USE OF ZINC TREATED PRECIPITATED CALCIUM CARBONATE IN HYGIENIC PRODUCTS
20200046869 ยท 2020-02-13
Inventors
Cpc classification
A61L2300/102
HUMAN NECESSITIES
C01F11/185
CHEMISTRY; METALLURGY
A61L15/46
HUMAN NECESSITIES
International classification
Abstract
The present invention relates to the use of zinc treated precipitated calcium carbonate (PCC), which is obtained by slaking calcium oxide with water to obtain a calcium hydroxide slurry, carbonating the calcium hydroxide slurry, and adding a Zn.sup.2+ ion provider before and/or during the carbonation, in hygienic products, to the hygienic products comprising said zinc treated precipitated calcium carbonate as well as to a process for the preparation of such hygienic products.
Claims
1-20. (canceled)
21. A method of making a hygienic product, the method comprising: forming a zinc-treated precipitated calcium carbonate, the forming comprising slaking calcium oxide with water to obtain a calcium hydroxide slurry, carbonating the calcium hydroxide slurry, and adding a Zn.sup.2+ ion provider before and/or during the carbonation; and applying or adding the zinc-treated precipitated calcium carbonate to a hygienic item, to form the hygienic product.
22. The method of claim 21, comprising applying or adding the zinc-treated precipitated calcium carbonate to a hygienic item to provide a dry coating weight of 0.05 to 15 mg/cm.sup.2.
23. The method of claim 21, wherein the hygienic item and the hygienic product are chosen from an ab/adsorbent product, a deodorant formulation, a nonwoven product, and a combination thereof.
24. The method of claim 23, wherein the ab/adsorbent product is chosen from a diaper, training panties, swim pants, a feminine hygiene product, an incontinence product, and a combination thereof.
25. The method of claim 23, wherein the ab/adsorbent product is a diaper.
26. The method of claim 23, wherein the ab/adsorbent product comprises one or several layers chosen from comprising a top sheet layer, one or more acquisition/distribution layer(s) (ADLs), a tissue wrap layer, an ab/adsorbent core, and a back sheet layer.
27. The method of claim 26, wherein the applying or adding of the zinc-treated precipitated calcium carbonate to the ab/adsorbent product comprises applying or adding the zinc-treated precipitated calcium carbonate to the one or the several layers of the ab/adsorbent product.
28. The method of claim 21, wherein the applying or adding of the zinc-treated precipitated calcium carbonate to the hygienic item comprises applying or adding the zinc-treated precipitated calcium carbonate to the hygienic item in the form of a slurry, dry, in the form of a formulation, or a combination thereof.
29. The method of claim 21, wherein the applying or adding of the zinc-treated precipitated calcium carbonate to the hygienic item comprises spray coating or printing the zinc-treated precipitated calcium carbonate onto the hygienic item.
30. The method of claim 21, wherein the applying or adding of the zinc-treated precipitated calcium carbonate to the hygienic item comprises applying or adding the zinc-treated precipitated calcium carbonate to the hygienic item in the form of an aqueous formulation.
31. The method of claim 30, wherein the aqueous formulation is chosen from a coating formulation, a spray coating formulation, a lotion, a printing ink formulation, or a combination thereof.
32. The method of claim 30, wherein the aqueous formulation has a solid content of from 15 to 70 wt % and/or a viscosity of from 50 to 3000 mPa.Math.s.
33. The method of claim 30, wherein the aqueous formulation further comprises one or more components chosen from a dispersing agent, a binding agent, a biocide, a defoamer, an oil, a pigment, a coalescing agent, a wetting agent, a neutralizing agent, an emulsifier, a solvent, a colorant, and combinations thereof.
34. The method of claim 21, wherein the Zn.sup.2+ ion provider is chosen from zinc sulphate, a zinc halide, zinc nitrate, a zinc phosphate, a zinc carbonate, zinc oxide, zinc hydroxide, hydrates thereof, and combinations thereof.
35. The method of claim 21, comprising adding the Zn.sup.2+ ion provider in an amount of from 0.1 to 30 wt % based on the dry weight of the calcium oxide.
36. The method of claim 21, comprising adding one or more Group I and/or Group II and/or Group III metal sulphates before and/or during the carbonation in an amount of from 0.1 to 30 wt % based on the dry weight of the calcium oxide.
37. The method of claim 21, comprising screening the calcium hydroxide slurry before the adding of the Zn.sup.2+ ion provider and/or after the carbonation.
38. The method of claim 21, wherein the carbonation comprises a carbonation gas flow rate of from 1 to 30 litres per minute.
39. The method of claim 21, wherein forming the zinc-treated precipitated calcium carbonate comprises concentrating a precipitated calcium carbonate slurry obtained from the carbonation, optionally in the presence of cationic and/or anionic dispersants.
40. A hygienic product formed using the method of claim 21.
Description
FIGURES
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EXAMPLES
[0091] 1. Measurement Methods
[0092] BET Specific Surface Area (SSA)
[0093] The BET specific surface area was measured via the BET process 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 was filtered, rinsed and dried at 110 C. in an oven for at least 12 hours.
