LAMINATE HAVING IMPROVED TENSILE PROPERTIES

Abstract

The present invention relates to a method of preparing an elastomeric laminate article, the method comprising: providing a first aqueous coating composition comprising a first polymer and discrete silicon dioxide nanoparticles, wherein the first polymer is a polyurethane; providing a second aqueous coating composition comprising a second polymer; coating a substrate with the first aqueous coating composition to form a first film on the substrate; coating the first film with the second aqueous coating composition to form a second film on the first film; and removing the substrate. In another aspect, the invention relates to an elastomeric laminate article which comprises a plurality of polymeric films and one or more interfaces, wherein each adjacent pair of films defines one of the interfaces, wherein at least one of the plurality of polymeric films comprises a polyurethane, wherein the laminate comprises silicon dioxide nanoparticles, and wherein at least 60 wt % of the silicon dioxide nanoparticles are present at one or more of the interfaces defined at least in part by a polyurethane-comprising film. In both cases the laminate article may be a condom, and the invention further relates to a condom obtained or obtainable by the inventive method.

Claims

1. A method of preparing an elastomeric laminate article, the method comprising: (i) providing a first aqueous coating composition comprising a first polymer and discrete silicon dioxide nanoparticles, wherein the first polymer is a polyurethane; (ii) providing a second aqueous coating composition comprising a second polymer; (iii) coating a substrate with the first aqueous coating composition to form a first film on the substrate; (iv) coating the first film with the second aqueous coating composition to form a second film on the first film; and (v) removing the substrate.

2. The method according to claim 1, wherein the second polymer is selected from a polyisoprene, a polyurethane and a mixture thereof.

3. The method according to claim 1, wherein the second polymer is a polyurethane.

4. The method according to claim 1, wherein the discrete silicon dioxide nanoparticles have a particle diameter of from 1 to 100 nm.

5. The method according to claim 1, wherein the discrete silicon dioxide nanoparticles have a BET surface area of at least 200 m.sup.2/g.

6. The method according to claim 1, wherein the discrete silicon dioxide nanoparticles comprise surface silanol groups.

7. The method according to claim 1, wherein the step of providing a first aqueous coating composition comprising a first polymer and discrete silicon dioxide nanoparticles comprises combining a source of the first polymer with a source of discrete silicon dioxide nanoparticles to form the first aqueous coating composition.

8. The method according to claim 7, wherein the source of the first polymer comprises an aqueous polyurethane dispersion.

9. The method according to claim 1, wherein the method further comprises providing a third aqueous coating composition comprising a third polymer, and, between the step of coating the first film with the second aqueous coating composition to form a second film on the first film and the step of removing the substrate, coating the second film with the third aqueous coating composition to form a third film on the second film.

10. The method according to claim 1, wherein the elastomeric laminate article is a condom.

11. (canceled)

12. An elastomeric laminate article which comprises a plurality of polymeric films and one or more interfaces, wherein each adjacent pair of films defines one of the interfaces, wherein at least one of the plurality of polymeric films comprises a polyurethane, wherein the laminate comprises silicon dioxide nanoparticles, and wherein at least 60 wt % of the silicon dioxide nanoparticles are present at one or more of the interfaces defined at least in part by a polyurethane-comprising film.

13. A condom comprising a laminate, the laminate comprising a plurality of elastomeric films and one or more interfaces, wherein each adjacent pair of elastomeric films defines one of the interfaces, wherein at least one of the plurality of elastomeric films comprises a polyurethane, wherein the laminate comprises silicon dioxide nanoparticles, and wherein at least 60 wt % of the silicon dioxide nanoparticles are present at one or more of the interfaces that are defined at least in part by the polyurethane-comprising film.

14. The elastomeric laminate article according to claim 12, wherein at least 70 wt % of the silicon dioxide nanoparticles are present at one or more of the interfaces, more preferably at least 80 wt %.

15. (canceled)

16. The method according to claim 3, wherein the first polymer and the second polymer are the same polyurethane.

17. The method according to claim 4, wherein the discrete silicon dioxide nanoparticles have a particle diameter of from 2 to 50 nm.

