DE102020005288B4 - Fireproof cladding material for flammable and/or combustible materials containing a foam resin composition based on novolaks, process for its preparation and use - Google Patents

Abstract

Refractory encasing material for flammable and/or combustible materials, comprising a foam resin composition based on novolaks, at least one endothermic blowing agent and a hardener, which absorbs heat during overheating and expands by foaming.

Description

The invention relates to a fireproof cladding material for flammable and/or combustible materials containing a foam resin composition based on novolaks.

Flammable and/or combustible materials pose a potential hazard during transport, operation, charging, and/or when not in use. They can self-ignite under mechanical or thermal stress and must be appropriately protected from the surroundings in the event of a fire to prevent them from accelerating the spread of the fire. Examples of flammable and/or combustible transportable materials include fireworks and chemical substances such as light metals such as lithium, sodium, potassium, rubidium, cesium, calcium, strontium, and barium.

The situation is particularly problematic when a large number of components are involved in the reaction, as is the case with a fire in a galvanic cell.

The galvanic cell is a technical device for converting chemical energy into electrical energy through a chemical redox reaction. It is particularly suitable for powering mobile electrical or electronic devices, such as flashlights, mobile phones, computers, power tools, and similar devices, as well as in motor vehicles.

Galvanic cells are classified according to their structure, for example, into batteries (e.g., zinc-carbon batteries, alkaline-manganese batteries), accumulators, and fuel cells. Unlike batteries, the redox reaction in accumulators is reversible. Applying an electrical voltage triggers the reverse reaction, and the accumulator can supply power again. Thus, accumulators are particularly used where temporary or permanent operation of electrical and electronic devices independent of the mains power supply is required or desired.

A common feature of almost all rechargeable batteries is that they release heat during charging and discharging. Depending on the age and type of battery, it may self-discharge even when not in use. This can lead to uncontrolled overheating of the battery, which can damage surrounding components and ultimately destroy the entire electronic or electrical device in a fire. Depending on the design of the galvanic cell, the problem of overheating can also occur with batteries.

In recent years, the use of lithium-based galvanic cells has progressed significantly. Lithium batteries (primary cells) as well as lithium-ion accumulators (lithium-ion batteries) and their further developments, such as lithium-ion polymer or lithium-ion titanate accumulators, are now in use. These are characterized by high energy density and are significantly lighter than, for example, nickel-cadmium accumulators. They are therefore used in, for example, mobile phones, digital cameras, camcorders, laptops, model vehicles, especially model airplanes, drones, power tools, and electric and hybrid vehicles.

Because lithium is a highly reactive metal and its compounds are also highly flammable, overheating can occur easily, and its effects should be minimized as much as possible. In addition, lithium-ion batteries are mechanically sensitive. The high current causes the casing to melt and burst into flames. The defect may not be immediately apparent, and a fire may break out some time later. Appropriate safety precautions must therefore be taken during transport, use, idle mode, and charging. Similar problems also arise when using other galvanic cells of the same type.

Until now, attempts have been made to solve the problem of flammability by using a casing around the accumulator/battery. These casings must not be electrically conductive when in contact with the accumulator/battery, must have high mechanical strength, and must be able to withstand fire for a certain period of time. Currently available materials include mineral granules based on silicon dioxide or foamed glass beads (e.g., ^Extover® ). The use of pure glass beads is advantageous for achieving fire-resistant properties, but only a small amount of heat energy is absorbed. In addition, the specific volume of the glass beads shrinks during melting, creating voids and cracks that allow reaction products to escape. Furthermore, there is no mechanical They provide support and no sealing function because the glass beads are loosely stacked. Furthermore, glass beads are heavy compared to other materials, which does not allow for every possible use of a battery embedded in glass beads. Foamed glass beads (e.g., ^Extover® ) absorb heat due to the melting of the glass only at considerably high temperatures, at which point thermal runaway of the battery is already fully underway, making containment almost impossible.

The use of phenol-formaldehyde materials for the insulation of accumulators is also known. US 2012/0003508 the use of a preformed foam, which, however, must be adapted to the geometry of the cells in the housing in order to develop its fire-resistant effect. The US 2015/0101289 a preformed foam based on phenolic resins. Both documents use liquid phenolic resoles in the production of the foam, which is inserted into the housing in a preformed form. In the production of foams from phenolic resoles, pentane is typically used as a blowing agent, which causes foam formation at 40°C. Any pentane remaining in the system would cause the foam to pop at higher temperatures (so-called "popping and spalling") and could contribute to the flammability of the system via the escaping pentane.

