Footwear assembly method using thermoplastic copolyamides as adhesive

Abstract

The invention relates to the use of a copolyamide of the following formula: Aa / (X.Y)b (formula I) wherein: A is at least one from among: (i) an alpha,omega-aminocarboxylic acid; (ii) a lactam; and X is at least one aliphatic diamine with 2 to 14 carbon atoms, a polyether or a polyetheramine comprising ether groups comprising 2 to 4 carbon atoms; Y is at least one aliphatic dicarboxylic acid with 6 to 22 carbon atoms; a is an integer from 1 to 3, in particular 1 or 2; and b is an integer from 1 to 3, in particular 1 or 2; said copolyamide having: • a melting temperature Tm of between 80°C and 150°C, • a melt volume-flow rate of 100 to 300 [mL / 10 min] at 160°C under 2.16 kg, as measured according to the ISO 1133 standard, - an enthalpy of crystallization of less than 5 J / g, as measured according to the ISO 307 standard by DSC on cooling at 20K / min, and - an enthalpy of fusion of at least 5 J / g, as measured according to the ISO 307 standard by DSC on heating at 20K / min, for the assembly of articles by hot spraying.

Description

[0001] Shoe assembly process using thermoplastic copolyamides as adhesive

[0002] technical field

[0003] This patent application relates to the use of particular thermoplastic copolyamides by hot spraying for the assembly of articles, in particular footwear, the associated article assembly process and the articles, in particular footwear, that can be obtained by this process.

[0004] Previous technique

[0005] Shoes, especially sports shoes, are generally made by assembling different parts, including an upper, a midsole, and an outer sole.

[0006] Various methods exist for assembling these shoe components. Historically, shoes were assembled, for example, by nailing or sewing. Modern shoes, particularly those made of synthetic materials, can also be assembled using adhesives.

[0007] Hot melt adhesives are substances that are solid at room temperature and are generally free of water and solvents. They are applied in a molten state and harden upon cooling, forming an adhesive bond that ensures the assembly of two substrates to be joined. These adhesives must have a melting point compatible with the material of the shoe components and develop sufficient adhesive strength to ensure a reliable bond. In addition to the thermoplastic polymer, hot melt adhesives may also contain a tackifying resin and / or a plasticizer.

[0008] Although it is possible to apply the adhesive using veils or films, it is advantageous to do so by hot spraying because this method is faster and more economical and is also compatible with automation of the assembly process.

[0009] Furthermore, the hot melt adhesives typically used for shoe assembly are thermoset adhesives, for example, polyurethane-based. These adhesives are incompatible with hot spray application and also present challenges during recycling. Therefore, these adhesives cannot be used in the manufacture of eco-designed products.

[0010] We are therefore looking for an adhesive for assembling items such as shoes that is suitable for hot spray application and that does not pose problems during the recycling of the items after use. Summary of the invention

[0011] The invention therefore aims to propose the use of copolyamides with a specific property profile that makes them suitable for solving the technical problem stated above. Indeed, the present invention is based on the observation that copolyamides with a melting temperature, hot viscosity, and crystallization rate as defined below allow both the deposition of a precise adhesive bead by hot spraying and also form a good quality bond, as evidenced by the energy required for separation and the observed mode of failure.

[0012] Also, according to a first aspect, the invention relates to the use of a copolyamide with the following formula:

[0013] HAS a / (XY)b (formula I) in which:

[0014] A is at least one of:

[0015] (i) an alpha-omega aminocarboxylic acid;

[0016] (ii) a lactam; and

[0017] X is at least an aliphatic diamine with 2 to 14 carbon atoms, a polyether or a polyetheramine comprising ether groups comprising 2 to 4 carbon atoms;

[0018] Y is at least one aliphatic dicarboxylic acid with 6 to 22 carbon atoms; a is an integer from 1 to 3, including 1 or 2; and b is an integer from 1 to 3, including 1 or 2; said copolyamide having: a melting temperature Tf between 80°C and 150°C, a hot melt volume index of 100 to 300 [mL / 10 min] at 160°C under 2.16 kg, as measured according to ISO 1133-1:2011, an enthalpy of crystallization of less than 5 J / g, as measured according to ISO 307 by DSC in cooling at 20K / min, and an enthalpy of fusion of at least 5 J / g, as measured according to ISO 307 by DSC in heating at 20K / min for the assembly of articles by hot spraying, in particular in a process known as "hot spraying" as defined below.

[0019] Advantageously, the copolyamide is of formula (I), where A is chosen from caprolactam, amino-11-undecanoic acid and lactam 12.

