GB2052305A - Reinforced plastics articles, a process for their manufacture and a reinforcing material - Google Patents

Abstract

The articles are made of isocyanate- based plastics materials in which is embedded a reinforcing mesh coated with an intumescent material which is preferably flexible. In particular, they are rigid isocyanurate foam panels of the type used in the building industry as sound and thermal insulating structures having improved fire resistant properties in terms of depth of charring, depth of scorching, surface cracking and dimensional stability. A favoured intumescent material is a mixture of ammonium polyphosphate; sorbitol or glucose or sucrose; and dicyandiamide or urea in water and/or polyvinyl acetate.

Description

SPECIFICATION Reinforced plastics articles, a process for their manufacture and a reinforcing material This invention relates to reinforced plastics articles, to a process for their manufacture and to a novel reinforcing material.

According to the present invention we provide a shaped isocyanate-based plastics article having embedded therein a reinforcing mesh coated with an intumescent material. The invention also includes a process for manufacturing the article and the coated mesh for use in the process.

The shaped article may be made of any isocyanate-based plastics including polyurethane, polyisocyanurate and polyurea plastics. These plastics materials and their methods of preparation are well known to those skilled in isocyanate and polyurethane technology.

Of particluar interest to us are rigid foamed plastics and more particularly such foams based on diphenylmethane-4,4'-diisocyanate (MDI), specially crude MDI, otherwise known as polymeric MDI, which is the product obtained by the phosgenation of aniline-formaldehyde condensates and contains mixtures of methylene bridged polyphenyl polyisocyanates. Isocyanate-based plastics include those based on isocyanate-ended prepolymers.

The article of the invention may take any desired shape and is obtained by moulding or otherwise shaping the isocyanate-based plastics-forming ingredients. Our special interest, however, is in the foam panels and laminates used in the building industry and sound and thermal insulating structures.

It is important, and a major concern amongst Fire Authorities, that these building elements do not readily burn and we are, therefore, concerned with providing building elements which have improved fire resistance properties and which moderate the spread of fire.

Polyisocyanurate rigid foams are inherently fire resistant; that is they do not burn much and form incombustible chars. However, there is a tendency for these chars to distort and split and fire can spread through the cavities and cracks thus formed.

In our UK patent 1,470,066 we provided isocyanurate foam laminates having improved fire resistant properties in which a mesh was embedded in the foam. The present invention provides, in a preferred embodiment, rigid isocyanurate foam panels and laminates with further improved fire resistant properties as expressed in terms of depth of charring, depth of scorching, surface cracking and dimensional stability.

Preferably the reinforcing mesh is placed near the surface of the laminate or panel which is most likely to be exposed to a fire to obtain maximum fire protection for the foam core.

The articles can be made by methods already well known for shaping mesh-reinforced plastics materials using a mesh pre-coated with the intumescent material. In particular, methods for making panels and laminates are described in, for example, UK Patents Nos 1,470,066 and 1,536,979.

Laminates may be faced with any suitable sheet materials many of which are listed in UK Patent No.

1,470,066. Non-combustible facings are to be recommended in building applications and we would especially mention the facings described in UK Patent No. 1,521,699 in which an outer metallic foil is bonded to an inner paper or fabric sheet by a flame resistant and low smoke-producing adhesive and a network of glass-fibre stands is interposed between the outer-foil and inner sheet.

The reinforcing mesh may be a network or lattice of metal, plastic or organic or inorganic fibrous material.

The network may be of regular design having, for example, square, rectangular or circular interstices, or it may be completely random as, for example, in continuous filament glass fibre swirl mat. The network may be substantially two-dimensional or it may be three dimensional, for example, in the form of "high loft" expanded glass fibre mats. It may be composed of single filaments, or of filaments formed into strands or entwined strands.

The interstices in the mesh should be large enough, when coated with the intumescent material, to allow the plastics forming ingredients to penetrate easily. In the case of plastics foam-forming mixtures the foam mix should be able to penetrate without causing excessive cell collapse and subsequent densification.

Preferably the interstices have minimum and maximum linear dimensions of 2 mm and 20 mm, respectively.

The mesh may be loosely knitted or woven with or without welding or bonding at the inter-sections.

The meshed material may be pre-coated with a processing aid, such as a size or, in the case of fibres, a spin finish.

Examples of materials from which the mesh can be made are metals, such as steel wire; organic fibres made from such materials as polypropylene, polyamides, such as 6:6-nylon and aramides, polyesters such as polyethylene terephthalate, cellulose, such as cotton, viscose rayon, jute, carbon, hemp, wool, acrylic materials and polyvinyl alcohol; inorganic fibres made from such materials as glass, asbestos, spun rock wool, "Ethringite" (calcium sulphate aluminate) Gypsum (calcium sulphate), alumina and zirconia, such as "Saffil" (RTM), and ceramics, such as alumino silicate fibre; and extruded thermoplastics made from polypropylene, H.D. polyethylene and polyamides, such as "Netlon" (RTM).

