Apparatus and method for providing a coating on a substrate

Abstract

 The invention provides for a printing press (10) having a coating smoothing station (28) at an inline position along a processing line for smoothing a coating (42) applied to a substrate (12). The coating (42) is applied at a printing station (20-26) and the smoothing station (28) effects smoothing of the coating (42) by way of roller means (48) without interfering with converting stations (30-32) located downstream and arranged to punch, slit or perforate the coated substrate.

Description

[0001] In the field of media products, it is common practice to provide recording materials or receiver stocks which include a substrate and a coating thereon. The coating enables data in the form of images to be transferred from a transfer medium and to be printed on the recording material or receiver stock to provide sharp and intense characters.

[0002] A common use of a coating applied to a substrate is in the field of thermal printing wherein a thermal print head causes transfer of coating material from a thermal transfer ribbon onto the receiving medium or stock. In this regard, it is extremely important that the transferred images assume a smooth surface so as not to cause smearing of the images when undergoing various processing operations.

[0003] In the past, attempts have been made to provide receiver stocks with good thermal transfer printing characteristics. In this regard, a coated receiver stock was used to obtain sharp and complete characters. One or more coatings were applied to a surface of the substrate in an attempt to make the surface smooth so that sharp and intense images could be thermally transferred onto the receiver stock from a thermal transfer ink ribbon. In the past, the coating and the smoothing of the coating had to be accomplished as one or more operations separate from the finishing and converting operations such as die cutting punching and slitting.

[0004] The receiver stocks were commonly coated with compositions which included clay or carbonate, a binder and other additives. For example, one knowncomposition consisted essentially of 75% clay pigment and 25% latex binder. However, a problem with these previous coatings was that the data printed on the receiver stock tended to smear because the surface of the receiver stock was not sufficiently absorbent to receive the thermally transferred ink from the thermal transfer ribbon. Another problem with such receiving stocks having a rough or non-smooth surface was that the stocks had to be used in printers that kept the thermally transferred ink in a molten state long enough for the ink to "fill in" or cover the rough surface. Thus, known coatings have a smoothness which is disadvantageously restricted and restrictive.

[0005] In the preparation of the recording material or receiving stock, it is common practice to use a printing press wherein a web of paper is moved past a plurality of processing stations. Such processing stations may include printing stations, coating application stations, and converting stations at which die cutting, punching, slitting, or perforating operations are performed in an in-line process.

[0006] U.S. Patent No. 4,581,278, discloses an imprinting device having a roller for a heat transfer laminate which is formed by a carrier and a coating, U.S. Patent No. 4,639,751, discloses an image-receiving sheet having a substrate and a coating comprising non-plate-shaped inorganic pigment and a binder and U.S. Patent No. 4,673,618, discloses a thermal recording medium having a coating which is homogeneous and smooth.

[0007] It is an object of the present invention to provide a substrate with a coating of improved smoothness and, advantageously, to provide a method and apparatus in which the smoothing operation can be performed in one pass along the process line of a printing press.

[0008] According to one aspect of the present invention, there is provided apparatus for coating a substrate comprising a printing press having at least one printing station for applying a coating to said substrate, at least one converting station located in series with said at least one printing station in a processing line, and means for transporting said substrate along said processing line, characterized by a smoothing station having roller means located downstream of said at least one printing station for engaging said coating and said substrate and adjustment means for selectively applying pressure thereto having regard to the thickness of the coating and the substrate.

[0009] According to another aspect of the present invention, there is provided a method of providing a coating on a substrate, comprising passing laid substrate through printing press means arranged to apply said coating to said substrate, characterized by applying pressure to said coating by way of roller means so as to smooth the surface of said coating.

[0010] The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings in which:

Fig. 1 is a side elevational view in diagrammatic form of a printing press embodying the present invention;

Fig. 2 is a side elevational view of certain members of the printing press utilized for smoothing the coating on a substrate; and

Fig. 3 is a view taken along the line 3-3 of Fig. 2.

