RU2805224C1 - Plywood board for cryogenic and low temperature applications - Google Patents

Abstract

FIELD: structural materials.

SUBSTANCE: invention relates to plywood board suitable for low temperature applications such as cryogenic applications. Plywood board (100) for use at temperatures less than minus 50°C comprises first, second and third veneer layers (110, 120, 130) containing hardwood, and the veneer layers (110, 120, 130) are attached to each other by an adhesive (200) containing resin. The resin (a) contains a polymerisable substance and a cross-linking agent, wherein (b) at least 50% by weight of the polymerisable substance is derived from lignin, (c) at least 10% of the molecules in the resin have a molecular weight greater than 10,000 Da, (d) by at least 10% of the molecules in the resin have a molecular weight of less than 1000 Da, (e) the number average molar mass of the resin is from 1000 to 1600 Da, and (f) the mass average molar mass of the resin is from 5000 to 14000 Da. The invention includes a method for manufacturing such a plywood board (100) and its use at a temperature of minus 50°C to support a container (410) containing liquefied petroleum gas (LPG) or liquefied natural gas (LNG), and application at minus 150°C to support the container containing LNG. The invention discloses a cargo storage system (CSS), such as a vessel (400), containing such a plywood board (100).

EFFECT: invention provides a plywood board that is strong and lightweight also at low temperatures and/or after being exposed to low temperatures, such as minus 50°C and below, and/or at cryogenic temperatures such as minus 150°C and below.

25 cl, 22 dwg, 3 tbl

Description

Technical field

The invention relates to plywood boards. The invention relates to plywood boards suitable for low temperature applications such as cryogenic applications. The invention relates to applications of such plywood boards. The invention relates to methods for manufacturing plywood boards.

State of the art

Plywood has been used as a construction material and has also been used as a construction material in liquefied natural gas (LNG) tanks. LNG tanks are examples of cargo storage systems (CSS). Plywood is particularly suitable for this application, as wood is a relatively strong and lightweight material that can also withstand very low temperatures. Compared to wood, plywood is more isotropic because it contains veneers oriented in different directions. In cryogenic applications such as LNG storage systems, the operating temperature range can be large, ranging from about +30°C when the container is empty to about -160°C when the container is loaded with LNG. Thus, isotropic properties are an advantage when considering thermal deformation.

Even though the wood veneer of plywood is adequately resistant to cold environments, it has been observed that the adhesive commonly used in plywood boards is not as resistant to cold environments. In particular, the adhesive may become brittle at low temperatures and/or after it has been exposed to low temperatures. Thus, the properties of plywood board, including strength, may become unacceptable for use at low temperatures. For these reasons, there is a need for a plywood board that is strong and lightweight also at low temperatures and/or after being exposed to low temperatures. Such problems may occur at low temperatures, such as -50°C and below, and/or at cryogenic temperatures, such as -150°C and below.

Brief description of the invention

It has been found that an adhesive containing a resin containing a polymerizable substance, where part of the polymerizable substance is derived from lignin, performs better at low temperatures and/or after exposure to low temperatures than a conventional plywood adhesive. Moreover, solid wood has been found to have beneficial properties for low-temperature applications, including above-ground liquefied gas storage, and cryogenic applications, such as LNG storage. Compared to softwood, hardwood is denser and much more durable. The plywood board according to the invention is described in more detail in independent claim 1 of the claims. The method for manufacturing such a plywood board is disclosed in more detail in independent claim 8 of the claims. A plywood board produced by this method is proposed in independent claim 14 of the claims. The applications of plywood board are disclosed in claims 20 and 21 of the claims. A preferred application relates to use as a carrier material in LNG storage systems. Thus, claim 22 relates to a cargo storage system, such as a vessel, containing a plywood board. In the dependent claim relating to the method, it is stated that the plywood board is suitable for use in cryogenic applications. The dependent claim discloses that the board or board-containing assembly contains an information storage medium or database containing information indicating that the plywood board is suitable for use in cryogenic applications.

Brief description of drawings

In FIG. 1 shows a side view of a plywood board according to the invention,

in Fig. 2 shows a side view of a plywood board according to the invention,

in Fig. 3a-3d show the orientation of the wood fibers of the veneer layers of a plywood board,

in Fig. 4a-4h show side views of the wood fiber orientations of the veneer layers of a plywood board,

in Fig. 5 shows a side view of the manufacturing process of a plywood board according to the invention,

in Fig. 6 shows a basic view of a vessel containing a plywood board according to the invention,

in Fig. 7a shows a plywood board with markings,

in Fig. 7b-7e show configurations comprising a plywood board and a storage medium or database, and

in Fig. 8 shows a side view of various areas of the adhesive layer.

Detailed Description of the Invention

Plywood is one of the most recognized material options for structural applications among wood-based panels because it offers advantages such as dimensional stability, excellent strength-to-weight ratio, and high chemical and impact resistance. Therefore, it has traditionally been widely used in light frame structures and was considered a reliable building product. In general, wood species, density, wood grain orientation, veneer quality, number of veneer layers, adhesive (including bonding resin and quantity), and the manner in which the adhesive is applied affect the overall properties of plywood. In sheets using the same number and quality of veneer layers, the mechanical properties of plywood are highly dependent on the type of adhesive because plywood is made by gluing together multiple thin sheets of veneer under heat and pressure. Phenol-formaldehyde resin has been widely used as a resin adhesive for plywood. At room temperature, plywood made with phenol-formaldehyde resin is highly resistant to peeling of adjacent layers.

In the case of offshore or offshore industries, phenol formaldehyde (PF) resin plywood has also been used for insulation boards in liquefied natural gas (LNG) carriers in cargo storage systems (CSS), such as ships, to ensure structural safety and reliability at LNG storage temperature -163°C. Partially filled LNG tanks are constantly exposed to liquid vibrations and liquid vibration-induced shock loads that are high pressures and short durations. Structural problems such as crack initiation and propagation, bulging and veneer failure in phenol-formaldehyde resin plywood used in LNG storage systems have been observed. Therefore, cryogenic applications (i.e. -150°C and below) require more durable plywood boards. In addition, similar problems were encountered at other low temperatures, that is, at -50 ° C and below.

In particular, such plywood boards which maintain their mechanical properties also at low temperatures (i.e. less than minus 150°C) and/or after they have been exposed to low temperatures (i.e. less than minus 150°C) are suitable for use in at least some cryogenic and low temperature applications. In the field of liquefied natural gas (LNG) cargo storage system (CSS), slabs for an application must go through a qualification process in order to determine their suitability for such application. The present invention relates to a plywood board 100 for use in a liquefied natural gas (LNG) cargo storage system (CSS) in the above sense. However, such boards are also suitable for other low temperature applications as mentioned above.

To obtain such plywood board 100, the effects of different adhesives, different amounts of adhesives, veneer materials, and veneer sheet orientation on mechanical properties after exposure to low temperature were studied. Among the various possibilities, a particularly feasible combination for cryogenic applications was identified. In particular, hardwood has been found to perform better than softwood. Moreover, cross-shaped layering of veneer layers is preferable to unidirectional adjacent veneer layers. It was also discovered that lignin resin adhesive (LR), containing a polymerizable substance, of which at least 50 wt. % comes from lignin, much better compared to phenol-formaldehyde (FF) resin.

In general, the adhesive 200 used to make plywood contains water, resin and a hardener. The hardener may contain clay, kaolin, starch, microcrystalline cellulose or wood flour. As for the resin, in general, the resin contains a polymerizable substance and a cross-linking agent. For example, in the prior art phenol-formaldehyde resin, phenol forms a polymerizable substance, and formaldehyde is used as a cross-linking agent. As stated above, the excellent adhesive resin contains a polymerizable substance, of which at least 50 wt. % comes from lignin. Such an adhesive is typically heat activated. Thus, by applying heat, the adhesive 200 is cured. Typically, heat and pressure are used to bond the layers of plywood veneer to each other.

Adhesive 200 is typically prepared by mixing resin, hardener and additional water. Note that the resin usually also contains water, so the term additional water was used above for other water. The dry matter content of the resin may be from 35 to 60%, preferably from 40 to 55%, and more preferably from 42 to 52%. The adhesive 200 typically contains from 60 to 80 wt. % resin (containing water), from 10 to 20 wt. % hardener and from 10 to 25 wt. % additional water. Preferably, the adhesive 200 contains from 65 to 75 wt. % resin. The hardener is usually substantially dry. Additional water is typically added in such an amount that the dry matter content of the adhesive 200 is the same as the dry matter content of the resin before mixing the adhesive. As stated below, due to the hydroxyl groups of the veneer layers, preferably the dry matter content of the adhesive 200 is between 35 wt. % up to 60 wt. %, for example, from 40 wt. % up to 55 wt. %, for example, from 42 wt. % up to 52 wt. %. This, on the one hand, ensures the adhesion of the adhesive 200 to the wood and, on the other hand, ensures a suitable viscosity of the adhesive 200.

It has been found that such adhesives function particularly well when (1) at least 50 wt. % polymerizable resin adhesive 200 is derived from lignin, (2) at least 10% of the molecules in the resin have a molecular weight above 10,000 Da, (3) at least 10% of the molecules in the resin have a molecular weight below 1,000 Da, (4) the number-average molar mass Mn of the resin is from 1000 Da to 1600 Da, and (5) the mass-average molar mass Mw of the resin is from 5000 Da to 14000 Da. In FIG. 1 and 2 show a plywood board where the adhesive 200 that was used to bond the veneer layers to each other is in cured form. No separate reference number is given for cured adhesive in the drawing. However, the terms adhesive and cured adhesive are used for the adhesive 200 before and after curing, respectively, as deemed necessary.

Regarding terms, as is known to one skilled in the art, the number average molar mass Mn is defined as (EN _i M _i )/(ΣN _i ), where N _i is the number of molecules of type i and M _i is the molar mass of molecules of type i. Accordingly, the mass-average molar mass Mw is determined as (ΣN _i M _i M _i )/(ΣN _i M _i ). Note that the product N _i M _i is the mass of molecules of type i and, in this document, also the weighting factor in the numerator.

