WO2013075918A1

WO2013075918A1 - A coated wrapping material

Info

Publication number: WO2013075918A1
Application number: PCT/EP2012/071621
Authority: WO
Inventors: Sandip Das; Sanjay Ghoshal
Original assignee: Unilever N.V.; Unilever Plc; Hindustan Unilever Limited; Conopco, Inc., D/B/A Unilever
Priority date: 2011-11-22
Filing date: 2012-10-31
Publication date: 2013-05-30

Abstract

The present invention relates to a coating composition for use on paper substrate and more particularly to water based barrier coating composition which provides improved seal strength and processing speed on automatic filling machines. It is an object of the present invention to provide for coated paper having high packaging speed on automatic ice-cream wrapping machine. It is another object of the present invention to provide for coated paper that can be sealed at low sealing temperature of 60 to 80°C. It is another object of the present invention to provide water based coating composition for a paper substrate. It is yet another object of the present invention to provide coated paper with good heat seal-ability and having good seal strength at relatively low sealing temperatures. It is still another object to provide a coated paper having good water barrier properties while still retaining the easy recyclability. We have found that addition of carnauba wax to a water based coating composition provides for a coated paper having good heat seal-ability at relativity low temperatures and with good seal strength. It was further found that the coated paper of the present invention provides high packaging speed on automatic ice-cream cone wrapping machines at low sealing temperature of 60 to 80°C. It was also found that paper coated with the water based coating of the present invention provides good water barrier properties and is recyclable.

Description

A COATED WRAPPING MATERIAL

Field of the invention

The present invention relates to a coating composition for use on paper substrate and more particularly to water based barrier coating composition which provides improved seal strength and processing speed on automatic filling machines.

The invention has been developed primarily for use in ice-cream cone wrapper application and will be described hereinafter with reference to this application.

However, it will be appreciated that the invention is not limited to this particular field of use.

Background of the invention

Packaged ice cream cone products, such as Cornetto (Trademark, ex Unilever), are popular and well-known. Such products are typically individually wrapped in a cone- shaped paper based sleeve which covers at least the cone portion of the product and which is sealed with a lid. Sleeve and lid provide structural protection for the cone during distribution and sale. Sleeves are commonly made from paper, metal (e.g.

aluminium) foil or paper / foil composites.

Sleeve is formed from flats. A flat being defined in industry as a pre-cut flat piece of wrapping material, for example paper, optionally having crease lines or folds, that can be formed into a shaped package. The flats on rolling form a cone shape having a tip at one end and being open at the other end. Wafer cones are placed into the cone- shaped sleeve. Then the wafer cone is filled with ice cream and the top of the sleeve is sealed with a lid. Sealing may be by gluing or heat-sealing. Sealing by gluing includes application of adhesives to the top open end of the sleeve and the lid and sticking them together. In another method sealing is achieved by crimping and heat-sealing the open end of the sleeve onto itself over the lid. Heat-sealing has the advantage of not requiring an adhesive, but places limitations on the type of material that can be used for the sleeve. Only materials such as metal foil which crimp easily, forming a tight, neat fold can be used. Providing a layer of metal foil on paper substrate makes it difficult to recycle.

Attempts at providing a coating composition onto a surface of paper to improve its heat seal-ability, moisture barrier and grease resistance are well known in the art. US4568574 A (Champion International Corporation, 1986) discloses a light refractive coated paperboard for packaging that conceals grease or oil stains formed by the penetration of oil or grease in the inner surface of paperboard. It discloses a coated paper board having a substrate material coated with a first coating layer of non-leafing silver ink and a second coating layer of highly pigmented white ink layer. The first coating layer includes a dispersion of aluminium powder in a nitro-cellulose resin and the second coating layer preferably includes titanium dioxide dispersed in a nitrocellulose resin. This disclosure does not teach of a coating composition for providing improved moisture barrier.

US5654039 A (International Paper Company, 1997) discloses a paper substrate coated on at least one surface with a primer coat and a top coat. It discloses that the coating improves the moisture barrier property while still retaining the easy re- pulpability characteristics of the paper substrate. The primer coat includes a water- based dispersion of a polymer and optionally waxes. The top coat includes 15 to 90% of polymer and 80 to 5% of wax on dry weight basis. The wax component is selected from paraffin wax, microcrystalline wax, polyethylene or a blend thereof. However, it does not disclose a coated paper for use in automatic-form fill machines.

