The present invention relates to a thermosetting hybrid coating system made of epoxy resin and a saturated polyester resin for its application as a heat-protective coating of a vehicle bottom plate and its application method. The coating system of the present invention is a crosslinked composite thick coating formulation that is resistant to mechanical, corrosion and high temperature influences.

The steel bottom plates of motor vehicles are exposed not only to corrosion, mechanical damage caused by stone chips, but also to strong heat effect, especially above the exhaust system, which may cause fire hazards.

To protect against corrosion, the steel is usually coated with some corrosion resistant formulation. It could be paint or synthetic resin.

Bodywork of motor vehicles is usually coated with a chassis protection coating which mainly carries out corrosion protection tasks. In addition to corrosive materials such as salt water, the impact of the chassis protection coating is primarily due to the protection against rock crushing.

In addition to these main tasks, the chassis protection coatings have a noise dampening effect. Relatively thick chassis layers are generally applied on the surface, i.e. liquid or pastelike masses which are cured after application to the chassis of the vehicle bodywork. Here, preference is given to the use of thermosetting chassis protection coatings which are then gelled in the furnace after application. Usually used materials are plastics mixed with plasticizers and bulking agents such as PVC or (meth)acrylates.

The chassis of motor vehicles is subjected to wear and corrosion effects helped by damage originating from rock crushing, gravel on the road, beside the winter salting. Those holes which are not subject to strong wear effect, are sprayed with coating containing wax and these are protected against the corrosion from moisture. The heavy-duty parts of the chassis which is subjected to corrosion and abrasive effects are usually coated with thick coatings containing bitumen, paraffin or thick coatings based on thermoplastic materials (for instance PVC, ABS, etc.). However, there are parts of the chassis which is not only subjected to the abovementioned corrosion helping effects, but the coating shall be resistant to heat as well. Such parts of the chassis are the areas nearthe exhaust system. In such places the coating containing bitumen or paraffin might become too soft, and would abrade from the surface to be protected; after a while these do not protect against corrosion effectively. In such locations the heat protection of the coated chassis or bottom plate consists of a heat shielding metal sheet, heat shield installed between the exhaust system and the bottom plate. Such solutions are introduced in the Audi Ag. (DE): DE19836970 Al number publication (Central tunnel for fitting exhaust system to vehicle chassis has a universal shape with a separate heat shield for each type of exhaust system) patent documentation. Daimler Ag. (DE): DE102012013876 Al publication (Motor vehicle e.g. passenger car has lining portion in intrusion case that is slid at heat shield and avoided collision with respect to exhaust system, and heat shield which is provided between exhaust portion and lining portion) patent documentation.

This solution requires time-consuming extra work with welding and assembly when assembling the car. At the same time, this steel sheet heat shield is subjected to increased corrosion due to the combined presence of winter salting and relatively higher temperature.

In order to avoid the abovementioned mounting disadvantages, products forming thick coating need to be manufactured which have very good heat resistance, and will protect the chassis surface of the motor vehicle that is subjected to strong heat for a long time; and will also protect against corrosion and rock crushing, and can be applied to the surface to be protected easily, by using the so-called "flat stream" technology.

In addition to the abovementioned thick coating products with high filler content, epoxy resin and unsaturated polyester resin based thick coatings are also widely used in the industry for corrosion protection of steel surfaces. The advantages of these coatings are known, but are not generally used to protect the chassis of motor vehicles. Different properties of both epoxy resin and polyester are known as well. The unsaturated polyester resins with relatively good mechanical properties are easy to handle during application. The epoxy resin systems have excellent mechanical and thermal characteristics, and they have highly water resistance, and their shrinkage is small during crosslinking. Their heat resistance might reach 140 °C when wet, and 220 °C when dry, but the coating is sensitive to the accurate ration of the measure of the epoxy resin and curing agent.

During application, due to the different crosslinking properties, the two systems crosslinking and hardening time can be set differently. The crosslinked system is formed in the unsaturated polyester resin by the polymerization of the unsaturated bonds. Crosslinking is controlled by the amount of accelerator and initiator. In case of epoxy resins, the epoxy groups react to the also multifunction crosslinking active groups (for instance amine groups, anhydrides) so the crosslinking reaction is very sensitive to compliance to the stoichiometric ratios.