In general, properties of adhesives that influence their resistance to cold temperatures include viscoelasticity, glass transition temperature, molecular size distribution, degree of cross-linking, and degree of crystallization. As described in detail below, in particular the lignin adhesive contains large molecules and small molecules, which may have a molecular size distribution advantageous for this application.

Without being bound by theory, the authors believe that the heterogeneous distribution of molecular sizes, indicated by the proportions of large molecules (high Dalton number) and small molecules (low Dalton number), improves the ductility of the adhesive at low temperatures. Moreover, the average molecular size indicated by the Mn and Mw numbers, combined with a significant proportion of small molecules, appears to ensure that the adhesive acts cooperatively with the wood veneer layers of the plywood so that the adhesive penetrates well into the veneer layers. The adhesive can penetrate into the cracks of the outer layer and into the micro grooves of the rough surface. In particular, a sufficient number of small molecules, indicated by the percentage of molecules with a low Dalton number, appears to allow the adhesive to penetrate into the cracks of the outer layer and into the microgrooves of the veneer layers.

With reference to FIG. 8, in general, when two objects, such as a veneer 110 and another veneer 130, are bonded to each other with an adhesive 200 that is cured, at least three different portions of the cured adhesive can be defined. First, as indicated by reference number 205a, the adhesion zone of the cured adhesive adheres to the surface of the veneer (110, 130) and, once bonded, forms an interface with the veneer (110, 130). Further from the interface there is a transition zone 205b in which the properties of the cured adhesive change from bulk properties to surface properties. Even further from the interface, in the adhesion zone 205 c, the adhesive has its bulk properties.

As stated above, small molecules can penetrate into the veneer layers. This improves adhesion, in particular in the adhesion zone 205a and in the transition zone 205b. However, it appears that small molecules of the adhesive, if the adhesive is composed of small molecules, tend to form a regular structure, which may tend to be self-repeating, similar to lattices or networks. However, such regular structures, even if strong, are usually fragile. Therefore, it appears that if the adhesive contains only small molecules, the adhesive must be brittle. Accordingly, it appears that larger adhesive molecules make the adhesive more pliable. Moreover, lignin in particular is known to contain molecules of various sizes and especially quite a lot of large molecules. Thus, since some of the resin comes from lignin, these large molecules are also present and the resulting adhesive is more flexible also at low temperatures. Large molecules also ensure that some molecules are present in the adhesion zone 205c, meaning that not all of the adhesive penetrates the veneer layers 110, 130.

Moreover, if the adhesive consists of small molecules, all molecules can easily penetrate into the veneer layers, since wood is a porous material. In the case where only the usual amount of adhesive was used, for this reason the adhesive layer became too thin and perhaps no adhesive zone was present. This layer does not have the required adhesive properties. Moreover, if the thickness was increased by using more adhesive, the resulting bond zone should be brittle, as stated above.

Moreover, it appears that if the adhesive is composed of large molecules, these large molecules tend to form a regular, brittle structure somewhat similar to that discussed above for small molecules. Moreover, in this case the molecules do not penetrate the veneer layers. The result is a thick and brittle engagement zone 205c that would be unreliable due to its fragility.

Thus, also the thickness of the grip zone affects the grip. Preferably, the thickness of the adhesion zone 205c is less than 0.2 mm or less than 0.15 mm. As shown in FIG. 8, the adhesion zone may be slightly thinner than the corresponding adhesive layer. However, considering the thickness ta (see FIG. 2) of the adhesive layer, preferably the thickness ta of the adhesive layer is less than 0.25 mm, for example 0.01 mm to 0.25 mm. More preferably, the thickness ta of the adhesive layer is less than 0.20 mm, for example from 0.01 mm to 0.20 mm, or less than 0.15 mm, for example from 0.01 mm to 0.15 mm. Thickness ta refers to the thickness of the adhesive layer between two adjacent layers. In plywood, especially regular non-reinforced plywood, thickness ta refers to the thickness of the adhesive layer between two adjacent layers of veneer. Moreover, preferably this thickness range applies to each adhesive layer between two adjacent layers, in particular, to the adhesive layers that are located between the first veneer layer 110 and the second veneer layer 120. In the case where another layer of material is attached to the board 100, for example, as a protective layer or cover, thicker layers of adhesive can be used for this purpose.

The greater penetration that is associated with the small molecules of the adhesive 200 is associated with a larger contact surface between the adhesive 200 and the wood substance (i.e., veneer layers 110, 130), thereby increasing the potential for secondary bonding and covalent bonding forces between the adhesive 200 and woody substance. Penetrating cracks and sealing damaged surface cells improves adhesion performance. Since the wood surrounding the interface of the adhesive joint contributes to the bonding characteristics, strengthening the wood at the interface has a positive effect on the strength and rigidity of the bond. Thus, the use of an adhesive having a non-uniform molecular size distribution cooperates with the surface structure of the veneer layers 110, 130 so that a strong cold-resistant plywood board is obtained.

Even if the lignin itself has a non-uniform size distribution, preferably the adhesive resin 200 contains lignin and at least one compound of phenol, cresol and resorcinol, more preferably the adhesive resin 200 contains lignin and phenol. Also preferably no more than 95 wt. 200% of the polymerizable substance of the adhesive resin comes from lignin.

In FIG. 1 shows a side view of a plywood board 100 according to one embodiment. In general, plywood board 100 has a length lp with a width wp and a thickness tp. As usual for these names, tp is less than the lesser of the length lp and the width wp. The thickness tp is shown in Fig. 2. The length 1p and width wp are shown in Fig. 1 and 3b. Typically, the length 1p is at least 1 m and the width wp is at least 1 m. In use, the board 100 can be cut to the required size. The thickness of tp is usually less than 100mm. The preferred tp thickness for low temperature and cryogenic applications is detailed below.

For the above reasons, plywood board 100 includes a first veneer layer 110 containing hardwood having a first wood fiber orientation D1, a second veneer layer 120 containing hardwood having a second wood fiber orientation D2, and a third veneer layer 130 containing hardwood. having a third orientation D3 of wood fibers.

The term hardwood refers to the wood of a deciduous tree. Specifically, in one embodiment, the veneer layers (plywood board 100) that contain hardwood comprise wood selected from ash, aspen, linden, beech, birch, cherry, pecan, mahogany, maple, oak, poplar, dipterocarp, teak, rosewood, oumea and shorewood, preferably birch or beech.

As for the names of these veneer layers, the third veneer layer 130 is located between the first veneer layer 110 and the second veneer layer 120 in the thickness direction tp of the plywood board 100. Accordingly, the first veneer layer 110 is the outermost veneer layer. Therefore, all of the veneer layers of board 100 that contain wood, with the exception of the very first veneer layer 110, are located on one side of the first veneer layer. In addition, also the second veneer layer 120 is the outermost veneer layer. Therefore, all of the veneer layers of board 100 that contain wood, with the exception of the second veneer layer 120 itself, are located on one side of the second veneer layer 120. This applies whether or not the board 100 is coated with a wood-free coating.

Typically, the plywood board 100 is not coated because the coating increases the weight of the board 100 without significantly improving its strength. Therefore, at least one of the major surfaces 112, 122 of the plywood board 100 may not contain a coating. Thus, in one embodiment, the first veneer layer 110 defines a first surface 112 of the plywood board 100, wherein the normal to the first surface 112 of the plywood board 100 is unidirectional with the thickness direction tp of the plywood board 100. Such first surface 112 is shown in FIG. 1 and 2. As discussed above, when uncoated, the wood material of the first veneer layer 110 forms a first surface 112. Moreover, in one embodiment, the second veneer layer 120 defines a second surface 122 of the plywood board 100, where the normal to the second surface 122 of the plywood board 100 is unidirectional with the thickness direction tp of plywood board 100. Such second surface 122 is shown in FIG. 1 and 2. As stated above, when uncoated, the wood material of the second veneer layer 120 forms a second surface 122.

Referring to FIG. 3a and 3b, in order for the plywood board 100 to have somewhat isotropic properties, the first wood fiber orientation D1 forms an angle α13 with the third wood fiber orientation D3, where the angle α13 is from 60 to 120 degrees. Typically, the angle α13 is 90 degrees or at least substantially 90 degrees (eg, 85 to 95 degrees). Angle α13 is shown in FIG. 3b. In a preferred embodiment, the first wood fiber orientation D1 is unidirectional with the second wood fiber orientation D2, or the first wood fiber orientation D1 makes an angle α12 of no more than 30 degrees with the second wood fiber orientation D2. As can be seen from FIG. 3b, the angle α12 is small, that is, the first wood fiber orientation D1 is substantially unidirectional with the second wood fiber orientation D2. Obviously, the first wood fiber orientation D1 may be unidirectional with the second wood fiber orientation D2. Having the first veneer layer 110 and the second veneer layer 120 oriented such that their wood fiber orientations D1 and D2 are at least substantially unidirectional (in the meaning described above) has the technical effect that the board 100 can use either the first surface 112 or the second surface 122 oriented in a predetermined direction, such as upward. In other words, the plate 100 responds to mechanical load in the same way, regardless of whether the first surface 112 or the second surface 122 is directed in a predetermined direction, for example, upward. For example, during bending, the orientation of wood fibers affects the bending modulus. In particular, during bending, the surface layers take the greatest deformation of the slab (compression or elongation depending on the side of the slab). Since each veneer layer is anisotropic, this has a direct impact on the properties of the board. Moreover, the bending of the veneer around an axis that is perpendicular to the orientation of the wood fibers of the veneer may have the effect that some wood fibers are partially broken out of the veneer, causing small chips to protrude from the veneer. Also for this reason, if the orientations D1 and D2 of the wood fibers were perpendicular, the board 100 should behave differently when used upside down and when used upside down. Thus, this improves the applicability of the slab 100 and makes it easier to manufacture designed structures from the slab 100.

