WO2000061244A1

WO2000061244A1 - Shock-absorbing composition and leg protector

Info

Publication number: WO2000061244A1
Application number: PCT/SE2000/000709
Authority: WO
Inventors: Stig Willner
Original assignee: Light Weight Support Ab; Camp Scandinavia Ab; WILLNER, Eva
Priority date: 1999-04-14
Filing date: 2000-04-14
Publication date: 2000-10-19
Also published as: AU4444500A; SE9901316D0

Abstract

The invention relates to a composition of at least four layers (1, 2, 3, 4) of alternating force distribution and force absorbing materials having the ability to distribute pressure and reduce the effects of a sudden impact. In a first aspect the composition is intended for use as a protection of body parts, such as the shin during football practice, whereas it can also be used during other athletic practices, e.g. soccer, cricket, riding, motor sports, skiing and ice hockey and used as a means for general damage prevention of a person or a property during professional practice.

Description

SHOCK-ABSORBING COMPOSITION AND LEG PROTECTOR

Technical field

The invention relates to a composition having at least four layers of alternating force distributing and force absorbing materials with the ability to distribute pressure and reduce the effects of a sudden impact, respectively. In a first aspect the composite is intended for use as a protection of body parts, such as the shin, during football practice, whereas it can also be used during other athletic practices, e.g. soccer, cricket, riding, motor sports, skiing or ice hockey, and as a means for general damage prevention of a person or a property, e.g. during professional practice.

Prior art

Material compositions consisting of alternating hard and soft materials, with the purpose to be used as a means for protecting varying body parts, are previously known.

A composition has previously been disclosed in US-A-4,710,984 for use in moped and motorcycle helmets. According to said patent document the composition consists of four alternating hard and soft layers. This type of material composition is intended for disposable use in the meaning that it cannot be reused after impact take up, which is impractical during e.g. athletic practice when every occasion of practice probably results in a number of impacts against the body parts to be protected. Furthermore, it is a bulky and ungainly composition not suitable as e.g. football protection. Another solution is proposed in FR-A-2 340 066 where a composition is described having five different layers, in which the two innermost layers are soft. This composition is as well intended for use in helmets, where the outermost layer is deformed after a blow. This is also a relatively thick composition.

In GB-A-2 281 024 a protective device is described for use during sport practice. Said protective device consists of one outer relatively hard material, which on the inside has a collection of several soft layers containing a number of tubes, being longitudinally arranged in the protective device. These tubes are intended to disperse the energy from the spot of the impact on the protective device over a larger area. However, the pressure dispersion and the reducing effect may only occur where the tubes are presented, and is only attained in the longitudinal direction of the tubes. Accordingly, the disadvantages with the previously above mentioned known constructions are i.a. that they are bulky, heavy and often intended for disposable use.

WO 95/11731 describes a shock absorbing device, which is i.a. intended for use as a leg protection, comprising a hard outer layer and at least two inner soft layers, which show decreasing impact reducing values.

US 4 484 369 describes a shock absorbing shin guard consisting of a rigid shell applied to a carrier of foamed material and provided with a hard insert. US 5 454 780 describes a rigid curable and formable leg protective pad being built up of several layers of rigid material.

One disadvantage with these known leg protective devices is that they must be made unacceptably thick, in order to give a satisfactory force reducing effect which fulfil the national and international demands. This results in that they become both ungainly and heavy.

As regards football protective devices there are two types available on the market today.

One type having longitudinal sheets of hard material and the sheets being covered with fabric. The distribution of forces occurs only along these sheets. Another type is a football protective device, which consists of an outer shell of hard plastic and an inner layer of foamed plastic. The inner layer is intended as comfort layer only and the construction may just take up relatively small forces.

One disadvantage with these two types of protective devices are that they cannot take up greater forces and the type of protection using longitudinal sheets is also dependent on the force hitting the sheets to give an effect.

According to the present invention a material composition is provided which solves the above mentioned problems.

Accordingly, one object of the present invention is to provide a new material composition, which may be used as a protection for property or body parts during e.g. athletic practice and which protection is intended for multiple use.

