RU2765450C1 - Cardboard for flat layers of corrugated cardboard and method for production thereof - Google Patents

Abstract

FIELD: paper.

SUBSTANCE: group of inventions relates to the pulp and paper industry, namely to cardboard for flat layers of corrugated cardboard, which consists of not less than 70 wt. % of waste fibre, as well as to a method of making said fibre. Such cardboard is intended for manufacture of packing containers in the form of boxes and trays for packing vegetables, fruits, as well as cooled and frozen products. Cardboard contains hydrophobic adhesive and reinforcing starch in the mass and/or on the surface and moisture-resistant polyamide-polyamine-epichlorhydrin resin in the mass. Cardboard additionally contains a polyacrylamide-based cationic resin. Method of producing cardboard consists in the fact that hydrophobic adhesive and moisture-resistant polyamide-polyamine-epichlorhydrin resin are diluted with water and mixed with each other. Obtained mixture, cationic starch and cationic resin based on polyacrylamide are then added to the paper mass. Layer of cardboard is formed and subjected to surface treatment with a composition containing hydrolysed starch and hydrophobic glue.

EFFECT: technical result of the invention consists in providing an increase in the strength of the cardboard in a wet state due to the acceleration of the reaction of formation of moisture-resistant chemical bonds, increase in the number of such bonds between the fibres of the raw material, without increase in the consumption of the moisture-resistant polyethylene resin, as well as in the reduction of water absorption during prolonged contact therewith.

4 cl, 1 tbl, 11 ex, 2 dwg

Description

SUBSTANCE: group of inventions relates to the pulp and paper industry, namely to a cardboard for flat layers of corrugated cardboard, consisting mainly of recycled fibers, and a method for its manufacture. Such cardboard is intended for the manufacture of packaging containers in the form of boxes and trays for packaging vegetables, fruits, as well as chilled and frozen products.

From the prior art, packaging materials in the form of cardboard, in particular corrugated, or paper, and methods for their manufacture, which make it possible to impart moisture-resistant properties to these materials, are known.

So, to improve the properties of wet strength, i.e. wet mechanical strength, wet-strength resins can be added to the board composition and paper composition, which form additional water-resistant, namely, wet strength, chemical bonds between cellulose fibers. Such resins include, in particular, PPE (polyaminepolyamide-epichlorohydrin) resins. In particular, PPE resins are produced under the trademarks: “Maresin”, “Kymene”, “Biores” and others.

Hydrophobic adhesives, such as AKD (based on alkyl ketene dimer), ASA (alkenyl succinic acid anhydride), and rosin glue, are used to reduce water absorption when cardboard is exposed to moisture for a long time, which make the cardboard water-repellent. Due to the water repellency and reduced water absorption, the paperboard also gains some wet strength, but without the formation of chemical bonds between the fibers.

Also, to reduce water absorption, cardboard made from cellulose raw materials may contain a surface coating, including modified (hydrolyzed) starch and hydrophobic adhesives based on copolymers of styrene and maleic anhydride and other types, which are added to compositions for surface sizing of cardboard on cardboard machines. Such adhesives include, for example, "Prosize SP", "Basoplast", "Fennosize" or similar adhesives.

In addition, modified (cationic) starch or modified medium molecular weight polyacrylamide dry strength resin, for example, grades such as: “Lycrid XH 43”, or "Metrix 64111", or similar reinforcing agents, which are added to paper stock prior to board molding. Any modified starch is known to increase dry strength of paperboard. At the same time, cationic starch is added to the mass, and hydrolyzed starch, in which the molecular weight and viscosity are reduced, is added from the surface. The latter is achieved by such methods of starch modification as oxidation or enzymatic hydrolysis. Modified starches are mainly added to paperboard from recycled paper, that is, from recycled materials, where the strength of the fibers is reduced in comparison with the strength of kraft paperboard from virgin pulp. Modified starches themselves do not add wet strength to cardboard, as they are water-soluble polymers.

