IE45743B1 - Absorbent articles - Google Patents

Abstract

The absorbent structure (60) which can be placed against the body serves for absorbing body fluids. It has an absorbent insert (72) which contains a fibrous mass (90), synthetic particles (92) being melted with the fibres in the insert (72). This increases the strength and resilience of the fibrous mass (90) and prevents clumping of the latter during use. In order to minimise the cost and thickness of the insert (72), the synthetic particles are arranged only in the upper side or inside thereof.

Description

The present invention relates to absorbent articles. ..Various absorbent articles of the disposable type, such as diapers and sanitary towels, have been proposed which are discarded after a single use. Several factors are of importance in determining whether such articles will be acceptable to the consumer. The articles should rapidly receive and dissipate body fluids without a significant amount of back-wetting to the wearer's skin, dnd should be inexpensive since they are not reused.

Much of the cost and deficiencies in prior articles may be attributed to the structure of and the materials used in the articles. In the case of disposable diapers, structures are often provided having an absorbent pad, a fluid-impervious backing sheet covering a back surface of the pad, and a fluid-pervious top sheet covering a front surface of the pad. Particularly in the case where the absorbent pads are made of a mass of fibres, such as comminuted wood pulp known in the art as fluff, an absorbent wadding sheet is often placed over the front surface of the pad to prevent balling and maintain structural integrity of the pad during use. In addition to adding to the cost of the diapers, such top wadding sheets impair the function of the diaper in a number of respects. The wadding sheets impede the rapidity of fluid passage from th'e top sheet into the pad, and retain fluid adjacent the front - 2 4 5 7 4 3 surface of the diaper, thus increasing the amount of back-wetting from the diaper to the infant. The wadding sheet also adds stiffness to the diaper, thus making it uncomfortable to wear. In addition to lacking structural integrity, the fibres in the fluff pads collapse when wetted and placed under loads, thus decreasing the absorbent capacity of the pads.

According to one aspect of the invention an absorbent article of sufficient pliability for placement against a wearer to capture body fluids comprises an absorbent pad comprising a mass of fluff fibres and particles of a thermoplastic material attached by fusion and solidification to fibres in the pad to increase the integrity and resiliency of the fibrous mass, a fluid-pervious top sheet covering at least a portion of the front surface of the pad, and a backing sheet of fluid-impervious material covering at least a portion of the back surface of the pad.

The increased structural integrity of the fibrous mass minimizes the possibility of breaking up and balling of the pad during use, minimizes collapsing of fibres when the pad is wetted and placed under loads in use, and eliminates the necessity for top and bottom wadding sheets for the pad, thereby permitting rapid passage of fluid into the pad from the fluid-pervious top sheet, reducing back wetting from the pad, and improving the pliability and hand of the article so that'it is more comfortable to the skin of the wearer.

As indicated above, many absorbent pads are currently made from wood fluff, which is normally formed by fiberizing or comminuting pulp board.

The pulp board itself is normally formed from trees through a pulping process.

The pulping processes may be categorized as chemical, semichemical, mechanical and thermochemical. All of the wood fluff used in absorbent articles sold in the United States known to the applicants has been exclusively formed from a chemically produced pulp. For a given species of wood, the chemical pulping process produces a pulp having fibres with a longer length than the fibres produced by the other pulping processes, particularly the mechanical pulping process. Accordingly, the industry has sought chemically produced pulp for use in disposable pads since the long fibres enhance the structural integrity and loft of the pad. - 3 45743 < ί Although the chemical pulp results in a pad with desirable characteristics, a number of disadvanatages are inherent in the use of such pulp. First, the chemical pulping process is relatively inefficient in that the yield of pulp to the amount of wood used in pulping is in the range of 40 to 55%, whereas the yield of the mechanical and thermomechanical pulping processes is as high as 90 to 95%. The disparity in yields between » * the processes is due to the removal of lignin, cellulose and hemicellulose from the wood during digestion in the chemical procedure. Accordingly, chemically produced pulps are significantly higher in cost than mechanical and thermo10 mechanical pulps, necessarily resulting in a more costly item to the consumer. Also the vital raw materials are not used to the desired extent in chemical pulps, thus being wasteful of natural resources.

Second, environmental considerations favour the use of pulps which are not produced by the cheitrical process. In the chemical sulphite process, it is difficult to reclaim the chemicals used during pulping. Hence, the manufacturer must dispose of the chemicals, which can be a problem where contamination of water by the chemicals must be avoided. Although it is less difficult to reclaim the chemicals used in a Chemical kraft pulping, this process is characterised by the emission of gases containing malodorous substances, such as mercaptans and organic sulphides.

