TECHNICAL FIELD

The present invention relates to a method and a system for creating apertures with melted edges in a web shaped material comprising: feeding a web-shaped material through a nip between a rotational ultrasonic horn and a rotational anvil roller, so as to create melted regions in said web-shaped material, while the web is residing on the anvil roller having a rotational speed.

BACKGROUND OF THE INVENTION

Apertured surface materials are often used in disposable personal care products such as diapers, sanitary napkins, or the like. The apertured materials could be used e.g. as topsheets, as intermediate layers in the products or at the edges thereof. For certain applications it is desired to have apertured web-shaped materials with sealed edges. For instance, this could be the case for materials that are to be used as topsheets or acquisition layers in absorbent products. The edges being sealed ensures that any liquid received on the topsheet passes through the apertures without being absorbed via the edges of the apertures.

The application of apertured materials is however not limited to materials intended to allow liquid to pass therethrough. For example, apertured materials could also be absorbent, having apertures so as to allow the materials to breathe.

Known processes for forming apertured web-shaped materials with sealed edges include thermobonding followed by aperturing the regions of the thermobond, needling, mechanical cutting, laser cutting, water jet cutting etc.

Usually, the apertured materials are acquired separately and brought to a product manufacturing process where they are bound to form a product, such as a disposable personal care product. Accordingly, the manufacturer of absorbent products must order and stock sufficient amounts of apertured materials, and have limited capability of adjusting the acquired apertured materials to the needs e.g. of new products. Alternatively, the product manufacturer may have their own aperturing equipment, although said aperturing equipment is then separate from the equipment for forming the complete absorbent product

In view of the above, it is desired to provide a method for creating an apertured web material which is suitable for inclusion in an in-line manufacturing process of a personal care product To this end, the method should be applicable to different line speeds, as may be required for the manufacture of different types of personal care products

Moreover, regardless whether the apertured surface material is created in an in-line process or not, there is generally a need for providing apertured surface materials in a cost-efficient and quick manner

There is also a need for providing apertured laminated surface materials in a cost-efficient and quick manner

The object of the invention is to provide a method for creating an apertured web with sealed edges, which is advantageous in view of one or more of the above-mentioned aspects

SUMMARY OF THE INVENTION

The above-mentioned object is achieved by a method for creating apertures with sealed edges in a web shaped material comprising

- feeding a web-shaped material through a nip between a rotational ultrasonic horn and a rotational anvil roller, so as to create melted regions in said web-shaped material,

-while the web is residing on the anvil roller having a rotational speed, and controlling the rotational speed of the ultrasonic horn to a speed other than that of the anvil roller, such that a speed difference is created between the horn and the anvil roller, the speed difference being selected such that the stress created in the web acts to rupture the centres of the melted regions in the web-shaped material, whereby apertures with melted edges are created

A method as described above has the advantage of being susceptible to inclusion in an in-line process for manufacturing an absorbent product As the method relies on control of a speed difference between the horn and the roller, the method may be used in a wide range of anvil roller speeds, and may easily be adapted to the requirements of an in-line process

The method utilises the stress created in the web by the speed difference between the ultrasonic horn and the anvil roller to create apertures Simply put, the ultrasonic energy will create melted regions in the web-shaped material, which are relatively brittle As the web is affected by the stress created by the speed difference, the brittle centres of the regions will rupture However, the edges of the melted regions will remain intact Accordingly, apertures having melted edges are created

That regions being melted by ultrasonic technology may unintentionally rupture has been known in the past However, this process has been regarded as a randomly occurring fault which is to be avoided when e g forming ultrasonically laminated products

The present invention aims to provide a reliable and controllable method for deliberately producing apertures with melted edges in a web material, which is clearly different than such apertures occurring randomly as a fault in a process e g for lamination

In particular, the speed difference is actively controlled and selected so as to purposely arrive at the desired apertures with melted edges

The production of apertures could be made continuously over a web area or intermittently, e g in selected regions of the web area

The versatility of the ultrasonic welding technology in combination with the advantage that the proposed method is suitable for a wide range of manufacturing speeds, including such that are used for in-line manufacturing of absorbent articles, make the proposed method particularly suitable for including in a production line for in-line manufacturing of articles When the method is implemented in this context, the manufacturer is only required to purchase and stock standard, un-apertured web material, to be used in the in-line manufacturing process Via the proposed method, the standard web materials may be provided with selected apertures in-line, said apertures being suitably adapted to the needs of the absorbent product which is manufactured in the in-line process Advantageously, the nip may be a non-contact nip. This is preferred since use of a non- contact nip results in reduced wear of the components involved. However, the method per se is not restricted to non-contact nips but may be used also in a contact nip.

