Method and system for manufacturing a coated paperboard and a coated paperboard

Abstract

The present invention relates to a method for manufacturing coated paperboard suitable for packaging paperboard applications. The method comprises coating a first surface of the paperboard web by applying a) a first coating composition in a precoating unit for forming a precoating layer comprising inorganic mineral pigment particles and least one binder for sealing the first surface of the paperboard web; and b) a second coating composition in a curtain coating unit for forming at least one barrier coating layer on the first surface of the paperboard web; and c) a third coating composition comprising a polymer dispersion in the curtain coating unit for forming at least one heat sealable coating layer on the first surface of the paperboard web. The temperature of the coated paperboard web is controlled and adjusted, and the paperboard web is cooled in at least one cooling unit.

Claims

1. A method for manufacturing coated paperboard suitable for packaging paperboard applications, the method comprising coating a first surface of the paperboard web by applying a. a first coating composition in a precoating unit for forming a precoating layer comprising inorganic mineral pigment particles and least one binder for sealing the first surface of the paperboard web, and b. a second coating composition in a curtain coating unit for forming at least one barrier coating layer on the first surface of the paperboard web, and c. a third coating composition comprising a polymer dispersion in the curtain coating unit for forming at least one heat sealable coating layer on the first surface of the paperboard web, controlling and adjusting the temperature of the coated paperboard web, and cooling the paperboard web in at least one cooling unit.

2. The method according to claim 1, wherein the temperature of the heat sealable coating layer is adjusted to a temperature level, where the dispersed polymer in the coating layer is at least partially melted during film forming.

3. The method according to claim 2, wherein the temperature of the coated paperboard web is adjusted to at least 90 C., preferably at least 100 C., more preferably in the range of 100-150 C., even more preferably in the range of 100-130 C., most preferably in the range of 110-120 C.

4. The method according to claim 1, wherein the temperature of the paperboard web after the temperature adjustment is cooled down to a temperature below 50 C., preferably below 45 C., more preferably below 40 C., before winding the coated paperboard web.

5. The method according to claim 1, wherein the paperboard web is calendered after the precoating unit and/or before and/or after the cooling unit.

6. The method according to claim 1, wherein the paperboard web is coated by applying the first coating composition on both the first surface and on a second surface of the paperboard web.

7. The method according to claim 1, wherein at least the first surface of the paperboard is exposed to electrical surface modification treatment before winding the said coated paperboard web onto jumbo reel.

8. The method according to claim 7, wherein the surface energy of the first surface of the coated paperboard web is changed by the electrical surface modification treatment.

9. The method according to claim 7, wherein the electrical power used in the electrical surface modification treatment is less than 50 W/m.sup.2/min, more preferably less than 40 W/m.sup.2/min, most preferably 15-30 W/m.sup.2/min.

10. A coated paperboard comprising a base paperboard and at least a first precoating layer and at least two successive coating layers at least on a first surface of the base paperboard, wherein the first precoating layer comprises at least inorganic mineral filler particles and a binder, a second barrier coating layer having barrier properties is arranged on top of the first precoating layer, and a third heat sealable coating layer is arranged on top of the second coating layer, the third coating layer comprising a heat sealable polymer.

11. The paperboard according to claim 10, wherein the inorganic mineral filler particles are selected from particles of calcium carbonates, kaolin and titanium dioxide.

12. The paperboard according to claim 10, wherein the binder in the first precoating layer is synthetic polymer latex, polyvinyl alcohol or starch.

13. The paperboard according to claim 10, wherein the weight of the precoating layer on the first surface is less than 30 g/m.sup.2, preferably 7-20 g/m.sup.2, more preferably 4-12 g/m.sup.2.

14. The paperboard according to claim 10, wherein the weight of the second coating layer is less than 20 g/m.sup.2, preferably 3-10 g/m.sup.2, more preferably 4-9 g/m.sup.2.