Third, the energy required to fiberize pulp board solely of the chemical type is greater than that necessary for a pulp board containing I mechanical or thermomechanical produced pulp. This is because lignin of the fibres is removed during chemical pulping, thus increasing hydrogen bonding between dry fibres of the chemical pulp.

The invention enables short fibres,such as fluffs formed from mechanical, thermomechanical, or semichemically produced pulps to be used in the pad because the plastics material maintains sufficient structural integrity of the pad.

The invention also includes methods of making such absorbent articles.

One method includes making the absorbent pad of the article by a procedure including the steps of forming a mass of wood fluff fibres, positioning particles of the thermoplastic material in the mass, and heating and cooling the - 4 45743 mass whereby the thermoplastic particles become attached to fibres in the mass by fusion and solidification. Another method includes making the absorbent pad by a procedure including the steps of forming a mass of wood fluff fibres, spraying a thermoplastic material in molten form on the mass, and permitting the thermoplastic material to solidify as particles attached to fibres in the mass.

The invention may be performed in various ways and some embodiments will now be described by way of example, with reference to the accompanying drawings, in which:Figure 1 is a diagrammatic view illustrating an apparatus for making an absorbent article according to a method of the invention; Figure 2 is a fragmentary front plan view illustrating an article in the form of a disposable diaper embodying the invention; Figure 3 is a fragmentary sectional view of the diaper of Figure 2; and Figures 4 to 6 are fragmentary sectional views of three other articles embodying the invention.

Although, for convenience, the absorbent article of the present invention will be described as a disposable diaper, it will be understood that the description is applicable to other absorbent articles, for example, sanitary towels, maternity napkins and wound dressings.

Referring now to Figure 1, there is shown an apparatus, generally designated 10, for making an absorbent article, such as a disposable diaper, according to a method of the present invention. The apparatus 10 has a first section 12 which receives pulp board from a plurality of feed rolls 14, and fiberizes the pulp board into a mass of fibres termed by the art commounted wood pulp or wood fluff. The types of wood pulp utilized in the feed rolls 14, or fed into the first section 12 by other suitable means, will be described in greater detail below. The first section 12 also receives a supply 16 of thermoplastic particles 18, and mixes the particles with fibres in the wood fluff. The particles of plastics material may be in any suitable form, such as powder, fibres, flakes, spheres or shredded material, and may be, for example, polyethylene, polypropylene, and Vinyon, (a Trade Mark of Union Carbide Corp., Charleston, West Virginia, U.S.A.). - 5 457 43 As shown, the first section 12 forms a mixture of fluff and plastics particles into a web 20, and passes the web 20 onto an endless belt 22 which is supported and driven by a pair of rollers 24 in a direction such that the web 20 is carried from the first section 12. The web 20 may be cut into lengths by suitable» means, such as reciprocating knife 26, in order to define pad sections 28.

The pad sections 28 pass from the belt 22 into a second section 30 where the pads are heated in order to fuse the plastics particles and cause them to adhere to fibres in the pad. The second section may comprise an oven, a hot air applicator or other suitable heating device. After the plastics materials have been melted in the heating section 30, the pad sections pass between upper and lower endless belts 32 and 34, respectively, which are respectively supported and driven by associated pairs of rollers 36 and 38. The belts 32 and 34 are driven in a direction such that the pad sections 28 are carried between the belts and are compressed by the belts while the plastics particles are still hot. In this manner, the plastics particles are pressed into closer engagement with the fibres and after solidification are firmly attached to the fibres. However, the pad sections may be heated and compressed simultaneously by suitable means, such as by heated rolls. Alternatively, the pad sections need not be compressed if the sections are heated to a sufficient temperature or the proportion of the plastics material relative to the fibrous mass is sufficiently large.

After compression, the pad sections 28 pass from the belts 32 and 34 into a third section 40 where final steps in the formation of the absorbent article take place. For example, in the case of a disposable diaper, a backing sheet of fluid-impervious material is placed against a back surface of the pad section, a fluid-pervious top sheet is placed against the front surface of the pad section, the top and backing sheets are secured together, and the diaper folded into the desired configuration, after which the diaper 42 passes from the third section 40 onto a belt 44 which carries the diapers to suitable apparatus for packaging the diapers.

