JPS593256B2 - Manufacturing method for propylene resin molded products - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new method for producing propylene resin molded articles.

More specifically, the present invention relates to a manufacturing method capable of obtaining a propylene-based resin molded article with excellent stiffness and transparency. Propylene resin molded products have five advantages, including better heat resistance than other general-purpose thermoplastic resin molded products, no hygiene concerns, and no harmful gases generated when incinerated. It is mainly used for frozen food applications.

However, conventional propylene resin molded products do not necessarily have satisfactory performance as food packaging containers, which has slowed down their widespread use. That is, the conventional polypropylene sheet molded article 10 had poor transparency, and the contents could not be seen through sufficiently from the outside of the container. Transparency is slightly improved by using an ethylene-propylene copolymer, but this copolymer is not practically used because it is weak and requires a thick sheet. 15 Under these conditions, there has been a great demand for molded products that have good rigidity and transparency, and that maintain the heat resistance inherent to propylene resins.

As a result of intensive study, the present inventors found that ethylene was 0.5 to 4.
A sheet made of an ethylene-propylene random 20 copolymer containing 0% by weight and having an average shrinkage stress of 3 to 20/9/Cfi in the longitudinal and transverse directions (hereinafter referred to as "vertical" and "horizontal") was heated to atmospheric pressure. It has been found that a molded product obtained by molding at the above pressure satisfies the above requirements, and the present invention has been developed. The content of the present invention will be explained in detail below. The propylene resin used in the present invention needs to be an ethylene-propylene random copolymer containing 0.5 to 4.0% by weight of ethylene. If the ethylene content is less than 0.5% by weight, netting is likely to occur during stretching, and the average value of vertical and horizontal shrinkage stress is 3 to 20 kg.
Even if it is difficult to stabilize the /d sheet,
Even if a sheet is obtained by overcoming this difficulty, the transparency is not sufficient, and furthermore, if an ethylene-propylene random copolymer exceeding 4.0% by weight is used, the stiffness is not sufficiently improved. The bonding method of ethylene and propylene must be random, and block copolymers do not improve transparency. The sheet used for molding must be stretched so that the average value of vertical and horizontal shrinkage stress is 3 to 20k9/Cli.

This stretching improves the stiffness (tensile modulus according to ASTM D882) by 1.5 to 2.5 times, and the stiffness (ASlMD
lOO3) is improved to 2/3 to 1/2. The degree of stretching of the sheet is expressed by the shrinkage stress. If the average value of the vertical and horizontal shrinkage stress of the sheet is less than 3.0 kg/c#f,
The degree of improvement in rigidity and transparency is so low that the present invention cannot be achieved. If the average value of the vertical and horizontal shrinkage stress of the sheet exceeds 20k9, the moldability is poor and satisfactory mold reproducibility cannot be obtained. It is preferable that the vertical and horizontal shrinkage stresses are well balanced; if they are too unbalanced, punctures may occur during molding, and the resulting molded product will have low tear strength. The preferred vertical/horizontal ratio range is ZO~1
%. In order to obtain a good molded product, it is necessary to mold the sheet at a pressure higher than atmospheric pressure.

Good shape reproducibility cannot be obtained by molding performed below atmospheric pressure, so-called vacuum molding. 1 to 8 commonly called pressure forming
A method of pressure molding using compressed air of approximately kg/Cli is optimal. In some cases, the use of a plug also helps to obtain a good molded product. The ethylene-propylene random copolymer referred to in the present invention can be prepared by adjusting the ethylene content to the required level during polymerization, or by mixing an ethylene-propylene copolymer containing 10% or less of ethylene with a propylene homopolymer. can get.

The melt flow index is not particularly limited, but is 0.5 to 109/10 minutes (ASTM Dl23823O
℃2.16 kg load) is preferable. Sheet shrinkage stress is the tensile stress that occurs when the orientation of the sheet is released.
When a sheet sampled as a strip of 0Tfr1n is placed in a tensile force meter and exposed to air adjusted to the crystal melting point of the sheet, the maximum shrinkage stress that occurs during the process of the sheet temperature rising from room temperature to the crystal melting point. is divided by the cross-sectional area of the sheet. The content of the present invention will be further clarified using Examples and Comparative Examples below.

