Drying method for composite films containing polyvinyl acetal resin and polyvinyl ethylene acetal resin

Abstract

The present invention provides a composite film obtained by drying a composite film containing polyvinyl acetal on a carrier. [Solution] A composite film comprising i) a carrier film and ii) film A comprising polyvinyl acetal and / or polyvinyl ethylene acetal and optionally a plasticizer, wherein film A has a total residual solvent content of less than 2000 ppm when measured in accordance with JIS K 5601-5-1, and the residual solvent content of each individual residual solvent is less than 250 ppm when measured in accordance with JIS K 5601-5-1.

Description

[Technical Field]

[0001] The present invention relates to a method for drying a composite film comprising polyvinyl(ethylene) acetal on a carrier, and to a composite film and a polyvinyl acetal film obtained by such a method.

[0002] Interlayer films containing polyvinyl acetal have long been known as adhesive layers for laminating glass. In particular, plasticized polyvinyl butyral (PVB) films are widely used as adhesive layers for glass-glass laminates, for example for windshields in automobiles.

[0003] It is also known to use patches of fairly thin opaque plastic films in combination with conventional plasticized PVB films in order to introduce specific functions into windshields. For example, WO 2019 / 038043 discloses a thin non-plasticized PVB film provided with a printed shielding area for protecting the sealant or adhesive that mechanically bonds the windshield to the chassis from ultraviolet radiation and for hiding the sensor system from view from the outside of the vehicle for aesthetic reasons.

[0004] Conventionally, PVB films are produced by melt extrusion using equipment such as a twin-screw extruder. The production of PVB films by solvent casting is also known in the art. For this purpose, U.S. Patent No. 7,012,746 discloses a solvent casting process for producing PVB films on a PET carrier. This process comprises drying the coated film at temperatures below 95°C in different zones in order to avoid discoloration due to thermal degradation. While residual solvent content levels are reported to be less than 10% by weight, the most preferred embodiment has less than 1% by weight.

[0005] However, the inventors have found that even very low levels of residual solvent content can cause problems in the production of glass laminates from polyvinyl acetal films. This is particularly true in the production of windshields. The automotive industry is constantly striving to improve the optical quality of laminates to enable the use of advanced sensors, for example, for fully autonomous driving technology. While we do not wish to be bound by theory, it is conceivable that low-boiling-point residual solvents could cause optical defects such as bubble formation during the lamination process, which requires heating of the polyvinyl acetal film to bond the glass plies. In addition, residual solvents are thought to adversely affect the adhesion between the polymer film and the glass surface.

[0006] Therefore, the industry is seeking improved methods for manufacturing polyvinyl acetal films, particularly those used in vehicle windshields.

[0007] Therefore, an object of the present invention was to provide a method for producing a polyvinyl acetal film having improved properties, in particular low residual solvent content, low manufacturing cost, and / or high optical quality, in particular high optical quality against optical defects such as wrinkles, bubbles or granules, low haze, and / or low yellowness.

[0008] The above and other problems are solved by the present invention.

[0009] A first aspect of the present invention is a method for manufacturing a composite film, wherein the composite film is i) Film A comprising polyvinyl acetal and / or polyvinyl ethylene acetal and optionally a plasticizer, ii) Carrier film and, Includes, a) Steps to prepare the carrier film, b) A step of coating one side of a carrier film with a solution comprising a solvent, polyvinyl acetal and / or polyvinyl ethylene acetal, and optionally a plasticizer. c1) A step of drying the composite film on a roll support at a temperature of 25 to 90°C, and d) A process that involves performing one or more drying steps selected from IR (infrared) drying, UV drying, microwave drying, vacuum drying, roll-supported drying at a temperature greater than 130°C but less than 180°C, and air flotation drying at a temperature greater than 130°C but less than 180°C. The method comprising the following in this order.

