Process for manufacturing shaped objects by filament winding

Abstract

The invention relates to a process for manufacturing a shaped object by a winding process, comprising the steps of: - winding resin-containing fibers under tension to form a shaped fibrous object, the resin comprising at least 50 wt% polyester, calculated on the basis of the polymer component of the resin, said polyester being derived from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms, - subjecting the shaped fibrous object to a curing step. In one embodiment, the resin-containing fibers are provided by a process comprising the steps of: - contacting the fibers with a liquid resin composition to obtain resin-containing fibers, the resin composition comprising a polyester, said polyester being derived from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms, - subjecting the resin-containing fibers to a drying step, the drying step being carried out until the resin-containing fibers are tacky and the resin-containing fibers have a diluent content of at most 25 wt%, calculated on the basis of the weight of the resin composition in the resin-containing fibers. Also claimed is the tacky fibers obtained by this intermediate process, as well as the shaped fibrous object which can be obtained by the process according to the invention.

Description

Technical Field

[0001] This invention relates to a process (method) for manufacturing shaped objects by filament winding. Background Technology

[0002] Filament winding processes are well known in the art. They are used to create open or closed end structures by winding resin-impregnated filaments under tension to form shaped fibrous objects. Winding can be performed on a mandrel or in a coreless winding process. In a coreless winding process, the fibers are wound onto a frame that provides the shaped structure by winding under tension. Once the object reaches its desired shape and thickness, the resin is cured, and the mandrel is removed where appropriate.

[0003] Glass and carbon fiber are commonly used as filaments, especially when high-strength objects are targeted. High-strength polymer fibers, such as polyaramid fibers, have also been used. A relatively new development in this field is the use of natural fibers, such as flax.

[0004] The resins used in the filament winding process are typically epoxy resins, although other resins have also been used.

[0005] There is a need in the art for a process for manufacturing shaped objects by filament winding, which exhibits increased flexibility and / or allows for the manufacture of objects having shapes not directly produced by the winding step. This invention provides such a process. Summary of the Invention

[0006] This invention relates to a process for manufacturing shaped objects by winding, comprising the following steps:

[0007] - Winding resin-containing fibers under tension to form a shaped fibrous object, the resin comprising at least 50% by weight polyester based on the polymer composition of the resin, said polyester being derived from aliphatic polyols having 2 to 15 carbon atoms and aliphatic polycarboxylic acids having 3 to 15 carbon atoms.

[0008] - and then perform a curing step on the shaped fiber object.

[0009] In this invention, a specific resin is used, namely, a resin comprising at least 50% by weight of polyesters derived from aliphatic polyols having 2 to 15 carbon atoms and aliphatic polycarboxylic acids having 3 to 15 carbon atoms. It has been found that using this specific resin has many advantages, particularly due to its specific curing properties.

[0010] The first advantage associated with using this resin is that the resin-impregnated fibers can be stored at room temperature. This allows the step of impregnating the fibers with resin to be separated from the step of winding the fibers to form a shaped fibrous object. Separating the step of impregnating the fibers with resin from the step of winding the fibers is advantageous because the two steps can be carried out at different rates. Furthermore, it has been shown that, particularly in the case of manufacturing non-cylindrical objects, resin absorption in a direct winding process can be uneven because the winding rate can vary with the diameter of the object. Separating the step of impregnating the fibers with resin from the step of winding the fibers solves this problem. Moreover, the step of impregnating the fibers with resin requires different operating conditions and may require different health, safety, and environmental (HSE) concerns than the step of winding the impregnated fibers. The resin-impregnated fibers used in filament winding processes are known in the art. They are generally referred to as prepreg. However, known prepregs require storage and transport under refrigerated conditions (e.g., at temperatures below 0°C), while the prepreg of the present invention can be stored and transported under ambient conditions (regarding both temperature and humidity). This not only means lower storage and transportation costs, as fewer measures will be needed to keep the prepreg in suitable storage conditions, but also that the prepreg is less susceptible to changes in storage conditions.

[0011] A second advantage associated with the use of a specific resin is that the resin's specific curing properties allow for curing only a portion of the material on the mandrel. This makes it possible to manufacture fibrous objects whose shape does not directly correspond to the shape produced by the winding step of forming the object. More specifically, it has been found that using the specific resin described herein allows for a process comprising the following steps: subjecting the shaped fibrous object to a first curing step to form a partially cured shaped fibrous object; removing the partially cured shaped fibrous object from the mandrel, if present; subjecting the partially cured shaped fibrous object to a step of changing its shape; and subjecting the resulting object to a further curing step. Attached Figure Description

[0012] Figure 1a and Figure 1b A fiber object obtained according to Example 1 is shown;

[0013] Figure 2 The prepreg material according to Example 2 is shown;

[0014] Figure 3a and Figure 3b The objects formed in Tables 3.1 and 3.3 of Example 3 are shown respectively;

[0015] Figure 4 A fiber object obtained according to Example 5 is shown. Detailed Implementation

[0016] In addition to the advantages described above, the process of the present invention produces shaped fiber objects with excellent properties. Other advantages of the present invention and specific embodiments thereof will become apparent from the further description.

[0017] The invention will now be discussed in more detail.

