Reduced density impact protector

Abstract

Various aspects of the invention relate to methods for manufacturing impact protectors of reduced density for the same performance, and protectors or garments comprising protectors formed by such meth

Description

FIELD OF THE INVENTION The present invention relates to a method of reducing the density of an impact protector compliant with one of EN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018, as well as impact protectors obtained or obtainable therefrom, and garments comprising said impact protectors. BACKGROUND OF THE INVENTION An impact protector generally comprises one or more energy absorbing and / or impact spreading materials designed to offer impact attenuation to areas of protection, for example, a part of the human body such as a limb or the back. Impact protectors may be worn on the body or incorporated into layers of protective clothing. An impact protector may be worn for safety where it is anticipated that a wearer may be involved in an impact such as a collision. If the wearer of the impact protector is involved in such an impact event, the impact protector absorbs and / or dissipates the forces created by the impact and attenuates the forces being transmitted to the body. Accordingly, impact protectors, when worn, may reduce injuries in subjects involved in impact collisions, such as impacts resulting from falling off a motorcycle. As such, impact protectors find utility in a wide variety of applications such as protective clothing for motorcyclists and workers in various industries. EN 1621-1:2012, EN 1621-2:2014, and EN 1621-3:2018 are European Standards for motorcyclists' protective clothing against mechanical impact. EN 1621-1:2012 relates to limb joint protectors, such as shoulder, elbow, hip, and knee protectors, EN 1621-2:2014 relates to back protectors, such as full back, central back, and lower back protectors, and EN 1621-3:2018 relates to chest protectors. Amongst other requirements, such as sizing, ergonomics, and innocuousness, EN 1621-1:2012, EN 1621-2:2014, and EN 1621-3:2018 each provide a standardised requirement for impact attenuation provided by the impact protector. Testing of an impact protector for compliance with either of these standards, as well as preparation of an impact protector which complies with either of these standards is within the capabilities of the skilled person. These standards are readily available can be found on the respective Catalogues of the European Committee for Standardisation (CEN). A variety of materials are known to provide energy absorbance and / or impact spreading to an impact protector. Of these materials, polyurethanes are widely used. Polyurethane is a strong material that can provide sufficient resistance to impact by absorbing forces generated by a collision. Polyurethanes are alternating copolymers that are typically synthesized by reacting a polyol with a polyisocyanate, such as a diol and diisocyanate. An Example of a common polyurethane formed by polymerisation of ethylene glycol with 4,4'-methylenediphenyl diisocyanate (MDI) is shown below. Polyurethanes made using various polyol and various polyisocyanate monomers are well known in the art. In some applications a mixture of different polyols and / or a mixture of different polyisocyanates can be used. The specific type of monomers from which a polyurethane material is derived may affect various physical properties of the polyurethane composition. Catalysts are typically used to induce the reaction of the polyols with the polyisocyanates so as to form the polyurethane material (a process known as curing). Catalysts also typically affect the rate of curing. Heat is also typically used in the curing process. In a typical procedure for making a polyurethane article, a liquid polyol composition containing one or more polyols, a catalyst and optionally other additives is mixed with one or more polyisocyanates to form a resin which is then shaped using known process such a molding or extrusion. Heat may then be applied, for example, to a mold causing the resin to cure into a solid polyurethane article shaped in the shape of the mold. Polyurethane may have a foamed structure to some degree which may occur when gas is introduced, either via reaction of the isocyanate with water to form carbon dioxide, and / or with the introduction of other blowing agents, such as nitrogen, fluorinated hydrocarbons, or dimethyl ether. The density can be easily adjusted by the introduction of water, or other blowing agents during polymerisation. Additionally, the density may be adjusted by controlling the shot weight, which refers to the mass of the mixture of monomers which is introduced into a mold compared to the capacity of the mold. A larger shot weight will provide a denser polyurethane material. Polyurethane densities can range very broadly, for example, from approximately 0.03 to 0.9 g / cm3. There are also various processing parameters known to the skilled person which can be used to adjust the density of a polyurethane, for example, features such as molding temperature, reaction time, and catalysis can be used to fine tune the density of a polyurethane material. Polyurethane materials of various densities are known in the art and methods of fine tuning the density of a polyurethane to a desired value are within the capabilities of the skilled person. A relatively low density is a desirable property in an impact protector. Reduction in weight gives the user a more comfortable experience and reduces the overall weight of the impact protector or garment comprising one or more impact protectors that they wear. This becomes increasingly significant in applications where multiple impact protectors may be worn around various parts of the body, for example, a jacket containing, shoulder and elbow pads or a pair of trousers containing knee and hip pads. Reduction in the density of an impact protector additionally provides environmental benefits due to reduced energy usage to transport the product, for example, from factory to the end user. Reduction of density also allows for a reduced mass of materials to be consumed in order to produce the impact protector thus conserving resources as well as reducing waste and pollution once the impact protector is disposed of at the end of its life. However, reduction in density comes at the significant cost of reduced energy dissipation and thus reduced impact attenuation properties. For example, if the polyurethane has an increasingly foamed structure with larger pores, this will reduce the stiffness of the material which will ultimately lead to the impact protector no longer satisfying the impact attenuation requirements of EN 1621-1:2012, EN 1621-2:2014, orEN 1621-3:2018. Various methods of reducing the weight of an impact protector without reducing the density have been used in the art, however, such methods provide significant drawbacks. For example, a smaller coverage area reduces protection and may contravene the coverage area requirements of EN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018, a thinner impact protector will reduce impact attenuation properties, and reduced volume will also reduce energy dissipation. As impact protectors will usually be designed to have the minimum weight possible whilst still satisfying the desired impact attenuation requirements of EN 1621-1:2012, EN 1621-2:2014, orEN 1621-3:2018, any one of the above issues can lead to an unacceptable failure to meet these standards. The present inventors have devised a new method of reducing the density of an impact protector whilst surprisingly avoiding the loss of impact attenuation properties desired, thus maintaining compliance with, for example, EN 1621-1:2012, EN 1621-2:2014, orEN 1621-3:2018. This method allows for density optimisation without making any physical changes to the design of the impact protector or to the species of monomers used in synthesis of the polyurethane. As discussed above, polyurethanes are typically prepared from a combination of monomers of one or more polyols and one or more polyisocyanates. The relative amounts of polyols and polyisocyanates used can be defined with respect to a stoichiometric ratio. In the context of the present invention, the stoichiometric ratio is defined as the ratio of alcohol groups in the one or more polyols to the isocyanate groups in the one or more polyisocyanates, from which the polyurethane material is derived. A stoichiometric ratio of 100:100 indicates an equivalent amount of hydroxyl groups of the polyols and of isocyanate groups. If the stoichiometric ratio is 100: >100 then some of the isocyanate remains unreacted, if the stoichiometric ratio is 100: <100 then some of the polyol is left unreacted. In the context of the present invention, the term stoichiometric ratio is used to describe the ratio of hydroxyl groups of the polyols : isocyanate groups in both a mixture of polyol and polyisocyanate monomers (either pre- or post-mixing of the monomers), from which the polyurethane product is derived. It is important to appreciate that this ratio is not necessarily the same as the molar ratio of polyol to polyisocyanate, but is the ratio of hydroxyl groups to isocyanate groups. Typically, the polyol and the polyisocyanate monomers will contain two alcohol groups, and two isocyanate groups, respectively. However, a polyol may contain three or more alcohol groups, and polyisocyanate may contain three or more isocyanate groups. Additionally, either or both of the one or more polyols, and / or the one or more polyisocyanates may be a mixture of different species. The stoichiometric ratio of a polyurethane may be easily calculated based on the mass and molecular structure of known precursor monomers. Additionally, the equivalent weights (eq. wt.) of the polyol and polyisocyanate can be used to determine stoichiometric ratio based on the ratio of reactive groups in a given weight of monomer compound. The equivalent weight tells you how many grams of a product you need to provide one equivalent of reactive group. The isocyanate and polyol equivalent weights can be calculated as shown below. 