WO2022185115A1

WO2022185115A1 - An adhesive composition and a process for its preparation

Info

Publication number: WO2022185115A1
Application number: PCT/IB2021/061027
Authority: WO
Inventors: Prem Kumar Nautiyal; Atul Kumar; Vilas Karande
Original assignee: Uflex Limited
Priority date: 2021-03-04
Filing date: 2021-11-27
Publication date: 2022-09-09

Abstract

The present disclosure relates to an adhesive composition and a process for its preparation. The adhesive composition comprises a first component and a second component. The first component comprises an OH component, at least one pigment and at least one additive. The second component comprises an NCO prepolymer compound. The first component and the second component are heated at a temperature in the range of 35 °C to 50 °C and then mixed together in a weight ratio in the range of 70:100 to 90:100 before application to obtain the adhesive composition. The adhesive composition of the present disclosure is solvent free and works well on existing solvent less lamination machines and drastically reduces the requirement of white inks. The process for the preparation of the adhesive composition is simple, efficient and environment friendly.

Description

AN ADHESIVE COMPOSITION AND A PROCESS FOR ITS PREPARATION

FIELD

The present disclosure relates to an adhesive composition and a process of its preparation.

DEFINITIONS

As used in the present disclosure, the following ter s are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used to indicate otherwise.

OH (polyols) component: The term “OH (polyols) component”, also known as hydroxyl terminated polyester compound or esterified hydroxyl terminated product or OH component, as used herein refers to a component obtained via esterification reaction of diacids and dihydric alcohols.

NCO component: The term “NCO component”, also known as isocynate component, as used herein refers to an isocyanate functionalized crosslinker monomer. It reacts with an esterified hydroxy terminated product (obtained via esterification reaction of diacids and dihydric alcohols) to form NCO prepolymer component.

Hegman gauge: The term “Hegman gauge”, also known as a grind gauge, refers to an instrument which indicates the fineness of grind or the presence of coarse particles and agglomeration, in dispersion.

Bead mill: The term “bead meal” refers to a grinding and dispersing machine designed to grind and disperse particles down to micro and nano scales.

Bond strength: The term “bond strength” refers to an average force required to peel the two films. Unit of measurement of bond strength is gf. BACKGROUND

The background information herein below relates to the present disclosure but is not necessarily prior art.

The adhesion of the bonded substrates such as laminates depends mainly on the intermolecular forces between the substrates and adhesive. There are different types of adhesives available commercially which are commonly used in the flexible packaging applications. Typically, the solvent based adhesives are used commercially. The use of such adhesives affects the environment adversely because of the high content of volatile organic solvents. Moreover, the necessity of high energy consuming equipment’s for drying these solvents to achieve the desired properties increases the overall cost.

Further, the conventional adhesives are generally applied on the reverse printed substrates and bonded with another substrate. While printing such reverse printed substrates, generally white ink is used in most of the commercial jobs. The application of adhesive and white ink, separately, is time consuming, requires extra labour, required in a huge amount and is expensive. Furthermore, the introduction of white pigments into 100% solid resin is a big challenge as it impacts wettability, hiding properties of the substrates, stability of the adhesive, flow control, specific gravity and bond strengths to the laminates used. Still further, the use of white pigment along with adhesives lead to the formation of spots during high speed printing.

The conventional adhesives have NCO terminated polymeric chains of varying chain length, i.e. short chains and long chains. If these NCO terminated polymeric chains comes in contact with moisture, it forms primary aromatic amines and carbon dioxide gas. If these amines are of short chain length then it has possibility of migration from intermediate layer to inner layer. Thus, when the adhesive is used in the food packaging, it is required to ensure the quality of the food material so that the aromatic amines from the adhesives should not migrate to the food material. In the food packaging adhesives, the amount of residual migration of aromatic amines should be less than 10 mg/dm . Further, the conventional polyurethane based adhesives used in flexible packaging applications are associated with the drawback of the occurrence of primary aromatic amines in the laminated food packaging materials, which originates from the polyurethane based adhesives used for binding the multilayer films.

Therefore, there is felt a need to provide an adhesive composition that mitigates the drawback mentioned herein above.

OBECTS

Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows.

It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.

Another object of the present disclosure is to provide an adhesive composition.

Yet another object of the present disclosure is to provide an adhesive composition which is free from solvent.

Still another object of the present disclosure is to provide an adhesive composition which serves the purpose of an ink.

Still another object of the present disclosure is to provide a cost effective and ecofriendly process for the preparation of the adhesive composition.

Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY

The present disclosure provides an adhesive composition. The composition comprises a first component and a second component. The first component comprises: (i) OH (polyol) component in an amount in the range of 55 wt% to 65 wt% with respect to the total weight of the first component; (ii) at least one pigment in an amount in the range of 30 wt% to 60 wt% with respect to the total weight of the first component; and (iii) at least one additive in an amount in the range of 0.05 wt% to 1 wt% with respect to the total weight of the first component. The second component comprises an NCO prepolymer component. A weight ratio of an NCO component to an OH component in the NCO prepolymer component is in the range of 1:1 to 2:1. The first component and the second component are heated at a temperature in the range of 35 °C to 50 °C and then mixed together in a weight ratio in the range of 70:100 to 90:100 before application to obtain the adhesive composition.

