US1972307A - Uniting synthetic resin and metal - Google Patents

Description

P 1934- E. c. LOETSCHER 1,972,307

UNITING SYNTHETIC RESIN AND METAL Filed Feb. 2, 1932 Patented sq. 4, 1934 UNITED STATES PATENT oF -uca.

The primary object of this invention is to secure a satisfactory bond between a metal base and bakelite or bakelized material, thereby overcoming the persistent tendency toward blistering and separation of the bakelite or bakelized material from the metal due apparently to the great difference in the co-eflicient of expansion between the layers.

A further object of the invention is to produce a perfectly fiat, smooth surface on the bakelite or bakelized material, which has heretofore been found diflicult when preparing products of relatively large surface areas, owing to the variations in the thickness of the metal used and the variations in the accuracy of the presses employed.

With these and other objects in view, as will be pointed out as the description progresses, reference will be had to the accompanying drawing forming a part of this specification and wherein,

Fig. 1 is a diagrammatical view of the disposition of parts in making a product covered on one side only, and,

Fig. 2 is a similar view with respect to,a product covered on both sides.

In the drawing, reference numeral 1 designates a metal base plate, iron and aluminum being specific examples, and this plate is first roughened, preferably by sandblasting, the blast being desirably directed at a sharp angle to the metal base to give the added advantage of undercutting to the roughen ng, whereby the adhesive applied to the metal base will find a better opportunity of securing a permanent hold upon the same. Sandblasting is followed by pickling or etching, this being practised by subjecting the roughened metal base to a bath of 540% concentrated hydrochloric acid to 90-95% of water. These two steps leave the metal base with a roughened and perfectly clean surface.

Reference numeral 2 represents a sheet of kraft or other paper, desirably unsized, which is treated, preferably by impregnation, with a synthetic resin of the phenol formaldehyde carbohydrate type such as is set forth in an application, filed February 11, 1931 and bearing Serial Number 515,144. After impregnation, the water solvent in which this synthetic resin is dissolved is only partially dried out so that some of the solvent remains for a purpose to be later elaborated.

Instead of impregnating the kraft paper 2 with the phenol formaldehyde carbohydrate resin, the sheet 2 may be first treated with bakelite by immersion, impregnation, or by incorporating the same at the time of manufacture of the paper, and then coating the bakelized paper 2 with the phenol formaldehyde carbohydrate resin, and as before, only partially drying out the water solvent therefrom.

The sheets 33 of paper treated with phenolic condensation products such as bakelite, are juxtaposed upon the layer 2, and upon these layers of bakelized paper 33, is then placed a layer 4 of fibrous material such as paper or textile material, wood veneer or the like, either decorated or plain. The material of layer 4 is treated with phenolic condensation products, such as bakelite, preferably by impregnation in a solution thereof diluted to the extent of approximately 50% with an alcohol solvent. When wood veneer is employed for the layer 4, its thickness is preferably 1/100" and impregnation is preferably conducted under hydrostatic pressure, but when materials such as paper or textiles are used for this layer 4, its porosity or capillary qualities" makes impregnation by mere immersion satisfactory. In fact, treatment of any of the layers employed herein may even be by brush coating, though complete saturation rather than mere surface coating of the layers is productive of a more completely satisfactory product.

A layer 5, of tissue paper, cellophane, or the like, preferably impregnated, when possible, with bakelite or other phenolic condensation product may then be applied to the layer 4 to provide a transparent protective covering therefor, but the use of this layer 5 is optional.

When the pack of layers 1, 2, 3--3, 4, 5, has been made up, it is ready for the press. The pressure plates 6 and 8 are respectively placed against the top and bottom of the pack and a compound layer made up of a layer or layers 9 of felt attached to a sheet of rubber 10 is applied to the bottom of the pressure plate 8, and the entire pack, including the plates and layers 6, 8, 9, 10 is inserted between the upper and lower platens 7 and 11 of a hydraulic press. These platens are equipped with usual provision for steam heating and water cooling. The lower face of the pressure plate 6 is highly polished to aid in preventing the same from becoming bonded with the product. The lower pressure plate 8 which is against the metal plate 1 need not be polished.

The press is then operated to force the platens 7 and 11 toward each other and to compact the pack. Steam is circulated through the upper platen '7, the lower platen 11 remaining cool to avoid overheating-the rubber to a degree that will destroy it or its elastic qualities. The felt layer 9 prevents the heat from the upper platen 7 being transmitted through the pack to the rubber layer 10 to similarly destroy the qualities thereof.

