US3573085A

US3573085A - Abrasive-containing capsular coating composition for pressure-sensitive record paper

Info

Publication number: US3573085A
Application number: US742181A
Authority: US
Inventors: Glen A Hemstock
Original assignee: Engelhard Minerals and Chemicals Corp
Current assignee: BASF Catalysts LLC; Phibro Corp
Priority date: 1968-07-03
Filing date: 1968-07-03
Publication date: 1971-03-30
Anticipated expiration: 1988-03-30

Abstract

INERT NON-ABSORPTIVE, RIGID MICROSCOPIC PARTICLES ARE SCATTERED AMONG MICROSCOPIC PRESSURE-RUPTURABLE OIL-CONTAINING CAPSULES IN A COATING ON PRESSURE-SENSITIVE RECORD SHEET MATERIAL.

Description

Patented Mar. 3 9, 119W.

3,573,085 ABRASlVE-CONTAINING CAPSULAR COATING COMPOSITION FOR PRESSURE-SENSITIVE RECORD PAPER Glen A. Hemstock, Princeton, N.J., assignor to Eugelhartl Minerals & Chemicals Corporation, Woodbridge, NJ. No Drawing. Filed July 3, 1968, Ser. No. 742,181 Int. Cl. B41m 5/22 US. Cl. 11736.2 8 Claims ABSTRACT OF THE DISCLOSURE Inert, non-absorptive, rigid microscopic particles are scattered among microscopic pressure-rupturable oil-containing capsules in a coating on pressure-sensitive record sheet material.

BACKGROUND OF THE INVENTION A type of widcly-used pressure-sensitive recording paper utilizes the reaction between normally colorless colorreactant dye material such as a mixture of crystal violet lactone and benzoyl leuco methylene blue and sensitive pigment material such as attapulgite clay to form the colored mark. An oily solution of the dye material is encapsulated in rupturable microscopic capsules usually made of hydrophilic colloid such as gelatin. The colored mark is formed when the capsules are ruptured by printing pressure and the contents of the capsules come into contact with the reactive pigment particles. In present commercial adaptations of this printing system, one side of the sheet is coated with a profusion of the microscopic capsules and the back of the sheet is coated with attapulgite clay, a colloidal clay material. The sheets are stacked so that the capsular coating is in face-to-face relation with the sensitive clay coating on another sheet which receives the printed image when the capsules are ruptured.

It has also been proposed (US. 2,730,457 to Barrett K. Green et al.) to provide the capsular layer with an overlay coating or an underlay coating of particles of a color-reactant solid such as attapulgite clay. This results in self-contained, pigment-coated record sheet material.

Irrespective of the arrangement that is used, it is apparent that in order to obtain a clear printed image, the capsules must rupture upon application of the printing pressure and the oily content of the ruptured capsules must come into adsorptive contact with the sensitive pigment. Failure of the capsules to rupture is especially likely to occur with self-contained pressure sensitive record material in which the capsules are proximate the base sheet and the sensitive pigment is coated over the capsular coating. With such an arrangement, a printed image of uniform intensity may not be obtained unless a relatively heavy coating of capsules is employed. Since the microscopic capsules are costly in comparison to the other constituents of the record material, it is highly desirable to minimize the coat weight of the capsules.

THE INVENTION Stated briefly, in accordance with the present invention, discrete, microscopically-dimensioned, rigid particles of a poorly oil-receptive material are scatered among individual oil-containing microscopic capsules of gelled hydrophilic-colloid material contained as a coating on pressure-sensitive record material. The rigid particles are inert to the oil contained within the capsules and they function to rupture the walls of the capsules when the coated paper containing the capsules is subjected to printing pressure. A coating of sensitive pigment may be provided as an overlay coating (so that pigment is proximate the sheet) or the sensitive pigment may be provided on a separate sheet. It is also within the scope of the invention to incorporate the sensitive pigment with the capsules and the rigid non oil-receptive particles so that the three types of particles are substantially uniformly interspersed on the sheet and in contact with each other.

The invention is of special benefit when employed in so-called self-contained printing sheet material in which the capsular coating is proximate the base sheet and the sensitive pigment is provided as a coating over the capsular coating. As mentioned, difficulty is especially likely to be experienced in rupturing the capsules in this form of pressure-sensitive record material.

