JPS58210929A - Manufacture of slippery sheet - Google Patents

Abstract

PURPOSE:To manufacture a curved slippery sheet having excellent shape stability, and suitable for a video cassette, etc., by slicing a block made of an ultra- high-molecular-weight polyethylene powder, winding the sheet around a core, and irradiating with radiation. CONSTITUTION:A block manufactured by the compression molding of ultra-high- molecular-weight polyethylene powder is sliced in the form of a sheet (preferably having a thickness of 0.05-0.5mm.), and the sheet is wound around a cylindrical core (preferably made of a radiation permeable material such as paper). The sheet is irradiated with radiation (preferably gamma-ray, etc.) to effect the crosslinking until the gel fraction of the sheet reaches 60-90%. The slippery sheet thus manufactured has a curvature corresponding to the state of winding. When the sheet is wrinkled, it can be smoothed by the heat-treatment at preferably 110- 125 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a sliding sheet, and in particular, an object of the present invention is to provide a sliding sheet suitable for use by being incorporated into audio cassettes, video cassettes, and the like.

In audio cassettes and video cassettes, a low-friction sliding sheet is interposed between the inner wall of the case and the magnetic tape wound on the reel.This reduces the amount of sliding between the end surface of the tape and the inner wall of the case when the tape is running. This may be used to reduce dynamic resistance, avoid excessive tension on the tape, prevent tape elongation, or stabilize tape running. In this case, it is common to use a curved sliding sheet as described in Japanese Utility Model Publication No. 49-6571. In the method of using a curved sliding sheet, the sliding sheet can moderately press the end face of the magnetic tape and maintain good contact between the two at all times, thereby preventing the occurrence of irregular winding of the tape and the application of excessive tension to the tape. This is preferable because it can further stabilize tape running.

By the way, as a material for forming the sliding sheet, ultra-high molecular weight polyethylene (hereinafter referred to as U
HPK (referred to as HPK) has attracted attention, and various applications are being considered for its application to sliding sheets, but UHPE has unique properties that are different from general thermoplastic resins, and it is difficult to shape UHPK sheets into a predetermined curved shape. No useful technology has yet been developed to do so.

In view of the above-mentioned current situation, the inventors of the present invention have conducted extensive studies, and as a result, the UHPK
The powder is formed into a block shape under pressure, cut to a predetermined thickness to form a notebook, and then this sheet-like material is wrapped around a core and irradiated with radiation to remove the gel content of the 7-tate-like material. It was discovered that by crosslinking the sliding sheet so that the ratio falls within a predetermined range, a sliding sheet shaped into a curved shape that approximately corresponds to the curvature when wrapped can be obtained, and this led to the completion of the present invention. 8゜That is, the method for manufacturing the lubricant sheet according to the present invention is based on UHPFi
The block-like material obtained by molding the powder under pressure is cut into a sheet, and then the sorted material is wrapped around a core and irradiated with radiation to remove the gel content of the sheet. rate is 60
Characteristic 2 is that it is crosslinked to 90%.

In the present invention, first, UHPFi powder is molded into a block shape under pressurized conditions. Due to the characteristics of UHPK, this molding is performed by filling a mold with UHPK powder and applying pressure at room temperature.
After compression preforming under conditions of 50-300 kg/at, the pressure is lowered to about 50-100 kg/1m and the temperature is raised above the melting point of UHPE to melt and sinter the UHPK powder, and then the pressure is lowered to about 150-100 kg/at. 300 kQl
This can be carried out by raising the temperature to the desired temperature, then slowly cooling it to room temperature while maintaining this pressurized state.

The UHPlii used here has a molecular weight of about 1 million or more by the viscosity method, which is larger than that of general polyethylene, which is about 20,000 to 100,000.
It is commercially available under trade names such as Heise Kusmilion (manufactured by Mitsui Petrochemicals) and Hostalen GUR (manufactured by Hoechst).