US5763100 A (International Paper Company, 1998) discloses a coated paper for use in food packaging and beverage containers which is recyclable and provides water resistance and grease resistance. It discloses a substrate coated on at least one surface with water based emulsion coating having 20 to 90 dry wt. % of an acrylic- styrene copolymer and 5 to 70 dry wt. % of a wax. The wax component is selected from paraffin wax, microcrystalline wax, polyethylene wax or a blend of two of more of the said waxes. However, it does not disclose a coated paper for use in automatic-form fill machines. GB1039540A (Reed Paper Group Limited, 1966) relates to a method of applying a coating on a surface of a web of paper or board having the step of forming a foam of a liquid coating composition having atleast one coating component with a gas or vapour and applying the foam to a surface and mechanically disintegrating the foam to form a continuous surface coating. The coating component disclosed in the application may be paraffin wax, microcrystalline wax, halo-waxes, bee wax and carnauba wax. The application is silent of a water-based coating composition having a mixture of carnauba wax and paraffin wax and/or microcrystalline wax.

Though above coating compositions are reported to provide for a paper substrate with improved water and grease resistance while still retaining their recyclability, it has been found by the present inventors that addition of such coating composition reduces the process-ability and run-ability on automatic machines. These coated papers are not reported to be used in automatic form-fill seal machines. A coating composition that runs smoothly on automatic form-fill machines remains to be desired. It is thus an object of the present invention to provide for coated paper having high packaging speed on automatic ice-cream wrapping machine.

It is another object of the present invention to provide for coated paper that can be sealed at low sealing temperature of 60 to 80°C.

It is another object of the present invention to provide water based coating composition for a paper substrate.

It is another object of the present invention to provide coated paper with good heat seal-ability and having good seal strength at relatively low sealing temperatures.

It is another object of the present invention to provide coated paper having good water barrier properties while still retaining the easy recyclability. Surprisingly it is found that addition of carnauba wax to a water based coating composition having paraffin wax and/or microcrystalline wax provides for a coated paper having good heat seal-ability at relativity low temperatures and with good seal strength. It was further found that the coated paper of the present invention provides high packaging speed on automatic ice-cream cone wrapping machines at low sealing temperature of 60 to 80°C. It was also found that paper coated with the water based coating of the present invention provides good water barrier properties and is recyclable.

Summary of the invention

According to a first aspect, disclosed is a coated paper having a paper substrate having a first surface and a second surface with atleast one surface coated with a water-based coating composition comprising, on dry weight basis of the coating composition: a 30 to 90% acrylic polymer or acrylic copolymers;

b 5 to 30% of wax selected from paraffin wax, microcrystalline wax, or a blend thereof;

c 2 to 20% ground up mica; and,

d 1 to 10% alkaline agent;

wherein the water-based coating composition includes a further 2 to 5% of carnauba wax on dry weight basis of the coating composition.

According to a second aspect, disclosed is a method of manufacturing a coated paper according to the first aspect including the steps of:

i. applying atleast to one surface of a paper substrate atleast one layer of a water-based coating comprising, on dry weight basis the water-based coating composition comprising:

a. 30 to 90% acrylic polymer or acrylic copolymers;

b. 5 to 30% wax selected from paraffin wax or microcrystalline wax or a blend thereof;

2 to 20% ground up mica; and,

1 to 10% alkaline agent;

wherein the water-based coating composition comprises a further 2 to 5% of carnauba wax on dry weight basis of the coating composition,

drying the coated paper. According to a third aspect, disclosed is a use for the coated paper as provided in first aspect for wrapping of food product.

According to a fourth aspect, the present invention provides a use for coated paper as provided in first aspect for wrapping of ice-cream cones. These and other aspects, features and advantages will become apparent to those of ordinary skill in the art from a reading of the following detailed description and the appended claims. For the avoidance of doubt, any feature of one aspect of the present invention may be utilised in any other aspect of the invention. The word "comprising" is intended to mean "including" but not necessarily "consisting of" or "composed of." In other words, the listed steps or options need not be exhaustive. It is noted that the examples given in the description below are intended to clarify the invention and are not intended to limit the invention to those examples per se. Similarly, all percentages are weight/weight percentages unless otherwise indicated.

