Patent Application
20240133119
The present invention relates generally to coated substrates which have been coated with two different coating compositions. The present invention further relates to the use of two different coating compositions to coat a substrate and a method of making a coated substrate.
Coating compositions are used widely to coat numerous types of substrates (e.g. different materials) which are used for numerous applications. In particular, coating compositions may be used to coat substrates which are used to package goods such as food and beverage products, electronic products, automotive products, medical/pharmaceutical products and cosmetic products. The coated substrate may, for example, be paper or the like.
It is often desirable or necessary that the coating composition reduces or prevents the permeation of gases, vapours and liquids through the substrate. For example, it is often desirable or necessary to reduce or prevent the permeation of water and/or organic substances such as oils (e.g. mineral oils) through the substrate. This may, for example, prevent contamination and/or spoilage of the packaged products (e.g. food/beverage) by the transmitted substances.
In some situations it is desirable or necessary to prevent the permeation of both water and oils through a substrate. However, many coated substrates are not able to effectively reduce or prevent the permeation of both water and oil through the substrate. It is therefore desirable to provide improved or at least alternative coated substrates that can reduce or prevent the permeation of both water and oil through a substrate. For example, it may be desirable to provide a coated substrate which demonstrates improved water barrier properties and/or improved oil barrier properties. This may, for example, allow a reduced coat weight to be used. It may also be desirable to provide a coated substrate that has been coated with water-based coating compositions and may, for example, be easily recyclable.
In accordance with a first aspect of the present invention, there is provided a substrate coated with a first coating comprising an alcohol-based binder and an inorganic particulate material, and a second coating comprising a latex binder and a phyllosilicate.
In accordance with a second aspect of the present invention, there is provided a use of a first coating composition comprising an alcohol-based binder and an inorganic particulate material and a second coating composition comprising a latex binder and a phyllosilicate to coat a substrate (e.g. to make a substrate in accordance with the first aspect of the present invention).
In accordance with a third aspect of the present invention, there is provided a method of coating a substrate (e.g. to make a substrate in accordance with the first aspect of the present invention) comprising coating the substrate with a first coating composition comprising an alcohol-based binder and an inorganic particulate material and a second coating composition comprising a latex binder and a phyllosilicate.
In accordance with further aspects of the present invention, there is provided a coating composition comprising an alcohol-based binder and an inorganic particulate material and a coating composition comprising a latex binder and a phyllosilicate.
In certain embodiments of any aspect of the present invention, the substrate is paper.
In certain embodiments of any aspect of the present invention, the alcohol-based binder is polyvinyl alcohol.
In certain embodiments of any aspect of the present invention, the inorganic particulate material is selected from an alkaline earth metal carbonate or sulphate (e.g. calcium carbonate, magnesium carbonate, dolomite, gypsum), a phyllosilicate, an aluminosilicate (e.g. hydrous kandite clay including kaolin, halloysite clay, ball clay, anhydrous (calcined) kandite clay including metakaolin, fully calcined kaolin and mica), talc, chlorite, pyrophyllite, serpentine, perlite, diatomaceous earth, magnesium hydroxide, aluminium trihydrate and combinations thereof. In certain embodiments, the inorganic particulate material is an aluminosilicate. In certain embodiments, the inorganic particulate material is kaolin.
In certain embodiments of any aspect of the present invention, the inorganic particulate material has a shape factor equal to or greater than about 10. In certain embodiments, the inorganic particulate material has a shape factor equal to or greater than about 30.
In certain embodiments, the inorganic particulate material has a shape factor equal to or greater than about 90.
In certain embodiments of any aspect of the present invention, the inorganic particulate material and alcohol-based binder are present in the first coating in a weight ratio of from about 5:1 to about 1:5. In certain embodiments, the inorganic particulate material and alcohol-based binder are present in the first coating in a weight ratio of from about 2:1 to about 1:1.
In certain embodiments of any aspect of the present invention, the latex binder is a styrene butadiene binder.
In certain embodiments of any aspect of the present invention, the phyllosilicate is selected from clays (e.g. kaolin), talc, mica, chlorite, pyrophyllite, serpentine and combinations thereof. In certain embodiments, the phyllosilicate is talc.
In certain embodiments of any aspect of the present invention, the phyllosilicate has a shape factor equal to or greater than about 10. In certain embodiments, the phyllosilicate has a shape factor equal to or greater than about 30. In certain embodiments, the phyllosilicate has a shape factor equal to or greater than about 90.
In certain embodiments of any aspect of the present invention, the phyllosilicate and latex binder are present in the second coating in a weight ratio of from about 5:1 to about 1:10. In certain embodiments, the phyllosilicate and latex binder are present in the second coating in a weight ratio of from about 2:1 to about 1:1.
In certain embodiments of any aspect of the present invention, the first coating has a coat weight equal to or less than about 30 gsm (g/m2). In certain embodiments, the first coating has a coat weight equal to or less than about 15 gsm or equal to or less than about 10 gsm. In certain embodiments of any aspect of the present invention, the second coating has a coat weight equal to or less than about 30 gsm (g/m2). In certain embodiments, the second coating has a coat weight equal to or less than about 15 gsm or equal to or less than about 10 gsm. In certain embodiments of any aspect of the present invention, the first and second coatings have a total coat weight equal to or less than about 50 gsm (g/m2). In certain embodiments, the first and second coatings have a total coat weight equal to or less than about 30 gsm or equal to or less than about 20 gsm.
In accordance with any aspect of the present invention, the first and second coatings are layered such that the first coating is closer to the substrate than the second coating (e.g. wherein the first coating is directly in contact with the substrate and the second coating is directly in contact with the first coating). In certain embodiments, the first and second coatings are layered such that the second coating is closer to the substrate than the first coating (e.g. wherein the second coating is directly in contact with the substrate and the first coating is directly in contact with the second coating). Thus, in certain embodiments, the first and second coating compositions are applied sequentially to the substrate. In certain embodiments, the first coating composition is applied to the substrate before the second coating composition is applied to the substrate. For example, the first coating composition may be applied directly to the substrate and the second coating composition may be applied directly to the first coating. In certain embodiments, the second coating composition is applied to the substrate before the first coating composition is applied to the substrate. For example, the second coating composition may be applied directly to the substrate and the first coating composition may be applied directly to the second coating.
In certain embodiments of any aspect of the present invention, the substrate has a moisture vapour transmission rate (MVTR) equal to or less than about 200 gsm (g/m2) per day. In certain embodiments, the substrate has a MVTR equal to or less than about gsm (g/m2) per day. In certain embodiments, the substrate has a MVTR equal to or less than about 1 gsm (g/m2) per day. In certain embodiments, the substrate has a MVTR equal to or less than about 0.2 gsm (g/m2) per day.
