JP5904442B2 - Molding method of high density polyethylene resin container - Google Patents

Description

The present invention is excellent also high stiffness has a surface gloss, to method of molding a high density polyethylene resin container having a low moisture permeability as well.

A high density polyethylene (hereinafter abbreviated as HDPE) resin designed for blow molding, particularly direct blow molding (hereinafter simply referred to as blow molding), has good blow moldability and rigidity. It has advantages such as high, chemically stable, excellent chemical resistance, and low material cost. For example, it has been used in a wide range of fields as a resin material for blow molded containers for shampoos. Yes.
On the other hand, HDPE resin blow-molded containers generally have poor surface gloss compared to polypropylene (PP) resin, which is also a polyolefin-based resin. There are difficulties in that.

Here, HDPE resin has a faster crystallization speed than general-purpose resins such as low-density polyethylene (LDPE) resin and PP resin. Therefore, if a mold with a mirror finish is used by blow molding, adhesion to the mold will be improved. It is difficult to obtain uniform gloss because the surface of the molded product is poor, sink marks are generated on the surface of the molded product, and air accumulation occurs.
Therefore, when HDPE resin is used in blow molding, it is common to use a mold with a blasted cavity surface. This is a blow molded container made of HDPE resin, and the surface gloss is sufficiently increased. This is the main cause that cannot be done.
In addition, for blow molding, considering the draw-down property when extruding a cylindrical parison and the shapeability of the parison in a molten state into a container, the molecular weight is relatively higher than that of HDPE resin for injection molding. Since HDPE resin having a high molecular weight distribution and a high molecular weight distribution is used, so-called fine irregularities due to rough skin are easily formed on the surface of the parison to be extruded, and it is difficult to obtain a high surface gloss from this point.

  In Patent Document 1, in order to solve the above-mentioned problem of surface gloss of a blow molded container made of HDPE resin, a relatively high crystallization speed of an ethylene-propylene random copolymer or the like on the outside of a base layer made of HDPE resin. Means such as laminating a slow polyolefin resin is described.

Patent Document 2 describes an invention about an HDPE resin for biaxial stretch blow molding, and is excellent in surface gloss and surface smoothness by using an HDPE resin having a specific range of density and fluidity. In addition, a container made of HDPE resin by biaxial stretch blow molding can be provided.
In the case of biaxial stretch blow molding, a test tube preform, which is a precursor, is injection molded, and this preform is biaxially stretched to shape the container. Compared with the HDPE resin for blow molding described above. It is possible to use HDPE resin with a low molecular weight and a narrow molecular weight distribution, and because the preform is injection-molded, its outer peripheral surface can be made smooth, and the container has a relatively good surface gloss. Can be formed.
Further, since the mouthpiece portion of the preform that has been injection-molded becomes the mouthpiece portion of the container that is the final product, the dimensional accuracy of the mouthpiece portion of the container can be increased.
In addition, the molding cycle is faster than blow molding, and molding can be performed with high productivity.

JP-A-2-215529 JP-A-9-194534

Here, in the configuration in which another resin such as a polyolefin resin having a low crystallization rate is described in Patent Document 1 to obtain surface gloss, it is necessary to mold a laminated parison, and HDPE resin originally has Since blow moldability is impaired, there is a problem that productivity is lowered and manufacturing and material costs are increased.
Moreover, although biaxial stretch blow molding can provide a container made of HDPE resin having a relatively good surface gloss, the surface gloss is still poor compared to a container made of PP resin or the like.
In the example of Patent Document 2, the surface glossiness of a bottle made of HDPE resin by biaxial stretch blow molding using a blended material of two types of HDPE or a blend of low density polyethylene (LDPE) is described. However, the value is at most about 78%, and its glossiness is considerably insufficient as compared with a PP resin container.

Therefore, the present invention is a biaxial stretch blow molding using an HDPE resin, and has excellent surface gloss without blending other types of synthetic resins or laminating other layers, and has a high level. It is a technical object to provide a rigid HDPE resin container.

