WO2015140374A1 - Procédé de fabrication de mousses de polyoléfines réticulées à alvéoles ouvertes, et mousses ainsi obtenues - Google Patents

Procédé de fabrication de mousses de polyoléfines réticulées à alvéoles ouvertes, et mousses ainsi obtenues Download PDF

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Publication number
WO2015140374A1
WO2015140374A1 PCT/ES2015/070177 ES2015070177W WO2015140374A1 WO 2015140374 A1 WO2015140374 A1 WO 2015140374A1 ES 2015070177 W ES2015070177 W ES 2015070177W WO 2015140374 A1 WO2015140374 A1 WO 2015140374A1
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Prior art keywords
foam
polyolefin
open cell
skin
phr
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PCT/ES2015/070177
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English (en)
Spanish (es)
Inventor
Miguel Ángel RODRÍGUEZ PÉREZ
Cristina SAIZ ARROYO
Josías TIRADO MEDIAVILLA
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Cellmat Technologies, S.L.
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Publication of WO2015140374A1 publication Critical patent/WO2015140374A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/02—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles
    • B29C44/027—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles the foaming continuing or beginning when the mould is opened
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
    • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/02—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles
    • B29C44/08—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles using several expanding or moulding steps
    • B29C44/083—Increasing the size of the cavity after a first part has foamed, e.g. substituting one mould part with another
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/34—Auxiliary operations
    • B29C44/56—After-treatment of articles, e.g. for altering the shape
    • B29C44/569—Shaping and joining components with different densities or hardness
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/04—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent
    • C08J9/06—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a chemical blowing agent
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/34—Chemical features in the manufacture of articles consisting of a foamed macromolecular core and a macromolecular surface layer having a higher density than the core

Definitions

  • the present invention relates to a new process for producing highly expanded, open cell crosslinked polyolefin foam with good temperature resistance by the compression molding method.
  • the invention also relates to the foam obtained by means of this method and its uses in general.
  • An additional 20 in a second phase is heated at atmospheric pressure to finish decomposing the foaming agent.
  • the polyolefin foam that is obtained by this method and similar ones has a closed cell cell structure. It is very difficult to obtain an open cell structure in this type of foam, the opposite of what happens with
  • the conventional method of achieving an open cell structure in crosslinked polyolefin foams is by breaking the walls.
  • Japanese Patent No. 54-63172 is characterized by adding an inorganic filler in large proportions to the formulation to produce a closed cell foam that can be subsequently broken by deformation.
  • Japanese patent No. 55-42100 describes a process of preparing a
  • US 4,424,181 and US 4,499,210 disclose a formulation suitable for directly producing open cell crosslinked polyolefins foams by reversing the decomposition temperature of the crosslinking agent and the foaming agent. That is presumably achieved by the
  • US Patent 4,435,346 is characterized by the expansion of the material containing the foaming agent and the crosslinker at atmospheric pressure under conditions where the peak of the ratio between the degree of crosslinking and the percentage of decomposition of the foaming agent is less than twenty. This prepares the foam for the subsequent rupture of its cell walls when subjected to mechanical stress.
  • European patent EP 0 452 527 A1 partially resolves the low temperature resistance by irradiation of the open cell foam already made with ionizing radiation.
  • European Patent EP 0 043 052 discloses a foamable formulation based on an ethylene ionomer resin that provides an open cell foam.
  • International patent application WO 98/21252 describes a method that includes a cell rupture stage after the expansion of a silane crosslinked polyolefin foam and additionally also with organic peroxides, increasing the percentage of open cell by more than 50% up to more than 80%.
  • the method may include a puncture stage to further increase the percentage of open cell.
  • Figure 1 Schematically represents the process of the present invention.
  • the figure shows the following stages of the process: step (i) of preparing a forming composition (A); step (ii) of obtaining a preform (B); preexpansion stage (iv) (C); and stage (v) of second expansion (D), where the following numerical references refer to the following elements:
  • components of the foam-forming composition that are introduced into an internal mixer (2) (it can also be an extruder); (3) homogeneous and molten mixture of the components; (4) calender; (5) laminated solid preform; (6) skin or preform coating; (7) press mold where the first expansion takes place; (8) closing and opening the press mold; (9) crosslinked and pre-expanded block; (10) press mold where the second expansion takes place; and (1 1) final foam of the invention.
