Method for producing shaped objects by filament winding

Abstract

The present invention provides a method for producing a shaped object through a winding process, comprising the steps of: winding a resin-containing fiber under tension to form a shaped fibrous body, wherein the resin comprises at least 50% by weight, calculated on the polymeric constituents of the resin, 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; and subjecting the formed fibrous body to a curing step. The method relates to the above method, which comprises the steps of: In one embodiment, the resin-containing fiber is contacting a fiber with a liquid resin composition to obtain a resin-containing fiber, wherein the resin composition comprises a polyester derived from an aliphatic polyol polyester derived from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms, calculated on the polymer constituents of the resin; subjecting the resin-containing fiber to a drying step, wherein the drying step is carried out until the resin-containing fiber becomes tacky and the resin-containing fiber has a diluent content of 25% by weight or less, calculated based on the weight of the resin composition in the resin-containing fiber; provided through a process that includes the steps of The adhesive fibers obtainable by this intermediate process are also claimed as are the shaped fibrous objects obtainable by the process according to the invention.

Description

[Technical Field]

[0001] The present invention relates to a method for producing shaped objects by filament winding. [Background technology]

[0002] Filament winding processes are well known in the art. They are used in the manufacture of open-ended or closed-ended structures by winding resin-impregnated filaments under tension to form a shaped fibrous body. The winding can be done on a mandrel or in a coreless winding process. In a coreless winding process, the fibers are wound onto a framework, thereby providing a shaped structure by winding under tension. Once the body has reached its desired shape and thickness, the resin is cured and, if appropriate, the mandrel is removed.

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

[0004] The resin used in filament winding processes is often an epoxy resin, although other resins have also been used. Summary of the Invention [Problem to be solved by the invention]

[0005] There is a need in the art for a method for producing shaped objects by filament winding that exhibits increased flexibility and / or allows for the production of objects having shapes that do not result directly from the winding process. The present invention provides such a method. [Means for solving the problem]

[0006] The present invention provides a method for producing a shaped object through a winding process, comprising the steps of: winding a resin-containing fiber under tension to form a shaped fibrous body, wherein the resin comprises at least 50% by weight, calculated on the polymeric constituents of the resin, 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; and subjecting the formed fibrous body to a curing step. The method comprises the steps of:

[0007] In the present invention, a specific resin is used, namely, a resin containing 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 use of this specific resin has been found to have several advantages, particularly due to its specific curability characteristics.

[0008] The first advantage associated with the use of this resin is that the resin-impregnated fibers can be stored at room temperature. This allows the process of impregnating the fibers with the resin to be separated from the process of winding the fibers to form a shaped fibrous object. Separating the process of impregnating the fibers with the resin from the process of winding the fibers is advantageous because the two processes can be performed at different speeds. In addition, it has been found that, particularly when non-cylindrical objects are produced, resin uptake in direct winding methods can be non-uniform because the winding speed can vary with the diameter of the object. Separating the process of impregnating the fibers with the resin from the process of winding the fibers solves this problem.

[0009] Furthermore, the process of impregnating the fiber with the resin requires different operating conditions than the process of winding the impregnated fiber, and potentially different associated health, safety, and environment (HSE) concerns. Resin-impregnated fibers for use in filament winding processes are themselves known in the art. The fibers are often referred to as prepregs. However, while the known prepregs require storage and transportation under refrigerated conditions, e.g., at temperatures below 0°C, the prepregs of the present invention can be stored and transported at ambient conditions, both in terms of temperature and humidity. This not only means that storage and transportation are cheaper, since fewer measures are required to maintain the prepreg under suitable storage conditions, but also that the prepreg is less likely to change under the storage conditions.

[0010] A second advantage associated with the use of the particular resin is that the particular curing characteristics of the resin allow for only partial curing on the mandrel. This makes it possible to produce fibrous objects having shapes that do not directly correspond to the shape resulting from the winding process in which the object is formed. More particularly, it has been found that the use of the particular resin described herein makes it possible to carry out a method that includes the steps of 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 a mandrel, if one is present, subjecting the partially cured shaped fibrous object to a step in which its shape is changed, and subjecting the object thus obtained to a further curing step.

[0011] In addition to the advantages mentioned above, the method of the present invention results in a shaped fibrous body having good properties. Further advantages of the present invention and its specific embodiments will become apparent from the further specification.

[0012] The invention will be discussed in more detail below. DETAILED DESCRIPTION OF THE INVENTION

[0013] In the process of the present invention, a resin-containing fiber is wound under tension to form a shaped fibrous body, wherein the resin comprises a polyester derived from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms. Resin-containing fibers are fibers in which a starting fiber (discussed below) has been provided with the particular resin (to be discussed below).

[0014] The fibers used in the present invention can be any fibrous material that can be wound around a mandrel. Examples include monofilament and multifilament yarns, tapes, and any other longitudinal shapes that can be wound around a mandrel. Suitable fibers (hence, the term for purposes of this specification also includes tapes) can be glass fibers, carbon fibers, polymer fibers such as polyester fibers, e.g., aramid fibers, polyalkylene fibers, e.g., polyethylene fibers and polypropylene fibers. Natural fibers, such as fibers derived from flax, hemp, palm, or other plant- or animal-based fibers, can also be used. Fibers suitable for use in filament winding methods are known in the art. Combinations of various types of fibers can also be applied. In one embodiment, the use of glass fibers can be preferred.

[0015] In one embodiment, layers of various types of fibers are applied, and in particular the use of natural fibers as the outer layer can be attractive to provide an attractive visual appearance and / or to aid in removing water from the system.

