Oil-based ink composition for writing board and writing utensil containing same

Abstract

Disclosed are: an oil-based ink composition for a writing board, the oil-based ink composition containing at least a pigment, an organic solvent, a polyvinyl acetal resin that is represented by general formula (1) and has a glass transition temperature of 75°C to 120°C inclusive, and a release agent; and a writing utensil which contains the oil-based ink composition for a writing board. In the formula, p, q, r, and s represent composition ratios, p may be 0, but q, r, and s each have a value that is greater than 0, and the sum of p, q, r, and s is 100.

Description

Oil-based ink composition for writing boards and writing implements containing the same

[0001] The present disclosure relates to an oil-based ink composition for a writing board and a writing instrument containing the same, and more particularly to an oil-based ink composition for a writing board with excellent erasability and a writing instrument containing the same.

[0002] Conventionally, in oil-based inks for writing boards (so-called whiteboards or blackboards) made of materials such as enamel, metal, or plastic, an adhesive resin is added to impart adhesiveness to the handwriting formed on the writing board so that writing and erasing can be repeated, and a release agent is added to make the handwriting erasable by rubbing with a board eraser (an erasing part made of felt or cloth), etc. Polyvinyl butyral resin has been widely used as the adhesive resin because of its excellent adhesive properties.

[0003] This type of resin is described as a marking ink composition for writing boards (e.g., Patent Document 1), which is characterized by containing a pigment, a polyvinyl butyral resin, ethyl alcohol, and further a compound having a salicylic acid skeleton as an additive, or as an oil-based marking pen ink composition for writing boards (e.g., Patent Document 2), which contains a pigment, an organic solvent, a polyvinyl butyral resin, and one or more release agents selected from polyoxyalkylene glyceryl ethers and polyoxyalkylene polyglyceryl ethers.

[0004] JP 2010-144064 A JP 2017-214519 A

[0005] In the oil-based ink compositions for writing boards described in the aforementioned patent documents, the addition of polyvinyl butyral resin improves the adhesion of handwriting, but the resulting highly tough handwriting coating strongly adheres to the writing surface, making it difficult to erase with light force. Furthermore, changes in the physical properties of the handwriting coating formed on the writing board over time and / or due to external factors can cause the handwriting to adhere to the writing board, resulting in problems such as some handwriting remaining undone during rubbing or the handwriting spreading and staining the writing board. Furthermore, handwriting that remains undone may not be erasable even with a commonly used eraser or a wet rag, requiring the use of solvents and / or special removers to erase the handwriting. However, these solvents and special removers are difficult to obtain and require separate preparation, which is time-consuming. Therefore, an oil-based ink composition for writing boards that can form handwriting that can be completely erased with a commonly used eraser without using these solvents and special removers is preferred.

[0006] The present disclosure overcomes the above-mentioned drawbacks and provides an oil-based ink composition for writing boards that forms a handwriting coating film with excellent erasability regardless of the type of solvent or release agent, and that can always be erased with light force even after a long period of time has passed since the handwriting was formed, regardless of the material of the writing board, and regardless of the material and pile length of the eraser, and a writing instrument containing the same.

[0007] Aspect 1 of the present invention is an oil-based ink composition for a writing board, characterized by containing at least a pigment, an organic solvent, a polyvinyl acetal resin represented by 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 the formula, p, q, r, and s represent composition ratios, and p may be 0, but q, r, and s all have values ​​greater than 0, and the sum of p, q, r, and s is 100.

[0008] A second aspect of the present invention is the oil-based ink composition for a writing board according to the first aspect, wherein the mass ratio of the polyvinyl acetal resin to the pigment is 0.34 or more.

[0009] A third aspect of the present invention is the oil-based ink composition for a writing board according to the first or second aspect, wherein the content of the polyvinyl acetal resin is more than 1.0% by mass.

[0010] A fourth aspect of the present invention is the oil-based ink composition for a writing board according to any one of the first to third aspects, further comprising a second resin other than the polyvinyl acetal resin.

[0011] A fifth aspect of the present invention is the oil-based ink composition for a writing board according to the fourth aspect, wherein the second resin is a polyvinyl butyral resin.

