Fiber-reinforced composite molding containing internal release agent

Abstract

A fiber-reinforced composite molded article which is obtained by molding reinforcing fibers and an epoxy resin, while containing a silicone oil as an internal mold release agent, and which is characterized in that the fragment ion intensity ratio A / B as detected if the molded article surface is analyzed by time-of-flight secondary ion mass spectrometry is expressed by the relational expression 3 ≤ A / B ≤ 20. A: The intensity of a fragment ion that has the highest intensity among the fragment ions derived from the silicone oil B: The intensity of a fragment ion that has the highest intensity among the fragment ions derived from the epoxy resin A fiber-reinforced resin molded article according to the present invention is capable of achieving high productivity and high quality by effectively exhibiting releasability from a mold with a small addition amount of a mold release agent without using an external mold release agent, while being capable of exhibiting high adhesion to other members without requiring a special surface treatment such as sanding.

Description

Technical Field

[0001] The present invention relates to a fiber-reinforced composite molded article using a mold release agent for fiber-reinforced composite materials.

Background Art

[0002] Fiber-reinforced resin materials are used in a wide range of fields such as the aircraft field, the automotive field, and industrial uses such as sports and leisure applications because of their high strength and high rigidity. Such fiber-reinforced resin materials are molded by various molding methods such as resin transfer molding, autoclave molding, pultrusion molding, compression molding, injection molding, and filament winding molding according to their uses and shapes. When these molding methods are selected, since it is necessary to demold the molded article from the mold after molding, mold release agents are widely used.

[0003] For example, in Patent Document 1, a mold release agent (external mold release agent) is applied (or sprayed) to the mold, and a thin film made of a mold release agent component is formed on the mold surface to ensure mold release from the molded article. On the other hand, as in Patent Document 2, a mold release agent (internal mold release agent) is added in advance to a resin composition made of a thermosetting resin, and when the resin composition cures in the mold, the mold release agent component bleeds out on the surface of the molded article to exhibit mold release from the mold. This method is also adopted.

[0004] In addition, as in Patent Document 3, a technique of adding liquid silicone to provide a liquid epoxy resin composition that facilitates mold release from the mold and a liquid epoxy resin molding material having excellent continuous moldability, and as in Patent Document 4, there are also examples that can provide a fiber-reinforced composite material capable of exhibiting excellent mold release properties using a fluorine-based mold release agent.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] On the other hand, in the molding method using an external release agent as shown in Patent Document 1, the releasability from the mold surface decreases with each molding, so it is necessary to frequently apply (or spray) the release agent on the mold surface, leading to an increase in the cost and labor of molding. In particular, when the resin is an epoxy resin, the adhesiveness to metal is strong, and resin may remain on the mold surface as burrs after molding, which requires time and cost for deburring and may also damage the surface quality of the molded product.

[0007] Also, in the method of adding an internal release agent into an epoxy resin composition as shown in Patent Document 2, in order to ensure sufficient releasability depending on the release agent, it is necessary to add a large amount of up to about 10 parts by mass of the release agent with respect to 100 parts by mass of the total resin. However, since not all of the added internal release agent bleeds out to the surface of the molded product during curing and most remains in the molded product, a decrease in the physical and mechanical properties of the molded product is also a concern when the addition amount is large.

[0008] In addition, the polyether and epoxy-modified liquid silicone used in Patent Document 3 do not have a sufficient effect of expressing releasability with respect to epoxy resin, and it is difficult to obtain a molded product with a small amount of addition without using an external release agent in molding for industrial applications based on thin-walled and complex shapes.

[0009] Furthermore, the release agent used in Patent Document 4 is described as having a melting point or softening point of 25°C or higher and 100°C or lower in order to reduce bleedability for materials that are stored at low temperatures before curing, such as prepregs and sheet molding compound materials. For a release agent that solidifies at room temperature like this, it may increase the hardness of the material itself, leading to a decrease in handleability and potentially lowering the mechanical properties after molding. Also, although there is a description that it becomes unnecessary to frequently apply an external release agent because there is no index for a good release state, it has not reached the point of providing a material that can be molded without applying an external release agent.

[0010] On the other hand, in post-processing steps such as the adhesion step or painting step of the molded product with other parts (made of metal or fiber-reinforced resin), the adhesiveness and adhesion to adhesives and paints are required, which is completely opposite to the molding process. Since the release agent layer formed on the surface of the molded product may cause poor adhesion or paint peeling, it is necessary to sufficiently remove the surface release agent layer by sanding or the like. The removal of this release agent leads to a large amount of time and cost as the release agent layer formed on the surface of the molded product becomes thicker.

[0011] Therefore, there is a demand for a process that can release from the mold with the minimum necessary amount of internal release agent and can be adhered with a simpler adhesion pretreatment, but there has been no material or molded product that can achieve both the contradictory properties of release property and adhesiveness.

[0012] In view of the various problems in the prior art mentioned above, an object of the present invention is to provide a fiber-reinforced composite molded product that, when using an epoxy resin composition added with an internal release agent as a molding material for a fiber-reinforced composite molded product, can effectively exhibit release property from the mold with a small amount of internal release agent added without using an external release agent, achieving high productivity and quality, and can exhibit high adhesiveness to other parts without performing special surface treatment such as sanding treatment.

Means for Solving the Problems

[0013] As a result of various studies on the formulation and adhesiveness of internal release agents in order to solve the above problems, the present inventors have found that in the fiber-reinforced composite molded article shown below, while the mold release property from the mold is good, a fiber-reinforced composite molded article that exhibits high adhesiveness with only a simple degreasing treatment without sanding, and a joined structure in which it is joined to other members can be realized.

