NO133586B - - Google Patents

Description

The present invention relates to a method for coloring or color modification of glass products which contain reducing ions by diffusion of a compound into the surface layer of the glass product from a contact medium.

One can produce colored vitreous by walking

from a vitrifiable composition with added suitable coloring agents.

However, such a method is only usable - in some cases, because you then have to use a different composition for each glass color to be produced. In the glass industry and particularly for the manufacture of flat glass, it is usually much more practical to color the glass product during or after it has been shaped so that the color treatment can be controlled independently of the composition of the vitrifiable mixture and the processing process for the glass.

Various methods are known for coloring glass products during and after forming. Such methods consist of coating the glass product with a film of a metal or metal oxide by evaporation in a vacuum. In this way, you can get a very thin film that only slightly reduces the light transmission of the glass. However, the film is subject to degradation or rubbing and otherwise to mechanical and chemical stress.

A satisfactory known method consists in

to indiffuse coloring substances in the glass at high temperatures.

In this way, the glass can be colored to a certain depth from the surface and the coloring cannot be removed by rubbing. However, this diffusion method is only of limited use if one wants to color a series of glasses with different colors. E.g.

There are different metals that can be indiffused in ionized

form in a vitreous body and which give different colors to the glass, but most of them, although of possible interest because of the special color which they give, will only be able to form a rather poor color when the compound is used according to barrel process- ways of coloring ordinary drawn sheet glass. This applies at least if you want to follow economical production methods.

E.g. silver is a special example of a valuable coloring agent. However, this metal only forms a rather weak yellow color in ordinary drawn plate glass when silver is used as a coloring agent in the known diffusion methods, and one must use a large amount of silver in salt farm in the treatment medium or use a relatively long treatment time. This weak yellowing is not sufficient to provide protection against actinic light.

The purpose of the present invention is to present a diffusion method which offers great possibilities of variation with regard to shades and color densities and which can be used on glass of different composition, including ordinary drawn glass.

According to the present invention, a method for coloring or color modification of vitreous bodies containing reducing ions is produced by diffusion of a compound into the surface layers of the vitreous body from a contact medium containing a mixture of metallic salts which supply reducible metal ions which can be reduced by the reducing ions, and the method is characterized by the fact that the contact medium contains a mixture of molten metal salts containing less than 0.5% by weight of salt(s) which supply the reducible metal ions, which ions are silver ions, and that after the diffusion of reducible metal ions into the vitreous from the contact medium achieves the final coloring by heating the vitreous body to a temperature above the lower relaxation temperature of the glass.

The method according to the invention is much more versatile than the known color processes by diffusion, in that with the help of the method of the invention a series of different colors can be obtained for glass that has many different compositions, and this on an industrial economic scale. This result is due to the application of two separate treatment

step, namely the diffusion step where the quantity of dye which

is available for indiffusion in the vitreous body is restricted

and on the other hand the development step during which the dye

which has diffused into the body forms the color or modifies or changes the color in the body or under which the color effect or the modifying effect is induced.

In addition to the versatility of the process, another important advantage is that the amount of colorant required to achieve a particular color is much smaller than the amount required by other methods. During the first stage of the process, at least part of the reducible metal ions that diffuse into the vitreous body are reduced by said reduction ions present in the body, but this reduction is not sufficient to give the final color and in certain cases the first treatment step could not observe any color at all. When you e.g. treat ordinary plate glass in a processing medium containing silver ions, you can use a very low concentration of silver in the medium, namely a concentration that

and with may be insufficient to give visible color in the glass after the first treatment step. In these cases, the method can be carried out on an industrial scale very cheaply.

In the most important applications of the invention, the treated glass consists of ordinary soda-lime glass. Such glass is essentially uncoloured and by using the invention it is possible to give the glass different colors which can be determined according to the method of the invention.

The invention can also be used for coloring plate glass made of soda-lime glass and glass products that are formed from flat soda-lime glass. The problems in staining vitreous bodies with regard to achieving a completely controllable color correspond

special optical requirements are often encountered when coloring glass objects that consist of or are made up of e.g.

ordinary plate glass made of soda-lime glass, in the production of flat or curved windows or sunglass lenses. One can e.g. profitably use the invention for coloring flat soda-lime glass formed according to the "float<n> method, whereby the plate glass is formed from a bath of molten glass which flows out to a layer of liquid glass on a substrate with a higher specific gravity, or for coloring of laminated soda-lime glass.