The thickly applied chassis protection layer shall be at least 200 μιη thick on 30 % of the application surface. It is especially advantageous, if the coating is minimum 200 μιη thick on 80 % of the surface area, but preferably 350-2000 μιη thick layer is applied.

The usual, wet application coating materials can be used as chassis protection. These are mostly PVC or acrylate based, which are configured to a paste substance by adding extenders. Here mostly coatings which are hardened by heat (thermosetting, turn into gel) are used.

The Nippon company shows examples of various thick coatings in JPH 1129133 (A) -STRENGTH POLYURETHANE HEAVY-DUTY CORROSIONPROOF COATED STEEL MATERIAL); JPH 1158609 (A) (HEAVY-DUTY CORROSION-INHIBITIVE STEEL MATERIAL COATED WITH POLYESTER) and of epoxy resin coating in JPS 87158267 (A) number patent documentation titled (PREVENTION OF STRESS CORROSION CRACKING OF STEEL PRODUCT). The solution introduced in patent description under number JPH 1129133 (A), the 1 to 6 mm of polyurethane layer is applied to the steel surface treated with primer, then a polyester layer containing glass fibers is laminated on it. In patent description under number JPH 1158609 (A), polyester layers of 1 to 10 mm, containing glass fibers, are applied as stress-resistant thick coating against corrosion. In patent description under number JPS 87158267 (A), to protect high-strength steel sheets against stress corrosion an epoxy resin thick coating is applied on epoxy or polyurethane based primer coating, containing corrosion resisting chromate, molibdate, and phosphate based pigment and coupling agents.

The object of the present invention is to provide a synthetic resin thick coating composition which is suitable to work as a protection, applied on the steel sheet surfaces of a motor vehicle in such areas where corrosion protection is already in place or not, to be resistant against the heat coming from the exhaust system, and to protect the surfaces coated or not coated from overheating, enhance their corrosion resistance, and therefore lengthen their lifespan. Our goal was as well to combine many benefits as possible of the earlier coating systems. Another requirement of the product according to our goal is that it shall be applicable by the flat stream method so widely used in the car industry for applying thick coating.

We recognized that we can combine the advantageous properties of the epoxy resin and the unsaturated polyester resin coatings by forming a coating composition consisting of the two different types of resin systems. It is well-known that epoxy resin products usually consist of two components, namely the epoxy resin part (component A) and crosslinking part (component B) selected from the compounds having two or more function groups that react with epoxy group. Polyester resin compositions can be crosslinked by initiator and accelerator, or just accelerator. In case of polyester compositions, the compositions are prepared in a number of ways by mixing the initiator with a carrier (which may be the filler which is part of the formulation) when mixed with the polyester resin, apparently as a second component B. This makes it easier to set the mixing ratio.

By combining the two systems into a two-component formulation, the advantages of both heat-curing resin systems can be used to protect steel plates against heat and corrosion. Of course, such systems can be also used perfectly in other application.

The synthetic resin system according to the invention consists of two components, component A and component B. Both components are liquids containing filler materials and other additives, and when mixing with each other, they harden irreversibly and form crosslinking. In case of setting on a solid surface, the resin mixture of A and B can be removed from the solid surface only by destructive methods.

The two main components of the synthetic resin system according to the present invention is epoxy resin and unsaturated polyester resin. For the crosslinking of the epoxy resin well-known crosslinking substances are used, mostly we choose from the following crosslinking agents: metaphenylenediamine, methylhexahydrophthalic anhydride (MHHPA), phthalic anhydride, maleic anhydride, bis(4-aminophenyl)-methane. Peroxides are generally used as initiators for the initiation of polyester crosslinking, preferably lauroyl peroxide, acetylbenzoyl peroxide, benzoyl peroxide, 2-butanone peroxide, methyl ethyl ketone peroxide, methylisobutyl peroxide.