[0016] When the fibers used are not endless, but rather have a limited length, such as fibers constructed from natural products such as flax, hemp, or fibers derived from other natural fibers, it has been found that the presence of the resin also contributes to the strength of the fibers when subjected to the winding process. This is especially true when a partial curing step has been performed, as will be discussed in more detail below.

[0017] The resin used in the present invention comprises a polyester derived from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms, a polymeric constituent, and optionally a diluent, if present in the fiber.

[0018] At least 50 wt. %, particularly at least 60 wt. %, and more particularly at least 70 wt. % of the polymeric constituents present in the resin composition are polyesters derived from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms. More particularly, when the advantages of the present invention are related to the properties of the resin, it may be preferred that at least 80 wt. %, particularly at least 90 wt. %, and more particularly at least 95 wt. % of the polymeric constituents present in the resin are polyesters derived from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms. It should be noted that in the context of this specification, the term "polymeric constituent" also includes monomers that can polymerize under the conditions encountered in the resin-containing fiber during the process according to the present invention.

[0019] The resin composition contains a polyester derived from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms.

[0020] The aliphatic polyol used in the present invention, also sometimes referred to herein as a polyalcohol, contains at least two hydroxy groups, particularly at least three hydroxy groups. Generally, the number of hydroxy groups is 10 or less, more particularly 8 or less, or even 6 or less, particularly 2 or 3. The polyalcohol has 2 to 15 carbon atoms. More particularly, the polyalcohol has 3 to 10 carbon atoms. Preferably, the polyalcohol does not contain heteroatoms. More particularly, the polyalcohol is an aliphatic polyalkanol containing only C, H, and O atoms. Preferably, the polyalcohol does not contain non-carbon groups other than hydroxy groups. In a preferred embodiment of the present invention, the polyalcohol contains a relatively large number of hydroxy groups compared to its number of carbon atoms. For example, the ratio of the number of hydroxy groups to the number of carbon atoms is 1:4 (i.e., one hydroxy group per four carbon atoms, or 8 carbon atoms per dialcohol) to 1:1 (i.e., one hydroxy group per carbon atom). In particular, the ratio of the number of hydroxy groups to the number of carbon atoms is 1:3 to 1:1, more particularly 1:2 to 1:1. Particularly preferred polyalcohol groups are those in which the ratio is 1:1.5 to 1:1. Compounds in which the ratio of hydroxy groups to carbon atoms is 1:1 are considered particularly preferred. The aliphatic polyols are preferably saturated, i.e., do not contain carbon-carbon double or triple bonds.

[0021] Examples of suitable polyalcohols include polyalcohols selected from glycerol, sorbitol, xylitol, mannitol and sorbitan, and dialcohols selected from 1,2-propanediol, 1,3-propanediol, 1,2-ethanediol, butanediol, hexanediol and isosorbide. The use of compounds selected from the group consisting of glycerol, sorbitol, xylitol and mannitol is preferred, and the use of glycerol is particularly preferred.

[0022] The preference for glycerol is based on the following: First, glycerol has a melting point of 20°C, which allows for easy processing, especially compared to xylitol, sorbitol, and mannitol, which all have melting points well above 90°C. Furthermore, glycerol has been found to result in high quality polymers, thus combining the use of readily available sources of material with good processing conditions and a high quality product. Mixtures of various types of alcohols can also be used.

[0023] However, it is preferred that the polyalcohol 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, in particular glycerol. In one embodiment, the polyalcohol consists essentially of glycerol.

[0024] The use of glycerol, a by-product of the production of biodiesel by the transesterification of glycerides with monoalcohols, is a specific embodiment of the present invention. Suitable monoalcohols include C1-C10 monoalcohols, particularly C1-C5 monoalcohols, more particularly C1-C3 monoalcohols, especially methanol. The glycerides are mono-, di-, and esters of glycerol with fatty acids, the fatty acids generally having 10 to 18 carbon atoms. Suitable methods for producing biodiesel with associated glycerol are known in the art.

[0025] The aliphatic polycarboxylic acid used in the present invention contains at least two carboxylic acid groups, particularly at least three carboxylic acid groups. Generally, the number of carboxylic acid groups is 10 or less, more particularly 8 or less, or even 6 or less. The polycarboxylic acid has 3 to 15 carbon atoms. More particularly, the polycarboxylic acid has 3 to 10 carbon atoms. Preferably, the polycarboxylic acid does not contain N or S heteroatoms. More particularly, the polycarboxylic acid is an aliphatic polycarboxylic acid containing only C, H, and O atoms. Preferably, the aliphatic polyol is saturated, i.e., does not contain carbon-carbon double or triple bonds.

[0026] In one embodiment, dicarboxylic acids are used. When used, the dicarboxylic acid can be any dicarboxylic acid having two carboxylic acid groups, generally 15 or less 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 can be preferred.

[0027] In one embodiment, a tricarboxylic acid is used. When used, the tricarboxylic acid can be any tricarboxylic acid having three carboxylic acid groups, generally 15 or fewer carbon atoms. Examples include citric acid, isocitric acid, aconitic acid (both cis and trans), and 3-carboxy-cis,cis-muconic acid. The use of citric acid is considered preferable for reasons of both cost and availability. Where applicable, the polycarboxylic acid can be provided in whole or in part in the form of an anhydride, such as citric anhydride.

