DE2741824A1 - PROCESS FOR TREATMENT OF PAPER AND CARDBOARD TO IMPROVE THEIR WATER AND WATER VAPOR RESISTANCE - Google Patents

Description

The invention relates to a method for treating paper and cardboard in order to make them water and steam resistance to improve.

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. About the water vapor resistance To improve paper and cardboard, these are generally treated with various impregnation and Coating materials treated. The most widely used paper coating agent is wax. Wax-coated paper or cardboard repels water; its resistance to Water is bad and too much water vapor penetrates, especially after folding. The fragility of wax is too high and when folding the wax layer breaks, so that water vapor through the corresponding cavities or interruptions can penetrate the wax layer. Regarding the other shortcomings of wax-coated products, note the minor one Friction, difficulty gluing and the fact that it cannot be reprocessed resp. be pulped can. In addition, wax-coated material does not result in a hard and resistant surface.

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Attempts have also been made to coat paper with bitumen. It is true that a good resistance to water vapor can be achieved which, however, becomes small after folding. In addition, bitumen is black and poisonous Material so its use as paper coating, particularly in the food packaging industry, is limited is. In addition, bitumen coatings tend to soften when the temperature rises.

Polyethylene film has also been applied as a paper coating. It was observed that the thus obtained, polyethylene-coated paper has a lower water vapor resistance possesses as a wax-coated paper when the coating is examined flat or in the unfolded state will. In the case of folded polyethylene-coated paper, it has been shown that its resistance is better than that of wax-coated paper is. If the manufacture of corrugated cardboard is considered, it must be taken into account: that the polyethylene-coated material cannot be processed in the production machines for corrugated cardboard, because the Polyethylene melts at the temperature of the counter pressure elements (double facer) of the corrugated cardboard manufacturing machines. The one with polyethylene Coated material is also not reprocessable, as is the case with the material provided with wax applies.

Of the other products on the market, those are coated with a high-melting veil or curtain Packaging products mentioned, in which mostly a mixture of wax and polyethylene as a coating substance was used. These products have relatively good water vapor resistance. However, the disadvantage of these products is the fact that the veil wax treatment only

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can be applied to complete box boards, which affects the competitiveness of these products. It is also not possible to tamp down or reprocess packaging material that has been treated with a wax veil.

It is also a process known as the "Secor" process known that is well suited for improving the water resistance of corrugated board. With the Secor procedure the corrugated cardboard completely impregnated with wax. The material thus treated has good moisture resistance and it retains its stiffness relatively well, even in high humidity. However, the prices for such products are high and these products cannot be pulped or reprocessed either.

With regard to current developments in the field According to the invention, it has been found that it would be extremely desirable to find a packaging material which has the following properties:

(1) It retains its strength, in particular its rigidity, even in the case of high humidity for a long period of storage.

(2) It has good water vapor resistance to prevent moisture penetration of the packaged product.

(3) It can be pulped or reprocessed. This property becomes even more important as the reprocessing of fibers increases.

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In addition to the above-mentioned essential properties, the following properties are worth mentioning, for example:

The material can be printed with normal inks / it can be glued with normal adhesives,

it can be processed under normal processing conditions, for example for the properties of the lining layer applies to processing in corrugated cardboard manufacturing machines,

it has a sufficiently high coefficient of friction with respect to the storage of boxes, and

it does not contain any harmful substances, which is essential for food packaging.

The invention is therefore based on the object of providing a way of treating paper or cardboard to propose that will allow the requirements mentioned above to be met. To solve this problem, the method proposed according to the characterizing part of claim 1, wherein the further claims contain preferred procedural measures.

The coating substance can be applied to the fibrous substrate in one methods known per se are applied. These known processes include dipstick coating, Blade coating or air knife coating.

As fibrous substrates to which the coating substance according to the invention can be applied, all types of Paper or cardboard or cardboard in the qualities required for packaging and wrapping purposes are used.

