JP2904797B2 - Polymer molded body - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a molded product obtained by molding a polymer composition, and particularly to a molded product obtained by injection molding of a household detergent container, food, and the like. It relates to a suitable polymer molded article.

[Background of the Invention]

2. Description of the Related Art Conventionally, various types of molded containers made of synthetic resin for accommodating and storing detergents, foodstuffs, and other powders, granules, liquids or semi-solids have been known.

In order to obtain such a molded container, molding and processing into a container shape are performed using various synthetic resin materials.
For example, when a container is molded by injection molding, materials such as vinyl chloride resin, polyethylene, polypropylene, styrene resin, ABS resin, and acrylic resin are widely used as the thermoplastic resin used as a molding material.

Conventionally, a composite container has been known in which a container is formed by combining a material other than plastic such as paper and a plastic material. In manufacturing such a composite container, for example, a blank plate made of paper or the like constituting a container body (body) is set in a cavity of a molding die,
Synthetic resin is injected into the cavity so as to fill the gap and the bottom of the part where both side edges of the blank plate face each other and to form the peripheral edge of the upper opening of the blank plate, and this synthetic resin is integrally attached to the blank plate and molded. Let it be done. Further, the lids constituting the lids of these container bodies are similarly formed by injection molding.

In various synthetic resin containers and composite containers as described above, it is important to improve the molding characteristics of the synthetic resin raw material. In particular, when the shape of the container has an asymmetric shape, or when it has a thin-walled portion or a constricted portion, in order to obtain a molded product having a uniform material and no residual strain, and having excellent mechanical properties. It is necessary to examine production conditions in consideration of various molding characteristics. When molding a container having such an asymmetrical shape or a thin-walled portion, various characteristics such as flow characteristics, molding shrinkage, and orientation of raw materials at the time of injection molding are important factors. It is difficult to find a material that has all of the above to a sufficiently satisfactory degree. For example, polyethylene is widely used as a raw material resin for these containers because it covers a wide range of mechanical properties from soft to hard and has relatively good moldability. Polyethylene is known to have various properties depending on its density, melt flow rate (MFR), and manufacturing method, and a material obtained by mixing these different types of polyethylene is also known.
In containers having an asymmetric shape or a thin portion as described above, conventionally used polyethylene materials are not always satisfactory, and the moldability during injection molding, the mechanical properties when used as a container, and the rigidity However, not all properties such as impact resistance, deformation resistance, and strength of a thin portion are harmoniously satisfied.

[Summary of the Invention]

The present invention has been made in view of the problems associated with the conventional technology described above, and has as its object to provide a polymer molded body exhibiting particularly excellent characteristics as a molded body having an asymmetrical shape or a thin portion. In particular, in addition to excellent molding characteristics during injection molding, all the properties such as excellent mechanical properties, rigidity, impact resistance, deformation resistance and strength of thin-walled parts of the obtained molded body are all The purpose is to provide a polymer molded body that is harmoniously satisfied.

In order to achieve the above-mentioned object, a polymer molded article according to the present invention comprises a polymer composition containing (a) 70% by weight or more of linear low-density polyethylene and (b) 30% by weight or less of low-density polyethylene. It is characterized by being made by injection molding a product.

In the present invention, in order to further improve the properties, the composition comprising the two-component system may further contain less than 10% by weight of high-density polyethylene.

[Specific description of the invention]

Hereinafter, the material for a molded container of the present invention will be described in more detail. In the following description, “%” representing a quantitative ratio is a weight ratio unless otherwise specified.

In the material for a molded container of the present invention, three kinds of polyethylenes of linear low-density polyethylene, low-density polyethylene and high-density polyethylene are blended in a specific quantitative ratio.

In the present invention, the above-mentioned linear low-density polyethylene, low-density polyethylene and high-density polyethylene are:
Each of them means those satisfying the following conditions.