15. The paperboard according to claim 10, wherein the weight of the third coating layer is less than 20 g/m.sup.2, preferably 5-12 g/m.sup.2, more preferably 6-9 g/m.sup.2.

16. The paperboard according to claim 10, wherein the base paperboard has a grammage in the range of 150 to 500 g/m.sup.2, preferably from 175 to 400 g/m.sup.2, more preferably 175 to 350 g/m.sup.2.

17. A packaging paperboard product made of paperboard according to claim 10.

18. The product according to claim 17, wherein the product is hot cup, cold cup, espresso cup, medicine pill dosing cup, cereal or powder box, cereal or powder bag, food service board package or a barrier coated paperboard products.

19. A paperboard manufacturing system for processing lignocellulosic pulp stock into coated paperboard, the system comprising at least a wire section, a press section and a drying section, wherein the system further comprises a coating section, which includes (i) a precoating unit, which is configured to close the pores of at least a first surface of a paperboard web by applying a first coating composition on the first surface of the web, (ii) at least one curtain coating unit, which is configured to provide at least two coating layers on at least the first surface of the paperboard web using a second coating composition, and (iii) at least one adjustable heating unit, which is configured to control and adjust the temperature of the paperboard web and to remove water therefrom, (iv) at least one cooling unit, wherein all the said sections and the said units are included in the same online manufacturing system ending at a jumbo reel wherein the coated paperboard web is wound for the first time.

20. The system of claim 19, wherein the adjustable heating unit comprises means for controlling the temperature by using a predetermined algorithm calculating the energy output of said unit.

21. The system of claim 19, wherein the adjustable heating unit comprises sensing means for measuring the actual temperature of the paperboard web surface at said unit.

22. The system of claim 19, wherein the system further comprises an electrical surface modification unit, which is configured to modify the energy of at least the first surface of the coated paperboard web.

23. The system of claim 19, wherein the said system further comprises at least one calendering unit, preferably said calendering unit is installed after the precoating unit and/or before and/or after the cooling unit.

24. The system of claim 19, wherein said system further comprises means for removing air from at least one coating composition used in the coating section, preferably said means comprises an underpressure pump.

25. The system of claim 19, wherein said system further comprises means for measuring the amount of coating composition applied, preferably said means comprises a mass flow meter.

Description

[0069] Some embodiments of the present invention are described in more detail below with reference to the enclosed schematical figures, in which

[0070] FIG. 1 depicts schematically an online system according to one embodiment of the present invention,

[0071] FIG. 2A-2B depict schematically coated paperboards obtained according to some embodiments of the present invention,

[0072] FIG. 3A depicts measured temperature from the paperboard surfaces, and

[0073] FIG. 3B depicts the predetermined temperature setting profile according to the present invention.

[0074] An exemplary embodiment depicting an online system according one embodiment of the present invention is depicted in FIG. 1 schematically. In FIG. 1 the following abbreviations are used: A=wire section; B=press section; C=drying section; D=coating section; and E=winding to jumbo reel.

[0075] In an exemplary embodiment of the present invention the coating section comprises a precoating unit, where the web enters in between the rolls of the precoater, and subsequently the web is guided through the post drying section.

[0076] The coating unit comprises a curtain coater. A preferred curtain coater may coat two or three layers simultaneously on a base paper web. The curtain coating unit is followed by a heating unit.

[0077] The sections of FIG. 1 are further explained in example 1.

[0078] FIGS. 2A and 2B depict the some embodiments of the preferred coated paperboard structures. In FIG. 5A three layers of coating are on the both sides and in FIG. 5B three layers of coating are only on one side.

[0079] The resulting multilayer structure is depicted in FIGS. 2A and 2B wherein 1=base paperboard, 2=precoating layer, 3=barrier layer and 4=heat sealable coating layer.

[0080] In one embodiment the heat sealable coating layer on top of the precoating and barrier layers if heated according to the heating profile of FIG. 3B. The three heating units whereby the web is passing after application of the third coating composition for forming the heat sealable coating layer are adjusted to 130 C., 60 C. and 40 C. The actual measured temperature experienced by the web is disclosed in FIG. 3A.

