DD155621A1 - THERMAL CONTAINERS - Google Patents

Abstract

Heat-insulating coating compositions for tempering temperatures between 60 and 80 degrees C with relatively short hardening times on the basis of binder mixtures of conventional amino-formaldehyde condensates and alkyd resins, optionally alkyd resin-acrylic polymer mixtures are improved without impairing the storage stability and processing ability in their durability. For this purpose, the coating compositions 1 to 10 wt .-%, based on the amino-formaldehyde condensate, multivalent amines and / or amides or their derivatives, which are not or only weakly basic, zugefuegt.Fuer special Anwendungsfaelle can additionally org. Acids are used as hardening catalysts.

Description

6497

Title of the Invention Thermosetting Coating Compositions

Field of application of the invention

The invention relates to thermosetting coating compositions for curing temperatures between 60 and 80 ⁰ C at relatively short curing times based on a binder combination of • alkoxylated Araino-formaldehyde condensates and fatty acid-modified alkyd resins.

Characteristic of the known technical solutions

Binder-based coating compositions of alkyd-melamine resin combinations having higher crosslinking reactivity are known. These coating agents can be thermally cured at 80 to 90 C within 30 to 60 minutes. For this purpose, alkoxylated melamine-pormaldehyde condensates are prepared by hitherto unreached very low levels of free formaldehyde and these used in combination with fatty acid-modified alkyd resins as a binder for the mentioned thermally curable coating compositions according to new methods · The preparation of the alkoxylated melamine-pormaldehyde condensates improved hardenability or combinations of the coating compositions which are curable as from 80 ° C. are described in detail in DE-AS 1 278 051, DE-AS 1 494 507, DE-OS 1 494 509, DE-AS 1669868, CH-PS 491 187, US Pat On the other hand. Special alkyd resins are prepared, which are used with conventional melamine-formaldehyde condensates in certain mixing ratios and then at 80 C in 30 minutes give good curing coatings (DD-PS 121 126).

2 6 4 9

However, all previously known, based on alkoxylated melamine-formaldehyde condensates formulated with alkyd resins coating agents can not fall below the curing temperature of 80 ⁰ C, because the cure rate decreases rapidly even in the presence of acidic curing catalysts with falling temperature and consequently below 80 ⁰ C. technologically unacceptably long curing times are required ·

For economic reasons, energy-saving hardening processes and technological rationalization measures with a shortening of the curing times are aimed at. However, curing temperatures below 80 ° C. are also desired for the coating of heat-sensitive objects, such as, for example, thermoplastic materials and shaped articles as well as some precision workpieces and electrical layer circuits.

To solve these problems, more than 80 C curable coating compositions have recently been proposed in which substantially alkoxylated Methylolmelamine perceived in modified form as precondensates or in combination with other organic film formers, the function of the binder. These binders have been specially created for use at low curing temperatures. Their main disadvantage is that these binders must always be produced with greater technological and energetic effort, and the purpose of a significant energy saving pursued by the application of low curing temperatures is called into question.

The crosslinking of alkoxylated methylol melamines at temperatures below 8O ⁰ C to sufficiently hard coatings is possible if these are converted via polyols, polycarboxylic acids or polyamines in precondensates and the precondensates are crosslinked in the presence of acidic curing catalysts. Although hard coatings suitable for the protection of plastic surfaces are obtained in this way, they do not have the necessary flexibility to be able to provide sufficient resistance to impacts such as impact and impact.

- 3 - 2 2 6497

In addition, acidic curing catalysts should be used to accelerate the cure at low temperatures sufficiently. These must be added to the coating agent immediately prior to their processing, whereby the processing ability of the finished coating agent is limited in time to hours to a few days. Both the addition of precisely metered amounts of catalyst immediately prior to processing and the limited processability of the finished coating compositions are disadvantageous for the processor.

In BE-AS 2 417 915 a coating agent is proposed for coating the surface of a molded article made of cellulose plastic, which is curable in the temperature range of 60 C to the heat distortion temperature of the article with an acidic catalyst. The coating composition contains as binder a precondensate of a partially alkoxylated methylamine and butanediol-1,4-ethylene glycol or diethylene glycol dissolved in a polar organic solvent. Similar proposals can be found in DE-OS 1 745 483, PR-PS 1 288 682 and GB-PS 1308697.

