Beverage infusion packages and materials therefor

Abstract

A beverage infusion package (e.g. a tea bag) is formed of porous, fibrous cellulosic material and has a closure seam produced by a mechanical compression action without heat sealing. The porous material contains thermoplastic fibres which are amorphous or are only partially crystalline and which make the package eminently suitable for infusion in a microwave oven. The porous, fibrous material may have a basis weight of 10 to 30 g m−2 and be comprises of a single wet-laid layer of an admixture of cellulosic fibres and the thermoplastic fibres.

Description

[0001] The present invention relates to a beverage inffusion packages (e.g. tea bags, coffee bags and the like) as well as to porous, fibrous web materials for use in producing such packages.

[0002] Beverage infusion packages such as tea bags comprise a particulate beverage precursor material, e.g. tea leaves or coffee granules, in a bag, sachet, pouch or the like (all conveniently referred to herein as a bag) of a porous, fibrous cellulosic material. This material typically has a basis weight of 10 to 30 g m−2 and is often referred to as “tissue” or “tissue paper”. The tissue may be of the “heat seal” or “non-heat seal” type and the invention is primarily concerned with the production of beverage infusion packages by techniques which do not involve heat sealing although a description of “heat seal” tissue is given below for the sake of completeness.

[0003] “Heat seal” tissue comprises two or more layers wet-laid in succession one on top of the other. One layer contains only cellulosic fibres and the other incorporates thermoplastic fibres. A beverage infusion package is produced from such tissue by forming the bag such that layers of the tissue incorporating thermoplastic fibres are juxtaposed and then heat sealed.

[0004] “Non-heat seal” tissue generally (but not necessarily) comprises a single wet-laid layer of cellulosic fibres produced from mixtures of well known paper-making fibres which may include both woody and non-woody materials, e.g. Manila hemp, sisal, jute, bleached and unbleached soft wood and hard wood species and in some instances approved synthetic fibres such as viscose rayon. The material is typically manufactured by the wet laid process on an inclined wire paper-making machine. The material is generally treated with classic wet and dry strength chemical enhancing products, such as CMC (carboxymethyl cellulose) and Kymene (epichlorohydrin).

[0005] Beverage infusion packages (eg. tea bags) produced from such “non-heat seal” material incorporate a seam formed by a mechanical compression action (e.g. involving crimping). Examples of such packages are those of the “double-chamber” type having attached string and tag as produced by both Constanta and Perfecta machines the world over.

[0006] Briefly, such double chamber packages are produced by longitudinally folding a strip of the non-heat seal tissue so that the free longitudinal edges are adjacent to each other. These two edges are then folded over together several times and the fold then reinforced by means of a pressure controlled toothed wheel known to those skilled in the art as a Crimp Wheel. The thus formed tube is then formed into the final double-chamber beverage infusion package (incorporating beverage precursor material). Such a package comprises, in effect, a short length of the tube folded transversely so that the widthwise ends are adjacent to each other and with the crimped seal extending lengthwise along the inner sides of the package which is closed at its transverse ends by a staple to which may be attached a string and tag.

[0007] To produce a beverage, the package is infused with hot water. This may be done, for example, by immersing the package in hot water, pouring hot water onto the package, or heating water and the bag in a microwave oven. This action, of infusing the package with hot water, causes the bag to inflate and float due to water bridging the pore structure of the tissue and creating a gas barrier film entrapping the atmosphere and volatiles generated du the brewing process. The inflation of the package increases stress on the mechanically formed seam to a degree dependent, at least in part on the type and dosage of the beverage precursor material in the package, e.g. black tea or herbal tea. The stress on the mechanical seam may be such as to result in failure thereof causing tea leaves, coffee grounds or the like to be released into the beverage and this is obviously undesirable. The problem of seam failure occurs when the wet crimp strength of the scam is not sufficiently high and is exaserpated in the microwave method of infusing the beverage where the extended period of energy input (e.g. for two minutes) increases the stress placed on the mechanical seam both in a cold and hot environment and has a detrimental effect on most classical wet and dry chemical systems employed.

[0008] It is an object of the present invention to obviate or mitigate the above mentioned disadvantages.

