A straw multilayer simulated plywood and preparation method thereof

Abstract

The embodiment of the present application discloses a straw multi-layer simulated plywood and a preparation method thereof, comprising a plurality of layers of veneers stacked and mutually bonded, wherein the veneers are formed by self-bonding of straw fibers, the veneers are subjected to high temperature heat treatment, and among the veneers constituting the plywood, at least two adjacent layers of the veneers are heated to different degrees. The veneers of the straw multi-layer simulated plywood of the present application are formed by self-bonding of straw fibers, and the veneers only include straw fibers, so large-scale and industrialized application of straw can be achieved; at the same time, the value of the multi-layer plywood is relatively high, so high value-added utilization of straw can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of plywood, and more specifically to a straw multilayer plywood; the invention also relates to a method suitable for preparing the straw multilayer plywood. Background Art

[0002] The technology of replacing wood with straw refers to the technology of using straw materials instead of wood to prepare solid wood boards or composite boards, which can not only achieve high added value and industrial utilization of straw, but also reduce the use of wood. This technology has generally gone through three stages. In the first stage, traditional adhesives were used to glue crop straw fragments or fibers, but they could not be well promoted due to their poor waterproof performance. For example, the technical solution recorded in the publication number CN1473691A in the Chinese Patent Library, entitled "Straw Medium and High Density Artificial Boards and Production Process Methods and Uses".

[0003] In the second stage, isocyanate adhesive is used to bond the straw fragments. However, due to the strong bonding property of isocyanate to metal and the relatively expensive raw material price, many practical production problems such as demoulding and loose slabs need to be solved, as well as the problem of how to reduce the manufacturing cost. For example, the technical solution recorded in the publication number CN108189192A in the Chinese patent library, entitled "A Straw-Based Artificial Board"; such as the adhesive and its use method recorded in the publication number CN104293274A, entitled "A Special Adhesive for Straw-Based Artificial Board and Preparation of Straw-Based Artificial Board".

[0004] In the third stage, straw is made into powder by wood-plastic composite technology and then co-extruded with plastic to make waterproof material, but the role of straw is to replace wood powder, and the added value is still relatively low. For example, the product and preparation method recorded in the Chinese patent library with publication number CN102153801A and the name "A straw plastic and its production method"

[0005] In summary, there is currently a lack of a high value-added, industrializable approach to straw utilization. Summary of the invention

[0006] The present application provides a straw multilayer plywood and a preparation method thereof.

[0007] In the first aspect of the present application, a straw multi-layer simulated plywood is provided, comprising a plurality of layers of veneers stacked and bonded to each other, the veneers being formed by self-bonding of straw fibers, the veneers being subjected to high-temperature heat treatment, and at least two adjacent layers of the veneers constituting the plywood being subjected to different degrees of heating.

[0008] In some embodiments, the straw fiber is treated to remove hemicellulose.

[0009] In some embodiments, the hemicellulose content of the straw fiber is quantitatively measured by liquid chromatography and is no higher than 20%.

[0010] In some embodiments, the single board has a thickness of 0.2 to 1.0 mm.

[0011] In some embodiments, the plurality of layers of the veneer are bonded together by an adhesive.

[0012] In a second aspect of the present application, a method for preparing the straw multilayer simulated plywood as described above is provided, comprising a process for preparing a veneer and a process for gluing the veneer, wherein the process for preparing the veneer is to lay a layer of the straw fiber on a lower pressing plate at room temperature to form a paving layer, wherein the paving layer is restricted on all sides, and an upper pressing plate with a temperature of 250 to 290° C. contacts the surface of the paving layer without pressure, and the upper pressing plate is withdrawn after a period of time; the above-mentioned actions are repeated to obtain a square blank formed by stacking a plurality of the paving layers; finally, the upper pressing plate presses the surface of the square blank at a temperature of 250 to 290° C. and a certain pressure, and the upper pressing plate is withdrawn after a period of time to obtain the square material; and the square material is cut at an angle to the upper pressing plate to obtain the veneer.

[0013] In some embodiments, the lower pressing plate is heated up starting from when the upper pressing plate contacts the surface of the second pavement layer; with each additional pavement layer, the temperature of the lower pressing plate increases by a fixed value until the upper pressing plate contacts the surface of the last pavement layer, at which time the lower pressing plate is isothermal with the upper pressing plate.

[0014] In some embodiments, the contact time between the upper pressing plate and the pavement layer satisfies the following formula:

[0015] t = 30 + a × (b - 5);

[0016] Wherein, t is the contact time, unit is s; a is any constant between 5 and 7, unit is s / mm; b is the thickness of the pavement layer, unit is mm.

[0017] In some embodiments, the upper pressing plate is maintained at 280-290° C. until the laying of all the paving layers is completed, and then the temperature of the upper pressing plate is reduced to 250-260° C. until the pressing of the square materials is completed.

[0018] In some embodiments, the pressure applied by the upper pressing plate to the square blank is 5-7 MPa.

[0019] In some embodiments, the veneer gluing process includes a gluing step, an assembling step, and a pressing step. In the gluing step, the surface of the veneer is fixed and kept flat by a vacuum adsorption plate, and an adhesive coating is formed on the back of the veneer by spraying.

[0020] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The veneer of the straw multi-layer simulated plywood of the present application is formed by self-bonding of straw fibers, and the veneer only includes straw fibers, so large-scale and industrialized application of straw can be achieved; at the same time, the value of the multi-layer plywood is relatively high, so high value-added utilization of straw can be achieved.

[0022] 2. In the preparation method of the straw multilayer simulated plywood of the present application, firstly, by laying the paving layer layer by layer and applying high temperature without pressure to the paving layer, it can be ensured that each paving layer is heated evenly. At the same time, the high temperature can remove the hemicellulose from the straw fiber (1) in the paving layer, so that the lignin therein can replace the adhesive to play a bonding role, at least in the process of cutting, so that the square material can maintain its shape; (2) coloring has a dark brown color similar to wood, and each paving layer is heated for a different time, which can form a color difference, and the thickness of the layer near the upper pressing plate and the thickness near the lower pressing plate is also heated differently, so a single board with simulated wood grain can be obtained by cutting at a suitable angle and method.

[0023] 3. Furthermore, the lower pressure plate gradually heats up as the pavement layers are laid layer by layer, which is conducive to the formation of color differences between the pavement layers.

[0024] 4. Furthermore, in the step of applying glue, a vacuum adsorption plate is used to fix the surface of the veneer and keep it flat, and the adhesive is sprayed from the back of the veneer to form an adhesive coating, which can (1) allow the adhesive to penetrate into the straw fibers of the veneer under the driving force of vacuum adsorption, thereby promoting the stability of the structure and shape of the veneer and avoiding the problem of straw fiber falling off due to the possible instability of the self-adhesion of the straw fibers; (2) there is sufficient adhesive in the veneer, and the excess adhesive that cannot adhere to the back of the veneer falls into the recovery pool under the action of its own weight, ensuring that an appropriate amount of adhesive is applied to the back of the veneer, so that the bonding interface (i.e., the back) of the veneer has relatively good adhesive properties, and achieves the purpose of saving adhesive usage and reducing manufacturing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative labor.

[0026] Figure 1 This is a schematic diagram of the structure of the straw multi-layer simulated plywood of Example 1 of the present application.

[0027] Figure 2 This is a surface picture of the straw multi-layer simulated plywood of Example 1 of the present application.

[0028] Figure 3 This is a process flow chart of the process of preparing the single board of Examples 1 to 12 of the present application.

[0029] Figure 4 This is a process flow chart of the sizing steps of Example 12 of the present application.

[0030] In the figure: 100, plywood, 110, veneer, 201, 202, 220 paving layer, 300, square material blank, 400, square material, 510, lower pressure plate, 520, side plate, 530, upper pressure plate, 600, vacuum adsorption plate, 700, spraying mechanism, 710, glue tank, 720, nozzle. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this application.

[0032] Example

[0033] Reference Figure 1 , Figure 2 The straw multi-layer simulated plywood 100 shown includes multiple layers of veneers 110 stacked and bonded to each other. The veneers 110 have the color and texture of wood. The color and texture of the veneers 110 at the top and bottom layers are the color and texture of the surface and bottom of the straw multi-layer simulated plywood; the 11 layers of veneers 110 together constitute the color and texture of the side and end surfaces of the straw multi-layer simulated plywood.

[0034] The single board 110 is formed by self-bonding of straw fibers that have been treated to remove hemicellulose. Typically, the length of the straw fibers is 2 to 5 mm, and the hemicellulose content quantitatively measured from the straw fibers constituting the single board 110 by liquid chromatography is about 19%.

[0035] The product structure of the plywood 100 of each embodiment is shown in Table 1, and the thickness of the adhesive layer is about 0.2 mm. Among them, the control group 1 is a poplar multilayer plywood prepared by applying urea-formaldehyde resin adhesive on one side of 11 layers of poplar veneer and using the existing technology, with a total thickness of 15 mm; the control groups 2 and 3 are straw density boards with a thickness of 15 mm prepared by using straw fiber mixed with urea-formaldehyde resin adhesive and phenolic resin adhesive and using the existing technology.

[0036] Table 1. Product structure comparison table of plywood 100 in various embodiments

[0037]

[0038]

[0039] Reference Figure 3 As shown, the embodiment of the present application also provides a method for preparing the aforementioned straw multi-layer simulated plywood 100, including a single board preparation process and a single board gluing process.

[0040] The equipment used in the process of preparing single board includes at least one mold with an opening on the top surface, and an upper pressing plate 530 with the same width as the opening on the top surface of the mold. The bottom plate of the mold can be used as a heat source and is regarded as a lower pressing plate 510. The four side plates 520 of the mold can provide restrictions on the pavement layer around.

[0041] During preparation, the lower pressing plate 510 is at room temperature (room temperature, T b0 =25°C), a layer of straw fiber is laid on the lower pressing plate 510 to form the first paving layer 201, and the upper pressing plate 530 has a temperature of T a The upper pressing plate 530 contacts the surface of the first pavement layer 201 without pressure after descending, and the upper pressing plate 530 is withdrawn after a period of time t. The contact time between the upper pressing plate 530 and the pavement layer satisfies the following formula:

[0042] t = 30 + a × (b - 5);

[0043] Wherein, t is the contact time, unit is s; a is a constant, unit is s / mm; b is the thickness of the pavement layer, unit is mm.

[0044] A second layer of straw fiber is laid on the first paving layer 201 to form a second paving layer 202. At the same time, the temperature of the lower pressing plate 510 is raised by ΔT. b, the upper pressing plate 530 contacts the surface of the second paving layer 202 without pressure after the original temperature drops, and after a period of time t, the upper pressing plate 530 is withdrawn. In this embodiment, the thickness of each paving layer is the same, so the time t is equal. Repeat the above steps, and when each layer of straw fiber is paved, the temperature of the lower pressing plate 510 is increased by △T b , until 20 paving layers 201, 202, 220 are paved to obtain the square material blank 300, at which time, the temperature of the lower pressing plate 510 is substantially the same as the temperature of the upper pressing plate 530. In practice, it may be difficult to point out a clear boundary between two adjacent paving layers, but their paving orders are different, and macroscopically visible color differences can be formed due to different heating times and different heating times in the same layer. The dividing line formed by the color difference can be understood as the boundary of each paving layer. At the same time, those skilled in the art can understand that at this boundary, the straw fibers of adjacent paving layers may penetrate and blend with each other. At the same time, after a thermal contact period of time t, the hemicellulose content quantitatively measured by liquid chromatography on the straw fibers in any paving layer is not higher than 20%, so as to improve the bonding performance between the straw fibers and enable the square material 400 to maintain its shape at least during the cutting process of the square material 400.

[0045] After obtaining the square blank 300, the upper pressing plate 530 presses the surface of the square blank 300 at the original temperature and a certain pressure P for 30 minutes to obtain the square blank 400. Finally, the square blank 400 is sliced ​​at an angle perpendicular to the surface of the square blank 400 to obtain a veneer 100 with a thickness of 1 mm. Of course, those skilled in the art will know how to obtain veneers 110 with different colors and textures by changing the cutting angle.

[0046] As a preferred embodiment, during the thermal contact process of the pavement layer, the upper pressing plate 530 has a relatively high temperature T a , and before the square material 400 starts to be pressed, it drops to a relatively low temperature T a ’ That is, the difference between Example 11 and Example 10 is that during the thermal contact process of the pavement layer, the temperature T of the upper pressing plate 530 is a = 285 ± 2 ° C; after the laying of all the paving layers, the temperature of the upper pressing plate 530 drops to T a ’ =255±2℃, and always keep T during the pressing process of the square material 400 a ’ temperature.

[0047] The process of gluing the veneers of Examples 1 to 11 adopts the means of the prior art, specifically including the steps of gluing, assembling and pressing. The gluing step is to apply phenolic resin adhesive or urea-formaldehyde resin adhesive (see Table 1) to one side of each veneer 100 by roller coating; the assembling step is to stack the veneers 100 after gluing according to the set number of layers; the pressing step is to obtain the plywood 100 of each example by hot pressing.

[0048] As a preferred embodiment, in the step of applying glue, the surface of the single board 110 is fixed and kept flat by the vacuum adsorption plate 600, and the back of the single board 110 is formed with an adhesive coating by spraying. Figure 4 As shown, in the step of applying glue, the surface of the single board 110 is fixed and kept flat by the vacuum adsorption plate 600, and the back of the single board 100 is sprayed by the spraying mechanism 700 to form an adhesive coating. Among them, the vacuum adsorption plate 600 is a part of the vacuum adsorption mechanism of the prior art, and the vacuum adsorption plate 600 has a format substantially the same as that of the single board 110, so that the single board 110 can be fixed and kept flat by the vacuum adsorption force. The spraying mechanism 700 is a glue spraying device of the prior art, which is arranged below the vacuum adsorption plate 600 and has a nozzle 720 connected to the glue pool 710 pipeline through a hydraulic pump. The nozzle 720 can be a hanging cup type, an atomizing type, or an ordinary nozzle, but preferably an atomizing nozzle, and the nozzle 720 is at an angle of 40 to 50 degrees with the single board 110, so as to spray uniformly on the back of the single board 110 to form an adhesive coating. It is further preferred that the glue pool 710 is located below the nozzle 720 to recover and recycle excess adhesive.