- In addition, in order to impart conductivity to the sliding sheet and prevent it from being charged due to sliding with a mating member during use, napw
Molding can be carried out by adding conductive powder such as carbon, graphite, metal powder, etc. to a powder content of up to about 20% by weight.

The thus obtained strip-like material is then cut using a lathe or the like to form a sheet-like material with a diameter of about 0.05 to 5 mm. This note-like material may be caused by the residual stress applied when molding the UHPFi powder into a pouch shape, and may result in wavy spots, etc. In such cases,
In the present invention, it is preferable to heat treat the notebook-shaped article.The notebook-shaped article is preferably heat-treated by fixing the sheet-shaped article in a frame and heating it, or by heating the sheet-shaped article by fixing it to a frame. This is done in such a way that the dimensions of the sheet-like material do not change, such as by placing it along a heated roll or drum with a smooth surface.

The heat treatment temperature is determined by the pressure applied during molding into a block and the heat treatment time, but is usually 9.
0℃～UHPF! The melting point is preferably 110 to 125°C.

The sinite-like product thus obtained is then cylindrical,
After being wound a predetermined number of times on a core such as a round bar, gamma
By irradiation with radiation having a large effective range such as X-rays and X-rays, crosslinking is carried out so that the gel fraction is 60 to 90%, preferably 70 to 80%.

The core is preferably made of plastic such as polyvinyl chloride, polyacetal, or polycarbonate, or a radiolucent material such as paper. It is also possible to use a core made of impermeable material.

The UHPE sheet is cross-linked by Jin's radiation irradiation method,
The irradiation dose required to bring the gel fraction to the above predetermined value is U
It is determined depending on the molecular weight of HPK, sheet thickness, irradiation conditions, etc., but in the case of gamma rays, it is usually about 2 to IO megarads, preferably about 3 to 5 megarads.

Honppatsu Dan 1 (In terms of gel fraction of the UHPE sheet after crosslinking is less than 60%, a sliding sheet with excellent shape stability during high temperature use cannot be obtained; Both are undesirable because the sheet becomes brittle and its mechanical strength decreases.

In the present invention, UHPE heat-treated with radiation irradiation
It is important to wrap the sheet into a roll along the outer surface of the core. By performing radiation irradiation in such a state, the UHPK sheet can be wrapped and shaped into a curved shape that roughly corresponds to the state.

Note that when the UHPK sheet is wound around the core many times and the thickness of the wound layer is increased, the radius of curvature changes between the inner layer and the outer layer, and the sliding sheet obtained from the inner layer has a curved radius of curvature of the same shape. Therefore, by cutting to lengths with curl heights, sliding notes with different curl heights can be obtained at the same time.

Furthermore, even if the UHPK'7-t is wound around the core many times, if the thickness of the spinning layer is not very thick,
Since there is not much difference in the radius of curvature between the inner layer and the outer layer, by unwinding and cutting into predetermined lengths after irradiation, it is possible to simultaneously obtain a large number of sliding sheets with substantially uniform blade heights.

Although the sliding sheet obtained by the method of the present invention is shaped into a curved shape, the sheet has excellent shape stability. Shape stability is an important characteristic of a curved sliding sheet made of UHPK, and if the shape stability is poor, for example, if an audio cassette incorporating this is used in a car stereo in the summer, the sliding sheet may be exposed to high temperatures. As a result, the curl height gradually increases and excessive pressure is applied to the magnetic tape, which may cause the tape to stretch due to excessive tension or cause tape running to become unstable, which may have a negative impact on sound quality. However, the product of the present invention has excellent shape stability,
No such inconvenience will occur.

In the present invention, the beak is formed as described above, and a block-like object obtained by molding IJHPE powder under pressure conditions is cut into a sheet shape, and this sheet-like object is wrapped around a core body and irradiated with radiation. By crosslinking, a curved sliding sheet can be obtained, and the sliding sheet is characterized by excellent shape stability.

Hereinafter, the present invention will be explained in more detail with reference to Examples. Note that parts in the examples are parts by weight.