The present invention is biaxially stretch blow molding method of HDPE plastic container (hereinafter, sometimes simply referred to as molding method.) Relates,
First, forming the shape method of the present invention to solve the above technical problem,
Using a blow mold with a mirror-finished cavity surface,
After setting this mold temperature (Tmold) to the range shown in the following formula (1),
By setting a preform made of a high-density polyethylene resin in a preheated state in a blow mold, and then performing biaxial stretch blow molding of the preform, the glossiness of the outer peripheral surface of the barrel peripheral wall of the container can be increased by JIS Z8741. A container having a density reduction rate DR (%) of the average density of the body peripheral wall of the container with respect to the density of the high-density polyethylene resin represented by the following formula (2) is 0.5% or less is 80% or more. to one in which it says.
Tc ≦ Tmold ≦ Tc + 10 ° C. (1)
In the above formula (1), Tc is the crystallization temperature of the HDPE resin used when the temperature is lowered, and is used for crystallization in the temperature-falling crystallization measurement at 10 ° C./min by a differential scanning calorimeter (hereinafter abbreviated as DSC). It is the temperature at the peak position of the accompanying exothermic curve.
DR = (d−da) / d × 100 (2)
Here, d is the density (g / cm ³ ) of the high-density polyethylene resin used for molding, and da is the average density (g / cm ³ ) of the barrel peripheral wall of the container after biaxial stretch blow molding .

In biaxial stretch blow molding of HDPE resin, generally, a mold having a blasted cavity surface is used and the mold temperature is set to 20 to 80 ° C.
The inventors of the present application set the mold temperature to a temperature lowering crystallization temperature of HDPE resin or a slightly higher temperature while studying the molding conditions for biaxial stretch blow molding, and thus a mold whose mirror surface is mirror finished. However, it has been found that the adhesiveness to the cavity surface can be maintained, and there is no gloss unevenness and excellent surface gloss can be achieved.
The above molding method is based on this examination result,
By setting the mold temperature for biaxial stretch blow molding within the range of the above formula (1), even molds with mirror-finished cavity surfaces can be expanded and shaped into a stretch by biaxial stretch blow molding. Adhesion to the cavity surface of the outer surface of the product can be sufficiently retained,
In particular, without blending or laminating other types of resins, only HDPE resins which are conventionally used, uneven gloss even without are possible to Rukoto a surface gloss above 80%, manufactured PP resins It has become possible to provide a container made of HDPE resin comparable to that of the above container.

Further, by setting the mold temperature within the range of the above formula (1), the crystallinity can be increased by the heat setting effect in the mold as compared with the conventional molding method in which the mold temperature is 20 to 80 ° C. It is possible to provide a container having a large rigidity, that is, a high density and having a high rigidity while using the same HDPE resin , and a container having a small moisture permeability.
Further, with the same rigidity and moisture permeability standard, it is possible to reduce the weight by making the peripheral wall thinner.

Here, when the mold temperature is lower than Tc−10 ° C., the adhesion of the outer surface of the container to the cavity surface becomes insufficient, and sufficient gloss cannot be obtained. In an insufficient area, the surface gloss becomes uneven and gloss spots appear.
Also, when the temperature exceeds Tc + 10 ° C, it approaches the melting point of the HDPE resin, so it sticks to the mold, making it difficult to remove from the mold, and deforming when removing the molded product from the mold. There arises a problem of lowering.

In the case of biaxial stretch blow molding, the outer surface side of the molded product is in contact with the cavity surface of the mold, but the inner surface side is in contact with air blow air, and the cooled air is used for air blow. Circulates air, so-called air circulation technology can be used to increase the cooling efficiency of the entire molded product,
Even if the mold temperature is set higher than in the conventional method as in the molding method of the present invention, it is not necessary to greatly extend the molding time including the mold holding time, and the productivity is maintained at a certain level. be able to.

  According to the above-described biaxial stretch blow molding method of the present invention, a container made of HDPE resin by biaxial stretch blow molding having an unprecedented excellent glossiness in which the gloss of the peripheral wall of the body portion is 80% or more. It becomes possible to provide.

According to the biaxial stretch blow molding method of the present invention described above, the average density of the barrel peripheral wall of the container after blow molding is equal to the density of the HDPE resin used for molding, or the density reduction rate DR (%) is 0. .5% or less, a container having higher rigidity than the case where the mold temperature is set to 20 to 80 ° C. and biaxial stretch blow molding as in the prior art, and further, moisture permeability is small. A container can be provided, and the weight can be reduced by thinning the peripheral wall.
Here, when the biaxial stretch blow molding is performed at a mold temperature of 20 to 80 ° C. as in the prior art, the heat setting effect at the mold temperature is poor, and the average density of the peripheral wall of the container body is the HDPE used for molding. compared to the density of the preform made of the resin significantly reduced, it is impossible to suppress the density reduction rate DR (%) of less than 0.5%.

