FR2930946A1 - Structure, useful in packaging, greenhouses or tubes, comprises a layer of a composition comprising semi-crystalline polymer and polyolefin, where the semi-crystalline polymer comprises repetitive units containing one amide or ester - Google Patents

Abstract

Structure comprises at least a layer of a composition comprising a semi-crystalline polymer (50 mass%) and polyolefin, where the semi-crystalline polymer comprises repetitive units containing at least one amide or ester.

Description

Field of the invention

The present invention relates to a structure with improved barrier properties, this structure comprising a composition based on a semi-crystalline polymer and a polyolefin. It also relates to a multilayer structure comprising at least one layer of said composition and on packages comprising these structures. The invention also relates to the use of structures in packages, greenhouses or tubes.

In the field of food, foods (meat, fruits, vegetables, dairy products, cereals) are usually placed in a package to facilitate their transit. These packaging are structures that can take very different forms (film, tray, cup, etc ...). These structures also allow the conservation of these foods: to limit the degradation, it is necessary to limit the contact of food with oxygen (02) and / or with the water of the external environment. For this purpose, protective structures, for example protective films, whose gas or liquid barrier properties, more particularly water, are used to improve the preservation of foodstuffs. Food can be packed in atmospheric air. To further improve their conservation, they can be vacuum packaged or inside a controlled atmosphere of inert gases, such as carbon dioxide (CO2) or dinitrogen (N2).

In the same way, electronic equipment (for example a semiconductor, a computer component, a music player, etc ...) must be stored away from moisture to prevent damage. This component can thus be packaged by a protective structure to limit its contact with the outside atmosphere. As with food, the component can also be placed in an inert atmosphere or in a dry atmosphere. 2930946 -2 In the agricultural sector, greenhouses are used to grow plants whatever the external conditions. These greenhouses are made from transparent or translucent structures. To allow a faster growth of plants, it is also possible to use a humidity and / or gas controlled atmosphere (for example in CO2). This controlled atmosphere allows a better performance of the greenhouse. It is advantageous for the structures to have water and gas barrier properties in order to preserve this controlled atmosphere.

To transport a fluid (ie a gas or a liquid), tubes are used. These tubes must allow the transit of the fluid, without there being any loss of fluid along the tube, or infiltration of another fluid inside the tube, for example external water.

In all these cases, it is necessary that the structures used have good gas and / or water barrier properties in order to preserve intact the fluid, the atmosphere, the food or the electronic component, all these terms being grouped under the term contained below in the description.

These structures are generally formed from polymers. Indeed, among the advantages that can be mentioned for these polymers, they are recyclable, lightweight, and can be easily shaped. However, their barrier properties are not always sufficient.

25 State of the art

To improve the barrier properties of the protective structures, a first solution is to increase their thickness. However, this leads to an increase in polymer consumption and thus an additional cost of production.

The barrier properties of the structures depend on the nature of the polymer (s) used: for example, a saponified acid-olefin / acid ester 2930946 -3 carboxylic copolymer has excellent gas barrier properties. On the other hand, it is sticky and fragile, which makes it difficult to use as such in the form of a monolayer structure. In addition, their water barrier properties are very inadequate. To partially solve these problems, they can be used in alloy with a polyolefin. For example, patent EPO441666 describes a food package using a mixture of a ethylene-saponified vinyl acetate copolymer (EVOH) and polypropylene. This composition has good barrier properties to gases and mechanically resistant to hot water. However, for this package to have barrier properties, there is a need for compatibility between the polypropylene and the EVOH copolymer; therefore, a compatibilizing agent is added. In addition EVOH, which is the main constituent, has a high cost. Polyolefins which have good barrier properties to water can also be mentioned. In US5536773, an alloy based on polypropylene (PP) and terpene resin is used. However, these polyolefins have a low impermeability to gases.

Polymer-based structures comprising repeating units containing amide or ester functions are also used. Among these polymers, mention may be made, for example, of polyamide (PA) or polyesters, for example poly (lactic acid) (PLA). These polymers have poorer water barrier properties than those of polyolefins, but better than those of the α-olefin / saponified carboxylic acid ester copolymers. Conversely, the gas barrier properties of the polymers having an acid function and / or an amine function are less good than those of the α-olefin / saponified carboxylic acid ester copolymers and better than those of the polyolefins.

The gas barrier properties of these polymers can be improved by the addition of mineral additives. For example, mention may be made of the application EP0358415 which describes structures of a mixture of PA and silicates in sheets (clays). These PA films have barrier properties to those 2930946 -4 containing no clays. However, these clays are relatively expensive. In addition, for the structure to be transparent, it is necessary that these clays are dispersed in nanometric order, which makes the process complex.

