GB2256219A - Moisture-absorbent self-adhesive strip - Google Patents

Description

3 J:-, 1 1 1 Moisture-Absorbent Materials This invention relates to

moisture-absorbent materials and in particular to a moisture-absorbent material in the form of a self-supporting tape, web or sheet and comprising a water-absorbing layer containing a highly water-absorbent polymeric material and an attachment surface comprising a pressure-sensitive adhesive.

A continuing problem with windows, especially single-glazed windows, is the presence of condensation. In cold weather, the interior surface of the window is frequently at a much lower temperature than that of the air inside the building. Where the warm, humid air contacts the cold glass, moisture condenses thereon and runs down the pane. This is unsightly and ultimately leads to the rotting of wooden frames and the staining of adjacent decor. Furthermore, the cold water supply is also at a much lower temperature relative to the air inside the building during periods of cold weather resulting in condensation forming on toilet cisterns, pipes, taps etc., especially ceramic cisterns. The condensed water may drip off the cistern onto the floor producing unsightly puddles of water on non-absorbent flooring, such as linoleum, and wet sodden patches on absorbent flooring, such as carpets etc.

Since little can be done to prevent condensation occurring, attempts to solve the problem have centred around methods of collecting the water. various devices have been described, which may be attached to the bottom of a window to collect condensation, e.g., as disclosed in British Patent Specification No. 2045845 and US Patent Nos. 4064666, 4065884 and 4408425. These devices generally comprise a trough or related construction containing an absorbent material which may be removed when saturated. However, such devices are bulky and obtrusive and do not adapt easily to different sizes and shapes of window.

2 A water-absorbent foam strip is commercially available from Spontex for laying at the bottom of windows to absorb water running down the window pane and collecting on the sill. The foam material has a limited absorptive capacity, such that the strip must be periodically removed from the sill and wrung out by hand when saturated. Consequently, the strip tends to distort on drying, warping into a twisted shape that cannot be repositioned neatly, making it rather unsightly.

European Patent Specification No. 59062 discloses a caulking material comprising particles of a waterabsorbent polymer dispersed in a rubbery matrix laminated to a second, non-swelling, rubbery layer. The material may be prepared in the form of a sheet of unit size or as a continuous length sheet in a roll and is designed to swell in a single direction on contact with moisture in order to seal gaps in crevices.

European Patent Publication No. 262230 discloses a water-absorbent composite comprising a ribbon-shaped laminate of a high-melting polymer and a low-melting polymer, the latter having particles of a water absorber fusion-bonded to its surface. The laminate may be slit into yarn and further processed into useful articles or used as a water-absorbing ribbon, e.g., as part of the protective sheathing of telecommunications cables and optical fibres.

Japanese Patent Application No. 1-129087 describes a water-stop tape comprising particles of absorbent polymer and inorganic filler dispersed in an organic binder and coated on paper or film for sealing gaps or crevices against moisture penetration.

Canadian Patent Specification No. 1220638 discloses super-absorbent materials enclosed by a porous envelope, e.g., of cloth, in the form of a bag, tube etc., which materials swell on contact with water and are intended as a replacement for sandbags in flood-prevention.

According to one aspect of the present invention there is provided a moisture-absorbent material in the form of a self-supporting tape, web or sheet and having a 3 water-absorbing layer comprising a highly water-absorbent polymeric material and an attachment surface comprising a pressure-sensitive adhesive.

The present invention provides a moisture-absorbent material (referred to hereafter simply as the "material") which can be readily and simply applied by a user to surfaces, e.g., windows, which are prone to condensation or otherwise regularly wetted, e.g., bath surrounds. The material is able to absorb and retain large amounts of water to prevent or at least substantially reduce the aforementioned problems. The absorbed water is then released into the atmosphere over an extended period, typically a matter of hours, without the need to remove the material; the rate of release varying with the ambient temperature and humidity (and on the ease with which air can permeate the water-absorbing layer). The material can be readily removed from a surface when dirty or when it is no longer required and is advantageously re-usable.

