IE84670B1

IE84670B1 - A process for preparing a waterproof composite material

Info

Publication number: IE84670B1
Application number: IE2004/0241A
Authority: IE
Inventors: Hughes Harry; Peter Kirby Anthony
Original assignee: Mayo Workwear Research & Development Limited
Filing date: 2004-04-02
Publication date: 2007-08-22

Abstract

ABSTRACT A process for preparing a waterproof composite material consisting of a fabric, an inner resin layer, a central resin layer, and an outer resin layer. Each resin layer comprises pores of different sizes allowing the permeability of the composite material to be controlled. The invention also relates to a waterprooof composite material. The invention further relates to a garment produced from the waterproof material.

Description

A process for preparing a waterproof composite material The present invention relates to a process for preparing a waterproof composite material consisting of a fabric, an inner resin layer, a central resin layer and an outer resin layer. The invention also relates to the waterproof composite material prepared by that process, and further to a garment produced from that waterproof composite material.

In the specification the term "polyurethane resin" refers to solid or semisolid polyurethane of natural or synthetic origin with no deﬁnite melting point, i.e. having no definite temperature at which solid polyurethane resin turns to liquid. In the specification the term "paper" refers to sheets of cellulose ﬁbres.

It is well known to laminate fabrics with a layer of polyurethane resin. US Publication No. US 2003/0027472 discloses a waterproof and moisture-permeable cloth structure for a wader comprising an outer cloth layer of material, a cloth layer of a waterproof and moisture-permeable material made of rubber or vinyl, a cloth material treated with a coating of polyurethane resin and an inner layer of a lining material. The disadvantage of this cloth structure is that the layer coated with polyurethane resin is not sufﬁcient to prevent water from passing therethrough. Therefore a further layer of material having waterproof properties such as rubber is required to render the material waterproof.

The disadvantage of using a material such as rubber either on its own or as part of a composite material is that it is non-porous and therefore does not allow the flow of air therethrough. Therefore if the material is worn for any considerable length of time, this will cause the wearer to perspire, which accordingly causes the wearer discomfort. Additionally the moisture remaining on the material from the wearer encourages the growth of microorganisms such as fungi. This results in an offensive odour and is unfavourable to the health of the wearer.

It is also well known to provide a layered waterproof structure comprising a layer of polyurethane. US Patent No. 5,402,540 discloses a footwear article which is of three- ply the intermediate ply being made from an elastomeric polyurethane ﬁlm. The inner and outer plies however are made of fabric. The three plies are bonded together using adhesive. The disadvantage of layered structure as disclosed in this document however is that as there is only one layer of resin, more water can permeate the garment.

It is further well known to provide a layered waterproof structure comprising multiple UK patent no. GB 2 036 642 discloses a method for producing a stretchable coated fabric comprising a number of layers of aromatic layers of polyurethane. polyurethane. This fabric is produced however in a manner so as to prevent thin areas appearing in the coating which give rise to discrete holes of pin-prick dimensions when the fabric is stretched.

UK patent no. 2 169 241 discloses an apparatus for the manufacture of polyurethane coated materials comprising applying layers of polyurethane material and at least partially drying the material after each process stage by short-wave infra-red heating means. This type of heating means however is used to prevent the top surface of the polyurethane covering being heated to the same intense heat effect as the bottom surface.

US patent no. 6,383,325 discloses a method for manufacturing a polyurethane product which is gas permeable. The permeability is provided by means of air vents, some of which are pattern cavities formed by the releasing sheet which require the addition of fluoride to act as a water repellent and to prevent droplets from attaching to the surface layer.

US patent no. 3,650,880 discloses a porous breathable polymer coated fabric, comprising a number of layers, each layer being repellent to the liquid phase.

There is therefore a need for a waterproof composite material and a process for preparation thereof which overcomes the above-mentioned disadvantages.

