EP0506807B1 - Flexible, tear-resistant and burst-resistant sheet, with reduced liquid absorbancy and controlled porosity - Google Patents

Abstract

The supple sheet according to the invention, which is resistant to tearing and bursting, has a low water- or other liquid-absorbing power, controlled porosity and is printable, comprises: at least cellulosic fibers, optionally synthetic fibers, at least one binder, at least one moisture-retaining agent in a proportion less than about 20% by dry weight of the sheet, at least one sizing agent. The invention finds an application in sterilizable packages.

Description

The present invention relates to a flexible sheet which can be used especially for sterilizable packaging.

We already know flexible sheets that are used to form packaging for example for surgical materials, probes, scalpels, forceps, and all materials usable by doctors and / or surgeons.

These flexible sheets must present simultaneously and necessarily several properties.

A first property is that the sheet must be flexible to ability to form sachets into which objects of various shapes and sizes.

A second property is that the sheet must be resistant to tearing as well as bursting. Indeed, it is intended for contain objects which may be heavy and blunt or sharp. In addition, it is intended in the form of a sachet, during sterilization with gases, for example ethylene oxide, to be subjected to pressure during gas injection and strong posterior depression during the evacuation of gases, which must be complete.

A third property is that the sheet must be slightly absorbent especially with regard to water, so that water or other products liquids do not penetrate through the sachet formed by the sheet, from outside to inside, by defiling the wrapped object, in the bag.

A fourth property is that the sheet must be permeable to gas. When you put the object in the bag, then that we have sealed this one, we submit the assembly to the action of gas sterilants and / or sterilizing ionic rays. However the permeability should be low enough for bacteria or other microorganisms do not get inside the sachet.

We already know sheets used especially to form surgical equipment packages, which consist of paper obtained by the wet method by draining an aqueous suspension of cellulose fibers on a grid (Foudrinier process) then drying of the sheet.

Such sheets of paper are sold to manufacturers of sterilizable sachets or packaging that make up the sachet having a layer of lacquer which ensures the connection between the edges of the sheet and a transparent film.

Other processors apply heat-sealable lacquer, aqueous or solvent medium, so as to preserve a certain gas permeability of paper. The bags or pouches are then heat-sealed with plastic films.

A disadvantage of these papers is that they are generally not very flexible and moderately resistant to tearing and bursting.

These papers are not very absorbent of water or other liquids because that are introduced during their manufacture, either in the suspension aqueous, either by surface treatment, a bonding agent, by neutral example, of the dimeric ketene type which decreases the absorption of water through the leaf.

In the prior art, we have therefore tried to improve the physical resistance of the sheet and more particularly its resistance to tearing and bursting. To this end, we thought to increase the bond between the cellulose fibers. We have for this introduces a binder of the polyvinyl alcohol type by coating the sheet with a composition containing this polyvinyl alcohol. But a disadvantage of this resistant sterilization paper mechanically is that the introduction of the binder gives a little appearance aesthetic to the final packaging due to the existence of folds because the packaging then does not suit the shape of the objects properly packed. The inflexibility of the sheet of paper can lead to the opening of the seals when handling the finished packaging.

We also know sheets of paper that are made more resistant to tearing and bursting by introduction into mass and / or surface of polymer latex, for example acrylic. These sheets are manufactured and sold by the company KIMBERLY CLARK. These sheets are flexible and have a touch plastic. However, their manufacture is difficult and expensive and gives a non-homogeneous paper in its characteristics. In addition, this paper is relatively permanent and much less biodegradable than usual paper. These papers have little water barrier, because little bonded.

We also know sheets of paper that are processed in sorbitol sizing press to make them flexible. The problem with these sheets is that the tear resistance and the burst is relatively low and that obtaining the bonding is difficult.

Sheets have also been made of the dry non-woven type, that is to say that a mattress of synthetic fibers, for example polyethylene, is made, which is bonded together, when hot. These sheets are manufactured by the company DU PONT DE NEMOURS and sold under the name of TYVEK ^R. These sheets are resistant to tearing and bursting. In addition, they are flexible. However, a major drawback of these sheets is that their thickness is very heterogeneous, that is to say that the distribution of the fibers per unit area is irregular, which means that the porosity of the sheet is not uniform. Thus, in certain places, the sheet will have pores of too large diameter, which will have the effect that the microorganisms will be able to penetrate inside the packaging produced using this sheet. On the contrary, in certain places, the sheet will have pores of too small diameter, which will hinder the penetration of the molecules of sterilizing gas. In addition, these sheets are absolutely permanent, that is to say non-biodegradable.

The invention is remarkable in that, according to a person skilled in the art, it it is difficult to combine the requisite qualities simultaneously. Indeed, the products that improve mechanical characteristics increase the rigidity, therefore decrease flexibility.

To improve flexibility, the skilled person thinks of adding softeners. However, there are two types of fabric softeners: products which reduce the bonds between fibers and agents of humidity maintenance (cf Pulp and Paper, Volume III, 1981, pages 1763-1764 - 3rd edition, edited by J.P. CASEY).

