soluble dyes classified as solvent dyes in the Color Index, can be used in combination with the pigment. It should be noted that the content of components other than pigments (such as resins) included in the processed pigment is not included in the "pigment content" mentioned above, but rather in the content of components other than pigments (such as resins).

[0085] <Second resin (or also known as "adhesive resin")>

[0086] In embodiments of the present invention, the oil-based ink composition preferably further comprises a second resin other than polyvinyl acetal resin. By adding the second resin, in the formed ink coating, the second resin enters the gaps between the structures formed by the polyvinyl acetal resins and bonds with them respectively, thereby maintaining excellent erasability and adhesion, suppressing ink bleeding, and improving durability.

[0087] As the second resin mentioned above, it can be used without particular restrictions as long as it is soluble relative to the preceding organic solvent. Specific examples include: ketone resins, amide resins, alkyd resins, rosin-modified resins, rosin-modified phenolic resins, phenolic resins, xylene resins, terpene resins, coumarone-indene resins, polyvinylpyrrolidone, polyvinyl butyral resins, polyethylene oxide, polymethyl methacrylate, ketone-formaldehyde resins, α-pinene and β-pinene / phenol condensation resins, acrylic resins, polyacrylic acid polymethyl methacrylate copolymers, etc.

[0088] These resins can be used alone or in combination of two or more. The second resin can be used in the ink composition at a rate of 0.01 to 5% by mass, preferably 0.1 to 5% by mass.

[0089] It should be noted that the aforementioned resin can be added in the form of processed pigments. It should also be noted that the content of the second resin contained in the processed pigment is not included in the "pigment content," but rather in the "second resin content."

[0090] Polyvinyl butyral resin

[0091] From the viewpoint of improving the adhesion of the ink and further enhancing the color rendering of the ink in the embodiments of the present invention, polyvinyl butyral resin is preferred among the second resins described above.

[0092] By adding polyvinyl butyral resin, in the formed ink coating film, the polyvinyl butyral resin enters the gaps in the coating structure formed by the polyvinyl acetal resins and bonds with them individually. This maintains a gentle adhesion and excellent erasability, suppresses ink bleeding, and further improves durability. Furthermore, due to the structure that enters the gaps, the physical property changes that occur in conventional ink coating films formed using only polyvinyl butyral resin are less likely to occur. Even if the physical properties of the polyvinyl butyral resin change in the ink coating film, the structure that enters the gaps will not affect the formed ink coating film, preventing the ink from adhering to the writing board and enabling the formation of an ink coating film with excellent erasability. Therefore, polyvinyl butyral resin can be used without being particularly limited by its glass transition temperature. Additionally, because its molecular structure is similar to that of the polyvinyl acetal resin, it easily overlaps with each other in the ink coating film, forming a denser and more uniform ink coating film, thus further improving color development.

[0093] The aforementioned polyvinyl butyral resin can be synthesized appropriately or commercially available products can be used. Examples of commercially available products include: "S-LEC BL-10", "S-LEC BL-1", "S-LEC BL-1H", "S-LEC BL-S", "S-LEC BL-2H", "S-LEC BL-5H", "S-LEC BL-7Z", "S-LEC BM-1", "S-LEC BM-5(Z)", "S-LEC BM-2(Z)", "S-LEC BM-SHZ", "S-LEC BM-5", "S-LEC BH-S", "S-LEC BH-A", "S-LEC BH-6", and "S-LEC BH-3(Z)" manufactured by Sekisui Chemicals Co., Ltd.; and "Mowital B14S", "Mowital B16H", "Mowital B20H", "Mowital B30T", "Mowital B30H", "Mowital B30HH", and "Mowital" manufactured by Kuraray Co., Ltd. B45H", "Mowital B60T", "Mowital B60H", "Mowital B60HH", "Mowital B75H", etc.

[0094] These polyvinyl butyral resins can be used alone or in combination of two or more. The content of polyvinyl butyral resin relative to the total oil-based ink composition is preferably 0.01 to 10% by mass, and more preferably 0.1 to 5% by mass from the viewpoint of obtaining superior discharge stability.

[0095] <Other Additives>

[0096] In the oil-based ink composition for writing instruments according to embodiments of the present invention, in addition to the above-mentioned components, various additives such as drying resistance agents, antioxidants, ultraviolet absorbers, rust inhibitors, viscosity modifiers, and defoamers may be used as needed.

[0097] The aforementioned additives are referred to as conventional additives, which may be appropriately used from known compounds as needed.

