JP2668549B2 - Molding thermoplastic resin sheet and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a molding thermoplastic resin sheet useful as an embossing material and a method for producing the same.

[Conventional technology]

JP-A-57-28135 proposes a molding thermoplastic resin sheet reinforced by reinforcing fibers and a method for producing such a molding thermoplastic resin sheet by utilizing a papermaking technique. This conventional technology uses polyolefin pulp that promotes the cohesiveness required for papermaking technology when mixing thermoplastic fibers with mineral fibers such as glass fibers shorter than 30 mm or organic fibers such as metal fibers or polyester fibers shorter than 30 mm. Do it.

When a molding thermoplastic resin sheet using a metal fiber as a reinforcing fiber is used as a molding material, the molded product comes to have conductivity, so that the strength of the metal fiber is improved and the electromagnetic wave shielding effect is excellent. In order to exhibit these properties satisfactorily, the metal fibers are uniformly dispersed in each part of the molded product, and the bondability between the metal fibers and the thermoplastic resin and the bondability between the thermoplastic resins are uniform in each part. It is necessary to be.

In view of the above, the above prior art employs a means for dispersing a reinforcing fiber such as a metal fiber and a thermoplastic resin powder by utilizing an agglomeration method. That is, a high-concentration aqueous suspension is first prepared by adding a dispersant, a binder or a coagulant in the presence of a polyolefin pulp to a main body composed of reinforcing fibers such as metal fibers and a thermoplastic resin powder and stirring the mixture. The solid component is dispersed by diluting the aqueous suspension, and the dispersed solid component is formed into a sheet by a known papermaking technique. Therefore, in the manufactured sheet, in addition to the reinforcing fibers and the thermoplastic resin, a binder and a coagulant are inevitably included, and if the thermoplastic resin is a resin other than the polyolefin resin, the binder or the coagulant is used. Polyolefin pulp is inevitably contained in addition to the agent.

[Problems to be solved by the invention]

 However, the prior art has the following problems.

That is, since the solid component is dispersed using the agglomeration method, when the aqueous suspension is diluted, the reaggregation of the solid component is likely to occur. PH adjustment of the medium becomes indispensable, and even in such a case, it is difficult to obtain a uniform dispersion state of the solid components. Further, since a flocculating agent is used, when the dispersing action stops, the movement of the reinforcing fiber in the aqueous suspension stops very quickly and becomes immobile, and when a reinforcing fiber having a large difference in specific gravity from the thermoplastic resin, for example, a metal fiber is used. It is difficult to disperse uniformly. Therefore, even though the preliminary treatment before entering the papermaking process is complicated, a solid component, particularly a solid component having a large specific gravity difference, cannot be uniformly dispersed, and the produced thermoplastic resin sheet for molding is not provided. There is a problem that extra components such as a coagulant are unavoidably included as foreign substances, and the bonding strength of the thermoplastic resin tends to be weakened at the interposition of these solid components.

The present invention has been made in view of the above problems, and has been made by focusing on a separation method of mineral particles, that is, a flotation method, in which solid particles are separated using the difference in physicochemical properties of the surfaces of the solid particles. The metal fiber or powdery or granular thermoplastic resin is suspended and uniformly dispersed in a liquid medium regardless of its specific gravity difference, and the solid component thus dispersed is sheeted using a papermaking technique. It is an object of the present invention to provide a method for producing a thermoplastic resin sheet for molding by molding into a shape. Another object of the present invention is to obtain a molded product which does not contain an extra component such as a coagulant and which exhibits uniform strength and electromagnetic wave shielding effect by uniform dispersion in each part when used as a molding material. It is an object of the present invention to provide a molding thermoplastic resin sheet capable of performing the following.

[Means for solving the problem]

The thermoplastic resin sheet for molding of the present invention holds powder or granules of the thermoplastic resin in gaps between structures in which conductive fibers such as metal fibers or metal-plated non-metal fibers are randomly entangled. The conductive fiber has a diameter of 1 to 18 μm.
The length is 5 to 50 mm and the content is 20 to 60% by weight, and the thermoplastic resin powder or granule has a particle size of 0.3 to 2.0 mm.
The thermoplastic resin sheet for molding has a diameter of 12 μ or less and a length of 5 to 50 mm.
The glass fiber may contain not more than 20% by weight of the glass fiber, or may contain not more than 20% by weight of the inorganic filler.

The method for producing a thermoplastic resin sheet for molding according to the present invention is performed by introducing conductive fibers having a length of 5 to 50 mm and a thermoplastic resin powder or granules having a particle diameter of 0.3 to 2.0 mm into a liquid medium, The method includes a step of introducing bubbles into the mixture, stirring and dispersing them while causing them to float, and a step of forming a web by removing the suspended matter and removing the liquid component.

