JP2002160275A - Injection molding method for crystalline resin moldings - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection molding method by which moldings of a recrystalline resin with high heat resistance and high rigidity are obtained. SOLUTION: This injection molding method for crystalline resin moldings comprises the step to mold a crystalline resin material by controlling the temperature of a mold 10-80 deg.C lower than the crystallization temperature of the material, when the material is injection-molded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an injection molding method for obtaining a crystalline resin molded article having high heat resistance and high rigidity.

[0002]

2. Description of the Related Art Crystalline resins, for example, polyethylene terephthalate resins, are widely used in fields such as bottles, films and fibers due to their excellent properties. Above all, bottles are widely used as containers for beverages, food, cosmetics, and medical use, etc., because the resulting molded products exhibit excellent transparency and surface gloss, and the amount of use is increasing year by year. Is shown.

[0003] Conventional polyethylene terephthalate (PE)
T) In order to obtain the transparency of the molded product, the temperature of the mold was usually reduced from room temperature to about 40 ° C., and crystallization was prevented by rapid cooling during molding. However, according to the method, since the resin of the PET molded article is amorphous, the rigidity thereof is low, and there has been a problem that thermal deformation is caused by heating.

[0004] Therefore, there has been proposed an invention in which glass fibers are added to improve the rigidity (Japanese Patent Laid-Open No. 8-239).
562, JP-A-8-59967 and the like). However, in these inventions, since a certain amount, for example, about 30% by weight, of glass fiber is added to the resin material, the material cost is increased, and the recycling of the waste may be difficult. Further, a similar problem occurs when the general waste of a crystalline resin such as a PET bottle is treated by so-called material recycling in which the waste is melted to produce a molded product.

[0005]

Accordingly, a method for improving heat resistance and rigidity by promoting crystallization of a crystalline resin such as polyethylene terephthalate resin without adding glass fiber, and a waste thereof. It has been strongly desired to provide a method for effectively reusing the same.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, in an injection molding method of a crystalline resin material, a method of setting a crystallization temperature of the material and holding the material for a predetermined time has been described. The present invention has been found by an injection molding method having a first step and a second step of controlling the temperature to be higher than 10 ° C. and lower by 80 ° C. than the crystallization temperature and maintaining the temperature for a predetermined time as a subsequent step.

The resin material used in the present invention is not particularly limited as long as it is a crystalline resin. For example, polyamide resin nylon 6, nylon 6,6, nylon 6,12
And polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate, and copolymer resins thereof. Also includes those recycled materials. The polyethylene terephthalate preferably used in the present invention includes recycled polyethylene terephthalate in addition to so-called virgin polyethylene terephthalate.

In the present invention, molding at a mold temperature of more than 10 ° C. and 80 ° C. lower than the crystallization temperature of the material resin means that, for example, when molding a PET resin having a crystallization temperature of 150 ° C. The mold temperature is controlled at 70 to 140 ° C. The crystallization of the crystalline resin is promoted by maintaining the crystallization temperature for a predetermined time, and then the temperature is lowered to the above temperature range, and the crystallization of the crystalline resin is further promoted by maintaining the crystallization temperature for a predetermined time. The heat resistance and rigidity of the molded product can be improved, and sufficient strength for removing the molded product is provided. If it is lower than 10 ° C. or higher than 80 ° C., it is not possible to obtain crystallization that provides the desired heat resistance and rigidity to the molded article. In addition, the mold used in the present invention may be any shape currently used, and is not limited to a specific shape.

The nucleating agent that can be used in the present invention serves as a nucleus at the time of crystal formation.
The nucleation rate is promoted, and the crystallization is further promoted by using the temperature control together with the mold temperature control, so that the molding cycle time can be shortened. The nucleating agent may be any of inorganic type such as calcium carbonate and talc or organic type, and is not particularly limited as long as it is suitable for each crystalline resin material.

[0010] The crystalline resin of the present invention may optionally contain a predetermined stabilizer. As a stabilizer,
For example, known antioxidants such as hindered phenols, thioethers and amines, benzophenones and hindered amines are preferable, and hindered phenol stabilizers are particularly preferable. It is preferable to add a stabilizer to the PET of the present invention because the heat resistance and rigidity exhibited by the method of the present invention are maintained.

Further, it is effective to incorporate a release agent into the crystalline resin of the present invention. As the release agent, paraffin wax, polyethylene wax, montanic acid ester wax, metal montanate, metal stearate,
Examples include silicone oils and fluorine-containing polymers.

In the present invention, a method of foaming at the time of injection molding can also be adopted. Specific examples of the foaming agent include diisopropyl hydrazodicarboxylate, 5-phenyltetrazole, hydrazodicarbonamide, barium azodicarboxylate, and trihydrazinotriazine.
0 ° C. or higher is preferable, and 200 ° C. or higher is more preferable.
Particularly preferred is 40 ° C. or higher. The amount of the nucleating material, glass fiber, stabilizer, release agent and foaming agent is not particularly limited,
Appropriate amounts can be used.