[0018] In the process of this invention, resin-containing fibers are wound under tension to form a shaped fibrous object. The resin comprises polyesters derived from aliphatic polyols having 2 to 15 carbon atoms and aliphatic polycarboxylic acids having 3 to 15 carbon atoms. The resin-containing fiber is a fiber in which the starting fiber (discussed below) already has a specific resin (discussed below).

[0019] The fibers used in this invention can be any fibrous material capable of being wound around a mandrel. Examples include monofilament yarns and multifilament yarns, tapes, and any other longitudinal shape capable of being wound around a mandrel. Therefore, the term "suitable fiber" in this specification also includes tapes, and suitable fibers can be glass fibers, carbon fibers, polymer fibers, such as polyester fibers (e.g., polyaramid fibers), and polyalkylene fibers (e.g., polyethylene fibers and polypropylene fibers). Natural fibers, such as those derived from flax, hemp, palm, or other plant or animal-based fibers, can be used. Suitable fibers for filament winding processes are known in the art. Combinations of different types of fibers can also be applied. In one embodiment, glass fibers may be preferred.

[0020] In one embodiment, layers of different types of fibers are applied. In particular, using natural fibers as the outer layer may be attractive for providing an appealing visual appearance and / or aiding in the removal of water from the system.

[0021] It has been found that the fibers used are not loop fibers, but fibers composed of fibers with a finite length, such as fibers derived from natural products, such as flax, hemp, or other natural fibers. The presence of resin, provided by the winding process, also contributes to the strength of the fibers. This is particularly applicable when a partial curing step has already been performed, as will be discussed in more detail below.

[0022] The resins used in this invention comprise polyesters derived from aliphatic polyols having 2 to 15 carbon atoms and aliphatic polycarboxylic acids having 3 to 15 carbon atoms. Resins present in fibers comprise polymer components and optionally include diluents.

[0023] In the polymer component present in the resin composition, at least 50% by weight, particularly at least 60% by weight, and more particularly at least 70% by weight, are polyesters derived from aliphatic polyols having 2 to 15 carbon atoms and aliphatic polycarboxylic acids having 3 to 15 carbon atoms. More particularly, since the advantages of the invention are associated with the properties of the resin, it may be preferable that, in the polymer component present in the resin, at least 80% by weight, particularly at least 90% by weight, and more particularly at least 95% by weight, are polyesters derived from aliphatic polyols having 2 to 15 carbon atoms and aliphatic polycarboxylic acids having 3 to 15 carbon atoms. It should be noted that, in the context of this specification, the term polymer component also includes monomers capable of being polymerized under the conditions that the resin-containing fibers will encounter during the process according to the invention.

[0024] The resin composition comprises polyesters derived from aliphatic polyols having 2 to 15 carbon atoms and aliphatic polycarboxylic acids having 3 to 15 carbon atoms.

[0025] The aliphatic polyols used in this invention (sometimes referred to herein as polyols) comprise at least two hydroxyl groups, particularly at least three hydroxyl groups. Typically, the number of hydroxyl groups will be 10 or fewer, more particularly 8 or fewer, or even 6 or fewer, particularly two or three. The polyol has 2 to 15 carbon atoms. More particularly, the polyol has 3 to 10 carbon atoms. The polyol preferably does not contain heteroatoms. More particularly, the polyol is an aliphatic polyalkane containing only C, H, and O atoms. The polyol preferably does not contain non-carbon groups other than hydroxyl groups. In a preferred embodiment of the invention, the polyol contains a relatively large number of hydroxyl groups compared to its number of carbon atoms. For example, the ratio between the number of hydroxyl groups and the number of carbon atoms ranges from 1:4 (i.e., one hydroxyl group for every four carbon atoms, or eight carbon atoms for a diol) to 1:1 (i.e., one hydroxyl group for every carbon atom). Specifically, the ratio of the number of hydroxyl groups to the number of carbon atoms is in the range of 1:3 to 1:1, more specifically in the range of 1:2 to 1:1. A particularly preferred group of polyols is the group in which the ratio is in the range of 1:1.5 to 1:1. Compounds in which the ratio of hydroxyl groups to carbon atoms is 1:1 are considered particularly preferred. Aliphatic polyols are preferably saturated, i.e., they do not contain carbon-carbon double or triple bonds.

[0026] Examples of suitable polyols include those selected from glycerol, sorbitol, xylitol, mannitol, and anhydrosorbitol, and diols selected from 1,2-propanediol, 1,3-propanediol, 1,2-ethylenediol, butylene glycol, hexanediol, and isosorbide. Compounds selected from the group consisting of glycerol, sorbitol, xylitol, and mannitol are preferred, with glycerol being particularly preferred.

[0027] The preference for glycerol is based on the following: First, glycerol has a melting point of 20°C, which makes it easy to process, especially compared to xylitol, sorbitol, and mannitol, whose melting points are all much higher than 90°C. Furthermore, glycerol has been found to provide high-quality polymers, thus combining readily available source materials with favorable processing conditions and high-quality products. Mixtures of different types of alcohols can also be used.

[0028] However, the polyol preferably consists of at least 50 mol%, preferably at least 70 mol%, more particularly at least 90 mol%, or even at least 95 mol% of glycerol, xylitol, sorbitol, or mannitol, especially glycerol. In one embodiment, the polyol is substantially composed of glycerol.

