Expanded polymer foam particle

Abstract

The present invention relates to expanded polymer foam particles provided with a functional skin layer and to a process for producing expanded polymer foam particles provided with a functional skin layer. The present invention also relates to moulded products manufactured on basis of such particles.

Description

[0001] Title: Expanded polymer foam particle

[0002] Description:

[0003] The present invention relates to expanded polymer foam particles provided with a functional skin layer and to a process for producing expanded polymer foam particles provided with a functional skin layer. The present invention also relates to moulded products manufactured on basis of such particles.

[0004] Expanded polymer foam particles provided with a functional skin layer are known in the art.

[0005] For example, US 2012 / 052127 discloses expanded polystyrene particle provided on the surface thereof with a skin layer with superior moldability wherein the skin layer comprises a binder selected from the group consisting of a thermoplastic resin-based adhesive, a thermosetting resin-based adhesive, an inorganic adhesive, a protein-based adhesive, and a mixture thereof, wherein the skin layer further comprises methylene diphenyl diisocyanate.

[0006] EP 1 709 110 discloses an expanded polystyrene particle with a functional skin layer wherein the functional skin layer is formed by coating the surface of the inner expanded polystyrene layer with a functional coating composition having 10 to 99 wt. % of a vinyl acetate based polymer and 0.1 to 90 wt. % of at least one functional additive, such as ultraviolet stabilizers, fillers, reinforcing agents, colorants, impactresistant agents, flame retardants, antistatic agents, and thermal conductivityimparting agents.

[0007] EP2656995 discloses a skin-covered foamed molded article, comprising: a skin having an interior surface defining a hollow interior space; and a foam layer of expanded polystyrene beads which are fuse-bonded to each other, said foam-layer being provided within the hollow interior space and fuse-bonded to the interior surface.

[0008] WO 2008 / 090333 discloses an aqueous gel-forming composition comprising from 5% to 40% by weight of an aluminosilicate comprising alkali metal aluminate and alkali metal silicate and from 0.1% to 10% by weight of an organic liquid. The aqueous gel-forming composition is coated onto the expanded polystyrene beads by spraying into a fluidized bed followed by drying in the bed to a moisture content of 12% by weight. WO 2010 / 128797 relates to a method for producing non-flammable expandable polystyrene particles wherein expandable polystyrene particles and 10 to 60% by weight of incombustible material powder having a particle size of 1 to 70 pm, such as metal oxides, non-metal oxides, metal hydroxides, silicon dioxide-containing materials, graphite, and vermiculite, are mixed and a mixture of a solvent capable of dissolving polystyrene and water is sprayed to form expandable polystyrene particles. A surface layer of the polystyrene particles in a softened state is formed and the incombustible material powder will penetrate and coat the surface of the expanded polystyrene particles. An amount of 0.1 to 10% by weight of a water-soluble resin is additionally coated on the expandable polystyrene particles that have been infiltrated and coated, wherein the water-soluble resin includes a vinyl acetate based resin, an acrylic-based resin, a polyvinyl alcohol resin, and an ethylene vinyl acetate based resin. The water-soluble resin contains 0.1 to 10% by weight of one or more selected from bromine-based flame retardants, phosphorus-based flame retardants, and antimony trioxide. The expanded polystyrene particles having been infiltrated and coated are additionally coated with a sodium silicate solution.

[0009] KR 2022 0021801 relates to a flame retardant composition for manufacturing EPS beads, the flame retardant composition containing, per 100 parts by weight of water, 30 to 45 parts by weight expanded graphite, 5 to 15 parts by weight gypsum, 0.5 to 15 parts by weight talc, 3 to 7 parts by weight of calcium carbonate, 10 to 20 parts by weight of ammonium polyphosphate, 3 to 7 parts by weight of decabromodiphenylethane, 1 to 3 parts by weight of M DI, 3 to 7 parts by weight of melamine cyanurate, 3 to 7 parts by weight of pentaerythritol, and 50 to 60 parts by weight of an organic binder selected from the group consisting of polyvinyl acetate, ethylene vinyl acetate copolymers, melamine resin, epoxy resin, and acrylic resin.

