GB2083050A

GB2083050A - Aqueous Emulsion Polymer Adhesive Compositions

Info

Publication number: GB2083050A
Application number: GB8125340A
Authority: GB
Original assignee: Kimberly Clark Corp
Current assignee: Kimberly Clark Corp
Priority date: 1980-08-28
Filing date: 1981-08-19
Publication date: 1982-03-17
Also published as: FR2489142A1; DE3130868A1; JPS5774375A; AU7335681A; KR830006396A; ZA815601B; NL8103668A; BR8105355A

Abstract

Adhesive compositions adapted to penetrate and strengthen a porous substrate and adhere a surface of the substrate to another surface comprise (1) a water emulsion polymer of polyvinyl acetate homopolymers, vinylacetate-ethylene copolymers, polyvinyl acetate-maleate copolymers, polyvinyl acetate or acrylic copolymers and (2) a water soluble polymer of polyvinyl-pyrrolidone, a partially hydrolyzed polyvinyl alcohol or completely hydrolyzed polyvinyl alcohol. The adhesive has particular utility for adhering portions of sanitary napkins and the invention also extends to such a sanitary napkin.

Description

SPECIFICATION Improvements in and Relating to Adhesive Compositions and Sanitary Napkins Including Such Adhesive Compositions This invention relates to an adhesive composition and particularly to an adhesive composition useful for laminating and reinforcing porous absorbent substrates.

Recently a new type of feminine napkin has attained substantial commercial success. This particular type of feminine napkin known as a panty liner is of limited capacity and is designed for use with intermenstrual vaginal discharge or, at other times when low levels of menstrual discharge occur.

Feminine napkins of the panty liner type, because they are designed to retain only minimal amounts of fluid, are smaller and more compact than the larger more absorbent conventional sanitary napkins.

Napkins of this type are designed to be flexible and soft. Flexibility is necessary so that the panty liner conforms to the perineal configuration, particularly as the wearer moves. Flexibility is important particularly at the peripherai edges because of the possibility of chafing which may result from the roughened edges contacting the tender skin in the perineal area.

One panty liner provides softness along its longitudinal sides by folding over the outer wrap and the absorbent material to provide a soft edge along the sides of the napkin. This can be accomplished without particular difficulty along the sides, but not at the longitudinal ends. These ends feature coterminous layers of the wrap and absorbent pad which may chafe. The layers also may separate which not only increases chafing by exposing a plurality of ends to delicate tissue but also tend to destroy the integrity of the napkin and, even with the low levels of flow contemplated for use of the napkin could provide areas of leakage.

Attempts to eliminate the delamination at the ends of the panty liner type of product have been directed into two general areas. The first involves the use of compression or embossing of the layers at the end. The second approach is to apply adhesive to the ends to adhere the wrap to the absorbent pad in the area. Both of these solutions have produced problems. While the adhesive does effectively prevent delamination it also stiffens the end portions eliminating the flexibility desired and decreasing the ability to maintain position during movement of the wearer.

Contrarily, when embossing only is used, softness is maintained but when the ends are wet, delamination frequently occurs. Delamination, in fact, even occurs in the dry state after some period of storage as the pad reaches moisture equilibrium. Delamination may also occur during use due to the motion applied to the ends during movement of the wearer.

According to this invention, an adhesive composition particularly adapted to penetrate and strengthen a porous substrate and adhere a surface of that substrate to another surface is provided in which a two-component adhesive system is utilized. The first component is a water emulsion polymer of polyvinyl acetate (PVAc) homopolymers, vinylacetate-ethylene (VA-E) copolymers, polyvinyl acetate-maleate (PVAcM) copolymers, acrylic copolymers or PVAc acrylic copolymers. The water emulsion polymers are mixed with a water soluble polymer of polyvinylpyrrolidone (PVP) or a partially or completely hydrolyzed polyvinyl alcohol (PVA).

