U.S. patent application number 09/909066 was filed with the patent office on 2003-01-23 for bonding of granular materials to polyolefin surfaces.
Invention is credited to Reeves, Robert Alan, Stevenson, Michael J..
Application Number | 20030017272 09/909066 |
Document ID | / |
Family ID | 25426593 |
Filed Date | 2003-01-23 |
United States Patent
Application |
20030017272 |
Kind Code |
A1 |
Stevenson, Michael J. ; et
al. |
January 23, 2003 |
Bonding of granular materials to polyolefin surfaces
Abstract
A permanent roughened or textured surface is applied to parts
molded from polyolefins, particularly from polyethylene by applying
to the surface of the part a coating mixture of a tackifier resin
and polyolefin particles in a liquid carrier and incorporating a
granular or particulate matter in the coating, either by
application to the coating or by admixing the granular or
particulate matter into the coating mixture. The coated surfaced is
heated to the melt temperature of the polyolefin for a short time,
sufficient to gel the polyolefin particles of the coating into the
surface of the part, but insufficient to cause any thermal
distortion of the part.
Inventors: |
Stevenson, Michael J.;
(Sedona, AZ) ; Reeves, Robert Alan; (Cottonwood,
AZ) |
Correspondence
Address: |
Robert E. Strauss
74527 Moss Rose Drive
Palm Desert
CA
92260
US
|
Family ID: |
25426593 |
Appl. No.: |
09/909066 |
Filed: |
July 20, 2001 |
Current U.S.
Class: |
427/385.5 ;
526/352 |
Current CPC
Class: |
Y02E 60/10 20130101;
C08J 7/0427 20200101; C08J 7/043 20200101; C08J 2323/02 20130101;
B05D 7/02 20130101; H01M 50/20 20210101; B05D 5/02 20130101; C08J
2423/00 20130101; H01M 50/24 20210101 |
Class at
Publication: |
427/385.5 ;
526/352 |
International
Class: |
B05D 003/02 |
Claims
What is claimed is:
1. The method of treating a polyolefin object to obtain a
permanently textured surface which comprises: a. coating the
surface with a mixture of a tackifier and polyolefin powders in a
liquid carrier; b. incorporating particulate solids having a size
range passing a 15 mesh standard screen size into the coating; c.
drying the coating and heating the coating and polyolefin surface
to the polyolefin melt temperature for a sufficient time to gel the
coating into the surface but insufficient to cause thermal
distortion of the polyolefin object.
2. The method of claim 1 wherein the polyolefin object is a
polyethylene object.
3. The method of claim 2 wherein the polyolefin powder is
polyethylene powder.
4. The method of claim 3 wherein the particles of the polyethylene
powder have a size range less than 140 microns.
5. The method of claim 1 wherein said tackifier is an aliphatic or
cycloaliphatic hydrocarbon resin.
6. The method of claim 1 wherein said active ingredients comprise
from 15 to 30 weight percent tackifier and from 85 to 70 weight
percent polyolefin powder.
7. The method of claim 6 wherein said liquid carrier is a
hydrocarbon solvent.
8. The method of claim 6 wherein said liquid carrier is water and
including sufficient surfactant to disperse the active ingredients
in water.
9. A coating mixture comprising: a. active ingredients comprising
from 15 to 30 weight percent tackifier and from 85 to 70 weight
percent polyolefin powders having a size range from 1 to about 140
microns; and b. a liquid carrier selected from the group consisting
of hydrocarbon solvents and surfactant containing water in an
amount from 1 to about 2 weight parts per part of active
ingredients.
10. The coating mixture of claim 9 wherein the polyolefin powder is
polyethylene powder.
11. The coating mixture of claim 10 wherein the particles of the
polyethylene powder have a size range from 5 to about 40
microns.
12. The coating mixture of claim 1 wherein said tackifier is an
aliphatic or cycloaliphatic hydrocarbon resin.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] This invention relates to surface treatment of polyolefin
parts, in particular, to permanently bonding granular materials to
surfaces of polyethylene parts such as containers and outdoor
signs.
[0003] 2. Brief Statement of the Prior Art
[0004] Polyolefin surfaces, particularly polyethylene surfaces,
resist acceptance of coatings. These polymers are commonly used to
form large, hollow-form parts such as outdoor signs, tanks and
containers by rotational molding. The surfaces of these parts are
smooth and difficult to coat.
[0005] In many instances, it is desirable to apply granular or
particulate materials to the surfaces of such parts, e.g.,
containers which also function as steps need a roughened or
abrasive texture and outdoor signs can be enhanced with reflective
glass beads or microspheres.
