HK1123523A - Getter systems comprising a gas-sorbing phase in the pores of a porous material distributed in a permeable means - Google Patents

Description

Getter systems comprising a gas-sorbing phase in the pores of a porous material distributed within a permeable means

The present invention relates to a getter system comprising a phase active for gas sorption in the pores of a porous material distributed within a permeable means.

Getter materials and systems are widely used in industry for all applications where it is necessary to maintain a vacuum or control the composition of a gaseous atmosphere by absorbing traces of undesired gases.

Getter materials widely used for this purpose are porous materials, such as activated carbon, in particular for the sorption of organic substances, or zeolites, silica or alumina for the sorption of gas molecules of small size. Another class of compounds of particular interest consists of anhydrous chemical desiccants which specifically adsorb moisture, for example oxides of alkaline earth metals, or some hygroscopic salts, for example chlorides (for example calcium chloride CaCl)₂) Perchlorate (e.g., magnesium perchlorate Mg (ClO))₄)₂) Or sulfates (e.g., calcium sulfate CaSO)₄)。

One problem common to some materials used to remove gaseous impurities, such as water, oxygen, or organic substances, is that they are typically in powder form and do not have sufficient cohesion to form a compact object; this is particularly true in the case of desiccants that adsorb moisture. This is a problem associated with almost all foreseeable industrial applications, requiring the absence of free particles.

This problem is in some cases solved by inserting a getter material inside a permeable container (for example a non-woven fabric casing, as for example shown in patent US4668551 relating to insulating panels).

Another possible approach to this problem is to distribute the getter material in a dispersion matrix capable of retaining the getter particles in a fixed position, while allowing the gas to flow towards the getter itself. Examples of the second solution are listed in many documents. Japanese patent application JP60-132274 discloses desiccant materials dispersed in a polysiloxane matrix; patent US3704806 discloses a desiccant composition comprising a zeolite dispersed in a matrix formed of a thermosetting polymer (such as an epoxy resin, etc.); patent US4081397 discloses a desiccant system comprising oxide particles of alkaline earth metals dispersed in an elastomeric polymer; patent US5304419 discloses a desiccant composition comprising a desiccant material dispersed in a matrix which may be formed of a polysiloxane, polyurethane or similar polymer; patent US5591379 discloses a desiccant composition comprising a desiccant selected from zeolites, alumina, silica gel, alkaline earth metal oxides and alkali metal carbonates dispersed in a porous glass or ceramic matrix; patent US6226890B1 discloses a desiccant system in which a desiccant material (e.g. an alkaline earth metal oxide) is dispersed within a polymer, such as a polysiloxane, an epoxide, a polyamide, polymethyl methacrylate or other polymer, etc., which is believed to have the property in that patent of not reducing or even increasing the rate of adsorption of the desiccant material to water; patent US6819042B2 discloses a desiccant system consisting of a desiccant material dispersed in a resin, such as a polyethylene, polypropylene, polybutadiene or polyisoprene resin.

One limitation common to many of the systems disclosed in these patents is that, due to the reaction with the gas to be sorbed, the getter material is generally subjected to structural and morphological modifications, such as swelling, which can be significant, in particular in the case of desiccants; the presence of a matrix around the grains of getter material may hinder the modification of these morphologies and inhibit or delay the gas sorption reaction.

In addition, some industrial applications may impose other requirements on the getter system. For example, the latest generation of Organic Light Emitting Displays (OLEDs) require getter systems that are transparent and have constant optical properties over the entire lifetime of the device, i.e. shortly after manufacture (when the getter material has not adsorbed moisture, but at a minimum content), near the end of the lifetime of the device (when the getter device has adsorbed a relatively large amount of moisture, even until the system is saturated) and also in intermediate steps of the lifetime of the OLED, i.e. when the various getter particles dispersed within the matrix adsorb different amounts of moisture; during the lifetime of the OLED, different levels of moisture absorbed by the getter particles can change the optical properties of the system, such as its light transmittance or refractive index, thus impairing the quality of the display. This problem is discussed, for example, in patent US6465953, which discloses a getter system for OLEDs consisting of getter particles in a transparent matrix, wherein the particles have a size sufficiently small not to interact with the luminescent radiation. In view of the importance of this application, reference should be made in particular to the use in OLEDs, in order to illustrate the use of the getter systems of the invention, but the getter systems of the invention have general application and can also be used in other applications.

