U.S. patent application number 13/376201 was filed with the patent office on 2012-04-12 for resin pellet and method for producing the same.
This patent application is currently assigned to DU PONT-MITSUI POLYCHEMICALS CO., LTD.. Invention is credited to Kazuyuki Chiba, Izumi Sasai.
Application Number | 20120088105 13/376201 |
Document ID | / |
Family ID | 43356153 |
Filed Date | 2012-04-12 |
United States Patent
Application |
20120088105 |
Kind Code |
A1 |
Chiba; Kazuyuki ; et
al. |
April 12, 2012 |
RESIN PELLET AND METHOD FOR PRODUCING THE SAME
Abstract
A resin pellet of the present invention includes a resin base
material and a plurality of microparticles embedded in the resin
base material. The resin pellet is covered with the plurality of
microparticles on the surface of the resin base material. According
to the present invention, it is possible to prevent detachment of
the microparticles to be applied on the resin base material and to
effectively suppress blocking of resin pellets.
Inventors: |
Chiba; Kazuyuki; (Chiba,
JP) ; Sasai; Izumi; (Chiba, JP) |
Assignee: |
DU PONT-MITSUI POLYCHEMICALS CO.,
LTD.
Minato-ku, Tokyo
JP
|
Family ID: |
43356153 |
Appl. No.: |
13/376201 |
Filed: |
June 14, 2010 |
PCT Filed: |
June 14, 2010 |
PCT NO: |
PCT/JP2010/003920 |
371 Date: |
December 5, 2011 |
Current U.S.
Class: |
428/403 ;
427/180; 427/222 |
Current CPC
Class: |
C08J 2323/08 20130101;
Y10T 428/2991 20150115; C08J 3/124 20130101 |
Class at
Publication: |
428/403 ;
427/180; 427/222 |
International
Class: |
B32B 5/16 20060101
B32B005/16; B05D 7/02 20060101 B05D007/02; B05D 7/24 20060101
B05D007/24; B05D 1/00 20060101 B05D001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 19, 2009 |
JP |
2009-146065 |
Claims
1. A resin pellet comprising a resin base material and a plurality
of microparticles embedded in said resin base material, wherein the
surface of said resin base material is covered with said plurality
of microparticles.
2. The resin pellet according to claim 1, wherein said
microparticles are embedded in said resin base material by
dispersing said microparticles and said resin base material in a
softened state in a liquid.
3. The resin pellet according to claim 1, wherein said
microparticles contain a resin component.
4. The resin pellet according to claim 1, wherein said resin base
material and said microparticles contain the same resin
component.
5. The resin pellet according to claim 1, wherein said resin base
material contains an ethylene-vinyl acetate copolymer.
6. The resin pellet according to claim 5, wherein the content of
vinyl acetate in said ethylene-vinyl acetate copolymer contained in
said resin base material is 25 to 50 mass %.
7. The resin pellet according to claim 1, wherein said
microparticles contain an ethylene-vinyl acetate copolymer.
8. The resin pellet according to claim 7, wherein the content of
vinyl acetate in said ethylene-vinyl acetate copolymer contained in
said microparticles is 5 to 20 mass %.
9. The resin pellet according to claim 1, wherein both said resin
base material and said microparticles comprise an ethylene-vinyl
acetate copolymer.
10. The resin pellet according to claim 1, wherein the average
particle size of said microparticles is equal to or less than 20
.mu.m.
11. The resin pellet according to claim 1, wherein the shore
hardness of said microparticles is higher than the shore hardness
of said resin base material.
12. The resin pellet according to claim 1, wherein the degree of
crystallinity of said microparticles by the X-rays is higher than
the degree of crystallinity of said resin base material by the
X-rays.
13. The resin pellet according to claim 1, wherein the Vicat
softening point of said microparticles is higher than the Vicat
softening point of said resin base material.
14. The resin pellet according to claim 1 wherein said resin base
material is a particle.
15. A method for producing a resin pellet comprising preparing a
resin base material and embedding a plurality of microparticles in
said resin base material, wherein, in embedding a plurality of
microparticles in said resin base material, the surface of said
resin base material is covered with said plurality of
microparticles.
16. The method for producing a resin pellet according to claim 15,
wherein, in embedding a plurality of microparticles in said resin
base material, said microparticles are embedded in said resin base
material by dispersing said microparticles and said resin base
material in a softened state in a liquid.
17. The method for producing a resin pellet according to claim 15,
wherein, in embedding a plurality of microparticles in said resin
base material, said resin base material is come into contact with
said microparticles at a temperature of equal to or more than 35
degrees centigrade and equal to or less than 80 degrees centigrade.
Description
TECHNICAL FIELD
[0001] The present invention relates to a resin pellet and a method
for producing the resin pellet.
BACKGROUND ART
[0002] In the past, blocking of resin pellets has been a problem,
so that various measures have been taken.
[0003] Patent Document 1 discloses that anti-adhesive powder is
attached on the surface of EVA particles in a post-treatment step
of the manufacturing process of resin pellets having ethylene-vinyl
acetate copolymer particles as a base material by feeding EVA
particles which have been cut in water into a transportation tube,
and contacting with an anti-adhesive powder slurry in the
transportation tube. It is described to be found that blocking is
not occurred by such a manner even though a large amount of resin
pellets are accumulated in a large hopper.
[0004] Patent Document 2 discloses that EVA microparticles is
attached on the surface of EVA particles in a post-treatment step
of the manufacturing process of resin pellets having EVA particles
as a base material by adding an aqueous EVA dispersion into
circulating water used for transportation of EVA particles, and the
resulting resin pellets are further attached EVA particles even in
the step of free feeding of resin pellets by spraying the aqueous
EVA dispersion. In this manner, it is described that decrease in
anti-blocking performance due to detachment of EVA microparticles
in a free feeding pipe of resin pellets is suppressed, and
reduction of the pressure loss and pinching of resin pellets to a
rotary valve fitted in the free feeding pipe are prevented.
[0005] Patent Document 3 discloses a poor crystalline copolymerized
polyester resin pellet having a glass transition point of equal to
or more than 40 degrees centigrade. This resin pellet is coated
with a powder layer of a copolymerized polyester resin having a
glass transition point of equal to or more than 40 degrees
centigrade and an average particle size of equal to or less than 35
.mu.m, and capable of being dissolved in a general-purpose solvent.
In this manner, it is described in such a manner that blocking of
pellets is prevented, blocking is not occurred over a long period
of time and the solution stability is excellent even though the
resin is dissolved in a general-purpose solvent.
[0006] Patent Document 4 discloses that the emulsion polymer latex
and the hardened tallow fatty acid are respectively attached to
polymer particles by mixing an emulsion polymer latex to a slurry
containing a (meth)acrylic block copolymer before mixing a hardened
tallow fatty acid thereto, and heating at a predetermined
temperature. In this way, it is described that blocking of adhesive
resin pellets having a small hardness is thus suppressed.
