US3329523A - Process for coating flexible sheet with amylose - Google Patents

Description

July 4, 1967 R. w. BEST ETAL 3,329,523

PROCESS FOR COATING FLEXIBLE SHEET WITH AMYLOSE Filed June 29, 1964 United States Patent O 3,329,523 PROCESS FOR COATING FLEXIBLE SHEET WITH AMYLOSE Roland W. Best and Robert M. Powers, Decatur, Ill., as-

signors to A. E. Staley Manufacturing Company, Decatur, 11]., a corporation of Delaware Filed June 29, 1964, Ser. No. 378,924 19 Claims. (Cl. 117-64) This is a continuation-in-part of application Ser. No. 296,660, filed July 22, 1963, and now abandoned.

This invention relates to a continuous process of forming an amylosic film or coating on paper.

For many years there has been a demand for low-cost grease-resistant coatings for paper. When amylosic material first became commercially available, it was thought that amylosic material might satisfy the need for a lowcost grease-resistant coating for paper. Insofar as we have been able to ascertain, this has only been conjecture. Until now, no one has disclosed any method for forming smooth, grease-resistant amylosic coatings on paper webs.

A variety of processes have been used for the continuous production of amylosic films. These processes include the extrusion of amylosic solutions into a coagulating bath, which precipitates the film; the extrusion of superficially 'dry amylosic material; casting amylosic solutions on a moving belt or roll under conditions where solvent is evaporated, forming an amylosic film; etc. However, all of these processes are designed for the preparation of self-supporting amylosic films and are not suitable for the preparation of'smooth, grease-resistant amylosic coated paper webs. Further, the tendency of amylosic material to gel rapidly, which is often advantageous in casting self-supporting amylosic films, is a drawback in the preparation of grease-resistant paper.

While it might appear that grease-resistant coatings could be applied to paper by passing the paper Web through an amylosic solution, such is not the case. When a paper web is passed through an amylosic solution, the web must be passed through a nip in order to remove excess treating material and to form a smooth surface. In this treatment the amylosic material is forced into the interior of the paper. When such paper is in contact with a greasy substance, the cellulosic fibers seem to act as a wick, for the grease passes through the paper. It is almost impossible to form a smooth amylosic coating with a spray applicator because of the tendency of aqueous solutions of amylosic material to gel prematurely before the active material can uniformly cover the paper.

Our own work has shown that it is virtually impossible to form an aesthetically acceptable smooth grease-resistant coating on a single sheet of paper (for example, 45 pound paper stock) using any of the commonly used laboratory hand coaters, such as a Bird applicator, Gardner applicator, doctor blade, Nordson Airless spray applicator, wire wrapped rod, etc. These failures are due to a combination of the porous, uneven character of paper and the tendency of aqueous solution of underivatized amylosic material to gel rapidly as the concentration of amylosic material increases and/or as the temperature of the aqueous solution decreases. The rapid gelling properties of amylose make it almost impossible to smooth a single sheet of paper prior to the gelation of the amylosic layer.

The object of this invention is to provide a continuous method of forming grease-resistant amylosic-coated paper webs.

We have now found that grease-resistant amylosic coated paper webs can be produced continuously and efliciently by applying an aqueous solution of amylosic material to the paper web with a roll applicator, followed ICC almost immediately by a smoothing operation before the amylosic coating can gel. Any excess coating material can be removed with an air blast from an air knife or by passing the coated side of the paper web over a rotating r-od. In this way a smooth grease-resistant sheet is obtained. The combination of roll applicator and air-knife smootheris known as an air-knife coater, while the combinat-ion of a roll applicator and rotating-rod smoother is known as a Champion knife coater. Of these two, the air-knife is preferred since it is possible to apply a much heavier amylosic coating in a single pass.