[0010] Roll-supported drying As used in relation to the present invention, roll-supported drying is an air-drying method in which a composite film is supported by a roll, and heated air comes from only one side of the composite film, i.e., the side opposite the roll support. Any conventional air nozzle can be used. Examples of suitable nozzle types include jet nozzles, floating nozzles, and airfoil nozzles.

[0011] Air flotation drying As used in relation to the present invention, air flotation drying is a non-contact drying method in which the composite film is kept suspended between heated airflows from both sides of the composite film. Any conventional air nozzle can be used. Examples of suitable nozzle types include jet nozzles, floating nozzles, and airfoil nozzles.

[0012] Infrared drying In relation to the present invention, infrared drying is a method in which infrared rays emitted from a light source pass through a coating film, and the absorbed energy causes molecules to vibrate, generating heat. Therefore, the entire coating film can be heated and dried simultaneously. It is characterized by a faster heating rate compared to hot air drying. Preferably, in the present invention, a gas IR dryer or an electric IR dryer is used.

[0013] microwave drying In relation to this invention, microwave drying refers to a method in which a composite film is exposed to a microwave electric field. Heat is generated at the molecular level, and the entire composite film is heated. This is an internal heating method in which the material itself acts as a heat source.

[0014] Vacuum drying As used in relation to the present invention, vacuum drying refers to a method of drying a composite film under vacuum or reduced pressure. When the atmospheric pressure around the coating film is lowered, the boiling point of the solvent decreases, the evaporation rate increases, and the drying of the coating film can be accelerated.

[0015] UV drying In relation to the present invention, UV drying refers to a method in which heat transfer to the composite film is achieved by UV irradiation of the composite film.

[0016] Preferably, at least one of the one or more drying steps in step d) is an IR drying step or an air flotation drying step at a temperature greater than 130°C but less than 180°C.

[0017] Preferably, at least one additional drying step c2) is performed between step c1) and step d), wherein the additional drying step c2) is an air flotation drying step at a temperature greater than 90°C but less than 130°C.

[0018] Surprisingly, a combination of an initial roll-supported drying process at low to medium temperatures and at least one process at temperatures above 130°C yielded excellent levels of residual solvent content, and it was found that no noticeable yellowing occurred in film A, especially when using air flotation drying and / or IR drying.

[0019] The term "composite film" means a film comprising at least two layers, one of which is attached to the other during manufacturing. In relation to the present invention, film A is attached to the carrier film by solvent casting.

[0020] The carrier film material can be selected from any material that is compatible with polyvinyl (ethylene) acetal and also compatible with the manufacturing method used to obtain the composite film. Therefore, the carrier material may be glass or metal. However, it is preferable to use a polymer material selected from the group consisting of polylactic acid, acrylonitrile-butadiene-styrene copolymer, polyamide, polycarbonate, polyethylene terephthalate (PET), polyethylene terephthalate copolymer, polyhydroxyalkanoate, polyurethane, polyolefin, such as polyethylene or polypropylene, acrylonitrile styrene acrylate, polyacrylate and polymethacrylate, polyvinyl alcohol, and TAC (cellulose triacetate). Most preferably, the carrier contains polyethylene terephthalate (PET), and in particular, the carrier is a film made of PET.

[0021] Preferably, the thickness of the carrier film is 10 to 500 μm, more preferably 25 to 250 μm, and most preferably 50 to 100 μm.

[0022] Film A used in accordance with the present invention comprises polyvinyl (ethylene) acetal, which is produced by acetalization of polyvinyl alcohol or ethylene vinyl alcohol copolymer.

[0023] The film may contain different polyvinyl acetals, each of which has a different polyvinyl alcohol content, degree of acetalization, residual acetate content, ethylene percentage, molecular weight, and / or different chain lengths of acetal group aldehydes.

[0024] In particular, the aldehyde used in the production of polyvinyl acetal may be linear or branched (i.e., of "n" or "iso" type) containing 2 to 10 carbon atoms, which results in the corresponding linear or branched acetal groups. The polyvinyl acetal is accordingly referred to as "polyvinyl (iso) acetal" or "polyvinyl (n) acetal".