18. The method according to claim 5, wherein the discrete silicon dioxide nanoparticles have a BET surface area of at least 250 m.sup.2/g.

19. The method according to claim 7, wherein the source of discrete silicon dioxide nanoparticles is colloidal silica.

20. The condom according to claim 13, wherein at least 70 wt % of the silicon dioxide nanoparticles are present at one or more of the interfaces.

21. The method according to claim 1, wherein the first aqueous coating composition comprises the discrete silicon dioxide nanoparticles in an amount of 0.1 to 3 wt %.

22. The method according to claim 1, wherein the first aqueous coating composition comprises the first polymer and the discrete silicon dioxide nanoparticles in a weight ratio of the first polymer to the discrete silicon dioxide nanoparticles of from 5:1 to 200:1.

Description

[0127] The present invention will now be described in relation to the following non-limiting figures.

[0128] FIG. 1 shows the tensile and burst properties of the condoms prepared in accordance with Example 1, as measured in accordance with Example 2. In each graph, the data points from left to right are for the control formulation (U228), 1 wt % SiO.sub.2, 2 wt % SiO.sub.2 and 3 wt % SiO.sub.2.

[0129] In FIG. 1A, the bars represent force at break (N, left hand axis) and the lines represent thickness (m, right hand axis).

[0130] In FIG. 1B, the bars represent tensile strength (MPa, left hand axis) and the lines represent elongation at break (%, right hand axis).

[0131] In FIG. 1C, the left hand bars represent modulus at 300% elongation (MPa) and the right hand bars represent modulus at 500% elongation (MPa).

[0132] In FIG. 1D, the right hand bars represent burst volume (L) and the left hand bars represent burst pressure (kPa).

[0133] FIG. 2 shows the tensile and burst properties of the condom prepared in accordance with Example 3, as measured in accordance with the methods disclosed in Example 2 and compared with the 2 wt % SiO.sub.2 and control condoms of Example 1. In each graph, the data points from left to right are for the control formulation (U228) at 26.3 m wall thickness, 2 wt % SiO.sub.2 at 24.8 m wall thickness and 2 wt % SiO.sub.2 at 20.0 m wall thickness.

[0134] In FIG. 2A, the bars represent force at break (N, left hand axis) and the line represents thickness (m, right hand axis).

[0135] In FIG. 2B, the bars represent tensile strength (MPa, left hand axis) and the line represents elongation at break (%, right hand axis).

[0136] In FIG. 2C, the left hand bars represent modulus at 300% elongation (MPa) and the right hand bars represent modulus at 500% elongation (MPa).

[0137] In FIG. 2D, the right hand bars represent burst volume (L) and the left hand bars represent burst pressure (kPa).

[0138] The present invention will now be described in relation to the following non-limiting Examples.

EXAMPLE 1

[0139] An aliphatic polyether polyurethane aqueous dispersion (Alberdingk U228 (50% solids), commercially available from Alberdingk Boley) was diluted with deionised water to 35% solids and mixed with a water-based carbodiimide cross-linking agent (Carbodilite SV-02 (40% solids), commercially available from Nisshinbo Chemical Inc.) in an amount of 3 wt % solid carbodiimide based on the total solids content of the diluted polyurethane dispersion. The resulting mixture was stirred for 30 minutes. Then, Ludox SM colloidal silica with a surface area of 363 m.sup.2/g (a 30 wt % suspension of SiO.sub.2 nanoparticles in H.sub.2O, commercially available from Sigma-Aldrich) was added in an amount of 1 wt %, 2 wt % or 3 wt % solids based on the weight of solid polyurethane, and the resulting mixture was stirred for 30 minutes and then sonicated for 30 minutes. A liquid polyether-modified siloxane surfactant (BYK-348, commercially available from BYK) was added in an amount of 0.2% w/v and the resulting mixture was stirred for 30 minutes.

[0140] A condom was prepared by dipping a glass former into the mixture three times to form three layers of material on the former using a dipping robot. Between each dipping step, the material was dried on the former at 60 C. for 5 minutes in a circulating air oven to form a film. After the final film-forming step, the material was dried on the former at 120 C. for 12 minutes in another circulating air oven. After cooling down to room temperature, a starch-based finishing slurry was applied and the condom was stripped from the glass former before drying in a dryer. The three-layered condom had a wall thickness of 25-30 m.

