CN1510214A - Method for producing coated paper or paperboard - Google Patents

Abstract

The present invention relates to a method for producing a coated paper or paperboard other than a photosensitive paper, comprising the steps of: forming a free-flowing curtain comprising at least one layer, wherein the composition forming the at least one free-flowing curtain layer has a high shear viscosity of at least 50 mPa-s, and (b) contacting the curtain with a continuous base substrate of base paper and paperboard.

Description

Process for producing coated paper or paperboard

technical field

The present invention relates to a method of producing coated paper or board. In addition, the present invention also relates to a method of applying a coating composition having a high viscosity to a substrate under high shear conditions.

Background technique

Pigmented coating compositions having a considerably higher solids content and viscosity than photosensitive solutions or emulsions are usually used in the manufacture of printing paper, for example by knife coating, rod (rod) or counter coating at high line speeds above 1000 m/min. Roll (film) coating method for coating. Either or all of these methods typically involve the continuous application of a pigmented coating to the surface of a moving paper or paperboard.

However, virtually every method used above suffers from a series of problems that lead to poor quality of the coated surface. In the case of knife coating methods, the settling of particles under the blades can lead to streaks in the coating, which will reduce the quality of the coated paper or board. Additionally, the high pressure on the blade to achieve the required coat weight creates a very high stress on the substrate and can lead to breakage of the substrate, thereby reducing production efficiency. Also, due to the highly abrasive nature of the pigmented paint, the scraper blades must be changed frequently in order to keep the coating surface flat. Likewise, unevenness of the substrate surface can affect the distribution of the coating on the surface of the paper or paperboard substrate. Uneven distribution of the coating on the surface of the paper or board can cause spots or mottling on the surface, resulting in poor print quality.

Rod (rod) coating methods are limited by the solids content and viscosity of the pigmented coating pigment being applied. The solids content and viscosity of pigmented coatings suitable for rod coating methods are generally lower than those used for blade coating methods. Therefore, it is not possible to vary the amount of coating that can be applied to the surface of a paper or paperboard substrate at random for the rod coating method. When the parameters of solids content, viscosity, and coat weight of the coating are not balanced, the surface quality of the coated paper or board is undesirably degraded. Also, to keep the painted surface even, the rods abraded by the coloring paint need to be replaced periodically.

The roll-coat (film) coating method is a particularly complex method of applying pigmented coatings to paper or board, due to the fact that for each operating speed and each required coat weight, the Process conditions for substrate surface characteristics, substrate porosity, coating solids content, and coating viscosity are narrow. An imbalance between these variables can result in an uneven film crack pattern on the surface of the coated paper, resulting in poor print results, or small droplets of coating that can be released as the web leaves the coating nip. These droplets, if redeposited on the sheet surface, can lead to poor print results. Furthermore, the maximum amount of coating that can be applied to a paper or board surface in one process using a roll coating method is generally lower than that applied using a knife or rod coating method. This coating weight limitation is very noticeable when coating at high speeds.

The common feature of all the above methods is that the surface of the paper base usually has irregular hills and valleys, and the amount of coating liquid to coat the paper base depends on whether it coats hills or valleys. Thus, the thickness of the coating, and its associated ink holding properties, will vary with the surface of the coated paper, resulting in non-uniformity of the printed image. Despite these disadvantages, these coating methods still dominate the paper industry because of their economical nature, especially at high line speeds.

A common feature of all the above-mentioned coating methods is that a coating composition with a high viscosity in the case of high shear and/or shear thickening behavior cannot be used to coat a substrate because such a coating composition would cause inability to Acceptable coating defects, such as streaking in the coating or failure to achieve the desired coat weight. Furthermore, such coating compositions generally exhibit poor water retention and low cured solids content. Coatings with poor water retention generally cannot be applied using the coating methods described above without reducing the solids content of the coating and/or adding a water retaining agent. Coating at high coating solids close to cured solids is also required for drying efficiency. This means that coatings with low cured solids and low water retention are particularly difficult to apply by the aforementioned coating methods.

On the other hand, there is a tendency in the paper industry that the engineered pigments used usually have a narrow particle size distribution and shapes such as high aspect ratio, needle-like or other irregular shapes and internal porosity such as occurs with calcined clay . Engineering coatings referred to below as so-called co-structured coatings have also been developed. The term "co-structured pigment" is understood to mean that the pigment has been modified, e.g., by agglomerating specific particles with other specific particles; Properties such as opacity, gloss and printability. Moreover, this coating helps to improve the mechanical properties of the paper.

When more than 20% by weight of an engineering pigment is added to a coating composition, the composition typically has a high viscosity under high shear and/or shear thickening behavior. This is because the pigments cannot squeeze into an efficient compact structure at high shear rates. Similar extrusion effect volumes at high shear rates occur in conventional coating formulations as their solids content approaches the cure point. This phenomenon makes it difficult or even impossible to apply such coating compositions to paper or board using the aforementioned coating techniques. Typically, flow capability becomes an issue when shear rates are greater than 100,000 s ^-1 and viscosities are greater than 50 mPa·s. It is generally considered that the paint with a viscosity exceeding 75mPa·s is difficult to flow, and the paint with a viscosity exceeding 100mPa·s is very difficult to flow.

Furthermore, it is almost impossible for paints with shear thickening behavior to flow on the aforementioned equipment. Shear thickening behavior is a phenomenon in which viscosity increases with increasing shear rate. Both the shear rate at which shear thickening begins and the degree to which viscosity increases with increasing shear can vary widely. These two aspects of shear thickening behavior are important and are entirely dependent on the solids content of the coating. In the present invention, a shear-thickening coating formulation is defined as a formulation whose viscosity increases by at least 20% when the shear rate changes by more than one order of magnitude (10 times) when the shear rate exceeds 1000 s ^-1 .

For some coatings, the onset and extent of shear thickening behavior is a sudden jump and represents a severe form of shear thickening (thixotropic) behavior. In the present invention, this behavior is called shear retardation behavior, which is defined as the behavior of a coating whose viscosity increases by at least 100% when the shear rate is increased by less than one order of magnitude, the shear rate is measured by the parallel plate viscosity measured by measurement. The shear rate at which shear-blocking behavior is initiated can vary widely and is particularly dependent on the solids content of the coating as well as the coating factors and its particle size distribution.

Curtain coating is a relatively new coating technology. EP-A517223 and Japanese patent applications JP-94-89437, JP-93-311931, JP-93-177816, JP-93-131718, JP-92-298683, JP-92-51933, JP-91-298229, JP -90-217327 and JP-8-310110 disclose coating one or more colored paint layers on the surface of moving paper by curtain coating method. More specifically,

The existing technologies are:

(i) The curtain coating method is used to apply a single layer of pigmented coating on a raw paper substrate to produce a single layer of pigmented coating on the paper.

(ii) A base coat of pigmented paint is applied to the base paper substrate by curtain coating prior to the application of a single layer of pigmented top coat by knife coating. Therefore, multi-layer colored coated paper can be produced by continuously performing colored coating.

(iii) The curtain coating method is used to apply a pigmented top layer to a raw paper substrate which has initially been precoated with a single layer of pigmented coating by a knife coating method or a metered roll coating method. Therefore, multi-layer colored coated paper can be produced by continuously performing colored coating.

