Bending-resistant thermoplastic hybrid injection molding composite structure and forming method thereof

Abstract

The invention discloses a bending-resistant thermoplastic hybrid injection molding composite structure which comprises continuous fiber reinforced thermoplastic resin and short fiber reinforced thermoplastic resin injected to the surface of the continuous fiber reinforced thermoplastic resin, adjacent interfaces of the continuous fiber reinforced thermoplastic resin and the short fiber reinforced thermoplastic resin have crystal bonding surfaces obtained by synchronous crystallization of the continuous fiber reinforced thermoplastic resin and the short fiber reinforced thermoplastic resin. The invention also provides a preparation method of the bending-resistant thermoplastic hybrid injection molding composite structure. According to the bending-resistant thermoplastic hybrid injection molding composite structure, the continuous fiber reinforced thermoplastic resin and the short fiber reinforced thermoplastic resin have matched crystallization pace, and finally, in the cooling process of the two materials, the two composite materials are crystallized at the same time, so that interfaces can be better fused, and the bonding surfaces have excellent adhesive force; and the product has good bending strength.

Description

Technical Field

[0001] The present invention belongs to the field of polymer composite materials, and in particular relates to a thermoplastic composite structure and a molding method thereof. Background Art

[0002] Thermoplastic composites have the advantages of light weight, high strength, heat resistance and recyclability, and are gradually becoming the preferred technology route for achieving lightweight automotive structural parts worldwide. Thermoplastic hybrid injection molding structures have the characteristics of continuous fiber sheets that are heated and formed into a skeleton and then injection molded. They do not require a time-consuming cross-linking curing process, so the molding cycle is short and the efficiency is high. A typical thermoplastic hybrid injection molding structure uses continuous fiber reinforced thermoplastic composites as the main load-bearing parts and short fiber reinforced homologous resins as secondary load-bearing parts. During the processing of thermoplastic composites, the long / short fiber hybrid injection molding structure can be easily and flexibly molded into various parts and components of varying complexity and precision, including parts for automobiles, aviation, electrical / electronic components, household appliances, etc.

[0003] Continuous fiber reinforced thermoplastic composites require a good impregnation effect, so relatively low viscosity resins are generally selected during the sheet production stage. Later, they need to undergo long-term heating, impregnation, and hot pressing. During the product molding stage, the resin needs to be rapidly overheated, which greatly reduces the molecular weight. The low molecular weight resin crystallizes faster during the cooling process, while the short fiber reinforced thermoplastic resin used for overmolding does not undergo a long-term thermal aging process and has a slow crystallization rate, which leads to different crystallization rates between the two. In addition, during the hybrid injection molding process, the continuous fiber reinforced thermoplastic sheet is heated to soften and then placed in the mold, and then the mold is closed and hot pressed. During this process, heating and insulation cannot be performed, which will result in a large amount of heat loss. The surface temperature is lower than the temperature during transfer, and finally injection molding is performed, resulting in a temperature difference between the continuous fiber sheet and the short fiber reinforced composite material, resulting in inconsistent cooling and crystallization of the melt. After many experiments, it has been shown that due to the inconsistent crystallization pace, the adhesion between the surfaces of the hybrid injection molded composite structure is relatively low. Under such weak adhesion conditions, the interface between the primary load-bearing component of the continuous fiber-reinforced composite and the short fiber-reinforced resin is damaged first, making the overmolded composite structure weaker than either of its components alone. Cracks may form at the interface of the overmolded composite structure, leading to problems such as mechanical performance degradation, premature aging, and product delamination during use. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology, and provide a bending-resistant thermoplastic hybrid injection molding composite structure with strong interface adhesion and strong bending resistance between the main load-bearing parts of continuous fiber reinforced thermoplastic composite materials and the secondary load-bearing parts of short fiber reinforced homologous resins, and its molding method.

