GB1562298A

GB1562298A - No-gel latex foam

Info

Publication number: GB1562298A
Application number: GB4507276A
Authority: GB
Original assignee: Uniroyal Inc
Current assignee: Uniroyal Inc
Priority date: 1975-10-29
Filing date: 1976-10-29
Publication date: 1980-03-12
Also published as: NL7611995A; FR2329431B1; FR2329431A1; ES452847A1; AU1909276A; IT1075979B; LU76101A1; AU505123B2; JPS5759254B2; BE847836A; JPS5271561A; DE2649691A1

Description

(54) NO-GEL LATEX FOAM (71) We, UNIROYAL, INC., a corporation organized under the laws of the State of New Jersey, United States of America, having an office at 1230 Avenue of the Americas, New York, New York 10020, United States of America, 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 a method for making no-gel rubber latex foam, and to foam made by the method.

No-gel rubber latex foams are distinguishable from conventional rubber latex foams by the absence of a gelling agent from the com- pounded latex, although a foaming agent is used to help maintain the cellular structure during manufacture. Cured no-gel rubber latex foams are distinguished by a soft hand or feel at the exposed surfaces, which are free from the congealed skin that is present on cured rubber latex foams prepared using a gelling agent.

According to the present invention a method for making no-gel rubber latex foam comprises the steps of coating a water vapor permeable supporting means with a water vapor permeable release agent comprising a polyethylene glycol polymer having a molecular weight range of 1,500 to 20,000, depositing a froth of uncured no-gel rubber latex foam onto the supporting means over the coating, heating the froth to dehydrate, cure and form the no-gel rubber latex foam, and separating the cured latex foam from the supporting means.

The release agent prevents the latex foam froth from adhering to the supporting means and thus functions as a parting layer between the latex foam froth and the supporting means.

The release agent also permits water vapor to escape from the latex foam froth through the supporting means so that the deposited froth is dehydrated and cured through its upper free surface as well as its lower supported surface. When the no-gel latex froth is fully cured it can be easily removed from the supporting means and the resultant product is substantially smooth and free of congealed polymer skin, and has a soft feel and hand at both the upper and lower surfaces. The foam body has a substantially open cell structure.

For continuous operation of the disclosed method the supporting means preferably includes a conveyor belt and desirably also includes a sheet of backing material which may be supported by the conveyor belr. For batch operation of the disclosed method the supporting means can comprise a backing material supported by a peripherally framed water vapour permeable base, which base may be a conveyor belt.

Various embodiments of the invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a simplified schematic diagram of an apparatus for carrying out continuous operation of a method according to the present invention; Figs. 2 to 8 are enlarged sectional views taken along lines 2-2 to 8-8 respectively of Fig. 1; Fig. 9 is an enlarged view of the fragmentary portion 9 in Fig. 7; Figs. 10 and 11 are enlarged views of the fragmentary portions 10 and 11 in Fig. 8; Fig. 12 is a simplified schematic diagram of an apparatus for carrying out batch operation of a method according to the present invention; Fig. 13 is an enlarged sectional view taken along the line 13-13 of Fig. 12; and Fig. 14 is a flow diagram; of the invention.

Referring to the drawings an apparatus for carrying out continuous operation of a method for making no-gel rubber latex foam is generally indicated by reference number 10 in Fig.

1.

The apparatus 10 includes a supporting means 12 upon which a rubber latex foam froth 14 is deposited and upon which a release agent 16 is coated prior to deposition of the rubber latex foam froth 14.

The supporting means 12 comprises a water vapor permeable backing material 18 sup ported, over part of its length, on an endless conveyor belt 20 driven in a circuitous path.

The backing material 18 is formed of a suit able woven or non-woven fabric such as Burlington 116 glass fabric manufactured by Burlington Mills, 6135 rayon manufactured by Scott Paper Co., or heat set polyester sheeting manufactured by Acme Mills. The backing material 18 must be permeable to water vapor, should withstand the hot moist conditions prevalent during curing of the foam froth 14, and desirably is capable of being reused.