[0029] The glycerol used is a byproduct of biodiesel production via transesterification of glycerol esters with monools, which is a particular embodiment of the invention. Suitable monools include C1 to C10 monools, particularly C1 to C5 monools, and more particularly C1 to C3 monools, especially methanol. Glycerol esters are monoesters and diesters of glycerol and fatty acids, which typically have 10 to 18 carbon atoms. Suitable processes for producing biodiesel with glycerol associations are known in the art.

[0030] The aliphatic polycarboxylic acids used in this invention comprise at least two carboxylic acid groups, particularly at least three. Typically, the number of carboxylic acid groups will be 10 or fewer, more particularly 8 or fewer, or even 6 or fewer. The polycarboxylic acids have 3 to 15 carbon atoms. More particularly, the polycarboxylic acids have 3 to 10 carbon atoms. The polycarboxylic acids preferably do not contain N or S heteroatoms. More particularly, the polycarboxylic acids are aliphatic polycarboxylic acids containing only C, H, and O atoms. The aliphatic polyols are preferably saturated, i.e., they do not contain carbon-carbon double or triple bonds.

[0031] In one embodiment, a dicarboxylic acid is used. If used, the dicarboxylic acid can be any dicarboxylic acid having two carboxylic acid groups and typically up to 15 carbon atoms. Examples of suitable dicarboxylic acids include itaconic acid, malic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, and oxalic acid. Itaconic acid and succinic acid may be preferred.

[0032] In one embodiment, a tricarboxylic acid is used. If used, the tricarboxylic acid can be any tricarboxylic acid having three carboxylic acid groups and typically up to 15 carbon atoms. Examples include citric acid, isocitric acid, aconitic acid (both cis and trans), and 3-carboxy-cis and cis-mucoconic acid. Citric acid is considered preferred for both cost and availability reasons. Where applicable, the polycarboxylic acid may be provided wholly or partially in the form of anhydrides, such as citric anhydride.

[0033] It has been found that tricarboxylic acids produce polyesters with attractive properties. Therefore, in one embodiment, the polyacid comprises at least 10% by weight of a tricarboxylic acid, whether or not in combination with dicarboxylic acids, other tricarboxylic acids, or mixtures thereof. In one embodiment, the polyacid comprises at least 30% by weight, preferably at least 50% by weight, of a tricarboxylic acid based on the total amount of the polyacid. In one embodiment, the amount of tricarboxylic acid is at least 70% by weight, more particularly at least 90% by weight, or even at least 95% by weight. In one embodiment, the polyacid consists essentially of a tricarboxylic acid, wherein the term "essentially" means that other acids may be present in amounts that do not affect the properties of the material.

[0034] In another embodiment of the invention, the acid comprises at least 10% by weight, preferably at least 30% by weight, and more preferably at least 50% by weight of a dicarboxylic acid, calculated based on the total amount of the acid. In one embodiment, the amount of the dicarboxylic acid is at least 70% by weight.

[0035] In one embodiment, the acid comprises a combination of at least 10 wt% tricarboxylic acid and at least 2 wt% dicarboxylic acid, more particularly a combination of at least 10 wt% tricarboxylic acid and at least 5 wt% dicarboxylic acid, or a combination of at least 10 wt% tricarboxylic acid and at least 10 wt% dicarboxylic acid. In this embodiment, the weight ratio between the two types of acid can vary over a wide range, depending on the desired properties of the material. In one embodiment, the dicarboxylic acid accounts for 2 wt% to 90 wt% of the total dicarboxylic acid and tricarboxylic acid, particularly 5 wt% to 90 wt%, more particularly 10 wt% to 90 wt%, depending on the desired properties of the material. It should be noted that the preferred range of tricarboxylic acids specified above also applies to this embodiment. It has been found that the use of tricarboxylic acids, particularly citric acid (especially in combination with triols such as glycerol), results in the formation of high-quality composite materials.

[0036] The combination of tricarboxylic acid and triol is considered particularly preferred because it has been found to produce high-strength polymer materials. In one embodiment, at least 50% by weight, more particularly at least 70% by weight, and even more particularly at least 90% by weight, of the polyol is a triol, particularly glycerol, and at least 50% by weight, more particularly at least 70% by weight, and even more particularly at least 90% by weight, of the polycarboxylic acid is a tricarboxylic acid, particularly citric acid.

[0037] The molar ratio between polyols and polyacids is controlled by the ratio between the number of reactive groups in the alcohol(s) and acid(s) used. Typically, the ratio between the number of OH groups and the number of acid groups is between 5:1 and 1:5. More specifically, this ratio may be between 2:1 and 1:2, more specifically between 1.5:1 and 1:1.5, and more preferably between 1.1:1 and 1:1.1. The theoretical molar ratio is 1:1.

[0038] Polyesters are formed by combining alcohols and acids to form a liquid phase. Depending on the nature of the compounds, this can be done, for example, by heating the mixture of components to a temperature at which the acid will dissolve in the alcohol, particularly in glycerol. Depending on the nature of the compounds, this can be done, for example, at temperatures in the range of 20°C to 250°C, such as 40°C to 200°C, such as 60°C to 200°C, or 90°C to 200°C. In one embodiment, the mixture can be heated and mixed at temperatures in the range of 100°C to 200°C, particularly in the range of 100°C to 150°C, more particularly in the range of 100°C to 140°C, for a period of 5 minutes to 2 hours, more particularly in the range of 10 minutes to 45 minutes.

