MX2008005482A - Gas barrier coating having high thermal resistance - Google Patents

Abstract

A coating composition comprising a silylated polyvinyl alcohol and colloidal silica in an aqueous vehicle, where the solids content of the composition is not greater than 7.5%w/w, the silyl monomer content of the silylated polyvinyl alcohol is not greater than 3.0%(based on the monomers forming the silylated polyvinyl alcohol), the silylated polyvinyl alcohol comprises at least 50%w/w of the solids content of the composition, and the average particle size of the colloidal silica is from 5 to 80nm, may be coated on a substrate with a layer of an inorganic compound to form a gas barrier lamella.

Description

BARRIER COATING AGAINST GASES THAT HAVE HIGH THERMAL RESISTANCE FIELD OF THE INVENTION The present invention relates to a coating composition which can be used to produce plastic flakes, which can be a single sheet or a laminated material, which is heatable, which has anti-gas barrier properties. and which can be used as packaging for a variety of materials, in particular food and pharmaceutical products, where exposure to oxygen needs to be eliminated or restricted and where the packaged material needs to be heated in order to be sterilized.

BACKGROUND OF THE INVENTION Synthetic plastic materials have been used for a long time for the packaging of food and other materials which need protection from handling and moisture. However, in recent years, it has been appreciated that, in addition, many foods and other sensitive materials benefit from being protected from atmospheric oxygen. A wide variety of multilayer laminated structures have been developed to provide barrier properties and other characteristics of performance suitable for the purpose of a package. These laminated materials may be any combination of plastic, metal or cellulosic substrates and may include one or more coating or adhesive layers. Laminated materials which include polymeric films having metals or inorganic compounds, such as silicon oxides, deposited thereon have been found to provide good general barrier properties and are widely used. However, their properties tend to be very temperature dependent and may lose their capacity to prevent the entry of oxygen completely at high temperatures, for example when the packaged material is heated in order to sterilize and / or cook it. In addition, the inorganic layer of these types of laminate material is preferably brittle and can crack or break when the laminate flexes, resulting in a loss of gas barrier properties. As a result, a variety of other laminated films have been proposed for this purpose. For example, EP 0 878 495 describes and claims a laminated gas barrier material comprising a substrate, a thin film, composite, inorganic layer and a protective layer which are laminated in that order, where the protective layer is way through of the coating on the thin, composite, inorganic film layer of a water-based coating composition containing a water-soluble polymer and at least one of (a) a metal alkoxide or a hydrolyzate thereof and (b) a tin chloride, followed by drying by heating. Other patents that use similar techniques include EP 1 211 295 (JSR), EP 0 960 901 (Nakato) and US 6,337,370. Although good barrier performance against oxygen is achieved, there are a variety of disadvantages with this technology. These disadvantages include having to prepare the hydrolysed silane pressure side (due to poor long-term stability), the exothermic nature of the hydrolysis reaction and the potential hazards associated with having to handle silane and hydrochloric acid or other acid . In addition, the water resistance of these coatings may be insufficient. US 2004/0014857 (acker) discloses the use of polyvinyl alcohols containing silane to achieve abrasion resistant coating paints, in particular coating paints for coating ink jet recording materials. EP 0 123 927 describes and claims the synthesis of a silylated polyvinyl alcohol (PVA) and its formulation in water resistant compositions. The PVA Silylated is produced by the copolymerization of vinyl acetate and vinyl alkoxy silanes (such as vinyl triethoxysilane), followed by hydrolysis of the acetate groups. The water resistant compositions are obtained by combining this silylated PVA with an inorganic particulate material such as clay or silica. It is said that these compositions have excellent demisting properties. Other patents describing similar compositions include JP2005194600A2, JP2005194471A2, JP2000290580A2 and US 2004/0054069.

BRIEF DESCRIPTION OF THE INVENTION It has now been surprisingly discovered that the compositions of the type disclosed in EP 0 123 927 have excellent gas barrier properties and can thus be used as components of packaging materials for food products, products Pharmaceuticals and other materials that need to be protected from the atmosphere. However, in order to achieve good gas barrier properties combined with a good capacity for heating, it is necessary to keep the components of the coating composition within strict limits.

