SE514710C2 - Absorbent articles containing superabsorbent material - Google Patents

Abstract

Absorbent structure in an absorbent article such as a diaper, sanitary napkin, incontinence guard, wound dressing, bed protection etc., said structure containing a superabsorbent material possibly in combination with other absorption- or carrier materials and where the superabsorbent material has a content of renewable and/or biodegradeable raw material of at least 20 % by weight, calculated on the dry weight of superabsorbent material, and has a phase angle # # 8‹ defined as the phase shift between deformation and strain measured at rheological measurements.

Description

lO 15 20 25 30 '514 710 2 chitosan, pectin, guargurnmi. Proteins and peptides are also possible polymers from a renewable source.

The function of a particular superabsorbent in an absorbent structure depends on many factors, such as where and how the superabsorbent is mixed into the absorbent structure, particle shape, particle size, and physical and chemical properties such as absorption capacity, absorption rate, gel strength and fluid retention.

A phenomenon called gel blocking can also adversely affect the absorption capacity of, for example, a ers berstruldur containing superabsorbents. Gel blocking means that superabsorbent particles during wetting form a gel that blocks the pores in the fi ber structure or between the particles and thus complicates the liquid transport from the hydrogen dryer to the rest of the absorption body and liquid transport to all particles. This entails a poor utilization of the total absorption capacity of the absorbent body and entails a risk of leakage.

A high gel strength - crosslinking of the superabsorbent reduces the risk of gel blockage. However, too high a gel strength gives too low an absorption capacity. By gel strength is meant the tendency to gel deformation, which can be defined as the shear modulus of the gel. This is measured in a rheometer and is calculated as the ratio between (a) the shear stress / deformation imposed on the sample and (b) the relative deformation / shear stress exhibited by the sample. The shear nodule, G ', is measured in the unit Pa. This is described, inter alia, in EP-B-254 476.

Another common method of characterizing a superabsorbent and its ability to function in an absorbent article such as a diaper, incontinence guard, bandage and the like is to measure its ability to absorb liquid under compressive load, so-called AUL (absorbency under load). This is described in, for example, EP-B-O, 339.46l. Here, in a special measuring device, the superabsorbent's ability to absorb a salt solution according to the so-called “demand wettability” principle is measured under a certain load, usually 2kPa, which is an accepted standard load in the industry. 10 15 20 25 30 - 514 at 3 Other common measuring pairs are the free swell capacity (FSC), which is measured in absorbed liquid per g of superabsorbent when it is allowed to swell, and the ability to retain liquid after centrifugation (CRC). ). According to the latter method, the superabsorbent is allowed to absorb liquid freely to saturation, depending on whether the sample is centrifuged and how much of the absorbed liquid is retained after centrifugation.

However, none of these methods of characterizing the properties of a superabsorbent tell the whole truth and do not always correlate with the function of the superabsorbent in a product concept. In particular, this applies to superabsorbents based entirely on renewable and / or biodegradable raw materials, which usually have a low AUL value and a low gel strength and where neither AUL nor any of the other measuring methods mentioned above constitute a good measure of the function of the superabsorbent in an absorbent article.

Object and main features of the invention The object of the present invention is to provide an absorbent structure in an absorbent article of the above kind where the absorbent structure contains a superabsorbent material wholly or partly based on renewable and / or biodegradable raw materials and which has a very good function in the absorbent structure measured as absorbency and inlet velocity. According to the invention, this has been achieved in that the superabsorbent material has a phase angle ö s8 ° measured in rheological measurements.

The superabsorbent material preferably has a phase angle δ s6 °, more preferably s4 ° and most preferably S3 °.

The superabsorbent material should preferably have a content of renewable and / or biodegradable raw material of at least 20, preferably at least 40, more preferably at least 60 and most preferably at least 80% by weight, based on the dry weight of superabsorbent material. 5 15710 4 According to an alternative, the superabsorbent material comprises a crosslinked polymer, wherein the polymer is based on renewable and / or biodegradable raw material and the crosslinker is either renewable and / or biodegradable or non-degradable / non-biodegradable.

