The present invention relates to infusion packets. More particularly, the present invention is directed towards the manufacture of infusion packets (such as tea bags) having a three-dimensional shape.

BACKGROUND

In the past, conventional infusion packets (e.g. tea bags) have typically been flat, comprising a single chamber filled with infusible material (e.g. leaf tea, herbal mixtures). Such packets are essentially flat and thus restrict the movement of the infusible material within the packet to substantially two dimensions. As a result, the infusion performance of these infusion packets is limited. US 3,549,381 discloses a tea bag comprising tea leaves enclosed in an impervious, flexible, thermoplastic protective film, at least a portion of said film having a regularly spaced embossed pattern on at least one surface which has been drawn sufficiently to develop a preferential weakness in one direction. The tea bag is impervious until it is stretched by the end user. As the thermoplastic material is stretched, it opens up forming a netlike material. Thus the embossed thermoplastic material is stretched in a first direction during manufacture (to develop a preferential weakness in one direction) and then stretched to some extent in a second direction by the end user (to form a netlike material). Since these tea bags are substantially flat, the movement of the tea leaves enclosed therein is restricted to substantially two dimensions during infusion. Furthermore, since formation of the netlike material relies on the consumer stretching the thermoplastic material, such tea bags will not be as uniform as conventional tea bags. For example, too little stretch may limit the performance of the tea bag due to only a part of the packaging material becoming porous. On the other hand, too much stretch may introduce openings which are large enough to permit leakage of the tea leaves into the beverage itself. Thus the performance of the tea bags disclosed in this document is likely to be far from optimal. The past few decades have seen the development of infusion packets which have a more three-dimensional shape and which allow greater circulation and mixing of the infusion liquid and the infusible material. Of particular success have been tetrahedral-shaped packets such as those described in WO 04/033303 and WO 95/01907. In the manufacture of tetrahedral packets, the tetrahedral shape is conventionally formed by making mutually perpendicular transverse seals in a tube of filter material. Apparatus designed for such manufacture is ill-suited to the manufacture of other three-dimensional shapes. Other three-dimensional shapes have been considered, such as those described in GB 2 408 252, which are manufactured by forming porous webs into three- dimensional shapes via the application of heat and/or moisture. The packages are made from webs of conventional infusion packet material, and the resulting packages are said to inherently have some folding, pleating and gathering of the web material, e.g. at the base of the shape being formed. Therefore, some areas in the package are not porous and/or have a tendency to trap the infusible material. This can limit the infusion performance of such packages, as well as being visually unappealing to consumers. Therefore, there remains scope for improvements regarding the design and manufacture of three-dimensional infusion packets.

SUMMARY OF THE INVENTION

Known thermoforming processes (e.g. for producing capsules) are capable of forming thermoplastic material into a variety of three-dimensional shapes. However, materials conventionally used to manufacture infusion packets are often not suitable for thermoforming. Firstly, infusion packets are commonly made of paper, which is not thermoformable. Secondly, even if they are made from a thermoformable material, the porosity and thinness of the material makes thermoforming a challenge.

In order to thermoform a material, it is necessary to heat the material to a temperature which is sufficient to allow the thermoplastic material to deform under thermofornning stresses. Very thin material is liable to tear under the stresses applied, particularly when being formed into a three-dimensional shape comprising sharp features. There is also the possibility that the thermoforming process will increase the size of the perforations and/or holes in the material to such an extent that fine particles of infusible material will leak out of the packet. On the other hand, it is important that heating the material does not close the perforations in the material, since this would reduce the porosity of the infusion packet.

Thus it would seem that thermoforming is not a practical method of generating infusion packets. However, the inventors have overcome these barriers by using a non-conventional material as the substrate for thermoforming.

