Vacuum bag for autoclave molding

Abstract

Provided is a vacuum bag for autoclave molding with which it is possible to reduce solid waste after autoclave molding and save labor in peeling work. This vacuum bag for autoclave molding has a polyvinyl alcohol film containing polyvinyl alcohol as a main component. A heat-treated film obtained by heating the polyvinyl alcohol film at 130°C for 120 minutes is completely dissolved in pure water at 70°C or lower.

Description

Vacuum bag for autoclave molding

[0001] The present invention relates to a vacuum bag for autoclave molding.

[0002] Molded bodies in which reinforcing materials such as natural fibers and carbon fibers are solidified with a base material (matrix) such as a resin are known. For such molded bodies, various molding methods are selected according to the final form and properties. Among the molding methods, autoclave molding is a molding method with a high degree of freedom in materials and shapes, and is the molding method that can most easily bring out the characteristics and performance of the molded body.

[0003] A typical procedure outline of autoclave molding is as follows. A prepreg in which a thermosetting resin is impregnated into fibers (reinforcing fibers) serving as a reinforcing material is cut into a predetermined shape. A mold release agent is applied to a mold having a desired shape, and the required number of prepregs are laminated at a predetermined position inside the mold. A release film and a breather are sequentially arranged on the surface of the laminated prepregs, and these are covered and sealed with a bagging film. By covering and sealing with such a bagging film, a vacuum bag is formed. By discharging the air inside the vacuum bag and making the inside of the vacuum bag into a vacuum state, the adhesion of the laminated prepregs to the mold is enhanced. Then, the molded body is obtained by curing the thermosetting resin while heating and pressurizing in an autoclave.

[0004] Generally, resin films such as nylon films are used as the bagging films used in autoclave molding. Patent Document 1 describes a film made of a resin composition mainly composed of a polyamide resin and a thermoplastic elastomer as a bagging film used in autoclave molding.

[0005] Japanese Patent Application Laid-Open No. 2016-190404

[0006] While autoclave molding is a method capable of producing high-quality molded products, it presents challenges in the disposal of the auxiliary materials used. Many of the auxiliary materials used in autoclave molding (release film, breather, bagging film, etc.) are not reused after molding and become waste. Because these auxiliary materials are in film form, they are bulky, and there are limitations to how much they can be reduced in size, requiring dedicated disposal space. Furthermore, in autoclave molding, the heat curing of the thermosetting resin inside the vacuum bag causes the bagging film and other materials to adhere strongly to the molded product, resulting in the problem of time-consuming removal work.

[0007] This invention was made based on these circumstances, and the object of this invention is to provide a vacuum bag for autoclave molding that enables the reduction of solid waste after autoclave molding and the saving of labor in peeling operations.

[0008] In other words, the present invention relates to [1] to [9]. [1] An autoclave-molding vacuum bag having a polyvinyl alcohol film mainly composed of polyvinyl alcohol, wherein a heat-treated film obtained by heating the polyvinyl alcohol film at 130°C for 120 minutes completely dissolves in pure water at 70°C or below. [2] The autoclave-molding vacuum bag according to [1], wherein the average thickness of the polyvinyl alcohol film is 25 to 200 μm. [3] The autoclave-molding vacuum bag according to [1] or [2], wherein the heat of fusion of the polyvinyl alcohol film, measured at a heating rate of 10°C / min using differential scanning calorimetry (DSC) in accordance with ISO 11357-2,3 (2011), is 10 to 35 J / g. [4] The autoclave-molding vacuum bag according to any of [1] to [3], wherein the polyvinyl alcohol contains modified polyvinyl alcohol. [5] The autoclave-molding vacuum bag according to [4], wherein the modified polyvinyl alcohol is at least one selected from the group consisting of sulfonic acid-modified polyvinyl alcohol and carboxylic acid-modified polyvinyl alcohol. [6] The autoclave-molding vacuum bag according to any of [1] to [5], wherein the degree of saponification of the polyvinyl alcohol is 70 to 98 mol%. [7] The autoclave-molding vacuum bag according to any of [1] to [6], wherein the content of vinyl alcohol units relative to the total monomer units of the polyvinyl alcohol is 70 to 98 mol%. [8] The autoclave-molding vacuum bag having a polyvinyl alcohol film mainly composed of polyvinyl alcohol, wherein the content of vinyl alcohol units relative to the total monomer units of the polyvinyl alcohol is 70 to 98 mol%. [9] The autoclave-molding vacuum bag according to [8], wherein the average thickness of the polyvinyl alcohol film is 25 to 200 μm.

[0009] The vacuum bag for autoclave molding of the present invention makes it possible to reduce solid waste after autoclave molding and to save labor in the peeling process.

[0010] Figure 1 is a schematic cross-sectional view showing a vacuum bag for autoclave molding, etc., according to one embodiment of the present invention. Figure 2 is a schematic cross-sectional view showing a vacuum bag for autoclave molding, etc., according to an embodiment different from that of Figure 1.

[0011] In this specification, numerical ranges indicated using "~" include the values ​​indicated before and after "~" as the lower and upper limits. In this specification, the upper and lower limits of numerical ranges (content, physical properties, etc.) can be combined as appropriate. In this specification, "main component" refers to the component with the highest content by mass. Polyvinyl alcohol may be abbreviated as "PVA," polyvinyl alcohol film as "PVA film," autoclave molding as "AC molding," and vacuum bags for autoclave molding as "AC molding vacuum bags" or "vacuum bags."

