One-step process for making a polymer composite coating with high barrier

Abstract

This invention relates to a one-step process for making a polymer composite suspension for coating plastic films characterized in that a first polymer is synthesized in-situ optionally in the presence of other polymers and in the presence of clay. Preferably the polymer composite suspension comprises a) 1.0 to 11.0 wt % of clay or silane modified clay, b) 0.1 to 10.0 wt % of poly (acrylic acid), which is a copolymer of acrylic acid (AA) with at least one other monomer selected from 2-ethylhexyl acrylate (EHA), β-carboxyethyl acrylate (β-CEA), methacrylamidoethyl ethylene urea (WAM II) and ethoxylated behenyl methacrylate (β-FM), c) 1.0 to 15.0 wt % of other polymers, preferably poly (vinyl alcohol) and d) 70 to 97 wt % of water or mixture of water with 2-propanol. The coating films made from the suspensions show good barrier capabilities against water vapor and oxygen can be used to make barrier layers on or within plastic films for packaging applications. The invention also relates to methods for making silane modified clay usable in the process for making the suspensions.

Claims

1. A method for making silane modified clay by dispersing the clay in an aqueous solution and adding a silane or a mixture of silanes by injection at a flow rate of 0.1 to 3.0 ml/min and at a homogenization speed in the range of 10,000 to 20,000 rpm.

2. The method according to claim 1 which comprises a heating step after the addition of the silanes.

Description

EXAMPLES

(1) Non-limiting examples of the invention and a comparative example will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

(2) Materials and Methods

(3) In the examples described below, unless otherwise indicated, all temperatures in the following description are in degrees Celsius and all parts and percentages are by weight, unless indicated otherwise. Reagents useful for synthesizing compounds may be purchased from commercial suppliers as mentioned in the examples.

(4) Test Methods Used

(5) Oxygen Transmission Rate (OTR)

(6) Oxygen permeability of nanocomposites coated PET film was measured by using Mocon oxygen permeability OX-TRAN Model 2/21 according to ASTM D3985 standard. Each film was placed on a stainless steel mask with an open testing area of 5 cm.sup.2. Oxygen permeability measurements were conducted at 23° C. (1 atm) and 0% relative humidity by placing coated surface of films to the oxygen rich side.

(7) Water Vapor Transmission Rate (WVTR)

(8) Water vapor permeability of nanocomposites coated PET film was measured by using Mocon water vapor permeability PERMATRAN-W Model 3/33 according to ASTM F1249 standard. Each film was placed on a stainless steel mask with an open testing area of 5 cm.sup.2. Water vapor permeability measurements were conducted at 37.8° C. (1 atm) and 90% relative humidity by placing coated surface of films to the water vapor rich side.

Example 1

Preparation of Silanes Modified Clay Suspension (SMMT[1])

(9) 5.0 g of pristine clay (montmorillonite) obtained from Nanocor Inc. of Arlington Heights of Illinois of the United States of America was mixed with 125 ml deionised water and stirred for 6 hours, followed by ultrasonication in a water-bath for 30 minutes. Then, 0.1875 ml of acetic acid was added to the solution and stirred for another 12 hours. To exchange water with acetone, acetone was added to the suspension. The clay suspension was homogenized with acetone using an IKA T18 Basic Ultra Turrax homogenizer at 15,000 rpm for 5 minutes. Thereafter, the slurry precipitate was filtered with a Buchner funnel and washed with acetone. The collected slurry precipitate was re-suspended into 500 ml of acetone and homogenized for 5 minutes at 15,000 rpm, followed by filtration and washing. Each cycle should use at least 500 ml of acetone. After second cycle, the collected precipitate was transferred to a round bottom flask, and then topped up with appropriate amount of acetone. 0.1 g of (3-aminopropyl)trimethoxysilane (97%, Aldrich) and 0.15 g of (3-glycidoxypropyl)trimethoxysilane (98%, Aldrich) were added to the solution. After stirring for 8 hours at room temperature, the mixture was ultrasonicated for 30 minutes and stirred at 50° C. for 8 hours. Then, 125 ml of deionized water was added into clay-acetone-silanes mixture and all the acetone was then removed by rotary evaporation at 60° C.

