DRYING PROCESSES FOR COMPOSITE FILMS COMPRISING POLYVINYL ACETAL AND POLYVINYL ETHYLENE ACETAL RESINS

Abstract

The present invention relates to drying processes for composite films comprising a polyvinyl acetal on a carrier as well as to composite films and polyvinyl acetal films obtained in such processes.

Claims

1. A process for the manufacture of a composite film, said composite film comprising: i) a film A comprising a polyvinyl acetal and/or a polyvinyl ethylene acetal and, optionally, a plasticiser, and ii) a carrier film, said process 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 and/or polyvinyl ethylene acetal, and the optional plasticizer; c1) drying the composite film on roll support at a temperature from 25 to 90 C.; and d) performing one or more drying steps selected from a list consisting of the following steps: IR drying, UV drying, microwave drying, vacuum drying, roll supported drying at a temperature of more than 130 C. and less than 180 C., air floatation drying at a temperature of more than 130 C. and less than 180 C.

2. The process according to claim 1 wherein at least one of the one or more drying steps of step d) is an IR drying step or an air floatation drying step at a temperature of more than 130 C. and less than 180 C.

3. The process according to claim 1 wherein at least one additional drying step c2) is performed between step c1) and step d) and wherein said additional drying step c2) is an air floatation drying step at a temperature of higher than 90 C. and less than 130 C.

4. The process according to claim 1 wherein the total drying time of step c1) and step d) is from 1.0 min to 5.0 min.

5. The process according to claim 1 wherein the drying time of step d) is from 1.0 min to 1.5 min.

6. The process according to claim 1 wherein the air flow in each of step c1) and step d) is independently from 2.5 m/s to 60 m/s.

7. The process according to claim 1 wherein the air flow in step d) is from 7.5 m/s and 60 m/s.

8. The process according to claim 1 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, polyolefins, acrylonitrile styrene acrylate, polyacrylates, polymethacrylate, polyvinyl alcohol, TAC (cellulose tri acetate), and mixtures thereof.

9. A composite film comprising i) a carrier film, and ii) a film A comprising a polyvinyl acetal and/or a polyvinyl ethylene acetal and, optionally, a plasticizer, wherein film A has a total residual solvent content of below 2000 ppm as measured according to JIS K 5601-5-1.

10. The composite film according to claim 9 wherein the total residual solvent content is below 500 ppm as measured according to JIS K 5601-5-1.

11. The composite film according to claim 9 wherein the residual solvent content of each individual residual solvent is below 250 ppm as measured according to JIS K 5601-5-1.

12. The composite film according to claim 9 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, polyolefins, acrylonitrile styrene acrylate, polyacrylates, polymethacrylate, polyvinyl alcohol, TAC (cellulose tri acetate), and mixtures thereof.

13. A film A1 obtained by separating the carrier film and the film A of the composite film according to claim 9, wherein the film A1 comprises a polyvinyl acetal and/or a polyvinyl ethylene acetal and, optionally, a plasticizer, and wherein the film A1 has a total residual solvent content of below 2000 ppm as measured according to JIS K 5601-5-1.

14. An interlayer for a laminate comprising at least two plies of glass and the film A1 according to claim 13.

15. A windshield for a motor vehicle comprising the laminate according to claim 14.

Description

EXAMPLES

Preparation of the PVB Solution 1

[0077] 16.0% by weight solution of polyvinyl butyral (PVB) powder (commercially available grade Mowital B60H) dissolved in a mixture of methanol/ethyl acetate (50:50% by weight) was prepared as coating fluid PVB solution 1.

Preparation of the Composite Film

[0078] A polyethylene terephthalate (PET) film with a matt surface (grade #50-X42G commercially available from Toray Industries, Inc.) with a thickness of 50 m was used as carrier. The surface roughness (Rz) was 4.0 m.

[0079] 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 of PVB solution 1 on the moving substrate was 200 m. The coating was conducted at a temperature of 26 C. The gap between the coating lip and the moving substrate was 300 m.

[0080] The drying was performed in three sections. The roll supported drying unit was used at the first drying zone of 1.5 m length. The temperature of first zone was set to 80 C. and the air flow was set to 5 m/s. Two air floatation drying units were used as the second and third drying zone with a length of 1.5 m each. The temperature of the second and the third zone was set to 110 C. and 140 C., respectively. In both zones, the air flow was set to 10 m/s. The total drying time in the three zones combined was 4 min.

[0081] No wrinkles and bubble defect could be identified in the composite film by visual inspection (visual inspection 1).

