EP1019296A1

EP1019296A1 - Valve sack

Info

Publication number: EP1019296A1
Application number: EP98909510A
Authority: EP
Inventors: Mikko Heitanummi; Valter Sievers; Kimmo Santamäki; Kari Nurmi
Original assignee: UPM Kymmene Oy
Current assignee: UPM Kymmene Oy
Priority date: 1997-03-18
Filing date: 1998-03-11
Publication date: 2000-07-19
Also published as: HUP0001933A2; SK128399A3; CZ9903259A3; WO1998041454A1; FI109290B; FI971130A; FI971130A0

Abstract

The invention relates to paper sacks and applies to the closing of a valve sack mouth. The valve has a valve tube (12) which can be closed by heatsealing after the filling of the sack, and/or the valve has a closing flap (14) which after the filling of the sack can be folded over the valve mouth and attached to the bottom by heatsealing. Both the valve tube and the closing flap are of material suitable for defibration. The sack is thus made completely tight and can therefore be used for storing both material that must be protected from the outside environment and material that is harmful to the environment. The sack can also be made to be refiberable.

Description

Valve sack

Field of the technology

The invention relates to paper sacks and applies to a valve sack equipped with a barrier film. Sacks according to the invention can be used particularly for storing products that require as tight packaging as possible. The sack material can be refϊbered.

Background to the technology

When manufacturing valve sacks of paper, a tube is formed of the paper web and cut into pieces of desired length, the ends are closed to form the bottom by first folding inwards the thinner end flaps and, on top of these, the wider side flaps. In all ends except the valve end, the side flaps are attached to the end flaps. The valve end can be supplemented with a separate paper-formed valve piece. In addition, the valve can have a closing flap which after the filling of the sack is folded over the valve mouth and attached to the bottom of the sack.

Moisture-proof valve sacks have been manufactured from paper coated with plastic film. A preferred plastic has been polyethylene. This type of sack material is unsuitable for the manufacture of recycled paper. In the defibration the plastic tends to form rather large particles and to separate the particles from the pulp is very difficult. In the manufacture of paper, these particles melt when the paper web is being dried by heating. The molten and tacky plastic material causes problems in the process. Furthermore, holes are formed to the paper in the region of molten particles.

The patent publication FI-C-92922 presented a moisture-proof sack paper applicable also to the manufacture of recycled paper. There the moisture barrier layer contains modified starch and synthetic polymer. Starch can be modified by grafting synthetic polymer into it. The grafting can be performed by an emulsion polymerization of the monomer solution in the presence of starch. The starch used can be degradated starch. The synthetic polymer can contain styrene- butadienecopolymer or vinyl acetate-acrylatecopolymer.

General description of the invention

A paper sack according to claim 1 has now been invented. Preferred embodiments of the invention are presented in the other claims.

The outer layer of the sack has a barrier layer preventing the penetration of moisture and grease, for example. This barrier layer is degradable which enables the refibering of the sack. Preferably the barrier layer is also heatsealable.

In the refibration of the sack material, the barrier layer is dispersed into the pulp and no harmful plastic particles are formed. An additional advantage is that also the biodegradation of the barrier layer is faster than that of all-synthetic plastics.

Since the sack layers are defϊberable material the sack is also suitable for the manufacture of recycled paper. The barrier layer can preferably contain modified starch and synthetic polymer. Starch can be preferably modified by grafting synthetic polymer into it. The grafting can be preferably performed by an emulsion polymerization of the monomer solution in the presence of starch. The starch used can be preferably degradated starch. The synthetic polymer can contain preferably styrene-butadienecopolymer or vinyl acetate- acrylatecopolymer. The sack has a valve closable by heatsealing. The valve is closed either by closing the inner side of the valve channel by heatsealing, or by folding a closing flap over the valve mouth and attaching the flap to the bottom by heatsealing. This will also ensure perfect valve tightness.

The sacks can be manufactured on tube and bottom machines of a conventional sack production line with no additional units. Extra material is not needed.

Drawings

The attached drawings are a part of the detailed description of the invention. In the drawings:

Fig. 1 shows the bottom to be closed of the sack blank, to which bottom the creases are marked with broken lines,

Fig. 2 shows the bottom with the flaps partly folded, and

Fig. 3 shows the bottom after the filling of the sack.

Detailed description

The manufacture of the barrier material

The barrier layer is formed of a mixture containing modified starch and synthetic polymer. The modified starch can be, for example, graft copolymer which has polymer chains formed of synthetic polymers attached with covalent bonds to a starch body. The polymer can contain, for example, styrene and alky lacry late or copolymers of different alkylmetacrylates or alkylacrylates. The starch can be preferably micromolecular, degradated by oxidation, for example. The degradation can also be carried out as the first stage in connection to the grafting reaction. In this case, attempts should be made to keep the degree of degradation a constant.

