FR2510628A1 - ABSORBENT SHEET STABILIZED, IN PARTICULAR FOR HYGIENIC PADS AND LAYERS - Google Patents

Abstract

THE INVENTION RELATES TO A STABILIZED ABSORBENT SHEET. THE SHEET, CONTAINING HYDROCOLLOIDAL FIBERS SERVING TO INCREASE RESISTANCE TO DEFORMATION IN A WET STATE, IS DRYED UNTIL AMBIENT CONDITIONS, THEN IS HEATED TO A TEMPERATURE BETWEEN ABOUT 150 AND 200C FOR A PERIOD OF ABOUT 3 TO 30 MINUTES. APPLICATION TO THE FIELD OF HYGIENIC BUFFERS AND LAYERS.

Description

251062-8

  The present invention relates to a method and products using absorbent fibrous bodies for absorbing fluids. In particular, the invention relates to products such as catamenial tampons, diapers, sanitary buffers and the like and relates more particularly to

  fibrous absorbent bodies that are easy to handle.

  in manufacturing processes of these products and which retain their integrity when wet by

fluids of the human body.

  The vast majority of fluid-absorbing products

  of the human body used at present include, at least in their training stage, buffers of

  fibrous absorbents, loosely and generally associated with

  such as ground wood pulp, rayon fiber, cotton, cotton floss and

  similar subjects For several generations, these

  have been found to be useful and effective in clothing, diapers, and sanitary articles because such materials are absorbent, poorly storytelling, and in the case of absorbent products to be worn by the user for a long time. These time-varying materials are flexible and comfortable Unfortunately, in contradiction with these highly desirable properties, there is the fact that buffers made of loosely associated fibrous materials are relatively fragile, because their tensile strength is low. , and they must be handled with care during their process of

manufacture -

  The manufacturing problems concerning these

  loosely associated with a certain degree of desire to incorporate into the mass of such fibrous materials certain cellulosic materials (called

  'hydrocolloldes'), which have properties of

  sorption substantially increased under the effect of a chemical modification Examples of such materials include: grafted cellulosic copolymers described in the patent

  U.S. No. 3,889,678 and cellulosic-carboxy

  Alkyl crosslinked agents described in U S Nos.

  3,731,686 and 3,858,585 and in U.S. Patent 3,589,364.

  These hydrocollold materials are in the form of

  highly inflatable fibers with strong retention effect.

  It is desirable to combine these fibers with more conventional absorbent materials such as rayon, wood pulp, cotton or the like, to produce an absorbent body having better properties.

  fluid retention properties Unfortunately, when

  that such fibrous materials are mixed, it is not easy

  to obtain a uniform distribution and this increases the co-

  plexity of manufacturing an absorbent body for the products concerned. In U.S. Patent Application Serial No. 8,200, filed October 5, 1979, there has been described a method for avoiding the difficulty of handling such materials and a process according to which the materials are arranged has been specifically described. in the form of a sheet which is made flexible by dry compression after its formation Although this method has obviously made it possible to use fibrous systems in an easier to process form and to produce products which are comfortable for the user, there are still disadvantages with these products Specifically, it has been found that when

  sheets of fibrous systems comprising modified fibers

  chemically as described above are wetted by fluids of the human body, such as urine or menstrual fluid, the leaves deform strongly, especially under the influence of pressures commonly occurring during the use of products such as tampons, diapers and similar items Under the influence of user pressure during the normal use of such products, leaves tend to flatten, flake and

  to deform, which greatly reduces their ability to em-

  trapping fluids in the interstices between the fibers

  and to allow the penetration of additional fluid.

  In other words, the deformation tends to limit the possibility of fluid penetration and, therefore, the full exploitation of the absorption capacities of these fluids.

  materials in the form of absorbent sheets.

  As a result, there is a need to produce a

  absorbent material in the form of a compact sheet, which can

  be easily handled during treatment, which is

  good when incorporated into absorbent products worn by the user, and resistant to deformation

  when subjected to pressure in the wet state.