The present disclosure also provides a process for the preparation of the adhesive composition. Initially, a diacid is reacted with dihydric alcohol at a first predetermined temperature for a first predetermined time period in the presence of a first catalyst and a first anti-oxidant to obtain an esterified hydroxy terminated compound (OH component). Then, at least one pigment and at least one additive are mixed with the OH component to obtain a first mixture. The first mixture is then grinded to obtain a first component. Separately, a diacid is reacted with a dihydric alcohol at a second predetermined temperature for a second predetermined time period in the presence of a second catalyst and a second antioxidant to obtain an esterified hydroxy terminated compound (OH component). An isocyanate functionalized cross-linker monomer (NCO component) is reacted with the esterified hydroxy terminated compound (OH component) in a predetermined weight ratio at a third predetermined temperature for a third predetermined time period to obtain a second mixture. The second mixture is then subjected to vacuum drying to obtain a second component (NCO prepolymer component). The first component and the second component are heated at a temperature in the range of 35 °C to 50 °C and then mixed together in a weight ratio in the range of 70:100 to 90:100 before application to obtain the adhesive composition.

DETAILED DESCRIPTION

Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, known processes or well-known apparatus or structures, and well known techniques are not described in detail. The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure are not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.

The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.

As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements.

Conventional adhesives are solvent based, which adversely affects the environment. Further, in the conventional adhesives, adhesives and ink are applied separately. Thus, requires a huge amount of adhesives as well as ink. The application process of these adhesives is time consuming, requires extra labour and is expensive. Furthermore, the introduction of pigments into 100% solid resin for preparing the adhesive composition is a big challenge as it impacts wettability, hiding properties of the substrates, stability of the adhesive, flow control, specific gravity and bond strengths to the laminates used. Still further, the use of white pigment along with adhesives is associated with the drawback of forming spots during high speed printing.

In an aspect, the present disclosure provides an adhesive composition.

The adhesive composition of the present disclosure comprises a first component and a second component. The first component comprises: (i) an OH (polyol) component; (ii) at least one pigment; and (iii) at least one additive. The second component comprises an NCO prepolymer component.

The first component and the second component are heated at a temperature in the range of 35 °C to 50 °C and then mixed together in a weight ratio in the range of 70: 100 to 90: 100 before application to obtain the adhesive composition.

In accordance with the present disclosure, the OH (polyol) component is in an amount in the range of 55 wt% to 65 wt% with respect to the total weight of the first component. In an exemplary embodiment, the amount of the OH (polyol) component is 61.4 wt% with respect to the total weight of the first component.

In accordance with the present disclosure, the pigment is at least one selected from titanium dioxide, zinc oxide, calcium carbonate, talc and silica. In an exemplary embodiment, the pigment is titanium dioxide (white pigment). In accordance with an embodiment of the present disclosure, the pigment is in an amount in the range of 30 wt% to 60 wt% of the total weight of the first component. In an exemplary embodiment, the amount of the pigment is 38.4 wt% with respect to the total weight of the first component.

In accordance with an embodiment of the present disclosure, the additive is at least one selected from dispersing agent and wetting agents. The dispersing agent is at least one selected from the group consisting of multifunctional silicone resin dispersion and dicarboxylic acid ester. In an exemplary embodiment, the dispersing agent is multifunctional silicone resin dispersion. In accordance with an embodiment of the present disclosure, the amount of at least one dispersing agent is in an amount in the range of 0.05 wt % to 0.2 wt% with respect to the total weight of the first component. In an exemplary embodiment, the amount of the dispersing agent is 0.05 wt% with respect to the total weight of the first component.

In accordance with an embodiment of the present disclosure, the wetting agent is polyether modified poly dime thylsiloxane. The amount of wetting agent is in the range of 0.05 wt% to 1 wt% with respect to the total weight of the first component. In an exemplary embodiment, the amount of wetting agent is 0.05 wt% with respect to the total weight of the first component. In accordance with the present disclosure, a weight ratio of an NCO component to an OH (polyol) component in the NCO prepolymer is in the range of 1:1 to 2:1. In an exemplary embodiment, the weight ratio of the NCO component to the OH (polyol) component is 1.8:1.

In another aspect, the present disclosure provides a process for the preparation of adhesive composition. The process is described in detail as follows:

In a first step, a diacid is reacted with a dihydric alcohol at a first predetermined temperature for a first predetermined time period in the present of a first catalyst and a first antioxidant to obtain an esterified hydroxy terminated compound (OH component).

In accordance with an embodiment of the present disclosure, the first predetermined temperature is in the range of 130 °C to 260 °C. In an exemplary embodiment, the first predetermined temperature is up to 235 °C. The first predetermined time period is in the range of 20 hours to 35 hours. In an exemplary embodiment, the first predetermined time period is 28 hours.

In accordance with the present disclosure, the first catalyst is selected from the group consisting of titanium butoxide, butylstannoic acid, monobutyltin oxide and monobutyltin hydroxide oxide. In an exemplary embodiment, the first catalyst is titanium butoxide.

In accordance with the present disclosure, the first antioxidant is selected from the group consisting of butylated hydroxy toluene, tris(2,4-di-tert.-butylphenyl)phosphite, and pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate). In an exemplary embodiment, the first antioxidant is butylated hydroxy toluene.

In accordance with the embodiment of the present disclosure, the molar ratio of the diacid to the dihydric alcohol is in the range of 1:1 to 1:2. In an exemplary embodiment, the molar ratio of the diacid to the dihydric alcohol is 1:1.4.