[0012] Aspect 6 of the present invention is the oil-based ink composition for a writing board according to any one of Aspects 1 to 5, wherein the release agent comprises at least one selected from the group consisting of carboxylic acid esters, silicone surfactants, anionic surfactants, nonionic surfactants, polyoxyalkylene glyceryl ethers, polyoxyalkylene polyglyceryl ethers, sulfates of polyoxyalkylene alkyl ethers, sulfates of polyoxyethylene alkylene alkyl ethers, sulfates of polyoxyalkylene alkylaryl ethers, polyoxyethylene alkyl ether phosphates or salts thereof, and polyalkylene glycol esters.

[0013] A seventh aspect of the present invention is the oil-based ink composition for a writing board according to the sixth aspect, wherein the carboxylic acid esters include a compound represented by the following general formula (3): Here, R in the formula １ ~R ２ are either an alkyl group having 6 to 18 carbon atoms or an alkoxypolyglycol group having 2 to 18 carbon atoms and 2 to 10 oxygen atoms.

[0014] Aspect 8 of the present invention is the oil-based ink composition for a writing board according to any one of Aspects 1 to 7, wherein the glass transition temperature is 109°C or lower.

[0015] A ninth aspect of the present invention is a writing implement containing the oil-based ink composition for a writing board according to any one of the first to eighth aspects.

[0016] According to an embodiment of the present invention, it is possible to provide an oil-based ink composition for a writing board, which has excellent erasability of handwriting formed on the writing board, regardless of the type of solvent and release agent, and a writing instrument containing the same.

[0017]

[0023] The embodiments of the present invention will be described in detail below. In this specification, "parts," "%," "ratio," and the like, which indicate the composition, are based on mass unless otherwise specified. However, the "composition ratio" in general formulas (1) and (2) is a percentage of the number of repeating units, not based on mass.

[0018] An oil-based ink composition for a writing board in an embodiment of the present invention (hereinafter sometimes referred to as "oil-based ink composition" or "oil-based ink") is characterized by containing at least a pigment, an organic solvent, a polyvinyl acetal resin represented by general formula (1) and having a glass transition temperature of 75°C or higher and 120°C or lower, and a release agent (also referred to as an erasability-imparting agent).

[0019] <Polyvinyl Acetal Resin> The polyvinyl acetal resin according to an embodiment of the present invention is represented by the following general formula (1).

[0020]

[0021] In general formula (1), p, q, r, and s represent composition ratios, and p may be 0, but q, r, and s all have values ​​greater than 0, and the sum of p, q, r, and s is 100. Here, the "composition ratio" in general formula (1) is a percentage of the number of repeating units.

[0022] In the general formula (1), when p is 0, the polyvinyl acetal resin is represented by the following general formula (2).

[0023]

[0024] In general formula (2), q, r, and s represent composition ratios, and q, r, and s all have values ​​greater than 0, and the sum of q, r, and s is 100. Here, the "composition ratio" in general formula (2) is a percentage of the number of repeating units.

[0025] The glass transition temperature of the polyvinyl acetal resins represented by general formulas (1) and (2) used in the present invention is 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, and particularly preferably 100°C or higher, with the upper limit being 120°C or lower, preferably 110°C or lower, more preferably 109°C or lower, and even more preferably 108°C or lower. The glass transition temperature is measured using the method described in the Examples below. Generally, handwriting coatings formed on a writing surface by evaporation of a solvent are prone to changes in physical properties due to a variety of factors, such as temperature and sunlight. In particular, handwriting coatings are prone to changes in physical properties after long-term aging, resulting in a significant decrease in erasability. In the case of conventional oil-based inks using polyvinyl butyral resins, the glass transition temperature of the polyvinyl butyral resin is low, and so the handwriting coating film is likely to rise above the glass transition temperature due to ambient temperature and / or sunlight, which causes changes in the physical properties of the polyvinyl butyral resin in the handwriting coating film, resulting in part of the handwriting remaining on the written surface, a phenomenon known as deterioration. In the handwriting coating film formed by the oil-based ink of the present invention, the glass transition temperature of the polyvinyl acetal resin is as high as 75°C or higher, and so changes in physical properties due to external factors are unlikely to occur, and erasability does not decrease even after long-term aging.

