JPS6315129B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing thermoformed products, and more particularly to a method for producing thermoformed products such as containers with improved surface gloss and transparency, which are produced by thermoforming an oriented thermoplastic synthetic resin sheet using a contact type face plate thermoforming machine. Regarding the manufacturing method. Conventionally, polystyrene or polyvinyl chloride sheets obtained by thermoforming such as compressed air or vacuum forming have been used for food containers, pharmaceutical containers, etc., and these resins have excellent moldability. Furthermore, it is well known that the product has excellent transparency. However, in recent years, problems such as heat resistance, hygiene, and incineration pollution during disposal have been raised in these resin molded products. Techniques have also been developed for thermoforming sheets of resins such as polyolefin resins such as polypropylene, nylon, and polyester to produce molded products. However, for any of the above-mentioned resins, when a conventional contact type face plate thermoforming machine is used as a thermoforming machine, transparency, surface gloss, etc. are impaired. In other words, in conventional contact-type face plate thermoforming machines, if the heating face plate is smoothed to improve transparency, the contact between the sheet and the heating face plate is reduced when the sheet is heated, that is, when the sheet is brought into contact with the heating face plate. Air remains locally in the form of bubbles, causing uneven heating of the sheet and leaving a pattern on the molded product such as a container (this condition is called a raindrop phenomenon). Therefore, conventionally, in order to prevent this raindrop phenomenon, the surface of the heating face plate has been roughened to some extent to make it easier to remove air. However, if the surface roughness of the heating face plate is large, the sheet surface becomes rough and transparency, surface gloss, etc. are impaired, and this is particularly noticeable in polyolefin resins. An object of the present invention is to provide a method for manufacturing thermoformed products such as containers that have excellent surface gloss and transparency. As a result of intensive studies to solve the above problems, the inventors of the present invention found that using an oriented sheet as a thermoplastic synthetic resin sheet reduces uneven contact of the sheet to the heating face plate and reduces raindrops, although the reason is unknown. Focusing on the fact that this phenomenon is less likely to occur, the inventors have discovered that by using an oriented sheet, a heating face plate with a smoother sheet contact surface can be used in a contact type face plate thermoforming machine, and the present invention has been achieved. That is, the present invention provides a method for manufacturing a thermoformed product such as a container by thermoforming an oriented sheet of thermoplastic synthetic resin with a contact type face plate thermoforming machine, in which the surface of the contact heating face plate of the contact type face plate thermoforming machine is Roughness (JIS B-
0601) has dramatically improved transparency and surface gloss by using a molding machine that finishes the product to a smoothness of 3S or less. The oriented sheet used in the present invention consists of a sheet uniaxially oriented, and in the case of uniaxially oriented,
Preferably, by keeping the reduction rate of the sheet width after orientation to the sheet width before orientation to 10% or less, distortion and uneven thickness of molded products such as containers can be prevented. As an example of the method for manufacturing the above-mentioned oriented sheet, a method using roll rolling will be described in detail. That is, the present invention obtains a thermoplastic synthetic resin sheet by a conventional method, and rotates the sheet in opposite directions at a temperature lower than its melting point or below its flow initiation point, and at intervals smaller than the thickness of the sheet. An oriented sheet is obtained by passing through a set gap between a pair of rolling rolls. Further, the sheet used in this rolling process may be obtained by any molding method and is not limited in any way. That is, a commonly used extrusion molding method may be used, or a method such as press molding or calendar molding may be used. Such a sheet is rolled to form a thermoformable sheet, and the thickness of the sheet is not essentially limited, but usually
The final rolled sheet thickness is preferably in the range of 0.02 mm to 2.0 mm, particularly preferably 0.1 mm to 1.5 mm. If the thickness is excessive, the required rolling pressure during roll rolling will be excessive, and the rolling rolls will have to be extremely large.
The advantage of implementation must be judged from an economic perspective. Further, the rolling method may be any conventionally known method. Since the oriented sheet made in this way is less likely to cause raindrop phenomenon, it is possible to make the contact surface of the sheet in the thermoforming machine smoother, and the smoother the surface, the better the transparency of the resulting molded product. However, in the thermoforming machine of the present invention, the surface roughness of the contact heating face plate (JIS
(according to Test Method B-0601) should be 3S or less.
In this case, a more favorable result can be obtained by smoothing the surface of the mold. Further, the sheet temperature when shaping the oriented sheet using a contact type face plate thermoforming machine is preferably maintained at a temperature lower than the melting point or flow start point of the sheet. As described above, by using an oriented sheet, the present invention not only avoids the raindrop phenomenon and dramatically improves transparency and surface gloss, but also prevents sagging of the sheet during pre-stretching (preheating) during thermoforming. A molded product is produced without wrinkles, distortion, or uneven thickness. Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples. Examples 1 to 2 and Comparative Examples 1 to 4 As shown in Table 1, iso-polypropylene resin was used as the thermoplastic synthetic resin sheet, and in particular, in Examples 1 and 2 and Comparative Example 4, the sheets were oriented by roll rolling. . This sheet is thermoformed using a contact-type face plate thermoforming machine (mold surface roughness: 5S) that uses heating face plates with different surface roughness to form a molded product (a rectangular tray with an opening surface of -170 mm x 100 mm and a depth of 11 mm). I got it. The contact time between the sheet and the heating face plate was 5 seconds, and the air pressure was 5 kg/cm ² . The haze value (HAZE VALUE) of the obtained molded article was measured and compared with the haze value of the original fabric sheet. In addition, the presence or absence of raindrop phenomenon in this molded article was investigated. The results are shown in Table 1.

[Table] As is clear from Table 1, the raindrop phenomenon may occur in molded products thermoformed by a contact type face plate thermoforming machine that uses a uniaxially oriented sheet and a heating face plate with a small surface roughness. In addition, the haze value on the container wall is low.

Claims (1)

[Scope of Claims] 1. A method for producing a thermoformed article by thermoforming a thermoplastic synthetic resin sheet using a contact type face plate thermoforming machine, wherein a uniaxially oriented sheet is used as the sheet, and the contact type face plate thermoforming machine The surface roughness of the heating face plate is
The method for producing the thermoformed product, characterized in that the product is finished to a smoothness of 3S or less. 2. The method for producing a thermoformed article according to claim 1, wherein the width reduction rate of the oriented sheet (the reduction rate of the sheet width after orientation relative to the sheet width before orientation) is 10% or less. 3. Claim 1, wherein the oriented sheet is a uniaxially oriented sheet oriented by roll rolling at a temperature lower than the melting point or flow initiation point of the sheet.
A method for producing a thermoformed article according to item 1 or 2. 4. Production of a thermoformed article according to claim 1, 2, or 3, wherein the sheet temperature during shaping is maintained at a temperature lower than the melting point or flow start point of the sheet, and thermoforming is performed. Method.