In accordance with an embodiment of the present disclosure, the diacid is at least one selected from the group consisting of hexanedioic acid, nonanedioic acid, butanedioic acid, decanedioic acid, octadecanoic acid, benzene-1, 3-dicarboxylic acid and benzene- 1,4- dicarboxylic acid. In an exemplary embodiment, the diacid is a mixture of hexanedioic acid and benzene- 1 ,4- dicarboxylic acid. In accordance with an embodiment of the present disclosure, the dihydric alcohol is at least one selected from the group consisting of ethane- 1,2-diol, 2,2'-oxydi(ethan-l-ol), propane- 1, 2-diol, 2,2-dimethylpropane-l,3-diol, butane- 1,4-diol, hexane- 1,6-diol, propane- 1, 2, 3-triol and 2-(hydroxymethyl)-2-ethylpropane-l,3-diol. In an exemplary embodiment, the dihydric alcohol is a mixture of 2,2'-oxydi(ethan-l-ol), 2,2-dimethylpropane-l,3-diol and propane- 1, 2, 3-triol.

In a second step, at least one pigment and at least one additive is mixed to the OH (polyol) component to obtain a first mixture.

In accordance with the present disclosure, the amount of OH (polyol) component is in the range of 55 wt% to 65 wt% with respect to the total weight of the first component. In an exemplary embodiment, the amount of OH (polyol) component is 61.4 wt% with respect to the total weight of the first component.

In accordance with an embodiment of the present disclosure, the pigment is at least one selected from titanium dioxide, zinc oxide, calcium carbonate, talc and silica. In an exemplary embodiment, the pigment is titanium dioxide (white pigment). The amount of pigment is in the range of 30 wt% to 60 wt% with respect to the total weight of the first component. In an exemplary embodiment, the amount of pigment is 38.4 wt% with respect to the total weight of the first component.

In accordance with an embodiment of the present disclosure, the additive is at least one selected from dispersing agent and wetting agent.

The dispersing agent is at least one selected from the group consisting of multifunctional silicone resin dispersion and dicarboxylic acid ester. In another exemplary embodiment, the dispersing agent is multifunctional silicone resin dispersion. In accordance with an embodiment of the present disclosure, the amount of at least one dispersing agent is in an amount in the range of 0.05 wt % to 0.2 wt % of the total weight of the first component. In an exemplary embodiment, the amount of the dispersing agent is 0.05 wt % of the total weight of the first component.

The dispersing agent is incorporated in the OH component in order to have long term stability. In accordance with the present disclosure, the wetting agent is polyether modified polydimethylsiloxane. In accordance with an embodiment of the present disclosure, the amount of wetting agent is in the range of 0.05 wt% to 0.1 wt% with respect to the total weight of the first component. In an exemplary embodiment, the amount of the wetting agent is 0.05 wt% with respect to the total weight of the first component.

The function of the wetting agent is to reduce the surface tension between adhesive composition and pigment, which results in better wettability.

In a third step, the first mixture is grinded to obtain a first component.

In accordance with an embodiment of the present disclosure, the first mixture is grinded to obtain a first component having a particle size in the range of 1 to 5 pm.

In an embodiment, the grinding is done by bead milling. Bead mill is basically dispersing and grinding machine designed to grind and disperse particles down to micro and nano scales. This is one of the very important steps in the white adhesive making, as stability of the product is governed by level of pigment grinding. In an embodiment, the grinding is done for 30 min and the level of dispersing and grinding is checked with the help of Hegman gauge. Hegman gauge is an instrument which gives idea about the particle size of the pigment in dispersed state. In order to get uniform and stable OH component, the desired particle size is less than 5 pm.

Separately, in order to obtain second component (NCO prepolymer component), firstly a diacid is reacted with a dihydric alcohol at a second predetermined temperature for a second predetermined time period in the present of a second catalyst and a second antioxidant to obtain an esterified hydroxy terminated compound (OH component).

In accordance with an embodiment of the present disclosure, the second predetermined temperature is in the range of 130 °C to 260 °C. In an exemplary embodiment, the second predetermined temperature is up to 225 °C. The second predetermined time period is in the range of 20 hours to 35 hours. In an exemplary embodiment, the second predetermined time period is 28 hours. In accordance with an embodiment of the present disclosure, a molar ratio of diacid to dihydric alcohol is in the range of 1:1 to 1:2. In an exemplary embodiment, the molar ratio of the diacid to the dihydric alcohol is 1 : 1.4.

In accordance with the present disclosure, the second catalyst is selected from the group consisting of titanium butoxide, butylstannoic acid, monobutyltin oxide and monobutyltin hydroxide oxide. In an exemplary embodiment, the second catalyst is titanium butoxide.

In accordance with the present disclosure, the second antioxidant is selected from the group consisting of butylated hydroxy toluene, tris(2,4-di-tert.-butylphenyl)phosphite, and pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate). In an exemplary embodiment, the second antioxidant is butylated hydroxytoluene.

In an embodiment, the first catalyst and the second catalyst are same. In another embodiment, the first catalyst and the second catalyst are different.

In an embodiment, the first antioxidant and the second antioxidant are same. In another embodiment, the first antioxidant and the second antioxidant are different.

In accordance with an embodiment of the present disclosure, the diacid is at least one selected from the group consisting of hexanedioic acid, nonanedioic acid, butanedioic acid, decanedioic acid, octadecanoic acid, benzene-1, 3-dicarboxylic acid and benzene- 1,4- dicarboxylic acid. In an exemplary embodiment, the diacid is hexanedioic acid.

