CN100347375C - Coated paper possessing silky feel - Google Patents

Abstract

The invention concerns a coating composition for coated paper designed to be offset printed, characterized in that the coating pigments are polyurethane microbeads having a size less than 10 micrometers, and advantageously, close to 7 micrometers. The invention also concerns a paper having a silky feel, comprising at least one side coated with said coating composition, and advantageously, both sides. Said paper is characterized in that it can be offset printed with little, even without, set-off or powdering.

Description

Coated paper with a silky feel

technical field

The present invention relates to a coating composition comprising polyurethane microspheres, and paper coated with the coating composition on at least one side, preferably on both sides.

Background technique

Papers of various types or with various compositions can be coated to enhance their surface properties.

Coating compositions commonly used for this purpose are dispersions comprising pigments, which may be organic or inorganic.

The coating composition may also contain other additives.

Paper used for printing, such as for books, magazines, brochures, or annual reports, or for packaging, is often made by coating base paper with one or more coating devices, sometimes Calendering is then carried out.

For its application, the final product should generally have higher surface properties.

These surface properties are mainly reflected in an improvement in the appearance of the paper, for example an increase in its whiteness, gloss or opacity.

The study of certain surface sensations of coated paper sheets is relatively new.

In the prior patent FR 2 791 368, the applicant company mainly proposes a wrapping paper with a property that recalls the characteristics of the packaged goods, especially for cosmetic products to be applied on the skin.

Therefore, the applicant company proposes to provide a property that recalls the place of final application, ie the skin, that is to say has a skin feel or softness.

The desired feel can be achieved by applying a coating comprising expandable thermoplastic microspheres to the surface of the paper.

The purpose of this patent is mainly to solve the problem of the machinability of these sheets during printing, especially the separation of the stacked sheets, due to the anti-slip properties of the added microspheres.

Typically, thin coated papers often create serious problems during printing or paper converting operations, most commonly in offset printing: chalking and smudging.

Chalking corresponds to the release of the coating as a dry powder during printing and becomes more pronounced as the sheet passes through the printing press or paper converting machine.

This phenomenon occurs due to poor binder/pigment metering, with a large excess of pigment relative to binder.

It may also be due to the size and shape of the pigment particles.

Staining corresponds to the transfer of printed matter from one sheet to another, especially when stacked.

It is often possible to observe thick or light ink stains on the left page of the paper, which are caused by the ink on the right page of the following paper.

When the stacked sheets are separated, there may be an audible creaking or creaking of the sheets.

If it is light, this phenomenon becomes staining.

If paper elements participate in the separation, it is picking.

If it is no longer possible to separate the sheets from one another, there is superposition bonding.

Paper is also likely to participate in this phenomenon, since paper that is not compatible with the ink is likely to have poor ink receptivity, and paper with an uneven surface requires too much ink for proper printing.

In view of these considerations, the applicant company has endeavored to provide a paper with a silky feel, preferably coated on both sides, which does not exhibit the printability and machinability problems as described above.

Contents of the invention

Therefore, the first object of the present invention is to provide a coating composition for offset printing coated paper, characterized in that the pigment used in the coating composition has an average particle size of less than 10 microns, preferably about 7 micron polyurethane microspheres.

In particular, the invention is characterized in that the binder used in the coating composition is an aqueous emulsion of polyurethane, preferably soft polyurethane with an elongation greater than or equal to 500%.

In particular, the invention is characterized in that the ratio of binder to pigment is greater than or equal to 40%, preferably greater than or equal to 200%, by dry weight.

Another object of the present invention is to provide a coated paper having a silky feel comprising at least one side, preferably both sides coated with a coating composition as described above.

The paper is characterized in that it can be printed in offset printing with low or even non-existent chalking and smudging.

The paper is based on cellulose fibers and has a grammage between 70-500 g/m ² , preferably between 100-300 g/m ² .

Depending on the case, the paper is transparent or translucent.

More specifically, the paper constitutes tracing paper.

The term "tracing paper" is to be understood as paper as defined in part 6.94 of the International Standard ISO 4046-1978.

