HK1107115A - Coated packaging materials - Google Patents

Description

Coated packaging material

Technical Field

The present invention relates to coated packaging materials.

Background information

It is often desirable for the packaging material to contain one or more layers for decorative and/or protective purposes. For example, packaging materials often include the name of the product, nutritional information, decorative pictures, and the like. Such decoration may be imparted to the packaging material, for example, using an ink. However, adhesion of the ink to the packaging material can be problematic. Improved adhesion of the ink to the packaging material is therefore desirable.

The packaging material also typically includes one or more protective layers, such as coatings that impart gas barrier properties. Many plastics used as packaging materials tend to be breathable. It is therefore also generally desirable to provide protection for the packaging material from the effects of breathability.

Summary of The Invention

The present invention relates to a packaging material comprising at least one coating layer having one or more thermally curable groups and one or more radiation curable groups. Radiation curable moieties containing ethylenic unsaturation may be used as a gas barrier layer for packaging materials, as oxygen may be added between double bonds. The present invention also relates to a packaging material comprising a first coating layer comprising one or more thermally curable groups and one or more radiation curable groups and a second coating layer comprising a radiation curable colorant. In these embodiments, the enhanced adhesion is believed to be due to cross-curing of the radiation curable groups in the first coating with the coating comprising the radiation curable colorant, although the inventors do not wish to be bound by any mechanism.

Detailed Description

The present invention relates to packaging materials comprising a thermally curable coating comprising one or more thermally curable groups and one or more radiation curable groups. In certain non-limiting embodiments, this coating comprises a film-forming resin having attached one or more thermally curable groups and one or more radiation curable groups. In other non-limiting embodiments, the thermally curable group and the radiation curable group are not attached to the same resin. The weight percent of radiation curable groups in this coating is less than the weight percent required to radiation cure the coating. This coating is sometimes referred to herein as the first coating.

The first coating may be a one-component or "1K" system or a two-component or "2K" system. For 1K systems, the thermally curable group may be self-curing, e.g., self-curing at ambient or elevated temperature, or may be cured at ambient or elevated temperature in the presence of a curing agent. For 2K systems, the curing agent ("curing agent component") remains separate from the reactive heat-curable groups ("resin component"); these components were combined shortly before application. After the resin component and the curing agent component are mixed and the resulting mixture is applied to a substrate, the substrate is then optionally heat treated (e.g., at ambient or elevated temperatures) to facilitate curing of the curing agent with the thermally curable groups.

As noted above, in certain non-limiting embodiments, the thermally curable groups and the radiation curable groups are on the same film-forming resin, which is sometimes referred to herein collectively as the "first film-forming resin". Any film-forming resin having one or more thermally curable functional groups can be used according to the present invention. According to certain embodiments of the present invention, this resin either has or may be modified to have radiation curable groups attached thereto. According to other embodiments of the present invention, the thermally curable groups may be on one resin and the radiation curable groups may be on another resin. As used herein, the term "thermally curable" and variations thereof refers to coatings and/or groups that can be cured or crosslinked at ambient or elevated temperatures and that do not cure or crosslink due to actinic radiation. Examples of polymers having thermally curable groups include hydroxyl-or carboxylic acid-containing acrylic copolymers, hydroxyl-or carboxylic acid-containing polyester polymers, isocyanate-or hydroxyl-containing polyurethane polymers, and amine-or isocyanate-containing polyureas. These polymers are further described in U.S. patent No. 5,939,491, column 7, line 7 to column 8, line 2; this patent and the patents referenced therein are incorporated herein by reference. Curing agents for these resins are also described in the' 491 patent at column 6, lines 6-62. Combinations of curing agents may be used. Resins containing isocyanate groups and curing agents containing hydroxyl groups are particularly suitable, and vice versa.