[0020] Preferably, the copolyamide is of formula (I), where X is selected from linear aliphatic diamines such as ethylene diamine, putrescine, cadaverine, 1,6-hexamethylene diamine, 1,10-decamethylene diamine; branched diamines; and cyclic diamines such as piperazine.

[0021] Preferably, the copolyamide is of formula (I), where Y is a linear aliphatic dicarboxylic acid, preferably selected from adipic acid, pipelic acid, suberic acid, azelaic acid, sebacic acid, 1,11-undecanedioic acid, 1,12-dodecanedioic acid and brassylic acid.

[0022] Advantageously, the copolyamide has formula (I) with a = 1 or 2 and b = 1 or 2, in particular with a = 2 and b = 1.

[0023] In particular, the copolyamide may have formula (I) and comprises at least one XY unit in which X is 11l,6-hexamethylene diamine.

[0024] In particular, the copolyamide can be PA 6 / 6.12 / 12.

[0025] Advantageously, the copolyamide has a melting point (Tf) between 85 and 130°C.

[0026] In particular, copolyamide can exhibit a glass transition temperature (Tg) below 60°C.

[0027] Preferably, the copolyamide allows a peel force, measured according to the t-peel test described in the examples, of at least 30N / mm.

[0028] According to a second aspect, the invention relates to a method for manufacturing articles, comprising the following steps:

[0029] (a) supply of the parts of the article to be assembled;

[0030] (b) application of a copolyamide according to the invention, on at least one of the surfaces of at least one of the parts to be assembled, by hot spraying; and

[0031] (c) assembly of the parts to be assembled, where appropriate under application of pressure.

[0032] Preferably, the polymer component of the finished article comprises at least 70%, preferably at least 80% and in particular at least 90% by weight of thermoplastic polymer.

[0033] According to a third aspect, the invention relates to an article that can be obtained by said manufacturing process, preferably a shoe, in particular a sports shoe.

[0034] Description of the implementation methods

[0035] Definition of terms

[0036] The term "copolyamide" refers to a polymer resulting from the copolymerization of at least two chemically distinct types of monomers, called comonomers, of which at least one, preferably two or three, and in particular all, are polyamide monomers as defined below. A comonomer other than polyamide monomers may, in particular, be a polyether monomer as defined later. A copolymer is therefore formed of at least two distinct repeating units or motifs. It may also be formed of three, four, five, or more repeating units. The copolyamide in the sense of the present invention is preferably a block copolymer, in which each repeating unit forms a segment of a certain length.

[0037] The term "monomer," as used in the description of polyamides, should be understood as the monomer necessary to form a repeating unit. The case where the repeating unit of the polyamide is formed by the association of a diacid with a diamine is a special one. In this case, the diamine / diacid pair (in equimolar quantities) is considered the monomer, since individually, the diacid and the diamine are not capable of polymerizing.

[0038] In the following description, any reference to a standard means the version of said standard in force on the filing date (or priority date if priority is claimed) of this application.

[0039] The term "melting temperature" refers to the temperature at which a polymer, at least partially crystalline, transitions to a viscous liquid state, as measured by differential scanning calorimetry (DSC) according to the standard NF EN ISO 11 357-3.

[0040] The term "glass transition temperature" refers to the temperature at which a polymer, at least partially amorphous, transitions from a rubbery to a glassy state, or vice versa. Glass transition temperature is conventionally measured by differential scanning calorimetry (DSC) according to standard NF EN ISO 11357-2. The minimum temperature measurable by DSC depends on the equipment used and is generally around -30°C. Below this minimum temperature, or as an alternative to DSC, glass transition temperature can be measured by dynamic mechanical analysis (DMA) according to standard ISO 6721-4 with a frequency of 1 Hz and an amplitude of 20 pm (voltage).

[0041] The term "enthalpy of crystallization" refers to the latent heat of crystallization, as measured by differential scanning calorimetry (DSC) according to the standard NF EN ISO 11 357-3.

[0042] The term "enthalpy of fusion" refers to the latent heat of fusion, as measured by differential scanning calorimetry (DSC) according to the standard NF EN ISO 11357-3.

