JPS6330071B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating metal surfaces using certain types of resins which are preferred in order to obtain layers exhibiting particularly satisfactory properties, in particular smoothness.

French Patent No. 2304690 describes a method for treating a metal surface to be coated with aluminum, in particular for the production of a headlight reflector for use in motor vehicles, which first comprises applying a layer of powdered resin on said surface. a process characterized in that it is applied, secondly, the resin layer is melted and solidified on the support, and thirdly, a shiny aluminum coating is deposited on the pretreated surface in a known manner. Regarding the method. According to this method, in particular polyurethane, polyester or epoxy resins are used to form the resin layer.

The inventors have now discovered according to the invention the following resins: polyurethane resins obtained by reticulation from polyol-based adducts of masked polyisocyanates and saturated polyesters with hydroxyl groups, polyesters with carboxyl groups and epoxies. It has been discovered that resin layers exhibiting excellent properties can be obtained using polyester epoxy resins obtained from mixtures of resins, or epoxy resins solidified with optionally promoted or substituted polyamides.

To form a polyester with hydroxyl groups,
The aliphatic polyacids used are, for example, adipic acid, and the aromatic polyacids used are terephthalic acid, isophthalic acid or orthophthalic acid, as well as esters and hydrogenated and halogenated derivatives of these acids, and in particular tetrahydrophthalic acid and hexahydrophthalic acid. be able to. As polyols it is possible to use, inter alia, ethylene glycol, propylene glycol, neobentyl glycol, trimethylolpropane or pentaerythritol.

The polyester containing hydroxyl groups formed starting from these components advantageously contains about 50
It will have a hydroxyl index between ~80 and an acid index of about 4-6. Preferably, terephthalic acid and neopentyl glycol are used to form the polyester.

The polyesters containing hydroxyl groups are then reticulated with adducts based on polyols and masked polyisocyanates, such as toluene diisocyanate, hexamethylene diisocyanate or isophorone diisocyanate masked with caprolactam. The product obtained by this reticulation preferably has a melting range of 65-100°C and a deblocking temperature of 160-180°C.
de'blocage).

In order to obtain a resin layer with particularly favorable smoothness, a small amount (0.5-10%) is added to this polyurethane resin.
It is desirable to add an epoxy resin such as epichlorohydrin and bisphenol A resin, in which case the melting interval is on the order of 80 DEG to 110 DEG C.

To produce the second type of resin used according to the invention, a polyol and preferably an aliphatic or aromatic polyacid selected from among the polyacids mentioned above are combined with an acid index of 30 to 50. to immediately form a polyester having carboxyl groups. Advantageously, the carboxyl-containing polyester will have an average molecular weight of about 1000-6000 and a melting point of the order of 80-100°C.

Terephthalic acid, optionally in mixtures with isophthalic acid, hexahydrophthalic acid and/or tetrahydrophthalic acid, and neopentyl glycol, optionally in mixtures with trimethylolpropane, can be used to form polyesters with carboxyl groups. preferable.

In order to obtain a polyester-epoxy, a polyester having carboxyl groups is preferably used with an epoxy resin having a molecular weight of about 1100 to 2000 and a melting interval of the order of 90 to 100 °C, so that the acid index and the epoxy index are equivalent. Mix in appropriate proportions.

Finally, the third type of resin used according to the invention is obtained by reticulation of epoxy resins with optionally promoted or substituted polyamides such as dicyandiamide. starting epoxy resin,
For example, it is advantageous for the resins based on epichlorohydrin and bisphenol A to have a molecular weight between 1100 and 2000, preferably between 1300 and 1500.

In order to produce the powdered resins which can be used in the process according to the invention, the various resins mentioned above are of course combined with customary additives such as extenders, in particular extenders of the polyacrylate type, and ,
Optionally, inert pigments or anticorrosive agents are added if it is desired to obtain a pigmented, non-colorless resin layer. Extending agents include, inter alia, the product "Modaflow" manufactured by Monsanto, which is used in amounts of about 0.5-2%.

The components, resin and additives in solid form are mixed and dispersed in an extruder, for example of the Buss PR100 type. After the mixture is rolled and cooled,
Next, for example, Micropul's ACM type crusher (un
broyeur type ACM de Mikropull) about 2~
Milled to a particle size of 100μ.

The powder thus obtained is preferably applied by an electrostatic method as described in FR 2304690 and, after calcination at about 180-220°C, completely smooth with an average thickness of about 30-80 μ. Give a membrane. The inventors believe that in order to obtain good smoothness, the polymerization reaction of the resin composition must be completed after a sufficient period of time has passed after the melting of the resin composition, and therefore the reactivity of the powdered resin is too large. I made sure that it was not too much. Of course, this last must likewise exhibit some degree of reactivity so that the required polymerization temperatures are not too high.

As described in FR 2304690, before depositing aluminum on the metal surface, a varnish is applied on top of the resulting resin layer to improve the adhesion of the aluminum layer, and the metal piece is brought to a sufficiently high temperature, i.e. approx. 160
If the temperature is raised above 0.degree. C., the resin layer can be isolated to avoid the risk of salting out phenomena.

