NL9001548A - PRINTABLE MULTILAYER FOIL. - Google Patents

Description

Printable multi-layer film

The invention relates to films, in particular self-adhesive films, which can be printed with different printing systems.

Self-adhesive films are often printed for decorative purposes. Various techniques can be applied for applying such printing, such as screen printing, letterpress printing, offset printing, flexography, pad printing, laser printing, rotogravure, etc. A choice can also be made from different inks, such as one- and two-component inks, oxidative or UV-drying inks, dissolved or dispersed or 100% ink systems. In this way, the combination possibilities of foil / printing ink / printing technique seem to be largely available. In practice, however, uses have been developed in which certain films are printed for specific purposes using specific printing ink / printing technique combinations. For example, self-adhesive polyvinyl chloride (PVC) films for outdoor applications are typically printed with screen printing techniques, using traditional PVC solvent inks or UV-curable inks.

In addition to the many advantages of PVC, such as durability, chemical resistance, mechanical properties, flame resistance, etc., there are also some drawbacks to using PVC as a foil: PVC can contain plasticizers that can be harmful to health; PVC contains heavy metals as a heat stabilizer; PVC causes hydrochloric acid formation upon aging and combustion; PVC can generate dioxins under certain circumstances.

Therefore, there is a need for a product which does not have these drawbacks, but which has the physical properties of PVC, in particular the flexibility and printing characteristics. The person skilled in the art is generally open to the manufacture of such a product in two ways: a) the production of a film on which a printable top layer is applied and b) the production of a multi-layer film with a printable top layer by means of coextrusion. As for method a), it is already known to make polyethylene terephthalate (PET) films suitable for printing with PVC screen printing ink by providing them with a thin top layer of polyvinylidene chloride (PVDC). It is also known to provide polyolefin films for this type of printing with a nitrocellulose or acrylic top layer. The application of such top layers usually takes place in the production process after the foil has been formed. It would be advantageous if a film with a top layer printable by PVC screen printing ink could be obtained in one step, for example by coextrusion. In addition, and most importantly, it would be advantageous to provide a film which can be printed not only with PVC screen printing ink but also with other ink / printing systems.

It has now been found that a particular mixture of polymers is excellently suitable as a top layer for a multilayer film with the above desired properties.

In one aspect, the invention provides a multilayer film comprising a top layer A, which consists of a mixture of one or more polyesters and one or more polyacrylates, and one or more other layers.

The polyacrylate is printable in itself with PVC screen printing ink, but it does not have the mechanical properties that could make it suitable for flexible film. Deformation causes hairline cracks and breakage relatively quickly. Also, it has not been possible to achieve sufficient adhesion between the pure polyacrylate and an adhesive layer commonly used in multi-layer films. The mixture of polyester and polyacrylate gives good adhesion to adhesive layers common in polyolefin-containing coextruded materials. The top layer mixture according to the invention surprisingly appears to be very well printable with a large number of different printing ink systems.

The polyesters that can be used in the top layer A can be any conventional polyester or copolyester. Preferably, copolyesters composed of terephthalic acid or 1,4-cyclohexanedicarboxylic acid as diacid and 1,4-cyclohexanedimethanol, polyalkylene glycol and / or alkylene glycol as diol are used. Such copolyesters are described, for example, in U.S. Patents 3,523,923, 3,943 189 and 2,901,466. Examples are copolyesters commercially available under the name Ecdel® from Eastman Kodak, Arnitel® from Akzo, Hytrel® from DuPont de Nemours and Kodar® from Eastman Kodak Company. Suitable copolyesters are, for example, polymers consisting of 1,4-cyclohexane dicarboxylic acid, 1,4-cyclohexane dimethanol and polytetramethylene glycol; polyethylene terephthalate (PET); PETG (terephthalic acid + ethylene glycol + polyalkylene glycol); polybutene terephthalate (PBT). In addition to the diacids and diols mentioned, other diacids and diols may optionally be present. Mixtures of the said polyesters can also be used.