[0081] The present invention is further illustrated by the following non-limiting examples.

EXAMPLES

Example 1

[0082] FIG. 1 shows schematically the sections of one paperboard system according to the present invention. The sequence of the sections is the following:

A Wire section wherein water is removed from stock with gravity and suction through a wire. Dry content about 0.5% to about 20%
B Press section wherein water is removed by pressing web. Dry content about 20% to about 50%.
C Drying section wherein water is removed by heating paperboard with the help of steam in drying cylinders. Dry content about 50% to about 95%.
D Coating section wherein web is coated and dried several times. Final dry content is about 90%. The coating section further comprises the following units: [0083] precoating [0084] calendering [0085] 1st curtain [0086] 2nd curtain [0087] calendering [0088] cooling [0089] optional surface charging
E Winding to jumbo reel

Example 2

[0090] The paperboard production system according to the invention was used to produce cups for hot beverages, such as coffee.

[0091] Final caliper of the paperboard product aimed at was 300 m. The following production parameters and sequence were applied: [0092] Base paper thickness was 200 g/m.sup.2 [0093] Precoating layer thickness was 10 g/m.sup.2 on each side of the paperboard [0094] Calendering was performed after precoating to close the surfaces [0095] Curtain coating was used to coat the inside surface of the cup paperboard by 6 g/m.sup.2 barrier coating layer and 8 g/m.sup.2 heat sealable coating layer, the dispersions were applied accordingly based on flow meter measurement results. [0096] Temperature was controlled and adjusted for the paperboard web for 150 C. and then the web was cooled down to 50 C. [0097] Final calendering was performed to reach the required target caliper of paper before directing the paperboards to winding.

[0098] A structure according to FIG. 2A was thus obtained.

[0099] This on-line produced product was used to successfully to make cups by the cup producer. The cups were rigid and their sealing properties were excellent (heat sealable function). Barrier properties were good as hot water or coffee did not penetrate into the paperboard product within a time period of 12 h.

[0100] Possible waste in production was reused as the paperboard product produced by the present method is recyclable without requiring any intermittent processing or treatment.

Example 3

[0101] The paperboard production system according to the invention was used to produce cups for cold beverages.

[0102] Final caliper of the paperboard product aimed at was 330 m. The following production parameters and sequence were applied: [0103] Base paper 200 g/m.sup.2. [0104] Precoating 10 g/m.sup.2 on each side. [0105] Calendering to close the surface. [0106] Curtain coating on inside surface: 6 g/m.sup.2 for barrier coating layer, 8 g/m.sup.2 for heat sealable coating layer. [0107] Temperature control, web 150 C and then cooled down to 50 C. [0108] Curtain coating on outside surface: 3 g/m.sup.2 for barrier coating layer, 3 g/m.sup.2 for heat sealable coating layer. [0109] Temperature control for web 150 C. and then cooled down to 40 C. [0110] Final calendering to reach needed caliper of paper. [0111] Outside surface of the paperboard for the cup was treated electrically using 25 W/m.sup.2/min to reach 60 dyn/cm surface tension.

[0112] A structure according to FIG. 2B was thus obtained.

[0113] This on-line produced paperboard product was used to successfully make cups by the cup producer. The cups were rigid and sealing properties were excellent (heat sealable function). Barrier properties were good as liquids did not penetrate into the product within a time period of 12 h. Outside of cup provided enough barrier against condensate water.

[0114] Possible waste in production was reused as the paperboard product produced by the present method is recyclable without requiring any intermittent processing or treatment.

Example 4

[0115] Fast food company used two different waste cups: a dispersion coated cup according to the present invention and a PE(polyethylene)-extruded cup. The traditional PE-extruded cups had to be treated as waste and therefore the fast food company had to pay an external party to collect the used cups and either burn or process them in a PE eliminating process. Dispersion coated cups were treated as recyclable paperboard and they could be sold accordingly.