Process and apparatus for registered embossing of extensible printed film or of a laminate comprising an extensible printed film

Abstract

In an embodiment, a process for synchronized embossing of an extensible printed film or of a laminate product including an extensible printed film is disclosed. The process includes pre-heating the film; possible coupling of the pre-heated film with a substrate; passage of the film or of the laminate between an engraved embossing cylinder; and a pressing counter-cylinder, in which the extensible film is subjected to a controlled elongation, in the longitudinal direction only, during the pre-heating step, during which the film is in a thermoplastic state, and said controlled elongation is such as to synchronize the decoration printed on the film with the position of the embossing cylinder.

Claims

1. A process for synchronized and continuous embossing of an extensible printed film or a laminate including an extensible printed film, wherein the extensible printed film is printed with a decoration having a pitch of repetition (printing pitch), and includes a plurality of reference marks printed on the extensible printed film, the process comprising: a first step of pre-heating the extensible printed film; embossing the extensible printed film by means of the action of at least one engraved rotary embossing cylinder; acquiring a measure which is directly or indirectly correlated to the angular position of the at least one engraved rotary embossing cylinder relative to at least one reference mark of the extensible printed film; while pre-heating a portion of the extensible printed film, subjecting the portion of the extensible printed film to a controlled elongation by passing the extensible printed film around at least two adjacent pairs of cylinders prior to the at least one engraved rotary embossing cylinder, the adjacent pairs of cylinders having different respective peripheral speeds, the extent of the controlled elongation being determined as a function of the measure, and such as to bring the decoration printed on the extensible printed film in registration with respect to the angular position of the at least one engraved rotary embossing cylinder; wherein the controlled elongation is obtained through a deformation of the portion of the extensible printed film in a longitudinal direction of advance motion of the extensible printed film, and the deformation of the portion of the extensible printed film having a substantially null component in the transversal direction substantially perpendicular to the longitudinal direction, so as to leave the width of the film unaltered; and wherein the embossing cylinder having an outer circumference for contact with the extensible printed film that is greater than the printing pitch of the extensible printed film.

2. The process according to claim 1 wherein the measure of the relative position between the extensible printed film and the at least one engraved rotary embossing cylinder comprises detection of the relative position between the at least one reference mark printed on the extensible printed film, and an impression generated by the at least one engraved rotary cylinder on the extensible printed film.

3. The process according to claim 2, further comprising at least one of: detecting the position of the at least one reference mark printed on the extensible printed film, carrying out the detection before the controlled elongation step; detecting an impression generated on the extensible printed film; or detecting the position of a reference associated directly with the at least one engraved rotary embossing cylinder.

4. The process according to claim 3 wherein at least one of the at least one reference mark on the extensible printed film, the position of the impression, or the position of the reference associated directly with the at least one engraved rotary embossing cylinder is detected by means of optical reading.

5. The process according to claim 1 wherein the adjacent pairs of cylinders include a first pair of pre-heating cylinders and a second pair of pre-heating cylinders, and the controlled elongation of the portion of the extensible printed film is caused by at least a stretching of the portion of the extensible printed film during the passage from the first pair of pre-heating cylinders, having a first peripheral speed, to the second pair of pre-heating cylinders, having a second peripheral speed greater than the first speed.

6. The process according to claim 5 wherein the controlled elongation is also caused by a change of temperature between the first pair of pre-heating cylinders and the second pair of pre-heating cylinders, the first and the second pairs of pre-heating cylinders having a temperature higher than room temperature and such as to take the portion of the extensible printed film to a plastic state.

7. The process according to claim 1 wherein the embossing is carried out directly on the extensible printed film, obtaining a printed and embossed extensible printed film.

8. The process according to claim 1, further comprising coupling the pre-heated printed film with a substrate, thereby producing a laminate.

9. The process according to claim 8 wherein the embossing is carried out on a laminate comprising the extensible printed film coupled with the substrate.

10. The process according to claim 8 wherein the measure of the relative position between the extensible printed film and the at least one engraved rotary embossing cylinder comprises detection of the relative position between the at least one reference mark printed on the extensible printed film, and an impression generated by the at least one engraved rotary embossing cylinder on the laminate comprising the extensible printed film.

11. The process according to claim 10, further comprising at least one of: detecting the position of the at least one reference mark printed on the extensible printed film, carrying out the detection before the controlled elongation step; detecting an impression generated on the laminate; or detecting the position of a reference associated directly with the at least one engraved rotary embossing cylinder.

