DE1179320B - Heat-curable coating agent based on polyvinyl acetal - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school KIj C09d

German class: 22h-3

Number: 1179 320

File number: S 65646IV c / 22 h

Filing date: October 29, 1959

Opening day: October 8, 1964

The invention relates to coating compositions which can be hardened by heat, in particular for electrical coating Head based on polyvinyl acetal with the addition of phenolic resins and organic Solvents.

Various modified polyvinyl acetals have already become known, which in extensive 'measure be used as coating compounds for various purposes, for example for lining Food cans and for insulating electrical conductors. Depending on the intended use the type of modification changes. The one based on polyvinyl acetal with the addition of Coating agents made from phenolic resins are particularly suitable for heat curing.

Most of the coating agents recently developed on the basis of polyvinyl acetal contain only extremely small amounts of various additives to improve certain properties of the commercially available products, which generally consist of about 100 parts of polyvinyl acetals and 50 parts of a phenolic resin consist.

Coating agents have also already become known, which contain polyvinyl acetals together with certain polyurethanes. Such coating agents have the weldability that phenol-modified polyvinyl acetals lack.

It is the aim of the invention to provide coating compositions based on polyvinyl acetals with the addition of To create phenolic resins that have better resistance to various organic solvents demonstrate. The coating compositions according to the invention should also have a better thermal stability, measured by flexibility and impact resistance. In addition, the coating agents should after of the invention to be elastic so that it can be used as a coating agent for electrical wires to insulate them can be.

According to the invention, these objectives are achieved in a thermosetting coating agent by a composition which is characterized in that it contains 100 parts by weight of polyvinyl acetal, 1 to 50 parts by weight of thermosetting phenol-aldehyde resin and 2 to 80 parts by weight of capped polyisocyanate, which is a polyurethane of the general formula Av Heat curable coating agent on the
Based on polyvinyl acetal

Applicant:

Shawinigan Resins Corporation,

Springfield, Mass. (V. St. A.)

Representative:

Dr.-Ing. E. Hoffmann, patent attorney,

Munich 8, Maria-Theresia-Str. 6th

Named as inventor:

Edward Lavin,

Andrew F. Fitzhugh, Longmeadow, Mass.,

Robert N. Crozier, Wilbraham, Mass. (V. St. A.)

Claimed priority:

V. St. v. America April 13, 1959 (805 656)

C _n H

(2n + 2-m)

O H

HO

-O-C-N-R-N-C-O-X

/ m

where R is a phenylene, methylphenylene, dimethylphenylene, naphthylene or methylnaphthylene group, a phenyl or alkali metal phenyl group containing alkyl groups from 1 to 6 atoms, m is an integer greater than 1, but not greater than η and η is a positive integer from 2 to 10.

Upon curing of the coating compositions according to the invention is represented over 150 ° C, the isocyanate groups-containing compound and removed in a higher side temperature range of between about 200 and 500 ° C, the organic solvent from the coating and is equal to _T time cured the coating composition by heating to.

Such coating agents differ in an advantageous manner from the previously known coating agents. It was already known to initiate the reaction of blocked polyisocyanates with the OH groups of organic substances to heat these compounds and also blocked isocyanates to be used for the production of wire enamels. For example, a product has a trade name Desmodur TH and Desmodur AP (phenol) from Bayer AG gained practical importance for the production of wire enamels. Desmodur However, TH has a chain structure with one side chain with all three ends substituted Benzene rings, namely l-methylbenzene-2-isocyanate,

409 690/329

are attached. These compounds differ from the polyurethanes used according to the invention. Based on the simplest conditions, namely η = 2, m = 2 (m = ή), R = phenylene, X = phenyl, a polyurethane of the following structure is obtained for the above formula:

O-CO-NH

NH-CO-O -CH ₂ -CH ₂ -O -CO-NH

NH - CO - O

In this formula are the conditions

1 < m ^ n,

Fulfills.

If one compares this formula with the formula of known diisocyanates, for example with that on p. 33 of the plastic book from Bayer from 1955 in the top row given formula, so one can see that both formulas are symmetrical to the one drawn in dash-dotted lines in the above formula Line of symmetry are. However, while the known polyurethane formula has six methylene groups form the middle part of the chain, there are only two methylene groups in the polyurethane according to the invention summarized in the middle of the chain, which bonded to phenylene groups on both sides Connect isocyanate radicals.

