JP4316258B2 - Plastic lightweight molded body and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is used for heat insulation / cooling containers used indoors and outdoors, oil and water tanks, floaters, etc., which is excellent in durability, light weight and rigidity, heat insulation, cushioning, and levitation plastic lightweight The present invention relates to a molded body and a manufacturing method thereof.
[0002]
[Prior art]
Conventionally, a heat insulating / cold container, a tank for oil supply / water supply, a floater, etc. are composed of a skin portion and an inner layer portion, and have been made by combining a metal of the skin portion and a plastic foam of the inner layer portion. In recent years, however, the skin has also been made of plastic materials for the purpose of weight reduction and cost reduction.
[0003]
As shown in FIG. 1, a conventional plastic lightweight molded body 10 includes an outer skin portion 2 and a highly foamed inner layer portion 3. In order to manufacture such a plastic lightweight molded body 10, the skin part is molded by vacuum molding or injection molding, and the plastic part of the inner layer part is combined with this, or the skin part is molded by blow molding or rotational molding. A method of producing an inner layer portion by injecting a foam of a two-component reaction type such as urethane foam into the inside and foaming is used. However, in the method in which the skin portion and the inner layer portion are separately produced as described above and combined later, there is a problem in the adhesion between the skin portion and the foamed portion of the inner layer, and the molded body itself is difficult to obtain rigidity. There is a problem.
[0004]
Therefore, in order to solve these problems, a method is adopted in which a reinforcing body is provided in advance on the skin portion and the inner layer portion by blow molding or rotational molding, and foam is injected. However, in this case, there is a problem that the foam cannot sufficiently fill the inner layer portion, and a void portion is partially generated, resulting in a decrease in strength, and man-hours are required and the cost is increased.
[0005]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a light weight and rigid plastic lightweight molded body having no voids and a method for producing the same.
[0006]
[Means for Solving the Problems]
A plastic lightweight molded body according to an aspect of the present invention is a plastic lightweight molded body including a skin portion and an inner layer portion, wherein the inner layer portion includes a non-foamed portion and a foamed portion, and the non-foamed portion is a gel component. The ratio is 0.5 to 15%, and the non-foamed part is mixed in the foamed part in a mesh form or a particulate form.
[0007]
The method for producing a plastic lightweight molded body according to another aspect of the present invention includes a plastic particle having a particle size of 1.5 mm or less and a plastic particle having a gel fraction of 0.5 to 15% and a particle size of 3 mm or more. The foamable resin particles having a particle diameter of 3 mm or more are simultaneously charged into a mold and heated while rotating the mold. The MFR (melt flow rate) of the plastic particles having a particle size of 3 mm or more is preferably in the range of 0.1 g / 10 min to 5 g / 10 min.
[0008]
The plastic lightweight molded body according to a preferred embodiment of the present invention comprises a skin portion and an inner layer portion, the inner layer portion comprises a non-foamed portion and a foamed portion, and the non-foamed portion and the foamed portion have a sea-island structure. Features.
[0009]
A method for producing a plastic lightweight molded body according to a preferred embodiment of the present invention comprises a foaming property in which a plastic particle having a particle size of 1.5 mm or less and a surface coated with a non-foaming resin having a gel fraction of 0.5 to 15%. The resin particles are simultaneously charged into a mold and heated while rotating the mold. The MFR of the non-foamable resin is preferably in the range of 0.1 g / 10 min to 5 g / 10 min. The average particle diameter of the expandable resin particles whose surfaces are coated with the non-expandable resin is 4 to 10 mm, and the thickness of the non-expandable resin layer covering the expandable resin particles is 0.5 to 5 mm Most preferably it is.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to FIGS.
