"A METHOD OF MOULDING AN OBJECT IN POLYURETHANE , IN PARTICULAR A SOLE FOR FOOTWEAR, OBTAINED FROM

POLYURETHANE SCRAPS, AND MOULDED OBJECT IN POLYURETHANE

THEREOF"

FIELD OF APPLICATION

[0001] The present invention relates to a method of moulding an object in polyurethane, in particular a sole for footwear, obtained from polyurethane scraps, and a moulded object in polyurethane, such as a sole for footwear .

PRIOR ART

[0002] As is well known, in recent years there is increasing consumer and market awareness to the issue of green economy, i.e. an economy that in addition to the goal of profit also supports the search for processes aimed to lower the impact on the external environment, protecting the environment in every possible form (energy, mining, ecological), making it sustainable. A theme strongly felt in art is that of the recovery of production waste.

[0003] In particular, in the field of soles for footwear, there are various operations under investigation or already implemented for the reuse of waste materials avoiding disposal thereof, in a manner dependent on the individual materials used as main components and/or accessories (vulcanised rubber, TPR, TPU, EVA, PVC, PC, ABS, PU) . The particular industry to which the present invention is directed is that of polyurethane foam, widely used in footwear.

[0004] The production of this type of sole employs a polymer (reaction product of two components called isocyanate and polyol) whose cross-linked (i.e. vulcanised) nature prevents the reuse of production waste, either they are by-products (burrs, drain pre- casting for colour change) or non-compliant finished parts. Therefore, it is not possible to grind the waste for reuse in small size with the raw material, as is the case with thermoplastic polymers.

[0005] In the field of polyurethane foam, therefore, there are primarily two ways of implementing the reuse of waste materials: glycolysis and agglomeration.

[0006] Glycolysis is the reaction between ground polyurethane and propylene (MonoEthyleneGlycol , DiEthyleneGlycol , or low molecular weight hydroxylated resins) which, under the action of heat and stirring, leads to a liquid product of low molecular weight which preserves hydroxyl functions. This product can be mixed in shearing with raw polyol and undergo a new polymerization reaction. [0007] Agglomeration uses shredded waste of polyurethane of flexible foams that are mixed with raw polyurethane, which by foaming incorporates them at its interior.

[0008] A third way is shredded waste agglomeration with the addition of a binder which acts as a glue where, inside a mould by the action of heat, the granules adhere to each other to produce a single piece.

DISCLOSURE OF THE INVENTION

[0009] The above known techniques have drawbacks and limitations.

[0010] In particular, the waste recovery technique by glycolysis includes a preliminary process which is obtaining the glycolized polyurethane, which requires a reactor in which the granules and glycol must react at high temperature for many hours. The result is a highly viscous liquid, with low technical characteristics due to the high diversity of components, which can be directly inserted into the polyol part only, in that are more technically disadvantageous as they are higher. Therefore, the final product will have a percentage of recovered on the finished product that, in the best case, does not reach 50%.

[0011] Considering the cost and complexity of the preliminary preparation reaction of the glycolized and the concentration limit on the total, such waste recovery method is not satisfactory from the point of view of both the commercial value and the ecological impact.

[0012] In the agglomeration technique of soles ground with raw polyurethane, an ISOCYANATE/POLYOL mixer should be arranged which provides for the introduction of this third component. The balance to be respected for the agglomeration to be moulded does not exceed concentrations of granules on the finished product of more than 20-30%, since these hinder the flow of material inside the mould, producing filling defects with respect to the original shape of the mould. Of course, the above percentages of granules are even more penalizing than those obtained with the glycolysis technique.

[0013] As for the agglomeration of the ground with a binder, the prior art allows a high percentage of recovered materials to be obtained since the binder envelopes the granules and is able, in minimum quantity, to glue them in one piece. Currently, this process is used to recover ground waste of various types, including polyurethane.