In certain embodiments of any aspect of the present invention, the substrate has an oil vapour transmission rate (OVTR) equal to or less than about 200 gsm (g/m2) per day. In certain embodiments, the substrate has an OVTR equal to or less than about 8 gsm (g/m2) per day. In certain embodiments, the substrate has a OVTR equal to or less than about 5 gsm (g/m2) per day. In certain embodiments, the substrate has a OVTR equal to or less than about 1 gsm (g/m2) per day.
Certain embodiments of any aspect of the present invention may provide one or more of the following advantages:
The details, examples and preferences provided in relation to any particular one or more of the stated aspects of the present invention apply equally to all aspects of the present invention. Any combination of the embodiments, examples and preferences described herein in all possible variations thereof is encompassed by the present invention unless otherwise indicated herein, or otherwise clearly contradicted by context.
There is provided herein a substrate coated with a first coating and a second coating. The first coating comprises an alcohol-based binder and an inorganic particulate material and the second coating comprises a latex binder and a phyllosilicate. Thus, there is provided herein a first coating composition comprising an alcohol-based binder and an inorganic particulate material. There is also provided herein a second coating composition comprising a latex binder and a phyllosilicate. The first and second coatings on the substrate may, for example, be a dry residue of the first and second coating compositions respectively.
The inclusion of inorganic particulate material (e.g. phyllosilicate, talc, kaolin) in the coating compositions may advantageously provide benefits such as reduced liquid phase mineral oil transmission, making the system cheaper, improving water barrier properties (i.e., reducing moisture vapour transmission rates through coated substrates such as coated paper) and improving the applicability of the barrier coating composition to the substrate (e.g. paper substrate). The inclusion of inorganic particulate material (e.g. phyllosilicate, talc, kaolin) in the coating compositions may also reduce the energy required for drying of the coating compositions.
The first coating composition comprises an alcohol-based binder and an inorganic particulate material. For example, the first coating composition may consist essentially of an alcohol-based binder and an inorganic particulate material, or may consist of an alcohol-based binder and an inorganic particulate material.
The first coating composition may, for example, be an aqueous suspension/dispersion. The solids content of the first coating composition may suitably be as high as possible whilst still giving a suitably fluid composition which may be used in coating a substrate. The solids content of the first coating composition may, for example, range from about 10% to about 90% by weight of the composition. For example, the solids content of the first coating composition may range from about 10% to about 80%, for example from about 10% to about 70%, for example from about 10% to about 60% by weight of the composition. After application of the aqueous coating composition to the substrate, the coating composition may be allowed to dry. Thus, the first coating may be in the form of a dry residue comprising an alcohol-based binder and an inorganic particulate material.
The term “alcohol” is used herein to mean an organic compound in which a hydroxyl functional group (—OH) is bonded to a carbon atom. Therefore, an alcohol-based binder is a composition or compound which contains a hydroxyl functional group bonded to a carbon atom, which is capable of functioning as a binder in a coating composition, for example a barrier coating composition, which may be suitable for coating a paper product.
The alcohol-based binder may comprise a primary alcohol having the general formula RCH2OH, a secondary alcohol having the general formula RR′CHOH, a tertiary alcohol having the general formula RR′R″COH, or a combination thereof. R, R′ and R″ represent alkyl groups having from one to twenty carbon atoms. For example R, R′ and R″ may represent alkyl groups having from one to ten carbon atoms. The alcohol-based binder may, for example, comprise primary, secondary and/or tertiary alcohol groups, which may be attached to a polymer backbone.
The alcohol-based binder may, for example, be a polymer comprising a carboniferous backbone having hydroxyl functional groups appended therefrom. For example, the alcohol-based binder may be polyvinyl alcohol. Polyvinyl alcohol may be obtained by conventional methods known in the art, such as, for example by partial or complete hydrolysis of polyvinyl acetate to remove acetate groups. Thus, a person of skill in the art will understand that polyvinyl alcohol obtained by hydrolysis of polyvinyl acetate may contain pendant acetate groups as well as pendant hydroxy groups. Thus, in embodiments, the polyvinyl alcohol is derived from partially or fully hydrolysed polyvinyl acetate. The extent of hydrolysis may be such that at least about 50 mole % of the acetate groups are hydrolysed, for example, at least about 60 mole % of the acetate groups are hydrolysed, for example, at least about 70 mole % of the acetate groups are hydrolysed, for example, at least about 80 mole % of the acetate groups are hydrolysed, for example, at least about 85 mole % of the acetate groups are hydrolysed, for example, at least about 90 mole % of the acetate groups are hydrolysed, for example, at least about 95 mote % of the acetate groups are hydrolysed or, for example, at least about 99 mole % of the acetate groups are hydrolysed.
The polymer may, for example, be a copolymer of polyvinyl alcohol and other monomers, such as, for example, acetate and acrylate. Hereinafter, the invention may tend to be discussed in terms of polyvinylalcohol. However, the invention should not be construed as being limited to such embodiments.
The alcohol-based binder component of the first coating composition may serve not only as binder when applied to the substrate (e.g. a paper substrate), but may also enhance the barrier properties of the first coating composition. The moisture vapour transmission rate of the coated substrate may, for example, be improved (e.g. reduced) in comparison to the moisture vapour transmission rate of a coated substrate coated with a first coating that does not comprise an alcohol-based binder.
The first coating composition may, for example, comprise at least about 20% by weight alcohol-based binder, based on the total weight of the barrier coating composition, for example, at least about 25% by weight alcohol-based binder, for example at least about 30% by weight alcohol-based binder, for example at least about 35% by weight alcohol-based binder, for example at least about 40% by weight alcohol-based binder, for example at least about 45% by weight alcohol-based binder, for example at least about 50% by weight alcohol-based binder, for example at least about 55% by weight alcohol-based binder, for example at least about 60% by weight alcohol-based binder, for example at least about 65% by weight alcohol-based binder, for example at least about 70% by weight alcohol-based binder or, for example at least about 75% by weight alcohol-based binder.
The first coating composition may, for example, comprise up to about 99% by weight, for example up to about 98% by weight, for example up to about 95% by weight, for example up to about 90% by weight, for example up to about 85% by weight, for example, up to about 80% by weight alcohol-based binder.
The inorganic particulate material may, for example, be selected from an alkaline earth metal carbonate or sulphate (e.g. calcium carbonate, magnesium carbonate, dolomite and gypsum); a phyllosilicate, an aluminosilicate (e.g. hydrous kandite clay including kaolin, halloysite clay, ball clay, anhydrous (calcined) kandite clay such as metakaolin, fully calcined kaolin and mica); talc, chlorite, pyrophyllite, serpentine, perlite, diatomaceous earth, magnesium hydroxide, aluminium trihydrate and combinations thereof.