Therefore according to a further aspect of the present invention there is provided a method of rendering a surface absorbent to moisture which comprises applying to that surface a moisture-absorbent material of the invention.

The material generally comprises a support imparting mechanical strength to the construction bearing on one side the water-absorbing layer and on the other side the adhesive attachment surface. The material is capable of absorbing -many times its own weight of water and generally has an absorption capacity of at least 10. The absorption capacity is defined as:

[Saturated weight of material - dry weight of material] dry weight of material Preferably, the material has an absorption capacity of at least 20, more preferably at least 50.

4 The water-absorbing layer generally comprises a layer of a porous material forming a water-permeable matrix into which is dispersed or otherwise contained the highly water-absorbent polymeric material. Suitable porous materials include non-woven webs, e.g., fabrics, and polymeric foams e.g., polyurethane or polyamide foams.

Polymeric materials that strongly absorb water are known. They include naturally occurring materials, such as different kinds of gums, alginates, pectins and gelatins (e.g., as disclosed in R6mpps Chemie-Lexikon 8th Edition, 2, p.1559/2558). These materials are usually cross-linked using techniques known in the art so that they are able to absorb water but without being converted to colloidal solutions.

Preferred highly water-absorbing polymeric materials for use in the invention are fully synthetic materials such as homopolymers of acrylic and methacrylic acid (or other modified acrylic acids) and copolymers of acrylic and methacrylic acid with one or more ethylenically unsaturated monomers. The carboxyl groups of these cross-linked polymers may also be in the monovalent salt form, in particular as alkali metal salts. Such materials are known and include cross-linked polyacrylate salts, such as those commercially available from Allied Colloids under the trade names SALSORB and ALCOSORB, starch-acrylic acid graft copolymers, such as those commercially available from Hoechst Celanese under the trade name SANWET, and saponified acid-vinyl acetate copolymers.

Examples of suitable water absorbent polymers are disclosed in the U.S. Patent Nos. 3983095_, 3954721, 4017653 and 4018951. Such material are used in disposable diapers and related products and in absorbent sheets for food packaging, e.g., as disclosed in Japanese Patent Specification Nos. 62-286725 and 63-267545. They are known in the art as "super- absorbers" or "superabsorbent polymers". This applies in particular to the copolymers of acrylic or methacrylic acid with acrylamide, methacrylamide and acrylonitrile, such as those described in German Patent Specification No. 2706135 and commercially available under the trade name 5 FAVOR.

other highly water-absorbent polymeric materials suitable for use in the invention are cross-linked polymers and copolymers of ethylene oxide and propylene oxide.

The highly water-absorbing polymeric material is preferably a polymer comprising, as a monomeric constituent thereof, an a, p-unsaturated compound containing one or two carboxyl groups (or groups that are convertible to carboxyl groups, such as carboxylic acid salts, carboxylic acid amides, carboxylic acid imides or carboxylic acid anhydrides). Suitable a,punsaturated compounds include, for example, acrylic acid, methacrylic acid, acrylamide, methacrylamide, maleic anhydride, maleic acid, maleinamide, maleinamic acid, maleinimide, itaconic acid, crotonic acid, fumaric acid and mesaconic acid.

The highly water-absorbent polymeric material may also comprise a mixture of two or more a,fl-unsaturated compounds as well as mixtures with one or more different copolymerisable monomers provided that the desired waterabsorption performance is reached. Suitable copolymerisable monomers include a- olefins, vinyl compounds and vinylidene compounds, such as ethylene, propylene, isobutylene, 1-butylene, diisobutylene, methylvinyl ether, styrene, vinyl acetate, acrylic esters, methacrylic esters, acrylonitrile and methacrylonitrile. When the highly water- absorbing polymeric material comprises a copolymer of a carboxylcontaining a,fl-unsaturated monomer with a copolymerisable monomer, the material preferably comprises at least 40% by mole of the a, fl-unsaturated compound(s).

6 Preferred highly water-absorbing polymeric materials include polymers of acrylic and methacrylic acid (and other modified acrylic acids), and copolymers of a olefins or vinyl compounds with maleic anhydride.