For example, corrugated cardboard selected as a prototype and a flat layer of this cardboard in the form of a sheet are known, which, during its manufacture, is glued and/or impregnated in the mass with a wet-strength resin and hydrophobic glue. Polyamidamine-epichlorohydrin or formaldehyde resins are used as a wet-strength resin, and dimers of alkyl or alkenyl ketene or alkenyl succinic anhydrides, rosin, starch, maleic anhydride, acrylic acid, acrylamide (RU 121512, class D21H 27/18, publ. 27.10) are used as a hydrophobic adhesive. .2012).

The known solution is aimed at imparting simultaneously wet-strength and hydrophobic properties to corrugated cardboard, as well as cardboard and paper layers used for the production of corrugated cardboard, which will increase the resistance to water. According to this decision, the complex use of hydrophobic and wet-strength chemicals will reduce the absorbent properties of paper materials, maintain their wet strength and thereby increase water resistance.

The disadvantages of the closest analogue include the following: wet-strength PPE resins in paper do not mature (form chemical bonds) immediately, but within several days, and maturation continues for weeks and even months. Therefore, for a quick effect of wet strength in cardboard, the consumption of resins must be increased. And this entails over time an excessively high wet strength, which makes it difficult to dissolve and recycle corrugated packaging from such cardboard as waste paper. In addition, PPE resins are highly cationic and can lead to a so-called recharging of the paper stock into the cationic region, which is highly undesirable as it causes increased foaming, problems with board molding on the board machine, and leads to a decrease in board dry strength. Another important circumstance is the fact that PPE resins contain a small (permissible) amount of harmful organochlorine compounds (epichlorohydrin interaction products) in their composition.

The technical problem solved by the invention is to create conditions for accelerating the maturation of wet-strength PPE resin and reducing the consumption of PPE resins while maintaining the effect of high wet strength cardboard.

The technical result, which allows solving this problem, is to increase the strength of the cardboard in the wet state due to the acceleration of the reaction of formation of wet-strength chemical bonds, to increase the number of such bonds between the fibers of the raw material without increasing the consumption of wet-strength PPE resin, and also to reduce the water absorption during prolonged contact with it.

In addition, the invention makes it possible to increase the strength of cardboard in a dry state, which is important when storing dry products in a cardboard container in a dry warehouse.

The technical result of the invention for the object of the method of manufacturing cardboard is to enable the production of cardboard with the above properties.

The named technical result is achieved in the invention due to the following combination of features.

Cardboard for flat layers of corrugated board contains a hydrophobic adhesive and reinforcing starch in the mass and/or on the surface and a wet strength polyamide polyamine epichlorohydrin resin in the mass. In contrast to the known cardboard, it additionally contains a cationic resin based on polyacrylamide in the mass.

The content of the cationic resin based on polyacrylamide is mainly 2-6 kg of marketable (diluted with water in accordance with the recipe) resin per ton of finished board.

Said paperboard consists of at least 70% by weight of waste paper.

The method for producing cardboard for flat layers of corrugated cardboard consists in diluting hydrophobic glue and wet-strength polyamide-polyamine-epichlorohydrin resin with water and mixing with each other. Then the obtained mixture, cationic starch and cationic resin based on polyacrylamide are introduced into the paper stock. A layer of cardboard is formed and subjected to its surface treatment with a composition including hydrolyzed (partially enzymatically or oxidized) starch and a hydrophobic adhesive.

When implementing the method, the hydrophobic adhesive and the wet-strength polyamide-polyamine-epichlorohydrin resin are diluted with water 4-10 times.

During the surface treatment of the paperboard, a dye is additionally included in the above composition in order to match the color of the recycled paperboard with the virgin kraft paperboard.

When implementing the method, paper pulp is used, consisting of at least 70 wt.% of waste paper.

The novelty of the proposed solution lies primarily in the fact that, in addition to adhesives, starch and wet-strength resin, dry-strength resin is added to the cardboard composition, providing the necessary combination of wet-strength PPE resin and dry-strength resin based on modified polyacrylamide.

It should be noted that the polyacrylamide-based dry-strength cationic resin in the proposed combination with PPE wet-strength resin has two important advantages: 1) approximately 1.5-2.0 times lower charge of cationic groups than wet-strength PPE resin; 2) has practically no harmful organochlorine impurities, since it does not contain epichlorohydrin products.