In certain embodiments, the first coating layer comprises a second film-forming resin in addition to the first film-forming resin. Any film-forming resin having one or more thermally curable functional groups can be used as the second film-forming resin according to the present invention, including those discussed above. The first and second film-forming resins may be the same except that the radiation curable groups are present on the first but not the second film-forming resin. In addition to the presence of radiation curable groups, the first and second film-forming resins may differ in several respects; for example, the resin backbone may be the same or different and/or the thermally curable groups on each resin may be the same or different. One skilled in the art can select a suitable curing agent depending on the thermally curable groups on the film-forming resin. One curing agent may be sufficient if the thermally curable groups on each film-forming resin are the same, but two or more curing agents may be used if the thermally curable groups on each film-forming resin are different. There is no limitation on the number of curing agents used according to the present invention. Similarly, there is no limit to the number of film-forming resins used in accordance with the present invention, and the use of one or two film-forming resins reflects just some non-limiting embodiments.

As noted above, in certain embodiments, the first film-forming resin comprises, or is "modified" to comprise, radiation curable groups. In other embodiments, the thermally curable group and the radiation curable group are on different resins. The term "radiation curable group" as used herein refers to any functional group that can react, e.g., via an addition reaction, upon exposure to actinic radiation, e.g., UV radiation or electron beam radiation. Examples of such groups include, but are not limited to, acrylates, methacrylates, vinyl ethers, ethylenically unsaturated resins, maleic unsaturated polyesters, fumarates, thiols, olefins, epoxy resins, and the like. "(meth) acrylate" and like terms are used herein to refer to both methacrylate and acrylate. "modified" and like terms mean that the radiation curable groups are covalently bonded to the resin. Thus, in certain non-limiting embodiments, the radiation curable groups are physically attached to the resin, while in other non-limiting embodiments, the radiation curable groups and the thermally curable groups are not physically attached to the same resin. It should be understood that in those embodiments in which the radiation curable group is covalently bonded to the resin, the bonding is such that the radiation curable group remains reactive upon exposure to radiation.

The first coating of the present invention comprises radiation curable groups in a weight percentage less than that required to render the coating radiation curable. Suitable amounts of radiation curable groups in the first coating can be determined by one skilled in the art. In certain embodiments, the amount of carbon-carbon double bonds on the resin is 7% or less; that is, 7% or less of the total weight of the coating, based on solids, is carbon-carbon double bonds.

It goes without saying that "dual cure" resins are known in the art, which comprise both thermally curable and radiation curable groups. As the name implies, these resins undergo two different types of curing. One curing mechanism is thermal curing, for example by using a curing agent and/or applying thermal curing; the second curing mechanism is curing by exposure to actinic radiation. The result of the dual cure is the formation of two interpenetrating networks, one of which is based on thermally cured groups and the other of which is based on radiation curable groups. The weight percentage of radiation curable groups used in the first coating according to the invention is not high enough to double cure the first coating; the first coating is only thermally curable. Thus, if the first coating is exposed to actinic radiation, it will not cure; "curing" as used in connection with coating refers to reaction between the components such that they resist melting when heated. Thus, the reaction between radiation curable groups in the first coating, which may occur in discrete spots when exposed to actinic radiation, is not sufficient to impart melt resistance to the coating upon heating. The first film-forming resin is cured by crosslinking of the thermally curable group.

The first film-forming resin comprising one or more thermally curable groups and one or more radiation curable groups may be prepared by reacting a first material and a second material. The first material may comprise at least one radiation curable group and at least one non-radiation curable group capable of reacting with the second material. The second material may comprise at least one functional group capable of reacting with the non-radiation curable group on the first material. One non-limiting embodiment includes the reaction of a hydroxyl functional acrylate with a polyisocyanate to produce a resin containing isocyanate functionality and acrylate functionality on the same molecule. Acrylate functional isocyanates are also commercially available from Bayer as their ROSKYDAL line. Alternatively, the resin comprising thermally curable groups and the resin comprising radiation curable groups may be mixed together.

