JPS6022615B2 - Container manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a thermoplastic synthetic resin molded article.

More specifically, the present invention relates to a method of ripening a sheet obtained by rolling a thermoplastic synthetic resin sheet obtained by a conventionally known method without causing problems such as wrinkling or sagging of the sheet during ripening. Conventionally, food containers,
Polystyrene and polyvinyl chloride sheets obtained by conventional aging processes such as compressed air and vacuum forming have been used for pharmaceutical containers, etc., and these resins have excellent moldability and the transparency of the product is also very high. It is well known that it is an excellent product.

However, in recent years, issues such as heat resistance, hygiene, and incineration pollution during disposal of these resin molded products have been raised.
Techniques have been developed for producing molded products by aging sheets of resins that, unlike these resins, do not have the above-mentioned problems, ie, polyolefin resins such as polyethylene and polypropylene, nylon, and polyester resins. However, when pressure-forming or vacuum-forming a resin sheet obtained by a conventional method, the sheet may sag during the heating and melting stage during ripening, or wrinkles may form around the periphery, resulting in a molded product with wrinkles. The only thing you can get is something that is distorted.

Recently, as a method for obtaining good molded products by removing the sagging and wrinkles of sheets during molding as mentioned above, Tokukan Sho 47-114
As seen in Publication No. 8y, a polyolefin with a high melt flow value is used, and the sheet obtained by highly finely controlling the melting temperature, cooling rate, roll surface roughness, etc. during sheet forming is processed into a solid state below the melting point. proposed a method of obtaining molded products using the plugassist method.

However, in this case, the polyolefin used in the first place is limited to those with extremely high melt flow values, and sheet forming requires advanced technology, which means that the sheet thickness cannot be easily changed, etc., which is still unsatisfactory. It has various points. Also, recently, as seen in Samurai Publication No. 50-158652, an opaque polypropylene sheet is obtained by heat-melting and rapidly cooling, and the transparent polypropylene sheet is aged at a temperature below its melting point. A method has also been proposed. This method is simple and effective, and is not limited to the melt flow value of polypropylene, so it can be said to be a useful method.However, since this technique heats and melts the sheet for molding, the sheet itself may change in thickness. is likely to occur,
Furthermore, it is extremely difficult to obtain a sheet with a uniform thickness due to uneven heating and cooling, and therefore it is difficult to obtain a good molded product even by normal aging. The present invention solves such problems, that is, it is not limited to materials, but also uses a simple method and device to prevent sheet sagging and wrinkles during molding.
The purpose of this invention is to provide a method for obtaining a good molded product that does not have uneven thickness.

The present inventors have developed a sheet obtained by rolling a thermoplastic synthetic resin sheet at a temperature lower than its melting point or lower than its flow initiation point (used only for resins that do not have a clear melting point). Alternatively, we found that the above-mentioned problems during molding can be solved by aging at a temperature higher than the flow start point, almost unaffected by various factors such as material and molecular weight, and based on this knowledge, This led to the present invention.

That is, a pair of thermoplastic synthetic resin sheets obtained by the usual method of the present invention, rotated in opposite directions at a temperature lower than the melting point or flow start point, and set at an interval smaller than the thickness of the sheet. A thinned sheet is obtained by passing the rolled sheet through a nip between rolling rolls, and then the rolled sheet is heated under tight conditions to a temperature higher than its melting point or flow initiation point and not more than 20°C higher than that. The aim is to improve moldability by air pressure forming or vacuum forming, and to obtain a good product using a conventional general-purpose air pressure forming machine or vacuum forming machine. In order to reduce the degree of wrinkling and sagging of the sheet, one effective method is to keep the sheet temperature low. However, in this case, especially when obtaining thick-walled containers, etc., the pressure required during sheet shaping becomes large, and it may be necessary to strengthen the ripening machine. That is, specifically, there are cases where it is not possible to use atmospheric pressure such as vacuum forming, and it is necessary to use air pressure forming and to increase the air pressure considerably (see Comparative Example 2 below). This process, particularly at a temperature lower than the melting point or lower than the flow start point, is advantageous in obtaining a molded product with particularly good transparency, but it increases the pressure required for molding during ripening, and It is disadvantageous to large players in terms of cost. However, even if the sheet temperature is made higher than the melting point or flow start point during ripening, the sheet tensioning ability due to heat shrinkage due to its orientation will not decrease, so it can be used in situations where a high degree of transparency is not particularly required. By utilizing this fact in pressure forming or vacuum forming, the above-mentioned problem can be solved. The thermoplastic synthetic resin used in this method is not particularly limited, and includes, for example, polyamide resin, polyester resin, polyolefin resin, polystyrene resin, polyvinyl chloride resin, and the like.

