JPH0247032A - Manufacture of bottle of biaxially oriented polyolefin - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a biaxially stretched polyolefin bottle. Specifically, the present invention relates to a method for producing a biaxially stretched bottle with excellent transparency and low heat shrinkability using polyolefin such as polypropylene or polyethylene.

[Conventional technology]

In recent years, blow-molded containers using polyolefin resins such as polypropylene have been used for applications such as food containers, pharmaceutical containers, and cosmetic containers.

Transparency is an important performance for containers, but
Compared to vinyl chloride resin, polyethylene terephthalate resin, etc., polyolefin such as polypropylene has poor transparency because it is a highly crystalline resin. However, it is an advantageous material in terms of rigidity, food hygiene, etc., and various studies are being conducted to improve its transparency. Seven methods include improving transparency by changing the crystal structure through a stretching process such as biaxial stretch blow molding.

[Problem to be solved by the invention]

As a biaxial stretch blow molding method, there is a method in which the parison is cooled and solidified in an injection mold, the parison is taken out from the mold, the parison is then heated to a predetermined temperature, and then biaxial stretch blow molding is performed. There is a problem in that the injection molding time becomes longer due to the cooling time required for the parison, resulting in poor productivity, and there is also a problem in that there is a large energy loss because the temperature of the parison must be raised again after it has been cooled.

In order to solve this problem, there is a method of taking the parison out of the mold in a molten state, but when the high-t parison is in a molten state, its viscosity is too low and the releasability from the mold is poor.
The surface smoothness of the parison released from the mold may be disturbed.
When this parison is biaxially stretched and blow molded, there is a problem that transparency unevenness and horizontal wrinkles occur in the molded product, and the transparency is rather reduced. Furthermore, as a method to improve the releasability between Parinon and the mold, coating the mold with a mold release agent such as silicone oil has been done, but this method has been found to actually worsen the appearance of the molded product. There is a problem.

[Means to solve the problem]

In view of the above-mentioned problems when molding bottles using biaxial stretch blow molding using polyolefins such as polypropylene, the inventors of the present invention aimed to improve transparency, especially by improving the releasability between Parinone and the mold in the molten state. As a result of extensive research into methods for manufacturing superior bottles, we found that by using an injection mold for parinon molding, the inner surface of the mold (the contact surface of the parison) was coated with a fluorine-based resin. The releasability between the parison and the mold has been significantly improved, the stretch molding temperature range in the high temperature range has been greatly expanded, the transparency of the resulting molded product (bottle) has been significantly improved, and the heat shrinkability has also been improved. They have discovered that this is the case and have completed the present invention.

That is, the gist of the present invention is to manufacture a container by biaxial stretch blow molding polyolefin, by injection molding a molten polyolefin into an injection mold whose inner surface is coated with a fluorine-based resin. A product made of polyolefin characterized by forming a bottom parison, taking it out from an injection mold while at least a part of the parison is in a molten state, and then biaxially stretching and blow molding the bottomed parison in the longitudinal and transverse directions. The invention consists in a method for manufacturing a biaxially stretched bottle.

The present invention will be explained in more detail below.

The polyolefins used in the present invention include homopolymers, copolymers, or two of α-olefins such as ethylene, propylene, /-butene, goomethyl-/-pentene, /-hexene, /-octene, and /-decene. It is a mixture of more than one species and is crystalline.

The biaxial stretch blow molding method using the above polyolefin raw material will be explained in detail with reference to the drawings.

FIGS. 1 to 6 are vertical sectional views sequentially showing steps from injection molding of a parison of polyolefin resin to completion of blow molding.

In the figure, / indicates the upper mold, C indicates the lower mold, 3 indicates the injection molding machine, G indicates the bottomed parison, J indicates the lip mold, 6 indicates the rotary table, 2 indicates the stretching rod, and ♂ indicates the blow mold. .

Figure 1 shows the upper mold (core) whose surface is coated with fluorine resin.
The injection mold consisting of a lower mold (cavity) 2 is closed, and molten resin is injected into the mold from an injection molding machine 3. The parison is kept in this state for an appropriate period of time to stabilize it.

Figure 2 shows that a bottomed parison formed by an injection mold is not cooled down to a solidified state, but the parison shape can be maintained, but at least a part of the parison is still in a molten state. While the inner layer side of the parison is in a molten state at a temperature ranging from the melting point of the polyolefin to -20°C to the melting point, preferably from the melting point -/j°C to the melting point -s°C, the bottomed parison is removed from the upper mold/and the lower mold 2. The mold is released and taken out, and the mold rips from the mouth! Indicates the state maintained by.

In the present invention, since the inner surface/a of the upper mold/, that is, the contact surface with parison is coated with a fluorine-based resin, the sliding property with the parison in the molten state is improved, and the mold release property is significantly improved, compared to the conventional 9. The range of molding parts that can be released at a temperature higher than the mold release temperature between the metal surface and the parison has been expanded, and it has also become possible to mold polypropylene homopolymer and the like.