Except in the operating and comparative examples, or where otherwise explicitly indicated, all numbers in this description indicating amounts of material or conditions of reaction, physical properties of materials and/or use are to be understood as modified by the word "about". Numerical ranges expressed in the format "from x to y" are understood to include x and y. When for a specific feature multiple preferred ranges are described in the format "from x to y", it is understood that all ranges combining the different endpoints are also contemplated.

Detailed description of the invention

The present invention provides for a coated paper which includes a paper substrate coated with a water based coating on atleast one surface and preferably a clay coating on the other surface.

Paper substrate

Any paper or paperboard may be used for subsequent coating. Any type of fibre based material may be coated, example include bleached or unbleached, hardwood or softwood, virgin or recycled, uncoated forms of paper or paperboard. Preferably the paper substrate has a basis weight in the range of 20 to 200 grams per square meter, more preferably in the range of 50 to 200 grams per square meter, still more preferably in the range 60 to 150 grams per square meter, further preferably in the range of 70 to 100 grams per square meter, and optimal paper substrate has a basis weight in the range of 80 to 100 grams per square meter.

Coating

Atleast one surface of the paper substrate is coated with a water-based coating composition. Alternatively, one surface of the paper is coated with the water-based coating composition according to the invention, while the second surface of the paper substrate may be coated with a clay coating.

Water-based coating composition

Water based coating composition includes acrylic polymer, wax, ground up mica, alkaline agent and carnauba wax.

Acrylic polymer: The water based coating composition includes 30 to 90 % on dry weight basis of an acrylic polymer or acrylic copolymer. Preferred compositions include 50 to 80 % on dry weight basis of the acrylic polymer or acrylic copolymer. More preferred compositions include acrylic polymer includes 60 to 70 % on dry weight basis of the acrylic polymer or acrylic copolymer. Preferably the acrylic polymer is from a monomer selected from a group of ethyl acrylate, methyl acrylate, butyl acrylate and butyl methacrylate.

Preferably the molecular weight of acrylic polymer is 3600 to 4500 more preferably 3800 to 4300 and still more preferably 3900 to 4200.

Wax: The water based coating composition includes 5 to 30% of wax on dry weight basis of the coating composition. Preferred compositions include 10 to 30% of wax on dry weight basis of the coating composition, more preferred compositions includes 15 to 25% of wax on dry weight basis of the coating composition.

The wax is a paraffin wax or microcrystalline wax or a blend thereof.

As known in the art microcrystalline waxes are a type of wax produced by de-oiling petrolatum, as part of the petroleum refining process. In contrast to the more familiar paraffin wax which contains mostly unbranched alkanes, microcrystalline wax contains a higher percentage of isoparaffinic (branched) hydrocarbons and naphthenic hydrocarbons. Microcrystalline wax is characterized by the fineness of its crystals in contrast to the larger crystal of paraffin wax and consists of high molecular weight saturated aliphatic hydrocarbons. Microcrystalline wax is generally darker, more viscous, denser, tackier and more elastic than paraffin waxes, and has a higher molecular weight and melting point. The elastic and adhesive characteristics of microcrystalline waxes are related to the non-straight chain components which they contain. Typical microcrystalline wax crystal structure is small and thin, making them more flexible than paraffin wax.

It is preferred to have a blend of microcrystalline wax and paraffin wax to enable the right balance in the above mentioned characteristics. A paraffin to microcrystalline wax ratio of between 1 :10 and 10:1 is preferred, more preferably between 1 :5 and 5:1 .

Ground up mica: The water based coating composition includes 2 to 20% on dry weight basis of ground up mica. Preferred compositions include 5 to 15% on dry weight basis of ground up mica. More preferred compositions include 8 to 10% on dry weight basis of ground up mica.

