WO1992021521A1 - Polymer material printing method - Google Patents

Abstract

A method providing monochrome or multicoloured printing of polymer materials to be optionally subjected to anamorphosis by the dry hot sublimation of pigments from release paper. For this purpose, transfer is performed at below-normal pressure.

Description

 PROCESS FOR PRINTING POLYMERIC MATERIALS

The subject of the invention is a process for printing mono or polychromic quality plastic materials based on polymers, rigid or semi-rigid which it is then desired to thermoform or not, and the products thus obtained.

By extension, the invention also applies to rigid or semi-rigid supports made of any material which has been previously coated with a varnish - film or polymeric coating - and which one wishes to print before a transformation of form other than thermoforming, such as stamping ...

At the present time and by way of example, to print decorative and advertising patterns on thermoformed plastic packaging, the food industry uses two technical solutions:

1) The first one, which mainly concerns thermoformed yogurt jars and joined in packs of several jars, consists of laminating - after thermoforming - on the parts of the object that one wishes to decorate, a label or banner made of preprinted paper. This solution requires the addition of a pre-printed paper support and the carrying out of a laminating operation which can only be carried out on smooth cylindrical surfaces and not on more complex surfaces.

2) The second which concerns the individual pots consists - always after thermoforming - of printing the parts to be decorated by means of printing techniques such as offset dry or flexography, which consists of scrolling each pot individually against printing rollers fitted with plates engraved and inked with the corresponding colors. This second solution does not, however, make it possible to print several jars which are joined together.

Furthermore, the decorative patterns obtained by these techniques are easily scratched and are sensitive to external aggressive agents (solvents for example).

3) Another example which the applicants have been confronted with is that of textured (non-smooth) panels of all sizes, made of rigid polymers thermoformed after printing, which are used for dubbing transport vehicles and which are decorated by screen printing. .

Here too, the patterns obtained on the surface of the material are easily scratched and sensitive to wear or to solvents, which in this case is more critical due to the necessary longer lifespan of these products compared to lost packaging such as than yogurt pots.

The applicants directed their research towards a printing technique - before thermoforming likely:

1) to authorize the printing of polychromic patterns resistant to wear and to solvents and not sensitive to heat during thermoforming,

2) to be inserted, whatever the type of object to be produced, in a mass production line, without modifying the flow rate, 3) to allow the greatest flexibility with regard to the subsequent modification of the printing patterns, without causing any modification of the production line, therefore without any additional cost,

4) to arrive at a technical solution where the correction of the printing patterns linked to the deformation of the thermoforming of the material is:

- independent of the production chain; faithful, therefore without alteration, as for the restitution of the decorative or advertising motif as one wishes to see it appear on the object to be produced, and this whatever the * complexity of its form.

In the textile industry, for polyester fiber fabrics which it is desired to print, there is a technique for printing by transfer of sublimable inks when hot (between 140 degrees C and 300 degrees C). This already old technique is described in particular in French patent No 1223330, and it has not stopped being improved since.

It consists in first of all carrying out a mono or polychromic impression on a paper support by using dyes which sublime hot.

The sublimation transfer operation is carried out by placing the printed paper and the virgin fabric in close contact around a drum heated to 200 degrees C. The delamination of the paper after sublimation takes place immediately at the pressure outlet, and this continuously. The pre-printing operation of the paper support to be transferred is carried out in a conventional manner and is independent of the printing of the fabric.

Due to the sublimation of dyes in the fabric, there is penetration of these into the polyester and the patterns thus obtained are therefore perfectly integrated into the final support, without alteration, and are resistant to various aggressions (washing, wear, solvents, heat ...)

When this same type of printing is carried out on a rigid plastic support, it is necessary to carry out this between two flat supports (metal trays), which are heated by a suitable means, and then exerts pressure on the paper and the plastic to be decorated.

For example, French patents No 2230794, 2521489, and English patents No 2120168 in their descriptions, specifically seek to use this printing technique on rigid or semi-rigid flat supports.

Applicants have found that these solutions are limited to the printing of defined materials made of homogeneous synthetic materials.

When we try to print composite plastics, consisting of several superimposed polymers obtained by coextrusion, the materials obtained as commonly used in industry, no longer meet the conditions defined in the patents mentioned above . Or made of the temperatures used (200 degrees) and the transfer time equal to or greater than one minute, rigid or semi-rigid materials generally used in industry (food industry for example) soften and expand resulting in elongation of the product and burrs outside the pressing supports, which causes dimensional variations which prohibit the faithful reproduction of the desired decorations. Furthermore, due to the pressure exerted on the material which tends to expand, the transfer paper adheres to the material after cooling. The solution indicated in French Patent No. 2230794, which consists of delaminating the paper from the material to be decorated before cooling, is not suitable, because this operation will stretch the still soft material by deforming it, which causes distortion of the patterns of decor and material itself.