By intumescent material we mean a material which swells when heated to form a non-flammable multicellular insulating barrier.

Suitable intumescent materials are described in the following publication: (i) Intumescent Coating Systems; Their Development and Chemistry by H.L. Vandersall in the Journal of Fire and Flammability, Volume 2 (April 1971) at page 97; and (ii) The Chemistry and Uses of Fire Retardants, by J.W. Lyons (1970) Wiley-lnterscience at pages 256 to 272.

Preferred intumescent materials are mixtures of three compounds, one from each of the following three categories: In organic Acids and Acid Salts: 1. (a) Acids: Phosphoric, sulphuric and boric acids.

(b) Ammonium Salts: Monoammonium phosphate, diammonium phosphate, ammonium polyphosphate, ammonium sulphate, ammonium chloride and ammonium bromide.

(c) Amine/Amide Phosphates: Urea Phosphate, guanyl urea phosphate, melamine phosphate, polyphosphorylamides having the repeat unit

phosphoryl trianilide.

(d) Amine Sulphates: p-Nitroaniline bisuiphate.

(e) Organophosphorus Compounds: Triphenyl phosphate, trixylyl phosphate, tricresyl phosphate, alkyl phosphates, alkyl phosphonates, haloalkyl phosphates such as tris[ss-chloroethyl] phosphates and tris[chlornprnpyl] phosphate, and oligomeric chloroalkyl phosphonates and phosphates e.g.

2. Polyhydric alcohols rich in carbon: Starch, dextrin, glucose, sucrose, maltose, arabinose, sorbitol, arabitol, inositol, mannitol, pentaerythri tol (monomer, dimer or trimer), triethylene glycol, methylol melamine, resorcinol, phenol-formaldehyde resins and linseed oil.

3. OrganicAmines orAmides: Urea, urea-formaldehyde, alkyl ureas, dicyandiamide, melamine, glycine (aminoacetic acid) and polyamide resins.

Other components may also be included in the intumescentformulation to improve the efficiency of the non-flammable, insulating barrier. These include halogenated compounds (resins or non-resins) to permit release of non-flammable gases (usually hydrogen chloride) to assist foaming of the intumescent coating, for example chlorinated paraffins, tetrachlorophthalic polyesters, and pentachlorophenyl glyceryl ether; and nucleating agents to improve the cell structure of the intumesced foam such as inert fillers of fine particle size, for example, titanium dioxide, silica, china clay, zinc oxide and mica.

Normally a binder is added to facilitate the application of the intumescent material to the mesh and to improve its coating characteristics. This is highly desirable when coating flexible meshes, such as glassfibre meshes, which will be stored on rolls and where there is a risk that the coating will flake off if the surface adhesion or flexibility of the intumescent material is poor. It is preferred, therefore, that the intumescent material is itself flexible. Care should be exercised in selecting a resinous binder because some thermosetting resins will reduce intumescence. Alkyl resins may be used as binders although halogenated alkyds are preferred as they are usually less thermosetting than their non-halogenated counterparts.

Examples of suitable binders are polyvinyl chloride, polyvinyl acetate, polyvinylidene chloride, epoxies and chlorinated rubber resins.

Particularly good results have been obtained using intumescent materials comprising mixtures of ammonium polyphosphate; sorbitol or glucose or sucrose; and dicyandiamide or urea in water and/or polyvinyl acetate.

Many intumescent agents are soluble in water and hydrolytically unstable. This is a disadvantage where they are used as coatings on surfaces exposed to the weather. However, it is not a disadvantage in the present invention since water solubility or dispersability facilitates the coating of some meshes, for example, glass-fibre mats, and the intumescent agent will be encapsulated in the plastics material and hence protected against water vapour or rain.

The intumescent agent may be applied to the reinforcing mesh in a variety of ways; in solid or liquid form.

For example, an intumescent powder can be blended with a binder, such as a thermoplastic or thermosetting resin, and applied with the binder to the mesh material. A short fusion or cure stage in an oven below the temperature of intumescence may be desirable.

In another, preferred method the intumescent material is applied as an aqueous emulsion or solution by, for example, spraying or immersion. In some cases the intumescent material may be more appropriately applied in a solvent medium.

The emulsion or solution may be blended with a spin finish or size. For example, it may be blended with the size used by glass fibre manufacturers for binding filamentary glass fibres into strands so that each filament is completely coated.