  In accordance with the present invention, it has now been discovered that an absorbent material comprising hydrocollold fibers can now be provided in the form of a sheet having substantial structural integrity both in the dry state and after it has been formed. wetted by human body fluids Specifically, it has been discovered that a sheet of hydrocolloidal fibers can be

  a subtantial resistance to the deformation in the hu-

  mide and which is therefore able to still absorb fluids from the human body without flattening and without stopping the

penetration of fluids.

  According to the present invention, a sheet comprising

  Hydrocolloidal fibers are subjected to a thermal treatment in which the sheet is heated, in the dry state, at a temperature of between about 1500 ° C. and 2000 ° C., for a period of about 3 to 30 minutes, preferably

  a temperature of 170 to 180 ° C for 10 to 15 minutes.

  The sheet may be formed by conventional means, such as a wet formation process in which a wet web of hydrocolloidal fibers is formed from a slurry by depositing means

  the mud on a sieve and suck up the water using a vacuum.

  The wet web is then dried to form a non-flexible and relatively hard sheet. As described in the aforementioned US patent application, the sheet is

  can now be compacted and made flexible by applying

  The resulting sheet is then subjected to the heat treatment claimed so that

  this sheet is made resistant to deformation when

that she is wet.

  Figure 1 is a graphical representation of the relationship between load and time when leaves

  are subjected to wet pressure.

  FIG. 2 is a graphical representation giving the relationship between the relaxation percentage and the heat treatment time, in accordance with the method according to the invention; Fig. 3 is a graphical representation giving the same relation as in Fig. 2, but further showing the influence of the variation of the heat treatment temperature; Fig 4 is a graphical representation giving the same relationship as in Fig 2, when using a different hydrocolloid material; and Fig. 5 gives the same graphical representation, when

  the use of a hydrocollold material still different.

  The sheets concerned by the present invention

  hold fibers characterized by the term "hydrocollol-

  The base of said fibers may consist of commonly used cellulosic materials such as, for example,

  wood pulp, cotton, cellulosic fiber,

  and similar substances. It is generally

  said fibers have lengths between about 100 and 3000 microns.

  cellulosic fiber from wood pulp because of

  both its cost and its availability.

  The base fibers are made hydrocolloidal by a

  chemical modification, so that they become

  water-soluble and capable of absorbing water in an amount at least about ten times their own weight, in the dry state and preferably about

  fifteen to thirty times their dry weight

  It consists of a chemical fixation on the polymer backbone of the raw materials, hydrophilic groups

  or polymers containing hydrophilic groups.

  This class of materials includes

  which are modified by carboxyalkylation, by phosphono-

  alkylation, by sulfoalkylation or by phosphorylation so as to render them highly hydrophilic. Such modified polymers may also be crosslinked to improve their

  hydrophilic nature and to render them insoluble in water.

  The same basic materials may also be used, for example, as a backbone on which other polymer moieties may be attached by graft copolymerization techniques. Graft polysaccharides and their method of manufacture have been described in US Patent No. 3,889,678. ,

  and they can be seen as chains of polysac-

  charides onto which a hydrophilic chain of the general formula has been grafted: - (CH 2) q CRI (CHF 2) p CR 2

C = O C = O

  IIX m Y no: R 1 and R 2 are selected from the group containing hydrogen and an alkyl radical containing from 1 to 4 carbon atoms, x and y are selected from the group consisting of -OH, -O (metal alkaline), and -N Hz, m is an integer of between 0 and 5000, n is an integer of between 0 and 5000, the total number of m and N fractions in a chain being at least 500, p is an integer of a value of 0 or 1, and q is an integer of a value between let preferably the hydrophilic chain is a hydrolye copolymer of acrylonitrile and monomers of methyl methacrylate or ethyl acrylate, as defined in US Pat.

  The graft polysaccharides described above and, in particular

  particular, grafted cellulose and carboxymethyl-

  cellulose constitute hydrocolloidal fibers of choice.

  Hydrocolloid fibers can be combined with

  other cellulosic or non-cellulosic absorbent fibers

  for the production of the sheet according to the invention.

  The fibers are combined with water in a sludge formation station so as to form a sludge which can

  be transported to a slick formation station.

