JPS6128701B2 - - Google Patents

Description

Detailed Description of the Invention The present invention provides gypsum needle crystals (general term for α-type hemihydrate gypsum needle crystals, type anhydrite gypsum needle crystals, and type anhydrous gypsum needle crystals) suitable for compounding with synthetic resins. and a synthetic resin. Gypsum needle crystals and their industrial utility are known from Japanese Patent Application Laid-Open No. 49-30626. Gypsum needle crystals are expected to be used, for example, as a filler for paper making, as a heat insulating material, or as a reinforcing material for organic polymers. Of course, the properties expected of gypsum needle crystals vary depending on the application, but
Mechanical properties such as elastic modulus and strength are important when composited with organic polymers, especially thermoplastic resins. One factor that determines these mechanical properties is the aspect ratio (vertical/width ratio) of the gypsum needles in the composite. Generally, as shown in short fiber reinforcement theory, the larger the aspect ratio, the higher the elastic modulus. Tensile strength etc. are improved. Therefore, preferred gypsum needles for reinforcing the thermoplastic resin are those having a large aspect ratio in the composite. In other words, strong gypsum needle crystals that are difficult to break during the process of kneading and compounding thermoplastic resin and gypsum needle crystals are expected. However, the reinforcing properties of gypsum needle crystals are insufficient. In particular, when gypsum needle crystals are kneaded and dispersed in polyvinyl chloride resin, the elastic modulus and dimensional stability (coefficient of thermal expansion) improve because the aspect ratio of the gypsum needle crystals in the composite becomes smaller. Reinforcement of the mechanical strength of the material is small. In particular, in the case of tensile strength, there is no reinforcing property and it is lower than the base strength (strength of only polyvinyl chloride resin without gypsum needle crystals added). On the other hand, one of the important physical properties of polyvinyl chloride resin composites is impact strength. In the case of impact strength,
When the gypsum needle crystals are kneaded and dispersed, the strength is significantly lower than the base strength. Furthermore, it has been impossible to simultaneously improve the tensile strength (approaching the base strength) and the impact strength in the gypsum needle crystals. In view of the above points, the present inventors have conducted intensive research and have created a new gypsum needle crystal that has tensile strength and impact strength comparable to that of polyvinyl chloride resin when combined with polyvinyl chloride resin. succeeded in. In other words, the rigidity and dimensional stability of the molded body composited with polyvinyl chloride resin are improved to the same level or higher than that of conventional gypsum acicular crystals, while the tensile strength and impact strength of the molded body are improved compared to the polyvinyl chloride resin. The gypsum needle crystal that can improve the strength to be comparable to that of vinyl chloride resin is a new gypsum needle crystal that has the properties shown below. It has an average diameter of about 1.2μ
and the adsorption amount of water per unit surface area is about 0.3 mg/m ² or less, more preferably 0.265 mg/m ² or less. Since the average diameter of gypsum needle crystals must be determined as a macroscopic quantity, it is determined from the settling start time. Here, the sedimentation start time is a value defined by the method described below. 2 g of classified anhydrous gypsum needle crystals are added to 1.00 ml of distilled water and stirred for 5 minutes to disperse well in the water. Next, the slurry in which the gypsum needle crystals are dispersed is poured into a 100 ml measuring cylinder with a depth of about 16 cm and left to stand still. Eventually, precipitation of gypsum needles occurs. The sedimentation volume of gypsum needle crystals decreases with time, but when the sedimentation volume is about 90 ml or more, the rate of temporal decrease is small, and when the sedimentation volume is less than about 90 ml, the temporal decrease rate of the sedimentation volume is large. Based on the above phenomenon, the standing time required for the settling volume to decrease to 90 ml is defined as the settling start time. The above-mentioned sedimentation volume refers to the volume of the slurry portion in which gypsum needle crystals are dispersed, that is, the volume obtained by subtracting the supernatant from 100 ml at a certain arbitrary standing time. It is not the volume of solid content settling after standing. Now, the sedimentation start time defined as described above is a macroscopic value that depends on the shape of the gypsum needle crystals. According to the research of the present inventors, the settling start time depends only on the diameter of the gypsum needles, and the length
If it is 20μ or more, it does not depend on the length. The smaller the diameter of the gypsum needles, the longer the settling start time. The correspondence between the diameter of gypsum needle crystals and the settling start time can be determined from electron micrographs. The average diameter of the volume was determined for several electron micrographs in which hundreds of gypsum needle crystals were dispersed in one field. The sedimentation start time of about 5.3 minutes corresponds to an average diameter of about 1.2μ determined from electron micrographs. Gypsum needle crystals having an average diameter of 1.2 μm or less as measured by the above method are the small diameter gypsum needle crystals according to the present invention. The amount of water adsorbed per unit surface area is measured by the method shown below. First, the sample is fired at 800°C for 60 minutes. This firing is called pretreatment. The specific surface area of the pretreated anhydrous gypsum needles is measured by the usual BET method using nitrogen. Let the value be A (m ² /g). Next, determine the amount of water adsorbed. The amount of water adsorbed when the vapor pressure of the system is changed at 20℃, i.e.