Example 1 The raw material resin (ethylene-propylene random copolymer) shown in Table 1 was melt-extruded using a T-die, cooled with a cooling roll kept at L3O ℃, reheated L, and stretched under the conditions shown in Table 1. Then, the obtained sheet was subjected to air pressure forming using compressed air of 4k9/Clft.

All of these sheets had good moldability, and the resulting molded products had good transparency and stiffness. However, the evaluation of stretchability, moldability, transparency, hexagram and stiffness was performed as follows. 1) Stretching stability: Stable and continuous stretching is possible without necking.

△ Netting sometimes occurs during continuous stretching.

× Almost impossible to stretch. Samburu collection is becoming popular in spots. 2) Formability Formability: Hot plate heating type air pressure molding Molding temperature: 110°C to 150°C in 10°C increments Heating time: 2 seconds Molding pressure: 4k9/Cli Mold size: Opening 12C77! ×12cm depth 6
C71 Formability display Good mold reproducibility is obtained within the above condition range.

X Cannot be molded within the above condition range.

Or good mold reproduction cannot be obtained. 3) Cut the side of the transparent molded product and remove the IO! The degree of haze is measured by 0AS'IMDlOO3.

When the cloudiness exceeds 15 (!), it feels opaque. 4
) Based on the tensile modulus of waist ASTM D882 (4) method.

The test piece was taken from the side of the molded product, and the distance between the chucks was 10
It was named C771. In order to notice improvement in waist, the tensile modulus must be 110k9/Clt or more. Comparative Example 1 Similar to Example 1, the raw resin shown in Table 1 (propylene homopolymer or ethylene-propylene block copolymer) was extruded, stretched or unstretched sheets were obtained under the conditions shown in Table 1, and pressure molded. I went.

As shown in Jikkenya 7, molded products obtained from unstretched sheets of propylene homopolymer had poor transparency and stiffness;
As shown in Jikkenya 8 and 9, propylene homopolymer has poor stretching stability and does not improve transparency sufficiently within the moldable range. Experiment Black 10 to 13 show the binding of molded products obtained from unstretched sheets of ethylene-propylene random copolymers with various ethylene contents, but both transparency and stiffness were inferior to the examples of the present invention. It's on. When an ethylene-propylene random copolymer with too high ethylene content is used, the stiffness is not sufficient as shown in Experiment Black 14. or,
Even if the ethylene content was appropriate, if the shrinkage stress was too high, molding was impossible as shown in Experiment Black 15. Example 2 The sheet of Experiment Black 2 of Example 1 was molded using the mold of Example 1 by two molding methods: radiant heating pressure forming and contact heating pressure forming.

The pressure of compressed air used for pressure forming is 1.2 gauge pressure.
, 4.6 kg/d. Molding was possible at all pressures, whether it was a radiation heating type or a contact heating type. Comparative Example 2 Experiment X) of Example 1. Attempts were made to form the sheet No. 2 using the mold of Example 1 using the radiation heating vacuum forming method (it was impossible to form the sheet using this method).

The present invention has the above-described structure, which is not found in conventional propylene resin molded products.

Claims (1)

[Claims] 1. Consists of an ethylene-propylene random copolymer containing 0.5 to 4.0% by weight of ethylene, and has an average value of longitudinal shrinkage stress and transverse shrinkage stress of 3 to 20 kg/cm^
2. A method for producing a propylene resin molded product, comprising molding the sheet according to item 2 at a pressure equal to or higher than atmospheric pressure. 2 The ratio of longitudinal shrinkage stress to lateral shrinkage stress is 1/1
The method according to claim 1, wherein the ratio is 0 to 10/1. 3. The method according to claim 1 or 2, wherein the ethylene-propylene random copolymer has a melt flow index of 0.5 to 10 g/10 minutes.