GB2099448A

GB2099448A - Grease compositions for ball pens

Info

Publication number: GB2099448A
Application number: GB8116810A
Authority: GB
Original assignee: Labofina SA
Current assignee: Labofina SA
Priority date: 1981-06-02
Filing date: 1981-06-02
Publication date: 1982-12-08
Also published as: IT8221570A0; GB2099448B; BE893076A; FR2506780A1; JPS581772A; DE3219106A1

Abstract

Grease compositions which are used as ink follower in ball pen refills or cartridges where they are disposed on the back of the ink column for providing positive pressure or weight behind the ink comprise a major amount of base oil gelled to a grease with a lower amount of water-proofed clay, and from 5% to 20% by weight, based on the total weight of composition, of a filler comprising a non-corrosive and water insoluble pigment, said composition having a consistency such that the unworked penetration after 24 hours is between 285 and 305 tenths of a millimeter when measured by the ASTM D.217-48 method.

Description

SPECIFICATION Grease compositons This invention relates to grease compositions which are used in ball pen refills and which are designed to provide positive pressure or weight behind the ink and to prevent ink seperation, thus facilitating consistent and uniform ink flow under all conditions of use.

The invention relates also to ball pen refills or cartridges wherein said grease compositions are disposed on the ink column in the tubular reservoir containing said ink.

Grease compositions generally comprise a vehicle, usually a lubricating oil, and a thickening agent, which is dispersed in the oil. Conventional grease compositions which are widely established are particularly employed as lubricants and they have been adapted for use over wide temperature or pressure ranges. Ink follower grease compositions are however unique for the reasons described in the text.

Where it is sought to obtain compositions which can satisfactorily perform their function in ball pen refills, some specific factors have to be considered. The compositions must fulfil the following requirements: non-miscibility with the ink solvent, oil bleed characteristics which must be tightly controlled, be of suitable consistency, have a high drop point, be of low toxicity, have a specific gravity less than that of the particular ink which is to be used, and have no detrimental effect on the ink flow during writing.

Some lubricating grease compositions of the conventional type meet one or other of the above requirements, but they can and do give rise to serious problems when they are used in ball pen refills. For instance, one problem encountered with silicone greases is the tendency to form a skin at the grease-ink interface, the skin being strong enough to prevent the grease from following the ink so causing loss of pressure over the ink with subsequent inconsistent ink flow.

The present invention is therefore directed to new grease compositions which meet the aforementioned requirements and which can provide high standards of performance in ball pen refills thus endowing the writing instrument with the special characteristics required.

To this end, the invention provides grease compositions comprising a major amount of base oil gelled to a grease with a lower amount of water-proofed clay and which contains from about 5% to about 20% by weight, based on the total weight of composition, of a filler comprising a non-corrosive and water-insoluble pigment, said composition having a consistency such that the unworked penetration after 24 hours is between 285 and 305 tenths of a millimeter when measured by the ASTM D.217-48 method.

According to another aspect of the invention there is provided ball pen cartridges or refills comprising a tubular reservoir containing a writing ball at one end, an ink column above said ball and a grease composition on the back of said column, the grease composition being as hereinbefore described.

The base oil employed in the grease compositions of the present invention may be any of the conventional oils, including mineral and synthetic lubricating oils. The oil may have a viscosity ranging from about 100 to 2,000 SSU at 38 C and suitably be between about 200 and 750 SSU at 38 C. The grease compositions of the present invention should contain as little toxic impurity as possible, because some users of graphic instruments, particularly children, could play with and suck the refills and swallow the contents. The base oil itself should therefore be substantially free from any toxic impurity. For this reason, highly refined oils, such as hydrofined white oils having a viscosity in the range of 300-400 SSU at 38"C are established as bases.

The base oil may also contain a synthetic lubricating oil such as a polyalphaolefin, a polyester or a polyglycol. Examples of synthetic oils which can be used in conjunction with mineral oils are polypropylene and alkyl esters of sebacic or adipic acid.

It is advantageous to include in the composition of the present invention, more particularly when the base oil is a refined white oil, a viscosity index improver. This additive is generally a substantially linear polymer which is soluble in all proportions in the base oil. Particularly suitable results are obtained using a poly-isobutene, hydrogenated or not, having a molecular weight in the range of about 850 to about 1 250, typically a polyisobutene having a mean molecular weight of about 1100 and a viscosity of about 140,000 SSU at 38 C. The amount of viscosity index improver depends upon the nature of this latter compound, the viscosity of the base oil, and the desired consistency of the grease composition. This amount can be easily determined by the skilled worker.According to the embodiment of the present invention where the base oil is a white oil, the viscosity index improver consisting in a polyisobutene with an average molecular weight of about 1100 and a viscosity of 140,000 SSU at 38 C is used in an amount corresponding to about 3-10% by weight of the base oil.

