Method for the prevention of mist formation in a device comprising rolls during the coating of flexible media with a crosslinkable liquid silicone composition

Abstract

Approaches are described for coating various flexible media, such as sheets of paper, synthetic polymer (polyolefin, polyester, etc.) sheets or fabric sheets, with a silicone on high-speed rolls. For example, an efficient method is described for minimizing and/or reducing mist formation when coating flexible supports with a liquid silicone composition precursor of crosslinked coatings. The coating process can be performed using a coating device that includes a roll operating at a high speed.

Claims

1. A method of minimizing mist formation during the coating of flexible media, the method comprising the following steps I) and II): I) preparing a liquid silicone composition X that is a precursor of silicone coating(s), the liquid silicone composition X comprising: at least one organopolysiloxane A crosslinkable by polyaddition, by dehydrocondensation, by polycondensation, cationically or radically, optionally at least one crosslinking organosilicon compound B, optionally at least one catalyst or photoinitiator C, the nature of which is chosen according to the type of reaction envisaged for said organopolysiloxane A, optionally at least one adhesion-modulating system K, and optionally at least one crosslinking inhibitor D; and II) coating said liquid silicone composition X onto a flexible medium by means of a roll coating device, wherein in step I) an anti-misting additive E is added to said liquid silicone composition X and wherein the anti-misting additive E is obtained by reacting, at a temperature of from 10° C. to 100° C., at least one compound F and at least one chemical compound comprising at least one primary or secondary amine function, wherein: each compound F is an organic compound comprising at least one alkene or alkyne function of which at least one of the substituents is an acid function, and the organic compound comprises at least one acid function and at least one alkene or alkyne function of which at least one of the substituents is an electro-attractive group.

2. The method according to claim 1, wherein the anti-misting additive E is obtained by reacting, at a temperature of from 10° C. to 100° C., at least one compound F and at least one organopolysiloxane O, wherein: each compound F is an organic compound comprising at least one alkene or alkyne function of which at least one of the substituents is an acid function, and the organic compound comprises at least one acid function and at least one alkene or alkyne function of which at least one of the substituents is an electro-attractive group; and each organopolysiloxane O is an organopolysiloxane comprising siloxy units (I.1) and (I.2) of the following formulae: $\begin{array}{cc}{Y}_a{Z}_b^1{\mathrm{SiO}}_{\frac{4-\left(a+b\right)}{2}};& \left(I\mathrm{.1}\right)\\ Z_c^2{\mathrm{SiO}}_{\frac{4-c}{2}}& \left(I\mathrm{.2}\right)\end{array}$ wherein: a=1 or 2, b=0, 1 or 2 and a+b=1, 2 or 3; c=1, 2 or 3; each Y independently represents a functional group of formula (I.3):
-E.sup.1-(NH-G).sub.h(NH.sub.2).sub.i  (I.3) wherein: h=0 or 1; i=0 or 1; h+i=1 or 2; E.sup.1 represents a divalent aliphatic, cycloaliphatic or aromatic hydrocarbon radical containing from 1 to 30 carbon atoms; G, when present, represents an aliphatic hydrocarbon radical containing from 1 to 10 carbon atoms, which is monovalent when i=0 or divalent when i=1; and the symbols Z.sup.1 and Z.sup.2, which are identical or different, represent a monovalent hydrocarbon radical having from 1 to 30 carbon atoms and optionally containing one or more unsaturated bonds and/or one or more fluorine atoms, a hydroxyl group, or a radical —OR.sup.1 wherein R.sup.1 represents a linear, cyclic or branched C.sub.1-C.sub.10 hydrocarbon radical, each organopolysiloxane O comprising, per molecule, at least one siloxy unit (I.1) carrying at least one functional group of formula (I.3).

3. The method according to claim 1, wherein each compound F is an organic compound comprising at least one carbon-carbon double bond and at least one carboxylic acid function.

4. The method according to claim 1, wherein each compound F is a compound of formula (II) ##STR00009## wherein: R.sup.2, R.sup.3 and R.sup.4, which are identical or different, represent a hydrogen atom, a COOH group, or a C.sub.1 to C.sub.6 alkyl group; and R.sup.5 represents a hydrogen atom, an alkyl group comprising at least one COOH group, or an aryl group comprising at least one COOH group.

