Glass fibre mat and use thereof for built-up roofing

Abstract

The invention relates to a fibre-based mat that can be used for making up bituminous membranes, comprising glass fibres, organic fibres and a binder, characterized in that the organic fibres have a shrinkage at 130.degree. C. of less than or equal to 5%. The invention also relates to a bituminous membrane comprising a substrate coated, covered or impregnated with a bituminous matrix, in which the substrate is a mat as above. The mat and the membrane can be used for the production of roofing and/or damp-proofing.

Description

[0001] The present invention relates to the field of fibre-based sheet materials and more particularly to a glass mat that can be used as a substrate for the production of products coated, covered or impregnated with bitumen, especially for roofing and/or damp-proofing applications.

[0002] In the field of roofing or damp-proofing, it is known to use bituminous membranes that are applied to the surface to be roofed or damp-proofed. These membranes generally consist of a substrate in the form of a sheet coated or impregnated with a bituminous matrix.

[0003] Sheet materials may be of various types and are usually obtained from organic or mineral fibres, preferably in the form of nonwovens.

[0004] Among materials that can be used, glass mats or veils are of great interest as they guarantee the dimensional stability of the bituminous membrane over time.

[0005] Glass mats can be obtained by any technique known per se, in particular the so-called wet technique described especially in the reference work "The Manufacturing Technology of Continuous Glass Fibres" by K. L. Loewenstein, Publ. Elsevier, 2nd edition, 1983, pp. 315-317. This technique, which is similar to papermaking techniques, consists in preparing an aqueous suspension of chopped glass fibres, in depositing this suspension as a film on a filter belt to which suction is applied in order to-remove some of the water from the film deposited, in applying a binder composition to the wet film, in drying the mat and crosslinking the binder in an oven, and then packaging the mat in the desired manner. The final product is in the form of quite a thin sheet (with a thickness of about 0.2. to 0.8 mm) and generally packaged in rolls.

[0006] The binder is often an aqueous composition based on a urea-formaldehyde resin, this resin having a satisfactory temperature withstand at the temperatures used subsequently for the bitumen impregnation.

[0007] However, glass mats have the drawback of having a relatively low tear strength, which detracts from the ease of use and especially forces the user to take precautions when handling it for making up the membrane or for laying it on a roof.

[0008] To remedy this drawback, there are complex substrates which combine a mat based on organic fibres and having a high tear strength with a glass mesh which gives the combination dimensional stability. However, these complexes combining two intermediate products are complicated to manufacture.

[0009] The object of the invention is to provide a glass-based material with an improved tear strength, without its manufacture being more complicated than that of a conventional mat.

[0010] EP-A-0 763 505 describes a glass fibre mat for the manufacture of asphalt roof shingles, the strength of which is improved thanks to a urea-formaldehyde binder modified by a self-crosslinkable vinyl additive. In this mat, a minor proportion of fibres may not consist of glass, and may especially be chosen from organic fibres such as nylon, polyester, polyethylene and polypropylene fibres. That document provides no specific information about these organic fibres and contains no particular example illustrating this possibility.

[0011] The present invention is based on the discovery that many organic fibres are not suitable for the manufacture of a mat and even have a very negative effect on the properties of the mat in bituminous roofing applications, but this drawback may be overcome by very carefully selecting the synthetic materials.

[0012] In this regard, the subject of the invention is a fibre-based mat that can be used for making up bituminous membranes, comprising glass fibres and organic fibres bound together by a binder, characterized in that the fibres have a shrinkage at 130.degree. C. of less than or equal to 5%.

[0013] It shall be noted that the wording <<glass mat>> or <<glass veil>> encompasses according to the invention materials well known from the person skilled in the art of glass fibre-based products. These are thin sheet-like materials, of an essentially isotropic structure, that is to say that there is no preferred orientation of the fibres. Practically, a veil can be characterized through the so-called 1 anisotropy ratio = tensile strength of the veil in the machine direction tensile strength of the veil in the cross direction ,

[0014] which is generally about 1, especially about 1 to 1.5, sometimes up to 2. This essentially random orientation of the fibres is generally achieved through providing the glass fibres in the form of chopped strands for the production of the veil, for instance using the above mentioned wet technique.

[0015] Choosing organic fibres according to the above criterion results in the mat being of high quality, and in particular having mechanical and thermal strength compatible with its being used subsequently for impregnation with bitumen, whereas other fibres result in the mat having insufficient thermal and/or mechanical strength.

[0016] Firstly, the organic fibres used in the mat manufacture have a high melting point in order to prevent them from degrading during the thermal steps in the manufacture of the mat, especially oven drying and crosslinking, and in the use of the mat, particularly when in contact with the bituminous binder. In general, the synthetic organic material is chosen to have a melting point above about 220.degree. C.

[0017] According to the invention, the fibres are selected according to their thermal shrinkage: this parameter corresponds to the dimensional variation, in this case the shortening, of the fibre after it has been exposed to a given temperature for a defined time. To do this, the initial length Li of the fibre before heating and then the final length Lf are measured, the shrinkage r being equal to

[0018] r=(Li-Lf)/Li(expressed as a percentage).

