Preparation method of LWRT composite board, LWRT composite board and application thereof

Abstract

This invention relates to the field of LWRT composite panel preparation technology, and particularly to a method for preparing LWRT composite panels, LWRT composite panels, and their applications. Glass fibers and polypropylene fibers are sequentially opened, dry-carded, cross-laid, and needle-punched to obtain a composite felt. The obtained composite felt is then passed through a first heating zone, while the nonwoven fabric and hot melt adhesive layer simultaneously follow the composite felt from its upper and lower surfaces through a second heating zone. After further hot lamination and cold setting, the LWRT composite panel is obtained. This invention significantly improves the bending performance, interlayer cohesion, and thickness uniformity of the composite panel by controlling the selection and specific gravity of the nonwoven fabric, hot melt adhesive layer, resin fibers, and glass fibers, and by combining material mixing, needle-punching, hot lamination, and cold setting processes. This overcomes many challenges of existing LWRT panels in the interlayer of RVs, buses, and vans.

Description

Technical Field

[0001] This invention relates to the field of LWRT composite material preparation technology, and in particular to a method for preparing LWRT composite materials, LWRT composite materials and their applications. Background Technology

[0002] Forest resources, as one of the most precious natural resources on Earth, not only provide habitats for countless organisms but are also crucial for maintaining the Earth's ecological balance. Like the lungs of the Earth, they absorb carbon dioxide and release oxygen through photosynthesis, effectively regulating climate, conserving soil and water, and mitigating or even preventing natural disasters such as droughts, floods, sandstorms, and hailstorms. Furthermore, forests have multiple functions, including purifying air, eliminating noise, protecting soil, and maintaining biodiversity, making them vital to human survival and development. However, with the rapid development of human society, the over-exploitation and utilization of timber resources has led to the increasing depletion of forest resources. Although the global emphasis on forest protection has increased in recent years, and the rate of forest degradation and loss has slowed, a large area of ​​forest (nearly 200 square kilometers) is still disappearing every day, posing a significant threat to the Earth's ecological environment. In the manufacturing of RVs, buses, and vans, traditional partition and sandwich panels are primarily made of wood. While these materials possess a certain degree of strength and stability, with the growing awareness of environmental protection, the increasing scarcity of timber resources, and problems such as mold growth, the need for alternatives to wood is becoming increasingly urgent. Against this backdrop, Light Weight Reinforced Thermoplastic (LWRT) sheets have begun to be used in this industry.

[0003] LWRT (Low-Waste Glass Fiber) sheets are a type of felt material made from chopped glass fibers and thermoplastic short fibers, which are then laminated into sheets through hot bonding and cold setting processes, making them an ideal alternative for sandwich panels in RVs, buses, and vans. However, existing LWRT sheets still have many problems in application, such as insufficient bending performance, poor surface flatness, lack of thickness uniformity, and insufficient interlayer cohesion, which to some extent limits their widespread use in the sandwich panel field for RVs, buses, and vans. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a method for preparing LWRT composite panels, LWRT composite panels, and their applications. By controlling the selection and proportioning of nonwoven fabric, hot melt adhesive layer, polypropylene fiber, and glass fiber, and optimizing the mixing, needle punching, hot bonding, and cold setting processes of the materials, this invention effectively improves the bending performance, interlayer cohesion, thickness uniformity, and the problem of wood mold growth in composite panels. This provides a higher-quality and more environmentally friendly solution for RV, bus, and van partition sandwich panels.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing an LWRT composite board, wherein the LWRT composite board comprises, from top to bottom, a nonwoven fabric, a hot melt adhesive layer, a composite felt, a hot melt adhesive layer, and a nonwoven fabric, and includes the following steps:

[0007] 1) Glass fiber and polypropylene fiber are sequentially opened, dry carded, cross-laid and needle-punched to obtain composite felt material;

[0008] The mass ratio of glass fiber to polypropylene fiber is 40-60:40-60;

[0009] The glass fiber has a fiber length of 50–130 mm and a surface oil content of 0.15–0.35%.

[0010] The polypropylene fiber has a fiber length of 46-76 mm, a surface oil content of 0.35-0.55%, a crimp number of 7-12, a melt index of 22-40 g / 10 min, a melting point of 166-175 °C, and a crystallization temperature of 160 °C.

