JPH0447699B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a crystalline syndiotactic device 1 for producing a highly elastic foam molded article by in-mold molding.
This invention relates to pre-expanded particles made of 2-polybutadiene resin (hereinafter referred to as 1,2-polybutadiene resin). Foam molded products made using the so-called bead foam molding method, in which pre-expanded particles of thermoplastic synthetic resin are filled into a mold and heated to re-foam and simultaneously fuse the particles together, are lightweight, have cushioning properties, and have good heat insulation properties. etc., and the molding method is suitable for mass production.
It is widely used in cushioning materials, packaging materials, insulation materials, building materials, etc. However, the production of foam molded products using the conventional bead foaming method is limited to those using polystyrene resins, polyethylene, polypropylene, etc. as raw materials, and it is difficult to manufacture foam molded products that exhibit rubber elasticity using thermoplastic elastomer resins. has not been carried out. This is because when trying to mold thermoplastic elastomer resin in a mold using the bead foaming method, although it foams and fuses, the subsequent shrinkage is large, resulting in severe deformation (including shrinkage) and the formation of coarse bubbles. This is because a very satisfactory molded product cannot be obtained. Therefore, foamed molded products with rubber elasticity have conventionally been made by polymerizing while foaming in a mold, like polyurethane foam, but this method has low productivity and the product is Since the cells were open cells, there was a problem in that the compression properties were poor. An object of the present invention is to enable the production of a highly elastic foam molded article by bead foam molding, which has conventionally been difficult to implement with thermoplastic elastomers, as described above. The present invention, which has succeeded in achieving the above object,
The intrinsic viscosity is 0.7 or more, the density is 0.900 to 0.925 g/cm ³ , and in differential scanning calorimetry, T ₂ −T ₁ ≧35°C (However, T ₁ [°C] is the endothermic amount Qmax [at the maximum endothermic point of the DSC curve] A non-crosslinked crystalline synthetic resin that exhibits an endothermic property that satisfies the lower limit of the temperature range that exhibits an endothermic amount of 1/2 or more of [cal/g°C], and T ₂ [°C] is the upper limit of the above temperature range. The present invention provides pre-expanded particles made of otakutic 1,2-polybutadiene resin. In the differential scanning calorimetry analysis, approximately 10 mg of the sample is placed in a capsule of a differential scanning calorimeter, and the temperature is increased from room temperature to approximately 170°C.
This is done by increasing the temperature at a rate of 20°C/min. The DSC curve is a curve obtained by plotting the results of the differential scanning calorimetry analysis described above, with temperature on the horizontal axis and heat absorption per 1°C on the vertical axis. If the DSC curve has multiple endothermic peaks and there are multiple temperature ranges in which the amount of endothermic energy is more than half of Qmax, the lower limit of each temperature range is taken as T ₁ , and the lower limit of each temperature range is taken as T ₂ . Take the higher upper limit of each temperature range. Curve I in the drawing is a DSC curve of a representative example of pre-expanded particles according to the invention. The pre-expanded particles of the present invention, which are particularly preferred in relation to the purpose of the present invention, are further characterized in differential scanning calorimetry with Qtotal≧3.0 cal/g (where Qtotal [cal/g] is the period from the start of melting to the end of melting of the sample). The pre-expanded particles are made of a 1,2-polybutadiene resin that exhibits endothermic properties satisfying the following conditions (total endothermic amount), and pre-expanded particles with such endothermic properties exhibit moldability almost equivalent to that of crosslinked polyethylene. 1,2-polybutadiene resin is known as a flexible thermoplastic resin that exhibits properties intermediate between those of rubber and plastic. This resin has a hydrogen atom bonded to a tertiary carbon atom and a vinyl group in each structural unit, so like general rubber materials, it may be affected by sulfur, peroxides, or the presence of photosensitizers. It has the characteristic that it can be easily crosslinked by irradiating the bottom with ultraviolet rays. Therefore, there are many molding methods and uses that take advantage of this feature, but the pre-expanded particles of the present invention are made of non-crosslinked particles. A method for producing a foam from a 1,2-polybutadiene resin includes a method of producing a low-foam molded product by adding a blowing agent to a blend of this resin and an ethylene-vinyl acetate copolymer and injection molding the mixture; Although a method for manufacturing sponge from a vulcanizate is known, it is not known to foam only this resin without crosslinking by a bead foaming method to form a high-magnification foam molded product. The pre-expanded particles of the present invention, unlike the pre-expanded particles of many other thermoplastic elastomer resins, have extremely good moldability in in-mold molding, and the foamed articles obtained from them have excellent flexibility, cushioning properties, and It has compression recovery properties. Even if it is a pre-expanded particle made of 1,2-polybutadiene resin, if the density of the resin is less than 0.900 g/ ^cm3 , the degree of crystallinity is low, resulting in poor moldability in the mold and poor shape retention of the molded product. Heat resistance is also poor. Also, if the density exceeds 0.925 g/cm ³ , the temperature at which fusion is possible is too high, resulting in poor in-mold moldability. Particularly preferred are those with a density of 0.905 to 0.920 g/ ^cm3 , and most preferred are those with a density of 0.905 to 0.920 g/cm3.
It has a weight of 0.915g/ ^cm3 . In addition, 1,2-polybutadiene resins with an intrinsic viscosity of less than 0.7 have a small molecular weight and therefore a low degree of crystallinity, so pre-expanded particles made of such resins have poor in-mold formability and shape retention of molded objects. It is bad, and its heat resistance is also poor. Conventionally, in the case of polyolefin resins, which are difficult to bead foam molded compared to polystyrene resins, it is common practice to crosslink the resin to improve moldability. The moldability of 1,2-polybutadiene resin, which was expected to be effective, was not improved by crosslinking, and good results were obtained only by imparting the above-mentioned specific endothermic properties without crosslinking. It was surprising. The reason why the 1,2-polybutadiene resin pre-expanded particles having the above-mentioned endothermic properties have particularly excellent in-mold moldability is considered as follows. First of all, Qtotla is
As is clear from the fact that this value is proportional to the crystallinity of the 1,2-polybutadiene resin, increasing the value above a certain value allows the 1,2-polybutadiene resin to exhibit its physical properties to a high degree. is essential on. However, when this value is too high, there are disadvantages in that poor fusion between expanded particles tends to occur during molding, and a large amount of thermal energy is required for molding. Therefore, Qtotal