The drawing illustrates a typical roll applicator of the air-knife coater variety. In a typical coating operation utilizing the principles of this invention, an aqueous slurry of from about 1% by weight to 15% by weight amylosic material is prepared. The amylosic material is then dissolved by heating the aqueous slurry under pressure in a continuous heat exchanger to about 120 C. to 160 C. or higher in order to dissolve the amylosic material. The dissolved amylosic material is continuously discharged into a ooacting pan 1 which is maintained above the gelation temperature of the amylosic solution (typically 60- C.). The roll applicator 3, which can be heated if desired, almost immediately reaches the temperature of the amylosic solution in the coating pan 1 as the roll applicator 3 revolves. The roll applicator 3 transfers the hot amylosic solution to the paper web 5. The paper web 5 which is typically moving at about 50 to 2500 feet per minute passes over the top of the applicator roll 3 and around the breast roll 7. An air knife 9 removes excess treating material and smoothes the surface of the paper by propelling a blast of air against the paper passing around the breast roll 7. Because of the speed at which the web is moving, the smoothing operation takes place immediately after the coating has been applied, before the amylosic material can gel. The excess treating material is caught in the catch pan 11 which can be heated to keep the amylosic material in fluid form. The amylosic material caught in the catch pan can then be recycled to the coating pan. The coated paper is then dried and wound upon a suitable roll. If desired, prior to or after the drying step the amylosic coated paper web can be coated with one or more additional coatings of amylosic material and/or other treating materials.

For the purpose of this invention, the term amylosic material refers to the amylose resulting from the separation of the amylose and amylopectin components of starch, or the whole starch which is composed of at least 50% amylose. Commercially available sources of amylose include Nepol amylose (the amylose fraction of corn starch), Superlose (the amylose fraction of potato starch), Amylomaize or Amylon (high-amylosic material corn starch containing approximately 54% amylose), Amylon VII (high-amylose corn starch containing up to 70% amylose), etc. The amylosic coatings based on high-amylose corn starch can be simulated by mixing corresponding concentrations of separated amylose with separated amylopectin. Preferably, the amylopectin content of the amylosic material is less than 20% by Weight since the higher the concentration of amylose the better the flexibility and strength of the coating. Various derivatives of amylosic material (amylose acetate, hydroxyethyl amylose, hydroxypropyl amylose, etc.) such as those described in US. Patent 3,038,895 can also be employed.

As indicated above, the coating composition is usually prepared by first forming an aqueous slurry of from about 1% to 15 by weight amylose and then dissolving the amylosic material at about C. to 200 C. in a continuous heat exchange unit, such as a Votator or any of the common types of starch cooker. In general, the higher the concentration of amylosic material in the coating composition the heavier the coating of amylosic material that can be applied to the paper in a single pass and correspondingly the more grease-resistant the paper. However, the higher the concentration of amylosic material the higher the viscosity of the coating composition and the greater the tendency of the amylosic material to gel prematurely in the coating pan or before the smoothing step. Accordingly, it is preferred to employ aqueous coating compositions containing from about 6 to 12% by weight dissolved amylosic material.

In order to prevent premature gel formation and high viscosity, the amylosic solution in the coating pan is kept hot, preferably at a temperature of about 60 C. to 100 C. However, the temperatures as low as 25C. can be employed with dilute aqueous solutions of the order of about 1% by weight amylosic material. In general, the temperature and amylose concentration should be selected in a manner to provide a coating composition having a maximum viscosity of about 400 cps. as measured on a Brookfield viscometer. However, in some cases, viscosities as high as 1,000 cps. can be employed.

