JPH08302058A - Production of cellulose acetate-based foam - Google Patents

Abstract

PURPOSE: To extremely readily obtain a cellulose acetate-based foam having sufficient uniformity and a high expansion ratio and suitable as a packing material by hydrating a polyoxyalkylene glycol-containing cellulose acetate composition, melting, foaming and extruding. CONSTITUTION: A hydrated cellulose acetate composition containing a polyoxyalkylene glycol (preferably one having 200-1,000 molecular weight) is melted, foamed and extruded by preferably a single screw extruder or a twin- screw extruder. The content of the polyoxyalkylene glycol in the composition is preferably 20-40 pts.wt. based on 100 pts.wt. of the cellulose acetate and the water content of the composition is preferably 10-30wt.%. The melt extrusion temperature and the melting temperature are 160-190 deg.C for 2-7 minutes in the case of the blend of 30 pts.wt. of the polyoxyalkylene glycol having 400 molecular weight. When the melting composition is extruded to an atmosphere controlled in the vicinity of the glass transition temperature once, a highly foamed molding is preferably obtained.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a cellulose acetate type foam. More specifically, the present invention relates to a cellulose acetate-based foam that can be uniformly and highly foamed and can impart properties particularly suitable as a packing material (for example, excellent lightness, cushioning property, heat insulating property, etc.). Regarding manufacturing method.

[0002]

2. Description of the Related Art Conventionally, synthetic resin foams have been used in a wide range of fields such as packing cushioning materials and heat insulating materials. However, these synthetic resin foams have a problem that they generate high heat during incineration to damage the furnace wall or generate toxic combustion gas, and on the other hand, if they are exposed, they are difficult to decompose for a long period of time. There is a problem of deteriorating the global environment, and it is desired to develop a foam that can be easily disposed of.

In response to such a request, for example, Japanese Patent Laid-Open No.
JP-A-269875 and JP-A-5-306349 propose a method of foaming a biodegradable resin such as a hydrolyzed esterified product of cellulose, which is brought into contact with oil heated above the boiling point of water. ing. However, since the foam obtained by this method is soiled with oil, it is troublesome to handle. Furthermore, when the water-containing resin is cellulose acetate, the expansion ratio is small, so that it is not suitable as a packing material as it is. There was a problem of being appropriate. On the other hand, even if the water-containing resin is melt-extruded and foam-molded as it is, the expansion ratio is small and the expansion is not uniform, so that a satisfactory foam cannot be obtained.

Further, in Japanese Patent Publication No. 63-65367 and Japanese Patent Laid-Open No. 6-32928, cellulose acetate,
It has been proposed to produce a foam by foam extruding a molten mixture containing a plasticizer and a foaming agent. But,
In these methods, an organic solvent such as pentane, acetone, or Freon is press-mixed as a foaming agent from the middle of the cylinder of an extruder into a mixture of melted cellulose acetate and a plasticizer, so that the dispersion state of the foaming agent in the melted mixture is Is likely to be non-uniform, and it is difficult to obtain a uniform foam, and there is a problem that the working environment is deteriorated by the organic solvent gas.

[0005]

SUMMARY OF THE INVENTION The present invention has been made against the background of the above-mentioned prior art, and an object thereof is to provide a method capable of easily producing a uniform and high foaming rate cellulose acetate foam. To do.

[0006]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that cellulose acetate containing polyoxyalkylene glycol is melt-extruded after water-absorption in advance. The present invention has been reached by finding that foaming can be performed uniformly and highly highly easily.

Thus, according to the present invention, there is provided a method for producing a cellulose acetate-based foam which comprises melt-foaming and extruding a water-containing cellulose acetate composition containing polyoxyalkylene glycol.

The cellulose acetate used in the present invention is
The degree of acetylation of cellulose represented by bound acetic acid is 45% or more. Particularly, the degree of acetylation is 47 to 60% (the number of bound acetyl groups per unit of cellulose is 1). .9 to 2.8) are preferable. When the degree of cellulose acetylation is less than 45%, the melting temperature becomes too high and stable melt molding becomes difficult.