One solution is to associate different polymers in multilayer structures, this structure making it possible to obtain gas and / or water barrier properties. For example, the application WO0103922 discloses a multilayer film having barrier properties to oxygen. This structure comprises a layer of semi-aromatic and amorphous polyamide and polyolefin layers. The water barrier properties are not improved. In addition, this solution requires the use of a specific type of polyamide whose cost is relatively high.

There is therefore a need to find an economical solution for improving barrier properties and / or limiting the thickness of monolayer structures or multilayer structure layers. The present invention solves at least one of the disadvantages and problems discussed above.

Brief description of the invention

The invention relates to a structure comprising a layer of a composition comprising a polymer (A), this polymer comprising repeating units which contain at least one amide and / or ester function. This polymer is semi-crystalline. The composition comprises more than 50% by weight of the polymer (A) relative to the total mass of the composition and further comprises a polyolefin (B). The structure according to the invention has barrier properties to water and gases are improved compared to a structure of the same thickness based on a composition consisting of the polymer (A). The improvement of the gas barrier properties is all the more surprising that those of the polyolefins (B) are lower than those of the polymer (A). For equivalent barrier properties, it is possible to reduce the thickness of the layers. EP1191067 discloses a composition comprising a thermoplastic polymer, which may be a polyamide or a polyester, and an impact modifier comprising an ethylene-alkyl (meth) acrylate copolymer whose carbon number in the alkyl chain is greater than 5. This composition has improved shock properties. Nothing is described on structures based on this composition, nor on the fact that these structures have barrier properties to water and / or gases that allow their advantageous use in greenhouses, packaging or tubes. Preferably, the mass ratio of the polyolefin (B) is in the range from 0.1 to 10% relative to the total weight of the composition included in the structure and preferably from 1 to 7%. Surprisingly, even when the polyolefin (B) is added in such small proportions, the gas or / and water barrier properties are improved over those of the semicrystalline polymer (A).

Preferably, the polyolefin (B) is a copolymer obtained from monomers including at least one non-functional monomer. Advantageously, the copolymer is obtained from monomers comprising ethylene and alkyl (meth) acrylate.

According to one embodiment, the polyolefin (B) is a copolymer obtained from monomers including at least one functional monomer (Y). When the polyolefin is obtained from monomers including at least one functional monomer (Y), the barrier properties and the transparency of the resulting structures are improved over those of the semicrystalline polymer (A). According to this embodiment, the functional monomer (Y) can be copolymerized in the polyolefin (B) chain. According to this same embodiment, the functional monomer (Y) can also be grafted onto the polyolefin (B).

Preferentially, when the polymer (A) comprises an amine functional group (X1) at the end of the chain, the functional monomer (Y) is a carboxylic acid anhydride and more preferably a maleic anhydride. The barrier properties and the transparency of the structures obtained are further improved in comparison with the structures based on a composition comprising this same polymer (A), but whose polyolefin is not obtained from monomers comprising d carboxylic acid.

Advantageously, when the polymer (A) comprises an acidic function (X2) at the end of the chain, the functional monomer (Y) is an unsaturated epoxide and more preferentially glycidyl methacrylate. The barrier properties and the transparency of the structures obtained are further improved in comparison with the structures based on a composition comprising the same polymer (A), but whose polyolefin is not obtained from monomers comprising the unsaturated epoxide. As the polymer (A), a semi-crystalline polyamide is preferred.

Advantageously, the layer of the composition has a thickness of less than 4 mm, advantageously in the range from 1 μm to 3 mm, preferably from 5 μm to 1 mm.

A particular structure of the invention comprises at least one layer of the composition and is of multilayer type.

Advantageously, at least one of the layers of the structures according to the invention comprises an anti-fogging agent. Water condenses less on the structure than when it does not contain an anti-fogging agent. Advantageously, at least one of the layers of the structures according to the invention comprises one of the elements chosen from plasticizers, diffusing nature fillers, dyes, brighteners, antioxidants, slip agents, flame or UV stabilizers.

The invention also relates to a package comprising a structure according to the invention. The invention also relates to the use of these structures in packages, tubes or greenhouses.

DETAILED DESCRIPTION OF THE INVENTION The invention relates to a structure comprising a layer of a composition comprising more than 50% of the total mass of the composition of a semicrystalline polymer (A) comprising repeating units which contain at least minus an amide and / or ester function, said composition further comprising a polyolefin (B).