The use of phenol resoles for the production of foams is also discussed in the DE 25 49 441 A1 , the DE 25 49 219 A1 and in the DD 81 224 A5 described. The WO 2010/133610 A1 describes a laminated material made of wood and foamed novolak and the DE 2 253 246 A the production of granulated phenol-formaldehyde resins as core binders in the shell molding process. Neither document discloses fire-resistant encasing materials for flammable and/or combustible materials. DE 1 230 557 A discloses a novolak composition from which a foam is produced in a closed metal mold, which can be used as an insulation panel. Accordingly, this document also does not disclose a fire-resistant wrapping material for flammable and/or combustible materials, which expands during use due to foam formation.

The object of the present invention is to provide a composition for producing fire-resistant encasing materials for flammable and/or combustible materials, which can be used easily regardless of the geometry of the material to be encased and at the same time ensures effective flame protection in the event of internal and external overheating.

The object is achieved according to the invention in that the fireproof cladding material for flammable and/or combustible materials comprises a foam resin composition based on novolaks, containing at least one endothermic blowing agent and a hardener, which absorbs heat during overheating and expands by foam formation.

The foam resin composition according to the invention provides a highly effective flame retardant system. The foam resin composition is a free-flowing, lightweight granulate that can serve as a fire protection and protective material. It can protect the environment from burning materials or, in confined spaces, protect flammable and/or combustible materials from fire for a specific period of time. It can therefore be used as hazardous goods packaging, e.g., for damaged lithium batteries/accumulators or other hazardous substances, particularly due to its low weight in air freight shipments.

The foam resin composition according to the invention is based on the principle that it is capable of absorbing heat during overheating and expands through foam formation. The resulting foam seals the fire-endangered space, preventing a fire from occurring or smothering it. Oxygen is kept out, and reaction products (e.g., vapors) are contained within. The granules do not cause damage to the extinguishing agent and are harmless. The primary extinguishing effect is based on smothering and isolating the fire source.

Since the foam resin composition is a granular material, it can be easily filled, for example, into the housing of a galvanic cell and is independent of its geometry. Thus, even the smallest cavities can be filled with the foam resin composition according to the invention, ensuring complete enveloping of the flammable and/or combustible transportable material. However, it is also possible to use the foam resin composition according to the invention outside the housing of a flammable and/or combustible transportable material, namely as a filling system in boxes and other means of transport. It can be positioned loose as granular material or packed in packages of various sizes outside the housing and function as a fire-resistant enveloping material. The foam resin composition is lightweight and can be reused when the foam function is not in use. It thus represents an environmentally friendly fireproof encasing material.

The novolak used for the foam resin composition according to the invention is a condensation product of a phenolic compound, e.g., selected from phenol, cresol, and/or xylenol, with an aldehyde, such as formaldehyde and/or acetaldehyde, using an acidic catalyst. The ratio of phenolic compound to aldehyde is greater than 1, preferably a ratio of 2:1 to 1.1:1, since the melting point of the novolak and the flame-retardant properties are optimal for the intended use within this range. It has surprisingly been found that novolak-based foam resin compositions exhibit better flame smoke and toxicity properties than other known phenol-formaldehyde resins. The novolak used is produced using processes well known in the art.

The foam resin composition according to the invention further contains an endothermic blowing agent. Endothermic blowing agents are chemical blowing agents that decompose by absorbing heat energy and releasing a gas. These blowing agents are therefore capable of expanding the foam resin composition upon heat generation in its environment, causing it to increase in volume and fill the fire-hazardous space. This blowing agent preferably develops its effect in the temperature range of approximately 110°C to 180°C, i.e., in the temperature range in which, for example, thermal runaway of a galvanic cell is accelerated. The initial foam formation stabilizes the galvanic cell, for example, while still being compressible in the event of expansion.

Carbonate mixtures are preferably used as endothermic blowing agents. These release carbon dioxide upon application of heat, which counteracts the further supply of oxygen to the fire source. NaHCO ₃ and/or NH ₄ HCO ₃ and/or Na ₂ CO ₃ and/or (NH ₄ ) ₂ CO ₃ are particularly preferred because they are easily accessible. These blowing agents are also lightweight and thus contribute to the excellent properties of the foam resin composition according to the invention.

The foam resin composition according to the invention contains a hardener (e.g., hexamethylenetetramine, resoles, or paraformaldehyde) as a further component. Upon application of heat, this creates a crosslinked polymeric structure in the novolak. With increasing curing, the flame retardancy of the foamed composition is ultimately further increased. Hardeners that also act as blowing agents or exhibit flame retardant properties are preferred. For example, hexamethylenetetramine decomposes into ammonia and formaldehyde upon curing, which are capable of further reacting with the free phenol of the novolak. The ammonia serves as an additional blowing agent or flame retardant. A further advantage of using hexamethylenetetramine is that it is inexpensive and highly functional.