4202 Isocyanate equivalent weight =--------------------g / eq 7 6 weight percent NCO6 / M 56100 Polyol equivalent weight = -— ---------—g / eq hydroxyl value The hydroxyl value (OHV) can be determined experimentally using the following equation: OHV = 56.1 x N x (Vb - Vac) ------—+AV ^ac Where OHV is the hydroxyl value; Vb is the amount (ml) potassium hydroxide solution required for the titration of the blank; Vac is the amount (ml) of potassium hydroxide solution required for the titration of the acetylated sample; Wac is the weight of the sample (in grams) used for acetylation; N is the normality of the titrant; 56.1 is the molecular weight of potassium hydroxide (g / mol); and AV is a separately determined acid value of the chemical substance. The content of free hydroxyl groups in a substance can also be determined by methods other than acetylation. ASTM D4274, ASTM D 1957 and ASTM E222-10 describe several versions of methods of determining hydroxyl value. The number of functional groups, such as isocyanate (NCO) or hydroxyl (OH) groups in a given mass of polyisocyanate or polyol monomer can be calculated as shown below. Number of NCO groups Number of OH groups mass of polyisocyanate monomer (g) isocyanate equivalent weight (g / eq) mass of polyol monomer (g) polyol equivalent weight (g / eq) The number of OH and NCO groups can then be used to calculate a ratio of OH : NCO groups, or an isocyanate index. The "isocyanate index" sometimes referred to as the “index” is a term of art used in the field of polyurethane chemistry and manufacturing. Isocyanate index describes the amount of reactive NCO groups present, relative to the amount of reactive OH groups in a polyurethane formulation, and is expressed as a single number, calculated by (NCO groups / OH groups) x 100. An isocyanate index of 100 indicates equivalent amounts of OH and NCO groups, which are thus in a stoichiometric ratio of 100:100. If the isocyanate index is greater than 100, then some of the isocyanate remains unreacted and the stoichiometric ratio of OH : NCO groups is 100: >100. If the isocyanate index is less than 100, then some of the polyol is left unreacted and the stoichiometric ratio of OH : NCO groups is 100: <100. These isocyanate index and stoichiometric ratio calculations are within the common general knowledge of the skilled person, who would be able to prepare a polyurethane from a chosen stoichiometric ratio. The present inventors have discovered that increasing the isocyanate index of a polyurethane material has a positive impact on the stiffness of the polyurethane material. It has been found that as the isocyanate index of the polyurethane material is increased, the stiffness of the polyurethane material will also increase, which provides increased impact attenuation properties. SUMMARY OF THE INVENTION The present inventors have devised a method of reducing the density of an impact protector without the associated unacceptable loss in impact attenuation properties which result from said reduced density. An impact protector prepared or preparable by this method will therefore enjoy a hitherto unachievable reduced density, as compared to a corresponding comparative impact protector, whilst maintaining impact attenuation properties. According to a first aspect of the invention, there is provided a method of reducing the density of an impact protector compliant with one ofEN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018, the method comprising the steps of: i) preparing a first impact protector compliant with one of EN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018, from a first polyurethane material having a density of Y g / cm3 and a stoichiometric ratio of 100:X; wherein the stoichiometric ratio is defined as the ratio of alcohol groups in the one or more polyol : isocyanate groups in the one or more polyisocyanate from which the polyurethane material is derived; ii) preparing a second polyurethane material by reacting the same one or more polyol and the same one or more polyisocyanate monomers from which the first polyurethane material is derived, in a stoichiometric ratio of 100 : (1.033 X or more); and iii) controlling the density of the second polyurethane material to be 0.95 Y g / cm3 or less; so as to produce a reduced density impact protector compliant with the same one of EN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018. According to a second aspect of the invention, there is provided an impact protector obtained or obtainable by the method of the present invention. According to a third aspect of the invention, there is provided a garment comprising an impact protector obtained or obtainable by the method of the present invention. DETAILED DESCRIPTION OF THE INVENTION According to the first aspect of the invention, there is provided a method of reducing the density of an impact protector compliant with one ofEN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018, the method comprising the steps of: i) preparing a first impact protector compliant with one of EN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018, from a first polyurethane material having a density of Y g / cm3 and a stoichiometric ratio of 100:X; wherein the stoichiometric ratio is defined as the ratio of alcohol groups in the one or more polyol : isocyanate groups in the one or more polyisocyanate from which the polyurethane material is derived; ii) preparing a second polyurethane material by reacting the same one or more polyol and the same one or more polyisocyanate monomers from which the first polyurethane material is derived, in a stoichiometric ratio of 100 : (1.033 X or more); and iii) controlling the density of the second polyurethane material to be 0.95 Y g / cm3 or less; so as to produce a reduced density impact protector compliant with the same one of EN 1621-1:2012, EN 1621-2:2014 or EN 1621-3:2018. Preparing a polyurethane material by reacting one or more polyol and one or more polyisocyanate monomers in a stoichiometric ratio of 100 : X will lead to a polyurethane material having an isocyanate index of (X / 100) x 100 = X. So for example, Preparing a polyurethane material by reacting one or more polyol and one or more polyisocyanate monomers in a stoichiometric ratio of 100 : 1.033 X will lead to a polyurethane material having an isocyanate index of (1.033 X / 100) x 100 = 1.033 X. Any of the stoichiometric ratios as disclosed herein may thus also be expressed as isocyanate indexes and vice versa. EN 1621-1:2012, EN 1621-2:2014, and EN 1621-3:2018 each specify two separate performance levels, as well as some optional tests under extreme conditions. In each case, Level 1 is a lower standard under which higher peak transmitted force values are acceptable, and Level 2 is a higher standard under which lower peak transmitted force values are acceptable. In the context of the present invention, the terms “compliant with one of EN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018” and “compliant with the same one of EN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018” are understood to refer to compliance any one of the tests outlined in EN 1621-1:2012, EN 1621-2:2014, and EN 1621-3:2018, for example, the Level 1 standard, unless otherwise specified. Where reference is made to “compliant with the same one of EN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018” this is understood to refer to compliance with the same specific test or combination of tests as the first oneofEN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018 referred to in that context. For example, the method of the present invention includes a method of reducing the density of an impact protector compliant with one of EN 1621-1:2012 (Level 1), EN 1621-2:2014 (Level 1), or EN 1621-3:2018 (Level 1), in this case, the first impact protector and the reduced density impact protector produced in step iii) are both compliant with one of EN 1621-1:2012 (Level 1), EN 1621-2:2014 (Level 1), or EN 1621-3:2018 (Level 1). Nevertheless, it is preferable that the first impact protector and the reduced density impact protector produced in step iii) are both compliant with one of EN 1621-1:2012 (Level 2), EN 1621-2:2014 (Level 2), or EN 1621-3:2018 (Level 2). Compliance with Level 2 will necessarily include compliance with the lower standard of Level 1. For Level 1 and Level 2 of each of EN 1621-1:2012, EN 1621-2:2014, and EN 1621-3:2018, the impact protector must not exceed the given maximum peak transmitted force values under both ambient conditions (temperature of (23 ± 2) °C and relative humidity of (50 ± 5) %), as well as under wet conditions after hydrolytic ageing. EN 1621-1:2012, EN 1621-2:2014, and EN 1621-3:2018 each also specify certain optional test criteria, these are similar impact attenuation tests at a high temperature (40 °C), and / or a low temperature (-10 °C). The exact conditions necessary to perform wet, high temperature, and low temperature testing are outlined in the relevant EN standard. Preferably, the first impact protector is compliant with one or both of the high temperature (40 °C) impact test and / or the low temperature (-10 °C) impact test requirements of one ofEN 1621-1:2012, EN 1621-2:2014, orEN 1621-3:2018, and the reduced density impact protector is also compliant with the same one or both of the high temperature (40 °C) impact test and / or the low temperature (-10 °C) impact test requirements of the same one ofEN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018. More preferably, the first impact protector is compliant with both of the high temperature (40 °C) impact test and the low temperature (-10 °C) impact test requirements of EN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018, and the reduced density impact protector is also compliant with both of the high temperature (40 °C) impact test and the low temperature (-10 °C) impact test requirements of the same EN 1621-1:2012, EN 1621-2:2014, orEN 1621-3:2018. As high temperature (40 °C), and low temperature (-10 °C) conditions both change the impact attenuation properties of the impact protector, more fine-tuned impact attenuation properties may be required in order to maintain the suitable impact protection needed to pass one of EN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018, at high and / or low temperature conditions, in addition to the standard ambient and wet conditions. An impact protector that is designed to pass a higher standard of impact attenuation test, such as Level 2, or for example, the high temperature (40 °C) standard will require a higher degree of impact attenuation than an impact protector that is designed to pass only the lower Level 1 standard. In order to minimise density, most impact protectors will be designed with the minimum density required to still pass the desired impact attenuation standard. Therefore, no matter which impact attenuation standard is desired, the present invention may be used to provide a reduced density impact protector that passes that same given impact attenuation standard. As would be appreciated high temperature (40 °C) or low temperature (-10 °C) conditions would generally change the impact attenuation properties of a polyurethane impact protector. Passing one or more of these optional tests thus represents an even more advantageous and unexpected conservation of impact attenuation properties. The practical advantages of this are obvious, as the impact protectors may thus reliably retain protection in more extreme conditions which may be encountered by motorcyclists and workers in various industries. In the context of an impact protector intended for protection of the human body, a zone of protection is specified which corresponds to a part of the human body which is protected. Preferably, the first impact protector and the