Sized Transfer Sheet

Abstract

The invention is concerned with coated paper. By precoating paper with starch and insolubilized alginate, the amount of transferable coating e.g. in record materials, needed per unit area can be reduced. This advantage can be achieved with small amounts of alginate, e.g. less than 0.05 gram per square meter per side, and high starch to alginate weight ratios e.g. 85:1. 7 Claims, No Drawings

Description

The invention relates to treated paper and like fibrous sheet material and the treatment may take the form of sizing.

It is known to treat paper for example to effect sizing by application thereto of an aqueous composition comprising starch and a water soluble alginate, such as sodium alginate. We have now discovered that useful treatments of fibrous sheet material such as paper can be effected using smaller amounts of alginate than those previously employed.

Accordingly the present invention provides a porous fibrous sheet material one or both surfaces of which have a coating comprising insolubilised alginate and starch, the weight ratio of starch to alginate being from 12:1 to 240:1 and to one or both coated surfaces of which sheet material there is adhered a layer of microscopic, pressure-rupturable capsules containing a transferable material. The amount of alginate in both surface layers can be 0.5, 1.02 or 3.0 grams per square meter although a preferred amount is not more than 0.05 gram per square meter. Smaller amounts of alginate may be employed, for example, 0.025 grams per square meter may be used, and amounts down to 0.005 grams per square meter may be used with some advantage. In general it is usually found to be convenient to use about 0.0125 grams per square meter.

In general it is desirable to use a weight ratio of starch to alginate of from about 12:1 to about 240:1, preferably from 16:1 or 25:1 to 160:1, more preferably about 75:1 to about 85:1 e.g. about 80:1.

Although the invention has particular usefulness with respect to paper, other like porous fibrous sheet materials comprising woven or nonwoven fibers may be treated similarly, for example, cardboard or even woven or nonwoven fabrics. The alginate present in the treated material according to the invention must be insolubilized and this may be achieved by converting a soluble salt into the free acid, alginic acid, or by one of the well known insolubilizing techniques which involve the reaction of the alginate with a polyvalent metal ion such as that of aluminum.

The fibrous sheet material according to this invention is preferably obtained by applying to the material an aqueous composition containing starch and a water soluble alginate. The starch in the aqueous composition may comprise from 6 to 12 percent by weight and preferably about 8 percent by weight. When such a composition is applied to a fibrous sheet material such as paper using a size press, each side of the material treated will usually pick up about 1.5 to 3 percent and desirably about 2 percent, the percentage being by weight based on the dry weight of the material treated. On the basis of the aforementioned starch to alginate ratios, the aqueous composition may also contain from 0.05 to 0.5 percent by weight of water soluble alginate and generally about 0.1 percent is preferred.

Although for convenience the alginate will normally be employed as the sodium salt, any soluble salt can be used, for example, the salts of other alkali metals, magnesium, ammonium and secondary amines.

Although it is convenient and preferred to prepare the material of this invention by applying an aqueous composition containing both starch and alginate, the two materials can be incorporated separately and in a variety of ways. For example, the required starch may be incorporated into paper during normal paper making techniques prior to laying the beaten fibers on a wire surface through which the water drains. Also an aqueous solution of an alginate salt may be applied to paper immediately the fibers of such material have settled into their configuration on a paper making machine during or after the draining off of the water but before the fibers are compacted. In another mode of obtaining products according to the invention a starch composition may be applied first and an alginate solution applied onto the layer of starch. Where the starch and alginate are added separately, however, it is preferred to apply the alginate first and then the starch.

The insolubilization of the alginate material may be achieved by the alginate reacting with aluminum ions present in a paper, for example, by virtue of the use of alum in the paper making operation. Alternatively or additionally an insolubilization treatment may be effected by direct application of an aqueous solution of a salt of a polyvalent ion such as aluminum.