[0012] A vacuum bag is a container that has a shape that creates a vacuum inside when the contents are evacuated. A vacuum bag may be, for example, a bag shape, but is not limited to that shape. A vacuum bag may be composed of, for example, only a bagging film, or it may be composed of a bagging film and other components (for example, a mold). A vacuum state does not refer only to a completely vacuum state, but to a state where the pressure is sufficiently reduced compared to atmospheric pressure. A vacuum state may be, for example, a state of 0.1 atmospheres or less, or a state of 0.01 atmospheres or less or 0.001 atmospheres or less. Furthermore, "molding material" refers to the material before curing, and "molded body" refers to the cured product after curing.

[0013] An AC molding vacuum bag according to one embodiment of the present invention is an AC molding vacuum bag having a PVA film mainly composed of PVA, wherein the heat-treated film obtained by heating the PVA film at 130°C for 120 minutes completely dissolves in pure water at 70°C or below.

[0014] The vacuum bag for AC molding enables a reduction in solid waste after AC molding and simplifies the peeling process. The reasons for this are as follows: In this vacuum bag for AC molding, the PVA film used as the so-called bagging film retains good water solubility even after heating during AC molding. Therefore, the PVA film can be dissolved and removed by washing with water after AC molding. Consequently, this vacuum bag for AC molding reduces the amount of bagging film that would normally become solid waste, leading to space savings in waste disposal areas (waste storage areas, etc.). Furthermore, since the PVA film, which is the bagging film, dissolves when washed with water after AC molding, it is not necessary to physically peel off the bagging film, and even if the film remains after washing, it can be easily peeled off, thus saving labor in the peeling process.

[0015] (PVA Film) First, the PVA film used in the AC molding vacuum bag will be described in detail below. This PVA film is used as a so-called bagging film. The PVA film is mainly composed of PVA. The PVA film has moderate hardness and is easy to work with. In addition, the PVA film has excellent conformability to the molding material, making it possible to manufacture molded products with a good surface appearance. Furthermore, since PVA has low affinity with the base material used in the molding material (especially thermosetting resins such as epoxy resin), it has the advantage of being easy to remove with water after molding.

[0016] PVA stands for vinyl alcohol unit (-CH ２ It is a polymer having -CHOH-). PVA may have monomer units other than vinyl alcohol units. As PVA, a vinyl ester polymer obtained by polymerizing vinyl ester monomers and then saponifying that polymer can be used. Polymerization and saponification can be carried out by conventionally known methods.

[0017] Examples of vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versaticate, with vinyl acetate being preferred.

[0018] The degree of polymerization of PVA is not particularly limited, and may be, for example, 500 to 8,000, 1,000 to 6,000, or 1,500 to 4,000. Here, the degree of polymerization of PVA refers to the viscosity-average degree of polymerization (Po) measured in accordance with the description in JIS K6726-1994, and is determined by the following formula from the intrinsic viscosity [η] (deciliters / g) measured in water at 30°C after resaponification and purification of polyvinyl alcohol.

[0019] The degree of saponification of PVA is not particularly limited, and is usually 70 to 100 mol%, may be 70 to 99.9 mol%, and preferably 70 to 98 mol%. By having a degree of saponification of 70 to 98 mol%, the appropriate hardness of the PVA film and the water solubility after AC molding can be optimized in a well-balanced manner. The upper limit of the degree of saponification is more preferably 95 mol%, even more preferably 93 mol%, and even more preferably 91 mol%, from the viewpoint of the water solubility of the PVA film after AC molding. The lower limit of the degree of saponification is more preferably 75 mol%, even more preferably 78 mol%, even more preferably 80 mol%, and may be 82 mol%, 84 mol%, or 86 mol%, from the viewpoint of flexibility, etc. The degree of saponification refers to the ratio (mol%) of moles of vinyl alcohol units to the total number of moles of monomer units (typically vinyl ester units) and vinyl alcohol units that can be converted into vinyl alcohol units by saponification. The degree of saponification of PVA can be measured in accordance with the description in JIS K6726-1994.

[0020] The PVA may contain modified PVA, or it may be modified PVA alone. Using modified PVA tends to increase the water solubility of the PVA film after AC molding. Modified PVA refers to PVA that has monomer units derived from monomers other than vinyl esters. Modified PVA may also be a saponified product of modified polyvinyl ester. Furthermore, modified PVA may be obtained by post-modifying unmodified PVA.Other monomers include, for example, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, and itaconic acid, their salts, or their anhydrides; unsaturated sulfonic acids such as acrylamide alkyl sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid, their salts, or their anhydrides; ethylene; olefins having 3 to 30 carbon atoms such as propylene, 1-butene, and isobutene; methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, and 2-butyl acrylate. Acrylic acid esters such as -ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate; acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamide Acrylamide derivatives such as dopropyldimethylamine or its salts, N-methylolacrylamide or its derivatives; methacrylamide derivatives such as methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid or its salts, methacrylamidepropyldimethylamine or its salts, N-methylolmethacrylamide or its derivatives; N-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-prop Examples include vinyl ethers such as polyvinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid esters; itaconic acid esters; vinyl silyl compounds such as vinyltrimethoxysilane; and isopropenyl acetate.

[0021] As the modified PVA, acid-modified PVA such as carboxylic acid-modified PVA, sulfonic acid-modified PVA, and phosphate-modified PVA is preferred, and at least one selected from the group consisting of sulfonic acid-modified PVA and carboxylic acid-modified PVA is more preferred. Using such modified PVA tends to increase the water solubility of the PVA film after AC molding.