  • the invention relates to a process for the manufacture of a highly expanded open cell crosslinked polyolefin foam.
  • the process is based on the fact that the inventors have surprisingly discovered that it is possible to obtain a highly expanded open cell crosslinked foam by working with a very low degree of crosslinking to produce the intercommunication of the foam cells and using a quantity of foaming agent greater than the usual one to compensate for the loss of gas that is produced by obtaining an open cell and to help cell opening, while using a skin with particular characteristics, defined below, which is used to coat the preform that it results in the open cell foam as detailed below.
  • crosslinked refers to the presence of carbon-carbon covalent bonds between chains of linear or branched polymers of polyolefin type. This cross-linking is typically achieved by the use of organic peroxides or by irradiation of polyolefin with electrons or gamma radiation.
  • high expanded foam in relation to a polyolefin foam is a conventional term used in the field of art.
  • 5 highly expanded foam is understood as a foam with a degree of expansion (increase in volume versus starting solid) of between 6 and 55 times, which typically equals material densities between 15 and 150 kg / m3.
  • open cell in relation to polyolefin foam refers to the foam having an open cell content, equal to or greater than 90%, preferably equal to or greater than 95%, more preferably equal to or greater than 97 %, and even more preferably equal to or greater than 99%. In an even more preferred embodiment it is 100%. Open cell content characterizes
  • open cell content was determined by gas pycnometry following the procedure of ASTM D 2856-94 (1998). According to this regulation a material with 100% open cell has all the cells of the same connected to the outside of the material through holes in the
  • the foam of the present invention is characterized by having an open cell content that reaches 100%.
  • closed cell refers in the present invention, in relation to a polyolefin foam, to an open cell content equal to or less than 20%, measured according to ASTM D 2856-94 (1998)
  • the process for the manufacture of a highly expanded open cell crosslinked polyolefin foam comprises the following steps:
  • step (ii) Mold one or more solid preforms from the one or more of the compositions prepared in step (i);
  • a foam precursor to be obtained which comprises a core prepared from one or more solid preforms obtained in the previous stage at least partially covered by a skin of a material
  • the highly expanded open cell crosslinked polyolefin foam forming composition that is prepared in step (i) comprises at least 20 a polyolefin, at least one crosslinking agent, at least one foaming agent, and optionally one or more additives, and characterized by presenting:
  • X and Y refer to parts per 100 parts of polyolefin.
  • the person skilled in the art knows how to obtain a foaming composition of Highly expanded closed cell crosslinked polyolefin, and determine the amount X of crosslinking agent and the amount Y of foaming agent, in the case of wishing to obtain a highly expanded crosslinked polyolefin foam of closed cell from a previously polyolefin
  • the expert can determine the contents of X and Y, so that cross-linking is achieved in a range that on the one hand allows the generation of stable cell walls during the expansion process, that is, walls Cell phones that offer a resistance that allows them to stretch without breaking in the expansion phase and a sufficient gas generation in the temperature range of the procedure to reach the desired relative density and degree of expansion.
  • the content of crosslinking agent X ' is between X / 7 and X / 1, 5, more preferably between X / 5 and X / 1, 75 and even more preferably between X / 4 and X / 1, 8 .
  • the content of foaming agent Y ' is between 3Y and 1, 2Y, more preferably between 2.5Y and 1.3Y, and even more preferably between 2.0Y and 1.4Y.
  • step (i) of the process of the invention one or more 25 open-cell cross-linked polyolefin foam forming compositions, hereinafter, forming composition depending on the type of foam, must be prepared.
  • the person skilled in the art first determines the amounts of X and Y that should be used to obtain a highly expanded cross-linked cross-linked polyolefin foam, from a certain polyolefin, with a certain density and using certain conditions of the process of obtaining, and from said values of X and Y determines the necessary amounts (X 'and Y') that the corresponding polyolefin foam forming composition must present highly expanded open cell crosslinked from the same polyolefin, with the same density and using the same or similar conditions in the process of obtaining.