This method is particularly effective for crystalline thermoplastic resins. In other words, crystalline thermoplastic resins generally have low melt tension above their melting point, and therefore lack self-holding power during pre-stretching (ripening) when ripening sheets, and are prone to curling and wrinkles. However, by providing orientation according to the present invention and increasing the self-retention force by the heat shrinkage force, the effect of removing the above-mentioned inhibiting factors is great. For example, crystalline polyolefin resins such as polyethylene and polypropylene are particularly suitable resins for this method. The molecular weight of these materials does not pose a hindrance to the implementation of this method. The sheet used in the rolling process of this method may be obtained by any forming 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 sheet for ripening, and although the thickness of the sheet is not essentially limited, the final rolled sheet thickness is usually 0. The range of .02 side to 2.0 ribs is preferable, especially 0.02 side to 2.0 ribs.
1 to 1.5 fences is preferred. If the thickness is excessive, the required rolling pressure during roll rolling becomes excessive, and the rolling rolls must be extremely large, so the advantage of implementation must be judged from an economical point of view. When roll rolling a sheet, the sheet must be in a solid state when rolled between the rolls, but if the rolling temperature is significantly lower than the melting point or flow initiation point, the required rolling pressure will increase significantly. invite. Usually, rolling is carried out at a temperature up to 5 mm lower, preferably 3 mm lower than the melting point or flow initiation point of the material of the sheet. Within this temperature range, rolling at as high a temperature as possible is better in terms of rigidity. The roll rolling method may be any conventionally known method, but the circumference of the pair of rolling rolls is effective in preventing elastic recovery of the material after rolling and increasing rolling efficiency by reducing the required rolling pressure. So-called non-uniform circumferential speed rolling, in which the speeds are made different from each other, is preferred. More preferably, the shearing speeds of both rolls are made different, and the thinned rolled sheet discharged from the rolling roll is passed along the surface of the roll having a higher circumferential speed and then taken off, or Better results are obtained if it is pulled at the same speed as the surface speed. Since there is virtually no change in the rolling process in the present invention, the rolling ratio is expressed as (seal thickness before rolling/seal thickness after rolling), but in the case of the above rolling, the rolling ratio does not exceed 5. is good. When the number exceeds 5, the molecular orientation of the rolled seal progresses significantly in the rolling direction, and as a result, the strength in the longitudinal direction of the sheet increases, and the difference is larger than that in the middle direction, and due to this directionality, aging is difficult. The shape decreases.

Usually, a rolling ratio of 1.0a or less of 3.0 or less, preferably 1.5 or less, and 2.0 or less gives good results. That is, good results are obtained in that the sheet does not sag, wrinkles, etc., and does not have any directional problems during the preheating of the matured sheet. In addition, the smoother the surface of the rolling roll, the smoother the surface of the resulting rolled sheet, which usually has a 0.
．． Surface roughness of 4S or less, preferably 0. The purpose can be fully achieved by setting the surface assembly degree (indicated by JIS test method B-0601) to be less than $. The thus-produced rolled sheet is subjected to pressure forming or vacuum forming, and in the case of relatively thick, deep-drawn products, it is preferable to use a plug in combination. Regardless of the molding method, there is no need to set any special conditions; the sheet is heated to a temperature higher than its melting point or flow start point, but not higher than 20 qC or more, and preferably kept at this temperature. Aging is performed within 5 minutes. Preheating of the rolled sheet during ripening is not particularly limited, but non-contact heating devices such as infrared rays and contact methods such as hot plates are used. In the present invention, no sagging, wrinkles, etc. are observed during heating, but the green around the die must be tightened. The mold for molding may be made of metal, wood, or plaster of any material commonly used, but the smoother the contacting part of the sheet, the better; therefore, metal with a mirror finish will give better results. .

