Acoustic interlayer comprising a transparent viscoelastic damping adhesive core layer

Abstract

The present invention relates to an interlayer for laminated glasses comprising two outer layers of a material selected from poly(vinyl butyral) (PVB) and poly(ethylene-vinyl acetate) (EVA), assembled by means of a viscoelastic damping adhesive layer formed by a material comprising from 21% to 62% by weight of at least one acrylic polymer, relative to the total weight of the dry material; from 22% to 60% by weight of at least one tackifier, relative to the total weight of the dry material; and from 7% to 43% by weight of at least one plasticizer, relative to the total weight of the dry material.

Description

[0001] Description

[0002] Title: Acoustic interlayer comprising a transparent viscoelastic damping adhesive core layer

[0003] The present invention relates to an interlayer for laminated glass having good vibration damping properties and good optical properties, as well as its manufacturing method. It also relates to a laminated glazing comprising such an interlayer as well as the use of said glazing as a vehicle windshield and / or as building glazing to dampen vibrations and / or increase the transmission loss of noise, in particular of airborne origin, in particular over the audible frequency decade between 1 kHz and 10 kHz, at room temperature. In particular, the laminated glazing may be a vehicle windshield.

[0004] Laminated glazing is commonly used in the transportation sector, particularly in windshields for automobiles, ships, and aircraft, as well as in construction. The role of laminated glazing is to eliminate the risk of fragments being thrown out in the event of sudden breakage and to act as a burglar-resistant material. Laminated glazing also offers the advantages of reducing the transmission of UV and / or infrared radiation and reducing the transmission of noise from the outside to the inside of vehicles, thereby improving the vibration and acoustic comfort of passengers or occupants.

[0005] Such glazing also has good optical properties.

[0006] Laminated glass units are generally composed of a first sheet of glass and a second sheet of glass, between which there is an interlayer. These units are manufactured using a known process, for example by hot and pressure assembly.

[0007] In the case of laminated glazing with vibration damping properties, a three-layer interlayer has been described comprising two layers of poly(vinyl butyral) (PVB), also called "outer layers" or "skins", assembled by means of a layer of PVB, also called "inner layer" or "core". The PVB of the inner layer has a different physicochemistry than the PVB of the two outer layers (see for example, US patent Nos. 5,340,654, 5,190,826, US 2006 / 0210782 and US 2016 / 0171961). Indeed, the PVB of the core has a lower residual hydroxyl content (-OH group) (generally between 8% and 10%) than that of the PVB of the skins (generating between 18 and 20%). Residual hydroxyl content refers to the amount of hydroxyl groups remaining as side groups on the vinyl chain of PVB after acetalization of poly(vinyl alcohol) by butyraldehyde.The higher hydroxyl content of the outer PVB layers results in a reduced affinity for the plasticizer compared to the inner layer, leading to a migration of the plasticizer to the PVB of the inner layer during the autoclaving step. The plasticizer increases the viscous component and thus improves the vibration damping properties of the viscoelastic inner layer, while the outer layers are rigid, thus ensuring the handling and mechanical strength of the interlayer. Rigid outer layers generally contribute little to the vibration damping properties compared to the inner layer.

[0008] In order to improve the sound insulation performance of laminated glazing units comprising a three-layer interlayer as described above, it was considered to further reduce the residual hydroxyl group content of the PVB of the inner layer in order to increase its plasticizer content. This, however, led to a shift in the glass transition temperature (Tg) value of the PVB of the core towards too low temperatures and therefore towards higher frequencies, leading to effective damping of vibrations outside the initial targeted frequency range (i.e. outside 1 kHz to 10 kHz). Vibration damping over the frequency interval of interest was therefore reduced at the operating temperatures of the glazing.

[0009] An increase in the residual hydroxyl group content of the inner layer PVB and a decrease in its plasticizer content were also considered. However, this led to a decrease in the viscous component of the core PVB and a shift in the glass transition temperature (Tg) of said PVB towards too high temperatures, also reducing the vibration damping power over the frequency range of interest at room temperature.

[0010] These two approaches, which involve playing on the hydroxyl group content of the internal PVB layer of the interlayers, have thus led to an impasse linked to the undesirable, but inevitable, increase / decrease in the glass transition temperature (Tg).The idea behind the present invention is to replace, in a three-layer interlayer (as defined above), the internal PVB layer with a viscoelastic damping adhesive layer of specific composition, different from PVB, which is transparent and which has a damping factor (or loss factor "tan 5") high (preferably greater than or equal to 2) over the frequency decade between 1 kHz and 10 kHz, at temperatures between 0°C and 40°C; thus giving laminated glazing provided with such a layer not only good acoustic insulation performance (more particularly high acoustic attenuation properties for airborne noise or high vibration damping properties) but also good optical properties (such as high light transmission and clarity factor and low haze factor).In the present application, the term "viscoelastic damping adhesive layer" means: a vibration damping adhesive layer of a viscoelastic material or an adhesive layer of a viscoelastic material having vibration damping.

