The present invention relates to methods for forming foamed polymeric articles and articles produced by such methods. In particular, the invention relates to a method of forming a foamed polymeric article comprising a foamed polymeric material sandwiched between two layers in a mold, wherein the polymeric material comprises a chemical blowing agent, and the expansion of the polymeric material during foaming causes the outer layers of the article to deform so as to provide good contact with the surfaces of the mold. The present invention further relates to foamed polymeric articles formed by the method of the invention having complex surface geometry and/or good continuity of the foam.

Foamed polymeric articles have many uses, including providing cushioning for impact and vibration dampening, resistance to compression, deflection, friction reduction and the like. Depending on the intended use, foamed polymeric articles having various simple structures may be suitable. However, in many cases more complex structures are required, for example if the foamed polymeric articles are intended to fit closely against structures having an uneven surfaces, such as body parts or complex mechanical components, or if additional properties are to be provided by the inclusion of regions having significantly different thicknesses, such as extra thickness to provide improved impact protection in certain areas and reduced thickness to provide greater flexibility in other areas. Such complex foamed polymeric articles may be produced as a single object or may be formed by combining smaller articles on a common base. However, small thin and intricate parts are difficult to manufacture from materials such as polyurethane, and in order to save costs in material and production time, it is preferable to form a number of such parts using a single large forming tool, such as a mold, the individual parts then being separated by cutting after forming. However, the larger the mold, the greater is the differential in density obtained by using traditional polyurethane processing methods. In particular, by the time the reacting/foaming polyurethane reaches the perimeter of the mold, some of the gelling/curing will have already started, and the material in continuous expansion can start ripping, creating an uneven cell structure. Similar problems occur in the manufacture of larger articles having complex structures, i.e. multiple regions of relatively increased thickness and relatively decreased thickness. Thus, traditional methods of forming small, thin and intricate parts and/or complex larger parts in polyurethane generate very large manufacturing reject rates, pushing the price per unit to non-commercial levels and sometimes reaching as high as 50%. Additionally, traditional methods of forming small, thin and intricate parts and/or complex larger parts in polyurethane may also result in the formation of bubbles in the polyurethane, particularly when the polyurethane is sandwiched between two layers, because as the material expands across the complex tool surface air bubbles become trapped. These bubbles can also result in deficiencies in the molded parts, such as weakness or non-uniform protection, and/or may render the parts unsuitable for sale due to aesthetic considerations. Reject rates caused by bubble production are often greater than 30%.

US 201 1/0277923 discloses a molding system that is said to be suitable for molding very thick products by controlling the rate of mold closure and/or interrupting the mold closure. However, this process is restricted to the use of mechanically frothed foams, and is not applicable to chemically foamed polymeric materials, such as chemically foamed polyurethane. In addition this process also relies on a vacuum system within the mold to help conform surface layers to the structure of the mold. Reject rates due to inconsistent foam structure and/or the presence of bubbles using the processes disclosed in US201 1/0277923 are not economically acceptable.

According to the present invention there is provided a method of forming a foamed polymeric article comprising a foamed polymeric material sandwiched between two layers, the method comprising the steps of:

i. applying a layer to a mold comprising at least first and second sections, at least one of the sections comprising a mold cavity having a mold profile, the layer being applied to the section comprising the mold cavity such that the profile of the layer is smoother than the mold profile;

ii. applying a charge of polymeric material onto the layer, the polymeric material comprising a chemical blowing agent;

iii. applying a further layer onto the charge of polymeric material so as to sandwich the polymeric material between the layers; iv. closing the mold thereby spreading the charge of polymeric material between the layers; and

v. chemically blowing the charge of polymeric material on the layer thereby filling the mold cavity.

