A PROCESS FOR PRODUCING A WATER SOLUBLE PACKAGE

Abstract: A process for producing a thermoformed package comprises the steps of placing a first sheet of film over a forming die having at least one cavity; heating the film to mould the film into the at least one cavity thereby forming at least one recess in the film, placing a composition in the at least one formed recess and sealing a second sheet of film across the at least one formed recess to produce at least one closed package. Each cavity includes a curved edge at least a portion of which comprises a resiliently deformable material.

Description: A PROCESS FOR PRODUCING A WATER SOLUBLE PACKAGE The invention relates to a process for producing a thermoformed package of the type comprising the steps of placing a first sheet of formable film over a forming die having a cavity, moulding the film into the cavity thereby forming a recess in the film, placing a composition in the thus formed recess, and sealing a second sheet of film across the recess to close the package. In particular, the invention relates to such a process for producing a water- soluble package containing a detergent composition. Detergent compositions for the machine washing of laundry are provided in many forms. Probably the most prevalent form of laundry detergent is washing powder or granules. A problem with the use of these forms of detergent is that the product needs to be dosed into the machine in such a way that the detergent is quickly and thoroughly dissolved in the wash water of the machine without coming into contact with the laundry in a solid form. In this regard many dosing devices which overcome this problem have been proposed. One such device disclosed in European Patent Nos . 0 343 070 and 0 343 069 teaches the use of a flexible fabric sock which holds the particulate detergent in the machine, the fabric of the sock being permeable to water so as to allow water enter the sock and carry the detergent out of the sock through the fabric walls in the form of an aqueous solution. More recently unit dose forms of detergent have been proposed in the form of compressed tablets of detergent powder. A problem encountered with the provision of detergent tablets is that the tablets need to be strong enough to withstand storage and transport, yet weak enough to disintegrate and dissolve quickly in the washing machine. A further problem is the need to prevent the tablets "posting" in the porthole and between the drums of conventional washing machines. More recently these problems have been overcome by the provision of detergent tablets having specific chemical disintegrants which allow quick disintegration of the tablets in the aqueous environment of a washing machine, and by the provision of loosely fitting net bags which aid tablet disintegration and prevent "posting" . However, as many of the current detergent tablets contain bleach and other irritant substances, the problem of handling the tablets remains. The provision of detergent compositions in water-soluble films has been known for some time. Most of the documents relating to this subject describe water soluble film envelopes formed using a vertical form-fill-seal (VFFS) route. A problem with envelopes produced using this VFFS method is that, due to the constraints of the process, the resultant envelopes have seals which incorporate defined weak points where the seals overlap at corners. This results in envelopes, which are easily corrupted as a result of impacts suffered during transport. In an attempt to overcome the problems associated with such VFFS envelopes, European Patent Application No. 0 608 910 describes thermoformed water soluble packages for pesticidal compositions of the above mentioned type, which packages include a seal which does not have any angular intersections with itself. While this specification does provide a partial solution to the problem of weak seals, the thermoforming of water-soluble films results in formed packages having many other weak points. Moreover, the packaging and transport of such packages subjects the formed packages to considerable impact forces . It is an object of the invention to overcome at least some of the above problems Statements of Invention According to the invention, there is provided a process for producing a thermoformed package of the above mentioned type, the process being characterised in that the or each cavity in the forming die has a curved edge, wherein at least a portion of the curved edge is formed from a material which is less hard and more deformable than the material of the cavity. Ideally, at least a portion of the curved edge comprises a resiliently deformable material. Generally, a predominant portion, and most preferably a whole, of the curved edge is formed of a resiliently deformable material. In one embodiment of the invention, the curved edge comprises an annular gasket of resiliently deformable material, which gasket is mounted in a