JPH0236141B2 - NETSUSEIKEISEINOSUGURETAHORIPUROPIRENKEIHATSUHOSHIITO - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polypropylene foam sheet. More specifically, the present invention relates to a polypropylene foam sheet with a smooth surface, high product uniformity, excellent thermoformability, and high mechanical strength such as bending strength. Conventionally, when manufacturing polypropylene foam sheets by kneading inorganic fillers with polypropylene resin, a relatively large amount of polyethylene resin is mixed to prevent defoaming (bubble destruction) and produce polypropylene foam sheets with a good appearance. It is known that a sheet can be obtained (Japanese Patent Publication No. 18608/1983). However, although such a filler-containing polypropylene foam sheet has a good appearance, it is intended to have a closed cell structure, which is the opposite of the cell structure intended by the present invention, and its mechanical strength (rigidity) is poor. There were also problems in that the holding strength of the sheet during heating was low and thermoformability was poor. There has also been a proposal to obtain foam molded products with high rigidity and impact resistance by adding polyethylene to a specific ethylene-propylene block copolymer and adjusting the density etc. (Japanese Patent Publication No. 57-59252). However, sheets made of such foamed products are not fully satisfactory in terms of mechanical strength other than impact resistance, and the magnification is as high as 3 to 6 times, surface smoothness is poor, and thermoformability is poor. There was also the problem that it was defective. The present invention was made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a polypropylene foam sheet that has high mechanical strength such as rigidity and good thermoformability. As a result of various studies and examinations, the inventors found that the specific properties obtained by reducing the amount of polyethylene resin mixed when kneading the inorganic filler with polypropylene resin and controlling the foaming conditions, etc. The inventors have discovered that a sheet-like foam having a thickness, bulk density, cell shape, density uniformity, and continuity ratio of 100 to 1000 has high rigidity and excellent thermoformability, and have arrived at the present invention. Thus, according to the present invention, (a) 99 to 70 parts by weight of a crystalline polypropylene resin, (b) 1 to 30 parts by weight of a polyolefin resin whose melting point is 10°C or more lower than the above polypropylene resin, and (c) an inorganic filler. Thickness: 0.1 to 100 parts by weight of resin composition
8 mm, with a bulk density of 0.23 to 1.2 g/ ^cm3 , the foamed cells are mainly composed of flat voids that spread approximately parallel to the sheet surface, and the coefficient of variation in the width direction of the density is 7. % or less, and a polypropylene foam sheet with excellent thermoformability characterized by a continuity rate of 30% or more. A crystalline propylene homopolymer is suitable as the crystalline polypropylene resin, but other polypropylenes such as a crystalline propylene-ethylene copolymer and a crystalline ethylene-propylene-diene terpolymer are also suitable. Examples include polymers. Although the melting point of the copolymer is lower than that of the homopolymer, it is usually appropriate to use a copolymer having a melting point of 135°C or higher, preferably 150°C or higher (DSC melting peak end point). Note that "crystalline" means that it is substantially crystalline and may partially contain an amorphous portion. Generally, an isotactic index of 90 or higher is suitable. On the other hand, the above polyolefin resins include high density polyethylene, low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-unsaturated carboxylic acid ester copolymer (e.g. ethylene-methyl methacrylate copolymer), ethylene-unsaturated Carboxylic acid metal salt copolymers (e.g. ethylene-
magnesium acrylate (or zinc) copolymer),
Propylene-olefin copolymer (propylene-
Examples include ethylene copolymer, propylene-butene-1 copolymer), polyethylene or polypropylene modified with unsaturated carboxylic acid (e.g., maleic anhydride), ethylene-propylene rubber, atactic polypropylene, etc. Preferably, propylene copolymers, propylene-butene-1 copolymers, and atactic polypropylene are used. It is more preferable to use a resin having a melting point 20° C. or more lower than the polypropylene resin. The inorganic filler may be in powder form, such as silica, diatomaceous earth, alumina, titanium oxide, iron oxide, zinc oxide, magnesium oxide,
Oxides such as pumice powder, hydroxides such as aluminum hydroxide, magnesium hydroxide, basic magnesium carbonate, carbonates such as calcium carbonate, magnesium carbonate, dolomite, sulfates such as calcium sulfate, barium sulfate, calcium sulfite, and talc. , clay, mica, asbestos, calcium silicate montmorillonite, bentonite and other silicates. Among these, it is preferable to use silicates or carbonates, most preferably talc, mica or calcium carbonate. In addition, the appropriate particle size is an average particle size of 30 μm or less.
Preferably, the thickness is 8 μm or less. The amount of these additions is
15 to 90 parts by weight is preferred. It is appropriate to keep the blending ratio of polyolefin resin to polypropylene resin in a small amount.
It is preferable that the amount of the latter is 1 to 15 parts by weight relative to 99 to 85 parts by weight of the former. However, the suitable blending ratio of the polyolefin resin is greatly influenced by the type and amount of the inorganic filler. The preferred blending ratio of polyolefin resin and filler depends on the feeding method to the extruder. For example, when supplying a filler to an extruder after melting and dispersing it in a resin in advance, it is preferable to use a ratio of 0.1 to 0.7 (weight ratio) to 1 filler. In the case of so-called dry blending where the agent is directly supplied, the same applies.
It is preferable to set it as 0.3-2.0 (weight ratio). If the amount of polyolefin resin is too small (for example,
