US3924022A

US3924022A - Method of applying an organic coating onto an inorganic coated steel sheet for a magnetic laminate application

Info

Publication number: US3924022A
Application number: US444859A
Authority: US
Inventors: Siegfried H Schroeter; Winkle Jon Van; Carroll B French
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1974-02-22
Filing date: 1974-02-22
Publication date: 1975-12-02
Anticipated expiration: 1992-12-02
Also published as: CA1042383A

Abstract

A continuous method is provided for improving the insulating characteristics of oriented steel strip having an inorganic surface coating to produce an organic resin-inorganic coatingoriented steel strip composite. Certain irradiation curable solventless organic resins can be continuously applied to the surface of the oriented steel strip in a pollution free manner. The resulting composite can be used to make power transformer core laminate.

Description

United States Patent 1 Schroeter et a1.

1 1 METHOD OF APPLYING AN ORGANIC COATING ONTO AN INORGANIC COATED STEEL SHEET FOR A MAGNETIC LAMINATE APPLICATION [75] Inventors: Siegfried I'I. Schroeter, Schenectady,

N.Y.; Jon Van Winkle, Dalton; Carroll B. French, Lenox, both of Mass.

[73] Assignee: General Electric Company,

Schenectady, NY.

{22] Filed: Feb. 22, 1974 [21] Appl. No.: 444,859

[52] US. Cl. 427/54; 204/159.15; 204/159.19; 336/219; 427/127; 427/403; 427/409 [51] Int. Cl. B05D 3/06; HOlF 27/24 [581 Field of Search 117/9331, 218, 219, 222, 117/215; 336/234, 219; 204/15915, 159.19;

[561 References Cited UNITED STATES PATENTS 2,354,123 7/1944 Horstman et a1. 148/6 1 1 Dec. 2, 1975 2,533,351 12/1950 Carpenter 148/635 3,531,317 9/1970 Patheiger et 211..v 117/9331 3,600,290 8/1971 Fitko 117/9331 3,666,568 5/1972 Shimanaka et a1. 117/218 3,721,617 3/1973 Watt 117/9331 3,770,490 11/1973 Parker 1. 117/9331 Primary Examiner l. H. Newsome Attorney, Agent, or Firm-William A. Teoli; Joseph T. Cohen; Jerome C. Squillaro [57] ABSTRACT 3 Claims, 2 Drawing Figures US. Patent Dec. 2, 1975 FIG.

METHOD OF APPLYING AN ORGANIC COATING ONTO AN INORGANIC COATED STEEL SHEET FOR A MAGNETIC LAMINATE APPLICATION The present invention relates to the use of certain irradiation curable solventless organic resins for imparting improved insulating characteristics to oriented steel having an inorganic insulating coating. More particularly, the present invention relates to a continuous, pollution free process for making power transformer core laminate.

Prior to the present invention, transformer core laminate was generally made from oriented steel strip commonly referred to as magnetic or silicon steel having an inorganic surface insulating coating such as a magnesium oxide or silicate, shown, for example, in Carpenter, et al., U.S. Pat. Nos. 2,385,332 and 2,533,351, or having an inorganic phosphate coated oriented steel as shown by Gifford U.S. Pat. Nos. 2,492,095 and 2,501,846. etc. Further examples of inorganic coating materials for imparting improved insulating characteristics to magnetic sheet material are shown by I-Iirst U.S. Pat. Nos. 3,562,011, 3,705,549 and 3,705,826, assigned to the same assignee as the present invention.

Although oriented steel processed by the abovedescribed methods provides useful transformer core laminate, it was found that in many instances the inorganic coating did not insure adequate insulation. The inorganic coating, for example, often had surface imperfections which caused variations in surface resistivity, when oriented steel strip was subjected to standard electrical and mechanical tests such as the Franklin test ASTM A344-68. Those skilled in the art also know that if the transformer core is not properly insulated, severe core damage can occur in the event the transformer is struck by lightning. A high voltage surge can result in permanent core insulation breakdown, resulting in higher core losses.

