Untitled record

GERMAN

The invention relates to methods for producing transparent, electrically conductive layers on inorganic objects.

Electrically conductive layers are generally applied to vehicle windows, instrument windows, lenses and other objects such that the surfaces of the articles can be heated to reduce fogging or icing. Experience has taught that for many purposes, the electrical resistance of the electrically conductive layer should be less than 100 ohms per square, and preferably not more than 150 ohms per square, to provide the proper heating effect without excessive stress. Of course, in order to meet these requirements, it is highly desirable that it be possible to control the resistance of the layer within certain limits so as to adapt the layer to different and variable uses.

In addition, it is desirable that the electrically conductive layer be hard, durable and adherent to the glass surfaces. In addition, when used for optical purposes, it is desirable that the conductive layers be extremely transparent and free of defects and distortions.

It is therefore a principal object of the invention to provide an electrically conductive layer which is hard and durable.

It is another object of the invention to provide a method of changing the resistance characteristics of an electrically conductive layer.

It is another object of the invention to provide a method of enhancing the light transmission of an electrically conductive article after the electrically conductive layer has been deposited thereon.

In the drawings is

Figure 1 is a schematic, an electrically conductive inorganic article with an inventive, electrically conductive, applied thereto layer representing view, and

Fig. 2 is a cross-sectional view of the article taken along line 2-2 in Fig. 1, illustrating the various coatings comprising the electrically conductive layer.

According to the invention there is provided a process for producing an electroconductive article which comprises applying an adhesive layer to a body having a smooth, continuous surface in a known manner, to which film a metal film is applied in a conventional manner the group gold, silver, copper, iron and nickel · heard that a second adhesive layer in contact with this metal process for manufacturing

an electrically conductive, transparent,

inorganic article

with increased hardness and translucency

applicant:

Libbey-Owens-Ford Glass Company, Toledo, Ohio

Representative: Dipl.-Ing. B. Wehr, Dipl.-Ing. H. Seiler,

Berlin-Grunewald, Lynarstr. 1,

and Dipl.-Ing. H. Stehmann, Nuremberg 2,

patent attorneys

Claimed priority: V. St. v. America of December 23, 1955

Stephen Holmes Harwig, Pittsburgh, Pa. (V. St. Α.), Has been named as an inventor

film is applied, a second metal film of chromium, nickel or an alloy thereof is applied in contact with the second adhesive layer and then the article is heated to elevated temperature.

In Fig. 1 of the drawings there is shown an electrically conductive article 10 comprising a support body 11 made of glass or the like, and an electroconductive film 12 on one of its surfaces and electrodes 13 distributing the current on the electroconductive film. The conductive film comprises, in particular, successively an adhesive layer 14 in contact with the carrier 10, a layer of gold, nickel, copper, silver or iron 15, a second adhesive layer, a layer of chromium or similar material 17 and, if desired, a protective layer 18 , such as quartz, aluminum oxide, magnesium fluoride od. Like.

The adhesive layer 14 is preferably made of a metal compound, e.g. A metal oxide, a metal sulfide, a metal sulfate or other metal compound. Of these, the metal oxides are the typical ones and adhere to the smooth glass or other silicon dioxyd containing surface with moieties.

009 589/211

Kulkräften and act by strong molecular adhesion also to keep the metal film. For best results, the adherent metal oxides may be those of lead, silver, aluminum, magnesium, nickel, zinc, boron and other rare earth metal oxides and the oxides of cadmium, antimony, bismuth, mercury, copper, gold, platinum, palladium and other oxides of heavy metals which adhere to vitreous silica-containing surfaces and to the above-mentioned metals.

The adhesive layers 14 of metal compounds are preferably very thin and only a few molecules thick and invisible, nor otherwise detectable except for the fact that they permit the formation of the high-tack articles described herein. It has been found that the layer thickness required to develop the adhesive forces and to provide a surface on which a continuous metal deposition layer can be formed is only a few molecules thick, so that the presence of the same on the glass can not be detected by any optical effects can.