In an alternative form, the thermoplastic particles are placed against a surface of the web 20 or pad sections 28 by a supply 46 of plastics - 6 457 43 material. The thermoplastic material may be spread in solid particulate form on the pad section, or it may be sprayed in molten form on the pad sections to form the particles, in which case further heating by the section 30 is not required. The plastic material may be placed against either of the outer surfaces of the pad section, or may be placed against both outer surfaces by inverting the pad or in another suitable manner. If desired, a carrier web 48 of tissue, such as a wadding sheet, may be unwound from a roll 50, and may be placed against the lower surface of the web 20, as shown, in order to facilitate movement of the web 20 prior to heating, particularly in the case where the plastics material is placed against the opposed surface by the supply 46.

An absorbent article in the form of a disposable diaper is illustrated in Figures 2 and 3 in which different reference numerals are utilized for clarity. The diaper generally' designated 60 comprises an absorbent pad assembly 62 having a backing sheet 64 of fluid-impervious material, such as polyethylene, defining a back surface 66 of the pad assembly 62, a fluidpervious top or cover sheet 68, such as a pervious non-woven material, defining a front surface 70 of the pad assembly 62, and an absorbent pad 72 located between the backing sheet 64 and cover sheet 68. The pad assembly 62 has a pair of side edges 74 and a pair of end edges 76. The absorbent pad 72 has a front surface 78, a back surface 80, a pair of side edges 82 and a pair of end edges 84. In a preferred form, as shown, the side edges 82 of the pad 72 are located adjacent the side edges 74 of the pad assembly 62, and the backing sheet 64 has lateral side margins 86 folded over and secured to the front of the pad assembly and covering lateral side margins of the absorbent pad 72. The diaper 60 may have tape fasteners 88 for use in securing the diaper about an infant.

As previously described, the absorbent pad 72 is made from a mass of fibres 90, and has particles 92 of thermoplastic material attached by fusion and solidification to the fibres 90 in the fibrous mass of the absorbent pad 72.

In the embodiment shown, the plastics particles 92 extend substantially throughout the pad, and are dispersed between the side and end edges 82 and 84, respectively, of the pad 72, and between the opposed front and back surfaces 78 and 80, respectively, of the pad 72. As shown, the particles 92 are spaced - 7 45743 throughout the pad in order to permit passage of fluid into the pad.

The fused and resolidified plastics particles hold the pad fibres together and maintain the structural integrity of the pad without the necessity of top and back wadding sheets, and may be used with the same results to maintain structural integrity of fluffs formed from pulps other than chemical pulp. Accordingly, the cost of the pad 72 and diaper is reduced, since the top and back wadding sheets have been eliminated, and the non-chemical fluffs are significantly cheaper than chemical fluffs.

Elimination of the top wadding sheet permits a more rapid passage of fluid from the top sheet into the pad, and reduces back wetting from the pad which is normally caused by the presence of the top wadding sheet.

Further, the article is pliable and has a better hand due to elimination of the top wadding sheet, thus providing additional comfort to the skin of the wearer. In addition to adding structural integrity to the pad 72, the fused and solidified plastics particles 92 increase the resiliency of the pad when wetted and placed under loads during use. In the past, the fibres in the usual chemical fluff collapse when wetted and placed under loads, thus reducing the interfibre spacing of the fluff and the ( absorbent capacity of the pad. In contrast, the fused and solidified particles 92 provide the pads 72 with resiliency, and increase the bulk and absorbent capacity during use.

As indicated above, the fused and solidified plastics particles 92 may be used to maintain the structural integrity of the pad even when formed from a non-chemical fluff having relatively short fibres. As will be discussed below, the pad 72 may be formed from a single type of such lower cost pulps, or the fibres from various pulps may be mixed into the pad.

As a background, the various pulping processes are - 8 4 5743 discussed as follows. Pulping itself may be defined for the present purposes as a procedure for rupturing the fibres of wood. The resulting pulp may be used for making paper or in this case absorb ent pads. The separated fibres of the pulp are normally formed into pulp board which may be wound into the feed rolls for conveni ence of handling during shipment and by the user. As discussed above, the rolls are fiberized or comminuted by the user to form the loosely formed fibrous mass which is cut into lengths as absorbent pads for the disposable articles.

Wood itself is primarily composed of cellulose, hemicellulose, and lignin. Lignin is an amorphous polymer of relatively high molecular weight that serves to hold the fibres of wood together. Cellulose is highly hydrophilic, while lignin has a significantly reduced affinity for liquid than cellulose and is relatively hydrophobic. Since pulping is concerned with rupturing the bonds between the wood fibres, the middle lamella between the fibres, which is composed mostly of lignin, must be ruptured during the procedure.

