Patent Application
20240199870
The invention relates to a flame retardant (meth)acrylate composition combining (meth)acrylic polymer with a synergistic flame retardant blend containing at least one organic phosphinate and at least one phosphonate ester. The (meth)acrylate composition is useful as a flame retardant cap layer in multi-layer polymer composites.
(Meth)acrylic polymers (PMMA), such as Trinseo SOLARKOTE® resins, has been widely used as a cap layer over many different substrate materials (e.g., ABS, PVC, HIPS) to improve weatherability, scratch and mar resistance, and aesthetics in many applications including decking, window profiles, and car interiors and exteriors.
However, PMMA is combustible, limiting its use in applications where flame resistance is required. There is a growing demand for a flame retardant (meth)acrylic cap layer having good processability and mechanical properties in the electrical, building and construction, and automotive fields, electric vehicle EV charging station and bath wall covering.
Flame retardant compounds for use in thermoplastics are well known. Most of these involve iodine and/or bromine compounds, such as aliphatic and aromatic bromine compounds, as for styrenic resins as described in US 2012-0184638, or a compound based on antimony. The problem with these flame retardants is that they tend to have toxicity issues, and with the recommended usage levels of 5-30 weight percent, these flame retardants adversely affect the physical properties (such as tensile strength) of the polymer.
Non-halogenated flame retardants for use in thermoplastics are also known, such as phosphonic acid derivatives (WO2018/137883), organic phosphorous-containing compounds with hindered amines (EP3002311), and dialkylphosphinic salts (EP 1544206). Acrylates are not described as the thermoplastic in these references.
EP1777257B1 describes the use of phosphinate flame retardants in (meth)acrylic polymers, with a UL-94 V-1 rating obtained for a 3.2 mm thickness sample. The reference describes the use of the flame-retardant (meth)acrylate as a top layer coextruded over acrylonitrile-butadiene-styrene (ABS). The total thickness of the multilayer sheet was 3 mm with flame-retardant (meth)acrylate layer thickness of 0.3 mm. The flame performance of the obtained multilayer sheet is similar to the substrate material.
Increased levels of flame retardant can improve the flame resistance of a (meth)acrylic thermoplastic. However, increased level of flame retardant tends to adversely affect the physical and mechanical properties of the thermoplastic, including reduced melt flow, reduced elongation at break, and an increase in yellowness.
There is a need for improved flame retardancy in an acrylic capstock, without adversely affecting the physical properties of the (meth)acrylic polymer, and without the use of halogens or other toxic additives.
It has now surprising been found that a blend of organic phosphinate with low levels of phosphonate ester compounds provided a synergistic effect in PMMA, with improved flame resistance, flowability, and reduced yellowness index may be achieved. In one example, a formulation passed UL94 V-0 test at ⅛″ thickness and UL94 V-1 test at 1/16″ thickness. A co-extruded sheet of the novel flame-resistant PMMA composition over a PC/ABS substrate passed the UL-94 V-0 test. In one example, a 2% addition of a phosphonate ester to the organic phosphinate in a PMMA composition unexpectedly provided a flame retardant increase equal to an extra 4% of phosphinate, yet without a penalty to the physical and mechanical properties.
The present invention provides a flame-retardant PMMA that can be co-extruded over a thermoplastic substrate to produce a multilayer structure having superior flame performance (without halogenated flame retardants), impact resistance, flowability and weatherability. The obtained multilayer structure can be further thermoformed into useful profiles and structures, such as the exterior housing of EV charging stations and car wash stations, bath wall covering, automotive applications, sanitary, aerospace, and building and construction applications.
The (meth)acrylic flame-retardant composition of the invention is a blend of one or more (meth)acrylic polymers (PMMA), one or more organic phosphinate, one or more phosphonate esters, and optionally other additives.
(Meth)acrylic polymers, as used herein, include, but are not limited to, homopolymers, copolymers and terpolymers (meaning more than two different monomer units) comprising alkyl (meth)acrylates. Blends of two or more different (meth)acrylic polymers are also contemplated.