[0006] U.S. Pat. No. 5,840,142 discloses and claims a method for
the permanent application of indica to the surface of a molded
polyethylene part using a transfer which is screen printed with a
wax, polyethylene and pigment mixture. After application to the
surface of a polyethylene part, the transfer is coated with a
mixture of polyethylene and wax and the part is heated to fuse the
coating and transfer into the surface of the part. Unfortunately,
the method of this patent cannot be used to create a part with a
roughened or textured surface, since the method achieves complete
integration of the applied coatings into the surface of the part,
forming a smooth clear surface.
OBJECTIVES OF THE INVENTION
[0007] It is an objective of this invention to provide a method to
apply granular or particulate material to the surface of parts
molded of polyolefins, particularly of polyethylene.
[0008] It is a further objective of this invention to provide
permanently roughened or textured surfaces to parts molded from
polyolefins, particularly from polyethylene.
[0009] It is an additional objective of this invention to provide a
coating composition which is useful in the method for applying
granular or particulate material to the surface of polyolefins,
particularly of polyethylene.
[0010] Other and related objectives will be apparent from the
following description of the invention.
BRIEF DESCRIPTION OF THE INVENTION
[0011] This invention is a method to impart a permanent, roughened
or textured surface to parts molded from polyolefins, particularly
from polyethylene. The method comprises coating the selected
surface of the part with a coating mixture of a tackifier resin and
polyolefin particles in a liquid carrier and incorporating a
granular or particulate matter in the coating, either by
application to the coating or by admixing the granular or
particulate matter into the coating mixture. The invention also
includes the composition of the coating mixture. The coated surface
of the polyethylene part is heated to the melt temperature of the
polyolefin for a short time, sufficient to gel the polyolefin
particles of the coating into the surface of the part, but
insufficient to cause any thermal distortion of the part. The
heating permanently incorporates the coating into the surface of
the part, with the granular solids bonded to the surface to impart
a roughened or textured surface.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0012] The invention is applicable to the treatment of surfaces of
polyolefins such as polymers and copolymers of ethylene, propylene,
butene, isobutene, with minor amounts of other comonomers such as
vinyl acetate, vinyl chloride, etc. Polyethylene is the most common
and advantageously treated polyolefin and is preferred, however,
the surfaces of other polyolefins can be likewise treated.
[0013] The treatment of the invention is applicable to provide a
roughened or textured surface to polyolefins in any form or shape,
including films and sheets and molded objects such as containers,
e.g., boxes, tanks, and outdoor signs, which are commonly
rotationally molded from polyethylene.
[0014] The method employs a coating adhesive mixture which is
applied to the polyolefin surface as a thin coating approximately
several mils or less, preferably one mil, in thickness. The coating
can be applied by any conventional method such as spraying,
brushing, rolling, etc. Spraying is preferred for ease of
application.
[0015] The active ingredients in the coating mixture are powders of
a polyolefin, preferable polyethylene and a tackifier. The
polyethylene powder and tackifier are present in relative
proportions of 15-30 weight parts tackifier and 85-70 weight parts
polyethylene powder per 100 weight parts. These ingredients are
dispersed in a suitable liquid carrier to permit application to the
polyolefin surface. The liquid carrier can be water or a
hydrocarbon solvent such as hexane or toluene.
[0016] The tackifier should be compatible with the polyolefin and
preferably should be white to neutral in color to avoid staining
the polyolefin surface. It should also have a softening temperature
less than the melting temperature of the polyolefin, which for
polyethylene should be less than 250 degrees F. Useful tackifiers
include polyacrylic acid polyacrylates, polyurethanes,
poly(vinyl)acetate and copolymers and mixtures thereof.
Particularly preferred tackifiers are hydrocarbon resins such as
aliphatic or cycloaliphatic petroleum resins from five carbon
monomers containing minor amounts of aromatics, synthetic terpene
resins, chlorinated polyolefins and hydrogenated rosin and rosin
esters. The tackifier should be of light color to avoid staining
the polyolefin surface, should have high heat and ultraviolet light
stability and be soluble in hydrocarbon solvents or be readily
emulsifiable in water. The softening point of the tackifier should
be from 75 to 135 degrees F., preferably from 85 to 120 degrees
F.
