WO2011087438A1

WO2011087438A1 - Mouldable material

Info

Publication number: WO2011087438A1
Application number: PCT/SE2011/050028
Authority: WO
Inventors: Mikael Ankerfors; Tom Lindström
Original assignee: Innventia Ab
Priority date: 2010-01-12
Filing date: 2011-01-12
Publication date: 2011-07-21

Abstract

The invention relates to highly extensible mouldable materials based on mixtures of lignocellulosic fibre materials and thermoplastic latex. A two-step process is disclosed, in which a paper material is first formed on a paper-machine and pressed and dried to a solids content between 30 and 100 % (pre-form), after which the so produced material is subjected to heat-pressing (moulding), or alternatively pressing followed by heat-activation.

Description

Mouldable material

Field of invention The invention relates to highly extensible mouldable materials, a method for their manufacture and methods for moulding of the materials.

Background Methods to impart a large strain to failure are well known to papermakers and several methods are available and are usually combined in the commercial manufacture of paper, because the strain at break is a critical property of paper materials in several converting operations and in many end-use situations. Sack-paper is for instance required to have a high strain at break in order to give sacks high- energy absorption capacity when subjected to load impacts. Tissue manufacturers use e.g. creping to get fluffy and extensible paper structures. Paper materials that are folded may exhibit surface cracking, a problem that makes the product unattractive and may result in leakages of packaging products. The most frequently used method to improve the extensibility of paper materials is based on the observation that the magnitude of the allowed shrinkage during drying of the paper material is directly proportional to the strain at break of the final sheet. The palette of technical operations used by papermakers can be listed as:

Minimization of restraint during the paper drying process, leading to a high extensibility of the fibre network. Several different tecliniques are used, such as use of low web tension between the press and the drying sections, alteration of the geometry of the free draws, Flakt- drying. • The use of dry strength agents (e.g. modified starches) to reinforce the fibre-fibre joint strength, leading to an increased extensibility of the sheet.

• High consistency (HC) refining in combination with low-consistency (LC) refining. HC- refining introduces curl/kinks on fibres, which improves the extensibility of the free fibre segments. LC-refining makes the fibres more flexible allowing the bonded area to increase, which improves the fibre-fibre joint strength and the extensibility of the sheet.

• Among the more important methods, mechanical shrinking of a moist paper web is a frequently used method. The most common method is Clupak-treatment of the paper in the drying section. The Clupak unit is normally installed in the dryer section of a paper- machine, where the dry content of the web is between 60-65%. The paper is subjected to a compressive force in the machine direction by the frictional effect of the recoiling rubber band in the Clupak device. This results in compaction of the web without any radical buckling or creping. Several variations in this area are known and have been the subject of many patent applications.

• Embossing methods, where mechanical structuring is utilised to geometrically enhance the extensibility of the paper material.

HC/LC-refining, combined with Clupak and drying under low restraint, constitutes the state of the art teclmology for achieving a high strain at break today. One drawback of this assembly of strategies for enhancing the extensibility of the paper material is the resulting rough low-quality printing surfaces. Print quality is a high and ubiquitous demand for boards today and is a most important requirement for packaging materials with a high marketing appeal.

Boards are generally restraint during drying in order to produce a material with high tensile stiffness, smooth surfaces, and high-quality print surfaces. This strategy also results in low extensibility of the produced board and related problems such as surface cracking in converting processes. Increased extensibility of the surface layers would generally involve the use of thicker middle layers, which would result in increased specific bending stiffness of the board material. Hence, paper materials with improved extensibility and methods for their manufacture are needed. Description of the Invention

In accordance with the invention, there is in a first aspect provided a mouldable material comprising Hgnocellulosic fibres and at least one thermoplastic latex. This material, which is in the form of a sheet, is highly extensible and may be formed into a 3-dimensional shape without cracking.

In one embodiment the Hgnocellulosic fibres are chosen among hardwood fibres, softwood fibres, a mixture of hardwood and softwood fibres, recycled fibres, virgin fibres (i.e. fibres that are not recycled), non-wood plant fibres, individually or in a mixture. Hence, the Hgnocellulosic fibres may consist of a mixture of hardwood and softwood fibres. The Hgnocellulosic fibres may also consist of a mixture of virgin and recycled fibres. The Hgnocellulosic fibres may e.g. constitute a mixture of pine and spruce fibres or a mixture of birch and spruce fibres.