Statements of Invention According to the invention there is provided a process for preparing a waterproof composite material consisting of a fabric, an inner resin layer, a central resin layer, and an outer resin layer, the process comprising: mixing a polyurethane resin, an antibacterial agent in the range 0.5% to 2.0% by weight of the resin and a solvent in the range 35% to 40% by weight of the resin to form a ﬁrst polyurethane resin composition; laying down a sheet of backing paper and adding an amount sufficient of the first polyurethane resin composition to the paper to provide an outer resin layer having a thickness of between 0.10mm and 0.15mm; baking the outer resin layer and the paper at a temperature in the range of between 125°C and 135°C for 3 to 5 minutes to form a resin layer comprising pores; coating the outer resin layer with a further amount of the first polyurethane resin composition to provide a central resin layer having a thickness of between 0.1mm and 0.15mm; baking the central resin layer, the outer resin layer and the paper at a temperature in the range of between 130°C and 145°C for 3 to 5 minutes, the central resin layer forming a layer comprising pores; mixing a polyurethane resin, an antibacterial agent in the range 0.5% to 2.0% by weight of the resin and a solvent in the range 13% to 23% by weight of the resin to form a second polyurethane resin composition; coating the central resin layer with an amount of the second polyurethane resin composition to provide an inner resin layer having a thickness of between 0.25mm and 0.35mm to form a composite polyurethane layer; adhering the composite polyurethane layer to a fabric by an adhesive to form the composite material; baking the material at a temperature in the range of between 145°C and 155°C for 3 to 5 minutes; the inner layer forming a layer comprising pores, the pores having a smaller diameter than the pores in the outer and central resin layers; removing the backing paper layer; and further drying the material at a temperature in the range of between 130°C and 140°C for 3 to 5 minutes.

The advantage of using a sheet of backing paper to provide the outer resin layer is that the use of the paper aids in providing a smooth surface to the composite material and also aids in absorbing moisture from the outer resin layer. A further advantage of the paper is that it can be easily removed from the composite material after baking.

The advantage of using polyurethane resin is that it has breathable properties, as well as tensile strength and tear propagation resistance.

The advantage of adding antibacterial agent is to prevent the build-up of mildew residues which can build-up in moisture pockets or within the pores contained within the material contained in the material.

The advantage of adding solvent is that it allows for the formation of pores in the resin layers. The pores are the spaces that the solvent once occupied before it was evaporated out by baking. The pores are substantially spherical in shape and randomly located throughout the resin layers. Adding solvent to the resin composition and baking each of the resin layers formed from the resin composition provides permanent porous resin layers which persist in the dry state.

Preferably the outer and central resin layers comprise pores having a diameter in the range of between 100 to 2000nm.

Further preferably the inner resin layer comprises pores having a diameter of less than 100nm.

The advantage of modifying the amount of solvent in the resin composition used to form each of the resin layers is that this results in the layers having different pore sizes. It has been found that polyurethane in particular is remarkably sensitive to small changes in the quantity of solvent added to the resin composition. It has further been found that a higher percentage of solvent in the resin composition results in a greater number of pores with larger diameters after baking than if less solvent is included in the resin composition. This is particularly advantageous in that it allows the diameter of the pores to be modified therefore allowing for a number of different resin layers having different pore sizes to be provided. The advantage of providing pores is that the resultant material has greater breathability. A further advantage of providing pores is that the resultant material has a lower density than a non-porous polyurethane composite material. The resultant material is also lighter than non- porous material.

The advantage of having different layers having different pore sizes is that the permeability of the overall material can be controlled. The permeability of the material is controlled by the pore sizes of the individual resin layers. As the inner resin layer is prepared such that it has pores which are substantially smaller than the pores of the central and outer resin layers, this results in the material being permeable to air in both directions but prevents the permeation of water droplets.

The advantage of having a pore size in the region of between 100 to 2000nm is that pores of this size are larger flow through pores which are permeable to air and some moisture such as water droplets. The advantage of allowing some water droplets to permeate the outer layers of the material is that the outer layer of the material remains drier and the material can be worn for a longer time in comfort. The advantage of having a pore size of less than 100nm is that pores of this size are small diffusive pores which are impermeable to water droplets but permeable to air and vapour moisture therefore allowing breathability of the layer.

The temperature also has an effect on the size of the pores formed. It has been found that lower temperatures result in larger pore size formation whereas higher temperatures result in the formation of smaller pores. A further advantage of increasing the temperature at each stage is that it ensures that all the resin is properly baked and that all of the solvent is sufficiently removed.

A further advantage of adding solvent is that it allows a more uniform application of the resin. The addition of solvent increases the smoothness and regularity of the resin.

The advantage of baking the outer resin layer and the central resin layer is that the solvent vapourises and is removed from the composition to form the porous layers.

