JP3012937B2 - Method for producing foam for cushioning - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an elliptical cushioning foam curved in a saddle shape. More specifically, the present invention provides
The present invention relates to a manufacturing method capable of obtaining an oval foam suitable for use as a stackable cushioning material in a high-quality state without depressions and through holes.

[Conventional technology and issues]

As a cushioning foam for packaging, foamed polystyrene resin is extremely useful, and various shapes have conventionally been proposed. Usually, in-mold bead foam molded products having a space corresponding to the outer shape of the contents are used, but since a mold that matches the contents is required each time, except when mass-producing the same type products, Has the disadvantage of being uneconomical. As an alternative to this, it is known to use a large number of irregularly shaped relatively small foams (rose cushions) obtained by cutting extruded foamed moldings, but these are specially extruded during production. There are drawbacks such as the necessity of a nozzle or the movement of articles inside the package during transportation. In order to remedy these drawbacks, Japanese Patent Publication No. 55-44700 discloses a non-foamed cylindrical rod-shaped body of foamable polystyrene resin, which is 70-90.
Expandable polystyrene that gives a saddle-curved elliptical plate upon foaming by rolling at ℃ by rolling into a rod having an elliptical cross section and cutting in the direction of the short axis of the elliptical cross section of the rod. A method for producing a resin has been proposed.

According to this method, the two mutually perpendicular axes of an oval or elliptical disk cut out of a rod that is still partially plastic are curved upon foaming depending on the thickness of the elliptical plate, Or, before foaming, it bends due to internal tension towards the opposite side, so that a saddle is obtained. This foam saddle has good cushioning and effective interengagement,
It is disclosed as a protective packaging material that guarantees the fixation of the package in the container.

However, according to this method, through holes or depressions having a diameter of about several mm appear in the obtained saddle-shaped elliptical foam, and when these are actually used as a cushioning material, the appearance is poor, the strength is insufficient, and cracks occur. There is a problem such that pulverization occurs and pulverization occurs.

[Means for solving the problem]

The present inventors have conducted various studies to solve the above problems, and as a result, have found that a good quality foam can be obtained by adjusting the water content in the polystyrene resin immediately before foaming.

That is, the present invention is to transform a cylindrical rod-shaped body extruded from a foamable polystyrene resin under substantially no foaming conditions into a rod-shaped body having an elliptical cross-section by rolling at 70 to 90 ° C. The rod-shaped body is cut in the direction of the short axis of the elliptical cross-section to form an elliptical plate, and then foamed to produce a saddle-shaped curved elliptical cushioning foam. An object of the present invention is to provide a method for producing a foam for cushioning, wherein the water content immediately before is 0.05 to 0.25% by weight.

 Hereinafter, the present invention will be described in more detail.

(Polystyrene resin) The polystyrene resin used in the present invention means a styrene homopolymer and a copolymer of at least 50% by weight, preferably at least 75% by weight of styrene and another copolymerizable monomer. . Examples of the copolymerizable monomer include ethylenically unsaturated copolymerizable compounds such as α-methylstyrene, nuclear halogenated styrene, nuclear alkylated styrene having 1 to 4 carbon atoms in the alkyl group, Acrylonitrile, methacrylonitrile, esters of alcohols having 1 to 10 carbon atoms with acrylic acid, methacrylic acid or fumaric acid, butadiene or N-vinyl compounds such as N-vinylcarbazole, N-vinylpyridine or small amounts (0.5% by weight) The following divinyl compounds such as butanediol diacrylate and divinylbenzene are used.

(Blowing agent) The expandable polystyrene resin contains a blowing agent. Foaming agents for this purpose are those used in the production of ordinary foamed polystyrene, i.e., aliphatic or cycloaliphatic hydrocarbons or halogenated hydrocarbons having a boiling point of up to about 90 ° C. and the use of polystyrene resins. Those which do not dissolve but can be uniformly dispersed therein, such as n-, i- or neopentane, hexane, cyclohexane, n- or i-
Butane, propane, difluorodichloromethane or a mixture thereof is about 2.5 to 9% by weight, preferably 4.5 to 9% by weight.
6.5% by weight is used.

The blowing agent may be added by any means at any time, for example, during the polymerization of the styrene monomer, or may be added and mixed with the polystyrene resin only in an extruder in which a cylindrical rod is extruded. it can.

The polystyrene resin can further contain other additives, such as dyes, fillers, stabilizers and flame retardants, etc. The flame retardant itself is composed of several components, for example, a co-acting additive. It may consist of a halogen compound, especially a bromine compound, in the combination.