is preferably in the range of about 3 to 15 cal/g (a particularly desirable value is 4 to 12 cal/g). Furthermore, the fact that the value of T ₂ - _{T 1} is as large as 35°C or more, and that the DSC curve typically shows two endothermic peaks as shown in curve I in the drawing, indicates that the resin constituting the pre-expanded particles is composed of multiple types of resin. It means containing a crystal structure. All or most of the crystals of 1,2-polybutadiene resin are a certain type of crystal and the DSC curve has a sharp single peak, resulting in T ₂
- Pre-expanded particles with T ₁ less than 35°C (a typical example DSC curve is shown as a curve in the drawing),
Because the temperature range from the actual start of melting to the end of melting is narrow, virtually all the crystals tend to melt when heated to the temperature required to fuse the foamed particles during molding, and therefore, the melting between the foamed particles tends to melt. However, the pre-foamed particles of the present invention, which have the above-mentioned crystal structure and endothermic properties (i.e., melting properties) based on the crystal structure, can be used from the substantial start of melting to the end of melting. Since the temperature range is wide, if molding is performed at a temperature near the middle of this temperature range, the low melting point crystalline portion will melt and contribute to the fusion between the foamed particles, while the high melting point crystalline portion will not melt and will allow pre-foaming. The foamed structure of the particles is maintained, resulting in good molding. It is particularly preferable for the pre-expanded particles of the present invention to be 20°C higher than the melting end temperature on the DSC curve.
When the total heat absorption at a higher temperature side than a low temperature is defined as Qh [cal/g], 0.15≦Qh/Qtotal≦0.5, and those with such characteristics have the above-mentioned low melting point. There is no excess or deficiency in the functions of the high melting point portion and the high melting point portion, and the moldability is particularly excellent. In the pre-expanded particles of the present invention, the average cell diameter is about 20 to 2000μ (preferably 50 to 1500μ), the average number of cells is 300 or less/mm ² (preferably 100 ^or less), and the expansion ratio is 3 or more. 50 times (preferably 5-40
times), average particle size is 1 to 20 mm (preferably 3 to 15 mm)
It can be appropriately selected within this range depending on the physical properties of the foamed product to be molded. The pre-expanded particles according to the present invention include particles of 1,2-polybutadiene resin having a density within the above range, 100 to 500 parts by weight of water per 100 parts by weight, and 3.
Place in a closed container with ~50 parts by weight of a blowing agent (e.g. dichlorodifluoromethane), 0.1-3 parts by weight of a dispersant (e.g. finely divided aluminum oxide),
After increasing the temperature to a temperature higher than the melting start temperature of the crystals and lower than the melting end temperature in the DSC curve of the raw resin under the measurement conditions to impregnate the resin with the foaming agent, the discharge hole at the bottom of the container is opened under pressure. It can be manufactured by releasing the contents into an atmosphere at a lower pressure than the inside of the container. Note that the pre-expanded particles having the preferable endothermic properties as described above are
In the manufacturing process using the above method, it can be manufactured by maintaining the temperature in the above temperature range for about 0.5 to 3 hours, but the heating conditions necessary to impart the desired endothermic properties are determined by the crystallinity of the raw resin ( density)
It depends. The pre-expanded particles according to the present invention are cured in pressurized air, similar to when pre-expanded particles of polystyrene resin or polyolefin resin are molded in a mold.
After maintaining an internal pressure of 0.01 to 5 kg/cm ² (G), it can be easily molded by filling it into a mold and heating it with hot water or steam. In particular, those having preferable endothermic properties as described above have a wide range of suitable molding temperatures, so they are easy to mold, and even when producing a large molded product, it is possible to easily obtain a homogeneous product over the entire molded product. Since the in-mold molded product obtained from the pre-expanded particles of the present invention exhibits superior performance in many properties such as flexibility, cushioning properties, and compression recovery properties, it can be used as a cushioning material, It is particularly suitable for packaging materials, automobile bumper core materials, interior materials, etc. The present invention will be explained below with reference to Examples and Comparative Examples. Examples and Comparative Examples 400 g of 1,2-polybutadiene resin particles with an average particle size of 2.5 mm, 1200 g of water, finely divided aluminum oxide
1.5g and blowing agent (dichlorodifluoromethane)
is placed in a sealed container, heated to a predetermined temperature t, and heated to 1.
After maintaining the temperature for a period of time to impregnate the resin with the foaming agent, the pressure inside the container is increased to 30 kg/cm ² with nitrogen, and then the discharge hole at the bottom of the container is opened to release the contents into the atmosphere. Foam the resin particles. In the above manufacturing method, various pre-expanded particles were manufactured by variously changing the raw material resin, the amount of the blowing agent, and the heating temperature. Table 1 shows the foaming conditions and the properties of the pre-expanded particles obtained. Further, each pre-expanded particle was pressurized and cured with air to give an internal pressure of 1.2 kg/cm ² (G), and then its moldability was tested using a mold having an internal diameter of 30 mm x 300 mm x 300 mm. Table 1 also shows the moldability and characteristics of typical molded bodies obtained in the test. The test method for moldability and the evaluation criteria for the characteristics of the molded article are as follows. Formability test method Multiple molding tests are performed while changing the molding temperature in stages, and the molding temperature at which the in-plane shrinkage rate of the molded product does not exceed 7% and the surface is uniform and smooth is determined as the "appropriate molding temperature".
shall be. The size of the width from the upper limit to the lower limit of the suitable molding temperature,
The quality of moldability is determined from the characteristics of the molded article molded at the appropriate molding temperature. Flexibility Tested in accordance with the Defense Agency standard (DNS Z-0503) and judged based on the following criteria (however, the test was omitted for Comparative Examples 3 to 6 in which a satisfactory molded product could not be obtained). ○: No breakage or cracking at all ×: Compressive elastic recovery that causes cracking Tested in accordance with JIS K6767 and judged based on the following criteria (However, Comparative Examples 3 to 6 in which a satisfactory molded product was not obtained) (examination was omitted for some cases). ○: Compression set 5% or less ×: Compression set exceeds 5%