[0014] That is, the present invention has the following configurations. (1) A fiber-reinforced composite molded article formed by containing silicone oil as an internal release agent in a reinforcing fiber and an epoxy resin, wherein when the surface of the molded article is analyzed by time-of-flight secondary ion mass spectrometry, the ratio of the fragment ion intensities detected is represented by the following formula (I). A fiber-reinforced composite molded article characterized by this. 3 ≦ A / B ≦ 20 ··· (I) A: The intensity of the fragment ion having the highest intensity among the fragment ions derived from the silicone oil B: The intensity of the fragment ion having the highest intensity among the fragment ions derived from the epoxy resin (2) The fiber-reinforced composite molded article according to (1), which further satisfies the following formula (II). 3 ≦ A / B ≦ 5 ··· (II) (3) The fiber-reinforced composite molded article according to (1) or (2), wherein the contact angle of the surface of the fiber-reinforced composite molded article with respect to water is 90 degrees or more. (4) The fiber-reinforced composite molded article according to any one of (1) to (3), wherein the silicone oil is a terminally modified silicone oil. (5) The fiber-reinforced composite molded article according to any one of (1) to (4), wherein the viscosity of the silicone oil is 50 mm 2 / s or more and 1,000 mm 2 / s or less. (6) The fiber-reinforced composite molded article according to any one of (1) to (5), wherein the functional group equivalent of the silicone oil is 300 g / mol or more and 2,000 g / mol or less. (7) The fiber-reinforced composite molded article according to any one of (1) to (6), wherein the addition amount of the silicone oil is 0.1 part by mass or more and 1 part by mass or less with respect to 100 parts by mass of the epoxy resin. (8) A joined structure in which the fiber-reinforced composite molded article according to any one of (1) to (7) is joined to another member with an adhesive. (9) The joined structure according to (8), which is joined without performing pretreatment other than degreasing.

Advantages of the Invention

[0015] The fiber-reinforced resin molded article in the present invention can achieve high productivity and quality by effectively exhibiting mold release properties with a mold with a small addition amount of a mold release agent and without using an external mold release agent, and can exhibit high adhesiveness to other members without performing special surface treatment such as sanding treatment.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0017] The fiber-reinforced composite molded article of the present invention is a fiber-reinforced composite molded article formed by containing silicone oil as an internal mold release agent in reinforcing fibers and an epoxy resin, and when the surface of the molded article is analyzed by time-of-flight secondary ion mass spectrometry, the ratio of the fragment ion intensities detected is represented by the relationship of the following formula (I), and more preferably, it is a fiber-reinforced composite molded article characterized by satisfying the relationship of formula (II). 3 ≦ A / B ≦ 20 ··· (I) 3 ≦ A / B ≦ 5 ··· (II) A: Intensity of the fragment ion with the highest intensity among the fragment ions derived from the silicone oil B: Intensity of the fragment ion with the highest intensity among the fragment ions derived from the epoxy resin

[0018] Hereinafter, the present invention will be described in detail with reference to the drawings together with embodiments. (Matrix resin) The epoxy resin used in the fiber-reinforced composite molded article of the present invention is not particularly limited as long as it is a compound having two or more epoxy groups in the compound. For example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD type epoxy resin, naphthalene type epoxy resin, biphenyl type epoxy resin, glycidylamine type epoxy resin, dicyclopentadiene type epoxy resin, phenol novolac type epoxy resin, aliphatic epoxy resin, alicyclic epoxy resin, prepolymers of the above epoxy resins, and copolymers of the above epoxy resins and other polymers such as polyether-modified epoxy resins and silicone-modified epoxy resins can be mentioned. These may be used alone or in combination of two or more.

[0019] In addition, the epoxy resin in the present invention is preferably cured using various curing agents, such as acid anhydride-based curing agents, amine-based curing agents, phenol-based curing agents, and thiol-based curing agents, because the curability and the properties of the cured product can be adjusted. In particular, when an acid anhydride-based curing agent is used, it is generally preferable from the viewpoint of improving heat resistance and chemical resistance, and when an amine-based curing agent is used, it is generally preferable from the viewpoint of low-temperature curability and high adhesiveness.

[0020] An isocyanate component may be used as another component in the present invention to increase heat resistance. The isocyanate compound is not particularly limited as long as it has an average of two or more isocyanate groups in one molecule, and known aliphatic isocyanates and aromatic isocyanates can be used. Polyisocyanate compounds and the like may be used alone or in a mixture of two or more.

[0021] Also, when using these isocyanates and adding an internal mold release agent having a reactive functional group, it is desirable that the reactivity with the functional group be appropriate. In particular, when using aromatic isocyanates, since the reactivity is higher compared to aliphatic isocyanates, it is likely to react with the modified group of the added silicone mold release agent, and it is necessary to increase the addition amount of the internal mold release agent itself or the functional group equivalent. On the other hand, it is difficult to control for mold release properties and the expression of high physical properties of the fiber-reinforced composite molded article, but the mold release agent can regularly and uniformly form a layer on the surface of the molded article.

[0022] Furthermore, the resin may contain other fillers and additives within a range that does not impair the object of the present invention according to the required properties. For example, curing accelerators, inorganic fillers, flame retardants, conductivity imparting agents, crystal nucleating agents, ultraviolet absorbers, antioxidants, vibration damping agents, antibacterial agents, insect repellents, deodorants, anti-coloring agents, heat stabilizers, lubricants, antistatic agents, plasticizers, coloring agents, pigments, dyes, foaming agents, foam suppressants, coupling agents, and the like can be mentioned.

[0023] [Reinforcing fiber] The reinforcing fiber in the present invention is not particularly limited, and carbon fiber, glass fiber, aramid fiber, etc. can be used, and furthermore, a mixed reinforcing fiber thereof can be used. Among them, from the viewpoints of preferably expressing high mechanical properties and ease of designing such properties, it is preferable to contain carbon fiber. Also, regarding the fiber form, a continuous fiber form, a short fiber form, etc. can be appropriately selected.

