A membrane with a weld quality indicator

Abstract

The invention is directed to a membrane (1) comprising a waterproof layer (2) having opposed top and bottom surfaces and a weld quality indicator (3) 5 deposited on one of the opposed surfaces of the waterproof layer (2), wherein the weld quality indicator (3) comprises one or more discontinuous lines running substantially parallel and adjacent to an edge (e1, e2) of the waterproof layer (2), wherein the discontinuous line(s) is / are composed of a series of spaced apart areas (on the surface of the waterproof layer) covered 10 with an ink comprising a thermochromic system.

Description

[0001] A MEMBRANE WITH A WELD QUALITY INDICATOR

[0002] Technical field

[0003] The present invention relates to use of heat sensitive indicators on thermoplastic membranes which indicate whether the temperature required to achieve a quality weld joint formed between two overlapped membrane portions has been reached. Particularly, the invention relates to membranes having a heat sensitive indicator deposited on a surface of the membrane adjacent to an edge of the membrane.

[0004] Background of the invention

[0005] In the field of construction, waterproof polymeric sheets, which are often referred to as membranes or panels, are used to protect underground and above ground constructions, such as basements, tunnels, and flat and low-sloped roofs, against penetration of water. Commonly used materials for waterproof membranes include plastics, in particular plasticized polyvinylchloride (p-PVC), thermoplastic olefins (TPE-O, TPO), and thermoset elastomers such as ethylene-propylene diene monomer (EPDM).

[0006] Roofing membranes are typically delivered to a construction site in rolls, transferred to the place of installation, unrolled, and adhered or affixed to the substrate to be waterproofed. Roofing membranes must be securely fastened to the roof substrate to provide sufficient mechanical strength to resist the shearing forces applied on it due to high wind loads. Furthermore, the edges of adjacent roofing membranes are overlapped to form sealable joints. These joints can then be sealed by bonding the bottom surface of the first overlapping edge portion of the first membrane with the top surface of a second overlapped edge portion of the second membrane. Typically, the overlapping regions are sealed by heating the adjacent surfaces of the overlapping membranes and then pressing the heated surfaces together, merging the material of the membranes and providing a strong seal.

[0007] The quality of the heat sealing depends on appropriate and sufficient heat application to achieve appropriate melting of the membrane material. The quality of the seals can be checked either visually or mechanically and either on a spot or continuous basis, by manually probing and lifting the edge of the upper membrane to determine if it is properly secured to the lower membrane. Spot wise checking of the weld seals can miss unexamined unsealed areas and a full inspection of every seal is often overlooked, potentially causing leaks and expensive corrective work.

[0008] In order to assist the applicators, roofing and waterproofing membranes having a heat sensitive indicator deposited to a membrane surface at the proximity of an edge have been developed. These types of weld quality indicators provide immediate, positive, and visually perceptible indication that a joint or seam between overlapped membranes has been raised to a sufficiently high temperature to achieve a proper seal. As the adjacent surfaces of the overlapped membrane portions are heated, heat passes through the membrane to the heat seal indicator resulting in color change provided that a target temperature range has been reached. Use of the heat sensitive indicators provides an additional quality control for the applicator making the roofing or waterproofing job more reliable and reduces the risk of costly leak repairs.

[0009] The weld quality indicators are typically based on use of heat sensitive coatings, inks, or polymer layers that change their color when the material is heated to threshold temperature. The heat sensitive formulation can also be designed to have a colorless appearance after the heat-induced color change, which is typically an advantage in roofing and waterproofing applications. It is also essential for the weld quality indicator to have a color-memory property, which enables the indicator to retain the color change upon a decrease in temperature from said temperature threshold.

[0010] A published patent application WO 2021 / 158997 A1 discloses a thermochromic indicator and use thereof to provide a roofing membrane with weld quality indicator. The thermochromic indicator comprises a reversible color-changing system comprising a dye, developer, and a solvent and it can be incorporated into a coating or ink. The formulation comprising the color-changing system is printed onto a roofing membrane at the time of manufacture as one or more continuous lines and cured, for example, using an UV-lamp.

[0011] However, using the continuous line weld indicator of WO 2021 / 158997 A1 for a roofing membrane can be problematic. This is because the presence of a weld indicator as a continuous line may interfere with weld formation between the overlapped edge portions of membranes. Even though the weld indicator is typically present only on the upper (exposed) surface of an overlapping membrane, during the installation of any roof the applicator will inevitably need to weld some membrane over the surface of the seam having the weld indicator. This is especially the case in the areas where three membranes are overlapped to form a T-joint.

[0012] When a T-joint is formed over a region comprising a weld indicator in form of a coated continuous line, the result is that the area of the weld indicator will extend perpendicularly across the entire weld seam. This may result in a region extending across the weld seam where the formation of the weld has been blocked and the continuous weld seam is interrupted, which may have a significant negative effect on weld quality and thus an increased risk of water leaks.

[0013] A coated weld indicator can be easily removed from the surface of a membrane by the applicators, but this adds a time-consuming step to the installation process. Furthermore, if the applicator forgets to remove the coating, they will need to be called to return to the installation site to resolve the situation, which is generally not acceptable and should be avoided. Another issue with using a continuous line is that it only shows the quality of the weld over a portion of the width of the weld. Using a line that is as wide at the entire weld would be impractical and would consume an unnecessary amount of ink.

[0014] Considering that the sole purpose of a weld quality indicator is to reduce installation time and reduce the risk of leaks from poor welds, there is a need for a novel type of weld quality indicator which does not suffer from the limitations of prior art solutions as discussed above.

[0015] Summary of the invention

[0016] The object of the present invention is to provide a membrane with a weld quality indicator enabling visually determining whether a seam formed between two overlapped portions of membranes has been sufficiently heated to a preselected threshold temperature ensuring appropriate seal strength. Particularly, it is an object of the present invention to provide a novel type of weld quality indicator, which solves or at least mitigates the problems of the prior art solutions as discussed above.

[0017] Surprisingly it has been found out that the objects can be achieved with the features of claim 1 .

[0018] Specifically, according to the invention, a membrane is proposed, the membrane comprising a waterproof layer having opposed top and bottom surfaces and a weld quality indicator deposited on one of the opposed surfaces of the waterproof layer, wherein the weld quality indicator comprises one or more discontinuous lines running substantially parallel and adjacent to an edge of the waterproof layer, wherein the discontinuous line(s) is / are composed of a series of spaced apart areas (on the surface of the waterproof layer) covered with an ink comprising a thermochromic system.

