US3416943A - Coating of paper and the like - Google Patents

Description

Dec. 17, 1968 N. O. CLARK ET L COATING OF PAPER AND THE LIKE 2 sheets-sheet 1' Filed April 29. 1965 FIGJ De c.17, l968 Filed April 29, 1965 N. O. CLARK ET A.-

COATING OF PAPER AND THE LIKE 2 Sh e'e ts -Sheet 2 United States Patent 3,416,943 COATING OF PAPER AND THE LIKE Norman Owen Clark and William Windle. Cornwall. England, assignors to English Clays Lovering Pochin & Company Limited, Cornwall, England, a British company Filed Apr. 29, 1965, Ser. No. 451.877 Claims priority, application Great Britain, May 4, 1964, 18,510/64 Claims. (Cl. 117-44) ABSTRACT OF THE DISCLOSURE An apparatus for coating sample sheet material comprises a backing roll for a sample sheet which is rotated to produce a peripheral speed equal to the linear speed at which the sheet material will travel in a full scale coating apparatus. A coating head with a reservoir for a coating composition and a flexible blade for applying the coating composition to a sample sheet on the backing roll moves parallel to the axis of rotation of the backing roll with the blade in contact with the sheet material in such a manner that a sample sheet material mounted on the backing roll is coated with a coating composition in the form of a helical strip of coated sheet material having uncoated gaps left between successive turns of said helical strip.

This invention relates to apparatus for, and a method of, coating paper and like fibrous sheet materials.

It is known to apply coatings to paper and similar sheet materials for a numberof purposes, for example to increase the gloss, smoothness. opacity and brightness of the material, or to hide surface irregularities thereof, and in particular to improve the surface of the material so that it is capable of taking print in the best possible manner.

Such coatings generally consist of pigment bound with an adhesive. The pigment which is used is principally kaolin or china clay, but alternatively others are used such as calcium carbonate, calcium silicate. satin white, and titanium dioxide. The adhesive may be a natural protcin such as casein or soya, animal glue, starch, or a synthetic adhesive such as styrene butadiene, acrylonitrile or polyvinyl acetate. These pigments and adhesives may be used as desired in a number of combinations, and other additives may also be employed in the coatings. The coatings may be applied in one or more layers.

The apparatus presently used for applying the coatings are of relatively high capital cost. Furthermore they are costly to operate during the initial starting-up period during which the working of the apparatus is investigated to ascertain the optimum conditions for operation using any particular machine, sheet material, and coating composition. In a similar manner, the apparatus is expensive to operate for the purpose of obtaining experimental data when designing new apparatus.

Hitherto, for experimental purposes, a small apparatus has been used, this apparatus being essentially a scaleddown version of production apparatus. Such a scaleddown apparatus may have disadvantages, especiallywith regard to interpretation of results obtained therewith. In production apparatus, a blade is often used to spread the coating composition, and such blade coating machines operate at high speed. A web of paper or the like sheet material may be run through the machine at a speed of between 1500 and 3000 feet per minute, and such high speeds are difficult to attain in a scaled-down apparatus. Since the performance of a blade coating machine is dependent partially upon the speed at which the machine Patented Dec. 17, 1968 ICC is run, the results obtained with a scaled-down apparatus may not be reliable. On the other hand, if full-size or scaled-down conventional apparatus is run at a high speed, relatively large quantities of sheet material and coating composition are necessary for a test, with the additional, consequential, problem that a large quantity of coated sheet material needs to be dried before laboratory testing. Laboratory testing is, however, generally carried out on small samples of material so that much wastage may occur.

It is an object of the invention to provide apparatus and a method for the experimental coating of paper and like sheet materials for test purposes under conditions closely resembling those which prevail during the coating of sheet materials on a large scale.

According to one aspect of the present invention, there is provided for coating sheet material, the apparatus comprising a rotatable backing roll upon which a sample of sheet material may be mounted to form a cylinder. a coating head including a blade and a reservoir for reception of coating composition. and means for enabling the coating head to be moved in operation parallel to the axis of rotation of the backing roll and in contact with the sheet material mounted thereon whilst the backing roll is rotated, whereby a helical strip of sheet material may be coated.

According to an other aspect of the present invention, there is provided a method of coating sheet material, the method of comprising rotating the sheet material in the form of a cylinder about the axis of the cylinder and applying a coating to the sheet material by a coating head loaded with coating composition, the head being moved parallel to the axis of the cylinder whilst the latter is rotated, thereby applying the coating composition to a helical strip portion of the cylinder of sheet material.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made by way of example to the accompanyin g drawings in which:

FIGURE 1 shows a general perspective view of apparatus for coating sheet material,

FIGURE 2 is a perspective view of part of the apparatus, and

FIGURE 3 is a diagrammatic elevation illustrating the operation of the apparatus.

