WO1980000928A1 - Method and apparatus for the double-sided coating of a moving web of material,preferably a paper web - Google Patents

Method and apparatus for the double-sided coating of a moving web of material,preferably a paper web Download PDF

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Publication number
WO1980000928A1
WO1980000928A1 PCT/SE1979/000226 SE7900226W WO8000928A1 WO 1980000928 A1 WO1980000928 A1 WO 1980000928A1 SE 7900226 W SE7900226 W SE 7900226W WO 8000928 A1 WO8000928 A1 WO 8000928A1
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WO
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Application
Patent type
Prior art keywords
web
coating
surface
roller
characterised
Prior art date
Application number
PCT/SE1979/000226
Other languages
French (fr)
Inventor
H Wallsten
Original Assignee
H Wallsten
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Filing date
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Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B05SPRAYING OR ATOMISING IN GENERAL; APPLYING LIQUIDS OR OTHER FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05CAPPARATUS FOR APPLYING LIQUIDS OR OTHER FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05C9/00Apparatus or plant for applying liquid or other fluent material to surfaces by means not covered by any preceding group, or in which the means of applying the liquid or other fluent material is not important
    • B05C9/04Apparatus or plant for applying liquid or other fluent material to surfaces by means not covered by any preceding group, or in which the means of applying the liquid or other fluent material is not important for applying liquid or other fluent material to opposite sides of the work

Abstract

Method and apparatus for double-sided coating of a moving web (1) of material with an aqueous coating composition. At least two coating stations are used for the purpose, spaced from each other and located one after the other in the direction of movement of the web, each station comprising a support roller (2, 6) and a coating means (3, 7), one side of the web (1) being brought into abutment with the support roller (2) in the first coating station and the other side of the web (1) being supplied with said coating composition, whereas in the second coating station the side of the web (1) which is already coated is brought into abutment with the support roller (6) and its uncoated side is provided with said coating composition. According to the invention due to the controlled, separate supply of a moist atmosphere on at least a part of the surface of the support roller in the second coating station which is temporarily not in contact with the paper web, a thin film of water is formed on said surface wholly or partly by condensation.

Description

Method and apparatus for the double-sided coating of a moving web of material, preferably a paper web.

The present invention relates to a method and an apparatus four double-sided coating of a moving web of material with an aqueous coating composition in at least two coating stations arranged one after the other in the direction of travel of the web and spaced from each other, each comprising a support roller and a coating means, one side . of the web being brought into abutment with the support roller in the first coating station and the other side of the web being supplied with said coating composition, whereas in the second coating station the side of the web already coated is' brought into abutment with the support roller and its uncoated side is coated with said coating composition.

It is already known to use the blade coating technique for coating, for instance, both sides of a paper web. In the case of blade coating and other similar methods of coat¬ ing, a rotating roller is used as support roller in a blade coating station. The paper web passes the coating station, whereupon the side of the paper web facing away from the roller is coated with a coating composition by means of a coating means, the coating compound being spread evenly by a flexible blade. Since such arrange- ments require a support roller, the paper web thus coated on one side is dried before the other side of the web is coated in a second, similar coating station with support roller and blade to prevent coating compound from being deposited on the second roller. Since, therefore, such plants- require two separate coating stations with inter¬ mediate drying, they take up a considerable amount of space and are also extremely complicated in structure.

Recent new developments of interest now aim at effecting

OMPI IPO simultaneous coating of both sides of a paper web using, for instance two opposing blades or one blade acting against a support roller. Such arrangements have the advantage that they require little space and are usually easy to serve as well as providing simultaneous impregna¬ tion through the liquid phase of the coating composition. However, one drawback is that it is difficult to set dif¬ ferent quantities of coating composition on each side of the weh if desired.

It has also been proposed (Swedish Patent No. 396,558) to arrange two separate blade coating stations in order to coat both sides of a web of material with an aqueous coating composition, these stations each being provided with a support roller in such a way that no intermediate drying is required. "According to the method proposed it is possible by pronounced cooling of the support roller in the second coating station to separate the layer of coating compound from the support roller in a film of con¬ densate produced on the cold surface of the roller. The film of condensate is produced due to the difference in temperature between the cooled surface of the support rol¬ ler and the hot layer of coating compound and is produced mainly by the water existing in said layer. When coating the web with thick compositions it is desirable to increas the difference in temperature between the cooled support roller and the warmer layer of composition by means of infrared radiation or by heating the coating composition, in some other way. The water vaporized from the composi¬ tion by the heating process condenses on the cooled sur- face of the support roller and also contributes to pro¬ ducing the film of condensate. The cooled support roller consists suitably of steel or metal and is cooled by means of a coolant supplied to.the roller through pipes.

However, there are several disadvantages associated with the method just described. When paper is coated with a

O .WI water dispersion the water is absorbed into the web and must be removed by drying after the coating process, as described above.- In all types of coating this is done by supplying heat in various drying arrangements. However, according to the method now described the subsequent drying- process is offset since condensation is effected on the surface of the second roller only by a pronounced cooling of the roller so that a temperature difference is obtained between the warmer coated paper web entering and the chilled roller surface. When coating in paper mills, for instance, the paper web has often a certain over tem¬ perature and the coating compound is often hot in order to improve penetration, but also to facilitate the sub¬ sequent drying. By keeping the roller surface according to the known method well cooled, the heat will be conduct¬ ed away from the coated paper web. This means that even more thermal energy is required in the subsequent drying process, which is uneconomical and may limit the capacity since the rate of travel of the web must be reduced if the drying capacity is to suffice. In certain cases, therefore, it may be necessary to compensate for this cooling of the paper web by an increase in the capacity of the subsequent cooling equipment.

