JPH0554855B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to pre-expanded polypropylene resin particles and a method for producing the same. For more details,
The present invention relates to pre-expanded polypropylene resin particles having excellent in-mold foamability and a method for producing the same. [Prior art] If the cell diameter of the polypropylene resin pre-expanded particles used for in-mold foam molding is 200 μm or less, the shrinkage rate of the molded product after in-mold foam molding tends to be large, and the shape of the molded product There are disadvantages such as distortion (commonly referred to as sink marks or warpage in the industry), leading to a decrease in the commercial value of the molded product and deterioration of the production technology of the molded product. [Problems to be Solved by the Invention] Therefore, as a result of intensive research in view of the above-mentioned prior art, the present inventors incorporated a specific polymer into a polypropylene resin, and created a cell diameter of 200 to 500 μm in the pre-expanded particles. The inventors have found that the above-mentioned problems after in-mold foaming can be solved by adjusting the temperature, and have completed the present invention. [Means for solving the problems] That is, the present invention provides polypropylene resin 100
carboxyl selected from ethylene-acrylic acid-maleic anhydride terpolymer, iomer formed by cross-linking the molecules of ethylene-methacrylic acid copolymer with metal ions, ethylene-acrylic acid copolymer and ethylene-methacrylic acid copolymer based on the weight part Polymers containing groups from 0.1 to
Pre-expanded polypropylene resin particles consisting of a base resin mixed with 10 parts by weight and characterized by having bubbles of 200 to 500 μm, and a thermoplastic resin containing a volatile foaming agent in a pressure-resistant container. In a production method in which particles are dispersed in water while stirring, heated under pressure, and then the aqueous dispersion is discharged into a low pressure area to pre-foam thermoplastic resin particles, 100 parts by weight of polypropylene resin as a thermoplastic resin is used. On the other hand, it contains carboxyl groups selected from ethylene-acrylic acid-maleic anhydride terpolymer, ionomer formed by cross-linking ethylene-methacrylic acid molecules with metal ions, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer. The present invention relates to a method for producing pre-expanded polypropylene resin particles, which uses a base resin mixed with 0.1 to 10 parts by weight of a polymer. [Function and Examples] As described above, the polypropylene resin pre-expanded particles of the present invention have a polypropylene resin of 100%
It is made of a base resin mixed with 0.1 to 10 parts of a specific carboxyl group-containing polymer per part (by weight, same hereinafter), and has a cell diameter of 200 to 500 μm. When such pre-expanded polypropylene resin particles are used for in-mold foam molding, the above-mentioned problems after in-mold foam molding can be solved. Examples of the polypropylene resin used in the present invention include ethylene-propylene random copolymer, ethylene-propylene-butene random terpolymer, ethylene-propylene block polymer, and homopolypropylene, but these polymers can be used alone as usual. or two or more types may be used in combination. Further, the polypropylene resin may be used in a non-crosslinked state, but it may also be used after being crosslinked with peroxide, radiation, or the like. The carboxyl group-containing polymer used in the present invention is an ethylene-acrylic acid-maleic anhydride polymer, an ionomer obtained by crosslinking the molecules of an ethylene-methacrylic acid copolymer with metal ions, an ethylene-acrylic acid copolymer, an ethylene- methacrylic acid copolymers, these polymers are usually used alone, but
More than one species may be used in combination. Among these carboxyl group-containing polymers, ethylene-
Alrylic acid-maleic anhydride terpolymers and ionomers can be suitably used. The amount of the carboxyl group-containing polymer used is 0.1 to 10 parts per 100 parts of the polypropylene resin.
Department. When the amount of the carboxyl group-containing polymer used is less than 0.1 part, the cell size of the pre-expanded polypropylene resin particles is unlikely to exceed 200 μm, and when the amount exceeds 10 parts, the cell diameter will decrease.
In addition to not becoming very large from around 500 μm,
This is not preferred because the properties of the polypropylene resin are impaired. In particular, when the amount of the carboxyl group-containing polymer used is 0.3 to 5 parts, it is preferable from the viewpoint of the effect of increasing the cell diameter and economic efficiency, but the amount is more preferably 0.5 to 3 parts. Polypropylene resin and a polymer containing carboxyl groups are usually melt-mixed using an extruder, kneader, Banbury mixer, roll, etc.
Then, it is formed into a desired particle shape that is easy to use for pre-foaming, such as a columnar shape, an elliptical shape, a spherical shape, a cubic shape, and a rectangular parallelepiped shape. Traditionally, thermoplastic resin particles containing a volatile blowing agent are dispersed in water while stirring in a pressure-resistant container such as an autoclave, and then released into a low-pressure area at high temperature and high pressure to prepare thermoplastic resin particles. Foaming methods are known, such as those described in West German Published Patent Application No. 2107683 and Japanese Patent Publication No. 56-1344. However, when pre-foaming is carried out by these methods, the cell diameters of the resulting pre-foamed particles are extremely non-uniform;
It is difficult to obtain particles with a diameter of 200 μm or more, and when in-mold foam molding is performed using such pre-expanded particles, only molded products with poor appearance and low commercial value can be obtained. However, in a pre-foaming technique for thermoplastic resin particles, thermoplastic resin particles containing a volatile blowing agent are dispersed in water while stirring in a pressure-resistant container, and after heating under pressure, the aqueous dispersion is released into a low pressure region. , when using a base resin in which 0.1 to 10 parts of a carboxyl group-containing polymer is mixed with 100 parts of a polypropylene resin as thermoplastic resin particles, a polyolefin-based resin having uniform bubbles with a cell diameter of 200 to 500 μm is used. Pre-expanded resin particles can be easily obtained. If the amount of the polymer containing a carboxyl group is less than 0.1 part, it will be difficult for the bubble diameter to exceed 200 μm, and if it exceeds 10 parts, the bubble diameter will decrease.
Although it is 200 μm or more, it is not preferable because it increases the dimensional shrinkage rate of the molded product and the distortion of the shape of the molded product. Volatile blowing agents used in the present invention include, for example, aliphatic hydrocarbons such as propane, butane, pentane, and hexane; cyclopentane,
Alicyclic hydrocarbons such as cyclobuntane; halogenated hydrocarbons such as trichloromonofluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane, trichlorotrifluoroethane, methyl chloride, methylene chloride, and ethyl chloride. However, these blowing agents may be used alone or in combination of two or more. The amount of these blowing agents to be used is not particularly limited, and is appropriately adjusted depending on the degree of foaming of the desired polyolefin resin pre-expanded particles. Normally, the amount used is the base resin (polypropylene resin 100%
Polymer containing carboxyl group per part
Contains 0.1 to 10 parts) 5 to 100 parts
There are 50 copies. In the present invention, polypropylene resin particles are made to contain a volatile blowing agent in a pressure-resistant container, and then dispersed in water while being stirred. , calcium carbonate, etc., and small amounts of surfactants such as sodium dodecylbenzenesulfonate, sodium n-paraffinsulfonate, sodium α-olefinsulfonate, etc. may be used. Other methods for producing the pre-expanded particles of the present invention include a method in which polypropylene resin particles are impregnated with a volatile blowing agent and then heated with steam or the like (for example, Japanese Patent Publication No. 48-34391, Japanese Patent Publication No. 58 −
65734) may be used. The pre-expanded polypropylene resin particles obtained by the production method of the present invention usually have a closed cell ratio of 80% or more, but if necessary, the pre-expanded particles are treated in a pressure-resistant container under superheating and pressure for a certain period of time. Possibly after air impregnation, the pre-expanded particles may be filled into a mold and heat-foamed by steam heating to produce a foam molded article as per the mold. The foamed molded product thus obtained has a small dimensional shrinkage rate and small shape deformation, so it has extremely high commercial value. Next, the present invention will be explained based on Examples and Comparative Examples, but the present invention is not limited only to these Examples. Examples 1 to 7 and Comparative Examples 1 to 4 100 parts of ethylene-propylene random copolymer (Noblen, manufactured by Sumitomo Chemical Co., Ltd., ethylene content: 4.5% by weight) was mixed with ethylene-acrylic acid-maleic anhydride in the amount shown in Table 1. 100 parts of base resin pellets prepared by mixing an acid terpolymer, 30 parts of dichlorodifluoromethane, 0.5 part of powdered basic calcium triphosphate as a dispersant, and 0.006 part of sodium n-paraffin sulfonate in a pressure-resistant container with 300 parts of water. and heated to 136℃. The pressure at this time was approximately 26 kg/cm ² G. Thereafter, while maintaining the pressure inside the container at 26 to 26.5 Kg/cm ² G while pressurizing dichlorodifluoromethane, the valve at the bottom of the pressure container was opened to release the aqueous dispersion to atmospheric pressure to perform pre-foaming. As a result, pre-expanded particles with an expansion ratio of about 30 times were obtained in each case.The obtained pre-expanded particles were impregnated with air for 2.0 hours at 80℃ x 8.5Kg/cm ² G (in air). After processing and adjusting the particle internal pressure to approximately 2.0 to 2.5 atm, 290
Fill a block mold of mm x 270 mm x 50 mm, approx.
A molded product was obtained by heating at a water vapor pressure of Kg/cm ² G. As for the physical properties of the obtained molded article, the average cell diameter, uniformity of cell diameter, dimensional shrinkage rate, and shape distortion of the molded article were measured by the following methods. The results are shown in Table 1. (Average cell diameter) Thirty pre-expanded particles are arbitrarily taken out of the obtained pre-expanded particles, the cell diameter is measured in accordance with JIS K 6402, and the average cell diameter (d) is calculated. (Bubble uniformity) The ratio of the average bubble diameter (d) to the standard deviation (σ) representing the variation in bubble diameter (hereinafter referred to as U) is evaluated as follows: U=(σ/d)×100(%). The smaller U is, the more uniform the bubbles are. ○: U value is less than 35% △: U value is 35 to 45% ×: U value is more than 45% (dimensional shrinkage rate) Measure the molded product dimensions and mold dimensions to determine the dimensional shrinkage of the molded product Find the rate. ○: 3% or less △: 3-5% ×: More than 5% (distortion of the shape of the molded product) Measure the thickness along the cross-sectional shape of the molded product (Figure 1), and calculate the maximum thickness L and the maximum thickness. Ratio to thickness L': Evaluate from S = (1-L'/L) x 100. ○: S is 3% or less △: S is 3-5% ×: S is over 5%