DETAILED DESCRIPTION OF THE INVENTION Thus, in a first aspect, the present invention consists of a coating composition comprising a silylated polyvinyl alcohol and colloidal silica in an aqueous vehicle, wherein the solids content of the composition is not greater than 7.5% in w / w, the content of silyl monomers of the silylated polyvinyl alcohol is not greater than 3.0% (based on the monomers that form the silylated polyvinyl alcohol), the silylated polyvinyl alcohol comprises at least 50% in p / p of the solids content of the composition and the average particle size of the colloidal silica is from 5 to 80 nm. In a second aspect, the invention comprises a process for preparing a gas barrier sheet, which comprises applying a composition of the present invention to a flexible substrate and removing the aqueous vehicle. In a further aspect, the invention comprises a gas barrier sheet comprising a flexible plastic film coated with a first coating comprising an inorganic compound and a second coating comprising a silylated polyvinyl alcohol having dispersed therethrough a particulate silica, where the content of silyl monomers of the silylated polyvinyl alcohol is not greater than 3.0% (in based on the monomers that form the silylated polyvinyl alcohol), the silylated polyvinyl alcohol comprises at least 50% w / w of the solids content of the total weight of silylated polyvinyl alcohol and silica and the average particle size of the colloidal silica is 5 to 80 nm. As used herein, the term "silylated polyvinyl alcohol" means a polymer that contains both vinyl alcohol units and silyl units. In addition, it may contain units derived from other monomers, for example: olefins, such as ethylene or propylene; esters of acrylic or methacrylic acid, such as methyl acrylate or ethyl methacrylate; other vinyl monomers, such as vinyl acetate; or styrene or derivatives thereof, such as methylstyrene. There is no particular restriction on the character of the silylated polyvinyl alcohol that is used in the present invention, other than that it should be appropriate for the proposed use of the gas barrier coating and can be any polyvinyl alcohol having a silicon atom in the molecule. This silylated polyvinyl alcohol can be prepared, for example, by: silylating a polyvinyl alcohol or a modified polyvinyl acetate which contains hydroxy and / or carboxy groups; saponifying a copolymer of a vinyl ester and an olefinically unsaturated monomer containing groups silyl; or saponifying a polyvinyl ester having one (a) terminal silyl group (s), which can be obtained by the polymerization of a vinyl ester in the presence of a silyl mercaptan. More generally, they can be prepared as described in EP 0 123 927, JP2005194600A2, JP2005194471A2, JP2000290580A2 and US 2004/0054069. It can also be prepared by the copolymerization of vinyl alcohol (or a precursor thereof) with a monomer containing silyl groups, such as vinyltrimethoxysilane. The proportion of silyl groups in the silylated polyvinyl alcohol is critical for the present invention. In this way, according to the present invention, the content of silyl monomers of the silylated polyvinyl alcohol is not greater than 3.0% (based on the monomers that form the silylated polyvinyl alcohol) and is preferably at least 0.2%. In this way, the preferred range is 0.2 to 3.0%. More preferably, the content of silyl monomers is less than 2.0% and thus an additionally preferred range is from 0.2 to 2.0%, much more preferably from 0.4 to 2.0%. These percentages are calculated as the proportion of monomer units containing silyl groups with respect to the total monomer units. The degree of saponification can vary from the same mode over a wide range, for example 70 to 100% mol. The amount of the silylated polymer is at least 50% of the dry weight of the coating comprising a silylated polyvinyl alcohol and the silica, more preferably at least 60%. Preferably, the amount does not exceed 90 or 95%. A preferred range is from 90 to 50%, more preferably from 90 to 60%. Scattered through the silylated polyvinyl alcohol is a particulate silica. This is used in the coating composition of the present invention as a colloidal silica. The amount of the silica used is also important for obtaining the benefits of the present invention. On the one hand, if very little is present, the beneficial effect may be too small to be of a very practical benefit. On the other hand, if much is present, it will adversely affect the properties of the film on which it is coated. The amount should not exceed 50% of the dry weight of the coating comprising the silylated polyvinyl alcohol and the colloidal silica, more preferably should not exceed 40% of the dry weight of the coating comprising a silylated polyvinyl alcohol and the inorganic compound. On the other hand, it is preferred that the amount should not be less than 5% of the dry weight of the coating comprising an alcohol polyvinyl silylated and the inorganic compound. More preferably, the amount is from 10 to 50% of the dry weight of the coating comprising a silylated polyvinyl alcohol and the inorganic compound. In order that the coating composition of the present invention does not gel while stored, the solids content should not exceed 7.5%. More preferably, it is at least 0.5% and a preferred range is 0.5 to 7.5%, much more preferably 1.5 to 5.0% w / w. The particle size of the silica should be from 5 to 80 nm, more preferably from 5 to 50 nm, even more preferably from 5 to 40 nm and much more preferably from 10 to 30 nm. In the process of the present invention, this coating composition is applied to a substrate and then the aqueous vehicle is removed, for example by heating. The resultant gas barrier sheet can be a single layer laminate or it can be part of a more complex multi-layer laminate structure which can include one or more additional substrates, adhesive coatings, ink and varnish layers, etc. It is well known to those experts in the field. It is preferred that the lamella of the present invention should adhere to a 1 additional flexible plastic sheet. There is no particular restriction on the character of the flexible substrate, although it is preferably a plastic film and any suitable material can be used for the proposed use. However, where the material that is packaged with the lamella of the present invention is a food product or pharmaceutical product, it will normally be preferred that the plastic film or other substrate must be food grade. Examples of suitable materials include: polyolefins, such as polyethylene or polypropylene; polyesters, such as polyethylene terephthalate, polybutylene terephthalate or polyethylene naphthenate; polyamides, such as nylon-6 or nylon-66; and other polymers, such as polyvinyl chloride, polyimides, acrylic polymers, polystyrenes, celluloses or polyvinylidene chloride. It is also possible to use copolymers of any of two or more of the compatible monomers used to produce these polymers. Polyesters are especially preferred. Where there is an additional plastic sheet, it must also be flexible and can be selected from any of the materials exemplified in the previous paragraph. Where the barrier film against gases of the present invention has a first coating on the flexible plastic film, this is an inorganic compound. As with plastic film, the character of this may be determined by the proposed use of the gas barrier sheet of the present invention, and where the sheet is for use as packaging for food products or pharmaceutical products, the inorganic compound must be food grade. Examples of these compounds include: aluminum compounds, such as aluminum oxide and silicon compounds, such as SiOx silicon oxides. The thickness of this first coating will depend in part on the character of the inorganic compound and its ability to form a coherent, continuous coating layer. However, in general, it is preferred that the coating should be from 1 nm to 1000 nm thick, more preferably from 20 to 100 nm thick. Where a first coating exists, the second coating on the plastic film may be on the same side of the film as the first coating or may be on the opposite side. In the first case, the second coated coating is on the surface of the first coating. The second coating comprises a silylated polyvinyl alcohol having dispersed therein a particulate inorganic compound having a maximum transverse dimension of 100 nm. The thickness of this second coating is preferably 0.05 μm to 2.5 μm, more preferably 0.1 μm to 1.0 μm (thickness of the dry coating film). The invention also provides a process for preparing the gas barrier sheet of the present invention, which comprises: applying to a flexible plastic film a first coating (where used) comprising an inorganic compound and a second coating comprising the coating composition of the present invention; and heating the resulting coated film to a temperature sufficient to cure the silylated polyvinyl alcohol. The first coating (where it is used) and the second coating can be applied in any order, ie the first coating can be applied first and the second coating can be applied second or the first coating can be applied secondly and the second can be applied first or the first and second coating can be applied at the same time. Also, the first coating can be applied before or after the film coated with the second coating is heated to cure the alcohol polyvinyl silylated The invention still further provides a food product, pharmaceutical product or other packaged material sensitive to the atmosphere, wherein the package comprises a gas barrier sheet of the present invention. The invention is further illustrated by the following non-limiting examples.

