JP3527538B2 - Core resin composition and method for producing hollow molded article using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin composition for cores and a method for producing a hollow molded article using the same, more specifically, the rigidity does not decrease with time due to moisture absorption, heat resistance, The present invention relates to a resin composition for cores, which has an excellent rate of water dissolution and water removability and a good finish accuracy of a hollow molded article, and a method for producing a hollow molded article using the same.

[0002]

2. Description of the Related Art Various proposals have been made for forming a core from a water-soluble resin in order to obtain a hollow molded article.

For example, JP-A-3-230927 and JP-A-3-227609 disclose, as water-soluble resins, polyacrylamide, polyacrylic acid, polymethacrylic acid, polyitaconic acid, polyvinyl alcohol (hereinafter P.
(Abbreviated as VA), polyethylene oxide, polyvinylpyrrolidone, polyvinyl methyl ether, isoprene-based resin soluble in alkaline aqueous solution, ethylene acrylate-acrylic acid copolymer, and the like are disclosed.

Further, in JP-A-6-39844, a vinyl acetate polymer having a degree of polymerization of 200 to 2000 is saponified as a water-soluble resin composition which can be easily molded into a core by injection molding or the like. A resin composition for cores is disclosed which comprises 100 parts by weight of a polymer obtained by saponification at 65 to 95 mol%, 0.5 to 50 parts by weight of a plasticizer, and 0 to 100 parts by weight of an inorganic filler.

Regarding the oxyalkylene group-containing vinyl alcohol-based polymer itself used in the present invention, US Pat. Nos. 1,917,662 and 2,844,570 are cited.
And No. 2990398 (oxyethylene group-containing PVA obtained by addition reaction of ethylene oxide with PVA), US Pat. Nos. 3,033,841 and 4,369,281 (with vinyl acetate in the presence of polyalkylene glycol). Oxyalkylene group-containing PVA obtained by saponifying a graft-polymerized polymer, US Pat. No. 46.
18648 and 4675360 (copolymer of vinyl alcohol and poly (alkyleneoxy) acrylate), JP-A-59-155408 (unsaturated monomer containing oxyalkylene group and acetic acid). Modified PVA obtained by saponifying a copolymer with vinyl), JP-A-1-158016 (water-resistant flexible film composed of vinyl alcohol-based polymer film containing oxyalkylene group), JP-A-3-203932 (oxyalkylene). There is a document such as a method of melt-molding a group-containing vinyl alcohol-based copolymer under substantially anhydrous conditions), but regarding the use of this oxyalkylene group-containing vinyl alcohol-based polymer as a core in injection molding. There is no description or suggestion, let alone blended with an inorganic filler and used as a core No mention at all in relation to Rukoto.

[0006]

Although various types of water-soluble resins for cores are used as described above, a core having a well-balanced finish accuracy and water-dissolving removability of a hollow molded product is used. It was very difficult to make. Further, it is rarely used for hollow molding immediately after the core is produced, and it is often left outside for a certain period of time.
In the technology disclosed in Japanese Patent Laid-Open No. 39844, there is a problem that the rigidity is lowered due to moisture absorption and the like, and the finish accuracy of the hollow molded article is lowered.

There is no decrease in rigidity over time due to moisture absorption,
It is desired to develop a resin composition for cores which is excellent in heat resistance, water dissolution rate and water dissolution removal property, and which can obtain a hollow molded article having good finishing accuracy, and a method for producing a hollow molded article using the same. Was there.

[0008]

However, as a result of intensive investigations by the present inventors in order to solve such problems, as a result, the PVA-based resin (A) containing an oxyalkylene group has an aspect ratio.
By blending 1 to 60% by weight of the inorganic filler (B) having a ratio of 20 or more, rigidity does not decrease with time due to moisture absorption, etc., and heat resistance, water dissolution rate and water dissolution removal property are excellent, and hollow. It was found that a resin composition for cores having a good finished precision of a molded product and a method for producing a hollow molded product using the same can be obtained, and the present invention has been completed.