[0028] The use of tricarboxylic acids has been found to result in polyesters with attractive properties. Thus, in one embodiment, the polyacid comprises at least 10% by weight of tricarboxylic acid, whether in combination with dicarboxylic acids, other tricarboxylic acids, and mixtures thereof. In one embodiment, the polyacid comprises at least 30% by weight, preferably at least 50% by weight, of tricarboxylic acid, calculated based on the total amount of 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 tricarboxylic acid, where "essentially" means that other acids may be present in amounts that do not affect the properties of the material.

[0029] In another embodiment of the invention, the acid comprises at least 10% by weight, preferably at least 30% by weight, more preferably at least 50% by weight, of dicarboxylic acids, calculated on the total amount of acids. In one embodiment, the amount of dicarboxylic acids is at least 70% by weight.

[0030] In one embodiment, the acid comprises a combination of at least 10% by weight of a tricarboxylic acid and at least 2% by weight of a dicarboxylic acid, more particularly at least 10% by weight of a tricarboxylic acid and at least 5% by weight of a dicarboxylic acid, or at least 10% by weight of a tricarboxylic acid and at least 10% by weight of a dicarboxylic acid. In this embodiment, the weight ratio between the two types of acid can vary widely depending on the desired material properties. In one embodiment, the dicarboxylic acid comprises a total of 2 to 90% by weight of the dicarboxylic acid and tricarboxylic acid, particularly 5 to 90% by weight, more particularly 10 to 90% by weight, depending on the desired material properties. Note that the preferred ranges for the tricarboxylic acid identified above are also applicable to this embodiment. The use of tricarboxylic acids, particularly citric acid, has been found to result in the formation of high-quality composite materials, especially in combination with the use of a trialcohol, such as glycerol.

[0031] A combination of a triacid and a trialcohol is considered particularly preferred, as it has been found to result in high strength polymeric materials. In one embodiment, at least 50 wt.%, more particularly at least 70 wt.%, even more particularly at least 90 wt.% of the polyalcohol is a trialcohol, especially glycerol, and at least 50 wt.%, more particularly at least 70 wt.%, even more particularly at least 90 wt.% of the polycarboxylic acid is a tricarboxylic acid, especially citric acid.

[0032] The molar ratio of the polyalcohol to the polyacid is controlled by the ratio of the number of reactive groups in the one or more alcohols used to the number of reactive groups in the one or more acids. Generally, the ratio of the number of OH groups to the number of acid groups is 5:1 to 1:5. More particularly, the ratio may be 2:1 to 1:2, more particularly 1.5:1 to 1:1.5, more preferably 1.1:1 to 1:1.1. The theoretical molar ratio is 1:1.

[0033] The polyester is formed by combining the alcohol and the acid to form a liquid phase. This can be done, depending on the nature of the components, by heating the mixture of components to a temperature at which the acid dissolves in the alcohol, particularly glycerol. This can be done at a temperature of, for example, 20 to 250°C, e.g., 40 to 200°C, e.g., 60 to 200°C, or 90 to 200°C, depending on the nature of the components. In one embodiment, the mixture can be heated and mixed at a temperature of 100 to 200°C, particularly 100 to 150°C, more particularly 100 to 140°C, for 5 minutes to 2 hours, more particularly 10 minutes to 45 minutes.

[0034] Optionally, a suitable catalyst can be used for preparing the polyester. Catalysts suitable for producing polyesters are known in the art. Preferred catalysts are heavy metal-free catalysts. Useful catalysts include, but are not limited to, strong acids such as hydrochloric acid, hydroiodic acid (also referred to as hydroiodic acid), and hydrobromic acid, sulfuric acid (H2SO4), nitric acid (HNO3), chloric acid (HClO3), boric acid, perchloric acid (HClO4), trifluoroacetic acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid. Catalysts such as zinc acetate and manganese acetate can also be used, but may be less preferred.

[0035] The resin composition, when present in the resin-containing fiber, may or may not contain a diluent. A suitable diluent, if present, must meet several requirements: it must be a low viscosity liquid; it must have no or low reactivity with the polyol and the carboxylic acid; it must be a good solvent for the polyol and the carboxylic acid; and it must evaporate easily from the resin-containing fiber.

[0036] Although other liquids are possible, the use of water is considered preferable for technical, economic, and environmental reasons. Thus, the diluent, when present, generally consists of at least 50% by weight, in particular at least 70% by weight, more in particular at least 90% by weight, and even more in particular at least 95% by weight of water.

[0037] An advantage of the present invention is that the resins currently used herein can be diluent-free or rely on water as a diluent, compared to resins conventionally used in filament winding, eliminating the need for precautions required when handling resins based on volatile organic solvents, such as acetone.

[0038] When the diluent is present in the resin composition present in the resin-containing fiber when it is provided to the winding process, it is generally present in an amount of 90% by weight or less, particularly 70% by weight or less, calculated based on the resin composition. The presence of some diluent may be inherent due to its presence in the composition when applied to the fiber, or may be advantageous because it can maintain the flexibility of the fiber, but the presence of too much diluent will not provide any additional benefit and will have to be removed from the composition. Therefore, it may be preferred that the resin composition in the resin-containing fiber when it is provided to the winding process contains 50% by weight or less of diluent, particularly 40% by weight or less.

[0039] In one embodiment, the diluent content of the resin composition present in the resin-containing fiber when it is provided to the winding process is 20% by weight or less, particularly 15% by weight or less, more particularly 10% by weight or less.This is particularly applicable when the fiber provided to the winding process is a separately prepared prepreg.However, this can also be applicable in the direct winding method, for example, when a drying step is performed between applying the resin to the fiber and providing the resin-containing fiber to the winding process, or when the resin applied to the fiber has a low diluent content.