With regard to the polymer (A), the term "semi-crystalline" covers homopolymers and copolymers which have both a glass transition temperature Tg and a melting temperature Tf. By repetitive unit is meant a pattern which is found at least twice in the polymer, these two units being able to be juxtaposed next to one another or separated by other patterns.

A preferred group of semi-crystalline polymers (A) is the group of semi-crystalline polyamides. These semi-crystalline polyamides comprise amine (Xl) and / or acid (X2) functions at the end of the chain. 10 - 8 In particular, the term "semi-crystalline polyamides" refers to aliphatic homopolyamides which result from the condensation of: • a lactam, • or an aliphatic alpha, omega-aminocarboxylic acid, • or a diamine aliphatic and an aliphatic diacid. Examples of lactam include caprolactam, oenantholactam and lauryllactam. Examples of aliphatic alpha, omega-aminocarboxylic acid include aminocaproic acid, 7-amino-heptanoic acid, 10-amino-1-undecanoic acid, and 12-amino-1-amino acid. dodecanoic. As examples of aliphatic diamine, mention may be made of hexamethylenediamine, dodecamethylenediamine and trimethylhexamethylenediamine. As examples of aliphatic diacid, mention may be made of adipic, azelaic, suberic, sebacic and dodecanedicarboxylic acids. Among the aliphatic polyamides, mention may be made, by way of example and in a nonlimiting manner, of the following polyamides: polycaprolactam (PA6); polyundecanamide (PA11); polylauryllactam (PAl2); polybutylene adipamide (PA4.6); polyhexamethylene adipamide (PA6.6); polyhexamethylene azelamide (PA6.9); polyhexamethylene sebacamide (PA-6.10); polyhexamethylene dodecanamide (PA6.12); polydecamethylene dodecanamide (PA10.12); polydecamethylene sebacanamide (PA10.10) and polydodecamethylene dodecanamide (PA12.12). PA6, PA6.6, PAl1 (sold by the Applicant under the trademark Rilsan®) and PAl2 (also marketed by the applicant under the trademark Rilsan®) are each preferred polyamides of the invention. Also referred to as "semicrystalline polyamides" are cycloaliphatic homopolyamides. Mention may in particular be made of cycloaliphatic polyamides which result from the condensation of a cycloaliphatic diamine and an aliphatic diacid. As an example of a cycloaliphatic diamine, mention may be made of 4,4'-methylene-bis (cyclohexylamine), also called para-bis (aminocyclohexyl) methane or PACM, 2,2'-dimethyl-4,4 Methylenebis (cyclohexylamine), also called bis- (3-methyl-4-aminocyclohexyl) -methane or BMACM. Thus, among the semi-crystalline polyamides, mention may be made of polyamides PACM.12, resulting from the condensation of PACM with diacid C12, BMACM.10 and BMACM.12 resulting from the condensation of BMACM with, respectively, the aliphatic diacids in Cl0 and in C12.

Also referred to as "semi-crystalline polyamides" are semi-aromatic homopolyamides which result from the condensation of: • an aliphatic diamine and an aromatic diacid, such as terephthalic acid (T) and acid isophthalic (I). The polyamides obtained are then commonly called "polyphthalamides" or PPA; An aromatic diamine, such as xylylenediamine, and more particularly metaxylylenediamine (MXD) and an aliphatic diacid. Thus, and without limitation, mention may be made of polyamides 6.T, 6.1, MXD.6 or MXD.10.