The present invention will be described in detail below. Oxyalkylene group-containing PVA resin (A) used in the present invention
Is typically a fatty acid vinyl ester and a polyoxyalkylene (meth) allyl ether such as polyoxyethylene (meth) allyl ether or polyoxypropylene (meth) allyl ether represented by the following general formula 1 or the following general formula It can be obtained by copolymerizing a polyalkylene vinyl ether such as polyoxyethylene vinyl ether and polyoxypropylene vinyl ether represented by Formula 2, and then saponifying the resulting copolymer. Among them, the PVA-based resin (A) containing an oxyalkylene group, which is obtained by saponifying a vinyl acetate-based copolymer, is economically most preferable.

As the polymerization method for obtaining the oxyalkylene group-containing PVA-based polymer, a solution polymerization method is usually adopted, and a suspension polymerization method, an emulsion polymerization method or the like can be adopted depending on the case. As the saponification reaction, an alkali saponification method, an acid saponification method or the like is adopted.

The oxyalkylene group content of the oxyalkylene group-containing PVA polymer is 1 to 60% by weight,
It is preferably from 2 to 50% by weight, particularly preferably from 3 to 40% by weight, and when it is less than 1% by weight, extrusion moldability is deteriorated.
There is a problem in that the water-dissolving rate and the water-dissolving removability are lowered, and if it is more than 60% by weight, there is a problem in that the precision moldability of the core is lowered and the thermal rigidity is lowered. The polyoxyalkylene group has an average degree of condensation of 3 to 100, and those having an average degree of condensation of less than 3 are inferior in extrusion moldability, and also have low industrial productivity when introducing the oxyalkylene group and water. There are problems such as a decrease in dissolution rate and water-dissolving removability, and when the average degree of condensation is more than 100, problems such as a decrease in extrusion moldability occur, preferably 3 to 50, particularly preferably 5 to 3.
It is 0. The average degree of condensation referred to herein means the following chemical formula 1,
N in the chemical formula shown in Chemical formula 2 is shown.

[0012]

[Chemical 1] However, R ₀ , R ₁ , R ₂ and R ₃ represent hydrogen or an alkyl group.

[Chemical 2] (X = H or -C-R _3, or R _{3) where, R 1, R 2, R} 3 represents hydrogen or an alkyl group.

The degree of saponification of the fatty acid vinyl ester units in the PVA-based resin (A) containing an oxyalkylene group is 60 to 100 mol%. There is a problem such as a decrease in finishing accuracy (a decrease in heat distortion temperature), a decrease in thermal stability, a decrease in moldability, a decrease in affinity with an inorganic filler, a decrease in rigidity, etc., preferably 80 to 100 mol% Is appropriate.
The weight average degree of polymerization is 100 to 2000,
If the amount is less than 2000, the strength of the core becomes insufficient, and if it exceeds 2000, there is a problem in that the melt viscosity is large and the finish accuracy of the hollow molded product is deteriorated, and the inorganic filler is poorly dispersed. It is particularly preferable because of the influence on the melt viscosity of the resin composition after blending the base filler (B) and the influence on the smoothness of the surface of the core (floating of the filler such as glass fiber) when the resin composition is molded as a core. Is 10
0 to 600.

Further, as a copolymerization component, in addition to polyoxyalkylene (meth) allyl ether, α-olefins (ethylene, propylene, long-chain α-olefins, etc.), ethylenically unsaturated carboxylic acid type monomers (acrylates,
Methacrylate, acrylonitrile, methacrylonitrile, vinyl chloride, vinyl ether, etc.) may be contained in an amount of about 30 mol% or less.

The oxyalkylene group-containing PVA-based resin (A) is, in addition to the above, a fatty acid vinyl ester, polyoxyethylene (meth) acrylate, polyoxypropylene (meth) acrylate, and polyoxyethylene (meth).
Polyoxyalkylene allylamine such as acrylamide, polyoxypropylene (meth) acrylamide, polyoxyethylene (1- (meth) acrylamide-1,1-dimethylpropyl) ester, polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinyl It can also be obtained by copolymerizing amine, polyoxyalkylene vinyl amine such as polyoxypropylene vinyl amine, and then saponifying.