The veneer layers of the plywood board 100, particularly the first, second and third veneer layers (110, 120, 130), were attached to each other using an adhesive 200 (see FIGS. 1 and 2). The details of the adhesive have been discussed above.

In FIG. 3a-3d show the structure of the plywood board 100 in more detail. FIG. 3a shows a side view of a board 100 with three layers of veneer 110, 120, 130. These veneer layers contain hardwood with wood grain orientations D1, D2, and D3, respectively. The arrows shown in layers 110 and 120 indicate the direction D1, D2 of wood fibers from left to right or right to left in FIG. 3a. The crosses shown in layer 130 in FIG. 3a indicate the direction D3, which is perpendicular to the plane of the paper on which the crosses are shown. Even though the adhesive 200 is not shown between the veneer layers, the veneer layers have been glued together using the adhesive 200 as detailed above.

In FIG. 3b shows an exploded view of the slab of FIG. 3a. In FIG. 3c shows how, in principle, the veneer layer 130 can be composed of more than one veneer layers 131, 132, 133. However, for purposes of illustration, the wood fiber direction D3 of FIG. 3c is different from that shown in FIG. 3b. Finally, in FIG. 3d shows the veneer layer 131, the growth rings observed on the veneer, and the orientation D3 of the wood fibers of the veneer layer 131 of FIG. 3s. As shown in FIG. 3d, in wood the annual rings extend, in a circular fashion, in the direction of the orientation of the wood fibers.

In FIG. 4a-4d show preferred wood fiber orientations of the veneer layers for plywood board 100 with three, four, five and six layers of veneer. The plywood board may contain, for example, from three to seventy-five (3 to 75) layers of veneer. In FIG. 4a-4d, the symbol N represents the number of veneer layers of the plywood board 100. In addition to the first, second and third veneer layers, the other veneer layers 140, 150, 160 contain wood. Preferably, the other veneer layers 140, 150, 160 also comprise hardwood. Preferably, the number N of veneer layers of plywood board 100 is at least five, for example from 5 to 75. In FIG. 4e and 4h show slabs with eight or ten layers of veneer.

Also in FIG. 4a-4h, arrows indicate wood grain orientations from left to right (or vice versa) and crosses indicate wood grain orientations perpendicular to the plane of the paper, respectively, as discussed above in connection with FIG. 3a-3d. As shown in FIG. 4a-4d, in one embodiment, the first number N1 of layers (110, 120, 130, 140, 150, 160) of veneer plywood board 100 are oriented in a first wood fiber orientation D1 (or in an orientation substantially unidirectional with the first wood fiber orientation D1 in the meaning , discussed above for D2). The second number N2 of layers (110, 120, 130, 140, 150, 160) of veneer plywood board 100 are oriented in a wood fiber orientation that is perpendicular to the first wood fiber orientation D1 (or in an orientation substantially perpendicular to the first wood fiber orientation D1 in the meaning discussed above for D3).

In order for the plate 100 to be substantially isotropic, preferably the first number N1 is substantially equal to N2. More precisely, the difference N1 - N2 between the first number N1 and the second number N2 is no more than two. Moreover, since N1 is the number of veneer layers oriented in the first wood fiber orientation D1, including at least the first veneer layer 110 and preferably the second veneer layer 120, the difference N1 - N2 is preferably at least zero. In other words, N1 is not less than N2. For example, in FIG. 4f and 4h show embodiments in which N1=N2.

Even more precisely, in the case where the number N of veneer layers is odd (that is, N can be expressed as 2M+1, where M is an integer), the first number N1 is greater than the second number N2 by one (that is, N1=N2+1). Such plates 100 are shown in FIG. 4a and 4c.

However, when the number N is even (that is, N can be expressed as 2M, where M is an integer), in order to have the outermost veneer layers 110, 120 oriented in the same direction, two adjacent intermediate veneer layers are oriented in in the same direction, as shown in Fig. 4b, 4d, 4e, 4f, 4g and 4h. Regarding the term "interlayer veneer", each intermediate veneer layer has two adjacent layers of veneer. With respect to the term "adjacent veneer", no wood-containing veneer is located between each pair of two adjacent veneers. However, in the case where multiple other non-wood structural layers, such as reinforcing layers, are used in the board 100, each other non-wood layer may be positioned between two adjacent veneer layers. In this case, the other structural layer is an adjacent layer to the veneer layer.

For example, in FIG. 4a, the intermediate veneer layer 130 has adjacent veneer layers 110 and 120. In this case, the outermost veneer layers 110, 120 are not intermediate veneer layers. Moreover, in all drawings, all veneer layers, with the exception of the outermost veneer layers 110, 120, are intermediate veneer layers.

Referring to FIG. 4b, 4d, 4e, 4f, 4g and 4h, preferably, when the number N is even, the first number N1 is equal to the second number N2 (that is, N1=N2) or the first number N1 is greater than the second number N2 by two (that is, N1=N2 +2). Moreover, as shown in the drawings, preferably the first wood fiber orientation D1 is perpendicular to the wood fiber orientation of a veneer layer that is adjacent to the first veneer layer 110. Also preferably, the second wood fiber orientation D2 is perpendicular to the wood fiber orientation of the veneer layer that is adjacent to the second veneer layer 120. Also preferably, the first 110 and second 120 veneer layers have unidirectional wood grain orientations.

Although the numbers N1 and N2 refer to the isotropy of the entire board 100 in the planar directions of the board (that is, in the length direction lp or the width direction wp or a linear combination of these directions), the distribution of veneer layers oriented in different directions in the thickness direction locally affects the isotropy . Since board 100 is preferably equally usable as upside down as upside down, preferably as many adjacent veneer layers are oriented transversely to each other as possible.

Referring to FIG. 4a-4h, unlike the outermost veneer layers (110, 120), each of the intermediate veneer layers 130, 140, 150, 160 has a first and a second adjacent veneer layer. For example, in FIG. 4b, the intermediate veneer layer 130 has adjacent veneer layers 110 and 140, and the intermediate veneer layer 140 has adjacent veneer layers 130 and 120.

In general, in order for the plywood board 100 to also be locally isotropic (locally in terms of position in the thickness direction), preferably as many intermediate veneer layers as possible have two adjacent veneer layers in which the orientation of the wood fibers is perpendicular to the orientation of the wood fibers the considered intermediate veneer layer. The limiting condition for this number is that the outermost veneer layers are even more preferably oriented in the same direction.

Referring in particular to FIG. 4a and 4c, when the number N of veneer layers of the board 100 is odd (that is, expressed as 2M+1, where M is an integer), preferably each of the intermediate veneer layers has two adjacent veneer layers in which the orientation of the wood fibers is perpendicular to the orientation of the wood fibers the considered intermediate veneer layer.

However, referring to FIG. 4b and 4d-4h, when the number N of veneer layers of the board 100 is even (that is, expressed as 2M, where M is an integer), preferably each of the intermediate veneer layers, except for the two intermediate veneer layers, has two adjacent veneer layers, in in which the orientation of the wood fibers is perpendicular to the orientation of the wood fibers of the interlayer veneer under consideration. Two layers not having such adjacent layers result from the fact that the directions of the wood fibers of the outermost layers (110, 120) of the veneer are unidirectional and the number N is even.

As shown in FIG. 4a-4h, each intermediate veneer layer has a first adjacent veneer layer and a second adjacent veneer layer. Moreover, the third number N3 of the intermediate veneer layers is such that

the direction of the wood fibers of the subject interveneer layer is perpendicular to the direction of the wood fibers of the first adjacent veneer layer of the subject intermediate veneer layer; and

the direction of the wood fibers of the subject intermediate veneer layer is perpendicular to the direction of the wood fibers of the second adjacent veneer layer of the subject intermediate veneer layer.

In FIG. 4a-4h show the total number N of veneer layers and the number N3 of such intermediate veneer layers that have two transversely oriented adjacent veneer layers. As shown in these drawings, the third number N3 of the intermediate veneer layers is less than the number N of veneer layers by two or four. In other words, the number N of veneer layers exceeds the third number N3 by two or four. Or, mathematically: N3=N-2 or N3=N-4.

Preferably, when the number N of veneer layers of the plywood board 100 is expressed as 2M+1, where M is an integer, the third number (N3) is less than the number N of veneer layers by two (N3=N-2), that is, N is greater than N3 by two.

It is also preferable that the number N of veneer layers of the plywood board 100 is expressed as 2M, where M is an integer, the third number N3 is less than the number N of veneer layers by four (N3=N-4), that is, N is greater than N3 by four.

In addition to the orientations of the wood fibers of the veneer layers, the isotropy of plywood board 100 may be affected by non-wood construction layers, particularly if such construction layers are anisotropic. Thus, what was said above about the numbers N1, N2 and N3 does not necessarily apply in all embodiments. However, the preferred plywood board 100 contains only layers of cured adhesive and intermediate veneer layers between the outermost veneer layers 110, 120. Thus, the core board 100, where the core is the portion between the first and second veneer layers 110, 120, preferably contains no wood-free structural layers other than cured adhesive 200. Moreover, the preferred plywood board 100 contains only layers of cured adhesive and intermediate veneer layers between the outermost veneer layers 110, 120 and what was said about the numbers N1, N2 and/or N3 applies. Even more preferably, the board 100 is not covered. In such a case, the plywood board 100 is composed of layers of cured adhesive and layers of veneer containing wood. Moreover, what was said about the numbers N1, N2 and/or N3 applies. It has been found that adhesive 200 also works well in cryogenic applications at least between the wood veneer layers of board 100.

With reference to FIG. 4b-4h, a preferred embodiment of plywood board 100 includes, in addition to the first, second and third veneer layers, an additional veneer layer (140, 150, 160) or additional veneer layers (140, 150, 160) located between the first veneer layer 110 and the second layer 120 veneer. The additional veneer layer contains wood and, if present, the additional veneer layers contain wood. Preferably, all layers (110, 120, 130, 140, 150, 160) that contain wood contain hardwood, such as one of ash, aspen, basswood, birch, cherry, pecan, mahogany, maple, oak, poplar, dipterocarpa, teak, rosewood, oumea and shorea, preferably birch or beech.