The present invention according to the biaxial stretch blow molding of HDPE plastic container,
A preheated preform is set in a mold having a mirror-finished cavity surface, and the mold temperature is set to fall in the range of the crystallization temperature Tc to Tc + 10 ° C., thereby blending or laminating other types of resins in particular. In addition, it is possible to provide a container having a high glossiness of uniform and high glossiness of 80% or more with the HDPE resin conventionally used.
In addition, while using the same HDPE resin, the density of the peripheral wall of the body of the container can be increased as compared with the conventional biaxial stretch blow molding method, and the container having high rigidity and further having low moisture permeability. A container can be provided, and the weight can be reduced by thinning the peripheral wall.

It is a front view which shows the Example of the biaxial stretch blow molding container by the shaping | molding method of this invention. It is a schematic explanatory drawing of temperature-fall crystallization by DSC. It is a table | surface which shows the evaluation result of the container of an Example and a comparative example collectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below along the examples with reference to the drawings.
FIG. 1 shows Example 1 of a biaxially stretched blow-molded container made of HDPE resin according to the molding method of the present invention. This container 1 is a casing having a cylindrical body portion 2 and has a high height. Is 120 mm, the capacity is 150 ml, and the average thickness of the body part 2 is 0.5 mm.

The HDPE resin used for the preform is the following resin A.
・ Resin A
(1) Density (according to JISK6760) 0.958 g / cm ³
(2) Melt index (MI) (according to JISK7210 (190 ° C., load 2.16 Kg)) 2.0 g / 10 minutes (3) Crystallization temperature (Tc) 117 ° C.

  Fig. 2 is a schematic illustration of temperature crystallization of HDPE resin by DSC. The horizontal axis is temperature (° C), the vertical axis is heat (mW), the resin is melted at a temperature of 190 ° C, and then the rate of temperature decrease to room temperature An exothermic curve accompanying crystallization when cooled at 10 ° C./min is shown, and the peak position of the exothermic curve is the above-described crystallization temperature Tc.

The container 1 shown in Example 1 above, using a mold which was mirror finished cavity surface, the mold temperature Tmold set at 120 ° C., a test tube-like above is a precursor was pre-heated to about 125 ° C. A preform made of resin A is set in a mold and biaxially stretched and blow molded, and its outer peripheral surface is uniform with no occurrence of sink marks or air pockets, gloss spots, and JIS Z8741 And the glossiness measured at an angle of 60 ° was 84.1% and the surface glossiness was high.
The average density da of the barrel 2 wall is 0.955 g / cm ^3, to 0.958 g / cm ³ is the density d of the HDPE resin used, the density reduction rate DR was 0.31% .

Next, for the preform using the following resin B which is another HDPE resin, the container of Example 2 was biaxially stretch blow-molded in the same manner as the container of Example 1 described above.
・ Resin B
(1) Density 0.951 g / cm ³
(2) Melt index (MI) 2.5 g / 10 min (3) Crystallization temperature (Tc) 115 ° C.
The gloss of the container 80.0%, the average density da is 0.949 g / cm ³ of the barrel 2 wall, to 0.951 g / cm ³ is the density d of the HDPE resin used, the density decreases The rate DR was 0.21%.

Furthermore, as a container of a comparative example, resin A and resin B were used, and the container of a total of four comparative examples (comparative examples 1 to 4) with a mold temperature (Tmold) of 80 ° C. and 50 ° C. As in the container of Example 2, it was prepared by biaxial stretch blow molding.
FIG. 3 shows the containers according to Examples 1 and 2 and Comparative Examples 1 to 4, the glossiness, the presence or absence of gloss spots visually, the average density da of the body 2 peripheral wall, the density reduction rate DR, and the container according to the following measuring method. It is the table | surface which put together the measurement result of the buckling strength and moisture permeability of.
-Method of measuring buckling strength: Using a precision universal testing machine autograph manufactured by Shimadzu Corporation, compress the container by applying a load in the axial direction of the container at a speed of 50 mm / min from the top of the container. Measure the load at the time when compression progresses and the container deforms.
Method for measuring moisture permeability: After filling with 150 g of water, a cap is attached, and then left in a constant temperature room at 40 ° C. for 90 days, and the rate of decrease in water weight after 90 days with respect to the initial water weight is measured.