[0019] The key shrinkages according to the invention are expressed for a temperature of 130.degree..degree.C., produced in an atmosphere of vapour, and for a time of 30 minutes.

[0020] According to the invention, the shrinkage is chosen to be less than or equal to 5%, preferably less than or equal to 4% and particularly less than or equal to 3%, for example about 2 to 3%.

[0021] Advantageously, this fibre quality may be obtained using semicrystalline polymer materials, particularly those in which the spinning process allows them to undergo drawing which increases the degree of crystallinity. Other manufacturing conditions such as presence of nucleation agents or the temperature factor may also lead to the organisation of the base macromolecules so that the polymer of initial amorphous structure starts to adopt a crystalline structure and to turn semi-crystalline.

[0022] Fibres satisfying the requirements of the invention may be found among polyester fibres, especially polyalkylene terephthalate and particularly polyethylene terephthalate fibres.

[0023] Organic fibres suitable for wet processes for manufacturing nonwovens are preferred, these fibres containing a sizing composition allowing the individual filaments to be dispersed in water.

[0024] The organic fibres may have variable dimensions, with a mean diameter of about 7 to 25 .mu.m for a linear density of about 0.5 to 2 dtex. The fibres are advantageously chopped to a length of the order of one millimetre to a few tens of millimetres, especially 6 to 30 mm.

[0025] The effect of the organic fibres is clearly perceptible above 5% by weight with respect to the total weight of fibres. The proportion of organic fibres is advantageously about 5 to 30%, especially 20 to 30% and particularly about 25% by weight with respect to the total weight of fibres.

[0026] The glass fibres used according to the invention are of a type conventional for the production of mat, preferably in the form of chopped yarns, having a length of the order of ten millimetres, especially 6 to 30 mm and preferably about 10 to 20 mm, for example 12 to 18 mm. It should be understood that a certain proportion of yarns (for example 5 to 10%) may be chopped to a length of up to 100 mm. Moreover, continuous yarn, especially glass yarn, may be introduced into the mat as reinforcement in the machine direction.

[0027] The binder used to form the mat is advantageously based on a urea-formaldehyde resin, preferably one which is modified by vinyl and/or acrylic additives in the manner known especially from U.S. Pat. No. 4,681,802 and EP-A-0 763 505. The amount of binder corresponds to generally a solids content of from 15 to 30% by weight with respect to the mat.

[0028] The mat is manufactured with a grammage, usual for glass mats, of about 30 to 150 g/m.sup.2, particularly 50 to 120 g/m.sup.2.

[0029] Given the difference in density between glass and organic fibres, the amount of material in the mat according to the invention for a given grammage is slightly greater than that contained in a glass mat, which means that the thickness is relatively greater and/or the porosity is less. For example, the porosity is about 1500 to 1900 l/m.sup.2.s for a 50 g/m.sup.2 mat.

[0030] Since the mat according to the invention is particularly suitable for damp-proofing and/or roofing applications, the subject of the invention is also a bituminous membrane comprising a substrate coated, covered or impregnated with a bituminous matrix, characterized in that the substrate is a mat as described above.

[0031] The bituminous matrix may be chosen from matrices known per se: natural, modified or unmodified bitumen, or a synthetic binder such as a "light-coloured binder" making it possible in particular to give the membrane a decorative colour.

[0032] The following examples, given non-limitingly, illustrate the invention.

EXAMPLE 1

[0033] An aqueous suspension of fibres is prepared, in which the fibres comprise:

[0034] 75% by weight of chopped E-glass yarn, having a filament diameter of 10 .mu.m and a linear density of 360 tex, the chopped length being 12 mm;

[0035] 25% by weight of chopped polyester yarn available from KURARAY under the reference EP 133, suitable for papermaking processes and water-dispersible. This yarn is characterized by a filament diameter of 12 .mu.m and a linear density of 1.4 dtex, the chopped length being 15 mm. The yarn is a polyethylene terephthalate yarn drawn to increase its crystallinity, having a shrinkage of about 2% at 130.degree. C. after exposure for 30 minutes in a wet environment and a shrinkage of 3% at 170.degree. C. after exposure for 15 minutes in a dry atmosphere.

[0036] The fibre suspension, which also contains the usual additives, namely antifoam, dispersant, viscosity modifier, etc., is processed under standard conditions on a mat manufacturing machine comprising (i) a hydroformer on which a partially dewatered wet film is formed, (ii) a station for applying the binder by spraying, coating [a curtain coater] or passing through a bath containing an aqueous composition based on a urea-formaldehyde resin plasticized by an acetate and an acrylic, which deposits on the mat an amount of binder corresponding to a solids content of 19% by weight with respect to the weight of mat, and (iii) a drying and crosslinking oven having several temperature zones from 135 to 215.degree. C. through which the mat runs with an average residence time of about 30 seconds, preferably slightly less than 30 seconds.

[0037] The mat poses no problem in manufacture and is obtained with a grammage of 50 g/m2, a thickness of 0.3 mm and a porosity of 1580 l/m.sup.2.s.

[0038] This mat is subjected to mechanical strength tests at room temperature and at high temperature, the results of which are given in Table 1 below.

