Patent Grant
7101438
This application is a 371 of PCT/JP02/08558 filed on Aug. 26, 2002, published on Mar. 6, 2003 under publication number WO 03/018210 A1 and claims priority benefits of Japanese Patent Application No. 2001-256454 filed Aug. 27, 2001.
The present invention relates to a coater for coating a dispersion slurry, containing solid particles dispersed in a dispersion medium where the said solid dispersion slurry is dispersed to the surface of a substrate running continuously using a coating roll being made, and, more specifically, to an improved coater which in case the dispersion slurry tends to adhere the surface of the coating roll or a dispersion slurry where such solid particles as are likely to settle down, providing stable dispersion slurry that can be applied stably and uniformly to the continuously running substrate.
An example of said dispersion slurry is such as has super absorbent polymer (hereinafter called “SAP”) dispersed in a medium and with such dispersion slurry being applied to a nonwoven fabric substrate, obtaining an absorbent sheet can be obtained.
With absorbent products being made super thin, such technologies as making SAP into a sheet form have become very important. Among such technologies, as a promising process, an attempt has been made to prepare a slurry by dispersing SAP in water, an organic solvent or an organic solvent/water mixed solvent using a viscosity adjusting agent such as CMC, MFC and PEO for coating a support. For example, in Patent Application Laid-open Hei 10-168230, an example where a coater and a kiss coater of a grid form, in Patent Application Laid-open Hei 11-34200, an example where coating is conducted from a nozzle of a tube type, in Patent Application Laid-open Hei 11-128825, an example where a die coater, a curtain coater, a knife coater or a spray coater is used, in Patent Application Laid open Hei 11-226467, an example where a slurry is guided from a buffer tank through to an overflow nozzle and in Japanese Patent Application Laid-open 2000-5674, an example where a pattern coating is conducted using a contact head are disclosed respectively.
In coating various types of substrate surfaces, the dispersion slurry in which solid particles are dispersed in a dispersion medium, unlike the case where a liquid to be applied for coating is a uniform solvent, is apt to have some partial variation in concentration due to phase separation, settling down, agglomeration and the like. In case the dispersion slurry is applied for coating, it is preferable to utilize a low cost roll coater of a relatively simple structure among various coaters available, but with such roll coater dispersed solid particles are apt to settle down in the dispersion slurry or to adhere to the surface of a coating roll. If such settling down or adhesion takes place, the coated surface may be uneven or clogging may take place during operation so that it becomes difficult to run a uniform and stable coating operation.
In order to diminish the settling down and adhesion of the dispersed solid particles, such actions for establishing making a condition where slurry may be made easier to be detached have been taken like treating of the surface of a coating roll with a material such as silicone and Teflon (registered trademark), scraping by means of a scraper, and rotating of a roll in a positive direction or a reverse direction.
Compared with such solid containing dispersion slurry, since the slurry in which SAP is dispersed is less fluid and thus apt to get of sludge like, it becomes more difficult to obtain stable and uniform coating with such SAP dispersion slurry and so far no commercial process therefor has been developed yet.
The objective of the present invention is to provide a coater enabling a SAP dispersion slurry to be coated uniformly both in a width direction and in a length direction at a wide range of speeds not causing any clogging over a wide range of basis weights.
A coater according to the present invention is provided with a apparatus for continuously running a nonwoven fabric substrate in a horizontal direction, a head bath whose top is opened, located over said running nonwoven fabric substrate and forming a bath for holding said dispersion slurry on the top surface of said nonwoven fabric substrate, a liquid seal plate for so sealing that said dispersion slurry may not leak from underneath of said nonwoven fabric substrate, and a coating roll rotating in a positive direction with respect to the running direction of said nonwoven fabric substrate, wherein said coating roll is so structured that a pressing pressure is exerted against said nonwoven fabric substrate and the dispersion slurry as coated onto the surface of said nonwoven fabric substrate while the surface coated with said dispersion slurry is made smooth.
A coater of a preferred form according to the present invention is provided further with a cover film provided as covering the peripheral surface of said coating roll in a range from the position of the topmost end vicinity of said coating roll extending through to the position of the bottom end vicinity thereof so that said dispersion slurry may be supplied between the top end of said cover film and the surface of said substrate.
A coater according to the present invention may be disposed in a position facing with said nonwoven fabric substrate as sandwiched between its top and bottom with said coating roll and provided with a support roll rotating in a positive direction with respect to the running direction of said nonwoven fabric substrate.
The top end portion of said cover film need not be fixed or said cover film except its top end portion may be so fixed by a side seal that said cover film is held in a prescribed position along the peripheral surface of said coating roll in both end portions in an axis direction of said coating roll.