In addition, none of these patents deals with printing on a flat support intended to be set in volume by thermoforming or stamping.

The present invention aims to solve the aforementioned problems.

To this end, the subject of the invention is a process for mono or polychromic printing of polymeric materials by hot and dry sublimation, for example by bringing the material to a temperature between approximately 140 degrees C and 300 degrees C for a duration of the order of one minute, of pigments from a transfer paper characterized in that the transfer takes place under a pressure less than the normal pressure, and preferably less than about 0.8. 10 ⁵ Pa.

Printing can in particular be done on sublimable semi-rigid materials by winding the material and the transfer paper in a reel which is steamed at said pressure below normal pressure. The applicants have found that by creating a vacuum hot between 140 degrees C and 300 degrees C between the planar material to be decorated and the printed paper, the following unexpected results were obtained: - the polymeric plastic materials soften without sinking or drooling even at high temperature and for periods equal to or greater than one minute, the transfer of sublimable dyes is carried out without alteration of the printing patterns and colors,

- the dyes penetrate the plastics thus ensuring the desired properties of resistance to friction and to solvents, - the transfer paper does not adhere to the support after cooling.

In addition, when it comes to sublimable plastic materials or covered on the surface with a sublimation-sensitive layer, the use of vacuum for flexible materials which are wound in reels with transfer paper , and this, in a closed oven kept hot, allows the transfer of sublimable dyes without altering the patterns and colors. After cooling, the paper does not adhere to the material, which allows after removal from the coil of the oven, delamination of the paper and the perfectly decorated and undistended material.

The process therefore adapts as well for rigid or semi-rigid planar products as for semi-rigid products which are wound in coils.

The material can, after printing, undergo any shape transformation such as thermoforming, stamping, ...

The solution to the problem of correcting printing patterns linked to the modification of shapes by thermoforming, or other process of transformation of the shape, has also been the subject of numerous research. For example, French patents No 2403201 and No 2469161 refer to it, but the solutions provided are, or very fragmentary or adapted to a particular implementation (molding). They are not independent of the object or its implementation chain.

To achieve the desired result, the patterns to be printed are subjected to a shape transformation, in particular by orthophotography and photographic straightening. Such techniques, in which the deformations of an object are determined numerically, and computerized digitization to automatically restore the plane image to be obtained, are known in the field of cartography by aerial photographs.

These seek, in fact, to correct the local variations in scales linked to the reliefs and the inclination of the shots.

These techniques are known by the name "orthophoto¬ graphie- ¹ and consist of successively performing the following operations:

- aerial shots of the subject,

establishment of a digital model thereof by digitizing the contour lines from a photogrammetry model and which is subsequently processed by computer,

restitution by "orthophotographic" transformation thanks to a numerically controlled projector,

The applicants were able to show that such an image correction technique is adapted to the problem of printing deformation due to thermoforming, as follows:

realization on the material to be thermoformed of the printing of a numbered millimeter fin,

- thermoforming of the material according to a standardized and reproducible procedure,

- realization of the photographic shooting and restitution of the nodes of the grid of mesh for a given interval, related to the desired precision, with a digital recording,

- identification of thermoformed surfaces to determine the deformation of the image,

- creation by the "orthophotographic ¹¹ " method of grids having undergone the reverse transformation,

printing on an identical material, of a well-marked non-regular grid, which results from this transformation,

- thermoforming of this material so as to note that all of the previously defined surfaces no longer have significant deformations.

It is understood that by this methodology, and for a given thermoformed object, one obtains once and for all the numerical determination of the corrections of the deformations; this digitization can then be computerized, thus making it possible to automate the reproduction of a plane image from patterns produced on the object to be decorated. There are, for example, computerized three-dimensional vision devices making it possible to establish the spatial coordinates of an object and of the patterns which appear on its surface; in order to achieve great precision, use is made in particular of an optical laser device which can scan the surface of the object.

By correcting the numerical values obtained by such vision devices, and this, by the values established as we have specified above, one can obtain the image which will have to be printed on the transfer paper. .

The applicants were therefore able, by the combination and adaptation of means which are:

the establishment, independently of the thermoforming chain, of the corrected planar image, linked to the deformation of the patterns, by means of the process which has just been described above,

the printing of this image, with hot sublimable inks on dry transfer support, adapted to the material to be thermoformed,

placing under vacuum between the plates or belts where the material to be treated and its transfer support will pass, while heating them with the temperature and the time necessary for the transfer of the patterns,

delamination after cooling of the transfer paper support and of the material before thermoforming, - the thermoforming of the material from which result the objects in volume reproducing the desired original decorations,

ensure the quality and productivity objectives corresponding to the existing equipment.