EXAMPLES In these examples, the coatings were prepared in an aqueous solution with 6% (w / w) isopropanol. Oxygen transmission rates of the coated samples were determined in a Mocon Oxtran 2 / 21MR gas permeability tester at 23 ° C and 50% relative humidity. The substrate used in all cases was a polyester substrate of 12 μm caliber (Melinex 800MR) with a surface treatment with aluminum oxide (approximately 40 nm thick). The coatings were applied with a K No. 2 bar and dried in a hot air flow (lab prints were dried with a hair dryer). Laminated materials were prepared by applying an adhesive to the polyamide surface of a laminated material of pre-formed polyamide 25 μm-75 μm cast polypropylene and then forming a final laminate Apply the coated surface of the aluminum / polyester oxide substrate to the adhesive layer on the polyamide surface. The adhesive used was supplied by Rohm & Hass, Adcote 811A together with Catalyst 9L10 and was prepared according to the manufacturer's instructions and applied to provide a final dry film weight of 4 gsm. The laminated materials were then stored for 10 days at 50 ° C to ensure complete cure of the isocyanate-based adhesive. The laminated materials were then tested by the bonding strength (N / 15mm) and the oxygen barrier both before and after heating. The heating test was 30 minutes at 130 ° C (a steam sterilization process at high temperature). Laminated materials were also visually inspected after heating to evaluate any sign of delamination. If the laminated materials showed severe delamination then the oxygen transmission rate was not always measured.

Example 1 (comparative) Aluminum oxide / polyester only substrate This was laminated to the polyamide-polypropylene sheet as described above.

