US2999787A

US2999787A - Machine glazed paper

Info

Publication number: US2999787A
Application number: US688142A
Authority: US
Inventors: Martin L Downs; Ralph A Nelson
Original assignee: Thilmany Pulp and Paper Co
Current assignee: Thilmany Pulp and Paper Co
Priority date: 1957-10-04
Filing date: 1957-10-04
Publication date: 1961-09-12
Anticipated expiration: 1978-09-12

Description

2,999,787 MACHINE GLAZED PAPER Martin L. Downs and Ralph A. Nelson, Appleton, Wis.,

assignors to Thilmany Pulp & Paper Company, a corporation of Wisconsin No Drawing. Filed Oct. 4, 1957, Ser. No. 688,142 7 Claims. (Cl. 1621'35) Unleveled base sheet formed (apparent density approx. 11 lbsJream/mil) Leveled Dried to substantially normal sheet dryness Hydrophilic colloid prepared which provides transparent film (water holding properties 3 see.)

Colloid set on leveled surface of sheet without substantial penetration Colloid on sheet dried against smooth dryer surface to provide Machine Glazed Paper In the paper art, it has been known for many years that if a wet cellulosic web is forced with suflicient pressure against a fiat surface and the web is allowed to dry in contact with the surface, a sheet will be provided having a side which conforms to the surface and which tends to reproduce the surface, i.e., a highly glazed surface.

In commercial paper making practice, it has been the practice to provide such a highly glazed surface on one side of a paper sheet by pressing a web onto the surface of a highly polished cast iron cylinder or dryer and hold the sheet in contact with the dryer until the moisture is substantially removed from the web. When sufficient moisture has been removed, the sheet automatically releases itself from the dryer and has a glazed surface which approximates the dryer surface.

The equipment used in the paper making art to produce such a highly glazed paper is known as a Yankee machine or Yankee dryer or is sometimes referred to as a Flying Dutchman machine. The paper manufactured on machines of this type is commonly known in the art as machine glazed or M.G. paper.

As above indicated, the machine glazed paper obtains its glaze characteristics by pressing of the cellulosic fibers, under high pressure, against a smooth polished dryer surface. The fibers on the surface, substantially individually, are conformed to the smooth polished surface. In order to obtain an improved glaze, the stock for the Web of Patented Sept. 12, 1961 paper is beaten, or refined. However, such beating cannot be carried too far, i.e. to a low freeness level sometimes referred to as a slow stock. If the porosity of the web is decreased by using such a slow stock, thereby providing a dense sheet, vapor pressure builds up between the dryer surface and the web so that the web, in certain areas during drying, is prematurely lifted away from the dryer surface, thereby providing an inferior glaze in the prematurely lifted areas resulting in a checked or non-uniformly glazed sheet. Accordingly, the porosity of the sheet must be maintained to a certain degree, so as to prevent this premature lifting. In view of this, the extent of development of glaze has been limited.

Furthermore, it has been recognized in the paper art that the Web and resulting sheet do not faithfully reproduce the profile of the dryer surface, not only because of the inherent fibrous nature of the web, with the concomitant impossibility of pressing the sheet with suflicient force to adhere every portion of the sheet to the dryer surface, but also because the sheet is a spongy mass with only portions of the fiber in actual contact with the dryer surface.

As will be seen from the foregoing, there are inherent limitations in the manufacture of machine glazed paper which necessarily limit the degree of glaze which can be developed on the sheet. In this connection, the development of vapor between the dryer and sheet is inherent in the drying operation, there are mechanical limitations upon pressure which can be brought to bear in contacting the sheet with the dryer surface, and the nature of the web limits the glaze which can be developed.

A principal object of this invention is the provision of an improved paper of the machine glazed type. A still further object of the invention is provision of an improved process for making a paper having a high gloss thereon. A particular object of the invention is the provision of a process for manufacturing a high gloss paper, the gloss being substantially transparent to thereby show the fibers of the cellulosic portion of the sheet.

These and other objects of the invention are accomplished by the formation of a web of paper or base sheet to which is applied an aqueous unpigmented mixture which includes a hydrophilic colloid. The colloid is set on the surface of the base sheet without substantial penetration of the base sheet, whereupon the combination is dried against a polished surface.