In one embodiment, the thermoplastic latex is chosen among polylactide latex,

polyhydroxyalkanoate latexes, individually or in a mixture.

Polyhydroxyalkanoate latexes comprise a large group of linear polyesters. In accordance with the invention, the copolymers of 3-hydroxybutyrates and 3 -hydroxy valeric acid with melting points below 100 °C are of particular interest.

The amount of thermoplastic latex is in the interval of from 1 to 20 % by weight of the

Hgnocellulosic fibres, e.g. in the interval from 1 to 5 % by weight of the Hgnocellulosic fibres.

In one embodiment, the solids content of the mouldable material is in the interval of from 30 to 100% by weight of the mouldable material, with the balance constituting water.

In one embodiment, the mouldable material is multi-layered, whereby the different layers may individually consist of or comprise various lignocellulosic fibres. For example, surface plies may comprise chemical pulp fibres (to impart high stiffness) and middle plies may comprise mechanical pulp fibres (to reduce the density of the material). Chemical pulp fibres can also be mixed with mechanical pulp fibres (for reinforcement of the material). The number of layers may be in the interval of from 1 to 10 layers.

According to a second aspect of the invention, there is provided a method of producing the mouldable material according to the invention, comprising the steps of:

(a) mixing pulp and at least one thermoplastic latex to obtain a mixture;

(b) pressing the mixture formed to obtain a mouldable material.

The pulp referred to above is pulp comprising lignocellulosic fibres. Chemical pulp, mechanical pulp, thermomechanical pulp (TMP) or chemi(thermo) mechanical pulp (CMP or CTMP), stone grounded wood (SGW) pulp may all be made use of in the present invention. The pulp may also be of non-wood origin. Furthermore, pulp used in accordance with the invention may be any mixture of the above listed pulp types.

The chemical pulps that may be used in the present invention include all types of chemical wood- based pulps, such as bleached, half-bleached and unbleached sulphite, kraft and soda pulps, and mixtures of these.

The method of the second aspect of the invention is contemplated to be used in a paper mill. Hence, in one embodiment there is a de-watering step (al ) between steps (a) and (b)

In one embodiment, the method of the second aspect comprises a final step of drying the mouldable material. Drying may be complete, or to a certain solids content of the mouldable material. It may be advantageous to have some residual moisture in the material to facilitate subsequent processing of the material.

In one embodiment of the method of producing the mouldable material, the thermoplastic latex is chosen among polylactide latex and polyhydroxyalkanoate latexes, individually or in a mixture. In one embodiment, retention agent(s) (for the thermoplastic latex, sizing agent(s), wet- strengthening agent(s), filler material(s) and/or dry-strengthening agent(s) are added to the mixture of (a). These additives are chosen to impart specific end-use properties of the mouldable material, and are well-known to the person skilled in the art.

Examples of retention aids are the condensation products such as epihalohydrins, polyamideamines and polyethyleneimines and their various condensation products and chain reaction products such as anionic, non-ionic and cationic polyacrylamides and polyethyleneoxides and natural product derivatives based on starches or gums. Retention aids may be used as single component systems, dual component systems comprising one cationic component (e.g. cationic polyacrylamide or cationic starch) and an anionic component (e.g. anionic polyacrylamide, silica sols or

montmorillonite sols. Examples of sizing agents comprise rosin sizes, alkenyl succinic anhydrides and alkyl ketene dimers. Examples of wet-strengthening agents include urea- formaldehyde resins, melamine-formaldehyde resins or polyamide-amine-epichlorohydrin resins. Examples of filler materials include kaolin clays, talk, ground calcium carbonate, and participated calcium carbonate. Examples of dry-strength agents include starch derivatives (e.g. cationic starch), gums (e.g.

galactomannans) or cellulose derivatives (e.g. carboxymethylcellulose).

In one embodiment of the method of producing the mouldable material, the mouldable material is pressed, de-watered and/or dried to a solids content in the interval of from 30 to 100% by weight of the mouldable material.

In a third aspect of the invention, the mouldable material is heat-pressed over a mould, at a heat- pressing temperature chosen to exceed the minimum film-forming temperature of the thermoplastic latex, or one of the thermoplastic latexes. The heat-pressing may be performed in one or several steps.

In a fourth aspect of the invention, the mouldable material is pressed over a mould, whereupon the material is heat-activated at a heat activation temperature chosen to exceed the minimum film- forming temperature of the thermoplastic latex, or one of the thermoplastic latexes.