[0011] The needle depth for acupuncture is 7–12 mm, and the needle density is 50–80 needles / cm. 2 ;

[0012] The nonwoven fabric contains 20-25% polyethylene by mass and has a basis weight of 40-80 gsm.

[0013] The hot melt adhesive layer is a polypropylene perforated adhesive film with a basis weight of 20-60 gsm, a pore size of 0.3-1 mm, and a pore spacing of 3-10 mm * 3-10 mm.

[0014] 2) The composite felt material obtained in step 1) is passed through the first heating zone, and the non-woven fabric and hot melt adhesive layer simultaneously follow the composite felt material from the upper and lower surfaces through the second heating zone. After hot bonding and cold setting, LWRT composite board is obtained.

[0015] The temperature of the first heating zone is 185–215°C, and the fan frequency is 50–80%.

[0016] The temperature of the second heating zone is 220-230℃, and the fan frequency is 90-100%.

[0017] The conditions for cold setting include: the gap between the impregnation rollers is 1.5 to 2.0 mm, and the cooling water recovery temperature is ≤30℃.

[0018] Preferably, in step 1), the glass fiber is a short-cut fiber with a diameter of 17 μm, a fiber length of 110 mm, a linear density of 2400 tex, and a surface oil content of 0.25%.

[0019] Preferably, in step 1), the polypropylene fiber is a short fiber with a fiber length of 60 mm, a linear density of 9 dtex, a surface oil content of 0.45%, a crimp number of 7, a melting point of 166℃, and an OIT ≥ 20 min.

[0020] Preferably, the conditions for step 1) of cross-laying the mesh include: a width of 2600mm, 28 layers of mesh, and a single mesh weight of 33g / m². 2 ;

[0021] The needle depth for acupuncture is 9 mm, and the needle density is 70 needles / cm. 2 ;

[0022] The feed rate for the dry combing process is 800–1100 kg / h.

[0023] Preferably, the thickness of the nonwoven fabric in step 1) is 0.04 mm, the breaking strength is ≥25 N, the dimensional shrinkage rate under thermal conditions is ≤2%, and the basis weight CV% value is ≤7%.

[0024] The hot melt adhesive layer has a basis weight of 30 gsm, a pore size of 0.5 mm, a pore spacing of 7 mm * 7 mm, a thickness of 28 μm, a melting point of 145 °C, and the pores are arranged in a diamond and / or square pattern.

[0025] Preferably, in step 2), the temperature of the first heating zone is 205°C and the fan frequency is 70%.

[0026] The temperature of the second heating zone is 225°C, and the fan frequency is 95%.

[0027] The conditions for cold setting include: the gap between the impregnation rollers is 1.7 mm, the pressure of the impregnation rollers is 20 t, the gap between the line pressure holding rollers is 2.9 mm, the pressure of the line pressure holding rollers is 10 t, the gap between the surface pressure holding rollers is 2.9 mm, and the pressure of the surface pressure holding rollers is 130 t.

[0028] The conditions for the thermal bonding in step 2) include: it is carried out in the second heating zone at a temperature of 225°C, a fan frequency of 95%, a hot roller gap of 1.5 mm, and a hot roller pressure of 3 t.

[0029] This invention also provides an LWRT composite board prepared by the preparation method described above, wherein the LWRT composite board has an areal density of 980-1080 gsm and a thickness of 2.9 mm. In this invention, the thickness of the nonwoven fabric in the LWRT composite board is 0.04 mm, the thickness of the hot melt adhesive layer is 0.03 mm, the thickness of the composite felt is 2.76 mm, the thickness of the hot melt adhesive layer is 0.04 mm, and the thickness of the nonwoven fabric is 0.03 mm.

[0030] The present invention also provides the application of the LWRT composite board described in the above technical solution in improving the mechanical properties of the board, wherein the mechanical properties include one or more of bending properties, interlayer cohesion, air permeability and interfacial bonding strength.

[0031] This invention also provides the application of the LWRT composite board described in the above technical solution in improving the board's resistance to mildew.

[0032] The present invention also provides the application of the LWRT composite board described in the above technical solution in improving the thickness uniformity of the board.

