Use of surface-reacted calcium carbonate as anti-blocking agent

Abstract

The present invention relates to the use of a surface-reacted calcium carbonate as an anti-blocking agent in polymer(s) containing compositions, wherein the surface-reacted calcium carbonate is a reaction product of natural ground or precipitated calcium carbonate with carbon dioxide and one or more H.sub.3O.sup.+ ion donors in an aqueous medium, wherein the carbon dioxide is formed in situ by the H.sub.3O.sup.+ ion donors treatment and/or is supplied from an external source, an anti-blocking agent comprising surface-reacted calcium carbonate or a combination of surface reacted calcium carbonate and mineral material, a method for controlling the blocking of polymer(s) containing compositions, a polymer(s) containing composition comprising surface reacted calcium carbonate or a combination of surface reacted calcium carbonate and mineral material, a coating composition comprising such polymer(s) containing composition, as well as a substrate coated with such coating composition.

Claims

1. A coating composition comprising a polymer containing composition comprising surface-reacted calcium carbonate, wherein the surface-reacted calcium carbonate is a reaction product of natural ground or precipitated calcium carbonate with carbon dioxide and one or more H.sub.3O.sup.+ ion donors in an aqueous medium, wherein the carbon dioxide is formed in situ by the H.sub.3O.sup.+ ion donor treatment and/or is supplied from an external source, wherein the composition further comprises a mineral material and the mineral material comprises one or more of precipitated calcium carbonate (PCC), natural ground calcium carbonate (GCC), dolomite, talc, bentonite, clay, magnesite, satin white, sepolite, huntite, diatomite, a silicate, and titanium dioxide, and the surface-reacted calcium carbonate has an intra-particle intruded specific pore volume of 0.1 to 1.3 cm.sup.3/g, calculated from a mercury intrusion porosimetry measurement.

2. The coating composition according to claim 1, wherein the mineral material is selected form natural ground calcium carbonate (GCC).

3. The coating composition according to claim 2, wherein the surface reacted calcium carbonate and the mineral material are present in a weight ratio of from 1:15 to 15:1.

4. The coating composition according to claim 2, wherein the surface reacted calcium carbonate and the mineral material are present in a weight ratio of from 1:4 to 4:1.

5. The coating composition according to claim 2, wherein the surface reacted calcium carbonate and the mineral material are present in a weight ratio of from 1:1 to 1:4.

6. The coating composition according to claim 2, wherein the combination of surface reacted calcium carbonate and mineral material is present in the polymer containing composition in a weight based ratio of the combination of surface reacted calcium carbonate and mineral material to polymer of 1:4.

7. The coating composition according to claim 2, wherein the surface-reacted calcium carbonate is in an amount of at least 5 wt %, based on the dry weight of the polymer.

8. The coating composition according to claim 2, wherein the polymer is selected from aqueous polymer dispersions comprising at least one copolymer obtained by emulsion polymerization of: (a) one or more principal monomers selected from the group consisting of C.sub.1-C.sub.4 alkyl (meth)acrylates, (b) 0.1 to 5 wt % of one or more acid monomers, (c) 0 to 20 wt % of acrylonitrile, and (d) 0 to 10 wt % of further monomers other than the monomers (a) to (c); wherein the glass transition temperature of the copolymer is in the range from 10 to 45° C., and wherein the emulsion polymerization is carried out in an aqueous medium in the presence of at least one carbohydrate compound.

9. The coating composition according to claim 2, wherein the surface-reacted calcium carbonate is a reaction product of natural ground calcium carbonate comprising marble, chalk, dolomite, limestone, and any mixture thereof, with carbon dioxide and one or more H.sub.3O.sup.+ ion donors in an aqueous medium, wherein the carbon dioxide is formed in situ by the H.sub.3O.sup.+ ion donor treatment and/or is supplied from an external source.

10. The coating composition according to claim 2, wherein the surface-reacted calcium carbonate is a reaction product of precipitated calcium carbonate comprising one or more aragonitic, vateritic, and calcitic mineralogical crystal forms, with carbon dioxide and one or more H.sub.3O.sup.+ ion donors in an aqueous medium, wherein the carbon dioxide is formed in situ by the H.sub.3O.sup.+ ion donor treatment and/or is supplied from an external source.