Said cover film may be constituted by a laminated film made by overlapping 2 sheets of film whose physical properties are different from each other.
Out of these two sheets of film, a first film extends preferably up to a position extending over said side seal and is fixed at said side seal, and a second film has preferably a width covering only the inner side of said side seal.
Said first film may be disposed in a position facing said coating roll, and said second film may be disposed in a position outside of said first film.
Alternately, said second film may be disposed in a position facing said coating roll, and said first film may be disposed in a position outside of said second film.
Said first film may be shorter than said second film with respect to the running direction of said substrate.
Said first and second films may be bonded to each other at least in parts.
Said first film is preferably a 50 μm or thicker PET film, and said second film is constituted by a 50 μm or thinner PET film.
The top end portion of said cover film may extend from the bottom end of the peripheral surface of said coating roll in its downstream side over a desired distance with respect to the running direction of said nonwoven fabric substrate.
On the other hand, with respect to said coating roll, it has preferably a diameter in a range of 100˜500 mm and the end portion of said cover film extends preferably only over a range of 1˜50 mm from said bottom end position down to its downstream side with respect to the running direction of said nonwoven fabric substrate.
It may be preferable to prevent the top end portion of said cover film from getting into contact with the peripheral surface of said coating roll, and a separator may be provided for that purpose.
In order to form a coating pattern on the surface of said nonwoven fabric substrate, a pattern spacer is further provided, thereby said dispersion slurry going from the top end portion of said cover film to its downstream that is to be supplied to the surface of said nonwoven fabric substrate is so regulated that the slurry is not supplied onto the surface of said substrate and thus a desired coating pattern may be formed.
Said coating roll surface may have some parts that are concave and convex, causing the areas in parts where the surface of said coating roll and said cover film do not get into contact to be provided so that any excessive contact friction between the two may be prevented from taking place.
Said dispersion slurry may contain as a solid component particulate, powdery or flaky SAP, and a preferable dispersion medium in such case is a mixture solvent of an organic solvent and water.
Said SAP may be particles having a diameter of 1000 μm or less, and said dispersion medium may be a mixture of water and a solvent of an organic solvent having a function of inhibiting swelling and water.
Said substrate may be of any nonwoven fabric, and may be a porous nonwoven fabric.
According to the present invention as explained above, during coating using dispersion slurry, a uniform thickness both in a width direction and a length direction, a wide range of speeds can be achieved with no clogging of the dispersion slurry taking place in coating nonwoven fabrics over a wide range of basis weights. Thus, the resulting coating film is uniform in thickness and smooth on the surface.
Furthermore, in case a cover film is applied, a problem common to any contact type coater such as a bar coater and a knife edge coater that is a substrate may get in contact with a coater, i.e. dispersion slurry may adhere to the surface of a coating roll, can be solved without any complicated coating equipment and resulting considerably increased costs involved. In particular, for any case where water absorbent solid particles of high surface adherence are applied as in case where a dispersion slurry which is made by dispersing absorbent solid particles in a dispersion medium of a water/organic solvent type, uniform and stable coating may be realized.
In the following, preferred embodiments of the present invention are explained with reference to the drawings:
Prior to making such explanation, it will be necessary to understand the characteristics of SAP and SAP dispersion slurry and of a nonwoven fabric substrate.
Coating of an even film or metal foil with slurry of high viscosity and high fluidity is already industrially established technology, and such technology is classified into an extrusion method such as die coating, curtain coating and nozzle coating and a head flowing method provided with a head bath. Coating heads such as a lip direct head, a comma direct head, a comma reverse head, a bottom feed reverse roll head, a direct gravure head, a kiss coating head, a squeeze coating head depending on the applications have been proposed.
It is extremely difficult, however, to achieve a stable and uniform coating by applying any such conventional coater in a process of coating a nonwoven fabric substrate having rough surface with SAP slurry.
(1) Characteristics of SAP and SAP Dispersion Slurry
SAP provides a spherical shape and a flaky shape depending upon the polymerization methods applied. If SAP of both shapes is measured in terms of approximated particles, the diameter of SAP has a wide distribution of 30˜1000 μm, and SAP is very irregular in shape and bulky. Also, SAP is naturally extremely sensitive to water.
SAP is apt to self coagulate if an attempt is made to disperse it into a slurry form (Japan Tappi Journal: 1079, Vol.52, No.8 (1998)), and it is extremely unstable, but it may be made into slurry in an organic solvent/water mixture. As it is, however, since it instantaneously settles down even if it is agitated, it is made stable by using a viscosity adjusting agent or a bonding agent. In conclusion, at this moment, it is most preferable condition to have SAP in coexistence with MFC (microfibrillated cellulose).
