Method for coating a support with a dispersion based on an acrylic polymer and a cross-linking agent

Abstract

A method for coating a support with an adhesion primer for improving the connection between the support and an active outer layer. To this end, the coating of the support with a layer of adhesion primer is carried out with an aqueous dispersion including (i) particles of at least one acrylic and/or methacrylic polymer having either a gel content of less than 50 wt. % and an acrylic and/or methacrylic acid copolymer content of at least 10 wt. %, or a gel content of at least 50 wt. %, and (ii) at least one cross-linking agent in an aqueous solution, that can allow interfacial cross-linking and leads to a residual content of free acid functions of the surface copolymer(s) of at least 5 wt. %.

Claims

1. Method for coating a support with at least one coat of bonding primer, comprising the implementation of the following steps: a) a support is implemented, b) optionally, a physical surface treatment of the corona or plasma type is carried out, c) at least one face of said support is coated with an aqueous dispersion comprising: particles of acrylic and/or methacrylic polymer(s) having: either (I) a gel content below 50% by weight relative to the total weight of acrylic and/or methacrylic polymer(s), and a content of copolymer(s) of acrylic and/or methacrylic acid(s) of at least 10% of the total weight of the polymers, or (II) a gel content of at least 50% by weight relative to the total weight of acrylic and/or methacrylic polymer(s), and at least one cross-linking agent, and the coating is made to cross-link in order to produce a primer coat allowing the bonding of a covering, the residual content of free acid functions of the copolymer(s) at the surface being at least 5% by weight relative to the total weight of polymer(s), wherein when the particles of acrylic and/or methacrylic polymer(s) are the particles having (I) a gel content below 50% by weight relative to the total weight of acrylic and/or methacrylic polymer(s), and a content of copolymer(s) of acrylic and/or methacrylic acid(s) of at least 10% of the total weight of the polymers, then a weight ratio of the particles of acrylic and/or methacrylic polymer(s) to the cross-linking agent is about 80/20 (weight/weight).

2. Method according to claim 1, wherein it further comprises two steps of perpendicular stretching of the support, at least one step of which is carried out before or after steps b) or c), in order to obtain a two-dimensional final stretching.

3. Method according to claim 1, wherein steps b) and c) are carried out in-line.

4. Method according to claim 1, wherein the support in step a) is a polyester film, with a thickness A such that:
A150 m.

5. Method according to claim 1, wherein the bonding primer coat has a thickness E such that:
E<200 nm.

6. Method for covering a support coated with at least one coat of bonding primer as obtained by the method as defined in claim 2, wherein it comprises a step of application of a covering capable of reacting with the bonding primer coat.

7. Method according to claim 6, wherein said covering comprises: at least one layer of at least one metal and/or at least one metal oxide, or at least one layer of ink, or at least one layer of adhesive.

8. Method according to claim 7, wherein the covering consists of a layer of metal and/or of metal oxide, the metal (or metals) being selected from aluminium, copper, nickel, silver, gold, and alloys thereof, and the metal oxide(s) being selected from the oxides of aluminium, silicon, copper, nickel, silver and mixtures thereof.

9. Method according to claim 1, wherein at least one portion of the surface of the support is modified by an electric discharge of the corona type under ambient air or gas, at high partial pressure.

10. Support obtained by the method as defined in claim 6, wherein an adhesion of the covering of at least 200 gF/38 mm measured by the adhesion test AT.

11. Support obtained by the method as defined in claim 8, wherein it has at least one of the following properties: an oxygen transmission rate at 23 C. and 50% moisture content at least less than 2 cc/m.sup.2/d, and/or a water vapour transmission rate at 38 C. and 90% moisture content at least less than 2 mg/m.sup.2/d.

12. Support according to claim 10, wherein it comprises recycled product from the support itself and/or from the coated support and/or from the coated and covered support.

13. Article selected from the group constituted by food and non-food packaging, films or sheets for graphic art (printing or drawing), films or sheets for decoration and films or sheets for support protection, wherein it comprises a support as defined in claim 10 or as obtained at the end of the method.

14. Aqueous dispersion, in particular for carrying out the method according to claim 1, wherein it comprises: i) particles of acrylic and/or methacrylic polymer(s) having either (I) a gel content below 50% by weight relative to the total weight of acrylic and/or methacrylic polymer(s), and a content of copolymer(s) of acrylic and/or methacrylic acid(s) of at least 10% of the total weight of the polymer(s), or (II) a gel content of at least 50% by weight relative to the total weight of acrylic and/or methacrylic polymer(s), and ii) at least one cross-linking agent, suitable for allowing interfacial cross-linking, present in an quantity such that the interfacial cross-linking of the particles of acrylic and/or methacrylic polymer(s) leads to a residual content of at least 5% by weight of free acid functions of the copolymer(s) at the surface relative to the total weight of polymer(s), wherein when the particles of acrylic and/or methacrylic polymer(s) are the particles having (I) a gel content below 50% by weight relative to the total weight of acrylic and/or methacrylic polymer(s), and a content of copolymer(s) of acrylic and/or methacrylic acid(s) of at least 10% of the total weight of the polymers, then a weight ratio of the particles of acrylic and/or methacrylic polymer(s) to the cross-linking agent is about 80/20 (weight/weight).