This known method also has other drawbacks. As mentioned, in certain cases extra heating of the paper web is necessa¬ ry during its passage from the first to the second station by means of infrared radiation, for instance. Such an arrangement is space-consuming and entails other con¬ siderable drawbacks as well. As is known, the paper web always swells to a certain extent when coated with a coating composition, due to the water absorption of the fibre material. This means that when the paper web has passed the first coating station in accordance with the known technique, it acquires longitudinal wrinkles caused by the swelling. With traditional coating means using two

OMPI WIPO separate stations with drying in between, this does not usually constitute any problem since the paper web is dried and smoothed before it passes the second coating station. In the arrangement described earlier for coating both sides of the paper, the formation of wrinkles is no problem either. However, according to the known method described last, without any intermediate drying, diffi¬ culties arise since the wrinkles appearing when the paper absorbs moisture while being coated in the first station must be smoothed out" before the web encounters the suppor roller in the second station in order to avoid uneven coating here. In this case a number of guide rollers, kno as clip tentering rollers, must be used which are spe¬ cially designed to smooth out the paper web by stretching it laterally. This constitutes a complication and, parti¬ cularly with relatively thin paper and high web speeds, it is difficult to ensure reliable operation, especially since the paper web is wet and fragile after being coated in the first station. Furthermore deposits often occur on the intermediate rollers.

Another disadvantage inherent in this known technique is that the support roller in the second coating station mus be made of a material having good thermal conductivity, such as steel. It has long been well known that steel is not a suitable material for the surface of a support roller in a blade coating station. It has been found that rubber rollers with a certain yield are preferable since they give a more uniform coating result, primarily becaus the elasticity of the roller contributes to smoothing out variations in the thickness of the paper web and thus. gives more uniform coating.

The object of the present invention, while eliminating the drawbacks and problems mentioned above, is to effect coating of both sides of a paper web with blades, for in-

O W stance, in two coating stations lying closely one after the other in the direction of travel of the web, each station comprising a support roller and a coating member with blades, for instance.

The invention solves the problems mentioned above accord¬ ing to the above described in that a controlled, separate supply of a moist, preferably warm atmosphere to at least a part of the surface of the support roller in the second coating station which is temporarily not in contact with the paper web, forms a thin film of water.

The surface of the roller may preferably he heated to a temperature exceeding the temperature of the web so that the web will be heated upon coming into contact with said surface.

In this manner the paper web is coated without being cooled down. Instead, the coating is performed in the se¬ cond coating station while heat is being supplied, which contributes to decreasing the energy consumption during the subsequent drying process and eliminates any need of extra drying capacity caused by the web being cooled down.

According to an alternative embodiment of the invention the surface of the roller in the second coating station is kept on such a temperature that a condensate film is maintained between this surface and the web laying against said surface.

By also eliminating the need for intermediate heating means in accordance with the invention, thus enabling the two support rollers to be placed so close together and with a straight stretch of web between so that there is no risk of wrinkles being formed in the web. No smoothing means are therefore required to eliminate the formation of wrinkles during transportation of the web between the first and second coating stations.

Another advantage with the present invention is that the surface of the support roller in the second coating sta- tion can be made of resilient rubber material having a yield which can be optimally adjusted to the resuire- ents of the blade coating technique.

Another advantage is gained since both the coating sta¬ tions together form an extremely compact, well-arranged and cheap unit. According to another embodiment of the invention the support rollers can easily be re-arranged- to form a size press for sizing or impregnating the paper web.

The invention also comprises an apparatus or a means for performing the method proposed, this means being substan¬ tially characterised in that two consecutive rollers are brought to assume such a position in relation to each other that the free stretch passed by the paper web between these support rollers is short enough . to allow the web to be passed without contact with support and/or guide rollers.

Other features of the invention will be revealed in the accompanying claims.

In the following the invention will be further described with reference to a number of embodiments shown in the drawings in which Figures 1 - 6 show schematically a number of different embodiments of the invention. According to a first principially embodiment and Figures 7 - 11 show schematically further embodiments princi- pially corresponding to those shown in Figures 1 - 5, but with the difference that the support rollers in the

^ OΕ WI second coating station are provided with means for supply and removal of heat.

Figure 1 illustrates one embodiment of the invention in which 1 designates a paper web to be treated by coating with a coating composition. 2 designates the support rol¬ ler in a first coating station, the coating means being designated 3 and comprising an application roller 4 and smoothing blade 5, all in accordance with known technique. The web travels in the direction of the arrows"A.

The paper web 1 thus coated on one side is caused to leave the support roller 2 and then passes with the coated side inwards partially around a support roller 6 consti¬ tuting the support roller in a second coating station, the coating means 7 here comprising an application roller 8 and a smoothing blade 9. The web is then carried further in the direction of the arrow A over a guide roller 10 to the subsequent drying process.

By means of a suitable member 11 a warm, moist atmosphere is supplied, for instance by blowing, to a suitable sec- tion of the roller surface 12 of the roller 6 which is not in contact with the web 1. The atmosphere applied by blowing, preferably consisting of hot, moist air, has a temperature exceeding the temperature of the coating layer on the web 1 leaving the first coating station and, due to the over-temperature and the water content, a controlled condensation of water vapour is obtained on the part of the surface of the roller 6 which is de¬ signated 12. Heat is liberated during the condensation process so that at least the outermost layer of the sur- face of the support roller 6 will be heated since the web 1 in the first coating station has a lower temperature than the surface layer of the roller surface 12 heated due to condensation and the paper web will take up heat from the roller surface. In balanced position the roller surface 12 will have a temperature prior to contact with the web which is higher than the temperature of the web, and after web contact, it will have at least the same temperature as the web. On average, therefore, the roller surface which have a temperature exceeding the tempera¬ ture of the paper web.

