Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to resilient water-
proof material, more especially in the form of sheet or
board, and its production by impregnation of material derived
from cellular or foamed synthetic plastics.
For a variety of applications, e.g. footwear,
building materials, gaskets and joint-sealing material~,
resilient waterproof materials are required.
; Previous developments in this field include the
following three kinds of flexible waterproof polyurethane
structures. Solid urethane rubbers are waterproof, flexible
and possess good compression and abrasion resistance, but
¦ they are of high density, notably in the region of 75 lb/ft3
and are therefore too costly for many applications. Micro-
~ cellular and skinned elastic polyurethanes are of lower
i 15 densi~y, e.g. 50 lb/ft3 and substantially waterproof, but
they are readily distorted under compression and their cell
¦ structure i8 difficult to control. As a third alternative,
! open-celled polyurethane structures of low density have
been impregnated with various agents, but these only acquire
their sealing properties under compression ~hen very high
¦ proportions of impregnants are used. In typical examples
the impregnation level varies between 75% and 200/~ of the
weight of polyurethane and, in addition, permanent com-
pression is necessary in order to form a liquid seal.
It is an object of this invention to provide a
flexible, polyurethane-based waterproof or sealing material
with good load-bearing properties, low compressibility and
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good abrasion resistance.
The material of the present invention comprises a porous
polyurethane material, preferably having a density in the range 20-50 lb/ft3
impregnated with elastomeric material to the extent of from 5 to 50% by
weight of the polyurethane.
The preferred material employs a porous polyurethane material
of a density in the range 25-50 lb/ft3 and an impregnation level of 15 to
35% by weight of polyurethane.
Any porous, impregnatable polyurethane material of the
appropriate density may be used as starting material, but the preferred
materials are so-called "reconstituted polyurethane foams" made by bonding
together particles of comminuted polyurethane foam with a polyurethane
binder. Suitable starting materials are those described in our British
Patent No. 1,337,413 which comprise polyurethane or other foam comminuted to
a particle size of less than 2 mm, bonded with a polyurethane composition
and moulded under pressure to give a density in the range 10-60 lb/ft3.
Such materials are not recognizably cellular in the sense in which the term
is ordinarily applied to polyurethane materials, but retain sufficient
porosity for impregnation to give the products of this invention. Foam
particles of other particle sizes can, however, be used, and the particle
size of the ccmminuted foam in reconstituted materials used in this
invention is preferably 1 to 4 mm and more especially 1 to 2 mm. Such
reconstituted materials may contain other materials such as comminuted
foam based on synthetic or natural rubber or vinyl polymer, or mineral
fillers, or fibres, or powdered cork, but being based on polyurethane
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and more especially on polyurethane binders, are here
comprehended within the term "polyurethane material".
The impregnant may be any of a wide range of
elastomers and may be selected with a given end use in view.
Examples of impregnants include rubbers of various kinds,
vinyl polymers and copolymers, acrylic elastomer6, butyl
rubbers, and especially carboxylated styrene-butadiene
rubbers. ~he impregnant may contain additives for various
purposes, for example colouring matters, stabilizers,
plasticizers, surface modifierY, U.V. stabilizers,
deodorants, fungicides or flame retardants.
~ he principal advantages of the materials according
to this invention are their flexibility, wear-resistance and
sealing qualities, which are achieved at low~r densities or
lower impregnation levels than previously proposed materials.
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This can be illustrated by comparing a typical material of
this in~ention with typical prior materials.
A material a~cording to the invention based on a
` 30 lb/ft3 porous polyurethane material and having 5 lb/ft3
impregnant has equivalent waterproof and sealing properties
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~, to a solid urethane rubber of 75 lb/ft' or a micro-cellular
polyurethane of 50 lb/ft3, giving advantages of lighter
weight and easier control of production. It is also note-
worthy that the material is lighter in weight and more
resistant to wear than rubber or vinyl sheet and has the
further advantages of flexibility and resistance to cracking,
breathability and a lower water absorption of the order of
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g%. It i8 noteworthy that at levels of impregnation
above the preferred ran~e, e g. at 7~!o, the product has an
even lower water absorption ~nd a lower breathability,
which is a disadvantage for such uses as shoe soles.