[0010] The problem with using a silicate based fire retardant composition for building insulation materials such as expanded polystyrene (e.g. roofing insulation) is that, until needed, such materials are often left exposed to the adverse weather conditions after delivery to the building site. Unless precautions are taken to protect them against the wet, such exposure can result in significant loss of the fire retardancy properties of the silicate-based composition.

[0011] The problem with the use of solvents is that it makes large scale production extremely difficult. An object of the present invention is to provide expanded polymer foam particles that meet the industrial requirements of fire resistance.

[0012] Another object of the present invention is to provide expanded polymer foam particles having a functional skin layer that is water resistant and does not leach out over time.

[0013] Another object of the present invention is to provide expanded polymer foam particles having a functional skin layer resulting in the formation of char when exposed to fire.

[0014] Another object of the present invention is to provide expanded polymer foam particles having a functional skin layer that does not melt when exposed to elevated temperatures.

[0015] Another object of the present invention is to provide expanded polymer foam particles having a functional skin layer that can be shape moulded.

[0016] Another object of the present invention is to provide expanded polymer foam particles having a functional skin layer that has a high water resistance.

[0017] The present invention as discussed above relates to an expanded polymer foam particle provided with a functional skin layer comprising: an inner expanded polymer foam layer and an outer functional skin layer, wherein the inner expanded polymer foam layer is formed by heating and expanding an expandable polymer foam bead or pellet, and the functional skin layer is formed by coating the outer surface of the inner expanded polymer foam layer with a functional coating composition, wherein the expanded polymer foam particle is chosen from the group of expanded polyethylene (EPE), expanded polypropylene (EPP), polylactic acid (PLA) and expanded polystyrene (EPS), the functional coating composition is based on 5 to 40 wt.%, preferably 10 to 25 wt.%, of a polyvinyl alcohol, 4 to 30 wt. %, preferably 7 to 15 wt.%, of an acid donor and 40 to 90 wt.%, preferably 50 to 80 wt.%, of at least one or more auxiliaries, the weight percentages are based on the total weight of the coating composition and all weight percentages add up to 100%.

[0018] On basis of the above specific coating composition one or more objects are achieved. The present inventors found that an unexpected advantage of the present coating composition is the excellent char formation as will be shown in the experimental section of this description. The present inventors found that a carbon or char structure around each bead is formed in a fire situation. Such a carbon structure around each bead prevents a further collapse of the bead and can thus be seen as a protective layer. The carbon structure has been obtained by the specific composition of the functional coating composition. If this structure is not formed, no fire-resistant properties can be recognized for the final product as will be discussed in the experimental section of this document.

[0019] In addition, the present coating composition is qualified as a non-hazardous, water based coating composition. In that context it is to be noted that a standard intumescent coating is activated at a temperature of approximately 250°C, which is well above the melting temperature of the polymer foam particle. Consequently, a standard intumescent coating cannot be used for the present polymer foam particles. A minimum amount of 5 wt.% polyvinyl alcohol is needed to create a sufficient char layer since the present inventors found that an amount lower than 5 wt.% of polyvinyl alcohol leads to a significant reduction of the fire properties.

[0020] The expanded polymer foam particle is a foam particle having a density of at most 100 kg / m3. The expanded polymer foam particle is a spherical particle wherein the diameter of the expanded polymer foam particle without the functional skin layer is between about 0,5 - 10 mm.

[0021] In an example polylactic acid (PLA) is a bio-based polylactic acid, preferably a bio-based biodegradable polymer that can be produced from renewable resources including starch from corn and potatoes, sugar from beets and sugar cane, and so forth. In this context biodegradable means that it will convert into natural material, such as water, carbon dioxide, and composite. This process is conducted by microorganisms and influenced by, inter alia, temperature and humidity.

[0022] In an example of the present invention the polyvinyl alcohol is a polyvinyl alcohol having an Mw of at least 5000, preferably at least 6000 and at most 120.000, preferably at most 100.000. The present inventors found that an Mw of at least 5000 is necessary for the formation of a strong char network char when exposed to fire. The Mw is measured via a viscosity measurement protocol on basis of a solution of 4 wt.% aqueous solution.

[0023] In an example of the present invention the polyvinyl alcohol is a polyvinyl alcohol having a hydrolysis degree in a range of at least 50, preferably at least 60 and more preferably of at least 80 and at most 100. The present inventors also found that a hydrolysis degree of at least 50 is necessary for the formation of a strong char network char when exposed to fire.