[0043] In the context of the copolyamides of the invention, the melting temperature, the glass transition temperature (when determined by DSC), the enthalpy of crystallization, and the enthalpy of fusion are determined by applying the following DSC cycle: 1) the sample temperature is equilibrated to 20°C, 2) the sample is cooled to -30°C using a cooling ramp of 10 K / min, 3) the sample is held at -30°C for 5 minutes, 4) the sample is heated to 250°C with a heating ramp of 20 K / min, 5) the sample is held at 250°C for 5 minutes, 6) the sample is cooled to -30°C with a cooling ramp of 20 K / min, 7) the sample is held at -30°C for 5 minutes, and finally 8) the sample is heated to a temperature of 250°C with a heating ramp of 20K / min.

[0044] The term "MVR" (English acronym for "melt volume rate") refers to the melt volume flow index. MVR is measured according to ISO 1133-1:2011, using an extrusion plastometer.

[0045] The nomenclature used to define polyamides is described in ISO 1874-1:1992 "Plastics - Polyamide (PA) materials for molding and extrusion - Part 1: Designation", particularly on page 3 (Tables 1 and 2), and is well known to those skilled in the art. In the PAL notation, PA designates polyamide and L designates the number of carbon atoms in the amino acid or lactam. Thus, polyamide is obtained by the polycondensation of the amino acid or lactam containing L carbon atoms. In the PAMN notation, M designates the number of carbon atoms in the diamine and N designates the number of carbon atoms in the diacid.

[0046] For the purposes of this invention, "hot spray" refers to a hot melt adhesive deposition technique in which the adhesive, introduced at room temperature in a solid state, is fluidized and / or liquefied during a short heating step to a high temperature, typically at least 20°C above the melting point of the adhesive, before being directly sprayed onto the substrate to be bonded. In a hot spray process, the heated / liquefied adhesive is sprayed onto the surface of the material immediately after being fluidized / liquefied, typically up to a few seconds after being fluidized and / or liquefied. In particular, the adhesive is not stored / maintained in a fluid / liquid state in a reservoir. The hot melt adhesive, heated to such a high temperature, has significant fluidity, so it is necessarily applied to the substrate continuously, typically in the form of one or more beads.

[0047] The hot spray technique of the invention differs from a printing technique, also called droplet projection technique, in several aspects.

[0048] The first difference lies in the temperature to which the adhesive is heated. In a printing process, the hot melt adhesive is heated to a temperature just high enough to make it fluid, generally close to its melting point. In a hot spray process, the adhesive is heated to a much higher temperature, typically at least 20°C above its melting point, so that it can be easily sprayed.

[0049] Furthermore, in a printing technique, a large quantity of adhesive is preheated and kept in a fluid state in a temperature-controlled tank. Conversely, in a hot spray process, the adhesive is continuously heated and directly applied / sprayed onto the substrate to be bonded. This direct application of the fluid / liquefied adhesive is essential because it prevents the degradation and / or oxidation of the adhesive that can occur at the high temperatures used in a hot spray process. This type of degradation does not occur at the temperature ranges used in printing techniques.

[0050] Finally, in a printing technique, the hot-melt adhesive is a viscous fluid that allows for the projection / application of the adhesive onto the substrate in a specific pattern, such as dots. However, this type of pattern is impossible to achieve with a hot-spray process, as the adhesive heated to such temperatures is too fluid. Therefore, adhesive applied using a hot-spray technique results in a continuous pattern, typically in the form of beads.

[0051] In the context of the present invention and unless explicitly stated otherwise, the ratios of each of the monomers are expressed by weight, relative to the total weight of the copolyamide.

[0052] As mentioned above, the invention aims, according to a first aspect, at the use of a copolyamide with the following formula:

[0053] HAS a / (XY)b (formula I) in which:

[0054] A is at least one of:

[0055] (i) an alpha-omega aminocarboxylic acid;

[0056] (ii) a lactam; and

[0057] X is at least an aliphatic diamine with 2 to 14 carbon atoms, a polyether or a polyetheramine comprising ether groups comprising 2 to 4 carbon atoms;

[0058] Y is at least an aliphatic dicarboxylic acid with 6 to 22 carbon atoms; a is an integer from 1 to 3, in particular 1 or 2; and b is an integer from 1 to 3, in particular 1 or 2; said copolyamide having: a melting temperature Tf between 80°C and 150°C, a hot melt volume index of 100 to 300 [mL / 10 min] at 160°C under 2.16 kg, as measured according to ISO 1133, an enthalpy of crystallization of less than 5 J / g, as measured according to ISO 307 by DSC cooling at 20K / min, and an enthalpy of fusion of at least 5 J / g, as measured according to ISO 307 by DSC heating at 20K / min, for the assembly of articles by hot spraying. Indeed, it has been found that these copolyamides have the properties required for the assembly of articles, particularly shoes, by hot spraying.The fact that it is a one-component hot melt adhesive makes the process more flexible, since it is not necessary to respect the open time as with HMPUR adhesives.