The PVA-based resin (A) containing an oxyalkylene group can be obtained by a reaction of alkylene oxide with PVA or polymerization of fatty acid vinyl ester with polyoxyalkylene glycol and subsequent saponification, in addition to the above method. I can.

The amount of the inorganic filler used in the core resin composition of the present invention is 1 to 60% by weight, preferably 10 to 55% by weight, and particularly preferably 20 to 50% by weight. If it is less than 1% by weight, heat resistance rigidity, water dissolution rate and water dissolution removability, stability with time of rigidity against moisture absorption, etc. are insufficient, and if it is more than 60% by weight, extrusion moldability, finish accuracy and surface of hollow molded product are obtained. It is not suitable because the smoothness etc. decreases.

Further, as the inorganic filler (B), talc, clay, silica, diatomaceous earth, kaolin, from the viewpoints of size, weight change and strength upon absorption of water, strength, elastic modulus, heat resistance, and improvement in hot water dissolution and removal property, Mica, asbestos, gypsum, graphite, glass fiber, glass balloons, glass beads, calcium sulfate, barium sulfate, ammonium sulfate, calcium sulfite, calcium carbonate, whisker-like calcium carbonate, magnesium carbonate, dawsonite, dolomite,
Potassium titanate, carbon black, alumina fiber,
Aramid fiber, boron fiber, processed mineral fiber, carbon fiber,
At least one selected from carbon hollow spheres, bentonite, montmorillonite, copper powder, etc. can be used, but strength, elastic modulus, heat resistance, water dissolution rate and water dissolution removal property, finish accuracy of hollow molded product From the standpoint of further improving the inorganic filler having an aspect ratio of 20 or more
It is necessary to adopt (B), and the average fiber diameter or average fiber
The rake diameter is preferably 1 to 30 μm , and talc, mica, glass fiber, and whisker-like calcium carbonate having a shape satisfying the above conditions are particularly preferable as the inorganic filler (B) in the present invention. The major axis of the inorganic filler is less than 50 mm, preferably less than 25 mm, more preferably less than 10 mm. If the major axis is 50 mm or more, the inorganic filler may be crushed during kneading during compounding or injection molding. Is not preferred.

Examples of the mica flakes used in the present invention include muscovite and phlogopite, as well as biotite, levidrite, paragonite, margarite, sericite, synthetic phlolovogrogite, and the like. , Non-alkali glass (E glass), chemical glass (C
In addition to (glass), alkali-containing glass (A glass) and the like are used. As the whisker-like calcium carbonate, for example, whiskers (manufactured by Maruo Calcium Co., Ltd.) are used.

The inorganic filler (B) is mixed with the oxyalkylene group-containing PVA-based resin (A) by the inorganic filler (B) and the oxyalkylene group-containing P.
A method in which the VA resin (A) is directly supplied to an injection molding machine or an extrusion molding machine to perform mixing and molding, or a mixture of the oxyalkylene group-containing PVA resin (A) and the inorganic filler (B). A method of supplying to an extruder and pelletizing is adopted.

The core is molded by melt-molding the oxyalkylene group-containing PVA resin (A) containing the above-mentioned inorganic filler (B). Examples of the melt molding method include an injection molding method, a blow molding method, an extrusion molding method, and a transfer molding method. At the time of melt molding, various additives such as a lubricant, a colorant, a stabilizer such as an antioxidant, and other polymers may be blended as necessary.
When the injection molding method is adopted, for example, the cylinder temperature is about 150 to 250 ° C, the mold temperature is about 30 to 100 ° C,
The conditions of injection pressure of about 500 to 2000 Kg / cm ² are adopted. When the extrusion molding method is adopted, it is desirable to set the die temperature to about 150 to 250 ° C. and the screw compression temperature to 5 to 30 ° C. higher than the discharge temperature, for example.