[0005] In order to solve the above technical problems, the technical solution proposed by the present invention is: A bending-resistant thermoplastic hybrid injection-molded composite structure comprises a continuous fiber-reinforced thermoplastic resin and a short fiber-reinforced thermoplastic resin injected onto the surface (partial or entire surface) of the continuous fiber-reinforced thermoplastic resin. The short fiber-reinforced thermoplastic resin has a higher crystallization temperature than the continuous fiber-reinforced thermoplastic resin. During injection molding, the injection temperature of the short fiber-reinforced thermoplastic resin is higher than the surface temperature of the continuous fiber-reinforced thermoplastic resin after compression molding. The adjacent interface between the continuous fiber-reinforced thermoplastic resin and the short fiber-reinforced thermoplastic resin comprises a crystallization bonding surface obtained by synchronous crystallization of the two resins.

[0006] In the above-mentioned bending-resistant thermoplastic hybrid injection-molded composite structure, preferably, the crystallization temperature of the short fiber reinforced thermoplastic resin is 3-35°C higher than that of the continuous fiber reinforced thermoplastic resin, and during injection molding, the injection temperature of the short fiber reinforced thermoplastic resin is 20-50°C higher than the surface temperature of the continuous fiber reinforced thermoplastic resin after compression molding.

[0007] In the aforementioned bending-resistant thermoplastic hybrid injection-molded composite structure, preferably, resin B in the short fiber-reinforced thermoplastic resin is a homologous substance, copolymer, or homologous mixture of resin A in the continuous fiber-reinforced thermoplastic resin. Resin A and resin B are homologous substances with the same polarity. Based on the principle of like dissolves like, their interfacial bonding is enhanced.

[0008] In the above-mentioned bending-resistant thermoplastic hybrid injection-molded composite structure, preferably, the resin A and the resin B are thermoplastic resins, including one or more of polypropylene, polyamide, polyester and polycarbonate, more preferably polypropylene and polyamide.

[0009] In the above-mentioned bending-resistant thermoplastic hybrid injection molding composite structure, preferably, a first additive for reducing the crystallization rate of the resin is added to the continuous fiber reinforced thermoplastic resin, or a similar polymerization monomer for reducing the crystallization rate of the resin is added during the polymerization of the continuous fiber reinforced thermoplastic resin. More preferably, the first additive includes a toughening agent and a similar resin to resin A, and the crystallization temperature of this similar resin is lower than that of resin A. The toughening agent can be POE grafted maleic anhydride. The crystallization temperature and crystallization rate of the similar resin of resin A are lower than those of resin A. For example, if resin A is PA6, the melting point of the blend of resin A and its similar resin must be lower than 210°C, preferably PA11, PA12, etc. When continuous fiber reinforced thermoplastic resin is polymerized, the same type of polymerization monomer is added to reduce the crystallization rate of the resin. This means that resin A adopts the same type of copolymer, has a lower crystallization temperature than resin A, and has better toughness. For example, if resin A is polyamide PA6, the copolymers can be PA6 / 66, PA6 / 12, PA6 / 10, PA6 / 1010, and terpolymers PA6 / 66 / 12, PA6 / 66 / 1010, etc. If resin A is polypropylene, the copolymer can be ethylene-propylene copolymer.

[0010] In the aforementioned bending-resistant thermoplastic hybrid injection-molded composite structure, preferably, a second additive for accelerating crystallization is added to the short fiber-reinforced thermoplastic resin. More preferably, the second additive is a nucleating agent comprising a metal carboxylate and / or an organic phosphate. For example, Clariant's nucleating agent Cav102 is used.

[0011] In the above-mentioned bending-resistant thermoplastic hybrid injection molding composite structure, preferably, the fibers in the short fiber reinforced thermoplastic resin and the continuous fiber reinforced thermoplastic resin include one or more of carbon fiber, glass fiber, basalt fiber, aramid fiber and natural fiber. At the same time, the fiber types in the short fiber reinforced thermoplastic resin and the continuous fiber reinforced thermoplastic resin are consistent.

[0012] As a general technical concept, the present invention also provides a method for preparing the above-mentioned bending-resistant thermoplastic hybrid injection-molded composite structure, comprising the following steps: (1) First, the continuous fiber reinforced thermoplastic resin sheet is rapidly heated until its surface temperature is higher than the melting point, and then it is quickly transferred to the injection mold, and the mold is closed and hot-pressed to obtain the continuous fiber reinforced thermoplastic resin main bearing component; (2) Short fiber reinforced thermoplastic resin is then injected onto the surface of the continuous fiber reinforced thermoplastic resin main load-bearing member to obtain a short fiber reinforced thermoplastic resin secondary load-bearing member. The injection temperature is higher than the temperature of the continuous fiber reinforced thermoplastic resin main load-bearing member after molding. During the cooling process, the interface between the continuous fiber reinforced thermoplastic resin and the short fiber reinforced thermoplastic resin is cooled and crystallized synchronously to obtain a crystallized bonding surface, that is, a bending-resistant thermoplastic hybrid injection-molded composite structure is obtained.