Alkaline agent: The water based coating composition includes 1 to 10% on dry weight basis of alkaline agent. Preferred compositions include 5 to 10% on dry weight basis of alkaline agent. Further preferred compositions include 8 to 10% on dry weight basis of alkaline agent. The alkaline agent is preferably a hydroxide salt, ammonium hydroxide is the most preferred alkaline agent.

Carnauba wax: Carnauba wax (also called Brazil wax and palm wax), is a wax obtained from the leaves of the carnauba palm by collecting them, beating them to loosen the wax, then refining and bleaching the wax.

Carnauba wax consists mostly of aliphatic esters (40 wt%), diesters of 4- hydroxycinnamic acid (21 .0 wt%), ω-hydroxycarboxylic acids (13.0 wt%), and fatty acid alcohols (12 wt%). The compounds are predominantly derived from acids and alcohols in the C₂6-C₃o range. Distinctive for carnauba wax is the high content of diesters as well as methoxycinnamic acid.

The water based coating composition includes 2 to 5% on dry weight basis carnauba wax. Preferred compositions include 2.5 to 5% on dry weight basis carnauba wax. More preferred compositions include 3 to 5% on dry weight basis carnauba wax.

Clay coating

Preferably a clay based coating (hereinafter clay coating) is coated on a second surface of the paper substrate.

Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations. Clays have structures similar to the micas and therefore form flat hexagonal sheets.

Clay minerals are very common in fine grained sedimentary rocks such

as shale, mudstone, and siltstone and in fine grained metamorphic slate and phyllite. A typical structure would be AI₂Si20₅(OI-l)4. Preferably the clay coating includes calcium carbonate or titanium dioxide. It is preferred that the coating composition is a water based slurry when applied on the paper with a water content of 50-70 % at the time of application.

Metallic ink coating Preferably a metallic ink coating is coated on a second surface of the paper substrate onto the clay coating.

Metallic ink coating composition includes a pigment, binder and a solvent. The pigment is preferably aluminium particles having a particle size (D50) from 1 1.5 micrometer to 12.5 micrometer. Preferably the metallic ink composition has 6% to 8% of the pigment.

Metallic ink composition preferably includes a solvent selected from alcohol, ester and methoxy propanol. The binder is preferably selected from ethylcellulose or

polyvinylbutyral.

Metallic ink layer preferably includes aluminium and a binder. Method of manufacturing a coated paper

According to a second aspect disclosed is a method of manufacturing a coated paper including the steps of applying atleast one layer of the water based coating composition and then drying the coated paper.

Applying the water based coating composition onto the paper substrate may be by any method of coating suitable for water based coating.

Examples of suitable coating methods include conventional methods such as air knife coating, blade coating, metering roll coating, gravure coating, rod coating, curtain coating, spraying. Drying after applying the water based coating is by any suitable drying method including hot air drying, infrared drying, direct flame drying and drying by contact with a heated drum.

Preferably a clay coated paper substrate of 90 grams per square meter thickness is coated with 4 to 5 grams per square meter of the water based coating composition. Paper substrate with the water based coating composition is then dried. The clay coated surface of the paper substrate is preferably coated with a metallic ink coating of 1 gram per square meter thickness.

Package and use of the coated paper According to a third aspect, the invention provides use of a coated paper of the first aspect for wrapping a food product. Preferred types of food products include ice-cream cones, fat, frozen products, confectionery and other products with low melting points. The wrapping and sealing may be carried in automatic machines. Such machines and the process to form wrappers are well known in the art.

Preferably the sealing is by conventional heat sealing methods such as heat sealing bars. The sealing temperature is preferably 60 to 90°C more preferably from 60 to 80°C still more preferably 70 to 80 °C and further preferably from 75 to 80 °C.

EXAMPLES

The invention will now be explained in details with the help of non-limiting examples

Evaluation of seal strength of coated paper used as sleeve for wrapping ice-cream cone:

Comparative Example A: A commercially available bleached kraft paper with a basis weight of 90 g/m² was taken. Water based coating, VaporCoat® 2200 E (Michelman Inc.) of 4 g/m² was applied on one surface of kraft paper using direct gravure printing and then dried using hot air oven set at a temperature of 70 to 90°C. A clay coating of calcium carbonate was then applied on the second surface. A layer of metallic ink, RotoStar UL-1016 from Eckart GmBH was applied over the dried clay coating. The coated paper was cut into a blank and rolled into a sleeve and wrapped around an ice cream cone in an automatic wrapping machine and sealed at different temperature, pressure and dwell time. The results of the seal quality are given in Table 1 .