Coating agents based on combinations of hydroxyl-containing polyurethane precondensates and amine resins are also already known for the coating of plastics, elastomers and other heat-sensitive articles. Thus, stretchable rubber article coverings are obtained according to US Pat. No. 3,954,899. It describes a coating agent consisting of a hydroxyl-containing polyurethane precondensate, an amine resin, a polymeric polyhydric alcohol and possibly an acidic curing catalyst, which is applied by a conventional method and cured with mild heat. Curing is usually achieved at 60 to 125 ° C within 20 to 40 minutes, curing time being shortened and curing temperature being kept low by the use of curing catalysts. Coating agents of a related kind, preferably used for the coating of heat-sensitive elastomers, are disclosed in US Pat 3,662,261, U.S. Patent 3,912,790 and U.S. Patent 3,542,718. Since the coating agents based on polyurethane

- 4 -. 2 2 6 A 9 7

Precondensates can be modified with amine resins in many ways, they can almost always be adapted to certain specific applications largely. However, the preparation of the polyurethane precondensates is not only technologically very complicated, but also requires special care and special plant technical prerequisites ·

Coating compositions based on acrylic polymer amine resin combinations that are curable between 60 and 80 ⁰ C within 20 to 30 minutes, are described in DE-OS 2,812,397. However, ordinary thermally curable acrylic polymers are not useful for this purpose. A particular feature of the acrylic polymers contemplated by the invention is that they have a low glass transition temperature. Acrylic polymer-amine resin combinations are also relatively expensive, so that the use of coating agents on this binder base remains limited to certain applications for this reason alone.

The curing of coating compositions based on condensing crosslinking amine resins or mixtures of these resins with other polymers can also be carried out in an energy-saving manner by a combined process. From DD-PS 134645 it is known that coatings of the type mentioned can be sufficiently crosslinked by thermal pre-curing at low temperatures or at low IR radiation densities and by short-time post-curing with UV rays. The use of lactic acid as a curing catalyst is required to achieve sufficiently high levels of crosslinking in such a short time under these curing conditions. However, the use of UV rays requires that the necessary facilities are available or created for this purpose. Radiation curing, however, can only be applied to those coated articles whose surfaces are directly accessible to the radiation. , , '

Object of the invention

The object of the present invention is mainly to eliminate the deficiency of the previously known, condensing crosslinking and low-temperature curable coating compositions by the already used for higher curing temperatures and proven for this purpose amine resins and alkyd resins are used as binders, so that on the Production of special binders with increased technological and energy costs can be dispensed with and the production of coating compositions for low curing temperatures is simplified and cheapened. In addition, the limitations on the processability and storage stability to be corrected or reduced, which inevitably occur as a result of the use of acidic curing catalysts.

Explanation of the essence of the invention

The object of the present invention is to provide a binder-based thermosetting coating composition of ordinary mixtures of an etherified amino-paromaldehyde condensate and a fatty acid-modified alkyd resin which is curable at low temperatures between 60 and 80 C in a relatively short time and has a processability and Has storage stability as exhibited by higher temperature curable coating agents on this binder base.

Purely the solution of the problem is a coating agent based on a Bindemitte.lgemisches

I amino-formaldehyde condensates, which are partially etherified by aliphatic monohydric alcohols having 1 to 4 carbon atoms, and

II alkyd resins having a fatty acid content of from 25 to 50% by weight and acid numbers below 35 mg KOH / g resin, alone or in admixture with condensing acrylic polymers which are predominantly hydroxy-functional,

- 6 - 2 2 6 4 9 7

and solvents, auxiliary substances and, if appropriate, pigments and extenders, 1 to 10% by weight, based on the amino-formaldehyde condensate, of a multivalent, non-weakly or only weakly basic amide and / or amine or their derivatives.

The coating compositions may additionally contain from 1 to 10% by weight, based on the amino-formaldehyde condensate, of one or more strongly organic acids as curing catalysts for particular applications.