[0094] Particle/Aggregate/Agglomerate Size Distribution (Volume % Particles/Aggregates/Agglomerates with a Diameter <X), d.sub.50 Value (Volume Median Particle/Aggregate/Agglomerate Diameter) and d.sub.98 Value of a Particulate Material:
[0095] The volume median particle or aggregate or agglomerate diameter and particle or aggregate or agglomerate diameter volume distribution of a particulate calcium carbonate-containing material was determined via laser diffraction, i.e. the particle or aggregate or agglomerate size is determined by measuring the intensity of light scattered as a laser beam passes through a dispersed particulate sample. The measurement was made with a HELOS particle-size-analyzer of Sympatec, Germany. The samples were prepared as follows: In case that the particulate calcium carbonate containing material was a powder, the powder was mixed with demineralized water to form a homogenous slurry having a solids content in the range of 20 to 25 wt. %. In case that the particulate calcium carbonate-containing material already was in the form of a slurry, it was brought to a solids content in the range of 20 to 25 wt. % by use of demineralized water, if necessary. Before starting the measurement it was ensured that the slurry to be measured did not contain any sediments. Alternatively, the measurement can be made with a Mastersizer 2000 or a Mastersizer 3000 of Malvern Instruments Ltd. (operating instrument software version 1.04).
[0096] Solids Content of an Aqueous Suspension
[0097] 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 seconds, standard drying of 5 to 20 g of suspension.
[0098] PH of an Aqueous Suspension
[0099] The pH of a suspension or solution was measured at 25 C. using a Mettler Toledo Seven Easy pH meter and a Mettler Toledo InLab Expert Pro pH electrode. A three-point calibration (according to the segment method) of the instrument was first made using commercially available buffer solutions having pH values of 4, 7 and 10 at 20 C. (from Sigma-Aldrich Corp., USA). The reported pH values are the endpoint values detected by the instrument (the endpoint was when the measured signal differed by less than 0.1 mV from the average over the last 6 seconds).
[0100] Brookfield Viscosity
[0101] For the purpose of the present invention, the term viscosity or Brookfield viscosity refers to Brookfield viscosity. The Brookfield viscosity is for this purpose measured by a Brookfield DV-III Ultra viscometer at 24 C.3 C. at 100 rpm using an appropriate spindle of the Brookfield RV-spindle set and is specified in mPa.Math.s. Once the spindle has been inserted into the sample, the measurement is started with a constant rotating speed of 100 rpm. The reported Brookfield viscosity values are the values displayed 60 seconds after the start of the measurement. Based on his technical knowledge, the skilled person will select a spindle from the Brookfield RV-spindle set which is suitable for the viscosity range to be measured. For example, for a viscosity range between 200 and 800 mPa.Math.s spindle number 3 may be used, for a viscosity range between 400 and 1600 mPa.Math.s spindle number 4 may be used, for a viscosity range between 800 and 3200 mPa.Math.s spindle number 5 may be used, for a viscosity range between 1000 and 2000000 mPa.Math.s spindle number 6 may be used, and for a viscosity range between 4000 and 8000000 mPa.Math.s spindle number 7 may be used.
[0102] SEM Images
[0103] Scanning electron micrographs (SEM) were carried out by diluting 150 l sample slurry with 20 ml deionized water, filtering through a 0.8 m filter, and air drying the filter residue. A sample carrier provided with carbon based, electrically conductive, double sided adhesive discs is pressed onto the filter, and, subsequently, sputtered with gold (8 nm) and evaluated in the SEM at various enlargements.
[0104] 2. Material
[0105] 2.1. Zinc Treated Precipitated Calcium Carbonate (Zn-PCC)
[0106] 150 kg of quicklime were added to 1300 litres of tap water having a temperature of 40 C. in a stirred reactor and slaked for 25 minutes under continuous stirring. The resulting slurry of calcium hydroxide (milk of lime) at 12.8 wt % solids was then screened on a 100 m screen.
[0107] The calcium carbonate precipitation was carried out in a 1000 litre baffled cylindrical stainless steel reactor equipped with a gassing agitator having a gas dispersion unit, a stainless steel carbonation tube to direct a carbon dioxide/air gas stream to the impeller, and probes for monitoring the pH and conductivity of the suspension.
[0108] 700 litres of the screened calcium hydroxide slurry were added to the carbonating reactor and the temperature of the reaction mixture was adjusted to the desired starting temperature of 20 C.
[0109] Before starting the carbonation reaction, 30 kg of 10 wt % aqueous solution of magnesium sulphate (MgSO.sub.4.7H.sub.2O) was added to the milk of lime.
[0110] The agitator was then adjusted to 1480 rpm, and the slurry was carbonated by passing a gas mixture of 26 vol. % carbon dioxide in air at 118 Nm.sup.3/h, corresponding to 19.7 litres per minute at standard temperature (0 C.) and pressure (1000 mbar) per kilogram of calcium hydroxide, through the slurry.
[0111] During carbonation, 100 kg of 10 wt % aqueous solution of zinc sulphate (ZnSO.sub.4.7H.sub.2O) were added continuously over the total carbonation time to the reaction mixture.
[0112] Completion of carbonation was reached after 1 hour 50 minutes reaction time and indicated by a drop in conductivity to a minimum accompanied by a drop in pH to a constant value below 8.
[0113] During carbonation the slurry temperature was allowed to rise resulting in a final slurry temperature of 58 C. due to the heat generated during the exothermic reaction.
[0114] The slurry was then screened on a 45 m screen before being fed to a dewatering centrifuge (operating at 4440 rpm) at a rate of 350 l/h providing a filter cake having a solids content of 42 wt %. This filter cake was collected and then redispersed with 2.5 wt % (active/dry) of a 100% sodium neutralized polyacrylate dispersing agent (Mw12000 g/mol; polydispersity index 3) in a mixing unit and the concentrated product was recovered as an aqueous slurry of the pigment.
[0115] The product of the carbonation and concentration step as stated above was an aqueous suspension of 38 wt % solids content of ultrafine primary calcium carbonate particles bound together to form aggregates/agglomerates.
[0116] Further properties of the obtained product are described in table 1 below.