11. The coating composition according to claim 2, wherein the surface-reacted calcium carbonate also has a specific surface area of form 20 m.sup.2/g to 200 m.sup.2/g, measured using nitrogen and the BET method according to ISO 9277.

12. The coating composition according to claim 2, wherein the surface-reacted calcium carbonate also has a volume median grain diameter d.sub.50(vol) of from 1 to 50 μm.

13. The coating composition according to claim 2, wherein the surface-reacted calcium carbonate also has a volume median grain diameter d.sub.50(vol) of from 1 to 8 μm.

14. The coating composition according to claim 2, wherein the polymer has a glass transition temperature T.sub.g in the range from 1 to 50° C.

15. The coating composition according to claim 2, wherein the polymer comprises one or more of homo- and/or copolymers of monomers selected from the group consisting of alkyl (meth)acrylates, methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, acid monomers, acrylic acid, methacrylic acid, esters of acylic acid, esters of methacrylic acid, ethylenically unsaturated nitriles, acrylonitrile, ethylene, propylene, butadiene, styrene, and salts thereof.

16. The coating composition according to claim 2, wherein the surface-reacted calcium carbonate is present in the polymer containing composition in an amount of 5 to 50 wt %, based on the dry weight of the polymer.

17. The coating composition according to claim 2, wherein the surface reacted calcium carbonate or a combination of the surface reacted calcium carbonate and the additional mineral material is present in the polymer containing composition in an amount of from 5 to 40 wt %, based on the dry weight of the polymer.

18. The coating composition according to claim 2, wherein the surface reacted calcium carbonate or a combination of the surface reacted calcium carbonate and the additional mineral material is present in the polymer containing composition in a weight based ratio of surface reacted calcium carbonate or a combination of surface reacted calcium carbonate and additional mineral material to polymer of 1:9 to 4:1.

19. The coating composition according to claim 2, wherein the polymer containing composition is coated on a substrate.

20. The coating composition according to claim 2, wherein the polymer containing composition is coated onto the substrate at a coat weight from 1 to 30 g/m.sup.2.

21. The coating composition according to claim 2, wherein the polymer containing composition is coated onto the substrate at a coat weight from 2 to 10 g/m.sup.2.

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows an SEM image of surface reacted calcium carbonate

(2) FIG. 2 shows the results of tack force measurements obtained for uncoated Synteape® paper and Synteape® paper coated with different coating compositions comprising polymer alone and in combination with MM 1 and SRCC 1.

(3) FIG. 3 shows the results of tack force measurements obtained for Synteape® paper coated with different coating compositions comprising polymer alone and in combination with MM 2 and SRCC 1.

(4) FIG. 4 shows the results of tack force measurements obtained for Synteape® paper coated with different coating compositions comprising polymer alone and in combination with MM 1 and SRCC 2.

(5) FIG. 5 shows the results of tack force measurements obtained for Synteape® paper coated with coating compositions comprising polymer alone and in combination with MM 1 and SRCC 4 at different coating weights.

(6) FIG. 6 shows the results of tack force measurements obtained for Synteape® paper coated with coating compositions comprising polymer alone and in combination with MM 1 and SRCC 4 at different coating weights

EXAMPLES

(7) I. Measurement Methods

(8) In the following, measurement methods implemented in the examples are described.

(9) Particle size distribution (mass % particles with a diameter<X), d.sub.50 (wt) value (weight median grain diameter) and d.sub.98 (wt) value of a particulate material:

(10) The d.sub.50 (wt) and d.sub.98 (wt) values were measured using a Sedigraph 5120 from the company Micromeritics, USA. The method and the instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurements were carried out in an aqueous solution comprising 0.1 wt % Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and supersonics.

(11) Particle size distribution (volume % particles with a diameter<X), d.sub.50(vol) value (volume median grain diameter) and d.sub.98(vol) value of a particulate material:

(12) Volume median grain diameter d.sub.50(vol) was evaluated using a Malvern Mastersizer 2000 Laser Diffraction System. The d.sub.50(vol) or d.sub.98(vol) value, measured using a Malvern Mastersizer 2000 Laser Diffraction System, indicates a diameter value such that 50% or 98% by volume, respectively, of the particles have a diameter of less than this value. The raw data obtained by the measurement is analysed using the Mie theory, with a particle refractive index of 1.57 and an absorption index of 0.005.