It is impossible to obtain paper, wood, metal or other sheets of. uniform thickness, or to produce a press of the kind used herein without inaccuracies, and because of these and other inaccuracies, it is impossible to make products with such relatively large surface areas as 12" x 12" without producing low pressure areas on the work, which result in dull spots in which the bakelite was not able to flow sufficiently to make a smooth and uniformly bright or polished surface film. A variation as low as .001 in the thickness of the pressure plates 6 and 8 and inequalities as low as .005" in the thickness of the press platens, are in themselves (not to mention the inaccuracies in the thickness of the layers forming the product), sufficient to cause certain areas to receive more pressure than others. Since the pressure plates 6 and 8 cannot, when directly against the platens 7 and 11, bend to take up the various inequalities, a uniform surface can only be obtained in the product by employing a compressible layer such as the rubber 10. Any compressiblematerial, such as fibre board, felted or textile material could be substituted for the rubber, but, because, these do not re-expand to their original thickness and soon lose all elasticity, they must be discarded, where as rubber in retaining its elasticity may be used over and over again so long as it is protected from destructive degrees of heat, for which protection the felt layer 9 is principally provided and only the upper platen 7 heated. During compression of the pack, the rubber layer 10 will compress in certain of its portions, becoming accommodated to the inaccuracies of the platens '1 and 11, of the pressure plates 6 and 8, and of the various layers of the product, thereby uniformly forcing the outer layer of the pack against the pressure plate 6 and eliminating the occurrence of dull surface spots. 1

When both sides of the metal plate 1 are to be covered, the various layers are prepared as before and reading top to bottom the layers constituting the product are juxtaposed in the following order; 5, 4, 33, 2, 1, 2, 3-3, 4, and 5. The pack thus constituted is then placed between the upper and lower platens 7 and 11 with the pressure plates 6 and 8 intervening between them and the pack respectively, and the compound sheet comprising the felt and rubber sheets 9 and 10 respectively, with the rubber next to the platen 11, is then placed between the pressure plate 8 and platen 11. The platens are closed upon the pack and, as before, steam is circulated through the upper platen 7 only and the applied heat transmitted through the entire pack to react the synthetic resins. The platen 11 is not heated by the application of steam, and remains cool as a protection to the rubber against vulcanizating the rubber 10. i

In both cases, after the synthetic resins have become reacted, the steam is cut ofi from the upper platen and water circulated therethrough to cool the product, after which the latter is removed for use.

Particular stress is placed upon the important part played by the phenol formaldehyde carbohydrate synthetic resin incorporated in layer 2 in obtaining a satisfactory bond between the bakelite or bakelized layers and the metal plate. Recognized authorities have expressed their inability to obtain a satisfactory bond between large surfaces of metal and bakelite or bakelized material. This they ascribe to the greater thermal expansion of the metal over the bakelite or bakelized material which results in the bakelite or bakelized layer separating from the metal as soon as the product is removed from the press. That is, the bakelite or bakelized layer which has been consolidated with heat and pressure, separates from the metal plate. On the other hand, applicant has discovered that his phenol formaldehyde carbohydrate synthetic resin not only clings tenaciously to the metal base plate, but also forms an inseparable bond with bakelite or bakelite coated or impregnated material. Like bakelite, it reacts under heat and pressure, and, being similar in many other respects to bakelite, forms a perfect bond therewith due either to mutual adhesion or combination, or both.

Bakelite, or the same in bakelized material, in small surfaces where the differences in the coefficient of expansion thereof and metal are slight, may show some tendency to adhere to a metal base, though not with the tenacity of applicants synthetic resin, but in large areas where the difference in expansion between these layers is material, bakelite will separate of its own accord from metal and when it does not naturally separate therefrom it can be easily peeled off by means of a knife or finger nail. The synthetic resin, employed by applicant, however, will not separate because of the extreme changes of temperature while in the press or because of any temperature changes encountered by the product in ordinary use, and clings so tenaciously to the roughened metal that it cannot be peeled off at all even with a knife. In fact, in attempting to remove applicants coating or covering from the metal, the same. must be scratched off and in instances actually dug out of the indentations in the metal plate.