(Extrusion, rolling and cutting) A cylindrical rod is formed by a conventional method, for example, a diameter of 3 to 10 m.
m, preferably through a circular nozzle having a cross section of 5 to 8 mm, the molten polystyrene resin containing the blowing agent for about 90 to 15
It is produced by extruding rods at a temperature of 0 ° C., especially 110-120 ° C., in a cooling liquid, usually at about room temperature. At this time, since the rod-shaped body is rapidly cooled at the surface, foaming does not substantially occur. The residence time in the cooling bath and its temperature are preferably coordinated with each other such that the rod leaves the bath while it is still hot and thus the interior is still plastic.

The extruded rods preferably pass between the pair of rolls in the partially plasticized state, preferably between 1: 1.2 and
Obtain an oval or elliptical cross section with an axial ratio of 1: 3, more preferably 1: 1.3 to 1: 2. It is known that a combination of one elastic roll and one inelastic roll, such as steel and rubber rolls, is preferred for this purpose. The running speed of the roll can be adjusted so that the rod is slightly stretched or not stretched at all. Stretching may also be performed by a pre-connected pair of rolls serving as feed ports for the cutting device. Also, several pairs of rolls for deforming the cylindrical rod may be sequentially connected. The surface of this roll is usually smooth,
An embossed pattern may be provided.

Preferably immediately after the roll, i.e. at substantially the same temperature, the bar is cut by a sharp rotating knife in the direction of the short axis of the bar cross-section, the thickness in the direction of the bar being preferably relative to the short axis of the bar cross-section. Is a foamable oval plate having a ratio of 1: 1.5 to 1:10, more preferably 1: 3 to 1: 6. The cutting is preferably performed in a plane perpendicular to the axis of the bar, but may also be performed in a plane inclined with respect to the axis of the bar.

Deformation and cutting by a roll are performed at a temperature of 70 to 90 ° C. In the preferred continuous operating method described above, the operating temperature can be set by measuring the temperature of the obtained ellipsoid. Immediately after the production of the obtained small piece of elliptical plate,
The thermometer inserted in this elliptical plate is 65-87 ° C, preferably
Indicates a temperature of 75-85 ° C. The 70-90 ° C., indicated as the temperature at which the bar passes through the roll and enters the cutting device, was estimated based on the temperature measurement of a small piece of elliptical plate.
This is because the direct measurement of the temperature of the bar is technically very tedious and the temperature of the bar is never uniform over its cross-section and increases inwards.
The designation 70-90 ° C. therefore relates to the estimated average temperature of the rod.

(Foaming) Foaming is performed on a small piece of the expandable elliptic plate by a known means in a commercially available prefoaming apparatus using, for example, steam at 100 to 150 ° C. In many cases, the particles are expanded until a bulk density of 4 to 15 g / bulk is reached.

Before foaming, the elliptical plate is usually 2-10mm and 3 ~
It has a short axis and a long axis of 20 mm, and a thickness of 0.8-3 mm. During foaming, this dimension grows three to four times.

(Water Content) In the present invention, the water content in the polystyrene resin of the small oval plate pieces immediately before foaming is important. The water content is 0.05 to 0.25% by weight, preferably 0.1 to 0.2% by weight. When this value is less than 0.05% by weight, the number of depressions generated on the surface of the elliptical cushioning foam curved in a saddle shape increases, and when the value exceeds 0.25% by weight, it penetrates the front and back of the saddle-shaped cushioning foam. The number of holes to be formed increases. When the number of these hollows and through-holes increases, the appearance of the cushioning foam is naturally impaired, the value as a product is reduced, and the physical properties are weakened, and crushed products may be generated during use. , Which cannot be used practically.

The moisture content of the expandable elliptical plate is measured by the following Karl Fischer method. That is: 50 ml of toluene and 25 ml of methanol are put into a titration flask, and hydranal is dropped to make the water content in the flask zero. Next, about 10 μm of distilled water is sucked in with a 25 μm micro syringe to measure the total weight (W1 mg), and then poured into a flask. The total weight after the injection is also weighed (W2 m
g). Start titration and determine end point volume (T ml).

 The titers (F) are as follows: F = (W1 / W2) / T Do this three times and average.

After precisely weighing (W g) about 1 g of the effervescent oval plate, it is poured into a flask set in accordance with the above method for determining the titer, and completely dissolved (about 20 minutes). Thereafter, titration is started and the end point amount is determined (T ml).