(iv) The curtain coating method is used to apply two single layers of specially colored coatings on a base paper substrate such that these single coatings are applied in a continuous coating process. Therefore, multi-layer colored coated paper can be produced by continuously performing colored coating.

As disclosed in the prior art discussed above, the use of curtain coating methods in which a single layer of pigmented coating is applied to the surface of a moving paper can produce a higher quality coated paper surface than using conventional coating methods. However, continuous application of single layers of pigmented coatings using curtain coating technology is limited by kinetic factors in the curtain coating process. Especially for light-weight coatings, it can only be used at coating speeds lower than those used in the traditional coating processes currently used, because at high coating speeds this coating curtain (curtain) becomes unstable to form a poorly coated surface. Unfortunately, regardless of any of the coating methods described above, due to the number of coating positions required and the number of auxiliary hardware required such as drive units, drying equipment, etc. and the space to place these machines, etc. The continuous application of single layers of pigmented coatings to paper or board remains a capital intensive manufacturing process.

The coating layer contains additives designed to impart functional properties such as release, printability, adhesion, release, and optical properties such as color and brightness to coated paper and paperboard. , opacity, gloss, etc., and their coatings are called functional coatings. Coating ingredients that bring these properties are also known as functional additives. Functional products include paper types such as self-adhesive papers, stamp papers, wallpaper, silicone release papers, food wrapping papers, greaseproof papers, moisture-proof papers, and saturated liners.

Curtain coating methods for simultaneous coating of multiple layers are well known and described in patents US3508947 and 3632374 for applying photosensitive compositions on paper and plastic webs. However, photosensitive solutions and emulsions have low viscosity and low solids content and can only be coated at low coating speeds.

In addition to photosensitive material coating applications, simultaneous multilayer coating by curtain coating methods is known in the field of pressure-sensitive copy paper production. For example, U.S. Patent No. 4,230,743 discloses that in one embodiment, a bottom layer and a second layer are simultaneously coated on a moving substrate, wherein the bottom layer contains microcapsules as a major component, and the second layer contains a color developing agent. However, such papers are reported to have the same properties as those obtained by continuous coating. In addition, this coating composition containing a color developer has a viscosity of 10-20 cps at 22°C.

JP-A-10-328613 discloses the simultaneous coating of two coatings on a paper base by a curtain coating method to produce inkjet paper. According to the teaching of this reference, the coating composition used was an aqueous solution with a very low solids content of 8% by weight. In addition, thickeners need to be added in order to obtain non-Newtonian properties of coating solutions. The examples described in JP-A-10-328613 demonstrate that the coating quality is acceptable only when the line speed does not exceed 400 m/min. Low operating speeds in coating processes are not suitable for the economical production of printing paper, especially plain printing paper.

None of the above documents discloses the application of high viscosity coating compositions on substrates under high shear conditions using curtain coating techniques. The above documents also do not disclose the method of applying a coating composition with shear thickening behavior to a substrate by curtain coating technology.

Contents of the invention

The underlying technical problem solved by the present invention is to provide a method for the production of coated paper and board in which a coating composition having a high viscosity under high shear is applied to said paper or board superior.

This technical problem is solved by a method for producing coated paper or paperboard excluding photosensitive paper, the method comprising the steps of: (a) forming a free flowing coating curtain comprising at least one layer, The composition wherein at least one free-flowing coating curtain layer is formed has a high shear viscosity of at least 50 mPa·s at a shear rate of 500,000 ^s , the high shear viscosity is defined by the capillary high shear viscosity described hereinafter Measurements Measure, and (b) contact the coating curtain with a continuous base paper and board substrate.

In another embodiment of the present invention, the method for producing coated paper or paperboard to solve said technical problem comprises the following steps: (a) forming a free-flowing coating curtain comprising at least one layer, wherein at least one The composition of the free-flowing coated curtain layer has a shear thickening coefficient of at least 1.2 at 25°C, and (b) the coated curtain is contacted with a continuous base paper and paperboard base substrate.

The shear thickening coefficient is determined by the ratio of the viscosity at a shear rate of 30,000s ^-1 to the viscosity at a shear rate of 3,000s ^-1 . These viscosity values are determined by parallel plate viscometry as described in detail below. If the viscosity at 30,000 s ^-1 is greater than the viscosity at 3,000 s ^-1 , then the value of the shear thickening coefficient at this time will be greater than the value of the shear thickening coefficient showing shear thickening behavior.

Surprisingly, successful coating of the coating curtain in step (a) on a substrate is possible when at least one layer comprises a composition having a shear thickening coefficient of at least 1.2. Preferably, the shear thickening coefficient is at least 1.3, more preferably at least 1.4, most preferably at least 1.5.

In another embodiment of the present invention, the method for producing coated paper or paperboard to solve said technical problem comprises the following steps: (a) forming a free-flowing coating curtain comprising at least one layer, wherein at least one The composition of the free-flowing coated curtain layer exhibits shear retardation behavior at 25°C, and (b) contacting the coated curtain with a continuous base paper and paperboard base substrate.

The presence of shear retardation behavior was confirmed by observing a viscosity increase of greater than 100% at a shear rate increase of less than 10-fold. The viscosity is measured by parallel plate viscometry as described in detail below. In a preferred embodiment, the free-flowing coating curtain in step (a) is a multilayer free-flowing coating curtain. According to the invention, the free-flowing coating curtain is preferably applied by a curtain coating apparatus equipped with sliding nozzles for delivering multiple liquid layers to form a continuous multilayer coating curtain. Alternatively, an extrusion-type feedblock, such as a slot die or nozzle having several adjacent extrusion nozzles, may be used in the practice of the invention.

It is preferred that at least one free-flowing coating curtain layer ⁱⁿ step (a) has a high shear viscosity of at least 75 mPa·s, preferably at least 100 mPa·s, most preferably at least 125mPa·s.

In a preferred embodiment, the coated paper or paperboard is not pressure sensitive copy paper. As used herein, the term "paper" also includes paperboard, unless such an interpretation cannot be clearly determined in the context in which the term is used. The term "excluding photosensitive paper" is understood to mean that all layers of the coating curtain used in the practice of the invention are free of silver-containing compounds. The term "excluding pressure-sensitive copying paper" is understood to mean that the combination of microencapsulated coupler and color developer is not included in a single layer or in different layers of the coating curtain used in the practice of the present invention.

The multilayer free-flowing coating curtain of the present invention has a bottom or interface layer, a top layer and optionally one or more inner layers. A free-fall coating curtain according to the teachings of the present invention may comprise other layers in addition to at least one layer having specific rheological properties. Conventional paint formulations used in industry as paint colorants can be used in the coating curtain. Each layer may comprise a liquid, emulsion, suspension, dispersion, solution, or combinations thereof. The coating coating curtain of the present invention comprises at least one layer, desirably at least two layers, at least three layers, at least four layers, at least five layers, or at least six or more layers. A coating curtain layer may include one or more paint layers, one or more functional layers, and/or one or more print layers.