A further object of the present invention is to provide a new material composition, which has an improved impact reducing effect due to a more effective force distribution without resulting in an increased thickness and/or weight for the protection.

Summary of the invention

The invention refers to a material composition, which is built up of at least four layers alternating hard elastic materials and soft elastic materials, in which the hard layers are force distributing and the soft layers are force absorbing. The composition comprises one outer layer of a force distributing material and further layers of alternating force absorbing and force distributing materials, whereby the alternating layers are at least three. Said force distributing and force absorbing materials are elastic and when an outer force acts on the composition a force reduction is obtained. Each of the layers is substantially an integral portion. Figures

Figure 1 schematically shows how the composition is built up, layers 1 and 3 being force distributing and 2 and 4 force absorbing. Figure 2 shows a shin protecting device 5 having four layers of material; two force distributing layers (l 'and 3 ') and two force absorbing layers (2 'and 4').

Detailed description of the invention.

The invention is described below with reference to the figures 1 and 2, which show preferred embodiments.

With reference to figure 1, a schematic composition is shown where layer 1 and 3 are force distributing and 2 and 4 are force absorbing. The force distributing layers will hereafter be referred to as the hard layers and the force absorbing referred to as the soft layers. Layers 1 and 3 and layers 2 and 4, respectively may either be made of the same material or be composed of different materials or combinations thereof.

The weight of the compositions is not critical but an important parameter in so far as e.g. a shin protective device intended for football players is not allowed to weight more than 300 g per leg protective device. The total weight of a body protecting composition is dependent on the field of application, i.e the impact reducing ability intended and thereby the number of layers of the composition and the thickness of the layers.

The hard force distributing materials have preferably a coefficient of elasticity (E-coefficient) of 0,5-100 GPa, more preferably 0,9-50 GPa and most preferably 1-30 GPa. Especially suitable materials are materials having an E- coefficient of 15-30 GPa. The E-coefficient for the hard materials may e.g. be obtained by the method described in SS-EN-ISO 527-1. The hard materials are preferably plastic materials and they may be fibre-reinforced. The different force distributing layers may be of the same or different materials and in the case of utilising fibre-reinforced materials, the fibre-reinforcements are preferably alternated so that the fibres in the different layers have different directions. The fibre content of the different layers may be varied as desired. Examples of suitable fibre contents are 10-30 %.

Suitable types of materials for the hard layers are e.g. composites of epoxi, polypropene or vinyl ester resin (unsaturated vinyl ester) being reinforced with fibres of Zylon, polyethene, carbon, aramide, glass or a corresponding high coefficient fibre. Even thermoformed shaped plastic may be used. Examples of coefficients of elasticity for different materials are Material E-coefficient

Polypropene 1.5 Gpa

Epoxy 3.6 Gpa

Aramide 69 Gpa

Glass fibre 24 Gpa

Zylen 180 Gpa

Carbon fibre 100 Gpa

The soft force absorbing materials have preferably a compressibility module of 10-250 kPa, most preferably 30-150 kPa. Furthermore the soft materials have preferably a density of 5-200 kg/m³, e.g. 10-100 kg/m³, preferably 20-80 kg/m³ and more preferably 30-50 kg/m³. The compressibility module for the soft materials may e.g. be obtained by the method described in SS-ISO-3386/1- 1986. The soft materials include foamed or cellular plastic materials, which preferably have closed cells.

Types of materials, which may be used in the soft layers are e.g. foams of ethylen vinyl acetate copolymer, polyether, polyester, polyurethane, or polyethene , such as Tempur®, Evazote EV 50 and Plastazote LD29. According to one embodiment the force absorbing layers may comprise materials having different reducing factors, giving a further possibility to control the total effect.

With reference to figure 2 a shin protective device 5, which is intended for use in sport practice such as football is shown. The protective device consists of four layers of materials, two hard layers 1 ' and 3 ^' and two soft layers 2 ^'and 4'. The outside of the protective device is made of a hard outer layer 1 'in a form suitable for the body part intended to be protected. Beneath this layer follows a soft material 2 ^'and thereafter furthermore a hard 3 'layer and a soft layer 4'. The layers may be joined by means of conventional joining methods such as e.g. gluing, hot air gluing, melt gluing etc, or be separate.

