阅读说明：本技术 具有间隔性能和高uv-灰化稳定性的层压材料颜料 (Laminate pigments with spacing properties and high UV-ashing stability ) 是由 福克·约根斯 福克·史密特 于 2019-09-16 设计创作，主要内容包括：本发明涉及一种具有高不透明度和UV-灰化抗性的二氧化钛颗粒,其包含两个二氧化硅涂层和至少一个氧化铝涂层,涉及获得所述颗粒的方法,涉及所述颗粒用在获得装饰纸层压材料或装饰箔的方法中的用途。本发明还涉及一种含有所述涂覆的二氧化钛颗粒的装饰纸层压材料或装饰箔。(The invention relates to titanium dioxide particles having high opacity and UV-ashing resistance, comprising two silica coatings and at least one alumina coating, to a method for obtaining said particles, and to the use of said particles in a method for obtaining decorative paper laminates or decorative foils. The invention also relates to a decorative paper laminate or a decorative foil containing the coated titanium dioxide particles.)

1. A process for obtaining coated titanium dioxide particles, said process comprising the steps of:

(i) providing an aqueous suspension of uncoated titanium dioxide particles;

(ii) adding phosphoric acid to the suspension to adjust the pH of the suspension to a value of 2 or less;

(iii) adding an alkaline silica precursor to the suspension such that, after said adding, the suspension has a pH of from 7 to 8, thereby forming a first silica coating on the particles;

(iv) adding an acid to the suspension to adjust the pH of the suspension to a value of 2 to 3;

(v) adding an alkaline silica precursor to the suspension such that, after said adding, the suspension has a pH of 4 to 5, thereby forming a second silica coating on the first silica coating; and

(vi) at least one alumina coating is applied over the second silica coating.

2. The method of claim 1, wherein the step of removing the metal oxide layer comprises removing the metal oxide layer from the metal oxide layer

(vii) adding an acidic alumina precursor to the suspension in order to form the at least one alumina coating on the second silica coating in step (vi).

3. The method of claim 2, wherein the step of removing the substrate comprises removing the substrate from the substrate

(vii) after step (vi), adding a basic alumina precursor to the suspension in step (vii) to form a second alumina coating on the first alumina coating.

4. A method according to any of claims 2 or 3, characterized in that

(vii) after addition of the acidic alumina precursor in step (vi), the pH of the suspension thus obtained is from 1 to 5, preferably from 2 to 4, more preferably 3; and/or

After addition of the basic alumina precursor in step (vii), the pH of the suspension thus obtained is 5 to 9, preferably 6 to 8, more preferably 7.

5. Method according to any of claims 2 to 4, characterized in that

(i) The acidic alumina precursor is selected from the group consisting of aluminum sulfate, aluminum nitrate, aluminum chloride, and preferably aluminum sulfate; and/or

(ii) The alkaline alumina precursor is selected from sodium aluminate, aluminum acetate, and preferably sodium aluminate; and/or

(iii) The alkaline silica precursor is selected from sodium silicate, potassium silicate, and lithium silicate, and is preferably sodium silicate.

6. Method according to any one of claims 1 to 5, characterized in that

In step (ii), in addition to the phosphoric acid used, an acid selected from the group consisting of: sulfuric acid, nitric acid, titanium oxychloride, titanyl sulfate, hydrochloric acid, and combinations thereof; and/or

In step (iv), the acid is selected from the group consisting of sulfuric acid, nitric acid, titanium oxychloride, titanyl sulfate, hydrochloric acid, phosphoric acid, and combinations thereof, preferably selected from the group consisting of sulfuric acid and titanium oxychloride, and more preferably titanium oxychloride.

7. Method according to any one of claims 1 to 6, characterized in that

In step (b)In step (ii), P represents the total weight of the uncoated titanium dioxide particles₂O₅Calculated, phosphoric acid is added in an amount of 1 to 4 wt.%, preferably 2 to 3 wt.%, more preferably 2.5 wt.%.