In accordance with an embodiment of the present disclosure, the dihydric alcohol is at least one selected from the group consisting of ethane- 1,2-diol, 2,2'-oxydi(ethan-l-ol), propane- 1, 2-diol, 2,2-dimethylpropane-l,3-diol, butane- 1,4-diol, hexane- 1,6-diol, propane- 1, 2, 3-triol and 2-(hydroxymethyl)-2-ethylpropane-l,3-diol. In an exemplary embodiment, the dihydric alcohol is a mixture of ethane- 1,2-diol, 2,2-dimethylpropane-l,3-diol, and propane- 1,2,3- triol.

An isocyanate functionalized cross-linker monomer (NCO component) is then reacted with so obtained esterified hydroxy terminated compound (OH) in a predetermined weight ratio at a third predetermined temperature for a third predetermined time period to obtain a second mixture. In accordance with an embodiment of the present disclosure, the third predetermined temperature is in the range of 50 °C to 100 °C. In an exemplary embodiment, the third predetermined temperature is 75 °C. The third predetermined time period is in the range of 2 hours to 10 hours. In an exemplary embodiment, the third predetermined time period is 5 hours.

In accordance with an embodiment of the present disclosure, a weight ratio of the isocyanate functionalized crosslinker monomer (NCO component) to the esterified hydroxy terminated compound (OH component) is in the range of 1:1 to 2:1. In an exemplary embodiment, the molar ratio of the esterified hydroxy terminated compound to the isocyanate functionalized crosslinker monomer is 1.8:1.

In accordance with an embodiment of the present disclosure, the isocyanate functionalized crosslinker is at least one selected from 2,2 methylene diphenyl diisocyanate (MDI), 2,4 methylene diphenyl diisocyanate (MDI), 4,4 methylene diphenyl diisocyanate (MDI), 5- isocyanato-l-(isocyanatomethyl)-l,3,3-trimethylcyclohexane (IPDI) and 1,6- diisocyanatohexane (HDI). In an exemplary embodiment the isocyanate functionalized crosslinkers is a mixture of 2,2-MDI (2-4%), 2,4-MDI (44-50%) and 4,4-MDI (44-50%).

There are different types MDI available depending on the percentage of MDI isomers present in it. A pure MDI contains 100% 4,4-MDI. The other form of MDI have a combination of 2,2-MDI, 2,4-MDI, and 4,4-MDI isomers with varying concentrations. Due to steric hindrances, reactivity of the 2,2-MDI is the least. 2,4-MDI is more reactive than 2,2-MDI; and 4,4-MDI is the most reactive amongst three isomers. Though 4,4-MDI is the most reactive, even a mixture of three isomers gives the desired result for the preparation of adhesive mixture.

The second mixture is then subjected to vacuum drying to obtain a second component (NCO component).

The first component and the second component are heated at a temperature in the range of 35 °C to 50 °C and then mixed together in a weight ratio in the range of 70: 100 to 90: 100 before application to obtain the adhesive composition. The adhesive composition prepared by the process of the present disclosure has a lower content of free isocyanate functionalized crosslinker (MDI) and hence migration of isocyanates is avoided.

The adhesive composition of the present disclosure works well on existing solvent less lamination machines and also reduces the requirement of white inks drastically. The white ink is four times costlier than other pigmented inks thereby giving substantial savings to the converters. The adhesive composition of the present disclosure provides good adhesion, and application suitability at low temperature. The adhesive composition of the present disclosure is environment friendly as it does not contain any solvent (solvent free). It can run at 300 - 350 meters/minute with excellent lay to the print and bonds are excellent. Ultimately convertor can get high productivity and per kg cost reduced in terms of consumption and power. If solvent-free adhesive composition of the present disclosure is compared with the solvent based adhesives, then solvent-free adhesives can run at higher production speeds like 300-350 m/min. However, the solvent based adhesives can run at production speed between 200-250 m/min. Also, as the adhesive of the present disclosure is solvent-free, there is no need to have extra heating zones for evaporation of solvents which is not the case with solvent based adhesives. There are different types of conventional solvent-free adhesives which are only used for adhesive purpose. However, white adhesive is used for dual purpose of ink as well as adhesive. The white adhesive can work on similar machines which are used for conventional solvent-free adhesives. Therefore, there is no need of modification of existing machines.

The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.

The present disclosure is further illustrated herein below with the help of the following experiments. The experiments used herein are intended merely to facilitate an understanding of the ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the experiments should not be construed as limiting the scope of embodiments herein. These laboratory scale experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial/commercial scale.

EXPERIMENTAL DETAILS:

EXPERIMENT 1: Optimization of the process for the preparation of adhesive composition

Example 1

Initially, 48.81 g of adipic acid (hexanedioic acid) and 1.5 g of terephthalic acid (benzene- 1 ,4-dicarboxylic acid) were added in a reactor followed by adding 38.41 g of diethylene glycol (2,2'-oxydi(ethan-l-ol)), 10.65 g of neopentyl glycol (2,2-dimethylpropane-l,3-diol) and 0.6 g of glycerol (propane- 1, 2, 3-triol) to obtain a mixture. The mixture was esterified in the presence of catalyst (titanium butoxide) and antioxidant (butylated hydroxytoluene) at a temperature of up to 235 °C for 28 hours to obtain an esterified hydroxyl terminated polyester compound (OH component) by eliminating water as a byproduct. The esterification temperatures generally start at around 130 °C.

