JP2012255082A - Curing method of polyolefin resin in-mold expansion molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the deformation and the shrinkage problem after in-mold expansion molding by a simple method, using neither execution of a special temperature control nor a special device in a curing step of a polyolefin resin in-mold expansion molded product.SOLUTION: The polyolefin resin in-mold expansion molded product is cured under the atmosphere in which a carbon dioxide concentration is adjusted, and thereby the shrinkage and deformation after the in-mold expansion molding can be controlled.

Description

  The present invention relates to a method for curing a foamed molded article in a polyolefin resin mold.

  Polyolefin resin pre-expanded particles are filled in a mold and heat-molded with water vapor, and the polyolefin resin in-mold foam molded product is an advantage of the in-mold foam molded product. It has characteristics such as sex. Polyolefin-based in-mold foam moldings are used in various applications such as heat insulating materials, shock-absorbing packaging materials, automobile interior members, and automotive bumper core materials.

  Conventionally, as a method for producing a polyolefin resin in-mold foam molded body, a method in which an inorganic gas such as air is previously injected into a polyolefin resin pre-expanded particle and foam molding is performed in a mold (so-called internal pressure application method), a polyolefin resin. A method of filling pre-expanded particles in a mold in a compressed state and foam-molding in the mold (so-called compression filling method) is performed.

However, the internal pressure application method requires a large-scale pressurization facility and has a problem that it takes time to apply the internal pressure. In addition, the compression filling method requires a device for compressing and filling the pre-foamed particles, and there is a problem that modification of an existing molding machine is required.
Because of these problems, there is a case where a method in which in-mold foam molding is performed using the polyolefin resin pre-expanded particles as they are without pretreatment in a state where the internal pressure is almost equal to the atmospheric pressure is sometimes used.

  By the way, the molded body molded by the in-mold foam molding method is filled with steam inside the foam at the time of molding. Therefore, when the molded body is left at room temperature after molding, the steam may be condensed and rapidly contracted or deformed.

  Even when the internal pressure application method or compression filling method is used, it may deform greatly after molding depending on the density of the molded body or molding conditions, etc., especially when performing in-mold foam molding without using pretreatment as it is However, there is a problem that it is difficult to obtain a molded article having a beautiful surface, such as sink marks and wrinkles remaining after drying because it is easily deformed after molding, and shrinkage does not return even after drying.

In order to solve these deformation and shrinkage problems after molding, methods for curing various polyolefin resin in-mold foam molded products have been studied so far.
In Patent Document 1, after taking out the polyolefin-based resin in-mold foam molded article, the temperature of the molded body is 25 to 55 ° C. lower than the melting point of the base resin while the volume of the molded article is 70 to 110% of the mold inner volume. A method of standing and curing is disclosed.
Patent Document 2 discloses a method for curing a polyolefin resin-in-mold foam-molded body using a cart-based curing device having an atmospheric temperature of 90 to 120 ° C.
In Patent Document 3, the curing initial temperature is kept at 15 ° C. or lower and higher than the melting temperature of the foamed molded article, and thereafter, curing is performed at a temperature of 75 to 85 ° C. 10 ° C. lower than the curing initial stage. A method is disclosed.

JP-A-60-166442 JP-A-2-130135 JP 2000-212320 A

A drying chamber of 60 to 80 ° C. is usually used to dry the polyolefin resin-in-mold foam-molded product, and the temperature is kept at a constant temperature. Further, usually, after the molded body is taken out and dried, it is left to stand at room temperature for a certain period of time in order to dry collectively.
Therefore, in order to implement the method of patent documents 1-3, there exists a problem that it is necessary to put in a drying chamber within the fixed time after shaping | molding, and a special apparatus is required.

  Therefore, the present invention solves the deformation and shrinkage problems after in-mold foam molding by a simple method without performing special temperature control or using a special device in the curing process having the above-mentioned problems. The purpose is that.