[0040] When the resin composition is present in the resin-containing fiber provided to the filament winding step, it may be preferred to include some diluent, as this can result in a more flexible fiber. This may be particularly true, but also in the case of a higher resin content and / or a higher degree of polymerization. Thus, in one embodiment, the resin composition, when present in the resin-containing fiber provided to the filament winding step, includes at least 0.5 wt. % water, particularly at least 1 wt. % water.

[0041] The resin composition may contain additional components.

[0042] In one embodiment, compounds are added to increase the interaction between the polymer and hydrophobic materials or to increase the water resistance of the final product. Suitable compounds include, for example, saturated or unsaturated C5-C22 fatty acids or their salts, saturated or unsaturated C5-C22 fatty alcohols, and dimeric and trimeric fatty acids or alcohols. For example, glycerol monostearate, triethyl citrate, and valeric acid can be used in the present invention. Compounds for increasing hydrophobicity will generally be added in an amount of 0.1 to 5% by weight, more particularly 0.3 to 3% by weight, calculated relative to the amount of the polymer. Additional ingredients for this purpose include saturated fatty acid mixtures obtained from the complete hydrogenation of vegetable oils, or vegetable oils in general.

[0043] Generally, the resin-containing fiber provided to the winding process comprises 1 to 90 volume % of the resin composition, calculated based on the total volume of the resin-containing fiber. The presence of too little resin will result in a molded object with insufficient properties. The presence of too much resin may impair the properties of the molded object, if the fiber is intended to provide specific properties to the molded object. In one embodiment, the resin-containing fiber provided to the winding process may preferably comprise 1 to 25 volume %, particularly 1 to 20 volume %, more particularly 1 to 15 volume %, and in some embodiments, 1 to 10 volume % of the resin composition. In another embodiment, the resin-containing fiber may preferably comprise 80 volume % or less of the resin composition, particularly 70 volume % or less of the resin composition. In one embodiment, the resin-containing fiber preferably comprises 25 to 90 volume %, particularly 25 to 80 volume %, more particularly 25 to 70 volume % of the resin composition.

[0044] The amount of resin composition relative to the fiber as provided to the winding process is calculated in volume percent from the weight of the resin composition relative to the fiber, the density of the resin composition, and the density of the material (glass, flax, etc.) from which the fiber is constructed.

[0045] The polyester present in the resin-containing fiber provided to the winding process generally has a degree of polymerization (DP) in the range of 0.05 to 0.6, where DP is the ratio of the number of reacted functional groups to the maximum number of functional groups that can react, and can be determined by using the acid value or by gravimetric measurement.

[0046] The desired degree of polymerization will depend on several factors. On the one hand, a higher degree of polymerization at the stage when the fiber is provided to the winding process has the advantage that less further curing is required in the process. On the other hand, a higher degree of polymerization may result in a more viscous resin composition, which may have a detrimental effect on the coating process. It may be preferred that the degree of polymerization of the resin relative to the fiber when provided to the winding process is at least 0.1, particularly at least 0.2, and more particularly at least 0.3.

[0047] In one embodiment, the resin-containing fiber is obtained by contacting a fiber with a liquid resin composition, as discussed above. The contacting step should be such that the resin composition adheres to the fiber. In one embodiment, this is done by passing the fiber through a resin bath. In another embodiment, the fiber is contacted with a lick roll to which the resin has been applied. Excess resin can be removed from the fiber, if desired. Other methods known in the art for coating a fiber with a liquid composition can also be applied. The liquid resin composition can be applied in a single step, but it can also be applied in two or more steps, with or without intermediate drying.

[0048] The viscosity of the liquid composition should be such that adequate coating of the fiber is achieved within a reasonable time frame. To achieve this goal, the viscosity should not be so low that significant coating is not achieved, nor so high that coating of the fiber is slow. The viscosity will depend on several 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 the presence of diluent, if any (higher amounts of diluent result in lower viscosity). In view of the above, preparing a liquid resin composition having the appropriate viscosity is within the purview of one skilled in the art.

[0049] In one embodiment of the present invention, the resin-containing fiber is contacting the fiber with a liquid resin composition to obtain a resin-containing fiber, wherein the resin composition comprises at least 50% by weight, calculated on the polymeric constituents of the resin, 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; subjecting the resin-containing fiber to a drying step, wherein the drying step is carried out until the resin-containing fiber becomes tacky and the resin-containing fiber has a diluent content of 25% by weight or less, calculated based on the weight of the resin composition in the resin-containing fiber; It is provided through a process including the steps of:

[0050] It may be preferred that the resin-containing fibers have a diluent content of 20 wt. % or less, more particularly 15 wt. % or less, even more particularly 10 wt. % or less, even more particularly 8 wt. % or less, and in some embodiments 5 wt. % or less.

[0051] In the context of this specification, tackiness is tested as follows: A 10 cm length of resin-containing fiber to be provided for the winding process is placed flat on a clean, dry, horizontal glass plate. Using a roller, a pressure of 200 g per mm of fiber width (determined on the fiber before rolling) is applied for 5 seconds. If necessary, the roller can be provided with a non-stick layer to prevent the fiber from adhering to the roller rather than the glass plate. The plate is then lifted and rotated so that the resin-containing fiber faces downward. If the resin-containing fiber falls off the glass plate within 15 seconds, the resin-containing fiber is considered non-tacky in the context of this specification. The test is performed at 20°C and 40-60% relative humidity.