[0082] The PET carrier was peeled off from a sample of the composite to measure the thickness of the dry PVB film. Measurement with a thickness gauge showed that the PVB film had a thickness of 25 m.

[0083] The residual solvent of PVB film was 60 ppm measured by gas chromatography according to JIS K 5601-5-1.

Preparation of the Laminated Glass

[0084] A stack of 20 sheets of the PVB film prepared above was made. A laminated glass of 3030 cm was prepared using this stack between two plies of common float glass using a vacuum bag and an autoclave. The temperature of the vacuum bag was set to 100 C. The pressure of the autoclave was set to 12 bar and the temperature was set to 140 C.

Heat Storage Test

[0085] The laminated glass was treated at 160 C. for 16 h. No defect was found by visual inspection (visual inspection 2).

Preparation of PVB Solutions 2 and 3

[0086] Two other coating solutions were prepared:

[0087] PVB solution 2 was prepared from a mixture of commercially available grades Mowital B75H and Mowital B60H (22/75, weight by weight) as a 17.0% by weight solution in a 50/50 (by weight) mixture of methanol and methyl ethyl ketone.

[0088] PVB solution 3 was prepared from a mixture of commercially available grades Mowital B75H and Mowital B30H (50/50, weight by weight) as a 13.5% by weight solution in a 50/50 (by weight) mixture of methanol and toluene.

Comparison of Drying Conditions

[0089] Example 1 as described above was repeated, however, using the PVB solutions 1, 2 and 3 and different drying conditions as described in table 1.

TABLE-US-00001 TABLE 1 Examples according to the invention Total PVB drying Drying Drying Drying Example solution time zone 1 zone 2 zone 3 1 1 4 min roll air air support float float 80 C. 110 C. 140 C. 2 1 4 min roll air air support float float 80 C. 110 C. 150 C. 3 2 4 min roll air air support float float 80 C. 110 C. 140 C. 4 2 4 min roll air air support float float 80 C. 110 C. 150 C. 5 2 2 min roll air air support float float 80 C. 110 C. 150 C.

TABLE-US-00002 TABLE 2 Comparative examples Total Comparative PVB Drying Drying Drying Drying Example solution time zone 1 zone 2 zone 3 1 1 4 min roll air air support float float 90 C. 110 C. 125 C. 2 1 2 min roll air air support float float 90 C. 110 C. 125 C. 3 1 4 min roll air air support float float 100 C. 120 C. 125 C. 4 2 2 min roll air air support float float 40 C. 130 C. 150 C. 5 2 2 min roll air air support float float 110 C. 110 C. 150 C. 6 3 9 min roll air air support float float 60 C. 70 C. 80 C. 7 3 2 min roll air air support float float 90 C. 110 C. 125 C.

TABLE-US-00003 TABLE 3 Test results: total residual solvent content, visual inspection of film A on carrier and laminate after heat storage Total residual visual visual solvent(ppm) inspection 1 inspection 2 Example 1 60 No defect No defect 2 20 No defect No defect 3 180 No defect No defect 4 50 No defect No defect 5 330 No defect No defect Comparative Example 1 570 Bubble defect No defect 2 3000 Bubble defect Bubble defect 3 240 Bubble defect No defect 4 170 Bubble defect No defect 5 260 Bubble defect No defect 6 20800 No defect Bubble defect 7 5800 No defect Bubble defect

Alternative Drying Conditions According to the Invention

[0090] The drying in zone 2 and 3 can also be performed using heating by infrared radiation according to the invention. Using infrared heating, the total drying time can be further reduced while obtaining the same low levels of residual solvent content as described for examples 1 to 5. Thus, the following drying conditions are used:

TABLE-US-00004 Total PVB drying Drying Drying Drying solution time zone 1 zone 2 zone 3 1 4 min roll Infrared Infrared support 110 C. 150 C. 80 C. 2 4 min roll Infrared Infrared support 110 C. 140 C. 80 C. 2 4 min roll Infrared Infrared support 110 C. 150 C. 80 C. 2 2 min roll Infrared Infrared support 110 C. 150 C. 80 C.

Alternative Drying Conditions not According to the Invention

[0091] Replacing the drying step in the first drying zone from roll support to air floatation drying, e.g. performing all three drying steps in air floatation mode, leads to comparable levels of residual solvent content as described for examples 1 to 5. However, omitting the roll support in zone 1 leads to the appearance of bubble defects.

TABLE-US-00005 PVB 4 min air air air solution float float float 1 80 C. 110 C. 150 C.