It is an object of the present invention to provide getter systems for gas sorption.

This and other objects of the invention are achieved according to the invention by a getter system comprising:

-polymer means (means) permeable to the gas to be adsorbed;

-a porous material powder distributed within the polymer device;

-a phase active in adsorbing the one or more gases within the pores of the porous material.

The invention is described below with reference to the accompanying drawings, in which:

figure 1 shows a getter system of the invention;

figure 2 shows one particle of a powder of porous material;

figures 3a and 3b illustrate the gas adsorption reactions that take place inside the pores of the particles of figure 2.

The getter system of the present invention is distinguished from the prior art in that the material active in the sorption of the gas is not directly dispersed in the matrix, but is present inside the pores of the "guest (guest)" phase, in the form of a powder dispersed in the matrix; this feature will ensure that the physical properties of the system are substantially unchanged with respect to gas adsorption, for example although the active material may undergo morphological modifications during gas adsorption, these modifications do not penetrate beyond the individual porous particles and as a result the interaction between the porous particles and the environment (matrix) is not modified.

With respect to the known getter systems, the system of the present invention offers a number of advantages in addition to the differences cited above. Firstly, if the dispersed porous material has well-defined geometrical characteristics (for example, in this case it is a natural or synthetic zeolite, fullerene or the like), it is able to convert a reversible reaction or process into an irreversible reaction or process due to steric effects of the product and/or due to particularly high chemical forces acting on the pore walls, with the result that the reaction product is tightly held within the pores. In addition, the porous material may receive the catalyst in addition to the active phase, thereby ensuring mutual proximity, which is a particularly clear advantage if both the active phase and the catalyst are solid, and furthermore they will have poor mobility if freely distributed within the polymer device. Finally, in the case where the porous material is a zeolite, the zeolite itself may act as a catalyst for a wide variety of reactions (acids or bases according to lewis and/or bronsted) supporting the reaction between the active phase and the gas to be adsorbed, as illustrated.

In fig. 1, the system of the present invention is shown in a general embodiment; in this case, the system 10 is shown in the form of a short parallelepiped in cross-section (brooken view), but it may have any other shape, such as a strip, a drop (drop), or it may be formed directly on the inner surface of the device whose atmosphere must be controlled, for example in the form of a thin layer, or a depression occupying this surface.

The getter system consists of a polymeric device 11 permeable to the gas to be sorbed, wherein a powder 12 of porous material is distributed inside said polymeric device. The device 11 may be formed of any polymeric material that is permeable to the gas species to be adsorbed; preferably, this polymer exhibits adhesive characteristics so that it can be fixed to the inner wall of the final device without the use of additional adhesive. Porous Materials suitable for forming the powder 12 that can be used for the purposes of the present invention are, for example, natural or synthetic zeolites, silicalites (i.e. zeolites substantially free of aluminium), aluminosilicates other than zeolites, fullerenes and organometallic frameworks (also known in the art as MOFs, see for example the article "Metal-organic frameworks: a new class of porous Materials" in j.l.c. roswell and o.m. yaghi, published online in "Microporous and Mesoporous Materials", No.73, p.3-14, 6 months 2004).

Fig. 2 illustrates an enlarged cross-sectional view of the particle 12: the particles of porous material exhibit pores 20, 20', … within which phases are arranged that are active for gas adsorption; the active phase is represented by the deposit 21, 21', 21 ", …; in the figures, the most general case is shown, in which the pores are substantially in the form of channels with variable cross-section (between different pores and in different positions within the pores) reaching the surface of the particles 12, and the deposits 21, 21', 21 ", … are bonded to the inner walls of the pores; alternatively, for example in the case of zeolites, the pores have dimensions that are strongly fixed by a crystalline structure that, as is known, may exhibit cavities interconnected by channels of reduced cross-section, and the active phase may simply be arranged within the cavities without bonding to the internal surface of the same cavity.