[0014] The current technique consists of three steps:

[0015] - pressing into large moulds granules consisting of scraps of polyurethane products (from insulation or packaging light foams) formerly wetted with a binder; then, the binder is baked with heat or steam, which is made using a significant amount of time,

[0016] - the resulting block is then cut into flat or rolled sheets,

[0017] - the sheets can be die-cut, shaped or coupled with other materials.

[0018] The limitation of the current scrap agglomeration technique with a binder lies in the fact that the products obtained from these sheets can have very geometrically simple shapes, and in order to obtain them, the agglomeration block must always be first moulded.

[0019] The need of solving the drawbacks and limitations mentioned with reference to the prior art is therefore felt.

[0020] Such a need is met by a moulding method according to claim 1.

DESCRIPTION OF THE DRAWINGS

[0021] Further features and advantages of the present invention will appear more clearly from the following description of preferred non-limiting embodiments thereof, in which:

[0022] figure 1 shows a schematic view of a mould system for implementing the moulding method according to the present invention.

[0023] Elements or parts of elements in common between the embodiments described below are referred to with the same reference numerals.

DETAILED DESCRIPTION

[0024] With reference to the above figures, reference numeral 4 globally indicates an overall schematic view of a mould for implementing the moulding method according to the present invention.

[0025] In the following description, explicit reference is made to a method for making a sole for footwear. However, the method can be extended to producing objects comparable in size to a sole to replace traditional materials where the properties of the agglomerate are sufficient, in particular in filling or containment uses. One can assume the production of a brick of such a shape that can be mechanically jointed with others identical ones, so as to form a larger structure that can be used as a weight, barrier or support. Therefore, in the following description, explicit reference will be made to an article such as a sole for footwear, without losing generality for the purposes of defining the scope of protection of the present invention.

[0026] Mould 4 comprises a body 8 and a cover 12 whch delimit, in closed configuration, a moulding chamber 16 which defines in negative the volume of product 20 to be moulded, in a known manner.

[0027] For example, mould 4 will be provided with handling means 24 of cover 12 and/or body 8, to allow the opening and closing thereof.

[0028] Mould 4 is provided with fluid inlet channels 28, typically steam (as best explained hereinafter) and one or more vent channels 32, fluidically connected to the moulding chamber 16 to allow the selective entry and expulsion of fluids, typically gas, in or from the moulding chamber 16.

[0029] Moreover, mould 4 may be provided with a steam generator 36 fluidically connected to mould 4, i.e. to the moulding chamber 16 by means of said fluid inlet channels 28.

[0030] The method of moulding an object in polyurethane, in particular a sole for footwear, according to the present invention, comprises the initial step of arranging polyurethane scraps in granular form.

[0031] Preferably, scraps are used which have an average particle size comprised between 4 and 7 mm, comprising extremes in the range 1-lOmm, of granular-pseudo spherical shape. The use of scraps having needle-shaped particle size is also contemplated, such as in the case of burrs, with lengths between 2 and 20mm and thicknesses less than a millimetre.

[0032] The selection of the scrap type is not random but a step is provided to select polyurethane scraps having a breaking load greater than 10 kg/cm2, and a density greater than 130 g/L.

[0033] Preferably, the polyurethane scraps have a breaking load of 10-60 kg/cm2; such a load is for example comprised between 10-20 Kg/cm2 when using drain pre- casting .

[0034] Moreover, according to one embodiment, the polyurethane scraps have a density of between 400-600 g/L, for example in the case of using scrap soles; moreover, drain pre-casting for colour change with a density of between 150 and 350 g/L may also be used.

[0035] As regards the type of material to be selected, according to an embodiment the hardness of said polyurethane scraps is between 5-70 ShoreA. Even more preferably, the hardness of said polyurethane scraps is between 35-55 ShoreA, in the case of scrap soles.

[0036] It is also possible to use drain pre-casting for colour change having a hardness of between 5-35 ShoreA.

