JPS5813575B2 - Goseimokuzai - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the creation of synthetic wood, and provides a synthetic wood with good cutting properties.

In particular, it is possible to provide a synthetic wood suitable for use in pencil shafts, which requires strong cutting properties.

Pencil barrels are generally made of natural wood, but in order to improve its cutting properties, this natural wood is selected from a special type of wood with specific annual rings, such as incense, and is also treated with complex treatments such as oil-impregnation treatment. I am using the one that has been given the following.

Furthermore, since it requires a special and complicated process to insert the core, it has drawbacks in terms of productivity, defective rate, price, etc.

On the other hand, synthetic pencil shafts based on plastic have been proposed to replace natural wood.

For example, Japanese Patent Publication No. 45-19124 proposes a lead equiaxed molded material made of a composition of polypropylene, fatty acid amide, Merck, etc.

Furthermore, Japanese Patent Publication No. 47-26014 proposes a pencil shaft made of foam such as styrene resin, and Japanese Patent Publication No. 49-2134 proposes a pencil shaft made of styrene resin foam containing short glass fibers. .

Japanese Patent Publication No. 49-12298 proposes a method for efficiently manufacturing pencils by continuously extruding the pencil shaft using a simple process and inserting the core by co-extrusion.

Furthermore, in Japanese Patent Application Publication No. 47-16214, there is
As an improvement on No. 2134, a composition in which fillers and glass fibers are added to a mixed composition of polystyrene and polyethylene has been proposed for use in lead shafts.

In particular, a composition estimated to be based on JP-A-47-16214 has been commercially available for several years.

The inventors of the present invention have carefully tried several patent examples related to the above-mentioned synthetic pencil shafts, and have also evaluated commercially available synthetic pencils in detail and compared them with pencils made of natural wood. Although it has many advantages, it has become clear that it still has drawbacks in terms of machinability.

In other words, when cutting with an electric cutting machine, the cutting resistance is
It is 20 to 30% larger than a natural wood shaft, and the joint between the shaft cores after cutting is difficult to scrape smoothly and tends to form a stepped structure.When manually cutting with a knife or safety razor, it is difficult to scrape like a plane. It was found that the scraps tended to resemble sawdust rather than plane shavings, making cutting inconvenient.

The present invention was created as a result of studies to eliminate the above-mentioned drawbacks of the conventional products, and its greatest feature lies in the use of a composition in which polyethylene and special reactive calcium carbonate are cross-wired. However, in order to further improve the cutting performance of the pencil shaft and also control other properties, such as extrusion processing characteristics, rigidity, bending strength, and pencil weight, to appropriate levels, reinforcement was applied. This material contains glass fiber, a foaming agent, etc., and the present invention was achieved by finding the optimum amount of these ingredients.

The inventors of the present invention first tried using inorganic fillers in combination with various plastic materials in order to obtain a pencil barrel with good machinability.
When using it as a base material, the material is hard and brittle, so when it is cut, it does not form a cutting layer and becomes powdery, resulting in high cutting resistance.It is difficult to improve the above drawbacks, so high-density polyethylene is used. was found to give the best results.

At room temperature, high-density polyethylene is less likely to break and is slightly softer than polystyrene or hard vinyl chloride resin.

However, this combination of high-density polyethylene and simple inorganic powder does not provide the effects of being hard to break, having high rigidity, and improving machinability, and results in only a very brittle composition.

The inventors of the present invention finally discovered a special reactive calcium carbonate after carrying out detailed experiments over a long period of time. We have discovered that the best effect can be obtained by using it as an inorganic filler.

Furthermore, in order to improve machinability and other various properties, we added glass fiber and found that foamed wood is good as a synthetic wood.

That is, the present invention uses 30 to 70 parts of high-density polyethylene having a melt index of 11/10 minutes or more and a density of 0.950 ff/crA or more, and 5 to 20 parts of glass fiber.
A synthetic wood consisting of 20 to 60 parts of special reactive calcium carbonate that exhibits binding properties with the polyethylene, the synthetic wood comprising at least an outer layer with a smaller expansion ratio and an inner layer with a larger expansion ratio than the outer layer, The foam cells of the inner layer exist independently of each other, and the inner layer and the outer layer are made of synthetic wood that is integrally formed.

Although the present invention relates to a synthetic wood designed for use in pencil shafts, the composition foam obtained by the present invention can be used as a substitute for wood other than pencil shafts by taking advantage of its properties. It is obvious that it can also be used.

The high-density polyethylene used in the present invention can be used in various commercially available brands, but in the present invention, it is necessary to blend a considerable amount of inorganic powder and perform extrusion processing, so it has high processing fluidity. In terms of physical properties, high rigidity and high impact strength are desirable.