[0039] Alternatively, a suitable catalyst can be used to prepare polyesters. Suitable catalysts for the manufacture of polyesters are known in the art. Preferred catalysts are those that do not contain heavy metals. Useful catalysts are strong acids, such as, but not limited to, hydrochloric acid, hydroiodic acid (also referred to as hydroiodic acid), hydrobromic acid, sulfuric acid (H₂SO₄), nitric acid (HNO₃), chloric acid (HClO₃), boric acid, perchloric acid (HClO₄), trifluoroacetic acid, toluenesulfonic acid, and trifluoromethanesulfonic acid. Catalysts such as zinc acetate and manganese acetate can also be used, although they may be less preferred.

[0040] Resin compositions may or may not contain a diluent when present in resin-containing fibers. A suitable diluent must meet several requirements: it is a liquid with low viscosity; it has little or no reactivity with polyols and carboxylic acids; it should be a good solvent for polyols and carboxylic acids; and it should readily evaporate from the resin-containing fibers.

[0041] Although other liquids are possible, the use of water is considered preferred for technical, economic, and environmental reasons. Therefore, if available, the diluent typically consists of at least 50% by weight, particularly at least 70% by weight, more particularly at least 90% by weight, and even more particularly at least 95% by weight of water.

[0042] One advantage of this invention is that, compared to resins conventionally used in filament winding, the resins currently used herein can be diluent-free or can rely on water as a diluent. This eliminates the need for measures required when dealing with resins based on volatile organic solvents such as acetone.

[0043] Diluents, if present in the resin composition, are typically present in an amount of up to 90% by weight, particularly up to 70% by weight, calculated based on the resin composition, because they are present in the resin-containing fibers supplied to the winding step. While the presence of some diluent may be inherent due to its presence in the composition when applied to the fibers, or advantageously because it helps maintain fiber flexibility, the presence of excessive amounts of diluent does not provide additional advantages and must still be removed from the composition. Therefore, the resin composition in the resin-containing fibers may preferably contain up to 50% by weight of diluent, particularly up to 40% by weight, when the resin-containing fibers are supplied to the winding step.

[0044] In one embodiment, because it is present in the resin-containing fibers supplied to the winding step, the diluent content of the resin composition is at most 20% by weight, particularly at most 15% by weight, and more particularly at most 10% by weight. This may be especially true when the fibers supplied to the winding step are prepreg materials that have been prepared separately. However, it may also be true when, in a direct winding process, for example, a drying step is performed between applying the resin to the fibers and supplying the resin-containing fibers to the winding step, or when the resin applied to the fibers has a low diluent content.

[0045] Preferably, the resin composition contains some diluent when it is present in the resin-containing fibers provided to the filament winding step, which can produce more flexible fibers. This may be especially, but not only, at higher resin contents and / or at higher degrees of polymerization. Thus, in one embodiment, the resin composition contains at least 0.5% by weight of water, particularly at least 1% by weight, when it is present in the resin-containing fibers provided to the filament winding step.

[0046] The resin composition may contain other components.

[0047] In one embodiment, a compound is added to increase the interaction between the polymer and the hydrophobic material, or to increase the water resistance of the final product. Suitable compounds include, for example, C5 to C22 saturated or unsaturated fatty acids or salts thereof, C5 to C22 saturated or unsaturated fatty alcohols, and dimer and trimer fatty acids or alcohols. For example, glyceryl monostearate, triethyl citrate, and valeric acid can be used in this invention. The compound that increases hydrophobicity is typically applied in an amount of 0.1% to 5% by weight, more particularly in an amount of 0.3% to 3% by weight, based on the amount of polymer. Other components for achieving this purpose include mixtures of saturated fatty acids obtained from fully hydrogenated vegetable oils or vegetable oils in general.

[0048] Typically, the resin-containing fibers provided to the winding step contain a resin composition between 1 vol% and 90 vol% based on the total volume of the resin-containing fibers. Too little resin will result in a molded article with insufficient properties. In cases where the fibers are intended to provide specific properties to the molded article, the presence of a very large amount of resin may degrade the properties of the molded article. In one embodiment, it may be preferred that the resin-containing fibers to be provided to the winding step preferably contain 1 vol% to 25 vol% of the resin composition, particularly 1 vol% to 20 vol%, more particularly 1 vol% to 15 vol%. In some embodiments, 1 vol% to 10 vol%. In another embodiment, the resin-containing fibers may preferably contain up to 80 vol% of the resin composition, particularly up to 70 vol%. In one embodiment, the resin-containing fibers preferably contain 25 vol% to 90 vol% of the resin composition, particularly 25 vol% to 80 vol%, more particularly 25 vol% to 70 vol%.

[0049] The amount of resin composition on the fiber during the winding step, expressed as a volume percentage, is calculated from the weight of the resin composition on the fiber, the density of the resin composition, and the density of the material constituting the fiber (glass, flax, etc.).

[0050] The polyester present in the resin-containing fiber supplied to the winding step typically has a degree of polymerization, which is the ratio of the fraction of reacted functional groups to the maximum number of reactive functional groups, in the range of 0.05 to 0.6. The degree of polymerization can be determined by acid value or gravimetric analysis.