Preferably, the thickness tbv of each of the intermediate veneer layers 130, 140, 150 is from 1.0 mm to 3.0 mm, more preferably from 1.0 mm to 2.0 mm. Preferably, the thickness of the first veneer layer 110 and/or the second veneer layer 120 is from 0.5 mm to 3.0 mm, more preferably from 0.5 mm to 2.0 mm. In one embodiment, at least one of the first veneer layer 110 and the second veneer layer 120 is thinner than the intermediate veneer layer 130, 140, 150. In one embodiment, the thickness tsv1 of the first veneer layer 110 is equal to the thickness tsv2 of the second veneer layer 120. The technical effect here is that the plate 100 is equally usable with the top side up and the top side down.

The thickness tp of the plywood board is preferably from 4 mm to 95 mm. The preferred number of veneer layers was indicated above.

As shown in more detail below, the surface veneer thicknesses tsv1 and tsv2 of board 100 may be less than the intermediate veneer thickness tbv, for example, due to sanding of at least one of the surface veneer layers. However, if the surface veneer layer 110, 120 is too thin, it may not sufficiently protect the underlying adhesive. Thus, the surface layer of the veneer may break during use or during transportation and expose the adhesive, which is generally unacceptable. Therefore, in one embodiment, the thickness tsv1 of the first veneer layer 110 is at least half of the thickness tbv of the third veneer layer 130, which is the intermediate veneer layer. It is also preferable that the thickness tsv2 of the second veneer layer 120 is at least half of the thickness tbv of the third veneer layer 130.

With respect to the amount of cured adhesive in plywood board 100, a preferred amount of (liquid) adhesive 200 is described below in terms of the manufacturing method. The adhesive 200 upon application contains water, a substantial portion of which evaporates during manufacture and/or storage, leaving a dry adhesive 200 between the veneer layers of plywood board 100. Moreover, when the dry matter cures, at least some of its resin undergoes polymerization. Considering the amount of adhesive 200 applied and its water content, in one embodiment, from 40 g/m ² to 120 g/m ² of cured adhesive is located between two adjacent layers. Preferably, from 50 g/ ^m2 to 100 g/ ^m2 of cured adhesive is located between two adjacent layers. This amount of cured adhesive has been found to work particularly well in plywood board 100 containing hardwood veneer layers (110, 120, 130). This amount has been found to be consistent with the suitable thickness ta of the plywood board adhesive layer, in particular the suitable thicknesses of the bond zone 205c as discussed above. Moreover, it has been found that this amount of cured adhesive works particularly well in plywood containing hardwood veneer layers such that the thickness of each intermediate veneer layer is from 1.0 to 3.0 mm, or from 1.0 to 2 .0 mm. Thus, even more preferably, from 40 ^gsm to 120 ^gsm or from 50 ^gsm to 100 ^gsm of cured adhesive is located in each space between two adjacent layers. The adjacent layers may be adjacent veneer layers such that no structural layer of material other than wood or cured adhesive is located between adjacent veneer layers. By definition, no wood layer is located between two adjacent layers of veneer.

The plywood board 100 described above has been found to be resistant to two types of heat treatment: thermal treatment and liquefied gas immersion treatment. As used herein, heat treatment resistance means that heat treatment does not significantly degrade the mechanical properties of plywood board 100. Such mechanical properties include flexural strength (measured in the longitudinal and transverse directions) and flexural modulus (measured in the longitudinal direction and in the transverse direction). These properties should not be significantly reduced by heat treatment. In addition, the board 100 may be resistant to heat treatments such that none of the heat treatments degrades other mechanical properties of the plywood board 100. Moreover, the inventors believe, given references [1] and [2], that the plywood board 100, which is resistant to these two types of heat treatment, is also suitable for LNG storage and other low temperature applications.

Flexural strength refers to the flexural strength defined in EN 310 (1993). It should be noted that the EN 310 standard refers to the longitudinal and transverse directions, which are sometimes referred to as the lengthwise direction and the crosswise direction, as stated above. Generally speaking, according to the EN 310 standard, test pieces are cut from plywood board 100 and the flexural strengths are measured in both the transverse direction and the longitudinal direction. The tensile strength in longitudinal bending and the tensile strength in transverse bending are indicated as the average values of the measured values. Before the samples are destroyed, the flexural moduli of the samples can be determined.

Regarding heat treatment resistance, generally speaking, the prototypes are cut from 100 plywood board and the prototypes are divided into two groups, so that the first group prototypes are heat treated before strength testing (such as EN310 or NFB51-123) and the prototypes the second group does not undergo heat treatment before strength testing (for example, EN 310 or NFB51-123). Moreover, since the strength is measured in both the longitudinal and transverse directions, the samples of the first group are further divided into a first set and a second set for longitudinal measurements and transverse measurements, respectively. For the same reason, the samples of the second group are further divided into a third set and a fourth set for longitudinal measurements and transverse measurements, respectively. If required, the size of the prototypes may differ from the dimensions specified in the standards.

Regarding the types of heat treatment, two types of treatments are known, for example, from references [1] and [2]: temperature shock treatment and liquefied gas immersion treatment.

Surge treatment was performed by immersing the first group of test samples in liquid nitrogen (LN2) for 1 hour and then placing the samples at room temperature (23°C) for 2 hours. This 3-hour cycle was repeated 3 times (total treatment time was 9 hours). The liquefied gas immersion treatment was carried out by immersing the first group prototypes in liquefied natural gas (LNG) for 15 days. Tests were then performed on samples at room temperature and at room temperature. These treatments were intended to comply with membrane-type LNG storage system approvals (including large storage tank and other liquid gas applications), which specify standards for the cryogenic test method. These and similar tests have been described, for example, in references [1] and [2].

Table 1 shows the flexural strengths measured similarly to EN 310 on eight slabs, so that half of the specimens cut from the slabs passed the thermal immersion test described above.

For the results of Table 1, four different types of plywood boards 100 were studied and two boards of each type were measured, whereby eight boards 100 were studied. The type is determined by the thickness of the board, which is either 9 mm or 12 mm, and the type of adhesive, designated FF and LC. FF corresponds to conventional phenol-formaldehyde adhesive. LC corresponds to lignin glue and it is the adhesive 200 described in detail above and below. Moreover, the lignin adhesive polymerizable substance used in the plywood boards 100 that were tested for Tables 1 to 3 contains phenol in addition to lignin.

The flexural strengths of two plywood boards of each of the four types are measured similarly to EN 310 and are described above. In Table 1, each row corresponds to results measured for one slab. As detailed above, figurative shapes were cut from each slab. The samples were divided into two groups, that is, into four sets. Samples of the first and second sets (i.e., the first group) were subjected to a thermal immersion test, the flexural strength was measured as the average of the samples from the first set of samples with longitudinal orientation of the wood grains, and the lateral bending strength was measured as the average of the samples from the second set samples with transverse orientation of wood fibers. These results are shown in Table 1 in the “After Dive” columns. Moreover, the samples of the third and fourth sets (i.e., the second group) did not undergo any heat treatment, the flexural strength was measured as the average of the samples from the third set of samples with longitudinal orientation of the wood fibers, and the lateral bending strength was measured as the average from samples from the fourth set of samples with transverse orientation of wood fibers. These results are shown in Table 1 in the “No Immersion” columns.

As shown in Table 1, when LK lignin adhesive was used, the flexural strength of the plywood board increased in the immersion test. Strength increased by an average of 3% and 4% in the longitudinal and transverse directions, respectively. On the contrary, when FF phenolic adhesive was used, the flexural strength of the plywood board decreased in the immersion test. Strength decreased on average by 8% and 4% in the longitudinal and transverse directions, respectively. This clearly indicates that the use of lignin adhesive to bond the veneer layers to each other helps the plywood board 100 withstand thermal immersion. It was found that boards with adhesive 200 (i.e. LK lignin adhesive) also performed well in the temperature swing test.

Table 2 shows the flexural moduli, i.e. "flexural modulus of elasticity", measured similarly to EN 310 on slabs. In addition to the flexural strength before failure, the flexural modulus (i.e., flexural modulus) can be measured. Half of the samples cut from the slabs underwent thermal immersion testing. These tests use the same slabs as those used in the tests whose results are shown in Table 1.

As shown in Table 2, when lignin adhesive “LK” was used, the flexural modulus of the plywood board remained virtually unchanged in the immersion test. On the contrary, when FF phenolic adhesive was used, the flexural modulus of the plywood board decreased in the immersion test. The bending modulus decreased on average by 5% and 1% in the longitudinal and transverse directions, respectively. This clearly indicates that using LC adhesive to bond the veneer layers together helps the board withstand thermal immersion.

In addition, the tensile strength of the plywood boards was measured in a manner similar to that discussed above. However, instead of measuring the flexural modulus and strength similar to EN310, the tensile strength was measured according to the NFB51-123 standard. Moreover, instead of subjecting the slab to a thermal immersion test, the slabs were subjected to a temperature shock test as detailed above. That is, the samples (those from the first group) that were heat treated underwent a sudden temperature change in which the samples were immersed in liquid nitrogen (LN2) and brought to a room temperature surface three times, as detailed above. The tensile strengths were measured for five slabs and the results are shown in Table 3.

As shown in Table 3, the tensile strength of plywood boards with lignin adhesive (“LG”) increases when tested with a sharp change in temperature, while the tensile strength of plywood boards with phenol-formaldehyde adhesive (“FF”) decreases when tested with a sharp change. temperatures This clearly indicates that using LC glue to join the veneer layers together helps the board withstand sudden temperature changes.

Although not shown in the tables, tensile strength perpendicular to the plane of the slab was measured according to EN-319 for both heat-treated and unheat-treated specimens. These results also showed that the use of LC glue to connect the veneer layers to each other helps the board withstand sudden temperature changes. In addition, shear strength was determined using a tensile shear test similar to EN-314 for both specimens that were heat treated and specimens that were not heat treated. These results also showed that the use of LC glue to connect the veneer layers to each other helps the board withstand sudden temperature changes.

