JPH07276372A - Core material and its use - Google Patents

Abstract

PURPOSE: To facilitate the precise molding of a core material for injection molding because of its heat resistance and flowability and to facilitate the removal of a core after use because of its water solubility by constituting the core material of a copolymer of polyvinyl alcohol and polyethylene oxide. CONSTITUTION: A core material is constituted of polyvinyl alcohol(PVA) and polyethylene oxide(PEO) and a molar ratio of PVA and PEO is set to 99-50:1-50 and a saponification value of PVA is set to 65-99 mol%. Because of this, the core material becomes high in water solubility. The glass transition temp. Tg of the core material is set to 40-100 deg.C and the melt index thereof is set to 0.1-50 to obtain flowability. Therefore, the flowability and water solubility of the core material can be enhanced without damaging the heat resistance thereof. This core material is used to form a core and this core is used to form an injection-molded product. As a result, the core can be formed into a fine shape and can be easily dissolved and removed after use because of its water solubility.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a core material made of a water-soluble material. The core material of the present invention is particularly useful for the manufacture of cores for injection molding of microstructured plastic products or parts, such as face-to-face fasteners used in the automotive industry.

[0002]

2. Description of the Related Art As a material for producing a core for injection molding of a polymer material product or parts having a fine structure, the core having a fine structure can be easily molded by itself, and the polymer material After injection molding a product or part, the used core must be easily dissolved and removed by water.

US Pat. No. 5,242,646 discloses a method for manufacturing a face-to-face engaging fastener composed of a head portion, a stem portion and a base portion. In this method, PVA is used as a core material. used. However, in PVA, melting and decomposition (thermal crosslinking) occur at the same time, so that core formation itself is difficult.

As a water-soluble core material for injection molding of polymer materials, JP-A-60-155212 and EP 0314 are used.
156 describes an acrylic polymer material having a carboxyl group. US Patent No. 4,990,146
And U.S. Pat. No. 4,870,148 describes an amino group-containing polymer material soluble in an acidic solvent or an alkaline solvent. Further, JP-A-1-198609 describes a material obtained by adding a filler to an acrylic polymer material having a carboxyl group as a water-soluble core material.

However, these water-soluble materials have problems in forming a core due to lack of heat resistance and fluidity, or are poor in water solubility when removing a used core with water. There was a problem.

[0006]

Accordingly, the present invention provides a core material for injection molding, which has sufficient heat resistance and fluidity when forming the core and has a fine structure. An object of the present invention is to provide a core material which can be precisely formed and is easily dissolved in water when the used core is dissolved and removed in water.

[0007]

As a result of various studies to solve the above problems, the present inventors have found that a composition comprising a copolymer of polyvinyl alcohol (PVA) and polyethylene oxide (PEO) The inventors have found that the above conditions are satisfied and completed the present invention. Accordingly, the present invention provides an injection molding core material comprising a copolymer of polyvinyl alcohol (PVA) and polyethylene oxide (PEO) and its use.

[0008]

[Detailed Description] In the present invention, a copolymer of polyvinyl alcohol (PVA) and polyethylene oxide (PEO) is used as a water-soluble core material used in a mold for injection molding. Polyvinyl alcohol (P
VA) has a melting point at 170 ° C to 230 ° C due to the difference in the degree of saponification.

However, all PVAs have the drawback that thermal decomposition begins to occur at temperatures above 200 ° C., and above 240 ° C., dehydration and crosslinking reactions proceed, resulting in a marked decrease in water solubility. Thus, during the thermal processing of PVA, the thermal processing was extremely difficult because the decomposition reactions occur in parallel. On the other hand, polyethylene oxide (PEO) is also known as a water-soluble resin. However, PV of the same average molecular weight
Compared with A, the injection fluidity is remarkably poor, and it is not suitable for the production of injection-molded products having a fine shape.

The polyvinyl alcohol (P
The copolymer of VA) and polyethylene oxide (PEO) has a hydroxyl group and an ether bond in its structure, so that while maintaining high water solubility, the concentration of the hydroxyl group causing a chemical reaction is relatively lowered. It is more stable than PVA because it can. Furthermore, the introduction of ether bonds gives a low melting point, which can solve the problem of thermal processability. The PVA part constituting this copolymer refers to a partially saponified PVA having an acetic acid group to a completely saponified PVA depending on the degree of saponification.

