Fibrous substrate for producing a porous coating base paper or prepreg, and method for the production thereof

Abstract

A fibrous substrate material for producing a porous coating base paper or prepreg comprises a planar impregnatable structure made of cellulose fibers, which contains at least one pigment species and optionally contains further additives conventional for paper. The cellulose fibers contain a proportion of 1 to 20 wt.-% of nanofibrillated cellulose (NFC). A method for producing the fibrous substrate material comprises the steps of: providing an aqueous suspension containing a cellulose containing material and an admixture of said pigment species and, optionally, further additives conventional for paper, sheet forming, drying.
The cellulose containing material contains a proportion of 1 to 20 wt.-% of NFC with a specific surface (SSA) of at least 125 m.sup.2/g.

Claims

1. A fibrous substrate material for producing a porous coating base paper or prepreg, comprising: a planar impregnatable structure made of cellulose fibers, which contains at least one pigment species and which optionally contains further additives conventional for paper, wherein the cellulose fibers contain a proportion of 1 to 20 wt.-% of nanofibrillated cellulose (NFC) with a specific surface (SSA) of at least 125 m.sup.2/g, wherein the fibrous substrate material is single-layered.

2. The fibrous substrate material according to claim 1, wherein the NFC portion is 5 to 10 wt.-%.

3. The fibrous substrate material according to claim 1, wherein the said pigment species is titanium dioxide.

4. The fibrous substrate material according to claim 1, wherein the said pigment species is iron oxide.

5. The fibrous substrate material according to claim 2, wherein the said pigment species is titanium dioxide.

6. The fibrous substrate material according to claim 2, wherein the said pigment species is iron oxide.

7. The fibrous substrate material according to claim 1, wherein the SSA of the NFC is at least 175 m.sup.2/g.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Examples of the invention will henceforth be described in more detail by reference to the drawings, in which are shown, in:

(2) FIG. 1 the specific surface area SSA in m.sup.2/g of NFC containing cellulose as a function of weight proportion of NFC; and

(3) FIG. 2 the light reflection (average taken in the band from 360 to 740 nm) on a black background as a function of the TiO2 content in wt.-%, for pressed sheets obtained with papers without NFC (triangles) and with papers with 5 wt.-% NFC (squares).

MODES FOR CARRYING OUT THE INVENTION

Example 1

(4) As shown in FIG. 1, the specific surface area SSA in m.sup.2/g of NFC containing cellulose increases linearly as a function of the weight proportion of NFC. While, in the example shown, it is only about 75 m.sup.2/g for conventional cellulose without NFC addition, it has values of around 225 m.sup.2/g in the case of 100% NFC; for more details see: Josset, S. et al. Energy consumption of the nanofibrillation of bleached pulp, wheat straw and recycled newspaper through a grinding process. Nordic Pulp & Paper Research Journal 29, 167-175 (2014).

(5) For a comparative evaluation of the properties of conventional coating base papers without NFC and of such base papers with NFC, paper blanks with a constant pulp density of 50 g/m.sup.2 and progressively larger TiO2 contents were produced by means of a sheet former (Estanit, Mlheim an der Ruhr, Deutschland, based on DIN EN ISO 5269-2-DIN 54358).

(6) Bleached pulp made of wood fibers was ground by a standard method to a Schopper-Riegler value of 35 SR.

(7) A first 1 wt.-% suspension of this pulp was prepared to produce standard paper blanks.

(8) A second 1 wt. pulp suspension with 5 wt.-% NFC (related to the total pulp amount) was prepared to produce modified paper blanks. The NFC made of softwood fibers (ECF, company Stendal, D) was produced by the method described in the following reference: Josset, S. et al. Energy consumption of the nanofibrillation of bleached pulp, wheat straw and recycled newspaper through a grinding process. Nordic Pulp & Paper Research Journal 29, 167-175 (2014).

(9) For sheet production, in each case, 150 mL of a suspension were diluted to 4 L (corresponding to 50 m.sup.2/g pulp in the paper produced). To this pulp, TiO2 was added in progressively increasing amounts (0.1 g to 2.0 g of a 10-wt. suspension). Each mixture was adjusted to a pH of about 6.3 by means of Al.sub.2SO.sub.4 and treated by means of a homogenization system (Ultraturrax) for 30 seconds at 15,000 rpm. Sheets were then produced by vacuum filtration (according to DIN EN ISO 5269-2) and subsequently vacuum-dried. A sample was taken from each leaf in order to determine its TiO.sub.2 content by ashing (900 C., 10 min).

(10) The remaining material was pressed onto a black background with an overlay paper impregnated with aqueous melamine resin to form a high gloss composite (60 bar, 2 min at 150 C., re-cooling: 5 min, to about 45-50 C.). The average light reflection of these pressed sheets was determined by means of a spectrophotometer (Konika Minolta, CM-2500D) between 360 and 740 nm.

(11) As shown in FIG. 2, the addition of 5 wt.-NFC results in a significant increase of the light reflection capacity. For example, at a TiO2 content of about 17 wt.-% the light reflection increases from about 49% (without NFC) to about 54% (with NFC). Moreover, the behavior in the flattening region of the curves at higher TiO2 content is particularly remarkable. For example, to achieve a reflection of 54%, conventional paper requires a TiO2 content of about 22 wt.-% which can be reduced to about 17 wt.-% in the case of addition of 5 wt.-% NFC. This corresponds to 22% saving of TiO2.

Example 2

(12) Several sections of monolayer fibrous substrate material were produced using NFC of various types, i.e. with different values of the specific surface area (SSA), in the above-mentioned manner. The ash content in wt.-% was used as a standard measure of the retention capacity of the mineral components, here in particular of titanium dioxide. The following results each are given as the mean of 3 measurements.

(13) For the production without NFC considered as reference base, an ash content of 30.8 wt.-% was found.

(14) Using an NFC with a SSA of about 95 m.sup.2/g (prior art), the ash content was 32.6 wt.-%, which corresponds to an absolute increase of 1.8 wt.-% compared to the reference.

(15) Using an NFC with a SSA of about 165 m.sup.2/g (according to the present invention), the ash content was 38.9 wt.-%, which corresponds to an absolute increase of 8.2 wt.-% compared to the reference.

(16) Using an NFC with a SSA of about 225 m.sup.2/g (according to the present invention), the ash content was 43.5 wt.-%, which corresponds to an absolute increase of 12.7 wt.-% compared to the reference.