EP1458930B1 - Coated paper having a silky tactile impression - Google Patents

Abstract

The silk feel paper, having a surface cotaing of pigments and a binding agent, has the pigments in the form of polyurethane microballs smaller than 10 microns in size in a binding agent of an aqueous solution of polyurethane, preferably with an elongation rate of at least 500 per cent. The proportion of binding agent to pigments is at least 40 per cent by weight, and preferably at least 200 per cent. The coating is applied to at least one, and preferably both sides of the paper, at a preferable rate of 3 - 6 g/sq m.

Description

The present invention relates to a coating composition comprising polyurethane and paper-coated microbeads on at least one side of said coating composition, and advantageously on both sides thereof.

Papers of various types or compositions can be coated to increase the quality of their surface.

A coating composition conventionally used for this purpose is a dispersion comprising pigments, which may be organic or inorganic.

The coating composition may also include other additives.

Printing papers such as paper for books, magazines, brochures, or annual reports, or papers for packaging are often made by coating a backing paper with one or more printing units. sleeping, followed sometimes by calendering.

The final product should generally have improved surface characteristics for its use.

These surface characteristics essentially result in a change in the visual appearance of the paper, either by increasing its whiteness, its brilliance, or its opacity.

The search for a certain surface touch for the sheet covered with the layer is in itself quite new.

In the prior patent FR 2791368 (Requirement EP -A 1 - 1,039,025 corresponding), the Applicant was interested in providing a packaging sheet which would include a characteristic that would recall one of the essential characteristics of the product to be packaged, particularly for cosmetic products to be applied to the skin.

The Applicant therefore proposed to provide a characteristic that evokes the destination, namely the skin, that is to say the touch, the softness of the skin.

The desired feel could be achieved by applying a layer to the sheet surface which included expandable thermoplastic microspheres.

This patent was intended, among other things, to solve the problems of machinability of these sheets during printing, in particular the problems of separation of sheets in the stacks due to the anti-slip properties of the added microspheres.

The documents US 4,091,130 and EP 0 425 975 disclose paper coating compositions comprising microbeads for breaking during a paper calendering step to release their contents.

The document EP 0 511 457 discloses a binding agent comprising a cross-linked urethane urea resin.

In general, coated fine papers often raise serious problems during printing or during processing operations, the most common being in the context of offset printing: dusting and smearing.

Dusting corresponds to the detachment of the layer in the form of a dry powder during printing, a phenomenon which can be accentuated with the successive passages of the sheet in the printing or converting machines.

This phenomenon comes from a poor binding / pigment dosage, the pigment being too large percentage relative to the binder.

It can also come from the size and shape of the pigment particles.

The smearing corresponds to the transfer of printing from one sheet to another during stacking in particular.

This is often seen on the back of a sheet more or less intense ink stains that come from the ink of the front of the sheet below.

When the pile is unraveled, the crunch of the leaves is heard more or less loudly.

This phenomenon, if it is weak, is called smearing.

This is picketing if paper elements participate in the detachment.

This is stacking if you can not separate the sheets from each other.

Paper may be involved in this phenomenon because paper that is not suitable for ink may have poor ink capacity and paper having an irregular surface condition requires too much ink for printing correct.

In view of these considerations, the Applicant has endeavored to provide a paper having a silky feel, preferably coated on both sides and not having the printability and machinability problems stated above.

A first object of the invention is therefore to provide a coating composition for coated papers intended to be printed in offset, characterized in that the pigments used in the layer are polyurethane microbeads having an average size of less than 10 micrometers, and advantageously close to 7 micrometers.

In particular, the invention is characterized in that the binder used in the layer is an aqueous emulsion of polyurethane, and preferably a soft polyurethane having an elongation rate greater than or equal to 500%.

In particular, the invention is characterized in that the level of binder with respect to the pigments is greater than or equal to 40% by dry weight, and preferably greater than or equal to 200%.

Another object of the invention is to provide a coated paper having a silky feel, comprising at least one face coated with a coating composition as defined above, and advantageously these two faces.

Said paper is characterized by the fact that it can be printed in offset with smearing and low dusting or nonexistent.

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

In one particular case, the paper is transparent or translucent.

More particularly, the paper constitutes a tracing paper.

Tracing paper means a paper as defined by International Standard ISO 4046-1978 in 6.94.

More particularly, the invention is characterized in that the said paper is a tracing paper, in particular obtained by a refined refining of the cellulose fibers component.

