US3914470A

US3914470A - Capsule-carrying sheets or webs

Info

Publication number: US3914470A
Application number: US327790A
Authority: US
Inventors: Benjamin Stanley Lewis
Original assignee: Wiggins Teape Research and Development Ltd
Current assignee: Arjo Wiggins Ltd
Priority date: 1972-01-31
Filing date: 1973-01-29
Publication date: 1975-10-21
Anticipated expiration: 1992-10-21
Also published as: BR7300734D0; GB1370081A; FR2170687A5; DE2304678A1; JPS557398B2; ES411102A1; AU5153173A; BE794831A; JPS4887908A; DE2304678B2; AU476079B2

Abstract

A capsule-carrying sheet or web such, for example, as is used in pressure-sensitive copying systems is produced by coating a surface of a base sheet or web with an aqueous coating mix which includes a rewettable binder material and a protective material. This coating is dried and then rewetted and a composite coating is formed by applying to the rewetted coating a coating of capsules. The composite coating is then dried.

Description

United States Patent [191 Lewis Y Oct. 21, 1975 CAPSULE-CARRYING SHEETS 0R WEBS v [75] inventor; Benjamin Stanley Lewis, Rhonnda,

Wales 73 .A's sig-nee: Wiggins Teape Research &

' Development, London, England [22 Filed: Jan. 29,1973

g 21 ,ApplnNoi: 327,790

[ 30] I Foreign Application Priority Data Jan. 31', 1972 UnitedKingdom 4472/72 References Cited UNITED STATES PATENTS 3,565,666 2/l97l Phillips 1 17/362 Primary Examiner-Th0mas .1. Herbert, Jr. Attorney, Agent, or FirmBurns, Doane, Swecker & Mathis [5 7] ABSTRACT A capsule-carrying sheet or web such, for example, as is used in pressure-sensitive copying systems is produced by coating a surface of a base sheet or web with an aqueous coating mix which includes a rewettable binder material and a protective material. This coating is dried and then rewetted and a composite coating is formed by applying to the rewetted coating a coating of capsules. The composite coating is then dried.

11 Claims, No Drawings lO/l972 Brown et al. ll7/36.4 X

CAPSULE-CARRYING SHEETS OR WEBS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to capsule-carrying sheets or webs and methods of producing such sheets or webs, and is particularly but not exclusively concerned with capsule-carrying sheets or webs for use in pressuresensitive copying systems.

2. Description of the Prior Art The art of encapsulation has in recent years achieved considerable commercial importance since encapsulation provides a method of maintaining a reactive material in an inert state by providing a non-reactive capsule wall between the reactive material and its surroundings. Encapsulation also enables the handling properties of solids to be conferred on liquids and gases.

It is known to encapsulate, for example, dyes, inks, chemical reagents, pharmaceuticals, flavourings, pesticides, herbicides and in fact any material which can be dissolved, suspended-or otherwise constituted in or as a liquid internal phase enclosed within a capsule wall. The capsule serves to maintain the internal phase in its liquid, or some other converted form, at least until the internal phase is released by rupture, melting, dissolving or other removal of the capsule wall, or until the internal phase is caused to diffuse out through the capsule wall.

Various methods of encapsulation are well known, the most commonly used methods involving either a coacervation reaction, a precipitation reaction, or a polymerisation reaction.

A disadvantage of capsules produced by known methods is that they are not sufficiently inherently strong to prevent accidental rupture thereof, this being a particular disadvantage, in pressure-sensitive copying systems where accidental rupture of capsules can result in undesirable marking of the copy sheet.

In order to increase the resistance of a capsulecarrying sheet or web, for use in a pressure-sensitive copying system, against accidental rupture of the capsules, it is known to coat a protective material in the form of cellulose fibres onto the sheet or web with the capsules, the protective material subsequently affording protection for the capsules against accidental rupture while still allowing rupture thereof by localised pressure from for example, writing, typing or printing on the sheet or web.