0.1 or less), not only the mechanical strength and thermoformability deteriorate, but also a sheet-like foam with a smooth surface cannot be obtained. The polypropylene foam sheet of the present invention can be obtained by foam-molding the resin composition.
At this time, the thickness must be 0.1 to 8 mm, and the thickness must be 0.3 to 8 mm.
~4 mm is preferred. If it is less than 0.1 mm, the rigidity is insufficient and it cannot be used as a molding sheet. Moreover, even if it exceeds 8 mm, it is difficult to perform thermoforming, making it unsuitable as a molding sheet. Also, the bulk density is 0.23 ~
It is necessary to set it as 1.2g/cm ^<3> , and 0.3-1.05g/cm ^<3> is preferable. If the thickness is less than 0.23 g/cm ³ , the desired rigidity cannot be obtained even if the thickness is increased, and if it exceeds 1.2 g/cm ³ , problems with sagging due to its own weight are likely to occur during thermoforming. On the other hand, the foamed cells are adjusted to have flat voids that extend substantially parallel to the sheet surface. Further, the coefficient of variation of density in the width direction is set to be 7% or less. Here, the variation coefficient of density in the width direction indicates a value measured by a method described later. Also, the communication rate is said to be 30% or more. What is continuity rate?
It is measured by ASTM D-2856 C method. Foamed sheets having the above characteristics are obtained by extrusion foaming the resin composition, and furthermore, the amount of foaming agent at that time, the amount of resin supplied, the nozzle interval, the cooling method, the resin temperature in the mold, the mold temperature, and the flow during foaming. It can be obtained by controlling extrusion conditions such as the expansion/stretching ratio in the direction, width direction, and thickness direction. In this case, when using a volatile blowing agent (for example, propane, butane, heptane, nitrogen gas, carbon dioxide gas, methylene chloride, fluorine-based hydrocarbon, etc.), the amount of blowing agent in the resin composition
0.5 to 10 parts by weight per 100 parts by weight is appropriate;
Chemical blowing agent (azodicarbonamide, N,N'-
Dinitrosopentamethylenetetramine, p, p′-
Oxybis (benzenesulfonyl hydrazide),
When using p,p'-oxybis(benzenesulfonylcarbazide) azobisisobutyronitrile, benzenesulfonylhydrazide, etc.), the appropriate amount is 0.1 to 10 per 100 parts by weight of the resin composition. Usually, it is preferable to use a combination blowing agent of sodium hydrogen carbonate and an organic acid (citric acid, etc.) or a volatile blowing agent. It is appropriate that the temperature of the resin when it enters the mold is about 180 to 240°C, and the temperature of the mold (the part near the discharge nozzle) is about 10 to 60°C lower. The expansion/stretching ratio during foaming is 1.1 to 5 times the nozzle gap in the thickness direction, and 1.5 to 3 times the nozzle opening length (circumferential length in the case of circular) in the width direction.
It is appropriate to control the flow direction to about 0.25 to 1.0 times the drawing speed ratio to the extrusion linear speed (non-foaming equivalent). Further, it is appropriate that the nozzle gap be 0.2 to 1.4 mm and that the extruded foam be forcedly cooled by the ejected gas. Of course, any known extruder can be used. The thus obtained polypropylene foam sheet of the present invention has high mechanical strength such as bending strength, excellent thermoformability, and has a beautiful surface with high smoothness. In particular, aged molded products obtained by press molding or vacuum molding have very good detailing, little local thinning, and a short molding cycle. Furthermore, the amount of extrusion per unit time can also be increased compared to the conventional method. The reason for this effect is not clear. However, the presence of a small amount of polyolefin resin ensures uniform dispersion of the inorganic filler.
In particular, considering that the filler embedded in the polyolefin is considered to be dispersed in the polypropylene resin, it is possible that the composition of such a resin composition has a uniformity and surface smoothing effect, and other effects. It is considered that excellent thermoformability and high mechanical strength are obtained due to the effects of adjusting the bulk density, thickness, communication rate, cell shape, etc. In particular, the density uniformity is high, and the bubbles are flat and parallel to the sheet surface, so expansion into the mold during thermoforming is uniform, and the high communication rate makes it easy to return the expanded molded product. It is believed that it exhibits ideal thermoformability. EXAMPLES This invention will be explained below with reference to Examples, but the invention is not limited thereby. Note that the measurement standards for each characteristic value are as follows. (a) Melting point of crystalline polypropylene resin and polyolefin resin: Temperature increase rate of 6℃ / DSC (differential scanning calorimeter)
Determined under conditions of minutes. For substances that do not have a clear melting point, a temperature that shows a value similar to the melt viscosity at the melting point of crystalline polypropylene is used as a substitute. However, the shear rate is 10 ^-1 sec
Let the melt viscosity be at (b) Surface roughness of foam sheet: Value measured according to JIS B 0601 (1982)
Adopts Rmax (μm) (vertical direction). (c) Communication rate: Value measured by ASTM D-2856 C method. The sample size is 25 x 200 mm and the thickness is approximately 5 mm when stacked. 5mm for items with a thickness of 5mm or more
Measure by cutting back and forth. (d) Coefficient of variation of density in the width direction (uniformity of density): Obtain a cut sample with a length of 250 mm in the machine direction and full width from a roll of foam sheet, and cut the sample at both ends (width direction) of 5.
Round down the mm and obtain specimens with a width of 10 to 25 mm and a total length (250 mm) so that n = 25 or more, measure the weight and thickness of each specimen, calculate the average value and standard deviation, and calculate the average value and standard deviation of each specimen. The coefficient of variation (CV) was calculated using the following formula. CV = standard deviation / average value × 100 (%) (e) Parallelism of foamed cells: From the micrograph of the cross section of the sheet, the longest end of the cell section is connected with a straight line, and the angle between the straight line and the sheet surface is
