SHOE INSOLE INCLUDING A KNITTED SPACER FABRIC

The invention relates to a shoe insole coupling acceptable cushioning properties to an appropriate minimal thickness suitable for aftermarket insertion into commercially available shoes.

Knitted spacer fabrics are known and have been employed in various applications, such as in clothing, mattresses, seats, and in medical applications, including patient support material. Shoe insoles that have dynamic cushioning properties have conventionally been made of inherently resilient materials, such as gels, elastomers or foams, to achieve the desired cushioning properties within the thickness limitations dictated by the constraints of commercially available shoes. While acceptable cushioning properties have been obtained by such elastomeric or foam material insoles, these have also been found uncomfortable to users over extended periods of use by not providing sufficient ventilation. Knitted spacer fabrics, that could provide the desired high value ventilation, have not before been considered suitable in the application of cushioning insoles, as these could only provide acceptable cushioning properties in thicknesses way beyond those that would be acceptable for thin aftermarket shoe insoles, which desirably should range between 3 mm and 5 mm in thickness, at least at the forefoot area. Another drawback of the known spacer fabrics with higher cushioning properties is that their exposed outer surfaces are rather stiff and experienced as uncomfortable to the human skin.

Accordingly it is an object of the present invention to propose an improved insole that includes a knitted spacer fabric. In a more general sense it is thus an object of the invention to overcome or ameliorate at least one of the disadvantages of the prior art. It is also an object of the present invention to provide alternative structures which are less cumbersome in assembly and operation and which moreover can be made relatively inexpensively. Alternatively it is an object of the invention to at least provide the public with a useful choice.

To this end the invention provides a shoe insole including a knitted spacer fabric, comprising: a top layer; a bottom layer; and a plurality of spacing threads extending between the top layer and the bottom layer, wherein the spacing threads include a monofilament yarn having a diameter of between 0.09 mm and 0.12 mm. This diameter of between 0.09-0.12 mm enables the knitted spacer fabric to be used as an insole. In a preferred embodiment the spacing threads preferably include a monofilament that is looped through the top layer. A monofilament is a relatively rigid single fibre material, which is more rigid compared to multifilament yarn, especially in the heavier qualities. Looping of the monofilaments through at least the top layer has the effect of increasing stiffness of the portions that extend as spacing threads between the top and bottom layers by improved anchorage. In particular it is advantageous when the monofilament has a diameter of at least 0.10 mm. With the spacing threads arranged in an appropriate density this monofilament thickness enables the desired cushioning properties to be achieved, within a thickness as little as 3 mm. The monofilament spacing threads are preferably of polyamide or polyester, more preferably of polyester.

In a preferred embodiment the shoe insole has a thickness of between 3 and 5 mm, and wherein the cushioning energy, measured between a top surface of the top layer and a bottom surface of the bottom layer, exceeds 60 milli Joule (mJ) using SATRA test method PM 159 for measuring cushioning properties. Such an embodiment provides in an open structure spacer material the correct, or at least acceptable, cushioning properties and is suitable as an insole that can be inserted in commercially available shoes. A desirable cushioning value for an insole starts at about 60 mJ (SATRA test) and higher, depending on its use. For sporting footwear the thickness may be greater, than for regular footwear. Thickness of insoles for male and functional footwear may also be slightly greater than that of insoles for female and fashionable footwear. Clearly sporting and functional shoes may require higher cushioning values than fashion shoes. Some commercially available footwear comes with a replaceable inner sole, and with those more latitude is available to use thicker spacer fabrics.

In a further preferred embodiment the top layer on one of its sides, exposed to the exterior and adapted to contact a shoe wearer's foot, has been given a softer feel by a sanding treatment. It has been found, that the sandpaper treatment will roughen the top surface, by controlled damaging of the yarns. This results in small loose yarn parts sticking out of the yarns that give a soft feeling. Preferably the sanding treatment has consisted of subjecting the exposed surface of the top layer to two passes of sandpaper, having a coarseness value of at least 150 and not exceeding 280, while applying a moderate pressure. Too much sanding, either by more passes, coarser sanding paper or too high sanding pressure will yield a raspy feeling. Excessive sanding will moreover destruct the textile structure of the knitted fabric, to the extend that holes are developed in the surface. Too little sanding, by less than two passes, too fine sanding paper, or too low sanding pressure, has been found not to produce the desired effect. With respect to the sanding treatment it is further preferred when a first pass of the two passes is in a first direction and a second pass is in a reverse direction. Running the knitted fabric through a sanding machine in a first run in one direction and in a second run in a reversed direction provides for a more equal treatment.