[0059] Furthermore, these copolyamides are more respectful of health and the environment since they contain neither solvents nor residual isocyanates.

[0060] Finally, the copolyamides used according to the invention are recyclable because they are thermoplastic. Thanks to the thermoplastic nature of these polyamides, articles assembled using them can be fully recycled. In particular, when articles contain a significant proportion of thermoplastic polymer or are even made entirely of thermoplastic polymer, the entire article can be ground and melted to provide a material that can be reused, thus greatly facilitating its recycling.

[0061] As mentioned above, the copolyamide proposed for the assembly of articles by hot spraying has the following formula:

[0062] HAS a / (XY)b (formula I) in which:

[0063] A is at least one of:

[0064] (i) an α,β-aminocarboxylic acid;

[0065] (ii) a lactam; and

[0066] X is at least an aliphatic diamine with 2 to 14 carbon atoms, a polyether or a polyetheramine comprising ether groups comprising 2 to 4 carbon atoms;

[0067] Y is at least one aliphatic dicarboxylic acid with 6 to 22 carbon atoms; a is an integer from 1 to 3, including 1 or 2; and b is an integer from 1 to 3, including 1 or 2.

[0068] Monomer A can be chosen from among α,β-aminocarboxylic acids having 8 to 16 carbon atoms, and lactams having 6 to 16 carbon atoms. Caprolactam, 11-aminoundecanoic acid, and 12-lactam are particularly preferred. It is possible to use several monomers A, including those mentioned above.

[0069] Monomer X is preferably a diamine with 2 to 10 carbon atoms, a polyether or a polyetheramine comprising ether groups comprising 2 to 4 carbon atoms.

[0070] The diamine is preferably an aliphatic diamine. In particular, it may be a linear aliphatic diamine, including ethylenediamine, putrescine, cadaverine, 1,6-hexamethylenediamine, and 1,10-decamethylenediamine. Alternatively, it may be a branched diamine. Another alternative is a cyclic diamine such as piperazine. 1,6-Hexamethylenediamine is particularly preferred. Of course, several diamines can be used, including those mentioned above. The polyether comprising ether groups of 2 to 4 carbon atoms is preferably a polyether containing ethylene glycol, propylene glycol, or tetramethylene glycol groups. Advantageously, polyether is essentially made up of these groups, and is therefore polyethylene glycol (PEG), polypropylene glycol (PPG) or polytetramethylene glycol (PTMG).Polyethylene glycol (PEG) is particularly preferred among these.

[0071] Polyetheramine comprising ether groups comprising 2 to 4 carbon atoms is preferably a polyether as described above but having amine groups at the end of the chain.

[0072] The polyether or polyetheramine preferably has a weight-average molar mass between 300 and 10,000, preferably between 500 and 5,000, and more preferably between 800 and 2,000, respectively. Preferably, X is a linear aliphatic diamine, in particular 1,6-hexamethylenediamine.

[0073] Monomer Y is preferably an aliphatic dicarboxylic acid having 4 to 20 carbon atoms, preferably 6 to 16, and particularly 6 to 13. Linear aliphatic dicarboxylic acids are especially preferred. Among these, adipic acid, pipelic acid, suberic acid, azelaic acid, sebacic acid, 1,11-undecanedioic acid, 1,12-dodecanedioic acid, and brassylic acid may be mentioned in particular. Of these, adipic acid is especially preferred. It is possible to use several dicarboxylic acids, particularly those chosen from among those mentioned above.

[0074] Preferably, the copolyamide has the formula (I) with a = 1 or 2 and b = 1 or 2. Particularly preferred are copolyamides with a = 2 and b = 1. In the latter case, we have a copolyamide obtained by copolymerization of two lactams, a dicarboxylic acid and a diamine, polyether or polyetheramine.

[0075] Advantageously, the copolyamide comprises an XY unit in which X is a polyether, notably polyethylene glycol (PEG).

[0076] The use of PA 6 / 6.12 / 12 copolyamide is particularly preferred.

[0077] The nature and ratio of monomers in the copolyamide can be varied to modulate its thermal properties. For example, PA 6 / 6.12 / 12 copolyamide with a ratio of 45 / 35 / 20 has a melting point of 145°C. With a ratio of 40 / 20 / 40, the same copolyamide has a melting point of 115°C, and with a ratio of 22 / 18 / 60, the copolyamide has a melting point of 128°C. Advantageously, the copolyamide has an A-membered content of 40 to 90% by weight, preferably 50 to 80% by weight, and particularly 60 to 70% by weight.