[0026] The handwriting coating film of the oil-based ink using the polyvinyl acetal resin has higher brittleness, so that handwriting does not adhere strongly to the writing surface and can be easily erased with light force. The reason for this is unclear, but it is thought to be as follows. Compared to the polyvinyl butyral resins that have been widely used in the past, the structure of the polyvinyl acetal resin of the general formula has an acetal structure having a methyl group with a smaller carbon number than a butyl group, and the composition ratio of the acetal structure having a butyl group is low, which creates a three-dimensional effect and allows the formation of a handwriting coating film with high brittleness. As a result, the formed handwriting coating film gently adheres to the writing board, and handwriting can be erased with light force when rubbed off without leaving any trace on the writing board.

[0027] Furthermore, by adding the polyvinyl acetal resin to an oil-based ink containing a pigment, the polyvinyl acetal resin is gently adsorbed onto the surface of the pigment, thereby improving the dispersion stability of the pigment in the oil-based ink. Improved pigment dispersibility in the oil-based ink can suppress aggregation and sedimentation of the pigment in the oil-based ink or at the pen tip of a writing instrument, thereby eliminating writing defects such as smeared handwriting and poor writing start.

[0028] The polyvinyl acetal resin also functions as a resin for improving the adhesiveness of handwriting and preventing handwriting from bleeding (that is, it also has the same function as the second resin described below).

[0029] The mass average molecular weight (hereinafter sometimes referred to as "molecular weight") of the polyvinyl acetal resin may be 150,000 or less, or may be 110,000 or less, or 100,000 or less, from the viewpoint of improving adhesiveness. The lower limit of the mass average molecular weight is not particularly limited, but may be 10,000 or more from the viewpoint of dispersion stability of the polyvinyl acetal resin.

[0030] Furthermore, the hydroxyl group content of the polyvinyl acetal resin (i.e., "s" in general formulas (1) and (2), hereinafter sometimes referred to as "hydroxyl group amount") may be 5 or more, 10 or more, or 14 or more, in order to obtain excellent ink ejection stability, and the upper limit may be 36 or less, 32 or less, or 27.

[0031] The polyvinyl acetal resin may be synthesized appropriately or a commercially available product may be used. The method for synthesizing the polyvinyl acetal resin is not particularly limited, but for example, polyvinyl acetate, which is a polymer obtained by polymerizing vinyl acetate, is saponified and the acetate group is replaced with a hydroxyl group to synthesize polyvinyl alcohol. An example of a method is to acetalize the synthesized polyvinyl alcohol using an aldehyde such as acetaldehyde (and, if necessary, butyraldehyde).

[0032] Commercially available polyvinyl acetal resins of the above general formula include those manufactured by Sekisui Chemical 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 "Mowital BA20S" manufactured by Kuraray Co., Ltd. These polyvinyl acetal resins may be used alone or in combination of two or more. In the oil-based ink composition for writing boards, the mass ratio of the polyvinyl acetal resin to the pigment is preferably 0.34 or more, more preferably greater than 0.50, and even more preferably 0.60 or more. This allows for further improvement in the erasure of handwriting formed on the writing board. The upper limit of the mass ratio of the polyvinyl acetal resin to the pigment is not particularly limited, but may be, for example, 20.00 or less, or 10.00 or less. The content of the polyvinyl acetal resin may be, for example, 0.01 to 10% by mass, or 0.1 to 5% by mass, relative to the total amount of the oil-based ink composition. The content of the polyvinyl acetal resin is preferably greater than 1.0% by mass, more preferably greater than 1.5% by mass, and even more preferably 1.7% by mass or greater. This further improves the erasure of handwriting formed on the writing board and increases the density of the handwriting. The polyvinyl acetal resin may be added in the form of a processed pigment, as described below. The content of the polyvinyl acetal resin contained in the processed pigment is not counted as the "pigment content," but as the "polyvinyl acetal resin content."