  • the forming composition is prepared by contacting the components, and mixing them until a homogeneous and molten mixture is obtained. Mixing and melting can be done in conventional manner in any conventional device or apparatus such as an internal mixer or an extruder.
  • the polyolefins that can be used in the present invention are for example low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), polypropylene (PP), ethylene vinyl acetate copolymer (EVA) ), ethylene-methyl acrylate (EMA) copolymer, ethylene-butyl acrylate (EBA) copolymer, ethylene-propylene (EPM) copolymer, ethylene-propylene-diene (EPDM) copolymer, TPE (thermoplastic ethylene elastomers), etc.
  • LDPE low density polyethylene
  • LLDPE linear low density polyethylene
  • HDPE high density polyethylene
  • PP polypropylene
  • EVA ethylene vinyl acetate cop
  • two or more polyolefins are used to obtain a forming composition in any proportions.
  • the polyolefin is LDPE.
  • the crosslinking agent introduced to produce cross-linking of the polyolefin allows to produce a stable low density foam.
  • crosslinking agents organic peroxides are typically used. Its selection in each particular embodiment is determined primarily by its decomposition temperature, which has to be significantly higher than the melting temperature of the polyolefin used.
  • organic peroxides examples include, among others, 1,1-bis (terbutylperoxy) -3,5,5-trimethylcyclohexane; terbutylperoxy benzoate; 2,2-bis (terbutylperoxy) butane; dicumyl peroxide; diteramyl peroxide; diterbutyl peroxide; 1, 2- bis (terbutylperoxy-isopropyl) benzene; 2,5-dimethyl-2,5-bis (terbutyl-peroxy) hexane, and mixtures thereof.
  • dicumyl peroxide is used.
  • DCP Dicumyl peroxide
  • DCP40 refers to a DCP mixed with calcium carbonate or other inorganic compound in a proportion 40% DCP / 60% calcium carbonate or inorganic compound.
  • the foaming agent is a chemical agent, which generates the expansion gas in stages (iv) and (v).
  • azodicarbonamide azobisisobutyl nitrile, oxybis (benzenesulfonyl hydrazine), 5-phenyltetrazole, bicarbonate, citric acid or mixtures thereof can be used among others.
  • azodicarbonamide is used.
  • the forming composition may also contain conventional additives in usual amounts for this type of polyolefin foams.
  • additives are the activators used to adjust the temperature of
  • 20 may be reinforcing charges, flame retardants, antistatic and electro-conductive agents, colorants, UV stabilizers, etc.
  • the additive is aluminum or magnesium hydroxide which is used, for example, in 40% contents in order to generate foams.
  • a composition of LDPE, DCP40 ie dicumyl peroxide with 40% by weight of active agent
  • azodicarbonamide ie dicumyl peroxide with 40% by weight of active agent
  • a highly expanded but closed cell crosslinked foam between 1, 1 and 2.2 parts of DCP40 is used per 100 parts of LDPE (equivalent to between 0.44 and 0.88 phr of peroxide of dicumyl in the mixture) and between 17 and 20 phr of azocarbonamide.
  • the person skilled in the art can determine in order to obtain the composition io forming of step (i) that the amount of DCP40 crosslinking agent necessary must be reduced with respect to the previously mentioned amounts and be between 0.1 1 and 2.0 phr , particularly between 0.16 and 1.47, more particularly between 0.22 and 1.26, and even more particularly between 0.28 and 1.22. so that respectively the content of dicumyl peroxide in the
  • the mixture corresponds to a value between 0.044 and 0.8 phr, preferably between 0.06 and 0.59, more preferably between 0.09 and 0.50 and even more preferably between 0.1 1 and 0.49.
  • the expert can determine that in order to obtain the forming composition 20 of step (i) the amount of azocarbonamide foaming agent must be increased with respect to the previously mentioned amounts and be between 18.7 and 80 phr, particularly between 20.4 and 60 phr, more particularly in the range between 22.1 and 50 phr, and even more particularly in the range between 23.8 phr and 40 phr.