reduced density impact protector are both configured to provide protection to the same zone of protection. EN 1621-1:2012 specifies the following body regions as zones of protection which limb joint protectors may be configured to protect: the shoulder (protector “S”); the elbow and forearm (protector “E”); the hip (protector “H”); the knee and upper tibia (Protector “K”); the knee, upper and middle tibia (Protector “L” + “K”); and the leg below protector “K” (protector “L”). Preferably, the first impact protector and the reduced density impact protector are both configured to provide protection to one of these zones of protection, more preferably the first impact protector and the reduced density impact protector are both configured to provide protection to the same one of these zones of protection. EN 1621-2:2014 specifies the following body regions as zones of protection which back protectors may be configured to protect: the central back and scapula area (full back protector); the central back (central back protector); and the lumbar region (lower back protector). Preferably, the first impact protector and the reduced density impact protector are both configured to provide protection to one of these zones of protection, more preferably the first impact protector and the reduced density impact protector are both configured to provide protection to the same one of these zones of protection. EN 1621-3:2018 specifies the chest as a zone of protection and categorises impact protectors as either a full chest protector or a divided chest protector. A full chest protector is designed as a single piece with dimensions and form to protect the rider’s chest. A divided chest protector is designed in two separate halves with dimensions and form to protect the rider’s chest. Either a full chest protector or one half of a divided impact protector can be considered an impact protector in the context of the present invention. Preferably, the first impact protector and the reduced density impact protector are both configured to provide protection to either the whole chest or half of the chest. Preferably, the first impact protector and the reduced density impact protector are both configured to provide protection to a substantially identical zone of protection. This means that both will provide a substantially identical coverage area when applied to the body. As would be appreciated, impact protectors may comprise various physical structures. For example, certain physical structures are well suited for aiding impact attenuation, for example, spacers, crumple zones, and protrusions are all physical structures which may be present on an impact protector to aid impact attenuation. Preferably, the first impact protector and the reduced density impact protector both have substantially the same overall physical structure. In the context of the present invention, the overall physical structure of an impact protector is understood to refer only to those features which aid impact attenuation and provide coverage over the zone of protection. For example, other differences in shape such as inconsequential modifications which do not contribute towards impact attenuation, coverage over additional areas other than the intended zone of protection, or minor features such as logos or text which may be engraved onto the impact protector are not considered to prevent an impact protector having the same overall physical structure. Additionally, several zones of protection exist on areas of the human body which have a symmetrical mirror image. As would be appreciated, limb joint protectors designed to protect the knee, shoulder, elbow etc, will usually be used in symmetrical pairs in order to provide protection to the left and right limb. Similarly, two separate halves of a divided chest protector will usually be used in a symmetrical pair. For the avoidance of doubt, in the context of the present invention, references to a pair of impact protectors having, the same zone of protection, a substantially identical zone of protection, and / or substantially the same overall physical structure are intended to encompass symmetrical pairs of impact protectors. An impact protector being a mirror image of, or symmetrical to, another impact protector is not considered to prevent the two impact protectors from having the same zone of protection, a substantially identical zone of protection, and / or substantially the same overall physical structure. This is because for the purposes of the present invention, a symmetrical impact protector would have the same impact attenuation properties with respect to a symmetrical body part. In step ii) of the method of the present invention a second polyurethane material is prepared by reacting the same one or more polyol and the same one or more polyisocyanate monomers from which the first polyurethane material is derived, in a stoichiometric ratio of 100 : (1.033 X or more). Preferably, the stoichiometric ratio is 100 : (1.035 X or more); more preferably 100 : (1.037 X or more); even more preferably 100 : (1.040 X or more); even more preferably 100 : (1.043 X or more); even more preferably 100 : (1.045 X or more); even more preferably 100 : (1.047 X or more); most preferably 100 : (1.050 X or more). A maximum increase in stoichiometric ratio may also be desirable in some applications. Depending on the specifics of the one or more polyols and / or one or more polyisocyanate monomers some isocyanate index values may lead to undesirable properties such as stickiness and difficulty in processing. For example, it is usually preferable that the stoichiometric ratio of the second polyurethane material does not exceed 100:140, in some applications it is preferable that the stoichiometric ratio does not exceed 100:120, and more preferably does not exceed 100:110. The skilled person would be able to determine an appropriate upper and lower limit for the stoichiometric ratio based on the one or more polyols and one or more polyisocyanates in question. For example, it may also be preferable that the stoichiometric ratio of the second polyurethane material is no lower than 100:70, preferably no lower than 100:80, more preferably no lower than 100:90. For example, the second polyurethane material may be prepared by reacting the same one or more polyol and the same one or more polyisocyanate monomers from which the first polyurethane material is derived, in a stoichiometric ratio of 100 : (1.033 X to 1.200 X); preferably 100 : (1.033 X to 1.175 X); more preferably 100 : (1.033 X to 1.150X); even more preferably 100 : (1.033 X to 1.125 X); even more preferably 100 : (1.033 X to 1.100 X); even more preferably 100 : (1.033 X to 1.075 X); most preferably 100 : (1.033 X to 1.050 X). For example, the second polyurethane material may be prepared by reacting the same one or more polyols and the same one or more polyisocyanate monomers from which the first polyurethane material is derived, in a stoichiometric ratio of from 100:1.035 X to 100 : 1.200 X; preferably from 100 : 1.037 X to 100 : 1.175 X; preferably from 100 : 1.040 X to 100 : 1.150 X; more preferably from 100 : 1.043 X to 100 : 1.125 X; even more preferably from 100 : 1.045 X to 100 : 1.100 X; most preferably from 100 : 1.047 X to 100 : 1.075 X. In step iii) of the method of the present invention the density of the second polyurethane material is controlled to be 0.95 Y g / cm3 or less. A larger decrease in density is more desirable. Preferably, the density of the second polyurethane material is controlled to be 0.94 Y g / cm3 or less; more preferably 0.93 Y g / cm3 or less; more preferably 0.92 Y g / cm3 or less; even more preferably 0.91 Y g / cm3 or less; even more preferably 0.90 Y g / cm3 or less; even more preferably 0.89 Y g / cm3 or less; even more preferably 0.88 Y g / cm3 or less; even more preferably 0.87 Y g / cm3 or less; even more preferably 0.86 Y g / cm3 or less; even more preferably 0.85 Y g / cm3 or less; even more preferably 0.84 Y g / cm3 or less; even more preferably 0.83 Y g / cm3 or less; even more preferably 0.82 Y g / cm3 or less; even more preferably 0.81 Y g / cm3 or less; most preferably 0.80 Y g / cm3 or less. A maximum decrease in density may also be desirable in some applications. Depending on the specifics of the one or more polyols and one or more polyisocyanate monomers some densities may lead to undesirable properties such as crumbliness and difficulty in suitably filling a mold or casting tool. As would be appreciated, the density cannot be reduced to zero. For example, it is usually preferable that the density is reduced no lower than 0.10 g / cm3, more preferably the density is reduced no lower than 0.20 g / cm3, even more preferably the density is reduced no lower than 0.30 g / cm3 The skilled person would be able to determine an appropriate lower limit for the density based on the one or more polyol and one or more polyisocyanate in question. For example, the density of the second polyurethane material may be controlled to be from 0.80 Y to 0.95 Y; preferably from 0.81 Y to 0.95Y; more preferably from 0.82 Y to 0.95Y; even more preferably from 0.83 Y to 0.95Y; even more preferably from 0.84 Y to 0.95 Y; most preferably from 0.85 Y to 0.95Y. By way of further example, the density of the second polyurethane material may be controlled to be from 0.80 Y to 0.94 Y g / cm3; preferably from 0.80 Y to 0.93 Y g / cm3; more preferably from 0.80 Y to 0.92 Y g / cm3; even more preferably from 0.80 Y to 0.91 Y g / cm3; even more preferably from 0.80 Y to 0.90 Y g / cm3; even more preferably from 0.80 Y to 0.89 Y g / cm3; even more preferably from 0.80 Y to 0.88 Y g / cm3; even more preferably from 0.80 Y to 0.87 Y g / cm3; even more preferably from 0.80 Y to 0.86 Y g / cm3; most preferably from 0.80 Y to 0.85 Y g / cm3. By way of yet further example, the density of the second polyurethane material may be controlled to be from 0.81 Y to 0.95 Y g / cm3; preferably from 0.82 Y to 0.95 Y g / cm3; more preferably from 0.83 Y to 0.95 Y g / cm3; even more preferably from 0.84 Y to 0.95 Y g / cm3; most preferably from 0.85 Y to 0.95 Y g / cm3. By way of yet still further example, the density of the second polyurethane material may be controlled to be from 0.81 Y to 0.94 Y g / cm3; preferably from 0.82 Y to 0.93 Y g / cm3; more preferably from 0.83 Y to 0.92 Y g / cm3; even more preferably from 0.84 Y to 0.91 Y g / cm3; most preferably from 0.85 Y to 0.90 Y g / cm3. Typically, a larger decrease in density will be offset by a larger increase in stoichiometric ratio. However, the exact relationship between these properties will depend on various factors such as the specifics of the one or more polyols and one or more polyisocyanates, or the overall physical structure of the impact protector. In a specific example, the density of the second polyurethane material is controlled to be from 0.80 Y to 0.90 Y g / cm3 and the second polyurethane material is prepared by reacting the same one or more polyol and the