Example 97 parts of UHPE powder (manufactured by Mitsui Petrochemical Co., Ltd., trade name: Izex Million 240M) and 3 parts of carbon powder were mixed uniformly, filled into a mold, and heated to 200 m2 at a temperature of 25°C.
Reduce the pressure to 50 kg/metre, raise the temperature to 210°C, maintain this condition for 120 minutes, and release UHPK.
The powder is melted and fired, then the pressure is increased to 200 kg/m
The block was then cut using a lathe to obtain a long sheet with a thickness of 100 μm, which was heat-treated along the surface of a metal roll heated to 120°C. (The contact time of the sheet-like material to the metal roll surface is 3 minutes).

Next, the sheet-like material is wound so that its longitudinal direction follows the outer peripheral surface of a paper cylindrical core body having an outer diameter of 200 mm, the thickness of the wrapped layer of the sheet-like material is approximately IQms, and cobalt 6
Gel fraction was 65 after irradiating 00 gamma rays at 2 Megaland.
%.

After that, the sheet-like material is rewound and the width direction dimension is 100.
mm, cut so that the longitudinal dimension is 59 mm,
A large number of sliding sheets (sample number l) were obtained which were shaped into curved shapes along the longitudinal direction. In this case, the thickness of the wrapped layer of the sheet-like material was relatively small, and the curl heights of the sliding sheet obtained from the inner layer portion and the sliding sheet obtained from the outer layer portion were almost uniform. .

The gel fraction of the above-mentioned sliding sheet was determined by immersing the sheet in xylene at 130°C for 24 hours to dissolve the uncrosslinked portion.
The crosslinked insoluble portion was filtered through a 50-mesh filter, taken out and dried, and its weight was measured, and the value was calculated using the following formula.

On the other hand, in the case of sample number 1, the above heat-treated sheet material was used, and the gamma ray irradiation dose was 4 megarads and 8 megarads. Two types of smooth sheets (sample numbers 4 and 5) having different curl heights were obtained by performing the same operation as in the case of sample number 2 except for using a core-shaped core.

The friction coefficient, curl height and tensile strength of these sliding sheets were measured by the following test methods and the results are shown in Table 1. In addition, the data of the curl height after heating in Table 1 is obtained by heating the sliding sheet at a temperature of 100°C for 48 hours.
Data is shown after being left in a room at 25°C for 1 hour. 0 tAI friction coefficient A Bauden-Leben type friction tester (manufactured by Toyo Baldwin, model KFM-4) was used, the mating material was a polyester film, and the sliding speed was 175. mm7fni le, load 200
g, measured at a temperature of 25°C.

(Bl Curl Height The sliding sheet was placed on a footboard, and the height of its curved top was measured using a hide gauge.

(C: Tensile strength) The maximum tensile strength of the sliding sheet in the curved direction was measured using a method similar to J-6888.

For comparison, heat-treated UHPI used to obtain the sliding sheet! ! Sample No. 2 except that the gamma rays were set to 1.5 and 12 megarads for the sheet.
Proceed as in the case of gel fraction 52 and 95%.
The data of the sliding sheets (sample numbers 6 and 7) obtained by crosslinking so as to be as follows are also shown.

Table 1 As is clear from the above Examples and Comparative Examples (According to the present invention, a sheet-like material obtained by cutting a block-like material is wrapped around a core body, and is shaped into a curved shape by being stretched by radiation irradiation. It is possible to obtain a ribbed sheet, and the shape stability of this sliding sheet is poor, and the curved state does not change even when exposed to high temperatures. It is also a big saving, and you can see that the practicality is multilayered.

Claims (1)

[Claims] A block-like product obtained by molding ultra-high molecular weight polyethylene powder under pressurized conditions is cut into a sheet, then the sheet-like product is wrapped around a core and irradiated with radiation to form a gel in the sheet-like product. A method for producing a sliding sheet, characterized by crosslinking so that the fraction is 60-90.