[0019] As it turned out, the suggested membrane enables visual inspection of the quality of welded seams between overlapped portions of adjacent membranes without having a significant impact on the total installation time. Furthermore, the use of the novel type of weld indicator does not result in formation of a continuous region of non-welded material even in case the weld indicator would be present on the surface of the lower membrane portion, which eliminates the risk of water leaks due to the presence of the weld indicator in the area of the welded seam.

[0020] Additional aspects of the present invention are presented in further independent claims. Preferred embodiments of the invention are outlined throughout the description and the dependent claims.

[0021] Brief description of the Drawings

[0022] Fig. 1 shows a membrane (1) composed of a waterproof layer (2) having long and short edges (e1 , e2) and a weld quality indicator (3) composed of one single discontinuous line running parallel to the long edge (e1) and composed of a plurality of spaced apart ink-covered areas separated by a distance (D1), wherein the discontinuous line is separated by distance (D2) from the long edge (e1) of the waterproof layer (2). Fig. 2 shows a membrane (1) composed of a waterproof layer (2) having long and short edges (e1 , e2) and a weld quality indicator (3) composed of first and second discontinuous lines running parallel to the long edge (e1) and composed of a plurality of spaced apart ink-covered areas separated by a distance (D11 , D12), wherein the first discontinuous line is separated by distance (D21 ) and the second discontinuous line is separated by a distance (D22) from the long edge (e1) of the waterproof layer (2) and wherein the discontinuous lines are separated by a distance (D3) from each other.

[0023] Fig. 3 shows a membrane (1) composed of a waterproof layer (2) having long and short edges (e1 , e2) and a weld quality indicator (3) composed of first and second discontinuous lines running parallel to the long edge (e1) and composed of a plurality of spaced apart ink-covered areas, wherein the ink-covered areas of the first and second discontinuous lines do not line up in rows.

[0024] Fig. 4a shows a first membrane strip (A) without a weld quality indicator and a second membrane strip (B) having a weld quality indicator deposited on one of its long edge portions positioned over the first membrane strip (A) to form a weldable seam.

[0025] Fig. 4b shows the membrane stirps of Figure 4a after a third membrane strip (C) has been positioned over the first and second membrane strips (A, B) in overlapping position along one of the short edges of the two other membrane strips to form a 3- way overlap joint (“T-joint”).

[0026] Figures 5a to 5d relate to testing of different types of weld quality indicators in case of a 3-way overlap joint shown in Figure 4b.

[0027] Detailed description of the invention

[0028] The subject of the present invention is a membrane (1) comprising a waterproof layer (2) having opposed top and bottom surfaces and a weld quality indicator (3) deposited on one of the opposed surfaces of the waterproof layer (2), wherein the weld quality indicator (3) comprises one or more discontinuous lines running substantially parallel and adjacent to an edge (e1 , e2) of the waterproof layer (2), wherein the discontinuous line(s) is / are composed of a series of spaced apart areas (on the surface of the waterproof layer) covered with an ink comprising a thermochromic system.

[0029] The term “polymer” designates a collective of chemically uniform macromolecules produced by a polyreaction (polymerization, polyaddition, polycondensation) where the macromolecules differ with respect to their degree of polymerization, molecular weight and chain length. The term also comprises derivatives of said collective of macromolecules resulting from polyreactions, that is, compounds which are obtained by reactions such as, for example, additions or substitutions, of functional groups in predetermined macromolecules and which may be chemically uniform or chemically non-uniform.

[0030] The term “elastomer” refers to any polymer or combination of polymers, which is capable of recovering from large deformations, and which can be, or already is, modified to a state in which it is essentially insoluble (but can swell) in a boiling solvent. Typical elastomers are capable of being elongated or deformed to at least 200% of their original dimension under an externally applied force, and will substantially resume the original dimensions, sustaining only small permanent set (typically no more than about 20%), after the external force is released. As used herein, the term “elastomer” may be used interchangeably with the term “rubber.”

[0031] The term “molecular weight” refers to the molar mass (g / mol) of a molecule or a part of a molecule, also referred to as “moiety”. The term “average molecular weight” refers to the number average molecular weight (Mn) of an oligomeric or polymeric mixture of molecules or moieties. The molecular weight may be determined by gel permeation chromatography.

[0032] The term “softening point” refers to a temperature at which compound softens in a rubber-like state, or a temperature at which the crystalline portion within the compound melts. The softening point is preferably determined by Ring and Ball measurement conducted according to DIN EN 1238 standard.

[0033] The term “melting temperature” refers to a peak melting temperature, i.e. the temperature at which a material undergoes transition from the solid to the liquid state. The melting temperature is preferably by differential scanning calorimetry (DSC) according to ISO 11357 standard using a heating rate of 2°C / min. The measurements can be performed with a Mettler Toledo DSC 3+ device and the Tgvalues can be determined from the measured DSC-curve with the help of the DSC- software. The term “melting point” may be used interchangeably with the term “melting temperature”.

[0034] The term “glass transition temperature” (Tg) refers to the temperature above which temperature a polymer component becomes soft and pliable, and below which it becomes hard and glassy. The glass transition temperature (Tg) is preferably determined by dynamical mechanical analysis (DMA) as the peak of the measured loss modulus (G”) curve using an applied frequency of 1 Hz and a strain level of 0.1 %.

[0035] The “amount or content of at least one component X” in a composition, for example “the amount of the at least one thermoplastic polymer” refers to the sum of the individual amounts of all thermoplastic polymers contained in the composition. Furthermore, in case the composition comprises 20 wt.-% of at least one thermoplastic polymer, the sum of the amounts of all thermoplastic polymers contained in the composition equals 20 wt.-%.

[0036] The term “room temperature” designates a temperature of 23°C.

[0037] The membrane and the waterproof layer are preferably sheet-like elements having top and bottom surfaces defining a thickness there between. The term “sheet-like element” refers in the present disclosure to elements having a length and width at least 15 times, preferably at least 25 times, more preferably at least 50 times greater than the thickness of the element.

[0038] The term “waterproof layer” refers in the present disclosure to continuous layers that are capable of acting as a barrier to water or other liquid penetration. Preferably, the top waterproofing layer exhibits a water resistance measured according to EN 1928 B standard of 0.6 bar for 24 hours.

[0039] The membrane is preferably a prefabricated membrane. The term “prefabricated membrane” refers in the present disclosure to membranes, which have been formed before being applied on a surface of a substrate. Such prefabricated membranes are prepared at a location that is typically remote from the construction site, brought to the site, for example, in the form of a roll and laid on a surface of a substrate to be waterproofed.