same one or more polyisocyanate monomers from which the first polyurethane material is derived, in a stoichiometric ratio of from 100:1.035 Xto 100 : 1.200 X. In a further specific example, the density of the second polyurethane material is controlled to be from 0.87 Y to 0.93 Y g / cm3 and the second polyurethane material is prepared by reacting the same one or more polyol and the same one or more polyisocyanate monomers from which the first polyurethane material is derived, in a stoichiometric ratio of from 100 : 1.040 X to 100 : 1.200 X. Step ii) of the method of the present invention involves preparing a second polyurethane material by reacting the same one or more polyols and the same one or more polyisocyanate monomers from which the first polyurethane material is derived. In the context of the present invention the feature of “the same one or more polyols” and “the same one or more polyisocyanates” is understood to refer to the same chemical compound, or the same combination of chemical compounds in the case of more than one polyol or polyisocyanate. For example, if the first polyurethane was prepared from 1,4-butanediol and 4,4’-methylenediphenyl diisocyanate, then the same one or more polyols and the same one or more polyisocyanate monomers must also be 1,4-butanediol and 4,4’-methylenediphenyl diisocyanate. Likewise, in the case that the one or more polyols is a mixture of 1,4-butanediol and ethylene glycol, then the same one or more polyols must be a mixture of 1,4-butanediol and ethylene glycol in substantially the same molar ratio. The term one or more polyols refers to the polyol compound or compounds which become part of the polyurethane chemical structure by virtue of polymerisation. Similarly, the term one or more polyisocyanates refers to the polyisocyanate compound or compounds which become part of the polyurethane chemical structure by virtue of polymerisation. In the context of the present invention, the term “polyol” refers to a molecule bearing two or more hydroxyl functional groups. Whilst diols, which have two hydroxyl groups are the most common form of polyol used in polyurethane synthesis, there are many examples of polyols bearing more than two hydroxyl groups. For example, glycerol, pentaerythritol, and xylitol have three, four and five hydroxyl groups, respectively, and are well known examples of polyols. Polymeric polyols such as polyvinyl alcohol may have many hydroxyl groups. Preferably, the one or more polyols comprises one or more diols; more preferably the one or more polyols comprises more than 50% by mass of one or more diols; even more preferably the one or more polyols consist essentially of one or more diols; even more preferably the one or more polyols consist of one or more diols. Examples of diols suitable for use in polyurethane synthesis include short chain diols, such as, ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, and hydroquinone bis(2-hydroxyethyl) ether (HQEE); as well as dimeric, oligomeric or polymeric diols, such as, diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polyester polyols. Ethylene glycol is a particularly suitable polyol. Preferably, the one or more polyols comprise ethylene glycol, more preferably the one or more polyols consist essentially of ethylene glycol, even more preferably the one or more polyols consist of ethylene glycol. 1,4-butanediol is also a particularly suitable polyol. Preferably, the one or more polyols comprise 1,4-butanediol, more preferably the one or more polyols consist essentially of 1,4-butanediol, even more preferably the one or more polyols consist of 1,4-butanediol. Polyethylene glycol is a particularly suitable polyol. Preferably, the one or more polyols comprise polyethylene glycol, more preferably the one or more polyols consist essentially of polyethylene glycol, even more preferably the one or more polyols consist of polyethylene glycol. The one or more polyols may be a single species or a mixture of species. For example, a particularly suitable mixture of polyols is a mixture of 1,4-butanediol and polyethylene glycol. Preferably, the one or more polyols comprises 1,4-butanediol and polyethylene glycol, more preferably the one or more polyols consists essentially of 1,4-butanediol and polyethylene glycol, even more preferably the one or more polyols consist of 1,4-butanediol and polyethylene glycol. In one example, the one or more polyols may comprise 1,4-butanediol, polyethylene glycol, and propoxylated ethylenediamine (CAS Number: 25214-63-5). Preferably, the one or more polyols has a hydroxyl value of from 150 to 180 mgKOH / g, more preferably from 162 to 172 mgKOH / g, for example 170 mgKOH / g. More preferably, the one or more polyols consist essentially of or consist of a polyethylene glycol having a hydroxyl value of from 162 to 172 mgKOH / g. Alternatively, the one or more polyols consist essentially of or consist of a mixture of 1,4-butanediol and polyethylene glycol, the mixture having a hydroxyl value of from 162 to 172 mgKOH / g. Various polyols may be derived from bio-based resources in order to obviate the use of petrochemicals. For example, many polyols such as sugars and glycerol are directly available from bio-based sources. Many other polyols can be readily prepared from biobased feedstocks. Bio-based polyols can be used to introduce bio-carbon into a polyurethane material and therefore an article, such as an impact protector made therefrom. In the context of the present invention, the feature of “the same one or more polyol” may be satisfied by a bio-carbon containing polyol so long as it is the same species. Thus, a bio-carbon containing polyol can be considered to be the same one or more polyol as a polyol of the same chemical structure, albeit containing only non-bio-carbon. The present invention therefore encompasses a method of preparing a reduced density impact protector having increased bio-carbon. The term “bio-based”, as used herein refers to a material that is derived in whole or in part from renewable biomass resources. Biomass resources are organic materials that are available on a renewable or recurring basis such as crop residues, wood residues, grasses, and aquatic plants. The term “biocarbon” as used herein describes an atom of carbon that is “bio-based”, i.e. that the atom of carbon in question is derived from a biomass resource. The skilled person is able to determine if a material is from a biomass resource, provided that the source of the material is known. Therefore, a skilled person is also able to determine if a material is derived from a from biomass resource, providing they have knowledge of the precursor material from which the material in question is derived. Nevertheless, objective tests may also be used to identify “biocarbon”. ASTM D6866 and ISO 16620-2 both provide methods of identifying “biocarbon” based on isotopic analysis. “Biocarbon” has a higher abundance of 14C than, for example, carbon derived from fossil fuels. Thus, the skilled person is also able to objectively test the biocarbon content of a given material. In the context of the present invention, the term “polyisocyanate” refers to a molecule bearing two or more isocyanate functional groups. For the avoidance of doubt, in the context of the present invention, the term “polyisocyanate” does not refer to substituted isocyanurates formed by trimerization of an isocyanate compound, which may be referred to as polyisocyanate, PIR, polyiso or ISO in other publications. Although it is possible that an isocyanurate may be substituted with two or more moieties bearing isocyanate groups, in which case such a compound is considered to be a polyisocyanate. A polyisocyanate has two or more isocyanate groups. For example, toluene-2,4,6-triyl triisocyanate, (1,3,5-benzenetriyl)tris(4,1-phenylene)trisisocyanate, and lysine triisocyanate are examples of well-known tri isocyanates having three isocyanate groups, suitable for use in polyurethane synthesis. Polyisocyanate having four or more isocyanate groups are also known, as well as oligomeric and polymeric isocyanates bearing many isocyanate groups, such as oligomeric and polymeric methylenediphenyl diisocyanate (MDI), the structure of which is shown below. MW's Diisocyanates are the most commonly used polyisocyanate in the preparation of polyurethane. A diisocyanate is a polyisocyanate bearing two isocyanate groups. Examples of diisocyanates suitable for use in polyurethane synthesis include, for example, aromatic diisocyanates, such as, toluene diisocyanate (TDI), methylenediphenyl diisocyanate (MDI), and tetramethylxylylene diisocyanate (TMXDI); as well as saturated diisocyanates, such as, 1,6-hexamethylene diisocyanate (HDI), 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate, IPDI), and 4,4'-diisocyanato dicyclohexylmethane (H12MDI or hydrogenated MDI). As would be appreciated, the term “saturated” refers to the carbon backbone of the polyisocyanate in question and not the isocyanate group itself. Preferably, the one or more polyisocyanates comprise one or more diisocyanates; preferably the one or more polyisocyanates comprise more than 50% by mass of one or more diisocyanates; more preferably the one or more polyisocyanates consist essentially of one or more diisocyanates; even more preferably the one or more polyisocyanates consist of one or more diisocyanates. Methylenediphenyl diisocyanate is a particularly suitable diisocyanate. A number of isomers of methylenediphenyl diisocyanate exist, such as 4,4’-methylenediphenyl diisocyanate, 2,4’-methylenediphenyl diisocyanate, and 2,2’-methylenediphenyl diisocyanate. 