Humidity resistant matches and process for the manufacture thereof

FIELD OF INVENTION

This invention relates to humidity resistant matches and to a process for the manufacture thereof.

BACKGROUND AND PRIOR ART

Typically, match head compositions contain a major proportion by weight of potassium chlorate in admixture with a proportion of combustible material, e.g. starch, sulphur, charcoal or phosphorus sesquisulphide; a binder; an inert filler e.g. ground glass, zinc oxide, calcium sulphate, felspar, diatomaceous earth or china clay; and minor ingredients such as a burning rate catalyst, potassium dichromate, a dye or colourant, and/or a dispersant. On a percentage basis (dry weight) a typical composition may contain

In the case of strike-anywhere matches a significant proportion of the combustible material is provided by potassium sesquisulphide, whereas a typical safety match will contain a higher proportion of potassium chlorate.

As the binder animal glues are extensively used, although other binders e.g. casein, albumen, alkyl vinyl ether/maleic anhydride copolymers, epoxy resins, polyvinyl acetate, polyvinyl alcohol, have been suggested from time to time. As match head compositions are usually applied to the match by dipping in an aqueous slurry or paste of the match head ingredients, a prime requirement of the binder is water- solubility or water-dispersibility. Also, since it is usual to incorporate into the match head a substantial quantity of air for the purpose of providing sensitivity a secondary requirement is for a binder of high foamability so that a slurry can be formed containing a high proportion of air bubbles which become incorporated into the match head. Also, of course, the binder must provide for the integrity of the head at all stages of storage, striking, ignition and combustion. Desirably also the binder is a combustible material. Although such criteria are met to a greater or lesser extent by the alternative binders mentioned, animal glue remains the binder of choice. Nevertheless animal glue possesses one major disadvantage, namely sensitivity to moisture, so that matches made therewith do not perform or store well in humid, e.g., tropical climates.

Various alternatives have been tried in order to provide a humidity resistant match head composition, including variations in the binder itself, and the provision of waterproof, e.g. shellac, coatings on the formed match head.

Typical prior art proposals for the production of humidity resistant matches are:

GB-A-2 098 975 which discloses humidity resistant matches comprising a conventional mixture of gelatin glue, sulphur, chlorate and conventional fillers to which has been added a proportion of an emulsified oil, e.g. linseed oil or liquid paraffin together with a proportion of hollow microspheres of a thermoplastic copolymer. Additionally, the binder in such compositions may contain 0-4% by weight of a water insoluble acrylate copolymer to increase the cohesion of the tip, such copolymer being added to the mix as an aqueous dispersion. The particular acrylate resins used in accordance with that proposal are not further identified.

Acrylate resins, more specifically acrylate ester copolymer resins, are also added to match head compositions in accordance with the teachings of FR-A-2 236 817 to provide humidity resistance.

Other additives providing humidity resistance in match head compositions are hollow ceramic microspheres (GB-B-1 506 185), epichlorohydrin or urea-formaldehyde resins (FR-B-1 515 152), polysulphides or epoxypolysulphide resins (GB-1 529 096), vinyl acetate (JP-A-74 92,209), casenite, viz a combination of casein and lime (JP-A-82 34,097), and various polymeric components inter alia methacrylate esters and glycerol chlorohydrin (USP 3 314 904), methyl vinyl ether/maleic anhydride copolymer (USP 3 441 456) and alkyl acrylate/catalyst combinations (Chem. Abs. 75, 152 504d, 1971

An alternative approach has been to provide the finished match head with a humidity resistant coating e.g. of cellulose acetate and a chlorinated hydrocarbon (JP-A-7447,510), methyl methacrylate/vinyl acetate copolymer (JP-A-75 04,222), shellac or nitrocellulose (JP-A-78 62,813).

Despite all such proposals, the need still remains for an effective humidity resistant match head composition, and the present invention seeks to fulfil that need.

SUMMARY OF THE INVENTION

In accordance with the invention humidity resistant matches having excellent and improved humidity resistance as well as excellent strike sensitivity are provided using a polyacrylic or substituted polyacrylic acid as the binder and zinc oxide as the filler, or as at least one of the components of the filler.

DETAILED DESCRIPTION

In accordance with the present invention it has been found that matches with improved humidity resistance and excellent strike sensitivity can be obtained from aqueous match head compositions containing, as the binder, a water-soluble or water-dispersible salt of polyacrylic or substituted polyacrylic acid, e.g. polymethacrylic acid, with ammonia or volatile amine, and, as the filler or as a component thereof, zinc oxide, the zinc oxide being present in an approximately stoichiometric amount relative to the carboxyl groups in the polymer or above. Amounts of polyacrylic or substituted polyacrylic acid substantially in excess of the stoichiometric requirement with respect to the zinc oxide result in a decrease in humidity resistance. For the avoidance of doubt, the stoichiometric amount of zinc oxide relative to the carboxyl groups in the polyacrylic acid is defined as one mole of zinc oxide for every two molar units of the polyacrylic or substituted polyacrylic acid, i.e. for every two carboxylic acid-containing units in the polymer.

For the purposes of this specification and claims, the term "polyacrylic acid" is deemed to include substituted polyacrylic acids, e.g. polymethacrylic and polychloroacrylic acid unless the context requires otherwise.