[0007] Patent Document 5 discloses a surface treatment method of
resin pellets. In this method, first, octadecyl isocyanate (1.0
equivalent in terms of the functional group) as a long-chain alkyl
compound was polymerized with polyvinyl alcohol (degree of
polymerization: 1,100, content of vinyl alcohol units: 98 mole %)
as a saponified material of a polyvinyl acetate (co)polymer, to
give a releasing agent component. Subsequently, this releasing
agent component, an ethylene-acrylic acid copolymer as an
acid-modified polyolefin copolymer and the like are put into water,
and then heat-melted at 120 degrees centigrade in advance.
Subsequently, its heat-melted material and water are uniformly
emulsified and dispersed at 135 degrees centigrade, and cooled to
give a desired aqueous releasing agent composition. With the use of
such a method, it is possible to easily obtain resin pellets having
excellent anti-blocking performance, without occurring separation,
precipitation, clogging or the like even after obtaining a final
product, and without deteriorating final performance of the final
product.
RELATED DOCUMENTS
Patent Documents
[0008] Patent Document 1: Japanese Laid-Open Patent Publication No.
Hei1 (1989)-288408 [0009] Patent Document 2: Japanese Laid-Open
Patent Publication No. 2007-153979 [0010] Patent Document 3:
Japanese Laid-Open Patent Publication No. 2008-248015 [0011] Patent
Document 4: Japanese Laid-Open Patent Publication No. 2008-13727
[0012] Patent Document 5: Japanese Laid-Open Patent Publication No.
Hei9 (1997)-77890
DISCLOSURE OF THE INVENTION
[0013] However, according to the technology described in Patent
Document 1, it is described that the stick temperature of the
obtained resin pellets is 5 to 25 degrees centigrade although
anti-blocking performance of resin pellets is improved. The stick
temperature refers to a temperature which perfectly prevents
blocking of pellets. Higher stick temperature make it easy handling
because the temperature condition during storage of pellets is
alleviated. Accordingly, in the technology of Patent Document 1,
storage of resin pellets needs to control the temperature to equal
to or less than room temperature (approximately 25 degrees
centigrade). Therefore, in summer when a temperature increases,
there is a problem of occurring blocking of resin pellets again if
the storage temperature is not controlled by an air conditioner or
the like, and re-grinding process before use is required.
[0014] When a volatile component resulting from unreacted raw
material monomer or decomposition product is contained in resin
pellets, the volatile component needs to be purged (removed). As
one example of this purge operation, the resin pellets are exposed
to a stream of air or inert gas. In this case, if the temperature
of the stream is increased or the temperature of the resin pellet
itself is increased, the volatile content in the resin pellets is
easily escaped and the purge time is thus shortened. However, in
the event that the stick temperature is equal to or less than room
temperature, the temperatures thereof may not be increased, so that
the resin pellets should be treated at a low temperature.
Therefore, it is required several tens of hours or sometimes over
hundreds of hours as the purge treatment time. Thus, there have
been demanded resin pellets having a stick temperature which can
reduce the purge time, that is, a high temperature exceeding room
temperature as much as possible.
[0015] Patent Document 2 requires a large scale process in which
EVA microparticles are attached many times during free feeding of
resin pellets. This indicates that, attached EVA microparticles are
easily detached simply by attaching EVA microparticles to pellets
in a common method. As a solution to the problem, EVA
microparticles are attached many times during free feeding.
According to this method, it is found that EVA microparticles
finally attached at the end of free feeding step might be easily
detached and blocking of pellets might occur in the transportation
and storage process after being transported from a silo storage
step. Furthermore, the present inventors have reviewed this method
and as a result, the stick temperature was also generally equal to
or less than 25 degrees centigrade in the same manner as in Patent
Document 1, so that storage of resin pellets was limited.
[0016] Also, in the technology described in Patent Document 3,
there was a problem such that a resin powder layer to be applied on
a copolymerized polyester resin was easily detached.
[0017] Also, in the technology described in Patent Document 4,
there was a problem such that an emulsion polymer latex and a
hardened tallow fatty acid attached to polymer particles were
easily detached.
[0018] Furthermore, in the technology described in Patent Document
5, there was a problem such that a releasing agent component, an
acid-modified polyolefin copolymer and the like were heat-melted,
so that resin layers having a simple layer structure were formed on
a resin base material, and resin layers were fused to each
other.
[0019] Accordingly, in the above-described conventional
technologies, blocking of resin pellets may not be fully
suppressed, and the storage temperature of resin pellets was
limited.
[0020] The present invention has been accomplished in view of the
above circumstances, and an object of the present invention is to
provide a resin pellet which prevents detachment of the
microparticles to be covered on the resin base material and
effectively suppresses blocking of resin pellets, and a method for
producing the resin pellet.
[0021] According to the present invention, there is provided a
resin pellet having a resin base material and a plurality of
microparticles embedded in the resin base material, wherein the
surface of the resin base material of the resin pellet is covered
with the plurality of microparticles.
[0022] According to the present invention, there is also provided a
method for producing a resin pellet including a step of preparing a
resin base material and a step of embedding a plurality of
microparticles in the resin base material, in which, in the step of
embedding a plurality of microparticles in the resin base material,
the surface of the resin base material is covered with the
plurality of microparticles.
[0023] According to the present invention, a plurality of
microparticles are embedded in the resin base material and the
surface of the resin base material is covered with the
microparticles. In this way, concavity and convexity are formed in
the surface of the resin pellet while preventing detachment of
microparticles from the resin base material. Accordingly, the
contact area of resin pellets may be decreased, and blocking may be
effectively suppressed.
[0024] By selecting a material having a softening temperature or
melting point higher than that of the resin constituting the resin
base material as microparticles, the resin base material to be a
core such as a core-shell structure may be protected even at a
temperature higher than the softening temperature of the resin base
material.
[0025] According to the present invention, blocking of resin
pellets is effectively suppressed. That is, blocking of resin
pellets is effectively controlled even though resin pellets are
stored or preserved at a high temperature.
[0026] As another effect in a preferred aspect, anti-adhesive
microparticles to be applied on the surface of the resin base
material are not detached even though they are transported by air
in the pipe.
[0027] As still another effect, since resin pellets can be dried at
a high temperature, the volatile component contained in the resin
pellets may be removed in a short period of time. Accordingly, the
time until the resin pellets having a volatile component in a small
amount are shipped may be reduced, so that the productivity is
improved. When the volatile component is removed before the molding
process, the time required for drying and molding after receiving
resin pellets is shortened, and a cycle from the step of receiving
of resins to the step of molding is improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The above and other objects, advantages and features of the
present invention will be more apparent from the following
description of certain preferred embodiments taken in conjunction
with the accompanying drawings.
[0029] FIG. 1 is a view illustrating the results of Example.
[0030] FIG. 2 is a view illustrating the results of Example.
[0031] FIG. 3 is an example of a device used for the production of
resin pellets according to the embodiment.
[0032] FIG. 4 is an example of a device used for the production of
resin pellets according to the embodiment.
DESCRIPTION OF EMBODIMENTS
[0033] Embodiments of the present invention will be illustrated
with reference to the drawings below.