[Table] Note: "〓" in the suitable molding temperature and suitable molding temperature range indicates that there is virtually no moldable temperature.
Comparative Examples 1 and 2 can be molded at the indicated temperature, but the shrinkage rate in the plane direction exceeds 7% and the molding condition is not good.

[Brief explanation of the drawing]

The figure is a DSC curve of pre-expanded particles according to the invention (I) and a control product ().

Claims (1)

[Claims] 1. Intrinsic viscosity of 0.7 or more, density of 0.900 to 0.925 g/
cm ³ and T ₂ −T ₁ ≧35°C in differential scanning calorimetry (however, T ₁ [°C] is the absorption amount that is more than half of the endothermic amount Qmax [cal/g°C] at the maximum endothermic point of the DSC curve). Pre-expanded particles made of a non-crosslinked crystalline syndiotactic 1,2-polybutadiene resin exhibiting endothermic properties that satisfy the lower limit of the temperature range indicating the amount of heat (T ₂ [°C] is the upper limit of the above temperature range) . 2 The 1,2-polybutadiene resin is subjected to differential scanning calorimetry under the condition that Qtotal ≥ 3.0 cal/g (where Qtotal [cal/g] is the total endothermic amount from the start of melting to the end of melting of the sample). 1,2-Polybutadiene resin pre-expanded particles according to claim 1, which exhibit satisfactory endothermic properties.