  As a result of intensive studies to solve the above problems, the inventor has obtained a polyolefin resin-in-mold foam-molded body molded from a mold based on the polyolefin resin pre-foamed particles under conditions where deformation and shrinkage easily occur. After taking out, by curing in an atmosphere of carbon dioxide concentration higher than the atmospheric partial pressure, more preferably in an atmosphere of carbon dioxide concentration of 20% by volume or more, the shrinkage of the in-mold foam molded product is small and the surface becomes beautiful. As a result, the present invention has been completed.

That is, this invention consists of the following structures.
[1] A polyolefin-based resin in-mold foam molded product formed by in-mold foam molding using polyolefin-based resin pre-expanded particles is taken out from the mold, and then in an atmosphere having a carbon dioxide gas concentration higher than the atmospheric partial pressure. Curing method of polyolefin resin in-mold foam-molded product, characterized by curing with
[2] The polyolefin resin-in-mold foam molded article curing method according to [1], wherein the carbon dioxide gas concentration atmosphere has a carbon dioxide gas concentration of 20% by volume or more.
[3] The time according to [1] or [2], wherein the time from the removal of the in-mold foam molded product from the mold until the start of curing in the carbon dioxide gas concentration atmosphere is 5 minutes or less. Curing method for foamed molded product in polyolefin resin mold.
[4] The polyolefin resin mold according to any one of [1] to [3], wherein the mold is cured in the carbon dioxide gas concentration atmosphere until just before the drying process of the in-mold foam molded body is started. Curing method for foamed molded products.
[5] The polyolefin resin mold according to any one of [1] to [4], wherein the internal pressure of the polyolefin resin pre-expanded particles filled by in-mold foam molding is substantially equal to the atmospheric pressure. Curing method for inner foam molding.

  According to the present invention, the polyolefin resin in-mold foam-molded body is cured under an atmosphere in which the carbon dioxide gas concentration is adjusted, so that shrinkage and deformation after in-mold foam molding can be performed without performing special temperature control. Can be suppressed.

It is an example of a DSC curve obtained when the polyolefin resin pre-expanded particles of the present invention are heated at a rate of 10 ° C./min from 40 ° C. to 220 ° C. with a differential scanning calorimeter (DSC). The low-temperature side melting peak, the low-temperature side melting peak calorie, which is the amount of heat enclosed by the tangent to the melting start baseline from the maximum point between the low-temperature side peak and the high-temperature side peak, is Ql, and the high-temperature side melting peak of the DSC curve Qh is the high-temperature side melting peak calorie, which is the amount of heat surrounded by the tangent line from the local maximum point between the low-temperature side peak and the high-temperature side peak to the melting end baseline. It is drawing explaining the measuring method for evaluating the state of sink. (A) has shown the midpoint of the length direction of the plate-shaped in-mold foaming body which is a position which measures a sink state. (B) has shown sectional drawing in this position, and measures thickness L1 in the edge part of a foaming molding, and thickness L2 inside 5 cm from an edge part using a digital caliper. In the evaluation of the present invention, the difference in thickness L1-L2 between the end portion and the inside is defined as “sink amount”.

  The in-mold foam molding method in the present invention is a method in which polyolefin resin pre-expanded particles are filled in a molding space that can be closed but cannot be sealed by two molds, and water vapor is used as a heating medium. Molded at a heating steam pressure of about 4 MPa (G) for about 3 to 60 seconds, fused the polyolefin resin pre-foamed particles together, then cooled the mold by water cooling, then opened the mold This is a method for obtaining a polyolefin resin-in-mold foam-molded product.

When using polyolefin resin pre-expanded particles for in-mold foam molding,
(1) A method of injecting an inorganic gas such as air into polyolefin resin pre-foamed particles in advance and using it for in-mold foam molding,
(2) A method in which polyolefin resin pre-expanded particles are filled in a mold in a compressed state and foamed in-mold
(3) Conventionally known methods such as a method of using polyolefin resin pre-expanded particles as they are without pretreatment in a state where the internal pressure is substantially equal to the atmospheric pressure can be used.
In particular, 3) the method of using the polyolefin resin pre-expanded particles as they are without pretreatment in a state in which the internal pressure is almost equal to the atmospheric pressure is greatly applied to the present invention because of the large shrinkage and deformation after molding.

