Field of the Invention

The invention relates to an apparatus for dispensing

absorbent sheet products comprising a store with an absorbent web which is to be dispensed, a conveying means with at least one rotatable conveying element in contact with the absorbent web for feeding the absorbent web, and means for severing the absorbent web so as to form absorbent sheet products.

Background Art

Dispensers for absorbent sheet products are well-known in the art. Such apparatus comprise a store with an absorbent web which is to be dispensed. The web is conveyed with at least one conveying element for feeding the absorbent web to a position where it is cut so as to form separate absorbent sheet products for a user. In dispensers for absorbent material, like tissue material, a build-up of electrostatic charge can be observed. When two bodies of different material are in contact which each other, there is migration of electrons between the two surfaces. The number of electrons that migrate is dependent on the difference in the so-called work function of the two materials. The term "work function" stands for the energy required to remove an electron from the surface of a specific material to infinite. Ά material with a lower work function acts as a donor. From such donor

material, the electrons migrate to the acceptor material with the higher work function. If the two bodies suddenly are separated from each other, the electrons try to return to their parent material. In the cases were the material is conductive, this is possible and the electrons migrate back to their parent material. However, if one or both of the two bodies are insulating materials, this will not happen. As a result, electrons get trapped In the surface of the material to which they have migrated. Thus, the factual charge is relatively small. Nevertheless, such static discharges still might be damaging to electronic components or unpleasant to a user.

Static electricity generates high voltages with low currents. Commonly accepted Standard IEC 61000-4-2 limits the allowable maximum voltage level to an amount smaller than +/- 8000V. If the electrostatic charge exceeds such maximum voltage, it might affect other electrical components. Further, it is even possible that a user might be exposed to unpleasant

discharges .

Various factors influence the build-up of electrostatic charges. The first factor is the type of material. In order to create an electrostatic build-up two bodies have to be in contact with each other, where at least one of them should be a bad conductor. When there are two bodies of dissimilar material it could cause the material to charge even more than when two similar materials are in contact with each other. This is the effect of the dielectric constant, or the work function. A material with high relative permittivity (the electric constant) becomes positively charged when it is separated from a material with low permittivity. A second factor is the contact area between dissimilar materials. The larger the contact area is the more electrons migrate between the materials. As a result of this, a large contact area promotes a high electrostatic charge build-up. A third factor is the separation speed. The higher the speed of separation of the two materials is the less is the possibility for the electrons to move back to the parent material. A higher separation speed results in a higher charge build-up. A further factor of influence is a possible motion between the materials. Firstly, the local heat generated by the friction between materials increases the energy level of the atoms making the escape of electrons easier. Secondly, a movement causes better surface contact by bringing the microscopic irregularities on both surfaces in contact with each other thus increasing the possibility of the electrons to migrate from one material to the other. The same applies for a higher temperature which results in easier release of electrons due to the higher energy level. Finally, atmospheric conditions can also influence the build-up of electrostatic charge. The more moisture there is in the atmosphere, the better is the ability of discharge. However, this is not true for all materials. For dispensers of the kind as stated above, however, the observation has been made that the electrostatic build-up tends to be higher in winter where the relative humidity of the ambient air is usually smaller.

Measurements show that the parts in a conventional dispenser which generate electrostatic charges are the conveying rolls and the knife or tear bar for severing the web into

individual sheets. The paper leaves a dispenser positively charged so that the dispenser apparatus itself experiences a build-up of negative electrostatic charges.

Summary of the Invention

It is an object of the invention to provide an apparatus for dispensing absorbent sheet products which, by simple means, effectively reduces the problems associated with

electrostatic build-up. This object is solved by an apparatus with the features of claim 1. Preferred embodiments follow from the other claims.

According to the invention, an apparatus for dispensing absorbent sheet products comprises a store with an absorbent web which is to be dispensed, a conveying means with at least one rotatable conveying element in contact with the absorbent web for feeding the absorbent web and means for severing the absorbent web so as to form absorbent sheet products. The apparatus is characterized in that the conveying element is designed such that the surface contact factor is less than 30%, preferably less than 20%, and most preferably less than 10%.

