WO2000042102A1

WO2000042102A1 - Acrylic materials

Info

Publication number: WO2000042102A1
Application number: PCT/GB2000/000014
Authority: WO
Inventors: Ian Michael Robinson; John Alan Mccluskey; Garry Stuart Hunt
Original assignee: Ineos Acrylics Uk Limited
Priority date: 1999-01-12
Filing date: 2000-01-06
Publication date: 2000-07-20
Also published as: AU1883600A

Abstract

An acrylic material comprising: a) 10-90 % wt. of an acrylic copolymer containing 80-99 % wt. of methyl methacrylate residues and 1-20 % wt. of a C1-C4 alkyl acrylate, b) 5-85 % wt. of a solid halogen-containing polymer which is compatibe with methyl methacrylate, and c) 5-20 % wt. of a phosphorous-containing organic fire retardant compound is disclosed which has improved performance on burning, particularly in relation to those burning characteristics which affect the hazard presented in the event of a fire.

Description

Acrylic Materials

The present invention relates to acrylic materials, particularly to acrylic materials having improved performance in fires.

Acrylic materials have been known and widely used for many years in a variety of applications, including building and glazing applications. The performance of such plastics materials in fire situations is highly important and such materials are often subjected to stringent testing to meet standard criteria set by various regulatory bodies. There are many aspects of a material's behaviour in fire situations which are important when assessing its safety. Although many fire tests are based upon a determination of the ease with which the material ignites, the way in which a material burns may be fundamental to the chances of any person escaping from a fire. For example, the amount of smoke and other toxic gases emitted when a material burns directly affects the likelihood of successful escape.

Acrylic materials which contain fire retardant compounds are already well known in the art. Typical fire retardant materials in widespread use include phosphorous and/or halogen-containing organic compounds, e.g. trischloroethyl phosphate (TCEP). GB-A-1064976 discloses casting resins comprising a blend of polymethyl methacrylate with polyvinyl chloride and TCEP to produce a self-extingiushing plastic. GB-A-1094874 discloses a polymerisable methyl methacrylate syrup comprising a methyl methacrylate monomer or mixture of copolymerisable monomers, and a copolymer of vinyl chloride and vinylidene chloride which may be polymerised to form compositions which are transparent and non-inflammable. US-A-5747569 discloses flame-retardant cast panels made of a composition comprising at least one methacrylic ester, methacryiic acid and an anhydrous phosphorous compound. GB-A-2138825 describes flame-resistant polymethylmethacrylate moulding materials comprising between 8 and 15 % of at least one chloroalkylphosphoracid ester of a specified formula and the resulting materials were contrasted with compositions containing halogen-containing polymers. GB-A-1031289 describes compositions containing PVC as a major component (50 - 80%) with a methyl methacrylate polymer with a chlorinated polyethylene, a dehydrochlorination inhibitor and a bivalent sulphur compound. GB-A-1033464 describes a self-extinguishing transparent thermoplastic material comprising 65 - 45 parts of polyvinyl chloride and 35 - 55 parts of an acrylic polymer. None of the above-mentioned references mentions the specific formulations of the present invention and which have been found to be particularly effective in providing an acrylic material having a good performance when tested for a number of different fire and burning characteristics.

According to the invention an acrylic material comprises: a) 10 - 90% wt of an acrylic copolymer containing 80 - 99% wt of methyl methacrylate residues and 1 - 20% wt of a C1 - C4 alkyl acrylate, b) 5 - 85% wt of a solid halogen-containing polymer which is compatible with methyl methacrylate, and c) 5 - 20% wt of a phosphorous-containing organic fire retardant compound.

In a second aspect of the invention a method of manufacturing an acrylic product comprises the steps of (i) dissolving in methyl methacrylate monomer a) 1- 20 wt % of a C1 - C4 alkyl acrylate b) a solid halogen-containing polymer c) a phosphorous-containing organic fire retardant compound such that the resulting mixture contains 5 - 25 % wt of b and 5 - 20 wt % of c based on the total (meth)acrylate content, d) a free-radical initiator and e) optionally a chain transfer agent, such as a mercaptan (ϋ) introducing the mixture into an enclosed mould and

(iii) heating the mixture at above 50 degrees C for at least two hours so that the mixture polymerises.

The methyl methacrylate monomer may contain some polymethylmethacrylate (PMMA) or methylmethacrylate/alkyl acrylate copolymer dissolved therein to optimise the viscosity of the mixture, to form a polymer/monomer syrup as is known in the art.