There is no particular need for heating or cooling the temperature of the mold, but it is preferable that the mold be cooled to shorten the molding cycle. In the case of a method using a plug, etc., the temperature at the tip of the plug is preferably close to the seat temperature.

Particularly in the case of metal, if the temperature is too low compared to the sheet temperature, the contact portion of the sheet to the plug will be cooled, making it difficult to stretch and deform, resulting in uneven thickness. Conversely, if the temperature at the tip of the plug is too high compared to the sheet (approximately 20 qo or more higher than the melting point or flow start point), the contact portion is likely to melt and break, making molding difficult. To explain the heating in detail, in general, in the case of ripening, sheet heating methods are roughly divided into a heat ray ray method (infrared heater, etc.) and a heat oven method.

When using a conventional non-oriented sheet such as poly-IJ olefin, it expands when heated, causing large undulations, resulting in sagging and wrinkles. If this situation were to occur under the radiation heating method, the temperature of the sheet near the heat source would rise further due to the large △T (temperature gradient between the heat source and the sheet), and there would be a large temperature difference between the sheet near the heat source and the sheet far away from the heat source. This results in a considerable temperature distribution in the sheet, making stable thermoforming difficult. On the other hand, in thermal open, ΔT is small, so the temperature does not have much effect on the distance between the sheet and the heat source. In this way, care must be taken in the heating method. However, in order to reduce ΔT with the thermal open method, if the hot air stove is used in a careless manner, temperature unevenness will occur in the atmosphere itself, and it is thought that a delicate design is required for the convection inside the furnace. In this respect, since the orientation sheet does not sag and is stretched horizontally, it can be used even with a simple spraying method, so strictness is not required. The present invention will be explained in detail below with reference to Examples and Comparative Examples, and the contents and testing methods used in the Examples are as follows.

Tensile modulus: This is a measure of rigidity; the higher the value, the greater the rigidity.

(Buckling strength according to ASTM D-882: This is a measure of the stiffness of a molded product container. The higher the value, the stronger the container is.) The container wall is crushed at a forward speed and the load at the start of buckling of the side wall is measured using a compression load cell. Thickness of the container wall: This is a measure of the quality of the molded product as well as its air formability (the container's (Average value of the thickness of 5 places on the top and bottom, evenly spaced in a fan-shaped manner with the arms open).

Thickness of the bottom of the container: This is a measure of air pressure moldability (the average value of the thickness at 5 locations on the bottom of the container).

Examples 1-2 MIO. 3 evenings/1 ridge, density 0.959 evening/Sakaki, melting point 1
Commercially available high-density polyethylene (referred to as HDPE) at 27°C was extruded to a thickness of 0.6 and 0.9, respectively (extrusion temperature 210°C, sheeting roll temperature 9000°C).
These sheets were then kept at a preheating temperature of 11,000 °C to obtain a surface roughness of 0. $, diameter 20
0 side 0, surface length 50mm, kept at a temperature of 125q0,
And non-uniform circumferential speed (high speed roll 5.2 kites/min, low speed roll 1
．． A maturing sheet of 0.3 skin thickness was formed by passing through a pair of rolling rolls (0.3 legs) at a speed of 0.2 mm/min.

The physical properties of the sheet are shown in Table 1. This rolling ratio is 2.03
．． After tightening the surrounding area of the 0 sheet, 1
The sheet was heated to a temperature of 134 qo.