[0141] A control was prepared in the same manner as above but without any added colloidal silica or surfactant.

[0142] The sample formulations are summarised in the following table:

TABLE-US-00001 TABLE 1 Formulations used to prepare condoms of Example 1 U228 SV-02 SM-SiO.sub.2 BYK Condom (phr) (wt %) (wt %) (% w/v) Control (U228) 100 3.0 0 0 1 wt % SiO.sub.2 100 3.0 1.0 0.2 2 wt % SiO.sub.2 100 3.0 2.0 0.2 3 wt % SiO.sub.2 100 3.0 3.0 0.2

[0143] The addition of colloidal silica was found to have no noticeable effect on the appearance of the condoms. All condoms appeared transparent after removal of the starch-based finishing powder.

EXAMPLE 2

[0144] The tensile (force at break, tensile strength, elongation at break, modulus) and air burst (burst pressure and burst volume) properties of condom samples obtained from condoms prepared in accordance with Example 1 were determined.

[0145] To determine the tensile properties, a ring-shaped sample was cut from each condom before being tested with a universal tensile tester in accordance with ISO 4074. The samples were tested with a 500 N load cell and stretched at a rate of 500 mm/min until break. The tensile stress was calculated by finding the ratio of force and the initial cross-sectional area of the specimen. The strain or elongation was defined as the ratio of the elongated length to the initial length of the sample. The moduli was defined as the stress at specific elongation e.g. modulus at 300% (M300) and 500% (M500) elongation are referred to as the stress at 300% and 500% elongation, respectively. The force, elongation and stress at breaking were defined as the force at break, elongation at break and tensile strength, respectively. Five replicate measurements for each sample were used to calculate mean average values for all properties.

[0146] The thickness of each condom (i.e. the wall thickness, excluding the bead) was measured at a right angle to the length of the condom, when it is unrolled and laid flat without any creases. Three thickness measurements were made for each sample condom by a thickness gauge, and a mean average was determined.

[0147] Burst pressure and burst volume of condom samples were assessed by inflating the condom like a balloon to measure the air pressure and air volume respectively needed to burst it according to ISO 23409:2011. The condom was unrolled and clamped to a stem, leaving about 150 mm to be inflated. The testing apparatus inflated the condom with a clean, oil-free and moisture-free air at a specified rate.

[0148] The results are shown in Table 2 and FIGS. 1A to 1D.

TABLE-US-00002 TABLE 2 Tensile and burst properties of PU condom produced in accordance with Example 1 with SM-SiO.sub.2 0, 1, 2 and 3 wt % Properties Control PU 1% SiO.sub.2-SM 2% SiO.sub.2-SM 3% SiO.sub.2-SM Thickness (m) 26 1 27 1 25 1 29 4 M300 (MPa) 3.15 0.09 3.07 0.16 3.47 0.17 3.36 0.08 M500 (MPa) 5.00 0.11 4.83 0.27 5.30 0.27 5.23 0.18 Force at break (N) 49.25 5.61 64.9 7.9 64.8 10.7 64.2 7.3 Tensile strength 46.93 4.88 59.62 6.86 65.42 11.02 56.47 2.4 (MPa) Elongation at break 447 5 462 8 462 8 453 8 (%) Burst pressure (KPa) 4.33 0.32 4.96 1.282 5.2 1.16 5.125 1.29 Burst volume (L) 3.13 0.25 3.20 0.91 3.70 0.75 3.00 0.816

[0149] The addition of SiO.sub.2 nanoparticles to the formulation was found to significantly increase the force at break and tensile strength of the condom samples. However, there was only a limited difference in modulus at 300% elongation, modulus at 500% elongation, elongation at break, burst pressure or burst volume as a result of the addition of SiO.sub.2 nanoparticles. It should be noted that the tensile strength peaked at 2 wt % SiO.sub.2. It is believed that increasing the SiO.sub.2 further increased the ductility of the material, ultimately reducing its tensile strength. It will be appreciated, however, that the tensile strength of the 3 wt % SiO.sub.2 condom was still significantly higher than the control.