5. The method according to claim 1, wherein each compound F is selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, 2-carboxyethyl acrylate, 3-carboxypropyl acrylate, maleic acid, fumaric acid, 2-(acryloyloxy)acetic acid, 2-(acryloyloxy)propanoic acid, 3-(acryloyloxy)propanoic acid, 2-(acryloyloxy)-2-phenylacetic acid, 4-(acryloyloxy)butanoic acid, 2-(acryloyloxy)-2-methylpropanoic acid, 5-(acryloyloxy)pentanoic acid, (E)-but-2-enoic acid, (Z)-prop-1-ene-1,2,3-tricarboxylic acid, cinnamic acid, sorbic acid, 2-hexenoic acid, 2-pentenoic acid, 2,4-pentadienoic acid, ethenesulfonic acid, vinylphosphonic acid, (1-phenylvinyl)phosphonic acid, 3-(vinylsulfonyl)propanoic acid, 2-(vinylsulfonyl)acetic acid, 2-(vinylsulfonyl)succinic acid, acetylenedicarboxylic acid and propiolic acid.

6. The method according to claim 2, wherein each organopolysiloxane O is an organopolysiloxane comprising siloxy units (I.1) and (I.2) of the following formulae: $\begin{array}{cc}{Y}_a{Z}_b^1{\mathrm{SiO}}_{\frac{4-\left(a+b\right)}{2}};& \left(I\mathrm{.1}\right)\\ Z_c^2{\mathrm{SiO}}_{\frac{4-c}{2}}& \left(I\mathrm{.2}\right)\end{array}$ wherein: a=1 or 2, b=0, 1 or 2 and a+b=2 or 3; and c=2 or 3.

7. The method according to claim 1, wherein said liquid silicone composition X comprises: at least one radically crosslinkable organopolysiloxane A1; at least one radical photoinitiator C1; and optionally at least one adhesion-modulating system K.

8. A liquid silicone composition X that is a precursor of silicone coating(s), the liquid silicone composition X comprising: at least one organopolysiloxane A crosslinkable by polyaddition, by dehydrocondensation, by polycondensation, cationically or radically, at least one anti-misting additive E, optionally at least one crosslinking organosilicon compound B, optionally at least one catalyst or photoinitiator C, the nature of which is chosen according to the type of reaction envisaged for said organopolysiloxane A, optionally at least one adhesion-modulating system K, and optionally at least one crosslinking inhibitor D, wherein the anti-misting additive E is obtained by reacting, at a temperature of from 10° C. to 100° C., at least one compound F and at least one chemical compound comprising at least one primary or secondary amine function, wherein: each compound F is an organic compound comprising at least one alkene or alkyne function of which at least one of the substituents is an acid function, and the organic compound comprises at least one acid function and at least one alkene or alkyne function of which at least one of the substituents is an electro-attractive group.

9. The liquid silicone composition X according to claim 8, wherein said silicone composition X comprises: at least one radically crosslinkable organopolysiloxane A1, optionally at least one radical photoinitiator C1, and optionally at least one adhesion-modulating system K.

10. A silicone coating exhibiting minimized misting, wherein the coating is formed with an anti-misting additive E in an amount effective to reduce mist formation when the coating is applied to a surface of a flexible medium, and wherein the coating is formed using a liquid silicone composition X that is a precursor of the silicone coating the liquid silicone composition X comprising: at least one organopolysiloxane A crosslinkable by polyaddition, dehydrocondensation, by polycondensation, canonically or radically, the anti-misting additive E, optionally at least one crosslinking organosilicon compound B, optionally at least one catalyst or photoinitiator C, the nature of which is chosen according to the type of reaction envisaged for said organopolysiloxane A, optionally at least one adhesion-modulating system K, and optionally at least one crosslinking inhibitor D; wherein the anti-misting additive E is obtained by reacting, at a temperature of from 10° C. to 100° C., at least one compound F and at least one chemical compound comprising at least one primary or secondary amine function, wherein: each compound F is an organic compound comprising at least one alkene or alkyne function of which at least one of the substituents is an acid function, and the organic compound comprises at least one acid function and at least one alkene or alkyne function of which at least one of the substituents is an electro-attractive group.