[0052] In this embodiment, the tacky resin-containing fiber having a specific diluent content can be stored before being used in the filament winding process. The tacky resin-containing fiber can also be transported. The advantage of this so-called resin prepreg compared to known prepregs for filament winding is that the prepreg can be stored at ambient conditions, for example, at a temperature of 4 to 35°C and a humidity of 10 to 90%, for at least 4 hours, particularly at least 24 hours, and still remain tacky. The tackiness of the polymer is a measure of the degree of polymerization of the polyester. When the resin-containing fiber is no longer tacky, the polymer will have polymerized to such an extent that further curing will not cause the fibers to adhere to each other when the fiber is wound around a mandrel to form a molded object that retains its shape sufficiently.

[0053] In a preferred embodiment, the tacky resin-containing fiber is wound around a spool to form a spooled tacky resin-containing fiber. The spool of tacky resin-containing fiber is easily stored, transported, and further processed. The tacky resin-containing fiber is provided to the mandrel after being unwound from the spool, if necessary.

[0054] The present invention also relates to the prepreg itself. More particularly, the present invention relates to a resin-containing fiber, wherein the resin fiber contains 1 to 25 volume % of a resin, calculated on the polymeric constituents of the resin, including at least 50 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 resin-containing fiber being tacky and having a diluent content of 25 weight % or less, calculated on the weight of the resin composition in the resin-containing fiber. In one embodiment, the fiber is a single spool. The preferences and further preferences set forth above regarding the nature and amount of the resin and the fiber also apply to this aspect of the invention.

[0055] In another embodiment, the resin-containing fibers are processed directly without the formation of a separate prepreg. In this embodiment, the resin-containing fibers are provided by a process comprising the steps of contacting fibers with a liquid resin composition to obtain resin-containing fibers, and subsequently subjecting the fibers thus obtained to the winding step, wherein the resin composition comprises at least 50% by weight, calculated on the polymeric constituents of the resin, 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.

[0056] Whether processed with a prepreg or directly with resin-containing fibers, the method of the present invention includes a step (also referred to herein as a winding step) in which the resin-containing fibers are wound under tension to form a shaped fibrous body. As noted above and known in the art, the winding can be performed around a mandrel or around a framework in a coreless filament winding process. This process is well known in the field of filament winding methods and does not require further elucidation. Suitable winding patterns are also known in the art and include hoop-like winding patterns, helical winding patterns, random winding patterns, etc.

[0057] The formed fibrous body resulting from the winding process is then subjected to a curing process.

[0058] If desired, the molded fibrous body can be subjected to a drying step before the curing step to remove excess diluent. When prepregs are used, a drying step will generally not be required. This can be attractive when resin-containing fibers containing substantial amounts of diluent are used. If drying is performed, it can be carried out at temperatures (air temperature), for example, between 15°C and 200°C, particularly between 15°C and 100°C. Depending on the temperature, the drying step can be carried out for a few minutes, for example, at least 2 minutes, particularly at least 5 minutes, but can also be carried out for longer periods, for example, between 0.25 hours and 3 days, depending on the size and shape of the body and the amount of water in the molded body. Selecting suitable drying conditions is within the skill of one skilled in the art. Applying a vacuum or providing an air current to enhance evaporation of the diluent may be considered.

[0059] The curing step is intended to further polymerize the polyester. The most important aspect of the curing step is that the polyester is at a reaction temperature, for example, a product temperature of 80 to 250°C, particularly 100 to 200°C. Curing can be carried out using heating techniques known in the art, for example, in an oven having an oven temperature of 80 to 450°C. Various 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 control the curing, it may be preferable to increase the product temperature during curing. The curing time is 5 seconds to 24 hours, particularly 5 minutes to 12 hours, depending on the size and shape of the object and the type and temperature of the oven used. Selecting appropriate curing conditions is within the skill of a person skilled in the art. Therefore, the resin composition used in the method according to the present invention is a thermosetting resin composition. No further curing step using ionizing or actinic radiation is performed.

[0060] Depending on the nature of the object being produced, the cured and shaped fibrous body may or may not be removed from the mandrel. Filament winding is often used to provide fiber reinforcement to objects, such as pressure vessels. In this case, the cured and shaped fibrous body would not be removed from the mandrel. Rather, the cured and shaped fibrous body and the mandrel would form a single object. In other embodiments, the cured and shaped fibrous body is removed from the mandrel.

[0061] In one embodiment, the curing step comprises: subjecting the shaped fibrous body to a first curing step to form a partially cured shaped fibrous body; removing the partially cured shaped fibrous body from the mandrel, if one is present; subjecting the partially cured, shaped fibrous body to a further curing step. The method is carried out in a multi-step manner, including the steps of

[0062] The primary advantage of this sequence is that removal of the mandrel, if present, may facilitate circulation of hot air through the formed fibrous mass, which may increase the rate of hardening.

[0063] In this method, the polymer in the partially cured, molded fibrous body generally has a degree of polymerization of at least 0.4, particularly at least 0.5. A minimum degree of polymerization is generally required to ensure that the molded fibrous body does not break down into separate fibers. For the same reason, the partially cured, molded fibrous body generally has a diluent content of 2% by weight or less, more particularly 1% by weight or less, calculated based on the total weight of the partially cured, molded fibrous body.

[0064] Typically, the partially cured fibrous mass has a degree of polymerization of 0.8 or less, in particular 0.7 or less, and further curing is carried out in the further curing step.

