JPH06145407A - Preexpanded bead for in-mold fuse molding and its production - Google Patents

Abstract

PURPOSE:To provide the subject thermoplastic preexpanded beads excellent in in-mold fuse moldability, capable of giving in-mold expanded foam having high-grade physical properties. CONSTITUTION:Perfectly cylindrical or ellipsoidally cylindrical resin beads are impregnated with a volatile foaming agent having a gas permeability constant of >=1X10<-10>cc. (STP).cm/cm<2>.sec.cmHg, followed by heating to effect expansion into primary expanded beads 1.5-5cm<3>/g in expansion ratio, which are then further expanded by a factor of >=3, thus affording the objective virtually spherical preexpanded beads. For the beads, one bandlike ring with relatively large film thickness at each hemisphere is found on the surface layer without crossing each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to so-called pre-expanded thermoplastic resin expanded particles for producing a thermoplastic resin expanded molded article by in-mold fusion molding and a method for producing the same.

[0002]

2. Description of the Related Art A method for producing a preformed foamed resin particle by in-mold fusion molding of a molded article made of a foamed thermoplastic resin has been widely practiced. And, as the pre-expanded particles to be subjected to the in-mold molding, spherical expanded particles having a uniform particle diameter are said to be ideal. This is because there is an angled portion when filling the inside of the mold of the molding machine and heating it to expand the expanded particles to form a densely fused molded product in which the spaces between the particles are filled. It is considered that the spherical pre-expanded particles are more uniform than the pre-expanded particles in the filling state in the mold cavity, and the properties of the obtained molded body are essentially good.

Therefore, several techniques relating to a method for producing spherical pre-expanded particles have been proposed. For example, Japanese Examined Patent Publication No. 52-41777 discloses a method of producing spherical particles by suspending ethylene resin particles in an aqueous suspension and heating to a high temperature above the melting point of the resin. JP-A-58-168626 and JP-A-60-453.
Similarly, Japanese Patent No. 4 discloses a method of producing spherical polypropylene resin particles by heating in a hot water suspension at high temperature. These technical ideals require that the pre-expanded particles to be used for in-mold molding have spherical expanded particles with little variation in particle size. When the particles are made uniform, and the foaming agent is impregnated into the particles and the mixture is heated and foamed, the pre-expanded particles to be obtained have a uniform shape because variations in the amount of the foaming agent impregnated in the resin particles and uneven heating temperature are reduced. Is teaching. However, in this method, since there is an independent spheroidizing step before the foaming step, there is a problem that the manufacturing step becomes complicated and a dedicated device and a large amount of heat energy are required, resulting in an increase in cost.

On the other hand, as a solution to the above problem, there is a method of producing pre-expanded particles having a substantially spherical shape by sphering the resin particles at the time of foaming by heating in order to make them spherical. For example, in JP-A-60-115413, JP-A-2-53837 and JP-A-2-67338, polyolefin resin particles having a special orientation are obtained, which are dispersed in a closed container together with a foaming agent in a dispersion medium. Preheated to a temperature close to the melting point of the resin, and then the resulting expandable particles are discharged into a low-pressure atmosphere together with a dispersion medium under high temperature and high pressure to form a substantially spherical prefoam. Techniques for making particles are described.

[0005]

However, the above-mentioned improved method has a drawback that expanded particles having a uniform particle diameter cannot be obtained. As a result, there still remains a problem that the filling property into the mold cavity is poor. This is considered to be due to the difficulties of the method for obtaining resin particles having a special orientation and the foaming method itself. That is, i) extruded as a strand and cut to obtain oriented resin particles, unevenness in the orientation of individual particles due to subtle fluctuations in the strand cooling rate and the draft take-up rate, and ii) a container generated when the expandable particles are discharged. The shape of the foamed particles depends on two factors: the amount of the foaming agent impregnated by the fluctuation of the foaming agent component and the pressure in the dispersion medium and the change of the orientation relaxation amount / shrinkage amount of the resin particles due to the fluctuation of the foaming temperature. It is presumed that the problems that tend to be uneven without being constant remain unsolved. Further, since the use of the pre-expanded particles having the particle shape as described above results in poor filling properties, the molded product obtained by filling the pre-expanded particles in the mold cavity and heat-molding has a surface appearance, compression set, and repeated compression. There is a problem in that the physical properties such as the recovery rate afterwards cannot be sufficiently satisfied.

An object of the present invention is to perform in-mold fusion molding in
It is an object of the present invention to provide pre-expanded particles having excellent moldability such as fusion property, filling property, dimensional shrinkage ratio with respect to mold and sink mark. Another object of the present invention is to provide pre-expanded particles capable of producing a foamed molded article having excellent surface appearance, compression recovery rate, compression strain, dimensional stability upon heating, dynamic cushioning properties, and the like. is there.

Another object of the present invention is to provide a method for producing pre-expanded particles which achieves the above objects.

[0008]

One of the present inventions is a substantially spherical pre-expanded particle made of a thermoplastic resin, in which a resin film covering the surface of the particle has a thick band-shaped ring. Two rings are formed, these rings do not intersect with each other, and the two rings are in a position where they can be bisected so as to exist one on each hemisphere when the particles are bisected, and The pre-expanded particles for in-mold fusion molding are characterized in that the angle formed by the two cut surfaces cut along the ring is 45 ° or less.

Another aspect of the present invention is that a thermoplastic resin in a molten state is extruded in a strand shape from an extruder through a nozzle and cut into a predetermined length to obtain cylindrical or elliptic columnar particles, and the particles are used as a base resin. Gas permeability coefficient is 1 × 10
^-10 cc. (STP). cm / cm ² . sec. cmH
A ridge which is an intersection of the end surface (corresponding to the above-mentioned strand cut surface) and the cylindrical side surface (corresponding to the above-mentioned strand surface) of the foamable resin particle by forming a foamable resin particle by impregnating with a volatile foaming agent of g or more. The volatile foaming agent present in the vicinity is volatilized preferentially to foam the expandable resin particles by heating to form primary expanded particles having an expansion ratio of 1.5 to 5 cm ³ / g, and then in the bubbles of the primary expanded particles. The method for producing pre-expanded particles for in-mold fusion molding is characterized in that a pressure of gas is applied to the pre-expanded particles, and the pre-expanded particles for in-mold fusion molding are heated and expanded at a foaming ratio of 3 or more with respect to the expansion ratio of the primary expanded particles.