The molar ratio of PVA and PEO in the copolymer is preferably 99-50 (PVA): 1-50 (P
EO). Within the range of this ratio, sufficient heat stability and sufficient fluidity during core formation and sufficient water solubility of the used core can be obtained, but when PEO is more than 50%, core material The viscosity becomes high and it becomes difficult to form a core having a fine shape. If PEO is less than 1%,
The heat stability of the core material is low, and thermal crosslinking occurs due to heating during core formation, and the water solubility of the used core tends to decrease.

The molar ratio of PVA to PEO in the polymer is more preferably 95-55 (PVA): 5-45 (PE
O). This is because the above features are emphasized in this range. The molar ratio of PVA and PEO in the polymer is more preferably 90 to 70 (PVA): 30 to 1
It is 0 (PEO). This is because the characteristics described above are further emphasized in this range.

The degree of saponification of PVA is preferably 65 mol% or more, for example 65 to 99 mol%. Here, 99 mol% means the maximum value of the saponification degree that is actually available.
This is because when the saponification degree is less than 65 mol%, the hydrophobicity is strong and the solubility in water tends to decrease. The degree of saponification of PVA is more preferably 70 mol% or more, for example 70.
˜99 mol%. This is because if it is 70 mol% or more, the water solubility becomes particularly high. The degree of saponification of PVA is more preferably 80 mol% or more, for example 80 to 99 mol%.
Is. This is because when the saponification degree is 80 mol% or more, the water solubility is maintained, the melting point rises, and the heat resistance during injection molding of parts and the like improves.

In a preferred embodiment of the water-soluble core material of the present invention, the water-soluble core material has a Tg of 40 ° C to 100 ° C. The reason is that if the temperature is lower than 40 ° C., the heat resistance is poor and it is not suitable as a core material used in a mold for injection molding. On the other hand, if the temperature exceeds 100 ° C., the injection molding of the core itself becomes difficult and, in addition, the water solubility decreases. for that reason,
In particular, it becomes difficult to use it for an injection molded product having a fine structure.

In a preferred embodiment of the water-soluble core material of the present invention, the MI of the water-soluble core material is 0.1 to 50 (A
It is a water-soluble polymer material according to STM D-1238 at 210 ° C. and under a load of 2160 g). In the present invention, the MI is limited to 0.1 to 50 because when it is less than 0.1, the fluidity in the mold for injection molding becomes poor, and in particular, it is used for an injection molded product having a fine structure. Will be difficult. On the other hand, when it exceeds 50, the average molecular weight of the core material is
This is because it becomes relatively low and the heat resistance decreases.

Specific commercially available PVA / PE
Examples of the O copolymer include water-soluble PVA / PEO copolymers Ax300 and Ax2000 manufactured by Nippon Synthetic Chemical Industry Co., Ltd. As the water-soluble core material of the present invention, an oxazoline compound, polyethylene oxide (PEO), and / or PVA can be added to the above core material. The oxazoline compound is defined as a polymer material having an oxazoline skeleton in the molecule, and for example, poly (2-ethyl-2-oxazoline) or the like can be used. Here, the reason for adding the oxazoline compound, PEO, or PVA is that it is possible to improve the fluidity and water solubility without impairing the heat resistance of the core material.

Particularly, for PVA, the hydroxyl group concentration is
70 to 95 mol% is preferable. The reason is 70
If it is less than mol%, the water solubility will decrease, while 95 mol%
If it exceeds, not only the water solubility is lowered but also the heat resistance is significantly deteriorated. The addition amount of the oxazoline compound, PEO or PVA is 100% by weight of the water-soluble copolymer 100.
5 to 60 parts by weight is preferable with respect to parts by weight. This is because if the amount of the oxazoline compound, PEO or PVA added is less than 5 parts by weight, the improvement effect is poor. on the other hand,
If it exceeds 60 parts by weight, the heat resistance is remarkably reduced, and it is not suitable for the production of injection-molded products having a fine structure.

A polyhydric alcohol compound, a filler, a pigment, and / or a dye may be further added to the water-soluble core material of the present invention. The polyhydric alcohol compound can improve the fluidity of the core resin by adding a small amount thereof. Also,
Since it has a hydroxyl group in the molecule, it has a relatively high boiling point, and even when it is used in the mold of the present invention, there is no problem such as foaming or bleeding. In particular, it is even more effective in improving the dispersibility of inorganic substances, fillers such as metal oxides, and coloring pigments.