In British Pat. No. l,252,858 there is described another method of affording protection against accidental rupture of capsules in a pressuresensitive copying system, in which method the previously described cellulose fibres are replaced, at least in part, by a different protective material in the form of granules of starch. Starch granules said to be suitable include those produced from wheat, potato,-sago, tapioca, rice and arrowroot.

It known methods of producing a capsule-carrying sheet or web also carrying cellulose fibres as protective material for the capsules, the capsules and cellulose fibres are coated together onto a base sheet or web in admixture with a gelatinised starch solution which is to serve as a binder between the capsules and cellulose fibre, and the base sheet or web. The sheet or web produced thus carries a coating including capsules, a protective material for protecting the capsules, i.e. the cellulose fibres, and a binder for the capsules and the protective material i.e. the gelatinised starch solution.

A disadvantage of known methods of producing a capsule-carrying sheet or web, in which the capsules are coated onto a base sheet or web in admixture with a binder material and a protective material, is that the binder material tends to form a film over the capsules, which film can interfere with the required release of the internal phase of the capsules on rupture of the capsules.

A further disadvantage of such known methods is that the binder material gives the single coating mix used a relatively high viscosity, and thus the coating mix must be coated at a relatively low solids concentration, the sheet or web thus having a relatively high moisture content after coating.

SUMMARY According to this invention a method of producing a capsule-carrying sheet or web comprising a base sheet or web having on a surface thereof a coating containing capsules, protective material for protecting the capsules against accidental rupture, and a binder material serving to bind the capsules and protective material to the base sheet or web, comprises the steps of:

a. forming a first coating on a surface of a base sheet or web by applying to the surface an aqueous coating mix including a rewettable binder material and a protective material;

b. drying the first coating;

c. rewetting the dried first coating;

d. forming a composite coating by applying a coating of capsules to the rewetted first coating; and

e. drying the composite coating.

Preferably steps 0 and d are carried out simultaneously by applying to the dried first coating an aqueous emulsion of capsules. Otherwise, steps 0 and d can be carried out consecutively, the capsules being applied in dry form, for example by spraying.

The mechanism by which the method of the invention operates is simple. The binder material applied at step a is rewetted at step c and then after drying at step e serves to bind the capsules and protective material to the base sheet or web.

Any suitable rewettable binder material can be used,

and examples of such binder material are dextrine, polyvinyl alcohol, or a mixture of dextrine and polyvinyl alcohol.

The protective material can be the commonly used cellulose fibres, or otherwise can be a granular polymeric material or, preferably, starch granules, as described above.

Preferably the base sheet or web is calendered between steps b and c of the method of the invention. Calendering considerably reduces the roughness of the coated sheet or web produced at step a, but rewetting of the coated surface at step 0 causes the coated surface to regenerate, but not completely, towards that existing prior to calendering.

The method of the invention, in addition to overcoming the disadvantages of known methods described above, has the advantage that the binder material/protective material coating can easily be applied using a size press on the machine on which the base sheet or web (which will normally be paper) is made. Further, a relatively high solids concentration can be used for the aqueous dispersion of capsules, if used, and thus drying of th sheet or web after application of the emulsion is simplified, and since less water is applied to the sheet or web during application of the dispersion appearance defects such as cockle, ribbing, curl, etc., all off which are related to the moisture content of the sheet or web, are reduced.

The aqueous dispersion of capsules, if used, can be applied by any means known for applying capsule coatings, for example by means of an air-knife coater.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will now be described by way of example with reference to specific workings thereof on a laboratory scale in relation to pressure-sensitive copying systems of the kind in which a colourless, chromogenic material of basic reactant chemical properties held in solution in an oily solvent in microcapsules is reacted, upon rupturing of the microcapsules by applied presbelow 30C and 5 g. of unburst arrowroot starch granules approximately 25 pm in size were then dispersed in the solution.

The suspension thus formed was applied as a surface size by means of a Meyer rod to one side of a 49 g/m base paper to give a coating weight of approximately 1.3 to 2.2 g/m The sized base paper was then dried, and calendered on a laboratory calender.