[0078] Furthermore, it is preferred that the copolyamide has a (XY)b motif content of 10 to 60% by weight, preferably 20 to 50% by weight, in particular 30 to 40% by weight.

[0079] The described copolyamide also exhibits a particular property profile, namely: a melting temperature Tf between 80°C and 150°C, a hot melt volume index of 100 to 300 [mL / 10 min] at 160°C under 2.16 kg, as measured according to ISO 1133, an enthalpy of crystallization of less than 5 J / g, as measured according to ISO 307 by DSC in cooling at 20K / min, and an enthalpy of fusion of at least 5 J / g, as measured according to ISO 307 by DSC in heating at 20K / min.

[0080] According to the invention, the copolyamide has a melting temperature (Tf) between 80°C and 150°C. Such a melting temperature allows for hot spraying at a temperature low enough to be compatible with substrates of very diverse nature. Advantageously, the melting temperature (Tf) of the copolyamide is between 85°C and 130°C, preferably between 87°C and 125°C, particularly between 90°C and 120°C, even more preferably between 92°C and 115°C, particularly between 95°C and 110°C, and especially between 100°C and 105°C.

[0081] The melt volume flow rate (MVR) of copolyamide is a parameter of particular importance in hot spray printing applications. When the melt volume flow rate is too low, the copolyamide does not pass easily or at all through the spray nozzle, making application difficult or even impossible with this technique. Conversely, when the melt volume flow rate is too high, the copolyamide penetrates too deeply into the substrate, and the amount remaining on the surface may be insufficient to ensure good adhesion.

[0082] It has been observed that a copolyamide with a hot melt index by volume, as measured according to ISO 1133-1:2011 at 160°C under 2.16 kg, of 100 to 300 [mL / 10 min], preferably of 120 to 280, particularly of 150 to 250 and especially of 175 to 225 [mL / 10 min] gave very satisfactory results when applied by hot spraying.

[0083] Furthermore, it was observed that a rather slow crystallization of the copolyamide promoted the formation of good adhesion and also contributed to a good quality of the assembly.

[0084] In the context of this presentation, we consider that a crystallization is slow when, in differential scanning calorimetry (DSC) analysis, no crystallization peak is observed during cooling with a rate of 20K / min, but on the other hand, an enthalpy of fusion is observed on subsequent heating (second heating), with an equivalent heating rate.

[0085] The copolyamide used according to the invention therefore has an enthalpy of crystallization, as measured according to standard NF EN ISO 11 357-3 by DSC under heating at 20 K / min, of less than 5 J / g, preferably less than 3 J / g, in particular less than 1 J / g and especially 0 J / g. Conversely, it has an enthalpy of fusion, as measured according to standard NF EN ISO 11 357-3 by DSC under heating at 20 K / min (second heating), of at least 5 J / g, preferably at least 10 J / g, in particular at least 20 J / g and especially at least 30 J / g.

[0086] As mentioned above, a sufficiently low glass transition temperature also ensures good flexibility of the parts and contributes to a sufficient hot melt flow index, which, as explained above, facilitates spraying. Preferably, the copolyamide has a glass transition temperature (Tg) below 60°C; advantageously, the Tg of the copolyamide is between -80°C and 60°C, preferably between -75°C and 50°C, particularly between -70°C and 40°C, and even more preferably between -65°C and 35°C.

[0087] Copolyamides used according to the invention are commercially available and can be manufactured using the usual processes described in the prior art. Reference may be made in particular to the process described in patent application EP 1 533 330 A1. In this process, all the reactants are introduced simultaneously into a suitable reactor, optionally with the addition of an acid such as phosphorous acid. The entire assembly is heated under nitrogen at a typical temperature of 235°C for a typical duration of 60 minutes, after which the reactor is placed under vacuum and the reaction is continued for a typical duration of 30 minutes. Of course, the temperatures and durations can be varied to take into account the reactivity of the chosen reactants.

[0088] Copolyamides can be obtained in the presence of a dicarboxylic acid or a diamine acting as a chain regulator, depending on whether a carboxylic acid or amine group is desired at the ends of the chain. If the precursors already contain a dicarboxylic acid or a diamine, it is sufficient to use it in excess, but another dicarboxylic acid or another diamine from the groups of dicarboxylic acids and diamines defined above can also be used.