(Operation)

When the above molding thermoplastic resin sheet is heated to a molding temperature to be softened, and when it is put into a stamping molding machine and embossed, there is a thickness variation of a thick portion or a thin portion of a molded article, or a rib portion. The conductive fibers flow evenly into the portions, and the electromagnetic wave shielding effect of the conductive fibers becomes uniform in each portion. When the conductive fibers are mainly made of metal fibers or non-metallic reinforcing fibers, the thick, thin and rib portions are uniformly reinforced by the conductive fibers. Furthermore, the thermoplastic resin sheet for molding does not contain an extraneous substance such as an aggregating agent. As a result, the bonding strength between the powdery or granular thermoplastic resins is improved, and the strength of the molded product is increased.

According to the method for producing a thermoplastic resin sheet for molding of the present invention, solid components such as conductive fibers and powdery or granular thermoplastic resin are suspended and uniformly dispersed on the surface of the liquid medium, and thus dispersed. The solid component is subjected to a papermaking process, that is, a process of removing a liquid medium and drying to form a web, and a thermoplastic resin sheet for molding in which conductive fibers are uniformly dispersed is produced.

〔Example〕

FIG. 1 and FIG. 2 are explanatory views of a specific configuration of a thermoplastic resin sheet for molding according to an embodiment of the present invention, wherein 1 is a conductive fiber, 2 is a powder or granules of a thermoplastic resin and others. Is shown. As can be inferred from the figure, the conductive fibers 1 are randomly entangled to form a gas-permeable structure A such as a mesh in which the conductive fibers 1 are in point contact or line contact with each other. The solid component 2 is held in the gap. Such a thermoplastic resin sheet for molding is heated and melted at a molding temperature, and is used as a molding material for embossing such as stamping molding.

The conductive fiber 1 is a discontinuous monofilament having a length of 5 to 50 mm and a lightness of 1 to 18 μm, and is made of a corrosion-resistant metal fiber such as copper, stainless steel, brass or the like, or an iron fiber plated with corrosion resistance; Alternatively, a non-metallic fiber such as glass fiber or polyester fiber plated with metal such as copper or nickel is used. The conductive fibers 1 may be mixed with reinforcing fibers such as ceramic fibers and glass fibers having the above-described length and diameter, and synthetic resin fibers having the above-described length and diameter. In such a case, the conductive fibers 1 and these fibers may be used. The structure A is formed by the reinforcing fibers and the synthetic resin fibers. When the synthetic resin fiber is mixed, the synthetic resin fiber is melted when heated to the molding temperature and fused with the powder or granules of the thermoplastic resin.
If the length of the conductive fiber 1 is shorter than 5 mm, the degree of entanglement tends to be insufficient, and not only is it difficult to maintain the shape retention when formed into a sheet, but also when the sheet is formed by embossing. The strength at the corner of the product tends to be insufficient, and the corner of the molded product is easily damaged. Further, when a reinforcing fiber such as a metal-plated glass fiber is used as the conductive fiber 1, it is difficult to obtain a sufficient reinforcing effect. If the length of the conductive fiber 1 is longer than 50 mm, the flowability of the conductive fiber 1 becomes poor when the fiber is too long to be embossed, and the thickness variation such as the thick wall portion, the thin wall portion and the rib portion is caused. Differences in conductivity are likely to occur between certain parts, and particularly when the conductive fiber 1 is insufficiently transferred to a thin portion or a rib portion, the conductivity is deteriorated, and there is a possibility that the electromagnetic wave shielding effect may be lost. In addition, strength tends to be insufficient. Even when the reinforcing fiber is used for the conductive fiber 1, the mechanical strength of the thin portion tends to be insufficient for the same reason as the length of the fiber is long. If the diameter of the conductive fiber 1 is smaller than the above range, the conductive fiber 1 is easily cut by embossing.

