GB2087942A - Capsule sheet for no-carbon copying paper - Google Patents

Abstract

In a capsule sheet for no-carbon copying paper having a coating layer containing microcapsules composed of a melamine-formalin resin film or a urea-formalin resin film, incorporating into said coating layer a latex (dry base) in an amount of 5 to 20% based on the weight of the microcapsules can prevent smudges due to undesired breakage of the microcapsules, and improve the water-, and heat resistance, and color- developing property of the capsule sheet.

Description

SPECIFICATION Capsule sheet for no-carbon copying paper This invention relates to a capsule sheet for no-carbon copying paper.

No-carbon copying paper is well known and usually composed of a combination of microcapsules containing a colorless electron-donative organic compound and a high-boiling organic solvent, and an acidic material which makes said colorless electron-donative organic compound develop color, and the demand therefor has increased more and more in recent years because of its usefulness.

The key technique in no-carbon copying paper is microcapsulation, which gives a great influence upon the performance characteristics of no-carbon copying paper. A coacervation method using gelatin has heretofore mainly been employed for microcapsulation in the production of no-carbon copying paper.

However, this method is disadvantageous, for example, in that only microcapsules with a low concentration can be obtained; complicated steps are required; stable production of microcapsules is difficult; the microcapsules obtained are perishable, have poor water resistance and are liable to be broken under the condition of high humidity; and the inner phase materials are easily extracted with a surfactant or the like. An improvement in said method has been desired, however no substitutive microcapsulation method has been found.

Recently, there have been put to practical use microcapsules produced by an interfacial polymerization method which have a film of polyurethane, polyurea or the like, the microcapsules produced by an in situ method which have a film of melamine-formalin resin or urea-formalin resin.

According to the interfacial polymerization microcapsulation, microcapsules can relatively easily be obtained at a high concentration and the microcapsules obtained are not perishable. However they cannot be said to have excellent resistance to polar solvents and chemicai agents.

The interfacial polymerization microcapsulation is disadvantageous, for example, in that highly reactive starting materials used are apt to give some side reactions which result in the difficulty of handling; fine uniform capsules are difficult to obtain; the starting materials used are poisonous; and the microcapsules obtained are expensive. Therefore, it is difficult to substitute the interfacial polymerization microcapsulation for microcapsulation by a gelatin coacervation method.

On the other hand, according to microcapsulation by an in situ method in which a melamine-formalin resin film or a urea-formalin resin film is used, microcapsules can easily and stably be obtained at å high concentration by a combination of a novel emulsifier (serving as a modifier) with the starting materials (for example, Japanese Patent Kokai (Laid-Open) Nos. 9079/1976, 84882/1978, 84883/1978, 84881/1978,49984/1979, etc.), and the microcapsules obtained are not perishable and have excellent heat-, solvent-, water-, and chemical resistance. Moreover they are inexpensive, and hence the in situ method is taking the place of the gelatin coacervation method.However, microcapsules obtained by the in situ method are disadvantageous in that they are very hard owing to the characteristics of the film material and hence are difficult to break by pressure applied by a pen or the like. Therefore, it has been investigated, for example, to make the film thin or modify the film.

However, for example, when the film is made thin, the microcapsules certainly become easy to break, but there tends to occur unnecessary or undesired breakage which results in smudges. It is possible to a certain extent to make the microcapsules easy to break by modifying the film. However also in this case, unnecessary or undesired breakage is caused and heat-, and solvent resistance which are characteristic of the in situ method are apt to be deteriorated.

These phenomena are more significant in microcapsules of a melamine-formalin resin film than in microcapsules of a urea-formalin resin film.

The present invention may enable the provision of a capsule sheet for no-carbon copying paper in which smudges due to unnecessary or undesired breakage of the microcapsules are prevented or minimised, and/or which is excellent in water-, and heat resistance and has a good coloring property.

According to the present invention there is provided a capsule sheet for no-carbon copying paper having a coating layer containing latex (dry base) and microcapsules composed of a melamine-formalin resin film or a urea-formalin resin film. Preferably said latex is present in an amount of 5 to 20% based on the weight of the microcapsules.

Such a sheet may have the advantages described above.

The reason why the above-mentioned advantages may be achieved by incorporating into said layer a latex (dry base) in an amount of 5 to 20% by weight based on the microcapsules in this invention is considered to be that hardness (in other words, brittleness) which is characteristic of the melamineformalin resin film or urea-formalin resin film is protected and sheltered owing to the soft latex which is present around the microcapsules composed of the aforesaid resin film.

Therefore, in this invention, the latex is desired to be soft, and it is recommended that its filmformation temperature should be equal to or lower than room temperature.

As the latex to be used, there are represented those which are very usually used as adhesives, and there may be exemplified, for example, very many commercially available latices such as acrylic ester-, vinyl acetate-, vinyl chloride-, styrene-butadiene-, and natural rubber latices.