Fibrous sheet material such as paper treated in accordance with the invention has a surface which is smoother and of reduced porosity compared with the untreated material. This is of considerable value in connection with record materials and one particular aspect of this invention is concerned with record materials, for example, record materials of the type described in British Pat. Specification No. 759,800. This specification in particular describes and claims a record member having provided, on a surface thereof, a coating comprising a plurality of microscopic, pressure-rupturable, oil-containing capsules of gelled hydrophilic colloid material formed by coacervation and wherein the oil contains a substance capable of producing a distinctive coloration when the capsules are ruptured. The microscopic pressure rupturable capsules may be made according to the techniques disclosed in British Pat. Specification Nos. 751,600 and 870,476.

In one form of the invention described in Specification No. 759,800 the internal phase of the capsules, that is the oil-containing composition, includes a colorless print-marking substance which forms blue marks when it comes into contact with a suitable receptor surface, for example, one containing an acidic material such as attapulgus clay. When the surface of the record material and a suitable receptor surface are in normal contact the substance capable of producing the distinctive coloration is, of course, kept away from the receptor surface by the capsule walls. However on rupture of the capsules by pressure the oil composition and the receptor surface come into contact and the appropriate mark is made on the receptor surface, for example, by the reaction of a leuco dye to give a blue-colored print.

In practice it is usually the case that the surface which bears the coating of the microscopic capsules is normally sized with starch prior to the provision of the layer of the microscopic capsules. It is believed, however, that with such starch sized papers the surface configuration is such as to provide shielding of capsules by fibers with the effect of loss of capsules into large surface holes which are larger than the average size of such capsules i.e. about 10 to 12 microns.

It has been surprisingly found that by using treated fibrous sheet material according to this invention as described above as the base for a record material a considerable saving of capsules may be effected, especially when optimum amounts of alginate and starch are used.

Accordingly, the invention includes a record material comprising a porous fibrous sheet material in accordance with the invention to one or both surfaces of which there is adhered a layer of microscopic, pressure-rupturable capsules containing a transferable material comprising a color transfer agent such as an oil which contains a substance capable of producing a distinctive coloration when the capsules are ruptured. The color transfer agent may be colored or a substance which develops a color either by exposure to air or when it is in contact with a reagent present in the receptor surface such as one of the acidic materials described in British Pat. Specification No. 759,800. With the record materials of this invention a smaller amount of microscopic capsules per unit area of base can be used to give a print intensity according to the required limits and this is surprising in view of the fact that other film forming materials which have been tested and which might be thought to be analogous to the alginates used herein gave no comparable improvement. (see example).

The record material of this invention may be formed from a paper base both sides of which have been treated by the application of an aqueous composition comprising both starch and an alginate.

It is to be understood that useful products can be achieved by arranging for the capsules to contain transferable materials other than a color transfer agent, for example, solids or liquids including shoe polish, perfume and adhesives. One form of color transfer agent which could be employed which is other than the type described in Specification No. 759,800 is a colored ink which may be constituted by a relatively low boiling organic solvent such as toluene and a colored dye or a leuco dye dissolved in the solvent.

Accordingly the invention includes a porous fibrous sheet material in accordance with the invention to one or both surfaces of which there is adhered a layer of microscopic, pressure rupturable capsules containing a transferable material such as a color transfer agent or one of the other transferable materials mentioned above.

Record materials of the type described herein are often used in the form of manifold sets which comprise a "CB Sheet," i.e. a record material having a coated back, the coating consisting of the said capsules containing a color transfer agent and a so-called "CF Sheet" which has a coated front, the coating of which normally contains an acidic material. Also in between a "CB Sheet" and a "CF Sheet" there may be interposed one or more so-called "CFB Sheets" which are coated on the front with an acid material and coated on the back with microscopic capsules. The invention also includes manifold sets including a record material as defined above as a "CB Sheet" or a "CFB Sheet."

Following is a description by way of example of a treated paper according to the invention.

EXAMPLE

White 49 g.s.m. base paper was treated at the size press with a size consisting of an 8 percent solution of a pre-oxidized corn starch, Amisol E. 1102 [ Amisol is a Registered Trade Mark ] and Manutex SX/RF (supplied by Alginate Industries Limited).

