Stock material or miscellaneous articles – Sheet including cover or casing – Complete cover or casing
FIELD OF THE INVENTION
This invention relates to an absorbent pad and particularly to an absorbent pad for use in the food industry as a biofluid absorbent, or a for a cooling pad.
Absorbent pads are well-known and widely used in the food industry. One type of absorbent pad is used as a biofluid absorber and is placed between fresh meat and the plastic meat tray. The pad functions to absorb biofluids exuding from the meat.
A second type of known pad is used as a cooling pad and is initially swelled with water, frozen and then placed with food or other produce which is to be kept cool.
Both types of pads have internal absorbents and typically use superabsorbent polymers (SAP). These polymers are also well-known and a typical polymer is a cross-linked sodium polyacrylate. In order to allow the internal absorbent to absorb fluid efficiently, the polymer is usually finely ground.
The internal superabsorbent polymer creates some difficulties which must be overcome if the pad is to be safe and commercially successful. Firstly, it is necessary to ensure that the polymer stays within the pad at all times, even when swollen into a gel-like state. Another problem with the superabsorbent polymers is that they are aggressive fluid absorbers and tend to desiccate the meat product by absorbing more than just the exuded biofluids.
To overcome the aggressive absorbing nature of the polymer, it is known to have absorbent pads formed with a bottom wall which is water permeable (and is typically a non-woven fabric), and a top wall formed from a totally liquid impermeable sheet.
A disadvantage with having a liquid impermeable top sheet is that biofluids run over the top sheet and fall away from the pad without the pad being able to absorb the biofluid through the bottom layer. This is particularly so if the meat product tray is stored or presented at an angle. Another disadvantage with the impervious top layer is that if the meat tray is level, biofluids can pool on the top layer and ruin the meat by promotion of bacterial growth.
Attempts have been made to provide a large slit or a number of slits in the top wall of the pad to overcome the above disadvantage. However the biofluids are still not efficiently absorbed and have a tendency to run off the top sheet, or to pool.
Another problem with cooling pads is that when the pads are swollen with water, the superabsorbent polymer turns into a gel and exerts considerable pressure on the wall of the pad and can extrude through the pad wall. This is particularly so if the top wall of the pad is formed with a large slit or slits.
OBJECT OF THE INVENTION
The present invention has been developed to provide an absorbent pad which can be used both as a biofluid absorber and also as a cooling pad and which can at least reduce the abovementioned disadvantages or provide the public with a useful or commercial choice.
In one form, the invention resides in an absorbent pad which has a top sheet and a bottom sheet, the sheets being joined to form at least one cell, a absorbent located within the cell, characterised in that at least one of the sheets is formed from a liquid impermeable material containing microperforations to allow fluid to pass through the microperforations and into the cell.
It is preferred that the top sheet is formed from the microperforated material. The bottom sheet may be formed from similar material, or different material such as a water-permeable non-woven sheet, a paper sheet, or a totally water impermeable sheet.
We find that the microperforations temper the aggressiveness of the superabsorbent polymer within the cell or cells. That is, the microperforations minimise the drawing effect which results in undesired desiccation of the meat product. The drawing effect appears to be minimised to an acceptable level by having a large number of extremely small perforations in the sheet of the absorbent pad which can then be placed under the meat product.
The microperforations also appear to reduce or prevent pooling of biofluids on top of the absorbent pad and if the microperforations are spread over the top sheet of the absorbent pad, biofluid absorption can occur over a larger surface area than might be the case if the pad was only slotted or slitted.
The microperforations are typically spread over the sheet in a substantially homogenous fashion. It is however envisaged that parts of the sheet may not include microperforations and these parts may include the joints between adjacent cells.
The microperforations may have various shapes and sizes and may be circular, elliptical (cigar-shaped), polygonal (including rectangular, triangular and diamond-shaped), irregular and the like. Depending on the process used to perforate the sheet, the formed perforations may have a flap or hinge portion adjacent the formed hole which still allows liquids to pass through the perforations.
The microperforations can be formed by hot pin perforating, cold pin perforating, open flame perforating, laser perforating, and by other suitable techniques. The different perforating processes may form different hole sizes and shapes.
A typical size of the microperforation can be between 10 to 200 microns. For instance, if the perforation is elliptical, it may have a size of approximately 20 microns×90 microns, but this can vary between 10 microns and 200 microns, possibly even more, the larger size being determined by the aggressiveness of the absorbing polymer or other type of absorbent.
The number of microperforations in the sheet may also vary as can be regularity or irregularity of the microperforations. There may be provided between 10 to 500 microperforations per square inch and we find a microperforation number of 330 per square inch to be suitable for our purposes. We find that the number of holes per square inch appears to affect only the absorbent rate of the product.
The size of the absorbent pad itself can also vary depending on its use. We find that a typical pad may be about 400 mm across and have an unlimited length with the consumer able to simply cut the pad lengthwise to suit. Each pad may have one or more cells, and we find that for a pad having a width of 400 mm, there may be provided 6 or so cells. Each cell can be of any shape or size and we find a suitable size to be between 40 mm to 100 mm across.
The sheet containing microperforations (which is typically the top sheet), can be formed from a plastic film. The plastic film can be a single film, a laminate film or other type of film. One type of useful film is a laminate formed from a polyester and a polyethylene. We find a suitable thickness to be a 12 micron polyester film laminated to a 30 micron polyethylene film. Other film thickness can be used if desired. We find that other types of plastics can be used such as nylon, other types of polyene film such as all types of polyethylenes and polypropylenes. We also find use for polyurethane and polyvinyl films. We find that the main property desired from the film is that it is able to be strong enough to resist wear and tear during use. We also find it desirable to choose a film which can accept printing inks such that the sheets of the pad, or at least one sheet of the pad, can be printed. We find it desirable from a consumer point of view that the films have a good opacity. If we form the pad by heat sealing the top sheet and the bottom sheet together, we prefer the films to be heat sealable.
If the absorbent pad contains a microperforated top sheet and a different type of bottom sheet, one type of preferred bottom sheet is a non-woven fabric. Many types of non-woven fabrics are known in the art, and a suitable fabric is a 40 g per square meter bi-component continuous filament which is pressure and temperature bonded. The filament can be made of a polyester core with a polyethylene sheath and this type of material is known. The filament may comprise a different type of sheath plastic such as polypropylene or a polypropylene polyethylene co-polymer. These filaments are desirable because a strong heat seal can be formed in the n
Hurley Jr. Rupert B.
Sealed Air Corporation (US)
Thomas Alexander S.
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