According to a preferred embodiment the hard layers of an aramide composition or a composite of glass fibre having 2-4 fibre sheets, and the soft layers comprise Tempur®, Evazote EV 50 or Plastozote LD29, which all are materials of foamed plastic with closed cells. In the embodiment according to figure 2 the hard layers 1 'and 3 ^'are made of the same material, i.e. a composite of glass fibre having four fibre sheets and epoxi as the matrix material, while the soft layers are made of Tempur® (2') and Plastozote LD29 (polyethene cellular plastic) (4'), respectively (see table 1). The hard layers have in this embodiment a total thickness of 1.2 mm, the soft layers a total thickness of 10mm and the weight of the protective device is approximately 130 g. The hard layers may according to the present invention be very thin and at the same time provide a great force reduction. One layer may e.g. have a thickness of approximately 0.5 mm, which with two hard layers give a total thickness for the hard layers of approximately 1mm.

According to a further embodiment of a leg protective device having 4 layers, the two outer layers may, due to weight requirements, be smaller than the two inner layers. The two outer layers are then concentrated to parts, which are extremely exposed areas.

The different layers and the different sheets may be joined by means of conventional joining methods such as e.g. gluing, hot air gluing, melt gluing etc. The layers may also be separated and only lie close to each other. Such a construction may be hold in place by e.g. a tight outer cover sheet.

The composition according to the present invention may, as mentioned above, be used within different areas as an impact reducing protective device. In a first aspect the composition is proposed for protection of body parts, such as the above mentioned shin protection during football practice. Obviously, the composition is suitable to be used within other athletic practices e.g. soccer, cricket, riding, motor sports, skiing and ice hockey. Furthermore, the composition may have the function of a general damage preventing impact reducing protector for persons or properties, e.g. during professional practice.

The individual layers of material, both the hard ones and the soft ones, are elastic and resume, within given stress ranges, in principal their form after a blow. This is important since the final product will have to be suitable for multiple use. Each layer constitutes a substantially integral part and preferably the different layers substantially cover each other. If required (e.g. to keep the weight low) the different layers may be of different sizes and furthermore all the hard layers may be provided with through holes.

Suitably, the hard layers are thinner than the soft ones, but the thickness of the different layers as well as the thickness of the total composition may be varied dependent on the purpose.

When the hard materials are made of a fibre composite material, e.g. a composite, these layers of composite may in their turn comprise one or more sheets. The number of coatings is i.a. dependent on the total thickness, the weight and impact reducing ability desired for a certain purpose.

One method to measure the force reduction which is suitable according to the present invention will be seen under the title "Definitions and safety demands according to the Swedish football association" below.

The composition according to the present invention provides a material giving an unexpectedly high impact reduction and at the same time the composition can be made thin and thereby light. For football protective devices rules according to the Swedish football association are applied and the definitions and safety demands applicable are as defined below. Furthermore, standardisation work is ongoing within Europe and the corresponding European standard CEN will be much the same. The composition according to present invention is preferably designed to fulfil the demands from the Swedish football association mentioned below.

Definitions and safety demands according to the Swedish football association

Content:

1. Introduction

2. Extent

3. Definitions

4. Testing

5. Demands

6. Labelling

1. Introduction This "standard" is intended to reduce damage, which can arise as a result of a kick to a leg protected with a leg protective device in football games.

2. Extent The "standard" comprises demands on the weight of the leg protective device, the sheet coverage of the lower part of the leg, the minimal length of the sheet and the force reduction at a simulated load.

3. Definitions The sheet refers to the plastic material or corresponding material on the front of the leg protective device used for force distribution.

Force reduction refers to the effect of the force distribution.

The force of penetration refers to the force, which passes through the leg protective device and records by the sensor.

4. Testing Before testing the sample bodies are conditioned in a room at a temperature of 23±1°C and a relative humidity of 50±2%. The conditioning is continued for at least 24 hours and until 2 consecutive weight measurements (5 minutes) show a deviation of no more than 0,1%.