4,4’-methylenediphenyl diisocyanate is a preferred isomer. In the context of the present invention, the general term “methylenediphenyl diisocyanate” in the absence of any specification of a specific isomer would be understood to refer to any methylenediphenyl diisocyanate isomer ora mixture thereof. The one or more polyisocyanates may comprise methylenediphenyl diisocyanate, preferably the one or more polyisocyanates comprises methylenediphenyl diisocyanate. The one or more polyisocyanates may consist essentially of methylenediphenyl diisocyanate, for example the one or more polyisocyanates may consist essentially of methylenediphenyl diisocyanate. The one or more polyisocyanates may also consist of methylenediphenyl diisocyanate. Where the one or more polyisocyanates may comprise methylenediphenyl diisocyanate, the one or more polyisocyanates preferably comprises 4,4’-methylenediphenyl diisocyanate. The one or more polyisocyanates may consist essentially of 4,4’-methylenediphenyl diisocyanate. The one or more polyisocyanate may also consist of 4,4’-methylenediphenyl diisocyanate. The one or more polyisocyanates may be a single species or a mixture of species. In a preferred embodiment, the one or more polyisocyanates may be a single species. However, certain mixtures of polyisocyanates are also particularly suitable. Preferably, the one or more polyisocyanates comprises, consists essentially of, or consists of one or more isomer of methylenediphenyl diisocyanate, oligomeric methylenediphenyl diisocyanate, polymeric methylenediphenyl diisocyanate, and combinations thereof; more preferably the one or more polyisocyanates comprises one or more isomer of methylenediphenyl diisocyanate. Preferably, where the one or more polyisocyanates include more than one polyisocyanate, and when there is a change in X, the ratio of isocyanate equivalent weights of the more than one polyisocyanate remains substantially constant. Step ii) of the method of the present invention involves preparing a second polyurethane material by reacting the same one or more polyols and the same one or more polyisocyanate monomers from which the first polyurethane material is derived. Preparation of a polyurethane material from a given combination of one or more polyols and one or more polyisocyanate monomers may be easily achieved by the skilled person. Polyurethanes are typically produced by mixing two or more liquid streams, one containing the one or more polyols and the other containing the one or more polyisocyanates. Typically, the polyol stream will contain any additives which may be used, such as catalysts, surfactants, blowing agents, flame retardants, pigments, fillers etc. The mixture of the one or more polyols and one or more polyisocyanate monomers, prior to polymerisation is often referred to a resin. Additives, such as catalysts, surfactants, blowing agents, flame retardants, pigments, fillers etc may also be added to the resin. The resin is typically poured into a mold or casting tool, or poured onto a surface and allowed to cure. The term cure in this context refers to polymerisation. The curing reaction may occur spontaneously or may be assisted by heating, depending on the specifics of the monomers involved and / or the potential use of catalysis. Typically, the step of preparing a second polyurethane material by reacting the same one or more polyol and the same one or more polyisocyanate monomers from which the first polyurethane material is derived further comprises addition of one or more of a silicone polymer, a polymerisation catalyst, and / or one or more pigments. Preferably, the silicone polymer, a polymerisation catalyst, and / or one or more pigments, where present, are mixed with the one or more polyol prior to contacting the one or more polyols with the one or more polyisocyanates. Typically, step of preparing a second polyurethane material includes the addition of from 0.01 to 3.0 wt% of a silicone polymer, preferably wherein the silicone polymer is 3-(polyoxyethylene)propylheptamethyltrisiloxane. Preferably the first and second polyurethane materials include the same silicone polymer, more preferably the first and second polyurethane materials include the same wt% of the same silicone polymer to within ±0.5 wt%, even more preferably to within ±0.1 wt%. Typically, step of preparing a second polyurethane material includes the addition of a polymerisation catalyst. Preferably the polyurethane polymerisation catalyst is an amine, more preferably the polyurethane polymerisation catalyst is a tertiary amine, such as diazabicyclo [5.4.0]undec-7-ene (DBU) or 1,4-diazabicyclo [2.2.2]octane (DABCO), dimethylaminopropyl urea, or any combination thereof. Alternatively, the polymerisation catalyst is an inorganic catalyst, such as zinc neodecanoate or bismuth neodecanaote. A mixture of any of the above discussed amine and inorganic catalysts may also be used. Preferably, the polymerisation catalyst is added to the one or more polyol in a total amount of from 0.1 to 2.0 wt%. Preferably, the first and second polyurethane materials are prepared using the same polymerisation catalyst, more preferably the first and second polyurethane materials are prepared using the same polymerisation catalyst in the same wt% to within ±0.5 wt%, even more preferably to within ±0.1 wt%. The polymerisation catalyst functions so as to catalyse curing of the polyurethane. In this respect, the catalyst may be used to initiate and control the reaction of the one or more polyols with the one or more polyisocyanates so as to form the cured polyurethane. Some polymerisation catalysts that are present in the composition will initiate the reaction with the one or more polyisocyanates as soon as it is mixed with the one or more polyols, and do not require the application of any heat. In contrast, some polymerisation catalysts only start functioning and catalysing the reaction between the one or more polyols and the one or more polyisocyanates once some degree of heat is applied to the resin. The different properties of different polymerisation catalysts allow a particular catalyst, or combination of catalysts to be optimised for a particular process. Typically, the step of preparing the second polyurethane material by reacting the same one or more polyols and the same one or more polyisocyanate monomers includes addition of from 0.01 wt% to 5.0 wt% of one or more pigments, preferably from 0.05 wt% to 2.5 wt%, more preferably from 0.1 wt% to 1.5 wt%, most preferably from 0.3 wt% to 1.0 wt%. The one or more pigments preferably have a hydroxyl value of from 20 to 40 mgKOH / g. Preferably the first and second polyurethane materials include the same pigment, more preferably the first and second polyurethane materials include the same wt% of the same pigment to within ±0.5 wt%, even more preferably to within ±0.1 wt%. Step iii) of the method of the present invention involves controlling the density of the second polyurethane material. One way that this may be achieved is by using one or more blowing agents. The density of a polyurethane material may be controlled by various factors of the manufacturing process. Typically, the density may be adjusted by controlling the shot weight, which refers to the mass of the mixture of monomers which is introduced into a mold compared to the capacity of the mold. The density of the second polyurethane material may be controlled by reducing the shot weight of the one or more polyols and the one or more polyisocyanate monomers in step ii) relative to the shot weight of the one or more polyols and the one or more polyisocyanate monomers in step i). A larger shot weight will provide a denser polyurethane material. Optionally, blowing agents may be used to impart a foamed structure on the polyurethane to some degree. The degree of foaming will correspond to reduced density as more voids are created in the polymer matrix which contribute to reduced density. Alternatively, the incorporation of fillers or additives can alter the density of polyurethane. Fillers, such as calcium carbonate or talc, can increase the material’s density, while hollow microspheres or other lightweight additives can decrease it. Temperature and pressure during the curing process can also impact the density of polyurethane. Higher temperatures and pressures can result in higher-density materials, while lower values may lead to lower-density products. As would be appreciated, multiple methods of controlling the density of a polyurethane material may be employed in combination. The skilled person is able to optimise these factors to achieve the desired density. Typically, the first and the second polyurethane material will have a foamed structure. This is typically achieved via the introduction of gas into the polyurethane material by a blowing agent. Various blowing agents are suitable for use in the present invention, for example, nitrogen, hydrocarbons, such as n-pentane, iso-pentane, or cyclopentane, fluorinated hydrocarbons, dimethyl ether, or combinations thereof may be used in the preparation of the first and / or second polyurethane material. Water may also act as a blowing agent via reaction of the polyisocyanate with the water to form carbon dioxide. Typically, water is used as a blowing agent, preferably 0.1 to 3.0 wt% of water is mixed with the one or more polyol prior to contacting the one or more polyol with the one or more polyisocyanate. Optionally, the blowing agent may further comprise one or more fluorinated hydrocarbons, such as 1,1,1,3,3-pentafluorobutane. The blowing agent, preferably water, may be in an amount of 0.1 to 0.5 wt% of the polyurethane material. The temperature at which polyurethane is prepared can vary depending on the specifics of the one or more polyols and one or more polyisocyanates, as well as the specifics of the catalysis and the manufacturing process. In general, polyurethane is manufactured at elevated temperatures to facilitate curing. For the purposes of molding, temperatures typically range from 40°C to 100°C, preferably from 40°C to 60°C, during the mixing pouring stage. The molds are typically heated to help with the curing and foaming processes. Typically, the mixture of monomers and any optional additives is poured into an open mold, followed by closing the mold and allowing curing to take place. Step iii) of the method of the present invention also involves producing a reduced density impact protector from the second polyurethane material. Typically, this is achieved by pouring the relevant resin into a mold or casting tool, or by pouring the relevant resin onto a surface and allowing curing to occur whilst the density is controlled as discussed above, such that the reduced density impact protector is formed. The reduced density impact protector may then, where applicable, be demolded and optionally undergo additional processing steps, such as cutting, trimming, or surface treatment. According to the second aspect of the invention, there is provided an impact protector obtained or obtainable by the method of the present invention. Such an impact protector may be characterised by its reduced density as compared to a comparative impact protector made without use of the present invention. According to the third aspect of the invention, there is provided a garment comprising an impact protector obtained or obtainable by the method of the present invention. For example, a motorbike jacket may comprise reduced density impact protectors of the present invention. Preferably, the reduced density impact protectors of the present invention are attachable to the garment by hook and look fasteners, or by fitting into pockets in the garment. This allows for easy replacement of the impact protector. The invention will now be described by reference to the following non-limiting Examples. Example 1 The method of the present invention was used to prepare a selection of reduced density knee protectors compliant with EN 1621-1:2012 at ambient, wet, hot (40 °C), and cold (-10°C) conditions. EN 1621-1:2012 Level 1 includes testing at ambient and wet conditions. Optional impact testing at hot (40 °C), and cold (-10 °C) conditions were also conducted in this example. A first polyurethane impact protector, made of first polyurethane material, was used as a reference point to prepare a reduced density impact protector made of a second