The multivalent amides or amines suitable for the inventive purpose must contain at least two amide or amine groups which are not or only very weakly basic. Unsuitable for the inventive purpose are the aliphatic amines with pronounced basic character, which are known and introduced as curing agents for epoxy resins. These include, for example, diethylenetriamine and triethylenetetramine. Other aliphatic diamines, such as hexamethylene-1,6-diamine, are not suitable. On the other hand, the amides of dibasic or polybasic aliphatic or aromatic carboxylic acids are suitable. These include, for example, urea, thiourea, oxalic acid diamide, malonamide, tartronamide, malic acid diamide, tartaric acid diamide, phthalic acid diamide, trimesic acid triamide and trimellitic triamide. Heterocyclic compounds such as the triazine derivatives melamine, formoguanamine, acetoguanamine and benzoguanamine are also suitable. But certain derivatives of urea and thiourea also cause the intended increase in reactivity and are therefore useful. These include biuret as well as the singly substituted urea and thiourea compounds such as monomethylolurea, monomethylurea, monophenylhumane, monomethylthiourea and monophenylthiourea, as well as the cyclic derivatives of urea, the cereals, such as barbituric acid and alloxan. From the group of aromatic amines, benzidine and semidine are particularly suitable, but also m-phenylenediamine and p-phenylenediarine.

-7 - 2 2 6497

The known amino-formaldehyde condensates which are suitable for the inventive solution are obtained in a conventional manner by condensation reactions of melamine, formaldehyde and monohydric aliphatic alcohols having 1 to 4 carbon atoms. Preferably condensates are used for the inventive purpose, which are etherified with n-butanoi (butanol-1) or i-butanol (butanol-2) and belong to the group of highly reactive, but at least the medium-reactive melamine resins.

In addition to etherified melamine-formaldehyde condensates, etherified urea-formaldehyde condensates or mixed condensates prepared from melamine, urea, formaldehyde and monohydric alcohols having from 1 to 4 carbon atoms are also suitable for the inventive purpose. Condensates of these two types have also been known for some time and are already being used for various purposes as paint binders.

Fatty acid-modified alkyd resins suitable for the invention are the polyester resins which have also been known for a long time and which are formed in the condensation of polybasic carboxylic acids, monobasic fatty acids, predominantly vegetable oil fatty acids, and polyhydric alcohols. It is preferred to use short-oil alkyd resins or mixtures of short-oil and medium-oil alkyd resins. There are no restrictions on the physical composition of the alkyd resins used, so that both unsaturated and saturated or both straight-chain and branched fatty acids can be contained in the alkyd resins. The use of other monocarboxylic acids, for example benzoic acid or derivatives of this acid, in addition to the fatty acids is possible. Alkyd resins of this type belong to the standard range of commercial alkyd resin manufacturers and have long been used in thermosetting coating compositions as a binder component. Instead of an alkyd resin alone, it is also possible to use mixtures of compatible alkyd resins. In addition, it is also possible to partially or completely replace the alkyd resin with a thermosetting acrylic polymer.

-β- 2 2 6497

The inventive use of multivalent amides or amines effected at curing temperatures between 60 and 8O ⁰ C considerable increases in hardness, which exceed the achievable by acid catalysis level · The additional use of acidic curing catalysts in addition to the amides or amines is not required. Only in the lower limit of curing at 60 ^° C. can the use of acidic curing catalysts in addition to multivalent amides or amines be advantageous if adequate curing is to be achieved in very short times. The addition of the curing catalysts must then take place immediately before processing the other known limitations in the application of acid catalysis must be considered. Suitable curing catalysts are high acidity organic acids such as p-toluenesulfonic acid, phthalic acid, maleic acid and other organic acids compatible with the binder components of the coating agent. In contrast, hydroxycarboxylic acids, such as, for example, lactic acid, glycolic acid or citric acid, are unsuitable.

The coating composition according to the invention can be applied by known application methods, such as spraying, dipping, flooding, casting, rolling and brushing. The coatings are curable at relatively low temperatures of between 60 and 80 G within 30 to 90 minutes and can be applied to any metal, plastic or wood-like material in thicknesses up to 50 μm without any complications or limitations for low temperature cure , They give weatherproof and sufficiently oil and fuel resistant coatings.

A significant advantage of the inventive solution is that not only highly reactive melamine resins are suitable for the coating agent, but also medium-reactive resins can be used. The elimination of this restriction, the production of coating compositions with hardenabilities from 60 C is no longer linked to the use of extremely reactive melamine resins, by which the storage stabilities of the coating compositions are known to be greatly reduced.

