Wet process chopped fiber mat production
The invention relates to a process for manufacturing a chopped strand mat that can be used for the reinforcement of thermosetting resins. The process comprises a step of dispersing strands, that are chopped and dried after sizing with a sizing liquid comprising an organosilane and a film former, in a white water, then a step of forming a web by passing the dispersion over a forming wire, through which the white water is drained, the strands being retained on said wire, then a step of applying a binder and then a heat treatment step. Chopped strand mats with a uniform mass per unit area of generally between 50 and 1100 g/m 2 are obtained. A few chopped strands are broken down into filaments within the mat.
1 . A process for preparing a chopped strand mat, comprising:
dispersing, in a white water, chopped strands that are dried after sizing with a sizing liquid comprising an organosilane and a film former; then
forming a web by passing the dispersion over a forming wire through which the white water is drained, the strands being retained on said wire; then
applying a binder; and then
heat-treating.
2 . The process as claimed in claim 1 , wherein the dried chopped strands comprise less than 0.2% water by weight.
3 . The process as claimed in claim 2 , wherein the dried chopped strands comprise less than 0.1% water by weight.
4 . The process as claimed in claim 1 , wherein the film former has a molecular mass of between 10000 and 100000 and, after drying at 105° C. for 2 hours, has a solubility in acetone at 20° C. ranging from 50 to 95%.
5 . The process as claimed in claim 1 , wherein the strands have a length ranging from 20 mm to 110 mm.
6 . The process as claimed in claim 1 , wherein, on passing onto the forming wire, the strands are dispersed in white water in an amount from 0.06 to 1% by weight of the sum of the weights of the strands and of the white water.
7 . The process as claimed in claim 6 , wherein, on passing onto the forming wire, the strands are dispersed in white water in an amount from 0.1 to 1% by weight of the sum of the weights of the strands and of the white water.
8 . The process as claimed in claim 1 , wherein the white water comprises a thickener in an amount such that the white water has a viscosity at 20° C. of between 1 and 20 mPa.s.
9 . The process as claimed in claim 8 , wherein the white water comprises a thickener in an amount such that the white water has a viscosity at 20° C. of between 5 and 12 mPa.s.
10 . The process as claimed in claim 1 , wherein the binder is applied in an amount such that the mat comprises between 2 and 20% binder by weight.
11 . The process as claimed in claim 1 , wherein the binder is applied in an amount such that the mat comprises between 3 and 6% binder by weight.
12 . The process as claimed in claim 1 , wherein the heat treating step is carried out by heating between 140 and 250° C.
13 . The process as claimed in claim 1 , wherein the mat has a mass per unit area of between 50 and 1100 g/m 2 .
14 . The process as claimed in claim 13 , wherein the mat has a mass per unit area of between 70 and 150 g/m 2 .
15 . The process as claimed in claim 1 , wherein the strands comprise glass.
16 . The process as claimed in claim 15 , wherein, at the moment of their dispersion in the white water, the sized, chopped and dried strands contain comprise 99% glass by weight.
17 . The process as claimed in claim 1 , wherein the strands comprise 10 to 300 filaments.
18 . The process as claimed in claim 1 , wherein the chopped strand/white water dispersion is permanently at a temperature ranging from 10° C. to 50° C.
19 . A chopped glass strand mat, wherein the mass per unit area of the mat varies by less than 20% over the surface of the mat and at least 80% by weight of the filaments comprised in the mat are in the form of strand comprising at least 10 filaments.
20 . The mat as claimed in claim 19 , wherein the mass per unit area varies by less than 10% over the surface of the mat.
21 . The mat as claimed in claim 20 , wherein the mass per unit area varies by less than 5% over the surface of the mat.
22 . The mat as claimed in claim 19 , wherein at least 90% by weight of the filaments are in the form of strand comprising at least 10 filaments.
23 . The mat as claimed in claim 19 , wherein at least 90% by weight of the filaments are in the form of strand comprising at least 25 filaments.
24 . The mat as claimed in claim 19 , wherein said mat has a mass per unit area of between 50 and 1100 g/m 2 .
25 . The mat as claimed in claim 24 , wherein said mat has a mass per unit area of between 70 and 150 g/m 2 .