[0011] The Applicant has thus developed a particular viscoelastic damping adhesive layer to form the core of a three-layer interlayer for laminated glass, said core layer being formed by a material comprising:

[0012] - from 21% to 62% by weight of at least one acrylic polymer, relative to the total weight of the dry material, preferably from 21% to 51% by weight, and more preferably from 21% to 35% by weight,

[0013] - from 22% to 60% by weight of at least one tackifying agent, relative to the total weight of the dry material, preferably from 22% to 35% by weight, and more preferably from 22% to 26% by weight, and

[0014] - from 7% to 43% by weight of at least one plasticizing agent, relative to the total weight of the dry material, preferably from 12% to 31% by weight and more preferably from 16% to 26% by weight.

[0015] Indeed, it was surprisingly found by the inventors that the combination of the following three components: at least one acrylic polymer with at least one tackifying agent and with at least one plasticizing agent, had to be present in the core layer of an interlayer for laminated glazing, and these in the proportions indicated above, in order to obtain laminated glazings having good acoustic insulation performance and good optical properties.The composition of the viscoelastic damping adhesive layer has in fact been chosen so that it is transparent (once in the laminated glazing) and so that the vibration damping (in other words the loss factor, also called damping factor "tan 5") is maximum over the frequency decade between 1 kHz and 10 kHz, preferably between 1 Hz and 10 kHz, at a temperature between 0°C and 40°C, preferably between 10°C and 30°C, more preferably between 15°C and 25°C and even more preferably for a temperature close to or equal to 20°C.

[0016] The present application therefore has as its first subject an interlayer for laminated glass comprising two external layers made of a material chosen from poly(vinyl butyral) (PVB) and poly(ethylene vinyl acetate) (EVA), assembled by means of a viscoelastic damping adhesive layer formed by a material comprising:

[0017] - from 21% to 62% by weight of at least one acrylic polymer, relative to the total weight of the dry material, preferably from 21% to 51% by weight, and more preferably from 21% to 35% by weight,

[0018] - from 22% to 60% by weight of at least one tackifying agent, relative to the total weight of the dry material, preferably from 22% to 35% by weight, and more preferably from 22% to 26% by weight, and

[0019] - from 7% to 43% by weight of at least one plasticizing agent, relative to the total weight of the dry material, preferably from 12% to 31% by weight and more preferably from 16% to 26% by weight.

[0020] The two outer layers of the interlayer are preferably layers of poly(vinyl butyral) (PVB).

[0021] The material of the viscoelastic damping adhesive inner layer may have a glass transition temperature of between -70°C and 10°C, in particular between -45°C and 0°C, and preferably between -45°C and -20°C. Thus, at approximately 20°C, a maximum loss factor (tan 5) may be included in an audible frequency range, located between 1 kHz and 10 kHz.

[0022] According to the invention, the glass transition temperature (Tg) of the viscoelastic damping adhesive inner layer can be measured by differential scanning calorimetry (DSC). The glass transition temperature can be determined using the midpoint method as described in ASTM-D-3418 for differential scanning calorimetry. The measuring device used by the applicant is the Discovery DSC model from TA Instruments.

[0023] Preferably, a glass transition temperature Tg is determined by dynamic mechanical analysis (DMA) or dynamic mechanical spectrometry (DMA). The value of Tg is determined by plotting an isofrequency curve of the loss factor as a function of the temperature of the material. The temperature at which the loss factor value is maximum is equal to the glass transition temperature Tg. The glass transition temperature depends on the excitation frequency of the material. In this document, the term "glass transition temperature" means the glass transition temperature measured at a frequency of 1 Hz by DMA.

[0024] As stated above, the internal viscoelastic damping layer, according to the invention, is formed by a material comprising at least one acrylic polymer, at least one tackifying agent, and at least one plasticizing agent, in proportions as defined above. The internal viscoelastic damping layer, according to the invention, is transparent.

