JPH03184825A - Preparation of biaxially stretched bottle made of 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.

1- [Prior Art] 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 resins, polyethylene terephthalate resins, etc., polyolefins such as polypropylene have poor transparency because they are highly crystalline resins. However, it is an advantageous material in terms of rigidity, food hygiene, etc., and various studies are being conducted to improve its transparency. One such method is to improve transparency by changing the crystal structure through a stretching treatment such as biaxial stretch blow molding.

[The problem to be solved by the invention is that the axial stretch blow molding method involves cooling and solidifying the parison in an injection mold, removing the parison from the mold, then heating the parison to a predetermined temperature, and then biaxially stretching blow molding. There is a method, but this method increases the injection molding time by the amount of time required to cool the parison, resulting in poor productivity.Additionally, the parison is heated again after it has been cooled, resulting in energy loss. The problem was that it was large.

In order to deal with this problem, there is a method of taking the parison out of the mold in a molten state, but when the high-temperature panoson is in a molten state, its viscosity becomes too low, making it difficult to release from the mold. The surface smoothness of the parison released from the mold is disturbed, and when this parison is biaxially stretched and blow molded, uneven transparency and horizontal wrinkles occur in the molded product, resulting in a problem in that the transparency is rather reduced. Furthermore, as a method to improve the releasability between the parison and the mold, a mold release agent such as silicone oil is applied to the mold, but this method actually worsens the quality of the molded product. There is a problem.

[Means for Solving the Problems 1] In view of the above-mentioned problems when molding a bottle by biaxial stretch blow molding using polyolefin such as polypropylene, the present inventors have solved the problem, especially in the separation between the parison and the mold in the molten state. As a result of intensive research into a method for manufacturing bottles with improved moldability and excellent transparency, we developed a ceramic coating on the inner surface of the injection mold for parison molding (the surface that contacts the parison). By using this material, the releasability between the parison and the mold in the molten state is significantly improved, the stretch molding temperature range in the high temperature range is greatly expanded, and the resulting molded product (bottle) is improved.
The present invention was completed based on the discovery that the transparency and heat-shrinkability of the material were significantly improved.

That is, the gist of the present invention is to manufacture a container by biaxial stretch blow molding polyolefin, by injecting molten polyolefin into an injection mold whose inner surface is coated with ceramic to form a bottomed parison. A polyolefin biaxial product, characterized in that the parison is formed and taken out 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. The invention consists in a method of manufacturing stretched bottles.

The present invention will be explained in more detail below.

The polyolefins used in the present invention include ethylene, propylene, 1-butene, 4-methyl-
It is a crystalline homopolymer, copolymer, or a blend of two or more of α-olefins such as 1-pentene, 1-hexene, 1-octene, and 1-decene.

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

Figures 1 to 6 are vertical sectional views sequentially showing the steps from injection molding of a parison of polyolefin resin to completion of blow molding, in which 1 is an upper mold, 2 is a lower mold, 3 is a 4 is an injection molding machine, 4 is a bottomed parison, 5 is a lip mold, 6 is a rotary table, 7 is a stretching rod, and 8 is a blow mold.

Figure 1 shows the upper mold (core) with ceramic coating on the surface.
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 to form a mold. The parison is kept in this state for an appropriate period of time to stabilize it.

Fig. 2 shows a bottomed parison 4 molded by an injection molding die without being cooled to a fixed state, while the parison shape can be maintained but at least a portion of the parison is still in a molten state. The surface temperature is between the melting point of the raw polyolefin -20'C and the melting point, preferably the melting point -1
While the inner layer side of the parison is in a molten state in the temperature range of 5°C to melting point -5°C, the bottomed parison is released and taken out from the upper mold 1 and the lower mold 2, and the lip mold is removed from the mouth. Type 5
Indicates the state maintained by.