In a third aspect of the invention a method of manufacturing an acrylic product comprises the steps of

(i) forming a molten mixture of a) an acrylic copolymer containing 80 - 99% wt of methyl methacrylate residues and

1 - 20% wt of a C1 - C4 alkyl acrylate, b) a solid halogen-containing polymer which is compatible with methyl methacrylate (ii) adding to said molten mixture a phosphorous-containing organic fire retardant compound such that the resulting mixture comprises 10 - 90% wt of said acrylic copolymer, 5 - 85% wt of said solid halogen-containing polymer, and 5 - 20% wt of said phosphorous-containing organic fire retardant compound; (iii) moulding the resulting mixture in molten form and subsequently cooling the mixture to form said acrylic product. The method of moulding may be by extrusion or by injection moulding or another melt-moulding technique, but is preferably by extrusion.

The acrylate comonomer is preferably ethyl acrylate. Preferably the acrylate comonomer is present at a concentration of at least 4% and less than 15 % especially less than 10% by weight of the total acrylic monomer present. We have found that a concentration of 4 - 8 % by weight, e.g. about 6% by weight is most preferred. The presence of an acrylate comonomer in the acrylic material results in a reduced rate of polymer decomposition compared to a methacrylate homopolymer. The presence of the acrylate therefore increases the time to ignition and decreases the rate of combustion of the acrylic material.

The solid halogen-containing polymer is preferably a polymer or copolymer of vinyl chloride with e.g. vinyl acetate, vinylidene chloride or acrylic monomers such as acrylates and methacrylates. Particularly preferred is a copolymer of vinyl chloride and vinyl acetate, i.e. PVC-coVA. The vinyl acetate content of the copolymer is preferably 0 - 40% wt, more preferably 5 - 20%, especially about 12 - 16% wt. The solid halogen-containing polymer must be compatible with the methyl methacrylate copolymer in such a way that it can be dissolved in the acrylic monomer or may be melt-blended into the acrylic polymer without undue difficulty. A molecular weight (Mw) of about 80,000 - 120,000 Daltons (D) is preferred, especially about 100,000 Daltons. When the molecular weight of the halogen-containing polymer is very high, e.g. above about 150,000 D then it may be more difficult to blend into the acrylic polymer. The vinyl acetate content is preferred in order to provide increased solubility in acrylic monomer and improved compatibility with acrylic polymer.

We have found that the presence of the halogen-containing polymer in the acrylic material leads to charring when the material is burned. When the material chars, the rate of heat release is relatively low compared with a material which does not char to the same extent. At higher levels of halogen-containing polymer, the time to ignition is relatively long. When the acrylic material is formed by dissolving the halogen-containing polymer in an acrylic monomer, the amount of solid halogen-containing polymer in the acrylic material of the invention is preferably 5 - 25 wt%, more preferably about 8 - 15%, e.g. 10%. As the amount of halogen-containing polymer is increased, the viscosity of the monomer + polymer mixture increases and it becomes more difficult to dissolve the polymer and operate the polymerisation process. These levels of halogen-containing polymer give a satisfactory balance of charring behaviour and smoke emission. When the acrylic material is formed by blending the halogen-containing polymer with the acrylic polymer in a molten state, the halogen-containing material may be present at a concentration >25% by weight of the total weight of the mixture, e.g. 40 - 85%, more specifically 50 - 80% by weight. At these higher levels of the halogen-containing material the resulting material may become more transparent than at lower levels of halogen-containing polymer, and transparent materials are desirable for certain applications such as glazing for example.

The acrylic material contains 5 - 20%, preferably about 12 - 17% by wt of a phosphorous-containing organic fire retardant compound. The fire retardant compound may be selected from a wide range of known and commercially available fire retardants which are known to be effective in acrylic materials. We have found that fire retardant compounds which also contain halogen are particularly effective in the invention. Examples of such materials include the linear or cyclic aliphatic organic phosphates, including halogen-containing organic phosphates, e.g. tris(chloroethyl) phosphate (TCEP) which is available from Akzo, aliphatic phosphoric acid esters with a phosphorinane structure (e.g. AMGARD™ P5085) , 2,2-bis (chloromethyl)-1,3-propanediol bis(bis(2-chloroethyl)phosphate) (CAS Reg. no = 38051-10-4) sold as AMGARD V6™ (Albright & Wilson), tris(dichloropropyl)phosphate (TDCP); aliphatic polyphosphate-phosphonates which contain chlorine such as chlorinated polyphosphates e.g. CR509 ™ available from Daihachi Chemical Industry Co Ltd, which is a chlorine-containing condensed phosphoric acid ester having a chlorine content of about 26% by weight, a phosphorous content of 14% by weight and a molecular weight of about 650 (CAS Registry number 78182-44-2) and related homologues, and other phosphate esters sold for use as fire retardants. Preferred fire retardant compounds are thermally stable above 200 °C. Thus relatively high molecular weight materials such as TDCP (onset temperature for thermal degradation = 221 °C, molecular weight = 432), Amgard V6 (onset temperature for thermal degradation = 250 °C molecular weight = 585) are particularly preferred since these generally exhibit higher thermal degradation temperatures than lower molecular weight materials such as TCEP (onset temperature for thermal degradation = 200 °C, molecular weight = 285.5).