[0033] <Organic Solvent> The organic solvent used in the present invention is not particularly limited, but a volatile (low boiling point) organic solvent is preferably used. Oil-based ink compositions using a volatile organic solvent exhibit excellent drying properties when used on writing boards such as whiteboards. Therefore, when touching the handwriting immediately after writing, problems such as wet ink adhering to the hand or staining of blank areas on the writing surface where no writing has been formed can be avoided, resulting in the formation of good handwriting. Examples of volatile organic solvents include lower aliphatic alcohol solvents and glycol ether solvents, and these are preferably used as the main solvent (accounting for 50% by weight or more of the total solvent). Specific examples of lower aliphatic alcohol solvents include aliphatic alcohol solvents having 2 to 4 carbon atoms, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, and isopropyl alcohol. Specific examples of glycol ether solvents include glycol ether solvents having 4 to 6 carbon atoms, such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether. More preferably, the lower aliphatic alcohol solvent is an aliphatic alcohol solvent having 2 to 4 carbon atoms, and the glycol ether solvent is a glycol ether solvent having 3 to 5 carbon atoms. These organic solvents may be used alone or in combination of two or more.

[0034] Further, if necessary, other solvents can also be used in combination. 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, ethyl methyl 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, glycol solvents such as ethylene glycol, diethylene glycol, propylene glycol, and benzyl glycol, benzyl alcohol, and γ-butyrolactone.

[0035] <Release Agent (Also Referred to as "Erasability Imparting Agent" or "Releasing Agent")> The release agent in the embodiment of the present invention is not particularly limited, and known ones can be used. Specific examples include one or more selected from the group consisting of carboxylic acid esters, silicone surfactants, anionic surfactants, nonionic surfactants, polyoxyalkylene glyceryl ethers and polyoxyalkylene polyglyceryl ethers, sulfates of polyoxyalkylene alkyl ethers, sulfates of polyoxyethylene alkylene alkyl ethers, sulfates of polyoxyalkylene alkylaryl ethers, polyoxyethylene alkyl ether phosphates or salts thereof, and polyalkylene glycol esters. One or more selected from the group consisting of carboxylic acid esters, polyoxyalkylene glyceryl ethers, and polyoxyalkylene polyglyceryl ethers are preferably used, and carboxylic acid esters are more preferably used. This can further improve the erasure of handwriting formed on the writing board. Examples of carboxylic acid esters include monobasic acid esters and dibasic acid esters. Examples of dibasic acid esters include aliphatic dibasic acid esters and aromatic dibasic acid esters such as diisononyl cyclohexane-1,2-dicarboxylate.Examples of monobasic acid esters include diglyceryl monoisostearate, as well as cetyl octanoate, cetyl isooctanoate, isopropyl myristate, butyl myristate, isocetyl myristate, octyldodecyl myristate, 2-hexyldecyl myristate, isopropyl isostearate, butyl isostearate, isocetyl isostearate, 2-hexyldecyl isostearate, isopropyl palmitate, 2-ethylhexyl palmitate, isooctyl palmitate, isooctadecyl palmitate, isocetyl palmitate, cetyl palmitate, isostearyl palmitate, isooctyl isopalmitate, isooctyl stearate, butyl stearate, isotridecyl stearate, 2-hexyldecyl stearate, 2-ethylhexyl stearate, isooctadecyl stearate, ethyl oleate, and cetyl 2-ethylhexanoate. Stearyl 2-ethylhexanoate, isostearyl 2-ethylhexanoate, oleyl 2-ethylhexanoate, ethyl linoleate, isopropyl linoleate, isobutyl oleate, lauryl oleate, myristyl caproate, isostearyl caproate, oleyl caproate, isostearyl caprylate, oleyl caprylate, isooctadecyl caprate, oleyl caprate, butoxyethyl palmitate, diglyceryl triisostearate, propylene glycol dicaprate, propylene glycol dicaprylate, pentaerythrityl tetraethylhexanoate, trimethylolpropane triethylhexanoate, trimethylolpropane triisostearate, glyceryl tri-2-ethylhexanoate, tri(capryl / capric)glyceryl, propylene glycol monocaprylate, 2-butyl-2-ethyl 1,3-propane 2-ethylhexanoate, and the like.Examples of aliphatic dibasic acid esters include dibutyl adipate, diisobutyl adipate, dioctyl adipate, diisononyl adipate, diisodecyl adipate, di-2-ethylhexyl adipate, ditridecyl adipate, dibutyl sebacate, dioctyl sebacate, di-2-ethylhexyl sebacate, dioctyl azelate, di-2-ethylhexyl azelate, di-2-ethylhexyl decanoate, dioctyl dodecanoate, di-2-ethylhexyl dodecanedioate, bis(2-butoxyethyl)adipate, bis(2-butoxyethyl)sebacate, and bis[2-(2-butoxyethoxy)ethyl] adipate.