In the present invention, since the inner surface 1a of the upper mold 1, that is, the contact surface with the parison is coated with ceramic, the sliding property with the parison in the molten state is improved and the mold releasability is significantly improved. It became possible to release the mold at a higher temperature than the mold release temperature of the mold, and the molding temperature range was expanded, making it possible to mold polypropylene homopolymer and other materials. Furthermore, the transparency and heat shrinkability of molded products obtained by stretching at high temperatures can be significantly improved. Ceramic coating methods used to coat the inner surface 1a of the mold 1 include a waxing method, a solution ceramic method, and a thermal spraying method (powder gas spraying method, rod gas spraying method, arc method). Thermal spraying method, plasma spraying method, discharge explosion spraying method, gas explosion spraying method, etc.), vapor phase coating formation method (PVD, CVD)
), and the thermal spraying method is particularly preferably used. Note that the ceramic coating treatment area is not limited to the mold 1a, but may be the cavity 2a and the mold 1a. As an example of the coating treatment for the molds 1a and 2a, for example, thermal spraying materials such as Al2O3, zrO2, Cr2O
+, Cr3C2, WC, TiC, TiC2, CeO2, etc.

FIG. 3 shows a state in which the parison 4 held by the lip mold 5 has been transferred onto the rotary table 6. FIG. 4 shows the state in which the stretching rod 7 is attached. FIG. 5 shows a state in which the bottomed parison 4 is stretched by the stretching rod 7 in the blow mold 8 and at the same time is stretch-blow-molded by blowing air.

FIG. 6 shows a state in which stretch blow molding has been completed, the blow mold 8 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 preliminaries performed as a stage before the hot parison is subjected to main blowing between FIGS. 3 and 5. 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 is injection molded while the parison retains its shape but is still at a fairly high temperature. Remove from mold,
This is subjected to biaxial stretch blow molding, and the bottomed parison taken out from the mold is, for example, taken out from an injection mold that can maintain the parison shape and is in a molten state.

That is, the parison is taken out from the injection mold while the surface temperature is within the temperature range of, for example, the melting point of the raw resin -20°C to the melting point, and the normal cooling time for the injection mold in this type of molding method is It is cooled for a shorter time than before and then removed from the mold. (The cooling time in the mold varies depending on various conditions such as parison wall thickness and mold temperature8-, so it is not possible to specify the time, but assuming that various conditions such as parison wall thickness and mold temperature are constant) (This is the case when the parison is completely cooled and solidified in the mold during injection molding of the bottomed parison, and then heated and raised to the stretching temperature again during biaxial stretch blow molding.) If biaxial stretch blow molding is carried out at a warm temperature, 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.

Although there are no particular restrictions on the size of the bottle produced by the method of the present invention, a parison with a wall thickness of about 1.5 to 5.5 mm, preferably about 2.5 to 4.5 mm is used, and About 1.2 to 3.5 times in the direction, 1.2 to 6.0 times in the horizontal direction
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 examples unless it exceeds the gist thereof.

91 Examples 1 to 2 Polypropylene A was a propylene-ethylene random copolymer (manufactured by Mitsubishi Chemical Corporation: 6200E1, degree of ethylene copolymerization: 3.2%, melt flow index (
MFI): 3.0g 710 minutes, density: 0.90g
/cm3, standard melt tension (MT): 2.5 g, melting point (Tm): 135°C, crystallization temperature: 95°C), and a biaxial stretch blow molding machine manufactured by Seisui Research Institute (
SB-150111 type) was used.

The parison contact surfaces (both surfaces of the male mold and female mold) of the injection mold of the above molding plate have a thickness of 300 mm. An Al2O3 coating is provided.

Polypropylene A at resin temperature, 240'C1 injection pressure =
After injection into a mold with a surface temperature of 20°C under the condition of 90 kg/cm 2 , it was taken out from the mold. The bottomed parison has an extended diameter portion 24. Ommφ, the stretched trunk length is 50 mm, and the trunk wall thickness is 4.0 mm. The molding conditions were an injection time of 3.0 seconds and a cooling time of 2.0 seconds, and the sample was taken out from the mold. The temperature of the body of the bottomed parison was 135°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 radiant temperature (IR-AH type) manufactured by Chino Co., Ltd. 10-.

