WO2005105467A1

WO2005105467A1 - Multicolour printing on glass/ceramic subtrates

Info

Publication number: WO2005105467A1
Application number: PCT/TR2004/000025
Authority: WO
Inventors: Muammer Erdirencelebi
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-04-29
Filing date: 2004-04-29
Publication date: 2005-11-10
Anticipated expiration: 2006-10-29

Abstract

A multicolour printing method using principles of both screen printing and pad printing. Ink is first screen printed on a silicone roller that is a roller coated with desired thickness of silicone rubber material, where the thickness and hardness of silicone rubber are determined according to the type and geometry of the substrate. Screen printed ink is then transferred to the substrate which is either moving horizantally if it is flat or rotating if it is cylindrical. Multicolor printings of flat glass/ceramic substrates like automotive or oven glasses during their travel (without stopping them) and without the need of drying inks between printing stations are possible with this invention. Also printing of cylindrical or flat substrates that have irregular geometries or embossed parts can be printed with present invention.

Description

Multicolour printing on glass/ceramic subtrates.

Technical Field

The present invention relates to multicolour printing on flat or cylindrical, glass or ceramic substrates that direct screen printing is either not applicable or is being applied within some limits.

Backround Art

Many printing techniques are being used as both a decorative process or as part of the functional design just like screen printing electrically conductive silver based enamels to backlites in automative industry.

Screen printing technique is may be the most widely used technique for those purposes. In this technique, the material to be printed is pressed through the openings of a screen fabric that has the shape of the desired pattern by a squeegee. The material to be printed differs a lot according to the type of the application therefore it'll be simply called as "ink" within the rest of the article.

Screen printing can be classified according to the geometry of the subtrate. In general, screen fabric is attached to a flat screen frame. If the substrate is flat, squeegee moves across the stationary screen while substrate also remains stationary under the screen. If substrate is cylindrical, this time screen moves across the stationary squeegee while substrate is rotating under the screen.

Another printing technique is pad (tampon) printing technique. Main principle of this technique is that pad material which is silicone rubber is an elastic material that can be deformed easily according to the geometry of the substrate and that pad material has an excellent release property. In this technique, desired pattern is engraved on a surface which is called cliche. The whole surface of the cliche is dispersed with ink and then ink is removed with a squeegee filling in the engravings only . Pad takes the ink from the engraved parts of the cliche and releases on the substrate. Multicolour pad printing is also possible because silicone rubber doesn't damage the previous printed colour(s).

Pad printing can also be classified according to the geometry of the cliche and pad used. For example, by using a cylindrical cliche and a cylindrical silicone pad, Rotary Tampon(Pad) Printing Technique(EP1251004) was introduced previously by Philipp Wilfried.

By using these two printing techniques together ,i.e. screen printing and pad printing, a new application palled Offset Screening Method was invented. In this technique, the ink is printed onto a flat, silicone coated surface with screen printing. Pad takes the ink from this flat surface and prints on the substrate. In this technique, temperature differences are very important to be able to increase the tackiness of the ink. Therefore, stainless steel screen fabric is used to heat the ink to 75-80°C. Although it is possible to get heavy ink deposits with this technique, the main difficulty in application is its being very sensitive to temperature and humidity variations. Disclosure of Invention

In screen printing of glass and ceramic substrates, there are some limits coming from the nature of the process. Actually many of those can be solved with pad printing processes that are also mentioned above but the reason of insisting on screen printing is mainly the ink deposit achieved. In all pad printing types including rotary pad printing, ink deposit or ink thickness can only be increased to a limited value since silicone rubber cannot take ink thicknesses beyond this limited value from the cliche. Therefore pad printing cannot be used in industial fields where thickness achieved with this technique is not satisfactory just like in glass and ceramic industries. Also, preparing the screen in screen printing is much easier than preparing the cliche in pad printing. This gives flexibility in production to work various patterns even the batch size is ery small. Considering these two conditions, focusing on the limits of screen printing can be understood clearly. Screen printing on flat substrates is a very common application. The main limit in this process is the necessity to print on stationary subtrate, i.e. the subtrate has to be stopped. Printing on a substrate in motion is impossible. With this invention, it is possible to print on flat substrates during their travel. In many applications, multicolour screen printing is achieved with special inks because after first colour is printed, this colour has to become dry to be able to print the second colour on it. To achieve this, some solutions are developed. In printing flat substrates, usually inks that dry with air are being used. However, drying with air takes time and this increases the whole process time a lot. To reduce the time, special inks are developed. UV or IR curable inks are being used for this purpose. They are pre-cured with UV or IR between each printing station letting the next colour printing available. But these inks are special therefore expensive inks compared to others and also curing units are necessary between each station which means, for example you have to add 3 curing stations to a 4 colour printing machine. Another very common application for multicolour screen printing of especially cylindrical substrates is using inks with thermoplastic mediums. These inks are solid in room temperature. When they are heated to 75-80°C on stainless steel fabrics they become liquid. As soon as they are printed, they loose their temperature and become dry again letting the next colours printing available. As can be seen, these inks are again special inks and can only be used with expensive stainless steel screen fabrics which makes the process very sensitive to temperature changes. With this invention, it is possible to make multicolour printing without waiting between stations or any pre-curing units or using hot inks and stainless steel fabrics. During screen printing, the squeegee can work properly only if there's no obstacle on the way of it. For example, if there's an embossed part on the substrate, the squeegee cannot work properly because of the height of the embossed part. With this invention, it is possible to print on embossed parts. With this invention, it is also possible to print on irregular shapes within some limits. Brief Description of Drawings