Example 2

Preparation of Silanes Modified Clay Suspension (SMMT[2])

(10) 5.0 g of pristine clay (montmorillonite) obtained from Nanocor Inc. of Arlington Heights of Illinois of the United States of America was mixed with 125 ml deionised water and stirred for 6 hours, followed by ultrasonication in a water-bath for 30 minutes. Then, 0.1875 ml of acetic acid was added to the solution and stirred for another 12 hours. After that, 0.1 g of (3-aminopropyl)trimethoxysilane (97%, Aldrich) was first slowly injected (0.1 ml/min) into the clay suspension, followed by 0.15 g of (3-glycidoxypropyl)trimethoxysilane (.sup.3 98%, Aldrich) under high speed of homogenizing process at 15,000 rpm by using an IKA T18 Basic Ultra Turrax for 15 minutes. Then, silanes modified clay suspension was heated at 50° C. for 6 hours under stirring.

Example 3

Preparation of Silanes Modified Clay Suspension (SMMT[3])

(11) 5.0 g of pristine clay (montmorillonite) obtained from Nanocor Inc. of Arlington Heights of Illinois of the United States of America was mixed with 125 ml deionised water and stirred for 6 hours, followed by ultrasonication in a water-bath for 30 minutes. Then, 0.1875 ml of acetic acid was added to the solution and stirred for another 12 hours. After that, 0.2 g of (3-aminopropyl)trimethoxysilane (97%, Aldrich) was first slowly injected (0.1 ml/min) into the clay suspension, followed by 0.3 g of (3-glycidoxypropyl)trimethoxysilane (.sup.3 98%, Aldrich) under high speed of homogenizing process at 15,000 rpm by using an IKA T18 Basic Ultra Turrax for 15 minutes. Then, silanes modified clay suspension was heated at 50° C. for 6 hours under stirring.

Example 4

Preparation of Silanes Modified Clay Suspension (SMMT[4])

(12) 5.0 g of pristine clay (montmorillonite) obtained from Nanocor Inc. of Arlington Heights of Illinois of the United States of America was mixed with 125 ml deionised water and stirred for 6 hours, followed by ultrasonication in a water-bath for 30 minutes. Then, 0.1875 ml of acetic acid was added to the solution and stirred for another 12 hours. After that, 0.3 g of (3-aminopropyl)trimethoxysilane (97%, Aldrich) was first slowly injected (0.1 ml/min) into the clay suspension, followed by 0.45 g of (3-glycidoxypropyl)trimethoxysilane (.sup.3 98%, Aldrich) under high speed of homogenizing process at 15,000 rpm by using an IKA T18 Basic Ultra Turrax for 15 minutes. Then, silanes modified clay suspension was heated at 50° C. for 6 hours under stirring.

Example 5

Preparation of Silanes Modified Clay Suspension (SMMT[5]-SMMT[7])

(13) The preparation method is analoguous to SMMT[2], except varying the clay to polymer ratio (wt %) and final total solid content concentrations. The composites solution can be diluted with water or mixture of water (75%) and 2-propanol (25%).

Example 6

Preparation of Poly(Vinyl Alcohol) (PVA) Solution

(14) 9.76 g of PVA (MW 44,000 completely hydrolyzed obtained from Wako Pure Chemical Industries, Ltd., Japan) was dissolved in 90 ml of deionized water under stirring at 100° C.

Example 7

Preparation of Poly(Acrylic Acid) (PAA) Solution

(15) 1.91 g of PAA (MW 450,000 obtained from Polysciences Asia Pacific, Inc., Taiwan) was dissolved in 23.14 ml of deionized water under stirring at room temperature (about 25° C.).

Example 8

Preparation of SMMT[2]/Polymer Nanocomposites

(16) First, PAA solution obtained from Preparation Example 7 was added into silanes modified clay suspension obtained from Preparation Example 2 under high speed homogenization process at 15,000 rpm for 5 minutes by using an IKA T18 Basic Ultra Turrax. Then, followed by addition of PVA solution obtained from Preparation Example 6 under same conditions. After addition, the mixture was continuously homogenized for 15 minutes at 15,000 rpm. For samples with isopropanol, 25% (v/v) of isopropanol to water may be added into the solution and homogenized for another 5 minutes.

Example 9

Preparation of Silanes Modified Clay/Polymer Nanocomposites Film

(17) SMMT[1]-SMMT[7]/Polymer coating solutions obtained from Preparation Example 1-5 were blade coated onto a PET film by using a film applicator with an applicator bar coating gap controlled at 50 μm. The applied nanocomposites layer was then dried by air flash at room temperature for 24 hours, followed by drying in a vacuum oven at 60° C. for 24 hours. For laminated films, another plastic film is coated with adhesive. Both of the coated plastic films were compressed together by using a laminator at 130° C.

Example 10

Synthesis of PVA/PAA/Clay Composite Suspension Via In Situ Polymerization

(18) PVA solution is prepared by dissolving 18.4 g PVA into 200 g water at 90° C. under stirring. Clay water suspension is prepared by dispersing 9.4 g clay into 200 g water under stirring followed by adding 0.3 ml acetic acid and further homogenizing for 30 minutes.