Figures 3a and 3b illustrate the mechanism of operation of the getter system of the present invention; fig. 3a shows, in a further enlarged view, a detail of the pores 20 in which the particles 12 and the deposits 21, 21', … of the particularly active phase are present, while the molecules of the gas species to be adsorbed are indicated by 30; during its movement, the molecules 30 contact the deposits 21, 21', … and react with them, thus becoming fixed on or by the deposits, according to different mechanisms of the nature of the constituents of the gas molecules/active phases specifically bound; this is illustrated by the "modified" deposits 31, 31' … in figure 3b, in the case of zeolites, the active phase may not be present as a deposit, but rather as particles "trapped" within the cavity of the zeolite, as previously described, and the products of reaction with the molecules 30 are in turn in the form of species trapped within the cavity.

The chemical nature of the active phase depends on the desired species to be adsorbed. For example, where the species to be adsorbed is oxygen, the active phase may be formed from readily oxidizable metals, such as alkali, alkaline earth or other metals, such as iron, tin and copper; low oxidation state metal oxides, such as manganese or copper oxides; salts with phosphite or phosphonite anions; or readily oxidizable organic compounds such as phenols, secondary aromatic amines, thioethers or aldehydes. In the case of carbon monoxide adsorption, deposits of metals that form complex species with this gas, such as nickel or iron, or alkenes, amines and ketones, these latter in the presence of lithium-based organometallic compounds, may be used. In the case of carbon dioxide, the active phase may be a hydroxide of an alkali metal or alkaline earth metal. In (unusual) cases where adsorption of nitrogen is required, inorganic materials may be used, such as lithium, barium or the compound BaLi₄Or porphyrins, i.e., metal organic molecules that can fix this gas to the central metal atom of the complex.

However, the most common and important situation is dehumidification. To this end, the active species may be selected from a broad spectrum of materials that act according to different adsorption mechanisms, as outlined in the following list:

-water-added material: epoxides belonging to this group; organic molecules with double or triple bonds (activated); alkali metal oxides, alkaline earth metal oxides or oxides of pseudoalkaline earth metals (i.e., substantially nickel, zinc and cadmium); organic (e.g., phthalic anhydride) and inorganic (e.g., boric anhydride) anhydrides;

-materials undergoing hydrolysis or nucleophilic substitution: belonging to this group are, for example, some alkoxides (e.g. aluminum alkoxides Al (OR))₃) Some halides, e.g. AlCl₃Acid halides (and in particular acid chlorides) of the general formula RCOX (in which X is a halogen atom), or else carbocationic compounds;

-materials that react with water, its decomposition products and form oxides and hydrides, or solid solutions; examples of such materials are iron which involves reaction with water, and yttrium, palladium or mixtures thereof which involve hydrogen adsorption;

materials solvated by water, such as magnesium sulfate, or metal centers present in zeolites in order to compensate for the loss of charge due to aluminum.

In a preferred embodiment, the getter system of the invention has the further property of being transparent to visible radiation throughout its lifetime, as previously mentioned; in this mode, the system of the invention is suitable for application to screens of the OLED type cited above.

These preferred getter systems include:

-an amorphous polymer device permeable to the gas to be adsorbed;

-a powder of porous material distributed within the polymer device, wherein the powder particles have an average particle size of less than 100 nm;

-a phase active in adsorbing the one or more gases within the pores of the porous material.

In this preferred embodiment, as an additional feature, the components of the system exhibit the following facts: the polymer device is amorphous, while the porous material dispersed within the polymer device is nano-sized, formed from particles having a size on the order of less than or equal to about 100 nanometers. The first of these two additional requirements is that the polymer is transparent only if it is perfectly crystalline or completely amorphous: since it is substantially impossible to obtain perfectly crystalline polymers, especially in the case of the invention where the powder has to be dispersed in the apparatus, it is necessary to resort to completely amorphous polymers. The second requirement comes from the fact that: particles having a size less than half the wavelength of the visible radiation do not cause interaction with it and thus do not change the transparency of the polymeric device.