The at least one free-flowing coating curtain layer in the present invention preferably includes at least one pigment. Examples of suitable pigments include clay, kaolin, calcined clay, co-structured pigments, talc, calcium carbonate, titanium dioxide, satin white, synthetic polymer pigments, zinc oxide, barium sulfate, gypsum, silica, synthetic magadisil Sodium stone (magadiite), alumina trihydrate, mica and diatomaceous earth. These pigments can be obtained naturally, synthesized, or processed. When these pigments are used in coating compositions, they exhibit improved paper properties, such as better opacity, improved gloss and/or better printability. These pigments can also be used in combination. These pigments can have different shapes, including blocks, dendrites, plates, needles, spheres, etc. as known in the art. An advantage of the present invention is its surprising ability to use pigments of any shape, including needle-like pigments which are difficult to use in knife-coating methods.

Unexpectedly, engineering pigments formulated in coating compositions having a high shear viscosity of at least 50 mPa·s at a shear rate of 500,000 s ^-1 can be readily applied to substrates using the process of the present invention.

The shape and structure of some pigments, such as co-structured pigments, can be destroyed at high shear rates, thereby adversely affecting the properties of these pigments. As a component of at least one free-flowing coating curtain layer, the shape and structure of these pigments are destroyed at a shear rate below 500,000 s ^-1 . Unexpectedly, the method of the present invention can include at least one such pigment. A composition of pigments is coated on a substrate. In a preferred embodiment, the shear rate that adversely affects the shape and structure of the pigment is less than 100,000 s ^-1 , more preferably less than 50,000 s ^-1 , most preferably at least 10,000 s ^-1 .

In another embodiment, at least one free-flowing coating curtain layer in step (a) includes at least one pigment having an aspect ratio of at least 1.5:1. Preferably, such pigments have an aspect ratio of at least 5:1, more preferably at least 10:1, even more preferably at least 15:1, and most preferably at least 20:1. In another preferred embodiment, the pigment has an aspect ratio of at least 30:1, more preferably at least 40:1, and most preferably at least 60:1.

Preferably, at least one free-flowing coating curtain layer of the present invention includes an adhesive. The adhesive can be any adhesive known to those skilled in the art. Examples of these binders include: styrene-butadiene latex, styrene-acrylate latex, styrene-butadiene-acrylonitrile latex, styrene-acrylate-acrylonitrile latex, styrene-butadiene - Acrylate-acrylonitrile latex, styrene-maleic anhydride latex, styrene-acrylate-maleic anhydride latex, polysaccharides, proteins, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate and cellulose derivatives. A wide variety of adhesives are commercially available.

The coating curtain of the invention comprises one or more functional layers. The purpose of the functional layer is to impart the desired functionality to the coated paper. For example, optional functional layers can provide printability, barrier properties such as moisture resistance, fragrance resistance, water resistance and/or water vapor resistance, solvent resistance, oil resistance, grease resistance and oxidation resistance properties, sheet stiffness, resistance to tearing, paper set properties, anti-adhesion, adhesion, and optical properties such as color, brightness, opacity, gloss, etc. Tacky functional coatings often cannot be applied by traditional continuous coating methods due to the tendency of the coating's tack to stick to the substrate on guide rolls or other coating equipment. In another aspect, simultaneous multilayer coating methods can apply the functional coating under the top coat to prevent the functional coating from contacting the coating machine.

The solids content of the functional layer can vary widely depending on the desired function. One functional layer of the present invention preferably has a solids content of up to 75% by weight, based on the total weight of the functional layer, and a viscosity of up to 3,000 cps (Brookfield viscosity at 5,100 rpm, 25° C.), more preferably 50-2,000 cps. Preferably the coating weight of the functional layer is from 0.1 to 10 g/m ² . More preferably, it is 0.5-3 g/m ² . In some cases, such as when a dye layer is used, the coat weight of the functional layer may be less than 0.1 g/m ² .

The functional layer of the present invention may comprise one or more materials such as: ethylene acrylic polymers; polyethylene; other polyolefins; polyurethanes; epoxy resins; polyesters; vinyl latex; styrene acrylate latex; carboxylated latex; starch; protein; etc.; adhesives such as starch, styrene-acrylic acid copolymer, styrene-maleic anhydride, polyvinyl alcohol, polyvinyl acetate, carboxymethyl fiber factor, etc.; anti-seepage agent (barrier) such as ethylene vinyl alcohol (ethylene vinyl alcohol), siloxane, or wax, etc. The functional layer may contain, but is not limited to, pigments or anti-bleeding agents, such as those previously described for each coating. .

In the present invention, the layer furthest from the base paper in the multilayer coating curtain is called the top layer. In a preferred embodiment, the free-flowing coating curtain in step (a) includes a top layer to ensure printability, since this layer is usually the one that will be printed. The coated paper of the present invention may also be further coated in a conventional manner, such as rod, doctor blade, roll, rod, or air knife coating techniques and the like. The top layer can be a paint layer or a functional layer, including a gloss layer. In a preferred embodiment of the invention, the top layer is very thin, with a coat weight of eg 0.5-3 g/m ² . This advantageously allows the use of less expensive materials under the top layer, but still produces paper with good printing properties. In one embodiment, the top layer is free of mineral pigments.

According to a particularly preferred embodiment, the top layer comprises a polish formulation. The new combination of polish formulation and simultaneous multilayer curtain coating combines the advantages of curtain coating with good gloss.

The formulations of the polishes used in the present invention include gloss additives such as synthetic polymer pigments including hollow polymer pigments obtained by polymerizing monomers such as styrene, acrylonitrile and/or acrylic. Suitable synthetic polymeric pigments have a glass transition temperature of 40-200°C, more preferably 50-130°C, and a particle size of 0.02-10 μm, more preferably 0.05-2 μm. The polish formulation contains 5-100% by weight gloss additive, more preferably 60-100% by weight, on a solids basis. Another polish formulation includes varnishes such as those based on epoxy acrylates, polyesters, polyester acrylates, polyurethanes, polyether acrylates, oleoresins, nitrocellulose, polyamides, vinyl copolymers and those of polyacrylate in various forms.

If the coating curtain has at least 3 layers, it has at least one intermediate layer. The viscosity of the intermediate layer is not critical so long as the coating curtain remains stable. When more than one intermediate layer is present, the functional layer and the paint layer can be used in combination. For example, these intermediate layers may comprise a combination of the same or different functional layers, a combination of the same or different paint layers, or a combination of paint layers and functional layers.

The interface layer is the layer that is in contact with the substrate to be coated. An important function of the interfacial layer is to facilitate the wetting of the substrate. An interface layer can have more than one function. For example, it can coat a substrate in addition to wetting, as well as improve properties such as adhesion, hold, stiffness, or a combination of these properties. In the multilayer coating curtains of the present invention, the interface layer is preferably a relatively thin coating. The suitable coating weight of the interface layer is 0.1-5 g/m ² , preferably 1-3 g/m ² . The interface layer suitably has a solids content of 0.1-65% by weight of the interface layer in the coating curtain. In a specific embodiment, the solid content of the interface layer is relatively low, preferably 0.1-40%.

The solids content of the coating curtain in step (a) ranges from 10 to 80% by weight, preferably from 20 to 75% by weight, based on the total weight of the coating curtain. Furthermore, it is preferred that the free-flowing coating curtain in step (a) has a solids content of at least 30% by weight, preferably at least 40% by weight, more preferably at least 50% by weight, even more preferably at least 55% by weight, and most preferably at least 60% by weight .