The highly water-absorbing polymeric material may be prepared by known methods using a free-radical polymerisation initiator. The material generally has a degree of polymerisation in the range from 10 to 5000.

The water affinity of the polymeric material may be further increased by reaction with a basic compound, such as a hydroxide, oxide or carbonate of an alkali metal, e.g., sodium and potassium, or an alkaline earth material, e.g., magnesium, calcium or barium, ammonia or a monoamine. The basic compound is generally admixed with a solution of the polymeric material in a suitable solvent, preferably water, under agitation. Preferred basic compounds are sodium hydroxide, potassium hydroxide and ammonia because of their reactivity and the increased durability of the water-absorbing properties of the resultant product.

The polymeric material containing the a,punsaturated compound(s) may then be subjected to a cross-linking reaction. Cross-linking agents suitable for this reaction include polyvalent epoxy compounds, polyvalent amines, polyhydric alcohols, amino-alcohols, polyisocyanates and polyvalent halohydrins. Polyvalent epoxy compounds and polyvalent amines are preferred because of their durability and the resulting high water absorptivity of the polymeric material. Suitable polyvalent epoxy compounds include glycerin diglycidyl ether, ethyleneglycol diglycidyl ether, polyethyleneglycol diglycidyl ether, glycerin triglycidyl ether, propyleneglycol diglycidyl ether, polypropyleneglycol diglycidyl ether and trimethylolpropane triglycidyl ether. polyvalent amines include ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine and polyethyleneimines generally having a molecular weight 7 no greater than 5,000. Although optional, in the practise of the present invention it is preferred, to cross-link the polymeric material.

Generally the cross-linking reaction is performed by admixing the polymeric material containing the a,punsaturated compound(s) with the cross-linking agent and optionally applying heat or adding a solvent as needed. For example, when a polyvalent epoxy compound or a polyvalent amine is used as the cross-linking agent, it is preferred to heat the reaction mixture in the presence of water. The product of the cross-linking reaction is normally dried or subjected to a further heat treatment. The degree of cross-linking is controlled (by adding an appropriate amount of the cross-linking agent) so as to ensure that the resultant high water-absorbing polymeric material has the desired ratio of water absorption. Several examples are given below of preferred highly water-absorbing polymeric materials for use in the present invention 20 (1) An optionally cross-linked material obtained from the reaction of a copolymer comprising maleic acid or a related compound (i.e., derivatives of maleic acid such as maleic anhydride, maleinamide or maleinimide), and an a-olefin of linear or branched structure and generally comprising from 2 to 12, preferably 2 to 8 carbon atoms (e.g., ethylene, propylene, butylene, isobutylene or diisobutylene) with a basic compound such as an alkali metal compound, alkaline earth metal compound, ammonia or a monoamine. 30 (2) An optionally cross-linked material obtained from the reaction of a copolymer comprising maleic acid or a related compound and a vinyl or vinylidene compound (e.g., styrene, vinyl acetate, methylvinyl ether, an acrylic acid ester, a methacrylic acid ester, acrylonitrile or methacrylonitrile) with a basic compound such as an alkali metal compound, alkaline earth metal compound, ammonia or a monoamine. (3) An optionally cross-linked material obtained from the reaction of a polymer of an acrylic acid or a 8 modified acrylic acid (e.g, methacrylic acid) and a basic compound such as an alkali metal compound, alkaline earth metal compound, ammonia or a monoamine.

(4) An optionally cross-linked material obtained from the reaction of a copolymer comprising acrylic acid or a modified acrylic acid and one or more of the vinyl or vinylidene compounds from (2) above and a basic compound such as an alkali metal compound, alkaline earth metal compound, ammonia or a monoamine.

Particularly preferred are the cross-linked materials obtained from the reaction of a co-polymer comprising isobutylene and maleic anyhydride with sodium hydroxide, potassium hydroxide or ammonia and the crosslinked material obtained from the reaction of polyacrylic acid and sodium hydroxide, i.e., sodium polyacrylate, because of their water absorbing power and durability.