[0011]
FIG. 2 is a view showing the structure of a plastic lightweight molded body according to the first embodiment of the present invention. As shown in FIG. 2, the plastic lightweight molded body 20 is composed of an outer skin portion 2 and an inner layer portion 3, the outer skin portion 2 and the inner layer portion 3 are fused, and the inner layer portion 3 is further bonded to the foamed portion 5. The non-foamed part 4 has a structure in which the non-foamed part 4 is mixed in a form close to a network structure. Since such a mesh-like non-foamed portion 4 functions as a reinforcing body, it has a strength superior to that of the conventional art. Note that the non-foamed portion 4 does not necessarily have a network structure, and may be present in the foamed portion 5 in a granular form. Further, in the present embodiment, the non-foamed portion 4 only needs to be able to function as a reinforcing body. Therefore, it is not required that the non-foamed portion 4 be foamed at all, and is regarded as substantially non-foamed compared to the foamed portion 5. If possible, it may be a low-foamed portion that is slightly foamed. On the other hand, the foamed portion 5 means a highly foamed highly foamed portion.
[0012]
Here, the relationship between the skin portion 2 and the inner layer portion 3 preferably satisfies A1 ≧ 1 mm and A2 ≧ 4A1 when the thickness of the skin portion 2 is A1 and the thickness of the inner layer portion 3 is A2. When A2 is smaller than 4A1, the bending strength is decreased.
[0013]
Further, when the density of the skin portion 2 is D1 and the density of the inner layer portion 3 is D2, it is preferable that D1 / D2 ≧ 2 is satisfied. When D1 / D2 is less than 2, heat insulation may be lost. Further, in the inner layer portion 3, the density of the foamed portion 5 is preferably 0.2 g / cm ³ or less, and the density of the non-foamed portion 4 is preferably 0.25 g / cm ³ or more.
[0014]
Furthermore, in the inner layer portion 3, it is preferable that the weight W1 of the non-foamed portion 4 and the weight W2 of the foamed portion 5 satisfy W1 / W2 ≧ 3. If W1 / W2 is less than 3, voids may occur in the inner layer portion 3.
[0015]
The manufacturing method of the lightweight plastic molded body of the present embodiment is such that three components of fine plastic particles, large plastic particles, and expandable resin particles are simultaneously put into a mold and rotated so as not to give an excessive centrifugal force to this material. It is heated and molded from the outside.
[0016]
Here, “fine plastic particles” are materials for the skin portion 2, “large plastic particles” are materials for the non-foamed portion 4 that function as a reinforcing body, and “foamable resin particles” are materials for the foamed portion 5. .
[0017]
First, fine plastic particles melt and adhere to the inner surface of the mold to form the skin portion 2. On top of that, expandable resin particles and large plastic particles adhere. Next, the foamable resin particles foam and fill the internal voids to form the foamed portion 5. At this time, the melt of large plastic particles adhering to the expandable resin particles is stretched along with the expansion of the expandable resin particles and fills the inside of the mold. And the structure close | similar to the mesh of a net | network is formed by extending | stretching, the non-foaming part 4 as a reinforcement is formed, and a rigid plastic molding is formed. The non-foamed portion 4 does not necessarily have a network structure, and may be mixed and present in the foamed portion 5 in a granular form.
[0018]
The fine plastic particles used as the skin material in the present invention are preferably fine particles having an average particle size of 1.5 mm or less, and more preferably plastic powder having an average particle size of 100 μm or less. The fine plastic particles are preferably fine particles or powder of a thermoplastic resin such as polyolefin resin, nylon, ABS, or polycarbonate. It is preferable to use a polyolefin resin having low hygroscopicity, more preferably a polyethylene resin, and most preferably a high-density polyethylene powder.
[0019]
The expandable resin particles used in the present invention are preferably crosslinked expandable granules. Here, the cross-linked foamable granular material is a plastic containing a cross-linking agent and a foaming agent, or a plastic containing a foaming agent that has been subjected to radiation cross-linking, and the resin expands into a foam when heated to a melting point or a softening temperature or higher. It is a granular material.