[0040] The distance between subsequent ink-covered areas in said discontinuous line(s) is preferably at least 0.5 mm, such as least 1 .5 mm, particularly at least 2.5 mm, especially at least 3.5 mm and / or not more than 100 mm, such as not more than 75 mm, particularly not more than 65 mm, especially not more than 50 mm. The expression “distance between subsequent ink-covered areas” is understood to mean the shortest distance between peripheries of two ink-covered areas in a discontinuous line.

[0041] A membrane (1 ) composed of a waterproof layer (2) having long and short edges (e1 , e2) and a weld quality indicator (3) composed of one single discontinuous line running parallel to the long edge (e1) of the waterproof layer (2) and composed of a plurality of spaced apart ink-covered areas separated by a distance (D1) is shown in Figure 1 .

[0042] In one or more embodiments, the distance between subsequent ink-covered areas in said discontinuous line(s) is 1 .5 - 65 mm, preferably 2.5 - 55 mm, more preferably 3.5 - 45 mm, even more preferably 5 - 35 mm, still more preferably 5 - 25 mm.

[0043] The spaced apart ink-covered areas can have any shape, for example a shape of a letter, logo, square, rectangle, circle, oval, or a triangle. A shape of letter, logo, square, or a rectangle may be preferred.

[0044] The size of the ink-covered areas may particularly be at least 2.5 mm2, such as at least 5 mm2, especially at least 10 mm2and particularly not more than 750 mm2, such as not more than 500 mm2, especially not more than 350 mm2.

[0045] In one or more embodiments, the size of the ink-covered areas is in the range of 1 .5 - 500 mm2, preferably 5 - 350 mm2, more preferably 15 - 250 mm2, even more preferably 25 - 150 mm2. In case of ink-covered areas having a shape of a square, the width / height of the square may be at least 0.5 mm, such as at least 1 .5 mm, particularly at least 3.5 mm and not more than 25 mm, such as not more than 20 mm, particularly not more than 15 mm.

[0046] The weld quality indicator is preferably deposited on a surface of the waterproof layer in the weld area, i.e. , in the area of the membrane that is overlapped with an adjacent membrane to form an overlapping membrane seam. Consequently, the discontinuous line(s) composed of the spaced-apart ink-covered areas are preferably positioned within a distance from the edge of the waterproof layer corresponding to the minimum width of an acceptable weld.

[0047] It may be preferred that the discontinuous line(s) is / are positioned a distance of not more than 50 mm, preferably not more than 45 mm, more preferably not more than 40 mm inward from the edge of the waterproof layer.

[0048] The distance between the edge of the waterproof layer and a discontinuous line composed of ink-covered areas refers to the width of the area covered with the discontinuous line measured from the edge of the waterproof layer in a direction perpendicular to the direction of the discontinuous line. In Figure 1 , the distance between the discontinuous line of the weld quality indicator (3) and the edge (e1) of the waterproof layer (2) is shown as “D2” whereas In Figure 2, the distances between the first and second discontinuous lines of the weld quality indicator (3) and the edge (e1) of the waterproof layer (2) are shown as “D21” and “D22”, respectively.

[0049] Furthermore, the preferred distance between discontinuous line(s) and the adjacent edge of the waterproof layer also depends on the number of discontinuous lines forming the weld quality indicator. For example, in case the weld quality indicator is composed of one single discontinuous line, it may be preferred that the discontinuous line is positioned approximately middle of the weld area, for example, 5 - 35 mm, particularly 10 - 30 mm inward from the edge of the waterproof layer. However, in case the weld quality indicator is composed of multiple discontinuous lines, such as of two discontinuous lines, it may advantageous that these are positioned in close proximity to the edges of the weld area. In one or more embodiments, the weld quality indicator is composed of two or more spaced apart discontinuous lines running substantially parallel to each other. The term “substantially parallel” is understood to mean that a first imaginary line running through the center of the ink-covered areas of the first discontinuous line forms an angle a with a second imaginary line running through the center of the ink-covered areas of the second discontinuous line, wherein the a has a value of not more than 5°, preferably not more than 2.5 °, more preferably not more than 1 .5°.

[0050] The distance between the two or more discontinuous lines of the weld quality indicator may be at least 1 .5 mm, particularly at least 2.5 mm, especially at least 3.5 mm and / or not more than 50 mm, such as not more than 40 mm, particularly not more than 30 mm, especially not more than 20 mm apart form each other. The expression “distance between the discontinuous lines” is understood to mean the shortest distance between peripheries of the ink-covered areas of two adjacent discontinuous lines.

[0051] Figure 2 shows a membrane (1) composed of a waterproof layer (2) having and short edges (e1 , e2) and a weld quality indicator (3) composed of two discontinuous lines running substantially parallel to each other and to the long edge (e1) of the waterproof layer (2) and composed of a plurality of spaced apart ink-covered areas separated by a distance (D11 , D12) from each other. Furthermore, the discontinuous lines are separated by a distance (D3) from each other.

[0052] In one or more embodiments, the distance between the two or more discontinuous lines of the weld quality indicator is 1 .5 - 30 mm, preferably 2.5 - 25 mm, more preferably 3.5 - 20 mm, even more preferably 5 - 15 mm.

[0053] It may further be preferred that the discontinuous lines are positioned on the surface of the waterproof layer such that the ink-covered areas of adjacent discontinuous lines do not line up in rows, meaning that they are offset. A membrane having a weld quality indicator (3) composed of two discontinuous lines composed of ink-covered areas that do not line up in rows is shown in Figure 3.

[0054] The ink used for obtaining the weld indicator comprises a thermochromic system providing the weld indicator properties of the thermochromic materials. Substances that change their color as response to a change in temperature are known as thermochromic materials. The temperature at which the change in color occurs is typically a temperature range and not a single temperature. Typically, the color of a thermochromic material starts to change ca. 4 °C below the threshold temperature. The change in color can either be irreversible or reversible. Irreversible thermochromic materials are suitable for one-time use providing evidence of attained temperature.

[0055] The thermochromic system preferably comprises at least one thermochromic dye, at least one color developer, and at least one solvent.

[0056] Such thermochromic systems are typically provided as thermochromic pigments, which are microencapsulated in a protective cover to protect the pigment from undesired effects from the environment. Each microcapsule is self-contained, having all of the components of the entire thermochromic system required to reproduce the color change. At lower temperatures, i.e. at temperatures below the full color point, the solvent is solid and the thermochromic dye and the color developer interact. At this stage the thermochromic dye absorbs light in the visible wavelength and is thus colored. The term “full color point” refers here to a temperature at which a thermochromic system has achieved maximum color density upon cooling and appears to gain no further color density if cooled to a lower temperature.