11. The method according to claim 2, wherein E1 is aliphatic and contains 1 to 10 carbon atoms.

12. The method according to claim 2, wherein Z.sup.1 and Z.sup.2 represent a monovalent hydrocarbon group selected from the group consisting of alkyl groups having from 1 to 8 carbon atoms, alkenyl groups having from 2 to 6 carbon atoms and aryl groups having from 6 to 12 carbon atoms optionally containing one or more fluorine atoms, a hydroxyl group, or a radical —OR.sup.1 wherein R.sup.1 represents a linear, cyclic or branched C.sub.1-C.sub.10 hydrocarbon radical.

13. The method according to claim 12, wherein Z.sup.1 and Z.sup.2 are selected from the group consisting of methyl, ethyl, propyl, 3,3,3-trifluoropropyl, vinyl, hydroxyl, methoxyl, xylyl, tolyl and phenyl group.

14. The method according to claim 4, wherein R.sup.2, R.sup.3 and R.sup.4 are identical or different and represent a C.sub.1 to C.sub.3 alkyl group.

15. The method according to claim 14, wherein R.sup.2, R.sup.3 and R.sup.4 are methyl.

Description

EXAMPLES

(1) I) Preparation of the Anti-Misting Additives E:

(2) In the examples below, which are given by way of illustration, reference is made to the following definitions: Mn represents the number-average molar mass.

(3) The organopolysiloxanes employed in the examples have the following formula:

(4) ##STR00007## organopolysiloxane (3): compound of formula (III), Mn 3000 g/mol, quantity of N—H bond per gram=1.33×10.sup.−3 mol/g; organopolysiloxane (4): compound of formula (III), Mn 50,000 g/mol, quantity of N—H bond per gram=8.0×10.sup.−5 mol/g; organopolysiloxane (5): compound of formula (III), Mn 30,000 g/mol; quantity of N—H bond per gram=1.33×10.sup.−4 mol/g.

Example 1

Preparation of an Anti-Misting Additive E1 According to the Invention

(5) In a 25 mL single-neck flask, 10.0 g of PDMS (5) and 0.039 g of acrylic acid are mixed, resulting in a molar ratio r=0.63 and a molar ratio J=1.26. The reaction mixture is stirred magnetically for 7 days at a temperature of 50° C. No post-reaction treatment was applied. .sup.1H NMR analysis of the product obtained in CDCl.sub.3 at 27° C. (128 scans) showed that the acrylic functions had disappeared.

Example 2

Preparation of an Anti-Misting Additive E2 According to the Invention

(6) In a 25 mL single-neck flask, 13.48 g of organopolysiloxane (4) and 0.022 g of acrylic acid are mixed, resulting in a molar ratio r=0.52 and a molar ratio J=1.03. The reaction mixture is stirred magnetically for 8 days at a temperature of 50° C. No post-reaction treatment was applied. .sup.1H NMR analysis of the product obtained in CDCl.sub.3 at 27° C. (128 scans) showed that the acrylic functions had disappeared.

Example 3

Preparation of an Anti-Misting Additive E3 According to the Invention

(7) In a 25 mL single-neck flask, 10.01 g of organopolysiloxane (3) and 0.461 g of acrylic acid are mixed, resulting in a molar ratio r=0.5 and a molar ratio J=0.99. The reaction mixture is stirred magnetically for 7 days at a temperature of 50° C. No post-reaction treatment was applied. .sup.1H NMR analysis of the product obtained in CDCl.sub.3 at 27° C. (128 scans) showed that the acrylic functions had disappeared.

Example 4

Preparation of an Anti-Misting Additive E4 According to the Invention

(8) In a two-neck flask, hexylamine and acrylic acid are mixed in proportions such that the acrylic acid/primary amine ratio is equal to 1. The mixture is stirred for 24 hours at a temperature of 50° C.

(9) The products E1, E2 and E3 obtained all have a viscosity which is at least 10 times greater than that of the respective starting organopolysiloxanes. The products obtained may be described as viscoelastic liquids.