[0024] [Internal mold release agent] Examples of the internal release agent added to the fiber-reinforced composite molded article of the present invention include metal soaps, polyethylene wax, animal and plant waxes such as carnauba wax, fatty acid esters, silicones, fluorine-based nonionic surfactants, etc. Among them, silicone-based release agents are preferred because they have excellent release properties. By using silicone oil among silicone-based release agents, the impregnation property of the resin composition into the reinforcing fibers can be improved. Since the release agent is liquid, it is possible to prevent the occurrence of unevenness due to the release agent being filtered by the fibers during impregnation into the reinforcing fibers. Furthermore, in materials handled in a semi-cured state such as prepregs and sheet molding compounds, the hardness of the semi-cured material can be kept soft. In particular, as the silicone oil, a modified silicone oil having reactivity in which a functional group R 1 from R 3 is introduced into the side chain or terminal of polysiloxane represented by the following formula (I) or (II) is more preferred.

[0025]

Chemical formula

[0026]

Chemical formula

[0027] Here, R 1 , R 2 represent a functional group containing any one of an amino group, an epoxy group, a carboxyl group, a thiol group, a carbinol group, a methacryl group, and a phenol group. R 3 is a methyl group, an amino group, an epoxy group, a carboxyl group, a thiol group, a carbinol group, a methacryl group, or a phenol group.

[0028] The presence of such a functional group R enables the functional group R to react with the matrix resin within the matrix resin after molding, thereby immobilizing the mold release agent component within the matrix resin. This suppresses the bleed-out of the mold release agent component to the surface of the molded article over time and also suppresses a decrease in adhesive strength during the adhesion step of the molded article. This is because when not immobilized by the matrix resin and the functional group R, due to changes over time, the mold release agent component remaining inside the molded article moves to the surface side, forming a weak layer at the adhesive interface or the coating film interface, leading to the progression of peeling. In contrast, the immobilization results in a peeling suppression effect.

[0029] Also, the length and structure of the siloxane present between two functional groups R in the same molecule or between the functional group R and the siloxane chain end have a significant impact on both mold release properties and adhesiveness. Examples of such functional groups R include an amino group, an epoxy group, a carboxyl group, a thiol group, a carbinol group, a methacryl group, a phenol group, etc., and these can be appropriately selected from among them. Among these, thiol group and carboxyl group modification have relatively low reactivity with epoxy resins compared to amino group and carbinol group modification, so a bleed amount sufficient to exhibit mold release properties can be ensured with a small amount of addition. Also, compared to ether and epoxy modification, the compatibility is high, and it can be well dispersed in the matrix resin, so it can bleed uniformly on the surface of the molded article, and good mold release properties can be stably obtained. Also, as the modification site, side chain modification as in formula (I) is common and can be selected according to the resin and molding conditions. If it is both-end or end modification as in formula (II), the variation in functional group equivalent is small, and it is easy to control the behavior within the matrix resin, so the variation in the degree of manifestation of mold release properties also becomes small.

[0030] Furthermore, in order to achieve demolding from the mold with the minimum necessary addition amount, it is necessary to finely disperse the internal release agent in the epoxy resin with a particle size in the nano- to several micrometer order. This is because only the release agent components existing at a very close distance to the mold surface can form a release agent layer when the epoxy resin cures. Therefore, when the release agent is dispersed in a coarse state in the uncured epoxy resin, the particle density of the release agent decreases, so the area where there is no release agent component, that is, the area where the epoxy resin directly contacts the mold, increases, resulting in extremely deteriorated mold release properties. Therefore, the viscosity of the release agent is preferably 50 mm 2 / s or more and 1,000 mm 2 / s or less. When the viscosity is lower than 50 mm 2 / s, it is difficult to handle during formulation and the separation from the matrix resin becomes faster. When it is higher than 1,000 mm 2 / s, it becomes difficult to finely disperse during stirring after stirring.

[0031] Also, the functional group equivalent, that is, the molecular weight per functional group R, is preferably 300 g / mol or more and 2,000 g / mol or less. When the functional group equivalent is smaller than 300 g / mol, the ratio of the siloxane chains that exhibit mold release properties with respect to the addition amount of the release agent decreases, so the addition amount must be increased. When it is larger than 2,000 g / mol, the compatibility with the epoxy resin decreases, so it aggregates in the resin and cannot bleed uniformly to the surface. In addition, it may cause poor appearance of the molded product and deterioration of the mechanical properties of the molded product.

[0032] Furthermore, the addition amount of these internal release agents is preferably 0.1 part by mass or more and 1 part by mass or less with respect to 100 parts by mass of the epoxy resin. If it is outside this range, when the resin composition for fiber-reinforced resin materials is being molded or in subsequent processes, there may be problems with mold release due to insufficient release agent, or excessive bleed-out of the release agent may hinder processes such as adhesion and painting of the molded product. Also, when using a two-component resin as the base for adding the internal release agent, it may be added to either the main agent or the curing agent, or it may be added after mixing the main agent and the curing agent. Furthermore, the temperature during addition is preferably below the temperature at which the release agent and the resin can react, and at a temperature at which the resin and the release agent can be stirred and mixed to a suitable viscosity.

[0033] (Fiber-reinforced composite molded product) Figure 1 is a diagram schematically showing the state of the release agent on the surface of a fiber-reinforced composite molded product, comparing the concept of the manifestation form of the effects of the present invention with the prior art. Conventionally, when a silicone release agent is used to achieve high mold release during the molding of fiber-reinforced composite molded products, it is considered sufficient to form a uniform release agent layer on the surface of the molded product, regardless of whether an external release agent or an internal release agent is used. When ensuring mold release by adding a large amount of a conventional internal release agent (Figure 1: Prior art (a)), a dense layer of the release agent component is formed on the epoxy resin. At this time, since the epoxy resin component is covered by the release agent layer, it is not exposed on the surface (a-1). At this time, since the hydrophobicity of the surface increases, the wettability with respect to polar liquids such as adhesives and paints deteriorates, and thus the contact angle (θ) with respect to water shows 90 degrees or more (a-3). On the other hand, since the release agent layer has extremely low reactivity, the adhesiveness with respect to adhesives and paints decreases.