Throughout the description, the surface factor is defined as the percentage relation between the contact area between the conveying element and the absorbent web, and the contact area between a cylindrical roll acting as the conveying element and the absorbent web. In order to properly define the surface contact factor, a full revolution of the conveying element and a corresponding amount of absorbent web fed by the conveying means have to be taken as a basis. The surface contact factor according to this definition could be

visualised in a simple way. If the contact area between the conveying element and the absorbent web left a colored marking on the absorbent web, the surface contact factor would be equal to the percentage area of the web which becomes colored. If there is more than one conveying element, the surface factor is calculated or measured for each

conveying element separately.

If the surface contact factor is less than 30%, one of the main factors for the build-up of undesired electrostatic load is greatly reduced. Depending on the specific design of the conveying means and especially the at least one rotatable conveying element, the surface contact factor might even be further reduced. According to a preferred range, the surface contact factor is less than 20% and most preferably less than 10%. If a surface contact factor being as small as 10% or less is used, care has to be taken that there still remains a sufficient grip of the at least one rotatable conveying element with the absorbent web so that the desired conveying function can still be realized.

The apparatus for dispensing is not limited to any particular type of dispenser and has utility for any dispenser wherein it is desired to reduce the generation of charges by providing a greatly reduced contact area between a conveying element and the absorbent web. The dispenser may be a "hands free" dispenser that is automatically actuated upon detection of an object placed within a defined detection zone. In alternative embodiments, the dispenser may be actuated upon the user pressing a bottom, switch or manual actuating device to initiate a dispense cycle. The dispenser may as well be of such type where the user grasps the absorbent material to be dispensed and pulls out a metered length of such absorbent material.

The store within the apparatus may be a roll on which an absorbent web is wound. It might as well be a store in which the web material is folded to a stack.

According to a preferred embodiment of the invention, the conveying element is a drive roll. As outlined above, the build-up of undesired static electricity depends on factors like the separation speed, a pressing force between the materials in contact with each other and the generation of friction between the materials. Therefore, a drive roll is especially prone to the build-up of undesired electrostatic load. Thus it is desirable to provide a drive roll with a surface contact factor within the inventive range.

Preferably, the store is a feed roller with the absorbent web wound thereon, and the drive roll creates a nip with the feed roller. Such an embodiment combines the conveying means with the store of the dispensing apparatus. The drive roll

directly cooperates with the feed roller so that no further conveying element is necessary. This also reduces the surface contact area between the absorbent web and the conveying means, simply by omitting a further conveying element.

According to an alternative embodiment of the invention, the conveying means comprises a second conveying element which is a guide roll. The guide roll has a surface contact factor less that 30%, preferably less than 20%, and most preferably less than 10%. If this alternative approach is selected, the conveying means comprises a drive roll and a cooperating guide roll. However, for the guide roll the same requirements exist as for the drive roll. Therefore, the guide roll also has a highly reduced contact area to the absorbent web resulting in a surface contact factor less than 30%. What is most preferred is the situation that the conveying means comprises a guide roll and a drive roll, both of which have a surface contact factor less that 30%, preferably less than 20% and most preferably less than 10%.

According to a preferred embodiment, at least one of the conveying elements is provided with a rotational shaft to which at least one wheel or cog wheel or cross-wheel

contacting the absorbent web is mounted. This leads to the situation that only very specific parts of the conveying elements are in contact with the absorbent web. If the contact area between the conveying element and the absorbent web is reduced too much, this also might have a negative impact. Firstly, a certain pressure will be needed in order to safeguard a transport of the absorbent web. This could leave undesirable marks or traces on the absorbent web.

Secondly, friction effects between the conveying element and the absorbent web might increase. In order to avoid such negative effects while maintaining a small surface contact factor, the use of cog wheels has been found to provide favourable effects. If the undulated peripheral surface of a cog wheel elastically presses somewhat into the yielding absorbent web, very small contact areas are sufficient to ensure a safe transport.