(10) In products E2 and E3, all the acid and amine functions are in ionic form (ammonium carboxylate) because the ratio J is equal to 1. In the case of compound E2, the ratio J=1.26 and consequently 25% of the acid functions will be in COOH form and not in ionic form.

(11) II) Test as Anti-Misting Additive

(12) The anti-misting additives E1 to E4 prepared in part I) were tested for anti-misting use.

(13) Description of the Test

(14) In order to analyze and quantify the mist produced in a roll coating device operating at high speed there was employed on the laboratory scale a “pilot misting machine” with a nephelometer (Portable Dust Monitor Series 1.100 from GRIMM), which allows the particles having a size greater than 0.5 μm, that is to say all the particles emitted into the atmosphere, to be measured.

(15) The coating device (supplied by Ermap, France) comprises 2 rollers and allows a strip of paper to run at a linear speed of from 50 to 920 m/min. The two press/coating rolls have a diameter of 10 cm. The press roll is covered with rubber and the coating roll is covered with chromium. The coating roll was shaped like a dumbbell so that the speed of the two rolls is synchronous. The press roll, which can be driven by a motor, is in contact with the coating roll under constant pressure. The silicone coating liquid is poured directly into the gap between the two rollers. The amount of fluid used is 0.25 ml.

(16) The nephelometer measures the concentration of particles in the mist or aerosol, expressed in μg/m.sup.3.

(17) The anti-misting performances of the various additives were tested in a radically crosslinkable silicone composition composed of 95 parts of compound A1 and 5 parts of compound A2, both having the following formula:

(18) ##STR00008##

(19) where for A1 (p=85 and q=7.5) and for A2 (p=220 and q=3.8), and one part ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate (CAS No. 84434-11-7) as photoinitiator.

(20) To the composition described above there is added zero, one or three parts by weight of the anti-misting additives E1 to E4 prepared in part I). The mixture is stirred in order to homogenize it.

(21) The results of the measurement of the mist density are expressed in μg/m.sup.3 and are shown in Table 1 below:

(22) TABLE-US-00001 TABLE 1 Measurement of mist density in μg/m.sup.3 E2 E3 E4 Speed Without E1 E2 E3 E1 3 3 3 m/min additive 1 part 1 part 1 part 3 parts parts parts parts 60 570 77 24 n.d.* 26 77 42 23 200 9560 2062 2163  5523 146 378 176 54 400 37696 3494 3867 25751 247 360 240 105 600 55074 3136 7828 23088 570 787 520 122 800 n.d.* n.d.* n.d.* n.d.* 1335 2316 1043 155 920 n.d.* n.d.* n.d.* n.d.* 2407 3868 1400 135 *n.d. not measured.

(23) Products E1, E2, E3 or E4 have very advantageous anti-mist behavior in the silicone compositions. With one part by weight of additive in the composition, mist is greatly reduced. With 3 parts by weight, the results are excellent.

(24) Products E1 and E2 have the advantage of being more readily incorporated than compound E3 into the tested formulation by simple stirring.

(25) II) Preparation of an Anti-Adhesive Silicone Coating on a Polymer Medium

(26) The silicone compositions comprising three parts by weight of additive E1 or E2 are coated by means of a Rotomec pilot coating machine onto a polyester medium. The machine speed is 50 m/min with a mercury lamp power fixed at 100 W/cm in order to effect crosslinking under UV. The deposit is between 0.9 and 1.1 g/m.sup.2. At the machine outlet, the tests carried out are smear, rub-off, dewetting and measurement of silicone extractables.

(27) Tests Carried Out on the Media Coated with Anti-Adhesive Silicone Coatings:

(28) Smear: Qualitative check of surface polymerization by the finger trace method, which consists in: arranging the sample of silicone-coated medium to be checked on a flat, rigid surface; making a trace with the fingertip by pressing moderately but firmly; and examining the trace so made with the naked eye, preferably in low-angled light. It is thus possible to see the presence of even a very slight trace from the difference in the shine of the surface.

(29) The evaluation is qualitative. The smear is quantified using the following grading:

(30) A: very good, no trace with the finger

(31) B: slightly less good, trace scarcely visible

(32) C: marked trace

(33) D: very marked trace and oily appearance of the surface, product scarcely polymerized, that is to say a grade from A to D, from the best result to the worst.