[Table] All of the molded products obtained in Examples 1 to 7 had small dimensional shrinkage rates and no distortion in the shape of the molded products. The molded product obtained in Comparative Example 1 was
It does not contain ethylene-acrylic acid-maleic anhydride terpolymer, and the uniformity of the cells in the pre-expanded particles is poor, and the average cell diameter is 200μm.
Because of the following, the obtained molded product had a large dimensional shrinkage rate and a large shape distortion. The molded products obtained in Comparative Examples 3 and 4 have large cell diameters in the pre-expanded particles and uniformity of the cells, but despite the large amount of ethylene-acrylic acid-maleic anhydride terpolymer used, The diameter was comparable to that of the molded products obtained in Examples 4 to 7, and the addition of the ethylene-acrylic acid-maleic anhydride terpolymer did not show any further effect, and the resulting molded products showed no dimensional shrinkage. Both the molding rate and the distortion of the molded product were poor. Examples 8 to 14 and Comparative Examples 5 to 7 Ionomers made by crosslinking the molecules of an ethylene-methacrylic acid copolymer with metal ions instead of 0.1 part of the ethylene-acrylic acid-maleic anhydride terpolymer used in Example 1 Pre-expanded particles were prepared in the same manner as in Example 1, except that Hymilan 1706 (Mitsui Polychemical Co., Ltd.) was used in the amount shown in Table 2, and then molded articles were prepared in the same manner as in Example 1. The physical properties of the obtained molded article were measured in the same manner as in Example 1. The results are shown in Table 2.