According to the most important embodiments of the invention, the method is used for coloring bodies that consist of or form part of drawn plate glass or a plate of curved glass produced by bending such plate glass. The advantages that the present invention entails are quite significant when the invention is used for coloring such glass products. Drawn soda-alk glasses usually only contain very small amounts

2+

reducing ions, e.g. Fe, so that if one tries to color these types of glass using certain substances according to known diffusion processes, one cannot give the glass satisfactory colors under the usual industrial conditions. The color is often too weak to carry out the desired projects. When a method according to the invention is used, a much stronger color is achieved and at a lower price. This is because the special treatment in two stages makes it possible to achieve the powerful colors that only require relatively small amounts of dye and without excessive heating requirements. It has been found that many different color densities can be produced in a total processing time of less than 24 hours and even less than 5 hours by using small amounts of colorant which, when used according to known diffusion methods even in large amounts, only give rather poor coloring.

The use of a treatment medium which contains not only the salt which supplies the reducible metal ions which give the colouring, but also one or more other salts is beneficial not only because the amount of disposable coloring agent for indiffusion in the glass is limited (the maximum amount of salt for supply of reducible metal ions is according to the invention 50% by weight of the treatment medium), but also because the weight-wise content of such salt can be chosen within a large range and as a function of the desired results. In other words, this quantity ratio is a regulation or control parameter in addition to . the temperature and treatment time. For any given colorant, these parameters have an impact both on the penetration depth of the reducible metal ions and on the final colouring.

The use of silver for coloring glass is particularly important, and especially when it comes to coloring vitreous bodies that make up or make up parts of drawn flat soda-lime glass. When the silver ions are reduced in the glass or during the subsequent temperature treatment of the glass, it acquires a yellow colour. The yellow color shows that the glass has certain absorbing properties towards actinic light. It is surprising to find that the method according to the invention can form such a strong yellow color and thereby give a strong absorption of actinic light to vitreous bodies consisting of drawn soda-lime glass with a common composition and that this can be achieved in a relatively simple way in industrial scale by using a processing medium containing a small amount of silver.

In such processes, the treatment medium can be very cheap. The very low amount of silver does not prevent the glass from taking on a strong yellow colour, also with the vitreous body consisting of or forming parts of ordinary drawn sheet glass made of soda-lime glass.

One can even achieve these results when the quantity ratio

of silver salt in the treatment medium is much lower than above.

According to the invention that one e.g. can be used for the treatment of ordinary drawn soda-lime glass (window glass) or "float" glass, the treatment medium contains less than 0.5% by weight of salt or salts that deliver reducible metal ions, as these salts consist of one or more silver salts. According to certain other very favorable embodiments for the treatment of "float" glass, the treatment medium contains less than 0.05, e.g. 0.01% by weight salt or salts which supply reducible metal ions, these salts being one or more silver salts. The indiffusion of the reducible metal ions in the <n>float<n->glass can take place during the continuous production of "float<w->glass despite the relatively high feed rate of the glass web and without having to take special precautions for to accelerate the diffusion rate of the reducible metal ions in the glass.

Although the present invention is described specifically with regard to silver, the method has also been shown to be applicable for dyeing or color modification using copper and gold.

Advantageously, the treatment medium, which comprises a mixture of salts not mentioned above, is in a molten state. The use of such a medium in a molten state is recommended to achieve a very satisfactory diffusion of reducible metal ions in the vitreous under normal atmospheric pressure. However, the invention can be carried out by using a treatment medium containing a mixture of metal salts in vapor form.

The invention can be carried out by showering or spraying the molten mixture on the vitreous bodies to be treated. You can advantageously immerse the glass in the molten mixture. Such dipping is beneficial because it is easy to achieve a uniform temperature over the treatment raft. The dipping technique is also in its place where you want to color or color modify the entire surface of the vitreous body. The invention is, of course, not limited to these cases. On the other hand, the invention encompasses all methods by which one colors or changes the color of only part of the surface of the vitreous body, e.g. one side of a plane or curved plate. If you only want to color part of a surface, you can immerse the body in a treatment medium by masking or covering the rest of the surface with e.g. a layer or coating that is temporary. As a variant, one can submerge or dip only a part of the body to be treated if the shape allows it. As another variant, the treatment medium can be kept in contact with only the part of the surface to be treated, containing the mixture between infinite walls running in contact with the glass product along the boundary surrounding the treatment surface. Another method is to pour the treatment mixture along the surface

to be dyed. You can of course also use the pouring technique when you want to color the entire surface of the product.