(34) Rub-off: Check of the ability of the silicone to adhere to the flexible medium by rubbing the finger to and fro, which consists in: arranging the sample of silicone-coated medium to be checked on a flat, rigid surface, the silicone being on the upper face; moving the fingertip to and fro 10 times (over a length of about 10 cm), pressing moderately but firmly; examining the appearance of rub-off with the naked eye. Rub-off corresponds to the appearance of a fine white powder or of tiny pellets which roll beneath the finger.

(35) The evaluation is qualitative. Rub-off is quantified using the following grading: 10: very good, no rub-off has occurred after 10 to-and-fro movements 1: very poor, rub-off after the very first movement

(36) The grade corresponds to the number of the to-and-fro movement (from 1 to 10) after which rub-off occurs.

(37) That is to say, a grade from 1 to 10, from the worst to the best result.

(38) Dewetting: Assessment of the degree of polymerization of the silicone layer by evaluating silicone transfer to an adhesive brought into contact with the coating by means of an ink of standardized surface tension. The method is as follows: Select an approximately 20×5 cm sample of the silicone-coated paper to be characterized, taken in the running direction (machine direction). Cut a length of adhesive tape of 15 cm and then arrange it with the adhesive side on the paper to be tested, without creasing, by exerting pressure 10 times by sliding the finger over the length of the adhesive tape. (“Scotch” adhesive tape from 3 M, reference 610, width: 25 mm). Remove the adhesive tape and lay it flat, adhesive part up. Deposit an ink mark on the adhesive part of the tape using a cotton swab (for single use) over a length of about 10 cm (inks of the SHERMAN or FERARINI and BENELI brand, of surface tension 30 dynes/cm and viscosity 2 to 4 mPa/s). Start the stopwatch immediately. The phase of the phenomenon of dewetting is deemed to be entered when the ink mark changes appearance, then stop the stopwatch. The ink must be deposited on the adhesive part of the tape within 2 minutes following coating with silicone. If the result obtained is <10 seconds, it is considered that migration of silicone onto the adhesive has taken place and that polymerization is incomplete. A grade of from 0 to 10 will be given, corresponding to the time which passes, in seconds, before the phenomenon of dewetting is observed. If the result obtained is 10 seconds, polymerization is deemed to be complete. In this case, a grade of 10 will be given, meaning that the result is very good. Note the grade obtained and the ink used (name, brand, surface tension, viscosity).

(39) Extractables: Measurement of the amount of silicone that is not grafted onto the network formed during polymerization. These silicones are extracted from the film by immersing the sample in MIBK for a minimum of 24 hours as soon as it leaves the machine. Measurement is carried out by flame absorption spectroscopy.

(40) The results of the various factory tests are shown in the following table.

(41) TABLE-US-00002 TABLE 2 Results of the factory tests on the coatings Without 3 parts 3 parts Formulation additive additive E1 additive E2 XRF coatweight (g/m.sup.2) 0.95 1.02 1.02 Smear A A B Rub-off 10 10 10 Dewetting 10 10 10 Extractables In-Line (100 cm.sup.2) % 1.2 1.4 1.3

(42) The factory tests of the two formulations comprising 3 parts of anti-misting additives E1 or E2 are satisfactory. There is no degradation of the properties of the coating obtained.

(43) Release: Measurements of peel forces were carried out using the standardized adhesives TESA 4651. The specimens of the multilayer article (adhesive in contact with silicone surface) were stored for 1 day at 23° C., 1 day at 70° C. and 7 days at 70° C. under the required pressure conditions and were then tested at a low peel speed in accordance with the FINAT 3 test (FTM 3) known to the person skilled in the art.

(44) The release force is expressed in cN/inch and is measured by means of a dynamometer, after compression of the samples either at ambient temperature (23° C.) or at a higher temperature for accelerated aging tests (generally 70° C.).

(45) The results are recorded in Table 3 below:

(46) TABLE-US-00003 TABLE 3 Release force in cN/inch Without 3 parts 3 parts Formulation additive additive E1 additive E2 TESA 7475 1 d @ 23° C. 9 11 11 1 d @ 70° C. 10 14 13 7 d @70° C. 12 17 17