[0011] The present invention is directed to a method for improving the smoothness of a coating on receiver stock. An example of a coating for which the apparatus and method of the present invention is applicable is disclosed in copending European patent application 92304089.3.

[0012] Referring now to Fig. 1 there is shown a side elevational view in diagrammatic form of a printing press 10 wherein a web 12 of paper or like media is unwound from a mill roll 14 supported on an unwind stand 15. The web 12 is trained around a compensating tension control unit 16 which includes rollers positioned in appropriate positions for controlling the tension in the web. The web 12 moves past an edge guide sensing unit 18 and then through a plurality of print stations 20, 22, 24 and 26, as shown by the arrows, for printing images or data on the web.

[0013] The web 12 then continues through a plurality of diecut stations or converting stations 28, 30 and 32 which may punch, slit or perforate the web 12 at specific locations or positions on the web. Waste material of the web, as a result of the converting operations, is trained around a matrix roll 34 and the finished product is then trained onto a rewind roll 36. The waste material of the web 12, after the converting operations, is shown as a dash line 37. The press 10 also includes a vertical perforating station 38 and a sheeter station 40. While the web 12 is shown as being trained around the several rolls of the vertical perforating station 38 and the sheeter station 40, the operations performed at either one or both of these stations are dependent upon the desired finished product. For example, it may be desirable to sheet the web 12 and rewind the finished product on the roll 36. The press 10 is manufactured as Model 650 by Webtron Corporation, Fort Lauderdale, Florida.

[0014] While the diecut station 28 is normally utilized for a diecut operation, such station 28 is modified to provide apparatus for effecting a web smoothing operation. Figs. 2 and 3 illustrate the mechanism and arrangement of the parts for the coating smoothing station.

[0015] As seen in Fig. 2, the web 12 with a coating 42 (shown with a rough surface) is driven over a base roll 44 journaled on a shaft 46 and under a smoothing roll 48 journaled on a shaft 50. A pressure transfer roll 52 (shown schematically as compared with Fig.3) is positioned above the smoothing roll 48 and has a pair of roller - type bearings 54 and 56 (Fig. 3) engageable with the surface of the smoothing roll 48 at the ends thereof. The roller bearings 54 and 56 are supported on respective shafts 58 and 60. A base roll gear 62 and a smoothing roll gear 64 are positioned to mesh for driving the base roll 44 and the smoothing roll 48 in the appropriate directions of rotation for advancing the web 12 in the direction, as shown by the arrow 66 in Fig. 2.

[0016] A pressure adjusting mechanism 70 (Fig. 2) is provided for bearing on the pressure transfer roll 52 and therethrough onto the smoothing roll 48 for adjusting the pressure for smoothing the coating 42 on the web 12. The surface of the smoothing roll (48) is particularly adapted for smoothing the coated paper media and, as such, has a smooth surface itself. The desired or required pressure is dependent upon the thickness of the substrate or web 12, the flow properties of the coating 42 and the degree of desired smoothness of the coating.

[0017] The pressure adjusting mechanism 70 includes a pair of screws 72 and 74 (Fig. 3) having shanks 76 and 78 extending through and threadedly engageable with a bridge 80 positioned over the pressure transfer roll 52. A pair of knobs 82 and 84 are threadedly engageable with the shanks 76 and 78 of the screws 72 and 74 for holding or locking a precise position of the screws so as to maintain the desired or required pressure.

[0018] A number of test examples are provided in the practice of the invention for establishing the results of a smooth coating 90 on the web 12, as seen in Fig. 2. The web 12 included a 50 pound electronic data processing (EDP) receiver stock which was coated by means of a flexographic process to a coated weight of 3 pounds per 3300 square feet (1.36 kg per 306.57 square meters) of surface. Several coating compositions were used and the process was exercised both with and without in-line press smoothing.