[0009] According to a first aspect of the present invention there is provided a beverage infusion package formed of porous, fibrous cellulsoic material and having a closure seam produced by a mechanical compression action without heat sealing characterised in that the porous material contains thermoplastic fibres which are amorphous or only partially crystalline.

[0010] Thus in accordance with the first aspect of the invention the beverage infusion package is formed from a material incorporating fibs of a thermoplastic which is amorphous or (more preferably) partially crystalline. We have found that such fibres produce a significant enhancement of mechanical seam integrity. The dry strength of the seam is sufficient to prevent the package bursting open and spilling the beverage precursor material during manufacture, packaging, delivery and or consumer use. Moreover, the wet crimp strength is such that there is no significant seam failure when infusion packages in accordance with the invention either when boiling water is poured onto the package to brew the beverage or when the infusion package is heated with water in a microwave oven.

[0011] We do not wish to be bound by theory but we believe that the success of the present invention is attributable to several reasons. Firstly, the thermoplastic fibres in the paper at the opposite sides of the seam are bent and form an inter-locked synthetic matrix which is impervious to boiling water and microwave energy. Secondly, the fact that the thermoplastic fibres are amorphous or only partially crystalline ensures that fibre recovery is limited which enables the crimped seam to be maintained under high stress in a hot aqueous environment.

[0012] The invention is particularly effective in the case where the mechanically formed seam is formed by folding over together adjacent edges of the porous material and applying a mechanical compressive force to the folded over edges. The compressive force may be applied by crimping, e.g. using a pressure controlled toothed wheel (a so-called Crimp Wheel). In such a case the fibres are crimped together providing an additional degree of interlocking and therefore enhancement of seam integrity.

[0013] The beverage infusion package of the invention may for example be a tea bag, e.g. of the double-chamber type, but is also applicable to other beverages, e.g. coffee.

[0014] The porous fibrous material will generally have a basic weight of 10 to 30gm−2, more typically 10 to 20 gm2, e.g. 10-13 gm2. For preference, the material will comprise 5 to 30%, more preferably 10% to 30%, and ideally 15% to 25% by weight of the thermoplastic fibres.

[0015] The material may be formed by conventional paper-making techniques by laying a suspension comprised of cellulosic and thermoplastic fibres onto a papers forming fabric of a paper-making machine (e.g. an inclined wire paper-making machine) and withdrawing water from the laid suspension through the fabric.

[0016] Cellulsoic fibres forming the suspension may be those conventionally used for producing non-heat paper for beverage infusion bags and may include both “woody” and “non-woody” materials such as manila hemp, sisal, jute, and bleached and unbleached soft wood and hard wood species.

[0017] Generally the relative amounts of non-woody material to woody material will be 40 to 80 parts of non-woody material to 20 to 60 parts woody material.

[0018] The material may be produced by laying successive layers of suspension (possibly of differing composition) one on top of the other, e.g. as described in WO-A-9601839. It is however more preferred that the material comprises only a single layer of the cellulosic and thermoplastic fibres. This is an important aspect of the invention in its own right and therefore according to the second aspect of invention there is provided a porous fibrous web material having a basis weight of 10 to 30 gm−2 and being comprised of a single, wet-laid layer of an admixture of cellulosic and thermoplastic fibres which are amorphous or are only partially crystalline.

[0019] Material in accordance with the second aspect of the invention is suitable, and primarily intended for, producing beverage infusion packages in accordance with the first aspect of the invention, However, the material is also suitable for any use where a porous, high wet strength, mechanically crimped seam is required.

[0020] Preferably the crystallinity of the thermoplastic fibres is less than 40% to reduce fibre recovery to 10% which enables the mechanical seam to be retained under high stress in a hot aqueous environment. More preferably the crystallinity is 10-20%.

[0021] Examples of thermoplastics which may be used are polypropylene, polyester, polyamide 6, 66, 11, 12 and high density polyethylene. Blocked or random copolymers or terpolymers of propylene and ethylene may also be used.

[0022] The thermoplastic fibres will preferably have a thickness of 0.5 to 6.0 denier although best results will generally be achieved with fibres in the 2 to 4 denier range.

[0023] The length of the thermoplastic fibres may be 0.5 mm to 12 mm, preferably 3 mm to 6 mm and more typically 5 mm.