Although the present invention is not to be restricted by any theory, the polyacrylic acid binder used in accordance with the invention is believed to undergo cross-linking with the zinc oxide during the drying stage with concomitant evaporation of the ammonia or volatile amine salt according to the following reaction scheme:

where R' is H or CH₃ or other low molecular weight substituent (e.g. CI or C₂-C₄ alkyl), n is an integer and NR₃ is ammonia or a volatile amine, i.e. a compound where R is H or a low molecular weight organic group, e.g. C,-C₄ alkyl, the R groups being the same or different, and optionally any two thereof being joined together to form with the N atom, a 5- or 6-membered heterocyclic ring compound e.g. pyridine or. piperidine. Suitable volatile amines include methylamine, ethylamine and pyridine, but for best results, the ammnonium salts are preferred.

Generally the molar ratio of carboxylic acid groups in the polymer to zinc oxide will be from 1.7:1 to 2.5: 1, preferably about 2: 1. The molecular weight of the polyacrylic acid will usually be in the range 100,000 to 1,000,000, preferably 200,000 to 300,000 in order to ensure adequate solubility or water dispersibility of the polymer salt in the aqueous match head composition used in the match dipping process. Preferably the polyacrylic acid is added to the match head composition as an aqueous solution or dispersion neutralised by the addition of a base, preferably ammonia or ammonium hydroxide, and preferably in an amount to provide an aqueous match head composition having a pH in the range 8-9. Moreover, since the polyacrylic acid salt possesses defoaming rather than foam-forming properties it will usually be necessary, in the aqueous slurry compositions used in this invention, to include a fomaing agent e.g. a surface active agent such as sodium dialkyl sulpho succinamate or triethanolamine lauryl sulphate in order to achieve a stable slurry with a sufficient degree of aeration. However, an adequate density and aeration by the slurry can also be achieved together with stability by incorporating as a filler or as a component thereof, glass or ceramic microspheres in the manner taught in our U.K. Patent Specification No. 1,506,185. Such microspheres may be present in amounts of from 1-33% by weight of the total composition (dry solids basis), preferably from 5 to 15%.

Further, in accordance with the invention, in order to obtain satisfactory cohesion of match heads containing polyacrylic acid as the binder it has been found desirable to incorporate into the composition a cohesion promoter,'preferably a combustible material, such as starch or modified starch derivative, e.g. a partially hydrolysed or esterified starch. Particularly suitable as cohesion promoters are starch acetate and thin boiling starches as are obtained from natural, unmodified starch by an acid and/or oxidation treatment which results in the breakdown of the starch macromolecules into smaller units. Other suitable cohesion promoters are water-soluble and water-dispersible cellulose derivatives and water-soluble and water-dispersible synthetic organic polymers and copolymers, e.g. ethylene/vinyl acetate copolymers, vinyl acetate/acrylic copolymers, styrene/acrylic copolymers, vinyl acetate/vinylchloride/ethylene terpolymers, poly(vinyl acetate), polyacrylates, and other vinyl ester polymers and copolymers with olefinic comonomers such as ethylene, e.g. polymers of the vinyl ester of versatic acid (a mixture of predominantly tertiary, cyclic carboxylic acids of 9 to 11 carbon atoms) with or without ethylene as a comonomer. The weight ratios of polyacrylic acid salt to cohesion promoter may range from 1:5 to 5: 1, preferably from 1:3 to 3:1, and most preferably about 1:1.

In order to obtain an aqueous match head composition of satisfactory rheology for the dipping process, i.e. suitable for the formation of a properly shaped match head by the dipping of the match splints into the aqueous match head composition to form a head thereon, and subsequent drying of the head, it may be necessary to include one or more viscosity modifying agents in the aqueous match head composition, particularly in those cases where a water-dispersible organic polymer, such as vinyl acetate/ ethylene copolymer, is used as the cohesion promoting agent. Any suitable viscosity modifying agent known in the art may be used, preferably combustible materials, e.g. water-soluble starch or cellulosic derivatives, such as the starch derivatives already mentioned. Such starches therefore serve both as a cohesion promoter and viscosity modifier and may hence be used alone in the compositions of the invention. Alternatively they may be used in combination with a water-soluble or water-dispersible copolymer, in which case their function is more that of a viscosity modifier than cohesion promoter, which purpose is served by the copolymer It is obvious for that reason that the compositions of this invention preferably contain a water-dispersible starch as a combined cohesion promoting and viscosity modifying agent. - _ .. .

In general, match head compositions used in accordance with this invention will contain, on a dry weight basis:

For application to the match stem in a traditional dipping process the above ingredients will be formed as a slurry in water and aerated as may be necessary to give the required density and sensitivity, and at a total solids, content of from 40-60% based on the total slurry weight. Suitable stabilizers which may be added, if necessary, to give the necessary stability to the aqueous match head composition include, in particular, water dispersible polyvinyl pyrrolidone and polyvinyl alcohol with molecular weights of the order of 44,000. Other aqueous foam stabilizers known in the art may also be used.

The procedures used in accordance with this invention to form the match head are entirely conventional, and do not need to be described herein, the novelty of the present invention residing in the compositions used, and particularly the binder component.

Specific formulations for use in accordance with the present invention are given in the following Examples: all percentages are by weight on a dry solids basis.

Example 1

Example 2

Yet further safety match compositions in accordance with the invention are illustrated by Examples 3-6 below:

An illustrative humidity resistant strike anywhere composition in accordance with this invention is illustrated by Example 7.

Example 7

Matches formed from the above compositions by dipping match splints into an aqueous and aerated dispersion of the specified ingredients to form a bulb thereon, and subsequently drying of the bulb to form the match head, are found to have good strike sensitivity and burning properties and good humidity resistance. After 24 hours storage at 95% relative humidity the success (ignition) rate on striking was excellent, approaching 100% successful ignitions. Under the same conditions, similar match head compositions but with animal glue as the binder fail completely, i.e. no successful ignition.