FI114977B - Printing paper and method for producing printing paper - Google Patents

Description

114977

Printing paper and method for producing printing paper

The invention relates to printing paper, in particular inkjet printing paper. The invention also relates to a method for producing printing paper, in particular ink-jet printing paper (so-called ink-jet paper).

As the use of personal computers and digital cameras increases, the need for high-quality prints has increased greatly and will continue to increase 10. Such print media has either a paper or a plastic film as a substrate on which is applied an ink-receiving layer, which may also be referred to as an absorption layer.

Em. device-generated images are commonly used to print ink-jet printers. As inkjet printers become more common, inkjet printing papers have begun to demand better features. The substrate for such printing papers is usually a substrate made of paper pulp. base paper with an absorbent layer on top. The purpose of the ab sorption layer is to receive the color jet of the ink jet printer 20 and to absorb the liquid in the ink, whereby the toner in the ink remains on the surface of the printing paper to form a sharp image. Due to the requirements for the absorption layer, the development of printing papers has focused specifically on the development of absorption layer materials and methods of application. Although the layer on top of the substrate 25 may be referred to as an absorption layer, it may: often have two or more layers which may differ from each other; * in composition and / or application step, and serve different purposes in the printing paper.

: 30 Ideally, the absorption layer would be such that it absorbs ink rapidly into the solvent layer vertically (Z), but does not spread the ink at all in the X and Y directions, i.e., in the plane of the image being printed. Further, the layer may be such that it chemically binds the ink dyes permanently to the receiving layer, and does not alter the dye nature or color tone of the ink.

2 1 1 4977

A long known method of making printing paper is to apply an aqueous solution or dispersion of an absorbent material to the substrate by some known coating method which, upon drying, forms an absorbent layer on the substrate. The printing paper produced in this way is shown e.g. EP-650850.

Care has been taken to avoid drying by selecting the material of the absorbent layer so that it can be applied by extrusion coating technology, whereby instead of dewatering it is sufficient to allow the layer applied in the molten space to cool. The basic raw material for the absorption layer is then a polymer applied in the molten state which, when solidified, forms an absorption layer. For example, EP-1018438 and WO 01/62510 disclose the formation of an absorption layer by extrusion coating, for example, from polyvinyl alcohol of extrudable quality. The polymer to be applied by extrusion provides a hydrophilic absorption layer which may also be doped with pigments. It is mentioned in the same publications that a thinner surface layer containing pigment and binder can be applied to the layer applied during the extrusion step, which first receives the ink jet of the resultant ink and produces a dye image. The separately applied topcoat can provide a surface paper of the printing paper; .. femininity (smoothness, shine) to fit. EP-1018438 discloses, for example, that the surface layer to be applied as an aqueous phase may have: *. up to about 10% by weight based on the dry weight of the pigments so as not to diminish the gloss. Only if nanoscale organic is used. ' pigments with such coatings, according to the publication, may be larger.

The surface layer pigments improve the absorbency of the surface as compared to only i. · * 30 solid binders which, on the other hand, achieve a higher gloss.

• V, · 'For inkjet printing purposes, a paper with good water absorption and good gloss and smoothness would be optimum! · ·. a picturesque solution.

35 In addition to the final characteristics of the print paper, you should pay attention '! manufacturing process. Thus, by replacing the application of the absorption layer with water by extrusion of molten polymer, process advantages have been achieved. Less attention has been paid to the optimization of the absorption layer raw materials and their mixing methods.

It is an object of the present invention to provide a printing paper made by extrusion coating technology in which the properties of the absorption layer are optimal. It is also an object of the invention to provide a process which makes it possible to produce printing paper under better process conditions in terms of the quality of the final product than before. To accomplish this purpose, the printing paper according to the invention is essentially characterized in what is set forth in the characterizing part of the appended claim 1.

The absorption layer contains talc or barium sulphate as pigment or a mixture thereof in which they may be present in a suitable ratio. These pigmen-15 teas can increase the absorbency and drying rate of printing paper, especially talc. Barium sulphate, on the other hand, has a lightening effect. By using a mixture of the above pigments, particles of different sizes are obtained in the absorption layer. When the pigment consists of two different fractions with different average particle sizes, a high degree of fill is achieved in the polymer matrix.

As an absorption layer extrudable matrix polymer, to which the above-mentioned matrix polymer.

; The pigments are distributed, using a polyvinyl alcohol having a degree of hydrolysis of 60-80%, a molecular weight of 10000-30000, preferably 15000-25000, and a degree of polymerization 300-1000, preferably 500-700.