[0024] In an example of the present invention the at least one or more auxiliaries are chosen from the group of graphite and fillers. The use of such fillers in a coating composition increases the fire resistance thereof.

[0025] In an example of the present invention the filler is selected from pulverulent inorganic substances such as talc, chalk, kaolin, aluminium hydroxide, aluminium nitrite, aluminium silicate, barium sulfate, calcium carbonate, titanium dioxide, calcium sulfates, silica, quartz flour, aerosil, alumina or wollastonite. Another example of a filler is expandable graphite resulting in an increase of the fire resistance and an improvement of the fire reaction. The incorporation of aluminium hydroxide in the present coating composition should be kept as low as possible since aluminium hydroxide is a weak base (pH= 8-9) and may interfere with other components resulting in less char formation.

[0026] In an example of the present invention the thickness of the functional skin layer is between 1 micrometre and about 300 micrometre. In an embodiment wherein the thickness of the functional skin layer is lower than 1 micrometre the fire resistance of the expanded polymer foam particle will be too low since there is a risk that the particle itself will be exposed to elevated temperatures resulting in a complete melt of the particles. If the thickness of the functional skin layer is more than about 300 micrometre no additional beneficial effects with regard to fire resistance will be observed. The thickness of the functional skin layer is at least 1 micrometre, preferably at least 50 micrometre, more preferably at least 60 micrometre and at most 300 micrometre, preferably at most 200, more preferably at most 110 micrometre.

[0027] The diameter of the expanded polymer foam particle provided with a functional skin layer according to the invention is in a range of 0,502 and 10,6 mm. The diameter of a foam particle without the functional skin layer is in a range of about 0,5 - 10 mm.

[0028] In an example of the present invention the functional coating composition is further based on 1 to 10 wt.%, preferably 2 to 8 wt.% of a cross linker, the weight percentages are based on the total weight of the coating composition and all weight percentages add up to 100%, to form a functional skin layer. The present inventors found that the water resistant of the functional coating composition can be improved by the incorporation of a cross linker in the functional coating composition. In an example of the present invention the cross linker is an 4,4'-methylene diphenyl diisocyanate (MDI) ether-based component. The incorporation of such a type of cross linker increases the wet bending strength of the polyvinyl alcohol present in the coating composition.

[0029] In an example of the present invention the acid donor is a phosphate, preferably chosen from the group of sodium pyrophosphate, calcium pyrophosphate, potassium pyrophosphate, ammonium polyphosphate and melamine polyphosphate, or a combination thereof.

[0030] The present invention also relates to a functional expanded polymer foam moulded product manufactured by heat expanding moulding of the expanded polymer foam particle with a functional skin layer as discussed above. The necessary heat can be provided via steam, hot air and of radio-frequency heating, or a combination thereof.

[0031] The present invention also relates to a process for producing expanded polymer foam particles provided with a functional skin layer, comprising the steps of: heating and expanding expandable polymer foam beads or pellets to produce expanded polymer foam particles; applying a functional coating composition to the outer surface of the above expanded polymer foam particles, the functional coating composition being prepared by mixing or dissolving 5 to 40 wt.%, preferably 10 to 25 wt.%, of a polyvinyl alcohol, 4 to 30 wt. %, preferably 7 to 15 wt.%, of an acid donor and 40 to 90 wt.%, preferably 50 to 80 wt.%, of at least one or more auxiliaries, the weight percentages are based on the total weight of the coating composition and all weight percentages add up to 100% to form a functional skin layer; and drying the thus coated polymer foam particles for obtaining the expanded polymer provided with a functional skin layer.

[0032] In an example the functional coating composition further comprises 1 to 10 wt.%, preferably 2 to 8 wt.% of a cross linker, the weight percentages are based on the total weight of the coating composition and all weight percentages add up to 100%, to form a functional skin layer.

[0033] The present invention will now be described in more detail with reference to the following several examples of the manufacture of functional expanded polymer foam particles and molded products manufactured thereof. Examples A-F

[0034] An amount of 150 g polyvinyl alcohol (manufactured by Sigma Aldrich) having an Mw of 70.000 and a degree of hydrolyse of 99,2-99,7% was dissolved in 850 g water using the following steps: filling a tank with demineralized water (Temp: <30°C), adding polyvinyl alcohol while stirring and dissolving the polyvinyl alcohol at elevated temperature. The number of dry solids in this example was 15% w / w.