[0020]
The size of the expandable resin particles used in the present embodiment is preferably a size that does not adversely affect the molding of the skin portion 2 and that has an average particle size of 3 mm or more. More preferably, a material of 5 mm or more and 10 mm or less is used. Although it is appropriately selected depending on the size of the molded body, in general, when the average particle diameter exceeds 10 mm, not only the molding time becomes longer but also voids are easily generated inside, and the rigidity and strength of the obtained molded body are reduced. This is not preferable.
[0021]
Large plastic particles used as a reinforcing material in the present embodiment are preferred because those having a melt index (MFR) in the range of 0.1 g / 10 min to 5 g / 10 min tend to have a network structure. The average particle size is preferably 3 mm or more larger than the powder used for the skin portion, and is preferably about the same as or smaller than the particle size of the expandable resin particles. Although it is appropriately selected depending on the size of the molded body, a size within the range of 3 mm to 10 mm is preferable. In general, when the average particle diameter exceeds 10 mm, the ratio of contact with the skin portion 2 of the non-foamed portion 4 decreases, and the strength and rigidity do not increase.
[0022]
Large plastic particles are required to have a gel fraction of 0.5 to 15%. When the gel fraction is within this range, the foamed resin particles can be pressed to suppress the foaming gas pressure to increase the thickness of the mesh portion. Can be obtained. When the gel fraction is less than 0.5%, the foaming gas pressure is too strong and voids may be formed. When the gel fraction exceeds 15%, foaming may not be sufficient.
[0023]
The gel fraction in the present invention is measured as follows.
(1) The weight-measured base film is wrapped in a stainless steel mesh (No. 400, manufactured by Nippon Wire Mesh Industry, Inc., weight measurement completed) and immersed in a 120 ° C. xylene solution for 24 hours.
(2) Leave at room temperature in a well-ventilated area for 2 hours.
(3) After vacuum drying at 10 Pa (7.5 × 10 ⁻² torr) or less at 80 ° C. for 16 hours, the total weight of the remaining base film and wire mesh is measured.
The value calculated by the following formula is defined as the gel fraction.
Gel fraction (%) = {(total weight of base film and wire mesh after immersion in xylene) − (weight of wire mesh)} ÷ (weight of base film before immersion in xylene) × 100.
[0024]
As the large plastic particles used in the present embodiment, what is so-called chemically cross-linked by using a peroxide, what has been cross-linked by introducing a functional group chemically (example of which is silane-modified), Examples thereof include those crosslinked by irradiation with radiation, and these techniques can also be combined. In addition, a recycled material of crosslinked and foamed resin can be used. In that case, a material with a reduced volume of crosslinked foamed polyethylene can be used, but such a material is preferably blended at about 1/2 or less of the plastic granular material.
[0025]
When high density polyethylene powder is used as the material for the skin part, the material for the inner layer part is cross-linked foaming polyethylene particles as foaming resin particles, and non-foaming or low foaming polyethylene particles as large plastic particles. Is preferably used.
[0026]
FIG. 3 is a view showing the structure of a plastic lightweight molded body according to the second embodiment of the present invention. As shown in FIG. 3, the plastic lightweight molded body 30 is composed of a skin portion 2 and an inner layer portion 3, the skin portion 2 and the inner layer portion 3 are fused, and the inner layer portion 3 is a non-foamed portion 4. And a sea-island structure with a foamed portion 5. Since such a sea-like non-foamed portion 4 works as a reinforcing body, it has a strength superior to that of the prior art. Here, the relationship between the skin portion 2 and the inner layer portion 3 is the same as that described above in the first embodiment.
[0027]
The method for producing a plastic lightweight molded body according to the present embodiment is such that fine plastic particles and expandable resin particles whose surfaces are coated with a non-foamed resin are simultaneously put into a mold, and an excessive centrifugal force is applied to the material. It is heated and molded from the outside while rotating so that there is no. By using such a method, a molded article having excellent strength can be easily obtained without using large plastic particles as the reinforcing material required in the first embodiment, and thus it is more preferable.