FIG.1 illustrates the steps of the process for printing flat substrates. FIG.2 illustrates the steps of the process for printing cylindrical substrates. FIG.3A and 3B represent isometric views of instants during printing of flat and cylindrical substrates respectively.

FIG.4A to 4E illustrate some examples to irregular shapes that can be printed with this process.

Best Mode for Carrying Out the Invention In the following description, the invention will first be described with reference to the accompanying drawing FIG.1. The main principles and how the process works will be described as if a flat substrate is being printed. Then, with the help of FIG.2, differences of the process to print a cylindrical substrate will be defined. Lastly, printing some irregular shaped substrates will be described with reference to FIG.4.

The present invention is a printing process which uses main principles of both screen printing and pad printing techniques together. These two techniques are well known from the prior art therefore the description will not focus on these. FIG.1 represents the steps of the process. In step a, just before the printing starts, parts are shown with numbers and directions of movements of parts are shown with thick arrows. With starting of the process, screen frame 2 on which screen fabric 4 is attached and in which ink 3 is put begins its linear motion in the direction shown . At the same time, squeegee 1 goes down and silicone roller 5 starts rotating around its stationary center that is at the same vertical line with the squeegee 1. Also flat substrate 6 moves in the opposite direction of screen frame 2. During the travel of the screen frame 2, squeegee 1 pushes ink 3 from the openings of screen fabric 4 to the surface of silicone roller 5. Actually, up to this part, everything is just the same as screen printing on a cylindrical subtrate. The only difference is a silicone roller 5 is printed instead of a cylindrical substrate. But why?

As can be recalled from the prior art, pad printing technique depends on two important properties of silicone rubber as a material. First, silicone rubber can be deformed easily according to the shape of the subtrate and second, it has an excellent releasing property that helps it to release ink to the surface it contacts very easily. These two properties of silicone rubber are also being used in present invention. Actually second one, releasing property is the reason of screen printing on a silicone roller as described above. Silicone roller 5 can be defined as a roller or a cylindrical material that is coated with a desired thickness of silicone rubber.

After ink 3 is printed on silicone roller 5, they start rotating together. Meanwhile, flat subtrate 6 comes under the silicone roller 5 and there exists a physical contact between silicone roller 5 and flat subtrate 6. During this contact, ink 3 on the silicone roller 5 is released on the subtrate 6 as can also be seen in steps b anc c of FIG.1. This is a continious process and it goes until the whole pattern on the screen fabric 4 is printed on the substrate by this way. Squeegee 1 goes up and screen frame 2 goes back to its initial position for printing of another substrate. In FIG. 2, instead of printing on a flat substrate 6, steps of printing on a cylindrical substrate 7 are represented. All of the parts described above and shown in FIG.1 are the same therefore same numbers are used in FIG.2. The only difference is that ; to print a cylindrical substrate 7, its center has to be stationary during printing just like the center of silicone roller 5. As can be seen from FIG.2, cylindrical substrate 7 rotates with silicone roller 5 in reverse direction to keep contact all over its periphery.

It has to be noted that during the process, absolute values of all the velocities have to be equal. This means, velocity of screen frame 2, linear velocity of silicone roller 5 on its surface and velocity of flat substrate 6 or in case of FIG.2, linear velocity of cylindrical subtrate 7 on its surface have to be equal although their directions are different. Actually, this is a very basic principle in all printing techniques. FIG.3A and 3B are used to represent instants during printing of a flat subtrate 6 and a cylindrical subtrate 7 respectively to describe the process more clearly. A pattern 8 consisting of small circles is used as an example pattern in both figures.

Answers to how the present invention solves problems of screen printing can be found above. First one was printing on flat subtrates without stopping them. From the description of the process, it is obvious that the substrate has to move under the silicone roller to be printed. Therefore, it is even impossible to print on a flat substrate if it stops. Second one was about multicolour printing. With this invention, multicolour printing will be easily performed. In description part, and also in figures, invention is described for single colour printing for simplicity. If two, three or more printing stations are put together respectively, following happens. In station one, first colour is printed as described. In second station, although first colour is still wet, it doesn't contact anything but the silicone rubber of second station. Just like in multicolour pad printing, silicone rubber contacts first wet colour but it does not damage the colour, it only releases second colour on the substrate. In following stations, same thing happens and by this way, desired number of colours are printed on the substrate. The biggest advantage of multicolour systems using this process is that the speed of the system doesn't change according to the number of colours. Whether a single colour or more colours are being printed, speed(pieces per minute) doesn't change because there are no loss of time for drying between stations.