The size was prepared by making up the alginate as a 6 percent solution using Calgon (sodium metaphosphate) as a dispersant in the ratio 2:1 Alginate to Calgon (weight/weight as delivered). The Calgon was first added to the water and then the alginate was stirred in with a high speed stirrer. The alginate was then blended with the starch mix at 50/60.degree. C. to give an 85:1 starch to alginate blend as an 8 percent solution.

A control experiment was run to produce a base paper sized in the same manner with an 8 percent starch solution. The pickup figures at the size press were similar in both cases.

Both the sized papers as produced above were further coated with an emulsion of microscopic, pressure rupturable oil containing capsules using an airknife coater. Sheets were produced with 5 g.s.m. and 6 g.s.m. coatings and the dried sheets were tested for print intensity. The print intensity of each coated sheet was measured as follows:

Each CB (emulsion coated back) sheet was placed against a standard CF (clay coated front) strip and the two run through a calender roll nip at standard speed. The nip width was 0.75 inches and the pressure was 83.5 lbs./linear inch.

This gave a "blued-up" strip of CF paper with a central image of 0.75 inches width. The print was allowed to develop for 30 seconds and the reflectance of the central blue image R.sub.image and of the background white R.sub.background were measured using an opacimeter.

Thus the lower the reflectance of blue image, R.sub.image, the stronger is the blue print, and it follows that the lower the print intensity, the better is the reactivity.

The results obtained for starch/alginate mix and starch control were as follows: CB Coating Print Intensity _________________________________________________________________________ _ 6 g.s.m. 5 g.s.m. _________________________________________________________________________ _ Starch only control 53.9 56.5 Starch/Alginate mix 49.3 53.5

Thus 0.1 percent of sodium alginate used in the starch mix at the size press resulted in a 16 to 17 percent saving in emulsion.

The above was repeated using an 8 percent solution of starch and a material other than alginate, the ratio of starch to each material being 9:1 (as recommended by suppliers). The print intensities obtained for 6 g.s.m. coatings were as follows: CB Coating Print Intensity Starch/polyvinyl alcohol mix 50.5 Starch/carboxymethyl cellulose mix 51.6 Starch/modified styrene maleic anhydride copolymer (Scripset) mix 53.7

Thus even with a high ratio of other material to starch, with a consequent increase in the cost of the size, there can still be a saving in emulsion by using a starch/alginate mix.

The above was repeated again using 0.2 percent of sodium alginate at the size press and all results were found to be comparable with those obtained using 0.1 percent of alginate. During further experiments with 0.1 alginate inclusion at the size press we found that the reduction in emulsion necessary did vary between 0.5 g.s.m. and 1.0 g.s.m.

The emulsion containing microscopic capsules referred to above consisted of the following ingredients: 100 p.b.w. Capsules 25 p.b.w. Solka Floc (Cellulose fiber) 10 p.b.w. Starch

The starch in the emulsion acted as an adhesive for the capsules and the cellulose fiber, and the cellulose fiber served to cushion the capsules during handling of the record member.

Claims

1. A porous fibrous sheet material one or both surfaces of which have a sizing coating comprising insolubilized alginate and starch, the weight ratio of starch to alginate being from 12:1 to 240:1, and to one or both coated surfaces of which sheet material there is adhered a layer of microscopic, pressure-rupturable capsules containing a transferable

2. A sheet material as claimed in claim 1 wherein the amount of alginate on at least one surface, and in its underlying layers, of the sheet material,

3. A sheet material as claimed in claim 2, wherein the amount of alginate

4. A sheet material as claimed in claim 1 wherein the transferable material comprises a color transfer agent which contains a substance capable of

5. A sheet material as claimed in claim 1, wherein the insolubilized

6. A sheet material as claimed in claim 1, wherein the weight ratio of

7. A paper sheet as claimed in claim 1 coated with about 0.0125 grams per square meter per side of aluminum alginate and about 1 gram per square meter per side of preoxidized corn starch.