GB1585664A

GB1585664A - Water activatible tapes

Info

Publication number: GB1585664A
Application number: GB30612/76A
Authority: GB
Original assignee: Evode Ltd
Current assignee: Evode Ltd
Priority date: 1977-07-22
Filing date: 1977-07-22
Publication date: 1981-03-11

Description

(54) WATER ACTIVATIBLE TAPES (71) We, EVODE HOLDINGS LIMITED, a British Company of Common Road, Stafford, Staffordshire, England do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to water activatible tapes and is an improvement or modification of the invention described in our Specification No.

1504124.

In Specification No. 1504124 there is des cribed a water-activatible tape comprising a web of foamed plastics material or fibrous material impregnated with a cementitious substance. In its dry state and when freshly wetted with water the impregnated tape is flexible and can be wrapped e.g. around a pipe or structural steel work, whereupon the cement will harden to form a tough protective encapsulating layer.

While the tape has proved to be extremely effective for these and other purposes, the process of manufacture described in Specification No. 1504124 involves production and environmental problems because of the difficulties of dealing with large volumes of volatile organic solvents. It is towards a solution to these problems that the present invention is primarily directed.

According to the present invention there is provided a method of manufacturing a wateractivatible tape which comprises contacting a carrier web with a mixture of a water-reactive substance, which is reactive with water to form a hardened mass, and a water-sensitive thermoplastic polymer and heating the mixture to cause the polymer to fuse to form a continous film containing the dispersed water-reactive substance.

By 'water-sensitive polymer' we mean a polymer which is at least swollen or made porous by contact with water so that on treating a tape according to the invention with water, the water can penetrate the polymer film and activate the cementitious substance.

The water-reactive substance may be a hydratable calcium sulphate such as gypsum or plaster of paris but is preferably a cementitious substance of the same kind as envisaged in our above co-pending application. Examples of suitable cementitious substances are Portland cement, white cement, Ciment Fondu, stearate coated cement. The cementitious substance may be mixed with inert diluents, fillers or pigments such as silica, clay, calcium carbonate, talc, fluorspar, barytes, pulverised fly ash, and metal oxides such as titanium dioxide.

One convenient method of applying the mixture of cementitious substance and polymer to the web is to form a dry blend of the cement, water-sensitive polymer and, optionally a watermiscible plasticiser. The resulting dry powder mixture is formed as a layer on one or both sides of the carrier web. The coating operation is completed by passing the web through a region where the polymer containing layer is heated to a temperature sufficient to cause fusion of the polymer particles to form a substantially continuous adherent film containing dispersed particles of water-reactive substance, such as cement. A heated nip roller has been found to be satisfactory. After cooling the tape may be wound onto a reel.

It has been found that a particularly useful procedure is to precoat the carrier web with an aqueous emulsion or aqueous solution of polymer at a rate of 20-2000g!m2 wet coating weight, optimally 300 glum2. The powdered mixture of cement, slurry components e.g.

Portland cement, water-sensitive polymer and, optionally plasticiser such as glycerol, are then applied as a powder layer by knife coating, fluidised bed, air spray or electrostatic spray and the composite is subjected to heat and pressure as described above to fuse the polymer particles to form a substantially continuous adherent film containing dispersed cement particles.

The dry powder blend of cement and watersensitive polymer is stable and may be stored indefinitely in a dry atmosphere.

Improvements in binding of the cement particles to each other and to the carrier web can be achieved by adding an aqueous emulsion or aqueous solution of an organic polymer to the dry powder blend prior to forming the layer on the carrier web. The quantity of emulsion or solution added to the dry powder blend is insufficient to form a liquid slurry but is sufficient to coat the particles so that they bind more readily to the carrier web. If the emulsion or solution is added just prior to application to the carrier web, it is not necessary to add a cement set retarder although this can be done if there are likely to be delays in carrying out the coating operation.Preferred set retarders are volatile set retarders such as water-soluble alcohols and ketones and ethylene glycol ethers, as described in our co-pending patent application No. 29507 & 6. (Serial No.1585663) Examples of water-sensitive thermoplastic polymers suitable for use in the method of the invention are cellulose esters and ethers, polyethylene oxide, polyethylene glycol, polymethyl vinyl ether and derivatives thereof, polyvinyl pyrrolidone, polyvinyl alcohol, polyvinyl acetate and polyhydroxy alkyl acrylates and methacrylates. In addition to providing the main agency for binding the cement to the carrier web, the water-sensitive polymer also improves the adhesion of the tape to surfaces when in use.

As indicated above an optional component of the cement-containing mixture applied to the carrier web is a plasticiser for the watersensitive polymer and this component ensures the flexibility of the finsihed tape. An example a suitable plasticiser for cellulose ethers and esters is glycerol.