Preferred water-absorbing polymeric materials have an absorption capacity of at least 20, preferably at least 100 based on the dry weight thereof.

Examples of suitable water-absorbing layers include: non-woven webs prepared from fibres impregnated with SALSORB or ALCOSORB, commercially available from M & J Paper Company; SANFOAM comprising a polyurethane foam loaded with a modified starch super-absorber, commercially available from Hoechst Celanese, and a range of non-woven webs comprising a blend of poly(propylene) and FIBERSORB super-absorbent fibres, commercially available from Arco Chemical Company.

The highly water-absorbent polymeric material is normally formed as particles or fibres although any other configuration offering a large surface area for contact with water is useful. The size distribution of the polymeric material is important as too fine particles may be leached out of the porous material, whereas, larger particles having a lower surface area:volume ratio may form a compact gel layer on their surface, thereby preventing further penetration of the water. Generally, at least one dimension of the polymeric material should be small enough to guarantee rapid water absorption.

9 When the polymeric material is formed as particles, the average diameter thereof is generally in the range from 10 to 1000 gm, preferably 50 to 500 gm and more preferably 50 to 300 gm. When the polymeric material is formed as fibres, the average length thereof is generally from 50 to 1000 gm, preferably 200 to 500 gm.

The moisture-absorbent material of the invention is manufactured by laminating the water-absorbing layer to a support such as conventional double-sided tape, e.g., 3M Type 415 adhesive tape comprising a poly(ethylene terephthalate) film with an acrylic-based, pressuresensitive adhesive coated on both sides, commercially available from Minnesota Mining and Manufacturing Co., using techniques well-known in the tape-manufacturing industry. Although the adhesive attachment surface may be applied directly to a self-supporting water-absorbing layer, e.g., by means of an adhesive transfer material, the preferred construction comprises a support preferably bearing adhesive on both sides, one side being bonded to the water-absorbing layer, the other being protected by a strippable carrier sheet.

The support may be formed from any material commonly used in tape manufacture, such as tissue, paper or polymeric films. The carrier sheet typically comprises a support bearing a release layer, e.g., a layer of poly(vinyl chloride- vinyl acetate) and optionally containing Si02 particles. such materials are well known in the art.

The adhesive used to bond the water-absorbing layer to the support is preferably a pressure-sensitive adhesive, capable of providing a permanent bond between the two that is unaffected by wet conditions. The attachment surface which may comprise a continuous or a discontinuous layer, desirably comprises a pressure- sensitive adhesive capable of bonding securely to glass under wet conditions, but remaining peelable from the glass when required. Although the adhesive for the attachment surface may comprise any pressure-sensitive adhesive known in the art, acrylic-based or modified acrylic acid-based adhesives are preferred.

The moisture-absorbent materials of the invention are preferably formed as an elongate tape or web which may conveniently be wound on itself or on a spool in the form of a roll. The user can then simply unwind and cut the desired length of material from the roll for use, removing the carrier sheet, if present prior to application. The web or tape would normally have a width of from 1 to 5cm, with a typical value of about 2.5cm, which is suitable for most household applications. Although the roll may contain any suitable length of moisture-absorbent material, it is preferred to include at least 5 metres. Alternatively, the moistureabsorbent material may be formed as individual strips. Where a greater surface area needs to be covered, as is the case with the underside of toilet cisterns and other bathroom surfaces, the moisture-absorbent material may be applied in the form of a sheet. The size of the sheet will depend largely on the surface area to be covered but sizes of at least A3 to A10 could be envisaged, typically A3 to A5.