[0025] The acrylic polymer(s) may be formed from monomers selected from the group consisting of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, pentyl acrylate, pentyl methacrylate, isoamyl acrylate, isoamyl methacrylate, hexyl acrylate, hexyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, octyl acrylate, methacrylate octyl, isooctyl acrylate, isooctyl methacrylate, nonyl acrylate, nonyl methacrylate, isononyl acrylate, isononyl methacrylate, isobornyl methacrylate, decyl acrylate, decyl methacrylate, dodecyl acrylate,dodecyl methacrylate, tridecyl acrylate, tridecyl methacrylate, hexadecyl acrylate, hexadecyl methacrylate, octadecyl acrylate, octadecyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, vinyl formate, vinyl acetate, vinyl propionate, 2-hydroxyethyl acrylate, hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, acrylic acid, styrene and acrylonitrile.,

[0026] The acrylic polymer(s) may be copolymers, formed from at least two monomers selected from the group formed by the monomers previously defined, or the acrylic polymer(s) may be formed by mixing at least two monomers selected from the group formed by the monomers previously defined. In one embodiment, the acrylic polymer(s) may be formed by mixing at least two homopolymers obtained from a monomer selected from the group formed by the monomers previously defined.

[0027] Preferably, the inner layer may comprise two different acrylic polymers. One of the two polymers may be 2-ethylhexyl acrylate (in English called 2-ethylhexyl acrylate or “2-EHA”) and / or butyl acrylate (in English called butylacrylate or “BA”). Preferably, one of the two polymers is 2-ethylhexyl acrylate (2-EHA) and the other of the two polymers is butyl acrylate (BA). The mass ratio between 2-ethylhexyl acrylate (2-EHA) and butyl acrylate (BA) may be between 2 and 4, and is preferably equal to 3.

[0028] The material may comprise another polymer that is not an acrylic polymer. Such another polymer may be formed from at least one monomer selected from styrene and methyl methacrylate.

[0029] The acrylic polymer(s) according to the invention may be in the form of polymer particles dispersed in water or in an aqueous solvent, also called "latex". The volume average diameter of a polymer particle is preferably between 100 and 10,000 nm, preferably between 250 and 2,500 nm and ideally between 700 and 900 nm. Said diameter is measured using a dynamic light scattering (DLS) device, which is a non-destructive spectroscopic analysis technique for accessing the size of particles suspended in a liquid or of polymer chains in solution with a diameter of approximately 1 to 10,000 nm. The measuring device used by the applicant is the Malvern Mastersizer® model. The small size of the particles makes it possible to limit the diffusion of light by the particles and to increase the transparency of the internal layer of the three-layer interlayer according to the invention.Thus, commercial latexes comprising at least one acrylic polymer can be used to form the inner layer. For example, it is possible to use Arkema ® Encor 4028, Arkema ® Encor 4517, Arkema ® Encor 4500 or Alberdingk ® A&B75070, or Alberdingk ® A&B75222 latexes.

[0030] The material may comprise a first acrylic polymer having a first glass transition temperature Tgi, and a second polymer, acrylic or non-acrylic, having a second glass transition temperature Tg2, higher than Tgi. The difference between the second glass transition temperature Tg2 and between the first glass transition temperature Tgi is preferably higher than 10°C, and preferably higher than 20°C. Thus, it is possible to increase the glass transition temperature of the material compared to the glass transition temperature of a material obtained solely with the first acrylic polymer. Indeed, the glass transition temperature obtained solely with the first acrylic polymer may be too low to present maximum damping of the material in an audible frequency range.

[0031] The acrylic polymer(s) provide the cohesion and adhesion properties necessary for the viscoelastic damping layer.

[0032] The tackifying agent combined with the acrylic polymer(s) and the plasticizing agent to form the viscoelastic damping layer preferably has a high hydrogen content (high degree of conversion of double bonds, by two hydrogen bonds), which results in the reduction of the amber color, on the Gardner color scale, according to ISO 4630. Thus, the Gardner index may be less than 1 or between 1 and 10, preferably between 1 and 2, on the Gardner color scale.

[0033] The tackifying agent may therefore comprise a hydrogenated resin, preferably chosen from rosins, rosin esters, hydrogenated rosin esters, hydrogenated rosin derivatives, terpenes and aliphatic or aromatic synthetic resins derived from petroleum. More preferably, the tackifying agent comprises a hydrogenated rosin resin, in particular a hydrogenated rosin ester, having a Gardner index of less than 1; and being for example of the brand Arakawa ® TFE045 or TFE019 or of the brand Foreverest ® HG90 or HG100. In preferred embodiments, the tackifying agent is used either in powder form in the presence or absence of a solvent, or in the form of solid particles dispersed in a solvent or co-solvent, such as water.

[0034] The tackifying agent used in powder form can be dissolved in a solvent, a co-solvent or even in plasticizing agents depending on their chemical affinity for these compounds.

[0035] The tackifying agent used in the form of solid particles in dispersion may be a glycerol ester of wood resin, preferably abietic acid, having a Gardner index of less than 1 on the Gardner color scale, such as Crystazene 110 produced by the company DRT, another possibility is the pinecrystal range from the company Arakawa. This tackifying agent may also be dispersed in a solvent, a co-solvent or even in plasticizing agents depending on their chemical affinity for these compounds and may also have a volume average diameter of between 100 and 10000 nm, preferably between 500 nm and 1000 nm.