[0034] Conversely, in the case of the surface of a molded product with low mold release property shown in the prior art (b), since the film of the mold release agent is distributed in a patchy manner on the surface of the molded product as shown in (b-1), the epoxy resin is exposed on the surface in an area of the order of several tens of micrometers square or more. Therefore, the mold and the resin adhere strongly at the exposed portion of the epoxy resin, and a large amount of energy is required to break this bond, resulting in a significant decrease in the mold release property. At this time, the wettability of the surface of the molded product is such that, since the epoxy resin itself has some polarity, the contact angle is lower than that in (a-3), and is approximately 70 to 80 degrees (b-3).

[0035] In contrast to these prior arts, the surface state of the fiber-reinforced composite molded product in the present invention (c) is in the state shown in (c-1). Briefly speaking, the surface (c-1) of the molded product of the present invention is in an intermediate state between (a-1) and (b-1), and the epoxy resin component is exposed in the gaps of the mold release agent component. The difference from the prior art (b) is that this gap region is very minute (on the order of several nanometers to several micrometers square) and is distributed without bias. Although the surface area of the mold release agent layer decreases due to the exposure of the resin component, a sufficient amount of the mold release agent is present on the surface of the molded product, and the macro surface property of wettability does not change (c-3). Further, since the resin components exposed in the gaps of the mold release agent layer are distributed without bias in a very narrow minute region (on the order of several nanometers to several micrometers square), an excessive amount of energy is not required to break the adhesion with the mold. Therefore, the molded product can be demolded from the mold with a load sufficiently low comparable to that in the prior art (a).

[0036] On the one hand, since mold release property is exhibited, it seems that adhesiveness with adhesives or paints cannot be exhibited without special treatment. However, the molded article of the present invention exhibits sufficient adhesiveness with only a pretreatment of degreasing level. Although the mechanism has not been fully elucidated, the present inventors presume that the modified group R of the mold release agent (silicone oil) described above contributes. In the mold release agent layer formed by bleeding out on the surface of the molded article, it is considered that there is a modified group R that remains without reacting with the epoxy resin, unlike the inside of the molded article. In particular, the outermost mold release agent component in contact with the adhesive is considered to precipitate from the molded article earliest, and it is presumed that there are relatively many unreacted residues R. Therefore, it is considered that this residue R forms a strong bond at the interface with the surface of the molded article by reacting with these molecules during curing when an adhesive or paint is applied, thereby exhibiting strong adhesiveness.

[0037] In order to exhibit both such mold release property and adhesiveness, it is necessary that both components derived from the internal mold release agent (silicone oil) and components derived from the epoxy resin are uniformly present on the surface of the molded article without bias. As an index for quantifying the component ratio, the fragment ion intensity measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS) is used.

[0038] TOF-SIMS analysis is an analytical method in which pulsed ions (primary ions) are irradiated onto the surface of a sample placed in ultra-high vacuum, and fragment ions (secondary ions) released with a certain kinetic energy from the sample surface are detected by a time-of-flight mass spectrometer. Secondary ions accelerated with the same energy pass through the analyzer at a speed corresponding to their mass. Since the distance to the detector is constant, the time (flight time) required to reach the detector is a function of the mass. By precisely measuring the distribution of this flight time, the mass distribution of the secondary ions, that is, the mass spectrum, can be obtained. By analyzing this mass spectrum, organic and inorganic substances present on the sample surface can be identified, and information regarding the abundance can be obtained from the peak intensity. Further, by converging the primary ion beam to 1 μm or less, analysis of minute parts and imaging measurement (distribution observation) with high spatial resolution are possible.

[0039] Regarding the fiber-reinforced composite molded article of the present invention, when analyzed by time-of-flight secondary ion mass spectrometry, it is necessary that the ratio of the fragment ion intensities detected satisfies the relationship of the following formula (I), and more preferably, is represented by formula (II). 3 ≦ A / B ≦ 20 ··· (I) 3 ≦ A / B ≦ 5 ··· (II) A: The intensity of the fragment ion having the highest intensity among the fragment ions derived from the silicone oil B: The intensity of the fragment ion having the highest intensity among the fragment ions derived from the epoxy resin

[0040] When the ionic strength ratio represented by formulas (I) and (II) is less than 3, as shown in Fig. 1(b-2), many fragment ions derived from the epoxy resin (indicated by "EP" in (b-2)) are detected. That is, since the silicone oil aggregates before the epoxy resin cures, it cannot be uniformly deposited on the surface of the molded product, indicating that the epoxy resin is overly exposed and the target mold release property cannot be achieved. Also, when the ionic strength ratio is greater than 20, it means that there are extremely many fragment ions derived from the silicone oil released from the surface of the molded product (indicated by "Si" in Fig. 1(a-2)), which means that the mold release agent component covers the entire surface of the molded product too much. Also, an increase in the ionic strength ratio means that the distribution of the mold release agent increases not only in the surface direction but also in the thickness direction of the molded product. When the high-concentration region of the mold release agent component spreads in the thickness direction, that region becomes a mechanically fragile region, so sufficient adhesiveness cannot be exhibited as it is, and it becomes necessary to physically remove the mold release agent layer by sanding or the like. If the ionic strength ratio is 20 or less, the mold release agent layer is appropriate in both the surface direction and the thickness direction, which is preferable because adhesiveness can be exhibited only by degreasing treatment with a solvent such as alcohols. Furthermore, if it is 5 or less, adhesiveness can be further enhanced while ensuring the mold release property.

