DE2741824C2 - Process for increasing the water resistance and reducing the water vapor permeability of paper products - Google Patents

Description

The invention relates to a method for increasing water resistance and reducing water vapor permeability of paper products, in particular packaging material, with the features according to the preamble of claim 1.

Fibrous substrates such as paper and cardboard are used extensively in the packaging industry. Paper and cardboard, however, offer very little resistance to the passage of water vapor and water opposite. In order to improve the water vapor resistance of paper and cardboard, it is known to use a coating to be made with wax. However, the brittleness of wax is high, so that especially folded paper for Water vapor is permeable. Another disadvantage of wax-coated products is the low friction, Difficulty trowels when gluing and the uselessness for re-stamping and reprocessing.

A method of the type mentioned has already become known in which an aqueous dispersion of a mixture of an acrylic polymer and a further agent is spread onto the paper product (GB-PS 12 23 251). Here, the water and water vapor barrier is formed as a layer between two webs of the paper product, the mixture consisting of a rubbery butadiene copolymer and wax being applied to two webs which are then connected to one another at the point of application. The mixture is spread onto the paper product in an amount of at least 50 g / m ^2.

Although this known method provides a paper product with good water vapor proofing effect, but the paper product does not receive any protection against it External moisture penetration and also the coefficient of friction of the external surface of the coated paper product is not affected in any catfish.

There is also already a known method that is not belongs to the genus mentioned at the outset, in which to increase the fat resistance on one side Paper web first applied a copolymer of acrylonitrile and ethyl acrylate and then the other Side of the paper web and the side coated with the copolymer is pulled through a paraffin bath (DE-AS 1146 352). As a result of the repulsion of the paraffin the polymer layer, the ropes of the web opposite the polymer layer are impregnated with paraffin. This creates a grease-repellent, water-vapor-impermeable paper product. However, this is well known The process is proportionate due to its two-stage nature complex and the paper product thus produced is therefore expensive.

Finally, it is known to use paper products such as canons, which are impregnated with a layer of wax, also made even more water-repellent with metal stearates make (Bärlocher "Metallseifen R 6/6/55 and R 9/4/57"), a combination with plastics is included not provided.

The invention is based on the object of a method for the treatment of paper and cardboard to create an increase in the water resistance and a decrease the water vapor permeable wedge of the paper results in a firm wedge for the paper even with strong humidification during longer storage tent and give a sufficiently high coefficient of friction so that no slip problems occur when the paper is used as wrapping paper or the like.

On the basis of the method described at the outset, this object is achieved by the features according to the characterizing part of claim 1.

The packaging material treated according to the invention has the following properties:

It retains its strength, especially its rigidity, even in high humidity for a long time Storage time. Because it has a low water vapor permeability, so that packaged products are prevented from becoming wet. It can also be tamped and reprocessed without the coated mixture interfering with reprocessing.

In addition to the properties described above, the packaging material can be printed with QbIi chen printing inks and glued with conventional adhesives. It can also be processed under normal processing conditions, which is important, for example, for the properties of the lining layer when processing in corrugated cardboard manufacturing machines, and above all it has a sufficiently high coefficient of friction, which is advantageous when stacking boxes made of the paper product like that. Finally, the packaging material does not contain any harmful substances, so that it can be used for the packaging of foodstuffs.

The mixture can be applied to the paper or cardboard in an amount of from 3 to 25 g / m ² , preferably from 5 to 10 g / m 2. The application can be carried out by methods known per se. These include measuring squeegee coating, doctor blade coating or air knife coating.

All types of paper or

Cardboard or cardboard in the same qualities as for packaging and university development purposes. Find use.

The field of application of the paper product treated by the process according to the invention includes the packaging and transport of frozen fish and meat, vegetables, tomatoes, lettuce, etc.) and fruit, the transport of pets, the cladding of facades of buildings, the wrapping of Wood, paper and cardboard rolls, and more generally packaging purposes that require good water resistance Requirement is.

The following example shows the preparation of a mixture as used in accordance with the invention and the production of a paper product coated therewith is described.