The resulting 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. Compressed air of 10 kg/cm 2 was blown into the bottle for 6 seconds to form a biaxially stretched bottle. The temperature of the blow mold at this time is 2
After blowing, it was cooled and taken out from the blow mold. The resulting bottle has an extended body height of approximately 100 m.
m, and the thickness is approximately 80 mmφ. The wall thickness of the body was approximately 0.4 mmt, and the transparency of this portion was 15% (haze value). (Example 1).

Body temperature (molding temperature) of the bottomed parison in the same manner as above
The transparency when cooled to 125°C was 20% (haze value). (Example 2) The measurement method for transparency and heat shrinkage rate is as follows.

[Transparency 1 Conforms to JISK 6714.

(Measure the haze of the body 0.4 mm t) [Heat shrinkage rate] Punch out the chest (0.4 mm t) into a strip (height 15 mm - circumference 50 mnn) and put it in an air oven at 120°
C- Perform annealing for 1 hr.

Thereafter, after being left in a constant temperature room at 23°065% for 24 hours, the shrinkage rate in the circumferential direction was measured.

The measurement results are shown in Table-1.

Comparative Examples 1 to 3 Molding was performed in the same manner as in Example 1 using an injection mold without ceramic coating.

Conventional injection molds have poor sliding properties with the parison in the molten state, so the molding conditions include injection time:
After injection for 3.0 seconds, the mold cannot be released unless the cooling time is 7.0 seconds or more, and in this way (7,0
After cooling for seconds), the temperature of the body of the bottomed parison that was taken out was approximately 1
It was 1000. Blow molding was performed in the same manner as in Example 1, and the transparency (haze value) was measured to be 30%. (Comparative Example 1) When the temperature of the body of the parison was set to 100°C (Comparative Example 2) and 90'C (Comparative Example 3) by increasing the cooling time and taking it out from the injection mold, When the transparency of the body was measured, it was 35% and 38% respectively.
Met.

The measurement results are shown in Table-1.

Table-l Example 3 In Example 1, instead of polypropylene A, polypropylene B (homopolymer, melt flow index (MF
I): 3. Og/10min, density: 0.91g/c
m”, standard melt tension crab 2.Og, melting point = 162°C1
The same procedure was performed except that a crystallization temperature of 117°C was used.

13- 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 slipperiness of the parison in the molten state is poor, so injection molding conditions are If the time is 3.5 seconds, the cooling time is 2
．． It was impossible to release the mold from the mold unless the time was 5 seconds or more. When the cooling time was set to 2.5 seconds, the temperature of the body of the bottomed parison was 130'C.

Al2O3 is applied to the parison contact surface 1a to a thickness of 300mm. In the coated injection mold, the parison and the sliding property in the molten state are improved, and the mold release property is significantly improved, so it is possible to release the mold 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 3.5 seconds, it was possible to take it out from the mold in a cooling time of 0.5 seconds. The temperature of the body of the bottomed parison taken out in this way was 155°.
It was C.

In this way, high-temperature stretch molding, which was previously impossible due to the inability to release the mold, is now possible, and the range of molding conditions for polypropylene B has been greatly expanded, and even for polypropylene homopolymer, the molding conditions have been greatly simplified. became.

Examples 4 to 9, Comparative Examples 4 to 6 The same procedures as in Example 1 were carried out except that polypropylene A was replaced with polypropylene C, D, and E having physical properties shown in Table 2 below.

The results are shown in Table-3.

15- JP-A-3-184825 (6) 4° [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 drawings]

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, 1 is an upper mold, 2 is a lower mold, 3 is an injection molding machine, 4 is a bottomed parison, 5 is a lip mold, 6 is a rotary table, 7 is a stretching rod, and 8 is a blow mold. .

Claims (1)

[Claims] (1) When producing a container by biaxial stretch blow molding polyolefin, the molten polyolefin is injected into an injection mold whose inner surface is coated with ceramic to form a bottomed parison. A method for producing a biaxially stretched polyolefin bottle, which comprises removing the bottle from an injection molding mold while at least a portion of the bottle is in a molten state, and then biaxially stretching the bottomed parison in the longitudinal and transverse directions. .