The term "semi-crystalline polyamides" also covers copolyamides, which result from the condensation of at least two of the above-mentioned groups of monomers to obtain homopolyamides. The monomer in the present description of the copolyamides is that which will form the repeating unit. Indeed, the case where a repeating unit of the PA consists of the combination of a diacid with a diamine is particular. It is considered that it is the combination of a diamine and a diacid, that is to say the diamine.diacide couple (in equimolar quantity), which corresponds to the monomer. This is because individually, the diacid or diamine is only one structural unit, which is not enough by itself to polymerize to give a polyamide. Thus, the copolyamides cover, in particular, the condensation products: of at least two lactams, at least two alpha, omega-aminocarboxylic aliphatic acids, at least one lactam and at least one alpha, omegaaminocarboxylic acid, aliphatic, • at least two diamines and at least two diacids, • at least one lactam with at least one diamine and at least one diacid, • at least one alpha, omega acid aliphatic aminocarboxylic amine with at least one diamine and at least one diacid, wherein the diamine (s) and the diacid (s) may be, independently of one another, aliphatic, cycloaliphatic or aromatic. Among the copolyamides, there may be mentioned for example PA6 / 1 1, PA 6/12 or PA6 / 1 1/12. The Melt Flow Index (MFI) of the polyamide is preferably in the range of from 1 to 400 g / 10 min (ASTM D 1238-86, 230 ° C., 2.16 kg). Its number-average molecular mass is preferably between 10,000 g / mol and 200,000 g / mol. The polycondensation of the various monomers is carried out according to the methods usually known, for example at a temperature of between 200 and 300 ° C., under vacuum or under an inert atmosphere, with stirring of the reaction mixture. Those skilled in the art may also use amine or acid monofunctional chain limiters, well known to those skilled in the art, to choose the final molar mass and the terminal function of the polyamide. It will suffice for one skilled in the art to select the types and ratio of monomers as well as to choose the molar masses of the polyamide to obtain the desired semi-crystalline polyamide. Preferably, in the case of the copolyamide, it is preferred that it be obtained from at least 75 mol% of a majority monomer relative to the total sum of the monomers.

Another group of semi-crystalline polymers (A) according to the invention is the group of polyesters. These semicrystalline polyesters comprise acid functions (X2) at the end of the chain. The polyesters may be condensation products of glycols and dicarboxylic acids. Examples that may be mentioned include polyethylene terephthalate (PET), polybutylene terephthalate (PBT) or PCT which is a copolyester obtained from monomers of cyclohexane dimethanol and dimethyl terephthalate. Among the polyesters, mention may also be made of poly lactic acid which can be formed from monomers (eg lactide) levogyrous (L) and / or dextrorotatory monomers (D), the level of monomers (L) and (D) being any. It may be a mixture of PLA (PLLA), which is formed from predominantly (L) monomers, and dextrorotatory PLA (PDLA), which is formed from predominantly (D) monomers. The synthesis of all these polyesters are well known to those skilled in the art; he will be able to choose the types and ratio of monomers to obtain the desired semi-crystalline polyester. It will suffice for those skilled in the art to select the types and ratio of monomers as well as to select the polyester molar masses to obtain the desired semi-crystalline polyester. Preferably, in the case of the copolyester, it is preferred that it be obtained from at least 75 mol% of a majority monomer relative to the total sum of the monomers. It is not within the scope of the present invention if the semicrystalline polymer is a polyesteramide copolymer.

With regard to the polyolefin (B), it is a polymer comprising as monomer an α-olefin. Α-olefins having from 2 to 30 carbon atoms are preferred. As α-olefin, mention may be made of ethylene, propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl- 1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicocene, 1-dococene, 1-tetracocene, 1-hexacocene, 1-octacocene, and 1-triacontene. Propylene and especially ethylene are preferred as α-olefins. This polyolefin may be a homopolymer when a single α-olefin is polymerized in the polymer chain. Examples include polyethylene (PE) or polypropylene (PP). This polyolefin may also be a copolymer when at least two comonomers are copolymerized in the polymer chain. One of the comonomers is an α-olefin; the other or the other comonomers are monomers capable of polymerizing with the α-olefin. These other comonomers capable of polymerizing with the α-olefin may be a functional monomer (then called functional monomer (Y)) and / or a non-functional monomer. By functional monomer (Y) is meant a monomer comprising a reactive functional group, this reactive functional group being capable of reacting under extrusion conditions, for example at 250 ° C., with an amine (X 1) and / or acid (X 2) function. of the polymer (A) when this monomer is grafted and / or copolymerized on the polyolefin (B): Among the functional monomers (Y), mention may be made of: • unsaturated epoxides, • unsaturated carboxylic acids and their salts, • the carboxylic acid anhydrides. Unsaturated epoxides include aliphatic glycidyl esters and ethers such as glycidyl allyl glycidyl ether, vinyl glycidyl ether, maleate and itaconate, acrylate and glycidyl methacrylate. These are, for example, alicyclic glycidyl esters and ethers such as 2-cyclohexene-1-glycidyl ether, cyclohexene-4,5-diglycidyl carboxylate, cyclohexene-4-glycidyl carboxylate, 5-norbornene-2-methyl 2-glycidyl carboxylate and endocis-bicyclo (2,2,1) -5-heptene-2,3-diglycidyl dicarboxylate. As the unsaturated carboxylic acid and its salts, there may be exemplified acrylic acid or methacrylic acid and the salts of these same acids. The acid anhydrides may be chosen, for example, from maleic, itaconic, citraconic, allylsuccinic, cyclohex-4-ene-1,2-dicarboxylic, 4-methylenecyclohex-4-ene-1,2-dicarboxylic anhydrides, 2930946 - 13-bicyclo (2,2,1) hept-5-ene-2,3-dicarboxylic acid, and x-methyl bicyclo (2,2,1) hept-5-ene-2,2-dicarboxylic acid. When the polyolefin (B) is obtained from monomers including at least one functional monomer (Y), the resulting structure is more transparent. The transparency of the structure is a particularly advantageous additional advantage for the structures used for example in the packaging: when the structure is transparent to the naked eye, the contents of the package can be seen. Glycidyl methacrylate or / and maleic anhydride is particularly preferred as the functional monomer (Y). It would not be departing from the scope of the invention if different functional monomers (Y) were copolymerized in the polyolefin (B).