[0033] This invention optimizes the characteristic morphologies of glass fiber and polypropylene fiber, feeds them in a specific ratio, and processes them through unpacking, carding, web laying, and needle punching to form a composite felt. Then, the composite felt is pressed into a board through a continuous lamination process with a preferred hot melt adhesive layer and a non-woven fabric layer. This results in not only entanglement points between the glass fiber and polypropylene fiber due to needle punching, but also the encapsulation of glass fiber by the molten polypropylene fiber and secondary consolidation of the molten polypropylene fiber at the entanglement points. Furthermore, the preferred needle punching process transforms a large number of glass fibers from a planar two-dimensional distribution to a three-dimensional distribution. Therefore, this LWRT composite board, used in the sandwich panels of RVs, buses, and vans, possesses characteristics such as high bending performance, interlayer cohesion, excellent thickness uniformity, no mold growth, and high air permeability.

[0034] This invention optimizes the composition of the nonwoven fabric, controlling the mass ratio of low-melting-point fiber components to be 20±5%. This ensures that the thermally rolled nonwoven fabric has a tensile strength ≥25N, while simultaneously maintaining its air permeability and plush feel, providing higher interfacial bonding strength when manufacturing partitions for RVs, buses, and vans.

[0035] The beneficial effects of this invention are:

[0036] 1. High Flexural Performance: This invention optimizes the characteristic morphology of glass fiber and polypropylene fiber, and feeds them in a specific ratio. The composite felt is then formed through unpacking, carding, web formation, and needle punching. The composite felt is then pressed into a board through a continuous lamination process with a preferred hot-melt adhesive layer and a non-woven fabric layer. Under the combined action of two high-temperature ovens (185℃-215℃ and 220℃-230℃), a 3t high-pressure hot roller, and a 20t high-pressure impregnation roller, the polypropylene fiber's encapsulation of the glass fiber after melting, as well as the secondary consolidation of the molten polypropylene fiber at the knot points, results in high flexural performance of the cold-pressed composite board.

[0037] 2. Interlayer Cohesion: The preferred needle-punching process transforms a large number of glass fibers from a planar two-dimensional distribution to a three-dimensional distribution. Simultaneously, the needle-punching creates numerous entanglement points between the glass and polypropylene fibers. During the board-making stage, the composite felt undergoes two heating zones, allowing the polypropylene fibers to fully melt. This results in not only entanglement points between the glass and polypropylene fibers from the needle-punching process, but also the encapsulation of glass fibers by the molten polypropylene fibers and secondary consolidation of the molten polypropylene fibers at these entanglement points. Therefore, the LWRT board of this invention possesses interlayer cohesion.

[0038] 3. Excellent Thickness Uniformity: The composite board of this invention is prepared through a continuous composite process including hot lamination, cold setting, and cutting. During the cold setting process, the composite board is cold-set using a double-layer protection system of 10t linear pressure and 130t surface pressure. Furthermore, the crystallization temperature of the polypropylene fibers is controlled at 100-120℃, and the low cooling water recovery temperature is ensured to be ≤30℃, allowing the core layer of the composite board to also achieve complete cooling and setting of the polypropylene fibers. Ultimately, the thickness tolerance of the board is controlled within ±0.1mm, achieving excellent thickness uniformity.

[0039] 4. Resistance to mold and mildew: The composite board of this invention is made of polymer materials such as polyolefins and polyesters and inorganic materials such as glass fibers, and does not contain any materials that are prone to mold growth. Therefore, it can eliminate the risk of mold growth in natural materials such as wood and bamboo during use.

[0040] 5. High air permeability: This invention strictly controls the proportion of low-melting-point components in the nonwoven fabric to 20±5%, with a melting point between 110℃ and 140℃. Furthermore, the hot melt adhesive layer of this invention is a perforated film. The perforated film is characterized by a pore size of 0.3-1mm and a pore spacing of 3-10mm*3-10mm. During the continuous lamination process, after passing through the second heating zone and then undergoing cold setting, the low-melting-point components in the nonwoven fabric and the hot melt adhesive layer are completely plasticized and re-shaped, forming countless discontinuous, irregular micropores on the surface of the board, thus giving the board air permeability. By controlling the selection of the nonwoven fabric, adhesive film, and the bulk density of the board, the specific fluid resistance of the composite board can be controlled within the range of 2449.8-11704.6 Pa*s / m.

