Fire Resistant Glazings

This invention relates to novel laminated glazings having fire resistant properties, to polymeric films useful as interlayers in such glazings and to additives which may be incorporated into these films in order to improve the fire resistance of laminated glazings incorporating such films.

In an increasing number of countries Building Regulations specify the fire resistance of glazings. Generally the regulations specify either a minimum time for which the glazing must form a barrier to the propagation of a flame when one side of the glazing is exposed to a fire and/or a minimum time for which the temperature and/or the intensity of radiated heat on the side of the glazing which is not exposed to the fire must remain below a specified figure.

Monolithic glazings comprising wired glass or toughened glass have been proposed for use as fire resistant glazings but generally they meet only the least stringent regulatory requirements and then only for relatively small glazings. Laminated glazings comprising at least two transparent panes and at least one interlayer which does not burn readily offer improved fire resistance. The interlayer is preferably formed from a material which forms a char when exposed to a fire. The char may assist in retaining the transparent panes in position and thereby ensures that the glazing constitutes a barrier to the fire for a longer period.

One type of laminated fire resistant glazing is produced by drying a solution of an alkali metal silicate waterglass on the surface of a glass pane. A second type is produced by filling the space between two opposed panes with a solution which is cured to form an interlayer. Both these manufacturing processes are labour intensive and time consuming and there is a need for a fire resistant glazing laminate which can be produced more economically and exhibit a fire resistance which meets the requirements of at least some of the applicable regulations.

One method by which laminated glazings may be produced relatively economically is autoclave lamination. Laminates comprising clear polymeric films such as polyvinylbutyral (PVB), ethylene vinyl acetate (EVA) and polyvinylchloride (PVC) may be produced using autoclave lamination. However these laminates exhibit no useful fire resistant properties. When exposed to a fire interlayers comprising these films burn readily and as a result the laminated glazing loses its integrity in a short time which does not meet any regulatory requirement.

We have now discovered additives which may be incorporated into PVC films to form an optically clear film which does not discolour even on prolonged exposure to sunlight and when incorporated into a laminated glazing results in the glazing having improved fire resistance.

The additives which we have discovered to be useful are compounds of boron which can form a homogeneous phase when incorporated into a PVC film.. Both organic and inorganic compounds of boron may be useful. Optically clear PVC films comprising a compound of boron are believed to be novel and accordingly from a first aspect this invention provides an optically clear polymeric film of a polymer or a copolymer of vinyl chloride which is characterised in that the film comprises a compound of boron.

The boron compound should be one which is compatible with the polymer film in a quantity which promotes the production of a char in a fire test without any phase separation. It is also preferably a compound which promotes adhesion between the char and the glass.

From a second aspect this invention provides a laminated glazing comprising at least two transparent panes and at least one interlayer which comprises an optically clear film of a polymer or copolymer of vinyl chloride and a compound of boron. The optically clear films should be essentially unaffected by the conditions which are used in the lamination process. They should also not discolour during the lamination process or during prolonged exposure to sunlight as part of a laminated glazing. The laminated glazings should have a light transmittance which is preferably greater than 70% and more

preferably greater than 85%. The glazings should preferably exhibit a haze value of less then 2% and more preferably less than 1%.

In order to be sufficiently flexible to form a film polymers and copolymers of PVC generally incorporate a plasticizer. A large number of compounds have been used as plasticizers for PVC including esters of carboxylic acids and esters of phosphoric acid, hydrocarbons, halogenated hydrocarbons, ethers, polyglycols and sulphonamides. The boron compounds which are useful in this invention may also function as plasticizers for the PVC. The boron compound may be the only plasticizer which is incorporated into the resin or it may be used in combination with other known plasticizers.

The boron compound should be one which is essentially unaffected by the conditions used in the processing of the polymer and in the autoclave lamination process. It should also be one which does not result in the discolouration of the polymer film during this processing or during prolonged exposure to sunlight as part of a fire resistant glazing.

The preferred boron compounds are organoboron compounds. In this specification the term "organoboron compound" is intended to mean a compound which contains boron and is soluble in an organic medium. The organoboron compound may be a boric acid ester or a boric anhydride. Inorganic boron compounds are useful provided that they are soluble in an organic medium or can be solubilised in an organic medium.

