DE69703721T2 - Ink for direct filling of ballpoint pens containing an aqueous ink composition - Google Patents

Description

The present invention relates to a direct filling ink that can be used in a ballpoint pen.

A ballpoint pen that is directly filled with ink using an ink cartridge or colorant is commonly known. Typically, inks used in these types of pens have a shear-thinning property, in other words, they have a high viscosity while not in use and a low viscosity during use due to the rolling (shearing) of the ballpoint pen. Such ballpoint pens are prone to many problems.

One problem, for example, is that when the water content of the ink is evaporated, the water-soluble (dispersible) resin in the ink thickens and/or forms a layer on the pen tip due to its very high molecular weight, thereby adversely affecting the writing quality with the pen. The use of an ink with cross-linked acrylic acid polymers, which has a relatively low thickening ratio and does not form a layer when the water content is evaporated, solves this problem. However, such inks with cross-linked acrylic acid polymers have low thixotropy. Thus, the viscosity is often not reduced to a desired level by the shear force during the writing process. This causes bleeding and smudging of the writing.

When a pigment is used as a colorant, light resistance and water resistance in the written ink are generally excellent. However, when the water content of the ink is evaporated, the pigment cannot be dispersed, thereby clumping the ink on the tip of the pen. It is therefore often difficult to make the pen write at the beginning of each use, or the pen does not write at all. Worse still, in the case of a pigment ink, the pigment is generally difficult to redisperse after the dispersion is lost or the pigment hardens, and even if fresh ink is added as such, usability is usually difficult to restore. Thus, there is currently no suitable ink for use in a ballpoint pen containing an aqueous ink composition having sufficient writing ability and resistance to drying.

Because of such problems, ballpoint pens using such aqueous ink compositions must be capped to prevent evaporation of water from the ink. However, a capless type of ballpoint pen capable of starting writing by a single touch is urgently desired.

It was therefore an object of the present invention to provide an aqueous ink composition having excellent resistance to drying and excellent writing ability, which can be used in a ballpoint pen without running or smudging.

According to these and other objects, there is provided an ink suitable for use in a ballpoint pen, the ink comprising: 2 to 10% by weight of a dye, 20 to 30% by weight of a wetting agent, 5 to 10% by weight of urea, 0.2 to 0.4% by weight of crosslinked acrylic acid polymer, 0.05 to 0.2% by weight of xanthan gum, 1.0 to 5.0% by weight of sorbitol, optionally other ingredients and the balance water.

Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description or by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

An ink suitable for the present invention is a direct-fill ink that can be used for a ballpoint pen and has excellent resistance to drying out and can be used for writing without noticeable bleeding and/or smudging.

A suitable direct fill ink for a ballpoint pen containing an aqueous ink composition according to the present invention consists essentially of 2 to 10% by weight of a dye, 20 to 30% by weight of a wetting agent for maintaining moisture, 5 to 10% by weight of urea, 0.2 to 0.4% by weight of a cross-linked acrylic acid polymer, 0.05 to 0.2% by weight of xanthan gum, 1.0 to 5.0% by weight of sorbitol, with the balance being water. Unless otherwise indicated, all percentages herein are by weight based on the total weight of the ink composition.

One aspect of the present invention relates to the use of a dye as a colorant. When a pigment is used, ink stability may be lost due to evaporation of water. Once the ink has hardened, the pigment is generally difficult to restore because the ink does not normally redisperse due to the presence of the pigment even after fresh ink is added. However, if a dye is used as a colorant and the ink hardens, the dye can generally be restored to its previous state when fresh ink is added because dyes have the ability to redisperse. In other words, even if the water content of an ink containing dye has evaporated so that the ink has hardened on the pen tip, the ink will dissolve again when fresh ink is added and successful writing can be performed again.

Another aspect of the present invention is the use of a cross-linked acrylic acid polymer in combination with xanthan gum to impart a shear-thinning property to the ink. A cross-linked acrylic acid generally does not thicken into a layer as the water content of the ink evaporates. However, cross-linked acrylic acids tend to have low thixotropy, which prevents the viscosity of the ink from being reduced to a desired level when writing and kept high when not in use. In addition, cross-linked acrylic acids generally have insufficient shear-thinning.

On the other hand, xanthan gum has high thixotropy and high shear thinning. Therefore, the viscosity of the ink can be adjusted to provide excellent writing quality without necessarily causing ink dripping from a ballpoint pen tip when used in a ballpoint pen. However, xanthan gum thickens considerably after the water in the ink evaporates, causing the ink to form a layer on the pen tip and rendering the pen incapable of writing, at least to some extent.