  • step (ii) one or more solid preforms are molded from the one or more of the molten compositions prepared in step (i).
  • one or more solid preforms are obtained from each molten composition.
  • two or more molten compositions 5 can be used together to obtain the same solid preform.
  • io Molding can be done by any conventional molding technique, such as calendering, extrusion, or pelleting and compacting.
  • a preform consisting of a calendering sheet is obtained.
  • the sheets can be obtained with thicknesses
  • a preform is obtained by extrusion.
  • the preform obtained by extrusion according to the present invention may in principle have any dimensions, shape, etc., such as circular, spheroidal, tubular, square, polygonal, block etc.
  • the preform is in the form of a three-dimensional block with a thickness therefore superior to the sheet
  • the preform obtained by extrusion or calendering can be used directly in the next step (iii) as a core to coat it with a skin and obtain a precursor.
  • a sheet obtained by calendering it is possible to obtain a core for the precursor in the next stage from several (same or different) sheets or overlapping (same or different) sheet fragments, one on top of the other, forming an assembly, as illustrated in Figure 1.
  • the number of overlapping sheets and their thickness will determine the thickness of the precursor obtained.
  • the core 30 comprises a single sheet.
  • the sheets obtained by calendering can have different thicknesses, in general, between 0.5 and 5 mm.
  • the core comprises 2 or more sheets, typically 4, 5, 6, 7, 8 for example.
  • the Overlapping sheets gives rise to a block-shaped core.
  • the block has lateral dimensions (XY: x and y axes) much greater than its thickness, (Z: z dimension) which in an even more particular case is between 5 and 60 mm.
  • the present invention contemplates the option of preparing two or more solid preform forming compositions from which solid preforms of different composition and properties are obtained. These preforms can be combined to form different cores that generate foams according to the present invention with differentiated parts. Thus, in a particular embodiment, two or more solid preforms are obtained in the form of sheets. These sheets or parts thereof can in principle be superimposed in any way by generating a multitude of different cores from which foams according to the invention can be manufactured in a very versatile way with compositions, properties, non-uniform structures throughout
  • sheets can be prepared from LDPE and EVA sheets, and a core with both types of sheets can be prepared, resulting in a foam according to the invention having different properties, depending on how the sheets have been placed, by example with different properties
  • step (iii) comprises preparing a precursor of the open cell foam to be obtained comprising said core coated at least in part by a skin comprising a material having a melting temperature lower than that used in the following stages (iv) and (v), an extensional viscosity greater than 10 4 Pas that typically corresponds
  • the viscosity of a low density polyethylene crosslinked with dicumyl peroxides using a DCP40 ratio of 1.9 phr
  • a nitrogen permeability of less than 4 sweeps corresponding to the nitrogen permeability of a low polyethylene Density measured at room temperature.
  • the extensional viscosity of the skin is greater than 5 10 4 Pas and more preferably greater than 10 5 Pas.
  • the nitrogen permeability is less than 3 sweep and more preferably less than 2 sweep.
  • the skin in the expansions of the process of the invention can melt, and also can be stretched without surfing significant breaks.
  • the material that forms the skin also has a viscosity such that neither it nor the constituent material of the molten core can escape from the molds used for expansion, and prevents or reduces the escape of gas generated during stages (iv) and (v ).
  • the skin allows for its properties that when the molds used in the process of the invention are metallic, the demolding of the pre-expanded shaped piece resulting from step (iv) and the expanded open cell crosslinked polyolefin foam resulting from step (v) is easy without the material adhering significantly to the mold.
  • skin refers in the context of the present invention to a solid preform that is used to at least partially coat the precusror of the highly expanded open cell polyolefin foam.
  • This generally in sheet form, can have different thicknesses depending on, for example, the method of production but in general the typical thickness
  • the skin can be easily obtained in a conventional manner by the person skilled in the art.
  • the person skilled in the art can select, for example, one or more polyolefins from those mentioned above and prepare a homogeneous and molten mixture including, one or more crosslinking agents, optionally one or more foaming agents, and optionally one or more additives in suitable proportions of the conventional compounds defined above for the forming composition.