As noted above, the reaction of the formation of wet-strength chemical bonds in cardboard (wet-strength maturation) occurs quite slowly, and the process of accelerating this reaction and the appearance of wet-strength cardboard is very important.

So, under normal storage conditions of cardboard (at 20 ° C), the maturation of wet strength occurs approximately as follows:

- in the first hour (at 20°C) about 20-30% of potential wet-strength bonds enter into the reaction of the resin with the cellulose fiber in the cardboard;

- in 24 hours (at 20°C) about 60-70% of bonds enter into the reaction;

- full maturation of wet strength can occur for several weeks and even months.

At high storage temperatures, the development of wet-strength bonds in the cardboard is accelerated. So in 5-10 minutes, at 105-110°C, almost 100% of the resin reacts with the fiber and the wet strength is fully matured. It can be noted that AKD glue ripens in a similar way (slowly), which interacts with cellulose and exhibits hydrophobic bonds and reduced water absorption by cardboard not immediately, but after a day or more.

An example of the manufacture of cardboard in an industrial environment.

In the fibrous mass, consisting of 100 wt.% of waste paper, cationic starch is added in the amount of 8 kg / t in the form of an aqueous solution, with a concentration of about 1%, then a mixture of AKD hydrophobic glue (brand "Aquapel 320A" pre-diluted 7 times with water) is added ) in the amount of 5 kg/t and wet-strength PPE resin (brand "Maresin VHP-200") in the amount of 6 kg/t. A cationic dry hardening resin based on PAA (Metrix 64111 brand) is added to the resulting mass in an amount of 3.6 kg/ton.

At the same time, the order of supplying the paper pulp with dry hardening resin of the “Metrix 64111” type and a mixture of AKD glue and PPE resin can be changed without a significant change in the result.

After all the chemicals have been supplied, the pulp is fed to the board machine and cardboard is produced in the traditional way: the web is cast, a layer of cardboard is formed and during the drying process it is surface treated in a size press with a composition including partially enzymatically decomposed starch, in an amount of about 27 kg / t and hydrophobic glue AKD (brand "Prosize SP") in the amount of 4.0 kg/t. The dosage of these chemicals is indicated in kilograms of commercial (liquid) chemical per ton of finished cardboard. For cationic and surface starch, this is a dry product, the rest of the chemicals are in commercial form - liquid products (aqueous solutions and dispersions) with a concentration of 20-30% by dry matter.

Below is a description of how cardboard samples were made in the form of paper castings at the stage of laboratory research, and how the finished castings were additionally subjected to surface treatment.

In FIG. 1 is a photograph of a sample of a cardboard casting (half of a casting) during surface treatment in a laboratory size press.

In FIG. 2 is a photograph of a sample of cardboard treated from the surface in a dryer.

To test cardboard for increased requirements for wet strength and reduced water absorption, samples were taken in the form of manual castings of cardboard weighing 135 g/m ² , which were made in laboratory conditions on a Rapid-Ketten sheeter. In this case, we used industrial paper pulp LLC "Aleksinskaya Paper and Cardboard Factory", 100% consisting of waste paper grade MS-5B.

Chemicals were added to the paper pulp before casting, both in the known and in the proposed combination, and, after drying, cardboard castings of various manufacturing options were obtained. According to the proposed method, the following chemicals were added to the mass:

- cationic corn starch "B-135" (ASTON company);

- wet-strength polyamine-polyamide-epichlorohydrin resin (PPE) “Maresin VHP-200” (TSC company);

- resin based on polyacrylamide (PAA) for dry strengthening "Metrix 64111" (Nalco company);

- hydrophobic glue AKD Aquapel 320 (Solenis company).

After the manufacture of cardboard castings, some of them were tested for the following indicators:

- breaking force in dry state;

- breaking force in the wet state 1 hour after manufacture (time not sufficient for the maturation of the AKD adhesive and for wet-strength resin);

- breaking force in the wet state 24 hours after manufacture (time sufficient for partial maturation of the AKD adhesive and for wet-strength resin);

- absorbency according to Cobb-60 (contact time with water 60 s). The test was carried out after preliminary heat treatment of cardboard in an oven for 5 minutes at a temperature of 110°C for complete maturation of the AKD adhesive and the development of hydrophobicity;

- absorbency according to Cobb-1800 (time of contact with water 1800 s). The test was carried out after preliminary heat treatment of cardboard in an oven for 5 minutes at a temperature of 110°C).

