JPH04101802A - Overlay plywood - Google Patents

Abstract

PURPOSE:To obtain the above overlay layer excellent in transparency by a method wherein the overlay layer to be provided on wooden board is made of specified powdered phenolic resin intercalative paper. CONSTITUTION:Powdered phenolic resin composing powdered phenolic resin intercallative paper is hot-melt-setting resin, which is produced by simultaneously carrying out the addition reaction and condensation reaction of phenolics and formaldehyde in the presence of excessive hydrochloric acid catalyst, and has methylol group in molecule, a weight average molecular weight of 3,500 or more and a gelling time of 3min or longer. The intercalative paper contains 50-90vol.% of powdered phenolic resin. Further, fibrous base material is made of pulp. The intercalative paper contains at least 10vol.% of wooden pulp, which is beaten to the extent so as to obtain the freeness of 500-50ml. Furthermore, the intercalative paper contains 0-20vol.% of synthetic resin and 10-30vol.% of powdered inorganic substance. The overlay layer concerned is produced by heating the intercalative paper put on wooden board under pressure so as to melt and harden the powdered phenolic resin and melt and bond the resin to the surface of the wooden board.

Description

DETAILED DESCRIPTION OF THE INVENTION [Background of the Invention] <Industrial Application Field> The present invention relates to an overlay plywood on which an overlay layer with excellent transparency is formed. More specifically, the present invention relates to an overlay plywood in which an overlay layer with excellent transparency is formed by pressurizing and heating a powdered phenolic resin-added paper made by adding an uncured powdered phenolic resin onto the plywood.

This overlay plywood can be used for various purposes such as box materials, building materials, furniture, etc., which require aesthetic appearance.

<Prior art> Plywood is useful as a material that takes advantage of its woody texture or as a base material on which decorative paper is to be applied. The surface was often coated with varnish for protection. However, since the plywood surface has a wide variety of small deformations, it is only possible to form a varnish coating film on an uneven surface, and even with varnishing, the plywood's cosmetic properties are insufficient. there were. Furthermore, since no reinforcing base material is added to the varnish coating film, there is a problem that the abrasion resistance is insufficient, and an improvement has been desired.

By the way, thermosetting resin-impregnated paper (Japanese Unexamined Patent Publication No. 5
A method has been proposed in which an overlay layer is formed on the surface of the plywood by pressurizing and heating the plywood. According to this method, the beauty and abrasion resistance of the plywood surface can be improved due to the transparency and strength of the phenolic resin in the overlay layer, and it is considered to be useful as an alternative to varnish coating methods. .

However, a method using phenol resin-impregnated paper (Japanese Patent Laid-Open No. 5
0-157464), phenolic resin-impregnated paper, which is paper impregnated with a thermosetting resin, such as semi-hardened phenol resin, is bonded to the surface of plywood with an adhesive, and the phenolic resin is cured in a short time by pressure heating. However, to the best of the inventors' knowledge, phenolic resin-impregnated paper must be stored refrigerated to prevent premature curing, and uncured phenolic resin must be dissolved. The problem with the manufacturing process is that a large amount of solvent vapor evaporates from the large amount of organic solvent used for impregnation, such as alcohol, which deteriorates the working environment, and the cost of recovering the organic solvent increases manufacturing costs. It also had some problems. Moreover, this method requires the additional and difficult work of applying the adhesive evenly to the uneven plywood surface when the phenolic resin-impregnated paper is placed on the plywood surface and heated under pressure. It also had points.

In addition, conventional phenolic resin inner-coated paper <c1 Kosho 63-2
The method of forming an overlay layer on the plywood surface by pressurizing and heating (Japanese Patent No. 8475) uses a low molecular weight resol resin, which lowers the drying temperature of papermaking wet sheets (120°C) that is encountered during the production of internally coated paper. This seems to have prevented premature or excessive curing, but the transparency of the overlay layer was insufficient.

The present inventor has discovered that the transparency of the overlay layer is greatly affected by the fluidity of the phenolic resin and the amount of internal addition of the phenolic resin. It became clear that the transparency of the overlay layer was insufficient.

Moreover, since the low molecular weight resol resin contains a large amount of free monomers such as phenol and formalin, during continuous paper making, free monomers are discharged from white water and rivers. There was a problem that there was a possibility of contamination.