[0028]
First, fine plastic powder melts and adheres to the inner surface of the mold to form the skin portion 2. The expandable resin particles are then expanded to fill the internal voids. At this time, the non-foamed layer covered with the expandable resin particles is also expanded at the same time and fused with the skin portion 2 to form a non-foamed portion having a sea structure. 5 is formed. Since this becomes a reinforcing body, a rigid plastic molded body is formed.
[0029]
The skin material and the expandable resin particle material used in the present embodiment are the same as those in the first embodiment described above.
[0030]
The average particle size of the expandable resin particles coated with the non-expandable resin used in the present embodiment is preferably in the range of 4 mm to 10 mm. If the average particle size is smaller than 4 mm, the foamable resin particles enter the skin portion 2 during the formation of the skin portion 2 during molding, and the skin portion 2 is not uniformly formed. For this reason, the thickness of the skin portion 2 of the molded product is difficult to be uniform, the appearance is poor, and the rigidity is likely to be lowered. On the other hand, if the thickness is 10 mm or more, the movement inside the mold is deteriorated during molding, and a gap is likely to be partially generated between the skin portion 2 and the foamed portion 5, which causes a decrease in strength. Most preferably, the average particle size is in the range of 5 mm to 8 mm.
[0031]
The non-foamable resin that covers the surface of the foamable resin particles used in the present embodiment is appropriately selected from those having a gel fraction of 0.5 to 15%, but is selected from the same resins as the foamable resin. Preferably. In this case, the MFR of the non-foamable resin is preferably within the range of 0.1 g / 10 min to 5 g / 10 min. The softening temperature of the foamable resin is preferably lower than the temperature at which the foamable resin particles foam. The thickness of the non-foamed layer covering the expandable resin particles is preferably 0.5 to 5 mm.
[0032]
In addition, when using a high density polyethylene powder as a material of an outer skin part, it is preferable to use what coated the cross-linked foaming polyethylene particle with the same polyethylene resin as a plastic material used for an inner layer.
[0033]
As described above, according to the method of the present invention, by simultaneously molding the three components, the skin portion 2, the reinforcing material (non-foamed portion 4), and the foamed portion 5 are well fused with each other. It is possible to prevent the formation of voids, and to obtain a plastic lightweight molded body having excellent heat insulation and strength. Even if it is used outdoors for a long period of time, there is little deterioration and dimensional change. Further, in the conventional manufacturing method, the skin portion and the inner layer portion are separately manufactured, or the step of providing the reinforcing body is separately provided, which requires man-hours and increases the cost. However, in the method of the present invention, the skin portion, the foamed portion of the inner layer, and the non-foamed portion as the reinforcing body can be simultaneously molded, and therefore, it can be produced at a low cost.
[0034]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to this.
[0035]
<Example 1>
High-density polyethylene powder having a particle size of 500 μm and a density of 0.96 g / cm ³ as the skin material, and dicumyl as 100 parts by weight of low-density polyethylene having a density of 0.92 g / cm ³ and an MFR of 1.5 g / 10 min as the foamable resin particles. A material obtained by mixing 0.5 parts by weight of peroxide and 20 parts by weight of azodicarbonamide into a granular material having an average particle diameter of 6 mm is a recycled material of a crosslinked polyethylene foam having a particle diameter of 4 mm (300 ° C.) as a reinforcing material. In the following, melted and mixed to reduce the gel fraction to 10%) was used. 76 g of the skin material, 21 g of the expandable resin particles, and 80 g of the reinforcing material were placed in a 100 mm × 100 mm × 50 mm rectangular parallelepiped mold (wall thickness: 4 mm). This is heated at a main rotation speed of 10 rpm, a sub-rotation speed of 5 rpm, and 230 ° C. for 40 minutes with an electric heating molding machine with oscillating rotation. It was. This molded body had a weight of 75 g and an apparent density of 0.35 g / cm ³ . The inner layer had fine air bubbles without voids, and the reinforcement made of recycled material had a structure close to the mesh. The 25% compressive strength of this molded product was as high as 2.5 kgf / cm ² . A cut surface obtained by dividing this half has a structure as shown in FIG.