In general it is also possible with advantage to have the spacer fabric additionally treated with a fabric softener. It has been shown however that the softening effect is limited in respect of that obtainable with the sanding treatment.

One insole 1 according to the invention is illustrated in FIG. 1. FIG. 1(A) is showing a bottom side 3 of the insole 1 and FIG. 1(B) is showing a top side 5 thereof. The bottom side 3 has a pattern that is composed of relatively large openings 7 and the top side 5 has a pattern of relatively large openings 9. The bottom side 3 is further covered by a support element 11 to provide a gradual reinforcement from a mid-foot portion to a heel portion. The heel portion is further provided with an additional cushioning and anti-slip insert 13. Thickness in the heel area can be allowed in the region of 7 mm. The support element 11 and heel insert 13 may also enhance handling of the insole when inserting same into a shoe and provide additional friction to prevent moving in the shoe, when in use. The support element 11 is attached by adhesive bonding.

Another variation of insole 21 is illustrated in FIG. 2. In this instance FIG. 2(A) shows a top side 25 of the insole 21 and FIG. 2(B) shows a bottom side 23 thereof. The bottom side 23, which corresponds with a lower surface of a spacer fabric material, is again provided with relatively large openings 27 in a pattern. The top side 25, which corresponds to an upper surface of the spacer fabric material, is provided with a pattern of relatively small opening 29. The pattern may be a regular or an irregular pattern depending on the type of braiding used. The bottom side 23 is partly covered by a support element 31, that is relatively inflexible and that extends from a mid-foot area towards the heel area to give a gradually increasing rigidity to the insole. The heel portion is provided with a cushioning and anti-slip insert 33.

Except for the form of the support elements 11, 31 the insole variants of FIGS. 1 and 2, are substantially identical. The insole 1 of FIG. 1 has been developed basically with male and functional footwear in mind, whereas the insole 21 of FIG. 2 has been designed principally for use in ladies and fashionable footwear. It should be clear however that other variations are within the scope of the invention, provided that these include as a major constituent a spacer fabric that has a top layer with relatively small opening and a bottom layer spaced there from with relatively large openings. The top layer and bottom layer use a denier that is preferably only slightly lower than that of the spacing threads, which will be discussed in more detail in reference to FIGS. 3 and 4. In this example both top and bottom layer are knitted from 150 denier polyester yarn. When colouring is required then alternatively polyamide yarns may be used but this is a more expensive option.

In shaping the perimeter of the spacer material of the insoles, to conform to a footprint, it has been found useful to employ laser cutting. This gives sharp and fine edges and fixates the braided structure after cutting. Additionally an anti-bacterial treatment may be given to the insoles of the invention and the known anti-bacterial agents have been found suitable for this purpose.

In FIG. 3 a side view of the spacer fabric shows it's cross-section in the warp direction, bottom layer 43 corresponds substantially to the bottom layers 3 and 23, as referred to in reference to FIGS. 1(A) and 2(B). A top layer 45 corresponds substantially to the top layers 5 and 25, as referred to in FIGS. 1(B) and 2(A). In-between the bottom and top layers 43, 45 is a cushioning layer that includes a plurality of spacing threads 55 that extend between the bottom layer 43 and the top layer 45.

The spacing threads 55 are each formed by polyester monofilaments having a diameter of between 0.09 mm and 0.12 mm, but preferably a polyester monofilament with a diameter of at least 0.10 mm. The monofilament yarn forming the spacing threads 55 may be a length of yarn that is knitted together with the yarns of the top and bottom layers 43, 45 and be looped back and forth between these layers.