It will be appreciated that various steps of the method of the present invention may be carried out in various different orders or substantially simultaneously. For example, the further layer may be applied to the section of the mold other than the section to which the layer has been applied, so that the step of applying the further layer onto the charge of polymeric material occurs by closing the mold, i.e. so that steps iii. and iv. are effectively a single step. Similarly, the chemical foaming of the charge of polymeric material may begin as soon as the charge is applied to the layer, so that step v. begins at the same time as, or even before, the closing of the mold (step iv.). Preferably however, no more than 10% of the foaming is completed before the mold is fully closed.

In a preferred embodiment of the present invention, the smoother profile is such that the layer is substantially spaced apart from the mold cavity, and preferably the layer is spaced apart such that it does not contact an inner surface of the mold cavity.

Because the profile of the layer is smoother than the mold profile, the charge of polymeric material may spread more evenly across the layer and, in particular, the formation of air bubbles between the polymeric material and the layer is completely avoided, or at least substantially reduced. This provides substantial improvements in the continuity of the foam, and the reduction or elimination of undesirable bubbles.

Furthermore, as the pressure generated by the chemical foaming of the polymeric material stretches the layer so that it comes into contact with the mold profile, the layer adheres well to the complex structure of the mold profile improving the definition of the surface structure of the foamed polymeric article. This step of the method is particularly facilitated by the inclusion of vents in the section of the mold comprising the mold cavity, the vents allowing air initially present between the layer and the mold profile to escape from the mold, so as to permit improved contact between the layer and the mold profile. The layer also creates a barrier between the polymeric material and the vents in the mold section, preventing the vents becoming blocked by the polymeric material, and avoids the need for release agents which can block vents, add extra cost and cause post process adhesion issues.

Once applied, the layer may be self-supporting in the mold section before foaming of the polymeric material.

Suitably the layer is held under tension after being applied to the section of the mold comprising a mold cavity and preferably it is held taut, providing a good surface for the charge of polymeric material to spread over.

The layer applied to the section of the mold comprising the mold cavity may comprise any material suitable to act as an outer layer of a foamed polymeric article. Suitably the layer comprises a polymer, textile and/or metal. The layer may also be formed from multiple layers of the same or different materials.

In a particular embodiment, the layer applied to the section of the mold comprising the mold cavity comprises a polymer comprising one or more materials selected from plastics, elastomeric materials, polyolefins, polyamides, polystyrenes, ethylene-vinyl acetates, nylons, polyesters, polyethylenes, polytetrafluroethylene, silicones, vinyls, polyurethanes, polyvinyl chloride, latex rubbers, synthetic rubbers, thermoplastic elastomers, or mixtures thereof. In an alternative embodiment of the method of the present invention, the layer comprises a textile which a woven or non-woven fabric comprising natural and/or artificial materials, preferably spandex or elastane, cordura, aramids, cotton or canvas.

The layer applied to the section of the mold comprising the mold cavity may be any suitable thickness, for example 0.001 mm to 3 mm, such as 0.05 to 0.01 mm.

Suitably, the layer applied to the section of the mold comprising the mold cavity will have a relatively low tensile modulus, such that it will stretch under the typical pressures generated by the chemical foaming of the polymeric material, such as 40 to 60 psi. However, a greater range of materials and/or thicknesses may be used in the method of the present invention compared to prior art processes, as in most prior art cases (for example using a vacuum to conform the film to the mold surface) much lower pressures are generated. The additional pressure produced in the method of the present invention also enables higher definition of complex products to be achieved.

Suitably in the method of the present invention, the charge of polymeric material may be applied to the layer in the mold by any suitable method, for example by being poured or injected onto the layer. Preferably, the charge of polymeric material is applied substantially in the middle of the layer, so that it spreads evenly across the layer during foaming.

Suitably the charge of polymeric material may be applied to the layer as a single charge. The size of the charge applied to the layer will depend upon the size of the article or articles to be formed and the size of the mold. Preferably the charge of polymeric applied to the layer is sufficient to cover from 10 to 100% of the layer before the mold is closed. Preferably, following closure of the mold and foaming of the charge of polymeric, the polymeric material will fill from 80 to 110% of the mold cavity.