[0022] Sulfonic acid-modified PVA is PVA having a sulfo group. The sulfo group may be in the form of a salt or an anhydride. Sulfonic acid-modified PVA may have monomer units derived from the unsaturated sulfonic acid, its salt, or its anhydride, or it may have a sulfo group introduced by post-modification. It is preferable that sulfonic acid-modified PVA has monomer units derived from an unsaturated sulfonic acid, its salt, or its anhydride.

[0023] Carboxylic acid-modified PVA is PVA having a carboxyl group. The carboxyl group may be in the form of a salt or an anhydride. Carboxylic acid-modified PVA may have monomer units derived from the unsaturated carboxylic acid, its salt, or its anhydride, or it may have a carboxyl group introduced by post-modification. It is preferable that carboxylic acid-modified PVA has monomer units derived from an unsaturated carboxylic acid, its salt, or its anhydride.

[0024] The modified PVA is preferably a saponified product of a modified polyvinyl ester (a copolymer of a vinyl ester and another monomer other than a vinyl ester). In other words, it is preferable that the modified PVA is not modified by post-modification. The main chain of the modified PVA may consist of vinyl alcohol units, arbitrary vinyl ester units, and units derived from other monomers. The other monomers are preferably monomers having acidic groups (sulfo groups, carboxyl groups, phosphate groups, etc.). The acidic groups may be in the form of salts or anhydrides. Examples of monomers having acidic groups include the unsaturated sulfonic acid, its salt or anhydride, the unsaturated carboxylic acid, its salt or anhydride, etc.

[0025] The degree of modification in modified PVA is, for example, 0.1 to 10 mol%. The lower limit of the degree of modification may be 0.5 mol% or 1 mol%. The upper limit of the degree of modification may be 5 mol% or 3 mol%. The degree of modification refers to the ratio of monomer units derived from monomers other than vinyl ester to the total monomer units constituting the modified PVA.

[0026] The upper limit of the content of vinyl alcohol units relative to the total monomer units of PVA is preferably 98 mol%, more preferably 95 mol%, even more preferably 93 mol%, and even more preferably 91 mol%. The lower limit of the content is preferably 70 mol%, more preferably 75 mol%, even more preferably 78 mol%, and even more preferably 80 mol% or 84 mol%. In this way, the presence of a moderate amount of monomer units other than vinyl alcohol units (vinyl ester units and monomer units derived from other monomers other than vinyl esters) tends to reduce the crystallinity of the PVA film and increase the water solubility of the PVA film after AC molding. In one embodiment of the present invention, the content of vinyl alcohol units relative to the total monomer units of PVA may be 70 to 98 mol%.

[0027] The lower limit of the PVA content in the PVA film is preferably 50% by mass, more preferably 60% by mass, and even more preferably 80% by mass. The upper limit of the PVA content in the PVA film may be 100% by mass, or 99% by mass, 95% by mass, or 90% by mass.

[0028] In addition to PVA as the main component, the PVA film may also contain water, plasticizers, surfactants, fillers, starch, hydrophilic polymers, etc., as long as they do not impair the effects of the present invention.

[0029] As plasticizers, polyhydric alcohols such as ethylene glycol, glycerin, diglycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, trimethylolpropane, and sorbitol are preferred from the viewpoint of being less likely to cause bleed-out to the film surface, and it is more preferable that at least one is selected from the group consisting of ethylene glycol, glycerin, diglycerin, propylene glycol, and diethylene glycol.

[0030] The amount of plasticizer contained in the PVA film can be appropriately adjusted according to the shape and surface properties of the molded article. The lower limit of the plasticizer content in the PVA film may be 0 parts by mass, preferably 1 part by mass, more preferably 3 parts by mass, and may also be 5 or 10 parts by mass per 100 parts by mass of PVA. By setting the plasticizer content in the PVA film to be above the lower limit, the flexibility of the PVA film can be increased. On the other hand, the upper limit of the plasticizer content is preferably 35 parts by mass, more preferably 30 parts by mass, even more preferably 25 parts by mass, and even more preferably 20 parts by mass per 100 parts by mass of PVA. By setting the plasticizer content in the PVA film to be below the upper limit, the strength of the PVA film can be increased.

[0031] The surfactant is not particularly limited as long as it does not impair the effects of the present invention, and examples include cationic surfactants, anionic surfactants, and nonionic surfactants.

[0032] The lower limit of the total content of PVA and optional components such as water, plasticizers, and surfactants in the PVA film may be, for example, 90% by mass, 95% by mass, 98% by mass, 99% by mass, 99.5% by mass, or 99.9% by mass. The upper limit of the total content of PVA and optional components such as water, plasticizers, and surfactants in the PVA film may be 100% by mass.

[0033] PVA film may contain fillers. By including fillers, the mechanical strength and handling properties of the PVA film can be improved.

[0034] Examples of fillers include carbon black, metal powder, silica, alumina, calcium carbonate, titanium dioxide, talc, mica, and clay minerals such as bentonite.

[0035] Examples of starches include natural starches such as corn starch, potato starch, sweet potato starch, wheat starch, rice starch, tapioca starch, and sago starch; and modified starches that have undergone etherification, esterification, oxidation, etc.

[0036] Examples of hydrophilic polymers include dextrin, gelatin, animal glue, casein, shellac, gum arabic, sodium polyacrylate, polyvinyl methyl ether, cellulose, acetylcellulose, acetylbutylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, and sodium alginate.

