JP2005035184A - Blow mold and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a blow mold which holds the durability and releasability of a mold surface and has excellent productivity, and also a manufacturing method of the blow mold excellent in operability and frictional resistance. <P>SOLUTION: The blow mold 10, which forms a hollow bottle by blowing compressed air into a preform P of a polyethylene terephthalate resin or the like held inside, is equipped with a pair of right and left split molds 11 and 11a holding the preform P, a panel tool 12 which is formed in projection into the split molds 11 and 11a and which is disposed to be fittable to and removable from the split molds 11 and 11a through a fixing member 12a and constituted of an aluminum alloy or the like, and an easy release layer 13 which is disposed on a preform contact face of the panel tool 12 and formed by a blast treatment, a specular finish treatment and a hard plating treatment. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a blow mold for forming a bottle or the like using a preform made of a thermoplastic resin or the like as a raw material and a method for manufacturing the same.

Conventionally, in blow molding of heat-resistant PET bottles and the like, heat set is performed to remove distortion during molding, so the bottle is easy to stick to the mold surface and the bottle deforms when released Will occur. As a countermeasure, a surface treatment for improving mold release properties such as forming irregularities on the mold surface using a sandblasting machine or a file is performed. Further, the following is disclosed in relation to the surface treatment technology of such a blow mold.
Patent Document 1 describes a technique in which the surface of a metal material is formed into a satin finish and the surface is subjected to porous plating or hard chrome plating.
Japanese Patent Application Laid-Open No. H10-228667 describes a mold surface that is coated with a fluororesin during blow molding.
JP 57-12607 A Japanese Patent Laid-Open No. 02-47032

However, in the molds described in Patent Documents 1 and 2, since the mold surface in contact with the preform is not properly formed, the convex portions of the mold surface and the fluororesin are worn or peeled off. Therefore, there is a problem in that the durability is low, the releasability is deteriorated from the initial state, dents and sink marks are generated, and the production yield is lowered.
In addition, since many of the conventional products have a mirror-finished surface, the contact area with the resin is increased, the bottle cannot be released at high speed, and productivity is lacking. was there.

  The present invention has been made in order to solve the above-mentioned conventional problems, and provides a blow mold having excellent productivity while maintaining the durability and releasability of the mold surface, and the workability. And it aims at providing the manufacturing method of the blow molding die excellent in friction resistance.

(1) A blow mold according to the present invention for solving the above-mentioned problems is a blow mold in which compressed air is blown into a preform such as polyethylene terephthalate resin held inside to form a hollow bottle. A pair of left and right split molds holding the reform,
The concavo-convex molded part formed in the split mold, and an easily releasable layer disposed and formed on the preform contact surface of the concavo-convex molded part.
As a result, an easily releasable layer that balances predetermined durability and friction resistance is formed on the contact surface with the preform of the concavo-convex molded portion, so that the durability of the mold surface can be improved and improved. It is possible to provide a blow molding die having excellent productivity while maintaining releasability.

(2) The blow mold according to the present invention is characterized in that, in the above (1), the area ratio between the mirror surface portion and the total surface area in the easy-release layer is 30 to 70%. . As a result, the mirror surface portion is secured at a predetermined ratio, so that the releasability from the preform on the mold surface can be maintained well.
Here, when the area ratio between the mirror surface portion and the total surface area is lower than 30%, the number of protruding acute angle portions is increased and it is easy to wear, and the releasability from the preform is constantly maintained stably. On the other hand, if the area ratio exceeds 70%, the contact surface with the preform becomes excessively mirror-finished to increase the contact resistance, and it is difficult to maintain good releasability.

(3) In the blow molding die of the present invention, in (1) or (2), the average surface roughness Ra (JIS B 0601-1994) in the easily releasable layer is 0.2 to 3 μm. It is configured. Thereby, it is possible to prevent the preform from coming into vacuum contact with the mold surface and to maintain the releasability more appropriately. Here, if the average surface roughness is less than 0.2 μm, it becomes difficult to secure a predetermined gap for storing gas between the preform surface and the mold surface, However, if it exceeds 3 μm, the change in surface properties due to wear tends to increase, which is not preferable.

(4) The blow mold according to the present invention is configured such that, in (3), the thickness of the hard plating in the easy-release layer is 1.5 to 50 times the average surface roughness. Has been. This enhances the durability of the mold surface and prevents the mold surface from being excessively mirror-finished by repeated blow molding, and good initial mold release properties over a long period of time. Can be secured.
Here, if the thickness of the hard plating is less than 1.5 times the average surface roughness Ra (JIS B 0601-1994), it becomes difficult to ensure a predetermined wear resistance, and conversely, 50 times. Exceeding this is not preferable because the preform contact surface is smoothed as a whole, and a predetermined air layer cannot be held here, and a vacuum contact state that deteriorates releasability is likely to occur.

