Claims:
1. A primer composition for lamination of a polymeric substrate selected from polypropylene (PP) or polyethylene (PE) with a polymeric woven sac film, comprising:
a. about 5 to 15% by weight, more preferably from about 8 to 12% by weight, and most preferably about 9 to 10% by weight of a linear triblock copolymer based on styrene and ethylene/butylene with a polystyrene content of about 25 to 35%, more preferably about 30%;
b. about 85 to 95% by weight of solvents, preferably aliphatic hydrocarbons selected from aliphatic alcohols and esters; and
c. about 0.1 to 1.0% by weight of an anti-blocking agent.

2. The anti-blocking agent according to claim 1, is a synthetic amorphous silica.

3. A printed laminate, comprising: a polymeric substrate selected from a polypropylene (PP) film or a polyethylene (PE) film, printed with an ink to form a printed polymeric substrate; a solvent based primer layer according to claim 1 over the ink layer; and an extrusion laminated polymeric woven sac film.

4. The polypropylene according to claim 3, is biaxially oriented polypropylene (BOPP).

5. The thickness of the solvent based primer layer in the printed laminate according to claim 3 is about 0.1 to 2.0 GSM, preferably about 0.3 – 0.6 GSM.

6. The thickness of the solvent based primer layer according to claim 3 is about 0.1 to 2.0 GSM, preferably about 0.3 – 0.6 GSM.

7. The printed laminate of claim 3, wherein the extrusion lamination bond strength between the polymeric substrate and the polymeric woven sac film is about 1 - 2 N/25 mm when the thickness of the solvent based primer is about 0.2 GSM; and the extrusion lamination bond strength between the polymeric substrate and the polymeric woven sac film is about 4 - 5 N/25 mm when the thickness of the solvent based primer is about 0.6 GSM.

8. The thickness of the ink layer according to claim 3, in case of colour inks is about 0.4 to 0.6 GSM, and in case of white ink is about 0.8 to 1.0 GSM.

9. The primer composition for lamination according to claim 3, wherein the polypropylene is biaxially oriented polypropylene (BOPP), and the polymeric woven sac film according to claim 6, is a polypropylene woven sac film.

10. A method of forming a printed laminate, comprising:
a. Providing a polymeric substrate selected from a polypropylene (PP) film or a polyethylene (PE) film,
b. printing the polymeric substrate with an ink to form a printed polymeric substrate;
c. applying a solvent based primer layer over the ink layer; and
d. extrusion laminating a polymeric woven sac film;
wherein, the solvent based primer includes about 5 to 15% by weight, more preferably from about 8 to 12% by weight, and most preferably about 9 to 10% by weight of a linear triblock copolymer based on styrene and ethylene/butylene with a polystyrene content of about 25 to 35%, more preferably about 30%; about 85 to 95% by weight of solvents, preferably aliphatic hydrocarbons selected from aliphatic alcohols and esters; and about 0.1 to 1.0% by weight of an anti-blocking agent.

Description:FIELD OF THE INVENTION:
The present invention relates to a solvent based primer for improved extrusion lamination bond strength of polypropylene (PP) or Polyethylene (PE) film substrates to polymeric woven sac films for packaging applications.

BACKGROUND OF THE INVENTION:
Extrusion lamination bond strength of polypropylene (PP) or Polyethylene (PE) films to ink applied on substrates such as biaxially oriented polypropylene (BOPP) is not optimum. Especially, such conventional PP or PE extrusion lamination fails to achieve the required lamination bond strength for certain heavy duty laminated bags, such as pet food, and other food and non-food packaging applications.

In order to achieve higher bond strength, often chlorinated inks such as chlorinated polypropylene and chlorinated EVA based resins are used, where aromatic hydrocarbon based solvents are necessary. These aromatic hydrocarbon based solvents and also halogens such as chlorine present in the ink resin is detrimental to the environment.

US20140370252A1 discloses a laminate structure that includes a primer coating comprising the reaction product of polyethyleneimine and formaldehyde on the surface of a polymeric substrate which is subsequently printed with an ink or toner image prior to lamination to another polymeric substrate.