[0037] The upper limit of the hydrophilic polymer content in the PVA film is preferably 15 parts by mass, and more preferably 10 parts by mass, per 100 parts by mass of PVA. The lower limit of the hydrophilic polymer content in the PVA film may be 0 parts by mass, 0.1 parts by mass, 0.5 parts by mass, or 1 part by mass, per 100 parts by mass of PVA. Note that the PVA content is not included in the hydrophilic polymer content.

[0038] The PVA film may further contain other components besides those described above, as long as they do not hinder the effects of the present invention. Examples of other components include antioxidants, ultraviolet absorbers, lubricants, crosslinking agents, colorants, preservatives, and fungicides. It is preferable that the PVA film does not contain any insoluble components that are visible to the naked eye when dissolved in 95°C hot water to prepare a 1% by mass aqueous solution. It is preferable that the PVA film does not contain components with a major diameter of 1 mm or more that are insoluble in 95°C hot water.

[0039] The surface of the PVA film may be physically and / or chemically treated as necessary, as long as it does not impair the effects of the present invention. Examples of physical treatments include embossing. Examples of chemical treatments include surface treatments to prevent blocking inside the film roll.

[0040] The average thickness of the PVA film is preferably 25 to 200 μm. From the viewpoint of ease of handling during AC molding, the lower limit of the average thickness is more preferably 30 μm. On the other hand, from the viewpoint of water solubility after AC molding, the upper limit of the average thickness is more preferably 160 μm, even more preferably 140 μm, and may also be 100 μm.

[0041] The PVA film may be a stretched film or an unstretched film, but an unstretched film is preferred. By using an unstretched PVA film as a bagging film, effects such as conformability are more fully realized. An unstretched film is a film that has not undergone substantially any stretching treatment. An unstretched film may be a film with a length-based stretching ratio of 1.0x or more and 1.1x or less, or a stretched film with a length-based stretching ratio of 1.00x or more and 1.01x or less.

[0042] A heat-treated PVA film, heated at 130°C for 120 minutes, dissolves completely in pure water at 70°C or below. In other words, the PVA film retains sufficient water solubility even after being heated under predetermined conditions. Hereinafter, the temperature of pure water at which the heat-treated film, heated at 130°C for 120 minutes, completely dissolves is also referred to as the complete dissolution temperature of the heat-treated film. The complete dissolution temperature of the heat-treated film is 70°C or below, but is preferably 60°C or below, more preferably 50°C or below, even more preferably 45°C or below, and even more preferably 40°C or below. The complete dissolution temperature of the heat-treated film may be 5°C or higher, or it may be 10°C or higher or 15°C or higher.

[0043] The upper limit of the time it takes for the heat-treated film to completely dissolve at its complete dissolution temperature (the time required for the complete dissolution of the heat-treated film at its complete dissolution temperature) is not particularly limited and may be 180 seconds, 90 seconds, or 60 seconds. The lower limit of the time required for the complete dissolution of the heat-treated film at its complete dissolution temperature may be 2 seconds or 10 seconds.

[0044] When the heat-treated film dissolves in pure water at 40°C (when the complete dissolution temperature of the heat-treated film is 40°C or lower), there is no limit to the lower limit of the complete dissolution time of the heat-treated film at 40°C, and it may be 2 seconds or 5 seconds. On the other hand, the upper limit of the complete dissolution time of the heat-treated film at 40°C is preferably 120 seconds, more preferably 60 seconds, and even more preferably 30 seconds. If the complete dissolution time of the heat-treated film at 40°C is within such a range, the workability when producing the vacuum bag, the water solubility after autoclave molding, etc. will be better.

[0045] Regarding the complete dissolution temperature and complete dissolution time of the heat-treated film, by lowering the degree of saponification of PVA, which is the main component of the PVA film, increasing the amount of modification, etc., the complete dissolution temperature of the heat-treated film tends to decrease, and the complete dissolution time of the heat-treated film tends to shorten. Also, by making the PVA film thinner, increasing the content of the plasticizer, etc., the complete dissolution temperature also tends to decrease, and the complete dissolution time tends to shorten. In addition, it can also be adjusted by the film-forming conditions, drying conditions, heat-treatment conditions, etc. when manufacturing the PVA film.

[0046] The complete dissolution temperature and complete dissolution time of the heat-treated film are specifically measured by the method described in the examples below.

[0047] The heat of fusion of the PVA film measured at a heating rate of 10°C / min using differential scanning calorimetry (DSC) in accordance with ISO 11357-2, 3 (2011) is preferably 10 to 35 J / g, more preferably 12 to 30 J / g. A low heat of fusion means a low crystallinity of the PVA film, etc. Such a PVA film has a higher water solubility of the PVA film after AC molding, and when attempting to remove the vacuum bag with water after AC molding, residues derived from the film are less likely to remain. Also, when the heat of fusion is within the above range, the PVA film has an appropriate hardness, which has advantages such as facilitating the production of the vacuum bag. The heat of fusion tends to decrease by lowering the degree of saponification of PVA, which is the main component of the PVA film, increasing the amount of modification, etc. Also, the heat of fusion tends to decrease by increasing the content of the plasticizer. In addition, it can also be adjusted by film-forming conditions, drying conditions, heat treatment conditions, etc. when manufacturing the PVA film.

[0048] (Vacuum Bag for AC Molding) The vacuum bag according to an embodiment of the present invention is a vacuum bag for AC molding having the above-described PVA film as a bagging film. Also, the vacuum bag has a space capable of accommodating a molding material inside. Usually, the vacuum bag has a portion capable of exhausting air and a portion capable of being sealed. The portion capable of exhausting air may be a vacuum valve or the like, which will be described later. The portion capable of being sealed may be a portion where a sealing member or the like, which will be described later, is provided.