The present invention will be described below with reference to the drawings. 1 to 5 are views showing various types of pre-expanded particles. FIG. 1 (Experiment No. 1 of Example 1): A diagram of pre-expanded particles of the present invention. 2-5: Figures of pre-expanded particles of the comparative product. Fig. 2 (same experiment No. 10): Cylindrical curved resin particles foamed using the foaming technique of the present invention. FIG. 3 (Experiment No. 11): Trigonal prismatic resin particles foamed using the foaming technique of the present invention. Fig. 4 (Experiment No. 9): Almost spherical resin particles obtained by subjecting elliptic columnar particles to a spheroidizing treatment in a high-temperature hot water suspension system and foamed using the foaming technique of the present invention. Fig. 5 (Experiment No. 6): Elliptic cylindrical resin particles foamed by a conventional foaming technique.

1 to 5, A is a view of the pre-expanded particles viewed from the front, B is a view of the pre-expanded particles from the side, and C is a central cross-sectional view of the pre-expanded particles. In C, S is a bubble,
U is a resin film, α _{1 to} α ₄ are thick belt-shaped portions, β ₁ ,
β ₂ represents the midpoint between the two strip rings (the midpoint between α ₁ and α ₂ , the midpoint between α ₃ and α ₄ ).

Comparing the structural differences of the above-mentioned five kinds of expanded particles, the pre-expanded particles shown in FIG. 1 are substantially spherical particles, and the resin film covering the surface thereof has two thick band-shaped rings. (R ₁ R ₂ ) are arranged. The pre-expanded particles in FIG. 2 are non-spherical, and as in FIG. 1, two thick band-shaped rings are arranged on the particle surface. The pre-expanded particles in FIG. 3 are composed of two thick film-like rings (R ₁ , R ₂ ) and 3
The book is not ring-shaped. Thick band film (R ₃ ,
R ₄ and R ₅ ) are present on the surface of the particle, and the thick band-shaped rings (R ₁ and R ₂ ) are the thick band-shaped films (R ₃ and R ₄ ,
It is connected to both ends of R ₅ ). The pre-expanded particles in FIG. 4 are almost spherical, and the surface film thickness is almost uniform. The pre-expanded particles in FIG. 5 have a drum-like shape, have no band-shaped thick portion, and have a substantially uniform thickness.

The pre-expanded particles of the present invention (FIG. 1) are substantially spherical, the two ring-shaped rings are not intersected, and the two rings are on each hemisphere when the particles are bisected. It is in a position where it can be bisected so that there is one at a time. Furthermore, the angle (θ) formed by the two cut surfaces cut along each ring is 45 ° or less. FIG. 2 is non-spherical, and the above-mentioned angle (θ) is 45 ° or more.

That is, the characteristic feature of the pre-expanded particles of the present invention is that two band-shaped rings with a large film thickness are formed on the resin film forming the skin layer, the two rings do not cross each other, and two particles are formed. When divided equally, the ring is in a position where it can be divided into two halves so that there is one ring on each hemisphere, and the angle between the two cutting planes cut along the individual rings is 45 ° or less. That is, the shape of the pre-expanded particles is almost spherical.

Is the most characteristic point of the present invention.
In the pre-expanded particles of the present invention, the thickness of the resin film covering the surface of the particles is not uniform, and a band of a thick film is formed in two places on the particle surface in a ring shape with respect to the film thickness other than the two places. As a result, the firmness of the waist that is not possible with conventional foamed particles is secured. That is, it means that the band-shaped ring having a large film thickness plays a role of a rib.

A band-shaped ring (α having a large thickness)₁, Α₂,
α₃, Α_FourThe band width of () is preferably 40 to 500 μm. band
Average film thickness (t₁) And the two strips
Point (β ₁, Β₂) Average film thickness (t₂) And (t₁/
t₂) Is preferably 3 to 20. And the position of the ring
Is a requirement that prescribes, and is different from FIGS.
Two cuts along the ring, as shown in Figure 2.
If the angle between the surfaces is 45 ° or more, the molded foam will be a ring.
The rib effect due to is not exhibited. Also, as shown in FIG.
A straight-lined thick-walled strip with two strip-shaped rings
When placed in connection with the membrane, the particles were not spherical
Therefore, the following effects cannot be exhibited.

Shows the shape of the expanded beads of the present invention. That is, the foamed particles of the present invention have a shape with almost no rounded flat surface portions, and are substantially spherical foamed particles. By making it substantially spherical, good filling properties can be secured in the in-mold fusion molding. In the present invention, the maximum value of the distance from the center of the expanded particles to the surface is A, and the minimum value is B, and the sphericity Y is calculated by taking the ratio.
Pre-expanded particles having a substantially spherical shape with (= A / B) of 1.5 or less are desirable. Moreover, the average particle size is about 1.5 to 8.0 mmφ.
It is desirable that the particles have a uniform particle size.

Since the pre-expanded particles of the present invention have two thick band-shaped rings in the skin layer, the pre-expanded particles have a mold shrinkage ratio with respect to a mold and a molding performance with a small sink mark, a compression recovery rate of 70%,
It becomes possible to produce a molded foam having excellent repeated compression set, dimensional change upon heating, tensile strength and dynamic impact characteristics. These performances show better results as the expansion ratio is higher.

Further, the rings do not cross each other but exist one by one on the hemisphere, and the angle between the two surfaces surrounded by the rings is 45 ° or less, so that the foamed particles having a strong elasticity can be achieved. . Further, since the shape of the pre-expanded particles is almost spherical, the filling property into the mold cavity is improved, the surface appearance of the obtained foamed molded product is excellent, and the compression set is small.

The above-mentioned effect is that when the in-mold fusion molding is performed using the pre-expanded particles of the present invention, the fusion-bonded film formed by fusion of the particle surfaces inside the foam-molded article has a large film thickness. It is presumed that the fusion-bonding film portion is three-dimensionally formed in a mesh shape, and that portion exerts a rib effect and plays a role of structurally reinforcing against mechanical deformation and thermal deformation. This is a surprising fact different from the conventional way of thinking about the skin layer thickness of the pre-expanded particles, that is, if the resin component occupying the skin layer is the same (same average film thickness), it is preferable to have a uniform film thickness. is there.