Any polymeric material capable of being chemically foamed to form a foamed polymeric article when sandwiched between two suitable layers may be used in the method of the present invention. Suitably the polymeric material is selected from ethylene vinyl acetate, an olefin polymer, an ethylene polymer, polypropylene, LDPE, HDPE, LLDPE, natural elastomer (e.g. latex), synthetic elastomer (e.g. silicone rubber, polyurethane, ethylene propylene rubber such as EPDM) or thermoplastic elastomer (e.g. polyester).

In a particular embodiment of the method of the present invention the polymeric material comprises a polymer-based material exhibiting dilatancy, preferably a silicone polymer, for example a borated siloxane polymer, such as PBDMS. ln a particular embodiment of the method according to the present invention, the foamed polymeric material is an elastic, energy absorbent material which exhibits a resistive load under deformation which increases with the rate of deformation, such as a composite material which comprises i) a first polymer-based material and ii) a second polymer-based material, different from i), which exhibits dilatancy in the absence of i), wherein the second polymer-based material ii) is entrapped in a matrix of the first polymer-based material i), and which is prepared by incorporating the second polymer- based material ii) with the first polymer-based material i) prior to foaming. Particularly suitable elastic, energy absorbent materials for use in the method of the present invention are disclosed in WO 03/055339 and WO 2005/000966.

Any suitable material may be used as the chemical blowing agent in the methods according to the present invention. A chemical blowing agent will cause the charge of polymeric material to foam and may also cause the resulting foam to cure and/or set. Suitable chemical blowing agents include hydrocarbons such as isopentane and cyclopentane or acetals such as dimethoxymethane If required, additional agents may also be included in the charge of polymeric material, such as separate cure/setting agents.

The concentration of chemical blowing agent used in the methods according to the present invention will depend upon the nature of the polymeric material and the chemical blowing agent and other factors, including the degree of foaming required and the molding conditions. Examples of suitable concentrations include from 0.1 wt% to 10 wt%, such as 3 wt% to 5 wt%.

Suitably the further layer is applied to the section of the mold to which the layer has not been applied and is self-supporting and/or is held under tension, and preferably held taut.

The further layer may comprise any material suitable to act as an outer layer of a foamed polymeric article. The further layer may be the same as or different to the layer applied to the section of the mold comprising a mold profile. Suitably the further layer comprises a polymer, textile and/or metal. The further layer may also be formed from multiple layers of the same or different materials.

In a particular embodiment, the further layer comprises a polymer comprising one or more materials selected from plastics, elastomeric materials, polyolefins, polyamides, polystyrenes, ethylene-vinyl acetates, nylons, polyesters, polyethylenes, polytetrafluroethylene, silicones, vinyls, polyurethanes, polyvinyl chloride, latex rubbers, synthetic rubbers, thermoplastic elastomers, or mixtures thereof. In an alternative embodiment of the method of the present invention, the further layer comprises a textile which a woven or non-woven fabric comprising natural and/or artificial materials, preferably spandex or elastane, cordura, aramids, cotton or canvas.

The further layer may be any suitable thickness, for example 0.001 mm to 3 mm, such as 0.05 to 0.01 mm.

In a particular embodiment, the layer applied to the section of the mold comprising the mold cavity, or the further layer applied to the other mold section, comprises or includes a layer of heat-sensitive adhesive, i.e. it may comprise a heat-sensitive adhesive or may be formed from a material that is not a heat-sensitive adhesive but to which a heat-sensitive adhesive is applied before, during or after the forming of the foamed polymeric article. The inclusion of a heat-sensitive adhesive on the outer surface of foamed polymeric article is particularly advantageous if the article is to be attached to a textile, as the heat sensitive-adhesive may be used to bond the article to the textile.

Preferably in the methods of the present invention spreading of the charge of polymeric material is caused by pressure from the mold, and particularly by the application of the further layer to the upper surface of the charge of polymeric material by the closing of the mold.