The first fabric softeners mentioned destroy connections interfibers, so they decrease the mechanical characteristics. The second cited do not have this disadvantage but they oppose the action of the bonding agents which give the barrier properties leaf.

• au moins des fibres cellulosiques,
• éventuellement des fibres synthétiques,
• éventuellement un agent de résistance à l'état humide,
• au moins un liant,
• au moins un agent de maintien de l'humidité en une quantité inférieure à 20% environ en poids sec de la feuille,
• au moins un agent de collage.

The Applicant has overcome this a priori and has surprisingly found that it is possible to manufacture a sheet having the properties mentioned above, by manufacturing a fibrous sheet containing:

• at least cellulosic fibers,
• possibly synthetic fibers,
• possibly a wet strength agent,
• at least one binder,
• at least one moisture-retaining agent in an amount of less than approximately 20% by dry weight of the sheet,
• at least one bonding agent.

To this end, the invention relates to a flexible sheet, resistant to tearing and bursting, very little absorbent with water or other liquid, with controlled porosity, printable, comprising a support based on cellulose fibers of which at least one of the faces is impregnated with a composition comprising at least one binder, characterized in that the composition contains at least one moisture-retaining agent and at least one bonding agent, such as the measured COBB ₆₀ bonding according to ISO535 standard, is less than 20 g / m ² , that the TABER stiffness, measured according to ISO 2493 standard is less than 2.5 and that the amount of moisture-retaining agent is less than about 20% by weight dry leaf.

The sheet preferably contains at least 1% moisture-retaining agent.

The humidity-retaining agent is preferably chosen from the group formed by urea, a nitrate salt or their mixtures. As urea-nitrate mixture, the mixture can preferably be used in a urea / sodium nitrate ratio of 2: 1.

The bonding agent is chosen from the group formed by wax or paraffin dispersions, alkyl ketene dimers, alkylene succinic anhydrides, stearic anhydrides and their mixtures.

The binder is chosen from the group formed by polyvinyl alcohol, native starch or its derivatives, cellulose ethers or esters, alginates, guaranates or mixtures thereof.

The impregnation composition is preferably carried out in the medium aqueous.

• jusqu'à 5% en poids sec d'un liant
• jusqu'à 5% en poids sec d'une dispersion aqueuse de paraffine
• jusqu'à 20% en poids sec d'urée ou d'un mélange urée-nitrate de sodium par rapport au poids de la feuille sèche.

The composition preferably contains:

• up to 5% by dry weight of a binder
• up to 5% by dry weight of an aqueous dispersion of paraffin
• up to 20% by dry weight of urea or of a urea-sodium nitrate mixture relative to the weight of the dry leaf.

The fibrous support is preferably a support formed mainly cellulose fibers. This support is preferably not bonded en masse; it can contain at least one wet resistance. The sheet is produced by a papermaking process. The support can be impregnated with the composition according to the invention, using a sizing press. Any other means of impregnation or bedding usually used in stationery may be suitable.

• une souplesse suffisante pour pouvoir former des emballages.
• une résistance à la déchirure et à l'éclatement suffisante pour résister à des objets lourds et contondants.
• un absorption faible à l'eau.
• une porosité contrôlée, c'est-à-dire des diamètres de pores réguliers et suffisamment grands pour permettre le passage de molécules gazeuses mais suffisamment petits pour empêcher le passage de micro-organismes.

The invention makes it possible to provide usable sheets, in particular for sterilizable packaging having simultaneously the following properties:

• sufficient flexibility to be able to form packages.
• sufficient tear and burst strength to withstand heavy and blunt objects.
• low water absorption.
• a controlled porosity, that is to say regular pore diameters and large enough to allow the passage of gaseous molecules but small enough to prevent the passage of microorganisms.

The invention makes it possible to provide printable sheets, preferably by heliographic printing, offset or flexographic.

Indeed, for sterilizable packaging, these include always a reference which can be obtained using inks reacting during sterilization.

The invention makes it possible to provide sheets whose physical characteristics are homogeneous, i.e. substantially the same in the cross direction as in the running direction.

The invention makes it possible to provide sheets which are the more easily biodegradable after use and the cost of manufacturing is competitive.

The invention is remarkable in that a sheet is obtained having a COBB of less than 20 g / m2 and up to 12 g / m2, and having a TABER stiffness of less than 2.5 and having an index of tear greater than 80 cNm2 / g.

The sheet obtained according to the invention can be heat sealed with plastic films. It is suitable for receiving lacquering in the middle aqueous or in solvent medium.

It is also peelable.

It complies with standards for sterilizable packaging (DIN 58953, BS 6256) and on packaging intended to come into contact with food (FDA, BGA).

EXAMPLES

The following examples are carried out on a paper machine of laboratory. We impregnate, using a sizing press, a support based on cellulose fibers, not mass bonded. The compositions for the impregnation bath are carried out in medium aqueous.

The characteristics of the sheets obtained are given in the table 1.

The tear index is measured according to ISO standard 1974.