Normal fluidity, melt index, stiffness, impact resistance,
Melt index: Ig/10 minutes or more, preferably 3 to 10 g/10 minutes, which is expressed by the density and Izod impact value of annealed or slowly cooled test pieces, in order to obtain good quality synthetic wood with the composition of the present invention. , density: 0.9 5 0
/cm3 or higher density polyethylene is used.

Furthermore, it is desirable to use a high-flow, high-rigidity product with an Izod impact strength (notched) of 4 or more.

(Physical property measurement methods are ASTM, D-1238, D-150
5, D-256, etc.) Next, the special reactive calcium carbonate referred to in the present invention is a metal of group Ⅰ of the periodic table, which is explained in detail in JP-A No. 48-67199. Surface-treated calcium carbonate produced by a method for producing active metal carbonate characterized by subjecting carbonate particles and an organic carboxylic acid to a heating reaction under dehydration conditions to bond the organic carboxylic acid to the surface of the metal carbonate particles. It is.

The surface-treated calcium carbonate has excellent affinity for organic substances and exhibits rapid and significant dispersibility, surface properties, and other performance-enhancing effects.

The surface-treated calcium carbonate produced by the above manufacturing method is produced by heating and reacting calcium carbonate and an organic carboxylic acid under dehydration conditions, and the activated calcium carbonate after the reaction is dried and
There is no need for re-grinding, the uniformity of the particle size of the obtained activated calcium carbonate is maintained, and the yield is very high, with a 5% mark.

Another feature is that by subjecting the metal carbonate particles such as calcium carbonate to a heating reaction with an organic carboxylic acid, the organic carboxylic acid forms a strong chemical bond on the surface of the metal carbonate particles. The layer consists of a homogeneous, completely reactive coated metal carbonate particle.

These characteristics give activated calcium carbonate particles an amazingly improved affinity for organic materials, and combined with the particle size and uniformity, they improve dispersibility in organic materials, surface properties, reinforcing properties, and other properties. This is a dramatic improvement.

FIG. 1 shows electron micrographs in which unprocessed calcium carbonate and the special reactive calcium carbonate of the present invention are kneaded into high-density polyethylene.

As can be seen from Figure 1, when polyethylene and calcium carbonate powder are heated and kneaded, the untreated calcium carbonate is not compatible with polyethylene and forms a simple blend system with a void structure (Figure 1). In contrast, in the case of the special reactive calcium carbonate referred to in the present invention (explained in JP-A No. 48-67199), polyethylene is strongly bonded to the surface of calcium carbonate powder. (See Figure 1-1B).

Furthermore, when using special reactive calcium carbonate,
The composition has dramatically improved bending strength.

In other words, untreated calcium carbonate is made into polyethylene,
As shown in Comparative Example 2, the bending strength of the structure obtained by simply blending was as low as 280 kg/cr; There is no such thing.

On the other hand, as shown in Examples 1 to 7, the bending strength of structures made using the special reactive calcium carbonate according to the present invention is as high as 430 to 590 kg/crtl, which is higher than that of natural wood. It shows a bending strength close to that of a pencil-making shaft.
It is fully usable for practical use.

Here, in order to further perfect the binding strength of the special reactive calcium carbonate to polyethylene, dicumyl peroxide, 2,5-dimethyl, 2,5-ditertiarybutylperoxyhexane, 2,5-dimethyl, 2.5-
0.0
It is also possible to use 1 to 0.1 part.

By appropriately selecting mixing conditions such as kneading temperature and time,
The amount of peroxide used can be reduced, and may even be zero.

The mixing amount of special reactive calcium carbonate is 20 to 60 parts.
This is within the scope of the department.

Desirably, the amount is in the range of 35 to 50 parts.

If the amount of special reactive calcium carbonate mixed is less than 20 parts, only a flexible and soft structure will be obtained.
It cannot be put to practical use as a pencil shaft.

Furthermore, if the amount of the special reactive calcium carbonate exceeds 60 parts, the volume occupied by the special reactive calcium carbonate exceeds the volume occupied by polyethylene, and the product becomes extremely brittle and the bending strength (maximum bending load) decreases, making it impractical for practical use. Not only can only a structure that cannot be used be obtained, but also the fluidity during melt extrusion deteriorates, making press molding extremely difficult, making it impossible to obtain a structure with the desired shape.

Further, the glass fiber used in the present invention is generally used for reinforcing plastics, and although there are no particular restrictions, a fiber diameter of approximately 5 to 20 microns is desirable.

By using glass fibers, the rigidity of the foamed structure obtained from the system of polyethylene and specially surface-treated calcium carbonate can be further improved.

