JPS62158025A - Manufacture of thermoplastic resin in-mold foam molded body - Google Patents

Abstract

PURPOSE:To manufacture a non-shrink foam molded body with favorable secondary expansibility by providing a process to vacuumize the interior of a mold and a process to pressurize a foam molded body in the mold with inorganic gas. CONSTITUTION:First, polyolefin-based thermoplastic resin pre-expanded particles with an intraparticle pressure of 1.2kg/cm<2> by absolute are filled in a mold. Secondly, the mold is vacuumized. Thirdly, vapor is fed in the mold for foam molding. Fourthly, the resultant foam molded body in the mold is pressurized with inorganic gas. For the heating of pre-expanded particles, vapor with a pressure of 2-5kg/cm<2> by gage is used normally. The pressure of the inorganic gas depends upon the material or the like of base material resin and lies within the range of about 0.01-5kg/cm<2> by gage, preferably of about 0.1-1.5kg/cm<2> by gage. The pressurizing with the inorganic gas prevents the gas in the molded part from escaping outside during the cooling period of the molded part and at the same time gives internal pressure to the molded part so as to prevent the molded part from shrinking.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a thermoplastic resin in-mold foam molded article.

[Conventional technology]

In-mold foam molding methods have traditionally been used in which pre-expanded particles of thermoplastic resin are filled into a mold and heated and foamed to form a molded product.For example, the pre-expanded particles are pressurized with an inorganic gas. , a method in which an inorganic gas is pressurized into particles to impart foaming ability, and then filled into a mold for heating and foaming (Japanese Patent Publication No. 52-22951, Japanese Patent Application Laid-Open No. 49-12806)
No. 5) or a method in which pre-expanded particles are compressed and filled into a mold for heating and foaming (Japanese Patent Publication No. 53-33996); A method of filling, heating and foaming, and then curing the obtained molded product at a predetermined temperature (Japanese Patent Publication No. 55-781
No. 6, JP-A-60-166442), etc. are known.

[Problem that the invention seeks to solve]

However, in the method described in Japanese Patent Publication No. 52-22951 or Japanese Patent Application Laid-open No. 49-128065, the time that the inorganic gas pressurized into the pre-expanded particles is retained within the particles is relatively short, and therefore After applying internal pressure through pressure treatment, it is necessary to mold the product in a short time, and as the pressure of the inorganic gas injected into the pre-expanded particles increases, the shrinkage rate of the resulting foam tends to decrease. This has the disadvantage that the molding cycle becomes longer and the manufacturing cost becomes higher.

Furthermore, in the method described in Japanese Patent Publication No. 53-33996, foaming ability is imparted to the pre-expanded particles by compressing the pre-expanded particles, and equipment for compressing and filling the pre-expanded particles is required. In addition, it is necessary to link the equipment for compression filling and the molding machine, resulting in a problem that the equipment becomes complicated.

Also, Japanese Patent Publication No. 55-7816, Japanese Patent Application Publication No. 60-166
If the pre-expanded particles are not pressurized and the pre-expanded particles are molded at an internal pressure approximately equal to atmospheric pressure as in the method described in Publication No. 442, the secondary foaming ability of the pre-expanded particles is poor. Only molded products with many voids can be obtained, and if methods such as lengthening the heating time or increasing the pressure of hot molding steam are adopted to solve this problem, the molded product can be removed from the mold into a room temperature atmosphere. The molded body expands once,
The shrinkage shrinks rapidly at just °. For this reason, in this method, it is necessary to cure the molded body at a predetermined temperature after molding, which requires complicated temperature control and time management during curing, lengthens the molding cycle, and makes it impossible to perform efficient molding. There was a problem.

[Means for solving problems]

As a result of intensive research into the above points, the present inventor found that after filling the mold with pre-expanded particles, the pressure inside the mold is reduced, and after foaming the particles, the foamed molded product is heated with inorganic gas. The inventors have found that the above problems can be solved by applying pressure, and have completed the present invention.

That is, the present invention includes a process of filling pre-expanded thermoplastic resin particles into a mold, reducing the pressure in the mold, and then supplying steam into the mold to perform foam molding. The gist of the present invention is a method for manufacturing a thermoplastic resin in-mold foam molded article, which comprises a step of pressurizing with gas.

The base resin of the thermoplastic resin pre-expanded particles used in the present invention includes low-density polyethylene, linear low-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, or a resin made of a mixture of two or more of these. Polyolefin resins such as polystyrene, polyP-
Methylstyrene, styrene-maleic anhydride copolymer,
Examples include styrene-acrylic acid copolymer, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, vinyl chloride, vinyl chloride-vinyl acetate copolymer, and vinylidene chloride resin.