Shows the percentage of objects whose angle is 45° or less. However, straight lines with a length of less than 100 μm will be omitted, and the length of the measured cross section shall be at least twice the thickness. (f) Flatness of bubbles: The thickest distance d among the bubble lengths l at the above parallelism was determined, d/l was calculated, and the average value was obtained (see Figure 4: In the figure, 1 indicates each bubble. show). (g) Moldability: A round container with a diameter of 120 mm and a depth of 60 mm was molded, and the evaluation was made by checking for problems during molding and the appearance of the product. The check items are as follows. Occurrence of pinholes and minute cracks Molding defects due to tears Excessive thinning of the wall in some areas Occurrence of wrinkles and overlapping areas Are corners and details clearly visible? (Comparative example 3 comparison) Trouble with sag during wide molding (continuous 640 mm width) Molding) Whether the molding cycle is long or not (Comparative Example 3 Control) Those that fall under any of the above check points were determined to be ×, and those that did not fall under any of the above check points were determined to be ○. Example 1 and Comparative Example 1 (Apparatus) The extruder used was a single screw type with a diameter of 65 mm and L/D = 35, and a mold with a cylindrical gap of about 105 mm and 0.4 mm was connected to the tip, and Immediately after the mold, a circular air nozzle was installed close to the mold to cool the sheet during foaming, and immediately after that, a 203 mm
An expansion mandrel with a diameter of . A cutter for incision was attached immediately after the mandrel, and a pulling machine was placed a few meters behind. (Method) Annex A, B, C and blowing agent (1 for all formulations)
The raw materials (parts by weight) were dry blended and supplied to an extruder. (However, B was not used in Comparative Example 1.) Extrusion foaming was performed at a rate of about 30 kg per hour, and the cylindrical foam sheet was cut open behind the mandrel and taken off. The product width was approximately 640 mm. Other product characteristics are shown in the attached table, but the differences in density distribution, surface roughness, good appearance (smooth and glossy), and thermoformability are particularly remarkable when comparing the two. Density non-uniformity is particularly likely to be large in filled foams. Uniformity of density is important from the economical point of view of obtaining the minimum basis weight (g/M ² ) in terms of strength, etc., but it also has an effect on thermoformability.
That is, if partial thinning occurs during molding and is severe, it may break and become impossible to mold. The appearance of Example 1 is very good, but Comparative Example 1 has severe unevenness, which not only makes it look bad as a product, but also creates cracks and holes where the dents widen when heat molding is performed, making it difficult to produce a good molded product. In the first embodiment, such a thing does not occur. A microscopic photograph of the cross section of the sheet obtained in Example 1 is shown in FIG. Examples 2 to 5 (The equipment and method were the same as in Example 1.) However, when the blowing agent was butane, it was added by injection at a rate of about 0.8 parts by weight to 100 parts of the total blend from the middle of the extruder. The quality of the obtained sheet is as shown in the attached table, and the same effects as in Example 1 were obtained. Example 6 (The equipment is the same as in Example 1.) A, B, and C were not simply dry blended, but were blended with B (polypropylene) using a high-speed stirrer (Super Mixer, manufactured by Kawada Seisakusho) at a temperature below the mp of A (polypropylene). (density polyethylene) mp or higher, i.e. approximately 120℃
By heating and stirring back and forth, fine particles integrated with talc (average particle size approximately 4μ) and polypropylene stabilizer are formed on the surface of approximately 600μ particle polypropylene through melted low-density polyethylene from powder (30 meshes). This was then fed to an extruder. As a blowing agent, butane gas was supplied from the middle of the extruder at a ratio of 0.8 parts by weight per 100 parts of resin. The quality of the obtained sheet was excellent as shown in the attached table. Example 7 Similar to Example 6, a mixture obtained using a high-speed stirrer with the same component ratio was further added with component A and a blowing agent, and dry blended to obtain the component ratio shown in the attached table. This mixture was then fed to an extruder. A foam sheet was obtained in the same manner as in Example 1. The quality of the obtained sheet was excellent as shown in the attached table. In particular, when this product is compared with Comparative Example 2 using a similar method, the superiority and inferiority are remarkable. That is, it has a small coefficient of variation in apparent density and is excellent in thermoformability and the like. Comparative Example 1 Produced in the same manner as in Example 1 (but without using component B). As shown in the attached table, the characteristics were not strong. Comparative Example 2 Filler-containing masterbatch (A component PP resin 60%,
Using 40% talc), component A and a blowing agent were further added and dry blended to obtain the component ratios shown in the attached table. This product was fed to the extruder of the example and a foamed sheet was obtained in the same manner. As shown in the attached table, the characteristics were not strong. Comparative Example 3 A foam sheet was produced using the same equipment and method as in Example 1. However, as a blowing agent, butane was supplied at a rate of about 0.8 parts from the middle of the extruder. The properties of the sheet are shown in the attached table. That is, it has good bulk density uniformity and low surface roughness (Rmax), but is inferior in heating dimensional stability and thermoformability.