Then, in the present invention, the core thus obtained is inserted into a mold, and a molding material is injection molded around the core. Examples of the molding material include various thermoplastic resins and thermosetting resins.

After injection molding, the core is cooled with cold water, normal temperature water,
A hollow molded article is manufactured by dissolving and removing with hot water, hot water, water such as steam. Examples of hollow molded products are hollow molded products having bent parts (intake manifold), complex shaped hollow manifolds, different diameter pipes, complex shaped hollow parts (bumpers, handles such as blades and kitchen utensils, golf club heads). ), Electronic parts and mechanical parts (propellers, blades, impellers), and the like.

[0024]

By blending 1 to 60% by weight of the organic filler (B) having an aspect ratio of 20 or more with the polyvinyl alcohol resin (A) containing an oxyalkylene group, such a resin composition can be obtained. For cores, the rigidity of the core made of is not deteriorated with time due to moisture absorption, etc., and is excellent in heat resistance, water dissolution rate, water dissolution removal property, and good finish accuracy. A resin composition and a method for producing a hollow molded article using the same are obtained, which is very useful.

[0025]

EXAMPLES The present invention will be described in more detail below with reference to examples. In the examples, "%" means weight basis unless otherwise specified. Example 1 Oxyalkylene group-containing PVA (A) Weight average degree of polymerization: 350 Polyoxyethylene monoallyl ether (X in formula 1 is H) (Copolymerization ratio of oxyethylene is 20) Average unit: 2.0 Mol% Ratio of oxyalkylene units in the whole polymer: 2
0% by weight Saponification degree of vinyl acetate component: 90 mol%

Inorganic filler (B) Glass fiber Average fiber diameter (μ): 10 Aspect ratio: 300

The above resin was supplied to a single-screw extruder (L / D = 28, 40 mmφ) at the compounding ratio shown in Table 1, and the supply section =
Pelletized resin composition was obtained by extruding at 180 ° C., compression part = 210 ° C., and metering part = 210 ° C. In order to evaluate the suitability of the core resin composition of the present invention as a core, the molding pellets are supplied to an injection molding machine, the cylinder maximum temperature is 220 ° C., the mold temperature is 60 ° C., and the injection pressure is 900 Kg /
The test piece having the shape shown below was prepared by injection molding under the condition of cm ^{2, and} the heat distortion temperature, the water dissolution time, and the bending strength retention rate after standing for 10 days at 25 ° C. and 65% RH under the following conditions: Was evaluated.

(Test piece) For heat distortion temperature measurement: Thickness 1 according to ASTM D648
A test piece of 2.7 mm, width of 12.7 mm, and length of 127 mm. For water dissolution time measurement: a disc-shaped test piece having a thickness of 3.2 mm and a diameter of 50 mm. For bending test: Thickness according to ASTM D790 6.
4 mm, width 12.7 mm, length 152.4 mm test piece.

(Test Conditions) Heat Deformation Temperature: Heat distortion tester manufactured by Yasuda Seiki Co., Ltd. was used. Load 18.6Kg, heating rate 2 ℃
/ Min. (Judgment Criteria) ◯: 60 ° C. or more Δ: 50 ° C. or more and less than 60 ° C. ×: less than 50 ° C. Water dissolution time: The test piece was immersed in a water bath having a water temperature of 25 ° C. and a water volume of 2 l, and stirred at a rotation speed of 300 rpm. . (Judgment Criteria) ○: 100 minutes or more and less than 200 minutes △: 200 minutes or more and less than 250 minutes X: 250 minutes or more Bending test: Shimadzu Corporation Autograph AG-5
Use 000A. Used load cell 500 kg, fulcrum span 101.6 mm Bending speed 2.5 mm / min. (Judgment Criteria) Judgment based on the retention rate of bending strength after leaving at 20 ° C. and 65% RH for 10 days ○: 86% or more △: 80% or more and less than 85% ×: less than 80%