In the practice of this invention, the base sheet may comprise any fiber furnish conventionally used in machine glazed papers. The surface should be levelled prior to application of the colloid. Such levelling permits the establishment of high glaze with relatively low amounts of colloid. The wire side of the base sheet, i.e., the side of the sheet which rides on or is carried by the Fourdrinier wire of the paper making machine, is levelled prior to coating with the colloid. Levelling may be accomplished by auxiliary wet pressing, a smoothing press, a breaker-stack, or by drying against a Yankee dryer. However, the levelling process should not increase the apparent density of the sheet to more than about 11 pounds per ream (24 inches by 36 inches500 sheets) per mil of thickness.

The basis weight of the base sheet should be in the range of from 15 pounds to pounds per ream (22 inches by 34 inches-500 sheets) finished weight, including the usual moisture content. This weight range of base sheet is necessary to provide the sheet of the invention.

The base sheet, when the colloid is applied, comprises less than 60 percent moisture. Higher moisture levels prevent the establishment of the high glaze surface because of difficulties in drying the sheet with the colloid on the surface. To establish this moisture level, some initial drying of the base sheet should be done to provide a base sheet having the desired moisture level. The base sheet preferably has less than 40 percent moisture, and may be dried to normal sheetdryness. i To provide satisfactory glazing of the sheet, the colloid should provide on the final sheet a continuous film over the surface of the base sheet. The establishment of such a continuous film can be determined by the uniformityof gloss and lac-k of imperfections in the finished sheet. .In this connection, the laboratory and semi-commercial work has shown that, with a 35 pound per ream base sheet, which has been levelled, as little as 2.5 pounds of dried colloid solids per ream are required to produce a high and uniform glaze, but as much as 8 pounds of colloid per ream has been successfully applied. In commercial practice with an air knife, a good level base sheet requires colloid to the extent of about 7 percent of the base sheet weight with a 35 pound per ream base sheet. With base sheets having lower basis weights, increased percentages of colloid are required. In this connection, a base sheet weighing 15 pounds per ream requires colloid to the extent of 10 percent of the weight of the base sheet. The amount even, high gloss. Amounts in excess of a minimum amount can be applied but there is an increase in the dry- The selection of a suitable colloid for appllcation to I the levelled sheet is of great importance. Likewise, the

adjustment of conditions to assure that the resulting dried colloid is a continuous film on the surface of the base sheet is of substantial importance. Not only must a continuous film be provided but, in addition, thefilrn should mirror the polished surface it is dried against. In

order to provide the desired film surface and film continuity, the film should be primarily on the surface .and

.of colloid will be kept as low as practical to insure the should not migrate into the base sheet. If the colloid mi- 3 grates into the base sheet, a condition known as strike-in occurs. The condition of strike-in is readily disconcerned as an area of different appearance. The migration can result from improper choice of colloid and/oncomditions of manufacture.

The overall spectral reflectance of the film carrying sheet is referred to as brightness, and strike-in results in loss of spectral reflectance with consequent loss of brightness as measured by a brightness tester, which may be a Photovolt instrument. By way of example, a white sheet having a basis weight'of 37.5 pounds per ream,

,and carrying a colloid film gave brightness readings of 67.5 to 68 on the brightness tester in areas not showing strike-in while readings 65 to 66 were obtained in areas showing strike-in. On a pastel yellow sheet having a basis weight of 38 pounds per ream and having the colloid film of the invention on its surface gave a brightness reading of 35 .5 to 36 in areas free of strike-in and 33.5

to 34.5 in areas of strike-in. One can detect a one point 'loss in brightness and rather easilyvisually detect .1.5

points loss in brightness.

The colloid materials used in the practice of this invention should have water holding properties and should test higher than about 3 seconds. In the test, 10 grams of a colloid is prepared in 280 cubic centimeters of distilled water and held at 73 F. to 75 F. for 3 hours; Approximately 25 cubic centimeters of the colloid mix is placed in a suitable porcelain dish. Straubel wet strength single fold kraft towels are cut into 1% inch squares andon'e side is dusted with a dry prepared mixture of finely ground corn starch, sugar and dye. The dusted sheet is dropped onto the colloid mix, dusted side up, and the time required applying the colloid solution is important.

Dow Chemical Company--Methocel l0 cps. (methyl cellulose) Of the above materials, methyl cellulose is an excellent water holder and provides most satisfactory results with minimum strike-in difficulties. However, those materials testing higher than 3 seconds can also provide satisfactory resutls.

To assure satisfactory filming, the colloid solution should have a viscosity of 200 to 1500 centipoises, as measured on a Brookfield 2M Spool at F. At lower viscosities, strike-in difficulties occur, while at higher viscosities, filming of the colloid solution onto the surface is difiicult to accomplish.