[0017] The polyolefin ingredient is used in a finely subdivided or
powdered state with a particle size from less than 1 micron to
about 140 microns, preferably from 5 to about 40 microns, maximum
particle diameter. The density of the preferred polyethylene powder
ranges from about 0.88 to 0.97 grams per cubic centimeter. Low,
high and linear high density and high to ultrahigh molecular weight
polyethylene can be used. Other suitable polyolefins include
polypropylene, ethylene/vinyl acetate copolymers, and metallocene
catalyst polyethylene.
[0018] The coating mixture has sufficient liquid carrier to provide
a solids content from 30 to about 50, preferably from 25 to 35,
weight percent, and can be thinned with additional liquid carrier
to provide an appropriate viscosity for application by spraying,
brushing, rolling, or dipping of the polyethylene surface with the
coating mixture.
[0019] When water is used as the liquid carrier, the active
ingredients are dispersed in water with surface active agents which
can include hydrocarbon silicone and fluorocarbon surfactants,
non-ionic surfactants and ionic surfactants. Sufficient amounts of
the surfactant are used to achieve a stable suspension of the
ingredients in the aqueous mixture. Typically, the effective
concentration of the surfactant will be from 0.1 to about 2 weight
percent of the solids content in the aqueous mixture, depending on
the particular surfactant which is used.
[0020] The granular solids can be of various sources, selected for
the particular application. Examples of suitable materials include
silica, e.g., sand, silicon carbide, aluminum oxide, aluminum
silicates, garnet, etc. If skid resistance is desired, sand or
garnet powders can be used. If an abrasive surface is desired,
silicon carbide or alumina can be used. In some applications, a
highly reflective surface may be desired and reflective glass beads
or microspheres, or metal flakes can be used. The particle size of
the granular solids can be varied considerably from 15 to about 300
mesh. The preferred size range is from 100 to about 300 mesh.
[0021] The granular solids can be admixed into the coating mixture
when the mixture is applied by brushing, rolling or dipping. In
such applications, the coating mixture can be loaded with granular
solids in amounts of 5 to 50 weight percent, preferably 15 to 30
weight percent. When the coating mixture is applied by spraying,
the granular solids are spread across the wetted surface of the
polyethylene part by dusting or other suitable techniques that will
ensure uniform distribution of the solids.
[0022] The coated surface is then heated to raise the temperature
of the coating and outer skin of the surface to the melt
temperature of the polyolefin powders, fusing the powders and
tackifier into the outer skin of the polyolefin surface. The
granular solids are thereby encased in the outer skin of the
polyolefin part, yet protrude from the surface of the part to
impart a roughened texture to the surface. In a typical
application, the coated polyolefin surface is heated to a
temperature from 250 to about 350 degrees F., taking care to avoid
excessive temperatures or temperature differentials which could
cause the polyolefin part to distort or warp.
[0023] The heating can be accomplished using a suitable radiant
source such as an open flame or a high temperature electrical
heater, e.g., an infrared heater. The heating step is practiced to
apply heat locally to the coated polyethylene surface sufficiently
to fuse the coating into the surface of the polyolefin part, a
condition which is reached when the coated surface appears to be
clear of any cloudiness.
[0024] Thereafter, the polyolefin part is cooled to ambient
temperature.
[0025] The invention is further described and illustrated in the
following example.
EXAMPLE
[0026] A battery container having a cover approximately two by
three feet in area and obtained by rotationally molding from
polyolefin is treated by the invention to provide skid resistance
suitable for use as a step. A coating mixture of active ingredients
comprising 30 weight percent of an aromatic modified C5 aliphatic
hydrocarbon resin and 70 weight percent polyethylene powders was
used to coat the outer surface of the container cover. The
polyethylene powder was high density polyethylene with a size range
from 1 to 80 microns. The active ingredients were dispersed in
toluene at a concentration of 25 weight percent and were sprayed
onto the polyethylene surface sufficiently to form a continuous
film over the surface. A pumice aggregate containing 70 weight
percent silica with a size range from 15 to 100 mesh was dusted
over the wet surface of the coating and a second coating of the
coating mixture was sprayed over the surface. The coating was
permitted to dry and then the surface was heated to approximately
250 degrees F., sufficiently to fuse the coating into the outer
skin of the polyethylene surface. After cooling the granular solids
were observed to have imparted a permanent, roughened texture to
the polyethylene surface.
[0027] The invention has been described with reference to the
illustrated and presently preferred embodiment. It is not intended
that the invention be unduly limited by this disclosure of the
preferred embodiment. Instead, it is intended that the invention be
defined by the method steps and ingredients, and their obvious
equivalents, set forth in the following claims.
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