Multi-layer films based on polyvinyl acetal with high plasticizer content Technical field

The invention relates to a plasticiser-containing film based on polyvinyl acetal, provided with least two layers of which at least one layer has a high plasticiser content for use in laminated glazing.

Prior art

It is well known that vibration and sound transmission behaviour of laminated safety glass composed of two plies of glass and a polymeric interlayer depends mostly on glass thickness, interlayer thickness and the coupling and damping effectiveness of the latter at a given temperature.

Conventional films from plasticized polyvinylbutyral (PVB) used as polymeric interlayer exhibit relatively high strong coupling but low damping at 20 °C and reduced coupling and increased damping at 40 °C thus rendering a laminated safety glass with a good sound barrier at this - relatively high - temperature.

So called "acoustic PVB" using modified plasticized polyvinylbutyral (PVB) offers reduced coupling and increased damping at lower temperature, i.e. around 20 °C. Since laminated glass will be exposed mostly to such temperatures, a better sound barrier will be experienced. In praxis, such modification is achieved by increased amounts of plasticizer, which lowers the glass transition temperature (Tg) of the PVB interlayer by about 15 - 25 °C compared to the conventional plasticized PVB film products. The increased amount of plasticizer can be present in the entire interlayer, which may cause problems of sticking, elongation during handling and lay-up operations and weakened mechanical properties in the laminate, unless the overall Tg is not too low.

The increased amount of plasticizer and a low Tg may be restricted to a core layer, which is embedded between outer layers of conventional PVB. In this case sticking, handling and interlayer toughness are governed by the outer layers having the desired "conventional" properties. This so-called acoustic tri-layer PVB is nowadays in widespread use for building applications and even more for automotive windscreens. Mainly driven by weight reduction efforts, windshield laminate construction changed in the past decade from two glass plies each having 2.1 mm thickness combined with conventional PVB interlayer to laminates comprising glass plies with 2.1 mm and 1.6 mm thickness combined with acoustic tri-layer PVB. Such asymmetric set-up provides lighter and thinner laminates with even better acoustic comfort than the more heavier versions.

It is a current target of research and development to further reduce glass thickness and glass weight, without compromising required safety properties. For example, the modification of acoustic tri-layer to impart stronger coupling to thin glass plies is disclosed in WO 2013/175 101A1. It appears that at the same time as coupling properties are increased, damping properties are slightly reduced. Such modification is achieved by reducing the total plasticizer content in an acoustic tri- layer PVB.

Surprisingly it has been found, that on the contrary, enhancing the total plasticizer content in an acoustic multi-layer PVB leads to significant improvement of the sound barrier properties in laminates if the plasticized poly vinyl butyral for the core and outer layers are properly selected. Object of the invention was therefore an interlayer film for laminated glazing, comprising at least one first and at least one second layer, each containing plasticized polyvinyl acetal, wherein the first layer comprises polyvinyl acetal having a polyvinyl alcohol content from 10 to 16 % by weight, a plasticizer content of at least 33% by weight and wherein the interlayer film has a total plasticiser content of at least 29 % by weight and, when laminated between two glass plies of 2.1 mm thickness, exhibits after 4 weeks aging after lamination a second mode frequency f2 according to ISO PAS 16940 of less than 720 Hz.

A surprising feature of the interlayer according to the invention is a significantly improved damping performance at reduced temperature such as 5 °C. This is a relevant additional advantage over normal acoustic tri-layer PVB since acoustic performance of a glazing is often measured and rated at 20 °C but naturally is desired to be good at lower and higher temperature as well which is particularly true for automotive glazing without the constancy of controlled air temperature as more typical for buildings.

In order to quantify the coupling and damping properties of the new interlayer according to the invention, the impedance test according ISO PAS 16940 is used on laminate beams of 25 x 300 mm with two plies of 2.1 mm soda lime glass. To reach equilibrium, the impedance test according ISO PAS 16940 is performed on such test laminate after 4 weeks aging after lamination . In such a layout, interlayers of the invention have a loss factor LF1 at 5 °C of more than > 0.10, more than 0,13, more than 0.16 or more than 0.20. LF1 is measured after the test laminate with the interlayer was stored to equilibrate for 2 weeks at 20 °C and then cooled down and measured at 5 °C.