Polymers suitable for the preparation of permeable and transparent devices are, for example, polyacrylates and polymethacrylates, Polyetherimides (PEI), Polyamides (PA), Cellulose Acetates (CA), cellulose Triacetates (TCA), polysiloxanes (also known as silicone resins), polyvinyl alcohols (PVAL), polyethylene oxides (PEO), polyethylene glycols (PEG), polypropylene glycols (PPG), polyvinyl acetates (PMAC), copolymers of polyethylene-vinyl alcohol and PA-PEO copolymers and polyurethane-PEO.

In general, in order to obtain permeable devices, the cited polymers and the preparation methods thereof are preferably selected from those which allow to obtain the maximum free volume of the polymeric device, the maximum order and regularity of the polymer chains, the minimum crosslinking speed, the minimum bulk density and the maximum interaction with the permeating species.

In addition to the components already cited, the system of the invention may also contain additional elements which improve some properties or support the achievement of these properties.

For example, within the pores of the porous material, there may be present a catalyst capable of promoting the reaction between the species to be absorbed and the active phase, for example in the case of unsaturated organic molecules which adsorb water by addition to double or triple bonds, the catalyst may be an acid or a base according to lewis or bronsted; metals such as platinum and palladium can catalyze the adsorption of hydrogen, and other metals such as nickel, iron, rhodium, ruthenium, copper, or silver can also catalyze various reactions in which organic compounds and gases are involved by forming coordination compounds involving the organic compounds and/or gases, and by redox mechanisms.

The system of the invention can be produced by pre-impregnating the active phase in the porous material and then forming a suspension of the porous material so impregnated in a polymeric device, if it has a sufficiently poor consistency. Alternatively, a suspension of the impregnated porous material particles in a solvent may be prepared, wherein it is also possible to solubilize the polymer. Suitable solvents depend on the polymer chosen and are well known in organic chemistry; examples of solvents are chloroform, acetone, tetrahydrofuran and toluene (for polyacrylates and polymethacrylates); formic acid and N-methylpyrrolidone (for polyamides); heptane or a toluene/diethyl ether mixture (for polydimethylsiloxane). Alternatively, a suspension may be formed between the porous material pre-impregnated with the active phase and a polymer precursor (e.g. an oligomer or monomer that will form the polymer) and the polymer formed in situ, for example by irradiation with UV radiation. To stabilize the suspension, suitable surfactants, which are well known in organic chemistry and do not require further explanation, may also be added thereto. The starting solution (if it contains a polymer or its precursor) or the low viscosity polymer in which the powder of porous material is already present can be poured in a suitable mould or directly in the final housing, for example on a suitable inner surface of the OLED screen; once the liquid mixture is poured into the desired enclosure, it can be "hardened" (called "solid", in which case the material has a very high viscosity in order to maintain a given shape) by extracting the solvent, polymerizing in situ, or if the polymer is maintained in the molten state by cooling, to give a low viscosity.

Claims (20)

1. Getter system (10) for the sorption of one or more gases, comprising:

-a polymeric device (11) permeable to the gas to be adsorbed;

-a powder (12) of porous material dispensed within the polymer device;

-a phase (21, 21 ', 21 ", …) which is active in adsorbing one or more gases within the pores (20, 20', …) of the porous material.

2. A getter system according to claim 1 wherein the porous material is selected among natural or synthetic zeolites, silicalites, aluminosilicates, fullerenes and metal-organic frameworks.

3. A getter system according to claim 1, wherein when the gas to be sorbed is oxygen, the active phase is selected among easily oxidizable metals, metal oxides with low oxidation state, salts with phosphite or phosphonite anions, and easily oxidizable organic compounds.

4. A getter system according to claim 3 wherein said easily oxidizable metals are selected among the alkaline, alkaline earth or other metals such as iron, tin and copper.

