JPH0214942B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application] The present invention provides a baking lacquer containing an acid catalyst based on a thermally crosslinkable acrylic, polyester or alkyd resin, which can be cured by the action of light and moisture by adding an N-substituted polyalkylpiperidine derivative. It concerns a method of stabilizing against [Prior Art] Depending on the circumstances, baking paints based on thermally crosslinkable acrylics, polyesters or alkyd resins are used, especially in the case of retouch finishing paints and high solids lacquers for the industrial finishing sector. An acid catalyst is added to the composition. The use of light stabilizers of the type consisting of polyalkylpiperazine derivatives in such compositions can lead to precipitation, delayed curing, agglomeration of pigments and a reduction in the light stabilizing effect due to the formation of salts caused by the light stabilizer and the acid catalyst. etc. are often observed. European Patent Application No. 6213 addresses these problems with polyalkylpiperidine light stabilizers in which the piperidine nitrogen is substituted, in particular with the following formula: (In the formula, R represents a hydrogen atom or a methyl group,
R ₁ is an alkyl group having 1 to 18 carbon atoms, a hydroxyalkyl group having 1 to 6 carbon atoms, an alkenyl group having 3 to 8 carbon atoms, or 3 carbon atoms;
It represents an alkynyl group having 7 to 8 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, the alkyl portion of which may be substituted with a hydroxyl group, an alkanoyl group having 1 to 8 carbon atoms, or an alkenoyl group having 3 to 5 carbon atoms. ) has been proposed as a solution by the single use of a light stabilizer having a group represented by: This type of N-
Substituted piperidine derivatives indeed have considerably more advantageous physical properties with respect to signs of visual deterioration than their N-unsubstituted derivatives, i.e. compounds having a group of the formula in which R ₁ represents a hydrogen atom. ing. [Problem to be Solved by the Invention] Many of the N-substituted light stabilizers described in European Patent Application No. 6213 do not meet the actual requirements in some cases in the field of paint technology. I found out something. When the catalyst concentration is very low and the stoving temperature is low, significant cure retardation can occur. When a cured lacquer is placed in a humid atmosphere, it becomes opaque and exhibits a phenomenon referred to by those skilled in the art as "blushing." Moreover,
Cured lacquers have insufficient stability to solvents and insufficient scratch resistance. However, a particularly selected group of compounds having a group of the formula has been found to be free of these disadvantages and are therefore suitable and preferred light stabilizers for stoving lacquers containing catalysts. SUMMARY OF THE INVENTION The present invention therefore provides light stabilizers for stoving lacquers containing acid catalysts based on thermally crosslinkable acrylic, polyester or alkyd resins of the following formula: [In the formula, n represents 1 or 2, R represents a hydrogen atom or a methyl group, and R ₁ represents an alkanoyl group having 1 to 8 carbon atoms, an alkenoyl group having 3 to 5 carbon atoms, a sorboyl group, a cinnamoyl group ,
an alkoxycarbonyl group having 2 to 5 carbon atoms or (R ₂ )(R ₃ )NCO—(wherein R ₂ is an alkyl group having 1 to 12 carbon atoms, a cyclohexyl group,
represents a phenyl group or a phenyl group substituted with a halogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms, R ₃ is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms; group, cyclohexyl group or benzyl group. ), R ₇ is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an allyl group, a benzyl group, a glycidyl group, or a group having 2 carbon atoms.