It has been found that improved insulating characteristics can be imparted to inorganic coated oriented steel strip by coating the steel strip with an organic resin. An organic resin-inorganic coating-oriented steel strip composite has been made by treating the oriented steel strip with a hydrocarbon solvent solution of a phenol-formaldehyde resin. Although transformer core laminate having improved insulating performance can be made by use of such organic resin, the cure of the resin requires a baking step. Cure of the organic resin can require 1 to 3 minutes, rendering the method undesirable for high-speed continuous operation. In addition, means for hydrocarbon solvent removal must be provided to avoid air pollution.

In addition to the requirement of insuring adequate insulation, those skilled in the power transformer art know that the core consisting of hundreds of thin laminations in the form of high grade silicon steel strips cut to size, must be immersed in C hydrocarbon oil. Oil immersion is required to improve heat transfer and to reduce corona around the core and coils which could seriously damage and impair the operating efficiency of the transformer. Experience has shown that the organic resin must be hydrolytically stable at temperatures up to about 100C for a period of about years in the hydrocarbon oil to satisfy manufacturing requirements. Premature breakdown of the organic resin not only will result in insulation failure of the transformer core, but

2 can also lead to the breakdown and reduction in the cffectiveness of the hydrocarbon oil to reduce corona.

A further criterion that a cured organic resin must possess before it will meet the specifications of power transformer manufacturers is that shrinkage upon cure will not have negative effects on properties. Those skilled in the transformer art know that shrinkage of certain coatings on the surface of the oriented steel strip can alter the magnetostriction characteristic of the steel. Even a slight increase in magnetostriction due to surface stress can result in substantial transformer hum.

The present invention is based on the discovery that certain solventless irradiation curable organic resins, which are defined more particularly hereinafter, and include both electron-beam curable and ultraviolet light curable resins, can be used to continuously make oriented steel-inorganic coating organic resin composites in a pollution free manner. The composites made in accordance with the practice of the invention can be used as power transformer core laminates and are equivalent or superior in all respects to the core laminates made in accordance with prior art procedures. This result is quite surprising since many available irradiation curable organic resins, such as shown by Patheiger et al., U.S. Pat. No. 3,531,317 cannot be employed to produce suitable power transformer core laminate. In addition to imparting improved resistivity to inorganic material coated oriented steel strip, one of the vital criteria required for operable solventless irradiation curable resins in accordance with the practice of the invention is hydrolytic stability or the ability to resist insulation breakdown during immersion in 10C hydrocarbon oil over a 30-year period under average operating conditions of C. A further criterion employed is heat-stability. A weight loss test using a cured resin sample can be used to screen for heat stability whereby a weight loss of up to 10% can be tolerated over a temperature range of to C over a 1,000 hour period.

A vital test for screening resins based on contamination of the transformer oil and alteration of its dielectric properties is the IFT test, ASTM D97l-50 Interfacial Tension of Oil Against Water, shown on page 322 of the 1970 Annular Book of ASTM Standards, part 17 (November). It has been found that the IFT test can readily identify operable solventless irradiation curable organic resins, which can be employed in the practice of the invention. A procedure which can be employed is as follows:

Four hundred fifty square inches of oriented steel strip having a 0.1 mil cured coating of said irradiation curable solventless organic resin and capable of providing a O ampere Franklin test reading is immersed in about 375 ml of 10C hydrocarbon oil which initially has about 9 39.0 dynes/cm interfacial Tension Reading as measured above, and the 10C hydrocarbon oil is heated at a temperature of 120C for 48 hours. In order to qualify, the oil must provide thereafter an interfacial tension reading of at least 30 dynes/cm.

A further surprising feature of the irradiation curable solventless resins employed in the practice of the invention is that when applied to the surface of oriented steel strip and cured in accordance with the practice of the invention, there is little or no change in the dimension of the strip sufficient to increase the magnetostriction of the transformer core material made therefrom. A test procedure which can be used to determine strain of the oriented steel strip resulting from the cured resin is the Epstein test ASTM A343.