It is desirable to have as high solids as possible in the colloid solution providing that a viscosity in the range specified is provided. Ten percent solids is the lower practical limit for colloid solutions, while there are colloids available which can be used even though they contain as high as about 35 percent solids.

The Penford 290 starch, at 20 percent solids in the colloid solution, is a very representative example of a suitable colloid mix. Protein and special gums such as Methocel have been successfully used but have practical limitations because of cost, color, or viscosity.

In addition to having the foregoing properties, the colloid fiim which is carried on the base sheet should have sufiicient flexibility so that the sheet can be embossed or printed. Furthermore, the flexibility of the colloid film should be such as to permit folding and bending of the sheet without cracking of the film. In addition, the colloid film should have acceptance to inks so as to provide a good printing surface.

In order to prevent sticking of the film to the dryer surface, to which the film conforms, the colloid should release itself from the dryer surface upon drying of the combined sheet of the invention. Any sticking of the film to the dryer surface results in lessening of gloss of the sheet.

It will be understood, of course, that the colloid film can be treated to develop a degree of insolubility in water so as to provide it with substantial resistance against retackifying upon redampening i.e., becoming stick; on wetting. V

.The term apparent density used herein refers to the weight per ream (dry basis) divided by the calipered thickness of the sheet.

In preparing the sheet of this invention, the manner of As before indicated, a highly desirable way of applying the colloid solution is by means of an air knife. However, coating rollers and other systems may be employed. It is important in the application of the colloid solution that the pressure be limited so as to reduce strike-in. Of course,

skill of the art to correlate these factors to provide the highly glazed sheet of the invention.

Not only. is it important to limit the pressure on the Lfil-m on the sheet in connection with the application of the jeo'lloid, but,,like'wise, it 'is important that the pressure .jonth'e' film be limited inthe early stages of drying on the face of the dryer. It will be understood, of course, that as the degree of drying increases, i.e., the sheet becomes dryer, greater pressures may be applied.

The conditions of pressure can best be adjudged by observation of the end sheet. In this connection, if insufficientpressure is being applied, flaked and skipped areas will appear on the face of the sheet of the invention. On the other hand, if the pressure is too great, the strike-in condition will appear, as above described.

Another important factor in the preparation of the sheet of the invention is the temperature of the dryer surface which, in the case of most commercial operations, will comprise a Yankee dryer. The temperature of the surface of the dryer must be lou enough to prevent blistering which causes loss of contact of a portion of the sheet with the dryer surface because of the build up of vapor pressure. This surface temperature, of course, is proportional to the speed of the dryer, the amount of moisture present, and the weight and porosity of the base sheet. In addition, the blistering can occur as a function of the thickness of film on the base sheet. Here again, the temperature of the dryer surface should be adjusted, and adjustment is effected in operation of the dryer to eliminate the blistering problem.

Blistering can be readily ascertained from inspection of the finished sheet. By way of example, a sheet of this invention was dried on a Yankee dryer having a temperature of about 190 F. to 220 F., the base sheet of the paper having a basis weight of 35 pounds per ream and the continuous film on this sheet weighing 3.5 pounds per ream.

It is also important that the apparent density be less than about 11 pounds per ream per mil thickness. At higher densities, the porosity is so reduced that the sheet cannot be satisfactorily made. Accordingly, it is difiicult to obtain the desired levelling with presses and breaker stacks. Likewise, levelling cannot be satisfactorily obtained by coating the base sheet.

To provide commercial results, the base sheet should be glossy. In this connection, the base sheet should have a gloss of points.

As an example of the practice of this invention, a base sheet is prepared on a Fourdrinier section of a Yankee machine, the base sheet having a basis weight of 35 pounds per ream, dry basis, and an apparent density of 10.5 pounds per ream per mil thickness. The sheet, in the Fourdrinier machine, is dried to a moisture content of about 35 percent. The base sheet is levelled in a pressing section in the Yankee machine.

A colloid solution is prepared from a Penford 290 starch, the solution comprising 20 percent solids. No pigments or other opaque substances are added to the colloid solution. The solution has a viscosity of 400 centipoises. The colloid solution is applied to the base sheet by means of an air knife to establish solids on one side of the base sheet at a level of 3.5 pounds per ream. The base sheet, carrying the colloid material, is passed into contact with a Yankee dryer, the colloid material contacting the dryer. The surface temperature of the dryer is about 190 F. When the sheet is dried, it releases from the dryer without difficulty and the sheet is prepared for sale.