The sheet temperature was measured by attaching a thermocouple to the bottom surface of the sheet using heat-resistant tape. Next, using a plug heated to 110°C, a circular cup-shaped molded product with a diameter of 4 ribs, a diameter of the bottom of 38 ribs, and a depth of 92 ribs was obtained under a pressure of 4.5 k9/ground using a plug-assisted pressure forming method. The thickness of each part of this molded article, the degree of haze of each part, and the buckling strength were measured. The results are shown in Table 1. The time that the sheet was held above its melting point during ripening was about 1 quartz (see Figure 1). Comparative Example 1 Using the same resin as that used in Examples 1 and 2, a 0.3-thick maturing sheet was obtained by extrusion molding, and then aged in the same manner as in Example 1 without rolling. performed the form.

Table 1 shows the physical properties of the sheet for ripening and the physical properties of the molded product.

Comparative Example 2 The same sheet as the sheet used for pressure forming in Example 1 (rolled at a magnification of 2.0) was maintained at a sheet temperature of 115 qC, lower than the sheet melting point, during ripening, and as a ripening machine, Example The cup obtained by using the same air pressure forming machine as in 1 had poor molding (mold fidelity), and the bottom corners were not rounded according to the mold dimensions, showing a gentle rounding. It was defective as a product.

The rolling pressure was further increased to 7k9/lump, and a molded product similar to that of Example 1 was obtained. 7k9
This pressure is too high for normal aging machines.

Example 3 Using commercially available isotactic polypropylene (referred to as jso-PP) having a MF of 12.0 m/1, a density of 0.910 m/m, and a melting point of 168°C, the extrusion temperature was 245°C.
q0, sieving roll temperature 10500, preheating temperature during sheet rolling 140qo, rolling roll temperature 1500○,
A circular cup-shaped molded product was obtained in the same manner as in Example 1, except that the sheet temperature during ripening was 170 qC, the rolling ratio of the 0.3 rib sheet was 2.0, and the plug temperature was 158 pm. Ta.

Table 1 shows the physical properties of the sheet and the molded product. The time the sheet was held above its melting point during ripening was approximately 1
It was Bansho. Comparative Example 3 The same resin as that used in Example 3 was used, and the extrusion temperature, sheeting roll temperature, and aging temperature were the same as in Example 3.
A circular cup-shaped molded product was obtained in the same manner as in Comparative Example 1 except that the same procedure was used as in Comparative Example 1.

Table 1 shows the physical properties of the sheet for ripening and the physical properties of the molded product. Example 4 Using commercially available nylon 6 (normal viscosity, density, 1.14 melting point 20 o), extrusion temperature 26 or 0, sheeting roll temperature 150°C, preheating temperature during sheet rolling 185°C, rolling temperature 190qo, aged type. A circular cup-shaped molded product was obtained in the same manner as in Example 1 except that the sheet temperature was 210 qo, the rolling ratio of the 0.3 rib sheet was 2.0, and the plug temperature was 195°C.

Table 1 shows the physical properties of the sheet for ripening and the physical properties of the molded product. The time that the sheet was held above its melting point during ripening was about 1 hour. Comparative Example 4 The same resin as that used in Example 4 was used, and the extrusion temperature, sheeting roll temperature, and ripening temperature were the same as in Example 4.
A circular cup-shaped molded product was obtained using the same machine as in Comparative Example 1, except that the machine was the same as that of Comparative Example 1.

The physical properties of the thermoformable sheet and the physical properties of the molded article are shown in Table 1. Table 1

[Brief explanation of the drawing]

Figure 1 shows the change in sheet temperature over time during ripening in Examples 1 to 2 and Comparative Example 1, and Figure 2 shows the presence or absence of sagging and wrinkles in the sheet during ripening in each Example and Comparative Example. The occurrence of sagging and wrinkles is shown. Figure 1 Figure 2

Claims (1)

[Claims] 1. A uniaxially oriented sheet obtained by rolling a thermoplastic synthetic resin sheet by passing it between a pair of rolls having a gap smaller than the thickness of the sheet at a temperature lower than its melting point or flow start point, and tightening the periphery. 1. A method for producing a container, which comprises air pressure forming or vacuum forming by heating to a temperature higher than the melting point or flow start point of the container, but not more than 20° C. higher than the melting point or flow start point of the container.