Wood logs are transported to the processor, after which bark from the logs may be removed. Generally, the logs are ground into chips, and the chips are used in the pulping procedure to separate fibres in the chips. The fibres are then washed to produce the unbleached pulp, after which the pulp may be bleached to a lighter colour pulp. The process differs primarily in the manner the wood is pulped.

The pulping procedures may be categorized as mechanical, chemical, semichemical and thermomechanical. In mechanical pulping, the logs themselves may be ground by a roughened stone to grind fibres out of the wood. Alternatively, wood chips may be - 9 45743 shredded or ground between metal shearing discs in a machine called a refiner. The mechanical pulps produced in this manner are characterized by relatively short fibres due to damage of the fibres during the procedure. Such groundwood processes are relatively efficient in that approximately 95% of the dry weight of the wood is converted into pulp, since materials, such as lignin, are not specially removed from the pulp.

In.chemical pulping, the wood chips are cooked in a vessel or digester with chemical reagents to separate the fibres, termed a digesting procedure. During digesting, the pulping reagents degrade and dissolve the lignin to break the bond between the fibres in order that they may be separated. However, the reagents also degrade some of the cellulose and hemicellulose, and( the loss of these, materials, including lignin, accounts for the relative inefficiency of chemical pulping. Thus, the yield from chemical pulping may range from 40 to 50% of the weight of the wood, with a maximum yield of 55%. Accordingly, chemically produced pulps are significantly higher in cost than mechanical and thermomechanical pulps, the yield of the latter also believed to approach 95%, not to mention the loss of valuable materials during chemical pulping.

The chemically produced pulp is characterized by relatively long fibres which are mostly completely separated. As noted above, the lignin is removed, and the hydrophilic fibres thus produced are susceptible to increased wetting.

The two most common chemical procedures are the sulphite and kraft processes. In the sulphite procedure, an acidic mixture is used as the reagent which is relatively difficult to reclaim, - 10 45743 thus posing a risk to the environment when disposed by the processor. In the kraft or sulphate process, the chips are cooked in a solution of sodium hydroxide, sodium carbonate and sodium sulphide. This process results in the emission of gases containing malodorous substances, and is also repugnant to the environment.

In the semichemical process, such as the neutral-sulphite process, the wood chips or logs are softened with a chemical, after which the wood is fiberized mechanically, frequently in disc refiners. The yield of the semichemical process is also higher than that of the chemical process.

Finally, in the thermomechanical procedure, wood chips are steamed at an elevated temperature and pressure to soften the lignin. Thus, the binding force between the fibres is greatly lessened through application of heat to permit separation of the fibres, . The fibres may be separated by a refiner under pressure or pressure changes.

For convenience, the fibrous mass formed from a mechanic ally produced pulp will be termed a mechanical fluff, the fibrous mass formed from a thermomechanically produced pulp will be termed a thermomechanical fluff, the fibrous mass formed from a semichemically produced pulp will be termed a semichemical fluff, while the fibrous mass formed from a chemically produced pulp will be termed a chemical fluff. The average fibre length of the mechanical fluff is less than that of the thermomechanical fluff, the average fibre length of the thermomechanical fluff is less than that of the semichemical fluff, while the average fibre length of the semichemical fluff is less than that of the chemical fluff. - 11 45743 Thus, under normal conditions the structural integrity and loft of the chemical fluff are1greater than those of the other fluffs which accounts for the widespread use of chemical fluff. However, relative to chemical fluffs, the fibres in the mechanical, thermomechanical, and semichemical fluffs contain a greater portion of their natural lignin, and the wet resilience of the fibres in the non-chemical fluffs is greater than that of the chemical fluff, thus providing the non-chemical fluffs with greater resiliency and fluid holding capacity when wetted and placed under loads.

In the embodiment of the invention shown in Figures 2 and 3, chemical, thermomechanical and semichemical fluffs may be used in the pad 72 with the fused and solidified plastics particles 92 providing the desired structural integrity of the pad, even though the fibres of the non-chemical fluffs have an average fibre length less than that of the usual chemical fluff. The pad may be made solely of mechanical fluff, thermomechanical fluff or semichemical fluff, or may comprise a mixture of the non-chemical fluffs, a mixture of the non-chemical fluffs and a chemical fluff, or, if desired, solely from the more costly chemical fluff. As explained above, due to higher pulp yields, the mechanical, thermomechanical and semichemical fluffs are less costly than the usual chemical fluff, and to the extent that the mechanical, thermomechanical or semichemical fluffs are used in the pad, the cost of the pad and of the diaper is reduced.

