WO2007048878A1

WO2007048878A1 - Multi-layered paper and a process for preparing it

Info

Publication number: WO2007048878A1
Application number: PCT/FI2006/050460
Authority: WO
Inventors: Patrick Sundholm
Original assignee: Dryad Ltd Oy
Priority date: 2005-10-26
Filing date: 2006-10-25
Publication date: 2007-05-03
Also published as: FI20055576A0; EP1941100A4; FI20055576L; EP1941100A1

Abstract

This invention relates to a multi-layered paper, which comprises a base paper, a first layer and a second layer. The first layer is an opacity layer comprising one or more dark colorants spray coated on at least one of the faces of the base paper, and the second layer comprises one or more white or near white pigments coated on the first layer. Further, this invention relates to a process for preparing a multi-layered paper. The process comprises providing a base paper, spraying a first layer of one or more dark colorants on at least one face of the base paper to form an opacity layer, and coating said first layer with a second layer of one or more white or near white pigments.

Description

MULTI-LAYERED PAPER AND A PROCESS FOR PREPARING IT

FIELD OF THE INVENTION

The present invention relates to a multi-layered paper, and more particularly to a high opacity paper. The present invention further concerns a process for preparing multi- layered paper and to the use of spray coating for applying an opacity layer on paper.

BACKGROUND OF THE INVENTION

In the paper industry, paper grades are divided in several different categories and in many different ways. This invention relates to printing and writing paper, including grades used for those paper grades which are used for newspapers, magazines, catalogs, books, commercial printing, copying, business forms, and stationery as well as for laser and digital printing. The printing and writing paper grades comprises newsprint, uncoated mechanical papers, which are mainly supercalandered (SC), coated mechanical papers, which are mainly light weight coated (LWC), uncoated woodfree papers and coated woodfree grades.

Newsprint is made largely from mechanical pulp and/or waste paper, with or without a small amount of filler. Newsprint is mainly used for newspaper manufacture, approximately 80%, and almost exclusively in reels. Recovered paper use in furnish has increased dramatically during the last decade.

Uncoated mechanical papers, mainly supercalandered (SC) papers, are used for magazines and advertising materials mainly in reels. Stable quality, a smooth printing surface for four color printing, and good runnability are the most important quality characteristics. Printing methods are offset and rotogravure. Coated mechanical papers, mainly light weight coated (LWC) papers, find the same uses as SC papers and also mainly in reels. High brightness is an additional quality factor for these papers. The printing methods are the same as for SC papers.

Coated woodfree papers are for high quality four color printing such as books, brochures, advertising materials and magazines. Two-thirds of the consumption is sheets and the remainder is in reels.

The uncoated woodfree papers: are used for printing and copying paper (e.g. A4), offset printing for books and brochures, continuous forms, etc. High brightness, stable quality and good formation are the most important quality requirements.

Writing paper, also known as business or office paper, is normally uncoated woodfree paper, which is suitable for printing or other graphic purposes, where at least 90% of the fibre furnish consists of chemical pulp fibres. Uncoated woodfree paper can be made from a variety of furnishes, with variable levels of mineral filler and a range of finishing processes such as sizing, calendering, machine-glazing and watermarking. This grade includes most office papers, such as business forms, copier, computer, stationery and book papers. Pigmented roll coated "coated" papers (coating > 6 g/m2 per side ) are covered by this heading.

The coated papers are all paper suitable for printing or other graphic purposes and coated on one or both sides with minerals such as china clay (kaolin), calcium carbonate, etc. Coating may be done by a variety of methods, both on-machine and off-machine, and may be supplemented by super-calendering.