[0041] 6. High Interfacial Bonding Strength: This invention optimizes the composition of the nonwoven fabric, controlling the mass proportion of low-melting-point fiber components to be 20±5%. While ensuring a tensile strength of ≥25N for the hot-rolled nonwoven fabric, it also guarantees air permeability and a plush feel. The plush feel enhances the board's ability to absorb adhesive, and suitable air permeability allows more adhesive to remain at the bonding interface while some adhesive seeps into the interior of the board. This results in higher interfacial bonding strength when manufacturing partitions for RVs, buses, and vans. Detailed Implementation

[0042] This invention provides a method for preparing an LWRT composite board, wherein the LWRT composite board comprises, from top to bottom, a nonwoven fabric, a hot melt adhesive layer, a composite felt, a hot melt adhesive layer, and a nonwoven fabric, and includes the following steps:

[0043] 1) Glass fiber and polypropylene fiber are sequentially opened, dry carded, cross-laid and needle-punched to obtain composite felt material;

[0044] The mass ratio of glass fiber to polypropylene fiber is 40-60:40-60;

[0045] The glass fiber has a fiber length of 50–130 mm and a surface oil content of 0.15–0.35%.

[0046] The polypropylene fiber has a fiber length of 46-76 mm, a surface oil content of 0.35-0.55%, a crimp number of 7-12, a melt index of 22-40 g / 10 min, a melting point of 166-175 °C, and a crystallization temperature of 160 °C.

[0047] The needle depth for acupuncture is 7–12 mm, and the needle density is 50–80 needles / cm. 2 ;

[0048] The nonwoven fabric contains 20-25% polyethylene by mass and has a basis weight of 40-80 gsm.

[0049] The hot melt adhesive layer is a polypropylene perforated adhesive film with a basis weight of 20-60 gsm, a pore size of 0.3-1 mm, and a pore spacing of 3-10 mm * 3-10 mm.

[0050] 2) The composite felt material obtained in step 1) is passed through the first heating zone, and the non-woven fabric and hot melt adhesive layer simultaneously follow the composite felt material from the upper and lower surfaces through the second heating zone. After hot bonding and cold setting, LWRT composite board is obtained.

[0051] The temperature of the first heating zone is 185–215°C, and the fan frequency is 50–80%.

[0052] The temperature of the second heating zone is 220-230℃, and the fan frequency is 90-100%.

[0053] The conditions for cold setting include: the gap between the impregnation rollers is 1.5 to 2.0 mm, and the cooling water recovery temperature is ≤30℃.

[0054] In this invention, the glass fiber is preferably chopped short fiber with a diameter of 17 μm, a fiber length of 110 mm, a linear density of 2400 tex, and a surface oil content of 0.25%. In this invention, the polypropylene fiber is preferably short fiber with a fiber length of 60 mm, a linear density of 9 dtex, a surface oil content of 0.45%, a crimp count of 7, a melting point of 166℃, and an OIT (out-of-place) time of ≥20 min. This invention does not have specific limitations on the source of the glass fiber and polypropylene fiber; conventional commercially available products are acceptable. In this invention, the nonwoven fabric has a thickness of 0.04 mm, a breaking strength ≥25 N, a thermal shrinkage rate ≤2%, and a basis weight CV% value ≤7%. In this invention, the nonwoven fabric is preferably a short-fiber hot-rolled nonwoven fabric, made by conventionally blending and hot-rolling black polyester fiber and white ES fiber. In this invention, the preferred basis weight of the hot melt adhesive layer is 30 gsm, the pore size is 0.5 mm, the pore spacing is 7 mm * 7 mm, the thickness is 28 μm, the melting point is 145 °C, and the pores are arranged in a diamond and / or square pattern. In this invention, the preferred conditions for the cross-laid mesh include: a width of 2600 mm, 28 mesh layers, and a single mesh basis weight of 33 g / m². 2 In this invention, the needle depth is preferably 9 mm, and the needle density is 70 needles / cm. 2 In this invention, the feed rate for the dry combing is preferably 800–1100 kg / h.