A latex used in usual paper processing has usually been selected from the above-mentioned latices in consideration of their respective characteristics. However, in a capsule sheet for no-carbon copying paper, the situation is different and the addition of a latex generally produces undesirable side effects, namely inhibition of color developability and increase of smudges. Therefore no latex has heretofore practically been used. [Except for the case of no-carbon copying paper, it is well known to add an aqueous emulsion as an adhesion-improving agent to microcapsules having a large size of 30 vim or more obtained by utilizing coacervation of gelatin. (Japanese Patent Kokai (Laid-Open) No.

11883/1978)1 Another reason why no latex has heretofore been used in producing a capsule sheet for no-carbon copying paper is not only that a dispersion of microcapsules obtained by the gelatin coacervation method per se contains a large amount of water-soluble highpolymers contributing to adhesion, such as colloid as a component of an equilibrium liquid, and does not require very large amounts of other adhesives, but also that when a latex is used, the properties of the microcapsule film are generally deteriorated by the surfactant which is contained in the latex in order to disperse (emulsify) and stabilize the latex.

According to our investigation, it was found that microcapsules composed of a urea-formalin resin film or particularly a melamine-formalin resin film were particularly resistant to surfactants and the like, and hence could coexist with a latex. However, it was found that even when a latex was added, it was not sufficiently usefui as an adhesive so that other water-soluble adhesives were needed. On the other hand, it was found that the softness of the latex in the coating layer compensated for the hardness (brittleness) of the microcapsules, and on the basis of this finding, this invention has been accomplished.

In this invention, when the latex (dry base) based on the weight of the microcapsules in the coating layer is 5% or less, little or no marked effect is dbtained, and when it is 20% or more, it is wasteful and sometimes gives bad influence.

The in situ microcapsulation by use of a melamine-formalin resin or a urea-formalin resin is well known. A dispersion of microcapsules having a high concentration can very easily be produced by, basically, emulsifying a solution of a colorless organic compound in a high-boiling organic solvent, in an aqueous solution of a macromolecular carboxylic acid, adding thereto urea and formalin, or their precondensation product, or a melamins-formalin precondensation product, and then allowing the resulting mixture to react under acidic conditions with heating. As representative well-known references, there may be exemplified Japanese Patent Kokai (Laid-Open) Nos. 49984/1979, 53679/1979, 84881/1978, 84882/1978, 84883/1978 and 9079/1976.

The microcapsule in this invention has the average particle size of approximately 2.0 to 8.0,um.

The microcapsules may contain an acidic material (e.g., a phenolic resin, a metal salt of a salicyclic acid derivative, or the like) in particular cases, and the particle size in this case is the same as the above.

In the capsule sheet for no-carbon copying paper of this invention which has a coating layer containing microcapsules composed of a melamine-formalin resin film or a urea-formalin resin film, said coating layer may contain a protecting agent (stilt material), a water-soluble adhesive and the like in addition to a fixed amount of latex.

As the protecting agent (stilt material), there are used those having a particle size which is a little larger than those of the microcapsules, such as starch particles, cellulose powder, inorganic powder, and the like. The amount of the protecting agent used is generally about 20 to 250 parts per 100 parts of the microcapsules, but about 20 to 80 parts in the case of usual transfer-type overlying paper, and often 1 50 parts in the case of self-contained pauper.

As the adhesive, there are used water-soluble high polymers such as starch or modified starch, polyvinyl alcohol, cellulose derivatives, carboxylic acid polymers and the like, and they are added in an amount required to obtain a necessary strength, for example, 5 to 40 parts per 100 parts of the microcapsules. In addition, various additives such as defoaming agents, for imparting water resistance, and the like are added, if required.

The preparation of these coating solutions needs no particular attention and may be carried out by a usual method and the coating method is not particularly limited.

The present invention is further explained below referring to experimental examples.

EXPERIMENT 1 (microcapsules produced by a gelatin coacervation method) An inner phase oil obtained by dissolving 3 parts of C.V.L. (crystal violet lactone = a colorless color-forming organic compound) in 100 parts of a high-boiling organic solvent N-296 (manufactured by Nihon Petrochemical Co., Ltd.) was emulsified in a solution of 20 parts of gelatin in 100 parts of water, and the resulting emulsion was added to 1,480 parts of a solution of 20 parts of gum arabic in 1 ,480 parts of warm water, after which the pH of thus obtained mixture was adjusted to 9.

Next, the pH was lowered to 4.5 with acetic acid under stirring, and the system was cooled to 1 OOC, after which 20 parts of glutaraldehyde (50%) was added thereto, and after a whole day and night, the pH of the resulting mixture was adjusted to 9, whereby a microcapsules-containing solution was produced by a gelatin coacervation method.

The average particle size of the microcapsules was 9.5 tom.