The polyacrylates that can be used in the top layer A can be a homopolymer, copolymer or terpolymer of acrylates, methacrylates, acrylic acid and methacrylic acid. Preferably, polyacrylates based on (C 1 -C 4 alkyl) methacrylates, such as methyl methacrylate (MMA), ethyl methacrylate (EMA), butyl methacrylate (BMA) and isobutyl methacrylate (IBMA), which give, for example, the following polymers : PMMA, ΡΕΜΑ, PBMA, PIBMA, P (MMA / IBMA), P (MMA / BMA), P (BMA / MMA), P (EA / MMA), P (EA / EMA / -MMA) and acrylic acid copolymers . Examples are polyacrylates commercially available under the name Paraloid® from Rohm and Haas, and Neocryl® from ICI.

The ratio of the polyester to the polyacrylate in the mixture forming the top layer A is not very critical to obtaining the desired printability properties. The ratio can vary from 1:99 to 95: 5. However, to obtain good adhesion to the underlying layer, it is desirable that the polyester be present in predominant amount. The polyester to polyacrylate ratio is preferably from 95: 5 to 50:50 and most preferably from 90:10 to 60:40.

The top layer A may, in addition to the polyester and the polyacrylate, optionally contain other polymers, such as rubbers, in small quantities to obtain special properties.

According to an embodiment, the multilayer film consists of three layers, successively the top layer A, a polymeric adhesive layer B and a central polymer layer C, the central layer C being the thickest layer.

The adhesive layer B serves to adhere the layers A and C together. The use of adhesive layers in multilayer films is known per se. The tie layers are usually modified polyolefins built from polyolefin backbones, such as polyethylene, polypropylene, ethylene vinyl acetate (EVA), etc., to which graft functional groups such as ethyl methacrylate, etc. are grafted. A block or terpolymer can also be made instead of a graft. Examples of suitable adhesive layers in the present multilayer films are the commercial products Admer® from Mitsui Petrochemical Industries, Ltd. and Lotader® from Orkem and Orevac® from Atochem.

The central layer C can consist of all kinds of materials, both plastics and non-plastics. Usually, for economic reasons, a material such as a polyolefin will be chosen. Common polyolefins are low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), propylene-ethylene copolymer, ethylene vinyl acetate and mixtures of such materials or mixtures containing such materials. Also, for example, polyamides, polyesters, polystyrene, etc. can be used as the central layer C.

As mentioned above, the central layer C is the thickest layer. This is at least 5 μπι thick and can also have any desired thickness. Usually the layer C will be about 30-90 mm thick. The adhesive layer usually has a thickness of 3-30 µl, usually 5-15 µl, and the top layer has a thickness of 4-30 µl, preferably 5-15 µl.

According to another embodiment of the invention, the multilayer film consists of two layers, the top layer A and the adhesive layer B. The composition and further properties of these two layers have been discussed above.

According to yet another embodiment, the multilayer film is a symmetrical five-layer film A / B / C / B / A. Such a film with a top layer A on both sides as defined above is therefore printable on both sides with many printing / ink systems.

According to a second aspect, the invention provides a self-adhesive multilayer film consisting of a multilayer film as described above, the back layer of which (in the case of a three-layer film layer C and in the case of a symmetrical five-layer film one of the top layers A) is provided with an adhesive glue layer. The glue can be any self-adhesive glue known in the art.

The self-adhesive multilayer film according to the invention is suitable for many applications, for example for labels and for outdoor applications, such as for advertising on shop windows, buses, etc.

The multilayer film according to the invention is transparent, but in some cases it may be desirable to color the film with, for example, titanium dioxide (white) or carbon black (black) or another desired pigment combination.

To improve the weather resistance of the film, the top layer A, the adhesive layer B and / or the central layer C can be stabilized with suitable UV absorbers / stabilizers, such as benzotriazole, benzophenone, hindered amines or combinations thereof, in concentrations up to 3 wt. .%.

According to a third aspect, the invention provides a method for the manufacture of the above-described multilayer films. In principle, any conventional multilayer film manufacturing method can be used, such as coextrusion, extrusion coating and lamination. Preference is given to coextrusion, because it allows the product to be obtained in one step.

