NO141549B - PROCEDURE FOR PREPARING AN IMPROPERABLE SURFACE LAYER OF A POROES FILM OF AN OXYBENZOYL POLYESTER ON A SUPPORT, PREFERRED METAL - Google Patents

Description

According to a recently invented technique it is

possible to produce high molecular weight oxybenzoyl polyesters which are highly resistant to acids and solvents at tempe-

temperatures up to and during the time exceeding 370°C. Due to the advantageous physical and chemical properties of these polyesters, considerable effort has been made in trying to find methods for providing substrates coated with these polyesters. A method that has had limited success,

is the application of the polyester in hot particle form to the substrate by various methods, e.g. flame spraying. Although such methods provide good adhesion of the polyester film to the substrate,

unfortunately they give a film of high porosity, mainly due to pores and small holes in the film. This porosity has an adverse effect on the electrical properties of the coating and allows the passage of acids, bases and solvents through the film, which can result in unwanted attack on the substrate. A further disadvantage of the method described above is that it results in a film which has a rough surface texture.

The invention therefore provides a method

for producing an impermeable surface layer of a porous film of an oxybenzoyl polyester on a substrate, the substrate preferably being metal.

The method according to the invention avoids the disadvantages of previously known methods, and it is characterized in that the surface of the porous film is exposed to a shear force that has sufficient strength to cause pla-

stiff deformation of the film, whereby the film's surface is made impermeable. The coating is also resistant to attack by acids, bases and solvents and has a smooth surface texture.

The oxybenzoyl polyester used in the process

the method according to the present invention, has a molecular

weight of at least approx. 3,500 and is either:

(a) a polyester of the formula

wherein R 1 is benzoyl, lower alkanoyl or hydrogen, and p is an integer from 30 to 200, or (b) a polyester having repeating structural units of formulas I, III and IV

where X is -0- or -SC^-, m is 0 or 1, n is o or 1, p is as above, q:r = 10:15 to 15:10, p:q = 1:100 to 100:1, p+q+r = 30 to 200, the carbonyl groups of the portion of formula I or III are linked to the oxy groups of the portion of formula I or IV, and the oxy groups of the portion of formula I or IV are linked to the carbonyl groups of the portion of formula I or III.

R"*" is preferably hydrogen or acetyl.

Further advantages of the present invention will be apparent from the following, detailed description of the invention and the accompanying drawing which is a schematic illustration of a preferred embodiment of the method according to the invention.

As mentioned, the film's surface is subjected to a shearing effect, preferably in a direction parallel to the film's surface. The shearing effect can be exerted in many different ways. For example, it can be carried out by grinding the film's surface with a polishing wheel or other rotating instruments containing fine, sharp grains, such as sandpaper. Alternatively, you can

IN

the shear force is applied by a smooth surface such as the surface of a smooth rotating roller or simply by hand using a laboratory spatula.

The invention will be better understood by reference to

the simple figure in the accompanying drawing in which an apparatus 10 suitable for carrying out the method according to the invention is schematically shown. In this embodiment, a flame spray gun 11 comprising a holder 12 for oxybenzoyl polyester and a nozzle 13 connected to the holder 12 by a pipe 14 is used to first mix oxygen and acetylene from a source not shown and then pass this mixture through the pipe 14 which draws the oxybenzoyl polyester from the holder 12 by venturi action and throws the mixture 15 of hot gases and oxybenzoyl polyester towards the substrate 16 while forming a film 17. The surface 18 of the film 17 is

rough, and the film mass itself contains small holes and pores due to an incomplete coalescence of the oxybenzoyl polyester particles present in the mixture 15. The substrate 16 is moved in the direction of the arrow 19 and passes under a roller 20 which moves in the direction of the arrow 21. The roller's surface can be highly polished or be a grinding wheel made of silicon carbide or other hard material that will grind the surface. When the substrate 16 passes under the roller 20, the film surface 18 is subjected to a shearing action by the roller 20 in a direction approximately parallel to the film's surface 18. The shearing action is preferably applied with sufficient force to cause a certain plastic deformation of the film 17 while producing a substrate 16 coated with a film 17 whose surface 22 is impermeable.

The production of the oxybenzoyl polyesters mentioned here is described in detail in US patent no. 3,579,870 respectively.

with the title "Polyesters Based on Hydroxybenzoic Acids" and Norwegian patent no. 129 301.

The oxybenzoyl polyesters which can be used in the present invention can also be chemically modified in different ways, such as by inclusion in the polyesters of monovalent reactants such as benzoic acid or trivalent or higher reactants such as trimesic acid or cyanuric chloride. The benzene rings in these polyesters are preferably unsubstituted, but can be substituted with non-disturbing substituents, examples of which include halogen such as chlorine or bromine, lower alkoxy, e.g. methoxy, and lower alkyl, e.g. methyl.

A large variety of substrates can be used in the method according to the present invention, examples of which include ferrous materials such as iron or steel, non-ferrous materials such as brass, titanium, aluminum or copper, and non-metals such as stone or concrete.

The polyesters that can be used in the present invention can be used in pure form, mixed with each other or with

a wide range of organic and/or inorganic fillers. Examples of suitable organic fillers include polyhalogenated addition polymers, such as polytetrafluoroethylene, and condensation polymers such as polyimides. Examples of suitable inorganic fillers include graphite, zinc, molybdenum disulphide and glass fibres. These fillers can make up to 70% by weight of the total weight of polyester and filler.