As described above, by using the pre-expanded particles of the present invention, an expanded molded article having a high degree of physical properties can be easily obtained, and the pre-expanded particles of the present invention are ideal for in-mold fusion molding. . The type of the thermoplastic resin constituting the pre-expanded particles of the present invention is not particularly limited as long as it can be extruded into pellets and can be pre-expanded, and examples thereof include low density polyethylene and linear low density polyethylene. , Medium density polyethylene, high density polyethylene, polypropylene, random copolymer polypropylene with ethylene, random copolymer polypropylene with α-olefin, block copolymer polypropylene with ethylene, α-
Block copolymerized polypropylene with olefin, ethylene-propylene copolymer, ethylene-α-olefin copolymer, ethylene ionomer, ethylene-vinyl acetate copolymer, polybutene-1, poly-4-methylpentene-1, etc. Examples thereof include a polyolefin resin, a polystyrene resin, a polycarbonate resin, a polyester resin, a polyamide resin, and a polyvinyl chloride resin, but a non-crosslinked or slightly crosslinked polyolefin resin is preferable.

The expansion ratio of the pre-expanded particles of the present invention is 5c.
m ³ / g or more and 100 cm ³ / g or less. Next, the method for producing the pre-expanded particles of the present invention will be described.
The main points of the production method of the present invention are: a) Use of true columnar or elliptic columnar particles obtained by extruding in a strand form, and b) Gas permeation coefficient of the above particles to the base resin is 1 × 1.
0 ^-10 cc. (STP). cm / cm ² . sec. cm
Forming expandable resin particles by impregnating a volatile foaming agent of Hg or more, c) End faces of the expandable resin particles (corresponding to the cut surface of the strand) and cylindrical side surfaces (corresponding to the surface of the strand).
The volatile foaming agent present near the ridge, which is the intersection point of the above, is volatilized preferentially to heat-expand the expandable resin particles, and d) Primary expansion particles of 1.5 to 5 cm ³ / g in expansion ratio. Then, (e) Next, a gas pressure is applied to the bubbles of the primary expanded beads to heat and expand the primary expanded beads at a foaming ratio of 3 or more with respect to the expansion ratio.

The two thick band-shaped rings do not cross each other,
The angle between the two faces cut along each ring is 4
In order to produce pre-expanded particles having a temperature of 5 ° or less as shown in FIG. 1, it is first necessary to use the cylindrical or elliptic cylindrical resin particles having the above-mentioned main point a). When non-cylindrical particles or triangular columnar particles are used, foaming is inferior to in-mold fusion molding as shown in FIGS. 2 and 3 and unsuitable for providing a molded foam having high physical properties. It becomes particles.

The cylindrical particles are obtained by heating and kneading a thermoplastic resin with an extruder, extruding it in a strand form from a die, cooling it, and cutting it into substantially cylindrical pellets having a desired diameter and height. . The molecular orientation of the pellet slightly changes depending on the structure of the die, the take-up speed (draft) of the strand, the extrusion rate, the cooling condition of the strand, etc., and as a result, the shape and size of the expanded particles vary. Therefore, it is desirable to obtain an extruded strand under the condition that molecular orientation is not applied as much as possible. Further, the shape is not limited to the columnar shape or the elliptic cylindrical shape, and it is sufficient that the shape is approximately elliptic and rod-shaped.

Even if the above-mentioned main point a) is satisfied, the gas permeation coefficient of the above particles to the base resin is 1 × 10 ^-10 c.
c. (STP). cm / cm ² . sec. Two thick band-shaped rings cannot be obtained without using a volatile foaming agent of cmHg or more. The gas permeability coefficient in this case is AST
It is measured by a gas permeability measuring device (manufactured by Toyo Seiki Seisakusho Co., Ltd.) according to MD 1434-72. As the volatile foaming agent of the above-mentioned main point (b), for example, the density is 0.920.
In the case of polyethylene resin of 0.945 g / cm ³ or ethylene-propylene random copolymer resin, carbon dioxide, propane, butane, pentane, 1,1-difluoroethane (F-152a), monochlorodifluoromethane (F-22), Examples thereof include methylene chloride and ethylene chloride. Among them, carbon dioxide, which is not combustible without the problems of CFC and HCFC regulations, is a desirable foaming agent.

The main point c) is to preferentially volatilize the volatile foaming agent existing in the vicinity of the ridge, which is the intersection of the end surface of the expandable particles and the side surface of the cylinder, in order to obtain two thick band-shaped rings. This phenomenon is caused by satisfying the above-mentioned main points a), b) and the volatilization treatment of the foaming agent described later. That is, the vicinity of the ridges of the expandable particles has a larger surface area per unit resin volume than the surface area of other particles, and the amount of the foaming agent volatilized is large. It is presumed that it is amplified by the use of the agent and the volatilization treatment. In this case, the blowing agent volatilization treatment is
For example, the expandable particles are exposed to the atmosphere in an open state for about 1 to 10 minutes, or the pressure in the system is rapidly reduced to atmospheric pressure at the stage of transferring the expandable particles to a foaming device, and then heat-foaming is performed. By blowing a heated gas below the starting temperature into the container to raise the temperature of the particles, or increasing the "heating rate or steam pressurization time" that indicates the speed until the expanded particles in the foaming device reach the foaming temperature. And foaming. The specific conditions in these methods vary depending on the type of the foaming agent used, the target expansion ratio, the average surface film thickness, etc., but the optimum conditions can be determined by simple preliminary conditions. Further, in the main point d), when the expansion ratio of the primary expanded particles exceeds 5 cm ³ / g, the thick band-shaped ring cannot be obtained because the expansion ratio is high, that is, the amount of the foaming agent impregnated is large. It is considered that it is difficult to increase the "difference in the amount of the foaming agent volatilized between the edge vicinity portion and the other surface portion of the functional particles". Under the foaming conditions in which the primary expansion ratio is less than 1.5 cm ³ / g, the obtained particles lack the bubble volume occupied in the resin component and become particles that are difficult to expand and use later. From the above phenomenon, the primary expansion ratio is 1.5 to 5 cm ³ / g.
It is necessary to control foaming within a narrow range.

The main point e) is that the pre-expanded particles having a thick-walled strip ring and having a substantially spherical shape are to appear.
When the foaming ratio of the primary foamed particles to the expansion ratio is 3 times or more, the drum surface of the drum-shaped particles and both surface portions thereof can be made spherical by the restraining force of the thick band-shaped ring.