[0117] The crystalline structure of the product was determined by SEM pictures and is exemplified by
[0118] 2.2. Spray Coating Formulations
[0119] From the above described zinc treated precipitated calcium carbonate having a solids contents of 38 wt %, a spray coating formulation was prepared by adding a carboxymethyl cellulose binder available under the tradename Finnfix CMC 5 from CP Kelco in a high shear mixer (Disperlux Pendraulik lab dissolver) for 15 minutes without temperature regulation, and 3000 rpm with a dispersion disc with a diameter of 60 mm, which, before its addition to the zinc treated precipitated calcium carbonate suspension, has been stirred with a paddle stirrer at a temperature of 90 C. in tap water at a solids content of 15 to 20 wt % for 20 to 30 min.
[0120] The composition and characteristics of the resulting coating formulation are summarized below:
TABLE-US-00001 TABLE 1 Formulation Composition Zn treated PCC [dry wt %] 25.5 Finnfix CMC 5 [dry wt %] 4.7 Dispersing agent [dry wt %] 1.3 Water [wt %] 68.5 Particle Size Distribution of the Zn-PCC in the formulation d.sub.50(vol) [m] 5.0 BET Specific Surface Area of the Zn-PCC in the formulation [m.sup.2/g] 70 Fluid characteristics of the formulation Solids Content [wt %] 31.6 pH 9.6 Brookfield Viscosity 460 100 rpm, Spindle 4 [mPa .Math. s]
[0121] 3. Pre-Trials
[0122] As it is essential to provide the hygienic product, such as a diaper, in an uncomplicated and flexible way with the zinc treated precipitated calcium carbonate containing coating formulation, the sprayability of the formulations was tested.
[0123] For this purpose, first, the dual beam technology was applied in order to generally test the sprayability of the coating formulations, which showed excellent atomization behaviour. Based on these results, the formulation was applied to diapers.
[0124] 3.1. Sprayability
[0125] For testing the sprayability of the coating formulations, the following parameters were set to be met for being suitable to be applied on hygienic products such as diapers:
TABLE-US-00002 TABLE 2 Coat weight (wet) 200 to 1000 mg Coat weight (dry) 60 to 310 mg Web speed 330 m/min Coating area length on substrate 185 15 mm Coating area width on substrate 45 5 mm Pulsation/spray burst 760 n/min Nozzle opening time 34 3 ms
[0126] For the trial, standard equipment applying the dual beam spray-technology was used, wherein purpose-built nozzles as described further below were used to realize the coat weight and coating area which was defined as mentioned above.
[0127] The formulations can be sprayed on any defined substrate using state of the art spray technology. As illustrated in
[0128] As regards the nozzles, two nozzle sizes were tested, 500 m and 650 m, and for both nozzles, the atomization was found to be excellent.
[0129] The mass output, i.e. the wet coat weight per piece, was controlled by varying the pressure of the vessel mass outputs at the given parameters such as nozzle opening time given above.
[0130] The spray coating of the coating formulation was carried out using two nozzle sizes and different pressure settings of the vessel. After the trials, the dry coat weight was determined by drying the coated material stored in the lab under ambient temperature (22 C.) and humidity (ca. 45%) for 20 h and determining its weight. The difference between the dried coated nonwoven sheet and the dried uncoated nonwoven sheet corresponds to the dry coat weight.
TABLE-US-00003 TABLE 3 Vessel Pressure Nozzle Diameter Coat Weight Trial [bar] [m] (dry) [mg] V1 24 650 404 V2 19 650 274 V3 15 650 204 V4 15 500 134 V5 12 500 124 V6 9 500 74
[0131] Accordingly, the target dry coat weight could be realized within the trial (V2 to V6).
[0132] Furthermore, considering the solids content of coating formulation 1 of 31.6 wt %, the achieved dry coat weights of V4, V5 and V6 displayed the calculated mass output. This finding indicates that almost all solids content remains on the surface of the nonwoven and is not penetrating through its pores.
[0133] 3.2. Zinc Retention Trials
[0134] For evaluating the amount of zinc remaining on the spray coated non-woven the same trials were carried out as described above with the following exceptions:
[0135] The coating formulation was applied and dry coat weights from 74 mg to 404 mg per piece were achieved. The remaining solids residue after ignition and the corresponding zinc content determined by the ICP MS method is displayed in the table below.
TABLE-US-00004 TABLE 4 Coat Vessel Nozzle Weight Top Sheet Weight Zn Pressure Diameter (dry) Residue on Ignition Content Trial [bar] [m] [mg] (570 C.) [g] [%] V1 24 650 404 0.3391 0.37 V2 19 650 274 0.2144 0.35 V3 15 650 204 0.1574 0.26 V4 15 500 134 0.1147 0.25 V5 12 500 124 0.1023 0.22 V6 9 500 74 0.0699 0.17
[0136] 3.3. Determination of of the Antimicrobial and Antifungal Activity of Zinc Treated Precipitated Calcium Carbonate
[0137] The microbial contamination (bacterial and fungi growth) of three different zinc containing powder samples was determined by the plate count method (spread count) according to the following procedure:
[0138] 3.3.1. Materials and Methods
[0139] Zinc Containing Powders
[0140] The powders used were: [0141] ZnCO.sub.3 (from Sigma-Aldrich) [0142] ZnO (from Sigma-Aldrich) [0143] Zn treated PCC (as described above)
[0144] Disruption Buffer (DB) Preparation
[0145] This buffer was used to detach the bacterial cells from the zinc containing powder particles.
[0146] 1.12 g of tris(hydroxymethyl)aminomethane (Tris) was dissolved in 800 ml of a 0.9% (w/v) saline solution. The pH was adjusted to 8 with HCl and made up to 1 litre with 0.9% (w/v) saline solution. The solution was then passed through a 0.2 m pore filter or autoclaved (121 C., 15 minutes) and aliquoted into 50 ml sterile tubes. The aliquots were stored at room temperature (21 C.).
