COMPOSITE FILMS WITH AN OBSCURATION AREA

Abstract

The present invention relates to a composite film comprising a polyvinyl acetal with an obscuration area which is provided on a carrier film.

Claims

1. A composite film comprising: a film A containing a polyvinyl acetal and optionally a plasticiser; and a carrier film, wherein film A is provided with an obscuration area.

2. The composite film according to claim 1 wherein the obscuration area is provided by a printed or coated ink layer on the surface of film A not facing the carrier film.

3. The composite film according to claim 1 wherein the carrier film contains a polymer selected from the group consisting of polylactic acid, acrylonitrile-butadiene-styrene copolymer, polyamides, polycarbonates, polyethylene terephthalate, polyethylene terephthalate copolymers, polyhydroxyalkanoates, polyurethanes, polyolefins, acrylonitrile styrene acrylate, polyacrylates and polymethacrylates, polyvinyl alcohol, and TAC (cellulose tri acetate).

4. The composite film according to claim 1 wherein a thickness of the film A is from 15 to 40 μm.

5. The composite film according to claim 1 wherein a thickness of the carrier film is from 25 to 250 μm.

6. The composite film according to claim 1 wherein film A is adhered to the carrier film with an adhesive strength from 0.05 to 10 N/3 cm.

7. The composite film according to claim 2 wherein a surface roughness Rz of the surface of film A to be coated or printed is from 0.01 to 10 μm, measured before said surface is coated or printed on.

8. The composite film according to claim 1 wherein a surface roughness Rz of the carrier film on the surface in contact with film A is from 1.0 to 10 μm, measured before the carrier film and the film A come into contact.

9. The composite film according to claim 2 wherein the ink comprises a binder selected from the group consisting of vinyl pyrrolidone, a water-soluble acrylic resin, an alcohol-soluble resin, an acrylic resin, a styrene-maleic resin, styrene-acrylate resin, a polyurethane resin, a polyvinyl acetal resin, a polyvinyl alcohol resin and a ketone resin.

10. A film A containing a polyvinyl acetal and optionally, a plasticiser; wherein one surface of the film A is provided with an obscuration area provided by a printed or coated ink layer and wherein the film A is obtained by peeling off a carrier film from the film A.

11. A process for the production of the composite film according to claim 1 comprising the following steps, in that order: a) providing a carrier film; b) coating one surface of the carrier film with a solution comprising a solvent, the polyvinyl acetal or polyvinyl ethylene acetal, and the optional plasticiser; c) evaporating the solvent to obtain the film A on the one surface of the carrier film; and d) providing an obscuration area by printing or coating the surface of the film A not in contact with the carrier film with an ink layer.

12. A process for the production of a windshield comprising two sheets of glass, combined by an interlayer film comprising a film A containing a polyvinyl acetal and optionally, a plasticiser; and a film B containing a polyvinyl acetal and a plasticiser in an amount of at least 22% by weight; comprising the following steps, in that order: a) positioning the composite film according to claim 1 to the first glass sheet with the film A facing the first glass sheet; b) peeling off the carrier film from the film A; and c) positioning the film B on the film A or on the second glass sheet; and d) providing a stack of the layers comprising first glass sheet-film A-film B-second glass in that order; and e) laminating the stack obtained in step d) to produce the windshield.

13. A process for the production of a windshield comprising two sheets of glass, combined by an interlayer film comprising a film A containing a polyvinyl acetal and optionally, a plasticiser; and a film B containing a polyvinyl acetal and a plasticizer in an amount of at least 22% by weight; comprising the following steps, in that order: a) positioning the composite film according to claim 1 to the film B with the film A facing the film B; b) peeling off the carrier film from the film A; c) providing a stack of the layers comprising first glass sheet-film A-film B-second glass in that order; and d) laminating the stack obtained in step c) to produce the windshield.

14. A process for the production of a windshield comprising two sheets of glass, combined by an interlayer film comprising a film A containing a polyvinyl acetal and optionally, a plasticiser; and a film B containing a polyvinyl acetal and a plasticizer in an amount of at least 22% by weight; comprising the following steps, in that order: a) providing the composite film according to claim 2 and peeling off the carrier film from the film A; b) positioning the film A on the first glass sheet with the surface of film A provided with a printed or coated ink layer away from the first glass sheet; c) positioning the film B on film A or on the second glass sheet; d) providing a stack of the layers comprising first glass sheet-film A-film B-second glass in that order; and e) laminating the stack obtained in step d) to produce the windshield.

15. A windshield obtained according to the process of claim 12.

Description

EXAMPLES

Preparation of the Composite Film

[0091] A polyethylene terephthalate (PET) film with a matt surface (grade #50-X42G commercially available from Toray Industries, Inc.) with a thickness of 50 μm was used as carrier. The surface roughness (Rz) was 4.0 μm.

[0092] A 15.5% by weight solution of polyvinyl butyral (PVB) powder (a 45:55 mixture of commercially available grades Mowital® B30H and Mowital® B75H) dissolved in a mixture of methanol/methyl acetate=50:50% by weight was used as coating fluid.

[0093] A commercially available standard solvent coating apparatus including an unwinder, a coater, a dryer and a winder was used in slot die coating mode. The substrate speed was 1.1 m/min and the wet thickness on the moving substrate was 200 μm. The coating was conducted at a temperature of 26° C. The gap between the coating lip and the moving substrate was 300 μm.

[0094] The drying was performed in three sections and the respective temperatures in the drying sections were set to 60° C., 70° C. and 125° C. The total drying time was approximately 4 min.

[0095] The composite film comprising the PVB film A and the PET carrier was wound into rolls. No wrinkles could be identified in the composite film when inspected by eye. The carrier was peeled off from a sample of the composite to measure the thickness of the dry film A. The measurement showed that the film A had a thickness of 25 μm.

[0096] A set of five 3 cm wide and 15 cm long specimens were cut from the composite film and the t-peel adhesive strength was measured with a tensile tester at 20° C. and at a pulling speed of 500 mm/min. The average from the 5 measurements was found to be 1.5 N/3 cm.

Printing onto the Composite Film

[0097] The composite film used in the first step was used in the following printing process.

[0098] A water-based printing ink comprising carbon black-based pigments and polyurethane-based binders was used in the printing process. The printing ink had a viscosity of 20 DIN-seconds (20° C., DIN 4 mm cup).

[0099] The printing ink was applied to the film A of the composite film using a flexographic printing machine. In a first step, the composite film went through an in-line corona treatment unit to improve the ink adhesion on the surface of film A. The corona treated film then went through four printing units which were all equipped with flexible Kodak Flexcel NX relief plates. Furthermore, the first printing unit was equipped with a Zecher 160 L/cm, 10 g/m2(60°) anilox roller, the second one with a Zecher 220 L/cm, 10 g/m2 (60°), the third one with an Apex 180 L/cm, 12 g/m2 (open) and the fourth one with a Zecher 120 L/cm, 20 g/m2 (60°). The drying temperature in the printing units was set to 55° C. After passing the printing units, the composite film went also through an additional drying zone (4 m), which was set to 70° C. During the whole printing process the composite film went through the printing machine with a speed of approximately 80 m/min.

[0100] At the end of the printing process, the composite film was wound on PVC roll core with a diameter of 6 inch.

[0101] Due to the PET carrier film no undried ink was transferred to the bottom side of the PVB film in the wound polymer film roll. The dried ink formed a homogeneously closed layer (dry film thickness of around 7 μm) on the PVB substrate, which appeared completely opaque after visual inspection. The optical density of the dried ink layer was measured with a transmission densitometer (x-rite, model 331C) and was above 3.5.