In a fourth aspect, the invention provides a composition consisting of a polyester and a polyacrylate as described above. When used as top layer A of a multilayer film, this mixture gives special properties, such as a very wide printability and good adhesion possibilities to conventional adhesive layers. This composition can exist in any desired form and also in the form of a foil. However, the use of such a foil is not obvious from an economic point of view.

Below are some examples that further illustrate the invention.

Example I

a) Three-layer film with a top layer of a mixture of Ecdel 9966 (copolyester of 1,4-cyclohexane dicarboxylic acid, 1,4-cyclohexane dimethanol and polytetramethylene glycol) and Paraloid B 48 N (copolymer of BMA and ΜΜΆ).

Ecdel 9966 granules and Paraloid B 48 N granules are scooped into a vessel in a 60:40 weight ratio. This vessel is placed in a so-called tumbler and tumbled for half an hour.

The macroscopically homogeneously tumbled material is dried in a hot air dryer (mol sieves) at 70 ° C for 4 hours. The dried mixture is now fed into an extruder at temperatures of 50-60 ° C.

The single screw extruder has a length of 27 L / D (> 20) and a screw diameter of 45 mm. The screw should preferably be equipped with a mixing element (so-called Maddock section and dispersion head); this is not necessary, however, since an ordinary screw "by nature" already has a mixing action. The mixture is extruded at melt temperatures around 250 ° C. Due to its mixing action, the screw ensures a homogeneous melt, which flows into the so-called feed block (according to Dow patent) after leaving the extruder. The extrudates from the other 2 extruders also flow in this feedblock. The main extruder (in this case 60 mm and 33 L / D) processes a polypropylene-ethylene random copolymer (Appryl 3080 FG3) and the other 45 mm extruder processes the adhesive layer material (Admer S 3000 from Mitsui Petrochemical Industries, Ltd.). In the feed block, these polymer streams are formed into an A / B / C sandwich.

The cooling roll that follows the flat foil head has a temperature between 10 and 60 ° C, so that the liquid film now solidifies. Depending on the surface structure of the cooling roller, a high-gloss or matt foil can be obtained. The polyester / acrylic blend preferably has contact with this cooling roller. After cooling, the side edges are cut and the foil is wound up. A transparent flexible foil is obtained in this way. The thicknesses of the layers A, B and C are 10, 10 and 60 µm respectively.

The rolls thus obtained can be unwound on a coater and provided with a layer of self-adhesive glue on the layer C. To this end, this layer of the film must first be treated with corona (surface tension increase due to partial surface oxidation), so that good adhesive adhesion is achieved. obtained. The glue can be a hot melt adhesive or based on solvent or water (emulsion). These rolls of self-adhesive film can be processed into sheets or labels that can then be printed again.

The sheets are printed with screen printing techniques and various screen printing inks, Visprox HSV (suitable for PVC; producer Visprox B.V., Haarlem) and Sericol Polydyne YD (suitable for plastics with a low surface tension; producer Sericol Group Ltd., Kent, England). The scratch resistance and the abrasion resistance of the print are assessed with the so-called "scratch test" and the "Taber abrasion test", and the adhesion of the print to the surface with the so-called "tape test". The scratch test is a subjective test in which a sharp object is passed over the print; the damage thus applied is a measure of the scratch resistance of the ink layer on the surface. The sharp object is often not standardized in printing practice (fingernail). For the ink adhesion to the surface, a so-called tape test is applied to the print in the so-called tape test. Then it is pulled with a jerk and the amount of ink adhered to this tape is a measure of the ink adhesion (no ink on the tape is good, ink on the tape is bad) .The Taber test uses the printed film sample glued to an aluminum plate and a hole is made in the middle so that the sample fits in the Taber tester. The abrasion test must be performed in a conditioned room (lab); the samples to be tested must be conditioned in this room for at least 24 hours. In the Taber test the combination of wheel CS 17 with the 500 g weights is preferably used. The device is set to 300 cycles. After 300 cycles, the sample is visually assessed; this can also be expressed in a number on the scale 1 to 5, where: 1 = very poor 2 = poor 3 = moderate 4 = sufficient 5 = good

The results of the different test methods are shown in the table which is included after the examples.