[0049] For example, the vacuum bag 2 shown in FIG. 1 is a bag-shaped vacuum bag formed from a PVA film 1 as a bagging film, and a molding material 3 is accommodated inside together with a mold 4. Also, the vacuum bag 2 shown in FIG. 2 is formed by the PVA film 1 as a bagging film and the mold 4. In the vacuum bag 2 of FIG. 2, a molding material 3 is accommodated inside.

[0050] Furthermore, the vacuum bag may use a combination of PVA film with a complete melting temperature of 70°C or lower and other bagging films as the bagging film. From the standpoint of reducing solid waste after obtaining the molded product, it is preferable that all of the bagging film in the vacuum bag be PVA film with a complete melting temperature of 70°C or lower.

[0051] According to a vacuum bag according to one embodiment of the present invention, it is possible to reduce solid waste after AC molding and to save labor in the peeling process. The method for manufacturing a molded body using a vacuum bag according to one embodiment of the present invention will be described below.

[0052] (Method for manufacturing a molded article) A manufacturing method using a vacuum bag according to one embodiment of the present invention includes, for example, the steps of: placing a molding material in a vacuum bag having a PVA film; curing the molding material; and dissolving the PVA film in water, in this order.

[0053] (Storage Process) There are no particular restrictions on the method of storing the molding material in the vacuum bag. For example, as shown in Figure 1, one method is to store the molding material 3 in a bag-shaped vacuum bag 2 formed from a PVA film 1. In this embodiment, the molding material 3 is placed on the mold 4, and the mold 4 is placed in the vacuum bag 2 together with the molding material 3. After storing the molding material 3 etc. in the vacuum bag 2, the vacuum bag 2 is sealed with a sealing member 5 such as sealing tape. The sealing means is not limited to using sealing tape, but adhesives etc. may be used, or the PVA films 1 may be directly bonded together by heat pressing etc. In addition, a vacuum valve 6 is provided in the vacuum bag 2 so that the air inside the vacuum bag 2 can be discharged. In order to store the molding material 3 in the vacuum bag 2 as shown in Figure 1, the mold 4, molding material 3 and second PVA film 1 may be placed on the first PVA film 1 in this order, and the vacuum bag 2 may be made by sealing the PVA films 1 together with a sealing member 5.

[0054] Furthermore, as shown in Figure 2, a method can also be employed in which a vacuum bag 2 containing the molding material 3 is produced by placing the molding material 3 on the mold 4, covering the molding material 3 with a PVA film 1, and sealing the space between the mold 4 and the PVA film 1 with a sealing member 5. In the configuration shown in Figure 2, a vacuum valve 6 is provided in the vacuum bag 2.

[0055] (Molding Material) The molding material is the material for the target molded body. Typically, the molding material contains a curable resin, and preferably contains both a curable resin and a reinforcing material. A typical form of the molding material is one in which a curable resin is impregnated into a fibrous reinforcing material. The curable resin used is uncured, but may be partially cured or semi-cured.

[0056] The curable resin is preferably a thermosetting resin. Examples of thermosetting resins include epoxy resins, phenolic resins, unsaturated polyester resins, cyanate ester resins, phenol-formaldehyde resins, and melamine resins, with epoxy resins being preferred. Water-soluble bagging films have particularly good release properties from such resins.

[0057] Thermosetting resins may contain various known curing agents. For example, if the curing resin is an epoxy resin, examples of curing agents include amines, amides, imidazoles, acid anhydrides, etc.

[0058] Various reinforcing fibers can be used as reinforcing materials. Examples of reinforcing fibers include artificially produced fibers such as carbon fibers, glass fibers, ceramic fibers, aramid fibers, boron fibers, basalt fibers, steel fibers, nylon fibers, fiber mats, scrim, and woven fabrics; natural fibers such as flax, hemp, jute, ramie, kenaf, sisal, bamboo, silk, cotton, and wood; and semi-natural fibers such as cellulose nanofibers. Two or more of these reinforcing fibers may be used in combination.

[0059] As the reinforcing fiber, carbon fiber or natural fiber is preferred, and carbon fiber is more preferred. The molded article obtained using the vacuum bag according to one embodiment of the present invention may be a reinforced fiber composite molded article or a carbon fiber composite molded article.

[0060] Considering the strength and dimensional stability of the molded object in each direction, a fibrous reinforcing material impregnated with a thermosetting resin (prepreg) may be used as the molding material.

[0061] The molding material may be in contact with the PVA film that constitutes the vacuum bag. Both the configurations in Figures 1 and 2 show the molding material 3 in contact with the PVA film 1. Normally, a release film is placed between the molding material and the bagging film to facilitate the removal of the bagging film after obtaining the molded product. However, in this manufacturing method, the PVA film, which is the bagging film, can be removed by dissolving it with water after obtaining the molded product, so a release film does not need to be placed. Not using a release film has advantages such as improved work efficiency and reduced waste.

[0062] (Other auxiliary materials, etc.) In the said manufacturing method, a release film may be placed between the molding material and the PVA film which is the bagging film. As the release film, a fluororesin (polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene hexafluoropropylene copolymer, etc.) film, PVA film, polymethylpentene film, polyolefin (polyethylene, polypropylene, etc.) film, etc. can be used. As the release film, a PVA film similar to the PVA film which is the bagging film can be used. When a release film is used, if it is the same type or different type of PVA film or other water-soluble film as the bagging film, the release film can be dissolved at the same time as the PVA film which is dissolved in water. It is preferable to use a PVA film of the same type as the bagging film as the release film because it makes recovery and reuse after dissolution easier. The specific form and preferred form of the PVA film which is the release film are the same as those described above for the PVA film which is the bagging film.