[0035] After preparing the aqueous polyvinyl alcohol solution additional components, namely acid donor Novaflam APP (ammonium polyphosphate, manufactured by Allinova), auxiliaries kaolin (manufactured by Sigma Aldrich) and crosslinker 4,4'- methylene diphenyl diisocyanate (manufactured by Sigma Aldrich) were added thereto according to Table 1 (See examples A-F). The final coating composition was coated onto expanded polystyrene particles by using a mixing device and the particles thus coated were dried by using an air flow stream.

[0036] The expanded polystyrene particles used in these Examples have an average diameter of 5 mm and a density of 15 kg / m3. These expanded polystyrene particles were obtained by pre-expanding expandable polystyrene particles having an average bead size range 95% between 0,9-1 , 8 mm (manufactured by BEWi RAW) in an expanding machine at a temperature of 103-105°C followed by drying and aging in a silo.

[0037] The expanded polystyrene particles provided with a functional skin layer were stored in big bags. The thickness of the functional skin layer was 60 micrometre.

[0038] The expanded polystyrene particles having a functional skin layer thus produced were charged into a steam moulder for expanded polystyrene, heated at a steam pressure of 0.6 kg / cm3for 40 seconds, sustained for 10 seconds, and cooled to manufacture an expanded polystyrene molded product having a density of 40 kg / m3.

[0039] The Mw was measured on basis of a viscosity measurement of an aqueous solution of 4 wt.%. The solution was transferred into a measurement cylinder at the measuring temperature, keeping it in a thermostatic bath at 20 ± 0.3°C. The viscosity was measured by a Brookfield LVT Viscometer and a Brookfield UL Spindle. The rotational speed of the spindle is 12rpm. This depends on the viscosity. An aqueous solution of 4 wt.% provided a viscosity of 28 to 32 cPs. Table 3 shows the relationship between the measured viscosity of the aqueous solution and the Mw. According to Table 1 several experiments were conducted as shown in Table 2. Table 2 refers to the physical properties of expanded polystyrene molded products according to Examples A-F. Examples A, B and F are examples according to the present invention. The amount of acid donor in Example C is too high. The amount of polyvinyl alcohol in Example D is too high. The amount of auxiliaries in Example E is too low.

[0040] Comparable results were obtained with other types of expanded polymer foam particles, such as expanded polyethylene (EPE), expanded polypropylene (EPP) and bio-based polylactic acid (PLA).

[0041] The inventors conducted an additional set of experiments according to the coating composition, except for another acid donor being potassium pyrophosphate (manufactured by Sigma Aldrich).

[0042] Table 1 : coating composition of Examples A-F

[0043] Table 2: physical properties of expanded polystyrene moulded products according to Examples A-F Table 3: relation between viscosity and Mw of a 4.wt% solution of PVA

[0044] From Table 2 it is clear that Example C does not meet the requirements of both fire test and water resistance due to the high amount of acid donor. From Table 2 it is clear that Example D does not meet the requirements of both fire test and water resistance due to the high amount of polyvinyl alcohol. From Table 2 it is also clear that Example E does not meet the requirements of both fire test and water resistance due to the low amount of auxiliaries.

[0045] The present inventors carried out additional fire test experiments with coating compositions based on ethylene vinyl acetate. Figure 1 shows four fire test experiments of EPS bead provided with a coating based on ethylene vinyl acetate, ammonium polyphosphate and an additional component (from left to right), i.e. starch, pentaerythritol, melamine, and cellulose. From the results shown in Figure 1 it is clear that for each coating composition no carbon structure has been formed around each pearl.

[0046] Figure 2 shows fire test experiments with three different coating compositions based on polyvinyl alcohol. The coating compositions further comprised ammonium polyphosphate and kaolin. In Figure 2, the amount of coating increases from left to the right. The reaction of polyvinyl alcohol and ammonium polyphosphate causes carbon formation around the bead in a fire situation, which is not possible with other combinations of water-based resins and fire retardants. Because this reaction only takes place at high temperatures (>200°C), the expanded polymer foam particles remain processable in moulding processes operating at temperatures <120°C.