Paper is distinguished from board or paperboard primarily on basis weight. The term "paper" is generally applied to sheets having basis weights of 20 to 170 g/m² while the term "board" or "paperboard" refers to basis weights of 130 to 450 g/m². Medium weight papers have a basis weight normally between 40 - 120 g/m² and light weight papers have basis weight normally less than 40 g/m². Paper has to fulfill certain requirements such as low basis weight, bulk, high whiteness, high opacity and the right surface ink absorbency properties. The set quality specifications are a compromise of these parameters. In paper manufacturing attention should be paid to visual out look of the paper in terms of brightness, shade, surface evenness and opacity. Also paper surface absorbency properties should match the printing process in question so that the penetration of ink into the paper surface is optimal from a quality and cost point of view.

To meet these demands, commercially available printing and writing paper can be constructed in layers. Typical layer constructions are:

1 ) one layer consisting of fibre and white pigments as fillers;

2) the base paper added with one layer on each side, so called sized paper, consisting of the base paper and a layer of chemicals, like starch;

3) the base paper added with one layer on each side of the paper, so called coated paper, consisting of the base paper and a layer of chemicals and white pigment, in which case the chemical act as a binder of the white pigment on to the paper; and

4) a base paper with two coated layers on each side, called double coated paper.

The additional white pigment layer improves whiteness and opacity, all other conditions remaining substantially unchanged.

Producing paper with improved properties requires more process stages, additional equipments, an increased amount of operating supplies and also more operating personnel. All of these increase the manufacturing costs. The aim is to provide a paper at low costs but with high quality. Highest priorities in paper quality are normally paper surface properties and whiteness. With existing methods one can achieve paper whiteness and adequate surface absorbency properties, at desired basis weights, depending on manufacturing concept chosen. Paper opacity is, however, always a compromise and an end result of choices made. US 6,387,500 discloses a method of increasing the brightness of a multi-layered coating and a multi-layered coated paperboard or paper comprising paperboard or paper, and a multi-layered coating. Also a method to reduce the amount of a white or near white pigment is disclosed. The multi-layered coating contains at least two layers. The first layer contains both dark colorant and white pigment. The second layer contains at least one pigment other than a dark colorant, such as a white or near white pigment. This publication does not disclose or suggest the use of spray coating technology for coating.

High opacity coated papers are used in various applications for which the paper must be printable and for which it is essential that the opacity of said paper is higher than the opacity of conventional coated papers with a comparable weight per square meter. It is known to make ultra opacity sheets by coating, traditionally using air-knife coaters, trailing-blade coaters or metering-bar coaters, at least one of the two faces of a three-ply paper support. The central ply of a three-ply support has a grey paper composition, which introduces ultra opacity by absorption of light. This central ply is surrounded by two plies with a white paper composition such that the assembly of each white ply supporting one or more white coats makes the ultra opaque sheet look white and uniform. One disadvantage of this technique is the difficult and expensive use of a multi-ply machine, particularly for manufacturing low grammage paper.

US 2005/0158570 discloses an ultra opaque coated sheet such as playing card, comprising a colored support made from a single ply of material (paper or plastic), the said support being coated on at least one of its faces with one or more white pigmented coats. Also a manufacturing process of this ultra opaque coated sheet is disclosed. According to this process opacification can be obtained by depositing a precoat of opacifying pigments using a curtain coating device on the paper surface.

Other ultra opaque coated sheets, such as lottery tickets scratch cards, have been disclosed in GB 2299036, EP 668092 and US 5213664. None of these publications are directed to manufacturing of printing and writing papers nor mentions the use of spray coating. The above processes do not solve the problem of poor opacity of medium or light weight papers. Problem with these papers is that they have very poor opacity. In medium and light weight papers the printed image or the text causes variations in opacity and so called "show through". Reduced reflection from a colored area on the reverse side of the paper, such as printed black image or text, changes the visual impression of the paper surface. The lower the paper opacity is the worse the negative effect.

The poor opacity is also present in printing and writing papers. It is obvious for a man skilled in the art that opacity can be improved by increasing the thickness of the paper i.e. increasing the grammage. Therefore higher grammage paper is used in these applications these days. However, the recent increase in transportation and mailing costs requires the development and use of lighter weight printing and writing papers.

