EP0398825B1 - Process for making a plane, supple and hardly tearable substrate, and the same - Google Patents

Abstract

Manufacture of a planar, fibrous, flexible substrate which is difficult to tear. The process consists in: - preparing by fibrillation natural cellulosic fibres until they have been given a Schopper-Riegler drainability higher than 60 DEG , - mixing into water a charge of cellulose fibres thus beaten and at least 30% by weight of artificial fibres, - diluting the mixture obtained, - and producing a substrate sheet using a paper making machine fed with the mixture. - Application to the manufacture of envelopes and bags.

Description

The present invention relates to the manufacture of a planar, fibrous, flexible substrate, of the sheet, sheet or film type and it relates, more particularly, to such flexible substrates having good tear resistance as well as good ability to l 'printability.

The invention relates, more specifically, to such substrates used as paper supports for printing, writing, or even packaging of various products and articles.

As a specific application, the invention is directed to planar, fibrous, flexible, hardly tearable substrates, intended for the manufacture of packaging envelopes, sachets, bags or pouches, maps, printed matter. .

Such articles have always been made from sheets of paper, of the conventional or particular type when it is desired to reinforce their resistance by their intrinsic quality or by the provision of reinforcements.

Papers have always been made from cellulosic fibers which are more or less refined in order to increase the specific surface and improve the potential to create interfiber bonds.

Papers are reputed to have certain positive characteristics such as printability and also negative characteristics such as low tear strength and hygroscopic sensitivity.

If it is possible to improve the resistance to humidity by adding specific additives during the manufacture of the papers, it turns out that the conventional manufacturing means do not allow an increase in the resistance to tear.

This negative characteristic poses real problems in many applications, in particular that of the manufacture of envelopes, sachets and bags.

To solve this problem, the prior art saw the birth of a product which is difficult to tear if not tear-proof, marketed under the registered trademark Tyvek® . This product is in the form of a sheet formed from plastic fibers deposited on a plane and calendered hot. The sheet has a flexible character, effectively difficult to tear, but has a number of drawbacks in addition to its high cost price.

Among these drawbacks, we must cite an unattractive plastic aspect, a great difficulty of printing-writing due to the raw material used and an elastic reaction posing real problems, for example, to the shaper responsible for executing on the sheets of pre-folds for making envelopes, sachets or bags.

These three drawbacks and the high production cost considerably limit the commercial development of such a product, in particular in the application to the production of envelopes, sachets or bags.

The prior art has also proposed a solution consisting in producing a paper having better tear resistance by incorporating into conventional cellulosic fibers synthetic fibers chosen from polyolefins, polyamides, polyesters, etc. The objective sought was to try to improve the physical characteristics of ordinary papers by the addition of synthetic fibers.

In reality, this technique does not seem to have experienced real industrial and commercial development. This lack of development is probably due to the incorporation of synthetic fibers which constitute non-binding fibers compared to the cellulose fibers commonly used in the paper industry. The presence of these synthetic fibers among the cellulosic fibers results in a loosening of the cellulosic interfiber bonds resulting in a lowering of the usual physical characteristics such as the breaking length according to the standard (I) Afnor NF Q 03-004 or ISO 1924/1 - 1983 , internal cohesion according to standard (II) Afnor NF Q 03-045 , bursting according to standard (III) Afnor NF Q 03-053 or ISO 2758 - 1983 . Only the resistance to tearing initiated according to standard (IV) Afnor NF Q 03-011 or ISO 1974-1974 and to tearing not primed according to standard (V) TAPPI T 470 os - 78 seems to have been improved in certain cases until '' at around 25%.

The tests which were carried out on the basis of such a technique made it possible to note an addition threshold close to 20% for synthetic fibers and the obligation to resort to the incorporation in the mixture of different adjuvant products in order to try to identify the different physical characteristics lowered by the presence of synthetic fibers. To this end, it is usual to incorporate latex to improve the interface cohesion between natural and synthetic fibers. Such incorporation significantly increases the cost of production and does not give satisfaction on the positive enhancement of the lowered physical characteristics.

We also know the teaching of patent BE-A-670,968 which consists, in order to improve the overall resistance of absorbent cleaning papers in wet conditions, of mixing long artificial non-fibrillatable fibers with short fibrillated fibers and adding one binder per point ensuring most of the improvement in strength. This prior art does not relate to a paper that is difficult to tear, having, moreover, an aptitude for printing-writing. Furthermore, the degree of refining of the cellulosic fibers is extremely low, of the order of 16 ° SR, which practically corresponds to a dispersed raw pulp. No lesson useful in obtaining better tear resistance can therefore be retained.