[0024] Preferably the thermoplastic fibres in the web have been “fused” or thermally bonded together, at a temperature greater tan the crystalline melt temperature of the thermoplastic fibres.

[0025] Such “fusing” can provide two effects. Firstly, the crystallinity of the thermoplastic fibres from which the web is manufactured may be reduced to a desired value. Thus for example the fibres may initially have significant crystallinity (e.g. greater then 50% and possibly greater than 80%) and this crystallinity may be reduced by the heat treatment to the preferred value of, say, 10-20%. Secondly the fibres become fused together at their junctions (or points of contact) to provide a cohesive reinforced crystalline matrix. The affect of fusing the thermoplastic web further improves the dry and wet crimp functionality by increasing web elasticity specifically in the cross machine direction orientation. However, the thermoplastic fibre can be used in an un-fused state, however, the improvement in wet crimp recovery is less, due to the higher recovery rate of the fibre to flexing and can lead to higher failure rates at the mechanical crimp fin seal during microwave brewing.

[0026] The thermoplastic fibres form which the web is produced may be of isotatic polypropylene drawn into fibres having a degree of crystallinity of at least 75%, the crystallinity subsequently being reduced during the above described “fusing” step.

[0027] The crystallinity of the fibres may be assessed colorimetrically. Thus, when polypropylene (a preferred thermoplastic for use in the invention) is crystallised from the melt and drawn under stress the arrays of crystallised, known as spherilites, become highly orientated in the longitudinal direction of the filament. Due to the highly orientated spherilites the fibres when viewed under polarised light show a distinctive bright yellow colouration demonstrating a degree of crystallinity.

[0028] When polypropylene is used in the current invention and is thermally bonded at a temperature greater than the crystalline melt temperature of the polypropylene the spherilites become more randomly orientated and under polarised light show only slight evidence of yellow colouration.

[0029] It is recognised for current beverage infusion bags formed having a seal produced by mechanical compression that if the initially formed dry seal is below a predefined value hen the strength of the crimp in the wet state (wet crimp) will be insufficient. However the current invention can produce a more than adequate wet crimp seal for microwave use for only a small increase in wet crimp strength.

[0030] The material of the second aspect of the invention or any other material from which a beverage infusion package in accordance with the first aspect of the invention is to be produced may be treated (by either addition to the wet pulp stock suspension or at a size press unit) with agents known per se for imparting wet and dry strength. e.g. carboxymethyl cellulose (CMC) and epichlorohydrin (e.g. available under the name KYMENE (Trade Mark). These agents may be used such as to provide at least 1% by weight thereof on the material.

[0031] Particularly in the case where the web is treated with epichlorohydrin, it is preferred that it is also treated with poly(vinyl alcohol) which acts to increase dry strength and (in conjunction with epichlorohydrin) improves wet crimp strength. The poly(vinyl alcohol) is preferably one having a degree of hydrolysis of at least 60%, more preferably at least 80%, and most preferably 95% to 99.9%.

[0032] The poly(vinyl alcohol) may for example of the type known as the “super-hydrolysed” variety, e.g. as available under the AIRVOL (Trade Mark) as available from Air Products.

[0033] Levels at which the poly(vinyl alcohol) will be applied to the web will generally be in the range 0.5 to 4% by weight typically 1.0 to 2% by weight

[0034] It is possible for the porous fibrous material (from which the infusion package is produced) to be relatively hydrophilic such that, during brewing of the beverage, the bag rapidly wets out and sinks in the brew liquor providing a satisfactory infusion rate. The hydrophilicity of the porous fibrous material may be measured by a water climb test in which the lower end of a vertically disposed strip (1″×5″ (2.54×12.70 cm)) of the material is dipped into water and then time taken for the water to rise 1″ (2.54 cm) up the material is measured. In accordance with the invention it is preferred that the porous, fibrous material has a water climb value of less than 70 seconds, e.g. 20 to 40 seconds, ideally about 30 seconds.

[0035] A further means of measuring, hydrophilicity is by the Water Drop Test in which a micro syringe is used to drop a small bead of water at ambient temperature on to a single layer of the infuser web, which is supported around its perimeter by a small diameter ring, typically 2″ (5.08 cms). The time taken for the droplet of water to spread out and collapse into the infuser web, i.e. zero contact angle, is timed by means of a stopwatch. It is preferred that the porous, fibrous material has a value in the Water Drop Test of less than 10 seconds, more preferably less than 5 seconds, and even more preferably less than 1 second.