[0055] In this invention, the temperature of the first heating zone is preferably 205°C, and the fan frequency is 70%. In this invention, the temperature of the second heating zone is preferably 225°C, and the fan frequency is 95%. In this invention, the preferred conditions for cold setting include: an impregnation roller gap of 1.7 mm, an impregnation roller pressure of 20 t, a line pressure holding gap of 2.9 mm, a line pressure holding pressure of 10 t, a surface pressure holding gap of 2.9 mm, and a surface pressure holding pressure of 130 t. In this invention, the preferred conditions for hot bonding include: being carried out in the second heating zone at a temperature of 225°C, a fan frequency of 95%, a hot roller gap of 1.5 mm, and a hot roller pressure of 3 t.

[0056] The present invention also provides an LWRT composite board prepared by the preparation method described above, wherein the LWRT composite board has an areal density of 980-1080 gsm and a thickness of 2.9 mm. In the present invention, the LWRT composite board comprises, from top to bottom, nonwoven fabric 1 (0.04 mm), hot melt adhesive layer 2 (0.03 mm), composite felt 3 (2.76 mm), hot melt adhesive layer 4 (0.04 mm), and nonwoven fabric 5 (0.03 mm).

[0057] The present invention also provides the application of the LWRT composite board described in the above technical solution in improving the mechanical properties of the board, wherein the mechanical properties include one or more of bending properties, interlayer cohesion, air permeability and interfacial bonding strength.

[0058] The present invention also provides the application of the LWRT composite board described in the above technical solution in improving the thickness uniformity of the board.

[0059] This invention also provides the application of the LWRT composite board described in the above technical solution in improving the board's resistance to mildew.

[0060] To further illustrate the present invention, the following detailed description is provided in conjunction with embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0061] Example 1

[0062] A method for preparing an LWRT composite board, comprising the following steps:

[0063] Step 1: Felt Making

[0064] Glass fiber and polypropylene fiber were selected as the raw materials for the composite felt. The glass fiber was chopped short fiber with a diameter of 17 μm, a length of 110 mm, a linear density of 2400 tex, and a surface oil content of 0.25%. The polypropylene fiber was short fiber with a length of 60 mm, a linear density of 9 dtex, a surface oil content of 0.45%, a crimp count of 7, a melt index of 40 g / 10 min, a melting point of 166℃, a crystallization temperature of 160℃, and an OIT (out-of-place) value ≥ 20 min. The mass ratio of glass fiber to polypropylene fiber was 47:53.

[0065] Pretreated glass fiber and polypropylene fiber are fed into the opening machine in proportion, and then sent to the blending bin after passing through multiple opening devices. They are weighed and continuously fed into the carding machine for carding. After carding, the blended fibers form a thin single fiber web, which is then cross-laid by the web laying machine and sent to the needle punching area. After needle punching and consolidation, it is rolled up to obtain the composite felt material.

[0066] The feeding rate of the cotton feeder in the mixing area is 900 kg / h. During the net laying process, the width is 2600 mm, the number of net layers is 28, and the weight of a single net is 33 g / m². 2 The needle depth is 9mm, and the needle density is 70 needles / cm. 2 .

[0067] The resulting composite felt material has a surface density of 860 gsm and a thickness of 9 mm.

[0068] Step 2: Plate Making:

[0069] Nonwoven fabrics 1 and 5 are made of the same short-fiber hot-rolled nonwoven fabric, which is made of black polyester fiber and white ES fiber blended and hot-rolled. The PE component accounts for 20% of the total weight of the nonwoven fabric, the basis weight is 40gsm, the thickness is 0.04mm, the breaking strength is ≥25N, the dimensional shrinkage rate in the hot state is ≤2%, and the basis weight CV% value is ≤7%.

[0070] Hot melt adhesive layers 2 and 4 are made of the same perforated polypropylene film. The adhesive layer has a basis weight of 30 gsm, a thickness of 28 μm, and a melting point of 145℃. The pore diameter is 0.5 mm, the pore spacing is 7 mm * 7 mm, and the pores are arranged in a diamond pattern.