The water film prevents deposits of coating agent applied on the web in the first coating station, on the support roller 6 but at the same time the paper web 1 absorbs heat from the surface 12 of the support roller 6 which, as mentioned, is utilized in the subsequent drying pro¬ cess.

As mentioned, it has been found that according to the in¬ vention rubber rollers can be used as supportrollers even in the second co-ating station, which is a great advantage.

The.means 11 mentioned in Figure 1 for the supply of hot, moist atmosphere is only shown schematically and consists of components known per se for processing air, for in- stance, such as means for heating the air, supplying moisture and forced blowing of the heated, moist air to¬ wards the roller surface.

The means also includes suitable control means, not shown, to enable optimal data on temperature, moisture content and air volume can be set and regulated.

A simple method of obtaining a constant and suitable film . of water is to control the adjustment of heat and moisture for instance, in relation to the temperature of the paper web and/or the coating composition. Starting with the temperature of the coating compound, the temperature of the web, the speed and so on, it is a simple matter to keep the water film at constant and op¬ timal values by means of suitable gauges and control means.

Figure 2 shows a second embodiment of the invention. The paper web is designated 1 here too, the support roller in a first coating station is designated 13 and the coating means 14. The support roller in the second coa¬ ting station is 15 and the blade coating means for the second support roller is 16. The blade coating station 16 is a puddle-type coater. Such a coater is well known and comprises a puddle of coating compound which is coated and smoothed out with the help of a downwardly directed blade pressing against the paper web.

The controlled, hot, moist atmosphere is blown on with a means designated 17. According to the embodiment in Fi¬ gure 2, the rollers 13 and 15 are placed extremely close together thus giving an extremely advantageous web passage with no risk of folds forming or abnormal strain on the paper web 1. This arrangement can also easily be altered so that it can be used as a size press, for in¬ stance. In this case a paper web 18 is guided - as shown by the broken lines - over -a guide- roller 19 between the rollers 13 and 15 which are pressed against each other and rotate in opposite directions. Traditional surface sizing with a starch solution, for instance, can thus be effected.

Figure 3 shows a third embodiment within the scope of the . invention. The paper web is again designated 1, the first coating means of puddle-type 20, the support roller for this 13 and a second coating means 20a. Hot, moist air is blown on by a means designated 17. The second coating means 20a also consists of a puddle-type coater, but the paper web 1 is bent in this case from the support roller 15 at an angle which is greater than the tangent through the point of contact of the blade on the surface of said roller. In this case too the two support rollers 13 and 15 are placed close together so that no intermediate equalizing roller is needed to prevent the formation of wrinkl s.

Figure 4 shows yet another embodiment according to the in vention. The paper web is designated 1 and passes over guide rollers 21 and 22 and is caused to pass around the support roller 13 in a first coating station having a blade coating means 14. The web is then passed on to the support roller 15 in a second coating station where a blade coating means of known type is designated 23. The paper web 1 then leaves the support roller 15 to pass between-two hot air driers 24 and 25. These may consist of airfoil driers, for instance, i.e. boxes provided with suitably blowing means through which hot, dry air flow to dry the paper web without contact. The means for blowing hot, moist air according to the invention has been designated 26. In this case the blowing means 26 is in communication with the hot air generator producing hot air for the boxes 24 and 25, which is not shown in the drawing. The hot air from the generator is, as mentioned, dry and an additional arrangement for moistening the hot, dry air is designated 27. This embodiment has the advantage that a common hot air source can be used both to heat the support roller 15 and for the subsequent con- tactless drying in the drying boxes 24 and 25.

According to the embodiments of the invention shown above a temperature difference shall be maintained between the surface of the support roller 15 and the paper web 1 coated in the first station so that by supplying hot, mois atmosphere on the surface of the roller 15 which is not in contact with the paper, the roller surface on average maintains a higher temperature than the coated paper web approaching the roller 15. In order to ensure good control so that the requisite temperature difference is 5 maintained the atmosphere should be set at suitable va¬ lues with respect to temperature, moisture content and volume. This can be done, for example, by performing a continuous temperature measurement on the coated paper web, which may be done without contact by means of an infra

10 radiation meter. One such means is designated 28 in Fi¬ gure 4. As mentioned earlier, in many cases it is suffi¬ cient for the temperature of the coating compound to control the adjustment of the hot, moist atmosphere. An¬ other method which gives extremely good control of the

15 process is for a temperature gauge measuring the surface temperature of the part of the roller not in contact with the paper to control the moisture content, temperature and volume of air blown on.

Figure 5 shows yet another embodiment of the invention.

20 The paper web has been designated 1 and passes the coating equipment in the direction of the arrows A. The web passes first a guide roller 21 and a support roller 13 pertaining to a first, lower coating station comprising a blade coa¬ ting station 14 of the type illustrated earlier. When the

25 side of the paper web 1 facing away from the support roller 13 has been coated with coating compound, it passes over a guide roller 29 and thereafter, with the coated side in, over the surface of a roller 15 constituting the support roller in a second coating station with a

30. blade coating means 23. The paper web then leaves the support roller 15 to pass between two hot air driers 24 and 25 to be dried without any contact.