  • the skin can be obtained by molding by any conventional technique such as calendering, extrusion, etc. also described above for solid preforms.
  • the skin can be a
  • Extruded sheet as defined above for the solid preform or being constituted by one or more sheets as also described above for the solid preform.
  • the skin can therefore be obtained by molding using chemical crosslinking, with the aforementioned crosslinking agents in conventional proportions 20 to generate closed-cell polyolefin foams with the necessary viscosity properties, etc. In a particular embodiment of the process of the invention.
  • the skin can be obtained by co-extrusion together with the solid preform of step (ii).
  • the skin can also be prepared by physical crosslinking (irradiation with electrons or gamma radiation) from a polyolefin mixture without crosslinking agent.
  • the skin and the core to be coated may comprise the same polyolefin.
  • the skin and the core comprise LDPE, and the mixture from which the skin is generated comprises a crosslinking agent and optionally foaming agent content that generates a closed cell polyolefin crosslinked foam.
  • the skin is obtained from a composition containing LDPE, and a DCP content sufficiently high to generate a high cross-linking such as between 1, 1 and 2.2 phr of DCP at 40% active substance per 100 parts of LDPE resin (phr).
  • the incorporation of foaming agent into the composition is optional.
  • the skin may be formed by a polyolefin different from that used to generate the core.
  • the skin may comprise a polyolefin selected from EVA, EBA, PP, HDPE, LLDPE, EPDM, TPEs, and mixtures thereof.
  • the coating of the core with the skin can be carried out by different methods.
  • the skin can cover all or part of the generated core surface.
  • the skin is positioned so that it covers the entire surface of the precursor. In another particular embodiment it is positioned so that it covers only a part of the surface thereof.
  • the skin can be placed on the upper and lower faces in the XY planes thereof.
  • the core is a three-dimensional block of XYZ dimensions.
  • the skin in a particular embodiment covers the entire surface of the core (including the upper and lower faces located in the XY period, as well as the lateral faces located in the XZ and YZ planes)
  • the skin covers only the two upper and lower faces of the core without covering the side faces located in the XZ and YZ planes.
  • the skin only covers one of the faces (the upper or lower) of the core without covering the lateral faces located in the XZ and YZ planes.
  • the precursor can be prepared directly by co-extrusion where in the outer layers of the material manufactured by co-extrusion the skins would be placed and in the center the core would be located.
  • the precursor prepared in the previous stage which is formed by a core and a skin (5 and 6) is introduced into the mold (7) of a press where a first expansion is to be carried out.
  • a press where a first expansion is to be carried out.
  • it is a hot plate press that transmits heat uniformly to the mold where the precursor material is housed.
  • the decomposition of the crosslinking agent causes the polymer to crosslink or crosslink, increasing the viscosity of the mixture.
  • the viscosity is therefore controlled by the concentration of the crosslinking agent, looking for a viscosity high enough for the foam to be stable and low enough for the cell walls to fracture during the expansion process.
  • the decomposition of the foaming agent causes a sufficient amount of gas to be generated that will allow the desired expansion to be achieved. Due to the effect of the applied pressure, as long as it is higher than the pressure of the gas generated by the foaming agent when it decomposes, the gas is dissolved inside the polymer without producing any type of foaming while the pressure continues exercising.
  • the pressure can be kept constant throughout the stage or it can be varied as long as it is higher than the gas pressure generated by the decomposition of the foaming agent.
  • the press (8) opens, producing a rapid expansion of the material.
  • the previous application of mold release solutions on the surface of the molds facilitates extraction.
  • the result of this stage is to obtain a pre-expanded and cross-linked shaped piece, (9).
  • the temperature can be applied by heating the upper and lower plates of the press, by means of external heating side jackets, by infrared heaters, by electrical resistors inserted in the mold body, by oil circuits thermostating into the mold body or by any other process.
  • the temperature must be such that the polymer matrix melts and the decomposition of the crosslinking agent and part of the foaming agent.
  • the heating process can be carried out by means of different steps of temperature if, for example, first it is desired to produce the fusion of the polymer and subsequently the decomposition of the crosslinking agent and the foaming agent.