Determine the adsorption isotherm and determine the amount of water adsorbed under the vapor pressure corresponding to 60% relative temperature. The value is B
(g/g), the amount of water adsorbed per unit surface area is B/A (g/m ² ). The pretreatment conditions are important. Generally, when α-type hemihydrate gypsum needle crystals or type anhydrous gypsum needle crystals are fired, the BET specific surface area and the amount of water adsorbed tend to decrease the longer they are fired at a higher temperature. However, according to the research of the present inventors, if the gypsum needle crystals are fired at an unnecessarily high temperature for a long time, the surface of the gypsum needle crystals becomes as if they were melted, and the surface condition of the gypsum needle crystals changes significantly. Because the width changes, it is unsuitable as a pretreatment for measuring the surface area of gypsum needle crystals. However, after firing at 800°C for 60 minutes, no evidence of melting of the surface of the gypsum needle crystals was observed. On the other hand, when producing type anhydrous gypsum needles industrially, firstly α-type hemihydrate gypsum needles or type anhydrous gypsum needles are produced, and then these gypsum needles are fired. Obtain type anhydrite acicular crystals. Therefore, the firing temperature is
Normally a temperature of 400 to 700°C is used. The reason for this is that, first, if the firing temperature is lower than 400°C, there is a strong possibility that α-type hemihydrate gypsum needle crystals or type anhydrite gypsum needle crystals remain unconverted, which is not preferable.
Second, the higher the firing temperature, the higher the energy cost. The temperature at which α-type hemihydrate gypsum needle crystals or type anhydrite gypsum needle crystals are converted into type anhydrous gypsum needle crystals is sufficient to be 600 to 700°C.
Therefore, the calcination temperature employed industrially is usually about
The temperature is below 700℃ and rarely exceeds 800℃. For the above reasons, 800
°C for 60 minutes was adopted. What is important is that whether the gypsum needles are α-type hemihydrate gypsum needles, type anhydrite gypsum needles, or type anhydrite gypsum needles (provided they are fired at a temperature below 800°C) That is, the fact that the reinforcing property of the gypsum needle crystals against the polyvinyl chloride resin is determined by the adsorption amount of water per unit surface area after the gypsum needle crystals are pretreated. That is, the effect of the present invention is exhibited when the amount of water adsorbed per unit surface area is 0.3 mg/m ² or less, preferably 0.265 mg/m ² or less. In general, the breaking (tensile) strength per unit cross-sectional area of inorganic fibers such as sapphire whiskers and glass fibers has diameter dependence. The breaking strength increases. According to the research conducted by the present inventors, the above-mentioned tendency was generally recognized also in the case of gypsum needle crystals. That is, in the process of kneading and compounding thermoplastic resin and gypsum needle crystals, the smaller the diameter of the gypsum needle crystals, the less breakage of the gypsum needle crystals, and as a result, the gypsum needle crystals in the composite are As the aspect ratio of the crystals becomes larger, the resin reinforcing properties of the gypsum needles increase. In particular, when the diameter of the gypsum needle crystals is about 2 to 1 μm or less, the degree of breakage of the gypsum needle crystals is significantly reduced. On the other hand, even if the diameters of the gypsum needles are approximately the same, the degree of breakage of the gypsum needles during the process of kneading and compounding the gypsum needles with a thermoplastic resin is not necessarily the same. . In other words, it has been found that the aspect ratio of the gypsum needle crystals in the composite and, as a result, the mechanical strength of the composite differ. The above general tendency also holds true for polyvinyl chloride resins. That is, the elastic modulus etc. are greatly improved and reinforced by kneading and dispersing the gypsum needle crystals. In a composite with a polyvinyl chloride resin, the tensile strength is usually not reinforced by the base strength, but if the average diameter is 2 to 1 μm or less, the decrease in strength is reduced. On the other hand, in the case of known gypsum needle crystals, the impact strength is significantly reduced even if the average diameter is about 1.2 μm or less. However, when the gypsum acicular crystals according to the present invention are adopted, not only the elastic modulus etc. are improved and reinforced more than the conventional gypsum acicular crystals, but also the impact strength is equivalent to the base strength. will be realized. That is, the present invention is unique in improving impact strength. Conventionally, filler dispersibility has been considered to be one of the factors that greatly influences the impact strength of PVC-based composite materials. The better the dispersion of the filler, the more remarkable the improvement in impact strength. However, in order to properly disperse conventional gypsum needle crystals in vinyl chloride resin, it is necessary to remove large particles and aggregates, and also to use processing methods that require large shearing force, such as roll kneading. Good dispersion of gypsum needle crystals was difficult to achieve unless the method was adopted. However, in the case of roll kneading, the gypsum needle crystals are significantly damaged and the aspect ratio of the gypsum needle crystals in the processed molded product becomes small, so that the reinforcing property of the mechanical strength of the