From the results summarized in the table in FIG. 3, biaxial stretch blow molding is performed at a temperature slightly higher than the crystallization temperature Tc of the HDPE resin used, as in the containers of Examples 1 and 2. Thus, the glossiness of 80% or more and unprecedented glossiness can be revealed in a state free from gloss spots , which is not found in conventional HDPE resin blow molded containers or biaxially stretched blow molded containers. It was confirmed that a container having excellent gloss comparable to a blow molded container made of PP resin can be provided.
Note that the gloss of the containers of Comparative Examples 3 and 4 where the mold temperature is 50 ° C., which is much lower than the crystallization temperature Tc, is about 30 to 70%, and the containers of Comparative Examples 1 and 2 which are 80 ° C. are also about 40 to 70%. In addition, it has glossy spots and is difficult to use for applications that require high appearance.

Further, regarding the average density da of the peripheral wall of the body part 2, in the container of Example 1, the density reduction rate DR is suppressed to 0.31% as small as the density of the HDPE resin used, whereas the same HDPE is used. In Comparative Example 1 in which the resin was used, the density reduction rate DR was 0.84%, and in Comparative Example 3, a large reduction was found to be 1.25%.
In the container of Example 2, the density reduction rate DR is suppressed to 0.21% as small as the density d of the HDPE resin used, whereas in Comparative Example 2 using the same HDPE resin as Example 2. The density reduction rate DR was 0.53%, and in Comparative Example 4, a large reduction of 0.84% was observed.
As described above, the density drop rate DR is kept small in the container of the example, and the average density da of the peripheral wall of the body part 2 is higher than that of the container of the comparative example while being made of the same HDPE resin. It can be seen that the strength is increased and the water permeability is suppressed.
For example, the buckling strengths of the containers of Example 1 and Comparative Example 3 are 288N and 277, respectively. If the same buckling strength is used as a reference, the container of Example 1 is about 4 compared to the container of Comparative Example 3. %, And the container of Example 2 and Comparative Example 4 is expected to be approximately 7% lighter.

In addition, the following facts have been found out by further finely changing the mold temperature.
1) In order to make the container have no gloss spots and high glossiness, the mold temperature Tmold needs to be set to the crystallization temperature Tc−10 ° C. or higher. Luster spots appear at temperatures below Tc-10 ° C.
2) By a mold temperature Tmold and higher than the crystallization temperature Tc, the glossiness can be Rukoto 80% or more.
3) When the mold temperature Tmold exceeds the crystallization temperature Tc + 10 ° C., the container is deformed when releasing the mold.

As mentioned above, although the structure of this invention and its operation effect were demonstrated along the Example, embodiment of this invention is not limited to the said Example.
The HDPE resin used for biaxial stretch blow molding is not limited to the resin used this time, but is used in the category of HDPE resin suitable for preform molding , and has various melting properties such as density and melt index. can do.
Further, the shape of the container is not limited to the case shown in FIG. 1 and can be various shapes and capacities.

As described above, the HDPE resin container by the biaxial stretch blow molding method of the present invention has excellent surface gloss comparable to that of a PP resin container, and is expected to be widely used.

1; Container 2; Body

Claims (1)

After using a blow mold with a mirror-finished cavity surface and setting the mold temperature (Tmold) to the range shown in the following formula (1), high-density polyethylene in a preheated state in the blow mold By setting a preform made of resin and then biaxially stretching blow-molding the preform, the glossiness of the outer peripheral surface of the barrel peripheral wall of the container is 80% or more according to JIS Z8741, and is represented by the following formula (2) A container having a density reduction rate DR (%) of an average density of the peripheral wall of the container with respect to the density of the high density polyethylene resin is 0.5% or less . forming shape method.
Tc ≦ Tmold ≦ Tc + 10 ° C. (1)
In the above formula (1), Tc is the crystallization temperature when the high-density polyethylene resin is cooled, and the temperature at the peak position of the exothermic curve accompanying crystallization in the temperature-falling crystallization measurement by a differential scanning calorimeter at 10 ° C./min. It is.
DR = (d−da) / d × 100 (2)
Here, d is the density (g / cm ³ ) of the high-density polyethylene resin used for molding, and da is the average density (g / cm ³ ) of the barrel peripheral wall of the container after biaxial stretch blow molding .

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