[0036] The hydrophilicity of the web may be achieved by treatment with epichlorohydrin and poly(vinyl alcohol).

[0037] The invention will be illustrated by the following non-limiting Examples in which porous fibrous material (in accordance with the second aspect of the invention) were produced as illustrated in Examples 4 and 5. Examples 1-3 represent comparative materials.

EXAMPLE 1-(COMPARATIVE)

[0038] A standard NHSTB 12.3-13.0 gsm infuser web was produced on an inclined pilot paper machine from 70% Manila and 30% soft wood and bonded with 1% Kymene and 2% CMC. This material was then slit to 94.3 mm coils and conditioned in a humidified laboratory to the typical industry standard of 7-8% moisture content, as low moisture is knows to significantly affect conversion parameters adversely.

EXAMPLE 2-(COMPARATIVE)

[0039] A USA style latex NHSTB prototype at 12.3-13.0 gsm infuser web was produced in the inclined pilot paper machine from 70% Manila and 30% softwood and bonded with 1% Kymene and 13.5% of a co-polymer of Ethyl and Butyl acrylate latex. This material was then slit to 94.3 mm coils and conditioned in a humidified laboratory to the typical industry standard of 7-8% moisture content.

EXAMPLE 3-(COMPARATIVE)

[0040] A European style latex NHSTB prototype at 12.3-13.0 gsm infuser web was produced on the inclined pilot paper machine from 60% Manila, 30% softwood, 10% hardwood and bonded with 1% Kymene and 13.5% of a co-polymer of methacrylate Styrene Butadiene latex. This material was then slit to 94.3 mm coils and conditioned in a humidified laboratory to the typical industry standard of 7-8% moisture content.

EXAMPLE 4-(INVENTION)

[0041] A standard NHSTB 12.3-13.0 gsm infuser web was produced on the inclined pilot paper machine from 55% Manila and 30% softwood, 15% Polypropylene (3 denier, 5 mm) and bonded with 1% Kymene. During the production of this material the polypropylene was “fused”/“thermally bonded” to an amorphous state by taking the polymer past its crystalline melt temperature. This material was then slit to 94.3 mm coils and conditioned in a humidified laboratory to the typical industry standard of 7-8% moisture content.

EXAMPLE 5-(INVENTION)

[0042] A standard NHSTB 12.3-13.0 gsm infuser web was produced on the inclined pilot paper machine from 55% Manila and 30% softwood, 15% polypropylene (3 denier, 5 mm) and bonded with 1% Kymene and 2% PVOH (Airvol 165). During the production of this material the polypropylene was “fused”/“thermally bonded” to an amorphous state by taking the polymer past its crystalline melt temperature. This material was then slit to 94.3 mm coils and conditioned in a humidified laboratory to the typical industry standard of 7-8% moisture content.

[0043] The materials produced in Examples 1 to 5 were subjected to a number of Tests as detailed below. Unless otherwise stated, tea bags for use in the Tests were produced on a Constanta NHSTB Machine at a speed of 140 bags/min. The bags were dosed with 1.8 grams of black tea equally between the two chambers and the enclosure made as standard using a steel staple.

[0044] Test 1- Microwave Crimp Failure

[0045] The energy out put of microwaves has increased dramatically over the recent couple of years and is now typically 850-1200 watts for domestic appliances. It has also been observed that the energy inputted to the fusion packet during the typical brew cycle can also vary for a given microwave wattage depending on make, model and whether the microwave is “cold” i.e. the first use or is “hot” i.e. the second and subsequent uses during a sustained period.

[0046] The test regime that has been adopted to evaluate the above observation and to provide a broad indication of infusion material acceptability over a range of conditions is outlined as follows:

[0047] Microwave used in a 1200 watt variable power domestic unit made by Philips Industries.

[0048] Water used is drawn from a domestic cold water supply common to the region

[0049] 5 replicate are performed with out any cool down ties between tests.

[0050] The bags are placed into 175 ml of water at ambient temperature, contained by a grade B 250 ml laboratory beaker.