The copolymer can also be obtained from monomers including at least one non-functional monomer. This monomer is a monomer different from the functional monomers (Y) and capable of polymerizing with an α-olefin. As non-functional monomer, it is preferred: one of the α-olefins already mentioned, this being different from the first α-olefin comonomer, dienes such as, for example, 1,4-hexadiene or ethylidene norbornene. butadiene; unsaturated carboxylic acid esters such as, for example, alkyl acrylates or alkyl methacrylates grouped under the term alkyl (meth) acrylates. The alkyl chains of these (meth) acrylates can have up to 30 carbon atoms. Mention may be made, as alkyl chains, of methyl, ethyl, propyl, n-butyl, sec-butyl, isobutyl, tert-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, undecyl and dodecyl. tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, hencosyl, docosyl, tricosyl, tetracosyl, pentacosyl, hexacosyl, heptacosyl, octacosyl, nonacosyl. Methyl, ethyl and butyl (meth) acrylates are preferred as unsaturated carboxylic acid esters, vinyl esters of carboxylic acids. As examples of vinyl esters of carboxylic acid, mention may be made of vinyl acetate, vinyl versatate, vinyl propionate, vinyl butyrate, or vinyl maleate. Vinyl acetate is preferred as the vinyl carboxylic acid ester. Advantageously, the non-functional monomer is an unsaturated carboxylic acid ester and / or a carboxylic acid vinyl ester. The resulting structure then has excellent transparency. Preferably, the non-functional monomer consists of one or more unsaturated carboxylic acid esters: the structure obtained has a very good resistance to light and / or heat. It is preferable that the structures included in the greenhouses have a very good resistance to light and / or heat. In fact, in the opposite case, the structures age faster with time and this aging results in their yellowing. However, this yellowing filters the light inside the greenhouse, which implies a loss of light radiation. This loss limits the yield of the greenhouse. Advantageously, the number of carbon atoms included in the alkyl chain of the alkyl (meth) acrylates is an integer in the range from 1 to 4. The cost of the composition is then less than when the number of carbon atoms is 5 or more. It would not be departing from the scope of the invention if different nonfunctional monomers were copolymerized in the polyolefin (B).

Advantageously, in the case of a copolymer, the polyolefin (B) comprises at least 50 mol% of α-olefin, preferably in the range of 60% to 98%, the sum of the moles of α-olefin. and comonomer being equal to 100%. When the polyolefin (B) is obtained from monomers including at least one non-functional monomer, the polyolefin (B) may comprise from 0.01% to less than 50% by mole of non-functional monomer and preferably from 2% to 40%, the sum of the moles of α-olefin and comonomer being equal to 100%. When the polyolefin (B) is obtained from monomers including at least one functional monomer (Y), the polyolefin (B) can comprise from (law% to 20% by mole of functional monomer (Y) and preferentially from 0.1% to 6%, the sum of the moles of α-olefin and comonomer being equal to 100%.

The polyolefin (B) can be obtained by polymerization of the various monomers (α-olefin, optional functional monomer (Y) and / or non-functional) by radical polymerization processes at high pressure or in solution, in an autoclave reactor or in a tubular reactor. which are techniques known to those skilled in the art. The functional monomer (Y) may also be grafted onto the polyolefin (B). The polyolefin can be grafted with a functional monomer (Y) using techniques well known to those skilled in the art. For example, a solution grafting method or a reactive extrusion method may be used. The density of the polyolefin (B) may advantageously be between 0.91 and 0.96. The polyolefin advantageously has an MFI in the range of 0.5 to 400 g / 10 min (ASTM D 1238, 190 ° C, 2.16 kg) and preferably 1 to 50 g / 10 min. It would not be departing from the scope of the invention if the polyolefin (B) consists of a mixture of polyolefins. In particular, the structure is in accordance with the invention if the polyolefin (B) obtained from monomers comprising a functional monomer (Y) is a polyolefin mixture of which at least one is obtained from monomers of which at least one monomer functional (Y).

