METHOD FOR PRODUCTION OF DISPOSABLE ABSORBENT ARTICLES
TECHNICAL FIELD
The present invention relates to a method for production of disposable absorbent articles attachable to the lower end of a torso, said method comprising assembling a continuous production web comprising chassis components, absorbent core components, a topsheet and a backsheet, and advancing the production web continuously in a machine direction, the machine direction coinciding with a main longitudinal axis of each absorbent article. The invention also pertains to disposable absorbent articles produced according to the method.
BACKGROUND ART
In the production of disposable absorbent articles, such as belted diapers, absorbent pants, open diapers and the like, cost is a critical factor. A disposable article is understood as meaning an article which is intended to be discarded when used and which is not washed or otherwise restored for absorption purposes. It is therefore important that absorbent articles of this type can be produced as easily and as efficiently as possible.
The main components in diapers of different kinds are usually an absorbent body which is arranged between two cover sheets, one of which is a liquid barrier sheet, for example a plastic film, and the other a liquid-permeable cover sheet, for example a nonwoven sheet. Further components, such as inner barriers, for example raised edge barriers, arranged in connection with the liquid-permeable cover sheet, or textile-like outer covers arranged outside the liquid barrier sheet can also be present. The diapers are designed with a front portion which, during use, is directed forwards on the user and lies across the latter's groin area, a rear portion which, during use, is directed rearwards on the user and lies across the latter's buttocks, and a crotch portion which is arranged between the front portion and the rear portion and is intended to be positioned at the user's crotch. The front portion, the rear portion and the crotch portion together provide the diaper with two leg openings and a waist opening.
In order to ensure that the absorbent article will fit a user's body shape and body size like an article of clothing, and in order to form closure seals preventing leakage around the leg openings and the waist openings, absorbent articles such as diapers are generally also provided with elastic members in the form of elastic threads or bands. The elastic threads and bands are generally secured, in a continuous process and in a stretched state, to one or more components of the absorbent article, generally to at least one cover sheet.
When producing comparatively large absorbent articles such as diapers, the articles have to be folded so that the size of the articles is reduced to a format that is practical for packaging and subsequent handling by a user. One problem encountered during the process is that once the finished elasticated articles have been cut loose from the running material web, they assume an irregular three-dimensional shape as soon as the tensioning of the elastic members ceases and the elastic members contract. For this reason, it is desirable to maintain the integrity of the running material web during as many of the production steps as possible before cutting the web into separate articles. In particular, folding of the elastically contracted individual articles after the web has been cut is extremely difficult, and is avoided by performing any longitudinal folding of the production web while the web is still intact. After the longitudinal folds have been made in the production web, the web is finally cut along a straight line across the running material web.
Although this production method solves the problem of keeping control of the individual products during the folding operation, it entails other problems. A particular problem is that due to the production web being cut when it has already been folded, the cut has to be made straight across the web. This means that the articles cannot be provided with a contoured waistline. A contoured waistline is highly desirable in order to improve the fit of the article and to give the article a tailored, clothes-like appearance resembling ordinary underwear. Accordingly, there is a strong need for an improved process for producing disposable absorbent articles of the kind having a waistline and being configured to be worn in the manner of underpants around the lower end of a wearer's torso.
The main object of the invention is to provide a method for producing disposable absorbent articles allowing the shape of the absorbent article adjacent the waist to be determined independent of the operation separating the running material web into separate articles.
DISCLOSURE OF INVENTION
The above problems have been solved by a method for production of absorbent articles, according to the appended claims.
The invention relates to a method for production of absorbent articles attachable to the lower end of a torso. The method may comprise the production steps of assembling a continuous production web from article components comprising chassis components, absorbent core components, a topsheet and a backsheet. The production web is being advanced continuously in a machine direction and has side edges parallel with the machine direction and a cross direction perpendicular to the machine direction. The production web has a machine direction along which the production web is advanced continuously in a direction coinciding with a main longitudinal axis of each absorbent article, whereby the method uses a longitudinal production of absorbent articles.
According to the invention, the method further comprises the steps of: - creating at least one weakening line across the width of the production web between joined individual articles, each comprising a leading portion and a trailing portion in the machine direction;
- folding a predetermined portion of each edge of the production web along at least one longitudinal folding line into contact with one of the topsheet or the backsheet; and
- separating individual absorbent articles from the production web along said weakened section.