[0036]
<Example 2>
High-density polyethylene powder having a particle size of 500 μm and a density of 0.96 g / cm ³ as the skin material, and dicumyl as an expandable resin particle having a density of 0.92 g / cm ³ and an MFR of 1.5 g / 10 min. A material obtained by mixing 0.5 parts by weight of peroxide and 20 parts by weight of azodicarbonamide into a granular material having an average particle diameter of 8 mm is a recycled material (300 ° C.) of a crosslinked polyethylene foam having a particle diameter of 5 mm as a reinforcing material. In the following, the mixture was melted and mixed to reduce the gel fraction to 10%. 76 g of the skin material, 21 g of expandable resin particles, and 80 g of the reinforcing material were mixed, and a molded body was produced under the same conditions as in Example 1. The obtained molded body was a molded body in which non-foamed portions were mixed and present in the foam and had no voids, and was lightweight and strong.
[0037]
<Example 3>
High-density polyethylene powder having a particle size of 500 μm and a density of 0.96 g / cm ³ as the skin material, and dicumyl as an expandable resin particle having a density of 0.92 g / cm ³ and an MFR of 1.5 g / 10 min. A mixture of 0.5 parts by weight of peroxide and 20 parts by weight of azodicarbonamide to form a granulate having an average particle diameter of 4 mm is coated with low density polyethylene having a gel fraction of 1.5% and a thickness of 2 mm. Was used to form a strand having an overall thickness of 8 mm and a length of 6 mm. 76 g of the skin material and 64 g of expandable resin particles were mixed, and a molded body was produced under the same conditions as in Example 1. The molded body had a weight of 75 g and an apparent density of 0.15 g / cm ³ . The inner layer had no voids and a sea-island structure . The 25% compressive strength was as high as 2.3 kgf / cm ² .
[0038]
<Example 4>
High-density polyethylene powder having a particle size of 500 μm and a density of 0.96 g / cm ³ as the skin material, and dicumyl as an expandable resin particle having a density of 0.92 g / cm ³ and an MFR of 1.5 g / 10 min. A mixture of 0.5 parts by weight of peroxide and 20 parts by weight of azodicarbonamide to form granules with an average particle diameter of 4 mm is extruded with a low density polyethylene with a gel fraction of 13% with a coating thickness of 1 mm. The material used was a strand having a total thickness of 6 mm and a length of 8 mm. 76 g of the skin material and 64 g of expandable resin particles were mixed, and a molded body was produced under the same conditions as in Example 1. The molded body had a weight of 78 g and an apparent density of 0.21 g / cm ³ . The inner layer had no voids and a sea-island structure . The 25% compressive strength was as high as 3.5 kgf / cm ² .
[0039]
<Comparative Example 1>
As the skin material, 76 g of high-density polyethylene powder having a particle size of 500 μm and a density of 0.96 g / cm ³ was used, and as foamable resin particles, a density of 0.92 g / cm ³ and an MFR of 1.5 g / 10 min of low-density polyethylene 100 parts by weight was used. Using 42 g of a material obtained by mixing 0.5 parts by weight of dicumyl peroxide and 20 parts by weight of azodicarbonamide into an average particle diameter of 6 mm, a molded body was obtained in the same manner as in Example 1. The obtained molded body had a skin thickness of 2.5 mm, and voids were observed in the inner layer portion. The 25% compressive strength was a low value of 0.28 kgf / cm ² .