According to a preferred embodiment, at least one layer forming the composite free-fall coating curtain has a solids content higher than 60% by weight of the total weight of the coating layer. In another embodiment of the present invention, at least one free-flowing coating curtain in step (a) has a solids content of at least 30% by weight, preferably at least 40% by weight, and most preferably at least 50% by weight.

In contrast to the technology of photosensitive paper and pressure sensitive copy paper, the method of the present invention can be operated with coating curtain layers having a wide range of viscosities and high solids content even at high coating speeds.

The method of the present invention advantageously allows modification of the composition and relative thickness of the individual layers in a multilayer composite structure. The multilayer components can be the same or different depending on the grade of paper being produced. For example, a thin layer close to the base paper designed for adhesion, a thick inner layer designed to provide sheet bulk, and a very thin top layer designed for optimal printability can be combined in a multilayer In coating curtains, the purpose is to provide a composite structure. In another embodiment, a specially designed inner layer for enhanced concealment may be used. Other embodiments of variable coat weight layers in a multilayer composite include a thin layer of less than 2 g/ ^m2 as at least one of the top, inner or bottom layers of the composite coating. With the method of the present invention, paper can be coated on one or both sides.

In a preferred embodiment, at least one free-flowing coating curtain layer in step (a) suitably comprises additives known to those skilled in the art, such as at least one surfactant, at least one dispersant, At least one lubricant, at least one water-retaining agent, at least one crosslinking agent, at least one optical brightener, at least one pigment, dye or colorant, at least one thickener, at least one defoamer , at least one antifoam agent, at least one antimicrobial agent and/or soluble dyes or colorants, and the like. Polyethylene oxide is one of the preferred additives and can be applied to any layer. In a preferred embodiment, polyethylene oxide is used as a thickener, preferably at least in the interface layer. Advantageously, the polyethylene oxide has a weight average molecular weight of at least 50,000, preferably at least 100,000, more preferably at least 500,000, most preferably at least 800,000. Preferably the polyethylene oxide is used in an amount sufficient to prevent cavitation, preferably less than 2% by weight, based on the weight of solids used in the layer.

In another embodiment, the at least one free-flowing coating curtain layer in step (a) has a coat weight dry weight of less than 10 g/m ² , preferably less than 8 g/m ² , most preferably less than 6 g/m ² .

In one embodiment of the invention, the continuous substrate in step (b) is neither pre-coated nor pre-calendered. In another embodiment, the base substrate is not precoated. In yet another embodiment, the base substrate is not pre-calendered. Preferably, the continuous web substrate in step (b) has a web speed of at least 300 m/min, even more preferably at least 400 m/min, most preferably at least 500 m/min. In another embodiment, the continuous web substrate has a speed of at least 800 m/min, preferably at least 1000 m/min.

The suitable grammage per square meter, or basis weight, of the continuous base material base is 20-350 g/m ² .

Description of drawings

FIG. 1 is a cross-sectional view showing a curtain coating apparatus 1 with a sliding nozzle arrangement 2 preferably for conveying multiple streams 3 of coating curtain layers to form a continuous multilayer coating curtain 4 . When a dynamic balance is reached, the flow rate of the coating curtain layer flowing into the sliding nozzle device 2 is completely balanced with the flow rate flowing out of the sliding nozzle device. The free-falling multilayer coating curtain 4 is in contact with the continuously running web 5 so that the web 5 is multilayered with the corresponding coating curtain layers. The web 5 changes direction of movement immediately before the coating zone by a roller 6 to minimize the effect of the air movement accompanying the fast moving web 5 .

Detailed ways

The invention is illustrated by the following examples. All parts and percentages are by weight unless otherwise indicated.

Example

formula

The following materials were used in the paint fluid:

Carbonate (A): 90% aqueous dispersion of calcium carbonate (HYDROCARB 90 ME from Plauess-Srauffer) with a particle size of less than 2 microns, 77% solids.

Carbonate (B): 60% aqueous dispersion of calcium carbonate (HYDROCARB 60 ME from Plauess-Srauffer) with a particle size of less than 2 microns, 77% solids.

• Carbonate (C): An aqueous dispersion of engineered calcium carbonate with a narrow particle size distribution and 75% of the particle size is less than 2 microns, (CARVERCARB 75 from Plauess-Srauffer), 72% solids.

· Carbonate (D): 36% calcium carbonate (MILLING CARB OG from Plauess-Srauffer) with a particle size of less than 2 microns, in powder form.

· Clay (A): water dispersion of calcined clay (ANSILEX 93, calcined kaolin fine particles, particle size distribution 86-90% of the particle size is less than 2 microns, average particle size of 0.8 microns, solid content 50%, from Engelhard Corporation, Iselin NJ).

· Clay (B): High aspect ratio clay dispersion in water (KSZ 81 from AKW-Kick, Hirschau Germany) with a solids content of 59.8% and an aspect ratio of 55-60:1.

· Clay (C): No. 1 high-brightness kaolin aqueous dispersion (HYDRAGLOSS 90 from J.M Huber Corp., Have de Grace, Maryland, USA) with a particle size of 98% less than 2 microns, solid content 71%.

• Latex: Carboxylated styrene-butadiene latex (DL 966 from Dow Chemical Company), 50% solids in water.

• Polyvinyl alcohol: 15% solution of low molecular weight synthetic polyvinyl alcohol (MOWIOL 6/98 from Clariant AG, Basel, Switzerland).

Thickener (A): acrylamide-acrylic acid copolymer anionic water-in-oil emulsion (STEROCOL BL, from BASF, Ludwigshafen, Germany), solid content 37%.

Thickener (B): 900,000 molecular weight non-ionic high molecular weight water-soluble polyethylene oxide polymer (POLYOX WSR-1105 from Dow Chemical Company), prepared as a 4% solids solution.

· Surfactant: Aqueous solution of sodium dialkylsulfosuccinate (AEROSOL OT from Cyanamid, Wayne, NJ, USA), 75% solids.

Brightener: Optical brightener derived from diamino-1,2-stilbene-disulfonic acid (TINOPAL ABP/Z from Ciba Specialty Chemicals Inc., Basel, Switzerland).

The pH of the pigmented paint formulation was adjusted by adding NaOH solution (10%). Water can be added to adjust the solids content of the formulation, if desired.

coating process

The formulations detailed below were coated on paper according to the following process. The equipment used was a multilayer slide die curtain coater manufactured by Troller Schweizer Engineering (TSE, Murgenthal, Switzerland). The curtain coater is equipped with edge guides lubricated by a trickle of water and a vacuum suction device to remove the edge lubricating water from the bottom of the edge guides above the edge of the coated paper. In addition, the curtain coater is equipped with vacuum suction equipment to remove interface surface air from the paper material upstream from the impingement zone of the coating curtain. The height of the coating curtain was 300 mm. Coating formulations are degassed prior to use to remove air bubbles. In each coating test, the coat weight obtained was based on the known volumetric flow rate of the pump delivering the coating to the curtain coater head, the speed at which the continuous paper web moved under the curtain coater head, the coat weight The density and percent solids of the curtain and the width of the coated curtain are calculated.

A comparative knife coating test was carried out using a conventional knife coater. Blade pressure is controlled by adjusting the head angle to a maximum of 24 degrees.

