JPS5858374B2 - expandable thermoplastic resin particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to highly foamable expandable thermoplastic resin particles with excellent properties.

The expandable thermoplastic resin particles are foamed in advance by heating (primary foaming), and then left for a certain period of time (ripening), then filled into a mold and heated more strongly than during the primary foaming (molding heating) to form the desired shape. It is said to be a shaped foam.

Conventionally, in this process, the foam has a bulk multiple of about 5 to 70.
(bulk density 0.2 to 0.014 g/a), but there were various problems when making highly foamed products with a bulk density of 60 times or more, especially 70 times or more. .

For example, large rectangular parallelepipeds, commonly known as blocks, are produced using a special method called two-stage foaming or cycle forming, which uses large expandable resin particles with a diameter of about 3 mrIt as a raw material and heats them twice.
Although it is possible to produce foams with a size of 0 times or more, this method is not suitable for producing small-sized foams because the raw material particles are large, and the molding and heating process is performed in two steps, which requires extra equipment. There were disadvantages such as requiring a long process.

In addition, small raw material particles have the disadvantage that the foam has poor stability, that is, shrinkage and deformation occur.

In addition, even if we try to manufacture highly foamed products by one-time molding and heating, there is little tolerance for fluctuations in working conditions.
The obtained foam was subject to shrinkage, deformation, etc.

Furthermore, in order to produce highly foamed products, methods such as increasing the amount of blowing agent in the raw material particles or strengthening the primary foaming conditions can be considered, but the former method allows stable impregnation into the particles. There is a limit to the amount of blowing agent (approximately 6.5 to 7.5 weight φ), and even if it is possible to achieve high foaming by impregnating more blowing agent, the bubbles in the foam may be uneven and the blowing agent may be lost during transportation. In the latter method, when the particles are cooled after primary foaming, the blowing agent and water vapor inside the particles condense, resulting in a reduced pressure inside the particles, causing the particles to shrink and deform.

The present invention solves these problems, and provides a highly foamable thermoplastic material that can produce highly foamed products and can be molded using a simple method, such as conventional methods. It relates to resin particles.

That is, the present invention relates to expandable thermoplastic resin particles obtained by impregnating a blowing agent into thermoplastic resin particles obtained by polymerizing a styrene monomer, diallyl phthalate, and an acrylic ester or a methacrylic ester.

Here, the styrene monomer is a styrene derivative such as styrene, α-methylstyrene, chlorostyrene, vinyltoluene, etc., and may contain monomers other than these.

Among these monomers, styrenic derivatives, particularly styrene, are used in a proportion of 50% by weight.

Unless a styrene derivative, particularly styrene, is used as the styrene monomer at a weight of 50 weight φ or more, the melt particle size characteristics and steam permeability necessary for the expandable resin particles cannot be obtained.

The above diallyl phthalates include diallyl, ortho,
There are phthalates, diallyl iso-phthalates, etc., and the amount used thereof is preferably 0.05 to 3 weight by weight in the raw material of the thermoplastic resin.

If it is less than 0.05 weight φ, it will tend to shrink after the completion of foam molding, and if it exceeds 3 weight, strong heating conditions that are not industrially advantageous will be required to achieve high foaming.

The above-mentioned acrylic ester or methacrylic ester is preferably one whose homopolymer has a softening point of 0°C or lower, and in this case, it can be used under a wide range of heating conditions, especially foaming in an open state, closed-heating state. Excellent stability in foaming during foaming and molding processes.

In particular, these include ethyl acrylate, isopropyl acrylate, n-propyl acrylate, isobutyl acrylate, n-butyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, n-hexyl methacrylate, and the like.

The amount of these used is 0.5 to 0.5 to
10 weight ratio.

If it is less than 0.5 weight φ, the effect of facilitating high foaming is small, and if it exceeds 10 weight φ, the highly foamed product tends to shrink and the foaming agent in the particles tends to escape.