Polyvinyl acetate homopolymer such as "Vinac XX-230" produced by Air Products and Chemicals, Inc., Allentown, Pa., U.S.A. is currently preferred. Due to the brittleness of this particular polymer, however, a plasticizer is required to provide the flexible adhesive film desirable for most types of adhesive applications. A suitable plasticizer is dipropylene glycol dibenzoate. This compound serves as an effective plasticizer and adhesion promoter. "Benzoflex 9-88" is a commercially available dipropylene glycol dibenzoate plasticizer supplied by Velsicol Chemical Corporation, Chicago, III., and is currently preferred.

Other plasticizers which may be used are dibutyl phthalate, "Santicizer 160" a butyl benzyl phthalate, "Saniticizer 141" a cresyl phenyl phosphate, "Saniticizer 8" an N-ethyl-ortho and paratoluenesulfonamides, all available from the Monsanto Chemical Company, St. Louis, Mo., U.S.A.

The (VA-E) copolymers are "suitable alternatives" and have similar adhesion characteristics to the (PVAc) polymers but due to the presence of the ethylene comonomer, little or no plasticizer is required to obtain flexibility and certain types of adhesion particularly to a nonporous substrate. A suitable (VA-E) copolymer is Airflex 400 produced by Air Products and Chemicals, Inc., Allentown, Pa., U.S.A.

Suitable water-soluble polymers for this adhesive combination are polyvinylpyrrolidone (PVP) which has excellent water solubility in conjunction with good substrate wetting properties. PVP is currently preferred as the water-soluble polymeric component. Alternative useful water-soluble polymers are partially hydrolyzed and completely hydrolyzed polyvinyl alcohols. Partially hydrolyzed PVA's are available in a variety of molecular-weight ranges from Monsanto Chemical Company and are sold as Gelvatol resins. Pva polymers are particularly useful because of their high cohesive strength and good film-forming properties. The choice of polymer grade in the partially hydrolyzed polyvinyl alcohol category is dependent upon the desired viscosity required for the adhesive application process.This will be discussed in more detail below but may in fact depend upon the method of application of the adhesive. For example, when the adhesive is applied by a spray the most highly soluble and lowest molecular weight grade of PVA polymer is preferred. Fully hydrolyzed PVA polymers are available from E. I. DuPont de Nemours a Company, Wilmington, Delaware, United States of America underthe Elvanol trade mark. It should be noted that polyvinyl alcohol polymers are manufactured by first forming the polyvinyl acetate polymer and then hydrolyzing the polyvinyl acetate polymer to form a PVA polymer. Partially hydrolyzed grades of polyvinyl alcohol, therefore, contain from 1025% of vinyl acetate groups while the fully hydrolyzed grades contain less than 1% of the vinyl acetate groups.

The fully hydrolyzed PVA polymers are useful in adhesive applications which require extra moisture resistance in the adhesive bond.

In addition to plasticizers, the adhesive mixture may contain small amounts, i.e. 0.10.2%, of wetting agents and/or defoamers to promote shelf stability of the liquid adhesive and to minimize foam generation during adhesive application. Suitable wetting agents are "Aerosol OT" by American Cyanamid Company, Wayne, N.

J., and "Triton X-100" by Rohm s Haas Company, Philadelphia, Pa. An alternative defoamer is Nopco JMY available from Nopco Chemical Company, Neward, N.J.

Generally, the adhesive composition may have from 2090% of the water emulsion polymer component and 550% of the water soluble polymer component. These percentages are percent by weight of the solid components of the adhesive mixture, rather than percent of the commercial ingredient purchased which includes water. The desired amounts of the components vary with the amount and rate of penetration of the porous substrate desired as well as the degree of residual adhesion necessary on the surface of the absorbent substrate as well as other factors well known in the adhesive art.A plasticizer is generally present between 540% by weight of the adhesive combination, the amount of plasticizer being dependent upon the particular choice of water emulsion polymer and the desired amount of flexibility present as well as the surface on which the porous substrate is to be attached.