Further, according to the present invention, a film with high strength (two-layered) having a high magnification of 25 times or less and a melting energy of a high temperature peak in a melting curve of differential scanning calorimetry (hereinafter referred to as rDscJ) of 8 J/g or more Ethylene (difficult to foam)
Even if pre-expanded particles made of a propylene random copolymer are used, it is possible to obtain a molded article with an excellent surface condition at a low particle internal pressure.

In addition, the high temperature peak in the DSC melting curve is the 030 curve obtained when the pre-expanded polypropylene resin particles 1 to 3 cm are heated to 220°C at a temperature increase rate of Iθ°C/min using a differential scanning calorimeter. For example, the first 030 curve is the 030 curve obtained when the sample is heated from room temperature to 220°C at a heating rate of 10°C/min, and then the sample is heated at a cooling rate of 10°C/min from 220°C to around 40°C. The second 030 curve is the 030 curve obtained when the temperature is lowered to 220° C. at a heating rate of 10° C./min, and the characteristic peak and high temperature peak can be determined from these 030 curves.

That is, the above-mentioned characteristic peak is an endothermic peak unique to the polypropylene resin constituting the expanded particles, and is thought to be due to the so-called endotherm during melting of the polypropylene resin. The characteristic peak appears in both the first DSC1lJll line and the second 030 curve, and the temperature at the top of the peak may be slightly different between the first and second times, but the difference is less than 5 ° C. Usually below 2°C.

On the other hand, the high temperature peak is an endothermic peak that appears on the higher temperature side than the characteristic peak in the first DSC curve, and the melting energy of the high temperature peak is the melting energy of an endothermic peak that appears on the higher temperature side than the solid peak. .

The pre-expanded particles used in the present invention can be obtained by foaming expandable resin particles containing a blowing agent under pressure in a pressure-resistant container, or by melt-kneading the resin and the blowing agent in an extruder.
A method in which resin particles and a foaming agent are dispersed in a dispersion medium in a pressure-resistant container, heated under pressure to impregnate the resin particles with the foaming agent, and then cut into a foamed strand. It can be obtained by, for example, a method of discharging it downward and foaming it.

The pre-expanded particles are pressurized with an inorganic gas, preferably nitrogen or an inorganic gas containing nitrogen as a main component, such as air, in the same way as in normal molding, so that the inorganic gas is contained in the particles, so that the internal pressure of the particles (usually 1. Although the particles may be subjected to molding after being given a pressure of more than 2kr/cd・abs (absolute pressure), in the present invention, the internal pressure of the pre-expanded particles to be heated and expanded is not necessarily higher than 1.2kg/-・abs. There is no need for pre-expanded particles that are pressurized with inorganic gas and then left under atmospheric pressure to reduce the internal pressure to below 1゜2 kg/cIa-abs. As with pre-expanded particles, which have an internal pressure equal to atmospheric pressure, the internal pressure of the particles can be reduced to 1 by using a gas mainly composed of inorganic gas.
Pre-expanded particles of less than 2 kg/crl-abs can also be used.

In the present invention, after the pre-expanded particles are filled into the mold, the pressure inside the mold is reduced, but the pressure reduction method includes a method using a vacuum pump, and a method in which the drain outlet of the mold is opened. Examples include a method of flowing steam and reducing the pressure by the flow of steam, but a method using a vacuum pump is particularly preferred because it can increase the degree of pressure reduction.

Further, the mold internal pressure when the pressure is reduced varies depending on the expansion ratio of the pre-expanded particles, but it is usually 710 m511 g or less, particularly preferably 66 QmsHg or less.

The pre-expanded particles filled in the mold are heated and foam-molded after the inside of the mold is reduced in pressure, and steam of 2 to 5 kg/cj HG is usually used to heat the pre-expanded particles. .

In the present invention, the pre-expanded particles are heated and foamed in a mold to obtain a foam molded article according to the mold, and then the molded article is pressurized with an inorganic gas in the mold. Pressurizing the molded body with inorganic gas is a process that prevents the gas inside the molded body from escaping to the outside until the molded body is cooled, and also applies internal pressure to the molded body to prevent shrinkage of the molded body. be.

Inorganic gases used for pressurization include air, carbon dioxide,
Examples include nitrogen gas, and among these, an inorganic gas containing nitrogen gas as a main component, for example, an inorganic gas containing 50 to 90% nitrogen gas, is the most preferred.

The pressure of the inorganic gas varies slightly depending on the material of the base resin, etc., but is approximately 0.01 to 5 kg/cnl.G, preferably 0.1 to 1.5 kg/am-G.
That's about it.

It is preferable to apply pressure to the molded body in the mold while the temperature of the molded body is high to some extent, for example, 60 to 120℃.
It is preferable to start applying pressure at a temperature of about 0.degree. C. while the molded body has a surface pressure. The time for applying pressure varies depending on the type of base resin, etc., but -a is most preferably about 1 to 5 minutes.