In the present invention, it is important to use diallyl phthalate and acrylic ester or methacrylic ester together. It serves to impart a plasticizing effect.

In particular, other compounds having two polymerizable double bonds such as divinylbenzene cannot be used in place of diallylphthalate.

In this case, good foaming properties at a temperature suitable for molding cannot be obtained.

The weight ratio of diallyl phthalate and acrylic ester or methacrylic ester is 1 to 3 to 10 for the latter, which is preferable in view of the balance between the rigidity of the thermoplastic resin and the effect of internal plasticization.

The polymerization for obtaining the above thermoplastic resin is preferably suspension polymerization.

In this case, the raw material monomers may be added to the aqueous medium all at once and polymerized, or may be added in portions and polymerized.

Alternatively, some polymer particles of a styrenic monomer are produced in advance, the particles are dispersed in an aqueous medium, and the styrenic monomer, diallyl phthalate, acrylic ester, or methacrylic ester is added to the particles. It may be added and impregnated and polymerized.

In addition, conventional methods relating to suspension polymerization can be used.

Polymerization catalysts used during polymerization include organic peroxides such as benzoyl peroxide, 1-butyl perbenzoate, lauroyl peroxide, and dicumyl peroxide, and azo compounds such as azobisisobutyronitrile. It can be used by dissolving it in a monomer.

The amount of polymerization initiator used is approximately 0.05 to 100% of the monomer.
It may be within the range of 1.5 weight or more.

Since unreacted monomers have an influence on foaming properties and molding properties, the polymerization is terminated so that the yield is approximately 0.5 weight.

During suspension polymerization, calcium carbonate,
Fine powder of poorly soluble inorganic salts such as bentonite, magnesium pyrophosphate, and tricalcium phosphate, water-soluble polymers such as polyvinyl alcohol, starch, and hydroxyethyl cellulose, or these together with water-soluble surfactants such as sodium alkylbenzenesulfonate. used in combination.

The amount of inorganic salt used is 0.1 to 1 weight per aqueous medium, and the amount of water-soluble polymer used is about 0.05 per weight per aqueous medium.
~3 weight φ, many surfactants are used in combination with inorganic salts, but the amount used may be 10 to 1100 pp in the aqueous medium.

The blowing agent to be impregnated into the thermoplastic resin particles includes low-boiling aliphatic hydrocarbons such as propane, butane, and pentane, and low-boiling halogenated hydrocarbons such as monochloromethane, monochlorodifluoromethane, and dichlorodifluoromethane. can be used.

Among these, isobutane, isopentane, and neopentane are preferably used in combination with other blowing agents.

In particular, it is preferable to use 40 to 80 parts by weight of Isobu, 5 to 30 parts by weight of Isopene, or 2 to 30 parts by weight of NeoPuff in the foaming agent.

The amount of the blowing agent impregnated into the thermoplastic resin particles is 6 to 10% by weight relative to the resulting expandable thermoplastic resin particles.

If the amount of foaming agent is too large, the foam state after foaming will be unstable and bubble unevenness will easily occur.

In order to stabilize the foam state after foaming, it is preferable to use about 8 weight cake or less.

In the above-mentioned suspension polymerization, impregnation with a blowing agent can be carried out by press-injecting the blowing agent during the polymerization or after the completion of polymerization, or by dispersing separately obtained thermoplastic resin particles in an aqueous medium and adding the blowing agent thereto. It may also be done by press-fitting.

The expandable thermoplastic resin particles according to the present invention are pre-foamed,
The pre-foaming may be performed by direct heating or by using steam, and may be performed in an open state or under pressure.

The expandable thermoplastic resin particles according to the present invention exhibit excellent properties in that they are easy to foam even when foaming under pressure and do not shrink after pre-foaming.

Next, examples of the present invention will be shown.

Example 1 6000 g of deionized water, 9 g of tricalcium phosphate, and 0.012 g of sodium dodecylbenzenesulfonate were placed in a 2011 pressure autoclave equipped with a rotary stirrer and thoroughly mixed.