As an alternative to the above-described embodiment of a conveying element provided with a rotational shaft to which wheels or cog wheels are mounted, it is also possible to provide a conveying element comprising a plurality of

radially arranged plates mounted to a rotational shaft, preferably four radially arranged plates. If this solution is used, it is important that either a sufficient number of radially arranged plates are provided or that the absorbent web is partially directed around the conveying element such that there is always at least one of the plates contacting the absorbent web so as to provide for a continuous conveying movement of the absorbent web.

According to a preferred embodiment of the invention, at least one of the conveying elements comprises a plurality of cross-wheels, the individual cross-arms of different

cross-wheels being preferably angularly shifted relative to each other. This specific embodiment is a combination of the two above-described basic shapes of the conveying element. It combines the idea of providing individual wheels or cog wheels on a rotational shaft with the basis idea to provide a plurality of radially arranged plates mounted to a rotational shaft, preferably four radially arranged plates. The

provision of cross-wheels bars reduces the contact area between the conveying element and the absorbent web to a minimum. If the individual cross-wheels bars are angularly shifted relative to each other, the positive effect can be achieved that despite of only four contact areas of each "wheel" made of two cross-shaped bars, a constant contact between at least one of the cross-shaped bars and the

absorbent web can be realized.

Preferably, the apparatus for dispensing is characterized in that the wheels or cog wheels or cross-wheels bars of the drive roll and of the guide roll are arranged such that the first contact areas between the drive roll and the absorbent web and the second contact areas between the guide roll and the absorbent web do not overlap in the plane of the web. Although the absorbent web to be conveyed has a certain thickness, reference to a "plane of the web" neglects the thickness of the web and considers the web to be a

two-dimensional structure. If the first contact areas and the second contact areas do not overlap, this means that the contact areas on the front side and on the backside of the web are at different positions. This, in turn, means that no nip forms between the drive roll and the guide roll but that drive roll and guide roll independently contact the absorbent web in order to convey it. This specific arrangement reduces the pressure on the absorbent web being one of the factors which is responsible for undesirable build-up of

electrostatic charges.

According to another preferred embodiment, the conveying means comprises a drive roll and a guide roll, the drive roll being provided with wheels or cog wheels or cross-wheels having a first radius, and the guide roll being provided with wheels or cog wheels or cross-wheels having a second radius, wherein the rotational axes of the drive roll and of the guide roll are parallel to each other, and the shortest distance between the parallel axes is smaller than the sum of the first radius and the second radius.

The radius of cross-wheels is considered to be the minimum inner diameter of a cylinder around such a structure with cross-wheels. If the shortest distance between the parallel axes is smaller than the sum of the first radius and the second radius, the absorbent web cannot run between the drive roll and the guide roll in a planar fashion. It has to assume an undulated shape in the cross-sectional plane including the rotational axes of the drive roll and of the guide roll. Such shape makes it possible to realise a very small contact area between both the guide roll and the drive roll and the absorbent web. Due to the tendency of the absorbent web to resume its initial, flat position, such arrangement of drive roll and guide roll relative to each other provide high frictional forces to achieve a safe transport of the

absorbent web even if the contact area should be very small with a surface contact factor being even less than 5%. According to a preferred embodiment, the contact surfaces of the at least one conveying web to the absorbent web are covered with an antistatic material, preferably antistatic rubber or PE HD Reg 1000-Antistat material. Antistatic rubber means the material commonly used as a backside base material for antistatic carpets. Such material is readily available and can be affixed to the contact surfaces of the conveying element. When providing the contact surfaces with an

antistatic material, not only the surface area being one factor of influence for the build-up of electrostatic charges can be minimized, but another measure is used in combination, namely to reduce the antistatic load by means of suitable surface materials.