[0051] The beaker is observed, through the glass door, during both microwaving and then in removal from the microwave and following recorded:

[0052] Does the crimp fin seal fail during the brewing process as indicated by tea leaf present in the beaker.

[0053] When the tea bag is removed and the top stapled seal opened does the crimped fin seal show signs of deforming such that the bag is on the verge of opening.

[0054] The test is then repeated immediately for the next replicate until the 5 samples have been tested.

[0055] The microwave is then allowed to cool down to ambient temperature and the test is then repeated at the next power setting (90%) until the fill range of setting (60-100%) have been evaluated for a given sample type,

[0056] The results are shown in Table 1. 1 Microwave Crimp Failure Vs Energy Input Table 1 Ex 2 Ex 3 Ex 4 Ex 5 Ex 1 Latex Latex Micro- Micro- % Energy JRC Product Product wave wave Input NHSTB USA EU NHSTB NHSTB 100  Total Total Total No failure No failure failure failure failure 90 Total Total Total No failure No failure failure failure failure 80 Total Total Total No failure No failure failure failure failure 70 Total Open on No failure No failure No failure failure inspection 60 Open on No failure No failure No Failure No failure inspection

[0057] Test 2-Tea Sift

[0058] The amount of tea that is allowed to pass through the infuser web is of critical importance as it limits how the tea bag producer can blend/mill the tea used. This impacts on both the final infusion rate of the tea bag and how much tea is lost into the package during transport (Tea sift).

[0059] To assess comparatively die differences between infuser tissues the following test regime has been adopted and is outlined as follows:

[0060] 3 discrete size ranges of sand are used (75-106, 106-150, 150-221microns)

[0061] The sand used is of the type produced by shot blasting and is fractionated in-house using graduated sieves.

[0062] The test is performed by weighing out 10.0 g±0.05 g of the sand and placing it in a catchpot for each of the sand fraction.

[0063] The catchpot is then covered by a square of the test tissue across the opening

[0064] The catchpots are then stacked one on top of cach other to form a column.

[0065] The stack is then carefully inverted.

[0066] The stack is then placed in an Endecote vertical shaker and vibrated for 10 minutes.

[0067] When the time is finished the catchpot stack is removed and carefully inverted so the tissue sample are again on top of each catchpot.

[0068] The residual sand in each catchpot is measured and the percentage “sift” of the paper determined by the product of the original and final sand weights.

[0069] The results are recorded under the appropriate sand range and the average “sift” ranking is established by taking the mean value of the 3 sand range results.

[0070] The results are shown in Table 2. 2 % Tea Sift Data Table 2 Ex 2 Ex 3 Particle EX 1 Latex Latex Ex 4 Ex 5 Size JRC Product Product Microwave Microwave Microns NHSTB USA EU NHSTB NHSTB  75-106 93.4 64.8 67.2 82.9 29.2 106-150 21.9 31.7 30.1 60.5 37.5 150-212 4.6 8.3 6.2 17.2 10.9 AVET 40.0 34.9 34.5 56.9 42.53

[0071] Test 3- Tea Infusion

[0072] The speed at which a specific tea blend infuses (Brews) is reliant on the impact of infusion packets and is obviously of key importance to the consumer.

[0073] To assess comparatively the impact in infusion rate of different infuser tissues the infusion rate is evaluated by measuring the colour change of the brew liquor of a period of time, typically 5-6 minutes, by colourimetry The following test regime has been adopted and is outlined as follows:

[0074] The tea bag is contained in a holding cage, to maintain submergence in the water, is placed into a 1000 ml beaker containing a photometer probe and a magnetic stirrer. 700 ml of boiling de-ionised water is poured into the beaker at which point the test begins.

[0075] The initial (Time=zero seconds) photometer reading is taken and then at intervals until the end of the test at 270 seconds.

[0076] The brew liquor in the beaker is maintained at 85° C. during the test by means of a heating plate.