According to an exemplary embodiment, the absorbent structure may contain a combination of hydro-fibers and superabsorbent materials, the hydro-fibers preferably consisting of cellulose pulp, tissue or hydro-synthetic fibers, and the absorbent structure contains between 5 and 80% by weight of the total absorbent material. weight.

According to another embodiment, the absorbent structure contains a combination of an absorbent scouring material and superabsorbent material.

According to a further exemplary embodiment, the superabsorbent material is in the form of a foam and according to a further exemplary embodiment, in the form of a coating on a material. preferably not more than 18 ml of an aqueous solution containing 0.9% by weight of saline solution, per g of superabsorbent material under a load of 2 kPa.

Description of the invention The absorbent structure according to the invention is intended to be used in an absorbent article of the type comprising a liquid-permeable cover layer, a liquid-tight cover layer and an absorbent structure interposed therebetween. The absorbent article may consist of a diaper, sanitary napkin, incontinence guard, bandage, bed pad, etc. The shape and construction of the absorbent article are, of course, completely optional and the invention can be applied to all types of such articles. 10 15 20 25 30 ~ 514710 5 The growing environmental awareness has meant that efforts are being made to replace the materials in absorbent articles, such as diapers, which are based on non-renewable / non-biodegradable raw materials with materials wholly or partly based on depletion and / or biodegradable raw materials. The materials in question are the liquid-tight casing of the ace layer in the form of a plastic film, the liquid-permeable casing of the ace layer in the form of a nonwoven and the superabsorbent.

Superabsorbents based on renewable and / or biodegradable raw materials, such as starch, cellulose, alginates, etc., often have a low gel strength and a low AUL value. Tests carried out have shown that such superabsorbents which have substantially equal FSC (swe swell capacity), CRC (centrifugal retention capacity) and AUL can have very different absorption capacities if combined with hydrophilic fibers, usually cellulosic pulp, in an absorbent structure. Therefore, according to the invention, another parameter has been sought which shows a clear correlation with the absorption capacity of the superabsorbent when it is incorporated in an absorbent structure, as it is intended to be made in an absorbent product, for example a diaper.

Rheology is the study of the deformation and surface properties of matter. The word rheology includes all deformation of a material that occurs when it is subjected to lQ-a fi er, whether it is enough with the usual gravity or if larger forces are needed. Rheology deals with the connections between KRAFI ", DEFORMAUON and TIME.

In the case where all defonation energy is spread as heat in the material, the material is referred to as VISKOST and it is said that it fl surface. In the event that the material stores all defonation energy, the material is referred to as ELASTIC and no sker surface occurs. A material where a certain part of defonation energy is stored and a certain part is spread as heat is called VISCOELASTIC.

In measurements of viscoelastic materials, the material is subjected to a sinusoidal stress (or deformation, depending on the type of instrument used) and the sinusoidal deformation (or stress) of the material is measured. The phase shift between the defonation and the stress is called the phase angle, ö. This is 0 ° for an ideal elastic material and 90 ° for an ideal viscous material.

By making a vector analysis of the stress-strain ratio, a component, G ', is obtained in phase with the deformation and a component, G ", 90 ° phase difference without the deformation.

The higher the values the modules G 'and G' 'assume, the more elastic and viscous the material, respectively. According to the above-mentioned EP-B-254 476, it is the module G's that is measured, which according to the invention has not proved to be sufficient to predict the function of the superabsorbent in an absorbent structure.

It has now been shown according to the invention that precisely the phase angle δ defined as tan δ = G "/ G 'constitutes such a parameter which shows a clear correlation with the properties of the superabsorbent in a concept in an absorbent structure. Especially good product function in terms of absorption capacity and supernatant velocities are those superabsorbents which have an island value of 8 °, and it is particularly surprising that this is also true for superabsorbents which have an AUL value as low as l0g / g at 2 kPa, which is deviated from in Table 1 below.

The rheological measurements are performed on a Carri Med CSLz 100 from TA Instruments.