Preferably, the rotational speed of the horn may be controlled in relationship to the speed of the anvil roller, so as to maintain a controlled speed difference regardless of the speed of the anvil roller. This provides a particularly adaptive system, where the speed of the process as a whole may be varied substantially without affecting the creation of the apertures. This is particularly beneficial when the method is to be included in an in-line product manufacturing process, as the speed of the complete manufacturing line may need to be varied for different purposes concerning different manufacturing steps in the procedure.

Advantageously, the web-shaped material may comprise at least two separate plies, which are fed through the non-contact nip such that the at least two plies are laminated together via the melted edges of said apertures. In this case, the web-shaped material is laminated and apertured in a one-step procedure. This provides is a simple and robust process for creating laminated, perorated plies, which moreover provides lamination and apertures in perfect register.

The web-shaped material may comprise any number of plies, for example at least 4, preferably at least 6 separate plies which are laminated together via the melted edges of said apertures. The proposed method is believed to be able to laminate and perforate a relatively large number of plies, as long as the thickness of the plies is such that the supplied ultrasonic energy is properly transmitted through all of them so as to melt the material therein.

Preferably, the rotational speed of the horn is other than 0, e.g. the horn is indeed intended to rotate.

Advantageously, the difference in rotational speed between the anvil roller and the horn in relation to the rotational speed of the anvil roller ((speed roller - speed horn)/speed roller) is in the range ±10-100 %, preferably ±10-90 %, most preferably ±30- 90 % of the speed of the anvil roller. The anvil roller and the horn may rotate in the same direction or in different directions If they rotate in different directions, it is understood that the speed difference between them is calculated as the true relative speed difference, using the anvil roller direction as the positive direction If e g the anvil roller rotates clockwise, a clockwise rotation will be 5 positive, and if the horn rotates counter-clockwise, the counter-clockwise rotation will be negative Accordingly, speed roller - speed horn will give the true difference in rotational speed

The above-mentioned speed differences are believed to be particularly suitable for 10 creation of the desired apertures

Advantageously, the difference in rotational speed between the anvil roller and the horn is in the range 20 - 300 m/min, preferably in the range 25 to 250 m/min, most preferred in the range 100 to 250 m/min 15

Advantageously, the rotational speed of the horn is in the range 5-500 m/min, preferably 50-450 m/min

Preferably, the total surface weight of the web-shaped material is between 10 gsm and 20 300 gsm

The web-shaped materials could be any materials susceptible to ultrasonic welding Preferably, such a material may comprise a thermofusible material

25 However, when multi-ply web shaped materials are formed as a result of the method (ι e lamination takes place), it is understood that all plies need not include meltable material Instead, it is sufficient that there is at least one ply which includes a material which does melt, whereby the desired lamination may be accomplished For example, a non-melting ply may be sandwhiched between two melting plies, and subject to the method for

30 creating apertures with sealed edges The method will then result in a multi-ply web where all three plies are laminated together along the sealed edges of the apertures

Preferably, the web-shaped material comprises at least one ply of a nonwoven material Nonwoven materials are fibrous materials including either homogenous or mixed fibres 35 Preferably some or all of the fibres may comprise polyolefins, e g polymer materials such as polyethylene and polypropylene, or alternatively materials made out of polyester, nylon or the like

Alternatively, or in addition to the non-woven material, the web-shaped material may comprise at least one ply of a film material Suitable films may be films of thermoplastic materials, e g polyethylene or polypropylene

The web-shaped material may also comprise at least one ply being in the form of materials made from natural fibres such as wood or cotton fibres, foam material or other materials that are capable of being welded using ultrasonic technology

With the proposed method it is possible to bond e g nonwoven materials to nonwoven materials, nonwoven materials to film materials, or film materials to film materials to form a multi-ply material

The web-shaped material could also comprise a multi-ply material which is already laminated before being subject to the method for creating apertures with sealed edges The lamination of the multi-ply material may then be enhanced by the creation of the melted regions surrounding the apertures Also, a laminated material could form one ply which is connected to one or more additional plies by means of the proposed method

Preferably, the web-shaped material as a whole comprises at least one of polypropylene, polyethylene, and polyester