The rigidity of the foamed structure can be improved by increasing the amount of special reactive calcium carbonate mixed, but if it exceeds 60 parts,
Brittleness (In addition to being easily broken, it also has the disadvantage of being difficult to extrude).

Therefore, in order to further improve the rigidity of the structure when the amount of calcium carbonate mixed is 60 parts or less, it is an effective method to mix an appropriate amount of glass fiber.

The amount of glass fiber mixed is 5 to 20 parts, preferably 10 to 20 parts.

If the amount of glass fiber mixed is less than 5 parts, the effect of improving the rigidity of the structure will be small.

Moreover, if the amount exceeds 20 parts, the blade of an electric pencil sharpener or manual knife will be significantly worn and damaged, which is not practical.

In addition, various silane treatments were applied to improve compatibility with plastics.

Preferably, glass fibers are used. Next, the structure according to the present invention is composed of at least two layers: an outer layer with a smaller foaming ratio and an inner layer with a larger foaming ratio than the outer layer, and the foam cells of the inner layer exist independently of each other, and The reason why the layer and the inner layer are integrally constructed is that
This is because it is most effective for synthetic wood for pencil barrels.

The surface layer, which is the outer layer, must be smooth so that painting will not be difficult in the subsequent painting process and to ensure a beautiful appearance.

On the other hand, the inner layer preferably has a foamed structure to the extent that rigidity and bending strength are not significantly reduced.

If the inner layer does not form a foam structure and is densely formed from a system of polyethylene and calcium carbonate, there will be a significant drawback in machinability.

In other words, manual cutting has a large cutting resistance, and not only does the cutting process become tiring, but when cutting with a commercially available electric pencil cutter, the cutting resistance is so large that the electric motor stops, making it impossible to continue cutting. A problem arises.

Therefore, forming the inner layer into a foamed structure is an effective means of imparting good machinability.

There is also the advantage that the weight of the product can be reduced.

The shape of the foamed cells must be independent of each other as single cells.

In other words, when the structure becomes open-celled, like a spongy structure, the rigidity decreases significantly, resulting in a structure that cannot be put to practical use as a pencil shaft.

When untreated calcium carbonate is used, the bonding force between polyethylene and calcium carbonate is extremely weak, and the gas generated from the blowing agent escapes through the defective voids between the polyethylene and calcium carbonate. It is difficult to obtain a structure with a high expansion ratio, and even if the foam is sufficiently foamed, only a soft and bendable structure with extremely low rigidity is obtained due to open cells.

In contrast, when special activated calcium carbonate is used as in the present invention, a structure with relatively little decrease in rigidity, little decrease in bending strength, and closed cells can be obtained simultaneously for the first time.

Furthermore, the degree of foaming of the synthetic wood of the present invention is preferably in the range of a foaming ratio (cell volume/solid volume) of 0.7 to 2.0.

More preferably, the expansion ratio is 1.0 to 1.7 times.

If the foaming ratio is less than 0.7, the cutting resistance during cutting is large, and the motor of a commercially available electric pencil cutter may stop, which may interfere with subsequent cutting.

If the foaming ratio exceeds 2, the foamed cells will become too coarse and the resulting product will be brittle and easily breakable (unsuitable for practical use).

Electron micrographs of the internal and external cross sections of the synthetic wood according to the present invention are shown in FIGS. 2A and 1B.

As shown in FIG. 2-A, it is clear that the foam cells in the inner layer exist as independent single cells.

The rod-like material shown in FIG. 2A corresponds to glass fiber mixed for the purpose of increasing the rigidity of the structure.

As shown in FIG. 2B, it is clear that the foam cells of the outer layer are smaller than those of the inner layer.

In order to reduce the foaming ratio of the outer layer, the temperature conditions and cooling conditions during extrusion processing can be appropriately set, and thereby a beautiful surface suitable for practical use can be obtained.

In order to obtain a more beautiful surface, a multilayer structure of three or four layers may be used.

The present invention is not limited to two layers consisting only of an outer layer and an inner layer.

A desired plastic is selected from a number of thermoplastic plastics other than the ethylene-calcium carbonate system, such as polyethylene, polypropylene, polystyrene, methyl methacrylate, etc., and a polyethylene-calcium carbonate foam structure is formed around the base material. Co-extrusion coating or other means of coating to achieve a beautiful appearance is a desirable method.

Pencil shafts using the synthetic wood of the present invention (can be continuously produced by ζ extrusion molding).

Therefore, improving extrusion speed is a major factor in increasing productivity.

In order to improve extrusion processability such as melt fracture, and to further improve the surface appearance, lubricants, colorants, stabilizers, etc. may be added.

In particular, using an inorganic substance such as talc powder as a lubricant is an inexpensive and effective method for improving extrudability.