The products obtained by this process are unique, due to the penetration of the inks into the material, giving the transferred patterns the qualities of resistance to friction and to solvents.

The process applies to any form of object that one would obtain on a thermoforming line, and one can, like what is done in the textile industry, independently print the supports of dry transfers, even outside the factory, using the "computer-aided printing" method described above. For an object of a given shape, the modification of the decoration patterns is flexible and rapid thanks to the computerized and automatic processing.

The process can easily be inserted into a continuous or discontinuous production line, it suffices to adapt the length of the metal or plastic mats resistant to heat, heating and the running speed of the production line, depending the temperature and the duration of treatment, themselves linked to the material to be therioformed, to the sublimable inks used, and to the nature of the dry transfer medium.

In the case where the material to be transformed is semi-rigid and sufficiently flexible to be wound in reels with the paper transfer support, the process also applies. The operation of evacuating and transferring sublimable hot inks can be carried out in a continuous process, immediately after extrusion when the material is still pasty, thus giving an entirely continuous printing and thermoforming process.

By extension, the process can also be applied to other shape transformations than the thermoforming of rigid or semi-rigid materials, and to any materials provided that they are coated with a polymeric varnish or a film. on which the technique of printing by means of sublimable inks is possible.

There will now be described, without implied limitation, examples of implementation of the method according to the invention with reference to the appended drawings in which:

FIG. 1. is a schematic cross-sectional view of the device used,

FIGS. 2a 2b and 2c represent one of the steps of example 1,

and Figures 3a, 3b and 3c show another step in this example.

The device of FIG. 1 comprises two rigid plates 1 and 2. The lower plate 2 has orifices 3 connected by pipes 4 to a vacuum pump 5.

A heating device 6 is arranged on the plate 1 and under the plate 2. The plastic sheet 7 is placed on the plate 2 surmounted by the sheet of transfer paper 8. A silicone seal 9 is placed between the two plates 1 and 2 at their periphery so as to produce a sealed enclosure 10 between the two plates .

A vacuum of the order of 0.75 × 10 ⁵ pascal is then produced in the enclosure 10 using the pump 5 and the heating means 6 are actuated so as to bring the sheets 7 and 8 to a temperature of l 'order of 200 degrees C for about a minute.

After this operation, the printing of the plastic sheet 7 is carried out, and the sheets 7 and 8 can be separated after cooling.

Of course, this process can be implemented continuously, for example between an extruding machine and a thermoforming machine.

Examples 1

Three objects in volumes were treated according to the process described above:

- a parallelepiped (Figures 2a and 3a) a cupola (Figures 2b and 3b) a cup in the shape of a yogurt pot (Figures 2c and 3c)

(Shaped objects commonly used in the food industry).

The different stages of treatment are as follows: 1. Choice of a material in plastic sheets to thermoform (sheets of 90 cm x 65 cm).

2. Monochrome (black) printing - before thermoforming - of a numbered millimeter mesh on the plastic sheets according to a conventional printing mode (identical to printing a paper sheet).

3. Production of three molds corresponding to the three shapes defined above.

4. Thermoforming of the millimeter plastic sheets on these three molds.

The shapes shown in Figures 2a, 2b and 2c are obtained.

The stability of deformations on thermoformed surfaces is perfect to the nearest 0.5 mm.

5. Shots and measurement of the grid nodes.

5.1. Each object is photographed from 3 different viewpoints x, y, z, located at

1.50 m from its center.

5.2. Digitization by half-centrimetic profile for each face from each x, y, z point of view, which gives rise to files on magnetic tape, organized as follows:

n profiles, x, y, z, x, y, z support points are recorded around each shape and identified on the thermoforming. 6. Identification of the chosen surfaces on the objects

6.1. Retrieving the profiles saved on the magnetic tape files to make one file per side:

n profiles number of points x y z x y z x y z the scanning was done on an Eclipse DC mini-computer. These files are not "rectangular".

6.2. From a central profile spotted by hand, we choose to keep a certain number of profiles on both sides, and points along the profiles, this constitutes a "regular" file.

No profile number of points x y z, xy z, y z,

6.3. The figures obtained being regular (m profiles of n points), exploitation of the profiles thanks to orthophotography.

The files are used for the constitution of the orthophotography control strip, this strip contains the transformed coordinates of the points of all the profiles.

7. On each zone, generation of an ortho-photographic film treating differently 2 types of deformation: 7.1. Flat face - parallelepiped.