Thus, even such stabilized slurry is likely to settle down unlike one normally available in industrial applications, and because of its poor fluidity, it easily becomes sandy or sludge-like, so that it needs to be continuously agitated in dispersion medium.
(2) Characteristics of Nonwoven Fabric Substrate
A nonwoven fabric substrate to be used in the present invention is preferably a porous and has a structure where solids in slurry are supported and a dispersion medium is easily permeated, such as a spun bonded nonwoven, a spun bonded/melt blown composite nonwoven, a spun laced nonwoven, a thermal bonded nonwoven, an airlaid matte, a crepe paper, a pile fabric and a towel fabric.
More preferable nonwoven fabric substrates are bulky and capable of supporting SAP in its structure. As described later, an example of such more preferable nonwoven fabric substrates is a nonwoven fabric made by overlapping a carded web onto a crepe paper and entangling both of them in parts resulting in a fluffy nonwoven fabric substrate with the resulting weight being approximately 20 g/m2 and thickness being approximately 1.5 mm, as obtained in
(3) Comparison Between Coating Directly Nonwoven Fabric in a Dry State and Coating Nonwoven Fabric Saturated with a Dispersion Medium
Table 1 shows two examples of coating a nonwoven fabric in a dry state and a nonwoven fabric with its voids filled with a dispersion medium for understanding the characteristics of SAP and a nonwoven fabric.
For these experiments the following substrate and SAP dispersion slurry were prepared:
Coating was performed in a process shown in
Table 2 shows the test results. In case coating was applied directly to a nonwoven fabric substrate in a dry state, the basis weight of SAP was nearly 300 g/m2, and there was almost no change in weight even when the clearance was changed. This weight was nearly comparable to the quantity of the dry web obtained when the web was first impregnated with the SAP dispersion medium and then the dispersion medium was removed with the web used as a filter. Meantime, in the case of the nonwoven fabric substrate saturated initially with the dispersion medium, the basis weight was proportionate to the clearance.
The present invention proposes, as shown in Table 2 above, an apparatus and a method for four different conditions such as stated of {circle around (1)} coating being done to a substrate in a dry state, {circle around (2)} coating being done to a substrate after it is saturated with a dispersion medium, {circle around (3)} the effect of the substrate as a filter being utilized, and {circle around (4)} emphasis being placed on the surface coating process by means of a coating roll with these four condition are combined in a very ingenious way.
The present invention will be explained in detail with reference to the drawings.
Basic Structure of Coater According to the Present Invention
This coater comprises rear gate 7 disposed having an appropriate rear gate clearance (C) on a net conveyor 6 for transferring a nonwoven fabric substrate 1, coating roll 4, support roll 5 disposed at a position facing the coating roll via the net conveyor, and nose plate 3 provided on the downside of the net conveyor 6 for sealing the bottom of head bath 2 formed on the upside of the nonwoven fabric substrate 1 between the rear gate 7 and the coating roll 4.
The head bath 2 is formed between the rear gate 7 and the coating roll 4. The head bath 2 provides a space for storing a slurry liquid at a first stage. The volume of the head bath 2 is determined by its longitudinal distance (hereinafter called “head length (L)”) if the width of the nonwoven fabric substrate 1 is given, and the quantity of the slurry stored in the head bath 2 is determined by the height of the head bath (H). This stored quantity is appropriately controlled depending upon such conditions as the desired basis weight and the running speed of the nonwoven fabric substrate 1.
In the coating job, the clearance (C) of the rear gate is adjusted by raising or lowering the rear gate 7 depending upon the apparent thickness (that is to say, bulkiness) of the used nonwoven fabric substrate. Generally speaking, the clearance should be set somewhat smaller than the bulkiness of the nonwoven fabric substrate 1. For example, the clearance is adjusted at approximately 3 mm for the bulkiness of 4 mm of web. The rear gate clearance (C) does not depend upon the running speeds, basis weights, etc. The clearance (D) is a very important controlling element and is finely adjusted depending upon such conditions as the basis weights, the properties of the substrate, its running speed and the coating patterns with respect to the height (H) of the head bath 2. The range of variation, however, is in a range of approximately 1.0˜2.0 mm. The position of the support roll is fixed and by raising or lowering the coating roll 4 with its distance to the support roll 5, the clearance (D) is adjusted and measured.
The nose plate 3 serves for sealing the bottom surface of the head bath 2 via the net conveyor 6, and, on the upstream side, covers the distance from the position of the rear gate 7 or its upsteam down to a position nearing to the support roll 5. On the downstream side, the top end of the nose plate 3 is made thin so that it may get near to the support roll 5 as much as possible and more easily seal the bottom surface of the support roll 5. Note that both edges of the nose plate 3 in the width direction are to preferably coupled and sealed to a side seal (not shown).
