METHOD FOR PRODUCING CORRUGATED CARDBOARD

Abstract

The present invention relates to a process for producing corrugated fiberboard from plies of paper which each have a grammage of 70 to 200 g/m.sup.2 and of which at least one ply of paper is obtained by a process comprising the addition of (A) 0.25 to 5 wt %, based on dry paper stock, of at least one cationic polymer comprising vinylamine units, and (B) 0 to 5 wt %, based on dry paper stock, of at least one polymeric anionic compound,

to a paper stock, draining the paper stock by sheet formation, coating the paper web obtained with (C) 0.1 to 3 wt %, based on dry paper stock, of at least one starch

and drying the coated paper web,

wherein the polymeric anionic compound is selected from a polymeric anionic compound (B1) and a polymeric anionic compound (B2),

wherein said polymeric anionic compound (B1) is obtainable by copolymerizing a monomer mixture comprising, preferably consisting of, (a) at least one monomer (a) selected from acrylamide and an N-vinylcarboxamide of the formula

##STR00001## where R.sup.1 and R.sup.2 are each H or C.sub.1 to C.sub.6 alkyl, (b) at least one acid-functional monoethylenically unsaturated monomer and/or its alkali metal, alkaline earth metal or ammonium salts (b), and (c) optionally one or more monoethylenically unsaturated compounds (c) other than said monomers (a) and (b), and (d) optionally one or more compounds having at least two ethylenically unsaturated double bonds in the molecule,

and said polymeric anionic compound (B2) is the hydrolysis product of said polymeric anionic compound (B1) whose carboxamide moieties have been partly or wholly hydrolyzed into amino groups,

and also the corrugated fiberboard thus obtained and its use in the manufacture of packaging boxes from corrugated fiberboard.

Claims

1. A process for producing corrugated fiberboard from plies of paper which each have a grammage of 70 to 200 g/m.sup.2 and of which at least one ply of paper is obtained by a process comprising: the addition of (A) 0.25 to 5 wt %, based on dry paper stock, of at least one cationic polymer comprising vinylamine units, and (B) 0 to 5 wt %, based on dry paper stock, of at least one polymeric anionic compound, to a paper stock; draining the paper stock by sheet formation; coating a paper web obtained with (C) 0.1 to 3 wt %, based on dry paper stock, of at least one starch,. to obtain a coated paper web; and drying the coated paper web, wherein: the polymeric anionic compound is selected from the group consisting of a polymeric anionic compound (B1) and a polymeric anionic compound (B2); and the polymeric anionic compound (B1) is obtainable by copolymerizing a monomer mixture comprising (a) at least one monomer selected from the group consisting of acrylamide and an N-vinylcarboxamide of the formula ##STR00007## where R.sup.1 and R.sup.2 are each H or C.sub.1 to C.sub.6 alkyl; (b) at least one acid-functional monoethylenically unsaturated monomer, an alkali metal, alkaline earth metal or ammonium salt thereof, or a mixture thereof; (c) optionally one or more monoethylenically unsaturated compounds other than said monomers (a) and (b); and (d) optionally one or more compounds having at least two ethylenically unsaturated double bonds in the molecule; and the polymeric anionic compound (B2) is a hydrolysis product of the polymeric anionic compound (B1) whose carboxamide moieties have been partly or wholly hydrolyzed into amino groups.

2. The process according to claim 1, wherein the cationic polymer comprising vinylamine units is obtainable by: polymerizing: (a) at least one monomer of the formula ##STR00008## where R.sup.1 and R.sup.2 are each H or C.sub.1 to C.sub.6 alkyl, (c) optionally one or more monoethylenically unsaturated monomers other than said monomers (a), and (d) optionally one or more compounds having at least two ethylenically unsaturated double bonds in the molecule; and then partially or completely hydrolyzing the monomer (I) units polymerized into the polymer, to form amino groups, and/or the cationic polymer comprising vinylamine units is obtainable by Hofmann degradation of polymers having acrylamide units, methacrylamide units, or both.

3. The process according to claim 1, wherein the cationic polymer comprising vinylamine units is polyvinylamine or an at least 10 mol % hydrolyzed homopolymer of N-vinylformamide.