Next, to 4900 g of styrene, 100 g of acrylic acid n-butyl ester, 10 g of diallyl phthalate, 6.0 g of benzoyl peroxide, 6.0 g of azobisisobutyronitrile,
3.0 g of t-butylhachenzoyl was mixed and dissolved, poured into the same autoclave, and stirred.Then, the temperature was raised to 85°C, and the stirring conditions were adjusted so that the oil droplets had a diameter of 0.8 to 1.0 mm.

Thereafter, in order to maintain this droplet size, 6 g of tricalcium phosphate was added in three portions within 4 hours to prevent the growth of droplets that would coalesce.

9 hours after reaching 85℃, i-butane 60%, n-butane 40%
450 g of a mixed blowing agent was injected over 30 minutes.

The pressure inside the autoclave was 12 kgf/d.

One hour after the injection of the foaming agent is completed, the temperature inside the autoclave is set to 12
The temperature was raised to 0°C in 2 hours and 20 minutes, maintained at this temperature for 4 hours, and then cooled to 35°C. Then, the excess blowing agent in the space was discharged, and finally, hydrochloric acid was injected to bring the hydrogen ion concentration (pH) to 4.
It was maintained for 20 minutes.

Next, the contents were taken out, washed with water, and dried to obtain expandable thermoplastic resin particles.

The particles contained 8.21% blowing agent (i-butane, n-butane) and 0.42% unreacted materials (styrene monomer, ethylbenzene).

This was left in an atmosphere at 15℃, and after 4 days the foaming agent was 6.6
When the volume had decreased significantly, the foamable particles that passed through a 12' mesh JIS sieve and remained on a 16 mesh were separated and their foaming properties were measured.

The measurement was carried out using a box-type autoclave with an internal volume 401 that could be opened and closed, and which was airtight and pressure-resistant when closed, and the sample was placed on a mesh and directly contacted and heated with the steel to be blown.

The purpose of performing such measurements is to find out how high foaming properties are maintained under foaming conditions ranging from normal pressure to elevated pressure.

This foaming characteristic is 67m1/at gauge pressure Okgf/d2min.
It became 9.

Increase the gauge pressure to 0.1 kgf/ca, 0.2
kgf/crib.

0.3kgf/ffl, 0.4kyf/ffl,
The foaming ratio when set to 0.5kyf/- is 76.
m1l/g, 84TLl/, 9°91m1/g, 96y
d! /g, 101 vertical /f! It became.

This foaming characteristic is illustrated as curve 1 in FIG.

Next, the foamable thermoplastic resin particles were foamed using a pressure foaming machine with rotating stirring blades.

Foaming conditions are internal steam pressure 0.2 kgf/criY
When the foaming reached a bulk ratio of 90 m 1/9, the blowing of steam was stopped.

The pre-expanded particles thus obtained were placed in a well-ventilated mesh and left in an atmosphere at 15° C. for 20 hours, and then molded.

The molding machine used was a machine designed for molding ordinary packaging materials and fish boxes (Barrier 10N, manufactured by Seki Seisakusho), and the mold had inner dimensions of 25 cm long, 30 cffL wide, and 25 cIfL deep.

Molding is done in the same way as conventionally used expanded polystyrene: mold preheating → foam particle filling → one-sided heating (steam is blown from one side of the mold until the back pressure on the steam inflow side rises to the set value) → both sides Heating (steam blowing from the entire surface of the mold)
The process was water cooling → cooling → mold opening (ejecting the molded product).

The molding conditions were set to 0.4 kgf / 0.4 kgf /
cr? t.

0.5kgf/-maximum pressure of heating steam 0.8ky
f/cra, 1, Okgf/shrine, double-sided heating time 1
Eight types of molded products were obtained by selecting and combining 0 to 20 seconds, and all of them were good, with no shrinkage deformation and no water content.