A further optional component of the mixture is an emulsion or aqueous solution of an organic polymer. Examples of suitable organic polymers are homo and co-polymers of vinyl acetate and acrylates, polystyrene, styreneacrylate copolymers, vinylidene chloride- acrylonitrile copolymers, homo and copolymers of vinyl chloride, ethylene-vinyl acetate copolymers, butadiene-acrylonitrile copolymers, butadiene-styrene copolymers, polychioro- prene, natural rubber, bitumen, polyvinyl alcohol, cellulose esters and ethers, poly-ethylene oxide polyethylene glycols, polyvinyl methyl ether and derivatives thereof and poly vinyl pyrollidone.

The material forming the carrier web of the tape may be of any of the material mentioned in our Specification No. 1504124 i.e. various types of fibrous or foamed plastics materials.

While not specifically mentioned in Specification No. 1504124 (although referred to generally as cellulosic fibres) paper carrier webs may be used. In addition to the carrier webs mentioned in this co-pending application, metal foils, such as aluminium foil, may be used and such foils may be perforated or unperforated.

When metal foils are used as carrier webs, the fusion of the thermoplastic polymer may be effected or assisted by induction or resistance heating of the carrier web.

The relative proportions of the cementitious substance and other additives used in preparing the slurry correspond generally with the proportions given in our co-pending application.

Thus the cementitious substance (e.g. Portland cement) may be present in an amount of 30 to 200 parts by weight, the water-sensitive polymer (e.g. cellulose ether) in an amount of 1 to 50 parts by weight, the polymer emulsion or solution (e.g. styrene-acrylic copolymer) 0.5 to 25 parts by weight (calculated as solids content) and other solid additives up to 50 parts by weight. Preferably the resulting slurry is applied to the carrier web in an amount of from 0.2 to 10 kgs. per square metre (dry basis).

The following example (in which all parts are by weight) is given to illustrate the invention and the manner in which it may be carried into effect.

EXAMPLE A dry powder blend was prepared by mixing together 100 parts of Portland cement, 20 parts of hydroxy propyl cellulose and 10 parts of glycerol. 20 parts of a styrene-acrylic copolymer emulsion (56 mass per cent solids) was added to the dry mixture and mixed thoroughly. The resulting blend, in which the emulsion had coated the particles of cement and cellulose ether, was a flowable particulate solid and was spread onto one side of a hessian carrier web.

The coated web was heated by passing it through a pair of electrically heated nip rollers having a surface temperature of 100 to 1700C, preferably 120 to 150or, and at a pressure of about 3 to 20 mega Pascals (approximately 500 to 3000 lbs per square inch). As a result, the coating on the tape was converted to a continuous adherent film of styrene-acrylic copolymer having particles of cement and cellulose ether dispersed therein.

In use the tapes prepared in accordance with the invention are activated by wetting with water or with an aqueous solution or emulsion containing a polymer, rubber or other additive such as setting accelerator, as described in our cited co-pending applications. In its wetted state, the tape is plastic and can be conformed to the desired shape, and, if required, adhered to the substrate by pressing it into place. After setting (12 to 48 hours) the tape forms a hard, resilient layer with good mechanical strength, abrasion and fire resistance and is also capable of protecting ferrous against a corrosive environment.

WHAT WE CLAIM IS: 1. A method of manufacturing a water-activatible tape which comprises contacting a carrier web with a mixture of a water-reactive substance which is reactive with water to form a hardened mass and a water-sensitive thermoplastic polymer and heating the mixture to cause the polymer to fuse to form a continuous film containing the dispersed water-reactive substance.

2. A method according to claim 1 in which the water-reactive substance is a cementitious substance.

3. A method according to claim 1 or claim 2 in which the carrier web is a web of fibrous

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

insufficient to form a liquid slurry but is sufficient to coat the particles so that they bind more readily to the carrier web. If the emulsion or solution is added just prior to application to the carrier web, it is not necessary to add a cement set retarder although this can be done if there are likely to be delays in carrying out the coating operation.Preferred set retarders are volatile set retarders such as water-soluble alcohols and ketones and ethylene glycol ethers, as described in our co-pending patent application No. 29507 & 6. (Serial No.1585663) Examples of water-sensitive thermoplastic polymers suitable for use in the method of the invention are cellulose esters and ethers, polyethylene oxide, polyethylene glycol, polymethyl vinyl ether and derivatives thereof, polyvinyl pyrrolidone, polyvinyl alcohol, polyvinyl acetate and polyhydroxy alkyl acrylates and methacrylates. In addition to providing the main agency for binding the cement to the carrier web, the water-sensitive polymer also improves the adhesion of the tape to surfaces when in use.

As indicated above an optional component of the cement-containing mixture applied to the carrier web is a plasticiser for the watersensitive polymer and this component ensures the flexibility of the finsihed tape. An example a suitable plasticiser for cellulose ethers and esters is glycerol.