(1) Linear low density polyethylene (LLDPE) The linear low density polyethylene (hereinafter referred to as LLDP) used in the present invention.
E may be abbreviated) is ethylene and carbon number 3-18
Is obtained by polymerizing the α-olefin of the present invention using a transition metal catalyst. The copolymerization reaction is usually 30
The polymerization is carried out at a polymerization temperature of 300300 ° C., a normal pressure to a polymerization pressure of 300 kg / cm ² , in the presence or absence of a solvent, or in a gas-solid, liquid-solid or homogeneous liquid phase.

As the α-olefin in this case, propylene, butene-1, 4-methylpentene-1, hexene-1, octene-1, decene-1 and the like are used.
~ 14 are preferred. These α-olefins are 1
Not only species but also two or more species can be used in combination.

The density (JISK6760) of the LLDPE used in the present invention is 0.9
It is less than 30g / cm ³ or more 0.942g / cm ^3, in particular, 0.930g~0.9
It is preferably in the range of 40 g / cm ³ . Density 0.930 / cm ³
If the amount is less than the above, the rigidity is inferior. On the other hand, if it exceeds 0.942 g / cm ³ , the strength is inferior.

The melt flow rate of the LLDPE used in the present invention (JIS
K6760) is from 10 to 100 g / 10 minutes, particularly preferably from 25 to 40 g / 10 minutes. Melt flow rate is 10g /
If it is less than 10 minutes, the moldability will be poor, while if it exceeds 100 g / 10 minutes, the strength will be poor, which is not preferable.

(2) Low-density polyethylene (LDPE) The low-density polyethylene (hereinafter sometimes abbreviated as LDPE) used in the present invention is obtained by polymerizing ethylene using a free radical generator such as an organic peroxide or oxygen. It is obtained by doing. The polymerization reaction is usually 130 to 3
It is carried out at a polymerization temperature of 00 ° C. and under a polymerization pressure of 500-3000 kg / cm ² .

The melt flow rate of the LDPE used in the present invention (JIS
K6760) is preferably 1 to 100 g / 10 minutes. If the melt flow rate is less than 1 g / 10 minutes, the fluidity is poor, while if it exceeds 100 g / 10 minutes, the strength is undesirably reduced.

(3) High-density polyethylene (HDPE) The high-density polyethylene (hereinafter sometimes abbreviated as HDPE) used in the present invention uses ethylene alone or ethylene and an α-olefin having 3 to 18 carbon atoms using a transition metal catalyst. And polymerized. The polymerization reaction is usually carried out at a polymerization temperature of 30 to 300 ° C., at a normal pressure to a polymerization pressure of 300 kg / cm ² , in the presence or absence of a solvent, or in a gas-solid, liquid-solid, or homogeneous liquid phase. Will be implemented.

As the α-olefin in this case, propylene, butene-1, 4-methylpentene-1, hexene-1, octene-1, decene-1 and the like are used.
~ 10 are preferred. These α-olefins are 1
Not only species but also two or more species can be used in combination.

The density of the HDPE (JIS K6760) used in the present invention is 0.9
It is preferably at least 42 g / cm ³ .

If the density is less than 0.942 g / cm ³ , particularly when obtaining a molded body having a thin portion formed thereon, the effect of improving the impact resistance of the thin portion is not preferable.

The polymer composition used for the production of the molded article of the present invention, the linear low-density polyethylene and the low-density polyethylene described above,
More preferably, the high-density polyethylene is complexly contained in the following quantitative ratio.

(1) 70% linear low-density polyethylene based on the total amount of linear low-density polyethylene and low-density polyethylene
As mentioned above, the content of the low-density polyethylene is more preferably 75 to 95%, and the low-density polyethylene is 30% or less, more preferably 5 to 25%.

(2) When high-density polyethylene is contained, the high-density polyethylene should contain less than 10%, preferably 1 to 8%, more preferably about 2 to 7%, based on the total amount of these three types of polyethylene.

In general, when injection molding a container having a longitudinal shape and a transverse direction such as a rectangle, the flow direction of the resin during molding is not uniform, and the shrinkage ratio during shrinkage depends on the direction. Will be different,
This causes warpage of the molded product. In the polymer composition used in the present invention, the above-mentioned linear low-density polyethylene (LLDPE) is a main raw material, which contributes to prevention of warping of the molded article as described above. Further, when molding a molded body having a thin portion, very high flow characteristics are required as a composition, but in the present invention, the higher the MFR of LLDPE, which is the main raw material, is more preferable. , And 30
The addition of less than 10% LDPE significantly improves the flow properties, especially in the high shear rate region.