molded product becomes low. In particular, the decrease in tensile strength becomes significant. Here, there is a difficulty in balancing tensile strength and impact strength. However, although the dispersion of the gypsum needles according to the present invention is better than that of conventional gypsum needles, the dispersion of the gypsum needles according to the present invention is better than that of conventional gypsum needles; , it is possible to achieve good dispersion. Therefore, according to the present invention, the mechanical strength, particularly the impact strength, of the molded article is significantly improved compared to the conventional case. In other words, if the gypsum acicular crystals according to the present invention are used, a composite material with tensile strength and impact strength balanced to the same level as the base strength can be obtained by using the powder extrusion, which is a common processing method for polyvinyl chloride resin. It is possible to obtain a body. Of course, the rigidity is greatly improved. Furthermore, when the gypsum needle crystals according to the present invention are composited with an organic polymer other than polyvinyl chloride resin, such as a polyolefin resin that is a thermoplastic resin, mechanical strength such as rigidity and tensile strength is lower than that of conventional gypsum. It was found that the reinforcement was significantly greater than in the case of needle-shaped crystals. For example, when a polypropylene resin, which is a typical polyolefin resin, is composited with the gypsum needle crystals of the present invention, the tensile strength of the gypsum needles is significantly reinforced compared to the case where conventional gypsum needle crystals are composited. The fracture strength of the gypsum needle-shaped crystals and, by extension, the reinforcing properties of the composite with the organic polymer depend on the diameter of the gypsum needle-shaped crystals, and even if the diameters are almost the same, the aspect ratios in the composite differ. It has already been explained that the reinforcing properties are different. The gypsum acicular crystals according to the present invention have significantly higher tensile strength of the composite than conventional gypsum acicular crystals even though the diameters are almost the same. That is, the present invention is distinctive in dramatically improving the mechanical strength of polyolefin resins. According to the single fiber reinforcement theory, the tensile strength TS of a fiber-reinforced composite is expressed by the first equation. TS=l/d・χ・τ・V _f +σ _n (1−V _f )...First equation l...Fiber length in the composite. However, l<l _c (critical fiber length) d...Fiber diameter χ...Constant related to fiber orientation τ...Interfacial shear strength between fiber and matrix V _f ...Fiber volume fraction σ _n ...Matrix Strength When the fiber is a gypsum needle crystal, l/d, that is, the aspect ratio in the first equation, is the average value after breakage in the compositing process. Therefore, the aspect ratio in the composite is considered to depend on the toughness of the gypsum needles themselves. That is, l/d∝σ _G ... Second equation Here, σ _G can be assumed to be the strength of the gypsum needle crystal itself, for example, the breaking strength. On the other hand, it has been confirmed that the breaking strength of whiskers and glass fibers is diameter dependent, and as the diameter becomes smaller, the breaking strength increases significantly and approaches the theoretical strength. The relationship between the breaking strength and the diameter can be approximated by, for example, an exponential relationship. Now, assuming that the fracture strength of gypsum needle crystals, which are whisker-like crystals, has the diameter dependence described above, it can be formally written as σ _G ∝l ^-d ……Equation 3 I can do it. Therefore, the above 1st to 3rd
From the formula, TS-σ _n (1-V _f )=χ・τ・V _f・l/d∝l ^-d ...4th formula, that is, l _o [TS-σ _n (1-V _f )]=- a・d+b...Equation 5 is considered to approximately hold true. constants a and b
is determined by substituting actual measured values for gypsum acicular crystals that are thought to have very few stress concentration points, such as steps, which will be described later. If the unit of tensile strength is Kg/cm ² and the unit of diameter is micron, then a = 0.60 and b = 6.41. According to research by the present inventors, conventional gypsum needle crystals have a large deviation from the fifth equation, that is, at a certain diameter, there is a large difference between the TS determined from the fifth equation and the actually measured TS. In particular, when the diameter is about 1.2μ or less, the deviation becomes very large. On the other hand, if such gypsum needle crystals are employed, even if the diameter is about 1.2 μm or less, the deviation from Equation 5 is small. Therefore, in the fifth equation, TS for any diameter d is defined as the tensile strength TS゜(d) of the composite when ideal gypsum needle crystals are adopted, and then Obtain the measured value TS(d) of the gypsum needle crystal complex, and calculate TS゜
Find the magnitude of the decrease from (d) and calculate it as ΔTS(d)≡
It is defined as TS゜(d)−TS(d). The tensile strength of the gypsum needle crystal composite is determined as follows. Type anhydrite acicular crystals after classification 40
Parts by weight were added to and mixed with 54 parts by weight of polypropylene resin powder, 6 parts by weight of acrylic acid-modified polypropylene resin, and some amount of stabilizer, and about
The pellets are extruded at 240°C, and the dried pellets are processed into JIS molds at a mold temperature of 60°C and an injection pressure of approximately 600Kg/ ^cm2 .