[0051] The required degree of polymerization will depend on many factors. On the one hand, a higher degree of polymerization at the stage of providing the fibers to the winding step has the advantage of requiring less further curing in this process. On the other hand, a higher degree of polymerization can produce a more viscous resin composition, which may adversely affect the coating process. When the fibers are provided to the winding step, the degree of polymerization of the resin on the fibers may preferably be at least 0.1, particularly at least 0.2, and more particularly at least 0.3.

[0052] In one embodiment, resin-containing fibers are obtained by contacting the fibers with a liquid resin composition as discussed above. The contacting step should cause the resin composition to adhere to the fibers. In one embodiment, this is accomplished by passing the fibers through a resin bath. In another embodiment, the fibers are contacted with a lick roll provided with resin. Excess resin can be removed from the fibers if necessary. Other methods of coating fibers with a liquid composition known in the art can also be applied. The liquid resin composition can be applied in a single step, or in two or more steps, whether or not intermediate drying is involved.

[0053] The viscosity of the liquid composition should allow for adequate fiber coating within a reasonable timeframe. Therefore, the viscosity should neither be too low to achieve meaningful coating, nor too high to result in slow fiber coating. Viscosity will depend on many factors, including the temperature of the liquid composition (higher temperatures result in lower viscosity), the degree of polymerization of the polyester (higher degrees of polymerization result in higher viscosity), and, if a diluent is present, a higher amount of diluent results in lower viscosity. Considering the above, preparing a liquid resin composition with an appropriate viscosity is within the capabilities of those skilled in the art.

[0054] In one embodiment of the invention, resin-containing fibers are provided by a process including the following steps:

[0055] - Contacting fibers with a liquid resin composition to obtain resin-containing fibers, the resin composition comprising at least 50% by weight of polyester, calculated based on the polymeric composition of the resin, the polyester being derived from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms.

[0056] - The resin-containing fiber is subjected to a drying step until the resin-containing fiber becomes sticky and has a diluent content of up to 25% by weight, calculated based on the weight of the resin composition in the resin-containing fiber.

[0057] The resin-containing fiber may preferably have a diluent content of up to 20%, more particularly up to 15%, even more particularly up to 10%, and even more particularly up to 8% by weight, and in some embodiments up to 5% by weight.

[0058] In the context of this specification, the tackiness test is performed as follows: When supplying the resin-containing fiber to the winding step, a 10cm length of the resin-containing fiber is laid flat on a clean and dry horizontal glass plate. A pressure of 200g per mm fiber width (determined on the fiber before rolling) is applied for 5 seconds using a roller. If desired, the roller may have a non-stick layer to prevent the fiber from adhering to the roller instead of the glass plate. The plate is then lifted and flipped so that the resin-containing fiber is facing down. If the resin-containing fiber falls off the glass plate within 15 seconds, it is considered non-sticky in the context of this specification. The test is conducted at 20°C and a relative humidity between 40% and 60%.

[0059] In this embodiment, fibers with a specified diluent content of viscous resin can be stored prior to the filament winding step. They can also be transported. Compared to known prepregs used for filament winding, this so-called resin prepreg has the advantage of being able to be stored for at least 4 hours, particularly at least 24 hours, under environmental conditions such as temperatures from 4°C to 35°C and humidity from 10% to 90%, while still maintaining viscous properties. The viscousness of a polymer is a measure of the degree of polymerization of the polyester. If the resin-containing fibers are no longer viscous, the polymer has polymerized to such a degree that further curing will not cause the fibers to adhere to each other to form a shaped object that adequately retains its shape when the fibers are wound around a mandrel.

[0060] In a preferred embodiment, the viscous resin-containing fibers are wound around a spool to form a wound viscous resin-containing fiber. The spool of viscous resin-containing fibers is easy to store, transport, and further process. If necessary, the viscous resin-containing fibers are provided to the mandrel after unwinding.

[0061] The present invention also relates to the prepreg material itself. More particularly, the present invention relates to resin-containing fibers, wherein the resin fibers contain 1 vol% to 25 vol% of resin, the resin comprising at least 50 wt% of a polyester derived from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms, calculated based on the polymer composition of the resin, the resin-containing fibers are tacky, and have a diluent content of up to 25 wt% calculated based on the weight of the resin composition in the resin-containing fibers. In one embodiment, the fibers are in a wound form. The above-described preferences for the properties and amounts of resin and fibers, and further preferences, also apply to this aspect of the invention.

[0062] In another embodiment, the resin-containing fibers are processed directly without forming a separate prepreg material. In this embodiment, the resin-containing fibers are provided by a process comprising the following steps: contacting the fibers with a liquid resin composition to obtain resin-containing fibers, and then providing the fibers thus obtained to a winding step, the resin composition comprising at least 50% by weight of polyester, calculated based on the polymer composition of the resin, the polyester being derived from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms.

[0063] Whether processed through prepreg or directly with resin-containing fibers, the process of this invention includes the step of winding the resin-containing fibers under tension to form a shaped fibrous object (also referred to herein as the winding step). As shown above, and as is known in the art, winding can be performed around a mandrel, or it can be performed around a frame in a coreless filament winding step. This step is well known in the field of filament winding processes and requires no further explanation. Suitable winding patterns are also known in the art and include annular winding patterns, helical winding patterns, random winding patterns, etc.

[0064] Then, the shaped fiber object produced by the winding step is subjected to a curing step.