According to the present invention, the cross-linked acrylic acid polymer is generally used as an additive for shear-thinning property to substantially prevent deterioration of the writing ability of the ballpoint pen due to evaporation of water. The xanthan gum is preferably added to compensate for disadvantages of the cross-linked acrylic acid polymer, to reduce the likelihood of ink dripping and to maintain high viscosity of the ink when not in use. This synergism between the cross-linked acrylic acid polymer and the xanthan gum results in an ink having excellent writing ability without significant bleeding or smudging during writing. The combination of these two components also provides the ink with, among other things, excellent resistance to drying without significant thickening and/or formation of a film after evaporation of the water content in the ink. Some thickening may occur when the ink drips from the pen tip or after the water has evaporated. A suitable measure of the thickening ratio of an ink according to the invention is preferably between 400 and 1000 mPas at 2.0 sec-1 and between 20 and 60 mPas at 400 sec-1. The ink of the present composition preferably has a thickening rate of up to about 30% in a preferred embodiment.

Yet another aspect of the present invention is the addition of urea to the ink. Urea has the ability to both prevent evaporation of water and dissolve dye, and therefore serves as a dissolving aid for redissolving the dye that has hardened after evaporation of water from the ink. Therefore, the combination of urea with the dye as a colorant is particularly conducive to improving resistance to drying and redissolving. However, when a pigment is used as a colorant, urea is preferably used only in an amount that does not significantly affect the stability of the ink. Moreover, the addition of urea is not critical when a pigment is used, since a pigment generally cannot be easily redissolved. However, the addition of urea is particularly advantageous in inks containing a dye to improve writing.

Yet another aspect of the present invention is the addition of sorbitol. The sorbitol is rich in hygroscopic properties and helps maintain the water content of the ink. In addition, its relatively low thickening ratio and drying properties contribute a lot to maintaining good performance of the ballpoint pen over a long period of time.

A direct fill ink for use in a ballpoint pen containing an aqueous ink composition of the present invention comprises a dye, a wetting agent, urea, cross-linked acrylic acid polymer, xanthan gum, sorbitol and water.

The dye used is used in an amount of 2 to 10% by weight based on the total weight of the ink composition. If no more than about 2% by weight of dye is used, the writing may blur under certain circumstances, and in cases where more than about 10% by weight of dye is used, the writing ability may begin to deteriorate.

The cross-linked acrylic acid polymer used is added in an amount of 0.2 to 0.4 wt% based on the weight of the ink composition. If less than about 0.2 wt% is used, the writing ability and drying resistance are adversely affected and produce undesirable ink viscosity, and if more than about 0.4 wt% cross-linked acrylic acid polymer is used, the writing quality of the ink may be affected due to the fact that the viscosity is not sufficiently reduced by the shearing force of the rolling ball during the writing process.

The xanthan gum is used in an amount of 0.05 to 0.2 wt% based on the total weight of the ink. If less than about 0.05 wt% is added, the performance of the ink may be reduced due to undesirable viscosity, and if more than about 0.2 wt% is used, a layer may form on the pen tip, which may result in deterioration of writing. In addition, the use of more than about 0.2 wt% of xanthan gum may create a deposit inside the pen tip when the ink dries out, thereby making the ink unstable.

The wetting agent preferably comprises a compound that serves to keep the ink composition moist. The wetting agent is preferably at least one compound selected from a dihydric alcohol, a trihydric alcohol, and a derivative of an alcohol, such as ethylene glycol, propylene glycol, glycerin, diethylene glycol, triethylene glycol, dipropylene glycol, polyglycerin, thiodiglycol, polyethylene glycol, polypropylene glycol, methyl cellosolve, butyl cellosolve, methyl carbitol, or ethyl carbitol. Most preferably, the wetting agent is at least one compound selected from ethylene glycol, polyethylene glycol, and glycerin. The wetting agent is used in an amount of 20 to 30% by weight based on the weight of the ink.

If less than about 20 wt% of wetting agent is used, the drying resistance of the ink may be reduced and the ink may harden on the pen tip. If more than about 30 wt% is added, the drying resistance of the ink is still excellent; however, the writing may include smudging and/or bleeding.

The urea is used in an amount of 5 to 10 wt.% based on the total weight of the ink composition. If less than about 5 wt.% is added, the hygroscopic property and dye solubility are reduced, possibly causing poor resistance to drying, and if more than 10 wt.% is used, the writing ability of the ink may be adversely affected due to the small change in viscosity when a shear force is applied. In addition, the use of excessive amounts of urea may affect the viscosity when no shear force is applied due to the possible precipitation of urea crystals after evaporation of some of the water content of the ink. If urea crystals form, they may impede ink flow.

Sorbitol is used in an amount of 1.0 to 5.0 wt% based on the weight of the ink. If less than about 1.0 wt% sorbitol is used, the hygroscopic property and the drying resistance may not be as pronounced as desired, and if more than about 5.0 wt% sorbitol is used, the thickening ratio of the ink after drying may be increased, resulting in reduced drying resistance of the ink.