Furthermore, baking also aids in the formation of consistent resin layers.

The advantage of having layers of polyurethane resin is that greater control of moisture and air permeability is permitted than with one layer of polyurethane resin.

The outer, central and inner resin layers interact to form a consistent resin layer. The layers interact in such a way so that the composite material is permeable to air and moisture in both directions but prevents the absorption of water. A further advantage of having layers of polyurethane resin is that the resin composition can be applied in such a manner to provide layers having different orientations. This provides greater strength to the material than if the material was comprised merely of one layer of polyurethane resin. Due to the orientations of the different layers providing greater strength it is possible to form a number of layers, the overall combined thickness of the layers being thinner than if one layer was formed. This also results in the associated advantage that the product material is lighter.

Furthermore as the pores are randomly formed in the individual layers during baking and therefore during removal of the solvent, more often than not the pores formed in one layer would not be directly on top of the pores formed in another layer. This would further prevent water passing through the pores but should not have any affect on the air passing therethrough. Furthermore as the composite material comprises a number of layers this enhances breathability of the composite material.

Ideally the solvent is selected from the group comprising one or more of solvents sold under the Trade Marks DUF®, TOL® and MEK®. The advantage of using solvents of this type is that they allow ﬁne control of the porous properties of the polyurethane resin.

Ideally the polyurethane resin has a molecular weight in the range of between 3,500 and 4,000 daltons.

The advantage of using polyurethane resin with a molecular weight of between 3,500 and 4,000 daltons is that polyurethane resins of this type provide better resistance to water penetration and resistance to flex cracking. The advantage of using identical resins to form each resin composition is that the quality of the resin is easy to control.

Furthermore, as the resins are identical the same type of solvent may be used to provide pores. This is further advantageous in that different solvents would have different effects on different types of resins and a solvent which may be useful for providing pores in a resin of one type may have a different and detrimental effect on a resin of another type.

Preferably the polyurethane resin composition used to form the outer resin layer comprises antibacterial agent in the range 0.5% to 1.5% by weight of the resin.

Further preferably the polyurethane resin composition used to form the inner and central resin layers comprises antibacterial agent in the range 1.0% to 2.0% by weight of the resin.

Ideally the antibacterial agent is ethyl-para-hydroxybenzene.

The advantage of adding a greater amount of antibacterial agent to the resin composition used to form the inner and central resin layer is that this provides a protective antibacterial barrier close to the wearer.

The fabric may be woven, knitted or non-woven. Preferably the fabric is knitted. The advantage of the fabric being knitted is that it facilitates impregnation of the fabric by the resin.

Ideally the fabric is selected from the group comprising polyester, polyamide, acrylic, rayon, lycra and non-woven fabric.

Preferably the composite polyurethane layer is adhered to the fabric so that the inner resin layer is in contact with the fabric.

The advantage of using polyester fabric is that it is porous and therefore allows the flow of air therethrough. This prevents the wearer perspiring and therefore can be worn for greater lengths of time in comfort. The inner resin layer is not subjected to baking until it has been applied to the fabric and therefore it can more readily impregnate the fabric upon contact.

Further preferably the adhesive is a powder adhesive having a particle size of between 200 and 300 pm. The advantage of using a powder adhesive having a particle size of between 200 and 300pm is that it allows greater control during application of the adhesive.

Preferably prior to adhering the composite polyurethane layer to the fabric, the fabric is dyed using a dye selected form the group comprising black dye selected from the group comprising black colour ex-sf and disperse dye stuff. Further preferably the fabric is stabilised by the addition of ex-sf. The advantage of stabilising the fabric is that it ﬁxes the colour provided by the dye to the fabric.

According to the invention there is further provided a waterproof composite material prepared by this process and a garment produced from the waterproof composite material.

Detailed Description of the Invention The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a cross sectional view of the composite material.

Figs. 2 and 3 are ﬂow diagrams of the process according to the invention.

In the invention the following equipment is used; mixing vessels, extruders, baking machines, all of which are known and require no further description.

Referring to the drawings and initially to Fig. 1 there is provided a waterproof composite material indicated generally by the reference numeral 100, comprising a fabric 101, an inner resin layer 102, a central resin layer 103, and an outer resin layer 104. The inner resin layer 102, partially impregnates the fabric 101.

Referring now to Fig. 2. In step 1 polyurethane resin is obtained. In step 2, antibacterial agent is added to the resin in the range 0.5% to 1.5% by weight of the resin. In step 3 solvent is added to the resin in the range 35% to 40% by weight of the resin. The polyurethane resin, antibacterial agent and solvent are mixed together in step 4, to form a ﬁrst resin composition. In step 5 paper is obtained in the form of a sheet and the paper is coated with an amount of resin composition sufficient to form a layer having a thickness of between 0.10mm and 0.15mm in step 6 to provide the outer resin layer.

The outer resin layer and paper are baked at a temperature of between 125°C and 135°C for 3 to 5 minutes in step 7 to form a porous resin layer. In step 8, a further amount of polyurethane resin is obtained. In step 9, antibacterial agent is added to the resin in the range of 1.0% to 2.0% by weight of the resin. In step 10 solvent is added to the resin in the range 35% to 40% by weight of the resin. The polyurethane resin, antibacterial agent and solvent are mixed together in step 11 to form a second resin composition. In step 12 the outer resin layer is coated with the second resin composition to provide a central resin layer having a thickness of between 0.1mm and 0.15mm. The central resin layer, the outer resin layer and paper are baked at a temperature of between 130°C and 145°C for 3 to 5 minutes in step 13 allowing the central resin layer to become a porous layer.

Referring now to Fig 3, a further amount of polyurethane resin, is obtained in step 14.

In step 15, antibacterial agent is added to the resin in the range 1.0% to 2.0% by weight of the resin. In step 16 solvent is added to the resin in the range 13% to 23% by weight of the resin. In step 17, the polyurethane resin, antibacterial agent and solvent are mixed together to form a third resin composition. In step 18 the central resin layer is coated with the third resin composition to provide an inner resin layer having a thickness of between 0.25mm and 0.35mm to form a composite polyurethane layer. In step 19 fabric is obtained. The fabric is dyed in step 20 to the required colour. In step 21 the fabric is stabilised. The composite polyurethane layer is adhered to the fabric in such a way that the inner resin layer is in direct Contact with the fabric to form a composite material in step 22. The composite polyurethane layer is adhered to the fabric by an adhesive.

In step 23, the material is baked at a temperature of between 145°C and 155°C for 3 to 5 minutes to allow impregnation of the inner resin layer into the fabric and to allow the inner resin layer to form a porous layer. The paper is removed from the outer resin layer in step 24 by tearing and rolling. The composition is dried further in step at a temperature of between 130°C and 140°C for 3 to 5 minutes. In step 26 the material is rolled and it is packaged in step 27.

Obviously it will be appreciated that certain of the steps such as dyeing and stabilisation are optional steps and do not always have to be carried out.

Table 1: Composition of materials in the composite material.

Material Percentage (°/o) Fabric 70 — 73 Composite Polyurethane layer 30 - 27 Example 1: Measurement of Water Repellency A composite material was prepared according to the above process and its water repellency was tested using the following protocol.

The water repellency was measured according to the method specified in the International Organisation for Standardisation, Test Method No. 150 81111981 which tests the determination of resistance to water penetration — Hydrostatic pressure test.

The rate of increase of water pressure was 60 cm/min and the temperature of the distilled water was 20°C. No cracking of the composite material was observed.

Example 2: Measurement of Flexing Endurance The flexing endurance was measured according to the method specified in the British and European Standards Test Method No. BS 3424 Part 9 Method 110 which tests for the determination of resistance to damage by ﬂexing.

The test parameters are outlined as follows: Apparatus Flexing Tester Test speed 90 :t 9 cpm No. of specimens 4 pcs. in size of 60mm X 60mm cut from submitted samples At 120°C for 7.5 hours Room temperature (specified by client) Storage condition Test condition After 10,000 cycles — no cracking of the composite material was observed.

Similar tests were also carried out using the SATRA Standard Test Methods (SATRA — TM) 25: 1 992 which tests for ﬂexing endurance and 259D:2001 which tests for water repellency, and the results are illustrated below in Table 2. SATRA is an independent testing house in the UK.

