IE47821B1

IE47821B1 - Absorbent materials

Info

Publication number: IE47821B1
Application number: IE1624/78A
Authority: IE
Original assignee: Beghin Say Sa
Priority date: 1977-09-13
Filing date: 1978-08-09
Publication date: 1984-06-27
Also published as: IT1107856B; GB2004201B; NL7809338A; FR2402474B1; DE2831211C2; IE781624L; NL189847C; NL189847B; IT7869061A0; GB2004201A; DE2831211A1; ES472418A1; FR2402474A1; BE868341A

Abstract

A method of manufacturing absorbent structures e.g. menstrual towels, nappies, surgical dressings and wiping towels, wherein a liquid- absorbing material e.g. in the form of a powder, is secured to a support e.g. a film or fibrous pad by depositing a binding agent for example poly(vinyl alcohol), particularly in the form of an aqueous solution or dispersion. In one procedure after the liquid-absorbing material and the binding agent have been applied to one pad, a second pad is applied to form an integral structure with the binding agent and in another procedure the liquid-absorbing material is incorporated between two pads, and a liquid binding agent is applied to the external surface of one pad and percolates through to form an integral structure.

Description

This invention relates to a method of making absorbent materials formed of a support associated with particles of a liquid-absorbing material.

During the last twenty years considerable develo5 pment has been applied to products for personal and domestic sanitary use. In particular the production of products utilizing cellulose fibres in the form of padding obtained by dry shredding of sheets or rolls of pulp has rapidly increased. Menstrual towels, nappies for babies and dressings are particular examples of such products.

Cellulose fibre pads, although possessing satisfactory capacity for absorbing liquids, have the disadvantage of a poor liquid retention capacity. Furthermore an increase in the quantity of liquid absorbed can only be obtained by an increase in the quantity of cellulose fibres.

Consequently attempts have been made to synthesize compounds, which are capable both of absorbing water and retaining it. Such compounds include modified poly20 saccharides and synthetic polymers. The methods usually ' employed for producing such material include converting a water-insoluble into a soluble compound, or in converting a 'water.-soluble compound by treatment with a cross-linking agent, to prevent solubilization in water. By such means it is possible to obtain a compound distending in the - 3 presence of water but not solubilizing, the water being absorbed in a quasi-irreversible way, under the usual conditions of use.

Such products include modified cellulose ethers, alginates and polyacrylates. Such so-called superabsorbent products occur in the form of powders, fibres or films.

Such powdery products are readily obtainable in the dry state by atomization, but they are of necessity very hygroscopic, which raises numerous difficulties.

For example French Patent Specification 2319434 describes a method of providing on a support, particles of a modified cellulose ether (carboxymethylcellulose treated by a polyfunctional derivative of acrylamide) consisting in moistening the support with a liquid (e.g. a solvent or water) and subsequently depositing the absorbent derivative thereon. The particles distend and adhere to the support and the assembly is dried to eliminate the liquid vehicle. The disadvantage of such a method lies in the distention of the absorbent particles followed by the drying operation. A large part of the effectiveness of the particles becomes lost because of the change in their surface state. Furthermore particles may adhere to each other which leads to the formation of a film even when depositing the particles of a single layer.

American Patent Specification 3919042 describes a similar method but for a different purpose which consists in spraying particles of starch by electrostatic process onto a sheet of cellulose fibres containing at least 25% water.

Another method consists in passing water vapour through a fibrous pad containing absorbent materials.

French Patent Specification 2066324 proposes shredding a sheet of cellulose fibres in the presence of - 4 an absorbent powder, and then moistening the assembly so as to cause the particles to adhere to the fibres.

The preferred means consists of a treatment by water vapour. It is still unfortunately necessary to dry the assembly which induces an appreciable loss of absorbent capacity. Furthermore industrial plant to carry out such method is very difficult to operate. When the absorbent powders are mixed with fibres in suspension in air in a chamber, the passage of water vapour inevitably draws a great quantity of powder towards the walls of the chamber on which they cohere.

A similar technique is described in British Patent Specification 1354406 whereby sheets of cellulose wadding, optionally impregnated with a cationic compound, are covered with a powder of a hydroabsorbent polymer, stacked and subjected to treatment by water vapour. The various layers are thus connected by a distending substance in the presence of an aqueous liquid.

Similarly German Patent Specification 489308 describes an absorbent structure such as a menstrual towel or dressing, comprising a layer of absorbent powder of starch, dextrin or gelatin between two pads of cellulose fibres. The layer of powder is fixed by moistening.

Another method consists in applying to a cellul25 ose substrate a gel distended with water (cross-linked polyacrylamide) and drying the laminate obtained. This technique however does not provide very satisfactory results as demonstrated in the table of Examples 1 to 3 of French Patent Specification 2122432.

French Patent Specification 2283255 is concerned with the improvement of the hydrophilicity of non-woven fabrics of synthetic fibre base having useful sanitary and cleaning applications. The fibrous structure is impregnated with a bath of dressing containing cellulose ether before the usual treatment with resins or binding - 5 agents. Thus fabrics are obtained exhibiting good hygroscopic properties even after several washings.