  Generally, the slurry should not contain more than about 0.1 and preferably not more than about 0.05% solids. The sludge can be formed in various ways known in the field of wet formation of

  For example, it may be prudent to form

  mud with a high concentration of solids, for example about 1.5% by weight solids, then further dilute the sludge by adding water to the desired concentration.

  Regardless of the formation of the mud,

  subsequently pass it in a web formation station where a wet web is formed, for example, by depositing the sludge on a continuous strip and maintaining a pressure difference on either side of the strip for evacuate a large proportion of the water and to leave a

  fiber web that is wet and loosely compacted.

  At this stage of the process, it is desirable that the web has a solids content of not greater than about 30% by weight of wet web and not less than about 6%. The wet web is then passed to a drying station where the web is is dried to a water content of less than about 10% by weight and preferably less than

about 5%.

  In accordance with the present invention, the web, now

  dried which corresponds to essential conditions

  It is then heat treated in the heated state at a temperature of about 150 ° C.

  C for a period of about 3 to 30 minutes.

  It goes without saying that, in the higher temperature range, the time may approach the lower limit of the time range, and vice versa The heat treatment of the water may be carried out by passing it through a tunnel tunnel dryer of air operating at temperature

  and at the appropriate band speed.

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  The resulting product is a sheet that is very

  resistant to deformation under pressure in the wet state.

  This property can be quantified by using a relaxation percent determination assay, as defined in the following. In such an assay, a sample of given size sheet is wetted completely and the excess

  water is removed by placing the sample between

  paper towels The wet sheet is then placed on a compression cell in a control device

  such as that known as "Instron" I.

  The head of the Instron came down to

  it comes touching the wet leaf and recording it

  The head of the device is then turned off.

  slowed until a maximum load of

  pressure corresponding to an arbitrary weight (eg 25 kilograms) is indicated on the chart of the recorder When a maximum compression load

  25 kilograms is reached, the Instron

  and allow the sample to assume its equi-

free under load.

  As the sample assumes the condition of equi-

  free of charge, the compressive load decreases because the

  is distorted by the forces exerted by the

  Instron head The deformation starts fast-

  then slowly decreases until

  blush a constant load in a distorted state.

  relaxation percentage is defined as the difference between the load of 25 kilograms and the load in equilibrium,

  divided by the load of 25 kilograms and multiplied by 100.

  Fig. 1 gives a graphical relationship between the compressive load and time The force exerted by the head of the Instron apparatus is gradually increased to the value of P for a period of time, P being

  arbitrarily chosen for example at 25 kilograms.

  After the leaf has reached its equilibrium condition, it reaches a constant compressive load of value R. The percentage of relaxation is then defined by the relation l (PR) / P) 1 X 100 It is obvious that the higher the percentage The hydrocolloidal fibrous material is formed into a sheet by first ensuring the dispersion of

  fibers in the water to produce a sludge with a

  1.17% by weight of solids 1 liter of slurry was placed in a conventional 185mm x 100mm sheet mold manufactured by Williams Apparatus Company, Watertown, New York. The slurry was then diluted at a consistency of 0.01% by weight solids, in accordance with the process defined in the standard method

TAP Pl T-2050571.

  After thorough mixing, the water is allowed to evacuate by gravity, and there remains a moist hydrocolloid fibrous web having a solids content of about 5%,

  value being based on the weight of the dry web.

  The wet pad is then dabbed with blotter leaves, compressed to remove excess water and then dried in a circulating air oven until

  water content of about 2% by weight of the dry matter.

  Resulting leaves having a weight of

base of 144 kg for 270 m 2.

  In accordance with the present invention, the different

  Leaf samples are submitted to a treatment stage.

  in which the leaves are heated

  at 1750 C for different periods of time.

  Leaf specks are then monitored to determine their percentage relaxation, as described above

for the compression test.

  FIG. 2 gives the results of this test for samples A, B and C of Table 1, these samples having been subjected to heat treatments at 1750 ° C. between 0 and 60 minutes. As shown in FIG. O minute, that is to say a

  the absence of heat treatment, the percentage of

  This is basically a function of the degree of hydrolysis or, in other words, the hydrophilicity of the hydrocolloidal material. Sample C, which has a high degree of hydrophilicity, has a relaxation percentage of 8 l,

  i.e., low wet stability.