The oxyalkylene group-containing PVA pellets containing the above-mentioned inorganic filler were fed to an injection molding machine and injection-molded under the following conditions to give a cylindrical shape with a branch pipe shown in FIG. The core was molded. Melt temperature: 200 to 230 ° C. Injection pressure: Primary 1000 kg / cm ² 2 primary 800 kg / cm ² 1 cycle: 28 seconds

Next, the core obtained above was set in a mold, and polypropylene (resin temperature: 250 ° C.) was injection-molded around the core under the following conditions. Melting temperature: 240 to 250 DEG ° C. Injection pressure: Primary 600 kg / cm ² 2 primary 600 kg / cm ² 1 cycle: 30 seconds

After the injection molding, the injection-molded product was taken out of the mold and allowed to stand in water at a temperature of 20 ° C. to dissolve and remove the core, and the melting time and the dimensional accuracy of the hollow-molded product were determined by the following methods. . Further, injection molding was similarly performed on the core after leaving the core at 20 ° C. and 65% RH for 10 days, and the melting time and the dimensional accuracy of the hollow molded product were determined.

Dissolving / removing time (20 ° C., standing): One molded product obtained by injection molding polypropylene around the core,
Immerse in a water tank containing 50 liters of water at 20 ° C,
The time until the core was completely dissolved was measured. Such a test was repeated 10 times and the average value was calculated. The evaluation results are shown in Tables 1 and 2. Hollow molded product dimensional accuracy: The inner diameter of the inner cylinder part of the core molded product after the core was dissolved and removed was measured with a caliper. 10 In this case, as shown in FIG. 2 (b), equally spaced points a ₁ ~a ₁₀
The inner diameter of the inner cylinder was divided into 16 equal parts for measurement, the fluctuation range of the deviation was determined, and the percentage of the mean value of the inner diameter was displayed.

Example 2 Weight-average degree of polymerization of PVA (A) containing oxyalkylene group : 350 Copolymerization ratio of polyoxyethylene monoallyl ether (X in formula 1 is H) (average degree of condensation of oxyethylene is 25) units: 2.4 mol% Ratio of oxyalkylene units in the whole polymer: 3
5% by weight Saponification degree of vinyl acetate component: 90 mol%

Inorganic filler (B) Glass fiber Average fiber diameter (μ): 10 Aspect ratio: 300

In order to evaluate the suitability of the resin composition as shown in Table 1 for the core of the resin composition for cores in the same manner as in Example 1, a pelletized resin composition was obtained, and the pellets for molding were obtained. Was supplied to an injection molding machine for injection molding, and the heat deformation temperature, the water dissolution time and the flexural modulus were evaluated.

The pellets of oxyalkylene group-containing PVA blended with the above-mentioned inorganic filler (B) are fed to a blow molding machine and blow molded under the following conditions, and the result is shown in FIG.
The bent core-shaped core shown in Fig. 3 was molded. Molding machine: Co. Tahara manufactured by blow molding machine TPF-403 Screw diameter 40mmφ, L / D = 24 cylinder _{temperature: C 1 / C 2 / C} 3 / C 4 / D (H) =
180/190/210/210/200 (° C) Screw rotation speed: 30 rpm Motor addition: 24 amp extrusion rate: 8.7 kg / hr parison descent time: 24 seconds Weight and wall thickness of molded product: weight 320 g, wall thickness 2 0.5 mm molding cycle: Mold clamping for about 17 seconds, air blow
About 20 seconds, total about 55 seconds

Next, the core obtained above was set in a mold, and polypropylene was injection-molded around the core under the same conditions as in Example 1. After injection molding, the injection-molded product was taken out of the mold, the core was dissolved in water at a temperature of 70 ° C. under flowing conditions, and the dissolution time and the dimensional accuracy of the hollow-molded product were determined by the following methods. Further, injection molding was similarly performed on the core after leaving the core at 20 ° C. and 65% RH for 10 days, and the melting time and the dimensional accuracy of the hollow molded product were determined.