The molecular weight (Mw) of the acrylic copolymer is at least 50,000 more preferably at least 100,000 D, most preferably at least 300,000 D. We have found that the high molecular weight reduces the tendency of the polymer to drip when burning. Drips of molten polymer represent an increased hazard in a fire because it may cause injury and lead to the fire spreading. In order to control molecular weight and improve the thermal stability of the acrylic polymer, a chain transfer agent (preferably an organic mercaptan, e.g. dodecyl mercaptan) may be added to the polymerisation mixture before polymerising the acrylic polymer. The amount of mercaptan added is typically 0 - 1%, preferably 0.1 - 0.6% by weight of the acrylic monomer(s).

When the acrylic article is formed by melting the acrylic copolymer, halogen containing polymer and fire retardant mixture and subsequently shaping the melt, e.g. by extrusion, the acrylic copolymer is preferably a moulding polymer containing residues of an organic mercaptan compound which was used as a chain transfer agent in the manufacture of the moulding polymer. Acrylic moulding polymers generally have molecular weights between 50,000 and 200,000, e.g. 80,000 - 150,000 and we have found that such polymers are suitable for use in the invention.

Other additives such as a UV stabiliser, colourants, impact modifiers, lubricants, cross-linking monomer residues etc commonly found in acrylic compositions may be present in the acrylic materials of the invention.

The acrylic polymers may be made in the form of sheets, powders or granules, e.g. for moulding resins. Fabricated sheets or moulded articles may be subjected to further processes such as shaping, particularly thermoforming or moulding or extrusion processes to make finished articles.

The invention will be further described in the following Examples.

Preparation of polymer samples

The composition of the acrylic polymers tested is shown in the Table. The PVC -co VA polymer had a Mw of about 100 kD and a vinyl acetate content of about 14%. Two different fire retardant compounds were used, CR509 (commercial product available from Daihachi) and TCEP (from Akzo). All components of the polymer were dissolved in methyl methacrylate (MMA). To the resulting monomer mixture was added 0.05 - 0.5% wt based on active monomer weight (depending on the desired molecular weight of the polymer) of AIBN free-radical initiator. The mixture was then cast between two glass plates held about 4 mm apart by a gasket and then polymerised at 63 °C for 18 hours. The resulting polymer sheet was then post-cured at 60 °C for 2 hours, 80 °C for 2 hours and finally 100 °C for 1 hour.

Burning properties by cone calorimetry The burning properties of the acrylic samples made were measured by cone calorimetry using a method described in ISO 5660 using an incident heat flux of 40 kW/m² and square samples measuring 100 x 100 mm x 4 mm thickness. The time to ignition (t,), Mass loss rate, Heat release rate, Heat of combustion, and carbon monoxide emission were all monitored. The amount of smoke generated was determined by measuring the smoke extinction area (area of shadows produced by the smoke particles).

Surface spread of flame test

The surface spread of flame was measured by BS 476 part 7.

Impact strength

Notched Izod impact strength was measured by ISO 180. Un-notched Charpy impact was determined according to ISO 179.

The results (Table 1 ) show that the time to ignition is relatively long in Example 4 and that this sample also shows a relatively low mass loss rate and heat release rate, i.e. it burns less easily and more slowly than other samples, demonstrating the synergistic effect of the PVC polymer, the fire retardant and the presence of acrylate comonomer in the material. Although on a mass basis, the smoke and CO generation is relatively high, the lower rate of burning results in an acceptable rate of generation of CO and smoke in the Example 4 material. The performance of Example 5 also gives acceptable results but less so than Example 4. The synergistic effect of the fire retardant additive with the PVC polymer is particularly evident if Example 6 & 7 are compared with Examples 2 & 4. When CR509 is used as a fire retardant, (Examples 6 & 7), the rate of combustion as evidenced by the peak heat release rate and heat of combustion is much lower when PVC is present than in its absence. The effect is less pronounced in Examples 2 & 4 which use TCEP.