The conveyor belt 20, which is also water vapor permeable, can be formed of any suitable material such as wire mesh, or metal links made by the LaPorte Company. The maximum size of the mesh or link openings is not critical as long as the conveyor adequately supports the backing material 18 when the layered of no-gel rubber latex foam froth is applied thereto.

The release agent 16 is a water vapour permeable ethylene glycol polymer having a molecular weight range of about 1500 to about 20,000. A suitable polymer is manufactured and sold by Union Carbide under the Trade Mark "Carbowax". Water solutions containing blends of one or more molecular weights of Carbowax can be used. The release agent is dispensed onto the backing material 18 in any suitable known manner, such as from a conventional dispensation vat 22 having a dispensing roller 23.

A pair of metermg rolls 24 and 26 coat or impregnate the release agent into the backing material 18. The coating of release agent is then dried by heating or evaporation (not shown) before being covered with the no-gel rubber latex froth 14. If desired the release agent can be applied by spraying or dipping the backing material 18. While portions of the release agent, during curing of the no-gel rubber latex foam froth, may decompose, sub lime or vaporize with the water vapor dehydrating from the froth, the release agent serves to shield the backing material 18 from the froth in its adherent state.

A rubber latex designed for use in the method of the present invention may be formulated of ingredients set forth in the following table: Parts by Weight, Ingredient Dry Basis Parts by Weight, Ingredient Dry Basis Neoprene (Type 60 or 357, DuPont) 100.00 Disodium N-octadecyl sulfosuccinamate (Cyanasol 18, American Cyanamid) 4.00 Sodium hexametaphosphate 0.50 (Calgon* Calgon Corp.) Dry ground nepheline syenite (Minex* 3, American Syenite Corp.) 50.00 Alumina trihydrate (Hydral C30BF, Alcoa) 25.00 Antimony Oxide 5.00 Potassium Hydroxide 0.25 Sodium salt of sulfate monoester of a mixture of various fatty alcohols, chiefly lauryl alcohol (Aquarex WAQ, DuPont) 2.00 Alkylated phenol non staining antioxidant (Naugawhite*, Uniroyal Chemical) 1.126 Zinc Oxide 7.50 Sodium polyacrylate (Modicol VD, Nopco Chemical) OAO Thiocarbanilide (A-l, Monsanto) 2.00 Pyrocatechol (Crown Zellerbach) 1.00 * Calgon, Minex and Naugawhite are all Trade Marks.

The neoprene latex has the following physical properties: Total Solids 60% by weight pH 10.5 Surface Tension 39 dynes per cm.

Viscosity (ambient temperature) 350 centipoises The latex formulation, without the addition of any gelling agent, is frothed by a suitable known apparatus such as disclosed in U.S.

Patents 2,695,246, 2,706,108 or 2,731,253.

The latex froth 14 is then poured or otherwise deposited onto the backing material 18 over the release agent 16 by a suitable known traversing spout or nozzle 28 such as disclosed in U.S. Patent 2,774,106. A doctoring arrangement 30 can be used, if desired, to facilitate deposition of the latex froth 14 to a uniform thickness on the backing material 18.

The cell structure of the no-gel neoprene latex froth 14 is not resistant to collapse despite the presence of foam stabilizers. It is preferable, therefore, to limit the thickness of the latex froth layer 14 to about 1-1/4 inches since densification, cell collapse and other similar problems may become evident in the cured foam when this layer thickness is exceeded. To minimize the possibility of cell collapse or cell densification the foam froth 14, should be cured and dehydrated rapidly and as soon as possible after it has been deposited onto the backing material 18. However, when the latex foam froth 14 is sub jected to a rapid cure cycle small fissures or blemishes otherwise known as surface checking can form in the foam surface.This condition is not generally objectionable, but can be substantially eliminated by preheating the latex froth 14 before subjecting it to a rapid cure.