Thus in a first aspect, the present invention relates to a process for the manufacture of infusion packets, the process comprising:

(a) providing a first sheet of thermoplastic material which is porous or non- porous;

(b) thermoforming portions of the first sheet into a three-dimensional shape;

(c) providing a second sheet of material;

(d) dosing an infusible substance into the thermoformed portions of the first sheet or onto the second sheet;

(e) sealing the first and second sheets together to form pockets containing the infusible substance such that each pocket includes at least one thermoformed portion of the first sheet;

(f) severing the pockets at the seals to form infusion packets each having a chamber containing the infusible substance,

wherein the first sheet is a polymer film with at least one embossed surface, and wherein the thermoformed portions of the first sheet are porous.

The process involves thermoforming a thermoplastic polymer film with at least one embossed surface. This type of thermoplastic material is not conventionally used in the manufacture of infusion packets. Indeed, the first sheet does not need be porous prior to being thermoformed (although the thermoformed portions of the first sheet are porous, i.e. permeable to aqueous liquids). By using this non- conventional material, it has been possible to develop a process which uses thermoforming to manufacture infusion packets having a wide variety of three- dimensional shapes. The inventors believe that this is the first time that anyone has recognised the possibility of using thermoforming to manufacture infusion packets with three- dimensional shapes from this material.

Thus in a second aspect, the invention relates to an infusion packet comprising a chamber that contains an infusible substance, wherein the packet comprises material that has been formed into a three-dimensional shape by thermoforming a thermoplastic polymer film having at least one embossed surface such that the thermoformed thermoplastic polymer film is porous. DETAILED DESCRIPTION

In a first aspect, the present invention relates to a process for the manufacture of infusion packets.

This process involves a first step in which a first sheet of thermoplastic material is provided. The first sheet of thermoplastic material may or may not be porous. In a second step, portions of this sheet are thermoformed into a predetermined three- dimensional shape (i.e. a shape having length, breadth and depth). The thermoformed portions of the first sheet are porous (i.e. permeable to aqueous liquids).

A variety of three-dimensional shapes are possible. For example, tetrahedral or hemispherical shapes and the like are possible. Hemispherical shapes are particularly preferred. The first sheet of thermoplastic material is a polymer film with at least one embossed surface. In certain embodiments the embossed film may be embossed on both surfaces. This first sheet need not be porous prior to being thermoformed. During thermoforming, portions of the first sheet (i.e. the portions being formed into three-dimensional shapes) experience stresses. These stresses are sufficient to introduce holes in the embossed polymer film. This allows the manufacture of a porous infusion packet from a non-porous material. Furthermore, since the holes are formed during the thermoforming process, this sheet can be stretched further than an equivalent porous sheet whilst ensuring that the holes present in the final packet are sufficiently small to minimise sift of the infusible material. Since the application of the thermoformed material is as infusion packets, the thermoformed thermoplastic material is permeable to aqueous liquids. More precisely, the thermoformed portions of the thermoplastic material are porous.

The polymer film preferably comprises polypropylene, polyethylene, or copolymers thereof. High-density polyethylene is particularly preferred.

The embossed surface preferably comprises small raised solid bosses (i.e. raised figures) arranged with spaces between adjacent bosses in longitudinal and transverse rows. Preferably the bosses in each longitudinal row are in staggered arrangement with the bosses in each adjacent row. The shape of the bosses is not critical, although in a particularly preferred embodiment the bosses are hexagonal in shape.

Preferably the embossed surface of the polymer film has a regular pattern of bosses. It is particularly preferred that the bosses are regularly spaced in longitudinal and transverse rows. In certain embodiments, the bosses are regularly spaced in mutually perpendicular rows.