Preferably, the horn and the anvil roller may be selected such that the width of the melted regions in the cross direction of the web is in the region 0 5-2 5 mm, preferably 0 6 to 2 0 mm The width of the melted regions is to be understood to be the width of the regions including the apertures (ι e the width of the aperture with the sealed edges) Hence, when measuring the width of a melted region in a finalised product, the measurement will take place in the machine direction and extending over an aperture It will be understood that the apertures per se will have a width in the cross direction which is smaller than that of the melted region

The proposed method is particularly suitable for creating relatively small, discrete apertures with sealed edges Such apertures with their sealed edges may have substantially the same extension in the cross direction as in the machine direction, having e g circular or square shapes The horn and the anvil roller may advantageously be selected such that the individual areas of the melted regions including the apertures are greater than 0 01 mm ² , e g in the range 0 2 mm ² to 3 5 mm ² , preferably 0 3 mm ² to 3 mm ²

However, the extension of the melted regions in the machine direction perpendicular to the cross direction may vary considerably For example, elongated melted regions including apertures may be created having a relatively large extension in the machine direction In this case, the individual areas of the melted regions may e g be greater than 3 mm ² , preferably greater than 5 mm ² , most preferred greater than 10 mm ²

Moreover, it will be understood that considerably larger apertures than those exemplified above may be created using the proposed method

Generally, for the measurement of sizes or areas of the melted regions and/or the apertures, image analysis methods may be used

The size of the melted regions may generally be controlled by the appearance of the anvil roller, which may be provided with protrusions having selected individual areas, which protrusions affect the formation of the melted regions The melted regions will appear in the web-shaped material opposing said protrusions, as is known in the prior art

In another aspect of the invention, there is provided a method for producing an absorbent article, wherein a web-shaped material is prepared to form a sheet in the article in an article forming process, and wherein the web-shaped material is apertured in-line with the article forming process and prior thereto in accordance with a method as described above Hence, in this case the aperturing process form part of an in-line process for producing an absorbent article

In such articles, the apertured web-shaped material may form any sheet which is typically apertured, such as a topsheet, a transition sheet or the like

In another aspect of the invention there is provided a system for continuously creating apertures with sealed edges in a web shaped material comprising - a rotational anvil roller

- a rotational ultrasonic horn, said anvil roller and said horn being arranged in an opposed relationship forming a nip through which a web residing on said anvil roller may be fed, for creation of melted regions in said web-shaped material, and means for controlling the rotational speed of said horn independently of the rotational speed of the anvil roller, enabling the system to be adjusted to create a stress in the web sufficient to create apertures in melted regions, resulting in a web being provided with apertures with melted edges Features and advantages as described above in relation to the method are equally applicable to the system

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in some more detail by reference to non-limiting examples and to the accompanying drawings wherein

Fig 1 illustrates an embodiment of a system for carrying out an embodiment of the method for creating apertures

Fig 2a illustrates an embodiment of an apertured web as obtained by an embodiment of a method in accordance with the invention, and Fig 2b illustrates another embodiment of an apertured web as obtained by an embodiment of a method in accordance with the invention

DETAILED DESCRIPTION

Fig 1 illustrates schematically a system for carrying out the method for continuously forming apertures with melted edges in a web-shaped material

A rotational anvil roller 2 and a rotational ultrasonic horn 1 are arranged to form a nip in which a web-shaped material 4 is apertured The rotational speeds of the anvil roller 2 and the horn 1 , respectively, are controlled by a controller 3 Advantageously, the controller 3 may keep the speed difference between the horn 1 and the anvil roller 2 constant, regardless of the speed of the anvil roller 2 The web-shaped material 4 is fed on the anvil roller 2, which is why the speed thereof will decide the feeding speed of the system If the system is arranged in-line with e g machinery for forming an absorbent article, then the speed of the anvil roller 2 will have to match the feeding speed of the absorbent article formation process Accordingly, it is advantageous that the speed of the system is variable

For the rotational anvil and the rotational ultrasonic horn, previously known technology may be used, such as described e g in EP 0 457 187 However, in prior art technology, rotational horns and anvils are generally controlled such that no speed difference appears between the horn and the anvil The control of the rotational speeds of the horn and the anvil may be adapted as described herein using conventional automatic control engineering

In the embodiment illustrated in Fig 1 , the web-shaped material 4 is directly fed into the nip between the ultrasonic horn 1 and the anvil roller 2 In the illustrated embodiment, the nip is a non-contact nip If desired, the web-shaped material may be compressed in a pre- compression unit before feeding into the nip