Here, when the compounding amount of LLDPE is less than 70%, and when the compounding amount of LDPE as the second component exceeds 30%, when the container having the asymmetric shape as described above is molded, This is not preferable because the difference in shrinkage ratio between the short direction and the short direction becomes too large. Further, in order to improve the rigidity of the molded product, the density of the linear low-density polyethylene is 0.93.
It is particularly preferred to use one of 5 g / cm ³ or more.

In the present invention, in order to further improve the characteristics, less than 10% of high-density polyethylene can be added as the third component as described above, but addition in this range adversely affects other physical properties. The rigidity can be further improved without exerting any effect.

As described above, in the molded article of the present invention, two or three kinds of polyethylene components are complexly contained in the above-described quantitative ratio, so that various types of containers, composite containers, and lids for molded containers can be used. In particular, in molding a container having a relatively planar shape portion and an asymmetrical shape portion or a thin-walled portion, all of the following characteristics are harmoniously provided.

(A) Deformation and torsion are less likely to occur in the molded body.

For example, even when molding a container having a rectangular planar shape, there is no difference in the shrinkage ratio of the molded body between the longitudinal direction and the transverse direction, so that a molded product without distortion or warpage is obtained. can get.

(B) Excellent moldability.

For example, in general, when obtaining a molded product having a thin portion over the entire periphery of the container peripheral portion, various conditions such as temperature and pressure become extremely high during injection molding, or imbalance in the flow of resin in the thin portion. Although the composition used in the present invention has a significantly improved α-melt viscosity at a high shear rate, the flow characteristics at the time of injection molding are greatly improved. Excellent
For this reason, a favorable state is maintained even under the load of the above-mentioned extreme molding conditions, and the flow in the thin portion does not become unbalanced, so that a molded article of good quality can be obtained.

(C) Since it has high rigidity and excellent impact resistance, it is suitable as a material for a molded article requiring such characteristics. Further, even with a molded product having a thin portion as described in (b) above, a molded product excellent in mechanical strength and impact resistance of the thin portion can be obtained.

Examples of Molded Articles Examples of the molded article of the present invention will be described with respect to a container containing powdery or granular materials such as foodstuffs and detergents, a liquid or solid, and a lid thereof.

In the molded container shown in FIG. 1, a container R and a lid C
Thus, a sealed state is realized. In particular, the lid C will be described. As shown in FIG. 1, the lid C has a top plate 1 and a peripheral edge 2 integrally formed. FIG. 2 is a partial cross-sectional view showing the detailed configuration of the peripheral edge. The peripheral edge portion 2 includes a peripheral top portion 3 and a peripheral descending wall 4 which is integrated therewith and descends along the inner surface of the upper opening peripheral portion of the container R. A peripheral skirt portion 5 is formed integrally with the peripheral top portion 3 and protrudes downward along the outer surface of the upper opening peripheral portion of the container. Further, the peripheral top 3 is in close contact with the top 21 of the peripheral edge of the upper opening of the container R. The peripheral edge descending wall 4 is integrally connected to the peripheral edge of the top plate 1 and integrally includes a sealing protruding rib 6 on the side facing the peripheral edge of the upper opening of the container R. On the other hand, an inward projecting edge 7 is formed on the inner surface of the peripheral skirt portion 5, and a concave groove 8 is formed above the projecting edge 7. In the state shown in FIG. 2 in which the lid C is fitted to the container R, the peripheral top 3 comes into close contact with the top 21 of the peripheral edge of the upper opening of the container, and the ridge 22 enters the inside of the groove 8. . In this way, the inner space of the container R is completely sealed from the outside by performing the sealing action at the three positions of the peripheral top portion 3, the sealing projection rib 6, and the projection edge 7.