[0034] The resin pellet of this embodiment has a resin base
material and a plurality of microparticles embedded in the resin
base material. In this resin pellet, the surface of the resin base
material is covered with a plurality of microparticles.
[0035] The aforementioned microparticles are dispersed in a liquid
along with the resin base material keeping the original shape with
at least its surface in a softened state. In this way, the
microparticles may be embedded in the resin base material.
Alternatively, as long as microparticles exhibit even a little
adhesiveness, microparticles are brought into contact with the
resin base material to make microparticles pseudo-bonded on the
resin base material, and the resin base material can maintain the
original shape although at least the surface of the resin base
material is softened. Therefore, microparticles may also be
embedded in the resin base material by heating at a temperature in
which microparticles are not softened. Incidentally, in this
embodiment, "softening" does not include a state in which the resin
base material is melted such that the shape of the resin base
material is not maintained.
[0036] The resin base material is a particle. Its shape may be
spherical or oval-spherical. The particle diameter is not limited
as long as it is a size used in a usual molding machine. It is
usually 1 to 10 mm and the most commonly 2 to 5 mm. When it is 2 to
5 mm, handling properties are excellent, the time for purging the
volatile content is also shortened because of large surface area,
and a strong and dense microparticle layer which is not relatively
easily detached may be formed on the surface.
[0037] The resin base material exhibits an effect of this
embodiment more remarkably when an amorphous or low-crystalline
thermoplastic resin is used. "Low-crystalline" mentioned herein
refers to the degree of crystallinity determined by differential
scanning calorimeter (DSC) of equal to or less than 30%, preferably
equal to or less than 20% and particularly preferably equal to or
less than 10%. The molecular weight of the thermoplastic resin may
be good as long as it is a molecular weight enough to maintain its
shape in a pellet form and hard to break on impact, and it is, for
example, 0.1 to 1,000 g/10 min, preferably 0.1 to 500 g/10 min, and
particularly preferably 0.5 to 200 g/10 min in terms of the melt
flow rate (JIS K6924-2, 190 degrees centigrade, a load of 2,160
g.
[0038] When a thermoplastic resin having a softening temperature
(Vicat softening point, JIS K7206) of equal to or less than 80
degrees centigrade, preferably equal to or less than 50 degrees
centigrade, further preferably equal to or less than 30 degrees
centigrade, and particularly equal to or less than standard room
temperature, that is, 25 degrees centigrade is used, the resin base
material exhibits an effect of the present invention more
remarkably. The lower softening temperature is, the lower the stick
temperature is. Therefore, cooling is required for storage, the
purge gas temperature is also lowered and the purge time tends to
be long. Thus, improvement effects of base material having the
lower softening temperature are greater.
[0039] Specifically, the resin base material may be a copolymer of
an ethylene monomer and a polar monomer selected from vinyl
acetate, methyl acrylate, ethyl acrylate, butyl acrylate, methyl
methacrylate and glycidyl methacrylate. In addition thereto, an
ethylene-.alpha.-olefin copolymer that is a copolymer of ethylene
and .alpha.-olefin having 3 to 10 carbon atoms (e.g. an
ethylene-propylene copolymer, an ethylene-1-butene copolymer, an
ethylene-1-hexene copolymer and an ethylene-1-octene copolymer
having ethylene as a main component) exhibiting amorphous or
low-crystalline behavior, or a propylene-.alpha.-olefin copolymer
that is a copolymer of propylene and ethylene or .alpha.-olefin
having 4 to 10 carbon atoms (e.g. a propylene-ethylene copolymer, a
propylene-1-butene copolymer and the like having propylene as a
main component) exhibiting amorphous or low-crystalline behavior,
may be used. Herein, "amorphous" means that the melting peak is not
measured by DSC. "Low-crystalline" means that the melting peak is
found by DSC, and that the area ratio of the peak is equal to or
less than 30% as compared to those exhibiting the maximum peak.
[0040] The resin base material is particularly preferably applied
to an ethylene-polar monomer polymer that is a copolymer of
ethylene and a polar monomer, and may further preferably be an
ethylene-vinyl acetate copolymer. In this case, as the content of
vinyl acetate in the ethylene-vinyl acetate copolymer is increased,
the degree of crystallinity and the softening temperature are
lowered, and the stick temperature tends to be lowered as well. In
case of an ethylene-vinyl acetate copolymer having the content of
vinyl acetate exceeding 40 mass % and ethylene of less than 60 mass
%, the crystal melting peak is not observed on the basis of DSC,
thus exhibiting amorphous. In case of an ethylene-vinyl acetate
copolymer having the content of vinyl acetate of equal to or more
than 20 mass % and equal to or less than 50 mass %, preferably 30
to 50 mass % and particularly 40 to 50 mass %, an effect of this
embodiment is remarkably exhibited; therefore, it is
preferable.
[0041] The resin base material can be produced by polymerization
according to a known method in combination with the above
monomers.
[0042] For example, the resin base material composed of an
ethylene-vinyl acetate copolymer can be produced by using a radical
polymerization method, an emulsion polymerization method or a
solution polymerization method.
[0043] The microparticles preferably contain a resin component, are
more preferably composed of a resin component as a main component,
and are further preferably composed of a resin component.
Furthermore, microparticles may be organic acid (salt) powder such
as calcium stearate, or inorganic compound powder such as silica,
talc or the like.
[0044] The microparticles in this embodiment may be dispersed in
water. The average particle size of microparticles properly varies
depending on the size of the resin base material to be covered.
However, it is preferable that the average particle size is
generally equal to or less than 20 .mu.m and particularly equal to
or less than 10 .mu.m, because the surface of the resin base
material can be densely covered with microparticles.
[0045] One of preferred aspects is that the shore hardness of
microparticles (JIS K7215, needle penetration angle: 90 degrees,
needle penetration speed: 0.8 mm/sec) is higher than the shore
hardness of the resin base material. Specifically, the difference
(.DELTA.HS=HS.sub.2-HS.sub.1) between the shore hardness (HS.sub.2)
of the microparticles and the shore hardness (HS.sub.1) of the
resin base material may be 30 to 100 and preferably 50 to 90.
[0046] When the microparticles contain a resin component, the shape
of microparticles may be truly spherical or oval-spherical. In an
extreme case, it may be irregularly polygonal. However, when it is
polygonal, for example, the friction with the inner wall of the
pipe becomes high when microparticles are transported in the pipe,
and there is greater risk of causing detachment of microparticles
even though they are embedded in the resin base material. Thus, the
shape is preferably truly spherical or oval-spherical without
having a corner.
[0047] Any resin component constituting the microparticles may be
good as long as it is polyester, polyolefin, polyurethane or the
like, is capable of being dispersed in water, or is capable of
being dispersed in water with the use of a dispersion aid such as a
surfactant or the like. The resin pellets in which the resin base
material is covered with microparticles of the present invention
are used for known melt molding or powder molding as it is.