In a particularly preferred embodiment, the method according to the present invention comprises deforming at least one of the layers, preferably the further layer, to form a convex shape with respect to the mold. In this embodiment, the deforming may be caused by a protrusion on the relevant mold section, preferably located substantially at the centre of the section. Preferably the protrusion is removable and/or retractable.

The protrusion used to deform the layer may be actively removed/retracted during the method or may be caused to retract by the expansion of the polymeric material during foaming.

By deforming the further layer to form a convex shape with respect to the mold portion, the relatively raised portion of the further layer comes into contact with the charge of polymeric material during the closing of the mold before other sections of the further layer, and, where the relatively raised portion is substantially central, this will cause air present between the upper surface of the charge of polymeric material and the further layer to move laterally away from the point of contact. This continues as more of the further layer is brought into contact with the charge of polymeric material during closing of the mold, effectively causing all of the air that might have been trapped between the charge of polymeric material and the further layer to be removed laterally, and avoiding or substantially reducing the formation of bubbles between the polymeric material and the further layer. Thus, the combination of this step with the expansion of the polymeric material during foaming and the employment of a relatively smooth profile for the layer to which the charge of polymeric material is applied can totally eliminate, or at least substantially reduce, the formation of bubbles in foamed polymeric articles produced by the method.

In a particular embodiment of the method according to the present invention, both sections of the mold comprise a mold cavity, enabling foamed polymeric articles having complex surface geometry on both the upper and lower surfaces to be produced, and undercuts in the geometry can be produced due to the central parting line where the mold shuts. Preferably in the methods according to the present invention, at least one section of the mold is heated, for example to a temperature of from 25 to 120°C, such as from 30 to 100, for example 40 to 60°C. Any suitable mold residence time may be used in methodes according to the present invention, depending upon the materials used and the molding conditions. However, suitable mold residence times are from 2 to 15 minutes, such as 10 minutes. Methods according to the present invention can produce much greater pressures within the mold compared to processes in which the surface of films are conformed to the mold only by a vacuum, for example 4 to 6 times greater pressures. However, in a particular embodiment of a method according to the present invention, the closed mold may be held under vacuum, for example so that the vacuum aids in conforming the layer applied to the section comprising the mold cavity to the mold profile, and in this case pressures of 5 to 7 times greater than conventional in mold pressures can be produced. This extra force can be used to reproduce finer details in the mold or to push thicker, stronger films into the mold cavity compared to prior art processes. The present invention also provides a foamed polymeric article comprising a foamed polymeric material sandwiched between two layers formed according to the method of the present invention.

By use of the methods of the present invention, foamed polymeric articles having very good foam consistency and with virtually no, or substantially reduced, undesirable bubbles may be produced. For example, where multiple parts are formed using a single tool, at least 20 parts can be produced all weighing within one gram of each other. Additionally, foamed polymeric articles produced by the method of the present invention may have complex geometries, including very thin regions or even regions of effectively zero thickness. Furthermore, where multiple components are formed in a single tool, very small parts may be produced accurately, for example parts having a volume of less than 1 cm ³ and/or parts having widths of as low as 1 mm.

The present invention further provides a protective pad formed from a foamed polymeric material according to the present invention. Such protective pads may be formed either as a single component having a complex surface geometry, or may be formed by combining a number of smaller components on a common base material. The present invention further provides a textile article comprising one or more foamed polymeric articles according to the present invention and/or one or more protective pads according to the present invention attached to a textile by a layer of heat- sensitive adhesive. The heat-sensitive adhesive may be applied to the foamed polymeric article or protective pad after it has been formed by a method according to the present invention or during the process of forming. For example, one of the layers between which the foamed polymeric material is sandwiched may comprise or include a heat-sensitive adhesive. After forming, the foamed polymeric article or protective pad may be attached to the textile by placing it in contact with the textile so that the heat- sensitive adhesive contacts the textile, and then heating so that the heat-sensitive adhesive fuses the article or pad to the textile.