[0098] The aforementioned ink composition can be filled into a marker pen with a nib attached to the writing tip for practical use. The structure and shape of the marker pen body are not particularly limited; examples include marker pens with the following structures: a marker pen nib such as a fiber nib, felt nib, or plastic nib attached to the writing tip, in which ink is impregnated in an ink-absorbing body composed of fiber bundles housed inside the pen barrel, and the ink is supplied to the writing tip; a structure in which ink is directly housed inside the pen barrel, and a given amount of ink is supplied to the writing tip via a comb-grooved ink flow regulating member or an ink flow regulating member composed of fiber bundles; and a structure in which ink is directly housed inside the pen barrel, and a given amount of ink is supplied to the writing tip via a valve mechanism. Alternatively, it can be housed in an ink reservoir that is removably and replaceably installed on the main body of the writing instrument.

[0099] It should be noted that, in addition to cap-type markers with a cap covering the tip, the markers mentioned above can also be telescopic markers with a press-type, rotate-type, or slide-type telescopic mechanism that can retract the tip into the pen barrel.

[0100] <Contributions to the SDGs>

[0101] Whiteboard teaching and learning are being conducted worldwide in various educational settings, including schools and seminars, based on the ease of writing on whiteboards and their portability and ease of deployment. Oil-based markers that can write on whiteboards are already widely used.

[0102] By using the oil-based ink composition and writing instrument containing it according to embodiments of the present invention, the time required to erase writing can be shortened, thereby enabling the provision of high-quality education. This high-quality education includes not only increased interaction time between educators and students, but also the elimination of stains and residues on the writing board during erasure, and the ability to use the writing board in a clean state at all times. In other words, embodiments of the present invention can be considered to contribute to Goal 4 of the United Nations Sustainable Development Goals (SDGs), namely, "Providing quality education for all."

[0103] Example

[0104] The ink compositions of the examples and comparative examples are shown in Tables 1 to 3 below.

[0105] It should be noted that the numerical values ​​in the table represent parts by mass.

[0106]

[0107]

[0108]

[0109] Please describe the contents of the raw materials in the table according to the labeled numbers.

[0110] (1) Carbon black

[0111] (2) CI Pigment Red 254

[0112] (3) A processed pigment composed of 50% CI Pigment Black 7 and 50% polyvinyl butyral.

[0113] (4) Processed pigment consisting of 45% CI Pigment Red 58 and 55% polyvinyl butyral.

[0114] (5) Polyvinyl alcohol acetal resin represented by general formulas (1) and (2) [glass transition temperature 108°C, manufactured by Sekisui Chemicals Co., Ltd., trade name: S-LEC KS-1]

[0115] (6) Polyvinyl alcohol acetal resin represented by general formulas (1) and (2) [glass transition temperature 103°C, manufactured by Sekisui Chemicals Co., Ltd., trade name: S-LEC KS-10]

[0116] (7) Polyvinyl alcohol acetal resin represented by general formula (1) [glass transition temperature 83°C, manufactured by Kuraray Co., Ltd., trade name: Mowital BA20S]

[0117] (8) Polyvinyl alcohol acetal resin represented by general formula (1) [glass transition temperature 79°C, manufactured by Sekisui Chemicals Co., Ltd., trade name: S-LEC BX-L]

[0118] (9) Polyvinyl alcohol acetal resin represented by general formulas (1) and (2) [glass transition temperature 110°C, manufactured by Sekisui Chemicals Co., Ltd., trade name: S-LEC KS-5Z]

[0119] (10) Polyvinyl butyral resin [glass transition temperature 70°C, manufactured by Sekisui Chemicals Co., Ltd., trade name: S-LEC BL-1]

[0120] (11) Polyvinyl butyral resin [glass transition temperature 70°C, manufactured by Sekisui Chemicals Co., Ltd., trade name: S-LEC BM-1]

[0121] (12) Polyvinyl butyral resin [glass transition temperature 61°C, manufactured by Sekisui Chemicals Co., Ltd., trade name: S-LEC BH-S]

[0122] (13) Cyclohexane-1,2-dicarboxylic acid diisononyl ester

[0123] (14) Diglyceride monoisostearate

[0124] (15) Di(2-ethylhexyl) azelaate

[0125] (16) Phosphate ester [18 carbon atoms, manufactured by Toho Chemical Co., Ltd., trade name: Phosphhanol ML-240]

[0126] The glass transition temperatures of the raw materials listed in the table were determined under the following conditions.

[0127] • Measuring apparatus: Differential scanning calorimetry (DSC) apparatus

[0128] [Made by METTLER TOLEDO, product name: FP900 Thermo System (a device consisting of an FP90 Central Processor and an FP85 TA Cell)]

[0129] • Sample volume to be measured: 10 mg

[0130] • Measurement conditions:

[0131] (A) Hold the sample at 10°C for 2 minutes.

