Veil with a PVOH fibre binding agent
View Patent ↗The process according to the invention comprises: a step in which chopped filaments and discontinuous PVOH fibers are dispersed in a process water, followed by a step in which a bed is formed in a forming device by passing the dispersion over a forming cloth through which the process water is drained, the filaments and fibers being retained on said cloth, followed by a heat treatment step in a stoving device. The PVOH fibers impart rigidity to the bed of fibers being formed. This process provides a veil with a very high tensile strength for low proportions of binder.
1. A continuous process for the manufacture of a veil comprising:
a. forming a dispersion of chopped filaments comprising glass filaments and discontinuous PVOH fibers in a process water, then
b. forming a bed in a forming device by passing the dispersion over a forming cloth through which the process water is drained, said cloth being a conveyor belt, the filaments and fibers being retained on said cloth, then
c. subjecting the bed to a heat treatment on a conveyor belt in a stoving device, wherein said veil comprises glass filaments and 1.5 to 15% by weight of a binder which comprises PVOH,
wherein the passage from the forming device to the stoving device causes the bed to undergo at least one belt hop.
2. A process as claimed in claim 1 , wherein the weight of PVOH fibers comprises 1.5 to 20% of the total weight of chopped filaments and PVOH fibers.
3. A process as claimed in claim 1 , wherein the chopped glass filaments are introduced into the process water in the form of yarns comprising 10 to 2000 dispersible filaments.
4. A process as claimed in claim 1 , wherein the weight of PVOH fibers comprises 2.5 to 15% of the total weight of chopped filaments and PVOH fibers.
5. A process as claimed in claim 1 , wherein the PVOH fibers have a length ranging from 3 to 15 mm.
6. A process as claimed in claim 1 , wherein at the beginning of the forming step, the total weight of filaments fibers represents 0.01 to 0.5% of the weight of the dispersion.
7. A process as claimed in claim 6 , wherein at the beginning of the forming step, the total weight of filaments+fibers represents 0.02 to 0.05% of the weight of the dispersion.
8. A process as claimed in claim 1 , wherein the process water comprises a thickener and has a viscosity of between 1 and 20 mPa·s at 20° C.
9. A process as claimed in claim 8 , wherein the process water comprises a thickener and has a viscosity of between 5 and 12 mPa·s at 20° C.
10. A process as claimed in claim 1 , wherein the veil comprises 2.5 to 10% by weight of binder.
11. A process as claimed in claim 1 , wherein the PVOH fibers form 25 to 100% of the total weight of binder in the veil.
12. A process as claimed in claim 1 , wherein the binder is exclusively PVOH.
13. A process as claimed in claim 1 , wherein the veil comprises at least 80% by weight of glass in the form of filaments.