The above processing conditions are most suitable when the now commercially available forms of underivatized amylose and granular high-amylose corn starch are employed. However, other forms of amylosic material, which dissolve in cold water or boiling water (100 C.), such as many of the amylosic derivatives described in U.S. Patent 3,038,895 and unretrograded amylosic material described in U.S. Patent 3,086,890, can be dissolved at lower temperatures. Likewise, the coating composition itself can be maintained at a lower temperature if an amylosic derivative of reduced tendency to gel is employed. In addition to various amylosic derivatives, which dissolve in water at less than 100 C., amylosic derivatives of the type described in commonly assigned application Ser. Nos. 65,295, now U. S. Patent 3,127,392, and 73,190, now U.S. Patent 3,208,998, which dissolve in water at temperatures above 100 C. but form stable aqueous solutions can be used. Further, some amylosic derivatives which are less viscous than underivatized amylosic material, can be employed at higher concentrations up to about 20% by weight. However, for best results, the temperature and concentration of amylosic derivatives should be selected in a manner to provide a coating composition having a maximum Brookfield viscosity of about 400 cps.

The amylosic coating composition can, of course, have additional ingredients. For example, plasticizers, such as glycerol, sorbitol, choline chloride, etc., are useful for increasing the flexibility and elongation of the amylosic coating. Polyvinyl alcohol and/or 1,2,6-hexanetriol are particularly effica-cious additives.

As indicated above, the amylosic coating can be applied in a single pass or in several passes. However, for forming effective grease-resistant paper, We have found that the amylosic coating (amylosic material and other additives, such as plasticizers) must weigh at least one pound per 1000 square feet of paper and preferably at least two pounds per 1000 square feet of paper. At lower coating weights the paper can be used in offset printing, where it is noly necessary to slow down the penetration of the hydrophobic printing ink.

The following examples are merely illustrative and should not be construed as limiting the scope of our invention.

Example I An aqueous solution of defatted amylose was prepared at 155 C. by passing a total solids aqueous slurry (8.5 parts by weight amylose and 1.5 parts by weight amylopectin) through a starch cooker of the type described in application Ser. No. 790,487 filed Feb. 2, 1959, now U.S. Patent 3,101,284. The solution was continuously supplied to a preheated coating pan (70 C.) of an airknife coater. (The air-knife coater was one station on a 40 foot long pilot plant coater.) The aqueous solution of amylose was continuously applied to a surface of a roll, which was partially immersed in the coating pan. The surface of the roll was not water absorptive. The amylose, while in an ungelled state, was transferred from the surface of the roll to a paper web (a roll of 45 pound paper), which was moving at 250 feet per minute. Immediately thereafter, before the overlying amylose coating composition gelled, the coating was smoothed by passing the paper web between a roll surface and an air blast from a jet. The coated side of the paper was exposed to the air blast. The coated paper was dried and then run through the air-knife coater a second time. The paper, which was dried a second time, had an amylose coating of about 1.1 pounds per 1,000 square feet of paper.

A 4 inch by 4 inch square of paper passed the standard grease-proofing test of the Technical Association of the Pulp and Paper Industry. The backside of the coated paper showed no passage of dye when 1.1 ml. turpentine containing an oil soluble red dye was dropped on a five gram mound of sand, which was placed on the coated side of the paper.

Example 11 Example I was repeated except that a roll of bleached kraft paper was used and the first amylose coating solution was prepared from a 12% by weight aqueous slurry of amylose. Paper having one layer of amylose, about 0.6 pound per 1,000 square feet of paper, failed the test described in Example I. Paper coated with a second layer of amylose, with a coating weight of about 2.0 pounds per 1,000 square feet of paper, passed the test described in Example I.

Example III Example I was repeated except that a roll of bleached kraft paper was used and three coats of amylose was applied to most of the roll. The paper which had been coated with two layers of amylose had a coating weight of about 2.3 pounds while the paper which had been coated with three layers of amylose had a coating weight of about 3.4 pounds per 1,000 square feet of paper. Both coated papers passed the test described in Example I.

Example IV This example illustrates coating the polyethylene side of commercially available corona discharge treated polyethylene coated natural kraft paper, the polyethylene layer being approximately 0.50 mil thick. An aqueous solution of amylose was prepared by heating to 155 C. a 11% solids aqueous slurry of 7.2 parts by weight corn amylose, 0.8 part by weight corn amylopectin and 3 parts by weight polyvinyl alcohol having about 2 acetyl groups per each monomeric units. The amylose composition was applied to the polyethylene side of the flexible sheet in the manner described in Example I, dried and a second coat applied in the same manner. The coated sheet passed the grease-proofing test described in Example I.

