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Dec. 2, 1969 D. A. Ostlie 3,481,759
IMPACT MARKING CARBONLESS PAPER
Filed Aug. 22, 1966
United States Patent Office
Patented Dec. 2, 1969
IMPACT MARKING CARBONLESS PAPER Dean A. Ostlie, White Bear Lake, Minn., assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware
Filed Aug. 22,1966, Ser. No. 574,130 Int. CI. B41m 5/22 U.S. CI. 117—36.2 9 Claims
ABSTRACT OF THE DISCLOSURE
Self-marking papers of the transfer or manifolding type operate by having a dye precursor within microscopic capsules carried as a transfer coating on one sheet of paper, the dye precursor within the capsules reacting with a receptor coating on a mating sheet of paper to produce a visible mark on such mating sheet of paper upon impact against the contacting transfer and receptor coatings when the two sheets of paper are mated, the microcapsules at the point of impact rupturing and releasing their contents onto the receptor coating of the mating sheet. To prevent the inadvertent marking or backgrounding during handling, a co-reactant for the dye precursor is included in the transfer coating containing the capsules but externally of the capsules so that upon the inadvertent rupture of capsules in the transfer coating the contents will react with the colorless co-reactant before passage through the sheet or transfer to the receptor sheet coating and thus prevent inadvertent marking of the paper. Scuff capsules to help further prevent inadvertent marking may also be included in the transfer coating along with the dye precursor containing capsules.
The invention relates to self-marking impact papers of the transfer or manifolding type wherein one marking ingredient is carried on one sheet of paper to react with a second marking ingredient carried on a mating sheet of paper. More particularly, this invention relates to selfmarking impact transfer or manifolding papers which have greatly increased resistance to inadvertent coloration or backgrounding during handling, particularly during printing or similar operations, and storage.
Impact or pressure sensitive self-marking carbonless transfer papers have come into wide usage over the past ten or twelve years. Ordinarily, these papers are printed and collated into form sets for producing multiple copies, impact on the top sheet causing each of the remaining sheets to form a mark thereon corresponding to the mark applied by machine key or stylus on the top sheet without carbon paper interleaves or carbon coatings. Of course, this sequence can be carried out through a number of sheets just as if carbon paper is used. The top sheet of paper upon which the impact is immediately made usually has its back surface coated with tiny microscopic capsules containing one of the reactive ingredients which produce a mark. A receiver sheet, placed in contact with such backface of the top sheet has its front surface coated with a material having a component reactive with the contents of the capsules so that when capsules are ruptured upon impact by stylus or machine key the contents of the ruptured capsules react with a coreactant therefor on the receiver sheet and a mark forms corresponding to the mark impressed by the stylus or machine key. In the trade, these self-marking impact transfer papers are des^ ignated by the terms CB, CFB, and CF, which stand respectively for "Coated Back," "Coated Front and Back," and "Coated Front." Thus, the CB sheet is usually the top sheet and the one on which the impact impression is directly made; the CFB sheets are the intermediate sheets
which form a mark on the front surface thereof and transmit the contents of ruptured capsules from the back surface thereof to the front of the next succeeding sheet; the CF sheet is the last sheet used which is only coated on the g front surface to form an image thereon and is not coated on the back surface as no further transfer is desired. While it is customary to coat the capsules on the back surface and coat the coreactant for the capsules on the front surface, this procedure could be reversed if desired. 10 In fact, with some systems, e.g. those using urea-formaldehyde polymer shelled capsules and dithiooxamide derived image forming dye precursors, coatings need not be used at all, and the coreactive ingredients may be carried in the sheets themselves, or one may be carried in one of 15 the sheets and the other may be carried as a surface coating. Further, the reactants may both be in capsules and may both be liquid. Patents illustrative of the various kinds of systems that may be used in the production of carbonless transfer papers are, for example, Patent No. 20 1,781,902 to Gill issued Nov. 18, 1930, Patent No. 2,168,098 issued to Groak, issued Aug. 1, 1939, Patent No. 2,299,694, to Green, issued Oct. 20, 1942, and Patent No. 2,712,507, to Green, issued July 5, 1955. The most common variety of carbonless impact trans25 fer paper and the type with which this invention is primarily concerned is the type illustrated in Green Patent No. 2,712,507 wherein tiny microscopic capsule are coated on the back of one sheet with microscopic capsule containing liquid fill having chemically reactive color forming 30 dye precursor coated on the back surface of the sheet, and a dry coating of a coreactant chemical for such dye precursor is coated on the front surface of a receiving sheet. In these capsule containing papers, which are preferred because of the speed and adequacy of the marks 3^ produced, a persistent backgrounding problem is encountered when the sheets, are printed to provide forms which are thereafter collated, stacked and cut to size in the formation of multiply copy form sets. This backgrounding, ^0 which occurs through inadvertent capsule rupture and transfer of fill contents through the sheet from the back surface thereof to the front surface or from sheet to sheet (CB to mating CF or CFB), although not sufficient to render the sheets unusable, does discolor the sheets. Thus, white sheets have been heretofore avoided and colored sheets have been used to mask this backgrounding while maintaining good contrast between the desired marking color and the paper color. While this problem has been a known problem since the inception of these 50 papers, until this invention it is not believed that any satisfactory solution had been found,
I have discovered that such backgrounding can be greatly reduced and very often eliminated by including in the capsule containing coatings of each of the mating 55 sheets a minor amount of a further coreactive additive for the liquid fill contents of the capsules which reacts therewith to form a colorless or nearly colorless, reaction product. Not only has this discovery enabled the production of white capsule containing impact marking papers 60 which remain that way through manufacture, printing, cutting, collation and storage, but it also reduces the extent of the severe discoloration which usually results around the cut edges of the sheets. Further, these beneficial results are achieved without any significant deterio65 ration of the normal impact marking ability of the transfer paper.