[0036] According to the invention, the amount of tackifying agent is between 22% and 60% by weight, relative to the total weight of the dry material, preferably between 22% and 35% by weight, and more preferably between 22% and 26% by weight.

[0037] The tackifying agent, according to the invention, provides tack, making the viscoelastic damping layer sticky to the touch. The tackifying agent also provides other properties such as: transparency, haze, clarity and UV resistance, necessary for the viscoelastic damping layer for a glazing-type application.

[0038] The plasticizing agent may comprise at least one member selected from a citrate, an adipate, a glycol, or a triethylene glycol derivative. The citrate may be acetyl tributyl citrate. The triethylene glycol derivative may be triethylene glycol bis(2-ethylhexanoate), marketed as Celanese® WVC 3800.

[0039] According to the invention, the quantity of plasticizing agent is between 7% and 43% by weight, relative to the total weight of the dry material, preferably between 12% and 31% by weight, and more preferably between 16% and 26% by weight.

[0040] The presence of the plasticizing agent in the composition of the viscoelastic damping adhesive layer, according to the invention, makes it possible, among other things, to provide mobility to the acrylic polymer chains and thus to shift the Tg of said layer towards lower temperatures, i.e. towards a temperature between 70°C and 10°C, preferably between -45°C and -20°C, as desired.

[0041] The inventors noted with surprise that the combination of the following three components: at least one acrylic polymer with at least one tackifying agent and with at least one plasticizing agent as described above, in the specific quantities stated above, gave the core viscoelastic damping adhesive layer and therefore the three-layer interlayer provided with it, good vibration damping properties, contributing to improved acoustic insulation of the laminated glazing containing this interlayer (more particularly to greater acoustic attenuation of airborne noise), as well as good optical properties, and this:

[0042] - compared to a three-layer interlayer whose inner layer comprises the same components but in different proportions, and

[0043] - compared to a three-layer interlayer whose internal layer is a PVB layer with a low residual level of hydroxyl groups (i.e. between 8% and 10%).

[0044] The improvement in the acoustic insulation of the laminated glazing obtained using an interlayer according to the invention is due to a loss factor tan 5 (determined by dynamic mechanical analysis) of the particular viscoelastic damping adhesive layer of a three-layer interlayer according to the invention, the value of which is greater than or equal to 2, preferably greater than or equal to 3, over the frequency decade between 1 kHz and 10 kHz, preferably over the frequency interval between 1 Hz and 10 kHz, for a temperature range between 0°C and 40°C, preferably between 10°C and 30°C, more preferably between 15°C and 25°C and even more preferably for a temperature close to or equal to 20°C.

[0045] Thus, the inventors have demonstrated that the viscoelastic damping adhesive layer according to the invention, after drying, in a three-layer interlayer according to the invention, made it possible to obtain a loss factor advantageously between 2 and 3, or even 3 and 4 for the internal layer of said interlayer, i.e. 1.5 times to 2 times more than for an internal layer comprising the same components but in different proportions, and 3 times to 4 times more than for a conventional PVB internal layer. The loss factor tan 5 of a material corresponds to the ratio between the energy dissipated in caloric form and the elastic deformation energy. It therefore corresponds to a technical characteristic specific to the nature of a material and reflects its capacity to dissipate energy, in particular acoustic waves. The higher the loss factor, the greater the dissipated energy, the more the material therefore plays its vibration damping function.This loss factor tan 5 varies depending on the temperature and frequency of the incident wave. For a given frequency, the loss factor reaches its maximum value at a temperature, called the glass transition temperature, determined by dynamic mechanical analysis. This loss factor tan 5 can be estimated using a rheometer or any other suitable known device. The rheometer is a device that allows a material sample to be subjected to deformation stresses under precise temperature and frequency conditions, and thus to obtain and process all the rheological quantities characterizing the material. More precisely, the loss factor is measured using a rotation rheometer in oscillation mode, where the sample is subjected to a sinusoidal stress for angular velocities w of 1 to 1000 rad / s in a temperature range from -100°C to 100°C with steps every 5°C.The rheometer used by the Applicant is the MCR 302 model from Anton Paar. It should be noted that the loss factor tan 5 of the inner layer determines the loss factor tan 5 of the interlayer, which is substantially the same value, as long as the volume fraction of the inner layer is not too low.

[0046] Thus, the implementation of an interlayer with an internal layer which has a relatively higher tan 5 loss factor makes it possible to further improve the acoustic insulation performance of the glazing fitted with it.