[0057] At elevated temperatures, i.e. near the threshold temperature of the thermochromic system, the solvent starts to melt and the interaction between the color developer and the thermochromic dye is interrupted. At this stage the thermochromic dye undergoes a chemical transformation (such as deprotonation) that causes it to lose its color. The term “threshold temperature” refers here to a temperature above which the thermochromic system has almost achieved its final clear or light color end point. The color starts to fade at approximately 4°C. below the threshold temperature and will be in between colors within the threshold temperature range. Generally, the threshold temperature of a thermochromic system is defined as the temperature at which the human eye can perceive that the pigment is starting to lose its color, or alternatively, starting to gain color. When the heating is continued, the thermochromic system becomes increasingly unordered and continues to lose its color until it reaches a level of disorder at which the pigment lacks any recognizable color. The temperature at which the color of a thermochromic system is diminished to a minimal amount and at which it appears to lose no further color density upon further heating, is also known as a “clearing point”.

[0058] It may be preferred that thermochromic system, as well as the ink comprising the thermochromic system, is colored below the temperature threshold and changes from the colored to a colorless state upon exposure to the temperature threshold.

[0059] Furthermore, the color change of the thermochromic system can be reversible, meaning that the temperature induced color change can be reversed, or irreversible, wherein the color change is permanent and cannot be reversed by cooling the system below the temperature threshold.

[0060] In one or more embodiments, the thermochromic system is a reversible or irreversible color-changing system, preferably an irreversible color changing system, preferably changing from one color to a colorless state upon exposure to a preselected temperature threshold.

[0061] The thermochromic dye can be a leuco dye, for example selected from crystal violet lactone (CAS No.: 1552-42-7); Pigment Blue 63 (CAS No.: 16521-38-3); 2'- (dibenzylamino)-6'-(diethylamino)fluoran (CAS No.: 34372-72-0); 7-(4-(Diethylamino)- 2-6 ethoxyphenyl)-7-(1-ethyl-2-methyl-1 H-indol-3-yl)furo[3,4-b ]pyridin-5(7H)-one (CAS No.: 69898-40-4); 6'-(diethylamino)-1',3'-dimethylfluoran (CAS No.: 21934-68- 9); 3,3-bis(l-butyl-2-methyl-IH-indol-3-yl)phthalide (CAS No.: 50292-91-6); or combinations thereof.

[0062] Suitable color developers for the thermochromic system include, particularly, weak acids, which act as proton donors, changing the color of the thermochromic dye between its leuco form and its protonated colored form. As non-limiting examples, the developer can be selected from: 3,5-di-tert-butylcatechol (CAS No.: 1020-31-1); 4,4'- (l,3-dimethylbutylidene)diphenol (CAS No.: 6807-17-6); or 2,2'-biphenol (CAS No.: 1806-29-).

[0063] Suitable solvents for use in the thermochromic system include, particularly solvents having a relatively large molecular weight, and which are relatively non-polar. Suitable solvents and co-solvents include, for example, aldehydes, thiols, sulfides, ethers, ketones, esters, alcohols, and acid amides. These can be used alone or as mixtures of at least two different solvents.

[0064] Further examples of suitable for providing the weld quality indicator are disclosed in WO 2021 / 158997 A1 , which is hereby incorporated by reference herein.

[0065] In one or more embodiments, the at least one thermochromic dye, the at least one color developer, and the at least one solvent are encapsulated within a capsule, preferably a microcapsule, such as a polymeric shell, to provide an / a (micro)encapsulated thermochromic system. The capsule has may have a mean particle diameter of 1 - 5 pm, preferably 1 - 3 pm.

[0066] The term “particle size” refers in the present document to the area-equivalent spherical diameter of a particle. The particle size distribution can be determined by sieve analysis according to the method as described in ASTM C136 / C136M -14 standard (“Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates).

[0067] The weld quality indicator may be obtained by applying a curable ink formulation comprising the thermochromic system to the surface of the waterproof layer, for example via printing, coating, or spraying. The thermochromic system may be present in the curable ink formulation in an amount of 5 - 60 wt.-%, particularly 5 - 50 wt.-%, based on the total weight of the ink formulation.

[0068] Suitable curable ink formulations to be applied via printing include at least flexographic inks, gravure inks, offset inks, and screen inks. The curable ink formulation can be water-based, solvent-based, or UV-curable, depending upon the chosen application method.

[0069] In one or more embodiments, the weld quality indicator is obtained by applying an UV-curable ink formulation comprising the thermochromic system to the surface of the waterproof layer. In these embodiments, the ink that is present in form of one or more discontinuous lines on the surface of the waterproof layer is a at least partially cured UV-curable ink.

[0070] Suitable curable ink formulations comprising the thermochromic system and methods for preparation thereof have been disclosed in WO 2021 / 158997 A1 . Furthermore, suitable ink formulations for use in present invention are commercially available, for example, from Chromatic Technologies Inc.

[0071] The waterproofing layer preferably comprises at least one polymer selected from polyvinylchloride, polyolefin, halogenated polyolefin, rubber, and ketone ethylene ester.

[0072] Suitable PVC resins for use in the membrane include the ones having a K-value determined by using the method as described in ISO 1628-2-1998 standard in the range of 50 - 85, preferably 65 - 75. The K-value is a measure of the polymerization grade of the PVC-resin, and it is determined from the viscosity values of the PVC homopolymer as virgin resin, dissolved in cyclohexanone at 30° C.

[0073] Suitable polyolefins for use in the membrane include, for example, polyethylene, ethylene copolymers, polypropylene, propylene copolymers. Especially suitable polyolefins include thermoplastic polyolefin elastomers (TPO-E), particularly heterophasic propylene copolymers. Heterophasic polymers are polymer systems comprising a high crystallinity base polyolefin and a low-crystallinity or amorphous polyolefin modifier. The heterophasic phase morphology consists of a matrix phase composed primarily of the base polyolefin and a dispersed phase composed primarily of the polyolefin modifier.