Lastly, how embossed parts qr some substrates having irregular geometries are printed with this process will be explained. FIG.5A, B, C, D and E are few examples to those geometries. In all example geometries, letters "X" and "Y" are used. In

FIG.5A and 5B, X is the maximum and Y is the minimum distance from an imaginary line. In FIG.5C, 5D and 5E, X is the maximum and Y is the minimum distance or radius from the center. It must be noted that geometries similar to FIG 5A and 5B have to be printed while they are travelling and geometries like FIG 5C, 5D and 5E while they are rotating. To print all of those geometries, present invention benefits from the first property of silicone rubber that it can be deformed easily. If a silicone roller is choosen such that the silicone layer on it can be deformed with a value of "X

- Y" , printing will be possible. All necessary adjustments are made as if a flat or cylindrical substrate having Y value of height or radius is being printed. During printing, silicone absorbs radius or height changes up to "X - Y" value which is the maximum difference. For a silicone roller, "X - Y" value depends on the thickness and hardness of the silicone rubber layer therefore silicone roller has to be choosen according to the application. If there's an embossed part on the surface, formula can be adapted such that "X - Y" value becomes the height of the embossed part. This time adjustments are made according to the surface of the substrate as if there's no embossing. During printing silicone deforms with a value of the height of the embossed part so printing occurs.

Industrial Applicability

Industrial applicability of the process depends on the possibility of establishing a system that uses the process. This is not difficult because from screen printing of cylindrical substrates, it's known that such multicolour systems with desired number of colours are already present in many industrial fields. The working principle is very similar to those screen printing systems. In present systems, using mechanisms and servo motors, screen frame is moved in horizontal direction and at the same time cylindrical substrate is rotated urtder the screen frame. With a small change, a silicone roller is rotated and subtrate is either moved in opposite direction to screen frame or is rotated in opposite direction to silicone roller according to its geometry in this new system.

This process όan be used in many applications in industry. In automotive glass industry, it's possible to print glasses without stopping the conveyors or taking them out of the line. They can be printed in-line and go directly to furnace to be bent or heat treated. Especially for backlites, this invention is very important because there're two colours on backlites one of which is the black one for decoration purpose and the other one is silver based for conductivity. This multicolour printing can be achieved in very short time period and as an in-line process. In multicolour printing of architectural glasses, oven glasses and similar flat glasses, or in flat ceramic articles, especially if high production rates are concerned, present invention is very advantageous. Four or six colours applications can be extensively used in these fields because more colours means more flexibility in designs. In glass/ceramic, tableware or container, bottle industries, especially being capable of printing irregular shapes and/or embossed parts, these products can be produced much more than today as those are being printed with very expensive methods(like decal applications) and in very small amounts because they are very expensive. This invention brings the advantage of printing those irregular parts like ordinary flat or cylindrical substrates.

This process may be used in present screen printing machines (especially for cylindrical ones) as last station with small changes on the machines. For example, regular surface of the substrate may be printed in previous stations and the irregular part or embossed part may be printed in last station that uses present invention.

In fact, this invention can be used not only in glass/ceramic industries but in all industrial fields where screen printing is being used and for which ink deposit achieved is important. Otherwise (if ink deposit is not important), other alternative printing methods may be considered as well.

Claims

1. A method for multicolour printing on substrates, the method comprising the steps of: screening ink from the openings of screen fabric onto the surface of a silicone roller by a squeegee; releasing said ink from silicone roller to a substrate;

2. the method of claim 1, wherein said openings of screen fabric is any desired pattern.

3. The method of claim 1 and 2, wherein said screen fabric is attached to a screen frame.

4. The method of claim 3, wherein said screen frame moves horizantally between said squeegee and said silicone roller.

5. The method of claim 1, wherein said silicone roller is a cylindrical roller of which surface is coated with desired thickness and hardness of silicone rubber.

6. The method of claim 5, wherein said silicone rubber can be deformed and has an excellent releasing property.

7. The method of claim 1 and 5, wherein said silicone roller rotates under the screen frame_;and below the subtrate.

8. The method of claim 7, there is physical contact between silicone roller and the substrate.

9. The method of claim 1 ,wherein the geometry of said substrate can be flat.

10. The method of claim 9, wherein said flat subtrate moves horizantally under the silicone roller.

11.The method of claim 1 , wherein the geometry of said substrate can be cylindrical.

12. The method of claim 11, wherein said cylindrical subtrate rotates under the silicone roller.

13. The method of claim 1 , wherein the geometry of said subtrate can be irregular.

14. The method of claim 1 , wherein there can be embossed parts on the said subtrate.

15. The system for multicolour printing using said method of claim 1 comrising the steps of the method of claim 1.

16. The system of claim 15, wherein said system comrise one or more printing stations for multicolour printing.

17. The system of claim 16, wherein said stations use the steps of said printing method of claim 1.

18. The system of claim 17, wherein said printing stations print consecutively.

19. The system of claim 17, wherein one or more said printing stations can be adapted as last printing station(s) of a screen printing machine.