[0065] If necessary, the shaped fibrous object can be subjected to a drying step prior to the curing step to remove excess diluent. If a prepreg material is used, a drying step is generally not required. This may be attractive if resin-containing fibers containing a large amount of diluent are used. If a drying step is performed, it can be carried out at temperatures, for example, between 15°C and 200°C (air temperature), particularly between 15°C and 100°C. Depending on the temperature, it can last for several minutes, for example at least 2 minutes, particularly at least 5 minutes, but can also last for longer periods, for example from 0.25 hours to 3 days, depending on the size and shape of the object and the amount of water in the shaped object. Choosing suitable drying conditions is within the capabilities of those skilled in the art. Applying a vacuum or providing an airflow can be considered to increase the evaporation of the diluent.

[0066] The curing step aims to further polymerize the polyester. The key to the curing step is that the polyester is at a reaction temperature, such as 80°C to 250°C, particularly a product temperature of 100°C to 200°C. Curing can be carried out using heating techniques known in the art, such as in an oven with a temperature ranging from 80°C to 450°C. Different types of ovens can be used, including but not limited to belt ovens, convection ovens, microwave ovens, infrared ovens, hot air ovens, conventional baking ovens, and combinations thereof. Curing can be carried out in a single step or multiple steps. To provide controlled curing, the product temperature can preferably be increased during curing. Curing time ranges from 5 seconds to 24 hours, depending on the size and shape of the object and the type of oven and the temperature used (particularly 5 minutes to 12 hours). Selecting suitable curing conditions is within the capabilities of those skilled in the art. Therefore, the resin composition used in the process according to the invention is a thermosetting resin composition. No further curing steps by ionization or photochemical radiation are performed.

[0067] Depending on the nature of the object being manufactured, the cured shaped fiber object may or may not be removed from the mandrel. Filament winding is commonly used to provide fiber reinforcement for objects such as pressure vessels. In this case, the cured shaped fiber object will not be removed from the mandrel. Instead, the cured shaped fiber object and the mandrel will form a single object. In other embodiments, the cured shaped fiber object is removed from the mandrel.

[0068] In one embodiment, the curing step in a multi-step process includes the following steps:

[0069] - Perform a first curing step on the shaped fiber object to form a partially cured shaped fiber object.

[0070] - In the presence of the mandrel, partially cured shaped fiber material is removed from the mandrel.

[0071] - To further cure the partially cured shaped fiber object.

[0072] The first advantage of this sequence is that, if a mandrel is present, removing the mandrel allows hot air to circulate more easily through the shaped fiber object, which can increase the curing rate.

[0073] In this process, the polymer in the partially cured shaped fibrous object typically has a degree of polymerization of at least 0.4, and more particularly at least 0.5. A minimum degree of polymerization is usually required to ensure that the shaped fibrous object does not break down into individual fibers. For the same reason, the partially cured shaped fibrous object typically has a diluent content of at most 2% by weight, and more particularly at most 1% by weight, calculated based on the total weight of the partially cured shaped fibrous object.

[0074] Typically, partially cured fibrous materials have a degree of polymerization of up to 0.8, and more particularly up to 0.7, which is further cured in a further curing step.

[0075] After removing the partially cured fibrous material from the mandrel, it can be further cured under the curing conditions specified above.

[0076] In one embodiment, a step of changing the shape of a partially cured object is performed. The partially cured object can still be relatively flexible, so it can be shaped into a form that would otherwise be impossible using a filament winding process. Examples of methods for changing the shape of an object include cutting, pressing, molding, vacuum forming, etc. After changing the shape, the object can be cured as described above.

[0077] For coreless filament winding processes, achieving curing in a two-step process may also be attractive, especially when a shape-changing step occurs between the first and second curing steps.

[0078] It is apparent to those skilled in the art that the curing step requires the formation of esters through the reaction of alcohols with carboxylic acids, resulting in water as a byproduct. This water must be removed from the formed fibrous object. It has been found that, particularly in cases where fibers have limited water absorption capacity—for example, in the case of glass fibers, carbon fibers, or polymer-based fibers such as polyamide fibers—and / or where the filament winding layer is relatively thick, measures to ensure that the water formed during the curing step can be readily evaporated can be attractive. Various examples of these measures can be mentioned. In one embodiment, the mandrel is porous, for example due to the presence of pores, or the mandrel is ribbed to allow water evaporation. In another embodiment, an absorbent material, such as a layer of paper or cardboard, woven or nonwoven fabric, or other absorbent material, is provided on the mandrel. In yet another embodiment, the mandrel itself can be an absorbent material, such as cardboard. Choosing a relatively open winding pattern can also help ensure adequate water removal. Sub-pressure curing can also be applied to promote water evaporation.

[0079] Using fiber combinations can also be attractive, for example, by combining synthetic fibers (such as glass fibers or carbon fibers) that typically have low water absorption capacity with natural fibers (such as cellulose-based fibers) that typically have higher water absorption capacity. The natural fibers can then be used as water pipes. In this embodiment, the natural fibers are typically present in an amount ranging from 1% to 40% by weight, particularly from 1% to 25% by weight, and more particularly from 1% to 10% by weight, based on the total fiber weight. The amount of natural fibers should not be too high, as this may degrade the properties of the object to be made from the synthetic fibers. Natural and synthetic fibers can be combined as needed. In one embodiment, natural and synthetic fibers are applied together in a single layer. In another embodiment, one or more layers of natural fibers are combined with one or more layers of synthetic fibers. It is preferable to use a layer of natural fibers on the exterior of the object to aid in water removal. Of course, the fiber layer can also be mixed with layers containing only natural fibers or only synthetic fibers.

