EP0005921B1

EP0005921B1 - Mark-recording systems

Info

Publication number: EP0005921B1
Application number: EP79300801A
Authority: EP
Inventors: Pierre Jean Allart; Claude Andre Guillaume
Original assignee: Monsanto Europe NV SA
Current assignee: Bayer Agriculture BVBA
Priority date: 1978-05-31
Filing date: 1979-05-10
Publication date: 1982-10-27
Also published as: FI791647A; AU4747879A; JPS552090A; FI70180C; FI70180B; CA1126026A; ATE1699T1; AU528695B2; DE2963924D1; EP0005921A1

Abstract

The invention relates to mark-recording systems, for example carbonless copying paper, in which a colourless chromogen is brought into contact with a chromogen-sensitizing agent in the presence of a liquid solvent for the chromogen, thereby producing a visible mark. In a system of the invention, the chromogen is a derivative of diphenylmethanol or diphenylmethylamine, the sensitizing agent is an acid clay, and the solvent comprises an aliphatic benzyl phthalate.

Description

This invention relates to pressure-sensitive mark-recording systems. The most familiar form of pressure-sensitive mark-recording system is the so-called carbonless copying paper which comprises a two-sheet system in which the under surface of the top sheet has a coating of microcapsules of a solution of a colourless chromogen, while the upper surface of the lower (receiver) sheet has an absorbent coating including a sensitizing agent for the chromogen. When a marking instrument is applied to the top sheet, the microcapsules are locally ruptured, thereby releasing the chromogen solution from the affected microcapsules to react with the underlying sensitizing agent and form coloured marks on the receiver sheet corresponding to the marks applied to the top sheet.
A successful carbonless copying paper system needs to meet a number of criteria. For example the marks on the receiver sheet should develop rapidly to a legible intensity of colour and a legible mark should persist for as long as the sheet is required to be kept. Whether the various criteria are met depends on a number of factors including the nature of the chromogen, the solvent and the sensitizing agent, and many different materials of each category have been proposed. Chromogens which have been proposed include phthalide derivatives, for example crystal violet lactone, and Malachite green lactone, indole-substituted pyromellitides, leucauramines, and diphenylmethane derivatives such as Michier's hydrol. Solvents which have been proposed include hydrocarbons, for instance petroleum fractions or synthetic hydrocarbons such as hydrogenated terphenyls: halogenated hydrocarbons, for instance chlorinated biphenyls, and esters, for instance alkyl adipates and. alkyl phthalates. The sensitizing agent is usuaHy an acid clay for example an attapulgite or bentonite clay, or an acidic organic polymer, for example a phenol-aldehyde polymer or a partially or wholly hydrolysed styrenemaleic anhydride or ethylene-maleic anhydride polymer.
The chromogens which are probably most frequently referred to in the art are the phthalide derivatives, especially crystal violet lactone. These chromogens are usually used in solution in a hydrocarbon type solvent. One reason for this choice of solvent is that although the phthalide colour- formers are soluble in esters, for example, it is found that esters and certain other solvents having similar polarity to the esters, show too great a tendency to compete with the chromogen in affinity for the sensitizing agent, so that in some cases, no colour development occurs. This is especially so with certain acid clay sensitizing agents.
Certain chromogens that are diphenylmethane derivatives are less subject to this limitation and can be used in conjunction with solvents such as esters, advantages of the latter over hydrocarbons being that the chromogens dissolve more readily and have higher solubilities. The use of diphenylmethane derivatives, for instance Michler's hydrol, as chromogens in pressure sensitive mark-recording systems, and the use of dibutyl phthalate as a solvent for the chromogen, is described in, for example, British Patent Specification 1,381,928 and U.S. Patent Specification 4,000,087.