[0147] Sample Preparation
[0148] 1 g of the respective powder and 9 ml sterile disruption buffer (DB) were weighed into a sterile 50 ml test tube (Greiner) under aseptic conditions using an autoclaved disposable spatula (VWR) in order to obtain suspensions of the zinc containing powder samples. To detach the microorganisms from the zinc containing powders samples, the suspensions were shaken on a vortex for 60 sec. at 2500 rpm before being put on a shaker for 30 minutes at motor setting 1400 (at room temperature, i.e. 21 C.).
[0149] Plating Procedure
[0150] The sample to be analyzed was appropriately diluted and a defined volume no greater than 0.1 ml was spread over the surface of an agar plate using a sterile glass/plastic spreader. The agar plates were then incubated upside down (condensed water) for a defined period of time at a defined temperature.
[0151] a) Bacteria (Aerobe Total Viable Count)
[0152] The following parameters are specifically defined: [0153] Diluent: Phosphate buffered saline (PBS) (from Fluka) [0154] Agar: Tryptic Soy Agar plates (TSA) (ready made from Biomrieux)
[0155] The sample to be analyzed was diluted 1:10 in PBS and 100 l of the dilution was spread onto the TSA plate which was incubated for 48 hours at 30 C.
[0156] b) Fungi
[0157] The following parameters are specifically defined: [0158] Diluent: PBS (Phosphate buffered saline) (from Fluka) [0159] Agar: Sabouraud-Glucose (4%)-Agar plate (with chloramphenicol) (from BIOTEST/Heipha)
[0160] The sample to be analyzed was diluted 1:10 in PBS and 100 l of the dilution were spread onto the plate which was incubated for 7 days at 25 C.
[0161] Evaluation
[0162] The plates were evaluated by counting the grown colonies, thereby taking into account that only plates containing between 30-300 colonies have a high statistical significance.
[0163] The results are given in cfu/ml (colony-forming unit per ml sample) or cfu/g (colony-forming unit per g sample).
[0164] 3.3.2. Results and Discussion
[0165] Total Viable Count
TABLE-US-00005 TABLE 5 Determination of aerobe bacterial and fungal growth. TVC [cfu/g] Sample Aerobe.sup.1) Fungi.sup.2) ZnCaCO.sub.3 <100 <10 ZnO <100 <10 Zn-PCC <100 <10 .sup.1)TSA: Tryptic Soy Agar for the determination of bacterial growth. .sup.2)SDC for the determination of fungal growth. 1 ml was plated to lower the detection limit.
[0166] As can be taken from table 5, no bacterial (detection limit 100 cfu/g) and no fungal (detection limit 10 cfu/g) contamination were found in the three samples.
[0167] This means that all of these samples show antimicrobial and antifungal activity, wherein the content of Zn in the Zn-PCC sample was the lowest indicating an increase of microbial effectivity by the use of Zn-PCC.
[0168] 4. Application of Zinc Treated Precipitated Calcium Carbonate in Baby Diapers
[0169] In the following trials, a spray coating formulation containing zinc treated precipitated calcium carbonate (PCC) was applied on baby diapers under industrial conditions, focussing on: [0170] 1. Sprayability with spray equipment installed in the machine at full speed [0171] 2. Impact of the spray coating on relevant diaper properties [0172] 3. Product stability and storage stability with respect to microbiological contamination.
[0173] The results of the determination of relevant diaper properties like rewet, absorption time, pH and microbiological investigations showed very good results.
[0174] 4.1. Spray Coating Formulation
[0175] From the above described zinc treated precipitated calcium carbonate having a solids contents of 38 wt %, a spray coating formulation was prepared by adding a carboxymethyl cellulose binder available under the tradename Finnfix CMC 5 from CP Kelco in a high shear mixer (Disperlux Pendraulik lab dissolver) for 15 minutes without temperature regulation, and 3000 rpm with a dispersion disc with a diameter of 60 mm, which, before its addition to the zinc treated precipitated calcium carbonate suspension, has been stirred with a paddle stirrer at a temperature of 90 C. in tap water at a solids content of 15 to 20 wt % for 20 to 30 min.
[0176] The composition and characteristics of the resulting coating formulation are summarized below:
TABLE-US-00006 TABLE 6 Formulation Composition Zn treated PCC [dry wt %] 27.4 Finnfix CMC 5 [dry wt %] 4.1 Water [wt %] 68.5 Fluid characteristics of the formulation Solids Content [wt %] 31.5 pH 10 Brookfield Viscosity 600 100 rpm, Spindle 4 [mPa .Math. s] Temperature 19 C.
[0177] 4.2. Spray Coating Procedure
[0178] The following parameters were set to be met for being suitable to be applied on diapers:
TABLE-US-00007 TABLE 7 Coat weight (wet) 40 to 300 mg Coat weight (dry) 12.6 to 94.5 mg Web speed 330 m/min Produced diapers 760 n/min Coating length on top sheet 200 15 mm Coating width on top sheet 45 5 mm Pulsation/spray burst 760 n/min Nozzle opening time 34 3 ms
[0179] The trial was realized on a conventional industrial diaper line.
[0180] The spray coating equipment (valve carrier, valve, nozzle and connectors) was provided by FMP TECHNOLOGY GMBH as described above (cf. also
[0181] Two nozzle sizes were chosen for the trial to transfer an adequate fluid amount onto the top sheet: 200 m and 500 m.
[0182] The diaper to be coated was a standard baby diaper maxi size 4 as illustrated in
[0183] The spray coating equipment was positioned in a section of the diaper line where the top sheet was already merged with the ADL (acquisition/distribution layer), absorbent core (fluff pulp and super-absorber layer) and the back sheet layer to allow the coating application onto the top sheet. Trial points V7 to V10 were run in this setup. During the trial, the application was slightly changed and adjusted to another position where the backside of the nonwoven top sheet could be coated. Trial point V11 was conducted in this setup. A dryer was not installed due to the limited space within the machine.