The inorganic particulate material may, for example, be an aluminosilicate, for example, kaolin. The inorganic particulate material may, for example, be kaolin having a high shape factor. The inorganic particulate material may, for example, be a magnesium silicate. Hereinafter, the invention may tend to be discussed in terms of kaolin. However, the invention should not be construed as being limited to such embodiments.
A kaolin product of high shape factor is considered to be more “platey” than a kaolin product of low shape factor. “Shape factor”, as used herein, is a measure of the ratio of particle diameter to particle thickness for a population of particles of varying size and shape as measured using the electrical conductivity methods, apparatuses, and equations described in U.S. Pat. No. 5,576,617, which is incorporated herein by reference. As the technique for determining shape factor is further described in the '617 patent, the electrical conductivity of a composition of an aqueous suspension of orientated particles under test is measured as the composition flows through a vessel. Measurements of the electrical conductivity are taken along one direction of the vessel and along another direction of the vessel transverse to the first direction. Using the difference between the two conductivity measurements, the shape factor of the particulate material under test is determined.
The shape factor of the inorganic particulate material, for example, kaolin, may be equal to or greater than about 10. For example, the shape factor may be equal to or greater than about 20, or equal to or greater than about 30, or equal to or greater than about 40, or equal to or greater than about 50, or equal to or greater than about 60 or equal to or greater than about 70. The shape factor may be equal to or greater than about 80, for example equal to or greater than about 90 or equal to or greater than about 100. For example, the shape factor of the inorganic particulate material may be up to about 95 or up to about 100 or up to about 110 or up to about 150. For example, the shape factor may lie in one or more of the following ranges: 20 to 150; 20 to 110; to 100; 30 to 150; 30 to 110; 30 to 100; 40 to 150; 40 to 110; 40 to 100; 50 to 150; 50 to 110; 50 to 100; 60 to 150; 60 to 110; 60 to 100; 70 to 150; 70 to 110; 70 to 100; 80 to 150; 80 to 110; 80 to 100; 90 to 150; 90 to 110; 90 to 100.
Unless otherwise stated, the mean (average) equivalent particle diameter (d50 value) and other particle size properties referred to herein for the inorganic particulate materials are as measured in a well known manner by sedimentation of the particulate material in a fully dispersed condition in an aqueous medium using a Sedigraph 5100 machine as supplied by Micromeritics Instruments Corporation, Norcross, Georgia, USA (telephone: +1 770 662 3620; web-site: www.micromeritics.com), referred to herein as a “Micromeritics Sedigraph 5100 unit”. Such a machine provides measurements and a plot of the cumulative percentage by weight of particles having a size, referred to in the art as the ‘equivalent spherical diameter’ (esd), less than given esd values. The mean particle size d50 is the value determined in this way of the particle esd at which there are 50% by weight of the particles which have an equivalent spherical diameter less than that d50 value. The term d 90 is the particle size value less than which there are 90% by weight of the particles.
The inorganic particulate material may, for example, have a mean equivalent particle diameter (d50) less than or equal to about 10 microns (μm) (by Sedigraph), e.g. less than or equal to about 8 μm, or less than or equal to about 6 μm, or less than or equal to about 4 μm, or less than or equal to about 2 μm, or less than or equal to about 1.5 μm, particularly less than or equal to about 1 μm, e.g. less than or equal to about 0.5 μm, e.g. less than or equal to about 0.4 μm or, e.g., less than or equal to about 0.3 μm. The value of d50 may, for example, be in the range of about 0.2 μm to about 2 μm, for example about 0.3 to about 1.5 μm, for example about 0.3 to about 1 μm, or for example about 1 μm to about 2 μm.
The inorganic particulate material may, for example, have a d 90 of less than or equal to about 5 particularly less than or equal to about 3 μm, e.g., less than or equal to about 2 μm. The value of d 90 may, for example, be in the range of about 0.5 μm to about 3 μm, for example about 1 μm to about 3 μm or, for example, about 0.5 μm to 2 μm.
The range of fine content of inorganic particulate, i.e. the wt % less than 0.25 μm may lie in the range of about 5 wt % to about 95 wt %, for example about 40 wt % to about 90 wt % or about 5 wt % to about 20 wt %.
The kaolin may, for example, have a shape factor equal to or greater than about 30 and a d go of less than about 2 μm. For example, the kaolin may have a shape factor equal to or greater than about 60, or 70, or 90, and a d 90 of less than about 2 μm.
The kaolin may, for example, have a shape factor between about 10 and about 20 and a d50 of less than about 1 μm, for example, less than or equal to about 0.5 μm.
The kaolin may, for example, have a shape factor between about 25 and about 50 and a d50 of less than about 0.3 μm.
The inorganic particulate material may, for example, be an aluminosilicate having a shape factor between about 20 and 40, and a d50 of less than about 0.5 μm.
Kaolin clay used in this invention may be a processed material derived from a natural source, namely raw natural kaolin clay mineral. The processed kaolin clay may typically contain at least about 50% by weight kaolinite. For example, most commercially processed kaolin clays contain greater than about 75% by weight kaolinite and may contain greater than about 90%, in some cases greater than about 95% by weight of kaolinite.
Kaolin clay used in the present invention may be prepared from the raw natural kaolin clay mineral by one or more other processes which are well known to those skilled in the art, for example by known refining or beneficiation steps.
For example, the clay mineral may be bleached with a reductive bleaching agent, such as sodium hydrosulfite. If sodium hydrosulfite is used, the bleached clay mineral may optionally be dewatered, and optionally washed and again optionally dewatered, after the sodium hydrosulfite bleaching step.
The clay mineral may be treated to remove impurities, e. g. by flocculation, flotation, or magnetic separation techniques well known in the art. Alternatively the clay mineral may be untreated in the form of a solid or as an aqueous suspension.
The process for preparing the particulate kaolin clay used in the present invention may also include one or more comminution steps, e.g., grinding or milling. Light comminution of a coarse kaolin is used to give suitable delamination thereof. The comminution may be carried out by use of beads or granules of a plastic (e. g. nylon), sand or ceramic grinding or milling aid. The coarse kaolin may be refined to remove impurities and improve physical properties using well known procedures. The kaolin clay may be treated by a known particle size classification procedure, e.g., screening and centrifuging (or both), to obtain particles having a desired d50 value or particle size distribution.
When the inorganic particulate material is obtained from naturally occurring sources, it may be that some mineral impurities will contaminate the ground material. For example, naturally occurring kaolin may be present in association with other minerals. Thus, the inorganic particulate material may include an amount of impurities. In general, however, the inorganic particulate material will contain less than about 5% by weight, preferably less than about 1% by weight, of other mineral impurities.