  The curing method of the polyolefin resin in-mold foam molded product according to the present invention is a special method in which the in-mold foam molded product is removed from the mold and then cured in an atmosphere having a carbon dioxide gas concentration higher than the atmospheric partial pressure. Even if temperature control is not performed, mold shrinkage and deformation of the in-mold foamed molded product can be suppressed.

The carbon dioxide gas concentration in the curing atmosphere in the present invention is more preferably 20% by volume or more, further preferably 30% by volume or more, and particularly preferably 50% by volume or more.
The carbon dioxide gas concentration in the curing atmosphere is a value measured using, for example, a high-concentration gas detector for carbon dioxide gas (manufactured by Shin Cosmos Electric Co., Ltd., XP-3140).

In the present invention, there is no particular limitation on the method of curing in an atmosphere in which the carbon dioxide concentration is adjusted, for example,
Place the in-mold foam molding in a sealable container, container, bag, etc., adjusted to the carbon dioxide concentration in advance.
Inject carbon dioxide into containers, containers, and bags containing in-mold foam moldings to adjust the carbon dioxide concentration.
And the like.

  The method of curing an in-mold foamed molded article in an atmosphere in which the concentration of carbon dioxide gas of the present invention is adjusted is because it is only necessary to fill a container, container, bag, etc. with carbon dioxide gas using a carbon dioxide cylinder, dry ice, or the like. No special equipment is required, and this is a very simple method.

In the curing method for an in-mold foam molded body of the present invention, it is desirable that the time until the curing under the carbon dioxide gas concentration atmosphere is started is 5 minutes or less after taking out from the mold, and is 2 minutes or less. It is more desirable.
When the time until the curing under the carbon dioxide gas concentration starts exceeds 5 minutes, the effect of suppressing shrinkage and deformation tends to be small.

In the curing method for an in-mold foam molded body of the present invention, after the curing step under a predetermined carbon dioxide gas concentration atmosphere, the in-mold foam molded body left at room temperature for the purpose of water removal, shape recovery, etc. You may heat (what is called a drying process) at the temperature of about -80 degreeC.
Although there is no restriction | limiting in particular in drying time, Preferably it is 4 to 48 hours. If the drying time is less than 4 hours, the desired effect tends to be poor, and if it exceeds 48 hours, the productivity is remarkably lowered, which is not desirable.
In the drying step, it is not necessary to be in an atmosphere in which the carbon dioxide concentration is adjusted, but drying may be performed in an atmosphere in which the carbon dioxide concentration is adjusted.

The density of the polyolefin resin-in-mold foam-molded product to which the present invention is applied is preferably 10 kg / m ³ or more and 300 kg / m ³ or less. In particular, in a molded body having a high foaming ratio and having a density of 10 kg / m ³ or more and 45 kg / m ³ or less, deformation is likely to occur, and therefore the application of the present invention is effective.

  As the resin constituting the in-mold foam molded body in the present invention, a polyolefin resin is employed. Polystyrene resins and the like are also used for in-mold foam molding, but polyolefin resins have low rigidity, and the shrinkage and deformation after in-mold foam molding are significant. Useful.

  The polyolefin resin used in the present invention is a polymer containing 75% by weight or more of an olefin monomer.

Specific examples of the olefin monomer include, for example, ethylene, propylene, butene-1, isobutene, pentene-1, 3-methyl-butene-1, hexene-1, 4-methyl-pentene-1, 3, 4 Examples thereof include α-olefins having 2 to 12 carbon atoms such as dimethyl-butene-1, heptene-1, 3-methyl-hexene-1, octene-1, and decene-1. These may be used alone or in combination of two or more.
Specific examples of other monomers copolymerizable with the olefinic monomer include, for example, cyclopentene, norbornene, 1,4,5,8-dimethano-1,2,3,4,4a. , 8,8a, 6-octahydronaphthalene and the like, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1 , 6-octadiene and the like. These may be used alone or in combination of two or more.

Specific examples of the polyolefin resin used in the present invention include, for example, polyethylene resins mainly composed of ethylene, such as high density polyethylene, medium density polyethylene, low density polyethylene, and linear low density polyethylene, and propylene as a major component. And a polypropylene-based resin.
These polyolefin resins may be used alone or in combination of two or more.