[0071] The composite felt 3 obtained in step one is first passed through the first heating zone. The continuous roll of nonwoven fabric 1 and the hot melt adhesive layer 2 follow the composite felt from the upper surface of the composite felt into the second heating zone. At the same time, the continuous roll of nonwoven fabric 5 and the hot melt adhesive layer 4 follow the composite felt from the lower surface of the composite felt into the second heating zone. Then, through hot bonding, cold setting and cutting, a composite board is obtained.

[0072] The process parameters for the first heating zone include: a temperature of 205℃ and a fan frequency of 70%.

[0073] The process parameters for the second heating zone include: a temperature of 225℃ and a fan frequency of 95%.

[0074] The process parameters for thermal bonding include: the process is carried out in the second heating zone at a temperature of 225℃, a fan frequency of 95%, a hot roller gap of 1.5mm, and a hot roller pressure of 3t.

[0075] The process parameters for cold setting include: impregnation roller gap: 1.7mm, impregnation roller pressure: 20t, line pressure holding gap: 2.9mm, line pressure holding pressure: 10t; surface pressure holding gap: 2.9mm, surface pressure holding pressure: 130t, and cooling water recovery temperature: ≤30℃.

[0076] The continuous lamination speed is 10 m / min. Finally, composite boards of suitable dimensions are obtained through online cutting. The board surface density is 1000 gsm, and the thickness is 2.9 mm.

[0077] Examples 2-7

[0078] Based on the embodiments, the structure, felt-making process, and board-making process were modified according to Table 1.

[0079] Table 1 Test data for Examples 1-7

[0080]

[0081]

[0082] Note: MD indicates the machine's production output direction, and CD indicates the direction perpendicular to the machine's production output direction.

[0083] The test data from Examples 1, 2, and 3 show that the longer the glass fiber, the higher the oil content; and the longer the polypropylene fiber, the higher the oil content and the greater the crimp number, resulting in slight mixing inhomogeneity between the two fiber components. A low melt flow index and a high melting point mean that some polypropylene fibers do not fully melt and encapsulate the glass fiber. An excessively high glass fiber ratio leads to insufficient polypropylene fibers for bonding, resulting in some glass fibers being unbonded. Shorter glass and polypropylene fibers have weaker stress conduction capabilities within the board after forming, and lower oil content in both components leads to weaker interfacial compatibility after mixing. An excessively high polypropylene fiber ratio results in insufficient glass fibers for skeletal support. In summary, the length of the glass fiber, the oil content, the length of the polypropylene fiber, the oil content, the crimp number, the melt flow index, the melting point, and the mass ratio of glass and polypropylene fibers all affect the final flexural modulus and interlayer cohesion of the board. The preferred fiber is 110 mm long with an oil content of 0.25%; the polypropylene fiber is 60 mm long with an oil content of 0.45%, has 7 crimps, a melt index of 40 g / 10 min, and a melting point of 166 °C. The mass ratio of glass fiber to polypropylene fiber is 47:53.

[0084] The test data from Examples 1, 4, and 5 show that the felt-making process involves a needle depth of 9 mm and a needle density of 70 needles / cm. 2 Increase the needle depth to 12mm; the needle density to 80 needle counts / cm. 2 Excessive needle punching in the felt material causes some fibers to break, reducing the actual fiber length, bending performance, and interlayer cohesion. The felting process involves a needle depth of 9mm and a needle density of 70 needles / cm. 2 Reduce needle depth to 7mm; needle density to 50 needle counts / cm. 2 Insufficient needle punching in the felt material results in insufficient fiber entanglement points between the two components, reducing bending performance and interlayer cohesion.

[0085] The test data from Examples 1, 6, and 7 show that reducing the board-making process from a first heating zone temperature of 205°C and a fan frequency of 70%, and a second heating zone temperature of 225°C and a fan frequency of 95%, to a first heating zone temperature of 185°C and a fan frequency of 50%, and a second heating zone temperature of 220°C and a fan frequency of 90%, resulted in insufficient melting of the polypropylene fibers in the felt material. Increasing the gap between the impregnation rollers from 1.7mm to 2.0mm prevented the melted polypropylene fibers from moving properly to the knot points, ultimately leading to reduced bending performance and interlayer cohesion. Increasing the board-making process from a first heating zone temperature of 205°C and a fan frequency of 70%, and a second heating zone temperature of 225°C and a fan frequency of 95%, to a first heating zone temperature of 215°C and a fan frequency of 80%, and a second heating zone temperature of 230°C and a fan frequency of 100%, and reducing the gap between the impregnation rollers from 1.7mm to 1.5mm, improved the board's bending performance and interlayer cohesion, but the rate of improvement slowed down.