The polymer has a melt index of 1-20 g / 10 min, preferably 2-7 g / 10 min (190 ° C; 2.16 kg). The relatively low degree of hydrolysis of polyvinyl alcohol increases the absorptive capacity.

, ·. The amount of inorganic pigment in the absorption layer is preferably 20-50% by weight, more preferably 25-40% by weight. The pigment may contain pigments other than talc and / or barium sulphate, but preferably at least 90% by weight of the total inorganic pigments are present.

The absorption layer is applied on a substrate by coextrusion with an intermediate layer through which the absorption layer is adhered to the substrate. In this way, in one extrusion step, layers can be applied to the substrate, one of which (absorption layer) can be selected according to its absorption properties and the other (intermediate layer) according to its adhesion properties (both substrate and absorption layer). fit.

The absorbent layer preferably has a basis weight of 10-40 g / m 2, more preferably 20-30 g / m 2. The thickness of the layer and the size and amount of inorganic pigment particle coils are preferably selected so that the absorption layer has an average of at least 3 layers in the Z direction (thickness direction).

On top of the absorption layer, a surface layer obtained by applying an aqueous pigment-containing binder solution to the surface of the printing paper may be provided.

When a large amount of finely divided pigment, e.g. colloidal silica, is used on the surface layer of the absorption layer applied by extrusion, a good gloss, smoothness and absorbency are obtained.

The process for producing the printing paper according to the invention is characterized in that the absorption layer is formed by extrusion of a compound having the aforementioned polyvinyl alcohol and the said pigment. -i in a solid granulate obtained by laser mixing. The proportions of the constituents of the granulate correspond to the ratio of polymer to pigment in the absorption layer. By using a compound in which the substances are premixed with one another, a product having a better homogeneity of the absorption layer can be obtained. Such a compound is applied by coextrusion with a / 30 interlayer, e.g., a barrier interlayer. at the same time to the surface of the substrate such that the interlayer remains as a continuous layer between the substrate and the absorption layer formed of the compound while attaching the latter to the substrate.

»35 The invention will be described in more detail below with reference to the accompanying drawing" · in cross-sectional view.

114977 5

The drawing shows a ready-to-print paper comprising a tray 1 serving as a support structure for the paper. An absorbent layer 2 of molten polymeric material is applied as an extrusion coating on the substrate. There is a special intermediate layer 2a between the absorption layer 2 and the substrate 1, which is also formed of a plastic applied in the same extrusion coating step. This interlayer 2a attaches the absorbent layer 2 to the substrate 1 and its significance is explained below.

10 The purpose of Tray 1 is to form a support and support structure for printing paper, and is most commonly of paper or paperboard. Although paper or board made from various fiber raw materials are commonly used materials, other materials than the actual paper products, such as polymer films, can be used. When using paper or board, it may be coated by known paper and board coating methods. The paper or board may also be coated with a layer of plastic on the side that comes in contact with the absorption layer 2. Such a plastic layer may also be pigmented. In selecting the plastic layer, sufficient adhesion to the material of the intermediate layer 2a should be considered. The plastic layer on the paper or cardboard can also act as a barrier layer to prevent water: .. from being absorbed from the absorption layer to the paper, so that the intermediate layer 2a applied simultaneously with the absorption layer 2 does not necessarily have to have barrier properties. According to a preferred embodiment, * ·! · '·! The absorption layer 2 and the intermediate layer 2a are applied to bare paper (not coated with plastic I) by coextrusion, whereby a coating which acts as a barrier layer can be obtained at the same time.

»*

The material of the absorption layer 2 should be of suitable polymeric polymeric grade. In selecting the absorption layer, it should be noted that in printing, the colors remain mostly on the topsheet 3, which will be described below, and the water acting as a solvent will penetrate the absorbent layer below, and water may return to the surface as the ink dries. The raw material for absorption sugar 35 is a thermoplastic hydrophilic compound containing polyvinyl alcohol and finely divided inorganic pigments to improve the drying rate and increase the absorption capacity.

114977 6

The matrix polymer forming component of the absorption layer (polyvinyl alcohol) has a certain melt-processing temperature at which it can be applied by extrusion to a substrate. The temperature profile (temperatures of the various parts of the extruder) in the extruder of the polyvinyl alcohol compound is typically 5 140-230 ° C.

The compound contains pigments as a filler to control the absorption properties of the absorption layer 2. In a compound in the form of a solid granulate, the polymer to be extruded is doped with pigments in the desired proportion. The pigments are present in an amount of 20-50% by weight in the absorption thio layer, preferably 25-40% by weight. The pigment is talc or barium sulphate or a mixture thereof to improve the drying rate and increase the absorption capacity of the printing.