12. An apparatus for embossing an extensible printed film or a laminate including an extensible printed film, the apparatus comprising: a section for pre-heating the extensible printed film; a section for embossing the extensible printed film the section comprising at least one engraved rotary embossing cylinder, the section for embossing the extensible printed film being downstream of the section for pre-heating; measuring means arranged to acquire a measure correlated directly or indirectly with the angular position of the embossing cylinder relative to at least one reference mark printed on the extensible printed film; and means for stretching the extensible printed film disposed in the section for pre-heating the extensible printed film, as the extensible printed film is pre-heated, and control means associated with the stretching means, arranged to subject the extensible printed film to a controlled elongation during pre-heating, and the extent of the controlled elongation being determined by the control means as a function of the measurement, with the effect of registering the position of the decoration printed on the extensible printed film with respect to the embossing cylinder; wherein the stretching means is located upstream from the section for embossing and the at least one engraved rotary embossing cylinder, the stretching means includes adjacent pairs of cylinders, and the stretching means is suitable for applying a purely longitudinal deformation of the extensible printed film, in the direction of forward motion of the extensible printed film itself, and with a substantially null component in the transversal direction, so as to leave the width of the extensible printed film unaltered during stretching; and wherein the at least one engraved rotary embossing cylinder has an outer circumference of contact with the extensible printed film, which is greater than the printing pitch of the extensible printed film.

13. The apparatus according to claim 12 wherein the measuring means comprise at least one of the following: a sensor arranged upstream of the pre-heating section, and configured to detect the passage of reference marks printed on the extensible printed film; a sensor arranged to detect the position of a reference directly associated with the at least one engraved rotary embossing cylinder; or a sensor arranged to detect the passage of an impression generated by the embossing cylinder on the extensible printed film.

14. The apparatus according to claim 12 wherein the adjacent pairs of cylinders of the means for stretching the extensible printed film comprise at least a first pair of pre-heating cylinders, during use having a first peripheral speed, and a second pair of pre-heating cylinders, during operation having a second peripheral speed greater than the first speed, so that the extensible printed film undergoes a longitudinal stretching during the passage from the first pair of pre-heating cylinders to the second pair of pre-heating cylinders.

15. The apparatus according to claim 14 wherein the first and the second pairs of pre-heating cylinders, have different temperatures during operation.

16. The apparatus according to claim 12, further comprising a coupling section for coupling the pre-heated extensible printed film with a substrate obtaining a laminate, the coupling section being downstream of the pre-heating section.

17. The apparatus according to claim 16 wherein the at least one engraved rotary embossing cylinder has an outer circumference in contact with the laminate, which is greater than the printing pitch of the extensible printed film.

18. The apparatus according to claim 16 wherein the measuring means comprises a sensor arranged to detect the passage of an impression generated by the at least one engraved rotary embossing cylinder on the laminate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a diagram of a continuous registered embossing process according to an embodiment of the invention. The figure schematically shows an apparatus for continuous embossing comprising an engraved cylinder and a pressing counter-cylinder.

(2) FIG. 2 schematically shows a positioning error of an embossing impression with respect to a printed mark, the detection of which is used to determine the controlled elongation of the film and/or a transversal centring.

(3) FIG. 3 shows a diagram of a process according to another embodiment of the invention in which an extensible film is coupled with a substrate to form a laminate, subsequently embossed.

(4) FIG. 4 shows another embodiment of the invention in which the last cylinder of the pre-heating step also represents the coupling cylinder between film and laminate.

(5) FIG. 5 shows an example of a film with a print that imitates wood, highlighting the printing pitch.

DETAILED DESCRIPTION

(6) FIG. 1 is a scheme of a process according to an embodiment of the invention in which an extensible film F passes through a pre-heating section 100 and then passes through an embossing section 200.

(7) The film F can be made for example from PVC. Said film F carries a printed decoration that repeats with a printing pitch (also known as development) determined essentially by the diameter of a cylinder previously used for printing. For example FIG. 5 shows a wood-like decoration that repeats with a printing pitch A. The example indicates sections 10 of width equal to the pitch A, after each of which the pattern is repeated, and separated by joining portions 11, if intended for cutting like in the case of laminates produced for imitation wood flooring.

(8) Going back to FIG. 1, the pre-heating section 100 includes a series of pre-heating cylinders. Preferably, the cylinders are arranged in pairs or groups. In the example six cylinders namely three pairs are depicted, indicated with reference numerals 101 to 106. The pre-heating cylinders 101-106 have a small diameter, more preferably about 150 mm. The symbols V.sub.1, . . . V.sub.n and T.sub.1, . . . T.sub.n denote the peripheral speeds and the temperatures of said cylinders.