Samples of the base paper, and the sized base paper before and after calendering were tested, using standards tests, for thickness and Bendtsen roughness.

Raw capsule dispersion (i.e. dispersion containing only capsules) was then coated onto the coated side of samples of the calendered sized base paper using a Meyer rod, and the capsule-carrying samples thus produced were, after drying, tested using standard tests for roughness, thickness, frictional smudge intensity, calender intensity and adhesion.

The results of the tests were as shown in the following Table I:

TABLE I Physical or Functional Property Tested Test Method Units Mean Result Range of Results Base paper thickness S.I.G. um 65.0 (62.5 to 67.5) Base paper roughness Bendtsen ml/min 200 160 to 220) Sized base paper thickness before calendering S.I.G. pm 80.0 (75.0 to 82.5) Sized base paper roughness before calendering Bendtsen ml/min 1350 l 100 to 1650) Sized base paper thickness after calendering S.l.G. urn 67.0 (62.5 to 72.5) Sized base paper roughness after calendering Bendtsen ml/min 205 130 to 300) Sized base paper thickness after coating S.I.G. um 77.5 (75.0 to 77.5) with capsules Sized base paper roughness after coating Bendtsen ml/min 405 (300 to 500) with capsules Frictional Smudge Intensity obtained from Bausch & Lomb Refl. 82.6 (76.0 to 88.3) capsule-coated samples Calender Intensity obtained from capsule- Bausch & Lomb Refl. 61.6 (52.0 to 69.0) coated samples Adhesion in capsule-coated samples Visual 60 Estimated capsule coating weight Substance g/rn 3.4 2.9 to 4.3

Measurements sure, with a coreactant material, such as attapulgite EXAMPLE II clay, acid treated montmorillonite clay, or particles of an oil-soluble, acidic, phenolic, polymeric material, to provide distinctive coloured marks. The microcapsules can be carried on one surface of a transfer sheet, known as a CB sheet, and the coreactant material carried on one surface of a separate record sheet, known as a CF sheet, and the invention will be described in relation to such a system.

Otherwise, the microcapsules and the co-reactant material can be carried together on the same surface of a single sheet.

In working the invention as hereinafter described the capsules used were approximately 12 pm in size, and had walls of gelatin and gum arabic enclosing an internal phase comprising the dye substances crystal violet lactone and benzoyl leuco methylene blue dissolved in a dibenzylbenzenes admixture, and diluted with kerosene. However, many different kinds of capsules are known which could otherwise be used.

EXAMPLE 1 A solution was formed by adding 5 g. of dextrine to 150 mls. of hot water. The solution was left to cool to A solution was formed by slowly adding 5 g. of Elvanol 52-22 (Registered Trade Mark) polyvinyl alcohol to mls. of cold water and then heating the dispersion formed to increase the rate of solution. The solution was left to cool to below 30C and 5 g. of unburst arrowroot starch granules approximately 25 pm in size were then dispersed in the solution.

The suspension thus formed was applied as a surface size by means of a Meyer rod to one side of a 49 g/m base paper to give a coating weight of approximately 1.8 to 2.2 glm The sized base paper was then dried, and calendered on a laboratory calender.

The same tests as in Example I were than applied to samples of the base paper, and the sized base paper before and after calendering.

Raw capsule dispersion was then coated onto the coated side of samples of the calendered sized base paper, as in Example I, and the capsule-carrying samples thus produced were, after drying, subjected to some of the tests detailed in Example I.

