DE2228288A1 - Heat-curable coating compsn - esp for the insides of food-conserving tins - Google Patents

Abstract

The coating consists of 50-95 wt % PF resin, which may be etherified, and 50-5 wt. % of an alkyd-type, polyester contg. functional OH gps and prod. by condensn of aliph. 5-15C di-/polybasic acids, opt contng a propn. of phthalic acid and/or fatty acids with di-/polyols. Compsn avoids the 'marking' effect normally formed in tins that share S-releasing foods.

Description

Thermosetting coating agent The invention relates to a thermosetting coating agent Coating agent that can be used as packaging varnish, in particular can or Inner tube lacquer for filling goods that split off sulfur, containing a binder system and optionally a solvent and / or customary additives, e.g. Lubricants, pigments and leveling agents.

For packaging varnishes that are used for painting the inside of tubes or cans made of tinplate, especially canned food, must be used in particular iohe requirements with regard to sulfur resistance and deep-drawing strength are made will.

arise during the sterilization of protein-containing foods namely, due to the resulting thermal degradation, various sulfur-containing Fission products, especially mercaptans and hydrogen sulfide.

If such a sterilization is now carried out in a tinplate extension, the tin on the surface of the tinplate reacts with the sulfur-containing tin Decomposition products with the formation of tin sulphide, which is visually characterized by a so-called "Marbling" makes noticeable. Through this sulphide formation the inner surface gets the can has a brownish-bluish appearance.

If the duration of action of the sulfur-containing cleavage products increases, this can also lead to the formation of iron sulphide, which adheres to the inner surface of the Canned food forms black spots and the contents can also flocculate the inner surface of the cans as well as their contents against such sulfurization phenomena To protect, a layer of varnish is applied to the tinplate. The general for this The types of paint used can be divided into pigmented and non-pigmented.

The pigmented paint types contain a filler that the sulfur-containing Chemically binds degradation products or which optically hides the tin sulfide formed.

By adding such a filler, however, the mechanical Properties of the applied paint film and its chemical resistance are essential worsened.

The well-known non-pigmented paint types, e.g. epoxyphenol, epoxy urea-formaldehyde or polybutadiene lacquers, the sulfur-containing degradation products, i.e. the formation of tin sulphide, does not ensure in a satisfactory manner, e.g. on sheet metal parts deformed after painting, such as l) corner corners, rebated edges and deep-drawn can parts.

The object of the invention is to create a coating agent that has particularly good deep-drawing properties and the aforementioned sulphonation phenomena avoids.

In the case of a coating agent, this task becomes the one mentioned at the beginning Kind according to the invention in that the binder system 50 to 95 wt.% Of a thermosetting reactive phenol-formaldehyde condensation product, optionally Is etherified, and 50 to 5 wt.% Of a higher molecular weight polyester of the alkyd resin type with functional hydroxyl groups, produced by condensation of aliphatic organic di- or polybasic acids with 5 to 15 carbon atoms, e.g.

Adipic or sebacic acid, optionally with a proportion of phthalic acid and / or fatty acid, and di- or polyhydric alcohols.

The functioning of this binder system is that the sulfur-containing degradation products released during the sterilization of the contents the baked-in coating or. Paint film cannot wander through, which also the formation of tin or iron sulfide is avoided.

I) this effect is probably due to a special favorable geometric Arrangement of the atoms within the binder molecule achieved.

This alkyd-polyester-phenolic resin combination according to the invention possesses apart from the sulfur resistance also the special advantages that they are uncrosslinked State - i.e. before the stoving - in the common lacquer solvents It is readily soluble1 that it uses a coating material with a high solids content, e.g. 50 % By weight, can be produced at low viscosity and that such coating agents easily in the usual way, e.g. by salting or spraying, onto the surface to be coated @etall can be applied. Other advantages are that the after after baking, e.g. 15 minutes at @ 00 ° C, the coating film formed @hvsiologically harmless, Is sterilization-proof and tasteless and is characterized by high chemical resistance as well as deep drawability. Finally, the one for the creation and the effort required to transport the coating agent according to the invention is lower, because the binder system used is less solvent and therefore less Transport container required.

In the practical implementation of the invention, it is advantageous if the binder system 70 to 90 wt. 7c 'phenol-formaldehyde condensation products and 30 to 10% by weight of higher molecular weight polyester of the alkyd resin type with functional Contains hydroxyl groups.

The properties of the coating composition according to the invention can by Usual additives, e.g. catalysts, e.g. zinc octoate, leveling agents, e.g. polyvinyl butyral, anti-crater agents and lubricants, e.g. polyethylene, may be further improved. To increase the scratch resistance, e.g. an addition of polyvinyl butyral favorable.

The invention is explained below with reference to examples.

I; e i s p i e 1 l: 70 parts by weight of thermosetting phenol-formaldehyde condensation product, which is commercially available under the name "PHENODUR PR 897", 30 parts by weight higher molecular weight polyester of the alkyl resin type with functional hydroxyl groups, with unbranched molecular chains and a hydroxyl content of about 1.2 wt. (Trade name "Desmophen 1700") and 100 parts by weight of Ethylglykol as a solvent were on one mixer mixed with one another and then formed a coating agent low viscosity.

In order to test the sulfurization resistance in the laboratory, this Coating agent with the usual dry application of approx. 6 g / m2 on the usual Tinplate (both hot-dip and electrolyte-tinned) applied and 15 minutes self-fired at 200 ° C. The sheet with the now crosslinked coating film was deep-drawn and sterilized for 2 hours at 130 ° C in the sulphide solution listed below, which is commonly used as a sulfide test solution and as a criterion for sulfur resistance of a coating is considered representative.

Composition of the sulphide solution used: 2 g Na2S 10 g NaCl 10 g gelatin 978 g water This mixture is made up with an acetic acid (3 wt.%) adjusted to a pH of 6.5 to 7.0.

After performing this test, it was found that neither in the deep-formed nor in your non-deformed part of the coated test sheets there were slightest signs of marbling.

The above-mentioned mixing ratio of the binder system brought thus absolute sulfur resistance and excellent deep tensile strength of the coating agent.

Example 2: 80 parts by weight of phenol-formaldehyde condensation product of the aforementioned type and 20 parts by weight of a higher molecular weight Polyester of the alkyd resin type with functional hydroxyl groups, with weakly branched molecular chains and a hydroxyl content of about 1.8% by weight (trade name "Desmophen 1800") with lOf) parts by weight of ethyl glycol as a solvent for about 30 minutes by means of a mixer mixed together.

This coating agent was, as described in Example 1 l) c, on retraren, hardened and tested. The samples showed no signs of narcosis, absolute sulfur resistance and good deep tensile strength.

Example 3: 90 parts by weight of the aforementioned phenol-formaldehyde condensation product and 10 ew.-parts of the polyester according to Example 1 were together with a solvent, e.g. 100 parts by weight of butyl glycol, mixed together. This coating agent was as described in Example 1, applied, cured and tested. The samples showed slight signs of marbling and sufficient deep tensile strength.

B e i 5 p i e 1 4: 50 parts by weight of the aforementioned phenol-formaldehyde condensation product and -50 parts by weight of the polyester according to Example l were together with a solvent, e.g. 120 parts by weight of ethyl glycol mixed.

This coating agent was applied as indicated in Example 1, hardened and tested. The samples showed no signs of marbling, absolute sulfur resistance and excellent deep-drawing properties.

@ e i s p i e 1 5:30 parts by weight of the aforementioned phenol-formaldehyde condensation product and 70 parts by weight of the polyester according to Example 1 were together with a solvent e.g. 100 parts by weight of ethyl glycol, mixed. This coating agent was made accordingly Applied to the information in Example i, cured and tested. The samples showed slight signs of marbling and route deep tensile strength; the coating film was, however, depending on the type of polyester of the aforementioned type used, if necessary sticky.

B e i 5 p i e 1 6: 70 Ciew. Parts of an etherified phenol-formaldehyde condensation product, which is commercially available under the name "PHENO-DTJR PR 722", and 30 wt. -Parts of the polyester mentioned in Example l were together with 100 parts by weight Ethylglycol as a solvent mixed with one another on a stirrer. This Coating agent was applied as described in Example 1 and cured and tested. The samples showed no signs of marbling, absolute Sulfur resistance and good deep tensile strength.

In addition to these examples, it should be noted that the use various thermosetting reactive phenol-formaldehyde condensation products (Resole), which can also not be etherified, and / or the use of different higher molecular weight polyester of the alkyl resin type with functional hydroxyl groups and the use of different solvents has practically no effect on the test results had analogous examples, in which, for example, also a strong A branched polyester of this type with a hydroxyl content of about 7.5% by weight (trade name "Desmophen 800") and a linear such polyester with a hydroxyl content of about 8.5% by weight (trade name "Desmopehn 850") were used. A change too the amount of solvent used had no effect on the quality of the tested coating. The amount of solvent could therefore depend on the type of application selected of the coating agent, e.g. rolling, spraying or brushing. Preferred however, the coating agent contains at least 40% by weight of solvent, advantageously 40 to 6 (!% By weight binder package.

The fiction geinäß coating agent results in We ißblech or aluminum gold or silver colored coatings, but can be pigmented as required, e.g. with aluminum powder.

Claims (4)

P a t e n t a n s p r ü c h e: 1.; dye-hardenable coating agent that can be used as packaging lac1 is, in particular can or tube inner lacquer for sulfur-releasing products, containing a binder system and optionally at least one solvent and / or usual additives, e.g. lubricants, pigments and flow agents, d a d u r c h g e k e n n n z e i c hn e t that the binder system 50 to 95 wt. a thermosetting reactive phenol-formaldehyde condensation product, which is optionally, etherified, and 50 to 5 Gew.0ó of a higher molecular weight polyester of the alkyd resin type having hydroxyl functional groups produced by condensation of aliphatic organic di- or polybasic acids with 5 to 15 carbon atoms, e.g. Adipic or sebacic acid, optionally with a proportion of phthalic acid and / or fatty acids and di- or polyhydric alcohols. 2. coating agent according to claim l, d a d u r c h g e k e n n z e i c h n e t that the binder system is 10 to 30 wt.% higher molecular weight polyester of the alkyd resin type having hydroxyl functional groups. 3. Coating agent according to claim l or 2, d a du r c h g e k e n n notices that the binder system is higher molecular weight polyester of the alkyd resin type with functional hydroxyl groups with unbranched or weakly branched molecular chains and with a hydroxyl content of at most 0.5% by weight, preferably between 1.2 and 2.5% by weight. 4. Coating agent according to one of claims 1 to 3, d a d u r c h it is not noted that it contains 40 to 60% by weight of the binder system.