If several thermoplastic latexes are used, e.g. in mixture or in different layers of the mouldable material, the heat-pressing temperature is chosen to exceed the highest film-forming temperature of the group of thermoplastic latexes used, or to exceed only the lowest film-forming temperature of the group, or alternatively a temperature anywhere in between is chosen. In the first case, all types of thermoplastic latexes comprised in the mouldable material would be heat-activated.

If a temperature exceeding only the lowest film-forming temperature is chosen, possibly only one thermoplastic polymer would be heat-activated, with the remainder of the thermoplastic latexes remaining in their non-activated state.

The pulp(s) and the at least one thermoplastic latex are chosen to impart advantageous moulding characteristics to the material. Moreover, optional retention agent(s) for the thermoplastic latex, sizing agent(s), wet-strengthening agent(s), filler material(s) and/or dry-strengthening agent(s) are chosen to impart specific end-use properties of the final, heat-pressed material.

In one embodiment, the mould is a 3-dimensional mould, enabling the production of 3-dimensional moulded materials in accordance with the invention. In one embodiment, the heat-pressing temperature is in the interval of from 10 to 220°C, e.g. in the interval of from 40 to 220^°C. Polyhydroxyalkanoate latexes have a minimum film-forming temperature within said intervals.

In another embodiment, the heat-pressing temperature is in the interval of from 90 to 200°C, e.g. in the interval of from 100 to 180^°C. Polylactide latex has a minimum film-forming temperature within said intervals.

The invention shall now be described in the following examples with reference to the accompanied figures, the intention of which is merely to illustrate the inventive concept and not to limit the scope of the invention in any way whatsoever.

Short description of the Figures

Figure 1 shows the equipment used for heat-pressing (shaping) the flat sheets of the mouldable material into 3D. To the left; the whole equipment. To the right; the mould that can be changed.

Figures 2, 3 and 4 show the three different moulds that were used to shape the mouldable material.

Figure 5 shows results from case 27 after heat-pressing (strain of 6%). The curved surface is pointing downwards on the middle picture and upwards on the right picture.

Figure 6 shows results from case 28 after heat-pressing (strain of 12%). The curved surface is pointing downwards on the middle picture and upwards on the right picture.

Figure 7 shows results from case 29 after heat-pressing (strain of 21 %). The curved surface is pointing downwards on the middle picture and upwards on the right picture.

Figure 8 shows results from case 30 after heat-pressing (strain of 21 %). The curved surface is pointing downwards on the middle picture and upwards on the right picture. Figure 9 shows results from case 32 after heat-pressing (strain of 12%). The curved surface is pointing upwards.

Figure 10 shows results from case 33 after heat-pressing (strain of 12%). The curved surface is pointing upwards.

Figure 1 1 shows results from case 34 after heat-pressing (strain of 12%). The curved surface is pointing upwards.

Figure 12 shows results from case 35 after heat-pressing (strain of 12%). The curved surface is pointing upwards.

Figure 13 shows results from case 36 after heat-pressing (strain of 12%). The curved surface is pointing upwards. Figure 14 shows results from case 37 after heat-pressing (strain of 12%). The curved surface is pointing upwards.

Examples

In all the below cases, a never-dried bleached softwood kraft pulp from Husum mill, M-real was used.

Cases 1-3

1 . Sheets were made according to the sheet preparation standard ISO 5269- 1 : 1 998. NaHCCh, with a concentration of 0.001 M, was added to the water suspension when making the sheets to buffer the system. In all cases the fibre grammage was around 80 g/m². In case 1 and 2, 20 % polylactide latex (LANDY PL-2000, Miyoshi Oil & Fat Co., LTD, Japan) was added to the fibres resulting in a total grammage of around 96 g/m² and 17 % latex calculated on the total weight. An amount of 0.4 % cationic polyacrylamide (C-PAM) (EKA PL 1520, Eka Chemicals. Sweden) was used as retention aid. In case 3, no latex or C-PAM was added.

2. The sheets were then wet pressed at 400 kPa.

3. Finally the sheets were dried at 23 °C and 50 % relative humidity (RH). In cases 1 and 3, the sheets were dried under restraint. In case 2, the sheets were dried freely.

Cases 4-18

In these cases, all sheets were prepared in the same way as in case 1 , but with different amounts of polylactide latex added and different total grammage. The dried sheets were then heat-pressed at different temperatures, times, and pressures as described in the table below.