The first coating composition may, for example, comprise at least about 20% by weight inorganic particulate material, based on the total weight of the barrier coating composition, for example, at least about 25% by weight inorganic particulate material, for example at least about 30% by weight inorganic particulate material, for example at least about 35% by weight inorganic particulate material, for example at least about 40% by weight inorganic particulate material, for example at least about 45% by weight inorganic particulate material, for example at least about 50% by weight inorganic particulate material, for example at least about 55% by weight inorganic particulate material, for example at least about 60% by weight inorganic particulate material, for example at least about 65% by weight inorganic particulate material, for example at least about 70% by weight inorganic particulate material or, for example at least about 75% by weight inorganic particulate material. The first coating composition may, for example, comprise no more than about 99% by weight, for example no more than about 98% by weight, for example no more than about 95% by weight, for example no more than about 90% by weight, for example no more than about 80% by weight, for example no more than about 70% by weight, for example no more than about 60% by weight, for example no more than about 50% by weight inorganic particulate material. The first coating composition may, for example, be applied as a single layer.
The weight ratio of inorganic particulate material to alcohol-based binder may, for example, range from about 5:1 to about 1:10, for example, from about 5:1 to about 1:9, for example, from about 5:1 to about 1:7, for example, from about 5:1 to about 1:5, for example, from about 4:1 to about 1:4, for example, from about 3:1 to about 1:3, for example, from about 2:1 to about 1:2, for example, from about 1.5:1 to about 1:1.5, for example, from about 1.25:1 to about 1:1.25. The weight ratio of inorganic particulate material to alcohol-based binder may, for example, be about 1:1.
The second coating composition comprises a latex binder and a phyllosilicate. For example, the second coating composition may consist essentially of or consist of a latex binder and a phyllosilicate, or may consist of a latex binder and a phyllosilicate.
The second coating composition may, for example, be an aqueous suspension/dispersion. The solids content of the second coating composition may suitably be as high as possible whilst still giving a suitably fluid composition which may be used in coating a substrate. The solids content of the second coating composition may, for example, range from about 10% to about 90% by weight of the composition. For example, the solids content of the second coating composition may range from about 10% to about 80%, for example from about 10% to about 70%, for example from about 10% to about 60% by weight of the composition. After application of the aqueous coating composition to the substrate, the coating composition may be allowed to dry. Thus, the second coating may be in the form of a dry residue comprising a latex binder and a phyllosilicate.
The term “latex” is used herein to mean a dispersion/suspension (e.g. aqueous dispersion/suspension) of one or more polymer(s). The polymers may, for example, be natural or synthetic. Therefore, the term “latex binder” means any composition comprising, consisting essentially of or consisting of one or more polymers, which is capable of functioning as a binder in a coating composition, for example a barrier coating composition, which may be suitable for coating a paper product.
The latex binder may, for example, be natural rubber latex obtained from, for example, rubber trees. The latex binder may, for example, be a synthetic latex. The latex binder may, for example, be a styrene polymer, for example copolymers including styrene monomers. For example, the latex binder may be a copolymer comprising, consisting essentially of or consisting of alkene monomers (e.g. ethylene, propylene, butylene, butadiene) and styrene monomers. For example, the latex binder may be styrene butadiene. The latex binder may, for example, be polyurethane, polyester and/or polyethyleneacrylate dispersions. Hereinafter, the invention may tend to be discussed in terms of styrene butadiene. However, the invention should not be construed as being limited to such embodiments.
The second coating composition may, for example, comprise at least about 20% by weight latex binder, based on the total weight of the barrier coating composition, for example, at least about 25% by weight latex binder, for example at least about 30% by weight latex binder, for example at least about 35% by weight latex binder, for example at least about 40% by weight latex binder, for example at least about 45% by weight latex binder, for example at least about 50% by weight latex binder, for example at least about 55% by weight latex binder, for example at least about 60% by weight latex binder, for example at least about 65% by weight latex binder, for example at least about 70% by weight latex binder or, for example at least about 75% by weight latex binder.
The second coating composition may, for example, comprise up to about 99% by weight, for example up to about 98% by weight, for example up to about 95% by weight, for example up to about 90% by weight, for example up to about 85% by weight, for example up to about 80% by weight latex binder.
The phyllosilicate may, for example, be selected from clays (e.g. kaolin), talc, mica, chlorite, pyrophyllite, serpentine and combinations thereof. For example, the phyllosilicate may be talc. For example, the phyllosilicate may be a combination of two or more phyllosilicates, for example a combination of talc and another phyllosilicate, for example talc and kaolin. Hereinafter, the invention may tend to be discussed in terms of talc. However, the invention should not be construed as being limited to such embodiments.
Talc may comprise, consist essentially of, or consist of natural talc particulate or synthetic talc particulate or a mixture of natural talc particulate and synthetic talc particulate.
As used herein, the term “natural talc” means talc derived from a natural resource, i.e., natural talc deposits. Natural talc may be either the hydrated magnesium silicate of formula Si4Mg3O10(OH)2, which is arranged as a stack of laminae, or the mineral chlorite (hydrated magnesium aluminium silicate), or a mixture of the two, optionally associated with other minerals, for example, dolomite. Natural talc occurs as rock composed of talc crystals.
As used herein, the term “synthetic talc” means talc that has been synthesized using a man-made synthetic process. The talc used in the present invention may be a macrocrystalline talc or microcrystalline talc.
The phyllosilicate mineral may, for example, be bleached with a reductive bleaching agent, such as sodium hydrosulfite. If sodium hydrosulfite is used, the bleached phyllosilicate mineral may optionally be dewatered, and optionally washed and again optionally dewatered, after the sodium hydrosulfite bleaching step.
The phyllosilicate mineral may be treated to remove impurities, e.g. by flocculation, flotation, or magnetic separation techniques well known in the art. Alternatively the phyllosilicate mineral may be untreated in the form of a solid or as an aqueous suspension.
The process for preparing the phyllosilicate may include one or more comminution steps, e.g., grinding or milling. Light comminution of a coarse phyllosilicate is used to give suitable delamination thereof. The comminution may use beads or granules of a plastic (e.g. nylon), sand or ceramic grinding or milling aid. The coarse phyllosilicate may be refined to remove impurities and improve physical properties using well known procedures. The phyllosilicate may be treated by a known particle size classification procedure, e.g., screening and centrifuging (or both), to obtain particles having a desired particle size distribution.
The phyllosilicate may be calcined or non-calcined. For example, the phyllosilicate may be calcined talc or non-calcined talc.
When the phyllosilicate is obtained from naturally occurring sources, it may be that some mineral impurities will inevitably contaminate the ground material. In general, however, the phyllosilicate material used in embodiments of the present invention will contain less than 5% by weight, preferably less than 1% by weight of other mineral impurities.