Prior to heating, the oxygen transmission rate was measured at 4.5-6.5 cm3 / m2 / 24h and the test for bond strength resulted in tearing of the polyester film. After heating, the oxygen transmission rate was measured between 10.0 - 15.0 cm3 / m2 / 24h and the polyester film was torn during the bond strength test.

Example 2 (comparative) Aluminum oxide / polyester substrate coated with a composition prepared according to EP 0 878 495 8.9 g of tetraethyl orthosilicate in 18.4 g of water and 18.4 g of ethanol together with 0.8 g of 0.1 N HCl they were stirred for 30 minutes. Then, 3.9 g of 12% (w / w) of PVA (Celvol 103) was added and the subsequent coating was applied to the aluminum oxide / polyester substrate at a wet film thickness of approximately 10 μm. The coating was then dried at 120 ° C for 90 seconds before preparing the laminate. Before heating, the oxygen transmission rate was 1.5 cm3 / m2 / 24h and the polyester film was torn during the resistance test of link. After heating, the oxygen transmission rate was 7.1 cm3 / m2 / 24h and the polyester film was torn during the bond strength test.

EXAMPLE 3 (comparative) Aluminum / polyester oxide substrates coated with a silated polyvinyl alcohol (PVA) 'A' The aluminum / polyester oxide substrate was coated with a 4% solution (w / w) of a functional PVA with silyl groups, defined as XA 'in Table 1, where the concentration of the monomer containing silyl groups in the main structure of the polymer was 1.6% (w / w of the monomer composition). Prior to heating, the laminate had an oxygen transmission rate of 0.25 cm3 / m2 / 24h and the polyester film was torn during the bond strength test. After heating, the laminate showed severe delamination with a bond strength of less than 0.5N / 15mm. Due to the severe delamination, it was not possible to obtain an accurate reading of the oxygen transmission rate.

Example 4 A coating was prepared by combining 3.0 g of isopropyl alcohol with 19.3 g of water, 17.1 g of a 7.25% (w / w) solution of the PVA described in Example 3 and 0.46 g of a colloidal silica with a particle size of 15 nm, a concentration of 40% and a pH of 9.5 (Bindzil 40/220, ex. EKA). This coating was applied to the aluminum / polyester oxide substrate at a wet coating film weight of 10-12 gsm and dried with air. The laminate was formed in the usual manner. Prior to heating, the oxygen transmission rate was less than 0.1 cm3 / m2 / 24h and the bond strength test resulted in a tearing of the polyester film. After heating, there were no observable signs of delamination and the oxygen transmission rate was 0.20 cm3 / m2 / 24h and the polyester film was torn during the bond strength test.

Examples 5 to 30 Using the silylated PVA as described in Example 3, the coatings were prepared with alkali colloidal silicas of different particle sizes and concentrations as summarized in Table 1. Laminated materials were prepared and subjected to test the usual way and the results are provided for the tests after heating.

Table 1 Effect of Colloidal Silica Particle Size on Material Properties co fifteen fifteen A, B: Concentrations provided in terms of% by weight in a 94/6 combination of water / Isopropanol. The PVA used in this series of examples (A ') had a nominal Si-monomer content of 1.6% (w / w) 1. The observation describes any visible signs of delamination after 5 heating at 130 ° C for 30 minutes 2 The bond strength is provided as the required force to separate the coated polyester from the rest of the laminate material in N / 15mm. Where the bond strength is very large and results in the polyester film tearing or tearing this is given as 'FT' in Table 1. 10 3. OTR (Oxygen Transmission Rate): Measure on an Examiner Mocon Oxtran 2 / 21MR at 23 ° C and 50% relative humidity. (cm3 / m2 / 24h) Examples 31 to 48 Using colloidal silica 15 nm (Bindzil 40/220), coating compositions with a total solids content of 4% (w / w) were prepared with a variety of different silylated PVA as described in the Table 2. The laminates were tested in the usual manner and the results after heating are shown in Table 2.