The coating roll 4 rotates in a positive direction with respect to the running direction of the nonwoven fabric substrate 1, and thus serves to push out the SAP slurry which otherwise is apt to get clogged.
In a conventional coater, in order to improve the metering accuracy, generally speaking, a coating roll is fixed as in the case of a comma coater, or is reverse rotated as in the case of a reverse coater. As against this conventional approach, in the present invention the coating roll 4 is made to rotate in a positive direction, and thus to push out the SAP dispersion slurry in a positive manner. The rotating speed of the coating roll 4 is changed from 0˜200% depending upon the conditions based on the running speed of the substrate being 100. Normally, the rotating speed is preferably adjusted in a range of 100% ±20%.
Another function of the coating roll 4 is to force the SAP slurry into the voids within the fibrous network of the nonwoven fabric substrate 1 and to make the surface of the coating smooth by regulating the coating thickness of the slurry. In a conventional method, since this part is a fixed edge, if small blocks of SAP are mixed even in a very small quantity, a coating roll may easily be clogged, and if such clogging takes place, the coated surface may be made fluffy resulting in a poor product quality and also in causing the surface of a drying roll in a drying step to get stained. In this sense, by rotating the coating roll 4, i.e. an outlet roll, the SAP dispersion slurry may be smoothly pushed out and at the same time getting a smooth, coated surface.
For the above-mentioned reasons, the structure of the coating roll 4 is preferably such that the surface is of a mirror finish, and yet for reducing adhesion to the surface the coating roll 4 may advantageously utilize polytetrafluoroethylene [Teflon (registered trademark)] coating, silicone coating, or a pearskin finish. In addition, in order to remove stain from the surface of the coating roll 4 or to prevent the substrate from being wound up by the surface of the coating roll 4, a scraper may be provided.
In a system of a film or a metal foil where no slurry permeates a substrate, the coated quantity on a substrate is primarily regulated by the clearance (D), but in a nonwoven fabric substrate, in particular in a bulky substrate preferable in the present invention, first of all, the actions of impregnating into the network of a substrate and of filtering by means of the substrate take place at the same time, and at approximately the same time when the SAP dispersion slurry is supported into by the substrate, depending upon the clearance a slurry layer coated on the surface is formed.
Which of these two zones plays a primary role is very much dependent upon such conditions as the properties of the substrates, coating speeds, and shapes of the head bath.
Coating System With the Coater Incorporated
In the foregoing, a basic structure of the coater has been explained, but, in order to form a coating system, other important units such as a precoater unit and a solvent suction apparatus are required to be incorporated.
Firstly, in case a nonwoven fabric substrate 1 is bulky and for example a hairy web, such step that coating the substrate beforehand, the voids in the substrate are filled with a dispersion medium and then coating is done by applying a slurry, so that a uniform coating may be realized on the substrate in the same way as for tissue and a spun bonded nonwoven fabric having a relatively thin and smooth surface.
Secondly, the precoater functions to make the substrate as a whole, i.e. from its inside structure to its surface, smooth by making microscopic roughness on the surface of the substrate even or by replacing air contained inside the substrate with a solvent.
Thirdly, by getting the conveyor 6 and the substrate 1 into close contact with each other and thus integrating both of them, it will be possible to secure a uniform contact-by-pressure state on the coater.
In case a relatively thin, uniform and nonbulky nonwoven fabric such as tissue and spun bonded web is used, the first function of the precoat, i.e. filling of voids, is not very important, but the second and the third functions are important.
In the present invention, therefore, although the quantity of the dispersion medium to be precoated depends upon the characteristics of the substrate, it is preferable to always apply the precoat for any type of the substrates. As methods of applying precoats, a spraying and a contact transferring are available, but since the hairy state or the bulkiness may change by getting in contact with the roll, it is preferable to employ an overflow type precoat as shown in
Agitating of the slurry in the head bath 2 is particularly important for the slurries that are apt to settle down and thus become sludge-like such as the SAP dispersion slurry used in the present invention, and in case the flow rate should be lowered, such slurries immediately settle down and deposit, thus a careful attention is needed.
A scraper is not indispensable, but if prevention of staining or of wrapping up is needed, the scraper is preferably provided. A solvent suction solvent suction apparatus is important in the sense that by such operation, SAP and the nonwoven fabric substrate are made in an integrated form and at the same time the load on the subsequent drying step can be lowered. The solvent suction apparatus is provided by disposing a suction box underneath the net conveyor. By the vacuum pressure of the suction box, almost all of the liquid dispersion medium contained in the SAP dispersion slurry is removed, and any residual solvent and water are removed in the following drying step, so that a SAP sheet in a dry state can be obtained.