[0074] Suitable commercially available heterophasic propylene copolymers include reactor blends of the base polyolefin and the polyolefin modifier, also known as “in-situ TPOs” or “reactor TPOs or “impact copolymers (ICP)”, which are typically produced in a sequential polymerization process, wherein the components of the matrix phase are produced in a first reactor and transferred to a second reactor, where the components of the dispersed phase are produced and incorporated as domains in the matrix phase. Heterophasic propylene copolymers comprising polypropylene homopolymer as the base polymer are often referred to as “heterophasic propylene copolymers (HECO)” whereas heterophasic propylene copolymers comprising polypropylene random copolymer as the base polymer are often referred to as “heterophasic propylene random copolymers (RAHECO)”. The term “heterophasic propylene copolymer” encompasses in the present disclosure both the HECO and RAHECO types of the heterophasic propylene copolymers. Suitable rubbers for use in the membrane include, for example, styrene-butadiene rubber (SBR), ethylene propylene diene monomer (EPDM), butyl rubber, polyisoprene, polybutadiene, natural rubber, polychloroprene rubber, ethylenepropylene rubber (EPR), nitrile rubber, acrylic rubber, and silicone rubber, and chemically crosslinked versions of the aforementioned rubbers.

[0075] According to one or more embodiments, the waterproofing layer comprises at least at least 35 wt.-%, preferably at least 45 wt.-%, more preferably at least 55 wt.-%, based on the total weight of the waterproofing layer, of at the least one polymer selected from polyvinylchloride, polyolefin, halogenated polyolefin, rubber, and ketone ethylene ester, preferably from polyvinylchloride, polyolefin, and rubber, more from preferably polyvinylchloride resin and polyolefin, even more preferably from polyvinylchloride resin, polypropylene, and propylene copolymers, still more preferably from polyvinylchloride resin and heterophasic propylene copolymers.

[0076] According to a first embodiment, the waterproofing layer comprises at least one polyvinylchloride-based waterproofing layer comprising:

[0077] - 25 - 65 wt.-%, preferably 30 - 60 wt.-% of a polyvinylchloride resin, - 15 - 50 wt.-%, preferably 25 - 45 wt.-% of at least one plasticizer for polyvinylchloride resin, and

[0078] - 0 - 30 wt.-%, preferably 0 - 25 wt.-% of at least one inorganic filler, all proportions being based on the total weight of the waterproofing layer.

[0079] Suitable polyvinyl chloride resins include those produced by suspension polymerization (also referred to as S-PVC) as well as those produced by emulsion polymerization (also referred to as E-PVC).

[0080] The polyvinylchloride resin may have a K-value determined by using the method as described in ISO 1628-2-1998 standard in the range of 50 - 85, more preferably 65 - 75. The K-value is a measure of the polymerization grade of the polyvinylchloride and it is determined from the viscosity values of the polyvinylchloride homopolymer as virgin resin, dissolved in cyclohexanone at 30°C.

[0081] The type of the at least one plasticizer for polyvinylchloride resin is not particularly restricted in the present invention. Suitable plasticizers for the PVC-resin include but are not restricted to, for example, linear or branched phthalates such as di-isononyl phthalate (DINP), di-nonyl phthalate (L9P), diallyl phthalate (DAP), di-2-ethylhexyl- phthalate (DEHP), dioctyl phthalate (DOP), diisodecyl phthalate (DIDP), and mixed linear phthalates (911 P). Other suitable plasticizers include phthalate-free plasticizers, such as trimellitate plasticizers, adipic polyesters, and biochemical plasticizers. Examples of biochemical plasticizers include epoxidized vegetable oils, for example, epoxidized soybean oil and epoxidized linseed oil and acetylated waxes and oils derived from plants, for example, acetylated castor wax and acetylated castor oil.

[0082] Particularly suitable phthalate-free plasticizers to be used in the waterproofing layer include alkyl esters of benzoic acid, dialkyl esters of aliphatic dicarboxylic acids, polyesters of aliphatic dicarboxylic acids or of aliphatic di-, tri- and tetrols, the end groups of which are unesterified or have been esterified with monofunctional reagents, trialkyl esters of citric acid, acetylated trialkyl esters of citric acid, glycerol esters, benzoic diesters of mono-, di-, tri-, or polyalkylene glycols, trimethylolpropane esters, dialkyl esters of cyclohexanedicarboxylic acids, dialkyl esters of terephthalic acid, trialkyl esters of trimellitic acid, triaryl esters of phosphoric acid, diaryl alkyl esters of phosphoric acid, trialkyl esters of phosphoric acid, and aryl esters of alkanesulphonic acids.

[0083] According to one or more embodiments, the at least one plasticizer for the PVC resin is selected from the group consisting of phthalates, trimellitate plasticizers, adipic polyesters, and biochemical plasticizers.

[0084] According to a second embodiment, the waterproofing layer comprises:

[0085] - 25 - 65 wt.-%, preferably 30 - 60 wt.-% of at least one polyolefin, - 10 - 50 wt.-%, preferably 15 - 45 wt.-% of at least one flame retardant, and - 0 - 30 wt.-%, preferably 0 - 25 wt.-% of at least one inorganic filler, all proportions being based on the total weight of the waterproofing layer.

[0086] According to one or more embodiments, the at least one polyolefin comprises at least one propylene copolymer and / or at least one thermoplastic polyolefin elastomer (TPO). Preferably, the at least one propylene copolymer has a propylene content of at least 60 wt.-%, more preferably at least 70 wt.-%, based on the weight of the propylene copolymer.

[0087] In one or more embodiments, the at least one propylene copolymer is a is a propylene-ethylene copolymer, preferably a random propylene-ethylene copolymer, preferably having an ethylene content of 5 - 20 wt.-%, more preferably 9 - 18 wt.-%, even more preferably 12 - 18 wt.-%, based on the weight of the propylene copolymer.

[0088] Suitable propylene ethylene copolymers are commercially available, for example, under the trade name of Versify® (from Dow Chemicals) and under the trade name of Vistamaxx® (from Exxon Mobil).

[0089] In one or more embodiments, the at least one thermoplastic polyolefin elastomer is a heterophasic propylene copolymer, preferably comprising:

[0090] - A) at least one polypropylene having a melting temperature (Tm) of 100°C or more, preferably a propylene homopolymer and / or a random copolymer of propylene having a comonomer content of less than 10 wt.-%, preferably less than 5 wt.-%, based on the weight of the copolymer and

[0091] - B) at least one polyolefin having a glass transition temperature (Tg) of -20°C or less, preferably an ethylene copolymer having a comonomer content of at least 5 wt.- %, preferably at least 10 wt.-%, based on the weight of the copolymer, preferably having a glass transition temperature (Tg) of -25°C or less, more preferably -35°C or less, preferably an ethylene-propylene rubber (EPR), wherein the heterophasic propylene copolymer comprises a matrix phase composed primarily of A), and a dispersed phase composed primarily of B).

