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Publication numberUS3622364 A
Publication typeGrant
Publication dateNov 23, 1971
Filing dateNov 12, 1968
Priority dateNov 12, 1968
Also published asDE1809778A1, DE1809778B2, US3753761
Publication numberUS 3622364 A, US 3622364A, US-A-3622364, US3622364 A, US3622364A
InventorsMasahiro Maeno, Kaichiro Miyazawa, Tadahisa Nakazawa, Yujiro Sugahara
Original AssigneeMizusawa Industrial Chem
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Color former for pressure sensitive recording paper and process for producing same
US 3622364 A
Abstract
A pressure sensitive recording paper comprising a paper substrate and a coating thereon comprising a color former which comprises a member selected from the group consisting of acid-treated dioctahedral montmorillonite clay minerals and mixtures of such minerals with natural dioctahedral montmorillonite clay minerals, the minerals having a secondary color development property, K2, of at least 1.40, the value of K2 being represented by the formula K2 = R430/R 550 + 1/2 (1-R550) wherein R430 and R550 are reflectances of light having wavelengths 430 m mu and 550 m mu , respectively, when the minerals are developed by benzoyl leuco methylene blue.
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United States Patent 72] Inventors Yujiro Sugahara Tokyo; Kaichiro Miyazawa, Tsuruoka-shi; Tadahisa Nakazawa, Niigata-ken; Masahlro Maeno, Niigata-ken, all of Japan [2]] Appl. No. 775,126 [22] Filed Nov. 12, 1968 [45] Patented Nov. 23, 1971 [73] Assignee Kabushiki Kalsha Mizusawa Kagaku Kogyo l-llgashi-ku, Osaka, Japan [54] COLOR FORMER FOR PRESSURE SENSITIVE RECORDING PAPER AND PROCESS FOR [50] Field of Search 106/72, 288 B; 252/450 [56] References Cited UNITED STATES PATENTS 2,903,434 9/1959 Gloss 252/450 3,213,037 10/1965 l-lodgkiss 252/450 3,369,993 2/1968 Mills et al. 252/450 Primary Examiner-James E. Poer Attorney-Sherman and Shalloway ABSTRACT: A color former for pressure sensitive recording paper which comprises a member selected from the group consisting of acid-treated dioctahedral montmorillonite clay minerals and mixtures of said minerals with natural dioctahedral montmorillonite clay minerals and a process for producing the same.

COLOR FORMER FOR PRESSURE SENSITIVE RECORDING PAPER AND PROCESS FOR PRODUCING SAME This invention relates to a color former which demonstrates pronounced color development effects when used in making manifold record paper, i.e. the pressure sensitive recording paper, which can reproduce copies by handwriting, printing or typing without the necessity of the conventional carbon paper, The invention also relates to a process for producing such a color former.

The pressure sensitive recording papers, with a few exception in the case of special papers, are in all cases those in which the color development reaction ascribable to the transfer of electrons between the colorless compound of organic coloring matter having electron donating property and a color former, the electron acceptor. (US. Pat. No. 2,548,366).

As the colorless compound of organic coloring matter, the color reaction substance, two classes of coloring matter each of which exhibit different behaviors of coloration are used cojointly. One of them is that which, as in the case, for example, of the triphenyl methane coloring matter, develops color intensity immediately upon contacting a solid acid, but which has a tendency to fade easily (primary color development coloring matter). The second coloring matter used is one which does not immediately develop color upon contacting a solid acid but develops its color completely after several days have elapsed and exhibits adequate fastness to sunlight. As such a coloring matter, for example, the acyl leucomethylene blue coloring matter are used (secondary color development coloring matter).

On the other hand, as the color former, the electron acceptor, the solid acids are generally used. In the past, known are such, for example, as kaolin, bentonite, attapulgite, aluminum sulfate, natural zeolite, silica gel, feldspar, pyrophyllite, halloysite, magnesium trisilicate, zinc sulfate, zinc sulfide, calcium fluoride, calcium citrate as well as the organic acids as tannic acid and benzoic acid.

The pressure sensitive recording paper using these color development coloring matter and color formers is made up of two classes of papers: one the transfer sheet (referred to as the coated back of CB), a paper which has been coated with the coloring matter in solution in oil and encapsulated by such as gelatin, gum arabic or synthetic resin the size of which capsules is several microns in diameter, and the other the receiving sheet (referred to as the coated front or CF a paper coated with the color former. Now, when the foregoing two papers are superpose facing each other and pressure is applied with either a steel pen or typewriter, the capsules of that portion to which the pressure has been applied rupture and the oil and the colorless coloring matter come into contact with the color former to develop color and thus impress that portion with a mark. On the other hand, when three or more copies are required, an one or more intermediate sheets which we generally referred to as a coated front and back back sheet (or CFB) i.e. one which has the front coated with the color development coloring matter and the back coated with the color former, are used interleaved between the transfer sheet and the receiving sheet.

According to the disclosures made heretofore, it can be seen that in all cases, the researches concerning the pressure sensitive recording paper have laid their emphasis on the process of synthesizing the organic coloring matter and capsulation thereof and practically no studies have been made regarding the color former of the pressure sensitive recording paper. Thus, in the present state of the art the practice is to use attapulgite, a kind of naturally obtained clay, in its as-obtained state.