EXPERIMENT 2 (melamine-formalin resin microcapsules produced by an in situ method) An inner phase oil obtained by dissolving 3 parts of C.V.L. in 100 parts of N-296 was emulsified in 11 5 parts of an aqueous solution (pH 5) containing 5 parts of a styrene-maleic anhydride copolymer. To the resulting emulsion was added 50 parts of an aqueous solution containing Sir613 (a melamine: formalin precondensation product manufactured by Sumitomo Chemical Co., Ltd.) in an amount of 20% in terms of solid, and the resulting mixture was adjusted to 700C, allowed to react for 2 hours, and then adjusted to pH 9, whereby a microcapsules-containing solution was produced from the melarnineformalin resin by an in situ method. The average particle size of the microcapsules was 4.0,1tom.

EXPERIMENT 3 (production of overlying paper for no-carbon copying paper) To each of two kinds of thus obtained microcapsules-containing solution were added wheat starch, starch and latex according to the formulation given in the following Table, and the resulting coating color was applied to plain paper having a weight per centare of 41 g/m2 by means of an air-knife coater so that the applied amount of the capsules might be about 2.3 g/m2, to obtain four kinds of overlying papers for no-carbon copying, A (comparative example 1), B (comparative example 2), C (comparative example 3) and D (example 1).

Formulation (in terms of solids)

A (Comparative B (Comparative C (Comparative.

example 1) example 2) example 3) D (Example 1) Microcapsules Microcapsules Microcapsules Microcapsules Microcapsules in Experiment 1 in Experiment 1 in Experiment 2 in Experiment 2 100 parts 100 parts 100 parts 100 parts (1) Wheat starch 35 parts 35 parts 35 parts 35 parts (2) Starch 10 parts 10 parts 15 parts 15 parts (3) Latex - 10 parts - 15 parts Note: (1) Wheat starch: Wheat starch having an average particle size of about 20 was used.

(2) Starch: Oxidized starch (MS-3800 manufactured by Nisshoku Co., Ltd.) was used.

(3) Latex: An ethylene-vinyl acetate copolymer (Kuraray OM-4000) was used.

EXPERIMENT 4 Four kinds of thus obtained overlying paper A, B, C and D were tested for the undermentioned items. As the sheet coated with an acidic material, commercially available underlying paper (Mitsubishi NCR Paper Resin N-40 Underlying Paper manufactured by Mitsubishi Paper Mills Ltd.) was used.

(I) Color-developing property Each of the overlying papers was placed upon the underlying paper and the color was developed by means of a super-calender, and after 1 hour, the depth of the developed color was measured by means of a color-difference meter, and is shown in terms of reflectivity.

(II) Heat resistance Each of the overlying papers and the underlying paper were placed one upon another in an oven at 1 05oC for 6 hours, and the breakage of the microcapsules due to heat was evaluated by measuring the smudge on or the reflectivity of the underlying paper.

(III) Water resistance Each of the overlying papers and the underlying paper were placed one upon another, immersed in water, and then dried in an oven, after which the smudges on or the reflectivity of the underlying paper were measured.

(IV) Smudges due to friction The underlying paper was put on each of the overlying papers (so that color might be developed), and a 3Kg weight was put on the underlying paper, after which the underlying paper was slid by 50 cm on the overlying paper, and the breakage of the microcapsules due to friction was determined by measuring the smudges on or the reflectivity of the underlying paper.

(V) Smudges due to pressure Each of the overlying papers and the underlying paper were placed one upon another and cut by means of a guillotine cutter, after which the smudges on or the reflectivity of the underlying paper due to, for example, pressing-down pressure in the vicinity of the cut end, were assessed. Measurement data and evaluation

A B C D (Comparative (Comparative (Comparative example 1) example 2) example 3) (Example 1) Kind of capsules Gelatin film capsules Melamine-formalin resin film capsules (I) Color-developing o o o o property % 35 36 33 33 (II) Heat resistance o x o o % 95 80 100 100 (III) Water resistance x x o o % 38 40 90 92 (IV) Smudges due to friction o x o o % 86 60 90 89 (V) Smudges due to pressure o x # o % 93 85 90 95 o: Satisfactory #: Unsatisfactory x: Inferior It was found from the above results that the overlying paper D (example 1 of this invention) was excellent in all the points; in the case of the gelatin capsules, the smudges are increased by the addition of the latex; and the effect of addition of the latex in the case of the melamine formalin resin capsules was quite contrary to that in the case of the gelatin capsules. The useful effect of this invention was realized for the first time in the microcapsules produced by the in situ method.

Claims (5)

1. A capsule sheet for no-carbon copying paper having a coating later containing latex (dry base) and microcapsules composed of a melamine-formalin resin film or a urea-formalin resin film.

2. A capsule sheet for no-carbon copying paper according to claim 1, wherein said latex is present in an amount of 5 to 20% based on the weight of the microcapsules.

3. A capsule sheet for no-carbon copying paper according to claim 1 or claim 2 wherein the latex is selected from acrylic ester-, vinyl chloride-, styrene-, butadiene-, and natural rubber latices.

4. A capsule sheet for no-carbon copying paper according to claim 1 and substantially as described and exemplified herein.

5. No-carbon copying paper including a capsule sheet according to any one of the preceding claims.