The rheometer is a "controlled stress" instrument. The measurements have been carried out using accepted theological methods, so that those skilled in the art can easily repeat the measurements.

In all measurements, the materials are sample prepared according to the principle of absorbent material to 20 g of synthetic urine. In order for the materials to be tested at the iron weight position during the swelling process, the mixture of sample + synthetic curin must be left for 2 hours and then tested, but within 6 hours of the mixture being prepared. 10 15 20 25 30 - 514t71o 7 The measurements are divided into two steps, where step one includes a so-called “stress sweep” with which you can adjust the linear area of the material. The linear viscoelastic region occurs when the deformation is so small that the material only negligibly changes from its equilibrium position. From this linear range, the shear stress at which the material is to be tested is selected in the next frequency sweep. From the frequency sweep O, l-10II-Iz the quantities G ', G' 'and ö are obtained. All G', G "and Ö values shown in the table below are taken at 1.13 Hz.

The superabsorbent based superabsorbents tested were a number of test substances based on crosslinked CMC (carboxymethylcellulose), A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13 and A14. Preparation of superabsorbents based on crosslinked CMC is described, inter alia, in EP-B-201 895. In addition, some test substances based on crosslinked carboxymethyl starch, B1, B2 and B3, were tested, which can be prepared substantially analogously to crosslinked carboxymethylcellulose (CMC) based on some test substances crosslinked. polyaspartate C1, C2 and C3, which can be prepared, for example, in accordance with WO96 / 08523. As a reference material, a commercially available superabsorbent from Hoechst called Sanwet IM 7100 was also tested, which is a cross-linked sodium polyacrylate and pure cellulose fluff without superabsorbent admixture.

The absorption concept tested consisted of 20% by weight of superabsorbent mixed with cellulose fl ufñnassa of chemical type. The basis weight of the mass structure was 500 g / m 2 In addition to the island value, the superabsorbents FSC (gl g), CRC (gl g) and AUL (g / g) were measured at 2 kPa. The test liquid in all cases consisted of synthetic urine according to the following recipe: 60 mmol KCl (4.5 g), 130 mmol NaCl (7.6 g), 3.5 mmol MgSO 4 (0.42 g), 2.0 mmol CaSO 4 * 2H 2 O (0.34 g), 300 mmol urea ( 18 g) and 1 g 0.l% -it triton are dissolved in 1 liter of dest.water. The measurement methods used to test the function of the superabsorbents in an absorbent structure as above were as follows: Absorbance in inclined plane: The specimen was placed at 30 ° inclination to mimic the position of the diaper during use and the lower end was in contact with a liquid bath (synthetic urine) and fi ck absorb liquid. The specimen was weighed before and after the liquid suction and the absorption was recorded as g of absorbed liquid per g of absorbent body.

Intake time: Three additions of 60 ml of liquid each (synthetic urine) were made with a time interval of 10 minutes. The time it took until all the liquid absorbed was measured (visual observation).

The results of the completed measurements are reported in Table 1 below.

Table l Material FSC CRC AUL Ö (°) Absorption in release time (s) (g / g) (g / g) (2/3) inclined Plan 1, 2, 3 (s / g) Mass - - - - 6.5 31 , 87, 127 IM 46 28 28 1.9 13.5 20, 15, 22 7100 A1 27 13 13 13.0 9.2 19, 34, 58 A2 29 22 11 16.0 8.8 21, 73, 134 A3 39 23 9 13.0 9.5 21, 45, 98 A4 40 20 13 15.0 9.0 19, 38, 81 A5 45 27 7 16.0 3.9 24, 75, 145 A6 43 25 13 15.0 9.1 22, 53, 123 10 15 20 25 30 '5 1 4 7 1 0' 9 A7 27 13.6 14 14.0 9.0 20, 44, 83 A8 25 13 14 15.0 9.2 20, 41, 97 A9 30 18 14 15.0 9.8 18, 50, 77 A10 54 32 11 20 9.6 21, 67, 210 A11 32 13 16 8.8 10.0 13, 23, 36 A12 58 18 12 21 9.0 18, 90, 960 A13 37 21 14 14 10.7 16, 60,131 A14 29 16 12 8.8 9.6 24, 24, 40 Bl 26 14 15 6.0 10.7 22, 28, 42 B2 27 17 6 9.9 9.4 25 , 60, 79 B3 20 12 9 - 10.2 23, 40, 63 Cl 31 17 8 2.9 12.1 22, 30, 49 C2 28 13 14 2.4 11.3 21, 30, 49 C3 23 10 18 2.0 9.8 21, 33, 54 Correlation studies on these dry test results show that the island value correlates positively with the entry times 2 and 3, ie. low inlet times at low Ö values, and negative with the absorption capacity, ie. high absorption capacity at low island values.

