GB2031797A - Process for making pressure- sensitive copying sets - Google Patents

Abstract

A process for separating a collated stack of pressure-sensitive copying sets comprises pre-treating the edge of a stack of sheets of pressure-sensitive copying paper to be padded with a liquid pre-treating composition, drying the edge, applying an adhesive composition to the edge, drying the adhesive composition and separating the unit sets. The pre-treating composition may be water, an aqueous solution, an aqueous dispersion, a hydrocarbon or a paint, selected to enhance bonding between sheets by the adhesive where adjacent surfaces are reactant-coated and to inhibit it where adjacent surfaces are not coated.

Description

SPECIFICATION Process for making pressure-sensitive copying sets This invention relates to a process for making a pressure-sensitive copying set from a stack of sheets of pressure-sensitive copying paper arranged in the sequence desired in the set.

In one widely used pressure-sensitive copying system, upper sheets of each set are coated on their lower surfaces with a reactant in the form of microcapsules containing a solution of colourless colour former (coated back or CB sheets), and lower sheets of each set are coated on their upper surfaces with a reactant in the form of a colour developing material such as an acidic clay or a phenolic resin (coated front or CF sheets). In most form sets, a number of intermediate sheets are also provided, each of which is coated on its lower surface with microcapsules and on its upper surface with colour developing material (coated front and back or CFB sheets).When localized pressure is applied to the form sets, for example by writing or typing, the microcapsules are ruptured and the colour former solution is released onto the colour developing material on the adjacent lower sheet and a chemical reaction ensues in which the colour of the colour former is developed. When sheets of pressure-sensitive copying paper are to be made into sets, a stack of sheets is assembled in the desired sequence, for example CB-CF, or CB-CFB-... -CF. It is conventional to make the sets of forms by applying an adhesive to one edge of the stack of sheets of paper, drying the edge, and separating the sheets into sets, for example by fanning the treated stack. This operation is often called edge padding.It is thought that separation into sets occurs because the adhesive forms a bond where two coated surfaces are adjacent but not where two uncoated surfaces are adjacent.

It has been found that, occasionally, some sheets of paper within a stack do not respond satisfactorily to the above described treatment with the result that some bonding occurs between sheets having adjacent uncoated surfaces-an effect known as blocking. In addition, bonding between adjacent coated surfaces may be insufficient so that, when the stack of sheets is fanned, separation occurs at coated interfaces-an effect known, in the case of 2-part forms, as reverse padding. The desired lack of bonding between uncoated surfaces may also be accompanied by weak bonding between adjacent coated surfaces. In this case, when the stack is fanned, the stack separates, in part, back into individual sheets-an effect known as fallapart.

It has now been found that these drawbacks are alleviated if, prior to the application of the edge padding adhesive, a pre-treatment is carried out in which a liquid composition is applied to the stack and then dried.

Accordingly, the present invention provides a process for making pressure-sensitive copying sets from a stack of sheets of pressure-sensitive copying paper arranged in the sequence desired in said sets, comprising the steps of applying an adhesive to said edge, drying the adhesive, and separating the sheets into said sets, wherein, prior to the application of the adhesive, a pretreating liquid is applied to the edge of the stack and said edge is then dried, said pre-treating liquid being compatible with the pressure-sensitive copying sets and effective to enhance bonding between adjacent sheets in the stack where adjacent surfaces of said adjacent sheets are reactant coated surfaces and/or to inhibit bonding between adjacent sheets in the stack where adjacent surfaces of said adjacent sheets are not reactant coated surfaces.

The pre-treating liquid may comprise any of a wide variety of materials although it will be understood that the pre-treating liquid composition must be compatible with the pressuresensitive copying set, for example in that it should not interfere with the functioning of the adhesive to be applied subsequently, should not interfere with normal image formation of the copying paper and should not discolour the copying paper. Desirably, the pre-treatment agent should dry relatively quickly so that subsequent application of the adhesive may be effected with the minimum delay.