U.S. Patent Specification 3,684,549 describes a record material sensitized with acidic electron acceptors and a dye transfer layer comprising a leucoauramine dye homogeneously distributed throughout an inert hot melt layer plasticized such that the dye can be easily transferred to the acidic electron acceptor layer for marking without transfer of the hot melt. The leucoauramine dyes are derivatives of bis(p-dialkylaminoaryl)methane, and amongst the plasticizers disclosed are butyl benzyl phthalate and octyl benzyl phthalate.
A pressure-sensitive mark-recording system of the invention comprises (a) sheet material, (b) mark-forming components supported by the sheet material and arranged in juxtaposition but in unreactive condition, the said components comprising a chromogen which is a, derivative of diphenylmethanol or of diphenylmethylamine and an acid clay sensitizer for the chromogen which produces a colour from the chromogen when brought into contact with the chromogen in the presence of a liquid solvent for the chromogen comprising an aliphatic benzyl phthalate or an aliphatic substituted-benzyl phthalate, that is to say a phthalate ester in which one of the carboxyl groups is esterified by an aliphatic group and the other by a benzyl or substituted benzyl group, and (c) the said liquid solvent supported by the sheet material but separated from the sensitizing agent by a physical barrier which is rupturable on the application of a marking instrument to the sheet material.
Compared with the solvents, for example xylene or dibutyl phthalates, hitherto proposed for use in conjunction with chromogens that are diphenylmethane derivatives, use of solvents in accordance with the present invention results in an improvement in the resistance to fading of the marks on the receiver sheet during storage, particularly if storage occurs under conditions where fading is due to the action of oxygen.
In an aliphatic benzyl or substituted-benzyl phthalate useful in the present invention, the aliphatic group can, for example, contain up to 24 carbon atoms, and may have a straight or a branched chain. It can, for example, be an alkyl group, for example an ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec- butyl, n-hexyl, isohexyl, n-octyl, 2-ethylhexyl, decyl, tetradecyl or octadecyl group. Preferred alkyl groups contain from 2 to 12 carbon atoms. Alternatively, the aliphatic group may be an alkoxyalkyl or a group derived from an alkyl group by the replacement of more than one -CHZ group by the same number of oxygen atoms, and it may thus be, for instance, an ethoxyethyl or a 3,6,9-trioxaundecyl group. A third possibility is that the aliphatic group is one derived from an alkyl ester of a hydroxy-carboxylic acid, for example a C_1-18 alkyl ester of glycollic acid, beta-hydroxypropionic acid or gamma- hydroxybutyric acid; or from a hydroxyalkyl ester of an aliphatic carboxylic acid, where the hydroxyalkyl radical and the aliphatic carboxylic acid may each contain up to 12 carbon atoms. Examples of such aliphatic groups are .butoxycarbonylmethyl, (2-ethylhexyloxy)carbonylmethyl, 2(ethylcarbonyloxy)ethyl .and 2,6,6,8-tetramethyl-4-oxa-3-oxonon-7-yl.
Preferred aliphatic substituted-benzyl phthalates are aliphatic alkylbenzyl phthalates. In an alkylbenzyl group, the nucleus of the benzyl group may, for instance, contain up to three alkyl substituents, each, for example, being an alkyl group having up to four carbon atoms, for instance methyl or ethyl; or one or both methylene hydrogen atoms of the benzyl group may be replaced by a similar alkyl group.
Specific examples of aliphatic benzyl phthalates useful in the present invention are butyl benzyl phthalates, for instance n-butyl benzyl phthalate and isobutyl benzyl phthalate, octyl benzyl phthalates, for instance n-octyl benzyl phthalate and 2-ethylhexyl benzyl phthalate, and 2,6,6,8-tetramethyl-4-oxa-3-oxonon-7-yl benzyl phthalate.