[0041] Such fragment ions derived from silicone oil and epoxy resin can detect many ions with various masses. Examples of the fragment ions detected as being derived from silicone oil include, for example, 73 SiC 3 H 9 +、 147 SiC 5 H 15 O+、 207 Si 3 C 5 H 15 O 3 + and so on. Also, since the fragment ions derived from the epoxy resin vary depending on the types of the epoxy resin and curing agent used, they cannot be uniquely shown. However, for example, in the case of bisphenol A type epoxy resin × amine-based curing agent, 107 C 7 H 7O+, 135 C 9 H 11 O+, 42 C 2 H 4 N+, 44 C 2 H 6 N+, 58 C 3 H 8 O+, C, H, O+, C, H, N+, C, H, N+, C, H, N+, CxHy+ etc. are detected as fragment ions. Note that the calculation of ion intensity is performed by Poisson correction on the observed intensity. Poisson correction is to supplement the ion intensity led to the mass spectrometer during the dead time in TOF-SIMS, and the intensity increases after correction compared with before correction. Among various fragment ions derived from silicone oil and epoxy resin calculated in this way, the ratio of the fragment ion with the highest intensity (i.e., the largest number) is taken as an index of the surface state. However, the method of taking the ratio is not limited to this, and the intensity ratio can also be taken with the sum of a plurality of ion intensities.

[0042] Also, in the fiber-reinforced composite molded product according to the present invention, it is preferable that the contact angle of the molded product surface with respect to water is 90 degrees or more. As described above, the contact angle is an index for ensuring mold release property. When it is less than 90 degrees, it means that the mold release agent layer cannot exhibit the mold release property, and when it is 90 degrees or more, a high mold release property can be exhibited.

[0043] The base material for forming the fiber-reinforced composite molded product of the present invention and the forming method are not particularly limited, and known materials and forming methods can be applied. For example, as an application example of the base material for forming, a sheet molding compound (SMC) base material in which chopped strands cut to a fiber length of about 0.1 mm to 5 mm are dispersed in a mat shape and impregnated with a matrix resin, or a prepreg base material in which continuously aligned reinforcing fibers in one direction are impregnated with a matrix resin can be used. Further, in these base materials, in the fiber-reinforced resin molded product obtained by press molding or autoclave molding, excellent mold release properties can be obtained and high productivity can be achieved. However, not limited to these reinforced fiber base materials, the resin composition of the present invention can also be applied to various molding methods such as resin transfer molding, drawing molding, injection molding, and filament winding molding. And in the fiber-reinforced resin molded product obtained from these above-mentioned base materials and molding methods, high productivity can be similarly realized.

[0044] In particular, in the fiber-reinforced composite molded product of the present invention, it is preferable that the volume ratio of the reinforcing fiber to the resin composition is 10 to 90%. If the volume ratio is less than 10%, even if the mold release property is good, it is likely to break under the local load applied to the molded product during demolding. If it is more than 90%, the absolute amounts of the resin and the mold release agent present on the surface of the molded product decrease, which may cause demolding failure.

[0045] Furthermore, the molding temperature during the curing molding of the fiber-reinforced composite molded product of the present invention is preferably 30°C or higher and 200°C or lower. When the molding temperature is less than 30°C, the curing reaction proceeds while the viscosity during molding remains high. When the molding temperature exceeds 200°C, in the case of a fast-curing resin, the molding time becomes too short, and the bleed-out of the mold release agent is suppressed.

[0046] Furthermore, when the fiber-reinforced composite molded article of the present invention is molded by press molding, it is preferable to flow the resin so that the area ratio after molding to the area before molding is 300% or less. High-cycle molding that requires reduction of the release agent treatment time often selects press molding. However, when molding is performed at a flow rate greater than 300%, flow bias is likely to occur, and accordingly, resin and release agent contained therein are biased, resulting in poor release.

[0047] Furthermore, when the fiber-reinforced composite molded article of the present invention is obtained by a method of disposing a reinforcing fiber laminate in a cavity of a mold and injecting the resin into the cavity from a resin injection port provided in the mold, it is preferable to stir the resin immediately before the start of injection. This is because, in a one-component or two-component resin composition added with an internal release agent, molding is carried out in a state where the internal release agent is well dispersed in the resin composition, so that the variation in the release property expression effect is reduced.

[0048] Furthermore, the fiber-reinforced composite molded article of the present invention can exhibit its effect even when obtained from a material in which it is difficult to control the release agent in the resin composition, such as a prepreg or a sheet molding compound (SMC). When molding is performed based on such an intermediate substrate, the time until molding is preferably within 3 months after the preparation of the resin composition before curing. This is because, in a material that requires long-term storage in a semi-cured state such as a prepreg or SMC, the degree of curing varies due to the long continuation of the semi-cured state, so that the flow during molding becomes non-uniform, and therefore, the bleed of the release agent to the surface of the molded article is also non-uniform, resulting in deterioration of the release property. Furthermore, in order to ensure better release property, it is preferably within 2 months after the preparation.

[0049] [Bonding structure] The fiber-reinforced composite molded product in the present invention can be used as a joined structure joined by an adhesive to a part made of metal or another fiber-reinforced composite molded product. Particularly in combination with a fiber-reinforced composite molded product, a structure that is lighter and has higher rigidity than metal can be realized by joining with an adhesive. Further, when performing adhesive bonding, high adhesive strength can be achieved without requiring a special pretreatment process other than degreasing. However, in order to achieve higher adhesive quality, energy ray treatments such as atmospheric pressure plasma treatment, corona treatment, and ultraviolet treatment can also be employed. These energy ray treatments enable faster processing and automation of the process compared to pretreatment by polishing such as sanding treatment. Further, by imparting high energy to the surface of the molded product, a part of the structure of the mold release agent component on the surface of the molded product is destroyed, a hydrophilic functional group that has a favorable effect on adhesion is introduced, or the surface is roughened on the nano-order to exhibit an anchor effect, thereby further enhancing the reliability of adhesion.