  As relaxation decreases, the stability of the sheet under humid conditions is greater and, conversely, the greater the percentage of relaxation, the lower the wet stability and the greater the risk of the sheet becoming deformed under pressure. it is moistened.

EXAMPLE I

  A series of sheet samples were prepared from a hydrocolloidal fibrous material made in accordance with Example III of the aforementioned U.S. Patent No. 3,889,678. This material is a grafted cellulose copolymer consisting of a skeleton in cellulose

  on which were grafted hydrophilic polymer fractions

  lysed from poly (acrylonitrile) and poly (ethyl acrylate) by combining raw materials consisting of wood pulp, acrylonitrile and ethyl acrylate in the following proportions by weight: 1 part of wood pulp for 1.40 parts of ethyl acrylate and 0.8 parts of acrylonitrile This hydrocolloidal material is in a fibrous form, the fibers having an average length of about 0.89 mm. According to US Patent No. 3,889 678 mentioned above, the grafted material is subjected to a hydrolysis step. Table 1 defines the

  conditions in which these samples were hydro-

  lysed to produce a hydrolysed product with degrees

  hydrolysis variables, and therefore varying degrees of

hydrophilic properties.

Table 1

HYDROLYSIS SAMPLE

Time (Hours) Temperature (OC

At 1.75 80

B 2.75 80

C 3.75 80

  Sample A, having a low degree of hydrophilicity, pre-

  feels a relaxation percentage of 44, which indicates

  relatively high stability in the wet state.

  Sample B, which has a medium degree of hydrophilicity, has a relaxation percentage of 71, which corresponds to wet intermediate stability. When these samples are subjected to heat treatment for periods between 0 and 50 minutes, it is found that the percentage of relaxation decreases considerably and tends to stabilize, for these samples, at values between 15 and 25% after a heat treatment of between 10 and 20 minutes. stabilize and he does

  decreases more when the treatment time increases.

  As a control, a sample of wood pulp was also subjected to the same sheet forming process and subsequent heat treatment. As shown in Figure 2, this wood pulp sample exhibited approximately the same percentage of relaxation for a heat treatment of 0 minutes (no treatment)

  sample A, that is to say that the sample has

  However, in strong opposition to the hydrocolloidal sheet according to the invention, the wood pulp gives rise to practically no decrease in the percentage of relaxation when the duration of the heat treatment is increased and, conversely it remains much less stable when wet

  that the hydrocolloidal sheets according to the invention.

EXAMPLE II

  To illustrate the time-temperature relationship of the materials treated in accordance with the present invention, Sample C of Example I is subjected to

  of 150, 1750, and 200 ° C The results of the test of

  These figures are given in Figure 3. As shown in this figure, it takes 60 minutes to reach a relaxation coefficient of 20 when the

  heat treatment is carried out at 150 ° C.

  For a heat treatment carried out at 1750 C, it takes 10 minutes to reach this percentage of relaxation, and for a heat treatment at 200 ° C, it takes only 5 minutes As a control, the sample of wood pulp subjected to a heat treatment at 1750 C also

  shown in Figure 3, and it can be seen that the

  percentage of relaxation does not vary essentially with

  the duration of the heat treatment of this sample.

EXAMPLE III

  A sample D of hydrocollold material of the type described with reference to Exemp 1 is heat-treated

  at a temperature of 1750 C for varying periods.

  This sample D was prepared according to the process described in Example 1, except that the raw materials used were in the weight ratio of 1 part of cellulose to 2.75 parts of ethyl acrylate and 1.6 parts of ethyl acetate. acrylonitrile The sample is hydrolysed

  at 800 C for two hours Figure 4 shows graphically

  The variation of the relaxation percentage as a function of the duration of the heat treatment at 1750 C. As shown in this figure, the samples stabilized after about 10 to 15 minutes at a relaxation percentage of about 20%. FIG. 4 shows the results of Example 1 and, with regard to the percentage of relaxation, an equivalence

  more or less good with the sample of this Exempt 1.

  The results for the sample were also superimposed

  wood pulp, as a control.