15. Method according to claim 1, wherein the particles of acrylic and/or methacrylic polymer(s) have a gel content below 50% by weight relative to the total weight of acrylic and/or methacrylic polymer(s), and a content of copolymer(s) of acrylic and/or methacrylic acid(s) of at least 10% of the total weight of the polymers.

16. Method according to claim 1, wherein the particles of acrylic and/or methacrylic polymer(s) have a gel content of at least 50% by weight relative to the total weight of acrylic and/or methacrylic polymer(s).

Description

FIGURES AND TABLES

(1) FIG. 1 shows a support (PET film) coated and covered according to the present invention.

(2) FIG. 2 shows a diagram of the adhesion of the metal covering under dry or damp conditions to latex A with or without addition of cross-linking agent and at different ratios (latex/cross-linking agent).

(3) FIG. 3 shows a diagram of the adhesion of the metal covering under dry or damp conditions to latex B with or without addition of cross-linking agent and at different ratios (latex/cross-linking agent).

(4) FIG. 4 shows a scheme of the interfacial cross-linking of carboxyl groups sited at the interface of polymer particles with a cross-linking agent of the melamine-formol type.

(5) FIG. 5 shows a diagram combined with a table illustrating the adhesion properties under dry and damp conditions, and the barrier properties (O2TR and MVTR) as well as the optical density of a film coated and cross-linked with a latex B with or without cross-linking agent at different coating thicknesses.

(6) FIG. 6 represents the method of production of a coated film according to the present invention, and in particular the method of in-line coating (a) and in-line coating by reverse gravure (b).

(7) FIG. 7 shows a schematic diagram of the PET/DAP complex in the adhesion test AT.

(8) FIG. 8 shows a schematic diagram of the test specimen fixed on a plate between the jaws of the dynamometer, used in the adhesion test AT.

(9) Table 1 shows different coating compositions according to the invention applied on a support according to the invention and their gel content values (in percentage by weight/total weight of polymers) after drying the coating at 110 C.

(10) Table 2 shows the values of barrier properties of a coating containing or not containing a cross-linking agent and according to different coating thicknesses.

EXAMPLES

Example 1Properties of the Dispersions According to the Invention

(11) The dispersions according to the invention (latex A prepared as in example 1 of application EP 0260203 B1 and latex B marketed under the name BT-67 by the company DSM, to which the cross-linking agent X or Y is added in proportions of 90/10 or 80/20 corresponding to the Latex/Cross-linking Agent ratio in dry/dry weight) are investigated for their capacity for cross-linking as a function of the temperature (MFFT in C. which is the minimum film-forming temperature), and as a function of the glass transition temperature of the copolymer (Tg in C.).

(12) The latex A without cross-linking agent corresponds to an aqueous dispersion comprising particles of acrylic and/or methacrylic polymer(s) and having either, on the one hand, a gel content below 50% by weight relative to the total weight of acrylic and/or methacrylic polymer(s) and, on the other hand, a content of copolymer(s) of acrylic and/or methacrylic acid(s) of at least 10% of the total weight of the polymers.

(13) The latex B without cross-linking agent corresponds to an aqueous dispersion comprising particles of acrylic and/or methacrylic polymers having a gel content of at least 50% by weight relative to the total weight of acrylic and/or methacrylic polymer(s).

(14) The cross-linking agent used is Cymel 303 LF (called C303 LF or X hereinafter) or Cymel 1123 (called C1123 or Y hereinafter) from Cytec Industries Inc.

(15) Below the glass transition temperature, the molecules have low relative mobility. The glass transition temperature Tg of a polymer is a useful indicator of flexibility. If Tg is too high (>80 or 90 C.) it may be expected to encounter problems of microcracks in the bonding primer, thus generating coating defects, which in their turn generate metallizing or printing defects.

(16) If the size of the particles in nanometers is small, this makes it possible to limit the water sensitivity of the bonding primer. In fact, the smaller the size at constant dry extract, the greater is the number of particles. This helps to reduce the space between the particles and thus decrease the voidage where water may be trapped or absorbed when the coated PET film is brought into contact with water.

(17) The gel content is measured after drying the coating at 110 C. in % by weight relative to the total weight of polymers.