The pre-treating liquid may be aqueous or non-aqueous. Aqueous pre-treating liquids which may be used include water and aqeuous solutions and dispersions of organic and/or inorganic compounds. Suitable inorganic compounds include inorganic salts, a preferred inorganic compound being sodium tetraborate decahydrate. Preferred organic compounds include organic dyes, more particularly the dyes represented by the colour indices 29200, 29175 and 47035 in the Colour Index (3rd edition) published by the Society of Dyers and Colourers with acknowledgements to the American Association of Textile Chemists and Colourists for its contribution of technical information. Dye 29200 has the following formula

and an example of this dye is Direct Scarlet 4SWN marketed by Crompton and Knowles.Dye 291 75 has the following formula

and an example of this dye is Pergasol Orange 3RSP marketed by Ciba Geigy. Dye 47035 has the following formula

and an example of this dye is Calcomine Chinoline Yellow marketed by American Cyanamid.

A preferred aqueous dispersion is a dispersion of an acrylic latexcontaining adhesive, an example of such a water-based dispersion having the following composition (wt%): 10.6% acrylic latex solids 20% ethylene glycol monomethylether 8% denatured alcohol (denatured with 5 gallons of commercial methanol per 1 OQ gallons of 95% ethanol known as "Formula 3A").

The aqueous pre-treating liquid may be applied by brushing or spraying.

Non-aqueous pre-treating liquid which may be used include non-aqueous solutions and.

dispersions. Again, the pre-treating liquids may be applied by brushing or spraying. Pre4ratiflg liquids which may be applied by brush include volatile aliphatic hydrocarbons, for example those having from 7 to 10 carbon atoms, such as heptane, octane, nonane and decane; a mixture of long chain saturated hydrocarbons such as that sold as Nujol; solution of silicone resins in organic solvents such as organosiloxane in methylene chloride; and solutions or resins in aliphatic hydrocarbon solvents such as "Piccolastic" resins (resins produced from a mixture of styrene and styrene homologues) in mineral spirits. It should be noted that, in the case of the aliphatic hydrocarbons, the adhesive should be applied before complete evaporation af the hydrocarbon being used. Pre-treating liquids which may be applied as a spray include pigmented paint sprays and silicone resin solutions, the latter being particularly preferred.

Pigmented paint sprays which may be used include paints containing titanium dioxide, carbon black, talc, diatomaceous silica, aluminium powder or various mixtures thereof as the pigment in a suitable vehicle (for example a hydrocarbon resin or a vinyl toluene alkyd resin) and solvent (for example an aliphatic or aromatic hydrocarbon, a ketone or a mixture thereof). Such paint compositions may further contain conventional driers such as tung oil and conventional drying accelerators.

Numerous edge padding adhesives have been proposed. For example, British Patent No. 1 263 510 discloses a mixture of an aqueous solution of a gelatin derivative and an aqueous emulsion of a polymer as an edge padding adhesive. U.S. Patents Nos. 3 960 638, 3 963 553, 3 970 500, 3 970 501 and 4 041 193 disclose the use of a naphthalene sulphonic acid formaldehyde condensate as an edge padding adhesive in various combinations with materials such as water-soluble polymers, binders, metal salts, polymer emulsions, surface active agents and latices. Japanese Patent Publication Nos. 12844/1978 and 12845/1978 disclose the use of a surface active agent with an aqueous solution of a synthetic polymer adhesive or an aqueous emulsion of a synthetic polymer adhesive, respectively, as an edge padding adhesive.

Japanese Patent Disclosure No. 99635/1974 discloses an aqueous adhesive composition comprising a vinyl acetate-maleic acid copolymer with various alcohols. The edge padding adhesive used in the present process is not critical and may be any of the foregoing.

The theory underlying the process of this invention is not, at present, completely elucidated and the applicants do not wish to be bound by any theory about the particular mechanism involved. However, it is thought that the pre-treating liquid probably seals, and hence makes less absorbent, the margins of the reactant-coated surfaces of the sheets, allowing more of the subsequently applied adhesive to be effective in bonding. This does not appear to happen in the case of surfaces which are not reactant-coated, and hence blocking is less likely to occur.