However, the conventional color formers such as indicated above were either those in which notwithstanding their good color development effect relative to the primary color development coloring matter their color development effect relative to the secondary color development coloring matter was poor or those in which notwithstanding their good color development efi'ect relative to the secondary color development coloring matter their color development effect relative to the primary color development coloring matter was poor. Thus, there has not been found to date a color former which demonstrates excellent color development effects relative to the primary as well as secondary color development coloring matter.

It is therefore a primary object of the present invention to provide a color former for use with the pressure sensitive recording paper, which demonstrates excellent color development effects relative to the primary as well as secondary color development coloring matter. Another object is to provide a process by which the foregoing color former is produced. A still another object is to provide a color former for use with the pressure sensitive recording paper, which not only excels in its color development effects relative to the primary as well as secondary color development coloring matter but also causes fewer smudges. A further object is to provide a process for producing such a color former. Smudge, as here used, refers to a nonintended color development phenomenon (soiling) which occurs, for example, during preservation, carrying, handling, etc. An additional object is to provide a color former for pressure sensitive recording paper in which the exfolidation phenomenon after its application to the paper is less.

Other objects and advantages of the present invention will become apparent from the following description.

The foregoing objects and advantages are achieved according to the present invention by a color former for pressure sensitive recording paper which comprises a dioctahedral montmorillonite clay mineral and/or the acid-treated products thereof the specific surface area of which is at least mF/g. of the total particles at least 75 percent by weight having a particle diameter 10 microns or less, and not more than 45 percent by weight being those of diameter one micron or less, said mineral and/or its acid-treated products having a secondary color development property, K of at least 1.40, preferably at least 1.60, the value of K being represented by the formula wherein R and R are reflectances of light having wavelengths 430 my. and 555 mp., respectively when said mineral and/or its acid-treated products are developed by benzoyl leucomethylene blue.

As a result of our extensive researches concerning the color former for pressure sensitive recording paper, we found that the following interesting facts.

According to our investigations, it was found that the color development effects of the color former in the secondary color development coloring matter, e.g. acyl leucomethylene blue, was controlled to a great extent by the inherent properties of the natural solid acid, and that though the color development property of the natural solid acid relative to the secondary color development coloring matter could be improved somewhat by such chemical treatments as, say, acid, alkali, oxidation and reducing treatments, a substantial improvement of the color development property could not be attained. Further, as the solid acids, which are the color former, the natural clay minerals, such as hereinbefore indicated, e.g. kaolin, bentonite, attapulgite and natural zeolite, are known, but actually attapulgite is principally used.

However, it was found according to our investigations that the secondary color development property of these natural clay minerals was very irregular, there being a marked difference in the color development property even among those of the same class depending upon such as their locale of production or their position of burial within the same deposit.

Hence, when the natural clay minerals generally referred to as, for example, attapulgite or bentonite, are used nonselectively, little, if any, color development property is noted n some instances or the extent of the color development is not adequate in some instance, and thus a uniform secondary color development effect is not demonstrated. In addition, these natural clay minerals have the shortcoming that their primary color development efiect is on the whole uniformly poor.

We however found according to our studies that of the natural clay minerals the dioctahedral montrnorillonite clay mineral had a unique property in that a certain class of the montmorillonite clay minerals had as its inherent property an excellent color development property relative to the secondary color development coloring matter (secondary color development property). It was also found that it differed from the other clay minerals in that its color development property relative to the primary color development color-ing matter (primary color development property) could be enhanced remarkably by an acid treatment. Further, it was continued by our studies that a practically proportional relationship holds between the primary color developments property of the hereinbefore indicated clay minerals and their specific surface area; and that the specific surface area of dioctahedral montmorillonite clay minerals adopted by the present invention is generally increased by its acid treatment though there is a difference in degree depending upon its class and that an enhancement of the primary color development property takes place in concomitance with this increase in specific surface area.

We found that a color former for pressure sensitive recording paper use which excels in both in its primary and secondary color development property could be obtained by first choosing from among the dioctahedral montmorillonite clay minerals those which excel in secondary color development property and thereafter subjecting these chosen montmorillonite clay minerals to an acid treatment until the desired specific surface area is obtained.

Further, we found according to our investigations that the color development property of the aforesaid montmorillonite clay minerals could be readily determined by measuring in accordance with the measurement method given below the reflectances R and R of light having wavelengths 430 my. and 550 mp. when said minerals are developed by benzoyl leucomethylene blue of the formula and comparing the value of K calculated as follows:

'primary color development property,

thereof Five grams of this powder is then placed in a weighing bottle and is dried in a 1 10 C. constant temperature dryer for 1 hour followed by allowing it to cool in a desiccator.

The particle diameter of the color former is measured by means of the Andreasen sedimentation pipet. For particulars, reference shall be made to the Encyclopedia of Chemical Technol gy (RE. Kirk, D. Othmer), Vol. 12, p. 490 (1954). The particle diameters used herein have all been made by this method of measurement.

2. Preparation of the color development coloring matter solutron.

Five grams of benzoyl leucomethylene blue are dissolved in grams of g.p. benzene.

