Films for the transfer print

Description

[0001] The present invention relates to new films for the use in the transfer print through colour sublimation.

[0002] More specifically it relates to films which are used in the transfer print preferably on tridimensional articles, in particular having curved surfaces, such as for example pendant lamps or bell-shaped lamps, pots, bottles, plates, etc., or having irregular surfaces, such as for example ornamental articles.

[0003] It is known in the prior art that the transfer print on tridimensional articles having curved surfaces is carried out by techniques which allow, by applying vacuum, the complete adhesion of the film with the drawing to be transferred to the tridimensional support which is to be printed. For this kind of transfer print a rubber membrane, under the form of a case, can be used, in which the film to be printed, placed on the support which is to be printed, is introduced. Vacuum is made in the membrane and then it is transferred in an oven at a suitable temperature, so as to obtain the print by colour sublimation. This print technology of tridimensional articles has the drawback that the adhesion between the support and the film can vary depending on the article shape, wherefore the obtained article may show print defects. Besides the membrane must be periodically replaced with a frequency depending on the use conditions, for example on the temperatures at which the transfer print occurs, on the mechanical wear of the rubber by which the membrane is formed, etc. Another technology available on the market used in the transfer print by colour sublimation is the so called bag technology, wherein the vacuum is directly created inside the film. The film forming substance must have suitable mechanical properties to this purpose. The article to be printed is wrapped in the printed film which is sealed on one edge, for example by an adhesive or ultrasounds. The print quality on the tridimensional article depends also on the film flexibility. Furthermore, by using a film with unsuitable adhesion features during the vacuum creation step, folds in the film can form, or small air bubbles can be held between the film and the article. In these cases the print defects on the printed article are such that the obtained article has to be duscarded.

[0004] In EP 921,014 in the name of the Applicant, the transfer print by colour sublimation is made by a composite film formed of a polymer film, which is metallized on one side with a thin aluminum layer, on which the colour drawing to be transferred is printed. The film allows to obtain the colour transfer with a high imagine definition and high chromatic yield. However the Applicant has found that by using this film to print tridimensional articles having curved surfaces, by the so called bag vacuum technology above mentioned, the film sometimes does not result perfectly adaptable to the particular shape of the article, wherefore the obtained print is defective.

[0005] The same drawbacks occur by using as a support of the drawing to be transferred also other substances of the prior art, such as for example paper.

[0006] From the above, it is clear that in order that the transfer print on tridimensional articles having curved surfaces can be made with the utmost definition and can be free from defects, it is necessary that the film has a perfect adhesion to the article, and therefore it must be formed by a substance which remains flexible at the temperature at which the transfer print occurs.

[0007] WO-A 99/O4982 discloses a composite for the print by color sublimation made by an air permeable base film of extensible material, such as a fabric, a superimposed insulating layer (11), on which it is printed the color to be transferred, that can be made by polyvinyl alcohol, paraffin or silicone. DE-A 3 229 288 discloses a composite made by a detachable base layer, that can be made of materials such as plastic, metal or paper; a separation layer, which is optional, that can be made of silicon or polyvinyl alcohol; a coloured drawing that can be printed both on the base layer or on the optional separation layer, or on the intermediate layer; an intermediate layer made of nitrocellulose, plastic, caoutchouc or silicon caoutchouc.

[0008] In this field of the prior art the need was therefore felt to have available a film, having on the surface which comes into contact with the article the printed drawing to be transferred, which put into contact by vacuum, in particular by the bag technology, with any tridimensional article having curved surfaces, warranted the colour transfer with high imagine definition and chromatic yield, without showing the drawbacks of the films used in the prior art for these applications.

[0009] This technical problem has been solved with the film of the present invention.

[0010] An object of the present invention is the use of a film of polyvinyl alcohol (PVA) having a thickness in the range 100-300 µm, and having on one surface a printed drawing to print articles, as described hereinafter, preferably tridimensional articles.

[0011] It has been found by the Applicant that when the film has a thickness lower than 100 µm the chromatic yield of the transfer process decreases and that with a thickness higher than 300 µm no further advantage is obtained as regards the chromatic yield or the imagine definition.

[0012] With chromatic yield it is meant the colour amount transferred on the article with respect to the colour amount which remains on the film after the transfer print. In practice the chromatic yield can be visually observed from the amount and quality of the colour transferred on the printed article with respect to the original one.