The results of the tests were as shown in the following Table II:

TABLE II Physical or Functional Property Tested Method Unit Mean Result Range of Results Base paper thickness S.I.G. um 65.0 (62.5 to 67.5) Base paper roughness Bendtsen ml/min 200 to 220) Sized base paper roughness before calendering Bendtsen ml/min 1500 1450 to 1600) Sized base paper roughness after calendering Bendtsen ml/min 340 (250 to 400) Sized base paper roughness after coating Bendtsen ml/min 450 (400 to 650) TAB LE 11 Continued Physical or Functional Property Tested Method Unit Mean Result Range of Results Frictional Smudge Intensity obtained from capsule-carrying samples Bausch & Lomb Refl. 92.2 (91.4 to 94.0)

Calender Intensity obtained from capsulecarrying samples Bausch & Lomb Refl. 53.6 (51.2 to 63.0)

Adhesion in capsule-coated samples Visual 100 Estimated capsule coating weight Substance g/m 4.0 (3.4 to 4.6)

Measurements EXAMPLE III A first solution was formed by slowly adding 0.5 g. of Elvanol 5222 (Registered Trade Mark) polyvinyl alcohol to 50 mls. of cold water and then heating the dispersion formed to increase the rate of solution.

A second solution was formed by adding 4.5 g. of dextrine to 100 mls. of hot water.

The first and second solutions were then mixed and the resulting solution left to cool to below 30C. 5 g. of unburst arrowroot starch granules approximately um in size were than dispersed in the solution.

The suspension thus formed was applied as a surface size by means of a Meyer rod to one side of a 49 g/m base paper to give a coating weight of approximately 1.2 to 2.3 g/m The sized base paper was then dried and calendered on a laboratory calender. The same tests an in Example I and 11 were then applied to samples of the base paper, and the sized base paper before and after calendering.

Raw capsule dispersion was then coated onto the coated side of samples of the calendered sized base paper, as in Examples 1 and I1, and the capsule-carrying samples thus produced were, after drying, subjected to the same tests as the similar samples of Example 11.

The results of the tests were as shown in the following Table 111:

Background reflectance x X00 a value of indicating no smudging at all; the lower the value, the more the smudging, that is the poorer the protection against accidental rupture of the capsules by horizontally-applied pressures.

Calender Intensity Test A capsule-carrying sample and a sta' dard CF sheet (as described above) are superposed with their coated surfaces in contact and a strip of the two sheets then passed between two rollers. After a waiting period the reflectance of the coloured mark thus formed on the CF sheet and the reflectance of the background around the coloured mark are measured with an opacimeter. The Calender Intensity or Cl value of the capsule carrying sample is then determined from the equation:

Coloured mark reflectance I I Background reflectance a value of 100 indicating no visible mark and thus the lower the value the more distinct the coloured mark.

TABLE III Physical or Functional Property Tested Method Units Mean Result Range of Results base paper thickness S.l.G. p.111 65.0 62.5 to 67.5 base paper roughness Bendtsen ml/min 200 to 220) sized base paper roughness before calendering Bendtsen ml/min 1500 1300 to 1650) s zed base paper roughness after calendering Bendtsen ml/min 290 (230 to 350) sized base paper roughness after coating with Bendtsen ml/min 430 (400 to 550) capsules (73.4 to 86.5) Frictional Smudge Intensity obtained from Bausch & Lomb Refl. 79.2 capsule-carrying samples Calender Intensity obtained from capsule- Bausch & Lomb Refl. 48.8 (45.1 to 52.0) carrying samples Adhesion in capsule-coated samples Visual 70+ Estimated capsule coating weight Substance g/m 4.2 (3.9 to 4.5)

Measurements The three most important tests of those mentioned above, to which the capsule-carrying sheets or webs produced in the'above described Examples 1, II and III were subjected are the frictional smudge intensity test, the calender intensity test, and the adhesion test and these tests will now be briefly described.

Frictional Smudge Intensity Test Adhesion Test A standard piece of black cloth is laid on the coated surface of a capsule-carrying sample; a weight is placed on the cloth and the cloth is then dragged across the coated surface of the capsule-carrying sample. The pattern thus produced on the cloth is then visually compared with a set of number standards, a value of 60 or above indicating acceptable adhesion of the coating on the capsule-carrying sample to the base paper.

Although the method of this invention has been described above in relation to only laboratory workings thereof, no difficulty is experienced in scaling up the described Examples for commercial production of capsule-carrying sheets or webs.