(13) Solids Content of an Aqueous Suspension

(14) The suspension solids content (also known as “dry weight”) was determined using a Moisture Analyser MJ33 from the company Mettler-Toledo, Switzerland, with the following settings: drying temperature of 160° C., automatic switch off if the mass does not change more than 1 mg over a period of 30 s, standard drying of 5 to 20 g of suspension.

(15) Specific Surface Area (SSA)

(16) The specific surface area was measured via the BET method according to ISO 9277 using nitrogen, following conditioning of the sample by heating at 250° C. for a period of 30 minutes. Prior to such measurements, the sample is filtered within a Büchner funnel, rinsed with deionised water and dried overnight at 90 to 100° C. in an oven. Subsequently the dry cake is ground thoroughly in a mortar and the resulting powder placed in a moisture balance at 130° C. until a constant weight is reached.

(17) SEM Images

(18) Scanning electron micrographs (SEM) were carried out by adjusting the solids content to a concentration of 20 wt % in water using an ultraturax (rotor-stator-mixer). A few drops (approximately 100 mg) were diluted in 250 ml distilled water and filtered through 0.2 μm pore membrane filter. Preparations obtained on the membrane filter in this way were sputtered with gold and evaluated in the SEM at various enlargements.

(19) Tack Force

(20) The tack force of the coatings to be evaluated was determined by measurements with an Ink Surface Interaction (ISIT) Tester (SeGan Ltd., UK).

(21) Principle of the Test

(22) Surface tack is measured by a special attachment (SeGan Ltd., UK) which consists of a solenoid, a coil spring, a load cell and a contact disc (P. A. C. Gane, E. Scyler, and A. Swan. Some novel aspects of ink/paper Interaction in offset printing. International Printing and Graphic Arts Conference, Halifax, Nova Scotia. Atlanta: Tappi Press. 209-228, 1994). The contact disc is pressed against the surface of the sample platen by electromagnetic force acting on the solenoid. This action applies an extensional force on the coil spring mounted in parallel with the solenoid. Contact time and force can be varied by electronic controls to optimize adhesion between contact disc and the surface.

(23) At cessation of the electromagnetic force the contact disc is retracted from the surface by the strain force of the extended coil spring, strong enough to achieve separation of the disc from the surface. The strain gauge, fixed between contact disc and coil spring, generates a load-dependent signal which is recorded as the measured tack force. The sequence is automatically repeated for a predefined number of cycles chosen to span the regions of the tack force under study. The build-up of the tensile force required to achieve each individual separation is recorded with time and can be analysed through specifically designed software. The maximum level of tensile force at each test point is plotted as measured tack force development with time.

(24) II. Material

(25) 1. Substrate Synteape®: white half-matt PP foil; 62 g/m.sup.2 (available from YUPO (Art.: 675227))

(26) 2. Surface-Reacted Calcium Carbonate (SRCC) SRCC 1

(27) Surface reacted calcium carbonate SRCC 1 was prepared as follows:

(28) 10 litres of an aqueous suspension of ground calcium carbonate were provided in a mixing vessel by adjusting the solids content of a ground marble calcium carbonate from Hustadmarmor having a weight based median particle size of 90% less than 2 μm, as determined by sedimentation, such that a solids content of 16 wt %, based on the total weight of the aqueous suspension, is obtained.

(29) Whilst mixing the slurry, 1.8 kg phosphoric acid was added in form of an aqueous solution containing 30 wt % phosphoric acid to said suspension over a period of 9 minutes at a temperature of 70° C. Finally, after the addition of the phosphoric acid, the slurry was stirred for additional 5 minutes, before removing it from the vessel and drying.

(30) The obtained SRCC 1 had a rose-like structure (cf. FIG. 1) and the following properties: d.sub.50(vol)=5.1 μm, d.sub.98(vol)=9.9 μm, and SSA=48 m.sup.2g.sup.−1. The intra-particle intruded specific pore volume is 1.224 cm.sup.3/g (for the pore diameter range of 0.004 to 0.51 μm). SRCC 2

(31) SRCC2 is a surface reacted calcium carbonate that is commercially available in dry form from Omya AG, Switzerland.