The alkyl methacrylate monomer is preferably methyl methacrylate, which makes up from 60 to 100 of the monomer mixture. 0 to 40 percent of other acrylate, methacrylate, and/or other vinyl monomers may also be present in the monomer mixture. The comonomers generally make up from 0.5 to 40 weight percent, preferably from 0.5 to 30 weight percent, and preferably from 2 to 20 weight percent of the (meth)acrylate copolymer. Other methacrylate, acrylate, and other vinyl monomers useful in the monomer mixture include, but are not limited to, methyl acrylate, ethyl acrylate and ethyl methacrylate, butyl acrylate and butyl methacrylate, iso-octyl methacrylate and acrylate, ethyl hexyl acrylate and methacrylate, lauryl acrylate and lauryl methacrylate, stearyl acrylate and stearyl methacrylate, isobornyl acrylate and methacrylate, methoxy ethyl acrylate and methacrylate, 2-ethoxy ethyl acrylate and methacrylate, dimethylamino ethyl acrylate and methacrylate monomers, styrene and its derivatives. Alkyl (meth) acrylic acids such as (meth)acrylic acid and acrylic acid can be useful for the monomer mixture. Small levels of multifunctional monomers as crosslinking agents may also be used. A preferred acrylic polymer is a copolymer of methyl methacrylate and 2-16 percent of one or more C1-C4 acrylates.
The (meth)acrylic polymer may be impact modified. Common impact modifiers useful in the invention include, but are not limited to, block copolymers, and core-shell impact modifiers. The core-shell impact modifier may have a soft-hard morphology, a hard core-soft-hard morphology, or similar other morphology. For many outdoor applications, a non-impact (meth)acrylic polymer could be too brittle for use, and an impact modified (meth)acrylic would be preferred.
The melt flow rate (MFR) of the (meth)acrylic polymer or the impact modified (meth)acrylic polymer of the invention is preferably greater than 0.6 g/10 min, preferably greater than 0.8 g/10 min, and more preferably greater than 1 g/10 min when testing under 230° C./3.8 kg. The (meth)acrylic polymer or the impact modified (meth)acrylic polymer of the invention further has a Vicat temperature preferably greater than 90° C., preferably greater than 95° C., and more preferably greater than 100° C. when testing under 10N, and a Vicat temperature greater than 85° C., preferably greater than 90° C., and more preferably greater than 95° C. when testing under 50N. The Tg of the (meth)acrylic polymer or the impact modified (meth)acrylic polymer of the invention is preferably greater than 90° C., preferably greater than 95° C., and more preferably greater than 102° C.
The invention requires a flame retardant blend of at least one organic phosphinate flame retardant and at least one phosphonate ester flame retardant.
The organic phosphinate flame retardant has the formula:
where:
Two or more different flame retardants having Formula [I] and/or [II] may also be used.
R1 and R2 are preferably alkyl groups including, but not limited to, methyl, ethyl, n-propyl, n-butyl, tert-butyl, n-pentyl, and/or phenyl groups.
R3 is preferably methylene, ethylene, n-propylene, isopropylene, n-butylene, tert-butylene, n-pentylene, n-octylene, or n-docecylene. It may also be phenylene, methylphenylene, ethylphenylene, tert-butylphenylene, methynaphthylene, pentylethylene, phenylpropylene or naphalene.
Advantageously, M denotes Ca, Al or Zn, and preferably M denotes Al.
Preferably the organic phosphinate flame-retardant agent of Formula (I) is one in which M denotes Al, and R1 and R2 both denote independently a C1-C6 alkyl group. Preferably R1 and R2 are both ethyl groups, or an ethyl group and a methyl group, as in Formulas [III] and [IV].
The weight % phoshorous in the phosphinate flame retardant is preferably greater than 16%, more preferably greater than 18%, more preferably greater than 20%, and most preferably greater than 22%.
Preferably the organic phosphinate flame retardant has a weight average particle size distribution D50 (measured by laser diffraction in acetone) of between 0.5 and 10 microns, advantageously between 1 and 5 microns. This particle size range provides good dispersion in the (meth)acrylic polymer.
The organic phosphinate flame retardant is present in the PMMA composition at from 20 to 45 parts by weight, advantageously from 25 to 45 parts by weight, more advantageously from 25 to 36 parts, and preferably from 29 to 32 parts, based on 100 parts of the (meth)acrylic polymer matrix.