The solvents used in the present invention can contain more than one aliphatic benzyl or substituted-benzyl phthalate, for example mixtures of alkyl benzyl or substituted-benzyl phthalates having a range of alkyl group sizes, for instance a CS-C7, a C₇-C₉ or a C₈-C₁₂ range. The solvents may optionally contain other components, for instance dialkyl' phthalates such as dibutyl phthalate and dioctyl phthalates, and various hydrocarbons, for example C_S-12 alkylbenzenes, kerosene or other petroleum fractions which are useful as diluents in certain circumstances to reduce the viscosity of the solvent. Preferably the solvent contains at least 50% by weight of an aliphatic benzyl or substituted benzyl phthalate or of a mixture of aliphatic benzyl or substituted-benzyl phthalates. Thus the solvent can be a mixture of at least one aliphatic benzyl or substituted-benzyl phthalate and a hydrocarbon diluent, the said mixture containing at least 50% by weight of the phthalate or phthalates. The proportions by weight of the aliphatic benzyl or substituted benzyl phthalate or phthalates and the diluent in mixtures may, for example, range from 50:50 to 90:10, for example 60:40, 70:30, 75:25 or 80:20. For rapid development of print intensity, the solvent is preferably one having a viscosity in the range 5 to 15 x 10^-2m²s^-1 (centistokes) at 38°C.
The concentration of the chromogen in a solution of the invention is generally of the same order as that in known solutions of chromogens which are diphenylmethanol or diphenylmethylamine derivatives, for example from 0.25 to 5%, more particularly from 0.4 to 4.0% by weight of the solution.
Chromogens which are especially suitable for use in the present invention include Michler's hydrol, i.e. bis(p-dimethylaminophenyl) methanol, its ethers, for example the methyl ether of Michler's hydrol and the benzyl ether of Michler's hydrol, aromatic sulfonic and sulfinic esters of Michler's hydrol, for example the p-toluene-sulfinate of Michler's hydrol, and derivatives of bis(p-dimethylaminophenyl)methylamine, for example N(bis(p-dimethylaminophenyl)methyllmorpholine.
Several encapsulation systems have been proposed for the encapsulation of the chromogen solution for use in carbonless copying paper, and the capsule walls in such systems generally may be formed from either natural or synthetic polymeric material. In the present invention, the capsule wall or shell is preferably made from a synthetic polymer, for example a polyurethane resin, a ureaformaldehyde resin, a melamine-formaldehyde resin or a polyamide resin. The use of such resins as shell-forming material in encapsulation is described in, for example, U.S. Patent 3,016,308, British Patent 989,264 and U.S. Patent 3,429,827. Shells of this kind can be made significantly less permeable to the aliphatic benzyl phthalates used in the present invention than shells made of natural polymeric material such as gelatin.
The acid clay used as sensitizing agent for the chromogen in the present invention can be any of those conventionally used for this purpose, including bentonite and attapulgite. The naturally occurring clay may be subjected to various treatments such as acid extraction or calcination before use as the sensitizing agent.
The mark-recording system of the present invention can be prepared according to well known conventional procedures. Descriptions of methods for preparing both the dye-carrying paper and clay-coated receiving paper are to be found in the literature.
Although a preferred embodiment of this invention comprises a two-sheet system wherein the acid is carried by one sheet and a marking fluid comprising a chromogen and solvent is carried by a second sheet, the invention is not limited to such systems alone. The only essential requirement is that the chromogen and the acid clay be maintained in a separate or unreactive condition until pressure is applied to the system and that upon the application of pressure the chromogen and acid clay are brought into reactive contact. Thus it is possible to have the chromogen and acid clay present in a dry and unreactive state on a common sheet and to have the solvent alone carried on a separate sheet whereupon the application of pressure would release the solvent into the chromogen-acidic material mixture and promote localized reaction and colour development. Obviously, many other arrangements, configurations and relationships of the solvent and the mark forming materials with respect to their encapsulation and location on the supporting sheet material can be envisaged, and such arrangements are within the scope of the present invention. For example, it is possible to coat a single sheet of paper with all the components of this system to form a single self-contained unit which can be marked by the movement of a stylus or other pressure-imparting means upon the surface of the paper. Such papers are particularly useful for use in inkless recording instruments.
Solutions for use in the invention were evaluated by the following technique:

A 0.5% by weight solution of Michler's hydrol p-toluene-sulfinate in the solvent was prepared. To estimate print intensity, a plate engraved with a pattern of dots was coated with sufficient of the solution to give a coating 18 microns in thickness, using a doctor blade. A carriage-supported roller having a paper sheet coated with an acid clay sensitizing agent wrapped round the roller was then moved slowly across the solution-coated plate under constant pressure. Colour developed on the paper. The paper was removed from the roller, and the intensity of colour was measured using a Macbeth RD 514 reflectometer calibrated against a "perfect white" of 0.07 units of optical density and a "perfect black" of 1.78 units of optical density, using standard "perfect white" and "perfect black" plates supplied by the manufacturer. After the initial reading, the paper was transferred to a cabinet at 75°C. and 40% relative humidity. It was removed at intervals for further colour intensity measurements.

To obtain the results shown in the tables below, the colour intensity was measured each time at 25 different points on the paper surface and the values were averaged.
The following abbreviations are used:

DBP - dibutyl phthalate
DOP - dioctyl phthalate
BBP - butyl benzyl phthalate
OBP - octyl benzyl phthalate
TBP - 2,6,6,8-tetramethyl-4-oxa-3-oxonon-7-yi benzyl phthalate
ALB - (C₈-alkyl)benzene

Table 1 shows the results obtained using one manufacturer's day-coated receiver sheets, the solvent in each case being a blend of the phthalate with either ALB in the proportions by weight 7:3 or with kerosene in the proportions by weight 8:2.
Comparison of Solvent 1 with Solvents 2-5, or of Solvent 6 with Solvent 7 shows that the colour intensity fades significantly more slowly when the phthalate is an aliphatic benzyl phthalate than when the phthalate is dibutyl phthalate.
Table 2 shows the results obtained using a second manufacturer's clay-coated receiver sheets.
The superiority of the alkyl benzyl phthalates over dibutyl phthalate is shown by a comparison of Solvent 11 with Solvent 10.
Table 3 shows the results obtained using the second manufacturer's clay coated receiver sheets, the solvent being in each case a blend of the phthalate with ALB in the proportions by weight 7:3.
Colour intensities are again shown to fade more slowly when the solvent comprises an aliphatic benzyl phthalate than when the solvent comprises a dialkyl phthalate.

Claims

1. A pressure-sensitive mark-recording system comprising (a) sheet material, (b) mark-forming components supported by the sheet material and arranged in juxtaposition but in unreactive condition, the said components comprising a chromogen which is a derivative of diphenyl methanol or of diphenylmethylamine and an acid clay sensitizer for the chromogen which produces a colour from the chromogen when brought into contact with the chromogen in the presence of a liquid solvent for the chromogen and (c) the said liquid solvent supported by the sheet material but separated from the sensitizing agent by a physical barrier which is rupturable on the application of a marking instrument to the sheet material, characterised in that the liquid solvent comprises an aliphatic benzyl phthalate or an aliphatic substituted-benzyl phthalate, the said phthalate being a phthalate ester in which one of the carboxyl groups is esterified by an aliphatic group and the other by a benzyl or substituted benzyl group.

2. A system according to Claim 1 in which the aliphatic substituted-benzyl phthalate is an- aliphatic alkylbenzyl phthalate.

3. A system according to either of Claims 1 and 2 in which the aliphatic group of the aliphatic benzyl or substituted-benzyl phthalate is an alkyl group containing up to 24 carbon atoms.

4. A system according to Claim 3 in which the aliphatic group of the aliphatic benzyl or substituted-benzyl phthalate is an alkyl group containing from 2 to 12 carbon atoms.

5. A system according to Claim 1 in which the solvent comprises a butyl benzyl phthalate or an octyl benzyl phthalate.

6. A system according to either of Claims 1 and 2 in which the aliphatic group of the aliphatic benzyl or substituted-benzyl phthalate is derived from an alkyl ester of a hydroxy-carboxylic acid or from a hydroxy (C,_-12 alkyl) ester of an aliphatic C,_-12-carboxylic acid.

7. A system according to Claim 1 in which the solvent comprises 2,6,6,8-tetramethyl-4-oxa-3- oxonon-7-yl benzyl phthalate.

8. A system according to any of Claims 1 to 7 in which the solvent is a mixture of at least one aliphatic benzyl or substituted-benzyl phthalate and a hydrocarbon diluent, the said mixture containing at least 50% by weight of the phthalate or phthalates.