Problems with the known methods are that they are expensive or unsuitable for the production of medium or light weight papers.

BRIEF DESCRIPTION OF THE INVENTION

It is thus an object an object of the present invention to provide a method and a paper for so as to overcome the above problems or at least as to alleviate the above disadvantages. For this purpose a multilayer paper and the production method thereof is provided.

One of the main aspects of this invention is paper quality and especially a manufacturing stage aimed to improve and control printing and writing paper opacity. The invented method is suitable for manufacturing coated sheets with higher opacity. These high opacity papers can be used in various applications for which the sheets must be printable and for which it is advantageous that the opacity of said sheets be higher than the opacity of conventional coated sheets with a comparable weight per square meter. The produced multilayer paper has unique properties. It is an advantage of the method of the invention that the paper can be produced at lower or at least at competitive costs compared to any other coated paper of today, while at the same time the opacity of said paper is higher than the opacity of conventional coated papers with a comparable weight per square meter.

The objects of the invention are achieved by a process and paper which are characterized by what is stated in the independent claims. The preferred embodiments of the invention are disclosed in the dependent claims.

The invention is based on the idea that adding a darker layer in the paper would increase the opacity. Opacity is an optical property of the paper. It is a measure of the degree to which paper transmits light. A paper with low opacity allows more light to pass through the paper, a paper with high opacity allows less light to pass through the paper. Opacity characterizes the ability of paper to hide text or pictures on the back side of the sheet. Opacity characterizes the ability of a single sheet to hide the background. Practically, the opacity determines how much of the image on the opposite side of the paper is shown through on the other side. When light hits a paper surface, a fraction of the intensity reflects back, and the remainder enters the sheet. Inside the sheet, light spreads or scatters in all directions. Some light eventually reflects back from the sheet, another part transmits through the sheet, and the remainder absorbs. Reflectance measurements can determine the reflected, transmitted, and absorbed intensities. International standards specify the procedures for the reflectance measurements including the spectral characteristics of the incident light, the standards for the calibration of the instruments, and the measurement geometry.

Most opacity problems experienced by papermakers involve the visibility of images printed onto the reverse sides or subsequent sheets of a magazine, newspaper, or book. Within the printing and writing paper field, a multilayer paper with one layer specifically aimed at increasing the opacity does not exists. This invention provides a new paper structure, which is constructed in layers and one layer is specifically aimed to improve opacity. This layer is called an "opacity layer".

Accordingly the present invention provides as a first aspect multi-layered paper, which comprises a base paper, a first layer and a second layer, wherein the first layer is an opacity layer comprising one or more dark colorants spray coated on at least one of the faces of the base paper, and the second layer comprises one or more white or near white pigments coated on the first layer.

In a second aspect the invention provides process for preparing a multi-layered paper. The process comprises providing a base paper, spraying a first layer of one or more dark colorants on at least one face of the base paper to form an opacity layer, and coating said first layer with a second layer of one or more white or near white pigments.

In a third aspect the invention provides the use of spray coating for applying an opacity layer on paper.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached drawings, in which

Figure 1 illustrates a diagrammatic section of a multi-layered paper according to this invention;

Figure 2a illustrates a diagrammatic view of a two-sided coating station; and

Figure 2b illustrates a diagrammatic view of a coating station with a doctoring blade; and

Figure 2c illustrates a diagrammatic view of a double coating station with an infrared dryer. SUMMARY OF THE INVENTION

Figure 1 illustrates a multi-layered paper (1), which comprises a base paper (2), a first layer (3) and a second layer (4), wherein the first layer (3) is an opacity layer comprising one or more dark colorants spray coated on at least one of the faces of the base paper (2), and the second layer (4) comprises one or more white or near white pigments coated on the first layer (3). In one embodiment of the invention the base paper (2) comprises pigments and mechanical pulp, chemical pulp, recycled paper or mixtures thereof. The base paper (2) is non-colored, thus the pigments used in the base paper are white or near white pigments. The coating of first (3) and second (4) layers is preferable done on both sides of the base paper (2).

