Liquid (meth)acrylic syrup, method for impregnating a fibrous substrate with said syrup, and composite material produced after polymerisation of said impregnation syrup

1. A viscous liquid (meth)acrylic syrup, whose dynamic viscosity is within a range from 10 mPa.s to 10,000 mPa.s at 25° C., comprising:

a) 10 to 60 parts by weight of a (meth)acrylic polymer having a molecular weight of greater than 100,000 g/mol,

b) 40 to 90 parts by weight of a (meth)acrylic monomer,

c) 0.1 to 3 parts by weight of an initiator to start the polymerization of the (meth)acrylic monomer, said initiator being in the form of a peroxide compound that is liquid in a temperature range of between 0° and 50° C.,

said syrup being characterized in that the initiator is combined with an accelerating system comprising:

d) 0.0005 to 0.1 part by weight of vanadium salt and

e) 0.05 to 1 part by weight of a tertiary amine,

the parts by weight relative to the sum of the (meth)acrylic monomer and of the (meth)acrylic polymer, the two together representing 100 parts by weight.

2. The (meth)acrylic syrup as claimed in claim 1 , wherein the vanadium salt d) is a salt comprising phosphorus ligands.

3. The (meth)acrylic syrup as claimed in claim 2 , wherein said vanadium salt d) comprising phosphorus ligands is selected from the group consisting of trialkyl phosphates, and dialkyl phosphates with alkyl chains comprising between 2 and 20 carbon atoms.

4. The (meth)acrylic syrup as claimed in claim 1 , wherein the tertiary amine e) is chosen from N,N-dimethyl-p-toluidine (DMPT), N,N-dihydroxyethyl-p-toluidine (DHEPT), N,N-diethyl-p-toluidine (DEPT) and para-toluidine ethoxylate (PTE).

5. The (meth)acrylic syrup as claimed in claim 1 , wherein the liquid peroxide compound c) is an organic peroxide comprising 2 to 30 carbon atoms, chosen from hydroperoxides, ketone peroxides and peroxyesters.

6. The (meth)acrylic syrup as claimed in claim 5 , wherein the peroxide compound is a hydroperoxide chosen from: tert-butyl hydroperoxide, monohydroperoxide, para-methane hydroperoxide, tert-amyl hydroperoxide and cumene hydroperoxide.

7. The (meth)acrylic syrup as claimed in claim 1 , wherein the constituent monomers of the syrup comprise between 0 and 5 parts by weight of aromatic vinyl monomer.

8. The (meth)acrylic syrup as claimed in claim 7 , wherein the aromatic vinyl monomer is not styrene.

9. The (meth)acrylic syrup as claimed in claim 1 , wherein the constituent monomers of the syrup comprise between 0 and 5 parts by weight of multifunctional monomers.

10. The (meth)acrylic syrup as claimed in claim 1 , wherein the constituent monomers of the syrup comprise futhermore between 0 and 5 parts by weight of oligomers bearing methacrylate functionalities.

11. The (meth)acrylic syrup as claimed in claim 1 , wherein said syrup has a dynamic viscosity with a value within the range from 50 mPa.s to 5000 mPa.s.

12. A fibrous substrate impregnated with the (meth)acrylic syrup of claim 1 , said fibrous substrate consisting of long fibers, the fibers of which have a length ratio of at least 1000.

13. A process for polymerizing a viscous liquid (meth)acrylic syrup as claimed in claim 1 , said syrup being a two-component system comprising a first component resulting from the mixing of compounds a), b), d) and e) and a second component comprising the initiating compound c), said process consisting in mixing the first and second component of the two-component system less than 10 minutes before injection into a mold or impregnation of a fibrous substrate.

14. A process for manufacturing structured mechanical parts or articles, wherein said process comprises the following steps:

a) impregnating a fibrous substrate with a viscous liquid (meth)acrylic syrup as claimed in claim 1 ,

b) polymerizing said viscous liquid (meth)acrylic syrup impregnating said fibrous substrate.

15. The process as claimed in claim 14 , wherein the impregnation of the fibrous substrate in step a) is performed in a closed mold.

16. The process as claimed in claim 14 , wherein step a) of impregnating a fibrous substrate and step b) of polymerization are performed in a closed mold.

17. The process as claimed in claim 14 , wherein the process is chosen from resin transfer molding and infusion.

18. The process as claimed in claim 14 , wherein the temperature of the polymerization in step b) is below 120° C.