The supply means for moist atmosphere to the surface of the support roller 15 is designated 30. In this case,

- SEX"

OMPI R l therefore, a guide roller 29 has been placed between the support rollers .13 and 15, . As mentioned previously, it is a great advantage is the guide roller between the two support rollers can be avoided and the risk of folds being formed on the type of paper liable to swell upon absorption of moisture and form folds can be avoided by placing the rollers close to each other as shown, for in¬ stance, in Figures 1, 2, 3 and 4. The embodiment in Fi¬ gure 5 with intermediate guide rollers 29 is suitable for less delicate paper such as paper with high surface weight or cardboard. In this case a greater distance between the two support rollers 13 and 15 can be accepted without risk of folds. In the means according to Figure 5 a larger space has been obtained between the coating means 14 and 23 which may be an advantage from the operating point of view, by placing the rollers further apart.

Figure 6 shows an embodiment of a supply means for hot, moist air against the support roller in the second coating station according to the invention. In this case the supp- ly means consists of a central container 31 extending across the paper web. The container is connected by pipes to a means for supplying hot, moist air under pressure. This connection is illustrated in the dotted circle 32. The air volume in the supply pipes can be regulated by dampers, for instance. Another method is to regulate the volume of air by regulating the speed of rotation of a fan. The container 31 has two parallel walls 33 and 34 forming a gap 35 directed towards the roller surface 36. The container 31 is surrounded by two box-shaped spaces 37 and 38, each with a gap 39 and 40, respectively sur¬ rounding the gap opening 35 on each side. Due to the over¬ pressure, hot moist air is forced in the direction of the arrows 41 towards the gap opening 35. The air meets the part of the roller surface 36 substantially opposite the gap opening 35. Since the quantity, moisture content and temperature of the air in the gap have been adjusted in accordance with the invention to the outer temperature of the roller surface 36, the air will be immediately condensed thereon, thus liberating heat. Most of the air will then flow in through the gaps 39 and 40 since a ' certain under-pressure is maintained in the spaces 37 and 3'8. This under-pressure is most easily achieved by allowing the spaces to communicate with the suction side of the fan mentioned earlier but not shown, which blows air into the container 31.

The method proposed in accordance with the above embodi¬ ments of the invention has also been tested in practice and these tests are described in detail in the two following examples.

In Example 1 an apparatus was used corresponding most closely to that described in Figure 1 and in Example 2 the apparatus corresponds to that shown in Figure 2.

OMPI

^Run Example 1 Example 2

Grade of paper Woodless printing Woodless printin paper paper

Mass per unit area, base paper 60 g/m^ 37 q/m

Diameter of support roller in second coa¬ ting station 750 mm 800 mm

Roller surface natural rubber natural rubber

Rubber hardness 75 P & J 75 P & J

Web temperature entering 45°C 40°C

Coating compound temperature 45°C 40°C

Web speed 300 m/min 500 m/min

COATING COMPOUND

Dryness content 60% 65%

Constituents kaolin, starch kaolin, starch latex

AIR BLOWN ON

Air speed 6 m/s 9 m/s

Dry thermometer temperature 8Q°C 95°C

Calculated moisture content 90% 95%

Average temperature of roller surface (estimated) 60°C 80°C

Shortest distance between support rollers (2 and 61 10 mm 0 mm

O The experiments described above show that a high standard of coating is obtained when use is made of the invention in accordance with the above examples. Experiments have also indicated that in many cases it is possible to operate with support rollers placed very close together which, as mentioned earlier, is a great advantage espe¬ cially with thin paper. If the nature of the paper and coating compound is such that an extra long time is re¬ quired for the liquid phase of the coating compound to penetrate the paper (dwell timel it may be necessary, however, to increase the distance between the rollers.

As a further example that the free length of web between the two rollers can be kept extremely short, the following may be mentioned. In a construction in accordance with Figure 1 the free length of web, i.e. the distance between the last point of contact on roller 13 and the first point of contact with the roller 15, was only 100 mm. In a means corresponding to that in Figure 2, the free web length was 0 since the paper web was in contact with the support rollers 13 and 15 during its entire transport through the coating equipment.

• In an equipment corresponding to that shown in Figure 4 the free web length of the paper was varied in a series of experiments and reached 1 m without there being any risk of wrinkles forming.

The moisture in the air blown on may consist partly of water vapour and partly of extremely fine, uniformly di¬ stributed water drops. If the air has a relatively high content of water vapour and little or no water drops, the film of water will be produced primarily through condensa¬ tion. In certain cases this may be preferable but if con¬ siderable quantities of water film are required for fast- running machines, vast quantities of heat will be liberated when the water vapour condenses on the roller surface, which may be a drawback. In other cases it may be more suitable for the water film to be achieved primarily by non-vaporized water, i.e. atomized drops of water. In the latter case, little heat is liberated when the film of water is formed, which in some cases may be an advantage. In other cases, however, it may be advisable for the mois¬ ture in the air blown on to produce the water film to consist of a mixture of water vapour and extremely fine water drops.

The device 11 shown in Figure 1 for the supply of hot, moist atmosphere is shown only schematically and may con¬ sist of conventional components for treating air, for in¬ stance, such as arrangements for heating the air, supply- ing moisture, means for forced blowing through nozzles or gaps onto the roller surface. Conventional moisturizing means can be used to enable a suitable combination of the moisture in the air to be reached in the form of atomized water drops and water vapour to suit the circumstances prevailing. One such suitable means is a humidifier con¬ sisting of nozzles atomizing water supplied to them. The nozzles are suitably placed in the top of the humidifier while the air, heated to suitable temperature, is caused to pass the humidifier in horizontal direction. A re- ceptacle is placed at the bottom of the humidifier to collect water. The device functions in such a way that the hot air supplies energy upon its passage through the humidifier so that at least some of the small drops of water are vaporized. Other drops of water remain in liquid form and the smallest are caught up by the air flow and distributed therein. Larger drops of water either fall to the bottom of the humidifier or can be removed in a spe¬ cial separator for water drops through which the moistened air flow passes after passing the humidifier. By a suitable choice of heating method, adjustment of the supply of moisture to the humidifier and adjustment of the air flow, this means enables the moist atmosphere to be adjusted to suit the temperature of the roller surface, web speed and other circumstances prevailing in the coating process.