Test Methods

Brookfield viscosity

Viscosity was measured using a Brookfield RVT viscometer (from Brookfield Engineering Laboratories, Inc., Stoughton, MA, USA). In order to measure the viscosity, inject 600ml of the sample into a 1000ml beaker at 25°C and 100rpm

Measure the viscosity.

Parallel Plate Viscosity Test

Said viscosity is measured using a Physica UDS200 viscometer (ex Paar Physica). The samples were tested at 25° C. using a parallel plate with a diameter of 50 mm and a measuring gap of 0.03 mm. Within two minutes, the shear rate was jumped from 10 s ⁻¹ to 100,000 s ⁻¹ using 10 steps of shear rate / logarithmic step of shear rate. The viscosities at shear rates of 3000 s ^-1 and 30,000 s ^-1 were determined by interpolation of the measured values. The shear-thickening coefficient is obtained by dividing the viscosity at a shear rate of 30,000 s ^-1 by the viscosity at a shear rate of 3000 s ^-1 . A shear-thickening coefficient value greater than 1 indicates shear-thickening behavior. A coating is considered to have shear retarding behavior if the flow curve of viscosity versus shear rate exhibits a sharp rise in viscosity (greater than 100% increase in viscosity and less than 10 times increase in shear rate).

Capillary High Shear Viscosity

High shear viscosity was measured with an ACAV II capillary viscometer (from ACA Systems, Finland). A sample of approximately 1000 cc is placed in a graduated cylinder and the measurement temperature is 25°C. A glass capillary with a diameter of 0.5 mm and a length of 50 mm was used in the measurement. Using a capillary with a length/diameter ratio of 100 minimizes the effect of tip impact on the measurement. The viscosity of the samples was measured using the 12 logarithmic scale of the shear rate, ranging from 100,000 s ⁻¹ to 1,500,000 s ⁻¹ . The measurement is terminated if the maximum measurement pressure (300 bar) is reached before the shear rate reaches 1,500,000 s ^-1 . Viscosity was calculated from the measured pressure versus flow rate curve. ACAV II software corrected kinetic energy data. The viscosity at a shear rate of 5000,000 s ^-1 was determined by interpolation of experimental data.

water retention

The water retention of paint colorants is measured by AA-GWR gravimetric water retention meter (from OY Gradek, Ab Kauinianen, Finland). The test cell was placed on a non-hygroscopic polycarbonate filter (Nucleopore brand, from Sterico AG, Dietikon, Switzerland) with a pore size of 0.8 micron, which was placed on a pre-weighed absorbent paper (Whatman chromatography paper , 17CHR, from VMR International AG, Dietikon, Switzerland). Place the unit on the support table and secure. Then 10 ml of paint colorant was added to the test tank, which was immediately closed with a stopper. start the timer. After 15 seconds the test cell pressure is 1 bar. After the 90 seconds are complete, remove the pressure and plug. After an additional 15 seconds, the absorbent paper was detached from the filter. The amount of liquid absorbed was obtained by weighing the absorbent paper using a balance accurate to 0.0001 gram. The amount of absorbed liquid per square meter is obtained by calculating the average value of 3 measurements.

Immobilization solids content

Measured with a Coesfeld Minimum Film Forming Temperature device (Coesfeld, Dortmund, Germany). A metal plate was placed on a 50 cm long glass plate with a temperature gradient such that one end was heated to 50°C while the other end was maintained at 10°C. A 14 cm wide, 0.4 mm wet layer of paint pigment is placed on the board by a squeegee. Gradually dry from the hot end to the cold end. After 15 minutes, remove the paint sample from the dry end with a spatula. The solids content of the samples was measured, and the average of six measurements was taken as the cured solids content.

Coating weight

In each paper coating test, the coat weight obtained was based on the known volumetric flow rate of the pump delivering the coating to the curtain coating head, the speed of the continuous paper web under the curtain coating head, the curtain coating head The density and percent solids content and the width of the coating curtain are calculated.

Cavity degree

The degree of cratering was determined by visual inspection of completely burned samples. A water/isopropanol (50/50) solution containing 10% ammonium chloride was used. Soak one-sided coated paper in the above solution for 30 seconds, and soak double-sided coated paper for 60 seconds. The samples were air dried overnight after removing excess solution with blotting paper. In an oven at 225°C for 3.5 minutes for complete combustion. Use a magnifying glass (magnification 10 times) to count the pits on a 3 x 3 cm cross-section of the completely burnt sample. Very small uncoated spots with perfect circles are not considered to be pits; they are considered to be small holes created by microbubbles caused by air entrapment in the paint. Also not considered to be pits are those elliptical areas of uncoated film along the long axis of the machine (direction of paper travel) that result from larger air bubbles present in the coating formulation that were not removed during degassing.

Coating Density

The density of the coating curtain was determined by weighing 100 ml of the coating sample in a pycnometer.

paper roughness

The roughness of the coated paper surface can be measured using a Parker PrinterSurf roughness gauge. A sample sheet of coated paper was sandwiched between a cork-mylar platen and the measuring head at a clamping pressure of 1000 kPa. Compressed air of 400 kPa was supplied to the device, and the leakage of air between the measuring head and the surface of the coated paper was measured. A higher measured value indicates a higher roughness of the coated paper surface.

brightness

Brightness was measured on a Zeiss Elrepho 2000. Brightness is measured on a stack of paper sheets according to the ISO2469 standard. The result is like R457.

opacity

Opacity is measured on a Zeiss Elrcpho 2000. Opacity is measured on a single sheet against a black standard (R ₀ ) and on a stack of sheets (R _∝ ). The result is represented by R ₀ /R _∝ ×100%.

the size of granule

The median Stokes equivalent spherical particle size and particle size distribution were measured by X-ray sedimentation (sedigraph) equipment (Sedigraph 5100 Particle Size Analysis System from Micromeritics, Norcross, Georgia, USA). Raw material manufacturers provide particle size and particle size distribution data for the raw materials used in the examples.

aspect ratio

The aspect ratio is found in "Aspect Ratios of Pigment Particles Determined by Differential Method", Nordic Pulp and Paper Research Journal , Vol.15, No.3/2000, pp.221-230 Measured by the electron microscope image analysis method described.

Example 1

The above components were mixed in the amounts given in Table 1 to show that a high aspect ratio clay was used.

Table 1 Gap 1 Gap 2 Carbonate (A) 100 Clay (B) 100 latex 13 13 polyvinyl alcohol 1 3.5 Surfactant 0.4 0.2 brightener 1 pH 8.5 8.6 Solid content (percentage) 60.1 55.7 Density (g/cm ³ ) 1.51 1.43 Brookfield viscosity [mPa·s] 120 755 Viscosity at 3,000s ^-1 [mPa·s] 29.9 114 Viscosity at 30,000s ^-1 [mPa·s] 13.5 150 Viscosity at 500,000s ^-1 [mPa·s] 13.6 57.9 shear thickening coefficient 0.45 1.32 The viscosity of the coating in gap 2 at a shear rate of 500,000 ^s was out of observation range, problematic to run on a knife coater (greater than 50 mPa·s), and had a shear thickening coefficient greater than 1.2.

The test speeds and coat weights for each layer in Example 1 are listed in Table 2. The base paper used is wood-containing paper with a surface roughness of 4.3 microns.