The first coating composition may, for example, comprise at least about 20% by weight phyllosilicate, based on the total weight of the barrier coating composition, for example, at least about 25% by weight phyllosilicate, for example at least about 30% by weight phyllosilicate, for example at least about 35% by weight phyllosilicate, for example at least about 40% by weight phyllosilicate, for example at least about 45% by weight phyllosilicate, for example at least about 50% by weight phyllosilicate, for example at least about 55% by weight phyllosilicate, for example at least about 60% by weight phyllosilicate, for example at least about 65% by weight phyllosilicate, for example at least about 70% by weight phyllosilicate or, for example at least about 75% by weight phyllosilicate. The first coating composition may, for example, comprise no more than about 99% by weight, for example no more than about 98% by weight, for example no more than about 95% by weight, for example no more than about 90% by weight, for example no more than about 80% by weight, for example no more than about 70% by weight, for example no more than about 60% by weight, for example no more than about 50% by weight phyllosilicate. The second coating composition may, for example, be applied as a single layer.
The weight ratio of the latex binder and phyllosilicate may be chosen so that the maximum weight of phyllosilicate particles is obtained in the coating without creating pores in the coating. This may, for example, depend on the particle size of the phyllosilicate. The weight ratio of phyllosilicate to latex binder may, for example, range from about 5:1 to about 1:10, for example, from about 5:1 to about 1:9, for example, from about 5:1 to about 1:7, for example, from about 5:1 to about 1:5, for example, from about 4:1 to about 1:4, for example, from about 3:1 to about 1:3, for example, from about 2:1 to about 1:2. For example, the weight ratio of phyllosilicate to latex binder may be from about 2:1 about 1:1.
The phyllosilicate may, for example, have a high shape factor. Thus, the phyllosilicate may be considered to be more “platey” than a phyllosilicate product of low shape factor. “Shape factor”, as used herein, is as described above in relation to the first coating composition.
The shape factor of the phyllosilicate (e.g. talc) may suitably be equal to or greater than about 10. For example, the shape factor may be equal to or greater than about 20, or equal to or greater than about 30, or equal to or greater than about 40, or equal to or greater than about 50, or equal to or greater than about 60 or equal to or greater than about 70. The shape factor may be equal to or greater than about 80, for example equal to or greater than about 90 or equal to or greater than about 100. For example, the shape factor of the phyllosilicate (e.g. talc) may suitably be up to about 95 or up to about 100 or up to about 110 or up to about 150. For example, the shape factor may lie in one or more of the following ranges: 20 to 150; 20 to 110; 20 to 100; 30 to 150; 30 to 110; 30 to 100; 40 to 150; 40 to 110; 40 to 100; 50 to 150; 50 to 110; 50 to 100; 60 to 150; 60 to 110; 60 to 100; 70 to 150; 70 to 110; 70 to 100; 80 to 150; 80 to 110; 80 to 100; 90 to 150; 90 to 110; 90 to 100.
The phyllosilicate (e.g. talc) may, for example, have a mean equivalent particle diameter (d50) less than or equal to about 10 microns (μm) (by Sedigraph), e.g. less than or equal to about 8 μm, or less than or equal to about 6 μm, or less than or equal to about 4 μM. For example, the phyllosilicate may have a d50 of less than or equal to about 2 μm, for example equal to or less than about 1.5 μm. The phyllosilicate may, for example, have a d50 ranging from about 0.1 μm to about 10 μm, for example from about 0.1 μm to about 5 μm, for example from about 0.1 μm to about 2 μm, for example from about 0.1 μm to about 1.5 μm, for example from about 0.5 μm to about 2 μm or from about 0.5 μm to about 1.5 μm.
The phyllosilicate may, for example, have a d 90 of less than or equal to about 20 μm, for example less than or equal to about 15 μm, for example less than or equal to about μm. For example, the phyllosilicate may have a d 90 of less than or equal to about 9 μm, for example less than or equal to about 8 μm, for example less than or equal to about 7 μm, for example less than or equal to about 6 μm. The value of d 90 may, for example, be in the range of about 1 μm to about 10 μm, for example about 1 μm to about 8 μm or, for example, about 1 μm to 6 μm.
The range of fine content of phyllosilicate particles, i.e. the wt % less than 0.25 μm may lie in the range of about 5 wt % to about 95 wt %, for example about 40 wt % to about 90 wt % or about 5 wt % to about 20 wt %.
The phyllosilicate (e.g. talc) may, for example, have a shape factor of greater than about 30 and a d50 equal to or less than about 2
The first and/or second coating compositions may contain one or more optional additional components, if desired. The first and/or second coating compositions may optionally comprise one or more further additive components, as discussed below. The first and/or second coating compositions may be in the form of an aqueous suspension of the binder and inorganic particulate material components defined above, and optionally one or more further additive components, as discussed below.
Such additional components, where present, may suitably be selected from known additives for coating compositions (e.g. paper coating compositions). Some of these optional additives may provide more than one function in the coating composition. Examples of known classes of optional additives are as follows:
Any of the above additives and additive types may be used alone or in admixture with each other and with other additives, if desired.
For example, the first and/or second coating compositions may further comprise one or more crosslinker(s). For example, the first coating composition may further comprise one or more crosslinker(s).
For example, the first or second coating compositions may further comprise one or more surfactant(s). For example, both the first and second coating compositions may further comprise one or more surfactant(s). The use of one or more surfactant(s) in the first and/or second coating compositions may, for example, improve the application of one coating on another (e.g. the recoatability of the coatings). The use of one or more surfactant(s) may, for example, improve the interaction between the two coatings.
Surfactants include, without limitation, ionic (e.g. anionic and/or cationic) and non-ionic surfactants. Anionic surfactants include, for example, sulphate, sulphonate and phosphate esters (e.g. ammonium lauryl sulphate, sodium lauryl sulphate, sodium lauryl ether sulphate) and carboxylates (e.g. alkyl carboxylates such as sodium stearate). Cationic surfactants include, for example, primary, secondary, tertiary and quaternary amines and quaternary ammonium species. Non-ionic surfactants include, for example, fatty alcohols, cetyl alcohol, stearyl alcohol, cetostearyl alcohol, oleyl alcohol, polyoxyethylene glycol alkyl ethers, polyoxypropylene glycol alkyl ethers, glucoside alkyl ethers, polyoxyethylene glycol octylphenol ethers, polyoxylene glycol alkylphenol ethers, glycerol alkyl ethers, sorbitan alkyl esters, dodecyldimethylamine oxide and block copolymers of polyethylene glycol and polypropylene glycol.
