FIELD OF THE INVENTION:
The present invention relates to a volatile organic compound (VOC) free,
environment-friendly and solvent-free lamination adhesive composition for lamination
of flexible substrates. Especially, the present invention relates to a two-component
adhesive composition for lamination of flexible substrates 5 comprising a –NCO
component and an –OH component in a defined ratio.
BACKGROUND OF THE INVENTION:
In order to better protect the environment, the release of volatile organic solvents to
10 the environment needs to be reduced and the use of solvent-based adhesives needs
to be eliminated.
Solvent-free adhesives possess the advantages of simple process flow, no emission
of volatile organic compounds to the environment ensuring better environmental
15 protection, less raw material consumption, low energy requirement, low maintenance
cost, less complicated machinery, high production speed and lesser risk of fire.
There are various uses of adhesives in today’s world. For example, adhesive
compositions are used to bond together sheet or film like substrates such as
20 polyethylenes, polypropylenes, polyesters, polyamides, metals, papers, or
cellophanes to form laminates also known as composite films. The extensive use of
adhesive compositions in diverse laminating applications is well known. For example,
adhesives are instrumental in the manufacture of laminates of flexible sheets used in
packaging of materials, particularly for packaging of food materials. Adhesives used
25 in laminating applications, or “laminating adhesives,” are commonly placed into three
categories: solvent-based, water-based, and solvent-free. The performance of an
adhesive varies by category or type of the adhesive and by the end application where
the adhesive is used.
30 Solvent-free laminating adhesives are applied using up to 100％ solid components
without the need of any of organic solvents or aqueous vehicles. Because of the fact
that organic solvent or water is not used in making the adhesives, there is no need of
drying the adhesive after application onto a substrate. Solvent-free adhesives are run
at high line speeds, hence are preferable in purposes requiring speedy adhesive
35 application. Solvent-based and water-based laminating adhesives are limited by
[3]
using the rate at which the solvent or water vehicle are efficiently dried and
eliminated after application. For environmental, health, and safety reasons,
laminating adhesives are ideally required to be solvent-free if not aqueous.
Within the category of solvent-free laminating adhesives, there are 5 many variations.
One particular variety includes two-component polyurethane-based laminating
adhesives. Usually, a two-component polyurethane-based laminating adhesive
includes a first component comprising an isocyanate-containing prepolymer and a
second component comprising one or more polyols. The first component is obtained
10 by the reaction of an isocyanate monomer with a polyether polyol and/or polyester
polyol. The second component is a polyether polyol and/or a polyester polyol. Each
component can optionally include one or more additives. The two components are
combined in a predetermined ratio for laminating biaxially oriented polypropylene
(BOPP) films, cast polypropylene (CPP) films, Metallized films, Nylon, Aluminium,
15 Polyester, Polyethylene, Polyvinylidene chloride (PVDC) and acrylic coated films and
other unprinted or reverse printed packaging substrates.
WO2018049672A1 discloses a two-component solventless adhesive composition
comprising a polyol component and an isocyanate component, where the polyol
20 component comprises a phosphate functional compound, and at least one polyol
selected from polyester, polyether, and the isocyanate component comprises a
isocyanate prepolymer.
US8022164B1 discloses a two-component solvent-free polyurethane laminating
25 adhesive including a first Component that acts as a resin, includes two vegetable oil
based polyols, and a Polyisocyanate. The Second Component, which acts as a
hardener, includes a vegetable oil based Polyol and another polyol.
US2014107287A1 discloses a solventless two component laminating adhesive
30 comprising a prepolymer and a curative. The prepolymer is a combination of a lower
molecular weight polyether polyol and a higher molecular weight polyether polyol.
The commercially available two-component solvent-free polyurethane-based
lamination adhesives based on the existing technologies have major limitations of
35 high viscosity of the –NCO component (usually 6000-10000 cps at 250°C) which
[4]
takes longer heating time to bring the adhesive composition to printing viscosity
during application. Another disadvantage of the technologies available in the prior-art
is short pot life and longer curing time of the adhesive mixture which drastically
reduces the overall productivity during printing. Yet another disadvantage of the
existing technology is poor wettability particularly when the secondary 5 lamination
layer is metallised, for example vacuum metallization on polyethylene terephthalate
(PET) films, biaxially oriented polypropylene (BOPP) films and cast polypropylene
(CPP) films.
10 Therefore, a two-component solvent-free polyurethane-based laminating adhesive
composition with improved printing viscosity, better pot life, faster curing, better
wettability on metallised layers, and methods of making the same, is desirable.
The present disclosure provides a two-component solvent-free lamination adhesive
15 composition comprising a –NCO component and an –OH component.