The apparatus shown in FIGURE 1 comprises a frame 1 upon which are mounted two aligned bearing blocks 2, only one of which may be seen in FIGURE 1. An axle 3 for a rubber-covered backing roll 4 is mounted for rotation in the bearing blocks 2. The backing roll 4 may be driven in the direction indicated by arrow R by an electric motor 5 through variable speed gearing 6, pulleys and a belt 7. A carriageway comprising two parallel bars 8 is mounted on the frame 1 so as to extend parallel to the horizontal axis of the axle 3 and at a level slightly below such axis.

Movably mounted by way of bobbin-shaped rollers 9 on the bars 8 is a coating head indicatedgenerally at 10. The coating head 10 is movable along the carriageway with the aid of a hydraulic cylinder 11 and ram 12, the cylinder 11 being mounted on the frame through the intermediary of a bracket 11a. Power for the hydraulic cylinder and ram may be supplied from a hydraulic pump 13 mounted on the base of the frame 1 of the apparatus. Passage of hydraulic fluid from the pump 13 to the cylinder 11 is by way of pipes (such as the pipe ilb in FIGURE 2) in known manner, and may be regulated by a control valve 14.

The construction and arrangement of the coating head 10 are more fully illustrated in FIGURE 2. A platform is carried by the rollers 9 and has mounted thereon two side pieces 16 between which is carried a blade support 17. A

curved blade 18 is clamped in known manner to the bot- 3 tom of the blade support 17. The blade is of spring steel of 0.2 to 0.4 mm. thickness, and comprises essentially a very short portion of a conventional coatingblade so that the vertical dimensions and configuration of the blade are conventional, whereas the width is greatly reduced. The backing roll 4 is also of conventional dimensions, and may be 2 feet (60 cm.) in diameter and 3 feet (90 cm.) in length, whereas the blade 18 is only 3 or 4 inches in length, say 3 to 4 inches (about 8 to 10 cm.). A coating chamber 19 is formed by the blade 18 and two extentions 16a to the side pieces 16, such extension being curved to accommodate the adjacent arc of the backing roll 4. The inner walls of the coating chamber are electroplated to resist chemical attack. The extensions 160 forming the sides of the chamber 19 are fitted with felt edge seals 20. The blade 18 may be adjusted on a slider 21 by a toggle arm 22 in a direction towards or away from the backing roll. Adjusting means (not shown) are also provided in known manner for varying the angle of the blade 18 with respect to the surface of the backing roll 4, for varying the pressure of the blade on the backing roll, and for varying the vertical position of the blade with respect to the equator of the backing roll. A tray (not shown) is disposed below the backing roll and the coating head for receiving excess coating composition in operation.

For commencing operation, the coating head 10 is moved by conventional means away from the backing roll 4, and is then brought to one end of the backing roll. it will be assumed for the purpose of this description that the coating head 10 is brought to the left-hand end of the roll as seen in the figures. A sample of the sheet material which is to be coated, and which may be of paper, for example, is wrapped around the backing roll 4 and held in position by adhesive tape. The sample has a width approximately equal to the length of the backing roll 4, and the length of the sample is such that it may be wrapped completely around the backing roll, with or without a little overlap. Thus the sample of sheet material assumes the form of a circular cylinder. The backing roll 4 carrying the sample is rotated in the direction indicated by the arrow R with the coating head 10 retracted away from the surface of the backing roll until the latter has reached the desired speed of rotation. The peripheral speed of the backing roll and itssample may be equal to the linear speed of the web of paper or-like sheet material in a full-scale coating apparatus. The coating head 10 is moved towards the sample of sheet material on the backing roll and is adjusted as desired in respect of its position and its pressure on the sample.

When the various adjustments are complete, the appropriate coating composition is poured into the reservoir 19 and the coating head 10 is caused to traverse the backing roll 4 in the direction indicated by the arrow T by admitting hydraulic fiuid to the cylinder ll and thereby actuating the ram 12. At the end of the traverse of the coating head 10, the backing roll 4 is braked and the head 10 is removed from the surface of the sheet material on the stationary backing roll, thus dropping the unused coating composition into the tray (not shown) below the coating head 10. The speed of movement of the coating head 10 in the direction of the arrow T is controlled by the valve 14 in such a way as to produce a spiral path of coated paper on the sample, which path if desired may cover substantially the whole surface area of the sample. Thus, for a higher speed of rotation in the direction R, a higher speed of traverse in the direction T is required.

FIGURE 3 shows diagrammatically the product of complete traverse of the coating head 10. the coating head being shown in a position part way along the traverse.

