Sealable sachets

Abstract: A container having at least one opening seal, which seal is mechanically strong in the dry state but disintegrates in water at temperature of 40°C or below under the influence of mechanical agitation. The seal is formed from a homopolymer or copolymer of N-vinylpyrrolidone.

Description: FIELD OF THE INVENTION The present invention relates to sealable sachets and especially to sealable, detergent containing sachets. BACKGROUND AND PRIOR ART EP 143 476A (Akzo N.U.) discloses an opening sachet having seams with a coating comprising an anionic and/or a nonionic water binding polymer, and a cationic polymeric adhesive. EP-A-0 246 897 (Unilever), published 25.11.87 and filed 21 May 1987, claiming the priority of British Patent Application No. 86 12 706 filed 23 May 1986 discloses a sealable container especially in the form of a sachet provided with a heat sealable, liquid-labile seal. The seal is formed from a mixture of an adhesive component labile in water at temperatures of 40°C or below and a heat-sealable component insoluble in water at temperatures of 40°C or below. EP-A-40931 discloses a fabric treatment product formed of water-insoluble, water impermeable synthetic plastic sheet material containing a fabric treatment composition comprising a liquid, the bag having a weak seal that will be opened by the mechanical action of a washing machine. Various possibilities are given for the formation of this seal including the possibility of a weak heat seal. Ullmanns Encyklopädie der technischen Chemie, 4th edition (1977), vol. 14, pages 234, 238 and 239 teaches that polyvinylpyrrolidone may be included in pressure sensitive adhesive compositions. Vol. 19 of the same work, at page 386 mentions that polyvinylpyrrolidone has adhesive properties and is known for use in hot melt adhesives. Surprisingly, we have now found that a heat-sealable, liquid-labile seal can be formed by use of only one of certain homopolymers and copolymers. DEFINITION OF THE INVENTION The present invention provides a heat-sealable, liquid-labile closure. According to the invention there is provided a sachet having at least one opening seal mechanically strong in the dry state but which disintegrates in water, especially under the influence of mechanical agitation, the seal being formed from and consisting exclusively of a polymer of N-vinylpyrrolidone with 0 to 95wt% of a polymerisable co-monomer. DETAILED DESCRIPTION OF THE INVENTION Sealant The sealant is a polymer of N-vinylpyrrolidone with 0 to 95wt% of a co-monomer. The sealant may be poly N-vinylpyrrolidone (hereinafter PVP) itself or a N-vinylpyrrolidone/co-monomer copolymer. The co-monomer is preferably vinyl acetate but other co-monomers are suitable, for example butyl acrylate. Preferably the vinylpyrrolidone comprises 30 to 100 wt% of the polymer, more preferably 40 to 100 wt% and especially 50 to 70 wt%. A suitable polymer is the N-vinylpyrrolidone/vinyl acetate (30/70) copolymer supplied by the Aldrich Chemical Company Inc under the reference 19,083-7. An even more preferred polymer is the N-vinylpyrrolidone/vinyl acetate (60/40) co-polymer supplied by the Aldrich Chemical Company Inc under the reference 19,084-5. The sealant can be in the form of a viscous emulsion which is applied to one side of the surface and dried to give a coating which is flexible enough not to crack when the surface is flexed. This is especially valuable in embodiments where the surfaces to be sealed together are themselves flexible, and, for example, allows sachets to be manufactured on high-speed sachet-making apparatus. A coating of sealant may be a continuous or a discontinuous coating. If the sealant mixture is applied in viscous form, then one coat is generally sufficient. However, if the mixture is less viscous then two coats of the sealing composition may be advantageously applied to each wall. The first coat sizes the surface and the second coat forms a layer on the surface. Superior heat-sealing occurs, in general, if both surfaces to be sealed are coated with the composition. The sealant composition is preferably applied to the surface using conventional roller coating equipment to give a dry, flexible coating which can be heat-sealed at 170 to 200°C at a pressure of 3 bar and a time of 0.5 seconds on a conventional sachet forming machine. Such machines enable flexible containers of the invention to be made rapidly and easily. Other ways of applying the sealant and sealing the substances will, of course, readily suggest themselves to one skilled in the art. Preferably, the dry bond formed between the wall and the sealant composition should be strong enough that eventual failure of the bond on the application of a pulling force will result in tearing of the non-heat-sealable material rather than rupture of the bond. Preferred bond strengths in the dry state, as measured by means of an Alwetron (Trade Mark) Tensiometer, of a seam having the dimensions of 1.5 x 0.5 cm are in excess of 0.5N, especially in excess of 2N and still more especially in excess of 5N. After immersion the bond strength is preferably less than 0.4N, especially less than 0.1N. The wet strength of the bond is preferably 40% or less of the dry strength, more preferably 30% or less and especially 5% or less. By appropriate choice of sealant delayed or sequential release is possible. Nature of the container walls The walls of the sachet are preferably of non-heat-sealable material. By non-heat-sealable material it is meant that the material does not heat-seal to itself at temperatures up to 30°C greater than the lowest temperature at which