The degree of hydrolysis of the polyvinyl alcohol in the compound is 60-80%, the molecular weight is 10000-30000, preferably 15000-25000, and the degree of polymerization is 300-1000, preferably 500-700. Compound melt index 1-20 g / 10 min, preferably 2-7 g / 10 min (190 ° C; 2.16 kg).

The compound (particles containing the polymer and filler) is melt-melted in an extruder and extruded onto the surface of substrate 1. .. to form an absorption layer. The absorption layer 2 is applied by coextrusion with a polyolefin based plastic:. forming a lower intermediate layer 2a which acts as a barrier layer,! In selecting a polymeric material for the ESA * * layer 2a, it should be noted that it attaches the absorption layer 2 to the substrate 1. The total amount of absorption layer 2 to be extruded onto the substrate 1 may be 10-40 g / m 2, preferably 20-30 g / m 2, and the amount of interlayer or barrier layer 30 2a is 2-30 g / m 2, preferably 8-20 g / m 2. The basis weight of the barrier layer 2a is normally lower than the basis weight of the absorption layer 2.

• * ·

On the surface of the absorption layer 2 there is applied a so-called. top-coating layer, namely: · 35 top coat 3. The top coat can be applied as a water-based composition; as described in more detail below. The topsheet 3 can also be applied in several successive stages. These sub-layers of surface layers formed in successive application steps are described in the drawing by reference numerals 3a, 3b and 3c. The compositions of the various sublayer layers of the topsheet may vary, and in particular the topsheet 3c, which forms the outer surface of the finished printing paper, which the ink 5 first hits in inkjet printing, and which forms the image, may be of a different composition. The surface layer 3 is usually thinner on a basis weight basis than the absorption layer 2 applied by extrusion, e.g. 1-7 g / m 2, preferably 2.5-4.5 g / m 2. Possible ways of applying the topcoat are described below.

10

The surface layer 3 acts as an ink-receiving layer (Tintenaufnahmeschicht) on the finished printing paper. Such a layer, when it has good smoothness and gloss, reproduces, for example, ink remaining in inkjet ink printing with good resolution and high color density. The top layer has a pigment for absorbency and a binder for attaching the pigment. The ratio of pigment to binder and the choice of the above ingredients can influence the surface properties.

In the drawing, the topsheet 3 has three layers, a bottom layer 3a, a middle layer 3b and a top layer 3c applied to the surface of the absorption layer 2, which forms the outer surface of the finished printing paper. The surface layer 3 contains pigment such that its proportion is the size of the surface layer 3; ·; at least 40 wt%, preferably between 40 and 80 wt%, of the total dry weight.

25 Inkjet printing results have been particularly good at printing paper. in pigments with a pigment to binder ratio close to 1: 1, e.g. between 45:55 and 55:45. Other binder materials usually contain more than 90% by weight of binder. Other possible agents include cationic additives (eg, polydadmac), optical brighteners, antifoams, crosslinkers (eg, glyoxal and zirconates) and wetting agents. The different layers of the topsheet 3 are applied in different stages and their compositions may be different, or at least the top one, forming the outer surface. layer 3c may differ from one or more of the lower layers 3b, 3a, which are usually one or two layers of the same composition.

114977 8

The pigment used is colloidal silica. Due to the large amount of pigment and the quality of the pigment, a good gloss and good water absorption of the ink are obtained on the surface, despite the fact that under the surface layer 3 there is a non-gloss absorption layer 2 formed by extrusion coating. Colloidal silica may be anionic or cationic.

The topsheet 3 can be applied over the absorption layer in one or more successive steps, in which case two or more sublayer layers are obtained. The layer-forming composition may be applied by the aqueous solution or dispersion method. The application may be by gravure printing, flexo printing, roller coating, reverse engraving, blade coating, airbrushing or a combination of methods. The topsheet may be applied on-line in the same line where the absorption layer 2 is formed by extrusion 15 onto the substrate, or off-line on a previously extruded and intermittently rolled substrate.

The topsheet 3 may be applied as an aqueous solution in which the pigment is dispersed and in which the binder is a polymer such as polyvinylalcohol, polyvinylpyrrolidone, carboxymethylcellulose, polyethylene oxide or polyoxyalkylene. The pigment in the finished layer is at least 40 wt% dry weight, preferably between 40 and 80 wt%. The total thickness of the topsheet 3 may be 1-7 g / m2, preferably 2.5-4.5 g / m2.

* ♦

The amount of water to be evaporated is small due to the thin layer.