From dispersion monomers are best produced by emulsion polymerization in the presence of starch, thus forming both synthetic polymer and grafted starch. In the polymerization conventional facilities can be used, such as initiators and surface-active agents.

In the heatsealable moisture barrier layer, the proportion of starch of the dry content of the coating mixture is approx. 40 % at the most, for example 10 - 40 %, preferably 20 - 30 %.

A filler can also be used in the mixture, such as talcum, calcium carbonate or kaolin. The proportion of filler of the mixture is 40 % at the most, for example 10 - 40 %, preferably 20 - 30 %. In particular, the use of a filler decreases sticking of coated paper reeled in rolls.

Example 1. Styrene-butylacrylate-starchcopolymer

118.3 g of native starch (moisture content 16 %) is elutriated into 220 g of water. In the suspension, 0.05 U/starch gram B.licheniformis temperature stable alfa-amylase (activity 984 U/ml) is added. Little by little, the temperature of the suspension is elevated, at the same time properly stirring, to 90 C° which temperature is then maintained for 30 minutes. Then 0.5 ml of 30 percentage hydroperoxide is added, and the temperature is dropped to 60 C°. A stream of nitrogen is lead to the mixture, 0.2 g of CuSO₄ is added, and 50.8 g of styrene, 101.6 g of butylacrylate and 6 g of 30 percentage hydroperoxide solution is dropped within 1.5 hours. The reaction is allowed to continue for another 2 hours after which the white dispersion achieved is cooled to room temperature. The viscosity of the dispersion in 25 C° is 1600 mPas and the solid matter content 51 %.

Example 2. Metylmetacrylate-butylacrylate-starchcopolymer

The polymer is made according to example 1 using metylmetacrylate (50.8 g) and butylacrylate (101.6 g) as monomers. A pale yellow dispersion is achieved, the viscosity of which is 1650 mPas and the solid matter content 51 %.

The manufacture of coated sack paper

A desired amount of the dispersion is applied on the surface of the paper and dried to form a barrier layer. The layer properties, such as vapour permeability, can be controlled by changing the composition and thickness of the layer. A suitable additive is, for example, wax dispersion. A suitable water vapour permeability for a conventional sack material can be, for example, approx. 20 g/m²/d.

The coating can be carried out preferably as presented in the publication FI-C- 92922. ^'

The barrier layer is preferably formed only on one side of the paper. Then, to prevent the curling of the paper it is recommendable to mechanically fold (i.e. break) the film prior to the manufacture of the sack. The manufacture of a valve sack

Valve sacks according to the invention can be made of paper coated as described above using conventional manufacturing technology. When multilayer sacks are concerned, the barrier layer can be placed between paper layers. Especially suitable is a two-layer sack where the moisture barrier layer is placed on the inner surface of the top layer.

In the following, the manufacture of a two-layer sack is described as an example, with reference to the attached drawings.

A two-layer sack is made, the inner layer of which is made of conventional, relatively porous sack paper, the outer layer of paper equipped with a barrier layer. The barrier layer is on the inner surface of the outer layer.

Paper webs are lapped in and in with their edges together and glued to form a tube. The end of the blank cut from the paper tube on a tube machine is closed on a bottom machine. There the forming of the diagonal creases (3) reaching from the edges (1) to the end (2) of the blank and the transverse center crease (4) is carried out, the end flaps (5) of the bottom are folded inwards along the diagonal creases, and the transverse side creases (6) are formed.

On the end flap (5) of the blank, a cut (7) is made reaching perpendicularly from the end (2) of the blank to the diagonal crease (3). The extra flaps (8) thus formed on the end flaps (5) are folded open. On the inner surfaces of the side flaps (9) and (9') and on the outer surface of the end flaps (5), an end glue line (10) is formed reaching from the side edge of the extra flap (8) to the diagonal crease (6). On the side of the side flap (9') which will be placed on top, an additional side glue line (1 1) is formed to the edge of the side flap (9¹). The glue lines (10) and (1 1) on the side of the side flap (9') form a consistent area. On top of the valve-side end flap (5), a separate valve (12) is glued.

When the side flaps (9) and (9') are folded, the end glue line (10) secures the side flaps to the end flap (5) or correspondingly to the valve (12) tightening the structure also in the region of the side crease (6). Furthermore, the glue spread on the surface of the end glue line closes the edge of the cut (7) by forcing itself between the fold layers on the pressure direction, making sure that the material packaged in the sack does not have access between the layers. In addition, the extra flaps (8) make the sack steadier and stronger.

The valve (12) is a flattened paper tube of the bottom width. It is made of the paper equipped with a heatsealable coating described above so that the coating is placed inside the tube. The outward edge is folded in two with the coating side outwards. On the inner edge, cuts can be made on the side that will be placed inside the bottom to form flaps (13), if desired.