TABLE-US-00008 TABLE 8 Vessel Nozzle Coating side Pressure Diameter Coat Weight Trial on Top Sheet Modus [bar] [m] (wet) [mg] V7 Top Pulsing 20 500 500 V8 Top Pulsing 10 500 250 V9 Top Continuous 9 200 113 V10 Top Pulsing 9 200 43 V11 Bottom Pulsing 9 200 43
[0184] 4.3. Tests and Results
[0185] Important properties of the diaper were evaluated such as rewet, absorption time and pH. These methods are common in the industry and allow a performance evaluation with respect to the final application on babies. Furthermore, microbiological examinations have been carried out.
[0186] 4.3.1. Rewet Test
[0187] The rewet test is designed to show the intrinsic ability of the absorbent core of a diaper to prevent fluids from resurfacing.
[0188] For evaluating the rewet properties of the treated diaper, 370 ml of a urine substitute (0.9 wt % NaCl solution) were poured with a delay of 20 min. after each addition onto each of the samples with a funnel. The micturition point is situated 2.5 cm ahead of the middle of the absorbent core. Between the beginning of the respective liquid application and the rewet measurement there was a delay of 20 min. in order to allow for the distribution and absorption of the liquid in the diaper sample. The surface moisture is determined quantitatively with a stack of filter papers of a known weight after 15 s under a weight of 4 kg. After having determined the final weight of the soaked filter papers, the weight of the liquid uptake could be calculated. The median values including standard deviation were indicated. A decreasing rewet value corresponds to an increasing surface dryness/skin friendliness as well as wearing comfort of the product.
[0189] As can be taken from table 9, the results of the rewet test indicate that a spray coated diaper shows an slightly improved performance compared to the reference diaper without coating. This means, that the ability of a diaper to hold the fluid and prevent it from resurfacing is unaffected. The target value was <0.5 g.
TABLE-US-00009 TABLE 9 Rewet after Rewet after production [g] drying [g] Reference 0.28 0.28 (untreated diaper) V8 0.18 0.12 V10 0.19 0.21
[0190] In this respect, Rewet after production means, a diaper sample was taken directly after the production process (ejection opening at the end of the machine), where the sample still had some residue moisture due to the coating. Rewet after drying means, that the diaper sample from the production trial was dried under ambient conditions until there was no residue moisture on the top sheet and was tested afterwards.
[0191] 4.3.2. Absorption Time
[0192] The absorption time describes the time a diaper needs to distribute and absorb a defined quantity of a urine substitute applied on a defined area on the top sheet.
[0193] The baby diaper is mounted flat onto a foam support on the examination table in order to ensure a planar surface during measurement. The micturition point of the urine substitute is situated 2.5 cm ahead of the middle of the absorbent core.
[0194] The dosage unit consisting of a plate (1030 cm, m=500 g) and a cylinder with an integrated funnel having an addition nozzle connected to an opening in the plate having an inner diameter of 40 mm mounted thereon and a time measuring device is placed onto the diaper and weighted with 24 kg (ca. 27 g/cm.sup.2). Subsequently, an amount of liquid urine substitute is added to the baby diaper (total liquid amount: maxi size: 370 ml). The time required for complete absorption of the liquid is determined. After a defined waiting time of 5 min. the addition is repeated two times. The mean value of 5 individual measurements is given including standard deviation.
[0195] As can be taken from table 10, the results of the absorption time measurement show that a wet coating weight of 43 mg (V10) does not affect the absorption properties of the diaper. If applying higher wet coat weights, like in this case 250 mg (V8), the time to full absorption increases. However, the values still remain within the required time (<200 s).
TABLE-US-00010 TABLE 10 First Addition Second Addition Third Addition Reference 34 79 114 (untreated diaper) V8 46 108 171 V10 35 76 113
[0196] 4.3.3. pH Value
[0197] The pH value on the diaper top sheet was determined by applying a defined quantity of a urine substitute and bringing a pH measuring stripe in contact with the non-woven surface after rinsing the diaper 1 to 3 times with the urine substitute.
[0198] As can be taken from table 11, the pH values are unobtrusive with respect to a wet coat weight of 43 mg (V8). At higher coat weights, the initially taken pH value increases, but is reduced after one rinsing to about 7. The pH on the diaper top sheet is a critical value because, values above 8 may increase the risk of the development of skin disorders.
TABLE-US-00011 TABLE 11 pH after first pH after second pH after third rinsing rinsing rinsing Reference 7 7 7 (untreated diaper) V8 7 7 7 V10 8 7 7
[0199] 4.3.4. Microbiological Investigation
[0200] The contamination of the final, industrially coated diapers was examined following the European Pharmacopoeia (01/2011:50104; Microbiological quality of non-sterile pharmaceutical preparations and substances for pharmaceutical use), which requires [0201] a max. count of 200 (TVC/TAMC=Total Aerobe Microbial Count) and [0202] a max. count of 20 (TYMC=Total Yeast and Mould Count).
[0203] As can be taken from table 13, the testing results of the up to four weeks old diapers indicate no contamination as far as the method and the corresponding detection limits are set-up. The analysis of TAMC in V10 in Week 4 was declared as an error. The analysis of TAMC in V11 in Week 4 counted 5 TYMC, which is still within the requirements.
[0204] Aerobe bacteria Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans are completely absent.