Furthermore, the transparency and heat shrinkability of molded products obtained by stretch molding at high temperatures can be significantly improved. Examples of the filtrate and thread resins used for coating the inner surface/a of the mold/mold are polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, and hexafluoropropylene. Tetrafluor/L
, :r-f V-copolymer, chlorotrifluoroethylene-vinylidene fluoride copolymer, etc., and polytetrafluoroethylene is particularly preferably used. Note that the coating treatment with the fluorine-based resin is not limited to the above mold/a, and may be used in combination with the cavity 2a.

As an example of the coating treatment for the molds /a and 2a, for example, polytetrafluoroethylene (molecules f7110oo to
There is a method in which a fluorotelomer dispersion obtained by diluting fluorocarbon-based solvent (for example, trichlorotrifluoroethane) to a concentration of about 20% by weight is applied to the molds/a and 2a. These include, but are not limited to.

Figure 3: Beam, mold! This shows the Paris song being held by the holder and being moved onto the rotating table. FIG. 9 shows the state in which the stretching rod 7 is installed. FIG. 5 shows a state in which the bottomed parison Z is stretched by the stretching rod 7 in the blow mold ♂ and at the same time is stretch-blow molded by blowing blow air. FIG. 4 shows a state in which the stretch blow molding has been completed, the blow mold ♂ has been opened, and the container (bottle) has been released.

The biaxial stretching molding method using the hot parison method mentioned here is an example of the molding method, and the preheating or preparatory process performed as a stage before the hot parison is subjected to the main flow between FIG. 3 and FIG. It may also be an apparatus that includes a blowing process or the like.

An important point in the method of the present invention is the heating state of the parison. In the method of the present invention, the bottomed parison formed by injection molding is not completely cooled in the injection mold, and as described above, the parison retains its shape but is injection molded while it is still at a fairly high temperature. Remove from mold,
This is biaxially stretch blow molded, and the bottomed parison taken out of the mold is one that can maintain its parison shape and is taken out of the injection mold while still in a molten state. be.

In other words, the temperature of the parison surface is equal to or less than the melting point of the raw resin by 20
It is taken out from the injection mold while the temperature is within the temperature range of ℃ to melting point, and it is taken out from the mold after cooling for a shorter time than the normal cooling time of the injection mold in this type of molding method. be. (The cooling time in the mold varies depending on various conditions such as the wall thickness of the parinon and the mold temperature, so it cannot be specified in terms of time, but when the various conditions such as the wall thickness of the parinon and the mold temperature are constant) ) Instead of using this method, the parison is completely cooled and solidified in the mold during injection molding of the bottomed parison, and then the parison is heated and heated to the stretching temperature again during biaxial stretch blow molding. If biaxial stretch blow molding is performed, the product will only have a cloudy surface, and the desired transparent bottle will not be obtained.

This is due to the difference in stretching properties between the surface layer and the interior of the injection-molded parison thus obtained.

The size of the bottle produced by the method of the present invention is not particularly limited, but is usually 3.0~! ,! Throat level, preferably 3. Sunset! Use a parison that is as thick as a parison, and fold it 2 to 2.2 times vertically and horizontally! ~! It is suitably used for bottles obtained by biaxially stretching to approximately double the original size.

The present invention will be explained in more detail with reference to Examples below.
The present invention is not limited to the following nine embodiments as long as the gist of the present invention is not exceeded.

Example/2 As polypropylene A, propylene-ethylene random copolymer (manufactured by Mitsubishi Kasei ■: ≦200E/, x tyrene copolymerization degree: 3.2%, melt flow index (MF I
): LOt/ / 'min, density: 00901/l
ri, standard melt tension (MT) = 2. J-f, melting point (Tm
):/jj°C, crystallization temperature: 9j°C), and a biaxial stretch blow molding machine (SB-/l
Om type) was used.

The parison contact surfaces (both surfaces of the male and female molds) of the injection mold of the above-mentioned molding machine were provided with a Teflon coating with a thickness of 100 μm.

Polypropylene A resin temperature = 24tθ℃, injection pressure = 9
After injecting into a mold with a surface temperature of 20° C. under the condition of θ cape/d, it was taken out from the mold. The bottomed parison has a stretched diameter of 2 degrees and a stretched body length of 2 degrees. θ■, the body thickness is DA, 0
It is the throat. The molding conditions were: injection time 3.1 seconds, cooling time! It was taken out from the mold in seconds. The temperature of the body of the bottomed parison was 730°C.

The temperature of the body of the bottomed parison was determined by measuring the temperature of the surface of the body of the parison using a digital radiation thermometer (model IR-AH) manufactured by Chino Corporation.