[0063] Although the mold 4 in Figures 1 and 2 is shown as a plate, its shape can be appropriately changed according to the desired shape of the molded product. The method for manufacturing the molded product can also be applied to molding using molds with complex shapes that have uneven surfaces. The material of the mold is not particularly limited, and metal molds such as aluminum and steel, pearl board molds, FRP (Fiber Reinforced Plastics) molds, etc., can be used.

[0064] A release agent may be placed between the mold and the molding material. That is, a release agent may be applied to the mold surface (the surface on which the molding material is placed) and the molding material may be placed on top of it. The molding material may be placed directly on the mold or via other components such as a release agent. There are no particular restrictions on the release agent, and it can be selected according to the material of the mold or prepreg. Examples of release agents include silicone-based, acrylic-based, urethane-based, urethane acrylate-based materials, fluoropolymer-based materials, or combinations thereof.

[0065] In this manufacturing method, a breather may be placed inside the vacuum bag for efficient disposal. When a breather is used, its placement is not particularly limited, for example, between the mold and the molding material, between the molding material and the bagging film (PVA film), or between the mold and the bagging film (PVA film). The breather may be placed in only one location or in multiple locations. Conventional breathers can be used as the breather. For example, a nonwoven fabric called a breather cloth can be used as the breather. The breather can be made of one or more layers of nonwoven fabric.

[0066] On the other hand, in this manufacturing method, it is not necessary to place a breather inside the vacuum bag. In particular, in this manufacturing method, PVA film is used as the bagging film, and PVA film has good release properties and conformability to the molding material or the molded article formed from the molding material. Furthermore, when PVA film is used as the bagging film, sufficient exhaust is possible even without placing a breather.

[0067] After placing the molding material in a vacuum bag and sealing the vacuum bag, the air inside the vacuum bag is expelled through a vacuum valve. For example, the vacuum valve may be connected to an exhaust device to expel the air from the vacuum bag.

[0068] (Curing process) The molding material is placed in a vacuum bag, the vacuum bag is evacuated, and then the molding material inside the vacuum bag is cured. By curing the molding material, the desired molded body is obtained. The curing of the molding material may be by thermosetting. The curing of the molding material can be carried out in the same manner as conventionally known autoclave molding. That is, after referring to the general manufacturing conditions for molded bodies, for example, the curing temperature and curing rate of the thermosetting resin constituting the uncured molding material used should be considered, and the pressure and temperature inside the autoclave should be adjusted according to the desired shape and properties of the molded body.

[0069] When heating is performed during the curing process, the heating temperature is preferably below the decomposition temperature of the PVA film used as the bagging film. For example, the upper limit of the heating temperature is preferably 200°C, more preferably 180°C, and even more preferably 150°C. The lower limit of the heating temperature is preferably 110°C.

[0070] When an autoclave is used in the curing process, the internal pressure of the autoclave is preferably above atmospheric pressure, more preferably 0.2 MPa or higher, and even more preferably 0.3 MPa or higher. The pressurization time is preferably 60 minutes or more, and more preferably 120 minutes or more.

[0071] (Dissolution process) After the molding material has hardened, the PVA film, which is the bagging film, is dissolved in water. Through this process, the PVA film, which is the bagging film, can be recovered as an aqueous solution. Therefore, this manufacturing method can reduce solid waste, and as a result, waste space can be saved.

[0072] There are no particular restrictions on the method of dissolving the PVA film with water. The PVA film covering the molded body formed from the hardened molding material may be directly sprayed with water to dissolve it, the entire vacuum bag containing the molded body may be immersed in water, or the PVA film may be peeled off the molded body and the PVA film may be immersed in water.

[0073] In one embodiment, the PVA film covering the molded body may be dissolved in water. In other words, the PVA film constituting the vacuum bag may be dissolved in water while the molded body is still in the vacuum bag. Dissolving the PVA film covering the molded body in water eliminates the need to peel off the PVA film, thus improving work efficiency. Alternatively, the PVA film covering the molded body may be brought into contact with water to partially dissolve it, then the PVA film may be peeled off, and the peeled-off PVA film may be dissolved in water. Methods for bringing the PVA film into contact with water include pouring water on it or immersing it in water. When the PVA film covering the molded body is brought into contact with water in this way, the adhesion between the PVA film and the molded body decreases due to the partial dissolution of the PVA film, making it easier to peel off the PVA film and improving work efficiency. In particular, bagging film is generally strongly adhered to the molded body and can be difficult to peel off. Therefore, this method, which involves dissolving at least a portion of the PVA film covering the molded body with water, is useful as it has the advantage of eliminating the need for peeling or making the peeling process easier.

[0074] When dissolving PVA film by immersion in water, the water may be agitated or water pressure may be applied to dissolve the PVA film. This allows the PVA film to dissolve quickly.

[0075] The water used to dissolve the PVA film may be an aqueous solution or aqueous dispersion containing other components besides water in which other components are dissolved or dispersed.

[0076] The lower limit of the water temperature used to dissolve the PVA film is preferably 4°C, more preferably 20°C, and even more preferably 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, or 80°C. By setting the water temperature above the lower limit, the PVA film can be dissolved in a short time. On the other hand, the upper limit of the water temperature may be, for example, 95°C, 90°C, 80°C, 70°C, 60°C, or 50°C. By setting the water temperature below the upper limit, it is possible to reduce costs and save energy in the manufacturing of molded products.