The invention is further illustrated and described with reference to the accompanying wherein: FIGURE 1 represents a collated form set of carbon70 less impact transfer paper;
FIGURE 2 is a greatly enlarged, partially schematic view of the collated form set of FIGURE 1 illustrating
the manner in which a mark is made on each sheet of the form; and
FIGURE 3 is a greatly enlarged, partially schematic view of one of the intermediate CFB sheets of the collated set of FIGURE 1 illustrating one manner in which inadvertent marking may take place while printing the sheet.
Referring now to the accompanying drawing in more detail, collated form set 10 as shown in FIGURE 1 as comprising a CB sheet 12, an intermediate CFB sheet w 14, and a CF back sheet 16. Of course, the number of intermediate CFB sheets is limited only by the requirements of the form set and the efficiency of the color forming transfer system.
The character of each of the sheets and the manner 15 in which impact forms a mark on each of the sheets of the form without carbon is illustrated in FIGURE 2. The top sheet 12, has a coating 20 on the undersurface thereof comprising tiny microscopic capsules having liquid fill therein, which fill comprises one of the reactive 20 ingredients for producing a mark. The intermediate sheet, or sheets 14, the CFB sheet, has a coating 18 on the top surface thereof containing a coreactant for the liquid contents of the capsules 22 to form a mark thereon when the capsules of a mating coating 20 are ruptured as by 2g the pressure of a stylus key such as 15 on the top sheet of the form. The pressure of the stylus 15 carries through to the back coating of the CFB sheet 14 rupturing the capsules 22 therein, the contents of which in turn react with the coreactant on the coating 18 of the bottom 30 sheet 16, the CF sheet, to form a mark there. The top sheet 12 is, of course, marked by the ink on the stylus or type key 15. However, although not shown, when the capsules have urea-formaldehyde polymer shells and a suitable color forming system, as noted hereinafter, the 35 top sheet may also have on the front surface thereof a coating or coatings, or partial impregnant, of a combination of the capsules of coating 20 and of the substance of coating 18 in contact with one another so that even if the type key or stylus does not contain any ink 4Q or other marking material the pressure alone will cause the capsules in the top of the sheet to rupture and react with the coreactant contiguous therewith so that this area of the sheet marks itself without the necessity of further mating sheet. Such a sheet is classified as an SCCB sheet, a self-contained, coated back sheet. The 45 front surface of the sheet is self-contained to produce its own mark without the necessity of any other agency such as a mating sheet, which accounts for the shorthand description, SC. The back sheet is coated with CB coating 20, such as illustrated in the drawing. 50
One way that backgrounding of the sheets occurs is when the sheets are cut to size. The cutting operation ruptures some of the capsules adjacent the cut edge whereupon, due to migration of fill through the sheets 14 the areas adjacent the cut edge become severely 55 discolored.
Undesirable backgrounding may occur on the SCCB and CFB sheets during manufacture, printing, or storage by migration. One way this occurs is illustrated in FIGURE 3. Thus, observing FIGURE 3 it will be seen that 60 as the sheet is pulled over the roller 26 to be printed by the printing roller 24 in an offset press or the like, some of the capsules of the coating 20 may be ruptured and migrate through the sheet to react with the front coating 18, and cause some backgrounding therein. The 65 number of capsules ruptured may be considerable but they are spread out far enough that the resulting inadvertent marking is more in the form of a background color on the sheet than an actual vividly contrasting mark such as occurs when the capsules are specifically rup- 70 tured through an area of type key impact as illustrated in FIGURE 2.
