GB2342354A

GB2342354A - Fillers for sponge rubber carpet underlay

Info

Publication number: GB2342354A
Application number: GB9821577A
Authority: GB
Inventors: Steven Chamberlain
Original assignee: Duralay Ltd
Current assignee: Duralay Ltd
Priority date: 1998-10-05
Filing date: 1998-10-05
Publication date: 2000-04-12
Also published as: GB9821577D0

Abstract

A sponge rubber carpet underlay comprises a sheet-like layer of a vulcanised blown rubber incorporating a filler system which is an admixture of a first particulate filler having a density of 20 to 200 kg m<SP>-3</SP> and a second particulate filler having a density of at least 1500 kg m<SP>-3</SP> the relative amounts of the two fillers and the total amount of the filler system being such that the sponge rubber has a density of 150 to 200 kg m<SP>-3</SP>. The first filler maybe cork. The underlay has the advantage of being of relatively light weight. Preferably the second filler is calcium carbonate.

Description

CARPET UNDERLAY The present invention relates to a carpet underlay, i. e. a material which is intended to be laid on a floor prior to the laying of a carpet so as to provide underfoot comfort and extension of carpet life.

The invention is concerned more particularly with so-called sponge underlay which is comprised of a vulcanised blown rubber incorporating a particulate filler system. Sponge rubber underlay is to be distinguished from the other principal types of carpet underlay, namely"Crumb Rubber"underlay and"Latex Foam"underlay.

Crumb Rubber underlay comprises bonded particles of a solid rubber material (e. g. obtained by shredding tyres). Latex foam underlay comprises a set latex foam incorporating fillers.

Sponge rubber underlay is manufactured by mixing a solid rubber (usually SBR) with a particulate filler such as calcium carbonate, extender oil, a curing system and blowing agents. The mixed formulation (the"compound") is fed via a calender into and through a curing oven in which the compound (in sheet form) is heated resulting in production of gas from the blowing agents to produce a blown material which becomes vulcanised by the curing system. Typically the calendered compound is transported through the curing oven on a metallic belt comprised of chain links which allow the compound to drape into the gap between the links (resulting in the production of"waffle underlay"). A backing medium, usually stitch reinforced paper or spun bonded non-woven fabric, is generally laid onto the top surface of the compound as it enters the over and is adhered to the compound by utilising the inherent tack thereof and/or light pressure from an air inflated bladder.

The finished sponge underlay generally has a density in the range 300-400 kg mi 3 an is typically wound into rolls having a running length of 8 or 11 linear metres.

However such rolls (which are of the most convenient length for supply and carpet laying purposes) are of considerable weight which is a disadvantage given that the rolls need to be lifted by carpet fitters and personnel in the supply chain. It would of course be possible to produce a roll of lesser weight by reducing the length of carpet underlay on the roll but this would not be regarded as economical for the purposes of storage and supply.

It is therefore an object of the present invention to obviate or mitigate the above mentioned disadvantages.

According to the present invention there is provided a sponge rubber carpet underlay comprising a sheet-like layer of a vulcanised blown rubber incorporating a filler system which is an admixture of a first particulate filler having a density of 20 to 200 kg m~3 and a second particulate filler having a density of at least 1500kg m~3 the relative amounts of the two fillers and the total amount of the filler system being such that the sponge rubber has a density of 150 to 250 kg rri 3.

Thus in accordance with the invention we are able to provide sponge rubber underlay whereof the sponge rubber has a density of 150 to 250 kg m~3. i. e. considerably less than in conventional sponge rubber underlays. Thus, for a given length, a roll of the underlay in accordance with the invention is considerably less than one of the conventional underlay.

Preferably the underlay of the invention has a density of 150 to 200kg in-'.

The underlay of the invention may for example be a waffle underlay.