As an alternative preferred embodiment, the contact surfaces of the at least one conveying element to the absorbent web are covered with a material of similar dielectric behaviour as cellulose, preferably sandpaper. The absorbent web in dispensers is basically made of cellulose material for which the dielectric behaviour is known and can be taken from text books. A similar dielectric behaviour means that the absolute value of the dielectric constant of the material differs from that of cellulose only by a maximum of 20% and preferably only by a maximum of 10%. When using sandpaper, there is a further advantage. Firstly, the paper base provides for a similar dielectric behaviour as cellulose. Secondly,

sandpaper with a rough surface further reduces the surface contact area between the conveying element and the absorbent web and, at the same time, also reduces friction effects between the conveying element and the absorbent web. In such a way, many different factors negatively influencing the build-up of electrostatic load can be reduced: a small surface contact area can be covered with a covering having a similar dielectric behaviour as cellulose, wherein the covering material further reduces the effective contact area and leads to a high friction for the transport of the

absorbent web. In the above-described preferred embodiments, special emphasis was placed on the conveying means according to claim 1. However, it is also possible to further optimize the means for severing according to claim 1. Usually, this is a tear bar either fixedly mounted to the housing of the dispenser or operated such as to sever the absorbent web by means of a cutting motion. If such a tear bar is made of a chromate coated material, it has been found that the build-up of electrostatic load at the tear bar can be considerably limited in comparison to a conventional tear bar made of uncoated metal material, like stainless steel.

Brief Description of the Drawings

In the following, several embodiments of the invention will be described, by reference to specific examples shown in the accompanying drawings, in which:

Fig. 1 schematically shows the relevant parts of a

dispenser;

Fig. 2 shows the major components of the conveying means as well as a tear bar of an apparatus for dispensing;

Fig. 3 schematically shows a first embodiment of the

invention with a drive roll directly cooperating with a feed roll;

Fig. 4a schematically shows a second embodiment of the

invention in which both the feed roll and the drive roll are provided with cog wheels;

Fig. 4b schematically shows an alternative outer

circumferential shape of a cog wheel which could also be used in the embodiment schematically shown in Fig. 4a;

Fig. 5 schematically explains another embodiment of the invention by schematically showing an alternative shape of a drive roll and a guide roll;

Fig. 6 schematically shows another embodiment of the

invention incorporating a specific shape of the guide roll cooperating with a guide surface within a conveying means; and

Fig. 7 schematically shows the mutual positions of a drive roll and guide roll according to another embodiment of the invention.

Description of Preferred Embodiments

Throughout the following embodiments the same elements will be denoted by the same reference numerals.

Fig. 1 schematically shows a dispenser without its front shell removed in order to see the main parts of such

dispenser.

The dispenser generally denoted by reference numeral 10 has a housing which consists of at least two parts. The back shell 12 as shown in Fig. 1 can be affixed to a wall. The front shell (not shown) closes the dispenser and only leaves a slot through which the product can be dispensed.

Inside the dispenser, there is a feed roll 14 on which an absorbent web 16 is wound. This is just an example and, as outlined above, other types of dispensers can also be used to realise the invention, like dispensers in which the absorbent web is stored as a folded stack. In the example dispenser as shown in Fig. 1, the absorbent web 16 is wound from the feed roll 14 and passes through a conveying unit 18 which mainly includes a drive roll 20, a guide roll 22 and a tear bar 24, as shown in Fig. 2. The absorbent web 16 leaves the dispenser at position 26 where there is a slot in the front shell of the dispenser through which the absorbent product extends and can be removed by a user.

The main parts of the conveying unit 18 as shown in Fig. 1 are individually exemplified in Fig. 2. The absorbent web to be dispensed passes through the nip between a drive roll 20 and a guide roll 22 which _/ in Fig. 2, are individually shown without the correct mutual arrangement. In an attempt to provide for a good friction between the conveying unit and the absorbent web, the drive roll 20 might be provided with wheels or rings 28 of a high friction component, like suitable plastic material or rubber. The guide roll 22 can be made of any suitable material which cooperates with the drive roll to achieve a safe transport of the absorbent web between drive roll 20 and guide roll 22.