[0080] The present invention also relates to shaped fibrous articles comprising wound resin-containing fibers, wherein the resin comprises at least 50% by weight polyester, calculated based on the polymer composition of the resin, the polyester being derived from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms, the polyester having a degree of polymerization of at least 0.8, the degree of polymerization being the ratio of the portion of reacted functional groups to the maximum number of reactive functional groups. Depending on the intended use, the polyester may preferably have a degree of polymerization of at least 0.9, particularly at least 0.95.

[0081] Preferences regarding the properties and amount of resin, the type of fiber, and other preferences also apply to this embodiment.

[0082] The purpose of this invention can be applied to many fields, from high-durability applications such as lantern poles and windmill components to design applications including furniture.

[0083] In one embodiment, the fiber is glass fiber having a resin based on glycerol and citric acid. In particular, when the resin has been polymerized to a degree of polymerization of at least 0.9, it has been found that durable objects can be obtained. The preferences expressed above also apply to this embodiment, unless they are mutually exclusive.

[0084] In one embodiment, the fiber is a natural fiber, particularly flax or hemp fiber, containing resins based on glycerol and citric acid. Objects based on this combination have been found to have an appealing look and feel, making them particularly attractive for design applications. The preferences expressed above also apply to this embodiment, unless they are mutually exclusive.

[0085] The invention will be illustrated by the following examples, but is not limited thereto or thereby restrictive.

[0086] Example 1: Fiberglass - Direct Wrap

[0087] A resin composition comprising a polyester based on glycerol and citric acid is provided, having a degree of polymerization of about 0.4 (based on mass balance) and a water content of 21% by weight. The bath temperature is 54°C. Glass fibers with a linear weight of 2400 tex are passed through the resin bath, and excess resin is removed. This forms a resin-containing fiber containing about 50% by volume of resin.

[0088] Resin-containing fibers are wound around a steel pipe with a diameter of 100 mm.

[0089] The steel pipe has been coated with a release agent. Alternatively, release paper or a release coating (such as a Teflon coating) can be used.

[0090] The winding process occurs in a circular pattern at a constant speed of 5.5 revolutions per minute and a constant angle of nearly 90°. Upon completion of the winding step, the mandrel containing the fibrous object is cured at 120°C for 1 hour, at 140°C for 1 hour, and at 160°C for 2 hours. The fibrous object is then cooled and removed from the mandrel.

[0091] The final object contains 43% resin by volume, calculated based on the total volume of the object composed of resin and fibers. An image of the resulting fiber object is shown in [the image / description]. Figure 1a and Figure 1b middle.

[0092] Example 2: Glass fiber prepreg

[0093] A resin composition is provided as described in Example 1, with the resin bath at room temperature. Glass fibers are passed through the resin bath. Excess resin is removed. The fibers contain 50% by volume of resin.

[0094] The resin-containing fibers are passed through an air channel. The residence time is four minutes. The air temperature is between 135°C and 150°C. The resulting product is viscous. It has a water content of less than 10% by weight. The degree of polymerization of the resin in the resulting prepreg is slightly higher than that of the resin in the polymer bath.

[0095] The resulting prepreg material was stored for four days under ambient conditions (temperature 18°C ​​to 22°C, relative humidity 40% to 60%). After four days, the prepreg material remained sticky, but otherwise unchanged. Similar materials have been stored under these conditions for several weeks without adverse effects. The prepreg material can be... Figure 2 I saw it in the middle.

[0096] Prepreg material is used to create cylindrical objects, in this case, carbon nanotubes, by winding it around a mandrel. After winding, a curing step is performed by placing the mandrel with fibers in an oven for 4.5 hours while the temperature is slowly increased from 80°C to 180°C. After 4.5 hours, the mandrel with the formed fiber object is removed from the oven, and the object is removed from the mandrel. The resin in the formed fiber object has a degree of polymerization greater than 0.95.

[0097] Example 3 - Flax Fiber - Direct Wrapping

[0098] A resin composition comprising a polyester based on glycerol and citric acid is provided, having a degree of polymerization of about 0.4 (based on mass balance) and a water content of 21% by weight. The bath temperature is 54°C. Linen fibers with a linear weight of 1000 tex are passed through the resin bath to remove excess resin. This results in a resin-containing fiber containing 60% by volume of resin.

[0099] Resin-containing fibers are wound around the steel pipe.

[0100] The winding is performed at a constant speed of 5.5 revolutions per minute and a constant angle.

[0101] Upon completion of the winding process, the mandrel containing the fibrous object is cured at 160°C for 30 minutes, followed by curing at 180°C for 60 minutes. The fibrous object is then removed from the mandrel. The final object contains 47% by volume of resin.

[0102] The table below shows the process conditions and results for various experiments. Images of the objects formed in 3.1 and 3.3 are shown in [the table]. Figure 3a and 3b middle.

[0103]

[0104] The material is lightweight and has an appealing natural look and feel.

[0105] Example 4: The effect of curing temperature

[0106] Repeat the program from Example 1, with the following differences:

[0107] - The temperature of the resin bath is 47℃.