After leaving the molded product in a dryer at 50°C for 6 hours, test pieces were cut out from each part of the box and the density (bulk expansion ratio) was measured.
, 9 g/l (bulk magnification: 92 times).

Example 2 0 of polyvinyl alcohol (GH20 manufactured by Nippon Gosei Kagaku)
．． 45 kg of a 3% aqueous solution and 21.0 kg of polystyrene manufactured by suspension polymerization (PS-LBZ manufactured by Denki Kagaku Kogyo) were placed in a container with an internal volume of 130 A? The mixture was placed in a pressure-resistant stainless steel autoclave and heated to 75° C. with stirring.

Next, styrene monomer 8.4 ky, acrylic acid n
A mixed solution of 0.60 kp of -butyl ester and 0.09 kg of diallylphthale was divided into four equal parts, and the mixture was added dropwise over a period of 20 minutes every hour to be absorbed into polystyrene particles suspended in water.

At this time, the fourth monomer mixture contained 0.009 kg of benzoyl peroxide and 0.0 kg of azobisisobutyronitrile.
09 kg and 0.0045 ky of t-butyl perbenzoic acid were dissolved and added dropwise.

Two hours after the fourth dropwise addition of the monomer mixture,
The temperature inside the autoclave was raised to 85° C. and maintained for 3 hours, at which time 5 kg of a mixture of i-butane and n-butane was injected under pressure.

The internal pressure was 11 kgf/d.

After 1 hour, the temperature inside the autoclave was raised to 120°C, maintained for 5 hours, and then cooled.

When the internal temperature decreased to 40° C., residual gas remaining in the space was released, and the contents were taken out, washed, dehydrated, and dried to obtain expandable thermoplastic resin particles.

The particles contained 7.8% blowing agent (i-butane, n-butane) and 0.38% unreacted substances (styrene monomer, ethylbenzene).

This was left in an atmosphere at 15°C, and the foaming properties were measured in the same manner as in Example 1 when the foaming agent amount was 6.6%.

The result is that the gauge pressure (kgf/kiln) is 0°0.1,
The bulk ratio (TIll/g) was 73, 87, 97, 106°104 and 98 at 0.2, 0.3, 0.4 and 0.5, respectively.

This foaming characteristic is illustrated as curve 2 in FIG.

Next, the pre-foamed particles were heated at a pressure of 0.2 kyf/i as in Example 1 to obtain pre-foamed particles with a density of 0.01 g/ynl.

After this was left to ripen, two pieces were molded using the same molding machine, mold, and heating conditions as in Example 1 under the same conditions.

The appearance of the molded product boxes was good.

Next, one of the molded products under the same conditions was left in an atmosphere at 15°C, and the other in a greenhouse at 50°C.

In both cases, the molded products continued to be slightly deformed until 2 hours had passed after molding.

However, for those left in an atmosphere of 15℃, after 12 hours,
Those in the 50°C greenhouse recovered from the deformed state to the complete state after 4 hours.

When samples were cut out from these boxes and their densities were measured, they were uniformly 10 g/l.

Comparative Example 1 Same as Example 1 except that n-butyl acrylate and diallyl phthalate were not used and only styrene was used as the monomer.
000g, and 100.0g of toluene was used as a plasticizer.
9 was dissolved and suspension polymerized in the same manner as in Example 1 to obtain expandable polystyrene particles.

This contained 8.3% blowing agent, 1.62% toluene, and 0.41% unreacted substances (styrene, ethylbenzene).

The particles were left in an atmosphere at 15°C until the foaming agent concentration was 6.6%, and then the foaming properties and molding properties were evaluated.

The foaming properties were measured according to Examples 1 and 2.

Gauge pressure (kyf/CrIL is 0.0.1, 0.2°, bulk magnification (ml
7g) can be foamed without shrinkage in 70, 76.71, 62, 50 and 45 under low heating conditions, and does not reach 80m7/7, and is 0.1kg f /
Shrinkage was significant under heating conditions exceeding cnt.

The above foaming characteristics are shown as curve 3 in FIG.