!: 25 ♦ *

The surface layer 3 can be formed as follows (parts in dry weight):

Lower layer 3a and middle layer 3b: 45-55 parts of colloidal silica and 45-55 parts of a binder, for example polyvinyl alcohol, forming 100 parts by weight of 1-3 g / m 2 on each layer.

: 30 Top layer 3c: 45-55 parts colloidal silica and 45-55 parts binder, for example polyvinyl alcohol, forming a total of 100 parts. In addition, 1-4 parts of the crosslinker, e.g. glyoxal or zirconate, are added. The basis weight is 1-3 g / m2.

ί 35 The layers are dried in between before the next application.

114977 9

When the pigment and the binder are used in the surface layer 3 in the above ratios, the paper is optimal for printing. When using a crosslinker on the top layer (no need to use on the layers below), there is also a universal printing paper 5 that does not distort black with any printer, thus avoiding the copper phenomenon (discoloration) especially in Epson black. A particularly good inhibitor of the copper phenomenon is the glyoxal crosslinker.

The polyolefin-based plastic 10 used as the material of the barrier layer 2a may be a copolymer, a terpolymer or an ionomer. This co-extrusion layer, which is formed simultaneously with the absorber layer, prevents ink solvent or ink from entering paper or board substrate 1, thereby eliminating the cockling effect on paper or board due to moisture, the barrier layer may have 15 color pigments to adjust 0.1-20%, e.g. The layer thickness may be from 2 to 30 g / m 2, typically 8 to 20 g / m 2. The barrier layer 2a also reduces the roughness caused by the paper or board-based substrate. The barrier layer also improves the runnability in extrusion, since the runnability of polyvinyl alcohol per se is poor, as well as its adhesion to paper or board, which would require the use of water or an aqueous dispersion to increase the likelihood of the aforementioned cockling phenomenon. It is essential to achieve good adhesion of the barrier layer 2a to both paper or board and thermoplastic:. hydrophilic absorption layer 2 polymer (PVOH).

25

• I

.! The temperature profile (temperatures of the various parts of the extruder) of the polyolefin-based resin is typically 180-300 ° C.

* · »·

One example of a barrier layer material that can be used, in particular, for extrusion of paper or paperboard by coextrusion: 30 is a maleic anhydride / ethylene / acrylic ester terpolymer. The random copolymer of this ethylene, alkyl acrylate and maleic anhydride is suitable for use in coextrusion, for example with polyvinyl alcohol, due to its good adhesion, and also provides good adhesion to substrate 1.

114977 10

The barrier layer 2a may also consist of a plurality of plastic layers having different compositions. These layers are coextruded simultaneously with the absorption layer.

5

The molten mixing compound may also be used as a starting material for the barrier layer 2a, but conventional dry mixing techniques may also be used to mix its materials prior to extrusion in the ratio required by the layer 2a composition.

10

During the coextrusion of the absorption layer and the barrier layer, the surface of the cooling cylinder is shiny (Rmax value 0.1-0.9 µm).

The extrusion or coextrusion process may be known, that is, where a molten polymer film is applied to the surface of the substrate in the form of a continuous moving web from the extruder die, which, when solidified, forms the desired layers on the substrate.

On the back of paper or paperboard tray 1 (opposite side to print side 20), a plastic protective layer can be used to prevent water from being absorbed from that side and to improve the mechanical properties of the paper during printing. This layer is marked with vii -: # # 1a in the drawing. The backing can be applied, for example, by extrusion po-: ·. a layer of ethylene which can be applied by coextrusion in a combination of two different qualities /.), eg LDPE against the surface of substrate 1 and further: * hdpe.

'·' Although the invention is referred to as printing paper, the substrate 1 can be a non-paper product and thus describes a product used in the same way as paper.

•

The invention will now be described by the following non-limiting examples. The backing resin in all products was 15 gsm PE-HD (density 940 kg / m3). The base paper in all examples was 35,100 gsm (g / m2) woodfree supercalendered. The barrier layer was all: in the Examples, 10 g Lotmer 3210 (terpolymer of ethylene acrylic ester and maleic anhydride), comonomer content 9%, melt index 114977 115 g / 10min (190 ° C / 2.16 kg). Parts or percentages are by weight unless otherwise indicated.

Example 1 5

Absorption layer 25 gsm: Vinex2144 70% (PVOH, density 1250 kg / m3) + Blanc fixe super F 30% (barium sulphate, average particle size 1 µm, density 4.4 kg / dm3).