[0040]
<Comparative example 2>
High-density polyethylene powder having a particle size of 500 μm and a density of 0.96 g / cm ³ as the skin material, and dicumyl as an expandable resin particle having a density of 0.92 g / cm ³ and an MFR of 1.5 g / 10 min. A mixture of 0.5 parts by weight of peroxide and 20 parts by weight of azodicarbonamide is made into granules having an average particle diameter of 4 mm, and low density polyethylene with a gel fraction of 0% is extruded with a coating thickness of 2 mm. The material used was a strand having a total thickness of 8 mm and a length of 6 mm. 76 g of the skin material and 64 g of expandable resin particles were mixed, and a molded body was produced under the same conditions as in Example 1. The molded body had a weight of 75 g and an apparent density of 0.15 g / cm ³ . The inner layer had no voids and the network structure was clean. The 25% compressive strength was as low as 0.18 kgf / cm ² .
[0041]
<Comparative Example 3>
High-density polyethylene powder having a particle size of 500 μm and a density of 0.96 g / cm ³ as the skin material, and dicumyl as an expandable resin particle having a density of 0.92 g / cm ³ and an MFR of 1.5 g / 10 min. A mixture of 0.5 parts by weight of peroxide and 20 parts by weight of azodicarbonamide to form granules with an average particle diameter of 4 mm is extruded with a low density polyethylene with a gel fraction of 19% at a coating thickness of 2 mm. The material used was a strand having a total thickness of 8 mm and a length of 6 mm. 76 g of the skin material and 64 g of expandable resin particles were mixed, and a molded body was produced under the same conditions as in Example 1. The molded body had a weight of 75 g and an apparent density of 0.65 g / cm ^3, and the inner layer had many voids.
[0042]
【The invention's effect】
As described above in detail, according to the present invention, there is provided a lightweight and rigid plastic lightweight molded body having no voids and a method for producing the same.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a conventional molded body with a skin.
FIG. 2 is a schematic cross-sectional view of a plastic lightweight molded body according to the first embodiment of the present invention.
FIG. 3 is a schematic cross-sectional view of a plastic lightweight molded body according to a second embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Conventional plastic lightweight molded object, 20 ... Plastic lightweight molded object in 1st Embodiment of this invention, 30 ... Plastic lightweight molded object in 2nd Embodiment of this invention, 2 ... Skin part, 3 ... Inner layer part 4 ... non-foaming part, 5 ... foaming part.

Claims (7)

It is a plastic lightweight molded body composed of a skin part and an inner layer part, wherein the inner layer part consists of a non-foamed part and a foamed part, and the non-foamed part has a gel fraction of 0.5 to 15%, A non-foamed portion is a plastic lightweight molded body in which the foamed portion is mixed in the form of a mesh or particles. Mold of plastic particles having a particle size of 1.5 mm or less and plastic particles having a gel fraction of 0.5 to 15% and a particle size of 3 mm or more and expandable resin particles having a particle size of 3 mm or more at the same time A method for producing a lightweight plastic molded article, wherein the plastic mold is heated while being rotated. 3. The method for producing a plastic lightweight molded article according to claim 2, wherein the MFR of the plastic particles having a particle diameter of 3 mm or more is in the range of 0.1 g / 10 min to 5 g / 10 min. A plastic lightweight molded body comprising an outer skin part and an inner layer part, wherein the inner layer part comprises a non-foamed part and a foamed part, and the non-foamed part and the foamed part have a sea-island structure. Plastic lightweight molded body. Plastic particles having a particle size of 1.5 mm or less and foamable resin particles coated with a non-foamable resin having a gel fraction of 0.5 to 15% are simultaneously put into a mold, and the mold is The method for producing a plastic lightweight molded article according to claim 4 , wherein the heating is performed while rotating. 6. The method for producing a plastic lightweight molded article according to claim 5, wherein the non-foamable resin has an MFR in a range of 0.1 g / 10 min to 5 g / 10 min. The average particle diameter of the expandable resin particles whose surface is coated with a non-expandable resin is 4 to 10 mm, and the thickness of the non-expandable resin layer that covers the expandable resin particles is 0.5 to 5 mm. The method for producing a plastic lightweight molded article according to claim 5 or 6, wherein

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