This solvent suction solvent suction apparatus may be one unit if the production speed is slow and that a full width coating is done, but in the case of a pattern coating or in a higher speed operation even with the full width coating, it may be necessary to install two sets of such solvent suction apparatus.
Now, turning back to the solvent suction apparatus solvent suction apparatus, in installing the first and the second solvent suction apparatus solvent suction apparatus, it is preferable to set the vacuum pressure higher and the air flow lower for the first solvent suction apparatus solvent suction apparatus than for the second solvent suction apparatus solvent suction apparatus. As the first vacuum pump for suction, such pumps that can keep the vacuum relatively high like a Nash roots pump and a root pump are employed preferably, and as the second vacuum pump for suction, such pumps that can keep the vacuum relatively low, but the air flow relatively high like a turbo blower are employed preferably.
To show an example of the specific performance of an solvent suction apparatus solvent suction apparatus, this apparatus is constituted by a first suction zone and a second suction zone, and the vacuum pressure of the first suction zone is kept at 26.6 kPa˜53.2 kPa (200 mmHg˜400 mmHg) and the vacuum pressure of the second suction zone at 6.65 kPa˜33.3 kPa (50 mm Hg˜250 mm Hg), and thus the vacuum pressure of the first suction zone is kept higher than that of the second suction zone.
<Changing of Coating Patterns>
In case the whole area of a substrate is coated uniformly, the coating with the SAP slurry can be done using such coater as has been described in the foregoing. In case coating of patterns in lines or patterns in horizontal stripes or patterns with thick and thin areas provided is desired, some or other scheme is required.
Generally speaking, as proposed by the inventors of the present invention in Patent Application Laid-open 2000-5674, a method of inserting a comb is simple and easy to apply. In this case, as shown in
<Manufacturing Process of SAP Sheet with the Coater Incorporated>
A process of manufacturing a SAP sheet with a coater according to the present invention incorporated will be explained below.
1. Step of preparing a non-bonded carded web;
2. Step of transferring the web onto a net conveyor;
3. Step of stream entangling said web at water beam intervals of at least 5 mm or more on said net conveyor by means of a high pressure water of 2.06 mPa (20 kg/cm2) or more;
4. Step of saturating said water stream entangled web with a SAP dispersing medium comprising an organic solvent/water mixed solvent by means of a precoater;
5. Step of coating said web saturated with said dispersing medium with said SAP dispersion slurry prepared of said organic solvent/water mixed solvent as a dispersing medium;
6. Step of removing by suction the solvent from said SAP coated web obtained by said coating; and
7. Step of thermally drying in a dryer said SAP coated web from which the solvent is removed.
<Basic Structure of Coater According to the Present Invention with a Cover Film Applied>
The coater and the process with such coater incorporated of the present invention have been explained. There is a means available for covering the surface of a coater with a film in order to fundamentally solve adhering of solids on the coating roll. Such means is explained in detail below:
In addition, a dispersion slurry 24 to be coated on the surface of the substrate 12 is made to continually supplied to the surface of the substrate 12 at a discharge position determined near the downstream from a position in the vicinity of the bottom end of the peripheral surface of said coating roll with respect to the running direction of said substrate through a slurry storage 14 provided as necessary in the rotating cycle of the coating roll 11.
Furthermore, a cover film 15 is disposed so that the dispersion slurry 24 to be supplied from the slurry storage slurry storage 14 may cover the coating roll 11 not getting into contact with the peripheral surface of the coating roll 11 and its end is made to pass over the bottom end of the coating roll 11. The dispersion slurry is made to be supplied to the space between the end of this cover film 15 and the surface of the substrate 12, and this space provides a discharge position of the dispersion slurry.
In example shown in
The coater of the dispersion slurry as such constituted will be explained in terms of its components below:
First of all, the coating roll 11 has a clearance (a gap) formed of a prescribed distance from the surface of the substrate 12 running continually underneath of the coating roll at the bottom end of the peripheral surface thereof, and by means of this clearance the thickness of the dispersion slurry 24 to be coated on the surface of the substrate 12 can be regulated to any desired value. Also, by the friction resistance with the cover film one end of which is fixed, the cover film 15 is given an appropriate tension and some or other concavity and convexity caused by the occurrence of creases or the sucking of air are prevented from taking place, so that the film may be positioned in close contact with the peripheral surface of the coating roll. Note that if the friction resistance is too large between the coating roll 11 and the cover film 15, the cover film 15 may deform or be damaged or, due to excessive braking, the rotational energy of the roll may be lost, so that the friction resistance needs to be adjusted to an appropriate value.