[0036] The carboxylic acid ester preferably contains a compound represented by the following general formula (3), which can further improve the erasability of handwriting formed on the writing board. Here, R in the formula １ ~R ２are either an alkyl group having 6 to 18 carbon atoms or an alkoxypolyglycol group having 2 to 18 carbon atoms and 2 to 10 oxygen atoms. The compound represented by the general formula (3) is a cyclohexanedicarboxylic acid ester in which a cyclohexanedicarboxylic acid having a carboxylic acid group at the ortho, meta, or para position is ester-bonded to an alkyl alcohol having 6 to 18 carbon atoms or an alkoxypolyglycol having 2 to 18 carbon atoms and 2 to 10 oxygen atoms. This compound can be uniformly present in the writing, thereby exhibiting a high release effect. Furthermore, due to the structure of the cyclohexane skeleton and two carboxylic acid esters, the compound represented by the general formula (3) is presumed to easily form weak bonds due to intermolecular forces with the acetal structure having a methyl group in the polyvinyl acetal resin, resulting in high compatibility. Therefore, the compound represented by the general formula (3) is more compatible with polyvinyl acetal resin than higher fatty acids such as cetyl isooctanoate, and therefore does not precipitate even when the solvent evaporates. Therefore, by using the compound of general formula (3), pigment dispersion by the polyvinyl acetal resin is not easily hindered even when the concentration increases due to solvent evaporation in the marker pen tip portion, which has a large ink-exposed surface, and therefore dry-up resistance is easily imparted, and handwriting can be formed without smearing during writing even when the pen tip is left exposed for a long period of time. Examples of the alkyl group having 6 to 18 carbon atoms include a 2-ethylhexyl group, a lauryl group, and an isononyl group. Preferred are alkyl groups having 6 to 16 carbon atoms, and more preferably alkyl groups having 8 to 14 carbon atoms. Furthermore, the alkyl group having 6 to 18 carbon atoms is preferably liquid at room temperature, and may be either a branched alkyl group or a linear alkyl group. The alkoxypolyglycol group having 2 to 18 carbon atoms and 2 to 10 oxygen atoms is R—(O—(CH ２ ) ｎ１ ) ｎ２-O- [wherein R represents an alkyl group, n1 is 1 to 4, and n2 is 1 to 9.] Examples of the alkoxy polyglycol group having 2 to 18 carbon atoms and 2 to 10 oxygen atoms include a methoxypropanol group, a methoxydipropanol group, and an ethoxydiglycol group. Preferably, it is an alkoxy polyglycol group having 2 to 16 carbon atoms and 2 to 10 oxygen atoms, and more preferably an alkoxy polyglycol group having 2 to 12 carbon atoms and 2 to 6 oxygen atoms. Furthermore, the alkoxy polyglycol group having 2 to 18 carbon atoms and 2 to 10 oxygen atoms is preferably liquid at room temperature, and the alkoxy group may be a branched alkoxy group or a linear alkoxy group.

[0037] The release agent may be used alone or in combination of two or more. The content of the release agent is not particularly limited, but may be, for example, from 1.0 mass % to less than 15.0 mass %, or from 1.0 mass % to 14.0 mass %, relative to the total amount of the oil-based ink composition.

[0038] <Pigment> As the pigment in the embodiment of the present invention, a general-purpose pigment that has been conventionally used in oil-based inks may be appropriately used. Specific examples include inorganic pigments such as carbon black, ultramarine, and titanium dioxide pigments; organic pigments such as azo pigments, phthalocyanine pigments, indigo pigments, thioindigo pigments, threne pigments, quinacridone pigments, anthraquinone pigments, threne pigments, diketopyrrolopyrrole pigments, dioxazine pigments, perylene pigments, perinone pigments, and isoindolinone pigments; metallic pigments such as aluminum powder and aluminum powder whose surface has been treated with a colored resin; metallic luster pigments in which a metal vapor-deposited film of aluminum or the like has been formed on a transparent or colored transparent film; metal pigments having a thickness of 0.01 to 0.1 μm obtained by peeling off a metal vapor-deposited film of aluminum or the like formed on a substrate such as a film; colloidal particles having an average particle size of 5 to 30 nm selected from gold, silver, platinum, and copper; fluorescent pigments, phosphorescent pigments, thermochromic pigments; and pearl pigments in which the surface of natural mica, synthetic mica, glass flakes, alumina, or transparent film flakes is coated with a metal oxide such as titanium oxide as a core material. Furthermore, pigments whose surfaces have been modified with resins and / or surfactants (i.e., processed pigments) may also be used. The pigments may be used alone or in combination of two or more. For example, in pigments whose surfaces have been modified with resins, the mass ratio of resin to pigment is not particularly limited, but may be, for example, 20:1 to 1:4. The content of the pigment is preferably 1 to 40 mass% and more preferably 3 to 40 mass% based on the total amount of the ink composition. Furthermore, the pigment may be used in combination with a general-purpose dye, such as an organic solvent-soluble dye classified as a solvent dye in the Color Index. Note that the content of components other than the pigment (e.g., resins) contained in the processed pigment is not counted as the "pigment content" above, but is counted as the content of components other than the pigment (e.g., resins).