It was unexpectedly discovered according to the present invention that it is possible to manufacture absorbent materials by applying a powdered liquid-absorbing material to a support and by depositing a binding agent on the thus supported powder.

The support can be a synthetic film or may be a fibrous material. Deposition of the binding agent may be effected by spraying or by transfer, e.g. a thin layer of a solution or dispersion of the binding agent on a roller surface is transferred to the supported liquid-absorbing product by applying the roller thereto.

Preferably particles of said powdered liquidabsorbing material are uniformly distributed on one surface of a surface consisting of a fibrous material.

The fibrous material may be formed of a padding obtained by dry process or by shredding of a sheet of cellulose fibres or of a sheet of cellulose wadding (tissue-wadding) or of a sheet of paper or of any other support comprising fibres.

While any type of binding agent may be used, particularly good results are obtained with a binding agent which is an aqueous solution of poly(vinyl alcohol). A 15% solution produces absorbent materials of good quality. Another type of binding agent composition which may be used according to the invention is in the form of an aqueous dispersion e.g. latex, for example an acrylic latex to fix the particles of liquid-absorbing material without substantially changing their absorbent power.

The liguid-absorbent material may be present on 2 the support at a loading of between 20 and 350 g/m . The binding agent may be deposited at a loading of from 2 to g/m based on dry binding agent. However a loading of - 6 2 binding agent as low as 2 g/m can provide satisfactory fixing of the absorbent material.

An advantage of the present invention is that the powdered liquid absorbing material may be deposited in an amount which corresponds substantially to more than one single layer of powders. Thus for powders of a volume mass of 1 and a diameter of 0.1 mm. a deposit of a single layer corresponds to a loading of 50 g/m t and by the method according to the invention, a deposit exceeding a 2 loading of 250 g/m may be obtained.

According to a particular embodiment of the invention, it is advantageous to deposit on the layer of liquid absorbing material a second fibrous pad. The binding agent thus serves both to fix the powders and to render the two pads integral.

A particular method of effecting the application of the binding agent is by depositing the binding agent on a composite formed by a layer of the liquid-absorbing material between two fibrous pads. By this procedure the moist binding agent percolates through the composite to render it an integral structure.

If desired the structure obtained can be dried.

The following examples of the invention are provided.

Example 1 Alginate powder obtained under the Trade Mark ALGUM 2600 sifter 100 was deposited at a loading of 70 g/m on a pad of cellulose fibres of the type used in the making of menstrual towels.

The deposit was then fixed by spraying an aqueous solution of 15% of poly(vinyl alcohol) obtained under the Trade Mark RH0D0VI0L 4/125. The structure obtained was then dried. By this procedure a loading of 6 g/m of the - 7 poly(vinyl alcohol) was obtained.

The absorptivity of the pads was not affected, and a substantial improvement in dry cohesion thereof was obtained.

Example 2 250 g/m of an alginate powder used in Example 1 was deposited on a pad of fibrous material and an aqueous solution of 15% of poly(vinyl alcohol) sprayed thereon to provide a film of loading 7 g/m on the surface. Under these conditions only 2/3 of the powder became fixed.

The deposition of a second pad of fibrous material onto the treated pad allowed the unfixed portion of the powder to become fixed thereto, thus securing an integral structure.

Example 3 By means of a spraying of 9 g/m of poly(vinyl 2 alcohol) onto a fibrous pad a deposit of 250 g/m of polycarboxyled synthetic absorbent obtained under the Trade Mark PERMASORB 10 was fixed to the pad.

Example 4 On a pad of cellulose fibres obtained by dry 2 shredding of a sheet of pulp, 250 g/m of alginate and of PERMASORB were applied, and fixed by spraying of poly (vinyl alcohol) thereon.

A 5 g sample was placed in a cylindrical basket provided with a conical portion, and plunged for 3 minutes in water and then drained for 1 minute.

The absorption results are set forth in Table 1. - 8 Table 1 Absorption of water Test fibre pad 105 g. Pad + poly(vinyl alcohol) 96 g· Pad (50) + Alginate (50) + poly(vinyl alcohol) 124 g. Pad (50) + PERMASORB (50) + poly(vinyl alcohol) 255 g.

Example 5 On a 300 g. pad of cellulose fibres a modified starch obtained from GRAIN PROCESSING CORPORATION under their Reference 35A 100 was deposited at a loading of 2 160 g/m , and was fixed by spraying an aqueous dispersion of a 22% acrylic latex obtained under the Trade Mark 2 PRIMAL P 339 at a loading of 10 g/m .

The formation of a thin peelable skin was observed. 5 g samples were tested as in Example 4. The results obtained are set forth in Table 2.

Table 2 Absorption of water Test fibre pad 104 g· Pad (65) + Powder (35) + (physical mixture 189 g. Pad (65) + Powder (35) + Latex 184 g.

It is consequently observed that the deposition of a not particularly absorbent film of latex does not substantially change capacity for absorption of structures obtained according to the invention.