The dry burst index is measured according to the ISO 2758 measurement.

The wet burst index is measured according to ISO standard 3686 (after immersion in water for ten minutes).
(after immersion in water for ten minutes).
Burst REH (wet strength) is the ratio of the wet burst and dry burst indices, multiplied by 100.

TABER stiffness is measured according to ISO 2493.

BENDTSEN porosity is measured according to ISO 5636/3.

The dry recovery expresses the quantity of sauce by dry weight absorbed per sheet per square meter.

COBB C ₆₀ is measured according to ISO standard 535 (water, 1 minute, at 23 ° C). EXAMPLE 1 2 3 4 Impregnation bath : . binder: polyvinyl alcohol (% by dry weight / bath) 1 1 1 1 . sizing agent: aqueous dispersion of paraffin (% by dry weight / bath) 2 2 2 2 . humidity maintenance agent: (% by dry weight / bath) - urea 20 20 14 14 - sodium nitrate 6 6 Dry recovery (g / m2) 13 5 14 7 Weight 103 107 105 109 Thickness 133 133 146 135 COBB C ₆₀ 12.5 12 14 13 Tear index 88 99 84 93 Dry burst index 43.5 50 46 51.5 Wet burst index 15.5 21 19.5 23 REH burst 36 42 42 45 TABER rigidity 1.61 2.49 1.21 2.25 BENDTSEN porosity 300 330 350 310

The sheets obtained are sterilizable. They are sealable and peelable.

The sheets obtained according to Examples 1 to 4 were sterilized at the water vapor, ethylene oxide or gamma rays, and then we have measured their characteristics.

The results obtained are presented in Table 2. EXAMPLE 1 2 3 4 Weight - steam 104 112 - 105 - ethylene oxide 104 112 106 106 - gamma rays 103 111 104 106 Tear index - steam 91 109 - 97 -Ethylene oxide 88 106 89 96 - gamma rays 65 62 62 67 Dry burst index - steam 42 45 - 31 - ethylene oxide 47 50 48 34 - gamma rays 36 38 41 25 Wet burst index - steam 12 10 - 15.5 - ethylene oxide 16 20 23 22 - gamma rays 11 13.5 16.5 17 REH burst - steam 29 38 - 34 - ethylene oxide 34 44 43 45 - range departments 31 40 42 40 TABER rigidity - steam 1.25 2.19 - 2.09 ethylene oxide 1.70 2.50 1.27 2.11 - range departments 1.71 2.37 1.11 2.22 BENDTSEN porosity - steam 605 350 - 340 - ethylene oxide 310 330 360 330 - gamma rays 340 340 360 325

COMPARARATIVE EXAMPLES

The paper is coated with an aqueous composition containing sorbitol and dimeric ketene. We measure the COBB. It can be seen from Table 3 that the bonding is much easier to obtain with the compositions containing urea and / or nitrate salt according to the invention. COMPOSITION PV alcohol 1% 1% 1% Sorbitol 58% 58% 58% Urea 13% 16% 14% 23% 16% 20% 23% Nitrate 7% 8% 7% 8% Dimer cetene 3% 10% 3% 3% 6% 3% Paraffin 9% 5% 5% 5% 5% Overall dry recovery 23% 29% 18% 14% 15% 15% 15% 13% 14% 15% Cobb 1 minute 32 55 22 23 15 23 14 14 23 13

Claims (8)

1. A supple, tear-resistant and burst-resistant sheet, with very little water- or other liquid-absorbency and controlled porosity, which is printable and which has a cellulosic fibre-based support, at least one side of which is impregnated with a composition which comprises at least one binder, characterised by the fact that the composition contains at least one moisture-retaining agent and at least one sizing agent, such that the COBB₆₀ sizing value, measured according to the standard ISO 535, is less than 20 g/m², and the TABER stiffness, measured according to the ISO 2493 standard, is less than 2.5, and by the fact that the amount of moisture-retaining agent is less than about 20% by dry weight of the sheet.
2. The sheet according to claim 1, characterised by the fact that it contains at least 1% of moisture-retaining agent.
3. The sheet according to one of claims 1 to 2, characterised by the fact that the moisture-retaining agent is urea, a nitrate salt, or mixtures thereof.
4. The sheet according to one of claims 1 to 3, characterised by the fact that the moisture-retaining agent is a urea/sodium nitrate mixture in a ratio of 2:1.
5. The sheet according to one of claims 1 to 4, characterised by the fact that the sizing agent is selected from the group consisting of wax or paraffin dispersions, alkylketene dimers, succinic alkylene anhydrides, stearic anhydrides, and mixtures thereof.
6. The sheet according to one of claims 1 to 5, characterised by the fact that the binder is selected from the group consisting of poly(vinyl alcohol), native starch or its derivatives, cellulose ethers or esters, alginates, guaranates, or mixtures thereof.
7. The sheet according to one of claims 1 to 6, characterised by the fact that it contains a water-resistant agent.
8. A sterilisation package, characterised by the fact that it comprises at least one sheet according to one of claims 1 to 7.