The hydroxyl value and viscosity achieved for the esterified hydroxyl terminated polyester compound (OH component) were in the range of 150 to 170 mg of KOH per g of resin sample and 1200-2100 cps at 25 °C respectively. The viscosity of the samples was measured using Brookfield viscometer (the hydroxyl values and the viscosity values are provided in ranges because it is so sensitive that result can always vary with the number of measurements).

The hydroxyl value is most important parameter as the reactivity of the first component with the second component is governed by the same. If it is not matching as per stoichiometric amounts, the drying of the adhesive will not be proper. In order to obtain the desired drying properties, stoichiometric proportions of the first component and the second component have to be matched. Viscosity is also another important property as it decides the amount of pigment that can be added in to the system. 61.5 g of so obtained hydroxyl terminated polyester (OH (polyol) component) was taken in a high speed mixer. Then, 38.5 g of titanium dioxide pigment was slowly added in the high speed mixer in such a way that homogeneous slurry was formed. The homogeneous slurry was then subjected to high speed mixing for 30 min at 1500 rpm to obtain a homogeneous mixture.

The viscosity of the so obtained mixture was measured and it was 2000 cps at 25 °C.

The homogenous mixture (first component) so obtained by the above process was subjected to stability study at different temperatures of -15 °C, 25 °C and 50 °C to understand its separation behavior. It was observed that, after 7 days, resin and pigment particles got separated. It clearly indicated that the interaction between titanium dioxide pigment and OH component was not adequate enough to obtain a stable product.

The second component was prepared by obtaining hydroxy terminated polyester polyol in the first step, which was then reacted with isocynates in the second step to obtain the NCO terminated prepolymer. So, in the first step, 56.18 g of adipic acid (hexanedioic acid) was charged in a reactor followed by adding 19.48 g of monoethylene glycol (ethane 1,2 diol), 24 g of neopentyl glycol (2,2-dimethylpropane-l,3-diol ), 0.3 g of glycerol (propane- 1, 2, 3-triol) to obtain a mixture. The mixture was then esterified in the presence of catalyst (titanium butoxide) and antioxidant (butylated hydroxytoluene) at a reaction temperature of up to 235 °C for 28 hours by eliminating water as a byproduct to obtain a hydroxy terminated polyester polyol (esterified hydroxy terminated compound or OH component). The esterification reaction started at 130 °C.

The hydroxyl value of the hydroxy terminated polyester polyol was in the range of 200-220 mg of KOH per gm of resin sample. The acid value of the so OH component was below 2 mg of KOH per gram of the hydroxy terminated polyester polyol.

In the second step, 34.5 g of hydroxy terminated polyester polyol (esterified hydroxy terminated compound), so obtained was reacted with 65.4 g of Methylene diphenyl diisocyanate (MDI) having 2-4% of 2,2 MDI, 44-50% of 2,4 MDI and 44-50% of 4,4 MDI at 75 °C for 5 hours to obtain an NCO component (second component).

The % NCO content of the prepolymer is designed in the range of 12-18%. In the present embodiment, its value was 15%. % NCO is one of the properties of the PU prepolymer and its stoichiometric amount has to be matched with the stoichiometric amounts and hydroxyl value of the first component. The first component and the second component are heated at 40 °C followed by mixing in a weight ratio of 80:100 to obtain an adhesive composition. The viscosities were then measured to determine the pot life of the adhesive composition.

Pot life of an adhesive composition is determined by measuring the viscosity of a mixture of a first component and a second component, when mixed at temperature 40 °C. The mixing of the first component and the second component is an exothermic reaction. It gives idea about the time up to which mixture of first component and second component can be in usable state. If mixed viscosity increases rapidly then application of such adhesive mixture becomes very difficult. Pot life data of the above adhesive composition having the first component and the second component has been tabulated as below:

Table 1: Pot life data of the adhesive composition of example 1

Generally, when the viscosity of the adhesive composition is below 3000 cps then the adhesive composition is considered as suitable for application. In this case, the adhesive composition was suitable for application till 15 minutes, after which viscosity starts increasing and application becomes difficult.

Example 2

The first component in Example 2 was prepared similar to Example 1, except that the slurry (homogenous slurry of OH component and pigment) was subjected to high speed mixing (at 1500 rpm) for increased time duration (60 min instead of 30 min) so that homogeneous mass is achieved.

The viscosity of the so obtained first mixture was measured and it was 1800 cps at 25 °C.

The so obtained first component was subjected to stability study at different temperatures of - 15 °C, 25 °C and 50 °C to understand its separation behavior. It was observed after 15 days that stability of the mixture was intact as no separation was noticed. Stability test was continued and samples were examined after completion of one month. It was observed that slight separation of the pigments started however it was better than the first component mentioned in the example 1. Based on the observation, it was concluded that the increased duration of mixing improved stability of the mixture dramatically. It clearly indicated that the interaction between titanium dioxide pigment and OH component was improved, however it was not adequate enough to obtain product which will be stable for more than one month.

Further, the second component (NCO component) was prepared in the same way as given in Example 1.

Example 3

The first components in Example 3 was prepared similar as in Example 2, except that the homogeneous mass of OH component and titanium dioxide pigment obtained after high speed mixing was processed with bead mill. The grinding by bead mill was done for 30 min and level of grinding was checked by using Hegman gauge. The particle size of the first mixture was less than 5 pm.