The present ink composition can be prepared using a suitable method known to those skilled in the art. For example, the ink can be prepared by mixing ion exchange water and 20 to 30% by weight of a wetting agent (moisture retaining agent). Then, 5 to 10% by weight of urea, 1.0 to 5.0% by weight of sorbitol, 2 to 10% by weight of dye are added and mixed for one hour at 60°C. A polymerizable acrylic acid polymer or a cross-linked acrylic acid polymer and xanthan gum are added, and the mixture is stirred with a homogenizing stirrer to form a uniform ink.

Other optional ingredients that may be added to the present composition include 0.2 to 2.0% by weight of a rust-resistant lubricant, 0.5 to 2.0% by weight of a pH-adjusting agent, and 1.0 to 2.0% by weight of an antifungal agent. Each of these weights is based on the total weight of the ink composition. The rust-resistant agent, if employed, may comprise one or more compounds selected from a phosphoric ester surfactant, phosphoric ester-type surfactants, benzotriazoles, and fatty acid esters. The pH-adjusting agent, if employed, may preferably comprise triethanolamine. The antifungal agent may comprise any compound known to be effective in preventing or reducing fungi, as known to those skilled in the art, e.g. B. 1,2-Benzoisothiazolin-3-one (PROXEL XL-2, Zeneca, Ltd.).

The present invention will be described with reference to the following examples.

example 1

Direct Black 154 7.5 wt.%

Ethylene glycol 20.0 wt.%

Urea 5.0 wt.%

Sorbitol 1.0 wt.%

rust-resistant lubricant 0.5 wt.%

pH-regulating agent 0.5 wt.%

antifungal agent 1.0 wt.%

cross-linked acrylic acid polymer 0.25 wt.%

Xanthan gum 0.15 wt.%

Ion exchange water rest

Ion exchange water was mixed with ethylene glycol, followed by addition of urea, sorbitol, dye, rust-resistant lubricant, pH adjusting agent and antifungal agent to mix by stirring, and followed by addition with mixing of cross-linked acrylic acid polymer and xanthan gum to prepare ink.

Examples 2 to 10

Inks were prepared as in Example 1, but the proportions and components in each composition and dye were modified as shown in Table 1.

The ink quality is also shown in Table 1.

Writing performance:

- particularly excellent writing without running or smudging

- available for practical use

Δ - relatively poor

X- particularly bad

Resistance to drying: Evaluated by writing a line with a ballpoint pen which was left lying on its side without a cap at 50ºC under 30% relative humidity for more than 3 months, and then with the ink-receiving tube (inner core) thereof at room temperature

- Ability to start writing within 3 cm without a broken line, smudging or similar.

- Ability to start writing within 3 to 5 cm

Δ - Ability to start writing within 5 to 10 cm

X - no writing start within 10 cm

Ink stability: Assessed after the pen is left uncapped on its side at 50ºC under 0% relative humidity

- stable for 3 months or more (no deposits in the ink after not less than 3 months, and the thickening rate is within 30%)

- stable for 2 to 3 months

Δ - stable for 1 to 2 months

X - outside the above conditions within 1 month

As is clear from the examples, according to the present invention, a dye is preferably used as a colorant. It is advantageous to use a wetting agent to maintain the moisture content of the ink, urea and sorbitol are advantageously used to obtain excellent resistance to drying, and cross-linked acrylic acid polymer is advantageously used in combination with xanthan gum to obtain both excellent writing ability and ink stability upon drying.

Comparative examples 1 to 19

Ink was prepared as in Example 1, but the ink compositions are shown in Table 2.

The performance is also shown in Table 2. Table 2

Comparison example 1 shows an example of an increased concentration of dye, and Comparative Example 14 shows an example of a decreased concentration of dye. The increased concentration of dye shows a weak pseudoplastic ability, and therefore a desired ink viscosity is difficult to obtain. The writing ability is adversely affected, the ink stability upon drying is poor, and the drying resistance ability is reduced. In addition, the decreased concentration of dye shows excellent ink stability, but has a decreased writing ability at the beginning of writing due to the properties of the resin upon drying.

Comparative Examples 2, 3, 15 and 16 show examples of using a pigment instead of a dye as a colorant. The pigment ink cannot be fully recovered after drying and has reduced ink stability. In addition, the use of pigment can have a wear effect on the ball element in a ballpoint pen, potentially shortening the writing life of the pen.

Comparative Example 5 shows an example employing an increased amount of the wetting agent, and Comparative Example 4 shows an example employing a reduced amount of the wetting agent. The example with the increased quantity thereof shows an excellent drying resistance ability, but has a slightly inferior writing ability with some smudging and bleeding. Moreover, the ink has a reduced stability due to abnormal thickening of the ink after drying. On the other hand, the reduced amount thereof shows an absence of ink lubricity, causing some smearing or tearing in writing, and also shows a poor drying resistance due to the reduced amount of hygroscopic wetting agents.