The polypropylene resin is not particularly limited as long as it contains propylene as a main component of the monomer. For example, propylene homopolymer, α-olefin-propylene random copolymer, α-olefin-propylene block copolymer Etc. These may be used alone or in combination of two or more.
In particular, since the α-olefin is ethylene, a polypropylene-based resin containing ethylene as a comonomer component is easily available and excellent in process moldability, so that it can be used for in-mold foam molding. Liked.

The polypropylene resin is not particularly limited as long as it contains propylene as a main component of the monomer, and examples thereof include a propylene homopolymer, an olefin-propylene random copolymer, and an olefin-propylene block copolymer. .
These may be used alone or in combination of two or more.

Examples of the polyethylene resin used in the present invention include ethylene homopolymer, ethylene-α-olefin random copolymer, ethylene-α-olefin block copolymer, low density polyethylene, high density polyethylene, and linear low density polyethylene. Is mentioned. The α-olefin referred to herein includes α-olefins having 3 to 15 carbon atoms, and these may be used alone or in combination of two or more.
Among these polyethylene-based resins, good foamability when ethylene-α-olefin block copolymer has a comonomer content other than ethylene of 1 to 10% by weight or is a linear low density polyethylene And can be suitably used for in-mold foam molding.

  The polyolefin-based resin used in the present invention further includes a cell nucleating agent such as talc, an antioxidant, a metal deactivator, a phosphorus-based processing stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, and a fluorescence as necessary. Brighteners, stabilizers such as metal soaps, or crosslinking agents, chain transfer agents, lubricants, plasticizers, fillers, reinforcing agents, inorganic pigments, organic pigments, conductivity improvers, flame retardant improvers, interfaces It can be used as a polyolefin resin composition to which an additive such as an activator type or a polymer type antistatic agent is added.

  The polyolefin resin composition used in the present invention is usually melted with an additive, if necessary, with a polyolefin resin in advance using an extruder, kneader, Banbury mixer, roll, etc. so as to be easily used for pre-foaming. The mixture is mixed and molded into a polyolefin resin particle having a desired particle shape such as a cylindrical shape, an elliptical shape, a spherical shape, a cubic shape, a rectangular parallelepiped shape, or the like.

  The method for producing the polyolefin resin pre-expanded particles used in the present invention is not particularly limited, but the polyolefin resin particles are dispersed in a dispersion medium together with a dispersant in the presence of a foaming agent in an airtight container. A method of releasing and foaming the dispersion in a sealed container to a low pressure region while maintaining the temperature and pressure in the container constant, after heating to a predetermined foaming temperature under pressure and impregnating the resin particles with a foaming agent, So-called decompression foaming is preferred.

  The heating temperature in the sealed container is preferably the melting point of polyolefin resin particles −25 ° C. or higher and the melting point of polyolefin resin particles + 25 ° C. or lower, more preferably the melting point of polyolefin resin particles −15 ° C. or higher and the melting point of polyolefin resin particles +15. The temperature is in the range of ℃ or less. After heating and pressurizing to this temperature and impregnating the foaming agent into the polyolefin resin particles, one end of the sealed container is opened to release the polyolefin resin particles into a lower pressure atmosphere than in the sealed container. Thus, polyolefin resin pre-expanded particles can be produced.

  In producing the polyolefin resin pre-expanded particles, the blowing agent is not particularly limited. For example, aliphatic hydrocarbons such as propane, isobutane, normal butane, isopentane, and normal pentane; inorganic gases such as air, nitrogen, and carbon dioxide; Water or the like and a mixture thereof can be used.

  The polyolefin resin pre-expanded particles used in the present invention are heated from 40 ° C. to 220 ° C. at a temperature increase rate of 10 ° C./min in 5-6 mg of polyolefin resin pre-expanded particles as measured by differential scanning calorimetry. It is preferred to have two melting peaks in the resulting DSC curve.