[0039] <Second Resin (or Adhesive Resin)> The oil-based ink composition according to an embodiment of the present invention preferably further contains a second resin other than the polyvinyl acetal resin. By adding the second resin, the second resin penetrates into the gaps formed between the polyvinyl acetal resins in the resulting handwriting coating film and bonds with them, thereby improving the resistance to bleeding and robustness of the handwriting while maintaining excellent erasability and adhesive properties. The second resin may be any resin that is soluble in the organic solvent described above, without any particular limitation. 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, polymethacrylic acid esters, ketone-formaldehyde resins, α- and β-pinene-phenol polycondensation resins, acrylic resins, and polyacrylic acid-polymethacrylic acid copolymers. These resins may be used alone or in combination of two or more. The second resin may be present in an amount of 0.01 to 5% by mass in the ink composition, preferably 0.1 to 5% by mass. The resin may be added in the form of a processed pigment. The content of the second resin contained in the processed pigment is not counted as the "pigment content," but as the "second resin content."

[0040] <Polyvinyl butyral resin> In the oil-based ink composition according to an embodiment of the present invention, a polyvinyl butyral resin is preferably used as the second resin, in view of achieving superior adhesion of handwriting and further improving the color development of handwriting. By adding a polyvinyl butyral resin, the polyvinyl butyral resin penetrates into the gaps in the coating film structure formed by the polyvinyl acetal resins in the formed handwriting coating film, bonding with each other, thereby further improving the suppression of bleeding and robustness of handwriting while maintaining gentle adhesion and excellent erasability. Furthermore, due to the aforementioned structure in which the polyvinyl butyral resin penetrates into the gaps, the physical property changes that occur in handwriting coating films formed by conventional oil-based ink compositions using only polyvinyl butyral resin are unlikely to occur. Even if the physical properties of the polyvinyl butyral resin change in the handwriting coating film, due to the aforementioned structure in which the polyvinyl butyral resin penetrates into the gaps, the formed handwriting coating film can be formed without causing the handwriting to stick to the writing board, and a handwriting coating film with excellent erasability can be formed. Therefore, polyvinyl butyral resin can be used without any particular limitation on the glass transition temperature. In addition, since the molecular structure of polyvinyl butyral resin is similar to that of polyvinyl acetal resin, the respective molecules easily overlap each other in the handwriting coating film, and a denser and more uniform handwriting coating film can be formed, thereby further improving color development.

[0041] The polyvinyl butyral resin may be suitably synthesized or may be a commercially available product. Commercially available products include those manufactured by Sekisui Chemical Co., Ltd. under the trade names "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)"; and those manufactured by Kuraray Co., Ltd. under the trade names "Mowital B14S," "Mowital B16H," "Mowital B20H," "Mowital B30T," "Mowital B30H," and "Mowital B40H." Examples of suitable polyvinyl butyral resins include "Mowital B30HH", "Mowital B45H", "Mowital B60T", "Mowital B60H", "Mowital B60HH", and "Mowital B75H". These polyvinyl butyral resins may be used alone or in combination of two or more. The content of the polyvinyl butyral resin is preferably 0.01 to 10% by mass, and more preferably 0.1 to 5% by mass, based on the total mass of the oil-based ink composition, in terms of obtaining better ejection stability.