The base oil, optionally blended with a viscosity index improver, is thickened to a grease by employing water-proofed or organophilic clays. These clays are prepared by treating montmorrilonites or bentonites with onium compounds, more particularly ammonium compounds. The treated clays are organophilic and swell in organic liquids, such as the above mentioned base oils with a formation of stable gels. The thickening agents may comprise a mixture of organophilic clays. The minimum amount of organophilic clay is generally about 5% by weight of the composition. Grease compositions containing an amount of thickening agent higher than about 15% weight are too hard and are not suitable for the aforementioned specific use.

Satisfactory results have been obtained by employing a thickening agent in an amount comprised between about 6 and 12% by weight of grease composition. According to an embodiment of the present invention where a white oil is used as a base oil in admixture with 3-10% by weight of polyisobutene as a viscosity index improver, an organophilic montmorrilonite is employed as a thickening agent in an amount of about 8 to 12% based on the total weight of the base oil and polyisobutene.

For their specific use in ball pen refills, the compositions of the present invention must possess a well defined consistency. The consistency is determined by penetration test method ASTM D.217-48, which consists of measuring the distance in tenths of a millimeter a standard cone will penetrate by free fall the surface of the composition placed in a cup of standard dimension. The test is carried out at a constant temperature of 25 C. For the compositions of the present invention, the range of suitable penetration values is preferably between 285 and 305 and is relatively narrow (results on compositions after standing 24 hours in the cup, i.e.

unworked penetration).

It has also been found that the compositions of this invention must be structurally stable, i.e.

they must not "bleed" to a significant extent or, in other words, they must not tend to separate so producing a substantially amount of oil. On the other hand, a slight oil bleed is helpful to obtain a composition which can easily follow down behind the ink in the cartridge as the ink is used. It is generally advantageous that the oil bleed be stabilised between 0.3% and 0.8% by weight at a temperature of 60 C.

In order to obtain a composition which can satisfactorily meet these requirements with respect to consistency and stability, it has been found that a water-insoluble filler must be incorporated in the formulation. The filler which is generally in powder form must be inert, no-corrosive and non-miscible with the ink solvents. Particularly suitable fillers are water-insoluble pigments, which provide an additional advantage in giving a grease formulation exhibiting a uniform colour. Such fillers are exemplified by zinc oxide and titanium dioxide. Since the choice of the filler depends both on technical and cost considerations, zinc oxide can be advantageously employed.

The amount of filler to be incorporated in the formulation depends upon the nature and the respective amounts of the other components. It is however preferable to use an amount of filler in the composition giving a total weight concentration of between about 5% and 20%. When zinc oxide is used as filler, the amount is more generally controlled in the range of about 7% to 1 5% weight.

The compositions of the present invention exhibit not only the required consistency and structure, but they remain structurally stable in cases of increased temperature, which may reach about 70 C. This stability is also an important requirement for grease compositions which are used in ink refills. Furthermore, the present invention compositions do not substantially flow under gravity, so preventing leakage if the refill is stored point up. These compositions have been found to be superior, when compared with other greases, such as for example soap greases which tend to become fluid in cases of increased temperature.

It is often advantageous to further improve the properties of the compositions by incorporating small amounts of the usual additives. Antioxidants can be used, such as amines or phenols, for example ditertiarybutylcresol, in proportions of about 0.5% to 1.0% based on the total weight of the composition. Lubricity improving agents such as fatty acids or their esters can also be employed. The products resulting from a partial oxidation of petrolatum or vaselines are particularly useful, because they also act as rust-preventive agent. They can be used in amounts which generally do not exceed about 1% weight.

To ensure that the thickening agent is homogeneously dispersed in the oil, a dispersing agent is employed. Suitable dispersants are methylcellosolve, cellosolve acetate, glycol diacetate, methyl- or ethyl acetoacetate, propylene carbonate and their mixtures. The amount of dispersant does not generally exceed 1.5% by weight of the total composition. Good results have been obtained with an amount of dispersant in the range of about 0.75 to 1.0% weight.

The process for manufacturing the compositions of the present invention comprises adding to a kettle approximately one-third of the base oils and the total amount of organophilic clay. The mixture is heated while being stirred. The dispersing agent is then added, with constant stirring of the mixture. When the mixture becomes thick, the balance of the base oil is added, together with the filler while the mixture is being stirred, in such a manner as to obtain a homogeneous mixture. The viscosity index improver and the aforementioned additives are thereafter incorporated in the formulation. The mixture is then passed through a colloid mill or any other homogenizer.