3. Color development conditions.

Two grams of the foregoing dried specimen are weighed onto a watch glass 8 cm. in diameter and spread out thinly. Four cc. of the aforesaid benzoyl leucomethylene blue solution are then dropped in such a manner as to completely wet the whole specimen, after which stirring is carried out with a spatula to ensure that the whole becomes homogeneous. lf complete wetting of the specimen cannot be accomplished by 4 ml. of the solution owing to the greatness of the oil absorption value of the specimen, the foregoing operation is carried out after first adding benzene to the coloring matter solution in a necessary amount. This is followed by allowing the specimen to stand for 24 hours in a room of temperature l5-20 C. into which the direct range of sunlight do not shine. During this time specimen is mixed two or three times with a spatula to ensure that the whole becomes homogeneous. The so obtained specimen is used for measuring the degree of color development.

4. Method of measuring the degree of color development.

The degree of color development of the specimen whose color has been developed in the foregoing manner is measured with a spectrophotometer. The specimen is packed in a powder cell of quartz and its reflectances of lights having wavelengths of 430 and 550 mp. are measured. The reflectance is expressed in percent using as the basis percent for the reflectance of an alpha-alumina shaped product. 5. Method of indicating the secondary color development property.

When the reflectances of the lights of 430 my and 550 mu are designated respectively R and R the secondary color development property is defined by the following equation:

Thus, the greater the value of H the better the secondary color development property. While as the method of accurately indicating color, the methods of indication of the Commission International dEclar-iage or International Commission on Illumination are used. The determinations of color development by means of the value of K,, as defined herein above and the results of determinations by means of the naked eye were found to be in very good agreement in our experiments.

Next, for clarifying the fact that the specific surface area secondary color development property and decolorizing property of the natural clay minerals differ greatly depending upon such conditions as their class locale of production and position of production is the same locale and that there is a change over a broad range in these properties after the acid treatment of the minerals, these properties of the various classes of natural clay minerals are shown in table I,

TABLE I Property of untreated specimen Acid treatment Specific Secondary Decoloriz- Specific Prim surface Primary color deg surface color deve S iccimen Class of the clay Name of the clay Locale in which area color develvelopment ability, area opment umber mineral mineral clay produced (rnJ/g.) opment (K (K2) percent (mi/g.) (K 5 Attapulgite fittfiifihlltglte llorid a (X -8 2k.) 32 2. 89 1.68 34.4 160 2.65 ao e eorg a 2. 6 1.17 39. 5 40 2.38 3 iKmun mineral '{Halloysite iigate 72 2. 20 1. 35 29. 3 2g 4 Mica clay mineral... Sericite Niigata. 24 2. 71 1. 20 39. 5 24 3.03 ale mineral Talc. kayama 2.02 1. 18 0 10 2.08 Bentomlte (I) Okayama 1.74 1.19 0 1.78 Bentomite (II) Tsugawa 60 2.40 1. 70 6.8 136 2. 50

(Niigata). Bentomite (III) Gunma 72 2.63 1.84 6.8 100 2.22 Sub-hentonite (I) MESlSSSlRp; 104 2. 40 1. 80 5. 7 280 3.04 Sub-hentonlte (II) Utah U. S:A.) 72 2.48 1. a0 1.1 232 2.96 Dioctahedralmont- Japanese-acid clay (I)- N akajo (Niigat 104 2.45 2.15 9. 1 200 3. 15 12 morillonite J apanese-acid clay do 96 2. 48 1.63 18.2 240 2. 70 1a {firgmese-acid clay Shibata (Nligata) 12s a. 10 1. 29 42. 1 160 a. 43 14 Japanese-acid clay Tsuruoka 104 2. 42 2.15 33. 0 350 3. 21

IV (Yamagata). 15 Jagpese-acid clay .do 136 2.19 1. 39 18. 2 144 2. 35

Property of acid-treated specimen (A) Property of acld-treated specimen (B) Secondary Decolor- Acid Specific Primary Secondary Decolor- Acid color deizing treatsurface color decolor deizing treat- Suitability for use as color former Specimen velopment ability, ment acid velopmeut velopment ablllty, ment for pressure sensitive recording Number (K2) Percent time (mfi/g.) (K1) (K1) percent time paper 1. 65 52. 1 1 160 2. 65 1. 65 47.0 2 Satisfactory (primary color develop ment efiect inferior) 1. 21 47. 8 3 72 2. 38 1. 22 54. 2 6 Poor. 1. 33 74. 4 3 190 2. 33 1. 32 79. 7 6 Poor (decolorizlng property very good). 1. 20 39. 6 1 32 3. 11 1. 20 42. 5 5 P001". 1.16 0 1 10 2.19 1.14 2.0 4 D0. 1.18 0 l 1.90 1. 15 0 2 D0. 1. 80 72. 0 1 185 3. 10 1. 82 73. 2 3 Excellent. 1. 82 66.2 1 120 2. 23 1. 71 70. 2 3 Poor. 2. 22 87. 1 5 350 3. 41 2. 26 75.7 9 Excellent (grade become acceptable as a result of acid treatment). 1.30 73.3 2 328 3.03 1. 25 80.3 4 Poor (decolorizing property very good). 1.89 75. 3 2 280 3. 47 1. 72 80. 7 5 Excellent (grade become acceptable as a result of acid treatment). 1. 98 68.0 3 340 3. 03 1.89 78. 2 7 Do. 1. 64. 7 4 168 3. 69 1. 32 70. 4 8 Poor. 2. 29 70. 8 3 400 3. 42 1. 57 73. 8 6 Excellent (grade become acceptable as a result of acid treatment). 1. 35 68.7 2 295 3. 20 1.33 78. 9 4 Poor (decolorizing property good).