Example 1 : A commercially available bleached kraft paper with a basis weight of 90 g/m² was taken. Water based coating composition prepared according to the present invention was made by mixing 1 kg of VaporCoat®2200 (Michelman Inc), a water based acrylic- wax emulsion and 0.05 kg of Michem®Lube160 (Michelman Inc). The kraft paper was then coated with 4 -5 g/m² of the coating composition on one of its surface using direct gravure printing and then dried using hot air oven set at 70-90°C. A clay coating of calcium carbonate was then applied on the second surface. A layer of metallic ink, RotoStar UL-1016 from Eckart GmBH was applied over the clay coating.

The coated paper was cut into a blank and rolled to a sleeve and wrapped around an ice cream cone in an automatic wrapping machine and sealed at different temperature, pressure and dwell time. The results of the seal quality are given in Table 1.

Table 1

Example Sealing Dwell time Pressure Seal Quality Seal temperature (seconds) (Bar) Strength

(°C) (N)

Comparative 80 0.55 4 No seal

Example A

85 0.75 4 No seal

90 1 .00 4 No seal ^—

95 1 .00 4 Poor 1 .2

1 10 1 .00 4 Good 5.91

Example 1 80 0.5 4 Good 5.85

85 0.5 4 Good 5.90

90 0.5 4 Good 5.92

95 0.5 4 Very Good 5.93

1 10 0.5 4 Excellent 5.98 It is evident from Table 1 that coated paper according to the present invention provides better seal strength at lower temperature of sealing and lesser sealing time as compared to coated paper of comparative example A.

Although the invention has been described with reference to specific embodiments for use in wrapping ice-cream cones, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims

1 . A coated paper comprising a paper substrate having a first surface and a

second surface with atleast one surface coated with a water-based coating composition said composition comprising on dry weight basis:

a. 30 to 90% acrylic polymer or acrylic copolymers;

b. 5 to 30% wax selected from paraffin wax, microcrystalline wax, or a blend thereof;

c. 2 to 20% ground up mica;

d. 1 to 20% alkaline agent; and,

wherein the water-based coating composition comprises a further 2 to 5% of carnauba wax on dry weight basis.

2. A coated paper as claimed in claim 1 wherein the alkaline agent is preferably ammonium hydroxide.

3. A coated paper as claimed in any one of the preceding claims wherein the paper substrate has a basis weight in the range of 50 to 200 grams per square meter.

4. A coated paper as claimed in Claim 1 wherein the second surface of the paper substrate is coated with a clay coating.

5. A coated paper as claimed in Claim 4 wherein the clay coating comprises of calcium carbonate or titanium dioxide.

6. A coated paper as claimed in Claim 4 or 5 wherein the clay coated second surface is imprinted with a metallic ink.

7. A coated paper as claimed in claim 6 wherein the metallic ink comprises aluminium powder and binder.

8. A coated paper as claimed in Claim 7 wherein the binder is selected from

ethylcellulose or polyvinylbutyral.

9. A coated paper as claimed in any one of the preceding claims wherein the coated surface may be sealed at a sealing temperature of 60 to 80°C.

10. A method of manufacturing a coated paper as claimed in claim 1 comprising the steps of:

a. applying atleast to one surface of a paper substrate atleast one layer of a water-based coating comprising, on dry weight basis of the coating composition:

i. 30 to 90% acrylic polymer or acrylic copolymers; ii. 5 to 30% wax selected from paraffin wax, microcrystalline wax, or a blend thereof;

iii. 2 to 20% ground up mica;

iv. 1 to 20% alkaline agent; and,

wherein the water-based coating comprises a further 2 to 5% of carnauba wax on dry weight basis.

b. drying the coated paper.

1 1 . Use of coated paper as claimed in claim 1 for wrapping of food product.

12. Use of coated paper as claimed in any of the preceding claims for wrapping of ice-cream cones.