Prior to thermoforming, the embossed surface of the polymer film preferably has at least 60 bosses per 25 mm, more preferably at least 80 bosses per 25 mm, most preferably at least 100 bosses per 25 mm. The embossed polymer film can be produced by extruding polymer film, usually as a molten film, into the nip between two suitable rollers. Embossing is achieved by passing the polymer film between pair of rollers wherein at least one of the pair is engraved. The engraving pattern determines the shape and spacing of the bosses on the embossed surface of the film. In order to produce a polymer film which is embossed on both surfaces, the polymer film is passed between a pair of rollers wherein both of the rollers are engraved. As set out above, it is not necessary for the embossed polymer film to be porous prior to thermoforming. However, in certain embodiments the embossed polymer film is porous prior to thermoforming. This can be achieved by simultaneous or sequential stressing of the embossed film in two directions in the plane of the film. For example, this type of porous material can be produced as described in GB 914,489, GB 1 ,055,963 and GB 1 ,106,254.

In a third step of the process, a second sheet of material is provided. This second sheet of material need not be the same material as the first sheet. In fact the second sheet of material need not be thermoformable, and as such can be a material conventionally used for the manufacture of infusion packets. In order to facilitate manufacture of the final infusion packet it is preferred that the second sheet of material is heat-sealable. In particular, it is preferred that the second sheet of material is a sheet of thermoplastic material. Suitable examples include polyethylene terephthalate (PET) and poly lactic acid (PLA).

In one preferred embodiment the second sheet of material is also a polymer film with at least one embossed surface. This permits thermoforming of portions of the second sheet. In this embodiment, the second sheet of material may be porous or non-porous prior to being thermoformed. The thermoformed portions of the second sheet are preferably porous.

In a fourth step, the process involves dosing an infusible substance. The infusible substance can be dosed into the thermoformed portion of the first sheet or onto the second sheet. For convenience of manufacture, it is preferred that the infusible material is dosed into the thermoformed portion of the first sheet.

Preferred examples of infusible substances are tea plant material, herb plant material, fruit pieces and/or flower material (e.g. petals). The term "tea plant material" refers to leaf and/or stem material from Camellia sinensis var. sinensis or Camellia sinensis var. assamica. It also includes rooibos obtained from Aspalathus linearis, as well as the product obtained by blending any of these tea plant materials. The leaf material may be fermented (i.e. black tea), partially fermented (i.e. oolong tea), or substantially unfermented (i.e. green tea).

In a fifth step, the first and second sheets are sealed together to form pockets. The pockets contain the infusible substance. Each pocket includes at least one thermoformed portion of the first sheet. The first and second sheets can be conveniently sealed together around the perimeter of the thermoformed portion of the first sheet.

As mentioned above, the second sheet need not be thermoformed. Therefore, in one preferred embodiment the pockets comprise a thermoformed portion of the first sheet sealed together with a non-thermoformed portion of the second sheet (i.e. the portion of the second sheet is essentially flat).

In embodiments where portions of the second sheet have also been thermoformed, it is preferred that each pocket includes a thermoformed portion of the first sheet and a thermoformed portion of the second sheet. Once again, the first and second sheets can be conveniently sealed together around the perimeter of the thermoformed portions.

Sealing may be achieved by any suitable method known in the art. Since the process necessarily involves thermoplastic material heat-sealing is particularly preferred. Alternatively, sealing the first and second sheets together may be achieved by other methods. For example, ultrasonic sealing allows the seal to be very narrow, which can improve the appearance of the infusion packet. A sixth step of the process involves severing the pockets at the seals to form infusion packets. Each infusion packet has a chamber containing the infusible substance. It should be noted that this step is not necessarily performed subsequently to the fifth step of sealing, and in a preferred embodiment, the sealing and severing steps of the process can be performed simultaneously.

As the thermoformed portions of the sheet form part of an infusion packet, typically the sheet of thermoplastic material will be very thin. Prior to being thermoformed, it is preferred that the sheet of thermoplastic material has an average thickness of less than 1 .0 mm, more preferably less than 0.5 mm, still more preferably less than 0.2 mm, most preferably from 0.01 to 0.1 mm. The thermoforming may be carried out by any suitable means known in the art. However, since the infusion packet produced by the process is porous, it is impractical to use air pressure to thermoform the sheet of thermoplastic material. Therefore, it is preferred that the sheet is thermoformed using a mould, more preferably by pressing a male former into the sheet.