I claim:

1. A method of producing a capsule-carrying sheet or web comprising a base sheet or web having on a surface thereof a composite coating containing capsules, protective material for protecting the capsules against accidental rupture, and a binder material serving to bind the capsules and protective material to the base sheet or web, comprising the steps of:

a. forming a first coating on a surface of a base sheet or web by applying to the surface an aqueous coating mix consisting essentially of a rewettable binder material and a protective material;

b. drying the first coating;

c. rewetting the dried first coating;

d. forming a composite coating by applying a coating consisting essentially of capsules to the rewetted first coating; and

e. drying the composite coating.

2. A method as claimed in claim 1, in which steps (c) and (d) are carried out simultaneously by applying to the dried first coating an aqueous dispersion of capsules.

3. A method as claimed in claim 1, in which the capsules are applied in dry form.

4. A method as claimed in claim 1, in which the binder material is selected from the group consisting of dextrine, polyvinyl alcohol, or a mixture of dextrine and polyvinyl alcohol.

5. A method as claimed in claim 1, in which the protective material is selected from the group consisting of cellulose fibres, granular polymeric material, or starch granules.

6. A method as claimed in claim 4, in which the protective material is selected from the group consisting of cellulose fibres, granular polymeric material, or starch granules.

7. A method as claimed in claim 1, in which the base sheet or web is calendered between steps (b) and (c).

8. A method according to claim 2, in which the base sheet or web is a 49 g/m paper, the aqueous coating mix applied thereto consists of a suspension formed by preparing a solution of 5g of dextrine in 150 mls of hot water, cooling the solution to below 30C, dispersing in the cooled solution 5g of unburst arrowrrot starch granules having a size of approximately 25 um and the suspension is applied to the paper to provide thereon a coating weight of approximately 1.3 to 2.2 glm 9. A method according to claim 2, in which the base sheet or web is a 49 g/m paper, the aqueous coating mix applied thereto consists of a suspension formed by slowly adding 5g of polyvinyl alcohol to 150 mls of cold water, accelerating the rate of solution by heating the dispersion so formed, cooling the solution to below 30C, dispersing in the cooled solution 5g of unburst arrowroot starch granules having a size of approximately 25 um, and the suspension is applied to the paper to provide thereon a coating weight of approximately 1.8 to 2.2 g/m 10. A method according to claim 2, in which the base sheet or web is a 49 g/m paper, the aqueous coating mix applied thereto consists of a suspension formed by preparing a first solution by slowly adding 0.5g of polyvinyl alcohol to 50 mls of cold water, accelerating the rate of solution by heating the dispersion so formed, preparing a second solution by adding 4.5g of dextrine to mls of hot water, mixing the first and second solutions, cooling the resulting solution to below 30C, dispersing in the cooled solution 5g of unburst arrow root starch granules having a size of approximately 25 pm, and the suspension is applied to the paper to provide thereon a coating weight of approximately 1.2 to 2.3 g/m 11. A method of producing a capsule-carrying sheet or web comprising a base sheet or web having on a surface thereof a composite coating containing (a) a binder material, (b) protective material, and (0) capsules, said protective material protecting said capsules against accidental rupture, and said binder material serving to bind said capsules and said protective material to said base sheet or web, which method consists essentially of the steps of:

a. forming a first coating on a surface of a base sheet or web by applying to the surface an aqueous coating mix consisting essentially of (a) said binder material, said binder material being rewettable and se lected from the group consisting of dextrin, polyvinyl alcohol, and a mixture of dextrin and polyvinyl alcohol, and (b) said protective material, said protective material being selected from the group consisting of cellulose fibers, granular polymeric material and starch granules;

b. drying said first coating;

0. rewetting said dried first coating;

d. forming a composite coating by applying a coating consisting essentially of said capsules to said rewetted first coating; and

e. drying said composite coating.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION q Patent No. 319141470 D d October 21, 1975 Inventor(5) Benjamin Stanley Lewis It is certified that error appears in the above-identified patent a and that said Letters Patent are hereby corrected as shown below:

At page 1, item No. [73] "Wiggins Teape Research & Development" should read Wiggins Teape Research & Development Limited Signed and Sealed this eighteenth Day of May 1976 a {SEALI A nest:

v RUTH C. MiSON C. MARSHALL DANN Q Amstmg ()jjm'r (nmmissimu'r nj'lalenrs and Trademarks

Claims

1. A METHOD OF PRODUCING A CAPSULE-CARRYING SHEET OR WEB COMPRISING A BASE SHEET OR WEB HAVING ON A SURFACE THEREOF A COMPOSITE COATING CONTAINING CAPSULES, PROTECTIVE MATERIAL FOR PROTECTING THE CAPSULES AGAINST ACCIDENTAL RUPTURE, AND A BINDER MATERIAL SERVING TO BIND THE CAPSULES AND PROTECTIVE MATERIAL TO THE BASE SHEET OR WEB, COMPRISING THE STEPS OF, A. FORMING A FIRST COATING A SURFACE OF A BASE SHEET OR WEB BY APPLYING TO THE SURFACE AN AQUEOUS COATING MIX CONSISTING ESSENTIALLY OF A REWETTABLE BINDER MATERIAL AND A PROTECTIVE MATERIAL, B. DRYING THE FIRST COATING, C. REWETTING THE DRIED FIRST COATING, D. FORMING A COMPOSITE COATING BY APPLYING A COATING CONSISTING ESSENTIALLY OF CAPSULES TO THE REWETTING FIRST COATING, AND E. DRYING THE COMPOSITE COATING.

8. A method according to claim 2, in which the base sheet or web is a 49 g/m2 paper, the aqueous coating mix applied thereto consists of a suspension formed by preparing a solution of 5g of dextrine in 150 mls of hot water, cooling the solution to below 30*C, dispersing in the cooled solution 5g of unburst arrowrrot starch granules having a size of approximately 25 m and the suspension is applied to the paper to provide thereon a coating weight of approximately 1.3 to 2.2 g/m2.

9. A method according to claim 2, in which the base sheet or web is a 49 g/m2 paper, the aqueous coating mix applied thereto consists of a suspension formed by slowly adding 5g of polyvinyl alcohol to 150 mls of cold water, accelerating the rate of solution by heating the dispersion so formed, cooling the solution to below 30*C, dispersing in the cooled solution 5g of unburst arrowroot starch granules having a size of approximately 25 m, and the suspension is applied to the paper to provide thereon a coating weight of approximately 1.8 to 2.2 g/m2.

10. A method according to claim 2, in which the base sheet or web is a 49 g/m2 paper, the aqueous coating mix applied thereto consists of a suspension formed by preparing a first solution by slowly adding 0.5g of polyvinyl alcohol to 50 mls of cold water, accelerating the rate of solution by heating the dispersion so formed, preparing a second solution by adding 4.5g of dextrine to 100 mls of hot water, mixing the first and second solutions, cooling the resulting solution to below 30*C, dispersing in the cooled solution 5g of unburst arrowroot starch granules having a size of approximately 25 m, and the suspension is applied to the paper to provide thereon a coating weight of approximately 1.2 to 2.3 g/m2.

11. A method of producing a capsule-carrying sheet or web comprising a base sheet or web having on a surface thereof a composite coating containing (a) a binder material, (b) protective material, and (c) capsules, said protective material protecting said capsules against accidental rupture, and said binder material serving to bind said capsules and said protective material to said base sheet or web, which method consists essentially of the steps of: a. forming a first coating on a surface of a base sheet or web by applying to the surface an aqueous coating mix consisting essentially of (a) said binder material, said binder material being rewettable and selected from the group consisting of dextrin, polyvinyl alcohol, and a mixture of dextrin and polyvinyl alcohol, and (b) said protective material, said protective material being selected from the group consisting of cellulose fibers, granular polymeric material and starch granules; b. drying said first coating; c. rewetting said dried first coating; d. forming a composite coating by applying a coating consisting essentially of said capsules to said rewEtted first coating; and e. drying said composite coating.