As stated above, plywood board 100 is particularly suitable for use in both low temperature (i.e., below minus 50°C) and cryogenic applications, such as below minus 150°C, such as for use in LNG storage facilities. Therefore, the manufacturer of the board 100 may indicate to the consumer this possibility of use. Moreover, the manufacturer may sell the board 100 together with information indicating this suitability. Such information may be indicated on the board 100 itself or separately, as explained in detail below.

With reference to FIG. 7a, in one embodiment, plywood board 100 includes an information carrier 590 carrying information indicating that plywood board 100 is suitable for use at temperatures below minus 50° C. and/or for use in cryogenic applications. For example, the surface 112, 122 of a plywood board may contain markings indicating such use. Thus, the outermost veneer layer 110, 120 can serve as information carrier 590. Alternatively, a label, such as a removable label, may be attached to the plate 100 to indicate its suitability for use at temperatures below minus 50° C., such as in an LNG storage facility.

With reference to FIG. 7b-7d, alternatively or additionally, a manufacturer of plywood board 100 may form an assembly 500 comprising plywood board 100 and further comprising an information medium 590 carrying information relating to the fact that plywood board 100 is suitable for use in low temperature and/or cryogenic applications. . For example, slab 100 may be arranged in a stack of slabs (100a, 100b, 100c, 100d, 100e, 100f) as in FIG. 7b, and the wrapper or tray of the stack of slabs may be marked to indicate that the slab 100 of the stack of slabs is suitable for such low temperature and/or cryogenic applications. Thus, for example, a wrapper or sticker may be a carrier 590 of information. Such markings may be applied directly to at least one of the plates 100.

With reference to FIG. 7c, alternatively or additionally, the storage medium 590 may be a brochure. Thus, the arrangement 500 may include a brochure indicating that the plate 100 is suitable for such use in low temperature and/or cryogenic applications. This brochure can be distributed electronically. For example, a computer readable storage device may serve as a storage medium. The database containing the information may be stored in a computer-readable storage device. For example, in FIG. 7c, storage medium 590 may be a computer readable storage device, such as a flash drive. The storage medium may carry information indicating that the plywood board 100 is suitable for use in a vessel 400 configured to transport liquefied natural gas.

With reference to FIG. 7d, the storage medium 590 may be a storage device accessible to the computer 594 via an interface 592. The storage storage device 590 may contain a database 580. The interface 592 may be a wireless interface. The information in the storage medium can be called the first information. As stated above, the first information may indicate that the plywood board is suitable for use in low temperature and/or cryogenic applications such as LNG storage.

With reference to FIG. 7e, the storage medium 590 may include first information indicating an identification (ID) of the plywood board 100 or a stack of plywood boards (100a, 100b, 100c). The database 580 may contain second information, where the second information contains, in connection with the identification, information that the plate 100 or stack of plates with a given identification is suitable for use in low temperature and/or cryogenic applications such as LNG storage. Thus, by connecting the database 580 containing the second identification information (i.e., the first information), information may be obtained indicating that the plate 100 or stack of plates is suitable for use in low temperature and/or cryogenic applications (particularly , LNG storage facility). The database may be accessible to computer 594 via interface 592. In this case, both the first and second information in combination indicate that the plywood board is suitable for use in low temperature and/or cryogenic applications such as LNG storage gas.

Thus, in one embodiment, plywood board 100 or assembly 500 containing plywood board 100 further includes (a) an information storage medium 590 carrying first information indicating the identification of the board 100 and/or (b) a database 580 containing second information , where the second information, possibly in combination with the first information, indicates that the plate with this identification is suitable for use in low temperature and/or cryogenic applications such as LNG storage gas storage. Thus, the first and/or second information, possibly in combination, may indicate that the plywood board 100 is suitable for use in a low temperature and/or cargo storage system (CSS) configured to transport liquefied natural gas (LNG).

Plywood board 100 can be manufactured using a method for making plywood board 100. The method includes arranging available a first veneer layer 110 comprising hardwood having a first wood fiber orientation D1, a second veneer layer 120 containing hardwood having a second wood fiber orientation D2, a third a veneer layer 130 containing hardwood having a third wood fiber orientation D3, and an adhesive 200.

As stated above, adhesive 200 is an aqueous binder composition and contains a resin, a hardener and water, some of which is present in the resin and some of which is make-up water. The resin contains a polymerizable substance and a cross-linking agent. At least 50 wt. % of the polymerizable substance comes from lignin, at least 10% of the molecules in the resin have a molecular weight greater than 10,000 Da, at least 10% of the molecules in the resin have a molecular weight less than 1000 Da, the number average molar mass Mn of the resin is from 1000 Da to 1600 Da, and The mass average molar mass Mw of the resin ranges from 5000 Da to 14000 Da.

As described in detail below, preferably the adhesive 200 has been manufactured such that the content of additional water in the adhesive 200 is between 10 wt. % up to 25 wt. % (relative to the total mass of the adhesive, as usual). Thus, the water content of the adhesive 200 may range from 40% to 65% (including also the water present in the resin). It has been found that an adhesive with this water content often has such a viscosity that the adhesive 200 flows well into the roughness and/or longitudinal cracks of the surfaces of the veneer layers during hot pressing. Suitable viscosity values are detailed below. In addition to affecting viscosity, the water of the adhesive affects the bonding to the wood veneer layers. In particular, the wood material of veneer layers contains hydroxyl groups (OH), which typically form bonds with adhesive molecules. Wetting the wood veneer layers with adhesive water has a positive effect on bond strength, possibly because sufficient wetness of the veneer layers reduces the surface tension between the veneer and the adhesive and thus allows the molecules at the interface to become fairly close to each other.

Preferably, the polymerizable substance contains lignin and at least one compound of phenol, cresol and resorcinol. More preferably, the polymerizable substance contains lignin and phenol. More preferably at least 90 wt. % of the polymerizable substance is lignin and phenol. Preferably, the polymerizable substance contains lignin that is derived from the kraft process (ie kraft lignin). Preferably, the polymerizable substance contains lignin, which is derived from the kraft process, and at least one compound of phenol, cresol and resorcinol. More preferably, the polymerizable substance contains kraft lignin and phenol. All material that comes from lignin can come from kraft lignin. Preferably, the crosslinking agent is an aldehyde such as formaldehyde, paraformaldehyde, or a combination thereof.

Typically, material that comes from lignin, especially lignin obtained from the kraft process, contains sulfur. Thus, the use of kraft lignin in the adhesive 200 can be determined from the sulfur content of the resin or adhesive. In this regard, the sulfur content of the resin can be determined before mixing the adhesive 200, although the sulfur content of the adhesive 200 can be measured after mixing, and the sulfur content of the cured adhesive can be measured, for example, from plywood board 100 by sanding it off. sand sample of the cured adhesive. In general, the amount of sulfur can be measured, for example, by taking a sample (from the resin or adhesive or board), burning it to ash, and analyzing the ash content. This method is usually called SEM-EDS, short for scanning electron microscopy (SEM) - energy dispersive spectroscopy (EDS). After performing SEM-EDS analysis, the ratio of elements that are as heavy as or heavier than sodium can be determined.

In one embodiment of the method, the ash obtained from the resin contains at least 1 wt. % sulfur, preferably at least 2 wt. % sulfur and more preferably at least 3 wt. % sulfur. In one embodiment of the method, the resin ash contains 1-20 wt. % sulfur, preferably 2-10 wt. % sulfur. Accordingly, when the adhesive 200 is cured, the cured adhesive may also contain sulfur. However, due to the hardener of the adhesive 200, the sulfur content of the cured adhesive may be lower. Thus, in one embodiment of the plywood board, the cured adhesive contains sulfur. In one embodiment, plywood board 100 contains a cured adhesive such that, after burning the cured adhesive to an ash, the ash of the cured adhesive contains at least 0.25 wt. % sulfur, preferably at least 1 wt. % sulfur and more preferably at least 1.5 wt. % sulfur. The sulfur content of the cured adhesive ash can be analyzed using SEM-EDS as described above. Naturally, also the entire plywood board 100 can be burned to ash and the sulfur content therein can be determined. Plywood board 100 or its cured adhesive does not need to be burned prior to SEM-EDS analysis. Thus, sulfur content can be analyzed by SEM-EDS from a sample of plywood board or from a sample of cured adhesive.

With regard to the preferred properties of the adhesive 200, we note the following. Preferably, the number average molar mass of the Mn resin is from 1100 Da to 1500 Da. Preferably, the mass average molar mass Mw is from 6000 Da to 12000 Da. Preferably, at least 15% of the molecules in the resin have a molecular weight of less than 1000 Da. Preferably, at least 15% of the molecules in the resin have a molecular weight greater than 10,000 Da. Most preferably, the adhesive has all of these features. In one embodiment, at least 18% of the molecules in the resin have a molecular weight greater than 10,000 Da.

With regard to the hardener, it is advantageous if the different veneer layers become bonded to each other to some extent also before hot pressing of the stack 300. In this regard, starch has been found to improve the bonding of the veneer layers before hot pressing. Thus, in one embodiment, the adhesive 200 contains a hardener that contains starch. Also, starch can have a heterogeneous size distribution. Therefore, the presence of starch in the adhesive 200 may improve the low temperature properties of the adhesive 200 due to the same principles as discussed above for lignin. However, although lignin is generally part of the resin of the adhesive 200, starch can be added as a hardening agent when mixing the adhesive 200.

The method includes applying an adhesive 200 to at least one surface of the third veneer layer 130. The adhesive 200 can be applied to two opposing surfaces of some of the intermediate layers 130, 140, 150 (eg, every other one), with the result that no adhesive is required to be applied to the outermost veneer layers 110, 120. Alternatively, adhesive 200 may be applied to only one side of all of the intermediate veneer layers 130, 140, 150 and only one side of only one of the outermost veneer layers 110, 120. In this way, surfaces 112, 122 (see FIG. 1) remain free of adhesive 200.