7.2. Circular faces - dome, cylinder.

The transformation to be applied at each point must ensure the deformation opposite to that of thermoforming.

The transformation is the projection on the face to be deformed.

7.1. Calculation of the characteristics of the plane of the plane face. We take a part of the coordinates of 3 points of the face, we determine the normal to the face and from there the angles characterizing an orientation of space, then we project each point on the plane.

7.2. We choose for these 2 forms - dome, cylinder - the projection on a cylinder tangent to the form.

Calculation of the cylinder axis: we take

"handcrafted" the barycenter of the upper face, then we project each point on the cylinder.

8. We choose among the files appearing on the magnetic strip, those which allow processing by orthophotography, that is to say those whose transformed coordinates have the value of the coordinates of the points of the face.

Films are produced according to the orthophotography method. In these films, there are millimeters having undergone the reverse deformation - after ther oformage, the millimeter will become regular on the selected areas.

The films are then mounted at their location on the millimeter which will be printed as described with reference to Figure 1, then thermoformed by any known means.

These examples demonstrate that the method according to the invention makes it possible to reveal printed patterns which are not deformed on a thermoforming which is carried out after printing on the determined material.

Examples 2

- Two objects in volume were treated to obtain pre-defined shapes decorated in polychromy.

- a box intended to contain cosmetic products and decorated in the colors of the perfumer (not shown) a sink for aircraft, coach, ... decorated in the colors of the transport company (not shown).

1. Choice of a plastic sheet material corresponding to the uses specified above, and the surface of which consists of a sublimable polymeric layer (polyester for example).

2. Full color printing of sheets of paper with sublimable ink. 3. Wedging between two rubber mats of a blank plastic sheet and a printed sheet of paper.

Vacuum created between the two mats, then heating to 200 degrees C (using radiant heaters arranged over the entire surface of the mat), for a period of one minute of the materials caught between the two mats.

Cooling to room temperature and delamination of the paper.

4. The flat plastic sheets are sublimated in polychromy, reproducing identically the original decorations.

5. Introduction of flat and printed plastic sheets to thermoform, in the molds, after location.

Thermoforming of printed plastic sheets.

Obtaining 2 objects in volume decorated in polychromy.

The two objects were anamorphic, showing distortion rates from 1 to 5, and the colors obtained are faithful despite the irregular anamorphosis of the subjects.

The intensity of the colors is nowhere altered by the anamorphosis.

No cracks appear, neither on the distended surfaces, nor on the angular forms. Examples 1 demonstrate the effectiveness of the process which makes it possible to reveal printed patterns which are not deformed after ther oformage.

Examples 2 demonstrate that the anamorphosis respects the colors of the original decorations as soon as the printing is done by sublimation before thermoforming.

The final object obtained after shape transformation can be smooth or textured, of regular or irregular shape, convex or concave.

Claims

1. A method of producing objects in volume decorated with patterns, from sheets of polymeric materials, characterized in that the patterns are subjected to. To cause a geometric transformation to appear, that the pattern is printed transformed on said sheets by hot and dry sublimation of pigments from a transfer paper at a pressure below normal pressure, and which is effected after printing a shape transformation of said sheet, such as thermoforming or stamping, giving its volume to said object and restoring the shapes of the original pattern, said geometric transformation being the reverse of the shape transformation. 2. Method according to claim 1 wherein the transfer is carried out at a pressure of less than approximately, 0.8 × 10 ⁵ Pa. 3. Method according to any one of claims 1 and 2, wherein the transfer is carried out by bringing the material to a temperature between about 140 degrees C and about 300 degrees C for a period of the order of one minute. 4. Method according to any one of claims 1 to 3, in which the delamination of the transfer paper takes place after cooling. 5. Method according to any one of claims 1 to 4, in which the printing is done on semi-rigid materials which can be sublimated by winding the material and the transfer paper in a reel which is steamed at said pressure below the normal pressure. Method according to any one of claims 1 to 5, in which the geometric transformations are obtained by photogrammetric calculation and rectification of the pattern by orthophotography. Method according to any one of claims 1 to 6, used continuously at the outlet of the machine for extruding the polymeric material while the material is hot. 8. Method according to any one of claims 1 to 7, used continuously at the entrance to a thermoforming machine. 9. Method according to any one of claims 1 to 8, in which the printing of a millimeter mesh is carried out on the material to be thermoformed, the material is thermoformed, the positions of the mesh are determined after its shape transformation by direct measurements in three-dimensional space, we create a grid of the inverse geometric transformation of the shape transformation, using measurements, we deform the pattern to be printed according to this grid, we print the pattern thus deformed on a flat material and we thermoform this material .