[0077] The results are shown in Table 3. 3 Infusion Data Table No. 3 Light Transmission Ex 4 Ex 5 Infusion Ex 2 Ex 3 Micro- Micro- Time Ex 1 Latex Latex wave wave Sec NHSTB Product Product NHSTB NHSTB 30 0.129 0.015 0.13  0.125 0.132 90 0.523 0.321 0.299 0.481 0.300 120 0.639 0.541 0.442 0.588 0.642 150 0.721 0.690 0.569 0.669 0.729 240 0.895 0.807 0.797 0.835 0.918 270 0.935 0.859 0.853 0.968 0.958

[0078] Test 4 Hydrophilicity

[0079] Water Climb and Water Drop Tests were conducted as described above.

[0080] The results are shown in Table 4. 4 Water Climb & Water Drop, Test Data Table 4 Ex 2 Ex 3 Ex 4 Ex 5 Water Water Ex 1 Latex Latex Micro- Micro- Climb to Drop Test JRC Product Product wave wave 1″ (Secs) (Secs) NHSTB USA EU HSTB HSTB  30   <1 ✓ ✓  50   <60 ✓ 300   >250 ✓ 400+ >450 ✓

[0081] Test 5- Wet Crimp

[0082] The dry strength of the crimp fin seal is of critical importance to both dry functionality in manufacture, packaging and end use, while the wet integrity of the crimped fin seal is obviously the key factor in brewing functionality.

[0083] To assess comparatively the differences between dry and wet crimp strengths of different infuser tissues, the following test regime has been adopted:

[0084] Tea bags are manufactured without tea being dosed to the individual bags,

[0085] The top seal is cut off 5 bags which are opened flat.

[0086] A 50 mm section is cut from ostensibly each chamber side of the bag. Each section is then cut to give the side of the chamber section containing the crimped fin seal alone.

[0087] The sample is then loaded into the jaws of a tensile testing machine, such that the crimped fin seal is situated between the jaws.

[0088] A standard tensile assessment of the seal is then under taken and the results reported as grams/50 mm.

[0089] The wet crimp test is identical to the above except that once loaded into the jaws of the tensile tester the sample is sprayed lightly with a mist of water at ambient temperature.

[0090] The results are shown in Table 5. 5 Wet Crimp Data Table No. 5 Typical Crimp Tensile Range (g/50 mm) Ex 1 Ex 2 Ex 3 Ex 4 Crimp Type NHSTB Latex Product Latex Product Microwave Dry 125-200 160-242 110-165 123-300 Wet  9-13 20-36 16-21 17-25

[0091] Test 6-Hot Water On Cup Brew

[0092] Herbal teas are of high bulk for a given grammage. The amount of tea dosed to herbal tea is still typically 1.5 g-2.0 g however the tea expands significantly during brewing and contains significant volumes of both ambient atmosphere and gases produced during the brewing process. The effect of this is to put an increased stain on the crimped fin seal, which with standard paper grades causing a rupture of this seam.

[0093] To assess comparatively the differences between infuser tissues the following test regime has been adopted and is outlined as follows:

[0094] Tea bags are manufactured without tea being dosed to the individual bags,

[0095] 2 grams of peppermint tea is dosed between the two chambers and the top enclosed as standard with a steel staple.

[0096] The bags are placed in a 500 ml b grade laboratory beaker

[0097] 200 ml of boiling domestic fresh water is poured on to the bag to determine if the bag:

[0098] Inflates (Balloons)

[0099] The crimped fin seal ruptures, as defined by tea leaves in the brew liquor.

[0100] The test is normally the result of 5 replicates and is reported as a percentage of the total tested.

[0101] The results are shown in Table 6 6 Hot Water On Cup Brew Test Table 6 Ex 2 Ex 3 Ex 1 Latex Latex Ex 4 Ex 5 Pour on Typical Product Product Microwave Microwave Test NHSTB US EU HSTB HSTB Ballooning 100%  20% 30% 100%  100%  Open on  0% 20% 20% 5% 5% Inspection Burst 90% 10% 15% 5% 0%

Claims

1. A beverage infusion package formed of porous, fibrous cellulsoic material and having a closure seam produced by a mechanical compression action without heat sealing characterised in that the porous material contains thermoplastic fibres which are amorphous or are only partially crystaline.

2. A package as claimed in claim 1 wherein the thermoplastic fibres are present as a fused or thermally bonded network.

3. A package as claimed in claim 1 or 2 wherein the thermoplastic has a crystallinity of less then 40%, preferably 10% to 20%.