Among the copolymers which have just been described, the composition according to the invention may in particular comprise those sold by the Applicant: mention may be made of the ethylene-vinyl acetate copolymers known under the trade name Evatane or the ethylene-(meth) copolymers Lotryl ° alkyl acrylate in the case where the polyolefin is not obtained from any functional monomer. Among the polyolefins grafted with a functional monomer (Y), mention may be made of those sold under the trademark Orevac®. Among the copolymers obtained by copolymerization of a functional monomer (Y), mention will be made of the copolymers sold under the Lotader brand.

The composition of the structure according to the invention may also contain compounds, called additional compounds, chosen from plasticizers, diffusing-type mineral fillers, dyes, brighteners, antioxidants, slip agents and anti-fogging agents. , flame retardants or UV stabilizers. The compounds may be in the form of masterbatches. Those skilled in the art will know how to adapt the quantities of the different compounds in order to obtain the various desired properties. For example, with regard to the composition of the structure according to the invention, the total amount of these additives is less than or equal to 49% by weight of the total composition, preferably in the range of from 0.01 to 30. % by mass. As plasticizers, mention may be made of aliphatic or naphthenic oils. The term "mineral filler with a diffusing nature" is intended to mean inorganic molecules having light-scattering properties. For example, these fillers may have a volume average diameter of from 1 to 6 μm measured by laser particle size, preferably from 2 to 4 μm. The size of these particles can be easily determined by conventional particle size techniques by those skilled in the art. Advantageously, the amount of these fillers will be between 1 and 6% of the total mass of the composition. For example, mention may be made of calcium carbonate fillers. In a greenhouse, it is advantageous for the structure to be able to diffuse the light in order to better distribute the light inside the greenhouse. This diffusion is all the more important when the plant grows vertically (for example in the case of tomato cultivation): if the light is not diffused, it reaches the lower part of the plant more difficultly. When light is diffused through the structure, the distribution of light to the inside of the greenhouse is more efficient. As an example of a dye, mention may be made of titanium dioxide. As an antioxidant, mention may be made of phosphites or phenolic compounds. Silica can be given as an example of a slip agent. As the anti-fogging agent, for example, the glycerol esters can be used. Examples of flame retardants are metal hydroxides or ammonium polyphosphate additives. Advantageously, the composition of the structure according to the invention comprises anti-fogging agents, for example in proportions ranging from 0.01 to 15% by weight and preferably from 1 to 10%. These agents prevent condensation of water on the structure. Indeed, in the field of packaging, it is preferable that the water does not condense inside the package so that we can see its contents without being hindered by the presence of condensation. Similarly, when the water condenses in the form of droplets on the structure of a greenhouse, the bacteria develop inside these droplets, these bacteria can spread inside the greenhouse when the droplets drop down. on plants. It is therefore preferable that the water does not condense. The composition comprises more than 50% by weight of polymer (A) relative to the total mass of the composition. Advantageously, this amount is greater than or equal to 80% by weight. Preferably, the mass ratio of the polyolefin (B) is in the range from 0.1 to 10% relative to the total weight of the composition included in the structure and preferably from 1 to 7%. This level is very preferably between 1 and 5%. The composition comprising the polymer (A) and the polyolefin (B) may optionally be in admixture with other polymers other than (A) and (B), so-called additional polymers. The production of the composition according to the invention requires the mixing of the polymer (A), the polyolefin (B) as well as any additional compounds and / or additional polymers. This mixing can be carried out by extrusion or kneading which are well known techniques. Those skilled in the art will easily adapt the processing parameters (temperature, speed of rotation of the screws) to the melting or softening temperatures of the components