IMPROVED RESIN SYSTEM FOR INTUMESCENT COATINGS

Abstract

An innovative reactive resin system can be used for intumescent coating. Intumescent coatings are used in particular for fire protection of metallic components, such as girders in structural engineering. In a fire scenario, these coatings are reactively foamed and so form a fire-resistant insulating layer with low thermal conductivity around the metal girder, with the resultant insulation retarding premature failure of this component. The resin systems are prepared by an innovative process where the monomer fraction is polymerized only up to a maximum degree of 70%. The glass transition temperature of this polymeric component of the resultant composition is particularly low.

Claims

1. A process for preparing a reactive resin for intumescent coatings, the process comprising: polymerizing a monomer mixture comprising at least one acid-functional monomer to a degree of polymerization of not more than 70%, and discontinuing polymerization, to obtain a resultant polymer, wherein the resultant polymer has a glass transition temperature of less than 23° C.

2. The process according to claim 1, wherein the monomer mixture comprises at least 90 wt % of acrylates and/or methacrylates.

3. The process according to claim 1, wherein the at least one acid-functional monomer comprises acrylic acid, methacrylic acid, itaconic acid, and/or 2-carboxyethyl acrylate.

4. The process according to claim 1, wherein the monomer mixture comprises 20 to 60 wt % of MMA.

5. The process according to claim 1, wherein the monomer mixture consists of the at least one acid-functional monomer and at least one further monomer selected from the group consisting of MMA, n-butyl (meth)acrylate, isobutyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, ethylhexyl (meth)acrylate, and styrene.

6. The process according to claim 1, wherein the monomer mixture contains up to 3 wt % of di- or trifunctional (meth)acrylates.

7. The process according to claim 1, wherein after discontinuing the polymerization, the polymeric constituent has a weight-average molecular weight Mw of between 10,000 and 200,000 g/mol.

8. The process according to claim 1, wherein the resultant polymer has a glass transition temperature of between −20° C. and 20° C.

9. The process according to claim 1, wherein the degree of polymerization on discontinuation of the polymerization is between 10 and 50 wt %.

10. A formulation for a 2-component intumescent coating, wherein the formulation after mixing of the 2-component system contains: 30 to 50 wt % of the reactive resin preparable according to claim 1, 35 to 60 wt % of a blowing agent, 0.1 to 2.5 wt % of a peroxide and/or azo initiator, optionally up to 2 wt % of an accelerator, optionally 4.9 to 15 wt % of at least one additive, and 5 to 30 wt % of at least one filler.

11. The formulation according to claim 10, wherein the formulation additionally contains pigments.

12. A method for intumescent coating of a metal surface, the method comprising: preparing the formulation according to claim 10, applying the formulation within 1 to 20 minutes to the metal surface, and curing the formulation within 60 minutes at a temperature of between 0 and 30° C.

13. The process according to claim 3, wherein the at least one acid-functional monomer comprises 2-carboxyethyl acrylate.

Description

EXAMPLES

[0032] The glass transition temperatures reproduced in the claims were calculated using the Fox equation and are authoritative. As a check the glass transition temperature was determined via DSC. Deviations from the values determined using the Fox equation were found to be less than 2° C.

[0033] The measurement of the glass transition temperatures using DSC is made according to DIN EN ISO 11357-4 with the following measurement programme:

[0034] 1.) Cooling to −30° C. and temperature hold for 10 min

[0035] 2.) Heating from −30° C. to 60° C. at 10 K/min

[0036] 3.) Temperature hold at 60° C. for 5 min

[0037] 4.) Cooling to 0° C. and temperature hold for 5min

[0038] 5.) Heating of sample from 0° C. to 120° C. at 10 K/min

[0039] 6.) Temperature hold at 120° C. for 5 min.