[0077] The molded articles obtained by this manufacturing method can be widely applied to a variety of products, from aircraft such as airplanes and helicopters, to vehicles such as motorcycles and automobiles, wind turbine blades, fishing rods, golf shafts, rackets, and other leisure goods.

[0078] <Other Embodiments> The present invention is not limited to the embodiments described above, and its configuration can be modified without altering the gist of the present invention.

[0079] The present invention will be described in detail below with reference to examples, but the present invention is not limited in any way by these examples. The evaluation methods used in the examples and comparative examples are shown below.

[0080] [Late of Fusion (DSC Measurement)] In accordance with ISO 11357-2,3 (2011), 3.6 mg of the PVA film to be measured was placed in an aluminum pan, and the late of fusion was determined by measuring the thermogram using differential scanning calorimetry (DSC) at a heating rate of 10°C / min. The PVA film used for measurement was first vacuum-dried in a vacuum dryer set to 52°C for 90 minutes, and then subjected to measurement.

[0081] [Solubility Test of Unheated Film] The unheated film refers to the PVA film obtained in the manufacturing example described later. The solubility test of the unheated film was measured using the following procedure: (1) A rectangular sample measuring 40 mm in length and 35 mm in width was cut from the PVA film. The sample was sandwiched and fixed between two 50 mm x 50 mm plastic plates, each with a rectangular window (hole) measuring 35 mm in length and 25 mm in width, so that the length of the sample was parallel to the length of the window and the sample was located approximately in the center of the width of the window. (2) 500 mL of deionized water (pure water) prepared to each temperature was placed in a 750 mL beaker, and the water temperature was adjusted to the measurement temperature ± 1.0 °C while stirring with a magnetic stirrer equipped with a 5 cm bar so that the vortex caused by stirring was approximately one-fifth of the water volume. (3) The sample fixed to the plastic plate in (1) was immersed in the deionized water in the beaker, taking care not to let it come into contact with the bar of the magnetic stirrer. (4) The time it took for the sample to completely disappear after being immersed in deionized water was measured. The water temperature was started at 30°C, and if the sample did not completely dissolve in 3 minutes, the temperature was increased by 10°C increments. That is, for example, if the sample did not completely disappear in 3 minutes in 30°C deionized water, a new sample was immersed in 40°C deionized water, and the time it took for the sample to completely disappear was measured. Following the above procedure, the complete dissolution temperature and the complete dissolution time at the complete dissolution temperature of the unheated film were measured. Note that "the sample completely disappears" means that no visible undissolved PVA film remains. If the PVA film contains visible fillers, such fillers are not included in the undissolved material.

[0082] [Solubility Test of Heat-Treated Film] A heat-treated film refers to a film obtained by heating an unheated film under the following conditions. The PVA film obtained in the following manufacturing example was heat-treated in a hot air dryer at 130°C for 120 minutes to obtain the heat-treated film. The complete dissolution temperature and complete dissolution time at the complete dissolution temperature of the heat-treated film were measured using the same method as the solubility test of the unheated film described above. In addition, a solubility test was performed using pure water at 40°C, and the complete dissolution time of the heat-treated film at 40°C was measured.

[0083] [Manufacturing Example 1] (Manufacturing of Film A) An aqueous solution containing 100 parts by mass of PVA (degree of polymerization 1,700, degree of saponification 88.0 mol%, unmodified PVA), 15 parts by mass of glycerin as a plasticizer, 1.0 part by mass of sodium alkyl sulfonate as an anionic surfactant, 0.5 parts by mass of polyoxyethylene alkyl ether as a nonionic surfactant, and 3.0 parts by mass of starch, with a PVA content of 11.0% by mass, was prepared as a film-forming stock solution. The film-forming stock solution was cast onto a metal drum at 60°C and dried for 20 minutes. The dried film was peeled from the surface of the metal drum to produce film A with an average thickness of 35 μm. The film obtained here is considered an unheated film. Melting heat determined from DSC, solubility tests of the unheated film, and solubility tests for heat treatment were performed. The results are shown in Table 2.

[0084] [Production Example 2] (Production of Film B) Film B was produced and evaluated in the same manner as in Production Example 1, except that the PVA was changed to itaconic acid-modified PVA (saponified copolymer of vinyl acetate and itaconic acid) with a degree of polymerization of 1,700, a degree of saponification of 88.0 mol%, and an itaconic acid modification amount of 1.3 mol%. The results are shown in Table 2.

[0085] [Production Example 3] (Production of Film C) Film C was produced and evaluated in the same manner as in Production Example 1, except that the PVA was changed to AMPS-modified PVA (saponified copolymer of vinyl acetate and AMPS) with a degree of polymerization of 1,700, a degree of saponification of 88.0 mol%, and an AMPS ((meth)acrylamide alkyl sulfonic acid) modification amount of 2.0 mol%. The results are shown in Table 2.

[0086] [Production Example 4] (Production of Film D) Film D with an average thickness of 80 μm was produced and evaluated in the same manner as in Production Example 1, except that the PVA was changed to AMPS-modified PVA (saponified copolymer of vinyl acetate and AMPS) with a degree of polymerization of 1,700, a degree of saponification of 88.0 mol%, and an AMPS modification amount of 2.0 mol%, and the film-forming stock was cast onto a metal drum at 60°C and dried for 40 minutes. The results are shown in Table 2.