By way of another example, to a finished M.G. paper having an apparent density of 10.5 pounds per ream per mil thickness is applied the above described colloid solution. The M.G. paper carrying the film is dried on a polished Yankee dryer, as above described. Through the application of the colloid film, the gloss of the paper increases from about 25 points to about 65 points.

The base sheet may be sized or other wise treated in accordance with known paper making procedures. Such sizing aids in limiting strike-in. Of course, the base sheet may be made from bleached pulp or unbleached pulp. The base sheet may be colored, if desired.

The colloid film may likewise be colored but, as before indicated, it should not be pigmented. Likewise, other inorganic fillers or materials should not be utilized in the colloid solution which materials break or interfere with the filming characteristics of the colloid. The colloid should provide a glaze on the sheet and, therefore, various of the elastomers cannot be used because they cannot be satisfactorily handled on the drier surface to provide the desired glaze.

It will be seen from the foregoing that a highly improved paper product can be prepared by applying a colloid film to a levelled sheet of paper. The prior levelling of the sheet permits the establishment of unusually high glaze on the sheet. This levelling coacts with the colloid film, Which is carried on the surface of the sheet, to provide this high degree of glaze when dried in contact with a polished dryer surface.

The various features of this invention which are believed to be new are set forth in the following claims.

We claim:

1. A process for the manufacture of machine glazed type paper comprising the steps of forming a base sheet having an apparent density of less than about 11 pounds per ream per mil of thickness, said base sheet being leveled and having a glossy surface, said base sheet being dried to substantial normal sheet dryness to thereby maintain the leveled surface, preparing an aqueous mixture including a hydrophilic colloid which mixture provides a transparent film, said hydrophilic colloid mixture having water holding properties higher than about 3 seconds, setting said colloid on the said glossy surface of said base sheet without substantial penetration of said base sheet, and drying the combined sheet with the colloid contacting a smooth drier surface whereby machine glazed paper having improved gloss is provided.

2. A process for the manufacture of machine glazed type paper comprising the steps of forming a base sheet having a basis weight of between about 15 pounds per ream and about pounds per ream and having an apparent density of less than about 11 pounds per ream per mil of thickness, levelling at least one side of said base sheet to provide a glossy surface, said base sheet being dried to substantial normal sheet dryness to thereby maintain the leveled surface, preparing an aqueous mixture including an hydrophilic colloid which mixture provides a transparent film, setting said colloid on the levelled surface of said base sheet without substantial penetration of said base sheet, said hydrophilic colloid mixture having water holding properties higher than about 3 seconds, and drying the combined sheet with the colloid contacting a smooth drier surface whereby machine glazed paper having improved gloss is provided.

3. A process for the manufacture of machine glazed type paper comprising the steps of forming a base sheet having a basis weight of between about 15 pounds per ream and about 120 pounds per ream and having an apparent density of less than about 11 pounds per ream per mil of thickness, levelling at least one side of said base sheet, said base sheet being dried to substantial normal sheet dryness to thereby maintain the leveled surface, preparing an aqueous mixture including a hydrophilic colloid which mixture provides a transparent film, said aqueous mixture having a viscosity of between about 200 centipoises and 1500 centipoises, setting said colloid on the levelled surface of said base sheet without substantial penetration of said base sheet, said hydrophilic colloid mixture having water holding properties higher than about 3 seconds, and drying the combined sheet With the colloid contacting a smooth dryer surface whereby machine glazed paper having improved gloss is provided.

4. A process for the manufacture of machine glazed type paper comprising the steps of forming a base sheet having a basis Weight of between about 15 pounds per ream and about 120 pounds per ream and having an apparent density of less than about 1 1 pounds per ream per mil of thickness, levelling at least one side of said base sheet, drying the base sheet to finished sheet dryness '7 to thereby maintain the leveled surface, preparing an aqueous mixture including a hydrophilic colloid which mixture provides a transparent film, said aqueous mixture having a viscosity of between about 200 centipoises and 1500 centipoises, setting said colloid on the levelled surface of said base sheet without substantial penetration of said base sheet, said hydrophilic colloid mixture having water holding properties higher than about 3 seconds, and drying the combined sheet with the colloid contacting a smooth dryer surf-ace whereby machine glazed paper having improved gloss is provided.