The preheating is preferably accomplished by any suitable known means of radiant heat such as a bank of "CaIred" (Trade Mark) heaters 32 (Figs. 1 and 5) near the backing material 18, preferably directly above the latex foam froth 14 immediately before a curing area 34. The surface temperature of the no-gel neoprene latex froth is usually about 70"F before being preheated and about 200"F after being preheated by for example, a five foot long bank of the Calrod heaters 32.The surface temperature rise from 70"F to 2OOF can occur in a time duration of about 25 seconds to about 200 seconds depending upon the composition of the latex, the thickness of the deposited froth layer 14 and the desired density of the cured no-gel neoprene latex foam, all of which determine the speed of movement of the conveyor belt 20 past the bank of Calrod heaters 32. For example a neoprene latex froth one half inch thick is preheated for about 100 seconds. The preheating effects a preliminary dehydration of the no-gel latex froth 14 to a depth of about 1/16 to 1/8 of an inch from the upper free surface of the froth. In instances where surface checking is a tolerable condition in the cured foam 22 the preheating step can be eliminated.

The latex froth 14 and the backing material 18 are conveyed by the conveyor belt 20 to the curing area 34 for subjection to substantially dry heat at a temperature which can range between about 260"F to about 300"F, depending upon the thickness of the deposited froth layer 14, the desired density of the cured foam, the heat tolerance of the backing material 18 and the heat tolerance of the release agent 16. The no-gel latex foam froth formulations can be cured at temperatures in excess of 300"F, but the Carbowax decomposes at temperatures exceeding this level.

The cure cycle duration for the no-gel latex foam froth 14 is essentially dependent upon the thickness of the froth layer and is not generally affected by the release agent 16. For example a neoprene no-gel latex froth layer 1/2 inch thick, backed by an "Acme" (Trade Mark) 4244X polyester sheet, can be dehydrated and cured at about 300"F for about 75 minutes. The release agent 16, which can have a coating density of about 5.40 grams/ft.2 may be prepared as follows: Weight Ingredient Percentage Water 64.64 Carbowax 4000 21.88 Carbowax 1500 13.13 10% HQMME in alcohol (Hydroquinone monomethyl ether, Eastman Chemical) .35 100.00 The HQMME retards decomposition of the Carbowax. The cured no-gel latex foam layer may be characterized by the following properties: Density 7.4 lbs./ft.' Compression 26 Ibs/50 sq.in.

(RMA) Tensile 5.6 psi Elongation 300% Tear .95 Ibs/linear inch Compression Set (22 hrs. at 158"F) based on deflected height 10coo Although any suitable known curing apparatus can be used, an open-ended tunneltype hot air oven schematically indicated by reference number 36 is prefererd. A relatively rapid cure is accomplished since the heat applied during cure causes the frdth 14 to dehydrate at its lower supported surface through the release agent 16, the backing material 18, and the conveyor belt 20 as well as at its upper surface as shown in Fig. 7. A possibility of cell collapse or cell densification in the cured foam 38 is thus minimized.

After the cure cycle is completed the cured no-gel latex foam 38 is conveyed by the conveyor belt 20 out of the oven 36 for stripping of the foam from the backing material 18. The Carbowax tends to slightly adhere the foam 38 to the backing material 18 when it cools.

It is thus preferred to strip the cured foam 38 from the backing material 18 while the release agent 16 is still hot. However, hot neoprene foam is usually tender. Therefore, to minimize the possibility of damage to the neoprene during the stripping operation cool air is blown onto the upper foam surface by means (not shown) to toughen it at the separation point.

A residue of the release agent 16 is left on the backing material 18 and on the undersurface of the foam at the separation point (Fig. 11), the residue 16 on the foam surface usually being an insignificant amount. However cool air can be blown against the undersurface of the stripped foam to minimize any tackiness between overlapping foam surfaces as where the foam stock is wound into a roll.

The separated foam 38, if desired, can also be cut, or otherwise handled in preparation for its intended use.