US7470736B2 discloses a water-based primer coating for use on polymeric substrates that includes a dispersion of a copolymer of ethylene and acrylic or methacrylic acid, and a compatible adhesion enhancer selected from an aliphatic polyurethane dispersion, a hydrogenated hydrocarbon rosin or rosin ester dispersion, and an amorphous acrylic polymer dispersion. The primer coating may be applied to a variety of polymeric substrates including polypropylene, biaxially oriented polpypropylene, polyethylene terephthalate, and polyvinyl chloride.

OBJECTS OF THE INVENTION:
The principal objective of the present invention is to provide a solvent based primer for improved extrusion lamination bond strength between polymeric substrates selected from polypropylene (PP) or Polyethylene (PE) and a polymeric woven sac film.

Another objective of the present invention is to provide an aromatic hydrocarbon free solvent based primer for improved extrusion lamination bond strength between polymeric substrates selected from polypropylene (PP) or Polyethylene (PE) and a polymeric woven sac film.

A further objective of the present invention is to provide a printed article using the solvent based primer that exhibits excellent extrusion lamination bond strength of polypropylene (PP) or Polyethylene (PE) films to a polymeric woven sac film.

Yet another objective of the present invention is to provide an appropriate GSM of the said primer coating to minimize the blocking problem in the printed laminate.

SUMMARY OF THE INVENTION:
The present invention provides a solvent based primer composition for a laminate structure comprising polypropylene (PP) or Polyethylene (PE) films laminated to polymeric substrates.

In one embodiment of the present invention, the solvent based primer coating comprises from about 5 to 15% by weight of a linear triblock copolymer based on styrene and ethylene/butylene, from about 85 to 95% by weight of solvents, preferably aliphatic hydrocarbons selected from aliphatic alcohols and esters and about 0.1 to 1.0% by weight of one or more additives.

In a further aspect of the present invention, the solvent based primer is substantially free of aromatic hydrocarbon solvents for improved extrusion lamination bond strength between polypropylene (PP) or polyethylene (PE) substrates and polymeric woven sac films.

In another embodiment, the present invention provides a polypropylene (PP) film or a polyethylene (PE) film printed with an ink, which is subsequently coated with a solvent based primer layer of the present invention, the printed substrate is further extrusion laminated to a polymeric woven sac film.

The primer coating provides good adhesion to ink and excellent extrusion lamination bond strength between polyethylene or polypropylene film e.g. biaxially oriented polypropylene (BOPP) and a polymeric woven sac film.

DETAILED DESCRIPTION OF THE INVENTION:
The preferred embodiments of the present invention will be described in detail with the following disclosure and examples. The foregoing general description and the following detailed description are provided to illustrate only some embodiments of the present invention and not to limit the scope of the present invention. The invention is capable of other embodiments and can be carried out or practiced in various other ways.

Unless otherwise specified, all the technical and scientific terms used herein have the same meaning as is generally understood by a person skilled in the art pertaining to the present invention. All the patents published patent applications referred to throughout the entire disclosure herein, unless specified otherwise, are incorporated by reference in their entirety.

It is to be understood that the ranges provided herein include the stated range and any value or sub-range within the stated range. For example, a range from greater than 0 % by weight to about 25 % by weight should be interpreted to include not only the explicitly recited limits of greater than 0 % by weight to about 25 % by weight, but also to include individual values, such as 0.05 % by weight, 0.9 % by weight, 7 % by weight, 21 % by weight, etc., and sub-ranges, such as from about 1 % by weight to about 24 % by weight, from about 5 % by weight to about 20 % by weight, etc. Furthermore, when “about” is utilized to describe a value, this is meant to encompass minor variations (up to +/-10%) from the stated value.

Reference throughout this specification to “one embodiment,” “an embodiment,” “one example,” or “an example” means that a particular feature, structure, or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present disclosure. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” “one example,” or “an example” in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable combinations and/or sub-combinations in one or more embodiments or examples. In addition, it should be appreciated that if any figures are provided herewith, they are for explanation purposes to persons ordinarily skilled in the art and that the drawings of them are not necessarily drawn to scale.

In this specification, certain aspects of one embodiment include process steps and/or operations and/or instructions described herein for illustrative purposes in a particular order and/or grouping. However, the particular order and/or grouping shown and discussed herein are illustrative only and not limiting. Those of skill in the art will recognise that other orders and/or grouping of the process steps and/or operations and/or instructions are possible and, in some embodiments, one or more of the process steps and/or operations and/or instructions discussed above can be combined and/or deleted. In addition, portions of one or more of the process steps and/or operations and/or instructions can be re-grouped as portions of one or more other of the process steps and/or operations and/or instructions discussed herein. Consequently, the particular order and/or grouping of the process steps and/or operations and/or instructions discussed herein do not limit the scope of the disclosure.