The polyoxyalkylene glycol contained in the cellulose acetate is a polymer composed of ethylene oxide and / or propylene oxide,
Alternatively, a mixture thereof can be used, and specific examples thereof include polyoxyethylene glycol, polyoxypropylene glycol, and an ethylene oxide / propylene oxide random copolymer. The molecular weight of the polyoxyalkylene glycol is not particularly limited, but it is 2 from the viewpoint of compatibility with cellulose acetate.
It is preferably about 0000 or less, particularly preferably 200 to 1000.
If the molecular weight exceeds 20,000, the compatibility with cellulose acetate decreases and uniform foaming tends to be difficult.

The polyoxyalkylene glycol content in the cellulose acetate composition varies depending on the foamability of the cellulose acetate used, the molecular weight of the polyoxyalkylene glycol, and the water content of the composition. However, it is preferably 10 to 60 parts by weight, particularly 20 to 4 parts by weight based on 100 parts by weight of cellulose acetate.
The range is 0 parts by weight. If the proportion of polyoxyalkylene glycol is less than 10 parts by weight, not only molding becomes difficult, but also the expansion ratio of the resulting foam tends to decrease, while if it exceeds 60 parts by weight, the glass transition temperature of the cellulose acetate composition is increased. Is too low, and even if it is sufficiently foamed at the time of molding, it tends to shrink when cooled, making it difficult to obtain a highly foamed foam.

Further, the above composition may contain other substances within the range not impairing the object of the present invention. For example, a thermoplastic resin having good compatibility with cellulose acetate, a plasticizer, and a thermosetting resin. Examples include stabilizers and foaming regulators. Among them, talc, titanium oxide, calcium silicate, silica,
Foaming regulators such as calcium carbonate and metal stearates, especially talc, can impart a more suitable foaming property to the composition, so that a uniform and highly foamed foam can be easily obtained. Therefore, it is preferable.

Next, in order to form the composition by mixing the above-mentioned cellulose acetate with polyoxyalkylene glycol and an additive such as a foaming regulator, these may be melted and kneaded by heating according to a conventional method, and the heating temperature at that time. The conditions such as the melt-kneading time and the melt-kneading means are not particularly limited as long as they do not cause thermal decomposition of cellulose acetate or polyoxyalkylene glycol. For example, the heating temperature may be equal to or higher than the temperature at which the mixture melts, and the melting temperature of the mixture varies depending on the type of cellulose acetate and the type and mixing amount of polyoxyalkylene glycol used. Good. The melt-kneading time cannot be unconditionally determined because it depends not only on the types of cellulose acetate and polyoxyalkylene glycol and the mixing ratios thereof, but also on the melt-kneading means used, but the obtained mixture is uniformly dispersed. The time required to be taken is taken. As the melt-kneading means,
Usually, a single-screw or twin-screw type extruder is adopted.

In the present invention, the cellulose acetate composition obtained as described above is required to be positively hydrated with water in advance, and the hydrated state must be melt-extruded. The method of making water hydrate is not particularly limited, and any method can be adopted. For example, after immersing the pelletized cellulose acetate composition in water for a sufficient time, a method of removing water droplets adhering to the chip surface and supplying it to the next melt extrusion foaming step, and leaving it in a high humidity atmosphere for a long time to absorb moisture There is a method of making it. At this time, it may be heated appropriately, and by doing so, the time for absorbing water is shortened, and the equilibrium water content of the obtained chips is increased, so that a highly foamed foam is easily obtained, which is preferable. Of course, if the equilibrium water content in the air is sufficient for the required expansion ratio, it is not necessary to purposely provide a step of hydrating, and the composition containing the equilibrium water left in the air may be used as it is.

If the water content of the composition hydrated by the above-mentioned method is too small, the expansion ratio will be insufficient, and the properties of the resulting foam, especially the properties such as light weight, cushioning property, and heat insulating property will be insufficient. On the other hand, if it is too large, the molding stability during melt extrusion decreases, the expansion ratio tends to decrease, and the energy cost also increases, so it is in the range of 5 to 40% by weight, particularly 10 to 30% by weight. Preferably.