The Component A (–NCO component) of the solvent-free lamination adhesive
composition uses a reaction product of a Methylene diphenyl diisocyanate (MDI) with
a polyester-polyol component.
20
The polyester polyol composition in the Component A (–NCO component) of the
solvent-free lamination adhesive composition includes a polyethylene glycol (PEG)
with a molecular weight of 200 g/mol as the critical component, and neopentyl glycol
and adipic acid as the other major constituents.
25
These two parts are combined in a definite ratio to provide the desired properties of
the solvent-free lamination adhesive.
OBJECTS OF THE INVENTION:
30 The principal objective of the present invention is to provide a two-component
solvent-free lamination adhesive with better curing, pot-life.
Another objective of the present invention is to provide a two-component solvent-free
lamination adhesive with better wettability on metallised secondary layer.
35
[5]
A further objective of the present invention is to provide a two-component solventfree
lamination adhesive with lower printing viscosity of the NCO component.
Other objectives, features and advantages will become apparent to those skilled in
the art from the detailed description and the 5 appended claims.
SUMMARY OF THE INVENTION:
The present invention relates to a volatile organic compound (VOC) free,
environment-friendly and solvent-free two component adhesive composition for
10 lamination of flexible substrates comprising a –NCO component and an –OH
component.
The Component A (–NCO component) of the adhesive composition particularly
includes a reaction product of Methylene diphenyl diisocyanate (MDI) and a
15 polyester-polyol component.
The polyester polyol composition in the Component A (–NCO component) of the
solvent-free lamination adhesive composition includes a polyethylene glycol (PEG)
with a molecular weight of 200 g/mol as the critical component, and neopentyl glycol
20 and adipic acid as the other major constituents.
The Component B (–OH component) is a combination polyol composition containing
both polyether polyol and a polyester polyol based on mono-ethylene glycol, 2-methyl
1,3-propane diol, adipic acid and isophthalic acid as the principal components.
25
Polyether polyols suitable for use in the Component A (–NCO component) of the
present invention have a molecular weight of about 1,000 g/mol.
Polyether polyols suitable for use in the Component B (–OH component) of the
30 present invention have a molecular weight of about 700 g/mol.
The polyethylene glycol (PEG) in the Component A (–NCO component) has, a
molecular weight of about 200 g/mol.
[6]
The two components are combined in a predetermined ratio and applied on a film or
a metallised film substrate for lamination of the film or metallised film substrate onto
another substrate. Application may be from a solution in a suitable solvent using
gravure or smooth roll coating cylinders or from a solvent-free state using special
application 5 machinery.
The two components are combined in a definite ratio to provide the solvent-free
lamination adhesive composition of the present invention with improved properties
including better pot-life, faster curing, improved wettability, better storage stability.
10
The solvent-free lamination adhesive composition of the present invention is applied
on a film or a metallised substrate, where the adhesive applied film or adhesive
applied metallised film substrate is laminated onto another substrate by any suitable
method known in the art.
15
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
20 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
25 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.
30 Definitions of terms used in this specification:
As used herein, an “isocyanate monomer” is any compound that contains two or
more isocyanate groups. An “aromatic isocyanate” is an isocyanate that contains one
or more aromatic rings. An “aliphatic isocyanate” contains no aromatic rings.
[7]
Isocyanate monomers suitable for use according to the present invention are
selected from aromatic isocyanates, carbodiimide modified isocyanates, and the
combinations thereof. Examples of aromatic isocyanates suitable for use according to
this invention include, but are not limited to, isomers of methylene diphenyl
dipolyisocyanate (MDI) such as 4, 4-MDI, 2, 4-MDI and 2, 2’-MDI, 5 or modified MDI
such as carbodiimide modified MDI or allophanate modified MDI. Preferably the
aromatic isocyanates suitable for use according to this invention is methylene
diphenyl dipolyisocyanate (MDI) such as 4, 4-MDI, 2, 4-MDI and 2, 2’-MDI.
10 The use of methylene diphenyl dipolyisocyanate (MDI) is preferred over toluenedipolyisocyanate
(TDI) because MDI has the advantages of large molecular weight,
low volatility, less odour and low toxicity compared with TDI. Together with meeting
the environmental needs, MDI also contributes to the health of workers. Moreover,
compared to TDI, the price of MDI is much lower, which is helpful in saving the cost
15 of manufacturing, and also the curing agent made using MDI possess improved
mechanical properties.
A chemical compound with two or more hydroxyl (-OH) groups is known as a “polyol”
in this disclosure. A polyol with exactly two -OH groups is a “diol”. Similarly a polyol
20 with just three -OH groups is a “triol”.