(19) 109.7 g of the above prepared PVA solution and 0.5 g EHA (Solvay Singapore Pte Ltd) are added in a 500 ml round bottom flask, and the mixture is stirred for 5 minutes. Then 0.1 g β CEA (Solvay Singapore Pte Ltd), 0.1 g WAM II (Solvay Singapore Pte Ltd), 0.1 g β EM (Solvay Singapore Pte Ltd) and 1.7 g AA (Solvay Singapore Pie Ltd) are mixed into the PVA solution. 104.7 g clay suspension and 100 g water are added into the round bottom flask and homogenized for 5 minutes. After inletting N.sub.2 for 30 minutes, the mixture is heated up to 60° C. under stirring. Finally, 0.05 ml BHPO and 0.5 ml Isoascorbic acid (5 wt % in water) are injected into the mixture, respectively, and stirred at 60° C. overnight. The total solid concentration of the prepared PVA/PAA/Clay composite suspension is 4.4 wt %.

(20) OTR and WVTR of PET film coated with the above prepared PVA/PAA/Clay composite suspension are measured as 0.46 cc/m.sup.2.Math.day and 19.2 g/m.sup.2.Math.day, respectively; OTR and WVTR of PP film coated with the above prepared PVA/PAA/Clay composite suspension are measured as 1.3 cc/m.sup.2.Math.day and 4.4 g/m.sup.2.Math.day, respectively.

(21) Results:

(22) Table 1 showed the transmission rate of oxygen and water vapor for plastic films with or without composites coating. Oxygen transmission rate was measured at 23° C. and 0% relative humidity, and water vapor transmission rate was measured at 37.8° C. at a 90% relative humidity for a number of test films. The thickness of the composites layer is controlled in a range of about 0.3 to 3.5 μm, which is dependent on the final total solid content concentration. Meanwhile, the thickness of a PET plastic film is about 12 μm. As revealed in Table 1, the oxygen transmission rates of composites layer coated PET films were significantly reduced in comparison to that of pure PET film. In the present invention, the lowest OTR of the composites/plastic film was achieved at 0.19 cc/(m2.Math.day), which in overall is 99.7 to 99.9% of reduction as compared to pure PET film. On the other hand, the water vapor transmission rates of composites layer coated plastic films were reduced to about 49.3 to 72.4% in comparison to that of pure PET film. In addition, the barrier property of composites layer prepared from present invention (SMMT

(23) TABLE-US-00001 TABLE 1 Oxygen and Water Vapor Transmission Rates of Films Silanes to Solid dry clay content Clay/polymer ratio OTR WVTR Type of Film* (wt %) (wt %) (wt %) (cc/[m.sup.2 .Math. day]) (gm/[m.sup.2 .Math. day]) PET — — — 130.65 46.49 SMMT[1]_Polymer/PET 5 7 30/70 0.33 15.02 SMMT[2]_Polymer/PET 5 7 30/70 0.30 12.89 SMMT[3]_Polymer/PET 10 7 30/70 0.24 12.85 SMMT[4]_Polymer/PET 15 5 30/70 0.19 14.43 SMMT[5]_Polymer/PET 5 5 30/70 0.28 14.85 SMMT[6]_Polymer/PET 5 4 50/50 0.31 17.50 SMMT[7]_Polymer/PET 5 4 75/25 0.22 23.55 *Thickness of the composite layer was controlled at about 2.5-3.5 μm

INDUSTRIAL APPLICABILITY

(24) The one-step process for making polymer composite suspensions may find a multiple number of applications in the manufacturing of barrier films for plastic films of packaging. For example, the methods as defined above may be used to manufacture packaging films with good barrier property. A good barrier layer against oxygen and moisture is important to protect the produces packaged from fast oxidation and deterioration. With the present invention, a barrier layer against oxygen and moisture can be made. It is to be appreciated that the presence of silane modified clay/polymer composites layer coated on the plastic substrate may substantially inhibit the permeation of gases and water vapor molecules to pass through the film. It is envisaged that silanes modified clay sheets that well intermix with polymer matrix form a hierarchical structure, which creates a longer tortuous path for molecules diffusion. The composites may also adsorb and retain part of the molecules on the surfaces, thus resulting in a reduced transmission rate of gas and water vapor molecules. Moreover, the laminated composites film is mechanically flexible to contour for multiple packaging applications due to the bending ability of the film.

(25) It will be apparent that various other modifications and adaptations of the invention are available to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.