The invention is further illustrated by the following examples where all parts and percentages are based on weight unless otherwise stated. These non-limiting examples are illustrative of certain embodiments suitable for practicing the invention and represent the best ways of carrying it out.

EXAMPLE 1

A mixture of 856 grams of phenyl-para-hydroxybenzoate, 0.015 grams of tetra-n-butyl orthotitanate and 1800 grams of polychlorinated poly-phenyl solvent (b.p. 360-370°C) was heated with constant stirring and under an atmosphere of flowing nitrogen at 170-190° C for 4 hours and then at 340-360°C for 10 hours. Early in this heating cycle, the mixture became a homogeneous liquid. During the heating cycle, condensation occurred followed by the distillation of phenol, and the resulting polyester formed a precipitate. The mixture was cooled to room temperature and extracted with acetone to remove polychlorinated polyphenyl solvent, and the product was dried overnight in vacuo at 60°C. A yield of 377 grams of polyester powder, consisting essentially of para-oxybenzoyl polyester, was obtained.

EXAMPLE 2

This example illustrates the synthesis of a copolymer useful in the present invention.

The following quantities of the following ingredients were combined as indicated:

Components A-D were placed in a four-necked, round-bottomed flask equipped with a thermometer, stirrer, a combined nitrogen and HCl inlet and an outlet connected to a condenser. Nitrogen was passed slowly through the inlet. The flask and its contents were heated to 180°C, after which HCl was bubbled through the reaction mixture. The outlet temperature was maintained at 110-120°C by external heating during the p-hydroxybenzoic acid/phenylacetate esterification reaction.

The flask and its contents were stirred at 180°C for 6 hours, after which the feed of HCl was shut off, the outlet temperature was raised to 180-190°C and the mixture stirred at 220°C for 3 1/2 hours. Up to this point, 159 grams of distillate was collected in the condenser. Component F was then added and the temperature gradually raised from 220°C to 320°C over a period of 10 hours (10°C/hour). Stirring was continued at 320°C for 16 hours and then for a further 3 hours at 340°C forming a slurry. The total amount of distillate, consisting of phenol, acetic acid and phenylacetate, amounted to 384 grams. Component G was added and the reaction mixture was cooled to 70°C. 750 ml of acetone was added and the slurry was filtered and the solids were extracted in a Soxhlet apparatus with <.-„ acetone to remove components C and G. The solids were dried in vacuo at 110°C overnight, after which the resulting copolymer (320 grams , i.e. 89.2% of theoretical yield) was recovered as a granular powder.

EXAMPLE 3

This example illustrates the method according to the present invention where the polyester film is subjected to a spooning action compared to a control film.

A 6.35 mm thick mild steel backing plate was flame sprayed with the granular polyester from Example 1 where

at the polyester was applied as a 0.076 mm thick film. The film was allowed to cool to room temperature, and the coated plate was cut in half

equal parts. The first part was immersed untreated in concentrated hydrochloric acid. Blisters formed on the surface of the polyester film, and

within a few minutes the entire film was lifted off the substrate.

The other part was lightly polished with a rotating, abrasive polishing wheel provided with No. 000 sandpaper and then immersed in hydrochloric acid of the same strength. No blisters appeared on the surface of the polyester film, which remained stubbornly attached to the substrate.

EXAMPLE 4

The procedure according to example 3 was repeated with the exception that the shearing effect was applied to the film by hand using a laboratory spatula instead of a polishing wheel, but with the same result.

EXAMPLE 5

The procedure according to example 3 was repeated with the exception that the film and the substrate were heated to 100°C before polishing, but with the same result.

EXAMPLE 6

This example illustrates the method according to the present invention where the film was applied by hot dipping.

A steel plate with dimensions 6.35 x 25.4 x 12 7 mm was heated to 600 oC and dipped into a container containing polyester according to Example 1. The plate was then pulled up, and the adhesive film was cooled and polished as in Example 3.

EXAMPLE 7

The procedures of Examples 3 to 6 were repeated, with the exception that the polyester from Example 1 was replaced by the polyester from Example 2, but with similar results.

EXAMPLE 8

The procedure according to example 3 was repeated with the exception that a plasma spray was used instead of flame spraying. The polyester stuck even better to the substrate.

Claims (3)

1. Method for producing an impermeable surface layer of a porous film of an oxybenzoyl polyester on a substrate, preferably metal, by subjecting the film to a shear force essentially parallel to the surface of the film, characterized in that the surface of the porous film is subjected to a shear force with sufficient strength to cause plastic deformation of the film, whereby the surface of the film is made impermeable, using an oxybenzoyl polyester with a molecular weight of at least approx. 3,500 and which is either (a) a polyester of the formula wherein R*" is benzoyl, lower alkanoyl or hydrogen, and p is an integer from 30 to 200, or (b) a polyester having repeating structural units of formulas I, III and IV n I where X is -O- or -SO 2 -, m is 0 or 1, n is 0 or 1, p is as above, q:r = 10:15 to 15:10, p:q = 1:100 to 100 :1, p+q+r = 30 to 200, the carbonyl groups of the portion of formula I or III are linked to the oxy groups of the portion of formula I or IV, and the oxy groups of the portion of formula I or IV are linked to the carbonyl groups of the portion of formula I or III. 2. Method as stated in claim 1, characterized in that a polyester is used where B?~ is hydrogen or acetyl. 3. Method as stated in claim 1 or 2, characterized in that the porous film is formed by flame spraying or plasma spraying of the oxybenzoyl polyester on the substrate.