By creating at least one weakening line across the entire width of the production web before the production web is folded it is possible to determine the shape of a leading and/or a trailing portion of the absorbent articles independent of the operation separating the running material web into separate articles. By selecting the curvature of the weakening line, the absorbent article may be given any desired shape adjacent a waist section of the finished product, which waist section is arranged around the waist of a wearer when the article is worn. Also, as the at least one weakening line is created prior to at least one folding operation, the articles are at least partially folded during the separating operation. This reduces the need for performing folding operations on the separated articles.
Thus, in accordance with the invention, the absorbent articles can be designed with a contoured waistline conforming to the body-shape of the user and giving the absorbent article a more tailored appearance with better fit without compromising production efficiency as the production web can be folded before individual articles are separated from the web.
A shaped waistline will facilitate for the user to identify the front and the rear portions of the article so that the user immediately can recognise the correct way of wearing the article. A further instance when a contoured waistline may be beneficial is for babies and children who often have a protruding belly and in diapers for new-born babies who still haven't lost their umbilical cord. One type of article that is fitted on the wearer's body as a pair of underpants is open-type diapers. In order to achieve a good fit of an open-type diaper and to allow the diaper to be used by persons with different body shapes and body sizes, diapers of this kind are provided with attachment means that allow the front and rear portions to be brought together and to be adjusted and fastened around the waist of a user. For this purpose, at least the rear portion of the diaper includes opposite side portions, each of which includes a fastening device usually in the form of fastening tapes which may be adhesive tapes or hook-and-loop fasteners. Because of the generally narrow width of the fastening tape in relation to the width of the side portions of the diaper, the top of the diaper along the waistline on the front portion tends to wrinkle and roll or fold over upon itself when the diaper is worn. This phenomenon is further enhanced if the wearer has a protruding belly which will push the waist edge of the diaper outwardly.
This is a negative factor for various reasons. A disadvantage is that the diaper becomes bulky at the waist and is difficult to conceal under normal clothes, which can be very embarrassing, especially for adult diaper users. The creased and bulky appearance also strengthens the immediate impression that the absorbent article is in fact a diaper, which is perceived as a negative factor both by adult incontinence sufferers and by children of toilet-training age. Another disadvantage of using the folded and creased absorbent pants is that folds and creases can cause discomfort in the form of chafing and irritation of the user's skin. It is therefore highly desirable to design the diaper with a contoured waistline so that the folding-over effect is eliminated or at least reduced.
According to the invention, the assembled production web of interconnected absorbent articles is provided with at least one weakening line between consecutive articles and is folded along at least one longitudinal folding line in a subsequent operation. After this initial folding operation, the production web is arranged to be separated into individual absorbent articles by pulling consecutive articles apart along the at least one weakening line. This may be achieved by providing a roller arrangement comprising cooperating holding rollers being in constant engagement with the production web and being rotated at a predetermined first speed, imparting a first line speed to the production web, and a subsequent roller nip with rollers being rotated at a predetermined second speed, intermittently imparting a second line speed to the production web. The intermittent action of the second roller nip may be accomplished by intermittently moving the rollers into engagement with the production web. Another way of obtaining the intermittent action of the second roller nip is by using a profiled roller that will move with different peripheral speed during a rotation. The tearing force applied to the weakening line is dependent on the difference between the first and the second line speed. By selecting suitable first and second line speeds the weakening line is caused to tear or rupture as the leading portion of the production web is passed through the roller nip and is accelerated to the second line speed. By arranging the holding rollers and the roller nip at a predetermined distance from each other, the roller arrangement may also be used for removing the intermediate section of the production web located between adjacent leading and trailing weakening lines. After separation, the individual articles are passed on to complete a predetermined folding operation and to be packaged. The intermediate sections may be removed from the process by suitable means.
According to one example of the invention, a contoured weakening line may be created adjacent at least each trailing portion of the absorbent articles. If the contour provided by the weakening line is desired at the trailing end only, then each separated article may be cut by a cutting means at right angles across the production web adjacent the leading portion of said article after the separation has been performed along the weakening line. Accordingly, after separation of a first absorbent article from the production web by breaking the web at the contoured weakening line, the resulting contoured leading portion of the next absorbent article is cut away and removed to provide the next absorbent article with a straight leading edge. According to a second example, the weakening line may be created adjacent at least each leading portion of the absorbent articles. If a contoured weakening line is desired at the leading end only, then each separated article may be cut by a cutting means at right angles across the production web adjacent the trailing portion of said article after the separation has been performed along the weakening line.