Examples of suitable organoboron compounds include esters having the general formula B(OR) ₃ wherein R represents an alkyl group, a cycloalkyl group or an aryl group comprising from 1 to 18 carbon atoms. Preferably the group R comprises from 1 to 8 carbon atoms. Examples of compounds having this general formula which are preferred for present use include tricresyl borates and trialkyl borates such as triethyl borate, tri n- propyl borate, triisopropyl borate, tri-n-butyl borate, tri-sec-butyl borate, tri-t-butyl borate, tri-n-octyl borate, tricyclohexyl borate and tris-2-ethylhexyl borate.

Also useful are the boroxines having the general formula I.

I wherein each group R which may be the same or different represents an optionally substituted alkyl or alkenyl group comprising from 1 to 18 carbon atoms. Preferably R represents an alkyl group comprising from 1 to 8 carbon atoms and most preferably R represents an alkyl group comprising from 1 to 6 carbon atoms. Trimethoxyboroxine (R represents a methyl group) and triethoxyboroxine (R represents an ethyl group) are liquid at room temperature while the higher trialkoxyboroxines are solids.

A preferred group of organoboron compounds useful in accordance with the present invention are those which comprise a greater proportion of boron and thus a greater number of BO bonds than the trialkyl or triaryl borates. Preferably, the organoboron compound comprises at least 5 wt% boron, usually from 5 to 20 wt% boron, more preferably from 5 to 14 wt % boron. Organoboron compounds having a relatively high boron content is preferred since this enhances the char forming effect on heating and reduces the amount of the compound which need be added to the PVC in order to provide a laminate having a particular degree of fire resistance.

One group of such preferred compounds are the polyborates. The preferred polyborates are biborates which have broad decomposition profiles when heated i.e. they tend to decompose over broad temperature ranges, and also at high temperatures. Such decomposition profiles can readily be determined by thermogravimetric analysis

Especially preferred polyborates are the trialkylene biborates wherein the alkylene group contains 2 to 8 carbon atoms, for example, tributyleneglycol biborate, dibutyleneglycol biborate, hexyleneglycol biborate, trihexyleneglycol biborate, tripropyleneglycol biborate

and trioctylene glycol biborate. Another preferred polyborate is 2,2'-oxybis- 1,3,2- dixaborinane C _O H _I2 B ₂ O _S .

Other boroesters which could be employed in the present invention are amino boresters, such as triethanolamine borate C _O H _I2 BNO ₃ , tri-iso-propanolamine borate C ₉ H18BNO3 and glycerol borate triethylamine complex C _I2 H _2S BNO ₆

Another group of organoboron compounds which may be useful in the present invention are organometallo borate compounds having the general formula II

II wherein M represents a tin atom, an antimony atom or a molybdenum atom; the groups R which may be the same or different represent hydrogen atoms or alkyl groups comprising from 1 to 3 carbon atoms and the groups R' which may be the same or different represent alkyl groups comprising from 1 to 4 carbon atoms. A preferred group of compounds having the formula II are those wherein both M atoms represent a tin atom.

A particularly preferred group of compounds having the formula II are those having the formula II wherein M represents tin and the groups R' represent butyl groups.

These preferred compounds have the formula III.

III

A particularly preferred compound having the above formula is the compound of Formula III wherein all the groups R represent hydrogen atoms. This compound is 1,2 bis(boryloxy)tetrabutyldistannoxane

The organoboron compounds having the general formula II and in particular the compounds having the general formula III are believed to be novel and comprise a second aspect of the present invention.

Another class of boron containing compounds which may be used are organic borate anions with non-metal cations which may be obtained by reacting an organoboronic acid or an organoborinic acid precursor with a tetraalkyl ammonium hydroxide or preferably a hydroxyalkyl ammonium hydroxide such as trimethylhydroxyethyl ammonium hydroxide. A preferred group of these compounds may be represented by the formula [R" _x B _y O _z ] [NR'"4] wherein x is an integer having a value of 4, y is an integer having a value of 3 or 4 and z is an integer having a value of 3 or 5, the groups R" which may be the same or different represent alkyl, alkenyl or aryl groups comprising from 4 to 6 carbon atoms and the groups R'" which may be the same or different represent alkyl or hydroxyalkyl groups comprising from 1 to 3 carbon atoms.