The obtained high-temperature bottomed parison is placed in a blow mold, a stretching rod is introduced into the bottomed parison, and the bottom of the bottomed parison is pressed to stretch it in the longitudinal direction. A biaxially stretched bottle was produced by blowing compressed air at /θ Cape/- for seconds. The temperature of the blow mold at this time was -20℃
After finishing blowing, it was cooled and taken out from the blow mold. The resulting bottle has an extended body height of approximately 100mm and a thickness of approximately ? 11. The wall thickness of the body was approximately o3■t, and the transparency of this portion was 20% (haze value).

(Example/) 0 Body temperature (molding temperature) of a bottomed parison in the same manner as above
When cooled to 72θ℃, the transparency is 2! % (haze value). (Example The measurement method for transparency and heat shrinkage rate is as follows.

〔transparency〕

Conforms to JIS K-t7/da.

(Measure the haze of the body part o, 4tt) [Heat shrinkage rate] Punch out the body part (O, l++m+t) into a short fence piece (height 13m - circumference j Om) and open it in the air at /20℃
-/ Perform annealing for hr.

After that, 23℃ 6! After being left in a constant temperature room for 24 hours, the shrinkage rate in the circumferential direction was measured.

The measurement results are shown in Table-/.

Comparative Examples/~3 Molding was carried out in the same manner as in Example/using an injection molding die not coated with Teflon.

Conventional injection molds have poor sliding properties with the parison in the molten state, so the molding conditions include injection time:
3. After injection in 3 seconds, cooling time is 6. ! The mold cannot be released from the mold unless it takes more than a second, so I did it like this (6, 3
After cooling for seconds), the temperature of the body of the bottomed parison taken out is approximately /
The temperature was 10°C. Blow molding was carried out in the same manner as in Example 1, and the transparency (haze value) was measured and was found to be 3θ.

(Comparative example/) The transparency of the body of the blow bottle was measured when the temperature of the body of the parison was 100°C and 0°C when the parison was removed from the injection mold by increasing the cooling time. %
1. ? (It was 5'%. The measurement results are shown in Table-7.

Table Example 3 In Example/, polypropylene A was replaced with polypropylene B (homopolymer melt flow index (M
FI): 109710 min, density: o, q/y
/ctd, standard melt tension crab, 2. The same procedure was carried out except that the following values were used: Of, melting point: / ℃, and crystallization temperature: 777°C.

When polypropylene B is used, looking at the temperature of the body of the parison that can be taken out from the injection mold, it is found that in conventional injection molds, the parison has poor slipperiness in the molten state, so the injection time is set to 3 as the molding condition. ,! If the cooling time is 2 seconds, then the cooling time is 2
．． ! It was impossible to release the mold from the mold unless it was held for more than a second. When the cooling time was set to 2.5 seconds, the temperature of the body of the bottomed parison was 730°C.

Thick fluorine resin (Teflon) on the Parinon contact surface/a!
Injection molds coated with 00μ have improved sliding properties with the parison in the molten state, and the mold release property has been significantly improved, so the mold can be released at a higher temperature than the conventional mold release temperature between the metal surface and the parison. When the molding conditions were an injection time of 38 seconds, it was possible to take out the product from the mold in a cooling time of 0.5 seconds. The temperature of the body of the bottomed parison taken out in this manner was 750° C. As described above, in the past, molding was impossible due to the inability to release the mold.

Since high-temperature stretch molding is now possible, the range of molding conditions for polypropylene B has been greatly expanded, and even for polypropylene homopolymer, the molding conditions have become much easier.

In Examples G to 2 and Comparative Examples G to B, the following cloth was used instead of polypropylene A.
The same procedure was carried out except that polybrene C, D, and E having the physical properties of 2 were used.

The results are shown in Table 3.

[Effect of the invention] According to the method of the present invention, using a polyolefin resin,
It is possible to produce biaxially stretched synthetic resin bottles with excellent transparency and low heat shrinkage, which is very effective in practice.

[Brief explanation of the drawing]

FIGS. 1 to 6 are vertical sectional views sequentially showing the steps from injection molding of a polyolefin resin parison to completion of blow molding. In the figure / is the stopper mold, 2 is the lower mold, 3 is the injection molding machine, G is the bottomed parison, Y is the lip mold, 6 is the rotary table, 7 is the stretching opening, C, ? indicate blow molds, respectively.

Claims (1)

[Claims] (1) When producing containers by biaxial stretch blow molding polyolefin, a parison with a bottom is formed by injection molding molten polyolefin into an injection mold whose inner surface is coated with a fluorine-based resin. A biaxially stretched bottle made of polyolefin, characterized in that the parison is removed from an injection molding mold while at least a portion of the parison is in a molten state, and then the bottomed parison is biaxially stretched and blow molded in the longitudinal and transverse directions. manufacturing method.