As a method for expanding pre-expanded particles having a target expansion ratio by expanding in multiple stages, which is the expansion method of the present invention,
For example, Japanese Examined Patent Publication No. 61-11253, Japanese Patent Publication No. 2-50
It is described in Japanese Patent Application No. 945 and Japanese Patent Application No. 3-174752. These technical thoughts require that pre-expanded particles having a closed cell structure and uniform particle shape are required during in-mold fusion molding (pre-expansion) of pre-expanded particles. It teaches you to avoid foaming. Regarding this point, the conventional foaming method (Experiment No. 1 of Example 1) was used.
6 and No. In contrast to 9), the foaming method of the present invention (Experiment Nos. 1 to 5 and Nos. 12 to 13 of Example 1) can provide pre-expanded particles having a uniform particle shape and rich in closed cell structure. Has been confirmed. However, in the above-mentioned conventional technology, there is no disclosure about the technical content regarding the method for obtaining pre-expanded particles having "a thick band-shaped ring in the skin layer", and the specific effect that the pre-expanded particles exhibit. And it is not possible to produce the pre-expanded particles of the present invention.

Based on the production method of the present invention, it is possible to provide an in-mold expansion-molded product having in-mold fusion molding performance and high physical properties which conventional pre-expanded particles do not have. It is possible to produce pre-expanded particles according to the invention of substantially spherical shape, which have a thick banded ring. Moreover, the manufacturing method of the present invention contributes to resource saving, energy saving, and pollution-free (solving the waste liquid treatment problem) by eliminating the conventional independent spheroidizing step, and the spherical shape is uniform by a simple method. Pre-expanded particles can be obtained, and the technical significance on the industrial world is extremely high.

Evaluation Method The evaluation method used in the present invention is shown below. 1) Foaming ratio Weight (Wg) Volume of known foamed particles and molded foam (V
cm ³ ) is measured by the water immersion method, and the value obtained by dividing the volume by the weight is taken as the foaming ratio (cm ³ / g). 2) Closed cell ratio Measured by an air pycnometer method (manufactured by BECKMAN, model 930) described in ASTM-D2856. (Average of n = 10) 3) Foaming ratio Calculated from the following formula.

The foaming ratio = (Sn-1) / ( S 1 -1) Sn: pre-expansion ratio of the foamed particle _{^{(cm 3 / g) S 1}} : The expansion ratio of the primary foamed particle (cm ³ / g) 4) shape Almost spherical As shown in FIG. 1, it means a shape with a rounded shape and almost no flat portion.

Taiko shape As shown in FIG. 5, the ridges of the resin particles are rounded with a small radius of curvature, but have a flat surface. Non-shape Refers to shapes that do not correspond to the above and. 5) Spheroidization degree It was calculated from the following formula. (Average of n = 50) Spheroidization degree Y = A / B A: Maximum value of distance from center of expanded particle to surface B: Minimum value of distance from center of expanded particle to surface 6) Variation in diameter of pre-expanded particles Randomly sample 200 foam particles,
The maximum diameter x of each particle was measured to a minimum unit of 10 μ with a digital caliper, and calculated and evaluated by the following equation.

[0033]

[Equation 1]

Evaluation scale Division No. Remarks When σ value is 0.2 or less ○ Excellent When σ value exceeds 0.2 × Poor 7) Skin layer thickness Near the center of foamed particles and two meats Electron micrographs (200 times) were taken of particle cut pieces cut along the surface formed by connecting the center of gravity of the thick band ring, and the following film thicknesses were measured. The expanded particles having no thick band-shaped ring were analyzed with respect to particle cut pieces cut in the longitudinal direction passing through substantially the center of the particles.

Thickness t ₁ (μ) of the thick strip portion The maximum film thickness at each of the thick strip portions in FIGS. 1 to 3C was measured, and this operation was carried out on 10 particle cut pieces. It is the value obtained by arithmetically averaging the measured values at the points. Thickness t ₂ (μ) of the central portion of the curve between the rings The thickness of two surface coatings located in the intermediate portion between the two strip-shaped rings in FIGS. 1 to 3 and C was measured, and this operation was performed on a cut piece of 10 particles. This is the value obtained by arithmetically averaging the measured values of these 20 points.

Average Surface Film Thickness For particles having a thick ring of the film layer as shown in FIGS. 1 to 3, the thickness t ₁ is 4 places, the thickness t ₂ is 2 places,
The thickness is measured at 14 places obtained by dividing the other skin curved surface portion into 14 equal parts, and this operation is carried out for cut pieces of 10 particles, and this is a value obtained by arithmetically averaging the measured values. For the expanded beads having no thick band-shaped ring, the thickness of 20 points obtained by dividing the skin curved surface portion into 20 equal parts was measured, and 200
The average value of the points was used.

[0037] which is the ratio of the epidermal membrane thickness ratio t ₁ / t ₂ thickness t ₁ and the ring between the thickness t ₂ of the curved central portion of the thick belt portion. 8) Molding performance 8-1) Degree of fusion 100 × 10 from a portion of the box-formed product having a thickness of 20 mm or more
A 0 mm square test piece was cut out, a cut with a depth of 2 mm was made in the center thereof, the bending molded product was split along the cut, and the material was broken for the total number of particles present in the cut cross section. The percentage of the number of particles was calculated.

Evaluation criteria Division No. Remarks When the material breakage rate is 90% or more ○ (excellent) When the material breakage rate is less than 90% 80% or more △ (Good) When the material breakage rate is less than 80% × (Not good Good) 8-2) Shrinkage rate of mold with respect to mold The shrinkage rate of the foamed molded product with respect to the mold is determined as follows.

Division No. Remarks If less than 2.5% ○ (Excellent) If 2.5% or more and less than 3.0% △ (Good) If 3.0% or more × (Poor) 8 -3) Sink The cavity is about 300 x 300 x 100 mm, and the thickness is about 20 m.
A straight-line ruler was applied to the bottom surface of the m-shaped box-shaped test piece in the diagonal direction, and the maximum distance between the test pieces and the ruler was determined, and evaluated as a percentage with respect to the length of the diagonal line.

Evaluation criteria Division No. Remarks When 0.5% or less ○ (Excellent) When more than 0.5% and less than 2% △ (Good) When 2% or more × (Poor) 8- 4) Fillability By observing a cut surface of 50 mm x 50 mm at any place of the foamed molded article, the following criteria is used depending on how many particle gaps (voids) have a length of 1 mm or more at the longest part. It was judged.