The water content (WC%) in the elliptical plate is calculated by the following formula: WC (%) = (F × T) / (W × 10) Thus, in the present invention, the water content is important. However, various methods can be used for this adjustment. For example, a predetermined amount of water is already contained in the polystyrene pellets for extrusion, or water is supplied from the middle of the extruder, so that the water content immediately before foaming can be adjusted. After being cut, it is immersed in water or placed in a water-containing atmosphere, and is optionally air-dried to obtain a predetermined water content.

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 Prepared by suspension polymerization in the presence of pentane and has a K of 59
Values (according to the method described in Her Huickencher's "Tsellose Chemie", Volume 13 (1932), p. 58) and
Polystyrene having an average particle size of 0.5 mm and containing 5.5% by weight of pentane as a blowing agent was added to butyl stearate 0.1%.
%, Plasticized in a heated single-screw extruder having a diameter of 90 mm, an extrusion length of 1350 mm and a conventional conveying screw and passing through a perforated plate with a 4.5 mm diameter nozzle cross section at a temperature of 137 ° C. It was extruded in a strand shape (rod shape) in a water bath at ℃. At this time, water was supplied from the middle of the extruder so that the water content in the extruded strand-like expandable polystyrene resin was 0.2% by weight.

After staying in a water bath for 12 seconds, the mixture was supplied to a rolling device comprising a steel roll and a roll made of foamed rubber having a Shore hardness of 80 ° and provided with a supply roll pair for providing an elliptical shape. Here, the strand is cut in the direction of the short axis of the cross section by a knife-type milling machine to form a thin elliptical plate. The small pieces of the foamable elliptical plate thus obtained had the shape of an elliptical, saddle-shaped disk having dimensions of 5 × 3.5 × 1 mm. The water content immediately before foaming was also approximately 0.2% by weight.

The elliptic plate was foamed under the action of steam at 120 ° C. until the bulk specific gravity reached 9 g /, to obtain a saddle-shaped curved elliptical cushioning foam piece. At this time, the saddle shape of the foam was largely retained and further emphasized. In addition, the appearance of this foam is smooth and almost free from scratches such as depressions and through holes,
Of the 10 foams of this elliptical plate, at a rate of only about 1 sheet,
There was one small hole of about 1 mm.

Further, when this foam for cushioning was used as a loose cushioning material for packaging, the movement of the contents was small and the cushioning property was sufficient even during transportation or vibration.

Example 2 Except for adjusting the water supply amount of the extruder so that the water content of the elliptic plate pieces immediately before foaming becomes 0.1% by weight, the same procedure as in Example 1 was carried out except that the amount of water supplied to the extruder was beautiful. I got

Comparative Example 1 An oval piece of expandable polystyrene resin was obtained in the same manner as in Example 1 except that water was not added from the middle of the extruder. Moisture content of this product immediately before foaming is 0.02% by weight
Met.

This was foamed in the same manner as in Example 1 to obtain a foam piece. This product had many small dents, had a dirty appearance, and had poor strength when used as a cushioning material, which was not satisfactory in practice.

Comparative Example 2 An elliptical foamed polystyrene resin buffer material was obtained in the same manner as in Example 1 except that water was supplied to polystyrene in the middle of the extruder, and the water content immediately before foaming was changed to 0.5% by weight. This elliptical piece had many large through holes having a diameter of 3 to 7 mm, had poor appearance, low strength, was easily crushed in use, and was not practical.

〔The invention's effect〕

According to the present invention, since the small pieces of the expandable polystyrene resin are foamed under the moisture content controlled as described above, almost no depressions or through holes are found on the foam surface, It is possible to produce a saddle-shaped curved elliptical cushioning foam small piece having excellent strength.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification code FI C08L 25:00 (56) References JP-A-58-176226 (JP, A) JP-A-59-81143 (JP, A) 55-44700 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 44/00-44/60 B29C 67/20 B65D 81/00-81/17 C08J 9/00 -9/42

Claims (1)

(57) [Claims] An extrudable polystyrene resin is extruded under a condition that foaming does not substantially occur.
Rolled at 90 ° C. to deform into a rod having an elliptical cross section, and then cut the rod in the direction of the short axis of the elliptical cross section to form a foamable elliptic plate. A method for producing a saddle-shaped curved elliptical cushioning foam by foaming, characterized in that the water content of the elliptic plate immediately before foaming is 0.05 to 0.25% by weight. Manufacturing method.