[0025] The polyvinyl acetal used according to the present invention is obtained in particular from the reaction of at least one polyvinyl alcohol with one or more aliphatic unbranched compounds containing 2 to 10 carbon atoms. n-Butyraldehyde is preferably used for this purpose.

[0026] The polyvinyl alcohol or ethylene vinyl alcohol copolymer used for producing the polyvinyl acetal in film A may be the same or different, may be pure, or may be a mixture of polyvinyl alcohols or ethylene vinyl alcohol copolymers having different degrees of polymerization or different degrees of hydrolysis.

[0027] The polyvinyl acetate content of the polyvinyl acetal in film A can be set by using appropriately saponified polyvinyl alcohol or ethylene vinyl alcohol copolymer. The polarity of the polyvinyl acetal is affected by the polyvinyl acetate content, which consequently also changes the compatibility of the plasticizer and the mechanical strength of each layer. It is also possible to carry out acetalization of polyvinyl alcohol or ethylene vinyl alcohol copolymer with a mixture of multiple aldehyde compounds.

[0028] Film A preferably comprises polyvinyl acetal in which the proportion of the same or different polyvinyl acetate groups is 0.1 to 20 mol%, preferably 0.5 to 3 mol%, or 5 to 8 mol%.

[0029] The polyvinyl alcohol content of the polyvinyl acetal used in film A may be 6-26% by weight, 8-24% by weight, 10-22% by weight, 12-21% by weight, 14-20% by weight, 16-19% by weight, preferably 16-21% by weight or 10-16% by weight.

[0030] In a preferred embodiment of the present invention, film A comprises polyvinyl acetal having a vinyl alcohol group proportion of 6 to 26% by weight, and film B comprises polyvinyl acetal B having a vinyl alcohol group proportion of 14 to 26% by weight.

[0031] The vinyl alcohol content and vinyl acetate content of polyvinyl (ethylene) acetal are determined in accordance with DIN ISO 3681 (acetate content) and DIN ISO 53240 (PVA content).

[0032] Film A used in accordance with the present invention may optionally contain the following plasticizers: - Esters of polyhydric aliphatic or aromatic acids, e.g., dialkyl adipates, e.g., dihexyl adipate, dioctyl adipate, hexylcyclohexyl adipate, mixtures of heptyl adipate and nonyl adipate, diisononyl adipate, heptylnonyl adipate, esters of adipic acid with alicyclic ester alcohols or ester alcohol-containing ether compounds, dialkyl sebacate, e.g., dibutyl sebacate, esters of sebacate with alicyclic ester alcohols or ester alcohol-containing ether compounds, esters of phthalates, e.g., butylbenzyl phthalate, or bis-2-butoxyethyl phthalate; - Esters or ethers of polyhydric aliphatic or aromatic alcohols or oligoether glycols having one or more unbranched or branched aliphatic or aromatic substituents, such as glycerol, diglycol, triglycol, or tetraglycol with linear or branched aliphatic or alicyclic carboxylic acids; examples of the latter group include diethylene glycol-bis-(2-ethylhexanoate), triethylene glycol-bis-(2-ethylhexanoate), triethylene glycol-bis-(2-ethylbutanoate), tetraethylene glycol-bis-n-heptanoate, triethylene glycol-bis-n-heptanoate, triethylene glycol-bis-n-heptanoate, tetraethylene glycol dimethyl ether, and / or dipropylene glycol benzoate; - Phosphates having aliphatic or aromatic ester alcohols, such as tris(2-ethylhexyl) phosphate (TOF), triethyl phosphate, diphenyl-2-ethylhexyl phosphate, and / or tricresyl phosphate; - Esters of citric acid, succinic acid, and / or fumaric acid It may contain one or more compounds selected from the following.

[0033] By definition, plasticizers are high-boiling point organic liquids. Therefore, other types of organic liquids with boiling points above 120°C can also be used as plasticizers.