(18) TABLE-US-00001 TABLE 1 Gel content MFFT, Tg, dp, after drying of Latex C. C. nm the coating Latex A.sup.1 40 64 50-80 9 Latex A + Cross-linking agent X (90/10).sup.2 50-80 80 Latex A + Cross-linking agent Y (90/10) 50-80 60 Latex A + Cross-linking agent X (80/20) 50-80 90 Latex A + Cross-linking agent Y (80/20) 50-80 70 Latex B.sup.3 17 20 <100 90 Latex B + Cross-linking agent X (90/10) <100 95 Latex B + Cross-linking agent Y (90/10) <100 90 Latex B + Cross-linking agent X (80/20) <100 95 Latex B + Cross-linking agent Y (80/20) <100 90 .sup.1Latex not cross-linked, comprising a di-acrylic monomer (ethylene glycol dimethacrylate) in the dispersion, contributing to formation of branchings in the resultant latex. .sup.2Latex/Cross-linking Agent ratio in dry/dry weight. .sup.3Commercial latex described as an acrylic latex already cross-linked.

(19) Cross-linking agent X makes it possible to obtain somewhat better results for obtaining gel after drying than cross-linking agent Y, which for its part develops better properties of resistance to chemicals or to water and better flexibility.

Example 2Preparation of a PET Film Coated with a Coat of Bonding Primer (Latex A+Cross-Linking Agent)

(20) The bonding primer dispersion according to example 1 is implemented: latex A (15 or 20% of dry extract)+cross-linking agent X or Y (with a latex/cross-linking agent ratio of 80/20 dry extract/dry extract). This dispersion is coated on the support by an in-line heliographic coating process according to FIG. 6b (pilot machine Toray Film Europe). The rotating helio roller leads to dispersion coating on the PET film. The small or large heliogravure rollers may be used for in-line coating. The coating is dried using infrared radiation at a wavelength of the order of 2 m. The results for the properties of this coated film are given in Table 2.

Example 3Preparation of a PET Film Coated with a Coat of Bonding Primer (Latex B+Cross-Linking Agent)

(21) Example 2 is implemented with a different dispersion, namely latex B (10-15 or 20% of dry extract)+cross-linking agent X or Y (with a latex/cross-linking agent ratio of 80/20 dry extract/dry extract). The results for the properties of this coated film are given in Table 2.

Example 4Preparation of a PET Film Coated with a Coat of Bonding Primer and Covered with a Layer of Metal

(22) The PET film coated with a coat of bonding primer according to example 2 or 3 is covered with a layer of aluminium obtained by evaporation under vacuum (410-4 mbar) in a conventional industrial metallizing process (TopMet machine from Applied Materials). In the course of metallizing, the thickness of the layer of metal is monitored by a measurement of film transparency expressed in terms of optical density OD. The OD selected for the present example is between 2.4 and 3.0, which corresponds to a thickness of the metal layer from 30 to 60 nm.

(23) By a similar method and using the same equipment, it is possible to prepare a PET film coated with a coat of bonding primer and a layer of aluminium oxide with a thickness of about 10 nm.

Example 5Adhesion Properties of a PET Film Coated with a Coat of Bonding Primer and Covered with a Layer of Metal According to the Invention

(24) The results are given in FIG. 2.

(25) C303LF and C1123 are the cross-linking agents used, from Cytec Industries Inc. The data in parentheses correspond to the latex A/cross-linking agent ratio in percentage by weight dry/dry.

(26) It can be seen that latex A without cross-linking agent does not allow sufficient adhesion of the metal covering under damp conditions. However, latex A combined with cross-linking agent X (C303 LF) and Y (C1123) in the proportions indicated (90/10 and 80/20) applied on a PET film gives very satisfactory results with adhesion of the metal of at least 200 gF/38 mm. Coating the PET film with a latex A combined with a cross-linking agent X (80/20) gives the best results of adhesion of the aluminium metal deposited by vacuum evaporation according to the standard process conditions.

Example 6Adhesion Properties of a PET Film Coated with a Coat of Bonding Primer and Covered with a Layer of Metal According to the Invention

(27) The results are shown in FIG. 3.

(28) C303LF and C1123 are the cross-linking agents used, from Cytec Industries Inc. The data in parentheses correspond to the latex A/cross-linking agent ratio in percentage by weight dry/dry.

(29) It can be seen that latex B without cross-linking agent does not allow sufficient adhesion of the metal covering. However, latex B combined with cross-linking agent X (C303 LF) and Y (C1123) in the proportions indicated (90/10 and 80/20) applied on a PET film gives very satisfactory results with adhesion of the metal of at least 250 gF/38 mm. Coating the PET film with a latex B combined with a cross-linking agent X (80/20) gives the best results of adhesion of aluminium metal to the PET film. The aluminium is deposited by vacuum evaporation according to the standard process conditions.