[0092] According to one or more embodiments, the heterophasic propylene copolymer is a reactor blend of A) and B), wherein the reactor blend has preferably been obtained by using a sequential polymerization process, wherein constituents of the matrix phase are produced in a first reactor and transferred to a second reactor where constituents of the dispersed phase are produced and incorporated as domains into the matrix phase. Particularly suitable heterophasic propylene copolymers include, for example, “reactor TPOs” and “soft TPOs” produced with LyondellBasell's Catalloy process technology, which are available under the trade names of Adflex®, Adsyl®, Clyrell®, Hifax®, Hiflex®, and Softell®, such as Hifax® CA 10A, Hifax® CA 12A, and Hifax® CA 60 A, and Hifax® CA 212 A. Further suitable heterophasic propylene copolymers are commercially available under the trade name of Borsoft® (from Borealis Polymers), such as Borsoft® SD233 CF.

[0093] Suitable flame retardants to be used in the waterproofing layer include, for example, magnesium hydroxide, aluminum trihydroxide, antimony trioxide, ammonium polyphosphate, and melamine-, melamine resin-, melamine derivative-, melamineformaldehyde-, silane-, siloxane-, and polystyrene-coated ammonium polyphosphates.

[0094] Other suitable flame retardants include, for example, 1 , 3, 5-triazi ne compounds, such as melamine, melam, melem, melon, ammeline, ammelide, 2-ureidomelamine, acetoguanamine, benzoguanamine, diaminophenyltriazine, melamine salts and adducts, melamine cyanurate, melamine borate, melamine orthophosphate, melamine pyrophosphate, dimelamine pyrophosphate and melamine polyphosphate, oligomeric and polymeric 1 ,3,5-triazine compounds and polyphosphates of 1 ,3,5- triazine compounds, guanine, piperazine phosphate, piperazine polyphosphate, ethylene diamine phosphate, pentaerythritol, borophosphate, 1 ,3,5- trihydroxyethylisocyanaurate, 1 ,3,5-triglycidylisocyanaurate, triallylisocyanurate and derivatives of the aforementioned compounds.

[0095] Suitable flame retardants are commercially available, for example, under the trade name of Martinal® and Magnifin® (both from Albemarle) and under the trade names of Exolit® (from Clariant), Phos-Check® (from Phos-Check) and FR CROS® (from Budenheim).

[0096] Suitable inorganic fillers for use in the waterproofing layer include sand, granite, calcium carbonate, clay, expanded clay, diatomaceous earth, pumice, mica, kaolin, talc, dolomite, xonotlite, perlite, vermiculite, Wollastonite, barite, magnesium carbonate, calcium hydroxide, calcium aluminates, silica, fumed silica, fused silica, aerogels, glass beads, hollow glass spheres, ceramic spheres, bauxite, comminuted concrete, and zeolites. The term “calcium carbonate” as inert inorganic filler refers in the context of the present document to calcitic fillers produced from chalk, limestone, or marble by grinding and / or precipitation.

[0097] The waterproofing layer can further comprise one or more additives, for example, UV- and heat stabilizers, antioxidants, flame retardants, dyes, pigments such as titanium dioxide and carbon black, matting agents, antistatic agents, impact modifiers, biocides, and processing aids such as lubricants, slip agents, antiblock agents, and denest aids.

[0098] The waterproofing layer may have a thickness of 0.5 - 5 mm, preferably 0.75 - 4 mm, more preferably 1 - 3.5 mm, even more preferably 1.2 - 3 mm. A thickness of a polymeric layer can be determined, for example, by using the measurement method as defined in EN 1849-2 standard.

[0099] In one or more embodiments, the membrane is a multi-ply membrane comprising, in addition to the waterproofing layer, a further waterproofing layer, wherein the waterproofing layer and the further waterproofing layer are preferably directly connected to each other over at least a portion of their opposing major surfaces. The composition of the further waterproofing layer may be same of different than the waterproofing layer. However, it is generally preferred that the waterproofing layers comprise the same polymer basis to ensure compatibility between the waterproofing layers.

[0100] It may further be preferred to include a reinforcing layer to the structure of the roofing membrane to improve mechanical properties of the membrane. The reinforcing layer may be fully embedded into the waterproofing layer or adhered to one of the major surfaces of the waterproofing layer or the further waterproofing layer. The expression “fully embedded” is understood to mean that the reinforcing layer is fully covered by the matrix of the waterproofing layer.

[0101] According to one or more embodiments, the membrane comprises a reinforcing layer that is fully embedded into the waterproofing layer or adhered to one of the major surfaces of the waterproofing layer, wherein the reinforcing layer is selected from non-woven fabrics, woven fabrics, and laid scrims comprising synthetic organic and / or inorganic fibers. The term “non-woven fabric” refers in the present disclosure to materials composed of fibers, which are bonded together by using chemical, mechanical, or thermal bonding means, and which are neither woven nor knitted. Non-woven fabrics can be produced, for example, by using a carding or needle punching process, in which the fibers are mechanically entangled to obtain the nonwoven fabric. In chemical bonding, chemical binders such as adhesive materials are used to hold the fibers together in a non-woven fabric. Typical materials for the non-woven fabrics include synthetic organic and inorganic fibers.

[0102] The term “laid scrim” refers in the present disclosure web-like non-woven products composed of at least two sets of parallel yarns (also designated as weft and warp yarns), which lay on top of each other and are chemically bonded to each other. The yarns of a non-woven scrim are typically arranged with an angle of 60 - 120°, such as 90 ± 5°, towards each other thereby forming interstices, wherein the interstices occupy more than 60% of the entire surface area of the laid scrim.

[0103] According to one or more embodiments, the synthetic organic fibers of the reinforcing layer are selected from polyethylene, polypropylene, polyester, nylon, and aramid fibers. According to one or more embodiments, the inorganic fibers of the reinforcing layer are selected from glass, carbon, metal, and wollastonite fibers.

[0104] The reinforcing layer may be a non-woven fabric, preferably a non-woven fabric having a mass per unit weight of not more than 300 g / m2, more preferably not more than 200 g / m2, such as 15 - 300 g / m2, preferably 25 - 250 g / m2, preferably 35 - 200 g / m2, more preferably 40 - 150 g / m2.

