GB1569070A - Polymeric cementing compositions - Google Patents

Description

(54) POLYMERIC CEMENTING COMPOSITlONS (71) We, SCOTT BADER COMPANY LIMITED. a British Company, of Wollaston, Wellingborough, Northamptonshire NN9 7RL, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to cementing compositions and particularly, though not exclusively, to rock anchors using them. Rock anchors are polymeric cements hardened in situ in boreholes or like cavities in rock and serving to secure an anchor member such as a bolt or stays embedded in them. Conventionally they are supplied as a sealed sausage-like film-wrapped capsule which is occupied by a mineral-filled unsaturated polyester resin system and also by a catalyst for the curing of the system. separated from the latter (for example in a plastics film or glass phial).

In use the capsule is put in place and the anchor member driven through the wrapping into it to break also the enclosure of the catalyst: the anchor member is then agitated in the composition to distribute the catalyst, and the system then gels and cures. The systems used have very fast gel and cure times.

Polyester resins are used because these are the only ones which are capable of having low enough gel and cure times. Most unsaturated polyester resins in use today contain styrene, as copolymerisable monomer. Styrene finds such wide use because it is a good solvent for unsaturated polyester resins giving easy-to-handle liquid resins at monomer contents appropriate for copolymerisation, whilst subsequently its particularly favourable copolymerisation characteristics give rise to durable high strength cured products. From a commercial point of view it has the advantage of ready availability and low cost.

One of the most serious disadvantages of the styrenated unsaturated polyester resins is their flammability, both in the liquid state and as solid fully cured products. A great deal of ingenuity and labour has been used to overcome this deficiency with respect to the flammability of the cured product, by means of additives or reactive components in the polyester which either shield the burning material from oxygen, or mechanically interfere with the mechanism of decomposition and burning to snuff out the flame. These methods are so successful that structures moulded from unsaturated polyester resins find wide use in building and transport and meet very stringent fire safety requirements. But where styrene or other volatile flammable monomer is present in the resin such expedients do not prevent the liquid resin from burning fiercely when ignited and do not reduce the hazard such volatile flammable materials present. In the production of glass fibre reinforced mouldings under factory conditions, these hazards are minimised by use of flameproof electrical equipment and removal of other potential sources of ignition. but away from such controlled environments the risk involved are often unacceptable. Thus the use of polyester resins as adhesives, grouts and cements for on-site applications is often circumscribed.

There is therefore a need for a polymeric composition which not only is non-flammable in its solid state (to which, as mentioned above. a great deal of attention has been paid) but also is of reduced flammability in its uncured liquid or pasty state. There is a need for a composition substantially lacking volatile flammable constituents even while uncured. Such compositions could then be used in for example flame-prrof areas of factories or mines.

As an example consider the use of polyester resins in coal mines. Whilst these are unlikely to be sources of ignition in a modern mining environment, the extra hazard created by the presence of styrene or other volatile flammable material of low flash point is barely tolerable and may well be prohibited by future legislation. It is in an attempt to alleviate this situation that the manufacturers of polyester resin bonded rock anchors have turned to the use of high flash point, low volatility monomers for use in their resin capsules. The use of ethylene glycol dimethacryate gives some measure of protection as this data suggests, because its flash point is 117"C while that of styrene monomer is 32"C.

Liquid unsaturated polyester resins based on ethylene glycol dimethacrylate are demonstrably less easy to ignite, but when ignited continue to burn. The cured product is flammable, but can be modified by the well-known fire retardants so as to become self extinguishing. So this approach represents only a partial solution to the problem.

Furthermore, at least at present, ethylene glycol dimethacrylate is a very expensive compound.

The resins include the polyester, the solvent monomer and the necessary accelerator(s) and stabilizer(s) (also known sometimes as inhibitor or retarder): the latter types of component being conventional for polyester resin systems. Our invention is characterised by the presence of bromostyrene as the solvent monomer.

We have discovered that if bromostyrene is used to replace styrene as copolymerisable monomer a liquid resin is produced which surprisingly is virtually non flammable. It is impossible to ignite a pool of this resin in air using a match or cigarette lighter. Exposure of the resin to a blow torch results in decomposition of the resin which imparts considerable luminosity to the blow torch flame and copious quantities of black smoke, but on removal of the flame the resin does not continue to burn. Similarly if the resin is poured in a thin film over crumpled paper it cannot be ignited by a match or cigarette lighter. Prolonged exposure to a blow torch flame causes luminous decomposition of the resin with copious smoke emission, but when the blow torch is removed the resin ceases to burn immediately.

We also provide in this invention a composition including the bromostyrene-containing resin as above and mineral filler(s), conventional for the forming of a pasty, curable polymeric cement. The flammability of these compositions is as low as or lower than that of the resin which they incorporate. Furthermore we provide in this invention a rock anchor which is a capsule containing the said composition and a separated catalyst, as well as the combination of that rock anchor with its metallic or other anchor member.

The following Examples illustrate the invention: Example I For an application requiring a fast cure time with a low viscosity resin an unsaturated polyester resin was prepared from maleic anhydride, phthalic anhydride and propylene glycol, reacted to an acid value of 30my KOHlg. This resin was suitably stabilised to provide good storage stability when pre-accelerated with amines and dissolved in either styrene (as comparison) or bromostyrene to give a viscosity at 25"C of 8 poise. The bromostyrene was a commercially available bromostyrene. which is a mixture of the ortho and para isomers.