Table 2 Speed [m/min] Gap 1 coating weight g/m ² (dry) Gap 2 coating weight g/m ² (dry) 1000 2 6 1000 2 8 1200 2 8 1500 2 8

A colored layer (slit 1) adjoins the paper. A second layer is added at the same time with slot 2, and this layer contains high aspect ratio clay. The multilayer coatings were successfully applied in all cases listed in Table 2 without running problems.

Example 2

The components described above were mixed in the amounts given in Table 3 to indicate the use of calcined clay.

table 3 Gap 1 Gap 2 Carbonate (A) 100 clay 100 Latex (A) 13 13 polyvinyl alcohol 1 3.5 Surfactant 0.4 0.2 brightener 1 pH 8.5 8.6 Solid content (percentage) 60.1 47.9 Density (g/cm ³ ) 1.51 1.36 Brookfield viscosity [mPa·s] 120 470 Viscosity at 3,000s ^-1 [mPa·s] 29.9 30.7 Viscosity at 30,000s ^-1 [mPa·s] 13.5 47.6 Viscosity at 500,000s ^-1 [mPa·s] 13.6 105.2 shear thickening coefficient 0.45 1.55

The viscosity of the coating in Gap 2 at a shear rate of 500,000 ^s was beyond the observed range, operation on a knife coater was very problematic (greater than 100 mPa·s), and the shear thickening coefficient was greater than 1.5.

The speeds and coat weights for each layer in Example 2 are listed in Table 4. The base paper used is wood-containing paper with a surface roughness of 4.3 microns.

Table 4 Speed [m/min] Gap 1 coating weight g/m ² (dry) Gap 2 coating weight g/m ² (dry) 1000 2 6 1000 2 8 1200 2 6 1200 2 8

A colored layer (slit 1) adjoins the paper. A second layer is added simultaneously with slot 2, and this layer contains calcined clay. The multilayer coatings were successfully applied without running problems in all cases listed in Table 4. Compared with the laboratory sample with clay (C) instead of clay (A) in the gap 2 formulation in Table 3 and applied with a doctor blade at a single coat weight of 8 g/ ^m2 , the first test condition in Table 4 The samples of coated paper obtained under significantly improved opacity (92.6 vs. 90.4) and brightness (80.4 vs. 73.7)

Example 3

The method of Example 1 was repeated with the thickener replacing a portion of the polyvinyl alcohol (PVOH) in the top layer (slot 2). The thickeners used in the comparative experiments were selected for their suitability for high-speed knife coating and their ability to provide a crater-free coating curtain coating at high coating speeds. Additionally, the amount of polyvinyl alcohol in the bottom layer (slot 1) was increased to two parts and the brightener was removed from the top layer (slot 2). The paint components were mixed in the amounts given in Table 5.

table 5 Gap 1 Gap 2 Carbonate (A) 100 Clay (B) 100 latex 13 13 polyvinyl alcohol 2 1.0 Thickener (A) 0.2 Surfactant 0.4 0.2 pH 8.5 8.6 Solid content (percentage) 60.3 55.8 Density (g/cm ³ ) 1.51 1.43 ABO water retention rate(g/m ² ) NM ^* 76 Brookfield viscosity [mPa·s] 350 740 Viscosity at 3,000s ^-1 [mPa·s] N M 153 Viscosity at 30,000s ^-1 [mPa·s] N M 214 Viscosity at 500,000s ^-1 [mPa·s] N M 96 shear thickening coefficient N M 1.39

( ^* NM = not measured)

The viscosity of the coating in gap 2 at a shear rate of 500,000 ^s was beyond the observed range, and it was difficult to run on a knife coater (greater than 75 mPa·s), and the shear thickening coefficient was greater than 1.2.

Each coat weight in slot 1 was 1.5 g/m ² (dry) and each coat weight in slot 2 was 6.5 g/m ² (dry). At coating speeds of 1250 m/min and 1500 m/min, the total coat weight of the multilayer coating was 8 g/m ² (dry). The base paper used was a 35 g/ ^m2 wood-containing paper with a surface roughness of 4.8 microns. The coating applied at a speed of 1250 m/min produced a crater-free coating and the coating applied at a speed of 1500 m/min produced a nearly crater-free coating with no other running problems. This demonstrates that coatings having high aspect ratio pigments and high high shear viscosities can be readily applied on a curtain coater at high coating speeds by the method of the present invention.

Comparative experiment A

Coatings containing high aspect ratio pigments (slit 2 of Example 3) were attempted to be coated with a jet applicator blade coater on the same base paper used in Example 3. Proper application of the coating at a coating speed of 1250m/min was not possible using this spray unit as the coating was deflected away from the paper substrate as it hit the substrate.

Comparative experiment B

The procedure of Comparative Example A was repeated, except that the coating mixture given in Table 6 was used. This coating composition is representative of the blend of pigment components in the two coatings used in Example 3 (Slots 1 and 2). The amounts of polyvinyl alcohol, surfactant, and thickener were the same as those used for the top layer (slot 2) in Example 3.

Table 6 Carbonate (A) 19 Clay (B) 81 latex 13 polyvinyl alcohol 1.0 Thickener (A) 0.2 Surfactant 0.2 pH 8.6 Solid content (percentage) 59.2 Density (g/cm ³ ) 1.46 ABO water retention rate(g/m ² ) 74 Brookfield viscosity [mPa·s] 1690 Viscosity at 3,000s ^-1 [mPa·s] 215 Viscosity at 30,000s ^-1 [mPa·s] 294 Viscosity at 500,000s ^-1 [mPa·s] 110 shear thickening coefficient 1.37

The same base paper used in Example 3 was coated with a total coating weight of 8.3 g/m ² (dry) at a speed of 1250 m/min using a spray knife coater. The measuring blade was a 0.4 mm thick blade with a 45 degree bevel, operating with a blade load (rake angle) of 12.1 degrees. The doctor blade showed extreme wet paint spreading (2 minute run time spreads 30g of paint). In addition, the paper had many skipped areas that were not coated. When the blade bevel angle was changed to 40 degrees, the blade ran cleanly, but the blade load was very high (coat weight 8.3 g/ ^m2 at maximum rake angle of 24 degrees). These doctor blade conditions will result in frequent web breakage and rapid wear of the doctor blades, resulting in unacceptably long downtimes of production equipment.

When coating with a 0.4 mm thick 45 degree angled doctor blade at a coating speed of 1500 m/min, the running problems were even more serious. The blade pressure (rake angle) required to achieve a total coat weight (dry) of 8.0 g/ ^m2 was 22.7 degrees. At this point the spread of paint was very noticeable (37.5 g spread after 2 minutes of running) and the level of skipping was unacceptable.

Example 4

The method of Example 2 was repeated, except that a part of the polyvinyl alcohol (PVOH) was replaced with a thickener in the top coat (slot 2). The thickeners used in the comparative experiments were selected for their suitability for high-speed knife coating and their ability to provide a crater-free coating curtain at high coating speeds. Additionally, the amount of polyvinyl alcohol in the bottom layer (slot 1) was increased to two parts and the brightener was removed in the top layer (slot 2). The paint components were mixed in the amounts given in Table 7.