8. The method according to any one of claims 1 to 7, characterized in that

In each of steps (iii) and (v), the silica precursor is added in an amount such that: each obtained silica coating is, independently of the other, from 0.6 to 8 wt.%, preferably from 1.6 to 6.5 wt.%, and more preferably from 2.6 to 5 wt.%, relative to the total weight of the coated particle.

9. Method according to any one of claims 1 to 8, characterized in that

In each of steps (vi) and (vii), the alumina precursor is added in an amount such that: each obtained alumina coating is, independently of the other, 0.8 to 4.2 wt.%, preferably 1.3 to 3.7 wt.%, and more preferably 1.8 to 3.2 wt.%, relative to the total weight of the coated particle.

10. Method according to claim 8 or 9, characterized in that

In step (iii), the silica precursor is added in an amount such that: the silica coating obtained is 2 to 8 wt.%, preferably 3.5 to 6.5 wt.%, and more preferably 5 wt.%, relative to the total weight of the coated particle;

in step (v), the silica precursor is added in an amount such that: the silica coating obtained is 0.6 to 4.6 wt.%, preferably 1.6 to 3.6 wt.%, and more preferably 2.6 wt.%, relative to the total weight of the coated particle;

in step (vi), the amount of the alumina precursor added is such that: the obtained alumina coating is 0.8 to 2.8 wt.%, preferably 1.3 to 2.3 wt.%, and more preferably 1.8 wt.%, relative to the total weight of the coated particle; and is

In step (vii), the alumina precursor is added in an amount such that: the obtained alumina coating is 2.2 to 4.2 wt.%, preferably 2.7 to 3.7 wt.%, and more preferably 3.2 wt.%, relative to the total weight of the coated particles.

11. Method according to any one of claims 1 to 10, characterized in that

The method further comprises the steps of separating the coated particles from the suspension, washing, drying, and grinding the coated particles, and using additives.

12. The method of claim 11, wherein the step of determining the target position is performed by a computer

Alkali metal nitrate salt is used as an additive and added to the titanium dioxide particles during drying and/or grinding, the alkali metal nitrate salt being selected from potassium nitrate and sodium nitrate.

13. Coated titanium dioxide particles obtained by the process according to one or more of claims 1 to 12.

14. Use of the coated titanium dioxide particles according to claim 13 in a process for obtaining a decor paper laminate or a decor foil.

15. A decorative paper laminate or decorative foil comprising the coated titanium dioxide particles of claim 13.

Technical Field

The invention relates to titanium dioxide particles having high opacity and UV-ashing resistance, comprising two silica coatings and at least one alumina coating, to a method for obtaining said particles, and to the use of said pigments in a method for obtaining decorative paper laminates or decorative foils. The invention also relates to a decorative paper laminate or a decorative foil containing the coated titanium dioxide particles.

Background

In paper laminate applications, white or light-colored papers are required to have high opacity and good UV-ashing resistance. Decorative papers and foils are widely used in the production of decorative surfaces and generally consist of a stack of papers impregnated with melamine resin and cured under heat and pressure. The laminate serves not only as a face paper covering the surface of the unsightly wood material, but also as a carrier for functional paper. Paper is usually made on a paper machine by mixing a pulp suspension with a white pigment or a suspension thereof with various additives. As a white pigment, titanium dioxide is commonly used in high-end laminates. The titanium dioxide pigment imparts a white color to the laminate and provides the opacity necessary to hide the aforementioned unsightly wood substrate. The finished paper laminate thus contains titanium dioxide pigment with a small amount of entrained moisture and oxygen. Titanium dioxide is known to have photocatalytic properties when exposed to UV-radiation. Incorporated into laminates and exposed to UV-radiation in the presence of moisture and oxygen, the laminates can be grayed out to varying degrees, which is undesirable.