4. The process according to claim 1, wherein the polymeric anionic compound is obtainable by polymerizing a monomer mixture comprising: (a) at least one monomer selected from the group consisting of acrylamide and an N-vinylcarboxamide of the formula ##STR00009## where R.sup.1 and R.sup.2 are each H or C.sub.1 to C.sub.6 alkyl; (b) at least one acid-functional monoethylenically unsaturated monomer, an alkali metal, alkaline earth metal or ammonium salt thereof, or a mixture thereof; (c) optionally one or more monoethylenically unsaturated monomers other than said monomers (a) and (b); and (d) optionally one or more compounds having at least two ethylenically unsaturated double bonds in the molecule.

5. The process according to claim 1, wherein the polymeric anionic compound is obtainable by polymerizing a monomer mixture comprising: (a1) N-vinylformamide; (b1) acrylic acid, methacrylic acid, alkali metal or ammonium salts thereof, or a mixture thereof; and (c1) optionally one or more monoethylenically unsaturated monomers other than the monomers of groups (a) and (b).

6. The process according to claim 1, wherein the polymeric anionic compound is an anionic copolymer of acrylamide.

7. The process according to claim 1, wherein the polymeric anionic compound is obtainable by copolymerizing a monomer mixture comprising: (a1) acrylamide; (b1) acrylic acid, methacrylic acid, alkali metal or ammonium salts thereof, or a mixture thereof; and (c1) optionally one or more monoethylenically unsaturated monomers other than the monomers of groups (a) and (b).

8. The process according to claim 1, wherein the paper web obtained is coated with an enzymatically degraded starch.

9. A corrugated fiberboard obtainable by the process of claim 1.

10. A method, comprising manufacturing a packaging box with the corrugated fiberboard of claim 9.

Description

EXAMPLES

[0146] The examples which follow illustrate the present invention. The percentages in the examples are by weight, unless otherwise stated.

[0147] The K-value of polymers was determined after Fikentscher, Cellulose-Chemie, volume 13, 58-64 and 71-74 (1932) at a temperature of 20 C. in 5 wt % aqueous sodium chloride solutions at a pH of 7 and a polymer concentration of 0.5%. It is to be noted that K=k1000.

[0148] The following polymers were used in the inventive and comparative examples.

[0149] Polymer (A)

[0150] Partially hydrolyzed polyvinylformamide (30% degree of hydrolysis) having a K-value of 90.

[0151] Polymer (B)

[0152] Anionic polymer with the monomer composition of 70 mol % acrylamide and 30 mol % acrylic acid, an M.sub.w of 800 000 g/mol and an anionic charge density of 3.8 meq/g.

[0153] Preparation of Starch Solution:

[0154] Merizet 120 maize starch (from Tate & Lyle) was enzymatically degraded as follows: A 12% slurry of Merizet 120 was prepared in hot water at 65 C. under agitation in a 1000 L vessel and 0.012% of PL 120 enzyme from Novozyme was added. After 20 minutes, 100 ml of acetic acid were added to the starch solution to terminate the process of starch degradation. The starch solution had a viscosity of 55 mPas at 100 rpm (spindle 2).

[0155] Further compounds used as auxiliaries: [0156] retention aid: polyvinylformamide (having a 20% degree of hydrolysis), a K-value of 160 and an anionic charge density of 25 mmol/100 g. [0157] Basoplast 450 P: 30 wt % solution of an anionic surface-sizing agent (from BASF SE)

[0158] Pretreatment of Paper Stock

[0159] Paper from 100% waste paper (a mixture of the varieties 1.02, 1.04, 4.01) was beaten with tap water in a pulper at a consistency of 4% until free of fiber bundles and ground in a refiner to a freeness of 40 SR. This stuff was subsequently diluted with tap water to a consistency of 0.8%.

[0160] Drainage Testing

[0161] One (1) liter of the paper stock described above was used in each inventive and comparative example and was in each case admixed in succession under agitation with the water-soluble polymers each specified in the table and thereafter drained using a Schopper-Riegler drainage tester by measuring the time in seconds for a quantity (filtrate) of 600 ml to pass through. The concentration of polymer A and of polymer B, which were each tested as dry strength agent for paper, was 1% in each case. The results of the measurements are reported in the table.