Dissolution and removal time (70 ° C., water flow): One molded product obtained by injection molding polyphenylene ether around the core was immersed in a water tank containing 50 liters of water at a temperature of 70 ° C. The water in the water tank was circulated at a rate of 50 liters per minute by a pump, and the time until the core was completely dissolved was measured. Such a test was repeated 10 times and the average value was calculated.

Dimensional accuracy of hollow molded product: The inner diameter of the inner cylinder part of the core molded product after the core was dissolved and removed was measured with a caliper.
In this case, as shown in FIG. 2 (b), equally spaced points b ₁
Perform measurement of the inner cylinder inner diameter 16 equal portions for 10 locations ~b _10, obtains the variation width of the deviation, 1 to the average value of the inner diameter
It is shown by the percentage display. The evaluation results are shown in Tables 1 and 2. Evaluations were performed for Examples 3 to 17 and Comparative Examples 1 to 3 according to Example 1 and Example 2. Table 1 shows the evaluation results.
And shown in Table 2.

Example 3 Weight average degree of polymerization of oxyalkylene group-containing PVA (A) : 350 Copolymerization ratio of polyoxyethylene monoallyl ether (X in formula 1 is H) (average degree of condensation of oxyethylene is 20) units: 2.0 mol% Ratio of oxyalkylene units in the entire polymer: 2
0% by weight Saponification degree of vinyl acetate component: 95 mol%

Inorganic filler (B) Glass fiber Average fiber diameter (μ): 8 Aspect ratio: 320

Example 4 Oxyalkylene group-containing PVA (A) Weight average degree of polymerization: 350 Polyoxyethylene monoallyl ether (where X is C
H ₃ ) (The average degree of condensation of oxyethylene is 22) Copolymerization ratio of units: 2.2 mol% Ratio of oxyalkylene units in the entire polymer: 2
0% by weight Saponification degree of vinyl acetate component: 90 mol%

Inorganic filler (B) Glass fiber Average fiber diameter (μ): 12 Aspect ratio: 300

Example 5 PVA (A) containing oxyalkylene group Weight average degree of polymerization: 500 Polyoxyethylene monoallyl ether (where X is C
H ₃ ) Copolymerization ratio of units (average degree of condensation of oxyethylene is 25): 2.4 mol% Ratio of oxyalkylene units in the whole polymer: 3
5% by weight Saponification degree of vinyl acetate component: 90 mol%

Inorganic filler (B) Glass fiber average fiber diameter (μ): 10 Aspect ratio: 300

Example 6 Weight-average degree of polymerization of oxyalkylene group-containing PVA (A) : 420 Polyoxyethylene vinyl ether (X in formula 2 is H)
(The average degree of condensation of oxyethylene is 22) Copolymerization ratio of units: 2.1 mol% Ratio of oxyalkylene units in the whole polymer: 2
2% by weight Saponification degree of vinyl acetate component: 92 mol%

Inorganic filler (B) Glass fiber Average fiber diameter (μ): 10 Aspect ratio: 300

Example 7 Evaluation was made in the same manner as in Example 1 except that the inorganic filler (B) was mica having an average filler diameter of 8 μ and an aspect ratio of 80. Example 8 Evaluation was performed in the same manner as in Example 1 except that the inorganic filler (B) was talc having an average filler diameter of 10 μ and an aspect ratio of 25. Example 9 Evaluation was performed in the same manner as in Example 1 except that the inorganic filler (B) was a whisker-like calcium carbonate having an average filler diameter of 1 μ and an aspect ratio of 30.

Example 10 The ratio of oxyalkylene units in the entire polymer was 6
Evaluation was performed in the same manner as in Example 1 except that 5% by weight of oxyalkylene group-containing PVA (A) was used. Example 11 PVA containing oxyalkylene groups in which the proportion of oxyalkylene units in the entire polymer is 1.7% by weight.
Evaluation was performed in the same manner as in Example 1 except that (A) was used. Example 12 Evaluation was performed in the same manner as in Example 1 except that the oxyalkylene group-containing PVA (A) having a weight average polymerization degree of 1100 was used.