According to a further example, a leading weakening line may be created adjacent each leading portion of the absorbent articles and a trailing weakening line may be created adjacent each trailing portion of the absorbent articles, which weakening lines are separated by a predetermined distance in the machine direction. In this way, two weakening lines can be provided if it is desired to provide a weakening line at both the trailing end and the leading end. Such an embodiment allows different contours to be provided at the leading and trailing ends, respectively. The predetermined distance separating the weakening lines should be made relatively short, in order to minimise material waste. At the same time the predetermined distance must be sufficient to allow an intermediate section between adjacent leading and trailing ends to be gripped by a roller nip, in order to remove the intermediate section from the leading end of a subsequent absorbent article.
The weakening lines adjacent each leading and trailing portion of the absorbent articles can be created at the same time in a single operation, or consecutively in separate operations. The strength of the respective weakening line may be the same, so that the same force is required when separating the individual absorbent articles from the production web along said weakened line. Alternatively, it is possible to make one weakening line weaker than the other weakening line. For instance, the leading weakening line may be weaker than the trailing weakening line, whereby less force is required when separating the trailing end of the individual absorbent articles from the production web. This method may be used to ensure that the weakening line along the trailing end of an absorbent article will separate before the weakening line along the leading end of a subsequent absorbent article.
The weakening lines may be created by mechanical deformation, for instance by perforating the production web or by partially cutting the production web along the weakening line. Combinations of partial cuts and perforations may also be used. Alternatively, the weakening line may be created by means of a welding seam across the production web. The perforation or welding seam will reduce the strength of the production web in the machine direction and allow consecutive individual absorbent articles to be separated from the production web, for instance by the application of a force in the longitudinal direction of the production web in the area of the weakening line. The force required to separate the absorbent articles can be controlled by the degree of perforation, for instance the number and size of adjacent perforations, or the width, penetration and/or heat applied to the welding seam. Should it be desired to reduce the required force further, the weakening line can be provided with a partial cut at one or more locations along the weakening line. The above methods of creating a weakening line may also be combined to a greater or lesser degree in order to control the force required for article separation.
According to a basic example, the weakening line can comprise a straight line at substantially right angles to the machine direction of the production web. However, according to the invention it is possible to provide at least one weakening line with a predetermined non-linear extension across at least part of the production web. The extension of the weakening line is defined as the shape of the weakening line as it extends across the production web. Such a predetermined non-linear weakening line may be provided at each trailing portion, at each leading portion, or at both the leading and trailing portion of the absorbent articles, depending on the desired effect to be achieved. For instance, the weakening line may be given a straight, linear extension when located parallel to a straight elastic element positioned in the waist section of the absorbent article. Such a weakening line may be provided at each trailing portion, at each leading portion, or at both the leading and trailing portion of the absorbent articles. Similarly, the weakening line may be given a non-linear, curved extension when located along a curved waist section of the absorbent article. Such a weakening line may be provided at each trailing portion, at each leading portion, or at both the leading and trailing portion of the absorbent articles. The weakening line may also be given a combined linear and non-linear extension to provide the respective trailing and leading portions with a predetermined shape. For instance, a trailing portion may be cut or be provided with a weakening line at right angles to the production web, while the leading portion may be provided with a weakening line having a non-linear extension, or curved shape across the production web. Alternatively, a predetermined non-linear weakening line may be provided adjacent the side edges of the production web. For instance, an absorbent article may comprise a waist section with side portions having free ends or "ears" with attachment means for fastening the absorbent article around the waist of a user. In this case it may be desirable to create rounded edges at the free ends of the side portions to reduce creasing and/or folding of the side portions adjacent the attachment means of the absorbent article.
The method may further comprise a cutting or weakening step providing each article with two leg openings, said leg openings being located in opposite side edges of the production web.
The invention also relates to an absorbent article produced according to the method described above. The absorbent article according to the invention will have at least one identifiable waist edge that has been created by tearing along a weakening line. In this manner the waist edge may be curved, for instance so that the waist edge on the front portion of the diaper has a lower cut than the rear waist edge and/or so that the waist edge on side portions of the article has been tailored to form rounded fastening flaps or "ears". The article according to the invention will have a good fit and a generally tailored appearance that allows a wearer or care-taker to easily understand how the article should be put on. In addition, the possibility of creating rounded edges on the side flaps at the waist portion of the article reduces the risk of sharp corners causing the wearer discomfort. Rounded side flaps will also reduce the risk of unwanted folding and wrinkling of the side flaps around fastening elements arranged on the flaps and will provide the article with a more aesthetically pleasing appearance.