in order to obtain the composition included in the structure according to the invention. For example, for a composition based on PA6, use an extrusion temperature close to 260 ° C. It is thus possible to produce, by mixing the constituents of the composition, a compound of this composition, this compound possibly being granulated directly at the outlet of the die. The invention also relates to a structure comprising several successive layers, said multilayer structure, at least one of the layers comprises the composition already described, this layer of the composition being called layer C. This multilayer structure also has improved barrier properties in comparison with the same multilayer structure whose layer C would be replaced by a layer of the polymer (A). When the structure is multilayer, it further comprises another layer, possibly having barrier properties to water and / or gases. For example, a metal-based layer (such as aluminum) or a polymer may be mentioned. Examples of polymers are: polyolefins, for example PE or PP, and in particular α-olefin / saponified carboxylic acid ester copolymers such as for example EVOH, polyamides, • polyesters, • fluorinated polymers, such as polyvinyl fluoride (PVF) and divinyl polyfluoride (PVDF). When the structure is multilayer, an intermediate binder layer 30 may allow adhesion of the layer of the mixture obtained according to the invention and the barrier layer. As an example of a binder, there may be mentioned ethylene-vinyl acetate, ethylene-alkyl (meth) acrylate copolymers or polyolefins comprising a functional monomer. Multilayer structures according to the invention can be advantageously obtained by coextrusion. As non-limiting examples of multilayer structures comprising layer C, there may be mentioned structures comprising successive layers: • Aluminum / Binder / C • PE / Binder / C • PP / Binder / C • PA / C 10 • EVOH / Binder / C • Polyester / Binder / C • Fluorinated Polymer / Binder / C With regard to the number of layers of the multilayer structure according to the invention, it is an integer greater than or equal to 2, preferably less than or equal to at 15, preferably from 3 to 9. Those skilled in the art will easily determine the binder to be used when it is necessary to combine the different layers according to the invention. Each of these layers can comprise the compounds already mentioned chosen from plasticizers, diffusing-type mineral fillers, dyes, brighteners, antioxidants, slip agents, anti-fogging agents, flame retardants or UV stabilizers. . These agents may be added to each of the layers in the same mass proportions as those already described for the composition comprising the polymers (A) and (B). Preferably, the layer comprising the anti-fogging agents is an outer layer. By outer layer is meant the layers of the structure of which at least one side is not in contact with the other layers of the structure. Water condenses less on the structure than when one of the layers does not contain, which allows for example its advantageous use in the field of packaging and greenhouses. Preferably, the anti-fogging agent is in the outer layer of the structure that is in contact with the contents. Preferably, the structures according to the invention have a thickness in the range from 1 μm to 30 mm, advantageously less than 4 mm. Films can advantageously be formed when the thickness of the structures is in the range from 1 μm to 2 mm, for example from 5 μm to 1 mm, more preferably from 25 μm to 500 μm. It would not be outside the scope of the invention if the structure was obtained directly without going through the compound step. The structure may take the form for example of a sheet, a tube, a film, a cup or a tray. The structure may form, alone or in combination with another structure, a package. These structures can be obtained from the compound described above by the conventional techniques of pressing, injection, extrusion blowing of the sheath, extrusion of hollow bodies which makes it possible, for example, to obtain bottles or reservoirs (again blow molding), extrusion lamination, extrusion coating, flat extrusion (also called cast extrusion) or sheet extrusion by calendering, these sheets may or may not be thermoformed later, for example to form trays or cups. All these techniques are well known to those skilled in the art and it will be able to adapt the conditions of implementation of the various techniques (temperature, speed of rotation of the screws, etc.) to form the structure according to the invention having the shape and desired thicknesses.