Polyhydric alcohol is defined as a compound having at least two or more hydroxyl groups in the molecule.
Glycerin, ethylene glycol, trimethylene glycol, tetramethylene glycol, propylene glycol, diethylene glycol, triethylene glycol,
2,3-butanediol, 1,3-butanediol, pentamethylene glycol and the like can be used.

The fillers are effective in improving the heat resistance, the mechanical strength, the effect of increasing the amount (reducing the cost), improving the fluidity and improving the solubility of the core material of the present invention. For example, talc, glass beads, Hollow glass beads, magnesium carbonate, silica particles, alumina oxide, calcium carbonate, mica, aluminosilicate, calcium phosphate, zeolite, metal salts and oxides of titanium, tin, magnesium, zinc and the like can be used. The amount of the filler added is not particularly limited, but is generally preferably 1 to 150 parts by weight with respect to 100 parts by weight of the water-soluble core material. Other than that, the improvement effect is poor. It is also preferable that the filler such as glass beads improves the compatibility with the core resin by the coupling treatment.

The pigments or dyes are extremely effective for visually recognizing the melted state of the core material of the present invention, that is, the adhesion of the core material to an injection molded article such as a face-to-face engaging fastener. Is. For example, by using a color different from the color of the injection-molded product for the core, it is possible to easily determine the adhesion of the core material to the product. Type is not particularly limited, carbon black, organic pigments, titanium white, organic dyes such as azo dyes, nitroso dyes, anthraquinone dyes, indigo dyes, sulfur dyes, acid dyes, basic dyes, thiazole dyes, Naphthol dye can be used.

The amount of the pigment or dye added is preferably 0.01 to 5 parts by weight with respect to 100 parts by weight of the water-soluble core material. If it is less than 0.01 parts by weight, the above-mentioned discrimination effect is poor, and if it exceeds 5 parts by weight, conversely, the pigment or
The dye adheres to the injection molded product, and conversely, it takes time to remove it. According to the present invention, the core material of the present invention is
Provided is a method for producing a core, which comprises melting at a temperature of 50 ° C. or higher, and injecting the melted core material into a mold for molding.

Here, heating the core material to a temperature of 150 ° C. or higher provides a low melt viscosity, and a mushroom shape connected to the base, a plurality of legs protruding from the base, and the ends of the legs. In order to enable precise and short-time production of precise injection-molded products such as face-to-face engaging fastener members having a plurality of headed protrusions that are provided upright with a predetermined spacing. is there.

As the heating means, a heater, infrared rays or the like can be used. Further, the melting temperature is 160 to 2
60 degreeC and 190-240 degreeC are suitable. Within the former range, a lower melt viscosity is obtained and the core material is
This is because there is no possibility that a crosslinking reaction or the like will occur due to overheating. Further, within the latter range, a lower melt viscosity can be obtained, and there is less risk of problems such as crosslinking and discoloration of the core material.

Further, as a method of manufacturing the core of the present invention,
It is preferable to mold the molten core material into a predetermined shape in a mold. This is because a molded product having a fine shape can be easily molded in a short time. In addition, in order to accelerate the solidification of the core and enable the mold to be molded in a short time, it is desirable to cool the mold to a certain temperature or lower with cooling air or the like. As described above, by using the core material of the present invention, it is possible to provide a water-soluble core for injection molding which is excellent in heat resistance, fluidity and water solubility.

Then, after that, the molten material for injection molding can be injected and molded while the core is placed in the same mold. As a result, complex microstructures such as face-to-face fastener members can be molded in a single step. When injecting the molten material for injection molding,
In order to maintain the shape of the core, it is desirable to carry out at a temperature below the melting temperature of the core. The molding method of the core and the method of manufacturing a molded product using the core are described in US Pat. No. 5,242,242.
No. 646 is described in detail.

[0027]

EXAMPLES Next, the present invention will be described more specifically by way of Examples and Comparative Examples. The materials used in the following examples and comparative examples are as follows.

[0028]

[Table 1]

[0029]

[Table 2]

Examples 1-2 and Comparative Examples 1-3. Water-soluble resin Ecomati and PVA manufactured by Nippon Synthetic Chemical Industry Co., Ltd.
24 using a hot air dryer whose temperature is controlled at 50 ° C.
After drying for more than an hour, a core mold 6 manufactured by Sumitomo 3M Co., Ltd. was used by an injection molding machine PS-40 manufactured by Nissei Plastic Industry Co., Ltd.
No. was used to produce cores at 210 ° C. Then, a standard face-to-face engaging fastener manufactured by Sumitomo 3M Limited was manufactured by using the injection molding machine PS-40 manufactured by NISSEI PLASTIC INDUSTRIAL CO., LTD. Using the core, and the following evaluations were performed.