Example

[0050] Hereinafter, the present invention will be described more specifically with reference to examples. For the contact angle on the surface of the molded product and the measurement by TOF-SIMS and calculation of the ion intensity ratio, for reasons of analysis, measurements were made on a resin plate not containing reinforcing fibers. At this time, the following results are considered to be the same even in the fiber-reinforced composite molded product containing reinforcing fibers. Further, fiber-reinforced composite molded products were molded using resins having the same composition as the resin molded product in the contact angle and TOF-SIMS analysis, and the results of evaluating the mold release property and adhesiveness by the following method are shown in Tables 1 and 2 together. Note that the present invention is not limited thereto.

[0051] [Resin material] In order to obtain the resin compositions of each example and comparative example, the following resin raw materials were used. Note that the numerical values of the internal mold release agent in the resin composition columns in Tables 1 and 2 indicate the content, and the unit is "parts by mass" with respect to other matrix resin raw materials.

[0052] <Formulation (1)> 49 parts by weight of bisphenol A type epoxy resin "Epotoate (registered trademark)" YD128 (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.), 49 parts by weight of 3 or 4-methyl-hexahydrophthalic anhydride HN-5500 (manufactured by Hitachi Chemical Co., Ltd.), 2 parts by weight of 1,2-dimethylimidazole "Curezol (registered trademark)" 1,2DMZ (manufactured by Shikoku Kasei Kogyo Co., Ltd.)

[0053] <Formulation (2)> 60 parts by mass of tetraglycidyl methylene aniline "Araldite (registered trademark) MY9655T (manufactured by Huntsman Japan Co., Ltd.), 15 parts by mass of 4,4'-methylenebis(2-isopropyl-6-methylaniline) "Lonza Cure (registered trademark)" M-MIPA (manufactured by Lonza Japan Co., Ltd.), 25 parts by mass of 2,2',6,6'-tetraethyl-4,4'-methylenedianiline "Lonza Cure (registered trademark)" M-DEA (manufactured by Lonza Japan Co., Ltd.)

[0054] <Formulation (3)> 6 parts by weight of aluminum trisdiethylphosphinate "Exolit (registered trademark)" OP935 (manufactured by Clariant Japan Co., Ltd.), 50 parts by weight of bisphenol A type epoxy resin "Epotoate (registered trademark)" YD128 (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.), 10 parts by weight of 1,6-hexanediol glycidyl ether YED216M (manufactured by Mitsubishi Chemical Corporation), 6 parts by weight of dicyandiamide "jER Cure (registered trademark)" DICY7 (manufactured by Mitsubishi Chemical Corporation), 12 parts by weight of 2,4-bis(3,3-dimethylureido)toluene "Omicure (registered trademark)" 24 (manufactured by PTI Japan Co., Ltd.), 5 parts by weight of 3,3-dimethyl-4,4'-diaminodicyclohexylmethane "jER Cure (registered trademark)" 113 (manufactured by Mitsubishi Chemical Corporation)

[0055] <Internal release agent> (Reactive silicone oil) ·Carboxyl-terminated silicone oil "DOWSIL (registered trademark)" BY 16-750 Fluid (manufactured by Dow Corning Toray Co., Ltd.) (indicated as 16-750 in Table 1 and Table 2), viscosity: 172 mm 2 / s, functional group equivalent: 742 g / mol · Bis-terminal amine-modified silicone oil X-22-161B (manufactured by Shin-Etsu Silicone Co., Ltd.), viscosity: 55 mm 2 / s, functional group equivalent: 1500 g / mol · Side-chain thiol-modified silicone oil KF-2001 (manufactured by Shin-Etsu Silicone Co., Ltd.), viscosity: 200 mm 2 / s, functional group equivalent: 1900 g / mol · Side-chain carboxyl-modified silicone oil “DOWSIL (registered trademark)” BY 16-880 Fluid (manufactured by Dow Corning Toray Co., Ltd.) (shown as 16-880 in Table 1), viscosity: 2500 mm 2 / s, functional group equivalent: 3500 g / mol (Non-reactive silicone oil) · Side-chain ether-modified silicone oil “DOWSIL (registered trademark)” L-7002 Fluid (manufactured by Dow Corning Toray Co., Ltd.) (shown as L-7002 in Table 2) (Non-silicone-based) · Phosphate ester derivative composition MOLD WIZ INT-EZ-6 (manufactured by Accel Plastic Research Laboratories) (shown as EZ-6 in Table 2)

[0056] [Reinforcing fiber substrate] <Substrate (1)>[[]] · Bi-directional carbon fiber fabric: BT70-30 manufactured by Toray Industries, Inc. (Yarn type: T700S, plain weave) <Substrate (2)>[[]] · Carbon fiber short fiber mat: manufactured by ZOLTEK, (Yarn type: “Panex35 (registered trademark)” carbon fiber bundle) <Substrate (3)>[[]] · Unidirectional carbon fiber prepreg: P3832-W19 manufactured by Toray Industries, Inc. (Yarn type: T700S)

[0057] (1) Preparation of resin composition According to the mixing ratios shown in the above resin formulations (1), (2), and (3), the resin raw materials were mixed at normal temperature environment. After adding the internal release agent according to Examples 1 to 12 in Table 1 and Comparative Examples 1 to 8 in Table 2, the mixture was stirred to prepare the resin composition.

[0058] (2) Resin molded plate forming​​​ Formulations (1) and (2): The resin composition prepared by the method described above was injected in a form sandwiched between release films ("Lumirror (registered trademark)" high-smooth grade, manufactured by Toray Industries, Inc.) in a mold set to a thickness of 2 mm, and cured under the conditions of 140°C for 2 hours to obtain a resin molded plate.