The means permits a certain quantity of water to be applied in a controlled manner on the roller surface in the form of a thin film. If a slight or moderate generation of heat is desired the means is preferably set so that the con¬ tent of atomized water particles in liquid form is rela¬ tively high in relation to vaporized water. If it is desired that the water film be effected primarily by means of condensation, the means should be set so that all or most of the water supplied is vaporized in the humidi¬ fier. In the first case a relatively cool, moist film is obtained whereas in the latter case the film formed re¬ leases relatively great quantities of heat.

In certain cases it is preferable for a thin water film to be effected by a preferably unheated atmosphere con¬ taining uniformly distributed, extremely minute water drops which are applied on the part of the roller surface in the second coating station which is temporarily not in contact with the paper web. This can be achieved, for instance, by supplying air to a humidifier of a type similar to that described above or by means of other known means for producing water in extremely finely distributed form, for instance spray nozzles.

The same reference numbers as in Figures 1 - 5 have been used for similar details in the embodiments shown in Figures 7 - 11. In the alternative embodiments shown in Figures 7 - 11 the support rollers in the second coating station have always been provided with supply - and removing means for heat - cp. the tubelike recess 6a in the centre of the support roll 6 in Figure 1. A suitable medium such as a liquid can be brought to supply heat through this recess or remove it depending on the temperature desired on the roller surface. This is not shown in detail in Figure 1 since it can be achieved in a number of ways known per se.

By means of the member 11 - which has been described above in Figure 1 - a moist atmosphere is blown on to a limited, selected part of the surface 12 of the support roller 6, i.e. the part which is temporarily not in contac with the web 1. The atmosphere blown on may consist of hot, humid air having a temperature preferably higher than the temperature of the roller surface 12. By means of a suitable choice of temperature and water content in the ai blown on, a controlled covering of water film is obtained on at least a part of the roller surface which is not in contact with the paper. The formation of a thin film of water prevents deposits on the support roller 6 from the layer applied on one side of the web in the first coating station. The method according to the invention enables the quantity of water in the film to be accurately set using means known per se, which is extremely important.

As mentioned, if the water film is too strong it may damage the coating layer from the first station, whereas if it is too thin or uneven, there will be deposits on the support roller in the second coating station.

The moisture in the air blown on may comprise partly water vapour and partly extremely fine and uniformly distributed drops of water. If the air has a relatively high contact of water vapour and little or no water drops the water film will be produced primarily through condensation. In certain cases this may be preferable but if large quanti¬ ties of water are required in the film, for instance in the case of high-speed machines, considerable quantities of heat will be liberated upon condensation of the water vapour against the roller surface, which may be a dis¬ advantage. In other cases it may be more suitable for the water film to be produced primarily by non-vaporized water, i.e. extremely finely distributed water drops. In the latter case small amounts of heat will be released when the water film is produced, which may be an advantage in certain cases. On the other hand it may be suitable in some cases for the moisture in the air blown on to produce the water film to consist of a mixture of water vapour and extremely small drops of water.

The means 11 in Figure 7 for supplying hot, moist atmos¬ phere is shown only schematically and may consist of con¬ ventional components for treating air, for instance, such as means for heating the air, supplying moisture, means for forced blowing through nozzles or gaps of the hot, moist air against the roller surface. Conventional- humidi¬ fiers may be used to enable a suitable combination of moisture in the air in the form of atomized water drops and water vapour to be achieved for the circumstances in question. One such suitable means, for instance, is a humidifier consisting of nozzles which atomize water di¬ stributed to them. The nozzles are preferably applied in the top of the humidifier while the air, heated to a suit¬ able temperature, is brought to pass the humidifier in horizontal direction. A container is provided at the bot- torn of the humidifier to collect the water. The means func¬ tions in such a way that the hot air supplies thermal energy upon its passage through the humidifier so that at least some of the small water drops are vaporized. Others remain in liquid form and the smallest are caught up by

OMPI WIPO the air flow and distributed therein. Large drops of water either fall down to the bottom of the humidifier or can be removed in a special separator for water drops through which the moistened air flow passes after it has passed through the humidifier.

By a suitable choice of heat supply to the air,- suitable adjustment of moisture supply to the humidifier and suit¬ able adjustment of the air speed, such a means enables the humid atmosphere to be adjusted in relation to the tempe- rature of the roller surface, speed and other circum¬ stances prevailing during coating.

The apparatus enables a certain quantity of water to be applied in a controlled manner on the roller surface in the form of a thin film. If a small or moderate heat gene- ration is desired the described means should be set so that the content of atomized water particles in liquid form is relatively high in relation to vaporized water. If the water film is to be primarily achieved by condensation the means should be set so that all or most of the water supplied is vaporized in the moisturizing arrangement. In the first case a relatively cool, moist film is ob¬ tained whereas in the latter case the film produced re¬ leases relatively large quantities of heat.

The apparatur also includes suitable regulating members, not shown, so that optial data can be set and regulated fo temperature, moisture content and air quantity.

A simple method of obtaining a constant and suitable film • of condensate is to control the adjustment of heat and moisture, for instance, in the air supplied in relation to the temperature of the roller surface, which should pre¬ ferably be kept constant. The latter method is simple sinc a temperature gauge can easily be introduced in the cir- culation system for the medium supplying or removing heat to or from the roller.