K-6745 specimens were injection molded at 250°C, then
Tensile tests are carried out at a temperature of approximately 23° C. and a tensile strength of 5 mm/min. On the other hand, the diameter d of the gypsum needle crystals is determined from the settling start time, and the ideal tensile strength TS at the same diameter is determined.
Find ゜(d) from equation 5, then ΔTS(d)=TS゜(d)
- Find TS(d). ΔTS(d) defined as above is considered to be a parameter of the toughness of the gypsum needle crystals. That is, Δ
Gypsum needles with a small TS are stronger than those with a large ΔTS(d). Strong gypsum needle crystals are gypsum needle crystals that are less likely to break during the kneading and compounding process with resin, in other words, there are fewer stress concentration points such as steps and dislocations on the crystal surface. Since the stress concentration points are considered to be active points on the crystal surface, it is thought that the adsorption capacity for highly polar water molecules is extremely large. In other words, Δ
It is thought that gypsum needle crystals with a large TS(d) also have a large adsorption amount of water molecules. In fact, while conventional gypsum needle crystals have a large ΔTS(d) and a large amount of water adsorption per unit surface area, the gypsum needle crystals according to the present invention have a small ΔTS(d) and a large adsorption amount of water per unit surface area. The amount of water adsorbed per unit surface area is also small. A clear first-order correlation is seen between ΔTS(d) and the amount of water adsorbed per unit surface area. This relationship is shown in FIG. The adsorption amount of water per unit surface area is 0.3 mg/m ² is Δ
Corresponding to TS = 60, the adsorption amount of water per unit surface area in the case of more preferable gypsum needle crystals is 0.265 mg/
m ² or less corresponds to ΔTS of 40 Kg/cm ² or less. Therefore, the gypsum needle crystal according to the present invention is practically
It is preferable to specify it in TS. Now, the gypsum needle crystal according to the present invention is defined by three items. The first condition, that the average diameter is about 1.2 μm or less, is considered to be based on the diameter dependence of gypsum needle crystals, as described above. When the diameter is about 1.2μ or less, the strength of the gypsum needle crystals generally increases significantly, so there is less damage during kneading processing.
As a result, it is thought that the aspect ratio of the gypsum needle crystals in the molded product increases, and the tensile strength is improved. The reason why the second condition, ie, "the amount of water adsorbed per unit surface area is approximately 0.3 mg/m ² or less", is not clear. However, the fact that the adsorption amount of water per unit surface area is different means that there is a field that preferentially adsorbs water molecules, which are more polar than nitrogen molecules, and the amount of water molecules that are present in the anhydrous gypsum needle crystals is It can be interpreted as being very different depending on the type. The adsorption point (field) can be assumed to be, for example, a step or a transition on the crystal surface. In other words, it is thought that gypsum needle crystals that adsorb a small amount of water per unit surface area are less likely to break due to fewer steps on the crystal surface. Particularly preferred gypsum needle crystals have an adsorption amount of water per unit surface area of 0.265 mg/m ² or less, have particularly few steps, and are considered to have close to ideal strength. As mentioned above, this is expressed as reinforcement of the strength (in other words, a reduction in ΔTS) when combined with PP. on the other hand,
As mentioned above, when composited with PVC, the strength and impact strength are not significantly reduced. Furthermore, if the gypsum needle crystals that satisfy the above two conditions "substantially do not contain particles or aggregates of about 20 microns or more", it is extremely advantageous from the point of view of improving impact strength. In general, it is thought that when large particles or aggregates are present, they become stress concentration points and cracks easily develop, resulting in a decrease in impact strength. Removal of particulates or agglomerates can be accomplished by classification, for example, in a forced vortex rotating wall classifier. The degree of classification may be determined as appropriate depending on the purpose of use, but it is desirable that the content of particles or aggregates be at least about 1% by weight. It has already been established that the dispersibility of the gypsum needle crystals according to the present invention in polyvinyl chloride resin is significantly better than that of conventional gypsum needle crystals, and one of the reasons for this is that , the adsorption point is considered. That is, while conventional gypsum needle crystals have many adsorption points, in other words, active points on the crystal surface, and the gypsum needle crystals themselves have a strong agglomeration property, the activity of the gypsum needle crystal surface according to the present invention is Since there are very few dots, it is thought that the gypsum needle crystals themselves have weak cohesiveness and are easily dispersed. It is believed that the impact strength is significantly improved as a result of good dispersion. The gypsum needle crystals defined as above can be produced as follows. An aqueous slurry containing 0.3 to 30% by weight of raw dihydrate gypsum is placed in an autoclave and heated under pressure while stirring to produce α-type hemihydrate gypsum needle crystals. Here, the properties of the raw material dihydrate gypsum must have the following characteristics. That is, the half width (integral width after correction) of the X-ray diffraction peak of the (002) plane is approximately 2.5 × 10 ^-4 radian, preferably 1.5 × 10 ^-4 radian or less, and the dispersion in water is After about 10
The solubility of calcium sulfate after minutes is approximately 0.204
%, particularly preferably 0.202% or less. X-ray diffraction was performed using X manufactured by Rigaku Denki Co., Ltd.