To achieve its object, the invention utilises a mixed filler system which comprises a first relatively low density (20 to 200 kg m~3) filler and a second relatively high density at least 1500kg m-3 filler. By use of the appropriate proportions of the first and second fillers and the total amount of the filler system it is possible to produce a vulcanised blown rubber having a density of 150 to 200 kg mi 3.

More specific details as to how sponge rubber underlays of the invention may be produced are given below but it will be appreciated that it is well within the capability of a person skilled in the art to calculate the relatively proportions of the first and second fillers, and the total amount of the filler system, required to achieve a particular density.

Typically the ratio of the weight of the particulate filler system to the amount of rubber (excluding other components of the underlay) will be in the range 1: 1 to 3 : 1, more preferably 1: 1 to 2: 1. This contrasts with amounts of about 6: 1 for conventionally used filler systems. Typically also in the filler system in accordance with the invention the second filler will be present in an amount (by weight) greater than the first filler, the weight ratio of first filler to second filler generally being in the range 1: 15 to 1: 5.

In addition to being of reduced density (providing the advantages outlined above), there are further advantages associated with the invention. In particular, it is possible to produce underlay with a higher % rubber content than conventional underlay (because of the lower ratio filler: rubber). This ensures that the underlay has better physical properties such as lower compression set and improved tensile properties. Moreover particle size distribution of the lower density fillers is greater with a reduction in specific surface area resulting in less physical interference with the polymer matrix. Furthermore there is less compression in storage due to the lower mass of the rolls.

The first filler may for example be granulated polyurethane foam (density 20 to 50 kg m~3). It is however more preferred that the first filler has a density in the range 50 to 180 kg m~3, more preferably 60 to 160 kg m~3, even more preferably 80 to 150 kg m~3. Particularly preferred materials for the first filler are cork (density 80-150 kg m~3) and vermiculite (density 60 to 160 kg m~3). It is particularly preferred to use cork having a density of 110 to 120 kg m~3. Mixtures of the aforementioned first fillers may also be used.

The first filler will for preference be such that the majority of the particles have a size in the range 0.2 mm to 0.5 mm with ideally there being less than 20% by weight (more preferably less than 15% by weight) having a particle size greater than 0.5 mm and/or less than 10% by weight (more preferably less than 8% by weight) having a particle size below 0.2 mm.

The second filler will generally have a density in the range 1500 to 4000 kg in- and even more preferably in the range 2000 to 3000 kg rri 3.

The second filler material is for preference calcium carbonate density ca 2700 ka "-3 as conventionally incorporated in sponge rubber underlay. It is however also possible to use other fillers such as barytes or alumina trihydrate (the latter being particularly useful when fine retarding is required). Mixtures of the above mentioned second fillers may also be used.

In addition to providing lightness for the finished underlay, the use of cork has the additional advantage of producing underlay with superior recovery characteristics (e. g. less than 2% thickness loss using the BS 4939 State Loading Test).

The rubber used for producing the underlay is preferably Styrene Butadiene Rubber (SBR) although other rubbers may be used. Components additional to the rubber and filler system used in the manufacture of the underlay of the invention include process oil (aromatic oil), curing agent, accelerators, blowing agent, blow promoter and moisture scavenger all as conventionally used in the production of sponge underlay.

The curing agent system may comprise zinc oxide and sulphur, the former acting as an activator and the latter serving to vulcanise (cross-link) the rubber.

Cure accelerators include tetromethylthiruam disulphide (TMTD) and Ncyclohexyl-2-benzothiazole sulphenamide (CBS).

Suitable blowing agents include sodium bicarbonate and oxybis benzene sulphonyl hydroxide.

A suitable blow promoter is stearic acid.

A suitable moisture scavenger is calcium oxide.

If desired, the formulation may incorporate a pigment.

One preferred embodiment of sponge underlay in accordance with the invention may be produced from the components identified in the following table in which the term"pphr"is to be understood as"part per 100 rubber".