[0013] The film of polyvinyl alcohol allows to obtain a tansfer print free from defects such as foldings, imagine definition, on tridimensional articles, independently from their shape, also with curved surfaces.

[0014] The PVA film is obtinable by known processes, such as for example by extrusion, and are available on the market. Another process is for example the following. A PVA solution in granules, as available on the market, is prepared, for example at 30-40% w/v in water, optionally in admixture with a hydroxylated organic solvent, preferably in an amount not higher than 5% by volume, for example aliphatic alcohols C₁-C₃, letting under mechanical stirring for 3-4 hours; the obtained paste is spread by a doctor blade, by using a spreading plant, on a surface of a plastic substance sheet having good mechanical properties, such as a polyester for example polyethylene terephthalate; subsequently, in line, by a suitable equipment, the obtained film is dried in an oven, preferably at about 100°C for about 1-2 minutes. The PVA film is then separated from the plastic substance sheet used as support.

[0015] Preferably the surface of the plastic substance sheet which is spread with polyvinyl alcohol is previously treated with known methods so as to result antiadherent, in order to facilitate the removal of the polyvinyl alcohol film, after the passage in the oven.

[0016] The film of the present invention is used for the transfer print process of tridimensional articles, in particular having curved surfaces, by colour sublimation, by the vacuum technique, preferably by the bag technology, said process comprising the following steps:

a) print of the coloured drawing to be transferred on a surface of the polyvinyl alcohol film, at a temperature in the range 80°-120°C, by mechanical compression, for example in a calender, by putting the polyvinyl alcohol film into contact with a sheet having impressed the coloured drawing with inks having thermoadhesive properties, said sheet being either of plastic substance such as to maintain good mechanical properties at the process temperatures, such as for example polypropylene or a polyester, polyethylene or polybutylene terephthalate type, or of paper,

b) wrapping of the printed film of polyvinyl alcohol around the tridimensional article to be printed and vacuum creation between the film and the article,

c) heating in an oven at 160°-190°C for a time comprised between 3 seconds and 5 minutes, preferably between 30 seconds and 2 minutes,

d) recovery of the printed article and optional separation of the polyvinyl alcohol film.

[0017] After step b) a preheating at temperatures lower than those indicated in step c) can be effected in order to favour the film adhesion to the article. Steps b) and c) of the above described transfer print process can be contemporaneously carried out.

[0018] The sheet used in a) can be printed by using the usual techniques, for example by rotogravure print.

[0019] It has been found by the Applicant that the PVA film cannot be used over 190°C, as it would instead be preferable for lowering the print process times and for obtaining the optimal colour chromatic yield.

[0020] More precisely it has been found by the Applicant that at temperatures higher than 190°C, for example 200°C, the PVA loses its properties and becomes rigid and brittle. In practice the PVA film loses its mechanical properties wherefore the film breaks during the transfer print.

[0021] By using the films of the present invention it is possible to reproduce by the transfer print the drawings on the surfaces of various articles, preferably tridimensional articles having curved sufaces, such as for example articles for pendant lamps, for example glass bells, article-holder boxes, pots, handles, ceiling light fixtures, ornamental articles, plates, etc..

[0022] The following examples illustrate-the invention with non limitative purposes.

EXAMPLE 1

[0023] By compression transfer as indicated in the description, using as a matrix the same red-coloured polyethylenterephthalate sheet on a surface by rotogravure print, a surface of the following films is coloured in red:

A. Polyvinyl alcohol film having a 150 µm thickness;

[0024] The process for preparing film A is carried out as indicated in the specification by using the spreading system by a doctor blade.

[0025] The receiving support is an aluminum sheet pretreated by electrostatic painting with polyester powdered thermosetting paint, having a thickness of 75 µm.

[0026] 3 supports are used for each of the above mentioned films.

[0027] As a colour reference standard, samples formed by the same substance and painted with amounts of colour equal to 100% , 90% , 80%, 70%, 60%, 50 % and 40% with respect to that applied on the samples printed by transfer.

[0028] The colour transfer process is carried out at 180°C for the sample A. The print time by sublimation is 30 seconds.