[0047] In a preferred embodiment, the viscoelastic damping layer is in direct contact with the two outer layers of PVB in an interlayer according to the present invention.

[0048] According to a particular aspect of the invention, the thickness of the internal viscoelastic damping layer has a thickness of between 5 μm and 50 μm, preferably between 10 μm and 30 μm, and more preferably between 15 μm and 25 μm. The use of a core layer whose thickness is of the order of a micrometer makes it possible to reduce the risks of flow of the material forming the core layer at the time of its deposition. This thickness also makes it possible to adjust the rigidity of the three-layer interlayer in order to obtain rigidity on the scale of the laminated glazing respecting the forming and curvature constraints of the final laminated glazing and to ensure the safety of passengers or occupants in the event of breakage of the laminated glass.

[0049] The thickness of the external PVB layers in a three-layer interlayer according to the invention may be between 200 pm and 500 pm, preferably between 300 pm and 400 pm, ideally around 380 pm.

[0050] According to a particular aspect of the invention, the inner layer represents a volume fraction of the interlayer of between 0.2% and 8%, preferably between 0.5% and 8%, and more preferably between 2.5% and 4%. The selection of such a value of volume fraction of the inner layer on the interlayer offers a satisfactory compromise between the requirement of rigidity on the one hand and the performance of the acoustic insulation on the other hand.

[0051] Another aspect of the invention is a method of manufacturing an interlayer for laminated glass as described above, the method comprising the following steps:

[0052] - supply of a first sheet made of a material chosen from poly(vinyl butyral) (PVB) and poly(ethylene vinyl acetate) (EVA),

[0053] - depositing on one of the faces of said first sheet a liquid composition comprising a latex, a tackifying agent, and a plasticizing agent, the latex comprising an emulsion, the emulsion comprising an aqueous continuous phase and a dispersed phase, the dispersed phase comprising at least one acrylic polymer,

[0054] - drying said liquid composition so as to form a viscoelastic damping adhesive layer,

[0055] - application to the viscoelastic damping adhesive layer thus formed of a second sheet made of a material chosen from poly(vinyl butyral) (PVB) and poly(ethylene vinyl acetate) (EVA).

[0056] The deposition of the liquid composition on one of the faces of said first sheet of PVB or EVA preferably takes place by spraying, more particularly by spraying with curtains or blades, or by the known method of liquid deposition from roll to roll, more precisely by the method of a reverse roll coater fed with the liquid composition via a slot (in English nip-fed reverse roll).

[0057] The drying step is preferably carried out continuously, at room temperature and / or in an oven at a temperature between 40°C and 120°C, preferably between 60°C and 100°C. Advantageously, this drying step is carried out under a reduced pressure between 0.01 atm and 1 atm, preferably between 0.1 atm and 0.5 atm, ideally at a pressure equal to 0.25 atm. A second sheet of PVB or EVA is then deposited above the viscoelastic damping adhesive layer resulting from the drying of the liquid composition. In the present application, “room temperature” means a temperature between 0°C and 40°C.

[0058] Thus, the viscoelastic damping adhesive layer is formed from the drying of a liquid composition comprising a latex, a tackifying agent, and a plasticizing agent. The latex comprises an emulsion. The emulsion comprises an aqueous continuous phase and a dispersed phase. The dispersed phase comprises at least one acrylic polymer. The composition may be a dilution of the latex, the tackifying agent, and the plasticizing agent in an aqueous phase.

[0059] The process parameters such as the tension of the PVB sheets in the process and the stability of the rollers and the feeding of the liquid composition through the slot can be controlled in such a way that the tri-layer interlayer according to the invention does not exhibit any waviness defects.

[0060] The invention also relates to laminated glazing comprising:

[0061] - a first sheet of glass,

[0062] - a second sheet of glass,

[0063] - an interlayer as described above, the interlayer being arranged between the first and second glass sheets.

[0064] In particular, laminated glazing can be a vehicle windshield.

[0065] According to a particular aspect of the invention, said first glass sheet has a thickness of between 0.5 and 3 mm, preferably between 1.4 and 2.1 mm, and said second glass sheet has a thickness of between 0.5 and 2.1 mm, preferably between 1.1 and 1.6 mm. The glass sheets are preferably made of soda-lime glass, as is customary for windows. The glass sheets can, however, also be made of other types of glass, for example quartz glass, borosilicate glass or aluminosilicate glass, or rigid transparent plastics, for example polycarbonate or polymethyl methacrylate.