The felt edge seals produce markings indicated at 23 in FIGURE 3. At the left-hand end of FIGURE 3, there is shown in broken lines an edge marking 230 which has been erased during the traverse. This marking 23a is one of the edge markings of an initial coated hoop 24 produced during the initial runningup period of the roll after the coating composition has been introduced into the reservoir 19 but before the traverse has occurred. After the traverse has been initiated, a helical path 25 is produced extending the length of the cylinder. of sheet material on the backing roll. A narrow gap 26 is left between each turn of the helix in the product shown, but this gap may be removed if desired by suitable adjustment of the control 14. At the end of the helical path, the coating head 10 is brought to a halt with the backing roll still rotating so as to produce a coated finishing hoop 27, thereby erasing the final part of the helical path. It will be seen that, apart from the ends of cylinder, the sheet material is coated with only one coat of composition and may be coated at a speed comparable with that of production apparatus without producing a large quantity of coated material. The helical path 25 is disposed at an angle A of only about 2% to the direction of motion R of the sample of sheet material, so that the departure from truly linear coating is negligible. It is found in practice that thereis no interference with the coating results, by virtue of the sideways movement of the coating head 10, if the length of the blade 18 is about one-tenth of the length of the backing roll 4, as

- described above. However, if desired the blade 18 may be longer, being up to about one-quarter or one-third of the length of the backing roll 4, or may be even shorter than one-tenth of this length.

After the coating head 10 has been withdrawn from the sheet material, the latter is dried. This may be done either in situ, for example by radiant heat, or may be done by removing the sample from the backing roll and drying in a drying chamber, with for example hot air. Since only a small quantity of coating composition is used on each sample, relatively little expenditure of heat energy is involved in the drying process. After drying, the sample is cut into strips for examination.

It will be appreciated that a number of modifications may be made to the apparatus described above. For example, the carriageway may be replaced by a lathe carriage for the coating head 10. if desired, a mirror (not shown) may be disposed at a suitable angle above the coating head 10 so that an operatormay be able to study the conditions prevailing within the reservoir 19. In this way the turbulence of the coating composition may be observed during operation.

We claim:

1. An apparatus, for coating sample sheet material, which comprises:

a rotatable backing roll upon which a sample of sheet material to be coated may be mounted to form a cylinder; 4 1 i first drive means for rotating said rotatable backing roll at a specific peripheral speed equal to a linear speed at which said sheet material will travel in a full scale coating apparatus;

a coating-head including a flexible blade having an edge which extends substantially parallel to the axis of rotation of said backing roll and having an operative length not more than one-third the operative length of said rotatable backing roll, and a reservoir for reception of a coating composition; and

a second drive means for moving said coating-head parallel to said axis of rotation of the backing roll with said blade in contact with the sheet material mounted thereon while the backing roll is rotated at said specific peripheral speed in a manner such that a-sample of sheet material mounted upon the backing roll may be coated with a coating composition to form a helical strip of coated sheet material having uncoated gaps left between successive turns of said helical strip.

2. An apparatus, for coating sample sheet material,

which comprises:

a rotatable backing roll upon whicha sample of sheet 6 material to be coated may be mounted to form a 5. A method of coating sheet material which comcylinder; prises the steps of: first drive means 'for rotating said rotatable backing roll mounting said sheet material on a rotatable backing at a specific peripheral speed equal to a linear speed roll to form a cylinder;

at which said sheet material will travel in a full scale 5 rotating said backing roll with the sheet material coating apparatus; mounted thereon at a specific peripheral speed equal a coating head mounted on rails and including a fiexto a linear speed at which said sheet material will ible blade of spring steel, which is 0.2 to 0.4 millitravel in a full scale coating machine;

meters thick and the edge of which extends substanapplying a coating composition to said sheet material tially parallel to the axis of rotation of said backing 10 from a coating-head loaded with a coating comporoll and has an operative length not more than onesition and including a flexible blade; having an edge third the length of said rotatable backing roll, and which extends substantially parallel to the axis of a reservoir for reception of coating composition; and rotation of said backing roll and having an operative length not more than one-third the operative length of said rotatable backing roll, and a reservoir for said coating composition; and moving said coating-head parallel to the axis of rotation of the backing roll, while the latter is rotated,

second drive means including a hydraulic rarn for enabling the coating-head to be moved in operation along said rails parallel to the axis of rotation of said backing roll with said blade in contact with the sheet material mounted thereon while said backing roll is rotated at said s cific ri heral speed in a manner such that a s iple heet material mounted of coawd having i gaps left upon said backing to" may bc coatcd with a coating between successive turns of said helical strip. composition to form a helical strip of coated sheet References Cited material having uncoated gaps left between succes- UNITED STATES PATENTS sive turns of said helical strip. I 3. Apparatus according to claim 2, wherein the operai'g gi g2 tive length of the edge of the flexible blade of spring steel 2235'250 3/1941 ggg 'zg 7 09 is approximately one-tenth the length of the-backing roll. 3.162082 2/1965 Krikorian 118413 4. An apparatus according to claim 2, wherein the coating-head is mounted on the rails through the inter- ALFRED L. LEAVI'IT, Rrimary Examiner. mediary of a slide which may be moved in a direction R L BROWDY (m-am x substantially perpendicular to the axis of rotation of the backing roll, whereby said flexible blade may be moved towards or away from said backing roll. 117-152, 118-409, 413

at a speed such that there is formed a helical strip

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