. There is provided by the present invention. a continuous. substantially pollution-free method for uniformly improving the surface resistivity of oriented steel strip having an inorganic material as a surface insulating coating to produce an oriented steel strip-inorganic coating-organic resin composite capable of providing an average Franklin test reading of from 0.1 to amperes at a pressure of up to 300 psi, which comprises, l. treating the oriented steel strip with an irradiation curable solventless organic resin to a thickness of up to 0.2 mil, and

2. passing the treated oriented steel strip through an irradiation curing zone at a rate of from 100 to 600 feet per minute, using an irradiation flux sufficient to effect the cure of the solventless organic resin to an organic resin with a hardness capable of being tested by the above-described Franklin test,

where said resin is characterized by having a viscosity of up to 3000 centipoises at 25C, and is a mixture consisting essentially of from 99l% by weight of organic monomer and correspondingly from l-99% by weight of organic polymer, where said irradiation curable solventless organic resin is capable of providing with C hydrocarbon oil, an interfacial tension reading of from 30 to 40 dynes/cm in accordance with ASTMD97l-50 1970).

Included by the irradiation curable solventless organic resins which can be used in the practice of the invention are UV curable wax containing polyesters as shown in copending application Ser. No. 444,860 of Seigfried H. Schroeter and Ona Valys Orkin, filed concurrently herewith and assigned to the same 'assignee as the present invention. These UV curable wax containing polyester can be more particularly defined as solventless organic-resins having a viscosity of from 500 centipoises to 3000 centipoises containing the following essential ingredients by weight:

A. to 40% of a vinyl aromatic material selected from styrene, vinyl toluene,tert-butylstyrene and mixtures thereof,

B. 80 to 60% of an unsaturated polyester reaction product of (i) a glycol and (ii) and aliphatically unsaturated organic dicarboxylic acid, where i. is a glycol selected from the class consisting of a. a mixture of 20-60 mole percent of neopentyl glycol and 40-80 mole percent of a member selected from propylene glycol, ethylene glycol and mixtures thereof, and

b. a mixture of (a) l to 40% by weight thereof of trimethylolpropane monoallyl ether, and

ii. is an aliphatically unsaturated organic dicarboxylic acid consisting essentially of a mixture of 50 to 65 mole percent of fumaric acid and 35 to 50 mole percent of a member selected from tetrahydrophthalic anhydride, endomethylene tetrahydrophthalic anhydride and mixtures thereof where there is utilized in making the unsaturated polyester reaction product of (B), up to at least about l0 mole percent excess of the glycol of (i) over the aliphatically unsaturated organic dicarboxylic acid of (ii) C. 1% to 5% based on the weight of (A) and (B) of a UV sensitizer, and D. 0.05% to 1% based on the weight of (A), (B) and (C) of paraffin wax.

The above described unsaturated polyester can be made by standard techniques involving either a onestep or two-step reaction procedure. The two-step procedure can involve reacting the total glycol at temperatures up to about 200C, which can consist ofa mixture of propylene glycol and neopentyl glycol, with tetrahydrophthalic anhydride. A hydrocarbon azeotroping solvent can be employed to facilitate removal of Water of reaction. Upon allowing the reaction mixture to cool, an acid number of from I to 25 indicates completion of the first stage of the reaction. The fumaric acid can then be added to the mixture with stirring and it is heated further until an acid number of 5 to 15 is obtained. In the one stage cook procedure, the acid number may be as high as 30.

In preparing the UV curable polyester composition, the vinyl aromatic solvent containing the paraffin wax and inhibitor can be added with stirring to the above prepared unsaturated polyester reaction product while it is warm. After the mixture has been allowed to cool to room temperature, an effective amount of the UV sensitizer can be added.

In addition to the above-described wax containing polyesters, there also can be used acrylic resins such as reaction products of acrylic or methacrylic acid with bisphenol A diglycidyl ether, known for example, as Shell Epocryl 301, dissolved in styrene, vinyl toluene, hydroxypropyl acrylate or hydroxypropyl methacrylate, or certain multifunctional acrylates such as trimethylol propane triacrylate, etc. Other acrylic resins may be those derived from the reaction of hydroxyl terminated polyester glycols, etc. with diisocyanates and hydroxyl containing acrylates and methacrylates, or may contain randomly pendant acrylate or methacrylate unsaturation. The cure of these resins is accomplished by the free radical polymerization or copolymerization of said pending groups with those of the monomer molecules, the free radicals being generated by the UV-activated sensitizer.