In the case where a large number of structural layers that do not contain wood are used, it may be sufficient to apply the adhesive 200 only to the surfaces of such structural layers.

The method includes arranging veneer layers 110, 120, 130 into a stack 300 such that

the third veneer layer 130 is located between the first veneer layer 110 and the second veneer layer 120 in the thickness direction tp of the plywood board 100 (that is, in the direction of the thickness of the stack 300),

adhesive 200 is located (a) between the first layer 110 and the third veneer layer 130 and (b) between the second layer 120 and the third veneer layer 130 and

the first wood fiber orientation D1 forms an angle α13 with the third wood fiber orientation D3, the angle α13 being from 60 to 120 degrees.

Such a stack 300 is shown in FIG. 5. The wood fiber orientations of the veneer layers 110, 130, 140, 150, 120 are shown using the same rule as in FIG. 3a and 4a-4h. To cure the adhesive 200 and form a solid plywood board 100, the method involves pressing the stack 300 for a period of time Δt with a pressure p and a temperature T. Such pressing is commonly referred to as hot pressing. The stack 300 may be compressed by using a first pressure surface 310 and a second pressure surface 320.

As a result of hot pressing, the adhesive 200 cures and bonds the veneer layers to each other. Curing of the adhesive also bonds the other layers to the veneer layers if such other layers are used. Thus, the veneer layers (110, 120, 130) of the final plywood board 100 were attached to each other by adhesive 200, possibly through other layers. Moreover, the plywood board 100 thus produced contains a cured adhesive between the veneer layers 110, 120, 130. However, for clarity, adhesive 200 is shown in FIG. 1 and 2. The properties of the cured adhesive are different from the properties of the adhesive 200 before curing. However, by analyzing the cured adhesive of the final (ie, manufactured) plywood board 100, it can be determined whether or not adhesive 200 was used to bond the veneer layers (110, 120, 130) to each other.

The temperature T, pressure p, and hot pressing time Δt are interrelated and may further be related to the board thickness tp and the amount of adhesive 200 used. For example, adhesive 200 cures faster at high temperature than at low temperature. Moreover, a thick layer of adhesive 200 requires a longer hot pressing time than a thin layer. The above adhesive has been found to cure to form layers of cured adhesive suitable for use in particular in cryogenic applications where the hot press temperature T is between 110°C and 190°C. More preferably, the hot pressing temperature T is from 120°C to 150°C. This temperature herein refers to the temperature of the pressure surfaces 310, 320. The air between the surfaces is not necessarily at this temperature since heat is conducted from the surfaces 310, 320 into the stack 300. However, it is also common for the environment near the stack to be heated to the above temperature within hot pressing, even if the stack 300 is located in a large factory that is at room temperature in at least most places.

At such a temperature T, a suitable length of time Δt (ie, hot pressing time) is usually from 3 minutes to 60 minutes, more preferably from 3 minutes to 15 minutes. Preferably the duration is from 5 to 10 minutes. However, as noted above, the exact duration may depend on the temperature T and the thickness tp of the plate 100 or stack 300 may influence the duration. A thick slab of 100 or a stack of 300 may require a longer period of time than a thin slab. Experience has shown that a duration of between half and two minutes per millimeter of thickness may be appropriate. The stack may be subjected to a pressure p that is at least the minimum pressure p _min and no more than the maximum pressure pmax (ie p _min ≤ p ≤ _{p max} ) for the aforementioned time.

Moreover, regarding the pressure p, the pressure may change during hot pressing. Typically, the pressure p reaches a maximum pressure p _max and is gradually reduced thereafter. Pressure p can be reduced stepwise or continuously. When the plate 100 is released from the hot pressing, the pressure p decreases to zero. However, when stack 300 and/or plate 100 are actually compressed, the pressure p may be at least the minimum pressure p _min . It has been found that the maximum pressure p _max is preferably not more than 3.5 MPa and more preferably not more than 2.0 MPa. This ensures that the veneer layers are not destroyed during hot pressing. Fracture would significantly reduce the load-bearing capacity of the plywood board 100. However, to achieve suitable indentation of the adhesive 200 into the surface of the veneer layers, the maximum ax pressure is at least 1.2 MPa, more preferably at least 1.5 MPa. Thus, the maximum pressure pmax may be from 1.2 MPa to 3.5 MPa, and more preferably from 1.5 MPa to 2.0 MPa. The pressure p refers to the force divided by the cross-sectional area of the stack 300. The cross-sectional area is the cross-sectional area having a normal in the thickness direction tp of the plywood board 100, which is unidirectional with the thickness direction of the stack 300. Thus, the cross-sectional area of the stack 300 is equal to the area cross-section of the plywood board 100. This pressure (in particular, p _max ) appears to be suitably high to force the adhesive 200 into the rough surface of the veneer layers 130, 140, 150, that is, into the wood fibers and/or longitudinal cracks of the veneer layers . Moreover, it appears that such pressure (in particular p _max ) is suitably low so as not to destroy the internal structure of the veneer layers by hot pressing. Both of these factors influence the mechanical properties of the plywood board 100. The term pressure p here refers to excess pressure, that is, a force per area above atmospheric pressure, such as a force per area where the force acts through a pressure plate having a pressure surface 310, 320 ( see Fig. 5). Regarding the minimum pressure pmin, pmin may be, for example, at least 0.1 MPa or at least 0.2 MPa.

The adhesive 200 is applied to the surface or surfaces of at least the intermediate veneer layer(s) as described above. Regarding the suitable amount of adhesive, preferably the adhesive is applied such that 100 g/ ^m2 to 200 g/ ^m2 of adhesive 200 is applied to the interface between two adjacent layers. Preferably, the adhesive is applied such that from 125 g/m ² to 170 g/m ² of the adhesive 200 is applied to the interface between two adjacent layers. Preferably, from 100 g/m ² to 200 g/m ² or from 125 g/m ² to 170 g/m ² of adhesive 200 is applied to each of the interfaces between two adjacent layers. If only veneer layers 110, 120, 130, 140, 150 and adhesive 200 are used, as detailed under board 100, 100 ^gsm to 200 ^gsm or 125 ^gsm to 170 gsm m ² of adhesive 200 is applied to each of the interfaces between two adjacent layers of veneer. This surface specific amount refers to the mass per cross-sectional area of the stack 300, that is, the largest flat surface area of the adjacent layers forming the interface. Thus, the aforementioned amount of adhesive 200 is placed between each two adjacent layers of veneer before said pressing. For example, in FIG. 5a, the aforementioned amount of adhesive is present between veneer layers 110 and 130, between veneer layers 130 and 140, between veneer layers 140 and 150, and between veneer layers 150 and 120. The adhesive is applied evenly. Thus, preferably the above-mentioned surface specific amount is applied to each part of the gap between two adjacent veneer layers. This amount has been found to be suitably high to bond the veneer layers to each other and still suitably low so as not to form a thick, brittle cured adhesive layer. In general, a thin layer can be flexible even if a thick layer of the same material was brittle. Moreover, as stated above, such an amount results in a suitably thick adhesive layer.

In the case where layers of other materials are used within the board, for example by replacing one or more intermediate veneer layers with a reinforcement layer (for example, a fiberglass layer or a carbon fiber layer), the adhesive 200 can also be applied to such spaces that are formed on both sides reinforcing layer(s). Moreover, if the reinforcement layer is used as a cover for the board 100, the reinforcement layer can be attached to the outermost veneer layer (110, 120) using an adhesive 200.

Moreover, it has been found that the above amount is particularly suitable for use in such a board in which the thicknesses of the veneer layers are from 1.0 mm to 3.0 mm, for example, from 1.0 mm to 2.0 mm, and the veneer layers contain hard wood. Typically, when a stack of 300 veneer layers 110, 120, 130 is formed, each veneer layer has the same thickness. Moreover, this thickness corresponds to the thickness tbv of FIG. 2. In other words, usually the veneer layers are not compressed in a hot press so that they become thinner. However, after hot pressing, the surface veneer layers PO, 120 can be sanded, whereby the thicknesses tsv1 and tsv2 of the board 100 can be less than the thickness of the surface veneer before said sanding. These thicknesses were also discussed in connection with plywood board 100, the surfaces 112, 122 of which could be sanded. Sand sanding is also beneficial in terms of manipulating the tp thickness of the slab 100. Sand sanding can be used to fine tune the tp thickness. However, preferably the outermost veneer layers 110, 120 (ie, the surface veneer layers if the board is not covered) are of a reasonable thickness, as detailed above. Therefore, in one embodiment, the board 100 is sanded such that only less than half of the wood material of the outermost veneer layers 110, 120 is sanded. Thus, more than half of the material remains in the slab. In the case where all veneer layers are of equal thickness before sanding, the thickness tsv1, tsv2 of the surface veneer layers 110, 120 is more than half of the thickness tbv of the intermediate veneer layer 130.

Moreover, the extent to which the adhesive 200 adheres to the veneer layers 110, 120, 130 may depend on the moisture content of the veneer layers 110, 120, 130 immediately before applying the adhesive 200 or during the application of the adhesive 200. It has been found that suitable The moisture content of layers 110, 120, 130 of veneer should be from 2% to 15%. preferably from 3% to 12%, where moisture content is calculated as a mass fraction of the dry weight of the veneer layers. It has been found that the adhesive 200 is otherwise unlikely to penetrate sufficiently into the veneer layers 110, 120, 130. Thus, one embodiment of the method includes drying the veneer layers 110, 120, 130. A preferred embodiment of the method involves drying the veneer layers 110, 120, 130 to a moisture content of 2% to 15%, preferably to a moisture content of 3% to 12%. In this document, moisture content refers to the moisture content relative to dry matter only.