One would have thought that it was enough to increase the refining of the pulp to obtain a paper that was difficult to tear. It is, on the contrary, well known in stationery and, in particular, according to PULP and PAPER , Chemistry and Chemical Technology, vol. II, 1960, Paper making, page 595-596, that on the contrary the resistance to tearing decreases with over refining paste. The same applies to the publication FUNDAMENTALS OF PAPER MAKING FIBERS, September 1957, page 387, in which it is also noted that the increase in refining results, at least from a certain limit, in a reduction in the resistance to tear.

The object of the invention is to remedy the drawbacks of the above techniques by proposing a new method for manufacturing a planar, fibrous, flexible, hardly tearable substrate, more particularly but not exclusively, intended for the production of envelopes. , pouches, sachets or bags.

The object of the invention is to produce, at an attractive cost price, a flat, fibrous, flexible, hardly tearable substrate, having, moreover, a good aptitude for printing-writing, as well as a resistance notably increased with variations in ambient humidity.

Another object of the invention is to provide a new substrate having good folding ability to facilitate the making of envelopes, pouches, sachets or bags.

• préalablement au mélange des fibres avec l'eau, on prépare, par fibrillation, des fibres naturelles cellulosiques provenant d'une pâte ordinaire, jusqu'à leur conférer une égouttabilité supérieure ou égale à 60° Schopper-Riegler,
• et on mélange ensuite dans de l'eau une charge de fibres cellulosiques ainsi raffinées et de 30 à 70 % en poids sur sec de fibres artificielles, par rapport à la charge totale de fibres cellulosiques et artificielles.

To achieve the above objectives, the manufacturing process according to the invention consists in:
mix the fibers in water, dilute the mixture obtained, pour it into a headbox of a paper-making machine and produce a sheet of substrate from said machine fed with the mixture and operating with respect for the parameters traditional driving,
characterized in that:

• prior to the mixing of the fibers with the water, cellulosic natural fibers from an ordinary pulp are prepared by fibrillation, until they give a drainability greater than or equal to 60 ° Schopper-Riegler ,
• and then mixed in water a load of cellulosic fibers thus refined and from 30 to 70% by dry weight of artificial fibers, relative to the total load of cellulosic and artificial fibers.

The subject of the invention is also, as a new industrial product, a planar, fibrous, flexible substrate, of the type based on cellulosic fibers, characterized in that it comprises natural cellulosic fibers originating from an ordinary and refined pulp. by fibrillation until reaching a drainability greater than or equal to 60 ° Schopper-Riegler and artificial fibers mixed at a rate of 30 to 70% by dry weight of the total load of cellulosic and artificial fibers.

The method according to the invention firstly consists in preparing cellulosic fibers preferably of the same species or plant varieties. Cellulose fibers from hardwoods or woody grasses are preferred, although good results can also be obtained with fibers from conifers.

By cellulosic fibers, it is necessary to consider the paper pulps ordinarily produced for the manufacture of papers, that is to say obtained by chemical means. The preparation of such a pulp according to the invention consists in refining the fibers by fibrillation, so as to give them a drainability greater than or equal to 80 ° Schopper-Riegler. The assessment of such drainability can be carried out by applying the conditions of the Afnor NF Q 50-003 or ISO 5267/1 - 1979 standard.

The objective is to microfibrillate the cellulose fibers so as to increase the specific surface for improve the ability to create hydrogen bonds.

A mixture is then prepared by incorporating into the paper pulp, super-refined compared to the ordinary treatment of conventional paper pulp, a load of artificial fibers of 30 to 70% by dry weight relative to the total load of cellulosic fibers and artificial. By artificial fibers, we should consider all unnatural fibers, such as plastics, regenerated, etc.

The mixing is carried out in an aqueous medium according to the usual conditions of the papermaking technique, for example at a rate of 2 to 4% by weight of cellulosic and artificial fibers.

The artificial fibers used may belong to one or more families and, preferably, to that of polyolefins, polyamides and polyesters for plastic fibers, and viscose or cellulose acetate for regenerated ones. Polyethylene terephthalate fibers are particularly suitable for the plastic family.