(9) The embossing section 200 essentially comprises an engraved embossing cylinder 201 and a counter-cylinder 202. The surface of the engraved cylinder 201 comprises suitable reliefs that, by contact, generate a pattern in relief on the surface of the suitably heated film F. The diameter of the cylinder 201, or rather its circumference, determines a pitch of the embossing. The counter-cylinder 202 is normally coated with rubber and is used to apply an embossing pressure. For example, said counter-cylinder 202 is connected to a hydraulic thrusting system, which can be made according to a known technique; said thrusting system is not essential for the purposes of embodiments of the present invention and it is not further described.

(10) The film F is fed with a linear speed of advance motion V.sub.1 and initial temperature T.sub.0. The embossed film leaving the engraved cylinder 201 has a speed generally indicated with V.sub.n (corresponding to the peripheral speed of the cylinder 201) which is greater than V.sub.1.

(11) The film F comprises a series of reference marks generated during the printing process and readable by suitable sensors, typically by optical reading. In FIG. 1, the distance L denoted the distance between two contiguous reference marks, measured upstream of the pre-heating section 100, that is upstream of the first cylinder 101. Said distance L can be measured, for example, with a mark reader 401.

(12) Said distance L in practice differs from the theoretical nominal distance between two marks (that is from the distance between the marks as generated in printing), being affected by an error (unknown) due to the causes that have been mentioned above and that include excessive tractions or shrinkage, over-heating, possible storage for a long time and/or at too high temperatures, etc.

(13) The speeds and/or temperatures of the cylinders 101-106 are determined so that, while passing in the section 100, the film F undergoes a controlled elongation L. Through the effect of this controlled elongation (also termed stretching), the distance between the same two marks assumes a value (L+L) downstream of the pre-heating section, and at the entry of the embossing section 200.

(14) During the process, the extent of the elongation L is controlled in such a way that said increased distance (L+L) is constant and in synchrony with the engraved cylinder 201. In other words, the variable elongation L absorbs the unknown deformation that initially affects the extensible film F, restoring the desired synchrony between the decoration already present on the printed film, and the embossing applied by the cylinder 201. More specifically, the distance (L+L) between two marks is equal to the outer circumference of the cylinder 201, providing the contact with the film F, said condition being necessary to maintain the synchrony between embossing process and printed decoration.

(15) Therefore, the controlled elongation L is not constant but can be continuously adjusted by varying the speeds and the temperatures of the pre-heating cylinders. In a preferred embodiment, the extent of said elongation L is calculated continuously with a feedback effect.

(16) The stretching of the film F takes place mainly through the effect of one or more accelerations of the transportation speed of the film. Acceleration takes place when the film F passes from a slower cylinder to a faster cylinder, in terms of peripheral speed.

(17) In the example of FIG. 1 the film F is conveyed to the section 100 with an initial linear speed V.sub.1 and initial room temperature T.sub.0 (not yet suitable for the stretching of the film). The cylinders 101 and 102, which form the first pair of cylinders, have a peripheral speed equal to said initial speed V.sub.1 and therefore do not stretch the film, but they have a temperature T.sub.1 that takes the film to a plastic state. The cylinders 103, 104 of the second pair, on the other hand, have a peripheral speed V.sub.2>V.sub.1, so that the film F undergoes a stretching substantially in the short passage area 109 where it leaves the contact with the cylinder 102, and before adhering to the subsequent, faster cylinder 103. Said stretching coincides with a proportional decrease in thickness of the film, to respect the continuity of the material.

(18) A second stretching, in an analogous way, takes place in the passage area 110 between the second pair of cylinders 103, 104 and the third pair of cylinders 105, 106, where the temperature of the film is further increased to T.sub.2. Said third pair has a final peripheral speed V.sub.n that equals the output speed of the section 100 and the peripheral speed of the cylinder 201, at a temperature T.sub.n which suitable for embossing or, in another case (FIG. 3), for coupling with the substrate.

(19) The closeness between the cylinders 102 and 103 (104 and 105, respectively) ensures that the film does not undergo a transversal necking (loss of width). Indeed, the film is particularly exposed to the undesired phenomenon of necking in the passage area, where it is free and not in contact with a cylinder; said area therefore is reduced to the essential minimum, bringing the said cylinders as close together as possible.

(20) In this example, consequently, the desired elongation L is the sum of two contributions or stretchingsa first stretching L.sub.1 in the area 109 and a second stretching L.sub.2 in the area 110, respectively. In other embodiments the number of said stretchings can be just one, or even greater than two. For example, in a simplified embodiment there is a group of cylinders with peripheral speed equal to the input speed V.sub.1 and a second group with peripheral speed equal to the output speed V.sub.n.