The structure according to the invention can be used in a package. The structures can also be used in a greenhouse. The structure can also be used in a tube for transporting a gaseous or liquid medium.

The present invention will now be illustrated by particular exemplary embodiments described below which employ PA6 as polymer (A). It should be noted that these examples are not intended in any way to limit the scope of the present invention. - 21 - Examples

To formulate the examples of the invention and comparative, the following products were used: Lotader 3410: it is an ethylene-butyl acrylate-maleic anhydride copolymer produced by ARKEMA, whose mass content of butyl acrylate is 17% and the mass ratio of maleic anhydride is 3.1%, which has a Tf equal to 89 ° C and of which the Melt Fluid Index (MFI) is 5g / l0min (ISO1133, 190 ° C, 2.16). kg).

Ultramid B3: This is a PA6 produced by BASF. Lacqtene 1003 FE 23: it is a polyethylene produced by Total Petrochemicals with a density equal to 0.923 g / cm3 of MFI equal to 0.3 g / l0 min (ISO 1133, 190 ° C., 2.16 kg) and whose melting point is equals 111 ° C.

In Table 1 are reported compositions composing structures according to the invention (EX1, EX2) and a comparative composition (CP) with the mass ratios of each product. Table 1 CP EX1 EX2 Ultramid ° B3 1 0.97 0.95 Lotader 3410 0 0.03 0.05 Multilayer films PE (inner layer) / Composition (intermediate layer) / PE (outer layer) were made by co- extrusion blow molding. In the EX1 and EX2 compositions, the Lotader 3410 was premixed in a bag with Ultramid B3. The PE of the inner and outer layers are extruded in two single screw extruders COLLIN at 220 ° C with a screw speed of 90 rpm. The compositions are extruded in a COLLIN single-screw extruder at 255 ° C with a screw speed of 45 rpm. The three extruders feed a Feedblock (box coextrusion) equipped with an annular die whose temperatures are set at 260 ° C. These conditions allowed the formation of a stable bubble thanks to the air flows injected at the base of the annular die, this bubble being drawn at a speed of 6.1 m / min to allow the manufacture of the film. multilayer. The PE layers are liners, that is to say, its role is to prevent the adhesion of the polyamide on itself during implementation. The adhesion between the PE and the compositions being very low, it is easy to peel off the PE layers in order to recover, after the manufacture of the multilayer film, a film of the composition and perform the permeability tests on these latter films. Under the operating conditions, the thickness of the films of composition 10 obtained is between 35 and 45 μm. The barrier properties to 1'02 (Flux 02 measured according to ASTM D 3985 at 23 ° C and a Relative Humidity Rate (RH) of 0%), CO2 (CO2 flow measured according to ASTM D 1343-75 , 23 ° C, HR = 0%) or water (Flux H2O measured according to ASTM E 96, BW method and inverted cup at 38 ° C and 50% RH) are related to the thickness of the films so 15 to be able to compare the values obtained. In Table 2 are reported the results obtained during these tests.

Table 2 Compositions Flux 02 CO2 Flux H2O Flux (cm3.25pm / m2.24h) (cm3.25pm / m2.24h) (g.mm/m2.24h) CP 48.8 178 19.7 EX 1 37.4 125 16.5 EX2 41.6 127 13 20 The gas and water barrier properties of the structures according to the invention are improved in comparison with the polyamide-based structures alone. For example, the water permeability of the EX2 film decreases by 34% and its CO2 permeability decreases by 29% compared to the properties of the polyamide CP. Although the polyolefin is present in very small proportions, the barrier properties are significantly increased. This is all the more surprising since polyolefins are more permeable to gases than polyamides.

Claims (11)

Revendications1. A structure comprising at least one layer of a composition, said composition comprising a semi-crystalline polymer (A) and a polyolefin (B), the semi-crystalline polymer (A) comprising repeating units which contain at least one amide or ester function and the composition comprising more than 50% by weight of polymer (A) relative to the total mass of the composition. 2. Structure according to claim 1 characterized in that the mass ratio of the polyolefin (B) is in the range of 0.1 to 10% relative to the total mass of the composition. 3. Structure according to claim 1 or 2 characterized in that the polyolefin (B) is a copolymer obtained from monomers including at least one non-functional monomer. 4. Structure according to claim 3 characterized in that the copolymer is obtained from monomers comprising ethylene and the alkyl (meth) acrylate. 5. Structure according to one of claims 1 to 4 characterized in that the polyolefin (B) is obtained from monomers including at least one functional monomer (Y). 6. Structure according to claim 5 characterized in that (Y) is copolymerized in the polyolefin (B). 7. Structure according to claim 5 characterized in that (Y) is grafted onto the polyolefin (B). 8. Structure according to one of claims 5 to 7 characterized in that the polymer (A) comprises an amine function (Xl) at the end of the chain and that 2930946 - 24 - that the functional monomer (Y) is an unsaturated epoxide or a carboxylic acid anhydride and more preferably a maleic anhydride. 9. Structure according to one of claims 5 to 7, characterized in that the polymer (A) comprises an acid terminus function (X2) at the end of the chain and in that the functional monomer (Y) is an unsaturated epoxide and more preferentially glycidyl methacrylate. 10. Structure according to one of claims 1 to 9 characterized in that the polymer (A) is a semi-crystalline polyamide. 11. Structure according to one of claims 1 to 10 characterized in that the thickness of at least one layer of the composition is less than 4 mm. 15 1 2. Structure according to one of claims 1 to 1 l characterized in that it is multilayer. 13. Structure according to one of claims 1 to 12 characterized in that at least one of the layers comprises anti-fogging agents. 14. Structure according to one of claims 1 to 13 characterized in that at least one of the layers comprises, in addition, at least one of the compounds selected from plasticizers, mineral fillers diffusing nature, dyes, brighteners antioxidants, slip agents, flame retardants or UV stabilizers. 15. A package comprising a structure according to any one of claims 1 to 14. 16. Use of a structure according to any one of claims 1 to 14 in a package, a greenhouse or a tube.