The foam resin composition according to the invention may contain additional additives (e.g., fibers for mechanical improvement, inorganic fillers for stabilization), flame retardants (e.g., polyphosphates, melamine derivatives, borates), and processing aids (e.g., metallic soaps). The use of vermiculite has proven advantageous because it is non-flammable and extremely well suited for heat absorption. Thus, it makes a significant contribution to the desired properties of the foam resin composition according to the invention.

Furthermore, it is advantageous if the components of the foam resin composition according to the invention are selected such that they release essentially non-combustible gases at temperatures above 150 °C, thereby further reducing the fire behavior.

1. a) 30 bis 75 Gew.% Novolak hergestellt aus Phenol und Formaldehyd
2. b) 2 bis 15 Gew.% Hexamethylentetramin
3. c) 0 bis 40 Gew.% Vermiculite
4. d) 1,5 bis 10 Gew.% endothermes Treibmittel
5. e) 0,5 bis 5 Gew.% Verarbeitungshilfsmittel
6. f) 0 bis 20 Gew.% weitere Zusatzstoffe.

A foam resin composition containing the following components (based on the total mass of all components) has proven particularly advantageous:

1. a) 30 to 75 wt.% novolak made from phenol and formaldehyde
2. b) 2 to 15 wt.% hexamethylenetetramine
3. c) 0 to 40 wt.% vermiculite
4. d) 1.5 to 10 wt.% endothermic blowing agent
5. e) 0.5 to 5 wt.% processing aid
6. f) 0 to 20 wt.% of other additives.

The specified combination, in particular of novolak, hexamethylenetetramine and endothermic blowing agent, preferably NaHCO ₃ , provides a foam resin composition which, during use, namely during heat absorption, is excellently suited to suppressing or suffocating an emerging fire (including smoke gas development) due to the foam morphology that forms.

The foam resin composition according to the invention is preferably prepared by mixing at least novolak, an endothermic blowing agent and a hardener in a dry mixer at room temperature, then further treating the mixture in a mixing process above the melting temperature of the novolak and grinding the cooled product to a particle size of 0.5 to 3 mm.

After the foam resin composition according to the invention has been produced, it can be placed in direct or indirect contact with the encapsulating flammable and/or combustible material, e.g., a galvanic cell. Direct contact means that the foam resin composition is loosely filled, e.g., into the galvanic cell, and fills all cavities and gaps. The grain size of the foam resin composition can be adjusted depending on the application. However, it is also possible to attach the foam resin composition to the flammable and/or combustible material, e.g., using an adhesive tape. This is particularly advantageous for encapsulating flammable and/or combustible materials of small dimensions, such as lithium-ion batteries for mobile phones. However, it is also possible for the foam resin composition according to the invention to be brought into indirect contact with the flammable and/or combustible material to be encased, i.e. for example, the galvanic cell is located in a housing and the housing is in contact with the foam resin composition, wherein here too the fixing of the foam resin composition to the housing, such as in a protective case for mobile phones, is possible.

It is also possible for the foam resin composition to enclose the flammable and/or combustible material, with or without packaging. The granular foam resin composition can be packaged in various packaging sizes, such as small bags, sized according to their specific application, thus simplifying the handling of the foam resin composition. The packaging material should melt before the endothermic blowing agent takes effect. When the foam resin composition is not in use, it can simply be reused with the packaging.

It is also conceivable to produce a preform from the foam resin composition according to the invention that has a shape close to the intended use but is not yet foamed. This preform can then serve, for example, as the inner shell of a protective cover for a device or be designed to form the entire protective cover.

The flammable and/or combustible transportable material to be encased is preferably one or more galvanic cells, in particular lithium batteries or lithium accumulators or battery packs containing lithium ions. When using galvanic cells containing lithium ions, oxygen is also released in the event of a fire, which means that these cells must be designed to be particularly fire-resistant. These can be used in various devices such as laptops, camcorders, mobile phones, power tools or electric vehicles, including model vehicles and drones. Due to the particularly flammable components, they are encased in a fire-resistant manner with the foam resin composition according to the invention both during transport and/or during operation and/or during charging and/or when not in use. Storage boxes for galvanic cells that are to be recycled, for example, can also be equipped with the foam resin composition according to the invention.