The phosphonate ester used in the invention has the generic formula:
Shorter chain R1, R2, and R3 tend to provide better flame retardancy, as the weight % of phosphorous in the phosphonate ester is higher. Methyl and ethyl groups are especially preferred.
The weight % phosphorous content of the phosphonate ester is preferably greater than 16%, preferably greater than 18%, more preferably greater than 20%, and most preferably greater than 22%.
The phosphonate ester flame retardant is present in the PMMA composition at from 0.1 to 17 parts by weight, advantageously from 0.2 to 12 parts by weight, based on 100 parts of the (meth)acrylic polymer matrix.
In one preferred embodiment, the phosphonate ester has formula [VI], with a phosphorous content of about 24 wt %.
The phosphonate ester can be granular or in powder form. It is used at from 0.1 to 10 percent by weight, preferably from 0.5 to 5 percent by weight, and more preferably from 0.5 to 3 percent by weight, in the PMMA composition, based on the total weight of the composition.
The weight ratio of phosphonate ester to organic phosphinate in the PMMA composition is in a range of from 1:100 to 1:2, preferably from 1:48 to 1:8.
Optionally other non-halogenated flame retardants may be present at low levels of from 0 to 5 weight percent, and preferably from 0.1 to 3 weight percent of the total PMMA composition. Useful other flame retardants include, but are not limited to, one or more compounds selected from below
The levels of flame retardants and additives used in the (meth)acrylic composition is optimized to balance the required level of flame retardancy, yet to minimize the amount of flame retardants, to reduce degradation of physical and mechanical properties of the composition. The composition of the invention surprisingly allows for an increase in flame retardancy, without the typical loss of physical and mechanical properties.
The (meth)acrylic polymer composition of the present invention may optionally contain, in one or more layers, one or more typical additives for polymer compositions used in usual effective amounts, including but not limited to processing aids such as zinc stearate, stearic alcohol and stearic acid, stabilizers, plasticizers, fillers, coloring agents, pigments, antioxidants, antistatic agents, surfactants, toner, refractive index matching additives, additives with specific light diffraction, light absorbing, or light reflection characteristics, dispersing aids, radiation stabilizers, carboxylic acids such as lactic acid, oxalic acid, and acetic acid, and light modification additives, such as polymeric or inorganic spherical particles with a particle size between 0.5 microns and 1,000 microns.
The flame-retardant (meth)acrylic composition of the invention may be blended by means known in the art, such as in a twin screw extruder.
As shown in Tables 1-5, the flame-retardant (meth)acrylic composition of the invention provides improved flowability (MFR increase), improved flammability and reduced yellowness.
The flame-retardant (meth)acrylic polymer matrix, whether impact modified or not, has a melt flow rate (MFR) greater than 0.4 g/10 min, preferably greater than 0.8 g/10 min, and more preferably greater than 1 g/10 min when testing under 230° C./3.8 kg. The polymer matrix, impact modified or not, further has a Vicat temperature greater than 90° C., preferably greater than 95° C., and more preferably greater than 100° C. when testing under 10N, and a Vicat temperature greater than 85° C., preferably greater than 90° C., and more preferably greater than 95° C. when testing under 50N. The Tg of the flame-retardant (meth)acrylic polymer is preferably greater than 90° C., preferably greater than 95° ° C., and more preferably greater than 100° C.
The thermoplastic flame-retardant (meth)acrylic composition can be transformed into useful objects, profiles and sheets, by typical means, such as, but not limited to, extrusion, and injection molding. Useful objects of the composition include covers for electrical devices, profiles, automotive parts and thermoformable sheets.
The flame-retardant (meth)acrylic composition of the invention may also be applied to a thermoplastic polymer, improving the resistance of the multi-layer composite to environmental factors, such as providing scratch and mar resistance, and UV resistance.
The flame-retardant (meth)acrylic polymer composition of the invention may be used as a cap layer on a thermoplastic substrate. A cap layer generally is much thinner than the structural plastic, typically being about 5 to about 25% of the total thickness of the multilayer structure comprising the capstock and structural plastic plies. For example, the thickness of the capstock can be about 0.05 to about 3 mm, preferably from 0.1 to 1 mm, whereas the thickness of the structural thermoplastic ply can be about 0.5 to about 20 mm, and preferably 1 to 10 mm.