When the sack is filled, the valve (12) can be closed by heatsealing.

Underneath the mouth of the valve (12), a closing flap (14) of the bottom width is glued as a part of the valve structure, extending outside the valve mouth. The closing flap (14) is intended to be folded over the valve (12) mouth of a filled sack to be pressed against the bottom and attached to it. The closing flap is also made of the paper equipped with a heatsealable coating described above and it is attachedunderneath the valve mouth with the coating side upwards. After the filling, the flap is folded over the valve mouth and attached to the bottom by heatsealing.

This way the sack can be closed perfectly after the filling. In operating conditions, heatsealing can be carried out more easily, reliably and practically than glueing with a separate glue and a glueing device. In addition, the closing technique presented here is more reliable.

The strength of the sack can be improved by glueing the layers together in certain regions as presented in the application publication FI-A-945727. The critical regions include particularly the end edges and corners of the bottom of the filled sack. In figure 1, the glue lines (15) and (16) are marked, added between the layers to strengthen the said regions.

Typically a so called bottom cover sheet (17) is further glued on top of the bottom. The bottom cover sheet (17) preferably has folded edges placed inside.

A multilayer sack can be made to be air permeable during the filling preferably as presented in the application publication FI-A-945831. Then the inner layer is strong sack paper with good air permeability. Between the layers, air channels are formed so that the air from inside the sack that during the filling of the sack gets entrapped between the layers can escape. The air can be discharged preferably from the edges of the layers in the bottom region, in which case the air channels are preferably grooves longitudinal of the sack. Then the end flap, if used, is glued with separate glue lines preferably longitudinal of the bottom, thus ensuring that the air that comes to the bottom underneath the end flap from between the layers can still easily escape from the bottom through the bottom ends.

All the necessary glueing is performed using degradable glue suitable for refibering, preferably a starch adhesive.

Preferably the sacks consist of two layers but more layers can be used if necessary.

If desired, the ends of the layers can be fitted in a suitable overlapping manner to further improve tightness.

Sacks according to the invention can be manufactured on conventional sack lines already in use. The cut (7) that is required can easily be made with conventional modified tools on the bottom machine in connection to the creasing. The end glue line (11) is also easily spread in the desired shape with conventional metering devices. No additional material is needed in the production and the production is not substantially slowed down.

The sacks are particularly suitable for the packaging of materials that must be isolated from the outside air as perfectly as possible. The material is then completely protected from the moisture or pollution of outside air, for example. Therefore the sack is very suitable for, for example, storing and transport of food stuffs. On the other hand, since no material can leak out of the sack, it can also be used in storing agents harmful to the environment.

Claims

1. A valve sack with a paper-based mante equipped with a degradable barrier film, and closed bottoms one of which has a valve on the end through which valve the sack can be filled, characterized in that the sack has a valve closable by heatsealing after the filling of the sack.

2. A sack according to claim 1, characterized in that the sack has

- a valve tube (12) which can be closed by heatsealing and which valve tube is material suitable for defibration, or

- a closing flap (14) which after the filling of the sack can be folded over the valve mouth and attached to the bottom by heatsealing and which closing flap is material suitable for defibration.

3. A sack according to claim 1, characterized in that the valve tube (12) or the closing flap (14) is paper with a heatsealable coating.

4. A sack according to claim 3, characterized in that the coating contains starch which has been modified by grafting synthetic polymer into it, and that the proportion of starch of the weight of the coating is 40 % at the most, such as 10

- 40 %, preferably 20 - 30 % .

5. A sack according to claim 4, characterized in that the starch used is degradated starch.

6. A sack according to one of the claims 3 - 5, characterized in that the synthetic polymer contains styrene and acrylate or alkylmetacrylatecopolymer or alkylacrylate copolymer.

7. A sack according to one of the claims 1 - 6, characterized in that the inner layer is paper with good air permeability and there are air channels formed between the layers so that the air from inside the sack that during the filling of the sack gets entrapped between the layers can escape.

8. A sack according to one of the claims 1 - 7, characterized in that it has a bottom closed by glueing, which bottom has end flaps (5) folded inwards along the diagonal crease (3) and side flaps (9, 9') folded on top of the said end flaps along the transverse side crease, that on the end flap there is a cut (7) reaching from the side crease (6) to the diagonal crease, and that the extra flap (8) thus formed on the side flap is folded open before the side flap is folded against the end flap.

9. A sack according to one of the claims 1 - 8, characterized in that the sack layers are also glued together in the region of the end edge (15) or the comer

(16) of the bottom.

10. The use of a sack according to one of the claims 1 - 9 for storing material that must be protected from the outside environment or that can be harmful to the environment.