[0108] - Continue winding until three double-layered fibers are formed.

[0109] - The mandrel has a diameter of 5cm.

[0110] Curing was carried out at 120°C for 1 hour, at 140°C for 1 hour, at 160°C for 1 hour, and at 180°C for 1 hour. The final product contained 45% by volume of resin.

[0111] To investigate the effect of curing temperature, the resulting object was divided into sheets with a length of 4 cm. Four of these sheets were further cured at 200°C for 1 hour. It was found that the post-cured sheets exhibited higher stiffness than the sheets that did not undergo the post-curing step.

[0112] Example 5: Absorption mandrel, stratified system

[0113] A cardboard tube with an outer diameter of 75 mm and a wall thickness of 2 mm is used as the mandrel. The purpose of the mandrel is to provide an inexpensive core, which also helps to remove water from the wound compound.

[0114] A resin composition comprising a glycerol- and citric acid-based polyester with a degree of polymerization of about 0.4 (based on mass balance) and a water content of 20% by weight is provided. The bath temperature is 50°C. Glass fibers with a linear weight of 2400 tex are passed through the resin bath to remove excess resin. The glass fibers are wound in a circular pattern around a cardboard mandrel at a constant speed of 5.5 revolutions per minute and a constant angle of almost 90° until a layer thickness of 8 mm is achieved.

[0115] Linen fibers with a linear weight of 2400 tex are passed through the same resin bath and used to provide a single-layer top layer on a glass fiber layer.

[0116] When the winding step is completed, the mandrel containing the fibrous object is cured at 120°C for 1 hour, at 140°C for 1 hour, at 160°C for 1 hour, and at 180°C for 1 hour. Figure 4 Images of the final fibrous object are provided. Using a flax outer layer on a glass fiber core allows for a product with an attractive visual appearance compared to a low-cost, high-strength glass fiber core. Additionally, flax fibers can aid in the transport of water from the glass fiber core.

Claims

1. A process for manufacturing a shaped object by winding, comprising the following steps: - Winding resin-containing fibers under tension to form a shaped fibrous object, said resin being a thermosetting resin comprising at least 50% by weight of polyester, calculated based on the polymer composition of said resin, said polyester being derived from aliphatic polyols having 2 to 15 carbon atoms and aliphatic polycarboxylic acids having 3 to 15 carbon atoms. - The shaped fiber object is cured at a product temperature of 80-250°C.

2. The process according to claim 1, wherein, The resin-containing fibers are provided by a process including the following steps: - Contacting fibers with a liquid resin composition to obtain resin-containing fibers, said resin composition comprising at least 50% by weight of a polyester derived from an aliphatic polyol polyester, wherein the aliphatic polyol polyester is derived from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms. - The resin-containing fiber is subjected to a drying step until the resin-containing fiber becomes sticky and the resin-containing fiber has a diluent content of up to 25% by weight, calculated based on the weight of the resin composition in the resin-containing fiber.

3. The process according to claim 2, wherein, The sticky resin-containing fibers are wound around a spool to form a wound sticky resin-containing fiber.

4. The process according to claim 1, wherein, The resin-containing fibers are provided by a process including the following steps: - Contacting fibers with a resin composition yields resin-containing fibers, said resin composition comprising polyester derived from aliphatic polyols having 2 to 15 carbon atoms and aliphatic polycarboxylic acids having 3 to 15 carbon atoms. The fibers are then wound under tension to form a shaped fiber object.

5. The process according to claim 4, wherein, Prior to the curing step, the shaped fiber object formed during the winding step is subjected to a drying step.

6. The process according to any one of the preceding claims, wherein, The step of winding resin-containing fibers under tension to form a shaped fibrous object is carried out by winding them on a mandrel.

7. The process according to claim 6, wherein, Remove the cured shaped fiber object from the mandrel.

8. The process according to claim 6, comprising the following steps: - The shaped fiber object is subjected to a first curing step on the mandrel to form a partially cured shaped fiber object. - Remove the partially cured shaped fiber object from the mandrel. - After being removed from the mandrel, the partially cured shaped fiber object undergoes a further curing step.

9. The process according to claim 8, wherein, After being removed from the mandrel and before the further curing step, the partially cured shaped fiber object is subjected to a step of changing the shape of the partially cured shaped fiber object.

10. The process according to any one of claims 1 to 5, wherein, The winding step is performed on the frame during the coreless filament winding step.

11. The process according to claim 10, comprising the following steps: - The shaped fiber object is subjected to a first curing step to form a partially cured shaped fiber object. - The step of changing the shape of the partially cured shaped fiber object, and - To further cure the partially cured shaped fiber object.

12. A fiber comprising a thermosetting resin composition comprising at least 50% by weight of a polyester derived from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms, the fiber being tacky and having a diluent content of up to 25% by weight based on the weight of the resin composition.

13. The fiber according to claim 12, wherein the fiber has a diluent content of up to 10% by weight, calculated based on the weight of the resin composition.

14. The fiber according to claim 12 or 13, wherein the fiber is present on a spool.

15. A shaped fibrous object comprising wound resin-containing fibers, wherein, The resin is a thermosetting resin comprising at least 50% by weight of polyester derived from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms, the polyester having a degree of polymerization of at least 0.8, the degree of polymerization being the ratio of the portion of the functional groups that have reacted to the maximum number of functional groups that can react.

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