Next, the slurry storage 14 for the dispersion slurry will be explained. This slurry storage 14 plays the role of a head bath for storing the dispersion slurry 24 temporarily as it is in a uniform and homogeneous state causing no concentration distribution nor coagulation as a preparatory step for obtaining a uniform coating condition both in the width and the length direction. Generally speaking, in this slurry storage 14 an agitator may be needed for preventing the concentration distribution possibly caused by the solid particles coagulating or settling down from taking place and for securing the uniformity in the width direction. If a slurry supplying apparatus used meets the conditions, the slurry storage may be omitted.
In a coater for a dispersion slurry according to the present invention as structured as described above, the supplying and coating of the dispersion slurry 24 onto the surface of the substrate 12 is performed not in the clearance between the coating roll and the surface of the substrate, as in the case of a conventional roll coating, but between the cover film 15 and the substrate 12. The coating roll 11 only regulates the position of the cover film 15 to the substrate 12, and does not get in contact with the dispersion slurry 24. Therefore, no problem on the difference of dispersion slurry adheres to the surface of the coating roll is found in the present invention.
In a coater for a dispersion slurry according to the present invention, it may be sometimes preferable to regulate the range of coating with respect to the width direction of the continuous running substrate just as in a conventional roller coating.
The side seal portion of this example shown by a numerical reference 13′ comprises a pair on the left and the right side consisting of both side gates of a slurry storage 14, and, in order to prevent leakage of liquid in close contact with the rear end plate portion 13 on the surface of the coating roll 11, is positioned inside of both side portions of the cover film 15 and fixed by a means such as welding and an adhesive to the rear portion plate 13 of the slurry storage 14.
This side seal portion 13′ is so provided preferably as to be in contact with the peripheral surface of the coating roll 11 in order to prevent the dispersion slurry 24 from leaking outside through a gap with the peripheral surface of the coating roll 11. In this case, however, the side seal portion 13′ preferably has sealability to the peripheral surface of the coating roll 11 and at the same time has lower friction resistance and less wearing. In order for the side seal portion 13′ to meet such requirements, it is preferably constituted by a resin material selected from a synthetic rubber, a foamed material, Teflon (registered trademark) and the like.
The dispersion slurry supplied to the slurry storage 14 is sealed by the rear end plate portion 13 on the rear portion and by the side seal portion 13′ on both sides and passes through the only exit formed between the slurry storage 14 and the cover film 15 to be used for coating the continuously running substrate 12.
In addition,
Hereunder, a cover film 15 used in a coater for a dispersion slurry according to the present invention is discussed.
First of all, the principal functions of the cover film 15 are as follows:
(1) The cover film 15 covers the area of the coating roll 11 which is in contact with the dispersion slurry 24 so that the dispersion slurry is prevented from getting into contact with the surface of the roll and from adhering on the surface of the roll.
(2) One end of the cover film 15 being fixed and the other end being free to move, by the action of edge effects provided by the free end portion, the dispersion slurry may easily be withdrawn from the surface of the cover film 15.
Out of the above-described functions, the one given in (2), i.e. the function provided by the free end of the cover film 15, is particularly important, which function will be explained in detail below:
<Developing of Effects of Sharp Edges at Rear End Portion>
The dispersion slurry which has partly deposited on the surface of the substrate 12 and is so in contact with the cover film 15 is separated from the cover film at the free end, and then is transferred onto the substrate 12 to complete the coating operation. On the transferring of the dispersion slurry at the end of the cover film, i.e. if the parting of the dispersion slurry parting from the edge of the cover film, is not smoothly done, the dispersion slurry may attach at the end portion of the cover film and may further deposit at the exposed surface of the coating roll 11 not covered by the cover film 15 causing lumps to be formed with the unfavorable result that the coated surface may become rough and since the surface is not uniformly coated. Furthermore, if this condition continues as it is, the dispersion slurry may be cause clogging, so that no continuous coating can be performed. Also, such condition may cause waves of concaves and convexes in the width direction which in turn causes non-uniformity in thickness in the width direction.
Thus, the cover film 15 is required to have an appropriate rigidity and at the same time its edge needs to be sharp. The reason therefore is that the edge of the cover film 15 needs to serve just like a sharp edge provided by a comma coater or an edge coater. What affects such function which is expected from the cover film are the material of the cover film and its thickness. The desirable materials as the cover film 15 are typically polyester, oriented polypropylene, Teflon (registered trademark), LDPE, polyvinyl chloride and the like.