Further, the extent to which the adhesive 200 adheres to the veneer layers 120, 130 may depend on the viscosity of the adhesive 200 and the water content of the adhesive 200. The viscosity of the adhesive 200 is highly dependent on the water content of the adhesive 200. As stated above, the adhesive substance 200 contains a hardener, additional water and resin. It has been found that the proper viscosity of the adhesive 200 is achieved when the additional water content of the adhesive 200 is between 13 wt. % up to 23 wt. % (relative to the total weight of the adhesive, as usual) and/or the water content of the adhesive 200 is from 40% to 65%. It has been found that the viscosity of the adhesive 200 with this water content is suitable for applying the adhesive 200 to the veneer layers and for the adhesive 200 to flow into the rough surfaces of the veneer layers during hot pressing. The viscosity of the applied adhesive 200 can range from 15 seconds to 60 seconds at a temperature of 23°C, measured using the Ford funnel test. Preferably, the viscosity of the applied adhesive 200 is from 25 seconds to 45 seconds at a temperature of 23°C, measured using the Ford funnel test. The Ford funnel test is described in ISO 2431 (1993-02-15). The above values refer to the funnel outlet size of 6 mm. In particular, the above values refer to a funnel outlet size of 6 mm in a test in which the temperature is 23°C. Moreover, preferably, when applying the adhesive 200 to at least one surface of the third veneer layer 130 or other layer, the viscosity of the adhesive 200 is from 15 seconds to 60 seconds, for example, from 25 to 45 seconds, measured using a Ford funnel test with using a funnel with a 6 mm outlet as described in ISO 2431 (1993-02-15). When the adhesive 200 cures, the dry matter of the adhesive 200 crosslinks and forms water. This water and the water of the adhesive 200 evaporate from the board 100 or stack 300 during hot pressing. Therefore, board 100 contains less cured adhesive than stack 300 contains adhesive 200.

Using this method, a plywood board 100 is produced. Thus, one embodiment relates to a plywood board 100 that has been manufactured using the above method.

As stated above, the board manufacturer may indicate to the consumer the suitability of plywood board 100 for use in low temperature and/or cryogenic applications, for example suitability for use at temperatures less than minus 50°C, for example suitability for use as a support for container 410 containing liquefied natural gas (LNG) or liquefied petroleum gas (LPG). The container 410 may be part of a cargo storage system (CSS), for example, it may be located on a vessel 400. Therefore, one embodiment of a method for making plywood board 100 includes an indication that the plywood board 100 is suitable for use at temperatures less than minus 50° C. and/ or in cryogenic applications. For example, one embodiment includes an indication that the plywood board 100 is suitable for use at temperatures less than minus 50°C. For example, one embodiment includes an indication that the plywood board 100 is suitable for use with cargo storage systems, for example, on a vessel 400 configured to transport liquefied natural gas. Suitability can be indicated in a variety of ways, as shown in FIG. 7a-7e and discussed above.

In the manufacture of plywood board 100, it has been discovered that the use of raw materials can be improved (i.e., manufactured more efficiently) by careful design in which veneer layers are used for the intermediate veneer layers 130, 140, 150 and in which they are used as the outermost layers 110, 120 veneer. In general, although the intermediate layer 130 can be composed of multiple veneer layers 131, 132, 133 (see FIGS. 3a-3d), the outermost veneer layers 120 typically contain only one veneer layer. However, for example, knots can be covered with wooden pieces.

In particular, it has been discovered that high quality veneer layers can be used as the outermost veneer layers 110, 120, that is, the veneer forming the main surface 112, 122 of plywood board 100. Accordingly, it has been found that lower quality veneer layers can be use in intermediate layers of veneer.

The term quality refers to many characteristics of the veneer layers 100, 120, 130 veneers. Applicable quality factors can be found, for example, in ISO 2426-1 (2000-12-01), ISO 2426-2 (2000-12-01) and ISO 2426-3 (2000-12-01). ISO 2426-2 is applicable for hardwood veneers, while ISO 2426-3 is applicable for softwood veneers. Since the plywood board 100 of the present invention contains at least three veneer layers 110, 120, 130 containing hardwood, at least the ISO 2426-2 standard is applicable.

One embodiment of the method includes determining that the quality of the third veneer layer 130 is lower than the quality of the first veneer layer and determining that the quality of the third layer 130 is lower than the quality of the second veneer layer 120. As stated above, the method includes positioning a third veneer layer 130 between the first veneer layer 110 and the second veneer layer 120. The quality of individual layers (110, 120, 130) is directly observed during the manufacture of plywood boards. Moreover, the quality of the intermediate veneer layer 130 can be determined from the plywood board 100, for example, by sanding the outermost veneer layers.

As stated above, such plywood board is particularly suitable for use as a structural material in low temperature and/or cryogenic applications. Therefore, embodiments of the invention relate to the use of plywood board 100 at a temperature of less than minus 50°C. Examples of such use include use in which the plywood board 100 is used to support a container 410 containing a liquefied gas, such as liquefied natural gas (LNG) or liquefied petroleum gas (LPG). With reference to FIG. 6, such a container 410 may be located on a vessel 400. Such a container 410 may also be located in another cargo storage system (CSS), such as an LNG storage system.

In particular, the plywood board 100 is suitable for use as a structural material in an LNG tanker. Therefore, one application of the invention is a ship 400 (see FIG. 6). Such vessel 400 includes the plywood board 100 described above. Such vessel 400 may also include other plywood boards 100a, 100b, 100c, 100d, 100e, 100f, 100g suitable for use in LNG storage facilities. In addition, the vessel 400 includes a container 410 configured for storing liquefied natural gas (LNG). On the vessel 400, the plywood board 100 supports the container 410. Typically, the container 410 is made of a thin steel plate (0.5 mm to 1.0 mm thick) and the shape of the container 410 matches the shape of a support leg made of plywood boards (100, 100a-100g ). In addition, a support support surrounds the container 410 in order to thermally isolate the container 410 from the environment.

Links

[1] Jeong-Hyeon Kim, Doo-Hwan Park, Chi-Seung Lee, Kwang-Jun Park, Jae-Myung Lee: "Effects of cryogenic thermal cycle and immersion on the mechanical characteristics of phenolic-resin bonded plywood", Cryogenics 72 (2015) 90-102

[2] Jeong-Hyeon Kima, Sung-Woong Choib, Doo-Hwan Parka, Seong-Bo Parke, Seul-Kee Kima, Kwang-Jun Parkd, Jae-Myung Leea: “Effects of cryogenic temperature on the mechanical and failure characteristics of melamine-urea-formaldehyde adhesive plywood", Cryogenics 91 (2018) 36-46

Claims (130)