(21) Each cylinder 101-106 or group of cylinders preferably has its own motors and/or transmission means and its own heating means, so that the cylinders (or groups) can have respective peripheral speeds V.sub.1, . . . V.sub.n and temperatures T.sub.1, . . . T.sub.n that are independent. A control system controls the speeds and temperatures of said cylinders or groups of cylinders.

(22) It should be noted that in FIG. 1 the section 200 is distanced from the cylinder 106 for the sake of representation; in practice, the cylinders 202, 203 are preferably in the immediate vicinity of the exit of the pre-heating section, i.e. close to the cylinder 106, to avoid leaving a portion of film without contact and therefore consequent risk of loss of width.

(23) The extent of the overall elongation L to be applied to the film is calculated based on a measurement of the relative position of the engraved cylinder 201 with respect to the film F or, more precisely, with respect to the decoration printed on the film itself. Said measurement can be acquired with suitable readers.

(24) The example of FIG. 1, for this purpose, shows: a first reader 401 upstream of the pre-heating section 100; a second reader 402 downstream of the embossing section 200; a third reader 403 located in the vicinity of the engraved cylinder 201.

(25) The first reader 401 is arranged to detect the passage of the marks printed on the film F, and allows the measure of the distance L. The second reader 402 is arranged to detect an embossing impression generated by the cylinder 201 on the film. The third reader 403 is arranged to directly detect the position of the cylinder 201, reading a reference 203 fixedly connected to the cylinder itself, and is also used for the pre-registering operation when production is started and every time the printed film has a junction.

(26) Preferably the readers 401 and 402 are optical readers; the reader 403 can be an optical reader as well, or possibly a magnetic reader sensitive to proximity passage of the reference 203.

(27) FIG. 2 schematically illustrates the regulation principle according to one of the embodiments of the invention. On a film F going from left to right according to the direction A, the figure shows a mark M printed on the extensible film and an embossing impression G generated by the cylinder 201. The mark M is first read by the reader 401 while the position of the impression G relative to the mark M is read by the reader 402. The example of FIG. 2 shows a positioning error of the impression G, corresponding to a synchrony error to be corrected. Said impression G is decentred with respect to the printed mark M by a longitudinal error E.sub.L and by a transversal error E.sub.T; the longitudinal error E.sub.L can be corrected with an increase in the described controlled elongation (L) of the film F; the error E.sub.T can be corrected by means of a transversal centring group (which is per se known and not illustrated) situated upstream of the pre-heating section 100.

(28) FIG. 3 refers to a second embodiment of the invention, where the film F is coupled with a substrate S, obtaining a laminate product LM. The coupling between film and substrate takes place in a station 300 comprising two cylinders 301 and 302, upstream of the embossing section 200. Like in the previous case and for the sake of ease of representation, the station 300 is depicted distanced from the last pre-heating cylinder 106, but preferably the cylinder 301 is as close as possible to said last pre-heating cylinder.

(29) The optical reader 402 in this second embodiment is situated downstream of the coupling cylinder 301. In other words, the centring measurement schematised in FIG. 2 is carried out immediately downstream of the coupling station 300.

(30) It should be noted that the controlled elongation of the film is carried out before the coupling (upstream of the station 300) since after coupling with a fibreglass reinforced substrate S, the laminate becomes inextensible and the correction would no longer be possible. The laminate LM therefore is delivered to the embossing section 200 already in a registered state, apart from a fine correction that can be made by acting on the angular position of the cylinder 201.

(31) In other words, the controlled stretching step is always carried out between the cylinders 101-106; the control step of the stretching is carried out at the exit of the coupling group 300 through the reader 402. This ensures that the reference marks (i.e. the printed decoration) has the correct pitch and position on a film that has become no longer extensible due to the coupling with an inextensible substrate.

(32) After the subsequent embossing step, readers 403, 404 are associated with the embossing station 200. The cylinder 201 has an impression generator, accompanied by an optical reader 404 and by a mark reader 403 fixedly connected to the cylinder itself, to carry out a verification and fine registering, intervening to correct a longitudinal error E.sub.L with a variation of the described controlled elongation (L) of the film F, and/or an error E.sub.T by means of a transversal centring group (per se known, not illustrated) situated upstream of the pre-heating section 100. The mark reader 403 is also used for the pre-registering operation each time production starts and each time the printed film has a junction.

(33) FIG. 4 shows a variant in which the coupling cylinder 301 coincides with the last cylinder of the pre-heating section 100, i.e. it replaces the cylinder 106 of FIG. 1 and FIG. 3.