[0034] Preferably, film A contains less than 10% by weight, more preferably less than 5% by weight, and most preferably less than 2.5% by weight of plasticizer.

[0035] In a particularly preferred embodiment, film A does not contain added plasticizers.

[0036] Preferably, the thickness of film A is 5 to 100 μm, more preferably 10 to 50 μm, and particularly 20 to 40 μm.

[0037] Similarly, preferably, film A is bonded to the carrier film with an adhesive strength of 0.05 to 10 N / 3 cm, preferably 0.1 to 5 N / 3 cm, and most preferably 0.5 to 3 N / 3 cm, as measured in accordance with JIS K 6854-3.

[0038] It has now been found that by using a specific carrier roughness Rz, it is possible to produce a film A having one surface that is very smooth and another surface that has a specific roughness. The specific roughness of the surface of film A can be adjusted by selecting a carrier with complementary roughness, and the other surface of film A is very smooth due to the production conditions of the film during solvent casting.

[0039] Preferably, the surface roughness Rz of the film A to be coated or printed is 0.01 to 10 μm, preferably 0.1 to 3.0 μm.

[0040] Similarly, preferably, the surface roughness Rz of the carrier film on the surface in contact with film A, measured before the carrier film and film A come into contact, is 1.0 to 10 μm, preferably 2.0 to 6.0 μm.

[0041] When printing, coating, or any other form of functionalization is performed on the surface of film A, it is advantageous to have one smooth surface in order to obtain a homogeneous pattern of the printed, coated, or functional film. However, the opposite side of film A that is not printed or coated is advantageously given a certain roughness Rz. This roughness can improve degassing during the lamination process.

[0042] The roughness Rz is measured in accordance with DIN EN ISO4288.

[0043] Preferably, at least one surface of film A is provided with a shielding area, conductive wiring for heating purposes, silver nanowires, quantum dots, IR and / or UV reflective coating, coating with light scattering particles, an antenna such as a 5G antenna, a print with decorative elements such as a company logo or color pattern, or a combination of these elements.

[0044] The term "shielding region" refers to a region of film A where the light transmittance in the visible spectrum (380-780 nm) is less than 10%. In modified forms, the shielding may gradually weaken toward transparency, for example, in the form of a dotted line region or a slope, or the shielding region may include a transparent region embedded therein to provide a field of view for, for example, a camera. In such modified forms, at least a portion of the shielding region must have a light transmittance of less than 10% in the visible spectrum.

[0045] The printed or coated layer contains inorganic or organic pigments. Preferred pigments include carbon black, iron oxide, polyaniline, perylene, or spinel pigments. The pigments can be dispersed in a carrier fluid such as water, alcohol, or a mixture of alcohol and water.

[0046] Another aspect of the present invention is a composite film, i) Carrier film and, ii) Film A comprising polyvinyl acetal and / or polyvinyl ethylene acetal and optionally a plasticizer. Includes, Film A has a total residual solvent content of less than 2000 ppm when measured in accordance with JIS K 5601-5-1. Regarding composite films.

[0047] Preferably, the total residual solvent content is less than 500 ppm when measured in accordance with JIS K 5601-5-1.

[0048] Preferably, the residual solvent content of each individual residual solvent is less than 250 ppm when measured in accordance with JIS K 5601-5-1.

[0049] A further aspect of the present invention relates to a film A1 obtained by separating a carrier film from film A of the composite film of the present invention described above, wherein film A1 comprises polyvinyl acetal and / or polyvinyl ethylene acetal and optionally a plasticizer, and has a total residual solvent content of less than 2000 ppm when measured in accordance with JIS K 5601-5-1. Thus, film A1 is a self-supporting film without a carrier. This can be obtained, for example, by peeling the carrier from film A.

[0050] The term "total residual solvent content" refers to the sum of all residual solvents present in the composite film. Water present in the film is not included in the total residual solvent content.