Therefore, it is preferable that the resin component constituting
the microparticles is selected from resin components of the same or
similar to the thermoplastic resin constituting the resin base
material, because there can be no risk of damaging performance of a
desired object to be molded that is the resin base material, or an
effect on the physical properties due to the presence of the
microparticle component can be controlled to a minimum.
[0048] For example, when the resin component of the resin base
material is an ethylene polymer, an ethylene polymer may be used as
the resin component contained in microparticles. In this way, an
effect on the physical properties of the resin base material may be
minimized. Of course, if microparticles are used as a resin
additive such as silica, silica may be used as it is. In this way,
it is also possible to exhibit an effect of preventing blocking in
a state that resin pellets are strongly covered with silica or an
effect as a slipping agent in a film after melt molding.
[0049] Further, as another example, it is preferable that an
ethylene-vinyl acetate copolymer as the microparticles is used when
the resin component of the resin base material is an ethylene-vinyl
acetate copolymer because an effect on the physical properties of
the resin base material may be minimized. The ethylene-vinyl
acetate copolymer constituting the microparticles in this case may
be selected among copolymers having the shore hardness (HS.sub.2)
which is higher than the shore hardness (HS.sub.1) of the
ethylene-vinyl acetate copolymer of the resin base material by 30
to 100 and preferably 50 to 90 as aforementioned. The shore
hardness is described in a product catalog of each company, so that
it is easy to select an appropriate product. Although there is a
variation in the content of vinyl acetate in the ethylene-vinyl
acetate copolymer depending on the polymerization method and
polymerization apparatus, one of preferred aspects is that the
content of vinyl acetate is generally equal to or less than 20 mass
%, and preferably equal to or more than 5 mass % and less than 20
mass %, because an effect of this embodiment is remarkably
exhibited. However, the kind of the ethylene-vinyl acetate
copolymer constituting the microparticles is determined based on
the relative relationship with the ethylene-vinyl acetate copolymer
constituting the resin base material, so that a copolymer with the
content of vinyl acetate of higher than 20 mass % may also be used
in some cases.
[0050] One of preferred aspects is that the degree of crystallinity
(a.sub.2) of the resin component constituting the microparticles by
the X-rays is higher than the degree of crystallinity (a.sub.1) of
the resin component constituting the resin base material by the
X-rays. Specifically, it is preferable that the difference
(.DELTA.a=a.sub.2-a.sub.1) in the degrees of crystallinity is 15 to
35% and preferably 20 to 30%, because the quality of the resin
pellets is less adversely influenced by a target final product of
this embodiment. The molecular weight of the resin component
constituting the microparticles is, for example, 10 to 500 g/10
min, preferably 50 to 300 g/10 min and particularly preferably 100
to 300 g/10 min in terms of the melt flow rate (JIS K6924-2, 190
degrees centigrade, a load of 2,160 g).
[0051] One or preferred aspects is that the Vicat softening point
(T.sub.2) of the resin component constituting the microparticles is
higher than the Vicat softening point (T.sub.1) of the resin
component constituting the resin base material. Specifically, the
difference (.DELTA.T=T.sub.2-T.sub.1) in the Vicat softening points
may be equal to or more than 3 degrees centigrade, preferably equal
to or more than 10 degrees centigrade, and more preferably equal to
or more than 15 degrees centigrade. Incidentally, when the Vicat
softening point is equal to or less than the lower limit of a
measuring device and it is not possible to measure the exact
number, the difference in the Vicat softening points may be
calculated with the use of the measurement lower limit. As
described below, when the resin component constituting the
microparticles is the same kind as that of the resin base material,
the Vicat softening point can be controlled by the amount of the
copolymer component. Within the temperature difference in the
aforementioned range, the resin pellets after being covered with
microparticles exhibit the target physical properties without
practically damaging the physical properties of the resin base
material.
[0052] Next, a method for producing a resin pellet of this
embodiment will be described. The production method of this
embodiment includes (1) a step of preparing a resin base material,
(2) a step of embedding a plurality of microparticles in the resin
base material and (3) a step of drying the resin pellets. The steps
(2) and (3) herein may be continuously but separately carried out,
or may be carried out at the same time.
[0053] First, it will be described about the step (1) of preparing
a resin base material. A typical pellet-like resin base material is
available by purchasing one of commercial products. In addition
thereto, a pellet-like resin base material which has been
pelletized by a commonly known polymer manufacturing process may be
used.
[0054] Next, it will be described about the step (2) of embedding a
plurality of microparticles in the resin base material. Herein,
there is used a dispersion obtained by dispersing microparticles in
a liquid. As the liquid, water is preferably used, and the liquid
may contain a dispersion aid such as a surfactant or the like for
the purpose of enhancing dispersibility and dispersion stability.
Or, the liquid may contain an organic solvent typified by alcohols
such as methanol, ethanol and the like. That is, water mentioned in
this embodiment may also be a mixture of mainly composed of water
with other component.
[0055] Stability of the microparticles in the dispersion is
preferably excellent, and microparticles may be dispersed in water
in a uniform and orderly manner.
[0056] As the aqueous dispersion, Chemipearl (registered trademark)
manufactured by Mitsui Chemicals, Inc. may be used as it is, or by
further being dispersed in water.
[0057] There are several brands of Chemipearl divided by the resin
component constituting the dispersed microparticles, and there are
specifically A series mainly composed of ethylene-.alpha.-olefin
copolymer elastomer, M series mainly composed of polyethylene, V
series mainly composed of an ethylene-vinyl acetate copolymer, S or
SA series mainly composed of an ionomer, and W series mainly
composed of low-molecular weight (wax) polyethylene or
polypropylene.
[0058] When the resin base material is an amorphous or
low-crystalline ethylene-.alpha.-olefin copolymer, the dispersion
is selected from Chemipearl A series; in case of polyethylene, the
dispersion is selected from Chemipearl M series; and in case of an
ethylene-vinyl acetate copolymer, the dispersion is selected from
Chemipearl V series, which are preferable combinations.
[0059] When the Vicat softening point is used as a guideline for
selection, they can be examined by using a catalog of the company,
selected and combined depending on the Vicat softening point of the
resin base material. For example, the Vicat softening point of A100
is 60 degrees centigrade, that of A400 is 55 degrees centigrade,
that of M200 is 75 degrees centigrade, that of 5100 is 60 degrees
centigrade, that of SA100 is 55 degrees centigrade, and that of
V200 is 40 degrees centigrade.
[0060] Commonly used is a dispersion in which microparticles are
dispersed in the range of 10 to 70 mass % relative to water. When
the concentration of the dispersion is increased, the solution
viscosity is increased, and handling properties and uniform
dispersibility tend to be lost. Thus, microparticles are contained
preferably in the range of 20 to 50 mass %, and particularly more
preferably in the range of 30 to 40 mass %.
[0061] The thus-prepared dispersion and the resin base material are
mixed. As the mixing amount, the amount of the dispersion is 0.001
to 20 times, and preferably 0.1 to 10 times of the total weight,
when the total weight of the resin base material is 100.