Claims

CLAIMS1. An expanded polymer foam particle provided with a functional skin layer comprising: an inner expanded polymer foam layer and an outer functional skin layer, wherein the inner expanded polymer foam layer is formed by heating and expanding an expandable polymer foam bead or pellet, and the functional skin layer is formed by coating the outer surface of the inner expanded polymer foam layer with a functional coating composition, wherein the expanded polymer foam particle is chosen from the group of expanded polyethylene (EPE), expanded polypropylene (EPP), polylactic acid (PLA) and expanded polystyrene (EPS), the functional coating composition is based on 5 to 40 wt.%, preferably 10 to 25 wt.%, of a polyvinyl alcohol, 4 to 30 wt. %, preferably 7 to 15 wt.%, of an acid donor and 40 to 90 wt.%, preferably 50 to 80 wt.%, of at least one or more auxiliaries, the weight percentages are based on the total weight of the coating composition and all weight percentages add up to 100%.

2. An expanded polymer foam particle according to claim 1 , wherein the polyvinyl alcohol is a polyvinyl alcohol having an Mw of at least 5000, preferably at least 6000 and at most 120.000, preferably at most 100.000.

3. An expanded polymer foam particle according to any one of claims 1-2, wherein the polyvinyl alcohol is a polyvinyl alcohol having a hydrolysis degree in a range of at least 50, preferably at least 60 and more preferably of at least 80 and at most 100.

4. An expanded polymer foam particle according to any one of claims 1-3, wherein the at least one or more auxiliaries are chosen from the group of graphite and fillers.

5. An expanded polymer foam particle according to claim 4, wherein the filler is selected from pulverulent inorganic substances such as talc, chalk, kaolin, aluminum hydroxide, aluminum nitrite, aluminum silicate, barium sulfate, calcium carbonate, titanium dioxide, calcium sulfate, silica, quartz flour, aerosil, alumina or wollastonite.

6. An expanded polymer foam particle according to any one of claims 1-5, wherein the thickness of the functional skin layer is at least 1 micrometre, preferably at least 50 micrometre, more preferably at least 60 micrometre and at most 300 micrometre, preferably at most 200, more preferably at most 110 micrometre.

7. An expanded polymer foam particle according to any one of claims 1-6, whereinthe acid donor is a phosphate, preferably chosen from the group of sodium pyrophosphate, calcium pyrophosphate, potassium pyrophosphate, ammonium polyphosphate and melamine polyphosphate, or a combination thereof.

8. An expanded polymer foam particle according to any one of claims 1-7, wherein the functional coating composition is further based on 1 to 10 wt.%, preferably 2 to 8 wt.% of a cross linker, the weight percentages are based on the total weight of the coating composition and all weight percentages add up to 100%, to form a functional skin layer.

9. An expanded polymer foam particle according to claim 8, wherein the cross linker is an 4,4'-methylene diphenyl diisocyanate (MDI) ether-based component.

10. A functional expanded polymer foam moulded product manufactured by heat expanding moulding of the expanded polymer foam particle with a functional skin layer according to any one of claims 1 to 9.

11. A process for producing expanded polymer foam particles provided with a functional skin layer, comprising the steps of: heating and expanding expandable polymer foam beads or pellets to produce expanded polymer foam particles, wherein the expanded polymer foam particle is chosen from the group of expanded polyethylene (EPE), expanded polypropylene (EPP), polylactic acid (PLA) and expanded polystyrene (EPS); applying a functional coating composition to the outer surface of the above expanded polymer foam particles, the functional coating composition being prepared by mixing or dissolving 5 to 40 wt.%, preferably 10 to 25 wt.%, of a polyvinyl alcohol, 4 to 30 wt. %, preferably 7 to 15 wt.%, of an acid donor and 40 to 90 wt.%, preferably 50 to 80 wt.%, of at least one or more auxiliaries, the weight percentages are based on the total weight of the coating composition and all weight percentages add up to 100% to form a functional skin layer; and drying the thus coated polymer foam particles for obtaining the expanded polymer foam particles provided with a functional skin layer.

12. A process according to claim 11 , wherein the functional coating composition further comprises 1 to 10 wt.%, preferably 2 to 8 wt.% of a cross linker, the weight percentages are based on the total weight of the coating composition and all weight percentages add up to 100%, to form a functional skin layer.

Images