[0105] The membrane can be provided in form of a roll, which is delivered to the construction site and unwound to provide sheets having a width of 1 - 5 m and length of several times the width. Moreover, the membrane can also be provided in the form of planar bodies, which are used for repairing damaged locations in existing adhered roofing systems.

[0106] In one or more embodiments, the membrane is a roofing membrane or flashing membrane, preferably a roofing membrane. The preferences given above for the membrane and to the weld quality indicator apply equally to all aspects of the present invention unless otherwise stated.

[0107] Another subject of the present invention is a method for preparing a membrane with a weld quality indicator according to any one of previous claims, the method comprising steps of: i. Providing a prefabricated membrane having a waterproof layer and ii. Printing a curable ink formulation comprising a thermochromic system to a surface of the waterproof layer, wherein the curable ink formulation is applied to the surface of the waterproof layer in a pattern comprising one or more discontinuous lines running substantially parallel and adjacent to an edge of the waterproof layer and composed of a series of spaced apart ink-covered areas.

[0108] The distance between subsequent ink-covered areas in said discontinuous line(s) is preferably at least 0.5 mm, such as least 1 .5 mm, particularly at least 2.5 mm, especially at least 3.5 mm and / or not more than 100 mm, such as not more than 75 mm, particularly not more than 65 mm, especially not more than 50 mm.

[0109] In one or more embodiments, the distance between subsequent ink-covered areas in said discontinuous line(s) is 1 .5 - 65 mm, preferably 2.5 - 55 mm, more preferably 3.5 - 45 mm, even more preferably 5 - 35 mm, still more preferably 5 - 25 mm.

[0110] In one or more embodiments, the method comprises a further step of curing the ink, preferably by UV curing and / or drying.

[0111] Step ii. of the method can be conducted using any conventional printing or coating technique that are known to the skilled person, such as by using a flexographic printer, ink jet printer, or a slot-die coater.

[0112] Step i. of providing the prefabricated membrane may include melt-processing a composition comprising the constituents of the waterproofing layer followed by meltshaping the thus obtained melted-processed composition using a suitable technique, such as extrusion and / or calendering. Suitable extrusion apparatuses comprising at least one extruder and an extruder die are well known to a person skilled in the art. Any conventional extruders, for example, a ram extruder, single screw extruder, or a twin-screw extruder may be used.

[0113] The further details of the step of providing the membrane depend on the embodiment of the membrane, in particular whether the membrane is a singly-ply or a multi-ply membrane.

[0114] Still another subject of the present invention is a method for covering a substrate comprising steps of:

[0115] I) providing a first sheet of a membrane according to the present invention,

[0116] 11 japplying said first sheet to a surface of the substrate,

[0117] III) providing a second sheet of a membrane according to the present invention,

[0118] IV) applying said second sheet to the surface of the substrate with a second edge portion of said second sheet resting on a first edge portion of said first sheet providing an overlapped edge portion,

[0119] V) bonding the opposing surfaces of said first and second edge portions to each other by using heat-welding means, wherein the weld quality indicator of the second sheet is present on a top surface of the second edge portion.

[0120] Step V) of the method may be conducted using a hot-air welding tool or an induction heat welding tool.

[0121] Furthermore, step V) preferably comprises heating the opposing surfaces of said first and second edge portions to a temperature above the melting point of said first and second sheet resulting in passing of the heat through the second sheet to the weld quality indicator causing it to change its color.

[0122] In one or more embodiments, the substrate is a roof substrate, preferably selected from a roof deck, insulation board, cover board, or a parapet wall.

[0123] Examples Preparation of test specimens

[0124] Test specimens composed of a strip of a roofing membrane and a weld quality indicator were prepared by printing an UV-curable ink formulation comprising a thermochromic system to the upper surface of the membrane strip having dimensions of 20.32 x 30.48 cm. The ink formulation was applied to the upper surface of the membrane strip in a pattern comprising one continuous line (reference example) or one or two discontinuous lines (inventive examples) running substantially parallel and adjacent to an edge of the membrane strip.

[0125] The membrane strips were cut from sheets of a commercially available multi-ply PVC-based roofing membrane (Sarnafil S327 60 mils) and an UV-curable thermochromic flexographic ink (from CTI Technologies Inc.) was used for preparing the weld quality indicators.

[0126] The dashed lines of the weld quality indicator were composed of spaced apart ink- coated areas having shape of a square and of dimensions of 6.35 x 6.35 mm (with, height). The weld quality indicator composed of one single continuous or dashed line was positioned approximately in middle of the planned weld seam ca. 10 mm from the edge of the membrane strip.

[0127] In case of a weld quality indicator composed of two dashed lines, the distance between two paral lelly running spaced apart discontinuous lines was approximately 6.35 mm and the first discontinuous line was positioned near the edge of the membrane strip and the second one near the edge of the planned weld seam ca. 20 mm from the edge of the membrane strip.

[0128] Testing of weld quality indicators

[0129] A first membrane strip (A) without a weld quality indicator was first laid against a surface of a substate. Another membrane strip (B) having a weld quality indicator deposited on one of its long edge portions was then positioned over the first membrane strip (A) to form a weldable seam having a width of at least 20 mm and running in longitudinal direction of membrane strips as shown in Figure 4a. The opposing surfaces of the edge portions of the first and second membrane strips (A, B) were then bonded to each other by heat welding using a Leister hand-held welding machine.

[0130] A third membrane strip (C) was then positioned over the first and second membrane strips in overlapping position along one of the short edges of the two other membrane strips (A, B) to form a 3-way overlap joint (“T-joint”) as shown in Figure 4b. The overlapped portion of the third membrane strip (C) was then bonded to the short edge portions of the first and second membrane strips (A, B) by heat welding using the hand-held welding machine.

[0131] The welding of the overlapped edge portions of the membrane strips was conducted using a welding speed of 2 - 4 m / s. The ink of the weld quality indicator had originally a light blue color, which vanished when the temperature of the ink reached a certain threshold temperature indicating that an appropriate temperature of the membrane materials and correspondingly a sufficient weld seam quality / strength should have been reached.

[0132] The quality of the heat-welded seams was tested by cutting a rectangular piece of the overlapping edge portion of the upper membrane and removing the piece by peeling. The rectangular piece had a long edge running perpendicular through the width of the welded seam as shown in Figures 5a - 5d. In case of good weld quality, removing the rectangular piece of the upper membrane resulted in:

[0133] 1) exposure of the back layer (black) of the lower membrane, since the interlayer bond strength between the welded membrane portions was higher than that between the top and back layers of the membrane (Figures 5a and 5d) or

[0134] 2) breaking of the rectangular piece before it could be pulled off, since the interlayer bond strength between the welded membrane portions was higher than the tensile strength of the membrane (Figure 5c).

