The present invention relates to a method and also to a device for determining the liquid retention of absorbent articles, such as sanitary napkins, diapers, incontinence napkins and like articles.
In order for an article to be felt dry and comfortable when worn, a very important factor is the liquid retention of the article, in other words its ability to retain liquid that has been absorbed by the absorbent body or pad of the article, when the article is subjected to load. It has been found that the ability of the article to retain absorbed liquid at the greatest loads occurring in normal use of the article is a decisive factor in respect of many users as to whether or not the article is felt to be comfortable.
Absorbent articles are generally able to absorb large quantities of liquid and are most often designed to transport discharged liquid quickly away from the surface of the article. It is important with respect to wearer comfort that the article has a dry top surface and that the liquid acquisition properties of the article, i.e. its ability to receive and transport discharged liquid quickly away from the top surface and into the absorbent body is therefore highly significant to the comfort of the wearer.
One way of determining the liquid retention of the article is to measure the amount of liquid that exits from an article which contains absorbed liquid, when the article is subjected to load. In known retention measuring processes, a liquid-containing article is subjected to a weight applied on top of the article wherewith the volume of liquid pressed from the article is drawn up by suction through the capillary forces of a fibre body, normally filter paper, disposed between the weight and the article. The liquid retention of the article is determined by weighing the fibre body. One problem with these known methods is that the capillaries in filter paper may vary in size. Moreover, when it is necessary to use several filter papers, the interfaces between the papers create problems. It has also been found that the measuring results depend on the person carrying out the measuring process, in other words different people obtain different results for one and the same article. Consequently, the reproducibility or certainty of retention measurement values obtained with these known processes is inadequate. Moreover, the suction properties of the fibre body used is liable to change in storage (ageing) or for some other reason, which can influence the result of the measuring process.
Another problem is that the load to which an article is subjected during use varies widely. This means that a number of weights must be available for the retention test, if it is to be possible to test for all feasible loads. Moreover, in the case of the known methods retention is normally measured at relatively low loads. This fails to give a clear picture of the retention properties of an article, since it has been found that an article which has good retention at low loads can have poor retention at high loads. User tests have also shown that retention at high load, e.g. the load experienced when the wearer sits on a chair or on the saddle of a bicycle, is decisive in determining whether the article is felt to be comfortable or not. Thus, these known methods of measuring retention under relatively low loads are poorly adapted to reality, in other words as to how a wearer judges the retention of the article concerned.
An object of the present invention is to eliminate or at least considerably reduce these problems, and to provide a flexible method for measuring retention of absorbent articles that has good reproducibility and that can be readily carried out. Another object is to provide an apparatus for carrying out the method that can be easily handled and that enables measurements to be made with loads that are close to reality.
The former object is achieved in accordance with the invention with a method of measuring the retention of absorbent articles that include an absorbent body having a top side which lies proximal to the wearer""s skin in use, and a bottom side which is covered by a liquid-permeable backing sheet, wherein the method comprises the steps of delivering a determined amount of liquid to one region on the top side of the article, urging a pressure body against a region on the top side of the article with a determined force, and collecting and measuring the amount of liquid therewith pressed from on the top side of said article, wherein the method is characterised by setting the determined force with which the pressure body is pressed against the top side of the article on a device that is adapted to urge the pressure body against the top side of said article with a selective pressure, and transporting the liquid pressed out from the top side of the article to a measuring vessel with the aid of sub-pressure.
According to one preferred embodiment of the invention, the liquid pressed from the top side of the article is transported to the measuring vessel via a space in the pressure body, this space communicating with the top side of the article via a liquid-permeable bottom of the pressure body. The device with which the pressure body is pressed against the top side of the article is conveniently computer controlled.
The invention also relates to a device for measuring retention of absorbent articles that include an absorbent body which has a top side that lies proximal to the wearer""s skin in use, and a bottom side which is covered by a liquid-impermeable backing sheet, wherein the device includes a pressure body and means for collecting liquid that gathers beneath the bottom of the pressure body, and wherein the device is characterised in that the pressure body includes a perforated bottom and a space which is delimited downwardly by said perforated bottom; in that the device includes a liquid collecting vessel in connection with the space in the pressure body, means for generating a sub-pressure in the collecting vessel, means for measuring the amount of liquid present in the collecting vessel, and means for selectively setting the pressure exerted by the pressure body against the top side of an absorbent article placed on a fixed supportive surface centrally beneath the pressure body.
In one preferred embodiment, the device includes means for delivering liquid to the absorbent body of an absorbent article, and a computer for controlling the various means. The pressure body is preferably connected to an arm that can be moved by means of a stepping motor. The collecting vessel is connected to a space in the pressure body interior which, in turn, is connected to a sub-pressure source, and is removably connected to the pressure body with the aid of an air-tight coupling element.
In another embodiment, the pressure body is connected to the arm for pivotal movement about a horizontal axis.