Table 1

Examples 8 - 11 The polymer samples were prepared as described above, using Amgard V6 (from Albright & Wilson) as a halogen and phosphorous-containing fire retardant compound. The compositions and test results are shown in Table 2.

Table 2

The sample containing the halogen-containing polymer, fire retardant and ethyl acrylate as a comonomer (Example 11 ) exhibits properties which are generally superior to those of the comparative samples of Examples 8 - 10 in that the time to ignite the sample is longer, whilst the mass loss rate, heat release rate, heat of combustion and generation of smoke and CO are all generally low.

Examples 12 - 15

A commercial polymethyl methacrylate - ethyl acrylate copolymer moulding resin, Diakon™ MG102 (Ineos Acrylics Ltd) having a molecular weight of approximately 90,000, was blended with a commercially available polyvinyl chloride resin (RXC377, available from EVC). The mixture was fed to a single screw extruder fitted with a liquid injection pump near the output end of the barrel and a vacuum take-off system for de-gassing. TCEP was fed to the molten mixture in the extruder by means of the liquid injection pump. The extruder was run at a temperature of between 150 - 160 °C at the feed and about 170 - 190 °C at the die. Samples were produced at a polymer feed rate of 2.5 kg per hour. The extruded lace was cut into polymer granules and then 100mm x 100mm plaques were prepared for cone calorimetry by injection moulding at 160 - 180 °C. The samples were tested as described in Example 1 and the results are shown in Table 3 together with results for comparative samples.

Table 3

Claims

1. An acrylic material comprising: a) 10 - 90% wt of an acrylic copolymer containing 80 - 99% wt of methyl methacrylate residues and 1 - 20% wt of a C1 - C4 alkyl acrylate, b) 5 - 85% wt of a solid halogen-containing polymer which is compatible with methyl methacrylate, and c) 5 - 20% wt of a phosphorous-containing organic fire retardant compound.

2. An acrylic material as claimed in claim 1 wherein said C1 - C4 alkyl acrylate comprises ethyl acrylate.

3. An acrylic material as claimed in claim 1 or claim 2, wherein said solid halogen-containing polymer comprises a polymer containing vinyl chloride residues.

4. An acrylic material as claimed in claim 3, wherein said polymer is a copolymer of vinyl chloride and up to 40 % of vinyl acetate residues.

5. An acrylic material as claimed in any preceding claim, wherein said acrylic copolymer has a molecular weight Mw of at least 80 kD.

6. An acrylic material as claimed in any preceding claim, further comprising mercaptan residues.

7. An acrylic material as claimed in any preceding claim, wherein said phosphorous-containing organic fire retardant compound comprises an aliphatic halogen-containing organic phosphate or a chlorinated polyphosphate.

8. An acrylic material as claimed in any preceding claim in the form of a sheet, powder or granules.

9. A method of manufacturing an acrylic product comprises the steps of (i) dissolving in methyl methacrylate monomer a) 1 - 20 wt % of a C1 - C4 alkyl acrylate b) a solid halogen-containing polymer c) a phosphorous-containing organic fire retardant compound, such that the resulting mixture contains 5 - 25 % wt of (b) and 5 - 20 wt % of (c) based on the total (meth)acrylate content, d) a free-radical initiator and e) optionally a chain transfer agent, such as a mercaptan (ii) introducing the mixture into an enclosed mould and

10. A method of manufacturing an acrylic product comprising the steps of (i) forming a molten mixture of a) an acrylic copolymer containing 80 - 99% wt of methyl methacrylate residues and

1 - 20% wt of a C1 - C4 alkyl acrylate, b) a solid halogen-containing polymer which is compatible with methyl methacrylate (ii) adding to said molten mixture a phosphorous-containing organic fire retardant compound such that the resulting mixture comprises 10 - 90% wt of said acrylic copolymer, 5 - 85% wt of said solid halogen-containing polymer, and 5 - 20% wt of said phosphorous-containing organic fire retardant compound;

(iii) moulding the resulting mixture in molten form and subsequently cooling the mixture to form said acrylic product.

11. A method as claimed in claim 10, wherein the molten mixture is moulded by extrusion.

12. A method as claimed in claim 10, wherein the molten mixture is moulded by injection moulding methods.