1. Measurement of saponification degree The saponification degree was calculated from the integrated intensity ratio measured using a nuclear magnetic resonance apparatus EX270 manufactured by JEOL Ltd. 2. Core material melting point (Tm) and glass transition temperature (Tg)
Measurement Using DSC-2C manufactured by Perkin Elmer, -60 to 3
The temperature was raised to 00 ° C. under the condition of 10 ° C./min, and Tm and Tg were measured from the change in specific heat.

3. Measurement of decomposition temperature (Td) of core material 10 ° C / mi using a thermogravimetric analyzer 951 manufactured by DuPont
The temperature was raised under the condition of n and the decomposition temperature in the air atmosphere was measured. 4. Melt Index (MI) Measurement of Core Material Using a melt indexer S-1001 manufactured by Toyo Seiki Co., Ltd., ASTM D-1238 (210 ° C., 2160 g)
The melt index (MI) of the core material was measured according to (under load condition).

5. Evaluation of Solubility The undissolved product in which the face-to-face engaging fastener member (1011CH5) and the core are integrated is immersed in water at 23 ° C or warm water at 70 ° C for 24 hours, and the dissolved state of the core material is visually checked. Was judged according to the following criteria. OK: Completely dissolved Fair: Almost dissolved NG: Undissolved substance present 6. Evaluation of heat resistance

The polymer materials described below were used as the face-to-face fastener members, and the face-to-face fastener members were manufactured under the temperature conditions shown. Next, one stem row is cut out from the surface fastener in the longitudinal direction, and the shape and uniformity of the stem group from the cross-sectional direction is judged by using a microscope according to the following criteria. The sex was evaluated.

Polypropylene 6800J 210 ° C manufactured by Mitsubishi Kasei Co., Ltd. 6 nylon 1011CH5 250 ° C manufactured by Mitsubishi Kasei Kogyo Co., Ltd. 66 nylon 1200S 280 ° C manufactured by Asahi Kasei Co., Ltd. OK: No problem NG: Partially defective Table 3 below.

[0036]

[Table 3]

Examples 3 to 7 and Comparative Examples 4 to 5. Water-soluble resin Ecomati and PVA manufactured by Nippon Synthetic Chemical Industry Co., Ltd.
Using a hot air dryer whose temperature is controlled at 50 ° C., 24
After drying for more than an hour, a polyhydric alcohol, an oxazoline compound, carbon black, and a filler were added and sufficiently mixed to obtain a core material. Next, the following evaluations were performed in the same manner as in Example 1 above. 1. Melt index (MI) measurement of core material 1. Evaluation of solubility 3. The evaluation results of heat resistance are shown in Table 4 below.

[0038]

[Table 4]

[0039]

As described above, according to the present invention, by using the copolymer of PVA and PEO, a core having a fine structure can be easily formed because of good thermal stability and fluidity. And, the used core can be easily dissolved and removed with water.

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Claims (11)

[Claims] 1. A core material for injection molding, which comprises a copolymer of polyvinyl alcohol (PVA) and polyethylene oxide (PEO). 2. The core material according to claim 1, wherein the molar ratio of PVA to PEO in the copolymer is 99 to 50:50 to 1. 3. The core material according to claim 1, wherein the PVA has a saponification degree of 65 to 99 mol%. 4. The core material according to claim 1, wherein the glass transition temperature (Tg) of the core material is 40 ° C. to 100 ° C. 5. The melt index (M
I) is 0.1-50, any one of Claims 1-4.
The core material described in the item. 6. The core material according to claim 1, further comprising an oxazoline compound, PVA and / or PEO. 7. A core molded using the core material according to any one of claims 1 to 6. 8. The core material according to claim 1, which is melted at a temperature of 150 ° C. or higher, and the melted core material is injected into a mold for molding. The manufacturing method of the core. 9. An injection-molded article formed by using the core according to claim 7. 10. The injection-molded article according to claim 9, which is a face-to-face engaging fastener member. 11. A method for manufacturing an injection-molded article, which comprises arranging the core according to claim 7 in a mold and then injecting an injection-molded article material.