The following data and examples further illustrate the present invention, but are not to be construed as limiting such invention.

Example 1 Grease compositions were prepared from the following components: -Base oil: a refined mineral-oil based composition (526 SSU at 38 C) in admixture with a hydrogenated polydecene-1 (148.4 SSU at 38 C) in a weight ratio 50:50.

-Thickening agent: dimethyl dioctodecyl ammonium bentonite (Bentone 34: registered trade mark of National Lead Company).

-Viscosity index improver: polybutene with viscosity of 140,000 SSU at 38 C.

-Dispersant: propylene carbonate.

The compositions of the grease and the results of tests were as follows: A B Comparative 1 Comparative 2 Base oil 75 74 82 64 Thickening agent 8 12 10 7 Dispersant 1 1 1.5 1 Viscosity index improver 5 5 5 4 ZnO 10 7 - 23 Additives (1) 1 1 1.5 1 (1) mixture of antioxidant and rust preventive agent (50:50 weight %) Compositions A and B meet the specific requirements of ball pen ink refills with respect to: -penetration index between 285 and 305 -oil bleed between 0.3% and 0.8% The comparative compositions 1 and 2 which are outside the scope of the present invention do not meet these requirements: Composition 1 without zinc oxide was too soft, while composition 2 contained a too large amount of zinc oxide and was too hard.

Example 2 A composition similar to composition A of example 1 was prepared, but by using TiO2 instead of ZnO. This composition also met the limiting requirements.

Example 3 A composition was prepared from the following components: -base oil: a refined mineral oil (345.7 SSU at 38 C) -thickening agent: a mixture of dimethyl-benzyl-tallow ammonium bentonite and dimethylditallow ammonium bentonite (Baragel: trade mark of the National Lead Company).

-V. I. Improver dispersant and additives : see example 1 The proportions of these components were: -base oil 75.2% -thickening agent 8 -dispersant 0.8 -V.l. improver 5 -ZnO 10 -Additives 1 The penetration was 295-305 and the oil bleed was 0.35%.

A comparative composition was prepared, but by substituting a lithium soap for the modified bentonite. The composition produced was not suitable for ink refills, because it becomes too soft in cases of increased temperature.

Another comparative composition was prepared by using: -base oil 80.% -thickening agent 10 -dispersant 1 -V.l. improver 6 -ZnO 2 -Additives 1 This composition had a penetration of 250 and an oil bleed of 1.2% which are outside the specification limits.

Claims

CLAIMS:

1. Grease compositions suitable for use in ball pen refills or cartridges and to be disposed on the back of the ink column to facilitate consistent and uniform ink flow during the writing process, said compositions comprising a major amount of base oil gelled to a grease with a lower amount of water-proofed clay, and from 5% to 20% by weight, based on the total weight of composition, of a filler comprising a non-corrosive and water-insoluble pigment, said composition having a consistency such that the' unworked penetration after 24 hours is between 285 and 305 tenths of a millimeter when measured by the ASTM D. 217-48 method.

2. Grease compositions according to claim 1, wherein the base oil has a viscosity ranging from 100 to 2,000 SSU at 38 C.

3. Grease compositions according to claim 2, wherein the base oil has a viscosity of betweeen 200 and 750 SSU at 38 C.

4. Grease compositions according to clainit wherein the base oil is a refined white oil having a viscosity in the range of 300-400 SSU at 38 C.

5. Grease compositions according to claim 1, wherein the base oil is blended with a viscosity index improver which is poly-isobutene having a mean molecular weight in the range of 850 to 1250.

6. Grease compositions according to claims 4 and 5 wherein the viscosity index improver is a poly-isobutene having a mean molecular weight of 1100 and a viscosity of 140,000 SSU at 38 C and is used in an amount corresponding about 3-10% by weight of the base oil.

7. Grease compositions according to claim 1, wherein the amount of water-proofed clay is comprised between 5 and 1 5% based on the total weight of the composition.

8. Grease compositions according to claim 1, wherein m'e pigment is zinc oxide and/or titanium dioxide.

9. Grease compositions according to claims 1 and 8, wherein the pigment is used in an amount ranging from 7 to 15% based on the total weight of the composition.

10. Grease compositions according to claim 1, having an oil bleed comprised between 0.3% and 0.8% by weight at a temperature of#O'C.

11. Grease compositions suitable for use in ball pen refills or cartridges substantially as hereinbefore described with reference to Examples 1, 2 and 3.

12. Ball pen refills or cartridges comprising a tubular reservoir containing a writing ball at one end, an ink column above said ball and on the back of said column, a grease composition according to claims 1 to 11.