[0029] The colour transferred on the receiving support is compared with that of the standard ones and classified according to the following scale:

10 =

Intensity of the red colour transferred on the samples of the pretreated aluminum sheet equal to that of the reference standard painted with a red amount equal to that present on the films (100%) before the transfer print.

9 =

Intensity of the red colour transferred on the samples of the pretreated aluminum sheet equal to 90% of that present on the films before the transfer print.

8 =

Intensity of the red colour transferred on the samples of the pretreated aluminum sheet equal to 80% of that present on the films before the transfer print.

7 =

Intensity of the red colour transferred on the samples of the pretreated aluminum sheet equal to 70% of that present on the films before the transfer print.

6 =

Intensity of the red colour transferred on the samples of the pretreated aluminum sheet equal to 60% of that present on the films before the transfer print.

5 =

Intensity of the red colour transferred on the samples of the pretreated aluminum sheet equal to 60% of that present on the films before the transfer print.

4 =

Intensity of the red colour transferred on the samples of the pretreated aluminum sheet equal to 60% of that present on the films before the transfer print.

[0030] Each coloured support obtained by using the above mentioned films is visually compared with the reference standards. By giving the values as above indicated, the following results are obtained:

Aluminum sheet coloured with the polyvinyl alcohol film having a thickness of 150 µm A) : 7;

EXAMPLE 2 (comparative)

[0031] A round-shaped glass bell to be used for pendant lamps, having an height of about 25 cm, a diameter at the base of about 18 cm and of about 8 cm at the top, is printed with one colour drawing formed by a rose-shaped blue-coloured flower.

[0032] A paper support printed by known methods for example by rotogravure print is used.

[0033] The article is wrapped in the paper. The vacuum is made by a membrane device. The transfer print is carried out at the temperature of 190°C for a time of 3 minutes.

[0034] The article is taken away from the oven, cooled and unwrapped from the paper.

[0035] The printed drawing does not show deformations. The print shows discontinuities due to folds formed in the paper during the vacuum formation step.

[0036] The article is not commercially accepted.

EXAMPLE 3

[0037] The same bell of Example 2 is printed with the same drawing, by using a polyvinyl alcohol film having a thickness of 150 µm of Example 1 (film A). The polyvinyl alcohol film is printed with the drawing by using the process described in the present application. The film is wrapped around the article directly in an oven, by an equipment which places the film directly on the article by lowering it from the oven top by tools which maintain the film perfectly horizontal until the film comes into contact with the article. In the oven there are some devices in order to automatically create the vacuum between the film and the bell when the film, lowered from the top, completely covers the article.

[0038] The transfer print is carried out at 190°C and lasts three minutes.

[0039] On the printed article the chromatic yield and the drawing definition result acceptable but the drawing visually appears vertically deformed of about 20% with respect to Example 2. The printed flower clearly results lengthened.

EXAMPLE 4 comparative

Print on a tridimensional article by using a polyvinyl alcohol film having a thickness lower than 100 micron.

[0040] A glass bell equal to that used in Example 2 is printed with the same one-colour drawing formed by a rose-shaped flower. In this case a polyvinyl alcohol film having a thickness of 80 micron is used. The film is applied to the article by using the procedure and conditions described in Example 3.

[0041] It is noticed that the film breaks during the transfer print process.

[0042] The test shows that the film thickness is not sufficient in this case to guarantee the mechanical properties which are required for its use in the transfer print process.

Claims

1. Use of a polyvinyl alcohol film having a thickness in the range 100-300 µm having on one surface a printed drawing for the transfer print of articles by colour sublimation, by the vacuum technique.

2. Use of polyvinyl alcohol according to claim 1 wherein the article has a tridimensional shape.

3. Use according to claim 2, wherein the vacuum technique is the bag technology.

4. Use according to claims 2-3, wherein the tridimensional articles have curved surfaces.

5. A transfer print process wherein it is used a polyvinyl alcohol film having a thickness in the range 100-300 µm, comprising the following steps:

a) print of the coloured drawing to be transferred on one surface of the polyvinyl alcohol film, at a temperature in the range 80°-120°C, by mechanical compression, by putting the polyvinyl alcohol film into contact with a sheet having impressed' the coloured drawing,

b) wrapping of the printed film of polyvinyl alcohol around the tridimensional article to be printed and vacuum creation between the film and the article,

c) heating in an oven at 160°-190°C for a time comprised between 3 seconds and 5 minutes, preferably between 30 seconds and 2 minutes,

d) recovery of the printed article and optional separation of the polyvinyl alcohol film.