[Table] All of the molded products obtained in Examples 8 to 14 had small dimensional shrinkage rates and no distortion in the shape of the molded products. The molded product obtained in Comparative Example 5 was
The amount of ionomer used is small, and the average cell size is
The diameter was 200 μm or less, and the evaluation of the molded product was poor. Furthermore, although the molded products obtained in Comparative Examples 6 and 7 used a large amount of ionomer, the average cell diameter was not larger than that of the molded products obtained in Examples 12 to 14. The evaluation of the molded product was also not favorable. From the results of Comparative Examples 2 to 7, there are upper and lower limits to the amount of polymer containing a carboxyl group, and especially if the amount exceeds 10 parts, the properties of the polypropylene resin will be lost. This is preferable in terms of average bubble diameter and bubble uniformity, but the evaluation of molded products becomes poor. [Effect of the invention] According to the invention, the bubble diameter is uniform between 200 and 500 μm.
The pre-expanded particles of polypropylene resin can be obtained, but the shrinkage rate of the molded product after in-mold foam molding using the pre-expanded particles is small, and the distortion of the molded product is also small, so there is no problem with the appearance such as surface appearance. Excellent, and the production yield of molded products is improved. Therefore, structural members such as vehicle shock absorbers that require dimensional accuracy,
It can be suitably used as a heat insulating building material, and is also useful as a cushioning packaging material.

[Brief explanation of the drawing]

FIG. 1 shows the cross-sectional shape of a molded article used to measure the distortion of the shape of the molded article. L: Maximum thickness of molded product, L′: Minimum thickness of molded product.

Claims (1)

[Claims] 1. Ionomer, ethylene-acrylic acid copolymer made by cross-linking the molecules of ethylene-acrylic acid-maleic anhydride terpolymer or ethylene-methacrylic acid copolymer with metal ions based on 100 parts by weight of polypropylene resin. and ethylene-
Consists of a base resin made by mixing 0.1 to 10 parts by weight of a carboxyl group-containing polymer selected from methacrylic acid copolymers, and has a cell diameter of 200 to 500 μm.
Pre-expanded polypropylene resin particles characterized by: 2 Claim 1 in which the polypropylene resin is an ethylene-propylene random copolymer
Pre-expanded polypropylene resin particles as described in . 3 Disperse thermoplastic resin particles containing a volatile foaming agent in water in a pressure-resistant container while stirring, heat under pressure, and then release the aqueous dispersion into a low pressure area to foam the thermoplastic resin particles. In the manufacturing method, polypropylene resin is used as the thermoplastic resin.
Carboxyl selected from ethylene-acrylic acid-maleic anhydride terpolymer, ionomer formed by cross-linking ethylene-methacrylic acid molecules with metal ions, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer per 100 parts by weight. 1. A method for producing pre-expanded polypropylene resin particles, which comprises using a base resin prepared by mixing 0.1 to 10 parts by weight of a group-containing polymer.