TABLE-US-00012 TABLE 13 Pseudomonas Staphylococcus Candida aeruginosa aureus albicans Sample Weeks TAMC TYMC [g.sup.1] [g.sup.1] [g.sup.1] Uncoated 1 .sup.>10.sup.4 <100.sup.ii absent absent absent Reference 2 <100 50.sup.ii absent absent absent [cfu/g] 3 <100 5.sup.iii absent absent absent V8 1 <100 <100.sup.ii absent absent absent 2 <100 <100.sup.ii absent absent absent 3 <100 <10.sup.iii absent absent absent V9 1 <100 <100.sup.ii absent absent absent 2 <100 <100.sup.ii absent absent absent 3 <100 <10.sup.iii absent absent absent V10 1 <100 <100.sup.ii absent absent absent 2 <100 <100.sup.ii absent absent absent 3 <100 <10.sup.iii absent absent absent V11 1 <100 <100.sup.ii absent absent absent 2 <100 <100.sup.ii absent absent absent 3 <100 5.sup.iii absent absent absent .sup.iiThe detection limit was too high (100 cfu/g). Therefore, it was not possible to verify whether the acceptance criteria were met. .sup.iiiAdditionally, the TYMC count was adjusted during the tests (in week 3) to verify the acceptance criteria of the EP: 1 g of the samples were mixed with 49 ml CASO-broth. 5 ml were plated by pour plate technique to lower the detection limit to 10 cfu/g.
[0205] 4.4. Drying Behaviour
[0206] In order to evaluate, whether the diapers coated with the inventive formulations according to the above described production process may also be dried during the coating process without affecting the top sheet substrate structure (PP fibres) due to melting or embrittlement, hence without deteriorating the performance of the diaper top sheet, the following trials were carried out.
[0207] For this purpose, not only spray coating, but also printing as alternative technology was tested to transfer the coating formulation to the nonwoven top sheet. This technology revealed to be a potential solution for an industrial upscale.
[0208] 4.4.1. Materials and Methods
[0209] Spray Coating Formulation
[0210] The spray coating formulation used for the coating of diapers and described in table 6 was used.
[0211] Nonwoven Material
[0212] The nonwoven top sheet substrate was a low bonded, soft PP (polypropylene) nonwoven top sheet typically used for standard baby diapers. Its average grammage is at 14 g/m.sup.2, with a width of 175 mm.
[0213] 4.4.2. Application of the Coating Formulation
[0214] The trial was realized on a lab printing machine (Testacolor 157, a laboratory printing press available from NSM Norbert Schlfli AG, Zofingen, Switzerland) using the above described spray coating equipment from FMP TECHNOLOGY GMBH. The spray equipment was assembled and installed on the printing machine.
[0215] Additionally, one flexo printing unit was installed (cf.
TABLE-US-00013 TABLE 14 Coat weight (wet) 20 to 200 mg Web speed 100 m/min Drying temperature 100 to 250 C. Coating length on top sheet continuous Coating width on top sheet 45 5 mm
[0216] Two nozzle sizes were tested: 100 and 200 m.
[0217] The pressure of the pressurized vessel was adjusted between 14 bar and 30 bar depending on the flowability of the operating nozzle. An observation of the abrasion tendency of coating material on machine parts was conducted on the transportation rolls, especially after the drying section.
[0218] In the subsequent printing application test, three different setups were used: [0219] Printing plate Flinn ART 2.54 mm, 360er Anilox roll [0220] Elastomer printing plate, 360er Anilox roll [0221] Elastomer printing plate, 120er Anilox roll
[0222] As a difference to the spray coating system which was adjusted to coat a width of 45 mm5 mm, the printing system transfers the coating formulation on a width of 150 mm and in specific pattern, depending on the characteristic of the printing plate. The Elastomer printing plate allows full area coating onto the substrate.
[0223] Samples were taken by cutting 210 mm long pieces of spray coated or printed nonwoven from the reels.
[0224] 4.4.3. Results and Discussions
[0225] Tables 15 and 16 give overviews of the results of trials V12 to V16 using spray coating and V17 to V19 using printing, the used equipment and different settings (pressure vessel, dyers, temperature, etc.). For all trial points, the machine speed was set to 100 m/min.
[0226] Furthermore, the results of the determined residual moisture, the zinc content and the recalculated dry- and wet coat weights are displayed. The weight values are based on samples cut to a length of 210 mm.
[0227] Residual Moisture after Coating and Drying
[0228] Different coat weights were determined using a four decimal digits lab balance (Mettler Toledo): [0229] Coat weight right after spraying/printing and drying [0230] Coat weight after storage under ambient conditions (air-dried, ca. 20 C.)
[0231] Based on these weights, the residual moisture after the coating and drying process was calculated
[0232] Zinc Content
[0233] The zinc content on the coated nonwoven was determined by extraction of solids on the coated top sheet in 25 ml of a 3% HNO.sub.3 solution, shaking and letting stand over night. After filtration over a 0.2 m regenerated cellulose syringe-filter, the solution was appropriately diluted before measuring. Zn-66 and Zn-68 were measured with an Inductively Coupled Plasma-Mass Spectrometer (ICP-MS) Elan DRCe from Perkin Elmer with an argon plasma flow of 15 l/min. Based on the zinc content, the dry- and wet coat weights were calculated
TABLE-US-00014 TABLE 15 V12 V13 V14 V15 V16 Coating Spray Spray Spray Spray Spray Nozzle size [m] 200 200 200 100 200 Pressure Vessel [bar] 14 14 12 30 14 Temp. Dryer 1 [ C.] 160 250 220 160 160 Temp. Dryer 2 [ C.] 130 230 200 140 140 Nonwoven Temp. 35 40-45 35-40 35 35 Coated Area [ C.] Nonwoven Temp. 45-50 60-65 45-50 45 45 Uncoated Area [ C.] Residual Moisture [%] 7.45 0.73 3.44 0 1.73 Zn content [mg] 0.49 0.64 0.68 0.19 0.37 Dry Coat Weight [mg] 38.04 49.27 52.62 14.31 28.38 Wet Coat Weight [mg] 120.76 156.41 167.03 45.42 90.11
[0234] To determine the temperature of the coated and uncoated nonwoven material after the drying section, the temperature measuring device Raynger ST2L from Raytek was used. The device uses non-contact, infrared measuring principle. The temperature is calculated based on the emitting radiation energy from the substrate. The measuring point was 30 cm after the last dryer. The distance from measuring device to substrate was ca. 20 cm.