For decorative purposes, letters and logos can be cut from these films with suitable equipment (Fasson-Graphix), which can then be glued on shop windows, etc. for advertising purposes.

For labels, the printing methods give letterpress printing (UV cured inks) and laser printing good results. The films can be die cut and matrix stripped, leaving a backing with printed labels.

b) Same as a) but now the Ecdel / Paraloid is tumbled together with a master batch, so that the final composition of the top layer is Ecdel / Paraloid (60/40) containing 1% -2% benzotriazole and 0 / 5-1% NECK. A master batch is also added to the PP, so that the HALS concentration is 0/3%. In this way a weather-resistant film is made which is suitable for a longer outdoor use than a). The results of the test methods are shown in the table.

c) Same as a) but now with 12% TiO 2 and 6% micro-talcum in the PP layer, so that a white opaque film is obtained.

d) Same as b) but now with 12% TiO2 and 6% micro-talcum in the PP layer, so that a white opaque film for long-term outdoor use is obtained.

Example II

Three-layer film with a mixture of Ecdel 9966 and Paraloid K 120 N (polymethyl methacrylate) as top layer

The procedure of Example I is followed, except that Paraloid K 120 N is now used instead of Paraloid B 48 N. The weight ratio of copolyester to polyacrylate is 90:10. The Ecdel / Paraloid K 120 N mixture is first premixed in a twin screw extruder due to the fact that the Paraloid K 120 N is a powder and the Ecdel is a granulate, so that mixing in the solid phase is impossible. The mixing ratio in the twin screw extruder is 50/50 and is realized by gravimetrically dosed feed systems. The extrudate is granulated.

The 50/50 granulate thus obtained can, according to Example I, be diluted again with Ecdel to a 90/10 composition in a tumbler, followed by drying and extrusion. The film thus obtained is translucent, because this Paraloid (PMMA) is less compatible with the Ecdel than B48N. In this case, another adhesive layer was used, namely Admer 469 from Mitsui Petrochemicals Industries Ltd., which gives the same result as Admer 3000. The layer thicknesses are the same as in Example 1. The results of the test methods are shown in the table.

Example III

Five-layer film with the outer (top) layers a mixture of Ecdel 9966 and Neocryl B 802 (copolymer from IBMA)

The procedure of Example I is followed, except that now Neocryl B 802 is used instead of Paraloid B 48 N. The weight ratio of copolyester to polyacrylate is 80:20. The central layer C consists of Eltex P KS 413, another propylene-ethylene random copolymer.

The Neocryl B 802 pearl granulate (fine granulate) is blended in the twin screw extruder with Ecdel (50/50). This granulate is diluted by the method of Example I to an 80/20 mixture. Coextrusion with Eltex P KS 413 takes place under similar conditions as in example I.

In the feed block, the polymer streams from both 45 mm extruders are split into 2 streams per material and the whole is combined into an A / B / C / B / A sandwich, which is formed in a flat foil head with adjustable gap width up to 80 µm thick foil, with respective coating thicknesses 10/5/50/5/10 µm. The results of the test methods are given in the table.

Example IV

Three-layer film with a mixture of Arnitel UX 4723 (polybutene terephthalate copolymer) and Paraloid B 44 (EA / MMA copolymer) as top layer.

The procedure of Example I is followed except that a polybutene terephthalate based thermoplastic elastomer is now used instead of Ecdel 9966. The weight ratio of polyester to polyacrylate is 70:30. The layer thicknesses of the film A / B / C are 20/10/50, respectively. An opaque film is produced, the printing results of which are stated in the table.

Example V

Three-layer film with a mixture of Kodar PETG 6763 and Paraloid B 48 N as the top layer.

The method of example I is followed, except that now a PETG is used as (co) polyester.

The miscibility of polyester and polyacrylate is poorer than in Example I, but a film with a higher hardness than that of Example I is formed. The results of the test methods are shown in the table. The film thicknesses of the A / B / C film 10/10/60 μια.

Comparative example

Three-layer film with a mixture of Nylon 6 (ültramid S3 from BASF) and Paraloid B 48 N as the top layer.