Table 7 Gap 1 Gap 2 Carbonate (A) 100 Clay (A) 100 latex 13 13 polyvinyl alcohol 2 2.0 Thickener (A) 0.2 Surfactant 0.4 0.2 pH 8.5 8.6 Solid content (percentage) 60.3 48.8 Density (g/cm ³ ) 1.51 1.38 Brookfield viscosity [mPa·s] 350 410 Viscosity at 3,000s ^-1 [mPa·s] NM ^* 595 Viscosity at 30,000s ^-1 [mPa·s] N M too high to measure Viscosity at 500,000s ^-1 [mPa·s] N M 137 shear thickening coefficient N M Unable to calculate Shear blocking behavior N M have

( ^* NM = not measured)

The viscosity of the coating in gap 2 at a shear rate of 500,000 s ^-1 was beyond the observed range, and it was difficult to run on the knife coater (greater than 100 mPa·s), and the coating exhibited shear thickening behavior.

The coating weight per layer of the coating in slot 1 was 1.5 g/m ² (dry) and in slot 2 6.5 g/m ² (dry) at a coating speed of 1500 m/min. The base paper used was a 35 g/ ^m2 wood-containing paper with a surface roughness of 4.8 microns. At a coating speed of 1500 m/min, the multi-layer coating was applied at a total coating weight of 8 g/m ² (dry) and provided an almost crater-free coating with no other running problems. This demonstrates that coatings with shear retarding behavior can be easily applied on a curtain coater.

Comparative experiment C

The coating containing the calcined clay pigment (slit 2 in Example 4) was applied to the same base paper as used in Example 4 using a spray knife coater equipped with a 0.4 mm thick doctor blade at an angle of 45 degrees. At a coating speed of 1500 m/min, the blade load (rake angle) required to achieve 8.4 g/ ^m2 (dry) was 21.4 degrees with a clean blade run. This justifies that calcined clay pigments require a relatively high doctor blade load.

Comparative experiment D

The procedure of Comparative Example C was repeated, except that the coating mixture given in Table 8 was used. This coating composition represents the admixture of the pigment components in the two coatings used in Example 4 (Slots 1 and 2). The amounts of polyvinyl alcohol, surfactant and thickener were the same as those used for the top layer in Example 4. At a coating speed of 1500 m/min, the blade load (rake angle) required to achieve 8.0 g/m ² (dry) was 22.4 degrees with a clean blade run.

Table 8 Carbonate (A) 19 Clay (A) 81 latex 13 polyvinyl alcohol 2.0 Thickener (A) 0.2 Surfactant 0.2 pH 8.6 Solid content (percentage) 51.7 Density (g/cm ³ ) 1.41 Brookfield viscosity [unit] 420 Viscosity at 3,000s ^-1 [mPa·s] 523 Viscosity at 30,000s ^-1 [mPa·s] too high to measure Viscosity at 500,000s ^-1 [mPa·s] 124 shear thickening coefficient Unable to calculate Shear blocking behavior have

Example 5

The procedure of Example 1 was repeated, except that the formulation in Table 9 was used. This example demonstrates the use of an engineered calcium carbonate pigment with a narrow particle size distribution compared to commonly used ground calcium carbonate. Coating formulations with low thickener levels at high solids impart low water retention and low cured solids to the coating.

Table 9 Gap 1 Gap 2 Carbonate (A) 100 Carbonate (C) 100 latex 13 11 polyvinyl alcohol 1.0 0.5 Thickener (A) 0.17 Surfactant 0.4 0.2 pH 8.5 8.6 Solid content (percentage) 60.0 67.2 Density (g/cm ³ ) 1.51 1.38 Water retention(g/m ² ) NM ^* 133 Cured solid content (percentage) N M 82.3 Brookfield viscosity [mPa·s] 240 1160 Viscosity at 3,000s ^-1 [mPa·s] N M 162 Viscosity at 30,000s ^-1 [mPa·s] N M 141 Viscosity at 500,000s ^-1 [mPa·s] N M 127 shear thickening coefficient N M 0.87

( ^* NM = not measured)

The viscosity of the paint colorant in gap 2 at a shear rate of 500,000 s ^-1 was beyond the observed range and was very difficult to run on a knife coater (greater than 100 mPa·s).

The coating weight of each layer in slot 1 was 1.5 g/m ² (dry) and in slot 2 6.5 g/m ² (dry). Multilayer coatings with a total coating weight of 8 g/m ² (dry) were coated at a coating speed of 1250 m/min on 35 g/m ² wood-containing paper with a surface roughness of 4.8 microns. The coating was free of craters and the coating had no other running problems. This demonstrates that a coating having a high dehydration rate and fast curing can be easily applied to a substrate by curtain coating.

Example 6

The procedure of Example 5 was repeated, except that the paint in gap 1 was replaced with the same paint as in gap 2 but diluted to 58.3% solids. This results in a multilayer coating curtain in which two layers are identical in composition, differing only in solids content. The as-applied coating exhibited no cratering and no other running defects.

Comparative experiment E

An attempt was made to coat the engineered carbonate containing coating (Slot 2 of Example 5) onto the same base paper used in Example 5 using a spray knife coater. At a maximum blade pressure (rake angle) of 24 degrees, the coat weight was 1.1 g/m ² (dry). The coating was diluted to 65.5% solids and had a Brookfield viscosity of 890 mPa·s, a viscosity of 107 mPa·s and a water retention of 137 at a shear rate of 500,000 s ⁻¹ . The coat weight at maximum doctor blade pressure (rake angle=24 degrees) was 9.3 g/m ² (dry). The paint used was further diluted to a solids content of 64.3% and had a Brookfield viscosity of 730 mPa·s, a viscosity of 88 mPa·s and a water retention of 146 at a shear rate of 500,000 s ⁻¹ . This coating was able to achieve a coat weight of 8.3 g/m ² (dry), but the doctor blade pressure was not a stable value. To maintain coat weight, blade pressure (rake angle) must be continuously increased to a maximum value during which time the coating exceeds the coat weight target of 8 g/ ^m2 (dry). Additionally, dried paint deposits accumulated on the blade tip (3.3 g from 3.75 minute run time). These dry "grooves" are very large and will eventually cause streaks on the surface of the coated paper. The poor runnability of this coating was attributed to its fast dewatering rate, and curing of the coating under the doctor blade.

Example 7

The previously described components were mixed in the amounts given in Table 10 to illustrate the use of Carbonate D, a coarse carbonate pigment. This carbonate pigment contains 2% by weight of particles with a diameter greater than 12 μm. This pigment cannot be applied with a knife coater without severe streaking because it contains large particles with a diameter close to the thickness of the wet paint.

Table 10 Gap 1 Gap 2 Gap 3 Carbonate (A) 25 30 Carbonate (D) 100 70 Clay (C) 75 latex 13 10 11 polyvinyl alcohol 1.0 0.8 0.8 Thickener (B) 0.2 0.15 0.07 Surfactant 0.4 0.2 pH 9.3 8.6 8.6 Solid content (percentage) 60.1 70.0 62.3 Density (g/cm ³ ) 1.50 1.67 1.54 Brookfield viscosity [mPa·s] 980 210 1120

Thickener (B) is added to the paint to prevent cratering. The speeds and coat weights tested for each coating in Example 7 are listed in Table 11. The base paper used was 75 g/ ^m2 wood-free paper with a surface roughness of 8.5 microns.