Another cause of backgrounding, of SCCB, CFB, CF and CB sheets collectively, and the most common cause, occurs upon storage of the sheets in collated form sets 75
as illustrated in FIGURES 1 and 2. When so collated (as the sheets must be to form sets which will mark properly) inadvertent discoloration results from transfer of fill from inadvertently ruptured capsules from sheet to sheet, as well as from migration of fill from surface to surface through the CFB sheets.
This inadvertent marking, I have discovered, is substantially reduced, and in many cases virtually eliminated when a further coreactant for the liquid fill contents of the capsules, which reacts therewith to provide a colorless image, is included. This color control additive is included in coating 20 with the capsules so that it immediately reacts with the ruptured capsule contents before such contents contact the coreactant of coating 18.
In general, the colorless product forming coreactant additive has been found to substantially reduce inadvertent backgrounding in carbonless impact transfer papers when used in amounts as small as 1% of the capsule coating weight and has maintained its effectiveness without undue harm to the functional characteristics of the sheet for desirable marking in amounts as high as 15%. Depending on the reactants used to produce a mark, this level may be very greatly varied. In a preferred system where dissolved derivatives of dithiooxamide are reacted with a metallic cations to produce a vivid mark, a level of about 5% background control additive, ± about 2%, has been found to be very satisfactory, and a general range of about 2 to 10% quite acceptable. With other reactive systems this may, of course, be changed and the amount can be readily adjusted with different systems simply by determining which reactive combinations yield colorless, or near colorless, reaction products, then adding the control additive which yields such a product to the capsule coating and visually determining at what point the functional properties of the paper are adversely affected to a degree to make the paper unsuitable for use (this would be with the higher amounts of additives) and the minimal amount necessary to provide some background reduction.
A presently preferred class of transfer papers is made wherein the capsule coating is comprised of capsules having a liquid fill containing an N,N'-di-substituted dithiooxamide complexing agent as a dye precursor which complexes with a metal cation, which may be included in the form of a metal salt in the coating 18 of the sheet material, to produce a vivid image. A particular N,N'di-organo-substituted dithiooxamide used is a combination of N,N'-di-benzyl-dithiooxamide (hereinafter sometimes referred to as DBDTO) and N,N'-bis (2-octanoyloxyethyl) dithiooxamide (hereinafter called DOEDTO). This material is usually present in an organic solvent such as cyclohexane within the capsule and is present in the amount of about 4% to 8% of the capsule fill.
A preferred cation is nickel, since many nickel salts provide fairly colorless coatings. Nickel rosinate is often used as the coating 18 since it is both colorless and reacts rapidly with the dye precursor to form a vivid blue image. Other metal cations such as mercury, cadmium, lead, zinc, copper, cobalt, and silver will also produce images. However, certain of these compounds such as cobalt, cadmium and zinc cation containing compounds reactwith the dithiooxamide derivatives to produce very nearly colorless products. Consequently, where white paper is desired they form images having very little, if any contrast with the background of the paper itself. Where tinted papers are used, one of the cations which reacts with the dye precursor to form a color matching the tint may be used, e.g. cobalt or cadmium for a yellow tinted sheet. Thus, these materials have been found to provide excellent background imaging control when used as additives for this purpose. Zinc salts, such as zinc rosinate, benzoate, octoate, laurate, salicylate, acetate, stearate, chloride, and sulfate, when used in concentrations of 1% or more and less than about 15% have been found to be excellent background color control additives for white papers.
Silver compounds have also been found effective but since most silver compounds are light sensitive their utility is much less.
With DBDTO-DOEDTO capsule fill in the capsule coating 20 and a nickel rosinate coreactant in the coating 18, approximately 5% zinc rosinate incorporated into the capsule coating provides very effective background control with essentially no effect on the imaging characteristics of the paper. As the concentration of the zinc rosinate is raised, for example to levels above 10%, the impact image tends to change somewhat from blue to red and above 15% the image becomes quite red rather than the more desirable blue, providing less contrast in the imaged sheets.
Other factors may affect the efficiency of the background control additive in the capsule coating. For example, if a strong film-forming binder such as a hydroxy ethylated starch is used to carry the capsules in the coating 20 some loss and effectiveness in the control additive will be found. It is believed this is due to the formation of films around the zinc rosinate particles prevent ing their reaction with ruptured capsule contents.