polyurethane material. The first impact protector is made of a first polyurethane material, in which the one or more polyols is a mixture of polyethylene glycol and 1,4-butanediol having a hydroxyl value of approximately 170 mgKOH / g, and the one or more polyisocyanates is 4,4’-methylenediphenyl diisocyanate. The first polyurethane material has an isocyanate index of 97.8 and a density of 0.50 g / cm3. The first impact protector is a knee protector compliant with EN 1621-1:2012 Level 1, as well as the high temperature (40 °C) impact test and the low temperature (-10 °C) impact test. The method of the present invention was used to prepare reduced density impact protectors as compared to the first impact protector. Samples 1 to 11 in Table 1 below represent test impact protectors made from polyurethane derived from the same one or more polyols and one or more polyisocyanates as the first impact protector but with differing densities and / or isocyanate indexes. The produced impact protectors were tested as per the requirements of EN 1621-1:2012 Level 1, as well as the high temperature (40 °C) impact test and the low temperature (-10 °C) impact test. This includes measuring the maximum peak transmitted force (Max PTF) at six (1 to 6) locations on the impact protector. The average maximum peak transmitted force is also shown (A). Table 1 also shows if the produced impact protector retained its ability to pass the requirements of all of EN 1621-1:2012 Level 1, the high temperature (40 °C) impact test, and the low temperature (-10 °C) impact test (Pass All = yes or no). The requirements of each of the EN 1621-1:2012 Level 1, the high temperature (40 °C) impact test and the low temperature (-10 °C) impact test, all include an average peak transmitted force (PTF) for each impact of <35kN; and with no single impact failures. Each sample is impacted in 6 locations and depending on the location the pass / fail criteria changes. Table 1 below shows the largest peak transmitted force value that was measured during impact testing at any one of the ambient, wet, hot (40 °C), and cold (-10 °C) conditions (Max PTF all conditions). Values highlight in bold represent failed values, and thus that impact protector would fail to satisfy the requirements of at least one of EN 1621-1:2012 Level 1, the high temperature (40 °C) impact test, or the low temperature (-10 °C) impact test. Table 1 Max PTF (kN) all conditions by location Sample impact protector Isocyanate index Density / g / cm3 1 2 3 4 5 6 A Pass All 1 102.6 0.45 28.4 33.8 31.9 30.8 26.1 26.2 28.7 Yes 2 102.6 0.475 25.5 32.7 25.3 27.9 22.5 23.5 25.2 Yes 3 97.8 0.425 56.0 68.2 71.4 43.3 48.3 55.1 49.7 No 4 97.8 0.45 47.6 56.8 48.2 31.2 35.9 41.6 37.1 No 5 97.8 0.47 36.6 45.1 34.6 31.0 36.0 38.0 34.5 No 6 99.4 0.45 42.5 56.5 55.4 40.7 44.1 50.5 43.6 No 7 99.4 0.47 39.2 49.5 42.1 30.3 33.7 35.0 33.7 No 8 99.4 0.50 25.6 31.7 30.1 29.7 26.5 29.3 27.5 Yes 9 101.0 0.45 48.6 57.5 32.0 30.2 34.9 38.2 35.7 No 10 101.0 0.50 29.9 31.1 29.9 28.4 24.4 27.7 27.3 Yes 11 102.6 0.50 34.3 30.1 28.6 27.4 22.4 25.6 25.4 Yes As can be seen from the results of Table 1, the method of the present invention allowed for new reduced density impact protectors to retain their ability to pass EN 1621-1:2012 Level 1, as well as the high temperature (40 °C) impact test and the low temperature (-10 °C) impact test. Samples 1 and 2 represent an increase in isocyanate index from 97.8 to 102.6, the new stoichiometric ratio is therefore 100 : 1.049 X, where 100 : X is the comparative stoichiometric ratio of the first polyurethane material. This increase in stoichiometric ratio allowed for the density to be reduced from 0.50 g / cm3to 0.475 g / cm3or 0.45 g / cm3 whilst retaining the ability to pass EN 1621-1:2012. In other words, where the original density of the comparative impact protector is Y, a reduced density of 0.95 Y, or 0.90 Y was achieved. For proof of concept, Samples 4 and 5 show the outcome when density is reduced but without any change in stoichiometric ratio. For Samples 4 and 5, changing the density Y to 0.90 Y or 0.94 Y without any change to isocyanate index caused the impact protectors to fail EN 1621-1:2012. This shows that the increase in isocyanate index, and thus stoichiometric ratio is essential in order to achieve reduced density whilst retaining impact attenuation. Samples 6 and 7 represent an increase in isocyanate index from 97.8 to 99.4, the new stoichiometric ratio is therefore 100 :1.016 X, where 100: X is the comparative isocyanate index of the first polyurethane material. As can be seen, this increase in isocyanate index did not allow for the density to be reduced from 0.50 g / cm3 to 0.475 g / cm3 or 0.45 g / cm3 whilst retaining the ability to pass EN 1621-1:2012. However, Sample 8 shows that this isocyanate index would be sufficient if the density were unchanged. This further demonstrates that reducing density alone will lead to failure of EN 1621 -1:2012. Table 2 below, shows the data for the average Max PTF (kN) of the worst performing sample under each of the ambient conditions, wet conditions after hydrolytic aging, cold conditions (-10 °C), and high temperature conditions (40 °C). As with Table 1, the ability to pass the requirements of all of EN 1621-1:2012 Level 1, the high temperature (40 °C) impact test, and the low temperature (-10 °C) impact test was assessed (Pass All = yes or no) with results highlighted in bold representing failed values. A value has also been included in Table 2 for the average Max PTF (kN) of worst sample for the comparative first impact protector, which was the average Max PTF (kN) under high temperature conditions. This allows for a percentage change (% change) in this property to be calculated for Samples 1 to 11. As the aim is to minimise peak transmitted 5 force, negative percentage change is considered a positive result, and positive percentage change is considered a negative result. Although a more minor positive percentage change does not necessarily lead to failure of EN 1621-1:2012, as can be seen from Sample 1. Table 2 Average Max PTF (kN) of worst sample Sample impact protector Isocyanate index Density / g / cm3 Ambient Wet Cold (-10 °C) Hot (40 °C) Pass All % change Comparative 97.8 0.5 - - - 27.9 Yes - 1 102.6 0.45 17.0 25.4 14.8 28.7 Yes +3 2 102.6 0.475 15.6 23.1 15.8 25.2 Yes -11 3 97.8 0.425 21.8 48.3 14.0 49.7 No +49 4 97.8 0.45 18.2 35.9 13.6 37.1 No +25 5 97.8 0.47 18.7 29.3 13.9 34.5 No +19 6 99.4 0.45 18.5 39.5 13.7 43.6 No +36 7 99.4 0.47 17.2 30.3 14.5 33.7 No +17 8 99.4 0.5 16.3 25.3 14.6 27.5 Yes -2 9 101.0 0.45 17.4 27.8 13.6 35.7 No +22 10 101.0 0.5 16.3 25.8 15.3 27.3 Yes -2 11 102.6 0.5 15.4 25.3 17.2 25.4 Yes -10 As can be seen, the impact protectors prepared in line with the method of the present invention also proved successful under various weather conditions. Example 2 The method of the present invention was used to provide reduced density versions of a 15 range of other first impact protectors. Various impact protectors, having different zones of protection were used. The first impact protectors were made of a first polyurethane material where the one or more polyols is a polyethylene glycol having a hydroxyl value of from 162 to 172 mgKOH / g, and the one or more polyisocyanates is 4,4’-methylenediphenyl diisocyanate. Reduced density impact protectors having identical overall physical structure were prepared using second polyurethane materials derived from the same one or more polyols and one or more polyisocyanates having an increased isocyanate index in combination with various reductions in density as outlined in Table 3 below. Table 3 also shows the EN standard and level that is passed by the comparative impact protector and the new impact protector prepared by the method of the present invention. Impact protectors compliant with various different EN standards were prepared, and in all cases, the reduced density impact protector is compliant with the same EN standard as the corresponding first impact protector (the specific standard applied is shown in the column labelled “Pass EN standard”). In line with the method of the present invention, in this example the stoichiometric ratio of the second polyurethane material is greater than 100 : 1.033 X. In this case the new stoichiometric ratio is 100 : 1.0368 X. Similarly, in each case, the density of the first impact protector is Y and the reduced densities of the new impact protectors formed by the method of the present invention are each less than 0.95 Y. The reductions in density achieved in this example ranged from 11 % to 17 %, which correspond to a range of 0.89 Y to 0.83 Y. Table 3 Entry Zone of Protection Change in Isocyanate Index / % Reduction in Density / % Pass EN Standard 12 Back 3.68 11 Yes (EN 1621-2:2014 level 1) 13 Chest 3.68 17 Yes (EN 1621-3:2018 level 1) 14 Back 3.68 15 Yes (EN 1621-2:2014 level 2) Example 3 The method of the present invention was again used to provide reduced density versions of a range of first impact protectors. Various impact protectors, having different zones of protection were used. The first impact protectors were made of a first polyurethane material where the one or more polyols is a mixture of polyethylene glycol and 1,4-butanediol having a hydroxyl value of approximately 170 mgKOH / g, and the one or more polyisocyanates is 4,4’-methylenediphenyl diisocyanate. Reduced density impact protectors having identical overall physical structure were prepared using second polyurethane materials derived from the same one or more polyols and one or more polyisocyanates having an increased isocyanate index in combination with reductions in density as outlined in Table 4 below. Table 4 also shows the EN standard and level that is passed by the comparative impact protector and the new impact protector prepared by the method of the present invention. Impact protectors compliant with various different EN standards were prepared, and in all cases, the reduced density impact protector is compliant with the same EN standard as the corresponding first impact protector (the specific standard applied is shown in the column labelled “Pass EN standard”). In line with the method of the present invention, in this example the stoichiometric ratios of the second polyurethane materials are greater than 100 : 1.033 X. The increased isocyanate indexes correspond to stoichiometric ratios of 100 :1.0491 X and 100:1.0475 X. Similarly, in each case, the density of the first impact protector is Y and the reduced densities of the new impact protectors formed by the method of the present invention are each less than 0.95 Y. The reductions in density achieved in this example ranged from 10 % to 20 %, which correspond to a range of 0.90 Y to 0.80 Y. Table 4 Entry Zone of Protection Change in Isocyanate Index / % Reduction in Density / % Pass EN Standard 15 Hip 4.75 20 Yes EN 1621-1:2012 (Level 1) 16 Elbow 4.91 15 Yes EN 1621-1:2012 (Level 2) 17 Shoulder 4.91 10 Yes EN 1621-1:2012 (Level 2)