[0042] <Other Additives> In addition to the above components, the oil-based ink composition for a writing instrument according to an embodiment of the present invention may contain various additives such as drying resistance imparting agents, antioxidants, ultraviolet absorbers, rust inhibitors, viscosity modifiers, antifoaming agents, etc. The additives are so-called conventional additives, and known compounds may be used as needed.

[0043] The ink composition is filled into a marking pen with a nib attached to its writing tip for practical use. The structure and shape of the marking pen itself are not particularly limited. Examples of marking pens include a structure in which a marking pen nib, such as a fiber nib, felt nib, or plastic nib, is attached to the writing tip, and ink is impregnated into an ink reservoir made of a fiber bundle housed inside the barrel, thereby supplying ink to the writing tip; a structure in which ink is directly housed inside the barrel, and a predetermined amount of ink is supplied to the writing tip via a comb-shaped ink flow rate regulator or an ink flow rate regulator made of a fiber bundle; and a structure in which ink is directly housed inside the barrel, and a predetermined amount of ink is supplied to the writing tip via a valve mechanism. The ink may also be housed in an ink reservoir that can be detachably attached to the writing instrument body. The marking pen may be a cap-type marking pen equipped with a cap that covers the nib, or a retractable marking pen with a retractable mechanism, such as a knock-type, rotary-type, or slide-type, that allows the nib to be housed inside the barrel.

[0044] <Contribution to SDGs> In various educational settings, such as schools and seminars, whiteboards are used in lessons and learning around the world due to the ease of writing on the board and their portability and ease of introduction, and oil-based marking pens that can be used to write on whiteboards are widely used. By using the oil-based ink composition according to an embodiment of the present invention and a writing instrument containing the same, the time required for erasing handwriting can be shortened, thereby increasing the time for communication between educators and students. Furthermore, the ink composition according to an embodiment of the present invention eliminates the staining and residual marks that occur when erasing the writing board, allowing the writing board to be used in a clean state at all times, thereby enabling the provision of high-quality education. In other words, it is believed that the embodiment of the present invention can contribute to the achievement of Goal 4 of the Sustainable Development Goals (SDGs) advocated by the United Nations, "Quality Education for All," and other goals.

[0045] The ink compositions of the examples and comparative examples are shown in the following Tables 1 to 3. The numerical values ​​of the compositions in the tables indicate parts by mass.

[0046]

[0047]

[0048]

[0049] The contents of the raw materials in the table are explained in order of the note number: (1) Carbon black (2) C.I. Pigment Red 254 (3) A processed pigment consisting of 50% C.I. Pigment Black 7 and 50% polyvinyl butyral (4) C.I. (5) Polyvinyl acetal resin represented by the general formulas (1) and (2) [glass transition temperature 108 ° C., manufactured by Sekisui Chemical Co., Ltd., trade name: S-LEC KS-1] (6) Polyvinyl acetal resin represented by the general formulas (1) and (2) [glass transition temperature 103 ° C., manufactured by Sekisui Chemical Co., Ltd., trade name: S-LEC KS-10] (7) Polyvinyl acetal resin represented by the general formula (1) [glass transition temperature 83 ° C., manufactured by Kuraray Co., Ltd., trade name: Mowital BA20S] (8) Polyvinyl acetal resin represented by the general formula (1) [glass transition temperature 79 ° C., manufactured by Sekisui Chemical Co., Ltd., trade name: S-LEC BX-L] (9) Polyvinyl acetal resin represented by the general formulas (1) and (2) [glass transition temperature 110 ° C., manufactured by Sekisui Chemical Co., Ltd., trade name: S-LEC KS-5Z] (10) Polyvinyl butyral resin [glass transition temperature 70°C, manufactured by Sekisui Chemical Co., Ltd., trade name: S-LEC BL-1] (11) Polyvinyl butyral resin [glass transition temperature 70°C, manufactured by Sekisui Chemical Co., Ltd., trade name: S-LEC BM-1] (12) Polyvinyl butyral resin [glass transition temperature 61°C, manufactured by Sekisui Chemical Co., Ltd., trade name: S-LEC BH-S] (13) Diisononyl cyclohexane-1,2-dicarboxylate (14) Diglyceryl monoisostearate (15) Di(2-ethylhexyl) azelate (16) Phosphate ester [carbon number 18, manufactured by Toho Chemical Industry Co., Ltd., trade name: Phosphanol ML-240]