Another class of resins may include UV-curable epoxy resins, for example, as described in US. Pat. Nos. 3,708,296; 3,721,6l6; and 3,721,617. Such resins may consist of bisphenol A diglycidyl ethers such as Epon Resins produced by Shell Chemical Co.; epoxidized phenol or cresol novolak resins such as produced by Dow Chemical Co. and Ciba Corporation or blends of such epoxy resins with epoxide monomers such as 1,2-epoxy-4( epoxyethyl) cyclohexane;( 3,4-epoxycyclohexyl)methyl 3,4-epoxy cyclohexane carboxylate, allyl glycidyl ether, etc., or mixtures thereof. These epoxy resins may be cured by a cationic mechanism initiated by the UV-activated sensitizer.

Among the UV radiation photosensitizers which can be used in the curable wax containing polyester compositions of the invention are, for example, ketones, such as benzophenone, acetophenone, benzil, benzyl methyl ketone; benzoins and substituted benzoins such as benzoin methyl ether, a-hydroxymethyl benzoin isopropyl ether; halogen containing compounds such as abromoacetophenone. p-bromoacetophenone, ozchloromethyl naphthalene. sulfur compounds such as aromatic disulfides. and other photosensitizers such as azides, dyes. thioketones, or mixtures or synergistic mixtures thereof. Other compounds, at levels which do not interfere with the cure, may also be added. Such compounds are, for example, inhibitors such as hydroquinone, tert-butyl hydroquinone, tert-butyl catechol, p-benzoquinone, 2.5-diphenylbenzoquinone, 2,6-ditert-butyl-p-cresol, etc.; various fillers, flatting agents. thixotroptic agents. dyes and pigments such as barytes. blanc fixe. gypsum. calcium carbonate, quartz, diatomaceous silica, synthetic silica, clay, talc. asbestine, mica, bentonite. aerogels, glass fibers, ultramarine blue, etc. In addition to the aforedescribed ingredients. up to 2% and preferably 0.05 to 0.3% of a wax. Suitable waxes include, for example, low melting paraffin waxes having a melting point of about 40 to 60C.

As shown in FIG. I of the drawing. a roller coater at 11 can be employed to continuously apply the irradiation curable organic resin onto the oriented steel strip at 10. The treated strip, in a preferred embodiment passes through a UV curing zone 12 to effect the cure of the organic resin on the surface of the oriented steel strip. However. if desired cure also can be effected by an electronbeam accelerator having an accelerator voltage of from about 150 to 3,000 KV. The electrode current should as a rule have a strength between about 50 and 100 ma.

As indicated, cure of the organic resin is preferably effected by using UV irradiation which can have a wavelength of from 1849 A to 4,000 A. The lamp systems used to generate such radiation can consist of ultraviolet lamps such as from 1 to 50 discharge lamps, for example, xenon, metallic halide, metallic are, such a low, medium or high pressure mercury vapor discharge lamp, etc., having an operating pressure of from a few millitor to about atmospheres, etc., can be employed. The lamps can include envelopes capable of transmitting light of a wavelength of from about 1,849 A to 4,000 A, and preferably 2,400 A to 4,000 A. The lamp envelope can consist of quartz, such as Spectrocil or Pyrex, etc. Typical lamps which can be employed for providing ultraviolet radiation are, for example, medium pressure mercury arcs, such as the GE l-I3T7 arc, etc. The cures may be carried out with a combination of various lamps. some or all of which can operate in an inert atmosphere,

In operating the lamp to achieve a desirable level of flux intensity required for effecting cures of the solventless resin in a pollution free manner, the lamps can be ballasted to provide a higher watts per inch input than that normally rated by the manufacturer. For example, the GE H3T7 lamp normally operated at 130 watts per inch, can be operated at up to 300 watts per inch input over a satisfactory operating life.