1. Plywood board (100) for use at temperatures less than minus 50°C, having a length (lp), a width (wp) and a thickness (tp), where the thickness (tp) is less than the lesser of the length (lp) and width (wp) , containing: a first veneer layer (110) containing hardwood having a first orientation (D1) of wood fibers, a second veneer layer (120) comprising hardwood having a second orientation (D2) of wood fibers, and a third layer (130) of veneer containing hardwood having a third orientation (D3) of wood fibers, where the third veneer layer (130) is located between the first veneer layer (110) and the second veneer layer (120) in the thickness direction (tp) of the plywood board (100), the first orientation (D1) of wood fibers forms an angle (α13) with the third orientation (D3) of wood fibers, the angle (α13) being from 60 to 120 degrees, and layers (110, 120, 130) of veneer are attached to each other by an adhesive (200) containing a resin, which contains a polymerizable substance and a cross-linking agent, where at least 50 wt.% of the polymerizable substance comes from lignin, at least 10% of the molecules in the resin have a molecular weight of more than 10,000 Da, at least 10% of the molecules in the resin have a molecular weight of less than 1000 Da , the number-average molar mass of the resin is from 1000 to 1600 Da, and the mass-average molar mass of the resin is from 5000 to 14000 Da. 2. The plywood board according to claim 1, containing a cured adhesive in the space between two adjacent layers, where the cured adhesive contains sulfur. 3. Plywood board according to claim 1 or 2, in which the thickness (ta) of the adhesive layer between two adjacent layers is less than 0.25 mm, for example from 0.01 to 0.25 mm, preferably the thickness (ta) of the adhesive layer between two adjacent veneer layers is less than 0.25 mm, for example from 0.01 to 0.25 mm, and/or the thickness (ta) of each adhesive layer between two adjacent layers and between the first veneer layer (110) and the second veneer layer (120) is less than 0.25 mm, for example from 0.01 to 0.25 mm. 4. Plywood board according to any one of paragraphs. 1-3, comprising an additional veneer layer (140) or additional veneer layers (140, 150, 160) located between the first veneer layer (110) and the second veneer layer (120), where additional layer(s) of veneer contains(contain) wood, a first number (N1) of layers (110, 120, 130, 140, 150, 160) of veneer plywood board (100) are oriented in a first orientation (D1) of wood fibers, a second number (N2) of veneer layers (110, 120, 130, 140, 150, 160) of plywood board (100) are oriented in a wood fiber orientation that is perpendicular to the first wood fiber orientation (D1), and the sum of the first number (N1) and the second number (N2) is equal to the number (N) of layers (110, 120, 130, 140, 150, 160) of plywood board veneer (100) and the difference (N1-N2) between the first number (N1) and the second number (N2) is no more than two and is at least zero, preferably all layers (110, 120, 130, 140, 150, 160) of veneer that contain wood contain hardwood such as one of ash, aspen, basswood, birch, cherry, pecan, mahogany, maple, oak, poplar, dipterocarpa, teak, rosewood, ocumea and shorea, preferably birch or beech, For example: (A) the number (N) of layers (110, 120, 130, 140, 150, 160) of veneer of plywood board (100) is expressed as 2M+1, where M is an integer, and the first number (N1) exceeds the second number (N2) by one (N1=N2+1) or (IN) the number (N) of layers (110, 120, 130, 140, 150, 160) of veneer of plywood board (100) is expressed as 2M, where M is an integer, and the first number (N1) is equal to the second number (N2) (N1=N2) or the first number (N1) exceeds the second number (N2) by two (N1=N2+2). 5. Plywood board according to claim 4, in which The veneer layer(s) (130, 140, 150, 160) of the plywood board (100) that are located between the first veneer layer (110) and the second veneer layer (120) are intermediate veneer layers, thus each intermediate veneer layer has a first adjacent veneer layer and a second adjacent veneer layer, where the third number (N3) of the intermediate veneer layers are such intermediate veneer layers that the direction of the wood grains of the subject inter-veneer layer is perpendicular to the direction of the wood fibers of the first adjacent veneer layer of the subject inter-veneer layer; and the direction of the wood grains of the subject inter-veneer layer is perpendicular to the direction of the wood fibers of the second adjacent veneer layer of the subject inter-veneer layer, and the third number (N3) is less than the number (N) of veneer layers by two or four (N3=N-2 or N3=N-4), preferably: (A) the number (N) of layers (110, 120, 130, 140, 150, 160) of veneer of plywood board (100) is expressed as 2M+1, where M is an integer, and the third number (N3) is less than the number (N) of veneer layers by two (N3=N-2) or (IN) the number (N) of layers (110, 120, 130, 140, 150, 160) of veneer of plywood board (100) is expressed as 2M, where M is an integer, and the third number (N3) is four less than the number (N) of veneer layers (N3=N-4). 6. Plywood board (100) according to any one of paragraphs. 1-5, in which intermediate veneer layers (130, 140, 150) containing wood are located between the first veneer layer (110) and the second veneer layer (120), the thickness (tbv) of each of the intermediate layers (130, 140, 150) of veneer is from 1.0 to 3.0 mm and thickness (tp) of plywood board (100) ranges from 4 to 95 mm, preferably each intermediate layer (130, 140, 150) of veneer contains hardwood. 7. Plywood board (100) according to any one of claims. 1-6, in which the thickness (tsv1) of the first veneer layer (110) is more than half of the thickness (tbv) of the third veneer layer (130) and the thickness (tsv2) of the second veneer layer (120) is more than half of the thickness (tbv) of the third veneer layer (130). 8. A method for manufacturing a plywood board (100) suitable for use at temperatures less than minus 50°C, comprising: the following layout: a first veneer layer (110) containing hardwood having a first orientation (D1) of wood fibers, a second veneer layer (120) comprising hardwood having a second orientation (D2) of wood fibers, and a third veneer layer (130) comprising hardwood having a third orientation (D3) of wood fibers, and adhesive (200), which contains a resin containing a polymerizable substance and a cross-linking agent, where at least 50 wt.% of the polymerizable substance comes from lignin, at least 10% of the molecules in the resin have a molecular weight of more than 10,000 Da, at least 10% of the molecules in the resin have a molecular weight mass less than 1000 Da, the number average molar mass of the resin is from 1000 to 1600 Da and the mass average molar mass of the resin is from 5000 to 14000 Da, the method includes arrangement of layers (110, 120, 130) of veneer and adhesive (200) in a stack (300), so that the third veneer layer (130) is placed between the first veneer layer (110) and the second veneer layer (120) in the thickness direction (tp) of the plywood board (100), the adhesive (200) is placed as between the first layer (110) and the third layer of veneer (130), and between the second layer (120) and the third layer of veneer (130), and the first orientation (D1) of wood fibers forms an angle (α13) with the third orientation (D3) of wood fibers, the angle (α13) being from 60 to 120 degrees, and hot pressing of stack (300). 9. Method according to claim 8, in which the adhesive (200) is applied in such a way that from 100 to 200 g/m ² of the adhesive (200) is placed between two adjacent layers before said hot pressing, preferably from 100 to 200 g/m ² of adhesive (200) is placed between two adjacent layers of veneer before said hot pressing and/or 100 to 200 g/m ² of adhesive (200) is placed between each two adjacent layers before said hot pressing. 10. The method according to claim 8 or 9, in which the dry matter content of the adhesive (200) is from 35 to 60 wt.% and/or the viscosity of the adhesive (200) is 15 to 60 seconds at 23°C, measured by the Ford funnel test using a funnel with a 6 mm outlet as described in ISO 2431 (1993-02-15), preferably when applying the adhesive (200), the dry matter content of the applied adhesive (200) is from 35 to 60 wt.% and the viscosity of the applied adhesive (200) is from 15 to 60 seconds, measured by the Ford funnel test using a funnel with 6mm outlet as described in ISO 2431 (1993-02-15). 11. Method according to any one of paragraphs. 8-10, comprising, after hot pressing the stack (300), sanding the first veneer layer (110), so that less than half of the material of the first veneer layer (110) is removed by sanding, preferably the method also includes sanding the second veneer layer (120) such that less than half of the material in the second veneer layer (120) is removed by sanding. 12. Method according to any one of paragraphs. 8-11, including markings indicating that the plywood board (100) is suitable for applications at temperatures less than minus 50°C, such as cryogenic applications, For example marking indicating that the plywood board (100) is suitable for use in a liquefied gas (LPG, LNG) cargo storage system (CSS), such as a storage facility designed to hold liquefied petroleum gas (LPG) or liquefied natural gas (LNG), for example , on a vessel (400) designed to transport liquefied petroleum gas (LPG) or liquefied natural gas (LNG). 13. Method according to any one of paragraphs. 8-11, including markings indicating that the plywood board (100) is suitable for use at temperatures less than minus 150°C, for example, in a liquefied natural gas (LNG) cargo storage system (SCS). 14. Method according to any one of paragraphs. 8-13, where the first layer (110) of veneer has the first quality determined according to the ISO 2426-2 standard, the second layer (120) of veneer is of the second quality determined according to the ISO 2426-2 standard, and the third layer (130) of veneer has a third quality, determined according to the ISO 2426-2 standard, while the first quality is higher than the third quality, also preferable the second quality is higher than the third quality. 15. Plywood board (100), which is manufactured by the method according to any one of claims. 8-13, wherein the plywood board (100) is suitable for use at temperatures less than minus 50°C, preferably at temperatures less than minus 150°C. 16. Plywood board (100) according to any one of paragraphs. 1-7 or 15, where the first layer (110) of veneer has the first quality determined according to the ISO 2426-2 standard, the second layer (120) of veneer is of the second quality determined according to the ISO 2426-2 standard, and the third layer (130) of veneer has a third quality, determined according to the ISO 2426-2 standard, while the first quality is higher than the third quality, also preferably the second quality over the third quality. 17. Plywood board (100) according to any one of paragraphs. 1-7, or 15, or 16, in which the plywood board (100) contains only layers of cured adhesive and intermediate veneer layers between the first veneer layer (110) and the second veneer layer (120), wherein the layers of cured adhesive are made by gluing layers of plywood board (100) to each other with an adhesive (200), preferably plywood board (100) consists of layers of cured adhesive and layers of veneer. 18. Plywood board (100) according to any one of paragraphs. 1-7 or 15-17, in which, when the first group of prototypes and the second group of prototypes are cut from the plywood board (100), the first flexural strength and the first lateral flexural strength were determined from the first group of test specimens according to EN 310 (1993) after the first group of test specimens had been heat treated by immersion in liquefied gas, and the second limit of longitudinal bending strength and the second limit of transverse bending strength were determined from the second group of test samples in accordance with the EN 310 (1993) standard without heat treatment of the samples of the second group of test samples, the first buckling strength is at least 97% of the second buckling strength and the first lateral bending strength is at least 97% of the second lateral bending strength, liquefied gas immersion treatment involves immersing samples of the first group of prototypes in liquefied natural gas (LNG) at a pressure of 100 kPa (1 atm) for 15 days. 19. Plywood board (100) according to any one of paragraphs. 1-7 or 15-18, wherein the plywood board (100) contains at least one of an information carrier (590) carrying the first information, and database (580) containing second information, where the first information and/or the second information indicates that the plywood board (100) is suitable for use at temperatures less than minus 50°C, for example in cryogenic applications, incarnate the first and/or second information indicates that the plywood board (100) is suitable for use in a cargo storage system (CSS) designed to contain liquefied gas (LPG, LNG), such as a system containing a container (410) configured to liquefied petroleum gas (LPG) or liquefied natural gas (LNG) content. 20. Plywood board (100) according to any one of paragraphs. 1-7 or 15-18, wherein the plywood board (100) contains at least one of an information carrier (590) carrying the first information, and database (580) containing second information, where the first information and/or the second information indicates that the plywood board (100) is suitable for use at temperatures less than minus 150°C, for example for use in a cargo storage system (CSS) configured to contain liquefied natural gas (LNG). 21. An arrangement (500) comprising a plywood board (100) according to any one of claims. 1-7 or 15-18, wherein the arrangement (500) contains at least one of an information carrier (590) carrying the first information, and database (580) containing second information, where the first information and/or the second information indicates that the plywood board (100) is suitable for use at temperatures less than minus 50°C, for example in cryogenic applications, incarnate the first and/or second information indicates that the plywood board (100) is suitable for use in a cargo storage system (CSS) designed to contain liquefied gas (LPG, LNG), such as a system containing a container (410) configured to liquefied petroleum gas (LPG) or liquefied natural gas (LNG) content. 22. An arrangement (500) comprising a plywood board (100) according to any one of claims. 1-7 or 15-18, wherein the arrangement (500) contains at least one of an information carrier (590) carrying the first information, and database (580) containing second information, where the first information and/or the second information indicates that the plywood board (100) is suitable for use at temperatures less than minus 150°C, for example for use in a cargo storage system (CSS) configured to contain liquefied natural gas (LNG). 23. Use of plywood board (100) according to any one of paragraphs. 1-7 or 15-20 at a temperature less than minus 50°C, such as an application in which a plywood board (100) is used to support a container (410) containing liquefied petroleum gas (LPG) or liquefied natural gas (LNG). 24. Use of plywood board (100) according to any one of paragraphs. 1-7 or 15-20 at a temperature less than minus 150°C, such as an application in which a plywood board (100) is used to support a container (410) containing liquefied natural gas (LNG). 25. A cargo storage system (CSS), such as a vessel (400), containing plywood board (100) according to any one of paragraphs. 1-7 or 15-20 and container (410) designed to contain liquefied gas (LPG, LNG), where a plywood board (100) supports the container (410).