The procedure of Example I is followed except that now Nylon 6 is used instead of the polyester. The miscibility of the top layer components is poorer than in Example 1. The film obtained does have a higher hardness than in Example I. However, the printing characteristics are poorer as can be seen from the results listed in the table.

The table below shows the results of the different test methods. The results obtained with a PVC film are also given for comparison.

TABLE

tape test scratch test Taber test

Example Kal screen printing

Sericol Polydyne YD good good 5

Visprox HSV well acceptable 4 water based flexography ink poor UV letterpress printing

Uvonyl well acceptable 2

Example Ifb)

Silkscreen

Sericol Polydyne YD good good

Visprox USV well acceptable

Example II Silkscreen

Sericol Polydyne YD good good 3

Visprox HSV good good 2

Example III screen printing

Sericol Polydyne YD good good 5

Visprox HSV good good 5

Example IV screen printing

Sericol Polydyne YD good good 4

Visprox HSV well acceptable 3 water based flexography ink bad bad 1

Example V screen printing

Sericol Polydyne YD good good 4

Visprox HSV good good 3 water based flexography ink bad bad 2

Comparative Example screen printing

Sericol Polydyne YD bad bad 1

Visprox HSV bad bad 1 water-based flexography ink bad bad 1 PVC film screen printing

Sericol Polydyne YD good good 5

Visprox HSV good good 4 water based flexography ink bad bad UV letterpress

Uvonyl good good

Claims (20)

Multilayer film comprising a top layer A # which consists of a mixture of one or more polyesters and one or more polyacrylates, and one or more other layers. Multilayer film according to claim 1, characterized in that the polyester of the top layer A is a copolyester of a diacid consisting of terephthalic acid or 1,4-cyclohexane dicarboxylic acid, and a diol consisting of 1,4-cyclohexane dimethanol, polyalkylene glycol and / or alkylene glycol. Multilayer film according to claim 1 or 2, characterized in that the polyacrylate of the top layer A is a copolymer of (C 1 -C 4 alkyl) methacrylates. Multilayer film according to claims 1-3, characterized in that the ratio of the polyester to the polyacrylate in the top layer A is from 95: 5 to 50:50. Multilayer film according to claim 4, characterized in that the ratio of the polyester to the polyacrylate in the top layer A is from 90:10 to 60:40. Multilayer film according to claims 1-5, consisting of a top layer A and a polymeric adhesive layer B. Multilayer film according to claims 1-5, consisting successively of a top layer A, a polymeric adhesive layer B and a central polymer layer C, wherein the central layer C is the thickest layer. Multilayer film according to claim 7, characterized in that the top layer A has a thickness of 4-30 µm, the adhesive layer B has a thickness of 3-30 µm, and the central layer C has a thickness of at least 5 µm. Multilayer film according to claims 1 to 5, consisting successively of a top layer A, a polymeric adhesive layer B, a central polymer layer C, a polymeric adhesive layer B and a top layer A. Multilayer film according to claims 6-9, characterized in that the adhesive layer B consists of a modified polyolefin. Multilayer film according to claims 6-10, characterized in that the central layer C consists of a polyolefin. Multilayer film according to claim 11, characterized in that the central layer C consists of polyethylene, polypropylene or ethylene-propylene copolymer. Self-adhesive multilayer foil consisting of a multilayer foil according to claims 1-12, the back layer of which is provided with an adhesive adhesive layer. A method of manufacturing a multilayer film according to claims 1-12 comprising the coextrusion of the two or more different polymers. 15. A composition consisting of one or more polyesters and one or more polyacrylates. Composition according to claim 15, characterized in that the polyester is a copolyester of a diacid consisting of terephthalic acid or 1,4-cyclohexane dicarboxylic acid, and a diol consisting of 1,4-cyclohexane dimethanol, polyalkylene glycol and / or alkylene glycol. Composition according to claim 15 or 16, characterized in that the polyacrylate is a copolymer of (Ο, -O 4 alkyl) methacrylates. A composition according to claims 15-17, characterized in that the ratio of the polyester to the polyacrylate is 95: 5 to 50:50. Composition according to claim 18, characterized in that the ratio of the polyester to the acrylate is from 90:10 to 60:40. A composition according to claims 15-19 in the form of a foil.