The polyolefin resin pre-expanded particles used in the present invention preferably have a DSC ratio of 7% to 60%. In particular, in the case of a low DSC ratio of 7% or more and 35% or less, the deformation is likely to be remarkable, so that the application of the present invention is effective.
As shown in FIG. 1, the DSC ratio is a low temperature surrounded by the tangent line and the DSC curve by drawing a tangent line to the DSC curve from the point where the endothermic amount is the smallest between the two melting peaks of the DSC curve. When the side portion is the low-temperature side melting peak calorie Q _l and the high-temperature side portion is the high-temperature side melting peak calorie Q _h , the ratio of the high-temperature side melting peak calculated from these [Q _h / (Q _l + Q _h ) × 100].

  Examples and comparative examples will be described below, but the present invention is not limited thereby.

In the examples and comparative examples, the substances used were as follows, but were used without any particular purification.
● Polypropylene resin: ethylene-propylene random copolymer [ethylene content 2.8%, MFR = 7.0 g / 10 min, melting point 145 ° C.]
● Powdered basic tricalcium phosphate [manufactured by Taihei Chemical Industry Co., Ltd.]
N-Paraffinsulfonic acid soda [Ramtel PS, manufactured by Kao Corporation]

  Evaluation in Examples and Comparative Examples was performed as follows.

(DSC ratio)
In a DSC curve (illustrated in FIG. 1) obtained when the polyolefin resin pre-expanded particles 5 to 6 mg are heated from 40 ° C. to 220 ° C. at a temperature rising rate of 10 ° C./min using a differential scanning calorimeter, Two melting peaks were calculated from the melting peak calorie Ql on the low temperature side and the melting peak calorie Qh on the high temperature side of the melting peak by the following equation.
DSC ratio = Qh / (Ql + Qh) × 100

(Foaming ratio)
The weight w (g) and ethanol submerged volume v (cm ³ ) of the polyolefin resin pre-foamed particles were determined, and the density d (g / cm ³ ) of the polyolefin resin particles before foaming was determined by the following equation.
Foaming ratio = d × v / w

(Molded body density)
The dimension and weight W (kg) of the obtained in-mold foam molded article were measured, and the volume V (kg / m ³ ) was calculated from the dimension, and was obtained by the following formula.
Compact density = V / W

(Surface)
The surface of the obtained in-mold foam molding was visually observed and evaluated according to the following criteria.
○: There are almost no wrinkles on the surface.
Δ: Not so noticeable, but there are small wrinkles on the surface.
X: Large wrinkles that stand out on the surface are present.

(Volume shrinkage)
The length, width, and thickness of the in-mold foam molded product after curing were measured with a digital caliper [manufactured by Mitutoyo], and the volume was calculated from the values.
For the volume shrinkage, the ratio of the obtained molded body volume to the volume calculated from the mold dimensions (length 400 mm × width 300 mm × height 50 mm) was obtained, and the second decimal place was rounded off.

(Sink amount)
As shown in FIG. 2, in the cross section at the midpoint of the length direction of the obtained molded body, the end thickness L1 and the thickness L2 inside 5 cm from the end are measured using a digital caliper [Mitutoyo]. did.
The amount of sink marks was evaluated as a difference in thickness L1−L2 between the end portion and the inside.

(Examples 1-8)
[Production of resin particles]
Addition and mixing of 0.03 parts by weight of talc as a nucleating agent to 100 parts by weight of a polypropylene resin, kneading with a 50 mmφ single screw extruder, granulation, and polypropylene with a particle weight of about 1.8 mg / grain Type resin particles were produced.
[Preparation of pre-expanded particles]
100 parts by weight of the obtained resin particles and 14 parts by weight of isobutane were mixed with 300 parts by weight of water, 1.6 parts by weight of powdered basic tribasic calcium phosphate and 0.03 parts by weight of sodium n-paraffin sulfonate in a 10 L sealed container. First, the inside of the container was heated to 142.5 ° C.
Next, while maintaining the temperature, isobutane was injected to adjust the internal pressure of the container to 1.85 MPa. Thereafter, while maintaining the internal pressure of the container with nitrogen, the valve at the bottom of the closed container is opened, and the aqueous dispersion is discharged under an atmospheric pressure through an orifice plate having an opening diameter of 4.0 mmφ to obtain polypropylene resin pre-expanded particles. Obtained. The pre-expanded particles obtained had a DSC ratio of 25% and an expansion ratio of 20 times.
[Production of in-mold molded foam]
The obtained polypropylene resin pre-expanded particles were filled into a mold having a length of 400 mm, a width of 300 mm, and a height of 50 mm without applying internal pressure and pre-processing for compression filling. Thereafter, the water vapor pressure is increased to 0.30 MPa (G) over 18 seconds, heated as it is for 5 seconds, the pre-expanded particles are fused together, water-cooled for 50 seconds, taken out from the mold, and the in-mold foam-molded product is obtained. Obtained. The resulting molded body density was 32 kg / m ³ .

