JPH0317868B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is used for producing prepreg of reinforcing fibers. In particular, the present invention relates to a double-sided release sheet having excellent moisture-resistant dimensional stability and heat-resistant dimensional stability. Prepreg materials made of carbon fibers and other reinforcing fibers have excellent mechanical properties and are lightweight, so they are used in a variety of applications, from aircraft parts to sports and leisure goods. Double-sided release sheets are widely used in the production of these reinforcing fiber prepreg materials. For example, in the production of unidirectional carbon fiber prepreg materials, carbon fibers arranged parallel to each other in a sheet shape in one direction are impregnated with a thermosetting resin, a release sheet is attached to this, and the resin is preliminarily applied. harden. When manufacturing a fiber-reinforced resin material, a release sheet-attached prepreg, that is, a prepreg material is cut into an arbitrary shape, the required number of sheets are laminated in a predetermined direction excluding the release sheet, and the resin is cured by heating. Release sheets used in the production of such prepreg materials are generally required to have the following properties. (a) It should have removability on both sides and exhibit appropriate temporary adhesion to the prepreg. (b) withstand the heat encountered in the manufacturing process of prepreg materials (e.g.
To withstand heat of 170℃. In other words, it has a low thermal shrinkage rate and good heat-resistant dimensional stability. (c) No deformation due to moisture absorption or dehumidification during prepreg manufacturing, processing, or use. In other words, it should have good moisture resistance and dimensional stability. Conventionally, there is no known double-sided release sheet that satisfies the above requirements among the double-sided release sheets used in the manufacturing process of prepreg materials for reinforcing fibers. For example, a double-sided release sheet that has been widely used in the past is known to consist of kraft paper, an undercoat layer formed on both sides of the kraft paper, and a release agent layer formed on the surface of each undercoat layer. It is being This release sheet easily absorbs moisture, expands and contracts significantly due to moisture absorption and dehumidification, and also contracts significantly when tension is released in the reinforcing fiber prepreg manufacturing process. This not only reduces the workability of preparing the prepreg, but also adversely affects the quality of the prepreg and, ultimately, the final fiber-reinforced resin material. JP-A-56-10532 proposes a unidirectional prepreg material using a paper release sheet that has an elongation of 0.5% or less relative to its bone-dry dimensions under 60% relative humidity. However, this publication does not provide any specific examples of paper release sheets with good moisture dimensional stability, and according to the results of the inventors' studies, conventional paper release sheets have been considered to have good moisture dimensional stability. Even if paper is used, it is difficult to avoid curling and channeling during manufacturing. In any case, there is no conventional double-sided release sheet using a paper base material that has both moisture-resistant dimensional stability and heat-resistant dimensional stability. An object of the present invention is to provide a double-sided release sheet that satisfies the above requirements and, in particular, has both moisture-resistant dimensional stability and heat-resistant dimensional stability. The double-sided release sheet used in the production of the reinforcing fiber prepreg according to the present invention has a polyvinyl alcohol undercoat layer formed on both sides of a base material made of glass fiber mixed paper, and a heavy release release sheet on one undercoat layer. A light release agent layer is formed on the other undercoat layer. The accompanying drawing is a sectional view showing a typical example of a double-sided release sheet according to the present invention. As shown in the figure, coating layers 4 and 4' of a release agent are formed on both sides of a paper base material 1 via undercoat layers (2) and (2) and undercoat layers (2) and (3), respectively. The base material constituting the double-sided release sheet of the present invention is glass fiber mixed paper, and is generally made of wood pulp of 70 to 70%.
97 parts by weight and 30-3 parts by weight of glass fiber.
Wood pulp includes softwood bleached kraft pulp (NBKP), hardwood bleached kraft pulp (LBKP),
is preferred, and a freeness of 550 to 400 C.SF is particularly preferred, particularly about 500 C.SF. The glass fiber to be mixed with wood has a fiber length of 1
~10mm, preferably 2-8mm, and L/D200
~1000 can be used advantageously. Note that, within a range that does not impair the achievement of the purpose of the present invention, the base material, glass fiber mixed paper, may be coated with an appropriate amount of a third fibrous material, such as synthetic resin pulp such as polyethylene or polypropylene, rayon, acrylic, or other material. It may also contain synthetic fibers, asbestos, gypsum fibers and other inorganic fibers. Glass fiber mixed paper can be manufactured according to commonly used wet papermaking methods. In general, a slurry of wood pulp and glass fiber mixture with a concentration of about 0.1 to 0.3% by weight is processed using a Fourdrinier multi-tube paper machine, a circular wire paper machine, or a Yankee paper machine to obtain a basis weight of 50 to 150 g/ ^m2 . Mixed paper making is sufficient. A particularly preferred example of glass fiber mixed paper is described in JP-A-51-102101. A release agent coating layer is formed on both sides of the glass fiber mixed paper via an undercoat layer. The undercoat layer is formed by applying an aqueous solution of polyvinyl alcohol that has good heat resistance and good adhesion to silicone. The application method can be carried out according to a conventional method, for example, using a roll coater. The application rate is about 1 to 20 g/m ² (solid content equivalent). A release agent coating layer is formed on glass fiber mixed paper with an undercoat layer formed on both sides, and a light release agent coating layer is formed on one side, and a heavy release agent coating layer is formed on the other side. As release agents, commonly used non-silicone resins such as silicone resins and long chain alkyl acrylate polymer resins are used. The amount of release agent applied may be about 0.3 to 2 g/m ² (solid content equivalent) for both the heavy release layer and the light release layer, and coating can be carried out according to a commonly used method. A reinforcing fiber prepreg is temporarily attached and supported on one side of the double-sided release sheet produced as described above, particularly on the heavy release agent coated side. Reinforcing fibers include carbon fiber, glass fiber,
Inorganic fibers such as metal fibers, and organic fibers such as aromatic polyamide fibers and polyamideimide fibers are used, and these may be used alone or in combination with
A combination of more than one species may be used. The reinforcing fibers are usually applied in the form of filament strands aligned in one direction, but they can also be applied in the form of a cross, and the appropriate thickness of the cloth is 0.05 to 0.5 mm.
The fineness of the filament used to manufacture prepreg,
The length, number, application form, etc. are not particularly limited. Prepreg is prepared by impregnating the above-mentioned reinforcing fibers with a thermosetting resin such as epoxy resin, unsaturated polyester resin, or phenolic resin. The impregnation treatment may be carried out according to a conventional method. Generally, the resin content of unidirectionally aligned prepreg is 10~
60% by weight, preferably about 30-45% by weight. The double-sided release sheet according to the present invention is particularly excellent in moisture-resistant dimensional stability and heat-resistant dimensional stability. Therefore, in the process of temporarily attaching carbon fiber unidirectional prepreg or other reinforcing fiber prepreg to the heavy release surface of this release sheet, curling or channeling may occur due to moisture absorption or dehumidification of the release sheet or heat exposure. This does not occur and high quality prepreg can be obtained. Hereinafter, the present invention will be described in more detail with reference to Examples. Example Hardwood bleached kraft pulp (Freeness 450c.c.,
CSF) 90% by weight and glass fiber (fiber length 3mm,
A base material 1 having a basis weight of 80 g/m ² was made from a mixture of 10% by weight of L/D330) using a Yankee paper machine. Separately, 90% by weight of hardwood bleached kraft pulp (freeness 450 c.c., CSF), glass fiber (glass fiber sizing agent removed by incineration by the method disclosed in JP-A-51-102107), fiber Major 3
mm, L/D330) and 10% by weight, a base material having a basis weight of 80 g/m ² was made into a mixed paper using a Yankee paper machine to form a base material 2. 65% by weight of clay, 10% by weight of CaCO ₃ on both sides of base materials 1 and 2, respectively.
A sealing undercoat layer with a concentration of 48% consisting of 25% by weight of Al(OH) ₃ and 22% by weight of SBR latex was applied at a coating amount of 15g/m ² (in terms of solid content). Furthermore, polyvinyl alcohol (“Denka Poval K-17E”,
(manufactured by Denki Kagaku Kogyo Co., Ltd.) was coated at 2 g/m ² (in terms of solid content) and dried to form an undercoat layer.
Apply a light release silicone release agent (SRX-357, manufactured by Toray Silicone Co., Ltd.) on one undercoat layer surface, and apply a heavy release silicone release agent (SRX-370, manufactured by Toray Silicone Inc.) on the other undercoat layer surface. Samples No. 1 and 2 were obtained by applying 1 g/m ² each using a roll coater, drying and curing. As samples for comparison, unbleached kraft paper (80 g/m ² , 85μ) and high-quality paper (80 g/m ² ,
85μ) were used separately and processed in the same manner as above to produce double-sided release sheets to obtain Samples Nos. 3 and 4. The heat resistance and moisture dimensional stability of the release paper obtained by the above treatment were measured, and the results shown in Table 1 were obtained.