Titanium dioxide pigments for decorative papers with low UV-ashability tendency are already well established and are characterized by the use of aluminium phosphate and alkaline nitrate to inhibit UV-ashability. For example, US 5,114,486 discloses coating zinc/aluminum phosphate to improve UV-ashing resistance. Document US 5,785,748 describes a method for obtaining a uniform coating on titanium dioxide with aluminium phosphate, wherein a mixture of concentrated phosphoric acid and an aluminium compound is added to a suspension containing titanium dioxide, and the aluminium phosphate is then precipitated at a pH of 3.5 or higher. Application WO 2004/061013 a2 discloses a titanium dioxide pigment with good UV-ashing resistance for use in decorative paper laminates which have an aluminium phosphate coating and exhibit particularly advantageous surface properties in terms of isoelectric point and zeta potential. The aluminum phosphate layer was precipitated while constantly maintaining the pH at 7. In an advanced development of the latter method according to DE 102006045244 a1, the coated pigment is finally subjected to a heat treatment. However, most of these pigments exhibit common opacity properties compared to pigments used in coating applications.

Those pigments used in coating applications have other targeted properties, such as high opacity, compared to pigments used in paper laminates. US 3,510,335 describes titanium dioxide pigments having a special type of post-treatment, which is particularly suitable for producing matt latex paints. The pigment particles are coated with a relatively high content of silica and alumina of at least 5 wt.%, relative to the total weight of the pigment. The coating is applied by a precipitation method aimed at obtaining a particularly voluminous, porous and "fluffy" surface coating. However, UV-ashing resistance is unsatisfactory in laminate applications, particularly in high end laminate applications.

Accordingly, there is a need in the art to provide coated titanium dioxide particles having excellent UV-ashing resistance and good opacity at the same level of coloration, which makes the particles particularly suitable for laminate applications.

Disclosure of Invention

The object of the present invention is to provide coated titanium dioxide particles which have excellent UV-ashing resistance and good opacity at the same level of coloration.

The object is achieved by coated titanium dioxide particles obtained by a process comprising the steps of: (i) providing an aqueous suspension of uncoated titanium dioxide particles; (ii) adding phosphoric acid to the suspension to adjust the pH of the suspension to a value of 2 or less; (iii) adding an alkaline silica precursor to the suspension such that, after said adding, the suspension has a pH of from 7 to 8, thereby forming a first silica coating on the particles; (iv) adding an acid to the suspension to adjust the pH of the suspension to a value of 2 to 3; (v) adding an alkaline silica precursor to the suspension such that, after said adding, the suspension has a pH of 4 to 5, thereby forming a second silica coating on the first silica coating; and (vi) applying at least one coating of alumina over the second silica coating.

The titanium dioxide particles obtained by the process of the invention show good opacity at the same level of coloration compared to the known particles used in laminate systems, but more excellent UV-ashing resistance compared to the ordinary particles. Furthermore, without wishing to be bound by any particular scientific theory, it is believed that the combination of process conditions, in particular the narrow pH ranges in steps (ii), (iii) and (v) and the use of phosphoric acid in step (ii), both provide good opacity and UV-ashing resistance.

Accordingly, in a first aspect, the present invention relates to a process for obtaining coated titanium dioxide particles, said process comprising the steps of: (i) providing an aqueous suspension of uncoated titanium dioxide particles; (ii) adding phosphoric acid to the suspension to adjust the pH of the suspension to a value of 2 or less; (iii) adding an alkaline silica precursor to the suspension such that, after said adding, the suspension has a pH of from 7 to 8, thereby forming a first silica coating on the particles; (iv) adding an acid to the suspension to adjust the pH of the suspension to a value of 2 to 3; (v) adding an alkaline silica precursor to the suspension such that, after said adding, the suspension has a pH of 4 to 5, thereby forming a second silica coating on the first silica coating; and (vi) applying at least one coating of alumina over the second silica coating.

In another aspect, the invention relates to a coated titanium dioxide particle obtained by the process disclosed herein.

In a further aspect, the invention relates to the use of the coated titanium dioxide particles according to the invention in a process for obtaining a decorative paper laminate or a decorative foil.

In a final aspect, the invention relates to a decorative paper laminate or decorative foil comprising the coated titanium dioxide particles of the invention.