  • the recommended pressure so that expansion does not occur when the mold remains closed is 15 MPa (150 bar) or higher.
  • the temperature can be applied in the same way as to the mold of the previous stage and will be higher than the decomposition of the foaming agent.
  • the foam When the foam has completed the mold, it begins a cooling cycle that ends when the material reaches a temperature that allows its demoulding without major deformations. Typically these temperatures are below 50 QC .
  • the cooling can take place in different ways, by means of air circulation, submerging the mold in a water bath or other liquid for rapid cooling, introducing circuits through which the entry or exit of water or oil can occur in the body of the mold, etc.
  • the mold is opened and the block (1 1) is removed.
  • the previous application of mold release solutions on the surface of the molds facilitates the extraction of the block.
  • the process of the invention optionally comprises an additional step for removing from the expanded crosslinked open cell polyolefin foam obtained in step (vi), the remains of material corresponding to the skin used in the process.
  • the removal of the material can be done, for example, by machining or cutting using the same means used today for cutting, and slicing the closed cell polyolefin foams.
  • the result of the process of the invention is a highly expanded crosslinked polyolefin foam (the ratio can reach up to 45 or what is the same, a density equal to or greater than 20 kg / m 3 , with a cellular structure of up to 100% open with high tortuosity and low permeability to 5 nitrogen, a good resistance to temperature (up to 100 ° C) and all this in a simple and direct way without requiring additional stages, such as cell rupture after obtaining the foam, which It constitutes a fundamental advantage of the process of the invention io
  • the invention relates to a highly expanded open cell crosslinked polyolefin foam obtainable by the process of the invention, hereinafter foam of the invention.
  • the polyolefin is low density polyethylene, and has a thermal resistance of at least 90 Q C, preferably at least 100 Q C.
  • the foam of the invention has an open cellular structure, with at least an open cell content equal to or greater than 90% and preferably equal to or greater than 95%, more preferably equal to or greater than 97%, and even more preferably equal to or greater than 99%, and still more preferably 100%
  • the average size of the foam cells of the invention can be controlled through various process parameters and their values are generally in the range between 50 microns and 3,000 microns.
  • the foam of the invention is characterized by its very high resistance to air flow. So while for example the airflow resistance of open-cell polyurethane foams is of the order of 10,000 rayls / m, that of the foams of this invention is equal to or greater than 50,000 rayls / m and preferably equal to or greater than 150000 rayls / m.
  • the foam also has very high tortuosity. In this sense, while the typical tortuosity of open-cell polyurethane foams is in the order of 2, that of the foams of the invention is equal to or greater than 5 5, preferably equal to or greater than 10. Tortuosity of an open cell cellular material is defined in the present invention as the distance that a gas molecule must travel to traverse the thickness of the material traveling through the pores of the structure divided by the geometric thickness of the material.
  • the foam also has high sound absorption;
  • the normalized sound absorption coefficient is equal to or greater than 0.3 and preferably equal to or greater than 0.5
  • the foam has a mechanical behavior in compression that is very dependent on the speed of deformation. So at low speeds of
  • the material behaves like a closed cell crosslinked polyolefin foam in which the stress in the post-collapse zone (deformation between 5 and 60%) increases with the deformation produced. Therefore the material behaves as a flexible polyurethane foam at low deformation rates and as a closed-cell polyoelfin foam at high
  • the foams of this invention have a coefficient of thermal expansion
  • the average cell size of the foams was determined using the intersection method, ASTM D3576-04 (2010) in which said size is determined by counting the number of cells intercepted by a grid drawn on foam micrographs.
  • the micrographs were obtained by scanning electron microscopy in a JSM 820 from Jeol.
  • Tortuosity was determined following the methodology explained in the following references: Laurikis, W. In Low Density Cellular Plastics: Physical Basis of Behavior; Hilyard, N. C; Cunningham, A., Eds .; Chapman & Hall: London, 1994; Chapter 10 or M.A. Rodriguez-Perez, M. ⁇ lvarez-Lainez, J.A. de Saja, Microstructure and physical properties of open-cell polyolefin foams, Journal of Applied Polymer Science, 1 14, 1 176-1 186, 2009.
