Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-06-01
2003-01-28
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S052000, C524S053000
Reexamination Certificate
active
06512028
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a gel material and to a method of making a gel material.
BACKGROUND OF THE INVENTION
Gels are known materials which have mechanical properties which enable them to be stored without flowing significantly. They can be self-supporting so that a sheet of a gel material can be handled without breaking or tearing. Weaker gel materials can be provided with a support, for example in the form of a fabric, and generally an open weave mesh.
Gel materials can include a component in their composition which enable the materials to absorb water (including water-based liquids). Such a material is sometimes referred to as a hydrogel. It can absorb several times its own weight in water, resulting in significant swelling of the gel. It can be important for many applications for the ability of the gel material to absorb water to be balanced against loss of physical properties due to swelling when the water is absorbed.
U.S. Pat. No. 3,898,143 discloses a method of making a gel material which involves co-crosslinking in aqueous solution an intimate mixture of polyethylene oxide and another water soluble polymer such as hydroxyethyl cellulose. The components of the mixture might be immiscible. However, the mixture is rendered homogeneous (or as a heterogeneous microphase) when the crosslinking reaction takes place, the crosslinking reaction being relied on to preserve the homogeneity of the mixture.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method of making a gel material has been provided which comprises mixing a water soluble crosslinkable matrix polymer, a particulate polymer material which has been crosslinked so that it has a gel content of at least about 55%, and an aqueous solvent to form a mixture, and crosslinking the matrix polymer so as to form a gel matrix of the matrix polymer in which the particles of the particulate polymer material are dispersed, each of the crosslinked matrix polymer and the crosslinked particulate polymer material being capable of absorbing water. In a preferred embodiment, the method includes drying the gel material after the crosslinking of the matrix polymer.
In accordance with one embodiment of the method of the present invention, the particulate polymer material is present in the mixture in an amount of at least about 0.5% by weight.
In accordance with another embodiment of the method of the present invention, the matrix polymer comprises polyethylene oxide. Preferably, the molecular weight of the polyethylene oxide is not more than about 5×10
6
.
In accordance with another embodiment of the method of the present invention, the particulate polymer material comprises an acrylic acid or an ester or a salt thereof.
In accordance with another embodiment of the method of the present invention, the particulate polymer material comprises a starch.
In accordance with another embodiment of the method of the present invention, the gel content of the particulate polymer material is at least about 75%.
In accordance with another embodiment of the method of the present invention, the size of at least about 60% by weight of the particles of the particulate polymer material is less than about 100 &mgr;m. Preferably, the size of at least about 85% by weight of the particles of the particulate polymer material is less than about 100 &mgr;m.
In accordance with another embodiment of the method of the present invention, the matrix polymer is present in the mixture in an amount of at least about 2% by weight.
In accordance with another embodiment of the method of the present invention, the ratio by weight of the matrix polymer to the particulate polymer material is at least about 0.1. In a preferred embodiment, the ratio by weight of the matrix polymer to the particulate polymer material is not more than about 10.
In accordance with another embodiment of the method of the present invention, the crosslinking of the matrix polymer is initiated by means of ultraviolet radiation.
In accordance with the present invention, a gel material has also been provided which comprises particles of a particulate polymer material which is capable of absorbing water and which is crosslinked so that it has a gel content of at least about 55% dispersed in a matrix of a polymer which has been crosslinked to reduce its solubility in water so that it swells rather than dissolves in water, the size of at least about 60% by weight of the particles of the particulate polymer material being less than about 100 &mgr;m. In a preferred embodiment, the gel content of the particulate polymer material is at least about 75%
In accordance with one embodiment of the gel material of the present invention, the matrix polymer comprises polyethylene oxide. Preferably, the molecular weight of the polyethylene oxide is not more than about 5×10
6
.
In accordance with another embodiment of the gel material of the present invention, the ratio by weight of the matrix polymer to the particulate polymer is at least about 0.1, and in another embodiment, it is not more than about 10.
In accordance with another embodiment of the gel material of the present invention, the gel material is in the form of a sheet.
In accordance with another embodiment of the gel material of the present invention, the particulate polymer material comprises an acrylic acid or an ester or a salt thereof.
In accordance with another embodiment of the gel material of the present invention, the particulate polymer material comprises a starch.
The present invention provides a gel material in which absorbency is maintained at a high level due to the use of a particulate polymer absorbent material that is crosslinked so that it retains its particulate form, in a matrix of a polymer (especially of a polyethylene oxide) which has been crosslinked so as to reduce its solubility in water so that it swells rather than dissolves in water.
Accordingly, in one aspect, the present invention provides a gel material which comprises particles of a particulate polymer material which is capable of absorbing water and which is crosslinked so that it has a gel content of at least about 55%, and which is supported in a matrix provided by a polymer which has been crosslinked to reduce its solubility in water so that it swells rather than dissolves in water.
The use of a particulate absorbent material in the gel of the present invention is believed to enhance the ability of the material to absorb water (including water based liquids such as solutions) compared with hydrogel compositions in which the matrix and absorbent materials are mixed homogeneously, for example as disclosed in U.S. Pat. No. 3,898,143. Thus, the gel material of the present invention can achieve higher water absorbencies than comparable materials while retaining appropriate physical properties so that it is capable of being handled, prior to and during use. In particular, the gel materials can be manipulated without losing their integrity even when significant quantities of water (or other aqueous materials) have been absorbed.
Preferably, the gel content of the particulate polymer material is at least about 60%, more preferably at least about 75%, for example at least about 90%. Gel content is measured by weighing accurately a sample of dry polymer (weighing about 0.1 g), and placing the sample in a Soxhlet extraction apparatus containing 200 ml of a 25:75 by weight mixture of water and ethanol. After 12 hours of extraction, the sample is placed in a drying oven at 60° C. until dry. The dry weight is recorded. The gel content is then calculated as follows:
Gel
content
(
%
)
=
Non
-
extracted
weight
original
weight
×
100
A high gel content has the advantage of ensuring that the particles of the polymer retain their particulate structure, at least to a large degree, when exposed to water, for example when a solution technique is used to make the gel material or when the gel is exposed to water in use. The particles of the polymer w
Bekkaoui Ali
Gentilcore Giovanni
Lancaster Ian Michael
Lerner David Littenberg Krumholz & Mentlik LLP
Rajguru U K
Scimat Limited
Seidleck James J.
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