The total amount of the one or more surfactant(s) in the first or second coating composition may, for example, be from about 0.01 wt % to about 5.0 wt %. For example, the total amount of surfactant in the first or second coating composition may range from about 0.1 wt % to about 3.0 wt % or from about 0.1 wt % to about 2.0 wt % or from about 0.1 wt % to about 1.0 wt %. For example, the total amount of surfactant in the first or second coating composition may range from about 0.5 wt % to about 3.0 wt % or from about 0.5 wt % to about 2.0 wt % or from about 0.5 wt % to about 1.0 wt %. For example, the total amount of surfactant in the first or second coating composition may be about 0.5 wt %.
For all of the above additives, the percentages by weight (based on the dry weight of inorganic particulate material (100%) present in the composition) can vary as understood by those skilled in the art. Where the additive is present in a minimum amount, the minimum amount may be about 0.01% by weight based on the dry weight of the inorganic particulate material. The maximum amount of any one or more of the above additives may, for example, be about 5.0% by weight based on the dry weight of the inorganic particulate material. For example, the maximum amount may be about 3.0% or 2.0% by weight based on the dry weight of the inorganic particulate material.
A substrate may, for example, be coated with the first and second coating compositions described above, including all embodiments thereof in all possible combinations. Thus, there is provided herein a substrate provided with a first coating comprising an alcohol-based binder and an inorganic particulate material, and a second coating comprising a latex binder and a phyllosilicate.
The substrate may, for example, be any material, for example selected from plastics (e.g. low density polyethylene, polypropylene, polyamides and the like), metals (e.g foils such as aluminium foil), textiles and paper. The material may, for example, be coloured, treated (e.g. varnished or laminated) or both. The coating of the substrates may, for example, comprise a dry residue of the first and/or second coating compositions described herein. Hereinafter, the invention may be defined in terms of paper substrates. However, the invention should not be construed as being limited to such embodiments.
The term paper substrate, as used in connection with the present invention, should be understood to mean all forms of paper, including board, such as, for example, white-lined board and linerboard, cardboard, paperboard, coated board, and the like. There are numerous types of paper, coated or uncoated, which may be coated using the compositions disclosed herein, including paper suitable for food packaging, perishable goods other than food, e.g., pharmaceutical products and compositions, books, magazines, newspapers and the like, and office papers. The paper may be calendered or super calendared as appropriate; for example super calendered magazine paper for rotogravure and offset printing may be made according to the present methods. Paper suitable for light weight coating (LWC), medium weight coating (MWC) or machine finished pigmentisation (MFP) may also be coated using the present compositions.
The paper substrate may have opposing first and second surfaces. The first and second coatings may, for example, be present on the first surface, the second surface, or both. For example, the first surface may be a surface which faces the interior of the paper product when it is formed into a three-dimensional product and the opposing second surface may face the exterior of the paper product. The first and/or second surfaces may or may not have other intermediary coatings or layers between each surface and the first and second coatings described herein. The first and second coatings may, for example, be applied directly to the paper substrate.
The first and second coating compositions may be applied to the substrate in any order. Thus, the first and second coatings may be layered such that the first coating is closer to the substrate than the second coating, or such that the second coating is closer to the substrate than the first coating. The first and/or second coating may be applied to the substrate directly with no other substances or coatings being applied before the first and second coatings are applied and no intermediate substances or coatings being applied between the first and second coatings. For example, the first coating may be in direct contact with the substrate and the second coating may be in direct contact with the first coating. For example, the second coating may be in direct contact with the substrate and the first coating may be in direct contact with the second coating.
The first coating on the substrate may, for example, have a coating weight between about 2 gsm and about 30 gsm (grams per m2), for example between about 3 gsm and about 28 gsm. The first coating may, for example, have a coating weight of less than about 15 gsm. For example, the first coating may have a coating weight of less than about 12 gsm, for example less than about 10 gsm. The first coating may, for example, have a coating weight of less than about 8 gsm, for example less than about 6 gsm, for example less than about 5 gsm.
The second coating on the substrate may, for example, have a coating weight between about 3 gsm and about 30 gsm (grams per m2), for example between about 2 gsm and about 28 gsm. The second coating may, for example, have a coating weight of less than about 15 gsm. For example, the second coating may have a coating weight of less than about 12 gsm, for example less than about 10 gsm. The second coating may, for example, have a coating weight of less than about 8 gsm, for example less than about 6 gsm, for example less than about 5 gsm.
The total coating weight of the first and second coatings on the substrate may, for example, range between about 2 gsm and about 50 gsm (grams per m2). For example, the total coating weight of the first and second coatings may range from about 2 gsm to about 40 gsm, for example from about 2 gsm to about 30 gsm. For example, the total coating weight of the first and second coatings on the substrate may be less than about gsm, for example less than about 25 gsm, for example less than about 20 gsm. For example, the total coating weight of the first and second coatings on the substrate may be less than about 15 gsm.
The first and second coating compositions used to coat the substrate may be barrier coating compositions. For example, the first and second coating compositions may reduce or prevent the permeation of gases and/or vapours and/or liquids through the coated substrate. For example, the coating compositions may reduce or prevent the permeation of water and/or organic oils through the coated product (i.e. reduce the moisture vapour and/or oil vapour transmission rate of the coated product).
Thus, the coated substrate may, for example, have a moisture vapour transmission rate (MVTR) which is equal to or less than about 200 gsm (g/m2) per day. For example, the coated substrate may have a MVTR which is equal to or less than about 150 gsm per day, for example equal to or less than about 100 gsm per day, for example equal to or less than about 50 gsm per day, for example equal to or less than about 30 gsm per day, for example equal to or less than about 20 gsm per day, for example equal to or less than about 10 gsm per day. For example, the coated substrate may have a MVTR of equal to or less than about 8 gsm per day, for example equal to or less than about 5 gsm per day, for example equal to or less than about 4 gsm per day, for example equal to or less than about 3 gsm per day, for example equal to or less than about 2 gsm per day, for example equal to or less than about 1 gsm per day. For example, the coated substrate may have a MVTR of equal to or less than about 0.9 gsm per day, for example equal to or less than about 0.8 gsm per day, for example equal to or less than about 0.7 gsm per day, for example equal to or less than about 0.6 gsm per day, for example equal to or less than about 0.5 gsm per day, for example equal to or less than about 0.4 gsm per day, for example equal to or less than about 0.3 gsm per day, for example equal to or less than about 0.2 gsm per day, for example equal to or less than about 0.1 gsm per day. For example, the coated substrate may have a MVTR ranging from about 0.01 gsm per day to about 200 gsm per day, for example from about 0.1 gsm per day to about 50 gsm per day, for example from about 0.2 gsm per day to about 5 gsm per day, for example from about 0.5 gsm per day to about 1 gsm per day.