[0051] Suitable solvents for polyvinyl butyral include, for example, chlorinated solvents (methylene chloride and 1,2-dichloroethane), alcohols (methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, isoamyl alcohol), ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, diacetone alcohol), esters (methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, isobutyl acetate, and n-butyl acetate), aromatics (toluene and xylene), and ethers (1,3-dioxolane and tetrahydrofuran). A polyvinyl butyral solution can be prepared using a blend of the aforementioned solvents. To achieve a low residual solvent content in film A, preferred solvents for PVB include methyl ethyl ketone, ethyl acetate, methanol, and ethanol.

[0052] Yet another aspect of the present invention relates to an automobile windshield, comprising the film A1 of the present invention described above.

[0053] There are several ways to use the film of the present invention in the manufacture of a windshield that is laminated together with a standard (=plasticized) polyvinyl acetal film (hereinafter referred to as "film B"). In one simple method, the carrier film is removed, the peeled printed film A is cut to size, stacked, and prepared for lamination by being attached to one of the surfaces or inner glass surfaces of the standard polyvinyl acetal film B before the final assembly of the glass and intermediate layer for the lamination process.

[0054] Alternatively, the composite film can be processed together with the carrier film material (such as PET) in processes where the thicker, less elastic, and more meltable properties of the carrier film material are advantageous, such as cutting, overlapping, and surface lamination. Even film A, which is less than 40 μm thick, can be handled safely until immediately before or during the assembly process when the carrier film is removed. It is also possible to remove any unnecessary cut portions / frames of film A from the carrier film, leaving only the necessary portion of the final size attached. It is possible to place such printed "stickers" together with a larger carrier film without requiring film A to come into contact with either standard polyvinyl acetal film B or the inner glass surface, and by utilizing the release properties of the carrier film, it is possible to 1) pre-bond the printed side of the thin film A to the surface of a blank cut to the appropriate size of standard polyvinyl acetal film B by applying heat and pressure or ultrasonic welding, 2) optionally stack and store multiple such integrated blanks, and 3) peel the carrier film from the back of the "sticker" during assembly before the start of the lamination process.

[0055] The composite film of the present invention can be easily stored in roll form and may help prevent the adhesion and transfer of surface contaminants to the back surface of film A.

[0056] The plasticizer-containing film B used in accordance with the present invention contains at least 22% by weight, for example 22.0 to 45.0% by weight, preferably 25.0 to 32.0% by weight, and particularly 26.0 to 30.0% by weight of plasticizer in its initial state before lamination.

[0057] In addition, films A, A1, and B may also contain additional additives such as residual water, UV absorbers, antioxidants, adhesion regulators, fluorescent whitening agents or fluorescent additives, stabilizers, colorants, processing aids, inorganic or organic nanoparticles, pyrolytic silicic acid, and / or surfactants.

[0058] In particular, film B may contain 0.001 to 0.1% by weight of an alkali metal salt and / or alkaline earth metal salt of a carboxylic acid as an adhesion control agent. Film B preferably contains magnesium ions in an amount of at least 10 ppm, preferably 20 ppm, and most preferably 30 ppm.

[0059] The lamination process for manufacturing laminated glass is preferably carried out by placing films A or A1 and B between two glass plates and pressing the resulting laminate under pressure or reduced pressure and at a high temperature to form a laminate.

[0060] For lamination of the laminate, methods well known to those skilled in the art can be used, with or without prior preparation of the pre-laminate.

[0061] So-called "autoclave processing" is carried out at a high pressure of approximately 10-15 bar and a temperature of 100-150°C for about 2 hours. For example, the vacuum bag method or vacuum ring method according to European Patent No. 1235683 operates at approximately 200 mbar and 130-145°C.

[0062] Vacuum laminators can also be used. These consist of a chamber that can be heated and evacuated, and can laminate glass in 30 to 60 minutes. A reduced pressure of 0.01 to 300 mbar and a temperature of 100 to 200°C, especially 130 to 160°C, have proven to be of practical value.

[0063] Film B may also have a wedge-shaped thickness profile. In the laminated glass laminate according to the present invention, a wedge-shaped thickness profile can be obtained even if the thickness profile is parallel to the surface of film A, and it can be used in automotive windshields for HUD displays.