22 64 9 7

From the new coating agent can be obtained even at higher curing temperatures than 80 C coatings with excellent properties. Under these conditions, sufficient hardening effects can be achieved even with small addition amounts of multivalent amides or amines. Relatively high hardnesses are obtained in a very short curing time, so that increased throughputs through the furnace installation are possible and as a result energy-saving measures under these circumstances can likewise be carried out.

The novel coating composition is prepared by a simple mixing process of known and commercially available etherified Me-Tamin-formaldehyde condensates and fatty acid-modified alkyd resins and commercially available, multivalent amides or amines and lacquer solvents, so that the otherwise necessary additional technological expenses for the production of special Binders are not required for this purpose.

The reactivity-increasing effect of multivalent amides or amines can ermit- in a simple manner from the Gelzeitverkürzung. which are produced by precisely metered additions of these substances in 50 #igen solutions of a highly reactive melamine resin in n-butanol. The melamine resin solution heated to 105 ^° C. gelled after addition of 8 ml of a 2 η p-toluenesulphonic acid solution (in butanol) to 50 g after a few minutes. This hull value and the changes caused by the addition of 1 g of various amides or amines are shown in the following overview. ·

- ίο - 2 2 6 4 9

Evaluation of the reactivity-increasing effect of multivalent amides or amines

Amide or Amiη gel time Gelzeitanderuns (56) (Min) (Min) -.- .. null 7:00 ...... - 71 urea 2:00 - 5.00 - 57 thiourea 3:00 - 4.00 - 57 melamine 3:00 - 4.00 - 32 monomethylolurea 4.75 - 2.25 - 9 Ν, Ν'-diphenyl , 6:35 - 0.65 0 Monocyclohexylharnstoff 7:00 00:00 - 35 m-phenylenediamine 4:53 - 2.47 - 35 barbituric 4:53 - 2.47

Exemplary embodiments ·

Example 1 .

Alkyd-melamine resin combinations made by blending a short oily soybean oil-modified alkyd resin with either a 70/30 high reactivity or medium reacting melamine resin are at additions of 1.3 and 2.2 wt % urea, based on the Pestharzanteil, has been added. The binder solutions have been applied to glass plates using a common device. After brief evaporation of the solvent, the films are cured at different temperatures for 30 minutes in the chamber furnace. Pendulum hardness determined by King's method is listed below.

Film hardness of alkyd-melamine resin combinations with and without urea additions after 30 minutes curing zwisctien 70 and 9O ⁰ C

Addition of urea (%) Melamine resin type 70 ⁰ C Film hardness (s) 80 ^D C · 85 C 65 50 at 9O ⁰ C 0 0 highly reactive 'medium reactive 32 25 52 40 87 67 81 69 1.3 1.3 highly reactive medium reactive 41 31 67 53 75 74 114 82 2.2 2.2 highly reactive medium reactive 36 36 60 60 95 90

Example 2

Alkyd-melamine resin combinations according to Example 1 were mixed with various multivalent amides or amines · by weight and lactic acid in amounts to 2.2 -.% Was added. The reactivity enhancing components were dissolved in methanol, dimethyl sulfoxide or other organic solvents and added to the binder solutions with vigorous stirring. After standing for several hours of the binder solutions of these films were mounted on glass plates with a conventional device. After brief evaporation of the solvent at normal temperature, the films .wurden cured in a chamber furnace at temperatures of 70 and 8O ⁰ G and times of 60 or 30 minutes. Pendulum hardness determined by König's method is given in the following overviews.

22 64

Film hardness of alkyd-amino resin combinations with additives of various amides or amines, as well as lactic acid after 60 minutes curing at 7O ⁰ C

additional component Melamine resin type Film hardness (s) at additional amounts 0 % 0.9 % 1. 54 53 from 5 % 2.2 % lactic acid highly reactive medium reactive 43 43 57 54 62 59 71 69 urea highly reactive medium reactive -43 43 45 57 79 74 81 77 thiourea highly reactive medium reactive 43 43 54 57 52 65 78 74 Barbitürsäure  highly reactive medium reactive 43 43 49 60 78 65 73 69 p-phenylenediamine highly reactive medium reactive 43 43 57 57 79 87 83 89 Monomethylolurea highly reactive medium reactive 43 43 CTiVJl VD 03 70 68