6. A process according to claim 5, wherein the sheet with impressed the coloured drawing is of plastic substance or of paper.

7. A process according to claims 5 and 6, wherein steps b) and c) are contemporaneously carried out.

Ansprüche

1. Verwendung eines Film aus Polyvinylalkohol mit einer Dicke im Bereich von 100 - 300 µm, der auf einer Oberfläche einen gedruckten Entwurf für den Transferdruck von Gegenständen durch Farbsublimation mittels der Vakuumtechnik besitzt.

2. Verwendung von Polyvinylalkohol gemäß Anspruch 1, wobei der Gegenstand eine dreidimensionale Form besitzt.

3. Verwendung nach Anspruch 2, wobei die Vakuumtechnik die Sacktechnologie ist.

4. Verwendung nach den Ansprüchen 2 - 3, wobei die dreidimensionalen Gegenstände gekrümmte Oberflächen besitzen.

5. Transferdruckverfahren, wobei ein Film aus Polyvinylalkohol mit einer Dicke im Bereich von 100 - 300 µm verwendet wird, enthaltend die folgenden Schritte:

a) Druck der zu übertragenden farbigen Zeichnung auf einer Oberfläche des Films aus Polyvinylalkohol bei einer Temperatur im Bereich von 80°-120°C durch mechanischen Druck, indem man den aus Polyvinylalkohol in Kontakt mit einem Blatt bringt das die farbige Zeichnung aufgedruckt hat,

b) Wickeln des bedruckten Films aus Polyvinylalkohol um den zu bedruckenden dreidimensionalen Gegenstand und Schaffung von Vakuum zwischen dem Film und dem Gegenstand,

c) Erhitzen in einem Ofen bei 160°-190°C für eine Zeit von 3 Sekunden bis 5 Minuten, vorzugsweise von 30 Sekunden bis 2 Minuten,

d) Erhalten des bedruckten Gegenstands und optionale Abtrennung des Films aus Polyvinylalkohol

6. Verfahren nach Anspruch 5, wobei das Blatt mit aufgedruckter farbiger Zeichnung aus Kunststoff oder Papier ist.

7. Verfahren nach den Ansprüchen 5 und 6, wobei die Schritte b) und c) gleichzeitig ausgeführt werden.

Revendications

1. Utilisation d'un film d'alcool polyvinylique ayant une épaisseur dans la gamme allant de 100 à 300 µm sur une face duquel se trouve un dessin imprimé pour l'impression par transfert d'articles par sublimation des couleurs, par la technique du sous vide.

2. Utilisation d'un film d'alcool polyvinylique selon la revendication 1, dans laquelle l'article a une forme tridimensionnelle.

3. Utilisation selon la revendication 2, dans laquelle la technique sous vide est la technique du sac.

4. Utilisation selon les revendications 2 et 3, dans laquelle les articles tridimensionnels ont des surfaces courbes.

5. Procédé d'impression par transfert dans lequel est utilisé un film d'alcool polyvinylique ayant une épaisseur dans la gamme allant de 100 à 300 µm, comprenant les étapes suivantes :

a) impression du dessin coloré à transférer sur une face du film d'alcool polyvinylique à une température dans la gamme allant de 80 ° à 120 °C par compression mécanique, par mise en contact du film d'alcool polyvinylique avec une feuille sur laquelle se trouve l'empreinte du dessin coloré,

b) enveloppement du film d'alcool polyvinylique imprimé autour de l'article tridimensionnel à imprimer et création d'un vide entre le film et l'article,

c) chauffage dans une étuve à 160°-190°C pendant une période de temps comprise entre 3 secondes et 5 minutes, de préférence entre 30 secondes et 2 minutes,

d) récupération de l'article imprimé et séparation facultative du film d'alcool polyvinylique.

6. Procédé selon la revendication 5, dans lequel la feuille sur laquelle se trouve l'empreinte du dessin coloré est en plastique ou en papier.

7. Procédé selon les revendications 5 et 6, dans lequel les étapes b) et c) sont effectuées au même moment.