Example V Example I was repeated with essentially the same results except that the amylose composition was applied to the coated side of a paper web which had been sized with a composition comprising clay and 14% by weight alkaline hypochlorite-oxidized starch based on the weight of the clay.

While the preceding examples illustrate the application of amylosic material to paper (coated and uncoated) with an air-knife coater the same coating technique can be used to coat any flexible sheet with amylosic material. For the purposes of this invention the term flexible sheet includes films or coatings of polyethylene, polypropylene, polyethylene terephthalate, polyvinylidene chloride, polyvinyl chloride, polyvinyl fluoride, aluminum foil, etc.

The term paper is used in a generic sense to include paper of all varieties, whether coated or uncoated, including paper board.

Since many embodiments of this invention may be made and since many changes may be made in the embodiments described, the foregoing is to be interpreted as illustrative only and our invention is defined by the claims appended hereafter.

We claim:

1. The process of forming a smooth, grease-resistant coated flexible sheet which comprises the steps of (1) providing an aqueous solution consisting essentially of an amylosic material containing at least 50% by weight amylose, wherein said amylosic material is present in a concentration of from 1 to 20% by weight of said aqueous solution and is selected from the group consisting of the separated amylose fraction of whole starch, Whole starch containing at least 50% by weight amylose and mixtures thereof, (2) applying said aqueous solution of amylosic material to a surface which is not water absorptive, (3) while said amylosic material is in an ungelled state transferring the coating composition from said surface to a flexible sheet, while said flexible sheet is moving at a rate of about 50 to 2,500 feet per minute, (4) immediately smoothing said coating before the overlying amylosic coating composition gels, and (5) drying said flexible sheet.

2. The process of claim 1 wherein said flexible sheet is a continuous paper web.

3. The process of claim 2, wherein said aqueous solution of amylosic material has a maximum Brookfield viscosity of 400 cps.

4. The process of claim 2, wherein said aqueous solution of amylosic material is at a temperature of from about 60 C. to 100 C.

5. The process of claim 4, wherein said amylosic material is the separated fraction of whole starch and comprises no more than 15% by weight of said aqueous solution.

6. The process of claim 5, wherein said amylosic material comprises from about 6% to 12% by weight of said aqueous solution.

7. The process of claim 4, wherein the amylopectin content of the amylosic material is less than 20% by weight and said amylosic material comprises no more than 15% by weight of said aqueous solution.

8. The process of claim 2, wherein excess amylosic treating material is removed from the coated paper in the smoothing operation and recovered.

9. The process of claim 8, wherein the excess amylosic material is recycled.

10. The process of forming a smooth, grease-resistant coated flexible sheet which comprises the steps of (1) providing an aqueous solution consisting essentially of an amylosic material containing at least 50% by weight amylose, wherein said amylosic material is present in a concentration of from 1 to 20% by weight of said aqueous solution and is selected from the group consisting of the separated amylose fraction of whole starch, whole starch containing at least 50% by weight amylose and mixtures thereof, (2) applying said aqueous solution of amylosic material to a surface which is not water absorptive, (3) while said amylosic material is in an ungelled state transferring the coating composition from said surface to a flexible sheet, while said flexible sheet is moving at a rate of about 50 to 2,500 feet per minute, (4) immediately smoothing said coating before the overlying amylosic coating composition gels by passing said flexible sheet between a surface and a blast of air with the coated side of the flexible sheet being exposed to the blast of air, and (S) drying said flexible sheet.

11. The process of claim 10 wherein said flexible sheet is a continuous paper web.

12. The process of claim 11, wherein said aqueous solution of amylosic material has a maximum Brookfield viscosity of 400 cps.