Claims

1. A method of reducing the density of an impact protector compliant with one of EN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018, the method comprising the steps of:i) preparing a first impact protector compliant with one of EN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018, from a first polyurethane material having a density of Y g / cm3 and a stoichiometric ratio of 100:X; wherein the stoichiometric ratio is defined as the ratio of alcohol groups in the one or more polyols : isocyanate groups in the one or more polyisocyanates from which the polyurethane material is derived;ii) preparing a second polyurethane material by reacting the same one or more polyols and the same one or more polyisocyanate monomers from which the first polyurethane material is derived, in a stoichiometric ratio of 100 : (1.033 X or more); andiii) controlling the density of the second polyurethane material to be 0.95 Y g / cm3 or less;so as to produce a reduced density impact protector compliant with the same one of EN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018.

2. The method of Claim 1, wherein the first impact protector is compliant with one of EN 1621-1:2012 (Level 2), EN 1621-2:2014 (Level 2), or EN 1621-3:2018 (Level 2), and the reduced density impact protector is also compliant with the same one of EN 1621-1:2012 (Level 2), EN 1621-2:2014 (Level 2), or EN 1621-3:2018 (Level 2).

3. The method of Claim 1 or Claim 2, wherein the first impact protector is compliant with one or both of the high temperature (40 °C) impact test and / or the low temperature (-10 °C) impact test requirements of one of EN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018, and the reduced density impact protector is also compliant with the same one or both of the high temperature (40 °C) impact test and / or the low temperature (-10 °C) impact test requirements of the same one of EN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018.

4. The method of Claim 3, wherein the first impact protector is compliant with both of the high temperature (40 °C) impact test and the low temperature (-10 °C) impact test requirements of one of EN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018, and the reduced density impact protector is also compliant with both of the high temperature (40 °C) impact test and the low temperature (-10 °C) impact test requirements of the same one ofEN 1621-1:2012, EN 1621-2:2014, or EN 1621-3:2018.