Generally the paper basis weight and bulk can be adjusted over a wide range, depending on mass flow, raw material used and calendering. This invention is especially related to multi-layered paper having basis weights (grammage) of 20 to 120 g/m², specifically less than 100 g/m² and more specifically 70 g/m² or less.

This invention is especially related to multi-layered printing and writing paper, which is used for printing. The paper according to the invention is preferable a news, magazine, printing or writing paper. Total visual outlook of the printed image is a function both of the outlook of the paper and the printed image on the paper, text or pictures. The outlook of the printed paper has to be even, sharp and there has to be a good contrast between paper and printed image.

The invention further relates to a process for preparing multi-layered paper, comprising providing a base paper, spraying a first layer of one or more dark colorants on at least one face of the base paper to form an opacity layer, and coating said first layer with a second layer of one or more white or near white pigments.

As will be appreciated by those skilled in the art, applying a pigment layer is technically the most cost efficient way of coating paper. Spray coating allows applying a coating layer with exact weight and thickness without having a reverse effect on production efficiency. Further, the spray can be applied in one or several layers. The advantage of spray coating is that the coating layer can be applied at desired amounts, for example from 1 g/m² to 15 g/m². Especially the coating layer is applied in amounts 2 g/m² to 12 g/m², more specifically from 3 g/m² to 10 g/m², and most specifically from 4 g/m² to 8 g/m².

The term "spray coating" used herein refers to coating that is done by using a spray coater. The term "spray coater" or "spray box" (5) used herein refers to an apparatus suited for applying coating to the surface of a web from a plurality of spray nozzles adapted over the cross-machine width of the web by way of spraying coating material under pressure via the nozzles onto the web. In a papermaking machine or coater, the spray nozzles are adapted in multiple rows at desired points along the web travel, spaced apart from each other at desired distances. The nozzles may be located in plural rows that are advantageously adapted into a hood serving to prevent at least a major portion of the coating mixture mist from escaping to the surroundings. Some spray-coating methods and apparatuses are described in WO 94/11116, WO 02/072952 and US 6,063,449.

According to the process of this invention, a layer of dark colorant is applied on the base paper surface by spraying, with the specific purpose of controlling opacity. The dark colorant can be sprayed on the base paper one side or both sides, simultaneously or as two separate stages. For purposes of the present invention, "a dark colorant" (e.g., a dark pigment and/or a dark dye) is a substance that imparts a black or blue color or tone to another material or mixture. The dark colorant can be a dye and/or pigment. Especially, the dark colorant can be a white pigment that has been dyed with a dark dye before applying onto the paper. Although the dark colorant might be formed from a white pigment and a dye, preferably the dark colorant used in this invention does not contain any white or near white pigments at the time it is applied onto the base paper.

The dark colorant can be composed of single particles like black iron oxide pigments. The dark colorant can also be structured single aggregate pigments as in carbon black pigments. Further, the dark colorant can be a mixture of single particles, structured pigments and dyes. Examples of dark colorants include, but are not limited to, carbon- containing pigments, iron oxide, and black or blue pigments or dyes. The carbon- containing pigments include carbon black (e.g., furnace and channel black), graphite, vitreous carbon, activated charcoal, activated carbon, and mixtures thereof.

In the process according to the invention, after the base paper is coated with a first layer, the surface is coated with a second coating layer containing white or near white pigments to achieve desired level of whiteness and desired level of paper absorbency properties for ink hold-out of the paper.