[0019] The coatings used in the process were identified as:

Coating A --

a commercial vinyl primer

Coating B --

a commercial print varnish

Coating C --

a vinyl acetate latex formulation

Coating D --

an 80% pigment/20% latex formulation

   The coated stocks were evaluated for smoothness by using a Parker Printsurf analyzer with a soft backing disc and a 20 kilogram clamping pressure. For the following Printsurf readings, the smoother the sheet, the lower the number.

[0020] Smoothness results were as follows:

	Printsurf Readings
	Stock (as is)	Press Smoothed Stock
Coating A	4.88	3.87
Coating B	4.86	3.52
Coating C	4.91	4.05
Coating D	3.89	3.23

[0021] It is thus seen that herein shown and described is a method for smoothing a coating on a web in-line on a printing press while maintaining subsequent converting operations. The coating and/or inks are applied at the normal print stations and the web is trained through a nip at the location which is normally occupied by the first die-cut station of the printing press. The nip is produced by inserting a solid roll identified as the smoothing roll 48, in place of a die and then using the pressure adjusting mechanism 70 for applying pressure and positioning the roll 48 in contact with the coating 42 on the web 12. The pressure applied at the nip is controlled by the mechanism 70 which adjusts how tight the roll is brought into contact with the coating 42 on the web 12. The pressure applied at the nip allows the above-described smoothing method to be used with various types of webs or substrates which include a tag stock wherein higher pressure levels can be applied, as well as pressure sensitive label stock wherein lower levels of pressure can be applied so as not to damage the facestock/adhesive/liner interfaces. After the web 12 passes through the nip at the coating smoothing station, the web 12 with the smooth coating 90 is driven through the die-cutting stations for the normal or traditional converting operations. This smoothing operation of course, is different from a calendering operation wherein cloth or paper or like media are pressed between rollers for providing a gloss to the media.

[0022] It is thus seen that herein shown and described is a method or process for improving the smoothness of a coating on a substrate or web. The method employs a printing press and includes a pressure adjusted roller for smoothing the applied coating in an in-line operation without interfering with subsequent converting operations.

Claims

1. Apparatus for coating a substrate (12) comprising a printing press (10) having at least one printing station (20-26) for applying a coating (42) to said substrate (12), at least one converting station (30-32) located in series with said at least one printing station (20-26) in a processing line, and means for transporting said substrate (12) along said processing line, characterized by a smoothing station (28) having roller means (44-48) located downstream of said at least one printing station (20-26) for engaging said coating (42) and said substrate (12) and adjustment means (72-78) for selectively applying pressure thereto having regard to the thickness of the coating (42) and the substrate (12).

2. Apparatus according to claim 1,
characterized in that said printing press (10) includes a plurality of printing stations (20-26) and a plurality of converting stations (28-32) and said roller means (44-48) is located at one of said converting stations (28).

3. Apparatus according to claim 1 or 2,
characterized in that said smoothing station (28) includes base roller means (44) fixed in position within said apparatus and smoothing roller means (48) facing said base roller (44) means and mounted so as to be movable relative thereto so as to vary said pressure.

4. Apparatus according to claim 3,
characterized by means for adjusting the pressure applied by said smoothing roller means (48) on said substrate (12) and said coating (42).

5. Apparatus according to claim 4,
characterized in that said smoothing roller means (48), comprises a solid roller and said pressure adjusting means includes a roller member (52) having bearing means (54;56) engageable with said solid roller (48).

6. A method of providing a coating (42) on a substrate (12), comprising passing said substrate (12) through printing press means (10) arranged to apply said coating (42) to said substrate (12), characterized by applying pressure to said coating (42) by way of roller means (48) so as to smooth the surface of said coating (42).

7. A method according to claim 6,
characterized in that said pressure is varied having regard to the thickness of said coating and substrate (12).

8. A method according to claim 6 or 7,
characterized in that the coated substrate (12) is finally transported to converting means (30-32) in said printing press means (10).

Drawing