Evaluation criteria Division No. Remarks Less than 2 ○ (excellent) 2 or more and less than 5 △ (good) 5 or more × (poor) 9) In-molded foam 9-1) Surface Appearance The surface appearance was evaluated as follows.

Evaluation Criteria Classification Code Smooth and beautiful with almost no surface irregularities ○ When surface irregularities are conspicuous but somehow manageable △ When surface irregularities are not very flat × 9-2) 70% compression strain recovery rate Thickness Is 40 mm and a 50 mm square plate-shaped test piece is fully compressed in the thickness direction at a compression speed of 10 mm / min to a thickness of 12 mm, and then decompressed at the same speed to obtain a thickness t when the compressive stress becomes zero. Is measured [[40-t) / 40] ×
100 is defined as 70% compression strain recovery rate.

9-3) Compression set Measured according to JIS K-6767 method. The experimental condition was 25% constant compression. 9-4) Repeated compression set Measured according to JIS K-6767 method. The experimental conditions were 25% compression and 80,000 repetitions.

9-5) Change in heating dimension A molded body sample cut out in a 200 mm square shape is heated to 25 ° C.
Let stand for 24 hours, draw a 100 × 100 mm square and a crosshair in the center, and carefully measure the length of each line segment.
Let stand for 96 hours in a constant temperature bath controlled to 00 ° C ± 1 ° C, take it out, and allow it to cool at 25 ° C for 1 hour, measure the dimensions of the marked lines, and measure the rate of change (%) from the original dimensions. The average value was calculated.

9-6) Tensile strength It was measured according to JIS K-6767, Method A. 9-7) Dynamic buffering property It was measured according to JIS Z-0234. The measurement conditions were a cushioning material thickness of 50 mm and a drop height of 60 cm, and the measurement values of the first drop were shown. 10) Comprehensive evaluation The following scale is evaluated as a comprehensive evaluation result.

Evaluation Criteria Division No. Remark All ○ ○ ○ (Quality required by the market) All ○ or △ without × mark △ (Conventional target quality) × 1 or more × (Conventional) quality)

[0047]

EXAMPLES The present invention will be described below with reference to examples.

[0048]