Table 2: Water Repellency and Flexing Endurance test results Test Method Property Result SATRA’s (Damage/ recommended no. of flexes) minimum guidelines SATRA TM Resistance to ﬂex Along No crackingi’ 100,000 ﬂexes with ; 1992 cracking—as received 100,000 no significant Across No cracking! damage .000 Resistance to ﬂex Along No crackingl 100,000 ﬂexes with cracking- after hydrolysis , 100,000 no significant according to SATRA TM damage 328: 1992, for 7.5 hours at Across Slight 120°C crackingl 100,000 SATRA TM Resistance to water Highly 2300 2593; 2001* penetration-Hydrostatic >459 water head test (cmH2O) resistant Water 280 resistant * The test was conducted with a rate of increase of water pressure equal to 60cm/minute, the temperature of the distilled water was 20°C. All the samples were tested with polyurethane coating face down.

In the specification the terms "comprise, comprises, comprised and comprising" or any variation thereof and the terms "include, includes, included and including" or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa.

The invention is not limited to the embodiments hereinbefore described. but may be varied in both construction and detail within the scope of the claims.

Claims

1. A process for preparing a waterproof composite material consisting of a fabric, an inner resin layer, a central resin layer, and an outer resin layer, the process comprising: mixing a polyurethane resin, an antibacterial agent in the range 0.5% to 2.0% by weight of the resin and a solvent in the range 35% to 40% by weight of the resin to form a ﬁrst polyurethane resin composition; laying down a sheet of backing paper and adding an amount sufficient of the first polyurethane resin composition to the paper to provide an outer resin layer having a thickness of between 0.10mm and O.15mm; baking the outer resin layer and the paper at a temperature in the range of between 125°C and 135°C for 3 to 5 minutes to form a resin layer comprising pores; coating the outer resin layer with a further amount of the first polyurethane resin composition to provide a central resin layer having a thickness of between 0.1mm and O.15mm; baking the central resin layer, the outer resin layer and the paper at a temperature in the range of between 130°C and 145°C for 3 to 5 minutes, the central resin layer forming a layer comprising pores; mixing a polyurethane resin, an antibacterial agent in the range 0.5% to 2.0% by weight of the resin and a solvent in the range 13% to 23% by weight of the resin to form a second polyurethane resin composition; coating the central resin layer with an amount of the second polyurethane resin composition to provide an inner resin layer having a thickness of between O.25mm and 0.35mm to form a composite polyurethane layer; adhering the composite polyurethane layer to a fabric by an adhesive to form the composite material; baking the material at a temperature in the range of between 145°C and 155°C for 3 to 5 minutes; the inner layer forming a layer comprising pores, the pores having a smaller diameter than the pores in the outer and central resin layers; removing the backing paper layer; and further drying the material at a temperature in the range of between 130°C and 140°C for 3 to 5 minutes. A process as claimed in claim 1 wherein the outer and central resin layers comprise pores having a diameter in the range of between 100 to 2000nm. A process as claimed in claim 1 wherein the inner resin layer comprises pores having a diameter of less than 100nm. A process as claimed in any preceding claim wherein the solvent is selected from the group comprising one or more of solvents sold under the Trade Marks DUF®, TOL® and MEK®. A process as claimed in any preceding claim wherein the polyurethane resin has a molecular weight in the range of between 3,500 and 4,000 daltons. A process as claimed in any preceding claim wherein the polyurethane resin composition used to form the outer resin layer comprises antibacterial agent in the range 0.5% to 1.5% by weight of the resin. A process as claimed in claims 1 to 5 wherein the polyurethane resin composition used to form the inner and central resin layers comprises antibacterial agent in the range 1.0% to 2.0% by weight of the resin. A process as claimed in any preceding claim wherein the antibacterial agent is ethyl-para-hydroxybenzene. A process as claimed in any preceding claim wherein the fabric is woven, knitted or non-woven. A process as claimed in any preceding claim wherein the fabric is selected from the group comprising polyester, polyamide, acrylic, rayon, Iycra and non- woven fabric. A process as claimed in any preceding claim wherein the composite polyurethane layer is adhered to the fabric so that the inner resin layer is in contact with the fabric. A process as claimed in any preceding claim, wherein the adhesive is a powder adhesive having a particle size of between 200 and 300 pm. A process for preparing a waterproof composite material substantially as described herein with reference to the accompanying drawings. A waterproof composite material prepared by the process as claimed in any of claims 1 to 13. A garment produced from the waterproof composite material as claimed in claim 14.