Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Nonwoven fabric – Including an additional nonwoven fabric
Reexamination Certificate
1999-12-06
2003-04-15
Morris, Terrel (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Nonwoven fabric
Including an additional nonwoven fabric
C428S316600, C426S077000, C426S084000
Reexamination Certificate
active
06548433
ABSTRACT:
The present invention relates to a fibrous, porous web material of the heat seal type intended for use particularly, but not exclusively, for the production of infusion sachets for brewing beverages such as tea, coffee and the like.
Infusion sachets for brewing beverages (e.g. so called teabags and coffee bags) are generally produced in either “heat seal” or “non-heat seal” generic types of fibrous porous web material (hereinafter also referred to as paper for convenience). Heat seal paper (with which the present invention is concerned) generally comprises two layers. One of these two layers is a bonding layer which includes fusible polymeric fibres which allow two layers of the paper to be heat sealed together in the production of infusion bags. The other layer is present as an insulation layer to prevent polymer (in the other layer) sticking to heated dies during conversion of the paper to produce an infusion sachet.
One example of commercially available heat seal paper is that manufactured by J.R. Crompton Limited under the name SUPERSEAL (Registered Trade Mark) which comprises a bonding layer incorporating relatively long (e.g. ca 5 mm) polypropylene, rayon and vegetable fibres, and a thermally inert layer of cellulosic fibres. Overall, the SUPERSEAL paper has a depth corresponding to a thickness of about 6-8 fibres with the bonding layer being of greater thickness than the thermally inert layer (in which the “long” fibres of the bonding layer are keyed).
There is however a problem in some areas with the known heat seal papers for use in the production of teabags in that fine tea dust (resulting from interaction of tea leaves during processing thereof) or fine particles of tea having a tendency to pass through the paper to the outside of the teabag. Since teabags are generally packaged in boxes or other types of “outer” packaging, the fine tea particles or dust are “loose” in the packaging and this is undesirable from the aesthetic viewpoint.
Depending on the packaging size, there may be up to a few milligrams of fine tea particles or dust “loose” in the packaging.
One strategy for overcoming this problem would be to increase the percentage of finer fibres (preferably hardwood fibres) in the stock from which the double ply paper is produced. This would result in a paper with smaller pores thus reducing the amount of fine tea or tea dust which can pass through the paper. Obviously the reduction in porosity would not be so high as to prevent passage of water through the material during infusion of the beverage.
However, an increased amount of hardwood or other short fibres in either of the two layers will reduce the strength of the paper possibly to the extent that (for the required pore size) the strength is insufficient for manufacture of the paper into infusion bags. A further disadvantage which would be associated with the use of hardwood or other short fibres would be the generation of “pin holes” in the paper resulting from general papermaking problems, e.g. air entrainment and wetness.
A further proposal for improving the particulate retention properties of a heat-sealable filter material to be used in the manufacture of beverage infusion bags is disclosed in U.S. Pat. No. 5,601,716. In accordance with this proposal, a filter material is produced by wet laying a first, fibrous layer on a paper-making machine and then depositing onto this layer, a plurality of individual synthetic or plastic fibres (which provide the heat-seal properties for the filter material) in a heated condition so that the synthetic or plastic fibres are able to fuse between themselves as well as with the fibres of the first layer. The synthetic or plastic fibres may be produced and deposited using a conventional melt spinning technique. The need to produce the heated synthetic or plastic fibres as separate process steps subsequent to the process of wet-laying and drying the first fibrous layer represents a disadvantage of this process. Furthermore, the random deposit of the synthetic or plastic fibres does not necessarily “target” large pores in the wet-laid layer so there may be an inconsistent improvement in filtration efficiency.
It is therefore an object of the present invention to obviate or mitigate the abovementioned disadvantages.
According to a first aspect of the present invention there is provided a fibrous, porous web material of the heat seal type having improved particulate retention properties for use in the manufacture of beverage infusion bags, the material comprising juxtaposed, successively wet laid first, second and third fibrous layers, at least one of said layers incorporating heat sealable fibres wherein the fibres in the first layer are of greater aspect ratio than those in the second layer which are of higher aspect ratio than those in the third layer.
According to a second aspect of the present invention there is provided a method of producing a fibrous, porous web material of the heat seal type of improved particulate retention properties for use in the manufacture of beverage infusion bags, the method comprising successively laying first, second and third fibrous layers whilst effecting drainage from formation of the first layer to formation of the third layer structure, at least one of said layers incorporating heat sealable fibres, wherein the fibres in the first layer are of greater aspect ratio than those in the second layer which are of higher aspect ratio than those in the third layer.
Materials in accordance with the first aspect of the invention have a reduced pore size so that when used for beverage infusion bags the passage of fine particles or dust of the beverage precursor material (e.g. tea leaves) is inhibited. Nevertheless, the material is of adequate strength for manufacture into beverage infusion bags and is of sufficient porosity so as to allow water to pass through the material used during infusion of the beverage.
The material is produced by successively wet laying the first, second and third layers (at least one of which incorporates the heat sealable fibres) onto a water pervious belt at spaced locations. This may be effected by three separate headboxes positioned such that there are free runs of the belt between the positions at which the successive headboxes lay their respective fibrous suspensions. Drainage through the belt is effected at least from formation of the first layer structure to formation of the third layer structure (i.e. over the regions of the free runs of the belt). Drainage of the free run between the first and second headboxes ensures that the first layer has a more coherent structure before the second layer is applied thereto. This ensures that disruption of the first layer by the laying of the second layer is prevented. Similarly the free run of the belt between the second and third headboxes ensures that disruption of the two layer structure by laying of the third layer is prevented.
These features of the method are an important aspect of the invention in their own right and therefore according to a third aspect of the invention there is provided a method of producing a fibrous porous web material of the heat seal type having improved particulate retention properties for use in the manufacture of beverage infusion bags comprising successively wet-laying first, second and third fibrous layers, at least one of which incorporates heat sealable fibres, at spaced locations along a water pervious belt such that there are free runs of the belt between the positions at which the first and second layers and between the positions at which the second and third layers are laid, and effecting drainage through the belt in said free runs from formation of the first layer to formation of the third layer structure.
It is preferred that the drainage of the fibrous web continues beyond the laying of the third layer.
The method of the invention have the advantage that any voids in the first layer caused by (for example) air-entrainment will be filled (as a result of drainage through the voids) by fibres of the second layer, and any remaining
Alston Joyce
Gbur Ivan
Tomkinson Brian
Guarriello John J.
J. R. Compton Limited
Morris Terrel
Woodard Emhardt Naughton Moriarty & McNett
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