[0059] Formulation (3): The resin composition prepared by the method described above was further held in an atmosphere of 40°C for 24 hours. After holding, the thickened composition was charged in a form sandwiched between release films ("Lumirror (registered trademark)" high-smooth grade, manufactured by Toray Industries, Inc.) in a mold set to a thickness of 2 mm by a 2-mm-thick spacer made of "Teflon (registered trademark)", and a resin molded plate was obtained by press molding under the conditions of 10 MPa and 140°C for 20 minutes.

[0060] (3) Contact angle measurement For the surface of the resin plate obtained by the method described above, measurement was carried out under the conditions of 23°C and 50% humidity using a Drop Master DMo-501 contact angle measuring device manufactured by Kyowa Interface Science Co., Ltd. 1 μL of pure water was dropped onto the surface of the resin plate, and the contact angle after 1 second was measured.

[0061] (4) Surface analysis of resin molded products by TOF-SIMS Small pieces of the resin molded plates in Table 1 and Table 2 were used with a TOF-SIMS device (TOF.SIMS 5: manufactured by ION-TOF) to obtain the mass spectrum of the outermost surface of the molded plate. The measurement was carried out for two different regions with a 300-μm square, and the measurement conditions were that the primary ion species was Bi 3++ , the primary ion irradiation density was 2.55e +10 ions / cm 2 , and only positive secondary ions were obtained. It was discriminated whether the obtained secondary ions were derived from silicone oil or epoxy resin, and the ion intensity ratio was calculated with the maximum intensity of each.

[0062] (5) Release property evaluation (Test piece preparation) Using the resin compositions of Table 1 and Table 2, mold release property evaluation was carried out. For the mold release property evaluation, the measuring jig 1 shown in Fig. 2(a) was used. The measuring jig 1 is circular in plan view and is composed of an upper jig 2 and a lower jig 3 having a cylindrical convex portion 4. Onto this lower jig 3, a cylindrical metal piece 6 having a cylindrical hole portion 5 that engages with the convex portion 4 and the upper jig 2 were placed, and the upper jig 2 and the lower jig 3 were fastened.

[0063] Formulation (1): After preheating the jig to 140 °C, the resin composition 7 prepared by the method described above was injected onto the metal piece 6 of the measuring jig 1, and heat-cured in an oven under the conditions of 140 °C × 2 hours to prepare an evaluation test piece 9 to which a resin cured product 8 was adhered to the metal piece.

[0064] Formulation (2): After preheating the jig to 100 °C, the resin composition 7 prepared by the method described above was injected onto the metal piece 6 of the measuring jig 1, and heat-cured in an oven under the conditions of 180 °C × 2 hours to prepare an evaluation test piece 9 to which a resin cured product 8 was also adhered to the metal piece.

[0065] Formulation (3): The resin composition 7 prepared by the method described above was further held in a 40 °C atmosphere for 24 hours. After preheating the assembled measuring jig 1 to about 140 °C, the resin composition 7 was placed on the surface of the metal piece 6, and heat-cured under the conditions of about 140 °C × 20 minutes with a pressure of about 10 MPa using a press machine to prepare an evaluation test piece 9 to which a resin cured product 8 was also adhered to the metal piece.

[0066] In addition, when molding the resin cured product 8, for reinforcement of the resin cured product during mold release force measurement, one 15 mm square base material (1) was placed on the metal piece 6 together with the resin composition 7 for molding. Also, when molding the evaluation test piece 9, a silicone rubber string 10 was arranged along the wall surface of the upper jig 2 so that the resin cured product 8 would adhere to the upper jig 2 and the mold release force would not be overestimated.

[0067] (Mold Release Force Measurement Test) As shown in Fig. 2(b), for the mold release property evaluation, after molding the cured resin 8, with the lower jig 3 and the rubber string 10 removed, a cylinder 11 with the same diameter was inserted into the hole 5 of the metal piece 6, and a load P was applied to the cylinder 11 to peel the cured resin 8 from the metal piece 6. The value obtained by dividing the maximum load at that time by the area of the cured resin 8 was defined as the mold release force. Furthermore, the fracture surfaces of the metal piece 6 and the cured resin 8 after the test were visually observed, and the removability of the resin burr remaining on the surface of the metal piece 6 was also evaluated. The measurement was performed using an electromechanical universal material testing machine Instron5565 manufactured by Instron Corporation. The evaluation criteria were as follows. ◎... The cured resin 8 peels off from the metal piece 6, and no burr remains on the metal piece 6. 〇... The cured resin 8 peels off from the metal piece 6, but burrs remain on the metal piece 6. The generated burrs can be removed by polishing with sandpaper. △... The cured resin 8 peels off from the metal piece 6, but burrs remain on the metal piece 6. The generated burrs can only be removed with a scraper. ×... The cured resin 8 causes matrix fracture and does not peel off from the metal piece 6.

[0068] (6) Adhesion evaluation (Test piece preparation) Formulation (1): Seven layers of substrate (1) were laminated on a metal tool plate, and the resin composition 7 prepared by the aforementioned method was impregnated into the substrate by the VaRTM (Vacuum Assisted Resin Transfer Molding) method. After curing at 140 °C for 2 hours in an oven, a fiber-reinforced resin molded plate (1) with a thickness of 2 mm was obtained.

[0069] Formulation (2): Seven layers of substrate (1) were laminated on a metal tool plate, and the resin composition 7 prepared by the aforementioned method was impregnated into the substrate by the VaRTM method. After curing at 180 °C for 2 hours in an oven, a fiber-reinforced resin molded plate (2) with a thickness of 2 mm was obtained.

[0070] Formulation (3): The resin composition 7 prepared by the method described above was impregnated into a previously prepared substrate (2) so that the fiber weight content Wf = 50%, and held in an atmosphere of 40 °C for 24 hours. When preparing the resin composition, the fiber-reinforced resin composition was charged into a press machine heated to 140 °C at a charge rate of 50% and heated and cured for 20 minutes to obtain a fiber-reinforced resin molded plate (3) with a thickness of 3 mm.