The invention will now be described with reference to the following Examples, in which a series of moisture absorbent tapes were prepared by laminating the water absorbing layer containing appropriate waterabsorbent polymeric material to 3M Type 415 double coated adhesive tape, commercially available from Minnesota Mining & Manufacturing Co. and comprising a poly(ethylene terephthalate) film with an acrylic-based pressure sensitive adhesive coated on each side thereof. Strips of each tape were applied to the interior wall of a beaker of known weight, which was then reweighed and filled with sufficient distilled water to fully immerse is the tape. After soaking the tape for 5 minutes, the distilled water was poured away and the beaker inverted and allowed to drain for a further 5 minutes. The beaker was then carefully dried without touching the saturated tape samples and weighed, thereby enabling the absorptive capacity of the tape to be calculated. This is expressed as the ratio of the weight of water absorbed to the dry weight of the tape:

Absorptive Capacity = [Saturated weight of tape - Dry weight of tape]/Dry weight of tape Example 1

This Example tests various absorbent materials supplied by the M & i Paper Co. and designated by their trade name, and also 3M Draught Excluder, commercially available from Minnesota Mining and Manufacturing Co., 20 as an example of an unmodified foam tape. of the M & J materials,, only Mil, MJ2 and MJ14890911 contain superabsorbent powder, the remainder being standard non woven absorbent webs, e.g., kitchen towels, serviettes etc. The absorptive capacity of the materials is shown 25 below in Table 1.

Table 1

Sample Absorptive Capacity Mil 38.1 MJ2 26.6 MJ 14890911 12.7 MJ 122143 1.6 MJ 122153 3.1 MJ 122156 3.4 MJ 127819 2.9 MJ 127841 2.4 MJ 147842 3.2 3M Draught Excluder 4.0 12 The moisture absorbent tapes in accordance with the invention, namely Mi 1, W 2 and W 14890911, containing the super absorbent powder show a clear advantage over the standard absorbent webs.

Example 2

This Example shows the use of a different type of absorbent material comprising super-absorbent fibres, commercially available from the Arco Chemical Co., under the trade name FIBERSORB blended with poly(propylene). Samples 1 to 3 below refer to different grades of the material with different weights (8.5 x 10-2, 1.7 x 10-1 and 3.4 x 10-1'kg M-2) and absorber contents (25, 10 and 30% w/w respectively). The absorptive capacity of the materials is shown below in Table 2.

Table 2.

Sample Absorptive Capacity 1 8.5 2 7.0 3 13.4 As expected, the absorptive capacity increases as 30 the loading of the absorbent material increases. ExamiDle 3 This Example shows the use of a foam-based vehicle for the superabsorbent particles. Samples 1 and 2 below refer to two grades of SAMFOAM absorbent material commercially available from Hoechst Celanese and comprising a polyurethane foam loaded with 24% by weight of a polyacrylate-modified starch. The two grades differ only in the surface treatment given to the foam. The absorptive capacity of the materials is shown below in Table 3.

13 Table 3

Sample 2 reverted to its original weight within a 48 hour period when left at 20C and 50% relative humidity.

IIALCOSORB11 (Allied Colloids), "FAVOR", IIFIBERSORBII 20 (Arco Chemical Co.), IISALSORBII (Allied Colloids), IISAMFOAMII (Hoechst Celanese) and IISANWETII (Hoechst Celanese) are all trade names.

Sample Absorptive Capacity 1 20.7 2 21.6 14

Claims (1)

1. A moisture-absorbent material in the form of a self-supporting tape, web or sheet and having a waters absorbing layer comprising a highly water-absorbent polymeric material, characterised in that the material has an attachment surface comprising a pressure-sensitive adhesive.

2. A material as claimed in Claim 1 comprising a support having coated on one side thereof the waterabsorbing layer and on the other side thereof the adhesive attachment surface.

3. A material as claimed in Claim 1 or Claim 2 in which the waterabsorbing layer comprises a water- permeable matrix containing the highly water-absorbent polymeric material.

4. A material as claimed in Claim 3 in which the matrix comprises a nonwoven web of a fabric material or a polymeric foam.

5. A material as claimed in Claim 4 in which the polymeric foam comprises a polyurethane or polyamide resin.

6. A material as claimed in any one of Claim 1 to Claim 5 in which the absorption capacity of the moisture- absorbent material is at least 10 based on the dry weight thereof.

7. A material as claimed in Claim 6 in which the absorption capacity of the moisture-absorbent material is at least 20 based on the dry weight thereof.