It has also proved possible according to the method of the invention to avoid the paper web being cooled down since the roller surface need not be cooled but can be kept relatively hot. This is a great advantage since energy losses are then avoided. The roller surface can be kept as hot as the paper web and in some cases considerably hotter than this, but still retain a uniform and suitably adjusted film of condensate. In the latter case, not only is the heat loss eliminated, heat is also supplied to the web, which contributes to drying it. This is an additional advantage since it facilitates the subsequent drying process.

Figure 8 illustrates an alternative embodiment of the appa¬ ratus shown in Figure 2. The paper web is designated 1, a first coating means 14, the support roller 13, the support roller in the second coating station 15, a recess for the supply of liquid 15a and a blade coating means for the second support roller 16. The blade coating means 16 con¬ sists in this case of a puddle-type coater. Such a coater is known within the coating technique field and consists of a pool of coating composition which is coated and smoothed out with the help of a downwardly directed blade which presses against the paper web. A controlled hot, moist atmosphere is blown on with a means designated 17. According to the embodiment in Figure 5 the rollers are placed extremely close together which gives an extremely advantageous transportation of the web with no risk of folds forming or abnormal strain on the web. This means can also easily be adapted for use as a size press, for instance. The paper web 18 (shown in broken lines) is conducted over a guide roller 19 (broken lines) and then between the rollers 13 and 15 which press against each other and rotate in opposite directions (arrows B in broke lines) . In this way surface sizing can be performed by supplying a starch solution, for instance, in known manner the sizing solution being preferably applied at the nip between the rollers. In this case one or both the stations 14 and 16 may be taken out of operation.

Figure 9 shows an alternative embodiment of the apparatus shown in Figure 3. The paper web is designated 1, the first coating means of puddle type 20, the support roller for this 13 and the second coating means 20a. A means for keeping the temperature constant on the surface of the roller 15 is designated 15a.

The second coating station 20a is also of puddle type but in this case the paper web is deflected from the support roller 15 at an angle which is greater than the tangent through the point of contact of the blade on the surface of said roller. Also in this case the two support rollers 13 and 15 are placed extremely close together so that no intermediate roller is required to smooth out wrinkles.

Figure 10 illustrates a further alternative embodiment of the apparatus shown in Figure 4. The paper web is designa¬ ted 1 and passes over the guide rollers 21 and 22 to pass around the support roller 13 in a first coating station where a blade coating means of known type is designated 41. The web is then conveyed to the support roller 15 in a second coating station where a second blade coating means is designated 23. The paper web then leaves the support roller 15 to pass between two hot air driers 24 and 25. These may consist of airfoil driers, for instance, i.e. boxes provided with suitable blowing means from which hot, dry air flows to dry the paper web without contact. The means for blowing hot, moist air according to the

- jR O invention is designated 26 and a means for maintaining a controlled temperature in the roller surface is designated 15a. In this case the blowing means 26 is in communica¬ tion with the hot air generator which produces hot air for the boxes 24 and 25 and which is not shown in the drawing. The hot air from the generator is dry and an addi¬ tional means for humidifying the hot dry air is designated 27. This embodiment has the advantage that a common source of hot air can be used both for heating the support roller 15 and for the subsequent contactless drying process in the drying boxes 24 and 25.

According to this apparatus a controlled and adjustable temperature difference is maintained between the surface of the support roller 15 and the hot, moist atmosphere ' which is directed towards the part of the surface of the roller 15 which is temporarily not in contact with the web. In order to ensure a good control so that the re¬ quisite temperature difference is maintained, the tempera¬ ture, moisture content and quantity of the atmosphere supplied should be set at suitable values. This can be achieved, for instance, by continuously measuring the temperature of the roller surface 15. This can be done in many ways such as in contactless manner with an infra radiation meter. Such a means has been designated 28 in Figure 4. The temperature gauge measuring the surface temperature of the part of the surface not covered by the web should preferably control the moisture content, tem¬ perature and/or quantity of the air blown on.

Figure 11 shows finally an alternative embodiment of the apparatus according to Figure 5. The paper web, designa¬ ted 1, passes the coating means in the direction of the' arrow A. The web first passes a guide roller 21 and a support roller 13 pertaining to a first, lower coating station comprising a blade coating means 14 of a type shown previously. When the side of the paper web facing away from the roller 13 has been coated with coating com¬ pound it passes over a guide roller 29 and thereafter, wit the coated side facing inwards, it passes over the surface of a roller 15 constituting the support roller in a second coating station having a blade coating means 23. The paper web then leaves the support roller 15 and passes between two hot air driers 24 and 25 to be dried without contact. A means for the supply and removal of heat-con- ducting medium to keep the surface temperature of the roller surface 15 constant is designated 15a.

A means for supplying moist, hot air to the surface of the support roller 15 is designated 30. In this case a guide roller 29 is located between the support rollers 13 and 15. As mentioned earlier, it is a great advantage if guide rollers between the two support rollers can be avoided and the risk of folds being formed in types of paper which have a tendency to swell and form folds upon absorption of moisture can be eliminated by placing the rollers close together as shown in Figures 1, 2, 3 and 4, for instancei The embodiment in Figure 11 with interme¬ diate guide rollers 29 is suitable for less delicate paper such as paper with high specific weight or card¬ board. In such cases a greater distance between the two support rollers 13 and 15 can be accepted without risk of folds forming. In the means according to Figure 5, since the rollers have been placed further apart, more space is obtained between the coating means 14 and 23 which may be an advantage in some cases.