5. A getter system according to claim 3, wherein said metal oxides with a low oxidation state are selected among the oxides of manganese and copper.

6. A getter system according to claim 3, wherein said readily oxidizable organic compound is selected among phenols, secondary aromatic amines, thioethers and aldehydes.

7. A getter system according to claim 1 wherein when the gas to be sorbed is carbon monoxide, the active phase is selected among nickel, iron, alkenes in the presence of lithium-based organometallic compounds, amines and ketones.

8. A getter system according to claim 1 wherein when the gas to be sorbed is carbon dioxide, the active phase is a hydroxide of an alkali or alkaline earth metal.

9. Getter system according to claim 1 wherein the active phase is selected among lithium, barium, the compound BaLi when the gas to be sorbed is nitrogen₄And porphyrins.

10. A getter system according to claim 1 wherein when the gas to be sorbed is water, the active phase is selected among epoxides, organic molecules with double or triple bonds; an alkali metal oxide; a carbocation-forming compound; an alkaline earth metal oxide, or an oxide of a metal selected from nickel, zinc and cadmium; organic and inorganic anhydrides; an alkoxide; hydrolyzable inorganic halides and acid halides; a mixture of iron and another element selected from yttrium, palladium or mixtures thereof, and magnesium sulfate.

11. Getter system according to claim 1, characterized in that the transparency is maintained when the quantity of gas sorbed is changed, comprising:

-an amorphous polymer device permeable to the gas to be adsorbed;

-a powder of porous material distributed within the polymer device, wherein the powder particles have an average particle size of less than 100 nm;

-a phase that is active in adsorbing one or more gases within the pores of the porous material.

12. A getter system according to claim 11, wherein said polymeric devices are selected from the group consisting of polyacrylates and polymethacrylates, Polyetherimides (PEI), Polyamides (PA), Cellulose Acetates (CA), cellulose Triacetates (TCA), polysiloxanes, polyvinyl alcohols (PVAL), polyethylene oxides (PEO), polyethylene glycols (PEG), polypropylene glycols (PPG), polyvinyl acetates (PVAC), copolymers of polyethylene-vinyl alcohols and PA-PEO copolymers and polyurethane-PEO.

13. Getter system according to any of claims 1 or 11, further comprising within said pores a catalyst capable of accelerating the reaction between the gas to be sorbed and the active phase.

14. A getter system according to claim 13, wherein said catalyst is selected among platinum, palladium, nickel, iron, rhodium, ruthenium, copper and silver.

15. A getter system according to claim 13, wherein said catalyst is an acid or a base according to lewis or bronsted.

16. A process for the preparation of a getter system according to claims 1 or 11, comprising the following steps: pre-impregnating an active phase within a porous material; and forming a suspension of the porous material so impregnated directly in the polymerization apparatus.

17. A process for the preparation of a getter system according to claims 1 or 11, comprising the following steps: pre-impregnating an active phase within a porous material; forming a suspension of the porous material so impregnated in a liquid, the liquid being a solvent for the polymer device; dissolving in the suspension a polymer to be used in forming a polymer device; and removing the solvent.

18. The method of claim 17, wherein when the polymer is selected from the group consisting of polyacrylates and polymethacrylates, the solvent is selected from the group consisting of chloroform, acetone, tetrahydrofuran, and toluene; when the polymer is a polyamide, the solvent is selected from formic acid and N-methylpyrrolidone; and when the polymer is polydimethylsiloxane, the solvent is selected from heptane or toluene diethyl ether.

19. A process for the preparation of a getter system according to claims 1 or 11, comprising the following steps: pre-impregnating an active phase within a porous material; forming a suspension of the porous material so impregnated in a liquid, the liquid being a solvent for a polymer precursor to be used in forming the polymeric device; dissolving the precursor in the suspension; causing the precursor to polymerize in suspension; and removing the solvent.

20. The method of any one of claims 17 or 19, wherein the suspension is stabilized by adding a surfactant.