While the invention is not limited thereto, a specific example of the preparation and formation of a transfer paper having color control additives therein in accordance with this invention is given hereinafter.
A paper coating slurry is prepared by mixing 344.5 parts of an imaging capsule slurry with 112 parts of 35% enzyme converted starch and 52.0 parts of 12.5% zinc rosinate. In addition, 66.4 parts of a scuff capsule slurry is included in this mixture. The imaging capsule slurry contains 24.5% imaging capsules. The second slurry, in the smaller amount, contained 18.5% capsules, the capsules being quite large, in the range of about 30 to 35 microns on an average size, their purpose being primarily to protect the capsule coating against inadvertent rupture of the imaging capsules. The imaging capsules, on the other hand, are of the size average in the range of about 5 to 15 microns. Ordinarily, such capsules to be useful in image forming papers are in the size average range of about 5 to 25 microns.
The coating is applied upon the paper by means of an air knife at a coating weight of 5 pounds per 3,000 square feet of surface. The large, inert scuff capsules act as bearing surfaces to minimize the capsule breakage due to 45 machine handling.
In the preparation of the coating slurry, the imaging capsule slurry is formed somewhat as follows:
jacket and the temperature control set at 160° F. then charges B and C are added in the order recited with continued agitation. After the batch reaches 160° F. it is reacted with continued agitation for 2Vz hours, then the temperature control is reduced to 75° F. Next charge D is added and the precondensate solution is ready for use. The concentration is about 24% solids.
The precondensate solution and the fill are combined to make capsules in a 300 gallon kettle as follows:
A __ Precondensate solution.._ 83.12
B. Hydrochloric acid (12.5)%) . 19
C Fill 15.10
D Hydrochloric acid (12.5%) . 19
E do .21
F Caustic (50% NaOH) .13
Q Soft water 1.06
Charge A was added and the agitator started, then 2Q Charge B was added. The temperature was adjusted to 89-90° F. and Charge C was added. The agitator was set for high shear agitation and Charge D was added over a five minute period. 30 minutes after Charge D was added, Charge E was added over a 30 minute period to adjust the pH of the system to 2.2 plus or minus .3. One hour after Charge E was added, the temperature was raised to 105° F. and the polymerization mixture was maintained at this temperature for a further nine hours. After the nine hour period, Charge F was added to neutralize the slurry and Charge G was added to flush the tanks as the slurry was removed therefrom and drummed for storage and use.
The scuff capsule slurry was prepared in general by use of the same precondensate solution used for the 35 imaging capsules in the following manner:
A 2,420.0 Prepolymer.
B 5.4 12.5% hydrochloric acid.
C 150.0 Cyelohexane.
D _ 5.4 12.5% hydrochloric acid.
E 6.0 Do.
F_ 29.5 Water.
Q- E.6 50% NaOH.
The Formalin is 37-38% formaldehyde and is stabilized with 7% methanol. The formalin is first added to a large
stainless steel kettle equipped with an agitator and heating 75 having liquid fill comprising a dye precursor, which cap
Charge A is added, the agitator is started, and then Charge B is added. The temperature is adjusted to the proper point (usually 90 to 95° F.) and Charge C is added. The agitator is set for high-shear agitation and Charge D is added over a 5 minute period. Five minutes after the addition of Charge D, Charge E is added over a five minute period. The pH is 2.2±.3 at this point. One hour after the addition of Charge E, the temperature is raised to 105° F. and maintained at this temperature for an additional 9 hours while maintaining highshear agitation. After this time period, Charges F and G are added to neutralize the reaction and bring the pH to 7.0±.5. The capsule slurry is drummed and stored for use in this form.
Similar capsule coatings were made as above utilizing as a color control additive, zinc rosinate, zinc benzoate, zinc octoate, zinc laurate, zinc salicylate, zinc acetate, zinc stearate, zinc chloride, zinc sulphate, cadmium rosinate, silver rosinate, and mercuric rosinate. All of these compounds exhibited some effectiveness in controlling the backgrounding of the sheet materials.
While the invention has been described in particular reference to the utilization of urea formaldehyde capsules and color forming systems of dithiooxamide derivatives as dye precursors reactive with metal cations, the system is as well practiced with capsules of other natures and other dye precursor-coreactive systems.
What I claim is:
1. An impact marking transfer paper having a transfer surfacing thereon comprising tiny microscopic capsules