The amount of intumescent material used will normally be sufficient to provide a continuous coating over the whole of the exposed surface area of the mesh material. Preferably there is sufficient intumescent material present to fill the interstices of the mesh and form a continuous barrier when intumescence takes place.

An additional benefit of our invention is that, during a fire, the intumescent foam affords protection to the reinforcing mesh as well as to the plastic foam below. This effect is important since many reinforcing meshes (especially organic fibres) will melt, burn and lose their mechanical strength and char-reinforcing properties if unprotected by the intumescent agent.

The coating must not, however, be so thick that it prevents the plastics-forming ingredients from easily penetrating the interstices when the shaped article is formed. The actual quantity of intumescent material used will depend interalia on the nature and method of application of the intumescent material, the type of mesh and plastics material used and the improvement in fire resistance required. It is a relatively simple matter for the skilled technologist to determine by trial and error. Some guidance is given in the following Examples which illustrate the invention. Parts and percentages are by weight unless otherwise stated.

Example 1 An aqueous emulsion of an intumescent material, Agent 'A', was prepared by blending the following ingredients at room temperature and milling the blend for about 18 hours.

Ingredients of Agent 'A' Parts Ammonium Polyphosphate 120 Sorbitol 50 Dicyandiamide 30 Polyvinyl acetate/Acrylic resin (90:10) in latex (50% solids) 40 Water 80 A web of continuous filament glass fibre mat (i.e. random mesh type B) of 140 g/m2 weight produced from strands composed of about 800 individual filaments was coated by immerising the web in a bath containing Agent 'A' and passing it between two nip-rollers. The web was then dried and weighed; 265 g/m2 intumescent agent had been deposited.

The mat was still flexible and there was no evidence of flaking. The open structure of the glassfibre mesh was retained.

A rigid polyisocyanurate foam panel reinforced with this intumescent-coated glassfibre mesh was then prepared by tacking the edges of the mesh to one side of a wooden frame; laying the frame on a silicone paper, with mesh adjacent the paper, to form an open mould of dimensions 25 cm by 25 cm by 4.3 cm; pouring a foam mix prepared as described below into the mould; and placing the mould in a press at 40"C for 30 minutes, before demoulding. The foam mix flowed into the glass fibre mesh on pouring and began to expand after 10 seconds.

The panel so formed had an overall density of 58 kg/m3 and a core density of 44 kg/m3.

The foam mix was prepared by mixing together, for 4 seconds with an electric stirrer, 100 parts of a polymeric MDI (isocyanate value 30%; viscosity at 25"C 1700 centistokes) and a blend of 26.9 parts of oxypropylated tolylenediamine (OH value 310 mg KOH/g) with 21 parts oftrichlorofluoromethane.

The fire resistance of the panel was tested subjecting it to thermal radiation having an intensity of 3.2 kW/cm2 in the apparatus hereinafter described with reference to the accompanying diagrammatic drawing.

In the drawing, test apparatus 11 consists of a radiator 12 and a specimen holder 13. The radiator 12 has a stainless steel heating tube 14 which is bent in a truncated cone shape and fixed together by NiCr-wire. The tube 14 is covered by a shade 15 consisting of two shells of heat resistant steel with an insulating ceramic fibre blanket interposed therebetween. The heating tube 14 is fastened to the shade 15 by NiCr-wires. Two clamps 16 and 17 serve to fix the radiator above the specimen holder 13 which is of stainless tubular steel construction. A mask 18 supported by the specimen holder has a circular opening (not shown) of 150 mm diameter. A press plate 19, covered with asbestos millboard 22, and counterweighted through a leverage system 20, holds a foam panel sample 21 against the mask 18.

The foam panel was held in the test apparatus, with its reinforced face nearest the radiator, for 1 minute.

After cooling, it was assessed for; (i) dimensional stability in respect of warping and expansion; (ii) cracking ofthecharformed; (iii) depth of charring; and (iv) depth of scorching behind the char.

A "control" foam panel made in the same way but without reinforcement and a "comparative" panel made in the same way but with uncoated fibre glass were subjected to the same test procedure. The results are shown in Table 1.

TABLE 1 Comparative Example 1 of Control Experiment Invention Panel not Glassfibre Panel rein reinforced reinforced forced with panel glassfibre coated with intumescent material Dimensional Stability gross- no distortion no distortion distortion Cracking of char severe not extensive limited to throughout surface layer Depth of char (mm) 8 4 Depth of scorching 14 6 behind char (mm) Example 2 A web of glassfibre mesh (type A) mat (54 g/m2) made by a process similar to that described in U.S. Patent 2,609,320 with 4% w/w saturated polyester binder was coated with Agent 'A' by the method used in Example 1. After drying, the mat was found to have 185 g/m2 intumescent agent deposited on it.