As the sheet of thermoplastic material is relatively thin, with a low capacity to store heat, it is preferred to heat the mould rather than the material.

In a preferred embodiment, thermoforming comprises the steps of bringing portions of the sheet of thermoplastic material at a temperature below that required for thermoforming into contact with a mould at a temperature above that of a thermoforming temperature of the thermoplastic material, pressing the mould into contact with the thermoplastic material, the contact between mould and thermoplastic material causing heat to transfer from the mould to the thermoplastic material and raising the thermoplastic material to a thermoformable temperature; such pressing causing thermoforming of the thermoplastic material to conform to the shape of the mould.

Thus no heating of the thermoplastic material is carried out until thermoforming begins. As the thermoplastic material has a low capacity to store heat, it will rapidly heat up once it comes into contact with the heated mould. Thus this method takes the potential disadvantage of low heat capacity and utilises this feature, resulting in effective thermoforming of the thermoplastic material. The temperature of thermoforming is sufficient to allow the thermoplastic material to deform under thermoforming stresses. Therefore, the temperature of the mould is preferably at least 60°C, more preferably at least 70°C. In order to ensure that the infusion packets produced by this process are porous, the thermoplastic material should not be exposed to temperatures which cause the perforations to close. Thus the temperature of the mould is preferably less than 150°C, more preferably less than 125°C, most preferably less than 100°C. In a second aspect, the invention relates to an infusion packet comprising a chamber that contains an infusible substance, wherein the packet comprises material that has been formed into a three-dimensional shape by thermoforming a thermoplastic polymer film having at least one embossed surface such that the thermoformed thermoplastic polymer film is porous.

It will be appreciated that such an infusion packet can be manufactured by the process of the invention.

The invention will now be illustrated by way of example and with reference to the following figures, in which:

Figure 1 is a schematic representation of an embodiment of an apparatus that is suitable for carrying out a process according to the present invention; and

Figure 2 is a schematic representation of the apparatus shown in Figure 1 during execution of a process according to the present invention.

Figure 1 shows a first sheet of thermoplastic material 2. The thermoplastic material is a film of high-density polyethylene which is embossed on one surface. The embossed film has 60 features per 25 mm.

The film is clamped in place by upper clamps 4 and lower clamps 6. The film is at ambient temperature. Positioned above the embossed film is a male former 8, at a temperature of 70°C.

In use, the male former 8 moves downwards to come into contact with the first sheet 2. As it makes contact, the portion of the first sheet 2 that comes into contact with the male former 8 rapidly heats up to 70°C.

The male former 8 continues to move downwards, heating and thermoforming the first sheet 2 simultaneously, until the male former 8 is in the position shown in Figure 2.

During thermoforming, portions of the embossed polymer file (i.e. those in contact with the male former) experience stresses. These stresses are sufficient to introduce holes in the embossed polymer film. Once the first sheet 2 is fully thermoformed, the male former 8 retracts and the first sheet 2 rapidly cools and sets. The formed portions of the first sheet are now porous, and hence permeable to aqueous liquids, due to the holes introduced during thermoforming. An infusible substance can subsequently be dosed into the thermoformed portion of the first sheet, and a second sheet of material used to seal the infusible material within a chamber. This second sheet can be a substantially planar sheet of material, or alternatively the second sheet can also have been thermoformed. As used herein the term "comprising" encompasses the terms "consisting essentially of and "consisting of. It should be noted that in specifying any range of values or amounts, any particular upper value or amount can be associated with any particular lower value or amount. The disclosure of the invention as found herein is to be considered to cover all embodiments as found in the following claims as being multiply dependent upon each other, irrespective of the fact that claims may be found without multiple dependency. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art in the relevant field.