The disclosed and shown methods and products in the appended figures should be understood as only being examples of the method and absorbent garments in accordance with the invention. Hence, the different method steps may be carried out in different order from that described, as explained above. The absorbent core may be part of a separately formed "core pack", with an absorbent core enclosed between a liquid permeable topsheet and a liquid impermeable backsheet. However, as this is only one way of incorporating the core in the chassis structure, alternative embodiments utilising parts of the chassis structure as topsheet and/or backsheet are also contemplated within the scope of the invention.
A production web as used herein is a running continuous multi-component web of subsequently arranged garment blanks. The garment-forming process may include application of features such as cover layers, barrier layers, liquid distribution layers, liquid storage layers, elastic elements, elastic webs, fastener elements elasticised or non-elasticised barriers, lotion, odour control agents, shaping elements, stabilising elements, etc.
BRIEF DESCRIPTION OF DRAWINGS The invention will be described in detail with reference to the attached figures. It is to be understood that the drawings are designed solely for the purpose of illustration and are not intended as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to schematically illustrate the structures and procedures described herein.
Figure 1a-b schematically illustrates a production line for carrying out the method according to the invention; Figure 2a-d schematically illustrates plan views of a production web comprising products being produced in the production line of Fig.1a-b, during consecutive steps of the production;
EMBODIMENTS OF THE INVENTION Figures 1a-b schematically illustrates a production line 100 for carrying out the method according to the invention. A first part of the production line is shown in Figure 1a.
The production line 100 in Figure 1a comprises a first conveyer unit 101 on which a backsheet with individual absorbent cores secured thereon, indicated by arrow A1 , is displaced towards a marriage point 111. In the marriage point 111 a topsheet, indicated by arrow A2, is placed on top of the absorbent cores and attached to the backsheet to form a production web. The production web has a machine direction MD along which the production web is advanced continuously in a direction coinciding with a main longitudinal axis of each absorbent article. The production web has side edges parallel with the machine direction MD and has a cross direction CD perpendicular to the machine direction. The method described in this example uses a longitudinal production of absorbent articles. In order to illustrate the principle of the invention as clearly as possible, the process shown in Figures 1a-b is highly simplified. Accordingly, the addition of components such as a fastening belt or fastening tapes, elastics, barrier means etc. has not been shown in the figures. It should be understood that all such components and production steps that are commonly used in the art may be included in the process without departing from the invention. In the example shown in Figure 1a, the production web is transferred from the first conveyer unit 101 to a second conveyer unit 102 on which the backsheet is joined to the topsheet in an edge sealing unit 112. The first and second conveyer units need not be separate units but may be combined into a single conveyer unit. The second conveyer unit 102 is followed by a perforation unit 113 used for creating at least one weakening line in the cross direction CD across the width of the production web between joined individual articles, each article comprising an absorbent core. The perforation unit 113 comprises a pair of counter rotating rollers 113a, 113b, wherein a first roller 113a is provided with perforating pins arranged to cooperate with a support roller 113b. Figure 2a schematically illustrates a plan view of a production web 200 comprising a line of products after leaving the perforation unit 113. In this example the perforation unit 113 creates a first, straight perforated line 201 at right angles to the production web 200, at the trailing end of a first absorbent article 211. The perforation unit also creates a second, curved perforated line 202 across the production web 200, at the leading end of a second absorbent article 212. Figure 2a also schematically indicates the relative positions of an absorbent core 213, a belt 214, located at the rear portion of the article, and leg elastics 215, 216, located substantially along the side edges of the production web 200. After the perforation unit 113, the production web is moved by a third conveyer unit 103 through a frontal hook applicator 114, where a fastening means for releasably attaching a front portion of the article to a fastening belt 214 is fixed to the topsheet. The hook applicator 114 is not an essential element of the invention and is only used when producing belted absorbent articles such as those shown in Figure 2a. The hook applicator is included in the process in Figure 1a in order to illustrate that additional production steps may be performed on the moving production web before the folding and separating steps according to the invention.