A rigid foam panel containing this treated glassfibre mesh was then prepared using the same foam formulation and method of Example 1.

A "comparative" rigid foam panel was made in the same way using the same mesh but untreated. The panels were subjected to the test procedure of Example 1 and the results are shown in Table 2.

TABLE 2 Depth of Depth of Black Scorched Char (mm) Foam (mm) Foam with untreated Glassfibre mesh (Comparative Experiment) 9 18 Foam with Glassfibre mesh coated 4 11.5 with intumescent agent The panel of the invention showed less surface cracking than the comparative experiment.

Example 3 A web of woven "Terylene" (Registered Trade Mark) polyester fibre net (mesh type C) (mesh size 4 mm x 4 mm) was coated with Agent 'A' and incorporated into a foam panel made using the same foam system as in Example 1. As a comparison a panel was made in the same way but with uncoated glass fibre. These panels were subjected to the test procedure of Example 1. The results are shown in Table 3.

TABLE 3 Weight of Depth of Intumescent Scorched Agent (g/m2) Foam (mm) Foam with uncoated "Terylene" net (comparative experiment) 0 16 Foam with "Terylene" Net coated 240 14 with intumescent material.

Example 4 The procedure of Example 1 was followed but using an extruded and oriented polypropylene net. A comparative panel was made in the same way but with uncoated net. Test results obtained are shown in Table 4.

TABLE 4 Weight of Depth of Intumescent Scorched Agent (g/m2) Foam (mm) Foam with uncoated Polypropylene 0 23 Net (comparative experiment) Foam with Polypropylene Net 442 14 Coated with intumescent agent Example 5 An aqueous emulsion of an intumescent material Agent B was prepared at room temperature by mixing together the following ingredients: Agent B Parts Ammonium Polyphosphate 36 Sorbitol 15 Dicyandiamide 9 Water 50 This blend was milled for approximately 18 hours.

Webs of continuous filament glassfibre random mesh (140 g/m2) were coated with various amounts of Agent B and foam panels made as in Example 1. These panels had a core density of 43 kg/m3 and were subjected to radiant energy at 4 kW/cm2 for 3 minutes in the apparatus of Example 1.

A "control" foam panel made in the same way but without reinforcement and a "comparative" panel made in the same way but with uncoated fibreglass mesh were subjected to the same test procedure. The results are given in Table 5.

TABLE 5

E C5 0 Zit E 't5 'iS 0 cn E SE ,, E Oo OCOLL Foam (unreinforced)-CONTROL 0 30 42 60 Foam with uncoated Glassfibre 0 23 49 54 mat - COMPARISON Foam with Glassfibre mat coated with Agent B (i) 49 20 43 54 (ii) 93 18 38 50 (iii) 140 11 32 46 (iv) 180 13 32 46 (v) 236 11 19 42 Discussion of results These results show that polyisocyanurate foam panels made with a reinforcing mesh coated with an intumescent material exhibit better fire resistance in terms of depth of charring, depth of scorching, surface cracking and dimensional stability, than foam panels made with the same reinforcement but devoid of an intumescent coating.

Claims (12)

1. A shaped isocyanate-based plastics article having embedded therein a reinforcing mesh coated with an intumescent material.

2. An article as claimed in claim 1 which is a rigid isocyanurate foam panel.

3. An article as claimed in claim 2 in which the reinforcing mesh is placed near one surface of the panel.

4. An article as claimed in any one of the preceding claims in which the interstices of the mesh have minimum and maximum linear dimensions of 2 mm and 20 mm respectively.

5. An article as claimed in any one of the preceding claims in which the intumescent material is a mixture of three compounds, one from each of the groups as herein defined, of (1) inorganic acids and acid salts, (2) polyhydric alcohols rich in carbon and (3) organic amines or amides.

6. An article as claimed in any one of the preceding claims in which the intumescent material is flexible.

7. An article as claimed in claim 5 in which the intumescent material comprises a mixture of ammonium polyphosphate; sorbitol or glucose or sucrose; and dicyanamide or urea in water and/or polyvinyl acetate.

8. An article as claimed in any one of the preceding claims in which the intumescent coating is sufficient to fill the interstices of the mesh and form a continuous barrier when intumescence takes place.

9. An article as claimed in claim 1 substantially as herein described with reference to any one of Examples 1 to 5.

10. A process for the manufacture of a shaped article as claimed in claim 1 which comprises embedding a reinforcing mesh coated with an intumescent material in an isocyanate-based plastics material and shaping said plastics material.

11. A process as claimed in claim 10 substantially as herein described with reference to any one of Examples 1 to 5.

12. A reinforcing mesh coated with an intumescent material for use in the manufacture of the shaped article claimed in claim 1.