Then, the length of the sheet and its relative dimension are measured. The method for measuring the force reduction for leg protective devices:

5 An apparatus consisting of a wooden dummy of the lower part of a leg, a power sensor, an amplifier, a missile, an electromagnet and fixation means belonging thereto. The wooden dummy has been penetrated by three holes each having a diameter of 10 mm. The holes are situated in the

10 centre of the "shin" and 30 mm from the upper part and the lower part of "shin", respectively. Through the holes a push rod is connected to a power sensor situated underneath. The leg protective device is placed on the wooden dummy during the test.

15

A missile is dropped from a defined height onto the push rod such that a force of 400 N is measured. The weight of the missile can be varied between 0,5 and 100 kg. The drop energy shall then be approximately 1.36 Nm. The missile

20 shall be equipped with a ball tip having a radius of 33 mm.

The leg protective device is placed over the push rod and is held snug against the wooden dummy, whereupon the missile is dropped. The force is recorded, in the upper part, in the lower part and in the middle.

25 Five body samples with five measurements per "hole" is measured. The three highest values per body sample are used to give a mean value for the force of penetration (P).

The force reduction is given in % according to following:

30 The force reduction = 100 x (l-P/4000)%

The object of the leg protective device is to reduce force resulting from a kick to the leg. Therefore, the force 35 reduction should be high. If the leg protective device is equipped with supplementary reinforcements on the force measuring spot, the force reduction is measured at another place along the leg. Measurements are also performed on the sheet, if present, otherwise as above. To get an idea of the size of the force reduction, 20 different protective devices have been examined as above on the behalf of the Swedish football association. These measurements form the basis for the demands mentioned below.

5. Demands The weight shall be less than 300 gram per leg protective device.

The length of the sheet shall for a person of < 160 cm be at least 17 cm(S)

160-180 cm 20 cm (S-M)

>180 cm 23 cm (L) (20 cm if an ankle protection is present)

The reach of the sheet shall be at least approximately 40% of the reach of the lower part of the leg, the standard being a leg circumference of 40 cm for a senior protection.

The force reduction shall be at least 50% in the lower part at least 50% in the upper part and at least 70% in the middle or exceed at least 170% as the total sum of the upper part, lower part and the middle.

Note: Protective devices provided with very elastic material on the inner side or with stretched fabric of the ice hockey type, are favoured by this method. Moreover, the sheet has to be stiff.

6. Labelling Protective devices, which fulfil the above mentioned demands, may be approved by the Swedish football association.

These demands may be fulfilled according to present invention through different combinations of materials. The composition according to present invention suitably gives a force reduction of at least 50%, preferably at least 70-80%. The force reduction is measured by means of the formula Force reduction = (l-P/4000)xl00, where P = force of penetration.

According to a preferred embodiment such materials are used, which in the form of a composition having four alternating layers, the two hard layers having a total thickness of 1 - 1.5 mm and the soft layers a total thickness of approximately 10 mm. result in a force reduction of 70%, whereby the force reduction is measured by means of the formula

Force reduction = (l-P/4000)xl00, in which P = force of penetration. According to a further preferred embodiment such materials are used, which in the form of a composition having four alternating layers, the two hard layers having a total thickness of 1.5-2 mm and the soft layers a total thickness of approximately 10 mm, result in a force reduction of 75 %, whereby the force reduction is measured by means of the formula. Force reduction = (l-P/4000)xl00, where P = force of penetration.

According to a still further embodiment such materials are used, which in the form of a composition having four alternating layers, the two hard layers having a total thickness of 2-2.5 mm and the soft layers a total thickness of approximately 10 mm, result in a force reduction of 80 %, whereby the force reduction is measured by means of the formula.

Force reduction = (l-P/4000)xl00, where P = force of penetration.

The force, i.e. the force of penetration (P), which is applied to the composition during the measurement should be below the ultimate stress limit for the outermost material in the composition, the force preferably being 5-10% below the stress limit.

The thickness of the total composition is preferably between 5 to 20 mm, preferably between 10 and 15 mm and more preferably between 10 and approximately 12 mm.

The example below shows the properties of different material compositions according to the present invention and two comparative compositions.