circumferential groove around the or each cavity. In such a case, the gasket should be dimensioned such that, when mounted in the groove, an exposed surface of the gasket should be flush with a surface of the cavity. In a further aspect of the invention, the or each cavity is surrounded by a raised flange, wherein at least a portion, and ideally most or all, of the raised flange comprises resiliently deformable material. In such a case, the curved edge and flange are preferably integrally formed. Thus, a single gasket preferably comprises the curved edge and the flange. In one embodiment of the invention, a ratio of a width of the flange to a minor diameter of the cavity is between 1:50 and 1:10, preferably about 1:12. The resiliently deformable material is preferably silicone rubber, however other suitable material performing the same function are envisaged. In the thermoforming step of the process of the invention, the film is heated by a heating plate. This may be flat but preferably has at least one concave depression which in use overlies the at least one cavity, wherein the heating step involves the step of bringing the film into intimate contact with the or each depression. The use of a heating plate having concave depressions helps to ensure that the film when heated thermoforms uniformly which results in a package having less weak spots. In one embodiment of the invention, intimate contact between the film and the concave depression is achieved by exerting a vacuum between the depression and the film. In this regard the depression may include holes through which the vacuum may be pulled. Alternatively, the heating plate may comprise a porous material. When a vacuum is exerted in this manner, the vacuum should ideally comprise a pressure of up to 1 Bar, and preferably be less that 0.6 Bar. In an alternative embodiment of the invention, the film is forced into intimate contact with the concave depression by blowing air against it. Typically the pressure of the blown air will be less than 5 Bar, preferably less than 3 Bar. The heating plate preferably has a temperature in the region of 100 to 120 degrees C, and ideally is approximately 110 degrees C. Although the time the film contacts the heating plate depends to a large extent on the type of film used and the temperature of the heating plate, the time of contact between the film and the plate should be in the region 0.1 to 5 seconds, preferably 0.5 to lseconds, ideally approximately 700 milliseconds. In one embodiment of the invention the film is a water- soluble film. Ideally the package contains a liquid, gel or other type of fluent composition. Preferably, the liquid comprises a detergent or any other type of active agent used in the machine washing of laundry or dishes . In another embodiment of the invention, the package contains a bathing or shower gel composition or any other type of personal care composition. Detailed Description of the Invention The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings in which: - Fig 1 is a sectional view illustration portions of a forming die and heating plate for use with the process of the invention; Fig 2 is a detailed sectional view of a concave depression of Fig 1 ; and Fig 3 is a detailed sectional view of an edge of a forming cavity according to the invention. EXAMPLE In this example a thermoforming process is described where a number of packages according to the invention are produced from a sheet of water soluble material, namely polyvinyl alcohol supplied under reference CC8534 from Chris Craft. In this regard recesses are formed in the sheet using a forming die having a plurality of cavities with dimensions corresponding generally to the dimensions of the packages to be produced. Further, a single heating plate is used for moulding the film for all the cavities, and in the same way a single sealing plate is described. A first sheet of polyvinyl alcohol film is drawn over a forming die so that the film is placed over the plurality of forming cavities in the die, the details of which are described in further detail below. In order to maximise package strength, the film is delivered to the forming die in a crease free form and with minimum tension. In the forming step, and referring to Figs 1 and 2, the film is heated to 110 degrees C, for approximately 700 micro seconds. A heating plate 1 is used to heat the film, which plate is positioned to superpose the forming die 2. The plate includes a plurality concave depressions 3 (only one is shown) which correspond to the cavity 4 on the forming die 2. Each concave depression is generally circular having a diameter of approximately 50mm and a depth of about 5mm. An edge 5 of the depression 3 is radiussed as is the base 6, the radius of the base being about 50mm and the radius of the edge being about 30 mm. During this preheating step, a vacuum is pulled through the pre-heating plate to ensure intimate contact between the film and the