[0013] A typical preparation method is as follows: First, a continuous fiber-reinforced thermoplastic resin is rapidly heated in an infrared or microwave device until its surface temperature is 30-80°C above its melting point. After equilibrium, it is quickly transferred to an injection mold, which is then closed and hot-pressed. Next, a short fiber-reinforced thermoplastic resin is injection-molded, with the injection temperature of the short fiber-reinforced thermoplastic resin being 20-50°C higher than the temperature of the continuous fiber-reinforced thermoplastic resin after molding. During the cooling process, the continuous fiber-reinforced thermoplastic resin and the short fiber-reinforced thermoplastic resin cool and crystallize, forming a flexurally resistant thermoplastic hybrid injection-molded composite structure.

[0014] The purpose of the present invention is to solve the problem of inconsistent temperature difference and crystallization speed between the two materials in a thermoplastic hybrid injection-molded composite structure, which leads to low bonding strength between the two materials. The structure includes structure (i) and structure (ii), and structure (i) and structure (ii) are connected by a hot-melt bonding surface of a certain area. Structure (i) is formed by hot pressing of a continuous fiber reinforced thermoplastic resin, and structure (ii) is formed by injection molding of a short fiber reinforced thermoplastic resin. Structure (i) is the main load-bearing member, and structure (ii) is a coating or a reinforcing rib structure. In order to ensure the bonding strength of structure (i) and structure (ii), in a more preferred embodiment, the present invention adds a first additive to the continuous fiber reinforced thermoplastic resin to reduce the crystallization speed of resin A (if the first additive uses a toughening agent, it can also increase the toughness at the same time), and adds a nucleating agent to the short fiber reinforced thermoplastic resin to accelerate the crystallization speed and reduce the crystallization time, thereby improving the matching degree of the crystallization of the two resins. At the same time, the crystallization temperature of the short-fiber-reinforced thermoplastic resin is higher than that of the continuous-fiber-reinforced thermoplastic resin. During the molding process, the processing temperature of the short-fiber-reinforced thermoplastic resin is raised, indirectly heating the surface of the continuous-fiber-reinforced thermoplastic resin. This synchronizes the crystallization reactions of the two structures, allowing the resins of the two composite materials to crystallize simultaneously. This hybrid structure exhibits excellent adhesion at the interface, and the finished product possesses good flexural strength. During use, the two structures will not experience interfacial delamination or degradation, and are widely used in automotive, aviation, electrical / electronic components, household appliances, and other parts.

[0015] In this invention, the nucleating agent in the short fiber-reinforced thermoplastic resin is heterogeneous nucleating, inducing the resin in the short fibers to participate in crystallization, resulting in higher strength while ensuring interfacial fusion. The continuous fiber-reinforced thermoplastic resin has lower crystallinity and relatively higher toughness. Under load, the forces at the bonding interface are transferred to the structure (ii) portion for buffering, protecting the relatively fragile bonding surface.

[0016] In the present invention, in order to ensure that the continuous fiber reinforced thermoplastic resin and the short fiber reinforced thermoplastic resin achieve certain functions, they both include one or more of the group consisting of anti-aging agents, antioxidants, and flame retardants.

[0017] Compared with the prior art, the advantages of the present invention are: The bending-resistant thermoplastic hybrid injection-molded composite structure of the present invention has a matching crystallization pace between the continuous fiber-reinforced thermoplastic resin and the short fiber-reinforced thermoplastic resin. Finally, during the cooling process of the two materials, the two composite materials crystallize at the same time, which can achieve better interface fusion, excellent adhesion on the bonding surface, and good bending strength of the product. During use, the two structures will not experience problems such as interface delamination and degradation. It can be widely used in spare parts such as automobiles, aviation, electrical / electronic components, and household appliances. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 Schematic diagram of the structure of the bending-resistant thermoplastic hybrid injection-molded composite structure in Example 1.