The present invention will now be described by way of example and with reference to the accompanying Figures, in which:

Figure 1 is a schematic diagram depicting a first mold section having a layer applied thereto in a first stage of a method according to an embodiment of the present invention; Figure 2 is a schematic diagram showing a second stage of a method according to the embodiment of the present invention;

Figure 3 is a schematic diagram showing a third stage of a method according to the embodiment of the present invention;

Figure 4 is a schematic diagram showing a fourth stage of a method according to the embodiment of the present invention; and

Figure 5 is a schematic diagram showing a fourth stage of a method according to an alternative embodiment of the present invention.

The following Examples illustrate the invention. Example 1

A first stage of a method according to an embodiment of the present invention is illustrated in Figure 1. A first mold section 1 comprising a mold cavity 3 defined by a mold profile 5 is provided, and a first layer 7 comprising a thermoplastic polyurethane (Bemis OT100) is disposed over the mold cavity 3 so that the profile of the first layer 7 is smoother than the mold profile 5.

A second stage in the method is shown in Figure 2. As shown in Figure 2, a second mold section 9 having a relatively smooth mold profile 1 1 is provided, and a second layer 13 comprising a thermoplastic polyurethane (Bemis OT100) is applied thereto. The second mold section 9 further comprises a retractable pin 15 which is extended so that the second layer 13 is deformed to form a convex shape with respect to the second mold section 9.

At substantially the same time, a charge of polymeric material 17 is applied to the first layer 7 at substantially the centre thereof. The charge of polymeric material 17 comprises a two part polyether based thermoplastic polyurethane, comprising a PU system, such as modelling foam referenced as J-Foam 7087, marketed by Jacobson Chemicals Ltd., premixed with a dilatant and a chemical blowing agent.

As the first layer 7 is taut, application of the charge of polymeric material 17 thereto does not substantially deform the first layer, so that it does not initially protrude into the mold cavity 3 or come into contact with the mold profile 5.

A third stage in the method of the present invention is shown in Figure 3. As shown in Figure 3, the first mold section 1 and the second mold section 9 are brought into contact, closing the mold cavity 3, and at the same time the charge of polymeric material 17 is spread outwards, so as to substantially cover all of the first layer 7, which is partially extended into the mold cavity 3 but which does not fully fill the cavity, so that the first layer 7 is in only partial contact with the mold profile 5. During the closure of the mold cavity 3, the retractable pin 15 at least initially remains extended from the second mold section 9, so that the central region of the second layer 13 contacts the charge of polymeric material 17 before the peripheral region of the second layer 13. This facilitates spreading of the charge of polymeric material 17 across the surface of the first layer 7, and also displaces air present between the second layer 13 and the charge of polymeric material 17 laterally, so that it is not entrapped between the second layer 13 and the polymeric material 17.

As the first layer 7 begins to protrude into the mold cavity 3 air present in the mold cavity 3 escapes therefrom via channels (not shown) in the first mold section 1.

During the forming process, the first mold section 1 and second mold section 2 are maintained at a temperature of 55°C A fourth stage of the method is shown in Figure 4. As shown in Figure 4, in the fourth stage illustrated, the retractable pin 15 has been displaced completely into the second mold section 9 so that the second layer 13 is flush with the mold profile 1 1 of the second mold section 9. Additionally, chemical foaming of the charge of polymeric material 17 has caused the polymeric material to expand so that the first layer 7 has been displaced fully into the mold cavity 3 and is in close contact with the mold profile 5 of the first mold section 1. All air previously present in the mold cavity 3 has been removed therefrom through channels (not shown) present in the first mold section 1 , and air present between the second layer 13 and the charge of polymeric material 17 before closure of the mold cavity 3 has been displaced laterally from between the first mold section 1 and second mold section 9.

The polymeric material 17 is retained in the mold for approximately 10 minutes. Following setting of the charge of polymeric material 17 a foamed polymeric article 19 is formed comprising a foamed polymeric material 17 sandwiched between the first layer 7 and the second layer 13.