In addition, when adding novolac type phenolic resin powder internally, it is necessary to add a hardening agent such as paraformaldehyde or hexamethylenetetramine internally in advance, but a hardening agent suitable for use (for example, hexamethylenetetramine) must be added internally. Since it is water-soluble, there is a problem in that it is impossible to add it internally. Even if it were possible to internally add a water-soluble curing agent by adsorbing it to a special substance and fixing that substance to the pulp, ammonia is removed from the curing agent when pressurizing and heating the phenolic resin. There was a problem in that gases such as the following were generated and a portion of the gases remained in the cured phenol resin, impairing the transparency of the overlay layer.

[Summary of the invention]

<Problems to be Solved by the Invention> The present invention solves the above problems and provides an overlay plywood in which an overlay layer having excellent transparency is formed by pressurizing and heating powdered phenolic resin internally added paper. The purpose is to

<Means for Solving the Problems> The overlay plywood according to the present invention is an overlay plywood in which an overlay layer is provided on a wooden board, in which this overlay layer presses paper added with a powdered phenolic resin defined as below. It is characterized by being formed on a wooden board by heating.

(a) Powdered phenol resin is a hot-melt curing resin obtained by simultaneously carrying out an addition reaction and a condensation reaction of phenols and formaldehyde in the presence of an excess hydrochloric acid catalyst, and has a methylol group in the molecule. and has a weight average molecular weight of 3,500 or more, and a gelation time of 3 minutes or more.

(b) The fiber base material constituting the powdered phenolic resin-loaded paper is substantially made of pulp, and the freeness is 500 ml to 5.
At least 10 ml of wood pulp beaten to 0 ml
% by volume (based on the total amount of all paper stock).

(c) Powdered phenolic resin content in the powdered phenolic resin-added paper is 50 to 90% by volume (based on the total amount of all paper stocks)
To be.

<Effects of the Invention> According to the present invention, an overlay plywood having an overlay layer having excellent transparency and planar smoothness can be obtained.

[Detailed description of the invention]

Main Requirements of the Invention The present invention consists of several quantitative conditions, where the unit "volume %" is a percentage based on the volume of a given component excluding air. It is calculated by the volume calculated by weight/true specific gravity.

Now, the overlay plywood according to the present invention is produced by pressurizing and heating a powdered phenolic resin-added paper containing a heat-melting hardening type powdered phenolic resin at a volume ratio of 50,150 to 10/90 to the fiber base material made of pulp. An overlay layer is formed on a wooden board.

That is, in the present invention, in the presence of a large amount of acid catalyst,
It is a hot-melt curing resin obtained by simultaneously carrying out an addition reaction and a condensation reaction of phenols and formaldehyde, and has a considerable number of methylol groups in the molecule, a weight average molecular weight of 3500 or more, and a degree of polymerization. is high, but the gelation time is 3
It has been discovered that an overlay layer with excellent transparency can be formed by internally adding a large amount of powdered phenolic resin, which is more than 100%.

In addition, this powdered phenolic resin has a high degree of polymerization, so
Since the amount of free monomers (phenol, formalin) remaining in the resin is extremely small (less than 500 ppm), there is no need to consider the volatilization of monomers from the dryer during paper-making with internal addition, making the work easier. The environment can be improved, and since the discharge of monomers from white water is eliminated, environmental pollution can also be prevented.

When paper is made by adding 50% or more of normal phenolic resin internally, most of the increased amount of phenolic resin will be liberated from the pulp sheet during the papermaking process, and the liberated phenolic resin will be absorbed by the paper machine. This causes various problems, such as clogging the wires of paper making it impossible to perform stable dewatering, staining papermaking blankets, and making stable dewatering from papermaking wet webs difficult. especially,
When paper is made using both inorganic fibers and organic fibers, the phenolic resin is difficult to fix on the inorganic fibers or organic fibers, and the amount of phenolic resin liberated from the pulp sheet increases accordingly, increasing the adverse effects. This will give rise to the problem.

Moreover, in the present invention, the fiber base material has a freeness of 50
10% by volume of fibrillated wood pulp beaten to 0ml to 50ml (representing the Canadian standard freeness (defeatness) specified in JIS-P-8121) (the total amount of all stock is 100% by volume) ), it was possible to fix an amount of 50 to 90 volume % (total paper stock is 100 volume %) of powdered phenolic resin, and succeeded in obtaining an overlay layer with excellent transparency. It is.