[0066] The technical advantages conferred by an interlayer according to the invention, as described in the present text, also relate to a laminated glazing containing such an interlayer. Thus, the Applicant proposes a laminated glazing comprising a particular interlayer as described above having good acoustic attenuation properties over the frequency decade between 1 kHz and 10 kHz, preferably over the frequency interval between 1 Hz and 10 kHz for a temperature range between 0°C and 40°C, preferably between 10°C and 30°C, more preferably between 15°C and 25°C, and even more preferably for a temperature close to or equal to 20°C; for which said laminated glazing is used.It was found that the interlayer according to the invention also gave the laminated glazing good optical properties, in particular a light transmission greater than 90% in the wavelength range of the visible spectrum, a blur factor of less than 1.5%, and a clarity factor greater than 95%.

[0067] Indeed, the inventors have discovered that a material formed by at least one acrylic polymer, by at least one tackifying agent and by at least one plasticizing agent, in the aforementioned specific proportions, can both have high acoustic attenuation properties and can also form a transparent viscoelastic damping adhesive layer allowing a laminated glazing to have a light transmission factor, a haze factor and a clarity factor suitable for vehicle glazing. In other words, preferably, the light transmission of the laminated glazing according to the invention is greater than 90%, in the wavelength range of the visible spectrum. Preferably, a haze factor of the laminated glazing according to the invention is less than 1.5%. Preferably, a clarity factor of the laminated glazing according to the invention is greater than 95%.

[0068] Generally speaking, light transmission is obtained according to the principles and methods described in standard NF EN 410 (2011).

[0069] In the present application, the term "haze factor" means the ratio between the intensity of all the light diffused by passing through a glazing (diffuse fraction or Id) at an angle greater than 2.5° and between the intensity of the light transmitted through a glazing ( / / .). The haze factor can be measured by spectroscopy techniques. The integration of the intensity over the entire visible range (from 380 nm to 780 nm) makes it possible to determine the normal transmission TL and the diffuse transmission Td. Such a measurement can also be obtained by using a Hazemeter. A glazing is generally considered to be transparent if its haze factor is less than 10%, in particular less than 5% and preferably less than 1.5%. The Hazemeter can be a "Haze-Gard ®" device marketed by the company BYK-Gardner.

[0070] The term "clarity factor" means the ratio defined by the following formula: [Formula 1] where is the intensity of light after passing through a window that has not been diffused, and l r is the intensity of light after passing through the glazing having been scattered at a small angle, preferably an angle equal to 15°. The clarity factor can be measured by spectroscopy techniques. Integrating the intensity over the entire visible range (from 380 nm to 780 nm) makes it possible to determine the normal transmission TL and the diffuse transmission Td. Such a measurement can also be obtained by using a Hazemeter. A glazing is generally considered to be transparent if its clarity factor is greater than 90% and preferably greater than 95%.

[0071] The interlayer according to the invention can also:

[0072] - have a cross-section tapering to a wedge shape from the top to the bottom of the laminated glazing to enable the laminated glazing to be used as a head-up display system screen (called HUD or Head Up Display), and / or

[0073] - include particles with an infrared radiation filter function to limit the temperature rise inside a vehicle due to infrared radiation from the sun, to improve the comfort of vehicle passengers or building occupants.

[0074] Another object of the invention is the use of a laminated glazing as described above as a vehicle windshield and / or as a building glazing to dampen vibrations and noise of solid origin between 1 Hz and 1000 Hz and / or increase the transmission loss to noise of airborne origin over the audible frequency decade between 1 kHz and 10 kHz, at room temperature. In the case where the glazing according to the invention is used as a windshield, it naturally meets all the conditions of United Nations Regulation No. 43 (known as Regulation R43) for resistance to hard impacts to ensure its mechanical strength.

[0075] Examples

[0076] Interleaves

[0077] Several different interlayers are prepared for laminated glazing.

[0078] Each of said interlayers comprises two outer layers of poly(vinyl butyral) (PVB), and these two outer layers are assembled by means of an inner adhesive viscoelastic damping layer formed by different materials including:

[0079] - either a commercial glue under the name “QuietGlue®”, with a milky appearance and yellow color, for interlayer no. 1, according to the prior art,

[0080] - either PVB having a residual hydroxyl content (-OH group) equal to 8%, lower than that of the PVB of the two external layers which is equal to 18%, for interlayer no. 2, according to the prior art,

[0081] - either 40% by weight of an acrylic polymer, 40% of a tackifying agent and 20% by weight of a plasticizing agent, relative to the total weight of the dry material, for interlayer no. 3, according to the invention,

[0082] - either 80% by weight of an acrylic polymer and 20% by weight of a plasticizing agent, relative to the total weight of the dry material, for interlayer no. 4, outside the invention (comparative), and

[0083] - or 81% by weight of an acrylic polymer, 2.4% of a tackifying agent and 16.6% by weight of a plasticizing agent, relative to the total weight of the dry material, for interlayer no. 5, outside the invention (comparative).