In particular, the invention is characterized in that the weight of said layer on at least one of the faces is between 2 and 10 g / m ² dry, preferably between 3 and 6 g / m ² .

Said paper is also characterized by a dynamic coefficient of friction between its front side lying down and its other side also facing back less than or equal to 1.0, measured according to standard NF-Q-03-082 with a pad of 200 g.

The dynamic coefficient of friction reflects the ability of the sheet to lock at the start of a displacement; the higher it is, the more difficult a movement of a leaf in a pile will be.

Comparative examples and nonlimiting examples of embodiment of the invention and other advantages, if any, are described below.

EXAMPLES Examples 1 to 5:

On a sheet of paper having a basis weight of 100 g / m ² , more specifically the CONQUEROR CX 22 marketed by the Applicant, is applied, using an air knife coater, a composition comprising microbeads of polyurethane of different sizes as mentioned in Table 1, at a rate of about 5 g / m ² per side.

• 24,7 parts d'eau
• 0,1 part d'agent mouillant
• 33,3 parts d'une émulsion aqueuse de polyuréthane Witcobond 290 H
• 20 parts de microbilles de polyuréthane
• 0,5 part de régulateur de pH
• 1 part d'épaississant.

The composition comprising polyurethane microbeads is produced in an aqueous medium and contains, in dry weight:

• 24.7 parts of water
• 0.1 part of wetting agent
• 33.3 parts of a Witcobond 290 H polyurethane aqueous emulsion
• 20 parts of polyurethane microbeads
• 0.5 part of pH regulator
• 1 part thickener.

Examples 6 to 13:

On a sheet of paper having a basis weight of 100 g / m ² , more specifically the CONQUEROR CX 22 marketed by the Applicant is applied, using an air knife coater, a composition comprising polyurethane microbeads of medium size close to 7 microns at a rate of 5 g / m ^{2 per} sec about per side, by varying the level of binder based on the weight of pigment as mentioned in Table 2.

• parts sèches variables d'une émulsion aqueuse de polyuréthane Rolflex PAD
• 20 parts de microbilles de polyuréthane Daiplacoat RHU 5070
• 0,5 part de régulateur de pH
• 1 part d'un épaississant

The composition comprising polyurethane microbeads is produced in an aqueous medium and contains, in dry weight:

• variable dry parts of an aqueous Rolflex PAD polyurethane emulsion
• 20 parts of polyurethane microbeads Daiplacoat RHU 5070
• 0.5 part of pH regulator
• 1 part of a thickener

REALIZATION OF THE TESTS:

• The touch of the face comprising the layer of polyurethane microbeads is manually appreciated.
• The response of the blank paper to the dust test is determined so as to show the propensity of the layer to disintegrate during a machine pass. The dusting test is done as follows:
  1. (a) a 40 mm x 40 mm and 2 kg sled mounted on a trolley and covered with a black cloth felt (mixture of 70% wool, 30% polyamide) on one or more sheets of paper coated with said layer,
  2. b) one pass on the paper to cover a total length of 6 m
  3. c) remove the felt from the skate
  4. d) the reflectivity of the felt is measured using an ELREPHO apparatus (the measured value being about 1.4 for the raw fabric)
• the response of the printed paper to the smear test is determined so as to highlight the propensity of the paper to smudge during machine stacking. The smearing test is carried out as follows:
  1. a) Test specimens of test paper 48 mm wide and 250 mm long are prepared.
  2. b) a PRUFBAU test device with a printing station No. 1 and a No. 2 post of printing transfer are used.
  3. c) the pressure of station No. 1 is adjusted to 1000 N and the pressure of station No. 2 to 400 N
  4. d) set the speed of the device at 0.5 m / sec
  5. e) the inking roll of station 1 is inked for 30 sec with a HUBER 408010 blue ink
  6. (f) a carrier fitted with a test-tube is placed in front of the post No. 1
  7. g) place a wheel not inked on the station n ° 2
  8. h) the specimen is printed on station 1
  9. i) the timer is started immediately after printing
  10. j) a specimen of the same paper is placed on the blank wheel of item 2
  11. (k) after 120 seconds has elapsed on the stopwatch, the conveyor equipped with the printed test-tube is engaged up to the level of the blanket
  12. l) the specimen from station 2 is immediately separated from its wheel
  13. m) the optical density of the cyan carried on the blank specimen is measured using an XRITE densitometer.