Comparative Example 8 shows an example of an increased amount of urea, and Comparative Example 6 shows an example of a decreased amount of urea. The increased addition amount thereof shows inferior writing ability due to the small difference between the viscosity of the ink when a shearing force is applied and the viscosity when no shearing force is applied. In addition, crystals may precipitate on the pen tip when drying. On the other hand, the decreased addition amount thereof shows reduced resistance to drying due to the smaller amount of hygroscopic properties and dye solubility.

Comparative Example 9 shows an example of an increased addition amount of sorbitol, and Comparative Example 7 shows an example of a decreased amount of sorbitol. The increased amount thereof shows a weak pseudoplastic ability, adversely affecting the writing ability. Moreover, due to the lack of solubility, crystals may precipitate when the water content evaporates. On the other hand, the decreased addition amount thereof shows a reduction in ink lubricity, resulting in a reduction in resistance to drying, and also shows inferior writing ability due to the reduction in viscosity of the ink.

Comparative Example 10 shows an example of an increased amount of cross-linked acrylic acid polymer. Comparative Example 11 shows an example of an increased amount of xanthan gum. The large addition amount of cross-linked acrylic acid polymer affects the writing ability because the viscosity is not sufficiently reduced due to the shearing force of the ball rolling during writing. In addition, the writing ability at the beginning of writing is also reduced for the same reason. If the amount of xanthan gum is too is high, not only does a layer quickly form on the pen tip, which initially leads to poor writing, but a deposit also forms inside the ballpoint pen when it dries out, which leads to unstable ink.

Comparative Example 12 shows an example of a reduced addition amount of cross-linked acrylic acid polymer. Comparative Example 10 shows an example of a reduced amount of xanthan gum. In Comparative Example 12, the desired ink viscosity is difficult to obtain in terms of the film-forming ability of the ink even if the xanthan gum is used in a maximum amount. This thus causes adverse effects on the writing ability. In addition, the water retention ability of the cross-linked acrylic acid polymer is reduced, resulting in a reduction in the resistance to drying. The reduced amount of xanthan gum shows inferior performance because the desired viscosity is difficult to adjust.

Comparative Example 18 shows an example of a reduced amount of both cross-linked acrylic acid polymer and xanthan gum. In this case, the ink easily drops out of the pen, it is difficult to maintain a high viscosity when the ink is not used, and the writing quality is adversely affected.

Comparative Example 19 shows an example of adding only cross-linked acrylic acid polymer without using xanthan gum as a viscosity control agent. Without xanthan gum, an adequate shear-reducing effect is difficult to obtain. In order to prevent smudging, writing tearing or dropping of ink, it is necessary to add additional amounts of cross-linked acrylic acid polymer, thus leading to deterioration of ink drying resistance. Therefore, the use of both xanthan gum and cross-linked acrylic acid polymer is preferred.

Ink according to the invention has excellent resistance to drying and writing ability without significant bleeding and/or smudging and is very suitable for use in a ballpoint pen application.

Claims (10)

1. An ink suitable for use in a ballpoint pen, comprising: 2 to 10 wt.% of a dye, 20 to 30% by weight of a wetting agent, excluding sorbitol, 5 to 10 wt.% urea, 0.2 to 0.4 wt.% of a cross-linked acrylic acid polymer, 0.05 to 0.2% by weight xanthan gum, and 1.0 to 5.0 wt.% sorbitol, if necessary other ingredients and remaining water. 2. Ink according to claim 1, comprising as a further ingredient 0.2 to 2.0 wt.% of a rust-resistant lubricant. 3. Ink according to claim 1 or 2, comprising as a further ingredient 0.5 to 2.0 wt.% of a pH-regulating agent which is not the wetting agent defined in claim 1. 4. Ink according to one of the preceding claims, comprising as a further ingredient 1.0 to 2.0 wt. % of a fungus-resistant agent. 5. The ink according to any preceding claim, wherein the wetting agent comprises at least one selected from a dihydric alcohol, a trihydric alcohol, and derivatives of dihydric alcohols and trihydric alcohols. 6. The ink of any preceding claim, wherein the wetting agent comprises at least one selected from ethylene glycol, polyethylene glycol and glycerin. 7. The ink according to any one of claims 2 to 6, wherein the rust-resistant agent comprises at least one selected from phosphoric acid ester surfactants, benzotriazoles and fatty acid esters. 8. The ink of any one of claims 3 to 7, wherein the pH regulating agent is triethanolamine. 9. A ballpoint pen containing an ink according to any one of the preceding claims. 10. Replaceable refill for a ballpoint pen, containing an ink according to one of claims 1 to 8.