In the production of the synthetic resin coating system suitable for the purpose of the present invention 1 to 2 t% aluminium flakes, 1 to 3 t% cork powders (Grain size: 0.2 to 1.5 mm), 30 t% aluminium hydroxide (Grain size: 0.02 mm) 5 to 10 t% Hollow glass spheres 'Q- ceir (Grain size: 0.02 to 0.07 mm) and 1 to 3 t% ground glass fibres (fibre length: 0.5 to 1.0 mm) are used as fillers.

The system according to the invention is created so that one of the components (Component A) contains the epoxy resin and one of the peroxides initiating the crosslinking of the unsaturated polyester resin is put with the other additives to be used. The other component (Component B) contains the unsaturated polyester resin and the crosslinking agent of the epoxy resin, also with the other additives.

The experiments were carried out in creating the epoxy-polyester synthetic resin hybrid system and it was found that unsaturated polyester based component can only be used in the system, if the mixture does not behave differently after mixing, meaning its viscosity does not increase, it does not warm up, that is it doesn't react to the other components. We found during our experiments that the unsaturated polyester blends into the system best if we mostly used anhydride type crosslinking agents as the crosslinking agent of the epoxy resin, that is we mixed this type of crosslinking agent with the unsaturated polyester into Component B. This type of crosslinking agents did not show any reaction to the unsaturated polyester resin.

The component A may also be incorporated into the peroxide initiator without reacting at room temperature with the epoxy resin. This component can be stored for several months without noticeable property change.

Following the mixing of Component A and B, the reaction does not start immediately at room temperature, since the peroxide (benzoyl peroxide) used in the invention decomposes very slowly at room temperature, so it does not initiate the polymerization / crosslinking of the polyester component. It is known that not only high temperatures, but ultraviolet light also can initiate the decomposition of peroxide, releasing free radicals, resulting in the polymerization of polyester. It means that following the mixing and application of mixed Components A and B, but before heat treatment, applying UV light, if necessary can accelerate the decomposition of the initiator, stabilizing the coating, significantly decreasing or preventing its drooping during heat treatment.

The synthetic resin hybrid system according to the invention is illustrated by examples. At the same time, it should be noted that experts can use the inventive idea for other areas of use without any modification, and find via routine experiments many compositions. The examples shown only illustrate the invention idea, without exclusively restricting to those the invention to be protected.

Examples of heat insulation, corrosion resistant hybrid synthetic resin coating systems: Resin basic materials used:

Bisphenol A diglycidyl ether epoxy resin:

- Ipox ER 1010: epoxy equivalent: 186 to 192 g/ekv; viscosity: 10000 to 14000 mPa.s (25 °C)

- manufacturer: Ipox Chemicals Kft, HU

Epoxy resin crosslinking agent

- methylhexahydrophthalic anhydride (MHHPA): viscosity 50 to 70 mPa.s (25 °C) Isophthalic acid based unsaturated polyester resin:

- Crystic 199: acid equalent: 27 mg KOH/g; viscosity 600 mPa.s {25 °C)

- manufacturer: Scott Bader, UK

Example 1

Component A: (215.6 tr)

epoxy resin Ipox ER 1010 100 parts by weight benzoyl-peroxide 50 wt % powder 0.6 parts by weight aluminium flakes 5 parts by weight

AI(OH)3 (20 μιη grain size) 100 parts by weight cork powder (1 mm grain size) 10 parts by weight

Component B: (280 tr)

polyester resin Crystic 199 50 parts by weight

MHHPA 80 parts by weight hollow glass spheres (Q-cell, 20 μιη grain size) 40 parts by weight

AI(OH)3 (20 μιη grain size) 100 parts by weight cork powder (1 mm grain size) 10 parts by weight Each of the two components above are mixed individually, using one of the known mixing methods. The components are individually stable, their consistency does not change, reaction, heat increase cannot be observed. Using MHHPA is advantageous because it is a liquid with a relatively small viscosity (50 to 70 mPa.s, 25 °C), and it makes it easy to mix the fillers into it.

The two components can be stored at room temperature for a long time without any change in their consistency. For application, Components A and B are thoroughly mixed in a 1 : 1.3 weight ratio. The two components mixed together can be stored at room temperature for several days, while at 80-120 °C temperature it will start to jellify for at least 5 hours.

