JPS5953851B2 - Method for manufacturing transparent containers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a transparent container from a polypropylene sheet for thermoforming, which has good transparency, is strong, and has good thermoformability. The present invention relates to a method for manufacturing a transparent polypropylene container having the above-mentioned excellent properties by plug-assisted pressure forming, matte molding, or the like.

Conventionally, polyvinyl chloride resin (hereinafter referred to as PVC) and polystyrene resin (hereinafter referred to as P, S-type).

In such a situation, for example, PVC has problems with its toxicity and low heat resistance, and P and S systems have problems with their low heat resistance, low impact resistance, and disposal, but these also have problems. However, other general-purpose resins were not able to fully satisfy any of the above three properties. Currently, the following proposals have been made to address this problem.

(1) Polyolefin (substantially polypropylene) is rapidly cooled to improve its transparency and then thermoformed at a temperature below its melting point (Japanese Patent Application Laid-open Nos. 50-158652 and 50-1603).
76).

However, the disadvantages of this method are poor thermoformability (sheet sagging and wrinkles during thermoforming, etc.), weak stiffness (molded product), and high technology required for the quenching process. 5(2) A polyolefin sheet (substantially made of polypropylene) is subjected to vacuum and pressure forming in a solid state using a plug (Japanese Unexamined Patent Publication No. 11489/1989).

The disadvantage of this case is that in order to obtain transparency, polypropylene with a low molecular weight is used, and the resulting molded product has low rigidity and impact resistance. (3) Thermoforming a high-density polyethylene blend and a polypropylene sheet in a solid state while stretching the sheet 5 to 15 times by setting the descending speed of a plug or punch at a temperature lower than the melting point (Japanese Patent Application Laid-Open No. 51-11001) -31761, 51-34956).

The disadvantage of this case is that it is difficult to industrialize and the detailed technology is still incomplete.

As mentioned above, while each method can certainly be expected to be effective, it cannot be denied that they also have various disadvantages at the same time.

In response to these problems, the present inventors have proposed a method in which a sheet that has already been uniaxially oriented is subjected to thermoforming. Needless to say, this method eliminates various disadvantages associated with the above proposals and is expected to be effective as a method for manufacturing transparent containers. That is, this method does not require sophisticated technology, the molecular weight of the raw material resin used is not limited, and no special thermoforming machine is required. On the other hand, the present inventors conducted further research on the method of manufacturing transparent containers, and found that isotactic polypropylene (hereinafter referred to as IsO-polypropylene) to which a small amount of nucleating agent was added as the raw material resin in the method proposed above. The inventors have discovered that the desired effect can be further dramatically enhanced by using the above-mentioned conventional methods, and that the various disadvantages seen in the conventional proposals can be overcome, leading to the present invention.

The present invention will be explained in detail below.

The method of the present invention involves adding 0.01 wt. to IsO-polypropylene to the weight of the resin (hereinafter the same shall apply) using a suitable means such as extruder kneading. %~2.0wt. A nucleating agent is dispersed and added in a range of 0.1%, the nucleating agent-added resin is melt-molded to form a sheet with a surface roughness of 0.7 μRMS or less, and then the sheet is subjected to, for example, roll rolling. It is characterized by imparting a slight orientation in the uniaxial direction with an elongation ratio of 1.02 times or more and 3 times or less by an appropriate means such as thermoforming at a sheet temperature lower than the melting point of the oriented sheet. This is a method to do so.

Examples of nucleating agents used in the present invention are as follows.

Nucleating agent Melting point (℃) Benzoic acid 122.3 Phthalic anhydride 132 Glutaric acid 98 Phenyl acetic acid 780 Phenyl salicylic acid 113 Phenyl benzoate
70 Phenyl salicylate
41.9P-Ethyl aminobenzoate
92 polyethylene terephthalate
265 polyamide (nylon-6) 21
5 It is generally known that by adding a small amount of a nucleating agent to 1s0-polypropylene, it is possible to improve the transparency of, especially injection molded products, or to shorten the molding time.