[0020] Figure 2 TEM images of the bending-resistant thermoplastic hybrid injection-molded composite structures in Example 3 and Comparative Example 1. DETAILED DESCRIPTION

[0021] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0022] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0023] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0024] Example 1: like Figure 1 As shown, the bending-resistant thermoplastic hybrid injection-molded composite structure of this embodiment includes a continuous fiber-reinforced thermoplastic resin and a short fiber-reinforced thermoplastic resin injected onto the surface of a portion of the continuous fiber-reinforced thermoplastic resin. The adjacent interfaces of the continuous fiber-reinforced thermoplastic resin and the short fiber-reinforced thermoplastic resin have a crystalline bonding surface obtained by synchronous crystallization of the two.

[0025] The materials for the preparation of the bending-resistant thermoplastic hybrid injection-molded composite structure of this embodiment are prepared as follows: 0.2% BASF antioxidant 1010 and Bruggemann antioxidant BRUGGOLEN H10 were added to both continuous fiber reinforced thermoplastic resin (PA6) and short fiber reinforced thermoplastic resin (PA66). At the same time, the glass fiber content in the continuous fiber reinforced thermoplastic resin was 67%, and the glass fiber content in the short fiber reinforced thermoplastic resin was 50%.

[0026] The molding process includes the following steps: A 3mm thick continuous fiber-reinforced thermoplastic resin is placed in an infrared heating furnace at the melting point of the main resin in the continuous fiber-reinforced thermoplastic resin + 30°C. It typically reaches the set temperature in 30 seconds and equilibrates for 40 seconds. The robot then quickly transfers the material to the injection mold of the injection molding machine, closes the mold, and performs hot pressing. Short fiber-reinforced thermoplastic resin is then injected onto the surface of the continuous fiber-reinforced thermoplastic resin. The injection temperature of the short fiber-reinforced thermoplastic resin is set at the melting point of the short fiber-reinforced thermoplastic resin + 30°C, forming a 1mm surface coating. The resin types used in the continuous fiber-reinforced thermoplastic resin and the short fiber-reinforced thermoplastic resin are shown in Table 1 below.

[0027] Example 2-4: As shown in Table 1, the resins of Examples 2-4 are nylon materials, and 4% wt of PoE-grafted maleic anhydride is added to some continuous fiber-reinforced thermoplastic resins; a nucleating agent is added to the short fiber-reinforced thermoplastic resin, such as 0.2% wt of Clariant nucleating agent Cav102 (carboxylate) added to polyamide.

[0028] Example 5-6: As shown in Table 1, the resins in Examples 5 and 6 are polyolefin materials, including copolymers and blends. The continuous fiber-reinforced thermoplastic resin in Example 5 is a copolymer with an ethylene content of 10%. The continuous fiber-reinforced thermoplastic resin in Example 6 is a blend of PP and EPDM with an EPDM content of 10%. The short fiber-reinforced thermoplastic resins are all PP supplemented with 0.2% by weight of Clariant's nucleating agent, Hostanox 4030.

[0029] Comparative Example 1-2: The main differences between Comparative Example 1-2 and Example 1 are shown in Table 1 below. In the comparative example, no first additive and no nucleating agent were added.

[0030] TEM images of the bending-resistant thermoplastic hybrid injection-molded composite structures in Example 3 and Comparative Example 1 are as follows: Figure 2 As shown in the figure, comparative example 1 has no crystallization at the interface, while example 1 produces obvious crystallization, which improves the interface bonding strength.

[0031] Flexural strength is generally used as an indicator of a material's ability to support (or withstand or sustain) a load when bent. When short-fiber-reinforced thermoplastic resins are overmolded into composite structures, flexural strength more readily reflects the level of good bonding strength achieved within the composite structure. Specimens were cut using a water jet to 80 mm in length, 10 mm in width, and 4 mm in thickness. Flexural testing was performed according to the GB / T 9341-2008 flexural test method, with no specified deflection, until test structure (i) and structure (ii) split, resulting in a sudden decrease in stress. The maximum stress was recorded. The results are shown in Table 2 below.