Pilm curing of alkyd-amine resin combinations with additions of various amides or amines and lactic acid after 30 minutes

O,

hardening at 80G

additional component Melamine resin type Film hardness (s) at additional amounts 0 % 0.9 % 1. 53 56 from 5 % 2.2 % lactic acid highly reactive medium reactive 52 40 VJl CTN OO VD VJL-J CJNVJI 82 76. urea highly reactive medium reactive 52 40 54 59 86 68 86 80 thiourea highly reactive 'medium reactive 52 40 VJlUl CTiVJI O CM C-C- 80 79 Barbituraäure highly reactive medium reactive 52 40 CJNVJI VJl OD 79 79 89 81 p-phenylenediamine highly reactive medium reactive 52 40 57 59 91 S5 84 87 Monomethylolurea highly reactive medium reactive 52. 40 79 74 80 79

_ ₁₃ _ 2 2 6497

Example 3

A pigmented alkyd-melamine resin coating agent is used. Mixing and diapering of the components produced in a grinding process on a Perl Mill. The coating composition has the following composition:

Short oily soybean oil alkyd resin 27 parts by weight

Highly reactive melamine resin 12 parts by weight

(partially butoxylated)

Pigments 18 parts by weight

Extender 4 parts by weight

Xylene 23 parts by weight

n-butanol · 13 parts by weight

Excipients' 3 parts by weight

Ratio of alkyd resin / melamine resin approx. 70/30

Plague content about 65% by weight

With 10 to 15 wt.% Of a special diluent consisting of a mixture of several common lacquer solvents, the coating agent is adjusted to processing consistency. Urea is added to the diluted coating agent as a multivalent amide in an amount of 1% by weight, based on the plague resin content. After thorough stirring, the coating agent is applied by pneumatic spraying on test plates made of Gla3 and deep-drawn sheet. After brief evaporation of the solvents (5 to 10 min), the coatings are thermally cured on the test plates in a chamber furnace. The characteristics of the cured coatings are shown in the following overview depending on the curing conditions. For the comparative evaluation of multivalent amides and acid curing catalysts, the characteristics of coatings are next stated, the weight instead of urea 1.5 -. Contain% of lactic acid, based on the Pestharzanteil, and were thermally cured under the same conditions.

649

Characteristics of pigmented alkyd-melamine resin coatings with addition of urea or lactic acid depending on the curing conditions

Hardening tempering cure time

additive

PH

Characteristics of the coatings

ET

GG

SD

70 ⁰ C 45 min 4 1 % HS 62 8.0 112 25 30 30 70 ⁰ C 45 min 1.5 % MS 62 7.6 96 30 30 40 8O ⁰ C 30 min 1 % HS 78 8.1 110 25 to 30 8O ⁰ C 30 min 1.5 % MS 66 8.3 93 25 to 30 8O ⁰ C 45 min 1 % HS 102 8.0 109 to 8O ⁰ C 45 min 1.5 % MS 83 8.0 86 25 to 30 80 ⁰ C 60 min 1 % HS 120 7.8 104 Skt. 30 80 ⁰ C 60 min - 105 7.0 109 to It means: HS MS PH ET GG SD Urea Lactic acid Pendulum hardness in s Erichsen cupping in gloss after long layer thickness in / um mm in example

A pigmented alkyd-melamine resin coating agent is prepared by mixing and dispersing the components in a mill scale on a Perl Mill. The coating composition has the following composition:

Short oily soybean oil alkyd resin

Highly reactive melamine resin (partially butoxylated)

Pigments Extender xylene n-butanol auxiliaries

23 parts by weight 6 parts by weight

21 parts by weight

13 parts by weight 20 parts by weight

14 parts by weight 3 parts by weight

22 64 9 7

Ratio alkyd resin / melamine resin solids content

about 80/20 about 65% by weight

0.6% by weight of urea, based on the amount of plague resin, is introduced into the coating composition with stirring with the residue to the friction material. The urea-containing coating composition is adjusted for processing consistency after two months of storage at normal temperature with a suitable special diluent. Test plates made of glass and deep-drawn sheet are coated by pneumatic spray application with the coating agent. The solvents are evaporated for 5 to 10 minutes at normal temperature from the coatings. The thermal curing of the coatings takes place in the chamber furnace at different temperatures. The characteristics of the cured coatings are shown below. In addition, the characteristics of coatings are listed, which were cured under the same conditions, but without added urea.