The thermoplastic resin contained in the solid component 2, for example, polypropylene (PP), polyethylene (PE), polystyrene (P
S), acrylonitrile-styrene-butadiene (AB
S), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polycarbonate (PC), polyphenylene sulfide (PPS), polysulfone (PS), polyether ether ketone (PEEK), etc. It has a grain size in the range of 0.3 to 2.0 mm. As shown in FIG. 2, the thermoplastic resin powder or granules are not integrally bonded to each other, but a large number of them are pressed into the gaps of the structure A and are solidified. Therefore, air permeability is ensured by the gaps inevitably present between the powders or granules, and when heated to the molding temperature, the air permeability allows the whole to be easily heated to a uniform temperature in a short time. The solid component 2 includes, for example, a binder and a filler in addition to the thermoplastic resin powder or granules. The binder binds the conductive fibers 1, the reinforcing fibers, and the synthetic resin fibers at the intersections, and preferable binders include polyvinyl alcohol, polyvinyl acetate, carboxymethyl cellulose, and starch. As the filler, various inorganic fillers contained in ordinary synthetic resin molding materials such as calcium carbonate and mica can be used. If the particle size of the thermoplastic resin powder or granules is set within the above range, the fluidity of the thermoplastic resin when heated to the molding temperature will be within just the right range, and the resin will flow too much and molding will become difficult. Also, there is no possibility that a uniform molded product cannot be obtained due to insufficient fluidity.

The amount of the conductive fiber 1 is 20 to 60% by weight. The amount of the thermoplastic resin powder or granule is 40 to 80% by weight. If necessary, the above-mentioned reinforcing fiber such as the glass fiber is not more than 20% by weight. Add within the range. For example, the mixing ratio is 40% by weight of metal fiber, 40% by weight of powder or granules of thermoplastic resin, 20% by weight of glass fiber
It is. If the blending amount of the conductive fibers 1 or the thermoplastic resin powder or granules is out of the above range, the strength may be insufficient, a sufficient electromagnetic wave shielding effect may not be obtained, or the solid component 2 of the structure A Insufficient holding power.

The thermoplastic resin sheet for molding is conveyed, for example, in a roll-wrapped form, and when it is used as a molding material, a predetermined amount is sampled and heated to a molding temperature.
In the case of (1), the resin in the molten state held in the gap between the structures A is charged into a stamping machine and stamped. Then, when the embossing is performed, the conductive fibers 1 and the reinforcing fibers flow into each part of the molded product and are uniformly dispersed, and a molded product having uniform mechanical strength and conductivity is obtained. Such an effect is satisfactorily exerted even when a thin portion or a rib portion is locally present in a molded product.

Further, since the molding thermoplastic resin sheet has air permeability, the vent holes, that is, the above-mentioned granules or gaps inevitably present between the granules are impregnated with the thermosetting synthetic resin. It is also possible. When a molding thermoplastic resin sheet impregnated with a thermosetting synthetic resin is used as a molding material, when the molding is performed by heating to the molding temperature to heat and melt the powder or granules of the thermoplastic synthetic resin, It is necessary to finish the embossing before the curable synthetic resin is cured. The molding thermoplastic resin sheet impregnated with the thermosetting synthetic resin as described above is useful as a molding material for a molding used as a substitute for a metal plate. The thermosetting synthetic resin includes known thermosetting synthetic resins such as phenol, polyester, urea, melanin, epoxy, and urethane.

FIG. 3 exemplifies an apparatus for manufacturing a thermoplastic resin sheet for molding of the present invention, and the manufacturing method of the present invention is continuously performed by the manufacturing apparatus shown in FIG. In FIG. 1, reference numeral 10 denotes a liquid tank, 11 denotes a liquid removing conveyor, and 12 denotes a molding conveyor. A liquid supply pipe 13, a hopper 14, and an overflow port 15 are attached to the liquid tank 10, and a bubble generator 16 is installed at the bottom of the liquid tank 10.

While supplying a liquid medium, for example, water, from a liquid supply pipe 13, a metal fiber M and a powder or granules P of a thermoplastic resin and necessary fillers and reinforcing fibers are charged into a liquid tank 10 from a hopper 14, and suspended. The metal fibers M and the powder or granules P of the thermoplastic resin are floated on the surface of the liquid medium by introducing bubbles from the bubble generator 16 into the liquid medium in the liquid tank 10 and simultaneously stirring the bubbles appropriately. By doing so, the metal fibers M and the thermoplastic resin powder or granules P floating on the surface of the liquid medium are uniformly dispersed. In addition, the gas content of the liquid medium is preferably 40 to 60% by volume percentage in order to uniformly disperse the metal fibers M. The dispersed metal fibers M and the powder or granules P of the thermoplastic resin (hereinafter referred to as suspended matter F) overflow from the overflow port 15 together with the liquid medium, and the web W is obtained by the papermaking technique. That is, the overflowing floating substance F is received by the dewatering conveyor 11 and sent to the molding conveyor 12 while being dewatered.
In the forming conveyor 12, the floating material F is formed into a sheet having a constant thickness to form a web W, which is wound as a forming thermoplastic resin sheet, for example, in a post process. Further, if necessary, the binder is held on the web W after dewatering by an appropriate means such as spraying to improve the shape retention. The length and diameter of the metal fibers used in this method and the particle size of the powder or granules of the thermoplastic resin are as described above. If such materials are used, the thermoplastic resin for molding described in FIGS. 1 and 2 will be used. A resin sheet is obtained.