[0065] After removal from the mandrel, the partially cured fibrous mass may be subjected to a further curing step under the curing conditions specified above.

[0066] In one embodiment, the partially cured object is subjected to a process to change its shape. The partially cured object can still be relatively flexible, and therefore can be formed into shapes that would otherwise be impossible to achieve using a filament winding method. Examples of methods by which the shape of the object can be changed include cutting, pressing, molding, vacuum forming, etc. After the shape has been changed, the object can be cured as described above.

[0067] For coreless filament winding processes, performing the curing in a two-step process can also be attractive, especially if a shape-changing step is performed between the first and second curing steps.

[0068] As will be apparent to those skilled in the art, the curing process inevitably involves the formation of water as a by-product, along with the formation of an ester by reaction of the alcohol with the carboxylic acid. This water must be removed from the formed fibrous body. It has been found that, particularly when the fibers have limited water absorption capacity, such as glass fibers, carbon fibers, or polymer-based fibers, such as polyamide fibers, and / or when the filament-wound layer is relatively thick, it can be attractive to take measures to ensure that the water formed during the curing process can easily evaporate. Various examples of such measures can be mentioned. In one embodiment, the mandrel is porous, e.g., due to the presence of holes, or is ribbed to allow water to evaporate. In another embodiment, a water-absorbing material, such as paper or cardboard, a layer of woven or nonwoven fabric, or other absorbent material, is provided on the mandrel. In a further embodiment, the mandrel itself can be made of a water-absorbing material, such as cardboard. Selecting a relatively open winding pattern can also help ensure adequate water removal. Curing at sub-atmospheric pressures, which promotes water evaporation, can also be applied.

[0069] The use of a combination of fibers can also be attractive, for example, by combining synthetic fibers, such as glass or carbon fibers, which generally have a low water absorption capacity, with natural fibers, such as cellulose-based fibers, which generally have a higher water absorption capacity. The natural fibers can then act as water conduits. In this embodiment, the natural fibers are generally present in an amount of 1 to 40% by weight, particularly in the range of 1 to 25% by weight, and more particularly in the range of 1 to 10% by weight, calculated on the total fiber weight. The amount of natural fibers should not be too high, as this can impair the properties of the object to be made from the synthetic fibers. If desired, the natural fibers and the synthetic fibers can be combined. In one embodiment, the natural fibers and the synthetic fibers are applied as a whole in a single layer. In another embodiment, one or more layers of natural fibers are combined with one or more layers of synthetic fibers. To aid in water removal, it may be preferable to use a layer of natural fibers on the outside of the object. Of course, it is also possible to mix fibrous layers with layers containing only natural or only synthetic fibers.

[0070] The present invention also relates to a molded fibrous body comprising wound resin-containing fibers, wherein the resin comprises at least 50% by weight, calculated on the polymeric components of the resin, 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, and the polyester has a degree of polymerization of at least 0.8, the degree of polymerization being the ratio of the number of reacted functional groups to the maximum number of functional groups that can react. Depending on the intended use, it may be preferred for the polyester to have a degree of polymerization of at least 0.9, particularly at least 0.95.

[0071] Preferences for the nature and amount of resin, fiber type, and other preferences also apply to embodiments of the present invention.

[0072] The objects of the present invention find application in many fields, ranging from heavy duty applications such as lantern poles and windmill components, to design uses including furniture.

[0073] In one embodiment, the fibers are glass fibers provided with a resin based on glycerol and citric acid. In particular, it has been found that durable objects can be obtained when this resin is polymerized to a degree of polymerization of at least 0.9. The preferences expressed above also apply to this embodiment, except where mutually exclusive.

[0074] In one embodiment, the fibers are natural fibers, particularly flax or hemp fibers, provided with a resin based on glycerol and citric acid. Objects based on this combination have been found to have an attractive appearance and feel, making them particularly attractive for design applications. The preferences expressed above also apply to this embodiment, except where mutually exclusive.

[0075] The present invention is illustrated by, but not limited to, the following examples.

[0076] Example 1 Glass Fiber - Direct Winding A resin composition was prepared containing a polyester based on glycerol and citric acid, having a degree of polymerization of about 0.4 (based on mass balance) and a water content of 21% by weight. The bath was at a temperature of 54°C. Glass fibers having a linear weight of 2400 tex were passed through the resin bath, and excess resin was removed. The resin-containing fibers thus formed contained about 50% by volume of resin.

[0077] The resin-containing fibre was wound around a 100 mm diameter steel pipe.

[0078] The steel pipe was coated with a release agent. Release paper can also be used as well as release coatings, such as Teflon coatings.

[0079] The winding was performed in a hoop pattern at a constant rpm of 5.5 rpm and a constant angle of approximately 90°. When the winding process was completed, the mandrel on which the fibrous mass was provided was cured at 120° C. for 1 hour, 140° C. for 1 hour, and 160° C. for 2 hours. The fibrous mass was then cooled and removed from the mandrel.

[0080] The final object contained 43% by volume of resin, based on the total volume of the object consisting of resin and fibers. Photographs of the fibrous object thus obtained are shown in Figures 1a and 1b.

[0081] Example 2 Glass fiber - prepreg A resin composition was prepared as described in Example 1. The resin bath was at room temperature. Glass fibers were passed through the resin bath. Excess resin was removed. The fibers contained 50% resin by volume.

[0082] The resin-containing fibers were passed through an air tunnel. The residence time was 4 minutes. The air temperature was 135-150°C. The resulting product was sticky. The product had a water content of less than 10% by weight. The degree of polymerization of the resin in the prepreg thus formed was slightly higher than that of the resin in the polymer bath.