Table 2 15 A. The silylated PVAs shown in Table 2 are commercially available from Kuraray. t OJ

Claims (30)

1. CLAIMS 1. A coating composition comprising a silylated polyvinyl alcohol and a colloidal silica in an aqueous vehicle, characterized in that the solids content of the composition is not greater than 7.5% w / w, the content of silyl monomers of the alcohol polyvinyl silylate is not greater than 3.0% (based on the monomers that form the silylated polyvinyl alcohol), the silylated polyvinyl alcohol comprises at least 50% w / w of the solids content of the composition and the average particle size of the polyvinyl alcohol. Colloidal silica is from 5 to 80 nm.
2. 2. The composition according to claim 1, characterized in that the solids content is at least 0.5% w / w.
3. 3. The composition according to claim 1 or claim 2, characterized in that the solids content is from 1.5 to 5.0% w / w.
4. 4. The composition according to any of the preceding claims, characterized in that the content of silyl monomers of the silylated polyvinyl alcohol is at least 0.2%.
5. The composition according to any of the preceding claims, characterized in that the content of silyl monomers of the silylated polyvinyl alcohol is less than 2.0%.
6. 6. The composition according to claim 5, characterized in that the content of silyl monomers of the silylated polyvinyl alcohol is from 0.4 to 2.0%.
7. The composition according to any of the preceding claims, characterized in that the silylated polyvinyl alcohol comprises at least 60% w / w of the solids content of the composition.
8. The composition according to claim 7, characterized in that the silylated polyvinyl alcohol comprises from 60 to 90% w / w of the solids content of the composition.
9. 9. The process for preparing a gas barrier sheet, characterized in that it comprises applying a composition according to any of the preceding claims to a flexible substrate and removing the aqueous vehicle.
10. 10. The process according to claim 9, characterized in that a coating comprising an inorganic compound is also applied.
11. 11. The process according to claim 10, characterized in that the inorganic compound is aluminum oxide.
12. 12. The process according to claim 10, characterized in that the compound Inorganic is silicon oxide.
13. The process according to any of claims 10 to 12, characterized in that the coating comprising the silylated polyvinyl alcohol and the colloidal silica is coated on the coating comprising the inorganic compound.
14. The process according to any of claims 10 to 12, characterized in that the coating comprising the silylated polyvinyl alcohol and the colloidal silica is coated on the side of the substrate opposite the coating comprising the inorganic compound.
15. 15. The process according to any of claims 10 to 14, characterized in that the substrate is a flexible plastic film.
16. 16. A gas barrier sheet, characterized in that it comprises a flexible plastic film coated with a first coating comprising an inorganic compound and a second coating comprising a silylated polyvinyl alcohol having dispersed therein a particulate silica, wherein the silyl monomer content of the silylated polyvinyl alcohol is not greater than 3% (based on the monomers forming the silylated polyvinyl alcohol), the silylated polyvinyl alcohol comprises at least 50% w / w of the solids content of the total weight of silylated polyvinyl alcohol and silica and the average particle size of the colloidal silica is from 5 to 50 nm.
17. 17. The foil according to claim 16, characterized in that the content of silyl monomers of the silylated polyvinyl alcohol is at least 0.2%.
18. 18. The foil according to claim 16 or claim 17, characterized in that the content of silyl monomers of the silylated polyvinyl alcohol is less than 2.0%.
19. 19. The lamella according to claim 18, characterized in that the content of silyl monomers of the silylated polyvinyl alcohol is from 0.4 to 2.0%.
20. The foil according to any of claims 16 to 19, characterized in that the silylated polyvinyl alcohol comprises at least 60% w / w of the total weight of the silylated polyvinyl alcohol and silica.
21. 21. The lamella according to claim 20, characterized in that the silylated polyvinyl alcohol comprises from 50 to 90% w / w of the total weight of the silylated polyvinyl alcohol and silica.
22. 22. The foil in accordance with any of claims 16 to 21, characterized in that the substrate is a polyester.
23. 23. The foil according to any of claims 16 to 22, characterized in that the inorganic compound of the first coating is aluminum oxide.
24. 24. The foil according to any of claims 16 to 23, characterized in that the inorganic compound of the first coating is silicon oxide.
25. 25. The foil according to any of claims 16 to 24, characterized in that the second coating is coated on the first coating.
26. 26. The foil according to any of claims 16 to 25, characterized in that the second coating is coated on the side of the flexible plastic film opposite the first coating.
27. 27. A multilayer lamella comprising a lamella according to any of claims 16 to 26, characterized in that it adheres to an additional flexible plastic sheet.
28. 28. The multi-layer lamella according to claim 27, characterized in that the additional plastic sheet is a polyolefin, polyester, polyamide, polyvinyl chloride, polyimide, acrylic polymer, polystyrene, cellulose, polyvinylidene chloride or a copolymer of any two or more of the compatible monomers that form these polymers.
29. 29. A package formed of a packaging material, characterized in that it comprises a foil according to any of claims 16 to 28.
30. 30. A food product, pharmaceutical product or other packaged material that is sensitive to the atmosphere, characterized in that the packaging comprises a foil according to any of claims 16 to 29.