The use of adhesive in accordance with the invention in a panty liner of this invention is illustrated in the accompanying drawings in which Figure 1 is a perspective view partially in cross section of the panty liner.

The pad is assembled by air laying wood pulp fluff 4 on a carrier layer of scrim 5. A thin layer of an adhesive of this invention is then coated on the upper portion of the fluff and a covering material such as a bonded carded web 2 having an embossed pattern 1 is overlaid on the adhesive coated fluff 4. The adhesive is then coated on the scrim support and permeates it to attach it to the fluff 4. The adhesive also provided integrity to the fluff layer 4 and bonds it to the cover material 2.

At this point in the process, all of the layers are coterminous around its entire periphery and is produced in long rolls approximately twice the width of the finished pad. Additional adhesive of this invention is then applied to the area 3. The structure is folded over along the sides so that the side peripheral edges abut each other. As can be seen from Figure 1 , this produces a configuration in which the outer layers, both top and bottom, are the cover material 2. Scrim support material 5; is folded over on itself as the innermost layer, and the fluff 4 is positioned between the cover 2 and the scrim support 5 on either side of the scrim.

The fold is maintained by gentle compression and the soft folded edge 10 is produced. The water impermeable baffle 6 is then adhesively attached in the abutted area.

Afterward the roll is embossed at each end to form the crimped end 3. Garment adhesive and release paper are then applied by conventional means and the ends formed. The napkin is then cut.

An example of a particularly preferred adhesive composition according to this invention for use as an end seal for panty liners is a mixture of 70% polyvinyl acetate homopolymer with 10% PVP and 10% partially hydrolyzed PVA and 10% of dipropylene glycol dibenzoate as a plasticizer. The PVP provides the substrate wetting and penetration properties necessary to maintain the integrity and prevent the delamination of the varying absorptive layers at the ends of the pad while the partially hydrolyzed PVA contributes adhesive film strength necessary to provide a desirable bond between the wrap and the absorbent materials.

Claims

1. An adhesive composition particularly adapted to penetrate and strengthen a porous substrate and adhere a surface of the substrate to another surface comprising, at least one water emulsion polymer of polyvinyl acetate homopolymers, vinylacetate-ethylene copolymers, polyvinyl, acetate-maleate copolymers, polyvinyl acetate-acrylic copolymers or acrylic copolymers and at least one water soluble polymer of polyvinylpyrrolidone, a partially hydrolyzed polyvinyl alcohol, or a completely hydrolyzed polyvinyl alcohol.

2. An adhesive composition according to Claim 1 wherein the water emulsion polymer is present in an amount between 20 and 90% by weight of the composition.

3. An adhesive according to Claim 1 or 2 wherein the water soluble polymer is polyvinylpyrrolidone present in an amount between 550% by weight of the composition.

4. An adhesive according to Claim 1 or 2 wherein the water soluble polymer is a partially hydrolyzed polyvinyl alcohol and is present at a level of 5 to 25% by weight.

5. An adhesive as claimed in any of the preceding claims wherein a plasticizer is present.

6. An adhesive according to any one of Claims 1 to 4 wherein dipropylene glycol dibenzoate is added at a level of 540% by weight.

7. A sanitary napkin containing an adhesive composition as claimed in any one of Claims 1 to 6.

8. A sanitary napkin according to Claim 7 which is a panty liner.

9. A napkin according to Claim 7 or 8 wherein the adhesive is used to attached a multilayered absorbent mat to a fluid permeable wrap.

10. A napkin according to any of Claims 7 to 9 wherein the adhesive composition has a water emulsion polymer present in an amount between 20 and 80% by weight of the adhesive composition.

11. A sanitary napkin substantially as hereinbefore described with reference to the accompany drawing.

12. An adhesive composition as substantially as hereinbefore described.