When carrying out the diffusion treatment by keeping a certain amount of treatment mixture in a molten state in contact with the glass product to be colored, a more even treatment can be achieved by stirring the mixture. As a variant, the mixture can be stirred by introducing gas.

During the indiffusion of reducible metal ions in the glass object from a mixture in a molten state, the desired concentration of reducible metal ions can be maintained by electrolytic dissolution of a certain amount of solid or liquid substance which supplies the necessary ions.

It has been found that the presence of one or more zinc salts in the mixture can favor the diffusion of reducible metal ions into the surface of the glass under certain conditions. Furthermore, color variations can be achieved with the help of zinc salts.

Advantageously, the reducible metal ions come from a metal salt selected from the group: nitrates, chlorides, sulfates. In general, these salts are easy to prepare, process and use. Furthermore, the salts can be easily melted and do not decompose at the relevant temperatures.

When treating with silver salts, the temperature during the first treatment step, i.e. the step where an indiffusion of reducible metal ions takes place in the gout of the vitreous surface, should preferably be below 350°C. By keeping the temperature lower than this level, a limited diffusion of reducible metal ions into the body is achieved during the first step which precedes the controlled development of color therein. second step. The second step of the process consists in heating the glass product to a temperature that is higher than the glass's "strain point". According to preferred embodiments, where the glass products consist of or are formed from drawn soda lime sheet glass, the glass products are heated to a temperature of at least 500°C after indiffusion of reducible metal ions in the glass body. By heating the glass to at least ^ >00°C during the second stage of the process, strong colors can be achieved during moderate or very short processing times even when using a processing medium where the reducible metal ions are silver ions in low concentration, e.g. lower than 0.5% by weight. During certain experiments it has been established that the amount of reducible silver ions that diffuse into the glass during the first step of the process has not been reduced even though a certain amount of reducing ions was still present in the surface layer of the glass. The effect achieved by the heating during the second stage of the process is likely to enhance the action of the reducible ions and the reducing ions so that the coloration which may be practically invisible after the first step is induced. This does not mean that the above conditions need to be the real and only reason for the success of the process. Other phenomena also probably play a significant role, e.g. the formation of crystallites. Whatever the reason, however, it is a fact that strong colors are obtained by combining the two steps mentioned, even when using a salt melter containing a relatively low amount of salt of the coloring metal.

As a function of the concentration of silver ions d the treatment medium and/or the influence of other factors such as any additive and any zinc salt, satisfactory colors can be achieved for protection against actinic light at treatment times such as e.g. is between 4 hours and a few minutes at temperatures of 500" to 600°C during the second stage of the treatment.

The development of the color during the second stage of the process can be accelerated by keeping the treated surface of the vitreous,

at least during part of the second stage of the treatment, in contact with a reducing liquid, e.g. a reducing gas such as hydrogen. However, this operation is of particular interest when the coloring agent is copper.

The salt(s) as the reducible metal ions

is mixed with until a treatment medium can play an additional role beyond that of diluent. E.g. the diluent may contain or consist of a metal salt which supplies metal ions which diffuse into the vitreous for exchange with other ions to effect other changes in the surface properties.

After you have heated the glass body and given it the final color, it is advantageous to quickly cool the glass so that surface pressure tensions are formed in the glass.

You can thus easily carry out coloring and hardening of the glass products during the same treatment process.

Furthermore, it is beneficial during the warm-up

of the glass and when this has reached a temperature that is above the glass's lower relaxation temperature and after the reducible metal ions have diffused into the glass, to diffuse into the glass's surface layer ions of the type lithium ions which give the glass's surface layer a lower thermal expansion coefficient, by exchange with other ions, so that surface tensions are introduced into the glass when the glass then cools.

In this way, the glass body is chemically hardened and consequently has great resistance to breakage and great tensile strength.

The glass bodies can of course be hardened in another way, either by a treatment which is carried out at least partially

during the color treatment, or by a treatment that is carried out after the color treatment, You can thus harden the glass thermally by heating and subsequent rapid cooling after it has cooled by

the end of the second color processing step. Alternatively, after the color treatment is completed, the vitreous can be chemically hardened by indiffusion of ions into the body from a contact medium to exchange for smaller ions, at a temperature not sufficient to allow complete equalization or relaxation of the surface compressive stresses which are induced in the glass. In ion exchange treatments of the type mentioned above, it is advantageous as a chemical curing medium to use a mixture containing an alkali metal salt which supplies the cations that must diffuse into the glass for exchange with other ions. Ref. is it beneficial to use a potassium salt melt. Suitable alkali metal salts for curing by ion exchange can e.g. can be chosen from among nitrates, chlorides and sulphates.