In addition, the cover film 15 may be constituted by one sheet of film of either of the above-mentioned materials, and also may be made by laminating 2 sheets of film of the same material. Also, 2 sheets of film of different materials may be used. For example, in case PET film is used, it is preferable that a first film is a PET film having a thickness of 50 μm or more and a second film is a PET film having a thickness of 50 μm or less. Also, combinations of 30 μm film and 100 μm film, of PET film/Teflon (registered trademark) film, and of PP film/metal foil are available.
Among them, a particularly preferable material is a polyester film, e.g. Lumilar (registered trademark, Toray Co., Ltd.) or its surface treated product.
The thickness of a film constituting the cover film depends upon the rigidity of the material, and if the film is too thin, its rigidity may be less than desired, it is apt to bend and deform. An appropriate thickness is 30 μm or more. Conversely, if the thickness is too thick, the film may not well match the coating roll 11. The thickness should be 300 μm or less. The thickness is preferably approximately 40˜200 μm. The preferable thickness also applies to a cover film consisting of two laminated sheets of film, depending upon the materials used.
The surfaces of the cover film 15 may be both smooth, and its roughness may also be treated it may be treated with a detaching agent such as Teflon (registered trademark) in order to lower the friction resistance on the surface in contact with the coating roll 11. Also, the dispersion slurry 24 may likely adhere by the action of electric adsorption on the surface of the cover film in contact with the dispersion slurry, so the surface of the cover film 15 in contact with the dispersion slurry is desired to be given an electrostatic or a metal vaporizing treatment.
<Positions of Free End of the Cover Film and Controlling of Such Positions>
The relation between the position of the bottom end of the coating roll 11 and the free end of the cover film 15 extending downstream with respect to the running direction of the substrate 12 affects the staining of the coating roll 11 or the easiness of dispersion slurry to separate from the edge of the cover film 15, so it is one of the very important elements.
In case a pattern spacer 31 is provided for forming a pattern, in addition to the above-mentioned distances a and b, as shown in
Note that
A distance ‘a’ from the bottom end of the coating roll 11 to the front end of the cover film 15 is desired to be more than 1 and preferably 3˜30 mm, and more preferably 5˜25 mm. If the distance is shorter than 3 mm, the edge effect is not sufficiently exhibited, and the disperse slurry may likely adhere onto the front end of the cover film 15 and to the peripheral surface of the coating roll 11 which is getting near to the front end of the cover film 15. Conversely, if the distance is longer than 30 mm, the dispersion slurry may adhere in solid form onto the surface of the cover film 15, and the coated surface may likely be non-uniform. On one hand, ‘b’ value, a distance in a vertical direction between the front end of the cover film 15 and the peripheral surface of the coating roll 11 is preferably long as much as possible in principle, but its appropriate value is approximately 1˜10 mm.
Distances c and d are selected appropriately depending upon the substrate 12 to be coated and the required coating patterns. Several examples of such distances are given in
Hereunder, principal conditions for coating a substrate with a dispersion slurry according to the present invention using a coater according to the present invention are explained:
First of all, the dispersion slurry is prepared by dispersing a super absorbent polymer (SAP) in a dispersing medium. Said SAP swells very much in water, but its swelling is controlled by adding an organic solvent such as methanol, ethanol, isopropyl alcohol, and propylene glycol, all being miscible with water, so the disperse slurry may be adjusted. To this system, as a viscosity adjusting agent or a coagulation inhibitor ethyl cellulose, PEO, or MFC may be added. Said SAP may be in such forms as fibrous, solid particulate, particulate or flaky form, but in making a slurry of such SAP, its forms are preferably particulate, powder or flake. A preferable form of SAP is a powdery form having an average particle diameter of 1000 μm or less, more preferably it has an average particle diameter of 100 μm or less.
As a substrate to be coated with this dispersion slurry, tissue, a generally used nonwoven fabric, a woven fabric and the like may be used. A preferable substrate is a bulky and porous substrate such as a bulky nonwoven fabric and a corrugated knitted fabric in which SAP particles can be contained in their network.
Next, a specific example is explained of coating a substrate with the above-described dispersion slurry using a coater for a dispersion slurry according to the present invention as shown in
In
Coating was performed using a coater of this configuration, and in a pattern of lines at intervals of 10 mm, a SAP coated substrate whose basis weight was 200 g/m2 was obtained. Note that, although in the course of coating there was no problem observed during the first several minutes, gradually later there was a tendency seen for lumps to be formed as the dispersion slurry adheres to the front end of the cover film and to the coating roll portion in close contact with the cover film, but as the speed was increased to 30 m/min, such lumps became smaller and less often happened.