Fig. 2 also exemplifies the possible size and shape of a tear bar which might be a part of the conveying unit 18 so that the servicing of the dispenser consisting of individual modules might be simplified. However, it is also possible to provide a tear bar 24 separately to the conveying unit. In that case, the tear bar 24 is separately affixed to the housing of the dispenser. Tear bar 24 is provided with cutting teeth 30 which can be used by a user to sever a suitable length of the absorbent web. The invention is not restricted to this specific type of dispenser and it is also possible to provide tear bars cooperating with the conveying unit in oder to automatically sever a metered length of absorbent sheet.

It has been found that, during operation, most static load builds-up at the three components as shown in Fig. 2. Drive roll 20, guide roll 22 and tear bar 24 get negatively charged, whereas the absorbent web, especially tissue paper, leaving the dispenser is positively charged.

Fig. 3 shows a first embodiment of the invention in which the conveying means comprises a drive roll 20 which is rotatable in the direction of arrow A. The drive roll is provided with a rotating shaft 32 to which a ring-shaped wheel 28, in the following denoted as a ring 28, is affixed such that it rotates together with a drive roll 22. The connection between ring 28 and drive roll shaft 32 as well as the connections between the other elements as described in the following embodiments can be made by any suitable means like form fit elements between the shaft and the ring or by a press fit between the shaft and the ring.

In Fig. 3 it can be seen that the ring 28 of the drive roll 20 directly cooperates with the feed roll 14 so as to turn the feed roll 14 and to convey the absorbent web 16 in direction of arrow B if the drive roll is rotated in

direction of arrow A. Fig. 3 further shows a guide rail 30 which serves to separate the absorbent web from the feed roller. The use of only one roller to feed the absorbent web makes the structure both simple and minimizes the surface contact factor. The center mounted ring 28 creates traction with minimal paper surface contact by pressing in the

direction of the center of the feed roll as the absorbent web is unwound. The feed roll could also be placed underneath the feed roll letting the feed roll weight create the pressure.

The embodiment schematically shown in Fig. 4a only shows a part of the guide roll 22 and drive roll 20. Both rolls are provided with parallel shafts 32 and 34 which are parallel and rotate in opposite directions A and C. Cog wheels are rotationally fixed to drive roll shaft 32 and the guide roll shaft 34. Such cog wheels provide for a small surface contact factor of the drive roll and of the guide roll and, at the same time, the teeth 36 on the outer circumferential surface of the cog wheels 38 provide for a good grip between the cog wheels 38 and the absorbent web to be conveyed. The absorbent web passing inbetween the drive roll 20 and the guide roll 22 runs through the nips 40 formed between cog wheels 38 on the drive roll shaft 32 and correspondingly arranged cooperating cog wheels 38 on the guide roll shaft 34. This establishes a safe transport using only the teeth 36 on the cog wheels which leads to a very low surface contact factor of less than 5% for both the guide roll 22 and the drive roll 20,

respectively.

Instead of a cog wheel 38 having teeth 36 as shown in Fig. 4a it is also possible to provide an alternative cog wheel 38 as shown in Fig. 4b having an undulated outer circumferential shape. Such softly rounded protections as shown in Fig. 4b have the advantage that they do not leave undesirable marks on the absorbent web. It becomes apparent that, depending on the specific needs and especially the characteristic

properties of the absorbent web to be transported, a suitable shape of the cog wheels can be selected.

Fig. 5 shows another embodiment of the invention also

exemplified by means of another embodiment of a drive roll 20 and guide roll 22. In the example as shown in Fig. 5, both rolls have thin, plate like wall sections 42 in the

longitudinal direction. The wall sections 42 are radially disposed with regard to the longitudinal axes of the rolls which are defined by the center axis of the drive roll shaft 32 and guide roll shaft 34. In the example as shown in

Fig. 5, each of the rolls 20 and 22 are provided with four radially arranged, longitudinal plates 24. The absorbent web 16 passes through the nip 40 between drive roll 20 and guide roll 22. The plates 42 of both rolls are arranged such that at least one of the plates are always in contact with the absorbent web 16 to be conveyed. In such a way, the rolls only may contact with the absorbent web four times per revolution. The contact surface area with the absorbent web is accordingly very small which ensures that there is low electrostatic generation like in the preceding embodiments.