PRIOR ART I am aware that it has been suggested in US. 2,730, 457 (supra) to incorporate sensitive attapulgite clay into a suspension of encapsulated dye material and to coat the mixture on paper to provide a single coating. Attapulgite, however, is a colloidal mineral and when it is interspersed wtih the capsules in the coating the clay particles merely serve the usual function of a sensitive pigment, i.e., to receive the printed image when the capsules are ruptured. The attapulgite particles do not promote the rupture of the particles since they are too small and are not sufficiently hard or abrasive. The present invention also differs in concept from the use, suggested in US. 2,665,453, of large glass beads or polymer particles in a rupturable film containing printing fluid for the purpose of providing a smudge-resistant coating.

DESCRIPTION In carrying out this invention, rigid particles Within the range of l to 44 microns, preferably finer than 10 microns, are used as the rupture-inducing agent. Optimum size within this range depends, inter alia, on the size of the rupturable capsules. The absence of substantial amounts of submicron size or colloidal particles in the rupture-inducing agent is preferable. The desired results are not realized when the rigid particles are too small to rupture the capsule walls. On the other hand, when the rigid particles are too large there will be a large spacing between adjacent capsules. Consequently, the resulting printed mark may lack the desired continuity. With representative capsules having a diameter of about 3 to 10 microns and walls about 1 micron thick, the use of particles largely within the range of about 1 to 2 microns is preferred.

Another requirement of the rigid particles is that they are white, off-white or transparent.

The rigid particles must have low oil absorption values in order to assure that when the capsules are ruptured the oily contents will be preferentially adsorbed by the color-reactant sensitive pigment particles. The rigid particles should have oil absorption values (Gardner Coleman) of 40 ml./ grams or below, preferably below 20 ml./ 100 gram. The Gardner Coleman method for measuring oil absorption (ASTM D2813) uses raw linseed oil. The test method is described by Gardner, H. A., and Sward, G. C., Physical and Chemical Examination of Paints, Varnishes, Lacquers and Colors, 9th ed., Inst. Paint Varnish Research, Washington, DC, 1939, page 209.

Rigid particles of various shapes, such as platelets, spheres or acicular form, may be employed.

Rigid, low density, poorly oil-retentive particles are exemplified by emulsified, high-glass transition tempera ture polymers such as high density polyethylene and acrylic plastics. These polymers are produced in suitable micron-size particles by emulsion polymerization technique. Products supplied as BS5 acrylic and Poly M which are emulsion polymerized acrylics and polyethylene, respectively, are examples of suitable polymeric particles.

Other particles which may be employed to promote the rupture of the capsules include glassy frits.

Minerals, exemplified by silica-containing minerals such as chrysotile asbestos shorts, quartz, and ground feldspar may be employed, as may be minerals such as rutile, anatase, calcined bauxite and alkaline earth carbonate minerals such as calcite and aragonite. Synthetic inorganic solids such as low surface area aluminas may be used. Hydrate aluminas of the CO30 series are suitable; these are finely divided, white crystals of synthetic alpha alumina trihydrate.

The rigid particles are employed in amount within the range of about to 300% based on the dry weight of the capsules. The quantity is preferably sutficient to provide at least one rigid particle between adjacent capsules when the mixture is coated on the sheet.

In putting the invention into practice, the rigid particles may be added dry or as an aqueous suspension to dry capsules or to an aqueous suspension (so-called emulsion) of the capsules. It will be noted that the suspension of capsules appears to be a milky fluid, although examination in a microscope reveals the presence of the discrete solid capsules. The capsules and the rigid particles are thoroughly mixed and the solids adjusted to a suitable level by addition or removal of water, if necessary. An adhesive suspension, usually a coked starch such as cornstarch, is incorporated with the capsular emulsion to produce the coating composition. Recommended, by way of example, is the use of a coating composition containing to 30% by weight combined capsules and rigid particles and starch in amount within the range of about 5% to 15 of the combined weight of the capsules and rigid particles. Optimum solids and composition of the coating composition will depend on whether the coating is applied by an on-machine process or an off-machine process.

In order to derive the benefits of the present invention, it is preferable, but not necessary, for the rigid particles to be in direct contact with the unruptured capsules with which they are interspersed on the coated sheet. It is essential, however, that the rigid particles be in sufficiently close proximity to the capsules so that the rigid particles are in surface-to-surface contact with adjacent capsules after the capsules have been deformed by printing pressure. In order to assure the required proximity of the capsules and rupture-inducing rigid particles, the coating composition should be applied to the base sheet at an adequate coat weight.

By employing the rigid particles as an additive, the coat weight of the capsular coating may be reduced from the amounts usually employed since more effective use is made of the capsules. Coat weights within the range of 1 to 5 lb./ream (3300 ft?) are suitable.