A further optional component of the mixture is an emulsion or aqueous solution of an organic polymer. Examples of suitable organic polymers are homo and co-polymers of vinyl acetate and acrylates, polystyrene, styreneacrylate copolymers, vinylidene chloride- acrylonitrile copolymers, homo and copolymers of vinyl chloride, ethylene-vinyl acetate copolymers, butadiene-acrylonitrile copolymers, butadiene-styrene copolymers, polychioro- prene, natural rubber, bitumen, polyvinyl alcohol, cellulose esters and ethers, poly-ethylene oxide polyethylene glycols, polyvinyl methyl ether and derivatives thereof and poly vinyl pyrollidone.

The material forming the carrier web of the tape may be of any of the material mentioned in our Specification No. 1504124 i.e. various types of fibrous or foamed plastics materials.

While not specifically mentioned in Specification No. 1504124 (although referred to generally as cellulosic fibres) paper carrier webs may be used. In addition to the carrier webs mentioned in this co-pending application, metal foils, such as aluminium foil, may be used and such foils may be perforated or unperforated.

When metal foils are used as carrier webs, the fusion of the thermoplastic polymer may be effected or assisted by induction or resistance heating of the carrier web.

The relative proportions of the cementitious substance and other additives used in preparing the slurry correspond generally with the proportions given in our co-pending application.

Thus the cementitious substance (e.g. Portland cement) may be present in an amount of 30 to 200 parts by weight, the water-sensitive polymer (e.g. cellulose ether) in an amount of 1 to

50 parts by weight, the polymer emulsion or solution (e.g. styrene-acrylic copolymer) 0.5 to 25 parts by weight (calculated as solids content) and other solid additives up to 50 parts by weight. Preferably the resulting slurry is applied to the carrier web in an amount of from 0.2 to

10 kgs. per square metre (dry basis).

The following example (in which all parts are by weight) is given to illustrate the invention and the manner in which it may be carried into effect.

EXAMPLE A dry powder blend was prepared by mixing together 100 parts of Portland cement, 20 parts of hydroxy propyl cellulose and 10 parts of glycerol. 20 parts of a styrene-acrylic copolymer emulsion (56 mass per cent solids) was added to the dry mixture and mixed thoroughly. The resulting blend, in which the emulsion had coated the particles of cement and cellulose ether, was a flowable particulate solid and was spread onto one side of a hessian carrier web.

The coated web was heated by passing it through a pair of electrically heated nip rollers having a surface temperature of 100 to 1700C, preferably 120 to 150or, and at a pressure of about 3 to 20 mega Pascals (approximately 500 to 3000 lbs per square inch). As a result, the coating on the tape was converted to a continuous adherent film of styrene-acrylic copolymer having particles of cement and cellulose ether dispersed therein.

In use the tapes prepared in accordance with the invention are activated by wetting with water or with an aqueous solution or emulsion containing a polymer, rubber or other additive such as setting accelerator, as described in our cited co-pending applications. In its wetted state, the tape is plastic and can be conformed to the desired shape, and, if required, adhered to the substrate by pressing it into place. After setting (12 to 48 hours) the tape forms a hard, resilient layer with good mechanical strength, abrasion and fire resistance and is also capable of protecting ferrous against a corrosive environment.

WHAT WE CLAIM IS: 1. A method of manufacturing a water-activatible tape which comprises contacting a carrier web with a mixture of a water-reactive substance which is reactive with water to form a hardened mass and a water-sensitive thermoplastic polymer and heating the mixture to cause the polymer to fuse to form a continuous film containing the dispersed water-reactive substance.
2. A method according to claim 1 in which the water-reactive substance is a cementitious substance.
3. A method according to claim 1 or claim 2 in which the carrier web is a web of fibrous

material, foamed plastics material or a perforated or unperforated metal foil.
4. A method according to any one of the preceding claims in which a dry blend of the powdered cementitious substance is formed with the water-sensitive polymer and the mixture applied to the carrier web, followed by heating to fuse the polymer to a substantially continous film adhered to the carrier web and having the cementitious substance dispersed therein.
5. A method according to claim 4 in which the carrier web is precoated with an emulsion or aqueous solution of a polymer and the dry blend of cementitous substance and watersensitive polymer applied to the polymer coating while it is still wet.
6. A method according to any one of claims 1 to 3 in which the cementitous substance and the water-sensitive polymer are mixed with an aqueous emulsion or solution of an organic polymer and the resulting mixture applied as a coating to the carrier web, the coating being thereafter heated to remove the water and form a substantially continuous adherent film on the carrier web.
7. A method according to claim 6 in which the polymer emulsion or dispersion is mixed with the cementituous substance and the watersensitive polymer in an amount sufficient to coat the particles thereof but not in an excess such that an aqueous slurry is formed.
8. A method according to any one of the preceding claims in which a water-miscible plasti ciser for the water-sensitive thermoplastic polymer is included in the mixture applied to the carrier web.
9. A method according to claim 8 in which the plasticiser is glycerol.
10. A method of manufacturing a wateractivatible tape substantially as described with reference to the Example.
11. A water-activatible tape which comprises a carrier web bearing an adherent film of a watersensitive thermoplastics polymer, said film having a powdered water-reactive substance dispersed therein.