Similarly, it is easy to think of a method of obtaining a transparent container by thermoforming a sheet with improved transparency by adding a nucleating agent to polypropylene. However, as a result of studies by the present inventors, although the IsO-polypropylene thermoformed containers obtained by this method are certainly more transparent than those to which no nucleating agent is added, optical distortion occurs in the walls of the transparent containers. As a result, the transparent light is finely refracted, giving the container a so-called "glaring" visual appearance, making it impossible to obtain a container with a clear, transparent appearance. Furthermore, the thermoforming conditions are narrow, and even under conditions that are considered appropriate, containers with localized dents in their walls are quite often produced after molding. Conventional polypropylene sheets warp and sag on the thermoforming mold due to thermal expansion and low melt tension of the sheet during heating during thermoforming.

This phenomenon is no exception even for sheets containing nucleating agents, which cause them to undulate and sag significantly. This results in uneven elongation of the sheet during deformation during thermoforming, or irregularities in the way deformation stress is applied, resulting in optical distortion within the wall of the molded container. In addition, rough surface conditions such as unevenness on the surface of the sheet are increased during deformation, and the surface condition becomes poor. It is considered that such a phenomenon significantly limits the contribution of the nucleating agent to increasing the transparency of the thermoformed sheet. Compared to this situation, when using the method of the present invention,
The above-mentioned problems have been completely resolved, and the container has excellent transparency and gloss due to the effects of surface smoothing, slight uniaxial orientation, and solid-state thermoforming at a temperature lower than the melting point. is obtained. There are no particular restrictions on the type of nucleating agent that can be used in the method of the present invention, but in particular, organic acids and their derivatives, or high molecular weight polymers with a higher melting point than polypropylene resin may be used to improve transparency. can get.

For example, organic acids include benzoic acid and salicylic acid, and derivatives of organic acids include metal salts of organic acids, such as sodium salts and aluminum salts. Examples of high molecular weight polymers include polyethylene terephthalate and polyamide. No special method is required for adding the nucleating agent, but since the amount added is small, care should be taken to disperse it within the resin ('-.).The amount added varies depending on the type of nucleating agent. is generally sufficient in the range of 0.01 to 2.0 wt.% based on the resin, more preferably 0.04 to 1.5 wt.%.
% is good. 0.01wt. %, it is difficult to expect a significant effect of improving transparency; If it is larger than %, the effect cannot be expected to be prolonged.

0.04wt. %, uniform dispersion into the resin is difficult; %, it is a little saturated, and compared to increasing the amount added, the degree of increase in effect is low, and there is little economic merit.

In addition, especially when a nucleating agent with a low melting point is added in too large a quantity, surging tends to occur during extrusion. Although sheet manufacturing equipment does not require any special structure, consideration should be given to smoothing the surface. For example, a molten sheet, typically extruded from a flat die, is wrapped around a polysyn roll,
There is a method of pulling the sheet, but in this case, in order to maintain the surface smoothness of the sheet at 0.7μRMS or less, the polysyn roll must have a surface roughness of 0.8S or less and a roll surface treatment at least equivalent to a cloth finish. Treatment should be done. Any known method may be used to uniaxially orient the sheet, but since the elongation ratio is as small as 1.02 to 3 times, unoriented portions may occur depending on the orientation method, making it difficult to achieve uniform orientation. This should be carefully considered, as it may make it difficult to grant. As a result of studies by the present inventors, a roll rolling method as shown in FIG. 1 is particularly suitable as an orientation method in this case. In the figure, 1 is a high-speed stretching roll, 2 is a low-speed stretching roll, 3 is a nip roll, 4 is a preheating roll, 5 is a sheet before orientation treatment, and 6 is a uniaxially oriented sheet. The advantages of the roll rolling method are: 1. Uniform orientation can be imparted even at low elongation ratios, 2. Even if the sheet is thick, there is no difficulty in stretching orienting due to tensile force, and 3. The surface of the sheet is smooth. There is no thickening phenomenon at the edge of the 4-oriented sheet, that is, the loss rate is small.
5. Transparency of oriented sheets is significantly improved compared to tensile stretching. As described above, it has many advantages. Roll rolling basically reduces the thickness of a raw sheet by passing the raw sheet through a gap between a pair of rolls that rotate in opposite directions, the gap being set at a distance smaller than the thickness of the raw sheet. It is.

This method also includes, for example, a hydraulic roll rolling method in which the surface of the roll is coated with a liquid film and the thickness is reduced by liquid pressure, and a non-uniform rolling method in which the circumferential speed of a pair of rolls is made different from each other. Roll rolling methods with various advantages are known, such as the rolling method and other multiple rolling methods, but there is no problem with any method, and in either method, the elongation ratio is 1.02 to 3 times, preferably 1.2. A factor of 2.5 to 2.5 times gives good results.