The material is cooled in the mold while being pressurized with inorganic gas or after the end of the pressurization, cooled until it can be easily released from the mold, and then taken out from the mold. In general, if the cooling is insufficient, the molded product expands too much when it is taken out from the mold, which tends to cause cracks on the surface. The degree to which the molded body has been cooled to the extent that it can be removed from the mold can be determined by the surface pressure of the foam. For example, in the case of ethylene-propylene random copolymer, the surface pressure is 1 to 0.5 +r/cII
It is preferable to take it out from the mold at about 1.1 G.

As a cooling method, in addition to normal water cooling, a combination of water cooling and cooling by vacuum drying may be used. When cooling by vacuum drying is used in combination, the surface hardness of the molded product increases, and mold release can be performed well. There is no need to dry the obtained molded body.

The molded product taken out from the mold is usually heated and dried after being taken out. For example, in the case of ethylene-propylene random copolymer, the appropriate temperature is generally 50 to 110°C, and in order to dry it in a short time, 60℃ or higher, especially 70℃
It is preferable to set it as above degreeC.

In the present invention, there is a step of depressurizing the mold after filling the pre-expanded particles and a step of pressurizing the molded body with an inorganic gas.
As mentioned above, excellent molded bodies can be obtained even by using pre-expanded particles with a low internal pressure of 1 or 2 kK/cnl-abs or less due to a gas containing an inorganic gas as the main component. When pre-expanded particles under internal pressure are used, molding can be carried out satisfactorily even with low-pressure steam, and economical molding can be performed. That is, in the case of normal molding methods, it is difficult to perform good foam molding when pre-expanded particles with low foaming ability are used, and for this reason, the internal pressure of the particles is 1 to 2 kg/all-a.
Although pre-expanded particles with a large foaming ability exceeding bs are used,
When low-pressure steam is used to heat such pre-expanded particles with high internal pressure, secondary foaming occurs before the particles are heated to a temperature at which they can fuse together due to the large foaming ability of the particles, and as a result, The gaps between the particles become smaller and steam cannot penetrate between the particles sufficiently, resulting in poor fusion of the particles in the molded body. For this reason, when using pre-expanded particles with high internal pressure, it is necessary to heat them all at once using high-pressure steam to a temperature that can cause the particles to fuse together, but in the case of particles with low internal pressure, the foaming ability is small, so low-pressure steam Even if the particles are heated by heating, there is no risk of large secondary foaming occurring before the particles are heated to a temperature that can cause mutual fusion, and the method of the present invention uses pre-expanded particles with low internal pressure for molding. Therefore, when pre-expanded particles with low internal pressure are used, efficient molding can be performed using low pressure steam. Therefore, in the present invention, it is preferable to use pre-expanded particles with a low internal pressure for economical molding, but even when pre-expanded particles with a high internal pressure similar to those used in the past are used, compared to the conventional molding method, An excellent molded body with less shrinkage can be obtained.

Moreover, in the present invention, when the above-mentioned pre-expanded particles are used, a highly foamed molded article having an expansion ratio of 5 to 70 times can be obtained.

In the above description, "kg/cA-abs J" indicates absolute pressure, and "rkg/cj-GJ" indicates gauge pressure.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples.

Examples 1 to 5 Pre-expanded particles shown in Table 1 using the thermoplastic resin shown in Table 1 as the base resin (however, particles made of ethylene-propylene random copolymer have a high temperature peak in the DSC melting curve) (with energy in the range of 10 to 12 J/g) was filled into a mold of 300 x 30 On + x 5 + 4 + n (inner dimensions), and the pressure inside the mold was reduced to the pressure shown in the same table using a vacuum device. Foam molding was performed by heating with steam. After heating and foaming, the mold was pressurized with air for 90 seconds, and then cooled with water until the surface pressure of the molded product was as shown in Table 1, and then taken out.

Table 1 shows the properties of the obtained molded product after drying it at 80° C. for 6 hours.

Comparative Examples 1 to 6 Pre-expanded particles shown in Table 1 using the thermoplastic resin shown in Table 1 as the base resin (however, particles made of an ethylene-propylene random copolymer have a high temperature peak in the DSC melting curve) An expanded foam molded body was obtained in the same manner as in the example except that the step of reducing the pressure in the mold and/or pressurizing with an inorganic gas (with energy in the range of 10 to 12 J/g) was not performed. . Table 1 also shows the properties of the obtained molded product after drying it in the same manner as in Examples.