These adhesive layers or coatings may be applied to the substrate by direct thermal evaporation, or a metal compound first applied to the substrate by thermal evaporation may be oxidized to form a metal oxide. Another way of producing the layers of metal oxide is to first apply a thin coating by spraying a metal onto the support body in a residual vacuum consisting in part of oxygen so that the metal will form with the oxygen remaining in the air of an oxide when precipitated on the glass.

After the adhesive layer 14 has been applied to the carrier body 11, the electrically conductive metallic layer 15 is applied to the adhesive layer in a thickness of at least 4 or 5 molecules. The conductive layer is preferably applied by thermal evaporation to form an extremely uniform coating since small changes in thickness result in areas of variable electrical conductivity and thus develop hot spots or areas of uneven heating on thicker portions of the layer.

By using thermal evaporation techniques to apply the electrically conductive layer 15, one molecule is applied to the other such that a smooth surface is formed over the adhesive layer. The adhesive layer located on the surface of the carrier body reduces the possibility of chemical reaction or mixing between the material of the carrier body and the metal of the electrically conductive layer; it is thus apparent that an extremely effective adhesive layer is created because of the inherent molecular attractive forces existing between the respective materials.

According to the invention, after the application of the electrically conductive layer 15 to the carrier body in contact with the adhesive layer 14, a second adhesive layer 16, preferably of a metal oxide having a thickness of generally at least ¹Iz molecule, applied, which may have the character of a layer of iron oxide od. Like. Then, a layer of chromium 17 having a thickness of 4 or S molecules or more is applied over the layer of metal oxide 16. It can be precipitated by thermal evaporation or other suitable method. If desired, a protective layer 18 of quartz, alumina, magnesium fluoride, or other suitable material may then be formed. the chromium layer are applied, which is known per se in only with an adhesive layer and a metal film coated glass sheets. Then, as shown in FIG. 1, electrodes or bus bars 13 may be mounted on a pair of opposite edge portions of the support body 11 in contact with the electrically conductive film. These electrodes may be made of any of a variety of materials and may be applied before the protective layer 18 has been applied to the chromium layer 17, but may also be applied to the substrate after the protective layer has been applied to the chromium except for the areas that correspond to the position of the electrodes. As examples of suitable materials for the electrodes or bus bars, sprayed copper, sprayed copper alloys, burned gold, silver and platinum flux, and combinations of these materials have been used satisfactorily.

According to the invention, it has now been found that the resistance properties of the electrically conductive film 12 can be changed by firing the film at elevated temperatures. In particular, it has been found that by firing the film at high temperatures, the resistance of the film decreases progressively within certain limits and according to the burning time. It is believed that this change in resistance is brought about by the growth of the crystals of the electrically conductive metal layer 15 at elevated temperatures which allow the crystals to expand and make better electrical contact with each other, thereby resulting in improved conductivity or, in other words, reduced resistance is effected.

The temperature at which the resistance change begins to take place is in the region of 26O⁰C has been determined as the lower limit. However, the temperature should not exceed a temperature at which the crystals tend to form at different levels, since they are obviously caused to overlap each other, thus breaking the electrical continuity in certain areas and the conductivity of the conducting ones Layer 15 to reduce or destroy. In general, this effect of overlapping crystallization occurs when the film is fired at temperatures generally greater than 330⁰C is burned, however, it is obvious that both the lower and the upper limit may change according to the type of the electrically conductive metal layer 15 used.

As a second feature of the invention, it has been found that the electrically conductive film 12 is substantially harder and more durable than previous electrically conductive films. It is believed that this is caused by a migration effect that occurs between the chromium layer 17 and the metallic conductive layer 15 during the burn process, wherein migration as the affinity of the molecules of one material for alloying with those of the other material is defined.

