GB2106529A - Solvent systems containing a high proportion of diluent for pressure-sensitive copying systems - Google Patents

Abstract

Solvent compositions for use in pressure-sensitive copying systems comprise 15 to 70 percent by weight of an alkylated diphenyl ether e.g. ethyl diphenyl ether, dimethyl diphenyl ether, or a mixture thereof, with 30 to 85 percent by weight of a diluent, preferably a monoalkyl- benzene or low odor kerosene.

Description

SPECIFICATION Solvent systems containing a high proportion of diluent for pressure-sensitive copying systems Background of the invention Field of the invention This invention relates to pressure-sensitive copying systems, e.g., the kind in which a substantially colorless colorformer (dye) held within microcapsules is reacted, upon rupturing of the microcapsules by an applied pressure, with a co-reactant material to form distinctive colored marks.

More particularly, the present invention relates to improved solvent systems useful in pressuresensitive copying systems.

Description of prior art Pressure-sensitive copying systems are well known, and have been developed in many variations.

These different variations have the same general types of colorless components arranged so that one or more of the components is isolated from the remainder of the components. The isolated components are released when localized pressure is applied. All of the components then become mixed, and a reaction occurs producing a material that forms a colored mark.

The colorless components of a basic pressure-sensitive copying system comprise a chromogenic material (also called the color former, color precurser, or dye), a co-reactant material (receiver), and a solvent system, all coated on one or more supporting surfaces, usuaily paper. The solvent system must be capable of dissolving the color former to provide the medium through which the colored mark is produced. Additionally, the solvent system must exhibit a variety of other properties such as low odor, storage stability, suitable viscosity, non-toxicity, promotion of color development, and promotion of color stability, all while maintaining sufficiently low cost for commercial success.

Those skilled in the art will recognize that a balance of the required properties is best obtained by using a solvent system comprising the actual dye solvent together with a diluent that may function to modify the properties of the system, to reduce cost, or both. The diluent comprises both substantially inert materials as well as materials with some dye solvent properties, but which cannot function alone as a dye solvent. The ability of a solvent system to exhibit good performance with a relatively low ratio of dye solvent to diluent is highly desirable due to the resulting flexibility and cost savings. Prior art patents routinely mention inclusion of diluents with dye solvents, and occasionally statements are made concerning the degree of dilution that is possible. However, these statements are seldom based upon included experimental data.As a practical matter, dye solvents that can be diluted beyond 1:1 ratio without dye solubility or color development becoming unsatisfactory, are rare.

U.S. Patent No. 3,627,581 which issued December 14, 1 971 discloses biphenyl and isopropyl substituted biphenyl as a dye solvent, with a mixture of C,O to C15 monoalkylbenzenes as a diluent, in the range of 2:1 to 1:2. solvent to diluent.

U.S. Patent No. 3,855,613, which issued February 11, 1975 discloses certain dibenzylbenzenes as dye solvents and comments that one advantage of these dye solvents is that they allow "high dilution", without being more specific.

U.S. Patent No. 3,996,405, which issued December 7, 1976, discloses ethyldiphenylmethane as dye solvent with a mixture of C" to C,2 monoalkylbenzenes as diluent in a 1:2 ratio, solvent to diluent.

U.S. Patent No. 4,130,229, which issued December 1 9, 1 978, discloses certain benzylated xylenes as dye solvents diluted in a 1:3 ratio with various diluents.

Japanese Patent Publication No. 49-95712, which was published September 11, 1974, but which never matured into a patent, describes a broad range of alkyl diphenyl ethers containing C1 to C40 alkyl groups, and mentions use of these solvents with a number of other solvents and diluents.

Although one example uses p-isopropyl diphenyl ether as a solvent with C10 to C12 paraffin as a diluent in a 4:1 ratio and another uses a mixture of tert-butyl and tert-pentyl diphenyl ether as the solvent with C12 to C14 isoparaffin as the diluent in a 7:3 ratio, no discussion of limits of dilutability is found, and there is no indication that high dilutability is either present or advantageous.

It is an object of this invention to provide improved solvent systems for use in pressure-sensitive copying systems.

It is a further object of this invention that the solvent systems contain a larger proportion of diluent than prior art solvent systems.