[0089] It was found that the described copolyamides possessed the properties required for the assembly of articles, particularly footwear, by hot spraying. The fact that it is a one-component hot-melt adhesive makes the process more flexible, since it is not necessary to observe the open time required for HMPUR adhesives.

[0090] Furthermore, these copolyamides are more environmentally friendly and better for health because they contain neither solvents nor residual isocyanates. The copolyamides used according to the invention are also recyclable because they are thermoplastic. Thanks to the thermoplastic nature of these polyamides, articles assembled using them can be fully recycled. In particular, when articles contain a significant proportion of thermoplastic polymer or are even made entirely of thermoplastic polymer, the entire article can be ground and melted to provide a material that can be reused, thus greatly facilitating its recycling.

[0091] Finally, the use of copolyamide according to the invention advantageously makes it possible to obtain assemblies exhibiting a peel force, measured according to the t-test described in the examples, of at least 30 N / mm, in particular of at least 40 N / mm, especially of at least 50 N / mm at 23°C, and most particularly of at least 60 N / mm.

[0092] Thanks to the advantages discussed above, the use of a described copolyamide makes it possible to obtain by hot spraying articles whose assembly interface has sufficient adhesion strength and robustness to withstand prolonged use.

[0093] According to a second aspect, the invention relates to a method of manufacturing articles by assembly in which the substrates are assembled by means of a copolyamide as described above, deposited by hot spraying.

[0094] A hot spraying process according to the invention typically comprises the following successive steps:

[0095] 1) heating a copolyamide as described above to a temperature at least 20°C above the melting point of the copolyamide, and

[0096] 2) the direct deposition by spraying of the heated copolyamide onto at least one substrate.

[0097] The spray nozzle temperature is preferably chosen to be at least 20°C, preferably at least 40°C, or even at least 60°C, and preferably at least 80°C above the melting point of the copolyamide. The copolyamide can be deposited on one or both of the substrates to be bonded. Advantageously, the copolyamide is deposited in the form of a bead. For the purposes of this invention, "bead" means a continuous, elongated pattern. This pattern can be deposited in any shape. In particular, it can be rectilinear, for example, in the form of one or more lines, and / or in a sinuous shape, for example, in the form of waves.

[0098] For the purposes of this invention, "direct deposition" means that the heated copolyamide obtained at the end of step 1) is not kept hot for a long period of time, but is applied to the substrate a very short time after reaching the required temperature. In particular, the copolyamide is not kept hot in a thermostatically controlled tank before being applied.

[0099] It may be useful to allow a copolyamide activation time before assembly, for example, an activation time between 5 and 60 seconds. This activation time then represents the maximum time allowed between the end of heating the copolyamide (step 1) and the deposition of the heated copolyamide onto the substrate (step 2).

[0100] Next, the substrates are assembled, preferably by applying pressure, for example, by passing them between two pneumatic rollers. The applied pressure can be between 2 and 15 bar, preferably between 4 and 12 bar. The applied force can be between 1 and 5 kN, preferably between 2 and 4 kN. Finally, the pressure application time can be selected between 10 and 1000 s, preferably between 50 and 250 s.

[0101] Thus, a method for manufacturing articles according to the invention typically comprises the following successive steps:

[0102] 1') supplying the parts of the article to be assembled, including the substrates of the article to be assembled, 2') heating a copolyamide as described above to a temperature at least 20°C above the melting point of the copolyamide,

[0103] 3') directly spray the heated copolyamide onto at least one of the parts, and 4') assemble the parts to be joined, preferably by applying pressure. The substrates to be assembled for the manufacture of the article may be of various kinds, and in particular include or be made up of thermoplastic polymers such as polyester, polypropylene, polyacrylate, polyether, polyamide, thermoplastic polyurethane elastomer (Lycra® or elastane), PTFE, PVDF, PEBA, polybutylene, polyisoprene, aramid (Kevlar®), polybenzimidazole (PBI), polyethylene, particularly ultra-high weight polyethylene, liquid crystal polymer or microfibers.

[0104] Substrates may also include or be made of fibers of inorganic materials, such as carbon, glass, copper, aluminum, or steel.

[0105] Preferably, at least one of the substrates to be assembled comprises or is made of a polyamide. Indeed, the copolyamides described generally exhibit particularly high adhesion to this substrate.

[0106] Advantageously, the substrates to be assembled comprise at least 60%, in particular at least 70%, even more preferably at least 80%, in particular at least 90% by weight of thermoplastic polymer or are composed of thermoplastic polymer.