[0083] The prepreg so obtained was stored for 4 days at ambient conditions (temperature 18-22°C, relative humidity 40-60%). After 4 days, the prepreg was still tacky but otherwise unchanged. Similar material has been stored under these conditions for several weeks without adverse effects. The prepreg can be seen in Figure 2.

[0084] The prepreg was used to make a cylinder by winding it around a mandrel, in this case a carbon tube. After winding, a curing process was carried out by placing the mandrel with the fiber in an oven for 4.5 hours while the temperature was slowly increased from 80°C to 180°C. After 4.5 hours, the mandrel with the molded fibrous body was removed from the oven and the body was removed from the mandrel. The resin in the molded fibrous body had a degree of polymerization greater than 0.95.

[0085] Example 3 Flax fiber - direct winding A resin composition was prepared containing a polyester based on glycerol and citric acid, with a degree of polymerization of about 0.4 (based on mass balance) and a water content of 21% by weight. The bath was at a temperature of 54°C. Flax fibers with a linear weight of 1000 tex were passed through the resin bath, and excess resin was removed. The resin-containing fibers thus formed contained 60% by volume of resin.

[0086] The resin-containing fiber was wound around a steel pipe.

[0087] The winding was performed at a constant rpm of 5.5 rpm and at a constant angle.

[0088] When the winding process was completed, the mandrel on which the fibrous mass was provided was cured at 160° C. for 30 minutes, followed by 180° C. for 60 minutes. The fibrous mass was then removed from the mandrel. The final mass contained 47% resin by volume.

[0089] The table below shows the processing conditions and results for the various experiments. Photographs of the objects formed in 3.1 and 3.3 are in Figures 3a and 3b, respectively.

[0090] [Table 1]

[0091] The material is lightweight and has an appealing natural look and feel.

[0092] Example 4 Effect of curing temperature The procedure of Example 1 was repeated with the following differences. The temperature of the resin bath was 47°C. The winding was continued until three double layers of fiber were formed. The mandrel had a diameter of 5 cm.

[0093] Curing was carried out as follows: 1 hour at 120° C., 1 hour at 140° C., 1 hour at 160° C., and 1 hour at 180° C. The final object contained 45% resin by volume.

[0094] To investigate the effect of curing temperature, the formed bodies were divided into pieces having a length of 4 cm, four of which were subjected to further curing at 200° C. for 1 hour. It was found that the post-cured pieces exhibited higher stiffness than pieces that were not subjected to the post-curing step.

[0095] Example 5 Absorbent mandrel, layered system A cardboard tube with an outer diameter of 75 mm and a wall thickness of 2 mm was used as a mandrel, the purpose of which was to provide a low-cost core that also contributed to the removal of water from the wound composite material.

[0096] A resin composition was prepared containing a polyester based on glycerol and citric acid, with a degree of polymerization of approximately 0.4 (based on mass balance) and a water content of 20% by weight. The bath was at a temperature of 50°C. A glass fiber having a linear weight of 2400 tex was passed through the resin bath, and excess resin was removed. The glass fiber was wound in a hoop pattern around the cardboard mandrel at a constant rpm of 5.5 rpm and a constant angle of approximately 90° until a layer thickness of 8 mm was reached.

[0097] Flax fibers having a linear weight of 2400 tex were passed through the same resin bath and used to provide a single top layer on the glass fiber layer.

[0098] When the winding process was completed, the mandrel on which the fibrous body was provided was cured at 120°C for 1 hour, 140°C for 1 hour, 160°C for 1 hour, and 180°C for 1 hour. A photograph of the final fibrous body is provided in Figure 4. The use of a flax outer layer on a fiberglass core allows for the provision of a product with an attractive visual appearance over a low-cost, high-strength fiberglass core. Additionally, the flax fibers may help transport water from the fiberglass core. In one embodiment, the present invention may be configured as follows. [Section 1] 1. A method for producing a shaped object via a winding process, comprising: winding a resin-containing fiber under tension to form a shaped fibrous body, wherein the resin comprises at least 50% by weight, calculated on the polymeric constituents of the resin, 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; and subjecting the formed fibrous body to a curing step. The method, comprising the steps of: [Section 2] The resin-containing fiber contacting a fiber with a liquid resin composition to obtain a resin-containing fiber, wherein the resin composition comprises at least 50% by weight, calculated on the polymer constituents of the resin, of a polyester derived from an aliphatic polyol polyester 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 fiber to a drying step, wherein the drying step is carried out until the resin-containing fiber becomes tacky and the resin-containing fiber has a diluent content of 25% by weight or less, calculated based on the weight of the resin composition in the resin-containing fiber; The method according to item 1, wherein the method is provided through a process including the steps of: [Section 3] 3. The method of claim 2, wherein the tacky resin-containing fiber is wound around a spool to form a spooled tacky resin-containing fiber. [Section 4] The method according to item 2 or 3, wherein the tacky resin-containing fiber is provided to a step of winding the resin-containing fiber, after being unwound from a spool if necessary, to form a shaped fibrous object. [Section 5] The resin-containing fiber contacting a fiber with a liquid resin composition to obtain a resin-containing fiber, wherein the resin composition comprises a polyester derived from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms; Subsequently, the fibers thus obtained are subjected to a winding process to form a shaped fibrous object. The method according to item 1, wherein the method is provided through a process including the steps of: [Section 6] Item 6. The method according to item 5, wherein the shaped fibrous body formed during the winding step is subjected to a drying step before the curing step. [Section 7] Item 7. The method of any one of items 1 to 6, wherein winding the resin-containing fiber under tension to form a shaped fibrous body is performed by winding on a mandrel. [Section 8] 8. The method of claim 7, wherein the cured, shaped fibrous body is removed from the mandrel. [Section 9] subjecting the shaped fibrous body to a first curing step on the mandrel to form a partially cured shaped fibrous body; removing the partially cured shaped fibrous body from the mandrel; subjecting the partially cured, shaped fibrous body to a further curing step after removal from the mandrel. Item 9. The method according to Item 7 or 8, comprising the steps of: [Section 10] 10. The method of claim 9, wherein after removal from the mandrel and before subjecting the partially cured shaped fibrous body to a step of changing its shape. [Section 11] Item 7. The method according to any one of items 1 to 6, wherein the winding step is carried out in a framework in a coreless filament winding step. [Section 12] subjecting the shaped fibrous body to a first curing step to form a partially cured shaped fibrous body; subjecting the partially cured, shaped fibrous body to a process in which the shape of the partially cured, shaped fibrous body is changed; and subjecting the partially cured, shaped fibrous body to a further curing step. Item 12. The method according to Item 11, comprising the steps of: [Section 13] 1. A fiber comprising a resin composition comprising 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 25% by weight or less, specifically 20% by weight or less, more specifically 15% by weight or less, even more specifically 10% by weight or less, still more specifically 8% by weight or less, and in some embodiments 5% by weight or less, calculated based on the weight of the resin composition in the resin-containing fiber. [Section 14] Item 14. The fiber according to item 13, which is present on a spool. [Section 15] 1. A molded fibrous body comprising wound resin-containing fibers, wherein the resin comprises 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 on the polymer constituents of the resin, and the polyester has a degree of polymerization of at least 0.8, the degree of polymerization being the ratio of the number of reacted functional groups to the maximum number of functional groups capable of reacting.