The base sheet may be conventional chemical wood pulp stock, typically about 15 to 50 lb. basis weight. When making self-contained record material it is preferable to use a base sheet that has been hornified and smoothed by passage through wet-calender rolls provided with water boxes on the stacks of upper jack rolls, as described in my copending application, Ser. No. 675,793, filed Oct. 17, 1967, now abandoned.

After the capsular coating has been applied and dried, the sheet may be provided with an overlay coating of sensitive pigment such as attapulgite clay as described in US. 2,730,457, calcined partially rehydrated kaolin, as described in my patent, US. 3,226,252, or a kaolin-acidic polymeric resin such as a phenylphenol-formaldehyde resin, as described in Netherlands application 6,511,224. It will be noted that the aforementioned sensitive pigment materials have higher oil absorption values than the abrasive inert particles which are contained in the capsular coating layer.

As mentioned above, the present invention is of special benefit when applied to the production of pressure-sensitive record material in which the capsular coating is proximate the base sheet and the coating of sensitive pigment is superimposed on the capsular coating. However, it is also within the scope of the invention to apply the coating of sensitive pigment to sheet material and employ the capsular coating mixture as an overlay coating. Also, the coating of sensitive pigment may be applied to the reverse side of a capsule-coated sheet and the resulting sheet may be used with another sheet coated with sensitive pigment in a manner such that the coating of sensitive pigment is in face-to-face relationship with the capsular coating. As another alternative, the sensitive pigment may be incorporated with the rigid particles and capsules in a single coating composition containing sufficient sensitive pigment to provide a smooth opaque finish to the paper and to assure continuity of the printed image. When the pig ment is incorporated with the capsules and rigid particles in a single coating, a coat weight within the range of 3 to 10 lbs. per ream is recommended.

EXAMPLE Equal weight proportions of crystal violet lactone (3,3 bis (p-dimethylaminophenyl) o-dimethylamino phthalide) and benzoyl leuco methylene blue are dissolved in trichlorodiphenyl to form a /2 (weight) solution. A sol containing 10% of pigskin gelatin is separately prepared. Twenty parts by weight of the oil solution is added to parts by weight of dispersed gelatin with stirring, forming an oil-in-water emulsion with the sol, as described in Reissue 24,899 to B. K. Green. Coacervation is induced, and the coacervate is gelled and hardened with formaldehyde, as described in said patent. The solids content of the emulsion is then adjusted to 50% by weight.

To 100 parts by weight of the 50% suspension of capsules, 20 parts by weight of a 50% aqueous suspension of emulsion-polymerized, high density polyethylene is added. The polyethylene is in the form of small spherical particles within the range of 1 to 5 microns and having a specific gravity of 0.95. The suspensions are mixed thoroughly and 40 parts by weight of a 10% suspension of cooked cornstarch is added. The suspensions are thoroughly mixed and diluted to 20% solids with water.

The coating composition, which resembles a creamy paste, is applied to 35 lb. per ream (25" x 40":500 sheets) bleached chemical wood cellulose fiber stock with an air-knife coater. Coat weight is 3 lb. per ream. The coating is dried and provided with a 1 lb. per ream overlay coating of a mixture of Attasorb RVM and Syloid by the procedure and with the ingredients described in my patent, U.S. 3,226,252.

It will be understood that the foregoing example is given for illustrative purposes only and the constituents of the capsule coated sheet may be varied within the scope of the appended claims.

I claim:

1. Pressure-sensitive record material comprising a sheet of paper on which is a coating of (a) discrete, microscopic pressure-rupturable capsules of oil-impermeable gelled hydrophilic colloid material containing therein an oily solution of dye-forming material, and uniformly interspersed among said capsules and in proximity thereto (b) discrete rigid particles of a solid material having a size within the range of 1 to 44 microns and a Gardner- Coleman oil absorption value below 40 ml./100 grams, said particles (b) being inert towards said oily dye-forming content of said capsules (a) when in contact therewith and functioning to rupture the walls of the capsules when the coated paper containing the capsules is subjected to printing pressure, said particles (b) being present in the amount of about 5-300% based on the weight of the capsules, said coating having a weight within the range of 1 to 5 lbs/ream.

2. The record material of claim 1 wherein said particles (b) are finer than 10 microns.

3. The record material of claim 1 wherein said particles (b) comprise glassy frit.

4. The record material of claim 1 wherein said particles (b) comprise a silica-containing mineral.

5. The record material of claim 1 wherein said particles comprise an alkaline earth carbonate mineral.

6. The record material of claim 1 wherein said particles are composed of aluminum oxide.

7. The record of claim 1 wherein said particles (b) are composed of an emulsified high glass transition 10 References Cited UNITED STATES PATENTS MURRAY KATZ, Primary Examiner US. Cl. X.R.