Table 1

Case 19

In case 19, the sheets were formed in the same way as in case 2, but the freely dried sheet were then warm pressed at 150 °C and 60 kPa for 30 minutes.

Cases 20-23

In these cases, all sheets were prepared in the same way as in case 1 , but only step 1 and 2 as described above. Hence, these sheets were not dried. The pressed and never dried sheets were then warm pressed at different temperature, times, and pressures as described in the table below. Table 2

Cases 24-26

In these cases, all sheets were prepared in the same way as in case 1 , but the total basis weights of the sheets were around 1 80 g/m^". The sheets were then shaped into a 3-dimensional-shape using a warm pressing equipment (see figure 1 ) which could be equipped with different moulds (see figure 2. 3 and 4). In case 24. the mould in figure 2 was used (approx. strain 6 %), in case 25, the mould in figure 3 was used (approx. strain 12 %) and in case 26, the mould in figure 4 was used (approx. strain 21 %). In all cases (case 24-26) the pressing in the equipment was performed at 150 °C and 400 kPa for 30 seconds.

Cases 27-29

In these cases, all sheets were prepared in the same way as in Case 20, but the basis weights of the sheets were around 1 80 g/m². The sheets were then shaped into a 3-dimensional-shape using a warm pressing equipment (see figure 1 ) which could be equipped with different moulds (see figure 2, 3 and 4). In case 27. the mould in figure 2 was used (approx. strain 6 %), in case 28, the mould in figure 3 was used (approx. strain 12 %) and in case 29, the mould in figure 4 was used (approx. strain 21 %). In all cases (case 27-29) the pressing in the equipment was performed at 150 °C and 400 kPa for 30 seconds.

Case 30-31 (Comparative examples)

In case 30, the sheets were prepared in the same way as in Case 1 , but the basis weights of the sheets were around 180 g/mf and did not contain any latex or C-PAM. In case 3 1 , the sheets were prepared in the same way as m Case 20, but the sheets were 180 g/m^" and did not contain any latex or C-PAM. The sheets were then shaped into a 3-dimensional-shape using a warm pressing equipment (see figure 1 ) which could be equipped with different moulds (see figure 2, 3 and 4). All three moulds were tried and the pressing in the equipment was performed at 150 °C and 400 kPa for 30 seconds. Case 32-36

In these cases, all sheets were prepared in the same way as in Case 7, but the basis weights of the sheets were around 150 g/m^" and different amounts of latex (5-20%) were tested. The sheets were then shaped into a 3-dimensional-shape using a warm pressing equipment (see figure 1 ) which was equipped with the mould showed in figure 3. In all cases (case 32-37) the pressing in the equipment was performed at 150 °C and 400 kPa. First, the sheets were pre-heated in the mould and then moulded under pressure. Before the actual moulding the samples were also wetted in different ways. Water was added to the sheets either by spraying or by immersing the sheets into water (see table 3). Table 3

Case Poly- Heat- Heat- Heat- Water Added Pre3D lactide pressing pressing pressing addition amount heating mouldlatex temperapressure time method of water time in ing additure (kPa) (min.) (%) 3D time tion re) mould (min.)

(% of (min.)

total)

32 20 1 50 60 4 Immersing 57 1.5 4

33 10 1 50 60 4 Immersing 52 1.0 4

34 20 150 60 4 Spraying 9 0.3 1

35 10 150 60 4 Spraying 15 0.3 3

36 10 150 60 4 Spraying 18 0.3 2 Case 37

In these cases, all sheets were prepared in the same way as in Case 19, but the basis weights of the sheets were around 150 g/m² and 5% were tested and the hot-pressing time was 30 min. The sheets were then shaped into a 3-dimensional-shape using a warm pressing equipment (see figure 1 ) which was equipped with the mould showed in figure 3. The pressing in the equipment was performed at 150 °C and 400 kPa. The 3-dimensional pressing was done in two steps. First, the sheets were preheated in the mould and then moulded under pressure. Before the actual moulding the samples were also wetted by spraying (see table 4). Table 4

Mechanical testing

Before mechanical testing of the sheets, they were stored at 23 °C and 50 RH over night. The mechanical testing was performed in accordance with ISO 1924-3 :2005, structural sheet density in accordance to SCAN-P 88 :01 , and grammage in accordance to ISO 536: 1995.

Results from the cases

The most crucial sheet property for allowing the sheet to be shaped from a flat sheet into a 3- dimensional-shape is the materials strain at break. The results from the mechanical testing and measurements of structural sheet density for the cases are listed in table 5 below.