It is a further object of this invention to provide solvent systems containing a high proportion of diluent with improved print speed and intensity over similarly diluted prior art dye solvents.

Further objects of this invention will become apparent from the following description and examples.

Summary of the invention The subject of this invention is a solvent system for use in pressure-sensitive copying systems, comprising: a) From about 15 percent to about 70 percent by weight of one or more alkylated diphenyl ethers having the general formula

where R1 is one or two alkyl groups, R2 is hydrogen or a methyl group, and the total number of carbon atoms of R1 plus R2 equals 2; and b) not less than about 30 percent nor greater than about 85 percent by weight of a diluent.

The solvent systems of this invention show excellent print speed and intensity and show a particularly marked improvement at a solvent to diluent ratio at which prior art solvents produce much poorer results.

Description of the preferred embodiments The pressure-sensitive copying systems utilizing the improved solvent systems of the present invention may be prepared according to conventional means well known to those skilled in the art. One common embodiment of the present invention is the formation of microcapsules containing the dye dissolved in the solvent system, which is then applied to the back surface of a transfer sheet. This is known as a CB (coated back) sheet.

The co-reactant material, which is usually an acidic inorganic clay or an acidic organic polymer, is applied to the front surface of the receiving sheet. Metallic salts of organic acids are frequently included as an activator for the co-reactant material. Compounds such as zinc salicylate, zinc dibenzoate and similar compounds can be used for this purpose. This is known as a CF (coated front) sheet. The CB sheet is juxtaposed with the CF sheet so that localized pressure, such as writing, typing, or printing on the front surface of the CB sheet causes the microcapsules to rupture, releasing the dye solution. This solution is transferred to the CF sheet where a colored mark is produced conforming to the area in which the localized pressure occurred.

Multiple copies can be made by inserting between the transfer sheet and the receiving sheet one or more intermediate sheets containing a receiver surface on the front face of the sheet and a transfer surface on the rear face. This is known as a CFB (coated front and back) sheet.

Additionally, the receiver and the microcapsules containing the dye dissolved in the solvent system may be applied to the front surface of the receiving sheet to produce a self-contained sheet.

One skilled in the art will recognize that many additional embodiments for pressure-sensitive copying systems are possible. The components of the pressure-sensitive copying system may be arranged in various configurations and combinations, and alternatives to microencapsulation are known. This invention does not include, and is not limited to any particular methods of production.

These solvent systems can be used in any of the pressure-sensitive copying systems known in the art.

The solvent systems of the present invention are preferably used with one or more conventional color formers of colorless or substantially colorless form. One class of color formers comprises colorless aromatic double bond organic compounds which are converted to a more highly polarized conjugated and colored form when reacted with an acidic co-reactant material. A particularly preferred class of color formers includes compounds of the phthalide type such as crystal violet lactone (CVL), which is 3,3-bis(p-dimethylaminophenyl)-6-dimethyl-aminophthalide, and malachite green lactone, which is 3,3-bis(p-dimethylaminophenyl) phthalide. In addition to phthalide derived color formers, other color formers useful in practicing this invention include indole substituted pyromellitides, leucauramines, substituted leucauramines, and other color formers known in the art.These color formers can be used either alone or in various combinations.

An auxiliary coloring agent can be employed with the above color formers to provide fade resistance where fading is a problem. Many phthalide compounds such as CVL are characterized by rapid color development with a normal tendency to fade during the course of time. One suitable auxiliary coloring agent is benzoyl leuco methylene blue (BLMB) which oxidizes when released on the paper to form a permanent blue color. The combination of a phthalide color former and an oxidizable auxiliary coloring agent provides a composition having both rapid color development and fade resistance.

The co-reactant is an acidic solid that reacts with the color former. The acidic material may be any compound that falls within the definition of a Lewis acid, i.e., an electron acceptor with reference to the color former, which promotes the polarization of the color former into a colored form. The solid acidic material further serves as an adsorbent of the marking fluid to receive the transferred image.

Commonly used acidic materials include acidic inorganic clays and acidic organic polymeric materials.

Superior results are achieved herein using phenolic polymeric materials as the co-reactant.

The solvent system, which provides the medium through which the color former reacts with the co-reactant, is composed of two major components, the dye solvent and the diluent. In this invention, the dye solvent comprises alkylated diphenyl ethers represented by the following formula:

in which R1 is one or two alkyl groups, R2 is hydrogen or a methyl group, and the total number of carbon atoms of R1 plus R2 equals 2.