It shall be understood that, when the web-shaped material 4 comprises several plies, the material for the separate plies may be fed from separate rollers and meet before the pre- compression unit (if present) or before being simultaneously fed into the nip between the horn 1 and the anvil roller 2

In the illustrated embodiment, the rotational anvil roller 2 and the rotational horn 1 are illustrated as rotating in the same rotational directions (see the arrows) This is believed to be particularly advantageous in particular as it facilitates control of the units However, the horn 1 and the anvil roller 2 may also rotate in different rotational directions

The precise speed difference to use will vary depending e g on the material of the web- shaped material, its thickness, and the number of plies therein However, the process for selecting the proper speed difference in a particular case is easily performed of a person skilled in the art As the frequency of the ultrasonic horn of a conventional system is usually not selectable, but remains within about 20 kHz to 40 kHz, the person skilled in the art is bound to the pre-selected frequency The welding power of the horn may be adjusted to the highest power available before contact with the anvil roll appears Contact with the anvil roll is generally not desired as it will lead to wear of the parts

Once the welding power is set, the person skilled in the art may start the process with the selected web material, and vary the speed difference between the anvil and the horn until the desired apertures with melted edges result The desired result, being the apertures with their melted edges, is easily verifiable by the person skilled in the art, which makes the setting of a correct speed difference easy Generally, suitable speed differences are believed to be those as specified in the above

Fig 2a illustrates a portion of an embodiment of an apertured web as obtained by an embodiment of the proposed method The web 10 is provided with apertures 20, each aperture being surrounded by a melted region 30 where the web material surrounding the aperture 20 is melted so as to form a seal around the aperture 20 Since the aperture 20 is created by stresses causing the initially integral melted region 30 to rupture, the precise borders of the actual aperture 20 may vary somewhat, although they will in general follow the contour of the melted region 30 The rupture is generally believed to involve some shattering of the material in the sealed Accordingly, the resulting aperture is not only a melted region including a crack or slit Rather, at least some of the melted material in the melted region is shattered and hence removed from the web, such that an aperture with sealed edges is formed

In view of the above, it will be understood that, when the method is used to create a plurality of apertures with sealed regions, said apertures having the same dimensions, measurements of the sizes of the apertures 20 per se, as could be made by image analysis methods, may reveal slight variations from aperture to aperture,

The melted regions 30 will have a more uniform appearance, as created by the ultrasonic process Their size could likewise be determined using image analysis methods

However, it will be understood that the difference in area between the melted region 30 and the aperture 20 will be relatively small, and moreover be approximately the same for different individual apertures 20 Accordingly, a measure of the dimensions of the melted regions including the apertures may be used for reflecting the dimensions of the apertures, and may in many practical applications be sufficient for serving the purpose of approximately determining the size of the apertures

Hence, for practical purposes, it is proposed to use the dimensions of the melted regions 30 including the apertures 20 rather than the dimensions of the apertures 20 as a relative measure of the properties of the apertured web 1

In Fig 2a, the web 1 is provided with a number of discrete apertures 20 The width a of the melted region 30 including an aperture 20 (ι e the width of the aperture with its sealed edges) as measured in the cross-direction CD of the web is approximately the same as the length b as measured in the machine direction MD of the web In this case, the width a and the length b may be in the region 0 5 - 2 5 mm, preferably 0 6 to 2 0 mm In other embodiments, the area of each discrete melted region 30 may be greater than 0 1 mm ² , preferably in the range 0 2 to 3 5 mm ² , most preferably 0 3 to 3 mm ²

In Fig 2b, the web 1 is likewise provided with a number of apertures 20 The width a of the melted region 30 including the aperture as measured in the cross-direction CD of the web is considerably smaller than the length b as measured in the machine direction of the web For example, the length b may be more than twice the width a The area of each melted region 30 may in this embodiment be greater than 3 mm ² , preferably greater than 5 mm ² , most preferred greater than 10 mm ²

Both embodiments as described above are suitable for forming a multi-ply web, that is, two or more web shaped materials are laminated via the melted regions 30

It will be understood, that the present invention may be varied within the scope of the appended claims For example, the invention is not restricted to web shaped materials in the form of essentially continuous webs of material alone Instead, it may also be used where the material consists of discrete items that are fed past an ultrasonic device Moreover, the apertures need not extend continuously over the entire length of the web shaped material but may be applied e g only to selected regions of the web shaped material