[0132] (B) Heat the sample to 280℃ at a rate of 10℃ / min.

[0133] (C) Hold the sample at 280°C for 2 minutes.

[0134] (D) Cool the sample to 10°C at a rate of 10°C / min.

[0135] (E) Hold the sample at 10°C for 2 minutes.

[0136] (F) Heat the sample again to 280℃ at a rate of 10℃ / min.

[0137] Following operations (A) to (F) above, the glass transition temperature (Tg) was determined based on the DSC curve obtained through the final operation (F). At this point, for the glass transition temperature, based on JIS K 7121, the midpoint glass transition temperature was taken as the glass transition temperature of the raw material in the table above.

[0138] <Ink Preparation>

[0139] The solvent and all components except the stripper were added to a mixing container for ink preparation. 70g of 2mm glass beads were then stirred at 40°C for 2 hours using a high-speed paddle mixer. The stripper was then added, and the mixture was stirred for another 5 minutes. The resulting product was filtered through a screen to remove the glass beads, thus obtaining the ink composition.

[0140] Making Markers

[0141] By filling 5g of each of the oil-based ink compositions of the above examples and comparative examples into the casing of a commercially available marker (manufactured by Pilot Co., Ltd.; WMBM-12L), an oil-based marker was obtained.

[0142] The following experiments were conducted using the obtained markers.

[0143] <Eraseability Test>

[0144] Using various markers, draw five spiral circles consecutively on two types of writing boards (whiteboards). Visually observe the erasability of the handwriting when a tissue carrying a 100g weight is moved across the handwriting, both immediately after writing and after being placed at 40°C for 14 days.

[0145] It should be noted that the writing board mentioned above uses a glossy enamel board with a surface gloss of 70° and an acrylic resin coating on the substrate surface.

[0146] The results are shown in Tables 4 to 6.

[0147]

[0148]

[0149]

[0150] It should be noted that the evaluation of the symbols in the table is as follows.

[0151] <Eraseability Test>

[0152] ◎: The ink marks can be erased by moving the pen once or twice.

[0153] ○: The ink can be erased by moving the pen three times.

[0154] △: Some traces of writing remain even after three moves.

[0155] ×: More than half of the writing cannot be erased by moving the brush three times, leaving some residue.

[0156] This application claims priority to Japanese Patent Application No. 2024-028794, filed on February 28, 2024. Japanese Patent Application No. 2024-028794 is incorporated herein by reference.

Claims

1. An oil-based ink composition for writing boards, comprising at least: pigment, organic solvent, polyvinyl acetal resin of the following general formula (1) having a glass transition temperature of 75°C or higher and 120°C or lower, and a release agent. in, In the formula, p, q, r, and s represent the composition ratios. p can be arbitrarily set to 0, while q, r, and s all have values ​​greater than 0. The sum of p, q, r, and s is 100.

2. The oil-based ink composition for writing boards according to claim 1, wherein, The mass ratio of the polyvinyl acetal resin to the pigment is 0.34 or higher.

3. The oil-based ink composition for writing boards according to claim 1 or 2, wherein, The content of the polyvinyl acetal resin exceeds 1.0% by mass.

4. The oil-based ink composition for writing boards according to any one of claims 1 to 3, further comprising a second resin other than the polyvinyl acetal resin.

5. The oil-based ink composition for writing boards according to claim 4, wherein, The second resin is polyvinyl butyral resin.

6. The oil-based ink composition for writing boards according to any one of claims 1 to 5, wherein, The stripping agent comprises any one or more selected from carboxylic acid esters, silicone surfactants, anionic surfactants, nonionic surfactants, polyoxyalkylene glycerol ethers, polyoxyalkylene polyglycerol ethers, sulfates of polyoxyalkylene alkyl ethers, sulfates of polyoxyethylene alkylene alkyl ethers, sulfates of polyoxyalkylene alkyl aryl ethers, phosphates of polyoxyethylene alkyl ethers or their salts, and polyalkylene glycol esters.

7. The oil-based ink composition for writing boards according to claim 6, wherein, The carboxylic acid esters include compounds represented by the following general formula (3). Where R in the formula 1 ~R 2 They are either alkyl groups with 6 to 18 carbon atoms or alkoxy polyethylene glycol groups with 2 to 18 carbon atoms and 2 to 10 oxygen atoms.

8. The oil-based ink composition for writing boards according to any one of claims 1 to 7, wherein, The glass transition temperature is below 109°C.

9. A writing instrument comprising an oil-based ink composition for a writing board as claimed in any one of claims 1 to 8.

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