[0062] Subsequently, a mixture of the dispersion and the resin base
material is exposed to warm wind of air or inert gas, (far)
infrared rays or the like, and heated. The heating temperature is
higher than the softening temperature of the resin base material,
and when the resin base material is a crystalline thermoplastic
resin, it becomes lower than its melting point. When an
ethylene-vinyl acetate copolymer is used as the resin base material
and microparticles, the mixture may be heated such that the
temperature of the resin pellet itself (hereinafter referred to as
the pellet temperature) is 35 to 80 degrees centigrade, and
preferably 40 to 60 degrees centigrade. A fluidized bed dryer, a
vibrating dryer, an infrared dryer or the like may be used for
heating. In this manner, the surface of the resin base material is
softened, and the microparticles are embedded in the resin base
material.
[0063] As one aspect of the method of mixing the resin base
material and the dispersion, the resin base material may be added
to the dispersion heated in advance and the mixture may be stirred.
In this case, the temperature of the dispersion is higher than the
softening temperature of the resin base material, and when the
resin base material is a crystalline thermoplastic resin, it
becomes lower than its melting point. Specifically, the temperature
is properly selected by the combination of the softening
temperature of the resin component constituting the resin base
material and the softening temperature of the resin component in
the dispersion. For example, in case of the ethylene-polar monomer
copolymer such as an ethylene-vinyl acetate copolymer, it may be 35
to 80 degrees centigrade, and preferably 40 to 70 degrees
centigrade. Such manner is more preferable because the surface of
the resin base material may be softened without agglomerating the
dispersion, and microparticles are easily embedded on the resin
base material. The dispersion is 1 to 20 times and preferably 2 to
10 times, based on the total weight of the resin base material.
[0064] As another aspect of the method of mixing the resin base
material and the dispersion, there may be a method including that
the dispersion is supplied like a rotational flow along the side
wall of the container into the resin base material present in the
container, and the resin base material and the dispersion are come
into contact with each other.
[0065] As another aspect, there may be a method including that the
resin base material and the dispersion are supplied in the same
direction like a rotational flow along the side wall of a
cylindrical-shaped or triangular cone-shaped container at the same
time, and the resin base material and the dispersion are come into
contact with each other.
[0066] As further another aspect, there may be a method including
that the dispersion is sprayed into the resin base material present
in the container using a sprayer, and the resin base material and
the dispersion are come into contact with each other.
[0067] According to these methods, microparticles may be attached
on the resin base material with a small amount of the dispersion to
be embedded. When the dispersion is equal to or less than the
equivalent, preferably 0.001 to 0.5 times and further preferably
0.01 to 0.1 time, based on the total weight of the resin base
material, an object of the present invention may also be achieved,
and the drying time thereafter may also be shortened. Thus, it is
favorable from the viewpoints of the productivity and energy
saving.
[0068] Microparticles collide against the surface of the softened
resin base material by dispersing microparticles and the softened
resin base material in the liquid as described above, and then the
surface of the resin base material having the viscosity from
softening is pushed by microparticles. In this way, microparticles
are embedded in the resin base material. The surface of the resin
base material is in a softened state so that the viscosity is
enhanced, and microparticles are embedded in the depth direction
from the surface of the resin base material. Therefore, detachment
of microparticles from the resin base material is suppressed.
[0069] In addition, in the aforementioned various methods, there is
also used a method in which the resin base material and
microparticles are come into contact with each other at normal
temperature without heating, microparticles are attached on the
resin base material simply by substantial point adhesion or point
sticking, and microparticles are embedded in the resin base
material and at the same time dried using the heat in the drying
step to be continuously carried out.
[0070] This method is suitably applied particularly to
microparticles exhibiting even a slight adhesiveness at normal
temperature.
[0071] Next, it will be described about the step (3) of drying
resin pellets.
[0072] In this embodiment, the resin pellets may be dried at a
temperature in which the resin base material component is softened
but the microparticle component is not softened, and drying by
using warm wind or (far) infrared rays or the like may be adopted.
In case of warm wind, air is used. When an organic solvent such as
alcohol is used in the step of embedding microparticles, inert gas
such as nitrogen or the like is preferably used. In this manner,
the microparticles embedded in the resin base material are more
firmly adsorbed and fixed on the resin base material.
[0073] Meanwhile, when the dispersion is used, the liquid
accompanying microparticles may also be removed.
[0074] Furthermore, in case that the resin base material and
microparticles are come into contact with each other at normal
temperature in the aforementioned step, microparticles attached on
the surface of the resin base material in a point adhesion state
are firmly adsorbed and fixed on the resin base material.
[0075] When resin pellets are stored under the condition of, for
example, a temperature of 25 to 35 degrees centigrade and
particularly 25 to 30 degrees centigrade after drying under such
dry conditions, microparticles are more firmly adsorbed and fixed
on the resin base material depending on the storage time (the
number of days). In this way, the surface of the resin base
material is covered with a plurality of microparticles.
[0076] Microparticles obtained by the air drying or cold wind are
simply attached on the surface of the resin base material, and less
likely to be embedded on the surface of the resin base material. Of
course, if the softening temperature of the resin base material is
equal to or less than normal temperature, the microparticle
component may possibly be firmly attached by spending time for air
drying. However it is not practical in consideration of the
productivity.
[0077] Meanwhile, in the method for producing pellets of this
embodiment, for example, a device illustrated in FIG. 3 may be
used. FIG. 3 is a schematic perspective view regarding a pellet
producing device 1. In the pellet producing device 1, a stirring
conveyance chamber 8 consisting of a cylindrical shell and a dry
section B consisting of an air permeable cylindrical screen are
respectively laterally arranged. In the dry section B, a main shaft
and a stirring blade driven to rotate around the shaft center of
the main shaft are rotatably installed.
[0078] Hereinafter, the method for producing rein pellets of this
embodiment using the pellet producing device 1 will be described in
detail with reference to FIG. 3. First, (1) the aforementioned step
is carried out, and the obtained pelletized resin base material is
put into a hopper 3 from a supply port 2. A predetermined amount of
the resin base material is continuously supplied to the stirring
conveyance chamber 8 of a covering section A by means of a rotary
valve 4. In the stirring conveyance chamber 8, the pellet-like
resin base material is conveyed in the longitudinal direction of
the stirring conveyance chamber 8 with stirring by a stirring
conveyance means such as a single thread roll. The stirring
conveyance chamber 8 is provided with a nozzle 17, the dispersion
obtained by dispersing microparticles in a liquid is sprayed on the
resin base material from the nozzle 17, and accordingly the surface
of the resin base material is covered with microparticles.