Some applications of the no-gel neoprene latex foam product include furniture cushions, presser pads in clothes pressing equipment, automobile trim pads, cosmetic foam, as in brassiers, and topper pads in mattresses.

No-gel rubber latex foam can be formed, according to another embodiment of the invention, in a batch method rather than a continuous method as previously described.

Accordingly in the batch method a supporting means 40 (Fig. 13) comprises a foraminous plate or wire screen 42 of finite area bounded by a peripheral frame 44 of any suitable shape and material mounted upon a foraminous conveyor belt 46 similar to the conveyor 20 as shown in Fig. 12. A flange 48 provided around the frame 44 catches any latex froth 14 overflowing the confines of the frame 44. The supporting means also comprises preshaped backing material 50 similar to the backing material 18, and covering the plate or screen 42. The backing material 50 is precoated with the release agent 16 in any suitable pre viouslv described manner. The frame 44, prior to use, is treated with a suitable conventional lubricant or mold release agent such as MR-214 manufactured by Green Chemical Products of Illinois.While MR-214 provides acceptable release of the no-gel rubber latex foam from a metal surface after curing, it does not release the foam from a textile surface such as the backing material 18 without causing damage to the foam layer.

Nozzles 52 (Fig. 12) deposit predetermined amounts of the neoprene latex foam froth 14 as previously formulated onto the precoated backing material 50 within the confines of the frame 44. The deposited froth is doctored, if desired, by a blade 54 and transported by the conveyor belt 46 into a dry air oven 56 similar to the oven 36. This arrangement permits dehydration of the undersurface of the latex foam froth 16 through the release agent (which is again desirably Carbowax), backing material 50, the wire screen 42 and the conveyor belt 46. Dehydration also occurs at the upper free surface of the latex foam froth 14. Curing times and temperatures may be as previously described and if desired, the foam froth can also be preheated by the Calrod heaters 32 as disclosed.

After curing is completed the cured foam 58 is removed from the backing material 50 for use as is or it can be trimmed or otherwise handled preparatory to formation of a finished article. The foam structure produced by either the continuous or batch methods described is characterized by a soft hand and feel at the upper and lower surfaces which are substantially smooth and free of congealed polymer skin.

As will be apparent to those skilled in the art the disclosed methods can be used with various other no-gel rubber latex formulations. For example latexes based on styrenebutadiene rubber, natural rubber and blends of natural rubber can be used to form the no-gel rubber latex foam froth in accordance with the present invention.

An advantage of the present method for forming no-gel rubber latex foam is that the resultant product does not have a backing material and is easily released from the supporting means after cure. Another advantage is the economy of the disclosed methods since the backing material is reusable.

WHAT WE CLAIM IS:- 1. A method for making no-gel rubber latex foam, comprising the steps of coating a water vapor permeable supporting means with a water vapor permeable release agent comprising a polyethylene glycol polymer having a molecular weight range of 1,500 to 20,000, depositing a froth of uncured no-gel rubber latex foam onto the supporting means over the coating, heating the froth to dehydrate, cure and form the no-gel rubber latex foam, and separating the cured latex foam from the supporting means.

2. A method according to claim 1 in which the supporting means includes a conveyor belt.

3. A method according to claim 1 or claim 2 in which the supporting means includes a backing material.

4. A method according to claim 3, in which the backing material moves from a first location to a second location and during said movement is, in a consecutive fashion, continuously coated with the release agent, continuously receives deposition of the foam froth over the release agent, and continuously conveys the foam froth to a heater to dehydrate, cure and form the no-gel rubber latex foam in a continuous sheet.

5. A method according to claim 3 or claim 4 in which the backing material is a textile.

6. A method according to claim 3 or claim 4 in which the backing material is glass or polyester.

7. A method according to any one of the preceding claims in which the release agent comprises a water solution including blends of polyethylene glycol polymers having different molecular weights.

8. A method according to any one of the preceding claims in which the release agent includes hydroquinone monomethyl ether.