5. A process for the manufacture of machine glazed type paper comprising the steps of forming a base sheet having a basis weight of between about 15 pounds per ream and about 120 pounds per ream and having an apparent density of less than about 11 pounds per ream per mil of thickness, levelling at least one side of said base sheet, said base sheet being dried to substantial normal sheet dryness to thereby maintain the leveled surface, preparing an aqueous pigment-free mixture including a hydrophi-lic colloid which mixture provides a transparent film, said base sheet having glossy surface, said aqueous mixture having a viscosity of between about 200 centipoises and 1500 centipoises, setting said colloid on the levelled surface of said base sheet without substantial penetration of said base sheet, said hydrophilic colloid mixture having water holding properties higher than about 3 seconds, and drying the combined sheet with the colloid contacting a smooth dryer surface whereby machine glazed paper with improved gloss is provided.

6. A process for the manufacture of machine glazed type paper comprising the steps of forming a base sheet having a basis weight of between about 15 pounds per ream and about 120 pounds per ream and having an apparent density of less than about 11 pounds per ream per mil of thickness, levelling one side of said base sheet, said base sheet being dried to substantial normal sheet dryness to thereby maintain the leveled surface, preparing an aqueous pigment-free mixture including a hydrophilic colloid which mixturerprovides a. transparent film, said aqueous mixture having a viscosity of between about 200 centipoises and 1500 centipoises, setting said colloid on the levelledsurface of said base sheet without substantial penetrationoi said base sheet, said hydrophilic colloid mixture having water holding properties higher than about 3 seconds, and drying the combined sheet with the colloid contacting a smooth dryer surface whereby machine glazed paper having improved gloss is provided.

7. A process for the manufacture of machine glazed type paper comprising the steps of forming a base sheet having a basis weight of between about 15 pounds per team and about pounds per ream and having an apparent density of less than about 11 pounds per ream per mil of thickness, levelling at least one side of said base sheet to provide a gloss of at least 10 points, said base sheet being dried to substantial normal sheet dryness to thereby maintain the leveled surface, preparing an aque: ous pigment-free mixture including a hydrophilic colloid which mixture provides a transparent film, said aqueous mixture having a viscosity of between about 200 centipoises and 1500 centipoises, said hydrophilic colloid haviug a water holding capacity of at least about three seconds and comprising carboxy methyl cellulose, setting said colloid on the levelled surface of said base sheet without substantial penetration of said base sheet, and drying the combined sheet with the colloid contacting a smooth dryer surface, whereby machine glazed paper having an improved gloss is provided.

References Cited in the file of this patent UNITED STATES PATENTS 1,753,565 Frank Apr. 8, 1930 1,992,996 Dodge Mar. 5, 1935 2,184,312 Merrill Dec. 26, 1939 2,227,494 Gold Jan. 7, 1941 2,313,491 Adrian Mar. 9, 1943 2,633,430 Kellgren Mar. 31, 1953 2,635,972 Azorloza et a1. Apr. 21, 1953 2,656,286 Fisher Oct. 20, 1953 2,711,156 Bauling June 21, 1955 2,930,106 Wrotnowski Mar. 29, 1960 FOREIGN PATENTS 297,098 Great Britain Aug. 8, 1929

Claims

1. A PROCESS FOR THE MANUFACTURE OF MACHINE GLAZED TYPE PAPER COMPRISING THE STEPS OF FORMING A BASE SHEET HAVING AN APPARENT DENSITY OF LESS THAN ABOUT 11 POUNDS PER REAM PER MIL OF THICKNESS, SAID BASE SHEET BEING LEVELED AND HAVING A GLOSSY SURFACE, SAID BASE SHEET BEING DRIED TO SUBSTANTIAL NORMAL SHEET DRYNESS TO THEREBY MAINTAIN THE LEVELED SURFACE, PREPARING AN AQUEOUS MIXTURE INCLUDING A HYDROPHILIC COOLOID WHICH MIXTURE PROVIDES A TRANSPARENT FILM, SAID HYDROPHILLIC COLLOID MIXTURE HAVING WATER HOLDING PROPERTIES HIGHER THAN ABOUT 3 SECONDS, SETTING SAID COLLOID ON THE SAID GLOSSY SURFACE OF SAID BASE SHEET WITHOUT SUBSTANTIAL PENETRATION OF SAID BASE SHEET, AND DRYING THE COMBINED SHEET WITH THE COLLOID CONTACTING A SMOOTH DRIER SURFACE WHEREBY MACHINE GLAZED PAPER HAVING IMPROVED GLOSS IS PROVIDED.