[0235] As can be taken from table 15, the residual moisture content of V15 was best. However, the 100 m nozzle tended to plug, such that a 200 m nozzle was used, which produced nearly equally good results. V12, V13, V14 and V16 showed a residual moisture from 0.73% to 7.45% depending on the adjusted temperature of the dryers.
[0236] The preferred drying temperature was found to be 160 C. and lower. Higher drying temperatures of up to 250 C. caused an increase of the temperature of the nonwoven itself and resulted in a fusing of the PP fibres.
[0237] This happened in the uncoated areas, where the temperature of the substrate reached 55 C. or higher. In coated areas, the fibres were unaffected because the substrate temperature at no time exceeded 45 C.
[0238] The detected zinc content on the samples reflects dry coat weights from 28 mg to 52 mg or wet coat weights from 90 mg to 167 mg (using the 200 m nozzle). With the 100 m nozzle a low dry coat weight of 14 mg (or 45 mg wet coat weight) could be achieved.
TABLE-US-00015 TABLE 16 V17 V18 V19 Coating Printing Printing Printing Printing Plates Flinn ART 2.54 mm Elastomer Elastomer Anilox Roll 360er Anilox 360er Anilox 120er Anilox Pick-up volume 4.9 m.sup.3/m.sup.2 4.9 m.sup.3/m.sup.2 15.2 m.sup.3/m.sup.2 Temp. Dryer 1 [ C.] 120 120 130 Temp. Dryer 2 [ C.] 0 0 0 Nonwoven Temp. 30-35 30-35 30-35 Coated Area [ C.] Nonwoven Temp. 30-35 30-35 30-35 Uncoated Area [ C.] Residual Moisture [%] dry dry dry Zn content [mg] 0.03 0.03 0.1 Dry Coat Weight [mg] 2.15 2.08 7.69 Wet Coat Weight [mg] 6.84 6.59 24.42
[0239] In V17 to V19 the coating was achieved by printing. Two different printing plates (Finn Art 2.54 mm and elastomer) where used combined with two different Anilox rolls having a difference in their pick-up volume (4.9 m.sup.3/m.sup.2 or 15.2 m.sup.3/m.sup.2). By this approach, the amount of coating formulation transferred to the substrate was significantly reduced to 2 mg (dry), and 6 mg (wet), respectively, using the Anilox roll with a lower pick-up volume. A coat weight of almost 8 mg (dry) or 24 mg (wet) was achieved with an elastomer printing plate and a 120er Anilox roll. Due to the low coat weights spread on a bigger area (150 mm width), the nonwoven could be dried to 100%. A drying temperature of 120 C. or 130 C. realized with one dryer was sufficient. The second dryer could be switched off.
[0240] As a consequence, low coat weights led to a lower amount of zinc on the substrate of 0.03 mg to 0.1 mg.
[0241] In contrast to the spray coating system, the coat weight would not be reduced by higher machine speeds in industrial scale, because the printing unit would operate at the same speed and transfer an unvarying amount of fluid. But, the coat weight, respectively, the transferred amount of fluid, can be adjusted depending on the design of the printing plate and the pick-up volume of the Anilox roll.
[0242] In V17 to V19, coating depositions within the machine or on machine parts could be reduced to a minimum, due to the fact that the nonwoven material could be effectively dried.
[0243] Microscopic Analysis
[0244] To examine the influence of coating and drying on the nonwoven material, SEM (Scattering Electron Microscopy) pictures were taken with back-scattering electron detector and secondary electron detector. The investigation allows a visualization of the PP fibres and calcium carbonate structures down to a size of 2 microns.
[0245] The SEM-analysis pictures of an uncoated reference nonwoven show a connection stripe, which is a results of the production process, in
[0246]
[0247] The connection stripes visualized in
[0248] Besides the connection stripes, solids can be found widely distributed and bonded onto the PP fibres spray coated according to V13 (see
[0249] A destruction of the fibres in coated areas by melting or embrittlement due to the drying process could not be observed, but a fusing of the PP fibres in uncoated areas, where the temperature exceeded 55 C. already became obvious by visual examination of the samples.
[0250]
[0251]
[0252] Compared to the spray coating application and as shown in the data table, lower amounts of solids were transferred by printing application which also becomes obvious in the SEM pictures of V17 in
[0253] Tensile Strength
[0254] As an indicative evaluation, the coated nonwoven samples were tested for their tensile strength using an ISO 527-3 tensile strength test method (typically applied on foils) on a Zwick Roell device with a 20 kN load cell. Stripes with a length of 150 mm and a width of 15 mm were punched out of the coated or uncoated area of the samples and placed into the sample holder. The test was conducted with a pre-load of 0.2 N and a test speed of 500 mm/min. The value are average values of 5 measurements, respectively.