Some of the cardboard castings of each variant were subjected to additional surface treatment in a laboratory size press immediately after production.

Surface treatment was carried out with an aqueous composition that included two main components:

- starch fermented with a concentration of 4.0 wt.% dry starch;

- hydrophobic glue "Prosize SP" (company "TSC") based on styrene acrylates with a concentration of 0.3 wt.% for commercial glue.

In this case, the application of components to the surface of the cardboard was:

- starch - 32 kg of dry starch per one ton of cardboard;

- hydrophobic glue "Prosize SP" 2.4 kg per commercial product per ton of cardboard.

In order to reduce the viscosity, the fermented starch was prepared according to the traditional technology with the addition of the enzyme preparation "Banzim 400A" (Banmark company) to the starch suspension before cooking.

The test results for cardboard castings without surface treatment and with surface treatment are shown in the table.

As you can see from the table:

- in the control example 0 without sizing chemicals, the absorbency of the cardboard is maximum, i.e. complete wetting is observed, and there is no wet strength;

- in the control example 0p with additional surface sizing with starch and hydrophobic (styrene acrylate) glue, the absorbency of Cobb-1800 cardboard is significantly reduced and, due to the decrease in absorbency, the wetting of the cardboard decreases and a slight wet strength appears. The dry strength of the cardboard is also significantly increased by the surface starch;

- in example 1, when 5 kg / t of AKD glue is added to the mass, the absorbency of Cobb-60 and Cobb-1800 cardboard decreases, but according to Cobb-1800 it remains at a very high level, since AKD glue without cationic starch does not work effectively enough;

- in example 1p with additional surface sizing, the absorbency values are reduced and due to this, wetting of the cardboard is reduced and the strength of the cardboard in the wet state is increased;

- in example 2, when an additional 4.0 kg / t of cationic starch is added to the mass, the absorbency of the cardboard decreases due to the improvement in the fixation of the AKD glue on the fibers, and the dry strength of the cardboard also increases. However, the strength of the board in the wet state remains insufficiently high. This is especially observed after 1 hour after manufacture, since maturation and AKD glue do not occur after 1 hour;

- in example 2p with additional surface sizing, all indicators are significantly improved - absorbency decreases, wet strength increases. However, the strength of the cardboard in the wet state remains at an insufficiently high level;

- in example 3 (prototype) when added to the mass of an additional 4.0 kg/t of wet-strength PPE resin, the wet strength of the cardboard in comparison with example 2 sharply increases and the absorbency of the cardboard is further reduced. This level of indicators already corresponds to cardboard with satisfactory, but insufficient wet-strength properties;

- in example 3p with additional surface sizing, all indicators are further improved and such a board corresponds to a good level of wet strength board. However, the maturation of the PPE resin after an hour is not efficient enough;

- in example 4, corresponding to the proposed solution, with the additional addition of dry-strength resin based on polyacrylamide to the mass, even lower absorbency values and high wet strength values are achieved. At the same time, the maturation of the wet-strength PPE resin is significantly accelerated, which is reflected in a higher strength of the cardboard in the wet state;

- in example 5, corresponding to the proposed solution, when pre-diluted with water and mixing wet-strength resin and AKD adhesive, in comparison with example 4, where the components were supplied separately, even lower absorbency values and high wet strength values \u200b\u200bare achieved, which is associated with more homogeneous mutual distribution of particles of AKD glue and resin, as well as their more uniform distribution on cellulose fibers;

- example 5p, most fully corresponds to the proposed solution.

Additional surface treatment of the resulting paperboard, in accordance with Example 5, results in the highest wet strength of the paperboard, the lowest Cobb-1800 absorbency, rapid maturation of the PPE wet strength resin, and the highest dry strength of the paperboard.

It can also be noted that if cationic starch is not added to the paper pulp, for example, in comparison with examples 5, 5p, then the wet strength indicators of the cardboard will also develop well, but the dry strength indicators of the cardboard will be lower. Therefore, in recycled boards, as a rule, cationic starch is added to the mass to increase the strength of the board in a dry state and positively influence the fixation of the AKD adhesive on the fibers.

