NL2032990B1 - Marker ink - Google Patents

Abstract

Ink for a marker pen and marker pen comprising such an ink. The ink comprises water, humectants and pigments, and optionally a film—forming binder. The water content is below the content of the one or more humectants, e.g., below 45 wt%. The humectants can for example comprise propylene glycol.

Description

35362-Zo/AV

Marker ink

The present disclosure relates to a composition of a marker ink for marker pens, and to a marker pen comprising an ink reservoir at least partly filled with such an ink.

A marker pen is a pen with an ink reservoir, a nib of a fibrous material, such as a hard felt, and a cap to prevent the marker from drying out. Marker pen inks can be solvent based or water based. Present day solvent borne inks are usually based on alcohols, such as 1-propanol, 1-butanol, diacetone alcohol or cresols. Such solvent based inks generally provide good adhesion and wetting, but have the drawback that they are less healthy for users and have an unpleasant odour. Water based inks generally do not wet all substrates and are often not water- resistant. Examples of water based inks for marker pens are disclosed in US 5,009,536, US 5,131,776 and US 5,512,623.

Pigments dispersed in water based inks tend to settle in the ink reservoir of the marker and block capillary channels of the nib of the marker pen. Stability is also important during storage in a refill bottle, before filling the marker. Settling of pigments tends to be different in a marker reservoir than in a refill bottle. Therefore, it is an object of the invention to provide an ink which is stable in the ink reservoir of a marker and also in a refill bottle or similar container.

Water soluble dyes are generally less affected by this stability problem, but compared to pigments, they lack light fastness, colour intensity, colour reproducibility in the marker and water resistance. Colour reproducibility is particular important in the professional use of marker pens. The colour produced by a marker pen should closely match a colour as defined in a given colour standardization system.

Another problem with water based marker inks is that ink in the nib of the marker pen tends to dry out. This is usually solved by adding a combination of humectants. However, it has been found that this has a negative impact on drying speed, water resistance and rheology.

In typical use of marker pens, the marker pen is usually drawn repetitively over the same spot of the substrate.

If water-based inks are used on paper, the ink slightly dissolves the binder of the paper. This can damage the paper, especially if a relatively hard nib is used and if the pen is drawn over the same spot more than once.

It is therefore an object of the invention to provide a water based ink for a marker pen which solves at least some of the above mentioned problems.

The object of the invention is achieved with an ink for a marker pen, comprising: - water; -— one or more humectants; - one or more pigments, wherein the water content is below the content of the one or more humectants.

It was found that inks with a relatively low water content do not damage a paper substrate if the ink is repetitively applied by means of a marker pen on the same spot of the paper substrate. Combining the relatively low water content with the relatively high content of humectants results in a rheology allowing capillary feed via the nib of a marker pen and preventing settling in the ink reservoir as well as in a refill bottle or vial with any type of pigment used in the usual amounts. The nib does not dry out too quickly when the cap is off. Notwithstanding the high content of humectants it was found that ink applied on paper still dries sufficiently fast.

The water content can for example be at most 45 wt, e.g., at most 35 wt%, e.g., at most 30 wt® by total weight of the ink.

The one or more humectants may for example include glycols, e.g., selected from the group of ethylene glycol, propylene glycol, dipropylene glycol, dipropylene glycol dimethylether, tripropylene glycol dimethylether, hexylene glycol, butylene glycol, glycerol or mixtures thereof. Propylene glycol is preferred since it is odourless and colourless, hygroscopic and allows accurate setting of the rheologic profile of the composition. Good results are obtained if the ink comprises at least 50 wtt, e.g., at least 60 wt%® propylene glycol.

The particle size of the pigments should preferably be small so as to improve the stability of the composition and to prevent settling and clogging of the ink reservoir and/or the nib. Good results are obtained with pigments having an average particle size below 100 nm, measured by dynamic light scattering.

Sufficient pigment should be included in the ink to provide an adequate colour intensity, but the viscosity should not become too high. The usual inks include between about 0,1 wt% and about 8 wt3 of pigments, e.g., between about 5 wt and about 7 wt%. Pigments that may be used in the invention include water dispersible pigments, optionally provided as an aqueous dispersion, for accurate measurement and uniform mixing.

In a specific embodiment, the composition further comprises a film-forming binder or resin. The film-forming resin can for example be an acrylic resin. In a specific embodiment, the acrylic resin comprises one or more water soluble acrylic polymers or copolymers, e.g., a water soluble styrene acrylate copolymer, e.g., having a molecular weight 7000 < Mw < 10000 Da, e.g., with an acid value of about 210 - 240 and a Tg of about 100 - 120, e.g., about 109 - 112°C. The styrene acrylate copolymer can for instance be neutralized with an organic amine having a boiling point of 150 - 400°C.