[0255] The results of the tensile strength test are summarized in tables 17 and 18:
TABLE-US-00016 TABLE 17 V13 V13 Ref. V12 center edge V14 V15 V16 Dry Coat Weight 38.04 49.27 52.62 14.31 28.38 [mg] Force max [N] 7.94 9.96 10.12 15.06 10.71 9.04 8.43 Standard 0.62 0.82 1.17 0.48 1.19 0.17 0.65 Deviation S [N] Variance V [%] 7.79 8.2 11.52 3.17 11.1 1.83 7.69
TABLE-US-00017 TABLE 18 Ref. V17 V18 V19 Dry Coat Weight 2.15 2.08 7.69 [mg] Force max [N] 7.94 7.98 7.42 7.27 Standard 0.62 0.24 0.64 0.68 Deviation S [N] Variance V [%] 7.79 3.07 8.61 9.34
[0256] This test, even if it is not standardized for nonwoven testing, indicates an increase of the tensile strength in machine direction (MD) by coating the substrate with the inventive formulations. Increased coat weights also increase the maximum force (at least for trial point V12 and V13 Center). This effect can be ascribed to CMC binder in the formulation, increasing the bonding force of the material. Lower coat weights as achieved in V17 to V19 do not have an influence on the tensile strength.
[0257] Testing the uncoated edges of samples of V13, where the high drying temperature led to a melting of the fibres, reveals that this structural change also affects the tensile strength properties. The maximum force in this case increases. However, the negative effects like embrittlement or increased roughness would probably impact other diaper properties negatively, which is not accepted by the customer.
[0258] 5. Application of Zinc Treated Precipitated Calcium Carbonate by Flexo Printing
[0259] In the following trials, a dispersion of zinc treated precipitated calcium carbonate was applied on nonwoven topsheets utilized for incontinence pads and diapers by flexo printing under industrial conditions at a target loading of 3-10 mg solids per product.
[0260] 5.1. Printing Dispersion
[0261] From the above described zinc treated precipitated calcium carbonate having a solids contents of 38 wt %, the same formulation was used as for the spray coating trials.
[0262] 5.2. Printing Procedure
[0263] The flexo printing trials were made on a Gallus type EM 280 printing machine (available from Gallus Ferd. Riiesch AG, St. Gallen, Switzerland) having a web width of 282 mm and a maximum mechanical machine speed of 150 ms.sup.1.
[0264] The dispersion was applied via a closed chamber doctor blade and corresponding Anilox rolls providing an application volume of 3.5-14 cm.sup.3m.sup.2. The printing cylinder was a solid area blanket cylinder having a Shore hardness A 45. After printing, the printed substrate passed two hot air driers allowing drying from both sides at a maximum temperature of 80 C.
[0265] The substrates were selected from: [0266] a) a polypropylene nonwoven substrate to be utilized as topsheet of incontinence pads, with a width of 152 mm and a weight of approx. 14.5 gm.sup.2. For an incontinence pad, a length of 350 mm was assumed, resulting in a printed area of 0.053 m.sup.2 per product. [0267] b) a polypropylene nonwoven substrate to be utilized as topsheet of a standard baby midi size diaper product, with a width of 145 mm and a weight of approx. 13.5 gm.sup.2. For a single diaper, a length of 315 mm was assumed, resulting in a printed area of 0.063 m.sup.2 per product.
[0268] The target amount per product was between 3.15 mg and 10 mg solids per product corresponding to between 0.050 gm.sup.2 and 0.159 gm.sup.2 (per diaper), and between 0.059 gm.sup.2 and 0.189 gm.sup.2 (per incontinence pad).
[0269] For determining the applied solids amount, 2 metres of unprinted and printed substrate, respectively were weighed on an analytical balance. The solids amount coated onto the substrate was determined by the weight difference.
[0270] 5.2.1. Incontinence Pads
[0271] The incontinence pad substrate was subjected to different printing conditions and evaluated with respect to the resulting coating amounts.
[0272] It can be taken from the results in table 19 that incontinence pad substrate may be successfully printed. The target solids application amounts may not only be achieved, but even be controlled within the defined target ranges by varying the roll volume (cf. trial V20 vs V21 and V23 vs. V24), as well as the web speed (cf. V23 vs V24).
[0273] Thus, the dispersion application was rather efficient, wherein residues on the roles could only be found on the parts not being covered by the substrate. Behind the drier, the roles were completely clean, and also the area around the Anilox Roll was free from dust and dispersion residues.
TABLE-US-00018 TABLE 19 Dry Coat Roll Web Temp. Dry Coat Weight/ Volume speed Drier Coating.sup.a Weight Product Trial [cm.sup.3/m.sup.2] [m/min] [ C.] [g] [g/m.sup.2] [mg] V20 12 20 45 0.0568 0.19 9.94 V21 14 20 45 0.0984 0.32 17.22 V22 6 20 45 0.0442 0.15 7.74 V23 3.5 20 45 0.0298 0.10 5.21 V24 3.5 120 45 0.0221 0.07 3.87 .sup.aWeight difference between unprinted and printed substrate measured for 2 m of substrate.
[0274] 5.2.2. Diapers
[0275] The diaper substrate was printed as described above providing the results in table 20.
[0276] It may be noted, however, that due to the higher and varying densities of and within the material, the printing process must be carefully controlled. Thus, web speed should not be too high due to the nature of the substrate, which otherwise tends to buckle.
[0277] Furthermore, due to the varying density within the diaper material, the weighed application amounts may not be determined as exactly as with the Inko Extra pads above.
[0278] Nevertheless, flexo printing may also be successfully applied to diapers, wherein the target solids application amounts may be achieved, and controlled, as well.
TABLE-US-00019 TABLE 20 Dry Coat Roll Web Temp. Dry Coat Weight/ Volume speed Drier Coating.sup.a Weight Product Trial [cm.sup.3/m.sup.2] [m/min] [ C.] [g] [g/m.sup.2] [mg] V25 3.5 60 45 0.0166 0.054 3.44 V26 3.5 80 50 0.0144 0.047 2.99 .sup.aWeight difference between unprinted and printed substrate measured for 2 m of substrate.