Detailed Description

These and other aspects, features and advantages of the present invention will become apparent to those skilled in the art upon review of the following detailed description and claims. Each feature of one aspect of the invention may also be used in any other aspect of the invention. Furthermore, it is a matter of course that the embodiments contained herein are intended only to describe and illustrate the present invention, not to limit it, and particularly, the present invention is not limited to these embodiments. The numerical ranges stated in the form of "x to y" include the values mentioned and those within the corresponding measurement accuracy ranges known to the person skilled in the art. If multiple preferred numerical ranges are recited in this form, all ranges subsumed by the combination of the different endpoints.

All percentages related to the compositions described herein relate to weight percentages (wt. -%) based on the mixture of the composition in question, respectively, unless explicitly stated otherwise.

As used herein, "at least one" means 1 or more, i.e., 1, 2, 3, 4, 5, 6, 7, 8, 9 or more. With respect to the coating, this value relates to the absolute number of molecules in the coating rather than the coating.

The titanium dioxide particles coated by the process of the present invention are preferably pigments based on titanium dioxide. "pigment" as used herein relates to an inorganic colorant which is practically insoluble in the application medium according to DIN 55943, undergoes neither chemical nor physical changes in the application medium and retains its particle structure. They are used for pigmenting based on the interaction of pigment particles with visible light by absorption and moderation.

The process disclosed herein is directed to coating titanium dioxide particles. The titanium dioxide disclosed herein can be obtained by the sulfate process or by the chloride process. Titanium dioxide may be present in the crystal structure of rutile, anatase or brookite, typically in the crystal structure of rutile or anatase. Rutile is particularly suitable compared to anatase, because of its lower photolytic catalytic activity. Preferably, the titanium dioxide particles used consist of at least 98 wt.%, preferably at least 99 wt.%, rutile, relative to the total weight of the particles.

Within the scope of the present invention, the titanium dioxide particles have a particle size that desirably scatters visible light to a high proportion (size). The particle size is the mass-related median d50 (hereinafter referred to as d50) from 200nm to 400nm as determined by disk centrifuge.

In step (i) of the process, an aqueous suspension of uncoated titanium dioxide particles is provided. As used herein, "aqueous suspension" refers to a suspension comprising at least 10 wt.%, preferably 20 wt.%, more preferably 30 wt.% water, based on the total weight of the aqueous suspension. The titanium dioxide particles are included therein at a concentration well known in the art of from 150g/L to 500g/L, preferably 400 g/L.

In general, the methods disclosed herein can be carried out in known apparatus suitable for such reactions. In addition, the suspension may be stirred, in particular during the addition of another compound such as a precursor, and brought to a specific temperature known in the art, in order to provide suitable conditions for the subsequent reaction and process steps. After each step, the suspension thus obtained may be aged for 5 to 60 minutes.

In a subsequent step (ii), phosphoric acid is added to the suspension to adjust the pH of the suspension to a value of 2 or less. Will be expressed as P relative to the total weight of uncoated titanium dioxide particles₂O₅Phosphoric acid is added in a calculated amount of 1 to 4 wt.%, preferably 2 to 3 wt.%, more preferably 2.5 wt.%. Phosphoric acid may be added over the course of 5 minutes to 30 minutes and preferably 15 minutes. If the pH is further lowered below 1, it is possible to use, in addition to the phosphoric acid used, other acids from the following group: sulfuric acid, nitric acid, titanyl chloride, titanyl sulfate, hydrochloric acid, and combinations thereof.

In step (iii), an alkaline silica precursor is added to the suspension such that the pH of the suspension after addition of the precursor is from 7 to 8. By doing so, a first silica coating is applied to the uncoated titanium dioxide particles. The addition is preferably carried out with stirring and may be carried out at elevated temperature. The precursor may be added to the suspension over the course of 5 to 60 minutes, and preferably over the course of 30 minutes.

Thereafter, in step (iv), an acid is added to the suspension obtained after step (iii) to adjust the pH of the suspension to a value of 2 to 3. Suitable acids include, but are not limited to, sulfuric acid, nitric acid, phosphoric acid, hydrochloric acid, titanium oxychloride, titanyl sulfate, or combinations thereof. Preferably, sulfuric acid or titanium oxychloride is used. Titanium oxychloride improves the UV-ashing resistance of the titanium dioxide particles obtained and used and is therefore particularly preferred. The acid may be added to the suspension during 5 minutes to 30 minutes, preferably 10 minutes.