[0013] In addition to the above-mentioned stabilizer, release agent and foaming agent, the crystalline resin of the present invention may contain, if necessary, a coloring agent such as a dye or a pigment, an ultraviolet ray blocking agent such as titanium oxide or carbon black, Reinforcing agents such as ordinary glass fibers, flica, mica, carbon fiber and potassium titanate, fillers such as silica, clay, calcium carbonate, calcium sulfate, glass beads, inorganic and organic nucleating agents, plasticizers,
An adhesive, an adhesion aid, a flame retardant, a flame retardant aid, and the like may be arbitrarily compounded. When the stabilizer, the release agent, the foaming agent, and the colorant include a certain amount, the stabilizer, the release agent, the foaming agent, and the colorant can also serve as a nucleating material.

The pressurized fluid that can be used in the injection molding method of the present invention is a gas or liquid that does not undergo a chemical change when pressurized. Specifically, air, nitrogen gas, carbon dioxide gas, helium gas, gas such as argon gas,
Liquids such as water, glycerin, and liquid paraffin are exemplified. Of these, nitrogen gas, air and the like are practically preferable.

[0015]

EXAMPLE 1 As shown in FIG. 2, the mold temperature was changed to the crystallization temperature of PET (1).
The temperature is set to 40 ° C., the plasticized resin is injected into the mold (time on the horizontal axis is 0 sec), and is held (area) for 60 sec to crystallize and mold PET in the mold. Next, the mold is quenched and lowered to 80 ° C. (area). While maintaining the temperature at 80 ° C. for 20 seconds, the mold is opened and the molded product is taken out (area). Finally, the mold is heated and returned to 140 ° C. (area). By controlling the mold temperature as described above, it is possible to crystallize and mold PET and then cool it to a temperature (about 80 ° C) with sufficient strength to take out the molded product, and take out the molded product I made it. Here, a PET bottle recycled material (recycled PET material) was used as a material, and molding of a propeller fan was performed under the conditions shown in Table 1. The properties of the obtained injection-molded product are also shown in Table 1.

[0016]

[Table 1] From the results shown in the above table, it was clarified that the injection molded product according to the present invention did not always undergo thermal deformation, was superior in cost, and was excellent in recyclability. Further, as shown in FIG. 1, an amorphous molded product obtained by a conventional molding method and Example 1 were used.
Was subjected to a tensile test while heating at 80 ° C. As a result, in the crystalline molded article according to the present invention, the yield stress (tensile stress) was significantly increased, and it was confirmed that the heat resistance and rigidity were improved.

Example 2 A PET bottle recycled material (recycled PET material) was used in the same manner as in Example 1 except that 0.1% by weight of calcium carbonate was added as a nucleating agent. Molding was performed. The characteristics of the obtained injection molded product are shown in Table 1 as in Example 1. According to the results, the molding cycle time could be reduced by 10 seconds.

Comparative Example 1 According to the conventional method, except that the temperature of the mold was set to 35 ° C.
PET bottle recycled material (recycled PE)
T material) was used to form a propeller fan under the conditions shown in Table 1. The characteristics of the obtained injection-molded product are also shown in Table 1 as in Example 1.

Comparative Example 2 Table 1 shows the results obtained by using a recycled PET bottle (recycled PET material) in the same manner as in Example 1 except that the temperature of the mold was set to 35 ° C. and 22.5% by weight of glass fiber was added. The propeller fan was molded under the conditions. The characteristics of the obtained injection molded product are shown in Table 1 in the same manner as in Example 1. In addition, when the temperature control of the present invention is performed and the injection molding of the crystalline resin is performed, the material cost is increased. However, if it is acceptable, by adding glass fiber to the resin material, the heat resistance can be further increased. And the rigidity is increased, and the mold temperature is increased to a high temperature (for example, about 140
(° C.).

[0020]

According to the method of injection molding a crystalline resin of the present invention, it is possible to obtain a molded article having improved heat resistance and rigidity and excellent in cost and recyclability. In addition, the addition of the nucleating agent not only provides the above effects, but also shortens the cycle time (molding time) and further facilitates crystallization. Further, the present invention can use a recycled material of a PET bottle as an injection-molded product, which leads to solving an environmental problem of effective use of waste, and the effect is remarkable.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a view showing the results of a tensile test performed on an amorphous molded product obtained by a conventional molding method and a crystalline molded product of Example 1 while being heated at 80 ° C.

FIG. 2 is a diagram illustrating a relationship between an elapsed time after injection and a mold temperature in Example 1.

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Claims (3)

[Claims] 1. A first step in which a mold temperature is set to a crystallization temperature of a crystalline resin material and held for a predetermined time, and as a subsequent step, the temperature is raised to a temperature exceeding 10 ° C. and 80 ° C. lower than the crystallization temperature. An injection molding method for a crystalline resin material, comprising a second step of controlling and holding for a predetermined time. 2. The injection molding method according to claim 1, wherein a nucleating material is added to the crystalline resin material. 3. The injection molding method according to claim 1, wherein glass fiber is added to the crystalline resin material.