For purposes of the present invention, the term "white pigment" can also encompass near white pigments as well. Preferably these white or near white pigments have a fine particle size and can be inorganic or organic. Examples of inorganic pigments include, but are not limited to, kaolin, finely ground natural calcium carbonate, precipitated calcium carbonate, calcined kaolin, titanium dioxide, aluminum trihydrate, talc, calcium sulfate (gypsum), precipitated silica, calcined clay, and the like. Organic pigments include, but are not limited to, styrene polymers, urea-formaldehyde resins and the like. Preferably, if titanium dioxide is used as a white pigment, an extender is also preferably used, such as kaolin or calcium carbonate.

In an effort to minimize cost by reducing use of this higher cost pigment, other white or near white pigments may be used to "extend" the effect of the higher cost pigment. These other white pigments are referred to herein as extenders, and may be functionally defined as any white or near white pigment (as defined above). In some cases, the extender can be used entirely; that is, in cases where the extender is able to completely eliminate the need for more expensive white pigments, such as titanium dioxide. Any extender commonly used by those skilled in the art in coatings for paperboard and paper can be used as the white or near white pigment.

In a preferred embodiment of the invention both the first and the second layer are applied by spray coating. Prior to the coating of the second layer, the first coating layer has to achieve a sufficient dryness. The applied layer of dark colorant must carry the following layer of white pigments without migration of the layers into each other. It is important that the two layers are not mixed into one layer, as the two layers have distinctively different purposes. Non contacting dryer, such as infrared dryer, is preferably used for drying. Figure 2c illustrates a diagrammatic view of a double coating station with an infrared dryer (8).

The manufacturing stage for forming opacity layer in the process according to this invention can be applied on-line with the paper machine. Alternatively this may be done as a separate off-line stage, before coating with white pigments for whiteness and surface properties. Thus, the coating stations can be either on-line with the paper machine or installed as off-line coating. In one embodiment of the invention the coating of the first and/or second layer is done in coating stations, which are installed on-line with the paper machine. In another embodiment of the invention the coating of the first layer is done online with the paper machine and the coating of the second layer is done off-line.

The coated paper can be calendered after the first and/or second coating layer has been applied. Although the paper can be machine calendered after the first coating layer has been applied, normally calendaring is done only after the second coating layer has been applied. The coated paper can also be super-calendered. In one embodiment of the invention, the first coating layer is applied on the paper and the coated paper is machine calendered on-line with the paper machine, and then off-line, the paper is coated with the second coating layer and super-caledenred. It is also possible to apply further coatings on top of the second coating layer and then super-calender the coated paper.

The coated paper is calendered to improve the paper gloss and smoothness to a desired level. Physically, gloss is the intensity ratio of specularly reflected light to the incident light. The specular reflection occurs in the surface layer of paper because light that enters the sheet undergoes many reflections and loses directionality. Gloss therefore strongly depends on the surface smoothness or roughness of paper. Instruments for measuring gloss have a fixed angle for the incident and the reflected light direction. The nominal angle is usually 75°.

The coated paper can further processed into news, magazine, printing or writing paper, especially to copy paper, computer paper or book paper. In one embodiment of invention the multilayered paper, comprising the first and the second coating layers, is further coated with one or more coating layers.

In spray coating the surface of the coated layer can be doctored (Fig. 2b) by using a doctoring unit (7) to create an even surface suitable for rotogravure. However, the coating can be done without doctoring (Fig. 2a). After applying the coatins with spray boxes (5), the coated paper can be pressed between two rotating rolls (6) or the like, to smooth the coating. The doctoring unit (7) can be a traditional doctoring blade, a smoothner, an air knife or air brush or any combination of these. The smoothing of the the coating surface can also be done in combination of doctoring and passing between two rolls. In one embodiment of the invention (Fig. 2c), the doctoring is done only after the second coating.

It is an advantage of the invention that no significant amount of coating is doctored away. Contacting application methods such as blade coating or film-transfer coating always need between the web surface and the excess-coating-doctoring element a gap that determines the thickness of the applied coat. Due to this and other factors, the final coat weight is affected by quality variations in the base sheet, among other things by its profile deviations and surface roughness. In contrast, a spray coater applies to the web under all circumstances a coating layer of constant weight entirely unaffected by base sheet quality variations.