The process of this invention may be used in conjunction with any of the various pressuresensitive copying paper systems known in the art. However, it should be emphasised that particularly good results are obtained with systems using a phenolic resin colour developer such as a metal modified phenolic resin. An example of this type of colour developing coating has the following composition.

Zinc-modified phenolic polymer 13.6 weight percent Paper coating kaolin 67.9 weight percent Calcium carbonate 6.0 weight percent Styrene-butadiene latex 6.0 weight percent Etherified corn starch 6.5 weight percent In order that this invention may be more readily understood reference will now be made to two examples which illustrate the process of the invention and do not impose any limitations upon it.

EXAMPLE 1 Bond strengths were evaluated on sets of forms produced from pressure-sensitive copying paper in the following way: a stack of collated sheets of the paper was jogged to the edge to be padded. Water was applied to this edge using a brush until a cascading effect was observed and the stack was allowed to dry. The sheets of paper were then fanned, jogged and an acrylic latex edge padding adhesive having the same composition as the pre-treating adhesive exemplified earlier was applied. After the adhesive had dried, the stack was fanned into sets of forms. The procedure was then repeated using a 1 % solution of Pergasol Orange 3RSP dye in water intead of the water. For comparative purposes, the process was repeated omitting the pretreatment step.

The resulting bonds in the form sets were evaluated by two practised observers. In order to evaluate the degree of bonding achieved in the example, the following bond scale was devised.

0 = no bond 1 = very weak bond 2 = weak bond 3 = satisfactory bond 4 = good bond 5 = excellent bond Each observer evaluated each bond five times. A total bond strength for each bond was calculated, as the limits being set as follows: 2 observers X 5 tests X 0 bond strength = 0 2 observers X 5 tests X 5 bond strength = 50 The results obtained are shown in the following table, the sheets being listed by type and basis weight (weight of 1 300 ft2 ream): Bond Strength Evaluation 1 % Pergasol Orange 3RSP dye in water Water pretreatment No pretreatment followed pretreatment followed by Form set Bond prior art by prior prior art Sequence Evaluated adhesive art adhesive adhesive 15 lb.CB CB-CFB 49 50 47 17 lib. CFB CFB-CFB 47 50 50 17 lib. CFB CFB-CFB 45 50 50 17 lib. CFB CFB-CFB 34 50 50 17 lib. CFB CFB-CF 30 44 46 15 lib. CF CF-CB (uncoated 0 0 0 sides) 15 lb. CB CB-CF 44 50 50 15 lib. CF CF-CB (uncoated 1 0 0 sides) As may be seen from these results, the omission of the pre-treatment stage, whilst resulting in reasonable bond strength for the first, second, third and seventh form sets, did not give satisfactory results for three of the remaining four form sets.A significant improvement was noted in these three cases for the padding process involving a water pre-treatment step, an even better result being obtained in the process involving pretreatment with the 1 % Pergasol Orange solution. Similar results were obtained when pre-treatment was effected using an aqueous solution of an acrylic latex adhesive composition which also contained a small amount (less than 1%) of a surface active agent such as "Tamol" (a sodium salt of a polymeric carboxylic acid).

EXAMPLE 2 Bond strengths were evaluated on sets of forms produced from pressure-sensitive copying paper in the following way: A stack of collated sheets of the paper was jogged to the edge to be padded. The edge was then sprayed with a silicone resin aerosol spray until it was visibly damp, and the stack was allowed to dry. The sheets of paper were then fanned, jogged and an adhesive having the same composition as pre-treating adhesive exemplified earlier was applied. After the adhesive had dried, the stack was fanned into sets of forms. The procedure was repeated twice for comparative purposes, the pre-treatment step being omitted in both cases, firstly with the adhesive used in Example 1 and secondly using an adhesive having the following compositions.