[0084] In the examples above:

[0085] - the acrylic polymer used to form the viscoelastic damping adhesive layer of interlayers No. 3, 4 and 5 is formed from 2-ethylhexyl acrylate (2-EHA) and butyl acrylate (BA) in a mass ratio equal to 3, - the tackifying agent used to form the viscoelastic damping adhesive layer of interlayers No. 3 and 5 comprises a hydrogenated rosin ester, and

[0086] - the plasticizing agent used to form the viscoelastic damping adhesive layer of interlayers No. 3, 4 and 5 comprises triethylene glycol bis(2-ethylhexanoate).

[0087] The aforementioned interlayers No. 1 to 5 are then subjected to the measurement of the loss factor “tan 5”, at a temperature of 20°C and at a frequency ranging from 10' 1 at 10 7 Hz. Thus Figure 1 [Fig. 1 ] illustrates the loss factor measurements for each of the spacers 1 to 5 in a frequency range from 10' 1 Hz to 10 7 Hz, at a temperature equal to 20°C.

[0088] The results reported in Figure 1 show that an interlayer, according to the invention, (interlayer No. 3) comprising a viscoelastic damping adhesive layer having specific quantities of: polymer, tackifying agent, and plasticizer, has higher vibration damping (in the desired audible frequency range, located between 1 kHz and 10 kHz, i.e. between 10 3 Hz and 10 4 Hz with a loss factor approximately equal to 3) compared to:

[0089] - an interlayer whose internal layer comprises quantities of: polymer, tackifying agent, and plasticizer outside the ranges of values ​​of the present invention, such as in interlayers No. 4 and 5,

[0090] - a three-layer interlayer formed solely of PVB, such as interlayer no. 2.

[0091] It is noted that the interlayer comprising the commercial glue, interlayer no. 1, has a loss factor equivalent to that of the interlayer according to the invention, but the latter is not capable of forming transparent glazing, as shown in table no. 1 below.

[0092] Laminated glazing

[0093] Then, laminated glazings No. 1 to 5 are prepared by placing each of the aforementioned interlayers between a first sheet of glass and a second sheet of glass.

[0094] For each of the laminated glazings, the light transmission, the haze factor and the clarity factor are measured by well-known spectroscopy techniques, in the visible range (from 380 nm to 780 nm). The results obtained are listed in Table 1 below:

[0095] [Table 1]

[0096] It is noted that the composition of the viscoelastic damping adhesive layer according to the invention in interlayer No. 3 not only makes it possible to obtain a high damping factor at room temperature and in the desired frequency range from 1 kHz to 10 kHz, but also to give the laminated glazing the desired transparency, in particular for a vehicle windshield; since the TL is greater than 90% (equal to 91.4%), the haze factor is less than 1% (equal to 0.35%) and the clarity factor is greater than 95% (equal to 98.4%).

[0097] Acoustic characterization of laminated glazing

[0098] In order to show the acoustic gain obtained between a laminated glazing No. 3, according to the invention, and a laminated glazing No. 2, according to the prior art, which comprises a tri-layer of PVB with different hydroxyl group contents and another laminated glazing No. 0, according to the prior art, which comprises a tri-layer of PVB with identical hydroxyl group contents, a numerical simulation was carried out. The acoustic model is based on the finite element method so as to reproduce the behavior of the acoustic attenuation according to the NF EN ISO 10140 standard.

[0099] Thus, Figure 2 [Fig. 2] illustrates the acoustic attenuation of laminated glazing of different configurations subjected to airborne noise produced according to standard NF EN 10140.

[0100] The results reported in Figure 2 show:

[0101] - an improvement in the acoustic attenuation of airborne noise, at a frequency of 10 kHz, of laminated glazing No. 3 according to the invention of at least 6 dB, compared to laminated glazing No. 2 according to the prior art and an improvement of at least 4 dB, compared to laminated glazing No. 0 according to the prior art,

[0102] - an improvement in the acoustic attenuation of airborne noise, at a frequency of 6 kHz, of laminated glazing No. 3 according to the invention of at least 3 dB, compared to laminated glazing No. 2 according to the prior art and of at least 2 dB, compared to laminated glazing No. 0 according to the prior art.