One can of course use the method according to the invention not only for coloring uncoloured glass, but also for changing or modifying the color of glass products that have already been coloured. The procedure applied to vitreous bodies that have already been colored is exactly the same as for uncoloured glass. The modification of the color can lead to a change in color or tone or to a simple strengthening or deepening of the color or tone in the glass, e.g. a color or tone obtained by a previous treatment which can of course be carried out according to the invention.

When the second stage of the process is carried out at a sufficiently high temperature, e.g. above 600 C, in certain cases, e.g. when the glass object consists of plate glass, curve or bend the vitreous body during this second processing step. Carrying out a bending operation during the color processing step is interesting because one can speed up the mass production of objects, e.g. increase the pace of serial production of vehicle windshields. By carrying out a hardening treatment during the color treatment step, one can give a glass plate a yellow color, harden the plate and bend it to the desired curve within a relatively short time.

The method of the invention can be used to give different color tones to different parts of the surface of the glass objects. E.g. plate glass can be treated according to the invention with a view to giving it different colors on each side of the plate. E.g. you can give the two opposite sides of the glass plate yellow colors of different density and strength. The invention includes vitreous bodies which are colored or have undergone a color change according to the method of the invention.

The invention also includes vehicle windshields

which consists of glass plates or at least one glass plate and at least one plastic plate, which glass plate or at least one glass plate, if there are more, is colored or has undergone a color modification on at least one of the surfaces according to the method of the invention, such composite panels are joined along the edges or over the entire surface with an intermediate layer of adhesive or plastic material.

One can e.g. use epoxy resins as glue or adhesive.

Advantageously, the intermediate layer consists of a pre-manufactured foil of e.g. polyvinyl butyral. Of particular importance is front glass that consists of two sheets of glass (of which at least one is colored or has undergone a color change) composed of at least one pre-manufactured intermediate foil of e.g. polyvinyl butyral.

The invention will be better understood with the help of the following non-limiting examples.

Example 1

A glass web essentially consists of SiO 2 72.5 ÅlgO^ 1.5 lo, Na 2 O 14%, CaO 7.5%, MgO 4 fo and smaller amounts of K^ O and iron oxide, drawn according to the Pittsburgh method.

Glass baneril^Bjfø thickness 3 rm'

Sheets of k x 0^5 m cut from this web are preheated and immersed in a bath of molten salts consisting of 58% by weight KNO^ and 42% by weight NaNO^, with 0.2% by weight AgNO^ added.

The bath is kept at a temperature of 330°C and the glass plate is immersed for 1 hour.

After pulling up the plates from the bathroom, they are still uncolored to the eye.

The plates then undergo a heat treatment at 550°C for 3 hours. The glass is then cooled and washed.

The plates have acquired a yellow colour. Other plates treated at 6 r 00 0 C for a few minutes are cooled well and washed.

The color obtained is yellow and one has an abrupt off- c 1

cooling achieved a thermal hardening on the two surfaces so that the bending resistance is increased.

A third plate series undergoes a temperature treatment at 650°C for a long enough time to allow the plates to be bent.

After cooling and washing, curved and yellow-coloured plates have been produced.

Example 2

In a first step, test plates (a) of ordinary glass with composition as in example 1, (b) glass with composition 80% Si02, 2% M20y 13% B2<0>3> 3.5% Na20, 1% KgO and containing a smaller amount of iron oxide, and (c) green colored "atherman" glass containing a larger amount of iron oxide than ordinary glass, immersed in a bath of NaNO^, containing 0.15% AgNO^ by weight, at 350°C. The plates were kept submerged for 2 hours.

After rinsing the test pieces, they were heated

to 600° in a mold that gave the glass a cylindrical shape.

After these treatments, the ordinary borosilicate glass, which was previously colorless before heating to 600°, had acquired a yellow color with a light transmission of almost 70%>, while the atherman glass, which had retained a green color after absorption from the salt melt, had turned brown with a much stronger absorption than ordinary glass (light transmission of around 20%).

The glass (a) after 2 hours immersion in the bath containing AgNO^ was practically colorless, and it was then dipped in a bath of molten salts containing 58% NaCl, 4% NaNO^

and 2 fo LiNO^, at 580°C.

The plates were immersed for 2 hours. The plates were pulled up, cooled and rinsed.