Table 11 Speed [m/min] Gap 1 coating weight g/m ² (dry) Gap 2 coating weight g/m ² (dry) Gap 3 coating weight g/m ² (dry) 1200 1.5 5.5 3 1200 2.5 12.5 5

The coating was free of craters and had no other running problems. A coating with a total coating weight of 10 g/m ² (dry) had an uncalendered surface with a surface roughness of 5.52 μm and a calendered surface with a surface roughness of 2.1 μm. A coating with a total coating weight of 20 g/m ² (dry) had an uncalendered surface with a surface roughness of 3.95 μm and a calendered surface with a surface roughness of 1.3 μm. This demonstrates that multi-layer coatings using coarse pigments in the main coating layer can be easily coated with a curtain coater and a smooth surface similar to paper coated with finer pigments can be obtained.

Claims (31)

1. the coated paper of a production except that sensitive paper or the method for cardboard, it may further comprise the steps:

(a) form one comprise one deck at least flow freely the coating curtain, wherein form composition that one deck at least flows freely coating curtain layer at 25 ℃ and 500,000s ^-1Shear rate under have 50mPas at least shear viscosity and

(b) described coating curtain is contacted with the continuous body paper or the web substrate of cardboard.

2. method according to claim 1 is characterized in that one deck at least in the step (a) flows freely coating curtain layer and has the shear viscosity of 75mPas at least, preferred 100mPas at least, most preferably 125mPas at least.

3. the coated paper of a production except that sensitive paper or the method for cardboard, it may further comprise the steps:

(a) form one comprise one deck at least flow freely the coating curtain, wherein form the composition that one deck at least flows freely coating curtain layer and comprise at least a pigment, the shape of described pigment and structure are being lower than 500,000s ^-1Shear rate under destroyed and

(b) described coating curtain is contacted with the continuous body paper or the web substrate of cardboard.

4. the coated paper of a production except that sensitive paper or the method for cardboard, it may further comprise the steps:

(a) form one comprise one deck at least flow freely the coating curtain, wherein form the shear-thickening coefficient value that one deck at least flows freely the composition of coating curtain layer and be at least 1.2 at 25 ℃, this shear-thickening coefficient is defined as 30,000s ^-1Viscosity under the shear rate and 3,000s ^-1The ratio of the viscosity under the shear rate and

(b) described coating curtain is contacted with the continuous body paper and the web substrate of cardboard.

5. according to the described method of aforementioned each claim, it is characterized in that the coating curtain that flows freely in the step (a) is that multilayer flows freely the coating curtain.

6. method according to claim 5 is characterized in that the coating curtain that flows freely in the step (a) comprises the top layer of guaranteeing printability.

7. according to claim 5 or 6 described methods, it is characterized in that the coating curtain that flows freely in the step (a) comprises at least three layers.

8. according to the described method of aforementioned each claim, it is characterized in that the one deck at least that flows freely coating curtain layer in the step (a) comprises at least a pigment.

9. method according to claim 8 is characterized in that described pigment is selected from clay, kaolin, calcined clay, co-structuredization pigment, talcum, calcium carbonate, titanium dioxide, satin white, synthetic polymer pigment, zinc oxide, barium sulfate, gypsum, silica, gibbsite, mica, synthetic magadiite and diatomite.

10. according to the described method of aforementioned each claim, it is characterized in that the one deck at least that flows freely coating curtain layer in the step (a) comprises the pigment that at least a length-width ratio was at least 1.5: 1.

11., it is characterized in that the one deck at least that flows freely coating curtain layer in the step (a) comprises adhesive according to the described method of aforementioned each claim.

12. method according to claim 11 is characterized in that described adhesive is selected from styrene-butadiene latex, styrene-acrylate latex, styrene-butadiene-acrylonitrile latex, styrene-acrylate-acrylonitrile latex, styrene-butadiene-acrylate-acrylonitrile latex, styrene-maleic anhydride latex, styrene-acrylate-maleic anhydride latex, polysaccharide, protein, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, cellulose derivative and their mixture.

13., it is characterized in that the one deck at least that flows freely coating curtain layer in the step (a) has the solids content of at least 30 weight % according to the described method of aforementioned each claim, be preferably at least 40 weight %, most preferably be at least 50 weight %.

14., it is characterized in that the coating curtain that flows freely in the step (a) has the solids content of at least 40 weight % according to the described method of aforementioned each claim, be preferably at least 45 weight %, most preferably be at least 50 weight %.

15., it is characterized in that the one deck at least that flows freely coating curtain layer in the step (a) comprises at least a fluorescent whitening agent according to the described method of aforementioned each claim.

16., it is characterized in that the one deck at least that flows freely coating curtain layer in the step (a) comprises at least a surfactant according to the described method of aforementioned each claim.

17., it is characterized in that the coating curtain that flows freely in the step (a) comprises at least 4 layers according to the described method of aforementioned each claim, be preferably at least 5 layers, and more preferably at least 6 layers.

18., it is characterized in that the one deck at least that flows freely coating curtain layer in the step (a) has less than 10g/m according to the described method of aforementioned each claim ²The coating weight dry weight, preferably less than 8g/m ², most preferably less than 6g/m ²

19., it is characterized in that the both not also not calenderings in advance of pre-coating of continuous web substrate in the step (b) according to the described method of aforementioned each claim.

20. according to the described method of aforementioned each claim, it is characterized in that the continuous web substrate in the step (b) has the base-material speed of 300m/min at least, preferred 400m/min at least, most preferably 500m/min at least.

21. according to the described method of aforementioned each claim, the every Gram Mass that it is characterized in that the continuous web substrate in the step (b) is 20-350g/m ²

A 22. coated paper or cardboard that makes by the described method of aforementioned each claim.

23. the coated paper of a production except that sensitive paper or the method for cardboard, it may further comprise the steps:

(a) form one comprise one deck at least flow freely the coating curtain, wherein form a composition that one deck at least flows freely coating curtain layer have the retardance behavior of shearing and

(b) described coating curtain is contacted with the continuous body paper and the web substrate of cardboard.

24. the coated paper of a production except that sensitive paper or the method for cardboard, it may further comprise the steps:

(a) form one comprise one deck at least flow freely the coating curtain, wherein form difference that one deck at least flows freely its paint solidification solids content of composition of coating curtain layer and coating applying solid content less than 15 and

(b) described coating curtain is contacted with the continuous body paper and the web substrate of cardboard.

25. the coated paper of a production except that sensitive paper or the method for cardboard, it may further comprise the steps:

(a) form one comprise one deck at least flow freely the coating curtain, wherein form pigment in the composition that one deck at least flows freely coating curtain layer have at least 2 microns particle size and

(b) described coating curtain is contacted with the continuous body paper and the web substrate of cardboard.

26. the diameter that method according to claim 25, the described pigment in the wherein said coating composition comprise at least 0.5 weight % is greater than 10 microns particle.

27. according to the described method of aforementioned each claim, wherein said continuous web substrate has 800m/min and the preferred speed of 1000m/min at least at least.

28. according to the described method of aforementioned each claim, wherein said coating curtain forms by a clearance type mouth mould.

29. according to the described method of aforementioned each claim, wherein said coating curtain forms by mouthful mould that slides.

30. according to the described method of aforementioned each claim, wherein the described coating curtain of one deck layer comprises poly(ethylene oxide) at least.

31. according to the described method of aforementioned each claim, wherein said coating curtain comprises poly(ethylene oxide) in its boundary layer.