[0040] The determination of the glass transition temperature is made in step 5.). Apparatus used was as follows:

[0041] DSC 1, dynamic heat-flow scanning calorimetry from Mettler Toledo Analytical balance accurate to 0.001 mg Crucible and universal crucible press from Mettler Toledo

[0042] The molar weight was determined using gel permeation chromatography (GPC) in line with DIN 55672-1: SDV columns Eluent: THF with 0.1 weight % addition of trifluoroacetic acid Measuring temperature 35° C. Universal calibration against polystyrene standards and conversion to PMMA equivalents via Mark-Houwink relationship.

Example 1:

[0043] The monomer mixture, consisting of 44.64 wt % of MMA, 46.24 wt % of ethylhexyl methacrylate, 8.81 wt % of n-butyl methacrylate and 0.31 wt % of beta-CEA, is mixed at room temperature with di(4-tert-butylcyclohexyl) peroxydicarbonate or 2,2′-azobis(isobutyronitrile) for the target molecular weight of 60 000 g/mol. A 50% fraction of the monomer mixture as a preliminary batch is heated with stirring to 74° C.: the heating is shut off and at 86° C., by continuous addition of the fraction of the monomer mixture accounting for the second 50%, polymerization takes place autothermally at 93° C. After a metering time of around 30 minutes, the procedure is at an end. Following the after-reaction time, the batch is slowly cooled to 30° C. and is stabilized with 15 ppm (15 mg/kg) of 2,6-di-tert-butyl -4-methylphenol (Topanol O).

[0044] The viscosity is determined via the 55 s flow time from cup 4, corresponding to 30-150 mP*s at 20° C. The target polymer content is around 25%. According to the Fox equation, the polymer formed has a glass transition temperature of −7.71° C. and is not crosslinked.

Example 2:

[0045] The monomer mixture, consisting of—based on the total amount of the monomers employed—15.09 wt % of ethylhexyl methacrylate, 8.81 wt % of n-butyl methacrylate and 0.31 wt % of beta-CEA, is introduced at room temperature into a 1L jacketed reactor and then mixed with the initiator, tert-butyl 2-ethylperoxyhexanoate (TBPEH), and the chain transfer agent, 2-ethylhexyl thioglycolate (TGEH). The amounts are adjusted for the target polymer weight of around 60 000 g/mol. This reaction mixture is heated with stirring at 75° C. (water bath).

[0046] The reaction commences after around 15 minutes, and a steady rise in temperature by around 15 to 20° C. is observed. After around 2.5 hours, the maximum temperature is reached and the procedure is at an end.

[0047] The internal temperature falls. At around 80° C., the thermostat is set to 80° C. and the batch is after-reacted for around an hour. During this time a rise in the viscosity is observed.

[0048] Before being cooled, the polymer is diluted with a second monomer mixture, consisting of 44.64 wt % of MMA and 31.15 wt % of ethylhexyl methacrylate, and is stabilized with 15 ppm (15 mg/kg) of 2,6-di-tert-butyl-4-methylphenol (Topanol O).

[0049] The viscosity is determined via the 30 to 80 s flow time (cup 4) at 20° C. This corresponds to a viscosity of 30 to 150 mPa*s. According to the Fox equation, the polymer formed has a glass transition temperature of 5.4° C. and is not crosslinked.

[0050] The target polymer content is around 25%.

[0051] Use example:

[0052] 42 wt % of the reactive resin from Example 1 are preformulated in each case with 29 wt % of ammonium phosphate, 8 wt % of pentaerythritol, 10 wt % of melamine and 10 wt % of titanium dioxide. These formulations are then divided into two fractions of equal size, with one fraction being admixed—based on the overall formulation—with 0.5 wt % of N,N-dimethyl-para-toluidine, and the other fraction being admixed with 0.5 wt % of benzoyl peroxide. These two fractions are subsequently mixed with one another and a small portion is removed. With the larger portion, a steel plate is coated in a coat thickness of 7 mm, while the smaller sample is used for measurement of the pot life and of the maximum temperature after mixing. The pot life, being the time within which the viscosity is ideal for application of the coating, was 13 min. The maximum temperature of 59.8° C. was attained after 40 min.