Then, in step (v), an alkaline silica precursor is added to the suspension so that, after the addition, the suspension has a pH of 4 to 5, thereby forming a second silica coating layer on the first silica coating layer. As a result, the second silica coating is applied over the first silica coating. The addition is preferably carried out with stirring and can be carried out at elevated temperature. The precursor may be added to the suspension over the course of 5 to 60 minutes, and preferably over the course of 30 minutes.

The alkaline silica precursors in steps (iii) and (v) are independently selected from sodium silicate, potassium silicate and lithium silicate. Preferably, sodium silicate is used.

In step (vi), at least one coating of alumina is applied on the second coating of silica. Any suitable alumina precursor may be used for the application of the alumina coating. In a preferred embodiment, an acidic aluminum precursor is added to the suspension in order to form the coating on the second silica coating. Preferably, the acidic alumina precursor is selected from the group consisting of aluminum sulfate, aluminum nitrate, and aluminum chloride, and preferably the precursor is aluminum sulfate.

Without wishing to be bound by a particular scientific theory, it is believed that the good opacity at the same level of coloration as compared to known particles used in laminate systems, but the superior UV-ashing resistance is due to the particular production process described herein, in particular due to the characteristics of the pH range in steps (ii), (iii) to (v) and the use of phosphoric acid in step (ii).

Preferably, in each step (iii) and (v), the amount of silica precursor added is such that: each obtained silica coating is, independently of the other, from 0.6 to 8 wt.%, preferably from 1.6 to 6.5 wt.%, and more preferably from 2.6 to 5 wt.%, relative to the total weight of the coated particle. Preferably, in addition to or instead of the aforementioned silica coating, in each of steps (vi) and (vii) the amount of alumina precursor added is such that: each obtained alumina coating is, independently of each other, 0.8 to 4.2 wt.%, preferably 1.3 to 3.7 wt.%, and more preferably 1.8 to 3.2 wt.%, relative to the total weight of the coated particle.

In addition to the coatings described above, other coatings may be applied. After step (vi), a basic alumina precursor is preferably added to the suspension in step (vii) to form a second alumina coating on the first alumina coating. Any suitable alumina precursor may be used to apply the alumina coating. Preferably, the alkaline alumina precursor is selected from sodium aluminate and aluminum acetate. More preferably, the precursor is sodium aluminate.

In an even more preferred embodiment, in step (iii), the silica precursor is added in an amount such that: the silica coating obtained is 2 to 8 wt.%, preferably 3.5 to 6.5 wt.%, and more preferably 5 wt.%; and in step (v), the amount of silica precursor added is such that: the silica coating obtained is 0.6 to 4.6 wt.%, preferably 1.6 to 3.6 wt.%, and more preferably 2.6 wt.%. Furthermore, in step (vi), the amount of alumina precursor added is such that: the alumina coating obtained is 0.8 to 2.8 wt.%, preferably 1.3 to 2.3 wt.%, and more preferably 1.8 wt.%, and in step (vii), the alumina precursor is added in an amount such that: the resulting alumina coating is 2.2 to 4.2 wt.%, preferably 2.7 to 3.7 wt.%, and more preferably 3.2 wt.%. All weight percentages in this even more preferred embodiment are relative to the total weight of the coated particle.

In a preferred embodiment, after addition of the acidic alumina precursor used in step (vi), the pH of the suspension thus obtained is from 1 to 5, more preferably from 2 to 4, even more preferably 3; alternatively or additionally, in another preferred embodiment, after addition of the basic alumina precursor in step (vii), the pH of the suspension thus obtained is 5 to 9, preferably 6 to 8, more preferably 7.

Other method steps known in the art may be performed. These include separating the coated titanium dioxide particles from the suspension, washing, sanding or bead milling, steam milling, drying, use of additives, or a combination of such steps. This serves to improve the physical properties, in particular the optical and chemical properties, of the particulate pigments.