Measurement was performed using a line diffraction device (Cat No. 2028) under the following conditions. Target; Cu (45KV 40mA) Filter; Ni Divergency; 1/2゜Receiving Slit; 0.3mm Scan Speed; 1/2゜/min Chart Speed; 80mm/min Time Const; 5sec The standard material for half width correction is , α-SiO ₂ with a particle size of 30–44μ annealed at 800 °C was used. The solubility of calcium sulfate is determined from the electrical conductivity at 19°C. That is, the electrical conductivity of an aqueous solution of calcium sulfate with a known concentration is measured at 19° C., and a calibration curve is created. Next, the electrical conductivity of the sample to be measured can be measured at 19°C, and the solubility of the sample can be determined from the above calibration curve. The particle size of the raw material dihydrate gypsum is several microns to 100 microns, more preferably several microns to 60 microns. The fine raw material dihydrate gypsum is obtained, for example, by hydrating calcined gypsum. The calcined gypsum used here does not substantially contain dihydrate gypsum or type anhydrous gypsum, and furthermore, from the half value width of the X-ray diffraction peak, Hall
It is preferable to use calcined gypsum, which has a large microcrystal grain size determined by the formula and has a small lattice strain of the microcrystals. The solubility (calcium sulfate equivalent) of fine hydrated dihydrate gypsum obtained by hydrating preferred calcined gypsum at a concentration of 0.3 to 30% by weight at room temperature with stirring is approximately 1 hour after the start of hydration. 0.204% or less, and furthermore, the half width of the X-ray diffraction peak of the (002) plane of the hydrated dihydrate gypsum crystal is about 2.5×10 ⁻⁴ radian or less. In addition to the raw material dihydrate gypsum, it may be possible to obtain favorable results by adding seed crystals. In particular, by adding seed crystals when the particle size of the raw material dihydrate gypsum is relatively large, the diameter of the resulting α-type hemihydrate gypsum needle crystals can be reduced to 1.2 μm or less. An example of such seed crystals is fine hydrated dihydrate gypsum obtained by hydrating calcined gypsum by the method described above. The calcined gypsum used here is obtained by calcining dihydrate gypsum in a conventional manner. Fine hydrated dihydrate gypsum obtained by hydrating calcined gypsum, which has a small microcrystal particle diameter determined from the half width of the X-ray diffraction peak of the calcined gypsum and has a large lattice strain of the microcrystals, is a seed crystal. It has a great effect as That is, a preferable seed crystal can produce small-diameter gypsum needle-like crystals even when added in a relatively small amount. Hydrated dihydrate gypsum, which is highly effective as a seed crystal, has a high solubility. In addition, hydrated dihydrate gypsum has a large half-value width of the X-ray diffraction peak of the (002) plane.
It is highly effective as a seed crystal. However, the solubility
If too many seed crystals are added that exceed 0.204% or that the half width of the X-ray diffraction peak of the (002) plane exceeds 2.5 x 10 ^-4 radians, the diameter of the resulting gypsum needle crystals will decrease. becomes thinner, but the amount of water adsorbed per unit surface area increases. Conversely, when the amount of seed crystals added is small, the diameter of the obtained gypsum needle crystals becomes thick. A preferred combination of the properties and amount of the hydrated dihydrate gypsum to be added is within the range shown below. Solubility of fine hydrated dihydrate gypsum (seed crystals) obtained by hydrating calcined gypsum (about 1 hour after the start of hydration, 19
°C) is 0.204% or less, and the half-value width (integral width after correction) of the X-ray diffraction peak of the (002) plane of the seed crystal is 2.5 × 10 ^-4 radian or less, the above-mentioned raw material Dihydrate gypsum (the solubility of calcium sulfate at 19℃ after about 10 minutes after being added and dispersed in water is approx.
