GB1563943A - Bituminous composition - Google Patents

Description

(54) BITUMINOUS COMPOSITION (71) We, THE BRITISH PETROL EUM COMPANY LIMITED, of Britannic House, Moor Lane, London, EC2Y 9BU, a British Company, 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 a bituminous composition suitable for use in sheet form as a sound insulating material.

Bitumen-backed felt is used as a sound insulating material in various situations, e.g.

on the floor of motor vehicles. It is normally used in the form of sheets having a total thickness of about 20 mm and a bitumen thickness of 2-5 mm. If the sheet has to fit over curved surfaces, e.g. the transmission tunnel of a car, the sheet has to have sufficient flexibility to be pressed out into the desired shape yet sufficient rigidity to maintain the shape in use. Bitumen itself tends to have the flexibility but not the rigidity. As bitumen is much cheaper than rubber and other known sound insulating materials it would be advantageous if the properties of bitumen could be modified to increase its rigidity sufficiently to ensure it holds its shape after moulding whilst retaining sufficient strength and pliability to withstand rough handling.

Various materials compatible with bitumen are potentially available to increase the rigidity of the bitumen but the bitumen must retain a certain flexibility so that it can still be moulded.

It has now been found that the required balance of properties can be obtained by incorporating with the bitumen a small but critical amount of a particular polymer.

According to the present invention a bituminous composition, capable of use in sheet form and capable of retaining a preformed moulded shape, consists essentially of bitumen, a styreneacrylonitrile copolymer present in an amount of from 2 to 8% wt by weight of bitumen and copolymer, and a filler present in an amount of from 20 to 80% wt by weight of total mixture.

The invention includes a bituminous sheet material capable of retaining a preformed moulded shape comprising a fabric, particularly a non-woven fabric, combined with a bituminous composition as defined above.

The bitumen may be derived from petroleum, e.g. the residue from the vacuum distillation of crude oil or an oxidised bitumen obtained by air blowing such a vacuum residue to a suitable penetration.

Oxidised bitumen is preferred to give the required stiffness. The bitumen (without filler) preferably has a penetration of from 25 to 100 at 250 C, more particularly 25 to 60, and a softening point (Ring and Ball) of from 50 to 1 100C, more particularly 70 to 100"C.

The styrene-acrylonitrile copolymer may have a styrene content of from 70 to 80% mole and an acrylonitrile content of from 20 to 30% mole and a number average molecular weight of at least 20,000. Suitable materials are sold by the B. F. Goodrich Co., under the name "Hycar" 2301, (Registered Trade Mark) by Monsanto under the name "Lustran" (Registered Trade Mark) SAN, or by Dow under the name "Tyril" (Registered Trade Mark).

Any of the normal fillers for bitumen may be used, and they may be powdered or fibrous, e.g. powdered limestone, Portland cement, talc, asbestos fibres, glass fibres or chopped organic fibres.

The components may be blended in a vessel equipped with a powerful stirrer and heaters capable of raising the charge to a temperature of from 100 to 200"C. The bitumen should first be melted to a mobile liquid and the copolymer and filler added, preferably in that order.

The blend may be formed into sheets by calendering on a 3 roll mill. If required as a backing for, e.g. felt, the felt and backing may be bonded by feeding both through the calender together. Slack wax may be used as an anti-blocking agent. The product may be press moulded into a preferred shape under pressure.

The invention is illustrated by the following comparative example.

Example.

A number of samples of a filled bitumen, suitable for use with backing felt to give a bitumen backed felt for use on the floors of motor cars, were prepared. The bitumen was a blown bitumen having a penetration of 40 at 25"C and a softening point (Ring and Ball) of 85"C. The samples contained 60% wt of powdered limestone filler based on the total weight of the mixture.

Included in the samples were differing amounts of a styrene-acrylonitrile copolymer, (Hycar 2301 sold by B. F.

Goodrich Co.).

A series of blends was made up as follows.

The bitumen was preheated in an oven at 1500C. It was then poured into a metal container and its temperature maintained at 1300C by heating on a hot plate. Styreneacrylonitrile powder was slowly added to the bitumen with stirring. The mixture was stirred rapidly using a propeller type stirrer.

The calcium carbonate filler was subsequently added and the whole stirred to a homogeneous consistency.

The blends were formed into moulded sheets 100 mm x 100 mm square and 2 mm thick by moulding in a press at 1000C using 3 minutes contact pressure and 5 minutes at 20 tonnes pressure.

Specimen sheets were tested for their ability to retain their shape after being moulded at room temperature under one ton pressure for one minute. The middle portions of the specimens were moulded into square cross-section with one open side around a square cross-section rod with 12.5 mm sides. The overall width of each specimen was thus reduced to 75 mm.

The ability of the material to retain its shape was judged by the amount of flattening which occurred when specimens were left standing in an inoubator at 150C.

All specimens were stood on a non-stick silicon paper.

Specimens formed from blends containing 0, 1, 3, 6 and 10% styreneacrylonitrile copolymer were prepared and moulded to the above shape for evaluation, the percentage of copolymer being by weight of the bitumen and copolymer.

The degree of flattening of the specimens in the incubator at 150C was measured after 24 hours and after 40 days. With no flattening the width would remain at 75 mm: if completely flattened the width would return to the original 100 mm.

TABLE 1

Styreneacrylo Width of Specimen nitrile copolymer content % wt After 24 hours t After 40 days 0 1 82-92 100 1 82 3 77-80 81-83 6 80 82 10 Broken Broken Several specimens were tested at each copolymer level, hence a range of widths is sometimes quoted in Table 1.

The table shows that the bitumen with no added copolymer showed appreciable flattening after 24 hours and had completely flattened after 40 days. The addition of 1% of copolymer effected some improvement but there was still significant flattening. With 3 and 6% of copolymer the amount of flattening was at its minimum, there being only an increase in width of 6-8 mm even after 40 days. When the amount of copolymer was 10%, however, the specimens were too brittle and, in fact, broke or cracked while being moulded.

Thus for specimens to have both the required flexibility to allow them to be moulded and the required rigidity for them to retain their shape after moulding, it was found that there was an optimum level of 3 to 6% wt of copolymer.

Claims (7)

WHAT WE CLAIM IS:

1. A bituminous composition, capable of use in sheet form and capable of retaining a preformed moulded shape, consisting essentially of bitumen, a styrene-acrylonitrile copolymer present in an amount of from 2 to 8% wt by weight of bitumen and copolymer, and a filler present in an amount of from 20 to 80% wt by weight of total mixture.

2. A bituminous composition as claimed in claim 1 wherein the bitumen is an oxidised bitumen.

3. A bituminous composition as claimed in claim 1 or 2 wherein the bitumen has a penetration of from 25 to 100 at 250C and a softening point (Ring and Ball) of from 50 to 1100C.

4. A bituminous composition as claimed in claim 3, wherein the bitumen has a penetration of from 25 to 60 at 25"C and a softening point (Ring and Ball) of from 70 to 100 C.

5. A bituminous composition as claimed in any of claims 1 to 4, wherein the styreneacrylonitrile copolymer has a styrene content of from 70 to 80% mole, an acrylonitrile content of from 20 to 30 /O mole and a number average molecular weight of at least 20,000.

6. A bituminous composition as claimed in claim I substantially as described in the- Example.

7. A bituminous sheet material capable of retaining a preformed moulded shape comprising a fabric, preferably a non-woven fabric, combined with a bituminous composition as claimed in any of claims 1 to 6.