JPH0336028B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for transferring onto objects made of plastic or provided with a surface layer, for example a paint layer or a surface layer made of plastic. In transfer, which is known primarily from the textile industry, ink is transferred by sublimation from a planar ink carrier onto the printing surface at elevated temperatures. During ink delivery, the ink carrier is pressed onto the printing surface.

The transfer of solid objects, for example sheet metal strips, onto painted surfaces is described in DE 29 14 704 A1. The transfer takes place when the painted sheet and the transfer paper pass through a calender. According to DE 26 42 350, the transfer is combined with the painting of the solid object, ie a thermoplastic plastic sheet is applied to the surface of the solid object and at the same time an ink is applied to the applied plastic layer from the ink carrier. metastasize. For bonding, various conventional methods are applied, such as high frequency bonding, ultrasonic bonding or hot air welding. Since lamination and ink transfer take place in the thermoplastic state of the plastic layer, the original gloss of the plastic surface is not maintained in this method.

When transferring onto objects made of plastic or objects with a plastic surface layer or a paint layer,
Surface gloss should essentially be maintained. A suitable method for this must be easily practicable under industrial conditions. This problem is solved by pressing the planar ink carrier to the printing surface with gas pressure above atmospheric pressure during the ink transfer, while maintaining that surface at a temperature below the thermoplastic range. It has been found. When mechanically pressing an ink carrier onto a printing surface at a temperature suitable for transfer, the pressure between the ink carrier and the surface is so high that areas inevitably arise where the surface gloss is permanently impaired; however, the present invention The method essentially achieves a more uniform pressure action and therefore the surface gloss is maintained.

With the method of the invention, all substrates that have sufficient affinity for the sublimation inks used for transfer can be printed. It is particularly advantageous to apply the method of the invention to the printing of objects with glossy surfaces or surfaces that are pressure-sensitive for other reasons.

The object to be printed must have, at least on its surface, a continuous, if necessary porous layer or matrix, which has sufficient affinity for the ink used during the transfer and at the application temperature. It consists of a plastic that may soften to a thermoelastic state, but not to a thermoplastic state. Particular preference is given to plastics which, because of their very high molecular weight or high branching or crosslinking properties, have no thermoplastic range and are thermoelastically soft at most.

Without exception, objects made of plastic with a closed plastic surface, especially flat plates, strips or sheets, are preferred. The plate or strip may, for example, have a thickness of 1 to 12 mm, in particular 2 to 8 mm. Curved, arched or otherwise three-dimensionally shaped materials, such as tubes, cupolas, health and hygiene parts, luminous guide markings, injection molded parts, etc., can be printed according to the invention. Furthermore, plastic foam having sufficient temperature stability can be obtained by the method of the present invention,
For example, polymethacrylimide plastic foam can be printed.

Other groups of printable objects include bases from other materials such as metal (board), ceramic, glass, asbestos cement board, leather, wood, wood chips, chipboard, hardboard, paper or paperboard. It contains a plastic surface layer on the body, for example a laminated sheet or a paint layer.

A particularly suitable plastic for the method of the invention is acrylic glass. It is a homopolymer of methyl methacrylate and the main proportion is in particular at least 70
% from this monomer and the remainder from other monomers copolymerizable with it and the acrylonitrile/methyl methacrylate monocopolymer.
Acrylic glass may be polymerized in sheet form; this so-called "cast acrylic glass" has a molecular weight of more than 1 million and therefore does not have a thermoplastic state range. However, acrylic glasses can also be extruded from thermoplastically meltable molding materials. In this case, the transfer step can be carried out directly after the production of the extruded plastic strip. Other suitable plastics are polyethylene, polypropylene, polyvinyl chloride, polystyrene and high impact butadiene/styrene plastics, polyoxymethylene, polycarbonate, fiberglass/polyester and aminoplast plastics.

Opaque white plastics are generally preferred, but transparent or other colored plastics or plastic layers are also suitable.

Planar ink carriers commonly used in textile printing or other transfer processes are also suitable for the method of the invention.
It may be printed in a single color or with any design in a single color or in multiple colors. Generally, it is produced on paper by intaglio, offset or screen printing methods, although plastic or metal sheets are also used as carrier materials. For printing, special sublimation inks are used which have sufficient affinity for the printing plastic.

If only part of the surface of the object is to be printed, the ink carrier may be smaller than the surface area of the object. In the case of non-planar materials, it is advantageous to use an ink carrier consisting of individual parts which can be better applied to the surface as a continuous piece. The individual parts can be used for transfer simultaneously or sequentially. Ink carriers made of elastic plastic sheets are often advantageous for printing spherically curved surfaces.