In addition to the above-described lamp means for generating ultraviolet radiation employed in the practice of the invention as shown in FIG. 2, the means for providing such ultraviolet radiation in the apparatus used therein also may include radiation filtering means, such as quartz windows at and 21, employed in combination with the lamp and reflector to provide means for ultraviolet radiation having a wavelength of from between about 1,849 A to 4,000 A, while effecting the removal of radiation greater than 7,500 A. The aforementioned windows can be made of any suitable material capable of transmitting ultraviolet at a wavelength of between 1,849 A to 4.000 A, such as quartz. Pyrex, Vycor, plastic sheets such as polymethylmethacrylate. etc. Typically, the filters can be approximately the same size as the lamps or larger.

The thermal control means at 22 and 23 optionally can include support means for the radiation filters, which when separated to a satisfactory degree. such as 1 inch or more, can provide a channel. to allow for the passage of air or water, to remove heat from the radia- 6 tion filters. Removal of heat also can be achieved by the employment of a cooling coil at 24 and 25 in instances where filter support means are employed.

The oriented steel strip which can be used in the practice of the invention can include any electrical or magnetic steel suitable as a core material for power transformers or magnetic core structures for motors, generators and the like. Such steel can include silicon steel strip having a thickness of 5 to 50 mil. preferably 11-25 mil, and a width of 2 to in.

It has been found advantageous to coat the oriented steel with up to 0.2 mil of resin and a rate of up to to 600 feet per minute.

When using UV lamps, the irradiation flux in the substrate can be at least 0.01 watts per square inch to effectively cure the organic resin within 1 to 20 sec. and permit the steel strip to be taken up at a rate of from 100 to 600 feet per minutes. The strip can be cut to a predetermined width for use as transformer laminate.

In order that those skilled in the art will be better able to practice the invention, the following examples are given by way of illustration and not by way of limitation. All parts are by weight.

EXAMPLE 1 A polyester was prepared by initially stirring and refluxing under nitrogen, a mixture of ingredients for about 4 hours at a temperature of up to about 200C. The mixture consisted of 0.50 mole of tetrahydrophthalic anhydride, 0.70 mole of propylene glycol, 0.40 mole of neopentyl glycol and 15 ml of toluene. At the termination of the reaction, the reaction product had an acid number of about 10. The reaction product was allowed to cool to room temperature.

There was added to the above reaction product, 0.50 mole of fumaric acid, and the mixture was then heated and stirred to a temperature of up to 200C until a final acid number of about 10 was obtained. Volatiles were removed from the final product by blowing with nitrogen.

The above polyester reaction product was heated to C and there was added 0.03 percent of hydroquinone. The polyester was allowed to cool to about 1 10C and there was added with stirring a 0.2 percent styrene solution of a paraffin wax having a m.p. of l33-135F. There was added sufficient styrene to produce a composition having about 30 percent by weight of styrene. When the mixture cooled to room temperature, there was added as a UV sensitizer, about 3 percent by weight of the mixture of a blend of iso-butyl and n-butyl ethers of benzoin. Based on method of preparation, the resulting mixture was a wax containing UV curable polyester composition. It had a viscosity of about 1,500 centipoises.

The viscosity of the resin at 24C measured with a Gardner Bubble Viscosimeter, is Y to Z, corresponding to 18 to 23 stokes. Resin viscosity did not change over 3 months at room temperature. The molecular weight of the resin was determined by gel permeation chromatography in methylene chloride against polystyrene with a 4 ft. column containing Pryrogel and Styrogel as support. The number average weight found by this method was 2,500 i 500.

The above UV curable solventless polyester resin is then used to charge a roller coater as shown in the drawing. A roll of oriented silicon strip steel. 24 inches wide and l 1 mil thick having a magnesium silicate inorganic surface coating is then coated on both sides with the polyester resin to a thickness of about 0.1 mil and at a rate of from 10 to 500 feet per minute. The treated strip is then passed through a UV curing zone having several H3T7 lamps operated at 750 watts in air. The lamps are spaced at a sufficient distance from the surface of the strip to provide at least 0.01 watts per in. light intensity.