The viscosity of the first component so obtained after passing through bead mill was in about 1600 cps at 25 °C.

The so obtained grinded first component was subjected to stability study at different temperatures of -15 °C, 25 °C and 50 °C to understand its separation behavior. It was examined after 1 month, 2 months and 3 months. It was observed that stability of the mixture was intact up to 2 months and no separation was noticed, however after 3 months slight separation was observed. Further, the second component in Example 3 was prepared in the same way as in Example 2. The adhesive composition was then obtained after mixing the first component and the second component in a ratio of 80: 100 at 40 °C.

The pot life of the adhesive composition was studied in the same way as performed in example 1. The viscosity was measured and it was less than 3000 cps after 15 min which was fair in terms of application.

Example 4

In order to understand the effect of dispersing agent on the stability of the first component, four different compositions of dispersing agents with varying concentrations were prepared. The first component was prepared in the similar way as in example 3 and further added the multifunctional silicone resin (Dow Corning® 3 Additive) as a dispersing agent with various concentrations.

Table 2 depicts the incorporation of different concentrations of dispersing agent in the first component

The so obtained first component (first component of example 3 + dispersing agent) were subjected to stability study at different temperatures of -15°C, 25°C and 50°C up to 9 months. This first component was examined after 3, 4, 5, 6, 7, 8 and 9 months. It was observed that the first component with no dispersing agent was separated, however the first component having 0.05%, 0.1% and 0.2% of dispersion agent were stable with no separation. Stability of the first component having dispersing agent in the concentration of 0.05%, 0.1 % and 0.2% was same. Therefore, the first component having 0.05 wt% of dispersing agent was the optimized concentration for further experiments.

The second component (NCO component) was prepared similar to example 3.

Application of the adhesive composition prepared in accordance with example 4 of the present disclosure

Substrates like printed PET (polyethylene terephthalate) to metallized PET (metallized polyethylene terephthalate), printed PET to metallized CPP (metallized cast polypropylene), printed PET to metallized BOPP (biaxially oriented polypropylene), printed BOPP to metallized BOPP are generally used for various applications. In the current embodiment, printed BOPP to metallized BOPP substrate was used for the application of the white adhesive.

The first component (with 0.05% dispersing agent) and the second component prepared in accordance with the example 4 of the present disclosure was kept in oven at 40°C. After attaining the temperature of 40°C, the first component and the second component were mixed in different ratios of 70:100, 80:100 and 90:100, and applied on the PET substrate with 2-4 gsm. GSM is gram of adhesive required to deposit 1 m area of substrate with 2-4 gsm weight depending on type of substrate as well opacity required. If more opacity required then higher gsm is needed and lower opacity is required then lower gsm is needed.

In the next step, the substrates were kept on it and nipped using the hand roller to form a laminate. The laminates made were passed through laminator to get a uniform laminate and kept under load of about 5 kg at 40 °C for 24-36 hours for curing to take place.

Cured laminates were tested for opacity and bond strength. Opacity is the hiding power of the substance, measured using an opacity meter. The unit of opacity is percentage (%) and if its value is above 60% then it is called a good opacity. Bond strength was measured using a Universal Testing Machine (UTM), Instron, Model no. R6570. 2-3 test specimens having 15 mm width were cut from the laminate. In the next step, they were partially delaminated so that two layers can fit into the upper and lower jaw of the UTM machine. Machine speed is 50 mm/rnin. Force required to separate the two layers was measured using UTM machine. It was found that laminates made using the adhesive composition having a ratio of first component to the second component of 80:100 were optimum in terms of curing. However, opacity of laminates made using all the mixing ratios (of the first component to the second component) 70:100, 80:100, and 90:100 was in the similar range, i.e., 65-66%. In case of the adhesive composition having the mixing ratio of 70:100, no tack was present. However, the bond and seal strength was on the lower side. In case of the adhesive composition having a mixing ratio of 90: 100, laminates had tack present in it, and bond and seal strength properties were also on the lower side.

Curing of the laminates is related to the amount of tackiness present in the laminate. If tackiness is present, it means curing of the adhesive is not complete. If there is no any tack means curing of the adhesive is complete and the laminates can be further processed. Having no tack is a desirable condition. Generally to be considered as the best laminate, tack should be as low as possible and seal strength should be on the higher side preferably more than 2 Kgf /15 mm which indicate the complete curing of the laminate. Tackiness is observed when polymerization is incomplete due incomplete curing time or lower curing temperature or higher GSM of the adhesive given.

The first component and the second component obtained as per example 4 were mixed in a ratio of 80:100 and sent for the trials on the commercial solventless laminating machines (Nordmeccanica and Uflex Model No. Simplex 1010). It was observed that curing of the adhesive was perfect after 24-36 hours with no tack as well as good bond and seal properties. Opacity of the laminates was also good (66%), however some speckling was observed at higher machine speeds.

The adhesive composition has a storage stability of at least nine months as it was evident from the appearance of the laminated substrate. If wetting is not good then lot of spots (speckling) can be observed on the laminate. Generally in case of metallized substrates, wetting becomes difficult and one can clearly see the dewetting behavior. The laminates prepared using adhesive composition of the present disclosure is free of speckling. Therefore, the adhesive composition demonstrated excellent wettability on metallized substrates.