[0086] Examples 8-10

[0087] Based on Example 1, the structure, felt-making process, and board-making process were modified according to Table 2.

[0088] Table 2 Test data for Examples 1 and 8-10

[0089]

[0090] The test data from Examples 1 and 8 show that when the cooling water temperature increases from 30°C to 80°C, the polypropylene fibers in the core layer of the board are not completely cooled and solidified, resulting in a decrease in the uniformity of the board thickness after exiting the cold setting zone. The test data from Comparative Examples 1 and 9 show that when the polypropylene fiber crystallization temperature decreases from 160°C to 110°C, the polypropylene fibers in the core layer of the board are not completely cooled and solidified, resulting in a decrease in the uniformity of the board thickness after exiting the cold setting zone. The test data from Comparative Examples 1 and 10 show that when the cooling line pressure decreases from 10t to 7t, the cooling surface pressure decreases from 130t to 70t, resulting in a decrease in the uniformity of the board thickness.

[0091] Comparative Example 1

[0092] Commercially available 2.5mm plywood

[0093] Table 3 Test data for Example 1 and Comparative Example 1

[0094]

[0095] The test data of Comparative Example 1 and Example 1 show that irregular mold appeared on the surface of Comparative Example 1 after being placed at 20°C for 12 days, while no mold or change was observed on the surface of Example 1 after being placed at 20°C for 20 days, indicating that the present invention has good resistance to mold.

[0096] Example 11

[0097] Using Example 1 as the substrate, 250g of two-component polyurethane adhesive was applied and adhered to XPS foam within 1 minute. A pressure of 0.1 MPa was applied and held for 24 hours to ensure that the polyurethane adhesive was completely cured.

[0098] Examples 12-16

[0099] Based on Example 11, the structure, felt-making process, and board-making process were modified according to Table 2.

[0100] Table 4 Test data for Examples 1 and 11-16

[0101]

[0102] The test data from Examples 11, 12, and 13 show that if the nonwoven fabric does not contain PE, the interlayer strength of the nonwoven fabric itself will be poor, resulting in poor interfacial bonding with XPS foam, and the failure site will appear in the interlayer of the nonwoven fabric. However, if the PE content in the nonwoven fabric is too high, after thermal lamination and cold setting, the specific flow resistance of the substrate will increase, making it difficult for the adhesive to fully wet the material interface, resulting in reduced interfacial bonding, and the failure site will be on the surface of the nonwoven fabric.

[0103] As can be seen from the test data of Examples 11 and 14, if the basis weight of the nonwoven fabric increases, the specific flow resistance of the substrate and the interfacial bonding force do not change significantly.

[0104] The test data from Examples 11, 15, and 16 show that if the basis weight of the adhesive film decreases, the pore size increases, and the pore spacing decreases, the specific flow resistance of the substrate decreases. Excessive adhesive penetration into the substrate results in less adhesive remaining at the interface for bonding, thus reducing interfacial adhesion. Conversely, if the basis weight of the adhesive film increases, the pore size decreases, and the pore spacing increases, the specific flow resistance of the substrate increases. Insufficient adhesive wetting of the material interface further reduces interfacial adhesion.

[0105] The composite board of the present invention has advantages such as high bending performance, interlayer cohesion, excellent thickness uniformity, mildew resistance, high air permeability and high interfacial bonding strength. It specifically solves the current pain points of the sandwich panels used in RVs, buses and vans, and further improves the product performance and customer satisfaction of such products.