8. A material as claimed in any preceding Claim in which the highly waterabsorbent polymeric material is in the form of particles, fibres or a mixture of both particles and fibres.

9. A material as claimed in Claim 8 in which the particles of the highly water-absorbent polymeric material have an average diameter of from 10 to 1000 gm.

10. A material as claimed in Claim 9 in which the particles of the highly water-absorbent polymeric material have an average diameter of from 50 to 500 gm.

is 11. A material as claimed in Claim 10 in which the particles of the highly water-absorbent polymeric material have an average diameter of from 50 to 300 Am.

12. A material as claimed in Claim 8 in which the fibres of the highly water-absorbent polymeric material have an average length of from 50 to 1000 Am.

13. A material as claimed in Claim 12 in which the fibres of the highly water-absorbent polymeric material have an average length of from 200 to 500 Am.

14. A material as claimed in any preceding claim in which the highly water-absorbent polymeric material is the optionally cross-linked reaction product of (a) a polymer comprising as a monomeric constituent an a,flunsaturated compound having one or more carboxyl groups or groups convertible to carboxyl groups and (b) a basic substance selected from alkali metal compounds, alkaline earth metal compounds, ammonia or monoamines.

15. A material as claimed in any one of Claims 1 to 13 in which the highly water-absorbent polymeric material is the optionally cross-linked reaction product of (a) a copolymer comprising an a-olefin and maleic anhydride and (b) a basic substance selected from alkali metal compounds, alkaline earth metal compounds, ammonia or monoamine.

16. A material as claimed in any one of Claim 1 to 13 in which the highly water-absorbent polymeric material is the optionally cross-linked reaction product of (a) a copolymer comprising maleic anhydride and a vinyl or vinylidene compound selected from styrene, vinyl acetate, methylvinyl ether, an ester of acrylic acid, an ester of methacrylic acid and acrylonitrile and (b) a basic substance selected from alkali metal compounds, alkaline earth metal compounds, ammonia or a monoamine.

17. A material as claimed in any one of Claims 1 to 13 in which the highly water-absorbent polymeric material is the optionally cross-linked reaction product of (a) a 16 polymer comprising acrylic acid or a modified acrylic acid and (b) a basic substance selected from alkali metal compounds, alkaline earth metal compounds, ammonia 5 or a monoamine.

18. A material as claimed in any preceding claim in which the highly water-absorbent polymeric material has an absorption capacity of at least 20 based on the dry weight thereof.

19. A material as claimed in Claim 18 in which the highly water-absorbent polymeric material has an absorption capacity of at least 100 based on the dry weight thereof.

20. A material as claimed in any one of Claim 2 to 19 in which the support comprises a poly(ethylene terephthalate) film.

21. A material as claimed in any one of Claim 2 to further comprising an interlayer of an adhesive between the water-absorbing layer and the support.

22. A material as claimed in Claim 21 in which the adhesive interlayer is a pressure sensitive-adhesive. 23. A -material as claimed in any preceding Claim in which the adhesive comprises an acrylate or modified acrylate based adhesive. 25 24. A material as claimed in any preceding claim further comprising a carrier sheet. 25. A material as claimed in Claim 24 in which the carrier sheet comprises a release layer. 26. A material as claimed in Claim 1 substantially as described herein.

claimed material or on a 28 claimed of from 27. A roll of a moisture-absorbent material as in any one of Claims 1 to 26 in which the is in the form of a tape or web wound on itself spool.

A roll of moisture-absorbent material as in Claim 27 in which the tape or web has a width 1 to 5 cm.

f 17 29. A roll of moisture-absorbent material as claimed in Claim 27 or Claim 28 in which the roll includes at least 5 metres of the moisture-absorbent 5 material.

30. A roll of moisture-absorbent as claimed in Claim 27 substantially as herein described.

31. A method of rendering a surface absorbent to moisture which comprises applying to that surface a moisture-absorbent material as claimed in any one of Claims 1 to 26.

32. A method as claimed in Claim 31 in which the surface is a window pane or a window sill.