Multiple correlation studies show that CRC in combination with the island value explains the result of the absorption capacity and of the inlet time 3.

In the above experiments, the superabsorbent was in the form of particles which were mixed with cellulose ün uünassa to form an absorbent body. However, the recovery is not limited to such absorbent bodies, but it is also conceivable to apply superabsorbent particles in the form of layers between layers of cellulose flute fi nassa or other choices fi- in hydrated fibers, natural or synthetic. The superabsorbent can also be applied between layers of tissue, nonwoven or other materials.

The superabsorbent may also be in the form of fibers, such as a liner, as a coating on other materials or as a foam. Instead of or in addition to cellulose fluff pulp, the absorbent body may contain other types of hydrolysers, absorbent scouring materials and the like.

Claims (12)

lO l5 20 25 30 35 "5-14 * 710 ll Paten tkrav An absorbent structure in an absorbent article, such as a diaper, sanitary napkin, incontinence guard, dressings, bed pads, etc., which structure contains a superabsorbent in material optionally in combination with other absorbent or carrier materials and that superabsorbent material has a content of renewable and / or biodegradable raw material of at least 20% by weight, calculated on the dry weight superabsorbent material, characterized in that the superabsorbent material has a phase angle δ s 8 ° defined as the phase shift between deformation and stress measured by rheological measurements. Absorbent structure according to claim 1, characterized in that the superabsorbent material has a phase angle δ: 6 °, preferably s4 ° and most preferably s 3 °. Absorbent structure according to Claim 1 or 2, characterized in that the superabsorbent material has a content of renewable and / or biodegradable raw material of at least 40, preferably at least 60 and preferably at least 80% by weight * l / b, based on the dry weight of superabsorbent material. Absorbent structure according to one or more of the preceding claims, characterized in that the superabsorbent material comprises a crosslinked polymer, wherein the polymer is based on renewable and / or biodegradable raw material and the crosslinker is either renewable and / or biodegradable or non-renewable / non-renewable. biodegradable. Absorbent structure according to one or more of the preceding claims, characterized in that it contains a combination of hydrophilic fibers and superabsorbent material. Absorbent structure according to Claim 5, characterized in that the hydro-fibers consist of cellulose pulp, tissue or hydro-synthetic fibers. lO 15 20 25 30 »514 rio 12 Absorbent structure according to Claim 5 or 6, characterized in that it contains between 5 and 80% by weight of superabsorbent material, based on the total weight of the structure. Absorbent structure according to one of Claims 1 to 4, characterized in that it contains a combination of an absorbent foam material and a superabsorbent material. Absorbent structure according to one of Claims 1 to 4, characterized in that the superabsorbent material is in the form of a foam. Absorbent structure according to one of Claims 1 to 4, characterized in that the superabsorbent material is in the form of a coating on a carrier material. Absorbent structure according to one or more of the preceding claims, characterized in that the superabsorbent material has an absorption capacity under a load of 2 kPa (AUL) of at most 25, preferably at most 20 and most preferably at most 18 ml of an aqueous solution containing 0, 9% by weight of saline solution, per g of superabsorbent material. Absorbent articles such as a diaper, sanitary napkin, incontinence guard, dressing, bedding, etc. comprising a liquid-permeable cover layer, a liquid-tight cover layer and an enclosed absorbent structure therebetween, characterized in that the absorbent structure is of the type specified in any of the claims. 1-1 l.