4. A package as claimed in any one of claims 1 to 3 wherein the thermoplastic is selected from polypropylene, polyester, polyamide and high density polyethylene.

5. A package as claimed any one of claims 1 to 4 wherein the fibrous material comprises 5 to 30% by weight of the thermoplastic fibres.

6. A package as claimed in claim 5 wherein the porous fibrous material comprises 10 to 30% by weight of thermoplastic fibres.

7. A package as claimed in claim 6 wherein the porous fibrous material comprises 15% to 25% by weight of the thermoplastic fibres.

8. A package as claimed in any one of claims 1 to 7 wherein the thermoplastic fibres have a thickness in the range 0.5 to 6.0 denier.

9. A package as claimed in claim 8 wherein the thermoplastic fibres have a thickness in the range 2 to 4 denier.

10. A package as claimed in any one of claims 1 to 8 wherein the porous fibrous material is hydrophilic.

11. A package as claimed in claim 9 wherein the porous fibrous material has a water climb value of least 70 seconds as measured by the time taken for water to rise 1 inch up that material.

12. A package as claimed in claim 10 wherein the porous fibrous material has a water climb value of 20 to 40 seconds.

13. A package as claimed in any one of claims 1 to 12 wherein the porous fibrous material has been treated with poly(vinylalcohol) having a degree of hydrolysis of at least 60%.

14. A package as claimed in claim 13 wherein the poly(vinylalcohol) has a degree of hydrolysis of at least 80%.

15. A package as claimed in claim 14 wherein the poly(vinylalcohol) has a degree of hydrolysis of 95% to 99%.

16. A package as claimed in any one of claims 1 to 15 wherein the porous fibrous material has a basis weight of 10 to 30 g m−2.

17. A package as claimed in any one of claims 1 to 16 wherein the mechanically formed seam has been formed by folding over together adjacent edges of the porous material and applying a mechanical compressive force to the folded over edges.

18. A package as claimed in any one of claims 1 to 17 wherein the seam is a crimped seam.

19. A package as claimed in any one of claims 1 to 18 which is of the double-chamber type.

20. A package as claimed in any one of claims 1 to 19 which is a tea bag.

21. A porous fibrous material having a basis weight of 10 to 30 g m−2 and being comprised of a single, wet-laid layer of an admixture of cellulosic and thermoplastic fibres which are amorphous or only partially crystalline.

22. A material as claimed in claim 21 wherein the thermoplastic fibres are present as a fused or thermally bonded network.

23. A material as claimed in claim 21 or 22 wherein the thermoplastic has a crystallinity of less then 40%.

24. A material as claimed in any one of claims 21 to 23 wherein the thermoplastic is selected from polypropylene, polyester, polyamide and high density polyethylene.

25. A material as claimed any one of claims 21 to 24 wherein the fibrous material comprises 5 to 30% by weight of the thermoplastic fibres.

26. A material as claimed in claim 25 wherein the porous fibrous material comprises 10 to 30% by weight of thermoplastic fibres.

27. A material as claimed in claim 26 wherein the porous fibrous material comprises 15% to 25% by weight of the thermoplastic fibres.

28. A material as claimed in any one of claims 21 to 27 wherein the thermoplastic fibres have a thickness in the range 0.5 to 6.0 denier.

29. A material as claimed in claim 28 wherein the thermoplastic fibres have a thickness in the range 2 to 4 denier.

30. A material as claimed in any one of claims 21 to 29 wherein the porous fibrous material is hydrophilic.

31. A material as claimed in claim 30 wherein the porous fibrous material has a water climb value of least 70 seconds as measured by the time taken for water to rise 1 inch up that material.

32. A material as claimed in claim 31 wherein the porous fibrous material has a water climb value of 20 to 40 seconds.

33. A material as claimed in any one of claims 21 to 32 wherein the porous fibrous material has been treated with poly(vinylalcohol) having a degree of hydrolysis of at least 60%.

34. A material as claimed in claim 33 wherein the poly(vinylalcohol) has a degree of hydrolysis of at least 80%.

35. A material as claimed in claim 34 wherein the poly(vinylalcohol) has a degree of hydrolysis of 95% to 99%.