[0135] In case of inacceptable weld quality, removing of the rectangular piece exposed the top layer (white) of the lower membrane indicating a too low interlayer bond strength between the welded edge portions (Figure 5b).

[0136] As can be seen in Figure 5b, the presence of a coated weld quality indicator in form of a continuous line results in formation of a region of non-welded material between the overlapped portions of the membrane strips in the area of the weld indicator. However, in case the coated weld indicator is composed of one discontinuous (dashed) line as shown in Figure 5c or of two discontinuous lines as shown in Figure 5d, no continuous region of non-welded material is formed in the weld area between the overlapped portions of the membrane strips enabling formation of a continuous welded seam.

[0137] The experimental data thus clearly demonstrates that a weld indicator obtained by coating an ink comprising a thermochromic system to a surface of a PVC-based roofing membrane will in some cases interfere with the weld formation between the overlapped portions of the membranes. Particularly, when a T-joint is formed over a region that contains a continuous line of the ink the result is that the coated region will extend perpendicularly across the entire weld seam. This will result in a region extending across the weld seam where the formation of the weld has been blocked and the continuous weld seam is thus interrupted.

[0138] However, when a dashed pattern of sufficient dimensions has been chosen instead, the coated region will never extend across the entire width of the weld seam, and thus there will be no region extending across the entire weld seam where the formation of the weld has been blocked. Consequently, by using a dashed line the continuous weld seam is never interrupted. There is thus no need to remove the ink from the surface of the membrane when a dashed pattern is used to ensure a continuous weld seam.

Claims

Claims1 . A membrane (1 ) comprising a waterproof layer (2) having opposed top and bottom surfaces and a weld quality indicator (3) deposited on one of the opposed surfaces of the waterproof layer (2), wherein the weld quality indicator (3) comprises one or more discontinuous lines running substantially parallel and adjacent to an edge (e1 , e2) of the waterproof layer (2), wherein the discontinuous line(s) is / are composed of a series of spaced apart areas (on the surface of the waterproof layer) covered with an ink comprising a thermochromic system.

2. The membrane according to claim 1 , wherein the distance (D1 , D11 , D12) between subsequent ink-covered areas in said discontinuous line(s) is at least 1 .5 mm, preferably at least 2.5 mm3. The membrane according to claim 1 or 2, wherein the distance (D1 , D11 , D12) between subsequent ink-covered areas in said discontinuous line(s) is 1 .5 - 65 mm, preferably 2.5 - 55 mm.

4. The membrane according to any one of previous claims, wherein the spaced apart ink-covered areas have a shape of a letter, logo, square, rectangle, circle, oval, or a triangle.

5. The membrane according to any one of previous claims, wherein the discontinuous line(s) is / are positioned a distance (D2, D21 , D22) of not more than 50 mm, preferably not more than 45 mm inward from the edge of the waterproof layer (2).

6. The membrane according to any one of previous claims, wherein the weld quality indicator is composed of two or more spaced apart discontinuous lines running substantially parallel to each other.

7. The membrane according to claim 6, wherein the distance (D3) between two discontinuous lines is at least 1 .5 mm, preferably at least 2.5 mm apart, particularly 1 .5 - 30 mm, especially 2.5 - 25 mm.

8. The membrane according to claim 6 or 7, wherein the discontinuous lines are positioned such that the ink-covered areas of adjacent discontinuous lines do not line up in rows (are offset).

9. The membrane according to any one of previous claims, wherein the thermochromic system comprises at least one thermochromic dye, at least one color developer, and at least one solvent.

10. The membrane according to claim 9, wherein the at least one thermochromic dye, at least one color developer, and at least one solvent are encapsulated within a capsule, preferably a microcapsule, to provide an / a (micro)encapsulated thermochromic system.

11. The method according to claim 10, wherein the capsule has a mean particle diameter of 1 - 5 pm, preferably 1 - 3 pm.

12. The membrane according to any one of previous claims, wherein the ink is a at least partially cured UV-curable ink.

13. The membrane according to any one of previous claims, wherein the waterproofing layer (2) comprises at least one polymer selected from polyvinylchloride, polyolefin, halogenated polyolefin, rubber, and ketone ethylene ester.

14. The membrane according to any one of previous claims, wherein the membrane is a roofing membrane or a flashing membrane.

15. A method for preparing a membrane with a weld quality indicator according to any one of previous claims, the method comprising steps of: i. Providing a prefabricated membrane having a waterproof layer and ii. Printing a curable ink formulation comprising a thermochromic system to a surface of the waterproof layer, wherein the curable ink formulation is applied to the surface of the waterproof layer in a pattern comprising one or more discontinuous linesrunning substantially parallel and adjacent to an edge of the waterproof layer.

16. The method according to claim 15, wherein the distance between subsequent ink-covered areas in said discontinuous line(s) is at least 1.5 mm, preferably at least 2.5 mm.

17. The method according to claim 15 or 16, wherein the distance between subsequent ink-covered areas in said discontinuous line(s) is 1 .5 - 65 mm, preferably 2.5 - 55 mm.

18. The method according to any one of claims 15-17 comprising a further step of curing the ink, preferably by UV curing and / or drying.

19. The method according to any one of claims 15-18, wherein step ii. is conducted using a flexographic printer, inkjet printer, or a slot-die coater.

20. A method for covering a substrate comprising steps:I) providing a first sheet of a membrane according to any one of claims 1 - 14,II) applying said first sheet to a surface of the substrate,III) providing a second sheet of a membrane according to any one of claims 1-14,IV) applying said second sheet to the surface of the substrate with a second edge portion of said second sheet resting on a first edge portion of said first sheet providing an overlapped edge portion,V) bonding the opposing surfaces of said first and second edge portions to each other by using heat-welding means, wherein the weld quality indicator of the second sheet is present on a top surface of the second edge portion.

21. The method according to claim 20, wherein step V) is conducted using a hot-air welding tool or an induction heat welding tool.

22. The method according to claim 20 or 21 , wherein step V) comprises heating the opposing surfaces of said first and second edge portions (to a temperature above the melting point of said first and second sheet) resulting in passing of the heat through the second sheet to the weld quality indicator causing it to change its color.

23. The method according to any one of claims 20-22, wherein the membrane is a roofing membrane or a flashing membrane and / or the substrate is a roof substrate.

Images