Na<+->ions in the glass had been exchanged for Li<+->ions in the salt melt and gave the glass's surface layer a smaller coefficient of thermal expansion than the rest of the glass, so that the glass's surface layer had compressive stresses after cooling.

It was found that after this second immersion the glass had a yellow color and, incidentally, that the fracture-bending resistance had increased (corresponding to a maximum tensile stress on a tensile-loaded plate equal to 97 kg/mm<2>).

Example

A sheet of glass with a thickness of 3 111111 °le produced by the "floatn" process.

This glass web contained on the surface in contact with the substrate of molten tin bath reducing tin ions.

While the path passed through the cooling chamber, an aerosol mixture of molten salts at 400° was sprayed onto the underside of the glass. The mixture had the following weight composition: 42% TJaNO^, 58% KNO^, 0.2% AgNO^. The mixture was kept in contact with the glass for a few seconds.

After cooling, the glass (which was uncoloured) was cut into sheets which underwent heat treatment for 15 minutes at 550°.

The side of the glass plate that was in contact with the tin bath had turned a bright yellow colour.

Example 4

Glass plates with a weight composition of 71% Si02, 1 fo Al20^, 14 fo Na20, 9 fo CaO, 4 fo MgO, smaller amounts of SO^, Fe^, Kr,0, were produced according to the float-glass process.

The plates were immersed for 5 minutes in a mixture of molten salts at 300°C

The smelt had the following composition: 58 KNO^, 42 fo NaNO^, added 0.2 fo AgNO^ on a weight basis. After cooling and washing, the plates, which were still uncoloured, were subjected to the following heat treatment:

500° for 2 hours

550° for 15 minutes

600° for 20 seconds.

The color formed was strongly yellow and localized to the surface which had ■ been in contact with the molten tin substrate.

The same operations were repeated with identical glass plates where, during the first step, the salt mixture used was replaced with a similar salt mixture which, however, only contained 0.01% by weight of AgNO^.

A yellow color was also obtained after the heat treatment step, but less strongly.

Example 5

Glass plates of the same composition as in example 1 were immersed for 1 hour in a mixture of molten salts at 3^0°,

consisting of NaNO^ and 0.2% by weight AgNO^.

After cooling and washing, the unstained glass plates were subjected to a heat treatment for 2 hours at $60°. It cooled slowly. The plate had turned yellow.

A new heat treatment was then carried out by immersing the same glass plates in a bath of KNO^ at 420°

for 8 hours.

After cooling and washing, the color of the glass plates had not changed, but the plates had achieved a mechanical strengthening by diffusion of K<+> ions. The reinforcement was equal on both sides of the glass and the bending fracture resistance, expressed as the maximum stretch on the surface of a plate under tensile load, was around 100 kg/mm 2.

Claims (6)

1. Method for coloring or color modification of vitreous bodies containing reducing ions by diffusion of a compound into the surface layers of the vitreous body from a contact medium containing a mixture of metallic salts which deliver reducible metal ions which can be reduced by the reducing ions, characterized in that the contact medium contains a mixture of molten metal salts containing less than 0.5% by weight of salt(s) which supply the reducible metal ions, which ions are silver ions, and that, after the diffusion of reducible metal ions into the vitreous body from the contact medium, the final coloring is achieved by heating the vitreous body to a temperature above the lower relaxation temperature of the glass. 2. Method as stated in claim 1, characterized in that said medium containing one or more salts which supply the reducible metal ions is selected from the group: nitrates, chlorides, sulphates. 3» Method according to claim 1 or 2, characterized in that the diffusion of the reducible metal ions into the glass body takes place while the body has a temperature of less than 350°C• 4» Procedure as specified in one or more of the above requirements, characterized by the aforementioned glass body is a body that consists of or is formed from drawn soda-lime plate glass and is heated to a temperature of at least 500°C after the indiffusion of reducible metal ions in the glass. 5. Method as stated in one or more of the above claims, characterized in that after the heating of the vitreous body, which gives the glass its final colour, the glass is rapidly cooled to introduce surface compression stresses. 6. Method as stated in one or more of the claims 1 to 5> characterized in that during the heating of the glass body while the glass maintains a temperature above the glass's "Strain point", after the diffusion of the reducible metal ions in the body, causes an indiffusion of ions, e.g. lithium ions, which give the glass's surface layer a lower thermal expansion coefficient when exchanged with other ions, so that surface compression stresses are introduced when the glass is then cooled.