Example 5 In this example first component obtained in example 4 was taken as such and effect of wetting agents at various concentrations was studied to understand its impact on wettability of substrates and speckling. The concentrations of wetting agents were varied from 0.05 to 0.1 wt%. Table 3 depicts the different concentrations of wetting agent (polyether modified polydimethylsiloxane) in the first component of example 4

Concentrations of wetting agents varied from 0.05% to 0.1% and it was observed that wetting behavior with 0.05 % and 0.1% was similar, but much improved than adhesive composition with no wetting agent. Therefore, concentration of wetting agent was optimized to 0.05%. The second component was prepared in the similar way as in Example 4.

The first and second components of adhesive composition so obtained as above were sent to trials on the commercial machines.

The first component and the second component were kept at a temperature in the range of 35- 50 °C, and then mixed together in a weight ratio of 80:100 before application to obtain the adhesive composition. Application of the above adhesive was done on PET and metallized PET substrate on Nordmeccanica and Uflex solventless machine speed of 200 m/min.

It was found that the hiding/opacity properties of the laminate were good. The curing properties such as tack, bond strength and seal strengths were as per desired criteria. It was observed that laminate obtained was free of speckling defects as well as any other lamination defects.

EXPERMIENT 2: Detection of migration of primary aromatic amines from the adhesive composition The adhesive composition of the present disclosure was detected for the migration of primary aromatic amines by using the following test procedure:

In order to understand distribution of the adhesive across the laminate, five pieces of 10 cm x 10 cm size from different part of laminates were cut for the testing. These pieces (specimen) were thoroughly cleaned and immersed in clean glass container having 2 liter capacity containing preconditioned simulant such that no two pieces touch each other. The specimens were separated by placing 2 to 3 mm diameter glass rods in between the specimens and the beaker was covered with glass plate/watch glass. The set was kept in a specified condition depending on the type of food packed. After exposure for the specified time, test specimens were removed from the extracted simulant with the help of clean tongs and washed with small amount of fresh simulant, which is then combined with the extracted simulant. A blank specimen was also carried out without the sample. There were different types of simulants being used depending on the nature of food packed. The simulant were selected from distilled water, 3% aqueous acetic acid solution, and 10% aqueous ethanol. Aqueous non-acidic foods without fat pH > 5) like honey and mineral water were tested using distilled water. Aqueous acidic foods without fat (pH <5.5) like fruit juices, and vinegar were tested using 3% aqueous acetic acid as a simulant. Alcoholic beverages having alcohol concentration less than 10% were tested using 10% aqueous ethanol. The amount of extractive extracted in the simulant is calculated using the following equation:

Amount of extractive (Ex) = (M/A) *100 mg/dm²

wherein,

M = mass of residue minus blank value in mg,

A = surface area exposed in each replicate in cm ,

The results obtained for printed/metallized PET for the above described foods were as follows:

Table 4: Migration study results of white adhesive used for bonding Printed PET/ metallized PET substrate

The result for the residual monomer of the adhesive composition samples in the extracted simulant was <1.5 mg/dm , which was far less than the permissible limit (10 mg/dm ). Thus, the adhesive composition of the present disclosure is safe for food packaging application. To measure the amount of primary aromatic amine, small of simulant is injected in to the GCMS to understand area under the peak corresponding primary aromatic amine.

TECHNICAL ADVANCEMENTS AND ECONOMICAL SIGNIFICANCE

The present disclosure described herein above has several technical advantages including, but not limited to, the realization of, an adhesive composition that:

• is solvent free, hence environment friendly;

• has excellent opacity;

• has excellent wettability on metallized substrates;

• has storage stability up to at least 9 months;

• serves the purpose of white ink as well as adhesive;

• is useful for all types of packings;

• reduces the use of the huge amount of costly ink, hence is cost effective;

• has good adhesion and excellent bonding;

• is suitable for low temperature applications; • has reduced the power consumption;

• works well on existing solvent less lamination machines

• has good freeze thaw stability; and the process for preparation of the adhesive composition:

• is simple and economical; and

• is environment friendly.

The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.

Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.

While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

One of the objects of the Patent Law is to provide protection to new technologies in all fields and domain of technologies. The new technologies shall or may contribute in the country economy growth by way of involvement of new efficient and quality method or product manufacturing in India.

To provide the protection of new technologies by patenting the product or process will contribute significant for innovation development in the country. Further by granting patent the patentee can contribute in manufacturing the new product or new process of manufacturing by himself or by technology collaboration or through the licensing.

The applicant submits that the present disclosure will contribute in country economy, which is one of the purposes to enact the Patents Act, 1970. The product in accordance with present invention will be in great demand in country and worldwide due to novel technical features of a present invention is a technical advancement in the adhesive. The technology in accordance with present disclosure will provide product cheaper, saving in time of total process of manufacturing. The saving in production time will improve the productivity, and cost cutting of the product, which will directly contribute to economy of the country. The product will contribute new concept in the adhesive wherein patented process/product will be used. The present disclosure will replace the whole concept of adhesive being used in this area from decades. The product is developed in the national interest and will contribute to country economy.

The economy significance details requirement may be called during the examination. Only after filing of this Patent application, the applicant can work publically related to present disclosure product/process/method. The applicant will disclose all the details related to the economic significance contribution after the protection of invention.