[Example 1, Comparative Example 1]Experiment No. 1 (invention) Non-crosslinked ethylene-propylene random copolymer resin [UNI
On Polymer FM821, density 0.90 g / c
m³, MFR 7g / 10min (230 ℃, 2.16k
g), ethylene content 2.7% by weight] 90 mm extruder
With a die nozzle diameter of 1.0 and a die hole number of 200
Polymer at an extrusion rate of 200 kg / Hr from the die
The molecular orientation is less likely to occur and the strand can be pulled stably.
At a minimum take-off speed of 18 m / min, cool and cool
Cut, elliptic cylinder with a length of 1.5 mm and an average diameter of 1.2 mmφ
Shaped particles were produced. Store the resin particles in a pressure container
As a foaming agent, the gas permeability coefficient is 9 × 10^-Tencc.
(STP). cm / cm²． sec. Two indicating cmHg
Injection of carbon oxide (gas) pressure 30kg / cm²G, warm
Carbon dioxide in the resin particles over a period of 4 hours at a temperature of 8 ° C
Was impregnated. Next, leave the expandable resin particles open for 2 minutes.
After exposing it to the atmosphere with
The temperature inside the chamber from 80 ° C to 130 ° C over 25 seconds.
While heating and maintaining that temperature, steam heating is started for 10 seconds.
It foamed and obtained the primary expanded particle. The expansion ratio of this expanded particle is
3.0 cm³/ G. The shape of the obtained expanded particles is
It is a drum shape, and the thickness of the surface coating near the edges of both ends is thick.
It was. The primary expanded particles are stored in a pressure heating device
8kg / cm using high pressure air at a temperature of 80 ℃²G
Up to 1 hour and hold that pressure for another 4 hours
As a result, the internal pressure of the bubbles of the primary expanded particles was increased and the expandability was imparted.
Next, the expandable primary expanded particles were stored in a foaming device and stored in a tank.
Raise the temperature from 80 ° C to 130 ° C over 10 seconds, and then
While maintaining that temperature, foam with steam heating for 8 seconds,
Next expanded particles were obtained. The secondary expanded particles have an expansion ratio of 6.
0 cm³/ G, which had a slightly drum-like shape. Further secondary
Expand the foam particles under the same conditions as those for obtaining the secondary expanded particles.
Tensioning and heat-foaming treatments were carried out to produce tertiary expanded particles (preliminary
Foam particles) were obtained. Shape of pre-expanded particles obtained in this experiment
FIG. 1 shows a schematic diagram of the membrane structure of the cortical and epidermal layers. According to FIG.
Then, the pre-expanded particles of the present invention are substantially spherical, and the surface is
The resin film (so-called skin layer) that covers it is a thick band
Two rings, not intersecting each other, surrounded by individual rings
It can be seen that the two surfaces are located almost parallel to each other.
ItExperiment No. 2 (invention) Experiment No. Change 130 seconds heating time of 10 seconds to 5 seconds
Furthermore, the expansion ratio is 1.5 cm³/ G of primary expanded particles
Experiment No. Additional pressure of air into the bubbles of primary expanded particles
Power, time 8kg / cm²G × 4 hours 30kg / cm²
Change to G x 15 hours and expand ratio 6 cm³/ G, almost
Experiment No. except that secondary expanded particles having a spherical shape were obtained. Same as 1
In this way, pre-expanded particles were obtained.Experiment No. 3 (invention) Experiment No. The volatile blowing agent and carbon dioxide used in 1
Nochlorodifluoromethane (F-22, gas permeability coefficient
1.1 x 10^-Tencc. (STP). cm / cm ²・ S
ec. cmHg) 60 ° C, 24 kg / cm²3 in G
Change to liquid impregnation for 0 minutes, foaming ratio 5 cm³/ G primary
Expanded particles were obtained, and the experiment No. 1 primary expanded particles into the bubble
Air pressure is 14kg / cm²Change to G and double foam
Rate 15 cm ³/ G of pre-expanded particles that are nearly spherical
Experiment No. except that obtained by step foaming. Obtained as in 1.Experiment No. 4 (invention) Experiment No. 1 elliptical columnar particles were replaced by true columnar particles (in the cooling water tank
Was obtained by changing the guide roll position of the
Change the temperature rise (steam pressure) time from 25 seconds to 15 seconds,
Experiment No. The same expansion ratio and shape as those of No. 1
Experiment No. Additional pressure of air into the bubbles of primary expanded particles
Force 8kg / cm²G is 10 kg / cm²Change to G,
Foaming ratio 7.2 cm³Secondary foamed granules of approximately spherical shape / g
Experiment No. except that I got a baby Pre-expanded particles in the same manner as 1
GotExperiment No. 5 (invention) Experiment No. The elliptic cylindrical particles of No. 1 are perfectly cylindrical particles (cooling water tank
Volatile foaming, which was obtained by changing the position of the guide roll inside
N-butane (gas permeation coefficient 12 x 10
^-Tencc. (STP). cm / cm²-Sec. cmH
g), and the experiment No. Same expansion ratio and shape as 1
After obtaining the primary expanded particles, the experiment No. 1 primary foam particles inside the bubbles
8kg / cm additional pressure to the air²G is 6 kg / cm²G
Change to, foaming ratio 5cm³/ G drum-shaped secondary
Experiment No. except that foamed particles were obtained. Spare in the same way as 1.
Foamed particles were obtained.Experiment No. 6 (conventional product) Experiment No. 100 parts by weight of resin particles 1 and n as a foaming agent
20 parts by weight of butane, 450 parts by weight of water, first as dispersant
Accommodates 3.0 parts by weight of calcium triphosphate in a pressure container
Then, raise the temperature to 130 ° C under stirring and hold for 1 hour to
After impregnating with the foaming agent, the internal pressure of the container is 10 kg / c for 20 seconds.
m²G, then 33 kg / cm²Add with nitrogen gas of G
While pressing, one end of the container is released and released into the atmosphere.
Magnification 15 cm³/ G of pre-expanded particles were obtained. Obtained
Fig. 4 shows a schematic diagram of the shape of the expanded beads and the membrane structure of the skin layer.
Show.Experiment No. 7 (Comparative example) Experiment No. The volatile blowing agent and carbon dioxide used in 1
Nochlorodifluoromethane (F-22), 60 ℃,
24 kg / cm²Liquid impregnation with G for 30 minutes,
Change the temperature rise (steam pressure) time from 25 seconds to 10 seconds
Foaming ratio 6cm³/ G primary foamed particles are obtained, and two-stage generation
Foaming expansion ratio 15 cm³/ G of pre-expanded particles was obtained.
Outside is the experiment No. Obtained as in 1.Experiment No. 8 (Comparative example) Experiment No. The volatile blowing agent and carbon dioxide used in 1
Nochlorodifluoroethane (F-142b, gas permeation agent)
Number 2 x 10^-Tencc. (STP). cm / cm ²・ Se
c. cmHg) and impregnated at 45 ° C for 5 hours.
Test No. Pre-expanded particles were obtained in the same manner as in 1.Experiment No. 9 (conventional product) Experiment No. 100 parts by weight of resin particles of 1 and 450 parts by weight of water
Parts, 3.0 parts by weight of tricalcium phosphate as a dispersant
Store in a pressure-resistant container, raise the temperature to 200 ° C with stirring and for 1 hour.
After holding, it was cooled to obtain substantially spherical resin particles. this
Experiment No. 3 except that resin particles having a substantially spherical shape were used.
Do the same as 1 and expand ratio 15 cm³/ G, almost a sphere
Pre-expanded particles in the form of particles were obtained.Experiment No. 10 (comparative example) Experiment No. The elliptic cylindrical particles of No. 1 are cylindrical curved particles (extrusion amount)
Was changed to 300 kg / Hr,
The melt fracture phenomenon occurred. This strand
Experiment No., except that it was obtained by cutting). Same as 1
To obtain pre-expanded particles.Experiment No. 11 (comparative example) Experiment No. 1 elliptical columnar particle is a triangular column (
The nozzle has a triangular cross section.
Experiment No. Same as 1
To obtain pre-expanded particles.

The shape of the pre-expanded particles and the film structure of the skin layer obtained in these experiments are shown in Experiment No. 2 to No. The product of the present invention of No. 5 has the same shape as that of FIG.
7 6 cm primary expansion ratio exceeds 5 cm ³ / g of ³ / g
The thick-walled band-shaped ring could not appear in the primary expanded particles of Experiment No. 8 has a gas permeability coefficient of 1 × 10 ⁻¹⁰ cc. (ST
P). cm / cm ² · sec. With the use of the foaming agent of less than cmHg, the thick band-shaped ring could not be revealed even if other conditions were satisfied. Experiment No. No. 10 cylindrical resin particles, Experiment No. 2 and 3 are schematic diagrams of the shape of the pre-expanded particles obtained by using 11 triangular prismatic resin particles and the film structure of the skin layer, respectively. FIGS. 2 and 3 show that a band-shaped ring having a large film thickness is unevenly distributed on one side on the curved surface of the particle, and the surfaces surrounded by the respective rings are not parallel (θ ₁ = 80
°) A non-spherical structure is shown in which three strip-shaped plane portions having a large film thickness are provided, the strip-shaped plane portions are intersected with and the strip-shaped rings having a thick film thickness are arranged at both ends thereof. It can be seen that even in the case of primary expanded particles having two thick band-shaped rings, substantially spherical pre-expanded particles cannot be obtained unless the expanded particles have a expansion ratio of 3 times or more with respect to the primary expanded particles.

The above experiment No. 1-No. The structure index of pre-expanded particles of No. 11 was evaluated by the method described in the text, and Table 1
It was shown to.