5. The method of any preceding claim, wherein the first impact protector and the reduced density impact protector are both configured to provide protection to the same zone of protection.

6. The method of Claim 5, wherein the zone of protection is selected from: the knee, the shoulder; the elbow and forearm; the hip; the knee and upper tibia; the knee, upper and middle tibia; the leg below the middle tibia; the central back and scapula area; the central back; the lumbar region; the whole chest; and half of the chest.

7. The method of any preceding claim, wherein the first impact protector and the reduced density impact protector both have substantially the same overall physical structure.

8. The method of any preceding claim, wherein the density of the second polyurethane material is controlled to be 0.94 Y g / cm3 or less; preferably 0.93 Y g / cm3 or less; more preferably 0.92 Y g / cm3 or less; more preferably 0.91 Y g / cm3 or less; even more preferably 0.90 Y g / cm3 or less; even more preferably 0.89 Y g / cm3 or less; even morepreferably 0.88 Y g / cm3 or less; even more preferably 0.87 Y g / cm3 or less; even morepreferably 0.86 Y g / cm3 or less; even more preferably 0.85 Y g / cm3 or less; even morepreferably 0.84 Y g / cm3 or less; even more preferably 0.83 Y g / cm3 or less; even morepreferably 0.82 Y g / cm3 or less; even more preferably 0.81 Y g / cm3 or less; most preferably 0.80 Y g / cm3 or less.

9. The method of any preceding claim, wherein the density of the second polyurethane material is controlled to be from 0.80 Y to 0.95 Y; preferably from 0.81 Y to 0.95 Y g / cm3; more preferably from 0.82 Y to 0.95 Y g / cm3; even more preferably from 0.83 Y to 0.95 Y g / cm3; even more preferably from 0.84 Y to 0.95 Y g / cm3; most preferably from 0.85 Y to 0.95 Y g / cm3.

10. The method of any one of Claims 1 to 8, wherein the density of the second polyurethane material is controlled to be from 0.81 Y to 0.94 Y g / cm3; preferably from 0.82 Y to 0.93 Y g / cm3; more preferably from 0.83 Y to 0.92 Y g / cm3; even more preferably from 0.84 Y to 0.91 Y g / cm3; most preferably from 0.85 Y to 0.90 Y g / cm3.

11. The method of any preceding claim, wherein the second polyurethane material is prepared by reacting the same one or more polyols and the same one or more polyisocyanate monomers from which the first polyurethane material is derived, in a stoichiometric ratio of 100 : (1.035 X or more); more preferably 100 : (1.037 X or more); even more preferably 100 : (1.040 X or more); even more preferably 100 : (1.043 X ormore); even more preferably 100 : (1.045 X or more); even more preferably 100 : (1.047 X or more); most preferably 100 : (1.050 X or more).

12. The method of any preceding claim, wherein the second polyurethane material is prepared by reacting the same one or more polyols and the same one or more polyisocyanate monomers from which the first polyurethane material is derived, in a stoichiometric ratio of 100 : (1.033 X to 1.200 X); preferably 100 : (1.033 X to 1.175 X); more preferably 100 : (1.033 X to 1.150 X); even more preferably 100 : (1.033 Xto 1.125 X); even more preferably 100 : (1.033 X to 1.100 X); even more preferably 100 : (1.033 X to 1.075 X); most preferably 100 : (1.033 X to 1.050 X).

13. The method of any preceding claim, wherein the second polyurethane material is prepared by reacting the same one or more polyols and the same one or more polyisocyanate monomers from which the first polyurethane material is derived, in a stoichiometric ratio of from 100 : 1.035 X to 100 : 1.200 X; preferably from 100 : 1.037 X to 100 : 1.175 X; preferably from 100:1.040 X to 100 : 1.150 X; more preferably from 100 : 1.043 Xto 100:1.125 X; even more preferably from 100 :1.045 Xto 100: 1.100 X; most preferably from 100 : 1.047 X to 100 : 1.075 X.

14. The method of any one of Claims 1 to 8, wherein the density of the second polyurethane material is controlled to be from 0.80 Y to 0.90 Y g / cm3 and wherein the second polyurethane material is prepared by reacting the same one or more polyols and the same one or more polyisocyanate monomers from which the first polyurethane material is derived, in a stoichiometric ratio of from 100 : 1.035 X to 100 : 1.200 X.

15. The method of any one of Claims 1 to 8, wherein the density of the second polyurethane material is controlled to be from 0.87 Y to 0.93 Y g / cm3 and wherein the second polyurethane material is prepared by reacting the same one or more polyols and the same one or more polyisocyanate monomers from which the first polyurethane material is derived, in a stoichiometric ratio of from 100 : 1.040 X to 100 : 1.200 X.

16. The method of any preceding claim, wherein the one or more polyisocyanates comprises one or more diisocyanates; preferably the one or more polyisocyanates comprises more than 50% by mass of one or more diisocyanates; more preferably wherein the one or more polyisocyanates consists essentially of one or more diisocyanates; even more preferably wherein the one or more polyisocyanates consists of one or more diisocyanates.

17. The method of any preceding claim, wherein the one or more polyisocyanates comprises, consists essentially of, or consists of one or more isomers of methylenediphenyl diisocyanate, oligomeric methylenediphenyl diisocyanate, polymeric methylenediphenyl diisocyanate, and combinations thereof; preferably wherein the one or more polyisocyanates comprises, consist essentially of, or consist of one or more isomers of methylenediphenyl diisocyanate.

18. The method of any preceding claim, wherein the one or more polyisocyanates comprises 4,4’-methylenediphenyl diisocyanate; preferably wherein the one or more polyisocyanates consist essentially of 4,4’-methylenediphenyl diisocyanate; more preferably wherein the one or more polyisocyanates consist of 4,4’-methylenediphenyl diisocyanate.

19. The method of any preceding claim, wherein the one or more polyols comprises one or more diols; preferably the one or more polyols comprises more than 50% by mass of one or more diols; more preferably wherein the one or more polyols consist essentially of one or more diols; even more preferably wherein the one or more polyols consist of one or more diols.

20. The method of any preceding claim, wherein the one or more polyols comprises polyethylene glycol; preferably wherein the one or more polyols comprises polyethylene glycol and 1,4-butanediol.

21. The method of any preceding claim, wherein the one or more polyols has a hydroxyl value of from 150 to 180 mgKOH / g, preferably from 162 to 172 mgKOH / g, for example 165 to 170 mgKOH / g (including 170 mgKOH / g).

22. The method of any preceding claim, wherein the first polyurethane material and the second polyurethane material have a foamed structure.

23. The method of any preceding claim, wherein the density of the second polyurethane material is controlled by reducing the shot weight of the one or more polyols and the one or more polyisocyanate monomers in step ii) relative to the shot weight of the one or more polyols and the one or more polyisocyanate monomers in step i).

24. The method of any preceding claim, wherein the density of the second polyurethane material is controlled using one or more blowing agents to control the density of the secondpolyurethane material, for example in an amount of 0.1 to 0.5 wt% of the polyurethane material.

25. The method of Claim 24, wherein the one or more blowing agents comprises water.

26. The method of Claim 25, wherein the one or more polyols is mixed with 0.1 to 0.5 wt% of blowing agent, preferably water, prior to contact with the one or more polyisocyanates.

27. The method of any preceding claim, wherein the step of preparing a second polyurethane material by reacting the same one or more polyols and the same one or more polyisocyanate monomers from which the first polyurethane material is derived further comprises addition of one or more of:i) from 0.01 to 3.0 wt% of a silicone polymer, preferably wherein the silicone polymer is 3-(polyoxyethylene)propylheptamethyltrisiloxane;ii) from 0.01 to 2.0 wt% of a polymerisation catalyst, preferably wherein the polyurethane polymerisation catalyst is an amine, more preferably wherein the polyurethane polymerisation catalyst is a tertiary amine, such as diazabicyclo [5.4.0]undec-7-ene or 1,4-diazabicyclo [2.2.2]octane, dimethylaminopropyl urea, or any combination thereof; and / oriii) from 0.01 to 5.0 wt% of one or more pigments, preferably wherein the one or more pigments have a hydroxyl value of 20 to 40 mgKOH / g.

28. An impact protector obtained or obtainable by the method of any one of Claims 1 to 27.

29. A garment comprising one or more impact protectors according to Claim 28.33