The alternative embodiments shown in Figures 7 to 11 in the invention has also been tested in practice. For example tests with the embodiment according to Figure 9 has been carried out with a support roller 15 of stain- less steel with a chromium plating. Water was supplied to the central pipe 15a. By way of example it may be mentio¬ ned that on one occasion the temperature of the water was 20 C and the atmosphere blown through the supply means 17 had a temperature of 60°C and an estimated moisture con¬ tent of 90% relative humidity. A simple adjustment of the air quantity by means of a damper enabled a water film of suitable proportions to be obtained on the roller sur¬ face 15. In spite of varying speed, temperature and moisture content in the paper web 1 entering and the coating medium applied in the coating station 20, an op¬ timal water film could be maintained by a simple adjust¬ ment of said damper in an extremely simply and rapidly adjustable manner. In the example cited the diameter of the roller 15 was 500 mm and the free length of web between its last point of contact on the roller 13 and its first point of contact with the roller 15 was only 100 mm, which guaranteed wrinklefree and reliable trans¬ port of the web.

In another series of experiments a test apparatus accord¬ ing to Figure 8 was used. In this case water having a temperature of around 40°C was supplied to the roller. The temperature of the web entering and of the coating medium was also 40°C. A moist atmosphere with a tempera- ture of about 75°C was supplied in the blowing means 17. In this case also it was a simple matter to maintain a suitably adjusted film of water on the roller surface. In this case the rollers 13 and 15 were so close together that they were almost touching, i.e. during its passage through the coating equipment the paper web 1 was all the time in contact with the support rollers 13 and 15, re¬ spectively, which is a great advantage particularly when coating at high speeds on paper with very low specific weight (down to 19 g/m ] .

-g ϊ E ?- OMPI In an experiment with an equipment substantially corre¬ sponding to that shown in Figure 10 hot water was supp¬ lied to the roller so that the outer temperature of the roller surface was about 70°C. The surface was covered with rubber which gave a good coating result. The moist atmosphere supplied through means 26 had a temperature of ca. 100 - 110°C, giving a suitable water film on the roller surface. In this case it was obvious that during its passage around the roller body 15 the paper web acquired a certain amount of heat from the surface of the roller. The free length of web between the rollers was varied up to a maximum of 1 meter without risk of wrinkle being formed.

The above shown and described embodiments are only a few examples of the use of the invention. Thus the supply of hot atmosphere to the surface of the support roller can be effected by various known devices and furthermore various known devices can be used for controlling the temperature of the support roller. Thus the temperature controll naturally must not be performed by supply or removal of heat through a central pipe in said roller bod

Another way is to blow cold, dry atmosphere through a slot of a suitable device, orientated before the hot air slot in the running direction of the roller, whereby the roller surface is cold down before passing the means for blowing hot moisture. Such method can normally only be used in slowly running apparatus.