(32) SRCC 2 has a rose type structure and the following properties: d.sub.50(vol)=2.4 μm; d.sub.98(vol)=9 μm; BET SSA=27 m.sup.2/g; The intra-particle intruded specific pore volume is 0.491 cm.sup.3/g (for the pore diameter range of 0.004 to 0.421 μm).

(33) SRCC 3

(34) SRCC 3 is a surface reacted calcium carbonate that is commercially available from Omya AG, Switzerland.

(35) SRCC 3 has a rose type structure and the following properties: d.sub.50(vol)=1.3 μm; d.sub.98(vol)=5 μm; BET SSA=45 m.sup.2/g; The intra-particle intruded specific pore volume is 0.18 cm.sup.3/g (for the pore diameter range of 0.004 to 0.09 μm).

(36) 3. Further Mineral Material (MM) MM 1: natural ground calcium carbonate; d.sub.50 (wt)=1.5 μm; d.sub.98 (wt)=10 μm; solids content 78 wt.-% (available from Omya AG, Switzerland) MM 2: very fine natural ground calcium carbonate powder, especially surface treated with a fatty acid; d.sub.50 (wt)=1.7 μm; d.sub.98 (wt)=5 μm; (available from Omya AG, Switzerland)

(37) 3. Polymers

(38) The polymer used in the following experiments was prepared according to Example 4 of WO 2013/083504 A1.

(39) A reactor was purged with nitrogen and 427.1 g of demineralized water and maltodextrin (C Dry MD 01915 (94.7% strength); Cargill) was added in an amount of 30 pphm (weight parts per hundred weight parts of monomers). The mixture in the initial charge was heated to 86° C. Then, 3.2 g of sodium peroxodisulphate (7%/strength) were added before stirring for 5 minutes. The emulsion feed consisting of 180.0 g of water, 20.0 g of emulsifier (Dowfax® 2A1, 45% strength) and 450.0 g of a monomer mixture of 55 wt % ethyl acrylate, 44 wt % methyl methacrylate, and 1 wt % acrylic acid was metered into the reactor over 2 hours. Concurrently with the emulsion feed the initiator feed was started (12.9 g of sodium peroxodisulphate, 7% strength) and likewise metered in over 2 hours. After the emulsion feed has ended, the system was allowed to polymerize for 45 min. The reactor was then cooled down to room temperature.

(40) The resulting dispersion had a solids content of 47 wt % and the obtained polymer had a T.sub.g of 30° C.

(41) III. Experiments

(42) 1. Sample Preparation

(43) The tackiness or stickiness of polymer coatings were tested by comparing the force development of samples measured using the Ink Surface Interaction Tester (ISIT) described above.

(44) The samples having the compositions given in the tables below were prepared as follows, unless indicated otherwise:

(45) In a 2 litres beaker, the polymer dispersion was provided at a pH of 8.5, which was adjusted using a 30% NaOH solution. Subsequently the mixture of surface reacted calcium carbonate and mineral material was added under vigorous stirring at 500 rpm for 10 min with a Pendraulik laboratory dissolver of the LD 50 type, from Pendraulik GmbH, Springe, Germany.

(46) The resulting mixtures were rod coated onto the substrate using an Erichsen Bar Coater (K-Control-Coater K202, Model 624/Fabr. No. 57097-4) with wire-wound rod No. 3 and air dried on a belt dryer at 7.0 mmin.sup.−1 at 150° C. The coating weight was about 7 g/m.sup.2, unless indicated otherwise.

(47) Subsequently, the surface of the samples was wetted by performing two passes of a gravure roller depositing 1 g/m.sup.2 of water with each pass at 300 N with a 5 s delay between each pass. The tack is measured at 500 N, comparable to the standard ISIT test method.

(48) Finally, tack force measurements were carried out as described above. The following results are the average of 3 measurements per sample, unless otherwise indicated.