Characteristics of pigmented alkyd-melamine resin coatings with and without addition of urea depending on the curing conditions

curing temperature 60 min additive -. % m % HS Characteristics of the ET coatings 40 curing 60 min 6 PH 6.5 SD 7O ⁰ C 45 min _ - · % HS 43 5.9 35 to 7O ⁰ C 45 min 0th 6 59 4.9 30 8O ⁰ C 30 min   _ - HS   66 4.2 30 30 80 ⁰ C 30 min 0th 6 73 4.0 30 100 ⁰ C - 70 3.0 25 to 100 ⁰ C 0th 83 30

It means:

HS urea

PH pendulum hardness in s

ET Erichsen cupping in mm

SD layer thickness in / um

_ · ₁₆ - 2 2 6Λ97

Example 5

A pigmented alkyd-melamine resin coating composition according to Example 3 is diluted with a special diluent for processing consistency with each

A) 2.0% by weight of p-toluenesulfonic acid

B) 1.6 wt -.% Lactic acid

C) 1.8% by weight urea

D) 2.0% by weight of p-toluenesulfonic acid plus 1.8% by weight of urea

added (additional amounts based on the'Pestharzanteil). After intensive stirring, the coating agent is applied by pneumatic spraying on test plates made of glass and thermoforming sheet. After brief evaporation of the solvent (5 to 10 minutes), the coatings are thermally cured on the test plates in a chamber furnace. The characteristics of the cured coatings are listed below depending on the curing conditions.

Characteristics of pigmented alkyd-melamine resin coatings with various hardness-increasing additives depending on the curing conditions

Curing temperature Addition Characteristics of the coatings Curing time 'PH ET GG SD

60 ^u C 60 min A 48 9.1 113 30 to 35 B- 45 9.0 113 25 to 35 C 42 9.2 109 25 to 30 D 47 9.4 110 25 to 35 49 9.4 113 30 7O ⁰ C 60 min A 72 9.3 112 30 to 35 B 75 8.9 114 25 to 35 C 69 9.0 111 30 to 40 D 80 9.2 112 35 --_ 86 9.0 109 25 to 30 80 ⁰ C 30 min A 63 9.1 114 30 B 74 8.6 113 30 to 35 C , 68 8.9 110 20 to 25 D 79 9.4 111 30 to 35 84 9.0 110 30

- 17 - 2 2 6 4 9 7

Example 6

Alkyd-melamine resin combinations according to Example 1, but deviating from it with a component ratio 65/35 "have been added with 1.8% by weight of urea plus 2.1% by weight of p-toluenesulfonic acid, in each case based on the plunger resin content. After vigorous stirring, the binder solutions were coated on glass plates using a conventional apparatus. Hach momentary evaporation of the solvent are cured the Pilme at 6O ⁰ C for various times in a chamber furnace. Pendulum hardness determined by King's method is listed below.

• o ^v

Pilmhärten of alkyd-melamine resin combinations with and without additives, after curing at 60 ⁰ C

Addition of melamine resin Pilmharden (s) after

Type 60 min 90 min 120 min

without addition

highly reactive '35 46 62

moderately reactive 29 36 42

with addition highly reactive 62 75 77

with added medium-reactive 59 80 88

Claims (2)

2 2 6Λ97 invention claims  Ό 1. Heat-curing coating compositions for curing temperatures between 60 and 80 ⁰ C based on a binder combination of (I) Amino-formaldehyde condensates produced by aliphatic monohydric alcohols with 1 to 4 carbon atoms partially •. , are etherified, and (il) alkyd resins having a fatty acid content of from 25 to 50% by weight and acid numbers below 35 mg KOH / g resin, alone or in admixture with condensing acrylic polymers which are predominantly hydroxyl functional, and solvents, excipients and optionally pigments and extenders, characterized in that they contain 1 to 10 wt .-%, based on the amino-formaldehyde condensate, of a multivalent, non-weakly or only weakly basic amide and / or amine or its derivatives. 2. Heat-curing coating compositions according to item 1, characterized in that they contain from 1 to 10% by weight, based on the amino-formaldehyde condensate, of one or more strong organic acids as curing catalyst.