EXAMPLE IV

  An absorbent fibrous sheet was prepared using

  reading the process described in Example 1, except that a fibrous mixture consisting of 50% wood pulp fibers and 50% by weight of crosslinked carboxymethyl cellulose fibers was used, these fibers being sold by the Hercules Company, Wilmington, Delware,

  under the commercial designation "Aqualon" I.

  The leaf produced by the process of Exempt 1 was checked with regard to the percentage of relaxation

  after having been heated to 1750 C during various

  The results are shown in Figure 5 and, as shown in this Figure, the carboxymethylated and heat-treated cellulose-containing sheet, ie Sample E, has reached a constant percentage of relaxation, which is ie a stability, after about 4 minutes of heat treatment at 1750 C. This process is much faster than for the copolymers

  grafted cellulose of the preceding Examples.

Claims (10)

  1. A method of treating a sheet containing hydrocollold fibers to increase the resistance to wet deformation, characterized in that said sheet is dried to ambient conditions and said sheet is heated to a temperature of between about 150 and 200 C for a period of about 3 to minutes.   2. Method according to claim 1, characterized in that said sheet is heated to a temperature between   about 170 and 180 C for about 10 to 15 minutes.   3. Method according to claim 1, characterized in that said hydrocolloidal fibers are chosen from the group consisting of carboxyalkylated cellulose fibers,   phosphoralcoylated, sulfoalkylated, phosphorylated or grafted.   4. Method according to claim 1, characterized in that said carboxyalkyl cellulose fibers are formed   of carboxymethyl cellulose insoluble in water.   Process according to claim 3, characterized in that   that the grafted cellulose fibers contain   on which are grafted hydrophobic polymer moieties of the formula: (CH 2) q CR 1 (CH 2) p CR I C = O C: O   II xymn LJL 1 = no: R 1 and R 2 are selected from the group containing hydrogen and an alkyl radical containing from 1 to 4 carbon atoms, X and Y are selected from the group consisting of -OH, -O ( alkali metal), and -NH 2, m is an integer from 0 to 5000, n is an integer of 0 to 5000, the total number of m and N fractions in a chain being at least 500, p is an integer of 0 or 1, and   q is an integer of a value between let 4.   Process according to claim 5, characterized in that   that said polymer fractions are copolymers, especially   hydrolyzed, acrylonitrile and acryl monomers. late ethyl.   7. Process according to claim 5, characterized in that   that said polymer fractions are copolymers, especially   hydrolyzed, acrylonitrile and methyl methacrylate.   8. Absorbent sheet, characterized in that it   holds hydrocolloidal fibers, in that it has been treated   thermally in the dry state and in that it has a   relaxation percentage less than 25% under a load of   maximum compression of 25 kilograms.   9. Sheet according to claim 8, characterized in that the value of the relaxation percentage is less than   20% under a maximum compressive load of 25 kilograms.   10. Sheet according to claim 8, characterized in that said hydrocolloidal fibers are chosen from the group consisting of carboxyalkyl cellulose fibers,   phosphoralcoylated, sulfoaloylated, phosphorylated or grafted.   Sheet according to claim 10, characterized in that said Uoylated carboxyalcohol fibers are formed   of carboxymethyl cellylose insoluble in water.   The sheet according to claim 10, characterized in that said grafted cellulose fibers contain   cellulose on which fractions of poly-   hydrophilic mother, of the formula: (CH 2) q CRIZ CH 2) p CR 2 C = oc = o L km 1 XY n o: R 1 and R 2 are chosen from the group containing hydrogen and an alkyl radical containing 1 to 4 carbon atoms, x and y are selected from the group consisting of -OH, -O (alkali metal), and -NH 2, m is an integer of from 0 to 5000, n is an integer of between 0 and 5000, the total number of m and N fractions in a chain being at least 500, p is an integer of 0 or 1, and q is a integer of a value between letd 13 Leaf according to whether said fractions are hydrolysed, late ethyl.   14. Sheet according to whether said fractions are hydrolysed, methylated. claim 12, characterized in that   of polymer are copolymers   acrylonitrile and acryl monomers   claim 12, characterized in that   of polymer are copolymers,   acrylonitrile and methacrylate