Surface layer in water dispersion 4 gsm: Mowiol 8-88 (PVOH) 60 parts + 10 Ludox SK-I (colloidal silica) 40 parts + CartabondTSI (Glyoxal) 2 parts

Example 2 Absorption layer 25 gsm: Vinex2025 70% (PVOH, density 1250 kg / m3) + FinntalcIO 30% (Talc, average particle size approx. 2 µm, density 2750 kg / m3).

Surface layer in aqueous dispersion 3 gsm: (Alcotex72.5 (PVOH) 90 parts + Gasil 35M (synthetic amorphous silica) 10 parts + Cartabond TSI 20 (glyoxal) 5 parts

Example 3; ·. Absorption layer 25 gsm: Ecomaty AX-2000 (PVOH, density 1270 kg / m3) 25 60% + Blanc fixe super F 10% (barium sulphate, average particle size 1 µm, density 4.4 kg / dm3) + FinntalcCIO 30% (talc) , Avg.

: particle size approx. 2 µm, density 2750 kg / m3).

Surface layer in aqueous dispersion 4 gsm: Imagel MA (gelatin) 80 parts + PVP K90 (polyvinylpyrrolidone) 20 parts + Zonyl FSN (fluoro-30 surfactant) 3 parts

Example 4

Absorption layer 25 gsm: Ecomaty AX-2000 (PVOH, density 1270 kg / m3) 35 60% + Blanc fixe super F 35% (barium sulfate, average particle size 1 µm, density 4.4 kg / dm3) + FinntalcCIO 5% (Talc, Avg.

particle size about 2 µm, density 2750 kg / m3).

1 1 4977 12

Surface layer in aqueous dispersion 3 gsm: IJ-2 (polyurethane) 50 parts + IJ-50 (polyurethane) 50 parts + Gasil 35M (synthetic amorphous silica) 10 parts + CR-5L (aliphatic epoxy, functional crosslinker) 2 parts.

5

Claims (9)

A printing paper, in particular for ink-jet printing, comprising a substrate (1) and on it an absorbent layer (2) spread by extrusion coating technology which contains as a melt-processable polymer a polyvinyl alcohol (PVOH) and a pigment distributed in the polymer, characterized in that the polyvinyl alcohol has the following properties: 10. degree of hydrolysis of 60-80% molecular weight of 10,000-30,000 degree of polymerization of 300-1000 melt index of 1-20 g / 10 min (190 ° C; 2.16 kg), and that the pigment is taik or barium sulphate or a mixture thereof, and an inorganic pigment, of which the above-mentioned substances form at least 90% by weight, is 20-50% by weight in the absorption layer, and that the absorption layer (2) is spread on the substrate in coextrusion with an intermediate layer (2a), by means of which the absorption layer is attached to the substrate (1). 20 Printing paper according to claim 1, characterized in that the intermediate layer (2a) has a weaker water absorption capacity than the absorption layer, in which it acts as a barrier layer between the absorption layer! '(2) and the substrate (1). ; 25 Printing paper according to claim 2, characterized in that the base material of the barrier layer (2a) is a polyolefin-based plastic. • · Printing paper according to any of the preceding claims, characterized in that the polyvinyl alcohol has a molecular weight of: 15,000-25,000, a degree of polymerization of 500-700 and a melt index of 2-7 g / 10 min. : 5. Printing paper according to any of the preceding claims, characterized in that the pigment is a mixture of barium sulphate and: and the average particle sizes of the above two pigment types are different. 114977 Printing paper according to any of the preceding claims, characterized in that the surface weight of the absorbent layer (2) is 10-40 g / m2, preferably 20-30 g / m2. 5 Printing paper according to any of the preceding claims, characterized in that on the absorption layer (2) there is a surface layer (3) having a lower surface weight, which contains adhesives and pigments. 10 8. A method of producing a print paper for use especially in ink jet printing, in which a polyvinyl alcohol and pigment containing absorbent layer (2) is spread on a substrate (1) by extrusion coating technology, characterized in that the absorbent layer (2) is formed. extrusion of a compound in which the polyvinyl alcohol polymer has the following properties: degree of hydrolysis of 60-80% molecular weight of 10,000-30,000 degree of polymerization of 300-1000 melt index of 1-20 g / 10 min (190 ° C; 2.16 and the pigment of Taik or Barium sulphate or a mixture thereof is in a mixture of solid particles which have been formed by melt mixing the components with each other, and absorption. the layer (2) is spread in coextrusion with the intermediate layer (2a), by means of which the absorption layer is attached to the substrate (1). ! 25 9. A process according to claim 8, characterized in that the compound:: contains 20-50% of an inorganic pigment, of which taik or barium sulphate or a mixture thereof forms at least 90% by weight.