Represents an alkoxyalkyl group of 3 to 6 carbon atoms, and when n represents 1, R ₈ is a hydrogen atom, an alkyl group of 1 to 12 carbon atoms, a glycidyl group, an alkenyl group of 3 to 5 carbon atoms, or an alkenyl group of 7 to 9 carbon atoms. represents an aralkyl group having 5 to 7 carbon atoms, a cycloalkyl group having 5 to 7 carbon atoms, an acyloxyalkyl group having 2 to 6 carbon atoms, or an aryl group having 6 to 10 carbon atoms, and when n represents 2;
R ₈ is an alkylene group having 2 to 12 carbon atoms, an arylene group having 6 to 12 carbon atoms, or -
CH ₂ CH (OR ₁ ) CH ₂ - (OCH ₂ - CH (OR ₁ )
Represents a group represented by CH ₂ ) ₂ . This invention relates to a method of using an N-substituted 2,2,6,6-tetraalkylpiperidine compound represented by the following formula, optionally together with other stabilizers. In the formula, R and R ₇ represent hydrogen atoms,
Compounds in which R ₁ represents an acetyl group and R ₈ represents a dodecyl group are preferred. Examples of this type of polyalkylpiperidine light stabilizers include the following. 3-dodecyl-1,3,8-triaza-7,
7,9,9-tetramethyl-8-acetyl-spiro[4.5]decane-2,4-dione, 3-benzyl-1,3,8-triaza-7,7,9,9-tetramethyl-8- Acetyl-spiro[4.5]decane-2,4-dione, 3-n-octyl-1,
3,8-triaza-7,7,9,9-tetramethyl-8-acryloyl-spiro[4.5]decane-
2,4-dione, 3-aryl-1,3,8-triaza-1,7,7,9,9-pentamethyl-8
-Propionyl-spiro[4.5]decane-2,4
-dione or a compound represented by the following formula: Polyalkylpiperidine light stabilizers that form chemical bonds with the lacquer binder can also be used. This occurs when the polyalkylpiperidine derivatives have reactive groups suitable for this purpose, such as glycidyl groups, hydroxyl groups or methylol groups. If the piperidine light stabilizer has a polymerizable group as R ₁ or at another position in the molecule, such as an acroyl or metaacroyl group, the lacquer binder also has a polymerizable group and becomes photostable. The agent can be copolymerized with the binder. This occurs, for example, with acrylic resins or acrylic-modified alkyd resins. The advantage in these cases is that the light stabilizer is not lost by extraction or migration and its effect is very permanent. Acrylic resin lacquers that are stabilized against light by the practice of the present invention are described, for example, by H. Kittel,
Lutz car and painting text book (H.Kittel's
Lehrbuch der Lackeund Beschichturigen), Volume 1, Part 2, pages 735-742 (Berlin, 1972)
and H. Wagner and HF Sarx, Synthetic Resins for Radicals (H. Wagner and HF Sarx,
Lackkunstharze) (1971) pages 229-238. The polyester lacquers which are stabilized against the action of light according to the practice of the invention are the customary stoving lacquers described, for example, in the above-mentioned book by H. Wagner and HF Zakes, pages 86-99. The alkyd resin lacquers stabilized against the action of light in accordance with the invention can be used in particular with the customary baking lacquers used in automotive lacquer coatings (so-called automotive finishing lacquers), such as alkyd melamine resins and alkyd-acrylic-melamine resins. It is a Lutzker based on
99-127) Baking lacquers stabilized by the practice of this invention may also include mixtures of acrylic, polyester and alkyd resins with each other or with other coating resins. Acrylic, polyester and alkyd resins are either self-crosslinked by heating or used in mixtures with other crosslinking agents, in which case melamine resins are particularly suitable. The stoving lacquer containing the acid catalyst stabilized according to the invention is suitable for finishes containing metallic pigments, finishes that appear internally homogeneous, and especially for retouching. The lacquer stabilized according to the invention is preferably applied in a conventional manner, either in one coat or in two coats. In the case of two-stage coating, a pigment-containing coating is applied first, and then a transparent lacquer is top-coated on top. When polyalkylpiperidine derivatives are used in a two-coat coating, they can be added only to the unpigmented topcoat lacquer or to both the unpigmented topcoat lacquer and the pigmented basecoat lacquer. The amount of polyalkylpiperidine derivative added is 0.01 to 5% by weight based on the solvent-free binder;
Preferably it is 0.5 to 1% by weight. The lacquer may be dissolved or dispersed in commonly used organic solvents or water, or no solvent may be used. The coating resin of the present invention is particularly suitable for use in high solids industrial lacquers, which are becoming increasingly important in the automobile industry and automobile repair, especially at low curing temperatures. In order to obtain the highest photostability, it is advantageous to use it in combination with other customary photostabilizers, such as UV absorbers or organic nickel compounds. The combination with synergistic UV absorbers of the type containing 2-hydroxybenzophenone, 2-(2-hydroxyphenyl)-benztriazole or oxalanilide is of particular interest. Examples of such UV absorbers include 2-(2-hydroxy-3,