[0071] Separately from the fiber-reinforced resin molded plate, 10 substrates (3) with all fiber directions aligned were laminated so as to have the same flexural rigidity as the fiber-reinforced resin molded plate, and a fiber-reinforced resin molded plate (4) with a thickness of 1.8 mm was obtained by a press molding method.

[0072] The obtained fiber-reinforced resin molded plates (1) to (4) were cut into strip pieces 12, 13, 14, and 15 each having a width of 25 mm and a length of 100 mm as shown in Fig. 3. After degreasing the strip pieces 12 to 15 with 2-propanol, the strip pieces 12, 13, and 14 were each adhered to the strip piece 15 with a two-component urethane adhesive (Pliogrip2400 / 2808B manufactured by Ashland) to prepare a single lap shear test piece 16 (adhesion width: 12.5 mm, adhesion length: 25 mm, adhesion thickness: 0.5 mm) described in JIS K6850 (2017). Tabs (width: 25 mm, length: 38 mm) were adhered to both ends of the test piece, and a tensile shear test was carried out using an electromechanical universal material testing machine Instron5589 manufactured by Instron, and the failure state of the joint was visually observed. In addition, only the strip piece 15 was sanded with #320 sandpaper before degreasing to prevent failure at the interface between the strip piece 15 and the adhesive. The evaluation criteria for the adhesion state were as follows. ◎... Cohesive failure progressed over the entire adhesion area. 〇... Interfacial failure progressed in part of the adhesion area (interfacial failure rate less than 50%). △... Interfacial failure progressed over 50% or more of the adhesion area. ×... Interfacial failure progressed over the entire adhesion area.

[0073] Examples 1 to 12, Comparative Examples 1 to 8 In Examples 1 to 12, the contact angle of the release surface was 90 degrees or more, and resin burrs did not occur, or even if they occurred, they could be removed with a slight force during polishing, exhibiting high releasability. Also, regarding the ratio of the fragment ion intensity derived from silicone oil to the fragment ion intensity derived from epoxy resin, the value was from 3 to 20, and it was found that in Examples 3 and 7, good results were shown for both releasability and adhesiveness.

[0074] In Comparative Examples 1 to 8, cases where a release agent that is non-reactive and not silicone oil was used, as well as cases where the addition amount of the silicone oil used in Examples 1 to 12 was extremely decreased and increased were examined. As a result, in Comparative Examples 1 to 3 and 5 to 6, the contact angle was 90 degrees or less, resulting in a non-water-repellent surface, and the cured resin 8 did not peel off from the metal piece 6 and caused base material fracture, exhibiting extremely high adhesiveness rather than releasability (in these comparative examples, since the adhesiveness was judged to be sufficient, the above-described adhesiveness evaluation was omitted). On the other hand, in Comparative Examples 4, 7, and 8, the ion intensity ratio was 20 or more, and there was no problem with releasability. However, it was visually confirmed that a large amount of the release agent that had bled excessively was present on the surface of the cured product and on the metal piece, and in the adhesiveness evaluation, it could not be adhered only by degreasing treatment and was broken by interfacial fracture over the entire adhesive surface.

[0075]

Table 1

[0076]

Table 2

[0077] The fiber-reinforced composite molded product of the present invention has good releasability for aircraft applications, automotive applications, sports applications, and other general industrial applications. Also, with a small addition amount of the release agent and without using an external release agent, it effectively exhibits releasability from the mold, achieving high productivity and quality. At the same time, it can exhibit high adhesiveness to other components and excellent mechanical properties without performing special surface treatments such as sanding treatment.

Explanation of Symbols

[0078] 1 Measuring jig 2 Upper jig 3 Lower jig 4 Protrusion 5 Hole 6 Metal piece 7 Resin composition 8 Cured resin 9 Release property evaluation test piece 10 Silicon rubber string 11 Cylinder 12 Strip piece 13 Strip piece 14 Strip piece 15 Strip piece 16 Single lap shear test piece

Claims

1. A fiber-reinforced composite molded product is formed by mixing reinforcing fibers and an epoxy resin with silicone oil as an internal mold release agent, the fiber-reinforced composite molded product being characterized in that the ratio of fragment ion intensities detected when the surface of the molded product is analyzed by time-of-flight secondary ion mass spectrometry is expressed by the relationship of the following formula (I), the functional group equivalent of the silicone oil is 300 g / mol or more and 2,000 g / mol or less, and the amount of the silicone oil added is 0.1 parts by mass or more and 1 part by mass or less per 100 parts by mass of the epoxy resin. 3≦A / B≦20...(I) A: The intensity of the most intense fragment ion among the fragment ions derived from the silicone oil B: The intensity of the fragment ion with the highest intensity among the fragment ions derived from the epoxy resin

2. The fiber-reinforced composite molded product according to claim 1, further satisfying the following formula (II): 3≦A / B≦5...(II)

3. 3. The fiber-reinforced composite molded product according to claim 1, wherein the contact angle of the surface of the fiber-reinforced composite molded product with water is 90 degrees or more.

4. The fiber-reinforced composite molded product according to any one of claims 1 to 3, wherein the silicone oil is a terminal-modified silicone oil.

5. The viscosity of the silicone oil is 50 mm ２ / s or more, 1,000mm ２ The fiber-reinforced composite molded product according to any one of claims 1 to 4, wherein the fiber-reinforced composite molded product has a viscosity of 1 / s or less.

6. A joined structure in which the fiber-reinforced composite molded product according to any one of claims 1 to 5 is joined to another member with an adhesive.

7. The bonded structure according to claim 6, which is bonded without any pretreatment other than degreasing.

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