EP0003186B1

EP0003186B1 - Moist packaged towelette and method of making same

Info

Publication number: EP0003186B1
Application number: EP79300077A
Authority: EP
Inventors: George Davidowich; Gerald Donald Miller; Wiley Edgar Daniels
Original assignee: Air Products and Chemicals Inc
Current assignee: Air Products and Chemicals Inc
Priority date: 1978-01-18
Filing date: 1979-01-17
Publication date: 1982-06-23
Also published as: EP0003186A1; DE2963135D1

Description

This invention relates to a moist packaged towelette and to a method of making the same.
Moist packaged towelettes are generally made by coating a sheet of nonwoven fabric, usually absorbent paper, with a binder and storing the coated fabric in contact with an aqueous solution in a container. The aqueous solution typically contains alcohol and, for example, a perfume or deodorant. The binder increases the structural integrity of the nonwoven fabric and prevents it disintegrating in the aqueous solution. (For the avoidance of doubt the term "nonwoven fabric" as used herein includes fabrics comprising carded or randomly orientated or cross-laid fibres. The fibres may comprise, for example, natural or regenerated cellulose, other synthetic or proteinaceous fibres of biodegrade materials, or mixtures of these).
Various binders have been proposed but all which are known to us have the disadvantage that the coated fabric maintains a high structural integrity even after prolonged exposure to water. This can result in blocked drains.
One known binder for nonwoven fabrics which are not intended to be exposed to moisture is polyvinyl alcohol. Whilst nonwoven fabrics provided with this binder have excellent structural integrity in the dry they disintegrate rapidly when immersed in water.
In order to use polyvinyl alcohol as a binder in applications where the non-woven fabric will be subjected to moisture it has been proposed to "insolubilize" the polyvinyl alcohol by the addition of, for example melamine formaldehyde and ammonium chloride such as disclosed in GB Patent Specification No. 1,510,667. Whilst the coated fabric has excellent wet strength it takes a substantial time to break down in excess water and can thus block drains. It has also been disclosed in US Patent 3,692,725 and 3,886,112 that a coating of polyvinyl alcohol and sodium tetraborate will increase the wet strength of a non-woven fabric in small amounts of water but will rapidly dissolve in large amounts of water thereby permitting the non-woven fabric to be disposed of via a toilet.
We have discovered that a nonwoven fabric provided with a binder comprising polyvinyl alcohol will retain a high structural integrity in contact with an aqueous solution provided that the aqueous solution contains a sufficient concentration of boric acid or sodium sulphate to prevent the polyvinyl alcohol dissolving in the aqueous solution. When the solution is diluted the polyvinyl alcohol dissolves thereby weakening the structural integrity of the towelette.
Accordingly, the present invention provides a moist packaged towelette comprising a sheet of nonwoven fabric provided with a binder and maintained in contact with an aqueous solution in a container characterized in that said binder comprises polyvinyl alcohol and said aqueous solution contains boric acid or sodium sulphate at a sufficient concentration to prevent said polyvinyl alcohol dissolving in said aqueous solution.
If boric acid is used it preferably comprises at least 1% (by weight) of the aqueous solution with 3% to 5% (by weight) being preferred and 4% to 5% (by weight) being more preferred.
If sodium sulphate is to be used it preferably comprises between 3% and 20% (by weight) of the aqueous solution and more preferably between 7% and 2096 (by weight) of the aqueous solution.
Polyvinyl alcohol is generally produced by the hydrolysis of polyvinyl acetate. Pure polyvinyl alcohol (i.e. 100% hydrolysed polyvinyl acetate) is relatively insoluble in water at room temperature when compared with 80% to 99% hydrolysed polyvinyl acetate. Accordingly, the binder preferably comprises a mixture of polyvinyl alcohol and polyvinyl acetate. If desired the polyvinyl alcohol may comprise as little as 1% (by weight) of such a mixture although it preferably comprises between 80% and 95% thereof.
Mixtures (emulsions) comprising vinyl acetate-ethylene copolymers and polyvinyl alcohol may also be used as a binder. In such a case the polyvinyl alcohol preferably comprises from 196 to 10% (by weight) of the binder and probably acts as a protective colloid. If desired the binder may also contain polyvinyl acetate and preferably between 5 and 25% (by weight) thereof. One particularly preferred range of binders comprises (by weight) 1 to 10% of 80―90% hydrolysed polyvinyl acetate and the balance vinyl acetate-ethylene copolymers. Preferably the vinyl acetate-ethylene copolymers contain (by weight) not more than 45% vinyl acetate and not more than 60% ethylene.
In all the above cases the weight of the binder is preferably between 5% and 50% of the weight of the untreated non-woven fabric.
The present invention also provides a method for making a moist packaged towelette which method comprises the step of wetting a sheet of nonwoven fabric provided with a binder by bringing said sheet into contact with an aqueous solution characterized in that said binder comprises polyvinyl alcohol and said aqueous solution contains a sufficient concentration of boric acid or sodium sulphate to prevent the polyvinyl alcohol dissolving in the aqueous solution.
The present invention also provides a method for making a moist packaged towelette which method comprises taking a sheet of nonwoven fabric which has been provided with a binder and packaging said sheet of treated material in contact with an aqueous solution in a container characterized in that said binder comprises polyvinyl alcohol and said aqueous solution contains a sufficient concentration of boric acid or sodium sulphate to prevent the binder from dissolving in the aqueous solution.
The container should preferably be impermeable to all the components of the aqueous solution. However, for economic reasons a container need only be sufficiently impermeable to the components of the aqueous solution for a limited period of time, for example, the anticipated time delay between manufacture and use. The container itself may be in the form of a sachet for accommodating a single towelette or a bag or box for accommodating a plurality of towelettes. In the latter cases the bags or boxes are preferably resealable to minimise evaporation of the aqueous solutions.
The binder may conveniently be applied to the nonwoven fabric by making an aqueous solution (or emulsion) of the binder and applying it to the fabric by, for example, a roller or a spray gun. Alternatively, the nonwoven fabric may simply be dipped in the aqueous solution (or emulsion).
Once treated the nonwoven fabric is preferably dried, and is then cut and, if desired, folded. The nonwoven fabric may then either be wetted by the aqueous solution and inserted in a container or inserted in a container and wetted. It should be understood that it is not essential to dry the nonwoven fabric after the application of the binder although drying is preferred for ease of handling.
For a better understanding of the invention reference will now be made to the following nonlimiting examples.