The loss factor (LF) is directly related to damping whereas resonance frequency (f) is related to the bending stiffness of the laminated beam which in turn depends on the strength of coupling provided by the interlayer. Due to redistribution of plasticizer between the different layers of multi-layer PVB after a "heat shock" such as the typical autoclave step of safety glass lamination, evaluation of impedance properties was performed after either 2 weeks or 4 weeks of equilibrating the laminates at precisely 20 °C in an humidity controlled (25 - 30 %RH) environment where necessary. A typical autoclave step has for example a 90 min total process duration, with a 30 min heating phase with pressuri zation up to 12 bar, 30 min hold time at 12 bar and 140 °C, 30 min cooling down phase to 40 °C with concomitant release of pressure.

In a first embodiment, interlayer films according to the invention have in the described test laminate a resonance frequency fl as defined in ISO PAS 16940 after equilibration at 20°C for 4 weeks of less than 160 Hz; less than 150 Hz; less than 140 Hz or less than 130 Hz when measured at 20 °C. Preferable, resonance frequencies fl are in a range of 100 - 140 Hz and most preferred in a range of 110 - 130 Hz. In a second embodiment, interlayer films according to the invention have in the described test laminate a loss factor LF1 as defined in ISO PAS 16940 after equilibration at 20°C for 4 weeks of more than 0.20; more than 0.22; more than 0.24; more than 0.26; more than 0.28 or more than 0.30 when measured at 20 °C.

In a third embodiment, interlayer films according to the invention have in the described test laminate a resonance frequency f2 as defined in ISO PAS 16940 after equilibration at 20°C for 4 weeks of less than 720 Hz; less than 680 Hz or less than 640 Hz when measured at 20 °C. Preferable, resonance frequencies f2 are in a range of 550 - 680 Hz and most preferred in a range of 600 - 660 Hz.

In a forth embodiment, interlayer films according to the invention have in the described test laminate a loss factor LF2 as defined in ISO PAS 16940 after equilibration at 20°C for 4 weeks of more than 0.20; more than 0.22; more than 0.24; more than 0.26; more than 0.28 or more than 0.30 when measured at 20 °C.

Surprisingly, combining the features of high plasticizer mono- layer PVB in the outer layers with an even stronger plasticized core layer leads to enhanced acoustic barrier properties of the laminated glass in direct acoustic testing according ISO 140 as illustrated in Fig. 1 in direct comparison with normal acoustic tri-layer. This is even more surprising in view of the fact, that the interlayer of the invention do not necessarily exhibit higher loss factor compared to normal acoustic tri-layer.

In Fig. 1, the term "8861" refers to an interlayer according to example 2, "VG-SC+" to an acoustic tri-layer film from Kuraray Europe GmbH and "VG" to an acoustic mono-layer film from Kuraray Europe. The term "1.6/1.6" refers the thickness of the glass sheets. A further surprising and beneficial effect of the invention is the reduction of time to equilibrium after producing the laminate of the invention involving in a high temperature step such as autoclaving. While the acoustic stiffness properties - as indicated by the second mode frequency f2 - of laminates with normal acoustic tri-layer will continue to change considerably even after 2 weeks of stabilization time at 20 °C due to slow processes of plasticizer diffusion until approaching the equilibrium distribution in the different layers, the new interlayer according to the invention approach such equilibrium faster. It means that f2 value can be initially high (just for example purpose 1000 Hz) , drops to lower value after some days (e.g. 900 Hz) and eventually stabilizes around a some minimum value (e.g. 800 Hz) . Long stabilization times (time elapsed until reaching the minimum value) are encountered with normal acoustic tri-layer, such as 4 weeks or more, whereas this stabilization process is significantly faster for the plasticizer richer interlayer of the present invention. This becomes evident when comparing f2 after 2 weeks with f2 after 4 weeks for laminated beams containing the interlayer of the invention respective conventional acoustic tri-layer. Accordingly, when laminated between 2 x 2.1 mm glass, f2 after 4 weeks of stabilization time at 20°C (f2w4) does not deviate more than 5%, preferably 4%, more preferably 3% and most preferably 2% from f2 after 2 weeks of stabilization time at 20°C (f2w2) for the interlayer of the invention when calculated with the formula below, whereas f2w4 of the laminated beam containing conventional acoustic tri-layer is found to deviate more than 5% from f2w2.