[0032] Table 1: Formulas of Examples and Comparative Examples

[0033] Table 2: Performance parameters of the composite structures of the embodiments and comparative examples

Claims

1. A bending-resistant thermoplastic hybrid injection-molded composite structure comprising a continuous fiber-reinforced thermoplastic resin and a short fiber-reinforced thermoplastic resin injected onto the surface of the continuous fiber-reinforced thermoplastic resin, characterized in that: The short fiber reinforced thermoplastic resin has a higher crystallization temperature than the continuous fiber reinforced thermoplastic resin. During injection molding, the injection temperature of the short fiber reinforced thermoplastic resin is higher than the surface temperature of the continuous fiber reinforced thermoplastic resin after compression molding. The adjacent interface between the continuous fiber reinforced thermoplastic resin and the short fiber reinforced thermoplastic resin has a crystallization bonding surface obtained by synchronous crystallization of the two.

2. The bending-resistant thermoplastic hybrid injection-molded composite structure according to claim 1, characterized in that: The crystallization temperature of the short fiber reinforced thermoplastic resin is 3-35° C. higher than that of the continuous fiber reinforced thermoplastic resin. During injection molding, the injection temperature of the short fiber reinforced thermoplastic resin is 20-50° C. higher than the surface temperature of the continuous fiber reinforced thermoplastic resin after compression molding.

3. The bending-resistant thermoplastic hybrid injection-molded composite structure according to claim 1 or 2, characterized in that: The resin B in the short fiber reinforced thermoplastic resin is a homologue, copolymer or homologue mixture of the resin A in the continuous fiber reinforced thermoplastic resin.

4. The bending-resistant thermoplastic hybrid injection-molded composite structure according to claim 3, characterized in that: The resin A and the resin B are thermoplastic resins, including one or more of polypropylene, polyamide, polyester and polycarbonate.

5. The bending-resistant thermoplastic hybrid injection-molded composite structure according to claim 3, characterized in that: The continuous fiber reinforced thermoplastic resin is added with a first additive for reducing the crystallization rate of the resin, or the continuous fiber reinforced thermoplastic resin is added with a similar polymerization monomer for reducing the crystallization rate of the resin during polymerization.

6. The bending-resistant thermoplastic hybrid injection-molded composite structure according to claim 5, characterized in that: The first additive includes a toughening agent and a resin similar to resin A, and the crystallization temperature of the resin similar to resin A is lower than that of resin A.

7. The bending-resistant thermoplastic hybrid injection-molded composite structure according to claim 3, characterized in that: A second additive for accelerating crystallization speed is added to the short fiber reinforced thermoplastic resin.

8. The bending-resistant thermoplastic hybrid injection-molded composite structure according to claim 7, characterized in that: The second additive is a nucleating agent, and the nucleating agent includes a carboxylic acid metal salt and / or an organic phosphate.

9. The bending-resistant thermoplastic hybrid injection-molded composite structure according to claim 1 or 2, characterized in that: The fibers in the short fiber reinforced thermoplastic resin and the continuous fiber reinforced thermoplastic resin include one or more of carbon fiber, glass fiber, basalt fiber, aramid fiber and natural fiber. At the same time, the fiber types in the short fiber reinforced thermoplastic resin and the continuous fiber reinforced thermoplastic resin are the same.

10. A method for preparing a bending-resistant thermoplastic hybrid injection-molded composite structure according to any one of claims 1 to 9, characterized in that: The following steps are involved: (1) First, the continuous fiber reinforced thermoplastic resin sheet is rapidly heated until its surface temperature is higher than the melting point, and then it is quickly transferred to the injection mold, and the mold is closed and hot-pressed to obtain the continuous fiber reinforced thermoplastic resin main bearing component; (2) Short fiber reinforced thermoplastic resin is then injected onto the surface of the continuous fiber reinforced thermoplastic resin main load-bearing member to obtain a short fiber reinforced thermoplastic resin secondary load-bearing member. The injection temperature is higher than the temperature of the continuous fiber reinforced thermoplastic resin main load-bearing member after molding. During the cooling process, the interface between the continuous fiber reinforced thermoplastic resin and the short fiber reinforced thermoplastic resin is cooled and crystallized synchronously to obtain a crystallized bonding surface, that is, a bending-resistant thermoplastic hybrid injection-molded composite structure is obtained.

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