Another diaper 60 embodying the invention is illustrated in Figure 4, in which reference numerals corresponding to those used in Figures 2 and 3 designate like parts. In this embodiment, the plastics particles 92 are placed on the front surface 78 of the pad 72, and are attached by fusion and solidification to the pad fibres at this location. Accordingly, the particles 92 maintain the structural integrity of the pad adjacent the front surface in a manner as previously described. If desired, a back wadding sheet 94 may be placed against the back surface 80 of the pad 72.

Another embodiment of the invention is illustrated in Figure 5, in which again, like reference numerals designate like parts. In this - 12 45743 embodiment, the particles 92 of plastics material are placed on the back surface 80 of the pad 72 and are attached by fusion and solidification to the fibres adjacent the lower part of the pad. Thus, the plastics particles 92 maintain the structural integrity of the lower portion of the pad. If desired, the pad 72 may have a top wadding sheet 96 by covering the front surface 78 of the pad 72.

Another embodiment of the invention is illustrated in Figure 6, in which, again, like reference numerals designate like parts. In this embodiment, the particles 92 of plastics material are placed on both the front and back surfaces 78 and 80 respectively, of the absorbent pad 72.

The particles 92 are attached to the pad fibres in a manner as previously described, and maintain the structural integrity of the front and back portions of the absorbent pad 72.

Claims (20)

1. An absorbent article of sufficient pliability for placement against a wearer to capture body fluids, comprising an absorbent pad comprising a mass of wood fluff fibres and particles of a thermoplastic material attached by fusion and solidification to fibres in the pad to increase the integrity and resiliency of the fibrous mass, a fluidpervious top sheet covering at least a portion of the front surface of the pad, and a backing sheet of fluid-impervious material covering at least a portion of the back surface of the pad.

2. An article as claimed in Claim 1, wherein the thermoplastic particles comprise a powder.

3. An article as claimed in Claim 1 wherein the thermoplastic particles comprise fibres.

4. An article as claimed in any of Claims 1 to 3 wherein the thermoplastic particles are dispersed substantially throughout the pad.

5. An article as claimed in any of Claims 1 to 3 wherein the thermoplastic particles are located adjacent the front surface of the pad.

6. An article as claimed in any of Claims 1 to 3 wherein the thermoplastic particles are located adjacent the back surface of the pad. - 13 4874-3

7. An article as claimed in any of Claims 1 to 3 wherein the thermoplastic particles are located adjacent both the front and back surfaces of the pad.

8. An article as claimed in any of the preceding claims wherein the wood fluff comprises fibres formed from a mechanically produced Pulp.

9. An article as claimed in any of Claims 1 to 8, wherein the wood fluff comprises fibres formed from a thermomechanically produced pulp.

10. An article as claimed in any of Claims 1 to 8, wherein the wood fluff comprises fibres formed from a semi chemically produced pulp.

11. An article as claimed in any of Claims 1 to 8, wherein the wood fluff comprises fibres formed from a chemically produced pulp.

12. An article as claimed in any of the preceding claims which is a disposable diaper.

13. An article substantially as described herein with reference to any of Figures 2 to 6 of the accompanying drawings.

14. A method of making an article as claimed in any of Claims 1 to 12 which includes making the absorbent pad by a procedure including the steps of forming a mass of wood fluff fibres, positioning particles of the thermoplastic material in the mass, and heating and cooling the mass whereby the thermoplastic particles become attached to fibres in the mass by fusion and solidification.

15. A method as claimed in Claim 14 including the step of compressing the heated mass.

16. A method as claimed in Claim 14 or Claim 15 wherein the positioning step comprises mixing the particles of the thermoplastic material with fibres in the mass.

17. A method as claimed in Claim 14 or Claim 15 wherein the positioning step comprises placing the particles of thermoplastic material against an outer surface of the mass.

18. A method of making an article as claimed in any of Claims 1 to 12 I which includes making the absorbent pad by a procedure including the steps - 14 4S743 of forming a mass of wood fluff fibres, spraying the thermoplastic material • i in molten form on the mass, and permitting the thermoplastic material to solidify as particles attached to fibres in the mass.

19. A method of making an article as claimed in any of Claims 1 to 12 5 which includes making the absorbent pad by a procedure substantially as described herein with reference to Figure 1 of the accompanying drawings.

20. An absorbent article which has been made by a method as claimed in any of Claims 14 to 19.