[0049] Since the back of the veneer 110 is glued, the veneer 110 after gluing can be directly placed on a veneer 110 used to form the bottom surface of the plywood 100. This process can be completed manually, or it can be realized by using a robot arm to drive the vacuum adsorption plate 600 to move the veneer 110. After repeatedly placing the veneer 110 after gluing to a set number of layers, the plywood of this embodiment is obtained by pressing through the hot pressing process of the prior art.

[0050] The process parameters of the single board preparation process of each embodiment are shown in Table 2. The thickness of the single board 110 obtained after cutting the square material 400 of embodiments 1 to 8 is shown in Table 1, and the thickness of the single board 110 of embodiments 9 to 12 is 1 mm.

[0051] Table 2. Comparison table of process parameters for the single board preparation process in each embodiment

[0052]

[0053]

[0054] The product performances of the plywood 100 of each embodiment and each control group are shown in Table 3.

[0055] Table 3. Product performance comparison table of plywood 100 in various embodiments

[0056]

[0057] The above description is intended to be illustrative and not limiting. Upon reading the above description, many embodiments and many applications beyond the examples provided will be apparent to those skilled in the art. Therefore, the scope of the present teachings should not be determined with reference to the above description, but should be determined with reference to the appended claims and the full scope of equivalents to which such claims are entitled. For the purpose of comprehensiveness, all articles and references, including disclosures of patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the preceding claims is not intended to be a waiver of the subject matter, nor should it be considered that the applicant has not considered the subject matter to be part of the disclosed application subject matter.

Claims

1. A straw multi-layer simulated plywood, comprising a plurality of layers of veneers stacked and bonded to each other, characterized in that: The veneer is formed by self-bonding of straw fibers, the veneer is subjected to high-temperature heat treatment, and at least two adjacent layers of the veneer constituting the plywood are subjected to different degrees of heat treatment; The method for preparing the straw multi-layer simulated plywood includes a process for preparing a veneer and a process for gluing the veneers. The process for preparing the veneer is to pave a layer of the straw fiber on a lower pressing plate at room temperature to form a paving layer, the four sides of the paving layer are restricted, an upper pressing plate with a temperature of 250 to 290° C. contacts the surface of the paving layer without pressure, and the upper pressing plate is withdrawn after a period of time; the above actions are repeated to obtain a square blank formed by stacking a plurality of the paving layers; finally, the upper pressing plate presses the surface of the square blank at a temperature of 250 to 290° C. and a certain pressure, and the upper pressing plate is withdrawn after a period of time to obtain the square material; and the square material is cut at an angle to the upper pressing plate to obtain the veneer.

2. The straw multilayer simulated plywood according to claim 1, characterized in that: The straw fibers are treated by removing hemicellulose.

3. The straw multilayer simulated plywood according to claim 1 or 2, characterized in that: The thickness of the single board is 0.2-1.0 mm.

4. The straw multilayer simulated plywood according to claim 1, characterized in that: The plurality of veneers are bonded together by adhesive.

5. The straw multi-layer simulated plywood according to claim 1, characterized in that: The lower press plate is heated from the moment the upper press plate contacts the surface of the second pavement layer; the temperature of the lower press plate increases by a fixed value each time a pavement layer is added, until the upper press plate contacts the surface of the last pavement layer, at which point the lower press plate becomes isothermal as the upper press plate.

6. The straw multi-layer simulated plywood according to claim 1, characterized in that: The contact time between the upper pressing plate and the pavement layer satisfies the following formula: t = 30 + a × (b - 5); Wherein, t is the contact time, unit is s; a is any constant between 5 and 7, unit is s / mm; b is the thickness of the pavement layer, unit is mm.

7. The straw multi-layer simulated plywood according to claim 1, characterized in that: The temperature of the upper pressing plate is maintained at 280-290° C. until the laying of all the paving layers is completed, and then the temperature of the upper pressing plate is reduced to 250-260° C. until the pressing of the square materials is completed.

8. The straw multi-layer simulated plywood according to claim 1, characterized in that: The pressure applied by the upper pressing plate to the square blank is 5-7 MPa.

9. The straw multi-layer simulated plywood according to claim 1, characterized in that: The process of gluing the veneers includes the steps of gluing, assembling and pressing. In the gluing step, the surface of the veneer is fixed and kept flat by a vacuum adsorption plate, and an adhesive coating is formed on the back of the veneer by spraying.

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