In a fifth embodiment, interlayer films according to the invention have in the described test laminate a ratio of decay of second mode resonance f2 as compared after 2 and 4 weeks of stabilization time at 20 °C based on the staring value f2w2 as defined by formula (f2w2 - f2w4)/f2w2 x 100 of less than 5 %, preferred less than 4%, more preferred less than 3%, and most preferred less than 2%. In a preferred embodiment, the first layer is embedded as core layer between two identical or different second layers. This embodiment can even be extended to 5 layers with a sequence second/third/first/third/second layer or second/first/third/first/second layer .

The total plasticiser content of the interlayer film is understood hereinafter as the content of plasticiser in relation to the total weight of the film. Interlayer films according to the invention have a preferred total plasticiser content of more than 29%, more than 29.5% more than 30%, more than 30.5% more than 31%, more than 32%, more than 33%, more than 34%, more than 34% and even more than 35% by weight. Since a plasticizer content of more than 40% by weight will usually lead to plasticizer exudation, a preferred range of total plasticiser content is between 31-36% by weight and a more preferred range is 32 - 34%.

The first layer of the interlayer film may have a plasticiser content of more than 33%, more than 35%, more than 37 % , more than 39% or more than 40% by weight with an upper limit of about 65% by weight, since sufficient damping properties are not maintained at too high dilutions of polymer. The second layer of the interlayer film may have a plasticiser content of more than 28%, more than 29%, more than 30 % , more than 32%, more than 33% or more than 34% by weight with an upper limit of about 40% by weight since mechanical properties and handling of film with higher plasticizer content rapidly degrade .

The interlayer according to the invention can be further described by the glass transition temperatures Tg (as determined with DSC) of the first layer and the second layer. While outer layers of conventional acoustic tri-layer have Tg values close to standard PVB film, i.e. in a range of 17 - 23 °C, the Tg of the second layer is lowered to values of less than 17 °C, preferably less than 16 °C, more preferably less than 15 °C and especially preferably less than 14 °C for the interlayer of the invention. The Tg of the first layer may be lower than 5 °C, 0 °C or preferably lower than - 5 °C. Since second outer and first inner layer and optionally additional layer can be present in several thicknesses (d in mm) in the interlayer of the invention, a thickness weighted average Tg is defined as follows:

Thickness weighted average Tg = [d( _firs t layer) x Tg _(firs t layer) + d(second layer) X Tg( _secon( j layer) + ··· + d( _n th layer) X Tg< _n th layer) ] / 01a1 film thickness. Total film thickness equals the sum of the thicknesses of all individual layers d( _firs t layer) + d _(seC ond layer) + ...

+ d (nth layer) ·

In another embodiment of the invention, the interlayer exhibits a thickness weighted average Tg of less than 12 °C, less than 10 °C and preferably less than 8 °C.

The interlayer film according to the invention may preferably have one or more first layers comprising polyvinyl acetal with a polyvinyl alcohol content of 10 - 16 % by weight 12 - 15 % by weight, and particularly preferably of 13 - 14 % by weight. The first layer may comprise polyvinyl acetal with different contents of polyvinyl acetate groups like a) 0 - 5 w% preferred 0 - 3 wght%, or b) 5 - 8 wght% or c) 8 - 30 wght%.

The interlayer film according to the invention may preferably have two or more second layers comprising polyvinyl acetal with a polyvinyl alcohol content of 14 - 24 % by weight 16 - 22 % by weight, and particularly preferably of 17 - 20 % by weight. The second layer may comprise polyvinyl acetal with contents of polyvinyl acetate groups in a range of 0 - 5 w% and preferably 0 - 3 w%

The layers may have different contents of polyvinyl alcohol groups to achieve different Tg and plasticizer content. Preferred, the difference in content by weight of polyvinyl alcohol groups between the layer having the highest Tg (usually the second layer) and the layer having the lowest Tg (usually the first layer) is less than 10 %; less than 8%; less than 7%; less than 6% or less than 5% and preferably in the range of 4 - 7 %.

The total thickness of the interlayer film may be between 0.3 - 3 mm or 0.35 - 2 mm or 0.45 - 1.8 mm or 0.75 - 1.35 mm or 0.85 - 1.2 mm or most preferably 0.9 - 1.15 mm. The thickness of layer with lowest Tg is preferred between 0.03 0.4 times of the total thickness of film, more preferred between 0.075 - 0.3 times of the total thickness of film and most preferred between 0.1 - 0.25 times of the total thickness of film.