FIG. 4 shows a side view of the spacer fabric of a cross-section in its weft direction. In the weft direction the openings in the top and bottom layers have a longer extend. The relatively large openings in the layer 43 are indicated as 49, whereas the relatively small openings in the top layer 45 are indicated as 49. The spacing threads 55 comprise oppositely inclined groups 55A, 55B, which helps to increase the stability of the cushioning layer that is formed of a possibly dense array of spacing threads 55 by preventing collapsing in a lateral direction. In general it also enhances stability when bias and orientation of the spacing threads introduces opposing forces.

In FIG. 5 is represented an enlarged detail view of the upper surface of the top layer 45 having a pattern of relatively small opening 49. A ruler 57 is superimposed on the top layer 45 to give an indication of its proportions along a centimeter (cm) scale. An arrow 59 indicates the weft direction and an arrow 61 indicated the warp direction.

In FIG. 6 an enlarge detail view of the lower surface of the bottom layer 43 is shown. The bottom layer 43 has a pattern of relatively large sized openings 47.

A ruller 57 is again superimposed on the bottom layer 43 to indicate its proportions in respect of a cm scale. The arrows 59, 61 indicate again the weft and warp directions, respectively.

The spacer material described in reference to FIGS. 1 to 6 has a thickness of 3.5 mm, measured from top to bottom surface. The yarns and threads used to form the top and bottom layers, as well as the “intermediate layer” of spacer threads are 100% polyester. The top and bottom layers each use a multifilament polyester fibre, denier 150, fibre count 72. The spacer threads in the “intermediate layer” are a monofilament polyester of 0.10 mm diameter. The density of the spacer material having this thickness per area is between 550 and 650 g/m². This calculates as an overall volumetric density of 0.165-0.18 g/cm³. In comparison it may be noticed here that a conventional gel material, as employed for insoles, has a density of about 1.0 g/cm³. The density with the specified yarns in the top and bottom layers, and the specified spacing threads there between, is attributed for 23-28% in the top layer, for 60-65% in the “intermediate layer” and for 12-15% in the bottom layer. Thus a significant aspect of the spacer material of the invention is a density of the spacer threads that exceeds 50% of the overall density. It is thereby also preferred that the proportion that the top layer attributes to the overall density, exceeds that of the bottom layer and is substantially double to that.

In general the multifilament polyester or polyamide yarns preferred for the top layer are within a range of 140 to 250 denier, while those of similar material for the bottom layer are preferably within a somewhat narrower range of 140-160 denier. The spacer threads are preferably formed of a polyester monofilament yarn having a diameter within the range of 0.09-0.12 mm. The preferred density, while respecting these ranges, works out at 0.165-0.50 g/cm³, which has be found necessary to achieve the minimum cushioning properties for use in insoles. In the preferred thickness range of 3-5 mm the monofilament spacer threads account for 60-65% of the total weight and result in a middle layer that has a volumetric density of 0.10-0.325 g/cm³.

Reference is now made to FIG. 7 which illustrates schematically the way in which a monofilament thread 63 is looped through the bottom and top layers 43, 45, to form the spacing threads 55. It is particularly important that the monofilament 63 is looped through the top layer 45 as this enhances the stability of the finished spacer fabric and insole product in achieving a high cushioning energy. This cushioning energy should be at least 60 milli Joules (mJ)—in accordance with SATRA's PM 159 test method for cushioning properties—for a thickness between the outer surfaces of the top and bottom layers that does not exceed 5 mm, and preferably does not exceed 4 mm.

To enable verification of the properties required from the spacer fabric to be useful for the insoles according to the invention reference is made to FIGS. 8 and 9. FIG. 8 schematically illustrates a measuring method developed by the British SATRA organization. According to this measuring method a predefined probe 65 engages a spacer material 67 that is being tested, with a constant speed and pressure. The strength of the spacer material 67 in Newtons (N) or kilo Pascall (KPa) and the nominal depression depth (Nominal strain) can then be recorded in a graph as shown in FIG. 9.

The graph of FIG. 9 shows the depression depth (nominal strain) and relative impact force (standard force) for repeated compressions of a single sample. The curved lines, one for each of the successive depressions, deviate slightly from one another, because the resilience of the knitted spacer material shows a certain delay in returning to its initial properties.