Testing procedures. 45 76.5 Grams each of the clay on a dry basis were weighed The several tests indicated in table I were conducted in the into eight 500-ml. conical beakers. After adding 200 ml. of 34 following manner: weight percent sulfuric acid to each beaker, they are heated in l Preparation of the specimen.

After the dried color former has been fully comminuted in a mortar or pot mill, it is winnowed and prepared such that a least 85 percent by weight of the total particles are those having a particle diameter 10 microns or less and not more than 35 percent by weight are those of a particle diameter one micron or less. Five grams of this powder are then weighed into a weighing bottle, dried for 1 hour in a 1 [0 C. constant temperature dryer and thereafter allowed to cool in a desiccator.

2. Acid treatment conditions. Specimens Nos. l-8.

Fifty grams each of the clay on a dry basis are weighed into six 500-ml. conical beakers. After adding 300 ml. of 16.2 weight percent hydrochloric acid to each beaker, they are heated in a 85 C. water bath. After the passage of each hour one of the beakers is taken out by turns from the water bath, and the contents are water-washed until no chloride ion remains, then dried at 110 C., comminuted and winnowed to obtain the specimen. Of these 6 specimens, the tests were conducted on (A) those demonstrating the greatest decolorizing property when a lubricating oil was decolorized at 250 C and (B) those demonstrating the greatest decolorizing property when soybean oil was decolorized at 1 10 C.

2. Specimens Nos. 9-15.

a C. water bath. After the passage of each hour, one of the beakers is taken out by turns from the hot water bath and the contents are water-washed until no sulfate ion remains, followed by drying at C., comminution and winnowing to obtain the specimens. Of these specimens, the tests were conducted on (A) those demonstrating greatest decolorizing property when a lubricant was decolorized at 250 C. and (B) those demonstrating the greatest decolorizing property when soybean oil was decolorized at 110 C. These (A) and (B) specimens are indicated in table I as acid-treated specimens (A) and (B), respectively.

3. Specific surface area.

The specific surface area of the several specimens were determined by the so-called BET method which is based on the adsorption of nitrogen gas. For details of this method, reference shall be made to the following literature:

S. Brunauer, P.H. Emmett, E. Teller, J. Am. Chem. Soc., 60,309 1938) perty. 1. Preparation of the solution of the color development coloring matter.

As the primary color development coloring matter, crystal violet lactone, a triphenylmethane coloring matter, is used. 0.5 Gram of this coloring matter is dissolved in 99.5 grams of g.p. benzene. The chemical nomenclature and structural formula of crystal violet lactone are as follows:

Crystal violet lactone [3,3-bis(p-dimethylaminophenyl)-6- dimethylphthalide] 2. Color development conditions.

Two grams of the hereinbefore described dried specimen are weighed into a watch glass 8 cm. in diameter and spread out thinly, after which 4 ml. of the aforesaid crystal violet lactone benzene solution are dropped onto the specimen in such a manner that the whole of the latter becomes completely wet. This is followed by mixing the whole with a spatula to achieve a homogeneous mixture and allowing the mixture to stand for 1 hour in a room temperature of l5-20 C. into which direct rays of sunlight do not shine. Thus is obtained the specimen for measuring the color development. In the case where the oil absorption of the specimen is great and complete wetting is not had by 4 ml. of the solution, the same operation is carried out after first having added the necessary amount of benzene to the coloring matter solution.

3. Method of measuring the degree of color development.

The degree of color development of the specimen whose color has been developed under the hereinbefore indicated conditions is measured using a spectrophotomer. The specimen is packed in a quartz cell having a diameter of 21 mm. and a height of [0 mm. and with the width of the slit 1 mm. the refiectances at wavelengths 390, 550 and 590 mp. are measured. The reflectance is indicated in percent using as the basis 100 percent for the reflectance of an alpha-alumina shaped article.

4. Method of indicating the primary color development property.

When the reflectances at 390, 550 and 590 mu are respectively designated R R and R the primary color development property, K,, is defined by the following equation:

Thus, it can be said that the larger the value of K,, the better the primary color development property. According to our experiments, there was a very good agreement between the determinations of the color development property as expressed by the value of K, and the results obtained by determinations by means of the naked eye.

5. Method of measuring the secondary color development property.

The method of measuring and indicating this property, as previously described herein, is used.

6. Decolorizing property.

Fifty grams of unrefined soybean oil are weighed into a hard glass ISO-ml. test tube, to which is then added 1 gram of the specimen. The test tube is then immersed in an oil bath heated at 1 10 C. and the contents are stirred vigorously for 20 minutes. The specimen is then filtered with a filter paper, after which the clarified oil is placed in a 20-mrn. cell. White light is directed against this cell and the light transmittance is measured with a photoelectric colorimeter. The light transmittance is indicated in percent or the basis of percent for the light transmittance of distilled water. The decolorizing property of oil when its light transmittance is T percent is defined by the following equation:

where 56 percent is the light transmittance of the unrefined soybean oil used in the present experiment. 7. Criterion of suitability.