Fig. 6 shows another embodiment which can be considered to be a combination of the provision of individual rings and the geometry as shown with reference to Fig. 5. The transport of the absorbent web is carried out by means of a cross traction concept which optimizes the contact area by using only one roll with thin cross-wheels 44 rotating with the drive roll shaft 32 in direction of arrow A. The cross shaped bars of the cross wheels feed the absorbent web which runs over the surface of a guide rail 46. In order to show the structure of the conveying means, the absorbent web in Fig. 6, like in Fig. 5 described above, is shown as if it were translucent. The concept as schematically exemplified in Fig. 6 is very simple and compact since there is only one rotating roll necessary. The contact surface with the guide rail 46 should not be larger than necessary for a safe feed. In order to make sure that there is a safe feed, the absorbent web 16 has to be gripped by at least one of the four rotating cross-arms 48 at any time so that the absorbent web is always moving forward. The design as shown in Fig. 6 could be alternated with two or one cross-wheel only as long as the specific absorbent web to be fed is safely transported. The fewer cross-wheels 44 are used, the smaller becomes the contact area.

In the embodiment as shown in Fig. 6, all cross-wheels 44 have the same angular orientation of the individual cross- arms 48. However, it is also possible to angularly shift the position of the cross-arms of a plurality of individual cross-wheels so that, at all times, the absorbent web is gripped in a good relative position by at least one the cross-wheels.

The embodiment of Fig. 7 shows a drive roll 20 and a guide roll 22 both being provided with rings 28 which are affixed to the drive roll shaft 32 and the guide roll shaft 34.

Between the rings 28 the absorbent web 16 is transported. In the cross-sectional view as shown in Fig. 7, the absorbent web 16 is not planar but has an undulated cross section. The reason is that the shortest distance between the parallel axes of the drive roll and the guide roll is smaller than the sum of the radius of the rings on the drive roll and the rings on the guide roll. This leads to the effect that the rolls are negatively offset which each other by the distance D. This causes the absorbent web 16 to form a wave-like appearance when it is fed between the drive roll 20 and guide roll 22. Such wave-shape of the absorbent web enables a feeding with a good grip. The concept as shown in Fig. 7 eliminates direct contact between the rings on the drive roll and the rings on the guide roll which consequently lowers the pressure between the absorbent web and the rolls. Ά reduction of direct pressure is another means to decrease the build-up of static load.

The embodiment as shown in Fig. 7 was exemplified by showing rings 28 on the drive roll and on the guide roll. However, it is also possible, instead of using the wheels in Fig. 7 to employ cog wheels or cross-wheels as shown in Fig. 6.

In all the above shown embodiments, there is a small surface contact factor between at least one conveying element and the absorbent web. In an attempt to even further decrease the risk of an undesirable build-up of electrostatic load, the contact surfaces of the at least one conveying element to the absorbent web can be further modified. One possibility is to cover such contact surfaces with an antistatic material.

Among such materials, PE HD Reg 1000 Antistat material or so-called antistatic rubber are preferred choices. Antistatic rubber is the rubber base of commercially available

antistatic carpets. This material has good leading ability as it is a semi-conductive material. Another possibility to decrease the build-up of static load is to provide contact surfaces which are covered with a material whose dielectric behaviour is similar to that of cellulose forming the major part of the absorbent web. In this respect, good results could be obtained by using sandpaper having, on the one hand a paper base and having, on the other hand, a good grip and low contact area to the absorbent web due to the surface topography of sandpaper.

All the above-described embodiments have in common that special measures have been taken to reduce the surface contact factor as much as possible in order to effectively reduce the undesirable build-up of static load. In such a way, surface contact factors as small as 5% can be realized.