Formulation of the solvent based primer
In one embodiment of the present invention, the solvent based primer coating comprises from about 5 to 15% by weight, more preferably from about 8 to 12% by weight, and most preferably about 9 to 10% by weight of a linear triblock copolymer based on styrene and ethylene/butylene, from about 85 to 95% by weight of solvents, preferably aliphatic hydrocarbons selected from aliphatic alcohols and esters and about 0.1 to 1.0% by weight of one or more additives.

A suitable linear triblock copolymer based on styrene and ethylene/butylene with a polystyrene content of about 25 to 35%, more preferably 30% is selected. Example of one such commercially available copolymer resin is Kraton, under the tradename Kraton FG1901.

Solvents
The non-limiting organic solvents for use in the present invention are selected from aliphatic alcohols, organic acid esters, glycol ethers, aliphatic hydrocarbons or cycloaliphatic hydrocarbons.

Suitable aliphatic alcohols include but are not limited to ethanol, Isopropanol, normal-propanol, isobutanol and 1-Methoxy,2-Propanol or mixtures thereof.

Suitable organic acid esters include but are not limited to methyl acetate, ethyl acetate, propyl acetate, butyl acetate and mixtures thereof.

Suitable glycol ethers include but are not limited to diethylene glycol mono-n-butyl ether (DEGMBE), propylene glycol n-butyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, dipropylene glycol methyl ether, dipropylene glycol n-butyl ether, propylene glycol methyl ether acetate, dipropylene glycol methyl ether acetate, propylene glycol n-propyl ether acetate, dipropylene glycol n-propyl ether, ethylene glycol n-butyl ether (or ethylene glycol monobutyl ether (EGMBE)), diethylene glycol n-butyl ether, triethylene glycol butyl ether, diethylene glycol methyl ether, tripropylene glycol monomethyl ether (TPGME), tripropylene glycol n-butyl ether (TPGBE), and triethylene glycol methyl ether.

Suitable aliphatic hydrocarbons include but are not limited to pentane, hexane, heptane, octane, nonane, decane, isopentane, isohexanes, isopentanes, isooctanes, 2,2-dimethylbutane, and mixtures thereof.

Suitable cycloaliphatic hydrocarbons include but are not limited to cyclopentane, cyclohexane, methylcyclopentane, methylcyclohexane and mixtures thereof.

Mixtures of any of the above solvents may also be used.

Preferably the organic solvents used are Non-toluene (NT), and Non-toluene-Non-ketone (NTNK) solvents. However, a person skilled in the art pertaining to the present invention may also use certain quantity of aromatic, ketonic solvents or a combination thereof. If used, suitable aromatic hydrocarbons include but are not limited to xylene and toluene. Suitable aliphatic ketones include but are not limited to methyl ethyl ketone, methyl isobutyl ketone.

Additives:
The primer composition of the present invention may also contain the usual additives such as anti-blocking agents to reduce the blocking issue in the laminated article.

Suitable anti-blocking agents may include a synthetic amorphous silica such as Syloid® ED-30.

However, a person skilled in the art pertaining to the present invention may also use other anti-blocking agents.

Laminate:
A printed laminate is formed using a polymeric substrate selected from a polypropylene (PP) film or a Polyethylene (PE) film printed with an ink, which is subsequently coated with a solvent based primer layer of the present invention, the printed substrate is further extrusion laminated to a polymeric woven sac film.

The polypropylene used as polymeric substrate includes biaxially oriented polypropylene (BOPP).

The polymeric woven sac is a polypropylene woven sac film.

The thickness or GSM of any ink and/or coating on applicable substrate has proportional impact on the blocking characteristics of the said ink or coating. Higher the GSM, more is the blocking issue.

The thickness of the solvent based primer layer is about 0.1 to 2.0 GSM. The most preferable thickness at which the minimum blocking of the ink occurs, is in between the range of 0.3 – 0.6 GSM.

At thickness about 0.2 GSM of the solvent based primer, the resulting extrusion lamination bond strength is up to 1 – 2 N/25 mm.