[Table] Epicoat on carbon fiber tow aligned in one direction
A solution consisting of 60 parts by weight of 828 (manufactured by Yuka Ciel Co., Ltd., a condensation product of bisphenol A and epichlorohydrin) and 40 parts by weight of methyl ethyl ketone was impregnated, and the content was adjusted using a squeezing roll. The heavy release side of the above-mentioned release sheet (width 420 mm in absolute dry state) was laminated to this resin-impregnated carbon fiber tow, and the sheet was passed through a hot air dryer maintained at 105°C to volatilize the solvent and B-stage the epoxy resin.
In this way, a unidirectionally aligned carbon fiber prepreg with a width of 400 mm was prepared and wound as it was. When the rolled sample was left at a relative humidity of 64%, the width of the release sheet (A) was as shown in Table 2. The prepreg manufacturing process described above was repeated. however,
After passing through a hot air dryer, an epoxy resin-impregnated plain weave glass fabric was laminated with a heated nip roll on the top surface of the prepreg just before being rolled up, and then wound up (Sample B). After storing Sample A in a cool place for one day, the same epoxy resin-impregnated plain weave glass fabric as that used in the production of Sample B was laminated to Sample A using a heated nip roll and rolled up (Sample C). Sample B and Sample C were left at a relative humidity of 64% or less, and the appearance of the samples was observed. The results were as shown in Table 2.

[Table] 〓
4 404

Claims (1)

[Claims] 1 An undercoat layer of polyvinyl alcohol is formed on both sides of a base material made of glass fiber mixed paper, and a heavy release agent layer is further formed on one undercoat layer,
A double-sided release sheet used for producing a reinforcing fiber prepreg, characterized in that a light release agent layer is formed on the other undercoat layer.