With such blocked polyisocyanates as a third reactant, heat-curable Represent coating agents that in their thermal, electrical and mechanical properties known polyurethane combination paints are superior.

The invention is illustrated in more detail by the following examples, in which the specified parts are parts by weight, without thereby the To want to limit the scope of the invention. Contain the substances in the examples labeled "Control" not a polyisocyanate, but are typical, commercially available wire coating compounds made from a polyvinyl acetal and a phenol-aldehyde resin.

example 1
Example 2
(Control)

Phenol-

AWehyd-

resin

(Parts)

10
50

Disguised
Polyisocyanate

(Parts)

60

Polyvinyl formal

(Parts)

100
100

The phenol-aldehyde resin was prepared in a manner known per se by adding a mixture of 100 parts of commercially available crude carbolic acid (a mixture of m-cresol and p-cresol with a smaller proportion of xylenols), 60 parts of formalin ( an aqueous solution of 37% formaldehyde) and 3.2 parts of triethanolamine at about 8O ⁰ C for about 2V treated _{for 2} hours at reflux. The reaction product was then dehydrated under vacuum, giving the resin as a dark, viscous mass.

The blocked polyisocyanate was a polyurethane with the following structural formula:

C ₂ H ₅ C (CHa) ₃

O H

in which Y is an m-methyl-phenyl group.

The polyvinyl formal contained about 10% acetate groups, calculated as polyvinyl acetate, about 6% Hydroxyl groups, calculated as polyvinyl alcohol, while the remainder consists essentially of formal groups duration.

The material according to Examples 1 and 2 was in a mixture of 170 parts of coal tar hydrocarbons of high solubility (with boiling points from 150 to 200 ⁰ C, composed mainly of alkylbenzenes, namely about 80% of it trimethyl- and tetramethyl-benzene) and 100 Share dissolved raw cresol. (The phenol-aldehyde resin is commercially available as a solution in raw cresol. The amount given in the example relates to the phenoplast without the solvent; the amount of solvent incorporated with this resin is included in the total amount of solvents given.)

Copper wire approximately 0.05 inches (1.27 mm) in diameter was coated with these compounds which were cured by conventional means well known in the wire insulation art (see U.S. Patent 2,307,588 ). The curing temperature was approximately 350 ^° C. in a zone of approximately 914 to 1219 mm of a vertical furnace approximately 3.66 m high. Six successive coatings were dried and cured on the wire.

Samples of the wire coated in this way were then crossed at an angle of 90 ° and loaded at the crossing point with a weight of 2.268 kg. The temperature was allowed to rise per 1O ⁰ C per minute until a result of a short circuit at the crossing point of the power circuit of a display device has been closed. In this way, the temperature at which the coating was severed was determined.

In Example 1, this temperature is that due to the presence of the capped polyisocyanate, the temperature of the throughput amounted to about 26O ⁰ C, in Example 2, only 212 ° C, from which it was seen

separately compared to the usual phenol-modified polyvinyl acetal coatings increased considerably became.

All other properties of these coatings were practically the same.

Similar insulating coatings on copper wire were made from the compositions in the following examples:

Blocked polyisocyanate

(Parts)

Polyvinyl formal

(Parts)

IO

Example 3 5 45 100

Example 4 2.5 67.5 100

Example 5 50-100

(Control)

The percentage of leaching from the insulating coatings was determined for various solvents certainly.

The percentage of extracted by methanol and toluene from the coatings substances was determined by measuring the weight loss of a coated wire after 2 hours immersion at reflux in the particular solvent and 1 hour drying at 150 ⁰ C in a conventional mechanical kiln.

The percentage of substances extracted by CHCIF2 was determined by inserting the coated wire into a U-tube and leaving the coating under the action of the solvent for 6 hours at a pressure of about 15.75 kg / cm ² and at a temperature of 40 ^° C., whereupon drying was carried out in a similar manner.

Percentage of leached substances askarele used in electrical equipment as insulating Lubricants are used; these are mixtures of chlorinated aromatic Compounds that are relatively stable at higher temperatures.