Example 1

A sheet of high groundwood, unsized paper (25 inchx38 inch) (63.5 cmx96.5 cm) was immersed in water for two minutes. (When dry 500 sheets of the paper weighed 24 pounds (10.9 Kg)). The wet sheet was found to have a tensile strength of approximately 0.59 pounds/inch (0.1 Kg/cm).

Example 2

A sheet of the same paper used in Example 1 was impregnated with a solution of VINOL (Trade Mark) 205 polyvinyl alcohol (PVOH) to the extent of 4 pounds (1.80 Kg) dry add-on and dried in a 120°C forced air oven. After immersion in water for two minutes the wet sheet was found to have a tensile strength of 0.59 pounds/inch (0.1 Kg/cm), i.e. approximately equal to the wet sheet in Example 1. (VINOL 205 is 87% to 89% hydrolysed polyvinyl acetate of low viscosity (4-6 cps) marketed by Applicants).

Example 3

Two sheets of paper were prepared and dried as in Example 2. However, instead of immersion in water both sheets were immersed in an aqueous solution containing 5% (by weight) boric acid at room temperature.
After immersion for two minutes one wet sheet was tested and found to have a tensile strength of 1.6 pounds/inch (0.29 Kg/cm), i.e. nearly 3 times the tensile strength in Example 1 and 2.
The other wet sheet was then immersed in a large quantity of water for a further two minutes and when tested was found to have a wet tensile strength of less than 0.8 pounds/inch (0.14 Kg/cm).

Example 4

A sheet of paper was prepared and dried as in Example 2. The sheet was then immersed in an aqueous solution containing 5% (by weight) boric acid at room temperature for 1 year. On removal from the solution there was no detectable reduction in tensile strength as measured by finger pull.