Advantageously, the ink carrier should be selected such that it does not form wrinkles or blisters under printing conditions. It is advantageous to predry the paper ink carrier at a temperature below the sublimation temperature. To avoid interference with the gloss of the printed surface, a fluid or particulate separating agent such as talc is dusted onto the ink carrier. Dusting plastic surfaces has been found to be less effective. The ink carrier is elastically moved at a small distance on the printing surface - approx.
It is recommended that the ink carrier be tensioned by ~2 mm and that the ink carrier in each case be in contact with the printing surface only in the area where the compressed gas acts.

Compressed gas generally consists of air. Inert gases such as nitrogen or carbon dioxide are used only in rare and exceptional cases. The compressed gas acts indirectly or directly on the back side of the ink carrier at a pressure slightly above atmospheric pressure, and circulates around the ink carrier so as not to affect the front side of the ink carrier that comes into contact with the object to be printed. should be. Compressed gas cushions can be used, the compressed gas being enclosed in pouches made of soft sheets or textiles that are less rigid than the ink carrier. It is more advantageous for the compressed gas cylinder to act directly on the ink carrier, in which case the bell-shaped hood containing the gas cylinder rests against the edge of the ink carrier or a narrow air gap can be formed. During this time, the compressed gas flowing out through the tube should be continuously replenished to maintain the required gas pressure.

Gas pressure is 3~200mm water injection (WS), especially 5~50mm
It may be at the level of WS. Higher pressures are not necessary with flat substrates and flexible ink carriers, which would result in disturbing printing or loss of gloss.

Advantageously, the gas pressure is generated by flowing gas. For example, compressed air from a number of single nozzles can be flowed to the backside of the ink carrier from small distances of, for example, 5 to 50 mm. For example, the nozzle may consist of holes in a perforated plate with a mutual spacing of 10 to 50 mm or correspondingly spaced slits. Especially advantageously,
The respective flowing compressed gas acts on a part of the backside of the ink carrier in a limited area and moves this area onto the backside of the ink carrier until the entire surface is pressed down. The residence time at each location must be sufficient as required for ink delivery. It is advantageous if the compressed air emerges from a slotted nozzle whose width spans the entire width of the printing area and which moves gradually over the substrate. The substrate can also be moved under a fixed slit nozzle.

The required flow rate of the flowing gas depends on the spacing from the ink carrier to the nozzle, the flexibility of the ink carrier, the dynamic pressure that occurs depending on the method of gas exit and other givens in the individual case. In any case, the flow rate must be sufficient to keep the ink carrier in intimate contact with the substrate surface for a sufficiently long period of time. If the ink carrier is flat and flat during the gas blowing, a lower flow rate is sufficient than if the ink carrier has a tendency to sag, wrinkle or blister. However, the flow velocity is
By crimping the ink carrier, it can be ensured that no impressions or loss of gloss occur on the substrate. Good results are achieved with flow rates of 5-20 m/sec. The relative velocity between the nozzle and the substrate ranges from 0.1 to 2.0 m/
It may take a minute.

Most transfer inks are 100-300℃, especially 150℃
Sublimes at ~250℃. During the action of the compressed gas, the ink carrier must reach the sublimation temperature of the ink and maintain this temperature until the desired ink transfer takes place. The higher the temperature of the printed surface, the more complete the transition, but the printed surface should be lower than the temperature of the ink carrier, in particular below the sublimation temperature of the ink. Generally, it is desirable for the ink to diffuse into the surface to be printed to a depth of about 20 to 100 micrometers.

Since the ink carrier is heated to the sublimation temperature for the first time just before the ink transfer begins, and since the sublimation process consumes heat, the ink carrier should be supplied with the heat necessary to maintain the sublimation temperature during the ink transfer from its back side. . For example, a thermal injection device can be provided in a bell-shaped hood containing the compressed gas cylinder, the injection direction of which is directed towards the rear side of the ink carrier. When operating with a flowing compressed gas, it can heat itself and act as a heat transfer medium. A thermal injection device can additionally be used. Ink transfer can be achieved with a contact time between the printing surface and the ink carrier of 2 seconds to 5 minutes. In particular the contact time is between 5 and 15 seconds. A contact time of the order of seconds preconditions not only a high temperature of the ink carrier but also a preheating of the printing surface to the highest possible temperature. For example, for thin objects such as plastic boards or sheets, plastic-coated sheets or laminates, it is often sufficient to place the object on a heated table for a while before transferring it. It is. Objects with thick walls or poor thermal conductivity are preheated in a heating box or with a heat injection device.

