JPH0325464B2 - - Google Patents

Description

[Detailed description of the invention]

This invention is based on reinforcing fiber prepreg (hereinafter referred to as
This invention relates to a double-sided release sheet that has a difference in peel strength between the front and back sides and is used in the production of prepreg (abbreviated as "prepreg"). 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. The release sheet used for producing such prepreg materials is required to have the following properties. That is, (a) removability on both sides with a difference between the front and back is required. (b) The heavy release surface of the release sheet must exhibit appropriate temporary adhesion to the prepreg. More specifically, when manufacturing the prepreg, the prepreg is laminated to the heavy release surface of a release sheet, and the prepreg is formed into a tape or sheet. Therefore, one surface (heavy release surface) must have heavy release properties so that the prepreg can be temporarily attached, and the other surface (light release surface) must be in the form of a tape or sheet, but the prepreg cannot be transferred to the opposite surface. It must be sufficiently easy to peel that it does not. In order to meet this required performance, it is necessary to have an appropriate difference in the peeling force between the front and back sides of the release sheet, which is essential for stable prepreg production. An object of the present invention is to provide a release sheet that has an appropriate difference in release force between the front and back surfaces and, as a result, has excellent processability in prepreg production. In a double-sided release sheet consisting of a base material made of uncoated paper or polymer film and a release agent layer formed on both sides of the base material via an undercoat layer, the The ratio of peeling force between the front and back surfaces is in the range of 1:2 to 1:50, preferably 1:
This is achieved by setting the ratio to 3 to 1 to 20 and increasing the peeling force of the heavy peeling surface to more than 75 g/25 mm. If the ratio of the front and back sides of the peeling force is within this range,
The prepreg has good temporary adhesion to heavy release surfaces,
There is no prepreg transfer to easily peelable surfaces. Therefore,
When such a release sheet is used, a prepreg can be stably produced. 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 3 and 3' of release agent are applied to both sides of the base material 1 via undercoat layers 2 and 2', respectively.
is formed. The base material constituting the double-sided release sheet of the present invention may be either uncoated paper or polymer film. These can be selected from those commonly used in prepreg production. Preferred paper base materials include kraft paper with a basis weight of 30 to 200 g/m ² and a thickness of 30 to 250 μm, high-quality paper, pure white roll paper, etc., and polymer films with a thickness of 10 to 250 μm.
Examples include 200μ polyethylene, polypropylene, polyester, etc. Alternatively, the base material may be a paper base material with a polymer film laminated on one or both sides of the paper base material. A release agent coating layer is formed on both sides of the base material via an undercoat layer (anchor treatment layer).
The anchor treatment layer on the paper base material is preferably one coated with a film-forming material such as polyvinyl alcohol that has barrier properties against silicone release agent coating liquids and dried. The layer preferably has a wettability index of 30 dynes/cm or more by corona discharge treatment, and a layer coated with polyvinyl alcohol or the like and dried, in order to impart adhesion to the silicone release agent. The anchor treatment can be carried out according to a conventional method, for example, using a roll coater. The application rate of the treatment agent is about 1 to 20 g/m ² (in terms of solid content). A release agent coating layer is formed on the base material with the 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. The ratio of the peel force between the heavy release layer and the light release layer is in the range of 1:2 to 1:50, preferably 1:3 to 1:20, as described above, and the peel force on the heavy release layer is 75 g. /Make it larger than 25mm. A release agent suitable for producing such a difference in release force can be selected from commonly used release agents. Examples of light-release silicones include SRX-357 (manufactured by Toray Silicone Co., Ltd.) and SRX-211 (manufactured by Toray Silicone Co., Ltd.), and examples of heavy-release silicones include SRX-345 (manufactured by Toray Silicone Co., Ltd.). (manufactured by Toray Silicone) and SRX-370 (manufactured by Toray Silicone). Reinforcing carbon fibers are temporarily attached and supported in the form of filament lands arranged in one direction on the heavy release agent coated surface of the double-sided release sheet produced as described above. There are no particular limitations on the fineness, length, number, application form, etc. of the filaments used for manufacturing the prepreg. Prepreg is manufactured by impregnating the above-mentioned reinforcing carbon fibers with thermosetting resins such as epoxy resins, unsaturated polyester resins, and phenolic resins. 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 has an appropriate difference in release force between both release surfaces, has excellent temporary adhesion of prepreg, and can stably produce prepreg. Hereinafter, the present invention will be described in more detail with reference to Examples. Example A base material of bleached kraft paper (basis weight 70 g/m ² ) coated with polyvinyl alcohol at 2 g/m ² (solid content equivalent) on both sides was used, and one side of this base material was coated with light release silicone SRX-211 (Toray).・Apply 1.0g/m ² (solid content equivalent) of Silicone Co., Ltd.), dry,
Harden and apply heavy release silicone SRX on the opposite side.
370 (manufactured by Toray Silicone) at 1.0 g/m ² (solid content equivalent) was applied, dried and cured, and designated as sample No. 1. Next, using the same base material, apply 1.0% of light release silicone SRX-357 (manufactured by Toray Silicone) on one side.
g/m ² (solid content equivalent) applied, dried and cured,
On the opposite side, apply heavy release silicone SRX-345 (manufactured by Toray Silicone) at 1.0 g/m ² (solid content equivalent).
Coat, dry, and harden to prepare sample No. 2. For comparison, silicone release agents SRX-357 and SRX-211 were applied to both sides of the same base material as above.
(manufactured by Toray Silicone Co., Ltd.) at 1.0 g/m ² (solid content equivalent) was applied, dried and cured, and designated as sample No. 3.
Apply SRX-345 and SRX-370 (manufactured by Toray Silicone) at 1.0 g/m ² (solid content equivalent), dry,
It was cured and designated as sample No. 4. The peeling force of the release paper obtained by the above treatment,
Prepreg temporary adhesion properties and prepreg transfer properties were measured, and the results shown in Table 1 were obtained.

[Table] * Comparative Example Peeling force, prepreg temporary adhesion and transferability were evaluated as follows. (1) Peeling force Scotch tape (manufactured by 3M) #28 was attached to the peeling surface and measured after aging under the following conditions. Γ Pressure 20G/cm ² Γ Temperature 70°C x 20 hours (2) Prepreg temporary adhesion Epicoat on carbon fiber tow pulled 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.
Then, at 20G/ ^cm2 pressure and 40℃ 65%RH for 24 hours.
After time aging, observe the peeling state of the prepreg. (Excellent) 〇＞△＞×(Not acceptable) (3) Prepreg transfer properties The prepreg produced as in the previous item (2) was sandwiched between a heavy release surface and a light release surface, and a pressure of 20G/ ^cm2 was applied. and 40℃
After aging in 65%RH for 24 hours, the state of adhesion to the heavily peeled surface was observed. (Excellent)〇＞△＞×(Not acceptable)

[Brief explanation of drawings]

The figure is a sectional view showing a typical example of a double-sided release sheet according to the present invention. Reference numbers are as follows. 1...Base material, 2,2'...Undercoat layer, 3,3'...
...Release agent coating layer.

Claims (1)

[Claims] 1 A double-sided release sheet consisting of a base material made of uncoated paper or polymer film and a release agent layer formed on both sides of the base material via an undercoat layer, with a peeling speed of 0.3 m/min to 20 m/min. Used for the production of reinforcing fiber prepreg, characterized in that the ratio of the peel force between the front and back surfaces is in the range of 1:2 to 1:50, and the peel force on the heavy peel side is greater than 75 g/25 mm. Double-sided release sheet.