Example 5

In order to determine the probable shelf life of the packaged towelette films of 15 ml. (0.038 cm) wet thickness were separately cast from VINOL 205 and VINOL 540 PVOH and dried at room temperature. Strips of the films of 1 x6 inches (2.54x 15.24 cm) were then immersed in an aqueous solution containing 5% (by weight) boric acid at various temperatures. The probable shelf life of the packaged towelette at various temperatures is indicated in Table 1.
In contrast all the films dissolved within 5 minutes when immersed in ordinary water. (VINOL 540 is 87% to 89% hydrolysed polyvinyl acetate of high viscosity (40-50 mPas) marketed by Applicants). 80% hydrolysed PVOH is commonly known to have reverse solubility, i.e. is insoluble in water above 20°C but is soluble at room temperature. For this reason towelettes should advantageously be coated with this material for use in high temperature atmospheres.

Example 6

A high groundwood stock paper substrate weighing 24 pounds (10.9 kg) per 3300 ft2 (307 m²) of its surface area (one face only) was treated with a 15% aqueous solution of VINOL 205 PVOH applied with a No. 10 Mayer rod separately to each side of the paper and dried at 250°F (120°C) for 30 seconds. The coated first side was dried before applying the coating to the other side.
The dried paper was then immersed for two minutes in a 5% boric acid solution and its wet tensile strength determined in Instron (C) and compound with that of the base stock (A) and the coated sheet without boric acid (B). The results are reported in Table 2 below. The resolubility was demonstrated by further immersion of the boric acid treated sheet in plain water for two minutes (D).

Example 7

Further studies were carried out to determine the effect of boric acid concentration on the wet tensile strength of PVOH in pregnated papers. These studies were made on paper sheets of a 42 pound/3300 sq. ft. stock (0.06 Kg/m²) each respectively immersed in boric acid solution of successively increasing concentrations. It was found that the wet tensile strength increased almost linearly with concentration from 0.72 pounds/inch (0.13 Kg/cm) at zero boric acid to 1.41 pounds/inch (0.26 Kg/cm) at 5% boric acid.

Example 8

Papers treated with other grades of polyvinyl alcohol were tested to determine the effect of boric acid in inhibiting disintegration. These included commercial grades identified as:
Each of these VINOL compositions were applied to a 24 Ib/3300 ft² (0.036 Kg/m²) base stock and dried at 250°F (120°C) for 30-90 seconds, as required. The amount of PVOH add-on varied due to viscosity differences so that the measured wet tensile values are not directly relatable between the grades.
All of these PVOH treated sheets exhibited wet tensile improvement with 5% boric acid immersion versus water immersion and all showed resolubility in plain water after short immersion in boric acid solution, as shown in Table 3.

Example 9

Cast films of VINOL 205 PVOH (1"×6"=2.5×15.24 cm) were separately tested to determine solubility respectively in boric acid solutions and in sodium sulphate solutions at different concentrations. The results are reported in Table 4.
The specific behaviour of boric acid in retaining solubilization of PVOH film is not attributable to the pH of the boric acid solution. Whereas a VINOL 205 film was insoluble in 5% boric acid solution, such film was readily dissolved respectively, in 5% aqueous solution of citric and phosphoric acid and a 0.7% solution of fumaric acid.

Example 10

A 60% vinyl acetate-40% ethylene copolymer emulsion containing 4% PVOH (75% VINOL 205 and 25% VINOL 523) (by weight) of the copolymer, and containing a total of 52% solids was cast to form a film of 15 mil (0.127 mm) wet thickness and air dried. While the film retained its definition when immersed in water, it exhibited practically no wet tensile strength as evidenced by the fact that it could not suspend its own weight.
When immersed in a 5% boric acid solution, the film exhibited surprisingly good wet tensile strength and was highly elastic. However, this film removed from the boric acid solution was redispersed in plain water in less than two minutes.
The treated film in contact with boric acid solution retained wet tensile strength for more than 30 days at 130°F (54.4°C). At 160°F (71.1 °C) the film retained wet tensile strength for 3 days indicating excellent film stability and shelf life at the elevated temperature that may be experienced under storage conditions.