[0039] Tensile Strength

[0040] Ten test pieces in the machine direction and 10 test pieces in the cross direction were cut in widths of 50 mm and lengths of 250 mm from the mat specimen. Each test piece was fixed between the jaws of a tensile testing machine and the system for driving the movable clamp was actuated until the specimen broke: the values of the tensile strength (in newtons) and of the elongation at break (as a percentage of the nominal length) were then measured. Also taken was a measurement of the tensile strength at 250.degree. C. under a fixed load equal to 10% of the strength value measured previously, and the time required for the test piece to break was measured.

[0041] Tear Strength

[0042] Ten test pieces in the machine direction and 10 test pieces in the cross direction were cut in widths of 50 mm and lengths of 100 mm from the mat specimen. A sharp cut was made on each test piece starting from the edge of a short side and parallel to the long sides halfway between the long sides, and 50 mm in length. The distance between the jaws of a tensile testing machine was set to be equal to 50 mm, the test piece was fixed in the jaws and the tensile tester was actuated, setting the pull rate at 100 mm/min. The maximum load (in N) when the test piece completely split into two parts was recorded. The tear strength was expressed as the average of the ten measurements.

[0043] The mat of Example 1 had very satisfactory mechanical properties and dimensional stability. It was processed on a continuous bituminous-membrane manufacturing line by impregnation with hot bitumen at about 200.degree. C., having a good amenability to impregnation, even giving the membrane a very attractive appearance.

[0044] Comparative Example 1

[0045] A mat was manufactured in the manner indicated in Example 1, but exclusively based on glass yarn. The mat had a grammage of 50 g/m.sup.2, a binder content corresponding to a 24% solids content by weight with respect to the weight of mat, a thickness of 0.3 mm and a porosity of 2000 l/m.sup.2.s. It was subjected to the same mechanical tests as the mat of Example 1.

[0046] Comparative Example 2

[0047] Example 1 was repeated with an organic fibre that does not meet the criteria of the invention. It was a polyester fibre sold by Tergal Fibres under the reference "1.6 dtex T110 mi-mat coup" [1.6 dtex T110 chopped half-mat], which is also water-dispersible, characterized by a linear density of 1.6 dtex, a chop length of 12 mm, a shrinkage at 130.degree. C. in a steam atmosphere of 7%.

[0048] A 50 g/m.sup.2 mat, with a binder content of 24% by weight, a thickness of 0.3 to 0.4 mm and a porosity of 1700 l/m.sup.2.s, was manufactured.

[0049] The manufacturing posed problems at the end of the line, since the formation of wrinkling, which may be ascribed to the phenomenon of thermal shrinkage of the organic fibre, was observed after the mat left the oven.

[0050] As the mechanical tests show, this mat has a low mechanical strength, less than that of the conventional glass mat. In particular, it may be seen that the anisotropy of the mat is greatly increased. Furthermore, the mechanical strength at 250.degree. C. is non-existent.

[0051] This mat is not suitable for the production of bituminous membranes.

1 TABLE 1 Ex. 1 Comp. Ex. 1 Comp. Ex. 2 TENSILE STRENGTH Machine direction (N/5 cm) 214 165 150 Cross direction (N/5 cm) 133 93 70 Anisotropy 1.6 1.7 2.1 Elongation (%) 1.9 1.1 1.2 TEAR STRENGTH Machine direction (N) 3.0 1.5 3.2 Cross direction (N) 3.5 1.7 3 STRENGTH at 250.degree. C. >4 min >4 min 0 WRINKLING on the line No No Yes

[0052] The invention was described in detail for the case of the wet manufacture of a mat having a particular grammage for application in the production of bituminous membranes, but it should be understood that the invention is not limited to this embodiment and in particular it encompasses other (dry) mat manufacturing techniques, other grades of mats, possibly reinforced with continuous glass yarns, and other products that can be used for roofing and/or damp-proofing.

Claims

1. Fibre-based mat that can be used for making up bituminous membranes, comprising glass fibres, organic fibres and a binder, characterized in that the organic fibres have a shrinkage at 130.degree. C. of less than or equal to 5%.

2. Mat according to claim 1, characterized in that the organic fibres have a shrinkage at 130.degree. C. of less than or equal to 3%.

3. Mat according to claim 1 or 2, characterized in that the organic fibres are based on a semicrystalline polymer.

4. Mat according to any one of the preceding claims, characterized in that the fibres are polyester, especially polyethylene terephthalate, fibres.

5. Mat according to any one of the preceding claims, characterized in that the organic fibres contain a sizing composition allowing the individual filaments to be dispersed in water.

6. Mat according to any one of the preceding claims, characterized in that the proportion of organic fibres is about 5 to 30% by weight with respect to the total weight of fibres.

7. Mat according to any one of the preceding claims, characterized in that the binder content is about 15 to 30% by weight with respect to the total weight of the mat.

8. Mat according to any one of the preceding claims, characterized by a grammage of 30 to 150 g/m2.

9. Bituminous membrane comprising a substrate coated, covered or impregnated with a bituminous matrix, characterized in that the substrate is a mat according to any one of the preceding claims.