[Curing of molded foam]
The obtained in-mold foam-molded product was placed in a polyethylene bag adjusted to a carbon dioxide gas concentration atmosphere and left at room temperature (23 ° C.) for 1 hour. At this time, the standing time from taking out the molded body to putting it into the bag and the carbon dioxide concentration in the bag are shown in Table 1.
The carbon dioxide atmosphere was adjusted by injecting carbon dioxide into a polyethylene bag from a carbon dioxide cylinder [manufactured by Air Water], sealing the bag mouth with a string, and filling the bag with carbon dioxide. . Then, using a high-concentration gas detector for carbon dioxide [manufactured by Shin Cosmos Electric Co., Ltd., XP-3140], while measuring the carbon dioxide concentration, air is introduced into a bag filled with carbon dioxide, thereby giving a predetermined carbon dioxide gas. The concentration was adjusted.
[Drying molded foam]
The molded body was taken out from the vinyl bag and dried in a drying room at 75 ° C. for 18 hours. The obtained molded body was allowed to stand at 23 ° C. for 4 hours for condition adjustment, and then the surface wrinkles, volume shrinkage rate, and sink amount were evaluated. The evaluation results are shown in Table 1.

Example 9
Even when it was dried in a drying chamber at 75 ° C. for 18 hours in the drying chamber, the foamed molded product in the mold was kept in a bag adjusted to a carbon dioxide atmosphere, as in Example 1, A molded body was obtained. The obtained molded body was allowed to stand at 23 ° C. for 4 hours for condition adjustment, and then the surface wrinkles, volume shrinkage rate, and sink amount were evaluated. The evaluation results are shown in Table 1.

(Comparative Example 1)
The obtained in-mold foam-molded product was allowed to stand at room temperature for 1 hour and then dried in a 75 ° C. drying room for 18 hours. After taking out from the drying chamber and leaving at 23 ° C. for 4 hours, the surface wrinkles, volume shrinkage, and sink amount were evaluated. The evaluation results are shown in Table 1.

  As is clear from Table 1, it can be seen that by curing in an atmosphere of carbon dioxide gas at a certain concentration or higher, wrinkles are improved and shrinkage is reduced. In addition, the amount of sink marks as an index of deformation could be reduced to half or less.

Claims (5)

  The polyolefin resin in-mold foam molded product formed by the in-mold foam molding method using the polyolefin resin pre-expanded particles is removed from the mold and then cured under an atmosphere of carbon dioxide concentration higher than the atmospheric partial pressure. A method for curing a foamed molded product in a polyolefin-based resin mold, characterized in that.   The method for curing a polyolefin resin-in-mold foam-molded article according to claim 1, wherein the carbon dioxide gas concentration in the curing atmosphere is 20% by volume or more of carbon dioxide gas.   3. The polyolefin resin in-mold foam-molded product according to claim 1 or 2, wherein the time from when the molded product is taken out of the mold until the curing under the carbon dioxide gas concentration atmosphere is started is 5 minutes or less. Curing method.   The polyolefin resin-in-mold foam-molded article according to any one of claims 1 to 3, wherein the foam-molded article in the mold is cured in the carbon dioxide gas concentration atmosphere until immediately before the mold-molded foam-molded body starts to rise to a drying temperature. Curing method.   The method for curing a polyolefin resin in-mold foam molded product according to any one of claims 1 to 4, wherein the internal pressure of the polyolefin resin pre-expanded particles filled by in-mold foam molding is substantially equal to atmospheric pressure.

Images