Example A number ( 1 - 10) of material compositions according to the present invention and two comparative compositions (11-12) have been tested to define the impact reducing ability of the compositions. The test has been performed according to the test for approval of leg protective devices according to the Swedish football association. The leg protective devices, which is to be tested is mounted on a wooden dummy of the lower part of a leg and a missile having a spherical impact area (diameter 66 mm) is dropped from a defined height onto the protective device. The force of penetration (P) applied to a circular area (diameter 10 mm) of the inner side of and in contact with the protective device is measured by the means of a piston in contact with the power sensor. The weight of the missile may vary between 0.5 and 100 kg and the missile is released from such a height that a force of 4000 N is measured when the protective device is mounted in the test equipment. The results are given as the force reduction in % and are calculated as follows:

Force reduction = (l-P/4000) xlOO

The force of penetration (P) is determined at three different spots on the protective device and five measurements are made at each spot. A mean value of the three highest values of the force of penetration are used to calculate the force reduction for the protective device. The accuracy of measurement of the test method is ± 1%. The results from 12 tested material compositions are seen in table 1.

The compositions according to the present invention have preferably an impact reducing ability (measured as the force reduction by the means of the above mentioned test method) of at least 50 %, preferably at least approximately 70 % and more preferably at least approximately 80 %.

The impact reducing ability of the protection according to figure 2 (corresponds to number 10 in the table 1) is ~ 100 % according to the examination method described above, i.e. no detectable pressure is applied to the measurement area during the test.

^a Hard material: Glass fibre composite, 1 fibre sheet (sgl); glass fibre composite, 2 fibre sheets (sg2); glass fibre composite, 3 fibre sheets (sg3); glass fibre composite, 4 fibre sheets (sg4); aramide composite, 1 fibre layer (sa). Each fibre layer has a thickness of 0,3 mm, which mean that sgl has a thickness of 0,3 mm, sg2 a thickness of 0,6 mm (2 x 0,3 mm), etc. ^b Soft material: Tempur ® (yellow), Evazote EV50 (grey), Plastazote LD29 (red). The soft materials each have a thickness of 5 mm.

From the above mentioned examples it may e.g. be concluded that the compositions 8 and 10 result in more or less a 100% force reduction. From the comparative examples it appears that the compositions 11 and 12 having only three layers, give approximately only half of the value reached with a fourth layer (see composition 4 and 3, respectively).

The material composition according to the present invention may also comprise more than four layers, e.g. 6,7 or 8, e.g. depending on the requested force reducing effect and the intended filed of application. Preferably an even number of layers is used.

Claims

1. Material composition for protection against impacts, comprising an outer layer (1,1 ^') of a force distributing material and further layers of alternating force absorbing and force distributing materials characterised in that the alternating layers are at least three (2, 2', 3, 3 ', 4, 4'), and that said force distributing and force absorbing materials are elastic, wherein a force reduction is obtained when an outer force is applied to the composition.

2. A composition according to claim 1 characterised in that the force distributing and force absorbing materials result in a force reduction of at least 50%, wherein the force reduction is measured by means of the formula Force reduction = (l-P/4000) x 100, and P = force of penetration.

3. A composition according to claim 1 characterised in that the force distributing and force absorbing materials result in a force reduction of at least 80%, wherein the force reduction is measured using the formula Force reduction = (l-P/4000) x 100, and P = force of penetration.

4. A composition according to any of the preceding claims, characterised in that said hard material has a coefficient of elasticity of 0,5 - 100 GPa.

5. A composition according to any of the preceding claims, characterised in that said soft material has a coefficient of elasticity of 10 - 200 GPa.

6. A composition according to any of the preceding claims, characterised in that said hard material is a glass fibre composite or an aramide composite.

7. A composition according to any of the preceding claims, characterised in that said soft material is a cellular or foamed plastic with closed cells.

8. A composition according to claim 6, characterised in that said glass fibre composite has 3 or 4 fibre sheets.

9. A leg protective device comprising the composition according to any of the previous claims.

10. A leg protective device according to claim 9, characterised in that it includes an outer layer of a glass fibre composite and thereafter three alternating layers of polyethene foam, glass fibre composite and ethylene vinyl acetate copolymer, respectively.