5-di-tertiary amyl-phenyl)-benztriazole, 2-[2-hydroxy-3,5-di(α-dimethylbenzyl)-phenyl]-benztriazole, 2-(2-hydroxy-5-tertiary tertiary octyl-phenyl)-benztriazole,
2-(2-hydroxy-3,5-di-tertiary octyl-phenyl)-benztriazole, 2,4
-Hydroxybenzophenone, 2-hydroxy-
4-octyloxy-benzophenone, 2-hydroxy-4-dodecyloxy-benzophenone,
2-ethyl-2'-ethoxy-4'-tertiary butyl-
Oxalanilide or 2-ethyl-2'-ethoxy-oxalanilide can be mentioned. When using such a combination, the total amount of all light stabilizers is from 0.2 to 5% by weight, preferably from 0.5 to 2% by weight, based on the coating resin. Further additives that can be included in the lacquer are antioxidants, such as those of the type consisting of sterically hindered phenol derivatives, phosphorus compounds such as phosphites, phosphines or phosphonites, leveling agents, curing accelerators, It is a viscous agent, a dispersant, or an adhesion promoter. EXAMPLES AND EFFECTS OF THE INVENTION The following examples describe the use of N-acylated polyalkylpiperidine derivatives in stoving lacquers containing acid catalysts. Parts and percentages are by weight. Example 1 Stabilization of metal pigment lacquer for two-stage coating against weathering. (a) Metallic pigment Lutzker polyester resin (L1850 Dynamite Nobel AG) 27 parts melamine resin (Maplenal RT, Farbwerke Hoechst AG) 3 parts cellulose acetobutyrate (CAB531, Eastman Chemical Company) 2 parts aluminum bronze (Alcoa 726, USA) Aluminum Co.) 8 parts toluene 10 parts xylene 7 parts butanol 3 parts butyl acetate 25 parts aromatic solvent mixture (Solbetsuso 150 parts
AG) 1.5 parts (b) Pigment-free Lutzker acrylic resin (Paraloid OL 42, Rohm & Haas) 56 parts Melamine resin (Shimel 301, American Cyanamid) 20 parts para-toluenesulfonic acid 0.3 parts ^*) Cellulose acetobutyrate (CAB551, Eastman Chemical Company) 2 parts leveling agent 3 parts butanol 11 parts butyl acetate 8 parts*) 0.5% on a solids basis 57mm x 79mm x 0.55mm painted with a polyester/epoxide resin based undercoat lacquer
The aluminum sheet was first coated with a metal-pigmented lacquer and then with a topcoat lacquer. The lacquer of the first stage coating was sprayed to obtain a coating approximately 15 microns thick and exposed to air for approximately 10 minutes. Next, a transparent lacquer was sprayed to obtain a coating film of approximately 30μ. After exposure to air for 15 min, the sample was baked at 120 °C for 30 min.
A weather resistance test consisting of 4 hours of ultraviolet irradiation at 60℃ and 4 hours of steam condensation treatment at 50℃ was conducted.
The tests were conducted using a UVCON weathering test device (sold by Atlas Inc.). Sample surface gloss according to ASTMD523
Measurements were made at 200 hour intervals. As the light stabilizer used in the method of the present invention, the following formula: 3-dodecyl-1,3,8-triaza-7,7,9,9-tetramethyl-8-acetyl-spiro[4.5]decane-2,4-dione expressed as a solid in an overcoating lacquer alone. 1% per minute and in combination with a benztriazole type UV absorber. The results are reported in Table 1.

[Table] Triazole

Claims (1)

Claims: 1. As a light stabilizer for stoving lacquers containing acid catalysts based on thermally crosslinkable acrylic, polyester or alkyd resins, the following formula: [In the formula, n represents 1 or 2, R represents a hydrogen atom or a methyl group, and R ₁ represents an alkanoyl group having 1 to 8 carbon atoms, an alkenoyl group having 3 to 5 carbon atoms, a sorboyl group, a cinnamoyl group ,
an alkoxycarbonyl group having 2 to 5 carbon atoms or (R ₂ )(R ₃ )NCO—(wherein R ₂ is an alkyl group having 1 to 12 carbon atoms, a cyclohexyl group,
represents a phenyl group or a phenyl group substituted with a halogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms, R ₃ is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms; group, cyclohexyl group or benzyl group. ), R ₇ is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an allyl group, a benzyl group, a glycidyl group, or a group having 2 carbon atoms.
Represents an alkoxyalkyl group of 3 to 6 carbon atoms, and when n represents 1, R ₈ is a hydrogen atom, an alkyl group of 1 to 12 carbon atoms, a glycidyl group, an alkenyl group of 3 to 5 carbon atoms, or an alkenyl group of 7 to 9 carbon atoms. represents an aralkyl group having 5 to 7 carbon atoms, a cycloalkyl group having 5 to 7 carbon atoms, an acyloxyalkyl group having 2 to 6 carbon atoms, or an aryl group having 6 to 10 carbon atoms, and when n represents 2;
R ₈ is an alkylene group having 2 to 12 carbon atoms, an arylene group having 6 to 12 carbon atoms, or -
CH ₂ CH (OR ₁ ) CH ₂ - (OCH ₂ - CH (OR ₁ )
Represents a group represented by CH ₂ ) ₂ --. A method of using an N-substituted 2,2,6,6-tetraalkylpiperidine compound represented by the following formula, optionally together with other stabilizers. 2. The method of using the light stabilizer according to claim 1, wherein R and R ₇ represent a hydrogen atom, R ₁ represents an acetyl group, and R ₈ represents a dodecyl group.