In principle, it is the opinion that the chromium molecules and the molecules of the metal layer 15

immigrate and interlock, causing the film to become firmer, denser and harder. The migration effect is controlled by the adhesive layer 16 between the respective layers, which provide some resistance to the flow of the molecules towards each other. While chromium has some effect on the resistance properties of the film, it should be understood that it is not essential since the amount of chromium which can migrate is relatively small relative to the thickness of the low resistance electrically conductive metal layer 15.

It is also believed that a migration action between the chromium layer 17 and the protective layer 18 takes place and the chromium layer is thus helpful in anchoring the protective layer. As a result of the migration action between the chromium and conductive metal layers 15 and the chromium and protective layers 18, which appears to cause interlocking of the molecules of the subject materials, a hard crust is formed over the film which is not easily damaged or distorted becomes, as it sometimes became in earlier films; the resistance of the electrically conductive film was found to be 29.6 ohms per square. Then the article was again placed in the oven for 3 hours and heated to 288 ° C; its resistance after heating was found to be 27.1 ohms per square. The article was returned to the oven and heated to 288 ° C for 3 hours, and the resistance was found to be 25.2 ohms per square.

Then the hardness of the article was checked and it was found that the previously used pencil eraser did not cause the slightest scratch or scratch on the electroconductive film at elevated pressure.

The article thus prepared had a light transmittance of 63% before heating and a light transmittance of 70 after heating¹¹Vo.

Example II

A glassy silicon-containing support of substantially square shape was coated in a manner somewhat similar to that described in Example I, except that the chromium layer was about 7 molecules thick. The counterpart

FaIl was, and thus the film is not so easy

crack or peel off, making him harder and harder, then put in an oven and become 2 stungers. heated to 177 ° C for a long time. The resistance of the still electrically conductive film as a further feature of the invention was set at that time to detect the light transmittance of 52.8 ohms per square. The article, generally after heating, was then placed in an oven and raised above 177 ° C. This is more markedly heated to 288 ° C for 2 hours and the identifiable at temperatures above 260⁰C; In the overall standing ability with 56.4 0hm per square meter fixed it has been established that the increase is made. After another 3 hours of heating at the light transmittance in the range of 4 to 10% 288 ° C, the resistance was 43.3 ohms per square, which is very substantial and desirable because area; after a further 3 hours warming with maximum light transmission in general 35,288⁰C, the resistance was 40.0 ohms per square

area; after another 3 hours of heating at 288 ° C, the resistance was 37.4 ohms per square area; and after an additional 8 hours, the resistance was 34.7 ohms per square.

The coating thus prepared was extremely hard and durable, and the pencil eraser used in Example 1 left no scratch marks on the coating. The light transmittance of the article was 64% before

is essential.

To explain and further clarify the characteristics of the invention, a number of embodiments will be given further. It will be appreciated that the electrical resistances mentioned throughout this specification, as well as those used in the examples, are given in ohms per square area; So if a film has an electrical resistance of 100 ohms per square, so

He has this resistance regardless of whether he is 45 to burning and 71% after burning, a few inches squared or a few decimeters squared. 'B eis ρ ie 1 III

A substantially square body made of glass was coated according to Example I and II,

A substantially square support body 50, but the chromium layer was about 5 molecules thick, was coated in succession with a layer of iron. Before heating, the electrically conductive oxide had coated with about 1 molecule of starch, the layer had a resistance of 47.0 ohms per square applied with the support surface and a light transmittance of 62%. The article was then heated to 288 ° C for 1 hour on a second approximately 1 molecule thick layer of 55, and its resistance was 41.5 ohms per square iron oxide, about 11.3 molecules thick surface detected. Then, the article was heated on a chromium layer and a quartz layer having a thickness of 316 ° C for 2 hours, followed by being about Vi wavelength. stood at 40.5 ohms per square and the light

E> ann, the bus bars were found to be in contact permeability of 68%. The elekmit the electrically conductive film along the surfaces 60 trically conductive film was extremely hard and where a

Example I

where the quartz and chromium were covered over the gold layer. After coating, the article thus made was quite soft, so that a pencil eraser marked clearly at low pressure and removed the electroconductive film. The resistance of the conductive film was measured between the bus bars and found to be 36.0 ohms per square. The object was then placed in an oven and 3 stun-steel band slightly scored the film before firing, he did not scratch it after firing.