(5) In the blow molding die of the present invention, in the above (1) to (4), the easily releasable layer is provided on the preform contact surface of the panel mold for molding the panel portion of the hollow bottle. Yes. As a result, it is possible to prevent yield defects due to sliding flaws or deformation due to mold release defects that occur particularly in the highly irregular panel portion of the bottle, and it is possible to provide a blow-molding mold that is further excellent in productivity.

(6) The blow mold of the present invention is the blow mold according to any one of (1) to (5), wherein the easily releasable layer is formed on the preform contact surface of the bottom mold for molding the bottom of the hollow bottle. It is also characterized by being provided. As a result, it is possible to prevent yield defects due to sliding scratches generated at the bottom of the bottle with severe irregularities and deformation due to defective mold release, and to provide a blow mold having further excellent productivity.

(7) The method for producing a blow mold according to the present invention is the method for producing a blow mold according to any one of (1) to (6) above, wherein the concavo-convex mold on which the easy-release layer is formed. A blasting process for forming a concavo-convex surface having a predetermined surface roughness Ra (JIS B 0601-1994) on the surface of the base metal of the portion, and a polishing process for polishing and removing a concavo-convex surface formed in the blasting process by a predetermined amount; And a plating process for applying hard plating with a predetermined thickness to the base metal polished and removed in the polishing process.
Thereby, it is possible to provide a method for producing a blow molding die having excellent productivity by balancing the durability, friction resistance, and mold release property on the die surface.

  According to the first aspect of the present invention, since the easily releasable layer that balances the predetermined durability and the friction resistance is formed on the contact surface with the preform of the concavo-convex molded portion, It is possible to provide a blow-molding die having excellent productivity while enhancing durability and maintaining good release properties.

  According to invention of Claim 2, since a mirror surface part is ensured by the predetermined ratio, the mold release property with the preform in a metal mold | die surface can be maintained favorable.

  According to the third aspect of the present invention, it is possible to prevent the preform from being in vacuum contact with the mold surface and to maintain the releasability more appropriately.

  According to the fourth aspect of the present invention, the durability of the mold surface is enhanced, and it is possible to prevent the mold surface from being excessively mirror-finished by repeating blow molding, for a long period of time. Thus, good initial release properties can be ensured.

According to the invention described in claim 5, blow molding that prevents a yield defect due to a sliding flaw occurring in a panel portion having particularly severe irregularities in a bottle or a deformation caused by a mold release failure, and is further excellent in productivity. Mold can be provided.
According to the sixth aspect of the present invention, it is possible to provide a blow mold that is excellent in productivity by preventing yield defects due to sliding scratches, dents, and the like that occur at the bottom of the bottle.

  According to invention of Claim 7, the manufacturing method of the blow molding die excellent in productivity can be provided by balancing the durability in a metal mold | die surface, friction resistance, and mold release property.

Hereinafter, a blow mold according to an embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a front cross-sectional view of the blow molding die of the present embodiment, FIG. 2 is a side cross-sectional view thereof, and FIGS. 3A to 3C are views taken along arrows AA and B in FIG. -B and CC plane sectional drawing.
1 to 3, a blow molding die 10 according to an embodiment is formed to protrude into a pair of left and right split molds 11 and 11a that sandwich a preform P to be supplied, and the split molds 11 and 11a. A panel mold 12 preform having four panel molds (concave-convex molding portions) 12 disposed at equal intervals of 90 degrees on the peripheral walls of the divided molds 11 and 11a via a fixing member 12a. On the contact surface, for example, an easily releasable layer 13 formed by blasting, mirroring, or hard plating is disposed.
Further, at the bottom of the blow molding die 10, a bottom die (unevenness forming portion) 14 that supports the bottom of the preform P, and air is blown to the bottom of the blow-molded bottle so that the bottle is placed in the bottom die 14. An air supply pipe 18 for discharging the gas and a thermocouple 15 for measuring the temperature of the divided molds 11 and 11a are provided.
Further, on the upper part of the blow mold 10, a cartridge heater 17 for heating the divided molds 11 and 11a to a predetermined temperature and a stretch for inserting the preform P in the longitudinal direction are inserted into the preform P. A rod 16 is provided.