It should be noted that the total paper stock means all of the components constituting the inner paper. Therefore, if the internal paper is made of powdered phenolic resin and pulp, it means all of these components and trace components (for example, fixing agent) added during paper making, but the entire paper stock is Most of the volume and weight will be occupied by the powdered phenolic resin and pulp.

In addition, when synthetic fibers and fillers are added, these are added.

Particularly in paper making, if a nonionic flocculant is added to a slurry in which powdered phenolic resin and pulp are dispersed, and then a cationic flocculant is added to form a slurry,
It has now become possible to stably perform continuous paper making of internally coated paper that can form a transparent overlay layer without releasing the resin from the pulp sheet.

Powdered phenolic resin> The powdered phenolic resin of the present invention is obtained by simultaneously carrying out an addition reaction and a condensation reaction of phenols and formaldehyde at a molar ratio of phenols/formaldehyde of 1 in the presence of an excess hydrochloric acid catalyst. The resulting hot-melt curing resin has a considerable number of methylol groups in the molecule, has a weight average molecular weight of 3,500 or more, and has a gelation time of 3 minutes or more.

In other words, powdered phenolic resin is obtained by simultaneously carrying out an addition reaction and a condensation reaction under specific conditions, so it has a different structure from ordinary novolac type and resol type phenolic resins, and This resin has unique physical properties that other phenolic resins do not have. This resin is typically obtained by reacting phenol with formaldehyde, but a mixture of phenol and a phenol derivative may be reacted with formaldehyde.

Examples of the phenol derivatives to be mixed include 0-m- or p-cresol, bisphenol A10-lm- or p-C2-C4 alkylphenol, p-phenylphenol, xylenol, resorcinol, and the like.

Powdered phenol resin itself, which is obtained by simultaneous addition reaction and condensation reaction from phenols and formaldehyde, is known (Japanese Patent Application Laid-Open Nos. 177011-1987, 114-1982, 1983-1983). 111
No. 822, ), it is known that powdered phenolic resins having a variety of different physical properties can be obtained. However, it has been discovered in the present invention that the obtained inner layer paper also has moldability, and the molded overlay layer also has excellent transparency.

"Weight average molecular weight" is measured by gel permeation chromatography after dissolving in methanol.

The particle size is from 1 to 150 μml, preferably from 1 to 150 μml.

The gelation time is 3 minutes or more, preferably 5 minutes or more.

<Fibre Base Material Substantially Made of Pulp> The powdered phenolic resin internalized paper according to the present invention is obtained by paper-making a slurry in which a powdered phenol resin and a fiber base material substantially made of pulp are dispersed in water. Here, "a fiber base material consisting essentially of pulp" means that synthetic fibers (inorganic fibers, organic fibers) may be included in addition to the pulp. That is, by adding synthetic fibers to the overlay layer according to the present invention, abrasion resistance, dimensional stability, and heat resistance are increased without impairing excellent transparency.

The pulp used in the present invention is typically wood pulp, but it may be made from plants other than wood, and both may be used in combination. Wood pulp is pulped (
There are various types classified according to the process (mechanical treatment, chemical treatment, and combination of both), and these may be used alone or in combination. Also, if the freeness is 50ml or more, 5
QOml or less, preferably 200-480ml. The total stock contains at least 10% by volume (based on the total amount of the total stock) of fibrillated wood pulp that has been beaten to a pulp. The volume of this fibrillated wood pulp is preferably 1/3 or more of the volume of the powdered phenolic resin.

As for pulp, LBKP and LUKP.

NUKPSNBKP, GP, RGP, CGP are preferred.

Synthetic fibers and fillers> Synthetic fibers that can be added to pulp include:
The present invention includes semi-synthetic fibers (for example, cellulose acetate fibers), and also includes inorganic fibers in addition to these normally organic fibers. Both can also be used together. Synthetic fibers are 20
Volume % or less (assuming the total HfA of all paper stocks is 100 volume %)
, preferably in an amount of 15% by volume or less. With this amount, the fixation of the powdered phenolic resin to the knob will not be impaired, and the transparency of the overlay layer will not be impaired. Furthermore, the abrasion resistance and dimensional stability of the overlay layer can be improved, and heat resistance and the like can be increased. In addition, from the viewpoint of mixing with pulp fibers, it is preferable to use synthetic fibers having an aspect ratio (fiber length/fiber diameter) of 1000 or less.

Specific examples of organic fibers include the following.