EXAMPLE 3

[0150] A further condom was prepared using the 2 wt % SiO.sub.2 formulation of Example 1 by the same method disclosed in Example 1 but having a lower wall thickness than the 2 wt % SiO.sub.2 condom of Example 1 (20 m as opposed to 25 m). The physical properties were measured in accordance with Example 2.

[0151] The results are shown in Table 3 and FIGS. 2A to 2D. The thicker 2% SiO.sub.2 condom and control condom from Examples 1 and 2 have been included for comparison.

TABLE-US-00003 TABLE 3 Tensile and burst properties of PU condom produced in accordance with Example 3 compared with reference condoms from Example 1 Control PU 2% SiO.sub.2-SM 2% SiO.sub.2-SM Properties (Example 1) (Example 1) (Example 3) Thickness (m) 26 1 25 1 20 1 M300 (MPa) 3.15 0.09 3.47 0.17 3.29 0.19 M500 (MPa) 5.00 0.11 5.30 0.27 5.18 0.33 Force at break (N) 49.25 5.61 64.8 10.7 41.5 3.49 Tensile strength (MPa) 46.93 4.88 65.42 11.02 52.23 8.25 Elongation at break (%) 447 5 462 8 450 14 Burst pressure (KPa) 4.33 0.32 5.2 1.16 3.08 0.55 Burst volume (L) 3.13 0.25 3.70 0.75 2.72 0.48

[0152] The 20 m thickness condom sample at 2 wt % SiO.sub.2 had a lower force at break than both the equivalent sample at 25 m thickness and the control sample at 26 m thickness. However, it was still within the acceptable range for a condom. Moreover, the tensile strength of the 20 um thickness condom sample at 2 wt % SiO.sub.2 was higher than the control sample, while the modulus at 300% elongation and the modulus at 500% elongation were comparable. The burst pressure for the 20 m thickness condom sample at 2 wt % SiO.sub.2 was slightly lower than for the other two samples, but still within the acceptable range.

[0153] Overall, the data demonstrates that the inclusion of SiO.sub.2 nanoparticles in the formulation allows for the thickness of the condom to be reduced while maintaining acceptable physical properties.

EXAMPLE 4

[0154] Scanning electron microscopy (SEM) images were taken of samples cut from condoms prepared in accordance with Example 1 to investigate the surface morphology of condom samples. Each sample was cut into small pieces and then immersed in liquid nitrogen for 1 minute before immediate breaking the sample to prepare a cross-sectioned sample. The sample was placed onto a sample stub before coating by gold under vacuum. Finally, the sample grid was subjected to surface micrograph analysis using a field emission scanning election microscope (FE-SEM).

[0155] SEM micrographs with magnitude of 5000, 10000 and 25000 were taken. For the SiO.sub.2-containing samples, SiO.sub.2 nanoparticles were visible at the interfaces between the polyurethane layers. This provides evidence of the ability of the SiO.sub.2 nanoparticles to migrate to the air-water interface during each coating step and to remain at the interface as each successive film is formed. At 1 wt % SiO.sub.2, the concentration of SiO.sub.2 nanoparticles dispersed in the bulk polyurethane matrix is very low. At 2 wt % and 3 wt % SiO.sub.2, the concentration of SiO.sub.2 nanoparticles dispersed in the bulk polyurethane matrix increases.

EXAMPLE 5

[0156] Scanning electron microscopy (SEM) with energy dispersive x-ray analysis (EDX) was performed on the samples imaged in Example 4 to investigate the elements distributed in the polyurethane matrix.

[0157] The condom sample without SiO.sub.2 mainly contained C and O as the main components of polyurethane. However, a Si component could be observed in the samples with SiO.sub.2, indicating the presence of SiO.sub.2. The SEM-EDX micrographs clearly showed that Si-containing particles are predominantly at the interface between the polyurethane layers. The SEM-EDX micrographs provide further evidence that discrete SiO.sub.2 nanoparticles are able to migrate to the interfaces between the films resulting from each dipping step.

[0158] The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.