(49) 2. Results

(50) First, the tackiness of uncoated Synteape® paper was compared with samples containing different amounts of MM 1 and SRCC 1 as given in table 1 below:

(51) TABLE-US-00002 TABLE 1 Sample Polymer [wt %] MM 1 [wt %] SRCC 1 [wt %] 1 — — — 2 75 — — 3 75 25 — 4 75 23 2 5 75 20 5 6 75 15 10 7 75 10 15 8 75  5 20

(52) As can be taken from FIG. 2, sample 1 representing the uncoated substrate has the lowest tack force, whereas the highest tack force is developed by sample 2 representing the polymer-alone coated substrate.

(53) By adding 25 wt % of MM 1 to the polymer (sample 3) the tackiness shows a bi-modal tack curve. This bi-modality is assumed to be the water initially being seen as surface moisture, then being absorbed and then resulting in the stickiness of the sheet by solubilising the polymer matrix.

(54) Replacing 2 wt/o of MM 1 by SRCC 1 (sample 4) reduces the stickiness slightly, whereas replacing 5 wt % by SRCC 1 (sample 5) almost entirely prevents stickiness.

(55) No stickiness can finally be observed for samples 6-8, wherein 10, 15 and 20 wt % of the mineral material was replaced by SRCC 1.

(56) In view of the above results, further experiments were carried out with coatings containing SRCC 1 only, and with an alternative mineral material and compared to the uncoated Synteape® paper of sample 1. The compositions can be taken from table

(57) TABLE-US-00003 TABLE 2 Sample Polymer [wt %] MM 2 [wt %] SRCC 1 [wt %] 9 95 —  5 10 90 — 10 11 75 25 —

(58) As can be taken from FIG. 3, the use of 5 wt % of SRCC 1 (sample 9) reduces stickiness, but only slightly, whereas the use of 10 wt % (sample 10) has a considerably stronger impact on stickiness comparable to sample 5 above containing 20 wt % MM 1 and 5 wt % of SRCC 1, but at a lower mineral material amount.

(59) Looking at sample 11, it can be seen that MM 2, which is a hydrophobic pigment that does not easily mix with the polymer, does not considerably reduce the stickiness of the coating even at an amount of 25 wt %.

(60) Further tests were made surface-reacted calcium carbonate SRCC 2 having the compositions given in table 3, and being coated onto Synteape®.

(61) TABLE-US-00004 TABLE 3 Sample Polymer [wt %] MM 1 [wt %] SRCC 2 [wt %] 12 75 20 5 13 75 15 10

(62) As can be taken from FIG. 4 showing the results of coatings containing SRCC 2 (samples 12 and 13) applied to Synteape® paper compared to paper coated with polymer only (sample 2) and paper coated with MM 1 only (sample 3), samples 12 and 13 showed an increasing reduction of tackiness with increasing amount of SRCC 2.

(63) Furthermore, the influence of the coat weight of the polymer(s) comprising composition was evaluated using MM1 and a SRCC 3 in the amounts given in table 4.

(64) TABLE-US-00005 TABLE 4 Coat weight Polymer MM 1 SRCC 3 Sample [g/m.sup.2] [wt %] [wt %] [wt %] 14 5 80 16 4 15 7 80 16 4 16 10 80 16 4 17 15 80 16 4 18 5 80 12 8 19 7 80 12 8 20 10 80 12 8 21 15 80 12 8

(65) As can be taken from FIGS. 5 and 6, the samples that show the best performance (most reduced tack response) as regards the coat weight applied to Synteape® paper are those with the lowest coat weights (samples 14 and 18). Samples 15 and 19 having a coat weight of 7 gm.sup.−2 require higher tack forces, which, however, are still below those of the paper coated with polymer only. Coat weights of 10 gm.sup.−2 (samples 16 and 20) provide about the same results, wherein sample 20 having a higher amount of SRCC 3 provides a lower tack response over the earlier time scale. At a coat weight of 15 gm.sup.−2, the tack response for both samples, sample 17 and 21 is higher at the peaks when compared to the tack response of the polymer alone, and thus not desirable.

(66) Thus, it can be seen that the coat weight should not be too high, wherein compositions containing a higher SRCC content provide better results as regards stickiness and the overall amount of mineral material.