0.204% or less, and the half width of the X-ray diffraction peak of the (002) plane is approximately 2.5 × 10 ^-4 radians or less), and the seed crystal is added in an amount of 3% or more by weight. The gypsum acicular crystals according to the present invention can be manufactured by this method. The solubility of fine hydrated dihydrate gypsum (seed crystals) obtained by hydrating calcined gypsum (at 19°C after approximately 1 hour from the start of hydration) exceeds 0.204%, or the hydrated dihydrate gypsum When adding hydrated dihydrate gypsum as a seed crystal, the half-width (integral width after correction) of the X-ray diffraction peak of the (002) plane of the (seed crystal) exceeds 2.5 × 10 ^-4 radians. When adding the seed crystals to the above-mentioned raw material dihydrate gypsum, the solubility of the seed crystals (fine hydrated dihydrate gypsum obtained by hydrating calcined gypsum) (approximately 1 After time, 19℃)
When is X percent and Z is the amount (percent) of the seed crystal added, in the (X, Z) coordinate,
It is a combination of the ranges shown by the shaded area in the figure, and when the half-width (integral width after correction) of the X-ray diffraction peak of the (002) plane of the seed crystal is set as Y radians, (Y , Z) coordinates, it is possible to produce the gypsum needle crystals according to the present invention by using as a starting material a mixture that satisfies the combinations shown in the shaded area in FIG. 2. . Now, the solubility of gypsum is considered to depend on the particle size and surface crystallinity of the gypsum. Therefore, it is possible to reduce the solubility of gypsum by washing the gypsum with water or leaving it to mature in a state in which it is dispersed in water. However, solubility is determined by a very small amount of very fine particles or lattice depressions on the crystal surface, so even if the solubility decreases significantly, It is inconceivable that there has been a drastic change to the (non-surface) state. On the other hand, the half width of the X-ray diffraction peak is a quantity that depends on the crystal grain size in the direction perpendicular to the crystal plane of interest and the average value of the lattice strain in the direction perpendicular to the crystal plane. Dihydrate gypsum obtained by hydrating calcined gypsum by the method described above generally becomes rod-shaped crystals extending in the C-axis direction. However, since the (002) plane of dihydrate gypsum is a plane perpendicular to the C axis, the half-value width of the X-ray diffraction peak of the (002) plane is determined by the size of the dihydrate gypsum in the elongation axis direction, and It depends on the average value of lattice strain.
Since the fine rod-shaped crystals of hydrated gypsum are considered to be single crystals, the size in the C-axis direction is several to several tens of microns, and their contribution to the half-value width is so small that it can be almost ignored. In other words, the X of the (002) plane of hydrated 2-gypsum
The half-width of the line diffraction peak is considered to be a parameter indicating the size of the average lattice strain in the C-axis direction, including the surface and inside of the dihydrate gypsum. According to the research of the present inventors, by aging hydrated dihydrate gypsum, which has a relatively high solubility, the solubility of hydrated dihydrate gypsum is greatly reduced.