To further improve the UV-ashing resistance, alkali metal nitrates may be added to the titanium dioxide particles during drying and/or grinding. The alkali metal nitrate is selected from potassium nitrate and sodium nitrate. Techniques and amounts for adding nitrate to improve the resistance are known in the art.

In another aspect, the present invention relates to a coated titanium dioxide particle obtained by the process of the present invention. In a preferred embodiment, the coated titanium dioxide particle is a titanium dioxide particle comprising at its surface 5 wt.% of a first silica coating, 2.6 wt.% of a second silica coating on the first silica coating, 1.8 wt.% of a first alumina coating on the second silica coating, and 3.2 wt.% of a second alumina coating on the first alumina coating, relative to the total weight of the titanium dioxide particle.

In a still further aspect, the invention relates to the use of coated titanium dioxide particles in a process for obtaining a decor paper laminate or a decorative foil. The coated particles are used in order to whiten the decor paper laminate or the decor foil into which they are incorporated. Furthermore, the particles can be used to improve the UV-ashing resistance of decorative paper laminates or decorative foils into which they are incorporated.

In a final aspect, the invention relates to a decorative paper laminate or decorative foil comprising the coated titanium dioxide particles of the invention.

All references cited herein are incorporated by reference in their entirety.

Examples

Example 1

A titanium dioxide pigment suspension was provided by mixing 15kg of titanium dioxide with 43L of water. Subsequently phosphoric acid was added to the uncoated particles during 15 minutes with stirring to obtain a suspension with a pH of 2. Then, an aqueous sodium silicate solution was added in an amount such that the obtained silica coating layer was 5

Subsequently added to the suspension under stirring so as to be in SiO with respect to the finally coated particles₂The final coated particles contained 5 wt.%.

During the addition, the pH was monitored. Stopping adding when pH is in the range of 7-8. In this range, the suspension is highly viscous. While stirring the suspension, sulfuric acid is added in an amount such that the pH is in the range of 2 to 3. Then, SiO was added in the course of 30 minutes₂2.6 wt.% sodium silicate, until the pH reaches a value of 4 to 5. Then 1.8 wt.% aluminium sulphate was added during 30 minutes and finally 3.2 wt.% sodium aluminate was added during 40 minutes. The coated particles thus obtained are filtered, washed, dried and ground. In the drying step, an aqueous solution of sodium nitrate was added so that the obtained granules contained 0.18 wt.% nitrate with respect to the titanium dioxide.

Example 2

The same process as in example 1 was carried out, except that titanium oxychloride was used instead of sulfuric acid to lower the pH in step (iv).

Comparative example 1

The same method as that of example 1 was performed except that sulfuric acid was used instead of phosphoric acid in step (ii) to lower the pH to a range of less than 2.

Comparative example 2

The same method as that of comparative example 1 was performed, except that each applied silica coating layer was 5.5 wt.% with respect to the total weight of the coated titanium dioxide particles.

Test method and test result

Particle size determination

The particle size of the titanium dioxide particles was determined by using a CPS butterfly centrifuge model DC 20000, available from CPS Instrument corporation, florida, usa. The sample was prepared by mixing 2g of dry pigment particles with 80g of sodium hexametaphosphate (0.06 mass% in water) commercially available from BK Giulini GmbH of raldenburg, germany under the name Calgon N until the resulting first premix was homogeneous. Subsequently, 2g of this first premix was added to 48g Calgon N and homogenized again well by mixing to obtain a second premix. 100 μ L of this second premix was used as a sample for determining particle size. The centrifuge was run at 3000 rpm. The calibration standard parameters were as follows:

particle density: 1.385g/mL

Peak diameter: 1.27 μ L

Peak width at half height: 0.08 μ L

The fluid parameters were as follows:

density of fluid: 1.045g/mL

Refractive index of fluid: 1.344

Fluid viscosity: 1.2 cps.