Polyester fiber, acrylic fiber, aramid fiber, phenolic fiber, rayon fiber, vinylon fiber, etc. These organic fibers contribute to increasing the dimensional stability of the overlay layer.

Specific examples of inorganic fibers include the following.

Glass fiber, alumina silica fiber, alumina fiber, carbon fiber, etc. These contribute to improving the abrasion resistance, heat resistance and dimensional stability of the overlay layer.

The powdered phenolic resin-loaded paper according to the present invention may also be a paper containing a filler. Fillers are commonly used in the paper manufacturing industry and generally consist of powdered inorganic substances, but in the present invention, a suitable filler can be selected from these to provide a unique or specific effect.

For example, silica powder can be used to give the overlay layer wear resistance, aluminum hydroxide powder can be used to give flame retardancy, indium oxide powder or tin oxide powder can be used to give electrical conductivity, or This can be done by adding titanium oxide powder that imparts electrical conductivity.

It is desirable to add such a filler within a range that does not impair the surface smoothness of the overlay layer, and generally the amount is 10 to 10.
30% by volume (based on the total amount of all stock), preferably 15-
20% by volume is appropriate. Note that the beauty of plywood with its transparency and surface smoothness is maximized when no filler is used.

Internally coated paper> The powdered phenolic resin internally coated paper according to the present invention is usually manufactured as follows. That is, 50 to 90% by volume of powdered phenol wood (based on the total amount of all paper stock)
, prepare a slurry consisting of at least 10% by volume (based on the total amount of all stock) of fibrillated wood pulp beaten to a freeness of 500 ml or less, a fiber base material, and water to fix the powdered phenolic resin to the pulp fibers. let The concentration of the slurry is 0.1 to 1% by weight, preferably 0.05 to 0.
1% by weight. Thereafter, the slurry is made into paper using a paper machine in a paper making process to obtain a dry paper coated with powdered phenolic resin. Typical paper machines include cylinder mesh paper machines, Fourdrinier paper machines, and inclined wire mesh paper machines. Note that fixing of the powdered phenol resin is effectively carried out by adding a nonionic flocculant or a cationic flocculant to the slurry. For the flocculant, first add a nonionic flocculant to a slurry in which powdered phenolic resin and pulp are dispersed, and then add a cationic flocculant to the slurry (preferably just before the papermaking process) to fix the powdered phenolic resin. let The amount of nonionic flocculant added is 0.05 to 0.5% by weight (based on the total amount of all paper stocks), preferably 0.1 to 0.5% by weight.
3% by weight, and the amount of cationic flocculant added was 0.
05 to 0.5% by weight (based on the total amount of all stock), preferably 0.1 to 0.3% by weight. Specific examples of nonionic flocculants include the following.

Polyethylene oxide, polyacrylamide, etc.

Specific examples of cationic flocculants include the following.

Polyethyleneimine, polyamide polyamine, cation-modified polyacrylamide, cationized starch, etc.

When powdered inorganic materials and/or synthetic fibers are added, it is common to add these flocculants to the slurry.

The resulting dry powdered phenolic resin-coated paper can be easily printed on the surface. Typical printing methods include offset printing and screen printing.

Wood Board> The overlay plywood according to the present invention is formed by forming an overlay layer on a wood board. Here, "wood board" refers to plywood made by gluing wood veneers together with adhesive, a board made by pressure-molding laminated wood chips or fine powder wood powder with resin, and a board made of a single piece of wood or Thin leaves pasted,
This includes ordinary wooden boards and the like. Moreover, this "wooden board" includes not only the above-mentioned boards but also those with decorative paper pasted on them. It goes without saying that such wood boards may be flame-retardant or preservative-treated.

Note that even though it is a wooden board, the length and width of the board can be any size relative to its thickness.

Formation of Overlay Layer> The overlay layer according to the present invention is formed by pressurizing and heating the internal paper layered on the wooden board to melt and harden the powdered phenol resin, and then melting and adhering it to the surface of the wooden board.

Although there are no particular restrictions on the pressurizing and heating device, for example, a hot press or the like can be used.

The heating temperature necessary for thermally melting the powdered phenolic resin and subsequently curing it is 120 to 180°C, particularly preferably 140 to 170°C.

The pressure is 5 to 70 kg/cd, preferably 10 to 50 kg/cd, in order for the hot melted powdered phenolic resin to fill the spaces (voids) in the pulp fibers and to obtain adhesion to the wood board.
, particularly preferably 30 to 40 kg/cd. The heating and pressurization can be carried out in a short period of time, preferably 5 to 10
It takes about a minute.