In general, based on the above examples, it was concluded that the dry hardening resin activates the wet strength resin. This makes it possible to increase the strength of the cardboard in the wet state by about 1.5 times, i.e. improve the efficiency of the PPE resin, and also allows you to accelerate the maturation of the PPE resin from several weeks to several days. Additionally, a reduction in water absorption is achieved by increasing the effectiveness of the hydrophobic AKD adhesive.

The cardboard obtained by this method has increased wet and dry strength and reduced water absorption, while the effect of wet strength, which depends on the development of wet-strength chemical bonds of the PPE resin, develops in the cardboard to a greater extent and much faster, namely by 50-60% in within a few hours and almost completely within 1-2 days.

The resulting cardboard, made from recycled materials (waste paper), due to increased wet strength and reduced absorbency, has properties similar to kraftliner - a more expensive cardboard made from primary cellulose fiber and allows you to partially or completely replace kraftliner in the manufacture of corrugated packaging for packaging vegetables, fruits, chilled and frozen foods.

Appendix: technical data sheets of major known chemicals such as: “Maresin VHP-200”, “Metrix 64111” and “Prosize SP” mentioned in the description.

table

No. Example Addition of chemicals to paper pulp, kg/t Ready-made cardboard without surface treatment Cardboard performance after additional surface treatment Cationic starch "B-135" Resin moisture-strong PPE
Meresin VHP-200 Glue AKD
Aqua-sang 320 Dry hardened resin PAA Matrix 64111 Breaking force in dry state, N Wet breaking force, N Absorbency of water, g / m ² Breaking force in dry state, N Breaking force in the wet state, N (24h) Absorbency, Cobb-1800 g/m2 Across
1 hour Across
24 hours Cobb-60 Cobb-1800 0 - - - - 74.1 <0.5 <0.5 > 240 > 240 - - - 0p - - - - 74.1 <0.5 <0.5 > 240 > 240 82.3 6.7 135 one - - 5.0 - 72.8 1.5 4.6 34.3 152 - - - 1p - - 5.0 - 72.8 1.5 4.6 34.3 152 81.4 10.6 110 2 4.0 - 5.0 - 77.2 1.7 6.4 27.8 137 - - - 2p 4.0 - 5.0 - 77.2 1.7 6.4 27.8 137 84.7 11.9 104 3 4.0 4.0 5.0 - 77.9 10.4 14.3 23.0 105 - - - 3p 4.0 4.0 5.0 - 77.9 10.4 14.3 23.0 105 85.0 16.5 one hundred 4 4.0 4.0 5.0 3.6 80.1 15.8 18.1 19.5 one hundred - - - 5 4.0 4.0+5.0
(premix) 3.6 80.2 16.4 18.8 18.7 98 - - - 5p 4.0 4.0+5.0
(premix) 3.6 80.2 16.4 18.8 18.7 98 88.1 20.2 83

Claims (4)

1. Cardboard for flat layers of corrugated cardboard, containing hydrophobic glue and reinforcing starch in the mass and / or on the surface and a moisture-resistant polyamide polyamine epichlorohydrin resin in the mass, characterized in that it additionally contains a cationic dry-strengthening resin based on polyacrylamide in the amount of 2-6 kg commodity resin per ton of finished cardboard, consisting of at least 70 wt.% of waste paper. 2. A method for producing cardboard for flat layers of corrugated cardboard, which consists in the fact that hydrophobic glue and wet-strength polyamide-polyamine-epichlohydrin resin are diluted with water and mixed together, introduced into the paper pulp, consisting of at least 70 wt.% of waste paper, the resulting mixture, cationic starch and a polyacrylamide-based cationic dry-strengthening resin, forming a layer of cardboard and subjecting it to a surface treatment with a composition including hydrolyzed starch and a hydrophobic adhesive. 3. The method according to claim 2, wherein the hydrophobic adhesive and the wet strength polyamide polyamine epichlorohydrin resin are diluted 4 to 10 times with water. 4. The method of claim 2, wherein the surface treatment composition further comprising a dye is used.

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