During cure, there is generated less than 5% by weight of volatiles based on the average weight of applied resin passing through the curing zone. The average exit temperature of the oriented steel strip substrate does not exceed 150C. There is obtained an organic resin-inorganic coating-oriented steel strip composite having a surface coating of organic resin of about 0.1 mil.

A 2 X 8 inch strip is cut from the above composite and measured for surface resistivity in accordance with ASTM A344 (Franklin'Test). It is found that the strip gives an average reading of 0 to 001 amps at a pressure of up to 300 psi. A 2 X 8 inch strip of the magnesium silicate coated oriented silicon steel free of the polyester resin has an average reading of 0 to 0.3 amps at the same pressure.

An interfacial tension test previously described is run in accordance with ASTM D97l-50 with 450 in on the above polyester coated composite in 10C hydrocarbon oil. A interfacial tension reading of at least 32 is obtained with the composite made in accordance with the practice of the invention.

A similar interfacial tension test is made with a composite strip made following the same procedure except that the polyester composition shown in the example of Patheiger et al., Pat. No. 3,531,317, is substituted for the UV curable polyester of the present. invention. There is obtained a reading of 23. As previously indicated, a reading of at least is required.

In addition to passing the above described Franklin Tests and IFT test, the composites made in accordance with the practice of the invention are measured for magnetostrictio'n and magnetic properties at power frequencies. A magnetostriction change of A2 -0.1 is obtained on the composite tested at inductions of 15.5 kilogausses. A-c permeability changes of composites at an induction of 10 orsteds are 0. There is no change in core loss at 15.0 kilogausses after preparing the composites.

In addition to the above tests, a heat stability test in terms of percent weight loss is run at 150C over 1,000 hours with a 10 mil cured sample of the polyester resin of the present invention and the polyester resin of Patheiger et al. The following results are obtained where Schroeter signifies the polyester of the invention and Patheiger et alQis the prior art resin:

Percent Weight Loss Schroeter Patheiger. et al 1001) hrs. Franklin Mugnctoat 150C.

(amps) ll-T striction (.2 wt. loss) phenolic 0 3H 0 l0 Schroeter 0 32 -0.1 2

As previously indicated Schroeter represents a weight loss of less than 5% volatiles during cure while phenolic can represent at least 65 /1. This dramatic reduction in weight loss percent of volatiles shows the substantially pollution free aspects of the method of the invention.

No loss of adhesion is observed when the composite film of the present invention is immersed in 100C water for 4 hours, boiling 5% KOH-solution for 30 min., or methylene chloride for 5 hours at room temperature.

EXAMPLE 2 The procedure of Example 1 is repeated except in place of the UV curable polyester resin, there is employed a UV curable acrylic resin. The aforesaid acrylic resin was prepared by effecting reaction between bisphenol A diglycidyl ether and acrylic acid employed in a l 2 mole ratio in the presence of about 0.01 mole percent of N,N-dimethylbenzylamine catalyst. A small amount of t-butyl catechol was added as a polymerization inhibitor. The reaction mixture was heated in a hot water bath at 90C with vigorous stirring. Periodically the reaction mixture was sampled and the acid number determined. When the acid number had fallen to 5 10, the reaction was terminated. The product was stored in the dark. Four hundred fifty parts of the above acrylic resin was blended with 55 parts of trimethylolpropane triacrylate monomer. To parts of the resulting blend, having a viscosity of 2,000 centipoises, were added 0.3 parts of Michlers Ketone, 4,4-Bis-(dimethylamino)benzophenone. During cure the temperature of the oriented steel strip is maintained below about 70C. There is obtained less than about 5% by weight loss of volatiles. A 2 X 8 inch strip of the acrylic resin-magnesium silicate-oriented silicon steel composite provide the following values in the respective tests as shown in Example 1.

Franklin 0.0 amps/1000 psi IFT 32 Heat Stability 8 wt. loss after 1000 hrs. at C.