The resulting overlay layer has excellent transparency, so it is possible to impart cosmetic properties to overlay plywood using only the overlay layer. However, it is preferable to add an inner layer of paper between the overlay layer and the wood board. Wooden board side and/or
If a printed layer is formed on a wood board, the printed layer can be visually recognized through the overlay layer, thereby imparting an aesthetic appearance to the plywood surface.

Experimental Examples The following experimental examples explain the present invention more specifically. The present invention is not limited by these experimental examples. Table-1 and Table-2 summarize the following experimental examples.

Example 1 Wood pulp (LBKP) is disintegrated at a concentration of 1% and then refined using a refiner to a freeness of 400 ml.

Thereafter, a powdered phenol resin (trade name: Bell Pearl S-890,
(Manufactured by Kanebo ■) Dispersed in water at a ratio of 50% by volume until the concentration is 0.
．． A 25% by weight slurry was prepared. After dispersion, apply a nonionic polymer flocculant (trade name N-210M, manufactured by Showa Denko ■)
was added to the slurry at a ratio of 0.3% by weight of the total paper amount to fix the powdered phenolic resin to the wood pulp. After that, 0.2% of a cationic flocculant (trade name: Clifix CP-633, manufactured by Kurita Industries ■) was added just before the cylinder of the cylinder paper machine.
The slurry was added to the slurry at a ratio of fr amount%, and paper was made using a circular mesh paper machine at a paper weight of 60 tr/rd. By laminating the made paper on the plywood and pressing it for 7 minutes at 150"CC140)c/Cj, the surface of the plywood itself was clearly shown.
An overlay plywood with a highly transparent overlay layer laminated on the surface was obtained.

Example 2 Highly beaten pulp (freeness -50ml) 10% by volume
, powdered phenolic resin (product name: Bell Pearl S-890,
Paper making was carried out in the same manner as in Example 1, except that the amount (manufactured by Kanebo Corporation) was 90% by volume (the total amount of both was 100% by volume), but continuous papermaking was possible. The internal paper obtained after papermaking was heated and pressed in the same manner as in Example 1 to obtain an overlay plywood with an overlay layer having excellent transparency laminated on the surface.

Example 3 The blending ratio was 50% by volume of powdered phenolic resin, 30% by volume of pulp (freeness -400ml), and glass fiber (product name UP).
GI/4ZA508, -L (manufactured by Nichika Yum Glass ■) was made in the same manner as in Example 1 except that the amount was 20% by volume (total amount is 100% by volume). After papermaking, hot pressing was performed in the same manner as in Example 1 to obtain an overlay plywood having a transparent overlay layer. This overlay plywood was subjected to a drop abrasion test using ASTM D673-
The wear resistance was evaluated based on the surface roughness according to the test method of No. 70, and compared with the overlay plywood of Example 1. The overlay plywood of this example containing inorganic fibers had improved wear resistance compared to the overlay plywood of Example 1.

Example 4 The blending ratio was 50% by volume of powdered phenolic resin, 30% by volume of pulp (freeness -400ml), and rayon fiber (1,
Paper making was carried out in the same manner as in Example 1, except that the paper size was 20% by volume (the total amount was 100% by volume). After papermaking, hot pressing was performed in the same manner as in Example 1 to obtain an overlay plywood having a transparent overlay layer.

Example 5 The blending ratio was 50% by volume of powdered phenolic resin, 20% by volume of indium oxide (In 203), pulp (freeness -
400ml) 20% by volume and highly refined pulp (freeness -
Paper making was carried out in the same manner as in Example 1, except that the total amount was 10% by volume (the total amount was 100% by volume). After papermaking, hot pressing was performed in the same manner as in Example 1 to obtain an overlay plywood having a transparent overlay layer.

The surface resistance of this overlay plywood was 1 ohm/hole.

Example 6 The blending ratio was adjusted to 50% by volume of powdered phenolic resin, 20% by volume of aluminum hydroxide (A12(OH)3), 20% by volume of pulp (freeness -400ml), and a fiber base material (freeness) consisting of highly refined pulp. Paper making was carried out in the same manner as in Example 1, except that the amount was 10% by volume (the total amount was 100% by volume). After papermaking, the paper was heated and pressed in the same manner as in Example 1 to obtain an overlay plywood having a heat-resistant overlay layer.