On the other hand, as shown in FIG. 2, a thin portion 9 is provided above the inwardly projecting edge 7, and this portion is particularly easily broken. In this embodiment, the thin portion is provided in the groove 8. In this embodiment, as shown in FIG. 1, the peripheral skirt portion 5 is notched as shown at 11 at the center of the short side of the lid C. Notch
11 is formed only on a portion below the thin portion 9, and a knob 12 is integrally formed on the upper portion of the notch 11.

In order to apply the lid C to the container R, since both are made of the above resin composition having elasticity, the lid C is
The lid is resiliently fitted to the container by being pushed down to the state shown in the figure. As a result, the inwardly projecting edge 7 of the lid engages with the lower side of the ridge 22 of the container, and the lid does not come off the container. In addition, the container and the lid come into contact with each other in a hermetically sealed state in conjunction with the peripheral top portion 3 and the rib 6 being pressed against the container.

In the above-described sealed state, since the inwardly projecting edge 7 has a sufficient strength, no problem occurs during normal handling (for example, during transportation or when the container is inadvertently dropped). . However, if the lid C is forcibly removed, the thin portion 9 is cut first, so that the opening of the lid due to mischief is immediately recognized. In recent years, crimes involving foreign substances such as poisons in the contents of products have been increasing. However, since such lids and containers using the lids have excellent virgin sealability, such crimes Is extremely useful in preventing the occurrence of

Further, when opening the lid of the container, the tearing tab 12 at the end of the peripheral skirt portion 5 is grasped with a finger and the notch 11 is cut.
Is used as a starting point, the thin portion of the peripheral skirt portion 5 is gradually cut off from the lid by cutting, and the opening is completed by cutting to the other end of the peripheral skirt portion 5.

In the molded article of the present invention, since the material constituting the molded article itself has the above-described excellent properties, not only is the thin-walled part excellent in tearability, but the cut end of the cut part is It is also excellent in that it is clean and does not generate cutting waste.

In other words, the above-mentioned lid is excellent in sealing properties, easy to open, and has a virgin sealing property, which is advantageous in the effect of preventing crime and the like, and is also excellent in appearance and sealing after opening. Can be said.

Molding method In order to obtain the polymer molded article of the present invention, for example, the above-mentioned linear low-density polyethylene, low-density polyethylene, and high-density polyethylene are subjected to a usual mixing operation, for example, a tumbler blender method, a Henschel mixer method, It can be obtained by mixing by a Banbury mixer method or an extrusion granulation method to obtain a raw material composition, and molding the composition thus obtained by an injection molding method.

During the molding, in the raw material composition described above, if necessary, in addition to the essential components, a neutralizing agent, a dispersant, an antioxidant, a weather resistance improver, an antistatic agent, other additives such as a pigment or a filler. Additional components can be added within a range that does not inhibit the above-mentioned effects of the present invention.

(Examples) Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

Examples 1 to 3, Comparative Examples 1 to 5 The compositions shown in Table 1 below were prepared using a tumble blender.
After mixing for 30 minutes, pellets were produced using a 30 mm diameter extruder set at a temperature of 200 ° C., and the physical properties of the composition were evaluated. The results are shown in Table 1.

Next, molded articles were molded from these compositions by an injection molding method and evaluated. Table 2 shows the evaluation results.

 The evaluation method is as follows.

(Physical properties of the composition) (1) Melt flow rate JIS-K6760 (2.16 kg load) (2) Density A 1 mm thick sheet was prepared with a hot press under pressure, and measured according to JIS-K6760.

(3) Flexural rigidity ASTM D7
A test piece was cut out with 47 and measured.

(4) Molding shrinkage ratio and molding shrinkage ratio Using an injection molding machine (trade name IS-80A, manufactured by Toshiba Machine Co., Ltd.)
The cylinder temperature is 180 ° C, the injection pressure is 600kg / cm ² , the molding cycle is 40 seconds, the mold temperature is 40 ° C, and the thickness is 2mm.
Was used to injection mold a flat plate of 90 × 150 mm. The resulting measured gauge length Lmm marked in the injection-molded article, between the reference lines marked on the mold length L ₀ mm from the molding shrinkage (%) = 100 × (L 0 -L) / L ₀ was sought.

