Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05C—APPARATUS FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05C9/00—Apparatus 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
  • B05C9/04—Apparatus 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

Definitions

• 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.
• 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.
• one drawback is that it is difficult to set dif ⁇ ferent quantities of coating composition on each side of the weh if desired.
• the cooled support roller consists suitably of steel or metal and is cooled by means of a coolant supplied to.the roller through pipes.
• 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.
• 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.
• 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-
• 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.
• 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.
• 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.
• 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 reserie- ents of the blade coating technique.
• 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.
• Figures 1 - 6 show schematically a number of different embodiments of the invention.
• 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
• ⁇ O ⁇ 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.
• 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.
• 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.
• 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.
• FIG. 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.
• 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.
• 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.
• FIG. 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.
• FIG. 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.
• 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.
• 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.
• 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
• 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.
• FIG. 5 shows yet another embodiment of the invention.
• 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.
• 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.
• the supply means for moist atmosphere to the surface of the support roller 15 is designated 30.
• a guide roller 29 has been placed between the support rollers .13 and 15, .
• 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.
• 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.
• FIG. 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.
• 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.
• 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.
• the free length of web between the two rollers can be kept extremely short, the following may be mentioned.
• 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.
• 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.
• 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.
• 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.
• a thin water film 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• FIG 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.
• 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) .
• 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.
• 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
• 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.
• 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.
• FIG 11 shows finally an alternative embodiment of the apparatus according to Figure 5.
• the paper web designa ⁇ ted 1
• the paper web 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.
• coating com ⁇ pound 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.
• a guide roller 29 is located between the support rollers 13 and 15.
• 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.
• 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.
• 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.

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• Application Of Or Painting With Fluid Materials (AREA)
• Coating Apparatus (AREA)

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• 1979
  • 1979-11-06 JP JP50196079A patent/JPS55500893A/ja active Pending
  • 1979-11-06 GB GB8016895A patent/GB2046640A/en not_active Withdrawn
  • 1979-11-06 WO PCT/SE1979/000226 patent/WO1980000928A1/en unknown
• 1980
  • 1980-05-20 EP EP19790901546 patent/EP0018994A1/en not_active Withdrawn

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