RESULTS:

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

It is found that even though most papers have a rather satisfactory response to smudging and dusting tests, only microbead sizes of less than 10 microns provide an acceptable silky feel.

The results of the tests for Examples 6 to 13 make it possible to conclude that by choosing a size of microbeads making it possible to obtain the desired silky touch, it is then necessary to choose a level of binder greater than or equal to 40% in order to have a dusting. correct and greater than or equal to 200% for correct smearing.

Indeed, the dusting is considered satisfactory below 2 and the smearing below 0.1.

We have shown on figures 1 and 2 a scanning electron microscope view of a paper presenting from the point of view of the plaintiff a silky touch.

• 2,8 kg d'eau,
• 0,03 kg d'agent mouillant TEXAPON Z95P,
• 81 kg de liant ROLFLEX PAD commercialisé par LAMBERTI,
• 6,1 kg de microbilles de polyuréthane DAIPLACOAT RHU 5070 commercialisé par PROMECOME,
• 1 kg d'un épaississant CMC BLANOSE 7M65 à 2,5 % commercialisé par AQUALON,
• à raison de 5,4 g/m² en poids sec par face, les quantités étant exprimées en poids commercial.

This paper was obtained by depositing on a CONQUEROR CX 22 support paper having a basis weight of 100 g / m ² the following layer composition on these two faces:

• 2.8 kg of water,
• 0.03 kg wetting agent TEXAPON Z95P,
• 81 kg of ROLFLEX PAD binder marketed by LAMBERTI,
• 6.1 kg of DAIPLACOAT RHU 5070 polyurethane microbeads marketed by PROMECOME,
• 1 kg of a 2.5% CMC BLANOSE 7M65 thickener marketed by AQUALON,
• at a rate of 5.4 g / m ² by dry weight per side, the amounts being expressed by commercial weight.

The paper obtained was then calendered.

The photographs represent respectively a top view magnified 200 times and a sectional view magnified 2000 times.

The paper obtained actually has a silky touch on both sides.

By measuring the coefficient of dynamic friction of the paper coated on itself according to standard NF-Q-03-082 with a pad of 200 g, a value of 0.8 is obtained which can ensure good machinability of the sheets on the sheets. printing or converting machines. <b> Table # 1 </ b> Particle name Daiplacoat Decolam F7 Decolam FT Decolam F Decolam W Particle Size (in micrometers) 7 10 28 28 50 Silky touch YES fair way way NO Powdering 1.8 1.6 1.6 1.6 1.4 Smear 0.4 0.32 0.41 0.39 0.2 Binder rate% Pigment 10% 20% 30 % 40% 50% 100% 150% 400% Silky touch YES YES YES YES YES YES YES YES Powdering 15.5 6 3.6 1.9 1.7 1.5 1.5 1.5 Smear 0.282 0.326 0.327 0.354 0.367 0.123 0.104 0.07

Claims (11)

1. Coating composition for coating papers intended to be printed in offset, comprising a binder and polyurethane microbeads having a size of less than 10 micrometers, characterized in that the polyurethane microbeads form pigments, and in that the binder is an aqueous emulsion of polyurethane having a degree of elongation of greater than or equal to 500%.
2. Coating composition as claimed in claim 1, characterized in that the polyurethane microbeads have a size of about 7 micrometers.
3. Coating composition as claimed in claim 1 or 2, characterized in that the level of binder with respect to the pigments is greater than or equal to 40% by weight.
4. Coating composition as claimed in claim 3, characterized in that the level of binder with respect to the pigments is greater than or equal to 200% by weight.
5. Coating composition as claimed in any preceding claim, characterized in that it comprises additives.
6. Paper having a silky feel, characterized in that it comprises at least one face coated with a coating composition as claimed in one of the preceding claims.
7. Paper as claimed in claim 6, characterized in that its two faces are coated with the coating composition.
8. Paper as claimed in the preceding claim, characterized in that the coefficient of dynamic friction between the coated recto face and the other verso face, also coated, of this paper is less than or equal to 1.0, which measurement is carried out according to the standard NF-Q-03-082 with a block weighing 200 g.
9. Paper as claimed in any one of claims 6 to 8, characterized in that the weight of the coating applied to at least one face is between 2 and 10 g/m² by dry weight.
10. Paper as claimed in claim 9, characterized in that the weight of the coating applied to at least one face is between 3 and 6 g/m².
11. Paper as claimed in one of claims 6 to 10, characterized in that it constitutes a tracing paper.

Images