A chemical compound that comprises at least two ester (R-CO-OR) linkages in the
same linear chain of atoms is known in this disclosure as a “polyester”. A chemical
compound that includes both multiple ester linkages and multiple –OH functional
25 groups is known in the present disclosure as a “polyester polyol”.
A chemical compound that comprises at least two ether (R-O-R) linkages in the same
linear chain of atoms is known in this disclosure as a “polyether”. A chemical
compound that includes both multiple ether linkages and multiple –OH functional
30 groups is known in the present disclosure as a “polyether polyol”.
As used herein, the terms “adhesive” or “lamination adhesive” is to mean the solventfree
adhesive composition prepared by mixing the two components i.e. Component A
(–NCO component) and Component B (–OH component) in a definite ratio to be used
35 for the purpose of lamination of flexible films and sheets.
[8]
Ratios, ranges, amounts: The ratios, ranges and amounts in this application often
expressed as "about" a certain number, value or range. "About" means the exact
amount or an amount within the limit of experimental error for the intended purpose.
Solvent-Free Lamination Adhesive 5 Formulation
The present invention provides a volatile organic compound (VOC) free,
environment-friendly and solvent-free lamination adhesive composition for lamination
of flexible substrates comprising two components i.e. a –NCO component and an –
OH component.
10
Component A (–NCO component)
The Component A (–NCO component) comprises a reaction product of reactants
comprising at least one “isocyanate monomer” and at least one polyester polyol.
15 The isocyanate monomer in the Component A (–NCO component) of the solvent-free
lamination adhesive composition is most preferably Methylene diphenyl diisocyanate
(MDI).
The amount of the isocyanate monomer in the Component A (–NCO component) is,
20 by weight based on the weight of the Component A (–NCO component), at least 55
wt％, or at least 57 wt％. The amount of the at least one isocyanate in the
Component A (–NCO component) is not to exceed, by weight based on the weight of
the Component A (–NCO component), 60 wt％, or 59 wt％.
25 The Component A (–NCO component) also comprises a polyether polyol as one of
the ingredients.
Polyether polyols suitable for use in the Component A (–NCO component) have a
molecular weight of about 1,000 g/mol.
30
Suitable polyether polyols for use in the Component A (–NCO component) is selected
from Polyethylene glycol, polypropylene glycol, ethoxylated and/or propoxylated
polyethers, poly-tetrahydrofuran (PolyTHF).
[9]
The amount of the polyether polyol in the Component A (–NCO component) is, by
weight based on the weight of the Component A (–NCO component), at least 9 wt％,
or at least 9.2 wt％. The amount of the polyether polyol in the Component A (–NCO
component) does not exceed, by weight based on the weight of the Component A (–
NCO component) 9.5 5 wt％, or 9.4 wt％.
The amount of the polyester polyol in the Component A (–NCO component) is, by
weight based on the weight of the Component A (–NCO component), at least 30
wt％. The amount of the polyester polyol in the Component A (–NCO component)
10 does not exceed, by weight based on the weight of the Component A (–NCO
component), 32 wt％, or 31 wt％.
The polyester polyol composition in the Component A (–NCO component) of the
solvent-free lamination adhesive composition includes a polyethylene glycol (PEG)
15 with a molecular weight of 200 g/mol as the critical component, and neopentyl glycol
and adipic acid as the other major constituents.
The Component A (-NCO Component) includes other additives such as stabilisers,
wetting agents, catalysts, adhesion promoters, cross-linkers etc.
20
Component B (–OH component)
The solvent-free lamination adhesive composition comprises at least one polyol
component comprising at least one polyol selected from the group consisting of a
polyester polyol, a polyether polyol, and the combination thereof.
25
Suitable polyether polyols for use in the Component B (–OH component) is selected
from Polyethylene glycol, polypropylene glycol, ethoxylated and/or propoxylated
polyethers, poly-tetrahydrofuran (poly-THF).
30 Polyether polyols suitable for use in the Component B (–OH component) have a
molecular weight of about 700 g/mol.
Preferably, the Component B (–OH component) comprises a combination polyol
composition containing both polyether polyol, and a polyester polyol. The polyester
[10]
polyol is based on adipic acid, mono-ethylene glycol, 2-methyl 1,3-propane diol (MP
Diol), and isophthalic acid.
The amount of the polyether polyol in the Component B (–OH component) is, by
weight based on the weight of the Component B (OH Component), 5 at least 35 wt％,
or at least 37 wt％. The amount of the polyether polyol in the Component B (–OH
component) does not exceed, by weight based on the weight of the Component B (–
OH component) 40 wt％, or 39 wt％.