[0087] [Manufacturing Example 5] (Manufacturing of Film E) Film E with an average thickness of 150 μm was manufactured and evaluated in the same manner as in Manufacturing Example 1, except that the PVA was changed to AMPS-modified PVA (saponified copolymer of vinyl acetate and AMPS) with a degree of polymerization of 1,700, a degree of saponification of 88.0 mol%, and an AMPS modification amount of 2.0 mol%, and the film-forming stock was cast onto a metal drum at 60°C and dried for 70 minutes. The results are shown in Table 2.

[0088] [Manufacturing Example 6] (Manufacturing of Film F) Film F was manufactured and evaluated in the same manner as in Manufacturing Example 1, except that the PVA was changed to unmodified, fully saponified PVA with a degree of polymerization of 2,400 and a degree of saponification of 99.9 mol%. The results are shown in Table 2.

[0089]

[0090]

[0091] [Example 1] Three layers of uncured carbon fiber composite material (W-3101-A / Q-1120E (manufactured by Teijin Limited), which consists of carbon fibers impregnated with epoxy resin, were placed on a flat mold as the molding material: A4 size 210 mm x 297 mm). Before placing the uncured carbon fiber composite material, a release agent (ChemLease 2166, manufactured by ChemTrend Japan Co., Ltd.) was applied to the surface of the mold that would come into contact with the uncured carbon fiber composite material. The mold was covered with a PVA film (film A, 400 mm x 600 mm) as a bagging film to form a vacuum bag, a vacuum valve for air release was installed inside the vacuum bag, and the vacuum bag was sealed with sealing tape. A small cut was made in the vacuum bag to expose the tip of the vacuum valve for air release to the outside of the vacuum bag.

[0092] A vacuum hose was connected to the vacuum valve for air discharge of the vacuum bag, and the air inside the vacuum bag was sucked out using a vacuum device. This was then placed in an autoclave. Heat curing was performed inside the autoclave while reducing the pressure inside the vacuum bag (130°C for 120 minutes, with an autoclave pressure of 0.5 MPa). After heat curing, the vacuum bag was removed from the autoclave and allowed to cool to room temperature. Subsequently, the entire vacuum bag containing the molded body obtained after heat curing was immersed in a water bath containing 40°C pure water at a mass 500 times the mass of the PVA film to dissolve the PVA film. The molded body was removed from the water bath to obtain the molded body. There was no film residue on the surface of the molded body. Furthermore, the appearance of the molded body was good.

[0093] [Example 2] A molded article was obtained in the same manner as in Example 1, except that film B was used instead of film A as the PVA film. The results (presence or absence of film residue after AC molding and immersion in water, and appearance of the obtained molded article) are shown in Table 3.

[0094] [Example 3] A molded article was obtained in the same manner as in Example 1, except that film C was used instead of film A as the PVA film. The results are shown in Table 3.

[0095] [Example 4] A molded article was obtained in the same manner as in Example 1, except that film D was used instead of film A as the PVA film. The results are shown in Table 3.

[0096] [Example 5] A molded article was obtained in the same manner as in Example 1, except that film E was used instead of film A as the PVA film. The results are shown in Table 3.

[0097] [Comparative Example 1] A molded article was obtained in the same manner as in Example 1, except that film F was used instead of film A as the PVA film. The results are shown in Table 3.

[0098]

[0099] In Examples 1 to 5, in which vacuum bags were made using films A to E, whose complete melting temperature is 70°C or lower, the film could be removed without leaving any residue by dissolving it in water after autoclave molding.

[0100] 1. PVA film (bagging film) 2. Vacuum bag 3. Molding material 4. Mold 5. Sealing component 6. Vacuum valve

Claims

1. An autoclave-molded vacuum bag having a polyvinyl alcohol film with polyvinyl alcohol as the main component, wherein a heat-treated film obtained by heating the polyvinyl alcohol film at 130°C for 120 minutes completely dissolves in pure water at 70°C or below.

2. The vacuum bag for autoclave molding according to claim 1, wherein the average thickness of the polyvinyl alcohol film is 25 to 200 μm.

3. The vacuum bag for autoclave molding according to claim 1 or 2, wherein the heat of fusion of the polyvinyl alcohol film, as measured using differential scanning calorimetry (DSC) in accordance with ISO 11357-2,3 (2011) at a heating rate of 10°C / min, is 10 to 35 J / g.

4. The vacuum bag for autoclave molding according to claim 1 or 2, wherein the polyvinyl alcohol comprises modified polyvinyl alcohol.

5. The vacuum bag for autoclave molding according to claim 4, wherein the modified polyvinyl alcohol is at least one selected from the group consisting of sulfonic acid-modified polyvinyl alcohol and carboxylic acid-modified polyvinyl alcohol.

6. The vacuum bag for autoclave molding according to claim 1 or 2, wherein the degree of saponification of the polyvinyl alcohol is 70 to 98 mol%.

7. The vacuum bag for autoclave molding according to claim 1 or 2, wherein the content of vinyl alcohol units relative to the total monomer units of the polyvinyl alcohol is 70 to 98 mol%.

8. An autoclave-molded vacuum bag having a polyvinyl alcohol film with polyvinyl alcohol as the main component, wherein the content of vinyl alcohol units relative to the total monomer units of the polyvinyl alcohol is 70 to 98 mol%.

9. The vacuum bag for autoclave molding according to claim 8, wherein the average thickness of the polyvinyl alcohol film is 25 to 200 μm.

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