[0050] The glass transition temperatures of the raw materials in the table were measured under the following conditions: Measurement apparatus: Differential scanning calorimetry (DSC) apparatus [Mettler Toledo Corporation, product name: FP900 Thermosystem (apparatus consisting of an FP90 Central Processor and an FP85 TA Cell)] Measurement sample amount: 10 mg Measurement conditions: (A) Holding the sample at 10°C for 2 minutes (B) Heating the sample to 280°C at 10°C / min (C) Holding the sample at 280°C for 2 minutes (D) Cooling the sample to 10°C at 10°C / min (E) Holding the sample at 10°C for 2 minutes (F) Heating the sample again to 280°C at 10°C / min After the above operations (A) to (F), the glass transition temperature (Tg) was determined from the DSC curve obtained in the last operation (F). In this case, the glass transition temperature was determined based on JIS K 7121, and the midpoint glass transition temperature was taken as the glass transition temperature of the raw material in the above table.

[0051] <Ink Preparation> Ink Preparation: The components other than the release agent were placed in a stirring vessel together with the solvent, and stirred together with 70 g of 2 mm glass beads in a high-speed blade mixer at 40°C for 2 hours, after which the release agent was added and stirred for a further 5 minutes, and the mixture was filtered through a mesh to remove the glass beads, thereby obtaining an ink composition.

[0052] <Preparation of Marking Pen> 5 g of each of the oil-based ink compositions of the Examples and Comparative Examples was filled into a commercially available marking pen case (WMBM-12L, manufactured by Pilot Corporation) to obtain an oil-based marking pen. The following tests were carried out using each of the obtained marking pens.

[0053] <Erasability Test> Using each marking pen, five consecutive spiral circles were written on two types of writing boards (whiteboards). The handwriting was visually observed immediately after writing and after leaving the board at 40°C for 14 days when a tissue paper carrying a 100g weight was moved over the handwriting. The writing board used was a gloss enamel board with a surface gloss value of 70°, the surface of which was coated with acrylic resin. The results are shown in Tables 4 to 6.

[0054]

[0055]

[0056]

[0057] The symbols in the table are used to evaluate the results as follows: <Erasability test> ◎: Handwriting can be erased with one or two moves. ○: Handwriting can be erased with three moves. △: Part of the handwriting remains after three moves. ×: More than half of the handwriting cannot be erased after three moves and remains.

[0058] This application claims priority from Japanese Patent Application No. 2024-028794, filed February 28, 2024. Japanese Patent Application No. 2024-028794 is incorporated herein by reference.

Claims

1. An oil-based ink composition for a writing board, comprising at least a pigment, an organic solvent, a polyvinyl acetal resin represented by 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 the formula, p, q, r, and s represent composition ratios, and p may be 0, but q, r, and s all have values ​​greater than 0, and the sum of p, q, r, and s is 100.

2. An oil-based ink composition for a writing board according to claim 1, wherein the mass ratio of said polyvinyl acetal resin to said pigment is 0.34 or more.

3. An oil-based ink composition for writing boards according to claim 1 or 2, wherein the content of the polyvinyl acetal resin is more than 1.0 mass%.

4. The oil-based ink composition for a writing board 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 a polyvinyl butyral resin.

6. The oil-based ink composition for writing boards according to any one of claims 1 to 5, wherein the release agent comprises at least one selected from the group consisting of carboxylic acid esters, silicone surfactants, anionic surfactants, nonionic surfactants, polyoxyalkylene glyceryl ethers, polyoxyalkylene polyglyceryl ethers, sulfates of polyoxyalkylene alkyl ethers, sulfates of polyoxyethylene alkylene alkyl ethers, sulfates of polyoxyalkylene alkylaryl ethers, polyoxyethylene alkyl ether phosphates or salts thereof, and polyalkylene glycol esters.

7. The oil-based ink composition for a writing board according to claim 6, wherein the carboxylic acid esters include a compound represented by the following general formula (3): Here, R in the formula １ ~R ２ are either an alkyl group having 6 to 18 carbon atoms or an alkoxypolyglycol group having 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 109°C or lower.

9. A writing implement containing the oil-based ink composition for writing boards according to any one of claims 1 to 8.

Images