Unless otherwise stated, the MVTR may be measured according to TAPPI T448. The opening of a pot containing silica gel or calcium chloride is covered with the coated substrate and the pot is weighed periodically over several hours or days depending on the expected MVTR level. The amount of water entering the pot is determined by measuring the change in weight of the silica gel or calcium chloride. The experiment is carried out at 23° C. and 50% humidity. Each coating composition may be present at a coatweight equal to or less than about 10 gsm (e.g. total coatweight equal to or less than about 20 gsm). The substrate used may be a woodfree base paper. The base paper may be pre-coated with a pre-coating composition to improve smoothness of the paper.
The coated substrate may, for example, have an oil vapour transmission rate (OVTR) which is equal to or less than about 200 gsm (g/m2) per day. For example, the coated substrate may have an OVTR which is equal to or less than about 150 gsm per day, for example equal to or less than about 100 gsm per day, for example equal to or less than about 50 gsm per day, for example equal to or less than about 30 gsm per day, for example equal to or less than about 20 gsm per day, for example equal to or less than about 20 gsm per day, for example equal to or less than about 10 gsm per day. For example, the coated substrate may have a OVTR of equal to or less than about 8 gsm per day, for example equal to or less than about 5 gsm per day, for example equal to or less than about 4 gsm per day, for example equal to or less than about 3 gsm per day, for example equal to or less than about 2 gsm per day, for example equal to or less than about 1 gsm per day. For example, the coated substrate may have a OVTR of equal to or less than about 0.9 gsm per day, for example equal to or less than about 0.8 gsm per day, for example equal to or less than about 0.7 gsm per day, for example equal to or less than about 0.6 gsm per day, for example equal to or less than about 0.5 gsm per day, for example equal to or less than about 0.4 gsm per day, for example equal to or less than about 0.3 gsm per day, for example equal to or less than about 0.2 gsm per day, for example equal to or less than about 0.1 gsm per day. For example, the coated substrate may have an OVTR ranging from about 0.01 gsm per day to about 200 gsm per day, for example from about 0.1 gsm per day to about 50 gsm per day, for example from about 0.2 gsm per day to about 5 gsm per day, for example from about 0.5 gsm per day to about 1 gsm per day.
Unless otherwise stated, the OVTR may be measured a method corresponding to that used to measure MVTR. The opening of a pot containing decane or heptane is covered with the coated substrate and the pot is weighed periodically over several hours or days depending on the expected OVTR level. The amount of decane or heptane leaving the pot is determined by measuring the change in weight of the pot. The experiment is carried out at 23° C. and 50% humidity. Each coating composition may be present at a coatweight equal to or less than about 10 gsm (e.g. total coatweight equal to or less than about 20 gsm). The substrate used may be a woodfree base paper. The base paper may be pre-coated with a pre-coating composition to improve smoothness of the paper
One advantage of using two different coating compositions may be that the barrier can be improved for both organic and water transmission. This may not be possible in the same way if only one type of coating is used (e.g. the one coating will only be optimized for either organic or water transmission but not both). Without wishing to be bound by theory, another advantage may be that the lower or inner layer may be protected from the detrimental influence of the substance which is blocked by the upper or outer layer. For example, an inner organic barrier layer may be protected from the detrimental effect of water by using an upper water barrier layer. Therefore, the inner layer (e.g. organic barrier layer) may perform better over time because it is not deteriorated (e.g. by water).
The coating compositions disclosed herein may be used to coat various materials and substrates to form coated substrate. Thus, there is provided herein a use of the first and second coatings described above to coat a substrate (to make a coated substrate) and a method of coating a substrate. The first and second coatings (first and second coating compositions) may be as described above, including all embodiments thereof and all possible combinations thereof.
The first and second coating compositions may be prepared by combining (e.g. mixing) the binder (e.g. alcohol-based binder or latex binder) and inorganic particulate material (e.g. kaolin or phyllosilicate such as talc) and other optional additives in appropriate amounts into an aqueous liquid to prepare a suspension of said components. The coating compositions may suitably be prepared by conventional mixing techniques, as will be known in the art. The inorganic particulate material may, for example, be an aqueous slurry. This may, for example, be prepared using a suitable mixer, following which the slurry is blended with a solution of the binder. The resulting mixture may be screened prior to coating.
Slurry make-down process may, for example, include the addition of one or more additives, for example which may be selected from one or more dispersants, one or more wetting agents, one or more pH-adjusting agents. The slurry make-down process may, for example, involve dispersing the inorganic particulate material in the aqueous medium at high shear, for example between 2000 and 3000 rpm. The final viscosity of the phyllosilicate slurry may, for example, range from about 200 cP (200 mPa·s) to about 400 cP (400 mPa·s). For example, the final viscosity of the phyllosilicate slurry may range from about 250 cP (250 mPa·s) to about 350 cP (350 mPa·s).
The method of coating a substrate may, for example, comprise coating the substrate with a first coating composition comprising an alcohol-based binder and an inorganic particulate material and a second coating composition comprising a latex binder and a phyllosilicate.
The first and second coating compositions may be applied in any order. For example, the first coating composition may be applied before the second coating composition or the second coating composition may be applied before the first coating composition. The first or second coating composition may be applied directly to the substrate. This coating composition may then be allowed to dry and/or crosslink before the other of the first and second coating composition is applied. The other of the first and second coating composition may then be applied directly to the coating composition already present on the substrate.
The coating process may be carried out using standard techniques which are known to the skilled person. The coating process may also involve calendaring or super-calendaring the coated substrate.
Methods of coating paper and other sheet materials, and apparatus for performing the methods, are widely published and well known. Such known methods and apparatus may conveniently be used for preparing coated paper. For example, there is a review of such methods published in Pulp and Paper International, May 1994, page 18 et seq. Sheets may be coated on the sheet forming machine, i.e., “on-machine,” or “off-machine” on a coater or coating machine. Use of high solids compositions is desirable in the coating method because it leaves less water to evaporate subsequently.
However, as is well known in the art, the solids level should not be so high that high viscosity and levelling problems are introduced. The methods of coating may be performed using an apparatus comprising (i) an application for applying the coating composition to the material to be coated and (ii) a metering device for ensuring that a correct level of coating composition is applied. When an excess of coating composition is applied to the applicator, the metering device is downstream of it. Alternatively, the correct amount of coating composition may be applied to the applicator by the metering device, e.g., as a film press. At the points of coating application and metering, the paper web support ranges from a backing roll, e.g. via one or two applicators, to nothing (i.e. just tension). The time the coating is in contact with the paper before the excess is finally removed is the dwell time—and this may be short, long or variable. The coating may added by a coating head at a coating station. According to the quality desired, paper grades are uncoated, single-coated, double-coated and even triple-coated. When providing more than one coat, the initial coat (precoat) may have a cheaper formulation and optionally coarser pigment in the coating composition. A coater that is applying coating on each side of the paper will have two or four coating heads, depending on the number of coating layers applied on each side. Most coating heads coat only one side at a time, but some roll coaters (e.g., film presses, gate rolls, and size presses) coat both sides in one pass.