Table 5

Strain at break value for the sheet after the paper was shaped into 3D. Hence, after the sheet had been strained 6 % (Cases 24 and 27) and 12 % (Cases 25 and 28), respectively. The reference materials (without latex and C-PAM) that were also shaped in the moulding equipment (cases 30 and 31 ) resulted in samples with very poor quality. Most of these samples broke during the moulding and those who did not break were very weak and could not keep their shape. Instead they collapsed. This problem occurred already using the mould with the lowest strain (see figure 2). The materials that contained latex and C-PAM (cases 24-29), on the other hand, could be shaped in all moulds and resulted in stiff paper materials, which retained their shape also at an applied compressive force to the moulded material. The figures 5-7 below illustrate examples of the appearance of shaped sheets containing latex (cases 27, 28 and 29). The sheets made in case Q, R and S, look and behave very similar to cases 27, 28 and 29, respectively.

A typical broken sheet from case 30 is illustrated by Figure 8. Case 3 1 sheets are very similar to case 30 sheets.

The results from cases 32-37 are presented in the form of photos of the 3-dimensional-shaped sheets are presented in figures 9- 14. The polylactide latex containing sheets that were immersed in water (case 32 and 33) were not successfully formed, probably because the high moisture content made them too weak to withstand the stresses that they were subjected to during the forming. These sheets were also pre-heated for longer times than the other polylactide latex containing sheets which might indicate that pre-heating is disadvantageous.

With less moistening the success was better. Case 34 containing 20% polylactide latex was successfully formed with an addition of 9% water. Cases 36 and 37 were also successfully formed despite only containing 10% and 5% polylactide latex, respectively.

Claims

Patent Claims

1 . Mouldable material comprising lignocellulosic fibres and at least one thermoplastic latex.

2. Mouldable material according to claim 1 , wherein the lignocellulosic fibres are chosen among hardwood fibres, softwood fibres, recycled fibres, virgin fibres, non-wood plant fibres, individually or in a mixture.

3. Mouldable material according to claim 1 , wherein the themioplastic latex is chosen among polylactide latex, polyhydroxyalkanoate latexes, individually or in a mixture.

4. Mouldable material according to claim 1 , wherein the thermoplastic latex amounts to 1 -20 % by weight of the lignocellulosic fibres.

5. Mouldable material according to claim 4, wherein the themioplastic latex amounts to 1 -5 % by weight of the lignocellulosic fibres.

6. Mouldable material according to claim 1 , wherein the solids content of the material is in the interval of from 30 to 100% by weight of the mouldable material.

7. Mouldable material according to claim 1 , wherein the mouldable material is multi-layered.

8. Method of producing the mouldable material of claim 1 , comprising the steps of:

(a) mixing pulp and at least one themioplastic latex to obtain a mixture;

(b) pressing the mixture formed to obtain a mouldable material.

9. Method according to claim 8, comprising a de-watering step (al ) between steps (a) and (b).

10. Method according to claim 8, comprising a final step of drying the mouldable material.

1 1 . Method according to claim 8, wherein the themioplastic latex is chosen among polylactide latex, polyhydroxyalkanoate latexes, individually or in a mixture.

12. Method according to claim 8, wherein retention agent(s) for the thermoplastic latex, sizing agent(s), wet-strengthening agent(s), filler material(s) and/or dry-strengthening agent(s) are added to the mixture of (a).

13. Method according to any one of claims 8- 10, wherein the mouldable material produced is pressed, de- watered and/or dried to a solids content in the interval of from 30 to 100% by weight of the mouldable material.

14. Method of moulding the mouldable material of claim 1 , wherein the mouldable material is heat-pressed over a mould, at a heat-pressing temperature chosen to exceed the minimum film-forming temperature of the thermoplastic latex, or one of the themioplastic latexes.

15. Method of moulding the mouldable material of claim 1 , wherein the mouldable material is pressed over a mould, whereupon the material is heat-activated at a heat activation temperature chosen to exceed the minimum film-forming temperature of the thennoplastic latex, or one of the thermoplastic latexes.

16. Method according to claim 14 or 1 5, wherein the mould is a 3-dimensional mould.

17. Method according to claim 14 or 15, wherein the heat-pressing or heat-activation

temperature is in the interval of from 10 to 220^°C.

18. Method according to claim 17, wherein the heat-pressing or heat-activation temperature is in the interval of from 90 to 200°C.