FIELD OF THE INVENTION

The invention relates to a process for producing a water disintegrable core which is used as a support for a roll of paper, especially for a toilet paper.

BACKGROUND OF THE INVENTION Papers for sanitary or household use are usually packaged in the form of rolls on a core. Said paper rolls, such as toilet paper roll or paper towel roll, are formed by winding the paper around a core that is generally made of cardboard.

Most of the cores that are used in conventional paper product rolls are disposed in the waste bins since they lead to a blockage of the soil pipe of toilets if they are thrown away down toilet bowls. However, in recent years consumers desire to throw said cores directly into the toilet bowl due to its ease of use and the need of decreasing amount of wastes produced by consumers. In this manner, the volume of waste to be destroyed or to be stored at dumps is decreased which results in a positive effect on the environment.

One of the most important features that water disintegrable cores must have is good stiffness characteristics. A core which does not have adequate strength cannot resist crushing from packaging, loading or transportation. This feature directly affects the quality of the products obtained.

Another important feature of a water disintegrable core is its disintegration time in water. Said cores must quickly disintegrate on contact with water in order to avoid the blockage of toilet drain lines. Water disintegrable cores which are suitable for throwing away down toilet bowls are known to date. For example, US 2010,167,889 describe a core which disintegrates in water and therefore can be thrown away into the toilet. The core is obtained by winding at least one strip made of tissue, wherein the strip is impregnated with starch. PCT patent application WO 2011/015951 describes a fibrous sheet which can be used to produce a water disintegrable core comprising 10% to 70% starch and at least 30% of papermaking fibers. To produce said fibrous sheet, the fibrous sheet containing starch is dried at a temperature high enough to gelatinize at least some of the starch.

It is, however, difficult to produce a water disintegrable core by methods presented by the prior art since they require specific drying temperatures and a lot of strip layers are required to produce a core having sufficient stiffness properties. Considering the amounts of starch used are exceeding by far starch amounts used for adhesion purposes. Moreover its application to the paper layers and drying process make the process overall cumbersome which brings about disadvantages in terms of the energy and material consumption.

Accordingly, there is a need for an improved method in order to produce a water disintegrable core to be used in paper product rolls such as toilet paper rolls, paper towel rolls, or the like.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide an improved method in order to produce a core which disintegrates quickly upon contact with water and has sufficient mechanical strength.

This object is solved in the present application by using alkali metal hydroxide selected from potassium hydroxide and sodium hydroxide.

This object is solved further by a method comprising the processing steps of suspending long cellulose fibers in aqueous alkali metal hydroxide solution, filtering and washing the filter repeatedly with water until the pH of filtrate reaches to neutral range. Obtained pulp is suspended in water, filtered through paper wire mesh, dried, spirally winded adhesively bonded and cut to obtain said water disintegrating core.

Moreover, this object is solved with another method comprising the processing steps of suspending long cellulose fibers in aqueous alkali metal hydroxide solution neutralizing the suspension with an acid, filtering the suspension through paper wire mesh, drying, spirally winding adhesively bonding and cutting to obtain said water disintegrating core.

In accordance with an embodiment of the invention, the objectives of the invention are successfully achieved with a paper sheet which can disintegrate in water with a basis weight of between 150 and 400 g/m 2 , preferably between 200 and 300 g/m 2 , more preferably around 260 g/m .

In accordance with another embodiment of the invention, the disintegration time in water belongs to the water disintegrable core is between 5 and 60 seconds, and preferably between 10 and 30 seconds.

In accordance with another embodiment of the invention, obtained cores can be used as a support in paper product rolls such as toilet paper rolls, paper towel rolls, or the like.

FIGURES

Figure 1: A view of disintegrable core of the present invention DETAILED DESCRIPTION OF THE INVENTION

The present inventors have surprisingly found that a water disintegrable core which quickly disintegrates upon contact with water can be produced by using alkali metal hydroxide in its preparation process. According to the present application, a method for producing a core which disintegrates in water comprising the following steps; a- providing long cellulose fibers,

b-adding an aqueous alkali metal hydroxide solution and suspending the cellulose fibers,

c-filtering the suspension,

d-adding water to the pulp on the filter, suspending and filtering,

e- repeating step (d) until the pH of the filtrate becomes neutral, f- adding water to the pulp on the filter suspending and filtering through paper wire mesh to form a paper sheet,

g- drying the paper sheet

h- spirally winding the paper sheet around itself,

i- adhesively bonding of the sheets to form a hollow tube,

j- cutting a section of said hollow tube to form a core.