The mixture is prepared by combining equal amounts of an acrylate monomer-styrene copolymer latex and a water dispersion of a metal searate, for example calcium stearate. About 10 g / m ^{2 of} the mixture is applied to the fibrous substrate, whereupon the product is dried. The product obtained can then be used for wrapping or as a top layer; however, it is also possible to process it into corrugated cardboard or similar products.

The physical properties of a kraft liner coated in the above-mentioned manner were tested and the results are set out in Table 1. The coated cardboard or cardboard is compared with such with uncoated lining or dry waxed lining (about 25 g / m ² wax). The procedures are described below.

example

Coating test for Kraftliner A) Test method:

Water absorption by glued paper and cardboard using the Cobb method SCAN-P 12: 64

The water absorption of paper (Cobb value) is defined as the amount of water, one or the other Side of the paper absorbed in a certain time from a 1 cm thick layer of water, which makes the paper evenly covered.

Water vapor permeability

ASTM 3-938 (tropical conditions), expressed in grams H ₂ CVm ² in 24 hours at relative humidity and 659b 2O ⁰ C and 90% relative humidity and 38 ° C.

Crushability:
B) Results:

Table 1

According to the invention treated Waxed Default- quality quality quality Roll 1 roll 2 Role 3 175 g / m ²

Coefficient of friction
static friction
kinetic friction
Cobb (30 min.)
g / m ²

Water vapor permeability
g / mV24h

65% RH, 20 ° C
90% RH, 38 ° C

11-2
0.15
0.78

2.15

21.83
155.3

0.16
0.18

2.30

15.15
162.7

0.14
0.19

2.26

17.36
176.1

0.17
0.12

11-11
0.16
0.11

11-2

0.53 0.47

47.6

52.0
391.0

11-11 0.54 0.49

276.1

575.0 2,462.0

The water-resistant quality produced according to the invention could be tamped or processed in the same way like uncoated material. The recyclability of wax-coated material was against it bad.

Corrugated cardboard boxes, which are coated with material according to the invention, e.g. B. as feed

Table 2

were checked. By exposing them to a relative humidity of 90% at 20 ^° C for 7 days as well as after artificial irrigation. They were compared with boxes made of uncoated or cast-coated material. The results are shown in Table 2.

t = 20 ° C. RF = 65 "/»

Basis weight

St ichein rei (3 strength

Flat crush strength

Compression resistance. N

iin treated pour
coated according to the invention
treated 528 571 561 4.4 4.4 4.4 357 290 350 2 290 2 223 2,685

Fortsctzunii

untreated cast according to the invention

coated treated

4.2 4th , 5 4.4 196 250 299 1044 2 122 2 281

t = 20 ° C, RH = 90%

Puncture tear resistance Flat crush resistance Compression resistance

t = 20 ° C, RH = 65% + 5 min. watering + 10 min. conditioning

Puncture resistance 4.2 4.4 4.5

Flat hose strength 200 255 298

Compression strength 1 086 2 476 2 804

Claims (5)

Patent claims: 1. Process for increasing the water resistance wedge and reducing water vapor permeability of paper products, especially packaging material, in which an aqueous dispersion is applied to the paper product a mixture of an acrylic polymer and another agent is applied, characterized in that a mixture is spread which consists of a) Copolymers of acrylate monomers with styrene, of acrylonitrile polymers or of acrylate monomers with styrene and butadiene and b) consists of metal stearates and / or wax, wherein the content of copolymers is 35 to 95%, and then the coated layer is dried will. 2. The method according to claim I, characterized in that the mixture in an amount of 3 to 25 g / m ² , preferably 5 to 10 ^{g / m!} is painted on. 3. The method according to claim 1 or 2, characterized in that a mineral wax is used Wax is used, the melting or softening point of which is between 50 and 80 ° C. 4. The method according to claim 3, characterized in that a macromolecular wax with straight Molecular chain is used. 5. The method according to any one of claims I to 4, characterized in that the metal stearate CaIcI-umstearat is used.