[0051]

[Table 1]

According to Table 1, the foaming agent on the surface of the particles is prioritized.
Volatilized conditions, such as heating foaming temperature rise (steam
The heating method in which the pressure) time is lengthened, the surface film thickness ratio (t
₁/ T ₂) Is a large value. Also conventional foaming
Experiment No. which is a method. With 6, the variation in particle size is large.
I understand that it is a problem. Then, in the above experiment No. 1 to N
o. 11 pre-expanded particles were used, and the internal pressure of each particle was
1.0 kg / cm²Empty to be (gauge pressure)
The air is pressed in, and the particles immediately get 305 × 30.
Inside the mold to form a box mold of 5 × 103 mm and thickness 21 mm
Full in a mold with internal dimensions of 305 x 305 x 52 mm.
Then, it was heated and foamed in a mold to obtain a molded foam. This place
Steam is used for heating for about 15 seconds, 2.0 kg /
cm²Pre-heating (gauge pressure) and 3.3 kg / cm²
(Gauge pressure), heating for 15 seconds, and after cooling
I took it out. The molded product taken out is aged in a room at 90 ° C for 8 hours.
Let This molding performance and the physical properties of the foamed molded product obtained are
Evaluation was carried out by the method described in the sentence, and the results are summarized in Table 2.

[0053]

[Table 2]

The 70% compression strain recovery rate was judged as a value of 18% or less as ◯, a value of more than 18% and 22% or less as Δ, and a value of more than 21% as ×. The compression set was 5%. The following values are judged as ◯, values exceeding 5% and 8% or less are evaluated as Δ, and values exceeding 8% are judged as ×, and the repeated compression set is ◯ for values of 6% or less and 10% or less for more than 6%. The value is judged as △, the value exceeding 10% is judged as ×, and the dimensional change at 100 ° C. is ○, the value less than 3.0% is ○, and the value of 3.0% or more and less than 5.0% is Δ,
A value of 5.0% or more is judged as ×, the tensile strength is 7 kg
/ Cm ² or more is ○, 6 kg / cm ² or more 7 kg / c
A value of less than m ² is determined as Δ, and a value of less than 6 kg / cm ² is determined as ×, and the dynamic deceleration characteristic has a maximum deceleration (G) of 34.
Values less than G are ○, values less than 37G and less than 37G are △, 37
The value of G or more was determined as x. Further, an effort was made to make the expansion ratio of the foamed molded product equal to the same level of 23 cm ³ / g, and the evaluation of the physical properties was evaluated.

According to Table 2, the pre-expanded particles of the present invention (Experiment No. 1 to No. 5) are comparative products (Experiment No. 7 to 8,
No. 10-11) and conventional products (Experiment No. 6 and No. 6).
9) which is superior in in-mold fusion molding performance (fusion degree, mold dimensional shrinkage ratio, sink mark, filling property) to those of 9), and the surface appearance of the foamed molded product obtained by in-mold molding, 70 % Compressive strain recovery rate,
It can be seen that various physical properties such as compression set, repeated compression set, 100 ° C. heating dimensional change, tensile strength, and dynamic buffering properties show high values with quality. This result is approximately spherical, which is a characteristic of the pre-expanded particles of the present invention,
There are two strip-shaped rings with a large thickness on the resin film that covers the surface.
The two surfaces surrounded by individual rings do not intersect with each other, and the angle between them is 45 degrees or less. Therefore, a thick skin is formed inside the foamed molded product obtained by fusion-molding the two surfaces. It is shown that the fusion-bonded part of 3) is three-dimensionally shaped like a mesh and exhibits a rib effect.

[0056]

Example 2 and Comparative Example 2 The experiment here shows that pre-expanded particles having a high expansion ratio and having a high closed cell ratio can be obtained by the production method of the present invention. . The expanded particles used in the experiment are the experiment No. 1 of Example 1 and Comparative Example 1. 1, No. 3, No. 5, No. 6, No. It is the expanded particles (expansion ratio 15 cm ³ / g) obtained in No. 9.
Air was added and adjusted so that the foaming ratio became 2.07 times in each bubble, and the experiment No. Heat-foaming was performed under the same conditions as the secondary foaming conditions of No. 1 to obtain pre-expanded particles having an expansion ratio of 30 cm ³ / g. This is No. 12, No. 13, N
o. 14, No. 15, No. It was set to 16.

The structural index of the obtained pre-expanded particles was evaluated and is shown in Table 3.

[0058]

[Table 3]

According to Table 3, the product of the present invention (Experiment No. 12)
~ No. 14) is a conventional product (Experiment No. 15, No. 1)
Compared with 6), pre-expanded particles having a higher closed cell rate were obtained, and it is surprisingly found that the expansion capacity is equal to or higher than that of the conventional product. The above experiment No. 12-No. 16 pre-expanded particles (expansion ratio 30 cm ³ / g) were used in Example 1 and Comparative Example 1.
In-mold molding was performed by the method described, the molding performance and the physical properties of the foamed molded product obtained were evaluated, and the results are summarized in Table 4.

[0060]

[Table 4]

The 70% compression set recovery rate is determined as ◯ for values of 10% or less, Δ for values of 10% or more and 13% or less, and x for values of 13% or more. The compression set is 8%. The following values are judged as ◯, values exceeding 8% and 10% or less are judged as Δ, values exceeding 10% are judged as x, and the repeated compression set is ◯ for values of 6% or less and 8% or less for 6% or more. The value is judged as △, and the value exceeding 8% is judged as ×. For the 100 ° C heating dimension change, the value of 8% or less is judged as ○, the value exceeding 8% and 12% or less is judged as Δ, and the value exceeding 12% is judged as ×. , tensile strength, maximum determination, the dynamic cushioning properties of 3 kg / cm ² or more values ○, 2 kg / cm ² or more at 3 kg / cm ² less than the value △, the value of less than 2 kg / cm ² as × If the deceleration (G) is 36 G or less, the value is ○,
A value exceeding 36 G and 38 G or less was judged as Δ, and a value exceeding 38 G was judged as x. The expansion ratio of the foamed molded product is 45c.
Efforts were made to make the same level of m ³ / g.

According to Table 4, even in the case of pre-expanded particles having a high expansion ratio, the product of the present invention is superior in the in-mold molding performance to the conventional product, and has a high expansion ratio (45 cm ³ / g) obtained by in-mold molding. It can be seen that the physical properties of the foamed molded product are significantly different from the conventional products and have high quality.