When using resins of the type described above, alkyd-melamine varnishes, especially of the water-soluble type, can be advantageously chosen as varnishes. Melamine-formaldehyde modified with fatty acids from plants (e.g. soybean) and etherified with alcohol to a binder with alkyd-type carboxyl groups neutralized with amines (e.g. dimethylethanolamine, triethanolamine, triethylamine, ammonia, etc.) It is made up of resin.

The following examples are illustrative of the invention and are not intended to limit its scope.

Example 1 Use of Polyurethane Resin To form the base hydroxyl-containing polyester, 55 parts of terephthalic acid are reacted with 45 parts of neopentyl glycol to obtain a product with a hydroxyl index of 50. 75 parts of this product plus 20 parts of an adduct based on isophorone diisocyanate masked with caprolactam, 2 parts of an extender (Modaflow from Monsanto)
1 part and 3 parts of epichlorohydrin-bisphenol type A epoxy resin (Epicoat 1004 resin from Schiel) are mixed.

This resin, applied on top of a metal substrate according to the technique described in FR 2304690, gives a layer which exhibits excellent smoothness after firing.

Example 2 Use of Polyester-Epoxy Resin 40 parts of terephthalic acid and 13 parts of tetrahydrophthalic acid are reacted with 47 parts of neopentyl glycol to produce a polyester with a base carboxyl group and an acid index between 40 and 50. Shows about
Gives a product with an average molecular weight of 1200. 60 parts of this product and an epichlorohydrin-bisphenol A type epoxy resin (Epicoat resin from Ciel)
1004) and 1 part of a polyacrylate type extender (Modaflow from Monsanto).

This resin, applied on a metal substrate according to the technique described in FR 2 304 690, gives a layer which exhibits excellent smoothness after firing.

Of course, numerous modifications can be made by those skilled in the art on the basis of known methods without departing from the scope of the invention.

Claims (1)

[Scope of Claims] 1. A method for treating a metal surface to be coated with aluminum for the production of a reflector for a headlight to be mounted on an automobile, comprising: first applying a powdered resin layer on the surface; , as a powdered resin, in a processing method, secondly by melting and solidifying the resin layer on the support and thirdly by depositing a shiny aluminum coating on the pretreated surface in a known manner. Using polyurethane resins obtained by reticulation from polyol-based adducts of masked polyisocyanates and saturated polyesters with hydroxyl groups or polyester-epoxy resins obtained by reaction of polyesters with carboxyl groups with epoxy resins. The above method is characterized in that: 2 A saturated polyester having a hydroxyl group is a polyacid selected from adipic acid, terephthalic acid, isophthalic acid, orthophthalic acid, tetrahydrophthalic acid and hexahydrophthalic acid, and neopentyl glycol, trimethylolpropane, pentaerythritol, ethylene. Process according to claim 1, characterized in that it is obtained by reaction with a polyol selected from glycol and propylene glycol. 3. Process according to claim 2, characterized in that the saturated polyester having hydroxyl groups is obtained by reaction of terephthalic acid and neopentyl glycol. 4 Saturated polyester with hydroxyl groups is approximately
4. Process according to any one of claims 1 to 3, characterized in that it exhibits a hydroxyl index lying between 50 and 80. 5. A method according to any one of claims 1 to 4, wherein the base polyisocyanate is selected from toluene diisocyanate, isophorone diisocyanate and hexamethylene diisocyanate. 6. The method according to any one of claims 1 to 5, characterized in that the polyisocyanate is masked with caprolactam. 7. The method according to any one of claims 1 to 6, characterized in that the polyurethane resin exhibits a melting interval of 65 to 100°C and a deblocking temperature of 160 to 180°C. 8. Process according to any one of claims 1 to 7, characterized in that from 0.5 to 10% by weight of an epoxy resin based on epichlorohydrin and bisphenol A is added to the polyurethane resin. 9 The polyester having a carboxyl group is a polyacid selected from adicipic acid, terephthalic acid, isophthalic acid, orthophthalic acid, tetrahydrophthalic acid and hexahydrophthalic acid, neopentyl glycol, trimethylolpropane, pentaerythritol, ethylene glycol and The method according to claim 1, characterized in that it is obtained by reaction with a polyol selected from propylene glycol. 10 The polyester having carboxyl group is about
Process according to claim 1 or 9, characterized in that it exhibits an acid index lying between 30 and 50. 11. The method according to any one of claims 1, 9 and 10, characterized in that the epoxy resin is based on epichlorohydrin and bisphenol A and has a molecular weight of about 1100 to 2000. 12. A method according to any one of claims 1 to 11, characterized in that an extender of the polyacrylate type is added to the resin. 13. The method according to any one of claims 1 to 12, characterized in that an inert pigment or anticorrosive agent is added to the resin. 14. A method according to claim 1, characterized in that an alkyd-melamine type varnish is applied on top of the resin layer. 15 Claim 14, characterized in that the alkyd-melamine varnish is a water-soluble varnish.
The method described in section.