Another benefit of spray coating methods is that they permit coating application to a paper web at any point of a papermaking machine or coater. It is also possible that the spray boxes (5) are installed on opposite sides of the paper web (Fig. 2a), which allows simultaneous coating of both sides of the paper. The spray coaters can be located on the press or dryer sections of the machine, whereby the length dimension of the machine will not become substantially longer. Therefore the method is especially suitable for multilayer coating.

The price and quantity of raw materials used in papermaking have a crucial impact on the competitiveness of paper grades produced. Herein, spray coating allows the production of the base sheet from a cheaper stock of lower strength without essentially compromising the end product quality. Inasmuch this coating method is free from streaking that typically is a handicap of other methods by occurring during coat smoothing and metering, it also permits the use of filler-grade calcium carbonate that is cheaper than coating-grade calcium carbonate. In the spray coating method, the penetration of binder into the base web is minimal thus leaving the pigment or size particles onto the web surface.

Accordingly, it is now possible to produce, e. g., such newsprint whose characteristics facilitate color printing at an improved quality level without an essential cost increase in the printing paper. Using the spray-coating method, it is possible to vary the coat weight in a wide range from a few grams per square meter to as heavy coats are required. A specific benefit of the spray coating technique has been found therein that controlled application now becomes possible also for coatings so lightweight that they have been impossible or at least extremely complicated to achieve by means of conventional coating techniques. Further, spray coating can provide a substantial brightness increase even at very low coat weights.

The spray coating method is capable of controlling the porosity and absorbency properties of the web surface in a fashion not offered by other application techniques. This is possible, because the amount of coating can be controlled very exactly. The coat weight becomes uniform over the entire area of the web irrespective of deviations in the web profile, thus making it possible to apply an equal amount of coating on both the valleys and the crests of the profile. Improved brightness and opacity result from the uniform coat. Further, since spray coating does not force the coating pigment particles into the interior structure of the base sheet fiber matrix, the consumption of coating furnish is smaller. Hence, a spray coating system provides: a good quality of applied coat, is capable of controlling the porosity of the web surface, and allows a wide range of applicable coat weights and the use of cheaper raw materials. Further, the spray-coating system is suitable for use at high web speeds, it does not force the coating pigment particles into the interior structure and as compared with conventional coating methods spray coating is easier to implement and involves lower investment costs.

It is a further advantage that spray coating can be performed to a base sheet whose moisture content is higher and, hence, whose strength is lower than what has been acceptable earlier. Thus, the qualities of spray coated paper are different from those of paper grades manufactured using conventional coating methods.

Owing to these benefits, spray coating method can be used for producing novel grades of paper.

In each of the coatings described above, additional optional ingredients, such as binders and dispersants that are traditionally used in coatings used for paper can also be present. The binder is present in an amount sufficient to bind the pigments to the substrate. Examples of binders include, but are not limited to, starch or latex. Suitable dispersing aids include but are not limited to, polyacrylates, polyphosphates, or other conventional dispersion aids. Other ingredients which can be present include thickeners, surfactants, biocides, defoamers, binder insolubilizers, lubricants and other ingredients that modify the properties of the coating color or the dry coating on the sheet. The types and amounts of each of these components that can be optionally present are known to or can be readily determined by those skilled in the art and these types and amounts of components can be used in the coatings of the present invention.