The ink may for example comprise at most 10 wt? of the acrylic copolymer, e.g., at most 5 wt%, e.g. at most 2 wt%, e.g., about 1 wt3, by total weight of the ink composition.

Optionally, the ink composition may comprise additives, such as for example surfactants, cosolvents, biocides, wetting agents or stabilisers.

The ink can for example have a Brookfield viscosity of at least 5 mPa.s, e.g., at least about 9 mPa.s, e.g., at most 14 mPa.s, e.g., at most 20 mPa.s, measured with a cup spindle viscometer with S42 spindle at 25°C and 30 rpm.

Good absorption by a paper substrate is achieved if the surface tension of the inks is between about 36 to about 42 mN/m.

With the ink composition of the present invention it is possible to formulate a wide range of ink colours, with different pigments but still with essentially the same rheological behaviour and the same surface tension.

The inks can be formulated with accurately reproducible colours with high colour intensity and very good coverage, in particular of paper substrates. It is possible to formulate inks accurately matching a given colour standardization system, such as RAL, NCS, PMS, among others.

The invention also pertains to a marker pen comprising a longitudinal pen body encasing an ink reservoir, at least one nib in capillary fluid connection with the ink reservoir, and a removable cap capping the nib. The ink reservoir may for example contain an ink composition according to the disclosure above.

In a specific embodiment, the marker pen comprises a nik at both opposite ends of the pen body. The nibs may be of different types. One nib may for example be a chisel tip while the other nib is a brush tip, a fine tip, a medium tip or a bullet tip. Other combinations can also be used. The respective caps can be shaped to indicate the type of nib they cap, so the user knows which cap he should remove to find a desired nib. For example, a chisel nib can be capped by a chisel shaped cap.

To prevent unintended rolling of the marker pen, the 5 pen body and/or the cap can be provided with a non-cylindrical section.

Opticnally, the cap can be provided with a slanted top face, which can for example be used for presenting information, such as a colour identification code, e.g., the brand and the colour number. This is particularly useful if a set of marker pens with inks of a different colour are presented in a holder, such as a display box, comprising at least one receiving cavity for holding a marker pen fitting within the receiving cavity exposing the cap with the slanted top face turned upward. If the cap has the same colour as the contained ink and/or presents a colour identification code, a buyer or user can directly see which one of the marker pens corresponds to the colour of his choice.

The ink composition of the present invention is particularly suitable for use on paper, in particular paper having a relatively high Cobb value, e.g., more than 20, e.g., more than 25. The paper should also have good whiteness for the pantone colour to be represented well, e.g., CIELAB a and b values being close to 0, and L close to 100.

EXAMPLES

A set of inks of different colours was formulated on basis of a base ink composition. The base ink composition comprised 1 wt% of film forming resin with a molecular weight Mw of 7000 - 10000 Da, an acid value of 222, and a Tg of 109°C. The base ink composition further contained 32,1 wt% water and 66,9 wt% of propylene glycol.

A coloured ink was formulated comprising 96 wt? of the base ink composition, 1,87 wt& of a yellow pigment PY83 and 2,13 wt% of a red pigment PR188.

A second coloured ink was formulated comprising 93 wt? of the base ink composition, 3,46 wt% of a blue pigment PB15 and 4,54 wt® of a green pigment PG7.

A third coloured ink was formulated comprising 99 wt® of the base ink composition, and 1,0 wt% of a black pigment

PBk7.

Drying out of marker nibs was tested by storing a set of markers having two nibs without cap at room temperature. Both nibs of each marker were tested by writing before and after 17 hours of storage. Both nibs still functioned properly after 17 hours.

Water resistance was tested by making a standardised drawdown of 4 micrometer thickness on a selected drawing paper using an automated applicator. After drying for 1 hour, a watercolour brush with water was used to brush the surface. If an ink is not removed after 5 seconds of brushing, such ink is confirmed to be water-resistant. The tested inks exceeded this limit significantly and were found to be water-resistant.

Damaging of paper was tested by applying the marker ink with the brush nib to the same spot on the Pantone paper for 10 seconds. The paper remained undamaged {no fibers coming loose).