Those in which the secondary color development property is above 1.40 and the specific surface area is above 180 mflg. are considered as being acceptable.

The following facts can be comprehended from the results of table I. Namely, l. the natural clay minerals other than the dioctahedral montrnorillorite clay minerals as used in the present invention are all inferior in their primary and secondary color development properties, the only exception being attapulgite (see specimen Nos. 2, 3 and 4 in table I). And even though their specific surface area is increased by an acid treatment, there is not much improvement of their primary color development property (see specimen No. 3 in table I).

2. While attapulgite demonstrates considerably good primary and secondary color development properties in its as-obtained natural state, its specific surface area is not increased to as much as 180 m. /g. even though it is subjected to the acid treatment, and its primary color development property is also scarcely improved (see specimen No. l in table I).

3. On the other hand, a certain class of the dioctahedral montmorillonite clays demonstrates good secondary color development property, which when acid treated increases its specific surface area greatly to also demonstrate concomitantly a marked improvement in its primary color development property as well (see specimen Nos. 7, 9, l l, 12 and I4 in table I).

4. However, there are those among the dioctahedral montmorillonite clay minerals which are unsuitable for use as the color former of the present invention because they are inferior in their secondary color development property although they excel in their specific surface area, primary color development property and decolorizing property (see specimen Nos. l0, l3 and 15 5. Further, there are those among the dioctahedral montmorillonite clay minerals which excel in their secondary color development property as in the case with attapulgite but whose specific surface area does not increase by means of the acid treatment and hence whose primary color development property is not improved (see specimen No. 8 in table I).

From the foregoing results it can be comprehended that the following general principles hold in the case of the dioctahedral montmorillonite clay minerals.

a. The secondary color development property being an inherent property of the material clay itself cannot essentially be improved though some improvement can be had by the acid treatment.

b. The primary color development property increases in proportion to an increase in the specific surface area by means of the acid treatment, the desirable primary color development property (K,=2.60) being attained when the specific surface area reaches or exceeds 180 m./g.

c. The decolorizing property is not related at all to the secondary color development property.

Hence, according to the present invention, a dioctahedral montrnorillonite clay mineral having the highest possible K,

value, at least above 1.40, and preferably above 1.60, it first chosen. This is then subjected to an acid treatment so as to increase its specific surface area to above 180 mP/g. while ensuring that its K value does not fall to below 1.40, and

preferably 1.60. Thus it becomes possible to produce the color 5 former having basically satisfactory primary and secondary color development properties. And, hence, as the aforesaid dioctahedral montmorillonite clay minerals can be mentioned the natural clay minerals such, for example, as the so-called bentonite, subbentonite, fullers earth, Florida earth and Japanese acid clay. However, it goes without saying that the dioctahedral montmorillonite clay minerals, as used herein, are not limited to only those which have been illustrated.

On the other hand, as the acid to be used in the acid treatment that is carried out in the invention process, any whether inorganic or organic may be used which is able to increase the specific surface area of the aforesaid montmorillonite clay minerals to above I80 m. /g. However, the inorganic acids are generally to be preferred over the organic acids for reasons of cost and ease of handling, and of the inorganic acids sulfuric and hydrochloric acids are particularly convenient.

Further, no particularly strict conditions are involved in the acid treatment. If an acid of dilute concentration is used, either the treatment time becomes longer or the quantity of the acid required becomes greater, whereas if the concentration is high, either the treatment time becomes shorter or the quantity of the acid required becomes less in correspondence to the increase in concentration. Again, if the treatment temperature becomes higher, the treatment time is correspondingly shortened. Hence, the acid concentration may be any in the range of the order of 180, percent, but from the standpoint of convenience in handling practice the acid treatment is preferably carried out at a concentration of the order of 1545 percent and a temperature ranging between 50 and l05 C. in short, in this invention, the acid treatment of the aforesaid dioctahedral montmorillonite clay mineral until its specific surface area becomes at least 180 mF/g. is the sole basically important conditions.

However, one thing which must be cautioned against the actually carrying out the acid treatment is that there are instances in which the secondary color development property makes a marked decline when the acid treatment proceeds to an excessive degree. For this reason, it is preferred that the acid treatment conditions be so controlled that the specific surface area of the clay after treatment comes within the range between 180 mF/g. and 350 mF/g.

Next, in table ll will be shown the changes in the specific surface area and the primary and secondary color development properties of acid-treated clay depending upon the it was also found by our investigations that the particle size of the color former to be used in the present invention was also a very important factor. That is to say, when the particle size of the color fonner becomes too large, there is an increase in the smudging phenomenon, whereas if there is an increase in those particles which are too small, the particles after having been applied to paper tend to exfoliate. Moreover, if considered from the standpoint of the color development effect, a greater color development effect is had when the particles of the color former is smaller in both cases of the primary and secondary color development properties.

As a result of extensive researches for the reasons for these phenomena, we found that by making the particle size of the color former such that the particles of a diameter 10 microns or less were present in an amount of at least 75 percent by weight, and preferably at least 85 percent by weight of the total particles and those of a diameter one micron or less were present in an amount not exceeding percent by weight, and preferably not exceeding 35 percent by weight of the total particles, the color development effect was greatly enhanced to yield an excellent color former for pressure sensitive recording paper use in which moreover the undesirable tendency to smudging and exfoliation of the applied particles was less.