 The molding shrinkage was measured in the direction perpendicular to the flow direction.

Molding shrinkage ratio = Molding shrinkage ratio in flow direction / Molding shrinkage ratio in vertical direction (5) Melt viscosity Capillary rheometer (Type 3211 manufactured by Instron)
And measured at 190 ° C.

Note that a capillary having an inner diameter of 0.05 inch and a length of 2 inches was used.

(Evaluation of molded products) (1) Injection molding conditions Injection molding machine (Osumi Claus Mafai, OKM150 / 600A)
Under the conditions of a cylinder temperature of 230 ° C., an injection pressure of 68 kg / cm ² , a molding cycle of 18 seconds, and a mold temperature of 21 ° C., a lid for a sealed container was injection-molded as a molding container.

As shown in FIGS. 1 and 2, the lid is formed by integrally forming a rectangular top plate and a peripheral portion, and a thin portion is formed over the entire peripheral portion. I have.

(2) Deformation Observation of the obtained molded container, も の indicates that there is no deformation, △ indicates that it is slightly deformed, and × indicates that it is very deformed.
And

(3) Rigidity A flexural rigidity of 3500 kg / cm ² or more is judged to be acceptable.

(4) Strength of thin portion The injection molded product used for evaluation of deformation was fitted, dropped from a height of 60 cm, and evaluated.

Good was evaluated as O, slightly poor as Δ, and poor as X.

(5) Moldability In order to evaluate deformation, moldability at the time of injection molding was evaluated.

Good was evaluated as O, slightly poor as Δ, and poor as X.

Example of Injection Molding of Ordinary Container The container shown in the sectional view of FIG. 3 was molded under the following injection conditions. Also in this container, the moldability was good.

Injection molding machine: Osumi Klaus Maffai OKM120 / 600A Cylinder temperature: 220 ° C Injection pressure: 82 kg / cm ² Molding cycle: 13 seconds Mold temperature: 17 ° C As is clear from the table, the molded articles of the examples show particularly excellent physical properties in all the items.

The molded article of the present invention has a remarkable improvement in flow characteristics particularly in a high shear rate region, and has a large contribution to the formability even though the peripheral part has a thin wall as in the examples.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a molded article according to an embodiment of the present invention, FIG. 2 is a partial cross-sectional view thereof, and FIG. 3 is a cross-sectional view of a container according to the embodiment of the present invention. . . C: lid, R: container, 1: top plate, 2: peripheral portion, 5: peripheral skirt portion, 7: inward protruding edge, 8: concave groove, 9: thin portion, 22: convex ridge.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Noriyoshi Shindo 5-17-8-501 Aoto, Katsushika-ku, Tokyo (72) Inventor Shigeichi Kobayashi 5-1 Anesaki Beach, Ichihara-shi, Chiba Sumitomo Chemical Industries, Ltd. ( 72) Inventor Yukio Yoshikawa 17-11, Fujikubo, Miyoshi-cho, Iruma-gun, Saitama A) JP-A-59-75933 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C08L 23/00-23/36

Claims (5)

(57) [Claims] (1) A linear low-density polyethylene of 70-95.
Injecting a polymer composition containing 5 to 30% by weight of a low-density polyethylene other than the linear low-density polyethylene and having a melt flow rate of 1 to 100 g / 10 minutes. A polymer molded article having a thin portion, which is formed by molding. 2. When the high-density polyethylene is further added to (a) the linear low-density polyethylene and (b) the low-density polyethylene other than the linear low-density polyethylene, the total amount of these three types of polyethylenes Against
Containing 1% by weight or more and less than 10% by weight of high-density polyethylene,
The polymer molded article according to claim 1. 3. A linear low-density polyethylene having a melt flow rate of 10 to 100 g / 10 min and a density of 0.930 g / cm ³ or more and 0.942 g / cm ³ or more.
The polymer molded article according to claim 1, which is less than ³ . 4. The polymer molded article according to claim 2, wherein the high-density polyethylene has a density of 0.942 g / cm ³ or more. 5. The polymer molded article according to claim 1, wherein the molded article is a container.