Once the first mold section 1 and the second mold section 9 are separated, the foamed polymeric article 19 may be removed from the mold cavity 3. The foamed polymeric article has a substantially flat first surface and a second surface having a complex geometry, as defined by the mold profile 5 of the first mold section 1. The foamed polymeric article 19 has a substantially uniform consistency across the article and is substantially free of unwanted bubbles.

Example 2

The fourth stage of an alternative embodiment of a method according to the present invention is illustrated in Figure 5. As shown in Figure 5, the first mold section 1 corresponds generally to the first mold section 1 shown in Figures 1 to 4, and comprises a mold cavity (no longer visible) and a mold profile 5 having a complex geometry. However, whilst the second mold section 21 corresponds generally to the second mold section 9 as shown in Figures 1 to 4 it differs therefrom, in that it also comprises a mold cavity (not visible) and a mold profile 23 having a complex surface geometry.

In this alternative embodiment, a first layer 7 corresponding generally to the first layer used in the method shown in Figures 1 to 4 is applied to the first mold section 1 and a second layer 13 corresponding generally to the second layer 13 used in the method illustrated in Figures 1 to 4 is applied to the second mold section 21. However, when the second layer 13 is applied to the second mold section 21 it does not initially protrude into the mold cavity of the second mold section 21 and does not contact the mold profile 23 of the second mold section 21. The displacement of the second layer 13 from the mold profile 23 may be facilitated by use of a retractable pin 15 present in the second mold section 21 ; however, if the second layer 13 is held taut the use of the retractable pin 15 is not necessary, and this may be retained in a retracted position within the second mold section 21.

As discussed with respect to Figures 2 and 3, a charge of polymeric material 17 corresponding to the charge of polymeric material 17 discussed with respect to Figures 2 and 3 is applied to the first layer 7, without causing the first layer 7 to substantially protrude into the mold cavity of the first mold section 1. The second layer 13 is then brought into contact with the upper surface of the charge of polymeric material 17 by bringing the second mold section 21 into contact with the first mold section 1. This causes the charge of polymeric material 17 to spread across the surface of the first layer 7 and the second layer 13, so as to substantially cover both surfaces. The foaming of the charge of polymeric material 17 causes the material to expand, so that the first layer 7 protrudes into the mold cavity of the first mold section 1 and comes into close contact with the mold profile 5 of the first mold section 1. Similarly, the expansion of the polymeric material during foaming also causes the second layer 13 to extend into the mold cavity of the second mold section 21 and to come into close contact with the mold profile 23 of the second mold section 21. Once foaming of the polymeric material 17 is complete, the first mold section 1 and second mold section 21 are separated, and a foamed polymeric article 25 is removed. The foamed polymeric article 25 comprises a foamed polymeric material 17 sandwiched between the first layer 7 and second layer 13 and both the first layer 7 and second layer 13 have complex surface geometries.

Example 3

Complex parts, in the form of protective gloves, were prepared by a method according to the present invention, corresponding to the method of Example 1. The products were inspected, and a defect rate was calculated, together with the total number of products considered to be unusable because of the presence of bubbles and/or being incomplete and/or having poor skin or foam. The results are shown in Table 1. Method According to the Invention - Table 1

Poor

Total parts Defect Incomplete

Bubbles product

made Rate part

skin/foam

Quantity 7603.0 130.0 1 19.0 7.0 4.0

Percentage 1.7% 1.6% 0.1 % 0.1 % A conventional prior art process was used to produce less complex parts by a polyurethane casting method, and these parts were assessed in the same manner as the parts produced by the method according to the present invention. The results are shown in Table 2.

Conventional Polyurethane Casting Method - Table 2

A comparison of the results shown in Tables 1 and 2 shows that the method according to the present invention has a much lower defect rate, and produces far fewer parts having unacceptable bubbles and/or being incomplete and/or having poor skin or foam characteristics. It is believed that if the complex parts produced by the method according to the present invention had been produced by the traditional polyurethane casting method, the reject rates would have been even higher.