The compatibility of plasticiser and polyvinyl acetal generally reduces with the decrease of the polar nature of the plasticiser. Plasticisers of higher polarity are thus more compatible with polyvinyl acetal than plasticisers of lower polarity. Alternatively, the compatibility of plasticisers of low polarity rises with an increase of the degree of acetalisation, i.e. with decrease of the number of hydroxyl groups and therefore the polarity of the polyvinyl acetal .

Due to the different content of polyvinyl acetal groups, the layers of the interlayer film can accommodate different quantities of plasticisers, without resulting in a bleeding of the plasticiser.

Interlayer films according to the invention can be produced by combining individually extruded layers or preferably by co- extrusion of the layers. The layers may contain identical or different plasticisers in an identical or different quantity prior to the combination with one another. The use of identical plasticisers is preferred, wherein the composition of plasticiser mixtures in the layers may change slightly on account of migration. The layers of the interlayer films may contain plasticisers or plasticiser mixtures formed from at least one of the following plasticisers known for PVB film: di-2-ethylhexyl sebacate (DOS), di-2-ethylhexyl adipate (DOA) , dihexyl adipate (DHA) , dibutyl sebacate (DBS) , triethylene glycol bis-n-heptanoate (3G7), tetraethylene glycol bis-n-heptanoate (4G7), triethylene glycol bis-2-ethylhexanoate (3GO or 3G8), tetraethylene glycol bis-n-2-ethylhexanoate (4GO or 4G8) , di-2-butoxy-ethyl adipate (DBEA) , di-2-butoxy-ethoxy-ethyl adipate (DBEEA) , di-2-butoxy- ethyl sebacate (DBES) , di-2-ethylhexyl phthalate (DOP) , di- isononyl phthalate (DINP) , triethylene glycol bis-isononanoate, triethylene glycol bis-2-propylhexanoate, 1 , 2-cyclohexane dicarboxylic acid diisononyl ester (DINCH) , tris (2-ethylhexyl) phosphate (TOF) and dipropylene glycol benzoate. In a preferred embodiment, the first and/or the second layer comprise a mixture of a plasticizer of low polarity, preferably triethylene glycol bis-2-ethylhexanoate (3G8), and at least one additional plasticizer, preferable 1 - 20 %, by weight of at least one plasticizer according to formula I or II

i^-O (-R ² -0) n-CO-R ⁵ I

R ^x -0 (-R ² -0) _n -CO-R ³ -CO- (0-R ⁴ -) _m O-R ⁶ II

With R ¹ ,R ⁵ ,R ⁶ : same or different, H, aliphatic or aromatic residue with 1 to 12 carbon atoms,

R ³ : a C-C bond, or an aliphatic or aromatic residue with 1 to 12 carbon atoms

R ² , R ⁴ : same or different, H, aliphatic or aromatic residue with 1 to 12 carbon atoms,

n, m: same or different integers from 1 to 10 or 1 to 5 Suitable are for example di- (2-butoxyethyl) -adipate (DBEA) , Di- (2-butoxyethyl) -sebacate (DBES) , Di- (2-butoxyethyl) -azelate, Di- (2-butoxyethyl) -glutarate, Di- (2-butoxyethoxyethyl) -adipate (DBEEA) , Di- (2-butoxyethoxyethyl) -sebacate (DBEES) , Di- (2- butoxyethoxyethyl ) -azelate, Di- (2-butoxyethoxyethyl) -glutarate, Di- (2-hexoxyethyl) -adipate, Di- (2-hexoxyethyl) -sebacate, Di- (2- hexoxyethyl) -azelate, Di- (2-hexoxyethyl) -glutarate, Di- (2- hexoxyethoxyethyl ) -adipate, Di- (2-hexoxyethoxyethyl) -sebacate, Di- (2-hexoxyethoxyethyl) -azelate, Di- (2-hexoxyethoxyethyl) - glutarate, Di- (2-butoxyethyl) -phthalate and/or Di- (2- butoxyethoxyethyl ) -phthalate .