  • Resistance to air flow is an important magnitude for open cell cellular materials; It measures the resistance offered by the cellular structure of the material to the passage of an air flow. In this document this magnitude was determined using the procedure described in ISO 9053: 1991.
  • the acoustic absorption of a specific material refers to the amount of energy that the material is able to dissipate when an acoustic wave hits it.
  • the acoustic absorption coefficient was determined following the methodology explained in ISO 10534-2. The result of this experiment are acoustic absorption coefficient curves as a function of frequency.
  • the parameter normalized absorption coefficient was defined as the arithmetic average of the values of the absorption coefficient in the measured range. This parameter was used for example in the publication M.A. Rodriguez-Perez, M. ⁇ lvarez-Lainez, J.A. de Saja, Microstructure and physical properties of open-cell polyolefin foams, Journal of Applied Polymer Science, 1 14, 1 176-1 186, 2009.
  • the mechanical behavior of the compression materials and the thermal expansion coefficient were determined as described in the MA document Rodriguez-Perez, M. ⁇ lvarez-Lainez, JA de Saja, Microstructure and physical properties of open-cell polyolefin foams, Journal of Applied Polymer Science, 1 14,1 176-1 186, 2009.
  • the temperature resistance of materials It was determined using the following procedure. Samples of the material under study of dimensions 5x5x5 cm 3 are conditioned under controlled conditions of humidity and temperature for 24 hours (typically 21 ⁇ 2 Q C and 50% ⁇ 10% relative humidity) and their geometric dimensions are measured. They are then placed in an oven at a certain temperature T res for a period of 24 hours.
  • the change in dimensions in each direction of space is determined as the percentage of difference between the initial and final dimensions using the initial one as a reference.
  • the thermal resistance of the material is determined as that temperature T res for which the dimensional change in some of the three directions of space is 5%. It is said that the material can be used below that temperature without the foam increasing its density significantly.
  • the particular structure of the foams of the present invention provides them with properties similar to flexible polyurethane foams, such as excellent resilience, very high acoustic absorption (better than that of low frequency polyurethane foams), excellent capacity as shock absorber and as thermal insulator, good impact behavior.
  • the polyolefin character of the material makes it act as a specific oil absorbent (interesting for applications to separate oil from water) and provides very good chemical and weather resistance, as well as a lower environmental impact than that of flexible polyurethane foam.
  • the open cell structure gives the material very different properties to those of closed cell foams, and all this however from a same material, that is, from a polyolefin.
  • the latter has important relevance in the separation of materials in the recycling of components using materials that are formed by an open cell foam with another closed cell foam.
  • these structures are constituted by an open cell polyurethane foam and a closed cell polyolefin foam; by using the open-cell polyolefin foam of this invention combined with a polyolefin closed-yield foam, a material of a unique chemical composition and therefore more easily reusable is obtained, which finds application in the recycling of components at the end of Its useful life.
  • the invention relates to the various applications or the use of the foam of the present invention derived from its advantageous properties.
  • the invention thus relates to the use of the foam of the invention as an acoustic absorbent, or as a thermal insulator, or as an oil absorber.
  • the foam of the invention is used in another particular embodiment as a material for the manufacture of seats, mattresses, etc., to provide comfort to them.
  • the foam of the present invention is used to obtain seals, since the material is normally hydrophobic and has a coefficient of thermal expansion equal to that of the starting polymer.
  • the foam of the invention is used to manufacture elements that contribute to the mechanical dissipation of vibrations in automobiles, machinery, etc.
  • Example 1 manufacturing process of an open cell crosslinked polyethylene foam.
  • a first composition was prepared by mixing the following components in a co-rotating twin screw extruder in the following proportions: low density polyethylene (Repsol PE003) with a flow rate of 2 g / 10 min measured at 190 Q C with 2, 16 kg 100 phr average particle size azodicarbonamide (D 50 ) of 10 microns
  • a second formulation was also prepared with the same ingredients in the proportions of 100 parts, 19 phr, 1, 8 phr, 0.025 phr and 0.5 phr, respectively.