[0079] Herein, when the resin base material and microparticles are
come into contact with each other in the stirring conveyance
chamber 8, it is preferable to heat the mixture at a temperature in
which the resin base material component is softened but the
microparticle component is not softened. In this way, attachment
(non-detachment) of microparticles to the resin base material may
be improved. Specifically, it is preferable that the resin base
material and microparticles are come into contact with each other
at equal to or more than the softening temperature of the resin
base material component, in case of a crystalline thermoplastic
resin used as the resin base material, at equal to or less than the
melting point and equal to or less than the softening temperature
of the microparticle component. For example, the pelletized resin
base material may be heated in advance in the range of less than
the temperature for melting it at a temperature for softening the
resin base material, and supplied to the stirring conveyance
chamber 8. In this case, for example, by mechanically heating the
inside of the hopper 3 and the rotary valve 4, the resin base
material may be heated. The heating temperature at this time may be
equal to or more than the softening temperature of the resin base
material component, in case of a crystalline thermoplastic resin
used as the resin base material component, may be equal to or less
than its melting point. For example, when the resin base material
is an ethylene-polar monomer copolymer, the heating temperature may
be 30 to 90 degrees centigrade and preferably 50 to 80 degrees
centigrade.
[0080] In order to improve attachment (non-detachment) of the
microparticles to the resin base material, the aforementioned
dispersion to be sprayed from the nozzle 17 may be heated in
advance. In this case, the liquid in which microparticles are
dispersed is preferably heated at a temperature in which
microparticles are not softened. The specific heating temperature
is automatically determined depending on the softening temperature
of the resin component constituting the microparticles. It is
required to be less than the boiling point of the liquid for
dispersing microparticles due to a dispersion liquid form. For
example, in case of the ethylene-polar monomer copolymer, the
liquid may be heated at a temperature of preferably 30 to 90
degrees centigrade and more preferably 50 to 80 degrees centigrade.
Incidentally, as the liquid for dispersing microparticles, water is
preferably used, and the liquid may contain a dispersion aid such
as a surfactant or the like, or may contain alcohols such as
methanol, ethanol and the like.
[0081] The resin base material thus covered with microparticles is
discharged from the stirring conveyance chamber 8 and diffused in a
conveyance path 27. The resin base material covered with
microparticles and diffused in the conveyance path 27 is contacted
with warm wind with stirring while being conveyed in the
longitudinal direction of the dry section B by means of the
stirring blade arranged in the dry section B. In this case, warm
wind is supplied from a hot wind supply port 28. In this way, the
surface of the resin base material covered with microparticles may
be dried. Warm wind is supplied from the aforementioned hot wind
supply port 28, and examples of warm wind include, for example, air
heated to 35 to 80 degrees centigrade, and inert gas such as
nitrogen or the like. In this manner, the surface area of the resin
base material is softened or melted, and microparticles may be
embedded in the surface of the resin base material.
[0082] In order to improve attachment (non-detachment) of the
microparticles to the resin base material, the conveyance path 27
may be mechanically heated. In this case, the heating temperature
may be equal to or more than room temperature, and may be, for
example, a temperature in which the resin base material component
is softened and microparticles are not softened. Furthermore, the
temperature may be properly controlled in relation to the retention
time in the conveyance path 27.
[0083] Subsequently, the resin base material covered with
microparticles is discharged from an outlet 47 and cooled to form
resin pellets of this embodiment. Cooling may be carried out by,
for example, immersing it in a liquid, spraying a liquid, or coming
into contact with cold wind. When a liquid is sprayed, water is
preferably used as the spraying liquid. The liquid may contain a
dispersion aid such as a surfactant or the like, or may contain
alcohols such as methanol, ethanol and the like. When a liquid is
sprayed, in addition to an effect of the liquid to be sprayed
directly contributing to cooling, a cooling effect is also expected
by evaporation by the heat of resin pellets and removing the latent
heat of vaporization. Examples of cold wind include, for example,
cold air, and inert gas such as nitrogen or the like. The cooling
temperature is reduced by preferably 5 degrees centigrade or less,
and more preferably 10 degrees centigrade or less, as compared the
softening temperature of the resin base material component. By
cooling in this manner, microparticles may be firmly attached to
the resin base material by residual heat of resin pellets, and
detachment of the microparticles from the resin base material may
be prevented.
[0084] According to the production method using the pellet
producing device 1, the aforementioned step (2) of embedding
microparticles in the resin base material and the aforementioned
step (3) of drying the resin pellets may be carried out
continuously or at the same time in a parallel manner, so that
resin pellets of this embodiment can be more efficiently
produced.
[0085] In the step (3) of drying the resin pellets in the method of
this embodiment for producing pellets, for example, one of
vibrating dryers illustrated in FIG. 4, that is, a spiral elevator
(also referred to as the vertical spiral conveyor) may be used.
[0086] The resin pellets on the spiral elevator are exposed to warm
wind and heated to 30 to 80 degrees centigrade as in the
aforementioned device. According to this spiral elevator, advantage
that the retention time is prolonged by extending the height of the
device in the vertical direction can be obtained. When the
retention time is prolonged in the drying step, the temperature of
warm wind may be lowered, and microparticles may be more firmly
attached to the resin base material, for example, by warm wind of
20 to 75 degrees centigrade and preferably 30 to 50 degrees
centigrade. In this case, the device is also distinctive in that
drying can be made by sending air without heating under weather
conditions, and drying can be made with energy saving because the
heating temperature is also lowered. Furthermore, the combined
advantage that the installation area is small and the retention
time is prolonged can be also obtained to be combined. As warm wind
blowing into the spiral elevator, air or inert gas such as nitrogen
or the like may be used. In this way, attachment (non-detachment)
of microparticles to the resin base material may be improved.
[0087] Next, an operational effect of this embodiment will be
described. According to this embodiment, a plurality of
microparticles are embedded in the resin base material and the
surface of the resin base material is covered with microparticles.
Accordingly, detachment of microparticles from the resin base
material is prevented, and unevenness is formed on the surface of
the resin pellets. Accordingly, the contact area between resin
pellets may be reduced, and blocking may be effectively
suppressed.
[0088] Furthermore, a non-blocking material is used as the
component constituting the microparticles, so that blocking may be
effectively inhibited.
[0089] Furthermore, the softening temperature (melting point or
sublimating temperature) of microparticles to be applied on the
surface is higher than that of the resin base material, so that
drying can be made in an environment having a temperature of equal
to or more than the softening temperature of the resin base
material and less than the softening temperature of the
microparticle component. Therefore, the volatile component such as
residual monomers contained in the resin base material may be
quickly removed.
[0090] While the embodiments of the present invention have been
described above with reference to the drawings, the disclosures are
presented for the purpose of illustrating the present invention,
and various constructions other than those described above are also
available.
EXAMPLES
(1) Evaluation of Physical Properties of Resin Pellet
[0091] i) Melt flow rate (MFR): JIS K7219-1999 (temperature
condition: 190 degrees centigrade, load: 2,160 g
[0092] ii) Vicat softening point: JIS K7206-1999 (measurement lower
limit: 25 degrees centigrade)
[0093] iii) Shore hardness: JIS K7215-1986
[0094] iv) Vinyl acetate content: JIA K 7192-1999
[0095] v) Degree of crystallinity: X-ray diffraction method
(2) Evaluation of Embeddability of Particles
[0096] The surface and cross section of the prepared resin pellets
were observed with an electron microscope, and embeddability was
determined with the attachment state of particles.
[0097] A: Particles were attached almost all over the surface of
pellets.