Example 13 Oxyalkylene group-containing PV having a weight average polymerization degree of 75
Evaluation was performed in the same manner as in Example 1 except that A (A) was used. Example 14 Oxyalkylene group-containing PVA having a saponification degree of 58 mol%
Evaluation was performed in the same manner as in Example 1 except that (A) was used. Example 15 Evaluations were made in the same manner as in Example 1 except that the oxyalkylene group-containing PVA (A) having an average degree of condensation of oxyethylene of 2 was used.

Example 16 Evaluations were made in the same manner as in Example 1 except that the oxyalkylene group-containing PVA (A) having an average degree of condensation of oxyethylene of 115 was used.

Comparative Example 1 Evaluation was carried out in the same manner as in Example 1 except that the blending amount of the inorganic filler (B) was 0% by weight. Comparative Example 2 Example 1 except that the glass fiber content was 70% by weight.
It evaluated similarly to. Comparative Example 3 Weight average polymerization degree of 35 containing 15% by weight of glycerin
The evaluation was performed in the same manner as in Example 1 except that polyvinyl alcohol having a vinyl acetate component saponification degree of 90 mol% was used. Comparative Example 4 Example 1 except that the aspect ratio of the glass fiber was 14.
It evaluated similarly to.

[0054]

[Table 1]

[0055]

[Table 2] (Note) α: Used for manufacturing hollow molded products without leaving after core production. β: Used to manufacture hollow molded products after leaving the cores at 20 ° C. and 65% RH for 10 days after manufacturing. A: Cylindrical shape with branches, B: Curved tube shape.

The polyvinyl alcohol resin (A) containing an oxyalkylene group has an aspect ratio of 20 or more.
That by inorganic filler (B) blending 1 to 60% by weight, such rigidity of the core of the resin composition without be decreased over time due to moisture absorption or the like, heat resistance, water dissolution rate and water solubility It is very useful to obtain a resin composition for cores which can obtain a hollow molded product having excellent removability and good finishing accuracy, and a method for producing a hollow molded product using the same.

[0057]

[Brief description of drawings]

FIG. 1 is a front view showing the shape of a core.

FIG. 2 is an explanatory view showing a measurement site for dimensional accuracy of a hollow molded product.

[Explanation of symbols]

a _{1 to} a ₁₀ : measurement points b _{1 to} b ₁₀ : measurement points

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C08K 3/34 C08K 3/34 (58) Fields investigated (Int.Cl. ⁷ , DB name) C08L 29/10 B29C 33/52 B29C 45/26 C08F 16/18 C08K 3/26 C08K 3/34

Claims (5)

(57) [Claims] 1. A polyvinyl alcohol-based resin (A) containing an oxyalkylene group having an aspect ratio of 20 or more.
A resin composition for a core, comprising 1 to 60% by weight of an inorganic filler (B). 2. The polyvinyl alcohol-based resin (A) containing an oxyalkylene group has a saponification degree of 60 to 100 mol%, and an average degree of condensation of the oxyalkylene group is 3 to 100,
The resin composition for a core according to claim 1, wherein the content of the oxyalkylene group is 1 to 60% by weight and the weight average degree of polymerization is 100 to 2000. 3. The resin composition for cores according to claim 1, wherein the inorganic filler (B) has an average fiber diameter or an average flake diameter of 1 to 30 μm . 4. The inorganic filler (B) is talc, mica,
The resin composition for cores according to claim 3, wherein at least one kind is selected from glass fiber and whisker-like calcium carbonate. 5. A hollow core is produced by inserting a water-soluble core into a mold, injection molding a molding material around the core, and dissolving and removing the core with water to produce a hollow molded article. A method for producing a hollow molded article, which comprises using the resin composition for a core according to any one of claims 1 to 4.