Next, in order to perform melt extrusion foam molding of the hydrated cellulose acetate composition, a known melt extrusion foam molding method which has been conventionally used for producing a foam molded article such as polystyrene may be adopted, but particularly, It is important to use an extruder having a structure in which the foaming gas does not escape, and a single-screw or twin-screw extruder is preferably used. At this time, the melt extrusion temperature and the melting time are determined by the type of cellulose acetate, the type and amount of polyoxyalkylene glycol, and the capacity of the screw extruder, but normally the mixture is melted uniformly without decomposition. Under the conditions, for example, when 30 parts by weight of polyoxyethylene glycol having a molecular weight of 400 is blended, a melting temperature of 160 to 190 ° C. and a melt kneading time of 2 to 7 minutes are selected.

The melt-kneaded cellulose acetate composition is
For example, it is extruded into a rod shape from a die having circular or elliptical discharge holes, and then cut into a desired length to obtain foam chips (pellets). At this time, it is preferable to extrude the melted composition into an atmosphere controlled at a temperature near the glass transition temperature so that foamed water vapor does not escape, because a highly foamed molded product can be obtained.

The characteristics of the foam obtained by the production method of the present invention are represented by, for example, the expansion ratio (pellet specific gravity before foaming / specific gravity of the foam), and are about 10 to 50 times, especially about 20 to 40 times. Is desirable. When the expansion ratio exceeds the above range, stable molding cannot be achieved,
Further, the mechanical strength tends to be poor, and on the other hand, if it is less than the above range, the properties as a foam cannot be exhibited.

When the expansion ratio of the obtained foam is insufficient, the expansion ratio can be improved by allowing the foam to absorb water appropriately and then reheating. Further, in the production method of the present invention, the obtained foam is shaped into chips (foamed pellets), the expansion ratio is made small, and the foamed pellets are packed in an appropriate mold and heated to form a shape. At the same time, additional foaming can be performed.
According to such a method, the water remaining in the cellulose acetate composition is heated to boil and vaporize, and
Since the cellulose acetate resin softens or melts, it further expands and foams due to its water vapor pressure, and the foamed lumps fuse together to create a molded product with any shape and a high expansion ratio. can do.

[0019]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

After crushing cellulose acetate flakes having an average degree of acetylation of 54.7%, polyoxyethylene glycol (PEG-400 manufactured by NOF CORPORATION) and talc (LMR-200 manufactured by Fuji Talc) in the proportions shown in Table 1. Mix and
This is 2m in diameter with a Japanese steel extrusion machine P90-28V.
It was melt extruded from a die having 20 circular holes of m and formed into pellets. The pellets thus obtained were immersed in water at 20 ° C. to absorb water at the ratios shown in Table 1, and then Ishina
Diameter of 3.5 with a single-screw extruder manufactured by ka Iron Works Co.Lid.
Melt extrusion was performed at a temperature shown in Table 1 to obtain foam chips from a die having 7 mm circular holes. The results are shown in Table 1.

[0021]

[Table 1]

[0022]

As described above, according to the method of the present invention, a uniform and highly foamed cellulose acetate-based foam can be obtained very easily without using a special foaming agent. It is possible to provide a foam that is particularly suitable as a packing material as compared with the body. Further, the polyoxyalkylene glycol used in combination is also excellent in biodegradability, so that it can be easily disposed of and does not deteriorate the global environment.

Claims (4)

[Claims] 1. A method for producing a cellulose acetate-based foam, which comprises melt-foaming and extruding a water-containing cellulose acetate composition containing polyoxyalkylene glycol. 2. The method for producing a cellulose acetate-based foam according to claim 1, wherein the water content of the composition is 5 to 40% by weight. 3. The method for producing a cellulose acetate-based foam according to claim 2, wherein the polyoxyalkylene glycol is polyoxyethylene glycol having an average molecular weight of 20,000 or less. 4. The method for producing a cellulose acetate-based foam according to claim 3, wherein the content ratio of polyoxyethylene glycol in the composition is 10 to 60 parts by weight based on 100 parts by weight of cellulose acetate.