The third conveyer unit 103 then moves the production web into the roller nip of a rotary die cutter 115, wherein a cutting roller 115a is arranged to cooperate with a die roller 115b. In the rotary die cutter 115, leg openings are cut in opposite side edges of the production web. The provision of curved leg openings is an optional feature of the process. Moreover, the cutting tool for the leg openings may alternatively be arranged on the perforation unit 113 such that the perforation step and the cutting of the leg openings may be performed simultaneously. Figure 2b schematically illustrates a plan view of a production web 200 comprising one product in a line of products after leaving a rotary die cutter 115. Figure 2b schematically indicates the relative positions of the absorbent core 213, a pair of leg openings 217, 218, and the leg elastics 215, 216, located substantially along the side edges of the production web 200. After the rotary die cutter 115, the production web is moved by a fourth conveyer unit 104 towards a folding unit 116, shown in Figure 1b.
Figure 1b shows a second part of the production line, where the fourth conveyer unit 104 transfers the production web in the direction of the arrow A3 to the folding unit 116. In the folding unit 116, the side edges of the production web 200 is folded along longitudinal fold lines, upwards and inwards into contact with the upper surface of the topsheet, as schematically indicated in Figure 2c. The first and second perforated lines 201 , 202 are indicated with dashed lines in Figure 2c. The first, straight perforated line 201 is created at the trailing portion of a first absorbent article 211 and the second, curved perforated line 202 is created at the leading portion of a second absorbent article 212 that follows the first absorbent article when the production web 200 moves in the machine direction, MD. After being folded in the folding unit 116, the production web is transferred to a holding conveyer 105. The holding conveyer 105 comprises an upper conveyer 106 and a lower conveyer 107 arranged to maintain the production web at a predetermined line speed. From the holding conveyer 115, the production web is delivered to a tearing unit 117 comprising a pair of counter rotating first and second rollers 117a, 117b. In the roller nip between the first and second rollers 117a, 117b the line speed is higher than the line speed of the holding conveyer 105. Hence, when the leading end of a first absorbent article 211 of the production web 200 enters the tearing unit 117 it will be accelerated by the first and second rollers 117a, 117b, causing the first perforated line 201 to tear. The first absorbent article 211 is then separated from the production web and is transferred by a fifth conveyer 108 towards additional folding conveyers and a packaging unit (not shown). Shortly after the separation of the first absorbent article 211 from the production web, the leading portion of the production web will reach the tearing unit 117. This leading portion is an intermediate portion 220 of the production web initially located between the first and second perforated lines 201 , 202, as indicated in Figures 2c and 2d. When reaching the first and second rollers 117a, 117b the intermediate portion 220 will be accelerated, causing the second perforated line 202 to tear. The intermediate portion 220 is then removed from the production line by a waste suction unit 118. The separating process is then repeated for the second and subsequent absorbent articles. The weakening lines adjacent each leading and trailing portion of the absorbent articles can be created at the same time in a single operation, as shown in Figure 1a, or consecutively by separate perforating or seam welding units. The strength of the respective weakening line may be the same, so that the same force is required when separating the individual absorbent articles from the production web along said weakened line. Alternatively, it is possible to make the leading weakening line weaker than the trailing weakening line, whereby less force is required when separating the trailing end of the individual absorbent articles from the production web in a tearing unit. This arrangement may be used to ensure that the weakening line along the trailing end of an absorbent article will separate before the weakening line along the leading end of a subsequent absorbent article. According to an alternative example, the weakening lines created adjacent each leading and trailing portion of the absorbent articles may be passed through separate tearing units. In this way, the absorbent articles would be separated from the production web in a first tearing unit and the intermediate portions would be separated from the absorbent articles in a second tearing unit.
According to a further alternative example, if a shaped weakening line is desired at a trailing end only, then each separated absorbent article may be cut by a cutting means at right angles across the production web adjacent the leading portion of said article after the separation has been performed in a first tearing unit. Similarly, the shaped weakening line may be created adjacent at least each leading portion of the absorbent articles. In this case, each separated absorbent article may be cut by a cutting means at right angles across the production web adjacent the trailing portion of said article after the separation has been performed along the weakening line.
A production line as described above can also be adapted to produce absorbent articles separated by a single straight line at right angles to the production web. This would merely require the replacement of the rollers in the perforation unit.
As is evident from the foregoing, the method according to the invention can be performed by means of a diaper machine or corresponding machine for longitudinal production. Such machines are commercially available, and it should not pose any difficulties to the skilled person having knowledge about the present invention to adapt such a machine in order to be able to implement the invention. Accordingly, it is not necessary to describe the basic technique and necessary equipment for manufacturing diapers herein.
The invention is not limited to the above examples, but may be varied freely within the scope of the appended claims. As an example, the production web may be folded only along a single fold line or along more than two fold lines before separating the individual articles from the production web.