9. A method according to any one of the preceding claims in which said rubber latex froth is based on a copolymer of styrene and butadiene.

10. A method according to any one of claims 1 to 8 in which said rubber latex froth is based on a polymer of neoprene.

11. A method according to any one of claims 1 to 8 in which the rubber latex froth is based on a latex of natural rubber or blends of natural rubber latices.

12. A method according to any one of the preceding claims in which, after the rubber latex froth is deposited onto the supporting means, it is preheated.

13. A method according to claim 12, in which the rubber latex froth is preheated from a temperature of 70"F to a temperature of 200so.

14. A method according to claim 13, in

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. means 40 (Fig. 13) comprises a foraminous plate or wire screen 42 of finite area bounded by a peripheral frame 44 of any suitable shape and material mounted upon a foraminous conveyor belt 46 similar to the conveyor 20 as shown in Fig. 12. A flange 48 provided around the frame 44 catches any latex froth 14 overflowing the confines of the frame 44. The supporting means also comprises preshaped backing material 50 similar to the backing material 18, and covering the plate or screen 42. The backing material 50 is precoated with the release agent 16 in any suitable pre viouslv described manner. The frame 44, prior to use, is treated with a suitable conventional lubricant or mold release agent such as MR-214 manufactured by Green Chemical Products of Illinois.While MR-214 provides acceptable release of the no-gel rubber latex foam from a metal surface after curing, it does not release the foam from a textile surface such as the backing material 18 without causing damage to the foam layer. Nozzles 52 (Fig. 12) deposit predetermined amounts of the neoprene latex foam froth 14 as previously formulated onto the precoated backing material 50 within the confines of the frame 44. The deposited froth is doctored, if desired, by a blade 54 and transported by the conveyor belt 46 into a dry air oven 56 similar to the oven 36. This arrangement permits dehydration of the undersurface of the latex foam froth 16 through the release agent (which is again desirably Carbowax), backing material 50, the wire screen 42 and the conveyor belt 46. Dehydration also occurs at the upper free surface of the latex foam froth 14. Curing times and temperatures may be as previously described and if desired, the foam froth can also be preheated by the Calrod heaters 32 as disclosed. After curing is completed the cured foam 58 is removed from the backing material 50 for use as is or it can be trimmed or otherwise handled preparatory to formation of a finished article. The foam structure produced by either the continuous or batch methods described is characterized by a soft hand and feel at the upper and lower surfaces which are substantially smooth and free of congealed polymer skin. As will be apparent to those skilled in the art the disclosed methods can be used with various other no-gel rubber latex formulations. For example latexes based on styrenebutadiene rubber, natural rubber and blends of natural rubber can be used to form the no-gel rubber latex foam froth in accordance with the present invention. An advantage of the present method for forming no-gel rubber latex foam is that the resultant product does not have a backing material and is easily released from the supporting means after cure. Another advantage is the economy of the disclosed methods since the backing material is reusable. WHAT WE CLAIM IS:-

1. A method for making no-gel rubber latex foam, comprising the steps of coating a water vapor permeable supporting means with a water vapor permeable release agent comprising a polyethylene glycol polymer having a molecular weight range of 1,500 to 20,000, depositing a froth of uncured no-gel rubber latex foam onto the supporting means over the coating, heating the froth to dehydrate, cure and form the no-gel rubber latex foam, and separating the cured latex foam from the supporting means.

14. A method according to claim 13, in

which the duration of preheating is from 25 seconds to 200 seconds.

15. A method according to any one of the preceding claims in which the curing of the rubber latex foam froth is carried out at a tem- perature range of from 260"F to 300so.

16. A method according to any one of the preceding claims in which the curing of the rubber latex foam froth is carried out at a temperature of 300"F for 75 minutes.

17. A method for making no-gel rubber latex foam substantially as herein described with reference to Figures 1 to 11 or to Figures 12 and 13 of the accompanying drawings.

18. A no-gel rubber latex foam prepared in accordance with a method according to any one of the preceding claims.