Alkylated diphenyl ethers have been known in the prior art as dye solvents. Surprisingly, it has been found that only certain alkylated diphenyl ethers can withstand the high dilution of the solvent systems of this invention, while maintaining excellent performance. Other alkylated diphenyl ethers show significant deterioration of image quality or otherwise perform unsatisfactorily when diluted to the extent possible in this invention.

Solvent systems of this invention also preferably contain a diluent. The use of diluents is well known in the art. Prior art dye solvents that are liquids at room temperature are frequently used with diluents, and dye solvents that are solid or semi-solid at room temperature must be used with a diluent to be effective. For purposes of this invention, the term diluent includes both inert or substantially inert materials and materials that may contribute to the ability of the solvent system to dissolve the color former. But, the term only includes materials that have little practical use alone as dye solvents either because they have poor solvating power for the chromogen or because they act in some way to inhibit the development of color.

Either type of diluent may be used as the diluent in the solvent systems of this invention. A dye solvent may be admixed with up to 5 parts of diluent for each part of dye solvent, using as the diluent a mineral or vegetable oil, such as kerosene, paraffin oil, mineral spirits, castor oil, cottonseed oil, neatsfoot oil, sperm oil, lard oil, olive oil, soybean oil, coconut oil, or rapeseed oil; C1-C15 alkylbenzene, or C1-C16 alkylaryl indane. Biodegradable monoalkylbenzene mixtures, sometimes called "alkylates", are particularly useful as diluents in the solvent systems of this invention. Such alkylates are commercially available as intermediates for the manufacture of anionic liquid and solid detergents. Typical is a mixture of C10-C15 monoalkylbenzenes.

The diluents referred to herein may function to alter physical properties of the solvent system as may be desired for handling or processing considerations. The diluents may also serve to reduce the total cost of the solvent system, or may be used to enhance the performance of the solvent system particularly with respect to speed of color development or resistance to fade.

In addition to the dye solvent and diluent, the solvent system may contain certain additives intended to alter or control the final properties of the solution, for example, odor masking agents, antioxidants, colored dyes, and the like. The solvent systems of this invention may be used with or without additives of this type.

Alkylated diphenyl ethers can be prepared by a number of known procedures. Among them are dehydration of alkyl phenols, with heating, in the presence of various dehydration catalysts such as thoria, or alkylation of diphenyl ether by reaction with an olefin in the presence of an alkylation catalyst such as aluminum chloride.

To test the imaging performance of solutions utilizing the solvent systems of this invention, solutions of crystal violet lactone (CVL) and benzoyl leuco methylene blue (BLMB) as indicated below, were prepared using solvent systems both within and outside of this invention. Print speed and intensity of the solutions applied to commercially available phenolic coated CF sheets were determined.

The laboratory procedure employed herein consisted of preparing a marking fluid comprising a solution of a chromogen (color former) in the solvent system to be tested, applying the fluid to CF paper coated with a phenolic resin co-reactant material, and measuring the print speed and color intensity.

The following dye solvents were used: (1) benzylated meta xylene (BMX) which is a prior art dye solvent; (2) a mixture of about 46 percent by weight of m-p' dimethyl diphenyl ether, about 41 percent m-m' dimethyl diphenyl ether and about 11% p-p' dimethyl diphenyl ether (DM DPO), a dye solvent used in this invention; and (3) a mixture of about 64 percent by weight of monoisopropyl diphenyl ether with about 36 percent by weight of polyisopropyl diphenyl ether (IP DPO), an alkylated diphenyl ether dye solvent outside the scope of this invention.

The following diluents were used: a mixture of C10-C15 monoalkylbenzenes (alkylate); and low odor kerosene. The dye solvents and diluents were admixed to form the indicated solvent systems.

In the test procedure the marking fluid was prepared by adding sufficient amounts of the indicated color former to the solvent system to achieve the indicated concentration of the color former.

This was followed by agitation and warming to 1000--1200C., if necessary to achieve solution. The solution was then cooled to room temperature, seeded with a few crystals of the color former, and allowed to stand for several days with occasional shaking to assure that the solution was not supersaturated.