the sealant used is heat-sealable. Although it is not essential that the walls are of non-heat-sealable material, it is important that the temperature, duration and pressure of the sealing process are such that the sachet walls are not directly bonded to one another over large areas without the involvement of an intermediate layer of sealant. The sachets are preferably heat-sealed but other methods of sealing including pressure, ultrasonics and high frequency induction may be used. The sachet will, in general, open more rapidly if at least one wall (or surface) is water-permeable than if all the walls are impermeable. The walls may be in any form although flexible materials such as webs or sheets of woven, knitted or non-woven fabric or paper are preferred. The wall material is preferably fibrous but may also be filamentary, slitted or foraminous. Suitable fibrous materials include cellulose, cellulose/regenerated cellulose mixtures, polyesters, and mixtures thereof. In preferred embodiments the walls are comprised of sausage casing paper, a viscose/cellulose mix, which is preferred because of its greater wet strength than many other papers, especially at elevated temperatures. The sachet walls preferably have a base weight of 5 to 100 gm⁻², more preferably 10 to 60 gm⁻² and especially 15 to 40 gm⁻². If the sachet walls are very permeable then the contents may be leached out before the sachet seals open. This may be a disadvantage if a delayed release of the container contents is required. The problem may be overcome by using less permeable walls. Sachets in accordance with the invention are preferably rectangular or square and made with four opening seals or one fold and three opening seals, although in principle one opening seal is sufficient. Sachets which also include non-opening seals as well as at least one opening seal are within the scope of the present invention but pattern coating may then be required. Sachets can be made by forming the material into a pouch with the coating on the inside. The contents are then introduced and the sachet sealed. The present invention is of use both for single compartment sachets which deliver their contents very rapidly and also for multicompartment sachets which deliver the contents of the compartments sequentially by the use of a number of seals opening at different times. In one preferred embodiment of the invention the sachet has two compartments. The compartments have one common non-opening seam and three opening seams each. The compartments may open at different times. Sachet Contents The contents of the sachet may be in any physical form. Preferably the contents are in particulate form. The sachet may contain any substances which are compatible with the materials of which the sachet of the invention is constructed. Aqueous liquids should, for example, be avoided as they would weaken the seal prematurely. The invention is of especial applicability to the home laundry process, and preferred contents of the article of the invention include fully formulated detergent compositions, bleaches, bleach precursors, fabric softeners, stain removing agents and anti-bacterial agents. The article of the invention is not only of use in the washing and dishwashing fields, and other contents and possible fields of use will, of course, be readily apparent to one skilled in the art. EXAMPLES The invention will be illustrated by the following non-limiting examples. All coating levels are on a dry basis. For the purpose of comparison the same substrate, sausage casing paper having a base weight of 21gm⁻², was used in each example and comparative example. One or two coats of sealant were applied to samples of the substrate, which were dried after each coat. Sachets 150mm square, each containing 40g detergent powder were formed by heat sealing the coated paper. To test opening times, sachets were placed in the drum of a Miele W756W washing machine on top of a 2.5Kg load of mixed cotton. The machine was operated on its 30°C wash cycle, and time durations were measured from when the machine had taken in water and drum agitation had commenced. The machine was stopped after periods of time to examine the sachet. The time until the sachet began to open was noted. Dry and wet bond strengths were also measured. The nature of the sealants used, the number of coats of sealant and the results observed are set out in the following Table. It may clearly be seen that PVP or PVP copolymers gave rise to seams which were strong in the dry state but weak after immersion in water. In contrast seams of PVA copolymers were strong both before and after immersion.

Claims: A sachet made of sheet material and having at least one opening seal mechanically strong in the dry state but which disintegrates in water under the influence of mechanical action, the seal being formed from a heat sealable coating layer on the sheet material, characterised in the coating layer consists exclusively of polymer of N-vinylpyrrolidone with 0 to 95 weight % of a polymerisable co-monomer. A sachet as claimed in claim 1 wherein the polymerisable co-monomer is vinyl acetate. A sachet as claimed in claim 1 wherein the polymerisable co-monomer is butyl acrylate. A sachet as claimed in any one of claims 1 to 3 wherein N-vinylpyrrolidone comprises 30 to 100 weight % of the polymer.

Inventors: NEWBOLD GEOFFREY, WAGNER JOHN DUNCAN, WRAIGE DOUGLAS, NEWBOLD, GEOFFREY, WAGNER, JOHN DUNCAN, WRAIGE, DOUGLAS
Applicants: UNILEVER NV, UNILEVER PLC, UNILEVER N.V.
Application year: 1988
Main classification: C11D17
IPC codes: C08F226, C11D17, B32B27, B32B7, B32B3, C08F26, B65D33