The relationship between the particle diameter of the color former and its primary and secondary color development properties and the relationship between the particle diameter and smudging are shown in table lll, below. It became apparent from these results that the color former should be preferably one containing at least 75 percent by weight of particles of a diameter 10 microns or less for achieving the color development efi'ect and prevention of the smudging phenomenon.

The specimens submitted to the experiment whose results have been presented in table [II were those prepared by adjusting the particle size by winnowing of the acid-treated specimen (B). (No. 12) of the previously given table I.

TABLE III Content of Color development particles 10 property Soil-resistant or less (wt. property Specimen N 0. percent) Primary Secondary (percent) Method of measuring the soil-resistant property. I

One hundred grams of the color former are suspended in 250 ml. of water, to which are then added 10 grams of starch.

degree of acid treatment given.

TABLE 11 Japanese acid clay A Japanese acid clay B Specific Primary Secondary Specific Primary Secondary Sulfuric acid surface color decolor desurface color decolor detreatment time area veloprnent velopment area velopmeni; velopment (hr.) (ml/g.) property property (ml/g.) property property 0 (untreated clay) 76 2. 45 2.13 62 2.36 1. 62 0.5 102 2. 2. 15 103 2. 42 1. 68 1 180 260 2. 15 142 2. 5O 1. 75 2 235 2. 99 2. 17 163 2. 84 1. 70 3 265 3. 28 2. 24 187 3. 09 1. 4 295 3. 39 2. 31 230 3. 21 1. 50 5 307 3. 47 2. 24 242 3. 3O 1. 38 6 325 3. 51 2. 15 248 3. 38 1.30 8..- 346 3.60 I. 88 263 3. 42 1. 28 370 3. 68 1. 65 271 3. 45 1. 25 384 3. 74 1. 60 280 3. 48 1. 20

ra s showninfable ll, above, thedioctahedral mSBESrii-" lonite clay minerals as used in the present invention are increased in their specific surface area by means of the acid treatment, and it can be seen that the primary color develop. ment property becomes good when the specific surface area becomes greater than 180 mF/g. When the specific surface area increases in this manner, the capacity to absorb and adsorb oil increases at the same time. Hence, the acid treatment is necessary and indispensable in the present invention.

This suspension is applied to paper of fine quality in an amount such that 7 grams of the color former are adhered per square meter of the paper, after which the paper is dried to thus obtain a coated front sheet. A coated back sheet is superposed on this coated front sheet, and a stainless steel cylinder 5 cm. in diameter and weighing 4 kg. is then placed on top of the superposed sheets and gently pulled across the sheets. The soiling of the coated front sheet thus resulting is measured for its reflectance of light of a wavelength 430 mp. using a spectrophotometer. The soil-resistant following equation:

property is defined by the Soil-resistant property That is to say, the greater the numerical value of the soil-resistant property (percent), the less is the soiling.

It is thus apparent from the results given in table III that a marked decrease in the smudging phenomenon takes place when the content of particles of a diameter microns or less is at least 75 percent by weight, and preferably at least 85 percent by weight of the total particles. It is also seen that the primary and secondary color development effects are also superior with this particle size.

A relationship between the particle diameter of the color former and the exfoliation property of the coated front sheet, such as shown in table IV, below, is observed. In this experiment the 1.G.T. (lnstrturt voor Grafische Techniek) test was employed for investigating the exfoliation property. In this test the tendency to exfoliation is less as the number becomes greater. The specimens used are those whose particle diameter has been adjusted as in table IV by winnowing the acidtreated specimen (A) (No. 12) of table 1.

The foregoing l.G.T. test was conducted on the specimen prepared in the following manner in accordance with the below-described measurement method. One hundred grams of the color former are suspended in 250 ml. of water, to which are then added 10 grams of starch. This suspension is applied to high quality paper such that the adhesion of the color former to the paper amounts to 7 grams per square meter, followed by drying the paper to obtain the coated front sheet. This sheet is submitted to the l.G.T. test and the rate at which the exfoliation of the color former takes place is measured. It can be seen that when the content of particles one micron or less in size exceeds 45 percent by weight the results of the l.G.T. test suddenly become worse.

It can be understood from the foregoing results that according to the present invention it is preferred from the standpoint of the color development efi'ect obtained and smudging that of the total particles at least 75 percent by weight, and preferably 85 percent by weight, are those whose particle size is 10 microns or less; and moreover that from the standpoint of the exfoliation property of the color former it is preferred that of the total particles not more than 45 percent by weight, and preferably not more than 35 percent by weight, are those one micron or less.

This exfoliation property is a considerably important matter in making good quality transfer sheets, because if the exfoliation of the color former is great a large amount of paste must be used for preventing this, with the consequence that a marked decline in the color development effect takes place.