[0107] Indeed, using thermoplastic-based substrates to manufacture the item allows for its complete recycling after use. More specifically, the item can be ground up and then melted down to produce a material that can be reused, particularly for manufacturing new items. However, it can also be worthwhile to recycle items that contain a small portion of non-thermoplastic material.

[0108] Advantageously, the assembly process for the article, particularly the shoe, is fully automated and requires no manual labor. The invention is particularly useful for manufacturing shoes, especially athletic shoes. Furthermore, it could be beneficial for manufacturing clothing, bags or baskets, furniture, blinds, leisure equipment such as backpacks and tents, and sporting equipment such as balls, kites, sails, and parachutes.

[0109] In general, the copolyamide is used according to the invention by hot spray application, i.e. in a molten state, directly onto the substrate(s) to be assembled.

[0110] According to a third and final aspect, the invention relates to an article that can be obtained by the process described above. Advantageously, this relates to shoes, particularly sports shoes. The invention will be explained in more detail in the examples that follow.

[0111] Examples

[0112] The copolyamides described in Table 1 below were first tested for their suitability for hot spray application. Subsequently, these copolyamides were used to bond different substrates, and the quality of the bond was evaluated by measuring peel strength and studying the interface failure mode.

[0113] Table 1 - Composition of the evaluated copolyamides Tf: melting point

[0114] Tg: glass transition temperature

[0115] Efusion: enthalpy of fusion

[0116] Ecrist. : enthalpy of crystallization

[0117] A. Application of an adhesive sealant by spraying

[0118] First, five horseshoe-shaped cords were formed on a 100x80mm substrate surface by spraying the different copolyamides using a hot spray device marketed by DESMA Schuhmaschinen (DESMA Sole Cell).

[0119] The depositions were carried out under the following conditions: atomization pressure (air): 1.75 bar; nozzle temperature: 80°C above the melting temperature of the copolyamide tested (between 185 and 210°C); distance between nozzle and substrate: 18 mm; and quantity of copolyamide: 2.5 g.

[0120] The quality of the deposited bead was visually inspected, particularly regarding the precision of the deposited bead. The results are summarized in Table 2 below.

[0121] Table 2 - Evaluation of hot spray deposition quality

[0122] It can be seen that the copolyamide in comparative example 4 does not allow for the deposition of a satisfactory bead, as the resulting bead pattern is wide and poorly defined. In contrast, the copolyamides in example 1 and comparative example 1 allow for the deposition of a bead of satisfactory quality with sharp contours. The copolyamides in comparative examples 2 and 3 are acceptable, although they exhibit less defined contours and a wider pattern. B. Assembly of substrates representative of the upper and the foamed midsole

[0123] Next, the different copolyamides were used to assemble a polyamide 11 textile with different substrates representative of materials used as a foamed midsole, and the quality of the assembly obtained was evaluated.

[0124] To achieve this, 0.6 mm thick beads were deposited by hot spraying, as explained in section A, onto representative substrates of the foamed midsole, cut into 100 mm x 100 m pieces. After an activation time of 25 s (12 s for example C4), the substrates were joined by applying a pressure of 2.8 kN for 120 s.

[0125] The adhesion strength of the assembled samples was evaluated using a T-peel test according to ISO 11339:2022 under the following conditions:

[0126] Travel speed: 200mm / min

[0127] One to two test tubes per reference

[0128] Sensor: 1 kN

[0129] Dynamometer: Synergy 200H

[0130] 90° peeling method imposed.

[0131] The interface formed was evaluated by observing the failure mode at the end of the previously described test. Adhesive failure occurs at the interface between the adhesive and one of the two substrates, while cohesive failure occurs within the adhesive layer itself. Cohesive failure indicates that the interface behaved more strongly than the adhesive material, and these bonds are considered more satisfactory.

[0132] Based on the peel strength and failure mode obtained for each copolyamide, the quality of the resulting bond was evaluated. More specifically, a peel strength of 15 N / cm or less was considered insufficient, and a cohesive failure mode was deemed to improve the overall quality of the bond.

[0133] The results are summarized in Table 3 below.

[0134] Table 3 - Upper / Midsole Assembly

[0135] It can be seen that the copolyamide in Example 1 allows for satisfactory bonding of the studied substrates in terms of peel strength. This copolyamide also ensures a cohesive failure mode. In comparison, the copolyamide in the comparison example

[0136] 2 exhibits a lower peel force, and sometimes a failure mode indicative of a weak interface.