Claims

Claims 1. Interlayer for laminated glass comprising two external layers made of a material chosen from poly(vinyl butyral) (PVB) and poly(ethylene vinyl acetate) (EVA), assembled by means of a viscoelastic damping adhesive layer formed by a material comprising: - from 21% to 62% by weight of at least one acrylic polymer, relative to the total weight of the dry material, preferably from 21% to 51% by weight, and more preferably from 21% to 35% by weight, - from 22 to 60% by weight of at least one tackifying agent, relative to the total weight of the dry material, preferably from 22% to 35% by weight, and more preferably from 22% to 26% by weight, and - from 7% to 43% by weight of at least one plasticizing agent, relative to the total weight of the dry material, preferably from 12% to 31% by weight and more preferably from 16% to 26% by weight.

2. Interlayer for laminated glass according to claim 1, characterized in that the two external layers are layers of poly(vinyl butyral) (PVB).

3. Interlayer according to claim 1 or 2, in which the material of the viscoelastic damping adhesive layer has a glass transition temperature (Tg) of between -70°C and 10°C, preferably of between -45°C and 0°C, and more preferably of between -45°C and -20°C.

4. Interlayer according to any one of the preceding claims, in which the acrylic polymer(s) are formed from monomers selected from the group formed by methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, pentyl acrylate, pentyl methacrylate, isoamyl acrylate, isoamyl methacrylate, hexyl acrylate, hexyl methacrylate, cyclohexyl acrylate, methacrylate cyclohexyl, octyl acrylate, octyl methacrylate, isooctyl acrylate, methacrylate isooctyl, nonyl acrylate, nonyl methacrylate, isononyl acrylate, isononyl methacrylate, isobornyl methacrylate, decyl acrylate, decyl methacrylate, dodecyl acrylate, dodecyl methacrylate, tridecyl acrylate, tridecyl methacrylate, hexadecyl acrylate, hexadecyl methacrylate, octadecyl acrylate, octadecyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, vinyl formate, vinyl acetate, vinyl propionate, 2-hydroxyethyl acrylate, hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, acrylic acid, styrene and acrylonitrile.

5. An interlayer according to any one of the preceding claims, wherein the material comprises a first acrylic polymer having a first glass transition temperature T gi, and a second polymer having a second glass transition temperature T g 2, greater than T gi , the difference between the second glass transition temperature T g 2 and between the first glass transition temperature T gi being preferably greater than 10°C, and preferably greater than 20°C.

6. Interlayer according to any one of the preceding claims, in which the tackifying agent comprises a hydrogenated resin, preferably chosen from rosins, rosin esters, hydrogenated rosin esters, hydrogenated rosin derivatives, terpenes, and aliphatic or aromatic synthetic resins derived from petroleum.

7. Interlayer according to any one of the preceding claims, in which the plasticizing agent comprises at least one element chosen from a citrate, an adipate, a glycol or a triethylene glycol derivative.

8. Interlayer according to any one of the preceding claims, in which the viscoelastic damping adhesive layer has a thickness of between 5 μm and 50 μm, preferably between 10 μm and 30 μm, and more preferably between 15 μm and 25 μm.

9. Interlayer according to any one of the preceding claims, in which the material of the viscoelastic damping adhesive layer has a loss factor tan ô greater than or equal to 2, preferably greater than or equal to 3, for a temperature range between 0°C and 40°C, for a frequency range between 1 kHz and 10 kHz.

10. An interlayer according to any one of the preceding claims, wherein the viscoelastic damping adhesive layer is in direct contact with the two outer layers.

11. A method of manufacturing an interlayer for laminated glass according to any one of claims 1 to 10, the method comprising the following steps: - supply of a first sheet made of a material chosen from poly(vinyl butyral) (PVB) and poly(ethylene vinyl acetate) (EVA), - depositing on one of the faces of said first sheet a liquid composition comprising a latex, a tackifying agent, and a plasticizing agent, the latex comprising an emulsion, the emulsion comprising an aqueous continuous phase and a dispersed phase, the dispersed phase comprising at least one acrylic polymer, - drying said liquid composition so as to form a viscoelastic damping adhesive layer, - application to the viscoelastic damping adhesive layer thus formed of a second sheet made of a material chosen from poly(vinyl butyral) (PVB) and poly(ethylene vinyl acetate) (EVA).

12. Method for manufacturing an interlayer for laminated glass according to claim 11, in which the drying step is carried out at room temperature and / or in an oven at a temperature between 40°C and 120°C, preferably between 60°C and 100°C.

13. Laminated glazing comprising: - a first sheet of glass, - a second sheet of glass, - an interlayer according to claims 1 to 10, the interlayer being arranged between the first and second glass sheets.

14. Laminated glazing according to claim 13, having a light transmission greater than 90% in the wavelength range of the visible spectrum, a haze factor less than 1.5%, and a clarity factor greater than 95%.

15. Use of laminated glazing according to claim 14, as a vehicle windshield and / or as building glazing to dampen vibrations and noise of solid origin and / or increase transmission loss to noise of airborne origin.

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