[0106] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing an LWRT composite board, wherein the LWRT composite board comprises, from top to bottom, nonwoven fabric, a hot melt adhesive layer, a composite felt, a hot melt adhesive layer, and nonwoven fabric, characterized in that, Includes the following steps: 1) Glass fiber and polypropylene fiber are sequentially opened, dry carded, cross-laid and needle-punched to obtain composite felt material; The mass ratio of glass fiber to polypropylene fiber is 40~60:40~60; The glass fiber has a fiber length of 50-130 mm and a surface oil content of 0.15-0.35%. The polypropylene fiber has a fiber length of 46~76mm, a surface oil content of 0.35~0.55%, a crimp number of 7~12, a melt index of 22~40g / 10min, a melting point of 166~175℃, and a crystallization temperature of 110℃. The needle depth for acupuncture is 7-12 mm, and the needle density is 50-80 needles / cm. 2 ; The nonwoven fabric contains 20% polyethylene by mass and has a basis weight of 40-80 gsm. The hot melt adhesive layer is a polypropylene perforated adhesive film with a basis weight of 20~60gsm, a pore size of 0.3~1mm, and a pore spacing of 3~10mm*3~10mm. 2) The composite felt material obtained in step 1) is passed through the first heating zone, and the non-woven fabric and hot melt adhesive layer simultaneously follow the composite felt material from the upper and lower surfaces through the second heating zone. After hot bonding and cold setting, LWRT composite board is obtained. The temperature of the first heating zone is 185~215℃, and the fan frequency is 50~80%. The temperature of the second heating zone is 220~230℃, and the fan frequency is 90~100%. The conditions for cold setting include: the gap between the impregnation rollers is 1.5~2.0mm, and the cooling water recovery temperature is ≤30℃.

2. The preparation method according to claim 1, characterized in that, In step 1), the glass fiber is a short-cut fiber with a diameter of 17µm, a fiber length of 110mm, a linear density of 2400tex, and a surface oil content of 0.25%.

3. The preparation method according to claim 1, characterized in that, In step 1), the polypropylene fiber is a short fiber with a length of 60 mm, a linear density of 9 dtex, a surface oil content of 0.45%, a crimp number of 7, a melting point of 166℃, and an OIT ≥ 20 min.

4. The preparation method according to claim 1, characterized in that, The conditions for step 1) of cross-laying the net include: a width of 2600mm, 28 layers of netting, and a single net weight of 33g / m². 2 ; The needle depth for acupuncture is 9 mm, and the needle density is 70 needles / cm. 2 ; The feed rate for the dry combing process is 800~1100 kg / h.

5. The preparation method according to claim 1, characterized in that, In step 1), the nonwoven fabric has a thickness of 0.04 mm, a tensile strength ≥ 25 N, a thermal shrinkage rate ≤ 2%, and a basis weight CV% value ≤ 7%. The hot melt adhesive layer has a basis weight of 30 gsm, a pore size of 0.5 mm, a pore spacing of 7 mm * 7 mm, a thickness of 28 µm, a melting point of 145 °C, and the pores are arranged in a diamond and / or square pattern.

6. The preparation method according to claim 1, characterized in that, In step 2), the temperature of the first heating zone is 205°C, and the fan frequency is 70%. The temperature of the second heating zone is 225℃, and the fan frequency is 95%. The conditions for cold setting include: the gap between the impregnation rollers is 1.7 mm, the pressure of the impregnation rollers is 20 t, the gap between the line pressure holding rollers is 2.9 mm, the pressure of the line pressure holding rollers is 10 t, the gap between the surface pressure holding rollers is 2.9 mm, and the pressure of the surface pressure holding rollers is 130 t. The conditions for step 2) thermal bonding include: it is carried out in the second heating zone at a temperature of 225°C, a fan frequency of 95%, a hot roller gap of 1.5 mm, and a hot roller pressure of 3 t.

7. An LWRT composite board prepared by the preparation method according to any one of claims 1 to 6, wherein the LWRT composite board has an areal density of 980 to 1080 gsm and a thickness of 2.9 mm.

8. The application of the LWRT composite board according to claim 7 in improving the mechanical properties of the board, wherein the mechanical properties include one or more of bending properties, interlayer cohesion, air permeability and interfacial bonding strength.

9. The application of the LWRT composite board according to claim 7 in improving the mildew resistance of the board.

10. The application of the LWRT composite board according to claim 7 in improving the thickness uniformity of the board.

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