【table】

【table】

[Table] In addition, samples of 50 x 150 mm were obtained for Examples 1 and 6, and the elastic modulus of the samples in the vertical direction, horizontal direction, back, and front were measured according to JIS-A-9511.The average values are as follows. It was hot on the street. The deformation speed is 50
mm/min, span 100 mm, and R of the pressurizing part was 3.5 mm, and the results were obtained when the span was deformed by 2%. Example 1: 12,000 Kg/cm ² Example 6: 15,600 Kg/cm ² Comparative Example 1: 13,400 Kg/cm ² Comparative Example 3: 8,300 Kg/cm ² Thus, in Examples 1 and 6, a sufficiently satisfactory elastic modulus was obtained. It can be seen that

[Brief explanation of drawings]

Figure 1 is a microscopic (x50) photograph showing the cross section of the polypropylene foam sheet obtained in Example 1, especially the structure of the bubble particles formed inside.
The figure shows the cross-section of a polypropylene foam sheet obtained in the same manner as in Example 1, except that the composition of Example 6 was used and the extruder mold dimensions and extrusion conditions were changed, and in particular, the structure of the cellular particles formed inside. Figure 3 is a microscope (x50) photograph showing the cross section of the polypropylene foam sheet obtained in Comparative Example 3, especially the structure of the bubble particles formed inside.
The photographic diagram and FIG. 4 are explanatory diagrams for measuring the flat state of foamed cells. 1... Foaming bubbles.

Claims (1)

[Scope of Claims] 1 (a) 99 to 70 parts by weight of a crystalline polypropylene resin; (b) a melting point of 10°C higher than the above polypropylene resin;
1 to 30 parts by weight of polyolefin resin and
(c) Made of a resin composition containing 5 to 100 parts by weight of an inorganic filler, with a thickness of 0.1 to 8 mm and a bulk density of 0.23 to 1.2.
g/cm ³ sheet-like foam, the foamed cells are mainly composed of flat voids that spread approximately parallel to the sheet surface, and the coefficient of variation in the width direction of the density is 7.
% or less, and a polypropylene foam sheet with excellent thermoformability, characterized by a continuity rate of 30% or more. 2 (a) 99 to 85 parts by weight of the polypropylene resin,
(b) 1 to 15 parts by weight of the polyolefin resin, and
The sheet according to claim 1, wherein the inorganic filler (c) is 5 to 100 parts by weight. 3. The sheet according to claim 1 or 2, wherein the polyolefin resin is a polyethylene resin. 4. The sheet according to any one of claims 1 to 3, having a bulk density of 0.3 to 1.05 g/cm ³ and a thickness of 0.3 to 4 mm.