[0064] The laminated glass according to the present invention can be used in windshields, backlights, and side windows of automobiles, buses, trucks, ships, trains, or airplanes. [Examples]

[0065] Preparation of PVB solution 1 A 16.0% by weight solution of polyvinyl butyral (PVB) powder (commercial grade Mowital® B60H) dissolved in a methanol / ethyl acetate (50:50 wt%) mixture was prepared as the coating fluid "PVB Solution 1".

[0066] Fabrication of composite films A polyethylene terephthalate (PET) film with a matte surface and a thickness of 50 μm (grade #50-X42G, commercially available from Toray Industries, Inc.) was used as a carrier. The surface roughness (Rz) was 4.0 μm.

[0067] A standard commercially available solvent coating apparatus, including an unwinder, coater, dryer, and winder, was used in slot die coating mode. The substrate speed was 1.1 m / min, and the wet thickness of PVB solution 1 on the moving substrate was 200 μm. Coating was performed at a temperature of 26°C. The gap between the coating lip and the moving substrate was 300 μm.

[0068] Drying was carried out in three sections. A roll-supported drying unit was used in the first drying zone, which was 1.5 m long. The temperature in the first zone was set to 80°C and the airflow to 5 m / s. Two air flotation drying units, each 1.5 m long, were used as the second and third drying zones. The temperatures in the second and third zones were set to 110°C and 140°C, respectively. The airflow in both zones was set to 10 m / s. The total drying time for all three zones combined was 4 minutes.

[0069] Visual inspection ("Visual Inspection 1") did not reveal any wrinkles or air bubble defects in the composite film.

[0070] The PET carrier was peeled from the composite material sample, and the thickness of the dried PVB film was measured. Measurements using a thickness gauge showed that the PVB film had a thickness of 25 μm.

[0071] The residual solvent in the PVB film, measured by gas chromatography in accordance with JIS K 5601-5-1, was 60 ppm.

[0072] Fabrication of laminated glass A stack of 20 PVB films prepared as described above was manufactured. Using this stack between two sheets of standard float glass, a 30 x 30 cm laminated glass was fabricated using a vacuum bag and an autoclave. The vacuum bag temperature was set to 100°C. The autoclave pressure was set to 12 bar and the temperature to 140°C.

[0073] Thermal storage test The laminated glass was treated at 160°C for 16 hours. No defects were found during visual inspection ("Visual Inspection 2").

[0074] Preparation of PVB solutions 2 and 3 The following two other coating solutions were prepared: "PVB Solution 2" was prepared as a 17.0% by weight solution in a 50 / 50 (by weight) mixture of methanol and methyl ethyl ketone, from a mixture (22 / 75, by weight) of commercially available grade Mowital® B75H and Mowital® B60H.

[0075] "PVB Solution 3" was prepared as a 13.5% by weight solution in a 50 / 50 (by weight) mixture of methanol and toluene, from a mixture (50 / 50, by weight) of commercially available grade Mowital® B75H and Mowital® B30H.

[0076] Comparison of drying conditions The above-described Example 1 was repeated, but using PVB solutions 1, 2, and 3 as shown in Table 1, and employing different drying conditions.

[0077] [Table 1]

[0078] [Table 2]

[0079] [Table 3]

[0080] Alternative drying conditions according to the present invention Drying in zones 2 and 3 can also be performed using infrared heating according to the present invention. Using infrared heating allows for a further reduction in total drying time while obtaining the same low levels of residual solvent content as described in Examples 1-5. Therefore, the following drying conditions are used: [Table 4]

[0081] Alternative drying conditions not covered by the present invention Replacing the drying process in the first drying zone from roll support to air flotation drying, for example, by performing all three drying processes in air flotation mode, results in a residual solvent content comparable to that described in Examples 1-5. However, omitting the roll support in zone 1 results in bubble defects.