  • the mixture of the first composition was pelleted, and 47 g of it was introduced into each of the four cavities present in a stainless steel mold and a cycle of 4 minutes was applied at 120 ° C and then others 4 minutes of cooling.
  • the mold cavities had dimensions of 155 x 75 x 4 mm 3 .
  • the process was repeated obtaining eight preforms with the dimensions of the mold cavities, of which 6 and a half were used as indicated below.
  • the mixture of the second formulation was calendered to obtain a sheet-shaped skin 1 mm thick.
  • a 290 g precursor was then made by placing six and a half preforms of the first composition (5) in a stack and a 1 mm sheet at the top and another at the bottom of the second formulation (6). Subsequently, the precursor was introduced into the mold of the phase 1 press (7) previously heated to 147 ° C.
  • the mold was made of aluminum with dimensions of 155x75x25 mm 3 .
  • the press (8) was closed with a force of 20 Tm and a 55 minute cycle was applied maintaining the closing force and the temperature.
  • the press (8) was opened releasing the pressure, which caused an expansion of the precursor. From the resulting pre-foam (9) the possible burrs were removed and without allowing time to cool it was introduced into the phase 2 mold (10).
  • This mold had a lid with lockable closure, was constructed of aluminum and the interior dimensions were: 410x205x103 mm 3 . The mold was then closed and placed in an oven at 165 ° C for 100 minutes. After the phase 2 cycle, the mold was removed from the stove and allowed to cool in the air until it reached room temperature.
  • phase 2 mold was opened and demoulded to obtain a foam block (1 1) of density 28 kg / m 3 , 100% open cell, an average cell size of 400 microns, a tortuousness of 18, a resistivity at the air flow of 149,000 rayls / m and a maximum operating temperature of 100 ° C.

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  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
  • General Chemical & Material Sciences (AREA)

Abstract

L'invention concerne un nouveau procédé pour l'obtention d'une mousse de polyoléfine réticulée hautement expansée à alvéoles ouvertes, comprenant les étapes consistant : (i) à préparer une ou plusieurs compositions moussantes de polyoléfine réticulée hautement expansée à alvéoles ouvertes, telle que le polyéthylène, (ii) à mouler une ou plusieurs préformes solides à partir de la ou des compositions, (iii) à obtenir un précurseur de la mousse finale à obtenir, qui comprend un noyau préparé à partir de la ou des préformes solides obtenues dans l'étape antérieure, recouvert au moins en partie d'une pellicule d'une polyoléfine réticulée présentant une température de fusion, une viscosité et une perméabilité au gaz spécifiques, (iv) à soumettre le précurseur à une pression et une température données dans un premier moule, puis à ouvrir ce dernier et à réaliser une première expansion, (v) à soumettre la pièce formée pré-expansée résultant de l'étape antérieure à une température donnée dans un second moule, puis à ouvrir ce dernier et à réaliser une seconde expansion, et à extraire la mousse de polyoléfine réticulée expansée à alvéoles ouvertes. L'invention concerne également la mousse de polyoléfine pouvant être obtenue au moyen dudit procédé, ainsi que son utilisation, par exemple, comme absorbant acoustique, comme isolant thermique ou comme absorbant d'huile, comme élément de confort dans des sièges et des matelas, comme joint d'étanchéité ou comme éléments pour dissiper les vibrations mécaniques et les chocs.
PCT/ES2015/070177 2014-03-18 2015-03-12 Procédé de fabrication de mousses de polyoléfines réticulées à alvéoles ouvertes, et mousses ainsi obtenues WO2015140374A1 (fr)

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ES201430377A ES2546218B1 (es) 2014-03-18 2014-03-18 Procedimiento de fabricación de espumas de poliolefinas reticuladas de celda abierta y espumas obtenidas
ESP201430377 2014-03-18

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Cited By (1)

* Cited by examiner, † Cited by third party
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WO2023161726A1 (fr) * 2022-02-28 2023-08-31 Braskem S.A. Composition de mousse polymère à alvéoles ouvertes à tortuosité ajustable et son procédé de fabrication

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