[0162] Base Paper Production and Treatment

[0163] The paper stock described above was admixed under agitation and in succession with the polymers specified in table 1 in the inventive and comparative examples. The amounts used in each case (parts by weight) of the polymer solids are reported per 100 parts by weight of waste paper solids.

[0164] The polymers (cationic polymer comprising vinylamine units, polymeric anionic compound and the retention aid) were each added to the paper stock in the form of a 1 wt % aqueous solution. The pH of the paper stock was kept at a constant pH7 (using 5% strength sulfuric acid).

[0165] Following the last addition of polymers to the paper stock, base papers 2 m in width, 5000 m in length and 133 g/m.sup.2 in basis weight were produced on a Fourdrinier machine from Voith. The base paper was subsequently size-pressed with a formulation consisting of a starch solution and size at different add-ons of 2.5 to 7 g/m.sup.2. The size-pressed paper was subsequently dried with contact dryers to a paper moisture content of 5%.

[0166] Table 1 hereinbelow summarizes the test liners (TLouter ply) and corrugated base papers (FLfluting) produced.

[0167] The paper stock treated wtih the polymers gave a Schopper-Riegler value of SR 40 in the drainage test.

[0168] Performance Testing of Base Papers

[0169] Paper was conditioned for 24 h at 50% relative humidity before the following strength tests were carried out: [0170] bursting pressure as per DIN ISO 2758 (up to 600 kPa) and DIN ISO 2759 (above 600 kPa) [0171] SCT as per DIN 54518 (Shortspan compression test) [0172] CMT as per DIN EN 23035 (Corona medium test)

TABLE-US-00001 TABLE 1 Specification of test liners or corrugated base papers Polymer A Polymer B Retention aid Starch (solids)/ parts by parts by parts by paper stock Size 0.15 Basis Starch/ weight of weight of weight of (solids) part by weight area Example solids solids solids [kg/ton] weight [g/m.sup.2] [g/m.sup.2] RP 1 - TL n.i. 0.046 50 (5 wt %) Basoplast 450 P 140 7 RP 2 - FL n.i. 0.046 50 (5 wt %) 140 7 RP 3 - TL n.i. 0.046 20 (2 wt %) Basoplast 450 P 140 2.8 RP 4 - FL n.i. 0.046 20 (2 wt %) 140 2.8 CM 1 - TL n.i. 1.3 0.023 50 (5 wt %) Basoplast 450 P 140 7 CM 1 - FL n.i. 1.3 0.023 50 (5 wt %) 140 7 CM 2 - TL n.i. 2.34 1.75 0.023 50 (5 wt %) Basoplast 450 P 140 7 CM 2 - FL n.i. 2.34 1.75 0.023 50 (5 wt %) 140 7 CM 3 - TL 1.3 0.023 20 (2 wt %) Basoplast 450 P 140 2.8 CM 3 - FL 1.3 0.023 20 (2 wt %) 140 2.8 CM 4 - TL 2.34 1.75 0.023 20 (2 wt %) Basoplast 450 P 140 2.8 CM 4 - FL 2.34 1.75 0.023 20 (2 wt %) 140 2.8 CM 5 - TL n.i. 1.3 0.023 Basoplast 450 P 136 CM 5 - FL n.i. 1.3 0.023 136 CM 6 - TL n.i. 2.34 1.75 0.023 Basoplast 450 P 136 CM 6 - FL n.i. 2.34 1.75 0.023 136 n.i. not inventive

[0173] Corrugated Fiberboard Production

[0174] The corrugated base papers (flutingFL) were formed to a B flute on a BHS board machine. Corrugated fiberboard production took place using Cargill 208 B 7 size, a speed of 125 m/min and a surface temperature of 63 C. for outer 1 and outer 2. Size add-on was 2.5 g/m.sup.2 in each case. Each run produced 2500 m of B flute. The corrugated fiberboard consists of the two outer layers (test liner A and test liner B with the flute in between).

[0175] Table 2 shows the composition of the corrugated fiberboards from the above-described test liners and corrugated base papers. The test liners in question were produced twice under the same conditions (test liner-A and test liner-B).