[0082] [Table 5]

Claims

1. A method for manufacturing a composite film, The aforementioned composite film is i) Film A comprising polyvinyl acetal and / or polyvinyl ethylene acetal, and optionally a plasticizer, ii) Carrier film and, Includes, a) Steps to prepare the carrier film, b) A step of coating one side of the carrier film with a solution comprising a solvent, the polyvinyl acetal and / or polyvinylethylene acetal, and optionally the plasticizer. c1) A step of drying the composite film on a roll support at a temperature of 25 to 90°C, and d) A process that involves performing one or more drying steps selected from the list consisting of an IR drying step, a UV drying step, a microwave drying step, a vacuum drying step, a roll-supported drying step at a temperature greater than 130°C but less than 180°C, and an air flotation drying step at a temperature greater than 130°C but less than 180°C. A method that includes these in this order.

2. The method according to claim 1, wherein at least one of the one or more drying steps in step d) is an IR drying step or an air flotation drying step at a temperature greater than 130°C but less than 180°C.

3. The method according to claim 1 or 2, wherein at least one additional drying step c2) is performed between step c1) and step d), and the additional drying step c2) is an air flotation drying step at a temperature greater than 90°C and less than 130°C.

4. The method according to any one of claims 1 to 3, wherein the total drying time of step c1), step d), and any step c2) is 1.0 minute to 5.0 minutes.

5. The method according to any one of claims 1 to 4, wherein the drying time in step d) is 1.0 to 1.5 minutes.

6. The method according to any one of claims 1 to 5, wherein the airflow in each of steps c1), d), and any step c2) is independently 2.5 m / sec to 60 m / sec.

7. The method according to any one of claims 1 to 6, wherein the airflow in step d) is 7.5 m / sec to 60 m / sec.

8. The method according to any one of claims 1 to 7, wherein the carrier film is made from a polymer selected from the group consisting of polylactic acid, acrylonitrile-butadiene-styrene copolymer, polyamide, polycarbonate, polyethylene terephthalate, polyethylene terephthalate copolymer, polyhydroxyalkanoate, polyurethane; polyolefin such as polyethylene or polypropylene; acrylonitrile styrene acrylate, polyacrylate, polymethacrylate, polyvinyl alcohol, TAC (cellulose triacetate), and mixtures thereof, and preferably the carrier is made from polyethylene terephthalate.

9. It is a composite film, i) Carrier film and, ii) A film A comprising polyvinyl acetal and / or polyvinyl ethylene acetal, and optionally a plasticizer, Includes, A composite film in which film A has a total residual solvent content of less than 2000 ppm when measured in accordance with JIS K 5601-5-1.

10. The composite film according to claim 9, wherein the total residual solvent content is less than 500 ppm when measured in accordance with JIS K 5601-5-1.

11. The composite film according to claim 9 or 10, wherein the residual solvent content of each individual residual solvent is less than 250 ppm when measured in accordance with JIS K 5601-5-1.

12. The composite film according to any one of claims 9 to 11, wherein the carrier film is made of a polymer selected from the group consisting of polylactic acid, acrylonitrile-butadiene-styrene copolymer, polyamide, polycarbonate, polyethylene terephthalate, polyethylene terephthalate copolymer, polyhydroxyalkanoate, polyurethane; polyolefin such as polyethylene or polypropylene; acrylonitrile styrene acrylate, polyacrylate, polymethacrylate, polyvinyl alcohol, TAC (cellulose triacetate), and mixtures thereof, and preferably the carrier is made of polyethylene terephthalate.

13. A film A1 obtained by separating the carrier film and the film A of the composite film according to any one of claims 9 to 12, comprising polyvinyl acetal and / or polyvinyl ethylene acetal and optionally a plasticizer, and having a total residual solvent content of less than 2000 ppm when measured in accordance with JIS K 5601-5-1.

14. An intermediate layer for lamination comprising at least two sheets of glass and the film A1 according to claim 13.

15. A windshield for an automobile, comprising the laminate described in claim 14.

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