The depression depth indicated by reference numeral 69 in FIG. 8 is represented by the horizontal axis of the graph of FIG. 9 and the sample tested had a thickness that accommodated a depression of about 4.5 mm. The curved lines 71, 73, 75, 77, 79, and 81 represent successive repeated depressions. Some slowness in recovery of the material is clearly evident from the different course between the first depression test curve 71 and the depression test curve 81. This somewhat slow recovery of the spacer fabric is not necessarily a drawback, as it may absorb the walking and running impacts in a manner unnoticed to the user, whereas a too quickly recovering material may convey too much a springy character to the user.

Cushioning can be defined as the ability of the insole material to conform elastically to the shape of the foot and distribute pressure, while standing, walking or running. Cushioning energy, expressed in milli Joules, is the energy that is absorbed by the insole during a single compression at a certain pressure. The cushioning energy is represented by the entire area to the right and below the curved lines in the graph illustrated in FIG. 9. A test method for determining cushioning energy has been developed by the SATRA institute and is known under their reference PM 159.

Manufacturing of the spacer fabric starts with providing the necessary yarns and monofilament and appropriately warping these for a knitting and/or conversion process. The so warped yarns are then knitted into a spacer fabric with monofilament spacing threads extending between top and bottom layers. The monofilament thereby is looped through at least the top layer. The knitted spacer fabric is then finished by one or more of colouring, adding softener and/or antimicrobial agents or the like. The so finished spacer fabric can then be subjected to a heat setting treatment and to sanding of its top surface. Optionally the produced quantity of spacer fabric can be subjected to quality inspection to ensure that it meets predefined specifications.

Sanding of the top surface can be accomplished in a conventional textile sanding machine that has a number of sandpaper rolls. A coarseness of the sandpaper of these rolls is selected to be one of 150 and 280, or any value there between. Pressure rolls may be employed to enhance the contact between the fabric top surface and the sandpaper rolls. It has been found that the uncomfortable feel of a top surface not treated by sanding can be attributed for an important part to the rather heavy and thick monofilaments being looped through the top layer of the knitted spacer fabric. By the sanding operation the yarns in the top layer, including notably also looped portions of the monofilament spacing threads, are damaged in a controlled manner so as to produce small loose yarn parts that stick out from the yarns. These sticking out elements soften the feeling on skin contact of the exposed upper surface. This effect is best achieved by two runs of the fabric through the sanding machine, with the second run in a direction opposite to the first run. Less sanding runs, or sanding with a sandpaper coarseness finer than 280 does not sufficiently produce the desired effect. On the other hand it has been found that sanding exceeding two successive runs, or at too high sanding pressure, and/or using too coarse a sandpaper (i.e. below 150) destroys the effect again. This is noticed by a raspy feeling that may be caused by uncontrolled damage to the monofilament loops, which presumably partly break and stick out from the top surface.

It is also an advantageous feature of the spacer material insole of the invention that it allows a high value ventilation in comparison to foam and gel material that are also used for insoles. Ventilation values in excess of 2,046,285 l/m² h have been achieved. Another benefit of the enablement of using spacer fabric as insoles is its low weight compared to the conventional foam and gel materials.

It is thus believed that the operation and construction of the present invention will be apparent from the foregoing description. The invention is not limited to any embodiment herein described and, within the purview of the skilled person; modifications are possible which should be considered within the scope of the appended claims. Equally all kinematic inversions are considered inherently disclosed and to be within the scope of the present invention. In the claims, any reference signs shall not be construed as limiting the claim. The term ‘comprising’ when used in this description or the appended claims should not be construed in an exclusive or exhaustive sense but rather in an inclusive sense. Thus the expression ‘comprising’ as used herein does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, the words ‘a’ and ‘an’ shall not be construed as limited to ‘only one’, but instead are used to mean ‘at least one’, and do not exclude a plurality. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage. Expressions such as: “means for . . . ” should be read as: “component configured for . . . ” or “member constructed to . . . ” and should be construed to include equivalents for the structures disclosed. The use of expressions like: “critical”, “preferred”, “especially preferred” etc. is not intended to limit the invention. Features which are not specifically or explicitly described or claimed may be additionally included in the structure according to the present invention without deviating from its scope.