Claims

1. 1. A method for producing a shaped object via a winding process, comprising: (a) winding a resin-containing fiber under tension to form a shaped fibrous body, wherein the resin comprises at least 50% by weight, calculated on the polymeric constituents of the resin, of a polyester derived from an aliphatic polyol having from 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having from 3 to 15 carbon atoms; and (b) subjecting the formed fibrous body to a curing step. The process includes the steps of: Here, the resin-containing fiber is (i) contacting a fiber with a liquid resin composition to obtain a resin-containing fiber, wherein the liquid resin composition comprises at least 50% by weight, calculated on the polymer constituents of the resin composition, of a polyester derived from an aliphatic polyol polyester derived from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms; (ii) subjecting the resin-containing fiber to a drying step, wherein the drying step is carried out until the resin-containing fiber becomes tacky and the resin-containing fiber has a diluent content of 25% by weight or less, calculated based on the weight of the resin composition in the resin-containing fiber; provided through a process that includes the steps of The method.

2. A method for producing a shaped object via a winding process, comprising: (a) winding a resin-containing fiber under tension to form a shaped fibrous body, wherein the resin comprises at least 50% by weight, calculated on the polymeric constituents of the resin, of a polyester derived from an aliphatic polyol having from 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having from 3 to 15 carbon atoms; and (b) subjecting the formed fibrous body to a curing step. The process includes the steps of: wherein step (a) is (1) contacting the fibers with a liquid resin composition, wherein the liquid resin composition comprises at least 50% by weight, calculated on the polymeric constituents of the resin, of a polyester derived from an aliphatic polyol polyester derived from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms; (2) winding the resulting fibers under tension to form a shaped fibrous body; and (3) drying the formed fibrous body prior to the curing step; performed by a process including the steps of The method.

3. The method described in claim 1, wherein the sticky resin-containing fiber obtained in step (ii) is wound around a spool to form a sticky resin-containing fiber wound on a spool.

4. 4. The method of claim 3, wherein the tacky resin-containing fibers are provided to a step of winding the resin-containing fibers to form a shaped fibrous body.

5. The method of any one of claims 1 to 4, wherein winding the resin-containing fiber under tension to form a shaped fibrous body is performed by winding on a mandrel.

6. The method of claim 5 wherein the cured shaped fibrous body is removed from the mandrel.

7. subjecting the formed fibrous body to a first curing step on the mandrel to form a partially cured formed fibrous body; removing the partially cured shaped fibrous body from the mandrel; subjecting the partially cured shaped fibrous body to a further curing step after removal from the mandrel. The method according to claim 5 or 6, comprising the steps of:

8. 8. The method of claim 7, wherein after removal from the mandrel and before subjecting the partially cured shaped fibrous body to the further curing step, the partially cured shaped fibrous body is subjected to a step in which the shape of the partially cured shaped fibrous body is changed.

9. The method according to any one of claims 1 to 5, wherein the winding step is carried out on a framework in a coreless filament winding step.

10. subjecting the shaped fibrous body to a first curing step to form a partially cured shaped fibrous body; subjecting the partially cured shaped fibrous body to a process in which the shape of the partially cured shaped fibrous body is changed; and subjecting the partially cured shaped fibrous body to a further curing step. The method of claim 9, comprising the steps of:

11. A fiber for use in the method of claim 1, the fiber comprising a resin composition comprising at least 50% by weight, calculated on the polymer constituents of the resin, 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 self-adhesive and having a diluent content of 25% by weight or less, calculated on the weight of the resin composition in the resin-containing fiber.

12. The fiber of claim 11 present on a spool.

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