*1 Particle internal pressure (kg/cIA-ab
s ) = (a-b) (g) Xo, 082 X (273 + t) (
'K) After foaming - 20℃ after curing for a week
Weight (g) of the above pre-expanded particles under atmosphere: 0.08
2 is a gas constant, t is room temperature (20°C in this example), 1.
0332 represents a coefficient for converting atm units to kg/cnl units.

In addition, the bubble volume (1) within the particle was determined by the equation: bubble volume (1) within the particle=true value of the pre-expanded particle.

However, the true volume (1) of the pre-expanded particles was measured by immersing the particles in water in a graduated cylinder.

*2 Measure the dimensions of the molded product after drying and leaving it at room temperature for 24 hours, and calculate the shrinkage rate with respect to the surface direction dimension of the mold. If the shrinkage rate is less than 3%...0 It was judged as 3% or more and less than 5%: △ 5% or more: ×.

*3 After drying and leaving at room temperature for 24 hours, measure the thickness of the center of the molded body, calculate the shrinkage rate relative to the mold thickness, and find that the shrinkage rate is less than 3%.・0 3% or more and less than 5%・・・Δ 5% or more・・・×

*4 Observe the surface of the molded product, Surface smoothness・・・・・・○ There are some voids on the surface...△ There are many voids on the surface...× It was judged as.

*5 The foam is tensilely fractured using Tensilon, and the fusion property is determined by the interparticle fracture and material fracture of the cross section, and the material fracture is 70% or more... ○ Less than 70% material fracture 40% or more...・△Material destruction 40%
Less than... It was judged as ×.

〔Effect of the invention〕

As explained above, the method of the present invention includes the step of reducing the pressure inside the mold and the step of pressurizing the foam molded product in the mold with inorganic gas.
Under conditions of low particle internal pressure of s or less, there is no shrinkage or secondary foaming even when using not only pre-foamed particles whose membrane strength is not very high but also pre-expanded particles whose membrane strength is high (hard to cause secondary foaming). It is possible to produce a foamed molded article with good properties.

In addition, since molding can be performed using pre-expanded particles with an internal pressure approximately equal to atmospheric pressure, large-scale force ■
Production of a molded product that does not require equipment such as a pressure device or a compression device for pre-expanded particles, and is sufficiently good to be used immediately without increasing the internal pressure by pressure treatment after producing pre-expanded particles. Moreover, there is no need to cure the molded body at a predetermined temperature after molding, and as a result, the molding cycle can be shortened and molding can be carried out with high efficiency. Further, when pre-expanded particles with low internal pressure are used, heating molding using low pressure air is possible, and molding can be performed economically. Furthermore, even when using pre-expanded particles with the same high internal pressure as used in conventional molding methods, it is possible to obtain molded objects with less shrinkage and excellent dimensional accuracy compared to conventional methods. have

Ko゛1-3Jε (City Official Book (Spontaneous) 7゜March 11, 1986 (1. Director General of the Patent Office, Uga Michibe 1, Indication of Incident Outside the House, Showa 61)
Patent Office No. 1103 2, Title of invention: Method for manufacturing thermoplastic resin in-mold foam molding (23,
Person who makes amendments (3
Relationship to the case Patent applicant address: 2-1-1 Uchisaiwai-cho, Chiyoda-ku, Tokyo Name: Kuchimoto Styrene Paper Co., Ltd. Representative: Masayo Uchiyama 4, Agent 101 Address: 2-7 Kanda Sakuma-cho, Chiyoda-ku, Tokyo 5. Date of amendment order → “Description of contents of amendment” on page 13, lines 10-11 and page 14, lines 4-5
"The melting energy of the high temperature peak is in the range of 10 to 12 J/g)" is corrected to "The melting energy of the high temperature peak is shown in Table 1.)".

:　Table 1 on page 15 of the same page is amended as shown in the attached sheet.

) Insert the following sentence between lines 9 and 10 on page 18.

*6 Gel fraction is the ratio of the weight of the xylene-free container after boiling the sample in boiling xylene for 8 hours to the weight of the sample before boiling, expressed as a percentage.

Claims (3)

[Claims] (1) After filling a mold with pre-expanded thermoplastic resin particles, the pressure inside the mold is reduced, and then steam is supplied into the mold to perform foam molding, and the foam molded product is heated in the mold with an inorganic gas. 1. A method for producing a thermoplastic resin in-mold foam molded article, comprising a pressurizing step. (2) The method for producing a thermoplastic resin in-mold foam molded article according to claim 1, wherein the thermoplastic resin is a polyolefin resin. (3) The pre-expanded particles filled into the mold are 1.2 kg/cm^2・ab by a gas whose main component is inorganic gas.
2. The method for producing a thermoplastic resin in-mold foam molded article according to claim 1, wherein the polyolefin resin pre-expanded particles have an internal particle pressure of s or less.