Examples of known coaters which may be employed include, without limitation, air knife coaters, blade coaters, rod coaters, bar coaters, multi-head coaters, roll coaters, roll or blade coaters, cast coaters, laboratory coaters, gravure coaters, kisscoaters, liquid application systems, reverse roll coaters, curtain coaters, spray coaters and extrusion coaters.
Water may be added to the solids comprising the coating composition to give a concentration of solids which is preferably such that, when the composition is coated onto a sheet to a desired target coating weight, the composition has a rheology which is suitable to enable the composition to be coated with a pressure (i.e., a blade pressure) of between 1 and 1.5 bar.
In one embodiment, the barrier coating is printed on the paper product, e.g., printed on a surface of the fibrous substrate of the paper product. The printing may utilize a technique selected from offset printing, flexographic printing or rotogravure printing, thereby allowing the coating composition to be applied to areas where it is required.
Offset printing is a widely used printing technique, as will be well understood by a person of ordinary skill in the art. The coating composition is transferred (or “offset”) from a plate to a rubber blanket, then to the surface of the substrate (e.g., paper substrate). The substrate may be sheet-fed or web-fed. The web-fed process may be heatset or coldset. Flexographic printing is a widely used printing technique, as will be well understood by a person of ordinary skill in the art. Using this technique, the coating composition is transferred from a first roll which is partially immersed in a tank comprising the coating composition. The coating composition is then transferred to the anilox roll (or meter roll) whose texture holds a specific amount of the coating composition since it is covered with thousands of small wells or cups that enable it to meter the coating composition to the printing plate in a uniform thickness evenly and quickly. The substrate is finally sandwiched between the plate and the impression cylinder to transfer the barrier coating. The coated substrate is then fed through a dryer, which allows the coating to dry. Advantageously, flexographic printing enables the coating composition to be applied in a series of thin layers (e.g., a series of fiver layers with a total coat weight of about 5 gsm) which has sufficient hold out to maintain good barrier properties (to liquid and/or vapour mineral oil transmission) for coating compositions comprising greater than about 60% by weight, for example, greater than about 65% by weight of inorganic particulate, based on the total dry weight of the composition. Rotogravure printing is a widely used printing technique, as will be well understood by a person of ordinary skill in the art.
The substrate (e.g. paper) may be formable or formed into a three-dimensional product, which may be suitable as food grade or pharmaceutical grade packaging, at least a portion of a first interior facing surface of the paper substrate is coated with the first and second coatings, and a second exterior facing surface of the paper substrate may be coated or printed with an ink-based product. The substrate (e.g. paper) may be derived from recycled pulp containing mineral oil and/or the ink-based product may comprise mineral oil.
Coated products (e.g. coated paper products) include brown corrugated boxes, flexible packaging including retail and shopping bags, food and hygiene bags and sacks, milk and beverage cartons, boxes suitable for cereals and the like, self adhesive labels, disposable cups and containers, envelopes, cigarette paper and bible paper.
The fibrous substrate may comprise virgin pulp (i.e., pulp which is not derived from a recycled material). Alternatively, the fibrous substrate may comprise a mixture of recycled pulp and virgin pulp.
A further aspect of the present invention is directed to packaged foodstuffs, pharmaceutical products or other perishable goods which are formed from the coated substrates (e.g. coated paper substrates) of the present invention. Foodstuffs are many and various and include, for example, grain based products such as breakfast cereals (e.g., oats, cornflakes and the like), flours (e.g., wheat flour and the like) and bakery products (e.g., breads, pastries and the like). Pharmaceutical products include, for example, tablets, powders suspensions and liquid-based products.
There is further provided a non-porous substrate coated with the first and second coating compositions described herein. The non-porous substrate may be a transparent paper, a translucent paper, a plastic film, such as polyethylene, polypropylene and the like, or a metal foil, such as aluminium foil. The substrate may be coloured, treated (e.g., varnished or laminated), or both. There is further provided a porous polyolefin substrate (e.g., polyethylene or polypropylene) coated with the coating compositions described herein.
Two different base papers (herein referred to as base paper 1 and base paper 2) were coated as shown in Table 1 below.
The first and second coating compositions were prepared by high shear mixing of the components.
The first and second coatings were applied to the base papers a hand draw down rod coater. The first and second coatings, where present, were each applied at a coat weight of 10 gsm.
Base paper 1 is a wood free paper, pre-coated on its back side on a paper machine online using a filmpress (Speedcoater).
Base paper 2 is a wood free paper, pre-coated on both sides on a paper machine online using a filmpress (Speedcoater).
The pre-coat is not considered as a barrier coating but only smoothens the paper surface for the following barrier coatings.
The kaolin used in the first and second coatings had a shape factor of 100, a GE brightness of 86 and an average particle size, d50 of 1.535 μm.
The talc used in the first and second coatings had a shape factor of 100, a talc/chlorite content of 98% and a d50 of 2 μm.
The polyvinyl alcohol used in the first and second coatings was either:
The term ester value referred to above denotes the number of mg of KOH needed to neutralize the acid released from the ester by saponification in 1 g of substance. The residual acetyl content is calculated from the ester value as follows: EV×0.0767. The degree of hydrolysis (saponification), H, indicated what percentage of the basic polyvinyl acetate molecule is saponified to polyvinyl alcohol. This is calculated as follows:
The styrene butadiene used was Styron DL1066.
The moisture vapour transmission rate and oil vapour transmission rate of these papers coated with the coatings described in Table 1 were measured according to the methods described above but at 38° C. and 90% humidity (e.g. according to TAPPI T464). The results are shown in Table 2 below.
It was found that the use of two coatings improved both the MVTR and OVTR. It was also found that the use of two coatings comprising kaolin and polyvinyl alcohol binder was not able to improve the MVTR as much as when at least one coating comprising talc and styrene butadiene binder was used. The use of two coatings comprising talc and styrene butadiene binder was not able to improve the OVTR as much as when at least one coating comprising kaolin and polyvinyl alcohol binder was used. By using one coating comprising kaolin and polyvinyl alcohol and one coating comprising talc and styrene butadiene, both the MVTR and OVTR were improved.
The foregoing broadly describes certain embodiments of the present invention without limitation. Variations and modifications as will be readily apparent to those skilled in the art are intended to be within the scope of the present invention as defined in and by the appended claims.
The following numbered paragraphs define particular embodiments of the present invention:
| Number | Date | Country | Kind |
|---|---|---|---|
| 14290367.3 | Dec 2014 | EP | regional |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15532661 | Jun 2017 | US |
| Child | 18400308 | US |