According to the invention, the incorporated artificial fibers are in the form of segments of determined length greater than 3 mm and preferably between 4 and 12. The fibers chosen are at most equal to 10 decitex and, preferably, between 1.1 and 2 decitex.

According to the invention, the load of artificial fibers is preferably equal to 50% by dry weight relative to the total load of cellulosic and artificial fibers.

The mixing between the cellulosic fibers and the artificial fibers in an aqueous medium is carried out with optionally the addition of adjuvants making it possible to subsequently improve the opacity, the hydrophobicity or even the insensitivity to water or humidity. The adjuvants used for this purpose can be considered as products known for these functions in the field of paper pulp and do not, strictly speaking, fall within the object of the invention, since their incorporation into the mixture, despite the presence artificial fibers, comes directly from the knowledge of those skilled in the art.

The mixture obtained, after homogenization under usual conditions, is diluted in water between 0.2 and 0.4% then is poured into the headbox of a paper-making machine, so as to be delivered from usual way on the drip cloth from which a sheet can be produced under traditional conditions.
Among these conditions, it is advisable to retain the draining, the drying, even the gluing and the calendering as a result of which the substrate in sheet produced can be stored in reel or, possibly, be precut in ream or ream of predetermined format.

An example of composition is certainly given below making it possible to compare the improvements in performance of the substrate in accordance with the invention compared with an ordinary paper and a substrate of the Tyvek® type.

EXAMPLE 1 :

The substrate according to the invention is, for example, produced from a mixture of paper pulp from a plant variety Eucalyptus sp and obtained by chemical means. Such a paste is superfine by fibrillation until it has a drainability equal to 95 ° SR.

A mixture is carried out, in an aqueous medium, by incorporating fibers at a concentration of 3% by weight, these fibers including 50% of cellulose fibers and 50% of artificial fibers of the polyester family of 6 mm in length and 1, 7 decitex. This mixture is then diluted to 0.45% in the headbox to produce a weight substrate 90 g / m².

The following table helps to highlight the different comparable characteristics between a paper 1 ordinary type, type 2 susbstrat Tyvek ®and a substrate 3 of the invention.

The values indicated are reduced to a grammage of 100 g / m².

EXAMPLE 2 :

The substrate according to the invention is the same as in the previous example, except that the artificial fibers consist entirely of viscose.

The values given are reduced to a grammage of 100 g / m².

It should be noted that the substrate according to Example 2 also has the advantage of being completely biodegradable.

The invention is not limited to the examples described and shown, since various modifications can be made thereto without departing from its scope.

Claims (10)

1. Process for manufacturing a flat, fibrous, supple substrate, based on natural and non-natural fibers and presenting an improved tear strength which consists in mixing the fibers in water, diluting the obtained mixture, pouring said mixture in a headbox of a paper-making machine and producing a substrate sheet from said machine supplied with the mixture and whose operation respects the conventional operational parameters,
      characterized in that:

   - before mixing the fibers with water, natural cellulosic fibers coming from an ordinary pulp are prepared by fibrillation until a drainability greater than or equal to 60° Schopper-Riegler is attained,

   - and a quantity of the thus refined cellulosic fibers are then mixed in water with 30 to 70% by dry weight of artificial fibers, with respect to the total quantity of artificial and cellulosic fibers.
2. Process according to claim 1, characterized in that the artificial fibers are selected from those of 1 to 10 decitex.
3. Process according to claim 1 or 2, characterized in that the artificial fibers present a length at least equal to 3 mm.
4. Process according to claim 1 to 3, characterized in that the artificial fibers present a length of between 4 and 12 mm.
5. Process according to claim 4, characterized in that the artificial fibers incorporate plastic fibers and regenerated fibers.
6. Flat, fibrous, supple substrate, based on natural and non-natural fibers, characterized in that it comprises natural cellulosic fibers which come from an ordinary pulp and which are refined by fibrillation until a drainability greater than or equal to 60° Schopper-Riegler is attained, as well as artificial fibers mixed at a rate of between 30 to 70% by dry weight of the total quantity of artificial and cellulosic fibers.
7. Flat substrate according to claim 6, characterized in that the artificial fibers are of 1 to 10 decitex.
8. Flat substrate according to one of claims 6 and 7, characterized in that the artificial fibers present a length at least equal to 3 mm.
9. Flat substrate according to one of claims 6 to 8, characterized in that the artificial fibers present a length of between 4 and 12 mm.
10. Flat substrate according to one of claims 6 to 9, characterized in that the artificial fibers are based on viscose.