The split molds 11 and 11a are made of aluminum alloy, steel, stainless steel, and the like, and are arranged so as to rotate about a rotation axis at a position eccentric from the center of the mold and to be divided from each other. As a result, the blow molded bottle is removed from the blow mold 10.
The panel mold 12 is made of aluminum alloy, steel, stainless steel or the like, is formed so as to protrude inward from the inner wall surfaces of the divided molds 11 and 11a, and is detachably fixed by a fixing member 12a.
In addition, a part or all of the preform contact surface of the panel mold 12 has an easily releasable layer formed by mirror-plating the blasted surface at a predetermined area ratio and then performing a hard plating process such as chrome plating. 13 is formed, and the mold releasability and durability with the molded preform P are favorably maintained.
As the preform P, a polyethylene terephthalate (PET) resin, a polyolefin resin such as polypropylene, a vinyl chloride resin or the like formed by injection molding is preferably used.

The preform P to be subjected to blow molding is formed into a test tube by injection molding and is manufactured as follows.
That is, when a slurry of ethylene glycol and terephthalic acid, which is a raw material for PET resin, is placed at 240 to 280 ° C., esterification proceeds and a polymer precursor called bishydroxyethyl terephthalate is formed. Next, polycondensation reaction is performed by removing excess ethylene glycol under high temperature and reduced pressure. Here, a PET resin having a number average molecular weight of about 10,000 (degree of polymerization of about 100) is produced. The high-viscosity molten PET obtained by this liquid phase polymerization is passed through cooling water, cooled, and then cut into chips (pellets).
Next, after drying PET resin pellets with a dehumidifying dryer, the preform P is molded with an injection molding machine. The molding temperature is 270 ° C. to 300 ° C. above the melting point of the PET resin.

The preform P thus obtained by injection molding is finished into a bottle shape in a blow molding process. First, the PET resin pellets are heated with an infrared heater so that the inside and outside are at the same temperature. Next, while being held in the split molds 11 and 11a of the blow molding mold 10 and being stretched in the longitudinal direction by the stretch rod 16, high-pressure air is blown and stretched in the lateral direction to form a bottle shape.
At this time, if the preform heating temperature, high-pressure air blowing timing, mold temperature, and the like are not appropriate, the product thickness distribution and transparency are affected, and the bottle thickness distribution affects the product strength. In addition, in products that require heat resistance, such as for hot coffee, the strain remaining in the molecular chain during stretching is relaxed and contracted during high-temperature filling, so a mold is used to remove this strain. The method of applying heat set is taken.
In order to further increase the heat resistance, after forming with a mold larger than the final product shape, it is heated with a heater to relieve strain. In order to improve the heat resistance, the mold temperature is increased, but in this case, cyclic trimers of diethylene glycol, terephthalic acid, and ethylene glycol are deposited on the mold surface to improve the transparency of the bottle. It is necessary to control the temperature within an appropriate range using the thermocouple 15 because it causes damage.

Subsequently, with respect to a method for manufacturing a blow mold having the panel mold 12 having the easy-release layer 13 on the preform contact surface, the bottom mold 14, and the like, the formation of the easy-release layer shown in FIG. This will be described with reference to a flow diagram.
First, as shown in FIG. 4A, the surface of the preform contact surface of the panel mold 12 is buffed as necessary in order to adjust the surface state smoothly.
Next, in the blasting process shown in FIG. 4B, the surface of the buffed panel mold 12 is subjected to blasting to form a textured surface. Such a blasting process is performed by spraying sandblast of a predetermined particle size on the surface of the panel mold 12 with a shot blasting machine. The average surface roughness Ra (JIS B 0601-1994) F on the blasted surface is determined by, for example, the target preform material and the material and shape of the blast material to be sprayed, the projection amount of the blast material, the blasting time, and the temperature. The size is determined by the processing conditions.

  In the polishing step shown in FIG. 4 (c), the average roughness of the protrusions of the satin-like convex portions formed by blasting by smoothly polishing the blasted uneven surface by buffing or the like. The surface is removed with a polishing allowance H of about 1/10 of the height, and the tip of the convex portion is smoothly mirror-finished (see FIG. 4D). Thereby, the area ratio of the mirror surface portion to the total surface area is maintained within a predetermined range, for example, 30 to 70%, so that the releasability by the surface shape can be favorably maintained.

The plating process shown in FIG. 4 (e) is a process of forming a hard plating layer M such as chrome plating on the processing surface from which the protrusion tip of the convex portion has been removed in the polishing process, The durability can be increased by increasing the hardness.
In addition, after this plating process, you may add the finishing grinding | polishing process which grind | polishes a plating process surface further with a thread | buff buff or a grindstone, and finishes a convex-shaped part to the smooth surface.
Furthermore, in the present embodiment, the easily releasable layer can be formed by executing the order of (i) blasting process → (ii) plating process → (iii) polishing process. In this case, the tip of the convex portion on the plated surface can be flattened without being rounded.
In addition, by blasting the surface of the panel mold,
By forming an uneven surface that becomes foamy and further improving its releasability,
It is also possible to prevent the formation of dents and scratches that occur when the preform P and the mold surface are in close contact with each other and the preform formed in a bottle shape is discharged from the divided molds 11 and 11a.