In certain non-limiting embodiments of the present invention, the first film-forming resin comprises at least one isocyanate having one or more ethylenically unsaturated moieties and one or more isocyanate ("NCO") groups. The NCO groups may be free or blocked. In these embodiments, the first film-forming resin will generally be in the first or resin component and the curing agent for the isocyanate will generally be in the second or curing agent component, with the two components being mixed immediately prior to application. Examples of ethylenically unsaturated isocyanates include (meth) acryloxy isocyanates. In other non-limiting embodiments, the resin comprises hydroxyl groups and radiation curable groups and the coating comprises an isocyanate. In other embodiments, the two components may comprise, for example, polyepoxides and carboxylic acid acrylates; anhydrides and hydroxyacrylates; or aminoplasts and hydroxyacrylates.

In addition to the one or more film-forming resins described above, the first coating may further comprise pigments, fillers, rheology modifiers, surfactants, light stabilizers, catalysts, oxygen scavengers, oxygen scavenging promoters and other additives known to those skilled in the art to achieve specific end-use performance properties. Additional resinous materials may also be present, such as crosslinking agents and film-forming resins other than the film-forming resins described above. Solvents and diluents may also be used. The film-forming resin typically comprises from 5 to 95 wt%, for example from 25 to 60 wt%, of the first coating. The curing agent (if used) typically comprises 5 to 95 wt%, e.g., 25 to 75 wt%, of the first coating. The other ingredients in the first coating, if used, are typically present in an amount of up to 50 wt% of the first coating. All of these weight percentages are weight percent solids of the total solids weight of the coating.

The present invention further relates to a packaging material comprising a first coating layer comprising one or more thermally curable groups and one or more radiation curable groups and a second coating layer comprising a radiation curable colorant. The term "radiation curable colorant" and like terms as used herein refers to any color-imparting compound that can be cured by actinic radiation, such as UV curable inks and the like. "colorants" may include, for example, inks, dyes, and/or pigments, and the like. Such products are commercially available, for example, from Sun Chemical Corporation, Fort Lee, NewJersey. Actinic radiation includes, but is not limited to, UV radiation, electron beam radiation, and even visible light curing, depending on the initiator used.

The second coating may also contain other additives such as one or more initiators such as photoinitiators, dispersants, dispersion carriers, accelerators and other standard additives.

The invention further relates to a method for coating the packaging material. The coatings described herein, as well as other coatings known in the art, can be applied to at least a portion of the packaging material, and can be applied directly to the packaging material or to at least a portion of a preexisting coating. Certain embodiments generally include applying a first coating to a packaging material. As described above, the first coating includes both thermally curable groups and radiation curable groups in a weight percentage less than that required to radiation cure the coating. The coating is formulated and mixed by means known to those skilled in the art and can be applied to the substrate by any means known in the art, such as spraying, rolling, brushing, dipping, casting/spin coating, electrostatic spraying, flow coating, and the like. After the first coating is applied, the substrate is subjected to a thermal curing process. Thermal curing can be carried out at ambient or elevated temperatures. The thermal curing is carried out in such a way that most of the thermally curable groups react with the curing agent. While most thermally curable groups will react, the art recognizes that some thermally curable groups may not react completely upon exposure to curing conditions, but may continue to react slowly over time (i.e., "post-cure"); it is further recognized that it is unlikely that 100% of the groups will react. Thus, the term "fully cured" as used herein does not mean that 100% of the groups have been cured, but that most have been cured as described above.

In certain non-limiting embodiments, after the thermal curing step is completed, a second coating comprising a radiation curable colorant is applied to the packaging material so as to be at least partially in contact with the first coating. The second coating is as described above and may also be applied using any suitable method. In certain non-limiting embodiments, it may be desirable to apply the second coating in a predetermined pattern or design. After the application of the second coating is complete, the packaging material is exposed to actinic radiation for a time sufficient to cure the radiation curable colorant. One skilled in the art can determine the appropriate dose, irradiance, source of actinic radiation, etc. to effect curing, depending on the colorant selected.