In addition, the interlayer film according to the invention may contain further additives known to the person skilled in the art, such as residual quantities of water, UV absorbers, antioxidants, adhesion regulators, optical brighteners, stabilisers, dyes, processing aids, organic or inorganic nanoparticles , pyrogenic silicic acid and/or surface-active substances . In a variant of the invention, all layers have the specified additives in largely identical concentration. In a preferred variant of the invention at least one of the layers does not comprise any anti-adhesion agent. Anti-adhesion agents are known to the person skilled in the art; in practice, alkaline or alkaline earth metal salts of organic acids, such as potassium/magnesium acetate, are often used for this purpose. It is also possible for a least one of the layers to contain 0.001 to 20 % by weight S1O ₂ , preferably 1 to 15 % by weight, in particular 5 to 10 % by weight, optionally doped with AI ₂ O ₃ or Zr0 ₂ , in order to improve rigidity. In another embodiment of the invention, the first and/or the second layer comprises a mixture of a plasticizer, preferred one of the before mentioned plasticizer, more preferably 3G8 or 1 , 2-cyclohexane dicarboxylic acid diisononyl ester (DINCH) , and at least one non-ionic surfactant, optionally with one or more of the additives as already disclosed.

The non-ionic surfactant is preferred an ethoxylated aliphatic or aromatic alcohol, containing at least 6 carbon atoms in the alcohol fraction, with an average degree of ethoxylation greater than or equal to 2. Particular preference is given to ethoxylated aliphatic or aromatic alcohols containing from 8 to 20 carbon atoms in the alcohol fraction, with an average degree of ethoxylation of from 3 to 10. Suitable non-ionic surfactants for the purposes of the invention are for example MARLOPHEN® NP 6, a nonylphenol whose average degree of ethoxylation is 6, MARLIPAL® 0 13/40, a fatty alcohol whose average degree of ethoxylation is 4, ISOFOL® 12 + 5 EO, a 2-butyloctanol whose average degree of ethoxylation is 5. Another example is Berol® 840, a narrowly distributed tetraethoxylated C8 alcohol from Akzo Nobel. Moreover, Ethylan 1003, Ethylan 1005 of Akzo Nobel (both ethoxylated CIO Guerbet alcohols carrying about 3 respective 5 EO units), Berol 260 or Berol 266 (ethoxylated C9-11 alcohols with about 4 respective 5.5 EO units) . In general, narrow distributed ethoxylates are preferred but standard etholylates like BASF' s Lutensol XP range of products are suitable as well (e.g. Lutensol XP 30, XP 40, XP 50, XP 60) The amount preferably used of the non-ionic surfactant ( s ) is from 1 to 25% by weight, in particular from 5 to 20 % by weight and more particularly 8 - 15 % by weight, based on the total film composition. Non-ionic surfactants act as a plasticizer at the same time enhancing the compatibility of the standard plasticizer and lowering the Tg of the layer (s) concerned. The sum of all plasticizer and non-ionic surfactants present in the film is considered total plasticizer content. Such mixtures present in the sublayers of the interlayer are thus considered "plasticizer".

In order to produce polyvinyl acetal, polyvinyl alcohol is dissolved in water and is acetalised with an aldehyde, such as butyraldehyde, with addition of an acid catalyst. The precipitated polyvinyl acetal is separated off, washed neutral, optionally suspended in an alkaline aqueous medium, then washed neutral again and dried.

The polyvinyl alcohol content of the polyvinyl acetal can be adjusted by the quantity of the aldehyde used during acetalisation . It is also possible to perform the acetalisation with other or a number of aldehydes having 2-10 carbon atoms (for example valeraldehyde) .

The films based on plasticiser-containing polyvinyl acetal preferably contain uncrosslinked polyvinyl butyral (PVB) , which is obtained by acetalisation of polyvinyl alcohol with butyraldehyde . The use of crosslinked polyvinyl acetals, in particular crosslinked polyvinyl butyral (PVB) , is also possible. Suitable crosslinked polyvinyl acetals are described for example in EP 1527107 Bl and WO 2004/063231 Al (thermal self-crosslinking of polyvinyl acetals containing carboxyl groups), EP 1606325 Al (polyvinyl acetals crosslinked with polyaldehydes ) and WO 03/020776 Al (polyvinyl acetals crosslinked with glyoxylic acid) . The disclosure of these patent applications is incorporated herein fully by reference.

In order to produce the films according to the invention, the layers can first be produced individually by extrusion and then combined mechanically, for example by being rolled jointly onto a film reel in order to form the intermediate layer film according to the invention.

It is also possible to produce the interlayer film by simultaneous co-extrusion of the layers. The co-extrusion can be performed for example with an appropriately equipped flat film die or a feed-block.

The interlayer films or single layers according to the invention are generally produced by extrusion or co-extrusion, moreover under certain conditions (melt pressure, melt temperature and die temperature) so as to obtain a melt fracture surface, i.e. a stochastic surface roughness.