In FIG. 4F, the easy-release layer 13 is formed on the panel mold 12 of the blow mold 10 by the above blasting process, polishing process, and plating process, and the preform P is contacted. It is a schematic diagram of a state.
As shown in the figure, the panel mold 12 has a textured surface formed on the surface of an aluminum alloy, and the surface of the convex portion is coated with a hard plating layer M to a predetermined thickness, for example, 1 to 10 μm. Yes. For this reason, the contact area is smaller than that in the conventional mirror surface state, the frictional resistance can be reduced, and the bottle that is in sliding contact with the panel mold 12 can be easily released without causing damage or deformation.
Further, since the hard plating treatment is performed, the frictional resistance can be further reduced, the durability can be improved, the workability and the maintainability can be improved, and the blow mold having excellent productivity can be obtained.

The data of the Example shown in Table 1 has shown the result of having formed 500 bottles using the blow molding die 10, measuring the number of occurrences of the dents, and evaluating the dent occurrence rate.
In Table 1, Comparative Examples 1 to 3 are formed on the steel mold surface under the same molding conditions as in the examples.
(1) Titanium nitride (TiN) coating,
(2) Kanak film, which is one of the vacuum nitriding methods,
(3) It is data of the result about what formed each QPQ film which performed soft nitriding treatment and oxidation treatment,
The comparative example 4 has shown the result measured on the same conditions using the aluminum alloy with a ground.
As is clear from Table 1, the number of dents in this example was zero, and it was found that a good production yield was obtained as compared with Comparative Examples 1 to 4.

In the blow molding die of the present invention, since the easily releasable layer that balances the predetermined durability and the friction resistance is formed on the contact surface with the preform of the concavo-convex molding portion, the durability of the die surface It has excellent productivity while maintaining good release properties.
In addition, since the mirror surface portion is secured at a predetermined ratio, the mold releasability from the preform on the mold surface can be maintained well for a long period of time.
Furthermore, the durability of the mold surface is enhanced, and by repeating blow molding, the mold surface is prevented from being worn and excessively mirror-finished. Can be secured.
In addition, it is possible to prevent yield defects due to sliding scratches generated in the panel portion having a particularly uneven surface and bottle bottom portions in the bottle and deformation due to defective release, thereby further improving productivity.

It is front sectional drawing of the blow molding die which concerns on embodiment of this invention. It is side surface sectional drawing of the blow molding die which concerns on embodiment of this invention. (A) is arrow AA plane sectional drawing in FIG. (B) is an arrow BB plane sectional view in Drawing 1. (C) is a CC cross-sectional view taken along the arrow in FIG. (A)-(f) is a formation flow figure of an easily peelable layer.

Explanation of symbols

10 Blow Molding Die 11, 11a Dividing Mold 12 Panel Mold (Unevenness Molding Section)
12a Fixing member 13 Easy release layer 14 Bottom mold (concave / convex molding part)
15 Thermocouple 16 Stretch Rod 17 Cartridge Heater 18 Air Supply Pipe F Average Surface Roughness H Polishing Allowance P Preform M Hard Plating Layer

Claims (7)

In a blow molding die that forms a hollow bottle by blowing compressed air into a preform such as polyethylene terephthalate resin held inside,
A pair of left and right split molds sandwiching the preform;
A concavo-convex molded portion formed in the split mold;
And a mold release layer disposed on the preform contact surface of the concavo-convex molded part. 2. The blow mold according to claim 1, wherein an area ratio between a mirror surface portion and a total surface area in the easily releasable layer is 30 to 70%. The blow mold according to claim 1 or 2, wherein an average surface roughness Ra (JIS B 0601-1994) in the easily releasable layer is 0.2 to 3 µm. The blow mold according to claim 3, wherein a thickness of the hard plating in the easy-release layer is 1.5 to 50 times the average surface roughness. The blow mold according to any one of claims 1 to 4, wherein the easily releasable layer is provided on a preform contact surface of a panel mold for molding the panel portion of the hollow bottle. The blow mold according to any one of claims 1 to 5, wherein the easily releasable layer is provided on a preform contact surface of a bottom mold for molding the bottom of the hollow bottle. It is a manufacturing method of the blow molding metal mold | die in any one of Claims 1-6, Comprising: Predetermined average surface roughness Ra (JISB) on the surface of the base metal of the uneven | corrugated molded part in which the said easy-release layer is formed. 0601-1994) is a blasting process for forming a concavo-convex surface of 0.2 to 3 μm, a polishing process for polishing and removing a predetermined amount of the concavo-convex surface formed in the blasting process, and polished and removed in the polishing process And a plating process for applying a hard plating of a predetermined thickness to the base metal.

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