It was also observed that the fixing of powders 2 was satisfactory by the deposition of 2 g/m of latex. - 9 Further tests showed that the forming on a fibre pad of a film obtained by the spraying of latex does not affect the qualities of absorption of the pad, as set forth in Table 3.

Table 3 Absorption of water Drainage ; 20 sec. Drainage 60 Test pad 113 g. 108 g. Pad + 8 g/m* 2 of PRIMAL 116 g. 108 g. Pad + 13.5 g/m2 of PRIMAL 112 g. 105 g. Pad + 20 g/m2 of PRIMAL 110 g. 103 g.

Example 6 Alginate powder was deposited uniformly at a loading of 15% by weight on a surface of a pad of cellulose fibres. Various techniques for the application of fixing powders were used as set forth in Table 4.

Table 4 Method of application Effectiveness of fixing Spraying with steam Spraying with water unsatisfactory unsatisfactory Spraying with an aqueous solution Example 7 On a support film of crinkled polypropylene, the powder used in Example 5 was deposited at a loading of 160 g/m and an aqueous dispersion of PRIMAL in the form of a fine mist was then sprayed thereon, until a deposit - 10 2 of loading 9 g/m was obtained. After drying it was possible to turn back the film of polypropylene without the powder becoming detached. When incorporated in a menstrual towel this modified film allowed both an increase in capacity for absorption and in a barrier effect comparable to an impermeable film.

Example 8 On a support formed of a thin non-woven layer of thermoplastic fibres fixed by thermosealing on a mesh of polypropylene reinforced by polyamide filaments, obtained under the Trade Mark SCRINYL, a powder obtained under the Trade Mark ALGUM 2600 filter 200 was deposited at a load2 ing of 50 g/m . 20% of the powder remained unfixed.

A deposit of 9 g/m of latex obtained under the Trade Mark COESOL 4, was sprayed using a dispersion 2 diluted 1/1, allowed the fixing of 40 g/m of the powder. After drying in air, the composite obtained was rolled up. The product can be used for example in agriculture to fix soils whilst retaining moisture.

Example 9 g/m of a dispersion of COESOL 4 diluted 1/1 was deposited on a sheet of TEFLON (Trade Mark). The film of damp latex was deposited by transfer onto a pad of 2 fibres including 160 g/m of ALGUM powder.

By means of a scraper, the composite of the sheet was detached. After drying it was established that the powder was satisfactorily held on the fibrous pad.

Many variants of the method according to the inven· tion may be used, for example to produce a uniform or patterned distribution of absorbent products.

The choice of binding agents used in the process of the invention may be determined by a satisfactory - 11 diffusing capacity of the liquid phase present and the rheological characteristics of a dispersion when used.

Absorbent materials obtained in accordance with the invention may be used as menstrual towels, nappies for babies, medical and surgical dressings, industrial wiping products and fixing agents for soils and for water retention.

The depositing of binding agent by transfer can be effected with embossed rollers allowing a patterned deposit to be obtained.

Claims

1. CLAIM S:1. A method of manufacturing an absorbent material which comprises a support and a powdered liquidabsorbing material deposited thereon, characterised in 5 that the said powdered material is deposited directly onto one surface of the support, and a binding agent is deposited on the thus supported powder.

2. A method according to claim 1, wherein the binding agent is applied by spraying. 10

3. A method according to claim 1, wherein the binding agent is applied by transfer.

4. A method according to any of claims 1 to 3, wherein the said powdered liquid-absorbing material is applied to the said support at a loading of between 20 and 15 350 g/m^.

5. A method according to any of claims 1 to 4, wherein the said binding agent is applied at a loading of 2 from 2 to 20 g/m , based on the dry binding agent.

6. A method according to any of claims 1 to 5, 20 wherein the said binding agent is applied in the form, of an aqueous solution of poly(vinyl alcohol).

7. A method according to any of claims 1 to 5, wherein the said binding agent is applied in the form of an aqueous dispersion. 25

8. A method according to any of claims 1 to 7, wherein the said support is a synthetic film.

9. A method according to any of claims 1 to 7, wherein the said support is a fibrous material. 47881 - 13

10. A method according to claim 9, wherein the said fibrous material is a pad of cellulose wadding.

11. A method according to claim 9, wherein the said fibrous material is a pad of dry-shredded cellulose fibres.

12. A method according to any of claims 9 to 11, wherein a second fibrous material is applied to the absorbent material after treatment with the binding agent, whereby the binding agent serves also to render the two materials integral.

13. A method according to claim 12, wherein the said second fibrous material is a pad of tissue-wadding.

14. A method according to Claim 12, wherein the said binding agent is deposited by transfer on a composite formed by a layer of the said liquid-absorbing material between two fibrous pads.

15. A method as claimed in any of claims 1 to 14, wherein a drying step is applied to the absorbent material obtained.

16. A method of manufacturing an absorbent material as claimed in claim 1, substantially as hereinbefore described, with particular reference to the Examples.

17. An absorbent material obtained by a method according to any of claims 1 to 16.

18. An absorbent material according to claim 17, which is a sanitary shield, diaper, surgical dressing or wiping towel.