1. A) Herstellung des Novolaks
   • 1085 g Phenol werden mit einer wässrigen Oxalsäurelösung mit 5,4 g Oxalsäure in den Reaktor vorgelegt und im Semi-Batch Verfahren mit 522 g einer 45 %-igen Formalinlösung bei 100 °C im Zulauf unter Rückfluss zur Reaktion gebracht. Nach 3 h Reaktionsdauer wird die überschüssige, nicht reagierte Phenolmenge unter Normaldruck bei Temperaturen bis 150 °C abdestilliert. Die folgende Vakuumdestillation reduziert den Gehalt an freiem Phenol auf unter 1 Gew %.
2. B) Erfindungsgemäße Schaumharzzusammensetzung:

Komponente Gew.% Prozent bezogen auf alle Komponenten Novolak (hergestellt unter A) 62 % Hexamethylentetramin 12 % Vermiculite 15 % Tracel NC 135 XF* 8 % Magnesiumstearat 2% Stearinsäure 1% Total 100 % * Produkt der Firma Tramaco GmbH The invention will be explained in more detail using an exemplary embodiment:

1. A) Production of the novolak
   • 1085 g of phenol are charged to the reactor with an aqueous oxalic acid solution containing 5.4 g of oxalic acid. The reaction is then carried out in a semi-batch process with 522 g of a 45% formalin solution at 100 °C under reflux. After a reaction time of 3 hours, the excess, unreacted phenol is distilled off under atmospheric pressure at temperatures up to 150 °C. The subsequent vacuum distillation reduces the free phenol content to below 1 wt. %.
2. B) Foam resin composition according to the invention:

component Wt% Percent based on all components Novolak (manufactured under A) 62% Hexamethylenetetramine 12% Vermiculite 15% Tracel NC 135 XF* 8% Magnesium stearate 2% Stearic acid 1% Total 100% * Product of Tramaco GmbH

All of these components were thoroughly blended in a dry mix stage for 10 minutes. The powdered mixture was then mixed for 2.5 minutes on an extruder at temperatures between 90°C and 110°C at 50 rpm. The cooled material was then ground to an average particle size of 1-2 mm.

The granular foam resin produced under B) is loosely filled into the casing of a lithium-ion battery, and the casing is then sealed. Tests using external heat at temperatures above 205 °C showed that the foam resin expanded and that the flammable lithium battery inside the casing did not catch fire.

Claims (12)

Refractory encasing material for flammable and/or combustible materials, comprising a foam resin composition based on novolaks, at least one endothermic blowing agent and a hardener, which absorbs heat during overheating and expands by foaming. Refractory cladding material according to at least one of the preceding claims, characterized in that the novolak is produced by condensation reaction of a phenolic compound selected from phenol, cresol and/or xylenol with formaldehyde and/or acetaldehyde in a ratio of 2:1 to 1.1:1 using an acid catalyst. Refractory cladding material according to at least one of the preceding claims, characterized in that it contains NaHCO ₃ and/or NH ₄ HCO ₃ and/or Na ₂ CO ₃ and/or (NH ₄ ) ₂ CO ₃ as endothermic blowing agent. Refractory cladding material according to at least one of the preceding claims, characterized in that it contains hexamethylenetetramine as a hardener. Refractory cladding material according to at least one of the preceding claims, characterized in that it contains, as further additives, flame retardants and processing aids. Refractory cladding material according to at least one of the preceding claims, containing the following components (based on the total mass of all components): a) 30 to 75 wt.% novolak produced from phenol and formaldehyde b) 2 to 15 wt.% hexamethylenetetramine c) 0 to 40 wt.% vermiculite d) 1.5 to 10 wt.% endothermic blowing agent e) 0.5 to 5 wt.% processing aid f) 0 to 20 wt.% other additives. A process for producing a fireproof cladding material for flammable and/or combustible materials, comprising a foam resin composition based on novolaks, at least one endothermic blowing agent and a hardener, which absorbs heat during overheating and expands by foaming, characterized in that : a) Mixing at least the novolak with an endothermic blowing agent and the hardener in a dry mixer at room temperature, b) then further processing the mixture produced in a) in a mixing process above the melting temperature of the novolak, c) grinding the cooled product to a particle size of 0.5 to 3 mm to form granules and d) encasing flammable and/or combustible materials with the granules so that they absorb heat when overheated and expand by foaming. Use of the refractory cladding material according to at least one of the Claims 1 until 6 , characterized in that it is arranged in direct or indirect contact with the surrounding flammable and/or combustible material. Use of the fireproof cladding material according to Claim 8 , enclosing the flammable and/or combustible material with or without packaging. Use of the fireproof cladding material according to Claim 1 for galvanic cells. Use of the fireproof cladding material according to Claim 10 for lithium batteries and lithium accumulators. Use of the fireproof cladding material according to Claim 10 for essential parts for transport and/or during operation and/or during charging and/or in the idle state of the galvanic cell.