Similarly, in the condition shown in
Furthermore, in the condition shown in
Note that, in
In addition, an example shown in
In case the coating roll 11 is so constituted that it rotates continuously in one direction with its axis center as the center, a relative difference in speeds between the running speed of the substrate and the peripheral speed of the coating roll is expressed with a case where such difference is in a range of −10%˜+10% as a constant speed. The relation between the running speed of the substrate and the rotational speed of the coating roll depends upon such factors as the thickness of the film, the running speed and the desired basis weight; when the rotational speed of the roll is zero, i.e. the roll is at a standstill, the film not being given any tension gets slackened so some or other scheme is required to give tension to the film and thus making the equipment more complicated. It is preferable to make the roll to rotate thereby allowing the film in close contact with the roll and its end portion is to be stable.
The rate of rotation depends upon the running speed, so it is difficult to regulate the range of the rates of rotation. A normal running operation is to change the running speed of the substrate appropriately at a constant rotational speed and a constant tension given to the film. Tables 3 and 4 show examples of setting such conditions.
Table 3 shows the relation of the running speed to the rotational speed of the roll at the running speed of 50 m/min. The running operation gets stabilized if the running speed is beyond approximately 5 m/min (10%). If a zone of 90% or higher and 110% or lower of approximately the equal speed as the speed of the substrate is made to be the equal speed zone, a zone of 10% or higher and 90% or lower is called a low speed zone and a zone of 110% or higher and 30% or lower is called an high speed zone.
The roll rotates always via the film, so what are being affected by the rotation of the roll are the contact of the film and a delicate change in the front end of the film. If the speed is higher than 75 m/min (150%), the tension gets high and at the same time sometimes the front end of the film may vibrate. If such vibration gets intense, the coating may get disturbed, but lumps may be prevented from developing and growing. Such vibration effect is highlighted by providing shallow grids on the surface of the coating roll.
In case the running speed of the substrate is changed over a wide range, as shown in Table 4, it becomes possible to make the substrate run independently of the speed of the coating roll by fixing the rotational speed of the coating roll at around 30 m/min and optimizing the material and the thickness of the film to such speed.
Fixing of Cover Film Onto the Coating Roll
The regulation of the position of the cover film 15 to the coating roll 11 is, as shown in
For fixing the cover film 15 by the side seal 13′, in addition to the positional regulation, a function for preventing leakage of the dispersion slurry is also needed, so an appropriate fixing means is desired preferably depending on some conditions such as whether the coating roll 11 rotates or not, the thickness of the cover film 15, etc.
Also, in case the coating roll 11 rotates, the cover film 15 is at all times given a tension, so for a stabilize operation incoming air is prevented by applying a small amount of PEG or the like to the cover film 15 when it is first installed.
An advantage of the method shown in
On the other hand, in the case of
Also, in the case of
<Multi Layered Cover Film>
As explained previously, the cover film may be of a single layer or of two laminated sheets of film. This multi layered cover film may be not only of two sheets of film wholly bonded together, but also of a combination of a longitudinally long film with a longitudinally short film, or a combination of a laterally wide film with a laterally narrow film.
In the present invention, no particular restrictions are imposed on the diameter of the coating roll, but generally speaking, the diameter of the coating roll is in a range of 100˜500 mm, and in this case, the distance of the edge of the second film extending from the bottom end position of the peripheral surface of the coating roll to the downstream side with respect to the running direction of the substrate is preferably 1˜50 mm.
As explained above, a coater according to the present invention enables a dispersion slurry to be coated in a uniform thickness in the width and the length direction at a wide range of speeds in the coating of nonwoven fabric substrates over a wide basis weight. Furthermore, in case a cover film is applied, such problem a dispersion slurry adheres to the surface of a coating roll can be solved without any complicated equipment and capital cost increases involved that, as is common to any contact type coater which is in direct contact with a substrate such as a bar coater and a knife edge coater. Therefore, a coater according to the present invention is suitable to the coating of nonwoven fabric substrates.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2001-256454 | Aug 2001 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP02/08558 | 8/26/2002 | WO | 00 | 2/25/2004 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO03/018210 | 3/6/2003 | WO | A |
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|---|---|---|---|
| 771998 | Pick | Oct 1904 | A |
| 3024948 | Rabl | Mar 1962 | A |
| 4239821 | McLean et al. | Dec 1980 | A |
| 4357373 | Cooper | Nov 1982 | A |
| 4978402 | Hallworth | Dec 1990 | A |
| Number | Date | Country |
|---|---|---|
| 5-41811 | Oct 1993 | JP |
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| 11-34200 | Feb 1999 | JP |
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| Number | Date | Country | |
|---|---|---|---|
| 20040211361 A1 | Oct 2004 | US |