The color former solution was thereupon saturated into a blotter. The blotter was daubed 7 times with a pencil eraser. The material on the pencil eraser, approximately 1 microliter of the color former solution, was transferred to a phenolic resin CF sheet and color intensity was measured.

A Macbeth digital read-out Reflection Densitometer was employed, using filters for color, to measure optical density. The optical density measurements obtained from the Reflection Densitometer were seen visually and were recorded on a Sanborn recorder which plots optical density versus time.

The color intensity data reported are the optical densities of the colored areas minus the optical densities of the CF sheets times 100.

Print speed is defined herein as the time (in seconds) from application of the color former solution until a color intensity of 40 is achieved on the CF sheet. It has been found difficult to visually distinguish color change above a value of 40.

Color intensity for each of the samples tested was derived from the recording at a defined elapsed time. Higher readings represent darker color.

Tables 1-5 contain the results of the tests. Tables 1 and 2 demonstrate that the solvent systems of this invention maintain a very high level of performance, even as the solvent to diluent ratio becomes small, while the performance of the other solvent systems is reduced.

Table 1 On Phenolic CF paper no. 1 using alkylate diluent Solvent/diluent Print speed Color intensity at seconds Dye Dye solvent ratio seconds 15 30 60 2-1/2% CVL BMX neat 9 54 65 70 3:1 9 61 72 75 1:1 10 58 71 75 1:3 13 47 67 71 DM DPO neat 2 76 79 80+ 3:1 2 78 80+ 80+ 1:1 3 76 80 80+ 1:3 7 70 80 80+ IP DPO neat 7 69 80 80+ 3:1 8 67 80+ 80+ 1:1 9 65 79 80+ 2-1/2% of 2/1 BMX neat 9 59 69 72 CVL/BLMB 3:1 10 56 66 69 1:1 11 55 66 68 1:3 14 43 61 64 DM DPO neat 4 62 71 76 3:1 5 60 70 76 1:1 7 53 64 70 1:3 7 55 67 74 Table 2 On Phenolic CF paper no. 2 using alkylate diluent Solvent/diluent Print speed Color intensity at seconds Dye Dye solvent ratio seconds 15 30 60 2-1/2% 2/1 BMX neat 19 37 48 57 CVVBLMB 3:1 17 38 49 59 1:1 19 37 47 55 1:3 17 38 50 60 DM DPO neat 4 62 71 76 3:1 5 60 70 76 1:1 7 53 64 70 1: :3 7 55 67 74 IP DPO neat 20 38 50 61 3:1 19 38 49 61 1:1 21 35 47 60 1:3 20 36 46 60 Table 3 demonstrates that the solvent systems of this invention perform slightly better than a prior art solvent system at low concentrations of color former.

Table 3 On CF paper no. 1 using alkylate at 1:1 dilution Dye Print speed Color intensity at seconds Dye solvent concentration seconds 15 30 60 BMX 0.5% 17 39 44 47 1.0% 10 50 55 58 2.0% 10 53 67 70 DM DPO 0.5% 14 45 60 64 1.0% 12 50 67 71 2.0% 12 54 74 78 Table 4 shows that, although dilutability with a kerosene diluent is not as high as with alkylate, solvent systems of this invention exceed the other solvent systems listed in performance.

Table 4 On Phenolic CF paper no. 1 using kerosene diluent Print speed Color intensity at seconds Dye Dye solvent Dilution seconds 15 30 60 2-1/2% CVL BMX 3:1 6 65 72 75 1:1 6 65 69 71 DM DPO 3:1 2 80+ 80+ 80+ 1:1 2 80+ 80* 80+ IP DPO 3:1 6 74 80+ 80+ 1:1 7 74 80+ 80+ 2-1/2% 2/1 BMX 3:1 7 62 68 70 CVL/BLMB 1:1 7 66 72 73 DM DPO 3:1 3 67 77 80 1:1 4 60 70 75 Table 5 shows that solvent systems of this invention are capable of completely dissolving the dye at concentrations of diluent at which solutions with the prior art solvent systems are clouded, evidencing incomplete solution of the dye. The receiver sheets used to obtain the data in Tables 1-4 had been freshly manufactured and purchased. The receiver sheets used to obtain the data in Table 5 had been in storage for almost 6 months longer than the other sheets.Storage of receiver sheets for this amount of time is known in the art to decrease sensitivity of the receiver sheets with resulting slower speed. By comparing Tables 1 and 5, this phenomenon can clearly be seen. Even with these receiver sheets that had been somewhat desensitized by age, the solvent systems of this invention produced results superior to prior art solvent systems, even at extreme dilution.