EXAMPLE 3 EXAMPLE 4 A 0.1 mil film of a polyester prepared from a resin of 0.6 mol of fumaric acid, 102 mol phthalic anhydride. 0.2 mol of tetrahydrophthalic anhydride, 0.6 mol neopentyl glycol and 0.4 mol propylene glycol having an acid number of is cut with styrene in a 60 weight ratio. The resin is cured at a dose of 4.8 Mr at 80 ft/min in an inert nitrogen atmosphere to give a composite which shows an IFT of 32.

Although the above examples are limited to only a few of the very many variables which can be used in the method of the invention, it should be understood that the present invention is directed to the use of a much broader variety of UV curable resins, and to conditions used to effect the cure of such resins on inorganic coated oriented silicon steel.

What we claimed as new and desire to secure by Letters Patent of the United States is:

l. A continuous, substantially pollution-free method for uniformly improving the surface resistivity of oriented steel strip having an inorganic material as a surface insulating coating to produce an oriented steel strip-inorganic coating-organic resin composite capable of providing an average Franklin test reading of from 0.1 to 0 amperes at a pressure of up to 300 psi, which comprises,

l. treating the oriented steel strip with an irradiation curable solventless organic resin to a thickness of up to 0.2 mil, and

2. passing the treated oriented steel strip through an irradiation curing zone at a rate of from 100 to 600 feet per minute, using an irradiation flux sufficient to effect the cure of the solventless organic resin to an organic resin hardness capable of being tested by the above-described Franklin test,

LII

where said resin is characterized by having a viscosityof up to 3,000 centipoises at 25C, and is a mixture consisting essentially of by weight from A. 20 to 40% of a vinyl aromatic material selected from styrene, vinyl toluene, tert-butylstyrene and mixtures thereof,

B. to 60% of an unsaturated polyester reaction product of (i) a glycol and (ii) an aliphatically unsaturated organic dicarboxylic acid, where i. is a glycol selected from the class consisting of a. a mixture of 20-60 mole percent of neopentyl glycol and 40-80 mole percent of a member selected from propylene glycol, ethylene glycol and mixtures thereof, and

ii. is an aliphatically unsaturated organic dicarboxylic acid consisting essentially of a mixture of 50 to 65 mole percent of fumaric acid and 35 to 50 mole percent of a member selected from tetrahydrophthalic anhydride, endomethylene tetrahydrophthalic anhydride and mixtures thereof where there is utilized in making the unsaturated polyester reaction product of (B), up to at least about 10 mole percent excess of the glycol of (i) over the aliphatically unsaturated organic dicarboxylic acid of (ii) C. 1% to 5%- based on the weight of (A) and (B) of a UV sensitizer, and

D. 0.05% to 1% based on the weight of (A), (B) and (C) of paraffin wax.

2. A method in accordance with claim 1, where the inorganic coating on the oriented steel strip is a magnesium oxide or a magnesium silicate.

3. A method in accordance with claim 1, where the cure of the irradiation curable resin is achieved with UV light having a wavelength of from 1,849 A to 4,000 A.

Claims

1. A CONTINUOUS, SUBSTANTIALLY POLLUTION-FREE METHOD FOR UNIFORMLY IMPROVING THE SURFACE RESISTTIVITY OF ORIENTED STEEL STRIP HAVING AN INORGANIC MATERIAL AS A SURFACE INSULATING COATING TO PRODUCE AN ORIENTED STEEL STRIP-INORGANIC COATING ORGANIC RESIN COMPOSITE CAPABLE OF PROVIDING AN AVERAGE FRANKLIN TEST READING OF FROM 0.1 TO 0 AMPERES AT A PRESSURE OF UP TO 300 PSI. WHICH COMPRISES,

1. TREATING THE ORIENTED STEEL STRIP WITH AN IRRADIATION CURABLE SOLVENTLESS ORGANIC RESIN TO A THICKNESS OF UP TO 0.2 MIL, AND