While curing the radiation curable colorant of the second coating, exposure to actinic radiation will also cause the radiation curable groups in the first coating to react and bond with the radiation curable groups in the second coating. The interlayer adhesion between the first coating and the second coating is believed to result from this cross-curing of the radiation curable groups in each layer. In those embodiments in which the radiation curable groups in the first coating are physically attached to the same resin as the thermally curable groups; interlayer adhesion is believed to be even greater; the cross-cured radiation groups are physically associated with the cured first coating and are therefore believed to be more permanent than, for example, when the radiation curable groups are merely mixed with the thermally curable resin. It is self-evident that in certain embodiments, some but not all of the radiation curable groups in the first coating may react and cross-cure with the second coating while others remain unreacted. In these embodiments, improved adhesion and gas barrier properties may be observed simultaneously.

The first coating may be deposited and cured and the second coating deposited and cured, or the second coating may be deposited on the uncured or partially cured first coating and the two layers may be cured simultaneously or sequentially with actinic radiation followed by thermal curing, or vice versa. In certain non-limiting embodiments, the second coating layer may be deposited first, and a thermally curable layer having radiation curable moieties is deposited on at least a portion of the uncured or partially cured second coating layer. The two layers can then be cured simultaneously or sequentially with actinic radiation followed by thermal curing, or vice versa. In these embodiments, the thermally curable layer will be unpigmented or slightly pigmented. "lightly pigmented" and like terms refer to pigmented systems from which actinic radiation may still penetrate; such systems may contain, for example, pigments that are lighter in color or pigments that have a lower concentration of pigment. Regardless of the application and curing sequence of the coating, in certain embodiments, most of the thermally curable groups in the thermally curable layer will react.

The multilayer coating system of the present invention can be applied to a variety of substrates and used in a variety of applications. "packaging material" and like terms refer to any material suitable for creating packaging, including but not limited to Mylar, metal foil, stretch wrap, cellophane, metal, glass, and polymers having gas permeability, including but not limited to polyesters, polyolefins, polyamides, cellulosics, polystyrenes, polyacrylics, polycarbonates, polyethylene terephthalate, poly (ethylene naphthalate), and any combination thereof.

Unless otherwise expressly stated, all numbers such as those expressing values, ranges, amounts or percentages used herein are to be understood as being preceded by the word "about", even if the term does not expressly appear. Any numerical range recited herein is intended to include all sub-ranges subsumed therein. Plural encompasses singular and vice versa. Also, as used herein, the term "polymer" refers to prepolymers, oligomers, and homopolymers and copolymers; the prefix "multi" refers to two or more.

Examples

The following examples are intended to illustrate the invention and should not be construed as limiting the invention in any way.

Example 1

Transparent coating: polyol component

Components	Dosage/pound
		Diisobutyl ketone	154.611
Methyl isobutyl ketone	254.116
		Fluorescent whitening agent1	1.674
Cellulose acetate butyrate2	10.087
		At this point good mixing is necessary to dissolve the CAB before proceeding.
TINUVIN 3283	9.367
		At this point it must be well mixed to dissolve TINUVIN 328 before continuing.
HRB 4856 polyol4	292.470
		TERATHANE 10005	30.610
Total of	752.935

¹RC-B thiopen from Wujin Fine Chemicals or Q-OB from NY Fine Chemicals.

²CAB 551.0.2PM3024 from Eastman Chemical

³Benzotriazole UV absorbers from Ciba Additives.

⁴Polyester-urethane polyols available from PPG Industries, Inc.