At thickness about 0.6 GSM of the solvent based primer, the resulting extrusion lamination bond strength is up to 4 – 5 N/25 mm.

The thickness of the ink layer (colour inks) is about 0.4 to 0.6 GSM. Any of the colour inks known to the printing ink Industries can be used not restricted to Cyan, magenta, yellow, black, orange, green.

The thickness of the ink layer (white ink) is about 0.8 to 1.0 GSM. Any of the white inks known to the printing ink Industries can be used, preferably white inks based on rutile TiO2, is suitable.

Examples:
The present disclosure will now be explained in further detail by the following examples. These examples are illustrative of certain embodiments of the invention without being limited to the specific examples given here.

Preparation of the Primer
The most preferred embodiments of the invention to prepare the solvent based primer composition are given in the examples below in Table 1, and Table 2.

Table 1
Examples 1 2 3
Primer-1
(wt%) Primer-2
(wt%) Primer-3
(wt%)
Copolymer based on styrene and ethylene/butylene (Kraton FG1901) 5 7.5 9.7
Solvents 94.9 92.3 90.2
Additive (Anti-blocking agent) 0.1 0.2 0.1
Total 100.00 100.00 100.00

Table 2
Examples 4 5 6
Primer-4
(wt%) Primer-5
(wt%) Primer-6
(wt%)
Copolymer based on styrene and ethylene/butylene (Kraton FG1901) 10.2 12.5 15
Solvents 89.7 87.2 84.8
Additive (Anti-blocking agent) 0.1 0.3 0.2
Total 100.00 100.00 100.00

Example 7.
Printed article
Separately BOPP substrates and PE substrates were printed with an ink, which were subsequently coated with the primer compositions of the above examples, the printed substrates were further extrusion laminated to a polymeric woven sac film. A lab simulation of extrusion lamination was conducted by laminating the substrates at a heat seal temperature of 200 °C using heated metal jaws at a pressure of 1 kg/cm2 (14.22 PSI) for 0.5 seconds.

The BOPP substrates and PE substrates were printed with both colour Ink and white Ink for evaluation purposes.

As a colour ink, SARJOLAM PLUS INKs from Yansefu Inks and Coatings Private Limited was used.

As a white ink, SARJOLAM PLUS WHITE RFL from Yansefu Inks and Coatings Private Limited was used.

Sample test result
The primer composition evaluation results have been provided in the following Table 3.
Table 3
Lamination Bond strength (N/ 25 mm) Primer-1 (GSM:0.1) Primer-2 (GSM:0.2) Primer-3 (GSM:0.3) Primer-4 (GSM:0.5) Primer-5 (GSM:0.6) Primer-6 (GSM:1.0)
(Polymeric substrate: BOPP printed with Colour Ink
Laminated to Woven sac) 1 1.5 2 3.5 4.5 Not separable
(Polymeric substrate: PE printed with Colour Ink
Laminated to Woven sac) 2 3 Not separable Not separable Not separable Not separable
(Polymeric substrate: BOPP printed with White Ink
Laminated to Woven sac) 1.5 2 2.5 4 5.5 Not separable
(Polymeric substrate: PE printed with White Ink
Laminated to Woven sac) 2 3 Not separable Not separable Not separable Not separable

Note:
* “Not separable” means the laminate layers could not be separated from each other.
* The numerical values in the above table indicate bond strength values expressed as N/25mm.

Advantages:
The primer coating provides good adhesion to ink and excellent extrusion lamination bond strength between polymeric substrates such as Polyethylene film or polypropylene film like biaxially oriented polypropylene (BOPP) and woven sac film.

Appropriate GSM of the said primer coating minimises the blocking problem in the printed laminate.

The solvent based primer despite being free of aromatic hydrocarbon solvents, exhibits improved extrusion lamination bond strength between polypropylene (PP) or Polyethylene (PE) substrates and a woven sac film. However, a person skilled in the art can use some amount of aromatic solvents such as toluene as per regulatory compliance requirement without departing from the teachings of the present invention.

Although the present disclosure is described in terms of certain preferred embodiments and examples, other embodiments and examples will be apparent to those of ordinary skill in the art, given the benefit of this disclosure, including embodiments and examples that do not provide all of the benefits and features set forth herein, which are also within the scope of this disclosure. It is to be understood that other embodiments may be utilized, without departing from the true spirit and scope of the present invention being indicated by the following claims.