The abrasion resistance was determined according to the test of the National Electrical Manufacturers' Association; the surface of the coating is repeatedly scraped with a rigid steel blade, and at a right angle to the wire until the enamel or the wire enamel is worn through. A weight of 780 g presses the needle against the cover, and the number of strokes that required to chafe through the coatings is a measure of the abrasion resistance.

Example 6
Example 7 ...
(Control)

Original abrasion resistance

89
62

Abrasion resistance

after pyranol treatment

71

These results again show the better solvent resistance of the three components existing wire enamels compared to the normal coatings made of polyvinyl formal and phenol-aldehyde resins .

As in Example 1, other wires were coated with the following enamels or wire enamels:

Example 3
Example 4 ...
Example 5 ...
(Control)

Methanol

0.56
0.30
2.76

toluene

1.17 0.00 4.16

CHCIF2

35 Phenol-
Aldehyde-
resin
(Parts) Disguised
Polyiso-
cyanate
(Parts) Polyvinyl
formally
(Parts) Example 8
40 Example 9
(Control) 10
50 60 100
100

0.44 0.30 1.48

Enamelled wires were produced as in Example 1 from the following materials:

Example 6
Example 7
(Control)

Phenol-

Aldehyde-

resin

(Parts)

10
50

Blocked polyisocyanate (parts)

60

Polyvinyl formal

(Parts)

100 100

Pattern of coated in the above manner wires were tested for their resistance to softening by means of the pyranol-test, by immersion of the coated wire in »Pyranol" for a period of 100 hours at a temperature of 100 ⁰ C and determining the decrease in Abrasion resistance.

"PYRANOL" is a registered trademark of General Electric for the so-called The ability of these coatings to bend when exposed to heat (bending time) was determined by storing samples of the coated wire at 150 ° C and determining the number of hours after which cracking occurred the coating occurred when the wire was wrapped around mandrels of circular cross-section, the diameter of which was once, twice or three times the diameter of the wire. Failed to put the coated wire over after a heat aging period ^! If a mandrel three times the diameter of the wire were wound without cracking the coating, the coating was considered unusable. On the other hand, if the heat-aged coated wire passes such a test with a mandrel three times the diameter of the wire, then successively thinner mandrels are used to determine the smallest diameter mandrel that the sample wire can be bent about after aging. In the test results below, the number 3 means that the mandrel with the smallest diameter by which the specimen can still be bent after the specified period of heat aging without cracks occurring is a mandrel three times the diameter of the wire.

The dielectric strength after aging was determined with covered wires wrapped around each other were, by periodically applying a voltage of 2000 volts for a duration of each a second. The samples were stored at elevated temperatures, and the number of hours that was required to cause the insulating coating to strike through was recorded.

Example 8 ...
Example 9 ...

(Control)

* F = unusable.

Flexural strength at 150 ^° C

64 I 80 I 96 I 112

hours

2
F *

F *

Dielectric

Old at MO ⁰ C

in hours

Phenol- Ver Polyvinyl Polyvinyl Aklenya-
resin cut it formally butyral (Parts) Pofyiso
cyanate (Parts) (Parts) 20th (Parts) _ 100 Example 15 .... 50 80 - 100 Example 16 .... 50 - 100 - Example 17 - (Control)

125

The dielectric aging at 160 ^° C. was determined in Examples 10 to 12 below:

Dielectric

Aged in hours at 60 ° C

From this it can be seen that polyvinyl butyral is also satisfactory for the invented

'5 coating agents according to the invention are used can, but the polyvinyl butyral-containing coating agents (Example 16) have a lower value Abrasion resistance as coating compositions containing polyvinyl formals (Example 17). That's why the Mass according to Example 15 still 0.006 parts of colloidal polytetrafluoroethylene (see US Pat. No. 2,668,157) and 0.001 part of dibutyl phosphoric acid was added.

The distinguishing features of the above

Masses are the following:

950 875 610

Example 10 ..

Example 11 ..

Example 12 ..

(Control)

The above results clearly show the improved dielectric aging resistance of the three Components of existing wire enamels.

The solvent resistance of the coatings of Examples 13 and 14 below were determined by immersing the coated wires in a refluxed one for 10 minutes Mixture of equal volumes of ethyl alcohol and toluene. The coatings were then put on Softening, stickiness, swelling, puckering, peeling, blistering or other signs of deterioration examined.

Example 15 Cut through Abrasion Bending Example 16 strength
in hours Example 17 at 150 ° C 3 ° (Control) 285 36 160 5 180 222 43 96 64

Blocked polyisocyanate

(Parts)

Polyvinyl formal

(Parts)

Example 13 .... 10 60 100

Example 14 - 60 100

(Control)

The wire enamels in these examples were heated slightly longer than in the other examples cured to a dark coating to make up the difference in solvent resistance after the to emphasize the respective composition more. The coating with the invention, from three Components existing wire enamel (Example 13) showed no harmful effect of the solvent, whereas the coating according to Example 14 softened noticeably and at the ends of the Wire loosened.

Wires were then coated with enamels of the following composition as in Example 1 :

The polyvinyl butyral-containing coating agents according to the present invention are preferable if both longer flex life and a higher sever temperature are desirable are. The percentage of substances extracted from these masses by solvents is lower, if higher proportions of the blocked polyisocyanates are used (e.g. 120 parts). Such masses are a little easier to harden, d. That is, the curing takes place with a shorter heating time or with a lower temperature.

It is not intended to apply the coating compositions according to the invention only to those in the preceding Limit the concentrations given in the examples. For example, if higher temperatures cutting through or rubbing through are particularly desirable, then this can be done in achieve the way that one for the inventive, consisting of three components wire

lacquers to 100 parts of polyvinyl acetal 2 to 80 parts of capped polyisocyanate are used without this any of the other desirable properties is adversely affected. Likewise, if increased solvent

and abrasion resistance are fundamental, the same in the inventive, out of three Components consisting of wire enamel from concentrations of 1 to 50 parts of the phenol-aldehyde resin to 100 parts of polyvinyl acetal obtained without

⁶ S adversely affecting the other desired properties. The critical concentrations for the improved compositions according to the invention are therefore 100 parts of polyvinyl acetal, 1 to 50 parts of phenol-alde-

hyd resin and 2 to 80 parts of blocked polyisocyanates. A coating agent with 100 parts of polyvinyl acetal, 1 to 20 parts of phenol-aldehyde resin and However, 40 to 80 parts of capped polyisocyanate is preferred because it is in this concentration range all desirable properties are best balanced. With a concentration the mass composed of three components of over 50 parts of the phenol-aldehyde resin for every 100 parts of polyvinyl acetal, the flexibility of the products decreases.

About the behavior of a mass of three components with lower proportions of blocked polyisocyanates To explain, wires were coated with the same enamel as in Example 1, however in the following proportions:

Polyvinyl formal

Example 18

100

The temperature for the severing of the coating of the enameled wires of the above composition amounted on average to more than 300 ⁰ C.

It will be readily apparent to those skilled in the art that many and widely differing embodiments of the present invention are possible without departing from the spirit of the invention or to move away from their area.

The polyvinyl acetal resins used in this invention are in U.S. Reissue Patent 20 430 to Morrison et al. described. The preferred polyvinyl acetals are those from the condensation of partially or fully hydroxylated polyvinyl esters with formaldehyde (polyvinyl formal), Acetaldehyde, propionaldehyde or butyraldehyde (polyvinyl butyral). Also condensates with higher Aldehydes can be used including those with aromatic aldehydes such as e.g. B. benzaldehyde. The preferred polyvinyl acetals can contain 1 to 35% ester groups, 3 to 15% hydroxyl groups and the remainder essentially contain acetal groups.

The phenol-aldehyde resins that can be used include very different resin condensates of a phenol with an aldehyde as described in U.S. Patent 2,307,588. This acts they are soluble, thermosetting substances. These resins can be made from various phenols such as B. Phenol, cresol, xylenol, ethylphenol, p-t-butylphenol, etc., as well as from various lower aidehydes, such as B. acetaldehyde, propionaldehyde and butyraldehyde can be produced. Is formaldehyde the more reactive aldehyde and is therefore preferred. To obtain thermosetting resins, it is it is desirable to use 0.5 to 3 moles of the aldehyde per mole of the phenol.