Wherein said alkali metal hydroxide are selected from potassium hydroxide and sodium hydroxide wherein sodium hydroxide is preferred for economic reasons.

According to an embodiment of the present invention, the method comprises the step of suspending long cellulose fibers in an aqueous sodium hydroxide solution having a concentration of less than 15%. The suspension of disintegrable core paper production comprises preferably 10% of pulp and 90% of water.

Long cellulose fibers are defined according to the present application as cellulose fibers having fibers of 0.5 - 2.5 mm, preferably 0.7 - 2.0 mm of length. Said fibers are not reduced in size, milled or crushed mechanically. In the present application, it is believed that alkali metal hydroxide base dissolves acidic group containing cellulose fiber and removed by filtering. These fibers are thought to have enhanced binding capabilities. Further, it is believed that in this manner treated cellulose fibers are having reduced hydrogen bonding capabilities which enables cellulose fibers to disintegrate quickly in water so that a water disintegrable paper can be produced.

In the present application method, repeated washings with water is aiming to remove residual acidic cellulose and alkali metal hydroxide for bringing the paper sheet to its inherent neutral pH ranges. Besides, deviation from neutral pH ranges causes corrosion on the machine and equipment used in paper production.

The pH of the cellulose fiber solution is about 12-13 when said fibers suspended in an aqueous sodium hydroxide solution. After addition of water to said cellulose suspension, performing washings and forming sheets, the pH is decreased to about 6.5-8 as in conventional paper production processes. According to the present application, another method for producing a core which disintegrates in water comprising the following steps; a- providing long cellulose fibers,

b- adding an aqueous alkali metal hydroxide solution and suspending the cellulose fibers,

c- adding acid to the suspension until pH reaches neutral ranges,

d- filtering the neutral suspension through paper wire mesh to form a paper sheet, e- drying the paper sheet

f- spirally winding the paper sheet around itself,

g- adhesively bonding of the sheets to form a hollow tube,

h- cutting a section of said hollow tube to form a core. Any acid suitable can be used to adjust the pH in neutral ranges, however hydrochloride acid, sulfuric acid, phosphoric acid are preferred due to economic reasons.

Compared to the previous process, in this process repeated washings are avoided. Instead, excess alkali metal hydroxide is neutralized with acid until reaching neutral pH ranges, below 8 or preferably 6.5 to 8. Subsequently the suspension is filtered whereby the paper sheet formed remains on the paper wire mesh.

In that manner, excess water use is avoided and filtering steps are eliminated which simplifies the process and eliminates the need for further equipment significantly. On the other hand, the previous process has the certainty that acidic cellulose and excess base are removed pretty well. Nevertheless both processes are working with the desired reliability. Remaining steps are same as the previous method.

The aqueous alkali metal hydroxide, preferably sodium hydroxide solution used in the methods according to the present invention has a concentration of less than 15%, due to the aggressive character at high concentration of said base. High alkali metal hydroxide solution concentrations are damaging both for paper sheet obtained and machine equipment used. Against the common practice, the cellulose fibers used in a method according to the present invention are not subjected to a step of milling before suspending in an aqueous sodium hydroxide solution. It is believed that milling increases the surface area between cellulose fibers resulting in an increase in hydrogen bonding capabilities of said fibers, which is not a desired effect in case of disintegrating core product.

It has been found that a core produced according to a method of the present invention disintegrates in water faster than a similar standard core of the prior art. The term "similar standard core" is understood to mean a core having substantially the same diameter and the same length as the core of the invention. The same core has not been specifically treated for becoming a fast disintegrating core.

Furthermore, it has been found that a core produced according to a method of the present invention disintegrates in water in similar time period and shows similar mechanical strength properties as the water disintegrating cores produced with extra starch.

The cellulose fibers used in a method according to the present invention include any fibre incorporating cellulose as a major constituent. Cellulosic fibres suitable for making the core of the present invention include: non wood fibres, such as cotton fibres or cotton derivatives, abaca, kenaf, sabai grass, flax, esparto grass, straw, jute hemp, bagasse, milkweed floss fibres, and pineapple leaf fibres; and wood fibres such as those obtained from deciduous and coniferous trees, including softwood fibres, such as Northern and Southern softwood Kraft fibres; hardwood fibres, such as Eucalyptus, maple, birch, aspen, or the like. Papermaking fibres used in connection with the invention include naturally occurring pulp-derived fibres as well as reconstituted cellulosic fibres such as lyocell or rayon, softwood fibres, pine, spruce and birch. Preferred fibre type of the present invention examples is eucalyptus tree fibres.