pre-heating plate 1, this intimate contact ensuring that the film is heated evenly and uniformly (the extent of the vacuum is dependant of the thermoforming conditions and the type of film used, however in the present context a vacuum of less than 0.6 bar was found to be suitable) Non-uniform heating results in a formed package having weak spots. As an alternative, or in addition, to the vacuum, it is possible to blow air against the film to force it into intimate contact with the preheating plate. In such cases the air should be blown at a pressure of less than 3 Bar. The thermoformed film is thus moulded into the cavities forming a plurality of recesses which, once formed, are retained in their thermoformed orientation by the application of a vacuum through the walls of the cavities. This vacuum is maintained at least until the packages are sealed. Once the recesses are formed and held in position by the vacuum, the composition, in this case a liquid detergent is added to each of the recesses. A second sheet of polyvinyl alcohol film is then superposed on the first sheet covering the filled recesses and heatsealed thereto using a heating plate. In this case the heat sealing plate, which is flat, operates at a temperature of about 140 to 160 degrees centigrade, and contacts the films for 1 to 2 seconds and with a force of 8 to 30kg/cm2, preferably 10 to 20kg/cm2. In more detail, and referring to Fig 3, each cavity 4 is generally dome shaped having a curved edge 10 with a radius of curvature. A raised flange 11 surrounds each cavity to ensure that the films are sealed together along the flange to form a continuous seal. In this embodiment, the radiussed edge 10 and raised flange 11 are both formed a by a resiliently deformable material gasket 12 of silicone rubber. This results in reduced force being applied at the inner edge of the sealing flange to avoid heat/pressure damage to the film. Once sealed, the packages formed are separated from the web of sheet film using cutting means. At this stage it is possible to release the vacuum on the die, and eject the formed packages from the forming die. In this way the packages are formed, filled and sealed while nesting in the forming die. In addition they may be cut while in the forming die as well . During the forming, filling and sealing steps of the process, the relative humidity of the atmosphere is controlled to ca . 50%. This is done to maintain the heat sealing characteristics of the film. When handling thinner films, it may be necessary to reduce the relative humidity ensure that the films have a relatively low degree of plasticisation and as such tend to be stiffer resulting in easier handling. The actual specific RH of the atmosphere needed will vary according to the temperature of the environment and the type of film used, however for temperatures in the region of 20 degrees C, the RH should be in the region of 30 to 50% depending on the thickness and elasticity of the film. The invention is not limited to the embodiment hereinbefore described which may be varied in both construction, detail and process step without departing from the process of the invention.

Claims: CLAIMS 1. A process for producing a thermoformed package comprising the steps of : - placing a first sheet of film over a forming die having at least one cavity; heating the film; moulding the film into the at least one cavity thereby forming at least one recess in the film; placing a composition in the at least one formed recess; and sealing a second sheet of film across the at least one formed recess to produce at least one closed package, the process being characterised in that the or each cavity in the forming die has a curved edge, wherein at least a portion of the curved edge is formed from a resiliently deformable material. 2. A process as claimed in claim 1 in which a predominant portion of the curved edge is formed of a resiliently deformable material . 3. A process as claimed in claims 1 or 2 in which the curved edge comprises an annular gasket of resiliently deformable material, which gasket is mounted in a circumferential groove around the or each cavity. 4. A process as claimed in any preceding claim in which the resiliently deformable material comprises silicone rubber . 5. A process as claimed in any proceeding claim in which the or each cavity is surrounded by a raised flange, wherein at least a portion of the raised flange comprises resiliently deformable material. 6. A process as claimed in claim 5 in which a predominant amount of the raised flange comprises resiliently deformable material . 7. A process as claimed in any of claims 5 or 6 in which a ratio of a width of the flange to a minor diameter of the cavity is between 1:50 and 1:10, preferably about 1:12.

Inventors: HARBOUR RICHARD, HARBOUR, RICHARD
Applicants: LEVER HINDUSTAN LTD, UNILEVER NV, UNILEVER PLC, HINDUSTAN LEVER LIMITED
Application year: 2000
Main classification: B65B11
IPC codes: B65B11