Thus, according to the present invention, success was achieved in the production of a color former for pressure sensitive recording paper by a procedure comprising choosing from among the dioctahedral montmorillonite clay minerals one whose secondary color development property, K value, relative to benzoyl leucomethylene blue as measured in accordance with the hereinbefore described measurement method is at least 1.40, and preferably at least 1.60, subjecting this chosen montmorillonite clay mineral to an acid treatment to increase its specific surface area to at least 180 m. /g., and preferably to a value in the range between 180 m. /g. and 350 mF/g. and moreover ensuring that the foregoing secondary color development property, K value does not become less than 1.40, and preferably not less than 1.60, followed by water-washing and drying, and thereafter either comminuting or classifying the foregoing clay mineral to render it into particle size in which of the total particles at least 75 percent by weight are those having a particle diameter 10 microns or less and moreover not more than 45 percent by weight of the total particles are those one micron or less in diameter.

In producing the invention color former, the procedure described above need not necessarily be followed however, it being also possible to produce it by the following method.

That is to say, the invention color former cal also be produced by mixing (A) a dioctahedral montmorillonite clay mineral which has been acid treated until its specific surface area is at least 180 m."/g., and preferably at least 220 m./g., with (B) a dioctahedral montmorillonite clay mineral or an acid-treated product thereof whose secondary color development property, K has a value of at least 1.40, and preferably at least 1.80 to obtain as a whole a specific surface area of at least 180 mF/g. and a value for said K of at least 1.40, and comminuting or classifying said clay minerals (A) and (B) either before or after their mixture either separately or at the same time to render the mixture into particle sizes in which at least 75 percent by weight of the total particles are particles having a diameter 10 microns or less and moreover not more than 45 percent by weight of the total particles are those one micron or less in diameter.

When the hereinabove described method of the present invention is followed, the aforesaid clay mineral (A) need not necessarily be one whose K value is at least 1.40. And on the other hand, the aforesaid clay mineral (B) or its acid-treated product need not necessarily be one whose specific surface area is at least 180 m.'*/g.

The invention color former prepared as hereinbefore described can be applied to paper using the natural or artificial pastes such, for example, as starch, casein, tragacanth gum, CMC, synthetic latex having a bonding property, such as styrene butadien latex and butadiene-acrylonitrille resin latex and polyvinyl alcohol to thus make the coated front sheet of pressure sensitive recording paper. Thus a good quality coated front sheet is obtained whose primary and secondary color development effects during copying are exceedingly good and moreover in which smudging is held to a minimum.

Further, for improving the color development effect still further or for increasing the amount of color former added, it is possible to suitably add such additives as other natural clay minerals or synthetic inorganic substances, e.g. calcium carbonate, silica, silicate; organic or inorganic pigments, e.g. ultramarine, persian blue, chrome yellow, iron oxide, lndanthrene, Rhodamine and Methyl violet; dyestuffs such as fluorescent bleaching agent, e.g. diaminostilbene and benzoimidazole; oxidants, e.g. chloroanyl, persulfates, dichromates, perhydrochlorides, perrnanganates, cupric salts, ferric salts, iodine, potassium ferrocyanide and organic acid peroxides; reducing agents, e.g., calcium sulfide and solid organic amines; solid acids, e.g. alumina, siloca, titania, zinc oxide, zinc chloride, titanium phosphate and zirconium phosphate; and alkaline substances such as sodium silicate, sodium pyrophosphate and alkaline earth metal hydroxides, e.g. slaked lime. It is to be understood that these instances wherein additives have been added are also comprehended by the present invention.

EXAMPLES l-5 The material clays indicated in table V were chosen, which were each dried, comminuted and winnowed to prepare them into specimens in which percent of the total weight were particles whose diameter was 10 microns or less and 30 percent of the total weight were those whose diameter was one micron or less.

EXAMPLE 6 Sixty-five percent by weight of the Japanese acid clay specimen B of table ll which had been acid treated for 12 hours and 35 percent by weight of specimen No. 8 of table I were mixed and then comminuted. This comminuted mixture When the test for secondary color development property, as fully described herein, was conducted on the foregoing specimens, the K, values shown in table V were obtained.

TABLE V was then winnowed and a specimen having the following partif gg y cle size was prepared; i.e., 92 percent by weight of particles g; whose diameter was l0 microns or less and 23 percent by Specimen property, No Materialclay and locale of its production K, 10 weight of particles whose d ameter was one micron or less. When the properties of this specimen were tested by the 1 3 1 55 3 acid i Nugata -1 A methods fully described in connection with table I, the follow- 2 B 53 ing results were obtained. 3.. .do C 1.31 Japanese acid clay-Tsuruoka, Yamagata A 2.15

Pref, Japan. 15 Specific surface area I97 m./g. 5 ..do B 1.39 K, 3.05 d0 C 1. 35 Kg 5g apanese acid clay-Shibata, Niigara. Pref, A 1. 29

apan. g "g8 B 53 The invention color former was thus obtained. 16: I 'iixitoriii 'isn swam elitism; 11;: I 1: 70 11 g p 1. so 20 EXAMPLE7 Sub-bentonite, M ssissippi, U.S.A

Specimen l (specimen No. l of table I) and specimen ll (Japanese acid clay specimen 8 of table II which had been acid treated for 12 hours) were each winnowed and specimens The Value of K in the Specimens L 4, 10 and l 1 in having the following particle sizes were prepared. table V were above 1.40. Hence, the acid treatment of these was carried out under the following conditions.