[0063]

Example 3 This experiment is intended to show that the foamed sheet of the present invention can be applied to any of the target "thermoplastic resins". Experiment No. 17 High-density polyethylene resin [Suntech H manufactured by Asahi Kasei Corporation
D, B770, density 0.955 g / cm ³ , MI 0.2
g / 10 minutes (190 ° C., 2.16 kg)]. 1 carbon dioxide was added to n-butane (gas permeation coefficient 5 × 10 ⁻¹⁰ cc. (STP) .cm / cm ²
-Sec. cmHg), foaming temperature 130 ° C to 126 ° C
Experiment No. except that each was changed to The same procedure as in 1 was carried out, and the primary expansion particles had an expansion ratio of 3.0 cm ³ / g, the secondary expansion particles had an expansion ratio of 6.0 cm ³ / g, and the expansion ratio 1
Pre-expanded particles of 5 cm ³ / g were obtained. Experiment No. 18 Low-density polyethylene resin [Suntech L manufactured by Asahi Kasei Corporation
D, F2130, density 0.921 g / cm ³ , MI3.
2 g / 10 minutes (190 ° C., 2.16 kg)] 0.15 parts by weight of dicumyl peroxide as a cross-linking agent was added to 100 parts by weight, and extrusion lightly cross-linked modified low density polyethylene resin (MI 0.5 g / 10 Min., Gel fraction 10% (boiling toluene × 8 hours extraction), Experiment No. 1 of Example 1
Experiment N except that the foaming temperature of 130 ℃ was changed to 104 ℃
o. The same procedure as in Example 1 was performed to obtain preliminary (tertiary) expanded particles having an expansion ratio of 15 cm ³ / g. In addition, LD of carbon dioxide
Gas permeation coefficient for PE (F2130) resin is 1.4
× 10 ^-9 cc. (STP). cm / cm ² · sec. c
It is the value of mHg. Experiment No. 19 polystyrene resin [Asahi Kasei Corp., GP680, density 1.05 g / cm ³ , MFR 7.5 g / 10 min (200
C., 5 kg)]. Change the foaming temperature 130 ° C of 1 to 100 ° C and expand the ratio of foam 3cm ³
/ G of primary expanded particles were obtained, and the experiment No. 1 Additional conditions for adding air into the bubbles of the primary expanded particles 80 ° C. × 8 kg / cm ² G 6
Change to 0 ℃ × 3kg / cm ² G and expand ratio 15cm
Pre-expanded particles of ³ / g were obtained by double-stage expansion. The gas permeability coefficient of carbon dioxide to PS (GP680) resin is 1.0 × 10 ^-9 cc. (STP). cm / cm ² · se
c. The value is cmHg.

These experiment Nos. The pre-expanded particles obtained in Nos. 17 to 19 were evaluated for the closed cell ratio by the method described in the text, and the values were 95%, 96%, and 100%. When the skin layer film structure of the expanded particles was observed in the same manner as in Example 1 and Comparative Example 1, two strip-shaped rings with a large film thickness, which were almost the same as in FIG. It was almost spherical in shape, with the two enclosed surfaces being located substantially parallel to each other.

[0065]

EFFECTS OF THE INVENTION The pre-expanded particles of the present invention, having the above-mentioned constitution, are excellent in in-mold fusion molding performance (fusion degree, mold dimension shrinkage ratio, sink mark, filling property), and surface appearance, 70
% Compression strain recovery rate, compression set, repeated compression set, 1
It is possible to easily obtain a molded foam having excellent mechanical and thermal characteristics such as dimensional change by heating at 00 ° C. and tensile strength and dynamic buffering characteristics. And in the fields that could not be used without conventional low-foam molded articles, such as structural materials and cushioning materials that have particularly large stresses on these characteristics, such as automobile seats and packaging cushioning materials when transporting light electrical equipment. Can be used as a high-magnification foam or a thin foam, and it is possible to reduce the weight and volume, and in addition, the physical properties of molded foam have been inferior. Can be used for many purposes.

Also as a manufacturing method, it has succeeded in obtaining substantially spherical pre-expanded particles having a uniform particle size without an independent spheroidizing step, which has heretofore been impossible to realize.
As a result, it contributes to resource saving, energy saving, and pollution-free, and its technical significance is extremely high.

[Brief description of drawings]

FIG. 1 is a front view (A), a side view (B), and a central sectional view (C) of pre-expanded particles of the present invention.

FIG. 2 is a front view (A), a side view (B) and a central sectional view (C) of particles obtained by pre-expanding cylindrical curved resin particles by the method of the present invention.

FIG. 3 is a front view (A), a side view (B), and a central cross-sectional view (C) of particles obtained by pre-expanding triangular columnar resin particles by the method of the present invention.

FIG. 4 is a front view (A), a side view (B), a central cross-sectional view (C) of particles obtained by pre-expanding particles obtained by spheroidizing elliptical columnar particles by a hot water suspension system at high temperature and high pressure by the method of the present invention. ).

FIG. 5 is a front view (A), a side view (B), and a central cross-sectional view (C) of particles obtained by pre-expanding elliptic columnar resin particles by a known method.

[Explanation of symbols]

U Resin film R ₁ , R ₂ Thick strip ring R ₂ , R ₃ , R ₄ Thick strip film S Bubble θ Angle between two cut surfaces cut along the ring

Claims (2)

[Claims] 1. A substantially spherical pre-expanded particle made of a thermoplastic resin, wherein a resin film covering the surface of the particle is formed with two band-shaped rings having a large film thickness. Two rings that do not intersect each other are located at two halves so that when the particles are bisected, they will be on each hemisphere, one on each hemisphere, and two halves cut along each ring. Pre-expanded particles for in-mold fusion molding, characterized in that the angle formed by the surfaces is 45 ° or less. 2. A method for producing pre-expanded particles comprising a thermoplastic resin, wherein a thermoplastic resin in a molten state is extruded from an extruder into a strand shape through a nozzle and cut into a certain length to obtain a cylinder or an elliptic cylinder. The particles have a gas permeability coefficient of 1 × 10 ⁻¹⁰ cc. (ST
P). cm / cm ² . sec. Near a ridge that is an intersection of the end surface (corresponding to the above-mentioned strand cut surface) and the cylindrical side surface (corresponding to the above-mentioned strand surface) of the foamable resin particle by forming a foamable resin particle by impregnating with a volatile foaming agent of cmHg or more. Part of the volatile foaming agent is volatilized preferentially to heat and foam the expandable resin particles, and the expansion ratio is 1.5 to 5 cm.
^{It is characterized in that 3} / g of primary expanded particles are formed, then gas pressure is applied to the bubbles of the primary expanded particles, and this is further expanded by heating at a foaming ratio of 3 times or more with respect to the expansion ratio of the primary expanded particles. A method for producing pre-expanded particles for in-mold fusion molding.