(30) As can be seen from FIGS. 2 and 3, adhesion of the metal covering obtained with a latex already cross-linked (latex B) is significantly increased after additional cross-linking obtained by adding the cross-linking agent. The effect of the cross-linking agent is confirmed by measuring the gel content (cf. Table 1), where an increase in gel content is observed when cross-linking agent X is added to latex B. In this case, interfacial cross-linking is promoted and the creation of polarity at the particle interface gives good results for adhesion of the metal to the support (see FIG. 4): the melamine groups generate interactions with the aluminium atoms, forming chelates. The adhesion performance is therefore increased since these polar groups are more accessible to the interface of the particles relative to the scenario with latex A since the cross-linking agent X is distributed in the polymer particles and at the interface of the particles owing to the low initial gel rate of latex A (cf. Table 1).

Example 7Adhesion Properties and Barrier Properties of a PET Film Coated with a Coat of Bonding Primer (Latex B+Cross-Linking Agent X) and Covered with a Layer of Metal According to the Invention

(31) FIG. 5 illustrates the adhesion performance of a metal covering (aluminium) under dry and damp conditions, oxygen transmission rate (PO2), water vapour transmission rate (PH2O), optical density (OD) of the metal layer coated on a latex B with or without cross-linking agent X (C303LF) at the ratio 80/20 and with different coating thicknesses: PG corresponds to small reverse gravure roller and GG corresponds to large reverse gravure roller.

(32) The measurements of permeability to oxygen are carried out with the OXTRAN 2/20 according to standard ASTM F-1927 Standard Test Method for determination of Oxygen Gas Transmission Rate, Permeance at Controlled Relative Humidity through Barrier Materials using a Coulometric Detector; the results are expressed in cc/m.sup.2/day.

(33) The measurements of permeability to water vapour are carried out according to standard ASTM F-1249 Standard Test Method for Water Vapour Transmission Rate through Plastic Film and Sheeting using a Modulated Infrared Sensor; the results are expressed in g/m.sup.2/day. The measurements of permeability to water vapour of the films are carried out on the Permatran-W3/31 with the MoconWater Vapor Permeation Analysis System software.

(34) As an example, FIG. 5 shows that all the performance data for this formulation (Latex B+Cross-linking agent X or C303 LF) are greatly influenced by the thickness of the coating. The thickness of the coating varies as a function of two parameters: the solids content of the formulation to be coated (10, 15 and 20% by weight of the total weight of the formulation to be coated, and/or the size of the rollers used for applying the dispersion with the cross-linking agent to be coated on the PET film.

(35) FIG. 5 shows a significant increase in adhesion of metal to latex B and the cross-linking agent X (C303 LF) when the coating thickness is small and when latex B is cross-linked even more during the step of drying the coating. FIG. 5 and Table 2 show that the barrier properties of latex B additionally cross-linked with cross-linking agent X (C303 LF) are significantly increased relative to the original latex B. The same applies to latex A cross-linked with cross-linking agent X (C303 LF) relative to the original latex A. Consequently, a more interpenetrating network of polymers forms, making it more difficult for oxygen and water vapour to penetrate through the coating.

(36) TABLE-US-00002 TABLE 2 Thickness of the Thickness of the coating estimated PO2 coating (produced on the basis of the (50% moisture PH2O on coated PET, consumption of the OD content, 23 C.), (90%, 38 C.), before the step of dispersion in the (optical cc/m.sup.2/d g/m.sup.2/d covering with metal) production line density) Latex B 11.14 0.86 >100 nm 2.4 (20% ES, PG) Latex B/X 1.97 0.28 130 20 nm 2.4 (80/20) (20% ES, PG) Latex B/X 1.45 0.18 63 20 nm 2.4 (80/20) (10% ES, PG) Latex B/X 3.00 0.27 126 20 nm 2.4 (80/20) (10% ES, GG) Latex B/X 1.00 0.30 80 nm 2.4 (80/20) (15% ES) Latex A <0.5 0.3-0.7 80 nm 2.4 Latex A/X <0.3 <0.3 60 nm 2.4 (80/20) (15% ES) Latex A/X <0.3 <0.3 80 nm 2.4 (80/20) (20% ES)

(37) In the above table:

(38) ES means dry extract

(39) PG means small gravure and indicates that coating was carried out with small rollers

(40) GG means large gravure and indicates that coating was carried out with large rollers

(41) X corresponds to the cross-linking agent used, namely Cymel 303.

(42) The Latex/Cross-linking Agent ratio by weight dry/dry is shown in parentheses, for example (80/20).

(43) This table also shows that the barrier properties improve with the decrease in thickness of the coating as far as a certain limit. This is correlated with the effectiveness of cross-linking in the coating drying step. With a coating of small thickness, more effective curing is observed between latex B and cross-linking agent X owing to the in-line coating process. Consequently, a more interpenetrating network of polymers forms, making it more difficult for oxygen and water vapour to penetrate through the coating.