The masked polyisocyanates used in the present invention are polyurethanes which, when heated above 150 ^° C., give a polyisocyanate. ^6s

Materials that can be used for this purpose are disclosed in U.S. Patent 2,797,232 and British Patent No. 2,797,232 U.S. Patent 755,942.

The polyurethanes are polyisocyanates, their isocyanate groups reacted with the reactive hydrogen of another organic compound where the polyurethane reacts like a polyisocyanate when subjected to elevated temperatures will. Suitable polyisocyanates include compounds such as phenylene diisocyanates, Tolylene diisocyanate, naphthalene diisocyanate, diphenylmethane diisocyanate, Cyclohexanediol diisocyanate, ethylene diisocyanate, tetramethylene diisocyanate, Hexamethylene diisocyanates, methylbenzene triisocyanates, polyisocyanates, which are the partial Reaction products of diisocyanates or triisocyanates with polyhydric alcohols, and the like. as well as mixtures of such substances. To the suitable, reactive hydrogen-containing substances, which combine with the polyisocyanates to form the desired polyurethanes Phenols such as B. phenol, cresol, xylenols, etc., secondary aromatic amines, mono- and polyfunctional tertiary alcohols, amides, lactams, mercaptans, enols and the like, including mixtures thereof can be used to cap the polyisocyanates. The preferred means of capping are Compounds with a hydroxyl group attached to an aromatic ring.

The blocked polyisocyanates are preferably used in the invention in a concentration _t of 40 to 80 parts of polyisocyanate per 100 parts of polyvinyl acetal. The optimal amounts depend on the type and amount of the polyvinyl acetal used and the phenol-aldehyde resin as well as the desired properties of the finished coating agent. The preferable proportion can easily be determined by those skilled in the art. By introducing the masked polyisocyanates into the customary polyvinyl acetal compositions modified by a phenoplast, the temperatures for cutting, the flexural strength and dielectric aging or dielectric strength are improved and the percentage of substances drawn out by solvents is reduced and excessively high proportions of masked polyisocyanates are set the flexibility of the coatings produced and can also reduce the strength of the product against a mixture of alcohol and toluene.

If the compositions according to the invention are to be used for coatings, the three resin components are dissolved in a substantially anhydrous organic solvent. The usual solvent consists of a phenol and a hydrocarbon, as this combination is responsible for dissolving of polyvinyl acetals is most effective. The phenol in question can be phenol itself or a cresol, be a xylenol or the like; the hydrocarbon can be an aliphatic compound, but is in the Usually an aromatic compound, such as. B. xylene, naphthalene or mixtures such as those in the examples used coal tar hydrocarbons with high solubility. The concentration of solids can be changed at will and depending on the expediency, from about 5 to 50%, based on the weight of the solution.

These compositions cure at about 150 ⁰ C and above from, but temperatures between 200 and 500 ° C are preferred; they can be used as surface coatings or as adhesives. The initial

409 690/529

materials or the solutions of the reagents can contain the usual additives, such as. B. fillers, Pigments, dyes, stabilizers, lubricants and the like can be added.

Claims (1)

Claim: Coating agent curable by heat, in particular for coating electrical conductors based on polyvinyl acetal with the addition of phenolic resins and organic solvents, characterized in that it contains 100 parts by weight of polyvinyl acetal, 1 to 50 parts by weight thermosetting phenol-aldehyde resin and 2 to 80 parts by weight of capped polyisocyanate contains, which is a polyurethane of the general formula O H H C "H _{(2re +} 2- _m ) -OCNRNCOX where R is a phenylene, methylphenylene, dimethylphenylene, naphthylene or methylnaphthylene group, a phenyl or alkali metal phenyl group containing alkyl groups from 1 to 6 atoms, m is an integer greater than 1, but not greater than η and η is a positive integer from 2 to 10. Considered publications: German Patent No. 946 173; U.S. Patent Nos. 2,499,134, 2,307,588, 730,466, 2,668,157, 2,574,313; Zeitschrift für angewandte Chemie, 1947, pp. 263-265; Bayer - Kunststoffe, 1955, p. 33. 409 690/329 9.64 Q Bundesdmckerei Berlin