10 The amount of the polyester polyol in the Component B (–OH component) is, by
weight based on the weight of the Component B (OH Component), at least 55 wt％.
The amount of the polyester polyol in the Component B (–OH component) does not
exceed, by weight based on the weight of the Component B (OH Component), 60
wt％, or 58 wt％.
15
The Component B (–OH component) includes other additives such as adhesion
promoters, wetting agents, adhesion promoters, cross-linkers etc.
The two components (Component A and Component B) are combined to make the
20 solvent-free lamination adhesive composition in a ratio of 1.0 : 0.50 to 1.0 : 0.80
wt/wt%, more preferably in a proportion of 1.0 : 0.55 to 1.0 : 0.70 wt/wt%, and most
preferably in a ratio of 1.0 : 0.60 wt/wt%.
The solvent-free lamination adhesive composition of the present invention with
25 improved properties including better pot-life, faster curing, improved wettability, better
storage stability.
The solvent-free lamination adhesive composition of the present invention is applied
on a film or a metallised substrate, where the adhesive applied film or adhesive
30 applied metallised film substrate is laminated onto another substrate by any suitable
method known in the art.
In a preferred embodiment of the invention, the solvent-free lamination adhesive
composition of the present invention includes the ingredients as given below. 3.2. Wettability test of the solvent-free adhesive composition:
In an embodiment, the solvent-free adhesive of Example 3 after 5 10 minutes of
mixing, (when the viscosity was measured as 1185 centipoise) was applied to the
surface of a 12 micron thin Polyethylene terephthalate (PET) film substrate.
The wettability was measured as the surface tension of the solvent-free adhesive
10 with the substrate. A contact angle of the substrate with the adhesive was found to
be less than about 5 degrees in air.
3.3. Pot life test of the solvent-free adhesive composition:
It would also be desirable to provide a polyurethane laminating adhesive that has a
15 long pot-life, for example greater than about 25 minutes, more preferably greater than
about 30 minutes or more at application temperatures. In comparison with the
adhesive dispersions described in the prior art, the solvent-free adhesive
compositions of the present invention have prolonged pot lives, or slower increases
in viscosity.
20
As shown in Table 9, the pot-life of the two-component solvent-free adhesive
composition is more than 30 minutes to reach a viscosity of 3000 centipoise (cps). It
takes more than 40 minutes for the adhesive composition of the present invention to
reach a viscosity of 4000 centipoise (cps), which makes the adhesive easy to handle
25 in laminating operations and easy to clean from laminating equipment.
3.4 Strength of Laminate formed by using the solvent-free adhesive
composition:
The adhesive as prepared as given in Example 3 was then applied to a 12 micron
30 thin Polyethylene terephthalate (PET) film substrate. A 55 micron thin Low Density 5. The two-component solvent-free lamination adhesive composition according to
claim 1, wherein, the polyether polyol in the NCO functional group containing
component and in the OH functional group containing component is selected
from Polyethylene glycol, polypropylene glycol, ethoxylated polyethers,
propoxylated, poly-tetrahydrofuran 5 (PolyTHF).
6. The two-component solvent-free lamination adhesive composition according to
claim 1, wherein, the Component A and Component B are combined in a ratio of
1.0 : 0.50 to 1.0 : 0.80 wt/wt%, more preferably in a ratio of 1.0 : 0.55 to 1.0 : 0.70
10 wt/wt%, and most preferably in a ratio of 1.0 : 0.60 wt/wt%.
7. The two-component solvent-free lamination adhesive composition according to
claim 1, wherein, the NCO functional group containing component additionally
comprises additives such as wetting agents, storage stabilisers, esterification
15 catalysts and processing stabilizer; and the OH functional group containing
component additionally comprises additives such as wetting agents, adhesion
promoters and esterification catalysts.
8. The two-component solvent-free lamination adhesive composition according to
20 claim 1, wherein said adhesive composition creates a surface tension with a 12
micron thin Polyethylene terephthalate (PET) film substrate producing a contact
angle of less than about 30 degrees in air, preferably less than about 10 degrees
in air and most preferably less than about 5 degrees in air.
25 9. A laminate formed by bonding two films with a two-component solvent-free
lamination adhesive composition comprising:
a NCO functional group containing component,
where, the NCO functional group containing component is a reaction product
of an isocyanate monomer, and a polyester polyol; and
30 a OH functional group containing component
where, the OH functional group containing component is a combination polyol
comprising a polyether polyol and a polyester polyol,
wherein, the amount of polyester polyol in the NCO functional group containing
component is, by weight based on the weight of the NCO functional group
35 containing component is about 30 wt％ to about 32 wt%; and the amount of
polyester polyol in the OH functional group containing component is, by weight