⁵Polyether polyols available from DuPont

Example 2

Clear coating at high solids: polyol component

Components	Dosage/pound
		Diisobutyl ketone	146.13
Methyl isobutyl ketone	224.99
		Fluorescent whitening agent	1.80
Cellulose acetate butyrate	10.87
		At this point good mixing is necessary to dissolve the CAB before proceeding.
TINUVIN 328	10.09
		Must be well mixed at this time to dissolve before continuingde-TINUVIN 328.
HRB 4856 polyol	315.12
		TERATHANE 1000	32.98
Methyl isobutyl ketone	17.32
		Total of	759.30

Example 3

Any of the polyol coatings may be mixed with a resin containing both thermally curable and radiation curable groups, such as the adduct of 2016 parts DESMODUR N3300 (a polyisocyanate crosslinker available from Bayer Corporation) and 106.1 parts hydroxyethyl acrylate (solid NCO equivalent weight 192; diluted to 60% solids in methyl isobutyl ketone). The mixture can be applied to packaging material, such as aluminum can stock, using a suitable draw down bar or wire wound bar. The coating can be cured in a laboratory convection oven at 200 deg.F for 10 minutes to a dry film thickness of about 0.5 mils. If desired, before application to the packaging material, 1000ppm cobalt (as Co) at 100-⁺⁺) Amount cobalt octoate was added to either coating. A decorative layer comprising a radiation curable colorant, such as EJ-81-505K (a blue UV curable ink available from PPG Industries, inc.) may then be applied using a suitable apparatus, such as a suitable draw down bar or wire wound bar, to partially or completely cover the first coating layer. The application may be, for example, according to a predetermined design or pattern. The ink may then be cured at a suitable dose, for example at 100 and 2000 mJ/cm. Good adhesion between the first layer and the ink will beAs would be expected.

While specific embodiments of the invention have been described above for purposes of illustration, it will be apparent to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.

Claims (18)

1. A packaging material comprising: a coating comprising one or more thermally curable groups and one or more radiation curable groups.

2. The packaging material of claim 1, wherein the thermally curable group comprises a hydroxyl group.

3. The packaging material of claim 1, wherein the thermally curable group comprises an isocyanate group.

4. The packaging material of claim 1 wherein said first coating comprises at least one isocyanate having one or more ethylenically unsaturated moieties and one or more isocyanate groups.

5. The packaging material of claim 1, wherein the radiation curable group comprises a (meth) acrylate functional group.

6. A packaging material comprising:

(a) a first coating comprising one or more thermally curable groups and one or more radiation curable groups; and

(b) a second coating comprising a radiation curable colorant.

7. The packaging material of claim 6, wherein the thermally curable group comprises a hydroxyl group.

8. The packaging material of claim 6, wherein the thermally curable group comprises an isocyanate group.

9. The packaging material of claim 6 wherein said first coating comprises at least one isocyanate having one or more ethylenically unsaturated moieties and one or more isocyanate groups.

10. The packaging material of claim 6, wherein the radiation curable group comprises a (meth) acrylate functional group.

11. The packaging material of claim 1 wherein the weight percent of radiation curable groups based on the total solids weight of the coating is 7 or less.

12. The packaging material of claim 6, wherein the weight percent of radiation curable groups based on the total solids weight of the first coating layer is 7 or less.

13. The packaging material of claim 1, wherein the coating further comprises cobalt octoate.

14. The packaging material of claim 6, wherein the first coating further comprises cobalt octoate.

15. A method of coating a packaging material comprising:

(a) applying the coating of claim 1 to a packaging material; and

(b) the coating is cured.

16. The method of claim 15, further comprising:

(c) applying a second coating comprising a radiation curable colorant; and

(d) the second coating is cured.

17. A method of coating a packaging material comprising:

(a) applying a coating comprising one or more thermally curable groups and one or more radiation curable groups onto the packaging material; and

(b) applying a coating comprising one or more radiation curable colorants to a packaging material;

wherein either step (a) or step (b) is performed first, but when step (b) is performed first, the coating comprising thermally curable groups and radiation curable groups is unpigmented or slightly pigmented.

18. The method of claim 17, wherein the first applied layer is fully cured before the second layer is applied.