(the figures refer to wt.% in an aqueous medium) Acrylic latex solids 10.9% Ethylene glycol monomethyl ether 20% Denatured alcohol (as previously defined) 8% "Tamol" Surface active agent 0.8% The results obtained in the edge padding of five form sets as just described are shown in the following table. The repeating units of the collated sheets of the form sets are shown in the table according to the basis weight of a 1 300 ft2 ream of paper.

Edge Padding Results Silicone Resin Spray Pre-treatment followed by First Form Sets First Adhesive Second Adhesive Adhesive 15 lib. CB Blocking Blocking Perfect 17 lib. CFB 17 lb. CFB 15 lb. CF 30 lb. CFB Slight blocking Blocking Good 1 7 Ib. CFB Good bonds Reverse Padding 15 lb. CF CB-CFB very weak bond 1 5 Ib. CB CB-CFB bond CB-CFB bond Good 17 lib. CFB fall-apart fall-apart 15 lb. CF 15 Ib. CB CFB (I)-CFB (II) bond CFB (Il)-CF Good 1 7 Ib. CFB (I) weak bond very weak 17 Ib. CFB (II) CFB(ll)-CF bond 15 lb. CF weak 22 lb. CB Blocking Reverse padding Good 1 5 lb. CF All bonds equal very slight blocking As may be seen from these results, the edge padding process of the invention produced in all cases a substantially more satisfactory result than did the prior art processes.

Claims (14)

1. A process for making pressure-sensitive copying sets from a stack of sheets of pressuresensitive copying paper arranged in the sequence desired in said sets, comprising the steps of applying an adhesive to said edge, drying the adhesive, and separating the sheets into said sets, wherein, prior to the application of the adhesive, a pre-treating liquid is applied to the edge of the stack and said edge is then dried, said pre-treating liquid being compatible with the pressure-sensitive copying sets and effective to enhance bonding between adjacent sheets in the stack where adjacent surfaces of said adjacent sheets are reactant coated surfaces and/or to inhibit bonding between adjacent sheets in the stack where adjacent surfaces of said adjacent sheets are not reactant coated sheets.

2. A process as claimed in claim 1, wherein the pre-treating liquid is water, an aqueous solution or an aqueous dispersion.

3. A process as claimed in claim 2, wherein the pre-treating liquid is an aqueous solution of an inorganic salt.

4. A process as claimed in claim 3, wherein the inorganic salt is sodium tetraborate decahydrate.

5. A proess as claimed in claim 2, wherein the pre-treating liquid is an aqueous solution of an organic dye.

6. A process as claimed in claim 5, wherein the organic dye is a dye represented by the Colour Index 29200, a dye represented by the Colour Index 29175, or a dye represented by the Colour Index 47035.

7. A process as claimed in claim 2, wherein the pre-treating liquid comprises an aqueous dispersion of an acrylic latex-containing adhesive.

8. A process as claimed in claim 1, wherein the pre-treating liquid is non-aqueous.

9. A process as claimed in claim 8, wherein the pre-treating liquid is a silicone resin solution.

10. A process as claimed in claim 9, wherein the silicone resin is organosiloxane.

11. A process as claimed in claim 8, wherein the pre-treating liquid is a volatile aliphatic hydrocarbon.

1 2. A process as claimed in claim 11, wherein the volatile aliphatic hydrocarbon comprises from 7 to 10 carbon atoms.

1 3. A process as claimed in claim 8, wherein the pre-treating liquid is a mixutre of long chain saturated hydrocarbons.

14. A process as claimed in claim 8, wherein the pre-treating liquid is a solution of a styrene resin in an organic solvent.

1 5. A process as claimed in claim 8, wherein the pre-treating liquid is a pigmented paint.

1 6. A process as claimed in claim 15, wherein the pigmented paint contains titanium dioxide, carbon black, talc, diatomaceous silica, aluminium powder or a mixture of any two or more of the foregoing in an organic vehicle and solvent.

1 7. A process for making pressure-sensitive copying sets as claimed in claim 1, substantially as hereinbefore described with reference to the foregoing examples.

1 8. A pressure-sensitive copying set, whenever made by the process claimed in any one of the preceding claims.