The properties of castings made from these resins are shown in the Table, wherein percentages are weight/weight.

Liquid Resin Test Method Units Styrene Bromo Properties styrene Monomer Content - % 35 50 Gel Times at 25"C 2% of 50% min 61/2 sol/2 Benzoyl peroxide Cast Sheet Properties Hardness Barcol 52 50 Heat Deflection Temperature BS2782 "C 77 63 Wt Tensile strength BS2782 N/mm2 54.0 51.4 Elongation at Break BS2782 % 1.55 1.5 Initial Tensile Modulus BS2782 N/mm2 4.08 4.24 Water absorption BS2782 502F mg% 20.5 (0.22) 15.2 (0.14) (24 hr) BS2782 502G mg% 20.5 (0.21) 15.3 (0.15) Bromostyrene is used in larger amounts than styrene would be to achieve a given viscosity of a resin (and therefore of a filled composition to be made from it) because it is a more viscous material than styrene. Typically contents of bromostyrene will be 35-55% by weight preferably 40-50%, in contrast to the usual styrene content of 30-40%.

Example 2 The bromostyrene resin of Example 1 was compounded with silica as inorganic filler to produce a pasty cement. On site, cure was initiated by mixing with benzoyl peroxide absorbed onto calcium sulphate. The cement gelled and set rapidly. being impossible to ignite either before or after admixture with the catalyst by matches or sparks. Combustion caused by a hot flame ceased as soon as the flame was removed.

Examples of other fillers are china clays. calcium carbonate.

Example 3 The composition of Example 2 was packaged in a plastics film together with a suitable catalyst such as benzoyl peroxide paste in glass phials to produce capsules for use in resin bonded rock anchors. The capsules were impossible to ignite with likely sources of ignition e.g. a match flame, a spark etc. If ignited by a very fierce hot flame they were immediately extinguished when the flame was removed.

They are used conventionally, by being penetrated and agitated on site by the metallic or other anchor member.

WHAT WE CLAIM IS: 1. A polyester resin including a polyester. a solvent copolymerisable monomer and at least one accelerator and stabilizer wherein the solvent monomer is bromostyrene. which resin is substantially non-flammable in the liquid state.

2. A resin according to Claim 1 wherein the bromostyrene content is 40-50% by weight of the resin.

3. A resin according to Claim 1 substantially as herein described and exemplified in Example 1.

4. A cement composition which consists of a resin according to Claim 1 or Claim 2 and an inorganic filler.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. Liquid Resin Test Method Units Styrene Bromo Properties styrene Monomer Content - % 35 50 Gel Times at 25"C 2% of 50% min 61/2 sol/2 Benzoyl peroxide Cast Sheet Properties Hardness Barcol 52 50 Heat Deflection Temperature BS2782 "C 77 63 Wt Tensile strength BS2782 N/mm2 54.0 51.4 Elongation at Break BS2782 % 1.55 1.5 Initial Tensile Modulus BS2782 N/mm2 4.08 4.24 Water absorption BS2782 502F mg% 20.5 (0.22) 15.2 (0.14) (24 hr) BS2782 502G mg% 20.5 (0.21) 15.3 (0.15) Bromostyrene is used in larger amounts than styrene would be to achieve a given viscosity of a resin (and therefore of a filled composition to be made from it) because it is a more viscous material than styrene. Typically contents of bromostyrene will be 35-55% by weight preferably 40-50%, in contrast to the usual styrene content of 30-40%. Example 2 The bromostyrene resin of Example 1 was compounded with silica as inorganic filler to produce a pasty cement. On site, cure was initiated by mixing with benzoyl peroxide absorbed onto calcium sulphate. The cement gelled and set rapidly. being impossible to ignite either before or after admixture with the catalyst by matches or sparks. Combustion caused by a hot flame ceased as soon as the flame was removed. Examples of other fillers are china clays. calcium carbonate. Example 3 The composition of Example 2 was packaged in a plastics film together with a suitable catalyst such as benzoyl peroxide paste in glass phials to produce capsules for use in resin bonded rock anchors. The capsules were impossible to ignite with likely sources of ignition e.g. a match flame, a spark etc. If ignited by a very fierce hot flame they were immediately extinguished when the flame was removed. They are used conventionally, by being penetrated and agitated on site by the metallic or other anchor member. WHAT WE CLAIM IS:

1. A polyester resin including a polyester. a solvent copolymerisable monomer and at least one accelerator and stabilizer wherein the solvent monomer is bromostyrene. which resin is substantially non-flammable in the liquid state.

2. A resin according to Claim 1 wherein the bromostyrene content is 40-50% by weight of the resin.

3. A resin according to Claim 1 substantially as herein described and exemplified in Example 1.

4. A cement composition which consists of a resin according to Claim 1 or Claim 2 and an inorganic filler.

5. A cement composition according to Claim 4 substantially as herein described and

exemplified in Example 2.

6. A rock anchor which is a capsule containing a composition according to Claim 3 and, separately, a catalyst for curing the resin of the composition.