[0098] B: Particles were attached on the surface of pellets, but
some of particles were detached.
[0099] C: Attachment of particles was not observed on the most of
the surface of pellets.
[0100] D: Attachment of particles was not observed on the surface
of pellets.
Example 1
[0101] An aqueous dispersion (solid content concentration: 40 mass
%) was prepared by dispersing microparticles composed of an
ethylene-vinyl acetate copolymer having the content of vinyl
acetate of 19 mass %, MFR of 150 g/10 min, a Vicat softening point
of 42 degrees centigrade, a shore hardness of 86 and the degree of
crystallinity of 26. 500 g of the aqueous dispersion was heated to
45 degrees centigrade, and 100 g of pellets (pellet temperature: 15
degrees centigrade) was added thereto, and the aqueous dispersion
and pellets were contacted under stirring for 30 seconds. The
pellets were composed of an ethylene-vinyl acetate copolymer having
the content of vinyl acetate of 46 mass %, MFR of 100 g/10 min, a
Vicat softening point of equal to or less than 25 degrees
centigrade (.DELTA.T.gtoreq.17), a shore hardness of 16 (.DELTA.HS:
70) and the degree of crystallinity of 0% (.DELTA.a: 26%) as a
resin base material. Subsequently, the obtained resin pellets were
cooled in cold water of 10 degrees centigrade and then dried at
normal temperature (25 degrees centigrade).
Example 2
[0102] To 10 kg of pellets (pellet temperature: 20 degrees
centigrade) was added 300 g (corresponding to 0.03 times relative
to total weight of base material) of an aqueous dispersion (solid
content concentration: 40 mass %), and the resulting mixture was
heated until the pellet temperature became 30, 40 and 50 degrees
centigrade respectively. The pellets were composed of an
ethylene-vinyl acetate copolymer having the content of vinyl
acetate of 46 mass %, MFR of 100 g/10 min, a Vicat softening point
of equal to or less than 25 degrees centigrade, a shore hardness of
16 and the degree of crystallinity of 0% as a resin base material,
while the aqueous dispersion was prepared by dispersing
microparticles composed of an ethylene-vinyl acetate copolymer
having the content of vinyl acetate of 19 mass %, MFR of 150 g/10
min, a Vicat softening point of 42 degrees centigrade
(.DELTA.T.gtoreq.17), a shore hardness of 86 (.DELTA.HS: 70) and
the degree of crystallinity of 26% (.DELTA.a: 26%). The mixture was
heated by coming into contact with air heated to 70 degrees
centigrade using a fluidized bed dryer or a vibrating dryer (spiral
elevator), or by putting into an infrared dryer regulated to 70
degrees centigrade. Subsequently, the obtained resin pellets were
cooled in cold water of 10 degrees centigrade, and the pellet
temperature was confirmed to be equal to or less than 20 degrees
centigrade, and then the resin pellets were dried at normal
temperature (25 degrees centigrade). The obtained resin pellets
were observed with an electron microscope to evaluate embeddability
of particles. The results are shown in Table 1. FIG. 1 illustrates
an electron microscope picture on the surface of resin pellets
prepared by heating to 40 degrees centigrade of the pellet
temperature, while FIG. 2(a) illustrates an electron microscope
picture on the surface of resin pellets prepared by heating to 50
degrees centigrade, and FIG. 2(b) illustrates a picture of the
cross-sectional surface of them. The average particle size of
microparticles was examined using the results from FIGS. 1 and 2,
and as a result, it was equal to or less than 20 .mu.m.
TABLE-US-00001 TABLE 1 Evaluation of Evaluation of embeddability
embeddability Pellet temperature (warm air) (infrared rays) 30
degrees centigrade C C 40 degrees centigrade B B 50 degrees
centigrade A A
Example 3
[0103] To 100 g of pellets (pellet temperature: 15 degrees
centigrade) was added 3 g (corresponding to 0.03 times relative to
total weight of base material) of an aqueous dispersion (solid
content concentration: 40 mass %), and the resulting mixture was
allowed to stand in an oven at a temperature of 45 degrees
centigrade and a humidity of 30% for 15, 30, 45, 50 and 60 minutes
respectively. The pellets were composed of an ethylene-vinyl
acetate copolymer having the content of vinyl acetate of 46 mass %,
MFR of 100 g/10 min, a Vicat softening point of equal to or less
than 25 degrees centigrade, a shore hardness of 22 and the degree
of crystallinity of 0% as a resin base material, while the aqueous
dispersion was prepared by dispersing microparticles composed of an
ethylene-vinyl acetate copolymer having the content of vinyl
acetate of 19 mass %, MFR of 150 g/10 min, a Vicat softening point
of 42 degrees centigrade (.DELTA.T.gtoreq.17), a shore hardness of
86 (.DELTA.HS: 64) and the degree of crystallinity of 26%
(.DELTA.a: 26%). The temperatures of resin pellets were
respectively measured over a predetermined period of time.
Subsequently, the obtained resin pellets were cooled in cold water
of 10 degrees centigrade, and the pellet temperature was confirmed
to be equal to or less than 20 degrees centigrade, and then the
resin pellets were dried at normal temperature (25 degrees
centigrade). The obtained resin pellets were observed with an
electron microscope to evaluate embeddability of particles. The
results are shown in Table 2.
TABLE-US-00002 TABLE 2 Time to allow to Evaluation of stand Pellet
temperature embeddability After 15 minutes 36.7 degrees centigrade
C After 30 minutes 39.6 degrees centigrade C After 45 minutes 40.9
degrees centigrade B After 50 minutes 41.3 degrees centigrade A
After 60 minutes 41.5 degrees centigrade A
Example 4
[0104] To 10 kg of pellets (pellet temperature: 15 degrees
centigrade) was added 300 g (corresponding to 0.03 times relative
to total weight of base material) of an aqueous dispersion (solid
content concentration: 40 mass %), and the resulting mixture was
heated until the pellet temperature became 50 degrees centigrade.
The pellets were composed of an ethylene-vinyl acetate copolymer
having the content of vinyl acetate of 41 mass %, MFR of 63 g/10
min, a Vicat softening point of equal to or less than 25 degrees
centigrade, a shore hardness of 40 and the degree of crystallinity
of 0% as a resin base material, while the aqueous dispersion was
prepared by dispersing microparticles composed of an ethylene-vinyl
acetate copolymer having the content of vinyl acetate of 19 mass %,
MFR of 150 g/10 min, a Vicat softening point of 42 degrees
centigrade (.DELTA.T.gtoreq.17), a shore hardness of 86 (.DELTA.HS:
46) and the degree of crystallinity of 26% (.DELTA.a: 26%). The
mixture was heated by coming into contact with warm air of 70
degrees centigrade using a fluidized bed dryer or a vibrating dryer
(spiral elevator), or by putting into an infrared dryer regulated
to 70 degrees centigrade. Subsequently, the obtained resin pellets
were cooled in cold water of 10 degrees centigrade, and the pellet
temperature was confirmed to be equal to or less than 20 degrees
centigrade, and then the resin pellets were dried at normal
temperature (25 degrees centigrade). The embeddability of particles
was evaluated and as a result, in any method of using a fluidized
bed dryer, a vibrating dryer and an infrared dryer, microparticles
were attached on the whole surface of resin pellets in the state
that some of microparticles were embedded. Evaluation of
embeddability was indicated as "A".