Example 11

The same emulsion as employed in Example 10 was diluted and applied to a paper substrate.
The emulsion was diluted with water to a 25% total solids content and applied to both sides of a 42 pound/3300 square foot (0.06 kg/m2) paper substrate, and the treated paper dried at 120°C in a forced air oven. The pick-up was 3.5 pounds (1.59 Kg) dry emulsion.
A sample of the dried emulsion treated paper, as determined by conventional Instron test, showed a wet tensile strength after immersion in water, of 1.08 pounds/inch (0.19 Kg/cm) as compared to the untreated stock which showed a wet tensile of 0.72 pounds (0.33 Kg).
A duplicate sample of the dried emulsion treated paper immersed in 5% boric acid solution for 2 minutes when tested by Instron exhibited a tensile of 1.41 pounds/inch (0.56 Kg/cm). When reimmersed in plain water for 2 minutes, the paper returned to about its initial wet strength, 1.09 pounds/inch (0.2 Kg/cm).
Another duplicate sample of the dried emulsion treated paper was immersed in 5% boric acid solution for 30 minutes maintained about the same tensile strength as that previously shown for the boric acid treatment while the water value on reimmersion decreased to 0.91 pounds/inch (0.16 Kg/cm).
It should be noted that the paper in the foregoing example had a relatively low dried emulsion add-on. At higher add-on levels or lower basis weight substrate greater relative increase in tensile strength may be realized.

Example 12

Cast films of the same emulsion as employed in Example 10 (1"x6"=2.5x15.24 cm) were separately tested to determine solubility respectively in boric acid solutions and in sodium sulphate solutions at different concentrations. The results are reported in Table 5.
From the foregoing results, it appears that while the soluble salts, sodium sulphate, can be employed to retard solubilization of polyvinyl acetate films, somewhat greater concentrations, i.e. about 3% to about 20%, are required than when using boric acid.

Claims

1. A moist packaged towelette comprising a sheet of non-woven fabric provided with a binder and maintained in contact with an aqueous solution in a container characterized in that said binder comprises polyvinyl alcohol and said aqueous solution contains boric acid or sodium sulphate at a sufficient concentration to prevent said polyvinyl alcohol dissolving in said aqueous solution.

2. A moist packaged towelette according to Claim 1, characterized in that said boric acid comprises at least 1 % (by weight) of said aqueous solution.

3. A moist packaged towelette according to Claim 2, characterized in that said boric acid comprises 3% to 5% (by weight) of said aqueous solution.

4. A moist packaged towelette according to Claim 3, characterized in that said boric acid solution comprises 4% to 5% (by weight) of said aqueous solution.

5. A moist packaged towelette according to any preceding claim, characterized in that said aqueous solution contains from 3% to 20% (by weight) of sodium sulphate.

6. A moist packaged towelette according to any preceding claim, characterized in that said binder comprises polyvinyl acetate.

7. A moist packaged towelette according to Claim 6, characterized in that said binder comprises between 80% and 99% (by weight) polyvinyl alcohol.

8. A moist packaged towelette according to Claim 6, characterized in that said binder comprises vinyl acetate-ethylene copolymer.

9. A moist packaged towelette according to Claim 8, characterized in that said vinyl acetate-ethylene copolymers comprises from 10% to 40% (by weight) vinyl acetate.

10. A moist packaged towelette according to Claim 8 or Claim 9, characterized in that said binder comprises from 196 to 10% (by weight) polyvinyl alcohol.

11. A method for making a moist packaged towelette which method comprises the step of wetting a sheet of nonwoven fabric provided with a binder by bringing said sheet into contact with an aqueous solution characterized in that said binder comprises polyvinyl alcohol and said aqueous solution contains a sufficient concentration of boric acid or sodium sulphate to prevent the polyvinyl alcohol dissolving in the aqueous solution.

12. A method for making a moist packaged towelette which method comprises taking a sheet of nonwoven fabric which has been provided with a binder, and packaging said sheets of treated material in contact with an aqueous solution in a container characterized in that said binder comprises polyvinyl alcohol and said aqueous solution contains a sufficient concentration of boric acid or sodium sulphate to prevent the polyvinyl alcohol from dissolving in the aqueous solution.