The colours of the inks were measured using a spectrophotometer and compared with a standard colour of a colour standardization system. For production quality control, the maximum allowable colour distance measured by the spectrophotometer is dE = 0,8. To test the inks, a standardised drawdown with thickness 4 micrometer of the ink on a selected paper was measured after 1 hour drying time with a UV-cut filter to compensate for optical brighteners in the paper. For all the tested inks, the measured colour distance dE was below 0,8.

Marker pens containing the inks were tested for writing durability on a writing machine with standard test paper (ISO 12757 test paper). The writing machine had a rotating bottom plate so that tested marker pens draw in a circular pattern with one circle having a circumference of 10 cm. The marker pens write under a 60° angle. The writing speed was set to 45 circles/minute, translating to 4,5 meters per minute. Paper movement was 150 mm / min. After every 100 m of writing the nibs of the marker pens were evaluated for wear, and the colour and ink flow were examined. The markers write for about 400 meters before showing loss of ink flow due to ink depletion.

The invention will be further explained with reference to the accompanying drawing, showing an exemplary embodiment.

Figure 1: shows a marker pen in longitudinal cross section;

Figure 2: shows a display box for marker pens.

Figure 1 shows an exemplary embodiment of a marker pen 1 comprising a longitudinal and mainly cylindrical pen body 2 encasing an ink reservoir 3. The pen body 2 has two opposite ends both comprising a nib 4, 5 in capillary fluid communication with the ink reservoir 3. The two nibs 4, 5 are hidden from view by a respective removable cap 6, 7. One nib 4 is a chisel nib capped by a cap 6 with a shape corresponding to the shape of the chisel nib 4. The other nib 5 is a brush nib, capped by a cap 7 with a shape corresponding to the shape of the brush nib 5.

The cap 6 of the chisel nib 4 has a rectangular cross section, so as to prevent unintended rolling of the marker pen 1. The cap © has a slanted top face 8 displaying a colour identification code corresponding to the colour of the contained ink. Also the colour of the caps 6, 7 corresponds to the colour of the contained ink.

Figure 2 shows a holder or display box 10 for presenting a set of nine marker pens 1 with inks of a different colour. The display box 10 has nine receiving cavities 11 for holding a marker pen 1. The marker pens 1 are held with a loose fit within the respective receiving cavities 11. The caps 7 with the slanted top faces 8 are turned upward to show the colour identification code. The display box 10 has a lid 12 for covering the cavities 11 and the contained marker pens 1.

The disclosure 1s not restricted to the above described embodiments which can be varied in a number of ways within the scope of the claims. Elements and aspects discussed for or in relation with a particular embodiment may be suitably combined with elements and aspects of other embodiments, unless explicitly stated otherwise.

Claims (12)

CONCLUSIONS 1. Ink composition for a highlighter, containing: - water; — one or more wetting agents; - one or more pigments, where the water content is lower than the content of the one or more humectants. 2. Ink composition according to claim 1, wherein the water content is a maximum of 45% by weight, for example a maximum of 35% by weight, for example a maximum of 30% by weight, based on the total weight of the ink composition. 3. Ink composition according to claim 1 or 2, wherein the one or more humectants comprise glycols, for example selected from the group of ethylene glycol, propylene glycol, dipropylene glycol, dipropylene glycol dimethyl ether, tripropylene glycol dimethyl ether, hexylene glycol, butylene glycol, glycerol or mixtures thereof. 4. Ink composition according to claim 1, 2 or 3, comprising at least 50 wt. propylene glycol. 5. Ink composition according to any one of the preceding claims, wherein the pigments have an average particle size of less than 100 nm (measured with dynamic light scattering). 6. Ink composition according to any of the preceding claims, further comprising a film-forming binder, for example an acrylic resin, for example comprising at least one water-soluble acrylate polymer or copolymer, for example a water-soluble styrene-acrylate copolymer. 7. Ink composition according to claim 6, comprising at most 5% by weight, for example at most 2% by weight of the styrene-acrylate copolymer. 8. Highlighter pen consisting of: - a longitudinal pen body enclosing an ink reservoir; - at least one nib in capillary fluid connection with the ink reservoir, - a removable cap covering the nib; wherein the ink reservoir contains an ink composition according to any of the preceding claims. 9. Marker pen according to claim 8, comprising two nibs of different types at opposite ends of the pen body. 10. Marker pen according to claim 9, wherein the pen body and/or cap comprises a non-cylindrical portion that prevents the marker pen from rolling away. 11. Marker pen according to claim 8, 9 or 10, wherein the cap has an oblique top surface. 12. Container for a marker pen according to claim 11, comprising at least one receiving cavity for holding a marker pen fitting within the receiving cavity with the sloping top facing upwards.