Although the half-width of the X-ray diffraction peak of the (002) plane is slightly reduced compared to the half-width before ripening, it is much smaller than the rate of decrease in solubility. The above phenomenon is considered to be evidence that solubility depends on the grain size and surface condition of gypsum, and that the half-width of the X-ray diffraction peak is the position that represents the average crystalline state of the entire gypsum crystal. . The production of gypsum needle crystals takes place under a dynamic equilibrium of dissolution of dihydrate gypsum in water and crystallization as α-type hemihydrate gypsum. As the dissolution of dihydrate gypsum progresses, the interior of the dihydrate gypsum crystals To form a new surface layer, the solubility of the system is
It is thought that the properties of the newly formed surface layer, that is, the properties of the initial interior of the dihydrate gypsum crystal, in other words, are determined by the half width of the X-ray diffraction peak. This is considered to be the importance of measuring the half-width of the X-ray diffraction peak. However, reducing solubility is beneficial. In α-type hemihydrate gypsum crystallization, the solubility of dihydrate gypsum,
Since the difference in solubility of α-type hemihydrate gypsum is considered to be the degree of supersaturation, the lower the solubility of dihydrate gypsum, the lower the degree of supersaturation and the realization of gradual crystallization. Conceivable. Generally, crystals with few impurities, lattice defects, steps, etc. are achieved by keeping the degree of supersaturation low and at a slow crystallization rate. Alpha-type hemihydrate gypsum needles are substantially produced at 115° to 130°C. It is preferable to stir the slurry at a low speed within a range that prevents sedimentation of the solid content of the slurry. When the stirring speed is low, the diameter of the obtained gypsum needles can be made smaller. The produced α-type hemihydrate gypsum needle crystals are dehydrated and separated, dried, and then calcined at 400 to 700°C to obtain stable anhydrous gypsum needle crystals. When adding gypsum needle crystals to synthetic resin,
5 to 75% by weight is suitable. If it is less than 5%,
There is little advantage in adding gypsum needle crystals to create a composite, and it is often difficult to create a composite that exceeds 75%. Next, examples will be described. Example 1 Dihydrate gypsum, a by-product of flue gas desulfurization, was calcined at 180° C. for 16 hours to obtain calcined gypsum having a microcrystalline particle diameter of approximately 0.125 microns and a microcrystalline lattice strain of approximately 1.4×10 ⁻³ . The calcined gypsum was hydrated. The solubility of calcium sulfate immediately before use, about 1 hour after the start of hydration, was 0.202%, and the half width of the X-ray diffraction peak of the (002) plane was about 1.45×10 ⁻⁴ radian. The hydrated dihydrate gypsum slurry having a slurry concentration of about 5% by weight was placed in an externally heated autoclave and heated under pressure while stirring. The slurry temperature was raised to about 130°C and maintained for 5 minutes to complete the reaction. After cooling the internal temperature to about 90°C, the mixture was quickly dehydrated and separated to obtain a dehydrated cake of α-type hemihydrate gypsum needle crystals. Next, the dehydrated cake was placed in a hot air baking oven at about 700°C.
By drying and firing for about 30 minutes, type anhydrous gypsum needle crystals were obtained. Then microplex
Approximately 20 by 132MP (Yaskawa-Alpine classifier)
Average diameter approximately 0.79, excluding particles and aggregates larger than μ
μ type anhydrous gypsum needle crystals were obtained. The classified anhydrous gypsum needle crystals were calcined (pretreated) at 800°C for 60 minutes, and the amount of water adsorbed per unit surface area was measured. The crystals are shown in Table 1. The classified anhydrous gypsum needle crystals were added in an amount of 10% by weight to lead-containing polyvinyl chloride (PVC) (Kanevinyl S1001 manufactured by Kanebuchi Chemical Co., Ltd.) using a 40 mm single-screw vent extruder. A belt-like strand was extruded. Next, a test piece with a thickness of about 3 mm was prepared by preheating at 175°C for 5 minutes and pressing at a pressure of 50 kg/cm ² for 5 minutes, and a test piece with a weight of 300 kg was prepared in a constant temperature room at a temperature of about 23°C.
g, and the Dupont impact strength (half height at failure, cm) using a 3/8-inch weight was measured. Table 1 shows the results.
Shown below. In addition, a tensile test piece was cut out from the belt strand and subjected to a tensile test in accordance with JIS K-6745. The results are shown in Table 1. On the other hand, 20% by weight of the classified anhydrous gypsum needle crystals were added to the lead-containing PVC and pelletized using a 40 mm vented extruder, and then a belt-shaped strand was extruded using the same extruder. A tensile test piece was cut out from the belt-like strand and subjected to a tensile test in accordance with JIS K-6745. The results are shown in Table 1. The above classified anhydrous gypsum needle crystals were added to 54 parts by weight of polypropylene resin (PP), 6 parts by weight of acrylic acid-modified PP, and a small amount of stabilizer.
40 parts by weight was added and pelletized using a 40 mm single-screw vent extruder.Then, the dried pellets were made into JIS K-6745 test pieces using an ordinary method using an injection molding machine, and subjected to a tensile test at a temperature of about 23°C. carried out. The results are shown in Table 1. Comparative Example 1 Different flue gas desulfurization byproduct dihydrate gypsum from Example 1 was used.