Example 2

Component A: (78 tr)

Ipox ER 1010 epoxy resin

benzoyl-peroxide 50 1% powder

aluminium flakes

AI(OH)3 (20 μιη grain size)

cork powder (1 mm grain size)

Component B: (107 tr)

Crystic 199 polyester resin

MHHPA

hollow glass spheres (Q-cell, 20

AI(OH)3 (20 μιη grain size )

cork powder (1 mm grain size)

Each of the two components shall be mixed individually according to the above. For application, Components A and B are mixed together in a 1 : 1.37 mass ratio. The two components mixed together can be stored at room temperature for days, but on 80-120 °C temperature it will start to jellify within 5 hours.

In the next example we present a heat insulation, corrosion resistant hybrid synthetic resin coating system that is suitable for the so called flat stream application technology of the car industry. Example 3

Component A:

!pox ER 1010 epoxy resin 50 parts by weight benzoyl-peroxide 50 1% powder 1.2 parts by weight aluminium flakes 5 parts by weight

AI(OH)3 (20 μιη grain size ) 40 parts by weight cork powder (1 mm grain size) 5 parts by weight

Component B:

Crystic 199 polyester resin 40 parts by weight

MHHPA 40 parts by weight hollow glass spheres (Q-cell, 20 μιη grain size) 20 parts by weight

AI(OH)3 (20 μιη grain size) 40 parts by weight cork powder (1 mm grain size) 5 parts by weight

Each of the two components shall be mixed individually according to the above. For application, Components A and B are mixed together in the ratio set above, 1 : 1.43 mass ratio. There is no change at room temperature for 3 hours. Above 80 0C, the crosslinking of the polyester starts due to the effect of benzoyl-peroxide, and because of the growing reaction heat the crosslinking of the epoxy resin also begins.

If the crosslinking is done at a higher temperature, according to the usage conditions purposefully at about 140 °C in case of coating, the hardening (setting) of the coating takes place in 10 minutes. Without polyester accelerator it would take place perfectly only in hours.

The storing time of the epoxy resin and MHHPA crosslinking mixture, without polyester resin content, is 12 months at room temperature. Its pot life is 5 hours at 80-140 °C (data: Broadview Technologies, Inc., USA). This also underlines the accelerator effect of mixing in the polyester resin system.

Application technology

The synthetic resin shall be mixed in the spraying device, and the necessary amount applied according to the above mentioned flat stream technology by a high pressure (5-50 x 106 Pa) gun on the plates or other parts on the bottom surface of motor vehicles in assembly and moving high above, in 1 to 6 mm thickness. Next the full hardening (setting) of the coating on the chassis or parts of the motor vehicle is completed by the usual method and at temperature in furnaces. If possible, following the application but before the heat treatment we can speed up the decomposition of the initiator into free radicals by using UV light, therefore the polyester component is partly polymerized, leading to the stabilization of the coating against possible extrusion during heat treatment.

The properties of the coating created by using the synthetic resin hybrid coating system as in example 3:

Density 0.65 to 0.85 g/cm3

Combustibility according to UL94 examination VO

Not soluble in water, oil, petrol

Does not contain hazardous materials

Measurement data regarding its heat insulation properties are shown in Table

I and II

The heat resistance of the coating according to the invention : measured in drying oven, at least: 160 °C

The heat resistance of the traditional coating: measured in drying oven, at most: 136 °C

Table 1 Geometric dimensions of the samples evaluated

Sample Surface

Thickness [mm] Length [mm] Width [mm]

number [m2]

1 2 3 4 averag 1 2 1 2

1 5.61 5.67 5.51 5.44 5.56 81.00 81.05 80.60 80.53 0.0065

2 4.36 4.40 4.29 4.30 4.34 80.10 80.25 80.10 80.15 0.0064

3 8.40 8.60 8.49 8.55 8.51 82.04 81.96 81.14 80.84 0.0066

Table 2

Temperature values measured and thermal conduction coefficient calculated when determining thermal conduction coefficient