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Paper or cardboard treated according to the invention can be used be for

Packaging and transport of frozen fish and meat,

Packaging and transportation of vegetables (tomatoes, lettuce, etc.) and fruit,

Transport of pets,

Facade material for buildings,

Wrapping paper for wood or paper and cardboard rolls and

in general, the purposes where the packaging material must have good moisture resistance.

The following example shows the production of a coating mixture as used in accordance with the invention, and the manufacture of a product coated with this is described.

The coating mixture is prepared by combining equal amounts of acrylic styrene latex and a water dispersion of a metal salt of stearate (e.g. calcium stearate). About 10 g / m ^a of Uberzugsmischung is applied to the fibrous substrate, after which the product is dried in a normal drying process.

The material as such can then be used for wrapping or used as a top layer; however, it is also possible to process it into corrugated cardboard or similar products.

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

example

Coating test for cardboard for heavy fodder

A) Examination procedure

Water absorption of glued paper and cardboard according to the Cobb method SCAN-PI2: 64

The water absorption of paper (Cobb value) is defined as the amount of water that goes to one side or the other of the paper Paper is absorbed in a certain time from a 1 cm thick layer of water that evenly covers the paper.

Permeability to moisture and water vapor

ASTM 3-988 (Tropical Conditions), expressed in grams of H _? O / m ² in 24 hours at 65% relative humidity and 20 ° C or 90% relative humidity and 38 ° C.

B) Results

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Tabel

ο co co

According to the invention
treated
quality Role 2 Role 3 Waxed
quality Role 1 11 -J_ Coefficient of friction 11 -J_ 0.16 0.14 11-J _- 11-11 static friction 0.15 0.18 0.19 0.17 0.16 kinetic friction 0.78 0.12 0.11 Cobb (30 mins) 2.30 2.26 g / m ² 2.15 47.6 Water vapor through
nonchalance g / m ² / 24h 15.15 17.36 65 % RH, 20 ° C 21.83 162.7 176.1 52.0 90 % RH, 38 ° C 155.3 391.0

Standard quality

175 g / m ²

11 -J_ 11-11 0.53 0.54 0.47 0.49

276.1

575.0 2,462.0

OO I

Crushability: The water-resistant quality produced according to the invention could be crushed or reprocessed in the same way as uncoated material. The reprocessability of wax-coated material, on the other hand, was poor,

The corrugated cardboard boxes, which are coated according to the invention Material, e.g. as food, were checked by using a relative Humidity of 90% at 20 ° C were exposed as well as after artificial irrigation. They were made with boxes uncoated or veil-coated material compared. The results are shown in Table 2.

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Table 2

t = 20 ° C, RH = 65 % untreated veil
coated according to the invention
treated Basis weight, g / m ² Puncture Resistance, J. 528 571 561 Flat crush strength, kN / m ² 4.4 4.4 4.4 Compression Strength, N. 357 290 350 t = 20 ° C, RH = 90 % 2,290 2.223 2,685 CD
σ Puncture resistance co
CD Flat crush strength 4.2 4.5 4.4 t * \ Compressive strength 196 250 299 O
00 t = 20 ° C, RH = 6 ⁵ % +
5 min. Watering +
10 min. Conditioning 1,044 2.122 2,281 Ul

Puncture resistance Flat crush resistance Compression resistance

4.2 4.4 4.5 200 255 298 1,086 2,476 2,804

Claims (4)

Patent claims: 1. Method of treating paper and cardboard for improvement of their water and water vapor resistance, characterized by the use of a composition for a Coating substance in the water phase, which consists of copolymers based on acrylic styrene, acrylonitrile or Acrylstyrene butadiene and metal salts of stearate and / or wax, the content of the copolymers 35 to 95%, preferably 50 to 80%. 2. The method according to claim 1, characterized in that the amount of coating substance on the paper or cardboard 3 to 25 g / m ", preferably 5 to 10 g / m *. 3. The method according to claim 1 or 2, characterized in that the wax is a mineral wax, preferably a macromolecular wax with a straight molecular chain, whose melting or softening point is between 50 and 80 ° C. 4. The method according to any one of claims 1 to 3, characterized in that that calcium stearate is used as the stearate metal salt. 8098 13/08 15 ORIGINAL