TABLE-US-00002 TABLE 2 Examples of corrugated fiberboard Example Composition of corrugated fiberboard Comment.sup.1) 1 n.i. RP 1 TL - A RP 2 FL RP 1 TL - B 5 wt % of starch 2 n.i. RP 3 TL - A RP 4 FL RP 3 TL - B 2 wt % of starch 3 n.i. CM 1 - TL - CM 1 - FL CM 1 - TL - Polymer A A B 5 wt % of starch 4 n.i. CM 2- TL - CM 2 - FL CM 2 - TL - Polymer A A B Polymer B 5 wt % of starch 5 CM 3 - TL - CM 3 - FL CM 3 - TL - Polymer A A B 2 wt % of starch 6 CM 4 - TL - CM 4 - FL CM 4 - TL - Polymer A A B Polymer B 2 wt % of starch 7 n.i. CM 5 - TL - CM 5 - FL CM 5 - TL - Polymer A A B 0% of starch 8 n.i. CM 6 - TL - CM 6 - FL CM 6 - TL - Polymer A A B Polymer B 0% of starch n.i.: not inventive .sup.1)the starch quantity is starch (solids) based on paper stock (solids)

[0176] Fefco Standard Box Production

[0177] The B flute corrugated fiberboard was formed in an in-line plotter and stamping machine from Meier at 30 m/min into Fefco standard boxes having the formats 302010 cm (type A), 403020 cm (type B) and 504030 cm (type C).

[0178] Strength Tests on Standard Box from Corrugated Fiberboard:

[0179] The sample materials to be tested were conditioned at 23 C. and 50% relative humidity to constant weight (for at least 24 h) before testing. Sample preparation was carried out as per the standard. The flat corrugated fiberboard boxes were uprighted and sealed with adhesive tape at the bottom and top flaps. Performance measurements for ECT and FCT were each carried out on 10 individual specimens (in conformity with the standard). The result reported is the mean from 10 measurements. [0180] ECT edge crush resistance to DIN EN ISO 3037 [0181] FCT flat crush resistance to DIN EN ISO 3035

[0182] On the corrugated fiberboard boxes: [0183] BCT box crush resistance to DIN 55440. BCT was determined as per said DIN standard for box types A, B and C.

[0184] The BCT measurements were carried out on 10 boxes in each case in conformity with the standard. The result reported is the mean from 10 measurements plus the related standard deviation.

[0185] Table 3 summarizes the performance test results of the treated base papers and the corrugated fiberboard box manufactured therefrom. The values reported for the treated base papers are the values of the test liner.

TABLE-US-00003 TABLE 3 Example Strength agent and starch SCT CMT Burst BCT - N BCT - N BCT - N ECT FCT content.sup.1) [kN*m.sup.2/g] [N*m.sup.2/g] [kPa*m.sup.2/g] Type A Type B Type C [kN/m] [kPa] Example 1 1.85 1.69 2.29 2407 2398 2443 5.37 322 n.i. 100% starch Example 2 1.7 1.61 2.17 2128 2255 2399 4.87 326 n.i. 2 wt % of starch Example 3 2 2.16 2.87 2707 2593 2669 6.06 448 n.i. Polymer A 5 wt % of starch Example 5 1.82 2.05 2.53 2128 2405 2439 5.88 411 Polymer A, 2 wt % of starch Example 7, 1.9 2 2.59 2027 2151 2282 4.95 394 n.i. Polymer A 0% starch Example 4 2.05 2.38 2.9 2563 2520 2611 6.36 424 n.i. Polymer A, Polymer B 5 wt % of starch Example 6 1.86 2.12 2.7 2408 2377 2439 5.59 438 Polymer A, Polymer B, 2 wt % of starch Example 8 1.9 2.2 2.82 2262 2532 2402 5.95 474 n.i. Polymer A, Polymer B, 0% starch n.i.: not inventive .sup.1)the starch quantity is starch (solids) based on paper stock (solids)

[0186] As is evident from the results in table 3, the use of polymer A combined with polymer B (Example 6) or polymer A (Example 5) while at the same time reducing the starch add-on from 50 kg/ton to 20 kg/ton provides comparable corrugated fiberboard strengths to the use of starch as sole strength agent.