2. PASSING THE TREATED ORIENTED STEEL STRIP THROUGH AN IRRADIATION CURING ZONE AT A RATE OF FROM 100 TO 600 FEET PER MINUTE, USING AN IRRADIATION FLUX SUFFICIENT TO EFFECT THE CURE OF THE SOLVENTNESS ORGANIC RESIN TO AN ORGANIC RESIN HARDNESS CAPABLE OF BEING TESTED BY THE ABOVE-DESCRIBED FRANKLIN TEST, WHRE SAID RESIN IS CHARACTERIZED BY HAVING A VISCOSITY OF UP TO 3,000 CENTIPOISES AT 25*C, AND IS A MIXTURE CONSISTING ESSENTIALLY OF BY WEIGHT FROM A. 20 TO 40% OF A VINYL AROMATIC MATERIAL SELECTED FROM STYRENE, VINYL TOLUENE, TERT-BUTYLSTYRENE AND MIXTURES THEREOF, B. 80 TO 60% OF AN UNSATURATED POLYSTER REACTION PRODUCT OF (I) A GLYCOL AND (II) AN ALIPHATICALY UNSATURATED ORGANIC DICARBOXYLIC ACID, WHERE I. IS A GLYCOL SELECTED FROM THE CLASS CONSISTING OF A MIXTURE OF 20-60 MOLE PERCENT OF NEOPENTYL GLYCOL AND 40-80 MOLE PERCENT OF A MEMBER SELECTED FROM PROPYLENE GLYCOL, ETHYLENE GLYCOL AND MIXTURES THEREOF, AND B. A MIXTURE OF (A) 1 TO 40% BY WEIGHT THEREOF OF TRIMETHYLOLPROPANE MONOALLY ETHER, AND II. IS AN ALIPHATICALLY UNSATURATED ORGANIC DICARBOXYLIC ACID CONSISTING ESSENTIALLY OF A MIXTURE OF 50 TO 65 MOLE PERCENT OF FUMARIC ACID AND 35 TO 50 MOLE PERCENT OF A MEMBER SELECTED FROM TETRAHYDROPHTHALIC ANHYDRIDE AND MIXENDOMETHYLENE TETRAHYDROPTHALIC ANHYDRIDE AND MIXTURES THEREOF WHERE THERE IS UTILIZED IN MAKING THE UNSATURATED POLYESTER REACTION PRODUCT OF (B), UP TO AT LEAST ABOUT 10 MOLE PERCENT EXCESS OF THE GLYCOL OF (I) OVER THE ALIPHATICALLY UNSATURATED ORGANIC DICARBOXYLIC ACID OF (II) C. 1% TO 5% BASED ON THE WEIGHT OF (A) AND (B) OF A UV SENSITIZER, AND D. 0.05% TO 1% BASED ON THE WEIGHT OF (A),(B) AND (C) OF PARAFFIN WAX.

2. passing the treated oriented steel strip through an irradiation curing zone at a rate of from 100 to 600 feet per minute, using an irradiation flux sufficient to effect the cure of the solventless organic resin to an organic resin hardness capable of being tested by the above-described Franklin test, where said resin is characterized by having a viscosity of up to 3,000 centipoises at 25*C, and is a mixture consisting essentially of by weight from A. 20 to 40% of a vinyl aromatic material selected from styrene, vinyl toluene, tert-butylstyrene and mixtures thereof, B. 80 to 60% of an unsaturated polyester reaction product of (i) a glycol anD (ii) an aliphatically unsaturated organic dicarboxylic acid, where i. is a glycol selected from the class consisting of a. a mixture of 20-60 mole percent of neopentyl glycol and 40-80 mole percent of a member selected from propylene glycol, ethylene glycol and mixtures thereof, and b. a mixture of (a) 1 to 40% by weight thereof of trimethylolpropane monoallyl ether, and ii. is an aliphatically unsaturated organic dicarboxylic acid consisting essentially of a mixture of 50 to 65 mole percent of fumaric acid and 35 to 50 mole percent of a member selected from tetrahydrophthalic anhydride, endomethylene tetrahydrophthalic anhydride and mixtures thereof where there is utilized in making the unsaturated polyester reaction product of (B), up to at least about 10 mole percent excess of the glycol of (i) over the aliphatically unsaturated organic dicarboxylic acid of (ii) C. 1% to 5% based on the weight of (A) and (B) of a UV sensitizer, and D. 0.05% to 1% based on the weight of (A), (B) and (C) of paraffin wax.