For the determination of opacity the amount of light reflected from a single sheet, when a black background absorbs all light transmitted through the sheet, is measured (RO). Opacity is then the ratio R0/R ¥. Both reflectances, RO and R ¥, are measured with a wavelength spectrum centred at 557 nm. Typical values for opacity are from 70% to 96%, normally being greater than 90%. Brightness is the reflectance of paper using blue light. Blue light is used because papermaking fibres have a yellowish colour and because the human eye perceives blue colours as brightness. Brightness (R¥), also called reflectance factor, is measured by adding sheets to a pile until there is no change in the intensity of reflected light at the wavelength of 457 nm. The value of R¥ is the measured reflectance relative to a perfect reflecting diffuser. R¥ = 1 corresponds to the maximum intensity of reflected diffuse light. Typical values for the brightness of printing papers are from 70% to 97%.

The multi-layered paper according to the invention has opacity, which is higher than the opacity of conventional coated paper with a comparable weight per square meter.

Claims

1. A multi-layered paper, which comprises a base paper, a first layer and a second layer, wherein the first layer is an opacity layer comprising one or more dark colorants spray coated on at least one of the faces of the base paper, and the second layer comprises one or more white or near white pigments coated on the first layer.

2. A paper according to claim 1, wherein the base paper comprises pigments and mechanical pulp, chemical pulp, recycled paper or mixtures thereof.

3. A paper according to claim 1 or 2 having basis weights of 20 to 120 g/m².

4. A paper according to any of the claims 1 to 3, wherein the dark colorant comprises carbon pigments, iron oxide, black or blue pigments or dyes, or mixtures thereof.

5. A paper according to claim 4, wherein the carbon pigment is carbon black, graphite, vitreous carbon, activated charcoal, activated carbon or a mixture thereof.

6. A paper according to any of the claims 1 to 3, wherein the dark colorant is a white or near white pigment dyed with a dark dye.

7. A paper according to any of the claims 1 to 6, wherein the white or near white pigment is selected from the group comprising kaolin, natural calcium carbonate, precipitated calcium carbonate, calcined kaolin, titanium dioxide, aluminum trihydrate, talc, calcium sulfate, precipitated silica, calcined clay, styrene polymers and urea-formaldehyde resins.

8. A paper according to any of the claims 1 to 7, which further comprises in the base paper, in the first layer and/or in the second layer other ingredients selected from the group comprising fillers, extenders, fibers, reinforcements, additives, binders, dispersants, thickeners, surfactants, biocides, defoamers, binder insolubilizers and lubricants.

9. A paper according to any of the claims 1 to 8, wherein the first and the second layer are both applied by spray coating.

10. A paper according to any of the claims 1 to 9, wherein the first and second coating layers are independently applied in amounts from 1 g/m² to 15 g/m².

11. A paper according to any of the claims 1 to 10, which is printing or writing paper.

12. A process for preparing multi-layered paper, comprising providing a base paper, spraying a first layer of one or more dark colorants on at least one face of the base paper to form an opacity layer, and coating said first layer with a second layer of one or more white or near white pigments.

13. A process according to claim 12, wherein the coating of first and/or second layer is done on both sides of the base paper.

14. A process according to claim 12 or 13, wherein the coating of first and/or second layer is done in coating stations, which are installed on-line with the paper machine.

15. A process according to any of the claims 12 to 13, wherein the coating of the first layer is done on-line with the paper machine and the coating of the second layer is done off-line.

16. A process according to any of the claims 12 to 15, wherein the coated paper is calendered after the first and/or second coating layer has been applied.

17. A process according to any of the claims 12 to 16, wherein the surface of the first and/or the second coating is doctored after the coating layer has been applied.

18. A process according to any of the claims 12 to 17, wherein the coated paper is further coated with one or more coating layers.

19. A process according to any of the claims 12 to 18, wherein the first and/or second coating is dried using a non-contacting dryer or dryer cylinder.

20. A process according to claim 19, wherein the non-contacting dryer is an infrared dryer.

21. A process according to any of the claims 12 to 18, wherein the coated paper is further processed into printing or writing paper.

22. Use of spray coating for applying an opacity layer on paper.

23. The use according to claim 22 for the manufacturing of printing or writing paper.