Claims

C" i a i _m s .
1. Method for double-sided coating of a moving web of material, preferably a paper web, with an aqueous coating composition in at least two coating stations arranged one after the other in the direction of travel of the web and spaced from each other, each comprising a support roller and a coating means, one side of the web being brought into abutment with the support roller in the first coating station and the other side of the web being supplied with said coating composition, whereas in the second coating station the side of the web already coated is brought into abutment with, the support roller and its uncoated side is coated with said coating composition, characterised in that by means of controlled, separate supply of a moist atmosphere on at least a part of the surface of the support roller in the second coating sta¬ tion which is temporarily not in contact with the paper
* web, a thin film of water is formed on said surface wholly or partially through condensation. »
2. Method according to claim 1, characterised in that the moist atmosphere supplied is warm so that the surface of the roller will be heated to a temperature exceeding that of the web so that the web is heated upon contact with said surface.
3. Method according to claim 1, characterised in that the thin film of water is effected by means of a preferably non-heated atmosphere containing uniformly distributed and extremely small drops of water applied on the part of the roller surface in the second coating station which is temporarily not in contact with the paper web.
4. Method according to claims 1 - 3, characterised in. that the surface of the support roller in the second coating station is brought to a temperature exceeding that of the web before coming into contact with the web and thereafter is caused to acquire a temperature which is at least in agreement with the web temperature.
5. Method according to claim 1, characterised-in that the surface of the support roller in the second coating sta¬ tion is maintained with such a temperature, that a film of condensate is maintained between said surface and the web laying against it.
6. Method according to claims 1 - 5, characterised in that the moist, warm atmosphere supplied is regulated with respect to quantity, moisture content and tempera¬ ture in order to achieve controlled heating of the surface of the support roller and controlled formation of the thickness of the film of condensate.
7. Method according to claims 1 - 6,- characterised in that a hot, moist air flow is blown against said surface of the second support roller.
8. Method according to claims 1 - 7, characterised in that the heat and moisture content of the hot, moist flow of air supplied are adjusted in relation to the tempera¬ ture of the web and/or coating composition.
9. Method according to one or more of claims 1 - 8, cha- racterised in that the moist flow of hot air is generated in a hot air generator for associated drying means, which is arranged for the purpose to cooperate with a moistu¬ rizer.
10. Method according to claims 1 - 9, characterised in that the two support rollers located one after the other are caused to assume such positions in relation to each other that the free stretch passed by the web between these support rollers is short enough to allow the web to travel without contact with support and/or guide rol-' lers.
11. Method according to claims 1 - 10, characterised in that the free length of the paper web between the support rollers does not exceed 1 meter.
12. Method according to claims 1 - 11, characterised in that the free length of the paper web is between 0 and
10 cm.
13. Apparatus for double-sided coating of a moving web of material, preferably a paper web, with an aqueous coating composition in at least two coating stations arranged one after the other in the direction of travel of the web and spaced from each other, each comprising a support roller and a coating means, one side of the web being brought into abutment with the support .Toiler in the first coating station and the other side of the web being supp- lied with said coating composition, whereas in the second coating station the side of the web already coated is brought into abutment with the support roller and its uncoated side is coated with said coating composition for performing the method of claim 1, characterised by mem- bers (11, 17, 26, 30) for controlled, separate supply of a moist atmosphere to the surface (12) of the support roller (6, 15) in the second coating station which is not in contact with teh web (1) .
14. Apparatus according to claim 13 characterised by means for maintaining of such a temperature of the surface (12) of said support roll (6, 15) in the second coating station, that a film of water is maintained between said surface and the web (1) laying against it. 15. Apparatus according to claim 13, characterised in that said supply members (11, 17, 26, 30) comprise an out¬ let directed towards the surface of the support roller
(6,
15), said outlet having outlet openings extending per- 5 pendicular to the generatrix of the roller surface and that the .supply member is connected to a heat source and a moisturizer ' (27) .
16. Aapparatus according to claims 13 - 15 characterised in that the heat source consists of a hot air generator Q for the associated drying equipment (24, 25) .
17. Apparatus according to claims 13 - 16, characterised in that the roller surface (12) consists of a rubber sheathing.
18. Apparatus according to one or more of claims 13 - 17, 5 characterised in that the supply.means comprises a central container (31) extending across the width of the paper web (1). and forming a gaplike opening (35) , as well as two box-shaped spaces (37, 38) which surround the ope¬ ning (35). and form gaplike spaces (39, 40) on each side thereof.
19. Apparatus according to one or more of claims 13 - 18, characterised by members for alternative arrangement of the support rollers so that they abut one another and with reverse directions of rotation form a size press.
20. Apparatus according to one or more of claims 13 - 19, characterised in that the support rollers arranged conse- ' cutively are spaced from each other in such a way that the free length of web between the rollers does not exceed 1 meter.
- R O Λ. .WI
^
21. Apparatus according to one or more of claims 13 - 20, characterised in that the free length of web between the rollers does not exceed 10 cm.
OMPI
PCT/SE1979/000226 1978-11-13 1979-11-06 Method and apparatus for the double-sided coating of a moving web of material,preferably a paper web WO1980000928A1 (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
SE7811722A SE427903B (en) 1978-11-13 1978-11-13 Method and arrangement for covering both sides of a moving material web at two consecutive coating stations
SE7811721A SE7811721L (en) 1978-11-13 1978-11-13 Seen and apparatus for double-sided coating of a traveling web, a paper web foretredesvis
SE7811721 1978-11-13

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE19792953280 DE2953280A1 (en) 1978-11-13 1979-11-06 Method and apparatus for the double-sided coating of a moving web of material, preferably a paper web

Publications (1)

Publication Number Publication Date
WO1980000928A1 true true WO1980000928A1 (en) 1980-05-15

Family

ID=26657150

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE1979/000226 WO1980000928A1 (en) 1978-11-13 1979-11-06 Method and apparatus for the double-sided coating of a moving web of material,preferably a paper web

Country Status (4)

Country Link
EP (1) EP0018994A1 (en)
JP (1) JPS55500893A (en)
GB (1) GB2046640A (en)
WO (1) WO1980000928A1 (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3313890A1 (en) * 1982-05-20 1983-12-15 Voith Gmbh J M size press
EP0336367A2 (en) * 1988-04-05 1989-10-11 Kanegafuchi Kagaku Kogyo Kabushiki Kaisha Double-side simultaneous coating equipment
US5630874A (en) * 1990-09-17 1997-05-20 Shell Oil Company Apparatus for resin impregnation of a fibrous substrate
US6416580B1 (en) 1996-02-21 2002-07-09 Voith Sulzer Papiermaschinen Gmbh Method and apparatus for applying a liquid or pasty medium on a traveling material web

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4712251B2 (en) * 2000-09-22 2011-06-29 帝人株式会社 Double-sided simultaneous coating method

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1427602A1 (en) * 1961-12-21 1968-11-07 British Cellophane Ltd Method and device for coating continuous tapes
US3470055A (en) * 1965-01-21 1969-09-30 Nat Distillers Chem Corp Extrusion coating method
SE396558B *

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE396558B *
DE1427602A1 (en) * 1961-12-21 1968-11-07 British Cellophane Ltd Method and device for coating continuous tapes
US3470055A (en) * 1965-01-21 1969-09-30 Nat Distillers Chem Corp Extrusion coating method

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3313890A1 (en) * 1982-05-20 1983-12-15 Voith Gmbh J M size press
EP0336367A2 (en) * 1988-04-05 1989-10-11 Kanegafuchi Kagaku Kogyo Kabushiki Kaisha Double-side simultaneous coating equipment
EP0336367A3 (en) * 1988-04-05 1990-08-08 Kanegafuchi Kagaku Kogyo Kabushiki Kaisha Double-side simultaneous coating equipment
US5630874A (en) * 1990-09-17 1997-05-20 Shell Oil Company Apparatus for resin impregnation of a fibrous substrate
US6416580B1 (en) 1996-02-21 2002-07-09 Voith Sulzer Papiermaschinen Gmbh Method and apparatus for applying a liquid or pasty medium on a traveling material web

Also Published As

Publication number Publication date Type
EP0018994A1 (en) 1980-11-26 application
GB2046640A (en) 1980-11-19 application
JPS55500893A (en) 1980-11-06 application

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