A stretch ratio of 1.02 times is the lower limit for achieving the desired effects (transparency, gloss, sheet tension); exceeding the upper limit of 3 times may cause the orientation to become too strong, requiring modifications to the thermoforming equipment, etc. In addition, a high-output orientation device is required. In addition,
1.2 to 2.5 times is a balance between the above upper and lower limits and provides a preferable effect. Conventionally, various thermoforming methods have been used, mainly vacuum forming, pressure forming, combined use of plugs, matted die method, etc., but in the method of the present invention, there are no restrictions on the selection. There is no. However, with the vacuum forming method that uses atmospheric pressure, the forming pressure may be insufficient for forming thick-walled containers, so consideration should be given to the thickness of the sheet used when carrying out the process.
From this point of view, as a thermoforming method particularly suitable for the method of the present invention, plug assist pressure 7 air molding gives good results.
Whichever method is used, the temperature of the sheet during thermoforming should be maintained below the melting point of the sheet. The optimal temperature conditions vary depending on the sheet thickness, container specifications (drawing ratio, shape, etc.) and thermoforming method2, but generally speaking, it is 130° to 160°C, especially 140° to
A range of 155°C is desirable. Although the preheating time also varies depending on the sheet thickness, for example, if the thickness is about 0.7 to 1 mm, the preheating time usually does not exceed 30 seconds. Needless to say, it is ideal to gradually heat the material to a predetermined temperature over a long period of time, but this is a trade-off with economic factors such as equipment costs. The shape of the plug cannot be determined universally, but one that is compatible with the shape of the container should be considered.

However, even if the shape of the plug used during implementation does not necessarily match the optimal shape in a strict sense,
It does not essentially affect the outcome. The surface temperature of the plug should be relatively close to the seat temperature if the plug surface material has a high specific heat (for example, metal), for example around 80° to 110°C, or if the specific heat is relatively low. (for example, cloth, etc.), even if the temperature is not controlled as strictly as described above, the result will hardly be affected. There are no restrictions on the molecular weight of the IsO-polypropylene used in the present invention.

Furthermore, although it is not essentially limited to homopolymers or copolymers, it is believed that block copolymer types in particular have extremely poor transparency and are of little practical value. However,
Since polypropylene is generally inferior in impact resistance, particularly in low-temperature impact properties, a mixed composition of a monopolymer and a copolymer may be effective in improving the impact resistance. The present invention is a particularly effective method for improving impact resistance.

That is, since the method of the present invention is not limited by the molecular weight of the IsO-polypropylene used, a resin having a relatively higher molecular weight than that conventionally considered appropriate as an IsO-polypropylene for thermoforming of transparent containers is used. It can be obtained because it is possible. This transparent container has good impact resistance properties that cannot be obtained with conventional transparent polypropylene containers. Ru. Therefore, it goes without saying that the low-temperature impact resistance properties are also greatly improved. For example, in the conventional polypropylene transparent container manufacturing method, M. F. The method of the present invention provides such transparency that M.I. is at least greater than about 5.0.
F. I. Even if it is about 0.3, it is possible to easily obtain transparency that is sufficiently higher than that. Additionally, the advantages of the present invention can be achieved using the same logic with respect to improving the rigidity of the container, that is, the buckling strength of the container.

Next, examples will be described.

Example 1 The influence of the molecular weight of the resin used and the concentration of the nucleating agent added in the method of the present invention was examined.

That is, samples of commercially available 1s0-polypropylene homopolymers of the following three types A to C are taken as shown in Table 1, and a predetermined amount of a nucleating agent (a commercially available benzoic acid reagent of first grade) as shown in Table 1 is added to each sample. After blending with a pen shell mixer, extrude through a T-die at a resin temperature of 230°C.
While still in the molten state, it was polished to a surface roughness of 0.4S and introduced into a pair of polysyn rolls whose surface temperature was maintained at 90°C, where it was cooled and solidified to form a sheet, with a sheet width of 400 mm. .