Comparative Example 2 Expandable thermoplastic resin particles were produced according to Example 1 except that diallyl phthalate was not used in Example 1,
Foaming properties were measured.

The results are shown as curve 4 in Figure 2, with a maximum of 75
Not only did it foam only at m1/g, but it also foamed at 0.2 kg.
Shrinkage occurred under steam pressure conditions of f/d or higher, and the range of foaming conditions was extremely narrow.

The molding characteristics also include shrinkage after being removed from the mold after molding,
The deformation was not favorable.

Comparative Example 3 Expandable thermoplastic resin particles were produced according to Example 1 except that 2.5 g of divinylbenzene was used instead of 10 g of diallylphthalate.

These particles contain 8.7% blowing agent, unreacted substances (styrene,
It contained 0.39% (ethylbenzene).

Using these particles, the foaming properties were measured in the same manner as in Example 1.

The results are shown as curve 5 in FIG. That is, foaming does not occur to a high expansion ratio under weak heating conditions.

The above particles were heated to 0.41y f /' using a pressure foaming machine.
After pre-foaming to a volume of 90 ml 1/9 at a pressure of 1.0 ml, the molding was carried out in the same manner as in Example 1, but the pressure of the heated steam in the mold was reduced to 1.0 ml.
If the pressure was not set at 1 kgf/crA, the inside and outside of the molded box would not be sufficiently fused internally, resulting in incomplete shaping.

Also, the heating steam pressure for molding is 1.1kyf/CI?
The molded product obtained by molding the L size has a weight of 3 on a dry weight basis.
It had a moisture content of 0 to 50, and was shrunk and deformed after being taken out from the mold.

Even after this was left in a dry house at 50° C. for 20 hours, the deformed state did not recover.

The conventionally widely used known technology of foaming expandable polystyrene particles under open atmospheric pressure can only obtain an expansion ratio of 65 to 70 Tll/g; When carried out under pressure, shrinkage tends to occur and it was not possible to stably obtain a foaming ratio of 60 ml near 9 or more.

The expandable thermoplastic resin particles according to the present invention can stably obtain an expansion ratio of 60 rnl/9 or more, particularly 80 TLl/g or more under steam heating and foaming conditions ranging from atmospheric pressure to pressurized state.

Moreover, as a result, it is possible to produce a significantly lighter molded body, which contributes to the reduction of packaging materials for lightweight items and thus to resource conservation.

[Brief explanation of the drawing]

FIG. 1 shows the foaming characteristics of Examples 1 to 2, and FIG. 2 shows the foaming characteristics of Comparative Examples 1 to 3. Explanation of symbols: 1...Curve showing the foaming characteristics of Example 1; 2...Curve showing the foaming characteristics of Example 2;
3...Curve showing the foaming characteristics of Comparative Example 1, 4...
...Curve showing the foaming characteristics of Comparative Example 2, 5...
- A curve showing the foaming characteristics of Comparative Example 3.

Claims (1)

[Scope of Claims] 1. Expandable thermoplastic resin particles obtained by impregnating a blowing agent into thermoplastic resin particles obtained by polymerizing a styrene monomer, diallyl phthalate, and an acrylic ester or a methacrylic ester. 2. The expandable thermoplastic resin particles according to claim 1, wherein the acrylic ester and methacrylic ester are acrylic esters or methacrylic esters whose homopolymer has a secondary transition point of 0° C. or lower. 3. The amount of diallyl phthalate used is 0.05 to 3% by weight based on the thermoplastic resin raw material.Acrylic acid ester and/or
Alternatively, the expandable thermoplastic resin particles according to claim 1 or 2, wherein the amount of methacrylic acid ester used is 0.5 to 10% by weight based on the thermoplastic resin raw material. 4. The expandable thermoplastic resin particles according to claim 1, 2, or 3, wherein the ratio of diallylphthalate and acrylic ester or methacrylic ester is 1 to 3 to 10 of the latter.