13. The process of claim 11, wherein said aqueous solution of amylosic material is at a temperature of from about 60 C. to C.

14. The process of claim 13, wherein said amylosic material is the separated fraction of whole starch and comprises no more than 15% by weight of said aqueous solution.

15. The process of claim 14, wherein said amylosic material comprises from about 6% to 12% by weight of said aqueous solution.

16. The process of claim 13, wherein the amylopectin content of the amylosic material is less than 20% by weight and said amylosic material comprises no more than 15% by weight of said aqueous solution.

17. The process of claim 12, wherein excess amylosic treating material is removed from the coated paper by the air blast.

18. The process of claim 17, wherein the excess amylosic material is recycled.

19. The process of claim 11, wherein said amylosic coating composition contains a plasticizing concentration of a polyhydric alcohol.

References Cited UNITED STATES PATENTS 2,325,798 8/1943 Porter 117156 X 2,798,990 7/1957 Davis 117165 X 2,822,581 2/ 1958 Muetgeert et al. 106-210 X 2,949,382 8/1960 Dickerman et a1. 117156 X 3,076,720 2/1963 Rice et al 11786 X FOREIGN PATENTS 6,410,751 9/ 1964 Netherlands.

OTHER REFERENCES Egan, F. W., Some Fundamentals of Coating Methods. The Paper Industry and Paper World, pp. 1142-4145, December 1944, copy in 117111.

Kaplan, Paul, Potential Industrial Use of Amylose. Cereal Science Today 3(8) pp. 206-209, October 1958, TH c 34.

WILLIAM D. MARTIN, Primary Examiner.

MURRAY KATZ, Examiner.

H. W. MYLIUS, M. LUSIGNAN, Assistant Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,329,523 July 4, 1967 Roland W. Best et a1.

d that error appears in the above numbered pat- It is hereby certifie tters Patent should read as ent requiring correction and that the said Le corrected below.

Column 2, line 21, for "coacting" read coating line 49, for "amylose", second occurrence, read amylosic material lines 52 and 53, for "(high-amylosic material corn" read (high-amylose corn line 68, for "amylose" read amylosic material column 3, line 17, for "amylose" read amylosic Signed and sealed this 18th day of June 1968.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

Claims (1)

1. THE PROCESS OF FORMING A SMOOTH, GREASE-RESISTANT COATED FLEXIBLE SHEET WHICH COMPRISES THE STEPS OF (1) PROVIDING AN AQUEOUS SOLUTION CONSISTING ESSENTIALLY OF AN AMYLOSIC MATERIAL CONTAINING AT LEAST 50% BY WEIGHT AMYLOSE, WHEREIN SAID AMYLOSIC MATERIAL IS PRESENT IN A CONCENTRATION OF FROM 1 TO 20% BY WEIGHT OF SAID AQUEOUS SOLUTION AND IS SELECTED FROM THE GROUP CONSISTING OF THE SEPARATED AMYLOSE FRACTION OF WHOLE STARCH, WHOLE STARCH CONTAINING AT LEAST 50% BY WEIGHT AMYLOSE AND MIXTURES THEREOF, (2) APPLYING SAID AQUEOUS SOLUTION OF AMYLOSIC MATERIAL TO A SURFACE WHICH IS NOT WATER ABSORPTIVE, (3) WHILE SAID AMYLOSIC MATERIAL IS IN AN UNGELLED STATE TRANSFERRING THE COATING COMPOSITION FROM SAID SURFACE TO A FLEXIBLE SHEET, WHILE SAID FLEXIBLE SHEET IS MOVING AT A RATE OF ABOUT 50 TO 2,500 FEET PER MINUTE, (4) IMMEDIATELY SMOOTHING SAID COATING BEFORE THE OVERLYING AMYLOSIC COATING COMPOSITION GELS, AND (5) DRYING SAID FLEXIBLE SHEET.

Images