[0137] C. Assembly of representative upper and outsole substrates Finally, copolyamides were tested for the assembly of polyamide 11 textile with Rilsan® BSR 30 (polyamide 11 loaded with carbon fibers), a material representative of materials used as outsole materials, as shown in Table 4 below.

[0138] The copolyamide was applied as described in section B, except that a 0.8 mm bead thickness was used. The quality of the resulting bond was evaluated according to the tests described in section B. The results are summarized in Table 4 below.

[0139] Table 4 - Upper / Outsole Assemblies

[0140] It can be seen that the copolyamide in Example 1 provides satisfactory bond quality for the substrate being evaluated. In comparison, the copolyamide in Comparison Example 2 exhibits insufficient peel strength and a failure mode indicating a weak interface.

[0141] The results as a whole highlight that the use of the copolyamide according to the invention makes it possible to solve the technical problem posed, namely to allow the application by hot spraying of a precise bead of glue on the substrate and to form a good quality assembly characterized by a substantial peel force and a cohesive mode of failure on the materials studied.

[0142] [List of cited documents]

[0143] EP I 533 330 Al

Claims

DEMANDS 1. Use of a copolyamide with the following formula: Aa / (XY) b (Formula I) in which: A is at least one of: (i) an alpha-omega aminocarboxylic acid; (ii) a lactam; and X is at least an aliphatic diamine with 2 to 14 carbon atoms, a polyether or a polyetheramine comprising ether groups comprising 2 to 4 carbon atoms; Y is at least one aliphatic dicarboxylic acid with 6 to 22 carbon atoms; a is an integer from 1 to 3, in particular 1 or 2; and b is an integer from 1 to 3, in particular 1 or 2; said copolyamide having: a melting temperature Tf between 80°C and 150°C, a hot melt volume index of 100 to 300 [mL / 10 min] at 160°C under 2.16 kg, as measured according to ISO 1133, an enthalpy of crystallization of less than 5 J / g, as measured according to ISO 307 by DSC cooling at 20K / min, and an enthalpy of fusion of at least 5 J / g, as measured according to ISO 307 by DSC heating at 20K / min for the assembly of articles by hot spraying.

2. Use according to claim 1, wherein the copolyamide is of formula (I), where A is selected from caprolactam, amino-11-undecanoic acid and lactam 12.

3. Use according to claim 1 or 2, wherein in the copolyamide is of formula (I), where X is selected from linear aliphatic diamines such as ethylene diamine, putrescine, cadaverine, 1,6-hexamethylene diamine, 1,10-decamethylene diamine; branched diamines; and cyclic diamines such as piperazine.

4. Use according to any one of claims 1 to 3, wherein the copolyamide is of formula (I), where Y is a linear aliphatic dicarboxylic acid, preferably selected from adipic acid, pipelic acid, suberic acid, azelaic acid, sebacic acid, 1,11-undecanedioic acid, 1,12-dodecanedioic acid and brassylic acid.

5. Use according to any one of claims 1 to 4, wherein the copolyamide is of formula (I) with a = 1 or 2 and b = 1 or 2.

6. Use according to any one of claims 1 to 5, wherein the copolyamide is of formula (I) with a = 2 and b = 1.

7. Use according to any one of claims 1 to 6, wherein the copolyamide is of formula (I) and comprises at least one XY unit in which X is 111,6-hexamethylene diamine.

8. Use according to any one of claims 1 to 1, wherein the copolyamide is PA6 / 6.12 / 12.

9. Use according to any one of claims 1 to 8, wherein the copolyamide has a melting temperature (Tf) between 85 and 130°C.

10. Use according to any one of claims 1 to 9, wherein the copolyamide has a glass transition temperature (Tg) below 60°C.

11. Use according to any one of claims 1 to 10, wherein the copolyamide enables a peel force, measured according to the t-peel test described in the examples, of at least 30N / mm.

12. A method for manufacturing articles, comprising the following steps: (a) supply of the parts of the article to be assembled; (b) application of a copolyamide as defined in claims 1 to 11 onto at least one of the surfaces of at least one of the parts to be assembled, by hot spraying; and (c) assembly of the parts to be assembled, where appropriate under application of pressure.

13. A method according to claim 12, wherein the polymer component of the finished article comprises at least 70%, preferably at least 80% and in particular at least 90% by weight of thermoplastic polymer.

14. Article which can be obtained by the process according to claim 12 or 13.

15. Article according to claim 14, characterized in that it is a shoe, in particular a sports shoe.

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