In the state of the art manufacturing of core polyvinyl alcohol is used as adhesive. The adhesive used in the present application may comprise starch, polyvinyl alcohol, and dextrin. Preferred adhesive is dextrin due to its fast dissolving characteristics.

A standard core comprise of two sheets which are adhesively tacked to each other. In the present application the disintegrable core is comprised of only one sheet. This fact reduces the adhesive use which is promotional for the fast disintegration. Only adhesive used in case of present invention cores is to bind winding sheets sidelong to form the tube form of the core. The present invention eliminates the need to form the core from two or more sheets, herewith related processing, equipment, energy time consumption is eliminated as well.

The method of the present invention product may comprise application of additional agents, such as binders, cleaning agents, disinfectants or fragrances. These additives can be applied by any methods known from state of the art.

The paper sheet produced by a method according to the present invention which can disintegrate in water has a basis weight of between 150 and 400 g/m , and preferably between 200 and 300 g/m ² . The water disintegrable core produced by a method according to the present invention has a disintegration time in water between 5 and 60 seconds, and preferably between 10 and 30 seconds.

The water disintegrable core produced by a method according to the present invention can be used as a support in paper product rolls such as toilet paper rolls, paper towel rolls, or the like.

EXAMPLES EXAMPLE 1: Preparation of water disintegrating core with NaOH and water washings

285 g of 0.7 mm long cellulose fibers are suspended under stirring in 108 mL of 2,5 % aqueous sodium hydroxide solution and stirred for 15 min. Obtained suspension is filtered from 2mm sieve diameter mesh filter. 100 mL water is added to the cellulose filter, stirred and again filtered, this washing procedure is repeated until pH of the filtrate is below 7 (4 washings necessary). To the cellulose filter 14362 ml water is added, suspended by stirring and filtered from paper wire mesh of 60 mesh size. The formed paper sheet is vacuum filtered and dried at 90°C until having water content below 6% by weight. Obtained paper sheet has been cut, spirally winded around itself and sidelongs adhesively bonded with dextrane to form hollow tube and cut to obtain the core of desired size.

EXAMPLE 2: Preparation of water disintegrating core with NaOH ve HC1 neutralization

285 g of 2.0 mm long cellulose fibers are suspended under stirring in 108 mlp of % 2,5 aqueous sodium hydroxide solution and stirred for 15 min. To the suspension, 1M HC1 is added until the pH of the solution is reached to 7 (approximately 60 ml), stirred further and sieved from the paper wire mesh of 60 mesh size. The formed paper sheet is vacuum filtered and dried at 90°C until having water content below 6% by weight. Obtained paper sheet has been cut, spirally winded around itself and sidelongs adhesively bonded with dextrane to form hollow tube and cut to obtain the core of desired size. TEST METHODS

1: Core Disintegration Time Tests

1.5 g of a sample excised from a core is put in 500 ml of water and mechanically stirred with a spatula. Start time of loosening of web and complete disintegration time of web are recorded.

Table 1: Measured Disintegration Times of Present Invention Examples and Related Prior Art Samples

As can be seen Ex 1 and Ex 2 core disintegration times are very similar and show close similarity with the starch containing disintegrating core. Starch containing core sample is provided from market. These cores are prepared by impregnation of starch solutions into cellulose web. Regular cores are the ones that made with the regular cellulose web. As already known cores made from this material are not disintegrating even within a few days and therefore prone to clogging the sewer pipe. In the present invention, the regular cellulose is treated with sodium hydroxide which presumably removes the short chain cellulose and acid containing chains. It is believed these removed stuffs are responsible for binding cellulose web.

Consequently with the present invention method prepared cores are disintegrating in proper disintegration times and as fast as in market available starch containing disintegration cores. The present invention products are having the advantage of eliminating the need of starch or any other chemicals, therefore simple, feasible and economical advantageous.

2: Strength Tests

The sample cores of present invention are compared with starch containing core and regular core with regard to its physical strength. The present invention samples are sufficiently strong against vertical and horizontal pressure applied to a core and fulfill market requirements.