Specimen I0 4. or less I p. or less Fifty grams on a dry basis of each of the foregoing five classes of clays were weighed into 500-ml. conical beakers and I 90 M 2| wt I their acid treatment was carried out under the conditions in- 93 w 4 m dicated in table lV, followed by water-washing, drying at 1 10 C., comminuting and winnowing to prepare the specimens. The particle size of each specimen was in all cases 90 percent of particles l0 microns or less in diameter and 25 percent of those one micron or less.

Next, 20 percent by weight of specimen 1 and 80 percent by weight of specimen II were well mixed, after which the proper- 5 ties of mixture was tested by methods which were fully described in connection with table I, with the following results: 7 7 TABLE VI Specific surface area 3 l0 m."/g.

Acid treatment conditions Concen- 'lemtration The invention color former was thus obtained. peigature (wt. Time Class of acid 0.) percent) (hr.) EXAMPLE 8 Sulfuric acid. 86 34 2 .do s5 34 3 The acid-treated specimen (B) (specimen No. l l of table I) gf gg g g8 is 2 was winnowed and a specimen having the following particle Acetic acidil. 85 27 6 size was prepared.

MWH w i U "*7 2 l0 microns or less 02 wt. k l micron or less 26 wt. I

To 50 grams of this specimen was then added 0.25 gram of e.p. sodium perborate as an oxidant followed by thorough The properties of the several specimens obtained by the foregoing acid treatment are shown in table Vll, below.

TABLE VII Color Specific development Decoior- Soil- Specimen surface value izing resistant number in area. ability property I.G.'I. Table V (m./g.) K1 K2 (Percent) (percent) (cam/sec.)

As apparent from the foregoing description, when those having a K, value of at least 1.40 are chosen from the various classes of the dioctahedral montmorillonite clay minerals and these chosen minerals are subjected to an acid treatment 70 mixing. When this mixture was tested for its properties in accordance with the testing methods fully described in connection with table I, the following results were obtained.

Specific surface area 280 m./g.

Thus was obtained the color former according to the 75 present invention.

. 5 EXAMPLE 9 The acid-treated specimen (B) (specimen No. 12 of table I) was winnowed and a specimen having the following particle sizes was prepared.

I0 microns or less 1 micron or less Next, to I00 grams of this specimen were added 4 grams of slaked lime as an alkaline substance followed by thorough mixing. When this specimen was tested for its properties by the test methods fully described in connection with table I, the results obtained were as follows:

Specific surface area 340 m.=/g. K, 3.15 K, 1.89

wherein R and R are reflectances of light having wavelengths 430 mu and 550 mu, respectively, when said minerals are developed by benzoyl leucomethylene blue. 2. A process for producing the color former for pressure sensitive recording paper, said process comprising treating a dioctahedral montmorillonite clay mineral having a secondary color development property, K of at least 1.40, the value of K being represented by the formula wherein R and R are reflectances of light having wavelengths 430 my and 550 m,u., respectively, when said mineral is developed by benzoyl leucomethylene blue, with an acid to increase the specific surface area of said mineral to at least 180 mF/g. while ensuring that said secondary color development property, K value does not decline .those of diameter 10 microns below 1.40; washing the acid-treated mineral with water and drying the acid-treated mineral; and thereafter comminuting and classifying the mineral to render it into particle sizes in which of the total particles at least 75 percent by weight are those of diameter 10 microns or less and of the total particles not more than 45 percent by weight are those of diameter one micron or less.

3. A process for producing a color former for pressure sensitive recording paper, said process comprising mixing:

A. a dioctahedral montmorillonite clay mineral which has been acid treated until its specific surface area has been increased to 180 m, lg. with B. dioctahedral montmon'llonite clay minerals having a secondary color development property, K; of at least 1.40, the value of K being represented by the formula wherein MEIER are wavelengths 430 mp. and 550 my respectively, when said member is developed by benzoyl leucomethylene blue, comminuting and classifying said mixture of minerals to render said mixture of minerals as a whole into one whose specific surface area is at least 180 m. /g., whose secondary color development property, K, is a value at least 1.40, and in which of the total particles at least 75 percent by weight are or less and of the total particles not more than 45 percent by weight are those of diameter one micron or less.

4. The process of claim 2 wherein the treatment with acid is conducted at a temperature of 50-l05 C. with an acid concentration of lpercent.

5. A color former for pressure sensitive recording paper which comprises a major portion of acid-treated dioctahedral montmorillonite clay minerals and a minor portion of natural dioctahedral montmorillonite clay minerals, said mixture as a whole having a specific surface area of at least m. /g., of the total particles at least 75 percent by weight of particle diameter 10 microns or less, and of the total particles not more than 45 percent by weight being those of diameter one micron or less, said mixture as a whole having a secondary color development property, K at least 1.40, the value of K being represented by the formula K2=%+i 1mw wherein R and R are reflectances of light having wavelengths 430 my. and 555 mu, respectively, when said mixtures are developed by benzoyl leucomethylene blue.

iw: a r

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Classifications
U.S. Classification106/468, 501/146
International ClassificationB41M5/155
Cooperative ClassificationC01B33/26, C01B33/46, C01B33/40, B41M5/1555, C01B33/42
European ClassificationC01B33/26, C01B33/46, C01B33/42, C01B33/40, B41M5/155B