Table 5 An older CF paper no. ? using alkylate diluent Dye Solvent/diluent Print speed Color intensity at seconds Dye solvent ratio seconds 15 30 60 Solution* 2-1/2% BMX 1:1 14 42 68 78 clear CVL 1:2 22 24 58 78 clear 1:3 27 13 47 77 sl. cloudy 1:4 28 13 45 76 sl. cloudy 1:5 36 8 29 71 sl. cloudy DM DPO 1:1 7 75 80+ 80+ clear 1:2 10 62 80+ 80+ clear 1:3 12 51 74 80+ clear 1:4 1 7 34 72 80+ v. sl. cloudy 1:5 20 23 63 80+ sl. cloudy IP DPO 1:1 17 33 71 80+ clear 1:2 20 25 60 78 clear 1:3 27 16 47 74 sl. cloudy 1:4 29 13 44 73 sl. cloudy 1:5 29 14 42 73 sl. cloudy *Visual inspection after 24 hrs. at room temperature.

All of the data in Tables 1-5 were taken using phenolic CF sheets. These solvent systems are also useful with clay CF sheets. Because they are the same molecular weight and exhibit very similar solvent properties as the dimethyl diphenyl ethers used to obtain the data in Tables 1-5, monoethyl diphenyl ether and other isomers of dimethyl diphenyl ether can be used as the dye solvent component of the solvent systems of this invention.

Although a preferred embodiment of this invention comprises a two-sheet system wherein the acidic receiving material is carried by one sheet and a marking fluid comprising a chromogen and solvent system is carried by a second sheet, this invention is not limited to such systems alone. The only essential requirement for a pressure-sensitive recording system is that the chromogen and the acidic sensitizing material 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 acidic material are brought into reactive contact.Thus, it is possible to have the chromogen and acidic material present in a dry and unreactive state on a common carrier and to have the solvent system alone carried on a separate sheet whereupon the application of pressure would release the solvent system into the chromogenacidic material mixture and promote localized reaction and color development. Obviously, many other arrangements, configurations and relationships of the solvent system and the mark forming materials with respect to their encapsulation and location on the supporting sheet or webs can be envisioned, and such arrangements are within the scope of the present invention.For example, it is possible to coat a single paper or support member with all the components of this system to form a single selfcontained 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 in inkless recording instruments.

A particularly preferred dye solvent for use in this invention is a p-p' dimethyl diphenyl ether, m-p' dimethyl diphenyl ether, m-m' dimethyl diphenyl ether, or a mixture thereof.

Many variations and combinations in the application of these reactants and dye solvent systems to prepare pressure-sensitive recording paper systems will be apparent to and within the knowledge of those skilled in the art and will depend upon such factors as the type of chromogenic material selected, the nature of the coating to be applied and its method of application. Also deemed important are the number of supporting substrates employed and the intended application of the system. Accordingly, the present invention is not to be limited by the specific details presented in the preceding descriptions and examples.

Claims (5)

Claims

1. A liquid composition for use as a dye solvent system in a pressure-sensitive copying system comprising: (a) From about 1 5 percent to about 70 percent by weight of a dye solvent containing one or more of the compounds having the general formula

where R, is one or two alkyl groups, R2 is hydrogen or a methyl group and the total number of carbon atoms of R, plus R2 equals 2; and (b) Not less than about 30 percent nor greater than 85 percent by weight of a diluent.

2. A composition of Claim 1 where the dye solvent is present from about 1 5 percent to about 50 percent by weight, and the diluent is present from about 50 percent to about 85 percent by weight.

3. A composition of Claim 1 where the dye solvent is p-p' dimethyl diphenyl ether, m-p' dimethyl diphenyl ether, m-m' dimethyl diphenyl ether, or a combination thereof.

4. A composition of Claim 1 where the diluent is C,0 to C13 monoalkylbenzene.

5. A composition of Claim 1 where the diluent is low odor kerosene.