When printing injection molded acrylic glass, the acrylic glass is preheated to 170-180°C and hot air at a temperature of 250-350°C is blown onto the back side of the ink carrier. Under these conditions sufficient ink delivery is achieved in 5 to 15 seconds without loss of surface gloss.
The same conditions apply for thermosetting plastics or thermally crosslinked coatings.

When printing thermoplastics with inks whose sublimation temperatures are within the plastic softening range of the plastic, carefully controlled temperature management is required. The plastic is at most in the thermoelastic temperature range and in each case can be preheated to a temperature clearly below the thermoplastic temperature range.
Further heating of the plastic surface during the contact time with the ink carrier is unavoidable, but should be maintained to such an extent that the plastic surface does not reach a thermoplastic state. The preservation of the surface gloss is a reliable sign that in any case the limits to the thermoplastic range have not been exceeded to such an extent that irreversible deformation of the surface can occur. The preheating temperature, the intensity of the thermal action during ink transfer, and the contact time are such that sufficient ink delivery is achieved without the ink carrier adhering to the plastic surface, which can be considered an indication of a thermoplastic state. mutually determined. The height of the gas pressure or gas flow rate also affects heat transfer to the plastic surface. If surface damage occurs due to adhesion of the ink carrier to the plastic surface, the injection heat supply can be reduced accordingly by lower preheating temperatures, by lowering the pressure, flow rate, temperature or duration of action of the compressed gas. It can be corrected by narrowing down.

Extruded acrylic glass is in a thermoplastic state at temperatures above 150℃, making it 120-135℃
The ink carrier can be printed according to the present invention when preheated to a temperature of 150 to 200 DEG C. and the ink carrier can be pressed with hot air at a flow rate of 5 to 20 m/sec for a contact time of 5 to 10 seconds. Predried boards made of polycarbonate plastic can be preheated to 180-200°C and tolerate hot air temperatures up to 350°C.

In practical application of the method, it should be possible to start ink delivery as soon as the compressed gas is applied. The printing surface should already be sufficiently preheated before the action of the compressed gas, or a suitable heat source should be applied immediately on the ink carrier. It is advantageous if both assumptions are met simultaneously.

The object to be printed can be preheated in an air circulation box and, if the object softens thermoelastically, is preheated to a suitable, in particular the same, temperature and placed on the stand. The object can also be placed on a table and heated, for example by means of a thermal injection device. The ink carrier is placed in a cold state and compressed gas is applied. The ink carrier can be mounted on a frame for easy handling. After the ink transfer, the ink carrier is removed and the printing object is optionally left on a stand until it has cooled to a temperature below its softening temperature. During continuous printing of a plastic strip placed on an endlessly rotating steel belt, a feed roller is placed over the strip at a location where the plastic strip is cooled from its thermoplastic state to a temperature suitable for transfer. A belt-shaped ink carrier sent out from the ink carrier is placed thereon and crimped by hot air jet through a slit nozzle provided perpendicular to the flow direction. Optionally, the strip passes under several slot nozzles one after the other. Thereafter, the ink carrier strip is removed and the printed plastic strip is cooled in a cooling zone.

Claims (1)

[Scope of Claims] 1. Transfer from a flat ink carrier to a solid object made of plastic or having a surface layer of paint or plastic under pressure of the ink carrier onto the printing surface of the object at a temperature suitable for ink transfer. A method characterized in that a planar ink carrier is pressed onto a printing surface by gas pressure at a pressure above atmospheric pressure during the ink transfer, the surface being maintained at a temperature not exceeding the thermoplastic range. Transfer method to solid objects. 2. The method according to claim 1, wherein the gas pressure is generated by gas flowing behind the ink carrier. 3. A method as claimed in claim 2, in which the gas pressure acts in each case only on a limited area of the back side of the ink carrier and gradually moves this area to other parts of the back side of the ink carrier. 4. Claims in which the ink carrier is spaced apart from the surface of the object to be printed at a small distance except in the area where the gas pressure acts, and in said area it abuts and presses against the surface of the object to be printed by the gas pressure. The method described in Section 3. 5. The method according to any one of claims 1 to 3, wherein a fluid or finely divided solid is applied as a separating agent before applying gas pressure to the surface of the ink carrier. 6. A method according to any one of claims 1 to 5, characterized in that the object to be printed or at least the printing surface is preheated to a temperature suitable for ink transfer before being subjected to the action of gas pressure. 7 Claim 1 printing a non-planar object
6. The method according to any one of Items 6 to 6. 8. A method as claimed in claim 7, in which several ink carriers, each covering only part of the printing surface, are arranged simultaneously or successively on a non-planar object.