[0037] After having arranged the polyurethane scraps, suitably selected as described, said scraps are wetted with a polyurethane binding agent in order to obtain an agglomerate of scrap material and binding agent.

[0038] Preferably, the polyurethane binding agent is isocyanate, suitable to react chemically with the steam, leading to the formation of ureic groups that increase the molecular weight of the binding agent, as better described hereinafter.

[0039] The step that provides for wetting the granules in advance is useful to ensure that the granules do not touching each other directly but there is always a thin layer of binding agent between them. On the one hand, this facilitates the flow of the granules in the liquid phase of the agglomeration, and thus allows for a correct and complete filling of the moulding chamber 16 of mould 4. On the other, the same layer of binder, as a result of heat treatment, will solidify and will constitute the matrix that permanently and elastically incorporates the polyurethane granules.

[0040] The method provides for the step of inserting the agglomerate in said mould 4, in particular in the moulding chamber 16, so that the percentage by weight of the binding agent is at least equal to 10% of the total weight of the agglomerate inserted in mould 4 itself.

[0041] For example, in order to fill mould 4, cover 12 is at least partially displaced from body 8 by the handling means 24, so as to access the moulding chamber 16 and fill it with the agglomerate.

[0042] Preferably, mould 4, or better the moulding chamber 16 thereof, is filled so that the compression ratio between the polyurethane granules to be moulded and the agglomerate obtained by moulding is about 2:1/3:1.

[0043] Preferably, the final agglomerate density is between

200-600 g/L.

[0044] After filling the moulding chamber 16, mould 4 is closed and the agglomerate is baked with steam blown inside the moulding chamber 16 of mould 4.

[0045] The steam is preferably water vapour, blown through the fluid inlet channels 28 at a pressure of between 2 and 4 bars .

[0046] Preferably, the steam is injected at a temperature of between 100 and 150 °C.

[0047] Due to the action of the steam, an increase in the molecular weight of the binding agent and the incorporation of the scraps inside a binding agent matrix is obtained.

[0048] In particular, since the polyurethane binding agent is isocyanate, it is suitable to react chemically with the steam, leading to the formation of ureic groups that increase the molecular weight of the binding agent.

[0049] It is also possible to provide the step of equipping the mould with heating means (not shown) and heating the mould from the outside at the same time as baking the agglomerate with steam inside mould 4. This increases the heating or shortens the duration of heating and baking of the agglomerate. [0050] For example, the baking time of the agglomerate inside the mould is 5-8 minutes.

[0051] At the end of the baking step, the cooling step of the mould and the extraction of the moulded part are carried out.

[0052] The cooling process can for example take place by by blowing of cold air.

[0053] The moulded part extracted from the moulding chamber 16 will have the shape and size of the latter and will be ready for use. In the case of a sole for footwear, it may for example be coupled to an upper.

[0054] As can be appreciated from the description, the present invention allows overcoming the drawbacks of the prior art.

[0055] In particular, the moulding method of the present invention allows:

[0056] either obtaining the finished piece with the desired shape in one step;

[0057] or reducing the baking time to a few minutes due to the small size of the mould;

[0058] or obtaining complex shapes due to the use of the final mould;

[0059] or using the ground scrap soles as a granule.

[0060] By virtue of the present invention it is possible to produce an article, and in particular a sole for footwear, starting from ground scrap and a binder that has a recycled content in the finished product higher than 75%, which is not possible with the prior art solutions .

[0061] Therefore, as seen, the present invention allows reaching concentrations higher than 75% of recycled material on the finished piece both with respect to glycolysis (with percentages lower than 50%) and to the agglomerate with polyurethane (with percentages lower than 25%) . The use of mould vulcanisation allows ample design opportunities with respect to the use of blocks to be cut, and times compatible with a reasonable hypothesis of productivity.

[0062] A man skilled in the art may make several changes and adjustments to the moulding methods described above in order to meet specific and incidental needs, all falling within the scope of protection defined in the following claims.