The surface roughness of all sheets is 0.25 to 0.3μRMS
It was hot. After preheating this sheet to 140℃, each roll with surface temperature maintained at 110℃ has dimensions of 220mmφ x 50mm.
0L passed between a pair of rolling rolls with a surface roughness of 0.4S to reduce its thickness, and the elongation ratio was 1.4 times, resulting in a thickness of 0.0L.
A 7 mm uniaxially oriented sheet was obtained. The sheet was thermoformed into a container using a far-infrared heating plug-assisted pressure forming machine, and the characteristics of the container were measured. The results are shown in Table 1. The general conditions for thermoforming are as follows. Seat preheating temperature
'::150℃ sheet preheating time
18 seconds sheet forming time
6 seconds pneumatic pressure 4k
g/Cml Plug surface Flannel cloth covered plug surface temperature 60℃ Plug volume Tip diameter = 45n1In Height "30!I]m Bottom diameter: -65w1m Cup volume Opening diameter 70mm Bottom diameter 60Wf1 Depth 40011n Number of molded pieces 4 cups Book table As is clear from the above, the method of the present invention makes it possible to obtain transparent containers regardless of the molecular weight of the IsO-polypropylene used, and it can be seen that the cup strength characteristics largely depend on the molecular weight.

Further, during thermoforming here, the uniaxially oriented sheet was stretched horizontally, and waviness and sag were completely removed.

The surface of the resulting cup had a high degree of photoselectivity, and no local refraction of the light beam transmitted through the vessel wall was observed. Example
2 and Comparative Example 1 As is clear from this table, the method of the present invention can obtain satisfactory results in terms of transparency and gloss when the surface roughness of the sheet before orientation is at least about 0.7 μRMS or less.

Furthermore, no local refraction of transmitted light was observed on the vessel wall of the resulting cup. The influence of elongation magnification in the present invention was investigated.

That is, M. F. I. 2. O
All nucleating agent concentrations were 0.1 Wt. Cups were obtained in the same manner as in Example 1, except that the elongation ratio was changed as shown in Table 2 and all 0.7 mm uniaxially oriented sheets were obtained. The results are shown in Table 2. The surface roughness of all orienter sheets was 0.25-0.3 μRMS. As is clear from this table, according to the method of the present invention, when the elongation ratio is at least 1.02 times to 3 times, transparency and
Satisfactory results can be obtained in terms of gloss.

In addition, within the range of the elongation ratio, the sheet during thermoforming was stretched horizontally and did not sag. Furthermore, no local refraction of transmitted light was observed on the wall of the resulting cup. When the elongation ratio was increased to 4 times, the transparency and surface gloss of the cup decreased significantly.

Example 3 and Comparative Example 2 The influence of sheet surface smoothness before orientation treatment in the present invention was examined.

That is, commercially available 1s0-polypropylene (melting point 168°C, density 0.90, M.F.I.2.O) was used, and the nucleating agent concentration was 0.1 wt. %, and the surface roughness of the polysynroll during melt forming of the sheet is 0.4S and 0.8, respectively.
Strength was obtained in the same manner as in Example 1, except that the sheet surface roughness was changed as shown in Table 3. The results are shown in Table 3. Ta.

The results are shown in Table 4. The surface roughness of all sheets before orientation was 0.25 to 0.3 μRMS. That is, the effect becomes saturated when the amount of the nucleating agent added exceeds a certain level. Example 5 Various changes were made to the nucleating agent in the present invention.

That is, as shown in Table 5, M. F. ．． Several types of IsO− with different
Polypropylene (both have melting points of 168°C) is combined with several types of nucleating agents, and the amount of nucleating agents added is all 0.1 wt%.
A cup was obtained in the same manner as in Example 1 except for the following.

The results are shown in Table 5. The surface roughness of all sheets before orientation was 0.25 to 0.3 μRMS. Example
6 A stretching method was utilized for the sheet orientation treatment in the method of the present invention.

That is, commercially available IsO-polypropylene (melting point 168°C,
Density 0.90M. F. I. 2.0), and uniaxially oriented using the close roll stretching method as shown in Fig. 1 to obtain an oriented sheet with a thickness of 0.7 mm, but everything was the same as in Example 1. I got a cup. The stretching conditions are as follows. High speed stretching roll peripheral speed
15m/Min low speed stretching roll peripheral speed
10.4m/Min stretching roll spacing
1mm stretching roll surface temperature
125℃ sheet preheating temperature 120
℃ Stretching roll diameter (both high and low speed) 220mmφ
The surface roughness of the sheet before orientation is 0.25 to 0.
It was 3 μRMS.