Example 5
[0105] To 10 kg of pellets (pellet temperature: 15 degrees
centigrade) was added 150 g (corresponding to 0.015 times relative
to total weight of base material) of an aqueous dispersion (solid
content concentration: 40 mass %), and the resulting mixture was
heated up to 60 degrees centigrade. The pellets were composed of an
ethylene-vinyl acetate copolymer having the content of vinyl
acetate of 46 mass %, MFR of 2.5 g/10 min, a Vicat softening point
of equal to or less than 25 degrees centigrade, a shore hardness of
28 and the degree of crystallinity of 0% as a resin base material,
while the aqueous dispersion was prepared by dispersing
microparticles composed of an ethylene-vinyl acetate copolymer
having the content of vinyl acetate of 19 mass %, MFR of 150 g/10
min, a Vicat softening point of 42 degrees centigrade
(.DELTA.T.gtoreq.17), a shore hardness of 86 (.DELTA.HS: 58) and
the degree of crystallinity of 26% (.DELTA.a: 26%). The mixture was
heated by coming into contact with warm air of 80 degrees
centigrade using a fluidized bed dryer, by coming into contact with
warm air of 70 degrees centigrade using a vibrating dryer (spiral
elevator), or by putting into an infrared dryer regulated to 80
degrees centigrade. Subsequently, the obtained resin pellets were
cooled in cold water of 10 degrees centigrade, and the pellet
temperature was confirmed to be equal to or less than 20 degrees
centigrade, and then the resin pellets were dried at normal
temperature (25 degrees centigrade). The embeddability of particles
was evaluated and as a result, in any method of using a fluidized
bed dryer, a vibrating dryer (spiral elevator) and an infrared
dryer, microparticles were attached on the whole surface of pellets
in the state that some of microparticles were embedded. Evaluation
of embeddability was indicated as "A".
Example 6
[0106] To 10 kg of pellets (pellet temperature: 15 degrees
centigrade) was added 150 g (corresponding to 0.015 times relative
to total weight of base material) of an aqueous dispersion (solid
content concentration: 40 mass %), and the resulting mixture was
heated up to 60 degrees centigrade. The pellets were composed of an
ethylene-vinyl acetate copolymer having the content of vinyl
acetate of 41 mass %, MFR of 2.0 g/10 min, a Vicat softening point
of equal to or less than 25 degrees centigrade, a shore hardness of
45 and the degree of crystallinity of 0% as a resin base material,
while the aqueous dispersion was prepared by dispersing
microparticles composed of an ethylene-vinyl acetate copolymer
having the content of vinyl acetate of 19 mass %, MFR of 150 g/10
min, a Vicat softening point of 42 degrees centigrade
(.DELTA.T.gtoreq.17), a shore hardness of 86 (.DELTA.HS: 41) and
the degree of crystallinity of 26% (.DELTA.a: 26%). The mixture was
heated by coming into contact with warm air of 80 degrees
centigrade using a fluidized bed dryer or a vibrating dryer (spiral
elevator), or by putting into an infrared dryer regulated to 80
degrees centigrade. Subsequently, the obtained resin pellets were
cooled in cold water, and the pellet temperature was confirmed to
be equal to or less than 20 degrees centigrade, and then the resin
pellets were dried at normal temperature (25 degrees centigrade).
The embeddability of particles was evaluated and as a result, in
any method of using a fluidized bed dryer, a vibrating dryer and an
infrared dryer, microparticles were attached on the whole surface
of pellets in the state that some of microparticles were embedded.
Evaluation of embeddability was indicated as "A".
Reference Example
[0107] To 10 kg of pellets (pellet temperature: 15 degrees
centigrade) was added 300 g (corresponding to 0.03 times relative
to total weight of base material) of an aqueous dispersion (solid
content concentration: 40 mass %), and the resulting mixture was
dried at normal temperature (25 degrees centigrade). The pellets
were composed of an ethylene-vinyl acetate copolymer having the
content of vinyl acetate of 46 mass %, MFR of 100 g/10 min, a Vicat
softening point of equal to or less than 25 degrees centigrade, a
shore hardness of 16 and the degree of crystallinity of 0% as a
resin base material, while the aqueous dispersion was prepared by
dispersing microparticles composed of an ethylene-vinyl acetate
copolymer having the content of vinyl acetate of 19 mass %, MFR of
150 g/10 min, a Vicat softening point of 42 degrees centigrade
(.DELTA.T.gtoreq.17), a shore hardness of 86 (.DELTA.HS: 70) and
the degree of crystallinity of 0% (.DELTA.a: 26%).
[0108] Evaluation of Blocking
[0109] With respect to resin pellets prepared in Reference Example
and resin pellets prepared in the above Examples 1 to 3, the stick
temperatures were compared, and blocking of respective resin
pellets was evaluated.
[0110] A cylindrical metal container with its inner surface having
a diameter of 40 mm and a height of 70 mm, and the inner surface
which is coated with Teflon (registered trademark) was allowed to
stand in an oven set to any temperature in advance for 30 minutes,
and then the resin pellets were put up to a height of 55 mm from
the bottom of the container and allowed to stand for 30 minutes.
After 30 minutes, the metal container was taken out from the oven,
and a load of 40.2 N was applied on the resin pellets for 1 hour
using a metal weight having an inner diameter slightly smaller than
that of the metal container. Thereafter, the load was removed and
the metal container was put upside down. Then, falling state of the
pellets was visually observed, and the container was back to the
original state after 1 minute and the inside of the container was
visually observed. When clusters of a plurality of resin pellets
remained inside the container, it was evaluated that sticking was
caused. This experiment was carried out in increments of 2.5
degrees centigrade, whereby the temperature in which the presence
and absence of sticking were distinguished at 2.5 degrees
centigrade was taken as the stick temperature. The results are
shown in Table 3.
TABLE-US-00003 TABLE 3 Stick temperature Reference Example 24
degrees centigrade Example 1 30 degrees centigrade Example 2 27 to
30 degrees centigrade Example 3 27 to 30 degrees centigrade
[0111] As shown in Examples above, it is found that the resin
pellet of the present invention has a resin base material and a
plurality of microparticles embedded in the resin base material,
wherein the surface of the resin base material is covered with the
plurality of microparticles. As a result, it is found that
microparticles obtained according to the conventional method have
the stick temperature increased by 3 to 6 degrees centigrade, as
compared to resin pellets attached without being embedded in the
resin base material. Thus, by increasing the stick temperature,
storage conditions and handling conditions of the resin pellets are
eased and in addition thereto, the production time can also be
reduced.
[0112] This application is based on Japanese patent application No.
2009-146065 filed on Jun. 19, 2009, the content of which is
incorporated hereinto by reference.
* * * * *