Claims

CLAIMS:

1. An adhesive composition comprising: a) a first component, wherein said first component comprises: i. OH (polyol) component in an amount in the range of 55 wt% to 65 wt% with respect to the total weight of the first component; ii. at least one pigment in an amount in the range of 30 wt% to 60 wt% with respect to the total weight of the first component; and iii. at least one additive in an amount in the range of 0.05 wt% to 1 wt% with respect to the total weight of the first component; and b) a second component comprising an NCO prepolymer component, wherein a weight ratio of an NCO component to an OH (polyol) component is in the range of 1 : 1 to 2: 1 ; wherein said first component and said second component are heated at a temperature in the range of 35 °C to 50 °C and then mixed together in a weight ratio in the range of 70:100 to 90:100 before application to obtain said adhesive composition.

2. The composition as claimed in claim 1, wherein said pigment is at least one selected from titanium dioxide, zinc oxide, calcium carbonate, talc and silica.

3. The composition as claimed in claim 1, wherein said additive is at least one selected from the group consisting of dispersing agent and wetting agent.

4. The composition as claimed in claim 3, wherein said wetting agent is at least one selected from the group consisting of polyether modified poly dime thylsiloxane; wherein said dispersing agent is at least one selected from the group consisting of a multifunctional silicone resin dispersion and dicarboxylic acid ester.

5. The composition as claimed in claim 1, wherein said OH (polyol) component is obtained via esterification reaction of diacid and dihydric alcohols.

6. The composition as claimed in claim 1, wherein said NCO prepolymer component is obtained via esterification reaction of diacid and dihydric alcohols to form an esterified hydroxy terminated product, followed by reacting said esterified hydroxy terminated product with at least one isocyanate functionalized crosslinker .

7. The composition as claimed in claims 5 and 6, wherein said diacid is at least one selected from the group consisting of hexanedioic acid, nonanedioic acid, butanedioic acid, decanedioic acid, octadecanoic acid, benzene- 1,3-dicarboxylic acid, and benzene- 1 ,4-dicarboxylic acid.

8. The composition as claimed in claims 5 and 6, wherein said dihydric alcohol is at least one selected from the group consisting of ethane- 1,2-diol, 2,2'-oxydi(ethan-l-ol), propane- 1,2-diol, 2,2-dimethylpropane-l,3-diol, butane- 1,4-diol, hexane- 1,6-diol, propane- 1 ,2,3-triol, and 2-(hydroxymethyl)-2-ethylpropane- 1 ,3-diol.

9. The composition as claimed in claim 6, wherein said isocyanate functionali ed crosslinker is at least one selected from 2,2 methylene diphenyl diisocyanate (MDI), 2,4 methylene diphenyl diisocyanate (MDI), 4,4 methylene diphenyl diisocyanate (MDI), 5-isocyanato-l-(isocyanatomethyl)-l,3,3-trimethylcyclohexane (IPDI) and 1 ,6-diisocyanatohexane (HDI).

10. A process for the preparation of an adhesive composition, said process comprising the following steps: i. reacting diacid with dihydric alcohol at a first predetermined temperature for a first predetermined time period in the presence of a first catalyst and a first antioxidant to obtain an esterified hydroxy terminated compound (OH component); ii. mixing at least one pigment and at least one additive to said OH component to obtain a first mixture; iii. grinding said first mixture to obtain a first component; iv. separately reacting diacid with dihydric alcohol at a second predetermined temperature for a second predetermined time period in the presence of a second catalyst and a second antioxidant to obtain an esterified hydroxy terminated compound (OH component); v. reacting an isocyanate functionalized crosslinker monomer (NCO component) with said esterified hydroxy terminated compound (OH component) in a predetermined weight ratio at a third predetermined temperature for a third predetermined time period to obtain a second mixture; vi. subjecting said second mixture to vacuum drying to obtain the second component (NCO prepolymer component); wherein said first component and said second component are heated at a temperature in the range of 35°C to 50°C followed by mixing in a weight ratio in the range of 70:100 to 90:100 before application to obtain said adhesive composition.

11. The process as claimed in claim 10, wherein the molar ratio of said diacid to said dihydric alcohol in step (i) is in the range of 1:1 to 1:2.

12. The process as claimed in claim 10, wherein said first predetermined temperature is in the range of 130°C to 260°C; wherein said first predetermined time period is in the range of 20 hours to 35 hours; and wherein said mixing in step (ii) is performed by using a stirrer at a speed in the range of 1000 rpm to 1500 rpm.

13. The process as claimed in claim 10, wherein the molar ratio of said diacid to said dihydric alcohol in step (iv) is in the range of 1:1 to 1:2.

14. The process as claimed in claim 10, wherein said second predetermined temperature is in the range of 130°C to 260°C; and wherein said second predetermined time period is in the range of 20 hours to 35 hours.

15. The process as claimed in claim 10, wherein said weight ratio of said isocyanate functionalized crosslinker monomer (NCO component) to said esterified hydroxy terminated product (OH component) to is in the range of 1:1 to 1:2.

16. The process as claimed in claim 10, wherein said third predetermined temperature is in the range of 50°C to 100°C; and wherein said third predetermined time period is in the range of 2 hours to 10 hours.

17. The process as claimed in claim 10, wherein said first catalyst and said second catalyst are same or different and are independently selected from titanium butoxide, butylstannoic acid, monobutyltin oxide and monobutyltin hydroxide oxide.

18. The process as claimed in claim 10, wherein said first antioxidant and said second antioxidant are same or different and are independently selected from butylated hydroxytoluene, tris(2,4-di-tert.-butylphenyl)phosphite, and pentaerythritol tetrakis(3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate).