Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2000-04-12
2002-02-12
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S065000, C521S068000
Reexamination Certificate
active
06346557
ABSTRACT:
The present invention relates to a spongy material, to a process for preparing it and to its applications, especially for the manufacture of household sponges and articles which include a spongy element, such as sponge cloths, squeezy mops and squeegees for cleaning surfaces.
In the household cleaning field, the sponges mainly used are plant-derived sponges, based on regenerated cellulose, and synthetic sponges which usually consist of polyurethane open-cell foams.
Although sponges based on regenerated cellulose have, as a general rule, very satisfactory properties, both in terms of water absorption and water retention capacities, ability to be wrung out, flexibility, toughness, mechanical strength and resistance to water, detergents and heat, their manufacture causes, however, major problems.
This is because these sponges are manufactured by processes which consist in firstly converting cellulose into a viscose pulp, which conversion is carried out by treating the cellulose with sodium hydroxide, dissolving the alkali cellulose thus formed in carbon disulphide and treating the resulting cellulose xanthate in sodium hydroxide. Next, after incorporating reinforcing fibres (hemp, flax, cotton, etc.), dyes and sodium sulphate crystals into the viscose pulp thus obtained and after forming by moulding or extrusion, the compound is heated, which makes it possible for the viscose to solidify and cellulose to be regenerated therefrom by evaporation of the carbon disulphide and causing the sodium sulphate crystals to melt which, by removing them, leave in their place a multitude of cells.
Thus, the implementation of these processes on an industrial scale, given the very corrosive and toxic nature of the products that they use, requires very specific plants which are very expensive both in terms of investment and of operating costs, is highly polluting despite the decontamination equipment that these plants include and the measures that are taken to limit the deleterious effect on the environment, and has relatively low production yields.
Polyurethane-foam sponges are obtained by markedly less constrictive manufacturing processes which are based on a condensation reaction between a polyol and a polyisocyanate in an aqueous phase, but they do have the drawback of being of a relatively hydrophobic nature which results in wettability, water-retention and wringing properties which are inadequate, despite the many treatments that have been proposed in the prior art for making polyurethane foams more hydrophilic.
Moreover, it has been proposed in U.S. Pat. No. 4,559,243 to produce spongy structures in the form of sheets a few mm in thickness by depositing, onto a support such as a woven, a nonwoven or a plastic sheet, a foam made of a mixture of a latex and of hydrophilic fibres, of the type comprising cellulose, viscose or even polyvinyl alcohol fibres, and then subjecting the compound to heating operations so as to coagulate the foam and to stabilize it into an open-cell structure by drying and crosslinking. Although the manufacture of these spongy structures, such as polyurethane-foam sponges, is free of the drawbacks of the processes for manufacturing plant-derived sponges, it proves to be the case, however, that these structures have a low absorbency which considerably limits their importance.
Consequently, the Applicant was set the task of providing sponges which have all the qualities required for household use and, especially, the ability to absorb a large volume of water and to retain the water thus absorbed for as long as it is desired not to actively expel it, the ability, however, to release this water under the effect of manual wringing and a high wipeability, the manufacturing of which sponges is simple to implement, requires no major industrial investment, uses neither corrosive substances nor toxic substances, is environmentally friendly and is characterized by economically advantageous productivity levels.
This objective is achieved, according to the present invention, by a spongy material comprising a mixture of cellulose fibres and of at least one elastomer, characterized in that it has:
a cellular structure formed by cells whose size is between 0.01 and 10 mm;
a relative density of between 0.03 and 0.1;
a water absorption capacity of at least 750%; and
a water retention capacity, after manual wringing, of less than 100%.
In the context of the present invention, the expression “water absorption capacity” should be understood to mean the ratio, expressed as a percentage, of the mass of water capable of being absorbed by the spongy material when it is entirely immersed in a volume of water to the dry mass of this spongy material and the expression “water retention capacity after manual wringing” should be understood to mean the ratio, also expressed as a percentage, of the mass of water retained in the spongy material after it has been manually wrung to the dry mass of the said spongy material.
The useful cellulose fibres according to the invention are all natural cellulose fibres such as wood cellulose fibres or papermaking fibres (coniferous or deciduous wood fibres, bleached or unbleached), cotton, flax, hemp, jute or sisal fibres or else regenerated fibres from rags.
They may, moreover, be long fibres (that is to say fibres more than 1 cm in length), short fibres (having a length of less than 3 mm) or fibres of intermediate length (between 3 mm and 1 cm in length) or else they may be composed of a mixture of fibres of various lengths. Thus, for example, excellent results have been obtained by using either long cellulose fibres, prepared by cutting sheets of cotton linters into shreds having a size of a few cm, by themselves or in combination with short cellulose fibres such as those sold under the brand name ARBOCELL® by Rettenmaier & Söhne and which measure about 900 &mgr;m in length, or cellulose fibres of intermediate length, which are also prepared by cutting sheets of cotton linters, but into shreds having a length of between approximately 8 mm and 1 cm.
Moreover, whatever their length, the cellulose fibres that can be used in the invention may advantageously have been subjected beforehand to a treatment suitable for promoting their entanglement within the elastomer and, consequently, their adhesion to this elastomer. Such a treatment may consist, for example, of a fibrillation treatment, that is to say mechanical agitation which has the effect of freeing the fibrils on the surface of the fibres, allowing them to catch on each other, or of an exposure to ultraviolet radiation which, by causing reactive sites to be formed on the surface of the fibres, allows chemical bonding of these fibres. By way of example of commercially available cellulose fibres that have undergone fibrillation, mention may be made of the fibres sold under the brand name LYOCELL® by Courtaulds Chemicals.
As regards the useful elastomer according to the invention, this may be chosen from very many elastomers as long as these elastomers are compatible with cellulose and therefore do not have a pronounced hydrophobicity.
Thus, the elastomer will advantageously be selected from polybutadiene rubbers, butadiene-styrene copolymers, butadiene-acrylonitrile copolymers (or nitrile rubbers), ethylene-propylene copolymers and terpolymers, styrene-butadiene or styrene-isoprene block copolymers, styrene-ethylene-butylene-styrene block copolymers, thermoplastic elastomers derived from polyolefins (such as SANTOPRENE® from AES or VEGAPRENE® from Hutchinson), octene-ethylene copolymers (such as those sold by DuPont-Dow under the brand name ENGAGE®), copolymers of ethyl acrylate and other acrylates, such as acrylate-ethylene-acrylic acid terpolymers (such as those sold by DuPont de Nemours and Exxon under the references VAMAC® and ATX® 325, respectively) or acrylate-acrylonitrile-styrene terpolymers (such as SUNIGUM® from Goodyear), polychloroprenes, chlorinated polyethylenes, and mixtures thereof.
Moreover, with regard to the aforementioned polyolefin elastomers, and especially polybutadiene, butadiene-styrene
Argy Gilles
Cheymol Andre
Garois Nicolas
Terrisse Jean
Alston & Bird LLP
Foelak Morton
Hutchinson S.A.
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