Material Pphr SG Comments Intol 1509 100 0.94 SBR-ex Enichem AP 637 10-30 0.115 Granulated Cork Calmote AD 145 2.68 Limestone Filler ex Croxton & Gary Process Oil 100 1 Extender Oil Zinc Oxide 6 5. 6 Cure Activator Sulphur 2. 1 Curative TMTD 2 1. 43 Cure Accelerator CBS 1. 7 1.28 Cure Accelerator Sodium Bicarbonate 12 2. 16 Blowing Agent OBSH 2 1. 55 Blowing Agent Stearic Acid 2 0. 84 Fatty Acid Blow promoter Calcium Oxide 3 2.36 Quicklime Moisture Scavenger Sponge underlay in accordance with the invention may be produced by the following steps.

(1) Mixing the ingredients together in a Bambury Internal Mixer or other suitable Internal Mixer. The mixed compound is dumped when a sufficient degree of mixing has occurred at a temperature of 70-80 C.

(2) Transferring the compound to a two-roll mill from which it is fed in the form of a sheet, via a transfer conveyer, to a calender where the sheet is calendered to the appropriate thickness. (3) Transferring the sheet to a patterned belt (e. g. comprised of chain links which allow the compound to drape into the gaps between the links) for passage through a curing oven. Prior to entering the curing oven, a backing layer may be applied to the top surface of the compound.

(4) After leaving the oven, the carpet underlay is trimmed, cut to length, rolled and wrapped.

Claims

CLAIMS 1. A sponge rubber carpet underlay comprising a sheet-like layer of a vulcanised blown rubber incorporating a filler system which is an admixture of a first particulate filler having a density of 20 to 200 kg m~3 and a second particulate filler having a density of at least 1500 kg m~3 the relative amounts of the two fillers and the total amount of the filler system being such that the sponge rubber has a density of 150 to 200 kg m-3.
2. An underlay as claimed in claim 1 wherein the ratio of the weight of the particulate filler system to the amount of rubber (excluding other components of the underlay) is in the range 1: 1 to 3: 1.
3. A underlay as claimed in claim 2 wherein the ratio of the weight of the particulate filler system to the amount of rubber (excluding other components of the underlay) is in the range 1 : 1 to 2: 1.
4. An underlay as claimed in any one of claims 1 to 3 wherein the second filler is present in an amount by weight greater than the first filler.
5. An underlay as claimed in claim 4 wherein the weight ratio of the first filler to the second filler is in the range 1: 15 to 1: 5.
6. A underlay as claimed in any one of claims 1 to 5 wherein the first filler has a density in the range 50 to 180 kg/m~3.
7. An underlay as claimed in claim 6 wherein the first filler has a density in range 60 to 160 kg/m~3.
8. An underlay as claimed in claim 7 wherein the first filler has a density in the range 80 to 150 kg/m~3.
9. An underlay as claimed in any one of claims 1 to 8 wherein the first filler is cork.
10. An underlay as claimed in any one of claims 1 to 9 wherein the majority of the particles of the first filler have a size in the range 0.2 mm to 0.5 mm.
11. An underlay as claimed in claim 10 wherein less than 20% by weight, more preferably less than 15% by weight, of the particles of the first filler have a size greater than 0. 5 mm.
12. An underlay as claimed in claim 10 or 11 wherein less than 10%, more preferably less than 8%, of the particles of the first filler have a particle size below 0.2 mm.
13. An underlay as claimed in any one of claims 1 to 12 wherin the second filler has a density of 1500 to 4000 kg m~3.
14. An underlay as claimed in claim 13 wherein the second filler has a density of 2000 to 3000 kg m~3.
15. An underlay as claimed in claim 14 wherein the second filler is calcium carbonate.
16. A sponge rubber carpet underlay comprising a sheet-like layer of a vulcanised blown rubber incorporating a filler system which is an admixture of a first particulate filler having a density of 20 to 200 kg m-3 and a second particulate filler which is calcium carbonate, the relative amounts of the two fillers and the total amount of the filler system being such that the sponge rubber has a density of 150 to 200 kg m-3.