Preparation of paper laminates (laboratory Scale)

The titanium dioxide pigments obtained according to examples 1 and 2 and comparative examples 1 and 2 were incorporated into decorative paper laminates and subsequently tested for optical properties and UV-ashing resistance. To this end, the titanium dioxide pigment to be tested is incorporated into the pulp and produced to have a mass of about 80g/m²And a tablet weight of about 30g/m²Titanium dioxide in mass content. The decorative paper is then impregnated with an aqueous melamine resin and pressed at temperature to form a paper laminate.

To evaluate the optical properties of the decor paper laminates and thus the quality of the titanium dioxide pigment, it is important to compare decor paper laminates with equal ash content. This requires the amount of titanium dioxide pigment used to form the sheet to be conditioned to be adjusted to the desired titanium dioxide content accumulated in the paper, in this case 30 + -1 g/m, depending on the retention (retention)²Or adjusted to the desired paper weight, in this case 80. + -.1 g/m². In these tests, 1.65g of oven-dried pulp was taken as the basis for sheet formation. The procedures and auxiliary equipment used are well known to those skilled in the art.

The titanium dioxide content (ash, expressed in [% ] of the sheet) was then determined. The content of titanium dioxide was determined by burning a defined weight of the produced paper in a fast incinerator at 800 ℃. The titanium dioxide content by mass (ash, expressed in [% ]) can be calculated by weighing the residue. The following formula is used as the basis for calculating the ash content:

ash content [ g/m²](ash [% ])]X paper weight [ g/m²])/100[％]。

Further processing of the paper includes its impregnation and pressing into laminates. The sheet to be impregnated with resin was completely saturated with melamine resin solution, then drawn between two doctor blades to ensure that a certain amount of resin was applied, and then pre-concentrated in a re-circulating air drying oven at 130 ℃. The amount of resin applied is 110 to 140 wt.% of the sheet. The sheet has a residual moisture content of 5.7 wt.% to 6.2 wt.%. The concentrated sheet is combined with a phenolic resin impregnated core paper and a white or black backing paper to form a stack (stack).

The stack for measuring optical properties has the following structure: decor paper laminates, white or black substrate paper, 6 core paper, white or black substrate paper, decor paper laminates.

The stack used to measure UV-ashing resistance had the following structure: decorative paper laminate, 5 sheets of core paper, white backing paper.

The stack was pressed at 140 ℃ and a pressure of 90 bar for 300 seconds by means of a Wickert Type 2742 lamination press.

Testing

The optical properties and UV-ashing resistance of the laminates were measured using commercially available equipment (spectrophotometer, Xenotest weatherometer). In order to evaluate the optical properties of the laminates, the use ofThe 3300 colorimeter measured the optical values (CIELAB L, a, b) according to DIN 6174 on white and black substrate papers. CIELAB optical values L (L) on a white substrate paper_{White colour}) Used as a measure of brightness. Opacity is a measure of the light transmission of the paper.

The following parameters were selected as a measure of the opacity of the laminate: CIELAB L_{Black color}The brightness of the laminate was measured on a black backing paper. Mixing CIELAB L_{Black color}Normalized to 30.0g/m²Ash content of (a). To evaluate the UV-ashing resistance (lightfastness) of the titanium dioxide pigments, corresponding laminate samples were exposed toIn Alpha machines. In thatOptical values CIELAB L, a and b according to DIN 6174 were measured before exposure and after 96 hours of exposure in Alpha. The light source has a radiation intensity of 70W/m²Xenon arc lamps. The temperature in the sample chamber of the machine was 45 ℃ and the relative humidity was 30%. The sample was rotated during exposure. Converting Δ L ═ L_{Before one}-L*_{After that}As a measure of UV-ashing resistance.

The results of the experiments are summarized in table 1.

Table 1: UV-ashing resistance and opacity values of the examples obtained

Examples of the invention	UV-ashing resistance DeltaL	Opacity LIn black color
			Example 1	-0.95	90.50
Example 2	-0.90	90.60
			Comparative example 1	-2.54	90.60
ComparisonExample 2	-2.36	91.00

Compared to the comparative examples prepared with prior art laminated titanium dioxide pigments, the laminates prepared according to the invention (examples 1 and 2) have significantly higher UV-ashing resistance and similar opacity compared to the prior art.