More specifically, the present invention is characterized in that the paper is tracing paper, in particular tracing paper obtained by heavy-blading cellulose fibers constituting the paper.

In particular, the invention is characterized in that the weight of the coating on at least one face is between 2-10 g/m ² , preferably between 3-6 g/m ² , calculated on dry weight.

The paper is also characterized in that its coefficient of kinetic friction between its coated right sheet and its other left sheet also coated is less than or equal to 1.0, measured according to standard NF-Q-03-082 , where the weight of the slider is 200g.

The coefficient of kinetic friction reflects the ability of the sheet to adhere when misalignment begins. The higher the coefficient of kinetic friction, the more difficult it is to initiate movement of the sheets in the stack.

Description of drawings

Further advantages of the invention will also be apparent from the following description of comparative examples and non-limiting examples for carrying out the invention with reference to the accompanying drawings. In the attached picture:

Figure 1 shows a scanning electron micrograph (top view, 200x magnification) of a paper with a silk feel according to the present invention, and

Figure 2 shows a scanning electron micrograph (section view, 2000 times magnification) of a paper with a silk feel according to the invention.

specific implementation plan

Example

Example 1-5

Use an air knife coater to coat the composition comprising polyurethane microspheres with different particle sizes as shown in Table 1 on a raw paper sheet with a grammage of 100 g/m ² , more specifically referring to the product sold by the applicant company Conqueror CX 22, the coating ratio is about 5g/m ² per side.

A composition comprising polyurethane microspheres is prepared in an aqueous medium and comprises, by dry weight:

-24.7 parts of water

-0.1 part of humectant

-33.3 parts of aqueous polyurethane emulsion Witcobond 290 H

-20 parts of polyurethane microspheres

-0.5 parts of pH adjuster

-1 part thickener

Example 6-13

Use an air knife coater to coat a composition comprising polyurethane microspheres with an average particle size of 7 microns on a raw paper sheet with a grammage of 100 g/m ² , more specifically Conqueror CX sold by the applicant company 22. The coating ratio is about 5 g/m ² per side on a dry weight basis, where the concentration of the binder varies as shown in Table 2 relative to the weight of the pigment.

A composition comprising polyurethane microspheres is prepared in an aqueous medium and comprises, by dry weight:

- Rolflex PAD, an aqueous polyurethane emulsion with variable parts by dry weight

-20 parts of polyurethane microspheres Daiplacoat RHU 5070

-0.5 parts of pH adjuster

-1 part thickener

Implementation of the experiment

The feel of the coated side containing polyurethane microspheres was assessed by hand.

The response of virgin paper to the pulverization test was determined to demonstrate the tendency of the coating to crumble when passed through the machine. The pulverization experiment was carried out in the following manner:

a) A slider with a size of 40mm×40mm and a weight of 2kg is mounted on a roller and covered with a black blanket made of fabric (a mixture of 70% wool and 30% polyamide), and then the slider is applied On one or more paper sheets coated with said coating,

b) one pass over the paper to cover a total length of 6m,

c) remove the felt from the slider,

d) The reflectance of the felt was measured using an Elrepho device (about 1.4 was measured for the untreated fabric).

The response of the printed paper to staining was determined, and it was demonstrated that the paper has a tendency to stain during mechanical stacking. Contamination experiments were carried out in the following manner:

a) prepare a paper test sample to be tested, the width is 48mm, and the length is 250mm,

b) using a Prufbau test rig with station 1 for printing and station 2 for transfer,

c) Adjust the pressure of station 1 to 1000N, and the pressure of station 2 to 400N,

d) adjust the speed of the device to 0.5m/sec,

e) The ink roller of station 1 is coated with Huber 408010 blue ink for 30 seconds,

f) the transport unit with the test sample is positioned before station 1,

g) The uninked roll is positioned on station 2,

h) printing test samples at station 1,

i) start the stopwatch immediately after printing,

j) Place a test sample of the same paper on the blank roll at station 2 using adhesive tape,

k) Once the stopwatch has elapsed 120 seconds, the transport unit with the printed test sample is brought into the blank roll,

l) the test sample at station 2 is immediately detached from its roll,

m) Measure the optical density of the blue pigment transferred onto the blank test sample using an Xrite densitometer. result

The test results for Examples 1-5 are shown in Table 1.