Roughening of the metal plate is not an essential to the success of this invention, since tenacious bonds have been made with metal sheets having the finish imparted to them by the rolling mill, which in the case of aluminum is quite lustrous. Satisfactory bonds for many purposes have been obtained with even very highly polished metal, but as with all adhesives the tenacity of bond decreases with the degree of polish present on the surface of the metal. It is pointed out, however, that whether polished or roughened, no satisfactory bond can be obtained at all between bakelite material and metal when the bakelite is depended upon to produce the bond,

whereas with applicants phenol formaldehyde carbohydrate synthetic resin interposed, a bond with polished as well as rough metals can be obtained that prevents separation of the parts without destruction of one or both of them.

The adhesive tenacity of the phenol formaldehyde carbohydrate synthetic resin is a natural characteristic thereof and requires no explanation but why its bond with the metal base is not broken as in the case of bakelite, due to the differencein the coefficient of expansion between the metal plate and the superimposed bakelite or bakelized material, finds its most probable explanation in that this resin has the property of not reacting into an absolutely rigid state as bakelite and of retaining a considerable degree of elasticity or plasticity due to retained moisture after reaction, which elasticity or plasticity is imparted to the entire layer 2. Hence the carbohydrate synthetic resin intervenes as a buffer between the metal and the rigid reacted bakelite yielding, to compensate for the difference of coeflicient of expansion between the metal and bakelite or bakelized material.

In a test, an aluminum sheet preparedand covered as in the example of Fig. 1, was placed in a cold storage room with a temperature of 10 below zero prevailing and maintained therein for a considerable period of time and no separation of the bakelite or bakelized material from the metal occurred. A similar test piece was then subjected to a temperature of 220 F. for several days and as in the previous test no separation occurred. The latter test, extending over a period sufllciently long to ordinarily dry off any solvent which may be remaining in the material, would seem to establish the fact that the. water is incorporated in the material in the form of combined water in sufiicient quantity to impart a considerable degree of elasticity to the carbohydrate synthetic resin or material impregnated therewith. The recited tests were under extremes of temperature under which a bakelite bond with metal, at least in products of considerable area, would show separation immediately upon removal thereof from the press, and applicant's bond in persisting throughout these extremes of temperature is capable of persisting throughout all the degrees of temperature that may be encountered in ordinary use of his product. Some of these uses being in the construction of furniture, building and car trim, and the like. 1

Applicant has been unable to separate the bakelized layers from the metal base of his products mechanically by any peeling operation or without actual destruction or disintegration. of the attached layer containing the carbohydrate synthetic resin.

While a number of layers have been specified as being present between the outer finishing layer 4 (the layer 5 being protective and optionali and the metal base 1, thenumber of' intervening layers may be varied since these may be considered padding layers employed principally to compensate for irregularities in the work- These layers, being impregnated with phenolic condensation product become more or less plastic during reaction of thecondensation product permitting the outer surfaces of the outer layers to adjust themselves perfectly to contour of the platens or pressure plates, and incidentally it is within the province of thk; invention to give the pressure plates molding configurations.

While the padding layers 2, 3-3 go a considerable ways toward producing a uniform surface, it is impossible without the use of the rubber layer 10 or a layer of other compressible elastic material to obtain a uniform surface finish in the product where large areas are involved because of the inaccuracies of the press platen and of the components of theproduct itself.

What is'claimed is:

1. The method of making a laminated body, 7 consisting in interposing between a metal plate and a body of phenolic condensation product of the bakelite type or a body impregnated with such condensation product a layer of water soluble phenol formaldehyde carbohydrate condensation product or a layer of material impregnated therewith, drying out from the phenol formaldehyde carbohydrate condensation product some of the water solvent but leaving a suflicient amount of solvent water therein to finally become incorporated in the phenol formaldehyde carbohydrate condensation product as combined water to prevent the latter condensation product from becoming as brittle and rigid after reaction as the phenolic condensation product, and reacting both condensation products under heat and pressure.

2. The method of making a laminated body, consisting intreating a simple or compound layer to cause the same to present a phenolic condensation product of the bakelite type on its exposed and concealed faces, juxtaposing the same to a layer of metal, interposing a layer treated to present on its opposite faces a water soluble phenol formaldehyde carbohydrate condensation product from which the water solvent no has been only partially dried out, the remaining water finally becoming incorporated in the phenol formaldehyde carbohydrate condensation prodnot as combined water, and finally reacting both ble condensation product from which the water solvent has been only partially dried out, and reacting both condensation products under heat and pressure. 5

EMJL C. LOE'ISCHER.

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