The results are shown in Table 6. No sagging of the sheet was observed during thermoforming in Example 6. Also, no local refraction of the transmitted light by the cup wall was observed. Comparative example
4 Cups were obtained in the same manner as in Example 1, except that the same resin as used in Example 1 was used and no nucleating agent was added.

The results are shown in Table 7. Note that the surface roughness of all sheets before orientation was 0.25 to 0.3 μRMS. As is clear from the table and the comparison with Example 1, it can be seen that the method of the present invention dramatically improves transparency.

Comparative Example 5 A cup was obtained in the same manner as in Example 1, except that the same resin used in Example 1 was used, no nucleating agent was added, and no uniaxial orientation treatment was performed.

The results are shown in Table 8. Note that the sheet thickness is 0.7 [N
In, and the surface roughness of all sheets is 0.25~
It was 0.3 μRMS. Comparative Example 6 The same resin used in Example 1 was used, the amount of nucleating agent (benzoic acid) added was 0.1 wt%, and the uniaxial orientation treatment was not performed. I made the same and got a cup.

The results are shown in Table 9. All sheet surface roughness is 0
．． It was 25-0.3 μRMS. As is clear from Comparative Examples 5 and 6, it can be seen that the transparency can be greatly improved by simply adding a nucleating agent.

This comparative example shows a limit to the extent of the transparency improvement effect, which is hindered by waviness or sagging during thermoforming, or its surface roughness, as described below. Compared to these, as is clear from the examples, it is clear that the method of the Buninvention can dramatically increase the transparency due to the synergistic effect of the sheet treatment and the nucleating agent. In this comparative example, the sheet immediately before thermoforming had waviness or sag.

Table 10 summarizes the results of these situations. Incidentally, a similar phenomenon was also observed in Comparative Example 5. Comparative Example 7 Commercially available 1s0-polypropylene was used, and the amount of nucleating agent (benzoic acid) added was 0.1 Wt. %, and a cup was obtained in the same manner as in Example 1 except that the sheet preheating temperature during thermoforming was 175°C.

The results are shown in Table 11. The surface roughness of each sheet before orientation was 0.25 to 0.3 μRMS.

All the test methods used in the above Examples and Comparative Examples were as described below.

1 Cloudiness level Based on ASTM D-1003, 2 Side wall thickness 10 points equally spaced in the circumferential direction at the center of the cup side wall. The average value of the measured values.

3 Place a plate on top of the buckling strength cup 7 and compress it at a speed of 50 mm/min using a tensilon tester. The load during buckling of the side wall is measured with a compression type load cell 8. Measured values for each of 10 cups. The average was calculated (see Figure 2).

4 Low temperature impact resistance In liquid at 10℃ and -30℃, (IPA)
After immersing for 0 minutes, a weight of 9 (152 g) was dropped to the bottom of the container and the degree of destruction was observed.

The number of pieces destroyed in each 10-piece test is displayed. (See Figure 3).

5 wall surface glossiness Compliant with JISZ874l.

45° specular gloss.

6 Sheet surface roughness Surface roughness meter (manufactured by Kosaka Institute, SE-4 type) measuring instrument.

7 Seal surface roughness Compliant with JISB6Ol-55.

[Brief explanation of drawings]

Fig. 1 shows a rolling roll apparatus preferably used to orient the resin sheet in the practice of the present invention, Fig. 2 shows a conceptual diagram of an apparatus for measuring buckling strength, and a conceptual diagram of a test apparatus for low-temperature impact resistance. It is a diagram.

Claims (1)

[Claims] 1. When manufacturing a transparent container from a sheet of isotactic polypropylene resin by thermoforming, 0.01 to 2.0 wt. A uniaxially oriented sheet obtained by stretching a sheet made of an isotactic polypropylene resin containing a nucleating agent of % and a surface roughness of 0.7 μRMS or less in one direction by 1.02 to 3 times at a temperature lower than its melting point. A method for producing a transparent container, characterized by thermoforming at a temperature lower than its melting point. 2. The method for manufacturing a transparent container according to claim 1, wherein the sheet is stretched by roll rolling. 3. The method for producing a transparent container according to claim 1 or 2, wherein the nucleating agent is an organic fatty acid or a derivative thereof. 4. The method for producing a transparent container according to claim 1 or 2, wherein the nucleating agent is a polymer having a melting point higher than that of the isotactic polypropylene resin.