Useful thermoplastic substrates for a multi-layer composite include, but are not limited to, saturated polyester (polyethylene terephthalate, polybutylene terephthalate), acrylonitrile/butadiene/styrene (ABS), styrene/acrylonitrile copolymer, acrylic/styrene/acrylonitrile (ASA) copolymer, polystyrene (PS), polycarbonate (PC), polypropylene oxide (PPO), polysulphone, polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), expanded PVC, polypropylene, polyethylene, high impact polystyrene (HIPS). The thermoplastic substrate could also be a mixture or alloy of two or more thermoplastics, such as, but not limited to, PPO/PS, PC/ABS.
In a preferred embodiment, the substrate layer is a PC/ABS. It was found that PC/ABS can provide a higher heat resistance than ABS alone, as well as better mechanical properties, increased toughness, strength and dimensional stability.
The flame-retardant (meth)acrylic composition and the thermoplastic substrate composition may be combined into a multi-layer structure sheet or profile by means known in the art, such as, but not limited to coextrusion (or multi-extrusion), hot compression, multi-injection molding.
Optionally, a tie layer may be imposed between the (meth)acrylic layer and the thermoplastic substrate, for example to improve adhesion of the layers. The intermediate layer is thinner than the thermoplastic substrate, generally in the range of from 10 to 700 microns.
The multi-layer composite of the invention is useful for producing thermoformable sheets by coextrusion. The sheets can be thermoformed into useful objects, including but not limited to, electric vehicle (EV) charging stations shells, car wash stations, automotive applications, automotive trim, aerospace applications, and building and construction applications such as bathroom wall coverings and shower stalls.
The formulations listed in Table 1 below were mixed and compounded using a 27 mm twin screw extruder. Testing specimens were prepared with a Demag injection molding machine at 360-445° F. Samples were tested, with the resulting properties shown in Table 1 below:
Formulations listed in Table 2 below were mixed and compounded using a 27 mm twin screw extruder. Testing specimens were prepared with a Demag injection molding machine at 360-445° F. Samples were tested, with the resulting properties shown in Table 2 below:
Formulations listed in Table 3 below were mixed and compounded using a 27 mm twin-screw extruder. Plexiglas® HFI-10 and Plexiglas® DR101 are commercial grades from Trinseo Altuglas. Testing specimens were prepared with a Demag injection molding machine at 360-445° F. Samples were tested, with the resulting properties shown in Table 3 below:
Formulations listed in Table 4 below were mixed and compounded using a 27 mm twin screw extruder. Testing specimens were prepared with a Demag injection molding machine at 360-445° F. Samples were tested, with the resulting properties shown in Table 4 below:
Comparing example M and N or O, with the same loading of OP935, generic phosphate such as Irgafos® 126 and Irgafos® 168 do not improve MFR and flame performance of the compound like Aflammit®PCO900 does. This may due to the unique chemical structure and high phosphorus content of Aflammit® PCO900.
Three extruders (two for the flame retardant PMMA and one for the PC/ABS) and a triple manifold die were used to coextrude FR PMMA over the PC/ABS to produce multi-layer sheet samples. The extrudates from each extruder were spread then combined at the die and finalized by passing a cooling station with three rollers. The extrusion rates of each extruder were finely adjusted so the obtained multilayer sheets met the desired layer thickness (0.6 mm for the PMMA or the flame-retardant PMMA layer, and 2.4 mm for the PC/ABS layer). These sheet samples were then cut to make specimens for testing.
Example Q proved that co-extruded flame-retardant PMMA with PC/ABS was successful (the formulation was processable). Compared to example P (same PC/ABS with non-flame-retardant PMMA cap layer), the flame performance of the sheet was improved from NR to V-0. Meanwhile, the flexibility and impact resistance were only slightly reduced so it is still suitable for thermoforming and used for EV charging station housing, bathroom wall covering, etc.
| Number | Date | Country | Kind |
|---|---|---|---|
| 22210851.6 | Dec 2022 | EP | regional |