A preferred tetraalkylammonium organoborinate salt for use in the present invention is the compound having the formula IV

IV

A second preferred tetraalkyl ammonium organoborinate salt is the compound having the general formula V

V

The tetraalkylammonium organoborinate salts and in particular the compounds having the formula IV and V are believed to be novel and comprise a further aspect of the invention.

The PVC films of this invention may comprise a homo or copolymer of vinyl chloride. Preferably the films comprise a homo polymer of vinyl chloride or a copolymer of vinyl chloride and one or more comonomers selected from the group comprising vinyl acetate, vinylidene chloride, propylene, methacrylic acid, acrylic acid, acrylonitrile, styrene, 2-

ethylhexyl acrylate, vinyl isobutyl ether, maleic anhydride, maleic acid, diethyl maleate, diethyl fumarate and mono and poly alkylene carbonates.

The PVC used to form the films of the present invention preferably has a melt viscosity (K Value) of from 60 to 75.

The PVC resin will preferably comprise a plasticizer in a quantity so as to ensure that the film is sufficiently flexible. Preferably the resins will comprise from 20 to 100 parts preferably from 20 to 40 parts per hundred by weight of plasticizer. In the preferred embodiments of the invention the plasticizer which is incorporated into the resin will comprise one or more boron compounds together with one or more compounds which do not contain boron and which function as a plasticizer for PVC. The boron compounds useful according to the present invention preferably comprise from 5 to 100%, preferably from 5 to 30% and more preferably from 5 to 25% by weight of the plasticizer.

A variety of materials are known to be useful as plasticizers for PVC. In the films of the present invention the plasticizer will be one which forms an optically clear film, which is stable under the conditions used in the lamination process and which is not degraded by long term exposure to sunlight. Preferably the plasticizer will be a compound in which the boron compound is sufficiently soluble to permit the latter to be incorporated with the former and used in the calendering process. The plasticizer may also preferably be chosen to be non flammable or not readily flammable in order not to detract from the fire resistance of the laminated glazing.

Examples of plasticizers which are known in the art and which may be used in the films of the present invention include phosphates, phthalates, isophthalates, terephthalates, adipates, azelates, mellitates and sebacates such as di (2-ethylhexyl) phthalate, diisooctyl phthalate, diisodecyl phthalate, butyl benzyl phthalate, butyl octyl phthalate, ditridecyl phthalate, diundecyl phthalate, trioctyl phophate, cresyl diphenyl phosphate, tricresyl phosphate tris (2-ethylhexyl) mellitate and triisooctyl mellitate.

The PVC film may also comprise other known conventional additives again provided that they can be incorporated into an optically clear film which is stable under the conditions used in the lamination process and which is not degraded by long term exposure to sunlight. Examples of such additives which may usefully be incorporated include flame retardants such as antimony oxide, halogenated hydrocarbons and phosphate esters (including those useful as plasticizers), processing aids such as soya bean oil, heat stabilisers particularly the salts of barium, calcium, tin or zinc with an organic acid, organometallic compounds such as tin mercaptides, dibutyl tin dilaurate, dibutyl tin maleate and compounds of phosphorus especially phosphites such as triphenyl phosphite and alkyl phosphines.

The PVC films may be prepared by thoroughly mixing the components and passing them through a roll mill in order to obtain high temperature mixing. The mixture may then be calendered to produce the PVC film. The film will preferably be from 0.1 to 2.0mm thick more preferably from 0.25 to 0.75mm thick.

The PVC is assembled between two panes which are normally glass panes. The glass panes are preferably float glass panes having a thickness of from 2.0 to 6.0mm. The panes may also be formed from borosilicate glasses or from ceramic glasses such as those sold by the Nippon Electric Glass under the Trade Mark FIRELITE. Excess film is trimmed from the edges of the panes and the assembly passed between a pair of nip rollers operating at elevated temperature, say up to 120 ⁰ C and exerting a pressure of around 14 bar. The assembled structure may be placed in a sealed vacuum bag to minimise the entrapment of air bubbles within the laminate and the bag placed within an autoclave. The lamination is then effected by heating to a temperature of up to 150 ⁰ C and a pressure of from 10 to 14 bar for a period of 4 to 5 hours.

The invention is illustrated by the following Examples

A series of formulations were made up having the compositions set out in Table 1. All proportions are expressed as parts per hundred to 100 parts PVC.

Table 1