Instead of the metal fiber M, a conductive fiber obtained by plating a glass fiber with metal or another type of conductive fiber may be used.
Further, reinforcing fibers such as ceramic fibers and glass fibers, and synthetic resin fibers having the above-described length and diameter may be mixed.

The specific gravity of the metal fiber M is 7.0 to 7.5, and the specific gravity of the thermoplastic resin powder or granule P is 0.9 to 1.4. The reason for the dispersion is assumed as follows. That is, the metal fibers M and the powder or granules P of the thermoplastic resin are mixed by the stirring action accompanying the introduction of bubbles into the liquid medium and the stirring of the liquid medium, and at the same time, the metal fibers M having a high specific gravity are mixed. This is probably because the liquid is adhered and held by the air bubbles, floats on the surface of the liquid medium, and is uniformly dispersed in the thermoplastic resin powder or granules P. A foaming agent or an activator may be mixed in the liquid medium. Examples of the foaming agent include sodium dodecylbenzenesulfonate, and examples of the activator include surfactants composed of higher alcohols such as isopropylbenzene alcohol, α-methyltricarpinols, and pine oil. The activator not only helps to improve the affinity (affinity) between the metal fiber M and the powder or granules P of the thermoplastic resin to increase the bonding strength between the two, but also adheres to the metal fiber M. It is helpful to remove the oil to further increase the binding force. In addition,
Needless to say, the powder or granules of the metal fiber M or the thermoplastic resin are specifically selected from the types described above.

〔The invention's effect〕

The molding thermoplastic resin sheet of the present invention, since conductivity is ensured by the conductive fibers such as the metal fibers or the metal-plated non-metal fibers contained therein, a molded article using this as a molding material has an electromagnetic wave. It has a shielding effect and can be suitably used as a casing or a cover member of an electric device which is an electromagnetic wave generation source such as a fluorescent lamp and various OA devices. The conductive fibers used in the molding thermoplastic resin sheet have a diameter of 1 to 18 μm and a length of 5 to 50 mm.
20 to 60% by weight, and the thermoplastic resin powder or granules have a particle size of 0.3 to 2.0 mm and 40 to 80% by weight. A good molded product can be obtained without the conductive fibers flowing uniformly throughout and the strength being partially reduced, and the conductivity and the electromagnetic wave shielding action being different in each part. Also,
When a metal fiber is selected as the conductive fiber or a glass fiber is selected as the non-metal fiber, the metal fiber or glass fiber acts as a reinforcing fiber and serves to strengthen the molded product.

The method for producing a thermoplastic resin sheet for molding of the present invention utilizes a floating method instead of the conventionally employed coagulation method, and does not use pulp or coagulant remaining as foreign matter in the manufactured product. There is no decrease in the bonding strength due to the presence of, and uniform strength is ensured in each part. In addition, since the floating method is used, there is an advantage that a thermoplastic resin sheet for molding in which powder or granular thermoplastic resin of metal fiber or the like having a large specific gravity is uniformly dispersed can be easily produced.

[Brief description of the drawings]

FIG. 1 and FIG. 2 are explanatory views of a concrete constitution of a thermoplastic resin sheet for molding according to an embodiment of the present invention, and FIG. 3 is a schematic explanatory view of an apparatus for continuously carrying out the method of the present invention. 1 ... conductive fiber, 2 ... solid component, F ... suspended matter, W
... web, A ... structure.

Claims (4)

(57) [Claims] 1. A thermoplastic resin powder or particle size is held in a gap between structures in which conductive fibers such as metal fibers or metal-plated non-metal fibers are randomly entangled. Its diameter is 1-18μ and its length is 5-50mm.
A thermoplastic resin sheet for molding, characterized in that the thermoplastic resin powder is contained in an amount of -60% by weight, the powder or stream diameter of the thermoplastic resin is 0.3-2.0 mm, and the content is 40-80% by weight. 2. The molding thermoplastic resin sheet according to claim 1, which contains 20% by weight or less of glass fibers having a diameter of 12 μm or less and a length of 5 to 50 mm. 3. The thermoplastic resin sheet for molding according to claim 1, wherein the filler contains 20% by weight or less of an inorganic filler. 4. A conductive fiber having a length of 5 to 50 mm and a particle size of 0.3
A powder or granules of a thermoplastic resin of ~ 2.0 mm into a liquid medium, introducing bubbles into the medium and stirring to disperse while floating, and after taking out the suspended matter, Removing the web to form a thermoplastic resin sheet for molding.