Alternatively, an interlayer film already produced in accordance with the invention can be embossed with a non- stochastic, regular roughness by means of an embossing process between at least one pair of rolls. Embossed films generally have improved deaeration behaviour during the laminated glass production and are used preferably in the automotive field. Films according to the invention have, independently of the production method, a surface structure applied on one side or particularly preferably on both sides, said surface structure having a roughness R _z from 15 to 150 ym, preferably R _z from 15 to 100 ym, particularly preferably R _z from 20 to 80 ym, and in particular R _z from 30 to 75 ym.

Use

The films according to the invention can be used to produce laminates comprising at least two glass sheets with at least one interlayer film according to the invention wherein the glass sheets have a different or the same thickness. The laminates according to the invention can be used as automobile and/ or architectural window, for example as a windscreen or in windows or transparent facade components, or in furniture making. For application of the interlayer in an automotive glazing unit, the glass plies may have same or different thickness, for example with a asymmetry of the plies is >10%; >20%; >30%; >50% wherein asymmetry is defined as [A mm - B mm / A mm + B mm]xl00 (A, B :glass plies) . One or more plies can be chemically hardened. Preferable, so called light weight laminates have a total glass thickness (i.e. sum of glass plies without interlayer) of less than 4.6 mm; less than 3.6 mm; less than 3.3 mm or even less than 3.0 mm. In such laminates, the glass sheets may have a degree of asymmetry of >10%; >20%; >30%; >50% (% asymmetry defined as [A mm - B mm / A mm + B mm] x 100) .

The general production of interlayer films based on polyvinyl acetals and laminated glass is known to the person skilled in the art or is described for example in EP 185 863 Bl, EP 1

258 Bl, WO 02/102591 Al, EP 1 118 258 Bl or EP 387 148 Bl .

Measurement methods

The polyvinyl alcohol content and polyvinyl acetate content of PVB were determined in accordance with ASTM D 1396-92. The degree of acetalisation (= acetal/butyral content) can be calculated as the remaining portion from the sum of polyvinyl alcohol content and polyvinyl acetate content determined in accordance with ASTM D 1396-92 needed to make one hundred. Conversion from % by weight into mol % is achieved by formulas known to the person skilled in the art.

The glass transition temperature of the different layers comprising partly acetalised polyvinyl alcohol and plasticizer was determined by means of differential scanning calorimetry (DSC) in accordance with DIN 53765 with use of a heating rate of lOK/min at a temperature interval of minus 50 °C to 150 °C. A first heating ramp, followed by a cooling ramp, followed by a second heating ramp was used. The position of the glass transition temperature was established on the measurement curve associated with the second heating ramp in accordance with DIN 51007. The DIN midpoint (Tg DIN) was defined as the point of intersection of a horizontal line at half step height with the measurement curve. The step height was defined by the vertical distance of the two points of intersection of the middle tangent with the base lines of the measurement curve before and after glass transition.

Measurement of the damping behaviour

In order to quantify the coupling and damping properties of the new interlayer according to the invention, the impedance test according ISO PAS 16940 is used on laminate beams of 25 x 300 mm with two plies of 2.1 mm soda lime glass. Due to redistribution of plasticizer between the different layers of multi-layer PVB after a "heat shock" such as the typical autoclave step of safety glass lamination, evaluation of impedance properties was performed after either 2 weeks or 4 weeks of equilibration the laminates at precisely 20 °C.

Examples

Interlayer films were produced by co-extrusion with the composition as shown in table 1. Hereby the core layer was centered in the middle of the film. Test laminates were produced with conventional 2.1 mm automotive grade soda lime glass ( Planiclear®) . After the given storage times, the acoustic properties were measured as disclosed according to ISO PAS 16940 with the results shown in table 2. In order to prove that the interlayer films according to the invention are suitable for production of laminated glass, safety test were performed and shown in table 3.

Table 1 with Comparative Examplel: VG-SC+ acoustic tri-layer film from Kuraray Europe GmbH, Ex 1-5 according to the invention

Table 2 with Comparative Examplel: VG-SC+ acoustic tri-layer film from Kuraray Europe GmbH, Ex 1-5 according to the invention

Table 3 with Comparative Examp el: VG-SC+ acoustic tri-layer film from Kuraray Europe GmbH, Ex 1-5 according to the invention