Example IV

An article was made in the same manner as the article in Example III. Before heating, the resistance was 37.5 ohms per square and the light transmittance was about

heated to 288 ° C for a long time, after which it removes 70 64%. After four consecutive 45 minutes

for long periods of heating at 260 ° C, the resistances involved were 34.5 ohms per square, 31.5 ohms per square, 29.0 ohms per square and 29.0 ohms per square. The light transmittance was 72% after the four heating times. The film was very hard, and scratches or scratches were not generated by rubbing with an eraser of Example I nor by pulling a steel band over the film.

10

Example V

An article was coated similar to Example III. Before heating, the resistance was 31 ohms per square area with a light transmittance of 63%. After 45 minutes of heating to 330 ° C, the resistance was 30 ohms per square, after a second 45 minute heating period at 300 ° C, the resistance was 28 ohms per square and after a third 45 minute heating period, the resistance was still 28 ohms per square area. After heating, the light transmittance was 70%.

Example VI

25

A glass plate was coated according to Example I. Before heating, the article had a resistance of 35 ohms per square. It was then heated to 338 ° C for 45 minutes and then had a resistance of 45 ohms per square. After a further 45 minute heating period to 338 ° C, the resistance was 60 ohms per square, and after a third 45 minute heating time at the same temperature, the resistance was 90 ohms per square. The increased resistance was evidently produced by a crystallization effect which causes the formation of individual crystals and their mutual overlap, thereby interrupting the electrical continuity between the crystals.

Example VII

An article was coated with layers similar to those in Example I and had a resistance of 33.5 ohms per square area before heating at 63% transmittance. The article was then heated to 243 ° C for 3 hours to give a resistance of 33.1 ohms per square. After two more consecutive hour heating periods at 243 ° C, the resistance remained at 33.0 ohms per square area with a light transmission of 66%. Thus, the resistance did not fall in stages, as was the case when the article was heated to about 260 ° C, although there was an increased light transmittance.

Example VIII

An article was coated with layers similar to those of Example I and had a resistivity of 35.1 ohms per square area before heating and a 63% transmittance. The article was then heated to 177 ° C for 4 hours. After this heating, the resistance of the film remained substantially at 35 ohms per square, but the light transmittance of the article increased to 66%. After a second heating of 45 minutes, the light transmission and resistance of the article remained substantially the same.

Example IX

An article was prepared in substantially the same manner as in Example III. Before heating, the resistance was 37.2 ohms per square and the light transmittance was about 67%. After heating to 177 ° C for 2 hours, the light transmission increased to 74%, while the resistance of the article remained the same.

From the Examples, it is apparent that the resistance properties of the electroconductive film can be controlled by heating the film so that the crystals of the film grow and make better contact with each other, thereby reducing the resistance. As can be seen from the examples, the resistance decreases by about 2 to 5 ohms per square area for multiple heating periods of about 45 minutes or longer to temperatures greater than about 260 ° C and less than about 330 ° C.

It is further noted that the electrically conductive film had excellent hardness and durability properties after undergoing the heating treatment. These features are highly desirable from the standpoint of military and civilian use, because of the abrasive particles in the air or the frictional properties of wipers used by operators, the electrically conductive films on windshields or instruments are very easily scratched or scratched. It is also important to note that the light transmission of the article increases after heating to high temperatures, which is generally desirable.

It is also apparent that, although chromium has been used in the examples, various equivalent metals, such as nickel or alloys of chromium or nickel, can also be used. Further, while gold has been used as the electrically conductive metal film, the other previously enumerated metals, such as especially silver and copper, with the chromium and the like metals can be used to produce the results of the present invention.