Next, a method for producing synthetic wood according to the present invention will be described.

When mixing and kneading the various raw materials explained above, first blend them with a mixer such as a Henschel mixer,
After that, in a melt mixer such as a Banbury mixer, a twin-screw extruder, or a continuous mixer with one rotor, generally 15
Kneading is carried out at a temperature of 0°C to 280°C, preferably 180°C to 260°C.

The kneading time may be appropriately selected depending on the composition of the raw materials, the performance of the mixer, etc., and can be determined by checking the physical properties, appearance, etc. of the product.

The composition obtained by kneading is formed into pellets using a sheet pelletizer or an extruder.

Next, 0.1 to 1.0 part of a foaming agent is blended with the pellets of the composition, and a foaming extrusion molding process is started.

Chemical blowing agents such as baking soda, ammonium bicarbonate, citric acid, azodicarbonamide, and azobisisobutyronitrile are usually used as blowing agents, but if special physical foaming extrusion equipment is available, butane and hexane can be used. It is also possible to use physical blowing agents such as Freon.

In addition, in order to control the hardness of the synthetic wood obtained by foam extrusion, it is possible to mix and extrude a small amount of different polymers such as polymethyl methacrylate, polystyrene, etc. in an amount of 50 parts or less per 100 parts of the composition. It is.

The present invention will be explained in more detail with reference to Examples below.

Examples 1-7 Melt index5. Of/10 minutes, density 0. 9
7 O r/cyd, high-density porous IJ for injection molding ethylene, special reactive calcium carbonate described in Example 1 of JP-A No. 48-67199, plate crystal type talc with an average particle size of 6.0μ, polyolefin Reinforcing glass fiber (9 microns, fiber length 3 mm) was kneaded with a Henschel mixer using 2,5-dimethyl and 2,5-di-t-butyl peroxyhexine as crosslinking agents at the composition ratio shown in Table 1. did.

Approximately 20 kg of this blend was mixed into 25 kg using a Banbury mixer.
The mixture was melt-kneaded at 0° C. for 10 minutes, and the molten material taken out was formed into a sheet using a roll, and after cooling, it was formed into pellets using a sheet pelletizer.

These pellets were dry-blended with azodicarbonamide in the proportions shown in Table 1 using a Henschel mixer, and then extruded into a hexagonal column shape from a modified die using a 65 mmφ single screw extruder to form a pencil shaft-like shape. I took it out.

The dimensions were approximately the same as a commercially available Mitsubishi 9800HB pencil.

Table 2 shows the results of evaluating the machinability of these pencil shaft-like molded products.

Comparative Example 1 As a natural wood pencil, Mitsubishi 9800HB pencil,
Table 2 shows the results of a comparative evaluation using a commercially available synthetic pencil based on polystyrene.

Comparative Examples 2 and 3 Pencil shaft-like molded products were produced and evaluated in the same manner as Examples 1 to 7, except that untreated calcium carbonate was used instead of the specially reactive calcium carbonate.

The blending composition is shown in Table 1, and the evaluation results are shown in Table 2.

Note 1: Sharpness of the tip angle: 5 items for natural wood products, 1 point is given when it is almost impossible to cut to an acute angle. Note 2: Cutting piece shape: A: Regular flake-like B: Irregular flake-like C. Sawdust-like shape As is clear from the above, the pencil shaft using the synthetic wood of the present invention has good cutting properties and good physical properties.
It has a performance closer to that of natural wood than conventional synthetic pencils based on amorphous polymers.

[Brief explanation of the drawing]

FIGS. 1A and 1B are electron micrographs of a fractured surface of a composition obtained by kneading calcium carbonate and polyethylene in a Banbury mixer (3000x magnification). A is the case where untreated calcium carbonate is used, and B is the case where the special reactive calcium carbonate referred to in the present invention is used. FIGS. 2A and 2B are cross-sectional electron micrographs of a foamed structure obtained by foaming and extruding a composition obtained by mixing glass fiber and using the special reactive calcium carbonate according to the present invention (magnification: 300). times). A is an inner layer with a large expansion ratio, and B is an outer layer with a small expansion ratio.

Claims (1)

[Claims] 1 Melt index is 1 g/10 minutes or more, density is 0. 950 g/cm3 or more, 30 to 70 parts of high-density polyethylene, 5 to 20 parts of glass fiber, 20 parts of special reactive calcium carbonate that exhibits bonding properties with the polyethylene.
60 parts to 60 parts of synthetic wood, the synthetic wood comprises at least an outer layer with a small foaming ratio; A synthetic wood comprising an inner layer having a larger expansion ratio than the outer layer, foam cells of the inner layer exist independently of each other, and the inner layer and the outer layer are integrally constructed.