Example 7 After offset printing was performed on the inner liner paper obtained in Example 1 using acrylic/urethane resin printing ink, the inner liner paper and plywood were laminated so that the printed surface was in contact with the plywood. By hot pressing under the same conditions as in Example 1, an overlay plywood on which the printed layer was projected was obtained.

Example 8 Plywood was produced by screen printing on plywood with acrylic/urethane resin printing ink, laminating the Tokuuchi paper of Example 1 on top of that, and hot pressing under the same conditions as Example 1. An overlay plywood was obtained in which the printed layer of was projected on the surface.

Comparative Example 1 Paper making was carried out in the same manner as in Example 1, except that the blending ratio was 45% by volume of powdered phenolic resin and 55% by volume of pulp (freeness -400ml) (the total amount of both was 100% by volume). . Continuous paper making was possible with this formulation, but when the obtained internally coated paper was heated and pressed in the same manner as in Example 1, the powdered phenolic resin could not completely fill the spaces between the paper fibers, so the overlay layer was It turned white and did not have sufficient transparency.

Comparative Example 2 The blending ratio was 95% by volume of powdered phenolic resin, 5% by volume of highly beaten (freeness -50ml) (the total amount of both was 100% by volume)
Paper making was carried out in the same manner as in Example 1, except that

With this ratio of blending, the powdered phenol resin was not fixed to the pulp fibers because the amount of fibers in the fiber base material made of pulp was insufficient, and continuous paper making was impossible.

Comparative Example 3 The blending ratio was 60% by volume of powdered phenolic resin, 20% by volume of pulp (freeness -400ml), and 30% by volume of glass fiber (trade name UPGI/4ZA508, manufactured by Unitika Um Glass ■) (the total amount of all was 100% by volume). Paper making was carried out in the same manner as in Example 1, except that the paper was made in the same manner as in Example 1. Continuous paper making was possible with this formulation, but when hot pressing was carried out in the same manner as in Example 1, the powdered phenolic resin could not completely fill the spaces between the paper fibers, so the phenolic resin layer turned white and was insufficient. Transparency was not achieved.

Comparative Example 4 The blending ratio was changed to 50% by volume of powdered phenolic resin and pulp (
Freeness - 550ml) 50% by volume (total amount of both 10
Paper making was carried out in the same manner as in Example 1, except that the amount was 0% by volume). Continuous paper making was possible with this formulation, but when hot pressing was performed in the same manner as in Example 1, the powdered phenolic resin could not completely fill the spaces between the paper fibers.
The overlay layer turned white and sufficient transparency could not be obtained.

Table-1 Table-2 Note 1. Numbers indicate volume %.

Note 2. ○ indicates excellent.

Note 1. Numbers indicate volume %.

Note 2. × indicates insufficient transparency;
In terms of papermaking properties, this indicates that continuous papermaking is impossible.

Claims (1)

[Claims] 1. In an overlay plywood in which an overlay layer is provided on a wooden board, the overlay layer is formed on the wooden board by pressurizing and heating a powdered phenolic resin-added paper defined as below. Overlay plywood characterized by being made of (a) Powdered phenol resin is a hot-melt curing resin obtained by simultaneously carrying out an addition reaction and a condensation reaction of phenols and formaldehyde in the presence of an excess hydrochloric acid catalyst, and has a methylol group in the molecule. and has a weight average molecular weight of 3,500 or more, and a gelation time of 3 minutes or more. (b) The fiber base material constituting the powdered phenolic resin-loaded paper is substantially made of pulp, and the freeness is 500 ml to 5.
At least 10 ml of wood pulp beaten to 0 ml
% by volume (based on the total amount of all paper stock). (c) Powdered phenolic resin content in the powdered phenolic resin-added paper is 50 to 90% by volume (based on the total amount of all paper stocks)
To be. 2. Synthetic fibers 0 to 20% by volume (based on the total amount of all paper stocks)
The overlay plywood according to claim 1, wherein the overlay plywood is contained in the range of . 3. The overlay plywood according to claim 1 or 2, wherein the powdered inorganic substance is contained in a range of 10 to 30% by volume (based on the total amount of all paper stocks). 4. Claims 1 to 3 further comprising a printed layer provided on one or both of the wood boards and the overlay layer, which can be visually recognized through the overlay layer.
Overlay plywood according to any one of the following paragraphs.