The present invention also provides a method Or
preparing a resilient waterproof material which comprises
impregnating a porous polyureth~ne material with from 5 to
5~/o of its own weight of an elastomeric material in the form
of a dispersion in a liquid medium, especially an aqueous
latex, or of a melt. Colouring matters or other additives
as mentioned above may be added to the wet impregnant.
In the preferred variants of the method, either an
i open-celled polyurethane material is prepared in which the
cells are precompressed and impregnated while under compression,
or a precompressed and set foam or porous material is impreg-
nated without further pressure. In the first case the
~ compressed impregnated structure is dried and fused while
; under compression, the pressure only being released after
the cure of the structure. In the second case the impregnated
structure is cured and dried without application of further
~i pressure.
~he actual process of impregnation can be carried out
- in several ways. It can be performed simply by dipping or
spraying a sheet of the porous material, though care has to
; Z5 be taken to prevent 'air locking' in the centre of the sheet.
The preferred method is one of compression to a sufficient
extent to expel the bulk of the air present in the structure
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and then releasing the pressure under the surface of the
liquid to allow the impregnant to permeate throughout the
sheet. This is followed by a final stage at which the
material is subjected to a controlled pressure to obtain
the adjustment to the required concentration of impregnant~.
~his process may be carried out either as a batch process
or as a continuous process. In the latter case, compression
can conveniently be applied using steel nip rolls.
~ he following examples illustrate the method of the
invention and the properties of the product.
.. ~camPle 1
A 13 x 13 inch piece of dry reconstituted polyure-
i thane material, prepared as described in the single Example
in British Patent No. 1,337,413, weighing 490 g., being 8 mm
thick, was passed through a series of driven steel nip
, rollers with a clearance of 3.6 mm immersed in a tank charged
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with an emulsion of rubber (REVIN~ 55DlO) containing 5~/'
solids. (REVINEX is a Trade Mark of Revertex Limited). After
' passing out of the tank the sample was passed through a
8eco~d similar nip to expel excess impregnant. The sheet of
q material after this further passage weighed 656 g. ~his was
then dried to constant weight at a temperature of 150~C.
The final weight of the sheet was 573 g. (corresponding to
17% impregnant). The water absorption of this sample was
measured by the SATRA ~est Method PM 75 (Water Absorption of
Cellular ~olings by the Compression Method) and the results
of this test and other physical properties are shown in the
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~ollowing Table.
TABLE
Property Unimpregnated Impregnated
` Density 35 lb/ft3 41 lb/ft3
Water Absorption Test over 100% 6.1%
Tensil~ Strength291 365
(lb/in )
;' Split Tear Resistance 11 20
(lb. per inch) _
Example 2
A further sample as above (dry weight 490 g.)
was treated in an identical manner except that the final
dry weight was 614 g. (25.3% impregnant). The water ab-
sorption of this sample was 4.9%.
Example 3
The following example employs a blend of impreg-
nating resins which is capable of producing a stiffened
sheet which does not crack on bending.
An impregnant composition was prepared from thefollowing constituents (parts by weight):
Carboxylated styrene-butadiene copolymer emulsion,
50-55% solids (REVI~EX 55D10) 100 parts
Carboxylated butadiene latex emulsion,
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., 50-55% solids (REVI~EX 14F70) lO0 parts
Colouring emulsion 2 parts
~ Water lO0 parts
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A 12 x 12 inch of reconstituted foam material (as before),
2 mm thick and weighing 7f,.5 g, was impregnated with this impregnant so
that after drying at 150C the final weight of the sheet was 102.2 g. This
corresponds to an impregnation level of 25%. The tensile strength of the
impregnated material, measured in accordance with British Standard 3379,
was 500 lb/in and double that of the unimpregnated material. The elong-
ation was 50%, which was not greatly different from the unimpregnated
material.
Similar products can be obtained at impregnation levels of
15-35% by weight of the dry impregnant solids, the preferred range being
25-30%.
These products, and particularly that of Example 3 itself,
are useful in the production of shoe materials, handbags, luggage and
motor car components. The material has the additional advantage of being
thermoformable and it can also be laminated to fabrics or faom materials
or to other suitable substrates.
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