By calcining at 220° C. for 4 hours, calcined gypsum with microcrystalline particles having a diameter of about 0.15 μm and a lattice strain of about 1.8×10 ⁻³ was obtained. The calcined gypsum was then hydrated. About 1 hour after the start of hydration, the solubility of calcium sulfate immediately before use was about 0.207%, and the half width of the X-ray diffraction peak of the (002) plane was about 3.9 x 10 ^-4 radians. Thereafter, in the same manner as in Example 1, classified anhydrous gypsum needle crystals having a thickness of about 0.65 μm were obtained. Next, the amount of water adsorbed per unit surface area was measured in exactly the same manner as in Example 1, and further,
Various physical properties of the composite with PVC and PP were measured. The results are shown in Table 1. Comparative Example 2 The microcrystalline particle size of airflow calcined calcined gypsum is approximately 0.06
μ, the lattice strain of the microcrystal was approximately 3.2×10 ⁻³ . The solubility of the dihydrate gypsum obtained by hydrating this calcined gypsum was approximately 0.235% immediately before use, and the half width of the X-ray diffraction peak of the (002) plane was approximately 5.8×10 ⁻⁴ radians. Hereinafter, by the same method as in Example 1, the thickness of approximately
Anhydrous acicular gypsum of type 0.59 μ after classification was obtained. The amount of water adsorbed per unit surface area and various physical properties of the composite with PVC and PP were measured in exactly the same manner as in Example 1. The results are shown in Table 1. Comparative Example 3 Flue gas desulfurization by-product dihydrate gypsum with a particle size of 10 to 60μ,
The solubility after about 10 minutes after being poured into water and stirring is approx.
The half width of the X-ray diffraction peak of the 0.200% (002) plane was approximately 1.1×10 ⁻⁴ radian. Using a slurry in which about 1.5% by weight of the hydrated dihydrate gypsum used in Comparative Example 1 was added to the raw dihydrate gypsum, it was classified to a thickness of about 1.5 μm in the same manner as in Example 1. Anhydrous gypsum needle crystals were obtained. Then,
The amount of adsorption per unit surface area and various physical properties of the composite with PVC and PP were measured in exactly the same manner as in Example 1. The results are shown in Table 1. Example 2 About 5% by weight of the hydrated dihydrate gypsum used in Comparative Example 2 was added to the raw material dihydrate gypsum used in Comparative Example 3.
Added. Thereafter, in the same manner as in Example 1, classified anhydrous gypsum needle crystals having a thickness of about 0.83 μm were obtained. Next, by the same method as in Example 1, the amount of water adsorbed per unit surface area and
Various physical properties of the composite with PVC and PP were measured.
The results are shown in Table 1. Example 3 The hydrated dihydrate gypsum slurry used in Example 1 was dehydrated and separated, washed with water, and dispersed in water again. The solubility was approximately 0.199%, and the half width of the X-ray diffraction peak of the (002) plane was approximately 1.4×10 ⁻⁴ radian. Thereafter, in the same manner as in Example 1, classified anhydrous gypsum needle crystals having a thickness of approximately 0.77 μm were obtained. Next, the amount of water adsorbed per unit surface area and various physical properties of the composite with PVC and PP were measured in exactly the same manner as in Example 1. The results are shown in Table 1. Example 4 The fine hydrated dihydrate gypsum used in Example 1 was added by weight to 15% of the raw material dihydrate gypsum used in Comparative Example 3.
% added. Thereafter, in the same manner as in Example 1, classified anhydrous gypsum needle crystals having a size of about 0.93 μm were obtained. Next, the amount of water adsorbed per unit surface area and PVC were determined in the same manner as in Example 1.
In addition, various physical properties of the composite with PP were measured. The results are shown in Table 1. 【table】

[Brief explanation of the drawing]

Figures 1 and 2 are graphs showing the combination ranges of (solubility) - (addition amount) and (half-value width) - (addition amount) of hydrated dihydrate gypsum, respectively, and Figure 3 is a graph showing the combination range of hydrated dihydrate gypsum. Graphs 4 and 5 showing the relationship between the adsorption amount of water per unit surface area of gypsum needle crystals and ΔTS when the gypsum needle crystals are composited with PP, respectively, are examples and comparisons. Hydration in example 2
Water gypsum (solubility) - (addition amount) and (half value width)
It is a graph showing combinations of - (addition amount). A...Example 1, B...Comparative example 1, C...Comparative example 2, D...Comparative example 3, E...Example 2, F...
Example 3, G...Example 4.

Claims (1)

[Scope of Claims] 1. A composite obtained by mixing gypsum needle crystals with an average diameter of about 1.2 μ or less and an adsorption amount of water per unit surface area of about 0.8 mg/m ² or less into a thermoplastic synthetic resin. composition. 2. The composite composition according to claim 1, which does not substantially contain particles or aggregates of about 20 microns or more in plaster. 3. The composite composition according to claim 1 or 2, wherein the amount of gypsum needle crystals mixed into the thermoplastic synthetic resin is 5 to 75% by weight based on the thermoplastic synthetic resin. 4. The composite composition according to claim 1 or 2, wherein the thermoplastic synthetic resin is a polyvinyl chloride resin. 5. The composite composition according to claim 1 or 2, wherein the thermoplastic synthetic resin is a polyolefin resin.