It was found that even though most papers had a substantially satisfactory response in the staining and chalking tests, only microspheres with a size below 10 microns gave an acceptable silky feel.

From the results of the experiments carried out on Examples 6-13 it can be concluded that in selecting the size of the microspheres to obtain the desired silk feel, in order to have correct chalking, the level of binder must be chosen to be greater than or equal to 40%, while to have correct staining, the level of binder must be selected to be greater than or equal to 200%.

This is because chalking below 2 and staining below 0.1 are considered satisfactory.

Scanning electron micrographs of paper with a silk feel from the applicant company's point of view are shown in Figures 1 and 2 .

The paper was obtained by coating on both sides of base paper Conqueror CX 22 having a grammage of 100 g/ ^m2 the following coating composition:

2.8kg of water

0.03kg of wetting agent Texapon Z95P

Adhesive Rolflex PAD 81kg, sold by Lamberti

6.1 kg of polyurethane microspheres Daiplacoat RHU 5070, sold by Promecome

1 kg of thickener CMC Blanose 7M65 at a concentration of 2.5%, sold by Aqualon

On a dry weight basis, the proportion is 5.4 g/m ² per side, the above amounts being expressed in commercial weights.

The resulting paper is subsequently calendered.

These photographs represent a top view at 200X magnification and a cross-sectional view at 2000X magnification, respectively.

The resulting paper exhibits a true silk feel on both sides.

The kinetic coefficient of friction of the coated paper was measured with a slider weighing 200 g according to standard NF-Q-03-082, giving a value of 0.8. This value ensures good machinability of the sheet on printing or paper converting machinery.

Table 1 particle name Daiplacoat Decolam F7 Decolam FT Decolam F Decolam W Particle size (micron) 7 10 28 28 50 Silky yes pass medium medium no chalking 1.8 1.6 1.6 1.6 1.4 stained 0.4 0.32 0.41 0.39 0.2

Table 2 Binder % Pigment 10% 20% 30% 40% 50% 100% 150% 400% Silky yes yes yes yes yes yes yes yes chalking 15.5 6 3.6 1.9 1.7 1.5 1.5 1.5 stained 0.282 0.326 0.327 0.354 0.367 0.123 0.104 0.07

Claims (13)

1. A coating composition for coated paper, which comprises a pigment and a binder, characterized in that the coating pigment is polyurethane microspheres with a particle size of less than 10 microns. 2. The coating composition according to claim 1, characterized in that the particle size of the polyurethane microspheres is 7 microns. 3. A coating composition as claimed in claim 1, characterized in that the binder used is an aqueous emulsion of polyurethane. 4. Coating composition according to claim 3, characterized in that the elongation of the polyurethane used is greater than or equal to 500%. 5. The coating composition according to claim 3, characterized in that the weight ratio of the binder to the pigment is greater than or equal to 40%. 6. The coating composition according to claim 5, characterized in that the weight ratio of the binder to the pigment is greater than or equal to 200%. 7. Paper comprising at least one side coated with a coating composition as claimed in one of claims 1 to 6. 8. Paper according to claim 7, characterized in that both sides are coated with said coating composition. 9. Paper as claimed in claim 8, characterized in that the coefficient of kinetic friction between the coated right page and the other left page which is also coated is less than or equal to 1.0 according to the French The standard NF-Q-03-082 is measured, and the weight of the slider is 200g. 10. Paper as claimed in any one of claims 7 to 9, characterized in that the weight of the coating layer on at least one side is between 2 and 10 g/ ^m2 on a dry weight basis. 11. Paper according to claim 10, characterized in that the weight of the coating layer on at least one side is between 3 and 6 g/ ^m2 on a dry weight basis. 12. Paper according to any one of claims 7 to 9, characterized in that the paper is tracing paper. 13. Paper according to claim 12, characterized in that said tracing paper is obtained by heavy knife beating of the cellulose fibers constituting the paper.

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